A progressive liquid-to-solid ratio convergence determination method for water-soluble fluoride content in lithium battery black powder

Abstract

This invention discloses a progressive liquid-solid ratio convergence determination method for the water-soluble fluoride content in lithium battery black powder. The method specifically includes: performing a first extraction with a standard liquid-solid ratio and detecting the fluoride content F1; performing an nth extraction with progressively increasing liquid-solid ratios and detecting the fluoride content Fn; calculating the fluoride content change rate Var_n and the standard content deviation rate Fpy_n between two adjacent extractions; terminating the extraction when Var_n ≤ Vt and Fpy_n ≤ 50%, where Vt is a preset threshold, and Fn is taken as the true water-soluble fluoride content Fbp of the black powder. The determination method provided by this invention can overcome solubility limitations, accurately determine the true total water-soluble fluoride content in the black powder, and calculate the amount of defluorinating agent to be added accordingly, achieving precise dosing of the solid fluoride process, effectively improving the defluorination treatment effect and product compliance rate of the black powder, while balancing detection costs and production application costs.

Description

Technical Field

[0001] This application belongs to the field of lithium-ion battery black powder technology, specifically relating to a progressive liquid-solid ratio convergence determination method for the water-soluble fluoride content in lithium battery black powder. Background Technology

[0002] Waste lithium-ion battery black powder is a core recycled raw material obtained from retired lithium-ion batteries through physical processes such as dismantling, sorting, and crushing. The content of its impurity components and effective metal components are key indicators determining the compliance of its import and resource utilization. Currently, the existing national standards in China clearly set access limits for the component content of waste lithium-ion battery black powder, specifically covering two core indicators: water-soluble fluoride impurities and main metal elements. Specifically, the water-soluble fluoride content in the black powder must be lower than the standard limit, while the lithium content in lithium iron phosphate battery black powder and the content of main metal elements such as lithium, nickel, and cobalt in ternary lithium-ion battery black powder must be higher than the standard limit. Only when all the above indicators meet the regulatory requirements can waste lithium-ion battery black powder be legally imported and subsequently processed and utilized.

[0003] Among the compliance testing indicators for lithium-ion battery black powder, water-soluble fluoride content is the most difficult to control and the key indicator with the most significant deviations in detection and regulation. The current national standard's standard method for testing water-soluble fluoride specifies fixed test conditions: weigh 100g of lithium-ion battery black powder sample, place it in 1L of deionized water, shake continuously for 18 hours, and then filter it. Finally, the concentration of fluoride ions in the filtrate is detected using a fluoride ion selective electrode, and the water-soluble fluoride content in the black powder is quantitatively calculated to determine whether the sample meets the standard.

[0004] The fluorine in lithium-ion battery black powder mainly originates from two core raw materials in the battery system: polyvinylidene fluoride (PVDF), the electrode binder, and lithium hexafluorophosphate (LiPF6), the electrolyte solute. The proportion of fluorine sources varies among different lithium-ion battery black powder systems. Specifically, in ternary lithium-ion battery black powder, binder-bound fluorine accounts for approximately 35% of the total fluorine content, while electrolyte-derived fluorine accounts for approximately 65%. In lithium iron phosphate battery black powder, binder-bound fluorine accounts for approximately 40% of the total fluorine content, while electrolyte-derived fluorine accounts for approximately 60%. Therefore, the electrolyte component is the main source of water-soluble fluorine in the black powder, and this portion of fluorine exists primarily as soluble lithium fluoride (LiF) salts.

[0005] According to physicochemical parameters, the solubility of lithium fluoride in water at 25℃ is approximately 1.5 g / L, corresponding to a theoretical upper limit of 1% soluble fluoride in 100g of lithium-ion battery black powder. Because the recycling and disposal of waste lithium-ion batteries involves multiple processes such as mechanical dismantling, physical sorting, organic solvent evaporation, and high-temperature pyrolysis, the occurrence and binding state of fluoride in the black powder are extremely complex, not simply a single soluble lithium fluoride salt form. Based on industry measurement data, the overall upper limit of total fluoride content in lithium-ion battery black powder is approximately 4%. Specifically, the upper limit of water-soluble fluoride content in black powder that has not undergone thermal pyrolysis is approximately 2.8%, while the upper limit of water-soluble fluoride content in black powder that has undergone thermal pyrolysis can reach 4%.

[0006] To meet national standards for water-soluble fluoride limits and achieve compliant utilization of spent lithium-ion battery black powder, the mainstream defluorination processes in the industry include three categories: water washing defluorination, thermal defluorination, and solid fluoride agent defluorination. Among them, solid fluoride agent defluorination has become a highly valuable defluorination technology solution in the industry due to its advantages of simple operation, low equipment investment, low processing cost, and strong adaptability. The core key to solid fluoride treatment lies in accurately matching the amount of solid fluoride agent added. The amount added must be strictly determined based on the actual total water-soluble fluoride content in the black powder. Insufficient solid fluoride agent will lead to incomplete defluorination, while excessive amount will result in waste of reagents and the introduction of new impurities, neither of which can meet the requirements for compliant treatment and resource utilization of black powder.

[0007] The core flaw in existing technologies lies in the fact that the industry generally uses the water-soluble fluoride data obtained from fixed-condition testing according to national standards as the benchmark for adding fluoride-fixing agents. This easily leads to the fluoride-fixing treatment effect being far below expectations, making it impossible to achieve stable compliance with standards for black powder. The reason for this is that the water-soluble fluoride testing method specified in the national standard uses a fixed liquid-to-solid ratio system (10mL:1g). This system is not an infinitely diluted aqueous solution environment. The testing process is limited by the solubility limit of metal fluorides (generally lithium fluoride), which cannot fully dissolve all the soluble fluoride in the black powder. The test value only represents a portion of the water-soluble fluoride content and cannot truly and completely characterize the actual total water-soluble fluoride content in the black powder.

[0008] Taking an extremely homogeneous sample as an example, if 2% of the fluorine in lithium-ion battery black powder exists entirely in the form of soluble lithium fluoride, when tested using the national standard fixed liquid-to-solid ratio method, only about 1% of the water-soluble fluoride content can be detected due to the limited solubility of lithium fluoride at room temperature. Based on this test data, the industry matches the dosage of solidifying fluoride agents, which can only precipitate and solidify the fluoride ions already dissolved in the system. The remaining undissolved lithium fluoride in the black powder will continue to dissolve in the water environment, keeping the water-soluble fluoride content in the system at the critical solubility value. Ultimately, this results in the water-soluble fluoride content of the black powder still exceeding the standard after solidifying fluoride treatment, failing to meet national standards for entry and use.

[0009] In summary, the national standard method for detecting water-soluble fluoride with a fixed liquid-to-solid ratio is suitable for standardized quality comparison and unified compliance assessment of different batches of lithium-ion battery black powder products, and can meet the standardized requirements for market access screening. However, this method has inherent limitations, and the test results are lower than the actual total water-soluble fluoride content of the black powder. In the process scenario of solid fluoride modification of black powder, relying on existing national standard test data to determine the dosage of solid fluoride agent will result in a serious mismatch between the agent dosage and the actual defluorination requirements, leading to poor solid fluoride defluorination effect and low product qualification rate, which seriously restricts the efficient and low-cost compliant resource utilization of waste lithium-ion battery black powder.

[0010] Therefore, there is an urgent need to develop a control technology that is compatible with solid fluoride processing and can accurately match the actual water-soluble fluoride content of black powder, so as to solve the pain points of existing technologies. Summary of the Invention

[0011] The purpose of this invention is to address the shortcomings of existing technologies by providing a detection and determination method suitable for the process scenario of adding defluorination agents to lithium-ion battery black powder for solid fluoride modification, which requires accurate acquisition of the true water-soluble fluoride content of the black powder. This method has the following advantages: it helps to overcome the systematic defects of existing methods and accurately obtain the true level of water-soluble fluoride content in lithium-ion battery black powder; it helps to accurately determine the amount of defluorination agent to be added, thereby improving the solid fluoride removal effect and product qualification rate; and it helps to understand the dynamic evolution law of water-soluble fluoride with liquid-solid ratio, thus balancing the detection cost and the cost of solid fluoride agent.

[0012] This invention provides a progressive liquid-to-solid ratio convergence determination method for the water-soluble fluoride content in lithium-ion battery black powder. This method is a progressive leaching detection method based on concentration convergence determination, used to determine the content of water-soluble fluoride, a component with limited solubility, in solid lithium-ion battery black powder, and includes the following steps: (1) Mix m1 g of lithium-ion battery black powder solid sample with the first volume V1 ml of extractant deionized water for the first extraction. The liquid-solid ratio is R1=V1:m1, unit ml / g. Detect the content of the target component water-soluble fluoride in the first extract and calculate the first content of water-soluble fluoride F1. (2) Increase the volume of deionized water as the extractant, perform the nth extraction, and detect the content of water-soluble fluoride, the target component, in the nth extract. Calculate the content F of water-soluble fluoride in the nth extraction. n Where n is a natural number greater than or equal to 2; (3) During the extraction process, calculate the rate of change V of the content of water-soluble fluoride, the target component, in the extract between two consecutive extractions. ar_n and standard content deviation rate F py_n The calculation formula is: , In the formula, F stIt is the upper limit requirement for water-soluble fluoride content specified in the standard, expressed as a percentage by mass. When the rate of change V ar_n Less than or equal to the preset threshold V t And the standard content offset rate F py_n When less than or equal to 50%, that is: V ar_n ≤V t And F py_n ≤50%, Then terminate the extraction, and determine the concentration of water-soluble fluoride F (n). n As a result of the measurement, the initial water-soluble fluoride content F of the lithium-ion battery black powder was obtained. bp =F n Otherwise, continue with the extraction process.

[0013] In the nth extraction process, the liquid-to-solid ratio R between the extractant deionized water and the lithium-ion battery black powder is... n =V n :m n R n The unit is ml / g, and it satisfies: Where n is a natural number greater than or equal to 2, and R1 is the liquid-to-solid ratio V1:m1 of the extractant deionized water and the lithium-ion battery black powder solid sample in the first extraction process; the preset threshold V t It is 5%-10%.

[0014] Preferably, it further includes: (4) Combining the initial water-soluble fluoride content F of lithium-ion battery black powder bp The upper limit requirement for water-soluble fluoride content specified in the standard F st The amount of fluoride reducing agent DF to be added is determined using the following formula: and In the formula, R DF It is the ratio of the mass of the fluoride reducing agent added to the mass of the lithium-ion battery black powder; F bp This refers to the water-soluble fluoride content (by mass) of the initial lithium-ion battery black powder; K sp It is a sparingly soluble fluoride, MeF n The solubility product constant; F st This refers to the upper limit requirement for water-soluble fluoride content specified in the standard, expressed as a percentage by mass; m is the mass of lithium-ion battery black powder sampled per 1L of aqueous solution, expressed in grams; t is the amount of sparingly soluble fluoride MeF. t The amount of fluorine in the molecular formula, t is a natural number 1, 2 or 3; M DF is the molecular weight of the defluorination agent; k is the addition coefficient of the defluorination agent; The fluoride reducing agent DF refers to a substance that can dissolve and release metal ions Me in aqueous solution and react rapidly with water-soluble fluoride ions to form insoluble fluoride MeF. t This reduces the water-soluble fluoride content in lithium-ion battery black powder.

[0015] In the process of determining the water-soluble fluoride content of lithium-ion battery black powder, the liquid-to-solid ratio R1 of the first extraction is the liquid-to-solid ratio specified in the standard. In the progressive leaching detection method, the leaching mode is oscillation and the detection method is fluoride ion selective electrode method.

[0016] The preset threshold V is the rate of change of the content of water-soluble fluoride, the target component, in two consecutive extractions. t Set to 5%-10%, this preset threshold V t This is based on a comprehensive consideration of the following factors: If the preset threshold V t If the threshold is set to less than 5%, another extraction may be required, increasing testing costs and reducing testing efficiency; if the preset threshold V is... t If the addition rate is set to greater than 10%, since the lower limit of the addition coefficient k of the defluorinating agent is 1.1, in this case, it is possible that the defluorinating agent is only 10% in excess, which is insufficient to fix and reduce the actual water-soluble fluoride content to exceed the detection value by more than 10%, which will lead to the water-soluble fluoride content exceeding the standard.

[0017] Among them, the deviation rate F of water-soluble fluoride standard content py Setting it to less than or equal to 50% is based on a comprehensive consideration of the following factors: Simply relying on the rate of change V of the target component water-soluble fluoride content in two adjacent extracts ar_n The criteria for determining whether extraction has been terminated have a key flaw: under conditions of high water-soluble fluoride content, even though the increase in water-soluble fluoride content between two consecutive measurements is not small (F... n -F n-1 However, compared to the previous water-soluble fluoride content (F) which had a high base, n-1 The rate of change V of water-soluble fluoride content between two consecutive tests. ar_n It can still reach a value less than or equal to the preset threshold V. t However, in this case, the increase in water-soluble fluoride content is far higher than the upper limit requirement for water-soluble fluoride content specified in the standard. st Therefore, it is necessary to limit the increase in water-soluble fluoride content between two consecutive tests relative to the upper limit requirement F for water-soluble fluoride content. st In this invention, the 50% value represents a balance between overall testing efficiency, cost, and the requirement for accurate determination of the defluorinating agent content.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects: (1) Eliminate the systematic errors of traditional detection systems and achieve accurate determination of the true content of water-soluble fluoride.

[0019] Current national standard testing methods for detecting water-soluble fluoride in lithium-ion battery powder using a fixed liquid-to-solid ratio parameter have inherent technical flaws. Fluorine in battery powder exists primarily as insoluble metallic fluorides such as lithium fluoride, nickel fluoride, and copper fluoride. Lithium fluoride, for example, has a solubility of only 1.5 g / L in water at 25°C. Under the standard-specified fixed liquid-to-solid ratio of 10 mL / g, when the water-soluble fluoride content in the sample is high, the extraction solution quickly reaches lithium fluoride saturation, preventing further dissolution of remaining soluble fluorides. This results in a false upper limit of approximately 1% in the detection results, with the detected value significantly lower than the true fluoride content of the sample, leading to a systematic detection bias.

[0020] The progressive liquid-solid ratio convergence determination detection method proposed in this invention uses two or more gradient extraction operations, with the adjacent detection content change rate Var_n and the standard content deviation rate Fpy_n as the determination criteria for iterative extraction. This method can completely restore the dynamic change law of water-soluble fluoride content in lithium-ion battery black powder as the liquid-solid ratio increases, accurately capture the dissolution characteristics of all soluble fluorides in the sample, effectively avoid the detection distortion problem caused by saturated dissolution limitation, eliminate the systematic defects of traditional detection methods from the root, and ensure that the detection results can truly reflect the actual water-soluble fluoride content level of the sample.

[0021] (2) Achieve precise matching of the amount of solid fluoride agent to improve the defluorination effect and resource utilization qualification rate of black powder.

[0022] Solid fluoride-based defluorination technology is the mainstream technology for compliant defluorination and resource-based treatment of lithium-ion battery black powder due to its advantages such as simple process, low equipment investment, low processing cost, and wide material compatibility. The core control point of the solid fluoride treatment process is the precise ratio of solid fluoride agent addition. The amount of agent used must be strictly matched with the actual water-soluble fluoride content of the black powder: insufficient agent dosage will lead to incomplete fluoride removal, and the fluoride content of the finished product will not meet the national standard limit requirements; excessive agent addition will not only cause material waste and increase processing costs, but also introduce impurities into the system, destroy the purity of the black powder material, and ultimately lead to substandard resource utilization of the product.

[0023] This invention utilizes a multi-stage extraction process with a gradient increasing liquid-to-solid ratio, combined with a dual-parameter collaborative judgment mechanism of Var_n and Fpy_n, to completely solve the technical pain points of insufficient fluoride dissolution and low test results in traditional single-stage fixed liquid-to-solid ratio extraction processes. It obtains true fluoride content data that is precisely matched with the national standard for water-soluble fluoride limit Fst, providing accurate data support for the quantitative addition of fluoride-fixing agents, achieving precise quantity control in the defluorination process, significantly improving the fluoride fixation and defluorination effect of black powder, and effectively improving the material compliance rate and resource utilization quality.

[0024] (3) Clarify the dynamic evolution of fluorine content and achieve a two-way balance between detection costs and production and application costs.

[0025] Current national standard testing methods set fixed parameters for black powder sampling quality and liquid-to-solid ratio. To ensure sample representativeness and avoid material composition deviations caused by small sample sizes, routine industry testing cannot arbitrarily reduce sample sizes. For black powder samples with unknown fluoride content, some industry scenarios employ an ultra-high liquid-to-solid ratio infinite dilution single-extraction testing method. While this can obtain high-precision fluoride content data, it has significant drawbacks: this testing mode uses a uniform ultra-high dilution standard for samples with both high and low fluoride content, resulting in extremely high solvent consumption and high testing costs; furthermore, this method only obtains the final fluoride content result and cannot reveal the evolution of water-soluble fluoride with changes in the liquid-to-solid ratio, lacking process reference value. The dosage of fluoride-fixing agents formulated based on this testing data is generally too high, easily leading to redundant and wasteful reagent resources and significantly increasing the cost of industrial defluorination treatment.

[0026] This invention utilizes a progressive gradient extraction detection mode to systematically summarize the dynamic evolution of water-soluble fluoride content in lithium-ion battery black powder with varying liquid-to-solid ratios. It can precisely terminate the detection process based on the actual fluoride leaching characteristics of the sample, eliminating the need for continuous ultra-high liquid-to-solid ratio extraction and significantly reducing solvent consumption and operational costs. Furthermore, the dosage of fluoride-fixing agent matched to the actual leaching patterns better aligns with actual production needs, accurately avoiding excessive reagent dosage. While ensuring the defluorination process meets standards, it effectively reduces the cost of industrial-scale fluoride treatment, achieving a multi-dimensional optimal balance between detection accuracy, detection cost, and production application cost. Attached Figure Description

[0027] Figure 1 This is a flowchart of the progressive liquid-to-solid ratio convergence determination method for the water-soluble fluorine content of lithium battery black powder according to the present invention. Detailed Implementation

[0028] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way.

[0029] Example 1 like Figure 1 As shown in the figure, this embodiment provides a progressive liquid-to-solid ratio convergence determination method for the water-soluble fluoride content of lithium battery black powder, as detailed below: A ternary lithium-ion battery black powder, type A, was selected, and its true water-soluble fluoride content was determined by testing. Based on this, the amount of fluoride-reducing agent to be added was determined. The upper limit requirement for the water-soluble fluoride content of ternary lithium-ion battery black powder stipulated by national standards is F. st =0.40% (mass percentage).

[0030] First, the first extraction was carried out according to the liquid-solid ratio R1=10ml / g specified in the standard. Specifically, m1=100g of lithium-ion battery black powder solid sample was mixed with the first volume V1=1000ml of deionized water as the extraction agent, and the mixture was turned and shaken for 17.5 hours. Then, the filtrate was taken and the water-soluble fluoride content was detected by the fluoride ion selective electrode method. The first water-soluble fluoride content F1=0.76% was calculated.

[0031] Secondly, the volume of deionized water as the extraction agent was increased for a second extraction. The liquid-to-solid ratio for the second extraction was R2 = 2R1 = 20 ml / g, that is, 100 g of lithium-ion battery black powder solid sample (m2) was mixed with 2000 ml of deionized water as the extraction agent, and the mixture was shaken for 18 hours. The filtrate was then collected and the water-soluble fluoride content was detected using a fluoride ion selective electrode method. The calculated second water-soluble fluoride content F2 = 0.83% was obtained. Simultaneously, the rate of change V of the water-soluble fluoride content between the two extractions was calculated. ar_2 and standard content deviation rate F py_2 The calculation formula is as follows: , , Therefore, V ar_2 ≤V t And F py_2 ≤50%, where the preset threshold V t The initial water-soluble fluoride content F2 of the ternary lithium-ion battery black powder A was 10%. The extraction was terminated, and the water-soluble fluoride content F2 was used as the determination result. bp =F2=0.83%.

[0032] Finally, MgSO4 was selected as the defluorination agent DF. This defluorination agent has a high solubility driving force, and releases metal ions Mg upon dissolving in aqueous solution. 2+ and water-soluble F - The rapid reaction generates the insoluble fluoride MgF2. When testing the water-soluble fluoride content of lithium-ion battery black powder, it can achieve full, rapid, and irreversible precipitation of fluoride ions in a very short time and under limited dissolution and diffusion conditions, so as to avoid exceeding the test results.

[0033] Based on the initial water-soluble fluoride content F of the ternary lithium-ion battery black powder A bp =0.83%, and the standard specifies an upper limit for water-soluble fluoride content F. st The amount of fluoride reducing agent DF can be determined by calculating its concentration as 0.40%, as detailed below: and In the formula, R DF =1.76% is the ratio of the mass of the fluoride reducing agent added to the mass of the lithium-ion battery black powder; K sp=6.5×10 -9 M is the solubility product constant of MgF2; m=100 is the mass of lithium-ion battery black powder sampled per 1L of aqueous solution as specified in the standard, in grams; t is the amount of fluorine in the molecular formula of the sparingly soluble fluoride MgF2, t=2; M DF =120.3 is the molecular weight of the defluorinating agent.

[0034] According to the determined ratio of defluorinating agent R DF =1.76%, the fluoride reducing agent was weighed and mixed with ternary lithium-ion battery black powder A, and then conditioned. The water-soluble fluoride content of the conditioned lithium-ion battery black powder A was then tested according to the sampling and testing methods specified in national standards. The water-soluble fluoride content of the conditioned ternary lithium-ion battery black powder A was ≤0.35%F. st =0.40%.

[0035] As can be seen from Example 1, by adopting the technical solution of the present invention, the true level of water-soluble fluoride content in lithium-ion battery black powder can be obtained relatively efficiently and at low cost, and it matches the requirement of determining the content of solid fluoride agent, so that the water-soluble fluoride content of the tempered lithium-ion battery black powder can meet the national standard requirements by using the simple method of adding solid fluoride agent.

[0036] Example 2 This embodiment provides a progressive liquid-to-solid ratio convergence determination method for the water-soluble fluoride content of lithium battery black powder, as detailed below: A lithium iron phosphate battery black powder B was selected, and its true level of water-soluble fluoride content was determined by testing. Based on this, the amount of fluoride-reducing agent to be added was determined. The upper limit requirement for the water-soluble fluoride content of lithium iron phosphate battery black powder stipulated by national standards is F. st =0.10% (percentage by mass).

[0037] First, the first extraction was carried out according to the liquid-solid ratio R1=10ml / g specified in the standard. Specifically, 100g of solid sample of lithium iron phosphate battery black powder B was mixed with the first volume V1=1000ml of deionized water as the extraction agent, and the mixture was turned and shaken for 18 hours. Then, the filtrate was taken and the water-soluble fluoride content was detected by the fluoride ion selective electrode method. The first water-soluble fluoride content F1=0.54% was calculated.

[0038] Secondly, the volume of deionized water as the extraction agent was increased for a second extraction. The liquid-to-solid ratio for the second extraction was R2 = 2R1 = 20 ml / g. Specifically, 100 g of solid lithium iron phosphate battery black powder B sample (m2) was mixed with 2000 ml of deionized water as the extraction agent. The mixture was then shaken for 18 hours. The filtrate was then analyzed using a fluoride ion-selective electrode method to determine the water-soluble fluoride content. The calculated second water-soluble fluoride content F2 = 0.57%. Finally, the rate of change V between the two water-soluble fluoride content analyses was calculated. ar_2and standard content deviation rate F py_2 , , , Therefore, V ar_2 ≤V t And F py_2 ≤50%, where the preset threshold V t The initial water-soluble fluoride content F of the lithium iron phosphate battery black powder B was 10%. The extraction was terminated, and the second water-soluble fluoride content F2 was used as the determination result. bp =F2=0.57%.

[0039] Finally, MgSO4 was selected as the defluorination agent DF. This defluorination agent has a high solubility driving force, and releases metal ions Mg upon dissolving in aqueous solution. 2+ and water-soluble F - The rapid reaction generates the insoluble fluoride MgF2. When testing the water-soluble fluoride content of lithium-ion battery black powder, it can achieve full, rapid, and irreversible precipitation of fluoride ions in a very short time and under limited dissolution and diffusion conditions, so as to avoid exceeding the test results.

[0040] Combined with the initial water-soluble fluoride content F of the lithium iron phosphate battery black powder B bp =0.57%, and the standard specifies an upper limit for water-soluble fluoride content F. st The amount of fluoride reducing agent DF can be determined by calculating its concentration as 0.10%, as detailed below: and In the formula, R DF =2.02% is the ratio of the mass of the fluoride reducing agent added to the mass of the lithium-ion battery black powder; K sp =6.5×10 -9 M is the solubility product constant of MgF2; m=100 is the mass of lithium-ion battery black powder sampled per 1L of aqueous solution as specified in the standard, in grams; t is the amount of fluorine in the molecular formula of the sparingly soluble fluoride MgF2, t=2; M DF =120.3 is the molecular weight of the defluorinating agent.

[0041] According to the determined ratio of defluorinating agent R DF =2.02%, the fluoride reducing agent was weighed and mixed with lithium iron phosphate battery black powder B, and then conditioned. The water-soluble fluoride content of the conditioned lithium-ion battery black powder B was then tested according to the sampling and testing methods specified in national standards. The water-soluble fluoride content of the conditioned lithium iron phosphate battery black powder B was ≤0.08%F. st =0.10%.

[0042] As can be seen from Example 2, by adopting the technical solution of the present invention, the true level of water-soluble fluoride content in lithium-ion battery black powder can be obtained relatively efficiently and at low cost, and it matches the requirement of determining the content of solid fluoride agent, so that the water-soluble fluoride content of the tempered lithium-ion battery black powder can meet the national standard requirements by using the simple method of adding solid fluoride agent.

[0043] Example 3 This embodiment provides a progressive liquid-to-solid ratio convergence determination method for the water-soluble fluoride content in lithium battery black powder, as detailed below: A ternary lithium-ion battery black powder, C, was selected, and its true water-soluble fluoride content was determined by testing. Based on this, the amount of fluoride-reducing agent to be added was determined. The upper limit requirement for the water-soluble fluoride content of ternary lithium-ion battery black powder stipulated by national standards is F. st =0.40% (mass percentage).

[0044] First, the first extraction was carried out according to the standard liquid-to-solid ratio R1=10ml / g. Specifically, 100g of lithium-ion battery black powder solid sample was mixed with 1000ml of deionized water as the first extraction agent, and the mixture was turned and shaken for 18.5 hours. Then, the filtrate was taken and the water-soluble fluoride content was detected by the fluoride ion selective electrode method. The first water-soluble fluoride content F1 was calculated to be 1.38%.

[0045] Secondly, the volume of deionized water as the extraction agent was increased for a second extraction. The liquid-to-solid ratio for the second extraction was R2 = 2R1 = 20 ml / g, meaning that 100 g of lithium-ion battery black powder solid sample (m2) was mixed with 2000 ml of deionized water as the first extraction agent, and the mixture was shaken for 18 hours. The filtrate was then analyzed using a fluoride ion-selective electrode method to determine the water-soluble fluoride content, and the second water-soluble fluoride content F2 was calculated to be 1.63%. The rate of change V of the water-soluble fluoride content between the two extractions was calculated. ar_2 and standard content deviation rate F py_2 , , , Therefore, V ar_2 >V t And F py_2 >50%, where the preset threshold V t The concentration was 10%, and a third extraction was performed. The liquid-to-solid ratio for the third extraction was R3 = 3R1 = 30 ml / g, meaning that 100 g of lithium-ion battery black powder solid sample (m3) was mixed with 3000 ml of deionized water (V3) as the extraction solvent. The mixture was shaken for 18 hours, and the filtrate was then analyzed using a fluoride ion selective electrode method to determine the water-soluble fluoride content. The calculated third water-soluble fluoride content was F3 = 1.72%. Simultaneously, the rate of change V between the second and third water-soluble fluoride contents was calculated.ar_3 and standard content deviation rate F py_3 The calculation formula is as follows: , , Therefore, V ar_3 ≤V t And F py_3 ≤50%, where the preset threshold V t The extraction was stopped at 10%, and the initial water-soluble fluoride content F3 of the ternary lithium-ion battery black powder C was determined using the third water-soluble fluoride content F3. bp =F3=1.72%.

[0046] Finally, CaSO4 was selected as the defluorination agent DF. This defluorination agent has a much higher solubility driving force than CaF2. The defluorination agent dissolves in aqueous solution and releases metal ions Ca. 2+ and water-soluble F - The rapid reaction generates insoluble fluoride CaF2. When testing the water-soluble fluoride content of lithium-ion battery black powder, it can achieve full, rapid, and irreversible precipitation of fluoride ions in a very short time and under limited dissolution and diffusion conditions, so as to avoid exceeding the test results.

[0047] Based on the initial water-soluble fluoride content F of the black powder C in this ternary lithium-ion battery bp =1.72%, and the standard specifies an upper limit for water-soluble fluoride content F. st The amount of fluoride reducing agent DF can be determined by calculating its concentration as 0.40%, as detailed below: and In the formula, R DF =5.41% is the ratio of the mass of the fluoride reducing agent added to the mass of the lithium-ion battery black powder; K sp =2.7×10 -11 M is the solubility product constant of CaF2; m=100 is the mass of lithium-ion battery black powder sampled per 1L of aqueous solution as specified in the standard, in grams; t is the amount of fluorine in the molecular formula of the sparingly soluble fluoride CaF2, t=2; M DF =136 is the molecular weight of the defluorinating agent.

[0048] According to the determined ratio of defluorinating agent R DF =5.41%, the fluoride reducing agent was weighed and mixed with ternary lithium-ion battery black powder C, and then conditioned. The water-soluble fluoride content of the conditioned battery black powder C was then tested according to the sampling and testing methods specified in national standards. The water-soluble fluoride content of the conditioned ternary lithium-ion battery black powder C was ≤0.36%F. st =0.40%.

[0049] As can be seen from Example 3, by adopting the technical solution of the present invention, the true level of water-soluble fluoride content in lithium-ion battery black powder can be obtained relatively efficiently and at low cost, and it matches the requirement of determining the content of solid fluoride agent, so that the water-soluble fluoride content of lithium-ion battery black powder after conditioning can meet the national standard requirements by using the simple method of adding solid fluoride agent.

[0050] The above provides a detailed description of a progressive liquid-to-solid ratio convergence determination method for the water-soluble fluoride content in lithium battery black powder, as provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the core ideas of this application. It should be noted that those skilled in the art can make various improvements and modifications to this application without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A progressive liquid-to-solid ratio convergence determination method for the water-soluble fluoride content in lithium battery black powder, characterized in that, The convergence determination method is a progressive leaching detection method based on concentration convergence determination, used to determine the content of water-soluble fluoride in lithium-ion battery black powder solids, including the following steps: (1) Mix m1 g of lithium-ion battery black powder solid sample with V1 ml of first volume of extractant deionized water for the first extraction, wherein the liquid-solid ratio is R1=V1:m1, unit ml / g; detect the content of water-soluble fluoride in the first extract and calculate the first content of water-soluble fluoride F1. (2) Increase the volume of deionized water as the extractant, perform the nth extraction, and detect the content of water-soluble fluoride, the target component, in the nth extract. Calculate the content F of water-soluble fluoride in the nth extraction. n Where n is a natural number greater than or equal to 2; (3) Calculate the rate of change V of the water-soluble fluoride content of the target component in two consecutive extracts. ar_n and standard content deviation rate F py_n The calculation formula is: ， ， In the formula, F st It is the upper limit requirement for water-soluble fluoride content specified in the standard, expressed as a percentage by mass. When the rate of change V ar_n Less than or equal to the preset threshold V t And the standard content offset rate F py_n When less than or equal to 50%, that is: V ar_n ≤V t And F py_n ≤50%, Then terminate the extraction, and determine the concentration of water-soluble fluoride F. n As a result of the measurement, the initial water-soluble fluoride content F of the lithium-ion battery black powder was obtained. bp =F n Otherwise, continue with the extraction process.

2. The progressive liquid-to-solid ratio convergence determination method for water-soluble fluoride content in lithium battery black powder according to claim 1, characterized in that, In the nth extraction process, the liquid-to-solid ratio R between the extractant (deionized water) and the lithium-ion battery black powder solid sample is... n =V n :m n R n The unit is ml / g, and it satisfies: Where n is a natural number greater than or equal to 2, and R1 is the liquid-to-solid ratio V1:m1 of the extractant deionized water and the lithium-ion battery black powder solid sample in the first extraction process; the preset threshold V t It is 5%-10%.

3. The progressive liquid-to-solid ratio convergence determination method for the water-soluble fluoride content in lithium battery black powder according to claim 1 or 2, characterized in that, Also includes: (4) Combining the initial water-soluble fluoride content F of lithium-ion battery black powder bp The upper limit requirement for water-soluble fluoride content specified in the standard F st The amount of fluoride reducing agent DF to be added is determined using the following formula: and In the formula, R DF It is the ratio of the mass of the fluoride reducing agent added to the mass of the lithium-ion battery black powder; F bp This refers to the water-soluble fluoride content (by mass) of the initial lithium-ion battery black powder; K sp It is a sparingly soluble fluoride, MeF n The solubility product constant; F st is the upper limit requirement for water-soluble fluoride content specified in the standard, expressed as a percentage by mass; m is the mass of lithium-ion battery black powder sampled per 1L of aqueous solution specified in the standard, expressed in grams. t is the sparingly soluble fluoride MeF t The amount of fluorine in the molecular formula, t is a natural number 1, 2 or 3; M DF is the molecular weight of the defluorination agent; k is the addition coefficient of the defluorination agent; The fluoride reducing agent DF refers to a substance that can dissolve and release metal ions Me in aqueous solution and react rapidly with water-soluble fluoride ions to form insoluble fluoride MeF. t This reduces the water-soluble fluoride content in lithium-ion battery black powder.

4. The progressive liquid-to-solid ratio convergence determination method for the water-soluble fluoride content in lithium battery black powder according to claim 1 or 2, characterized in that, In the determination of the water-soluble fluoride content of lithium-ion battery black powder, the liquid-to-solid ratio R1 of the first extraction is the liquid-to-solid ratio specified in the standard; the F in the convergence criterion py_n ≤50% is based on the standard limit F st The acceptable range of deviation.

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