A lithium-rich ferrite modified material, a preparation method and application thereof

Abstract

This invention discloses a lithium-rich ferric acid modified material, its preparation method, and its application. The lithium-rich ferric acid modified material comprises a lithium-rich ferric acid core and a coating layer; the coating layer covers at least a portion of the surface of the lithium-rich ferric acid core; the coating layer comprises lithium fluoride and lithium borate; the lithium-rich ferric acid core is doped with boron and fluorine. This invention constructs a lithium fluoride and lithium borate composite coating layer on the surface of a boron- and fluorine-doped lithium-rich ferric acid core. The resulting lithium-rich ferric acid modified material has the advantages of high charge / discharge specific capacity and good air stability, solving the problem of significant capacity reduction in lithium-rich ferric acid when exposed to air. This material can maintain a high specific capacity even after prolonged exposure to air, thus it can be used as a high-capacity lithium replenisher for lithium-ion batteries, achieving high lithium replenishment efficiency. Simultaneously, this material is prepared at low temperature, with short preparation time, simple process, low price, and is environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, and particularly relates to a lithium-rich iron acid modified material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are currently the mainstream electrochemical energy storage carrier. During the initial cycling phase, the solid electrolyte interphase (SEI) layer that forms consumes a large amount of active Li. + This results in low initial coulombic efficiency and significant capacity loss, becoming a key bottleneck for improving battery energy density. The antifluorite structure of lithium-rich iron oxide Li5FeO4 (LFO) allows for the formation of cations (Fe... 3+ / Fe 4+ ) and anions (O 2- / O 2n- LFO (Lithium-ionized oxygen) exhibits high irreversible specific capacity driven by the O2 redox process, along with a low delithiation potential (approximately 3.5V) and simple synthesis, making it a highly attractive pre-lithiation cathode material. However, LFO suffers from extremely poor air stability, readily reacting with airborne H2O and CO2 to generate inert impurities such as LiOH and Li2CO3. This not only leads to a loss of lithium content in the material itself (up to 15%-20%) but also introduces impurity phases that hinder lithium-ion transport, ultimately causing a significant decrease in lithium replenishment efficiency (from over 90% theoretically to below 60%), while also exacerbating side reactions at the battery interface. LFO's air sensitivity not only reduces its effectiveness in pre-lithiation but also complicates its handling and storage. Current research suggests that improving the air stability of LFO plays a crucial role in enhancing its electrochemical performance.

[0003] One study proposed using a sodium ion implantation strategy to enhance the lithium compensation capability of materials at high rates. This is achieved by triggering the redox reaction of oxygen anions. This enhancement stems from the introduction of sodium ions into tetrahedral lithium sites, which not only increases the lattice oxygen content but also promotes the oxidation of oxygen. 2- →O 2n- →O2 conversion process. Furthermore, the formation of the surface carbon layer significantly improves the air stability of LFO-Na. Experimental data show that the initial charging capacity of LFO-Na material reaches 763.8 mAh g⁻¹ at 0.1C and 1C rates, respectively. -1 and 584.2 mAhg -1 Compared to the original LFO material, it improved by 86.2 mAh g. -1 and 221.7mAhg -1 More notably, LFO-Na exhibited excellent air stability in a 20% humidity environment, maintaining a capacity of 531.0 mAh g after 8 hours of exposure. -1 The capacity is [missing information], while the capacity of the original LFO material is only 249.2 mAh g.-1 .

[0004] Further research has found that residual alkali readily forms on the surface of Li5FeO4 when exposed to air, which can be successfully converted into a lithium phosphate layer through one-step phosphorylation. Surface-phosphorylated Li5FeO4 (LP-LFO) exhibits excellent air stability, maintaining a capacity of 637.3 mAh g even after 3 hours of exposure to air. -1 The capacity.

[0005] While the above methods can improve the air stability of LFO to some extent, the improvement is limited and they do not take into account the electrochemical performance of the material under higher humidity (e.g., 70% humidity) conditions for longer protection (e.g., 24 hours). Summary of the Invention

[0006] In order to overcome at least one of the problems existing in the prior art, one of the objectives of the present invention is to provide a lithium-rich iron acid modified material, which has good electrochemical performance and good air stability, and can still maintain a high charge-discharge specific capacity after long-term exposure in high humidity air.

[0007] The second objective of this invention is to provide a method for preparing the above-mentioned lithium-rich ferric acid modified material.

[0008] A third objective of this invention is to provide a lithium supplement.

[0009] The fourth objective of this invention is to provide a positive electrode material.

[0010] The fifth objective of this invention is to provide a lithium-ion battery.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] A first aspect of the present invention provides a lithium-rich ferric acid modified material, the lithium-rich ferric acid modified material comprising a lithium-rich ferric acid core and a coating layer; the coating layer covers at least a portion of the surface of the lithium-rich ferric acid core; the coating layer comprises lithium fluoride and lithium borate; the lithium-rich ferric acid core is doped with boron and fluorine.

[0013] In some embodiments of the present invention, the coating layer is formed by calcining lithium hydroxide and ammonium fluoroborate.

[0014] After calcination, lithium hydroxide (LiOH) and ammonium fluoroborate (NH4BF4) can be transformed into a crystalline lithium fluoride (LiF) and an amorphous lithium borate (Li3BO3) composite coating layer, and some boron (B) and fluorine (F) elements are doped into the lithium-rich iron acid core phase to form B / F co-doping.

[0015] In some specific embodiments of the present invention, the coating layer is formed by calcining lithium hydroxide and ammonium fluoroborate on the surface of a lithium-rich ferric acid core.

[0016] In some embodiments of the present invention, the sum of the masses of the lithium hydroxide and the ammonium fluoroborate is 1 to 25% of the total mass of the lithium-rich iron acid modified material; for example, it can be any value or a range between any two of 1%, 3%, 5%, 7%, 10%, 12%, 15%, 17%, 20%, or 25%.

[0017] In some specific embodiments of the present invention, the sum of the masses of the lithium hydroxide and the ammonium fluoroborate is 5 to 20% of the total mass of the lithium-rich iron acid modified material.

[0018] In some more specific embodiments of the present invention, the sum of the masses of the lithium hydroxide and the ammonium fluoroborate is 7 to 12% of the total mass of the lithium-rich iron acid modified material.

[0019] In some embodiments of the present invention, the molar ratio of lithium hydroxide to ammonium fluoroborate is 1:(0.2~1.2); for example, it can be any value or a range between 1:0.2, 1:0.25, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.8, 1:1 or 1:1.2.

[0020] In some specific embodiments of the present invention, the molar ratio of lithium hydroxide to ammonium fluoroborate is 1:(0.25~1).

[0021] In some more specific embodiments of the present invention, the molar ratio of lithium hydroxide to ammonium fluoroborate is 1:(0.3~0.6).

[0022] By optimizing the dosage of ammonium fluoroborate and lithium hydroxide, the electrochemical performance of lithium-rich iron acid modified materials can be further improved, giving them better air stability.

[0023] A second aspect of the present invention provides a method for preparing a lithium-rich ferric acid modified material as described in the first aspect of the present invention, comprising the following steps: mixing lithium-rich ferric acid, lithium hydroxide and ammonium fluoroborate, and calcining in a protective gas to obtain the lithium-rich ferric acid modified material.

[0024] In some embodiments of the present invention, in the preparation method of the lithium-rich ferric acid modified material, the sum of the mass of lithium hydroxide and ammonium fluoroborate is 1 to 25% of the total mass of the lithium-rich ferric acid, lithium hydroxide and ammonium fluoroborate; for example, it can be any value or a range between any two of 1%, 3%, 5%, 7%, 10%, 12%, 15%, 17%, 20% or 25%.

[0025] In some specific embodiments of the present invention, in the preparation method of the lithium-rich ferric acid modified material, the sum of the mass of lithium hydroxide and ammonium fluoroborate is 5 to 20% of the total mass of the lithium-rich ferric acid, lithium hydroxide and ammonium fluoroborate.

[0026] In some more specific embodiments of the present invention, in the preparation method of the lithium-rich ferric acid modified material, the sum of the mass of lithium hydroxide and ammonium fluoroborate is 7-12% of the total mass of the lithium-rich ferric acid, lithium hydroxide and ammonium fluoroborate.

[0027] In some embodiments of the present invention, in the preparation method of the lithium-rich iron acid modified material, the molar ratio of lithium hydroxide to ammonium fluoroborate is 1:(0.2~1.2); for example, it can be any value or a range between any two of 1:0.2, 1:0.25, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.8, 1:1 or 1:1.2.

[0028] In some specific embodiments of the present invention, in the preparation method of the lithium-rich iron acid modified material, the molar ratio of lithium hydroxide to ammonium fluoroborate is 1:(0.25~1).

[0029] In some more specific embodiments of the present invention, in the preparation method of the lithium-rich iron acid modified material, the molar ratio of lithium hydroxide to ammonium fluoroborate is 1:(0.3~0.6).

[0030] In some embodiments of the present invention, the calcination temperature is 400~460°C; for example, it can be any value or a range between 400°C, 410°C, 420°C, 430°C, 440°C, 450°C or 460°C.

[0031] In some specific embodiments of the present invention, the calcination temperature is 410~450℃.

[0032] In some more specific embodiments of the present invention, the calcination temperature is 420~440°C.

[0033] In some embodiments of the present invention, the calcination time is 3 to 18 hours; for example, it can be any value of 3 hours, 5 hours, 7 hours, 10 hours, 12 hours or 15 hours or a range between any two.

[0034] In some specific embodiments of the present invention, the calcination time is 5 to 15 hours.

[0035] In some more specific embodiments of the present invention, the calcination time is 7 to 12 hours.

[0036] By optimizing the calcination temperature and time, the electrochemical performance of lithium-rich iron acid modified materials can be further improved.

[0037] In some embodiments of the present invention, the protective gas includes at least one of nitrogen, argon, or helium; in some specific embodiments of the present invention, the protective gas is selected from argon.

[0038] In some embodiments of the present invention, the flow rate of the protective gas is 300~700 mL / min.

[0039] In some specific embodiments of the present invention, the flow rate of the protective gas is 400~600 mL / min.

[0040] A third aspect of the present invention provides a lithium replenishing agent, the lithium replenishing agent comprising the lithium-rich ferric acid modified material described in the first aspect of the present invention.

[0041] A fourth aspect of the present invention provides a cathode material comprising the lithium replenishing agent described in the third aspect of the present invention.

[0042] A fifth aspect of the present invention provides a lithium-ion battery comprising the positive electrode material described in the fourth aspect of the present invention.

[0043] In some embodiments of the present invention, the negative electrode material of the lithium-ion battery is metallic lithium.

[0044] In some embodiments of the present invention, the separator of the lithium-ion battery is a glass fiber membrane.

[0045] In some embodiments of the present invention, the electrolyte of the lithium-ion battery includes lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), and dimethyl carbonate (DMC); wherein the concentration of lithium hexafluorophosphate is 0.5~1.5 mol / L; and the volume ratio of ethylene carbonate to dimethyl carbonate is 1:(0.5~1.5).

[0046] In some embodiments of the present invention, the lithium-ion battery has a first-cycle charging specific capacity of 600~900 mAh·g at a 1 / 3C rate. -1 For example, it could be 600mAh·g -1 650mAh·g -1 700mAh·g -1 750mAh·g -1 800mAh·g -1 850mAh·g -1 Or 900mAh·g -1 Any value in or a range of values ​​between any two.

[0047] In some specific embodiments of the present invention, the lithium-ion battery has a first-cycle charging specific capacity of 800~850 mAh·g at a 1 / 3C rate. -1 .

[0048] In some embodiments of the present invention, after the lithium-ion battery is exposed to air with 70% humidity for 24 hours, the specific capacity of the first charge at 1 / 3C rate is 500~700 mAh·g. -1 For example, it could be 500mAh·g -1 550mAh·g -1 600mAh·g -1 650mAh·g -1 Or 700mAh·g -1 Any value in or a range of values ​​between any two.

[0049] In some specific embodiments of the present invention, after the lithium-ion battery is exposed to air with 70% humidity for 24 hours, the specific capacity of the first charge cycle at a 1 / 3C rate is 600~650 mAh·g. -1 .

[0050] In some embodiments of the present invention, after the lithium-ion battery is exposed to air with 70% humidity for 24 hours, its capacity retention rate at 1 / 3C is 65-80%; for example, it can be any value or a range between 65%, 67%, 70%, 72%, 75%, 77% or 80%.

[0051] In some specific embodiments of the present invention, the lithium-ion battery retains 70-77% of its capacity at 1 / 3C after being exposed to air with 70% humidity for 24 hours.

[0052] The beneficial effects of this invention are as follows: This invention constructs a composite coating layer of lithium fluoride and lithium borate on the surface of a lithium-rich ferric acid core doped with boron and fluorine. The resulting modified lithium-rich ferric acid material has the advantages of high charge / discharge specific capacity and good air stability, solving the problem of significant capacity reduction in lithium-rich ferric acid when exposed to air. This material can maintain a high specific capacity even after prolonged exposure to air, thus it can be used as a high-capacity lithium replenisher for lithium-ion batteries, achieving high lithium replenishment efficiency. Simultaneously, this material is prepared at a low temperature, with a short preparation time, simple process, low price, and is environmentally friendly. Attached Figure Description

[0053] Figure 1 This is a flowchart of the preparation process for the sample in Example 1.

[0054] Figure 2 The graphs show the electrochemical performance of the samples from Example 1 and Comparative Examples 1-3 immediately after preparation.

[0055] Figure 3 The graph shows the electrochemical performance of the samples from Example 1 and Comparative Examples 1-3 after 24 hours of exposure to air.

[0056] Figure 4 The images show the XRD patterns of the samples from Example 1 and Comparative Examples 1-3 immediately after preparation and after 24 hours of exposure to air.

[0057] Figure 5 The graph shows the electrochemical performance of the samples from Examples 1 and 2 immediately after preparation.

[0058] Figure 6 The graph shows the electrochemical performance of the samples from Examples 1 and 3 immediately after preparation.

[0059] Figure 7 The image shows the electrochemical performance of the sample from Example 4 immediately after preparation. Detailed Implementation

[0060] The following specific embodiments further illustrate the content of the present invention in detail. It should also be understood that the following embodiments are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the principles described herein are all within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make selections within a suitable range based on the description herein, and are not intended to be limited to the specific data in the examples below. Unless otherwise specified, the raw materials, reagents, or apparatus used in the following embodiments and comparative examples can be obtained from conventional commercial sources or by existing known methods.

[0061] Example 1 A lithium-rich iron acid modified material (LFO-BF) is shown in the preparation flowchart below. Figure 1 As shown, the specific preparation steps are as follows: LiOH . H2O and NH4BF4 were used as additives. They were mixed at a molar ratio of 2:1 (total 10 mg) and ground thoroughly. Then, 90 mg of LFO was added according to the mass ratio of the resulting product to LFO of 1:9. The mixture was then ground thoroughly for 5 min to form a mixed powder. The total mass of the additives was 10% of the total mass of the mixed powder. The mixed powder was placed in a tube furnace and calcined at 430℃ for 10 h under an argon gas flow rate of 500 mL / min to obtain LFO-BF. The LFO-BF was then stored in a glove box and ground into powder for later use.

[0062] Example 2 A lithium-rich iron acid modified material differs from Example 1 in that the calcination temperature is modified to 410℃ or 450℃, while other conditions are the same as in Example 1.

[0063] Example 3 A lithium-rich iron acid modified material differs from Example 1 in that the calcination time is modified to 5h or 15h, while other conditions are the same as in Example 1.

[0064] Example 4 A lithium-rich iron acid modified material differs from Example 1 in that the total mass of additives used in this example is modified to 5%, 7%, 15%, or 20% of the total mass of the mixed powder (LiOH). . (The molar ratio of H2O and NH4BF4 remains unchanged), and all other conditions are the same as in Example 1.

[0065] Comparative Example 1 A lithium-rich iron acid modified material (LFO), namely LFO without coating treatment.

[0066] Comparative Example 2 A lithium-rich iron acid modified material (LFO-BH) differs from Example 1 in that NH4BF4 is replaced with H3BO3, while all other conditions are the same as in Example 1.

[0067] Comparative Example 3 A lithium-rich iron acid modified material (LFO-BHA) differs from Example 1 in that NH4BF4 is replaced with (NH4)3BO3, while all other conditions are the same as in Example 1.

[0068] Performance testing 1) Test the X-ray diffraction (XRD) patterns of the samples of each embodiment and comparative example immediately after preparation and after exposure to air (24h exposure in an air environment at 25°C and 70% RH).

[0069] 2) Samples from each example and comparative example were taken immediately after preparation and after exposure to air (24h exposure at 25°C and 70% RH) as positive electrode active materials. They were mixed with super P and polytetrafluoroethylene (PTFE) in a mass ratio of 6:3:1 to form a positive electrode. Lithium metal was used as the negative electrode, 1M LiPF6 in DMC:EC=1:1 Vol% was used as the electrolyte, and glass fiber was used as the separator. Lithium-ion batteries were assembled and constant current charge-discharge tests were conducted at 1 / 3C.

[0070] Figure 2 The graphs show the electrochemical performance of the samples from Example 1 and Comparative Examples 1-3 immediately after preparation. Figure 3 The graph shows the electrochemical performance of the samples from Example 1 and Comparative Examples 1-3 after 24 hours of exposure to air.

[0071] from Figures 2-3 As can be seen, the samples LFO, LFO-BH, LFO-BHA, and LFO-BF prepared using different boron sources exhibited good electrochemical performance with initial charge-discharge capacities of 721 mAh / g, 560 mAh / g, 793 mAh / g, and 844 mAh / g, respectively, immediately after preparation. However, after exposure to air at 70% relative humidity for 24 hours, the capacities of the three samples prepared in Comparative Examples 1-3 decreased to 365 mAh / g, 420 mAh / g, and 523 mAh / g, respectively, with increased polarization and significant plateau changes. The LFO-BF sample from Example 1, after air exposure under the same conditions, maintained a specific capacity of 632 mAh / g with minimal polarization change and a capacity retention rate as high as 75%, demonstrating that the method in Example 1 can significantly improve the air stability of LFO.

[0072] Figure 4 The images show the XRD patterns of Sample 1 and Comparative Examples 1-3 immediately after preparation and after 24 hours of air exposure. Figure 4 It is evident that the XRD patterns of freshly prepared samples LFO and LFO-BF conform to the standard card, indicating they are pure LFO phases. However, LFO-BH and LFO-BHA contain impurities such as LiOH and LiFeO2. Furthermore, after 24 hours of exposure to air, LFO, LFO-BH, and LFO-BHA showed significant peaks for LiO2, LiOH, and LiCO3 impurities, while only LFO-BF showed no significant change after 24 hours of air exposure, indicating good air stability.

[0073] XRD analysis shows that, compared to other boron sources, this application uses NH4BF4 to modify and introduce F element, which reacts with LiOH to form crystalline LiF, while B forms an amorphous lithium borate compound. Electrochemical results show that the synergistic effect of the two is more stable to air and moisture than a single boron source.

[0074] Example 1: Sample passed through LiOH . H2O and NH4BF4 coating modification can increase the lithium content retention rate of lithium-rich iron oxide Li5FeO4 from less than 50% before modification to 75% after 24 hours of exposure in an air environment of 25℃ and 70%RH. Moreover, the content of inert impurities such as LiOH and Li2CO3 generated is controlled within 2%, which completely solves the problems of traditional Li5FeO4 being easy to absorb moisture and react with CO2.

[0075] Figure 5 The graphs show the electrochemical performance of the samples from Examples 1 and 2 immediately after preparation. From... Figure 5It is evident that calcination temperature affects the electrochemical performance of LFO-BF samples, with samples calcined at 430℃ exhibiting higher specific capacity.

[0076] Figure 6 The graphs show the electrochemical performance of the samples from Examples 1 and 3 immediately after preparation. From... Figure 6 It is evident that calcination time also affects the electrochemical performance of LFO-BF samples, with samples calcined for 10 hours exhibiting higher specific capacity.

[0077] Figure 7 This is a graph showing the electrochemical performance of the sample from Example 4 after 24 hours of air exposure. (From...) Figure 7 It can be seen that ammonium fluoroborate (NH4BF4) and lithium hydroxide (LiOH) . The coating amount of H2O additives also affects the electrochemical performance of LFO-BF samples. When the coating ratio is 10%, LiOH... . The sample obtained when the molar ratio of H2O to NH4BF4 is 2:1 has a higher specific capacity.

[0078] LFO, as an ultra-high capacity lithium replenisher, is inexpensive and environmentally friendly, and can replenish the large amount of lithium ions irreversibly and permanently lost during the first charge-discharge cycle of lithium-ion batteries. However, it has a fatal flaw: it is extremely prone to reacting with air. Therefore, this invention addresses the problem of poor air stability of LFO in existing technologies by using LiOH... . The LFO-BF sample obtained by coating and modifying with H2O and NH4BF4 has significantly improved air stability, effectively solving the problems of traditional Li5FeO4 being hygroscopic and easily reacting with CO2.

[0079] In summary, the embodiments of this invention employ calcination coating of lithium hydroxide and ammonium fluoroborate on the surface of lithium-rich ferric acid. A composite coating layer of lithium fluoride and lithium borate is constructed on the surface of the boron- and fluorine-doped lithium-rich ferric acid core. The resulting modified lithium-rich ferric acid material exhibits advantages such as high charge / discharge specific capacity and good air stability, solving the problem of significant capacity reduction in lithium-rich ferric acid exposed to air. This material maintains a high specific capacity even after prolonged exposure to air, thus serving as a high-capacity lithium replenisher for lithium-ion batteries, achieving high lithium replenishment efficiency. Furthermore, this material is prepared at low temperatures, with short preparation times, simple processes, low cost, and is environmentally friendly.

Claims

1. A lithium-rich iron acid modified material, characterized in that, The lithium-rich ferric acid modified material includes a lithium-rich ferric acid core and a coating layer; the coating layer covers at least a portion of the surface of the lithium-rich ferric acid core; the coating layer includes lithium fluoride and lithium borate; the lithium-rich ferric acid core is doped with boron and fluorine.

2. The lithium-rich iron acid modified material according to claim 1, characterized in that, The coating layer is formed by calcining lithium hydroxide and ammonium fluoroborate.

3. The lithium-rich iron acid modified material according to claim 2, characterized in that, The sum of the masses of the lithium hydroxide and the ammonium fluoroborate is 1 to 25% of the total mass of the lithium-rich ferric acid modified material.

4. The lithium-rich iron acid modified material according to claim 2, characterized in that, The molar ratio of lithium hydroxide to ammonium fluoroborate is 1:(0.2~1.2).

5. A method for preparing a lithium-rich iron acid modified material as described in any one of claims 1 to 4, characterized in that, The process includes the following steps: mixing lithium-rich ferric acid, lithium hydroxide, and ammonium fluoroborate, and calcining them in a protective gas atmosphere to obtain the lithium-rich ferric acid modified material.

6. The preparation method according to claim 5, characterized in that, The calcination temperature is 400~460℃.

7. The preparation method according to claim 5, characterized in that, The calcination time is 3 to 18 hours.

8. A lithium supplement, characterized in that, The lithium replenishing agent includes the lithium-rich iron acid modified material according to any one of claims 1 to 4.

9. A positive electrode material, characterized in that, The cathode material includes the lithium replenishing agent as described in claim 8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode material as described in claim 9.

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