Method for measuring free carbon content in positive electrode material

Abstract

The present application relates to lithium battery material detection technology field, disclose a method for determining the content of free carbon in positive electrode material, positive electrode material includes at least one of lithium iron phosphate and lithium iron manganese phosphate, comprising: mixing glue liquid with magnetic member and appropriate amount of sample to be measured in the container; make the free carbon in the sample to be measured uniformly distributed in the glue liquid, and make the positive electrode material particles in the sample to be measured fully adsorbed to the surface of the magnetic member, then make the positive electrode material particles fully settle to the bottom of the container; take part or all of the glue liquid separated from the positive electrode material particles and dry to obtain dried glue powder; by testing the carbon content in the glue powder obtained after drying before and after the experiment, the content of free carbon in the sample to be measured is calculated according to the carbon content change amount. The method is simple and convenient, and the free carbon in the positive electrode material can be accurately detected.

Description

Technical Field

[0001] This invention relates to the field of lithium battery material testing technology, and more specifically, to a method for determining the free carbon content in cathode materials. Background Technology

[0002] Lithium iron phosphate (LiFePO4 or LFP) of the olivine type has become one of the most widely used cathode materials for lithium-ion batteries (LIBs) due to its high thermal stability, long cycle life, and low cost. LFP batteries account for more than one-third of the entire LIB market.

[0003] Lithium iron phosphate (LiFePO4) or lithium manganese iron phosphate (LFP) has a spatial framework consisting of MeO6 octahedra (Me being one or both of Fe and Mn) and PO4 tetrahedra. P occupies the tetrahedral positions, while Me and Li fill the octahedral voids. Me occupies octahedral positions sharing corners, and Li occupies octahedral positions sharing edges. Adjacent MeO6 octahedra are connected by sharing vertices, resulting in low electronic conductivity. The PO4 tetrahedra, located between the MeO6 octahedra, hinder the flow of Li. + The diffusion process of carbon is crucial. Therefore, carbon sources are introduced during the production of lithium iron phosphate (LFP) or lithium manganese iron phosphate (LFP) to reduce ferrous ions, prevent oxidation, and decrease the trivalent phase of Fe. This also inhibits internal particle contact, prevents abnormal grain growth, and improves electronic conductivity. However, LFP has a lower intrinsic conductivity than LFP, requiring more carbon coating to improve electrochemical properties such as conductivity. If the coating is uneven, the remaining carbon exists in a free form, failing to enhance conductivity and instead reducing the material's specific capacity. Therefore, given the total carbon content of the material, the amount of free carbon can reflect the coating condition. However, currently, there is no simple and quick method to test the free carbon content.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a simple and convenient method for determining the free carbon content in cathode materials.

[0006] This invention is implemented as follows:

[0007] This invention provides a method for determining the free carbon content in a cathode material, wherein the cathode material includes at least one of lithium iron phosphate and lithium iron manganese phosphate, comprising:

[0008] Mix the adhesive solution, the magnetic suction device, and an appropriate amount of the sample to be tested in a container;

[0009] The free carbon in the sample to be tested is evenly distributed in the adhesive solution, and the positive electrode material particles in the sample to be tested are fully adsorbed onto the surface of the magnetic chuck, and then fully settled to the bottom of the container.

[0010] The gel solution, which is partially or completely separated from the positive electrode material particles, is dried to obtain dried gel powder.

[0011] The carbon content in the adhesive powder obtained after drying the adhesive solution before and after the experiment was tested, and the free carbon content in the sample was calculated based on the change in carbon content.

[0012] In an optional implementation, the free carbon content in the sample to be tested is calculated based on the change in carbon content in the adhesive powder obtained after drying the adhesive solution before and after the experiment.

[0013] Take a mass of m1 of rubber powder and prepare it into a solution. Take a mass of m2 of the sample to be tested. The carbon content in the rubber powder used to prepare the solution is w1%, and the carbon content in the dried rubber powder is w2%. The free carbon content x in the cathode material is calculated by the formula: x% = (w2% - w1%) × m1 / m2.

[0014] In an optional implementation, the instrument used to test the carbon content in the rubber powder and the dried rubber powder is a carbon-sulfur analyzer.

[0015] In an optional embodiment, the magnetic force of the magnetic attractor is 8000 to 12000 GS.

[0016] In an optional implementation, the magnetic element is a magnetic ball or a magnetic rod.

[0017] In an optional embodiment, the viscosity of the adhesive solution is 1000 to 10000 mPa·s.

[0018] In an optional embodiment, a glue powder is used to prepare a glue solution for the experiment. The glue powder is selected from at least one of CMC, PAA and PUA powders.

[0019] In an optional embodiment, the solid content of the adhesive solution is 0.1 to 0.5 wt%.

[0020] In an optional implementation, the settling method is static settling, and the settling time is 12 to 36 hours.

[0021] In an optional embodiment, the method for uniformly distributing the free carbon in the sample to be tested in the adhesive solution and for fully adsorbing the positive electrode material particles in the sample to be tested onto the surface of the magnetic chuck is to stir at a speed of 600-1000 r / min for 1-3 hours.

[0022] In an optional embodiment, the drying temperature is 100–150°C.

[0023] The present invention has the following beneficial effects:

[0024] The testing method provided in this application utilizes magnetic attraction and gravity sedimentation to adsorb lithium iron phosphate (LFP) or lithium iron manganese phosphate (LMC) particles to the bottom of a container. Free carbon is uniformly distributed in the liquid due to adsorption and steric hindrance. After the free carbon is uniformly distributed and the LFP or LMC particles have been adsorbed and settled to the bottom of the container, the upper layer of liquid is dried. The free carbon content in the sample can be calculated by measuring the mass change between the original and dried liquid powder, or by measuring the change in carbon content between the original and dried liquid powder. This method is simple to operate, provides accurate results, and can measure the free carbon content in lithium iron phosphate or LMC cathode materials, thereby determining the quality of the cathode material. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0026] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0027] This application provides a method for determining the free carbon content in a cathode material, wherein the cathode material includes at least one of lithium iron phosphate and lithium iron manganese phosphate, comprising:

[0028] Mix the adhesive solution, the magnetic suction device, and an appropriate amount of the sample to be tested in a container;

[0029] The free carbon in the sample to be tested is evenly distributed in the adhesive solution, and the positive electrode material particles in the sample to be tested are fully adsorbed onto the surface of the magnetic chuck, and then fully settled to the bottom of the container.

[0030] The gel solution, which is partially or completely separated from the positive electrode material particles, is dried to obtain dried gel powder.

[0031] The carbon content in the adhesive powder obtained after drying the adhesive solution before and after the experiment was tested, and the free carbon content in the sample was calculated based on the change in carbon content.

[0032] Because lithium iron phosphate (LFP) and lithium iron manganese phosphate (LMC) particles are ferromagnetic, while free carbon is not, the determination method provided in this application utilizes magnetic attraction and gravitational sedimentation to adsorb LFP or LMC particles to the bottom of the container. Free carbon, due to adsorption in the adhesive solution and steric hindrance, can be uniformly distributed in the adhesive solution. Once the free carbon is uniformly distributed, the LFP or LMC particles are adsorbed and settle to the magnetic adsorption element. After drying the upper layer of adhesive solution, the free carbon content in the sample can be calculated from the mass change between the original adhesive powder and the dried adhesive powder. This method is simple to operate and provides accurate detection results.

[0033] Preferably, the specific calculation method can be:

[0034] Take a mass of m1 of rubber powder and prepare it into a solution. Take a mass of m2 of the sample to be tested. The carbon content in the rubber powder used to prepare the solution is w1%, and the carbon content in the dried rubber powder is w2%. The free carbon content x in the cathode material is calculated by the formula: x% = (w2% - w1%) × m1 / m2.

[0035] The above calculation method requires less data to test, is simple to operate, and has high accuracy.

[0036] Furthermore, the instrument used to test the carbon content in the rubber powder and the dried rubber powder is a carbon-sulfur analyzer.

[0037] The determination method provided in this application is described below in more detail.

[0038] The method for determining the free carbon content in the cathode material provided in this embodiment includes the following steps:

[0039] S1. Prepare the adhesive powder into an adhesive solution:

[0040] Take a mass of m1 and a carbon content of w1% of the adhesive powder and dissolve it in a solvent to obtain an adhesive solution with a volume of V1.

[0041] Preferably, the viscosity of the adhesive solution is 1000–10000 mPa·s, and the viscosity is tested at 25℃±2℃ using a Brookfield DV2T viscometer.

[0042] The above-mentioned viscosity range provides good steric hindrance for free carbon while ensuring its uniform distribution. The viscosity should not be too high; if it is, the steric resistance will exceed the magnetic attraction, preventing the positive electrode particles from being adsorbed onto the magnetic surface. Even if the magnetic attraction is greater than the resistance, the small difference will result in a prolonged adsorption and sedimentation process, making detection difficult. Conversely, the viscosity should not be too low, as this can prevent the free carbon from distributing evenly. For example, if the steric resistance is less than the weight of the free carbon, the concentration of free carbon may increase with decreasing height.

[0043] Preferably, the adhesive powder is selected from at least one of CMC, PAA and PUA.

[0044] The adhesive solutions prepared from the above-mentioned substances have a suitable steric hindrance effect on free carbon.

[0045] Furthermore, the solid content of the adhesive solution is 0.1–0.5 wt%.

[0046] The above-mentioned solid content of the adhesive solution has a better viscosity, which can ensure that free carbon is easily and evenly distributed in the adhesive solution, and can ensure that the magnetic attractor can adsorb the positive electrode particles onto its surface in a relatively short time.

[0047] Furthermore, the solvent used to prepare the adhesive solution can be deionized water.

[0048] S2. Mix the adhesive solution, the magnetic chuck, and an appropriate amount of the sample to be tested in a container:

[0049] First, add the magnetic component into a container containing a volume of adhesive liquid V1.

[0050] Then, add a sample of mass m2 to the container.

[0051] Preferably, the magnetic force of the magnetic attractor is 8000 to 12000 GS (for example, it can be 8000 GS, 10000 GS or 12000 GS).

[0052] The magnetic components within the aforementioned magnetic force range can generate sufficient attraction to the positive electrode particles, enabling the particles to overcome spatial steric hindrance and adhere to the surface of the magnetic components, thus preventing them from easily detaching from the surface of the magnetic components.

[0053] Specifically, the magnetic attractant can be a magnetic ball, a magnetic block, or a magnetic rod.

[0054] S3, Separation of Free Carbon

[0055] Stir the sample in the container with a plastic rod at a speed of 600-1000 r / min (e.g., 600 r / min, 800 r / min or 1000 r / min) for 1-3 hours (e.g., 1 hour, 2 hours or 3 hours) to ensure that the free carbon in the sample is evenly distributed in the liquid and that the positive electrode material particles in the sample are fully adsorbed onto the surface of the magnetic element.

[0056] Then let the container stand, allowing the magnetic components with positive electrode particles adsorbed on their surface to sink to the bottom of the container.

[0057] S4, Drying

[0058] Take a portion or all of the upper layer of adhesive liquid in a container with a volume of V3 and dry it to evaporate the solvent in the adhesive liquid to obtain dried adhesive powder.

[0059] Preferably, to ensure the drying rate while avoiding carbon loss, the drying temperature is 100-150°C (e.g., 100°C, 120°C, or 150°C), and the drying time is 12-36 hours (e.g., 12 hours, 24 hours, or 36 hours).

[0060] S5, Detect and Calculate

[0061] The mass m3 of the dried adhesive powder is measured, or the carbon content w2% of the dried adhesive powder is measured.

[0062] The free carbon content x% in the cathode material can be calculated using the formula: x% = (w2% - w1%) × m1 / m2.

[0063] Example 1

[0064] The carbon content in the CMC powder used in this embodiment was determined to be 39.67% using a carbon-sulfur analyzer.

[0065] Add 3g of CMC powder to a beaker containing 1L of deionized water and stir with a plastic stirring rod at 800r / min for 1 hour to obtain 1L of adhesive solution with a viscosity of 2350mPa·s.

[0066] Place a 10000GS small magnetic rod into 1L of the above-prepared adhesive solution, add 10g of the lithium iron phosphate powder to be tested, stir with a plastic stirring rod at 800r / min for 2 hours, and let stand for 24 hours.

[0067] After standing, samples were taken four times at different heights in the upper layer of the adhesive solution (at 1000ml, 800ml, 600ml, and 400ml of the beaker, with 150mL taken each time. After drying in an oven at 130℃, the samples were weighed and found to be 0.4752g, 0.4746g, 0.4755g, and 0.4764g, respectively. The carbon content was determined to be 40.51%, 40.49%, 40.52%, and 40.55% using a carbon-sulfur analyzer.

[0068] The free carbon contents were calculated to be 0.252%, 0.246%, 0.255%, and 0.264% using the formula x% = (w2% - w1%) × m1 / m2.

[0069] The test and calculation results above show that the quality of the dried adhesive powder obtained from sampling and drying at different heights is almost identical, and the measured carbon content is also almost identical. This demonstrates that the detection method provided in this embodiment can ensure that free carbon is uniformly distributed in the adhesive solution during the detection process.

[0070] The iron and lithium content in the dried adhesive powder was tested using the ICP (inductively coupled plasma) method. The results showed that no iron or lithium was detected in the dried adhesive powder, indicating that the lithium iron phosphate particles in the lithium iron phosphate powder were adsorbed and settled at the bottom of the beaker by the magnetic rod and were not distributed in the adhesive solution.

[0071] The above test results show that the test method provided in this application has high detection accuracy.

[0072] Example 2

[0073] The carbon content in the CMC powder used in this embodiment was determined to be 39.50% using a carbon-sulfur analyzer.

[0074] Add 1g of CMC powder to a beaker containing 1L of deionized water and stir with a plastic stir bar at 800r / min for 1 hour to obtain 1L of adhesive solution with a viscosity of 1250mPa·s.

[0075] Place a 10000GS small magnetic rod into 1L of the above-prepared adhesive solution, add 10g of the lithium iron phosphate powder to be tested, stir with a plastic stirring rod at 800r / min for 2 hours, and let stand for 24 hours.

[0076] After standing, samples were taken four times at different heights in the upper layer of the adhesive (at 1000ml, 800ml, 600ml, and 400ml of the beaker, with 150mL taken each time. After drying in an oven at 130℃, the samples were weighed and found to be 0.1755g, 0.1759g, 0.1751g, and 0.1760g, respectively. The carbon content was determined using a carbon-sulfur analyzer to be 42.05%, 42.09%, 42.01%, and 42.10%, respectively.

[0077] The free carbon contents were calculated to be 0.255%, 0.259%, 0.251%, and 0.260% using the formula x% = (w2% - w1%) × m1 / m2.

[0078] The test and calculation results above show that the quality of the dried adhesive powder obtained from sampling and drying at different heights is almost identical, and the measured carbon content is also almost identical. This demonstrates that the detection method provided in this embodiment can ensure that free carbon is uniformly distributed in the adhesive solution during the detection process.

[0079] The iron and lithium content in the dried adhesive powder was tested using the ICP (inductively coupled plasma) method. The results showed that no iron or lithium was detected in the dried adhesive powder, indicating that the lithium iron phosphate particles in the lithium iron phosphate powder were adsorbed and settled at the bottom of the beaker by the magnetic rod and were not distributed in the adhesive solution.

[0080] Example 3

[0081] The carbon content in the CMC powder used in this embodiment was determined to be 39.60% using a carbon-sulfur analyzer.

[0082] Add 5g of CMC powder to a beaker containing 1L of deionized water and stir with a plastic stir bar at 800r / min for 1 hour to obtain 1L of adhesive solution with a viscosity of 6480mPa·s.

[0083] Place a 10000GS small magnetic rod into 1L of the above-prepared adhesive solution, add 10g of the lithium iron phosphate powder to be tested, stir with a plastic stirring rod at 800r / min for 2 hours, and let stand for 24 hours.

[0084] After standing, samples were taken four times at different heights in the upper layer of the adhesive (at 1000ml, 800ml, 600ml, and 400ml of the beaker), with 150mL taken each time. After drying in an oven at 130℃, the samples were weighed and found to be 0.7750g, 0.7725g, 0.7765g, and 0.7740g, respectively. The carbon content was determined using a carbon-sulfur analyzer to be 40.10%, 40.05%, 40.13%, and 40.08%, respectively.

[0085] The free carbon contents were calculated to be 0.250%, 0.225%, 0.265%, and 0.240% using the formula x% = (w2% - w1%) × m1 / m2.

[0086] The test and calculation results above show that the quality of the dried adhesive powder obtained from sampling and drying at different heights is almost identical, and the measured carbon content is also almost identical. This demonstrates that the detection method provided in this embodiment can ensure that free carbon is uniformly distributed in the adhesive solution during the detection process.

[0087] The iron and lithium content in the dried adhesive powder was tested using the ICP (inductively coupled plasma) method. The results showed that no iron or lithium was detected in the dried adhesive powder, indicating that the lithium iron phosphate particles in the lithium iron phosphate powder were adsorbed and settled at the bottom of the beaker by the magnetic rod and were not distributed in the adhesive solution.

[0088] Example 4

[0089] The carbon content in the PAA powder used in this embodiment was determined to be 49.91% using a carbon-sulfur analyzer.

[0090] Add 3g of PAA powder to a beaker containing 1L of deionized water and stir with a plastic stir bar at 800r / min for 1 hour to obtain 1L of adhesive solution with a viscosity of 7609mPa·s.

[0091] Place a 10000GS small magnetic rod into 1L of the above-prepared adhesive solution, add 10g of the lithium iron phosphate powder to be tested, stir with a plastic stirring rod at 800r / min for 2 hours, and let stand for 24 hours.

[0092] After standing, samples were taken four times at different heights in the upper layer of the adhesive solution (at 1000ml, 800ml, 600ml, and 400ml of the beaker, with 150mL taken each time. After drying in an oven at 130℃, the masses were 0.4764g, 0.4761g, 0.4746g, and 0.4779g, respectively. The carbon content was determined to be 50.79%, 50.78%, 50.73%, and 50.84% ​​using a carbon-sulfur analyzer.

[0093] The free carbon contents were calculated using the formula x% = (w2% - w1%) × m1 / m2 to be 0.263%, 0.261%, 0.246%, and 0.279%, respectively.

[0094] The test and calculation results above show that the quality of the dried adhesive powder obtained by sampling and drying at different heights is almost the same, and the carbon content measured is also almost the same. This shows that the detection method provided in this embodiment can ensure that free carbon is evenly distributed in the adhesive liquid during the detection process.

[0095] The iron and lithium content in the dried adhesive powder was tested using the ICP (inductively coupled plasma) method. The results showed that no iron or lithium was detected in the dried adhesive powder, indicating that the lithium iron phosphate particles in the lithium iron phosphate powder were adsorbed and settled at the bottom of the beaker by the magnetic rod and were not distributed in the adhesive solution.

[0096] Example 5

[0097] The carbon content in the PAA powder used in this embodiment was determined to be 48.99% using a carbon-sulfur analyzer.

[0098] Add 1g of PAA powder to a beaker containing 1L of deionized water and stir with a plastic stir bar at 800r / min for 1 hour to obtain 1L of adhesive solution with a viscosity of 3360mPa·s.

[0099] Place a 10000GS small magnetic rod into 1L of the above-prepared adhesive solution, add 10g of the lithium iron phosphate powder to be tested, stir with a plastic stirring rod at 800r / min for 2 hours, and let stand for 24 hours.

[0100] After standing, samples were taken four times at different heights in the upper layer of the adhesive solution (at 1000ml, 800ml, 600ml, and 400ml of the beaker, with 150mL taken each time. After drying in an oven at 130℃, the masses were 0.1759g, 0.1749g, 0.1764g, and 0.1765g, respectively. The carbon content was determined to be 51.58%, 51.48%, 51.63%, and 51.64% using a carbon-sulfur analyzer.

[0101] The free carbon content was calculated to be 0.259%, 0.249%, 0.264%, and 0.265% using the formula x% = (w2% - w1%) × m1 / m2.

[0102] The test and calculation results above show that the quality of the dried adhesive powder obtained from sampling and drying at different heights is almost identical, and the measured carbon content is also almost identical. This demonstrates that the detection method provided in this embodiment can ensure that free carbon is uniformly distributed in the adhesive solution during the detection process.

[0103] The iron and lithium content in the dried adhesive powder was tested using the ICP (inductively coupled plasma) method. The results showed that no iron or lithium was detected in the dried adhesive powder, indicating that the lithium iron phosphate particles in the lithium iron phosphate powder were adsorbed and settled at the bottom of the beaker by the magnetic rod and were not distributed in the adhesive solution.

[0104] In summary, the method for determining the free carbon content in cathode materials provided in this application utilizes magnetic attraction and gravitational sedimentation to adsorb lithium iron phosphate or lithium iron manganese phosphate particles to the bottom of the container. Due to adsorption by the adhesive solution and steric hindrance, the free carbon can be uniformly distributed in the adhesive solution. After the free carbon is uniformly distributed in the adhesive solution, and the lithium iron phosphate or lithium iron manganese phosphate particles are adsorbed and settled to the bottom of the container, the upper layer of adhesive solution is dried. The free carbon content in the sample can then be calculated from the mass change between the original adhesive powder and the dried adhesive powder. This method is simple to operate, provides accurate results, and can determine the free carbon content in lithium iron phosphate or lithium iron manganese phosphate cathode materials, thereby assessing the quality of the cathode material.

[0105] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for measuring the content of free carbon in a positive electrode material, characterized by, The cathode material includes at least one of lithium iron phosphate and lithium iron manganese phosphate, comprising: Mix the adhesive solution, the magnetic suction device, and an appropriate amount of the sample to be tested in a container; The free carbon in the sample to be tested is evenly distributed in the adhesive solution, and the positive electrode material particles in the sample to be tested are fully adsorbed onto the surface of the magnetic suction device. Then, the positive electrode material particles are fully settled to the bottom of the container. The adhesive solution, which is partially or completely separated from the positive electrode material particles, is dried to obtain dried adhesive powder. The carbon content in the adhesive powder obtained after drying the adhesive solution before and after the experiment was tested. The free carbon content in the sample was calculated based on the change in carbon content. The method is as follows: Take m1 of the adhesive powder and prepare it into the adhesive solution. Take m2 of the sample to be tested and measure the carbon content w1% in the adhesive powder used to prepare the adhesive solution and the carbon content w2% in the dried adhesive powder. The free carbon content x in the cathode material is calculated by the formula: x%=(w2%-w1%)×m1 / m2.

2. The method of claim 1, wherein the method is characterized by, The instrument used to test the carbon content in the rubber powder and the dried rubber powder is a carbon-sulfur analyzer.

3. The method for determining the free carbon content in a positive electrode material according to claim 1 or 2, characterized in that, The magnetic force of the magnetic attractor is 8000~12000GS.

4. The method for determining the free carbon content in the cathode material according to claim 1 or 2, characterized in that, The viscosity of the adhesive solution is 1000~10000 mPa•s.

5. The method for determining the free carbon content in the cathode material according to claim 1 or 2, characterized in that, The adhesive solution was prepared using a powder selected from at least one of CMC, PAA, and PUA for testing.

6. The method for determining the free carbon content in the cathode material according to claim 5, characterized in that, The solid content of the adhesive solution is 0.1~0.5wt%.

7. The method for determining the free carbon content in the cathode material according to claim 1 or 2, characterized in that, The settling method is static settling, and the settling time is 12~36 hours.

8. The method for determining the free carbon content in the cathode material according to claim 1 or 2, characterized in that, The method for ensuring that the free carbon in the sample to be tested is uniformly distributed in the adhesive solution and that the positive electrode material particles in the sample to be tested are fully adsorbed onto the surface of the magnetic chuck is as follows: stirring at a speed of 600~1000 r / min for 1~3 h.

9. The method for determining the free carbon content in the cathode material according to claim 1 or 2, characterized in that, The drying temperature is 100~150℃.