Lithium metal phosphate-based positive electrode active material and method for producing same

Abstract

The present invention relates to a lithium metal phosphate-based positive electrode active material having an olivine structure in which pores are formed, and more particularly, to: a lithium metal phosphate-based positive electrode active material in which a combination index, reflecting the relative volume ratio occupied by micropores having a diameter in the range of 1.6 nm to 2.2 nm among all pores, the specific surface area of the positive electrode active material, and the average crystal size, is set in a predetermined range, and structural characteristics are defined on the basis of the balance between the pore ratio, the specific surface area, and the crystal size; and a method for producing same.

Description

Lithium metal phosphate-based cathode active material and method for manufacturing the same

[0001] The present invention relates to a lithium metal phosphate-based cathode active material and a method for manufacturing the same.

[0002] The present application claims the benefit of priority based on Korean Patent Application No. 10-2024-0130796 filed September 26, 2024 and Korean Patent Application No. 10-2025-0104051 filed July 30, 2025, and includes all contents disclosed in the documents of said Korean patent applications as part of this specification.

[0003] With the recent rapid proliferation of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for small, lightweight, and relatively high-capacity rechargeable batteries is increasing rapidly. In particular, lithium-ion batteries are gaining prominence as power sources for portable devices due to their lightweight nature and high energy density. Consequently, active research and development efforts are underway to improve the performance of lithium-ion batteries.

[0004] In a lithium secondary battery, electrical energy is produced by oxidation and reduction reactions when lithium ions are inserted into or removed from the positive and negative electrodes, which are composed of active materials capable of lithium ion intercalation and deintercalation, with an organic or polymer electrolyte charged between them.

[0005] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate compounds (LiFePO4) have been used as cathode active materials for lithium-ion batteries. Among these, lithium cobalt oxide (LiCoO2) is widely used and applied as a cathode active material for high-voltage applications due to its advantages of high operating voltage and excellent capacity characteristics. However, due to the rising price and supply instability of cobalt (Co), there are limitations to its mass use as a power source in fields such as electric vehicles, leading to the emergence of a need for the development of cathode active materials that can replace it.

[0006] Accordingly, a nickel-cobalt-manganese-based lithium composite transition metal oxide (hereinafter simply referred to as 'NCM-based lithium composite transition metal oxide') was developed in which a portion of the cobalt (Co) was substituted with nickel (Ni) and manganese (Mn).

[0007] However, conventionally developed NCM-based lithium composite transition metal oxides generally exist in the form of secondary particles formed by the aggregation of primary particles. Due to their large specific surface area, low particle strength, and high lithium byproduct content, they exhibit problems such as high gas generation and reduced stability during cell operation. In particular, in the case of high-nickel (High-Ni) NCM-based lithium composite transition metal oxides in which the nickel (Ni) content is increased to over 65 mol% to secure high capacity, structural and chemical stability are further degraded, and securing thermal stability becomes even more difficult.

[0008] Accordingly, there is still a need to develop a cathode active material with secured stability capable of realizing high capacity, while overcoming the disadvantages of high-nickel (High-Ni) NCM-based lithium composite transition metal oxides.

[0009] [Prior Art Literature]

[0010] [Patent Literature]

[0011] (Patent Document 1) Korean Published Patent Application No. 2012-0065192 (June 20, 2012)

[0012] The object of the present invention is a lithium metal phosphate-based cathode active material having an olivine structure containing pores, wherein a parameter (P) defined by the interrelationship between the volume ratio, specific surface area, and crystal size of micropores with a diameter of 1.6 nm to 2.2 nm mi As ) is set to a specific range, it provides a positive electrode active material that can balance the output characteristics and capacity characteristics of a lithium secondary battery.

[0013] Another objective of the present invention is to provide a method for manufacturing the lithium metal phosphate-based cathode active material.

[0014] One embodiment of the present invention is a lithium metal phosphate-based positive electrode active material having an olivine structure including pores, wherein P of the positive electrode active material is represented by the following formula 1. mi A lithium metal phosphate-based cathode active material having a value of 0.05 m / g to 0.5 m / g is provided.

[0015] [Equation 1]

[0016] P mi =(NV × BET) / S

[0017] In the above Equation 1,

[0018] NV is a normalized value obtained by normalizing the volume ratio of pores with a diameter of 1.6 nm to 2.2 nm to the total volume of pores within the range of a diameter greater than 0 nm and less than or equal to 10 nm in the above-mentioned positive electrode active material.

[0019] BET is the BET specific surface area of ​​the positive electrode active material, and

[0020] S is the average crystallite size of the positive electrode active material.

[0021] The above positive active material may be represented by the following chemical formula 1.

[0022] [Chemical Formula 1]

[0023] Li 1+a Fe 1-x-y Mn x My PO4

[0024] In the above chemical formula 1,

[0025] M is at least one element selected from the group consisting of B, Y, Ca, V, Ni, Co, Mg, Nb, Mo, W, Ti, Sr, and Zn, and

[0026] 0≤a≤0.05, 0<x<1, 0≤y<1, x+y<1.

[0027] The NV of the above Equation 1 can be 0.3 to 1.0.

[0028] The BET specific surface area of ​​the positive active material in Equation 1 above is 10 m² 2 / g to 40 m 2 / g can be.

[0029] The average crystal size (S) of the positive active material in Formula 1 above may be 90 nm to 130 nm.

[0030] The above positive active material may include at least one pore among micropores, mesopores, and macropores.

[0031] The above positive active material may have a higher volume ratio of micropores than mesopores or macropores.

[0032] P of the above positive active material represented by Formula 1 mi The value may be 0.05 to 0.3 m / g.

[0033] Another embodiment of the present invention provides a method for manufacturing a lithium metal phosphate-based positive electrode active material, comprising the steps of: (1) mixing an iron phosphate precursor, a manganese phosphate precursor, a lithium precursor, and a solvent to obtain a composition for forming a positive electrode active material; (2) spray-drying the composition for forming a positive electrode active material to produce a dried material; and (3) calcining the dried material to produce a positive electrode active material having an olivine structure containing pores.

[0034] The above iron phosphate precursor and manganese phosphate precursor may be a mixture of the iron phosphate precursor and the manganese phosphate precursor, or an iron-manganese phosphate complex precursor.

[0035] The above iron phosphate precursor and manganese phosphate precursor may include an olivine structure.

[0036] The above composition for forming the positive electrode active material may further include one selected from the group consisting of sucrose, glucose, fructose, mannose, carbon black, acetylene black, and graphite as a carbon source.

[0037] The step of obtaining the above-mentioned composition for forming the positive electrode active material may include adding at least one compound comprising at least one element selected from the group consisting of B, Y, Ca, V, Ni, Co, Mg, Nb, Mo, W, Ti, Sr, and Zn.

[0038] The above positive active material may be represented by the following chemical formula 1.

[0039] [Chemical Formula 1]

[0040] Li 1+a Fe 1-x-y Mn x M y PO4

[0041] In the above chemical formula 1,

[0042] M is at least one element selected from the group consisting of B, Y, Ca, V, Ni, Co, Mg, Nb, Mo, W, Ti, Sr, and Zn, and

[0043] 0≤a≤0.05, 0<x<1, 0≤y<1, x+y<1.

[0044] The firing of step (3) above may be carried out at a temperature of 600 ℃ to 900 ℃.

[0045] The lithium metal phosphate-based cathode active material according to the present invention has pores formed within an olivine structure, and in particular, a parameter P calculated by combining the volume ratio (NV), BET specific surface area, and average crystal size (S) of micropores with a diameter of 1.6 nm to 2.2 nm. mi By including the range of 0.05 m / g to 0.5 m / g, the diffusion and absorption / release characteristics of lithium ions are significantly improved compared to existing materials. This structural optimization results in a balanced improvement in the charge / discharge capacity and output characteristics of lithium secondary batteries in lithium metal phosphate-based cathode active materials, and in particular, it has the effect of achieving excellent electrochemical performance even in olivine structures where some of Fe is substituted with Mn and other metal elements.

[0046] Furthermore, the cathode active material according to the present invention can be prepared from iron phosphate and manganese phosphate, and since these precursors inherently contain an olivine structure, a stable olivine crystal structure of the cathode active material prepared therefrom can be formed and maintained. As a result, the micropore volume ratio within the total pore volume is secured above a certain level, and through the combination of BET specific surface area and crystal size, P mi It can be optimized to improve electrolyte accessibility and electronic conductivity within the electrode.

[0047] In addition, a lithium secondary battery incorporating the positive electrode active material according to the present invention can be expected to achieve overall performance improvements such as high power output, high capacity, and long cycle life. Furthermore, through the systematic control of the pore structure, a reduction in internal resistance and an increase in lithium ion mobility are realized, enabling stable operation even under rapid charge and discharge conditions.

[0048] Figure 1 is a graph showing the normalized value of the pore volume in the range of diameter greater than 0 nm and less than or equal to 10 nm in a lithium metal phosphate-based cathode active material according to one embodiment and a comparative example of the present invention.

[0049] FIG. 2 is a graph showing the normalized value of the volume ratio of pores with a diameter of 1.6 nm to 2.2 nm to the total volume of pores within the range of diameter greater than 0 nm and less than or equal to 10 nm in a lithium metal phosphate-based cathode active material according to one embodiment and a comparative example of the present invention.

[0050] Embodiments of the present invention will be described in detail below. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor can appropriately define the concepts of terms to best describe their invention, they should be interpreted in a meaning and concept consistent with the technical spirit of the present invention. Therefore, the configurations described in the embodiments of this specification are merely one preferred embodiment of the present invention and do not represent all aspects of the technical spirit of the present invention. It should be understood that various equivalents and modifications capable of replacing them may exist at the time of filing this application.

[0051] Throughout this specification, when a part is described as 'comprising' a certain component, it means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0052] In this specification, average particle size "D 50 " refers to a particle size corresponding to a volume accumulation of 50%. The above D 50 For example, it can be measured using the laser diffraction method. The laser diffraction method generally enables the measurement of particle sizes ranging from the submicron range to several mm, and can obtain results with high reproducibility and high resolution.

[0053]

[0054] Hereinafter, a positive electrode active material according to one embodiment of the present invention and a method for manufacturing the same will be described in more detail.

[0055]

[0056] positive electrode active material

[0057] The present invention relates to a lithium metal phosphate-based cathode active material having an olivine structure containing pores, wherein the cathode active material is characterized by being able to improve the capacity and high-rate discharge performance of a lithium secondary battery by particularly including micropores in a specific ratio or more, thereby expanding the diffusion path of lithium ions and improving electron transfer efficiency.

[0058] Typically, so-called LFP series cathode materials, such as lithium iron phosphate (LiFePO4), have high structural stability against volume changes caused by charging and discharging of the battery compared to other types of cathode materials, such as nickel-cobalt-manganese (NCM) ternary cathode materials, as oxygen and phosphorus atoms form strong covalent bonds (P=O) in the PO4 tetrahedral structure forming an olivine structure. Furthermore, they exhibit excellent characteristics in maintaining high thermal stability because oxygen atoms are not easily detached through thermal decomposition. Therefore, LFP series cathode materials are materials with excellent stability, exhibiting minimal capacity reduction due to the collapse of the crystal structure caused by overcharging and generating minimal gas, which can secure the stability required, especially for large lithium-ion batteries.

[0059] However, the above-mentioned olivine-structured LFP-based cathode material has a problem in that the oxygen atoms are strongly bonded in a hexagonal close-packed structure, which hinders the movement of lithium ions, and since the electrical conductivity is also relatively low, the flow of electrons is not smooth.

[0060] In this regard, the present invention provides an olivine-structured cathode active material in which a portion of Fe in a pure lithium iron phosphate (LFP) cathode material is substituted with Mn, etc., and which contains a specific amount of micropores among the pores formed in the cathode active material to increase the mobility of lithium ions and improve the charge / discharge capacity and efficiency of a lithium secondary battery.

[0061] The olivine-structured cathode active material according to the present invention comprises a porous structure having pores of various sizes, and in particular, aims to maximize the diffusion characteristics of lithium ions through a structure in which the ratio of micropores is controlled.

[0062] The above-described positive electrode active material may include at least one pore among micropores, mesopores, and macropores depending on its diameter, and preferably, the volume ratio of micropores may be adjusted to be higher than that of mesopores or macropores. When the proportion of micropores is set relatively high in this way, the adsorption and insertion reactions of lithium ions during initial charging can proceed more smoothly, thereby improving reactivity at the electrode surface and consequently improving the initial efficiency and output characteristics of the battery. In addition, by increasing the proportion of micropores, the lithium ion diffusion path within the entire electrode is homogenized, which can effectively lower the ion transfer resistance within the electrode.

[0063] Such pore structure characteristics can be calculated by obtaining a BET plot by performing nitrogen gas adsorption at liquid nitrogen temperature using, for example, Quantachrome’s Autosorb-1, and then calculating the pore size and volume through the Horvat-Kawazoe analysis method.

[0064] The positive electrode active material of the present invention quantifies this pore structure and incorporates P as a parameter as an indicator to simultaneously improve lithium ion mobility and electrode reactivity within the olivine-structured positive electrode active material. mi The value is used, and the above parameter is defined according to the following Equation 1.

[0065] [Equation 1]

[0066] P mi =(NV × BET) / S

[0067] In the above Equation 1,

[0068] NV is a normalized value obtained by normalizing the volume ratio of pores with a diameter of 1.6 nm to 2.2 nm to the total volume of pores within the range of a diameter greater than 0 nm and less than or equal to 10 nm in the above-mentioned positive electrode active material.

[0069] BET is the BET specific surface area of ​​the positive electrode active material, and

[0070] S is the average crystallite size of the positive electrode active material.

[0071] In Equation 1 above, parameter P miAmong the factors, NV (Normalized Value) is a quantitative measure of micropores that actually contribute to the reaction; it indicates that lithium ion reactivity is significantly enhanced during high-rate charging and discharging by playing a key role in securing the electrolyte retention capacity and rapid lithium ion adsorption and extraction pathways of micropores with a diameter of 1.6–2.2 nm. It refers to a value calculated by assigning '1' when all pores have a diameter of 1.6–2.2 nm relative to the total volume of pores with a diameter greater than 0 nm and less than or equal to 10 nm in the cathode active material, and '0' when no pores with a diameter of 1.6–2.2 nm exist relative to the total volume of pores with a diameter greater than 0 nm and less than or equal to 10 nm. BET (Specific Surface Area) represents the total amount of active surface formed by reactive pores to ensure a rapid reaction rate under high-rate discharge conditions, as contact with the electrolyte and electrochemical reactions cannot proceed smoothly if the surface area of ​​the cathode active material is not sufficiently secured even if the aforementioned micropores are present; and S (Crystal Size is a modifier representing the distance lithium ions diffuse into the crystal—that is, the length of the ion diffusion path—depending on the crystal size. As the crystal size decreases, high-speed charge / discharge characteristics are improved due to the shorter diffusion distance; conversely, if the crystal is large, internal diffusion resistance increases, which can degrade performance; thus, it serves as a normalization criterion for performance evaluation.

[0072] Since it is difficult to comprehensively evaluate the performance of a cathode active material based on a single factor—such as each factor of the aforementioned parameters—regarding the relationship between lithium ion and electron transport and micropores in porous lithium metal phosphate-based cathode active materials, the NV × BET term quantifies the active surface area of ​​the actually reactive micropores and the parameter P, which is obtained by dividing this by the average crystal size S. miAs an indicator reflecting the actual reactive pore structure per unit crystal size, it functions as a unique performance evaluation criterion that quantifies the interaction between micropore-based reactivity, the degree of activation of the electrode surface, and the diffusion distance within the particle, thereby effectively explaining the difference in high-rate charge / discharge performance that is difficult to explain with single physical properties such as BET, porosity, and crystal size.

[0073] P according to the above formula mi The value is preferably in the range of 0.05 m / g to 0.5 m / g, for example, 0.05 m / g or more, 0.06 m / g or more, 0.07 m / g or more, 0.08 m / g or more, 0.09 m / g or more, 0.10 m / g or more, 0.11 m / g or more, 0.12 m / g or more, 0.13 m / g or more, 0.14 m / g or more, 0.15 m / g or more, 0.16 m / g or more, 0.17 m / g or more, 0.18 m / g or more, 0.19 m / g or more, 0.20 m / g or more, 0.21 m / g or more, 0.22 m / g or more, 0.23 m / g or more, 0.24 m / g or more, 0.25 m / g or more, 0.26 m / g It may be greater than or equal to, 0.27 m / g or greater than or equal to, or 0.28 m / g or greater, and 0.50 m / g or less, 0.49 m / g or less, 0.48 m / g or less, 0.47 m / g or less, 0.46 m / g or less, 0.45 m / g or less, 0.44 m / g or less, 0.43 m / g or less, 0.42 m / g or less, 0.41 m / g or less, 0.40 m / g or less, 0.39 m / g or less, 0.38 m / g or less, 0.37 m / g or less, 0.36 m / g or less, 0.35 m / g or less, 0.34 m / g or less, 0.33 m / g or less, 0.32 m / g or less, 0.31 m / g or less, 0.30 m / g or less, or 0.29 m / g or less. There is. The above P miIf the value is less than 0.05 m / g, the NV value is extremely small, the BET value is too small, or the S value is too large, causing the lithium ion migration path to become narrow or long, which degrades battery output characteristics and may reduce capacity retention during high-speed charging and discharging; on the other hand, P mi If the value exceeds 0.5 m / g, the BET may become excessively large or the crystal size may become too small, which can adversely affect battery life due to excessive contact with the electrolyte or structural instability; therefore, parameter P according to the present invention mi It is desirable for NV to have a value within the above range, while reflecting the structural, porous, and surface characteristics of the cathode active material in a balanced manner, and considering high-speed charge / discharge characteristics, output retention rate, and thermal stability, which are directly related to actual battery performance. Therefore, in the present invention, it is desirable to control NV within the range of 0.3 to 1.0, while reflecting the structural, porous, and surface characteristics of the cathode active material in a balanced manner and considering high-speed charge / discharge characteristics, output retention rate, and thermal stability, which are directly related to actual battery performance. In addition, the BET specific surface area is 10 m² 2 / g to 40 m 2 It may be in the range of / g, preferably 10 m 2 / g to 30 m 2 / g, more preferably 11 m 2 / g to 25 m 2 / g, most preferably 12 m 2 / g to 20 m 2 It is preferable to include it within the range of / g. In addition, the average crystal size S can be controlled within the range of 90 nm to 130 nm, and as the crystal size becomes smaller, lithium ion diffusion becomes smoother, improving high-speed charge / discharge performance.

[0074] In one embodiment of the present invention, the positive electrode active material is based on an olivine crystal structure and may be composed of a lithium metal phosphate-based composition in which a portion of Fe is substituted with Mn or other metal elements, and specifically may be represented by the following chemical formula 1.

[0075] [Chemical Formula 1]

[0076] Li 1+a Fe 1-x-y Mn x M y PO4

[0077] In the above chemical formula 1,

[0078] M is at least one element selected from the group consisting of V, Ni, Co, Mg, Nb, Mo, W, Ti, Sr and Zn, and

[0079] 0≤a≤0.05, 0<x<1, 0≤y<1, x+y<1.

[0080] The above composition basically maintains the high thermal and structural stability of LiFePO4, while providing effects such as improved lithium ion diffusion coefficient, enhanced electrical conductivity, and increased electrode reaction rate by substituting some of the Fe with metal elements (Mn, Co, etc.) having similar or different oxidation states and ionic radii.

[0081] For example, Mn substitution can alter the symmetry of the crystal structure and the lithium ion diffusion pathway, thereby significantly improving electrochemical performance, particularly in high-speed charge / discharge environments.

[0082] In addition, in a preferred embodiment, the first positive active material having an olivine structure represented by the above chemical formula 1 may be represented by the following chemical formula 1-1.

[0083] [Chemical Formula 1-1]

[0084] Li 1+a Fe 1-x-y Mn x M y PO4

[0085] In the above chemical formula 1-1,

[0086] M is at least one element selected from the group consisting of V, Ni, Co, Mg, Nb, Mo, W, Ti, Sr and Zn, and

[0087] 0.01≤a≤0.04 and 0.1≤x≤0.9, 0≤y≤0.1 and x+y<1.

[0088] In addition, the positive active material according to the present invention has Fe present inside the crystal structure 2+ / Fe 3+ and Mn 2+ / Mn 3+ It provides a stable electron transfer pathway during the lithium ion insertion and extraction process through redox reactions, which can contribute to improving not only the initial efficiency of the battery but also the cycle life and power retention rate.

[0089] Furthermore, small-scale doping of polyvalent metals (M) can perform functions such as improving electrical conductivity, inhibiting grain growth, and stabilizing the structure, which can be a very important technical advantage in lithium secondary battery applications requiring high power and long lifespan characteristics.

[0090] In one embodiment of the present invention, the positive electrode active material having an olivine structure represented by Formula 1 may further include an amorphous carbon layer on its surface. Here, "amorphous" means not exhibiting a distinct crystal structure.

[0091] Through the above-mentioned surface amorphous carbon layer, the insertion and extraction of lithium ions into and out of the olivine-structured cathode active material in the core can be achieved, and since it also has high electronic conductivity, it can simultaneously serve as a conductive path to the olivine-structured cathode active material core. Therefore, high charge-discharge efficiency of the lithium secondary battery can be secured, and stability can be improved by preventing adverse reactions between the cathode active material in the core and the electrolyte.

[0092] For example, the amorphous carbon may include a material selected from soft carbon (low-temperature calcined carbon), hard carbon, pitch carbide, mesophase pitch carbide, calcined coke, and combinations thereof.

[0093] The above amorphous carbon may be included in an amount of 0.1 to 15 parts by weight per 100 parts by weight of the total anode active material, for example, 1 to 12 parts by weight, preferably 3 to 10 parts by weight.

[0094] In order to improve the smooth lithium ion mobility and electron conductivity to the above-mentioned positive electrode active material core, it is desirable to control the content of amorphous carbon within the above range.

[0095] The method for forming the above amorphous carbon layer is not limited to any specific method, but dry coating methods such as deposition and CVD (chemical vapor deposition), and liquid coating methods such as impregnation and spraying can be used.

[0096] In one embodiment of the present invention, the average particle size (D50) of the positive electrode active material may be 1 nm to 10 μm, for example 1 nm to 1 μm, preferably 50 nm to 1 μm.

[0097] The above positive active material may be in the form of primary particles or secondary particles comprising a plurality of primary particles.

[0098] When the above-mentioned positive active material has the above-mentioned average particle size, excellent rolling density can be achieved, and it includes particles having various particle sizes within the above range, with a narrow particle size distribution, so that the electrolyte can come into uniform contact with the positive active material, thereby enabling the realization of characteristics of a high-capacity, high-output lithium secondary battery.

[0099]

[0100] Method for manufacturing positive electrode active material

[0101] Another embodiment of the present invention provides a method for manufacturing the positive electrode active material.

[0102] In particular, the lithium metal phosphate-based cathode active material with an olivine structure according to the present invention is a high-rate specialized material having a porous structure, and has the advantage of easily inducing the formation of micropores and pore control even in the process for manufacturing it.

[0103] Specifically, the method for manufacturing an olivine-structured positive electrode active material according to the present invention comprises: (1) a step of obtaining a composition for forming a positive electrode active material by mixing an iron phosphate precursor, a manganese phosphate precursor, a lithium precursor, and a solvent; (2) a step of producing a dried material by spray-drying the composition for forming a positive electrode active material; and (3) a step of producing an olivine-structured positive electrode active material containing pores by calcining the dried material.

[0104] In the case of conventional olivine-structured lithium manganese iron phosphate-based cathode active materials (LMFP), micropores were hardly observed in the cathode active material formed through the structural reassembly process during manufacturing, in which precursors such as iron oxalate (Fe-oxalate) and manganese carbonate (Mn-carbonate) were mixed, ground, and calcined.

[0105] In contrast, the olivine-structured cathode active material according to the present invention is formed by a manufacturing method in which an iron phosphate precursor and a manganese phosphate precursor are mixed together with a lithium precursor to form a composition, and the composition is spray-dried, thereby enabling the cathode active material to include a plurality of micropore structures.

[0106] In one embodiment of the present invention, the iron phosphate precursor may mean a material including, for example, FePO4, and specifically may be iron phosphate hydrate, i.e., FePO4·2H2O.

[0107] In one embodiment of the present invention, the manganese phosphate precursor may refer to a material including, for example, MnPO4, and specifically may be manganese phosphate hydrate, i.e., MnPO4·H2O.

[0108] In one embodiment of the present invention, the iron phosphate precursor and the manganese phosphate precursor included in the composition for forming the positive electrode active material of step (1) may be a mixture of the iron phosphate precursor and the manganese phosphate precursor, or an iron-manganese phosphate composite precursor.

[0109] The above lithium precursor is preferably one or more selected from the group consisting of lithium phosphate (LiPO4), lithium carbonate (Li2CO3), lithium hydroxide (LiOH), and lithium acetate (CH3COOLi), but is not limited thereto.

[0110] The above solvent is not limited to any specific type as long as it can be well mixed without affecting each component included in the composition, and for example, water, methanol, ethanol, N-methylpyrrolidone, etc. may be used.

[0111] Generally, lithium manganese iron phosphate (LMFP)-based cathode active materials have an oxidation state of Fe that is Fe 2+ Since it is, Fe during the manufacturing process 2+ Ga Fe 3+ There is a problem that oxidation must be prevented, and also, the high-rate discharge characteristics are significantly lower than those of general cathode active materials due to the low Li-diffusion coefficient and electrical conductivity of LMFP.

[0112] Therefore, in order to manufacture an electrode using the olivine-based positive electrode active material according to the present invention, it is desirable to further increase the conductivity, and thus it is desirable to add a carbon source to the composition for forming the positive electrode active material of step (1).

[0113] As the above carbon source, one type selected from the group consisting of sucrose, glucose, fructose, mannose, carbon black, acetylene black, and graphite may be further included, but sucrose may be introduced as the carbon source of step (1) to maintain the crystallinity of the cathode active material.

[0114] In some embodiments, the step of obtaining the composition for forming the positive electrode active material of step (1) may include adding at least one compound comprising at least one element selected from the group consisting of B, Y, Ca, V, Ni, Co, Mg, Nb, Mo, W, Ti, Sr, and Zn. For example, the compound may be a salt (e.g., carbonate), hydroxide, or oxide of the elements. The elements may exist as dopants by substituting a portion of Fe and Mn inside the precursor particles, or may exist on the surface of the precursor particles as a surface coating agent.

[0115] Next, the composition for forming the positive electrode active material of step (1) above is spray-dried to produce a dried product.

[0116] When carried out according to the aforementioned spray-drying process, the sprayed composition becomes spherical due to surface tension, making it easy to obtain spherical particles with a large particle diameter range compared to conventional cases. Furthermore, the cathode active material manufactured according to this spray-drying process possesses porous characteristics, which not only suppresses the volume expansion of the electrode during charging and discharging but also enables the simultaneous synthesis of a carbon coating.

[0117] During the above spray drying process, the spray pressure of the composition may be 300 to 500 Pa. When the spray pressure of the composition is within the above range, the capacity and conductivity characteristics of the positive active material are excellent. During the above spray drying, the atmosphere may be carried out under an inert gas atmosphere such as nitrogen gas.

[0118] Next, (3) the above dried material is calcined to produce an anode active material containing pores.

[0119] In one embodiment of the present invention, the dried product obtained after the spray drying step may be calcined at a temperature of 600°C to 900°C, and crystallinity of the anode active material may be secured at this step. In addition, although it may be variable depending on the calcination temperature, the calcination time in the temperature range may be, for example, 8 to 15 hours.

[0120] In one embodiment of the present invention, the olivine-structured lithium metal phosphate-based active material produced through the above steps can be represented by the following chemical formula 1.

[0121] [Chemical Formula 1]

[0122] Li 1+a Fe 1-x-y Mn x M y PO4

[0123] In the above chemical formula 1,

[0124] M is at least one element selected from the group consisting of B, Y, Ca, V, Ni, Co, Mg, Nb, Mo, W, Ti, Sr, and Zn, and

[0125] 0≤a≤0.05, 0<x<1, 0≤y<1, x+y<1.

[0126]

[0127] Electrode for lithium secondary battery and lithium secondary battery

[0128] Another embodiment of the present invention provides an electrode for a lithium secondary battery comprising the positive active material.

[0129] As the above electrode includes the positive electrode active material according to the present invention, the degradation of characteristics of the lithium secondary battery in a high-temperature environment may be reduced and thermal stability may be significantly increased.

[0130] The above electrode includes the aforementioned positive active material and can be used as a positive electrode of a lithium secondary battery. The above electrode can be manufactured, for example, as follows.

[0131] First, a composition for forming an anode active material layer comprising an anode active material, a conductive agent, and a binder according to the above embodiments is prepared. An anode slurry is prepared by mixing the composition with a solvent, and then the anode slurry is directly coated and dried onto an anode current collector to produce an anode electrode plate. Alternatively, the anode slurry can be cast onto a separate support, and then a film obtained by peeling off from the support is laminated onto the anode current collector to produce an anode electrode plate.

[0132] The binder used in the composition for forming the positive electrode active material layer is a component that assists in the bonding of the active material and conductive agent, and in the bonding to the current collector. Examples of such binders include polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, and various copolymers. The content thereof is used in an amount of 1 to 5 weight percent based on the total weight of the composition for forming the positive electrode active material layer. When the content of the binder is within the above range, the bonding strength of the active material layer to the current collector is good.

[0133] The binder used in the composition for forming the positive electrode active material layer is a component that assists in the bonding of the active material and conductive agent, and in the bonding to the current collector. Examples of such binders include polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, and various copolymers. The content thereof is used in an amount of 1 to 5 weight percent based on the total weight of the composition for forming the positive electrode active material layer. When the content of the binder is within the above range, the bonding strength of the active material layer to the current collector is good.

[0134] When the above composition for forming the positive electrode active material layer is mixed with a solvent to form a slurry, N-methylpyrrolidone (NMP), acetone, water, etc., may be used as the solvent. The content of the solvent is used in an amount of 1 to 10 parts by weight based on 100 parts by weight of the composition for forming the positive electrode active material layer. When the solvent content is within the above range, the process of forming the active material layer is easy.

[0135] The positive current collector, to which the positive slurry is coated or laminated, has a thickness of about 3 to 500 μm and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. The current collector may also form fine irregularities on its surface to increase the adhesion of the positive active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible.

[0136] The anode is completed by directly coating and drying the anode slurry onto the anode current collector, or by laminating an anode film manufactured as a separate film onto the anode assembly and then pressing it.

[0137] Another embodiment of the present invention provides a lithium secondary battery comprising an electrode for the lithium secondary battery.

[0138] According to one embodiment, the lithium secondary battery comprises the positive electrode described above; a negative electrode disposed opposite to the positive electrode; and a separator disposed between the positive electrode and the negative electrode. The electrode and the lithium secondary battery employing the same can be manufactured, for example, as follows.

[0139] The anode and cathode are manufactured by applying and drying the anode slurry and cathode slurry, respectively, onto a current collector. The manufacturing of the anode is as described above.

[0140] To manufacture a cathode, a cathode slurry for forming a cathode is prepared by mixing a cathode active material, a binder, a conductive agent, and a solvent.

[0141] The above-mentioned cathode active material is not specifically limited to those generally used in the field, but more specifically, lithium metal, metals capable of alloying with lithium, transition metal oxides, materials capable of doping and undoping lithium, materials capable of reversibly inserting and extracting lithium ions, etc. may be used.

[0142] The above transition metal oxide may be, for example, tungsten oxide, molybdenum oxide, titanium oxide, lithium titanium oxide, vanadium oxide, lithium vanadium oxide, etc. The material capable of doping and dedoping the lithium is, for example, Si, SiO x(0<x≤2), Si-Y alloy (where Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element, or a combination thereof, and is not Si), Sn, SnO2, Sn-Y (where Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element, or a combination thereof, and is not Sn), etc., and at least one of these may be mixed with SiO2 and used. The above element Y may be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof.

[0143] The material capable of reversibly inserting and extracting the above lithium ions is a carbon-based material, and any carbon-based negative electrode active material commonly used in lithium batteries can be used. For example, it is crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon is, for example, amorphous, plate-like, flake-like, spherical, or fibrous natural graphite; or artificial graphite, and the amorphous carbon is, for example, soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0144] The conductive agent, binder, and solvent used in the cathode slurry may be the same as those used for the anode. In some cases, it is also possible to form pores inside the electrode plate by adding a plasticizer to the anode slurry and the cathode slurry. The content of the cathode active material, conductive agent, binder, and solvent is at a level typically used in lithium secondary batteries.

[0145] The negative electrode current collector is generally made with a thickness of 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, similar to the positive electrode current collector, fine irregularities may be formed on the surface to strengthen the bonding strength of the negative electrode active material, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

[0146] Similar to the manufacture of the anode, the prepared cathode slurry can be directly coated and dried onto a cathode current collector to manufacture a cathode plate. Alternatively, the cathode slurry can be cast onto a separate support, and then the film obtained by peeling off from the support can be laminated onto a cathode current collector to manufacture a cathode plate.

[0147] The above-mentioned positive and negative electrodes can be separated by a separator, and any separator commonly used in lithium secondary batteries can be used. In particular, it is suitable to have low resistance to ion movement of the electrolyte and excellent electrolyte wetting ability. For example, it may be a material selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or combinations thereof, and may be in the form of a non-woven fabric or a woven fabric. The separator used has a pore diameter of 0.01 to 10 μm and a thickness generally of 5 to 300 μm.

[0148] Lithium salt-containing non-aqueous electrolytes consist of a non-aqueous electrolyte and lithium. Non-aqueous electrolytes include non-aqueous electrolytes, solid electrolytes, and inorganic solid electrolytes.

[0149] As the above-mentioned non-aqueous electrolyte, for example, non-protic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl lactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, ethyl propionate, etc. may be used.

[0150] The above organic solid electrolyte may be, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, a polyester sulfide, a polyvinyl alcohol, polyvinylidene fluoride, a polymer containing an ionic dissociator, etc.

[0151] As the above-mentioned inorganic solid electrolyte, for example, nitrides, halides, sulfates of Li such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, and Li3PO4-Li2S-SiS2 may be used.

[0152] Any lithium salt commonly used in lithium secondary batteries may be used, and as a substance that dissolves well in the above-mentioned non-aqueous electrolyte, examples include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 One or more materials such as LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, (CF3SO2)2NLi, lithium chloroborate, lithium lower aliphatic carboxylate, and lithium 4-phenylborate may be used.

[0153] In addition to the above electrolyte components, various additives may be used in the above electrolyte for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity.

[0154] The above additives include imide-based salts such as lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide; borate-based salts such as lithium bis(oxalate)borate (LiBOB), lithium difluoro(oxalate)borate (LiOdFB), and tris(trimethylsilyl)borate (TMSB); phosphate-based salts such as difluorophosphate and tris(trimethylsilyl)phosphate; and haloalkylene carbonate-based compounds such as difluoroethylene carbonate. Alternatively, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride may be included, and the above additives may be used alone or in combination. In this case, the above additives may each be included in an amount of 0.1% to 10% by weight with respect to the total weight of the electrolyte.

[0155] In addition to existing applications such as mobile phones and portable computers, the above-mentioned lithium secondary battery is suitable for applications requiring high capacity, high output, and high-temperature operation, such as electric vehicles, and can also be used in hybrid vehicles by combining it with existing internal combustion engines, fuel cells, and supercapacitors. Furthermore, the above-mentioned lithium battery can be used in all other applications requiring high output, high voltage, and high-temperature operation.

[0156] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, these embodiments are merely illustrative of the invention and are not intended to limit the appended claims. It is obvious to those skilled in the art that various changes and modifications to the embodiments are possible within the scope and spirit of the invention, and that such variations and modifications fall within the scope of the appended claims.

[0157]

[0158] Preparation Example 1: Synthesis of Mn Precursor

[0159] First, 200 mL of ethanol was added to a 500 mL three-necked flask, a stirrer was set up, and stirring was started at 300 rpm at room temperature (approximately 25 ℃). 0.1 mol (24.8 g) of manganese(II) nitrate tetrahydrate (Mn(NO3)2·4H2O) was slowly added, and stirring continued for about 5 minutes until completely dissolved. Subsequently, 0.1 mol (approx. 5.9 mL) of 85 wt% phosphoric acid (H3PO4) was measured and injected dropwise while maintaining stirring at a constant speed (300 rpm) for an additional 10 minutes or more. At this time, Mn in the solution 2+ Ions and PO4 3- It was observed that a light pink or white precipitate formed depending on the reaction of the ions.

[0160] The generated precipitate was stabilized at room temperature for 10 minutes immediately after the reaction was finished, and then washed three times with deionized water (DI water). Afterwards, the precipitate was filtered using a vacuum filtration device, and the filter cake was dried at 60°C for more than 12 hours to finally obtain Mn PO4·H2O, which is a Mn precursor.

[0161]

[0162] Preparation Example 2: Synthesis of Fe Precursor

[0163] After adding 200 mL of ethanol to a 500 mL three-necked flask, a stirrer was set up, and stirring was initiated at 300 rpm at room temperature (approx. 25 ℃). 0.1 mol (approx. 40.4 g) of iron(II) nitrate cihydrate (Fe(NO3)2·9H2O) was slowly added, and stirring continued for about 5 minutes until completely dissolved. Subsequently, 0.1 mol (approx. 5.9 mL) of 85 wt% phosphoric acid (H3PO4) was metered and injected dropwise while maintaining stirring at a constant speed (300 rpm) for an additional 10 minutes or more. At this time, Fe in the solution 2+ Ions and PO4 3- It was observed that white or off-white precipitates formed depending on the reaction of ions.

[0164] The generated precipitate was stabilized at room temperature for 10 minutes immediately after the reaction was finished, and then washed three times repeatedly with deionized water (DI water). Afterwards, the precipitate was filtered using a vacuum filtration device, and the filter cake was dried at 60°C for more than 12 hours to finally obtain FePO4·H2O, an Fe precursor.

[0165]

[0166] Preparation Example 3: Synthesis of Mn-Fe Precursor

[0167] After adding 200 mL of ethanol to a 500 mL three-necked flask, a stirrer was set up, and stirring was initiated at 300 rpm at room temperature (approx. 25 ℃). Subsequently, 0.06 mol (approx. 14.9 g) of manganese(II) nitrate tetrahydrate (Mn(NO3)2·4H2O) and 0.04 mol (approx. 16.2 g) of iron(II) nitrate ctaryhydrate (Fe(NO3)2·9H2O) were added sequentially, and stirring was maintained for approximately 5 minutes until completely dissolved. Next, 85 wt% phosphoric acid (H3PO4) was weighed to achieve a 1:1 molar ratio with respect to the total moles of Mn and Fe (0.10 mol), and a total of 0.10 mol (approx. 5.9 mL) was injected dropwise while maintaining stirring at a constant speed (300 rpm) for an additional 10 minutes or more. During this process, Fe 2+ and Mn 2+ The ion is PO4 3- It was observed that a grayish-white or light pink precipitate formed upon reaction with ions.

[0168] The generated precipitate was stabilized at room temperature for 10 minutes immediately after the reaction was completed, and then washed three times repeatedly with deionized water (DI water). Subsequently, the precipitate was filtered using a vacuum filtration device, and the filter cake was dried at 60°C for more than 12 hours to produce the Mn-Fe composite precursor, Fe 0.6 Mn 0.4 PO4·H2O was finally obtained.

[0169]

[0170] Preparation Example 4: Synthesis of Mn-Fe Precursor

[0171] After adding 200 mL of ethanol to a 500 mL three-necked flask, a stirrer was set up, and stirring was initiated at 300 rpm at room temperature (approx. 25 ℃). Subsequently, 0.06 mol (approx. 14.9 g) of manganese(II) nitrate tetrahydrate (Mn(NO3)2·4H2O) and 0.04 mol (approx. 16.2 g) of iron(II) nitrate ctaryhydrate (Fe(NO3)2·9H2O) were added sequentially, and stirring was maintained for approximately 5 minutes until completely dissolved. Next, 85 wt% phosphoric acid (H3PO4) was weighed to achieve a molar ratio of 1:1.1 relative to the total moles of Mn and Fe (0.10 mol), and a total of 0.11 mol (approx. 6.5 mL) was injected dropwise while maintaining stirring at a constant speed (300 rpm) for an additional 10 minutes or more. During this process, Fe 2+ and Mn 2+ The ion is PO4 3- It was observed that a grayish-white or light pink precipitate formed upon reaction with ions.

[0172] The generated precipitate was stabilized at room temperature for 10 minutes immediately after the reaction was completed, and then washed three times repeatedly with deionized water (DI water). Subsequently, the precipitate was filtered using a vacuum filtration device, and the filter cake was dried at 60°C for more than 12 hours to produce the Mn-Fe composite precursor, Fe 0.6 Mn 0.4 PO4·H2O was finally obtained.

[0173]

[0174] Example 1: Preparation of positive electrode active material

[0175] Mn-Fe composite precursor (Fe prepared according to Preparation Example 3) 0.6 Mn 0.4 For 10 g of PO4·H2O, lithium carbonate (Li2CO3) was weighed and added in a molar ratio of Li : (Fe + Mn) = 1 : 1. At this time, 0.1 mol (approx. 7.39 g) of Li2CO3 was added based on 73.89 g per approximately 1.00 mol.

[0176] The mixture was placed in a 500 mL octagonal container, filled with zirconia beads (1 mm diameter), and then subjected to wet dispersion and mixing using a bead mill (Netzsch MicroSeries) at a speed of 1,500 rpm for 2 hours. Ethanol was used as a solvent for mixing, and after mixing, the ethanol was removed using a rotary vacuum concentrator. As a result, a slurry for forming an anode active material with evenly dispersed particles was obtained.

[0177] Subsequently, the above slurry was dried using a compressed air spray dryer (Buchi B-290). At this time, the spray pressure was set to approximately 400 Pa, the injection rate to 5 mL / min, the inlet temperature to 180 ℃, and the outlet temperature to approximately 90 ℃. The dried material obtained through spray drying exhibited a relatively uniform fine particle form.

[0178] The obtained dried material was placed in an alumina crucible, inserted into a tubular electric furnace, and calcined under a nitrogen atmosphere by heating to 700 ℃ at a heating rate of 5 ℃ / min and maintaining the temperature for 10 hours. After calcination, a dark brown calcined product was recovered through natural cooling, and XRD analysis revealed that the calcined product was a lithium metal phosphate-based cathode active material (LiFe) with an olivine structure containing some pores. 0.6 Mn 0.4 It was confirmed as PO4).

[0179]

[0180] Example 2: Preparation of positive electrode active material

[0181] An olivine-structured lithium metal phosphate-based cathode active material was prepared in the same manner as in Example 1, except that the Mn-Fe precursor according to Preparation Example 4 was used instead of the Mn-Fe precursor according to Preparation Example 3.

[0182]

[0183] Example 3: Preparation of positive electrode active material

[0184] A manganese precursor (MnPO4·H2O) prepared according to Preparation Example 1 and an iron precursor (FePO4·H2O) prepared according to Preparation Example 2 were weighed and mixed in a molar ratio of Mn : Fe = 0.4 : 0.6. Based on the total molar amount of metal in the mixed Mn·Fe precursor, lithium carbonate (Li2CO3) was added in a molar ratio of Li : (Mn + Fe) = 1 : 1. Approximately 0.10 mol (7.39 g) of Li2CO3 was weighed and added.

[0185] The mixture was placed in a 500 mL octagonal container, filled with zirconia beads (1 mm diameter), and then subjected to wet dispersion and mixing using a bead mill (Netzsch MicroSeries) at a speed of 1,500 rpm for 2 hours. Ethanol was used as a solvent for mixing, and after mixing, the ethanol was removed using a rotary vacuum concentrator. As a result, a slurry for forming an anode active material with evenly dispersed particles was obtained.

[0186] Subsequently, the above slurry was dried using a compressed air spray dryer (Buchi B-290). At this time, the spray pressure was set to approximately 400 Pa, the injection rate to 5 mL / min, the inlet temperature to 180 ℃, and the outlet temperature to approximately 90 ℃. The dried material obtained through spray drying exhibited a relatively uniform fine particle form.

[0187] The obtained dried material was placed in an alumina crucible, inserted into a tubular electric furnace, and calcined under a nitrogen atmosphere by heating to 700 ℃ at a heating rate of 5 ℃ / min and maintaining the temperature for 10 hours. After calcination, a dark brown calcined product was recovered through natural cooling, and XRD analysis revealed that the calcined product was a lithium metal phosphate-based cathode active material (LiFe) with an olivine structure containing some pores. 0.6 Mn 0.4 It was confirmed as PO4).

[0188]

[0189] Comparative Example 1: Preparation of positive electrode active material

[0190] Lithium carbonate (Li2CO3), manganese carbonate (MnCO3), iron phosphate (FePO4), and ammonium monohydrogen phosphate (NH4H2PO4) were weighed and mixed to achieve a molar ratio of Li : P = 1 : 1 and Mn : Fe = 6 : 4. At this time, 0.06 mol of MnCO3 and 0.04 mol of FePO4 were used as metal ion sources, and accordingly, 0.10 mol of Li2CO3 (approx. 7.39 g) and 0.10 mol of NH4H2PO4 (approx. 11.5 g) were added together. In addition, sucrose was added as a carbon source for carbon doping to a concentration of 5 wt% based on the total precursor mixture to prepare the mixture.

[0191] The above mixture was placed in a 500 mL octagonal container, filled with zirconia beads (diameter 1 mm), and then wet dispersed and mixed using a bead mill (Netzsch MicroSeries) at a speed of 1,500 rpm for 2 hours. Ethanol was used as a solvent for mixing, and after mixing, the ethanol was removed using a rotary vacuum concentrator.

[0192] Subsequently, the above slurry was dried using a compressed air spray dryer (Buchi B-290). At this time, the spray pressure was set to approximately 400 Pa, the injection rate to 5 mL / min, the inlet temperature to 180 ℃, and the outlet temperature to approximately 90 ℃. The dried material obtained through spray drying exhibited a relatively uniform fine particle form.

[0193] The obtained dried material was placed in an alumina crucible, placed in a tubular electric furnace, heated to 700 ℃ at a heating rate of 5 ℃ / min under a nitrogen atmosphere, and then calcined by maintaining the temperature for 10 hours. After calcination, a blackish-brown calcined product was recovered through natural cooling.

[0194]

[0195] Experimental Example 1: Analysis of Pore Characteristics and PMI Parameters of Anode Active Material

[0196] For the cathode active materials prepared according to Examples 1 to 3 and Comparative Example 1, pore characteristics and grain size were analyzed, and based on this, parameter P mi was calculated.

[0197] Pore ​​characterization was performed using a BET analyzer (Bel, BELSORP-mini), and each sample was vacuum-dried at 120 °C for 12 hours prior to measurement. Isothermal adsorption curves using nitrogen gas were obtained at 77 K, and based on these, the specific surface area (BET, m²) was determined according to the 6-point BET (Brunauer-Emmett-Teller) method. 2 / g) was calculated. For pore analysis, the Barrett-Joyner-Halenda (BJH) method was applied to calculate the total pore volume, volume by pore size, and volume ratio.

[0198] At this time, based on the total volume (A) of pores with a diameter greater than 0 nm and less than 10 nm among all pores, the volume ratio (%) of pores with a diameter of 1.6 nm or more and less than 2.2 nm was measured and normalized to obtain a normalized volume ratio B, which was defined as the NV (Normalized Value) value, a parameter term in the present invention.

[0199] Also, P mi The average crystal size (S, nm) of the cathode active material, which is the denominator term of the parameter, was measured by X-ray diffraction analysis (XRD). The analyzer used was Rigaku’s Ultima IV, and measurements were taken at 0.02° intervals in the range of 2θ = 10° to 80° using the Cu-Kα line (λ = 1.5418 Å). The average grain size was calculated by applying the Scherrer equation to the major diffraction planes among the measured XRD peaks, such as (111), (121), and (311).

[0200] Finally, the NV(B) and BET m measured above 2 Using the values ​​of / g), S(nm), P according to the following formula mi The values ​​were calculated, and the results are shown in Table 1 below.

[0201] Comparative Example 1 Example 1 Example 2 Example 3 Specific surface area (BET, m 2 / g)23.69 225.35 24.95 323.678 Pore volume (A, cm 3 / g)0.294 10.297 80.2917 0.3018 Normalized value(B, NV)0.165 0.558 0.413 1.00 Average crystal size(S, nm)128 195 197 410 1.8P mi 0.0310.1490.1060.233

[0202]

[0203] In addition, the volume ratio of pores with a diameter of 1.6 nm or more to 2.2 nm or less to the total volume of pores with a diameter greater than 0 nm to 10 nm or less after measurement was normalized, and the results are shown in Figures 1 and 2.

[0204] Referring to Table 1, Figure 1, and Figure 2 above, the cathode active materials according to Examples 1 to 3 maintain a high micropore volume ratio (NV) of 1.6 nm or more to 2.2 nm or less compared to the cathode active material according to Comparative Example 1, which means that among the total pores of the cathode active material, a pore structure that substantially contributes to electrolyte penetration and lithium ion diffusion has developed.

[0205] In particular, metal phosphate hydrate precursors having an olivine structure (MnPO4·H2O, FePO4·H2O, Fe 0.6 Mn 0.4In Examples 1–3 using PO4·H2O, uniform and fine micropores were formed due to the release of crystal water from the precursor and lattice stabilization characteristics during the calcination process, which was quantitatively confirmed through BJH analysis. Such structural differences showed a significant difference in the normalized ratio (NV) of micropore volume, and the parameter P, which also considered BET specific surface area (BET) and grain size (S), mi The value was also calculated to be significantly higher than that of the comparative example.

[0206] On the other hand, in the case of Comparative Example 1, commercial precursors (Li2CO3, MnCO3, FePO4, NH4H2PO4) were used, resulting in a non-uniform pore distribution and a low micropore ratio, which lowered the NV value; furthermore, despite some increase in specific surface area, the grain size (S) was relatively large, and consequently, P mi The value was found to be significantly lower than that of the example.

[0207] In summary, the positive electrode active material according to the embodiment of the present invention enables micropore-centered pore control by utilizing the structural characteristics of the precursor, and accordingly, P mi The parameter value can be adjusted within a range of approximately 0.05 m / g to 0.5 m / g, thereby allowing the parameter P according to the present invention mi It can be seen that this serves as an important technical indicator of performance in terms of forming high-speed pathways for lithium ions and securing electrolyte reactivity.

[0208]

[0209] Experimental Example 2: Evaluation of Lithium Secondary Battery Characteristics

[0210] A lithium secondary battery was manufactured using the positive active material prepared in the examples and comparative examples. Specifically, the positive active material, Denka Black as a conductive material, and PVDF as a binder were mixed in a mass ratio composition of 93:5:2, respectively, and a positive slurry was prepared using NMP (N-methyl-2-pyrrolidone) as a solvent. The positive slurry was coated onto an aluminum current collector (thickness: 20 μm), vacuum dried at 100°C, and then rolled to produce a positive electrode.

[0211] The cathode used 1.2 mm thick lithium metal (Li metal).

[0212] As described above, the anode and cathode manufactured were notched into circular shapes with diameters of Φ14 and Φ16, respectively, and stacked. An electrode cell was formed by interposing a separator (polyethylene, thickness 13 μm) notched to Φ19 between the anode and cathode. The electrode cell was placed inside a coin cell outer casing with a diameter of 20 mm and a height of 1.6 mm, and an electrolyte was injected to assemble it. The electrode was aged for at least 12 hours to allow the electrolyte to impregnate the inside of the electrode. The electrolyte used was prepared by dissolving 1 M LiPF6 in a mixed solvent of EC / EMC (30 / 70; volume ratio).

[0213] Formation charging and discharging were performed on the secondary battery manufactured as described above (charging conditions CC-CV 0.1C 4.3V 0.005C CUT-OFF, discharging conditions CC 0.1C 3V CUT-OFF).

[0214]

[0215] (1) Initial capacity measurement and initial capacity efficiency evaluation

[0216] The above-mentioned lithium secondary battery was charged (CC-CV 0.1C 4.3V 0.005C CUT-OFF) in a 25℃ chamber, and the battery capacity (initial charge capacity) was measured. Then, the battery capacity (initial discharge capacity) was measured after discharging (CC 0.1C 3.0V CUT-OFF), and the results are shown in Table 2 below.

[0217]

[0218] (2) Comparison of output characteristics according to increase in C-rate

[0219] The output characteristics of the above lithium secondary battery were measured according to the increase in C-rate. Specifically, the relative discharge retention rate (%) was calculated by comparing the discharge capacity under 1C and 4C conditions with the 0.1C / 0.1C charge / discharge capacity, and the results are shown in Table 2 below.

[0220] Comparative Example 1 Example 1 Example 2 Example 3 Capacity (mAh / g) Charge 148.2 151.2 152.4 152.9 Discharge 145.2 147.7 148.2 150.8 Output (%) 1C / 0.1C 89.2 090.2 890.8 792.1 44C / 0.1C 77.9 983.7 484.2 185.42

[0221]

[0222] Referring to Table 2, it can be seen that the lithium secondary batteries according to Examples 1 to 3 have higher initial charge / discharge capacities compared to Comparative Example 1, and are particularly improved in terms of initial capacity efficiency (discharge capacity / charge capacity). In addition, regarding high-rate discharge retention rate, the lithium secondary batteries using the cathode active materials according to the Examples showed superior results compared to the lithium secondary batteries using the cathode active materials according to the Comparative Example.

[0223] This is interpreted as a result demonstrating that the cathode active material of the example exhibits excellent high-speed lithium ion diffusion and reactivity by having a micropore-centered pore structure and highly reactive surface characteristics.

[0224]

[0225] Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims also fall within the scope of the present invention.

Claims

1. As a lithium metal phosphate-based cathode active material having an olivine structure containing pores, P of the above positive active material represented by the following Formula 1 mi A value of 0.05 m / g to 0.5 m / g, Lithium metal phosphate-based cathode active material: [Equation 1] P mi =(NV × BET) / S In the above Equation 1, NV is a normalized value obtained by normalizing the volume ratio of pores with a diameter of 1.6 nm to 2.2 nm to the total volume of pores within the range of a diameter greater than 0 nm and less than or equal to 10 nm in the above-mentioned positive electrode active material. BET is the BET specific surface area of ​​the positive electrode active material, and S is the average crystallite size of the positive electrode active material.

2. In Paragraph 1, The above positive active material is represented by the following chemical formula 1, Lithium metal phosphate-based cathode active material: [Chemical Formula 1] Li 1+a Fe 1-x-y Mn x M y PO4 In the above chemical formula 1, M is at least one element selected from the group consisting of B, Y, Ca, V, Ni, Co, Mg, Nb, Mo, W, Ti, Sr, and Zn, and 0≤a≤0.05, 0<x<1, 0≤y<1, x+y<1.

3. In Paragraph 1, The NV of the above Equation 1 is 0.3 to 1.0, Lithium metal phosphate-based cathode active material.

4. In Paragraph 1, The BET specific surface area of ​​the positive active material in Equation 1 above is 10 m² 2 / g to 40 m 2 / g person, Lithium metal phosphate-based cathode active material.

5. In Paragraph 1, The average crystal size (S) of the positive active material of Formula 1 above is 90 nm to 130 nm, Lithium metal phosphate-based cathode active material.

6. In Paragraph 1, The above positive active material comprises at least one pore among micropores, mesopores, and macropores. Lithium metal phosphate-based cathode active material.

7. In Paragraph 6, The above positive active material is one in which micropores have a higher volume ratio than mesopores or macropores. Lithium metal phosphate-based cathode active material.

8. In Paragraph 1, P of the above positive active material represented by Formula 1 mi A value of 0.05 to 0.3 m / g, Lithium metal phosphate-based cathode active material.

9. (1) A step of obtaining a composition for forming an anode active material by mixing an iron phosphate precursor, a manganese phosphate precursor, a lithium precursor, and a solvent; (2) A step of preparing a dried product by spray-drying the above-mentioned composition for forming an anode active material; and (3) A step comprising the step of producing an olivine structured positive active material containing pores by calcining the above-mentioned dried material, Method for manufacturing a lithium metal phosphate-based positive electrode active material according to claim 1.

10. In Paragraph 9, The above iron phosphate precursor and manganese phosphate precursor are, A mixture of iron phosphate precursors and manganese phosphate precursors, or an iron-manganese phosphate complex precursor, Method for manufacturing a lithium metal phosphate-based cathode active material.

11. In Paragraph 9, The above iron phosphate precursor and manganese phosphate precursor include an olivine structure, Method for manufacturing a lithium metal phosphate-based cathode active material.

12. In Paragraph 9, The above composition for forming a positive electrode active material further comprises, as a carbon source, one selected from the group consisting of sucrose, glucose, fructose, mannose, carbon black, acetylene black, and graphite. Method for manufacturing a lithium metal phosphate-based cathode active material.

13. In Paragraph 9, The step of obtaining the above-mentioned composition for forming a positive electrode active material comprises adding at least one compound containing at least one element selected from the group consisting of B, Y, Ca, V, Ni, Co, Mg, Nb, Mo, W, Ti, Sr, and Zn. Method for manufacturing a lithium metal phosphate-based cathode active material.

14. In Paragraph 9, The above positive active material is represented by the following chemical formula 1, Method for manufacturing lithium metal phosphate-based cathode active material: [Chemical Formula 1] Li 1+a Fe 1-x-y Mn x M y PO4 In the above chemical formula 1, M is at least one element selected from the group consisting of B, Y, Ca, V, Ni, Co, Mg, Nb, Mo, W, Ti, Sr, and Zn, and 0≤a≤0.05, 0<x<1, 0≤y<1, x+y<1.

15. In Paragraph 9, The firing of step (3) above is carried out at a temperature of 600 ℃ to 900 ℃, Method for manufacturing a lithium metal phosphate-based cathode active material.

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