Modified lithium-rich lithium iron phosphate lithium supplement and preparation method, application, lithium supplement positive electrode and lithium ion battery

Abstract

The application belongs to the field of batteries, and particularly relates to a modified lithium-rich lithium iron phosphate lithium supplement agent, a preparation method and application thereof, a lithium-supplemented positive electrode and a lithium ion battery, wherein the modified lithium-rich lithium iron phosphate lithium supplement agent comprises a core and a shell coated on the surface of the core, the core is lithium-rich lithium iron phosphate, and the shell comprises an oxygen scavenger, porous carbon and a fast ion conductor; the oxygen scavenger comprises at least one of potassium sulfide, zirconium disulfide, di-aluminum sulfide, cuprous sulfide and magnesium sulfide. The application provides a new material in which the lithium-rich lithium iron phosphate is coated with a shell of a synergistic composite material of an oxygen scavenger, porous carbon and a fast ion conductor, and based on the combination of the shell synergistic components and the core-shell structure, the problems of gas generation and poor air stability of the lithium-rich lithium iron phosphate can be solved from the root cause, and the first efficiency and long cycle stability of the battery assembled from the material can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to modified lithium iron ferrite lithium supplementing agents, their preparation methods, applications, lithium supplementing cathodes, and the field of lithium-ion battery technology. Background Technology

[0002] Lithium-ion batteries are increasingly widely used in the new energy field. However, during the first charge and discharge process, the electrolyte decomposes on the surface of the negative electrode to form an SEI film, which consumes a large amount of active lithium, resulting in low initial coulombic efficiency and insufficient energy density. This problem has become a core bottleneck restricting the improvement of battery performance. The initial irreversible capacity loss of graphite negative electrodes is about 10%, while the loss of high-capacity silicon-based and tin-based negative electrodes exceeds 30%.

[0003] To address this core bottleneck, lithium replenishment technology has emerged. Its core idea is to introduce a lithium replenishing agent into the battery system to provide additional active lithium to the battery, making up for the lithium loss during the first charge and discharge process, thereby improving the battery's first coulombic efficiency and energy density, and promoting the practical application of high-capacity anode materials. The performance of the lithium replenishing agent has thus become the key to determining the lithium replenishment effect.

[0004] Among numerous lithium replenishing agents, lithium iron phosphate (Li5FeO4) has become one of the most widely used commercially available cathode lithium replenishing agents due to its significant advantages. As a lithium-rich anti-fluorite material, it possesses an extremely high theoretical specific capacity, reaching 867 mAh / g after complete lithium removal, and can release over 700 mAh / g of irreversible capacity during actual charging. Furthermore, its lithium removal process exhibits two characteristic voltage plateaus of approximately 3.5 V and 4.0 V, demonstrating excellent compatibility with the charging platforms of mainstream cathode materials such as lithium iron phosphate, and is compatible with most existing battery electrolyte systems, requiring no disruptive modifications to battery production systems.

[0005] Currently, traditional lithium iron ferrite (LiFe) preparation processes primarily use lithium oxide (Li2O) as the core lithium source. This raw material is expensive and its cost is high, significantly increasing the economic cost of large-scale production and hindering its industrialization. Furthermore, existing processes produce LiFe materials with extremely poor air stability. During storage, transportation, and subsequent electrode processing in normal atmospheric environments, they are prone to side reactions with moisture and carbon dioxide, leading to surface degradation, structural decay, and a significant decrease in lithium replenishment activity. In addition, during battery charge-discharge cycles, the crystal structure of traditional LiFe materials is prone to irreversible phase transitions, continuously releasing oxygen. This not only easily causes internal cell swelling and bulging but also disrupts the interface stability of the battery system, posing safety hazards and severely limiting the practical application of LiFe lithium replenishment agents in high-performance lithium-ion batteries.

[0006] In view of this, existing technologies have also disclosed some methods for coating and modifying lithium iron phosphate. For example, patent CN121307031A discloses a lithium replenishing agent, which includes a lithium replenishing core and a carbon coating layer covering the surface of the lithium replenishing core, wherein the lithium replenishing core is doped with Al. Patent CN120413830A discloses a conductive lithium replenishing additive Li5FeO4, which is composed of 82-85 wt% Li5FeO4 and 15-18 wt% conductive slurry; the conductive slurry is composed of carbon material, aluminum additive, organic carbon source and solvent; the aluminum additive is nano-alumina; the organic carbon source is glucose; the mass ratio of carbon material to aluminum additive is 1:0.1-0.5; the mass ratio of carbon material to organic carbon source is 1:0.1-0.5.

[0007] Although some modification schemes for lithium iron ferrite rich in lithium have been disclosed in the existing technology, the existing schemes are difficult to fundamentally solve the gas generation problem of Li5FeO4, and the performance of the material, especially its stability, needs to be further improved. Summary of the Invention

[0008] To address the problems existing in the prior art, the primary objective of this invention is to provide a modified lithium iron ferrite lithium supplement agent, which aims to effectively solve the problems of gas generation and insufficient air stability of lithium iron ferrite, thereby significantly improving the cycle stability of batteries assembled from the material.

[0009] The second objective of this invention is to provide a method for preparing and applying the modified lithium iron ferrite lithium supplement agent.

[0010] A third objective of this invention is to provide a lithium-replenishing cathode and a lithium-ion battery comprising the modified lithium-rich lithium iron phosphate supplementing agent.

[0011] Lithium iron oxide (Li5FeO4) has become a highly promising lithium replenishment material due to its ultra-high theoretical lithium replenishment capacity, low raw material cost, and decomposition potential compatible with mainstream lithium battery systems. However, compared with conventional lithium replenishment agents such as Li2NiO2, lithium nitride, and organic lithium salts, it has several unique challenges: the delithiation process releases lattice oxygen, causing a much higher gas generation problem than other lithium replenishment agents, leading to electrode bulging, increased battery internal resistance, and cycle degradation; simultaneously, its extremely poor air stability and low intrinsic ionic and electronic conductivity result in significantly worse lithium replenishment kinetics and a sharp decrease in efficiency at low temperatures. Existing single coating and doping modification methods are insufficient to address these coupled defects. Given the difficulty of simultaneously suppressing lattice oxygen release and gas generation, improving material air stability, and enhancing lithium replenishment efficiency at low temperatures while retaining the high lithium replenishment capacity advantage of Li5FeO4, this invention provides the following solution:

[0012] A modified lithium iron ferrite-rich lithium supplement includes a core and a shell covering the surface of the core, wherein the core is lithium iron ferrite-rich; and the shell includes an oxygen scavenger, porous carbon, and a fast ion conductor.

[0013] Oxygen scavengers include at least one of potassium sulfide, zirconium disulfide, aluminum trisulfide, cuprous sulfide, and magnesium sulfide.

[0014] This invention provides a novel material for shell-coating lithium iron ferrite using a synergistic composite material of oxygen scavenger, porous carbon, and fast ion conductor. Based on the combination of the shell synergistic components and the core-shell structure, synergy can be achieved, enabling the capture and confined functionalization of generated oxygen, and optimizing the ion electron conduction pathway. This fundamentally solves the problems of gas generation and poor air stability of lithium iron ferrite, and effectively improves the first-efficiency performance and long-cycle stability of the battery assembled with the material.

[0015] The oxygen scavenger includes at least one of potassium sulfide, zirconium disulfide, and aluminum trisulfide; preferably, it includes zirconium disulfide; more preferably, it is a zirconium disulfide and aluminum trisulfide in a weight ratio of 1:0.5~2. Studies have shown that the preferred oxygen scavenger, in combination with other components and coating structures, can further solve the prominent gas generation problem of lithium iron phosphate and further enhance the stability of the assembled battery.

[0016] Porous carbon is at least one of activated carbon, coal-based porous carbon, pitch-based porous carbon, and biomass-based porous carbon; the specific surface area of ​​the porous carbon is greater than 1600 m². 2 / g or more; further, it can be 1600~2500 m 2 / g.

[0017] Fast ion conductors include one or more of the following: garnet type, NASICON type, sulfide type, and perovskite type; further, they can be Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li7La3Zr2O 12 At least one of them.

[0018] In the modified lithium iron ferrite lithium supplement, the mass percentage of porous carbon is 1-5%; the mass percentage of oxygen scavenger is 4-10%; and the mass percentage of fast ion conductor is 0.5-3%. Further, the mass percentage of porous carbon is 2-4%; the mass percentage of oxygen scavenger is 5-6%; and the mass percentage of fast ion conductor is 1-2%.

[0019] The present invention also provides a method for preparing the modified lithium iron ferrite supplement agent, wherein lithium iron ferrite, oxygen scavenger, porous carbon, and fast ion conductor liquid phase are mixed and spray-dried, followed by annealing treatment to obtain the modified lithium iron ferrite supplement agent.

[0020] The present invention uses the raw materials described above for spraying and annealing treatment, which can construct the material with the structure described above in one step. The material can retain the high lithium replenishment activity of Li5FeO4, while effectively suppressing its gas production, and can effectively improve the cycle stability of the battery assembled from the material.

[0021] In this invention, lithium source and iron oxide are ground and sintered to obtain lithium iron oxide rich in lithium.

[0022] The molar ratio of lithium to iron in the lithium source and iron oxide is 5.1~5.7:1;

[0023] The lithium source is a composite lithium source composed of lithium oxide and lithium hydroxide, with the proportion of lithium hydroxide being ≥70%.

[0024] Grinding is done by ball milling;

[0025] Preferably, the ball milling speed is 300 r / min to 400 r / min;

[0026] Preferably, the ball milling time is 4 to 5 hours;

[0027] Preferably, the particle size D50 of the material after ball milling is < 0.8 μm;

[0028] The sintering process is carried out in a protective atmosphere;

[0029] The sintering process includes a first sintering process and a second sintering process, wherein the heating rate of the first sintering process is 3~5℃ / min;

[0030] Preferably, the sintering temperature of the first stage of sintering is 400~450℃;

[0031] Preferably, the holding time for the first sintering stage is 8-15 hours;

[0032] Preferably, the heating rate of the second sintering stage is 3~5℃ / min;

[0033] Preferably, the sintering temperature of the second stage sintering is 800~900℃;

[0034] Preferably, the holding time for the second sintering stage is 8-10 hours.

[0035] The solvent in the liquid-phase mixture is an organic solvent;

[0036] The inlet air temperature for spray drying is 190~200℃, and the outlet air temperature is 100~110℃.

[0037] The annealing process is carried out in a protective atmosphere; the protective atmosphere can be at least one of nitrogen or a rare gas.

[0038] Preferably, the annealing heating rate is 3℃ / min to 5℃ / min;

[0039] Preferably, the annealing temperature is 300~400℃;

[0040] Preferably, the annealing and heat preservation time is 2 to 10 hours; more preferably, it can be 4 to 6 hours.

[0041] The present invention also provides an application of the modified lithium iron ferrite lithium supplement agent, which is used as a lithium supplement agent and mixed with a positive electrode active material to obtain a lithium supplement positive electrode active material.

[0042] Preferably, the lithium-supplemented positive electrode active material is compounded with a binder and a conductive agent to obtain the lithium-supplemented positive electrode material;

[0043] Preferably, a lithium-supplemented cathode material is composited onto a current collector to obtain a lithium-supplemented cathode;

[0044] Preferably, a lithium-ion battery is obtained by assembling a lithium-added positive electrode.

[0045] The present invention also provides a lithium-supplementing cathode material, comprising a cathode active material and a lithium-supplementing agent, wherein the lithium-supplementing agent is the modified lithium-rich lithium iron ferrite lithium-supplementing agent described in the present invention.

[0046] The present invention also provides a lithium-ion battery comprising the modified lithium iron phosphate supplementing agent described above; and further comprising the lithium supplementing cathode material described above.

[0047] Beneficial effects

[0048] 1. This invention provides a novel modified lithium iron ferrite (LFP) supplementary lithium material. It innovatively utilizes oxygen scavengers, porous carbon, and fast ion conductors as synergistic components as the shell material, combined with core-shell structure control. This synergy compensates for the loss of active lithium during lithium-ion battery cycling, suppresses and adsorbs oxygen released during cycling, and converts it into oxygen anions, thereby reducing oxygen release. Furthermore, the synergistic shell material provides abundant pores, optimizing ion transport and extraction capabilities. Moreover, the shell layer physically isolates the LFP core from the corrosion of carbon dioxide and water molecules in the air, improving the air stability of the LFP supplementary lithium material. The modified lithium supplementary lithium material of this invention effectively improves the battery's room temperature cycling stability and low temperature cycling stability.

[0049] 2. The lithium-ion battery provided by the present invention has significantly improved reversible specific capacity and cycle life due to the use of lithium-rich lithium iron phosphate supplement provided by the present invention, and the cell gas production is low during the cycle, thus significantly improving safety. Attached Figure Description

[0050] Figure 1This is the XRD pattern of the coated Li5FeO4 obtained in Example 1.

[0051] Figure 2 This is a graph showing the cycling performance of Example 1 in a full cell at low temperature. Detailed Implementation

[0052] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0053] Secondly, the present invention provides a method for preparing the aforementioned lithium-rich lithium iron phosphate supplement, comprising the following steps:

[0054] Step (1):

[0055] A first mixture is obtained by grinding a lithium source and iron oxide, followed by two-stage sintering to obtain a lithium-rich lithium iron ferrite core. This invention uses a composite lithium source primarily composed of low-cost lithium hydroxide and employs a two-stage sintering method. In the first stage sintering temperature (400-450°C), the lithium hydroxide in the first mixture undergoes a dehydration reaction to convert into lithium oxide. Upon reaching the second stage sintering temperature (800-900°C), the lithium oxide generated in the first stage sintering and the lithium oxide from the composite lithium source react together with iron oxide to form lithium-rich lithium iron ferrite. This method is more cost-effective than traditional methods using lithium oxide as the sole lithium source.

[0056] Preferably, the molar ratio of lithium to iron in the lithium source and iron oxide is 5.1~5.7:1;

[0057] Preferably, the lithium source is a composite lithium source composed of lithium oxide and lithium hydroxide, and the proportion of lithium hydroxide is ≥70%;

[0058] Preferably, the first grinding process is ball milling;

[0059] Preferably, the ball milling speed is 300 r / min to 400 r / min;

[0060] Preferably, the ball milling time is 4 to 5 hours;

[0061] Preferably, the particle size D50 of the material after ball milling is < 0.8 μm;

[0062] Preferably, the two-stage sintering in step (1) is carried out under an argon protective atmosphere;

[0063] Preferably, the heating rate of the first sintering stage is 3~5℃ / min;

[0064] Preferably, the sintering temperature of the first stage of sintering is 400~450℃;

[0065] Preferably, the holding time for the first sintering stage is 8-15 hours;

[0066] Preferably, the heating rate of the second sintering stage is 3~5℃ / min;

[0067] Preferably, the sintering temperature of the second stage sintering is 800~900℃;

[0068] Preferably, the holding time for the second sintering stage is 8-10 hours;

[0069] Step (2):

[0070] The lithium iron ferrite core, oxygen scavenger, porous carbon and fast ion conductor are dispersed in an organic solvent and subjected to a second grinding process. The slurry is then spray-dried to obtain a second mixture. The second mixture is then sintered to obtain the lithium iron ferrite lithium supplement.

[0071] Preferably, the porous carbon in step (2) is at least one of activated carbon, coal-based porous carbon, pitch-based porous carbon, and biomass-based porous carbon; the porous carbon accounts for 1-5% of the mass of the second mixture; and the surface area of ​​the porous carbon is 1600 m². 2 / g or more;

[0072] Preferably, the oxygen scavenger in step (2) includes, but is not limited to, at least one of potassium sulfide, zirconium disulfide, aluminum trisulfide, cuprous sulfide, and magnesium sulfide; the oxygen scavenger accounts for 4-10% of the mass of the second mixture.

[0073] Preferably, in step (2), the fast ion conductor is one or more of the following: garnet type, NASICON type, sulfide type, and perovskite type; the mass percentage of the fast ion conductor in the second mixture is 0.5~3%.

[0074] Preferably, the organic solvent in step (2) is a monohydric alcohol or a dihydric alcohol;

[0075] Preferably, the second grinding in step (2) is sand grinding and is carried out under an argon atmosphere;

[0076] Preferably, the milling speed is 500 rpm to 600 r / min;

[0077] Preferably, the grinding time of the sand mill is 3 to 4 hours;

[0078] Preferably, the particle size D50 of the material after sand milling is < 0.6 μm;

[0079] Preferably, the solid content of the grinding solution is controlled at 30-40%;

[0080] Preferably, the inlet air temperature of the spray drying in step (2) is 190~200℃ and the outlet air temperature is 100~110℃;

[0081] Preferably, the sintering in step (2) is carried out under an argon atmosphere;

[0082] Preferably, the sintering heating rate is 3℃ / min to 5℃ / min;

[0083] Preferably, the sintering temperature is 300~400℃;

[0084] Preferably, the sintering holding time is 2 to 10 hours.

[0085] In the description of the embodiments of this invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this invention, "multiple" means two or more, unless otherwise explicitly defined.

[0086] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0087] Example 1

[0088] 1. Preparation of lithium-rich lithium iron ferrite supplement

[0089] Step (1.1): Lithium hydroxide (LiOH) and lithium oxide (Li2O) were mixed at a mass ratio of 7:3 to obtain a composite lithium source. The composite lithium source was mixed with iron oxide (Fe2O3) at a lithium to iron molar ratio of 5.5:1 and placed in a ball mill. The mixture was ball-milled at 350 r / min for 4.5 hours to obtain a first mixture with a particle size D50 < 0.8 μm. The first mixture was placed in an argon-protected atmosphere furnace and heated to 420℃ (first stage calcination temperature T1) at a rate of 4℃ / min. The temperature was held for 13 hours, and then heated to 850℃ (second stage calcination temperature T2) at a rate of 4℃ / min. The temperature was held for 9 hours, and after natural cooling, a lithium-rich lithium iron ferrite core (Li5FeO4) was obtained.

[0090] Step (1.2): Combine the obtained lithium iron ferrite core, oxygen scavenger (potassium sulfide, K2S), and porous carbon (activated carbon with a specific surface area of ​​2000 m²) 2 / g), fast ion conductor (Li7La3Zr2O) 12The lithium iron ferrite was dispersed in anhydrous ethanol at a mass ratio of 90:5:3:2 and milled under an argon atmosphere at a speed of 550 r / min for 3.5 hours, with the solid content controlled at 35%. The particle size D50 after milling was <0.6 μm, yielding a second mixture. This second mixture was then spray-dried at an inlet air temperature of 195℃ and an outlet air temperature of 105℃ to obtain a dry powder. The dry powder was placed in an argon-protected atmosphere furnace and heated to 350℃ (annealing temperature) at a rate of 4℃ / min, held at that temperature for 5.5 hours, and then allowed to cool naturally to obtain a lithium-rich lithium iron ferrite supplement with a composite coating (composite lithium supplement). Room temperature and low temperature tests were conducted at 25℃ and -10℃, respectively.

[0091] Step 2, Positive Electrode Material

[0092] The positive electrode current collector is aluminum foil. After NCM811 (75 wt%), composite lithium supplement (5 wt%), Super P (10 wt%) and PVDF (10 wt%) are mixed evenly, the positive electrode sheet is obtained by slurry preparation, coating, drying and rolling.

[0093] Step 3, negative electrode material

[0094] The negative electrode current collector is copper foil. After uniformly mixing graphite (90 wt%), Super P (5 wt%) and PVDF (5 wt%), the negative electrode sheet is obtained by slurry preparation, coating, drying and rolling.

[0095] Step 4: Assembly

[0096] After obtaining the positive and negative electrodes, they were assembled into CR2025 coin cells. The separator was a 16 μm thick PP membrane, and the electrolyte formulation was 1.0 M LiPF6 in EC:DMC:EMC = 1:1:1. Lithium replenishment was achieved during the first charge-discharge cycle. The first charge was performed using a 0.05 C constant current or constant voltage charge with a cutoff voltage of 4.2 V, and the first discharge was performed using a 0.05 C constant current discharge with a cutoff voltage of 2.0 V. Room temperature and low temperature tests were conducted at 25℃ and -10℃, respectively.

[0097] Example 2

[0098] Compared to Example 1, the only difference is that in step (1.1), the mass ratio of lithium hydroxide (LiOH) to lithium oxide (Li2O) in the composite lithium source is 8:2. The total amount of Li in the composite lithium source and other conditions are the same as in Example 1.

[0099] Example 3

[0100] Compared to Example 1, the only difference is that in step (1.1), the mass ratio of lithium hydroxide (LiOH) to lithium oxide (Li2O) in the composite lithium source is 9:1. The total amount of Li in the composite lithium source and other conditions are the same as in Example 1.

[0101] Example 4

[0102] Compared to Example 1, the only difference is that in step (1.2), the oxygen scavenger is zirconium disulfide (ZrS2). All other conditions are the same as in Example 1.

[0103] Example 5

[0104] Compared to Example 1, the only difference is that in step (1.2), the oxygen scavenger is aluminum sulfide (Al2S3). All other conditions are the same as in Example 1.

[0105] Example 6

[0106] Compared with Example 1, the only difference is that in step (1.2), the porous carbon is coal-based porous carbon (specific surface area of ​​1800 m²). 2 / g). Other conditions are the same as in Example 1;

[0107] Example 7

[0108] Compared to Example 1, the only difference is that in step (1.2), the fast ion conductor is Li. 1.3 Al 0.3 Ti 1.7 (PO4)3. Other conditions are the same as in Example 1;

[0109] Example 8

[0110] Compared with Example 1, the only difference is that in step (2), the obtained lithium-rich lithium iron phosphate core, oxygen scavenger (potassium sulfide, K2S), porous carbon (activated carbon), and fast ion conductor (Li7La3Zr2O) are added. 12 Mix at a mass ratio of 90:6:3:1. Other conditions are the same as in Example 1;

[0111] Example 9

[0112] Compared with Example 1, the only difference is that in step (2), the cathode material consists of NCM811 (70 wt%), lithium supplementation material (10 wt%), Super P (10 wt%), and PVDF (10 wt%). Other conditions are the same as in Example 1;

[0113] Example 10

[0114] Compared with Example 1, the difference is that in step (1.1), the sintering temperature T1 of the first stage of the core is 450℃ and the time is 12h, and the sintering temperature T2 of the second stage is 800℃ and the time is 10h. Other conditions are the same as in Example 1;

[0115] Example 11

[0116] Compared with Example 1, the difference is that in step (1.2), the annealing temperature is 380°C and the time is 5 hours. Other conditions are the same as in Example 1;

[0117] Example 12

[0118] Compared to Example 1, the only difference is that in step (1.2), the oxygen scavenger is a combination of zirconium disulfide (ZrS2) and cuprous sulfide (Cu2S), with a mass ratio of 1:1. The amount of oxygen scavenger and other conditions are the same as in Example 1;

[0119] Comparative Example 1

[0120] Compared with Example 1, the difference is that step (1.2) is omitted, and the lithium-rich lithium iron ferrite obtained in step 1 is directly used as the lithium replenishing agent. Other operations and parameters are the same as in Example 1.

[0121] Comparative Example 2

[0122] Compared with Example 1, the difference is that step (1.2) does not contain porous carbon; other operations and parameters are the same as in Example 1.

[0123] Comparative Example 3

[0124] Compared with Example 1, the difference is that step (1.2) does not contain an oxygen scavenger (potassium sulfide, K2S); other operations and parameters are the same as in Example 1.

[0125] Comparative Example 4

[0126] Compared with Example 1, the difference is that step (1.2) does not contain a fast ion conductor; other operations and parameters are the same as in Example 1.

[0127] Comparative Example 5

[0128] Compared with Example 1, the difference is that in step (1.2), an equal weight of Li2S is used as the oxygen scavenger; other operations and parameters are the same as in Example 1.

[0129] Comparative Example 6

[0130] Compared with Example 1, the difference is that in step (1.2), cellulose of equal weight is used instead of porous carbon; other operations and parameters are the same as in Example 1.

[0131] Comparative Example 7

[0132] Compared with Example 1, the difference is that Li5FeO4, porous carbon, oxygen eliminator and fast ion conductor are ground and used directly as lithium replenishing agent without forming a coating structure. The ratio of Li5FeO4, porous carbon, oxygen eliminator and fast ion conductor and the amount of lithium replenishing agent are the same as in Example 1.

[0133] Performance data:

[0134] I. Air stability experiment

[0135] The first-charge specific capacity (mAh / g) of the lithium replenishment additives prepared in each case after being stored for different periods in an air atmosphere at 25℃ and 30% RH is shown in Table 1:

[0136]

[0137] Note: The term 0d refers to materials that are not exposed to air, for example, materials stored in an Ar atmosphere.

[0138] As shown in Table 1, the lithium-rich lithium iron ferrite supplement synthesized within the preferred range exhibits good delithiation capacity and excellent air stability. Examples 1, 4, and 12 demonstrate that the preferred oxygen scavenger can further improve air stability.

[0139] II. Full Battery Cycle Data

[0140] The test results at 0.05°C / 25°C are shown in Table 2:

[0141]

[0142] As can be seen from the results of the embodiments, within the preferred parameter range of the present invention, the composite lithium replenishing agent has both excellent ionic conductivity and electronic conductivity, can release sufficient lithium ions, make up for the active lithium lost by the negative electrode in the first cycle of the battery, and effectively improve the reversible capacity and cycle life of the battery.

[0143] III. Low-temperature cycling data:

[0144] The test results at 0.05°C / -10°C are shown in Table 3:

[0145]

[0146] In summary, the process described in this invention, through the combination of the aforementioned components and coating structure, achieves synergy, enhancing the air stability of the material and improving the stability of the assembled battery, such as low-temperature cycle stability. Furthermore, as demonstrated in Examples 1, 4, and 12, the preferred oxygen scavenger can further synergistically enhance the lithium replenishment effect and stability of the material.

Claims

1. A modified lithium-rich lithium iron ferrite lithium supplement agent, characterized in that, It includes a core and a shell covering the surface of the core, wherein the core is lithium iron ferrite rich in lithium; and the shell includes an oxygen scavenger, porous carbon, and a fast ion conductor. Oxygen scavengers include at least one of potassium sulfide, zirconium disulfide, aluminum trisulfide, cuprous sulfide, and magnesium sulfide.

2. The modified lithium-rich lithium iron ferrite supplement agent as described in claim 1, characterized in that, The oxygen scavenger contains at least one of potassium sulfide, zirconium disulfide, and aluminum trisulfide; preferably zirconium disulfide; more preferably zirconium disulfide and aluminum trisulfide in a weight ratio of 1:0.5~2. Preferably, the porous carbon is at least one of activated carbon, coal-based porous carbon, pitch-based porous carbon, and biomass-based porous carbon; Fast ion conductors include one or more of the following types: garnet, NASICON, sulfide, and perovskite.

3. The modified lithium-rich lithium iron ferrite supplement agent as described in claim 1 or 2, characterized in that, In the modified lithium iron ferrite lithium supplement, the mass percentage of porous carbon is 1-5%; the mass percentage of oxygen scavenger is 4-10%; and the mass percentage of fast ion conductor is 0.5-3%.

4. A method for preparing the modified lithium-rich lithium iron ferrite supplement agent according to any one of claims 1 to 3, characterized in that, The modified lithium iron ferrite lithium supplement agent is prepared by mixing lithium iron ferrite rich in lithium, oxygen scavenger, porous carbon, and fast ion conductor liquid phase, followed by spray drying and annealing.

5. The preparation method of the modified lithium-rich lithium iron ferrite supplement agent as described in claim 4, characterized in that, Lithium-rich lithium iron oxide is prepared by grinding and sintering lithium source and iron oxide. The molar ratio of lithium to iron in the lithium source and iron oxide is 5.1~5.7:1; The lithium source is a composite lithium source composed of lithium oxide and lithium hydroxide, with the proportion of lithium hydroxide being ≥70%. Grinding is done by ball milling; Preferably, the ball milling speed is 300 r / min to 400 r / min; Preferably, the ball milling time is 4 to 5 hours; Preferably, the particle size D50 of the material after ball milling is < 0.8 μm; The sintering process is carried out in a protective atmosphere; The sintering process includes a first sintering process and a second sintering process, wherein the heating rate of the first sintering process is 3~5℃ / min; Preferably, the sintering temperature of the first stage of sintering is 400~450℃; Preferably, the holding time for the first sintering stage is 8-15 hours; Preferably, the heating rate of the second sintering stage is 3~5℃ / min; Preferably, the sintering temperature of the second stage sintering is 800~900℃; Preferably, the holding time for the second sintering stage is 8-10 hours.

6. The preparation method of the modified lithium-rich lithium iron ferrite supplement agent as described in claim 4, characterized in that, The solvent in the liquid-phase mixture is an organic solvent; The inlet air temperature for spray drying is 190~200℃, and the outlet air temperature is 100~110℃.

7. The preparation method of the modified lithium-rich lithium iron ferrite supplement agent as described in claim 4, characterized in that, The annealing process is carried out in a protective atmosphere; Preferably, the annealing heating rate is 3℃ / min to 5℃ / min; Preferably, the annealing temperature is 300~400℃; Preferably, the annealing and heat preservation time is 2~10 hours.

8. The application of the modified lithium-rich lithium ferrite supplement agent according to any one of claims 1 to 3 or the modified lithium-rich lithium ferrite supplement agent prepared by the preparation method according to any one of claims 4 to 7, characterized in that, It is used as a lithium supplement agent and mixed with the positive electrode active material to prepare a lithium-supplemented positive electrode active material; Preferably, the lithium-supplemented positive electrode active material is compounded with a binder and a conductive agent to obtain the lithium-supplemented positive electrode material; Preferably, a lithium-supplemented cathode material is composited onto a current collector to obtain a lithium-supplemented cathode; Preferably, a lithium-ion battery is obtained by assembling a lithium-added positive electrode.

9. A lithium-supplemented cathode material, comprising a cathode active material and a lithium-supplementing agent, characterized in that, The lithium replenishing agent is the modified lithium-rich lithium iron ferrite replenishing agent according to any one of claims 1 to 3 or the modified lithium-rich lithium iron ferrite replenishing agent prepared by the preparation method according to any one of claims 4 to 7.

10. A lithium-ion battery, characterized in that, The modified lithium iron ferrite supplement agent according to any one of claims 1 to 3 or the modified lithium iron ferrite supplement agent prepared by the preparation method according to any one of claims 4 to 7; Preferably, it comprises the lithium-supplemented cathode material as described in claim 9.

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