A method for preparing a positive electrode lithium supplement and its application

Abstract

This invention provides a method for preparing a positive electrode lithium supplement, comprising the following steps: Step S1: Mixing and grinding lithium nitrate and lithium hydroxide monohydrate; Step S2: Melting the material after mixing and grinding in Step S1 to obtain a mixed lithium salt of lithium nitrate and lithium hydroxide; Step S3: Mixing the mixed lithium salt with an iron source and glucose, and then pressing it into tablets; Step S4: Calcining the material after tableting in Step S3 under inert gas protection; Step S5: Cooling and sieving the calcined material after Step S4 to obtain the positive electrode lithium supplement Li5FeO4. The method of this invention for preparing Li5FeO4 has excellent properties such as small particle size, low energy consumption, short sintering time, low cost, and low calcination temperature.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a method for preparing a positive electrode lithium replenishing agent and its application. Background Technology

[0002] Lithium-ion batteries are widely used due to their advantages such as high energy density, low pollution, and long lifespan. As one of the core materials of lithium-ion batteries, the anode material has a significant impact on the battery's cycle performance and energy density. In practical applications, the anode consumes the active lithium from the cathode during the first charge of a lithium-ion battery to form the SEI film, resulting in capacity loss and a decrease in initial coulombic efficiency. Carbon-based anodes experience 5% to 15% initial capacity loss, while silicon-based anodes experience 15% to 35%. This initial capacity loss reduces the energy density of the lithium-ion battery and can even worsen its cycle performance.

[0003] Pre-lithiation technology is an effective way to solve the above problems. Currently, lithium replenishment technology is divided into two main categories: positive electrode lithium replenishment and negative electrode lithium replenishment. Compared with negative electrode lithium replenishment technology, positive electrode lithium replenishment is compatible with existing battery processes. A small amount of high-capacity material is added during the positive electrode slurry preparation process. During charging, Li+ is extracted from the high-capacity material to replenish the irreversible capacity loss during the first charge and discharge. Li5FeO4 has a theoretical specific capacity as high as 867mAh / g, high irreversible capacity, and is compatible with existing lithium-ion battery binder systems, making it a promising material for positive electrode lithium replenishment. However, the existing high-temperature solid-state method for preparing Li5FeO4 has problems such as high calcination temperature, long sintering time, high lithium source consumption, high cost, and the need for multiple sintering cycles, resulting in large particle size, poor stability, and even inability to be stored externally. For example, CN110498449A discloses a lithium ferrite material and its preparation method, which involves mixing and grinding an iron source, a lithium source, a carbon source, and deionized water, followed by spray drying and sintering to obtain lithium ferrite with carbon coating on the surface. The lithium-iron molar ratio is large (5.89-12:1), the calcination temperature is high (650-1000℃), the calcination time is long (24-48h), and the cost is high. Summary of the Invention

[0004] To address the aforementioned technical problems in the preparation of Li5FeO4 in existing technologies, this invention provides a method for preparing a positive electrode lithium supplement, comprising the following steps:

[0005] Step S1: Mix and grind lithium nitrate and lithium hydroxide monohydrate;

[0006] Step S2: Melt the material after mixing and grinding in step S1 to obtain a mixed lithium salt of lithium nitrate and lithium hydroxide;

[0007] Step S3: The mixed lithium salt is mixed with an iron source and glucose and then compressed into tablets;

[0008] Step S4: The material after tableting in step S3 is heated under inert gas protection and then calcined.

[0009] Step S5: Cool and sieve the material after calcination in step S4 to obtain positive electrode lithium supplement Li5FeO4.

[0010] Further, in step S1, the lithium nitrate and the lithium hydroxide monohydrate are mixed in a molar ratio of 3:2-3:5.

[0011] Furthermore, in step S2, the melting is carried out in a high-temperature furnace, with the melting temperature set to 100℃-300℃ and the melting time to be 5 hours.

[0012] Furthermore, in step S3, the mixed lithium salt and the iron source are mixed at a lithium to iron molar ratio of 5-5.05:1.

[0013] Furthermore, the iron source is one or more of ferric oxide, iron(II) oxide, ferric hydroxide, ferric nitrate, and ferric citrate.

[0014] Furthermore, the tableting process in step S3 is carried out under a pressure of 0-20 MPa.

[0015] Furthermore, the heating in step S4 is carried out at a rate of 3℃ / min - 8℃ / min.

[0016] Furthermore, the calcination temperature in step S4 is 300℃-500℃, and the calcination time is 10h-24h.

[0017] In another aspect, the present invention also provides a lithium supplement prepared using the above method.

[0018] Another aspect of the present invention provides a lithium-ion battery prepared using the above-described method.

[0019] This invention uses a mixed lithium salt of LiOH and LiNO3 as the lithium source to prepare Li5FeO4 using a molten salt method. On one hand, selecting low-melting-point LiOH-LiNO3 (183℃) as the lithium source facilitates wetting of the precursor surface, increasing the reaction area and avoiding the problem of coating difficulties caused by residual alkali left from incomplete raw material reactions. On the other hand, the formation of the salt melt enhances the fluidity of the reactants, prevents interparticle bonding, and significantly shortens the reaction time and controls particle size. The method of this invention for preparing Li5FeO4 exhibits excellent properties such as small product particle size, low energy consumption, short sintering time, low cost, and low calcination temperature. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope image of the Li5FeO4 material obtained in an embodiment of the present invention;

[0021] Figure 2 This is a scanning electron microscope image of Li5FeO4 material obtained in the comparative example of the prior art;

[0022] Figure 3 This is a comparison chart of the first charging curves obtained by using Li5FeO4 material obtained in the present invention as a positive electrode supplementing agent and then manufacturing a battery, in accordance with the prior art. Implementation

[0023] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0024] The technical solutions of various embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0025] Example 1: The preparation method of a positive electrode lithium supplement provided in this example includes the following steps:

[0026] S1: Mix lithium nitrate and lithium hydroxide monohydrate in a molar ratio of 3:2. In this step, ball milling is the preferred mixing method. Ball milling is a grinding method that uses the impact, compression, and friction of grinding balls to pulverize materials. Generally, the diameter of the grinding balls can be set to 4-9 times the diameter of the material to be pulverized.

[0027] S2: The powder obtained after grinding in S1 is placed in a muffle furnace at 200°C and melted for 5 hours. The molten material is then ground again to obtain a mixed lithium salt of lithium nitrate and lithium hydroxide.

[0028] S3: The lithium salt, which has been melted and mixed in S2, is then rapidly mixed with the iron source and glucose. Before mixing, the molar ratio of each material is controlled to ensure that the molar ratio of Li to Fe is 5.05:1. After mixing, the materials are ground, and finally compressed into tablets under a pressure of 10 MPa. In step S3, ferric oxide is used as the iron source, but one or more of magnetite, ferric hydroxide, ferric nitrate, and ferric citrate can also be used.

[0029] The high-speed mixing in this step involves the high-speed rotation of the paddles, causing the material to move tangentially along the paddles. Under centrifugal force, the material is thrown against the pot wall and rises along the wall. Some of the rising material falls back to the center of the paddles under gravity, while the rest hits the pot lid and falls back down. It is then thrown up again. This combination of upward and tangential motion causes the material to collide and mix with each other. Additionally, baffles are installed during mixing to further turbulent the material flow, creating irregular motion and strong vortices near the baffles, promoting further uniform dispersion and mixing of the material.

[0030] S4: The mixture after tableting in step S3 is calcined in an inert gas atmosphere at a temperature of 5°C / min to 400°C for 24 hours. In this step, considering the safety, practicality, and economy of the inert gas, nitrogen is preferred. However, alternatively, one or more combinations of helium, neon, argon, krypton, xenon, radon, and nitrogen can also be used.

[0031] S5: After cooling the material calcined according to step S4, remove it and grind and sieve it to obtain the sample Li5FeO4. In this step, the sieve used for sieving is preferably 300 mesh. Of course, it is also possible to choose any of the following meshes: 60, 100, 150, 200, 300, 400, and 500 mesh. Using these types of sieves will not damage the structure of Li5FeO4 during the sieving process and can achieve the best sieving results.

[0032] Example 2: The main difference between this example and Example 1 is the ratio of the substances and the reaction conditions. All other aspects are the same as in Example 1. This example provides a method for preparing a positive electrode lithium replenishing agent, including the following steps:

[0033] S1: Mix lithium nitrate and lithium hydroxide monohydrate in a molar ratio of 3:2.

[0034] S2: The powder obtained after grinding in S1 is placed in a muffle furnace at 100°C and melted for 5 hours. The molten material is then ground again to obtain a mixed lithium salt of lithium nitrate and lithium hydroxide.

[0035] S3: The lithium salt after S2 molten mixing is mixed with iron source and glucose at high speed. Before mixing, the molar ratio of each material is controlled so that the molar ratio of Li element to Fe element is 5.05:1 before mixing. After mixing, the material is ground and finally compressed into tablets under a pressure of 0 MPa.

[0036] S4: The mixture after tableting in step S3 is heated to 300℃ at 3℃ / min and then calcined for 20h in an inert gas atmosphere.

[0037] S5: After cooling the material calcined according to step S4, take it out and grind and sieve it to obtain sample Li5FeO4.

[0038] Example 3: The main difference between this example and Example 1 is the ratio of the substances and the reaction conditions. All other aspects are the same as in Example 1. This example provides a method for preparing a positive electrode lithium replenishing agent, including the following steps:

[0039] S1: Mix lithium nitrate and lithium hydroxide monohydrate in a molar ratio of 3:4.

[0040] S2: The powder obtained after grinding in S1 is placed in a muffle furnace at 100°C and melted for 5 hours. The molten material is then ground again to obtain a mixed lithium salt of lithium nitrate and lithium hydroxide.

[0041] S3: The lithium salt, which has been melted and mixed in S2, is mixed at high speed with the iron source and glucose. Before mixing, the molar ratio of each material is controlled so that the molar ratio of Li to Fe is 5.02:1. After mixing, the materials are ground and finally compressed into tablets under a pressure of 0 MPa. In this embodiment, the iron source is iron(III) oxide (Fe3O4).

[0042] S4: The mixture after tableting in step S3 is heated to 400℃ at 8℃ / min and then calcined for 24h in an inert gas atmosphere.

[0043] S5: After cooling the material calcined according to step S4, take it out and grind and sieve it to obtain sample Li5FeO4.

[0044] Example 4: The main difference between this example and Example 1 is the ratio of the substances and the reaction conditions. All other aspects are the same as in Example 1. This example provides a method for preparing a positive electrode lithium replenishing agent, including the following steps:

[0045] S1: Mix lithium nitrate and lithium hydroxide monohydrate in a molar ratio of 3:5.

[0046] S2: The powder obtained after grinding in S1 is placed in a muffle furnace at 200°C and melted for 5 hours. The molten material is then ground again to obtain a mixed lithium salt of lithium nitrate and lithium hydroxide.

[0047] S3: The lithium salt, which has been melted and mixed in S2, is mixed at high speed with the iron source and glucose. Before mixing, the molar ratio of each material is controlled so that the molar ratio of Li to Fe is 5:1. After mixing, the materials are ground and finally compressed into tablets under a pressure of 5 MPa. In this embodiment, the iron source is ferric oxide.

[0048] S4: The mixture after tableting in step S3 is heated to 500℃ at 5℃ / min and then calcined for 15h in an inert gas atmosphere.

[0049] S5: After cooling the material calcined according to step S4, take it out and grind and sieve it to obtain sample Li5FeO4.

[0050] Example 5: The main difference between this example and Example 1 is the ratio of the substances and the reaction conditions. All other aspects are the same as in Example 1. This example provides a method for preparing a positive electrode lithium replenishing agent, including the following steps:

[0051] S1: Mix lithium nitrate and lithium hydroxide monohydrate in a molar ratio of 3:5.

[0052] S2: The powder obtained after grinding in S1 is placed in a muffle furnace at 200°C and melted for 5 hours. The molten material is then ground again to obtain a mixed lithium salt of lithium nitrate and lithium hydroxide.

[0053] S3: The lithium salt, which has been melted and mixed in S2, is mixed at high speed with the iron source and glucose. Before mixing, the molar ratio of each material is controlled so that the molar ratio of Li to Fe is 5.03:1. After mixing, the materials are ground and finally compressed into tablets under a pressure of 10 MPa. In this embodiment, the iron source is ferric oxide.

[0054] S4: The mixture after tableting in step S3 is heated to 300℃ at 3℃ / min and then calcined for 15h in an inert gas atmosphere.

[0055] S5: After cooling the material calcined according to step S4, take it out and grind and sieve it to obtain sample Li5FeO4.

[0056] Example 6: The main difference between this example and Example 1 is the ratio of the substances and the reaction conditions. All other aspects are the same as in Example 1. This example provides a method for preparing a positive electrode lithium replenishing agent, including the following steps:

[0057] S1: Mix lithium nitrate and lithium hydroxide monohydrate in a molar ratio of 3:5.

[0058] S2: The powder obtained after grinding in S1 is placed in a muffle furnace at 100°C and melted for 5 hours. The molten material is then ground again to obtain a mixed lithium salt of lithium nitrate and lithium hydroxide.

[0059] S3: The lithium salt, which has been melted and mixed in S2, is mixed at high speed with the iron source and glucose. Before mixing, the molar ratio of each material is controlled so that the molar ratio of Li to Fe is 5.02:1. After mixing, the materials are ground and finally compressed into tablets under a pressure of 10 MPa. In this embodiment, the iron source is ferric oxide.

[0060] S4: The mixture after tableting in step S3 is heated to 500℃ at 5℃ / min and then calcined for 20h in an inert gas atmosphere.

[0061] S5: After cooling the material calcined according to step S4, take it out and grind and sieve it to obtain sample Li5FeO4.

[0062] Example 7: The main difference between this example and Example 1 is the ratio of the substances and the reaction conditions. All other aspects are the same as in Example 1. This example provides a method for preparing a positive electrode lithium replenishing agent, including the following steps:

[0063] S1: Mix lithium nitrate and lithium hydroxide monohydrate in a molar ratio of 3:2.

[0064] S2: The powder obtained after grinding in S1 is placed in a muffle furnace at 200°C and melted for 5 hours. The molten material is then ground again to obtain a mixed lithium salt of lithium nitrate and lithium hydroxide.

[0065] S3: The lithium salt, which has been melted and mixed in S2, is mixed at high speed with the iron source and glucose. Before mixing, the molar ratio of each material is controlled so that the molar ratio of Li to Fe is 5.02:1. After mixing, the materials are ground and finally compressed into tablets under a pressure of 20 MPa. In this embodiment, the iron source is ferric oxide.

[0066] S4: The mixture after tableting in step S3 is heated to 300℃ at 5℃ / min and then calcined for 15h in an inert gas atmosphere.

[0067] S5: After cooling the material calcined according to step S4, take it out and grind and sieve it to obtain sample Li5FeO4.

[0068] Example 8: The main difference between this example and Example 1 is the ratio of the substances and the reaction conditions. All other aspects are the same as in Example 1. This example provides a method for preparing a positive electrode lithium replenishing agent, including the following steps:

[0069] S1: Mix lithium nitrate and lithium hydroxide monohydrate in a molar ratio of 3:2.

[0070] S2: The powder obtained after grinding in S1 is placed in a muffle furnace at 200°C and melted for 5 hours. The molten material is then ground again to obtain a mixed lithium salt of lithium nitrate and lithium hydroxide.

[0071] S3: The lithium salt, which has been melted and mixed in S2, is mixed at high speed with the iron source and glucose. Before mixing, the molar ratio of each material is controlled so that the molar ratio of Li to Fe is 5.01:1. After mixing, the materials are ground and finally compressed into tablets under a pressure of 20 MPa. In this embodiment, the iron source is ferric oxide.

[0072] S4: The mixture after tableting in step S3 is heated to 400℃ at 5℃ / min and then calcined for 20h in an inert gas atmosphere.

[0073] S5: After cooling the material calcined according to step S4, take it out and grind and sieve it to obtain sample Li5FeO4.

[0074] Comparative Example

[0075] This embodiment describes the preparation method of a conventional positive electrode lithium replenishing agent as follows:

[0076] A suitable amount of micron-sized LiOH•H2O and Fe2O3 were thoroughly mixed and ground, then pre-calcined in a box furnace at 470℃ for 10 hours. After pre-calcination and grinding, the mixture was calcined at 850℃ for 12 hours, and finally lightly ground to obtain the final sample Li5FeO4.

[0077] The Li5FeO4 samples obtained in the above embodiments were added to the manufacturing process of the positive electrode sheet. The specific process is as follows: Li5FeO4 samples, conductive carbon (Super P) and PVDF binder were mixed at a mass ratio of 9:0.5:0.5, and an appropriate amount of N-methylpyrrolidone (NMP) was added. The mixture was magnetically stirred for 4 hours until uniformly mixed to obtain Li5FeO4 lithium supplementation slurry. The lithium supplementation slurry was added to the positive electrode slurry to prepare the positive electrode sheet in the conventional way. The positive electrode sheets of appropriate size were selected and cut, and the above electrode sheets were assembled into button batteries for button cell testing.

[0078] Using the Li5FeO4 samples obtained in the above embodiments, positive electrode sheets were fabricated. These positive electrode sheets were then assembled into button batteries for coin cell testing, and the first charge curve was plotted to obtain the desired results. Figure 3 The comparison chart of the first charging curves shown is only comparing the samples Li5FeO4 obtained in Example 1 and the comparative example as lithium replenishing agents for the purpose of comparison and analysis.

[0079] The Li5FeO4 samples obtained in each embodiment and the comparative example were subjected to scanning electron microscopy for comparative analysis. For ease of comparison and explanation, only the scanning electron microscopy tests of the samples obtained in Example 1 and the comparative example were selected for comparative analysis. Figure 1 This is a scanning electron microscope image of the Li5FeO4 sample from Example 1; Figure 2 This is a scanning electron microscope image of the Li5FeO4 sample obtained for comparison.

[0080] The particle size of Li5FeO4 obtained in each embodiment and comparative example was measured, and the residual alkali on the alcohol phase surface and the powder resistivity were measured and analyzed. At the same time, the capacity of the battery obtained from the corresponding Li5FeO4 was tested.

[0081] The test results are shown in Table 1:

[0082] Group Capacity (mAh / g) Powder resistivity (Ω / cm) residual alkali on alcohol phase surface (ppm) Particle size D50 (μm) Example 1 752.8 1.58 354 2.5 Example 2 694.2 23.3 953 4.2 Example 3 683.6 25.6 2530 7.6 Example 4 611.3 2.38 680 6.3 Example 5 658.2 4.68 1672 9.4 Example 6 678.5 9.75 1300 5.6 Example 7 683.9 28.6 580 12.7 Example 8 735.6 46.5 2650 8.3 Comparative Example 1 520.4 287.76 5563 20.8

[0083] Based on the above test results, it was found that the residual alkali on the alcohol phase surface of Li5FeO4 prepared by the molten salt method described in Examples 1-8 was significantly reduced compared with that of Li5FeO4 prepared by the high temperature solid phase method in the comparative example. This can improve the problems of excessive residual alkali and difficulty in coating caused by incomplete reaction of raw materials, and improve the electrochemical performance of the material.

[0084] The particle size of Li5FeO4 prepared by the molten salt method described in Examples 1-8 is also significantly smaller than that of Li5FeO4 prepared by the high-temperature solid-state method in the comparative examples. Furthermore, according to... Figure 1 and Figure 2 The SEM images of Li5FeO4 prepared by the molten salt method and the high-temperature solid-state method show that the material prepared by the molten salt method exhibits an irregular granular morphology. Most of the particles are small, with a diameter of about 2 μm. A small number of large particles with a diameter of about 10 μm are formed due to crystal agglomeration. These large particles may be due to uneven mixing of some precursors, but overall, the particle size of Li5FeO4 is relatively small. In contrast, the SEM images of the Li5FeO4 sample prepared by the high-temperature solid-state method show that the material morphology is usually large blocky or plate-like particles. Most of the particles are large, with a diameter of about 20 μm, and a small number of small particles appear on the surface of the large particles.

[0085] from Figure 3 Analysis of the initial charging curve at 25℃@0.066C shows that the charging platform of Example 1 is smaller than that of the comparative example, indicating that the polarization of the electrode in Example 1 during the charging process is less than that of the comparative example.

[0086] Furthermore, considering the comprehensive properties such as powder particle size, powder resistivity, battery capacity, and residual alkali on the alcohol phase surface, the optimal production and preparation method for Li5FeO4 using the molten salt method of this invention, specifically step one, can yield Li5FeO4 with the best performance.

[0087] Furthermore, through analysis of the influence of various factors on the electrochemical performance of the material, it was found that the order of influence on the electrochemical performance of the material from largest to smallest is: the elemental ratio of lithium to iron, the pressing pressure, the sintering time, and the sintering temperature.

[0088] This invention prepares Li5FeO4 sacrificial lithium salt using a molten salt method with a mixed lithium salt of LiOH and LiNO3 as the lithium source. On the one hand, this avoids the coating difficulties caused by residual alkali from incomplete raw material reactions. On the other hand, it significantly shortens the reaction time and controls particle size. A lithium replenishing agent is then introduced through surface coating. The mechanism by which this agent improves the energy density of lithium-ion batteries is compared, and the electrochemical performance of the lithium-ion batteries is analyzed to illustrate its impact.

Claims

1. A method for preparing a positive electrode lithium supplement, characterized in that, Includes the following steps: Step S1: Mix and grind lithium nitrate and lithium hydroxide monohydrate; the lithium nitrate and lithium hydroxide monohydrate are mixed in a molar ratio of 3:2-3:5; Step S2: The material after mixing and grinding in step S1 is melted to obtain a mixed lithium salt of lithium nitrate and lithium hydroxide; the melting is carried out in a high-temperature furnace, the melting temperature is set to 100℃-300℃, and the melting time is 5h. Step S3: The mixed lithium salt is mixed with an iron source and glucose and then compressed into tablets; the mixed lithium salt and the iron source are mixed at a lithium to iron molar ratio of 5-5.05:

1. Step S4: The material after tableting in step S3 is heated under inert gas protection and then calcined. Step S5: Cool and sieve the material after calcination in step S4 to obtain positive electrode lithium supplement Li5FeO4; the iron source is one or more of ferric oxide, ferric oxide, ferric hydroxyl oxide, ferric nitrate and ferric citrate.

2. The method for preparing the positive electrode lithium replenishing agent as described in claim 1, characterized in that, In step S3, the tablet compression process is... The procedure is carried out under a pressure of 0-20 MPa.

3. The method for preparing the positive electrode lithium replenishing agent as described in claim 1, characterized in that, The heating in step S4 is carried out at a rate of 3℃ / min-8℃ / min.

4. The method for preparing the positive electrode lithium replenishing agent as described in claim 1, characterized in that, The calcination temperature in step S4 is 300℃-500℃, and the calcination time is 10h-24h.

5. A lithium supplement, characterized in that, It is prepared using the method for preparing the positive electrode lithium supplement as described in any one of claims 1-4.

6. A lithium-ion battery, characterized in that, Includes the lithium replenishing agent as described in claim 5.

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