Method for determining lithium content of failed lithium iron phosphate positive electrode powder based on lithium hydroxide assisted sintering-potentiometric titration combination

Abstract

This invention relates to a method for determining the lithium content of spent lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering and potentiometric titration. The method involves mixing spent lithium iron phosphate cathode powder with lithium hydroxide powder; sintering the mixture at high temperature; pulverizing the sintered product and dissolving it in a measured amount of deionized water; using hydrochloric acid standard solution as the titrant, potentiometric titration of the test solution is performed, and the amount of hydrochloric acid standard solution consumed is recorded. The residual alkali content in the test solution is calculated based on the concentration of the hydrochloric acid standard solution. The amount of lithium hydroxide involved in the reaction is calculated using stoichiometry based on the total amount of lithium hydroxide added and the amount of unreacted lithium hydroxide, and the lithium content in the spent lithium iron phosphate cathode powder is then derived. The beneficial effect is that by leveraging the synergistic reaction between excess lithium hydroxide and lithium in spent lithium iron phosphate, combined with the precise detection advantages of potentiometric titration, efficient and accurate determination of the lithium content in spent lithium iron phosphate cathode powder is achieved.

Description

Technical Field

[0001] This invention relates to the field of battery recycling and elemental analysis technology, specifically to a method for determining the lithium content of failed lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering-potential titration. Background Technology

[0002] Lithium iron phosphate (LFP) batteries are widely used in new energy vehicles and energy storage due to their advantages such as high safety, good cycle performance, and low cost. As power batteries reach the end of their lifespan, a large amount of spent LFP cathode material is generated. Recycling this material can not only alleviate resource shortages but also reduce environmental pollution. Lithium, as a key element in LFP cathode material, has a content that is a core indicator for evaluating the recycling value of spent cathode material. Therefore, establishing an efficient and accurate method for determining lithium content is of great significance.

[0003] Existing methods for determining the lithium content in failed lithium iron phosphate cathode materials mainly include inductively coupled plasma atomic emission spectrometry (ICP-AES) and atomic absorption spectrometry (AAS). These methods typically require complex digestion processes on the samples, such as high-temperature digestion using a mixed acid of sulfuric acid, perchloric acid, and hydrogen peroxide. The procedures are cumbersome, time-consuming, and require expensive large-scale analytical instruments. In addition, some methods may have errors in their measurement principles, leading to significant deviations in the measurement results.

[0004] Potentiometric titration is an analytical method based on a potential jump to determine the titration endpoint. It has advantages such as simple operation, high accuracy, and no need for complex pretreatment. It has been applied to the determination of indicators such as residual alkali content. However, there are currently no reports on the application of potentiometric titration to the determination of lithium content in spent lithium iron phosphate cathode powder. Summary of the Invention

[0005] To address the problems of cumbersome operation, high cost, and significant impact on accuracy of existing methods for determining the lithium content in failed lithium iron phosphate cathode powder, this invention provides a method for determining the lithium content in failed lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering and potentiometric titration, thereby overcoming the shortcomings of the prior art.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A method for determining the lithium content of spent lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering-potentiometric titration includes the following steps: S10, Material mixing: The spent lithium iron phosphate cathode powder and lithium hydroxide powder are mixed in a set ratio to obtain a uniform mixture. S20, high-temperature sintering: Under an inert gas atmosphere, the mixture is sintered at high temperature and then naturally cooled to room temperature to obtain the sintered product. High-temperature sintering can promote the reaction between exhausted lithium iron phosphate and lithium hydroxide, so that lithium element exists stably in the product system. At the same time, it removes residual organic matter in the material and avoids interference with subsequent titration detection. S30, Determination of residual alkali content: The sintered product was crushed and dissolved in a measured amount of deionized water. After centrifugation and filtration to remove insoluble matter, a clear test solution was obtained. The test solution was potentiometrically titrated with hydrochloric acid standard solution as titrant, and the amount of hydrochloric acid standard solution consumed at the titration jump point was recorded. The residual alkali in the test solution was calculated by combining the concentration of hydrochloric acid standard solution. The residual alkali is the alkali content corresponding to the unreacted lithium hydroxide. S40, Lithium Content Derivation: Based on the total amount of lithium hydroxide added and the amount of unreacted lithium hydroxide corresponding to the measured residual alkali amount, the amount of lithium hydroxide participating in the reaction is calculated through stoichiometry. Then, based on the reaction mechanism of spent lithium iron phosphate and lithium hydroxide, the lithium content in the spent lithium iron phosphate cathode powder is derived.

[0007] Based on the above technical solution, the present invention can be further improved as follows.

[0008] Furthermore, the spent lithium iron phosphate cathode powder in S10 is pre-treated by impurity removal and drying. Impurity removal mainly removes impurities such as electrolyte and binder adhering to the surface, while drying mainly removes moisture.

[0009] Furthermore, the drying temperature is 105℃~120℃, and the drying time is 2h~4h.

[0010] Furthermore, in S10, the failed lithium iron phosphate cathode powder and lithium hydroxide powder are ball-milled and mixed using a planetary ball mill.

[0011] Furthermore, the ball milling speed is 200 r / min to 400 r / min, and the ball milling time is 30 min to 60 min.

[0012] Furthermore, the amount of lithium hydroxide powder added is 10% to 50% excess relative to the stoichiometric ratio required for the theoretical lithium content in the failed lithium iron phosphate cathode powder. The purpose of using excess lithium hydroxide is to ensure that the lithium in the failed lithium iron phosphate can react completely, while ensuring that there is residual lithium hydroxide after sintering, so as to deduce the lithium content by measuring the residual alkali content.

[0013] Furthermore, when sintering the mixture at high temperature, the mixture is first placed in an alumina crucible, and then placed in a sintering furnace. After sintering, the sintering furnace is closed and allowed to cool naturally to room temperature to obtain the sintered product.

[0014] Furthermore, the inert gas is nitrogen or argon, and the gas flow rate is 50 mL / min to 150 mL / min.

[0015] Furthermore, the sintering temperature is 500℃~700℃, and the sintering time is 2h~6h.

[0016] Further, in S30, the sintered product is pulverized to a particle size of less than 100 mesh using an agate mortar, a quantitative amount of deionized water is added, and the mixture is stirred on a magnetic stirrer for 30 min to 60 min to fully dissolve it. Then, the mixture is centrifuged and filtered to remove insoluble matter. The centrifugation speed is 3000 r / min to 5000 r / min to obtain a clear test solution.

[0017] Furthermore, the potentiometric titration uses a glass electrode as the indicator electrode and a saturated calomel electrode as the reference electrode. The titration endpoint is determined by a potential jump curve, with the pH value corresponding to the jump point being 8.3–4.3. The concentration of the hydrochloric acid standard solution is 0.1 mol / L–0.5 mol / L. The solution temperature during the titration is 25℃±2℃. The potential value and hydrochloric acid consumption are recorded in real time. Based on the potential jump curve, the titration endpoint is determined. Combined with the concentration of the hydrochloric acid standard solution, the residual alkali in the test solution is calculated. This residual alkali corresponds to the content of unreacted lithium hydroxide.

[0018] Furthermore, the specific derivation process is based on the following reaction principle: Lithium hydroxide reacts with hydrochloric acid to produce lithium chloride and water. The stoichiometric relationship is based on the neutralization reaction equation of lithium hydroxide and hydrochloric acid: LiOH·H2O+HCl=LiCl+2H2O. The amount of unreacted lithium hydroxide can be calculated based on the amount of hydrochloric acid consumed. The amount of unreacted lithium hydroxide is the amount of lithium hydroxide that reacts with lithium in the dead lithium iron phosphate by subtracting the total amount of lithium hydroxide added. That is, the amount of unreacted lithium hydroxide is calculated by the amount of residual alkali, and then combined with the total amount of lithium hydroxide added, the amount of lithium hydroxide that reacts with lithium in the dead lithium iron phosphate is obtained. Finally, the lithium content in the dead lithium iron phosphate cathode powder is finally deduced based on the conservation relationship of lithium element.

[0019] The beneficial effects of this invention are: 1) Simple operation, no need for complicated sample digestion: High-temperature sintering replaces the traditional acid digestion process, simplifying the sample pretreatment process, avoiding the use of multiple strong acid reagents, and reducing the difficulty of operation and safety risks; 2) High accuracy and reliable results: By using excess lithium hydroxide to ensure the complete reaction of lithium in the failed lithium iron phosphate, the residual alkali content is accurately determined by potentiometric titration. That is, by combining the precise detection advantages of potentiometric titration with the lithium content in the failed lithium iron phosphate cathode powder based on the stoichiometric relationship, the lithium content in the failed lithium iron phosphate cathode powder is deduced, thereby achieving efficient and accurate determination of the lithium content in the failed lithium iron phosphate cathode powder, effectively avoiding measurement deviations caused by the measurement principle, and improving the accuracy and reliability of the detection results. 3) Low cost and easy to promote: The operation process is simple, no complex sample digestion equipment is required, and the required equipment is conventional sintering furnace, potentiometric titrator, etc. No expensive large-scale analytical instruments are required. The amount of reagents used is small and the detection cost is low. It is suitable for laboratory and industrial batch detection, and provides key elemental analysis technology support for the recycling of spent lithium iron phosphate. Detailed Implementation

[0020] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0021] Example 1 A method for determining the lithium content of spent lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering-potentiometric titration includes the following steps: S10, Material mixing: Take a sample of expired lithium iron phosphate cathode powder, remove the electrolyte and binder from the surface of the expired lithium iron phosphate cathode powder, and then dry it in an oven at 110℃ for 3 hours to remove moisture. Then accurately weigh 100g of the dried expired lithium iron phosphate cathode powder as a sample, mix it with 10g of lithium hydroxide monohydrate powder, and ball mill it at 300r / min for 45min using a planetary ball mill to obtain a uniform mixture. S20, high-temperature sintering: The mixture was placed in an alumina crucible and then placed into a sintering furnace. Nitrogen gas was introduced at a flow rate of 100 mL / min, and the temperature was raised to 550 °C. Sintering was carried out for 6 hours to allow the lithium in the exhausted lithium iron phosphate to react with the excess lithium hydroxide and form a stable product. After sintering, the mixture was allowed to cool naturally to room temperature to obtain the sintered product. S30, Determination of residual alkali content: The sintered product was pulverized to a particle size of less than 100 mesh. 0.55 g of the pulverized sintered product was accurately weighed and added to 50 mL of deionized water. After stirring magnetically for 45 min, the mixture was centrifuged at 4000 r / min and then filtered to remove insoluble matter, resulting in a clear test solution. A potentiometric titrator was used with 0.2 mol / L hydrochloric acid standard solution as the titrant, a glass electrode as the indicator electrode, and a saturated calomel electrode as the reference electrode. The titration was performed at 25 °C. The hydrochloric acid consumption corresponding to the potential jump point was recorded as 2.28 mL. The mass of unreacted lithium hydroxide corresponding to the residual alkali was calculated to be 3.83 g. S40, Lithium Content Derivation: The total mass of lithium hydroxide monohydrate added is 10g, and the mass of unreacted lithium hydroxide is 3.83g. Therefore, the mass of lithium hydroxide that participated in the reaction is 6.17g. Based on the stoichiometric relationship, the lithium content in the failed lithium iron phosphate cathode powder is calculated to be 3.5%.

[0022] Example 2 A method for determining the lithium content of spent lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering-potentiometric titration includes the following steps: S10, Material mixing: Take a sample of expired lithium iron phosphate cathode powder, remove the electrolyte and binder from the surface of the expired lithium iron phosphate cathode powder, and then dry it in an oven at 105℃ for 4 hours to remove moisture. Then accurately weigh 100g of the dried expired lithium iron phosphate cathode powder as a sample, mix it with 15g of lithium hydroxide powder, and use a planetary ball mill at a speed of 200r / min for 60min to obtain a uniform mixture. S20, high-temperature sintering: The mixture was placed in an alumina crucible and then placed into a sintering furnace. Nitrogen gas was introduced at a flow rate of 100 mL / min, and the temperature was raised to 600 °C. Sintering was carried out for 4 hours to allow the lithium in the exhausted lithium iron phosphate to react with the excess lithium hydroxide and form a stable product. After sintering, the mixture was allowed to cool naturally to room temperature to obtain the sintered product. S30, Determination of residual alkali content: The sintered product was pulverized to a particle size of less than 100 mesh. 0.575 g of the pulverized sintered product was accurately weighed and added to 50 mL of deionized water. After stirring magnetically for 30 min, the mixture was centrifuged at 4000 r / min and then filtered to remove insoluble matter, resulting in a clear test solution. A potentiometric titrator was used with 0.1 mol / L hydrochloric acid standard solution as the titrant, a glass electrode as the indicator electrode, and a saturated calomel electrode as the reference electrode. The titration was performed at 23 °C. The hydrochloric acid consumption corresponding to the potential jump point was recorded as 13.41 mL. The mass of unreacted lithium hydroxide corresponding to the residual alkali was calculated to be 11.25 g. S40, Lithium Content Derivation: The total mass of lithium hydroxide added is 15g, and the mass of unreacted lithium hydroxide is 11.25g. Therefore, the mass of lithium hydroxide that participated in the reaction is 3.75g. Based on the stoichiometric relationship, the lithium content in the failed lithium iron phosphate cathode powder is calculated to be 3.9%.

[0023] Example 3 A method for determining the lithium content of spent lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering-potentiometric titration includes the following steps: S10, Material mixing: Take a sample of expired lithium iron phosphate cathode powder, remove the electrolyte and binder from the surface of the expired lithium iron phosphate cathode powder, and then dry it in an oven at 120℃ for 2 hours to remove moisture. Then accurately weigh 100g of dried expired lithium iron phosphate cathode powder as a sample, mix it with 20g of lithium hydroxide powder, and use a planetary ball mill at a speed of 400r / min for 30min to obtain a uniform mixture. S20, high-temperature sintering: The mixture was placed in an alumina crucible and then placed into a sintering furnace. Nitrogen gas was introduced at a flow rate of 50 mL / min, and the temperature was raised to 700 °C. Sintering was carried out for 2 hours to allow the lithium in the spent lithium iron phosphate to react with the excess lithium hydroxide and form a stable product. After sintering, the mixture was allowed to cool naturally to room temperature to obtain the sintered product. S30, Determination of residual alkali content: The sintered product was pulverized to a particle size of less than 100 mesh. 0.6 g of the pulverized sintered product was accurately weighed and added to 50 mL of deionized water. After stirring magnetically for 60 min, the mixture was centrifuged at 4000 r / min and then filtered to remove insoluble matter, resulting in a clear test solution. A potentiometric titrator was used with 0.3 mol / L hydrochloric acid standard solution as the titrant, a glass electrode as the indicator electrode, and a saturated calomel electrode as the reference electrode. The titration was performed at 27 °C. The hydrochloric acid consumption corresponding to the potential jump point was recorded as 4.53 mL. The mass of unreacted lithium hydroxide corresponding to the residual alkali was calculated to be 11.41 g. S40, Lithium Content Derivation: The total mass of lithium hydroxide added is 20g, and the mass of unreacted lithium hydroxide is 11.41g. Therefore, the mass of lithium hydroxide that participated in the reaction is 8.59g. Based on the stoichiometric relationship, the lithium content in the failed lithium iron phosphate cathode powder is calculated to be 3.1%.

[0024] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for determining the lithium content of failed lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering-potentiometric titration, characterized in that, Includes the following steps: S10, Material mixing: The spent lithium iron phosphate cathode powder was mixed with lithium hydroxide powder to obtain a mixture. S20, high-temperature sintering: The mixture was sintered at high temperature in an inert gas atmosphere and then naturally cooled to room temperature after sintering to obtain the sintered product. S30, Determination of residual alkali content: The sintered product was crushed and dissolved in a measured amount of deionized water. After centrifugation and filtration to remove insoluble matter, a clear test solution was obtained. The test solution was potentiometrically titrated with hydrochloric acid standard solution as titrant, and the amount of hydrochloric acid standard solution consumed at the titration jump point was recorded. The residual alkali in the test solution was calculated by combining the concentration of hydrochloric acid standard solution. The residual alkali is the alkali content corresponding to the unreacted lithium hydroxide. S40, Lithium Content Derivation: Based on the total amount of lithium hydroxide added and the amount of unreacted lithium hydroxide corresponding to the measured residual alkali amount, the amount of lithium hydroxide participating in the reaction is calculated through stoichiometry. Then, based on the reaction mechanism of spent lithium iron phosphate and lithium hydroxide, the lithium content in the spent lithium iron phosphate cathode powder is derived.

2. The method for determining the lithium content of failed lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering-potential titration as described in claim 1, characterized in that, The failed lithium iron phosphate cathode powder in S10 has been pre-treated by removing impurities and drying.

3. The method for determining the lithium content of failed lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering-potential titration as described in claim 2, characterized in that, The drying temperature is 105℃~120℃, and the drying time is 2h~4h.

4. The method for determining the lithium content of failed lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering-potential titration according to claim 1, 2, or 3, characterized in that, The failed lithium iron phosphate cathode powder and lithium hydroxide powder in S10 were mixed by ball milling using a planetary ball mill.

5. The method for determining the lithium content of failed lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering-potential titration as described in claim 4, characterized in that, The ball milling speed is 200 r / min to 400 r / min, and the ball milling time is 30 min to 60 min.

6. The method for determining the lithium content of failed lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering-potential titration according to any one of claims 1 to 5, characterized in that, The amount of lithium hydroxide powder added is 10% to 50% in excess of the stoichiometric ratio required for the theoretical lithium content in the failed lithium iron phosphate cathode powder.

7. The method for determining the lithium content of failed lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering-potential titration as described in claim 1, characterized in that, The inert gas is nitrogen or argon, and the gas flow rate is 50 mL / min to 150 mL / min.

8. The method for determining the lithium content of failed lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering-potential titration according to claim 1, characterized in that, The sintering temperature is 500℃~700℃, and the sintering time is 2h~6h.

9. The method for determining the lithium content of failed lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering-potential titration as described in claim 1, characterized in that, Potentiometric titration uses a glass electrode as the indicator electrode and a saturated calomel electrode as the reference electrode. The titration endpoint is determined by a potential jump curve, with the pH value corresponding to the jump point being 8.3 to 4.

3. The concentration of the hydrochloric acid standard solution is 0.1 mol / L to 0.5 mol / L, and the solution temperature during titration is 25℃ ± 2℃.

10. The method for determining the lithium content of failed lithium iron phosphate cathode powder based on lithium hydroxide-assisted sintering-potential titration according to claim 1, characterized in that, The stoichiometric relationship is based on the neutralization reaction equation of lithium hydroxide and hydrochloric acid: LiOH·H2O+HCl=LiCl+2H2O. The amount of unreacted lithium hydroxide is calculated by the amount of residual alkali, and then combined with the total amount of lithium hydroxide added, the amount of lithium hydroxide that reacted with lithium in the dead lithium iron phosphate is obtained, and finally the lithium content is derived.