KR20210122195A - A cathode active material for an all solid type battery and an all solid type battery comprising the same - Google Patents

Abstract

The present invention relates to a positive electrode active material for an all-solid-state battery including secondary particles comprising a group of a plurality of primary particles, wherein the primary particles provided on the surface of the secondary particles among the primary particles are oriented particles provided in the form of a rod shape having a short axis and a long axis.

Description

A cathode active material for an all-solid-state battery and an all-solid-state battery comprising the same

The present invention relates to a cathode active material for an all-solid-state battery and an all-solid-state battery comprising the same, and more specifically, to a cathode active material for an all-solid-state battery and an all-solid-state battery comprising the same, which has improved interfacial properties with a solid electrolyte and exhibits excellent lifespan characteristics even in long-term cycles related to solid-state batteries.

With the development of portable mobile electronic devices such as smart phones, MP3 players, and tablet PCs, the demand for secondary batteries capable of storing electrical energy is increasing explosively. In particular, with the advent of electric vehicles, medium and large energy storage systems, and portable devices requiring high energy density, the demand for lithium secondary batteries is increasing. With such an increase in demand for lithium secondary batteries, various research and development for improving the characteristics of positive electrode active materials used in lithium secondary batteries are being conducted.

On the other hand, the existing lithium secondary battery uses a liquid non-aqueous organic electrolyte, which has a risk of ignition and explosion. In fact, since explosion accidents of products to which this is applied continue to occur, it is urgent to solve these problems.

All-solid-state batteries replace these organic electrolytes with solid electrolytes, and all of the battery's components, such as electrodes and electrolytes, are made of solid. it is possible to do

In the case of an all-solid-state battery to which such a solid electrolyte is applied, there is a problem in that capacity is not properly expressed due to high interfacial resistance occurring at the interface between the positive electrode active material and the solid electrolyte. The main causes of such interfacial resistance are the space charge layer phenomenon in which a lithium-deficient layer is formed at the interface of the solid electrolyte due to the potential difference between the positive electrode active material and the solid electrolyte, and the formation of an interfacial impurity layer by a chemical reaction at the interface of the positive electrode active material and the solid electrolyte. is becoming

That is, although stability can be obtained by using a solid electrolyte, electrochemical characteristics, particularly characteristics such as long-term cycle, are deteriorated, which is a problem, and various studies are being conducted to solve this problem.

(Prior Patent) US Patent 5,523,179

One technical problem to be solved by the present application is to provide a cathode active material for an all-solid-state battery having a stable microstructure and an all-solid-state battery using the same.

Another technical problem to be solved by the present application is to provide a cathode active material for an all-solid-state battery in which the interfacial resistance with a solid electrolyte is reduced, and a side reaction on the surface between the cathode active material and the solid electrolyte is reduced, and an all-solid-state battery using the same. .

The technical problem to be solved by the present application is not limited to the above.

The present invention provides an all-solid-state cathode active material and an all-solid-state battery comprising the same.

In one embodiment, comprising secondary particles consisting of a group of a plurality of primary particles, the primary particles provided on the surface of the secondary particles among the primary particles are provided in the form of a rod shape having a short axis and a long axis It may include a positive electrode active material for an all-solid-state battery that includes oriented particles.

In one embodiment, the long axis of the primary particles may be provided to face the central portion of the secondary particles to provide a diffusion path of lithium ions.

In one embodiment, the primary particles include a crystal structure having an a-axis and a c-axis, and the ratio of the length in the a-axis direction to the length in the c-axis direction increases from the center of the secondary particles toward the surface. may include

In one embodiment, the a-axis direction of the primary particles may be provided to face the central portion of the secondary particles to correspond to the diffusion path of lithium ions.

In one embodiment, the all-solid positive electrode active material is prepared by calcining a composite metal hydroxide containing at least one of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al) with a lithium compound. Including that, at least any one or more of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al) constituting the composite metal hydroxide has a concentration gradient in at least any part or more of the composite metal hydroxide It may be provided to have.

In one embodiment, the cathode active material may be any one or more of NC-based, NCM-based, NCA-based, LNO-based, NCMA-based, LCO-based and NM-based having a layered structure.

In one embodiment, the cathode active material is prepared by calcining a composite metal hydroxide including at least one of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al) with a lithium compound. However, the nickel (Ni), cobalt (Co), manganese (Mn), and added together with at least any one or more of aluminum (Al), or added together with the lithium compound may further include a different element that is fired have.

According to another aspect of the present invention, a positive electrode comprising the above-described positive electrode active material; and a solid electrolyte, wherein the solid electrolyte may include any one or more of a halogen-based solid electrolyte, a sulfide-based solid electrolyte, and an oxide-based solid electrolyte.

According to the present invention as described above, the cathode active material for an all-solid-state battery according to the present invention includes secondary particles formed by aggregation of a plurality of primary particles, and the secondary particles exhibit excellent cycle characteristics by having a stable microstructure. It may include a cathode active material for a solid battery.

In addition, the all-solid-state battery using the positive electrode active material for an all-solid-state battery according to the present invention can form a stable interface with the solid electrolyte by itself even though unnecessary processes such as surface treatment of the conventional positive electrode active material are omitted. can improve the electrochemical and mechanical properties of

1 is a view schematically showing secondary particles according to an embodiment of the present invention.
2 is a schematic diagram of a cross-section of a cathode active material according to an embodiment of the present invention.
3 is a view schematically showing the movement of lithium ions in the positive electrode active material according to an embodiment of the present invention.
4 is a diagram schematically showing the characteristics at the interface between the microstructure and the solid electrolyte of the positive electrode active material (a) according to the prior art and the positive electrode active material (b) according to the embodiment of the present invention in the same solid electrolyte.
5 is a SEM image of the positive electrode active material of Comparative Example 1 and Example 1.
6 is a graph showing the concentration of the metal constituting the positive electrode active material of Example 1. Referring to FIG.
7 is a graph confirming the cycle characteristics in the secondary batteries (a, c) using the liquid electrolyte and the all-solid batteries (b, d) using the solid electrolyte using the cathode active material for Comparative Examples 1 and 1 .
8 is an all-solid-state battery using the positive electrode active material of Comparative Example 1 and Example 1, the lifespan characteristics (a) at 0.5C, the capacity-voltage profile at each cycle (b), 2 cycles and 100 cycles It is a graph showing the Nyquist plot (c, d).
9 is an all-solid-state battery using the positive electrode active material of Comparative Examples 1 and 1, at 0.1C, 30°C, 0.05C, and 70°C, capacity-voltage profiles (a), Comparative Example 1 and Ex situ XRD pattern showing the (003) peak for Example 1.
10 is a graph showing lattice parameters and volumetric strain (a), a diagram schematically showing monitoring the pressure of a solid electrolyte using a pressure sensor (b), and 0.1C, 30°C It is a view showing the operando electrochemical pressiometry according to Comparative Example 1 and Example 1 in which 1 cycle was performed with the furnace. 15 is a cross-sectional SEM image according to Comparative Example 1 and Example 1. FIG.
In FIG. 11 , the microstructures of Example 1 and Comparative Example 1 were confirmed. SEM images of the positive electrode active material for all-solid-state batteries were shown before the cycle (pristine), 4.3V charge, 3V discharge, and after 100 cycles, respectively.
12 is an ex situ TEM image of the all-solid-state battery using Comparative Example 1 and Example 1 after 100 cycles of charging and discharging.
13 is a graph showing ex situ XPS results of all-solid-state batteries using Comparative Example 1 and Example 1. FIG.
14 is a graph confirming the discharge capacity (a) and cycle characteristics according to the nickel content in the lithium secondary battery using the positive electrode active material and the liquid electrolyte according to Preparation Examples 1 to 5, Comparative Example 1, and Example 1 ( b), a graph confirming the discharge capacity (c) and cycle characteristics according to the nickel content in the all-solid-state battery using the positive electrode active material and the solid electrolyte according to Preparation Examples 1 to 5, Comparative Example 1, and Example 1 ( d).

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the technical spirit of the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosed subject matter may be thorough and complete, and the spirit of the present invention may be sufficiently conveyed to those skilled in the art.

In this specification, when a component is referred to as being on another component, it may be directly formed on the other component or a third component may be interposed therebetween. In addition, in the drawings, thicknesses of films and regions are exaggerated for effective description of technical content.

In addition, in various embodiments of the present specification, terms such as first, second, third, etc. are used to describe various components, but these components should not be limited by these terms. These terms are only used to distinguish one component from another. Accordingly, what is referred to as a first component in one embodiment may be referred to as a second component in another embodiment. Each embodiment described and illustrated herein also includes a complementary embodiment thereof. In addition, in the present specification, 'and/or' is used to mean including at least one of the elements listed before and after.

In the specification, the singular expression includes the plural expression unless the context clearly dictates otherwise. In addition, terms such as "comprise" or "have" are intended to designate that a feature, number, step, element, or a combination thereof described in the specification is present, and one or more other features, numbers, steps, configuration It should not be construed as excluding the possibility of the presence or addition of elements or combinations thereof.

In addition, in the following description of the present invention, if it is determined that a detailed description of a related well-known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

In addition, in the present application, that the ratio of the first crystal structure in the specific part is higher than the ratio of the second crystal structure means that the specific part includes both the first crystal structure and the second crystal structure, but the specific part In , it is interpreted to mean that the ratio of the first crystal structure is higher than the ratio of the second crystal structure, and also means that the specific portion has only the first crystal structure.

In addition, in the present application, the crystal system (crystal system) is triclinic, monoclinic, orthorhombic, tetragonal, trigonal or rhombohedral, hexagonal. , and may be composed of 7 pieces of a cubic system.

In addition, in the present application, "mol%" refers to the content of any metal included in the positive electrode active material or the positive electrode active material precursor when it is assumed that the sum of the remaining metals except sodium and oxygen is 100% in the positive electrode active material or the positive electrode active material precursor. interpreted as meaning

1 is a view schematically showing secondary particles according to an embodiment of the present invention. 2 is a schematic diagram of a cross-section of a cathode active material according to an embodiment of the present invention. 3 is a view schematically showing the movement of lithium ions in the positive electrode active material according to an embodiment of the present invention.

1 to 3 , the positive electrode active material according to an embodiment of the present invention may be applied to an all-solid-state battery including an all-solid electrolyte, and the positive electrode active material may be formed of secondary particles 100 having an approximately spherical shape. . The secondary particles 100 are divided into a central portion 10 and a surface portion 20 and may be formed by aggregation of a plurality of primary particles 30 . The primary particles 30 may have a layered structure.

In the secondary particle 100, the primary particles 30 constituting the central portion 10 and the primary particles 30 constituting the surface portion 20 may have the same size or different sizes, and the surface portion 20 ) constituting the primary particles 30 have a long axis and a short axis, and extend in a direction from the surface portion 20 toward the central portion 10 to include oriented particles provided in the form of a rod shape. . The oriented particles may be arranged in a direction toward the central portion 10 of the secondary particles 100, and may be provided in a radiate form.

In the positive electrode active material, the oriented particles are provided in a rod shape, and the rod shape has a short axis and a long axis, and the average length of the short axis is 1.0 μm or less, and the average length of the long axis may be 1.0 μm or more. For example, in the positive electrode active material, the shape of the primary particle may be different from the central part and the surface of the secondary particle. Specifically, the primary particle may be provided so that the length of the long axis increases from the central part of the secondary particle to the surface part. can

A long axis of the primary particles may be provided to face a central portion of the secondary particles to provide a diffusion path for lithium ions. In addition, the primary particle includes a crystal structure having an a-axis and a c-axis, and the primary particle includes a ratio of a length in an a-axis direction to a length in the c-axis direction increasing from the center of the secondary particle toward the surface. can Specifically, the a-axis direction of the primary particles may be provided to face the central portion of the secondary particles to correspond to the diffusion path of lithium ions.

The cathode active material may include a crystal structure having a c-axis and an a-axis, wherein the c-axis approximately corresponds to a minor axis direction of the rod shape, and the a-axis approximately corresponds to a major axis direction of the rod shape. . In the rod shape of the primary particles, the length of the minor axis corresponding to the c-axis in a direction from the center of the secondary particles to the surface portion is substantially similar, and the length of the major axis corresponding to the a-axis is at the center. It may increase as it goes toward the surface part.

The long-axis direction or the a-axis direction of the primary particles is provided to face the center of the secondary particles, which is provided to correspond to the diffusion path of the lithium ions, so that the diffusion of the lithium ions can be performed more effectively.

The all-solid positive electrode active material is prepared by calcining a composite metal hydroxide containing at least one of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al) with a lithium compound, At least any one or more of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al) constituting the composite metal hydroxide may be provided to have a concentration gradient in at least any part or more of the composite metal hydroxide. . Specifically, the secondary particle 100 may be made of one or more metals including lithium, and at least some of the one or more metals may have a concentration gradient in the central portion 10 and/or the surface portion 20 . More specifically, the secondary particle 100 includes nickel (Ni), but the concentration of nickel (Ni) in the surface portion 20 of the secondary particle 100 is the central portion 10 of the secondary particle 100 . ) may be provided lower than the concentration in

Since the nickel (Ni) is provided low in the surface portion 20 of the secondary particle 100, a side reaction with the solid electrolyte on the outermost surface of the secondary particle 100 is reduced, and the all-solid-state battery including the positive electrode active material can improve the long-term cycle characteristics of In addition, since the nickel (Ni) is provided at a high concentration in the central portion 10 of the secondary particles 100, by increasing the total nickel (Ni) concentration of the secondary particles 100, the capacity of the all-solid-state battery is improved can do it

Alternatively, in the secondary particle 100, a hollow is formed between the central part 10 and the surface part 20, or the crystal form between the central part 10 and the surface part 20 is different, or the central part 10 ) by manufacturing the surface portion 20 so as to surround the central portion 10 after manufacturing, a difference in image between the central portion 10 and the surface portion 20 may be formed, whereby the core and the shell (shell) may be provided in the form divided.

Between the primary particles 30 having the rod shape, that is, between the primary particles 30 extending from the central portion 10 of the secondary particles in the surface portion 20 direction (D). , a path for movement of metal ions (eg, lithium ions) may be provided. Accordingly, the all-solid-state battery using the positive electrode active material for an all-solid-state battery according to an embodiment of the present invention can have high charge-discharge efficiency and excellent long-term lifespan characteristics.

The cathode active material for an all-solid-state battery may be any one or more of NC-based, NCM-based, NCA-based, and NCMA-based having a layered structure.

For example, the NC-based, NCM-based, NCA-based, and NCMA-based types are a type determined by the type of metal element other than lithium and a hetero element added as a dopant in the positive electrode active material, wherein N is nickel (Ni), C is Cobalt (Co), M represents manganese (Mn), and A represents aluminum (Al). The NC-based means a cathode active material made of nickel and cobalt excluding lithium and a hetero element added as a dopant, the NCM-based means a cathode active material made of nickel, cobalt and manganese, and the NCA-based is nickel, cobalt and It means a cathode active material made of aluminum, and the NCMA system may mean a cathode active material made of nickel, cobalt, manganese and aluminum.

The cathode active material includes one prepared by calcining a composite metal hydroxide containing at least one of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al) with a lithium compound, wherein the nickel ( Ni), cobalt (Co), manganese (Mn), and at least one or more of aluminum (Al), or added together with the lithium compound may further include a different element that is fired.

The average concentration of the heterogeneous element in the positive electrode active material may be 0.01 mol% to 2 mol%, specifically, 0.05 mol% to 2 mol%, or 0.1 mol% to 2 mol% or 0.5 mol% to 2 mol%. The average concentration of the heterogeneous element at the grain boundary of the primary particles may include 0.5 mol% to 12 mol%, specifically, 2 mol% to 12 mol%.

If the average concentration of the heterogeneous element in the whole of the positive electrode active material is less than 0.01 mol%, the heterogeneous element is not uniformly distributed throughout the primary particles constituting the secondary particles. . In addition, if the average concentration of the heterogeneous element at the grain boundary of the primary particles is less than 2 mol%, it is not possible to prevent aggregation of the primary particles in the process of firing at high temperature, and if it exceeds 12 mol%, the heterogeneous element at the grain boundary of the primary particles is excessively accumulated, so the movement of lithium ions is not easy, which may cause a problem.

4 is a view schematically showing the characteristics at the interface between the microstructure and the solid electrolyte of the positive electrode active material (a) according to the prior art and the positive electrode active material (b) according to the embodiment of the present invention in the same solid electrolyte.

4 is a positive electrode active material (a) including secondary particles consisting of a group of randomly formed primary particles without orientation as in the prior art in the case of using the same solid electrolyte (Li ₆ PS _{5 Cl), and an embodiment of the present invention} In the positive electrode active material (b) containing secondary particles as a group of primary particles provided to have an orientation according to

In the case of the positive electrode active material according to the prior art, an anisotropic volume occurs in the primary particles, and the grains of the primary particles are randomly oriented, thereby increasing the movement path of lithium ions. In addition, the primary particles are separated from each other by separating the primary particles. At this time, since the solid electrolyte is not liquid, it is difficult to penetrate into the inner space of the secondary particles, thereby reducing the movement speed of lithium ions. This phenomenon progresses more and more as the cycle progresses, and the lifespan characteristics and electrochemical characteristics of the positive electrode active material according to the prior art are deteriorated.

On the other hand, in the case of the positive electrode active material according to the present embodiment, the primary particles provided on the surface of the secondary particles among the primary particles may be provided in the form of a rod shape and arranged to have high orientation. In the case of the positive electrode active material according to this embodiment, since the orientation of the primary particles is approximately maintained even after charging and discharging a plurality of times, the grains of the primary particles are provided to contact each other to reduce the passage of lithium ions, thereby reducing the movement speed of lithium ions. can improve In addition, the positive electrode active material according to this embodiment is provided so that the primary particles constituting the secondary particles are in contact with each other from the surface portion in contact with the solid electrolyte to the center, so that the solid electrolyte does not need to penetrate into the interior of the lithium ion. It is possible to efficiently move from the solid electrolyte to the inside of the secondary particles. Accordingly, the secondary battery using the positive electrode active material according to the present embodiment can maintain excellent long-term lifespan characteristics and electrochemical characteristics.

According to another aspect of the present invention, an embodiment of the present invention includes a positive electrode comprising the positive electrode active material according to one of the preceding claims; and a solid electrolyte, wherein the solid electrolyte may include any one or more of a halogen-based solid electrolyte, a sulfide-based solid electrolyte, and an oxide-based solid electrolyte.

The halogen-based solid electrolyte may be Li _a MX _b , where 0<a<2, 0<b<5, M is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, It may be selected from the group consisting of Mg, Pb, Sc, Y, La-Lu, and alloys thereof, and X may be any one or more of F, Cl, Br, and I.

The sulfide-based solid electrolyte includes sulfide-based particles. The sulfide-based solid electrolyte may be prepared by coating or modifying the surface of the sulfide-based particles, and a mixture including the particles may be subjected to a dry or wet process. The sulfide-based particles are not particularly limited in the present invention, and all known sulfide-based materials used in the field of lithium batteries may be used. As the sulfide-based material, a commercially available material may be purchased and used, or an amorphous sulfide-based material manufactured through a crystallization process may be used.

Specifically, the sulfide-based solid electrolyte _{may be any one or more of Li 2} -P ₂ S ₅ binary system, LGPS family, Thio-LISICON, and Argyrodite. More specifically, the sulfide-based solid electrolyte is, for example, 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 SP ₂ S ₅ -Z _m S _n where m and n are positive numbers, Z is Ge , Zn or Ga, Li ₂ S-GeS ₂ , Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _p M ¹ O _q , p and q are is positive, M ¹ is P, Si, Ge, B, Al, Ga, or In, Li _7-x PS _6-x Cl _x (0<x<2), Li _7-x PS _6-x Br _x (0<x<2), or Li _7-x PS _6-x I _x (0<x<2).

_{When using a sulfide-based solid electrolyte material containing Li 2} SP ₂ S ₅ as the sulfide-based solid electrolyte material for forming the solid electrolyte _{, the mixing molar ratio of Li 2} S and P ₂ S ₅ is, for example, Li ₂ S : P ₂ S ₅ = It is in the range of about 50:50 to 90:10.

The sulfide-based solid electrolyte is, for example, Li _7-x PS _6-x Cl _x (0≤x≤2), Li _7-x PS _6-x Br _x (0≤x≤2), and Li _7-x PS It may be an Argyrodite-type compound including at least one selected from _6-x I _{x (0≤x≤2).} In particular, the sulfide-based solid electrolyte may be an Argyrodite-type compound including at least one selected _{from Li 6} PS ₅ Cl, Li ₆ PS ₅ Br, and Li ₆ PS _{5 I.}

The density of the Argyrodite-type solid electrolyte may be 1.5 to 2.0 g/cc. As the argyrodite-type solid electrolyte has a density of 1.5 g/cc or more, the internal resistance of the all-solid-state battery is reduced, and the penetration of the solid electrolyte layer by Li is effectively suppressed. can

The sulfide-based solid electrolyte may include, for example, Li ₆ PS ₅ Cl, Li ₆ PS ₅ Br, or Li ₆ PS ₅ I.

The oxide-based solid electrolyte is, for example, Li _1+x+y Al _x Ti _2-x Si _y P _3-y O ₁₂ (0<x<2, 0≤y<3), BaTiO ₃ , Pb(Zr _{(1 -x)} Ti _x )O ₃ (wherein, 0≤x≤1), Pb _1-x La _x Zr _1-y Ti _y O ₃ (wherein, 0≤x<1, 0≤y<1) _{), Pb (Mg 1/3 Nb 2/3} ) O 3 -PbTiO 3, HfO 2, SrTiO 3, SnO 2, CeO 2, Na 2 O, MgO, NiO, CaO, BaO, ZnO, ZrO 2, Y 2 O ₃ , Al ₂ O ₃ , TiO ₂ , SiO ₂ , SiC, Li ₃ PO ₄ , Li _x Ti _y (PO ₄ ) ₃ (wherein 0<x<2,0<y<3), Li _x Al _y Ti _z (PO ₄ ) ₃ (0<x<2, 0<y<1, 0<z<3), Li _1+x+y (Al _(1-m) Ga _m ) _x (Ti _{(1) -n)} Ge _n ) _2-x Si _y P _3-y O ₁₂ (0≤x≤1, 0≤y≤1, 0≤m≤1, 0≤n≤1), Li _x La _y TiO ₃ ( where 0<x<2, 0<y<3), Li _x Ge _y P _z S _w (wherein, 0<x<4, 0<y<1, 0<z<1, 0<w<5), Li _x N _y (wherein, 0<x<4, 0<y<2), SiS ₂ , Li _x Si _y S _z (wherein, 0<x<3, 0<y) <2, 0<z<4), Li _x P _y S _z (wherein, 0<x<3, 0<y<3, 0<z<7), Li ₂ O, LiF, LiOH, Li ₂ CO ₃ , LiAlO ₂ , Li ₂ O-Al ₂ O ₃ -SiO ₂ -P ₂ O ₅ -TiO ₂ -GeO ₂ Ceramics, garnet ceramics of the _{formula Li 3+x} La ₃ M ¹ ₂ O ₁₂ (wherein, M ¹ is Te, Nb or Zr, and x is an integer from 1 to 10), or a combination thereof.

On the other hand, in the positive electrode active material according to the present embodiment, the oriented particles maintain an approximately constant distance between neighboring particles, and microcracks occur due to volume changes of contraction and expansion of primary particles during charging and discharging. can be prevented from becoming That is, even when an all-solid-state battery is used, when the positive electrode active material is used, the positive electrode active material hardly generates microcracks and exhibits excellent cycle characteristics during the cycle.

The positive electrode active material for all-solid according to an embodiment of the present invention has a 2θ value in an X-ray diffraction (XRD) pattern when charging and discharging in 2 to 5 cycles and then discharging to 3.0V or less in the range of 18° to 19° It may have a single peak in In addition, the all-solid positive electrode active material according to an embodiment of the present invention, after performing 100 cycles of charging and discharging, the secondary particles include a layered structure and a rocksalt structure, wherein the rock salt structure is the secondary It may exist only in a region of 0.1 nm to 5 nm in thickness from the outermost surface of the particle to the inside. In the cathode active material according to this embodiment, even after the cycle, it can be confirmed that the rock salt structure formed on the surface of the secondary particles exists only in a narrow range of 0.1 nm to 5 nm, which is between the cathode active material and the solid electrolyte. It means that there is little change in the microstructure of the positive electrode active material due to the interfacial resistance.

Hereinafter, Examples and Comparative Examples of the present invention will be described. However, the following examples are only preferred examples of the present invention, and the scope of the present invention is not limited by the following examples.

1. Preparation of cathode active material

Comparative Example 1 (Bulk_NCA80)

After putting 10 liters of distilled water into the reactor (capacity 47L, output of the rotary motor 750W or more), N ₂ gas was supplied to the reactor at a rate of 6 liters/minute, and the temperature of the reactor was maintained at 45° C. while stirring at 350 rpm. Nickel sulfate aqueous solution (NiSO ₄ 6H ₂ O, Samjeon Chemical) and cobalt sulfate aqueous solution (CoSO ₄ 7H ₂ O, Samjeon Chemical) are mixed in an amount such that the molar ratio of nickel (Ni) and cobalt (Co) is 84:16. A metal solution having a concentration of 2M was prepared. The prepared metal solution was 0.561 liter/hour, 16M ammonia solution (NH ₄ OH, JUNSEI) was 0.11 liter/hour, and 4M sodium hydroxide solution (NaOH, Samjeon Chemical) was 0.60 liters/hour, respectively. It was continuously introduced into the reactor for 24 hours. The co-precipitation reaction was performed while maintaining the pH in the reactor in the range of 10 to 12 to prepare Ni _0.84 Co _0.16 (OH) ₂ composite metal hydroxide.

The prepared composite metal hydroxide was filtered, washed several times with distilled water, and dried in a vacuum dryer at 110° C. for 12 hours to prepare a powder. The complex metal hydroxide aluminum hydroxide (Al(OH) ₃ ) and lithium hydroxide (LiOH) prepared in powder form were mixed in a molar ratio of 1.01:0.96:0.04 (Li: Ni + Co: Al), and then the temperature was raised to 2° C./min. Preliminary firing was performed by heating at a speed of heating at 450° C. for 5 hours, followed by firing at 770° C. for 10 hours to prepare a cathode active material powder, which is shown in Table 1.

Example 1 (RS_FCG75)

After 10 liters of distilled water was put into the reactor (capacity 40L, output of the rotary motor 750W or more), N ₂ gas was supplied to the reactor at a rate of 6 liters/minute, and the temperature of the reactor was maintained at 45° C. while stirring at 350 rpm. Nickel sulfate aqueous solution (NiSO ₄ 6H ₂ O, Samjeon Chemical), cobalt sulfate aqueous solution (CoSO ₄ 7H ₂ O, Samjeon Chemical), and manganese sulfate aqueous solution (MnSO ₄ H ₂ O, Samjeon Chemical) were mixed with nickel (Ni), cobalt (Co ) and manganese (Mn) in a molar ratio of 1:0:0 to the first metal solution having a concentration of 2M mixed in an amount such that the molar ratio of nickel (Ni), cobalt (Co) and manganese (Mn) is 0.645:0.149: A second metal solution having a concentration of 2M mixed in an amount to be 0.206 was prepared. The prepared first metal solution was 0.561 liters/hour, 16M ammonia solution (NH ₄ OH, JUNSEI) was 0.08 liters/hour, and 4M sodium hydroxide solution (NaOH, Samjeon Chemical) was 0.60 liters/hour _{Each of the spherical Ni(OH) 2} particles was first prepared by continuously inputting the reactor for 14 hours to form a first concentration maintaining part. Thereafter, the second metal solution was added to the co-precipitation reactor at 0.561 liters/hour and continuously added for 10 hours while constantly changing the concentration of the metal solution fed into the reactor to the first concentration maintaining part (spherical Ni(OH) ₂ The second concentration gradient part was provided by accumulating particles made of nickel-cobalt-manganese having various compositions on the outside of the particle). The co-precipitation reaction was performed while maintaining the pH in the reactor in the range of 10 to 12 to prepare a concentration gradient-type metal composite hydroxide having _{an average composition of Ni 0.75} Co _0.1 Mn _0.15 (OH) _{2 .}

The prepared concentration gradient composite metal hydroxide was filtered, washed several times with distilled water, and dried in a vacuum dryer at 110° C. for 12 hours to prepare a powder. After mixing the composite metal hydroxide prepared in powder form and lithium hydroxide (LiOH) in a molar ratio of 1.01:1 (Li: Ni + Co), heated at a temperature increase rate of 2°C/min in an oxygen atmosphere, and then 450°C for 5 hours Pre-calcination was carried out by maintaining, followed by calcination at 790° C. for 10 hours to prepare a concentration gradient type cathode active material powder.

Category 1 Category 2 Ni (mol%) Co (mol%) Mn (mol%) Al (mol%) Li (mol%) Firing temperature (℃) Comparative Example 1 Bulk_NCA80 80 16 0 4 One 770 Example 1 RS_FCG75 75 10 15 0 One 790

Preparation Example 1 (NCM111)

After 10 liters of distilled water was put into the reactor (capacity 40L, output of the rotary motor 750W or more), N ₂ gas was supplied to the reactor at a rate of 6 liters/minute, and the temperature of the reactor was maintained at 45° C. while stirring at 350 rpm. Nickel sulfate aqueous solution (NiSO ₄ 6H ₂ O, Samjeon Chemical), cobalt sulfate aqueous solution (CoSO ₄ 7H ₂ O, Samjeon Chemical), and manganese sulfate aqueous solution (MnSO ₄ H ₂ O, Samjeon Chemical) were mixed with nickel (Ni), cobalt (Co ) and manganese (Mn) in a molar ratio of 1:1:1 were mixed to prepare a metal solution having a concentration of 2M. The prepared metal solution was 0.561 liters/hour, 16M ammonia solution (NH ₄ OH, JUNSEI) was 0.08 liters/hour, and 4M sodium hydroxide solution (NaOH, Samjeon Chemical) was 0.60 liters/hour, respectively. was continuously added for 24 hours. The co-precipitation reaction was performed while maintaining the pH in the reactor in the range of 10 to 12 to prepare Ni _0.1 Co _0.1 Mn _0.1 (OH) ₂ metal composite hydroxide.

The prepared metal complex hydroxide was filtered, washed several times with distilled water, and dried in a vacuum dryer at 110° C. for 12 hours to prepare a powder. _{Ni 0.9} Co _0.05 Mn _0.05 (OH) ₂ metal composite hydroxide prepared in powder form, and lithium hydroxide (LiOH) were mixed in a molar ratio of 1.01:1 (Li: Ni + Co + Mn), and then the temperature was raised to 2 ° C / min Preliminary firing was performed by heating at a speed of heating at 450° C. for 5 hours, followed by firing at 700° C. for 10 hours to prepare a cathode active material powder, which is shown in Table 2.

Preparation 2 (NCM523)

A metal solution with a concentration of 2M added to the reactor was mixed with nickel sulfate aqueous solution (NiSO ₄ 6H ₂ O, Samjeon Chemical), cobalt sulfate aqueous solution (CoSO ₄ 7H ₂ O, Samjeon Chemical), manganese sulfate aqueous solution (MnSO ₄ H ₂ O, Samjeon Chemical). ) to prepare a cathode active material powder in the same manner as in Example 1, except that the molar ratio of nickel (Ni), cobalt (Co) and manganese (Mn) was mixed in an amount of 5:2:3, and 2 is shown.

Preparation 3 (NCM622)

A metal solution with a concentration of 2M added to the reactor was mixed with nickel sulfate aqueous solution (NiSO ₄ 6H ₂ O, Samjeon Chemical), cobalt sulfate aqueous solution (CoSO ₄ 7H ₂ O, Samjeon Chemical), manganese sulfate aqueous solution (MnSO ₄ H ₂ O, Samjeon Chemical). ) to prepare a cathode active material powder in the same manner as in Example 1, except that the molar ratio of nickel (Ni), cobalt (Co) and manganese (Mn) was mixed in an amount of 6:2:2, and this 2 is shown.

Preparation 4 (NCM811)

A metal solution with a concentration of 2M added to the reactor was mixed with nickel sulfate aqueous solution (NiSO ₄ 6H ₂ O, Samjeon Chemical), cobalt sulfate aqueous solution (CoSO ₄ 7H ₂ O, Samjeon Chemical), manganese sulfate aqueous solution (MnSO ₄ H ₂ O, Samjeon Chemical). ) to prepare a cathode active material powder in the same manner as in Example 1, except that the molar ratio of nickel (Ni), cobalt (Co) and manganese (Mn) was mixed in an amount of 8:1:1, and this 2 is shown.

Preparation 5 (NCM900505)

A metal solution with a concentration of 2M added to the reactor was mixed with nickel sulfate aqueous solution (NiSO ₄ 6H ₂ O, Samjeon Chemical), cobalt sulfate aqueous solution (CoSO ₄ 7H ₂ O, Samjeon Chemical), manganese sulfate aqueous solution (MnSO ₄ H ₂ O, Samjeon Chemical). ) to prepare a cathode active material powder in the same manner as in Example 1, except that the molar ratio of nickel (Ni), cobalt (Co) and manganese (Mn) was mixed in an amount of 90:5:5, and this 2 is shown.

Category 1 Category 2 Ni (mol%) Co (mol%) Mn (mol%) Preparation Example 1 NCM111 33 33 33 Preparation 2 NCM523 50 20 30 Preparation 3 NCM622 60 20 20 Preparation 4 NCM811 80 10 10 Preparation 5 NCM900505 90 05 05

2. Manufacture of all-solid-state battery

(1) Preparation of solid electrolyte

As the solid electrolyte, Li ₆ PS ₅ Cl was used. To synthesize Li ₆ PS ₅ Cl, Li ₂ S (99.9 %, Alfa Aesar), P ₂ S ₅ (99 %, Sigma-Aldrich), and LiCl (99.99 %, Sigma-Aldrich) were mixed for each stoichiometry. The amount was measured and mixed, and the stoichiometric amount was ball milled at 600 rpm for 10 hours _{with a ZrO 2 mixing ball using a Pulverisette 7 PL (Fritsch GmbH).} The ball milled powder was heat-treated at 550 °C for 5 hours under Ar atmosphere.

(2) Manufacture of all-solid-state battery

For the all-solid battery, the positive electrode is prepared by mixing the powder prepared according to Examples, Comparative Examples, and Preparation Examples with a solid electrolyte (Li ₆ PS ₅ Cl) and a conductive carbon additive (super P) in a weight ratio of 70:30:3 in a mortar grinder (mortar and pestle) to prepare a positive electrode active material mixture by dry mixing. As the counter electrode (cathode), partially lithiated indium (nominal composition Li _0.5 In) or lithium metal foil (20 μm) was used.

Li _0.5 In was prepared by mixing Li (FMC Lithium corp.) and In (Sigma-Aldrich, 99.99%) powder.

An all-solid-state battery with a diameter of 13 mm made of a Ti rod current collector and a PEEK (polyaryletheretherketone) mold was prepared as follows.

First, 150 mg of Li ₆ PS ₅ Cl powder was prepared into pellets to form an SE layer (solid electrolyte layer). Then, the positive electrode active material mixture was applied to one side of the SE layer, and a counter electrode (Li _0.5 In) was applied to the other side of the SE layer to prepare an assembly. The prepared assembly was compressed to 370 MPa. In this case, the loading level in the case of the positive electrode active material of Examples and Comparative Examples was 11.3 mg/cm 2 .

(3) Liquid electrolyte secondary battery

A secondary battery using a liquid electrolyte, the positive electrode is N-methylpyrrolidone (N-methylpyrrolidone), the positive electrode active material according to Examples, Comparative Examples, and Preparation Examples, carbon black and polyvinylidene fluoride (poly(vinylidene fluoride)) was mixed in a weight ratio of 90:5.5:4.5 to prepare a slurry. The prepared slurry was coated on Al foil so that the loading level was 4 mg/cm 2 to prepare an electrode. The prepared electrode was compressed and vacuum dried at 120°C. As a liquid electrolyte, 1.2M LiPF ₆ was mixed with ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7, and vinylene carbonate 2wt% was added with A battery test was performed by manufacturing a 2032 coin-type half cell using lithium metal as an anode. The secondary battery was charged and discharged and cycled at 0.5C (100mA/g) at 3V-4.3V.

3. Evaluation of cathode active materials and all-solid-state batteries

(1) Material analysis of cathode active material (sintered body)

The microstructure, specific surface area, etc. of the positive electrode active material prepared according to Examples, Comparative Examples, and Preparation Examples were evaluated.

The microstructure of the positive electrode active material was confirmed by SEM (Verios G4UC, FEI). The specific surface area was confirmed by N2 adsorption/desorption isotherm using a Brunauer-Emmett-Teller (BET, 3 Flex, Micromeritics).

For cross-sectional SEM observation, electrodes (sampled electrodes) charged with different SOC (state of charge) were stored in a glove box filled with Ar, and cooled at -90°C with a cross-sectional polisher (CP, JEOL IB-). 19520CCP) was used to cut by Ar-ion beam milling. Then, in order to prevent exposure to external air, the electrode was moved from the end face polisher (CP) to the SEM equipment using the Air-Isolation system holder while maintaining the Ar atmosphere.

For TEM measurement, the electrode (discharged state), which was subjected to 100 cycles, was cut into a thin foil with a thickness of 70 nm with a focused ion beam (FIB, SCIOS, FEI) and seated on a Mo grid to measure TEM.

For XRD analysis (ex situ XRD), each all-solid-state battery was mounted in a holder and sealed with a Be window in a glove box filled with Ar. Ex situ XRD was performed using a Rigaku MiniFlex 600 diffractometer using Cu Kα radiation from 10° to 70° of 2θ with a step size of 0.02°. Ex situ XRD was performed with a monochromatic Al Kα source (1486.6 eV) at 12 kV and 6 mA using K-Alpha+ (Thermo Fisher Scientific). Each sample was mounted in a sample holder in a glove box filled with Ar, and moved to the XPS instrument without exposure to air.

(2) Confirmation of electrochemical properties

EIS was measured using Bio-Logic (VMP3) from 1.5 MHz to 10 Hz with an amplitude of 10 mV for an all-solid-state battery discharged to 3.8V (vs Li / Li +) at 0.1C. In the process of charging and discharging, the external pressure of the all-solid-state battery was within approximately 70 MPa and within approximately 7 MPa, respectively, when _{Li 0.5} In (or Li ₄ Ti ₅ O _{12 ) and Li metal were used as counter electrodes.} In the case of operando electrochemical pressiometry, a _{negative to positive (np) ratio was set to 13 with a zero strain Li 4} Ti ₅ O ₁₂ as a cathode, and a pressure sensor was used to monitor the pressure during charging and discharging. did.

Hereinafter, the microstructure, surface properties and electrochemical properties of the positive electrode active materials according to Examples and Comparative Examples were confirmed.

5 is a SEM image of the positive electrode active material of Comparative Example 1 and Example 1. 6 is a graph showing the concentration of the metal constituting the positive electrode active material of Example 1. Referring to FIG. 7 is a graph confirming the cycle characteristics in the secondary batteries (a, c) using the liquid electrolyte and the all-solid batteries (b, d) using the solid electrolyte using the cathode active material for Comparative Examples 1 and 1 . 8 is an all-solid-state battery using the positive electrode active material of Comparative Example 1 and Example 1, the lifetime characteristics (a) at 0.5C, the capacity-voltage profile at each cycle (b), 2 cycles and 100 cycles It is a graph showing the Nyquist plot (c, d).

Table 3 shows the results of confirming the electrochemical characteristics of the all-solid-state battery using the positive electrode active material according to Examples and Comparative Examples.

Category 1 Category 2 0.1C, 1st Dis-Cap (mAh/g) 1 ^st Efficiency 0.5C Capacity (mAh/g) 0.5C/0.1C Cycle number 0.5C Capacity Retention Comparative Example 1 Bulk_NCA80 156.1 71.2% 135 86.5% 200 46.9% Example 1 RS_FCG75 194.2 84.9% 169.8 87.4% 200 79.0%

Referring to 5, in the positive electrode active material of Comparative Example 1, primary particles are randomly oriented to form an overall spherical secondary particle. On the other hand, it was confirmed that the positive active material of Example 1 was composed of primary particles having a rod shape having a high aspect ratio, and in particular, the primary particles located on the surface of the secondary particles were radially arranged to face the ab side. . This is considered to be because the positive electrode active material of Example 1 has a concentration gradient, and at the same time, it is arranged as primary particles in the form of rods in the surface portion of the secondary particles.

Referring to FIG. 6 , in the cathode active material of Example 1, in the concentration of the metal confirmed by electron probe micro-analyzer (EPMA), for the secondary particles, nickel appeared at a higher concentration in the central portion than in the surface portion, and manganese compared to the central portion. It was confirmed that it appeared at a higher concentration on the surface part.

7 and 8 show the results of charging and discharging cycles from 3.0V to 4.3V (vs Li / Li +) at 30 ° C., respectively, the positive electrode active material of Comparative Example 1 (bulk_NCA80) and Example 1 (RS_FCG75) was used to compare the electrochemical performance of a lithium secondary battery prepared with a liquid electrolyte and an all-solid battery prepared with a solid electrolyte.

In the case of a lithium secondary battery prepared with a liquid electrolyte, it was confirmed that the charge capacity of the first cycle at 0.1 C was similar to 217mAh/g and 219mAh/g in Comparative Example 1 and Example 1, respectively ( a) see). When the lithium secondary batteries prepared with the liquid electrolyte prepared in Comparative Examples 1 and 1 were compared with each other while changing the c-rate of the charging current, Example 1 had a higher nickel content than Comparative Example 1 even though the nickel content was lower. It was confirmed that the discharge capacity was represented (see FIG. 8(c)). Example 1 is judged because it has a rod-shaped structure in which diffusion of lithium ions is advantageous.

When the solid electrolyte was used, the first discharge capacities of Example 1 and Comparative Example 1 were 194 mAh/g and 156 mAh/g, respectively (refer to FIG. , it was confirmed that Example 1 exhibited a higher value of 71.2%. In the capacity-voltage profile of the all-solid-state battery, Comparative Example 1 showed a discharge capacity that was 28.8% lower than that of the charged capacity, and Example 1 was 15.1%, indicating superior characteristics than Comparative Example 1. . When the cycle was performed at different c-rates, the characteristics according to the rate of charging current were similar to the liquid electrolyte and the solid electrolyte, but the solid electrolyte showed a lower capacity than that of the liquid electrolyte, which was carried out in Comparative Example 1 It was confirmed that a larger difference than Example 1 was exhibited.

In a half-cell using a solid electrolyte, a cycle was performed at 30° C. at 0.5C constant current and constant voltage (CC-CV). It was confirmed that both Comparative Example 1 and Example 1 exhibited a stable capacity profile up to 200 cycles. In 200 cycles, the capacity was maintained at 79.1% with respect to the initial capacity in Example 1, but it was confirmed that Comparative Example 1 was 46.9% lower than that of Example 1 with respect to the initial capacity.

In the process of performing the charging and discharging cycles, the nominal voltage polarization gradually increases, and it can be seen that the difference between Example 1 and Comparative Example 1 increases when it proceeds to 100 cycles rather than 50 cycles. there was. In (b) of FIG. 8 , it can be confirmed that Example 1 has a lower degree of increase in polarization compared to Comparative Example 1.

EIS (Electrochemical Impedance Spectroscopy) signals measured in a charged state at 3.8V (vs Li / Li +) at cycle 1 and cycle 100 are Nyquist plots (inhibited semicircles and connected to the ends of the depressed semicircles). (shown in the form of a tail) (FIG. 11 (c, d)), it shows the interface resistance between the grains in the solid electrolyte in Example 1 and Comparative Example 1, Comparative Example 1 (39.6Ω) is 1 cycle It was confirmed that there was a significant increase in cycle 2 compared to . In addition, it was confirmed that after 100 cycles, the increase in the R3 value was significantly increased in Comparative Example 1 (598Ω) compared to Example 1 (146Ω).

9 is an all-solid-state battery using the positive electrode active material of Comparative Example 1 and Example 1, at 0.1C, 30°C, 0.05C, and 70°C; It is an ex situ XRD pattern showing the (003) peak for Comparative Example 1 and Example 1.

In an all-solid-state battery using a solid electrolyte, the capacity of the primary charge is mostly generated by deintercalation of lithium ions (Li+) in the lattice of the positive electrode active material. On the other hand, oxidative decomposition of the solid electrolyte occurs as a side reaction, and this side reaction also affects the capacity of the primary charge.

In order to check the degree of influence of the oxidative decomposition of the solid electrolyte in Example 1 and Comparative Example 1, it was charged at 0.1C and 30°C in CC-CV mode, and discharged at 0.05C and 70°C to confirm the capacity. In the case of Example 1, the discharge capacity at 0.05C and 70°C was increased by 6mAh/g compared to 0.1C and 30°C (200mAh/g), but in Comparative Example 1, it was 31mAh/g from 156mAh/g to 187mAh/g. It was confirmed that g increased.

Ex situ XRD pattern was used to confirm the results with three different SOC all-solid-state batteries for one cycle (charged at 0.1C and 30°C and then discharged at 0.05C and 70°C) at 0.1C and 30°C. When the position of the (003) peak was compared with the position before the cycle after discharging to 3.0V (vs Li / Li +) at 30 ° C., it can be confirmed that Comparative Example 1 moved to a larger negative value compared to Example 1. there was. The shift of the (003) peak in the negative direction in Comparative Example 1 is relaxed when discharging at 70 ° C. It is determined that in Comparative Example 1, lithium ions were not fully inserted into the lattice while charging at 30 ° C. .

10 is a graph showing lattice parameters and volumetric strain (a), a diagram schematically showing monitoring the pressure of a solid electrolyte using a pressure sensor (b), and 0.1C, 30°C It is a view showing the operando electrochemical pressiometry according to Comparative Example 1 and Example 1 in which 1 cycle was performed with the furnace. 14 is a cross-sectional SEM image according to Comparative Example 1 and Example 1. FIG.

In (a) of FIG. 10 , the volumetric strain is calculated as _{(V final} -V _inital ) / V _{inital .} In the all-solid-state battery of Example 1 and Comparative Example 1, the performance difference in the initial cycle lies in the difference in overpotential. In the case of the lithium ion battery prepared with the liquid electrolyte of Comparative Example 1 and Example 1 at a cutoff voltage of 4.3V (vs Li / Li +), the volumetric strain was 4.2% and -3.4% (in situ XRD), respectively. result), and it was confirmed that the slope of the volume strain was greater than approximately 4.1V (vs Li / Li +), and this volume strain is predicted to be due to the occurrence of the H2-H3 phase transition, which is a poor phase transition.

In Comparative Example 1 and Example 1, the volume strain up to 4.1V (vs Li / Li +) was -1.9% and -1.8%, respectively. Comparative Example 1 and Example 1 have different electrochemical performances at a cutoff voltage of 4.3V (vs Li / Li +), but at a voltage of 4.1V, it can be seen that both Comparative Example 1 and Example 1 exhibit relatively good cycle characteristics. there was.

In FIG. 11, the microstructure was confirmed for Comparative Example 1 and Example 1. SEM images of the cathode active material for all-solid-state batteries were shown before the cycle (pristine), 4.3V charge, 3V discharge, and after 100 cycles, respectively.

In the case of Comparative Example 1, it can be confirmed that microcracks in the secondary particles constituting the positive electrode active material and spaces (voids) and cracks between the secondary particles of the positive electrode active material and the solid electrolyte are formed even after one cycle of charging. That is, in the case of Comparative Example 1, it means that the total shrinkage of the lattice volume is up to about 4.2%, and even when discharged in one cycle, microcracks in the secondary particles and the space between the secondary particles and the solid electrolyte remain without disappearing. was able to confirm

In the case of Example 1, it can be seen that the space between the secondary particles constituting the positive electrode active material and the solid electrolyte appears in one cycle of charging, which is considered to be due to volumetric shrinkage related to the H2-H3 phase transition. It can be seen that in Example 1, the space between the secondary particles and the solid electrolyte is smaller than that of Comparative Example 1, when it is charged at about 4.1V or more, which means that the degree of volume contraction is smaller in Example 1 than in Comparative Example 1. . In addition, in Example 1, it can be confirmed that microcracks do not occur inside the secondary particles, and after the discharge, the microstructure of the secondary particles is maintained as it is, and it can be confirmed that the space between the solid electrolytes of the secondary particles is eliminated.

Comparing 1 cycle and 100 cycles, both of Comparative Example 1 and Example 1 confirmed that microcracks generated inside the secondary particles and the space (cracks) between the secondary particles and the solid electrolyte further progressed.

In the case of Comparative Example 1, it can be seen that the microstructure is largely decomposed, such as the secondary particles and the solid electrolyte completely collapsed after 100 cycles. On the other hand, in the case of Example 1, it was confirmed that the pellet shape was maintained almost the same even after 100 cycles. Also, in Comparative Example 1, most of the primary particles constituting the secondary particles were separated, and the shape of the secondary particles was not maintained, but in Example 1, it was confirmed that the secondary particles were maintained as they are and microcracks hardly occurred.

After one cycle of discharging, the all-solid-state battery of Comparative Example 1 showed large cracks, but this phenomenon did not occur when the liquid electrolyte was used. This is considered to be because the solid electrolyte is elastically deformed and plastically deformed by the pressure applied in the process of manufacturing the all-solid-state battery, and thus the stress remains locally. In addition, it is determined that the disordered arrangement of the primary particles together with the anisotropic volume shrinkage occurring during the charge/discharge process of Comparative Example 1 greatly affects the space and/or cracks of the all-solid electrolyte during the initial charge/discharge process. In addition, in Comparative Example 1, it can be confirmed that even when the volume is expanded due to discharge, the space and/or cracks of the solid electrolyte are maintained without disappearing.

In Example 1, the primary particles provided on the surface of the secondary particles are provided in the form of a rod shape having a high aspect ratio, and the primary particles of the rod shape are radially aligned with high orientation. In the positive electrode active material as in Example 1, no cracks were formed in the secondary particles, and it was confirmed that large cracks were not formed in the solid electrolyte and maintained in a good state by effectively accommodating the reversible volume change occurring during the charging and discharging process.

In an all-solid-state battery using zero-strain Li ₄ Ti ₅ O ₁₂ as a negative electrode (counter electrode), the electrochemical pressure was measured using each of Comparative Example 1 and Example 1 as a positive electrode (Fig. 10 (b), ( c) see). According to the calculations obtained in the in situ XRD pattern (see (a) of FIG. 10), the volume strain rate of Comparative Example 1 was larger than that of Example 1 during the charging/discharging process. After the first charge, the decrease in pressure measured in Comparative Example 1 was -0.15 MPa, and the decrease in pressure measured in Example 1 was -0.30 MPa, confirming that Comparative Example 1 appeared smaller than Example 1. That is, in Comparative Example 1, it means that the microcracks of the secondary particles and the voids and cracks of the solid electrolyte are maintained without disappearing after they are formed.

It was confirmed that the increase in pressure in Comparative Examples 1 and 1 during discharge corresponds to the expansion of the grid volume (see (a) of FIG. 10). That is, after the cycle, the pressure of Comparative Example 1 was higher than that of Example 1, whereas Comparative Example 1 had less lithium ions inserted into the lattice than Example 1 and that mechanical deterioration such as formation of microcracks also occurred significantly. could check

12 is an ex situ TEM image of the all-solid-state battery using Comparative Example 1 and Example 1 after 100 cycles of charging and discharging. 13 is a graph showing ex situ XPS results of all-solid-state batteries using Comparative Example 1 and Example 1. FIG.

In FIG. 12, while changing the ex situ TEM image to high and low magnification, the surface (a) and central (b) and corresponding SAED patterns of the secondary particles of Comparative Example 1 were confirmed, and the secondary particles of Example 1 The surface (c), the center (d), and the corresponding SAED pattern were respectively confirmed.

In FIG. 13 , the S 2p XPS signal (a) and the P 2p XPS signal (b) were confirmed for Comparative Example 1 and Example 1 after 100 cycles with _{Li 6} PS _{5 Cl, respectively.}

Referring to the ex situ XRD results, it can be seen that the (003) peak of Comparative Example 1 largely shifts in a negative direction compared to Example 1 after discharging at 30°C. In addition, Comparative Example 1 shows a wider (003) peak after discharging, which means that Comparative Example 1 includes primary particles having various SOCs, whereby electrochemical, It means that the degree of contact between the ions is mechanically low (refer to FIG. 12 (b)).

In the all-solid-state battery using the positive electrode active material of Comparative Example 1 and Example 1, it was confirmed that the effect of electrochemical stability at the interface between _{each positive electrode active material and the solid electrolyte Li 6} PS _{5 Cl was particularly important in the initial cycle.} . In FIG. 12 , it can be seen that the surface region (i) in which the positive electrode active material of Comparative Examples 1 and 1 is in contact with the solid electrolyte has a different texture than that of the inner region (ii). In both Comparative Example 1 and Example 1, in the SAED pattern, the surface region (i) exhibits a rock salt structure having a space group Fm3m rather than a layered structure (R3m), and the inner region (ii) is a layered structure (R3m). was able to confirm Rock salt structure appearing in the surface region (i) has, it is determined by since, by oxidation of the Li ₆ PS ₅ Cl on the surface of the positive electrode active material in contact with the Li ₆ PS ₅ Cl layered structure that has been phase-transition to the rock salt structure.

Referring to the S 2p and P 2p ex situ XPS results after 100 cycles, _{SO 4} ^2- , PO ₄ ^3- , bound sulfur (P-[S] _n -P) and P ₂ derived from _{Li 6} PS _{5 Cl} It can be identified as S _5. Comparative Example 1 and Example 1 both show a slight positive shift in the Ni 2p XPS peak after cycling, which means that nickel ions with an oxidation state of nickel (Ni) exceeding 2+ exist. On the other hand, ex situ XPS results for cobalt (Co) and manganese (Mn) do not change even after cycling.

In the ex situ TEM image after 100 cycles, the thickness of the region where the rock salt structure exists was 13 nm to 15 nm in Comparative Example 1, and about 3 nm in Example 1 It was confirmed that Example 1 appeared less than Comparative Example 1. . This is judged because the content of nickel on the surface of Example 1 (about 70% or less) is less than the content of nickel on the surface of Comparative Example 1 (80%).

_{SO 4} ^2- , PO ₄ ^3- , bound sulfur (P-[S] _n -P) and P ₂ S ₅ derived from Li ₆ PS ₅ Cl do not differ significantly in the initial cycle, but after 100 cycles It can be seen that Comparative Example 1 shows more than Example 1, whereby it is determined that the performance of Comparative Example 1 is lower than that of Example 1 after 100 cycles.

That is, in the case of the comparative example in which the primary particles are randomly arranged and the difference in aspect ratio is not large, the anisotropic volume change of the primary particles causes cracks in the solid electrolyte along with the change in the microstructure of the secondary particles even in the initial cycle.

On the other hand, in the positive electrode active material according to this embodiment, the primary particles are formed in a rod shape having a high aspect ratio, and are provided to have a high orientation, so that the shape of the secondary particles is stably maintained even in the course of a cycle, and thereby the solid electrolyte is also It was confirmed that it was stably maintained and exhibited excellent cycle characteristics without mechanical deterioration. In addition, the positive electrode active material as in the embodiment is provided so that the grain boundaries of the primary particles present in the secondary particles are in contact with each other, and the contact between these grain boundaries is stably maintained even in the process of performing repeated cycles, whereby lithium ions are can move efficiently.

In addition, the positive electrode active material according to Example 1 exhibits high capacity characteristics despite a low nickel content compared to Comparative Example 1, and the concentration of nickel in the surface portion of the secondary particles is relatively lower than in the central portion of the secondary particles. By preventing side reactions at the interface with the electrolyte Li ₆ PS _{5 Cl, excellent cycle characteristics could be exhibited.}

Table 4 shows a case in which a lithium secondary battery was prepared with a liquid electrolyte using the cathode active material prepared according to Example 1, Comparative Example 1, and Preparation Examples 1 to 5, and a case where an all-solid battery was prepared using a solid electrolyte. This is the result of comparing the dose expression rate in 14 is a graph confirming the discharge capacity (a) and cycle characteristics according to the nickel content in the lithium secondary battery using the positive electrode active material and the liquid electrolyte according to Preparation Examples 1 to 5, Comparative Example 1, and Example 1 ( b), a graph confirming the discharge capacity (c) and cycle characteristics according to the nickel content in the all-solid-state battery using the positive electrode active material and the solid electrolyte according to Preparation Examples 1 to 5, Comparative Example 1, and Example 1 ( d).

Category 1 Category 2 liquid electrolyte solid electrolyte [B]/[A] 0.1C, 1st Dis-Cap (mAh/g)
[A] 0.5C Capacity Retention 0.1C, 1st Dis-Cap (mAh/g)
[B] 0.5C Capacity Retention capacity release rate Preparation Example 1 NCM111 161.8 97.7% 140.4 84.7% 86.8% Preparation 2 NCM523 170.5 92.1% 135.2 83.1% 79.3% Preparation 3 NCM622 180.4 92.4% 148.4 87.4% 82.2% Preparation 4 NCM811 207.8 91.3% 142 81.4% 68.3% Preparation 5 NCM900505 226.6 74.3% 189.8 68.5% 83.7% Comparative Example 1 Bulk_NCA80 205.4 97.6% 156.1 56.4% 76.0% Example 1 RS_FCG75 212.2 94.0% 194.2 85.7% 91.5%

Referring to Table 4 and FIG. 14 , the positive electrode active material according to Comparative Example 1 had a capacity expression rate in the solid electrolyte with respect to the liquid electrolyte of 76%, whereas the positive electrode active material according to Example 1 had the capacity in the solid electrolyte with respect to the liquid electrolyte. The expression rate was 91.5%. That is, in the case of Example 1, it was confirmed that the capacity was almost similar to that of the liquid electrolyte even when the solid electrolyte was used.

In the case of using a liquid electrolyte, it was confirmed that the discharge capacity increased as the nickel content increased. On the other hand, in the case of a solid electrolyte, it was confirmed that the nickel content was not proportional to the discharge capacity. This is considered to be caused by problems such as oxidation in the solid electrolyte and side reactions between the interface between the solid electrolyte and the positive electrode active material.

Those of ordinary skill in the art to which the present invention pertains will understand that the present invention may be embodied in other specific forms without changing the technical spirit or essential features thereof. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims described below rather than the above detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts are included in the scope of the present invention. should be interpreted

10: central
20: surface portion
30: primary particle
100: secondary particle

Claims (8)

Including secondary particles consisting of a group of a plurality of primary particles,
Of the primary particles, the primary particles provided on the surface of the secondary particles include oriented particles provided in the form of a rod shape having a short axis and a long axis. According to claim 1,
A cathode active material for an all-solid-state battery, wherein the long axis of the primary particle is provided toward the center of the secondary particle to provide a diffusion path of lithium ions. According to claim 1,
The primary particle includes a crystal structure having an a-axis and a c-axis, and the primary particle is an all-solid, wherein the ratio of the length in the a-axis direction to the length in the c-axis direction increases from the center of the secondary particle toward the surface. A cathode active material for batteries. 4. The method of claim 3,
A cathode active material for an all-solid-state battery that is provided so that the a-axis direction of the primary particles faces the center of the secondary particles to correspond to the diffusion path of lithium ions. According to claim 1,
The all-solid positive electrode active material is prepared by calcining a composite metal hydroxide containing at least one of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al) with a lithium compound,
At least any one or more of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al) constituting the composite metal hydroxide is provided to have a concentration gradient in at least any part or more of the composite metal hydroxide A cathode active material for a phosphorus all-solid-state battery. According to claim 1,
The positive electrode active material is a layered structure (layered structure) NC-based, NCM-based, NCA-based, LNO-based, NCMA-based, LCO-based and NM-based cathode active material for an all-solid-state battery of any one or more. According to claim 1,
The cathode active material includes those prepared by calcining a composite metal hydroxide containing at least one of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al) with a lithium compound,
For an all-solid-state battery further comprising a hetero element added together with at least one of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al), or added together with the lithium compound and fired cathode active material. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 7; and
comprising a solid electrolyte,
The solid electrolyte is an all-solid-state battery comprising at least one of a halogen-based solid electrolyte, a sulfide-based solid electrolyte, and an oxide-based solid electrolyte.

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