KR20180087102A - Composite Cathode Active Material and Secondary battery Comprising the Same - Google Patents

Abstract

Provided is a composite positive electrode active material which includes a core particle, a first coating layer and a second coating layer coating the core particle. The core particle comprises a positive electrode active material, and the first coating layer contains a first lithium-containing compound which includes at least one selected among zirconium (Zr), niobium (Nb), titanium (Ti) and aluminum (Al). The second coating layer contains a second lithium-containing compound which includes at least one selected among germanium (Ge), niobium (Nb), and gallium (Ga). The first lithium-containing compound and the second lithium-containing compound are different from each other.

Description

TECHNICAL FIELD The present invention relates to a composite cathode active material and a secondary battery including the composite cathode active material,

The present invention relates to a composite cathode active material and a secondary battery comprising the composite cathode active material.

BACKGROUND ART [0002] Recently, all solid secondary batteries using a solid electrolyte having lithium ion conductivity have attracted attention. As the solid electrolyte of such a pre-solid secondary battery, for example, a sulfide-based solid electrolyte having high lithium ion conductivity has been proposed.

However, the sulfide-based solid electrolyte may react with the cathode active material particles upon charging to cause an interface resistance component of the cathode active material particles. In this case, the interface resistance between the positive electrode active material particles and the solid electrolyte is increased and the conductivity of the lithium ion is lowered, so that the output of the all solid secondary battery is lowered. Also, the reaction at the interface between the cathode active material and the solid electrolyte is particularly effective when the load on the entire solid secondary battery is large (for example, when charging the battery to a higher voltage than the pre-solid secondary battery or discharging the entire solid secondary battery) And the like.

As a method for solving the above problem, there has been proposed an invention in which the surface of the positive electrode active material particles is coated with a coating layer. For example, there is an invention in which cathode active material particles are coated with Li ₂ OP ₂ O ₅ -Nb ₂ O ₅ -B ₂ O ₃ -GeO ₂ glass (Patent Document 1), an invention in which cathode active material particles are coated with an amorphous carbon film (Patent Document 2), an invention in which a cathode active material particle is coated with a solid electrolyte (Patent Document 3), an invention in which a cathode active material particle is coated with an oxide-based material containing lithium zirconium oxide (Patent Document 4) Patent Document 5 discloses an invention in which cathode active material particles are coated with an inorganic material (Patent Document 5), an invention in which cathode active material particles are coated with a Li-ion conductive oxide having a BO-Si structure (Patent Document 6) (Patent Document 7), a coating layer composed of a material having at least one polyanion structure of PO ₄ ^3- , SiO ₄ ^4- , GeO ₄ ^4- and BO ₃ ^3- is coated with 50% Of the positive electrode active material Invention for covering the particles (Patent Document 8), the invention for coating the positive electrode active material particle of Li-ion conductive oxide is Li ₄ SiO ₄ -Li ₃ BO _3, and LiNbO ₃ (Patent Document 9), the positive electrode active material particles, Li ₃ BO ₃ (Patent Document 10); a method of coating positive electrode active material particles with lithium ion conductive oxides (Li and Ti) (Patent Document 11); (Patent Document 12), which covers a cathode active material particle with a coating layer containing a Group 13 element (Al, B, and Ga) (Patent Document 13) Etc. have already been reported.

In the inventions disclosed in Patent Documents 1 to 13, the coating layers have a single-layer structure. Patent Literatures 14 and 15 disclose a coating layer having a two-layer structure. Specifically, Patent Document 14 discloses an invention for covering an upper coating layer including a lower coating layer containing a first lithium ion conductor and a second lithium ion conductor. Wherein the lithium ion conductivity of the first lithium ion conductor is 1 x 10 ^-7 S / cm or more and the second lithium ion conductor has a multiple anion structure including at least one of B, Si, P, Ti, Zr, Containing Li-containing compounds. Patent Document 15 discloses an invention in which a lower coating layer (layer near the cathode active material particles) is made of amorphous carbon and an upper coating layer is made of lithium-containing oxide.

[Patent Document 1] JP-A-2016-81822 [Patent Document 2] JP-A-2015-88383 [Patent Document 3] JP-A-2015-201372 [Patent Document 4] JP-A-2014-116149 [Patent Document 5] International Patent Publication No. 2012/105048 [Patent Document 6] International Patent Publication No. 2012/157119 [Patent Document 7] International Patent Publication No. 2014/013837 [Patent Document 8] Japanese Patent Publication No. 5455766 [Patent Document 9] Japanese Patent Publication No. 5578280 [Patent Document 10] Japanese Unexamined Patent Application Publication No. 2012-89406 [Patent Document 11] International Patent Publication No. 2007/004590 [Patent Document 12] JP-A-2016-024907 [Patent Document 13] Japanese Patent Publication No. 5551880 [Patent Document 14] JP-A-2016-103411 [Patent Document 15] Japanese Patent Publication No. 5737415

However, the inventions disclosed in Patent Documents 1 to 14 can not sufficiently improve the characteristics of the entire solid secondary battery. Therefore, it is presumed that the present invention can not sufficiently suppress the interfacial reaction between the sulfide-based solid electrolyte and the cathode active material. Although the invention disclosed in Patent Document 15 contributes to the improvement of the characteristics of the entire solid secondary battery, the amorphous carbon film can be coated by a blast method, an aerosol deposition method, a cold spray method , A sputtering method, a CVD method, a spraying method, or the like, must be used. Therefore, the productivity is low.

Accordingly, in order to solve the above problems, the present invention provides a novel and excellent composite positive electrode active material which is excellent in productivity while improving the characteristics of the entire solid secondary battery, and a secondary battery comprising the same.

According to one aspect of the present invention,

And a first coating layer and a second coating layer covering the core particles and the surface of the core particles,

Wherein the core particle comprises a cathode active material,

Wherein the first coating layer comprises a first lithium-containing compound,

Wherein the first lithium-containing compound includes at least one selected from zirconium (Zr), niobium (Nb), titanium (Ti), and aluminum (Al)

Wherein the second coating layer comprises a second lithium-containing compound,

Wherein the second lithium-containing compound comprises at least one selected from the group consisting of germanium (Ge), niobium (Nb), and gallium (Ga)

The first lithium-containing compound is different from the second lithium-containing compound, and a composite cathode active material is provided.

The surface of the core particle may be coated with the first coating layer and the surface of the first coating layer may be coated with the second coating layer.

The first lithium-containing compound may be a lithium-containing oxide or a lithium-containing phosphorus oxide.

The first lithium-containing compound is selected from lithium zirconium oxide (Li-ZO), lithium niobium oxide (Li-Nb-O), lithium titanium oxide (Li-Ti-O) and lithium aluminum oxide Lt; / RTI >

The lithium zirconium oxide may include aLi ₂ O-ZrO ₂ (where 0.1 ≦ a ≦ 2.0).

The first lithium-containing compound may be lithium zirconium oxide (Li-Zr-PO ₄ ) or lithium titanium oxide (Li-Ti-PO ₄ ).

The second lithium containing compound may be at least one selected from lithium germanium oxide (Li-Ge-O), lithium niobium oxide (Li-Nb-O) and lithium gallium oxide (Li-Ga-O).

The thickness of the first coating layer may be 1 nm or more and 50 nm or less.

The total thickness of the first coating layer and the second coating layer may be 1 nm or more and 500 nm or less.

The average particle diameter of the core particles may be 10 탆 or less.

The core particle may include a lithium transition metal oxide having a layered rock salt type structure.

The core particles may be LiNi _x Co _y M _z O _{2 where} M is Al or Mn and 0 <x <1, 0 <y <1, x + y + z = 1.

The core particles may have a composition of 0.5? X <1.

For example, the core particles may have a composition of 0.7 < x < 1.

According to another aspect of the present invention,

There is provided a positive electrode comprising the composite positive electrode active material.

According to another aspect of the present invention,

The anode;

cathode; And an electrolyte formed between the positive electrode and the negative electrode.

The lithium secondary battery is a pre-solid lithium secondary battery,

The electrolyte may be a sulfide solid electrolyte.

Wherein the sulfide solid electrolyte comprises at least sulfur and lithium,

Further contains at least one element selected from phosphorus (P), silicon (Si), boron (B), aluminum (Al), germanium (Ge), zinc (Zn), gallium (Ga), indium can do.

The sulfide solid electrolyte may be lithium sulfide; And at least one selected from silicon sulfide, phosphorus sulfide, and boron sulfide.

The sulfide solid electrolyte may include Li ₂ S and P ₂ S ₅ .

The sulfide solid electrolyte may have a particle shape.

According to the present invention, the core particle containing the positive electrode active material is coated with the first coating layer and the second coating layer, and the first coating layer and the second coating layer include specific components. Therefore, the reaction occurring at the interface between the composite cathode active material including the core particles, the first coating layer and the second coating layer and the solid electrolyte can be suppressed. Further, since the first coating layer and the second coating layer can be produced by applying an alkoxide salt of an element constituting such a coating layer to the surface of the cathode active material particles and firing it, it is easy to manufacture and therefore, the productivity is excellent.

1 is a cross-sectional view schematically showing a layer structure of a lithium secondary battery according to an embodiment.
2 is a cross-sectional view schematically showing the structure of a composite cathode active material according to one embodiment.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, and redundant description will be omitted.

<1. Outline of all solid secondary batteries>

A pre-solid secondary battery according to an embodiment of the present invention is a pre-solid secondary battery using a solid electrolyte as an electrolyte. Further, a pre-solid secondary battery according to an embodiment of the present invention is a so-called pre-solid lithium ion battery in which lithium ions move between an anode and a cathode.

Here, since the cathode active material and the electrolyte are solid, the entire solid secondary battery using the solid electrolyte is less likely to penetrate the electrolyte in the cathode active material as compared with the all solid secondary battery using the organic solvent as the electrolyte. Therefore, the area of the interface between the positive electrode active material and the electrolyte tends to be small in the entire solid secondary battery, and it is necessary to sufficiently secure the movement path of lithium ions and electrons between the positive electrode active material and the solid electrolyte.

Therefore, for example, a technique has been proposed in which the positive electrode layer is formed of a mixed layer of a positive electrode active material and a solid electrolyte to increase the area of the interface between the positive electrode active material and the solid electrolyte.

However, when a sulfide-based solid electrolyte is used, a reaction occurs at the interface between the positive electrode active material and the solid electrolyte at the time of charging to generate a resistance component, so that the interface resistance between the positive electrode active material and the solid electrolyte may increase. In addition, the reaction at the interface between the cathode active material and the solid electrolyte is particularly effective when the load on the entire solid secondary battery is large (for example, when the battery is charged to a higher voltage than the entire solid secondary battery or when the entire solid secondary battery is discharged with a large current And the like).

Therefore, all solid secondary batteries using a sulfide-based solid electrolyte are required to suppress the generation of interface resistance components between the positive electrode active material and the solid electrolyte.

The present inventors speculated that there is a possibility that the deterioration reaction of the cathode active material at the interface between the cathode active material and the solid electrolyte (for example, the number of atoms of the transition metal element included in the cathode active material) and the deterioration reaction of the solid electrolyte. Accordingly, the present inventors have reached the full solid secondary battery according to the present embodiment, taking into consideration that the coating layer for suppressing deterioration of the cathode active material and the coating layer for suppressing the deterioration reaction of the solid electrolyte are coated with the cathode active material core particles.

In the all-solid-state secondary battery 1 according to the present embodiment, the surface of the core particle 101 is coated with the first coating layer 102 and the second coating layer 103. The core particles 101 and the solid electrolyte 300 are prevented from being in direct contact with the core particles 101 and the solid electrolyte 300 by the first coating layer 102 and the second coating layer 103, It is possible to suppress the generation of the resistance component at the interface between the first electrode and the second electrode.

The first coating layer 102 and the second coating layer 103 formed of the lithium-containing compound have lithium ion conductivity while suppressing the reaction between the core particles 101 and the solid electrolyte 300. Therefore, the first coating layer 102 and the second coating layer 103 can secure the movement path of lithium ions between the core particles 101 and the solid electrolyte 300, Can be improved.

According to one embodiment, the surface of the core particle 101 may be coated with the first coating layer 102, and the surface of the first coating layer 102 may be coated with the second coating layer 103. In this case, the characteristics of the pre-solid secondary battery 1 can be improved as compared with the case where the stacking order of the first coating layer 102 and the second coating layer 103 is changed. That is, it is presumed that the first coating layer 102 mainly suppresses deterioration of the core particles 101, and the second coating layer 103 mainly suppresses the deterioration of the solid electrolyte 103.

<2. Configuration of all solid secondary batteries>

Next, the configuration of the all-solid-state secondary battery according to the present embodiment will be described with reference to Figs. 1 and 2. Fig. Fig. 1 is a cross-sectional view schematically showing the layer configuration of the all-solid-state secondary battery 1 according to the present embodiment. 2 is a cross-sectional view schematically showing the configuration of the composite positive electrode active material 100 of the all-solid-state secondary battery 1 according to the present embodiment.

1, the entire solid secondary battery 1 includes a positive electrode layer 10, a negative electrode layer 20, and a solid electrolyte layer 30 positioned between the positive electrode layer 10 and the negative electrode layer 20 And has a laminated structure.

[Anode layer]

The anode layer 10 includes a composite cathode active material 100 and a solid electrolyte 300. In addition, the anode layer 10 may further include a conductive agent to supplement the electronic conductivity. Further, the solid electrolyte 300 will be described later in the solid electrolyte layer 30.

2, the composite cathode active material 100 according to one embodiment includes a core particle 101, a first coating layer 102 covering the surface of the core particle 101, and a first coating layer 102 And a second coating layer 103 which further covers the second coating layer 103. The order of lamination of the first coating layer 102 and the second coating layer 103 is changed so that the surface of the core particle 101 is coated with the second coating layer 103, 2 The surface of the coating layer 103 may be coated with the first coating layer 102.

(Core particles containing a positive electrode active material)

The core particle 101 including the positive electrode active material is formed of a positive electrode material having a higher charge / discharge potential than the negative electrode active material contained in the negative electrode particles 200 described later and capable of reversibly intercalating and deintercalating lithium ions.

The core particles (101) may be any of those conventionally used in the art without any limitation. For example, Li _a A _1-b B _b D ₂ , where 0.90 ≤ a ≤ 1, and 0 ≤ b ≤ 0.5; Li _a E _1-b B _b O _{2 -c} D _{c where} 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05; LiE (in the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05) 2-b B b O 4-c D c; Li _a Ni _{1 -bc} Co _b B _c D _? Wherein, in the formula, 0.90? A? 1, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1- b c} Co _b B _c O _{2 -?} F _? Wherein? 0.90? A? 1, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1- b c} Co _b B _c O _2-α F ₂ wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _1-bc Mn _b B _c D _{? Where} 0.90? A? 1, 0? B? 0.5, 0? C? 0.05, 0 <?? 2; Li _a Ni _1-bc Mn _b B _c O _2-α F _α wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _1-bc Mn _b B _c O _2-α F ₂ wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _b E _c G _d O ₂ wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, and 0.001 ≤ d ≤ 0.1; Li _a Ni _b Co _c Mn _d G _e O ₂ wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1; Li _a NiG _b O ₂ (in the above formula, 0.90? A? 1, and 0.001? B? 0.1); Li _a CoG _b O ₂ (in the above formula, 0.90? A? 1, 0.001? B? 0.1); Li _a MnG _b O ₂ (in the above formula, 0.90? A? 1, 0.001? B? 0.1); Li _a Mn ₂ G _b O ₄ (in the above formula, 0.90? A? 1, 0.001? B? 0.1); QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO _4; Li _(3-f) J ₂ (PO ₄ ) ₃ (0? F? 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0? F? 2); In the formula of LiFePO ₄ may be used a compound represented by any one:

In the above formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or combinations thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

Of course, a compound having a coating layer on the surface of the compound may be used, or a compound having a coating layer may be mixed with the compound. The coating layer may comprise an oxide, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, or a coating element compound of the hydroxycarbonate of the coating element. The compound constituting these coating layers may be amorphous or crystalline. The coating layer may contain Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof. The coating layer forming step may be any coating method as long as it can coat the above compound by a method that does not adversely affect physical properties of the cathode active material (for example, spray coating, dipping, etc.) by using these elements, It will be understood by those skilled in the art that a detailed description will be omitted.

Specifically, for example, the core particles 101 are made of lithium cobalt oxide (hereinafter referred to as LCO), lithium nickel oxide, lithium nickel cobaltate, lithium nickel cobalt aluminum oxide (hereinafter referred to as NCA), nickel cobalt lithium manganese , NCM), lithium salts such as lithium manganese oxide and lithium iron phosphate, nickel sulfide, copper sulfide, sulfur, iron oxide, or vanadium oxide. Each of these cathode active materials may be used alone or in combination of two or more.

In addition, the core particles 101 may be formed of the above-mentioned lithium salt, including a lithium salt of a transition metal oxide having a layered salt-salt type structure. Here, &quot; layered &quot; refers to a thin sheet-like shape. The &quot; rock salt type structure &quot; refers to a sodium chloride type structure, which is a type of crystal structure, and specifically, a structure in which the face-centered cubic lattices formed by each of cation and anion are arranged to be shifted from each other by 1/2 of the unit lattice corner .

As the lithium salt of the transition metal oxide having such a layered rock salt type structure, for example, LiNi _x Co _y Al _z O ₂ (NCA) or LiNi _x Co _y Mn _z O ₂ (NCM) (0 <x <1 , 0 <y <1, 0 <z <1, and x + y + z = 1).

When the core particles 101 include a lithium salt of a ternary transition metal oxide having the layered rock salt type structure, the energy density and thermal stability of the entire solid secondary battery 1 can be improved.

The composite positive electrode active material 100 according to the present embodiment is characterized in that the structural change of the core particle 101 and the change of the structure of the core particle 101 and the solid electrolyte 300 by the first coating layer 102 and the second coating layer 103, The battery characteristics of the pre-solid secondary battery 1 can be further improved.

When the core particle 101 is formed of a lithium salt of ternary transition metal oxide such as NCA or NCM and contains nickel (Ni) as the cathode active material, the capacity density of the pre-solid secondary battery 1 is increased So that metal elution in the cathode active material can be reduced in a charged state. Thus, the all-solid-state secondary battery 1 according to the present embodiment can improve the long-term reliability and cycle characteristics in a charged state. Particularly, for example, when the range of x in the NCA and the NCM is 0.5? X < 1, preferably 0.7? X < 1 and a large amount of nickel is contained, a high capacity battery can be realized.

Here, the shape of the core particle 101 may be, for example, a particle shape such as a spherical shape or an elliptic spherical shape. The average particle diameter of the core particles 101 is preferably 0.1 탆 or more and 50 탆 or less, for example. For example, the average particle size of the core particles 101 may be, for example, 0.1 μm or more and 20 μm or less. For example, the average particle diameter of the core particles 101 may be, for example, 0.1 μm or more and 10 μm or less. Here, the &quot; average particle diameter &quot; refers to the number average diameter (D50) of the particle size distribution obtained by the scattering method or the like, and can be measured by a particle size distribution meter or the like.

The content of the core particles 101 in the anode layer 10 may be, for example, 10 wt% or more and 99 wt% or less, and more specifically 20 wt% or more and 90 wt% or less have.

(First coating layer)

According to one embodiment, the first coating layer 102 covers the surface of the core particle 101. Particularly, in the present embodiment, the first coating layer 102 can be formed of a compound described below to suppress the reaction occurring at the interface between the core particle 101 and the solid electrolyte 300, It is presumed that the deterioration reaction can be effectively suppressed. Further, the first coating layer 102 has lithium ion conductivity.

The first coating layer 102 includes a first lithium-containing compound.

The first lithium-containing compound may be, for example, a lithium-containing oxide or a lithium-containing phosphorus oxide. For example, the lithium-containing oxide may be at least one selected from the group consisting of lithium zirconium oxide (Li-Zr-O), lithium niobium oxide (Li-Nb-O), lithium titanium oxide (Li- O).

Here, the lithium zirconium oxide may include, for example, aLi ₂ O-ZrO ₂ (where 0.1 ≦ a ≦ 2.0). Since aLi ₂ OZrO ₂ (hereinafter also referred to as LZO) is a composite oxide of Li ₂ O and ZrO ₂ and is chemically stable, by forming the first coating layer 102 with aLi ₂ O-ZrO ₂ , And the solid electrolyte 300 can be further suppressed. Here, the range of a may be 0.1? A? 2.0. By setting a in the above range, the battery characteristics of the all-solid secondary battery 1 can be further improved.

When the first coating layer 102 is composed of LZO, the amount of the core particles 101 is controlled so that the molar ratio of LZO to the core particles 101 (that is, the coating amount of LZO) is 0.1 mol% or more and 2.0 mol% . &Lt; / RTI &gt; When the coating amount of the first coating layer 102 is in the above range, the discharge capacity and the load characteristics can be further improved. On the other hand, when the coating amount of the first coating layer 102 is less than 0.1 mol%, the effect of inhibiting the reaction between the core particles 101 and the solid electrolyte 300 may not be sufficient. If the coating amount of the first coating layer 102 exceeds 2.0 mol%, the lithium ion conductivity between the core particle 101 and the solid electrolyte 300 may be lowered.

The lithium-containing phosphorus oxide may be, for example, an oxide of lithium titanium (Li-Ti-PO ₄ ) or an oxide of lithium zirconium (Li-Zr-PO ₄ ).

The thickness of the first coating layer 102 may be, for example, 1 nm or more and 50 nm or less. For example, the thickness of the first coating layer 102 may be, for example, 5 nm or more and 30 nm or less. When the thickness of the first coating layer 102 is within the above range, the characteristics of the pre-solid secondary battery 1 can be improved without lowering the lithium ion conductivity. On the other hand, if the thickness of the first coating layer 102 is less than 1 nm, it may be difficult to sufficiently suppress the reaction between the core particles 101 and the solid electrolyte 300. If the thickness of the first coating layer 102 exceeds 50 nm, the lithium ion conductivity between the core particles 101 and the solid electrolyte 300 may be lowered.

The thickness of the first coating layer 102 may be measured using, for example, a transmission electron microscope (TEM) sectional image or the like. The thickness of the second coating layer 103 described later can be measured in the same manner.

(Second coating layer)

According to one embodiment, the second coating layer 103 covers the first coating layer 102. [ Particularly, in the present embodiment, the second coating layer 103 can be formed of a compound described below to suppress the reaction occurring at the interface between the core particles 101 and the solid electrolyte 300, It is presumed that the deterioration reaction can be effectively suppressed. In addition, the second coating layer 103 has lithium ion conductivity.

The second coating layer 103 includes a second lithium containing compound and the second lithium containing compound includes at least one selected from germanium (Ge), niobium (Nb), and gallium (Ga).

The second lithium containing compound may be at least one selected from lithium germanium oxide (Li-Ge-O), lithium niobium oxide (Li-Nb-O) and lithium gallium oxide (Li-Ga-O).

Here, the composition of the first coating layer 102 and the second coating layer 103, that is, the first lithium-containing compound and the second lithium-containing compound are different, whereby the characteristics of the pre-solid secondary battery 1 are further improved .

The total thickness of the first coating layer 102 and the second coating layer 103 may be 1 nm or more and 500 nm or less, for example, 15 nm or more and 70 nm or less. When the total thickness of the first coating layer 102 and the second coating layer 103 is within the above range, the reaction between the core particles 101 and the solid electrolyte 300 can be further suppressed without lowering the lithium ion conductivity . On the other hand, when the total thickness of the first coating layer 102 and the second coating layer 103 is less than 1 nm, the effect of inhibiting the reaction between the core particles 101 and the solid electrolyte 300 may not be sufficient. If the total thickness of the first coating layer 102 and the second coating layer 103 exceeds 500 nm, the lithium ion conductivity between the core particles 101 and the solid electrolyte 300 may be lowered.

The first coating layer 102 and the second coating layer 103 may cover at least a part of the core particles 101. [ That is, the entire surface of the core particle 101 may be covered with the first coating layer 102 and the second coating layer 103, and a part of the surface of the core particle 101 may be covered with the first coating layer 102 and the second coating layer 103. [ (103).

The anode layer 10 may be formed by appropriately adding additives such as a conductive agent, a binder, a filler, a dispersant, and an ionic conductive agent in addition to the composite cathode active material 100 and the solid electrolyte 300 described above .

Examples of the conductive agent that can be mixed into the anode layer 10 include graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder, and the like. Examples of the binder that can be blended in the anode layer 10 include polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, and the like. As a filler, a dispersant, an ionic conductive agent, and the like that can be mixed into the anode layer 10, a known material used for an electrode of a pre-solid secondary battery can be generally used.

[Cathode layer]

As shown in FIG. 1, the cathode layer 20 includes a cathode particle 200 solid electrolyte 300. The solid electrolyte 300 is described later in the solid electrolyte layer 30.

The negative electrode particles 200 are composed of a negative electrode active material that has a lower charge / discharge potential than the positive electrode active material contained in the core particles 101 and is capable of alloying with lithium or reversibly intercalating and deintercalating lithium.

The negative electrode active material is not limited as long as it can be used as a negative electrode active material of a lithium secondary battery in the related art.

Examples of the negative electrode active material include at least one selected from the group consisting of a lithium metal, a metal capable of alloying with lithium, a transition metal oxide, a non-transition metal oxide, a material capable of doping and dedoping lithium, can do.

The lithium-alloyable metal may be selected from the group consisting of Si, Sn, Al, In, Ge, Pb, Bi, , A rare earth element or a combination element thereof and not Si), an Sn-Y alloy (Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, Or the like). The element Y may be at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Se, Te, Po, or a combination thereof.

The transition metal oxide may be, for example, tungsten oxide, molybdenum oxide, titanium oxide, lithium titanium oxide, vanadium oxide, lithium vanadium oxide, and the like.

The non-transition metal oxide may be, for example, SnO ₂ , SiO _x (0 <x <2) or the like.

Examples of the material capable of doping and dedoping lithium include Sn, SnO ₂ and Sn-Y alloys (Y is an alkali metal, an alkaline earth metal, a Group 11 element, a Group 12 element, a Group 13 element, a Group 14 element, A Group 15 element, a Group 16 element, a transition metal, a rare earth element, or a combination element thereof, but not Sn). The element Y may be at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Se, Te, Po, or a combination thereof.

The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. Examples of the carbon-based material include natural graphite, artificial graphite, graphite carbon fiber, resin fired carbon, pyrolytic vapor grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin fired carbon, polyacene, Vapor grown carbon fiber, soft carbon or hard carbon, mesophase pitch carbide, or the like can be used. These may be used alone as the negative electrode active material 201, or may be used by mixing two or more thereof.

The carbon-based material may be amorphous, plate-like, flake, spherical, fibrous, or a combination thereof.

The negative electrode layer 20 is formed by adding appropriately selected additives such as a conductive agent, a binder, a filler, a dispersant, and an ion conductive agent in addition to the above-described negative electrode particles 200 and the solid electrolyte 300 .

As the additive to be incorporated into the negative electrode layer 20, the same additive as that to be added to the positive electrode layer 10 described above can be used.

[Solid electrolyte layer]

The solid electrolyte layer 30 includes a solid electrolyte 300 formed between the anode layer 10 and the cathode layer 20.

The solid electrolyte 300 is formed of a sulfide solid electrolyte material. The sulfide solid electrolyte material includes at least sulfur and lithium and is at least one selected from the group consisting of phosphorus (P), silicon (Si), boron (B), aluminum (Al), germanium (Ge), zinc (Zn) (In), and a halogen element.

Specifically, the solid electrolyte 301 includes lithium sulfide as a sulfide solid electrolyte material, and the second component may include at least one selected from silicon sulfide, phosphorus sulfide, and boron sulfide. For example Li ₂ SP ₂ S ₅ .

The sulfide solid electrolyte material may include sulfides such as SiS ₂ , GeS ₂ , and B ₂ S _{3 in} addition to Li ₂ SP ₂ S ₅ , which is known to have higher lithium ion conductivity than other inorganic compounds. The sulfide solid electrolyte may further contain Li ₃ PO ₄ , a halogen, a halogen compound, LISICON, LIPON (Li ₃ PO ₄ , Li ₂ PO ₄ ), or the like, to an inorganic solid electrolyte consisting of a combination of Li ₂ SP ₂ S ₅ , SiS ₂ , GeS ₂ , B ₂ S ₃ , _{+ y} PO _4-x N _x ), Thio-LISICON (Li _3.25 Ge _0.25 P _0.75 S ₄ ), Li ₂ O-Al ₂ O ₃ -TiO ₂ -P ₂ O ₅ (LATP) Can be used.

Specific examples of the sulfide solid electrolyte material include Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiX (X is a halogen element), Li ₂ SP ₂ S ₅ -Li ₂ O, Li ₂ SP _{2 S 5 -Li 2 O-LiI,} Li 2 S-SiS 2, Li 2 S-SiS 2 -LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li 2 S-SiS 2 - B ₂ S ₃ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ SB ₂ S ₃ , Li ₂ S -P ₂ S ₅ -ZmSn or one of _{Ga), Li 2 S-GeS} 2, Li 2 SSiS 2 -Li 3 PO 4, Li 2 SSiS 2 -Li p MO q (p, q is a positive number, M is p, Si, Ge, B , One of Al, Ga and In). Here, the sulfide-based solid electrolyte material is produced by treating the starting material (for example, Li ₂ S, P ₂ S _5, etc.) of the sulfide-based solid electrolyte material by a melt quenching method, a mechanical milling method or the like. Further, such post-treatment firing can be performed.

According to one embodiment, in the solid electrolyte 300, among the above-described sulfide solid electrolyte materials, those containing at least sulfur (S), phosphorus (P), and lithium (Li) can be used. Li ₂ SP ₂ S ₅ can be used.

In the case of using a material containing Li ₂ S-P ₂ S ₅ as a sulfide solid electrolyte material for forming the solid electrolyte 300, the mixing molar ratio of Li ₂ S and P ₂ S ₅ is, for example, Li ₂ S: P ₂ S ₅ = 50: 50 to 90: 10.

Examples of the shape of the solid electrolyte 300 include particle shapes such as a pseudo-spherical shape and an elliptic spherical shape. The particle size of the solid electrolyte 300 is not particularly limited. For example, the average particle diameter of the solid electrolyte 300 may be 0.01 占 퐉 or more and 30 占 퐉 or less, and specifically 0.1 占 퐉 or more and 20 占 퐉 or less. The average particle diameter represents the number average diameter (D50) of the particle size distribution of particles obtained by the scattering method or the like, as described above.

The configuration of the all-solid-state secondary battery 1 according to the present embodiment has been described in detail above.

<3. Manufacturing method of pre-solid secondary battery>

Next, a manufacturing method of the all-solid-state secondary battery 1 according to the present embodiment will be described. The pre-solidified secondary battery 1 according to the present embodiment can be manufactured by manufacturing the anode layer 10, the cathode layer 20, and the solid electrolyte layer 30, respectively, and then laminating the above layers.

[Preparation of anode layer]

First, a composite positive electrode active material 100 is produced by sequentially forming a first coating layer 102 and a second coating layer 103 on the surface of the core particle 101.

The core particles 101 can be produced by a known method. For example, when NCA is used as the core particle 101, Ni (OH) ₂ powder, Co (OH) ₂ powder, Al ₂ O ₃ .H ₂ O powder and LiOH.H ₂ O powder are mixed and ground with a ball mill or the like. Next, the mixed and pulverized raw material powder is mixed with a predetermined dispersant, binder or the like to adjust the viscosity or the like, and then formed into a sheet. In addition, the core particles 101 can be produced by calcining the sheet-shaped formed body at a predetermined temperature and pulverizing the formed body after sintering with a sieve (mesh) or the like. Here, the grain size of the core particles 101 can be adjusted by changing the fineness of the sieve used for crushing the compact.

Subsequently, the first coating layer 102 is formed on the surface of the core particle 101 prepared above. The first coating layer 102 is formed on the surface of the cathode active material particle 101, for example, in the following manner. That is, the alkoxide salt of the metal element constituting the first coating layer 102 is mixed with stirring in a solvent such as alcohol to prepare a solution. Then, the prepared solution is sprayed on the surface of the core particles 101 and dried. The spraying can be performed, for example, by using an electric fluidized bed granule coating machine FD-MP-01E manufactured by Powerlex Co., Ltd. Subsequently, the core particles 101 subjected to spray drying of the solution are baked. The first coating layer 102 is formed on the surface of the core particle 101 by the above process.

On the other hand, the second coating layer 103 may be formed on the first coating layer 102 by the same method as the first coating layer 102. In addition, the first coating layer 102 and the second coating layer 103 can be manufactured by a method other than the above-mentioned method.

The composite cathode active material 100 coated sequentially with the first coating layer 102 and the second coating layer 103 can be produced by the above method.

Next, the prepared composite cathode active material 100, the solid electrolyte 300 prepared by the method described below, and various additives are mixed and added to a solvent such as water or an organic solvent to form a slurry or a paste. The obtained slurry or paste is applied to a current collector, dried and then rolled to obtain a positive electrode layer 10.

[Production of cathode layer]

The cathode layer 20 can be manufactured in the same manner as the anode layer. Concretely, the negative electrode particles 200, the solid electrolyte 300 prepared by a method described later, and various additives are mixed and added to a solvent such as water or an organic solvent to form a slurry or a paste. The obtained slurry or paste is applied to a current collector, dried and then rolled to obtain a cathode layer 20. Further, the cathode particles 200 can be produced by a known method using a negative electrode active material.

The current collector used in the anode layer 10 and the cathode layer 20 may be any of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti) A plate or a thin body made of cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li) or an alloy thereof can be used. The positive electrode layer 10 or the negative electrode layer 20 may be formed by compression molding a mixture of the composite cathode active material 100 or the negative electrode particles 200 and various additives in the form of a pellet without using a current collector You may.

[Production of Solid Electrolyte Layer]

The solid electrolyte layer 30 can be produced by the solid electrolyte 300 formed of a sulfide-based solid electrolyte material.

First, a sulfide-based solid electrolyte material is produced by a melt quenching method or a mechanical milling method.

For example, in the case of using the melt quenching method, a predetermined amount of Li ₂ S and P ₂ S ₅ are mixed to form a pellet, which is reacted in a vacuum at a predetermined reaction temperature and then quenched to produce a sulfide-based solid electrolyte material . The reaction temperature of the mixture of Li ₂ S and P ₂ S ₅ is, for example, 400 ° C. to 1000 ° C., and more specifically, 800 ° C. to 900 ° C., for example. The reaction time is, for example, 0.1 hour to 12 hours, more specifically, for example, 1 hour to 12 hours. The quenching temperature of the reactant is usually 10 ° C or lower, preferably 0 ° C or lower, and the quenching rate is usually about 1 ° C / sec to 10000 ° C / sec, for example, about 1 ° C / sec to 1000 ° C / sec .

When a mechanical milling method is used, a predetermined amount of Li ₂ S and P ₂ S ₅ are mixed and stirred by using a ball mill or the like to conduct a reaction, whereby a sulfide-based solid electrolyte material can be produced. Although the stirring speed and stirring time of the mechanical milling method are not particularly limited, the higher the stirring speed, the faster the production rate of the sulfide-based solid electrolyte material, and the longer the agitation time, the more the conversion rate of the raw material into the sulfide- .

Thereafter, the sulfide-based solid electrolyte material obtained by the melt quenching method or the mechanical milling method is heat-treated at a predetermined temperature and then pulverized to produce the solid electrolyte 300 in the form of particles.

Next, the solid electrolyte 300 obtained by the above method is subjected to a heat treatment such as a known method such as a blast method, an aerosol deposition method, a cold spray method, a sputtering method, a CVD method, The solid electrolyte layer 30 can be produced by vapor deposition using the film forming method. Further, the solid electrolyte layer 30 can be produced by pressing the solid electrolyte 300 alone. Further, the solid electrolyte layer 30 may be produced by mixing and pressurizing the solid electrolyte 300 with a solvent, a binder or a support. Here, the binder or the support is added for the purpose of reinforcing the strength of the solid electrolyte layer 30 or preventing short-circuiting of the solid electrolyte 300.

[Production of all solid secondary batteries]

The positive electrode layer 10, the negative electrode layer 20 and the solid electrolyte layer 30 fabricated by the above method are laminated so as to sandwich the solid electrolyte layer 30 in the positive electrode layer 10 and the negative electrode layer 20, And pressurized to produce the all-solid-state secondary battery 1 according to the present embodiment.

The present invention will be described in more detail by way of the following examples and comparative examples. However, the examples are for illustrating the present invention, and the scope of the present invention is not limited thereto.

[Example]

(Example 1)

(Production of cathode active material)

LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM) was used as the core particle 101. The average particle diameter of the core particles 101 was measured by a scattering method and found to be 7 μm. Subsequently, a surface coating treatment was applied to the core particles 101 by using a mixed solution of lithium methoxide and zirconium propoxide and ethanol. Specifically, the amount of the mixed solution was adjusted so that the coating amount of Li ₂ O-ZrO ₂ (LZO) relative to the NCM was 0.5 mol% based on the total amount of NCM. Subsequently, the surface of the core particles 101 was coated with a mixed solution by using a motorized fluidized-bed granule coating machine FD-MP-01E manufactured by POWEREX CO., LTD. Specifically, the core particles 101 were weighed under conditions of a weight of 500 g, an air supply temperature of 90 ° C, an air flow rate of 0.23 m ³ / h, a rotor rotation speed of 400 rpm, an atomized air volume of 50 NL / min, The mixed solution was sprayed on the surface of the core particle (101). Subsequently, the core particles 101 coated with the mixed solution were dried. The coated particles obtained through the above-mentioned surface coating treatment were fired at 350 캜 for 1 hour in an air atmosphere to form a first coating layer 102 made of LZO on the surface of the core particles 101.

Subsequently, a mixed solution of lithium methoxide and germanium propoxide and ethanol was prepared. Specifically, the amount of the mixed solution was adjusted so that the coating amount of Li ₂ O-GeO ₂ (LGeO) relative to the NCM was 0.5 mol% based on the total amount of NCM. Then, a second coating layer 103 made of LGeO was formed on the first coating layer 102 by the above process. The composite cathode active material 100, that is, the double layer coated composite cathode active material in which the first coating layer 102 and the second coating layer 103 are coated on the core particles 101 was obtained by the above-described process. The thickness of the first coating layer 102 was in the range of 5 to 30 占 퐉 and the thickness of the first coating layer 102 and the second coating layer 103 ) Was in the range of 15 to 70 mu m.

(Preparation of all solid secondary batteries)

Initially, reagents Li ₂ S, P ₂ S ₅ , and LiCl, which are starting materials of a sulfide-based electrolyte material, were weighed so as to obtain a material having Li ₆ PS ₅ Cl composition. The reagents were then subjected to a mechanical milling treatment in a planetary ball for 20 hours. The mechanical milling process was carried out at a rotation speed of 380 rpm and in an argon atmosphere.

800 mg of a powder sample of Li ₆ PS ₅ Cl composition obtained by the mechanical milling treatment was pressed (pressure: 400 MPa / cm ² ) to obtain pellets having a diameter of 13 mm and a thickness of about 0.8 mm. The obtained pellets were covered with gold foil, and then placed in a carbon crucible to prepare a sample for heat treatment. The obtained sample for heat treatment was vacuum-sealed in a quartz glass tube. Then, the sample for heat treatment was placed in an electric furnace, and the temperature of the electric furnace was raised from room temperature to 550 DEG C at 1.0 DEG C / min. Then, the sample for heat treatment was heat-treated at 550 DEG C for 6 hours. Then, the sample for thermal treatment at 1.0 캜 / min was cooled to room temperature. After the recovered heat treatment, the sample was pulverized by an agate mortar. The pulverized sample was analyzed by X-ray diffraction to confirm that a desired argyrodite crystal was produced. Then, the sample after the heat treatment was used as the solid electrolyte 300.

Then, the composite cathode active material 100, the solid electrolyte 300, and the carbon nanofibers (CNF) as the conductive agent were mixed at a weight ratio of 83: 15: 3 to prepare a positive electrode mixture. Further, a metal Li foil (thickness 30 mu m) was used as the cathode. The positive electrode mixture (10 mg), the solid electrolyte 300 (150 mg), and a metal Li negative electrode were laminated in this order and pressed at a pressure of ³ ton / cm ² to obtain a test cell.

(Load characteristic evaluation)

The test cell thus obtained was charged at a constant current of 0.05 C at a temperature of 25 캜 to a maximum voltage of 4.0 V, and discharged at a constant current of 0.05 C until the discharge end voltage reached 2.5 V. The discharge capacity was measured, and the initial discharge capacity was determined. Then, the test cell was discharged at 0.05C, 0.5C, and 1C, respectively, and rate characteristics were measured. The ratio of the 1C discharge capacity to the initial discharge capacity was taken as an index of the load characteristics. The higher this value is, the smaller the internal resistance of the battery is, and thus the battery can be said to have an excellent load characteristic.

(Cycle life test)

The resulting test cell was charged and charged to a maximum voltage of 4.0 V at a constant current of 0.05 C at 25 캜 and discharged at 0.5 C to a discharge end voltage of 2.5 V for 50 cycles. The ratio of the discharge capacity in the 50th cycle to the discharge capacity in the first cycle was defined as the discharge capacity retention rate. The discharge capacity retention rate is a parameter showing the cycle characteristics. The larger the value, the better the cycle characteristics. The results are summarized in Table 1 below. The unit of "initial discharge capacity" shown in Tables 1 to 4 is "mAh / g ".

(Example 2)

(Production of cathode active material)

As the core particle 101, NCM used in Example 1 was used. Subsequently, a first coating layer 102 made of LZO was formed on the surface of the core particle 101 by the same process as in Example 1. Then,

Then, a mixed solution of lithium methoxide and niobium ethoxide and ethanol was prepared. Specifically, the amount of the mixed solution was adjusted so that the covering amount of Li ₂ O-Nb ₂ O ₅ (LNbO) to NCM was 0.5 mol% based on the total amount of NCM. Then, a second coating layer 103 made of LNbO was formed on the first coating layer 102 by the same process as in the first embodiment. The thickness of the first coating layer 102 was in the range of 5 to 30 占 퐉 and the thickness of the first coating layer 102, the second coating layer 103, and the second coating layer 103 were measured using a cross- Was in the range of 15 to 70 mu m. Thereafter, a test cell was fabricated by the same process as in Example 1, and the load characteristics and the cycle life were evaluated. The results are summarized in Table 1.

(Comparative Example 1)

The same treatment as in Example 1 was carried out except that the second coating layer 103 was not formed. That is, in Comparative Example 1, only the coating layer made of LZO was formed on the surface of the core particle 101. The results are summarized in Table 1.

(Comparative Example 2)

The same treatment as in Example 1 was carried out except that the first coating layer 102 was not formed. That is, in Comparative Example 2, only the coating layer containing LGeO was formed on the surface of the core particle 101. The results are summarized in Table 1.

(Comparative Example 3)

As the core particle 101, NCM used in Example 1 was used. Subsequently, a first coating layer 102 made of LGeO was formed on the surface of the core particle 101 by the same process as in Example 1. Then, Then, a second coating layer 103 made of LZO was formed on the first coating layer 102 by the same process as in the first embodiment. Thereafter, a test cell was prepared by the same process as in Example 1, and the load characteristics and the cycle life were evaluated. The results are summarized in Table 1.

(Comparative Example 4)

As the core particle 101, NCM used in Example 1 was used. Then, a first coating layer 102 made of LNbO was formed on the surface of the core particle 101 by the same process as in Example 2. [ Subsequently, a mixed solution of lithium methoxide and titanium isopropoxide and ethanol was prepared. Specifically, the amount of the mixed solution was adjusted so that the covering amount of Li ₂ Ti ₂ O ₅ (LTO) to NCM became 0.5 mol% based on the total amount of NCM. Then, a second coating layer 103 made of LTO was formed on the first coating layer 102 by the same process as in the first embodiment. Thereafter, a test cell was fabricated by the same process as in Example 1, and the load characteristics were evaluated. The results are summarized in Table 1. In Comparative Example 4, the cycle characteristics were not evaluated because the rate characteristics were not good.

(Comparative Example 5)

As the core particle 101, NCM used in Example 1 was used. Then, a mixed solution of lithium methoxide, zirconium propoxide, germanium propoxide and ethanol was prepared. Specifically, the amount of the mixed solution was adjusted so that the covering amount of Li ₂ O-ZrO ₂ -GeO ₂ (LZGeO) to NCM was 0.5 mol% based on the total amount of NCM. Then, a coating layer made of LZGeO was formed as the first coating layer 102 by the same process as in Example 1. [ Thereafter, a test cell was fabricated by the same process as in Example 1, and the load characteristics were evaluated. The results are summarized in Table 1. In addition, since the rate characteristic was poor in Comparative Example 5, the cycle life was not evaluated.

Initial discharge capacity Rate characteristics (1C / 0.05C) Cycle characteristics Example 1 153 0.80 0.98 Example 2 152 0.80 0.98 Comparative Example 1 145 0.80 0.94 Comparative Example 2 147 0.80 0.94 Comparative Example 3 149 0.80 0.94 Comparative Example 4 147 0.60 - Comparative Example 5 149 0.75 -

(evaluation)

In Examples 1 and 2, the initial discharge capacity, rate characteristics, and cycle characteristics were excellent. In comparison, in Comparative Examples 1 to 5, at least one of the initial discharge capacity, the rate characteristic and the cycle characteristic was lowered. In particular, the structure of the positive electrode active material of Comparative Example 3 is different from that of Example 1 in that the order of stacking the first coating layer 102 and the second coating layer 103 is changed, but the initial discharge capacity is lower than that of the first embodiment. Comparative Example 4 also changed the stacking order of the first coating layer 102 and the second coating layer 103, but the rate characteristics as well as the initial discharging capacity were lower than those of the Examples. In Comparative Example 5, the constituent elements of the first coating layer 102 and the constituent elements of the second coating layer 103 were the same as one layer, but also the initial discharge capacity was lowered.

(Example 3)

The test cell fabricated in the same manner as in Example 1 was charged at a constant current of 0.05 C at 25 DEG C to a maximum voltage of 4.1 V and then discharged at a constant current of 0.05 C up to the discharge end voltage of 2.5 V. [ The discharge capacity was measured, and the initial discharge capacity was determined. Then, the test cell was discharged at 0.05C, 0.5C, and 1C, respectively, and rate characteristics were measured. The ratio of the 1C discharge capacity to the initial discharge capacity was taken as an index of the load characteristics. For the cycle life test, the obtained test cell was charged and discharged at a constant current of 0.05 C at a constant current of 4.1 V at 25 DEG C, and discharged at 0.5 C to the discharge end voltage of 2.5 V for 50 cycles. The ratio of the discharge capacity in the 50th cycle to the discharge capacity in the first cycle was defined as the discharge capacity retention rate. That is, in Example 3, the same process as in Example 1 was carried out except that the charging voltage of the test cell was 4.1 V. The results are summarized in Table 2.

(Example 4)

The test cell produced in the same manner as in Example 2 was evaluated in the same manner as in Example 3. The results are summarized in Table 2.

(Comparative Example 6)

The test cell produced in the same manner as in Comparative Example 1 was evaluated in the same manner as in Example 3. The results are summarized in Table 2.

(Comparative Example 7)

The test cell produced in the same manner as in Comparative Example 2 was evaluated in the same manner as in Example 3. The results are summarized in Table 2.

(Comparative Example 8)

The test cell produced in the same manner as in Comparative Example 3 was evaluated in the same manner as in Example 3. The results are summarized in Table 2.

(Comparative Example 9)

The test cell produced in the same manner as in Comparative Example 4 was evaluated in the same manner as in Example 3. The results are summarized in Table 2. In Comparative Example 9, the cycle life was not evaluated because the rate characteristics were not good.

(Comparative Example 10)

The test cell produced in the same manner as in Comparative Example 5 was evaluated in the same manner as in Example 3. The results are summarized in Table 2. Further, in Comparative Example 10, the cycle life was not evaluated because the rate characteristics were not good.

Initial discharge capacity Rate characteristics (1C / 0.05C) Cycle characteristics Example 3 170 0.80 0.98 Example 4 170 0.78 0.96 Comparative Example 6 161 0.76 0.96 Comparative Example 7 168 0.80 0.92 Comparative Example 8 169 0.76 0.96 Comparative Example 9 167 0.51 - Comparative Example 10 170 0.71 -

(evaluation)

Even when the voltage was increased to 4.1 V, results similar to those at 4.0 V were obtained.

(Example 5)

The test cell fabricated in the same manner as in Example 1 was charged at a constant current of 0.05 C at a temperature of 25 캜 up to a maximum voltage of 4.2 V and then discharged at a constant current of 0.05 C up to a discharge end voltage of 2.5 V. The discharge capacity was measured, and the initial discharge capacity was determined. Then, the test cell was discharged at 0.05C, 0.5C, and 1C, respectively, and rate characteristics were measured. The ratio of the 1C discharge capacity to the initial discharge capacity was taken as an index of the load characteristics. For the cycle life test, the obtained test cell was charged and discharged at a constant current of 0.05 C at a constant voltage of 4.2 V at 25 DEG C, and discharged at 0.5 C to a discharge end voltage of 2.5 V for 50 cycles. The ratio of the discharge capacity in the 50th cycle to the discharge capacity in the first cycle was defined as the discharge capacity retention rate. That is, in Example 5, the same process as in Example 1 was carried out except that the charging voltage of the test cell was 4.2 V. The results are summarized in Table 3.

(Example 6)

The test cell produced in the same manner as in Example 2 was evaluated in the same manner as in Example 5. The results are summarized in Table 3.

(Comparative Example 11)

The test cell produced in the same manner as in Comparative Example 1 was evaluated in the same manner as in Example 5. The results are summarized in Table 3.

(Comparative Example 12)

The test cell produced in the same manner as in Comparative Example 2 was evaluated in the same manner as in Example 5. The results are summarized in Table 3.

(Comparative Example 13)

The test cell produced in the same manner as in Comparative Example 3 was evaluated in the same manner as in Example 5. The results are summarized in Table 3.

(Comparative Example 14)

The test cell produced in the same manner as in Comparative Example 4 was evaluated in the same manner as in Example 5. The results are summarized in Table 3. In Comparative Example 14, the cycle life was not evaluated because the rate characteristics were poor.

(Comparative Example 15)

The test cell produced in the same manner as in Comparative Example 5 was evaluated in the same manner as in Example 5. The results are summarized in Table 3. In Comparative Example 15, cycle life was not evaluated because the rate characteristic was poor.

Initial discharge capacity Rate characteristics (1C / 0.05C) Cycle characteristics Example 5 188 0.81 0.98 Example 6 186 0.78 0.94 Comparative Example 11 171 0.81 0.95 Comparative Example 12 175 0.80 0.93 Comparative Example 13 186 0.77 0.96 Comparative Example 14 185 0.43 - Comparative Example 15 187 0.69 -

(evaluation)

Even when the voltage was increased to 4.2 V, results similar to those at 4.0 V were obtained.

(Example 7)

LiNi _0.8 Co _0.15 Al _0.05 O ₂ (NCA) was used as the core particle 101. The average particle diameter of the core particles 101 was measured by a scattering method and found to be 7 μm. Subsequently, a surface coating treatment was applied to the core particles 101 by using a mixed solution of lithium methoxide and zirconium propoxide and ethanol. Specifically, the amount of the mixed solution was adjusted so that the coating amount of Li ₂ O-ZrO ₂ (LZO) relative to the NCA was 0.5 mol% based on the total amount of NCA. Subsequently, the surface of the core particles 101 was coated with a mixed solution by using a motorized fluidized-bed granule coating machine FD-MP-01E manufactured by POWEREX CO., LTD. Specifically, the core particles 101 were weighed under conditions of a weight of 500 g, an air supply temperature of 90 ° C, an air flow rate of 0.23 m ³ / h, a rotor rotation speed of 400 rpm, an atomized air volume of 50 NL / min, The mixed solution was sprayed onto the surface of the core particle (101). Subsequently, the core particles 101 coated with the mixed solution were dried. The coated particles obtained by the above-mentioned surface coating treatment were fired at 350 캜 for 1 hour in the air atmosphere to form a first coating layer 102 made of LZO on the surface of the core particles 101.

Subsequently, a mixed solution of lithium methoxide and germanium propoxide and ethanol was prepared. Specifically, the amount of the mixed solution was adjusted so that the coating amount of Li ₂ O-GeO ₂ (LGeO) relative to NCA was 0.5 mol% based on the total amount of NCA. Then, a second coating layer 103 made of LGeO was formed on the first coating layer 102 by the above process. The composite cathode active material 100, that is, the double coated composite cathode active material, in which the first coating layer 102 and the second coating layer 103 were coated on the core particles 101 was obtained by the above process. The thickness of the first coating layer 102 was in the range of 5 to 30 占 퐉 and the thickness of the first coating layer 102 and the second coating layer 103 ) Was in the range of 15 to 70 mu m.

(Preparation of all solid secondary batteries)

Initially, reagents Li ₂ S and P ₂ S ₅ , which are starting materials of a sulfide-based electrolyte material, were weighed so as to obtain a material having a Li ₃ PS ₄ composition. The reagents were then subjected to a mechanical milling treatment in a planetary ball for 20 hours. The mechanical milling process was carried out at a rotation speed of 380 rpm and in an argon atmosphere.

The sample obtained by the mechanical milling treatment was pulverized by an agate mortar. The pulverized sample was subjected to a crystal analysis by X-ray diffraction to confirm whether Li ₂ S and P ₂ S ₅ used as starting materials remained. The sample after the crushing was used as the solid electrolyte 300.

Subsequently, the composite cathode active material 100 solid electrolyte 300 and the carbon nanofibers (CNF) as a conductive agent were mixed at a weight ratio of 60: 35: 5 to prepare a positive electrode mixture. Further, graphite, a solid electrolyte 300 and vapor-grown carbon fibers (VGCF) as a conductive agent were mixed at a weight ratio of 60: 35: 5 to prepare an anode mixture. The positive electrode mixture (15 mg), the solid electrolyte (100 mg) and the negative electrode mixture (15 mg) were laminated in this order and pressed at a pressure of ³ ton / cm ² to obtain a test cell.

(Load characteristic evaluation)

The test cell thus obtained was charged at a constant current of 0.05 C at a temperature of 25 캜 to a maximum voltage of 4.0 V and then discharged at a constant current of 0.05 C until the discharge end voltage reached 2.5 V. The discharge capacity was measured, and the initial discharge capacity was determined. Then, the test cell was discharged at 0.05C, 0.5C, and 1C, respectively, and rate characteristics were measured. The ratio of the 1C discharge capacity to the initial discharge capacity was taken as an index of the load characteristics.

(Cycle life test)

The resulting test cell was charged and charged to a maximum voltage of 4.0 V at a constant current of 0.05 C at 25 캜 and discharged at 0.5 C to a discharge end voltage of 2.5 V for 50 cycles. The ratio of the discharge capacity in the 50th cycle to the discharge capacity in the first cycle was defined as the discharge capacity retention rate. The results are summarized in Table 4 below.

(Comparative Example 16)

As the core particle 101, NCA used in Example 7 was used. Then, a first coating layer 102 made of LGeO was formed on the surface of the core particle 101 by the same process as in Example 7. [ Then, a second coating layer 103 made of LZO was formed on the first coating layer 102 by the same process as in the seventh example. Thereafter, a test cell was prepared by the same treatment as in Example 7, and the load characteristics and the cycle life were evaluated. The results are summarized in Table 4.

(Comparative Example 17)

The same treatment as in Example 7 was carried out except that the second coating layer 103 was not formed. That is, in Comparative Example 17, only the coating layer made of LZO was formed on the surface of the core particles 101. The results are summarized in Table 4.

(Comparative Example 18)

As the core particle 101, NCA used in Example 7 was used. Subsequently, the same treatment as in Example 2 was carried out except that the first coating layer 102 was not formed, so that only the coating layer made of LNbO was formed on the surface of the core particle 101. Thereafter, a test cell was fabricated by the same process as in Example 7, and the load characteristics and the cycle life were evaluated. The results are summarized in Table 4.

(Comparative Example 19)

The same treatment as in Example 7 was performed except that the first coating layer 102 was not formed. That is, in Comparative Example 19, only the coating layer made of LGeO was formed on the surface of the core particle 101. The results are summarized in Table 4.

Initial discharge capacity Rate characteristics (1C / 0.05C) Cycle characteristics Example 7 140 0.79 0.99 Comparative Example 16 132 0.76 0.83 Comparative Example 17 117 0.62 0.98 Comparative Example 18 119 0.48 0.88 Comparative Example 19 131 0.69 0.86

(evaluation)

Similar results were obtained when the core particle 101 was replaced with NCA.

(Example 8)

(Production of cathode active material)

LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (NCM) was used as the core particle 101. The average particle diameter of the core particles 101 was measured by a scattering method and found to be 7 μm. Subsequently, a surface coating treatment was applied to the core particles 101 using a mixed solution of lithium methoxide and zirconium propoxide and ethanol. Specifically, the amount of the mixed solution was adjusted so that the coating amount of Li ₂ O-ZrO ₂ (LZO) relative to the NCM was 0.5 mol% based on the total amount of NCM. Subsequently, the surface of the core particles 101 was coated with a mixed solution by using a motorized fluidized-bed granule coating machine FD-MP-01E manufactured by POWEREX CO., LTD. Specifically, the mixed solution was prepared under the conditions that the weight of the core particles 101 was 500 g, the air supply temperature was 90 ° C., the air supply air volume was 0.23 m ³ / h, the rotor rotation speed was 400 rpm, the atomized air volume was 50 NL / min, Was sprayed on the surface of the core particle (101). Subsequently, the core particles 101 coated with the mixed solution were dried. The coated particles obtained through the above-mentioned surface coating treatment were fired at 350 캜 for 1 hour in an air atmosphere to form a first coating layer 102 made of LZO on the surface of the core particles 101.

Subsequently, a mixed solution of lithium methoxide and germanium propoxide and ethanol was prepared. Specifically, the amount of the mixed solution was adjusted so that the coating amount of Li ₂ O-GeO ₂ (LGeO) relative to the NCM was 0.5 mol% based on the total amount of NCM. Then, a second coating layer 103 made of LGeO was formed on the first coating layer 102 by the above process. The composite cathode active material 100, that is, the double layer coated composite cathode active material in which the first coating layer 102 and the second coating layer 103 are coated on the core particles 101 was obtained by the above-described process. The thickness of the first coating layer 102 was in the range of 3 to 30 占 퐉 and the thickness of the first coating layer 102 and the second coating layer 103 ) Was in the range of 6 to 70 mu m.

(Preparation of all solid secondary batteries)

Initially, reagents Li ₂ S and P ₂ S ₅ , which are starting materials of a sulfide-based electrolyte material, were weighed so as to obtain a material having a Li ₃ PS ₄ composition. The reagents were then subjected to a mechanical milling treatment in a planetary ball for 20 hours. The mechanical milling process was carried out at a rotation speed of 380 rpm and in an argon atmosphere.

A sample of the Li ₃ PS ₄ composition obtained by the mechanical milling treatment was pulverized by an agate mortar. The pulverized sample was subjected to a crystal analysis by X-ray diffraction, and it was confirmed that Li ₂ S and P ₂ S ₅ used as a starting material did not remain. Then, the sample after the heat treatment was used as the solid electrolyte 300.

Then, the composite cathode active material 100, the solid electrolyte 300 and the conductive agent VGCF were mixed at a weight ratio of 60: 35: 5 to prepare a positive electrode mixture. Further, graphite and solid electrolyte 300 and VGCF as a conductive agent were mixed at a weight ratio of 60: 35: 5 to prepare a negative electrode mixture. The positive electrode mixture (15 mg), the solid electrolyte 300 (100 mg), and the negative electrode mixture (15 mg) were laminated in this order and pressed at a pressure of ³ ton / cm ² to obtain a test cell.

(Load characteristic evaluation)

The test cell thus obtained was charged at a constant current of 0.05 C at a temperature of 25 캜 to a maximum voltage of 4.0 V and then discharged at a constant current of 0.05 C until the discharge end voltage reached 2.5 V. The discharge capacity was measured, and the initial discharge capacity was determined. Then, the test cell was discharged at 0.05C, 0.5C, and 1C, respectively, and rate characteristics were measured. The ratio of the 1C discharge capacity to the initial discharge capacity was taken as an index of the load characteristics.

(Cycle life test)

The resulting test cell was charged and charged to a maximum voltage of 4.0 V at a constant current of 0.05 C at 25 캜 and discharged at 0.5 C to a discharge end voltage of 2.5 V for 50 cycles. The ratio of the discharge capacity in the 50th cycle to the discharge capacity in the first cycle was defined as the discharge capacity retention rate. The results are summarized in Table 5 below.

(Comparative Example 20)

As the core particle 101, NCM used in Example 8 was used. Subsequently, a first coating layer 102 made of LGeO was formed on the surface of the core particle 101 by the same process as in Example 8. [ Then, a second coating layer 103 made of LZO was formed on the first coating layer 102 by the same process as in the eighth embodiment. Thereafter, a test cell was prepared by the same process as in Example 8, and the load characteristics and the cycle life were evaluated. The results are summarized in Table 5.

(Comparative Example 21)

The same treatment as in Example 8 was carried out except that the second coating layer 103 was not formed. That is, in Comparative Example 21, only the coating layer made of LZO was formed on the surface of the core particle 101. The results are summarized in Table 5.

(Comparative Example 22)

The same treatment as in Example 8 was carried out except that the first coating layer 102 was not formed. That is, in Comparative Example 22, only the coating layer made of LGeO was formed on the surface of the core particle 101. The results are summarized in Table 5.

Initial discharge capacity Rate characteristics (1C / 0.05C) Cycle characteristics Example 8 105 0.5 0.98 Comparative Example 20 103 0.45 0.97 Comparative Example 21 101 0.32 0.96 Comparative Example 22 101 0.33 0.96

(evaluation)

As shown in Table 5, the battery according to Example 8 exerts excellent capacity characteristics, rate characteristics, and cycle characteristics as compared with the batteries according to Comparative Examples 20 to 22.

As described above, according to the embodiment of the present invention, the core particles 101 are coated with the first coating layer 102 and the second coating layer 103, and the first coating layer 102 and the second coating layer 103 are coated with a specific Element. Therefore, the characteristics of the entire solid secondary battery including the core particles 101, the first coating layer 102, and the second coating layer 103 can be further improved. Further, since each coating layer is produced by applying the alkoxide salt of the element constituting the coating layer to the core particle 101 and firing it, the coating layer can be easily manufactured, and the productivity is also excellent.

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to these examples. It will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims. Accordingly, it should be understood that they fall within the technical scope of the present invention.

1 pre-solid secondary battery
10 anode layer
20 cathode layer
30 solid electrolyte layer
100 composite cathode active material
101 core particle
102 First coating layer
103 Second coating layer
200 cathode particles
300 solid electrolyte

Claims (20)

And a first coating layer and a second coating layer covering the core particles and the surface of the core particles,
Wherein the core particle comprises a cathode active material,
Wherein the first coating layer comprises a first lithium-containing compound,
Wherein the first lithium-containing compound includes at least one selected from zirconium (Zr), niobium (Nb), titanium (Ti), and aluminum (Al)
Wherein the second coating layer comprises a second lithium-containing compound,
Wherein the second lithium-containing compound comprises at least one selected from the group consisting of germanium (Ge), niobium (Nb), and gallium (Ga)
Wherein the first lithium-containing compound and the second lithium-containing compound are different from each other. The method according to claim 1,
Wherein the surface of the core particle is coated with the first coating layer and the surface of the first coating layer is coated with the second coating layer. The method according to claim 1,
Wherein the first lithium-containing compound is a lithium-containing oxide or a lithium-containing phosphorus oxide. The method according to claim 1,
The first lithium-containing compound is selected from lithium zirconium oxide (Li-ZO), lithium niobium oxide (Li-Nb-O), lithium titanium oxide (Li-Ti-O) and lithium aluminum oxide At least one compound cathode active material. 5. The method of claim 4,
Wherein said lithium zirconium oxide comprises aLi ₂ O-ZrO ₂ (provided that 0.1 ≦ a ≦ 2.0). The method according to claim 1,
Wherein the first lithium-containing compound is lithium zirconium oxide (Li-Zr-PO ₄ ) or lithium titanium oxide (Li-Ti-PO ₄ ). The method according to claim 1,
Wherein the second lithium-containing compound is at least one selected from lithium germanium oxide (Li-Ge-O), lithium niobate oxide (Li-Nb-O) and lithium gallium oxide (Li-Ga-O). The method according to claim 1,
Wherein the thickness of the first coating layer is 1 nm or more and 50 nm or less. The method according to claim 1,
Wherein the total thickness of the first coating layer and the second coating layer is not less than 1 nm and not more than 500 nm. The method according to claim 1,
And the average particle diameter of the core particles is 10 占 퐉 or less. The method according to claim 1,
Wherein the core particle comprises a lithium transition metal oxide having a layered rock salt type structure. The method according to claim 1,
Wherein the core particles are LiNi _x Co _y M _z O ₂ wherein M is Al or Mn and 0 <x <1, 0 <y <1, x + y + z = 1. 13. The method of claim 12,
Wherein the core particles satisfy 0.5? X <1. A positive electrode comprising the composite cathode active material according to any one of claims 1 to 13. A cathode according to claim 14;
cathode; And
And an electrolyte formed between the positive electrode and the negative electrode. 16. The method of claim 15,
The lithium secondary battery is a pre-solid lithium secondary battery,
Wherein the electrolyte is a sulfide solid electrolyte. 17. The method of claim 16,
Wherein the sulfide solid electrolyte comprises at least sulfur and lithium,
Further contains at least one element selected from phosphorus (P), silicon (Si), boron (B), aluminum (Al), germanium (Ge), zinc (Zn), gallium (Ga), indium Lt; / RTI &gt; 17. The method of claim 16,
The sulfide solid electrolyte may be lithium sulfide; And at least one selected from silicon sulfide, phosphorus sulfide, and boron sulfide. 17. The method of claim 16,
Wherein the sulfide solid electrolyte comprises Li ₂ S and P ₂ S ₅ . 17. The method of claim 16,
Wherein the sulfide solid electrolyte has a particle shape.

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