Method for manufacturing single-particle positive electrode with controllable exposed surface for lithium ion secondary battery

Abstract

The present invention relates to a method for manufacturing a single-particle positive electrode with a controllable exposed surface for a lithium ion secondary battery. According to one embodiment, a single particle positive electrode with a controllable exposed surface for a lithium ion secondary battery can be provided comprising a layered oxide single particle structure, which is represented by chemical formula 1 and has exposed crystal facets consisting of {003} facet, {012} facet, {104} facet, or a combination thereof. [Chemical formula 1] Li(NixMnyCoz)O2 (where x+y+z=1)

Description

Method for manufacturing a single-particle cathode for a lithium-ion secondary battery with controllable exposure surface area

[0001] The present invention relates to a method for manufacturing a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure surface.

[0002] The most widely used cathode material in conventional lithium-ion batteries is a layered oxide, and among these, LiCoO2 cathode has been actively researched and commercially used for the past several decades due to its robust structure and relatively excellent performance.

[0003] However, due to the recent high price of cobalt (Co), the lithium battery industry is putting a lot of effort into finding other elements that can replace Co in this layered structure, and in particular, nickel (Ni) and manganese (Mn) are attracting attention as substitutes that can contribute to improving energy density and power density.

[0004] LiCo x Ni y Mn 1-x-y Layered oxide anodes with the chemical formula O2 can offer high energy density and improved voltage platforms. To enhance the reversible capacity and structural stability of these layered oxides, an appropriate ratio of Ni and Mn is essential. Mn contributes to structural stability, while Co reduces the disorder of Li / Ni, helping to form a well-crystallized layered structure.

[0005] In current technologies pursuing high energy density, safety, and long life, surface reconfiguration optimization has become an important research topic. Surface reactivity is a key factor in determining the lifespan and stability of batteries, and is very important until actual instability of the battery appears.

[0006] Therefore, LiCo x Ni y Mn 1-x-ySolving problems such as surface and interelectrode interactions of O2 anodes and capacity loss at high voltages are essential challenges in realizing practical high-energy batteries.

[0007] The various exposed surfaces and properties of cathode materials critically impact the performance of lithium-ion batteries, requiring a thorough understanding. The particle surface and orientation of layered cathodes are critical factors that directly influence the rate of lithium transport and the stability of surface phase transitions. In this regard, appropriate chemical composition, crystal structure, and particle morphology control play a key role in determining the overall performance of the battery.

[0008] A method for manufacturing a single particle positive electrode for a lithium ion secondary battery with controllable exposure area according to one embodiment of the present invention is proposed to solve the above problems, and LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 The aim is to propose a method to simultaneously improve the rapid movement of lithium ions and lattice stability by precisely controlling the exposed surface of O2 cathode materials, and to improve the reversible capacity and cycle stability of lithium ion batteries by minimizing the surface lithium loss and structural instability that may occur during high-voltage operation.

[0009] In addition, the present invention aims to develop a technology that can be effectively applied even in large-scale manufacturing processes by providing a new manufacturing technology that optimizes various interfacial structures of layered oxide anodes and thereby improves the energy density and safety of the entire battery system.

[0010] According to one embodiment, a single-particle positive electrode for a lithium ion secondary battery with controllable exposure surface area can be provided, which comprises a layered oxide single-particle structure represented by the following chemical formula 1 and having an exposed crystal facet formed of a {003} plane, a {012} plane, a {104} plane, or a combination thereof.

[0011] [Chemical Formula 1]

[0012] Li(Ni) x Mn y Co z )O2

[0013] (Here, x+y+z=1.)

[0014] In addition, the layered oxide single particle structure can provide a single particle positive electrode for a lithium ion secondary battery with controllable exposure area, having any one crystal shape selected from a plate shape, a polyhedral shape, and an octahedral shape.

[0015] In addition, a single-particle positive electrode for a lithium ion secondary battery with controllable exposure surface and crystal shape can be provided, in which the exposure surface and crystal shape are controlled according to a change in at least one chemical potential selected from among a lithium chemical potential and an oxygen chemical potential.

[0016] In addition, a single-particle positive electrode for a lithium ion secondary battery with controllable exposure area can be provided, wherein the change in the chemical potential is induced by the type of a metal salt including at least one salt selected from a lithium salt and a mixed salt, the content of the metal salt, or the sintering temperature, wherein the lithium salt is any one salt selected from LiCl, LiOH, Li2CO3, LiNO3, Li2SO4, and combinations thereof, and the mixed salt is any one salt selected from NaCl, KCl, and combinations thereof.

[0017] According to one embodiment, a method for manufacturing a single-particle positive electrode for a lithium ion secondary battery with controllable exposure surface can be provided, comprising the step of manufacturing a layered oxide single-particle structure having an exposed crystal facet formed by a {003} plane, a {012} plane, a {104} plane, or a combination thereof, represented by the following chemical formula 1.

[0018] [Chemical Formula 1]

[0019] Li(Ni)x Mn y Co z )O2

[0020] (Here, x+y+z=1.)

[0021] In addition, a method for manufacturing a single-particle positive electrode for a lithium ion secondary battery with controllable exposure area can be provided, which comprises a first step of preparing an oxalic acid precursor compound; and a second step of mixing the prepared oxalic acid precursor compound with a metal salt and then sintering the mixture to obtain a layered oxide single-particle structure.

[0022] In addition, a method for manufacturing a single-particle positive electrode for a lithium ion secondary battery having a controllable exposure area can be provided, the first step comprising: step 1-1 of preparing a precursor aqueous solution by dissolving a nickel source, a cobalt source, and a manganese source in a solvent; step 1-2 of preparing an oxalate aqueous solution by dissolving sodium oxalate and manganese oxalate in a solvent; step 1-3 of preparing a stirred solution by adding the prepared oxalate aqueous solution to the prepared precursor aqueous solution and stirring at a temperature of 40 to 60°C; step 1-4 of forming an oxalic acid precipitate through a precipitation process using micro-ultrasonic treatment of the prepared stirred solution; and step 1-5 of drying the formed oxalic acid precipitate to obtain an oxalic acid precursor compound.

[0023] In addition, in the step 1-1, the nickel source is Ni(CH3COO)2, NiCl2, NiI2, NiSO4, Ni(NO3)2, NiSO4·6H2O or a mixture thereof, the cobalt source is CoCl2, CoBr2, Co(CH3COO)2, CoSO4, Co(NO3)2, CoSO4·7H2O or a mixture thereof, and the manganese source is MnI2, MnSO4, Mn(NO3)2, Mn(CH3COO)2, MnSO4·H2O or a mixture thereof, and a method for manufacturing a single-particle positive electrode for a lithium ion secondary battery with controllable exposure area can be provided.

[0024] In addition, the above step 1-1 is a step of dissolving a nickel source, a cobalt source, and a manganese source in a solvent so that the molar ratio of nickel:cobalt:manganese satisfies 1 to 3:1:1, and a method for manufacturing a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure area can be provided.

[0025] In addition, in the above steps 1-3, a method for manufacturing a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure area can be provided, wherein the molar ratio of cobalt:manganese in the stirring solution satisfies the range of 1:1.1 to 1.4.

[0026] In addition, the second step may include an addition step of adding an excess amount of a metal salt to a prepared oxalic acid precursor compound to obtain a mixed composite; a preheating step of preliminarily heat-treating the obtained mixed composite at a heat treatment temperature of 400 to 600°C for 5 to 8 hours; a pulverizing step of cooling the preliminarily heat-treated mixed composite to room temperature and then pulverizing the cooled mixed composite; and a sintering step of heat-treating the pulverized mixed composite at a sintering temperature of 750 to 900°C for 10 to 28 hours; a method for manufacturing a single-particle positive electrode for a lithium ion secondary battery having a controllable exposure area may be provided.

[0027] In addition, in the above-described adding step, a method for manufacturing a single-particle positive electrode for a lithium ion secondary battery with controllable exposure area can be provided, wherein the metal salt includes at least one salt selected from a lithium salt and a mixed salt, the lithium salt is any one salt selected from LiCl, LiOH, Li2CO3, LiNO3, Li2SO4, and combinations thereof, and the mixed salt is any one salt selected from NaCl, KCl, and combinations thereof.

[0028] In addition, in the above-described adding step, if the metal salt includes a lithium salt, the lithium salt is added so as to satisfy a content range of 105 to 125 wt% relative to 100 wt% of the prepared oxalic acid precursor compound, and if the metal salt includes both a lithium salt and a mixed salt, the lithium salt is added so as to satisfy a content range of 105 to 125 wt% relative to 100 wt% of the prepared oxalic acid precursor compound, and the mixed salt is added so as to satisfy a content range of 200 to 400 wt% relative to 100 wt% of the prepared oxalic acid precursor compound, a method for manufacturing a single-particle positive electrode for a lithium ion secondary battery with controllable exposure area can be provided.

[0029] In addition, in the above-described adding step, if the metal salt includes a lithium salt, the lithium salt is any one salt selected from LiNO3, a combination of LiNO3 and LiCl, and LiCl, and if the lithium salt is a combination of LiNO3 and LiCl, the combination of LiNO3 and LiCl is composed of 10 to 90 wt% of LiNO3 and 90 to 10 wt% of LiCl, and a method for manufacturing a single-particle positive electrode for a lithium ion secondary battery with controllable exposure area can be provided.

[0030] In addition, in the above-described adding step, if the metal salt includes both a lithium salt and a mixed salt, the lithium salt is LiNO3, the mixed salt is any one salt selected from NaCl, a combination of NaCl and KCl, and KCl, and if the mixed salt is a combination of NaCl and KCl, the combination of NaCl and KCl is composed of 25 to 75 wt% of NaCl and 25 to 75 wt% of KCl, a method for manufacturing a single-particle positive electrode for a lithium ion secondary battery with controllable exposure area can be provided.

[0031] A method for manufacturing a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure surface according to one embodiment of the present invention has the effect of providing a new method for improving the lithium transfer speed and efficiency by precisely controlling the exposed surface of a layered oxide used as a positive electrode material for a lithium-ion battery.

[0032] In addition, the technology for controlling the exposed surface of the cathode material can significantly improve the electrochemical performance of the battery by enabling rapid and efficient movement of lithium ions, and in particular, by controlling various lithium salts and sintering conditions to create an optimal exposed surface, it has the effect of improving the charge capacity and discharge efficiency of the battery.

[0033] In addition, the present invention can increase the structural stability of the positive electrode and minimize structural damage that may occur during high-voltage operation, which has the effect of extending the life of the battery and maintaining stable performance even after long-term use.

[0034] In addition, the present invention can improve the cycle stability of a lithium-ion battery by ensuring uniform distribution and stable diffusion of lithium ions, thereby having the effect of minimizing performance degradation during repeated charging and discharging processes.

[0035] FIG. 1 is a drawing for briefly explaining a manufacturing process of a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure area according to one embodiment of the present invention.

[0036] Figure 2 is a drawing for explaining the change in crystal shape according to chemical potential.

[0037] Figure 3 is a drawing for explaining the deterioration of the exposed crystal surface due to an electrochemical reaction.

[0038] FIG. 4 is a flowchart illustrating a method for manufacturing a single-particle positive electrode for a lithium ion secondary battery with controllable exposure area according to one embodiment of the present invention.

[0039] FIG. 5 is a drawing showing the results of XRD analysis and TEM analysis of a layered oxide single particle structure according to one embodiment of the present invention.

[0040] Figure 6 is a drawing showing the ratio of exposed crystal faces according to the crystal shape of the layered oxide single particle structure of the present invention.

[0041] Figure 7 is a diagram showing a voltage curve in a charge / discharge experiment of a battery including a single-particle positive electrode of the present invention.

[0042] Figure 8 is a diagram showing cycle life characteristics in a charge / discharge experiment of a battery including a single-particle positive electrode of the present invention.

[0043] Figure 9 is a diagram showing the microstructure of a single-particle anode according to sample B of Example 2 before and after 100 cycles.

[0044] Figure 10 is a graph showing the transition metal oxidation state and surface chemical changes of the single-particle anode according to sample B of Example 2 before and after 100 cycles.

[0045] Figure 11 shows the results of evaluating the microstructure of a single-particle structure according to the sintering temperature.

[0046] Figure 12 shows the results of evaluating the crystal shape of single particles according to the content of mixed salt.

[0047] Figure 13 shows the results of evaluating the electrochemical performance of single particles according to the content of mixed salt.

[0048] In order to fully understand the configuration and effect of the present invention, a preferred embodiment of the present invention will be described in detail with reference to the attached drawings.

[0049] The present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and subject to various modifications and changes. However, the description of these embodiments is provided to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the present invention of the scope of the invention. In the attached drawings, components are illustrated in enlarged size for convenience of explanation, and the proportions of each component may be exaggerated or reduced.

[0050] The terminology used herein is for the purpose of describing embodiments and is not intended to limit the present invention. In addition, the terms used herein can be interpreted as having the meaning commonly known to those of ordinary skill in the art, unless otherwise defined. In this specification, the singular also includes the plural unless specifically stated in the phrase. As used herein, the words "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components, steps, operations, and / or elements mentioned.

[0051] When a layer is referred to herein as being "on" another layer, it may be formed directly on the surface of the other layer, or a third layer may be interposed therebetween. Although terms such as first, second, etc. are used herein to describe various regions, layers, etc., these regions and layers should not be limited by such terms. These terms are used merely to distinguish a given region or layer from another region or layer. Thus, a part referred to as a first part in one embodiment may be referred to as a second part in another embodiment. The embodiments described and illustrated herein also include complementary embodiments thereof. Parts denoted by the same reference numerals throughout the specification represent like elements.

[0052] The present invention relates to a layered positive electrode active material including cobalt (Co), nickel (Ni), and manganese (Mn), and more specifically, to a single-particle positive electrode for a lithium-ion secondary battery including a layered oxide single-particle structure having a specific exposed crystal facet by controlling the type of metal salt, the content of the metal salt, or controlling the sintering temperature.

[0053] Furthermore, the single particle cathode for a lithium ion secondary battery of the present invention is designed to increase the electrochemical performance of the cathode while ensuring long-term stability by controlling the exposed crystal surface to optimal conditions.

[0054]

[0055] Single-particle cathode for lithium-ion secondary batteries with controllable exposure area

[0056] FIG. 1 is a drawing for briefly explaining a manufacturing process of a single particle positive electrode for a lithium ion secondary battery with controllable exposure surface according to one embodiment of the present invention, FIG. 2 is a drawing for explaining a change in crystal shape according to chemical potential, and FIG. 3 is a drawing for explaining deterioration of an exposed crystal surface due to an electrochemical reaction.

[0057] A single-particle positive electrode for a lithium ion secondary battery with controllable exposure surface according to an embodiment of the present invention may include a layered oxide single-particle structure having an exposed crystal facet formed by a {003} plane, a {012} plane, a {104} plane, or a combination thereof, represented by the following chemical formula 1.

[0058] [Chemical Formula 1]

[0059] Li(Ni) x Mn y Co z )O2

[0060] Here, x+y+z=1.

[0061] The above layered oxide single particle structure is a positive electrode active material having a single particle shape, and is structurally different from a multi-particle (polycrystal) formed by agglomerating small particles. Due to this structural difference, the problem of cracks easily occurring between particles during the rolling process and charge / discharge process for forming the positive electrode active material into a certain thickness can be solved.

[0062] In addition, a single particle positive electrode for a lithium ion secondary battery with controllable exposure area according to one embodiment of the present invention comprises Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, and a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure area according to another embodiment of the present invention may include a layered oxide single-particle structure (NCM 111) represented by the chemical formula of Li(Ni 3 / 5 Mn 1 / 5 Co 1 / 5 ) may include a layered oxide single particle structure (NCM 622) represented by the chemical formula O2.

[0063] More specifically, in one embodiment of the present invention, the layered oxide single particle structure has any one crystal shape selected from a plate shape, a polyhedral shape, and an octahedral shape.

[0064] Additionally, in another embodiment of the present invention, the layered oxide single particle structure may have a polyhedral shape.

[0065] Here, the plate shape may be a shape in which the layered oxide single particle structure has {003} planes, {012} planes, and {104} planes as exposed crystal planes, and the area ratio of the {003} plane satisfies 50 to 70%.

[0066] In addition, the polyhedral shape may be a shape in which the layered oxide single particle structure has {003} plane, {012} plane, and {104} plane as exposed crystal planes, and the area ratio of the {012} plane satisfies 50 to 60%, and the area ratio of the {104} plane satisfies 10 to 20%.

[0067] In addition, the octahedral shape may be a shape in which the layered oxide single particle structure has {003} planes and {012} planes as exposed crystal planes, and the area ratio of the {012} plane satisfies 70 to 80%.

[0068] At this time, the layered oxide single particle structure may have an exposed crystal plane, which is a major crystal plane among the crystal planes forming the crystal on its surface, and the electrochemical performance of the anode may be increased by controlling the exposed crystal plane.

[0069] For example, the {003} plane of the layered oxide single particle structure may be a base plane that can increase the structural stability of the single particle, and the {012} plane and the {104} plane may be side planes (lateral planes) that can more easily allow movement of reactants (e.g., lithium ions), and such exposed crystal planes may have the effect of improving long-term stability, charge capacity, and discharge efficiency.

[0070] In addition, the {003} plane and {012} plane of the layered oxide single particle structure can be easily controlled by adjusting the chemical potential, and the {104} plane may be a plane that is less affected by the chemical potential, but has a tendency to decrease when the {003} plane increases and to increase when the {003} plane decreases.

[0071] Referring to FIG. 1, in the manufacturing process of a single particle positive electrode for a lithium ion secondary battery with controllable exposure area according to an embodiment of the present invention, first, [Ni 1 / 3 Mn 1 / 3 Co 1 / 3 ]Oxalic acid precursor compound (Metal precursor) represented by C2O4 or [Ni 3 / 5 Mn 1 / 5 Co 1 / 5 ]Oxalic acid precursor compound (Metal precursor) represented by C2O4 is synthesized through microwave and ultrasonic precipitation processes.

[0072] The precipitation process can take from 6 to 24 hours. If the reaction time is less than 6 hours, the oxalic acid precursor compound cannot grow into a satisfactory single particle and cannot achieve strong crystallinity. If the reaction time exceeds 24 hours, the oxalic acid precursor compound grows into very large secondary particles, failing to achieve a uniform metal distribution.

[0073] Additionally, the initial precipitation liquid used in the ultrasonic precipitation process may include pure water, a solution of pure water mixed with a certain amount of ethanol, or a solution of pure water mixed with ethylene.

[0074] To obtain an oxalic acid precursor compound with a uniform distribution of metal material, an excess of Mn oxalate of 10% to 35% on a molar basis is required.

[0075] Next, the oxalic acid precursor compound is mixed with a lithium salt including LiCl, LiOH, Li2CO3, LiNO3, Li2SO4 and combinations thereof in a predetermined excess amount (e.g., 105%, 110%, 120%).

[0076] Additionally, a mixed salt containing NaCl, KCl and combinations thereof may be additionally mixed in a preset excess amount (e.g., 400%) to the oxalic acid precursor compound.

[0077] The sintering process for the mixture is performed in a one-step or two-step procedure, with the two-step procedure including a pre-sintering step at 400°C to 600°C for 5 to 8 hours. The pre-sintered compound is then cooled to room temperature and ground again.

[0078] Both the one-step and two-step procedures involve sintering in a muffle oven for 10 to 28 hours in an air or oxygen atmosphere, and sintering can be performed at, but is not limited to, 800°C, 825°C, 850°C, 875°C and 900°C.

[0079] Figures 2a) and 2b) are diagrams showing changes in the exposed crystal plane and crystal shape according to the lithium chemical potential and the oxygen chemical potential.

[0080] Referring to FIG. 2, in the layered oxide single particle structure, the exposed crystal plane and the crystal shape can be controlled according to a change in at least one chemical potential selected from among lithium (Li) chemical potential and oxygen (O2) chemical potential.

[0081] Specifically, in the layered oxide single particle structure, the area ratio of the exposed crystal face can be determined according to the surface energy.

[0082] For example, among the above exposed crystal planes, the {003} plane tends to have lower surface energy as the lithium chemical potential decreases, and among the above exposed crystal planes, the {012} plane tends to have lower surface energy as the oxygen chemical potential increases.

[0083] That is, when the lithium chemical potential decreases, the {003} plane among the exposed crystal planes may increase, and when the oxygen chemical potential increases, the {012} plane among the exposed crystal planes may increase.

[0084] Accordingly, in the layered oxide single particle structure, the crystal shape can be controlled by increasing or decreasing a specific exposed crystal plane (area of ​​a specific exposed crystal plane).

[0085] More specifically, in the layered oxide single particle structure, the lithium chemical potential can control the crystal thickness. As the lithium chemical potential increases, the {003} plane (the area or area ratio of the {003} plane) decreases, and the crystal can gradually change from a plate shape to a block-shaped polyhedron. That is, an increase in the lithium chemical potential causes an increase in the crystal thickness.

[0086] In addition, in the layered oxide single particle structure, the oxygen chemical potential can control the orientation of crystal planes or the ratio of exposed planes. As the oxygen chemical potential increases, the {012} plane (the area or area ratio of the {012} plane) increases, and the crystal can gradually change from a block-shaped polyhedron to an octahedron. In other words, the increase in the oxygen chemical potential causes a change in the crystal side surface shape.

[0087] Furthermore, in the layered oxide single particle structure, the change in the chemical potential can be induced by the type of metal salt including at least one salt selected from among lithium salts and mixed salts, the content of the metal salt, or the sintering temperature.

[0088] Here, the lithium salt is any one salt selected from LiCl, LiOH, Li2CO3, LiNO3, Li2SO4 and combinations thereof, and the mixed salt is any one salt selected from NaCl, KCl and combinations thereof.

[0089] For example, in one embodiment of the present invention, an increase in the sintering temperature can induce an increase in the lithium chemical potential and a decrease in the oxygen chemical potential.

[0090] Accordingly, as the sintering temperature increases, it induces an increase in the lithium chemical potential and a decrease in the oxygen chemical potential, that is, the {003} plane (the area or area ratio of the {003} plane) decreases and the {012} plane (the area or area ratio of the {012} plane) decreases, so that the thickness of the crystal increases and it becomes easy to form a polyhedron.

[0091] Conversely, when the sintering temperature decreases, it induces a decrease in the lithium chemical potential and an increase in the oxygen chemical potential, that is, the {003} plane (the area or area ratio of the {003} plane) increases and the {012} plane (the area or area ratio of the {012} plane) increases, so that the thickness of the crystal decreases and it becomes easy to form a plate.

[0092] In addition, in one embodiment of the present invention, an increase in the content of LiNO3 or LiOH can induce a decrease in lithium chemical potential and a decrease in oxygen chemical potential.

[0093] Accordingly, when the content of LiNO3 or LiOH increases, it induces a decrease in the lithium chemical potential and a decrease in the oxygen chemical potential, that is, the {003} plane (the area or area ratio of the {003} plane) increases and the {012} plane (the area or area ratio of the {012} plane) decreases, so that the crystal approaches a polyhedral shape, and the side surfaces may be the {012} plane and the {104} plane.

[0094] In addition, in one embodiment of the present invention, an increase in the content of LiCl or Li2SO4 can induce an increase in the lithium chemical potential and an increase in the oxygen chemical potential.

[0095] Accordingly, when the content of LiCl or Li2SO4 increases, it induces an increase in the lithium chemical potential and an increase in the oxygen chemical potential, that is, the {003} plane (the area or area ratio of the {003} plane) decreases and the {012} plane (the area or area ratio of the {012} plane) increases, so that the crystal increases in thickness, approaches an octahedral shape, and the side surfaces may be the {012} plane and the {104} plane.

[0096] Additionally, in another embodiment of the present invention, an increase in the content of NaCl or KCl can induce a decrease in the lithium chemical potential.

[0097] Accordingly, when the content of NaCl or KCl increases, a decrease in the lithium chemical potential is induced, that is, the {003} plane (the area or area ratio of the {003} plane) increases, so that the crystal increases in thickness and can approach a polyhedral shape.

[0098] Referring to Fig. 3, in the layered oxide single particle structure, the deterioration process of the exposed crystal plane of the {012} plane due to the electrochemical reaction can be confirmed.

[0099] In the case of the {012} plane and the {104} plane, unlike the {003} plane which provides structural stability, these are exposed crystal planes where lithium ion movement is more active, and are side planes (lateral surfaces) required to secure a high ion diffusion coefficient and improve electrochemical performance.

[0100] However, unlike the {104} plane, the {012} plane causes cation mixing as excessive reduction reaction occurs due to excessive loss of lithium cations and oxygen anions.

[0101] Furthermore, due to the above-mentioned cation mixing phenomenon, a rock salt layer is formed on the {012} plane, and the rock salt layer blocks the movement of lithium ions, causing electrochemical deactivation, which leads to a serious capacity reduction.

[0102] Accordingly, in the single-particle positive electrode for a lithium-ion secondary battery capable of controlling the exposure surface according to one embodiment of the present invention, it is preferable that the layered oxide single-particle structure has a polyhedral crystal shape, and more specifically, it is preferable that the exposed crystal planes of the layered oxide single-particle structure are maximized for {003} planes and {104} planes and minimized for {012} planes by controlling the lithium chemical potential and the oxygen chemical potential.

[0103]

[0104] Method for manufacturing a single-particle cathode for a lithium-ion secondary battery with controllable exposure surface area

[0105] FIG. 4 is a flowchart illustrating a method for manufacturing a single-particle positive electrode for a lithium ion secondary battery with controllable exposure area according to one embodiment of the present invention.

[0106] Referring to FIG. 4, a method for manufacturing a single-particle positive electrode for a lithium ion secondary battery capable of controlling the exposure surface according to an embodiment of the present invention may include a step (S10) of manufacturing a layered oxide single-particle structure having an exposed crystal facet formed by a {003} plane, a {012} plane, a {104} plane, or a combination thereof, represented by the following chemical formula 1.

[0107] [Chemical Formula 1]

[0108] Li(Ni) x Mn y Co z )O2

[0109] Here, x+y+z=1.

[0110] More specifically, the step (S10) of manufacturing the layered oxide single particle structure includes a first step (S100) of preparing an oxalic acid precursor compound; and a second step (S200) of mixing the prepared oxalic acid precursor compound with a metal salt and then sintering the mixture to obtain a layered oxide single particle structure.

[0111] The above first step (S100) relates to a process for manufacturing an oxalic acid-based precursor, and includes a process of preparing a precursor aqueous solution by mixing a nickel source, a cobalt source, and a manganese source, adding an oxalate aqueous solution to the prepared precursor aqueous solution, and then obtaining a precipitate through an ultrasonic precipitation process.

[0112] Specifically, the first step (S100) includes steps 1-1 (S110), 1-2 (S120), 1-3 (S130), 1-4 (S140), and 1-5 (S150), wherein in the first step (S100), a nickel source, a cobalt source, and a manganese source are dissolved in a solvent to prepare a precursor aqueous solution.

[0113] First, in the step 1-1 (S110), the nickel source may be Ni(CH3COO)2, NiCl2, NiI2, NiSO4, Ni(NO3)2, NiSO4·6H2O or a mixture thereof, the cobalt source may be CoCl2, CoBr2, Co(CH3COO)2, CoSO4, Co(NO3)2, CoSO4·7H2O or a mixture thereof, and the manganese source may be MnI2, MnSO4, Mn(NO3)2, Mn(CH3COO)2, MnSO4·H2O or a mixture thereof.

[0114] In a preferred embodiment of the present invention, the nickel source is NiSO4·6H2O, the cobalt source is CoSO4·7H2O, and the manganese source is MnSO4·H2O.

[0115] In addition, the above step 1-1 (S110) may be a step of dissolving a nickel source, a cobalt source, and a manganese source in a solvent so that the molar ratio of nickel:cobalt:manganese satisfies 1 to 3:1:1.

[0116] Next, the above step 1-2 (S120) is a step of preparing an oxalate aqueous solution by dissolving sodium oxalate and manganese oxalate in a solvent.

[0117] Step 1-2 (S120) may be a step of preparing excess Mn seeds to obtain an oxalic acid precursor compound having a desired composition and a uniform composition.

[0118] Additionally, in the above step 1-2 (S120), the weight ratio of sodium oxalate and manganese oxalate dissolved in the solvent may be 1:0.05 to 1.5.

[0119] Next, the above steps 1-3 (S130) are steps for preparing a stirred solution by adding the prepared oxalate aqueous solution to the prepared precursor aqueous solution and stirring at a temperature of 40 to 60°C.

[0120] In the above steps 1-3 (S130), the molar ratio of cobalt:manganese in the stirring solution can satisfy the range of 1:1.1 to 1.4.

[0121] Next, the above steps 1-4 (S140) are steps for forming an oxalic acid precipitate by subjecting the prepared stirred solution to a precipitation process using micro-ultrasonic treatment.

[0122] In the above steps 1-4 (S140), the micro-sonic treatment can be performed for a reaction time of 6 to 24 hours. If the reaction time is less than 6 hours, the oxalic acid precipitate cannot grow into single particles and cannot have strong crystallinity, and if the reaction time exceeds 24 hours, the oxalic acid precipitate grows into coarse secondary particles, and there is a problem that it is difficult to obtain an oxalic acid precursor compound having a desired and uniform composition.

[0123] Next, steps 1-5 (S150) may be a step of drying the formed oxalic acid precipitate to obtain an oxalic acid precursor compound.

[0124] In steps 1-5 (S150), the drying process may be a process of washing the formed oxalic acid precipitate, placing the washed precipitate in a vacuum oven, and drying it at a temperature of 50 to 70°C for 20 to 30 hours.

[0125] The above second step (S200) relates to a process for manufacturing a layered oxide single particle structure having an exposed crystal surface, and includes a process of obtaining single particles through a sintering process after adding a metal salt to an oxalic acid precursor compound.

[0126] Specifically, the second step (S200) includes an addition step (S210), a preheating step (S220), a grinding step (S230), and a sintering step (S240). In the second step (S200), an oxalic acid precursor compound and a metal salt are mixed and then heat-treated to obtain a layered oxide single particle structure.

[0127] First, the addition step (S210) is a step of obtaining a mixed complex by adding an excess amount of a metal salt to the prepared oxalic acid precursor compound to satisfy a preset content range.

[0128] Here, the metal salt may include at least one salt selected from a lithium salt and a mixed salt.

[0129] Specifically, the lithium salt is any one salt selected from LiCl, LiOH, Li2CO3, LiNO3, Li2SO4, and combinations thereof, and the mixed salt is any one salt selected from NaCl, KCl, and combinations thereof.

[0130] In one embodiment of the present invention, when the metal salt includes a lithium salt, the lithium salt may be added so as to satisfy a content range of 105 to 125 wt% relative to 100 wt% of the prepared oxalic acid precursor compound.

[0131] In a preferred embodiment of the present invention, when the metal salt includes a lithium salt, the lithium salt may be any one salt selected from LiNO3, a combination of LiNO3 and LiCl, and LiCl.

[0132] In addition, when the lithium salt is a combination of LiNO3 and LiCl, the combination of LiNO3 and LiCl may be composed of 10 to 90 wt% of LiNO3 and 90 to 10 wt% of LiCl.

[0133] As described above, in one embodiment of the present invention, the type of lithium salt and the content of lithium salt can induce a change in at least one chemical potential selected from the lithium chemical potential and the oxygen chemical potential, which can determine the crystal shape of the layered oxide single particle structure.

[0134] For example, when a lithium salt is used as a metal salt in the addition step (S210) and the lithium salt is added to satisfy a content range of 120 wt%, and LiNO3 is added to a content of 120 wt%, the layered oxide single particle structure of the present invention can have a plate shape.

[0135] In addition, when the lithium salt is added to satisfy the content range of 120 wt%, and a combination of LiNO3 and LiCl is added to a content of 120 wt%, the layered oxide single particle structure of the present invention can have a polyhedral shape.

[0136] More specifically, when the lithium salt is a combination of LiNO3 and LiCl, LiNO3 may be added to satisfy a content range of 20 to 100 wt% relative to 100 wt% of the prepared oxalic acid precursor compound, and LiCl may be added to satisfy a content range of 20 to 100 wt% relative to 100 wt% of the prepared oxalic acid precursor compound.

[0137] In addition, when the lithium salt is added to satisfy the content range of 120 wt%, if LiCl is added to a content of 120 wt%, the layered oxide single particle structure of the present invention can have an octahedral shape.

[0138] In another embodiment of the present invention, when the metal salt includes both a lithium salt and a mixed salt, the lithium salt may be added to satisfy a content range of 105 to 125 wt% relative to 100 wt% of the prepared oxalic acid precursor compound, and the mixed salt may be added to satisfy a content range of 200 to 400 wt% relative to 100 wt% of the prepared oxalic acid precursor compound.

[0139] In a preferred embodiment of the present invention, when the metal salt includes both a lithium salt and a mixed salt, the lithium salt may be LiNO3, and the mixed salt may be any one salt selected from NaCl, a combination of NaCl and KCl, and KCl.

[0140] In addition, when the above mixed salt is a combination of NaCl and KCl, the combination of NaCl and KCl may be comprised of 25 to 75 wt% of NaCl and 25 to 75 wt% of KCl. It is preferable that the combination of NaCl and KCl be comprised of 50 wt% of NaCl and 50 wt% of KCl.

[0141] As described above, in another embodiment of the present invention, the type of mixed salt and the content of the mixed salt can induce a change in the lithium chemical potential, which can determine the crystal shape of the layered oxide single particle structure.

[0142] For example, when a mixed salt is used as a metal salt in the addition step (S210), and the mixed salt is added to satisfy a content range of 400 wt%, if a salt of a combination of NaCl and KCl is added in a content of 400 wt%, the layered oxide single particle structure of the present invention can have a polyhedral (poly) shape.

[0143] More specifically, when the mixed salt is a combination of NaCl and KCl, NaCl may be added to satisfy a content range of 100 to 300 wt% relative to 100 wt% of the prepared oxalic acid precursor compound, and KCl may be added to satisfy a content range of 100 to 300 wt% relative to 100 wt% of the prepared oxalic acid precursor compound.

[0144] Next, the preheating step (S220) is a step of preliminarily heat-treating the obtained mixed composite at a heat treatment temperature of 400 to 600°C for 5 to 8 hours, and the crushing step (S230) is a step of cooling the preliminarily heat-treated mixed composite to room temperature and then crushing the cooled mixed composite.

[0145] Next, the sintering step (S240) is a step in which the pulverized mixed composite is heat-treated at a sintering temperature of 750 to 900°C for 10 to 28 hours.

[0146] As described above, in one embodiment of the present invention, the sintering temperature can induce a change in at least one chemical potential selected from the lithium chemical potential and the oxygen chemical potential, which can determine the crystal shape of the layered oxide single-particle structure.

[0147] Specifically, as the sintering temperature increases, the crystal shape of the single particle may become closer to a polyhedral shape or may show a tendency for the thickness to increase. This is because an increase in the sintering temperature induces an increase in the lithium chemical potential and a decrease in the oxygen chemical potential, i.e., the {003} plane may decrease and the {012} plane may increase.

[0148] In addition, in one embodiment of the present invention, it is preferable that the sintering temperature satisfies the range of 800 to 900°C. If the sintering temperature is less than 800°C, it is difficult to form an exposed crystal face, and if the sintering temperature exceeds 900°C, a problem of the exposed crystal face disappearing may occur.

[0149] In addition, in another embodiment of the present invention, it is preferable that the sintering temperature satisfies the range of 800 to 825°C. If the sintering temperature is less than 800°C, it is difficult for an exposed crystal surface to be formed, and if the sintering temperature exceeds 825°C, the crystals become large and thick, which may cause problems such as the formation of abnormally large particles and the disappearance of the exposed crystal surface.

[0150]

[0151] Example 1: Preparation of layered oxide single particle structure 1

[0152] S100: First, a precursor aqueous solution was prepared by dissolving NiSO4·6H2O, a nickel source, CoSO4·7H2O, a cobalt source, and MnSO4·H2O, a manganese source, in 180 mL of deionized water as a solvent.

[0153] Here, nickel source, cobalt source, and manganese source were dissolved in deionized water so that the molar ratio of nickel:cobalt:manganese was 1:1:1.

[0154] Next, an oxalate aqueous solution was prepared by dissolving 1 g of sodium oxalate and 0.1 g of manganese oxalate in 90 mL of deionized water.

[0155] Afterwards, the prepared oxalate aqueous solution was added to the prepared precursor aqueous solution, and stirred at 40 rpm at a temperature of 50°C to prepare a stirred solution.

[0156] Here, the molar ratio of cobalt:manganese in the stirred solution was set to 1:1.25.

[0157] Next, the prepared stirred solution was subjected to a precipitation process using microsonic treatment for 6 hours to form an oxalic acid precipitate. Thereafter, the formed oxalic acid precipitate was washed, placed in a vacuum oven, and dried at 60°C for 24 hours to obtain an oxalic acid precursor compound.

[0158] At this time, the obtained oxalic acid precursor compound is [Ni 1 / 3 Mn 1 / 3 Co1 / 3 ]C2O4.

[0159] S200: A lithium salt selected from LiNO3, a combination of LiNO3 and LiCl, and LiCl was added to the prepared oxalic acid precursor compound in an amount ranging from 120 wt% to 100 wt% of the oxalic acid precursor compound, thereby obtaining a mixed composite.

[0160] Here, when a combination of LiNO3 and LiCl is added to the prepared oxalic acid precursor compound, LiNO3 is added so as to satisfy a content range of 80 wt% relative to 100 wt% of the oxalic acid precursor compound, and LiCl is added so as to satisfy a content range of 40 wt% relative to 100 wt% of the oxalic acid precursor compound.

[0161] Next, the obtained mixed composite was preheat-treated at a heat treatment temperature of 500°C for 5 hours, and the preheat-treated mixed composite was cooled to room temperature and then pulverized. Thereafter, the pulverized mixed composite was sintered in a muffle oven at 825°C for 20 hours to obtain a layered oxide single-particle structure.

[0162] At this time, the obtained layered oxide single particle structure is LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 It is O2 (Example 1).

[0163] The layered oxide single particle structure obtained by adding LiNO3 is sample A of Example 1, the layered oxide single particle structure obtained by adding a combination of LiNO3 and LiCl is sample B of Example 1, and the layered oxide single particle structure obtained by adding LiCl is sample C of Example 1.

[0164]

[0165] Example 2: Preparation of a single-particle cathode for a lithium-ion secondary battery with controllable exposure area 1

[0166] The layered oxide single particle structure according to Example 1, PVDF (binder), and Super P (electronic conductor) were mixed in a weight ratio of 80:13:7 to obtain a mixed powder, and an NMP solution was added to the obtained mixed powder to prepare an electrode slurry.

[0167] Thereafter, the manufactured electrode slurry was coated on AI foil with a thickness of 200 μm, and the coated AI foil was dried in a vacuum atmosphere at a temperature of 120°C for 8 hours to obtain a positive electrode (Example 2).

[0168] The positive electrode including sample A of Example 1 is sample A of Example 2, the positive electrode including sample B of Example 1 is sample B of Example 2, and the positive electrode including sample C of Example 1 is sample C of Example 2.

[0169]

[0170] Example 3: Preparation of layered oxide single particle structures 2

[0171] S100: In Example 1, dissolving the nickel source, cobalt source, and manganese source in deionized water so that the molar ratio of nickel:cobalt:manganese is 1:1:1 was replaced with dissolving the nickel source, cobalt source, and manganese source in deionized water so that the molar ratio of nickel:cobalt:manganese is 3:1:1, and the same procedure as in step S100 of Example 1 was performed to obtain an oxalic acid precursor compound.

[0172] At this time, the obtained oxalic acid precursor compound is [Ni 3 / 5 Mn 1 / 5 Co 1 / 5 ]C2O4.

[0173] S200: LiNO3 was added to the prepared oxalic acid precursor compound in an amount ranging from 120 wt% to 100 wt% of the oxalic acid precursor compound, and a mixed salt selected from among NaCl, a combination of NaCl and KCl, and KCl was added in an amount ranging from 400 wt% to 100 wt% of the oxalic acid precursor compound, thereby obtaining a mixed complex.

[0174] Here, when a combination of NaCl and KCl is added to the prepared oxalic acid precursor compound, NaCl is added so as to satisfy the content range of 100 to 300 wt%, and KCl is added so as to satisfy the content range of 100 to 300 wt%.

[0175] Next, the obtained mixed composite was preheat-treated at a heat treatment temperature of 500°C for 5 hours, and the preheat-treated mixed composite was cooled to room temperature and then pulverized. Thereafter, the pulverized mixed composite was sintered in a muffle oven at 750 to 900°C for 20 hours to obtain a layered oxide single-particle structure.

[0176] At this time, the obtained layered oxide single particle structure is LiCo 1 / 5 Ni 3 / 5 Mn 1 / 5 It is O2 (Example 3).

[0177] Here, the layered oxide single particle structure obtained by adding a combination of NaCl (200 wt%) and KCl (200 wt%) and sintering at 750°C is sample A of Example 3, the layered oxide single particle structure obtained by adding a combination of NaCl (200 wt%) and KCl (200 wt%) and sintering at 775°C is sample B of Example 3, the layered oxide single particle structure obtained by adding a combination of NaCl (200 wt%) and KCl (200 wt%) and sintering at 800°C is sample C of Example 3, and the layered oxide single particle structure obtained by adding a combination of NaCl (200 wt%) and KCl (200 wt%) and sintering at 825°C is sample D of Example 3, and the layered oxide single particle structure obtained by adding a combination of NaCl (200 wt%) and KCl (200 wt%) and sintering at 900°C is The oxide single particle structure is sample E of Example 3.

[0178] In addition, the layered oxide single particle structure obtained by adding KCl (400 wt%) and sintering at 800°C is sample F of Example 3, the layered oxide single particle structure obtained by adding a combination of NaCl (100 wt%) and KCl (300 wt%) and sintering at 800°C is sample G of Example 3, and the layered oxide single particle structure obtained by adding a combination of NaCl (300 wt%) and KCl (100 wt%) and sintering at 800°C is sample H of Example 3.

[0179]

[0180] Example 4: Preparation of a single-particle cathode for a lithium-ion secondary battery with controllable exposure area 2

[0181] The layered oxide single particle structure according to Example 3, PVDF (binder), and Super P (electronic conductor) were mixed in a weight ratio of 80:13:7 to obtain a mixed powder, and an NMP solution was added to the obtained mixed powder to prepare an electrode slurry.

[0182] Thereafter, the manufactured electrode slurry was coated on AI foil with a thickness of 200 μm, and the coated AI foil was dried in a vacuum atmosphere at a temperature of 120°C for 8 hours to obtain a positive electrode (Example 4).

[0183]

[0184] Experimental Example 1: Evaluation of the Microstructure of Single-Particle Structures

[0185] XRD analysis and TEM analysis of the layered oxide single particle structure according to Sample A to Sample B of Example 1 were performed, and the results are shown in FIGS. 5 and 6.

[0186] FIG. 5 is a drawing showing the results of XRD analysis and TEM analysis of a layered oxide single particle structure according to one embodiment of the present invention, and FIG. 6 is a drawing showing the ratio of exposed crystal faces according to the crystal shape of the layered oxide single particle structure of the present invention.

[0187] Fig. 5a) is an XRD analysis result according to crystal shape, Fig. 5b) is a TEM analysis result according to sample A of example 1, Fig. 5c) is a TEM analysis result according to sample B of example 1, and Fig. 5d) is a TEM analysis result according to sample C of example 1.

[0188] As illustrated in Fig. 5, by controlling the type of lithium salt, layered oxide single-particle structures having similar particle sizes and morphologically distinct properties were confirmed. As a result of X-ray diffraction analysis, it was confirmed that both samples A to B of Example 1 had a hexagonal a-NaFeO2 structure (R3m space group), confirming that they had a layered structure.

[0189] More specifically, when examining the crystal shapes of Samples A to C of Example 1, it can be confirmed that they each have a plate shape, a polyhedral shape, and an octahedral shape, and an exposed crystal facet consisting of a {003} plane, a {012} plane, a {104} plane, or a combination thereof was confirmed.

[0190] As shown in Fig. 6, the ratio of the exposed crystal surface of samples A to C of Example 1 was confirmed.

[0191] In the case of sample A of Example 1, it was confirmed that it had an exposed crystal plane consisting of {003}, {012}, and {104}, and that the {003} plane occupied the largest proportion, followed by the {012} plane and the {104} plane.

[0192] In the case of sample B of Example 1, it was confirmed that it had an exposed crystal plane consisting of {003}, {012}, and {104}, and that the {012} plane occupied the largest proportion, followed by the {003} plane and the {104} plane.

[0193] For sample C of Example 1, it was confirmed that it had an exposed crystal plane consisting of {003} and {012}, and that the {012} plane accounted for the largest proportion.

[0194]

[0195] Experimental Example 2: Electrochemical Performance Evaluation of a Battery Containing a Single-Particle Anode

[0196] After manufacturing a secondary battery cell using a single-particle positive electrode and a lithium metal electrode according to Sample A to Sample B of Example 2, the electrochemical performance of the cell was evaluated, and the results are shown in FIGS. 7 and 8.

[0197] The evaluation of electrochemical performance was performed by conducting a charge / discharge experiment at a constant current, and the range of 2.5 to 4.5 V was used during charge / discharge, and the current size was 100 mAh / g.

[0198] Additionally, the current density was increased to 0.1C, 0.2C, 0.5C, 1C, 2C, etc., and 5 cycles were performed for each.

[0199] Figure 7 is a diagram showing a voltage curve in a charge / discharge experiment of a battery including a single-particle positive electrode of the present invention.

[0200] Figures 7a) and 7b) are diagrams showing the voltage curve of the 1st cycle in the charge / discharge experiment, and Figures 7c) and 7d) are diagrams showing the voltage curve of the 20th cycle in the charge / discharge experiment.

[0201] As the number of cycles increased, the single particle anode (Octa) according to sample C of Example 2 experienced the most severe irreversible overpotential (~0.3 V), the single particle anode (Plate) according to sample A of Example 2 showed the least overpotential (~0.1 V), and the single particle anode (Poly) according to sample B of Example 2 showed an intermediate level of performance degradation between the two samples.

[0202] Figure 8 is a diagram showing cycle life characteristics in a charge / discharge experiment of a battery including a single-particle positive electrode of the present invention.

[0203] Fig. 8a) is a graph showing the results of a speed characteristic experiment, Fig. 8b) is a graph showing the capacity retention rate at 1C, Fig. 8c) is a graph showing a charging curve according to a constant current intermittent titration technique in the second cycle, and Fig. 8d) is a graph showing a charging curve according to a constant current intermittent titration technique in the second cycle.

[0204] As illustrated in Fig. 8, charge-discharge experiments were conducted to confirm the relationship between the electrochemical degradation of single-particle positive electrodes according to Samples A to C of Example 2 and the electrochemical properties and microstructure. It was confirmed that at a low current density of 0.1 C, the battery including the single-particle positive electrode (plate) according to Sample A of Example 2 had the highest capacity (192.3 mAh / g).

[0205] In addition, when the current density increased to 2C, the battery including the single-particle positive electrode (Poly) according to sample B of example 2 showed the highest capacity (137.5 mAh / g), whereas the battery including the single-particle positive electrode (Octa) according to sample C of example 2 showed the worst capacity retention and rate performance due to rapid deterioration of the {012} plane.

[0206] This is because the {003} plane has higher electrochemical stability than the {104} plane and the {012} plane, that is, it was confirmed that an increase in the {003} plane improves the capacity retention rate and discharge capacity.

[0207] In addition, it was confirmed that the battery including the single-particle positive electrode (Poly) according to sample B of Example 2 maintained the highest capacity during the initial cycling, and the battery including the single-particle positive electrode (plate) according to sample A of Example 2 showed the highest capacity retention rate after 100 cycles due to the highest proportion of {003} planes, which are the main exposed crystal planes.

[0208] The results of the constant current intermittent titration technique technology experiment confirmed that the high exposure of {012} and {104} planes helps promote Li ion transport even when degraded during cycling.

[0209] That is, it was confirmed that exposure of the {003} plane is effective in improving the cycle retention rate and discharge capacity, and at the same time, exposure of the {012} plane and the {104} plane is necessary to improve the diffusion rate of Li ions, and since the {012} plane causes rapid deterioration during cycling, it was confirmed that exposure of the {012} plane should be minimized while exposure of the {104} plane should be maximized.

[0210]

[0211] Experimental Example 3: Evaluation of the microstructure of a single-particle anode (poly) after 100 cycles.

[0212] In order to confirm the structural changes of the {012} plane and the {104} plane during the preceding cycling experiment, the microstructure of the single-particle anode (Poly) according to sample B of Example 2 after 100 cycling was evaluated using TEM and EELS, and the results are shown in FIGS. 9 and 10.

[0213] Figure 9 is a diagram showing the microstructure of a single-particle anode according to sample B of Example 2 before and after 100 cycles.

[0214] FIG. 9a), FIG. 9b), and FIG. 9c) are drawings showing the microstructure of the {012} plane and the {104} plane according to the sample before cycling, and FIG. 9d), FIG. 9e), and FIG. 9f) are drawings showing the microstructure of the {012} plane and the {104} plane according to the sample after cycling.

[0215] As shown in Fig. 9, the {012} plane and the {104} plane, which are the exposed crystal planes, can be identified, and it was confirmed that the crystal shape was well maintained even after 100 cycles.

[0216] Additionally, it was confirmed that the grid pattern was well maintained even after 100 cycles on the {104} surface.

[0217] However, on the {012} plane, a new lattice pattern can be observed after 100 cycles, and specifically, a typical {012} lattice pattern and a lattice pattern related to a phase transformation can be identified. This phase transformation progresses from a layered structure to a spinel structure and finally to a rock salt structure (space group Fm3m), and thus, it can be inferred that after cycling, some of the {012} planes have a rock salt phase or a spinel phase.

[0218] In other words, the {104} plane does not appear to impair the stability of the anode because only slight structural distortion occurs during cycling, rather than surface reconstruction or structural degradation. On the other hand, surface reconstruction of the {012} plane causes structural degradation, and specifically, it is confirmed that it induces an irreversible phase transformation from the spinel phase to the rock salt phase as an intermediate phase. Accordingly, exposure of the {012} plane is likely to deteriorate the cycling stability despite its advantage of increasing the Li diffusion rate.

[0219] Figure 10 is a graph showing the transition metal oxidation state and surface chemical changes of the single-particle anode according to sample B of Example 2 before and after 100 cycles.

[0220] FIG. 10a) is an oxygen K-edge EELS spectrum for the {104} plane in the single-particle anode according to sample B of Example 2 before and after 100 cycles, FIG. 10b) is an oxygen K-edge EELS spectrum for the {012} plane in the single-particle anode according to sample B of Example 2 before and after 100 cycles, FIG. 10c) is a manganese K-edge EELS spectrum for the {104} plane in the single-particle anode according to sample B of Example 2 before and after 100 cycles, and FIG. 10d) is a manganese K-edge EELS spectrum for the {012} plane in the single-particle anode according to sample B of Example 2 before and after 100 cycles.

[0221] As shown in Fig. 10, there are two groups of peaks in the O K-edge region of the EELS spectrum, one is indicated as a minor peak (530 eV, peak a) and the other is indicated as a main peak (540 eV, peak b). At this time, the minor peak can be an indicator of TM (transition metal) oxidation, and it can be confirmed that the minor peak on the {104} plane does not change much after 100 cycles, but the minor peak on the {012} plane decreases. This indicates that some TM cations are reduced on the {012} plane during cycling.

[0222] Furthermore, it can be confirmed that the decrease in Mn and the formation of the rock salt phase on the {012} plane after 100 cycles are significantly related to the reduction or migration of Mn. In particular, the decrease in Mn causes the loss of oxygen and lithium, creating vacancies, which can promote cation mixing. In other words, the promoted cation mixing promotes the formation of the rock salt layer on the {012} plane.

[0223]

[0224] Experimental Example 4: Evaluation of the microstructure of single-particle structures according to sintering temperature, type of mixed salt, and content of mixed salt.

[0225] Samples A to E of Example 3 were prepared, and the formation process of the exposed crystal surface according to the sintering temperature was evaluated, and the results are shown in Fig. 11.

[0226] In addition, samples F, G, C, and H of Example 3 were prepared, and the crystal shapes of single particles according to the content of the mixed salt were evaluated, and the results are shown in Fig. 12.

[0227] Figure 11 shows the results of evaluating the microstructure of a single-particle structure according to the sintering temperature.

[0228] As shown in Fig. 11, in the case of the single particle structure according to Example 3, it can be confirmed that an exposed crystal face is formed at a sintering temperature of 800°C, and it can be confirmed that the exposed crystal face disappears at a sintering temperature of 825°C or higher.

[0229] Figure 12 shows the results of evaluating the crystal shape of single particles according to the content of mixed salt.

[0230] As shown in Fig. 12, it was confirmed that the single particles according to Sample F, Sample G, Sample C, and Sample H of Example 3 had a polyhedral crystal shape.

[0231]

[0232] Experimental Example 5: Evaluation of the electrochemical performance of single-particle structures according to the content of mixed salt.

[0233] Samples G, C, and H of Example 3 were prepared, and the electrochemical performance of the single particles according to the content of the mixed salt was evaluated, and the results are shown in Fig. 13.

[0234] Figure 13 shows the results of evaluating the electrochemical performance of single particles according to the content of mixed salt.

[0235] As illustrated in FIG. 13, it was confirmed that the single particles according to Sample G, Sample C, and Sample H of Example 3 had a polyhedral crystal shape that exposed the {104} plane as much as possible, balanced the {003} plane, and minimized the {012} plane, thereby exhibiting excellent discharge capacity and excellent capacity retention.

[0236]

[0237] Although the method for manufacturing a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure surface according to the above embodiments of the present invention has been described as a specific embodiment, this is merely an example, and the present invention is not limited thereto, and should be construed as having the widest scope according to the basic idea disclosed in this specification. Those skilled in the art may implement embodiments not specified by combining or replacing the disclosed embodiments, but this also does not exceed the scope of the present invention. In addition, those skilled in the art may easily change or modify the disclosed embodiments based on this specification, and it is clear that such changes or modifications also fall within the scope of the present invention.

Claims

1. A layered oxide single particle structure represented by the following chemical formula 1, which comprises an exposed crystal facet consisting of a {003} plane, a {012} plane, a {104} plane, or a combination thereof. [Chemical Formula 1] Li (Ni x Mr y Co z )O2 (Here, x+y+z=1) Single-particle cathode for lithium-ion secondary batteries with controllable exposure area.

2. In paragraph 1, The above layered oxide single particle structure is, Having a crystal shape selected from among a plate shape, a polyhedral shape, and an octahedral shape, Single-particle cathode for lithium-ion secondary batteries with controllable exposure area.

3. In paragraph 2, The above exposure decision surface and the above decision shape are, controlled by a change in at least one chemical potential selected from the lithium chemical potential and the oxygen chemical potential; Single-particle cathode for lithium-ion secondary batteries with controllable exposure area.

4. In paragraph 3, The change in the above chemical potential is, A type of metal salt comprising at least one salt selected from lithium salts and mixed salts, induced by the content or sintering temperature of the metal salt, The lithium salt is any one salt selected from LiCl, LiOH, Li2CO3, LiNO3, Li2SO4 and combinations thereof, and the mixed salt is any one salt selected from NaCl, KCl and combinations thereof. Single-particle cathode for lithium-ion secondary batteries with controllable exposure area.

5. A step of manufacturing a layered oxide single particle structure having an exposed crystal facet formed by a {003} plane, a {012} plane, a {104} plane, or a combination thereof, represented by the following chemical formula 1; [Chemical Formula 1] Li (Ni x Mr y Co z )O2 (Here, x+y+z=1) A method for manufacturing a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure area.

6. In paragraph 5, The step of manufacturing the above layered oxide single particle structure is: Step 1: preparing an oxalic acid precursor compound; and A second step of mixing a prepared oxalic acid precursor compound and a metal salt and then sintering the mixture to obtain a layered oxide single particle structure; A method for manufacturing a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure area.

7. In paragraph 6, The above first step is, Step 1-1: preparing a precursor aqueous solution by dissolving a nickel source, a cobalt source, and a manganese source in a solvent; Step 1-2 of preparing an aqueous oxalate solution by dissolving sodium oxalate and manganese oxalate in a solvent; Steps 1-3: adding the prepared oxalate aqueous solution to the prepared precursor aqueous solution and stirring at a temperature of 40-60°C to prepare a stirred solution; Steps 1-4 of forming an oxalic acid precipitate through a precipitation process using micro-ultrasonic treatment of the prepared stirred solution; and Step 1-5 of drying the formed oxalic acid precipitate to obtain an oxalic acid precursor compound; A method for manufacturing a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure area.

8. In paragraph 7, In step 1-1 above, The above nickel source is, Ni(CH3COO)2, NiCl2, NiI2, NiSO4, Ni(NO3)2, NiSO4·6H2O or a mixture thereof, The above cobalt source is, CoCl2, CoBr2, Co(CH3COO)2, CoSO4, Co(NO3)2, CoSO4·7H2O or a mixture thereof, The above manganese source is, MnI2, MnSO4, Mn(NO3)2, Mn(CH3COO)2, MnSO4·H2O or a mixture thereof, A method for manufacturing a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure area.

9. In paragraph 8, Step 1-1 above is, A step of dissolving nickel source, cobalt source and manganese source in a solvent so that the molar ratio of nickel:cobalt:manganese satisfies 1 to 3:1:

1. A method for manufacturing a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure area.

10. In paragraph 9, In steps 1-3 above, The molar ratio of cobalt:manganese in the above stirring solution satisfies the range of 1:1.1 to 1.

4. A method for manufacturing a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure area.

11. In paragraph 10, The second step above is, An addition step of obtaining a mixed complex by adding an excess amount of a metal salt to a prepared oxalic acid precursor compound to satisfy a preset content range; A preheating step in which the obtained mixed composite is subjected to a preheat treatment at a heat treatment temperature of 400 to 600°C for 5 to 8 hours; A crushing step of crushing the cooled mixed composite after cooling the preheat-treated mixed composite to room temperature; and A sintering step comprising heat treating a pulverized mixed composite at a sintering temperature of 750 to 900°C for 10 to 28 hours; A method for manufacturing a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure area.

12. In paragraph 11, In the above addition step, The above metal salt comprises at least one salt selected from lithium salts and mixed salts, The lithium salt is any one salt selected from LiCl, LiOH, Li2CO3, LiNO3, Li2SO4 and combinations thereof, and the mixed salt is any one salt selected from NaCl, KCl and combinations thereof. A method for manufacturing a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure area.

13. In paragraph 12, In the above addition step, When the above metal salt includes a lithium salt, the lithium salt is added to satisfy a content range of 105 to 125 wt% relative to 100 wt% of the prepared oxalic acid precursor compound. When the above metal salt includes both a lithium salt and a mixed salt, the lithium salt is added to satisfy a content range of 105 to 125 wt% relative to 100 wt% of the prepared oxalic acid precursor compound, and the mixed salt is added to satisfy a content range of 200 to 400 wt% relative to 100 wt% of the prepared oxalic acid precursor compound. A method for manufacturing a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure area.

14. In paragraph 13, In the above addition step, When the metal salt comprises a lithium salt, the lithium salt is any one salt selected from LiNO3, a combination of LiNO3 and LiCl, and LiCl; When the above lithium salt is a combination of LiNO3 and LiCl, the combination of LiNO3 and LiCl is composed of 10 to 90 wt% of LiNO3 and 90 to 10 wt% of LiCl. A method for manufacturing a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure area.

15. In paragraph 14, In the above addition step, When the metal salt includes both a lithium salt and a mixed salt, the lithium salt is LiNO3, and the mixed salt is any one salt selected from NaCl, a combination of NaCl and KCl, and KCl, When the above mixed salt is a combination of NaCl and KCl, the combination of NaCl and KCl is composed of 25 to 75 wt% of NaCl and 25 to 75 wt% of KCl. A method for manufacturing a single-particle positive electrode for a lithium-ion secondary battery with controllable exposure area.

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