Composite positive electrode active material, manufacturing method thereof, and all-solid-state battery comprising same

Abstract

The present invention relates to a composite positive electrode active material comprising: a first electrolyte layer disposed on the active material; and a second electrolyte layer disposed on the first electrolyte layer, wherein the first electrolyte layer is contained at 2.5 wt% to 5.0 wt% relative to the active material. The composite positive electrode active material of the present invention has thin and uniform electrolyte coating layers formed on the surface thereof, thereby enhancing electrochemical performance and rate capability in an all-solid-state battery.

Description

Composite cathode active material, method for producing the same, and all-solid-state battery comprising the same

[0001] The present invention relates to a composite cathode active material, a method for producing the same, and an all-solid-state battery including the same.

[0002] Lithium secondary batteries, which have high energy density and are easy to carry, are mainly used as batteries for small devices such as smartphones, tablets, and laptops. Recently, as they have begun to be used as batteries for electric vehicles or energy storage systems (ESS), related research is actively being conducted.

[0003] Lithium secondary batteries currently used in industry use electrolytes containing flammable organic solvents, posing safety concerns that can lead to explosions or fires in the event of collisions or penetrations. Therefore, all-solid-state batteries, which utilize solid electrolytes instead of the electrolyte, are being proposed. All-solid-state batteries are batteries composed entirely of solid materials, specifically those that utilize solid electrolytes. These all-solid-state batteries are safe, eliminating the risk of electrolyte leakage and explosion, and offer the advantage of being easy to manufacture in thin forms.

[0004] Meanwhile, in the case of all-solid-state batteries, the active material and solid electrolyte must be combined to provide an ion conduction path for the active material within the electrode. Furthermore, an electrolyte coating layer of appropriate thickness and ratio must be formed on the active material to facilitate contact between the active material and the solid electrolyte. However, conventional solid- or liquid-phase electrolyte coatings have the problem of difficulty in forming a thin, uniform coating layer on the surface of the active material.

[0005] The present invention provides a composite cathode active material capable of improving the electrochemical characteristics of an all-solid-state battery by thinly and densely coating an electrolyte on the surface of an active material to reduce the interfacial resistance between the active material and the electrolyte.

[0006] One embodiment of the present invention for achieving the above-described purpose relates to a composite cathode active material comprising an active material, a first electrolyte layer disposed on the active material, and a second electrolyte layer disposed on the first electrolyte layer, wherein the first electrolyte layer is included in an amount of 2.5 wt% to 5.0 wt% based on the active material.

[0007] The composite cathode active material of the present invention can improve the electrochemical characteristics and rate characteristics of an all-solid-state battery by forming a thin and uniform electrolyte coating layer on the surface.

[0008] FIG. 1 is a cross-sectional view schematically illustrating an example of a composite bipolar active material according to one embodiment of the present invention.

[0009] FIG. 2 is a flowchart schematically illustrating an example of a method for manufacturing a composite positive electrode active material according to another embodiment of the present invention.

[0010] Fig. 3 is a photograph of the surface of a composite cathode active material manufactured according to the method for manufacturing a composite cathode active material of Fig. 2.

[0011] Figure 4 is a flowchart schematically illustrating another example of the manufacturing method of Figure 2.

[0012] Figure 5 is a graph showing ionic conductivity.

[0013] Figure 6 is a graph showing the rate characteristics of Comparative Examples 1 to 3 and Example 1.

[0014] Figure 7 is a charge / discharge graph of Comparative Example 1 and Examples 2 to 4.

[0015] Figure 8 is a graph showing the life characteristics and rate characteristics of Comparative Example 1 and Examples 2 to 4.

[0016] Figure 9 is a graph showing the rate characteristics of Examples 1, 5, and 6.

[0017] Figure 10 is an XRD graph of Comparative Example 1 and Examples 3 to 6.

[0018] Figure 11 is a graph of the rate characteristics of Comparative Example 1 and Example 6.

[0019] One embodiment of the present invention for achieving the above-described purpose relates to a composite cathode active material, comprising a first electrolyte layer disposed on the active material and a second electrolyte layer disposed on the first electrolyte layer, wherein the first electrolyte layer is included in an amount of 2.5 wt% to 5.0 wt% based on the active material.

[0020] The thickness of the first electrolyte layer may be 100 nm to 1000 nm.

[0021] The second electrolyte layer includes first particles and second particles having different sizes, and the first particles may have a larger average particle diameter (D50) than the second particles.

[0022] The average particle diameter (D50) of the first electrolyte layer may be the same as the average particle diameter (D50) of the second particles.

[0023] The ratio of the first particle to the second particle may be 9:1 to 7:3.

[0024] The first electrolyte layer and the second electrolyte layer may contain the same material.

[0025] An intermediate layer may further be included between the active material and the first electrolyte layer.

[0026] Another embodiment of the present invention for achieving the above-described purpose relates to a method for producing a composite cathode active material, comprising the steps of preparing a solid electrolyte, mixing the solid electrolyte with an active material in a solvent to form a mixture, reacting the mixture to coat the solid electrolyte on the active material, and mixing the active material coated with the solid electrolyte, the solid electrolyte, and a conductive material.

[0027] In the step of preparing a solid electrolyte, the solid electrolyte may include a first solid electrolyte and a second solid electrolyte having different average particle diameters (D50).

[0028] The mixture includes the second solid electrolyte, and the second solid electrolyte may have a smaller average particle diameter (D50) than the first solid electrolyte.

[0029] The second solid electrolyte included in the mixture may be included in an amount of 2.5 wt% to 5 wt% based on the active material.

[0030] Additionally, a heat treatment step may be further included.

[0031] Another embodiment of the present invention for achieving the above-described purpose relates to an all-solid-state battery comprising a composite cathode active material and a cathode layer disposed on the composite cathode active material, wherein the composite cathode active material comprises an active material, a first electrolyte layer disposed on the active material, and a second electrolyte layer disposed on the first electrolyte layer.

[0032] Before describing in detail the preferred embodiments of the present invention below, it should be noted that the terms and 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 are consistent with the technical spirit of the present invention.

[0033] Throughout this specification, the terms first, second, etc. are used not in a limiting sense but for the purpose of distinguishing one component from another.

[0034] Throughout this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0035] Throughout this specification, terms such as “include” or “have” mean that a feature or component described in the specification is present, and do not preclude the possibility that one or more other features or components may be added.

[0036] Throughout this specification, when it is said that a part such as a film, region, component, etc. is on or above another part, it includes not only the case where it is directly on top of the other part, but also the case where another film, region, component, etc. is interposed between them.

[0037] The identifiers used in each step are for convenience of explanation and do not indicate the order of the steps. The steps may be performed in a different order than stated, unless the context clearly dictates otherwise. In other words, the steps may be performed in the same order as stated, substantially simultaneously, or in the opposite order.

[0038] Hereinafter, embodiments of the present invention will be described. However, the scope of the present invention is not limited to the following preferred embodiments, and those skilled in the art can implement various modified forms of the contents described herein within the scope of the present invention.

[0039] The present invention relates to a composite cathode active material, a method for producing the same, and an all-solid-state battery including the same.

[0040] FIG. 1 is a cross-sectional view schematically illustrating an example of a composite bipolar active material according to one embodiment of the present invention.

[0041] Referring to FIG. 1, the composite cathode active material (10) may include an active material (110), a first electrolyte layer (120) coated with the active material (110) on the surface, a second electrolyte layer (130) coated on the first electrolyte layer (120), and an intermediate layer (140).

[0042] The active material (110) refers to a material that directly takes charge of the electrochemical reaction of the positive or negative electrode of the battery, and may include a positive electrode active material and a negative electrode active material. For example, the active material (110) may include a positive electrode active material, and the positive electrode active material refers to a material that receives electrons and is reduced together with a cation. As a specific example, the active material may include a combination of any one or more selected from lithium transition metal oxides such as lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganese oxide, lithium iron phosphate, nickel sulfide, copper sulfide, lithium sulfide, iron oxide, or vanadium oxide, but is not necessarily limited thereto, and any material used as a positive electrode active material in the relevant technical field may be used.

[0043] The first electrolyte layer (120) may be disposed on the active material (110) and may include an oxide-based solid electrolyte and a sulfide-based solid electrolyte, and more preferably, may include a sulfide-based solid electrolyte.

[0044] Sulfide-based solid electrolytes include, for example, LGPS (Li 10 GeP2S 12 ) system, LPS(Li7P3S 11 ) system, LPSX(Li x P y S z X) system (X is a halogen element) solid electrolyte, and as a specific example, it may include Li6PS5Cl.

[0045] For example, in order to coat the first electrolyte layer (120) on the surface of the active material (110), at least one method selected from among dry ball milling, dry planetary milling, mechano-fusion, and wet coating may be used, and more preferably, wet coating may be used.

[0046] For example, wet coating involves placing the active material (110) in the above solution, placing it in a reactor capable of forming a vacuum state in an unsealed state with reduced pressure, and applying ultrasonic waves under the vacuum state, whereby coating and drying can be performed simultaneously. In this case, the vacuum state refers to a state in which the internal pressure is reduced in an unsealed space.

[0047] At this time, the average particle diameter (D50) of the electrolyte powder may be 0.1 µm to 5 µm, and preferably 2 µm to 3 µm.

[0048] As another example of a coating process, an electrolyte powder may be dissolved in a solvent to prepare a solution, and then an active material (110) may be placed in the solution, stirred and vacuum-coated using a rotary evaporator, and at this time, drying may be performed simultaneously to coat the surface of the active material (110) with a first electrolyte layer (120).

[0049] As an optional embodiment, in the coating process, a solvent such as n-heptane or acetonitrile (ACN) may be used, and the electrolyte powder may be included in an amount of 2.5 wt% to 5 wt% based on the active material. When the electrolyte coating layer is less than 2.5 wt% based on the active material, the electrolyte is not sufficiently coated on the surface of the active material, which may cause a problem in that the charge / discharge capacity of the battery is reduced due to pores that are generated, and when the electrolyte powder exceeds 5 wt% based on the active material, the electron conductivity of the electrolyte is not smooth, which may cause a problem in that not only the high-speed charge / discharge capacity but also the electrochemical characteristics are reduced at low speeds.

[0050] Meanwhile, when the electrolyte powder is included in an amount of 2.5 wt% to 5 wt% based on the active material, the thickness of the first electrolyte layer (120) coated on the active material (110) may be 100 nm to 1000 nm.

[0051] Meanwhile, the thicker the first electrolyte layer (120), the better the ionic conductivity of lithium ions can be. However, if the thickness becomes excessively thick, even if a conductive material is included, electron conduction may be difficult, which may reduce the performance of the battery.

[0052] Therefore, in the composite cathode active material (10) according to one embodiment of the present invention, the first electrolyte layer (120) is thinly coated with an appropriate thickness, thereby securing a movement path for lithium ions coming from and going into the active material (110), while at the same time allowing electrons to easily move through the conductive material described below.

[0053] The second electrolyte layer (130) may be formed by including first particles (131) and second particles (132) of different sizes in a slurry form on the first electrolyte layer (120). At this time, the materials forming the first electrolyte layer (120) and the second electrolyte layer (130) may be the same.

[0054] By forming a second electrolyte layer (130) on the surface of a first electrolyte layer (120) including first particles (131) and second particles (132) of different sizes, the second electrolyte layer (130) reduces the pores inside the electrolyte layer and is formed densely, so that even if the electrolyte layer is formed thick, the interfacial resistance does not increase, and the ionic conductivity is improved, so that the electrochemical stability of the all-solid-state battery increases and the rate capability can be improved.

[0055] Meanwhile, although the ionic conductivity may increase as the thickness of the electrolyte increases, in the case where it is formed by dry coating or wet coating, such as the first electrolyte layer (120), if the thickness is formed thick, it may be difficult to control the internal properties, such as pores, and thus the interfacial resistance may increase due to the pores. Therefore, by first coating the first electrolyte layer (120) thinly to secure a movement path for lithium ions coming into and going out of the active material (110) while simultaneously allowing electrons to move easily, and later forming a second electrolyte layer (130) on the first electrolyte layer (120) by including first particles (131) and second particles (132) of different sizes in a slurry form, the interfacial resistance may be reduced and the ionic conductivity may be improved compared to the case where the electrolyte is formed thickly on the surface of the active material (110) with only the first electrolyte layer (120).

[0056] Meanwhile, since the first particle (131) and the second particle (132) have lower intergranular resistance as their sizes increase, their ionic conductivity is high, but when physically forming a complex, many pores may be generated, which may increase the interfacial resistance. Therefore, when the first particle (131) is large in size and has high ionic conductivity and the second particle (132) is smaller in size and has lower ionic conductivity than the first particle (131) and is mixed at a certain ratio, the ionic conductivity may be improved, the contact area with the active material (110) may be increased, and the interfacial resistance may be reduced by controlling the pores. That is, by forming a bimodal electrolyte layer including particles of different sizes, the ionic conductivity of the electrolyte may be increased by the first particle (131) having a large size, and the electrolyte may be densely formed by the second particle (132) having a small size, thereby controlling the pores inside, thereby reducing the interfacial resistance.

[0057] In addition, when using first particles (131) and second particles (132) of different sizes, the interfacial resistance can be greatly reduced and the ionic conductivity can be improved while forming a thin electrolyte layer compared to when using only the first particles (131) of a large size, and when using only the second particles (132) of a small size, the ionic conductivity can be greatly improved and the density can be improved to reduce the interfacial resistance.

[0058] That is, when the active material (110) is coated using both the first particle (131) and the second particle (132), a uniform and thin coating can be achieved, so that the interfacial resistance can be greatly reduced and the ionic conductivity can be greatly improved.

[0059] For example, the ratio of the first particles (131) and the second particles (132) included in the second electrolyte layer (130) may be 9:1 to 7:3. In addition, the average particle diameter (D50) of the first particles (131) may be 30 µm to 70 µm, preferably 40 µm to 60 µm, and the average particle diameter (D50) of the second particles (132) may be 0.1 µm to 5 µm, preferably 2 µm to 3 µm.

[0060] Meanwhile, the average particle diameter (D50) of the second particles (132) may be the same as the average particle diameter (D50) of the electrolyte powder of the first electrolyte layer (120) described above.

[0061] Since the first particles (131) and second particles (132) included in the second electrolyte layer (130) have a ratio of 9:1 to 7:3, the second electrolyte layer (130) can be thin while improving ionic conductivity, and at the same time, by forming a dense coating layer, the contact area with the active material (110) can be increased, and the internal pores can be reduced, thereby reducing the interfacial resistance. In addition, since the average particle diameter (D50) of the first particles (131) is 40 µm to 60 µm and the average particle diameter (D50) of the second particles (132) is 2 µm to 3 µm, the second particles (132) can fill the space between the first particles (131) having a large size, so that the second electrolyte layer (130) can be formed thinly while being dense.

[0062] As an optional embodiment, the second electrolyte layer (130) may further include a conductive material.

[0063] The conductive material is a conductive material that can enable electrical conduction between the composite positive electrode active material (10) and the electrolyte. The conductive material may include, but is not limited to, carbon black, graphite fine particles, natural graphite, artificial graphite, acetylene black, Ketjen black, carbon fibers; metal powders or metal fibers or metal tubes such as carbon nanotubes, copper, nickel, aluminum, and silver; and conductive polymers such as polyphenylene derivatives. Any conductive material that can be used as a conductive material in the relevant technical field may be used, and a specific example thereof may include super p.

[0064] As an optional embodiment, an intermediate layer (140) may be formed between the active material (110) and the electrolyte layer (120).

[0065] The intermediate layer (140) is coated on the surface of the active material (110), thereby improving the electrochemical stability range of the active material (110), and by blocking contact between the positive active material (110) and the first electrolyte layer (120), it can prevent the solid electrolyte of the first electrolyte layer (120) from deteriorating or decomposing.

[0066] The intermediate layer (140) may include, for example, one or more selected from lithium, a transition metal, oxygen, and phosphorus, and may include, for example, lithium metal oxide, lithium metal phosphate, lithium phosphate, etc., and preferably, lithium metal oxide. As a specific example, the lithium metal oxide may include a form of Li-MO, and M may be Nb, Ni, Ti, Mo, Al, Zn, Cs, Cr, Ag, Mn, Rb, Sn, Cs, Sr, Hf, Sn, Ir, Rb, Cu, Ca, Ga, Cd, Ta, Re, Fe, Rh, Au, Zr, or a combination of any one or more selected from these.

[0067] As a result, the composite cathode active material according to one embodiment of the present invention can have a thin, uniform, and dense electrolyte layer coated on the active material, and by coating the first electrolyte layer thinly, a movement path of lithium ions coming into and going out of the active material is secured while at the same time electrons can easily move through the conductive material, and by additionally coating a second electrolyte layer including first and second particles of different sizes on the first electrolyte layer, the interfacial resistance can be greatly reduced and ionic conductivity can be greatly improved.

[0068] FIG. 2 is a flowchart schematically illustrating an example of a method for manufacturing a composite positive electrode active material according to another embodiment of the present invention.

[0069] Referring to FIG. 2, a method for manufacturing a composite cathode active material may include a step of preparing a solid electrolyte (S100), a step of mixing the solid electrolyte with an active material in a solvent to form a mixture (S200), a step of reacting the mixture to coat the solid electrolyte on the active material (S300), and a step of mixing the active material coated with the solid electrolyte, the solid electrolyte, and the conductive material (S400).

[0070] In the step of preparing a solid electrolyte (S100), the solid electrolyte may include an argyrodite-type solid electrolyte, and as a specific example, may include an argyrodite-type sulfide-based solid electrolyte.

[0071] Lithium precursors and phosphorus precursors can be used to synthesize solid electrolytes.

[0072] The lithium precursor may be, for example, one or more selected from lithium oxide (Li2O), lithium carbonate (Li2CO3), lithium halide (LiZ; Z is halogen), lithium sulfide (LiS), lithium nitrate (LiNO3), lithium phosphate (Li3PO4), and lithium hydroxide (LiOH), and the phosphorus precursor may include, for example, P2S5.

[0073] The solid electrolyte can be synthesized by mechanically milling a lithium precursor and a phosphorus precursor using n-heptane for 60 to 80 hours, drying, and then heat-treating at 500°C to 600°C for 10 to 14 hours. At this time, the synthesized solid electrolyte is a first solid electrolyte (SSE) having particles with a large average particle diameter (D50). large ) can be. This solid electrolyte (SSE) large ) is pulverized through ball milling to obtain a second solid electrolyte (SSE) having particles with a small average particle diameter (D50). small ) can be pulverized. Therefore, in the step of preparing a solid electrolyte (S100), two solid electrolytes having different average particle sizes (D50) can be prepared in the form of powder.

[0074] In the step (S200) of forming a mixture by mixing a solid electrolyte with an active material in a solvent, a second solid electrolyte (SSE) having a small particle size small) powder and the cathode active material can be mixed in a solvent to form a mixture. For example, n-heptane or acetonitrile (ACN) can be used as the solvent, and the cathode active material can include a combination of one or more selected from lithium transition metal oxides such as lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganese oxide, lithium iron phosphate, nickel sulfide, copper sulfide, lithium sulfide, iron oxide, or vanadium oxide.

[0075] Meanwhile, the second solid electrolyte (SSE) included in the mixture small ) The powder may be included in an amount of 2.5 wt% to 5 wt% based on the positive electrode active material.

[0076] As an optional embodiment, an intermediate layer acting as a passivation may be formed on the surface of the cathode active material, and the intermediate layer may include a form of Li-MO. In this case, M may be Nb, Ni, Ti, Mo, Al, Zn, Cs, Cr, Ag, Mn, Rb, Sn, Cs, Sr, Hf, Sn, Ir, Rb, Cu, Ca, Ga, Cd, Ta, Re, Fe, Rh, Au, Zr, or a combination of any one or more selected from the above.

[0077] In the step (S300) where the mixture is reacted to coat the solid electrolyte on the active material, the mixture is introduced into a reactor capable of forming an open vacuum in a state of reduced pressure in an unsealed state, and an ultrasonic wave of 30 kHz to 50 kHz is applied under the open vacuum atmosphere to form a second solid electrolyte (SSE) on the surface of the positive electrode active material. small ) can be coated. At this time, coating and drying can be performed simultaneously, and the temperature inside the reactor can be maintained at 50°C to 70°C.

[0078] In the step of mixing the solid electrolyte and the conductive material (S400), the second solid electrolyte (SSE) small ) on the surface of the cathode active material coated on the surface, that is, the second solid electrolyte (SSE) small ) on the first solid electrolyte (SSE) manufactured previously large ) and / or a second solid electrolyte (SSE small ) and the conductive material are mixed in a slurry state and applied, thereby producing a composite cathode active material.

[0079] Meanwhile, the conductive material is a conductive material that can enable electrical conduction between the composite positive electrode active material (10) and the electrolyte. The conductive material may include, but is not limited to, carbon black, graphite fine particles, natural graphite, artificial graphite, acetylene black, Ketjen black, carbon fibers; metal powders or metal fibers or metal tubes such as carbon nanotubes, copper, nickel, aluminum, and silver; and conductive polymers such as polyphenylene derivatives. Any conductive material that can be used as a conductive material in the relevant technical field may be used, and a specific example thereof may include super p.

[0080] Fig. 3 is a photograph of the surface of a composite cathode active material manufactured according to the method for manufacturing a composite cathode active material of Fig. 2.

[0081] Referring to Figure 3, it can be confirmed that the electrolyte is uniformly coated on the surface of the composite cathode active material.

[0082] Figure 4 is a flowchart schematically illustrating another example of the manufacturing method of Figure 2.

[0083] Referring to FIG. 4, a method for manufacturing a composite cathode active material may include a step of preparing a solid electrolyte (S100), a step of mixing the solid electrolyte with an active material in a solvent to form a mixture (S200), a step of reacting the mixture to coat the solid electrolyte on the active material (S300), and a step of mixing the active material coated with the solid electrolyte, the solid electrolyte, and the conductive material (S400), and may further include a heat treatment step (S450).

[0084] In the heat treatment step (S500), the coated cathode active material to which the slurry is applied is heat treated at 500°C to 600°C for 10 to 14 hours, so that a composite cathode active material can be manufactured. This heat treatment step is to prepare a composite cathode active material by coating the first solid electrolyte (SSE) on the surface of the cathode active material. large ) and a second solid electrolyte (SSE) small ) can further improve the performance of the composite cathode active material by increasing the lowered crystallinity and improving the ionic conductivity.

[0085] As a result, the composite cathode active material according to one embodiment of the present invention can have a thin, uniform, and dense electrolyte layer coated on the active material, and by coating the first electrolyte layer thinly, a movement path of lithium ions coming into and going out of the active material is secured while at the same time electrons can easily move through the conductive material, and by additionally coating a second electrolyte layer including first and second particles of different sizes on the first electrolyte layer, the interfacial resistance can be greatly reduced and ionic conductivity can be greatly improved.

[0086] Meanwhile, the composite cathode active material manufactured in this way can be applied to an all-solid-state secondary battery.

[0087] An all-solid-state secondary battery may include the composite cathode active material manufactured above. The all-solid-state secondary battery includes a cathode layer, an anode layer, and a solid electrolyte layer disposed between the cathode layer and the anode layer, wherein the cathode layer and the solid electrolyte layer may be a composite cathode active material according to an embodiment of the present invention.

[0088] The above positive electrode layer includes a positive electrode active material layer, and the positive electrode active material layer may include a composite positive electrode active material, a binder, and a solid electrolyte, and the negative electrode layer includes a negative electrode active material and a binder.

[0089] The cathode active material layer may include a composite cathode active material according to embodiments of the present invention, and by including the composite cathode active material, may include a solid electrolyte layer and a conductive material together.

[0090] The binder may include, but is not limited to, polyvinylidene fluoride, styrene butadiene rubber (SBR), polytetrafluoroethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, and polymethyl methacrylate, for example. Any binder used in the art may be used. In addition, the binder may be composed of a single binder or a plurality of different binders.

[0091] The above negative electrode layer may include a negative electrode active material and a binder.

[0092] The negative electrode active material may include, for example, one or more selected from a carbon-based negative electrode active material, a metal or metalloid negative electrode active material, and lithium metal itself. A specific example may include lithium and phosphorus metal.

[0093] The binder may include, but is not limited to, polyvinylidene fluoride, styrene butadiene rubber (SBR), polytetrafluoroethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, and polymethyl methacrylate, for example. Any binder used in the art may be used. In addition, the binder may be composed of a single binder or a plurality of different binders.

[0094] As a result, the all-solid-state secondary battery including the composite cathode active material according to the embodiments of the present invention can have improved electrochemical characteristics.

[0095]

[0096] (Comparative Example 1) Anode composite using only small-particle electrolyte

[0097] Li2S, P2S5, and LiCl were mixed in a 5:1:2 mol% ratio using n-heptane, and then mechanically milled for 72 hours. The mixture after mechanical milling was heat-treated at 550°C for 12 hours in an inert gas atmosphere to synthesize a solid electrolyte. The solid electrolyte thus synthesized was ball-milled with 3 mm balls in toluene, a non-reactive solvent, to manufacture electrolyte powder with an average particle size (D50) of 3 μm, and LiNbO3-coated cathode active material (Li[Ni 0.6 Co 0.2 Mn 0.2 ]O2) (hereinafter referred to as LNO-NCM622), 70% of the conductive agent, 30% of the electrolyte powder manufactured above, and 1.3% of the conductive agent Super P were mixed to make a composite cathode active material.

[0098]

[0099] (Comparative Example 2) Anode composite using only large-particle electrolyte

[0100] Li2S, P2S5, and LiCl were mixed in a ratio of 5:1:2 mol% using n-heptane, and then mechanically milled for 72 hours. The mixture after mechanical milling was heat-treated at 550°C for 12 hours in an inert gas atmosphere to synthesize a solid electrolyte. Using the solid electrolyte thus synthesized, an electrolyte powder with an average particle size (D50) of 50 μm was manufactured, and a positive electrode active material (Li[Ni 0.6 Co 0.2 Mn 0.2 ]O2) (hereinafter referred to as LNO-NCM622), 70% of the conductive agent, 30% of the electrolyte powder manufactured above, and 1.3% of the conductive agent Super P were mixed to make a composite cathode active material.

[0101]

[0102] (Comparative Example 3) Only small-particle electrolytes that have undergone chemical reactions in reactive solvents are used.

[0103] Li2S, P2S5, and LiCl were mixed in a ratio of 5:1:2 mol% using n-heptane, and then mechanically milled for 72 hours. The mixture after mechanical milling was heat-treated at 550°C for 12 hours in an inert gas atmosphere to synthesize a solid electrolyte. The solid electrolyte thus synthesized was added to an acetonitrile (ANC) solvent to form a solution, and dried by applying ultrasound at 40 kHz at a temperature of 60°C in an open vacuum atmosphere to manufacture an electrolyte powder with an average particle size (D50) of 6 μm, and a cathode active material (Li[Ni 0.6 Co 0.2 Mn 0.2 ]O2) (hereinafter referred to as LNO-NCM622), 70% of the conductive agent, 30% of the electrolyte powder manufactured above, and 1.3% of the conductive agent Super P were mixed to make a composite cathode active material.

[0104]

[0105] (Example 1) An electrolyte was used in which a large particle size electrolyte and a small particle size electrolyte were mixed in a mass ratio of 9:1 (large particle size electrolyte 90%).

[0106] The electrolyte powders manufactured in Comparative Example 2 and Comparative Example 1 were mixed in a mortar and pestle at a mass ratio of 9:1 to manufacture a bimodal electrolyte powder, and the positive electrode active material (Li[Ni) coated with LiNbO3 0.6 Co 0.2 Mn 0.2 ]O2) (hereinafter referred to as LNO-NCM622), 70% of the conductive agent, 30% of the bimodal electrolyte powder manufactured above, and 1.3% of the conductive agent Super P were mixed to produce a composite cathode active material.

[0107]

[0108] (Example 2) Only small-particle electrolyte was used, and an anode with 30 wt% of small-particle electrolyte coated on the anode surface was used.

[0109] 0.35 g of the cathode active material (LNO-NCM622) was added together with 0.15 g of the electrolyte powder manufactured in Comparative Example 1 in 200 cc of acetonitrile solvent, and 40 kHz ultrasonic waves were applied in an environment of 60°C while simultaneously creating an open vacuum atmosphere to perform coating and drying simultaneously, thereby manufacturing a cathode active material coated with 30 wt% of the electrolyte of Comparative Example 1 based on the cathode active material. A composite cathode active material was manufactured by mixing 100% of the cathode active material coated with this electrolyte and 1.3% of Super P, a conductive agent.

[0110]

[0111] (Example 3) Only small-particle electrolyte was used, and a cathode active material was used in which 5.0 wt% of small-particle electrolyte was coated on the cathode surface.

[0112] 0.4750 g of the cathode active material (LNO-NCM622) was added together with 0.0250 g of the electrolyte powder manufactured in Comparative Example 1 in 200 cc of the solvent acetonitrile, and while applying ultrasonic waves of 40 kHz in an environment of 60℃ and simultaneously creating an open vacuum atmosphere, coating and drying were performed simultaneously to manufacture a cathode active material coated with 5.0 wt% of the electrolyte of Comparative Example 1 based on the cathode active material. A composite cathode active material was manufactured by mixing 75% of the cathode active material coated with this electrolyte, 25% of the electrolyte powder of Comparative Example 1, and 1.3% of the conductive agent Super P. Finally, the overall ratio of the cathode composite was 70%, the overall ratio of the electrolyte was 30%, and the ratio of the conductive agent Super P was 1.3%.

[0113]

[0114] (Example 4) Only small-particle electrolyte was used, and a cathode active material was used in which 2.5 wt% of small-particle electrolyte was coated on the cathode surface.

[0115] 0.4750 g of the cathode active material (LNO-NCM622) was added together with 0.0125 g of the electrolyte powder manufactured in Comparative Example 1 in 200 cc of the solvent acetonitrile, and while applying ultrasonic waves of 40 kHz in an environment of 60℃ and simultaneously creating an open vacuum atmosphere, coating and drying were performed simultaneously to manufacture a cathode active material coated with 2.5 wt% of the electrolyte of Comparative Example 1 based on the cathode active material. A composite cathode active material was manufactured by mixing 72.5% of the cathode active material coated with this electrolyte, 27.5% of the electrolyte powder of Comparative Example 1, and 1.3% of the conductive agent Super P. Finally, the overall ratio of the cathode composite was 70%, the overall ratio of the electrolyte was 30%, and the ratio of the conductive agent Super P was 1.3%.

[0116]

[0117] (Example 5) A bimodal electrolyte was used in which large-particle electrolyte and small-particle electrolyte were mixed in a ratio of 9:1, and a cathode active material was used in which 5.0 wt% of small-particle electrolyte was coated on the cathode surface.

[0118] In the same manner as in Example 3, a cathode active material coated with 5.0 wt% of the electrolyte of Comparative Example 1 based on the cathode active material was manufactured, and a composite cathode active material was manufactured by mixing 75% of the cathode active material coated with this electrolyte, 25% of the bimodal electrolyte powder of Example 1, and 1.3% of the conductive agent Super P. Ultimately, the overall ratio of the cathode composite was 70%, the overall ratio of the electrolyte was 30%, and the ratio of the conductive agent Super P was 1.3%.

[0119]

[0120] (Example 6) A bimodal electrolyte was used in which large-particle electrolyte and small-particle electrolyte were mixed in a ratio of 9:1, and a cathode active material was used in which 2.5 wt% of small-particle electrolyte was coated on the cathode surface.

[0121] In the same manner as in Example 4, a cathode active material coated with 2.5 wt% of the electrolyte of Comparative Example 1 based on the cathode active material was manufactured, and a composite cathode active material was manufactured by mixing 72.5% of the cathode active material coated with this electrolyte, 27.5% of the bimodal electrolyte powder of Example 1, and 1.3% of the conductive agent Super P. Ultimately, the total ratio of the cathode composite was 70%, the total ratio of the electrolyte was 30%, and the ratio of the conductive agent Super P was 1.3%.

[0122]

[0123] (Experimental Example 1) Measurement of ionic conductivity

[0124] Each of the electrolyte powders manufactured in Comparative Examples 1 to 3 was placed in a mold, pressurized at 7 tons, and the thickness and EIS were measured to measure the ionic conductivity.

[0125]

[0126] (Experimental Example 2) Electrochemical charge / discharge rate evaluation

[0127] The composite cathode active materials of Examples 1 to 6 and Comparative Examples 1 to 3 were used, and a battery cell having a diameter of 13 mm was manufactured using a Li-In composite as a working electrode. Then, an experiment was conducted in which charge and discharge cycles were repeated using WonAtech in a voltage range of 2.38 V to 3.68 V vs. In / Li+ corresponding to 3.0 V to 4.3 V vs. Li / Li+ at charge and discharge rates of 0.1 C (1 C = 200 mA / g), 0.2 C, 0.5 C, 1.0 C, and 2.0 C at a temperature of 30°C.

[0128] Figure 5 is a graph showing ionic conductivity.

[0129] Referring to Fig. 5, the ionic conductivity of the electrolyte powders manufactured in Comparative Examples 1 to 3 can be confirmed.

[0130] It can be confirmed that Comparative Example 2, which has a small interface and a large particle size, has the highest lithium ion conductivity, and Comparative Example 1, which has a large interface and a small particle size, has a lower ion conductivity than Comparative Example 2. In addition, it can be confirmed that the electrolyte powder of Comparative Example 3, which was manufactured in the same way as coating an electrolyte on a positive electrode active material, has lower crystallinity and crystallinity, and the interfacial resistance increases, resulting in a lower ion conductivity by more than 1 / 10 compared to Comparative Examples 1 and 2.

[0131] Figure 6 is a graph showing the rate characteristics of Comparative Examples 1 to 3 and Example 1.

[0132] Referring to Figure 6, in the case of Comparative Example 1, which has low ionic conductivity but small particle size, it can be seen that high capacity is exhibited at relatively low rates such as 0.1C, 0.2C, and 0.5C because the contact area with the positive electrode active material can be increased, and at fast rates such as 1.0C and 2.0C, it can be seen that low capacity is exhibited due to low ionic conductivity.

[0133] On the other hand, in the case of Comparative Example 2, which has high ionic conductivity but large particle size, it can be seen that it exhibits a lower capacity than Comparative Example 1 at relatively low rates such as 0.1C, 0.2C, and 0.5C because the contact area with the positive electrode active material is small. However, at fast rates such as 1.0C and 2.0C, it can be seen that it exhibits a relatively high capacity despite the low contact area due to the high ionic conductivity. However, it can be seen that the capacity gradually decreases after only 5 charge / discharge cycles at a fast rate such as 1.0C.

[0134] In the case of chemically reacted Comparative Example 3, since the contact area with the positive electrode active material is smaller than that of Comparative Example 1 and larger than that of Comparative Example 2, a high capacity is exhibited like that of Comparative Example 1 at a slow rate of 0.1C, but since it has the lowest ionic conductivity, it can be confirmed that the capacity decreases very rapidly as the charge / discharge rate increases from 0.2C.

[0135] In the case of Example 1 (bimodal electrolyte) where Comparative Examples 1 and 2 were mixed at a mass ratio of 1:9, since there was a large amount of electrolyte with large particles, the contact area with the positive electrode active material was not sufficiently created, and thus a capacity higher than that of Comparative Example 2 and lower than that of Comparative Example 1 was exhibited at 0.1C, 0.2C, and 0.5C, but it was confirmed that as the charge and discharge became faster, a performance higher than that of Comparative Examples 1 and 2 was exhibited at 1.0C and 2.0C. In other words, it can be confirmed that the performance of the battery can be improved by increasing the density of the electrode.

[0136] Figure 7 is a charge / discharge graph of Comparative Example 1 and Examples 2 to 4.

[0137] Referring to Fig. 7, in the case of Example 2 where the electrolyte coating layer is 30 wt% based on the positive electrode active material, it can be confirmed that charging and discharging are not performed properly even at a low C-rate (0.1 C). This is because the ion conductive layer is sufficient but the electron conductivity is not good. Even if an additional conductive material is added, the distance between the positive electrode and the conductive material is too far to hinder electron conductivity, so it can be seen that charging and discharging are not performed properly even at a low C-rate (0.1 C).

[0138] In the case of Example 3, which is coated with 5.0 wt% of electrolyte based on the positive electrode active material, which is 1 / 6 of that of Example 2, electrons can move more smoothly than in Example 2, so charging and discharging can be performed smoothly. However, due to the electrolyte coating layer having an inappropriate thickness, it can be confirmed that although a higher discharge capacity is shown than that of Comparative Example 1 during discharge, the charging characteristics of electrons are not properly expressed during charging.

[0139] In the case of Example 4, where the electrolyte was coated at 2.5 wt% based on the cathode active material as the coating layer, it was confirmed that both the movement of lithium ions and the movement of electrons were smooth, and thus a higher capacity was shown compared to Comparative Example 1, where the cathode active material was not separately coated, during both charge and discharge.

[0140] Figure 8 is a graph showing the life characteristics and rate characteristics of Comparative Example 1 and Examples 2 to 4.

[0141] Referring to Figure 8, in the case of Example 2 where 30 wt% of the electrolyte was coated on the cathode active material based on the cathode active material, it can be confirmed that smooth charging and discharging is not performed even at a low c-rate of 0.2 C.

[0142] In Example 3, where 5.0 wt% of the electrolyte was coated on the cathode active material based on the cathode active material, the discharge capacity at 0.2 C was slightly higher than that of Comparative Example 1 without coating, but when the rate was increased to 0.5 C, the capacity decrease was very large. This can be inferred to be related to the decrease in ionic conductivity and the high interfacial resistance between the electrolytes caused by the decrease in crystallinity and crystallinity of the electrolyte during the coating process, which led to the decrease in capacity.

[0143] In the case of Example 4, where 2.5 wt% of the electrolyte was coated on the cathode active material based on the cathode active material, it can be confirmed that the discharge capacity was highest at 0.2 C and maintained constant. However, as in Example 3, the ionic conductivity decreased during the coating process, and the surface of the electrolyte reacted with the reactive solvent was wide, resulting in an overall larger interfacial resistance, so it can be inferred that the capacity decrease at 0.5 C was greater than that of other electrolytes.

[0144] On the other hand, in the case of Comparative Example 1, which did not coat the cathode active material, there was no deterioration of the electrolyte used, so it was confirmed that a lower capacity was shown at 0.2C, but the decrease in capacity at 0.5C was very small.

[0145] Figure 9 is a graph showing the rate characteristics of Examples 1, 5, and 6.

[0146] Referring to Figure 9, in the case of Example 1 where the electrolyte was not coated on the surface of the positive electrode active material, it can be confirmed that a low capacity is exhibited starting from a low rate of 0.1 C.

[0147] In the case of Example 5, where 5.0 wt% of electrolyte was coated on the cathode active material based on the cathode active material, a higher capacity was shown than Example 1 from 0.1 C due to the high contact area between the active material and the electrolyte, but as the rate increased, the difference with Example 1 narrowed, and a similar capacity was shown at 1.0 C, and a lower capacity was shown than Example 1 at 2.0 C due to a decrease in ionic conductivity caused by deterioration of the electrolyte coated on the surface of the active material.

[0148] In the case of Example 6, where 2.5 wt% of the electrolyte was coated on the cathode active material based on the cathode active material, it was confirmed that by maintaining a high contact area between the active material and the electrolyte and a thin coating thickness, the electronic conductivity was sufficiently improved due to the influence of the conductive agent that facilitates the movement of electrons, and thus a sufficiently high capacity could be expressed from a low rate of 0.1 C to a high rate of 2.0 C.

[0149] Figure 10 is an XRD graph of Comparative Example 1 and Examples 3 to 6.

[0150] Referring to FIG. 10, XRD graphs of the electrolyte used in Comparative Example 1, the cathode active material before coating (LNO-NCM622) (Reference Cathode), the electrolyte-active material composite coated with 5.0 wt% of the electrolyte (Examples 3 and 5), and the electrolyte-active material composite coated with 2.5 wt% of the electrolyte (Examples 4 and 6) can be confirmed.

[0151] Comparing Examples 3 to 6 with the electrolyte and the cathode active material (LNO-NCM622) (Reference Cathode) before coating used in Comparative Example 1 through the graph, it can be confirmed that the crystallinity of the electrolyte does not drop significantly after particle size control and that there are no impurities other than NCM622 and the electrolyte before and after coating.

[0152] Figure 11 is a graph of the rate characteristics of Comparative Example 1 and Example 6.

[0153] Referring to FIG. 11, when a composite cathode electrode is formed using an electrode composite in which an electrolyte is coated on a cathode active material as in Example 6, and this is mixed with a bimodal electrolyte to form a composite cathode active material and charge / discharge is performed, it can be confirmed that much higher charge / discharge characteristics can be exhibited from a low rate to a high rate compared to Comparative Example 1.

[0154] As a result, the composite cathode active material according to one embodiment of the present invention can have a thin, uniform, and dense electrolyte layer coated on the active material, and by coating the first electrolyte layer thinly, a movement path of lithium ions coming into and going out of the active material is secured while at the same time electrons can easily move through the conductive material, and by additionally coating a second electrolyte layer including first and second particles of different sizes on the first electrolyte layer, the interfacial resistance can be greatly reduced and ionic conductivity can be greatly improved.

[0155] While the present invention has been described with reference to the embodiments illustrated in the drawings, these are merely exemplary, and those skilled in the art will appreciate that various modifications and variations of the embodiments are possible. Therefore, the true scope of technical protection of the present invention should be determined by the technical spirit of the appended claims.

Claims

1. Active material; A first electrolyte layer disposed on the above active material; and comprising a second electrolyte layer disposed on the first electrolyte layer; The above first electrolyte layer is a composite cathode active material containing 2.5 wt% to 5.0 wt% based on the active material.

2. In paragraph 1, A composite cathode active material, wherein the thickness of the first electrolyte layer is 100 nm to 1000 nm.

3. In paragraph 1, The second electrolyte layer comprises first particles and second particles having different sizes, A composite positive electrode active material, wherein the first particles have a larger average particle diameter (D50) than the second particles.

4. In paragraph 3, A composite cathode active material in which the average particle diameter (D50) of the first electrolyte layer is the same as the average particle diameter (D50) of the second particles.

5. In paragraph 3, A composite cathode active material, wherein the ratio of the first particle to the second particle is 9:1 to 7:

3.

6. In paragraph 1, A composite cathode active material, wherein the first electrolyte layer and the second electrolyte layer contain the same material.

7. In paragraph 1, A composite cathode active material further comprising an intermediate layer between the active material and the first electrolyte layer.

8. Step of preparing solid electrolyte; A step of forming a mixture by mixing the above solid electrolyte with an active material in a solvent; A step of reacting the mixture so that the solid electrolyte is coated on the active material; and A method for manufacturing a composite cathode active material, comprising the step of mixing the active material coated with the solid electrolyte, the solid electrolyte, and a conductive material.

9. In paragraph 8, A method for manufacturing a composite cathode active material, wherein in the step of preparing a solid electrolyte, the solid electrolyte includes a first solid electrolyte and a second solid electrolyte having different average particle diameters (D50).

10. In paragraph 9, The mixture comprises the second solid electrolyte, A method for manufacturing a composite cathode active material, wherein the second solid electrolyte has a smaller average particle diameter (D50) than the first solid electrolyte.

11. In paragraph 10, A method for manufacturing a composite cathode active material, wherein the second solid electrolyte included in the mixture is included in an amount of 2.5 wt% to 5 wt% based on the active material.

12. In paragraph 8, A method for manufacturing a composite cathode active material, further comprising a heat treatment step.

13. Composite bipolar active material; and A cathode layer disposed on the above composite positive electrode active material; The above composite bipolar active material is an active material; A first electrolyte layer disposed on the above active material; and An all-solid-state battery comprising a second electrolyte layer disposed on the first electrolyte layer.

Images