Composite material for cathode active material comprising multi-component olivine material with added lithium ion conductor and manufacturing method thereof

Abstract

The present invention relates to a composite material for a positive electrode active material comprising a multi-component olivine material and a method for manufacturing the same. More specifically, the invention provides a composite material for a positive electrode active material comprising a lithium transition metal phosphate core having an olivine structure mixed with a lithium ion conductor; and a hybrid coating layer of a lithium ion conductor and a carbon material formed on part or all of the core, and a method for manufacturing the same, thereby enabling superior electrical performance in a lithium secondary battery using the same.

Description

Technology Field

[0001] The present invention relates to a cathode material for a secondary battery, and more specifically, to a composite material for a cathode active material comprising a multi-component olivine material to which a lithium ion conductor is added, and a method for manufacturing the same. Background Technology

[0002] Lithium-ion battery technology has revolutionized energy storage and utilization by offering various advantages, such as high energy density, lightweight design, and long lifespan. Despite significant improvements over the years, even higher energy densities are still required to meet the growing demand for renewable energy storage and utilization. Furthermore, lithium-ion batteries face several critical challenges related to high costs, including raw material and manufacturing expenses, as well as resource availability.

[0003] Cathode materials play a critical role in determining energy storage capacity, operating voltage, cycle life, rate performance, and the stability of energy storage devices. The successful commercialization of lithium-ion batteries is primarily based on advancements in cathode materials, such as olivine LiFePO4 (LFP), layered oxide LiCoO2 (LCO), nickel (Ni)-based materials (e.g., NCM, NCA), and spinel LiMn2O4. Olivine phosphate offers the advantages of relatively high operability, long cycle stability, low cost, and actual capacity close to theoretical limits. In practice, olivine phosphate batteries are more attractive for large-scale applications. High-voltage olivine cathodes rely on combinations of other transition metals to obtain multi-component olivine materials that utilize the relatively high conductivity of Fe and the high energy density provided by other elements such as Mn and Co. Advances in cathode material research and development are crucial for achieving higher energy density, longer cycle life, faster charging, enhanced safety, and more sustainable energy storage solutions.

[0004] Synthesis methods capable of controlling particle size, morphology, and cation order are critical to the success of electrode materials. Regardless of the synthesis method used, the synthesized material must satisfy the following three basic requirements: (1) unblocked lithium diffusion channels, (2) optimized particle size to provide a high surface area and short diffusion paths, and (3) a conductive coating to ensure the movement of electrons and lithium ions in all directions without noticeable polarization.

[0005] Although many approaches have been used for the synthesis of olivine cathode materials, solid-state reaction is the only method adopted for large-scale commercial production. However, in the case of solid-state reactions, there are limitations in controlling particle nucleation and growth, so materials synthesized based on solid-state reactions generally form as aggregates with a wide range of particle sizes and irregular shapes. Consequently, poor lithium ion diffusion kinetics are exacerbated by the contribution of intra-particle boundaries, which limit the actual performance of olivine cathode materials.

[0006] The movement of lithium ions from one electrode to another presents both physicochemical and electrochemical challenges because mass and charge transfer occur simultaneously. The lithium ion transport pathway is complex, proceeding through active material particles, the bulk electrolyte, and the electrode / electrolyte interface. Furthermore, inconsistent particle shapes and uneven particle packing lead to non-uniform electron conduction and lithium ion diffusion across the electrode, resulting in a complex electrode structure. Consequently, there is a need for cathode materials capable of exhibiting superior electrical performance with greater stability. Prior art literature

[0007] Korean Patent Publication No. 10-2010-0004797 (Published Jan. 13, 2010) The problem to be solved

[0008] The objective of the present invention is to provide a composite material for a positive electrode active material capable of exhibiting excellent electrical performance in a lithium secondary battery.

[0009] Another objective of the present invention is to provide the above-mentioned composite material for use as an electrode material.

[0010] Another objective of the present invention is to provide a method for manufacturing the above-mentioned composite material. means of solving the problem

[0011] To achieve the above objective, the present invention provides a composite material for a positive electrode active material comprising: a lithium transition metal phosphate core having an olivine structure mixed with a lithium ion conductor; and a hybrid coating layer of a lithium ion conductor and a carbon material formed on part or all of the core.

[0012] The present invention provides a positive electrode active material comprising the above-mentioned composite material as an active ingredient.

[0013] The present invention provides an electrode comprising the above-mentioned positive active material and a lithium secondary battery comprising the electrode.

[0014] In addition, the present invention provides a method for manufacturing a composite material for a positive electrode active material, comprising the steps of: mixing an olivine-structured lithium transition metal phosphate precursor and a lithium ion conductor precursor to produce an olivine-structured lithium transition metal phosphate core precursor mixed with the lithium ion conductor; and mixing the produced core precursor with a lithium ion conductor precursor and a carbon material to synthesize and coat a core. Effects of the invention

[0015] The composite material according to the present invention is manufactured from a multi-component olivine material mixed with a lithium ion conductor, and by establishing lithium ion pathways inside the olivine material particles and on the particle surface, lithium ion transport can be easily controlled, and the stability of the redox region is improved, thereby enhancing the overall performance of the olivine material.

[0016] The composite material according to the present invention can be utilized as a high-performance cathode material for lithium secondary batteries, and by using it, the problems of conventional lithium secondary batteries can be improved to provide a lithium secondary battery capable of exhibiting excellent electrical performance at high current rates during long cycles. Brief explanation of the drawing

[0017] Figure 1 shows pristine LiFe 0.4 Mn 0.6PO4 (LFMP), carbon-coated LFMP (LFMP@C), pure LiFe 0.4 Mn 0.6 PO4_Li 1.3 Al 0.3 Ti 1.7 This shows a schematic diagram of the synthesis of (PO4)3 composite (LFMP_LATP) and carbon and LATP-coated LFMP_LATP composite (LFMP_LATP@C_LATP). Figure 2 shows the crystal structure and morphology of pure LFMP, where (a) is XRD analysis and (b) is an SEM image. Figure 3 shows the crystal structure and morphology of carbon-coated LFMP (LFMP@C), where (a) is XRD analysis and (b) is an SEM image. Figure 4 shows the crystal structure and morphology of a pure LFMP_LATP composite, where (a) is XRD analysis, (b) is a high-resolution TEM image, and (c) and (d) are EDS images and elemental mappings of all related elements such as Fe, Mn, Ti, Al, P, and O, respectively. Figure 5 shows the crystal structure and morphology of a carbon and LATP-coated LFMP_LATP composite (LFMP_LATP@C_LATP), where (a) is the XRD analysis, (b) is the high-resolution TEM image, and (c) and (d) are the EDS images and elemental mappings of all related elements, such as Fe, Mn, Ti, Al, P, O, and C, respectively. Figure 6 shows the electrochemical performance of pure LFMP and LFMP@C, where (a) shows the discharge capacity at a current rate of 1.0 C during a long cycle (period), and (c) and (d) show the general charge-discharge profiles of LFMP@C at various current rates and 1.0 C during various cycles, respectively. Figure 7 shows the long cycle performance at 1.0 C along with the typical charge-discharge profile according to various cycles of the pure LFMP_LATP composite. Figure 8 shows the long cycle performance at 1.0 C along with typical charge-discharge profiles according to various cycles of a carbon and LATP-coated LFMP_LATP composite (LFMP_LATP@C_LATP). Figure 9 shows the long cycle performance at 5.0 C along with typical charge-discharge profiles according to various cycles of a carbon and LATP-coated LFMP_LATP composite (LFMP_LATP@C_LATP). Figure 10 shows the long cycle performance at 10.0 C along with typical charge-discharge profiles according to various cycles of a carbon and LATP-coated LFMP_LATP composite (LFMP_LATP@C_LATP). Specific details for implementing the invention

[0018] The present invention will be described in detail below.

[0020] To address the problem of battery performance degradation of olivine cathodes caused by the inherent characteristics of the solid-state process, the inventors synthesized a cathode material using a multi-component olivine material and a lithium ion conductor, and confirmed that by coating this material with carbon and a lithium ion conductor, the stability of the redox reaction can be improved and excellent electrochemical performance can be exhibited, thereby completing the present invention.

[0022] The present invention provides a composite material for a positive electrode active material comprising: a lithium transition metal phosphate core having an olivine structure mixed with a lithium ion conductor (Li-ion conductor); and a hybrid coating layer of a lithium ion conductor and a carbon material formed on part or all of the core.

[0024] The lithium transition metal phosphate of the above olivine structure may be a compound represented by the following chemical formula 1:

[0025] [Chemical Formula 1]

[0026] LiM 1 a M 2 (1-a) PO4

[0027] M in the above chemical formula 1 1 , M 2 Each may be the same or different, may be selected from metal elements consisting of Fe, Mn, Co and Ni, and may be 0≤a≤1.

[0028] Preferably, M 1 , M 2 can be Fe and Mn, respectively, and LiFe where a is selected as 0.4. 0.4 Mn 0.6 It may be PO4(LFMP), but is not limited thereto.

[0029] The lithium transition metal phosphate of the above olivine structure may further include one or more elements selected from the group consisting of Cr, Zr, Nb, Cu, V, Mo, Ti, Zn and Al, but the elements may be included in a trace amount of less than 5%.

[0031] The above lithium ion conductor may be a compound represented by the following chemical formula 2:

[0032] [Chemical Formula 2]

[0033] Li 1+x R x M 3 2-x (PO4)3

[0034] In the above chemical formula 2, R is selected from Al, B, Sn, or Ge, and M 3 can be selected from Ti, Ge, or Hf, and 0≤x<2.

[0035] Preferably, R is Al, M 3 Li where is Ti and x is 0.3 1.3 Al 0.3 Ti 1.7It may be (PO4)3(LATP), but is not limited thereto.

[0036] The above lithium ion conductor is not limited thereto and can be applied as long as it has high lithium ion conductivity, stability, and compatibility with olivine materials, for example, NASICON-based (Na super-ionic conductor) solid electrolytes can be applied as Li-conductors for coating.

[0038] The lithium transition metal phosphate core of an olivine structure mixed with the above lithium ion conductor can be represented by the following chemical formula 3:

[0039] [Chemical Formula 3]

[0040] LiM 1 a M 2 (1-a) PO4_γLi 1+x R x M 3 2-x (PO4)3

[0041] In the above chemical formula 3, M 1 , M 2 may be the same or different, and are selected from Fe, Mn, Co, or Ni; R is selected from Al, B, Sn, or Ge; and M 3 is selected from Ti, Ge, or Hf, and 0≤a≤1 and 0≤x<2.

[0042] Preferably, the core may be in a form where the lithium ion conductor is dispersed inside or on the surface of lithium transition metal phosphate particles having an olivine structure. The lithium ion conductor may be uniformly or non-uniformly dispersed in the phosphate.

[0043] In the above chemical formula 3, γ is the weight ratio (wt %) of the lithium ion conductor to the lithium transition metal phosphate of the olivine structure, which can be selected from 0.1≤γ≤5, preferably 5 wt %, but is not limited thereto.

[0044] By mixing a lithium ion conductor with an olivine-structured lithium transition metal phosphate in the above weight ratio, lithium ion transport in the olivine material can be controlled and improved, and furthermore, the redox reaction of the olivine material can be stabilized to improve the overall performance of the olivine material as a cathode material for lithium-ion batteries.

[0046] A composite material for a positive electrode active material comprising an olivine-structured lithium transition metal phosphate core mixed with the above-mentioned lithium ion conductor and a hybrid coating layer of a lithium ion conductor and a carbon material formed on part or all of the core can be represented as shown in Chemical Formula 4 below:

[0047] [Chemical Formula 4]

[0048] A@αC_βB

[0049] Here, A is a lithium transition metal phosphate core of an olivine structure mixed with a lithium ion conductor, B is a lithium ion conductor, C is a carbon material, and α and β represent the theoretical weight percentages of C and B relative to A. As described above, B is represented by Chemical Formula 2 and can be expressed as shown in Chemical Formula 5 below:

[0050] [Chemical Formula 5]

[0051] A@αC_βLi 1+x R x M 3 2-x (PO4)3

[0052] More specifically, the coating layer comprises a lithium ion conductor and a carbon material, and the amount of the lithium ion conductor and the carbon material may be 0.1 to 10 weight %, preferably 1 to 5 weight %, relative to the phosphate core, but is not limited thereto. Accordingly, the α and β values ​​may be expressed as 0.1 < α and β < 10, respectively.

[0053] The carbon material may use carbonaceous compounds, carbon-containing precursors, and some inorganic sources, and may be one or more selected from the group consisting of, for example, sucrose, glucose, lactose, acetylene black, carbon nanotubes, graphene, oxalate, acetate, carbonate, and citrate, but is not limited thereto.

[0054] The lithium ion conductor and the carbon material can simultaneously or sequentially coat the surface of the lithium transition metal phosphate core of the olivine structure, and preferably, the lithium ion conductor and the carbon material can be coated simultaneously to modify the core surface.

[0055] The lithium ion conductor and carbon material may coat or modify part or all of the core surface, and preferably, the coating of the lithium ion conductor and carbon material may be formed at certain parts of the core surface having lower surface energy and may be in a form that is directly bonded to the core surface.

[0056] The coating layer of the lithium ion conductor and carbon material protects the core and can improve its electrical properties by suppressing unwanted surface reactions and controlling surface electrochemical reactions.

[0058] The present invention provides a positive electrode active material for a secondary battery comprising the above-described composite material.

[0060] The present invention provides an electrode comprising the above-mentioned positive active material.

[0061] In addition to the above-mentioned positive electrode active material, the electrode may further include a conductive material, a binder, a solvent, etc.

[0062] The above conductive material is used to impart conductivity to the electrode, and may include graphite, carbon black, metal fibers, etc. In the battery being constructed, any material that possesses electronic conductivity without causing chemical changes can be used without any special limitations.

[0063] The above binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. Specifically, examples include polyvinylidene fluoride (PVDF), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, polypropylene, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, but are not limited thereto.

[0064] The above solvent may be selected from N-methyl-2-pyrrolidone, dimethylsulfoxide (DMSO), isopropyl alcohol, acetone, or water, but is not limited thereto and may include solvents commonly used in the art. The amount of the above solvent used may be adjusted considering the coating thickness of the slurry and the manufacturing yield.

[0066] The present invention provides a lithium secondary battery comprising the above-described electrode. In this case, the electrode may be a positive electrode of the lithium secondary battery.

[0067] More specifically, the above lithium secondary battery may include a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode may include the positive electrode active material and, preferably, may be manufactured from a slurry comprising the positive electrode active material, a conductive material, a binder, and a solvent. The negative electrode may be a lithium electrode comprising lithium metal and may include a negative electrode active material. The separator may use a porous polypropylene membrane, and the electrolyte may be a lithium salt-based solution in which ethylene carbonate / dimethyl carbonate is dissolved, but is not limited thereto and may be used without special limitation as long as it is a compound capable of providing lithium ions.

[0069] In addition, the present invention provides a method for manufacturing a composite material for a positive electrode active material, comprising a lithium transition metal phosphate core having an olivine structure mixed with the above-mentioned lithium ion conductor and a hybrid coating layer of a lithium ion conductor and a carbon material formed on part or all of the core.

[0070] A manufacturing method according to the present invention may include the steps of: mixing an olivine-structured lithium transition metal phosphate precursor and a lithium ion conductor precursor to produce an olivine-structured lithium transition metal phosphate core precursor mixed with the lithium ion conductor; and mixing the produced core precursor with a lithium ion conductor precursor and a carbon material to synthesize a core and coating the synthesized core.

[0072] The step of manufacturing the above core precursor can be performed by adding the lithium transition metal phosphate precursor with an olivine structure and the precursor raw materials of the lithium ion conductor to acetone and ball milling.

[0073] More specifically, the lithium transition metal phosphate precursor of the olivine structure may include a lithium precursor, a transition metal precursor selected from Fe, Mn, Co, or Ni, and a phosphate precursor as raw materials, for example, Li2CO3 or LiOH, FeC2O4·2H2O, MnC2O4·2H2O, and NH4H2PO4 in stoichiometric ratios. The precursor of the lithium ion conductor may include a lithium precursor, a metal precursor selected from Al, B, Sn, or Ge, a metal precursor selected from Ti, Ge, or Hf, and a phosphate precursor as raw materials, for example, Li2CO3 or LiOH, AlOH(OOCCH3)2, TiO2, and NH4H2PO4 in stoichiometric ratios.

[0074] In the above manufacturing method, a sufficient supply of lithium sources is very important for the synthesis of olivine structural materials. If lithium sources are insufficient or absent, amorphous phosphates of trivalent metal ions (MPO4 (M = Fe, Mn, etc.)) may be formed at low temperatures. Since MPO4 compounds are thermally stable and electrochemically inactive, they can consequently cause capacity loss and capacity degradation. Although trivalent compounds such as Fe2O3 and FePO4 are much cheaper and more stable than Fe(II) salts, Fe(III) precursors require the addition of reducing gases or reducing agents during synthesis to form LiFePO4, etc.

[0075] In the case of the ball milling above, the mass ratio of zirconia balls (Ø = 5 mm, SciLab) to raw materials may vary from 10:1 to 20:1, the rotational speed of the ball milling may be in the range of 200 to 300 rpm, and the ball milling time may be 3 to 5 hours, but is not limited thereto. Since short-duration milling requires long-duration heat treatment, long-duration milling only requires short-duration heat treatment, the time is not particularly limited as long as the relevant raw materials can be uniformly mixed with the desired precursor.

[0076] In addition, the step of manufacturing the core precursor is not limited to ball milling and may use a combination of other techniques such as dry milling, wet milling, and jet milling. Furthermore, homogenization using ultrasound or the like may be performed, and after the mixing process, fine powder may be obtained by drying through an oven or spray drying.

[0077] The core precursor manufactured above may be one in which the lithium ion conductor is mixed in an amount of 1 to 5 weight percent relative to the lithium transition metal phosphate having an olivine structure.

[0079] The manufacturing method according to the present invention may synthesize and coat the core through a solid-state process, but is not limited thereto, and various methods such as sol-gel, co-precipitation, hydrothermal, and solvothermal processes may be performed.

[0080] The step of synthesizing and coating the core can be performed by heat treatment in stages at a temperature of 100 to 800°C, and more specifically, by heat treatment in stages in a pipe under an inert gas at 100 to 140°C for 1 to 3 hours, at 330 to 370°C for 2 to 4 hours, and at 630 to 670°C for 7 to 9 hours. In particular, the synthesis and coating of the core require heat treatment for 6 to 24 hours at a high temperature of 400 to 800°C.

[0081] Inert gases such as Ar are used to protect against oxidation into divalent metal ions during sintering or to reduce trivalent metal ions to metal. Effective reduction can be achieved through such heat treatment, and since excessively high temperatures generate unwanted impurities that make it impossible to control particle growth and aggregation, the above temperature range is desirable.

[0083] Hereinafter, the present invention will be described in detail with reference to examples to aid in understanding. However, the following examples are merely illustrative of the content of the present invention and the scope of the present invention is not limited to the following examples. The examples of the present invention are provided to more completely explain the present invention to those with average knowledge in the art.

[0085] <Example 1> Synthesis of Composite Materials

[0086] Figure 1 shows a schematic diagram of the synthesis of various materials. The synthesis of materials includes the preparation of precursors and heat treatment at high temperatures.

[0087] LFMP precursors and LATP precursors were prepared separately by mixing stoichiometric amounts of the relevant raw materials. Pure (pristine) LiFe 0.4 Mn0.6 PO4 (LFMP) was synthesized from LFMP precursors. Li2CO3 (Aldrich, 99.0%), FeC2O4.2H2O (Junsei, 99.0%), MnC2O4.2H2O (Alfa Aesar, 99.0%), and NH4H2PO4 (Junsei, 99.5%) were used as LFMP precursors. Carbon-coated LFMP (LFMP@C) was synthesized from a mixture of LFMP precursors and sucrose (Junsei, 100%) as a carbon source. The amount of sucrose was theoretically predetermined to achieve a carbon coating of 5 wt% of the olivine LFMP material.

[0088] LiFe 0.4 Mn 0.6 PO4_Li 1.3 Al 0.3 Ti 1.7 (PO4)3 composite (LFMP_LATP) was synthesized from a mixture of LFMP precursors and LATP precursors. Li2CO3 (Aldrich, 99.0%), AlOH(OOCCH3)2 (Aldrich, 100.0%), TiO2 (Aldrich, 100.0%), and NH4H2PO4 (Junsei, 99.5%) were used as LATP precursors. In this example, the weight ratio of the LATP precursors was calculated so that a final LATP content of 5 wt% relative to LFMP was achieved. To prepare a mixture for coating carbon and LATP onto pure LFMP_LATP, the synthesized pure LFMP_LATP was mixed with an appropriate amount of sucrose and LATP precursors so that each coating component theoretically achieved 5 wt% relative to LFMP in the pure LFMP_LATP.

[0089] All relevant raw materials were mixed in acetone (Samchun, 99.7%) by ball milling (Pulverisette, Fritsch) for 3 hours. The mass ratio of zirconia balls (Ø = 5 mm, SciLab) to raw materials can vary from 10:1 to 20:1, the rotational speed of the ball milling is in the range of 200 to 300 rpm, and the ball milling time is about 3 to 5 hours.

[0090] After mixing, the mixture was dried in an 80°C oven to remove acetone and obtain a solid precursor. The solid precursor was heat-treated at a high temperature to synthesize the final target product. The solid precursor was purged at 120°C for 2 hours in a pipe under pure Ar gas, followed by treatment at 350°C for 3 hours, and then sintered at 650°C for 8 hours. The resulting material was collected and stored in a glove box filled with Ar gas.

[0092] <Example 2> Crystal Structure and Morphological Analysis

[0093] Figures 2 and 3 show the results of the crystal structure and morphology analysis of pure LFMP and carbon-coated LFMP (LFMP@C), respectively, confirming that both pure LFMP and LFMP@C have highly crystalline olivine structures, and Figures 4 and 5 show the crystal structures of pure LFMP_LATP composite and carbon and LATP-coated LFMP_LATP composite (LFMP_LATP@C_LATP), respectively, further confirming the successful synthesis of highly crystalline olivine materials by solid-state process.

[0094] All materials were synthesized as aggregates with irregular structures and varying initial particle sizes. Due to the low weight contribution, it is difficult to observe the crystalline phase of LATP within the composites. However, morphological characteristics based on EDS mapping for composites including pure LFMP_LATP and LFMP_LATP@C_LATP confirm the successful synthesis of the composites. Elemental mapping of the composites shows a uniform distribution of Fe and Mn reflecting the formation of LFMP olivines, and a less uniform distribution of Al and Ti reflecting the heterogeneous distribution of LATP components within the composites. The Al signal is weaker in intensity compared to Ti due to the relatively low elemental concentration. The distribution of P and O for the (Fe-Mn) and (Ti-Al) groups indicates the formation of phosphate-based compounds, including LFMP and LATP, within the composites. The carbon coating on the LFMP_LATP@C_LATP material can be represented by C mapping.

[0095] According to EDS analysis, LATP components can be formed inside or on the surface of the composite regardless of additional coating steps. Due to the nature of the solid-state process, LATP can nucleate and then grow at some favorable locations with relatively low surface energy. Although it is difficult to achieve a uniform distribution of LATP throughout the composite, the presence of LATP provides sufficient channels for the transport of lithium ions between LFMP particles in the aggregate or on the surface of LFMP particles, even in heterogeneous structures, thereby efficiently improving the electrochemical performance of the olivine active material.

[0097] <Example 3> Verification of Electrochemical Performance

[0098] The electrochemical performance of various active materials was investigated using a 2032 type coin cell assembled in an Ar-filled glove box, with a lithium metal foil as the counter electrode, a 1.0 M LiPF6 solution dissolved in ethylene carbonate / dimethyl carbonate (1:1 volume) as the electrolyte (Panax Etec Co. Ltd, Korea), and a porous polypropylene membrane as the separator. The active material electrodes were prepared from a slurry containing 80.0 wt% of the synthesized active material, 10.0 wt% Super P, and 10.0 wt% poly(vinylidene fluoride) (Aldrich, MW = 534,000) in N-methyl-2-pyrrolidone (Duksan, HPLC grade) solvent. Charge-discharge performance was evaluated at various current rates (1.0 C = 170.0 mA g⁻¹) at room temperature. -1 It was tested using a constant current automatic battery cycler (Galvanostatic automatic battery cycler, WonATech WBCS 3000, Korea) with a constant current-voltage charging protocol.

[0100] Fig. 6 shows the electrochemical performance of pure LFMP and LFMP@C; referring to this, the carbon-coated LFMP material exhibited improved capacity delivery (Fig. 6(a)) and capacity retention (Fig. 6(b)) of the LFMP material as a cathode for lithium-ion batteries at all current rates. Carbon coating is the most dominant approach among all conventional methods for improving the performance of olivine materials for lithium-ion batteries. At 1.0 C, LFMP@C initially [pronounced] 126.5 mAh g⁻¹ -1 It provides a discharge capacity and can have a 95% retention rate, and after 50 cycles, 119.8 mAh g -1 It provided a discharge capacity of . Under the same cycling conditions, the pure LFMP provided 113.6 mAh g⁻¹ in the first cycle. -1discharge capacity and 97.4 mAh g at 50 cycles -1 It provided a discharge capacity of 83.4% and a capacity retention rate of 83.4%.

[0101] More importantly, as shown in Figs. 6(c and d), despite the improvement in capacity transfer and capacity retention, the carbon coating is not sufficient to stabilize the redox reactions of various transition metals within the multi-component olivine LFMP material, even though (0.6 * 170.0 =) 102 mAh g -1 Despite having a molar contribution of 0.6 corresponding to the theoretical capacity, the actual capacity delivered by Mn activity is significantly less than its theoretical capacity, particularly at high current rates and after cycling, as reflected by the shortened operating voltage stabilizer of Mn activity after cycling. For example, Mn activity is 25.0 mAh g⁻¹ when cycling at 1.0 C. -1 It can provide a smaller discharge capacity (Fig. 6(d)), which means that Mn activity can be a major factor limiting battery performance.

[0103] The rate performance and cycling stability of olivine phosphate batteries are primarily limited by low electrical conductivity and low lithium ion diffusivity within aggregates, where large-sized particles, particularly the boundaries between initial particles, can raise the barrier for charge transport, especially lithium ion transport. The presence of LATP as a lithium ion conductor in the LFMP_LATP composite synthesized according to Example 1 can mitigate lithium ion diffusion within the composite and thus provide greater capacity by stabilizing the redox reactions of various transition metals within the olivine LFMP.

[0104] Referring to Fig. 7(a), the pure LFMP_LATP composite initially yields 139.8 mAh g at 1.0 C. -1 It provided a discharge capacity of and 139.5 mAh g after 50 cycles. -1A similar discharge capacity was achieved. Even after 400 cycles, the pure LFMP_LATP composite had a discharge capacity of 107.6 mAh g⁻¹, corresponding to a retention rate of 77.0%. -1 It provided a discharge capacity. These values ​​are superior to the performance of pure LFMP as well as LFMP@C, demonstrating the advantages of LATP in the LFMP_LATP composite. In particular, the Mn activity in the first cycle can be clearly recognized compared to the performance of LFMP@C (Fig. 6(d)). However, the capacity degradation and significant decrease in Mn activity due to cycling imply the need for a surface coating for long-cycle performance.

[0105] According to Example 1 above, the surface coating of composite particles using a hybrid conductive coating composed of carbon and lithium ion conductors can additionally provide a pathway for charge transport on the surface of lithium ion particles, where the redox reaction occurs initially and lithium ion insertion is more complex than in a mass process.

[0106] The surface coating applied to composite particles possesses various functions. First, the coating material has been proven to effectively protect the active material and suppress unwanted surface reactions. Furthermore, since olivine particles can be covered at least partially with hybrid electronic and lithium-ion conductive materials, this arrangement can enhance both the lithium-ion and electronic conductivity of the active material and regulate surface electrochemical reactions, which is essential for maximizing the utility of the active material and maintaining appropriate cycling performance.

[0107] The conductive coating can be synthesized in situ along with the synthesis of the LFMP_LATP composite, or by performing a separate coating step on the pure LFMP_LATP composite. To perform in situ coating, a precursor mixture must be prepared by thoroughly mixing an appropriate amount of LFMP precursor with an appropriate amount of LATP precursor and a carbon source. To perform coating on the pure composite, the synthesis pathway according to the formation of LFMP_LATP@C_LATP of FIG. 1 must be followed. In either case, a high-temperature heat treatment in an inert atmosphere must be carried out to obtain a stable coating. According to the present embodiment, a composite cathode material composed of an olivine material and a NASICON-type solid electrolyte can be closely coated wholly and / or partially with a hybrid conductive coating of carbon and the NASICON-type solid electrolyte to form a core-shell composite structure.

[0109] As shown in Fig. 8, the coated composite (LFMP_LATP@C_LATP) produced 141.2 mAh g during the first cycle at a current rate of 1.0 C. -1 It demonstrates excellent performance by providing a discharge capacity. After 500 cycles, the discharge capacity is 144.6 mAh g -1 It reaches. As shown in FIGS. 9(a) and FIGS. 10(a), respectively, the coated composite reaches 113.7 and 82.2 mAh g over 500 cycles at 5.0 and 10.0 C. -1 It can stably provide the average discharge capacity. In particular, the redox reaction of both Fe and Mn activity in the LFMP_LATP@C_LATP composite is stabilized during very high current rates and long cycle performance (Figs. 8(b), 9(b), 10(b)), demonstrating the importance of the present invention in achieving high-speed and high-performance cathode materials for lithium-ion batteries.

[0111] Foregoing, specific parts of the present invention have been described in detail. It is evident to those skilled in the art that such specific descriptions are merely preferred embodiments and do not limit the scope of the invention. That is, the actual scope of the invention is defined by the appended claims and their equivalents.

Claims

Claim 1 A lithium transition metal phosphate core of an olivine structure mixed with a lithium ion conductor; and a hybrid coating layer of a lithium ion conductor and a carbon material formed on part or all of the core, wherein the lithium transition metal phosphate of the olivine structure is LiFe 0.4 Mn 0.6 PO4(LFMP), and the lithium ion conductor is Li 1.3 Al 0.3 Ti 1.7 A composite material for a positive electrode active material, characterized in that the lithium ion conductor LATP is (PO4)3(LATP), the lithium ion conductor LATP is dispersed inside the lithium transition metal phosphate LFMP particle or on the surface of the particle to form a core, and the hybrid coating layer simultaneously comprises the LATP and a carbon material, thereby establishing a lithium ion pathway in both the core and the coating layer to regulate lithium ion transport and stabilize the redox reaction of the transition metal within the LFMP, resulting in improved electrochemical performance. Claim 2 delete Claim 3 delete Claim 4 A composite material for a positive electrode active material according to claim 1, wherein the lithium transition metal phosphate core having an olivine structure mixed with the lithium ion conductor is characterized by having LATP mixed at a content of 5 wt% relative to LFMP. Claim 5 delete Claim 6 A composite material for a cathode active material according to claim 1, wherein the carbon material is one or more selected from the group consisting of sucrose, glucose, lactose, acetylene black, carbon nanotube, graphene, oxalate, acetate, carbonate, and citrate. Claim 7 A positive active material comprising a composite material according to any one of claims 1, 4, and 6 as an active ingredient. Claim 8 An electrode comprising a positive electrode active material according to claim 7. Claim 9 A lithium secondary battery comprising an electrode according to claim 8. Claim 10 The method comprises the steps of: mixing an olivine-structured lithium transition metal phosphate precursor and a lithium ion conductor precursor to produce an olivine-structured lithium transition metal phosphate core precursor mixed with the lithium ion conductor; and mixing the produced core precursor with a lithium ion conductor precursor and a carbon material to synthesize a core and forming a coating layer on a part or all of the core, wherein the olivine-structured lithium transition metal phosphate is LiFe 0.4 Mn 0.6 PO4(LFMP), and the lithium ion conductor is Li 1.3 Al 0.3 Ti 1.7 A method for manufacturing a composite material for a cathode active material, characterized in that the lithium ion conductor LATP is (PO4)3(LATP), the lithium ion conductor LATP is dispersed inside the lithium transition metal phosphate LFMP particle or on the surface of the particle to form a core, and the hybrid coating layer simultaneously comprises the LATP and a carbon material, thereby establishing a lithium ion pathway in both the core and the coating layer to control lithium ion transport and stabilize the redox reaction of the transition metal within the LFMP, resulting in improved electrochemical performance. Claim 11 A method of manufacturing according to claim 10, wherein the manufactured core precursor is formed by mixing the lithium ion conductor in an amount of 1 to 5 weight percent relative to the lithium transition metal phosphate having an olivine structure. Claim 12 In claim 10, the step of manufacturing the core precursor is characterized by being performed by adding the olivine-structured lithium transition metal phosphate precursor and lithium ion conductor precursor raw materials to acetone and ball milling at a rotational speed of 200 to 300 rpm for 3 to 5 hours. Claim 13 A manufacturing method according to claim 10, wherein the step of synthesizing the core and forming a coating layer on part or all of the core is performed by heat treatment in stages at a temperature of 100 to 800℃.

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