CN111024681B - A kind of analysis method of ternary lithium-ion battery positive pole piece - Google Patents

Abstract

The invention relates to an analysis method of a ternary lithium ion battery positive pole piece, which comprises the steps of dissolving the pole piece by using acid liquor, filtering, carrying out ICP (inductively coupled plasma) test on filtrate, and carrying out thermogravimetric analysis test on filter residues. The component analysis method of the ternary lithium ion battery positive pole piece provided by the invention is combined with ICP, TG and other methods, analyzes the current collector and coating parameters of the positive pole piece, has the advantages of less sampling, simple operation, capability of effectively and accurately obtaining pole piece parameters, and important significance in pole piece verification, benchmarking and simulation parameter analysis work of the lithium ion battery.

Description

A kind of analysis method of ternary lithium-ion battery positive pole piece

technical field

The invention relates to the field of lithium-ion batteries, in particular to a method for analyzing positive pole pieces of ternary lithium-ion batteries.

Background technique

With the increasingly stringent regulations on energy conservation and emission reduction around the world, the new energy vehicle market is developing rapidly. As the power source of new energy vehicles, lithium-ion batteries have made breakthroughs in related technologies and products in recent years. Lithium-ion batteries are composed of four key parts: positive pole piece, negative pole piece, diaphragm and electrolyte. The positive and negative pole pieces are the places where lithium ions react and store. The role of ions and blocking electrons to prevent positive and negative short circuits. Positive and negative electrodes are usually mixed with active material, conductive agent, and binder and then coated on the current collector (the positive electrode usually uses aluminum foil, and the negative electrode usually uses copper foil). The current collector plays the role of connecting the external circuit, and its thickness has a significant impact on the current conduction of the external circuit of the battery and the temperature change during the charging and discharging process; the active material in the positive electrode sheet is the source of lithium ions, and the higher the mass fraction of it is , the higher the capacity and specific energy of the battery, the higher the nickel content of the ternary positive electrode material, the higher the battery capacity; the conductive agent is usually a carbon material, which carries out electron transmission between the active material particles, and increasing the content can improve the electrode internal However, if the content is too high, the specific energy of the battery will be reduced, and agglomeration may occur during the homogenization process, and the distribution in the electrode will be uneven; the positive pole piece usually uses polyvinylidene fluoride (PVDF) as a binder , the low content will lead to low cohesive force between the active material, conductive agent and current collector, and the pole pieces are prone to powder falling and crushing. In addition, due to the lack of conductivity, too high a binder content will increase the internal capacity of the battery. resistance, reducing the electrochemical performance of the battery.

As a key component of lithium-ion batteries, the composition parameters of the positive electrode sheet have a decisive impact on the characteristics of the battery such as capacity, energy, power, and life. In the battery simulation experiment, the parameters of the pole piece are necessary input items, and it is very important to clarify the parameters of the pole piece. In addition, in the battery benchmarking process, the design of the pole piece is the core content. At present, there are many related patents and documents on the preparation and process improvement of positive pole pieces. However, there is no unified test method or standard for parameter analysis of unknown positive pole pieces.

Usually, when analyzing the positive electrode sheet, the thickness of the aluminum foil is measured by scraping off the paint and using a micrometer to test the thickness of the foil; Component separation test. These methods are not only complicated to operate, but also cannot test accurate results due to low precision testing.

CN201410530716 discloses a method for the determination of three elements of a nickel-cobalt-manganese ternary material, by measuring the total amount of ions of nickel, cobalt, and manganese with EDTA titration, and then sampling in an alkaline medium of ammonium chloride and ammonia to form Nickel ammonium complex, then use hydrogen peroxide to oxidize cobalt and form trivalent cobalt ammonium complex with ammonia to form manganese dioxide precipitate, after filtration, titrate the filtrate with EDTA using ammonium violate as indicator to determine the content of nickel The solution after titration is heated to produce cobalt hydroxide precipitation, and the content of cobalt is measured with EDTA titration after acid dissolution. The contents of the three elements were calculated according to the volume and concentration of EDTA consumed in each step and the mass of the sample.

CN201611146766 discloses a method for detecting the content of nickel-cobalt-manganese in ternary materials or ternary precursors. The total amount of nickel-cobalt-manganese is obtained by complexation titration, the molar amount of manganese is obtained by redox titration and the potentiometric titration is used to obtain The total molar amount of cobalt and manganese.

The above method mainly focuses on the detection of the element content of the active substance or its precursor, but the titration operation is complicated, requires many reagents, and takes a long time.

Contents of the invention

Aiming at the defects and deficiencies in the prior art, the present invention provides a method for analyzing the positive pole piece of a ternary lithium ion battery.

The object of the present invention is to provide a method for analyzing the positive pole piece of a ternary lithium ion battery, comprising the steps of dissolving and filtering the pole piece with an acid solution, then performing an ICP test on the filtrate, and performing a thermogravimetric analysis test on the filter residue.

According to some preferred embodiments of the present invention, comprising the following steps:

Step 1), cutting the positive pole piece into disc-shaped pole pieces;

Step 2), testing the thickness of the pole piece;

Step 3), using acid solution to dissolve and filter the pole piece;

Step 4), carry out ICP test to the filtrate in step 3); determine through calculation and include the chemical formula of aluminum foil thickness and active material percentage and ternary active material;

Step 5), carry out thermogravimetric analysis test to filter residue in step 3); Determine the content of binder and conductive agent according to weight loss temperature and weight loss;

The positive pole piece is a positive pole piece of a ternary lithium ion battery.

According to some preferred embodiments of the present invention, in step 1), the diameter of the pole piece is 6-50 mm.

According to some preferred embodiments of the present invention, in step 2), a micrometer is used to test the thickness of 10-30 pole pieces, and an average value of the pole piece thickness is calculated.

According to some preferred embodiments of the present invention, in step 3), the weight of the pole piece is weighed, and after the pole piece is fully dissolved with an excessive amount of acid solution, it is transferred to the first volumetric flask, and deionized water is added to carry out Constant volume and shake well, use glass funnel and slow speed filter paper to filter, take a certain volume of filtrate and transfer to the second volumetric flask, add deionized water to dilute and constant volume, preferably, the temperature of the drying is 70 ~ 120 ℃.

According to some preferred embodiments of the present invention, in step 3), the acid solution is hydrochloric acid, the concentration of the hydrochloric acid is 0.1-10mol/L, preferably 2-5mol/L; the volume of the hydrochloric acid is 5-30mL, It is preferably 10.～20mL; the volume of the filtrate taken is 1～10mL, preferably 5mL, the volume of the first volumetric flask is 20～500mL, preferably 50～200mL, and the volume of the second volumetric flask is 20～200mL. 500mL, preferably 50-200mL.

According to some preferred embodiments of the present invention, in step 4), the quality of each element in the pole piece is determined by using an ICP test, and the pole piece includes four elements of Al, Li, Ni, Co, and Mn.

According to some preferred embodiments of the present invention, in step 4), the thickness of the aluminum foil, the chemical composition of the active material, the percentage of the active material, the chemical formula of the ternary active material, the coating surface density and the pole piece are calculated according to the mass of each element of the pole piece. compacted density.

According to some preferred embodiments of the present invention, in step 5), take the dried filter residue, and use a thermogravimetric analyzer to perform a thermogravimetric test; the test atmosphere is oxygen or air, the gas flow rate is 10-200mL/min, and the temperature is raised from normal temperature , the heating rate is 1-20°C/min, and the upper temperature limit is 800-1000°C.

According to some preferred embodiments of the present invention, in step 5), test the thermogravimetric curves of the conductive agent and the binder used in the pole piece respectively, according to the decomposition temperature and the weight loss rate of the conductive agent and the binder, Calculate and determine the mass ratio of the binder and the conductive agent in the filter residue.

According to some preferred embodiments of the present invention, hydrochloric acid is used to dissolve the aluminum foil and the active material in a certain mass of pole pieces, and after filtration, the concentration of Al, Li, Ni, Co, and Mn elements in the filtrate is tested by ICP, and the aluminum foil is determined through calculation. Thickness and proportion of active material in coating and chemical formula of ternary active material. The filter residue after filtration is subjected to a thermogravimetric analysis test, and the contents of the binder and the conductive agent are determined according to the weight loss temperature and weight loss.

The beneficial effects of the present invention are at least as follows: the present invention provides a method for analyzing the composition of the positive pole piece of the ternary lithium ion battery, combining ICP, TG and other methods to analyze the current collector and coating parameters of the positive pole piece. The traditional method of solvent dissolution, filtration, and weighing is used for analysis, and the operation is relatively complicated, and the error is relatively large. The method of the present invention overcomes the above problems, and has the advantages of less sampling and simple operation. The method proposed by the invention can effectively and accurately obtain pole piece parameters, and is of great significance in pole piece verification, benchmarking, and simulation parameter analysis of lithium-ion batteries.

Description of drawings

Figure 1 is the thermogravimetric curve of binder (PVDF) and conductive agent (SP, KS-6) in oxygen.

Figure 2 is the thermogravimetric curve of sample filter residue in oxygen.

detailed description

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all Example. The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination between the specific embodiments. Based on the embodiments of the present invention, all those skilled in the art obtained without creative work Other embodiments all belong to the protection scope of the present invention.

In the present invention, if no specific technique or condition is indicated in the examples, the technique or condition described in the literature in this field, or the product manual shall be followed. The instruments used and those whose manufacturers are not indicated are all conventional products that can be purchased through formal channels. The chemical raw materials used in the present invention all can buy conveniently in domestic chemical products market.

Example 1

1) Take the positive electrode piece to be tested (the ratio is: active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ): conductive agent (SP+KS-6): binder (PVDF) = 92.5 :5:2.5), cut the pole piece into a disc with a diameter of 14mm, test the thickness of 20 pole pieces, and calculate the average a result to be 65.3μm.

2) Take a pole piece and weigh it, m ₁ =30.9mg, area S ₁ =1.5393cm ² . Fully dissolve the pole piece with 5mL (V ₁ ) of hydrochloric acid with a concentration of 5mol/L for 30min, transfer to 50mL (V ₃ ) volumetric flask 1 and make constant volume with deionized water. The solution after constant volume was filtered, and the filter residue was washed 3 times with deionized water, and then transferred to an oven at 80° C. for 24 hours to dry. Take 5mL (V ₂ ) of the filtrate and transfer to 100mL (V ₄ ) volumetric flask 2 to make up to volume.

3) Take the solution in 10mL volumetric flask 2, use ICP to test the mass fraction of Al, Ni, Co, Mn, input mass m ₁ , dilution factor V ₄ /V ₂ =50, test result wt% _Al = 21.68%, wt % _Ni = 14.78%, wt% _Co = 14.74%, wt% _Mn = 13.64%.

The thickness of the aluminum foil is calculated by the mass of Al to be 16.1 μm. According to the mass fractions of Ni, Co, and Mn, the active material is LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , the proportion of active material is 92.42%, and the coating surface density of the pole piece is 7.55mg/ cm ² , the compacted density is 3.06g/cm ³ .

4) The filter residue in step 2) was subjected to a thermogravimetric test, the temperature range was 25-800°C, the heating rate was 5°C/min, the test was carried out in oxygen, the gas flow rate was 50mL/min, and the conductive agent was tested under the same conditions ( SP and KS-6) and binder (PVDF) thermogravimetric curve (as shown in Figure 1). According to the thermal weight loss curves of PVDF and conductive agent, the weight loss of PVDF is completed before 500°C, and the conductive agent begins to lose weight after 500°C. The thermal weight loss curve of filter residue (as shown in Figure 2) has a clear dividing line at 480°C. The weight loss rate before 480°C is 34.22%, and the weight loss rate after 480°C is 65.67%, which are the weight loss caused by the decomposition of PVDF and conductive agent respectively.

5) Through calculation, the proportion of the binder (PVDF) is 2.59%, and the proportion of the conductive agent (SP+KS-6) is 4.98%. Therefore, the ratio of each component of the positive pole piece is: active material: conductive agent (SP+KS-6): binder (PVDF) = 92.42:4.98:2.59. This analysis method has the advantages of small error, time saving, and comprehensive analysis items.

Example 2

This embodiment provides an analysis method for the positive pole piece of a ternary lithium-ion battery, which is different from the embodiment 1 in the analysis method for the content of the conductive agent and the binder.

1) Take the positive electrode piece to be tested (the ratio is: active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ): conductive agent (SP+KS-6): binder (PVDF) = 92.5 :5:2.5), cut the pole piece into a disc with a diameter of 14mm, test the thickness of 20 pole pieces, and calculate the average a result to be 65.3μm.

2) Take the pole piece to be tested with an area of 20*20cm, fully soak it with N-methylpyrrolidone (NMP), completely remove the coating on the surface of the aluminum foil with a dust-free paper, and use a micrometer to take 10 positions on the aluminum foil to test the thickness. The average value is 16 μm.

3) Take 10 cut pole pieces with a diameter of 14mm and weigh them, m ₁ =303mg, calculated according to the thickness of the aluminum foil measured in 2) of 16μm, the mass m _Al of Al in the 10 pole pieces is 66.5mg, single The sheet area is S ₁ =1.5393 cm ² .

4) Put the pole piece in step 3) into a 50mL centrifuge tube, take 20mL (V ₁ ) hydrochloric acid with a concentration of 5mol/L to fully dissolve the pole piece for 30min, centrifuge the solution, take 5mL supernatant, and Add deionized water to a volumetric flask with a volume of 100mL to make it constant, and use ICP to test the three elements of Ni, Co, and Mn. The test results show that the molar ratio of Ni, Co, and Mn is 1:1:1. It can be seen that the positive active material is LiNi _1/3 Co _1/3 Mn _1/3 O ₂ .

5) The residue after centrifugation in step 4) was washed with 30 mL of deionized water and then centrifuged to remove the supernatant, repeat the operation of washing, centrifuging, and removing the supernatant 3 times, and transfer the residue to an oven at 80°C for drying After 24 hours, the mass of the mixture of the conductive agent (SP+KS-6) and the binder (PVDF) was weighed to obtain m ₂ =16.03 mg. After calculation, the measured active material of the positive electrode sheet accounted for 93.22%. The coated surface density of the sheet was 7.68 mg/cm ² , and the compacted density was 3.11 g/cm ³ .

6) Transfer the dried filter residue to a 50mL beaker, add 20mL N-methylpyrrolidone (NMP), stir in an oil bath at 100°C for 1h, dissolve the binder (PVDF) through NMP, centrifuge, and remove the upper layer NMP, repeat the process of adding NMP, stirring in an oil bath, centrifuging, and removing NMP for a total of 3 times, and dry the residue obtained at the last time in a vacuum environment at 120° C., weigh it, and the mass is 4.81 mg. It can be calculated that the mass proportion of the conductive agent is 4.07%, and that of the binder is 2.71%. Therefore, the ratio of each component of the positive pole piece is: active material: conductive agent (SP+KS-6): binder (PVDF) = 93.22:4.07:2.71. Compared with Example 1, Example 2 separates the conductive agent and the binder by means of dissolution and centrifugation. The operation is tedious and time-consuming, and the error is relatively large during the operation, which causes the test results to deviate from the true value.

Although the present invention has been described in detail with general descriptions and specific embodiments above, it is obvious to those skilled in the art that some modifications or improvements can be made on the basis of the present invention. Therefore, the modifications or improvements made on the basis of not departing from the spirit of the present invention all belong to the protection scope of the present invention.

Claims (7)

1. an analytical method for a ternary lithium-ion battery positive pole piece, is characterized in that, comprises the following steps: Step 1), cutting the positive pole piece into disc-shaped pole pieces; Step 2), testing the thickness of the pole piece; Step 3), using an acid solution to dissolve and filter the pole piece; the acid solution is hydrochloric acid, and the concentration of the hydrochloric acid is 2 to 5 mol/L; Step 4), carry out ICP test to the filtrate in step 3); Calculate the thickness of aluminum foil, the chemical composition of active material, the percentage of active material, the chemical formula of ternary active material, the coating surface density and the pole piece according to the mass of each element of the pole piece compacted density; Step 5), take the filter residue dried in step 3), and use a thermogravimetric analyzer to perform a thermogravimetric test; the test atmosphere is oxygen, the gas flow rate is 10-200mL/min, and the temperature is raised from normal temperature, and the heating rate is 1-20°C /min, the temperature upper limit is 800-1000°C; respectively test the thermogravimetric curves of the conductive agent and the binder used in the pole piece, and calculate and determine the The mass ratio of the binder and the conductive agent in the filter residue; The positive pole piece is a positive pole piece of a ternary lithium ion battery. 2. The method according to claim 1, characterized in that, in step 1), the diameter of the pole piece is 6-50 mm. 3. The method according to claim 1, characterized in that, in step 2), the thickness of 10 to 30 pole pieces is tested with a micrometer, and the average value of the pole piece thickness is calculated. 4. The method according to claim 1, characterized in that, in step/step 3), the weight of the pole piece is weighed, and then the pole piece is fully dissolved with an excessive amount of acid solution, and then transferred to the first pole piece. Volumetric flask, add deionized water to constant volume and shake well, use glass funnel and slow filter paper to filter, transfer a certain volume of filtrate to the second volumetric flask, add deionized water to dilute and constant volume. 5. The method according to claim 4, characterized in that, in step 3), the drying temperature of the filter residue is 70-120°C. 6. The method according to claim 5, characterized in that, in step 3), the volume of the hydrochloric acid is 5-30 mL; the volume of the filtrate taken is 1-10 mL, and the volume of the first volumetric flask is 20-500 mL , the volume of the second volumetric flask is 20-500mL. 7. according to the method described in any one of claim 1 to 6, it is characterized in that, step 4) in, use ICP test to determine the quality of each element in the described pole piece, comprise Al, Li, Ni in the described pole piece , Co, Mn four elements.

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