KR102449815B1 - Cathode active material for all solid battery, manufacturing method thereof and all solid battery comprising the cathode active material - Google Patents

Abstract

The present invention relates to a cathode active material for an all-solid-state battery, a method for manufacturing the same, and an all-solid-state battery comprising the same, and more particularly, to a precursor solution in which precursors are dispersed in an organic solvent is mixed with lithium transition metal oxide, followed by drying and heat treatment By sequentially carrying out, it is possible to form a positive electrode active material in which the surface of the sulfide-based solid electrolyte is uniformly coated on the lithium transition metal oxide.
In addition, the positive active material for an all-solid-state battery of the present invention can improve the contact characteristics between the particles of the solid electrolyte and the active material by suppressing the formation of voids between the solid electrolyte and the positive active material in the electrode and increasing the density, and mass production is possible, and the stability of the electrode and lifespan characteristics can be improved.

Description

A cathode active material for an all-solid-state battery, a manufacturing method thereof, and an all-solid-state battery comprising the same

The present invention relates to a cathode active material for an all-solid-state battery, a manufacturing method thereof, and an all-solid-state battery comprising the same.

Lithium secondary batteries are widely used from small devices such as mobile phones and laptops to large devices such as electric vehicles and power storage systems, and their demand is increasing. In the case of a lithium secondary battery, since an organic liquid electrolyte to which lithium salt is added is used, there is a potential risk of not only electrolyte leakage but also ignition and explosion.

Recently, research on all-solid-state batteries in which a liquid electrolyte is replaced with a solid electrolyte to overcome the limitations of such lithium secondary batteries and to improve battery stability has been conducted. Since the all-solid-state battery uses a solid electrolyte, there is no evaporation of electrolyte according to temperature change or leakage due to external impact, and has very excellent stability from explosion and fire. In addition, it has high energy density, so it can be used in medium and large-sized devices such as electric vehicles and power storage systems.

In order to express the performance of such an all-solid-state battery, it is important to improve the contact characteristics between the particles of the solid electrolyte and the active material in the all-solid-state battery to the extent that the theoretical capacity of the active material, which is the basis thereof, can be fully expressed. However, studies so far have not been able to meet the required level.

On the other hand, solid electrolytes mainly used in all-solid-state batteries include oxide-based and sulfide-based solid electrolytes. In particular, sulfide-based solid electrolytes have superior lithium ion conductivity compared to oxide-based solid electrolytes and are stable over a wide voltage range. . The sulfide-based solid electrolyte is mainly manufactured using a solid-phase method. In the solid-phase method, starting materials and balls are put in a milling vessel and pulverized, and then heat-treated by providing high energy. However, the solid electrolyte using such a solid-phase method has problems in that it is difficult to uniformly disperse the starting material, there is a limit to amorphization, and it is difficult to enlarge the milling vessel, so that mass synthesis is not easy.

Therefore, there is a need for research and development to improve the performance of the all-solid-state battery by improving the limitations of the existing solid electrolyte and at the same time improving the contact characteristics between the particles of the active material and the solid electrolyte in the all-solid-state battery.

Korea Patent Publication No. 2014-0058165

In order to solve the above problems, an object of the present invention is to provide a positive electrode active material for an all-solid-state battery in which a sulfide-based solid electrolyte is coated on all or a part of a surface of a core including a lithium transition metal oxide.

Another object of the present invention is to provide a positive electrode for an all-solid-state battery comprising a high-density positive electrode active material by suppressing the formation of voids between the solid electrolyte and the active material in the electrode.

Another object of the present invention is to provide an all-solid-state battery including the positive electrode having improved stability and lifespan characteristics of the electrode.

Another object of the present invention is to provide a method for manufacturing a cathode active material for an all-solid-state battery.

The object of the present invention is not limited to the object mentioned above. The objects of the present invention will become more apparent from the following description, and will be realized by means and combinations thereof described in the claims.

The present invention includes a core comprising a lithium transition metal oxide; And a sulfide-based solid electrolyte represented by the following formula (1) coated on all or part of the surface of the core including the lithium transition metal oxide; A positive electrode active material for an all-solid-state battery comprising a, wherein the positive active material is lithium sulfide, phosphorus sulfide and halide To provide a cathode active material for an all-solid-state battery, which is obtained by mixing lithium transition metal oxide with a precursor solution containing the compound, drying it to obtain a mixed powder, and then heat-treating it.

[Formula 1]

L _a P _b S _c X _d

(In Formula 1, X is F, Cl, Br, or I, 0<a≤10, 0<b≤10, 0<c≤15, 0≤d≤20)

The lithium transition metal oxide is LiCoO ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNiO ₂ , LiCoPO ₄ , LiFePO ₄ , LiMn ₂ O ₄ , LiMnPO ₄ , LiFe _1-x Mn _x PO ₄ (0<x≤0.8), LiVOPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , LiNi _0.5 Mn _0.5 O ₂ , LixM ₂ (PO ₄ ) ₃ (M=Fe or Ti, and 0<x≤3) and Li _4+x Mn ₅ O ₁₂ (0<x≤3) may be at least one selected from the group consisting of have.

The sulfide-based solid electrolyte is one selected from the group consisting of Li ₃ PS ₄ , Li ₇ P ₃ S ₁₁ , Li ₆ PS ₅ F, Li ₆ PS ₅ Br, Li ₆ PS ₅ Cl and Li ₇ P ₂ S ₈ I. may be more than

The sulfide-based solid electrolyte may have a particle size of 0.1 to 10 μm and an ionic conductivity of 1 x 10 ^-5 to 5 x 10 ^-3 S/cm at 25 °C.

The sulfide-based solid electrolyte has an X-ray diffraction analysis result, 2θ is ① 13° to 14° range, ② 16° to 18° range, ③ 24° to 26° range, ④ 27° to 29° range, ⑤ 30° to 32° range, ⑥ 43° to 45° range, ⑦ 46° to 48° range, ⑧ 52° to 54° range, first effective peak, second effective peak, third effective peak, fourth effective peak, fifth an effective peak, a sixth effective peak, a seventh effective peak and an eighth effective peak; an intensity ratio of (first effective peak)/(second effective peak) is 1.6 to 1.8, and an intensity ratio of (second effective peak)/(third effective peak) is 0.1 to 0.4; The intensity ratio of (3rd effective peak)/(4th effective peak) is 0.7 to 1.1, the intensity ratio of (4th effective peak)/(5th effective peak) is 1.2 to 1.5, the (5th effective peak) The intensity ratio of /(6th effective peak) is 2.5 to 2.8, the intensity ratio of (6th effective peak)/(7th effective peak) is 1.2 to 1.5, the (7th effective peak)/(8th effective peak) is ) may have an intensity ratio of 0.5 to 0.8.

The positive active material may be coated with 0.01 to 10% by weight of a sulfide-based solid electrolyte based on the total weight of the positive active material.

The positive active material has an X-ray diffraction analysis result, 2θ is in the range of 16° to 20°, ② in the range of 35° to 37°, ③ in the range of 38° to 40°, ④ in the range of 44° to 47°, the first effective peak, the second an effective peak, a third effective peak and a fourth effective peak; an intensity ratio of (first effective peak)/(second effective peak) is 2.2 to 2.5, and an intensity ratio of (first effective peak)/(fourth effective peak) is 0.9 to 1.2, wherein An intensity ratio of (second effective peak)/(third effective peak) may be 4.9 to 5.2, and an intensity ratio of (second effective peak)/(fourth effective peak) may be 0.4 to 0.7.

Meanwhile, the present invention provides a positive electrode for an all-solid-state battery including the positive electrode active material.

In addition, the present invention is the positive electrode; cathode; and a solid electrolyte interposed between the positive electrode and the negative electrode.

In addition, the present invention comprises the steps of preparing a precursor solution by mixing a mixture containing lithium sulfide and phosphorus sulfide in an organic solvent; preparing a mixed solution by mixing a lithium transition metal oxide with the precursor solution; drying the mixed solution to obtain a mixed powder; and heat-treating the mixed powder in an inert atmosphere to prepare a positive electrode active material in which a sulfide-based solid electrolyte is coated on all or part of a surface of a lithium transition metal oxide;

In the mixture containing lithium sulfide and phosphorus sulfide, lithium sulfide and phosphorus sulfide may be mixed in a molar ratio of 3 to 7:1.

The mixture including lithium sulfide and phosphorus sulfide may further include a halogenated compound, and a halogenated compound to phosphorus sulfide of the mixture may be mixed in a molar ratio of 1:0.1 to 4 molar ratio.

The mixed solution may include 0.01 to 10% by weight of the precursor solution and 90 to 99.99% by weight of the lithium transition metal oxide.

In the step of preparing the mixed solution, the mixture may be mixed at room temperature to 80° C. at a rotation speed of 100 to 900 rpm for 6 to 24 hours.

The step of obtaining the mixed powder may be vacuum dried at room temperature to 160° C. for 1 to 4 hours.

The inert atmosphere may be performed in at least one inert gas selected from the group consisting of argon, hydrogen, nitrogen, helium, neon, xenon, and krypton.

In the step of preparing the positive active material, the heat treatment may be performed at 250 to 800° C. for 10 minutes to 5 hours.

The mixture including lithium sulfide and phosphorus sulfide is a mixture of lithium sulfide and phosphorus sulfide in a molar ratio of 4.3 to 5.7: 1, and the mixture including lithium sulfide and phosphorus sulfide further includes a halogenated compound, and phosphorus in the mixture A step of mixing a halogenated compound with respect to a sulfide in a molar ratio of 1: 1.5 to 2.5, wherein the mixed solution contains 4 to 7 wt % of the precursor solution and 93 to 96 wt % of the lithium transition metal oxide, and preparing the mixed solution is carried out for 10 to 14 hours at room temperature at 650 to 850 rpm at revolutions per minute, and the step of obtaining the mixed powder is vacuum dried at 95 to 140 ° C. for 1.5 to 3 hours, and the inert atmosphere is carried out in argon gas, , the heat treatment in the step of preparing the positive active material may be performed at 500 to 600 ℃ for 2.5 to 3.5 hours.

The mixture comprising lithium sulfide and phosphorus sulfide further includes a halogenated compound, wherein the lithium sulfide, phosphorus sulfide and halogenated compound are mixed in a molar ratio of 5: 1:2, and the mixed solution is 5 wt% of the precursor solution and Containing 95% by weight of the lithium transition metal oxide, the step of preparing the mixed solution is performed at room temperature at 700 rpm per minute for 12 hours, and the step of obtaining the mixed powder is vacuum dried at 120° C. for 2 hours And, the inert atmosphere may be performed in argon gas, and the heat treatment in the step of preparing the positive active material may be performed at 550° C. for 3 hours.

The cathode active material for an all-solid-state battery according to the present invention is obtained by mixing lithium transition metal oxide with a precursor solution in which precursors are dispersed in an organic solvent, followed by drying and heat treatment on the whole or part of the surface of the core including lithium transition metal oxide. A positive active material coated with a sulfide-based solid electrolyte may be formed.

In addition, the positive electrode active material for an all-solid-state battery according to the present invention can improve the contact characteristics between the particles of the solid electrolyte and the active material by suppressing the formation of voids between the solid electrolyte and the positive active material in the electrode and increasing the density, and there is an advantage that can be mass-produced.

In addition, the cathode active material for an all-solid-state battery according to the present invention has a high synthesis yield and purity of lithium transition metal oxide compared to the conventional solid-state process, and is surface-treated with a sulfide-based solid electrolyte with improved crystallinity and ionic conductivity, resulting in electrode stability and lifespan characteristics It is possible to improve the electrochemical performance such as

The effects of the present invention are not limited to the above-mentioned effects. It should be understood that the effects of the present invention include all effects that can be inferred from the following description.

1 shows the results of X-ray diffraction analysis (XRD) of the sulfide-based solid electrolytes prepared in Example 1 and Comparative Examples 1 and 2 according to the present invention.
FIG. 2 shows X-ray diffraction analysis (XRD) results of the sulfide-based solid electrolyte before (Before coated) and after (After coated) the cathode active material prepared in Example 1 according to the present invention.
3 is a scanning electron microscope (FE-SEM) photograph of the positive active material prepared in Example 1 according to the present invention.
4 shows electrochemical impedance analysis (EIS) results of the sulfide-based solid electrolytes prepared in Example 1 and Comparative Examples 1 and 2;
5 is a scanning electron microscope (FE-SEM) photograph of a cross-section of the all-solid-state battery prepared in Example 2 according to the present invention.
6 is a graph showing the charging and discharging results of the all-solid-state battery prepared in Example 2 according to the present invention.

Hereinafter, the present invention will be described in more detail by way of an embodiment.

In the present invention, "amorphous" means that atoms do not have a regular arrangement but show a disordered arrangement.

In the present invention, "crystalline" means that atoms have a regular arrangement, and the arrangement of atoms has a spatially repeated pattern.

In the present invention, "significant or effective peak" refers to a peak repeatedly detected in substantially the same pattern without being significantly affected by analysis conditions or an analysis performer in XRD data.

The present invention relates to a cathode active material for an all-solid-state battery, a manufacturing method thereof, and an all-solid-state battery comprising the same.

Specifically, the present invention includes a core comprising a lithium transition metal oxide; And a sulfide-based solid electrolyte represented by the following Chemical Formula 1 coated on all or part of the surface of the core including the lithium transition metal oxide; A positive electrode active material for an all-solid-state battery comprising a, wherein the positive active material is lithium sulfide, phosphorus sulfide and halide To provide a cathode active material for an all-solid-state battery obtained by mixing a lithium transition metal oxide with a precursor solution containing the compound, drying it to obtain a mixed powder, and then performing heat treatment.

[Formula 1]

L _a P _b S _c X _d

(In Formula 1, X is F, Cl, Br, or I, 0<a≤10, 0<b≤10, 0<c≤15, 0≤d≤20)

The lithium transition metal oxide is LiCoO ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNiO ₂ , LiCoPO ₄ , LiFePO ₄ , LiMn ₂ O ₄ , LiMnPO ₄ , LiFe _1-x Mn _x PO ₄ (0<x≤0.8) , LiVOPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , LiNi _0.5 Mn _0.5 O ₂ , LixM ₂ (PO ₄ ) ₃ (M=Fe or Ti, 0<x≤3) and Li _4+x Mn ₅ It may be at least one selected from the group consisting of O ₁₂ (0<x≤3). Preferably, the lithium transition metal oxide may be at least one selected from the group consisting of LiCoO ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNiO ₂ , LiCoPO ₄ , LiFePO ₄ , LiMn ₂ O ₄ and LiMnPO ₄ , and most preferably For example, it may be LiCoO ₂ .

The sulfide-based solid electrolyte is one selected from the group consisting of Li ₃ PS ₄ , Li ₇ P ₃ S ₁₁ , Li ₆ PS ₅ F, Li ₆ PS ₅ Br, Li ₆ PS ₅ Cl and Li ₇ P ₂ S ₈ I. may be more than Preferably, the sulfide-based solid electrolyte may be at least one selected from the group consisting of Li ₆ PS ₅ F, Li ₆ PS ₅ Br, Li ₆ PS ₅ Cl, Li ₆ PS ₅ I and Li ₇ P ₂ S ₈ I, , most preferably Li ₆ PS ₅ Cl.

The sulfide-based solid electrolyte may have a particle size of 0.1 to 10 μm and an ionic conductivity of 1 x 10 ^-5 to 5 x 10 ^-3 S/cm at 25 °C. Preferably, the particle size is 3 to 10 μm, the ionic conductivity is 3 x 10 ^-4 to 4 x 10 ^-3 S/cm, most preferably the particle size is 5 to 10 μm, and the ionic conductivity is 3.77 x 10 ^{- 3} S/cm.

The sulfide-based solid electrolyte has an X-ray diffraction analysis result, 2θ is ① 13° to 14° range, ② 16° to 18° range, ③ 24° to 26° range, ④ 27° to 29° range, ⑤ 30° to 32° range, ⑥ 43° to 45° range, ⑦ 46° to 48° range, ⑧ 52° to 54° range, first effective peak, second effective peak, third effective peak, fourth effective peak, fifth An effective peak, a sixth effective peak, a seventh effective peak and an eighth effective peak may be seen.

Here, an intensity ratio of (first effective peak)/(second effective peak) is 1.6 to 1.8, and an intensity ratio of (second effective peak)/(third effective peak) is 0.1 to 0.4, and , the (third effective peak)/(4th effective peak) intensity ratio is 0.7 to 1.1, the (4th effective peak)/(5th effective peak) intensity ratio is 1.2 to 1.5, the (5th effective peak) intensity ratio is The intensity ratio of peak)/(6th effective peak) is 2.5 to 2.8, the intensity ratio of (6th effective peak)/(7th effective peak) is 1.2 to 1.5, the (7th effective peak)/(8th effective peak) is effective peak) may have an intensity ratio of 0.5 to 0.8.

In the case of having the crystal structure of the XRD characteristics as described above, the sulfide-based solid electrolyte is an argyrodite-type Li ₆ PS ₅ Cl, and the sulfide-based solid electrolyte obtained is not explicitly described in the following Examples or Comparative Examples. It was confirmed that the purity and crystallinity of the solid electrolyte was very high, and the potential stability and ionic conductivity were greatly improved while having a high energy density by forming a stable interface with the electrode.

The positive active material may be coated with a sulfide-based solid electrolyte in an amount of 0.01 to 10% by weight, preferably 4 to 7% by weight, and most preferably 5% by weight based on the total weight of the positive active material. At this time, if the coating amount of the sulfide-based solid electrolyte is less than 0.01% by weight, void suppression and densification between the active material and the solid electrolyte in the electrode may not be sufficiently exhibited. Resistance is generated, and as a result, the performance of the battery may be deteriorated.

The positive electrode active material for all-solid-state batteries is coated with the sulfide-based solid electrolyte on all or part of the surface of the core including lithium transition metal oxide, so that the contact characteristics between the active material and the solid electrolyte can be improved, and the formation of pores in the electrode is suppressed and densification can be achieved.

The positive active material has an X-ray diffraction analysis result, 2θ is in the range of 16° to 20°, ② in the range of 35° to 37°, ③ in the range of 38° to 40°, ④ in the range of 44° to 47°, the first effective peak, the second An effective peak, a third effective peak and a fourth effective peak may be seen.

Here, the intensity ratio of the (first effective peak)/(the second effective peak) is 2.2 to 2.5, and the intensity ratio of the (first effective peak)/(the fourth effective peak) is 0.9 to 1.2, and , an intensity ratio of (second effective peak)/(third effective peak) may be 4.9 to 5.2, and an intensity ratio of (second effective peak)/(fourth effective peak) may be 0.4 to 0.7.

In the case of having the crystal structure of the XRD characteristics as described above, the positive active material did not have a side reaction at the interface between the electrode and the solid electrolyte layer, although not explicitly described in the following Examples or Comparative Examples, and reversible increase in discharge capacity The vortex characteristics were improved.

Meanwhile, the present invention provides a positive electrode for an all-solid-state battery including the positive electrode active material.

In addition, the present invention is the positive electrode; cathode; and a solid electrolyte interposed between the positive electrode and the negative electrode.

In addition, the present invention comprises the steps of preparing a precursor solution by mixing a mixture containing lithium sulfide and phosphorus sulfide in an organic solvent (S1); preparing a mixed solution by mixing a lithium transition metal oxide with the precursor solution (S2); drying the mixed solution to obtain a mixed powder (S3); and heat-treating the mixed powder in an inert atmosphere to prepare a positive electrode active material in which a sulfide-based solid electrolyte is coated on all or part of the surface of a lithium transition metal oxide (S4); do.

In the step (S1) of preparing the precursor solution, a precursor solution may be prepared by mixing a mixture containing lithium sulfide and phosphorus sulfide in an organic solvent. In the step (S1), by mixing and dispersing two or more kinds of precursors in an organic solvent, the dispersibility of the precursors is increased compared to powder mixing in the solid-state process, so that a fine-sized solid electrolyte can be synthesized.

The organic solvent may be at least one selected from the group consisting of acetonitrile, ethyl acetate, dibutyl ether, ethyl propionate, and tetrahydrofuran. . Preferably, the organic solvent may be at least one selected from the group consisting of acetonitrile, ethyl acetate and dibutyl ether, and most preferably acetonitrile. The acetonitrile has excellent dispersing properties, and can achieve superior particle size and distribution compared to other organic solvents when synthesizing a sulfide-based solid electrolyte. The organic solvent may be 30 to 90% by weight based on the total weight of the precursor solution.

In step (S1), the lithium sulfide may be lithium sulfide (Li ₂ S), and the phosphorus sulfide may be phosphorus pentasulfide (P ₂ S ₅ ). In the mixture containing lithium sulfide and phosphorus sulfide, lithium sulfide and phosphorus sulfide are present in a 3-7:1 molar ratio, preferably 4-6:1 molar ratio, more preferably 4.3-5.7:1 molar ratio, most preferably 5 It may be mixed in a molar ratio of 1:1. In this case, if the ratio of lithium sulfide is less than 3 moles, the ionic conductivity of the sulfide-based solid electrolyte may be rapidly reduced, and if it exceeds 7 moles, unreacted lithium sulfide may remain and act as an impurity.

The mixture including lithium sulfide and phosphorus sulfide may further include a halogenated compound. In the step (S1), a mixture containing lithium sulfide and phosphorus sulfide is mixed in an organic solvent and first stirred, and then the halogenated compound is additionally mixed to perform a second stirring process. When the step (S1) is stirred twice, the particle size of the obtained sulfide-based solid electrolyte can be minimized by maximally preventing aggregation of the starting materials.

In addition, the halogenated compound to phosphorus sulfide in the mixture may be mixed in a molar ratio of 1: 0.1 to 4, preferably 1: 1 to 3, more preferably 1: 1.5 to 2.5, and most preferably 1: 2 have. The halogenated compound may be mixed to increase the ionic conductivity of the sulfide-based solid electrolyte. In this case, when the ratio of the halogenated compound is less than 0.1 mol, the ionic conductivity of the solid electrolyte may be reduced. Conversely, if the ratio of the halogenated compound is more than 4 mol, further improved ionic conductivity cannot be expected, and the unreacted halogenated compound may act as an impurity.

The halogenated compound may be at least one selected from the group consisting of lithium fluoride (LiF), lithium bromide (LiBr), lithium chloride (LiCl) and lithium iodide (LiI), preferably lithium chloride (LiCl). . Compared to other halogen elements, the solid electrolyte containing lithium chloride has high ionic conductivity and forms a stable interface, thereby significantly reducing interfacial resistance and greatly improving battery performance.

In the step (S2) of preparing the mixed solution, the mixed solution may include 0.01 to 10% by weight of the precursor solution and 90 to 99.99% by weight of the lithium transition metal oxide. Preferably, 4 to 7 wt% of the sulfide-based solid electrolyte and 93 to 96 wt% of the lithium transition metal oxide may be mixed, and most preferably 5 wt% of the sulfide-based solid electrolyte and 95 wt% of the lithium transition metal oxide % can be mixed.

In the step (S2), the mixture may be mixed at room temperature to 80° C. at a rotation speed of 100 to 900 rpm for 6 to 24 hours. Preferably mixing and stirring at room temperature for 8 to 16 hours at 500 to 800 rpm at revolutions per minute, more preferably for 10 to 14 hours at 650 to 850 rpm at revolutions per minute, and most preferably at 700 rpm at revolutions per minute for 12 hours. can do.

At this time, when the stirring temperature is less than room temperature, the number of revolutions per minute is less than 100 rpm, or the stirring time is less than 6 hours, the dispersibility of the precursors is lowered, so that a solid electrolyte having a uniform particle size cannot be synthesized, and the lithium transition metal The solid electrolyte may not be properly coated on the surface of the oxide. Conversely, if the stirring temperature exceeds 80 ° C, the number of revolutions per minute exceeds 900 rpm, or the stirring time exceeds 24 hours, it is not preferable because the particle size of the solid electrolyte may grow excessively, and the solid electrolyte on the surface of the lithium transition metal oxide This excessive coating may interfere with the movement of lithium ions in the positive electrode active material. The step (S1) may be mixed and stirred using a magnetic stirrer or an ultrasonic disperser, preferably a magnetic stirrer.

The step (S3) of obtaining the mixed powder may be vacuum-dried at room temperature to 160°C for 1 to 4 hours, preferably at 95 to 140°C for 1.5 to 3 hours, and most preferably at 120°C for 2 hours. At this time, if the drying temperature is less than room temperature or the drying time is less than 1 hour, it is not dried properly and thus an amorphous precursor powder cannot be formed. As a result, it is difficult to control the particle size of the sulfide-based solid electrolyte and transition to a phase with low ionic conductivity may occur.

The vacuum drying may be performed using a vacuum dryer, a micro-evaporator or a rotary evaporator, preferably vacuum-drying using a micro-evaporator.

The inert atmosphere may be performed in at least one inert gas selected from the group consisting of argon, hydrogen, nitrogen, helium, neon, xenon, and krypton. Preferably, it may be at least one selected from the group consisting of argon, hydrogen and nitrogen, and most preferably, it may be carried out in argon gas.

In the step (S4) of preparing the positive active material, the heat treatment is performed at 250 to 800° C. for 10 minutes to 5 hours, preferably at 400 to 700° C. for 1 to 4 hours, more preferably at 500 to 600° C. for 2.5 to 3.5 hours. , most preferably at 550 °C for 3 hours. At this time, if the heat treatment temperature is less than 250 ℃ or the heat treatment time is less than 10 minutes, crystallization may not proceed sufficiently, on the contrary, if the heat treatment temperature is more than 800 ° C. is too large, so it may be difficult to manufacture particles of a uniform size. In addition, the ionic conductivity may be lowered due to the non-uniform particle size.

In particular, although not explicitly described in the following Examples or Comparative Examples, in the method for manufacturing a positive electrode active material for an all-solid-state battery according to the present invention, the molar ratio of lithium sulfide, phosphorus sulfide and halogenated compound, precursor solution and lithium transition After applying the cathode active material prepared by varying the mixing ratio of metal oxides, stirring conditions, drying conditions, and heat treatment conditions to an all-solid-state battery, charging and discharging 200 times at a temperature of 300 ° C. to analyze the cathode surface by scanning electron microscope (SEM) was confirmed through

As a result, unlike other conditions and other numerical ranges, when all of the following conditions were satisfied, the interfacial stability between the electrode and the solid electrolyte layer was excellent, and the stability and lifespan characteristics of the battery were improved by lowering the activation energy while maintaining high ionic conductivity. Confirmed.

① The mixture containing lithium sulfide and phosphorus sulfide is a mixture of lithium sulfide and phosphorus sulfide in a molar ratio of 4.3 to 5.7:1, ② the mixture containing lithium sulfide and phosphorus sulfide further includes a halogenated compound, and the mixture of phosphorus sulfide and halogenated compound in a molar ratio of 1: 1.5 to 2.5, ③ the mixed solution contains 4 to 7 wt% of the precursor solution and 93 to 96 wt% of the lithium transition metal oxide, ④ the mixed solution The manufacturing step is performed at room temperature at 650 to 850 rpm for 10 to 14 hours, ⑤ the step of obtaining the mixed powder is vacuum dried at 95 to 140 ° C. for 1.5 to 3 hours, ⑥ the inert atmosphere is performed in argon gas, and ⑦ heat treatment in the step of preparing the positive active material may be performed at 500 to 600° C. for 2.5 to 3.5 hours.

However, when any one of the above seven conditions was not satisfied, the ionic conductivity was maintained to some extent, but the activation energy was also increased, thereby deteriorating the stability and lifespan characteristics of the battery.

In particular, although not explicitly described in the following Examples or Comparative Examples, in the method for producing a sulfide-based solid electrolyte according to the present invention, after applying a sulfide-based solid electrolyte satisfying all of the following more desirable conditions to an all-solid-state battery The cathode surface was confirmed by scanning electron microscopy (SEM) analysis by carrying out charging and discharging at a temperature of 800° C. for 500 hours.

As a result, unlike in other conditions and other numerical ranges, it was confirmed that when all of the following conditions were satisfied, the positive active material in the electrode was not lost and maintained in a high-density state even after operation at a high temperature, which confirmed that the thermal stability and lifespan characteristics of the battery were very excellent. .

① The mixture including lithium sulfide and phosphorus sulfide further includes a halogenated compound, wherein the lithium sulfide, phosphorus sulfide and halogenated compound are mixed in a molar ratio of 5: 1:2, ② The mixed solution is the precursor solution by weight of 5 % and 95% by weight of the lithium transition metal oxide, ③ preparing the mixed solution is performed at room temperature at 700 rpm at revolutions per minute for 12 hours, ④ obtaining the mixed powder is 2 at 120 ° C. Vacuum drying for time, ⑤ the inert atmosphere is performed in argon gas, ⑥ heat treatment in the step of preparing the positive electrode active material may be performed at 550 ℃ for 3 hours.

However, when any one of the above six conditions is not satisfied, some of the sulfide-based solid electrolyte is lost by heat, and a number of pores are generated on the electrode surface, and the energy density is lowered, resulting in a sharp decrease in the lifespan of the battery.

As described above, the cathode active material for an all-solid-state battery according to the present invention mixes a lithium transition metal oxide with a precursor solution in which precursors are dispersed in an organic solvent, and then drying and heat-treating it sequentially. A positive active material in which all or part of a sulfide-based solid electrolyte is coated may be formed.

The positive active material can improve the contact characteristics between the particles of the solid electrolyte and the active material by suppressing the formation of voids between the solid electrolyte and the positive active material in the electrode and increasing the density, and has the advantage that mass production is possible. The positive electrode active material has a higher synthesis yield and purity than the conventional solid-state process of lithium transition metal oxide, and by surface-treating the lithium transition metal oxide with a sulfide-based solid electrolyte with improved crystallinity and ionic conductivity, electrochemical performance such as stability and lifespan characteristics of the electrode is improved can do it

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited by the following examples.

Example 1: Preparation of a cathode active material for an all-solid-state battery

All experiments were performed in a glove box not exposed to moisture and oxygen. Lithium sulfide (Li ₂ S), phosphorus pentasulfide (P ₂ S ₅ ) and lithium chloride (LiCl) were quantified at a molar ratio of 5::1:2 and put in acetonitrile to prepare a precursor solution. Then, 95 wt% of the precursor solution was mixed with 5 wt% of LiCoO ₂ , a lithium transition metal oxide, and stirred at room temperature at 700 rpm for 12 hours to prepare a mixed solution. At this time, the organic solvent was 40% by weight based on the total weight of the mixed solution. Then, the mixed solution was put into a micro-evaporator and vacuum dried at 120° C. for 2 hours to prepare a mixed powder. Then, the mixed powder was heat-treated at 550° C. for 3 hours in an argon atmosphere to prepare a cathode active material coated with a sulfide-based solid electrolyte (Li ₆ PS ₅ Cl) on all or part of the surface of LiCoO ₂ . At this time, the coated sulfide-based solid electrolyte was 5 wt% based on the total weight of the positive electrode active material, and the particle size was 5 to 10 μm.

Example 2: Preparation of an all-solid-state battery

0.15 g of the sulfide-based solid electrolyte (Li ₆ PS ₅ Cl) of Example 1 was put into a 15 ㅨ mold, the solid electrolyte layer was press-molded, and one surface of the solid electrolyte layer was surface-treated prepared in Example 1 0.03 g of a composite positive electrode in which NCM523 (nickel, cobalt, manganese), the sulfide-based solid electrolyte and VGCF (vapor grown carbon nanofiber) were mixed was pressurized. In addition, an all-solid-state battery was prepared by pressing 0.1 g of Li-In alloy powder on the other surface of the solid electrolyte layer.

Comparative Example 1: Preparation of a cathode active material using a sulfide-based solid electrolyte prepared by liquid synthesized

A precursor solution was prepared by mixing lithium sulfide (Li ₂ S), phosphorus pentasulfide (P ₂ S ₅ ) and lithium chloride (LiCl) in acetonitrile without forming an amorphous precursor powder. Then, a cathode active material was prepared in the same manner as in Example 1 using the precursor solution.

Comparative Example 2: Preparation of a positive active material using a sulfide-based solid electrolyte prepared by solid synthesized

Lithium sulfide (Li ₂ S), phosphorus pentasulfide (P ₂ S ₅ ) and lithium chloride (LiCl) were mixed and then ball milled to prepare a mixed powder. Then, 5% by weight of the mixed powder and 95% by weight of LiCoO ₂ , which is a lithium transition metal oxide, were mixed in acetonitrile in the same manner as in Example 1 to prepare a cathode active material.

Experimental Example 1: X-ray diffraction (XRD), scanning electron microscope (FE-SEM) and electrochemical impedance (EIS) analysis

XRD (X-ray diffraction) and FE-SEM (Scanning Electron) to confirm the composition and shape of the sulfide-based solid electrolyte prepared in Example 1 and Comparative Examples 1 and 2 and the cathode active material prepared in Example 1 Microscope) analysis was performed. The results are shown in FIGS. 1 to 4 .

1 shows the results of X-ray diffraction analysis (XRD) of the sulfide-based solid electrolytes prepared in Example 1 and Comparative Examples 1 and 2 above. Referring to FIG. 1 , in Example 1 and Comparative Examples 1 and 2, peaks were confirmed at the same position, and it was found that the components of the synthesized solid electrolyte were the same. In particular, in the case of Example 1 (dried after dispersion), it was confirmed that the intensity of each peak was relatively higher than Comparative Examples 1 (Liquid synthesized) and 2 (Solid synthesized). Through this, it was found that the yield and purity of the synthesized sulfide-based solid electrolyte were the best.

FIG. 2 shows the results of X-ray diffraction analysis (XRD) of the positive active material prepared in Example 1 before (Before coated) and after (After coated) the sulfide-based solid electrolyte was coated. Referring to FIG. 2, peaks were confirmed at the same position both before and after coating of the sulfide-based solid electrolyte, indicating that the sulfide-based solid electrolyte was well coated on the surface of the lithium transition metal oxide. could In addition, the intensity of each peak after coating (After coated) of the sulfide-based solid electrolyte was slightly lower than that of before coating (Before coated), as each sampling was performed, but it was confirmed that the ratio of peak intensity at each position was similar.

3 is a scanning electron microscope (FE-SEM) photograph of the positive active material prepared in Example 1. FIG. Referring to FIG. 3, in the positive active material of Example 1, it was confirmed that the elements contained in the sulfide-based solid electrolyte were uniformly dispersed on the surface of the lithium transition metal oxide.

4 shows electrochemical impedance analysis (EIS) results of the sulfide-based solid electrolytes prepared in Example 1 and Comparative Examples 1 and 2; With respect to the EIS analysis result, the ion conductivity was calculated by the following formula.

[Ion conductivity = thickness (mm)/{resistance (Ω) x area (mm ² )}]

Referring to FIG. 4, in Example 1 (dried after dispersion), the impedance resistance value was 48.76 Ω, and the ionic conductivity was 3.77 x 10 ^-3 S/cm. In addition, in Comparative Example 1 (Liquid synthesized), the impedance resistance value was 172.30 Ω, and the ionic conductivity was 1.85 x 10 ^-3 S/cm. In addition, in Comparative Example 2 (solid synthesized), the impedance resistance value was 131.42 Ω, and the ionic conductivity was 2.42 x 10 ^-3 S/cm. Through this, it was confirmed that Example 1 had the lowest impedance resistance value and the highest ionic conductivity compared to Comparative Examples 1 and 2.

Experimental Example 2: Charge/discharge evaluation and electrochemical impedance (EIS) analysis

A charging/discharging experiment was performed using the all-solid-state battery prepared in Example 2 under the condition of 0.1 C rate in the range of 2.0 to 3.6 V. The results are shown in FIGS. 5 and 6 .

5 is a scanning electron microscope (FE-SEM) photograph of a cross-section of the all-solid-state battery prepared in Example 2. FIG. Referring to FIG. 5 , in the all-solid-state battery of Example 2, it was confirmed that the elements contained in the sulfide-based solid electrolyte were uniformly dispersed on the electrode.

6 is a graph showing the charging and discharging results of the all-solid-state battery prepared in Example 2. Referring to FIG. 6 , in the all-solid-state battery of Example 2, it was confirmed that the sulfide-based solid electrolyte was formed at a high density without voids on the electrode, so that the battery was well driven.

Claims (19)

a core comprising lithium transition metal oxide; and
A positive electrode active material for an all-solid-state battery comprising; a sulfide-based solid electrolyte represented by the following Chemical Formula 1 coated on all or part of the surface of the core including the lithium transition metal oxide,
The positive active material is obtained by mixing a lithium transition metal oxide with a precursor solution containing lithium sulfide, phosphorus sulfide and a halogenated compound to prepare a mixed solution, drying the mixed solution to obtain a mixed powder, and then heat-treating,
The precursor solution is obtained by mixing a mixture containing lithium sulfide and phosphorus sulfide in an organic solvent and first stirring, followed by second stirring by further mixing the halogenated compound,
The precursor solution comprising lithium sulfide, phosphorus sulfide and halogenated compound is a mixture of lithium sulfide, phosphorus sulfide and halogenated compound in a molar ratio of 4.3 to 5.7: 1: 1.5 to 2.5,
The mixed solution contains 4 to 7% by weight of the precursor solution and 93 to 96% by weight of the lithium transition metal oxide,
The mixed solution is prepared by performing for 10 to 14 hours at room temperature at 650 to 850 rpm per minute,
The mixed powder is obtained by vacuum drying at 95 to 140 ℃ for 1.5 to 3 hours,
The heat treatment is to be performed for 2.5 to 3.5 hours at 500 to 600 ℃ in argon gas,
The sulfide-based solid electrolyte has a particle size of 5 to 10 μm, and an ionic conductivity of 3.77 x 10 ^-3 S/cm at 25° C. The cathode active material for an all-solid-state battery.
[Formula 1]
L _a P _b S _c X _d
(In Formula 1, X is F, Cl, Br, or I, 0<a≤10, 0<b≤10, 0<c≤15, 0≤d≤20)
According to claim 1,
The lithium transition metal oxide is LiCoO ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNiO ₂ , LiCoPO ₄ , LiFePO ₄ , LiMn ₂ O ₄ , LiMnPO ₄ , LiFe _1-x Mn _x PO ₄ (0<x≤0.8) , LiVOPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , LiNi _0.5 Mn _0.5 O ₂ , LixM ₂ (PO ₄ ) ₃ (M=Fe or Ti, 0<x≤3) and Li _4+x Mn ₅ O ₁₂ (0<x≤3) is at least one selected from the group consisting of a positive electrode active material for an all-solid-state battery.
According to claim 1,
The sulfide-based solid electrolyte is one selected from the group consisting of Li ₃ PS ₄ , Li ₇ P ₃ S ₁₁ , Li ₆ PS ₅ F, Li ₆ PS ₅ Br, Li ₆ PS ₅ Cl and Li ₇ P ₂ S ₈ I. The positive active material for an all-solid-state battery that is the above.
delete According to claim 1,
The sulfide-based solid electrolyte has an X-ray diffraction analysis result, 2θ is ① 13° to 14° range, ② 16° to 18° range, ③ 24° to 26° range, ④ 27° to 29° range, ⑤ 30° to 32° range, ⑥ 43° to 45° range, ⑦ 46° to 48° range, ⑧ 52° to 54° range, first effective peak, second effective peak, third effective peak, fourth effective peak, fifth an effective peak, a sixth effective peak, a seventh effective peak and an eighth effective peak;
an intensity ratio of (first effective peak)/(second effective peak) is 1.6 to 1.8, and an intensity ratio of (second effective peak)/(third effective peak) is 0.1 to 0.4; The intensity ratio of (3rd effective peak)/(4th effective peak) is 0.7 to 1.1, the intensity ratio of (4th effective peak)/(5th effective peak) is 1.2 to 1.5, the (5th effective peak) The intensity ratio of /(6th effective peak) is 2.5 to 2.8, the intensity ratio of (6th effective peak)/(7th effective peak) is 1.2 to 1.5, the (7th effective peak)/(8th effective peak) is ) of the positive active material for an all-solid-state battery that the intensity ratio is 0.5 to 0.8.
According to claim 1,
The cathode active material is a cathode active material for an all-solid-state battery in which 0.01 to 10% by weight of a sulfide-based solid electrolyte is coated based on the total weight of the cathode active material.
According to claim 1,
The positive active material has an X-ray diffraction analysis result, 2θ is in the range of 16° to 20°, ② in the range of 35° to 37°, ③ in the range of 38° to 40°, ④ in the range of 44° to 47°, the first effective peak, the second an effective peak, a third effective peak and a fourth effective peak;
an intensity ratio of (first effective peak)/(second effective peak) is 2.2 to 2.5, and an intensity ratio of (first effective peak)/(fourth effective peak) is 0.9 to 1.2, wherein The (second effective peak)/(third effective peak) intensity ratio is 4.9 to 5.2, and the (second effective peak)/(fourth effective peak) intensity ratio is 0.4 to 0.7. active material.
A positive electrode for an all-solid-state battery comprising the positive active material of claim 1 .
The positive electrode of claim 8;
cathode; and
a solid electrolyte interposed between the positive electrode and the negative electrode;
An all-solid-state battery comprising a.
preparing a precursor solution by mixing a mixture containing lithium sulfide and phosphorus sulfide in an organic solvent and first stirring, followed by additional mixing of a halogenated compound and second stirring;
preparing a mixed solution by mixing a lithium transition metal oxide with the precursor solution;
drying the mixed solution to obtain a mixed powder; and
preparing a positive electrode active material in which a sulfide-based solid electrolyte is coated on all or part of a surface of a lithium transition metal oxide by heat-treating the mixed powder in an inert atmosphere;
including,
The mixture containing lithium sulfide and phosphorus sulfide is a mixture of lithium sulfide and phosphorus sulfide in a molar ratio of 4.3 to 5.7: 1,
The mixture containing lithium sulfide and phosphorus sulfide further includes a halogenated compound, and a mixture of a halogenated compound with respect to phosphorus sulfide of the mixture in a molar ratio of 1: 1.5 to 2.5,
The mixed solution contains 4 to 7% by weight of the precursor solution and 93 to 96% by weight of the lithium transition metal oxide,
The step of preparing the mixed solution is performed at room temperature at 650 to 850 rpm for revolutions per minute for 10 to 14 hours,
The step of obtaining the mixed powder is vacuum-dried at 95 to 140 ℃ for 1.5 to 3 hours,
The inert atmosphere is carried out in argon gas,
In the step of preparing the positive active material, the heat treatment is performed at 500 to 600° C. for 2.5 to 3.5 hours,
The sulfide-based solid electrolyte has a particle size of 5 to 10 µm, and an ionic conductivity of 3.77 x 10 ^-3 S/cm at 25 °C.
delete delete delete delete delete delete delete delete 11. The method of claim 10,
The mixture comprising lithium sulfide and phosphorus sulfide further includes a halogenated compound, wherein the lithium sulfide, phosphorus sulfide and halogenated compound are mixed in a molar ratio of 5: 1:2,
The mixed solution contains 5% by weight of the precursor solution and 95% by weight of the lithium transition metal oxide,
The step of preparing the mixed solution is carried out at room temperature at 700 rpm at the number of revolutions per minute for 12 hours,
The step of obtaining the mixed powder is vacuum-dried at 120 ° C. for 2 hours,
The inert atmosphere is carried out in argon gas,
In the step of preparing the cathode active material, the heat treatment is performed at 550° C. for 3 hours.

Images