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

Abstract

The present disclosure relates to a method for manufacturing a surface-modified electrode active material capable of improving output characteristics, low-temperature characteristics and the like, and an electrode and a lithium secondary battery manufactured from the surface-modified electrode active material. The method for manufacturing a surface-modified electrode active material comprises the steps of: preparing a solid electrolyte dispersion containing an oxide-based solid electrolyte and a solvent; applying the solid electrolyte dispersion onto the surface of the electrode active material; and heat-treating the coated electrode active material to form a surface-modified electrode active material.

Description

TECHNICAL FIELD

[0001] Cross Reference to Related Applications

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0118577, filed on September 6, 2023, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

[0003] The present disclosure relates to a method for manufacturing a surface-modified electrode active material that can improve output characteristics and low-temperature characteristics of a lithium secondary battery, and an electrode and a lithium secondary battery manufactured thereby. BACKGROUND

[0004] Recently, as the application fields of lithium secondary batteries are rapidly expanding to energy storage power sources of large-area devices (e.g., automobiles and energy storage devices), and power, electronics, communication, and power sources of electronic devices (e.g., computers), the demand for lithium secondary batteries having high capacity, high output, long lifespan, and high stability is increasing.

[0005] A lithium secondary battery is generally configured to include a positive electrode, a negative electrode, a separator, and an electrolyte containing a lithium salt and an organic solvent, in which lithium ions move through the electrolyte during charging and discharging.

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

[0007] Meanwhile, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4), etc.), or lithium iron phosphate compounds (LiFePO4) have been used as positive electrode active materials of lithium secondary batteries. In particular, lithium composite transition metal oxides based on NCM have been developed to improve low thermal stability while maintaining the excellent reversible capacity of LiNiO2, however, conventional lithium composite transition metal oxides based on NCM are insufficient in capacity characteristics and thus are limited in application.

[0008] To address such limitations, research has recently been conducted to increase the nickel (Ni) content in lithium composite transition metal oxides based on NCM. However, in the case of high-concentration nickel positive electrode active materials, capacity is increased, but as the depth of charge increases, Ni 2+ oxidized to Ni 3+ / 4+Rapid oxygen desorption occurs, and the desorbed oxygen reacts with the electrolyte to change the inherent properties of the material, which may cause instability in the crystal structure and even structural collapse.

[0009] Therefore, there is a continued need to develop technologies that can accelerate the desolvation of lithium ions in the electrolyte, thereby improving the output characteristics of lithium secondary batteries and maintaining excellent low-temperature characteristics. Summary of the Invention

[0010] Technical issues

[0011] Therefore, one object of this disclosure is to provide a method for manufacturing a surface-modified electrode active material that can accelerate the desolvation of lithium ions in an electrolyte, thereby improving the output characteristics of a lithium secondary battery and maintaining excellent low-temperature characteristics, such as high output at low temperatures.

[0012] Another object of this disclosure is to provide electrodes and lithium secondary batteries made from the surface-modified electrode active material, which exhibit improved output characteristics and low-temperature characteristics.

[0013] Technical solution

[0014] In the following, a method for manufacturing surface-modified electrode active materials, etc., according to specific embodiments of the present disclosure will be described.

[0015] The terms or words used in the specification and appended claims should not be construed as limited to their ordinary or dictionary meanings, and this disclosure should be interpreted in a meaning and concept consistent with the technical concept of this disclosure, based on the principle that the inventor can appropriately define the concepts of the terms in order to best describe his own invention.

[0016] The terminology used herein is provided to describe exemplary embodiments and not to limit the inventive concept. Unless the context clearly indicates otherwise, the singular forms include the plural forms.

[0017] It should be understood that the terms “comprising,” “including,” “having,” etc., are used herein to specify the presence of the said feature, integer, step, component, or combination thereof, but do not exclude the presence or addition of one or more other features, integers, steps, components, or combinations thereof.

[0018] Method for manufacturing surface-modified electrode active materials

[0019] According to one embodiment of this disclosure, a method for manufacturing a surface-modified electrode active material is provided, the method comprising the steps of: preparing a solid electrolyte dispersion comprising an oxide-based solid electrolyte and a solvent; coating the solid electrolyte dispersion onto the surface of an electrode active material; and heat-treating the coated electrode active material to form a surface-modified electrode active material.

[0020] Specifically, refer to Figure 1 A method for manufacturing surface-modified electrode active materials involves pre-dispersing an oxide-based solid electrolyte in a solvent, allowing the oxide-based solid electrolyte to be uniformly distributed on the surface of the electrode active material. This differs from conventional surface-modified active materials where the oxide-based solid electrolyte particles aggregate and are unevenly distributed. Therefore, the oxide-based solid electrolyte particles can lower the activation energy associated with the desolvation process of lithium ions in the electrolyte at the interface where the electrode active material layer and the electrolyte contact each other, thus accelerating lithium ion desolvation. Furthermore, this can improve lithium-ion conductivity around the electrode active material particles.

[0021] First, an oxide-based solid electrolyte can be uniformly dispersed in a solvent to prepare a solid electrolyte dispersion comprising the oxide-based solid electrolyte and a solvent. Thus, the oxide-based solid electrolyte can be pre-dispersed in the solvent, and the oxide-based solid electrolyte can be uniformly distributed on the surface of the electrode active material in the coating steps described below.

[0022] In one exemplary embodiment, the step of preparing the dispersion 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 the oxide-based solid electrolyte and solvent are mixed within the above ranges, if the content of the oxide-based solid electrolyte is 70 parts by weight or more, it is difficult to control the D50 value between 100 nm and 1 μm, and if the content of the solid electrolyte is 5 parts by weight or less, the dispersion energy efficiency transferred to the particle surface may decrease, and the dispersion time may become longer.

[0023] In one exemplary embodiment, in the step of preparing the dispersion, an oxide-based solid electrolyte can be dispersed in a solvent using one or more of the following methods: ultrasonic treatment, high-shear mixer, high-pressure homogenizer, and bead milling.

[0024] In particular, in order to improve the dispersion efficiency of high-concentration oxide-based solid electrolyte dispersions with nanoparticle size and minimize the oxidation of oxide-based solid electrolytes due to heat generated during the dispersion process, bead milling can be used, wherein the temperature of the dispersion is up to 40°C and the dispersion time is up to 3 hours.

[0025] In one exemplary embodiment, the oxide-based solid electrolyte in the solid electrolyte dispersion may have one or more particle size distributions selected from D50 of 100 nm to 1 μm and D90 of 400 nm to 1.5 μm. The electrolyte may have, for example, one or more particle size distributions selected from D50 of 300 nm to 700 nm, D90 of 400 nm to 900 nm, and a 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 can be achieved.

[0026] In one exemplary embodiment, any solid electrolyte containing lithium in its structure, having a lithium-ion source, and in the form of lithium metal oxide or lithium metal phosphate, can be used as an oxide-based solid electrolyte.

[0027] Specific examples include at least one lithium metal oxide or lithium metal phosphate selected from: Nasicon-type solid electrolytes, Lisicon-type solid electrolytes, garnet-type solid electrolytes, perovskite-type solid electrolytes, and LiPON-type solid electrolytes. More specific examples include at least one of the following: compounds based on LAGP (lithium aluminum germanium phosphate), compounds based on LLZO (lithium lanthanum zirconium oxide), compounds based on LATP (lithium aluminum titanium phosphate), compounds based on LLZTO (lithium lanthanum zirconium tantalum oxide), compounds based on LLTO (lithium lanthanum titanium oxide), compounds based on LSTP (lithium silicon titanium phosphate), and compounds based on LGPO (lithium germanium phosphate).

[0028] From the perspective 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 lithium secondary batteries, Nasicon-type solid electrolytes, such as LAGP-based compounds or LATP-based compounds, can be appropriately used.

[0029] Next, the solid electrolyte dispersion can be coated onto the surface of the electrode active material. Specifically, the solid electrolyte dispersion can be mixed with the positive electrode active material to form a uniform coating, such that the nanoparticles of the oxide-based solid electrolyte dispersion are uniformly distributed on the surface of the positive electrode active material.

[0030] In an exemplary embodiment, the step of coating the solid electrolyte dispersion can be carried out by one or more of the following methods: spraying, high-speed homogenization mixing, and fluidized bed coating.

[0031] In an exemplary embodiment, the positive electrode active material can be a compound capable of reversibly intercalating and deintercalating lithium, and specifically, it can include a lithium metal oxide containing lithium and at least one metal (such as iron, cobalt, manganese, nickel, or aluminum).

[0032] Specifically, the lithium metal oxide can include lithium-manganese-based oxides (such as LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (such as LiCoO2, etc.), lithium-nickel-based oxides (such as LiNiO2, etc.), lithium-nickel-manganese-based oxides (such as LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (such as LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (such as LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt-based oxides (such as Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, and p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, and p1 + q1 + r1 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxides (such as Li(Ni p2 Co q2 Mn r2 M s2 )O2 (where M is selected from Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of each independent element, where 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1), etc.), lithium iron phosphate (for example, Li 1+a Fe 1-x M x (PO 4-b )Xb (where M is selected from at least one of Al, Mg and Ti, X is selected from at least one of F, S and N, -0.5≤a≤0.5, 0≤x≤0.5, 0≤b≤0.1), etc., and any one of them or a mixture of two or more of them may be used.

[0033] The positive electrode active material includes a lithium metal oxide containing lithium and two or more metals selected from nickel, manganese, cobalt, and aluminum. Based on the total metal content excluding lithium, the lithium metal oxide may contain 60 mol% or more, or 60 mol% to 99 mol%, or 70 mol% to 95 mol% of nickel. Such a lithium metal oxide can be represented, for example, by the following chemical formula 1:

[0034] [Chemical Formula 1]

[0035] Li x Ni a Co b M 1 c M 2 d O2

[0036] In chemical formula 1, M 1 It can be one or more of Mn and Al, or a combination thereof, M 2 It can be one or more of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, 0.90≤x≤1.1, or 0.95≤x≤1.08, or 1.0≤x≤1.08, and 0.60≤a≤1.0, or 0.70≤a≤0.99, or 0.80≤a≤0.95.

[0037] Meanwhile, the average particle size (D50) of the positive electrode active material can be 4 μm to 15 μm, or 7 μm to 13 μm, or 8 μm to 12 μm.

[0038] By using lithium metal oxides with such a high nickel content as the positive electrode active material and combining them with oxide-based solid electrolytes, the output and capacity characteristics of lithium secondary batteries can be further improved.

[0039] In one exemplary embodiment, from the perspective of accelerating the desolvation of lithium ions at the interface between the active material layer and the electrolyte and improving lithium ion conductivity without inhibiting the insertion and desorption process of lithium ions by the positive electrode active material, 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.

[0040] Next, the coated electrode active material can be heat-treated to form a surface-modified electrode active material.

[0041] In one exemplary embodiment, the heat treatment is preferably performed at a temperature equal to or higher than the glass transition temperature (Tg) of the oxide-based solid electrolyte, and after the heat treatment, the oxide-based solid electrolyte nanoparticles uniformly coated on the surface of the active material are sintered to form a uniform coated thin film layer, thereby forming a modified electrode active material.

[0042] In one exemplary embodiment, the heat treatment step may include firing at a temperature of 600°C to 1000°C for 1 to 3 hours to form a surface-modified electrode active material.

[0043] Simultaneously, the solvent can be removed before the firing process. Specifically, the electrode active material coated with an oxide-based solid electrolyte is first dried at 130°C for 2 hours to remove the NMP solvent. The dried active material coated with the oxide-based solid electrolyte can then be fired at 800°C for 2 hours to form a surface-modified electrode active material.

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

[0045] According to another embodiment of this disclosure, 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 comprising a surface-modified electrode active material manufactured by the method described above for manufacturing a surface-modified electrode active material.

[0046] The following will describe in more detail an electrode for a lithium secondary battery according to one embodiment and a lithium secondary battery including the same. However, the following description primarily focuses on one embodiment in which the electrode for the lithium secondary battery is the positive electrode, but it is obvious that the scope of this disclosure is not limited thereto, and the electrode of one embodiment may also be the negative electrode.

[0047] According to one embodiment, the positive electrode for a lithium secondary battery includes a metal current collector. There are no particular limitations on the metal current collector, as long as it is conductive and does not cause chemical changes within the battery. For example, stainless steel; aluminum; nickel; titanium; calcined carbon; or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc., can be used.

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

[0049] Meanwhile, the conductive material included in the active material layer is a component used to further improve the conductivity of the positive electrode active material. There are no particular limitations on such conductive materials, as long as they are conductive and do not cause chemical changes in the battery. For example, conductive materials that can be used include: carbon powder, such as carbon black, acetylene black, Ketjen black, celluloid black, furnace black, lampblack, or thermally cracked carbon black; graphite powder, such as natural graphite, artificial graphite, or graphite with a well-formed crystal structure; conductive nanomaterials, such as carbon nanofibers or carbon nanotubes; fluorinated carbon powder; conductive powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive materials such as polyphenylene derivatives. Among these, the conductive materials include conductive nanomaterials such as carbon nanotubes or carbon nanofibers, which can further reduce the resistance of the lithium secondary battery including the positive electrode of one embodiment and further improve output characteristics, etc.

[0050] Typically, based on the total weight of the positive electrode active material layer, the conductive material may be included in an amount of 1% to 20% by weight, or 1% to 15% by weight, or 1% to 10% by weight.

[0051] The binder selectively included in the active material layer is a component that facilitates bonding between the positive electrode active material and the conductive material, as well as bonding with the current collector. Examples of binders may include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, nitrile-based rubber, styrene-butadiene rubber, fluororubber, etc. Mixtures or copolymers selected from two or more of these may also be used.

[0052] Typically, the binder may be included in an amount of 1% to 20% by weight, or 1% to 15% by weight, or 1% to 10% by weight, based on the total weight of the positive electrode active material layer.

[0053] In addition, fillers may optionally be added to the positive electrode as a component to suppress its expansion. There are no particular limitations on such fillers, as long as they suppress electrode expansion without causing chemical changes in the battery, and examples may include: olefinic polymers, such as polyethylene and polypropylene; and fibrous materials, such as glass fiber and carbon fiber.

[0054] The positive electrode of one embodiment described above can be prepared, for example, by dispersing and mixing a positive electrode active material, an oxide-based solid electrolyte, a binder, a conductive material, etc., in a dispersion medium (solvent) to form a slurry, coating the slurry onto a metal current collector, and then drying and rolling it. In this case, the dispersion medium can be NMP (N-methyl-2-pyrrolidone), DMF (dimethylformamide), DMSO (dimethyl sulfoxide), ethanol, isopropanol, water, or mixtures thereof, but is not necessarily limited to these.

[0055] Furthermore, a lithium secondary battery is provided, comprising: a positive electrode; a negative electrode; and an electrolyte containing a lithium salt and a non-aqueous organic solvent, wherein the positive electrode of the aforementioned lithium secondary battery is included. Such a lithium secondary battery according to other embodiments can exhibit excellent output characteristics and low-temperature characteristics.

[0056] In other embodiments of the lithium secondary battery, the negative electrode may have a conventional configuration known in the art. For example, the negative electrode may include a negative electrode current collector and a layer of negative electrode active material formed on the negative electrode current collector, wherein the negative electrode active material layer may contain, for example, a negative electrode active material, and, if necessary, may contain additives such as conductive materials, binders, and fillers. Furthermore, such a negative electrode can be formed by a general method: dispersing and mixing the components of the negative electrode active material layer in a dispersion medium (solvent) to form a slurry, coating the slurry onto the negative electrode current collector, and then drying and rolling it.

[0057] At this time, the negative electrode current collector can be 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), or alloys thereof, or copper (Cu) or stainless steel whose surface has been treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag), but is not necessarily limited to these. The shape of the negative electrode current collector can be foil, film, sheet, stamped form, porous body, foam, etc.

[0058] Furthermore, compounds capable of reversibly inserting and de-intercalating lithium can be used as anode active materials. Specific examples include: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, or amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Sb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and metal oxides capable of doping and de-doping lithium, such as SiO₂. β(0<β<2), SnO2, vanadium oxide or lithium vanadium oxide; or composite materials containing metal compounds and carbonaceous materials, such as Si-C composite materials or Sn-C composite materials, and mixtures of any one or more of them may be used. Furthermore, a thin film of metallic lithium may be used as the negative electrode active material.

[0059] Furthermore, both low-crystallinity carbon and high-crystallinity carbon can be used as carbonaceous materials. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, sheet-like, flake-like, spherical, or fibrous natural or artificial graphite, crystalline graphite (Kish graphite), pyrolytic carbon, carbon fibers based on mesophase pitch, mesophase carbon microspheres, mesophase pitch, and high-temperature calcined carbon such as coke derived from petroleum or coal tar pitch.

[0060] Based on the total weight of the negative electrode active material layer, the aforementioned negative electrode active material may be included in an amount of 60% to 99% by weight, or 70% to 99% by weight, or 80% to 98% by weight.

[0061] In other embodiments, 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 that migrate from the positive electrode during charging and discharging are electrodeposited on the negative electrode current collector to form a lithium metal layer, and this lithium metal layer can be used as the negative electrode active material.

[0062] On the other hand, the binder and conductive materials included in the negative electrode active material layer can be the same as those previously described for the positive electrode, and therefore, further description thereof will be omitted. Furthermore, when the electrode for a lithium secondary battery according to the above embodiment is used as the negative electrode, the negative electrode active material layer may also include the aforementioned oxide-based solid electrolyte with a lithium-ion source. In this case, the oxide-based solid electrolyte can satisfy the D50 ratio of the aforementioned negative electrode active material particles.

[0063] Other embodiments of the lithium secondary battery described above also include an electrolyte containing lithium salts and non-aqueous organic solvents. Such an electrolyte serves as a transfer medium for lithium ions between the positive and negative electrodes, wherein the lithium ions exist in a solvated state within the electrolyte, and can be inserted into the electrode active material through desolvation at the interface between the electrolyte and the electrodes. Another embodiment of the secondary battery can accelerate this desolvation and exhibit even better output characteristics as described above.

[0064] The lithium salt contained in the electrolyte serves as a medium for transferring ions within the lithium secondary battery. For example, the lithium salt may contain Li. + It is a cation and may contain anion selected from the following: 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 - .

[0065] Specifically, the lithium salt may include at least one of the following: LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10LiAlCl4, 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 lithium salts can be appropriately varied within the normal usable range and can be included in the electrolyte at a concentration of 0.5 M to 6 M or 1 M to 5 M.

[0067] In a more specific example, the electrolyte may contain lithium salt at a relatively low concentration of 0.5 M or greater but less than 2 M, or 0.7 M to 1.5 M. Even in such cases, the lithium secondary battery of another embodiment can exhibit improved output characteristics due to the accelerated desolvation of lithium ions caused by the action of the electrode in one embodiment described above. Therefore, not only can problems such as increased electrolyte viscosity, reduced fluidity, and decreased electrolyte ion conductivity and battery output at low temperatures caused by the use of electrolyte compositions containing high concentrations of lithium salt be solved, but also excellent low-temperature characteristics of lithium secondary batteries can be achieved.

[0068] On the other hand, in some other embodiments of this disclosure, the electrolyte may contain lithium salt at a high concentration of 2 M to 6 M, or 2.5 M to 5.5 M. In such cases, by containing a high concentration of lithium salt and applying the electrode of one embodiment, the desolvation of lithium ions can be further accelerated, and the output characteristics of the secondary battery can be further improved.

[0069] Furthermore, by applying an electrode according to one embodiment, lithium-ion conductivity can be improved and resistance can be reduced even at low temperatures. This reduces the degradation of low-temperature output characteristics caused by high lithium salt concentrations.

[0070] On the other hand, there are no particular limitations on the types of non-aqueous organic solvents that can be included in the electrolyte, and any organic solvent known to be suitable for lithium-ion battery electrolytes can be used. Examples of such organic solvents include those selected from at least one of the following: carbonate-based solvents, ether-based solvents, nitrile-based solvents, phosphate-based solvents, and sulfone-based solvents.

[0071] More specifically, carbonate-based solvents may include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butyl carbonate, fluoroethylene carbonate, methyl propyl carbonate, methyl ethyl carbonate, ethyl propyl carbonate, methyl (2,2,2-trifluoroethyl) carbonate, etc., and phosphate-based solvents may include trimethyl phosphate, triethyl phosphate, 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxophosphazenecyclopentane 2-oxide, etc.

[0072] Furthermore, ether-based solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, or tetrahydrofuran derivatives such as 2-methyltetrahydrofuran, and nitrile-based solvents may include butadienenitrile, adiponitrile, sebacatenitrile, acetonitrile, propionitrile, etc. Additionally, sulfone-based solvents may include dimethyl sulfone, ethylmethyl sulfone, sulfolane, etc.

[0073] In addition to lithium salts and non-aqueous organic solvents, the electrolyte may also contain a diluent that exhibits lithium salt solubility at least 10 times lower than that of the non-aqueous organic solvent. Such a diluent is an organic solvent miscible with non-aqueous organic solvents but substantially insoluble in lithium salts. For example, it may be an ether-based solvent having fluorinated alkyl groups, and more specifically, it may include one or more of the following: 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), methoxynonfluorobutane (MOFB), and ethoxynonfluorobutane (EOFB).

[0074] When such a diluent is also included, locally high concentrations of lithium salt can exist in the non-aqueous organic solvent of the electrolyte, while lithium salt can be essentially absent in the diluent. Because the locally high concentration of lithium salt exists in the electrolyte in a solvated form, the output characteristics of the lithium secondary battery can be further improved, and the increase in electrolyte viscosity and decrease in fluidity can also be reduced. Furthermore, if an electrode of one embodiment is used with this locally high concentration of salt electrolyte, lithium-ion conductivity can be improved and resistance can be reduced even at low temperatures, thereby reducing the degradation of low-temperature output characteristics caused by high concentrations of lithium salt.

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

[0076] Meanwhile, the lithium secondary battery in some of the above embodiments may also include a porous separator membrane inserted between the positive and negative electrodes.

[0077] Such porous separators can be made from olefinic polymers (e.g., polyethylene and polypropylene) in the form of sheets, multilayers, microporous membranes, woven fabrics, and nonwoven fabrics, as well as glass fibers, but are not necessarily limited to these. However, porous polyethylene or porous glass fiber nonwoven fabrics (glass filters) are preferred as separators, and porous polyethylene is even more preferred. The separator can be an insulating film with high ion permeability and mechanical strength, and the pore size of the separator is typically in the range of 0.01 μm to 10 μm, and the thickness is typically in the range of 5 μm to 300 μm, but is not limited to these.

[0078] Furthermore, in some other embodiments of the lithium secondary battery, a separator membrane may not be inserted, but the electrolyte can be inserted 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 containing the aforementioned lithium salt and a non-aqueous organic solvent in a polymer matrix. Known polymer-based solid electrolytes can be used as the polymer matrix. In this case, other embodiments of the lithium secondary battery may be semi-solid-state batteries that combine liquid and solid electrolytes.

[0079] Meanwhile, other embodiments of the lithium secondary battery can be prepared according to conventional methods in the art. For example, the lithium secondary battery can be prepared by housing an electrode assembly including a positive electrode, a negative electrode, and a separator (or electrolyte membrane) in a housing, and injecting and impregnating the aforementioned electrolyte in the housing.

[0080] Such lithium secondary batteries can be used not only as battery cells for powering small devices, but also as cell batteries in battery modules for powering medium and large devices.

[0081] Beneficial effects

[0082] A method for manufacturing a surface-modified electrode active material according to one embodiment of this disclosure pre-disperses an oxide-based solid electrolyte in a solvent and uniformly distributes the oxide-based solid electrolyte on the surface of the electrode active material. Therefore, the oxide-based solid electrolyte particles can reduce the activation energy associated with the desolvation process of lithium ions in the electrolyte at the interface where the electrode active material and the electrolyte contact each other, thereby accelerating desolvation. This can also improve the lithium-ion conductivity around the electrode active material particles.

[0083] Furthermore, since the output characteristics of lithium secondary batteries can be improved even without the application of new electrolyte compositions such as those containing high concentrations of lithium salts, problems such as increased electrolyte viscosity, reduced fluidity, and decreased electrolyte ion conductivity and battery output caused by the application of new electrolyte compositions can be solved, and excellent low-temperature characteristics of lithium secondary batteries can be achieved.

[0084] Furthermore, even when used with an electrolyte composition containing a high concentration of lithium salts, the electrode disclosed herein can promote the desolvation of lithium ions, thereby improving lithium ion conductivity and reducing resistance.

[0085] Therefore, this disclosure can greatly contribute to the development of next-generation lithium secondary batteries that exhibit improved output and low-temperature characteristics. Attached Figure Description

[0086] Figure 1 A comparison is shown between the manufacturing method according to this disclosure (in which an oxide-based solid electrolyte is pre-dispersed in a solvent such that the oxide-based solid electrolyte is uniformly distributed on the surface of the electrode active material) and a conventional method (in which oxide-based solid electrolyte particles in the surface-modified active material aggregate rather than are uniformly dispersed).

[0087] Figure 2 SEM and EDS Ti elemental mapping images of the positive electrode active materials of Comparative Example 1 and Example 1 according to this disclosure are shown.

[0088] Figure 3 The results of evaluating the electrochemical properties of lithium secondary batteries manufactured using the cathodes of Examples 2 and 3 and Comparative Examples 2 and 3 according to this disclosure are shown.

[0089] Figure 4 A graph showing a comparison of the resistance measured at state of charge (SOC) of lithium secondary batteries manufactured using the positive electrodes of Examples 2 and 3 and Comparative Examples 2 and 3 according to this disclosure. Detailed Implementation

[0090] The present disclosure will be described in more detail below with reference to specific embodiments. However, the following embodiments are merely exemplary implementations to aid in understanding the present disclosure and are not intended to limit the scope of the disclosure.

[0091] Example 1-1: Manufacturing of surface-modified positive electrode active materials

[0092] 25 g of Li, an oxide-based solid electrolyte with a D50 of 300 nm, was used. 1.3 Al 0.3 Ti 1.7(PO4)3 (LATP) and 50 g of NMP were mixed, and the mixture was added to the mixture using a bead mill. The mixture was then subjected to dispersion treatment for 40 minutes using a pin mill to prepare a solid electrolyte dispersion.

[0093] A lithium nickel cobalt manganese composite oxide (NCM 603; D50: 5 μm) containing 80 mol% nickel in all transition metals was used as the positive electrode active material. The prepared dispersion was added to 5 kg of the positive electrode active material, and then mixed and stirred at 3000 rpm for 30 minutes using a homogenizer. 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 positive electrode active material with a uniform solid electrolyte coating film formed thereon.

[0094] Examples 1-2: Manufacturing of surface-modified positive electrode active materials

[0095] 50 g of Li, an oxide-based solid electrolyte with a D50 of 300 nm, was used. 1.3 Al 0.3 Ti 1.7 (PO4)3 (LATP) and 50 g of NMP were mixed, and the mixture was added to the mixture using a bead mill. The mixture was then subjected to dispersion treatment for 40 minutes using a pin mill to prepare a solid electrolyte dispersion.

[0096] A lithium nickel cobalt manganese composite oxide (NCM 603; D50: 5 μm) containing 65 mol% nickel in all transition metals was used as the positive electrode active material. The prepared dispersion was added to 5 kg of the positive electrode active material, and then mixed and stirred at 3000 rpm for 30 minutes using a homogenizer. 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 positive electrode active material with a uniform solid electrolyte coating film formed thereon.

[0097] Example 2: Manufacturing of Lithium Secondary Batteries

[0098] Carbon nanotubes were used as the conductive material, and polyvinylidene fluoride (PVDF) was used as the binder. A slurry of the positive electrode active material was prepared by mixing 97 parts by weight of the surface-modified positive electrode active material from Example 1-1, 1.5 parts by weight of the conductive material, and 1.5 parts by weight of the binder. The prepared slurry was coated onto an aluminum current collector and dried to prepare the positive electrode. At this time, the particle size distribution of the oxide-based solid electrolyte (LATP) was measured using a laser diffraction particle size analyzer (Malvern Mastersizer 3000), and it was found to be D10: 0.234 μm, D50: 0.345 μm, D90: 0.495 μm, and span: 0.757. Graphite was used as the negative electrode active material, and the negative electrode active material: conductive material: binder was mixed in a weight ratio of 96.5:1.5:2 without using the oxide-based solid electrolyte, and the same process as for the positive electrode was performed to manufacture the negative electrode.

[0099] The prepared positive and negative electrodes were positioned facing each other, a 15 μm thick polyethylene (PE) separator was inserted between them, and an electrolyte was filled to fabricate a bi-cell type lithium secondary battery. The electrolyte was prepared by dissolving LiPF6 at a concentration of 1.0 M in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate (EC / EMC mixed volume ratio of 3 / 7).

[0100] Example 3: Manufacturing a lithium secondary battery

[0101] Carbon nanotubes were used as the conductive material, and polyvinylidene fluoride (PVDF) was used as the binder. A positive electrode active material slurry was prepared by mixing 97 parts by weight of the surface-modified positive electrode active material from Examples 1-2, 1.5 parts by weight of the conductive material, and 1.5 parts by weight of the binder. The prepared slurry was coated onto an aluminum current collector and dried to prepare the 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 the negative electrode active material, and the negative electrode active material: conductive material: binder was mixed in a weight ratio of 96.5:1.5:2 without using the oxide-based solid electrolyte, and the same process as for the positive electrode was performed to manufacture the negative electrode.

[0102] The prepared positive and negative electrodes were positioned facing each other, a 15 μm thick polyethylene (PE) separator was inserted between them, and an electrolyte was filled to fabricate a dual-cell lithium secondary battery. The electrolyte was prepared by dissolving LiPF6 at a concentration of 1.0 M in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate (EC / EMC mixed volume ratio of 3 / 7).

[0103] Comparative Example 1: Positive Electrode Active Material

[0104] A lithium nickel cobalt manganese composite oxide (NCM 603; D50: 5 μm) containing 65 mol% nickel in all transition metals was used.

[0105] Comparative Example 2: Manufacturing Lithium Secondary Batteries

[0106] A positive electrode active material slurry 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 material, and 1.5 parts by weight of PVDF. The prepared slurry was coated onto an aluminum current collector and dried to prepare the positive electrode. The conductive material, binder, negative electrode, and electrolyte were the same as those used in Example 2.

[0107] The prepared positive and negative electrodes are positioned facing each other, and a 20 μm thick polyethylene (PE) separator is inserted between them and filled with electrolyte to manufacture a dual-cell lithium secondary battery.

[0108] Comparative Example 3: Samples without pre-dispersion

[0109] A positive electrode active material slurry was prepared by mixing 96 parts by weight of the positive electrode active material of Comparative Example 1, 1.5 parts by weight of the conductive material, 1.5 parts by weight of PVDF, and 1 part by weight of oxide-based solid electrolyte (LATP). The prepared slurry was coated onto an aluminum current collector and dried to prepare the positive electrode. The conductive material, 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.

[0110] The prepared positive and negative electrodes are positioned facing each other, and a 20 μm thick polyethylene (PE) separator is inserted between them and filled with electrolyte to manufacture a dual-cell lithium secondary battery.

[0111] Experimental Example

[0112] 1) Figure 2 SEM and EDS analyses of the surface-modified positive electrode active materials of Comparative Example 1 and Example 1 respectively show the Ti elemental mapping images of the oxide-based solid electrolyte.

[0113] As a result, it can be determined that, compared with unmodified positive electrode active materials, the surface-modified positive electrode active materials according to embodiments of the present disclosure enable the oxide-based solid electrolyte nanoparticles to be uniformly dispersed and subjected to heat treatment to form a uniform solid electrolyte coating on the surface of the positive electrode active material.

[0114] 2) In addition, the electrochemical characteristics of the lithium secondary batteries of Examples 2 and 3, as well as Comparative Examples 2 and 3, were evaluated. Specifically, for each sample, the capacity change and charge / discharge change were measured simultaneously during three repeated charge / discharge tests at room temperature (approximately 25°C) under the following conditions: 1) charging from 0.2 C to 0.33 C (cutoff: 4.2 V, 0.05 C) and 2) discharging from 0.2 C to 0.33 C (cutoff: 2.5 V), and the results are shown in... Figure 3 middle.

[0115] As a result, it can be determined that in Examples 2 and 3, which applied surface-modified positive electrode active materials, the desolvation rate of the electrolyte was accelerated and the ionic conductivity at low temperatures was improved, thereby improving battery resistance and output characteristics.

[0116] 3) For the lithium secondary batteries of Examples 2 and 3, and Comparative Examples 2 and 3, the resistance at each state of charge (SOC) was measured while repeatedly performing charge / discharge tests at room temperature (approximately 25°C) under the following conditions: 1) charging from 0.2 C to 0.33 C (cutoff: 4.2 V, 0.05 C) and 2) discharging from 0.2 C to 0.33 C (cutoff: 2.5 V). Specifically, the charge / discharge tests were repeated at SOC settings of 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, and 10%, and the DC resistance (2.5 C discharge (cutoff: 10 seconds or 2 V)) was measured after each charge / discharge. The resistance measurement results for each state of charge are shown in... Figure 4 The following are listed together in Table 1:

[0117] [Table 1]

[0118]

[0119] As a result, it can be determined that in Example 2, which uses a surface-modified positive electrode active material, the desolvation rate of the electrolyte is accelerated and the ionic conductivity at low temperatures is improved, thereby improving the battery resistance and output characteristics.

Claims

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

2. The method for manufacturing a surface-modified electrode active material according to claim 1, wherein: the step of preparing the dispersion includes mixing 5 parts by weight to 70 parts by weight of the solid electrolyte based on an oxide and 30 parts by weight to 95 parts by weight of the solvent.

3. The method for manufacturing a surface-modified electrode active material according to claim 1, wherein: in the step of preparing the dispersion, the solid electrolyte based on an oxide is dispersed in the solvent using a bead mill method.

4. The method for manufacturing a surface-modified electrode active material according to claim 1, wherein: the solid electrolyte based on an oxide includes at least one lithium metal oxide or lithium metal phosphate selected from among 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. The method for manufacturing a surface-modified electrode active material according to claim 1, wherein: the solid electrolyte based on an oxide includes at least one selected from among a LAGP (lithium aluminum germanium phosphate)-based compound, a LLZO (lithium lanthanum zirconium oxide)-based compound, a LATP (lithium aluminum titanium phosphate)-based compound, a LLZTO (lithium lanthanum zirconium tantalum oxide)-based compound, a LLTO (lithium lanthanum titanium oxide)-based compound, a LSTP (lithium silicon titanium phosphate)-based compound, and a LGPO (lithium germanium phosphate)-based compound.

6. The method for manufacturing a surface-modified electrode active material according to claim 1, wherein: the solid electrolyte based on an oxide has one or more particle size distributions of D50 of 100 nm to 1 μm and D90 of 400 nm to 1.5 μm.

7. The method for manufacturing a surface-modified electrode active material according to claim 6, wherein: in the solid electrolyte dispersion, the solid electrolyte based on an oxide has a particle size distribution of D50 of 300 nm to 700 nm, D90 of 400 nm to 900 nm, and a span of 1 or less.

8. The method for manufacturing a surface-modified electrode active material according to claim 1, wherein: the step of applying the solid electrolyte dispersion is performed by a spray method.

9. The method for manufacturing a surface-modified electrode active material according to claim 1, wherein: the solid electrolyte based on an oxide is included in an amount of 0.3 parts by weight to 5 parts by weight based on 100 parts by weight of the electrode active material.

10. The method for manufacturing a surface-modified electrode active material according to claim 1, wherein: the step of heat treatment includes heat treatment at a temperature equal to or higher than a glass transition temperature (Tg) of the oxide-based solid electrolyte.

11. The method for manufacturing a surface-modified electrode active material according to claim 1, wherein: the step of heat treatment includes firing treatment at a temperature of 600°C to 1000°C for 1 hour to 3 hours to form the surface-modified electrode active material.

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

13. A lithium secondary battery, comprising: a positive electrode; a negative electrode; and an electrolyte containing a lithium salt and a nonaqueous organic solvent, wherein the electrode for a lithium secondary battery according to claim 12 is included as a positive electrode.

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