Composite cathode active material, preparation method therefor, and lithium secondary battery comprising same

Abstract

The present invention relates to a composite cathode active material, a preparation method therefor, and a lithium secondary battery comprising same, the material having an oxide-based solid electrolyte attached thereto so that conductivity, capacity, and output characteristics of a lithium secondary battery can be improved without deterioration of physical properties of the cathode active material itself. The composite cathode active material comprises: cathode active material particles; oxide-based solid electrolyte particles formed on the cathode active material particles; and a crosslinked polymer binder, wherein the oxide-based solid electrolyte particles can be attached to the surface of the cathode active material particles by means of the crosslinked polymer binder.

Description

Composite cathode active material, method for producing the same, and lithium secondary battery comprising the same

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0075012, filed June 12, 2023, and Korean Patent Application No. 10-2024-0031896, filed March 6, 2024, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a composite cathode active material capable of improving the conductivity, capacity, and output characteristics of a lithium secondary battery by attaching an oxide-based solid electrolyte without deteriorating the physical properties of the cathode active material itself, a method for producing the same, and a lithium secondary battery including the same.

[0004] Recently, as the application areas of lithium secondary batteries have rapidly expanded to include not only power supply for electronic devices such as electric, electronic, communication, and computer devices, but also power storage for large-area devices such as automobiles and power storage devices, the demand for lithium secondary batteries with high capacity, high output, long life, and high stability is increasing.

[0005] Accordingly, in order to improve the capacity, output, and electrode conductivity of a lithium secondary battery and to enhance stability, it has been proposed to include inorganic solid electrolyte particles within the active material layer of the positive electrode, or to manufacture and use a coating or composite positive electrode active material by coating such inorganic solid electrolyte particles on the positive electrode active material particles.

[0006] Previously, methods for manufacturing the composite cathode active material were considered, including mixing cathode active material particles and inorganic solid electrolyte particles in a wet or dry manner, optionally milling them, and then calcining them. However, recently, cathode active materials containing a high nickel content have been mainly used to increase the capacity and energy density of lithium secondary batteries, and since such cathode active materials containing a high nickel content exhibit low moisture stability, the wet method has not been easily applied.

[0007] In addition, in the case of the existing method, there was a difficulty in the process because the sintering and re-sintering had to be performed at a considerably high temperature in order to attach the solid electrolyte particles, which are inorganic particles, on the positive electrode active material particles. In addition, during this high-temperature sintering process, the crystal structure of the surface of the positive electrode active material particles changed, which could deteriorate the electrochemical properties and stability, and there was a disadvantage in that large particles were created due to agglomeration during the high-temperature sintering, which required re-grinding, etc.

[0008] In addition, when the sintering temperature is lowered, a large number of the inorganic solid electrolyte particles are detached from the positive electrode active material particles, so there is a disadvantage in that it is difficult to sufficiently obtain the effect of improving capacity, output, or conductivity by coating the inorganic solid electrolyte.

[0009] Accordingly, there is a continuous demand for technology development regarding composite cathode active materials that can improve the capacity and output characteristics of lithium secondary batteries by favorably attaching oxide-based solid electrolytes without deteriorating the characteristics and stability of the cathode active material itself due to high-temperature sintering, etc.

[0010] Accordingly, the present invention provides a composite cathode active material capable of improving the conductivity, capacity, and output characteristics of a lithium secondary battery by favorably attaching an oxide-based solid electrolyte without deteriorating the physical properties and stability of the cathode active material itself.

[0011] In addition, the present invention provides a method for manufacturing a composite cathode active material, which can manufacture the composite cathode active material through a simplified process and a relatively low-temperature heat treatment process.

[0012] The present invention also provides a positive electrode and a lithium secondary battery exhibiting excellent capacity and output characteristics, including the composite positive electrode active material.

[0013] The present invention comprises a cathode active material particle; and

[0014] Comprising oxide-based solid electrolyte particles and a crosslinked polymer binder formed on the positive electrode active material particles,

[0015] The above oxide-based solid electrolyte particles provide a composite positive electrode active material attached to the surface of the positive electrode active material particles via the cross-linked polymer binder.

[0016] The present invention also provides a method for producing the composite positive electrode active material, comprising the steps of mixing positive electrode active material particles, oxide-based solid electrolyte particles, and a polymer binder; and the step of thermally curing the mixture.

[0017] In addition, the present invention provides a positive electrode for a lithium secondary battery, comprising: a metal current collector; and a positive electrode active material layer formed on the metal current collector and including the composite positive electrode active material and a conductive material.

[0018] The present invention also provides a lithium secondary battery including the positive electrode; the negative electrode; and the electrolyte.

[0019] The composite cathode active material of the present invention has oxide-based solid electrolyte particles attached to cathode active material particles via a cured and cross-linked polymer binder, and can be manufactured through a simplified process at a relatively low curing temperature.

[0020] Therefore, it is possible to suppress deterioration of the characteristics and stability of the positive electrode active material due to high-temperature heat treatment processes, etc., or the generation of large particles. At the same time, the oxide-based solid electrolyte particles are stably attached and maintained on the positive electrode active material particles, thereby improving the capacity, output, and conductivity of the lithium secondary battery.

[0021] Accordingly, the present invention can greatly contribute to the development of next-generation lithium secondary batteries exhibiting improved capacity and output characteristics.

[0022] Figure 1 shows the results of analyzing the particle size distribution of the composite positive electrode active material particles of Example 1 and the positive electrode active material particles of Comparative Example 1.

[0023] Figure 2 shows the results of evaluating resistance according to the state of charge for the lithium secondary batteries of Example 1 and Comparative Examples 1 and 2.

[0024] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best possible manner.

[0025] It should be understood that the terms “include,” “comprising,” or “having” used in this specification are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0026] According to one embodiment of the invention, a cathode active material particle; and

[0027] Comprising oxide-based solid electrolyte particles and a crosslinked polymer binder formed on the positive electrode active material particles,

[0028] The above oxide-based solid electrolyte particles are provided as a composite positive electrode active material attached to the surface of the positive electrode active material particles via the cross-linked polymer binder.

[0029] In the composite cathode active material of the above embodiment, oxide-based solid electrolyte particles are attached to the cathode active material particles via a cured and cross-linked polymer binder. In addition, as described in more detail below, the composite cathode active material of this embodiment can be manufactured at a relatively low temperature corresponding to the curing temperature of the polymer binder. As a result, the deterioration of the characteristics and stability of the cathode active material due to a high-temperature heat treatment process such as a plurality of existing high-temperature sintering processes, or the generation of large particles during the manufacturing process can be suppressed, and the material can be manufactured through a simplified process without additional heat treatment or additional grinding.

[0030] In particular, in the composite cathode active material, since a change in the crystal structure of the surface of the cathode active material (for example, a change from a rock salt structure of the surface to a layered structure, etc.) hardly occurs, the risk of battery fire or explosion due to the change in the crystal structure is reduced, and the safety of the lithium secondary battery can be greatly improved.

[0031] Furthermore, the oxide-based solid electrolyte particles can be firmly attached to the cathode active material particles by a cured and cross-linked polymer binder and stably maintained on the cathode active material particles. As a result, the capacity, output, conductivity, etc. of a lithium secondary battery can be further improved by coating the oxide-based solid electrolyte particles.

[0032]

[0033] Hereinafter, a composite cathode active material, a method for manufacturing the same, a cathode, and a lithium secondary battery according to implementation examples will be described in more detail.

[0034] In the composite cathode active material of the above embodiment, the cathode active material particles may include a compound capable of reversible intercalation and deintercalation of lithium, specifically, a lithium metal oxide containing one or more metals such as iron, cobalt, manganese, nickel, or aluminum and lithium.

[0035] Specifically, the lithium metal oxide is a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (e.g., LiNi 1-Y Mn Y O2 (here, 0 <Y<1), LiMn 2-Z Ni Z O4 (where 0<Z<2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2 (here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2 (here, 0 <Y2<1), LiMn 2-Z1 Co Z1 O4 (wherein, 0<Z1<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r )O2(wherein, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (wherein, 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2) etc.), lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2)O2 (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are atomic fractions of independent elements, respectively, 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc.), or lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (Here, M is at least one selected from Al, Mg, and Ti, X is at least one selected from F, S, and N, -0.5≤a≤+0.5, 0≤x≤0.5, 0≤b≤0.1), and any one or two or more compounds thereof may be included.

[0036] Among these, the positive electrode active material includes a lithium metal oxide including lithium and two or more transition metals including nickel, and the lithium metal oxide may include nickel in an amount of 80 mol% or more, or 80 to 99 mol%, or 85 to 95 mol%, based on the total metal transition content excluding lithium. Such a lithium metal oxide may be represented by, for example, the following chemical formula 1:

[0037] [Chemical Formula 1]

[0038] Li x Ni a Co b M 1 c M 2 d O2

[0039] In the above chemical formula 1, the M 1 Mn and Al may be one or more selected from or a combination thereof, and M 2may be at least one selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and may be 0.90≤x≤1.1, or 0.95≤x≤1.08, or 1.0≤x≤1.08, and may be 0.80≤a<1.0, or 0.80≤a≤0.99, or 0.85≤a≤0.95, and b, c, and d may each independently be 0 or more and less than 0.2 (however, excluding the case where b, c, and d are all 0).

[0040] By using a lithium metal oxide containing such a high nickel content as a cathode active material, the capacity and energy density of a lithium secondary battery can be further improved. In addition, the composite cathode active material of one embodiment can attach the oxide-based solid electrolyte particles without a change in the crystal structure of the cathode active material particles due to high-temperature sintering, etc., even when using such a high nickel content cathode active material particles. Therefore, while maintaining the high capacity and energy density, the capacity and output characteristics of a lithium secondary battery can be further improved by adding the oxide-based solid electrolyte particles.

[0041] In addition, as the oxide-based solid electrolyte particles attached on the positive electrode active material particles, any solid electrolyte having a lithium ion source by including lithium in its structure and having the form of a lithium metal oxide or lithium metal phosphate can be used.

[0042] Specific examples thereof include at least one lithium metal oxide or lithium metal phosphate selected from a Nasicon-type solid electrolyte, a Lisicon-type solid electrolyte, a Garnet-type solid electrolyte, a Perovskite-type solid electrolyte, and a LiPON-type solid electrolyte, and more specific examples thereof include at least one selected from the group consisting of a LAGP (lithium aluminum germanium phosphate) compound, an LLZO (lithium lanthanum zirconium oxide) compound, a LATP (lithium aluminum titanium phosphate) compound, an LLZTO (lithium lanthanum zirconium tantalum oxide) compound, an LLTO (lithium lanthanum titanium oxide) compound, a LSTP (lithium silicon titanium phosphate) compound, and a LGPO (lithium germanium phosphate) compound.

[0043] Among these, a NASICON-type solid electrolyte such as the LAGP-type compound or LATP-type compound can be appropriately used in terms of being well attached to the positive electrode active material particles by a cross-linked polymer binder and improving the conductivity and output of a lithium secondary battery.

[0044] The above-mentioned oxide-based solid electrolyte particles may be included in an amount of 0.1 to 5 parts by weight, or 0.5 to 4 parts by weight, or 1 to 3.5 parts by weight based on 100 parts by weight of the above-mentioned positive electrode active material particles. Accordingly, the oxide-based solid electrolyte particles may be well attached to the surface of the positive electrode active material particles, effectively improving the electrochemical characteristics of the lithium secondary battery, while not impairing the characteristics of the positive electrode active material particles.

[0045] In addition, in the composite cathode active material of the above-described embodiment, the cathode active material particles may have an average particle diameter (D50) of 3 to 15 μm, or 5 to 13 μm, or 7 to 12 μm, and the oxide-based solid electrolyte particles may have an average particle diameter (D50) of 100 nm to 1.3 μm, or 150 nm to 1.0 μm, or 200 to 800 nm. Accordingly, a plurality of oxide-based solid electrolyte particles may be favorably attached or bonded to the surface of the cathode active material particles, and the composite cathode active material of the embodiment may exhibit excellent electrochemical properties.

[0046] At this time, the average particle diameter (D50) of each particle can be calculated as a particle diameter corresponding to 50% of the volume accumulation amount in the particle size distribution curve when the particle size distribution of the positive active material particles or the oxide-based solid electrolyte particles is measured using, for example, a laser diffraction method and a laser diffraction particle size measuring device.

[0047] Meanwhile, the composite cathode active material of the above embodiment includes a crosslinked polymer binder that is bonded or attached to the cathode active material particles to favorably attach the oxide-based solid electrolyte particles to the surface thereof. This crosslinked polymer binder may be a polymer binder that has been cured and crosslinked in the presence or absence of a crosslinking agent, and the polymer binder before curing and crosslinking may be a polymer of the same type as the polymer binder separately included in the cathode active material described below.

[0048] In addition, the cross-linked polymer binder may be formed in a form attached or bonded to the surface of the positive electrode active material particle while covering at least a portion of the oxide-based solid electrolyte particle on the positive electrode active material particle.

[0049] By using such a cross-linked polymer binder, the oxide-based solid electrolyte particles are well bonded or attached to the surface of the positive electrode active material particles without a high-temperature sintering process, so that the composite positive electrode active material of one embodiment can exhibit improved stability and electrochemical properties.

[0050] The above cross-linked polymer binder is a polymer known to be usable as a binder in the active material layer of a lithium secondary battery, and may be any polymer that can be cured by a method such as thermal curing or photocuring, more specifically, a polymer that can be cured and cross-linked at a temperature of 100°C or higher, or 100 to 200°C. A specific example thereof may be a polymer that is cross-linked by curing, or a copolymer or mixture of two or more polymers selected from the group consisting of polyvinylidene fluoride polymers, polyvinyl alcohol polymers, cellulose polymers, polyvinylpyrrolidone polymers, polytetrafluoroethylene polymers, and polyolefin polymers. However, considering the characteristics of the positive electrode and the good adhesion of the oxide-based solid electrolyte particles, a polyvinylidene fluoride polymer cross-linked by thermal curing may be appropriately used.

[0051] The crosslinked polymer binder may be included in an amount of 0.03 to 2 parts by weight, or 0.05 to 1.5 parts by weight, or 0.1 to 1.0 parts by weight based on 100 parts by weight of the positive electrode active material particles. As a result, the oxide-based solid electrolyte particles can be favorably attached to the positive electrode active material particles, and the increase in resistance caused by the crosslinked polymer binder can be reduced.

[0052] The composite cathode active material of the above-described embodiment can exhibit a uniform particle size distribution as particle aggregation, etc., due to high-temperature firing, etc., is reduced during the manufacturing process. Specifically, the composite cathode active material can exhibit a small particle size deviation, for example, a SPAN derived from the particle size distribution analysis result of 0.3 to 5 ㎛, or 0.5 to 3 ㎛, or 0.5 to 1.5 ㎛.

[0053] Meanwhile, the composite cathode active material of the above-described embodiment can be manufactured by a method including a step of mixing cathode active material particles, oxide-based solid electrolyte particles, and a polymer binder; and a step of thermally curing the mixture.

[0054] In this manufacturing method, the thermal curing step may be carried out in the presence or absence of a crosslinking agent or a curing initiator depending on the type of the polymer binder, and may be carried out at a temperature range from the minimum curable temperature of the polymer binder to 20°C higher. Specifically, the thermal curing step may be carried out at a temperature of 100 to 200°C, or 105 to 180°C, or 110 to 150°C.

[0055] By this thermal curing, the polymer binder may be cured and crosslinked to form a crosslinked polymer binder, and the oxide-based solid electrolyte particles may be attached to the surface of the positive electrode active material particles by this crosslinked polymer binder, thereby manufacturing a composite positive electrode active material of one embodiment.

[0056] By this manufacturing method, the high-temperature re-firing process for attaching the oxide-based solid electrolyte particles can be omitted, and furthermore, the aggregation between the positive electrode active material particles during the manufacturing process can be reduced, thereby reducing the need for an additional grinding process. Accordingly, while the manufacturing process is simplified, the deterioration of the characteristics and stability of the positive electrode active material during the high-temperature re-firing process can be suppressed, and a composite positive electrode active material having a uniform particle size distribution can be manufactured.

[0057] Meanwhile, in some cases, if curing and adhesion between the cross-linked polymer binders occur, a step of crushing the composite positive electrode active material may be further included after the thermal curing step, if necessary.

[0058] Meanwhile, according to another embodiment of the invention, a positive electrode for a lithium secondary battery is provided, which comprises the composite positive electrode active material of the above-described embodiment. The positive electrode may comprise a metal current collector; and a positive electrode active material layer formed on the metal current collector, the positive electrode active material layer comprising the composite positive electrode active material of the above-described embodiment and a conductive material.

[0059] In the positive electrode of these other embodiments, the metal current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used.

[0060] In addition, the positive electrode active material layer may include the composite positive electrode active material and conductive material described above, and may optionally further include a polymer binder.

[0061] At this time, the composite positive electrode active material of the above embodiment may be included in an amount of 60 to 99 wt%, or 70 to 99 wt%, or 80 to 98 wt% based on the total weight of the positive electrode active material layer.

[0062] In addition, the conductive material included in the positive electrode active material layer is a component for further improving the conductivity of the composite positive electrode active material. The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive nanomaterials such as carbon nanofibers or carbon nanotubes; fluorinated carbon powder; conductive powder such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used. Among these, the conductive material includes a conductive nanomaterial such as carbon nanotubes or carbon nanofibers to further lower the resistance of a lithium secondary battery including the positive electrode and improve output characteristics, etc.

[0063] Typically, the conductive material may be included in an amount of 1 to 20 wt%, or 1 to 15 wt%, or 1 to 10 wt% based on the total weight of the positive electrode active material layer.

[0064] The polymer binder optionally included in the above-described positive electrode active material layer is a component that assists in bonding the composite positive electrode active material and the conductive material, and in bonding to the current collector. Examples of such polymer binders include polyvinylidene fluoride polymers; polyvinyl alcohol polymers; cellulose polymers such as carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyvinylpyrrolidone polymers; polytetrafluoroethylene polymers; polyolefin polymers such as polyethylene (PE), polypropylene, ethylene-propylene-diene, or sulfonated ethylene-propylene-diene; or rubber polymers such as nitrile rubber, styrene-butadiene rubber, or fluororubber. A mixture or copolymer of two or more selected from these may also be used.

[0065] In another embodiment, the positive electrode may include not only the polymer binder included in the positive electrode active material layer, but also the cross-linked polymer binder included in the composite positive electrode active material of one embodiment, which may function as a type of polymer binder. Accordingly, the polymer binder included in the positive electrode active material layer may be a polymer of the same type as the cross-linked polymer binder of the composite positive electrode active material, and for example, may be the same polymer as before the cross-linked polymer binder is cured and cross-linked. Accordingly, the content of the polymer binder included in the positive electrode active material layer may be reduced by the amount of the cross-linked polymer binder, thereby maintaining excellent electrical properties of the positive electrode.

[0066] The above polymer binder may be included in an amount of 1 to 20 wt%, or 1 to 15 wt%, or 1 to 10 wt%, based on the sum of the contents of the crosslinked polymer binder included in the composite positive electrode active material, relative to the total weight of the positive electrode active material layer.

[0067] Additionally, a filler may be optionally added to the positive electrode as a component that suppresses its expansion. Such filler is not particularly limited as long as it can suppress the expansion of the electrode without causing chemical changes in the battery. Examples of fillers that can be used include olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber; and the like.

[0068] The positive electrode of the above-described embodiment can be manufactured, for example, by dispersing and mixing the composite positive electrode active material, polymer binder, and conductive agent in a dispersion medium (solvent) to make a slurry, applying the slurry on a metal current collector, and then drying and rolling. At this time, the dispersion medium may be NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof, but is not necessarily limited thereto.

[0069] Meanwhile, according to another embodiment of the invention, a lithium secondary battery comprising the above-described positive electrode; negative electrode; and electrolyte is provided. The lithium secondary battery of this other embodiment can exhibit excellent stability, capacity, and output characteristics by including the composite positive electrode active material and positive electrode of the above-described embodiment.

[0070] In the lithium secondary battery of these other embodiments, the negative electrode may have a conventional configuration known in the art. For example, the negative electrode may include an negative electrode current collector and an negative electrode active material layer formed on the negative electrode current collector, and the negative electrode active material layer may include, for example, an negative electrode active material and, if necessary, additives such as a conductive material, a binder, and a filler. In addition, the negative electrode may be formed by a conventional method of dispersing and mixing each component of the negative electrode active material layer in a dispersion medium (solvent) to make a slurry, applying the slurry on the negative electrode current collector, and then drying and rolling the slurry.

[0071] At this time, the negative electrode current collector may be, but is not limited to, platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), copper (Cu), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO2), FTO (F doped SnO2), and alloys thereof, as well as copper (Cu) or stainless steel surface-treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag). The negative electrode current collector may have a form such as a foil, a film, a sheet, a punched form, a porous body, or a foam.

[0072] In addition, a compound capable of reversible intercalation and deintercalation of lithium may be used as the negative electrode active material. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Sb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metallic oxides capable of doping and dedoping lithium such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metallic compounds and carbonaceous materials such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may also be used as the negative electrode active material.

[0073] In addition, both low-crystalline carbon and high-crystalline carbon can be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0074] The above-described negative electrode active material may be included in an amount of 60 to 99 wt%, or 70 to 99 wt%, or 80 to 98 wt% based on the total weight of the negative electrode active material layer.

[0075] In another embodiment, the negative electrode may not include a negative electrode active material layer, but may only include a negative electrode current collector. In such a negative electrode, lithium ions moved from the positive electrode during the charge and discharge process may be deposited on the negative electrode current collector to form a lithium metal layer, and this lithium metal layer may function as a negative electrode active material.

[0076] Meanwhile, the binder and conductive material included in the negative electrode active material layer may be the same as those described above for the positive electrode, so further description thereof will be omitted.

[0077] The lithium secondary battery of another embodiment described above further includes an electrolyte. In one embodiment, the electrolyte may be a liquid electrolyte containing a lithium salt and a non-aqueous organic solvent. This electrolyte acts as a lithium ion transport medium between the positive and negative electrodes.

[0078] The lithium salt included in the above electrolyte is used as a medium for transferring ions within a lithium secondary battery. The lithium salt is, for example, Li as a cation. + Including, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - and SCN - It may include an anion selected from the group consisting of .

[0079] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB10 Cl 10 , LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (lithium bis(fluorosulfonyl) imide, LiN(SO2F)2), LiBETI (lithium bis(perfluoroethanesulfonyl) imide, LiN(SO2CF2CF3)2) and LiTFSI (lithium bis(trifluoromethanesulfonyl) imide, LiN(SO2CF3)2).

[0080] The concentration of the above lithium salt can be appropriately changed within a commonly usable range, and can be included in the electrolyte at a concentration of 0.5 M to 6 M, or a concentration of 1 M to 5 M.

[0081] Meanwhile, the type of non-aqueous organic solvent that can be included in the electrolyte is not particularly limited, and any organic solvent previously known to be applicable to electrolytes of lithium ion batteries, etc., can be used. Examples of such organic solvents include at least one selected from the group consisting of carbonate solvents, ether solvents, nitrile solvents, phosphate solvents, and sulfone solvents.

[0082] More specifically, as the carbonate solvent, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, methyl propyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate or methyl (2,2,2-trifluoroethyl) carbonate can be used, and as the phosphate solvent, trimethyl phosphate, triethyl phosphate or 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphosphorane 2-oxide can be used.

[0083] In addition, as the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxy ethane, or tetrahydrofuran derivatives such as 2-methyl tetrahydrofuran can be used, and as the nitrile solvent, succinonitrile, adiponitrile, sebaconitrile, acetonitrile, or propionitrile can be used. In addition, as the sulfone solvent, dimethyl sulfone, ethylmethyl sulfone, or sulforane can be used.

[0084] Meanwhile, the lithium secondary battery of another embodiment described above may further include a porous separator interposed between the positive electrode and the negative electrode.

[0085] These porous membranes can be made of olefin polymers such as polyethylene and polypropylene, glass fibers, etc. in the form of sheets, multi-membranes, microporous films, woven fabrics, and non-woven fabrics, but are not necessarily limited thereto. However, it may be preferable to use porous polyethylene or porous glass fiber non-woven fabric (glass filter) as the membrane, and it may be more preferable to use porous glass filter (glass fiber non-woven fabric) as the membrane. The membrane may be an insulating thin film having high ion permeability and mechanical strength, and the pore diameter of the membrane may generally be in the range of 0.01 to 10 ㎛, and the thickness may generally be in the range of 5 to 300 ㎛, but is not limited thereto.

[0086] In addition, in another embodiment of the lithium secondary battery, the separator may not be interposed, and the electrolyte described above may be interposed between the positive and negative electrodes in the form of an electrolyte membrane or an electrolyte film. In this case, the electrolyte membrane or the electrolyte film may be in the form of a polymer matrix containing the lithium salt, non-aqueous organic solvent, and / or solid electrolyte described above, or may be in the form of a solid electrolyte membrane or a solid electrolyte film containing a solid electrolyte such as a polymer-based solid electrolyte, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or a halide-based solid electrolyte. In a more specific example, the electrolyte membrane or the electrolyte film may contain an oxide-based solid electrolyte of the same type as the oxide-based solid electrolyte contained in the composite positive electrode active material of one embodiment. In addition, a well-known polymer-based solid electrolyte, etc. may be used as the polymer matrix. Meanwhile, since the type of the solid electrolyte or the composition of the electrolyte membrane or the electrolyte film may follow the composition of a general semi-solid battery or an all-solid-state battery, further description thereof will be omitted.

[0087] As described above, a battery in which an electrolyte membrane including a solid electrolyte is interposed between the positive and negative electrodes in place of or in addition to the separator interposed between the positive and negative electrodes can be a semi-solid battery using both a liquid electrolyte and a solid electrolyte, or an all-solid battery including only a solid electrolyte.

[0088] Meanwhile, the lithium secondary battery of the above-described other embodiment can be manufactured according to a conventional method in the art. For example, the electrode assembly including the positive electrode, negative electrode, and separator (or electrolyte membrane) can be manufactured by housing it in a case and injecting and impregnating the electrolyte described above.

[0089] These lithium secondary batteries can be applied to battery cells used as power sources for small devices, and are particularly suitable for use as unit cells in battery modules that serve as power sources for medium- to large-sized devices.

[0090]

[0091] The invention will be described in more detail below through specific examples. However, the following examples are provided solely to aid understanding of the invention and do not limit the scope of the invention.

[0092]

[0093] Example 1: Preparation of composite cathode active material, cathode, and lithium secondary battery

[0094] As a cathode active material, lithium nickel cobalt manganese composite oxide (NCM 811; D50: 10㎛) containing 80 mol% of nickel among the total transition metals was used, and LiAl with D50: 300nm was used as an oxide-based solid electrolyte. 0.3 Ti 1.7 (PO4)3(LATP series) compound particles were used respectively. In addition, polyvinylidene fluoride (PVdF) was used as a binder.

[0095] For 100 parts by weight of the above-described positive electrode active material particles, 3 parts by weight of the oxide-based solid electrolyte particles and 0.1 part by weight of the binder were mixed, and further mixed and heat-cured at a temperature of 150 to 180°C for 2 hours, followed by drying in a vacuum oven at 100°C for 24 hours, thereby manufacturing a composite positive electrode active material of Example 1 coated with the above-described positive electrode active material particles and the cured (cross-linked) binder.

[0096] The above composite cathode active material: conductive material (carbon nanotube): binder (PVdF) was mixed in a weight ratio of 97:1:2, dispersed in an NMP solvent at 3000 rpm to prepare a slurry, and then coated with a uniform thickness on a 25 ㎛ thick aluminum foil (Al foil) using a blade-type coating machine, a Labdryer / coater type LTE, Werner Mathis AG, dried in a vacuum oven at 130°C for 24 hours, and rolled using a roll press machine to prepare a cathode for a lithium secondary battery.

[0097] SiO was used as a negative electrode active material, and a negative electrode active material: conductive material: binder was mixed in a weight ratio of 96.5:1.5:2, and the same process as the positive electrode was performed to manufacture a negative electrode.

[0098] After the positive and negative electrodes were each formed, a separator made of a porous polyethylene (PE) film was interposed between them to form a stacked electrode assembly.

[0099] The manufactured electrode assembly was placed in a pouch, sealed, and dried in a vacuum oven at 60°C for 24 hours. An electrolyte was injected to manufacture a pouch-type lithium secondary battery. The electrolyte was prepared by dissolving 1.0 M LiPF6 in an organic solvent consisting of ethylene carbonate / ethyl methyl carbonate (EC / EMC mixing volume ratio of 3 / 7).

[0100]

[0101] Comparative Example 1: Manufacturing of a positive electrode and a lithium secondary battery

[0102] Instead of the composite cathode active material of Example 1, an uncoated lithium nickel cobalt manganese composite oxide (NCM 811; D50: 10 μm) was used as the cathode active material.

[0103] The above positive electrode active material: conductive material (carbon nanotube): binder (PVdF) were mixed in a weight ratio of 97:1:2, dispersed in an NMP solvent at 3000 rpm to prepare a slurry, and then coated with a uniform thickness on a 25 ㎛ thick aluminum foil (Al foil) using a blade-type coating machine, a Mathis coater (Labdryer / coater type LTE, Werner Mathis AG), dried in a vacuum oven at 130°C for 24 hours, and rolled using a roll press machine to prepare a positive electrode for a lithium secondary battery.

[0104] Using these positive electrodes, a lithium secondary battery was manufactured in the same manner as in Example 1.

[0105]

[0106] Comparative Example 2: Manufacturing of a positive electrode (mixture of positive electrode active material and oxide-based solid electrolyte) and a lithium secondary battery.

[0107] A non-aqueous organic solvent composition containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70 was prepared. 5 wt% of trimethylolpropane triacrylate (TMPTA) and 0.02 wt% of AIBN, a polymerization initiator, were added to the composition and mixed to prepare a gel polymer electrolyte composition.

[0108] In this gel polymer electrolyte composition, a cathode active material of lithium nickel cobalt manganese composite oxide (NCM 811; D50: 10㎛) containing 80 mol% of nickel among the total transition metals, and LiAl having a D50 of 300 nm 0.3 Ti 1.7 An oxide-based solid electrolyte of (PO4)3(LATP) compound was added in the same amount as in Example 1 and mixed. Then, this mixture was placed in a heating chamber and heated at 70°C for 5 hours, thereby producing a positive electrode active material.

[0109] In these positive electrode active materials, the positive electrode active material particles and oxide-based solid electrolyte particles were present in a mixed and dispersed state on the TMPTA-cured and cross-linked gel polymer.

[0110] The above mixed cathode active material: conductive material (carbon nanotube): binder (PVdF) was mixed in a weight ratio of 97:1:2, dispersed in an NMP solvent at 3000 rpm to prepare a slurry, and then coated with a uniform thickness on a 25 ㎛ thick aluminum foil (Al foil) using a blade-type coating machine, a Labdryer / coater type LTE, Werner Mathis AG, dried in a vacuum oven at 130°C for 24 hours, and rolled using a roll press machine to prepare a cathode for a lithium secondary battery.

[0111] Using these positive electrodes, a lithium secondary battery was manufactured in the same manner as in Example 1.

[0112]

[0113] Experimental Example 1: Preparation of composite cathode active material, cathode, and lithium secondary battery.

[0114] Using a particle size analyzer (Malvern Mastersizer), the particle size distribution of the composite positive electrode active material of Example 1 and the positive electrode active material of Comparative Example 1 was analyzed, and the analysis results are shown in Fig. 1. Referring to Fig. 1, the composite positive electrode active material of Example 1, like the positive electrode active material of Comparative Example 1, had a single peak of 9.0 μm corresponding to D50, and the SPAN value was confirmed to be 0.5 to 0.8 μm.

[0115] From this, it was confirmed that in the composite positive electrode active material of Example 1, the oxide-based solid electrolyte particles coated on the positive electrode active material particles were not detached, but were uniformly coated on the positive electrode active material particles by the cross-linked binder.

[0116]

[0117] Experimental Example 2: Resistance Evaluation by State of Charge (SOC)

[0118] For the lithium secondary batteries of Example 1 and Comparative Examples 1 and 2, charge and discharge tests were repeatedly performed at room temperature (approximately 25°C) under the conditions of 1) 0.2C - 0.33C charge (cut-off: 4.2V, 0.05C) and 2) 0.2C - 0.33C discharge (cut-off: 2.5V), and resistance was measured according to the state of charge (SOC).

[0119] Specifically, the above charge-discharge test was repeatedly performed under the SOC setting of 10% to 90%, and the DC resistance (2.5C discharge (cut-off: 10 s or 2 V)) was measured after each charge-discharge.

[0120] The results of resistance measurements at each state of charge are shown in Fig. 2, and the results of resistance evaluation at SOC 10% and 50% are also shown in Table 1 below:

[0121] SOC(%)Comparative Example 1(Ω)Comparative Example 2(Ω)Example 1(Ω)500.67450.650910.63909101.034540.988180.98364

[0122] Referring to Table 1 and FIG. 2 above, it was confirmed that the lithium secondary battery using the composite cathode active material of Example 1 exhibited lower resistance and higher ionic conductivity at different charge states compared to Comparative Example 1 (using a general cathode active material) and Comparative Example 2 (mixing cathode active material and oxide-based solid electrolyte), and in particular, exhibited a better effect in the SOC range of 50 to 70%.

[0123]

[0124] Experimental Example 3: Rate Evaluation

[0125] For the lithium secondary batteries of Example 1 and Comparative Examples 1 and 2, charge and discharge tests were conducted at a temperature of 25°C.

[0126] Specifically, charging was performed under the conditions of 0.2C (cut-off: 4.2V, 0.05C), and discharging was performed at different rates of 0.2C, 0.33C, 0.5C, 1C, 2C, and 3C (cut-off: 2.5V). Under each discharge rate, charge and discharge tests were performed for 3 to 30 cycles each, and then the capacity retention rate was evaluated. The results of the comparative evaluation of the capacity retention rate under the discharge rate of 3C (@ 16 to 18 cycles) are shown in Table 2 below:

[0127] Discharge rate comparison example 1 Capacity maintenance rate (%) Comparative example 2 Capacity maintenance rate (%) Example 1 Capacity maintenance rate (%) 3C61.1968.1470.05

[0128] Referring to Table 2, it was confirmed that the lithium secondary battery of Example 1 had a higher discharge capacity retention rate and superior output characteristics than Comparative Examples 1 and 2 under the high discharge rate of 3C.

Claims

1. Positive electrode active material particles; and Comprising oxide-based solid electrolyte particles and a crosslinked polymer binder formed on the positive electrode active material particles, The above oxide-based solid electrolyte particles are a composite positive electrode active material attached to the surface of the positive electrode active material particles via the cross-linked polymer binder.

2. In the first paragraph, the positive electrode active material particle comprises a lithium metal oxide including lithium and two or more transition metals including nickel, The above lithium metal oxide is a composite cathode active material containing nickel in an amount of 80 mol% or more based on the total transition metal content excluding lithium.

3. In the first paragraph, the oxide-based solid electrolyte particles are a composite cathode active material comprising at least one lithium metal oxide or lithium metal phosphate selected from a Nasicon-type solid electrolyte, a Lisicon-type solid electrolyte, a Garnet-type solid electrolyte, a Perovskite-type solid electrolyte, and a LiPON-type solid electrolyte.

4. In the first paragraph, the oxide-based solid electrolyte particles are a composite cathode active material comprising at least one selected from the group consisting of a LAGP (lithium aluminum germanium phosphate)-based compound, an LLZO (lithium lanthanum zirconium oxide)-based compound, a LATP (lithium aluminum titanium phosphate)-based compound, an LLZTO (lithium lanthanum zirconium tantalum oxide)-based compound, an LLTO (lithium lanthanum titanium oxide)-based compound, a LSTP (lithium silicon titanium phosphate)-based compound, and a LGPO (lithium germanium phosphate)-based compound.

5. In the first paragraph, the crosslinked polymer binder is a composite cathode active material comprising a crosslinked polymer in which at least one polymer, copolymer or mixture is cured and selected from the group consisting of polyvinylidene fluoride polymers, polyvinyl alcohol polymers, cellulose polymers, polyvinyl pyrrolidone polymers, polytetrafluoroethylene polymers and polyolefin polymers.

6. In the first paragraph, the positive electrode active material particles have an average particle diameter (D50) of 3 to 15 μm, The above oxide-based solid electrolyte particles are composite positive electrode active materials having an average particle diameter (D50) of 100 nm to 1.3 μm.

7. In the 6th paragraph, the composite cathode active material is a composite cathode active material having a particle size span of 0.3 to 5 μm.

8. A composite positive electrode active material in the first paragraph, wherein the oxide-based solid electrolyte particles are included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the positive electrode active material particles.

9. A composite positive electrode active material in the first paragraph, wherein the crosslinked polymer binder is included in an amount of 0.03 to 2 parts by weight based on 100 parts by weight of the positive electrode active material particles.

10. A step of mixing positive electrode active material particles, oxide-based solid electrolyte particles, and a polymer binder; and A method for producing a composite positive electrode active material of claim 1, comprising a step of thermally curing the above mixture.

11. A method for producing a composite positive electrode active material, wherein the thermal curing step is performed at a temperature of 100 to 200°C in the 10th paragraph.

12. A method for producing a composite positive electrode active material, wherein the thermal curing step is performed in the presence of a crosslinking agent or a curing initiator in the 10th paragraph.

13. A method for producing a composite cathode active material, further comprising a step of crushing the resultant product after the thermal curing step in the 10th paragraph.

14. Metal current collector; and A positive electrode for a lithium secondary battery, comprising a positive electrode active material layer formed on the above metal current collector and including the composite positive electrode active material of claim 1 and a conductive material.

15. A positive electrode for a lithium secondary battery, wherein the positive electrode active material layer further comprises a polymer binder of the same type as the crosslinked polymer binder of the composite positive electrode active material.

16. A positive electrode for a lithium secondary battery, wherein the polymer binder comprises at least one selected from the group consisting of a polyvinylidene fluoride polymer, a polyvinyl alcohol polymer, a cellulose polymer, a polyvinylpyrrolidone polymer, a polytetrafluoroethylene polymer, and a polyolefin polymer.

17. A lithium secondary battery comprising the positive electrode of Article 14; a negative electrode; and an electrolyte.

18. In the 17th paragraph, further comprising a separator interposed between the positive and negative electrodes, or A lithium secondary battery in which the electrolyte has the form of an electrolyte membrane or electrolyte film containing a solid electrolyte and is interposed between the positive electrode and the negative electrode.

Images