Positive electrode lithium supplement additive and preparation method and application thereof

Abstract

The invention discloses a positive electrode lithium supplement additive and a preparation method and application thereof. The positive electrode lithium supplement additive is of a coating structure, the inner layer is Li5FeO4 particles, and the coating layer is a carbon layer. The preparation method of the positive electrode lithium supplement additive comprises the following steps: 1) mixing a lithium salt and an iron salt with water to obtain a solution A; (2) carrying out mixed culture on fusarium oxysporum freeze-dried powder and the solution A to obtain a solution B, centrifuging and filtering the solution B, and drying filter residues to obtain a precursor; and 3) supplementing a lithium source B according to the molar ratio of Li to Fe elements in the precursor, mixing the supplemented lithium source B with the precursor, and calcining to obtain the positive electrode lithium supplementing additive. The positive electrode lithium supplement additive is applied to preparation of a lithium ion battery material. The lithium supplement additive prepared by the invention has good rate capability, is free of particle aggregation and overgrowth during preparation, is in full contact with other positive electrode materials in the processing process, and can significantly improve the energy density of the lithium ion battery.

Description

Technical Field

[0001] The invention belongs to the field of lithium ion batteries and relates to a positive electrode lithium supplement additive and a preparation method and application thereof. Background Art

[0002] In recent years, with the increasing demand for portable devices and electric vehicle endurance, higher requirements have been placed on the performance of lithium-ion batteries. However, due to the problem of first irreversible capacity loss, the application of many high-performance battery materials has been limited.

[0003] During the first charge, the solid electrolyte film (SEI film) formed on the surface of the negative electrode is an important reason for the first irreversible capacity loss. Therefore, how to replenish the Li consumed during the formation of the SEI film? + The positive electrode lithium replenishment method can effectively replenish the Li lost during the first charging process. + , and because of the high potential of the positive electrode lithium supplement material, good compatibility with existing lithium battery main materials, and easy use and operation, it has attracted widespread attention, especially the lithium supplement additive with an inverse fluorite structure. Although lithium supplement additives can effectively replenish the amount of active lithium lost due to the formation of the SEI film, due to its poor surface conductivity, high residual alkali, large polarization and other characteristics, it cannot exert its full capacity and seriously affects the slurry processing performance. In response to the above problems, some scholars have proposed a solution to coat the surface of the lithium supplement additive with a carbon layer, but problems such as uneven coating, enlarged particles after coating, and loose coating still limit the application of lithium supplement additives.

[0004] Therefore, the preparation of a small particle, uniformly and tightly coated inverse fluorite structure lithium supplement additive Li5FeO4 is the key to further breakthrough in the capacity of lithium batteries. Summary of the invention

[0005] The purpose of the present invention is to provide a positive electrode lithium supplement additive and a preparation method and application thereof.

[0006] The invention provides a positive electrode lithium supplement additive, which is a coating structure, wherein an inner layer is Li5FeO4 particles, and a coating layer is a carbon layer.

[0007] In the above-mentioned positive electrode lithium supplement additive, the coating layer may have a thickness of 0.3-0.5 μm.

[0008] In the above-mentioned positive electrode lithium supplement additive, the particle size D of the Li5FeO4 particles is 50 The particle size may be 1.5-2 μm. The specific purity of the Li5FeO4 particles is ≥95%, the total residual alkali is ≤2%, and the carbon content is ≤3 wt.%.

[0009] The present invention provides a method for preparing the above-mentioned positive electrode lithium supplement additive, comprising the following steps: 1) Mixing lithium salt and iron salt with water to obtain solution A; 2) mixing the freeze-dried powder of Fusarium oxysporum with the solution A to obtain a solution B, centrifuging the solution B, filtering it, and drying the filter residue to obtain a precursor; 3) According to the molar ratio of Li and Fe in the precursor, the supplementary lithium source B is mixed with the precursor and then calcined to obtain the positive electrode lithium supplement additive.

[0010] The present invention adopts a microbial method to prepare a composite material, introduces Fusarium oxysporum hyphae, provides nutrition to Fusarium oxysporum through an organic lithium source and an iron source so that it secretes extracellular protein, uses the extracellular protein as a hydrolysis and restriction template to accurately prepare a precursor, and then sinters to in-situ transform the protein layer into a graphite and amorphous carbon coating layer to prepare a composite material.

[0011] In the above preparation method, in step 1), the lithium salt is selected from one or more of lithium acetate, lithium oxalate, and lithium citrate; The iron salt is at least one of iron formate, iron acetate, and iron citrate; The mixing is performed by magnetic stirring, the rotation speed may be 400-500 rpm, specifically 400 rpm, the stirring time may be 0.5-1 h, specifically 40 min, 0.5-40 min or 40 min-1 h; The molar ratio of lithium element to iron element in the solution A may be 1.0-1.3:1, specifically 1.2:1.

[0012] In the above preparation method, in step 2), the conditions of the mixed culture are as follows: the temperature can be 20-35°C, the shaking speed can be 200-400 rpm, and the time can be 24-36 h.

[0013] In the above preparation method, in step 2), the mass ratio of the lyophilized powder of Fusarium oxysporum to the solute in the solution A can be 8-10: 1. The lyophilized powder of Fusarium oxysporum is purchased from Shanghai Ruichu Biotechnology Co., Ltd., and the product catalog number is ACCC37438.

[0014] In the above preparation method, in step 3), the molar ratio of the lithium source B to the lithium element and the iron element in the precursor may be 5.0-5.5:1; The lithium source B may be at least one of LiOH, LiOH·H2O, Li2O and Li2CO3.

[0015] In the above preparation method, in step 3), the lithium source B and the precursor are mixed by ball milling, the ball-to-material ratio can be 5-10:1, specifically 7:1, the rotation speed can be 300-500 rpm, specifically 400 rpm, and the time can be 0.5-1 h, specifically 30 min.

[0016] In the above preparation method, in step 3), the calcination temperature program is: heating rate 2~5 ℃ / min to 200~300 ℃, 200~300 ℃ insulation for 2~5 h; from 200~300 ℃ to 450~600 ℃ at a heating rate of 2~5 ℃ / min, 450~600 ℃ insulation for 5~15 h. The specific primary sintering program is: heating rate 3 ℃ / min to 200 ℃, 200 ℃ insulation for 180 min; from 200 ℃ to 550 ℃ at a heating rate of 3 ℃ / min, 550 ℃ insulation for 720 min, and the sintering atmosphere is nitrogen.

[0017] The calcination can be carried out in a tube furnace.

[0018] The positive electrode lithium supplement additive of the present invention is used in preparing lithium ion battery materials.

[0019] The present invention has the following beneficial effects: The particle size D of the lithium supplement additive Li5FeO4 prepared by the present invention is 50 1.5~2μm, purity ≥95%, total residual alkali ≤2%, carbon content ≤3 wt.%, within the above performance range, Li5FeO4 has good rate performance, Li + It has the characteristics of short transmission distance, high transmission efficiency, good surface conductivity, not easy to deteriorate in the air, easy to store and transport, etc. There is no particle agglomeration, overgrowth and other phenomena in the preparation process. It has sufficient contact with other positive electrode materials during processing and no gel phenomenon occurs. It can significantly improve the energy density of lithium-ion batteries and has no obvious effect on their cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The first charge and discharge curves of the lithium ion batteries prepared in Example 4 and Comparative Example 9 are shown; Figure 2 The cycle curves of the lithium-ion batteries prepared in Example 4 and Comparative Example 9 are shown. DETAILED DESCRIPTION

[0021] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0022] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0023] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0024] The present application provides a positive electrode lithium supplement additive, which is a coating structure, wherein the inner layer is Li5FeO4 particles, and the coating layer is a carbon layer.

[0025] Furthermore, the coating layer may have a thickness of 0.3-0.5 μm.

[0026] Furthermore, the particle size D of the Li5FeO4 particles is 50 It can be 1.5~2μm.

[0027] The present application also provides a method for preparing the above-mentioned positive electrode lithium supplement additive, comprising the following steps: 1) Mixing lithium salt and iron salt with water to obtain solution A; 2) mixing the freeze-dried powder of Fusarium oxysporum with the solution A to obtain a solution B, centrifuging the solution B, filtering it, and drying the filter residue to obtain a precursor; 3) According to the molar ratio of Li and Fe in the precursor, the supplementary lithium source B is mixed with the precursor and then calcined to obtain the positive electrode lithium supplement additive.

[0028] Embodiment 1: A method for preparing a high-performance positive electrode lithium supplement additive Li5FeO4 / CC (LFO) composite material comprises: Step S1: 2.5 g of lithium oxalate and 7.93 g of ferric acetate were added to 200 mL of deionized water, and stirred by magnetic stirring for 40 min at a speed of 400 rpm to prepare solution A (the molar ratio of lithium element to iron element in solution A was about 1.2:1).

[0029] Step S2: 85 g of Fusarium oxysporum freeze-dried powder (purchased from Shanghai Ruichu Biotechnology Co., Ltd., product catalog number ACCC 37438) was added to solution A, placed in a constant temperature shaking incubator for 36 h, the temperature was set to 25°C, the shaking speed was 250 rpm, and solution B was obtained after the incubation; solution B was centrifuged at 10,000 rpm for 15 min, filtered, and the filter residue was retained and dried at 120°C for 120 min to obtain an LFO precursor.

[0030] Step S3: 10 g of the precursor and 2.17 g of lithium oxide are placed in a ball mill with a ball-to-material ratio of 7:1 and a ball mill speed of 400 rpm for 30 min; the mixed material is placed in a tubular furnace for calcination, and the sintering procedure is as follows: heating up to 200 °C at a heating rate of 3 °C / min, and keeping at 200 °C for 180 min; heating from 200 °C to 550 °C at a heating rate of 3 °C / min, and keeping at 550 °C for 720 min. The sintering atmosphere is nitrogen, and a high-performance positive electrode lithium supplement additive Li5FeO4 / CC (LFO) composite material, referred to as LFO, is obtained.

[0031] LFO granularity D 50 , residual alkali, purity and carbon content are shown in Table 1.

[0032] Step S4: The positive electrode lithium supplement additive LFO prepared in this embodiment is combined with the positive electrode material LFP to prepare a soft-pack battery, the mass ratio of LiFePO4:Li5FeO4:conductive agent:PVDF is 95:1.5:1.5:2, the test voltage is 2-4.5V, and the charge and discharge are performed at 0.1C / 0.1C, and the first charge capacity and the capacity retention rate at the 200th cycle are recorded.

[0033] Embodiment 2: The lithium oxalate and ferric acetate in S1 in Example 1 of the present invention were replaced with 5 g of lithium acetate and 15.47 g of ferric citrate, respectively, the amount of the lyophilized powder of Fusarium oxysporum in S2 was changed to 163.76 g, the amount of lithium oxide in S3 was 1.67 g, and the other operations remained unchanged. The test data are shown in Table 1.

[0034] Embodiment 3: The culture temperature of the constant temperature shaking incubator of S2 in Example 1 of the present invention was adjusted to 30° C., and the other operations remained unchanged. The test data are shown in Table 1.

[0035] Embodiment 4: The 2.63 g of lithium oxide added in S3 in Example 1 of the present invention was adjusted to 3.53 g of lithium hydroxide, and the other operations remained unchanged. The test data are shown in Table 1. Figure 1 The first charge and discharge curves of the lithium-ion batteries prepared in Example 4 and Comparative Example 9 are shown. After adding 1.5% LFO, the first charge capacity reaches 173.43 mAh / g, which is 8.62 mAh / g higher than that of Comparative Example 9 without adding LFO. This shows that the LFO prepared in Example 4 has a good pre-lithiation effect and replenishes the Li consumed by the formation of the SEI film. + , which improves the energy density of the battery to a certain extent. A good cycle capacity retention rate is an important indicator for judging battery performance, such as Figure 2As shown, after adding the LFO prepared in Example 4, the capacity retention rate of the soft-pack battery after 200 cycles reaches 99.81%, which is better than that of Comparative Example 9 without LFO addition. Adding the LFO prepared in Example 4 can effectively improve the battery performance.

[0036] Embodiment 5: The tubular furnace sintering program of S3 in Example 1 of the present invention was changed to: heating up to 200 °C at a heating rate of 3 °C / min, and keeping at 200 °C for 240 min; heating up from 200 °C to 600 °C at a heating rate of 3 °C / min, and keeping at 600 °C for 900 min. The other operations remained unchanged. The test data are shown in Table 1.

[0037] Comparative Example 1: The lithium oxalate and ferric acetate in S1 in Example 1 of the present invention were replaced with 5 g of lithium hydroxide monohydrate and 15.86 g of iron oxide, respectively, the amount of the lyophilized powder of Fusarium oxysporum in S2 was changed to 166.88 g, and the amount of lithium oxide in S3 was 2.65 g. The other operations remained unchanged. The test data are shown in Table 1.

[0038] Comparative Example 2: The addition amount of the freeze-dried powder of Fusarium oxysporum in S2 of Example 1 of the present invention was changed to 77.6 g, and the other operations remained unchanged. The test data are shown in Table 1.

[0039] Comparative Example 3: The addition amount of the freeze-dried powder of Fusarium oxysporum in S2 of Example 1 of the present invention was changed to 155.16 g, and the other operations remained unchanged. The test data are shown in Table 1.

[0040] Comparative Example 4: The temperature of the constant temperature shaking incubator of S2 in Example 1 of the present invention was changed to 10° C., and other operations remained unchanged. The test data are shown in Table 1.

[0041] Comparative Example 5: The temperature of the constant temperature shaking incubator of S2 in Example 1 of the present invention was changed to 45° C., and other operations remained unchanged. The test data are shown in Table 1.

[0042] Comparative Example 6: The amount of lithium oxide added in S3 in Example 1 of the present invention was adjusted to 1.75 g, and the other operations remained unchanged. The test data are shown in Table 1.

[0043] Comparative Example 7: The tubular furnace sintering program of S3 in Example 1 of the present invention was changed to: 200°C, 60 min; 550°C, 240 min, and the other operations remained unchanged. The test data are shown in Table 1.

[0044] Comparative Example 8: The tubular furnace sintering program of S3 in Example 1 of the present invention was changed to: 550° C., 720 min, and the other operations remained unchanged. The test data are shown in Table 1.

[0045] Comparative Example 9: The ratio of the soft-pack battery material prepared in S4 in Example 1 of the present invention was changed to a mass ratio of LiFePO4: conductive agent: PVDF of 96.5:1.5:2, and the other operations remained unchanged. The test data are shown in Table 1.

[0046] From the specific data of the embodiments of the present invention in Table 1, it can be seen that the embodiments of the present invention achieve the following technical effects: Embodiments 1-5 all show relatively excellent lithium supplementation effects, and D 50 The particle size is 1.5-2 μm, the purity is ≥95%, the total residual alkali is ≤2%, and the carbon content is ≤2.5%. Compared with comparative examples 1-8, the lithium supplement additive Li5FeO4 / CC prepared according to the present invention has excellent physical and chemical properties and obvious processing performance advantages.

[0047] Comparison of Examples 1-2 of the present invention and Comparative Example 1 shows that the addition of organic lithium salts and iron salts to Solution A is crucial for the preparation of Li5FeO4 / CC, which is beneficial for reducing residual alkali, particle size, carbon content, and improving purity, electrochemical properties and processing performance.

[0048] By comparing Examples 1-3 of the present invention and Comparative Examples 2-3, it can be seen that limiting the amount of the added freeze-dried powder of Fusarium oxysporum to the preferred range of the present application is beneficial to improving the purity and controlling the surface carbon content, and improving the electrochemical properties and processing properties of the lithium supplement additive Li5FeO4 / CC.

[0049] Comparing Example 3 of the present invention with Comparative Examples 4-5, it can be seen that setting the temperature of the constant temperature incubator within the preferred range of the present application is beneficial to further improve the purity, electrochemical properties and processing properties of the lithium supplement additive Li5FeO4 and reduce the particle size.

[0050] Comparing Example 4 of the present invention and Comparative Example 6, it can be seen that controlling the quality of the added lithium source B within the preferred range of the present application is beneficial to further improve the purity, electrochemical properties and processing properties of the lithium supplement additive Li5FeO4 and reduce residual alkali.

[0051] Comparison of Example 5 of the present invention and Comparative Examples 7-8 shows that controlling the calcination conditions within the preferred range of the present application is beneficial to further reduce the particle size, residual carbon content, residual alkali, and improve purity, electrochemical properties and processing properties.

[0052] Comparison of Examples 1-5 of the present invention and Comparative Example 9 shows that adding the lithium supplement additive Li5FeO4 prepared by the present invention to the positive electrode slurry of the soft-pack battery is beneficial to significantly improve the battery capacity.

[0053] Table 1

[0054] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those described herein, for example.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A positive electrode lithium supplement additive, characterized in that: The positive electrode lithium supplement additive is a coating structure, the inner layer is Li5FeO4 particles, and the coating layer is a carbon layer.

2. The positive electrode lithium supplement additive according to claim 1, characterized in that: The coating layer has a thickness of 0.3-0.5 μm.

3. The positive electrode lithium supplement additive according to claim 1 or 2, characterized in that: The particle size D of the Li5FeO4 particles 50 1.5~2μm.

4. A method for preparing the positive electrode lithium supplement additive according to any one of claims 1 to 3, characterized in that: The following steps are involved: 1) Mixing lithium salt and iron salt with water to obtain solution A; 2) mixing the freeze-dried powder of Fusarium oxysporum with the solution A to obtain a solution B, centrifuging the solution B, filtering it, and drying the filter residue to obtain a precursor; 3) According to the molar ratio of Li and Fe in the precursor, the supplementary lithium source B is mixed with the precursor and then calcined to obtain the positive electrode lithium supplement additive.

5. The preparation method according to claim 4, characterized in that: In step 1), the lithium salt is selected from one or more of lithium acetate, lithium oxalate, and lithium citrate; The iron salt is at least one of iron formate, iron acetate, and iron citrate; The mixing is carried out by magnetic stirring at a speed of 400-500 rpm and a stirring time of 0.5-1 h; The molar ratio of lithium element to iron element in the solution A is 1.0-1.3:

1.

6. The preparation method according to claim 4 or 5, characterized in that: In step 2), the mixed culture conditions are as follows: temperature is 20-35°C, shaking speed is 200-400 rpm, and time is 24-36 h; The mass ratio of the freeze-dried Fusarium oxysporum powder to the solute in the solution A is 8-10:

1.

7. The preparation method according to claim 4 or 5, characterized in that: In step 3), the molar ratio of the lithium source B to the lithium element and the iron element in the precursor is 5.0-5.5:1; The lithium source B is at least one of LiOH, LiOH·H2O, Li2O and Li2CO3.

8. The preparation method according to claim 4 or 5, characterized in that: In step 3), the lithium source B and the precursor are mixed by ball milling, with a ball-to-material ratio of 5-10:1, a rotation speed of 300-500 rpm, and a time of 0.5-1 h.

9. The preparation method according to claim 4 or 5, characterized in that: In step 3), the calcination temperature program is: heating rate 2-5 °C / min to 200-300 °C, and keeping at 200-300 °C for 2-5 h; heating rate 2-5 °C / min from 200-300 °C to 450-600 °C, and keeping at 450-600 °C for 5-15 h.

10. Use of the positive electrode lithium supplement additive according to any one of claims 1 to 3 in the preparation of lithium ion battery materials.

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