Classification determination method for carbon content of lithium iron phosphate repair material and application

Abstract

The application discloses a kind of lithium iron phosphate repair material carbon content classification determination method and application, belong to material detection technical field.The method first lithium iron phosphate repair material is added NMP organic solvent, 40-50 ℃ stirring dispersion 1-2h, selectively dissolves PVDF, solid phase material is dried after 130-140 ℃ using the method of difference weight to quantify PVDF content;Again, hydrochloric acid / nitric acid mixed acid solution is added to solid phase material, 100-110 ℃ heating reaction 1-2h, dissolve lithium iron phosphate matrix, filter and dry to obtain carbon residue, quantify SP (CNT) and total content of coated carbon, combined with the typical value of coated carbon can further distinguish the proportion of each carbon source.The application does not need carbon sulfur instrument and other high-value equipment, and only uses conventional laboratory apparatus to realize the classification determination of PVDF, conductive carbon and coated carbon, solves the problem that traditional method can only measure total carbon and cannot distinguish carbon source and has high detection cost, is suitable for lithium iron phosphate positive material recycling repair and quality control, and has good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of testing by measuring the chemical or physical properties of materials, and particularly to a method and application for classifying and determining the carbon content of lithium iron phosphate remediation materials. Background Technology

[0002] Lithium iron phosphate (LiFePO4, LFP) is a mainstream cathode material for lithium-ion batteries, and the recycling of its repair materials is of great significance for reducing battery production costs and improving resource utilization. Carbon content is a key indicator determining the processing and electrochemical performance of lithium iron phosphate repair materials. The carbon components in repair materials have complex origins, mainly including binders such as PVDF (polyvinylidene fluoride), conductive agents such as SP (acetylene black), CNTs (carbon nanotubes), and carbon coatings (glucose carbonization products) on the material surface. Different carbon sources have significantly different functions in the battery system: PVDF mainly serves as an electrode binder, SP and CNTs are responsible for improving electronic conductivity, and the coated carbon is used to improve material interface stability and cycle life. Simply obtaining the total carbon content cannot distinguish the contribution of each carbon source, making it difficult to accurately guide the optimization of repair processes and cell preparation. Therefore, achieving classified and quantitative detection of different carbon sources is crucial for improving the quality of repair materials and expanding their application in power batteries, energy storage batteries, and other scenarios.

[0003] Currently, the carbon content detection of lithium iron phosphate remediation materials commonly employs the high-temperature combustion infrared absorption method using a carbon-sulfur analyzer, which is the mainstream method for total carbon detection in the industry. Its core process involves fully burning the sample at 1200-1600℃, converting all carbon-containing components into carbon dioxide, and then quantifying the CO2 using an infrared detector to output the total carbon mass fraction. While this method is relatively simple to operate and fast, it has fundamental technical limitations. During high-temperature combustion, different carbon sources such as PVDF, conductive agents, and coated carbon are completely oxidized, and the generated CO2 cannot be distinguished or identified. The instrument can only provide the total carbon content and cannot separate and determine the individual carbon sources. Furthermore, the purchase cost of carbon-sulfur analyzers is high, typically ranging from 80,000 to 200,000 yuan, placing a significant financial burden on small and medium-sized recycling companies and laboratories. The ongoing costs of instrument maintenance and combustion aid consumption are also high, hindering its widespread application in the recycling and remediation process.

[0004] Current total carbon detection technologies cannot meet the requirements for refined quality control of lithium iron phosphate (LFP) repair materials. Because they cannot separately quantify the carbon content of PVDF, SP, CNT, and coatings, production cannot optimize repair processes such as debinding, impurity removal, and recoating based on carbon composition data. This easily leads to problems such as poor batch-to-batch consistency of repair materials, unstable electrode peel strength, and uneven conductive network construction. When cell manufacturers use repair materials, the lack of precise carbon source content makes it impossible to design targeted slurry ratios, stirring processes, and drying parameters, resulting in fluctuations in key indicators such as battery rate performance and cycle life, limiting the application of repair materials in high-end battery fields. The industry urgently needs a low-cost, easy-to-operate method that can classify and determine different carbon sources to overcome the bottlenecks of existing technologies, such as only being able to measure total carbon, being unable to distinguish carbon sources, having high costs, and limited production guidance. This would provide reliable detection support for the efficient and high-value utilization of LFP repair materials. Summary of the Invention

[0005] To address the aforementioned technical problems, the first aspect of this invention provides a method for classifying and determining the carbon content of lithium iron phosphate remediation materials, comprising the following steps: S1. Add lithium iron phosphate repair material to organic solvent, use concentric twin-shaft dispersing mixer to stir and disperse, dissolve PVDF in lithium iron phosphate repair material, dry the insoluble solid material, weigh and calculate the PVDF content and the first carbon content. S2. Add acid solution to solid material, heat to boiling, react for 1-2 hours, cool and filter after reaction to obtain carbon slag containing SP and coated carbon, dry, weigh and calculate second carbon content.

[0006] This invention defines the measurement steps and conditions. The core of the invention lies in utilizing the characteristic that PVDF is selectively soluble in organic solvents, while lithium iron phosphate, conductive carbon, and coated carbon are insoluble. By stirring and dispersing for 1-3 hours, the PVDF is ensured to be fully dissolved. After drying and weighing, the PVDF is accurately quantified by differential gravimetric method, avoiding errors caused by insufficient dissolution or solvent residue. Adding a mixed acid solution to the solid material and heating it to boiling for 1-2 hours is to quickly and thoroughly dissolve the lithium iron phosphate matrix without oxidation or loss of SP and coated carbon. The boiling temperature and reaction time can balance dissolution efficiency and carbon residue integrity. The cooling, filtration, and drying steps are used to remove the liquid phase and moisture, ensuring the accurate and reliable weighing of carbon residue.

[0007] This technical solution enables the classification and quantification of PVDF, SP, and coated carbon in lithium iron phosphate repair materials, fundamentally solving the bottleneck of traditional carbon-sulfur analyzers that can only measure total carbon and cannot distinguish carbon sources. The detection process uses only conventional laboratory equipment, significantly reducing equipment and usage costs. The classification and detection results can accurately guide the optimization of repair processes and the formulation of cell homogenization processes, improve the consistency of raw materials and the electrochemical performance of batteries, and provide stable, reliable, and easily accessible detection support for the high-value utilization of lithium iron phosphate repair materials.

[0008] As an implementable example, the organic solvents include NMP (N-methylpyrrolidone), DMF (N,N-methylpyrrolidone), etc. Dimethylformamide), DMAc (N,N) One or more of the following organic solvents are selected: dimethylacetamide (DMC), THF (tetrahydrofuran), DMSO (dimethyl sulfoxide), acetone, and butanone (methyl ethyl ketone); NMP is the preferred organic solvent in this invention. NMP is a commonly used strongly polar aprotic solvent in the lithium battery industry, exhibiting excellent solubility for PVDF. It does not dissolve lithium iron phosphate, conductive agents, or coated carbon. NMP can rapidly and completely dissolve PVDF at mild temperatures, ensuring clean separation. Simultaneously, NMP has high chemical stability and does not react with any component in the sample under stirring and drying conditions, without damaging the carbon structure or introducing impurities. Furthermore, NMP has a moderate boiling point and is easily removed by drying, facilitating subsequent solid-liquid separation and quantification by weighing without affecting detection accuracy.

[0009] As an feasible example, the mass ratio of lithium iron phosphate remediation material to organic solvent is (1-2):(90-120). This invention controls the material-to-liquid ratio at (1-2):(90-120), ensuring sufficient but not excessive organic solvent. Insufficient solvent leads to excessively high system viscosity, incomplete PVDF dissolution, and difficulty in solid-liquid separation, resulting in lower measurement results. Excessive solvent increases drying load, prolongs operation time, wastes reagents, and increases detection costs. This range provides a sufficient dissolution environment for PVDF, ensuring the polymer chains fully extend and completely detach from the solid phase, while maintaining appropriate solid content and viscosity, allowing for efficient and thorough filtration / centrifugation separation, avoiding residue and entrainment errors, and ultimately ensuring accurate PVDF content quantification and good method repeatability.

[0010] As an feasible example, the stirring temperature in step S1 is 40-50℃, the stirring time is 1-2 hours, and the stirring speed is 50-500 rpm. Too low a stirring temperature will result in a slow and incomplete dissolution rate of PVDF, leading to lower test results; too high a temperature will cause a large amount of NMP to volatilize, abnormal system viscosity, and may also introduce thermogravimetric errors. A temperature of 40-50℃ can significantly improve the swelling and dissolution efficiency of PVDF in organic solvents, allowing the long PVDF chains to fully extend and achieve complete desorption and dissolution.

[0011] As an feasible example, the drying temperature in step S1 is 130-140℃, and the drying time is 1-2 hours. The drying temperature is higher than the boiling point of NMP, which can quickly evaporate the solvent and avoid residues that could lead to an overestimation of the solid phase weight and an underestimation of the PVDF content. At the same time, the moderate temperature will not cause residual PVDF decomposition, carbon structure oxidation, or lithium iron phosphate phase transformation, thus ensuring the stability of the components.

[0012] As an example of implementation, the acid solution includes at least one of hydrochloric acid, nitric acid, and hydrofluoric acid; preferably, it is a mixed acid solution of hydrochloric acid and nitric acid.

[0013] Furthermore, the mass concentration of the acid in the acid solution is 10-30%. This invention selects at least one of hydrochloric acid, nitric acid, and hydrofluoric acid as the acid solution because these acids can rapidly and completely dissolve the lithium iron phosphate matrix under mild heating conditions, and do not oxidize or dissolve SP, CNT, or coated carbon at appropriate concentrations and temperatures, thus achieving efficient separation of the inorganic phase and carbon slag. Controlling the acid mass concentration at 10%-30% ensures sufficient dissolution of lithium iron phosphate and a moderate reaction rate, while avoiding excessive concentration that could lead to oxidation and loss of carbon components or accelerated equipment corrosion. Simultaneously, it prevents incomplete dissolution and deviations in detection results due to excessively low concentration, thus balancing dissolution effect, detection accuracy, and operational safety.

[0014] As an feasible example, the heating temperature in step S2 is 100-110℃, and the heating time is 1-2 hours. This invention limits the heating temperature of step S2 to 100-110℃ and the heating time to 1-2 hours. Its core function is to completely dissolve the lithium iron phosphate matrix under mild conditions without oxidation or loss of conductive and coated carbon, ensuring the integrity of the carbon residue and accurate test results. The temperature range of 100-110℃ is close to the atmospheric boiling point of the hydrochloric acid-nitric acid mixture, which can significantly accelerate the acid dissolution rate of lithium iron phosphate and ensure complete matrix dissolution. If the temperature is below 100℃, the acid dissolution reaction is too slow and the dissolution is incomplete; if the temperature is above 110℃, it easily exacerbates acid volatilization and splashing, and may also cause slight oxidation of the carbon residue, resulting in lower test results. A heating time of 1-2 hours can ensure that lithium iron phosphate reacts fully and enters the liquid phase, avoiding interference from undissolved solid residues in the weighing of carbon slag. If the time is too short, the dissolution will be incomplete, and if the time is too long, the detection efficiency will be reduced and the acid consumption will be increased. 1-2 hours can balance the full dissolution, detection accuracy and operation efficiency, providing a stable and reliable basis for subsequent carbon slag quantification.

[0015] The second aspect of this invention provides an application of a method for classifying and determining the carbon content of lithium iron phosphate remediation materials, which can be applied to the recycling and remediation of lithium iron phosphate cathode materials.

[0016] Beneficial effects (I) This invention, through selective dissolution of PVDF and acid-soluble separation of the lithium iron phosphate matrix, can accurately distinguish and quantify PVDF, conductive carbon (SP / CNT), and coated carbon in lithium iron phosphate remediation materials, completely overcoming the shortcomings of traditional carbon-sulfur analyzers' high-temperature combustion method, which cannot identify carbon sources and can only measure total carbon content. This method can obtain the true content of each carbon component separately, providing more comprehensive and valuable data support for material quality evaluation, and significantly improving the scientific rigor and practicality of the test results.

[0017] (II) Traditional total carbon detection relies on carbon-sulfur analyzers costing 80,000 to 200,000 yuan, and also requires consumables such as combustion aids and high-purity oxygen, resulting in high maintenance costs. This invention only uses common laboratory equipment such as electronic balances, stirrers, drying ovens, and conventional glassware, without the need for large-scale precision instruments. It has low initial investment, low operating costs, and is easy to set up. The method has low requirements for site and operating environment, and can be directly used in various scenarios such as recycling companies, material plants, and battery cell factories, significantly lowering the threshold for quality testing of lithium iron phosphate remediation materials and facilitating widespread application.

[0018] (III) This invention is carried out entirely under low temperature, normal pressure, and non-strong oxidation conditions. The PVDF dissolution temperature is 40-50℃, and the acid dissolution temperature is 100-110℃. This will not cause oxidation, ablation, or loss of conductive carbon and coated carbon, nor will it trigger a phase change in lithium iron phosphate components. The organic solvent and mixed acid system are stable, with strong separation selectivity and thorough solid-liquid separation. Errors in the drying and weighing processes are controllable, ensuring high consistency of results from multiple parallel experiments. The method's precision, accuracy, and stability are significantly better than the traditional high-temperature combustion method, meeting the data reliability requirements for material quality control and process optimization.

[0019] (iv) By classifying and measuring the content of PVDF, conductive carbon, and coating carbon, the production end can clearly identify the impact of each carbon source on the material's processing performance and optimize repair processes such as debonding, cleaning, coating, and drying. For example, the debonding process can be adjusted based on the PVDF content to reduce the impact of residual adhesive; the carbon replenishment and recoating processes can be optimized based on the conductive carbon content to improve batch consistency. Stable and controllable carbon composition can significantly improve electrode processability, slurry stability, peel strength, and conductive network uniformity, bringing the quality of repaired materials close to that of new materials.

[0020] (v) Based on the classification and testing results, cell manufacturers can precisely design the homogenization process, conductive agent ratio, binder addition amount, and stirring regime to avoid problems such as poor rate performance, short cycle life, and large internal resistance fluctuations caused by unreasonable carbon source ratios. Clear carbon composition information can help cell manufacturers stabilize production, improve battery consistency and safety, and enable lithium iron phosphate remediation materials not only to be used in low-end energy storage fields, but also to enter mid-to-high-end application scenarios such as power batteries and small power tools, significantly increasing the added value of recycled materials and promoting the development of the lithium iron phosphate recycling industry towards high value, refinement, and large scale. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the classification and determination method for carbon content in lithium iron phosphate remediation materials in Examples 1-2. Detailed Implementation

[0022] Example 1 The first aspect of this example provides a method for classifying and determining the carbon content of lithium iron phosphate remediation materials, including the following steps: S1. Add 1.5000±0.01g of lithium iron phosphate repair material to 100g of NMP, and stir and disperse at 40℃ using a concentric twin-shaft dispersing mixer for 2h. The stirring speed is 80rpm and the dispersion speed is 1200rpm to dissolve the PVDF in the lithium iron phosphate repair material. Dry the insoluble solid material at 135℃ for 2h, weigh and calculate the PVDF content and the first carbon content. S2. Add 50 mL of acid solution (containing 13 wt% hydrochloric acid + 10 wt% nitric acid) to the solid material, heat to boiling, react for 1 h, cool and filter after the reaction to obtain carbon slag containing SP and coated carbon, dry, weigh and calculate the second carbon content.

[0023] The typical carbon content of lithium iron phosphate coating is 1.3%. The content of SP (CNT) and coating carbon can be fuzzily quantified through calculation. Actual testing yielded a PVDF mass content of 1.82%, and the total mass content of SP (CNT) plus coating carbon was 1.74%.

[0024] The second aspect of this example provides an application of a method for classifying and determining the carbon content of lithium iron phosphate remediation materials, which can be applied to the recycling and remediation of lithium iron phosphate cathode materials.

[0025] Example 2 The first aspect of this example provides a method for classifying and determining the carbon content of lithium iron phosphate remediation materials, including the following steps: S1. Add 1.5000±0.01g of lithium iron phosphate repair material to 100g of NMP, and stir at 40℃ using a concentric biaxial dispersing mixer for 2h (if not dispersed here, the long chains of PVDF will not open and will not break, resulting in a higher solution viscosity). The stirring speed is 80rpm to dissolve the PVDF in the lithium iron phosphate repair material. Dry the insoluble solid material at 135℃ for 2h, weigh it, and calculate the PVDF content (high viscosity indicates incomplete solid-liquid separation, resulting in a higher final result and a lower PVDF content) and the first carbon content. S2. Add 50 mL of 10 wt% HF acid solution to the solid material, heat to boiling, react for 1 hour, cool and filter after the reaction to obtain carbon slag containing SP and coated carbon, dry, weigh and calculate the second carbon content.

[0026] In this example, the actual test yielded a PVDF content of 1.11% and a total SP (CNT) content plus coated carbon content of 2.41%.

[0027] The flowcharts for the classification test methods in Examples 1-2 are as follows: Figure 1 As shown.

[0028] Comparative Example 1 The first aspect of this example provides a method for classifying and determining the carbon content of lithium iron phosphate remediation materials, including the following steps: S1. Weigh 0.1g±0.005g of the lithium iron phosphate repair material sample and place it in a crucible. Add a multi-component flux (a mixture of tungsten granules, tin granules, and pure iron filings) to a total weight of 1.5g-1.6g. S2. Press the lifting button of the carbon-sulfur analyzer to lower the crucible. Use the crucible clamp to pick up the weighed sample and place it in the quartz crucible holder in the crucible holder. S3. Start the instrument and enter the analysis stage; each sample is tested in parallel. S4. After the test is completed, check the carbon and sulfur content, lower the lifting furnace, take out the crucible, repeat the test 3 times, and then click the "dust removal" button to clean 2-3 times to remove the fallen dust. S5. Test results: The actual measured total carbon content was 3.57%.

[0029] The present invention compares and tests the results of Examples 1 and 2 with Comparative Example 1. The results show that the carbon content classification and determination method of lithium iron phosphate remediation material provided by the present invention can achieve accurate quantification of PVDF, conductive carbon and coated carbon, and solves the technical defect of traditional carbon-sulfur analyzers that can only measure total carbon and cannot distinguish carbon sources. At the same time, it verifies the significant influence of process parameters and solvent selection on the detection results.

[0030] Example 1 employed the optimal NMP selective dissolution method for PVDF followed by hydrochloric / nitric acid mixed acid dissolution, yielding stable and reliable detection data: the PVDF content was 1.82%, and the total content of SP (CNT) and coated carbon was 1.74%. Combined with the typical value of 1.3% for coated carbon, the contributions of conductive carbon and coated carbon can be further distinguished. The results show clear component composition and reasonable numerical values, with the total carbon content closely matching the 3.57% of Comparative Example 1, demonstrating the high accuracy of this method and its ability to accurately reflect the actual distribution of various carbon sources in the sample.

[0031] Example 2 is a comparative process. In step S1, insufficient dispersion was not performed (the concentric twin-shaft mixer only stirred, not dispersed), resulting in incomplete dissolution of PVDF, high system viscosity, and incomplete solid-liquid separation. The final measured PVDF content was only 1.11%, significantly lower than in Example 1, indicating that stirring and dispersion are crucial for the complete extraction of PVDF. Meanwhile, in step S2, 10wt% hydrofluoric acid was used instead of mixed acid. Although it could dissolve lithium iron phosphate, the strong corrosiveness of HF led to the loss of some carbon components or excessive dissolution of the matrix. The measured SP (CNT) and total coated carbon content was higher than 2.41%, deviating from the true value. This further proves that the mixed acid system is more suitable for the complete preservation and accurate quantification of carbon slag.

[0032] Comparative Example 1 uses the traditional carbon-sulfur analyzer method, which can only obtain a total carbon content of 3.57%, and cannot distinguish the contents of PVDF, conductive carbon, and coated carbon. It cannot provide refined guidance for the repair process and cell preparation. Moreover, this method relies on expensive instruments and multi-element co-solvents, resulting in high detection costs and complex operation, making it unsuitable for rapid on-site detection of recycled materials.

[0033] In summary, Example 1 provides accurate detection results, clear component differentiation, mild conditions, and low cost, effectively guiding the development of recycling and homogenization processes for lithium iron phosphate remediation materials. Example 2 verifies that thorough dispersion and a mixed acid system are crucial for ensuring detection accuracy. Comparative Example 1 demonstrates that traditional total carbon detection methods suffer from information gaps, high costs, and insufficient practicality. Overall, the method of this invention significantly outperforms existing technologies in terms of classification detection, data accuracy, operating costs, and industrial application, exhibiting outstanding technical advantages.

Claims

1. A method for classifying and determining the carbon content of lithium iron phosphate remediation materials, characterized in that, Includes the following steps: S1. Add organic solvent to lithium iron phosphate repair material, use concentric twin-shaft dispersing mixer to disperse and dissolve PVDF in lithium iron phosphate repair material, dry the insoluble solid material, weigh and calculate the PVDF content and first carbon content. S2. Add acid solution to solid material, heat to boiling, react for 1-2 hours, cool and filter after reaction to obtain carbon slag containing SP and coated carbon, dry, weigh and calculate second carbon content.

2. The classification and determination method according to claim 1, characterized in that, The organic solvents include one or more of NMP, DMF, DMAc, THF, DMSO, acetone, and butanone.

3. The classification and determination method according to claim 1, characterized in that, The mass ratio of the lithium iron phosphate repair material to the organic solvent is (1-2): (90-120).

4. The classification and determination method according to claim 1, characterized in that, The stirring temperature in step S1 is 40-50℃.

5. The classification and determination method according to claim 1, characterized in that, The stirring time in step S1 is 1-2 hours.

6. The classification determination method according to claim 1, characterized in that, The drying temperature in step S1 is 130-140℃.

7. The classification determination method according to claim 1, characterized in that, The drying time in step S1 is 1-2 hours.

8. The classification determination method according to claim 1, characterized in that, The acid solution includes at least one of hydrochloric acid, nitric acid, and hydrofluoric acid.

9. The classification and determination method according to claim 1, characterized in that, The heating time in step S2 is 1-2 hours.

10. The application of a method for classifying and determining the carbon content of lithium iron phosphate remediation materials according to any one of claims 1-9, characterized in that, It is used in the recycling and repair of lithium iron phosphate cathode materials.

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