Composite material for cathode active material comprising multi-component olivine material with added lithium ion conductor, and method for preparing same

Abstract

The present invention relates to a composite material for a cathode active material comprising a multi-component olivine material and to a method for preparing same. More specifically, the present invention provides a composite material for a cathode active material and a method for preparing same, the composite material comprising: a lithium transition metal phosphate core having an olivine structure and mixed with a lithium ion conductor; and a hybrid coating layer including a lithium ion conductor and a carbon material, and formed on at least a portion or all of the core. Accordingly, a lithium secondary battery using the composite material can exhibit superior electrical performance.

Description

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

[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 including a multi-component olivine material to which a lithium ion conductor is added, and a method for manufacturing the same.

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

[0003] Cathode materials play a critical role in determining the energy storage capacity, operating voltage, cycle life, rate performance, and stability of energy storage devices. The successful commercialization of lithium-ion batteries is primarily based on the advancement of cathode materials, including olivine LiFePO4 (LFP), layered oxide LiCoO2 (LCO), nickel (Ni)-based (e.g., NCM, NCA), and spinel LiMn2O4. Olivine phosphate offers the advantages of relatively high operability, long cycle stability, low cost, and a practical specific capacity close to the theoretical limit. Indeed, olivine phosphate batteries are more attractive for large-scale applications. High-voltage olivine anodes rely on the combination of different transition metals to achieve multi-component olivine materials that leverage the relatively high conductivity of iron and the high energy density offered by other elements such as manganese and cobalt. Advances in cathode material research and development are crucial for achieving higher energy density, longer cycle life, faster charging, improved safety, and more sustainable energy storage solutions.

[0004] Synthesis methods that allow for control over particle size, morphology, and cation order are crucial for the success of electrode materials. Regardless of the synthesis method used, the resulting material must satisfy three fundamental requirements: (1) unobstructed lithium diffusion channels, (2) an optimized particle size to provide 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] While many approaches have been used to synthesize olivine cathodes, solid-state reaction is the only method adopted for large-scale commercial production. However, solid-state reaction has limitations in controlling particle nucleation and growth, resulting in materials synthesized using solid-state reaction typically forming agglomerates with a wide range of particle sizes and irregular morphologies. Consequently, poor lithium ion diffusion kinetics are exacerbated by the contribution of intraparticle boundaries, which limits the actual performance of olivine cathodes.

[0006] The movement of lithium ions from one electrode to another presents both physicochemical and electrochemical challenges, as both mass and charge transfer occur simultaneously. Lithium ion transport pathways are complex, involving active material particles, bulk electrolyte, and the electrode / electrolyte interface. Furthermore, the irregular particle shape and non-uniform particle packing lead to uneven electronic conduction and lithium ion diffusion across the electrode, complicating the electrode structure. Therefore, there is a pressing need for a cathode material that can deliver superior electrical performance with greater stability.

[0007] The purpose of the present invention is to provide a composite material for a cathode active material that can exhibit excellent electrical performance in a lithium secondary battery.

[0008] Another object of the present invention is to provide a use of the above composite material as an electrode material.

[0009] Another object of the present invention is to provide a method for manufacturing the above composite material.

[0010] To achieve the above object, the present invention provides a composite material for a cathode 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.

[0011] The present invention provides a cathode active material comprising the above composite material as an active ingredient.

[0012] The present invention provides an electrode including the above-described positive electrode active material and a lithium secondary battery including the electrode.

[0013] In addition, the present invention provides a method for producing a composite material for a cathode active material, comprising the steps of: mixing a lithium transition metal phosphate precursor having an olivine structure and a lithium ion conductor precursor to produce a lithium transition metal phosphate core precursor having an olivine structure 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 the core.

[0014] The composite material according to the present invention is manufactured from a multi-component olivine material mixed with a lithium ion conductor, so that lithium ion transport can be easily controlled by establishing lithium ion paths inside and on the surface of olivine material particles, and the stability of the redox region can be improved, thereby improving the overall performance of the olivine material.

[0015] The composite material according to the present invention can be utilized as a high-performance cathode material for a lithium secondary battery, and by using the composite material, problems of conventional lithium secondary batteries can be improved, thereby providing a lithium secondary battery capable of exhibiting excellent electrical performance at a high current rate for a long cycle.

[0016] Figure 1 shows pristine LiFe 0.4 Mn 0.6 PO4(LFMP), carbon-coated LFMP (LFMP@C), pure LiFe 0.4 Mn 0.6 PO4_Li 1.3 Al 0.3 Ti 1.7 A schematic diagram of the synthesis of (PO4)3 composite (LFMP_LATP), carbon and LATP coated LFMP_LATP composite (LFMP_LATP@C_LATP).

[0017] Figure 2 shows the analysis of the crystal structure and morphology of pure LFMP. (a) is an XRD analysis and (b) is an SEM image.

[0018] Figure 3 shows the crystal structure and morphology of carbon-coated LFMP (LFMP@C), where (a) is an XRD analysis and (b) is an SEM image.

[0019] Figure 4 shows the analysis of the crystal structure and morphology of the pure LFMP_LATP composite, where (a) is an XRD analysis, (b) is a high-resolution TEM image, and (c) and (d) are EDS images and elemental mapping of all related elements such as Fe, Mn, Ti, Al, P, and O, respectively.

[0020] Figure 5 shows the crystal structure and morphology of the 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 mapping of all related elements such as Fe, Mn, Ti, Al, P, O, and C, respectively.

[0021] Figure 6 shows the electrochemical performance of pure LFMP and LFMP@C, where (a) shows the discharge capacity at various current rates, (b) shows the discharge capacity at a current rate of 1.0 C for a long cycle (cycle), and (c) and (d) show the typical charge-discharge profiles of LFMP@C at various current rates and various cycles at 1.0 C, respectively.

[0022] Figure 7 shows the long cycle performance at 1.0 C along with typical charge-discharge profiles for various cycles of pure LFMP_LATP composites.

[0023] Figure 8 shows the long cycle performance at 1.0 C along with typical charge-discharge profiles for various cycles of carbon and LATP coated LFMP_LATP composite (LFMP_LATP@C_LATP).

[0024] Figure 9 shows the long cycle performance at 5.0 C along with typical charge-discharge profiles for various cycles of carbon and LATP coated LFMP_LATP composite (LFMP_LATP@C_LATP).

[0025] Figure 10 shows the long cycle performance at 10.0 C along with typical charge-discharge profiles for various cycles of carbon and LATP coated LFMP_LATP composite (LFMP_LATP@C_LATP).

[0026] Hereinafter, the present invention will be described in detail.

[0027]

[0028] In order to improve the problem of deterioration of battery performance of olivine positive electrode due to the essential characteristics of solid-state process, the inventor synthesized a positive electrode material using a multi-component olivine material and a lithium ion conductor, and confirmed that by coating this with carbon and a lithium ion conductor, the stability of redox reaction can be improved and excellent electrochemical performance can be exhibited, thereby completing the present invention.

[0029]

[0030] The present invention provides a composite material for a cathode 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.

[0031]

[0032] The lithium transition metal phosphate having the above olivine structure may be a compound represented by the following chemical formula 1:

[0033] [Chemical Formula 1]

[0034] LiM 1 a M 2 (1-a) PO4

[0035] In the above chemical formula 1, M 1 , M 2 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.

[0036] Preferably, M 1 , M 2 can be Fe and Mn respectively, and a is LiFe selected as 0.4 0.4 Mn 0.6 It may be, but is not limited to, PO4(LFMP).

[0037] The lithium transition metal phosphate having 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 in this case, the elements may be included in a trace amount of less than 5%.

[0038]

[0039] The above lithium ion conductor may be a compound represented by the following chemical formula 2:

[0040] [Chemical Formula 2]

[0041] Li 1+x R x M 3 2-x (PO4)3

[0042] 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.

[0043] Preferably, R is Al, M 3 is Ti, x is Li which is 0.3 1.3 Al 0.3 Ti 1.7(PO4)3(LATP) but is not limited thereto.

[0044] 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, and for example, a NASICON-based (Na super-ionic conductor) solid electrolyte can be applied as a Li-conductor for coating.

[0045]

[0046] The lithium transition metal phosphate core having an olivine structure mixed with the above lithium ion conductor can be represented by the following chemical formula 3:

[0047] [Chemical Formula 3]

[0048] LiM 1 a M 2 (1-a) PO4_γLi 1+x R x M 3 2-x (PO4)3

[0049] 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.

[0050] The core may preferably be in a form in which the lithium ion conductor is dispersed within the lithium transition metal phosphate particle having an olivine structure or on the surface of the particle. The lithium ion conductor may be uniformly or non-uniformly dispersed in the phosphate.

[0051] In the above chemical formula 3, γ is a weight ratio (wt %) of the lithium ion conductor to the lithium transition metal phosphate of the olivine structure, and may be selected from 1 ≤ γ ≤ 5, and preferably 5 wt %, but is not limited thereto.

[0052] By mixing a lithium ion conductor with a lithium transition metal phosphate having an olivine structure in a weight ratio within the above range, lithium ion transport in the olivine material can be controlled and improved, and further, the redox reaction of the olivine material can be stabilized, thereby improving the overall performance of the olivine material as a cathode material of a lithium ion battery.

[0053]

[0054] A composite material for a cathode active material comprising a lithium transition metal phosphate core having an olivine structure mixed with the above 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 expressed as in the following chemical formula 4:

[0055] [Chemical Formula 4]

[0056] A@αC_βB

[0057] 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 with respect to A. As described above, B is represented by Chemical Formula 2 and can be expressed as Chemical Formula 5 below:

[0058] [Chemical Formula 5]

[0059] A@αC_βLi 1+x R x M 3 2-x (PO4)3

[0060] More specifically, the coating layer includes 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 wt%, preferably 1 to 5 wt%, based on the phosphate core, but is not limited thereto. Accordingly, the α and β values ​​may be expressed as 0.1 < α, β < 10, respectively.

[0061] The above carbon material may be a carbonaceous compound, a carbon-containing precursor, and some inorganic sources, and may be, for example, at least one selected from the group consisting of sucrose, glucose, lactose, acetylene black, carbon nanotubes, graphene, oxalate, acetate, carbonate, and citrate, but is not limited thereto.

[0062] 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.

[0063] The lithium ion conductor and carbon material can coat or modify part or all of the core surface, and preferably, the coating of the lithium ion conductor and carbon material can be formed at some specific portion with lower surface energy on the core surface, and can be in a form directly bonded to the core surface.

[0064] The coating layer of the lithium ion conductor and carbon material can protect the core, improve its electrical properties by suppressing unwanted surface reactions and controlling surface electrochemical reactions.

[0065]

[0066] The present invention provides a cathode active material for a secondary battery comprising the above composite material.

[0067]

[0068] The present invention provides an electrode comprising the above-described positive electrode active material.

[0069] In addition to the above-mentioned positive electrode active material, the above-mentioned electrode may further include a conductive material, a binder, a solvent, etc.

[0070] The above conductive material is used to provide conductivity to the electrode, and graphite, carbon black, metal fibers, etc. can be used. In the battery being constructed, any conductive material that does not cause chemical changes and has electronic conductivity can be used without special restrictions.

[0071] The above binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the current collector, and specifically, examples thereof include, but are not limited to, polyvinylidene fluoride (PVDF), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, polypropylene, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof.

[0072] The solvent may be selected from, but is not limited to, N-methyl-2-pyrrolidone, dimethyl sulfoxide (DMSO), isopropyl alcohol, acetone, or water, and may include solvents commonly used in the art. The amount of the solvent used may be adjusted in consideration of the coating thickness of the slurry and the manufacturing yield.

[0073]

[0074] The present invention provides a lithium secondary battery including the electrode described above. In this case, the electrode may be a positive electrode of the lithium secondary battery.

[0075] More specifically, the 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 including the positive electrode active material, a conductive material, a binder, and a solvent. The negative electrode may be a lithium electrode including lithium metal, and may include an 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 any compound capable of providing lithium ions may be used without particular limitation.

[0076]

[0077] In addition, the present invention provides a method for manufacturing a composite material for a cathode active material, which comprises a lithium transition metal phosphate core having an olivine structure mixed with the above 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.

[0078] The manufacturing method according to the present invention may include the steps of mixing a lithium transition metal phosphate precursor having an olivine structure and a precursor of a lithium ion conductor to manufacture a lithium transition metal phosphate core precursor having an olivine structure mixed with the lithium ion conductor; and the steps of mixing the manufactured core precursor with a precursor of a lithium ion conductor and a carbon material to synthesize a core and coating the synthesized core.

[0079]

[0080] The step of manufacturing the above core precursor can be performed by adding a lithium transition metal phosphate precursor of an olivine structure and a precursor raw material of a lithium ion conductor to acetone and ball milling them.

[0081] 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 may be included in a stoichiometric ratio. 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 may be included in a stoichiometric ratio.

[0082] In the above manufacturing method, a sufficient supply of lithium source is very important for the synthesis of olivine structure material. If lithium source is insufficient or absent, amorphous phosphate of trivalent metal ions (MPO4 (M = Fe, Mn, etc.)) can be formed at low temperatures. MPO4 compounds are thermally stable and electrochemically inactive, which can result in capacity loss and capacity degradation. Trivalent compounds such as Fe2O3 and FePO4 are much cheaper and more stable than Fe(II) salts, but Fe(III) precursors require the addition of reducing gas or reducing agent during synthesis to form LiFePO4, etc.

[0083] In the above ball milling, the mass ratio of zirconia balls (Ø = 5 mm, SciLab) to the raw material can vary from 10:1 to 20:1, the rotation speed of the ball milling can range from 200 to 300 rpm, and the ball milling time can be, but is not limited to, 3 to 5 hours. Short-time milling requires long-time heat treatment, while long-time milling only requires short-time heat treatment, so as long as the relevant raw material can be uniformly mixed with the desired precursor, the time is not particularly limited.

[0084] In addition, the step of manufacturing the core precursor is not limited to ball milling, and other techniques such as dry milling, wet milling, and jet milling can be used in combination. In addition, homogenization using ultrasound, etc. can be performed, and after the mixing process, the mixture can be dried using an oven or spray drying, etc. to obtain a fine powder.

[0085] The core precursor manufactured above may be a lithium ion conductor mixed with a lithium transition metal phosphate having an olivine structure in an amount of 1 to 5 wt%.

[0086]

[0087] 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.

[0088] The steps of synthesizing and coating the core can be carried out by stepwise heat treatment at a temperature of 100 to 800°C, and more specifically, by stepwise heat treatment in a pipeline 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 at a high temperature of 400 to 800°C for 6 to 24 hours.

[0089] An inert gas such as Ar is used to protect the metal from oxidation to divalent metal ions during sintering or to reduce trivalent metal ions to metal. Effective reduction can be achieved through heat treatment as described above. However, the above temperature range is preferred, as excessively high temperatures generate unwanted impurities and make it difficult to control particle growth and aggregation.

[0090] Hereinafter, to aid understanding of the present invention, examples will be given in detail. However, the following examples are intended only to illustrate the scope of the present invention and are not intended to limit its scope. These examples are provided to more fully explain the present invention to those of average skill in the art.

[0091]

[0092] <Example 1> Synthesis of composite materials

[0093] Figure 1 shows a schematic diagram of the synthesis of various materials. Material synthesis involves precursor preparation and high-temperature heat treatment.

[0094] LFMP precursor and LATP precursor were prepared separately by mixing stoichiometric amounts of the relevant raw materials. Pristine LiFe 0.4 Mn 0.6 PO4(LFMP) was synthesized from an LFMP precursor. 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 the LFMP precursor and sucrose (Junsei, 100%) as a carbon source. The amount of sucrose was predetermined to theoretically achieve a carbon coating of 5 wt% on the olivine LFMP material.

[0095] 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 precursor and LATP precursor. 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 precursor was calculated so that the final LATP content of 5 wt% with respect to LFMP was achieved. In order to prepare a mixture for coating carbon and LATP on pure LFMP_LATP, the synthesized pure LFMP_LATP was mixed with an appropriate amount of sucrose and LATP precursor so that each coating component in the pure LFMP_LATP theoretically achieved 5 wt% with respect to LFMP.

[0096] All relevant raw materials were mixed in acetone (Samchun, 99.7%) using a ball mill (Pulverisette, Fritsch) for 3 h. The mass ratio of zirconia balls (Ø = 5 mm, SciLab) to the raw materials could vary from 10:1 to 20:1, the rotation speed of the ball milling ranged from 200 to 300 rpm, and the ball milling time was approximately 3-5 h.

[0097] After mixing, the mixture was dried in an oven at 80°C to remove acetone and obtain a solid precursor. The solid precursor was heat-treated at high temperatures to synthesize the final target product. The solid precursor was purged in a furnace under pure Ar gas at 120°C for 2 hours, then treated at 350°C for 3 hours, and sintered at 650°C for 8 hours. The resulting material was collected and stored in a glove box filled with Ar gas.

[0098]

[0099] <Example 2> Analysis of crystal structure and shape

[0100] Figures 2 and 3 show the crystal structure and morphology analysis results of pure LFMP and carbon-coated LFMP (LFMP@C), respectively, and it can be confirmed that both pure LFMP and LFMP@C have highly crystalline olivine structures, and Figures 4 and 5 show the crystal structure analysis results of pure LFMP_LATP composite and carbon and LATP-coated LFMP_LATP composite (LFMP_LATP@C_LATP), respectively, which further confirm the successful synthesis of olivine materials with highly crystalline properties by solid-state processing.

[0101] All materials were synthesized as aggregates with irregular structures and various initial particle sizes. Due to their low weight contribution, it is difficult to observe the crystalline phase of LATP within the composites. However, morphological characterization based on EDS mapping for the composites containing pure LFMP_LATP and LFMP_LATP@C_LATP confirms the successful synthesis of the composites. Elemental mapping of the composites shows a uniform distribution of Fe and Mn, reflecting the formation of LFMP olivine, and a less uniform distribution of Al and Ti, reflecting the non-uniform distribution of LATP components within the composites. The Al signal is weaker than that of Ti due to the relatively low element concentration. The distribution of P and O in the (Fe-Mn) and (Ti-Al) groups indicates the formation of phosphate-based compounds containing LFMP and LATP in the composites. The carbon coating on the LFMP_LATP@C_LATP material can be depicted by C mapping.

[0102] EDS analysis revealed that the LATP component can form within or on the surface of the composite, regardless of the additional coating step. Due to the nature of the solid-state process, LATP can nucleate and then grow at favorable sites with relatively low surface energy. Although achieving uniform distribution of LATP throughout the composite is difficult, the presence of LATP can effectively enhance the electrochemical performance of the olivine active material by providing sufficient channels for lithium ion transport between the LFMP particles in the aggregate or on the surface of the LFMP particles, even in a heterogeneous structure.

[0103]

[0104] <Example 3> Electrochemical performance verification

[0105] The electrochemical performance of various active materials was investigated using 2032-type coin cells assembled in an Ar-filled glove box with lithium metal foil as the counter electrode, 1.0 M LiPF6 solution in ethylene carbonate / dimethyl carbonate (1:1 by 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. The charge-discharge performances were measured at room temperature at various current rates (1.0 C = 170.0 mA g -1 ) were tested using a galvanostatic automatic battery cycler (WonATech WBCS 3000, Korea) with a constant current-voltage charge protocol.

[0106]

[0107] Figure 6 shows the electrochemical performance of pure LFMP and LFMP@C, where the carbon-coated LFMP material exhibits improved capacity delivery (Figure 6(a)) and capacity retention (Figure 6(b)) at all current rates and as a cathode for lithium-ion batteries. Carbon coating is the most dominant approach among all the conventional methods to improve the performance of olivine materials for lithium-ion batteries. At 1.0 C, LFMP@C initially exhibits a capacity of 126.5 mAh g -1 It can provide a discharge capacity of 119.8 mAh g and have a 95% retention rate, and after 50 cycles, it can have a discharge capacity of 95% and a 95% retention rate. -1 It provided a discharge capacity of 113.6 mAh g in the first cycle under the same cycling conditions. -1 Discharge capacity of 97.4 mAh g at 50 cycles -1 It provided a discharge capacity of 83.4%, providing a capacity retention rate of 83.4%.

[0108] More importantly, as shown in Fig. 6(c and d), despite the improvement in capacity delivery and capacity retention, the carbon coating is not sufficient to stabilize the redox reactions of various transition metals in the multicomponent olivine LFMP material, although (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 the Mn activity is much less than its theoretical capacity, especially at high current rates and after cycling, which is reflected by the shortened operating voltage plateau of the Mn activity after cycling. For example, the Mn activity is 25.0 mAh g when cycled at 1.0 C. -1 It can provide a lower discharge capacity (Fig. 6(d)), which means that Mn activity can be a major factor limiting battery performance.

[0109]

[0110] The rate performance and cycling stability of olivine phosphate batteries are primarily limited by the low electrical conductivity and lithium ion diffusivity within the aggregates, where the large particle size, especially the boundaries between the initial particles, can increase 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, thereby stabilizing the redox reactions of various transition metals within the olivine LFMP, thereby providing higher capacity.

[0111] Referring to Fig. 7(a), the pure LFMP_LATP composite initially exhibited 139.8 mAh g at 1.0 C. -1 It provided a discharge capacity of 139.5 mAh g after 50 cycles. -1 A similar discharge capacity was achieved. Even after 400 cycles, the pure LFMP_LATP composite achieved 107.6 mAh g corresponding to a retention rate of 77.0%. -1 The discharge capacity was provided. These values ​​are superior to the performance of pure LFMP as well as LFMP@C, demonstrating the advantage of LATP in the LFMP_LATP composite. In particular, the Mn activity in the first cycle can be well 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.

[0112] Surface coating of composite particles using a hybrid conductive coating composed of carbon and lithium ion conductors according to the above Example 1 can provide additional pathways for charge transport at the surface of lithium ion particles, where redox reactions occur early and lithium ion insertion is more complex than bulk processes.

[0113] The surface coating applied to the composite particles has several functions. First, the coating material has been proven to effectively protect the active material and suppress undesirable surface reactions. Furthermore, since the olivine particles can be at least partially covered with a hybrid electronic and lithium-ion conducting material, this arrangement can enhance both the lithium ion and electronic conductivity of the active material and control surface electrochemical reactions, which are essential for maximizing the usability of the active material and maintaining adequate cycling performance.

[0114] The conductive coating can be synthesized in situ together with the synthesis of the LFMP_LATP composite or by performing a separate coating step on the pure LFMP_LATP composite. To perform the in situ coating, a precursor mixture should be prepared by thoroughly mixing an appropriate amount of the LFMP precursor with an appropriate amount of the LATP precursor and a carbon source. To perform the coating on the pure composite, the synthesis route according to the formation of LFMP_LATP@C_LATP in Figure 1 should be performed. In either case, a high-temperature heat treatment in an inert atmosphere is required 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 fully and / or partially closely coated with a hybrid conductive coating of carbon and a NASICON-type solid electrolyte to form a core-shell composite structure.

[0115]

[0116] As shown in Fig. 8, the coated composite (LFMP_LATP@C_LATP) exhibited a capacity of 141.2 mAh g in the first cycle under a current rate of 1.0 C. -1 It exhibits excellent performance by providing a discharge capacity of . After 500 cycles, the discharge capacity is 144.6 mAh g -1As shown in Fig. 9(a) and Fig. 10(a), the coated composites exhibited capacities of 113.7 and 82.2 mAh g over 500 cycles at 5.0 and 10.0 C, respectively. -1 It can stably provide an average discharge capacity of . In particular, the redox reactions of both Fe and Mn activities in the LFMP_LATP@C_LATP composite are 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-rate and high-performance cathode materials for lithium-ion batteries.

[0117]

[0118] While specific aspects of the present invention have been described in detail above, it should be apparent to those skilled in the art that these specific descriptions merely represent preferred embodiments and are not intended to limit the scope of the present invention. In other words, the substantial scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lithium transition metal phosphate core having an olivine structure mixed with a lithium ion conductor; and A composite material for a cathode active material, comprising a hybrid coating layer of a lithium ion conductor and a carbon material formed on part or all of the core.

2. In paragraph 1, The lithium transition metal phosphate of the above olivine structure is, A composite material characterized by being a compound represented by the following chemical formula 1: [Chemical Formula 1] LiM 1 a M 2 (1-a) PO4 In the above chemical formula 1, M 1 , M 2 may be the same or different, and are selected from Fe, Mn, Co or Ni, and 0≤a≤1.

3. In paragraph 1, The above lithium ion conductor is, A composite material characterized by being a compound represented by the following chemical formula 2: [Chemical Formula 2] Li 1+x R x M 3 2-x (PO4)3 In the above chemical formula 2, R is selected from Al, B, Sn or Ge, and M 3 is selected from Ti, Ge or Hf, and 0≤x<2.

4. In paragraph 1, The lithium transition metal phosphate core having an olivine structure mixed with the above lithium ion conductor is, A composite material characterized by being represented by the following chemical formula 3: [Chemical Formula 3] LiM 1 a M 2 (1-a) PO4_γLi 1+x R x M 3 2-x (PO4)3 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, 0≤a≤1 and 0≤x<2, and γ is the weight ratio (wt %) of the lithium ion conductor to the lithium transition metal phosphate of the olivine structure, selected from 1≤γ≤5.

5. In paragraph 1, The above lithium ion conductor is, A composite material characterized in that lithium transition metal phosphate particles having an olivine structure are dispersed within the particles or on the surface of the particles.

6. In paragraph 1, The above carbon material, A composite material characterized by comprising at least one selected from the group consisting of sucrose, glucose, lactose, acetylene black, carbon nanotube, graphene, oxalate, acetate, carbonate, and citrate.

7. A cathode active material comprising a composite material according to any one of clauses 1 to 6 as an active ingredient.

8. An electrode comprising a positive electrode active material according to Article 7.

9. A lithium secondary battery comprising an electrode according to Article 8.

10. A step of mixing a lithium transition metal phosphate precursor having an olivine structure and a lithium ion conductor precursor to prepare a lithium transition metal phosphate core precursor having an olivine structure mixed with the lithium ion conductor; and A method for producing a composite material for a cathode active material, comprising a step of mixing the above-mentioned manufactured core precursor with a lithium ion conductor precursor and a carbon material to synthesize and coat the core.

11. In paragraph 10, The core precursor manufactured above is, A manufacturing method characterized in that the lithium ion conductor is formed by mixing 1 to 5 wt% of a lithium transition metal phosphate having an olivine structure.

12. In paragraph 10, The step of manufacturing the above core precursor is: A manufacturing method characterized in that the above olivine structure lithium transition metal phosphate precursor and lithium ion conductor precursor raw materials are added to acetone and ball milled at a rotation speed of 200 to 300 rpm for 3 to 5 hours, 13. In paragraph 10, The steps of synthesizing and coating the above core are: A manufacturing method characterized in that it is performed by stepwise heat treatment at a temperature of 100 to 800℃.

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