Method for synthesizing phosphate-triple-composite cathode material assisted by ion accelerator

Abstract

The application relates to a preparation method of a phosphate-triple-composite positive electrode material assisted by an ion accelerator. Firstly, the phosphate positive electrode material is nano-sized to shorten an ion transmission path. Then, iron oxide is used as a bridge to realize effective connection of the nano-sized phosphate positive electrode material on the surface of the triple positive electrode material. The iron oxide serves as an "ion accelerator", so that the composite material not only has high energy density and cycle stability, but also can still work stably under extreme conditions such as high and low temperatures.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode materials, and in particular relates to a method for synthesizing phosphate-ternary composite cathode materials with the assistance of an ion accelerator. Background Technology

[0002] With the continuous development of the new energy field, electric vehicles have gradually become the main type of new energy vehicles, and lithium-ion batteries are the most common power source for them. Due to their characteristics such as low self-discharge frequency, high energy density, and long service life, lithium-ion batteries have gradually become the preferred choice for new energy vehicles. However, conventional lithium-ion batteries experience a rapid decline in specific capacity and cycle stability under low or high temperature conditions. Therefore, the development of high-energy-density, long-life lithium-ion batteries for extreme environments is urgently needed.

[0003] As is well known, cathode materials, as a key factor affecting various battery performance indicators, need to possess characteristics such as high potential, high specific capacity, high energy density, excellent safety, rate performance, and long lifespan. Currently, layered ternary cathode materials (NCM) and lithium iron phosphate (LiFePO4) are still the main cathode materials on the market. Although NCM has high energy density, it is expensive, has poor cycle performance, and low safety. While phosphate cathode materials have the advantages of low cost and long cycle life, they are limited by low conductivity. Therefore, combining the two electrode materials to complement each other's strengths will be the future development trend. CN104733708A and CN111653752B disclose a method for preparing a composite cathode material of LiFePO4 coated with NCM. Although the electrochemical performance is effectively improved, it does not consider the impact of extreme high or low temperature environments on the battery material. It is worth noting that battery performance is severely limited by extreme environments. When the battery operates at low temperatures, the increased viscosity of the electrolyte greatly limits the lithium-ion migration rate and causes capacity decay. High temperatures can effectively accelerate lithium-ion transport rates, but they also accelerate interfacial side reactions, ultimately leading to battery performance degradation. Therefore, there is an urgent market need for lithium-ion batteries that can operate for extended periods across a wide temperature range. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method for ion accelerator-assisted synthesis of phosphate-ternary composite cathode materials.

[0005] The technical solution adopted in this invention is as follows: A method for ion accelerator-assisted synthesis of phosphate-ternary composite cathode materials includes the following steps: (1) Using ternary cathode material LiNi x Co y Mn 1-x-yO2 is dispersed in a solvent to form solution A. The iron source is dissolved in the solvent to obtain solution B. Then, solution B is uniformly added dropwise to solution A and stirred thoroughly to obtain a mixture. After drying the mixture, it is transferred to an O2 atmosphere for calcination to obtain a ternary material coated with iron oxide. (2) The phosphate cathode material is nano-sized in a high-energy ball mill and freeze-dried to obtain nano-sized phosphate cathode material; the ternary cathode material coated with iron oxide obtained in step (1) is uniformly dispersed in a solvent, the nano-sized phosphate cathode material is added and stirred continuously, and dried until the solvent is completely evaporated to obtain phosphate cathode and iron oxide modified ternary material.

[0006] Preferably, in step (1) LiNi x Co y Mn 1-x-y In O2, 0.45≤x≤0.98, 0≤y≤0.55.

[0007] Preferably, in step (1), the amount of iron source added accounts for 1-10% of the mass of the ternary material.

[0008] Preferably, the iron source includes one or more of ferric chloride hexahydrate, ferrous chloride, ferric phosphate, ferrous phosphate, ferric ammonium citrate, ferrous oxalate, and ferric acetylacetone.

[0009] Preferably, the sintering temperature in step (1) is 200-600℃ and the sintering time is 1-5 h.

[0010] Preferably, in step (2), the amount of nano-sized phosphate cathode material added accounts for 2-6% of the mass of the ternary material coated with iron oxide.

[0011] Preferably, the phosphate cathode material is selected from one or more of lithium iron phosphate, lithium manganese iron phosphate, and lithium vanadium phosphate.

[0012] Preferably, in step (2), the high-energy ball mill adopts wet ball milling, and the solvent can be one or more of deionized water, anhydrous ethanol, and acetone; the power is 15-35 Hz, and the time is 1-5 h.

[0013] Preferred, LiNi x Co y Mn 1-x-y The preparation method of O2 ternary cathode material is as follows: lithium salt and ternary precursor LiNi x Co y Mn 1-x-y (OH)₂ was mixed in a specific molar ratio, and solvent was added and stirred thoroughly. After the solvent evaporated, the mixture was transferred to a tube furnace under an O₂ atmosphere. A two-stage sintering process was then used to obtain a high-nickel ternary cathode material (LiNi). x Co yMn 1-x- y O2).

[0014] Furthermore, the lithium salt can be selected from any one or more of lithium hydroxide, lithium carbonate, lithium acetate, and lithium bis(trifluoromethanesulfonyl)imide; the precursor LiNi x Co y Mn 1-x-y The elemental content of (OH)₂ is 0.45≤x≤0.98, 0≤y≤0.55; in the two-stage sintering process, the first stage is 350-500℃, and the sintering time is 3-6 h. The second stage is 700-950℃, and the sintering time is 10-18 h.

[0015] Furthermore, the selected solvent is one or more of deionized water, anhydrous ethanol, N-methylpyrrolidone, diethyl ether, acetone, and diethyl ether. Furthermore, O2 is introduced during the calcination process, with the gas flow rate controlled at 80-200 ml·min. -1 .

[0016] The beneficial effects of this invention are as follows: 1. This invention utilizes a high-energy ball mill and freeze-drying technology to achieve nano-sizing of phosphate-based cathode materials, effectively shortening the lithium-ion transport path. Furthermore, the smaller particle size increases the contact area between the phosphate-based cathode material and NCM83, which is beneficial for uniform material coating.

[0017] 2. The selected iron source is inexpensive and has a low decomposition temperature. The in-situ coated Fe2O3 layer is magnetic, and under the influence of a magnetic field, it can enhance the Li at the interface. + Transportation and structural stability, thereby mitigating Li under low-temperature conditions (-20°C). + The capacity decay problem is caused by low activity and slow diffusion.

[0018] 3. During the charging and discharging process, phosphate-based cathode materials can still provide additional capacity, and the PO4 in phosphate-based cathode materials... 3- The phosphate cathode material and Fe2O3 are uniformly coated on the ternary material under the action of electrostatic force, which reduces the direct contact between the ternary material and the electrolyte and inhibits the occurrence of side reactions. As a result, it still has excellent cycle stability under high temperature conditions (55℃). Attached Figure Description

[0019] Figure 1 XRD patterns of the modified NCM83 in Example 1 and the basic NCM83 in Comparative Example 1; Figure 2 SEM images of nano-sized LiFePO4, NCM83 modified in Example 1, and basic NCM83 in Comparative Example 1; Figure 3 The rate performance graphs are for the modified NCM83 of Example 1 and the base NCM83 of Comparative Example 1 at 0.1-5 C, 2.7-4.3 V, and 25 ℃. Figure 4 The graph shows the cycling performance of the modified NCM83 of Example 1 and the basic NCM83 of Comparative Example 1 at 1 C, 2.7-4.3 V, and 25 °C. Figure 5 The graph shows the cycling performance of the modified NCM83 of Example 1 and the basic NCM83 of Comparative Example 1 at 0.3 C, 2.7-4.3 V, and 55 °C. Figure 6 The graph shows the cycling performance of the modified NCM83 in Example 1 and the basic NCM83 in Comparative Example 1 at 0.5 C, 2.7-4.3 V, and -20 ℃. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] The high-nickel ternary cathode material used in the following specific embodiments is polycrystalline LiNi. 0.83 Co 0.12 Mn 0.05 O2 ternary cathode material, denoted as NCM83.

[0022] The specific method is as follows: LiOH·H2O was reacted with the ternary precursor LiNi 0.83 Co 0.12 Mn 0.05 (OH)₂ was mixed at a molar ratio of 1.05:1, and an appropriate amount of anhydrous ethanol was added as a solvent. After the solvent evaporated, the mixture was transferred to a tube furnace under an O₂ atmosphere, and the gas flow rate was controlled at 200 ml·min. -1 A two-stage sintering process was adopted, with the material being held at 450 ℃ for 5 h and then at 780 ℃ for 15 h to obtain the high-nickel ternary cathode material NCM83. This material was used as Comparative Example 1. Example 1

[0023] (1) 1 g of NCM83 was ultrasonically dispersed in 20 ml of anhydrous ethanol to form solution A. 5 wt% of Fe(C5H7O2)3 was dissolved in 10 ml of anhydrous ethanol to obtain solution B. Solution B was then uniformly added dropwise to solution A and stirred continuously for 30 min. The mixture was dried at 90 °C until the solvent was completely evaporated, and then transferred to a tube furnace under O2 atmosphere for sintering at 300 °C for 2 h to finally obtain Fe2O3-coated NCM83 material (NCM83@Fe2O3).

[0024] (2) Commercially available LiFePO4 was nano-sized in a high-energy ball mill, and then the nano-sized LiFePO4 was freeze-dried for 24 h. The NCM83@Fe2O3 obtained in step (1) was uniformly dispersed in NMP, and 4 wt% of nano-sized LiFePO4 was added and stirred for 2 h. The solution was then dried at 100 °C until the solvent was completely evaporated, and the solution was ground to obtain LiFePO4-coated NCM83@Fe2O3 material. Example 2

[0025] This embodiment uses commercially available LiMn 0.5 Fe 0.5 Replace LiFePO4 in step (2) of Example 1 with PO4, and follow the same procedure as in Example 1 to obtain LiMn. 0.5 Fe 0.5 PO4-coated NCM83@Fe2O3 material. Example 3

[0026] In this embodiment, commercially available Li3V2(PO4)3 is used instead of LiFePO4 in step (2) of Example 1, and the rest of the methods are the same as in Example 1, to obtain Li3V2(PO4)3 coated NCM83@Fe2O3 material. Example 4

[0027] The difference between this embodiment and embodiment 1 is that in step (2), 2 wt% of nano-sized LiFePO4 is added to obtain LiFePO4-coated NCM83@Fe2O3 material. Example 5

[0028] The difference between this embodiment and embodiment 1 is that in step (2), 6 wt% of nano-sized LiFePO4 is added to obtain LiFePO4-coated NCM83@Fe2O3 material. Example 6

[0029] (1) In this example, 3 wt% of Fe(C5H7O2)3 was dissolved in 10 ml of anhydrous ethanol to obtain solution B, and NCM83@Fe2O3 was prepared according to step (1) of Example 1.

[0030] (2) Following the method in Example 1, LiFePO4-coated NCM83@Fe2O3 material was prepared. Example 7

[0031] (1) In this example, 7 wt% of Fe(C5H7O2)3 was dissolved in 10 ml of anhydrous ethanol to obtain solution B, and NCM83@Fe2O3 was prepared according to step (1) of Example 1.

[0032] (2) Following the method in Example 1, LiFePO4-coated NCM83@Fe2O3 material was prepared. Example 8

[0033] (1) In this example, 5 wt% of FeCl3·6 H2O was dissolved in 10 ml of anhydrous ethanol to obtain solution B, and NCM83@Fe2O3 was prepared according to step (1) of Example 1.

[0034] (2) Following the method in Example 1, LiFePO4-coated NCM83@Fe2O3 material was prepared. Comparative Example 2

[0035] NCM83 was ultrasonically dispersed in 20 ml of anhydrous ethanol to form solution A. 5 wt% Fe(C5H7O2)3 was dissolved in 10 ml of anhydrous ethanol to obtain solution B. Solution B was then uniformly added dropwise to solution A, with continuous stirring for 30 min. The mixture was dried at 90 °C until the solvent was completely evaporated, and then transferred to a tube furnace under an O2 atmosphere for sintering at 300 °C for 2 h, finally obtaining Fe2O3-coated NCM83 material. Comparative Example 3

[0036] Commercially available LiFePO4 was nano-sized in a high-energy ball mill, and then the nano-sized LiFePO4 was freeze-dried for 24 h. NCM83 was uniformly dispersed in NMP, and 4 wt% of nano-sized LiFePO4 was added and stirred continuously for 2 h. The solution was then dried at 100 °C until the solvent was completely evaporated, and then ground to obtain LiFePO4-coated NCM83 material.

[0037] Application Example 1

[0038] Battery fabrication and performance testing: The main components of a battery include positive and negative electrode shells, separators, spring contacts, gaskets, positive and negative electrode materials, and electrolytes. The specific fabrication process is as follows: The prepared materials, conductive agent, and binder were mixed in a mass ratio of 8:1:1, with an appropriate amount of N-methylpyrrolidone added as a solvent. After grinding, the mixture was coated onto the current collector aluminum foil using a scraper. It was then placed in a vacuum oven and dried at 90°C for 24 hours. The dried material was then cut into 12 mm diameter discs using a slicer. Battery assembly was performed in a glove box filled with argon atmosphere. Pure lithium sheets were used as the negative electrode, and the assembly proceeded in the following order: positive electrode shell - positive electrode material - electrolyte - separator - lithium sheet - gasket - spring contact - negative electrode shell. After the assembled button batteries were left to stand for 12 hours, a series of tests were conducted.

[0039] The cathode materials used in the examples and comparative examples were fabricated into button cells and their electrochemical performance was tested on the NEWARE high-performance battery testing system. The test conditions were: 25°C, 2.7-4.3V, 1C. The test results are shown in Table 1.

[0040] Table 1. Cyclic test results of Examples 1-8 and Comparative Examples 1-3 Example 1 181.3 89.5 Example 2 178.4 86.2 Example 3 170.3 82.9 Example 4 181.9 83.8 Example 5 177.8 86.4 Example 6 180.6 82.5 Example 7 178.8 79.1 Example 8 179.6 88.3 Comparative Example 1 182.1 68.7 Comparative Example 2 180.7 82.1 Comparative Example 3 175.5 75.6 .

[0041] As shown in Table 1, the high-nickel ternary cathode material achieves a first-discharge specific capacity of 182.1 mAh g⁻¹ at 1C. -1 However, the capacity retention rate after 100 cycles was only 68.7%. With the addition of the "ion accelerator" Fe2O3, the capacity retention rate of Comparative Example 2 was significantly improved, indicating that an appropriate amount of magnetic Fe2O3 is more conducive to stabilizing the surface structure and lithium-ion transport. Meanwhile, the results of Examples 2 and 3 also confirmed that the addition of other nano-sized phosphate cathode materials slightly reduced the initial discharge specific capacity but significantly improved the cycle retention rate, mainly due to the superior structural stability of phosphate cathodes. The decrease in initial discharge specific capacity is due to the presence of LiFePO4, Li3V2(PO4)3, and LiMn. 0.5 Fe 0.5 The theoretical capacity of PO4 (approximately 170 mAh g) -1 133 mAh g -1 170 mAh g -1 The efficiency is far lower than that of high-nickel ternary materials (theoretical 280 mAh g). -1Examples 4 and 5 varied the coating amount of lithium iron phosphate. Although the cycle retention rates were higher than those of Comparative Examples 1 and 2, we found that only an appropriate amount of coating could achieve the optimal capacity retention. Examples 6 and 7 varied the thickness of the "ion accelerator". Similarly, an appropriate amount of iron oxide was needed to ensure the best ion transport rate. Furthermore, the results of Example 8 showed that Fe2O3 could be generated using different iron sources, but the slightly lower cycle retention rate compared to Example 1 was attributed to the lower decomposition temperature of Fe(C5H7O2)3.

[0042] Figure 1 The figures show the XRD patterns of Example 1 and Comparative Example 1. As can be seen from the figures, diffraction peaks belonging to LiFePO4 and Fe2O3 appear in Example 1, indicating the presence of these two substances in the material. Furthermore, the presence of these two substances does not affect the crystallinity and layered structure of the high-nickel ternary cathode material.

[0043] Figure 2 SEM images of nano-sized LiFePO4, Comparative Example 1, and Example 1 are shown. The SEM images confirm that wet ball milling and freeze-drying techniques can achieve the nano-sizing of lithium iron phosphate. In Example 1, fine lithium iron phosphate particles are clearly visible uniformly distributed on the secondary particles, demonstrating that LiFePO4 can be uniformly adhered to the surface of the high-nickel ternary material with the assistance of Fe2O3.

[0044] Figure 3 The graph shows the rate performance of the cathode materials of Example 1 and Comparative Example 1 at 0.1-5 C, 2.7-4.3 V, and 25 °C. Fe2O3, acting as an ion accelerator, can accelerate the Li ionization on the surface of LiFePO4 and NCM83 materials using its own magnetic field. + Diffusion improves the rate performance of the material.

[0045] Figure 4 The graphs show the cycling performance of the cathode materials of Example 1 and Comparative Example 1 at 1 C, 2.7-4.3 V, and 25 °C. The stability of the materials is significantly improved due to the presence of LiFePO4 and Fe2O3. Multiple coating layers effectively suppress the volume expansion of the high-nickel ternary material and hinder direct contact with the electrolyte, thereby achieving superior electrochemical performance.

[0046] Figure 5 The graph shows the cycling performance of the cathode materials of Example 1 and Comparative Example 1 at 0.3 C, 2.7-4.3 V, and 55 °C; Li at high temperature + It has high activity and fast transport rate, but with the increase in activity of Li +The lack of [something] and the continuous occurrence of interfacial side reactions cause the electrochemical performance to deteriorate. However, the presence of multiple coating layers of LiFePO4 and Fe2O3 greatly reduces the occurrence of side reactions and inhibits the dissolution of transition metals in ternary materials.

[0047] Figure 6 The graph shows the cycling performance of the cathode materials of Example 1 and Comparative Example 1 at 0.5 C, 2.7-4.3 V, and -20 °C. Low temperatures reduce the activity of lithium batteries, slow down the reaction rate, and deteriorate the conductivity of the electrolyte. However, the addition of Fe2O3 effectively improves lithium activity, enabling Example 1 to still provide 153.7 mAh g⁻¹ at -20 °C. -1 It has a high discharge specific capacity and a cycle retention rate of 94.5%.

Claims

1. A method for ion accelerator-assisted synthesis of phosphate-ternary composite cathode materials, characterized in that, Includes the following steps: (1) Using ternary cathode material LiNi x Co y Mn 1-x-y O2 is dispersed in a solvent to form solution A. The iron source is dissolved in the solvent to obtain solution B. Then, solution B is uniformly added dropwise to solution A and stirred thoroughly to obtain a mixture. After drying the mixture, it is transferred to an O2 atmosphere for calcination to obtain a ternary material coated with iron oxide. (2) The phosphate cathode material is nano-sized in a high-energy ball mill and freeze-dried to obtain nano-sized phosphate cathode material; the ternary cathode material coated with iron oxide obtained in step (1) is uniformly dispersed in a solvent, the nano-sized phosphate cathode material is added and stirred continuously, and dried until the solvent is completely evaporated to obtain phosphate cathode and iron oxide modified ternary material.

2. The method for synthesizing phosphate-ternary composite cathode materials with ion accelerator assistance according to claim 1, characterized in that, In step (1) LiNi x Co y Mn 1-x-y In O2, 0.45≤x≤0.98, 0≤y≤0.

55.

3. The method for synthesizing phosphate-ternary composite cathode materials with ion accelerator assistance according to claim 1, characterized in that, Step (1) The amount of iron source added accounts for 1-10% of the mass of the ternary material.

4. The method for synthesizing phosphate-ternary composite cathode materials with ion accelerator assistance according to claim 1, characterized in that, Iron sources include one or more of ferric chloride hexahydrate, ferrous chloride, ferric phosphate, ferrous phosphate, ferric ammonium citrate, ferrous oxalate, and ferric acetylacetone.

5. The method for synthesizing phosphate-ternary composite cathode materials with ion accelerator assistance according to claim 1, characterized in that, In step (1), the sintering temperature is 200-600℃ and the sintering time is 1-5 h.

6. The method for synthesizing phosphate-ternary composite cathode materials with ion accelerator assistance according to claim 1, characterized in that, In step (2), the amount of nano-sized phosphate cathode material added accounts for 2-6% of the mass of the ternary material coated with iron oxide.

7. The method for synthesizing phosphate-ternary composite cathode materials with ion accelerator assistance according to claim 1, characterized in that, Phosphate-based cathode materials are selected from one or more of lithium iron phosphate, lithium manganese iron phosphate, and lithium vanadium phosphate.

8. The method for synthesizing phosphate-ternary composite cathode materials with ion accelerator assistance according to claim 1, characterized in that, The high-energy ball mill uses wet ball milling with a power of 15-35 Hz and a time of 1-5 h.

9. The method for synthesizing phosphate-ternary composite cathode materials with ion accelerator assistance according to claim 1, characterized in that, LiNi x Co y Mn 1-x-y The preparation method of O2 ternary cathode material is as follows: lithium salt and ternary precursor LiNi x Co y Mn 1-x-y (OH) is mixed at a molar ratio of 1.01 to 1.09:1, and the solvent is added and stirred thoroughly. After the solvent evaporates, the mixture is transferred to an O2 atmosphere and sintered in two stages: the first stage is at 350-500℃ for 3-6 h; the second stage is at 700-950℃ for 10-18 h; and the result is obtained.

10. The method for synthesizing phosphate-ternary composite cathode materials with ion accelerator assistance according to claim 1, characterized in that, The solvent is one or more of deionized water, anhydrous ethanol, N-methylpyrrolidone, diethyl ether, acetone, and diethyl ether.

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