A high-rate lithium iron phosphate cathode material and its preparation method
By adding non-ferrous phosphates, grinding aids, and third-phase inhibitors to the preparation of lithium iron phosphate cathode materials, grain growth can be controlled, solving the problem of poor rate performance caused by excessive grain growth, and realizing efficient and safe production of nanomaterials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CAMEL GRP RESOURCE CYCLE XIANGYANG CO LTD
- Filing Date
- 2023-11-14
- Publication Date
- 2026-05-26
AI Technical Summary
Existing lithium iron phosphate cathode materials suffer from poor rate performance due to excessive grain growth during the preparation process, and the addition of ethanol increases costs and poses safety risks.
By adding non-ferric phosphates, grinding aids, and third-phase inhibitors, grain growth is controlled and carbon coating is improved to prepare nano-lithium iron phosphate materials.
This improved the rate performance of lithium iron phosphate cathode materials, reduced preparation costs and safety risks, and enabled efficient production of nanomaterials.
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Figure CN117486188B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery electrode materials, specifically to a high-rate lithium iron phosphate cathode material and its preparation method. Background Technology
[0002] Lithium iron phosphate (LFP) batteries have been widely used in power batteries and energy storage batteries. With the promotion of lithium battery applications, high-rate LFP batteries used as starting batteries have also attracted widespread attention. However, due to the low ionic and electronic conductivity of lithium iron phosphate, its rate performance is poor, which greatly limits the application of LFP batteries. Therefore, developing a high-rate LFP battery is of great significance.
[0003] Currently, industrial production technologies for lithium iron phosphate (LFP) cathode materials include the iron phosphate process, ferrous oxalate process, iron oxide red process, iron nitrate process, and hydrothermal process, with the iron phosphate process being the most prevalent. The iron phosphate process mainly involves batching (using iron phosphate and lithium carbonate as raw materials), coarse grinding, fine grinding, spray drying, sintering, pulverizing, batch mixing, demagnetization, and packaging. The processes before pulverization significantly impact the rate performance of LFP. In the preparation of high-rate LFP, the powder is typically ground to below 200 nm to ensure complete particle reaction. However, reducing the particle size makes it easier for particles to agglomerate, leading to excessive grain growth in subsequent sintering processes. When lithium carbonate dissolves in water, it is alkaline and ionizes to release hydroxide ions, which readily react with the ferric ions of iron phosphate dissolved in water to form red iron hydroxide. At around 400℃, the water vapor produced by the decomposition of ferric hydroxide reacts with the carbon source in the raw materials to generate water gas, reducing the carbon coating of the material and leading to excessive grain growth and a decrease in ionic conductivity. When only ferric phosphate and lithium carbonate participate in the reaction, a longer holding time is usually required to ensure complete reaction. However, the longer holding time results in larger lithium iron phosphate grains and more secondary growth. The grain size directly affects the rate performance of lithium iron phosphate; generally, materials with smaller grains have higher rate performance. Therefore, to prevent excessive ferric hydroxide production, some manufacturers add anhydrous ethanol during grinding to reduce the surface energy of the particles. Adding ethanol requires ethanol recovery equipment, and the factory construction level also needs to be upgraded, increasing costs and posing certain safety hazards for mass production. Summary of the Invention
[0004] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a high-rate lithium iron phosphate cathode material and its preparation method, thereby solving the technical problem of poor rate performance caused by excessive grain growth in the preparation of lithium iron phosphate cathode materials in the prior art.
[0005] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows:
[0006] In a first aspect, the present invention provides a method for preparing a high-rate lithium iron phosphate cathode material, comprising the following steps: (1) mixing powder raw materials with a solvent and stirring evenly to obtain material A; wherein the powder raw materials are a mixture of iron source, lithium source, non-ferrous phosphate, grinding aid, third phase inhibitor and organic carbon source, wherein the molar ratio of lithium iron phosphate is (1-1.5):(0.95-1):1; the non-ferrous phosphate accounts for 2-4% of the total phosphorus molar amount in the powder; the non-ferrous phosphate is a phosphate that does not contain iron phosphate; (2) grinding material A to obtain slurry B; (3) drying slurry B to obtain powder C; (4) calcining powder C under a protective atmosphere to obtain a high-rate lithium iron phosphate cathode material.
[0007] Secondly, the present invention provides a high-rate lithium iron phosphate cathode material prepared by the above-mentioned preparation method.
[0008] Compared with the prior art, the beneficial effects of the present invention include:
[0009] This invention reduces the amount of free ferric ions by adding non-ferrous phosphates, thereby reducing the amount of ferric hydroxide generated during slurry drying; it also adds grinding aids to reduce the initial particle size of the material and the generation of grinding by-reaction products, improving efficiency and thus enhancing carbon coating, inhibiting particle growth, and facilitating the preparation of nano-sized lithium iron phosphate; and it adds a third-phase inhibitor to suppress particle growth. Through the combination of these methods, the rate performance of lithium iron phosphate can be effectively improved (1C discharge specific capacity of 150–155 mAh / g, 3C discharge specific capacity of 143–148 mAh / g); moreover, no ethanol needs to be added during grinding, resulting in low-cost high-rate products and improved production safety. Attached Figure Description
[0010] Figure 1 This is a rate performance test diagram of the high-rate lithium iron phosphate cathode material prepared in Example 1 of the present invention. Detailed Implementation
[0011] 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.
[0012] This invention provides a high-rate lithium iron phosphate cathode material and its preparation method. By adding non-ferrous phosphates to reduce the dissolution of iron phosphate and decrease the content of ferric ions in the aqueous solution during grinding, and by adding grinding aids to shorten the grinding time while reducing the content of ferric hydroxide, a better carbon coating is formed on the surface of the lithium iron phosphate material. Finally, a third-phase inhibitor is added. The three factors work together to reduce excessive grain growth and improve the rate performance of the lithium iron phosphate cathode material.
[0013] The present invention discloses a method for preparing high-rate lithium iron phosphate cathode material, which mainly improves the rate performance of lithium iron phosphate cathode material through four processing steps, including the following steps:
[0014] (1) Mix the powder raw material with the solvent, and stir the material evenly with a stirring paddle to obtain material A;
[0015] The powder raw material is a mixture of iron source, lithium source, non-ferrous phosphate, grinding aid, third phase inhibitor and organic carbon source, wherein the molar ratio of lithium iron phosphate is (1~1.5):(0.95~1):1; and non-ferrous phosphate accounts for 2~4% of the total phosphorus molar amount in the powder.
[0016] Non-ferrous phosphates are phosphates that do not contain iron phosphate. The total phosphorus in material A comes from phosphorus-containing raw materials, such as iron phosphate and non-ferrous phosphates.
[0017] (2) Material A is pumped to the grinding chamber of the nano-sand mill by a vacuum pump and ground by the nano-sand mill to make the particle size of material A reach below 200nm, thus obtaining slurry B.
[0018] (3) The slurry B is dried into powder C by a centrifugal spray dryer.
[0019] (4) Powder C is sintered in a high-temperature atmosphere furnace to obtain high-rate lithium iron phosphate cathode material.
[0020] Preferably, in step (1), the iron source includes iron phosphate and iron oxide; the lithium source includes lithium carbonate; and the solid content in material A is 20-40%.
[0021] Preferably, in step (1), the amount of organic carbon source added accounts for 3wt% to 15wt% of the powder raw material, the amount of grinding aid added accounts for 0wt% to 1wt% of the powder raw material, and the amount of third phase inhibitor added accounts for 0.01wt% to 1wt% of the powder raw material.
[0022] Preferably, in step (1), the phosphate includes one or more of lithium dihydrogen phosphate, potassium phosphate, sodium phosphate, calcium phosphate, ammonium dihydrogen phosphate, and calcium dihydrogen phosphate.
[0023] Preferably, in step (1), the grinding aid includes one or more of carbon black, tricalcium phosphate, corundum, magnesium oxide, chromium oxide and diamond.
[0024] Preferably, in step (1), the third-phase inhibitor includes one or more of vanadium dioxide, yttrium oxide, cerium oxide, lanthanum oxide, corundum, magnesium oxide, and iron oxide.
[0025] Preferably, in step (1), the solvent is water; the organic carbon source includes one or more of polyethylene glycol and glucose.
[0026] Preferably, in step (2), material A is pumped to the grinding chamber of the nano-sand mill using a vacuum pump, and material A is ground by the nano-sand mill.
[0027] In a further preferred embodiment, the zirconium beads collide with material A by high-speed rotation (2000 rpm) inside the grinding chamber. This process lasts for 4 to 5 hours, so that the particle size of material A reaches below 200 nm, resulting in slurry B; or the material is first coarsely ground at 1500 rpm for 1 hour, and then finely ground at 2000 rpm for 4 hours, so that the particle size of material A reaches below 200 nm, resulting in slurry B.
[0028] Preferably, in step (3), the slurry B is transported to the atomizer at the top by a peristaltic pump. The atomizer centrifuges and atomizes the slurry B. Then, hot air at a temperature of 160-200°C is drawn in by an induced draft fan and a heating pipe to quickly dry the atomized slurry B. The resulting powdered precursor is cooled within 30 minutes (by means of air cooling, etc.) to avoid side reactions caused by high internal temperature.
[0029] Preferably, in step (4), the firing is carried out under a nitrogen atmosphere, with the temperature raised to 700-740°C and held for 7-9 hours; the third phase inhibitor plays a role in hindering grain boundary movement, consuming the energy of grain boundary movement, and making the grains smaller.
[0030] Main mechanism of action and advantages of this invention:
[0031] (1) The KSp of ferric hydroxide is = 1.0 × 10⁻⁶. -39 In an alkaline system, grinding easily produces ferric hydroxide, which easily generates water vapor during high-temperature sintering. Water vapor can cause abnormal particle growth, leading to a decrease in the rate performance of lithium iron phosphate. This invention reduces the solubility of ferric phosphate by adding phosphate (only non-ferrous phosphate substances), thereby reducing the content of ferric ions in the aqueous solution and achieving the purpose of reducing / inhibiting the formation of ferric hydroxide.
[0032] (2) The present invention improves grinding efficiency, reduces the initial particle size of materials and reduces the generation of grinding byproducts by adding grinding aids.
[0033] (3) The present invention adds a third phase inhibitor to hinder grain boundary movement and expansion during sintering, thereby reducing grain size and preventing abnormal grain growth by consuming the ability of grain boundary expansion.
[0034] By combining the above methods, this invention can also improve the carbon coating degree of the material, reduce the impact of excessive grain growth, and improve the rate performance of lithium iron phosphate.
[0035] The present invention will be further described in detail below through specific embodiments and comparative examples.
[0036] Example 1
[0037] In this embodiment, lithium dihydrogen phosphate is used to reduce the content of free ferric ions in the solution; carbon black is used as a grinding aid and vanadium dioxide is used as a third-phase inhibitor.
[0038] Step 1: According to the molar ratio of lithium iron phosphate to phosphorus of 1.02:0.97:1, take iron phosphate, iron oxide (to prepare the required iron), lithium dihydrogen phosphate, carbon black, vanadium dioxide and lithium carbonate and put them in water. Then, add polyethylene glycol and glucose in a mass ratio of (1:1.8) as organic carbon sources to obtain material A with a solid content of 23%.
[0039] Based on the total mass of iron phosphate, iron oxide, lithium dihydrogen phosphate, carbon black, vanadium dioxide, lithium carbonate, polyethylene glycol, and glucose, the addition amount of organic carbon source (polyethylene glycol and glucose) is 10%, the addition amount of grinding aid (carbon black) is 0.31 wt%, and the addition amount of third phase inhibitor (vanadium dioxide) is 0.74 wt%.
[0040] Lithium dihydrogen phosphate accounts for 3% of the total phosphorus molar amount in the powder raw material.
[0041] Step 2: Material A is first coarsely ground at 1500 rpm for 1 hour, and then finely ground at 2000 rpm for 4 hours to obtain particle size D. 50 Slurry B with a diameter of <200nm.
[0042] Step 3: Slurry B is fed into the spray dryer at a feed rate of 2500 ml / h, and the spray inlet air temperature is 180℃ to prepare powdered precursor C.
[0043] Step 4: Place the powdered precursor C in a graphite crucible, put it into a high-temperature atmosphere furnace, and heat it to 720°C at a heating rate of 2.5°C / min under a nitrogen atmosphere. Hold it at this temperature for 8 hours to perform solid-state sintering and obtain high-rate lithium iron phosphate cathode material.
[0044] One gram of the prepared high-rate lithium iron phosphate cathode material was mixed with conductive carbon black and PVDF at a mass ratio of 90:5:5, and NMP was added to form a slurry. This slurry was coated onto aluminum foil, dried, and pressed to form an electrode. Using lithium metal as the negative electrode, PP as the separator, and 1.1 mol / L LiPF6 as the electrolyte, a coin cell was assembled in a glove box. Capacity tests were conducted at 0.1C and 3C currents, with a voltage range of 2.0V to 3.9V. The charge / discharge method was as follows: constant current charging at 0.1C until the voltage reached 3.9V, followed by constant voltage charging to 0.01C cutoff; constant current discharging at 0.1C and 3C, with a discharge termination voltage of 2.0V.
[0045] Depend on Figure 1It can be seen that the lithium iron phosphate cathode material prepared in Example 1 has a discharge specific capacity of 162 mAh / g at 0.1C, a discharge specific capacity of 155 mAh / g at 1C, and a discharge specific capacity of 148 mAh / g at 3C.
[0046] Example 2
[0047] The only difference between Example 2 and Example 1 is that the amount of lithium dihydrogen phosphate added is reduced to 2.5% of the total molar amount of phosphorus in the powder raw material (the amount of lithium carbonate and iron phosphate is adjusted accordingly to ensure that the molar ratio of lithium, iron and phosphorus in the powder raw material is 1.02:0.97:1); the other steps and conditions are the same as in Example 1.
[0048] According to the coin cell test, the lithium iron phosphate cathode material obtained in Example 2 has a discharge specific capacity of 159 mAh / g at 0.1C, 150 mAh / g at 1C, and 143 mAh / g at 3C.
[0049] Example 3
[0050] The only difference between Example 3 and Example 1 is that the powder raw materials of Example 1 are used for formulation, but no grinding aid is added. The other steps and conditions are the same as those of Example 1.
[0051] According to the coin cell test, the lithium iron phosphate cathode material obtained in Example 3 has a discharge specific capacity of 162 mAh / g at 0.1C, 154 mAh / g at 1C, and 147 mAh / g at 3C.
[0052] Example 4
[0053] The only difference between Example 4 and Example 1 is that the powder raw materials of Example 1 are used for formulation, but no third-phase inhibitor is added. The other steps and conditions are the same as those of Example 1.
[0054] According to the coin cell test, the lithium iron phosphate cathode material obtained in Example 4 has a discharge specific capacity of 160 mAh / g at 0.1C, 151 mAh / g at 1C, and 143 mAh / g at 3C.
[0055] Comparative Example 1
[0056] The only difference between Comparative Example 1 and Example 1 is that iron phosphate is used as the sole source of phosphorus, and no phosphate (lithium dihydrogen phosphate) is added. The other steps and conditions are the same as in Example 1.
[0057] According to the coin cell test, the lithium iron phosphate cathode material obtained in Comparative Example 1 has a discharge specific capacity of 158 mAh / g at 0.1C, 146 mAh / g at 1C, and 137 mAh / g at 3C.
[0058] Comparative Example 2
[0059] The only difference between Comparative Example 2 and Example 1 is that iron phosphate is used as the sole source of phosphorus, and no phosphate (lithium dihydrogen phosphate), grinding aid, or third-phase inhibitor is added. All other steps and conditions are the same as in Example 1.
[0060] According to the coin cell test, the lithium iron phosphate cathode material obtained in Comparative Example 2 has a discharge specific capacity of 155 mAh / g at 0.1C, 143 mAh / g at 1C, and 133 mAh / g at 3C.
[0061] Compared with Example 1, Example 2 contains a small amount of phosphate, while Comparative Example 1 does not contain phosphate. The results show that the effects are not as good as those of Example 1 (with the addition of an appropriate amount of phosphate). In this invention, if too little phosphate is added, it will not be able to completely inhibit the dissolution of iron ions, while too much will act as an impurity and affect the performance of the material.
[0062] As can be seen from Examples 1 and 3, the grinding aid does not have a decisive effect on the production of ferric hydroxide in this invention, but mainly affects the grinding time. However, if too much is added, it will also be an impurity, and if too little is added, the grinding time will be longer.
[0063] As can be seen from Examples 1 and 4, the performance of the material obtained without adding a third-phase inhibitor is lower than that of Example 1, and excessive addition is also an impurity that affects the performance of the material.
[0064] In Comparative Example 1, no non-ferrous phosphate was used, which produced more ferric hydroxide during the drying process, resulting in a 11 mAh / g decrease in discharge specific capacity at 3C rate compared to Example 1. In Comparative Example 2, the grinding aid and third-phase inhibitor were further removed compared to Comparative Example 1, leading to a further decrease in discharge specific capacity at high rates. This indicates that the use of non-ferrous phosphate, grinding aid, and third-phase inhibitor in this invention produced a synergistic effect.
[0065] As can be seen from the examples and comparative examples:
[0066] 1) By adding phosphates to reduce the amount of free ferric ions, the amount of ferric hydroxide generated during the slurry drying process can be reduced. Lithium dihydrogen phosphate can be used to replace lithium carbonate, or any phosphorus source that does not produce hydroxide ions when dissolved in water can be used to reduce the amount of ferric hydroxide generated.
[0067] 2) Introduce grinding aids to reduce side effects during grinding while achieving the goal of rapidly reducing material particle size;
[0068] 3) The formation of a third phase can be achieved by using inhibitors, or by using impurities in low-grade raw materials or by forming a small amount of liquid phase to hinder the movement of grain boundaries. During sintering, this can hinder the expansion of grain boundaries, thereby reducing the grain growth rate, reducing the grain size, and improving the rate performance of the material.
[0069] In summary, the method for improving the rate performance of lithium iron phosphate cathode materials according to the present invention involves weighing the required materials, with the preferred molar ratio of lithium iron phosphate to phosphorus being 1.02:0.97:1. An organic carbon source (3wt%–15wt%) is then added, and the material is placed in a solvent for the next step. In this invention, the concentration of ferric ions in the solution is reduced by adding phosphate, thus reducing the generation of the grinding byproduct ferric hydroxide; a grinding aid (0wt%–1wt%) is added to improve grinding efficiency while reducing material particle size; and a third-phase inhibitor (0.01wt%–1wt%), typically an impurity or trace element in lithium iron phosphate, is added to hinder grain boundary expansion during sintering and prevent excessive grain growth. The amount of iron hydroxide produced during the drying process of the obtained sample was significantly reduced, thereby reducing the water vapor generated during the sintering process, enhancing the carbon coating on the surface of lithium iron phosphate grains, preventing excessive grain growth, and improving the rate performance of the material. In particular, Example 1, which contains appropriate amounts of phosphate and appropriate amounts of third-phase inhibitor, can produce a synergistic effect, reducing the primary particle size of lithium iron phosphate and significantly improving the rate performance. The 1C discharge specific capacity can reach 155 mAh / g, and the 3C discharge specific capacity can reach 148 mAh / g.
[0070] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.
Claims
1. A method for preparing a high-rate lithium iron phosphate cathode material, characterized in that, Includes the following steps: (1) Mix the powder raw material with the solvent and stir evenly to obtain material A; the powder raw material is a mixture of iron source, lithium source, non-ferrous phosphate, grinding aid, third phase inhibitor and organic carbon source, wherein the molar ratio of lithium iron phosphorus is (1~1.5):(0.95~1):1; the non-ferrous phosphate accounts for 2~4% of the total phosphorus molar amount in the powder raw material; Non-ferrous phosphates are phosphates that do not contain iron phosphate; the non-ferrous phosphate is lithium dihydrogen phosphate; the third-phase inhibitor is vanadium dioxide; the grinding aid is carbon black. The grinding aid is added at a rate of 0 wt% to 1 wt% of the powder raw material, and the third-phase inhibitor is added at a rate of 0.01 wt% to 1 wt% of the powder raw material. (2) Grind material A to obtain slurry B; (3) Dry slurry B into powder C; (4) Under a protective atmosphere, powder C is calcined to obtain high-rate lithium iron phosphate cathode material.
2. The method for preparing high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, In step (1), the iron source includes iron phosphate and iron oxide; the lithium source includes lithium carbonate; and the solid content in material A is 20-40%. The amount of organic carbon source added accounts for 3wt% to 15wt% of the powder raw material.
3. The method for preparing high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, In step (1), the solvent is water; the organic carbon source includes one or more of polyethylene glycol and glucose.
4. The method for preparing high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, In step (2), material A is ground to a particle size of less than 200 nm using a nano-grind mill to obtain slurry B.
5. The method for preparing high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, In step (3), slurry B is dried by centrifugal spraying, with the spray inlet air temperature being 160-200℃.
6. The method for preparing high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, In step (4), the firing is carried out under a nitrogen atmosphere by heating to 700-740°C and holding for 7-9 hours.
7. The high-rate lithium iron phosphate cathode material prepared by the preparation method according to any one of claims 1-6.