Battery-grade ferrous oxalate and its preparation method

Abstract

This invention discloses battery-grade ferrous oxalate and its preparation method. The preparation method includes a precipitation reaction, aging treatment, solid-liquid separation and vacuum drying in sequence. By constructing a comprehensive control model covering the entire process of precipitation, aging and drying, the reaction parameters, aging conditions and drying kinetics are uniformly correlated to achieve simultaneous optimization and precise control of multiple performance indicators of the product, maintain the stability of battery-grade ferrous oxalate performance, and take into account purity, particle size and tap density.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to battery-grade ferrous oxalate and its preparation method. Background Technology

[0002] Ferrous oxalate is a key precursor for the preparation of lithium iron phosphate, the cathode material for lithium-ion batteries. Its purity, particle size distribution, and crystal morphology directly affect the electrochemical performance of the final battery product. Currently, the industrial synthesis of ferrous oxalate mainly employs a liquid-phase precipitation method, which typically involves mixing and reacting ferrous sulfate solution with oxalic acid solution under specific conditions. However, traditional processes suffer from significant batch-to-batch product quality fluctuations; furthermore, purity, particle size, and tap density are often mutually restrictive, making it difficult to simultaneously achieve high purity, small particle size, and high tap density.

[0003] Therefore, there is an urgent need for a method for preparing ferrous oxalate that can maintain product stability while taking into account purity, particle size, and tap density.

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

[0005] The purpose of this invention is to provide battery-grade ferrous oxalate and its preparation method, which is beneficial to maintaining the performance stability of battery-grade ferrous oxalate while taking into account purity, particle size and tap density.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides a method for preparing battery-grade ferrous oxalate, comprising sequentially performing a precipitation reaction, aging treatment, solid-liquid separation and vacuum drying, wherein the precipitation reaction comprises: adding the ferrous sulfate solution and the oxalic acid solution into a reaction vessel containing a base liquid and stirring, wherein the precipitation reaction satisfies formula (1):

[0007] In formula (1): V Fe The feed rate of ferrous sulfate solution is expressed in mL / min. V C The feed rate of oxalic acid solution is expressed in mL / min. V Fe,ref The reference value for the ferrous sulfate solution addition rate is 100 mL / min; V C,ref The reference value for the oxalic acid solution addition rate is 100 mL / min; N represents the stirring speed, in rpm; N ref The reference value for stirring speed is 200 rpm; Tr The precipitation reaction temperature is expressed in °C. T0 is the initial temperature of the bottom liquid, in °C; ΔT ref The reference value for the reaction temperature difference is 10°C; The aging treatment and the vacuum drying also satisfy equation (2):

[0008] In formula (2): T a The aging temperature is expressed in °C. t a The aging time is expressed in hours (h). pH refers to the acidity or alkalinity of the aging treatment system. T d The drying temperature is expressed in °C. t d Drying time, in hours (h).

[0009] In an optional implementation, the T r The temperature is 60-80℃.

[0010] In an optional implementation, T0 is 40-60°C; And / or, the N It is 200-250 rpm.

[0011] In an optional embodiment, the concentration of ferrous ions in the ferrous sulfate solution is 50-100 g / L; And / or, V Fe The flow rate is 50-300 mL / min.

[0012] In an optional embodiment, the concentration of the oxalic acid solution is 0.8-1.2 mol / L; And / or, V C 50-300 mL / min; And / or, the substrate solution is water or dilute sulfuric acid with a pH of 1.0–3.0; And / or, in the precipitation reaction step, ferrous sulfate and oxalic acid are simultaneously added to the reaction vessel at a molar ratio of 1:1.15~1.4.

[0013] In an optional embodiment, the pH is 1.5-3.5; And / or, the aging process includes adjusting the pH to 1.5-3.5 with sulfuric acid or sodium hydroxide.

[0014] In an optional implementation, the T a 50℃ < T a ≤80℃; And / or, the t a It takes 1-5 hours.

[0015] In an optional implementation, the T d Temperatures range from 80 to 120℃. And / or, the t d For 3-12 hours.

[0016] Secondly, the present invention provides a battery-grade ferrous oxalate prepared by the battery-grade ferrous oxalate preparation method described in any one of the foregoing embodiments, wherein the battery-grade ferrous oxalate has a purity greater than 99.5%, a D50 of 0.8-1.5 μm, and a tap density ≥ 0.85 g / cm³. 3 .

[0017] Thirdly, the present invention provides a method for determining parameters in the preparation method of battery-grade ferrous oxalate according to any one of the foregoing embodiments, including the process of preparing battery-grade ferrous oxalate by sequentially performing precipitation reaction, aging treatment, solid-liquid separation and vacuum drying using ferrous sulfate solution and oxalic acid solution as raw materials: determining any one of the following according to formula (1): the feeding rate of ferrous sulfate solution, the feeding rate of oxalic acid solution, the stirring speed, the precipitation reaction temperature and the initial temperature of the bottom liquid;

[0018] In formula (1): V Fe The feed rate of ferrous sulfate solution is expressed in mL / min. V C The feed rate of oxalic acid solution is expressed in mL / min. V Fe,ref The reference value for the ferrous sulfate solution addition rate is 100 mL / min; V C,ref The reference value for the oxalic acid solution addition rate is 100 mL / min; N The stirring speed is expressed in rpm. N ref The reference value for stirring speed is 200 rpm; T r The precipitation reaction temperature is expressed in °C. T 0 represents the initial temperature of the base liquid, in °C; Δ T ref The reference value for the reaction temperature difference is 10°C; And / or, determine any one of the aging temperature, aging time, aging pH, drying temperature and drying time according to formula (2);

[0019] In formula (2): T a The aging temperature is expressed in °C. t a The aging time is expressed in hours (h). pH refers to the acidity or alkalinity of the aging treatment system. T d The drying temperature is expressed in °C. t d The drying time is expressed in hours (h).

[0020] The present invention has the following beneficial effects: The battery-grade ferrous oxalate preparation method provided in this application constructs a comprehensive control model covering the entire process of precipitation, aging, and drying, and uniformly links precipitation reaction parameters, aging conditions, and drying kinetics to achieve simultaneous optimization and precise control of multiple performance indicators of the product, maintain the stability of battery-grade ferrous oxalate performance, and take into account purity, particle size, and tap density. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 SEM images of battery-grade ferrous oxalate prepared at PI1=2.1 and PI2=0.1 in Example 1; Figure 2 The XRD patterns of battery-grade ferrous oxalate prepared at PI1=2.1 and PI2=0.1 in Example 1 are shown. Figure 3 This is a process flow diagram for preparing battery-grade ferrous oxalate in Example 1. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0024] This invention also provides a method for preparing battery-grade ferrous oxalate, comprising a precipitation reaction, aging treatment, solid-liquid separation and vacuum drying performed sequentially, wherein the precipitation reaction comprises: adding the ferrous sulfate solution and the oxalic acid solution into a reaction vessel containing the base liquid and stirring, wherein the precipitation reaction satisfies formula (1):

[0025] In formula (1): V Fe The feed rate of ferrous sulfate solution is expressed in mL / min. V C The feed rate of oxalic acid solution is expressed in mL / min. V Fe,ref The reference value for the ferrous sulfate solution addition rate is 100 mL / min; V C,ref The reference value for the oxalic acid solution addition rate is 100 mL / min; N represents the stirring speed, in rpm; N ref The reference value for stirring speed is 200 rpm; T r The precipitation reaction temperature is expressed in °C. T0 is the initial temperature of the bottom liquid, in °C; ΔT ref The reference value for the reaction temperature difference is 10°C; The aging and vacuum drying steps also satisfy equation (2):

[0026] In formula (2): T a The aging temperature is expressed in °C. t a The aging time is expressed in hours (h). pH refers to the acidity or alkalinity of the aging treatment system. T d The drying temperature is expressed in °C. t d Drying time, in hours (h).

[0027] The battery-grade ferrous oxalate preparation method provided in this application constructs a comprehensive control model covering the entire process of precipitation, aging, and drying. This model unifies the correlation between precipitation reaction parameters, aging conditions, and drying kinetics, achieving simultaneous optimization and precise control of multiple performance indicators of the product. This maintains the stability of the battery-grade ferrous oxalate performance while also considering purity, particle size, and tap density. Specifically: Formula (1) correlates multiple dynamic parameters such as feeding rate, stirring intensity, and reaction temperature difference, breaking the traditional isolated control mode. By controlling the nucleation and growth rates, this model effectively overcomes the problem of not being able to simultaneously achieve high product purity and small particle size. When the PI1 value is controlled within the range of 0.8-3.0, such as 0.8, 1.04, 1.29, 1.53, 1.78, 2.02, 2.27, 2.51, 2.76, and 3.0, it can simultaneously ensure that the prepared battery-grade ferrous oxalate has low impurity content and ideal submicron particle size.

[0028] By using formula (2) to correlate aging parameters such as temperature, time, pH and drying parameters such as temperature and time, and PI2 is 0.05-0.15, for example 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, it can suppress the hard agglomeration of particles caused by rapid evaporation of surface solvent, ensuring that the product has high purity and qualified particle size while having high tap density, thereby improving the compaction density and energy density of subsequent lithium iron phosphate cathode materials.

[0029] The method presented in this application exhibits good process reproducibility and is suitable for digital production. It transforms complex process experience into a quantifiable mathematical model, greatly reducing the uncertainty of human operation and improving batch-to-batch stability and reproducibility, thus laying the foundation for realizing intelligent manufacturing and digital factories.

[0030] In an optional implementation, the T r The temperature range is 60-80℃, for example, 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃, and 80℃. This temperature range is beneficial for promoting the kinetic rate of the ferrous oxalate crystallization reaction, increasing the yield and improving the crystal morphology, and reducing the formation of by-products.

[0031] In an optional implementation, T0 is 40-60°C, for example 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, 52°C, 54°C, 56°C, 58°C, or 60°C. And / or, the N200-250 rpm, such as 200 rpm, 206 rpm, 211 rpm, 217 rpm, 222 rpm, 228 rpm, 233 rpm, 239 rpm, 244 rpm, 250 rpm.

[0032] Controlling the temperature of the base solution and the intensity of stirring is beneficial to the stable growth of crystal nuclei.

[0033] In an optional embodiment, the concentration of ferrous ions in the ferrous sulfate solution is 50-100 g / L, for example, 50 g / L, 54 g / L, 58 g / L, 62 g / L, 66 g / L, 70 g / L, 74 g / L, 78 g / L, 80 g / L, 84 g / L, 88 g / L, 92 g / L, 96 g / L, 100 g / L; V Fe The flow rate is 50-300 mL / min, for example, 50 mL / min, 100 mL / min, 150 mL / min, 200 mL / min, 250 mL / min, and 300 mL / min.

[0034] A ferrous sulfate solution concentration of 50-100 g / L and a flow rate of 50-300 mL / min are beneficial for improving reaction efficiency and product yield, while maintaining solution stability and preventing excessive precipitation that could lead to particle agglomeration.

[0035] In an optional embodiment, the concentration of the oxalic acid solution is 0.8-1.2 mol / L, for example 0.8 mol / L, 0.84 mol / L, 0.88 mol / L, 0.92 mol / L, 0.96 mol / L, 1.00 mol / L, 1.04 mol / L, 1.08 mol / L, 1.12 mol / L, 1.16 mol / L, 1.20 mol / L; V C The flow rate is 50-300 mL / min, such as 50 mL / min, 100 mL / min, 150 mL / min, 200 mL / min, 250 mL / min, and 300 mL / min, which can match the amount of ferrous iron to achieve precise control of the molar ratio, ensure complete reaction, reduce residues, and improve product purity.

[0036] And / or, the base solution is water or dilute sulfuric acid, which helps to inhibit ferrous hydrolysis and oxidation, maintain pH stability of the system, provide a clean reaction environment, and facilitate the acquisition of a homogeneous precursor. The pH of the base solution can be controlled within the range of 1.0–3.0, preferably 1.5–2.5, and the base solution can be deionized water, with a volume of 10%–30% of the total volume of the reaction system, preferably 15%–25%.

[0037] And / or, in the precipitation reaction step, ferrous sulfate and oxalic acid are simultaneously added to the reaction vessel at a molar ratio of 1:1.15 to 1.4, for example, 1:1.15, 1:1.2, 1:1.25, 1:1.3, 1:1.35, or 1:1.4.

[0038] Matching the amounts of ferrous ions and oxalic acid helps reduce excess reactants. Simultaneous addition controls the nucleation rate, resulting in ferrous oxalate crystals with uniform particle size and high purity.

[0039] In an optional implementation, the pH is 1.5-3.5, for example 1.5, 1.72, 1.94, 2.17, 2.39, 2.61, 2.83, 3.06, 3.28, 3.5; And / or, the aging process includes adjusting the pH to 1.5-3.5 with dilute sulfuric acid or sodium hydroxide.

[0040] This pH range helps maintain the stability of ferrous ions, preventing their hydrolysis and oxidation, while promoting uniform precipitation of ferrous oxalate, thus improving product purity and crystal quality.

[0041] In an optional implementation, the T a The temperature range is 50-80℃, such as 50℃, 53℃, 56℃, 59℃, 62℃, 65℃, 68℃, 71℃, 74℃, 77℃, and 80℃. This temperature range is conducive to crystal growth during the aging process, promotes the uniformity and integrity of the grains, reduces defects, and takes into account purity, grain size, and tap density.

[0042] And / or, the t a The aging time is 1-5 hours, for example, 1 hour, 1.5 hours, 2.0 hours, 2.5 hours, 3.0 hours, 3.5 hours, 4.0 hours, 4.5 hours, and 5.0 hours. Appropriate aging time ensures sufficient crystal growth, improves product purity and crystallinity, while avoiding excessively long aging times that could negatively impact product performance.

[0043] In an optional implementation, the T d The drying temperature should be between 80-120℃, such as 80℃, 83℃, 86℃, 90℃, 93℃, 96℃, 100℃, 103℃, 106℃, 110℃, 113℃, 116℃, and 120℃. Drying within this temperature range can effectively remove moisture while avoiding damage to the product structure or affecting its performance, thus ensuring the stability and purity of the product.

[0044] And / or, the t dThe drying time should be 3-12 hours, for example, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h, 10 h, 10.5 h, 11 h, 11.5 h, and 12 h. Sufficient drying time ensures complete removal of moisture, preventing residual moisture from affecting product quality and subsequent processing, while avoiding excessively long drying times that could negatively impact product performance.

[0045] This invention also provides a battery-grade ferrous oxalate prepared by the method described in any one of the foregoing embodiments, wherein the battery-grade ferrous oxalate has a purity greater than 99.5%, for example 99.6%, 99.7%, 99.8%, 99.9%, 99.95%, or 99.99%; a D50 of 0.8-1.5 μm, for example 0.8 μm, 0.88 μm, 0.95 μm, 1.03 μm, 1.10 μm, 1.18 μm, 1.25 μm, 1.33 μm, 1.40 μm, 1.48 μm, or 1.5 μm; and a tap density ≥ 0.85 g / cm³. 3 For example, 0.85 g / cm 3 0.90 g / cm 3 0.95 g / cm 3 1.00 g / cm 3 1.05 g / cm 3 1.10 g / cm 3 1.15 g / cm 3 1.20 g / cm 3 .

[0046] The present invention also provides a method for determining parameters in the preparation method of battery-grade ferrous oxalate according to any one of the foregoing embodiments, including the process of preparing battery-grade ferrous oxalate by sequentially performing precipitation reaction, aging treatment, solid-liquid separation and vacuum drying using ferrous sulfate solution and oxalic acid solution as raw materials: determining any one of the following according to formula (1): ferrous sulfate solution feeding rate, oxalic acid solution feeding rate, stirring speed, precipitation reaction temperature and initial temperature of bottom liquid;

[0047] In formula (1): V Fe The feed rate of ferrous sulfate solution is expressed in mL / min. V C The feed rate of oxalic acid solution is expressed in mL / min. VFe,ref The reference value for the ferrous sulfate solution addition rate is 100 mL / min; V C,ref The reference value for the oxalic acid solution addition rate is 100 mL / min; N The stirring speed is expressed in rpm. N ref The reference value for stirring speed is 200 rpm; T r The precipitation reaction temperature is expressed in °C. T 0 represents the initial temperature of the base liquid, in °C; Δ T ref The reference value for the reaction temperature difference is 10°C; And / or, determine any one of the aging temperature, aging time, aging pH, drying temperature and drying time according to formula (2);

[0048] In formula (2): T a The aging temperature is expressed in °C. t a The aging time is expressed in hours (h). pH refers to the acidity or alkalinity of the aging treatment system. T d The drying temperature is expressed in °C. t d The drying time is expressed in hours (h).

[0049] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0050] The test methods for ferrous oxalate purity, D50, tap density, particle size distribution, and batch stability involved in this application are as follows: The purity of ferrous oxalate was determined by inductively coupled plasma optical emission spectrometry (ICP-OES, GB / T 36590-2018) to determine the content of impurity elements and calculate the purity of ferrous oxalate.

[0051] Particle size (D90, D10, and D50) and particle size distribution were determined using a laser particle size analyzer (GB / T 19077-2016 "Particle Size Analysis by Laser Diffraction"). A D90 / D10 ratio of <3.0 met the requirements for battery-grade materials; a D90 / D10 ratio of 3.0–4.0 was basically usable; and a D90 / D10 ratio of >4.0 did not meet the requirements for battery-grade materials.

[0052] Tap density was determined using a tap density meter (GB / T 5162-2021 "Determination of Tap Density of Metal Powders").

[0053] Particle morphology and aggregation state: Observation and analysis were performed using scanning electron microscopy (SEM, GB / T 16594 2008).

[0054] Batch stability is determined by combining multiple batch sampling inspections of the fluctuation range of product purity, particle size D50, and tap density for each batch. If the fluctuation range of product purity, particle size D50, and tap density is all <1.0%, it is recorded as excellent; if the fluctuation range of one or more of the product purity, particle size D50, and tap density is 1.0%-3.0%, it is recorded as good; if the fluctuation range of one or more of the product purity, particle size D50, and tap density is >3.0%, it is recorded as poor.

[0055] Comparative Example 1 This comparative example provides a method for preparing battery-grade ferrous oxalate, specifically including the following steps: Raw material preparation: Prepare 80g / L (with Fe) 2+ (Calculated) ferrous sulfate solution and 1.0 mol / L oxalic acid solution.

[0056] Precipitation reaction: The base solution is 100ml of deionized water, and the temperature of the base solution is set. T 0 = 50℃, target reaction temperature T =55℃, stirring speed N =200rpm, add ferrous sulfate solution and oxalic acid solution to the bottom liquid, ferrous sulfate feed rate V Fe =90mL / min, oxalic acid feed rate V C =100mL / min.

[0057] Calculate and verify:

[0058] Aging treatment: After the precipitation reaction, adjust the above slurry to pH=2.5, and set... T a =60℃ t a=2h.

[0059] Solid-liquid separation: After aging, solid-liquid separation is performed, and the filter cake is washed with deionized water until the conductivity of the filtrate is ≤300μS / cm.

[0060] Vacuum drying: setting T d =85℃, to ensure the drying process index PI2 is within the range of 0.05-0.15, take the target value PI2=0.1, and calculate the required drying time. t d .

[0061]

[0062] The PI1 value of 0.45 is much smaller than 0.8, indicating that under the current stirring and temperature difference conditions, the feeding rate is too slow, the system is not sufficiently supersaturated, the crystals have grown excessively, the particle size is large (D50 = 2.0 μm), the morphology is incomplete, the product purity is 99.66%, and the tap density is 0.60 g / cm³. 3 .

[0063] Comparative Example 2 This comparative example is based on Comparative Example 1 with only minor adjustments. V Fe =300mL / min, V C =320mL / min.

[0064] Re-verify:

[0065] The aging reaction, solid-liquid separation and vacuum drying procedures are the same as those in Comparative Example 1.

[0066] This PI1 value is much greater than 3.0, indicating that under the current stirring and temperature difference conditions, the feeding rate is too fast, the instantaneous supersaturation of the system is too high, which can easily lead to explosive nucleation, excessively fine particles (D50=0.5μm), easy agglomeration, increased risk of impurity encapsulation, and may cause temperature fluctuations in the reaction system. The product purity is 97.88%, and the tap density is <0.85g / cm³. 3 .

[0067] Example 1 This embodiment is based on Comparative Example 1 with only minor adjustments. V Fe =200mL / min, V C =210mL / min.

[0068] Final verification:

[0069] The PI1 value falls within the range of 0.8-3.0, which meets the model requirements.

[0070] The aging reaction, solid-liquid separation, and vacuum drying procedures were the same as in Comparative Example 1. The resulting product had a purity of 99.71%, a D50 particle size of 1.05 μm, and a tap density of 1.03 g / cm³. 3 .

[0071] Comparative Example 3 This comparative example provides a method for preparing battery-grade ferrous oxalate, specifically including the following steps: Raw material preparation: Prepare 80g / L (with Fe) 2+ (Calculated) ferrous sulfate solution and 1.0 mol / L oxalic acid solution.

[0072] Precipitation reaction: The base solution is 120ml of deionized water, and the temperature of the base solution is set. T 0 = 50℃, target reaction temperature T =60℃.

[0073] Set stirring speed N =250rpm, add ferrous sulfate solution and oxalic acid solution to the bottom liquid, ferrous sulfate addition rate V Fe =250mL / min, oxalic acid feed rate V C =265mL / min.

[0074] Calculate and verify:

[0075] The aging reaction, solid-liquid separation and vacuum drying procedures are the same as in Example 1.

[0076] This PI1 value is much greater than 3.0, indicating that under the current stirring and temperature difference conditions, the feeding rate is too fast, the instantaneous supersaturation of the system is too high, the nucleation phenomenon is prominent, the particles are too fine (D50=0.6μm), and they are more prone to agglomeration. Impurity ions (such as SO4²⁻) are also present. - It is easily encapsulated, reducing the product purity to 96.58% and the tap density to 0.90 g / cm³. 3 .

[0077] Example 2 This embodiment is based on Comparative Example 3 with only minor adjustments. V Fe =190mL / min, V C =200mL / min.

[0078] Re-verify:

[0079] The PI1 value falls within the range of 0.8-3.0, which meets the model requirements.

[0080] The aging reaction, solid-liquid separation, and vacuum drying procedures were the same as in Example 1. The resulting product had a purity of 99.89%, a D50 particle size of 1.25 μm, and a tap density of 1.15 g / cm³. 3 .

[0081] Conclusion: Under optimized PI1 values ​​(close to 2.5) and drying conditions, the product purity, particle size, and tap density all reached excellent levels.

[0082] Comparative Example 4 This comparative example provides a method for preparing battery-grade ferrous oxalate, which differs from Example 2 only in that the stirring speed of the precipitation reaction is adjusted. N =450rpm.

[0083] Calculate and verify:

[0084] This PI1 value is slightly less than 0.8, indicating that at the current feeding rate, the stirring speed is too fast and / or the feeding is too slow, resulting in insufficient supersaturation and excessive shear force in the system. This leads to predominantly growing crystals with large particles (D50 = 3.0 μm), irregular morphology, prolonged reaction time, and reduced efficiency. The product purity is 99.85%, and the tap density is 1.58 g / cm³. 3 This indicates that under high stirring intensity, the feeding rate needs to be further increased to maintain the same supersaturation.

[0085] Example 3 This embodiment is based on Comparative Example 4 with only minor adjustments. V Fe =250mL / min, V C =280mL / min.

[0086] Re-verify:

[0087] The PI1 value falls within the range of 0.8-3.0, meeting the model requirements. The resulting product has a purity of 99.55%, a D50 particle size of 0.9 μm, and a tap density of 0.93 g / cm³. 3 .

[0088] Conclusion: High stirring intensity (high) N The D50 value allows for a faster feeding rate and helps produce finer particles (reduced D50), but the tap density decreases due to the finer particles.

[0089] Example 4 This embodiment provides a method for preparing battery-grade ferrous oxalate, specifically including the following steps: The preparation of raw materials and the precipitation reaction are the same as in Example 2.

[0090] Aging treatment: After the precipitation reaction, adjust the pH to 2.5 and set... T a =70℃ t a =4h.

[0091] Solid-liquid separation: After aging, solid-liquid separation is performed, and the filter cake is washed with deionized water until the conductivity of the filtrate is ≤300μS / cm.

[0092] Vacuum drying conditions: set T d =90℃, to ensure the drying process index PI2 is within the range of 0.05-0.15, the target value PI2 = 0.15 is taken (to seek a denser structure by increasing the PI2 value), and the required drying time is calculated. t d .

[0093]

[0094] The obtained product has a purity of 99.75%, a D50 particle size of 1.48 μm, and a tap density of 1.28 g / cm³. 3 .

[0095] Conclusion: By increasing the aging temperature, extending the aging time, increasing the drying temperature, and adjusting the drying process index PI2, a product with higher tap density was successfully prepared, but the particle size increased, demonstrating the adjustability of process parameters on the physical properties of the product.

[0096] Comparative Example 5 The only difference from Example 2 is that the ferrous sulfate feeding rate was significantly reduced to 50 mL / min, and the calculated PI1 value was 0.64.

[0097] Conclusion: Although the product purity reached 99.60%, due to excessively long reaction time, crystals grew excessively, the D50 particle size increased to 3.5 μm, and the tap density decreased to 0.75 g / cm³. 3 .

[0098] Comparative Example 6 The only difference from Example 2 is that the ferrous sulfate feeding rate was significantly increased to 300 mL / min, and the calculated PI1 value was 3.84.

[0099] Conclusion: Due to excessively high instantaneous supersaturation, a large number of crystal nuclei were generated, resulting in excessively fine particle size (D50 = 0.4 μm), making filtration and washing difficult. The sulfur content in the product exceeded the standard, reducing the purity to 99.05%, and the tap density to 1.05 g / cm³. 3 .

[0100] Comparative Example 7 The only difference from Example 2 is that high-temperature short-time drying is used. T d =120℃, t d =3h.

[0101] Conclusion: The product exhibits severe hard agglomeration, with a tap density of only 0.70 g / cm³. 3 Furthermore, some of the ferrous oxalate underwent localized oxidation, resulting in a purity of 99.65% and a particle size D50 of 0.8 μm.

[0102] Comparative Example 8 The only difference from Example 2 is that it uses high-temperature, long-term aging. T a =80℃, t a =5h.

[0103] Conclusion: The product exhibits severe particle agglomeration, a wide particle size distribution, poor batch stability, and a tap density of 0.78 g / cm³. 3 Furthermore, some of the ferrous oxalate underwent localized oxidation, resulting in a purity of 99.3% and a particle size D50 of 2.2 μm.

[0104] Comparative Example 9 The only difference from Example 2 is that the ferrous sulfate solution and oxalic acid solution are not added synchronously during the precipitation reaction. Specifically, 600 ml of oxalic acid solution is first added to the base solution at a rate of 190 mL / min and stirred evenly. Then, the ferrous sulfate solution is added continuously at a rate of 200 mL / min. The other process parameters are the same as in Example 2.

[0105] Conclusion: Localized incomplete or excessive precipitation occurred, resulting in coarse and irregular product particles with poor packing properties, significantly increased impurity content, and a tap density of 0.75 g / cm³. 3 The purity is 98.6%, and the particle size D50 is 4.2 μm.

[0106] Comparative Example 10 The only difference from Example 2 is that no bottom liquid was added to the reaction vessel during the precipitation reaction.

[0107] Conclusion: The product has large crystals (D50=15.5μm), irregular particle morphology, poor flowability, and its purity is reduced to 98.8%, with a tap density of 1.45 g / cm³. 3.

[0108] Comparative Example 11 The only difference from Example 2 is that pH control was not performed in the aging process, resulting in a system pH of 5.0 and a calculated value of PI2 = 0.2.

[0109] Conclusion: The product has irregular particle morphology, a wider particle size distribution (D50=1.8μm, span D90 / D10=5.5), a purity reduced to 99.2%, and an impurity content that is approximately 5-8 times higher than in Example 2. The tap density is only 0.85 g / cm³. 3 Furthermore, the performance of different batches of products fluctuates significantly.

[0110] The ferrous oxalate products obtained in the above examples and comparative examples are compared and summarized in Table 1: Table 1 Comparison of ferrous oxalate preparation indicators between the examples and comparative examples.

[0111] As shown in Table 1, in Example 2 of this application, PI1 and PI2 are within a reasonable range, and the electron microscopy and XRD patterns of the prepared ferrous oxalate product are as follows. Figure 1-2 As shown, the particle size uniformity is good, the particle morphology is intact, and the D50 of the batch products is between 1.23-1.28 μm. The processes in Examples 1-4 of this application are as follows: Figure 3 As shown, when PI1 and PI2 are within a reasonable range, the prepared ferrous oxalate product exhibits excellent performance in the three key indicators of purity, particle size distribution, and tap density. Furthermore, its overall performance is balanced and coordinated, with strong batch stability. The purity, D50 particle size, and tap density of the ferrous oxalate all fluctuate within the range of <1.0%, fully meeting the requirements for battery-grade materials. However, in Comparative Examples 1-11, when PI1 and PI2 are not within a reasonable range, the prepared ferrous oxalate product exhibits significant defects in various aspects, illustrating the importance of adjusting the process parameters according to formulas (1) and (2) in this application.

[0112] This invention, through optimized synthesis routes and process control, successfully achieved a synergistic improvement in high purity, suitable particle size, and high tap density, resulting in battery-grade ferrous oxalate with excellent overall performance and strong batch stability. Data from various comparative examples show that if key process parameters such as dosing rate, pH, temperature, and time are changed, causing PI1 and PI2 to fall outside their reasonable ranges, although they may approach the requirements for a single indicator, it is difficult to achieve simultaneous optimization of multiple performance aspects. Therefore, the technical solution provided by this invention possesses integrity and indivisibility, and the combination of PI1 and PI2 produces a significant synergistic effect.

[0113] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing battery-grade ferrous oxalate, characterized in that, The process includes a precipitation reaction, aging treatment, solid-liquid separation and vacuum drying, using ferrous sulfate solution and oxalic acid solution as raw materials in sequence. The precipitation reaction includes: adding the ferrous sulfate solution and the oxalic acid solution into a reaction vessel containing the bottom liquid and stirring. The precipitation reaction satisfies equation (1). In formula (1): V Fe The feed rate of ferrous sulfate solution is expressed in mL / min. V C The feed rate of oxalic acid solution is expressed in mL / min. V Fe,ref The reference value for the ferrous sulfate solution addition rate is 100 mL / min; V C,ref The reference value for the oxalic acid solution addition rate is 100 mL / min; N The stirring speed is expressed in rpm. N ref The reference value for stirring speed is 200 rpm; T r The precipitation reaction temperature is expressed in °C. T 0 represents the initial temperature of the base liquid, in °C; Δ T ref The reference value for the reaction temperature difference is 10°C; The aging treatment and the vacuum drying also satisfy equation (2): In formula (2): T a The aging temperature is expressed in °C. t a The aging time is expressed in hours (h). pH refers to the acidity or alkalinity of the aging treatment system. T d The drying temperature is expressed in °C. t d Drying time, in hours (h).

2. The method for preparing battery-grade ferrous oxalate according to claim 1, characterized in that, The T r The temperature is 60-80℃.

3. The method for preparing battery-grade ferrous oxalate according to claim 1, characterized in that, The T 0 represents 40-60℃; And / or, the N It is 200-250 rpm.

4. The method for preparing battery-grade ferrous oxalate according to claim 1, characterized in that, The concentration of ferrous ions in the ferrous sulfate solution is 50-100 g / L; And / or, V Fe The flow rate is 50-300 mL / min.

5. The method for preparing battery-grade ferrous oxalate according to claim 1, characterized in that, The concentration of the oxalic acid solution is 0.8-1.2 mol / L; And / or, V C 50-300 mL / min; And / or, the substrate solution is water or dilute sulfuric acid with a pH of 1.0–3.0; And / or, in the precipitation reaction, ferrous sulfate and oxalic acid are simultaneously added to the reaction vessel at a molar ratio of 1:1.15~1.

4.

6. The method for preparing battery-grade ferrous oxalate according to claim 1, characterized in that, The pH value is 1.5-3.5; And / or, the aging treatment includes adjusting the pH to 1.5-3.5 with sulfuric acid or sodium hydroxide.

7. The method for preparing battery-grade ferrous oxalate according to claim 1, characterized in that, 50℃＜ T a ≤80℃； And / or, the t a It takes 1-5 hours.

8. The method for preparing battery-grade ferrous oxalate according to claim 1, characterized in that, The T d Temperatures range from 80 to 120℃. And / or, the t d It takes 3-12 hours.

9. A battery-grade ferrous oxalate prepared by the method according to any one of claims 1-8, characterized in that, The battery-grade ferrous oxalate has a purity greater than 99.5%, a D50 of 0.8-1.5 μm, and a tap density ≥0.85 g / cm³. 3 .

10. A method for determining parameters in the preparation method of battery-grade ferrous oxalate according to any one of claims 1-8, characterized in that, In the process of preparing battery-grade ferrous oxalate by sequentially carrying out precipitation reaction, aging treatment, solid-liquid separation and vacuum drying using ferrous sulfate solution and oxalic acid solution as raw materials: according to formula (1), determine any one of the following: ferrous sulfate solution feeding rate, oxalic acid solution feeding rate, stirring speed, precipitation reaction temperature and initial temperature of bottom liquid; In formula (1): V Fe The feed rate of ferrous sulfate solution is expressed in mL / min. V C The feed rate of oxalic acid solution is expressed in mL / min. V Fe,ref The reference value for the ferrous sulfate solution addition rate is 100 mL / min; V C,ref The reference value for the oxalic acid solution addition rate is 100 mL / min; N The stirring speed is expressed in rpm. N ref The reference value for stirring speed is 200 rpm; T r The precipitation reaction temperature is expressed in °C. T 0 represents the initial temperature of the base liquid, in °C; Δ T ref The reference value for the reaction temperature difference is 10°C; And / or, determine any one of the aging temperature, aging time, aging pH, drying temperature and drying time according to formula (2); In formula (2): T a The aging temperature is expressed in °C. t a The aging time is expressed in hours (h). pH refers to the acidity or alkalinity of the aging treatment system. T d The drying temperature is expressed in °C. t d Drying time, in hours (h).

Images