A magnesium-vanadium double-doped high-compaction lithium iron phosphate positive electrode material prepared by using a mixed iron source, a preparation method and applications

Abstract

The application relates to a magnesium-vanadium double-doped high-compaction lithium iron phosphate positive electrode material prepared by using a mixed iron source, a preparation method and application. A lithium source, a mixed iron source, a phosphorus source, a vanadium source, a magnesium source and a carbon source are added into a solvent, are ground, are spray dried to obtain a precursor, and the precursor is sintered under the protection of an argon-hydrogen atmosphere to obtain the double-doped high-compaction lithium iron phosphate positive electrode material. Different valence iron ions in the mixed iron source cause different local coordination environments, combined with the co-doping of Mg and V ions with different valences, non-uniform crystal nucleation and growth can be induced, the number of early LiFePO4 crystal nuclei is increased, part of the crystal nuclei grows faster to a certain extent, micron and nanometer particle grading states with a certain particle size distribution are formed, the micron and nanometer particle grading states are easy to be tightly packed, and the compaction density is improved. The magnesium-vanadium double-doped lithium iron phosphate positive electrode material with high compaction and high performance is obtained by adopting a one-time sintering process, the raw material cost is low, pollution is avoided, the preparation process is simple, the overall yield is high, and the method is suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of lithium iron phosphate preparation technology, and relates to a magnesium-vanadium dual-doped high-pressure lithium iron phosphate cathode material prepared using a mixed iron source, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries (LIBs) possess advantages such as high energy density, long cycle life, and high safety, making them one of the most important electrochemical energy storage devices. As a core component of power and energy storage networks, the volumetric energy density of LIB system cells directly determines the space utilization rate of energy storage modules, a parameter limited by the physicochemical properties of the cathode material. Lithium iron phosphate (LFP), as a mainstream cathode material, is widely used due to its excellent cycle stability, thermal stability, and cost advantages. However, its poor intrinsic conductivity and relatively low compaction density and volumetric energy density limit its application in high-range driving scenarios. Increasing compaction density can significantly reduce electrode porosity, increase the amount of active material per unit volume, and improve volumetric energy density. However, increasing compaction density often leads to a decrease in battery performance. Therefore, overcoming the compaction density bottleneck while maintaining battery performance is key to the further development of LFP batteries.

[0003] The technical solution disclosed in patent CN102916179B employs two separate batching and wet ball milling processes for lithium salt, iron source, and phosphate raw materials to obtain two sets of precursor slurries with different particle sizes. These are then mixed in a certain proportion, dried, pre-sintered, and subjected to a third wet ball milling before finally sintering to obtain lithium iron phosphate cathode material with high compaction density. While this solution achieves increased compaction density by utilizing the principle of particle size distribution, its overall process involves three ball milling processes and two sintering processes, making the steps complex and the production cycle long, significantly restricting large-scale production capacity. Patent CN103618083B obtains high-compact lithium iron phosphate through a three-stage pressing method, but this method requires multiple pressing, crushing, and sintering processes, making the process complex and resulting in high industrial production costs. Patent CN106744780A prepares high-compact lithium iron phosphate using a high-compact iron source, but this method has a low overall yield, affecting production capacity and incurring high costs. While the aforementioned existing technical solutions have improved the compaction density of lithium iron phosphate materials to varying degrees, they suffer from problems such as complex preparation processes, high production costs, and limited production capacity. They have failed to achieve an effective balance between process simplicity and material performance, and require further improvement and breakthroughs.

[0004] Therefore, overcoming the shortcomings of the existing technology is an urgent problem to be solved in this technical field. Summary of the Invention

[0005] To address the aforementioned problems in existing technologies, the present invention aims to provide a low-cost and simple method for preparing dual-doped high-compact lithium iron phosphate cathode materials. Utilizing the different local coordination environments constructed by iron ions of different valence states in a mixed iron source, combined with the co-doping effect of Mg and V ions of different valence states, non-uniform crystal nucleation and growth are induced during the sintering process. This method increases the number of early LiFePO4 nuclei, promotes differentiated growth of some nuclei, and can form a micron- and nano-particle gradation state with a wide particle size distribution through a single sintering, thereby improving the compaction density of the material. To achieve the above objective, the present invention adopts the following technical solution: In a first aspect, a method for preparing a dual-doped high-pressure lithium iron phosphate cathode material is provided, comprising the following steps: Step 1: Ball mill and mix lithium source, mixed iron source, phosphorus source, magnesium source, vanadium source, carbon source and solvent to obtain slurry; Step 2: Spray dry the slurry to obtain precursor powder; Step 3: The precursor powder is sintered under an argon-hydrogen atmosphere to obtain magnesium-vanadium dual-doped high-pressure lithium iron phosphate.

[0006] Furthermore, in step one, the lithium source is one or more of lithium phosphate, lithium carbonate, lithium hydrogen phosphate, lithium dihydrogen phosphate, and lithium hydroxide.

[0007] Furthermore, in step one, the iron source is one or more of the following: iron phosphate, ferric oxide, ferric oxide, ferrous oxalate, and iron powder.

[0008] Furthermore, in step one, the phosphorus source is one or more of lithium phosphate, lithium hydrogen phosphate, lithium dihydrogen phosphate, and iron phosphate.

[0009] Furthermore, in step one, the magnesium source is one or more of magnesium carbonate, magnesium acetate, and magnesium oxide.

[0010] Furthermore, in step one, the vanadium source is one or more of vanadium oxalate, vanadium pentoxide, and ammonium metavanadate.

[0011] Furthermore, in step one, the solvent is one or more of water, ethanol, methanol, and acetone.

[0012] Furthermore, in step one, with the molar amount of phosphorus source being 100 parts, the total molar amount of lithium source and magnesium source is 100-105 parts, and the total molar amount of iron source and vanadium source is 95-100 parts, of which the molar amount of vanadium source is 1-5 parts and the molar amount of magnesium source is 0.5-3 parts.

[0013] Further, in step one, the carbon source is one or more of sucrose, glucose, cellulose, cyclodextrin, polyethylene glycol, phenolic resin, and starch; the amount of carbon source added is 5-15% of the total mass of lithium source, phosphorus source, iron source, magnesium source, and vanadium source.

[0014] Furthermore, in step one, the ball milling speed is 200~800 r / min, the ball-to-material mass ratio is 5~15:1, and the time is 3~10 h.

[0015] Furthermore, in step two, the inlet temperature of the spray dryer is 110-320 ℃, and the outlet temperature is 60-160 ℃; Furthermore, in step three, the sintering conditions are as follows: heating from room temperature to 200-500 ℃ at a heating rate of 1-10 ℃ / min and holding at that temperature for 1-8 h; then heating to 650-850 ℃ at a heating rate of 1-10 ℃ / min and holding at that temperature for 3-15 h; and finally cooling to room temperature at a cooling rate of 1-20 ℃ / min.

[0016] In a second aspect, a magnesium-vanadium dual-doped high-pressure lithium iron phosphate cathode material is provided, wherein the magnesium-vanadium dual-doped high-pressure lithium iron phosphate cathode material is prepared by the preparation method described in the first aspect.

[0017] Thirdly, a lithium-ion battery is provided, comprising the magnesium-vanadium dual-doped high-pressure lithium iron phosphate cathode material described in the second aspect.

[0018] Fourthly, the application of the magnesium-vanadium dual-doped high-pressure lithium iron phosphate cathode material as described in the second aspect in the preparation of lithium-ion batteries is provided.

[0019] The beneficial effects of this invention over the prior art are as follows: (1) The synthesis method of mixed iron source co-doping with Mg and V utilizes the difference in local coordination environment caused by multivalent ions to induce non-uniform nucleation and growth of grains. Iron sources with different reaction paths form nano / submicron or micron particles respectively, and a graded state that is easy to be tightly packed is obtained through one sintering, which significantly improves the compaction density of the material while effectively reducing the production cost.

[0020] (2) Magnesium and vanadium are doped into the lithium iron phosphate lattice. Mg makes the Li-O bond length of the olivine structure LiO6 octahedron longer, making lithium ions easier to migrate; V, as a multivalent transition metal element, has strong electrochemical activity and conductivity improvement ability. Introducing high-valence V can increase vacancy defects through charge compensation mechanism, promote ion diffusion and improve lithium intercalation activity, and at the same time adjust the band structure to improve electronic conductivity.

[0021] (3) By adopting a mixed iron source and combining it with a dual-ion doping improvement strategy, large and small particle graded materials can be formed to increase compaction density, while increasing lithium intercalation activity and improving electron / ion transport, thereby improving the specific capacity, rate capability and cycle performance of the material. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is the SEM image of Example 1 of the present invention; Figure 2 This is the XRD pattern of Example 1 of the present invention; Figure 3 These are the 0.1 C charge-discharge curves of Example 1 and Comparative Examples 1-4 of the present invention; Figure 4 These are the 1C cycle performance diagrams of Example 1 and Comparative Examples 1-4 of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] As used in this invention, “about,” “approximately,” or “approximately” includes the stated value and the average value within an acceptable range of deviation from a particular value, wherein the acceptable range of deviation is determined by a person skilled in the art taking into account the measurement under discussion and the error associated with the measurement of the particular quantity (i.e., the limitations of the measurement system).

[0026] The present invention will be further illustrated below with reference to specific embodiments. However, these embodiments are merely illustrative and not intended to limit the scope of the invention.

[0027] Example 1 Lithium phosphate, iron phosphate, ferrous oxalate, ferric oxide, magnesium acetate, vanadium pentoxide, and 12% sucrose (by mass of the total six components) were added to water in a Li:P:0.95:0.01:0.02 molar ratio of Li, P, Fe, Mg, and V. The mixture was ball-milled at 400 r / min for 5 h. The slurry was then spray-dried at an inlet temperature of 140 ℃ and an outlet temperature of 70 ℃. The dried powder was placed in a tube furnace under an argon-hydrogen atmosphere and heated to 350 ℃ at a heating rate of 5 ℃ / min, held for 4 h, then heated to 700 ℃ at a heating rate of 5 ℃ / min, held for 10 h, and finally cooled to room temperature at a cooling rate of 10 ℃ / min to obtain double-doped high-density lithium iron phosphate.

[0028] Example 2 Lithium carbonate, lithium dihydrogen phosphate, iron phosphate, ferric oxide, magnesium oxide, vanadium oxalate, and 10% starch (by mass of the total six components) were added to water in a Li, P, Fe, Mg, and V molar ratio of 1.005:1:0.95:0.005:0.03. The mixture was ball-milled at 600 r / min for 4 h. The slurry was then spray-dried at an inlet temperature of 200 ℃ and an outlet temperature of 130 ℃. The dried powder was placed in a tube furnace under an argon-hydrogen atmosphere and heated to 400 ℃ at a heating rate of 2 ℃ / min, held for 3 h, then heated to 720 ℃ at a heating rate of 2 ℃ / min, held for 8 h, and finally cooled to room temperature at a cooling rate of 15 ℃ / min to obtain double-doped high-pressure lithium iron phosphate.

[0029] Example 3 Lithium carbonate, lithium dihydrogen phosphate, ferrous oxalate, ferric oxide, ferric oxide, ferric oxide, magnesium carbonate, vanadium aluminate, and 15% glucose (by mass of the total six components) were added to water in a Li, P, Fe, Mg, and V molar ratio of 0.995:1:0.96:0.015:0.01. The mixture was ball-milled at 350 r / min for 6 h. The slurry was then spray-dried at an inlet temperature of 270 ℃ and an outlet temperature of 160 ℃. The dried powder was placed in a tube furnace under an argon-hydrogen atmosphere and heated to 300 ℃ at a heating rate of 10 ℃ / min, held for 2 h, then heated to 700 ℃ at a heating rate of 10 ℃ / min, held for 12 h, and finally cooled to room temperature at a cooling rate of 8 ℃ / min to obtain double-doped high-pressure lithium iron phosphate.

[0030] Example 4 Lithium dihydrogen phosphate, lithium carbonate, iron phosphate, ferrous oxalate, magnesium acetate, vanadium oxalate, and 10% cyclodextrin (by mass of the total six components) were added to water in a Li, P, Fe, Mg, and V molar ratio of 0.99:1:0.95:0.02:0.02. The mixture was ball-milled at 700 r / min for 3 h. The slurry was then spray-dried at an inlet temperature of 180 ℃ and an outlet temperature of 100 ℃. The dried powder was placed in a tube furnace under an argon-hydrogen atmosphere and heated to 300 ℃ at a heating rate of 5 ℃ / min, held for 2 h, then heated to 700 ℃ at a heating rate of 10 ℃ / min, held for 10 h, and finally cooled to room temperature at a cooling rate of 20 ℃ / min to obtain double-doped high-pressure lithium iron phosphate.

[0031] Comparative Example 1 Lithium phosphate, iron phosphate, ferrous oxalate, ferric oxide, magnesium acetate, and 12% sucrose (by mass of the former) were added to water in a Li:P:Fe:Mg molar ratio of 1:1:0.974:0.015. The mixture was ball-milled at 400 r / min for 5 h. The slurry was then spray-dried at an inlet temperature of 140 ℃ and an outlet temperature of 70 ℃. The dried powder was placed in a tube furnace under an argon-hydrogen atmosphere and heated to 350 ℃ at a heating rate of 5 ℃ / min, held for 4 h, then heated to 700 ℃ at a heating rate of 5 ℃ / min, held for 10 h, and finally cooled to room temperature at a cooling rate of 10 ℃ / min to obtain double-doped high-pressure lithium iron phosphate.

[0032] Comparative Example 2 Lithium phosphate, iron phosphate, ferrous oxalate, ferric oxide, vanadium pentoxide, and 12% sucrose (by mass of the former) were added to water in a Li:P:Fe:V molar ratio of 1:1:0.95:0.01. The mixture was ball-milled at 400 r / min for 5 h. The slurry was then spray-dried at an inlet temperature of 140 ℃ and an outlet temperature of 70 ℃. The dried powder was placed in a tube furnace under an argon-hydrogen atmosphere and heated to 350 ℃ at a heating rate of 5 ℃ / min, held for 4 h, then heated to 700 ℃ at a heating rate of 5 ℃ / min, held for 10 h, and finally cooled to room temperature at a cooling rate of 10 ℃ / min to obtain double-doped high-density lithium iron phosphate.

[0033] Comparative Example 3 Lithium phosphate, iron phosphate, ferrous oxalate, ferric oxide, and 12% sucrose (by mass of the total four components) were added to water in a Li:P:Fe molar ratio of 1:1:0.96 and ball-milled at 400 r / min for 5 h. The slurry was then spray-dried at an inlet temperature of 140 ℃ and an outlet temperature of 70 ℃. The dried powder was placed in a tube furnace under an argon-hydrogen atmosphere and heated to 350 ℃ at a heating rate of 5 ℃ / min, held for 4 h, then heated to 700 ℃ at a heating rate of 5 ℃ / min, held for 10 h, and finally cooled to room temperature at a cooling rate of 10 ℃ / min to obtain double-doped high-density lithium iron phosphate.

[0034] Comparative Example 4 Lithium carbonate, lithium dihydrogen phosphate, iron oxalate, magnesium acetate, vanadium pentoxide, and 12% sucrose (by mass of the former) were added to water in a Li:P:Fe:Mg:V molar ratio of 1:1:0.95:0.01:0.02. The mixture was ball-milled at 400 r / min for 5 h. The slurry was then spray-dried at an inlet temperature of 140 ℃ and an outlet temperature of 70 ℃. The dried powder was placed in a tube furnace under an argon-hydrogen atmosphere and heated to 350 ℃ at a heating rate of 5 ℃ / min, held for 4 h, then heated to 700 ℃ at a heating rate of 5 ℃ / min, held for 10 h, and finally cooled to room temperature at a cooling rate of 10 ℃ / min to obtain double-doped high-pressure lithium iron phosphate.

[0035] Compaction density comparison: The powder compaction density of the sintered sample materials obtained in the test examples and comparative examples is shown in Table 1.

[0036] Table 1 Powder Compacted Density Table

[0037] As shown in Table 1, the powder compaction density of the lithium iron phosphate materials prepared in Examples 1-4 is significantly higher than that of the lithium iron phosphate materials prepared in Comparative Examples 1-4, indicating superior processing performance. This application achieves high-compactness, high-performance lithium iron phosphate materials through one-step sintering by controlling doping element design and precursor design.

[0038] SEM images of the Mg, V dual-doped high-pressure lithium iron phosphate cathode material prepared in Example 1 are shown below. Figure 1 As shown, the sample contains particles of different sizes. This wide particle size distribution allows small particles to tightly fill the pores between large particles, forming a particle size distribution that increases the compaction density of the material. At the same time, the sample exhibits a regular spherical morphology with a smooth surface. This morphology is conducive to the rearrangement and slippage of particles during the electrode rolling process, thereby obtaining a higher electrode compaction density.

[0039] The XRD pattern of the Mg, V dual-doped high-pressure lithium iron phosphate cathode material prepared in Example 1 is shown below. Figure 2 As shown, the characteristic diffraction peaks of the sample match the standard card of olivine structure LiFePO4, indicating that well-crystallized lithium iron phosphate was successfully synthesized and that dual-ion doping did not change the crystal structure.

[0040] The following describes the preparation process of the coin cell based on the lithium iron phosphate cathode material prepared in the aforementioned embodiments, and compares the electrical performance of coin cells prepared based on different lithium iron phosphate cathode materials.

[0041] Active material, PVDF, and conductive carbon black were mixed at a mass ratio of 8:1:1 and dissolved in N-methylpyrrolidone (NMP) to form a slurry. The slurry was then stirred on a stirring table for 10 h to ensure uniform mixing. The slurry was then uniformly coated onto aluminum foil and dried overnight in a vacuum oven at 80 °C. The electrode sheet was then removed, compacted on a tablet press, and finally cut into 14 mm diameter electrode discs using a slicing machine. The electrode sheet prepared based on lithium iron phosphate cathode material was used as the positive electrode, and lithium foil as the negative electrode. 1.0 M LiPF6 was dissolved in a solution of EC: EMC: DMC = 1:1:1 (v:v:v) as the electrolyte. A Celgard 2500 polypropylene organic microporous membrane was used as the separator. Coin cells were assembled in a glove box filled with high-purity argon gas, with each coin cell using 60 μL of electrolyte.

[0042] After assembling the button cell, the battery was charged and discharged using a NEWARE BTS (range: 0-5 V, 0-50 mA) charge and discharge tester at rates of 0.1 C and 1 C.

[0043] The comparison of charge-discharge curves at 0.1 C rate for lithium-ion batteries (i.e., the aforementioned coin cells) assembled using the lithium iron phosphate cathode material prepared in Example 1 and the lithium iron phosphate cathode materials prepared in Comparative Examples 1-4 is shown in the figure below. Figure 3 As shown, from Figure 3 It can be seen that lithium-ion batteries have a stable voltage plateau around 3.4 V, corresponding to Fe 2+ / Fe 3+ Redox pairs; furthermore, the 0.1 C discharge capacity of Example 1 is 162.8 mAh g. -1 The 1C discharge capacity is 140.2 mAh g. -1 ; Figure 4 The comparison of the 1C charge-discharge cycle curves of Example 1 and Comparative Examples 1-4 shows that the lithium-ion battery prepared in Example 1 has the best electrochemical performance.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing magnesium-vanadium dual-doped high-pressure lithium iron phosphate cathode material using a mixed iron source, characterized in that, Includes the following steps: Step 1: Ball mill and mix lithium source, mixed iron source, phosphorus source, magnesium source, vanadium source, carbon source and solvent to obtain slurry; Step 2: Spray dry the slurry to obtain precursor powder; Step 3: The precursor powder is sintered under an argon-hydrogen atmosphere to obtain magnesium-vanadium dual-doped high-pressure lithium iron phosphate.

2. The preparation method according to claim 1, characterized in that, The lithium source is one or more of lithium phosphate, lithium carbonate, dilithium hydrogen phosphate, lithium dihydrogen phosphate, and lithium hydroxide; the iron source is one or more of iron phosphate, ferric oxide, ferric oxide, ferrous oxalate, and iron powder; the phosphorus source is one or more of lithium phosphate, dilithium hydrogen phosphate, lithium dihydrogen phosphate, and phosphorus pentoxide; the magnesium source is one or more of magnesium carbonate, magnesium acetate, and magnesium oxide; the vanadium source is one or more of vanadium oxalate, vanadium pentoxide, and ammonium metavanadate; and the solvent is one or more of water, ethanol, methanol, and acetone.

3. The preparation method according to claim 1, characterized in that, With 100 parts of phosphorus source, the total molar amount of lithium and magnesium source is 100-105 parts, and the total molar amount of iron and vanadium source is 95-100 parts, of which the molar amount of vanadium source is 1-5 parts and the molar amount of magnesium source is 0.5-3 parts.

4. The preparation method according to claim 1, characterized in that, The carbon source is one or more of sucrose, glucose, cellulose, cyclodextrin, polyethylene glycol, phenolic resin, and starch; the amount of carbon source added is 5-15% of the total mass of lithium source, phosphorus source, iron source, magnesium source, and vanadium source.

5. The preparation method according to claim 1, characterized in that, The ball milling speed is 200~800 r / min, the ball-to-material mass ratio is 5~15:1, and the time is 3~10 h.

6. The preparation method according to claim 1, characterized in that, The inlet temperature during spray drying is 110-320℃, and the outlet temperature is 60-160℃.

7. The preparation method according to claim 1, characterized in that, The sintering conditions are as follows: heating from room temperature to 200-500 ℃ at a heating rate of 1-10 ℃ / min and holding at that temperature for 1-8 h; then heating to 650-850 ℃ at a heating rate of 1-10 ℃ / min and holding at that temperature for 3-15 h; and finally cooling to room temperature at a cooling rate of 1-20 ℃ / min.

8. A magnesium-vanadium dual-doped high-pressure lithium iron phosphate cathode material, characterized in that, The magnesium-vanadium dual-doped high-pressure lithium iron phosphate cathode material is prepared by the preparation method described in any one of claims 1-7.

9. A lithium-ion battery, characterized in that, Including the magnesium-vanadium dual-doped high-pressure lithium iron phosphate cathode material as described in claim 8.

10. The application of the magnesium-vanadium dual-doped high-pressure lithium iron phosphate cathode material as described in claim 8 in the preparation of lithium-ion batteries.

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