Positive electrode active material for lithium secondary battery and method for preparing same

Abstract

A positive electrode active material for a lithium secondary battery according to an exemplary embodiment includes a lithium metal oxide particle and a coating layer portion attached to a surface of the lithium metal oxide particle through a chemical bond. The coating portion includes a thiol group. The positive electrode active material for a lithium secondary battery according to an exemplary embodiment can suppress decomposition of an electrolyte and can improve life characteristics of a secondary battery.

Description

Technical Field

[0001] This invention relates to a positive electrode active material for lithium secondary batteries and a method for preparing the same. More specifically, it relates to a positive electrode active material for lithium secondary batteries comprising lithium metal oxide particles and a method for preparing the same. Background Technology

[0002] Rechargeable batteries are batteries that can be repeatedly charged and discharged. With the development of the information communication and display industries, rechargeable batteries are widely used as power sources for portable electronic communication devices such as portable cameras, mobile phones, and laptops. In addition, in recent years, battery packs including rechargeable batteries have been developed for use as power sources for environmentally friendly vehicles such as electric vehicles.

[0003] Secondary batteries can be categorized into, for example, lithium secondary batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among them, lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous for charging speed and lightweight design, so they are being actively developed and applied.

[0004] When all the materials constituting a secondary battery are solid, it can be called an all-solid battery. For example, an all-solid battery may include an electrode assembly comprising a positive electrode, a negative electrode, and an electrolyte. The electrolyte in an all-solid battery exists in solid form; as solid electrolytes, there are polymer-based solid electrolytes, oxide-based solid electrolytes, and sulfide-based solid electrolytes.

[0005] Solid electrolytes possess high energy density, physical stability, and long calendar life. However, side reactions may occur at the interface between the solid electrolyte and the positive or negative electrode. To suppress these side reactions, methods for coating the surfaces of the positive and negative electrodes and / or the active materials contained therein are being investigated and developed. However, problems such as uneven coating, precipitation of active materials, and high process costs still exist. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] One technical problem of the present invention is to provide a positive electrode active material for lithium secondary batteries that provides improved lifespan characteristics.

[0008] One technical problem of the present invention is to provide a lithium secondary battery with improved lifespan characteristics.

[0009] One technical problem of the present invention is to provide a method for preparing a positive electrode active material for lithium secondary batteries that provides improved lifespan characteristics.

[0010] (II) Technical Solution

[0011] According to an embodiment of the present invention, the positive electrode active material for a lithium secondary battery comprises lithium metal oxide particles and a coating portion, wherein the coating portion is attached to the surface of the lithium metal oxide particles by chemical bonds and comprises thiol groups.

[0012] According to an exemplary embodiment, the chemical bond may include an ester bond.

[0013] According to an exemplary embodiment, the coating portion may be derived from a thiol-based compound.

[0014] According to an exemplary embodiment, the thiol compound may contain one or more of thioglycolic acid, mercaptopropionic acid, mercaptobutyric acid, mercaptoundecanoic acid, mercaptosuccinic acid, and cysteine.

[0015] According to an exemplary embodiment, the thiol compound may comprise a thiol group at one end and a carboxyl group at the other end.

[0016] According to an exemplary embodiment, the thiol-based compound may comprise a compound represented by the following chemical formula 1.

[0017] [Chemical Formula 1]

[0018]

[0019] In the chemical formula 1, R 1 It is a straight-chain or branched alkylene group having 1 to 10 carbon atoms, or a straight-chain or branched alkenyl group having 2 to 10 carbon atoms.

[0020] According to an exemplary embodiment, the coating portion may further comprise a thiol-based compound containing a carboxyl group.

[0021] According to an exemplary embodiment, the thickness of the coating portion can be from 0.1 nm to 30 nm.

[0022] According to an exemplary embodiment, the lithium metal oxide particles may contain manganese, and the molar ratio of manganese among the metal elements other than lithium and oxygen may be 0.5 or more.

[0023] A lithium secondary battery according to an embodiment of the present invention includes: a positive electrode comprising a positive electrode active material for a lithium secondary battery according to the above embodiment; a negative electrode; and an all-solid-state electrolyte layer disposed between the positive electrode and the negative electrode.

[0024] According to an embodiment of the present invention, a method for preparing a positive electrode active material for a lithium secondary battery involves preparing a mixture of lithium metal oxide particles, a thiol compound containing a carboxyl group, and an acid. The mixture is then stirred.

[0025] According to an exemplary embodiment, the mixture may comprise lithium metal oxide particles with hydroxyl groups formed on their surface.

[0026] According to an exemplary embodiment, the content of the thiol-based compound can be from 0.1% by weight to 5.0% by weight of the total weight of the mixture.

[0027] According to an exemplary embodiment, the acid content can be from 0.01% by weight to 1.0% by weight of the total weight of the mixture.

[0028] According to an exemplary embodiment, the temperature of the step of stirring the mixture can be below 200°C.

[0029] (III) Beneficial Effects

[0030] The positive electrode active material according to an embodiment of the present invention can suppress the decomposition of the electrolyte. Therefore, the lifespan characteristics of the secondary battery can be improved.

[0031] In the method for preparing the positive electrode active material according to an embodiment of the present invention, a coating portion can be uniformly formed on the surface of the positive electrode active material, thereby achieving the effect of inhibiting the decomposition of the solid electrolyte. Furthermore, the method for preparing the positive electrode active material according to an embodiment of the present invention can form a uniform coating portion without additional processes such as high-temperature heat treatment or sputtering, thus improving process efficiency. Attached Figure Description

[0032] Figure 1 A schematic cross-sectional view of the positive electrode active material according to an exemplary embodiment is shown.

[0033] Figure 2 This is a schematic diagram illustrating an electrode assembly according to an exemplary embodiment.

[0034] Figure 3 This is a schematic diagram illustrating a lithium secondary battery according to an exemplary embodiment.

[0035] Figure 4 A graph showing the FT-IR analysis results of the positive electrode active materials according to Example 1 and Comparative Example 1.

[0036] Figure 5a and Figure 5b The figures shown are TEM images and EDS analysis images according to Example 1.

[0037] Figure 6a and Figure 6b The figures show the TEM image and EDS analysis image based on Comparative Example 1, respectively.

[0038] Figure 7a and Figure 7b The figures shown are the TEM image and the EDS analysis image based on Comparative Example 2, respectively.

[0039] Figure 8a and Figure 8b The figures show the TEM image and EDS analysis image based on Comparative Example 3, respectively.

[0040] Figure 9a and Figure 9b The figures show the TEM image and EDS analysis image based on Comparative Example 4, respectively.

[0041] Figure 10a and Figure 10b The figures shown are the TEM image and the EDS analysis image based on Comparative Example 5, respectively. Detailed Implementation

[0042] Embodiments of the present invention provide a positive electrode active material for lithium secondary batteries (hereinafter, simply referred to as "positive electrode active material"), the positive electrode active material for lithium secondary batteries comprising lithium metal oxide particles and a coating portion, the coating portion being formed on the surface of the lithium metal oxide particles and comprising thiol groups. Furthermore, a positive electrode for lithium secondary batteries (hereinafter, simply referred to as "positive electrode") comprising the positive electrode active material for lithium secondary batteries is provided. Furthermore, a lithium secondary battery (hereinafter, simply referred to as "secondary battery") comprising the positive electrode is provided. Furthermore, a method for preparing the positive electrode active material for lithium secondary batteries is provided.

[0043] The accompanying drawings and embodiments in this specification serve to further understand the technical ideas disclosed herein, and therefore should not be construed as limiting the technical ideas of the invention to the contents described in these drawings and embodiments.

[0044] Figure 1 A schematic diagram illustrating a positive electrode active material according to an exemplary embodiment.

[0045] Reference Figure 1 The positive electrode active material includes lithium metal oxide particles 100 and a coating portion 110 formed on the lithium metal oxide particles 100.

[0046] The positive electrode active material may contain compounds that enable reversible insertion and extraction of lithium ions.

[0047] According to an exemplary embodiment, the lithium metal oxide particles 100 may comprise lithium nickel metal oxide. The lithium nickel metal oxide may further comprise at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0048] In some embodiments, the lithium metal oxide particles 100 may include a layered or crystalline structure of a compound represented by the following chemical formula 2.

[0049] [Chemical Formula 2]

[0050] Li x Ni a M b O 2+z

[0051] In chemical formula 2, the values ​​can be 0.9≤x≤1.2, 0.01≤a≤0.99, 0.01≤b≤0.99, and -0.5≤z≤0.1. As mentioned above, M can contain Co, Mn, and / or Al.

[0052] The chemical structure represented by Formula 2 indicates the bonding relationships contained in the layered or crystalline structure of the lithium metal oxide particles 100, and does not exclude other additional elements. For example, M may contain Co and / or Mn, and Co and Mn may be provided together with Ni as the main active element of the positive electrode active material. Formula 2 is provided to represent the bonding relationships of the main active elements, and it should be understood that Formula 2 includes the introduction and substitution of additional elements.

[0053] In one embodiment, in addition to the primary active element, auxiliary elements may be included to enhance the chemical stability of the positive electrode active material or the layered / crystal structure. These auxiliary elements may be incorporated into the layered / crystal structure and form bonds; this should be understood to also include the chemical structures represented by Formula 2.

[0054] The auxiliary element may include at least one of, for example, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. The auxiliary element may function as an auxiliary active element, together with Co or Mn, to contribute to the capacity and rate performance characteristics of the positive electrode active material; for example, Al.

[0055] For example, the lithium nickel metal oxide may include a layered or crystalline structure of a compound represented by the following chemical formula 2-1.

[0056] [Chemical Formula 2-1]

[0057] Li x Ni a M1 b1 M2 b2 O 2+z

[0058] In chemical formula 2-1, M1 may contain Co, Mn, and / or Al. M2 may contain the aforementioned auxiliary elements. In chemical formula 2-1, the values ​​can be 0.9≤x≤1.2, 0.01≤a≤0.99, 0.01≤b1+b2≤0.99, and -0.5≤z≤0.1.

[0059] The lithium metal oxide particles 100 may further comprise coating elements or doping elements. For example, elements substantially the same as or similar to the auxiliary elements described above may be used as coating elements or doping elements. For example, one of the elements described above or a combination of two or more of the elements described above may be used as coating elements or doping elements.

[0060] The coating element or doping element may exist on the surface of the lithium metal oxide particles 100, or may penetrate through the surface of the lithium metal oxide particles 100 and be included in the bonding structure represented by chemical formula 2 or chemical formula 2-1.

[0061] The lithium metal oxide particles 100 may contain nickel-cobalt-manganese (NCM) based lithium oxide.

[0062] Nickel (Ni) can be provided as a transition metal relevant to the capacity of lithium secondary batteries. When a positive electrode active material containing a high nickel content is used, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0063] According to an exemplary embodiment, the lithium metal oxide particles 100 can maintain conductivity by including cobalt (Co), and can further improve lifetime stability and capacity retention characteristics by including manganese (Mn).

[0064] According to an exemplary embodiment, the positive electrode active material may also include lithium cobalt oxide-based active material, lithium manganese oxide-based active material, lithium nickel oxide-based active material, or lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0065] According to an exemplary embodiment, the positive electrode active material may include one or more of a Mn-rich based active material, a Li rich layered oxide (LLO) / Over Lithiated Oxide (OLO) based active material, and a Co-less based active material.

[0066] For example, the positive electrode active material may include a compound represented by Chemical Formula 3 below.

[0067] [Chemical Formula 3]

[0068] p[Li2MnO3]·(1-p)[Li q JO2]

[0069] In Chemical Formula 3, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J may include at least one element selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0070] According to an exemplary embodiment, the lithium metal oxide particle 100 may include an Over Lithiated Oxide (OLO) based active material. For example, in the lithium metal oxide particle 100, the molar ratio of lithium among the metal elements other than oxygen may exceed 1.

[0071] According to an exemplary embodiment, the lithium metal oxide particle 100 may include an over-lithiated nickel-cobalt-manganese (NCM) based lithium oxide. For example, the lithium metal oxide particle 100 may include an NCM based lithium oxide having a molar ratio of lithium among the metal elements other than oxygen of 1.1 or more.

[0072] In some embodiments, the molar fraction of manganese in the over-lithiated NCM based lithium oxide (e.g., the number of moles of manganese in the total number of moles of nickel, cobalt, and manganese) may be 0.5 or more, 0.55 or more, 0.6 or more, or 0.65 or more.

[0073] In some embodiments, the molar fraction of manganese in the over-lithiated NCM based lithium oxide may be from 0.5 to 0.9, from 0.55 to 0.85, from 0.57 to 0.82, from 0.60 to 0.80, or from 0.65 to 0.75.

[0074] Within the above range, the coating portion 110 containing a thiol group may be uniformly formed on the lithium metal oxide particle 100.

[0075] In some embodiments, the molar fraction of nickel in the over-lithiated NCM based lithium oxide may be from 0.05 to 0.25, from 0.07 to 0.22, from 0.09 to 0.2, from 0.1 to 0.2, or from 0.12 to 0.18.

[0076] In some embodiments, the molar fraction of cobalt in the overlithiated NCM-based lithium oxide can be 0.05 to 0.25, 0.07 to 0.22, 0.09 to 0.2, 0.1 to 0.2, or 0.12 to 0.18.

[0077] Within the aforementioned range, stability can be improved while maintaining high capacity and conductivity.

[0078] According to an exemplary embodiment, the lithium metal oxide particles 100 may include a secondary particle structure comprising a plurality of primary particles.

[0079] For example, the secondary particle can refer to a particle in which multiple primary particles aggregate but are essentially regarded or observed as a single particle. For instance, in the case of the secondary particle, the boundary of the primary particle can be observed in a SEM cross-sectional image.

[0080] For example, the secondary particles may be composed of more than 10, 30, 50, or 100 primary particles aggregated together.

[0081] For example, the term "secondary particle" can be used in a sense that it differs from a single-particle structure. For instance, in the case of a single particle, unlike the secondary particle, the boundary of the primary particle may not be observable in the SEM cross-sectional image.

[0082] Lithium metal oxide particles 100 with a secondary particle structure can provide high energy density and high power characteristics.

[0083] In some implementations, the surface of the lithium metal oxide particles 100 may also contain hydroxyl groups.

[0084] For example, it may contain a portion of hydroxyl groups that did not react with the thiol-based compounds described below during the formation of the coating portion 110.

[0085] The coating portion 110 can be attached to the surface of lithium metal oxide particles by chemical bonds. In addition, the coating portion 110 may contain thiol groups.

[0086] According to an exemplary embodiment, the lithium metal oxide particles 100 and the coating portion 110 can be chemically bonded by ester bonds.

[0087] For example, the linker of the lithium metal oxide particles 100 and the coating portion 110 may include a chemical structure containing ester bonds. For example, the linker may include a chemical structure represented by -RC(O)O- (e.g., R is a substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms).

[0088] According to an exemplary embodiment, thiol groups may be distributed on the surface of the coating portion 110.

[0089] For example, the connection base may include -R a -C(O)OR b -(For example, R) a and R b Each of the following chemical structures represents a hydrocarbon group (each consisting of substituted or unsubstituted carbon atoms, having a number of 1 to 20 hydrocarbon groups). In the chemical structure, R a R is positioned along the direction toward the lithium metal oxide particles 100. b By being arranged in an outward direction, and by combining with thiol groups, thiol groups can be distributed on the surface of the coating portion 110.

[0090] For example, the coating portion 110, within 50% of its thickness in a straight line from the outermost edge toward the center of the lithium metal oxide particles 100, may contain more than 60% thiol groups.

[0091] The thiol groups on the surface of the coating 110 can form SS bonds with the sulfur present in the electrolyte, thereby maintaining a uniform contact state. Furthermore, it can suppress oxygen generation, thus improving lifespan characteristics under high temperature and high voltage conditions.

[0092] For example, the high voltage can refer to a voltage of 4.4V or higher. Alternatively, the high voltage can refer to a voltage of 4.5V or higher, or 4.6V or higher.

[0093] According to an exemplary embodiment, the coating portion 110 may be derived from a thiol-based compound.

[0094] The thiol-based compound can refer to a compound containing a thiol group (-SH). The thiol-based compound can include all isomers having the same elements but different chemical structures.

[0095] For example, the thiol compounds may include alkyl thiols such as methanethiol, ethanethiol, 1-propanethiol, 2-propanethiol, 1-butanethiol, 2-butanethiol, and pentanethiol; olefin thiols such as propene-1-thiol, butene-1-thiol, and pentenene-4-thiol; alkynyl thiols such as propyne-1-thiol and butyne-1-thiol; and mercaptopropylamine. The list includes amine, benzenenethiol, benzenedithiool, 2-methylbenzenethiol, 2-ethylbenzenethiol, 4-methoxybenzenethiol, naphthalenethiol, mercaptobenzoic acid, cyclopentanethiol, mercaptobenzothiazole, mercaptopurine, mercaptoindole, thioacetic acid, thiosalicylic acid, glutathione, and cysteine.

[0096] According to an exemplary embodiment, the thiol-based compound may contain a carboxyl group.

[0097] For example, the thiol-based compounds may include thioglycolic acid, thiopropionic acid, thiobutyric acid, thioundecanoic acid and other thioalkyl acids, as well as organic acids containing thiol groups such as thiosuccinic acid and thiolactic acid.

[0098] The coating portion 110 can be uniformly formed by the reaction of the carboxyl group of the thiol-based compound with the hydroxyl group on the surface of the lithium metal oxide particles 100. Ester bonds can be formed through the dehydration condensation reaction of the hydroxyl and carboxyl groups. Therefore, the coating portion 110 can exist in a stable state, thereby improving the chemical and mechanical stability of the secondary battery.

[0099] For example, the thiol-based compound contains thiol groups and carboxyl groups, and the carboxyl groups combine with the hydroxyl groups on the surface of the lithium metal oxide particles 100, thereby allowing unreacted thiol groups to be distributed on the surface side of the coating portion 110.

[0100] According to an exemplary embodiment, the thiol-based compound may comprise one or more of mercaptoacetic acid, mercaptopropionic acid, mercaptobutyric acid, mercaptoundecanoic acid, mercaptosuccinic acid, and cysteine.

[0101] In some embodiments, the thiol compound may comprise one or more of mercaptoacetic acid, mercaptopropionic acid, and mercaptoundecanoic acid.

[0102] According to an exemplary embodiment, the thiol-based compound may comprise a terminal thiol group and a terminal carboxyl group. For example, the thiol-based compound may include more than one alkylene group between the thiol group and the carboxyl group.

[0103] By using a thiol-based compound with the above-described structure, the thickness of the coating portion 110 can be greater than a predetermined range. Therefore, the effect of inhibiting electrolyte decomposition can be further improved.

[0104] In some embodiments, the thiol compound may comprise a thiol group at one end, a carboxyl group at another end, and an alkylene group between the two ends.

[0105] The alkylene group may include substituted or unsubstituted alkylene groups having 1 to 10 carbon atoms, substituted or unsubstituted alkenylene groups having 2 to 10 carbon atoms, and / or substituted or unsubstituted alkynylene groups having 2 to 10 carbon atoms.

[0106] The alkylene, alkenylene, and ynylene groups may each include straight-chain or branched structures.

[0107] When a portion of the alkylene, alkenylene, and alkynylene groups is substituted, it may be replaced by an amino group, hydroxyl group, carboxyl group, halogen group, and / or alkoxy group.

[0108] For example, mercaptoacetic acid can be understood as comprising a thiol group at one end, a carboxyl group at the other end, and a methylene group between the thiol group and the carboxyl group.

[0109] For example, cysteine ​​can be understood as comprising a thiol group at one end, a carboxyl group at the other end, and an ethylene group between the thiol group and the carboxyl group, wherein a portion of the ethylene group is substituted with an amino group.

[0110] According to an exemplary embodiment, the thiol-based compound may comprise a compound represented by the following chemical formula 1.

[0111] [Chemical Formula 1]

[0112]

[0113] In chemical formula 1, R 1 It is a straight-chain or branched alkylene group having 1 to 10 carbon atoms, or a straight-chain or branched alkenyl group having 2 to 10 carbon atoms.

[0114] In some implementation schemes, R 1 It can be a straight-chain alkylene group having 1 to 10 carbon atoms. In some embodiments, R 1 It can be a straight-chain alkylene group with 1 to 5 carbon atoms.

[0115] The thiol-based compound containing the above-mentioned compound can suppress excessive increase in the thickness of the coating portion 110. Therefore, the increase in the volume of the secondary battery can be suppressed, thereby improving the energy density.

[0116] In some embodiments, the thiol-based compound may comprise monomers of polymers containing thiol groups and hydroxyl groups.

[0117] In some embodiments, the coating portion 110 may comprise a polymer containing thiol groups.

[0118] For example, the thiol-based compound can be polymerized to form a coating portion 110 in polymer form by polymerization of a monomer containing a thiol as a side chain. For example, a coating portion 110 containing a thiol group can be formed by introducing a portion of the thiol-based compound during polymerization of a monomer that does not contain a thiol.

[0119] In one embodiment, the coating portion 110 may further comprise a thiol compound containing a carboxyl group. For example, unreacted thiol compounds may be included in the coating portion 110 during the formation of the positive electrode active material.

[0120] According to an exemplary embodiment, the thickness of the coating portion 110 can be 0.1 nm or more. In some embodiments, the thickness of the coating portion 110 can be 0.1 nm or more, 0.2 nm or more, 0.5 nm or more, 0.8 nm or more, 1.0 nm or more, or 1.5 nm or more.

[0121] According to an exemplary embodiment, the thickness of the coating portion 110 can be less than 30 nm. In some embodiments, the thickness of the coating portion 110 can be less than 30 nm, less than 28 nm, less than 26 nm, less than 25 nm, less than 23 nm, less than 21 nm, or less than 20 nm.

[0122] For example, the thickness of the coating portion 110 can be 0.1 nm to 30 nm, 0.2 nm to 28 nm, 0.5 nm to 25 nm, 0.8 nm to 25 nm, 1.0 nm to 21 nm, or 1.5 nm to 20 nm.

[0123] Within the aforementioned range, the reduction in interfacial properties due to physical contact between the positive electrode active material and the electrolyte can be suppressed. Furthermore, the increase in resistance due to the decomposition of the coating portion 110 can be suppressed.

[0124] According to an exemplary embodiment, the positive electrode active material can be provided as a positive electrode active material for all-solid-state batteries.

[0125] In this specification, "all-solid-state battery" can refer to a battery that does not use a liquid electrolyte. The liquid electrolyte can refer to an electrolyte that is in a liquid phase at room temperature, for example, an electrolyte containing lithium salts (LiPF6, LiClO4, LiBF3, etc.) in an organic solvent such as dimethyl carbonate or diethyl carbonate.

[0126] The electrolyte of the all-solid-state battery may include gel polymer electrolytes, polymer solid electrolytes, and inorganic solid electrolytes, excluding organic liquid electrolytes and ionic liquid electrolytes.

[0127] The coating portion 110 of the positive electrode active material can maintain uniform contact with the solid electrolyte of the all-solid-state battery at the interface. For example, the sulfide-based solid electrolyte and the thiol groups of the coating portion 110 can maintain uniform contact through SS bonds. Therefore, the decomposition of the solid electrolyte can be suppressed, thereby improving the life characteristics of the secondary battery.

[0128] Figure 2 This is a schematic diagram illustrating an electrode assembly according to an exemplary embodiment.

[0129] Reference Figure 2 The electrode assembly may include a positive electrode 200 containing the above-mentioned positive electrode active material, a negative electrode 230, and an electrolyte layer 240 between the positive electrode 200 and the negative electrode 230.

[0130] The positive electrode 200 may contain the aforementioned positive electrode active material. For example, the positive electrode 200 may be a composite positive electrode containing conductive materials, solid electrolytes, etc. For example, the positive electrode 200 may optionally further contain binders, thickeners, etc.

[0131] For example, it can be used in the form of a composite positive electrode or positive electrode active material formed by pressurizing a mixture of the above-mentioned positive electrode active material and solid electrolyte.

[0132] The pressurization can be performed by flat plate pressurization in the form of uniaxial pressing or isostatic pressing in the form of triaxial pressing.

[0133] In one embodiment, the pressurization can be an isostatic pressing process, for example, the pressurization can be performed by warm isostatic pressing (WIP), cold isostatic pressing (CIP), or roll pressing. The pressurization can be performed by cold isostatic pressing (CIP), which, compared to flat plate pressing, applies stress uniformly in all directions, thereby suppressing bending of the composite cathode.

[0134] In one embodiment, the pressurization can be performed at a pressure of 200 MPa to 800 MPa for 10 seconds to 1 minute. Within this range, a composite positive electrode (particles with a density of 75% or more) with high adhesion between the positive electrode active material and the solid electrolyte can be formed.

[0135] The conductive material can be added to enhance the conductivity of the positive electrode and / or the mobility of lithium ions or electrons. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), and carbon fibers, and / or metal-based conductive materials including perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3. In one embodiment, a carbon-based conductive material may be used as the conductive material.

[0136] The adhesive may include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) copolymer, polyacrylonitrile, polymethyl methacrylate, nitrile rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, a PTFE-based adhesive may be used as the positive electrode adhesive.

[0137] Carboxymethyl cellulose (CMC) can be used as a thickener, for example.

[0138] Positive electrode 200 is a composite positive electrode, which may include a positive electrode current collector.

[0139] The positive current collector may include, for example, stainless steel, nickel, aluminum, titanium, copper or alloys thereof, preferably aluminum or aluminum alloys.

[0140] The negative electrode 230 can be used as a composite negative electrode or a negative electrode active material formed by pressurizing a mixture of negative electrode active material and solid electrolyte. Under pressurization, it can be carried out by flat plate pressing in the uniaxial pressing form or isostatic pressing in the triaxial pressing form described above.

[0141] The negative electrode active material can be any negative electrode active material known in the art that can absorb and release lithium ions, without particular restriction.

[0142] For example, the negative electrode active material can be carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers, lithium alloys, silicon, or tin.

[0143] Examples of amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB) calcined below 1500°C, and mesophase pitch-based carbon fiber (MPCF).

[0144] Examples of crystalline carbon include natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and other graphite-based carbons.

[0145] Lithium metal can be categorized as pure lithium metal or lithium metal with a protective layer formed to inhibit dendrite growth, etc.

[0146] Elements included in the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0147] The negative electrode 230 is a composite negative electrode and may include a negative electrode current collector.

[0148] The negative electrode current collector may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, preferably copper or copper alloys.

[0149] The electrolyte layer 240 may contain a solid electrolyte. The electrolyte layer 240 acts as a separator, preventing short circuits between the positive electrode 200 and the negative electrode 230, and maintaining ion flow. In this case, the secondary battery can be manufactured as an all-solid-state battery.

[0150] The solid electrolyte may include a sulfide-based electrolyte. As a non-limiting example, the sulfide-based electrolyte may include Li₂S-P₂S₅, Li₂S-P₂S₅-LiCl, Li₂S-P₂S₅-LiBr, Li₂S-P₂S₅-LiCl-LiBr, Li₂S-P₂S₅-Li₂O, Li₂S-P₂S₅-Li₂O-LiI, Li₂S-SiS₂, Li₂S-SiS₂-LiI, Li₂S-SiS₂-LiBr, Li₂S-SiS₂-LiCl, Li₂S-SiS₂-B₂S₃-LiI, Li₂S-SiS₂-P₂S₅-LiI, Li₂S-B₂S₃, and Li₂S-P₂S₅-Z. m S n (m and n are positive numbers, Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are positive numbers, M is P, Si, Ge, B, Al, Ga, or In), Li 7-x PS 6-x Cl x (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2), Li 7-x PS 6-x I x (0≤x≤2), etc. These can be used individually or in combination of two or more.

[0151] In one embodiment, the solid electrolyte may also include oxide-based amorphous solid electrolytes such as Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, and Li2O-B2O3-ZnO.

[0152] In some embodiments, the solid electrolyte contained in the positive electrode 200, the negative electrode 230, and the electrolyte layer 240 may include a sulfide-based electrolyte.

[0153] The sulfide-based electrolyte can maintain a uniform contact area with the coating portion 110 of the positive electrode active material through SS bonds. Furthermore, it can suppress the decomposition of the solid electrolyte, thereby improving battery life characteristics under high-temperature conditions.

[0154] Figure 3 This is a schematic diagram illustrating a lithium secondary battery according to an exemplary embodiment.

[0155] Reference Figure 3The electrode assembly 250 can be housed within the housing 260. Tabs (positive and negative tabs) can protrude from and extend to one side of the housing 260 from the positive and negative current collectors belonging to the electrode assembly, respectively. The tabs can be fused to said side of the housing 260 to form electrode leads (positive lead 207 and negative lead 227) extending to or exposed outside the housing 260.

[0156] According to an exemplary embodiment, a battery cell can be defined by a positive electrode 200, a negative electrode 230, and an electrolyte layer 240, and an electrode assembly 250, for example, in the form of a jelly roll, can be formed by stacking multiple battery cells. For example, the electrode assembly 250 can be formed by winding, lamination, folding, etc., of the electrolyte layer 240.

[0157] The all-solid-state battery can be manufactured in shapes such as cylindrical and prismatic cans, pouches, or coins.

[0158] According to the method for preparing the positive electrode active material of the present invention, a mixture of lithium metal oxide particles, a thiol compound containing a carboxyl group, and an acid is prepared. The mixture is stirred.

[0159] The lithium metal oxide particles and thiol-based compounds may respectively represent the lithium metal oxide particles and thiol-based compounds according to the above embodiments.

[0160] The acid can be any known acid compound. For example, the acid can be sulfuric acid, hydrochloric acid, nitric acid, acetic acid, citric acid, etc.

[0161] In the mixture, the number of functional groups formed on the surface of lithium metal oxide particles can be increased.

[0162] According to an exemplary embodiment, the mixture may comprise lithium metal oxide particles with hydroxyl groups formed on their surface.

[0163] For example, it may contain hydroxyl groups formed by the reaction of the lithium metal oxide particles with oxygen or moisture. For example, it may contain hydroxyl groups formed by dangling bonds resulting from coordination unsaturation on the surface of the lithium metal oxide particles.

[0164] For the surface coating of lithium metal oxide particles, the content of thiol compounds and acid content can be controlled.

[0165] According to an exemplary embodiment, the content of the thiol-based compound can be 0.1% by weight or more of the total weight of the mixture. In some embodiments, the content of the thiol-based compound can be 0.15% by weight or more, 0.2% by weight or more, 0.25% by weight or more, 0.27% by weight or more, or 0.3% by weight or more of the total weight of the mixture.

[0166] According to an exemplary embodiment, the content of the thiol-based compound may be less than 5.0% by weight of the total weight of the mixture. In some embodiments, the content of the thiol-based compound may be less than 4.8%, 4.5%, 4.3%, 4.2%, or 4.0% by weight of the total weight of the mixture.

[0167] For example, the content of the thiol compound may be from 0.1% to 5.0% by weight, 0.2% to 4.8% by weight, 0.25% to 4.3% by weight, or 0.3% to 4.0% by weight of the total weight of the mixture.

[0168] Within the aforementioned range, the thickness of the coating can be controlled, thereby further improving lifetime characteristics under high temperature and / or high voltage. For example, when the content of the thiol-based compound is less than the aforementioned range, the area where no coating is formed may increase, potentially increasing interfacial resistance and reducing lifetime characteristics. For example, when the content of the thiol-based compound exceeds the aforementioned range, the thiol-based compound may penetrate into the interior of the lithium metal oxide particles, potentially accelerating capacity reduction due to volume expansion.

[0169] According to an exemplary embodiment, the acid content can be 0.01% by weight or more of the total weight of the mixture. In some embodiments, the acid content can be 0.02% by weight or more, 0.03% by weight or more, 0.04% by weight or more, 0.045% by weight or more, or 0.05% by weight or more of the total weight of the mixture.

[0170] According to an exemplary embodiment, the acid content may be less than 2.0% by weight of the total weight of the mixture. In some embodiments, the acid content may be less than 1.9%, 1.8%, 1.7%, 1.6%, 1.5%, or 1.0% by weight of the total weight of the mixture.

[0171] For example, the acid content may be from 0.01% to 2.0% by weight, 0.02% to 1.9% by weight, 0.03% to 1.7% by weight, 0.05% to 1.5% by weight, or 0.05% to 1.0% by weight of the total weight of the mixture.

[0172] Within the aforementioned range, acid-mediated reactions can be activated on the surface of lithium metal oxide particles, thus forming a more uniform coating. For example, when the acid content is below the aforementioned range, thiol compounds may aggregate in some areas, or the area without a coating may increase. For example, when the acid content exceeds the aforementioned range, side reactions caused by the reaction between the lithium metal oxide particles and the acid may occur.

[0173] According to an exemplary embodiment, the weight ratio of the acid to the thiol compound may be 0.01 to 0.8, 0.02 to 0.6, or 0.03 to 0.5.

[0174] Within the aforementioned range, the coating on the surface of lithium metal oxide particles can be formed more uniformly.

[0175] According to an exemplary embodiment, the preparation and mixing of the mixture can be carried out at a temperature below 200°C. In some embodiments, the temperature during the preparation and mixing of the mixture can be 0°C to 180°C, 10°C to 150°C, 15°C to 100°C, or 20°C to 80°C.

[0176] Because the coating can be formed under mild conditions, the designed positive electrode active material can be easily realized.

[0177] According to an exemplary implementation, the stirring can be carried out for 1 to 24 hours, 2 to 18 hours, or 3 to 15 hours.

[0178] The preparation and stirring of the mixture can be carried out in a solvent.

[0179] The solvent is a known solvent, and ethanol, isopropanol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfite, etc., can be used without restriction. These can be used alone or in combination of two or more.

[0180] The mixing method is not limited, but can be carried out according to known methods such as a mixer, manual mixing, or mechanical grinding.

[0181] After stirring the mixture, it can be dried. The solvent can be removed by this drying process.

[0182] According to an exemplary embodiment, the drying can be performed under vacuum conditions. Vacuum drying minimizes changes in the composition of the positive electrode active material.

[0183] The positive electrode can be manufactured from the aforementioned positive electrode active material. For example, the aforementioned positive electrode active material, solid electrolyte, and conductive material can be dry-mixed to prepare a preliminary composite positive electrode. The preliminary composite positive electrode can be pressurized to form a positive electrode. The positive electrode can exist in the form of a composite positive electrode.

[0184] In some embodiments, the preliminary composite cathode may comprise 50% to 99% by weight of the cathode active material, 1% to 40% by weight of a solid electrolyte, and 1% to 10% by weight of a conductive material relative to the total content.

[0185] By using a dry method to manufacture the cathode, manufacturing efficiency can be improved because no additional drying or purification processes required for solvents are needed.

[0186] The following are embodiments that help to understand the present invention. However, these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the claims. Various changes and modifications can be made to the embodiments within the scope of the present invention and the technical concept. This is obvious to those skilled in the art, and it is natural that such variations and modifications fall within the scope of the claims.

[0187] Example 1

[0188] (1) Preparation of positive electrode active material

[0189] 0.995g of lithium metal oxide (Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2), 0.005 g of mercaptoacetic acid and 0.001 g of citric acid were added to 60 mL of acetonitrile and stirred at 60 °C for 5 hours. The solvent was then removed by vacuum drying at room temperature to prepare the positive electrode active material.

[0190] (2) Manufacturing of positive electrode and secondary battery

[0191] The positive electrode is manufactured by mixing the positive electrode active material, the sulfide-based solid electrolyte (Li6PS5Cl) as the electrolyte, and the carbon nanofiber as the conductive material in a weight ratio of 60:35:5.

[0192] The positive electrode is attached to one side of a sulfide-based solid electrolyte (Li6PS5Cl) serving as a separator, and an indium-lithium alloy (In-Li alloy) negative electrode is attached to the opposite side. Pressure is then applied to manufacture a 13mm pressed-out cell. The pressed-out cell is then encapsulated in a casing to manufacture a secondary battery.

[0193] Example 2

[0194] The positive electrode active material, positive electrode, and secondary battery were manufactured using the same method as in Example 1, except that the contents of the lithium metal oxide and mercaptoacetic acid were changed to 0.99 g and 0.01 g, respectively.

[0195] Example 3

[0196] The positive electrode active material, positive electrode, and secondary battery are manufactured using the same method as in Example 1, except that 3-mercaptopropionic acid is used instead of mercaptoacetic acid.

[0197] Example 4

[0198] The positive electrode active material, positive electrode, and secondary battery are manufactured using the same method as in Example 1, except that 11-mercaptoundecanoic acid is used instead of mercaptoacetic acid.

[0199] Comparative Example 1

[0200] The positive electrode active material, positive electrode, and secondary battery are manufactured using the same method as in Example 1, except that mercaptoacetic acid and citric acid are not included.

[0201] Comparative Example 2

[0202] The positive electrode active material, positive electrode, and secondary battery are manufactured using the same method as in Example 1, except that 1-propanethiol is used instead of thioglycolic acid.

[0203] Comparative Example 3

[0204] The positive electrode active material, positive electrode, and secondary battery are manufactured using the same method as in Example 1, except that propionic acid is used instead of mercaptoacetic acid.

[0205] Comparative Example 4

[0206] The positive electrode active material, positive electrode, and secondary battery are manufactured using the same method as in Example 1, except that thioglycolic acid is used instead of ethylene-acrylic acid.

[0207] Comparative Example 5

[0208] 0.98g of lithium metal oxide (Li 1.2 Ni 0.13 Co 0.13Mn 0.54 O2), 0.001 g of lithium powder and 40 μL of niobium(V) ethoxide as a coating material were added to 60 mL of ethanol and heat-treated at 350 °C for 3 hours to prepare the positive electrode active material.

[0209] Using the aforementioned positive electrode active material, a positive electrode and a secondary battery were manufactured using the same method as in Example 1.

[0210] Experimental Example

[0211] (1) Fourier transform infrared (FT-IR) analysis

[0212] The IR spectra of the positive electrode active materials according to Example 1 and Comparative Example 1 were analyzed. The analytical results are shown in... Figure 4 middle.

[0213] Reference Figure 4 SH bonds and C=O bonds were confirmed in the IR spectrum of the positive electrode active material according to Example 1. However, SH bonds and C=O bonds were not confirmed in the IR spectrum of the positive electrode active material according to Comparative Example 1. Therefore, it was confirmed that a coating was formed in the positive electrode active material according to Example 1, but no coating was formed in the positive electrode active material according to Comparative Example 1.

[0214] (2) Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) analysis

[0215] The positive electrode active materials according to the examples and comparative examples were analyzed by TEM and EDS. The elemental composition and distribution of the surface of the positive electrode active materials were confirmed by the analysis. The presence or absence of coating was confirmed by the elemental distribution of the images, and the evaluation results are shown as O or X in Table 1 below.

[0216] O: Coating formed on the surface of the positive electrode active material

[0217] X: No coating has been formed on the surface of the positive electrode active material.

[0218] Figure 5a to Figure 10a The figures shown are TEM images of Examples 1 and Comparative Examples 1 to 5, respectively. Figure 5b to Figure 10b The figures shown are EDS analysis images according to Example 1 and Comparative Examples 1 to 5, respectively.

[0219] Reference Figure 5a and Figure 5bAccording to Example 1, sulfur atoms of mercaptoacetic acid are uniformly distributed on the surface of the positive electrode active material.

[0220] Reference Figure 6a and Figure 6b In the positive electrode active material according to Comparative Example 1, sulfur atoms were not identified, and no surface coating was formed.

[0221] Reference Figure 7a and Figure 7b In the positive electrode active material according to Comparative Example 2, propanethiol does not contain a carboxyl group and cannot form an ester bond with the hydroxyl group on the surface of the positive electrode active material, so no surface coating is formed.

[0222] Reference Figure 8a , Figure 8b , Figure 9a and Figure 9b The distribution of carbon atoms on the surface of the positive electrode active material according to Comparative Example 3 and Comparative Example 4 was confirmed, but it was not uniformly distributed.

[0223] Reference Figure 10a and Figure 10b In Comparative Example 5, which uses a conventional positive electrode active material coating method, a niobium-containing coating was formed on the surface of the positive electrode active material, but the coating was not formed uniformly.

[0224] (3) Evaluation of lifespan characteristics

[0225] The lifetime characteristics of the secondary batteries manufactured according to the examples and comparative examples were evaluated. Specifically, in the formation process, the batteries were charged at 0.05C CC / CV (4.6V) at 60°C (relative to Li / Li). + ), 0.025C cut-off current) and 0.05C CC discharge (2.0V (relative to Li / Li) + This is repeated 5 times as a cycle. Afterwards, a 0.5C CC / CV charge (4.6V relative to Li / Li) is applied at 60°C. + ), 0.25C cutoff current) and 0.5C CC discharge (2.0V (relative to Li / Li) + As one cycle, the discharge capacity is measured according to the cycle.

[0226] Lifetime characteristics are evaluated as a percentage of the discharge capacity at the 100th or 200th discharge cycle divided by the discharge capacity after the formation process. The measurement results are shown in Table 1 below. Cases with capacity retention less than 60% are not shown.

[0227] [Table 1]

[0228]

[0229] As shown in Table 1, the lifespan characteristics of the secondary battery according to the embodiment are improved. Furthermore, the lifespan characteristics of the secondary battery according to the comparative example are reduced.

[0230] In Comparative Example 1, the initial capacity retention was relatively good, but due to the lack of a coating, the electrolyte layer decomposed due to oxygen generated in the positive electrode as cycling progressed. That is, the reduced storage stability of the secondary battery led to a decrease in its lifetime characteristics.

[0231] In Comparative Example 2, although propanethiol, as a thiol-based compound, was used, no thiol-based compound coating was formed on the surface of the positive electrode active material, and the life characteristics of the secondary battery were reduced.

[0232] In Comparative Examples 3 to 5, although a coating was formed on the surface of the positive electrode active material, the life characteristics of the secondary battery were reduced because it did not contain thiol compounds.

Claims

1. A positive electrode active material for a lithium secondary battery, comprising: lithium metal oxide particles; and a coating portion attached to a surface of the lithium metal oxide particles by a chemical bond and containing a mercapto group.

2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein The chemical bond includes an ester bond.

3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein, The coating portion is derived from a mercapto group compound.

4. The positive electrode active material for a lithium secondary battery according to claim 3, wherein The mercapto group compound contains one or more of mercapto acetic acid, mercapto propionic acid, mercapto butyric acid, mercapto undecanoic acid, mercapto succinic acid, and cysteine.

5. The positive electrode active material for a lithium secondary battery according to claim 3, wherein The mercapto group compound contains a mercapto group at one terminal and a carboxyl group at another terminal.

6. The positive electrode active material for a lithium secondary battery according to claim 3, wherein The mercapto group compound contains a compound represented by the following Chemical Formula 1, [Chemical Formula 1] In the formula 1, R 1 is a linear or branched alkylene group having 1 to 10 carbon atoms or a linear or branched alkenylene group having 2 to 10 carbon atoms.

7. The positive electrode active material for a lithium secondary battery according to claim 1, wherein The coating portion further contains a mercapto group compound containing a carboxyl group.

8. The positive electrode active material for a lithium secondary battery according to claim 1, wherein The thickness of the coating portion is 0.1 nm to 30 nm.

9. The positive electrode active material for a lithium secondary battery according to claim 1, wherein The lithium metal oxide particles contain manganese, and the molar ratio of the manganese to metal elements other than lithium and oxygen is 0.5 or more.

10. A lithium secondary battery, comprising: a positive electrode containing the positive electrode active material for a lithium secondary battery according to claim 1; a negative electrode; and a solid electrolyte layer provided between the positive electrode and the negative electrode.

11. A method for producing a positive electrode active material for a lithium secondary battery, comprising the steps of: preparing a mixture of lithium metal oxide particles, a mercapto group compound containing a carboxyl group, and an acid; and stirring the mixture. The mixture contains lithium metal oxide particles having a hydroxyl group formed on a surface thereof. The content of the mercapto group compound is 0.1 to 5.0% by weight based on the total weight of the mixture.

12. The method for producing a positive electrode active material for a lithium secondary battery according to claim 11, wherein The content of the acid is 0.01 to 2.0% by weight based on the total weight of the mixture.

13. The method of producing a positive electrode active material for a lithium secondary battery according to claim 11, wherein The temperature of the step of stirring the mixture is 200°C or lower.

14. The method of producing a positive electrode active material for a lithium secondary battery according to claim 11, wherein ​ 15. The method of producing a positive electrode active material for a lithium secondary battery according to claim 11, wherein ​

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