Method for manufacturing surface-modified electrode active material and electrode and lithium secondary battery manufactured thereby

Abstract

The present invention relates to a method for manufacturing a surface-modified electrode active material capable of improving output characteristics and low-temperature characteristics, and an electrode and a lithium secondary battery manufactured thereby. The method for manufacturing a surface-modified electrode active material comprises the steps of: preparing a solid electrolyte dispersion solution including an oxide-based solid electrolyte and a solvent; coating the surface of an electrode active material with the solid electrolyte dispersion solution; and forming a surface-modified electrode active material by heat-treating the coated electrode active material.

Description

Method for manufacturing surface-modified electrode active material and electrode and lithium secondary battery manufactured thereby

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0118577, filed September 6, 2023, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a method for manufacturing a surface-modified electrode active material capable of improving the output characteristics and low-temperature characteristics of a lithium secondary battery, and to an electrode and a lithium secondary battery manufactured thereby.

[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] A lithium secondary battery is generally composed of a positive electrode, a negative electrode, a separator, and an electrolyte including a lithium salt and an organic solvent, and lithium ions move through the electrolyte during the charging and discharging process.

[0006] Within the electrolyte, lithium ions exist in a solvated state, surrounded by an organic solvent. Therefore, for the lithium ions within the electrolyte to migrate and be inserted into the electrode active material, they must undergo a desolvation process, in which the lithium ions are separated or desorbed from the organic solvent molecules. Therefore, the smooth progress of this desolvation process can affect the output, resistance, or stability of the lithium secondary battery.

[0007] Meanwhile, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2, LiMn2O4, etc.), lithium iron phosphate compound (LiFePO4), etc. are used as positive electrode active materials for lithium secondary batteries. In particular, NCM-based lithium composite transition metal oxides have been developed to improve the low thermal stability while maintaining the excellent reversible capacity of LiNiO2. However, conventional NCM-based lithium composite transition metal oxides have insufficient capacity characteristics, which limits their application.

[0008] To improve such problems, research has been conducted recently to increase the content of Ni in NCM-based lithium composite transition metal oxides. However, in the case of high-concentration nickel positive electrode active materials, the capacity increases, but the Ni content decreases depending on the depth of charge. 2+ In Ni 3+ / 4+ Rapid oxygen desorption occurs due to oxidation, and the desorbed oxygen reacts with the electrolyte, changing the inherent properties of the material and causing instability of the lattice structure and even structural collapse.

[0009] Accordingly, there is a continuous demand for the development of technology that can improve the output characteristics of lithium secondary batteries by accelerating the desolvation of lithium ions within the electrolyte while maintaining excellent low-temperature characteristics.

[0010] Accordingly, the present invention provides a method for manufacturing a surface-modified electrode active material that can improve the output characteristics of a lithium secondary battery by accelerating the desolvation of lithium ions in an electrolyte, while maintaining excellent low-temperature characteristics such as high output at low temperatures.

[0011] The present invention also provides an electrode and a lithium secondary battery manufactured thereby, which exhibit improved output characteristics and low-temperature characteristics.

[0012] Hereinafter, a method for manufacturing a surface-modified electrode active material according to a specific embodiment of the invention will be described.

[0013] 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 idea 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 way.

[0014] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0015] In this specification, it should be understood that the terms “include,” “comprising,” or “having” 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.

[0016]

[0017] Method for manufacturing surface-modified electrode active material

[0018] According to one embodiment of the present invention, a method for producing a surface-modified electrode active material is provided, comprising: a step of producing a solid electrolyte dispersion comprising an oxide-based solid electrolyte and a solvent; a step of coating the solid electrolyte dispersion on the surface of an electrode active material; and a step of heat-treating the coated electrode active material to form a surface-modified electrode active material.

[0019] In particular, referring to FIG. 1, the method for manufacturing the surface-modified electrode active material can evenly distribute the oxide-based solid electrolyte on the surface of the electrode active material by pre-dispersing the oxide-based solid electrolyte in a solvent phase. This can be distinguished from the conventional surface-modified active material in which the oxide-based solid electrolyte particles aggregate with each other and are not evenly dispersed. Accordingly, the oxide-based solid electrolyte particles can accelerate the desolvation process of lithium ions in the electrolyte by reducing the activation energy involved in the desolvation process of lithium ions in the electrolyte at the interface where the electrode active material and the electrolyte come into contact. In addition, this can improve lithium ion conductivity around the electrode active material particles.

[0020] First, a solid electrolyte dispersion comprising an oxide-based solid electrolyte and a solvent can be prepared by uniformly dispersing the oxide-based solid electrolyte in a solvent phase. This allows the oxide-based solid electrolyte to be pre-dispersed in the solvent phase, and the oxide-based solid electrolyte can be uniformly distributed on the surface of the electrode active material in the coating step described below.

[0021] In an exemplary embodiment, the dispersion preparation step may include mixing 5 to 70 parts by weight of an oxide-based solid electrolyte and 30 to 95 parts by weight of a solvent. When mixing the oxide-based solid electrolyte and the solvent in the above range, if the oxide-based solid electrolyte is 70 parts by weight or more, it is difficult to control the D50 value to 100 nm to 1 μm, and if the solid electrolyte is 5 parts by weight or less, the efficiency of dispersion energy transferred to the particle surface may decrease, resulting in a longer dispersion time.

[0022] In an exemplary embodiment, in the dispersion preparation step, the oxide-based solid electrolyte may be dispersed in the solvent phase using one or more of sonication, a high-shear mixer, a high-pressure homogenizer, and a bead-milling method.

[0023] In particular, in order to increase the dispersion efficiency of a high-concentration oxide-based solid electrolyte dispersion of nanoparticle size and minimize oxidation of the oxide-based solid electrolyte due to heat generated during the dispersion process, the dispersion can be dispersed using a bead milling method at a temperature of up to 40°C and a dispersion time of up to 3 hours.

[0024] In an exemplary embodiment, the oxide-based solid electrolyte in the solid electrolyte dispersion may have a particle size distribution of at least one of D50 of 100 nm to 1 μm and D90 of 400 nm to 1.5 μm. For example, the oxide-based solid electrolyte may have a particle size distribution of at least one of D50 of 300 to 700 nm, D90 of 400 to 900 nm, and span of 1 or less. When the oxide-based solid electrolyte particles are uniformly distributed within the above ranges, excellent output characteristics and low-temperature characteristics may be achieved.

[0025] In an exemplary embodiment, the oxide-based solid electrolyte may be any solid electrolyte having a lithium ion source including lithium in its structure and having the form of a lithium metal oxide or lithium metal phosphate.

[0026] For example, 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 may be mentioned. More specific examples 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.

[0027] Among these, a NASICON-type solid electrolyte such as the LAGP-type compound or LATP-type compound can be appropriately used in terms of accelerating the desolvation of lithium ions at the interface between the active material layer and the electrolyte and improving the ion conductivity and output of a lithium secondary battery.

[0028] Next, the solid electrolyte dispersion can be coated on the surface of the electrode active material. Specifically, the solid electrolyte dispersion can be mixed with the positive electrode active material, and a uniform coating layer can be formed so that nanoparticles of the oxide-based solid electrolyte dispersion are uniformly distributed on the surface of the positive electrode active material.

[0029] In an exemplary embodiment, the solid electrolyte dispersion coating step may be performed by one or more of spray coating, high-speed homogeneous mixing, and fluidized bed coating methods.

[0030] In an exemplary embodiment, the positive electrode active material may include a compound capable of reversible intercalation and deintercalation of lithium, specifically a lithium metal oxide including lithium and one or more metals such as iron, cobalt, manganese, nickel, or aluminum.

[0031] 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.

[0032] Among these, the positive electrode active material includes a lithium metal oxide including lithium and two or more metals selected from the group consisting of nickel, manganese, cobalt, and aluminum, and the lithium metal oxide may include nickel in an amount of 60 mol% or more, or 60 to 99 mol%, or 70 to 95 mol%, based on the total metal content excluding lithium. Such a lithium metal oxide may be represented by, for example, the following chemical formula 1:

[0033] [Chemical Formula 1]

[0034] Li x Ni a Co b M 1 c M 2 d O2

[0035] 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 0.60≤a<1.0, or 0.70≤a≤0.99, or 0.80≤a≤0.95.

[0036] Meanwhile, the positive electrode active material may have an average particle diameter (D50) of 4 to 15 μm, or 7 to 13 μm, or 8 to 12 μm.

[0037] By using lithium metal oxide containing such a high nickel content as a cathode active material and combining it with an oxide-based solid electrolyte, the output and capacity characteristics of a lithium secondary battery can be further improved.

[0038] In an exemplary embodiment, the oxide-based solid electrolyte may be included in an amount of 0.3 to 5 parts by weight based on 100 parts by weight of the electrode active material, in order to accelerate the desolvation of lithium ions at the interface between the active material layer and the electrolyte and improve lithium ion conductivity without inhibiting the insertion and desorption process of lithium ions by the positive electrode active material.

[0039] Next, the coated electrode active material can be heat-treated to form a surface-modified electrode active material.

[0040] In an exemplary embodiment, it is preferable to heat-treat at a temperature higher than the glass transition temperature (Tg) of the oxide-based solid electrolyte, and after the heat-treating, the oxide-based solid electrolyte nanoparticles uniformly coated on the surface of the active material may be sintered to form a uniform coating thin film layer, thereby forming a modified electrode active material.

[0041] In an exemplary embodiment, the heat treatment step may be a sintering treatment at a temperature of 600 to 1000° C. for 1 to 3 hours to form a surface-modified electrode active material.

[0042] Meanwhile, the solvent may be removed prior to the calcination treatment. Specifically, the electrode active material coated with the oxide-based solid electrolyte is first dried at 130°C for 2 hours to remove the NMP solvent. The dried oxide-based solid electrolyte-coated active material may be calcined at 800°C for 2 hours to form a surface-modified electrode active material.

[0043]

[0044] Electrodes for lithium secondary batteries and lithium secondary batteries

[0045] According to another embodiment of the present invention, an electrode for a lithium secondary battery is provided, comprising: a metal current collector; and an active material layer formed on the metal current collector and including a surface-modified electrode active material manufactured by the above-described surface-modified electrode active material manufacturing method.

[0046] Hereinafter, a lithium secondary battery electrode according to one embodiment and a lithium secondary battery including the same will be described in more detail. However, the following description focuses on an embodiment in which the lithium secondary battery electrode serves as a positive electrode, but the scope of the invention is not limited thereto, and it goes without saying that the electrode of the above embodiment may serve as a negative electrode.

[0047] The positive electrode for a lithium secondary battery according to the above embodiment includes a metal current collector. The metal current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used.

[0048] In addition, the active material layer on the metal current collector may further include, in addition to the surface-modified electrode active material, an oxide-based solid electrolyte having a conductive material and a lithium ion source, and may optionally further include a binder.

[0049] Meanwhile, the conductive material included in the active material layer is a component for further improving the conductivity of the 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 can further lower the resistance of a lithium secondary battery including the positive electrode of one embodiment and improve output characteristics, etc. by including a conductive nanomaterial such as carbon nanotubes or carbon nanofibers.

[0050] 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 active material layer.

[0051] The binder optionally included in the above active material layer is a component that assists in the bonding of the positive electrode active material and the conductive material, and the bonding to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, nitrile rubber, styrene-butadiene rubber, or fluororubber, and a mixture or copolymer of two or more selected from these may also be used.

[0052] Typically, the 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 total weight of the positive electrode active material layer.

[0053] 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.

[0054] The positive electrode of the above-described embodiment can be manufactured, for example, by dispersing and mixing the positive electrode active material, oxide-based solid electrolyte, 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.

[0055] In addition, a lithium secondary battery is provided, which includes a positive electrode; a negative electrode; and an electrolyte including a lithium salt and a non-aqueous organic solvent, and includes the aforementioned lithium secondary battery electrode as a positive electrode. The lithium secondary battery of this other embodiment can exhibit low-temperature characteristics along with excellent output characteristics.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] Meanwhile, since the binder and conductive material included in the negative electrode active material layer can be the same as those described above for the positive electrode, further description thereof will be omitted. In addition, when the lithium secondary battery electrode of the embodiment already described above becomes the negative electrode, the negative electrode active material layer may further include an oxide-based solid electrolyte having the lithium ion source already described above, and in this case, the oxide-based solid electrolyte can satisfy the D50 ratio described above for the negative electrode active material particles.

[0063] The lithium secondary battery of another embodiment described above comprises an electrolyte comprising a lithium salt and a non-aqueous organic solvent. This electrolyte acts as a transport medium for lithium ions between the positive and negative electrodes. These lithium ions exist in the electrolyte in a solvated state, while at the interface between the electrolyte and the electrode, they can be desolvated and inserted into the electrode active material. As described above, in the secondary battery of another embodiment, this desolvation is accelerated, thereby exhibiting improved output characteristics, etc.

[0064] 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 Cl10 - , 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 .

[0065] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 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).

[0066] 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.

[0067] In a more specific embodiment, the electrolyte may include a lithium salt in a relatively low concentration of 0.5 M or more and less than 2 M, or 0.7 M to 1.5 M. Even in this case, since the desolvation of lithium ions is accelerated by the action of the electrode of the above-described embodiment, the lithium secondary battery of another embodiment may exhibit improved output characteristics. As a result, problems such as increased electrolyte viscosity, decreased fluidity, and decreased ion conductivity of the electrolyte and battery output at low temperatures due to the application of an electrolyte composition including a high concentration of lithium salt can be solved, and excellent low-temperature characteristics of the lithium secondary battery can be achieved at the same time.

[0068] Meanwhile, in another embodiment of the invention, the electrolyte may contain a lithium salt at a high concentration of 2 M to 6 M, or 2.5 M to 5.5 M. In this case, the desolvation of lithium ions can be further accelerated by containing a high-concentration lithium salt and applying the electrode of one embodiment, and the output characteristics of the secondary battery can be further improved.

[0069] In addition, by applying the electrode of the above embodiment, lithium ion conductivity can be improved and resistance can be reduced even at low temperatures. This can reduce the deterioration of low-temperature output characteristics due to high-concentration lithium salts, etc.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] Meanwhile, the electrolyte may further include, in addition to the lithium salt and the non-aqueous organic solvent described above, a diluent that exhibits a solubility in the lithium salt that is at least 10 times lower than that of the non-aqueous organic solvent. The diluent may be an organic solvent that is miscible with the non-aqueous organic solvent while exhibiting substantially no solubility in the lithium salt, for example, an ether solvent having a fluorine-substituted alkyl group, and more specifically, may include at least one selected from the group consisting of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether (BTFE), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), methoxynonafluorobutane (MOFB), and ethoxynonafluorobutane (EOFB).

[0074] When such a diluent is further included, a high-concentration lithium salt may be locally present in the non-aqueous organic solvent within the electrolyte, and substantially no lithium salt may be present within the diluent. In this way, since a high-concentration lithium salt is locally present in a solvated form within the electrolyte, the output characteristics of the lithium secondary battery can be further improved, while the increase in viscosity and decrease in fluidity of the electrolyte can be reduced. In addition, when the electrode of one embodiment is applied together with such a high-concentration salt electrolyte, lithium ion conductivity can be improved and resistance can be reduced even at low temperatures, thereby reducing the deterioration of low-temperature output characteristics due to high-concentration lithium salt, etc.

[0075] The amount of the diluent used can be adjusted depending on the type of non-aqueous organic solvent and lithium salt, or the overall concentration of the lithium salt, and for example, the diluent: non-aqueous organic solvent can be included in the electrolyte in a molar ratio of 1:0.2 to 1:5, or 1:0.5 to 1:2.

[0076] 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.

[0077] 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 polyethylene 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.

[0078] In addition, in another example 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 electrolyte film. In this case, the electrolyte membrane or electrolyte film may be in the form of a polymer matrix containing the lithium salt and a non-aqueous organic solvent described above, and a well-known polymer-based solid electrolyte or the like may be used as the polymer matrix. In this case, the lithium secondary battery of the other embodiment may be a semi-solid battery that uses a liquid electrolyte and a solid electrolyte in combination.

[0079] 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.

[0080] 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.

[0081] A method for manufacturing a surface-modified electrode active material according to an embodiment of the present invention can evenly distribute an oxide-based solid electrolyte on the surface of an electrode active material by pre-dispersing the oxide-based solid electrolyte in a solvent phase. Accordingly, the oxide-based solid electrolyte particles can accelerate desolvation by reducing the activation energy involved in the desolvation process of lithium ions within the electrolyte at the interface where the electrode active material and the electrolyte come into contact. In addition, this can improve lithium ion conductivity around the electrode active material particles.

[0082] Furthermore, since the output characteristics of a lithium secondary battery can be improved without applying a new electrolyte composition including a high concentration of lithium salt, problems such as increased electrolyte viscosity, decreased fluidity, and decreased ion conductivity of the electrolyte and output of the battery at low temperatures due to the application of the new electrolyte composition can be solved, and excellent low-temperature characteristics of a lithium secondary battery can be achieved.

[0083] Additionally, even when applying an electrolyte composition including the high-concentration lithium salt, etc., the electrode application of the present invention facilitates the desolvation of lithium ions, thereby improving lithium ion conductivity and reducing resistance. Accordingly, the output characteristics of a lithium secondary battery can be further improved by using the high-concentration lithium salt, etc., while reducing the deterioration of low-temperature characteristics.

[0084] Accordingly, the present invention can greatly contribute to the development of next-generation lithium secondary batteries exhibiting improved output characteristics and low-temperature characteristics.

[0085] Figure 1 compares a manufacturing method according to the present invention in which an oxide-based solid electrolyte is evenly distributed on the surface of an electrode active material by pre-dispersing the oxide-based solid electrolyte in a solvent phase, with a conventional surface-modified active material in which oxide-based solid electrolyte particles aggregate with each other and are not evenly dispersed.

[0086] Figure 2 shows SEM and EDS Ti element mapping images of the positive electrode active material according to Comparative Example 1 and Example 1 of the present invention.

[0087] FIG. 3 shows the results of evaluating electrochemical characteristics for lithium secondary batteries manufactured using positive electrodes according to Example 2, Example 3, and Comparative Example 2 and Comparative Example 3 of the present invention, respectively.

[0088] FIG. 4 is a graph comparing the results of resistance measurements according to state of charge (SOC) for lithium secondary batteries manufactured using positive electrodes according to Example 2, Example 3, and Comparative Example 2, Comparative Example 3 of the present invention.

[0089] 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.

[0090]

[0091] Example 1-1: Preparation of surface-modified cathode active material

[0092] D50: Li at 300 nm 1.3 Al 0.3 Ti 1.7 (PO4)3 oxide solid electrolyte (LATP) 25g and NMP 50g were mixed, a bead mill was added to the mixture, and dispersion treatment was performed for 40 minutes using a spike mill to prepare a solid electrolyte dispersion.

[0093] As a cathode active material, a lithium nickel cobalt manganese composite oxide (NCM 603; D50: 5 μm) containing 80 mol% of nickel among the total transition metals was used, and the prepared dispersion was added to 5 kg of the cathode active material, and the mixture was stirred at 3000 rpm for 30 minutes using a homogeneous mixer, and the NMP solvent was dried at 130°C for 1 hour and then calcined at 800°C for 2 hours to produce a surface-modified cathode active material having a uniform solid electrolyte coating film.

[0094]

[0095] Example 1-2: Preparation of surface-modified cathode active material

[0096] D50: Li at 300 nm 1.3 Al 0.3 Ti 1.7 (PO4)3 oxide solid electrolyte (LATP) 50g and NMP 50g were mixed, a bead mill was added to the mixture, and dispersion treatment was performed for 40 minutes using a spike mill to prepare a solid electrolyte dispersion.

[0097] As a cathode active material, a lithium nickel cobalt manganese composite oxide (NCM 603; D50: 5 μm) containing 65 mol% of nickel among the total transition metals was used, and the prepared dispersion was added to 5 kg of the cathode active material, and the mixture was stirred at 3000 rpm for 30 minutes using a homogeneous mixer, and the NMP solvent was dried at 130°C for 1 hour and then calcined at 800°C for 2 hours to produce a surface-modified cathode active material having a uniform solid electrolyte coating film.

[0098]

[0099] Example 2: Manufacturing of lithium secondary batteries

[0100] Carbon nanotubes were used as the conductive agent, and polyvinylidene fluoride (PVDF) was used as the binder, respectively. 97 parts by weight of the surface-modified positive electrode active material of Example 1-1, 1.5 parts by weight of the conductive agent, and 1.5 parts by weight of the binder were mixed to prepare a positive electrode active material slurry. The prepared slurry was coated on an aluminum current collector and dried to prepare a positive electrode. At this time, the particle size distribution of the oxide-based solid electrolyte (LATP) was measured using a laser diffraction particle size measuring device (Malvern Mastersizer 3000), and was D10: 0.234 μm, D50: 0.345 μm, D90: 0.495 μm, and span: 0.757. Graphite was used as the negative active material, and the negative active material: conductive material: binder was mixed in a weight ratio of 96.5:1.5:2 without using an oxide-based solid electrolyte, and the negative electrode was manufactured by performing the same process as the positive electrode.

[0101] The prepared positive and negative electrodes were positioned so that they face each other, a 15 μm thick polyethylene (PE) separator was interposed between them, and an electrolyte was filled to manufacture a bi-cell type lithium secondary battery. At this time, the electrolyte was prepared by dissolving 1.0 M LiPF6 in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate (EC / EMC mixing volume ratio of 3 / 7).

[0102]

[0103] Example 3: Manufacturing of lithium secondary batteries

[0104] Carbon nanotubes were used as a conductive material and polyvinylidene fluoride (PVDF) was used as a binder, respectively. 97 parts by weight of the surface-modified positive electrode active material of Example 1-2, 1.5 parts by weight of a conductive material, and 1.5 parts by weight of a binder were mixed to prepare a positive electrode active material slurry. The prepared slurry was coated on an aluminum current collector and dried to prepare a positive electrode. At this time, the particle size distribution of the oxide-based solid electrolyte (LATP) was D10: 0.237 μm, D50: 0.347 μm, D90: 0.497 μm, and span: 0.749. Graphite was used as an anode active material, and the anode active material: conductive material: binder was mixed in a weight ratio of 96.5: 1.5: 2 without using an oxide-based solid electrolyte, and the same process as for the positive electrode was performed to prepare an anode.

[0105] The prepared positive and negative electrodes were positioned so that they face each other, a 15 μm thick polyethylene (PE) separator was interposed between them, and an electrolyte was filled to manufacture a bi-cell type lithium secondary battery. At this time, the electrolyte was prepared by dissolving 1.0 M LiPF6 in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate (EC / EMC mixing volume ratio of 3 / 7).

[0106]

[0107] Comparative Example 1: Positive electrode active material

[0108] A lithium nickel cobalt manganese composite oxide (NCM 603; D50: 5㎛) containing 65 mol% of nickel among all transition metals was used.

[0109]

[0110] Comparative Example 2: Manufacturing of Lithium Secondary Battery

[0111] A slurry of positive electrode active material was prepared by mixing 97 parts by weight of the positive electrode active material of Comparative Example 1, 1.5 parts by weight of the conductive agent, and 1.5 parts by weight of PVDF. The prepared slurry was coated on an aluminum current collector and dried to prepare a positive electrode. The conductive agent, binder, negative electrode, and electrolyte were the same as those used in Example 2.

[0112] The prepared positive and negative electrodes were positioned so that they face each other, a 20 ㎛ thick polyethylene (PE) separator was interposed between them, and an electrolyte was filled to manufacture a bi-cell type lithium secondary battery.

[0113]

[0114] Comparative Example 3: Sample without pre-dispersion

[0115] A slurry of a positive electrode active material was prepared by mixing 96 parts by weight of the positive electrode active material of Comparative Example 1, 1.5 parts by weight of a conductive agent, 1.5 parts by weight of PVDF, and 1 part by weight of an oxide-based solid electrolyte (LATP). The prepared slurry was coated on an aluminum current collector and dried to prepare a positive electrode. The conductive agent, binder, negative electrode, and electrolyte were the same as those used in Example 2. The particle size distribution of the oxide-based solid electrolyte (LATP) was D10: 0.302 μm, D50: 0.512 μm, D90: 3.3 μm, and span: 5.766.

[0116] The prepared positive and negative electrodes were positioned so that they face each other, a 20 ㎛ thick polyethylene (PE) separator was interposed between them, and an electrolyte was filled to manufacture a bi-cell type lithium secondary battery.

[0117]

[0118] Experimental example

[0119] 1) In Fig. 2, the SEM images of the surface-modified positive electrode active materials of Comparative Example 1 and Example 1 and the EDS analysis of the surface of the active material show the Ti element mapping images of the oxide-based solid electrolyte, respectively.

[0120] As a result, it can be confirmed that, compared to a cathode active material without surface modification, the surface-modified cathode active material according to the embodiment of the present invention uniformly disperses oxide-based solid electrolyte nanoparticles and forms a uniform solid electrolyte coating layer on the surface of the cathode active material through heat treatment.

[0121]

[0122] 2) In addition, the electrochemical characteristics of the lithium secondary batteries of Examples 2 and 3 and Comparative Examples 2 and 3 were evaluated. Specifically, for each sample, a charge-discharge test was repeated three times 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 the capacity change and charge-discharge change were measured, and the results are shown in Fig. 3.

[0123] As a result, it can be confirmed that in Examples 2 and 3, where the surface-modified positive electrode active material was applied, the desolvation rate of the electrolyte was accelerated and the ionic conductivity at low temperatures was increased, thereby improving cell resistance and output characteristics.

[0124]

[0125] 3) For the lithium secondary batteries of Examples 2 and 3 and Comparative Examples 2 and 3, the resistance was measured by repeatedly conducting charge and discharge tests 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) according to the state of charge (SOC). Specifically, the charge and discharge tests were repeatedly conducted under the settings of 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, and 10% of SOC, and the DC resistance (2.5C discharge (cut-off: 10s or 2V)) was measured after each charge and discharge. The results of the resistance measurements according to the state of charge are illustrated in Fig. 4 and also shown in Table 1 below.

[0126] Sample Charge (mAh) Discharge (mAh) Efficiency (%) DC-IR (Ω, @SOC 50%) △DC-IR (%) Comparative Example 2106.5 105.49 9.0 0.780 Comparative Example 3110.8 110.49 9.6 0.73-7.0 Exemplary Example 2106.3 105.79 9.4 0.59-24.3 Exemplary Example 3110.0 109.79 9.70.70-10.9

[0127] As a result, it can be confirmed that in Example 2, where a surface-modified positive electrode active material was applied, the desolvation rate of the electrolyte was accelerated and the ionic conductivity at low temperatures was increased, thereby improving cell resistance and output characteristics.

Claims

1. A step of preparing a solid electrolyte dispersion comprising an oxide-based solid electrolyte and a solvent; A step of coating the solid electrolyte dispersion on the surface of the electrode active material; and A method for manufacturing a surface-modified electrode active material, comprising: a step of heat-treating the coated electrode active material to form a surface-modified electrode active material.

2. In paragraph 1, A method for producing a surface-modified electrode active material, wherein the dispersion preparation step comprises mixing 5 to 70 parts by weight of an oxide-based solid electrolyte and 30 to 95 parts by weight of a solvent.

3. In paragraph 1, A method for manufacturing an electrode for a lithium secondary battery, wherein an oxide-based solid electrolyte is dispersed in a solvent phase using a bead-milling method in the above dispersion manufacturing step.

4. In paragraph 1, A method for manufacturing an electrode for a lithium secondary battery, wherein the oxide-based solid electrolyte comprises 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.

5. In paragraph 1, A method for manufacturing an electrode for a lithium secondary battery, wherein the oxide-based solid electrolyte comprises 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.

6. In paragraph 1, A method for manufacturing an electrode for a lithium secondary battery, wherein the above oxide-based solid electrolyte has a particle size distribution of at least one of D50 of 100 nm to 1 ㎛ and D90 of 400 nm to 1.5 ㎛.

7. In paragraph 6, A method for producing a surface-modified electrode active material, wherein the oxide-based solid electrolyte in the solid electrolyte dispersion has a particle size distribution of D50 of 300 to 700 nm, D90 of 400 to 900 nm, and span of 1 or less.

8. In paragraph 1, A method for manufacturing a surface-modified electrode active material, wherein the above solid electrolyte dispersion coating step is performed by a spray coating method.

9. In paragraph 1, A method for producing a surface-modified electrode active material, wherein the above oxide-based solid electrolyte is included in an amount of 0.3 to 5 parts by weight per 100 parts by weight of the electrode active material.

10. In paragraph 1, A method for manufacturing a surface-modified electrode active material, wherein the heat treatment step includes heat treatment at a temperature higher than the glass transition temperature (Tg) of the oxide-based solid electrolyte.

11. In paragraph 1, A method for producing a surface-modified electrode active material, wherein the above heat treatment step is performed by firing at a temperature of 600 to 1000°C for 1 to 3 hours to form a surface-modified electrode active material.

12. Metal current collector; and An electrode for a lithium secondary battery, comprising an active material layer formed on the metal current collector and including a surface-modified electrode active material manufactured by any one of the manufacturing methods of claims 1 to 11.

13. Containing a positive electrode; a negative electrode; and an electrolyte including a lithium salt and a non-aqueous organic solvent; A lithium secondary battery comprising an electrode for a lithium secondary battery according to Article 12 as a positive electrode.

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