Composite lithium supplement additive and preparation method and application thereof

Abstract

The invention discloses a composite lithium supplement additive and a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. The composite lithium supplement additive provided by the invention comprises a lithium-rich lithium ferrite core; the conductive carbon coating layer and the pentafluoropropionamide coating layer are sequentially coated outside the lithium-rich lithium ferrite inner core from inside to outside, so as to form a core-shell structure. The composite lithium supplement additive prepared by the invention forms a three-dimensional interpenetrating electron transport network, significantly improves the material conductivity, optimizes the charge transfer dynamics, can effectively isolate lithium-rich lithium ferrite from contacting H2O and CO2 in the air, significantly reduces the generation of surface residual alkali, can adapt to the volume expansion of lithium-rich lithium ferrite in the charge-discharge process, and improves the lithium supplement efficiency. And material structure damage caused by interface stress is reduced, so that the cycling stability of the lithium ion battery is greatly improved, the service life of the lithium ion battery is greatly prolonged, and the material has a wide application prospect in the lithium ion battery.

Description

Technical Field

[0001] This application belongs to the field of lithium-ion battery technology, and in particular relates to a composite lithium supplementation additive, its preparation method and application. Background Technology

[0002] Lithium replenishment technology is a method of pre-storing lithium ions in the electrode to compensate for the initial capacity loss of the battery. It effectively solves the problem of low initial coulombic efficiency and improves battery capacity and cycle stability. Positive electrode lithium replenishment has the most promising industrial application prospects due to its high safety and the fact that it does not require changes to existing battery manufacturing processes. Antifluorite structure lithium-rich lithium iron phosphate (Li5FeO4) (LFO) serves as a new generation of positive electrode lithium replenishment reagent, utilizing Fe... 3+ / Fe 4+ Cation oxidation and O 2- / O2 n- Anion oxidation synergistic mechanism can provide up to 870 mAh g -1 The irreversible lithium release capacity of LFO is significantly superior to that of traditional lithium-rich materials, attracting increasing attention. However, the practical application of LFO still faces some challenges. When LFO is exposed to humid air, it readily reacts with H2O / CO2 to form LiOH and Li2CO3 surface layers, reducing the active lithium content and increasing electrode polarization.

[0003] Existing methods for improving the conductivity and stability of lithium supplements include carbon coating or polymer coating. The prior art disclosed in application publication number CN 118099569 A is a lithium supplement conductive additive that significantly improves the stability of the material in air by selecting a carbon material as the first coating layer and an organic long-chain fatty acid coating layer for lithium salt.

[0004] However, existing composite cathode lithium replenishment additives have the following problems: the bonding between their modified coating and the core material largely relies on physical adsorption, resulting in weak interfacial bonding strength. This makes the coating prone to peeling or even detachment during long-term charge-discharge cycles due to internal stress impacts and external environmental disturbances. Once the coating fails, it not only completely loses its protective function for the core material but also significantly weakens the overall performance of the lithium replenishment additive, ultimately leading to a substantial decrease in battery cycle stability. Summary of the Invention

[0005] This application discloses a composite lithium supplement additive, its preparation method and application, aiming to solve the technical problems of unstable air in positive electrode lithium supplement additives, which leads to a significant decrease in the specific capacity of the lithium supplement additive.

[0006] To achieve the above objectives, the technical solution of this application is:

[0007] The first aspect of this application provides a composite lithium supplementation additive, comprising: a lithium-rich lithium iron phosphate core;

[0008] And a conductive carbon coating layer and a pentafluoroacetamide coating layer that are sequentially wrapped around the lithium-rich lithium iron phosphate core from the inside out.

[0009] In conjunction with the first aspect, preferably, the conductive carbon material is one or more of carbon nanotubes, superconducting carbon black, Ketjen black, and acetylene black.

[0010] In conjunction with the first aspect, preferably, the conductive carbon material accounts for 5-20 wt% of the composite lithium supplementation additive.

[0011] In conjunction with the first aspect, preferably, the pentafluoropropionamide accounts for 0.01-5 wt% of the composite lithium supplementation additive.

[0012] The second aspect of this application provides a method for preparing the composite lithium supplementation additive described in the first aspect, the method comprising:

[0013] Lithium oxide, ferric oxide, and conductive carbon materials were ball-milled to obtain a precursor.

[0014] The precursor is calcined in an inert atmosphere to obtain a pre-lithium core;

[0015] The pre-lithi core and pentafluoropropamide are dissolved in an organic solvent and reacted. After solid-liquid separation and vacuum drying, the composite lithium supplement additive is obtained.

[0016] Preferably, in conjunction with the second aspect, the molar ratio of lithium oxide to ferric oxide is (5-6):1.

[0017] Preferably, in conjunction with the second aspect, the calcination treatment conditions are: heating to 500-900℃ at a heating rate of 3-10℃ / min and calcining for 5-20 h;

[0018] The conditions for ball milling are: ball-to-material ratio of (5-10):1, ball milling speed of 100-600 rpm, and ball milling time of 2-10 h.

[0019] Preferably, in conjunction with the second aspect, the organic solvent is one or more of tetrahydrofuran, N-methylpyrrolidone, ethanol, chloroform, and toluene.

[0020] The third aspect of this application provides a lithium-ion battery cathode, comprising the composite lithium-replenishing additive described in the first aspect or the composite lithium-replenishing additive prepared by the preparation method described in the second aspect.

[0021] A fourth aspect of this application provides a lithium-ion battery including a positive electrode sheet containing the composite lithium supplementation additive described in the third aspect.

[0022] Compared with the prior art, the advantages or beneficial effects of the embodiments of this application include at least the following:

[0023] The composite lithium supplement additive provided in this application forms a core-shell structure by coordinating and bonding a first layer of conductive carbon material and a second layer of pentafluoropropamide onto lithium-rich lithium iron ferrite. On one hand, the conductive carbon material layer permeates the entire lithium supplement additive, forming a three-dimensional interpenetrating electron transport network, significantly improving the material's conductivity and optimizing charge transport kinetics. On the other hand, the amide groups (-NH-CO-) in the pentafluoropropamide molecule interact with the metal ions (Fe2+) on the surface of the pre-lithiation material. 3+ Li + It forms coordination bonds, improving the adhesion strength of the coating layer to form a more uniform and compact coating layer, avoiding the "island coating" phenomenon; it can also effectively isolate lithium iron ferrite from contact with H2O and CO2 in the air, significantly reducing the generation of surface residual alkali (such as LiOH, Li2CO3), thereby reducing slurry gelation problems and improving the material storage and processing stability; at the same time, due to the flexibility of the molecular structure, it can adapt to the volume expansion of lithium iron ferrite during charging and discharging, reducing material structure damage caused by interfacial stress, thereby improving the safety performance of the battery. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 SEM image of the A1-composite lithium supplementation additive provided in the embodiments of this application;

[0026] Figure 2 XRD pattern of the A1-composite lithium supplementation additive prepared in the embodiments of this application;

[0027] Figure 3 The contact angle diagram between the A1-composite lithium supplementary additive provided in the embodiments of this application and water;

[0028] Figure 4 The contact angle diagram of the B3-additive prepared in the embodiments of this application with water;

[0029] Figure 5 SEM image of the B3-additive prepared in the embodiments of this application. Detailed Implementation

[0030] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0031] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0032] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0033] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0034] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0035] It should be noted that all raw materials and reagents in the embodiments of this application were purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0036] In a first aspect, embodiments of this application provide a composite lithium supplementation additive, comprising: a lithium-rich lithium iron phosphate core;

[0037] And a conductive carbon coating layer and a pentafluoroacetamide coating layer that are sequentially wrapped around the lithium-rich lithium iron phosphate core from the inside out.

[0038] On the one hand, the conductive carbon material layer penetrates the entire lithium-filling additive to form a three-dimensional interpenetrating electron transport network, significantly improving the material's conductivity and optimizing charge transport dynamics; on the other hand, the amide groups (-NH-CO-) in the pentafluoroacetamide molecule interact with the metal ions (Fe) on the surface of the pre-lithiation material. 3+ Li + It forms coordination bonds, improving the adhesion strength of the coating layer to form a more uniform and compact coating layer, avoiding the "island coating" phenomenon; it can also effectively isolate lithium iron ferrite from contact with H2O and CO2 in the air, significantly reducing the generation of surface residual alkali (such as LiOH, Li2CO3), thereby reducing slurry gelation problems and improving the material storage and processing stability; at the same time, due to the flexibility of the molecular structure, it can adapt to the volume expansion of lithium iron ferrite during charging and discharging, reducing material structure damage caused by interfacial stress, thereby improving the safety performance of the battery.

[0039] It should be noted that the dual composite mechanism of conductive carbon network reconstruction and fluorinated organic interface passivation overcomes the problems of limited electron transport and uncontrollable interfacial side reactions in existing lithium-replenishing additives. Introducing conductive carbon during material sintering accelerates kinetic transport through its dispersion effect and the construction of an efficient electron transport network. Simultaneously, the external coating of highly hydrophobic fluorinated organic compounds effectively mitigates the absorption of H2O / CO2 by the material surface in humid environments. Thanks to the synergistic effect of this composite system, the material's electronic conductivity and air stability are improved through material modification, enabling LFO to effectively compensate for active lithium loss and achieve the goal of improving battery specific capacity and cycle stability.

[0040] In this embodiment, the conductive carbon material is preferably one or more of carbon nanotubes, superconducting carbon black, Ketjen black, and acetylene black. The addition of conductive carbon during the synthesis process gives it the dual function of a conductive agent and a dispersant. Compared to traditional amorphous carbon, its conductivity is significantly enhanced, and this dispersing effect can inhibit the growth of cathode material particles, resulting in smaller particle sizes and effectively shortening the migration paths of electrons and lithium ions.

[0041] In this embodiment, the conductive carbon material preferably accounts for 5-20 wt% of the composite lithium supplementation additive. An appropriate amount of pre-lithiation ensures the formation of a continuous and efficient electronic conductive network. If the proportion of conductive carbon material is less than 5%, insufficient conductive pathways result in increased internal resistance, decreased lithium supplementation efficiency, and exacerbated polarization effects. If the proportion of conductive carbon material exceeds 20%, the excess conductive agent will act as "dead weight," significantly reducing the specific capacity.

[0042] In this embodiment, the pentafluoropropionamide is preferably present in the composite lithium-replenishing additive at a proportion of 0.5-5 wt%. By controlling the proportion of pentafluoropropionamide in the composite lithium-replenishing additive, the performance of the additive is optimized. This proportion ensures that the fluorinated organic compound pentafluoropropionamide exhibits good electrochemical stability within the coating layer, while effectively suppressing side reactions with the electrolyte and reducing unnecessary mass loss. A proportion that is too low may not fully realize its role in suppressing side reactions, improving interfacial stability, and mitigating volume expansion, while a proportion that is too high may result in an excessively thick coating layer, affecting the diffusion rate of lithium ions and thus impacting the overall battery performance. Optimizing this proportion can improve the conductivity of the composite lithium-replenishing additive and the overall cycle stability of the battery.

[0043] Secondly, embodiments of this application also provide a method for preparing the composite lithium supplementation additive described in the first aspect, the preparation method comprising:

[0044] Lithium oxide, ferric oxide, and conductive carbon materials were ball-milled to obtain a precursor.

[0045] The precursor is calcined in an inert atmosphere to obtain a pre-lithium core;

[0046] The pre-lithi core and pentafluoropropamide are dissolved in an organic solvent and reacted. After solid-liquid separation and vacuum drying, the composite lithium supplement additive is obtained.

[0047] It should be noted that the preparation method used in this application employs a two-step process of high-temperature calcination and liquid-phase coating. During the sintering of the pre-lithiated material, conductive carbon inhibits high-temperature particle agglomeration through physical barrier effects, reducing the particle size to the submicron level. Simultaneously, a three-dimensional interpenetrating electron transport network is constructed, effectively improving the material's conductivity and significantly optimizing charge transport kinetics. Secondly, through molecular-level interface engineering, the fluorinated organic compound pentafluoropropionamide (PFPA) is bonded to metal ions (such as Fe) on the LFO surface via its amide groups (-NH-CO-). 3+ Or Li + The fluorine atoms form coordination bonds, enhancing the bonding strength of the coating layer. Furthermore, the high proportion of fluorine atoms provides strong hydrophobicity and chemical inertness, effectively blocking H2O / CO2 corrosion. Through the synergistic effect of the conductive network and the interface passivation layer, the composite pre-lithiation additive maintains high specific capacity while suppressing capacity decay under air exposure, achieving a simultaneous improvement in energy density and cycle stability.

[0048] In this embodiment, the preferred molar ratio of lithium oxide to ferric oxide is (5-6):1. While the actual molar ratio of lithium oxide to ferric oxide is 5:1 based on the chemical formula, considering the loss of lithium oxide during calcination, an excess of lithium oxide is required to prevent the presence of Li in the product due to insufficient lattice lithium.5- x FeO4 is a lithium-deficient phase, which reduces the lithium replenishment capacity.

[0049] In this embodiment, the preferred calcination conditions are: heating to 500-900℃ at a heating rate of 3-10℃ / min for 5-20 h; the preferred ball milling conditions are: a ball-to-material ratio of (5-10):1, a ball milling speed of 100-600 rpm, and a ball milling time of 2-10 h. By controlling the calcination conditions, the conductive carbon material can be prevented from agglomerating at high temperatures through a physical barrier effect, reducing the particle size to the submicron level. Simultaneously, a three-dimensional interpenetrating electron transport network can be constructed, effectively improving the material's conductivity and significantly optimizing charge transport dynamics. When the ball milling speed is below 100 r / min, the energy is insufficient, making it difficult to form a pure-phase compound; when the ball milling speed is above 600 r / min, material agglomeration and excessively large particles are easily caused.

[0050] In this embodiment, the organic solvent is preferably one or more of tetrahydrofuran, N-methylpyrrolidone, ethanol, chloroform, and toluene. These organic solvents can form a homogeneous and stable solution, facilitating further reactions.

[0051] Thirdly, this application also provides a lithium-ion battery cathode, comprising the composite lithium-replenishing additive described in the first aspect or the composite lithium-replenishing additive prepared by the preparation method described in the second aspect. Based on the fact that the above additives can form a uniform, regular, and stable material structure, the lithium-ion battery cathode is endowed with higher lithium-replenishing capacity and stability.

[0052] Fourthly, this application also provides a lithium-ion battery, including a positive electrode sheet, wherein the positive electrode sheet contains the composite lithium replenishment additive described in the third aspect. The positive electrode of this lithium-ion battery possesses excellent lithium replenishment capacity and stability, thereby endowing the lithium-ion battery with high conductivity, excellent rate cycle performance and stability, and improved battery safety performance, thus exhibiting strong product competitiveness.

[0053] The technical solution of this application will be further described below with reference to specific embodiments.

[0054] Example 1

[0055] This embodiment provides a method for preparing A1-composite lithium supplementation additive, specifically including:

[0056] S101: 1.64 g of lithium oxide (Li₂O), 1.60 g of nano-Fe₂O₃, and 0.16 g of carbon nanotubes (CNTs) were placed in a ball mill jar and dry-milled at 500 rpm for 5 h, wherein the Li / Fe molar ratio was 5.5:1, and the mass of carbon nanotubes accounted for 5% of the total mass of Li₂O and Fe₂O₃. The ball-milled raw material powder was then pressed into tablets using a tablet press at a pressure of approximately 16 T to obtain the precursor.

[0057] S102: Place it under an argon atmosphere, heat it to 300 ℃ at a heating rate of 5 ℃ / min, hold it for 2 h, then heat it to 600 ℃, hold it for 12 h, cool it to room temperature, and then crush the material to obtain lithium iron ferrite pre-lithium material.

[0058] S103: 100 mg of hydrophobic organic compound pentafluoropropamide was added to 15 ml of organic solvent N-methylpyrrolidone (NMP) and stirred for 1 h to obtain a PFPA / NMP solution. The above-mentioned lithium-rich lithium iron phosphate pre-lithiation material was added to the above PFPA / NMP solution. The mass percentage of pentafluoropropamide in the total pre-lithiation additive was 0.5 wt%. The mixture was magnetically stirred for 5 h. The solid-liquid mixture was filtered to obtain a solid powder. The powder was dried in a vacuum oven at 80 ℃ for 12 h and then naturally cooled to obtain the A1-composite lithium supplementation additive.

[0059] The A1-composite lithium supplement additive has a core composed of a Li5FeO4 and CNT composite system, and an outer shell coated with pentafluoropropionamide (PFPA). The PFPA constitutes 0.5 wt% of the total pre-lithiation additive.

[0060] Example 2

[0061] This embodiment provides a method for preparing A2-composite lithium supplementation additive, specifically including:

[0062] S201: 1.64 g of lithium oxide (Li₂O), 1.60 g of nano-Fe₂O₃, and 0.16 g of carbon nanotubes (CNTs) were placed in a ball mill jar and dry-milled at 500 rpm for 5 h, wherein the Li / Fe molar ratio was 5.5:1, and the mass of carbon nanotubes accounted for 5% of the total mass of Li₂O and Fe₂O₃. The ball-milled raw material powder was then pressed into tablets using a tablet press at a pressure of approximately 16 T to obtain the precursor.

[0063] S202: Place it under an argon atmosphere, heat it to 300 ℃ at a heating rate of 5 ℃ / min, hold it for 2 h, then heat it to 600 ℃, hold it for 12 h, cool it to room temperature, and then crush the material to obtain lithium iron ferrite pre-lithium material.

[0064] S203: 100 mg of hydrophobic organic compound pentafluoropropamide was added to 15 ml of organic solvent N-methylpyrrolidone (NMP) and stirred for 1 h to obtain a PFPA / NMP solution. The above-mentioned lithium-rich lithium iron phosphate pre-lithiation material was added to the above PFPA / NMP solution. The mass percentage of pentafluoropropamide in the total pre-lithiation additive was 1 wt%. The mixture was magnetically stirred for 5 h. The solid-liquid mixture was filtered to obtain a solid powder. The powder was dried in a vacuum oven at 80 °C for 12 h and then naturally cooled to obtain the A2-composite lithium supplementation additive.

[0065] The A2-composite lithium supplement additive has a core composed of a Li5FeO4 and CNT composite system, and a shell layer coated with pentafluoropropionamide (PFPA). Furthermore, the PFPA accounts for 1 wt% of the total mass of the pre-lithiation additive.

[0066] Example 3

[0067] This embodiment provides a method for preparing A3-composite lithium supplementation additive, specifically including:

[0068] S301: 1.64 g of lithium oxide (Li₂O), 1.62 g of nano-Fe₂O₃, and 0.16 g of carbon nanotubes (CNTs) were placed in a ball mill jar and dry-milled at 500 rpm for 5 h, wherein the Li / Fe molar ratio was 5.5:1, and the mass of carbon nanotubes accounted for 5% of the total mass of Li₂O and Fe₂O₃. The ball-milled raw material powder was then pressed into tablets using a tablet press at a pressure of approximately 16 T to obtain the precursor.

[0069] S302: Place it under an argon atmosphere, heat it to 300 ℃ at a heating rate of 5 ℃ / min, hold it for 2 h, then heat it to 600 ℃, hold it for 12 h, cool it to room temperature, and then crush the material to obtain lithium iron ferrite pre-lithium material.

[0070] S303: 100 mg of hydrophobic organic compound pentafluoropropamide was added to 15 ml of organic solvent N-methylpyrrolidone (NMP) and stirred for 1 h to obtain a PFPA / NMP solution. The above-mentioned lithium-rich lithium iron phosphate pre-lithiation material was added to the above PFPA / NMP solution. The mass percentage of pentafluoropropamide in the total pre-lithiation additive was 2 wt%. The mixture was magnetically stirred for 5 h. The solid-liquid mixture was filtered to obtain a solid powder. The powder was dried in a vacuum oven at 80 °C for 12 h and then naturally cooled to obtain the A3-composite lithium supplementation additive.

[0071] The A3-composite lithium supplement additive has a core made of Li5FeO4 and CNT composite system, and a shell layer made of pentafluoropropionamide (PFPA). The mass percentage of pentafluoropropionamide in the total pre-lithiation additive is 2 wt%.

[0072] Example 4

[0073] This embodiment provides a method for preparing A4-composite lithium supplementation additive, specifically including:

[0074] S401: 1.64 g of lithium oxide (Li₂O), 1.62 g of nano-Fe₂O₃, and 0.16 g of carbon nanotubes (CNTs) were placed in a ball mill jar and dry-milled at 500 rpm for 5 h. The Li / Fe molar ratio was 5.5:1, and the mass of the carbon nanotubes accounted for 5% of the total mass of Li₂O and Fe₂O₃. The ball-milled raw material powder was then pressed into tablets using a tablet press at a pressure of approximately 16 T to obtain the precursor.

[0075] S402: Place it under an argon atmosphere, heat it to 300 ℃ at a heating rate of 5 ℃ / min, hold it for 2 h, then heat it to 600 ℃, hold it for 12 h, cool it to room temperature, and then crush the material to obtain lithium iron ferrite pre-lithium material.

[0076] S403: 100 mg of hydrophobic organic compound pentafluoropropionamide was added to 15 ml of organic solvent N-methylpyrrolidone (NMP) and stirred for 1 h to obtain a PFPA / NMP solution. The above-mentioned lithium-rich lithium iron phosphate pre-lithiation material was added to the above PFPA / NMP solution. The mass percentage of pentafluoropropionamide in the total pre-lithiation additive was 3 wt%. The mixture was magnetically stirred for 5 h. The solid-liquid mixture was filtered to obtain a solid powder. The powder was dried in a vacuum oven at 80 °C for 12 h and then naturally cooled to obtain the A4-composite lithium supplementation additive.

[0077] The A4-composite lithium supplement additive has a core made of Li5FeO4 and CNT composite system, and a shell layer made of pentafluoropropionamide (PFPA). The mass percentage of pentafluoropropionamide in the total pre-lithiation additive is 3 wt%.

[0078] Example 5

[0079] This embodiment provides a method for preparing A5-composite lithium supplementation additive, specifically including:

[0080] S501: 1.64 g of lithium oxide (Li₂O), 1.62 g of nano-Fe₂O₃, and 0.16 g of carbon nanotubes (CNTs) were placed in a ball mill jar and dry-milled at 500 rpm for 5 h, wherein the Li / Fe molar ratio was 5.5:1, and the mass of carbon nanotubes accounted for 5% of the total mass of Li₂O and Fe₂O₃. The ball-milled raw material powder was then pressed into tablets using a tablet press at a pressure of approximately 16 T to obtain the precursor.

[0081] S502: Place it under an argon atmosphere, heat it to 300 ℃ at a heating rate of 5 ℃ / min, hold it for 2 h, then heat it to 600 ℃, hold it for 12 h, cool it to room temperature, and then crush the material to obtain lithium iron ferrite pre-lithium material.

[0082] S503: 100 mg of hydrophobic organic compound pentafluoropropamide was added to 15 ml of organic solvent N-methylpyrrolidone (NMP) and stirred for 1 h to obtain a PFPA / NMP solution. The above-mentioned lithium-rich lithium iron phosphate pre-lithiation material was added to the above PFPA / NMP solution. The mass percentage of pentafluoropropamide in the total pre-lithiation additive was 5 wt%. The mixture was magnetically stirred for 5 h. The solid-liquid mixture was filtered to obtain a solid powder. The powder was dried in a vacuum oven at 80 °C for 12 h and then naturally cooled to obtain the A5-composite lithium supplementation additive.

[0083] The A5-composite lithium supplement additive has a core made of Li5FeO4 and CNT composite system, and a shell layer made of pentafluoropropionamide (PFPA). The mass percentage of pentafluoropropionamide in the total pre-lithiation additive is 5 wt%.

[0084] Meanwhile, to verify the comprehensive performance of the lithium supplementation additives prepared in the above embodiments, this application provides the following comparative examples for detailed illustration.

[0085] Comparative Example 1

[0086] This comparative example provides a material preparation method, component ratio, preparation operation, and process parameters that are basically the same as those in Example 1. The difference is that pentafluoropropionamide is not added in this comparative example, resulting in B1-additive.

[0087] Comparative Example 2

[0088] This comparative example provides a material preparation method, component ratio, preparation operation, and process parameters that are basically the same as those in Example 1. The difference is that carbon nanotubes are not added in this comparative example, resulting in B2-additive.

[0089] Comparative Example 3

[0090] This comparative example provides a material preparation method, component ratio, preparation operation, and process parameters that are basically the same as those in Example 1. The difference is that carbon nanotubes and pentafluoropropamide are not added in this comparative example, that is, only lithium-rich lithium iron ferrite is used to obtain B3-additive.

[0091] To verify the morphological characteristics of the composite lithium-supplementing additive prepared in the examples, SEM testing was performed. The test results are as follows: Figure 1 and Figure 5 As shown.

[0092] according to Figure 1 and Figure 5 It can be seen that the particle size of the A1-composite lithium supplementation additive is 1-3 μm, and the surface of the material becomes smooth after coating, and the CNTs are covered; the particle size of the B3-additive without carbon nanotubes is D50=25 μm, and the larger particle size will cause kinetic lag.

[0093] To verify the structural characteristics of the composite lithium-supplementing additive prepared in the examples, its structure was characterized by XRD. The test results are as follows: Figure 2 As shown.

[0094] according to Figure 2 It can be seen that the characteristic peaks of the PFPA surface modification are highly consistent with those of PDF#75-1253 Li5FeO4, indicating that the coating layer did not change the structure of the bulk material. Due to the low concentration and amorphous phase of the coated PFPA, no impurities were detected in the XRD spectrum of PFPA-LFO.

[0095] To verify the hydrophilic and hydrophobic properties of the composite lithium supplementation additive prepared in the examples, a water contact angle test was performed on it.

[0096] according to Figure 3 and Figure 4 As shown, the contact angle of the B3-additive is 60.6°, and the contact angle of the A1-composite lithium supplement additive is 121.8°. The hydrophobicity of the material is greatly improved after being coated with pentafluoroacetamide, which in turn can prevent the material from reacting with carbon dioxide and water in the air to generate byproducts such as Li2CO3 and LiOH to a certain extent.

[0097] Coin cell fabrication: The positive electrode sheet was prepared by mixing positive electrode material, conductive agent Super P, and binder PVDF (5 wt%, solvent NMP) in a mass ratio of 70:20:10 to form a slurry, which was then coated onto a current collector, dried, and sliced. Then, using the positive electrode sheet as the positive electrode and a lithium sheet as the negative electrode, coin cells (2032) were assembled in an argon glove box with water and oxygen content less than 0.1 ppm. The electrolyte was 1 M LiPF6 in DMC:EC:EMC = 1:1:1 Vol%, and the separator was a polypropylene (PP) membrane. Constant current charge-discharge tests were performed on a Blue Battery testing system, with voltage ranges from 2.5 to 4.5 V.

[0098] The above additives were exposed to an environment of 28 °C and approximately 40% RH for a period of time, and electrochemical tests were performed. The data obtained are shown in Table 1.

[0099] Table 1. Results of the first charge specific capacity test for button cells.

[0100]

[0101] As shown in Table 1, the first-cycle charge specific capacity test results of Examples 1-5 and Comparative Example 2 of this application indicate that the conductivity of the lithium-adding additive significantly affects its electrochemical performance. For materials without added conductive carbon, their inherently poor conductivity results in very low capacity utilization. The introduction of conductive carbon material can suppress excessively large particles, and the conductive agent can construct a denser conductive network and promote charge transfer, effectively improving the material's reactivity. From the first-cycle charge specific capacities of Examples 1-5 and Comparative Example 1 in Table 1, it can be seen that the first-cycle charge specific capacity decreases with increasing coating amount. This is mainly because the outer fluorinated organic compound is inactive, and coating causes a certain loss in the material's capacity. Under air exposure for a certain period, the unmodified material experiences a significant capacity decay due to air erosion, while the capacity decay of the material coated with hydrophobic organic compounds is less. The hydrophobic coating effectively improves its chemical environmental stability and inhibits the formation of residual lithium-based compounds.

[0102] Therefore, the composite lithium supplement additive prepared in this application can effectively isolate lithium iron ferrite from contact with H2O and CO2 in the air, significantly reduce the generation of residual alkali on the surface, adapt to the volume expansion of lithium iron ferrite during charging and discharging, reduce material structure damage caused by interfacial stress, thereby greatly improving the cycle stability and service life of lithium-ion batteries, and has broad application prospects in lithium-ion batteries.

[0103] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0104] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A composite lithium supplementing additive, characterized by, Comprising: a lithium-rich lithium iron phosphate core; and an electrically conductive carbon coating layer and a pentafluoropropionamide coating layer successively wrapped outside the lithium-rich lithium iron phosphate core from inside to outside.

2. The composite lithium supplement additive according to claim 1, characterized in that, The electrically conductive carbon material is one or several of carbon nanotubes, superconducting carbon black, Ketjen black, and acetylene black.

3. The composite lithium supplement additive according to claim 1, characterized in that, The proportion of the electrically conductive carbon material in the composite lithium supplement additive is 5-20 wt%.

4. The composite lithium supplement additive according to claim 1, characterized in that, The proportion of the pentafluoropropionamide in the composite lithium supplement additive is 0.5-5 wt%.

5. A method of preparing the composite lithium supplementing additive according to any one of claims 1 to 4, characterized in that, The preparation method comprises: ball milling lithium oxide, diiron trioxide, and electrically conductive carbon material to obtain a precursor; calcining the precursor in an inert atmosphere to obtain a pre-lithium core; reacting the pre-lithium core with pentafluoropropionamide dissolved in an organic solvent, followed by solid-liquid separation and vacuum drying, to obtain the composite lithium supplement additive.

6. The method of claim 5, wherein the lithium supplementing additive is prepared by mixing the lithium supplementing material and the carbon material in a weight ratio of 1 : 1 to 1 :

10. The molar ratio of lithium oxide to diiron trioxide is (5-6):

1.

7. The method of claim 5, wherein the lithium supplementing additive is prepared by mixing the lithium supplementing material and the carbon material in a weight ratio of 1 : 1 to 1 :

10. The calcination conditions are: heating at a rate of 3-10 ℃ / min to 500-900 ℃ and calcining for 5-20 h; The ball milling conditions are: a ball-to-material ratio of (5-10):1, a ball milling speed of 100-600 rpm, and a ball milling time of 2-10 h.

8. The method for preparing the composite lithium supplementation additive according to claim 5, characterized in that, The organic solvent is one or several of tetrahydrofuran, N-methyl pyrrolidone, ethanol, chloroform, and toluene.

9. A lithium-ion battery cathode, characterized by, A lithium ion battery comprising the composite lithium supplement additive of any one of claims 1-4 or prepared by the preparation method of any one of claims 5-8.

10. A lithium-ion battery, characterized by, A lithium ion battery comprising the positive electrode sheet of claim 9.

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