Lithium iron phosphate and a method for preparing the same
By using a composite carbon source in the lithium iron phosphate preparation process, a uniform conductive carbon layer and an oxidizing atmosphere are formed, solving the problem of iron phosphide formation at high temperatures and improving the battery performance and safety of lithium iron phosphate.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHANGZHOU LIYUAN NEW ENERGY TECH CO LTD
- Filing Date
- 2026-04-16
- Publication Date
- 2026-06-30
AI Technical Summary
In the process of preparing lithium iron phosphate by high-temperature solid-state method, how to effectively suppress the formation of iron phosphide in order to avoid its damage to battery performance, especially the rapid capacity decay and safety hazards.
Using conventional carbon sources, polyethylene glycol, and organic compounds containing sulfonic acid groups as composite carbon sources, a uniform conductive carbon layer and oxidizing atmosphere are formed on the surface of lithium iron phosphate particles to inhibit the excessive reduction of lithium iron phosphate to iron phosphide. This includes the use of sulfonic acid groups such as methanesulfonic acid, ethylsulfonic acid, and sodium dodecylbenzene sulfonate, combined with the surface activity and bridging effect of polyethylene glycol, to promote uniform mixing and carbon coating.
It significantly inhibits the formation of iron phosphide, improves the electronic conductivity and cycle stability of lithium iron phosphate cathode materials, enhances the battery's initial efficiency and rate performance, prevents electrolyte side reactions, and extends battery life.
Smart Images
Figure CN122301159A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a lithium-ion electrode material, and more particularly to a lithium iron phosphate that can effectively suppress the formation of iron phosphide and its preparation method. Background Technology
[0002] Lithium iron phosphate (LiFePO4, LFP) is widely used in the lithium-ion battery field due to its core advantages such as high safety, long cycle life, low cost, and good thermal stability. Moreover, its application areas are rapidly expanding from traditional markets to emerging fields. Its core application area is electric vehicles and electric transportation, which is the largest and fastest-growing market for LFP batteries. The second largest application area is large-scale energy storage systems, where LFP's lifespan and safety perfectly meet energy storage requirements. Currently, the most mature, highest-volume, and lowest-cost industrial route for lithium iron phosphate is the high-temperature solid-state method, which accounts for the vast majority of industrial production. Its core idea is to uniformly mix iron, lithium, phosphorus, and carbon sources, and then sinter them at an inert high temperature, resulting in a solid-solid reaction to directly synthesize lithium iron phosphate. As the demands for compaction and energy density in batteries increase, the sintering temperature in the lithium iron phosphate (LFP) material preparation process is gradually rising. The high temperature and the reducing atmosphere generated by carbon source decomposition inevitably lead to the formation of iron phosphide (FeP). The higher the calcination temperature, the easier it is for FeP to form, mainly because the reducing atmosphere at high temperatures has a stronger reducing effect, easily reducing LiFePO4. Iron phosphide (such as Fe3P, Fe2P, and FeP) is a highly harmful impurity in LFP cathode materials. Even trace amounts (typically at the ppm level) can cause severe or even fatal damage to battery performance; this damage is systemic, irreversible, and detrimental. Its harm stems from its high electronic conductivity as an inactive substance, which disrupts the inherent stable structure of the LFP system—an insulator that allows lithium ions to pass through. By establishing a conductive network within the cathode material, it triggers severe internal micro-short circuits, leading to abnormally high self-discharge, rapid capacity decay, and a sharp drop in cycle life, thus creating safety hazards. Lithium iron phosphate (LFP) batteries are renowned for their high safety and long lifespan, advantages built upon a stable olivine crystal structure and a lean electrolyte reaction system. The introduction of iron phosphide fundamentally disrupts this "insulating substrate," its presence signifying a loss of control in the production process and acting as a "poison" for battery performance. Suppressing iron phosphide formation is a crucial breakthrough for the further development of LFP materials. However, currently, there is no effective method to avoid a strong reducing atmosphere that promotes iron phosphide formation during the high-temperature LFP preparation process. Summary of the Invention
[0003] Purpose of the invention: The purpose of this invention is to solve the problem of how to effectively suppress the generation of iron phosphide and suppress the rapid decay of battery capacity in the high-temperature solid-phase production process of lithium iron phosphate, and to provide a method for synthesizing lithium iron phosphate; another purpose of this invention is to provide lithium iron phosphate prepared by the above method.
[0004] Technical solution: The method for preparing lithium iron phosphate according to the present invention includes the following steps:
[0005] (S1) Mix the iron source, lithium source, phosphorus source and carbon source evenly according to the stoichiometric ratio;
[0006] (S2) The uniformly mixed materials are ground, dried and sintered to obtain lithium iron phosphate;
[0007] The carbon source includes conventional carbon sources, polyethylene glycol, and organic compounds containing sulfonic acid groups.
[0008] Furthermore, the sulfonic acid-containing organic compounds include one or more of methanesulfonic acid, ethylsulfonic acid, sodium dodecylbenzenesulfonate, sodium p-toluenesulfonate, sodium 1-naphthalenesulfonate, and sulfonate esters.
[0009] Furthermore, the molar ratio of the iron source to the organic compound containing sulfonic acid groups is 1:0.0001~0.0005.
[0010] Furthermore, the conventional carbon source is selected from glucose and sucrose. The molar ratio of the iron source to glucose, polyethylene glycol, and organic compounds containing sulfonic acid groups is 1:0.02~0.03:0.007~0.01:0.0001~0.0005.
[0011] Glucose and sucrose are commonly used as primary carbon sources for lithium iron phosphate (LFP) due to their low cost. However, their poor coating properties on LFP affect its performance. Therefore, glucose needs to be used in combination with other small amounts of carbon source additives during LFP preparation to ensure the quality of the carbon layer. Polyethylene glycol (PEG) possesses surface activity, effectively reducing the surface tension at the solid-liquid interface in the slurry during raw material mixing, preventing material agglomeration, promoting uniform mixing, and facilitating the formation of LFP precursors with perfect crystal structure and uniform particle morphology. Simultaneously, the hydroxyl groups at both ends of PEG are active, acting as a bridge connecting one end to LFP particles and the other end to sulfonic acid groups, promoting the uniform distribution of sulfonic acid organic matter on the surface of LFP particles, thus laying the groundwork for the subsequent formation of a uniform carbon coating layer. During high-temperature sintering, polyethylene glycol and sulfonic acid-based organic compounds uniformly coated on the surface of the lithium iron phosphate precursor undergo pyrolysis and carbonization, compensating for the uneven coating of conventional carbon sources. This forms a uniform conductive carbon layer on the surface of the lithium iron phosphate particles, significantly improving the electronic conductivity of the finished lithium iron phosphate cathode material while suppressing electrolyte side reactions, thereby enhancing initial efficiency, rate performance, and cycle stability. Simultaneously, the sulfonic acid groups decompose at high temperatures to generate SO3, which has a certain oxidizing property. This SO3 counteracts some of the reducing atmosphere on the surface of the lithium iron phosphate particles, thus inhibiting the excessive reduction of lithium iron phosphate to iron phosphide. Polyethylene glycol acts as a bridge, promoting the uniform dispersion of a small amount of sulfonic acid-based organic compounds throughout the raw materials and ensuring sufficient contact between the generated small amount of oxidizing SO3 gas and lithium iron phosphate. Furthermore, the sulfonic acid-based compounds exhibit high chemical stability, remaining stable under certain temperature and acid / alkali conditions. This ensures that more sulfonic acid-based compounds decompose during the high-temperature calcination stage, thereby guaranteeing the thoroughness and effectiveness of inhibiting the excessive reduction of lithium iron phosphate to iron phosphide. Meanwhile, the uniform carbon coating can effectively block the contact between the reducing atmosphere and lithium iron phosphate, achieving a dual protection effect.
[0012] Furthermore, in step (S2), the particle size D after grinding... 50 The wavelength is 450~550nm.
[0013] Furthermore, in step (S2), the sintering temperature is 780~850℃ and the sintering time is 5~10h.
[0014] Furthermore, step (S1) also includes titanium dioxide, and the molar ratio of iron source to titanium dioxide is 1:0.01~0.02.
[0015] Furthermore, in step (S1), the iron source is selected from iron phosphate, the lithium source is selected from lithium carbonate, and the phosphorus source is selected from phosphoric acid; the molar ratio of iron phosphate to lithium carbonate and phosphoric acid is 1:0.5~0.55:0.005~0.01.
[0016] Beneficial Effects: Compared with the prior art, the present invention has the following significant advantages: 1. It selects conventional carbon sources, polyethylene glycol, and organic compounds containing sulfonic acid groups as composite carbon sources. Polyethylene glycol promotes the uniformity of raw material mixing and carbon coating. SO3, which has a certain oxidizing property, is generated by the decomposition of sulfonic acid groups. It counteracts and consumes a certain amount of reducing atmosphere on the surface of lithium iron phosphate particles, thereby inhibiting the excessive reduction of lithium iron phosphate to iron phosphide; 2. Polyethylene glycol and sulfonic acid group organic compounds undergo pyrolysis and carbonization, which makes up for the problem of uneven coating of conventional carbon sources. A uniform conductive carbon layer is formed on the surface of lithium iron phosphate particles, which can significantly improve the electronic conductivity of the finished lithium iron phosphate cathode material, while inhibiting electrolyte side reactions, thereby improving the first-efficiency and rate performance; 3. The sulfonic acid group compounds have high chemical stability and remain stable under certain temperature and acid-base conditions, ensuring that more sulfonic acid group compounds decompose during the high-temperature calcination stage, thereby ensuring the thoroughness and effectiveness of inhibiting the excessive reduction of lithium iron phosphate to iron phosphide. Attached Figure Description
[0017] Figure 1 This is a scanning electron microscope image of Embodiment 1 of the present invention;
[0018] Figure 2 This is a scanning electron microscope image of Comparative Example 1 of the present invention;
[0019] Figure 3 This is a comparison XRD pattern of Embodiment 1 and Comparative Example 1 of the present invention;
[0020] Figure 4 These are photographs of the YueMei cleanliness analyzer used in Embodiments 1-7 of the present invention;
[0021] Figure 5 These are photographs of the YueMei cleanliness analyzer used in Comparative Examples 1-4 of this invention. Detailed Implementation
[0022] The technical solution of the present invention will be further described below with reference to specific embodiments. All reagents used are commercially available. In the embodiments, iron phosphate is selected as the iron source, lithium carbonate as the lithium source, and phosphoric acid as the phosphorus source. The molar ratio of iron phosphate to lithium carbonate and phosphoric acid is 1:0.51:0.0078, and the molar ratio of iron source to titanium dioxide is 1:0.017 (the technical effect of the present invention can be achieved when the molar ratio of iron phosphate to lithium carbonate and phosphoric acid is in the range of 1:0.5~0.55:0.005~0.01, and the molar ratio of iron source to titanium dioxide is in the range of 1:0.01~0.02). Glucose (sucrose can also achieve the technical effect of the present invention) is a conventional carbon source. The effects of the type and amount of carbon source on inhibiting the production of iron phosphate and inhibiting the rapid decay of battery capacity are discussed.
[0023] Example 1
[0024] A method for preparing lithium iron phosphate includes the following steps:
[0025] (S1) Weigh 2000g (13.26mol) of ferric phosphate, 504g (6.82mol) of lithium carbonate, 88g (0.4mol) of glucose, 160g (0.106mol) of polyethylene glycol, 18g (0.225mol) of titanium dioxide, 12g (0.104mol) of 85% phosphoric acid, and 0.384g (0.004mol) of methanesulfonic acid. Add these to 8000g of demineralized water and stir evenly in a mixing tank. Transfer the mixture to a sand mill and grind it until D is achieved. 50 450-550nm;
[0026] (S2) The material after sand milling is spray dried at 180~220℃. The dried powder is transferred into a sagger and placed in a nitrogen atmosphere furnace and calcined at 780~850℃ for 5~10 hours. After cooling to room temperature, it is pulverized by air jet mill to obtain lithium iron phosphate.
[0027] Example 2
[0028] The carbon source differs from that in Example 1 in that it is: 58.67 g (0.27 mol) of glucose, 140 g (0.093 mol) of polyethylene glycol, and 1.39 g (0.004 mol) of sodium dodecylbenzenesulfonate.
[0029] Example 3
[0030] The carbon source differs from that in Example 1 as follows: 66g glucose (0.3mol), 200g polyethylene glycol (0.133mol), and 0.742g 98% ethyl sulfonic acid (0.0066mol).
[0031] Example 4
[0032] The carbon source differs from that in Example 1 in that it is: 88g glucose (0.4mol), 200g polyethylene glycol (0.133mol), and 0.24g sodium p-toluenesulfonate (0.0012mol).
[0033] Example 5
[0034] The carbon source differs from that in Example 1 as follows: 66g glucose (0.3mol), 160g polyethylene glycol (0.106mol), and 0.52g sodium 1-theasulfonate (0.0025mol).
[0035] Example 6
[0036] The carbon source differs from that in Example 1 in that it is: 66g (0.3mol) of glucose, 140g (0.093mol) of polyethylene glycol, and 0.932g (0.0066mol) of 2-hydroxyethyl methanesulfonate.
[0037] Example 7
[0038] The carbon source differs from that in Example 1 in that it is: 66g (0.3mol) of glucose, 160g (0.106mol) of polyethylene glycol, 0.192g (0.002mol) of methanesulfonic acid and 0.225g (0.002mol) of 98% ethylsulfonic acid.
[0039] Comparative Example 1
[0040] Unlike Example 1, only 88g of glucose was added as the carbon source.
[0041] Comparative Example 2
[0042] Unlike Example 1, polyethylene glycol is not added as the carbon source.
[0043] Comparative Example 3
[0044] Unlike Example 1, no methanesulfonic acid was added to the carbon source.
[0045] Comparative Example 4
[0046] The carbon source differs from that in Example 1 in that it is: 88g glucose (0.4mol), 140g polyethylene glycol (0.093mol), and 1.5g methanesulfonic acid (0.96mol).
[0047] The charge-discharge performance and iron phosphide content of the lithium iron phosphate prepared in the above examples and comparative examples were tested. The test results are detailed in Tables 1 and 2. Test method for charge-discharge performance: The lithium iron phosphate cathode material, Super-P, and PVDF prepared in the above examples and comparative examples were coated on aluminum foil in a 90:5:5 ratio. The anode was lithium metal. A 1 mol / L LiPF6 EC:DMC:EMC (volume ratio 1:1:1) solution was used as the electrolyte. A Celgard 2400 microporous polypropylene membrane was used as the separator. A coin cell was assembled in an argon-filled glove box and tested on a blue-light testing system. Test method for iron phosphide content: 1 kg of pulverized lithium iron phosphate was added to 6 L of demineralized water. A wrapped magnetic rod was added and stirred in a mill for 1 hour. The magnetic material on the magnetic rod was scraped off, and the magnetic material was filtered through a 0.2-micron filter membrane. The black particles observed by photographing with a YueMei cleanliness analyzer are iron phosphide. See details... Figure 4-5 .
[0048] Table 1. Performance test results of lithium iron phosphate prepared in each embodiment.
[0049]
[0050] Comparison of key indicator detection results for Examples 1-7 is shown in Table 1 and Figure 4As shown, comparing Examples 1 and 2, the inhibitory effect of organic compounds containing sulfonic acid groups on iron phosphide at the same temperature with the same proportion is basically the same. Comparing Examples 2 to 7, it can be concluded that the proportion of sulfonic acid groups has a significant impact on the inhibitory effect on iron phosphide. Within a certain range, the higher the proportion of sulfonic acid groups, the stronger the inhibitory effect on iron phosphide. In Example 4, when the molar ratio of sulfonic acid group dosage to iron source is close to 0.0001, the iron phosphide content increases slightly, while below this dosage, the iron phosphide content increases significantly.
[0051] Table 2. Performance test results of lithium iron phosphate prepared in each comparative example.
[0052]
[0053] From Table 1-2 and Figure 4-5 Comparing the data from Example 1 and Comparative Examples 1-3, Comparative Examples 1 and 3 did not use organic compounds containing sulfonic acid groups as a carbon source, resulting in a significant increase in the iron phosphide content in the finished lithium iron phosphate product. Although Comparative Example 2 used organic compounds containing sulfonic acid groups as a carbon source, which had a certain effect on inhibiting iron phosphide formation, it lacked the PEG synergistic effect compared to Example 1, leading to a weaker inhibition effect. Figure 1-3 As shown, the XRD and SEM comparisons of Example 1 and Comparative Example 1 also demonstrate that the novel carbon coating process used in Example 1 can effectively suppress the formation of iron phosphide. Comparing Example 1 and Comparative Example 4, the sulfonic acid-containing organic compound synergistically inhibits iron phosphide formation with PEG. However, excessively high proportions of the sulfonic acid-containing organic compound lead to excessively high carbon content, inhibiting particle growth and ultimately reducing the compaction density and capacity of lithium iron phosphate.
Claims
1. A method for preparing lithium iron phosphate, characterized in that, Includes the following steps: (S1) Mix the iron source, lithium source, phosphorus source and carbon source evenly according to the stoichiometric ratio; (S2) The uniformly mixed materials are ground, dried and sintered to obtain lithium iron phosphate; The carbon source includes conventional carbon sources, polyethylene glycol, and organic compounds containing sulfonic acid groups.
2. The method for preparing lithium iron phosphate according to claim 1, characterized in that, The sulfonic acid-containing organic compounds include one or more of the following: methanesulfonic acid, ethylsulfonic acid, sodium dodecylbenzenesulfonate, sodium p-toluenesulfonate, sodium 1-naphthalenesulfonate, and sulfonates.
3. The method for preparing lithium iron phosphate according to claim 2, characterized in that, The molar ratio of the iron source to the organic compound containing sulfonic acid groups is 1:0.0001~0.0005.
4. The method for preparing lithium iron phosphate according to claim 3, characterized in that, The conventional carbon source is selected from glucose and sucrose.
5. The method for preparing lithium iron phosphate according to claim 4, characterized in that, The molar ratio of the iron source to glucose, polyethylene glycol, and organic compounds containing sulfonic acid groups is 1:0.02~0.03:0.007~0.01:0.0001~0.0005.
6. The method for preparing lithium iron phosphate according to claim 1, characterized in that, In step (S2), the particle size D after grinding 50 The wavelength is 450~550nm.
7. The method for preparing lithium iron phosphate according to claim 1, characterized in that, In step (S2), the sintering temperature is 780~850℃ and the sintering time is 5~10h.
8. The method for preparing lithium iron phosphate according to claim 1, characterized in that, The step (S1) also includes titanium dioxide, and the molar ratio of iron source to titanium dioxide is 1:0.01~0.
02.
9. The method for preparing lithium iron phosphate according to claim 1, characterized in that, In step (S1), the iron source is iron phosphate, the lithium source is lithium carbonate, and the phosphorus source is phosphoric acid; the molar ratio of iron phosphate to lithium carbonate and phosphoric acid is 1:0.5~0.55:0.005~0.
01.
10. Lithium iron phosphate prepared by the method of claim 1.