Regeneration method and application of modified lithium ferrite treated by Lewis acid

Abstract

The invention discloses a regeneration method and application of modified lithium ferrite treated by Lewis acid, and the regeneration method comprises the following steps: in an inert atmosphere, mixing Lewis acid with a sulfonic acid-based solid acid catalyst to obtain a mixture; placing the modified lithium ferrite and the mixture in a closed reaction container, wherein the modified lithium ferrite is not in direct contact with the mixture; at the temperature of 60-120 DEG C, lewis acid in the mixture is decomposed to release lewis acid gas, the lewis acid gas reacts with impurities of the modified lithium ferrite, and after the reaction is finished, the regenerated lithium ferrite material is obtained. The catalytic induction Lewis acid treatment is adopted, alkaline impurities on the surface of the lithium ferrite material can be removed, the electrochemical activity of the lithium ferrite material is recovered, and meanwhile the air stability of the lithium ferrite material is improved. The regenerated lithium ferrite material provided by the invention is used as a positive electrode lithium supplementing agent, can supplement the consumption of active lithium of a lithium battery, prolongs the cycle life of the lithium battery, and improves the long cycle performance of the lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ferrite regeneration, and specifically relates to a regeneration method and application of treating deteriorated lithium ferrite with a Lewis acid. Background Art

[0002] As a high-performance energy storage technology, lithium-ion batteries have been widely used in many fields such as mobile electronic devices, electric vehicles, and renewable energy due to their high energy density, long cycle life, low self-discharge, and environmental protection characteristics. However, how to further improve the energy density and cycle life of lithium-ion batteries has always been an important topic in battery technology research and development. During the charge and discharge process of lithium-ion batteries, a solid electrolyte interface film (SEI) will form on the surface of the negative electrode, and the formation of this process will consume active lithium ions. At the same time, as the number of battery cycles increases, the active lithium ions will gradually be lost, resulting in a decrease in the cycle stability of the battery. Since the active lithium in lithium-ion batteries is mainly provided by the positive electrode material, increasing the amount of active lithium in the positive electrode has become the key to improving the energy density and cycle performance of lithium batteries.

[0003] In order to improve the battery capacity and long-term cycle stability, the pre-lithiation technology based on positive electrode lithium supplements has been proposed and widely used. Common positive electrode lithium supplements include lithium ferrite Li5FeO4 (abbreviated as LFO), lithium nitride Li3N, and lithium nickelate Li2NiO2, etc. Among them, as a common positive electrode lithium supplement, LFO has been widely used in the pre-lithiation process of lithium-ion batteries due to its low cost, high theoretical capacity, and good lithium release ability. However, there are still many problems with LFO in practical applications. First, the air stability of LFO is poor, and it is easy to react with H2O, CO2, and O2 in the air, resulting in the formation of a high-impedance, strongly alkaline impurity layer on the surface. These alkaline impurities will not only reduce the electrochemical lithium supplementation activity of LFO, but also interact with the binder during the electrode slurry preparation process, resulting in slurry gelation, seriously affecting the performance of the battery. Secondly, LFO is prone to side reactions with the electrolyte during charging, generating gas, leading to an increase in the internal pressure of the battery, and further affecting the stability and safety of the battery. In addition, the low conductivity of LFO is also one of the key factors restricting its lithium supplementation effect, resulting in the difficulty of fully exerting the lithium supplementation performance of LFO.

[0004] To solve these problems, Chinese Patent (Publication No.: CN119447310A) uses the low-temperature molten salt method to form a solid electrolyte coating layer on the surface of the carbon-doped LFO material, effectively isolating the air and improving the air stability of the material. However, the large-scale utilization of the low-temperature molten salt method has the disadvantages of difficult process control and high cost, restricting its application in actual production. In addition, Chinese Patent (Publication No.: CN119315135A) proposes a structure with an LFO core and a C@Li shell 7 / 4Ti 5 / 4 The core-shell structure of TiO3 aims to improve the stability of the material, reduce the residual alkali on the surface, and enhance the conductivity. However, the preparation process is complex and costly, and it is difficult to ensure the uniformity of the core-shell structure in large-scale production.

[0005] In summary, although existing research has made certain progress in improving the lithium compensation performance of LFO, how to solve the problem of air instability of LFO under the premise of high efficiency remains a key technical problem to be solved urgently. In addition, due to the poor air stability of LFO, deterioration during actual processing, transportation, and use is inevitable. Therefore, developing a simple and convenient regeneration method for LFO to improve its stability and lithium compensation activity in practical applications is of great significance for effectively enhancing the capacity, cycle stability, and safety of batteries. Summary of the Invention

[0006] To solve the above technical problems, the object of the present invention is to provide a regeneration method and application of treating deteriorated lithium iron oxide with a Lewis acid.

[0007] The above object of the present invention is achieved by the following technical solutions:

[0008] The first aspect of the present invention provides a regeneration method of treating deteriorated lithium iron oxide with a Lewis acid, comprising the following steps:

[0009] (1) In an inert atmosphere, mix a Lewis acid with a sulfonic acid group solid acid catalyst to obtain a mixture;

[0010] (2) In an inert atmosphere, place the deteriorated lithium iron oxide and the mixture obtained in step (1) in a closed reaction vessel, and the deteriorated lithium iron oxide and the mixture do not come into direct contact; at 60 - 120 °C, the Lewis acid in the mixture decomposes to release Lewis acid gas, which reacts with the impurities of the deteriorated lithium iron oxide, and after the reaction, a regenerated lithium iron oxide material (abbreviated as D-LFO) is obtained.

[0011] Lithium iron oxide (LFO) is a typical cathode lithium compensation material, but it is prone to deterioration in an air atmosphere, namely deteriorated LFO. The regeneration method of treating deteriorated lithium iron oxide with a Lewis acid based on catalytic induction provided by the present invention enables the Lewis acid to decompose into Lewis acid gas at 60 - 120 °C under the catalytic action of a sulfonic acid group solid acid catalyst, reacts with the carbonates and hydroxides on the surface of deteriorated LFO, thereby removing impurities and generating a modified interface layer, and restoring the electrochemical lithium compensation activity of LFO. This regeneration method can not only significantly improve the air stability and cycle stability of LFO, but also effectively reduce the gas generation amount of the battery, enhance the safety, capacity, and long-term use performance of the battery. In addition, this method has a simple process, convenient operation, and remarkable effects, is suitable for large-scale production, and has important practical application value.

[0012] Further, in step (1), the Lewis acid is lithium hexafluorophosphate (LiPF6) and / or lithium tetrafluoroborate (LiBF4). The Lewis acid can decompose under the catalysis of the sulfonic acid group solid acid catalyst to release Lewis acid gas (such as PF5, BF3, etc.). The Lewis acid gas reacts with the surface impurities of the deteriorated LFO to remove basic impurities such as oxides and hydroxides.

[0013] Further, in step (1), the sulfonic acid group solid acid catalyst is selected from one or more of sulfonated silica gel (SiO2-SO3H), sulfonated alumina (Al2O3-SO3H), and sulfonated polystyrene (PS-SO3H). The sulfonic acid group solid acid catalyst can reduce the decomposition temperature of the Lewis acid and improve the reaction efficiency.

[0014] Further, in step (1), the mass ratio of the Lewis acid to the sulfonic acid group solid acid catalyst is (1-20):1, preferably (3-15):1. This mass ratio helps to improve the decomposition efficiency of the Lewis acid and control the reaction rate.

[0015] Further, in step (2), the mass ratio of the deteriorated LFO to the mixture is (5-100):1, preferably (20-50):1. This mass ratio can ensure that the impurity layer of the deteriorated LFO reacts fully with the Lewis acid gas. When the mass ratio is too small, the Lewis acid decomposition reaction is too fast to control, and the excessive Lewis acid gas will erode the main body of the LFO; while when the mass ratio is too large, the Lewis acid gas cannot remove the impurities of the deteriorated LFO completely.

[0016] Further, in step (2), the reaction time is 1-24 h.

[0017] Further, in step (2), after the reaction, there is also a step of performing vacuum drying treatment.

[0018] Further, in step (2), the temperature of the vacuum drying treatment is 100-150 °C, and the time is 1-12 h. The vacuum drying treatment can remove the moisture and unreacted gas during the reaction.

[0019] In a specific embodiment, the deteriorated lithium ferrite and the mixture can be placed in a sealed double-layer reaction vessel. The upper layer is the deteriorated LFO, and the lower layer is the mixture, and the two do not come into direct contact.

[0020] The second aspect of the present invention provides a D-LFO material obtained by the regeneration method of treating deteriorated lithium ferrite with the Lewis acid described in the first aspect.

[0021] The D-LFO material provided by the present invention has high electrochemical lithium supplementation activity, air stability, and low interfacial reactivity with the electrolyte, which can reduce the decomposition of the electrolyte and inhibit the gas generation of the battery.

[0022] The third aspect of the present invention provides an application of the D-LFO material described in the second aspect in a lithium-ion battery.

[0023] As a cathode prelithiation material (cathode lithium supplement agent) for lithium-ion batteries, the D-LFO material provided by the present invention can effectively improve the capacity, cycle stability, and safety of the battery, and is applicable to lithium-ion batteries with high energy density and long life.

[0024] The fourth aspect of the present invention provides a prelithiated cathode electrode sheet, which includes the D-LFO material described in the second aspect.

[0025] Further, the prelithiated cathode electrode sheet is prepared by the following preparation method: adding the D-LFO material to the cathode active material, then mixing it with a conductive agent and a binder, and obtaining the prelithiated cathode electrode sheet after treatment.

[0026] Further, the addition amount of the D-LFO material is less than or equal to 1.5% of the total mass of the D-LFO material (lithium supplement agent), the cathode active material, the conductive agent, and the binder.

[0027] The fifth aspect of the present invention provides a lithium-ion battery, which includes the prelithiated cathode electrode sheet described in the fourth aspect.

[0028] Further, the lithium-ion battery is assembled from the prelithiated cathode electrode sheet, an electrolyte, a separator, and a negative electrode sheet.

[0029] Advantages of the present invention:

[0030] (1) By using catalytic induction Lewis acid treatment, the present invention can remove alkaline impurities on the surface of deteriorated LFO, restore its electrochemical activity, and improve the air stability of the LFO material at the same time.

[0031] (2) The regeneration method provided by the present invention can significantly reduce the phenomenon of gas generation when the LFO material reacts with the electrolyte, thereby improving the safety of the battery and reducing problems such as battery swelling or electrolyte leakage caused by gas generation.

[0032] (3) As a cathode lithium supplement agent, the D-LFO material provided by the present invention can supplement the consumption of active lithium in the lithium battery, extend the cycle life of the lithium battery, and improve the long-cycle performance of the lithium-ion battery. Description of the Drawings

[0033] Figure 1 It is a schematic diagram of the regeneration method of treating deteriorated lithium ferrite with Lewis acid in the present invention.

[0034] Figure 2 X-ray diffraction (XRD) patterns of LFO with impurity phases (metamorphic LFO), the D-LFO material prepared in Example 1, and the D-LFO after being exposed to air for 6 h and 12 h.

[0035] Figure 3 Scanning electron microscope (SEM) image of the D-LFO material prepared in Example 1.

[0036] Figure 4 High-resolution transmission electron microscope (HRTEM) images of the D-LFO material prepared in Example 1; where a is the HRTEM image of D-LFO, b is the high-magnification HRTEM image of the blue region in a, and c is the high-magnification HRTEM image of the orange region in a.

[0037] Figure 5 X-ray photoelectron spectroscopy (XPS) spectra of the D-LFO material prepared in Example 1; where a is the F 1s spectrum and b is the P 2p spectrum.

[0038] Figure 6 Charge-discharge curve comparison diagrams of the half-cells assembled with the LFO material and the D-LFO material prepared in Example 1 at a rate of 0.05C (1C = 832 mA·g -1 ).

[0039] Figure 7 Charge-discharge curve comparison diagrams of the half-cells assembled with the LFO material and the D-LFO material prepared in Example 1 at a rate of 0.2C (1C = 832 mA·g -1 ).

[0040] Figure 8 First charge-discharge curve diagrams of the LiFePO4 / graphite full cell and the LiFePO4-1.5% D-LFO / graphite full cell assembled by adding the D-LFO material prepared in Example 1.

[0041] Figure 9 Cycling performance curve diagrams of the LiFePO4 / graphite full cell, the LiFePO4-1.5% LFO / graphite full cell assembled by adding the LFO material, the LiFePO4-1.5% metamorphic LFO / graphite full cell assembled by adding the metamorphic LFO, and the LiFePO4-1.5% D-LFO / graphite full cell assembled by adding the D-LFO material prepared in Example 1.

[0042] Figure 10 Time-gas production curve diagrams of the LFO material and the D-LFO material prepared in Example 1 with LiPF6 solution at 60°C. Detailed implementation manners

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this invention belongs. The terms used in the description of this invention herein are for the purpose of describing specific embodiments only and are not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the related listed items.

[0044] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited are not intended to limit the present invention.

[0045] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods, and the materials, reagents, etc. used, unless otherwise specified, can be obtained from commercial channels.

[0046] The deteriorated LFO used in the following examples and comparative examples is the deteriorated LFO (Air-LFO) obtained after the LFO material is exposed to air for 48 h.

[0047] Example 1

[0048] A regeneration method for treating deteriorated lithium ferrite with a Lewis acid, comprising the following steps:

[0049] (1) In an inert atmosphere, 1 g of LiPF6 is mixed uniformly with 0.2 g of sulfonated silica gel (SiO2-SO3H) to obtain a mixture.

[0050] (2) In an inert atmosphere, 20 g of deteriorated LFO and 1 g of the mixture are placed in a sealed double-layer reaction vessel, ensuring that the deteriorated LFO is located in the upper layer and the mixture is located in the lower layer. Then the reaction vessel is placed in an oven and heated at 120 °C for 1 hour. During the reaction process, LiPF6 decomposes into PF5 acidic gas, which reacts with the impurities on the surface of the deteriorated LFO to remove carbonate and hydroxide impurities. After the heating is completed, the reaction product is taken out and vacuum dried at a temperature of 120 °C for 8 hours to obtain a regenerated LFO material (D-LFO).

[0051] Figure 1 It is a schematic diagram of the regeneration method for treating deteriorated lithium ferrite with a Lewis acid in the present invention.

[0052] In order to verify the subsequent air stability of the D-LFO material, the D-LFO material was exposed to air with 30% humidity for a 12-hour test, and the test results are as Figure 2 shown, Figure 2XRD patterns of the LFO with impurity phases (degraded LFO), the D-LFO material prepared in Example 1, and the D-LFO after being exposed to air for 6 h and 12 h. Figure 2 It shows that within 0 - 12 hours, the peak positions and intensities of the XRD patterns of the D-LFO material do not change significantly, proving that the D-LFO material has good stability in air and is not easily degraded.

[0053] Figure 3 SEM image of the D-LFO material prepared in Example 1, where it can be seen that the D-LFO material presents a coated flaky irregular shape.

[0054] Figure 4 HRTEM image of the D-LFO material prepared in Example 1. From Figure 4 a, it can be seen that the thickness of the modified interface layer of the D-LFO material is 20 - 50 nm. From Figure 4 b, the (0 2 3) crystal plane characteristics of Li5FeO4 are observed, and the corresponding interplanar spacing is which verifies the integrity of the internal lattice structure of the material. Figure 4 c further shows that the modified interface layer presents a typical amorphous structure, in sharp contrast to the internal crystalline region.

[0055] Figure 5 X-ray photoelectron spectroscopy diagrams of F 1s and P 2p of the D-LFO material prepared in Example 1. Figure 5 a in it is the F 1s spectrum, showing a peak at 686.1 eV, which is in good agreement with the characteristics of LiF. The presence of F corresponds to the process of PF5 gas reacting with Li2CO3 and LiOH to form LiF, indicating that PF5 treatment not only removes surface impurities but also forms a stable LiF coating, effectively improving the interface stability of the material. Figure 5 b in it is the P 2p spectrum, and the signal at 139.8 eV corresponds to the phosphorus signal in phosphate, indicating the presence of an interface coating containing phosphate (such as Li3PO4) on the surface. The formation of this phosphorus-containing coating not only enhances the air stability of the material but also may improve its electrochemical performance by inhibiting the oxidation reaction of the electrolyte. Figure 5 It proves that the regeneration method of treating degraded lithium ferrite with Lewis acid provided by the present invention regenerates the high-resistance and strongly basic interface layer of degraded LFO into a modified interface layer coated with a mixture of Li3PO4 and LiF.

[0056] Example 2

[0057] A regeneration method of treating degraded lithium ferrite with Lewis acid, comprising the following steps:

[0058] (1) In an inert atmosphere, 1.5 g of LiBF4 is taken and mixed evenly with 0.5 g of sulfonated alumina (Al2O3-SO3H) to obtain a mixture.

[0059] (2) In an inert atmosphere, 10 g of deteriorated LFO and 0.2 g of the mixture are placed in a sealed double-layer reaction vessel, ensuring that the deteriorated LFO is in the upper layer and the mixture is in the lower layer. The reaction vessel is placed in an oven and heated at 60 °C for 24 hours. During the reaction, LiBF4 decomposes into acidic gases such as BF3, removing the impurities on the surface of the deteriorated LFO. After heating, the reaction product is taken out and vacuum dried at a temperature of 150 °C for 1 hour to obtain the D-LFO material.

[0060] Example 3

[0061] A regeneration method for treating deteriorated lithium ferrite with a Lewis acid, comprising the following steps:

[0062] (1) In an inert atmosphere, 1.5 g of LiBF4 is taken and mixed evenly with 0.1 g of sulfonated polystyrene (PS-SO3H) to obtain a mixture.

[0063] (2) In an inert atmosphere, 10 g of deteriorated LFO and 0.5 g of the mixture are placed in a sealed double-layer reaction vessel, ensuring that the deteriorated LFO is in the upper layer and the mixture is in the lower layer. The reaction vessel is placed in an oven and heated at 100 °C for 8 hours. During the reaction, LiBF4 decomposes into acidic gases such as BF3, reacting with the impurities on the surface of the deteriorated LFO to remove oxides and hydroxides. After heating, the product is taken out and dried in a vacuum drying oven at a temperature of 100 °C for 12 hours to obtain the D-LFO material.

[0064] Example 4

[0065] A regeneration method for treating deteriorated lithium ferrite with a Lewis acid, comprising the following steps:

[0066] (1) In an inert atmosphere, 1 g of LiPF6 is taken and mixed evenly with 0.15 g of sulfonated silica gel (SiO2-SO3H) to obtain a mixture.

[0067] (2) In an inert atmosphere, 10 g of deteriorated LFO and 0.3 g of the mixture are placed in a sealed double-layer reaction vessel, ensuring that the deteriorated LFO is in the upper layer and mixture A is in the lower layer. The reaction vessel is placed in an oven and heated at 70 °C for 18 hours. During the reaction, LiPF6 decomposes into acidic gases such as PF5, reacting with the impurities on the surface of the deteriorated LFO to remove carbonate and hydroxide impurities. After the reaction, the product is taken out and dried in a vacuum drying oven at a temperature of 120 °C for 4 hours to obtain the D-LFO material.

[0068] Comparative Example 1

[0069] A regeneration method for treating deteriorated lithium iron oxide with a Lewis acid, comprising the following steps:

[0070] In an inert atmosphere, 20 g of deteriorated LFO and 1 g of LiPF6 are placed in a sealed double-layer reaction vessel, ensuring that the deteriorated LFO is in the upper layer and LiPF6 is in the lower layer. Then the reaction vessel is placed in an oven and heated at 180 °C for 1 hour. During the reaction, LiPF6 decomposes into PF5 acidic gas, which reacts with the impurities on the surface of the deteriorated LFO to remove carbonate and hydroxide impurities. After heating, the reaction product is taken out and vacuum dried at 120 °C for 8 hours to obtain the D-LFO material.

[0071] In the absence of a sulfonic acid group solid acid catalyst, LiPF6 does not undergo thermal decomposition at 90 °C, resulting in the inability to complete the regeneration of the deteriorated LFO; LiPF6 begins to thermally decompose above 180 °C.

[0072] Comparative Example 2

[0073] A method for treating deteriorated lithium iron oxide with a Lewis acid, comprising the following steps:

[0074] (1) In an inert atmosphere, 1 g of LiPF6 is mixed evenly with 0.2 g of sulfonated silica gel (SiO2-SO3H) to obtain a mixture.

[0075] (2) In air, 20 g of deteriorated LFO and 1 g of the mixture are placed in a reaction dish, ensuring that the deteriorated LFO does not come into direct contact with the mixture. Then the reaction dish is placed in an oven and heated at 120 °C for 1 hour. During the reaction, LiPF6 undergoes self-decomposition in air, generating HF while etching the impurity layer and the LFO material body, which is harmful to the lithium supplementation performance of the LFO material, resulting in the inability of the LFO material to complete normal charge and discharge.

[0076] Test Example 1

[0077] Test the lithium supplementation performance of the LFO material and the D-LFO material prepared in Examples 1-4 and Comparative Example 1. The test method is as follows: A composite electrode obtained by uniformly mixing the LFO material or D-LFO material, conductive agent carbon black, and binder in a mass ratio of 8:1:1 is used as the working electrode, a metal lithium sheet is used as the counter electrode, and a lithium-ion battery (half-cell) is assembled with a 1 M LiPF6 solution (volume ratio of ED:DMC:EMC 1:1:1, EC is ethylene carbonate, DMC is dimethyl carbonate, and EMC is ethyl methyl carbonate) as the electrolyte. Then, charge and discharge tests are carried out between 2.5 - 4.5 V. In Test Example 1, 1C = 832 mA·g -1 .

[0078] The test results are as Figure 6 shown, Figure 6 which is a comparison chart of charge-discharge curves of a half-cell assembled with an LFO material and the D-LFO material prepared in Example 1 at a rate of 0.05C. As can be seen from Figure 6 it, for the half-cell assembled with the D-LFO material prepared in Example 1 at a rate of 0.05C, the initial charge specific capacity is 772.82 mAh / g, the discharge specific capacity is 84.94 mAh / g, and the irreversible capacity is 687.88 mAh / g; while for the LFO material under the same conditions, the initial charge specific capacity is 707.15 mAh / g, the discharge specific capacity is 82.94 mAh / g, and the irreversible capacity is 624.21 mAh / g.

[0079] For the half-cell assembled with the D-LFO material prepared in Example 2 at a rate of 0.05C, the initial charge specific capacity of the first cycle is 769.64 mAh / g, the initial discharge specific capacity of the first cycle is 82.15 mAh / g, and the irreversible capacity is 687.49 mAh / g; for the half-cell assembled with the D-LFO material prepared in Example 3 at a rate of 0.05C, the initial charge specific capacity of the first cycle is 768.93 mAh / g, the initial discharge specific capacity of the first cycle is 82.11 mAh / g, and the irreversible capacity is 686.82 mAh / g; for the half-cell assembled with the D-LFO material prepared in Example 4 at a rate of 0.05C, the initial charge specific capacity of the first cycle is 769.92 mAh / g, the initial discharge specific capacity of the first cycle is 82.33 mAh / g, and the irreversible capacity is 687.59 mAh / g; for the half-cell assembled with the D-LFO material prepared in Comparative Example 1 at a rate of 0.05C, the initial charge specific capacity of the first cycle is 213.23 mAh / g, and the initial discharge specific capacity of the first cycle is 11.15 mAh / g.

[0080] The lithium compensation performance of the LFO material and the D-LFO material at high rates was further tested. The test results are as Figure 7 shown, Figure 7 which is a comparison chart of charge-discharge curves of a half-cell assembled with an LFO material and the D-LFO material prepared in Example 1 at a rate of 0.2C. As can be seen from Figure 7 it, for the D-LFO material prepared in Example 1 at a rate of 0.2C, the initial charge specific capacity of the first cycle is 553.13 mAh / g, the discharge specific capacity is 63.55 mAh / g, and the irreversible capacity is 489.58 mAh / g; while for the LFO material under the same conditions, the initial charge specific capacity of the first cycle is 246.84 mAh / g, the discharge specific capacity is 62.11 mAh / g, and the irreversible capacity is 184.73 mAh / g. This shows that the lithium compensation performance of the D-LFO material at high currents is significantly better than that of the LFO material, mainly due to its more excellent electrical conductivity.

[0081] Test Example 2

[0082] The regenerated LFO materials prepared in Test Examples 1-4 were applied to LiFePO4 / graphite full cells to test their actual application performance in cathode prelithiation. In Test Example 2, 1C = 172 mA·g -1 , and the test method was as follows: A composite electrode obtained by uniformly mixing LiFePO4, D-LFO material, conductive agent carbon black, and binder in a mass ratio of 78.5:1.5:10:10 was used as the working electrode, graphite was used as the counter electrode, and a lithium-ion battery (LiFePO4-1.5% D-LFO / graphite full cell) was assembled with a 1M LiPF6 solution (ED:DMC:EMC volume ratio 1:1:1) as the electrolyte. The control groups were lithium-ion batteries assembled without adding D-LFO material (LiFePO4 / graphite full cell), lithium-ion batteries assembled with 1.5% LFO material (LiFePO4-1.5% LFO / graphite full cell), lithium-ion batteries assembled with 1.5% deteriorated LFO (LiFePO4-1.5% deteriorated LFO / graphite full cell), and lithium-ion batteries assembled with the D-LFO material prepared in Example 1 (LiFePO4-1.5% D-LFO / graphite full cell). The first charge-discharge test was carried out between 2.8-4.3V, and the charge-discharge test in the cycling stage was carried out between 2.8-3.65V. The first charge was a three-stage charge. First, it was charged at a constant current mode of 0.05C for 1h, then charged at a constant current mode of 0.1C for 1h, and finally charged at a constant current mode of 0.2C until the cut-off voltage of 4.0V. The first 3 cycles in the cycling stage were activated at a small current of 0.2C rate, and a current of 1C rate was used in the subsequent cycling process.

[0083] The test results are as Figure 8 and Figure 9 shown. Figure 8 is the first charge-discharge curve of the LiFePO4 / graphite full cell and the LiFePO4-1.5% D-LFO / graphite full cell assembled with the D-LFO material prepared in Example 1. Figure 9 is the cycling performance curve of the LiFePO4 / graphite full cell, the LiFePO4-1.5% LFO / graphite full cell assembled with LFO material, the LiFePO4-1.5% deteriorated LFO / graphite full cell assembled with deteriorated LFO, and the LiFePO4-1.5% D-LFO / graphite full cell assembled with the D-LFO material prepared in Example 1. From Figure 8It can be seen that the initial charge specific capacity of the LiFePO4-1.5%D-LFO / graphite full cell is 176.81 mAh / g, which is 10.04 mAh / g higher than that of the LiFePO4 / graphite full cell without the addition of the D-LFO material. The discharge specific capacity also increases from 132.14 mAh / g to 145.1 mAh / g.

[0084] The initial charge specific capacity of the LiFePO4-1.5%D-LFO / graphite full cell assembled with the D-LFO material prepared in Example 2 is 176.81 mAh / g, which is 9.66 mAh / g higher than that of the LiFePO4 / graphite full cell. The corresponding discharge specific capacity also increases from 132.14 mAh / g to 145.3 mAh / g. The initial charge specific capacity of the LiFePO4-1.5%D-LFO / graphite full cell assembled with the D-LFO material prepared in Example 3 is 176.48 mAh / g, and the corresponding discharge specific capacity also increases from 131.96 mAh / g to 144.9 mAh / g. The initial charge specific capacity of the LiFePO4-1.5%D-LFO / graphite full cell assembled with the D-LFO material prepared in Example 4 is 176.73 mAh / g, and the corresponding discharge specific capacity also increases from 131.96 mAh / g to 149.6 mAh / g.

[0085] From Figure 9 It can be seen that the capacity retention rate of the LiFePO4-1.5%D-LFO / graphite full cell assembled with the D-LFO material prepared in Example 1 is 98.5% after 200 cycles, and the discharge specific capacity is 134.97 mAh / g. While the capacity retention rate of the LiFePO4 / graphite full cell without the addition of the D-LFO material is 97.6% after 200 cycles, and the discharge specific capacity is only 113.76 mAh / g. In addition, the LiFePO4-1.5% deteriorated LFO / graphite full cell will show significant capacity decay in the first 20 cycles. It should be noted that the conventional LFO material will deteriorate when stirred in the air, resulting in an increase in the capacity of the full cell in the early stage of cycling, but there will be continuous capacity decay after 120 cycles, and the performance is significantly inferior to that of the blank control group (LiFePO4 / graphite full cell).

[0086] The LiFePO4-1.5% D-LFO / graphite full cell assembled with the D-LFO material prepared in Example 2 had a capacity retention rate of 98.3% after 200 cycles, and the discharge specific capacity of the full cell after 200 cycles was 134.42 mAh / g; the LiFePO4-1.5% D-LFO / graphite full cell assembled with the D-LFO material prepared in Example 3 had a capacity retention rate of 98.8% after 200 cycles, and the discharge specific capacity of the full cell after 200 cycles was 134.98 mAh / g; the LiFePO4-1.5% D-LFO / graphite full cell assembled with the D-LFO material prepared in Example 4 had a capacity retention rate of 98.1% after 200 cycles, and the discharge specific capacity of the full cell after 200 cycles was 134.42 mAh / g.

[0087] In summary, the D-LFO material exhibits excellent lithium compensation performance and cycling stability in lithium-ion batteries, and is suitable for battery applications under high-rate charge and discharge conditions.

[0088] Test Example 3

[0089] Evaluate the interfacial stability of the LFO material and the D-LFO materials prepared in Examples 1-4 with the LiPF6 solution at 60 °C, and conduct a high-temperature reactivity test on the LFO material and the D-LFO materials. The test method is as follows: Place 1 g of the LFO material or D-LFO material and 10 mL of a 1 M LiPF6 solution (volume ratio of ED:DMC:EMC 1:1:1) in a reaction vessel with an external gas collection bag, and place the reaction vessel in a constant-temperature heater at 60 °C for a reaction of 0-12 d, and record and analyze every 1 d.

[0090] The test results are as Figure 10 shown, Figure 10 is the time-gas production curve of the LFO material and the D-LFO material prepared in Example 1 with the LiPF6 solution at 60 °C. It can be seen from Figure 10 the figure that the test results show that after the LFO material reacts with the LiPF6 solution for 8 d, the gas evolution amount reaches the peak value of 0.94 mL / g; in contrast, for the D-LFO material prepared in Example 1, the gas evolution amount reaches the peak value after 6 d, only 0.23 mL / g; for the D-LFO material prepared in Example 2, the gas evolution amount reaches the peak value after 6 d, only 0.21 mL / g; for the D-LFO material prepared in Example 3, the gas evolution amount reaches the peak value after 5 d, only 0.26 mL / g; for the D-LFO material prepared in Example 4, the gas evolution amount reaches the peak value after 7 d, only 0.22 mL / g.

[0091] It can be seen that the gas generation amount of the D-LFO material under high-temperature conditions is significantly lower than that of the LFO material, indicating that the interfacial stability with the electrolyte has been significantly improved. This characteristic makes the D-LFO material more suitable for the full-cell system in practical applications, and can effectively reduce the gas generation problem caused by electrolyte decomposition in a high-temperature environment, thereby improving the safety and cycle stability of the battery.

[0092] Obviously, the above-mentioned embodiments of the present invention are only examples for clearly explaining the present invention, rather than limitations on the implementation manners of the present invention. Those skilled in the art should understand that other different forms of changes or variations can be made on the basis of the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A method for regenerating lithium ferrite modified by Lewis acid treatment, characterized in that: The following steps are involved: (1) mixing a Lewis acid with a sulfonic acid-based solid acid catalyst in an inert atmosphere to obtain a mixture; (2) In an inert atmosphere, the modified lithium ferrite and the mixture obtained in step (1) are placed in a closed reaction vessel, wherein the modified lithium ferrite is not in direct contact with the mixture; at 60-120° C., the Lewis acid in the mixture decomposes to release Lewis acid gas, which reacts with impurities in the modified lithium ferrite, and after the reaction is completed, a regenerated lithium ferrite material is obtained.

2. The regeneration method according to claim 1, characterized in that: In step (1), the Lewis acid is lithium hexafluorophosphate and / or lithium tetrafluoroborate.

3. The regeneration method according to claim 1, characterized in that: In step (1), the sulfonic acid-based solid acid catalyst is selected from one or more of sulfonated silica gel, sulfonated alumina and sulfonated polystyrene.

4. The regeneration method according to claim 1, characterized in that: In step (1), the mass ratio of the Lewis acid to the sulfonic acid solid acid catalyst is (1-20):

1.

5. The regeneration method according to claim 1, characterized in that: In step (2), the mass ratio of the modified lithium ferrite to the mixture is (5-100):

1.

6. A regenerated lithium ferrite material obtained by the method for regenerating lithium ferrite modified by Lewis acid treatment as described in any one of claims 1 to 5.

7. Use of the regenerated lithium ferrite material according to claim 6 in a lithium ion battery.

8. A pre-lithiated positive electrode plate, comprising the regenerated lithium ferrite material according to claim 6.

9. The pre-lithiated positive electrode sheet according to claim 8, characterized in that: The pre-lithiated positive electrode plate is prepared by the following preparation method: the regenerated lithium ferrite material is added to the positive electrode active material, and then mixed with a conductive agent and a binder, and the pre-lithiated positive electrode plate is obtained after treatment.

10. The pre-lithiated positive electrode sheet according to claim 9, characterized in that: The added amount of the regenerated lithium ferrite material is less than or equal to 1.5% of the total mass of the regenerated lithium ferrite material, the positive electrode active material, the conductive agent and the binder.

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