Polymorphic battery-grade ferrous oxalate, a method for preparing the same, and a lithium battery cathode material
By preparing polycrystalline ferrous oxalate, the stress concentration problem during sintering of monocrystalline ferrous oxalate was solved, which improved the performance of lithium battery cathode materials and reduced the preparation cost, realizing efficient and environmentally friendly ferrous oxalate production.
Patent Information
- Application Number
- CN202510786042.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-12
- Publication Date
- 2026-02-13
- Estimated Expiration
- 2045-06-12
AI Technical Summary
In existing methods for synthesizing ferrous oxalate, single-crystal ferrous oxalate is prone to stress concentration during sintering with lithium sources, leading to product defects. Furthermore, the preparation cost is high and the pollution emissions are large.
Ferrous sulfate solution was mixed with excess oxalic acid to form C2/c seed crystals. Ferrous sulfate solution and dispersant were added to induce the formation of a new I2/a phase. The crystal phase ratio was adjusted by aging to obtain polycrystalline ferrous oxalate.
It effectively reduces the stress concentration problem of ferrous oxalate during sintering, improves the quality and performance of lithium battery cathode materials, and reduces manufacturing costs and pollution emissions.
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Figure CN120309466B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of materials, in particular to a polymorphic battery-grade ferrous oxalate, a preparation method thereof, and a lithium battery positive electrode material. BACKGROUND
[0002] As a green secondary battery with high energy density, high voltage, long cycle life and no memory effect, lithium battery is an important foundation of current power battery. The excellent performance of lithium iron phosphate battery in safety performance and cycle life has become one of the mainstream power batteries of electric vehicles.
[0003] The current mainstream production process of lithium iron phosphate includes iron phosphate process, iron red process, liquid phase method and ferrous oxalate process. As an important precursor of lithium iron phosphate, ferrous oxalate is currently mainly prepared by mixing high-purity ferrous salt and oxalate solution, and the process also needs to adjust pH. The preparation method has high cost, large water treatment capacity, and large amount of by-products and pollution emissions. The lithium iron phosphate battery material prepared by the ferrous iron process has excellent cycle performance and high rate performance, and can quickly respond to fast charging and discharging under large current, which has unique advantages compared to other processes. With the rapid development of economy and technology, the demand for fast charging response power batteries will further increase. Therefore, it is of great significance to develop a low-cost ferrous oxalate preparation technology.
[0004] Ferrous oxalate exists in multiple crystal structures, and its main synthesis method is to react oxalate with divalent iron ions. In the synthesis of lithium iron phosphate by the ferrous iron process, single crystal ferrous oxalate mainly has the following problems: single crystal ferrous oxalate is easy to form stress concentration and produce defects when sintered with lithium source. Mixed crystal ferrous oxalate can produce good synergistic effect due to the difference in bond energy decomposition, so that the sintered product lithium iron phosphate is more stable and uniform. Therefore, it is of great significance to prepare ferrous oxalate with multiple crystal types and controllable proportions. SUMMARY
[0005] The purpose of the present application is to provide a polymorphic battery-grade ferrous oxalate and a preparation method thereof, which is simple and convenient to operate, can efficiently obtain a battery-grade ferrous oxalate with multiple crystal types, and reduce the stress concentration problem of single crystal ferrous oxalate during sintering.
[0006] Another purpose of the present application is to provide a lithium battery positive electrode material which uses polymorphic battery-grade ferrous oxalate as an iron source, can effectively solve the stress concentration problem during sintering, reduce product defects, and improve quality.
[0007] Embodiments of the present application are implemented as follows:
[0008] A preparation method of a polymorphic battery-grade ferrous oxalate, comprising:
[0009] S1. mixing a solution of ferrous sulfate with excess oxalic acid to obtain a first slurry;
[0010] S2. supplementing the first slurry with a solution of ferrous sulfate and a dispersant to obtain a second slurry;
[0011] S3. aging the second slurry.
[0012] A polymorphic battery-grade ferrous oxalate is prepared by the above-mentioned method for preparing a polymorphic battery-grade ferrous oxalate.
[0013] A lithium battery positive electrode material is prepared by using the above-mentioned polymorphic battery-grade ferrous oxalate as an iron source.
[0014] The embodiment of the present application has the following beneficial effects:
[0015] The embodiment of the present application provides a polymorphic battery-grade ferrous oxalate and a preparation method thereof. The preparation method first mixes a solution of ferrous sulfate with excess oxalic acid to form a C2 / c crystal seed, and then supplements the solution of ferrous sulfate and a dispersant. The dispersant is used to induce a I2 / a new phase on the (001) crystal surface of the C2 / c crystal phase. Subsequently, aging is performed. Since the C2 / c and I2 / a crystal phases of ferrous oxalate are both metastable phases, they will gradually transform into the orthorhombic Cccm structure under the action of high-temperature aging. By adjusting the proportion and time, a polymorphic battery-grade ferrous oxalate mixed with three crystal phases can be obtained. The preparation method is simple and convenient, and can efficiently obtain a polymorphic mixed battery-grade ferrous oxalate, thereby reducing the stress concentration problem of single crystal ferrous oxalate during sintering, and obtaining a high-quality lithium battery positive electrode material. BRIEF DESCRIPTION OF DRAWINGS
[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.
[0017] Figure 1 A flow chart of a preparation method of a polymorphic battery-grade ferrous oxalate provided in the embodiment 1 of the present application;
[0018] Figure 2 A scanning electron microscope image of the polymorphic battery-grade ferrous oxalate provided in the embodiment 1 of the present application;
[0019] Figure 3 An XRD graph of the polymorphic battery-grade ferrous oxalate provided in the embodiment 1 of the present application. DETAILED DESCRIPTION
[0020] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. If specific conditions are not indicated in the embodiments, conventional conditions or conditions recommended by manufacturers are adopted. If manufacturers of reagents or instruments are not indicated, all are conventional products that can be purchased in the market.
[0021] The coated modified phosphate positive electrode composite material, the preparation method and the application thereof will be described in detail below.
[0022] A preparation method of a polymorphic battery-grade ferrous oxalate, comprising:
[0023] S1. mixing a solution of ferrous sulfate with excess oxalic acid to obtain a first slurry;
[0024] S2. supplementing the first slurry with a solution of ferrous sulfate and a dispersing agent to obtain a second slurry;
[0025] S3. aging the second slurry.
[0026] In the step S1, the molar ratio of ferrous sulfate to oxalic acid is 1:(0.8-1.0). As a simplest dicarboxylic acid, the structural formula of oxalate presents a straight line, forming a linear molecular structure, and the two carbon-oxygen double bonds and single bonds are in an alternating arrangement. At the same time, oxalate also has strong coordination, which can chelate with transition alkali metal ions. Therefore, in the reaction with ferrous sulfate, different crystal forms of ferrous oxalate will be generated according to the existence form, proportion and reaction temperature of oxalate. In the step S1, oxalic acid is in an excess state, and the strong coordination of oxalate and Fe 2+ , the special deformed octahedral structure formed by two water molecules forms a C2 / c crystal seed, and the structural formula is as follows
[0027] .
[0028] Further, the solution of ferrous sulfate can be a commercially available sulfuric acid liquid configured into a solution, or can be obtained by reacting an iron source with sulfuric acid. Alternatively, the iron source is selected from reduced iron powder, iron block and other industrial iron products with an iron content of more than 99%, and the concentration of sulfuric acid is 15%-20%. The molar ratio of sulfuric acid to iron element is 0.9-1.2:1. The concentration of the obtained iron liquid is 80-85 g / L (mass fraction Fe% is 7.0wt%-8.0wt%).
[0029] In the step S1, the oxalic acid directly participates in the reaction in the form of solid, without being configured into a solution, which can reduce the consumption of water. After aging is completed, the solid product can be filtered out, and the mother liquor can be further recycled.
[0030] Optionally, in the S1 and S2 steps, the amount of ferrous sulfate is 1:1~4. By adjusting the ratio of ferrous sulfate in the S1 and S2 steps, the proportion of monoclinic I2 / a and monoclinic C2 / c in the battery-grade ferrous oxalate can be adjusted. Increasing the amount of ferrous sulfate in the S2 step can obtain more monoclinic I2 / a.
[0031] In the S1 step, the reaction temperature of ferrous sulfate and oxalic acid is 40~90℃. At this temperature, the reaction can be promoted, and the C2 / c crystal seed is quickly formed.
[0032] Further, in the S2 step, the solution of the added ferrous sulfate is mixed with the dispersant to obtain a mixed solution, and then the mixed solution is mixed with the first slurry. In the mixed solution, the concentration of the dispersant is 1vol%~20vol%. The dispersant includes at least one of glycerol, propylene glycol and ethylene glycol. Preferably, the dispersant is glycerol. In the S2 step, the excess Fe 2+ forms an infinite chain structure with the oxalate group, and the structure is as follows
[0033] .
[0034] After the chain structure is saturated, the I2 / a new phase is formed on the (001) crystal surface of the C2 / c crystal phase under the induction of the dispersant.
[0035] Optionally, in the S2 step, the first slurry is added to the mixed solution at a rate of 200~500L / h, and the reaction temperature is maintained at 40~90℃. By controlling the reaction rate, the oxalate ferrous particles in the slurry can better adhere to the surface of the crystal seed for further growth, which is beneficial to the growth of the I2 / a new phase.
[0036] The aging time of the second slurry is 30~240 min, and the aging temperature is 40~90℃. The C2 / c and I2 / a crystal phases of ferrous oxalate are metastable phases, which will gradually transform into the orthorhombic Cccm structure under the action of high-temperature aging. By controlling the aging reaction time, the battery-grade ferrous oxalate with three crystal types can be obtained.
[0037] After the aging is completed, the mixed slurry is filtered and separated, the solid part is washed and dried to obtain the battery-grade ferrous oxalate product, and the separated mother liquor is recycled.
[0038] The embodiment of the application also provides a battery-grade ferrous oxalate with multiple crystal types, which is prepared by the above-mentioned preparation method of the battery-grade ferrous oxalate with multiple crystal types. It includes three crystal phases, orthorhombic Cccm, monoclinic I2 / a and monoclinic C2 / c, and the cell parameters of the three crystal phases are shown in Table 1.
[0039] Table 1: Cell parameters of orthorhombic Cccm, monoclinic I2 / a, monoclinic C2 / c crystal structures
[0040] Crystal structure a / nm b / nm c / nm α / ° β / ° γ / ° Orthorhombic Cccm 1.221 0.555 1.547 90 90 90 Monoclinic I2 / a 1.220 0.552 0.992 90 128 90 Monoclinic C2 / c 0.991 0.555 0.970 90 104 90
[0041] And by adjusting the preparation parameters, such as the ferrous sulfate ratio of S1 and S2 steps, pumping rate, reaction temperature, etc., the proportion of the three crystal phases can be further adjusted.
[0042] The embodiment of the application also provides a lithium battery positive electrode material prepared by using the above-mentioned polymorphic battery-grade ferrous oxalate as an iron source. The polymorphic battery-grade ferrous oxalate has a synergistic effect when being sintered to synthesize lithium iron phosphate material, so that the synthesized lithium iron phosphate has good rate performance and cycle performance.
[0043] The features and performance of the application are further described in detail below in combination with embodiments. Embodiment 1
[0044] The embodiment provides a polymorphic battery-grade ferrous oxalate, and a preparation method thereof is as shown in Figure 1 , which comprises:
[0045] S1. 20 kg of industrial pure iron products with a purity of more than 99% are used as iron powder, which is put into a 250 L dilute sulfuric acid solution with a concentration of 15.01%, stirring is started at 40 Hz, and reaction is carried out at 70 ℃ for 5 h, and a ferrous sulfate solution with a Fe% concentration of 7.21% is obtained by filtration.
[0046] S2. The ferrous sulfate solution is equally divided into 1# and 2# reaction kettles, nitrogen is introduced for protection, and stirring is started, and the reaction temperature is 60℃. 45 kg of oxalic acid is added to the 1# reaction kettle to form a first slurry, and a mixed solution of 15% volume fraction of glycerol is added to the 2# reaction kettle.
[0047] S3. The first slurry is pumped into the mixed solution in the 2# reaction kettle at a pumping speed of 500 L / h, and a second slurry is formed by reaction, and the reaction temperature is 60℃.
[0048] S4. Continue to age at 60℃ for 180 min to obtain a ferrous oxalate slurry with a particle size D50=26.3 um; centrifugal filtration is carried out, and after the mother liquor after separation is titrated for acidity, it is reconfigured and returned to leaching, and the filtered ferrous oxalate is washed, dried, crushed, and batch mixed to obtain a light yellow finished product battery-grade ferrous oxalate with a purity of 99.9%.
[0049] The electron microscope image of the battery-grade ferrous oxalate is as shown in Figure 2As shown in the figure, the ferrous oxalate has different morphological structures. At the same time, the prepared ferrous oxalate particles have regular morphology, and the particle surface is free of dust, indicating that the ferrous oxalate crystal has good crystallinity.
[0050] The XRD pattern of the battery-grade ferrous oxalate is shown in the figure. Figure 3 As shown in the figure, the peak position can correspond to the orthorhombic Cccm, monoclinic I2 / a and monoclinic C2 / c crystal phases in the database, indicating that the battery-grade ferrous oxalate obtained in this embodiment exists in three crystal phases at the same time. Example 2
[0051] This embodiment provides a polymorphic battery-grade ferrous oxalate, and the preparation method is as follows:
[0052] S1. 20 kg of industrial pure iron product with a purity of more than 99% is used as iron powder, which is put into a 250 L sulfuric acid solution with a concentration of 15.01%, and stirring is started at 45 Hz. The reaction is carried out at 80 ℃ for 3 h, and a ferrous sulfate solution with a Fe% concentration of 7.69% is obtained by filtration.
[0053] S2. The 40% and 60% ferrous sulfate solutions are respectively divided into 1# and 2# reaction kettles, and nitrogen is introduced for protection and stirring is started. The reaction temperature is 70 ℃. 40 kg of oxalic acid is added to the 1# reaction kettle to form a first slurry, and a mixed solution of 10% volume fraction of glycerol is added to the 2# reaction kettle.
[0054] S3. The first slurry is pumped into the mixed solution in the 2# reaction kettle at a pump speed of 300 L / h, and a second slurry is formed by reaction. The reaction temperature is 70 ℃.
[0055] S4. Continue to age at 70 ℃ for 60 min to obtain a ferrous oxalate slurry with a particle size D50=26.8 um. After centrifugal filtration, the mother liquor after separation is titrated for acidity and then reconfigured and returned to leaching. The filtered ferrous oxalate is washed, dried, crushed, and batch mixed to obtain a light yellow finished product of battery-grade ferrous oxalate with a purity of 99.8%.
[0056] S5. The filtered mother liquor is supplemented with concentrated sulfuric acid to a predetermined acidity value, and the mother liquor is returned to leaching 17 kg of iron powder. Stirring is started at 45 Hz, and the reaction is carried out at 80 ℃ for 3 h. A ferrous sulfate solution with a Fe% concentration of 7.4% is obtained by filtration.
[0057] S6. The ferrous sulfate solution in S5 is split into 40% ferrous sulfate solution into 1# reactor and 60% ferrous sulfate solution into 2# reactor, nitrogen is introduced for protection and stirring is started, the reaction temperature is 70℃. 40 kg of oxalic acid is added into 1# reactor to form the first slurry, and 10% glycerol by volume is added into 2# reactor to form the mixed solution.
[0058] S7. The first slurry is pumped into the mixed solution in 2# reactor at a pump rate of 400 L / h to form the second slurry.
[0059] S8. The second slurry is aged at 70℃ for 120 min to obtain the ferrous oxalate slurry with a particle size D50 = 32.5 um; centrifugation, filtration and separation are performed to obtain the secondary circulating mother liquor and ferrous oxalate, the filtered ferrous oxalate is washed, dried, crushed and batch mixed to obtain the light yellow finished product battery grade ferrous oxalate with a purity of 99.4%. Example 3
[0060] This example provides a polymorphic battery grade ferrous oxalate, and the preparation method is as follows:
[0061] S1. On the basis of Example 2, the secondary circulating mother liquor is acid-adjusted to the predetermined acidity, and the mother liquor is recycled back to leaching 19 kg of iron powder, stirring is started at 40 Hz, and the reaction is carried out at 80℃ for 5 h to obtain a ferrous sulfate solution with a Fe% concentration of 8.21%.
[0062] S2. 30% of the ferrous sulfate solution is split into 1# reactor and the rest is split into 2# reactor, nitrogen is introduced for protection and stirring is started, the reaction temperature is 80℃. 44 kg of oxalic acid is added into 1# reactor to form the first slurry, and 10% glycerol by volume is added into 2# reactor to form the mixed solution.
[0063] S3. The first slurry is pumped into the mixed solution in 2# reactor at a pump rate of 300 L / h to form the second slurry, and the reaction temperature is 80℃.
[0064] S4. Aging is continued at 80℃ for 30 min to obtain the ferrous oxalate slurry with a particle size D50 = 46.8 um; centrifugation and filtration are performed, and the separated mother liquor is reconfigured after acidity titration and returned to leaching, the filtered ferrous oxalate is washed, dried, crushed and batch mixed to obtain the light yellow finished product battery grade ferrous oxalate with a purity of 99.8%.
[0065] Comparative Example 1
[0066] This comparative example provides a battery grade ferrous oxalate, and the preparation method is basically the same as that of Example 1, except that in S2 step, no glycerol is added into 2# reactor.
[0067] Comparative Example 2
[0068] This comparative example provides a battery-grade ferrous oxalate, the preparation method of which is basically the same as that of Example 1, except that in the S3 step, the first slurry is pumped into the 2# reaction kettle at a rate of 2000 L / h.
[0069] Comparative Example 3
[0070] This comparative example provides a battery-grade ferrous oxalate, the preparation method of which is basically the same as that of Example 1, except that in the S4 step, no aging is performed.
[0071] Comparative Example 4
[0072] This comparative example provides a battery-grade ferrous oxalate, the preparation method of which is basically the same as that of Example 1, except that in the S4 step, the aging time is extended to 24 h.
[0073] Test Example 1
[0074] The battery-grade ferrous oxalates provided by Examples 1-3 and Comparative Examples 1-4 are detected by XRD to determine the proportion of the three crystal phases, and the detection results are shown in Table 2.
[0075] Table 2: Proportion of each crystal phase in the examples
[0076] Example Temperature / °C Seed crystal ratio / % Aging time / h Orthorhombic Cccm Monoclinic C2 / c Monoclinic I2 / a Example 1 60 50% 3 35.8% 51.7% 12.5% Example 2, first cycle 70 40% 1 33.9% 43.5% 22.6% Example 2, second cycle 70 40% 2 34.2% 45.0% 20.8% Example 3 85 30% 0.5 32.3% 38.0% 29.7% Comparative Example 1 60 50% 3 40.7% 59.3% 0 Comparative Example 2 60 50% 3 39.5% 56.8% 3.7% Comparative Example 3 60 50% 0 9.7% 68.9% 21.4% Comparative Example 4 60 50% 24 99.8% 0.2% 0
[0077] As can be seen from Table 2, using the preparation methods of Examples 1-3, a mixed ferrous oxalate of the three crystal phases can be obtained. Among them, Example 2 recycles the mother liquor, and the polymorphic battery-grade ferrous oxalate can be obtained after two cycles, and the proportion of each crystal phase changes little, indicating that the method of the example of the application can realize continuous cyclic production. In contrast, in Comparative Example 1, no glycerol is used for induction, and it can be seen that there is no monoclinic I2 / a crystal phase in the ferrous oxalate product. In Comparative Example 2, the pumping rate of the first slurry is accelerated, and the too fast pumping rate is not conducive to the growth of the monoclinic I2 / a crystal phase, also resulting in only a small amount of monoclinic I2 / a crystal phase in the product. In Comparative Example 3, the second slurry is not aged, and only a small amount of orthorhombic crystal phase Cccm is generated in the product. In Comparative Example 4, the aging time is extended, and under long-term aging, the metastable monoclinic crystal phase I2 / a and monoclinic crystal phase C2 / c are almost completely converted into orthorhombic crystal phase Cccm. As can be seen, by adjusting the preparation condition parameters, the proportion of the three crystal phases can be adjusted.
[0078] Test Example 2
[0079] The battery-grade ferrous oxalate prepared in Examples 1-3 and Comparative Examples 1-4, and commercially available ferrous oxalate (control) were used as the iron source, diammonium hydrogen phosphate was used as the phosphorus source, lithium carbonate was used as the lithium source, and glucose was used as the carbon source to prepare lithium iron phosphate battery cathode materials. The performances of the lithium iron phosphate battery cathode materials of each group were compared, and the comparison results are shown in Table 3.
[0080] Table 3. Performance comparison of lithium iron phosphate battery cathode materials
[0081] Experiment No. D50 / μm 0.1C discharge specific capacity (mAh / g) 1C discharge specific capacity (mAh / g) Example 1 1.28 161.0 142.0 Example 2, first cycle 1.16 159.3 140.7 Example 2, second cycle 1.32 160.7 141.5 Example 3 1.21 159.9 140.0 Comparative Example 1 1.41 156.4 135.8 Comparative Example 2 1.38 157.8 137.6 Comparative Example 3 1.27 158.6 138.8 Comparative Example 4 1.39 156.1 134.0 Comparative Example 1.32 156.6 133.6
[0082] As can be seen from Table 3, the battery cathode material prepared by using the ferrous oxalate provided in Examples 1-3 as the iron source has a bulk density of 1.21-1.32 μm, a 0.1C discharge specific capacity of 159.3 mAh / g or more, and a 1C discharge specific capacity of 140 mAh / g or more, and has a better rate performance. In contrast, the rate performance of the battery cathode material prepared by using the ferrous oxalate in the prior art as the iron source is significantly reduced, the 0.1C discharge specific capacity is only 156.6 mAh / g, and as the rate increases, the difference in discharge specific capacity becomes more obvious, and the 1C discharge specific capacity is only 133.6 mAh / g. Although Comparative Examples 1-4 also contain more than one crystal phase, the rate performance is poor due to the unbalanced proportion of each crystal phase, and the synergistic effect is not fully utilized, and the 0.1C and 1C discharge specific capacities are reduced to different degrees, which are slightly higher than those of the control. In particular, Comparative Example 4, the ferrous oxalate is basically composed of a single orthorhombic Cccm crystal phase, and the battery cathode material prepared therefrom has basically the same performance as the control. It can be seen that the multi-crystal battery-grade ferrous oxalate prepared in the examples has a positive promoting effect on the performance of the battery cathode material.
[0083] In summary, the examples of the present application provide a multi-crystal battery-grade ferrous oxalate and a preparation method thereof. The preparation method first mixes a solution of ferrous sulfate with excess oxalic acid to form a C2 / c crystal seed, and then adds a solution of ferrous sulfate and a dispersant to induce the formation of a I2 / a new phase on the (001) crystal face of the C2 / c crystal phase. Subsequently, aging is performed. Since the C2 / c and I2 / a crystal phases of ferrous oxalate are both metastable phases, they will gradually transform into the orthorhombic Cccm structure under the action of high-temperature aging. By adjusting the proportions and time, a multi-crystal battery-grade ferrous oxalate mixed with three crystal phases can be obtained. The preparation method is simple and convenient, and can efficiently obtain a multi-crystal battery-grade ferrous oxalate mixed with three crystal phases, reduce the stress concentration problem of single-crystal ferrous oxalate during sintering, and obtain a high-quality lithium battery cathode material.
[0084] The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.
Claims
1. A process for the preparation of a polymorph of battery grade ferrous oxalate characterized in that, Comprising: S1. mixing a solution of ferrous sulfate with excess oxalic acid to obtain a first slurry; S2. adding a solution of ferrous sulfate and a dispersant to the first slurry to obtain a second slurry; S3. aging the second slurry; In S1, the reaction temperature of ferrous sulfate and oxalic acid is 40-90℃; In S2, the reaction temperature is 40-90℃; the dispersant is selected from at least one of glycerol, propylene glycol and ethylene glycol; In S3, the aging time of the second slurry is 30-240 min, and the aging temperature is 40-90℃.
2. The production method according to claim 1, characterized by, In S1 and S2, the ratio of the amount of ferrous sulfate is 1:1-4, and the concentration of iron in the solution of ferrous sulfate is 7.0wt%-8.0wt%.
3. The preparation method according to claim 1, characterized in that, In S2, the added solution of ferrous sulfate and dispersant are mixed to obtain a mixed solution, and then the mixed solution is mixed with the first slurry; in the mixed solution, the concentration of the dispersant is 1vol%-20vol%.
4. The production method according to claim 3, characterized by, In S2, the first slurry is added to the mixed solution at a rate of 200-500L / h.
5. A polymorph of battery grade ferrous oxalate characterized by, Prepared by the method of any one of claims 1-4.
6. A lithium battery cathode material, characterized in that, Prepared by using the polymorphic battery-grade ferrous oxalate of claim 5 as the iron source.