KR20240037037A - Solid electrolyte and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a sulfide-based solid electrolyte that has an argyrodite-based crystal structure, at least a portion of the crystal structure is doped with oxygen, and is represented by the following formula (1).
[Formula 1]
Li _(6-5x) P _(1-x) S _(4.95-4x) A _1-2x O _4x+0.05
In Formula 1, A is a halogen element and 0 < x < 0.5.

Description

Solid electrolyte and lithium secondary battery containing the same {SOLID ELECTROLYTE AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a solid electrolyte and a lithium secondary battery containing the same, and more specifically, to a sulfide-based solid electrolyte and a lithium secondary battery containing the same.

Recently, as demand for IT mobile devices and small power-driven devices such as electric bicycles and small electric vehicles has rapidly increased, interest in high-capacity batteries is increasing. As demand for high-capacity batteries increases, research on the safety or energy density of high-capacity batteries is actively underway.

Accordingly, research on all-solid-state batteries is actively underway as a material to improve the safety of existing secondary batteries and increase energy density. An all-solid-state battery refers to a battery that replaces the liquid electrolyte used in existing lithium secondary batteries with a solid one. It does not use flammable solvents in the battery, so no ignition or explosion occurs due to a reaction such as the decomposition reaction of a conventional electrolyte solution. Since this is not done, the safety of the battery can be improved. Additionally, since lithium metal or lithium alloy can be used as the anode material, the energy density relative to the mass and volume of the battery can be improved.

The solid electrolyte used in the all-solid-state battery is generally an inorganic solid electrolyte, and various studies have been conducted on a sulfide-based solid electrolyte with a composition such as Li ₆ PS ₅ Cl, which is an azirodite structure among the all-solid-state batteries. It's in progress.

However, the sulfide-based solid electrolyte has problems that make it difficult to handle in general atmosphere, such as significantly lowering ionic conductivity due to side reactions with moisture.

In order to solve the above-mentioned problems, one object of the present invention is to provide a solid electrolyte in which deterioration of ionic conductivity can be minimized when exposed to the atmosphere.

Another object of the present invention is to provide a lithium secondary battery including a solid electrolyte having the above-mentioned advantages.

In order to achieve the above-mentioned problem, one embodiment of the present invention has an argyrodite-based crystal structure, at least a portion of the crystal structure is doped with oxygen, and is represented by the following formula (1), a sulfide-based crystal structure. A solid electrolyte is provided.

[Formula 1]

Li _(6-5x) P _(1-x) S _(4.95-4x) A _1-2x O _4x+0.05

In Formula 1, A is F, Cl, Br, I, or a combination thereof, and 0 < x < 0.5.

The solid electrolyte may satisfy Equation 1.

<Equation 1>

6.005 ≤ [Li]/[P] ≤ 6.5

In Equation 1, [Li] and [P] mean at% of Li and P, respectively.

The solid electrolyte may satisfy Equation 2.

<Equation 2>

4.9 ≤ [S]/[P] ≤ 5.4

In Equation 2 above, [S] and [P] mean at% of S and P, respectively.

The solid electrolyte may satisfy Equation 3.

<Equation 3>

0.5 ≤ [A]/[P] ≤ 0.995

In Equation 3 above, [A] and [P] mean at% of A and P, respectively.

The solid electrolyte may satisfy Equation 4 below.

<Equation 4>

0.01 ≤ [O]/[S] ≤ 0.4

In Equation 4 above, [O] and [S] mean at% of O and S, respectively.

In the solid electrolyte, when measuring an

The ionic conductivity of the solid electrolyte after exposure to the atmosphere may be maintained in the range of 60 to 83% of the ionic conductivity before exposure to the atmosphere.

Another embodiment of the present invention is an anode; cathode; and a solid electrolyte layer positioned between the positive electrode and the negative electrode, wherein at least one of the positive electrode, negative electrode, and solid electrolyte layer includes the solid electrolyte described above.

In the sulfide-based solid electrolyte according to an embodiment of the present invention, at least a portion of the azirodite-based crystal structure is doped with oxygen, so that side reactions with moisture are suppressed when exposed to the atmosphere, thereby minimizing deterioration of ionic conductivity.

However, the effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned can be explained by those who have ordinary knowledge in the technical field to which this disclosure pertains from the description of the claims (referred to as a “person skilled in the art”). can be clearly understood.

Figure 1 is a schematic diagram conceptualizing a method for manufacturing a solid electrolyte according to another embodiment of the present invention.

Hereinafter, with reference to the attached drawings, embodiments of the present invention will be described clearly and in detail so that those skilled in the art can easily implement the present invention. However, this is presented as an example, and the present invention is not limited thereby, and the present invention is only defined by the scope of the claims to be described later.

Terms or words used in this specification and claims should not be construed as limited to their common or dictionary meanings, and the inventor may appropriately define the concept of terms in order to explain his or her invention in the best way. It must be interpreted with meaning and concept consistent with the technical idea of the present invention based on the principle that it is.

In this specification, expressions such as “comprising” should be understood as open-ended terms that imply the possibility of including other embodiments.

As used herein, “preferred” or “preferably” refers to embodiments of the invention that may provide certain advantages under certain circumstances. However, under the same or different circumstances, other embodiments may also be preferred. Additionally, mention of one or more preferred embodiments does not mean that other embodiments are not useful, nor is it intended to exclude other embodiments from the scope of the invention.

In this specification, the term "combination(s) thereof" described in the Markushi format expression refers to a mixture or combination of one or more selected from the group consisting of the components described in the Markushi format expression, It means containing one or more selected from the group consisting of constituent elements.

In this specification, the description of “A and/or B” means A or B or both.

1. Solid electrolyte

One embodiment of the present invention provides a sulfide-based solid electrolyte that has an argyrodite-based crystal structure, at least a portion of the crystal structure is doped with oxygen, and is represented by the following formula (1).

[Formula 1]

Li _(6-5x) P _(1-x) S _(4.95-4x) A _1-2x O _4x+0.05

In Formula 1, A is F, Cl, Br, I, or a combination thereof, and 0 < x < 0.5.

The sulfide-based solid electrolyte according to one embodiment of the present invention has an argyrodite-based crystal structure. The azyrodite-based crystal structure has the advantage of high ionic conductivity. However, instead of having high ionic conductivity, this azyrodite-based crystal structure has a problem in that ionic conductivity is significantly deteriorated due to a side reaction with moisture when exposed to the atmosphere.

To solve this problem, at least part of the crystal structure of the sulfide-based solid electrolyte according to one embodiment of the present invention is doped with oxygen. By being doped with oxygen, moisture stability can be excellent. More specifically, when exposed to the atmosphere, side reactions with moisture are suppressed, and deterioration of ionic conductivity can be minimized.

The sulfide-based solid electrolyte according to one embodiment of the present invention is represented by the following formula (1).

[Formula 1]

Li _(6-5x) P _(1-x) S _(4.95-4x) A _1-2x O _4x+0.05

In Formula 1, A is a halogen element and 0 < x < 0.5.

Specifically, in Formula 1, O (oxygen) is a doping element. In this specification, “doping” may mean not only replacing some elements of a compound with new elements, but also allowing the doped element to become a component of the crystal phase of the compound.

And, in Formula 1, 4x+0.05 represents the doping amount of oxygen, a doping element, in moles. At this time, 0 < x < 0.5 is satisfied.

More specifically, x may be 0.005 to 0.4, 0.005 to 0.07, or 0.005 to 0.02. If x is too small, it may mean that the doping amount of oxygen is too small, and if x is too large, it may mean that the doping amount of oxygen is too large. At this time, if the doping amount of oxygen is too small, it does not differ significantly from the basic Li ₆ PS ₅ Cl azirodite composition, resulting in a doping effect, that is, an effect of increasing moisture stability when exposed to the atmosphere, that is, ions when exposed to the atmosphere. The effect of reducing the deterioration of conductivity (a measure of this may be the ionic conductivity before exposure to the air compared to the value of the ionic conductivity after air exposure converted into a percentage (%) (hereinafter referred to as retention rate)) may cause problems. You can. On the other hand, if the doping amount of oxygen is too large, the crystal structure of the azyrodite in the sulfide-based solid electrolyte with high ionic conductivity is greatly modified, resulting in poor lithium ion movement, which can eventually lead to a problem in which ionic conductivity is significantly lowered. there is.

In Formula 1, A refers to a halogen element, and may specifically be any one or more of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

More specifically, A may be chlorine (Cl). Among the halogen elements, chlorine in particular is used, which may have the advantage of stabilizing the structure of the azirodite-based solid electrolyte and making it easier to synthesize and cheaper than other elements.

The solid electrolyte may satisfy Equation 1 below.

<Equation 1>

6.005 ≤ [Li]/[P] ≤ 6.5

In Equation 1, [Li] and [P] mean at% of Li and P, respectively.

More specifically, [Li]/[P] refers to the ratio of the number of moles of lithium atoms to the number of moles of phosphorus atoms, and [Li]/[P] may be 6.005 to 6.5, 6.005 to 6.07, or 6.005 to 6.02. If [Li]/[P] is too small, conductivity may deteriorate due to impurities, and if [Li]/[P] is too large, battery performance may deteriorate due to moisture instability and structural instability due to high sulfide content in moisture. do.

The solid electrolyte may satisfy Equation 2 below.

<Equation 2>

4.9 ≤ [S]/[P] ≤ 5.4

In Equation 2 above, [S] and [P] mean at% of S and P, respectively.

More specifically, [S]/[P] refers to the ratio of the number of moles of sulfur atoms to the number of moles of phosphorus atoms, and [S]/[P] may be 4.9 to 5.4, 4.9 to 5.02, or 4.9 to 4.97. If [S]/[P] is too small, conductivity may deteriorate due to impurities, and if [S]/[P] is too large, battery performance may deteriorate due to moisture instability and structural instability due to high sulfide content in moisture. do.

The solid electrolyte may satisfy Equation 3 below.

<Equation 3>

0.5 ≤ [A]/[P] ≤ 0.995

In Equation 3 above, [A] and [P] mean at% of A and P, respectively.

More specifically, [A]/[P] means the ratio of the number of moles of halogen atoms A to the number of moles of phosphorus atoms. At this time, the halogen atom A may be F, Cl, Br, I, or a combination thereof. And, [A]/[P] may be 0.5 to 0.995, 0.93 to 0.995, or 0.98 to 0.995. If [A]/[P] is too small or large, moisture and electrochemical performance deterioration occurs due to structural instability.

The solid electrolyte may satisfy Equation 4 below.

<Equation 4>

0.01 ≤ [O]/[S] ≤ 0.4

In Equation 4 above, [O] and [S] mean at% of O and S, respectively.

More specifically, [O]/[S] refers to the ratio of the number of moles of oxygen atoms to the number of moles of sulfur atoms, and [O]/[S] may be 0.01 to 0.4, 0.01 to 0.07, or 0.01 to 0.03. If [O]/[S] is too small, it may react with moisture when exposed to the atmosphere, resulting in a decrease in ionic conductivity due to structural collapse of the solid electrolyte, and if [O]/[S] is too large, the polarity of Li in the structure may occur. becomes smaller and ionic conductivity may drop significantly.

In the solid electrolyte, when measuring an

The XRD peak value 2θ in the above range corresponds to the impurity peak, and since the impurity peak does not appear in the solid electrolyte, moisture stability and electrochemical stability can be improved when exposed to the atmosphere.

As the solid electrolyte according to one embodiment of the present invention satisfies the above-mentioned Chemical Formula 1 and Equations 1 to 4, the ionic conductivity after exposure to the atmosphere can be maintained in the range of 60 to 83% of the ionic conductivity before exposure to the atmosphere. there is.

2. Manufacturing method of solid electrolyte

Another embodiment of the present invention includes mixing a lithium-containing sulfide, a phosphorus-containing compound, a halogen-containing compound, and a doping raw material to form a mixture; and heat-treating the mixture to form a sulfide-based solid electrolyte.

Figure 1 is a schematic diagram conceptualizing a method for manufacturing a solid electrolyte according to another embodiment of the present invention.

Referring to FIG. 1, the orange oval-shaped area in FIG. 1 shows the composition range of the starting raw materials in the conventionally generally known method of manufacturing basic azirodite solid electrolyte.

On the other hand, the method for producing a solid electrolyte according to the present invention provides a sulfide-based solid electrolyte with the desired oxygen-doped azirodite-based crystal structure by further mixing the doping raw material in the mixing step of the starting raw material to dope oxygen. can do.

At this time, the blue sphere-shaped area in FIG. 1 shows the composition range of the starting raw materials in the method for producing a solid electrolyte according to the present invention.

Hereinafter, a method for producing a sulfide-based solid electrolyte according to another embodiment of the present invention will be described in detail in each step.

First, lithium-containing sulfide, phosphorus-containing compound, chlorine-containing compound and doping raw material are mixed to form a mixture.

The lithium-containing sulfide may be, for example, Li ₂ S, Li ₂ S ₂ or a combination thereof, but is not limited thereto. Specifically, the lithium-containing sulfide may be Li ₂ S.

The phosphorus-containing compound may be, for example, P ₂ S ₅ , P ₂ O ₅ or a combination thereof, but is not limited thereto. Specifically, the phosphorus-containing compound may be P ₂ S ₅ .

The halogen-containing compound may be, for example, LiF, LiCl, LiBr, LiI, or a combination thereof, but is not limited thereto. Specifically, the halogen-containing compound may be LiCl.

The doping raw material may be, for example, Li ₂ SO ₄ , Li ₃ PO ₄ , Li ₄ SiO ₄ , Li ₄ GeO ₄ , Li ₃ BO ₃ , Li ₃ AlO ₃ or a combination thereof, but is not limited thereto. no.

More specifically, the doping raw material may be Li ₂ SO ₄ . By using Li ₂ SO ₄ as a doping raw material, conductivity deterioration can be minimized as lithium is simultaneously doped with oxygen, and overall battery performance can be increased because oxide is doped at a high concentration.

The mixing can be performed by dry mixing or wet mixing.

Preferably, the mixing may be dry mixing. When performed by dry mixing, there is an advantage that no separate solvent is required as with wet mixing.

At this time, dry mixing can be performed using a dry milling method.

Dry milling may be a ball mill, vibrating mill, turbo mill, mechanofusion, disk mill, bead mill, or planetary mill. More specifically, it may be a planetary mill.

The mixing may be performed for 4 to 12 hours, specifically 6 to 10 hours, and more specifically 7 to 9 hours. If mixing is performed for too short a time, problems with undermixing may occur. On the other hand, if mixing is performed for too long, the mixing state may remain the same even if mixing is completed over a certain period of time and further mixing is performed, which may cause problems in process efficiency.

The mixing may be performed at a rotation speed of 100 to 500 rpm, specifically 150 to 450 rpm, and more specifically 200 to 400 rpm. If the rotation speed is too slow, the balls may not be able to enter the inside of the powder body, which may cause problems such as less overall mixing of the powder particles or less atomization of the powder particles due to low energy. On the other hand, if the rotation speed is too fast, the powder may be concentrated in one place, causing less even mixing.

Next, optionally, if necessary, after forming the mixture, a step of compressing the mixture to form pellets may be further included.

At this time, the compression may be performed at a pressure of 100 to 500 Mpa, specifically 150 to 450 Mpa, and more specifically 200 to 400 Mpa. If the pressure is too low, a problem may occur in which interfacial resistance may increase due to insufficient cohesion between powder particles. On the other hand, if the pressure is too high, the bonding between the powder particles has already occurred and the bonding state does not change even if more pressure is applied, which may cause problems in process efficiency. Therefore, forming pellets at an appropriate pressure is desirable in terms of productivity.

Next, the mixture is heat treated to form a sulfide-based solid electrolyte. Of course, when the step of forming pellets is further included, the pellets are heat treated to form a sulfide-based solid electrolyte.

The heat treatment may be performed at 300 to 800°C, specifically 400 to 700°C, and more specifically 500 to 600°C. If the heat treatment temperature is too low, the heat treatment effect may be insignificant, and if the heat treatment temperature is too high, the elements that make up the solid electrolyte may vaporize and the solid electrolyte may be lost.

The heat treatment may be performed in an inert gas atmosphere. More specifically, it may be performed in an argon (Ar) atmosphere.

3. Lithium secondary battery

Another embodiment of the present invention is an anode; cathode; and a solid electrolyte layer positioned between the positive electrode and the negative electrode, wherein at least one of the positive electrode, negative electrode, and solid electrolyte layer includes the solid electrolyte described above.

Since the solid electrolyte is the same as described above, the remaining components will be described in detail below.

The positive electrode may include a current collector and a positive electrode active material layer disposed on the current collector, and the positive electrode active material layer may include a positive electrode active material.

As the positive electrode active material, a compound capable of reversibly intercalating and deintercalating lithium (lithiated intercalation compound) can be used. Specifically, one or more types of complex oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof can be used. As a specific example, a compound represented by any of the following formulas can be used:

Li _a A _1-b B _b D ₂ (wherein 0.90 ≤ a ≤ 1.8 and 0 ≤ b ≤ 0.5); Li _a E _1-b B _b O _2-c D _c (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE _2-b B _b O _4-c D _c (wherein 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a Ni _1-bc Co _b B _c D _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Co _b B _c O _2-α T _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Co _b B _c O _2-α T ₂ (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B _c D _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Mn _b B _c O _2-α T _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B _c O _2-α T ₂ (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _b E _c G _d O ₂ (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li _a Ni _b Co _c Mn _d GeO ₂ (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a CoG _b O ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a MnG _b O ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li _(3-f) J ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); and LiFePO ₄ .

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

Of course, the above compound may have a coating layer on its surface, or a mixture of the above compound and a compound having a coating layer may be used.

The coating layer may include at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. You can. The compounds that make up these coating layers may be amorphous or crystalline. Coating elements included in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. For the coating layer formation process, any coating method may be used as long as these elements can be used in the compound to coat the compound in a manner that does not adversely affect the physical properties of the positive electrode active material (e.g., spray coating, dipping method, etc.). Since this is well-understood by people working in the field, detailed explanation will be omitted.

The positive electrode active material layer may further include a conductive material and/or binder along with the positive electrode active material described above.

The binder serves to adhere the positive electrode active material particles to each other and to the current collector, and representative examples include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, and carboxylated Polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic Teed styrene-butadiene rubber, epoxy resin, nylon, etc. can be used, but are not limited thereto.

The conductive material is used to provide conductivity to the electrode, and in the battery being constructed, any electronically conductive material can be used as long as it does not cause chemical change. Examples include natural graphite, artificial graphite, carbon black, acetylene black, and Ketjen. Carbon-based materials such as black and carbon fiber; Metallic substances such as metal powders such as copper, nickel, aluminum, and silver, or metal fibers; Conductive polymer materials such as polyphenylene derivatives; Alternatively, a conductive material containing a mixture thereof may be used.

Aluminum may be used as the current collector, but is not limited thereto.

The negative electrode includes a current collector and a negative electrode active material layer disposed on the current collector, and the negative electrode active material layer includes a negative electrode active material.

The negative electrode active material includes a material capable of reversibly intercalating/deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

The material capable of reversibly intercalating/deintercalating lithium ions is a carbon material. Any carbon-based anode active material commonly used in lithium ion secondary batteries can be used, and a representative example is crystalline carbon. , amorphous carbon, or a combination of these can be used. Examples of the crystalline carbon include graphite such as amorphous, plate-shaped, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon). Alternatively, hard carbon, mesophase pitch carbide, calcined coke, etc. may be mentioned.

The lithium metal alloy includes lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn. Any alloy of metals of choice may be used.

Materials that can dope and dedope lithium include Si, SiOx (0 < x < 2), Si-Y alloy (Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth An element selected from the group consisting of elements and combinations thereof, but not Si), Sn, SnO ₂ , Sn-Y (where Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth element) and an element selected from the group consisting of a combination thereof, but not Sn), etc., and at least one of these and SiO ₂ may be mixed and used. The element Y includes Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, It may be selected from the group consisting of Se, Te, Po, and combinations thereof.

Examples of the transition metal oxide include vanadium oxide and lithium vanadium oxide.

The anode active material layer also includes a binder and, optionally, may further include a conductive material.

The binder serves to adhere the negative electrode active material particles to each other and to the current collector, and representative examples include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, and carboxylated Polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic Teed styrene-butadiene rubber, epoxy resin, nylon, etc. can be used, but are not limited thereto.

The conductive material is used to provide conductivity to the electrode, and in the battery being constructed, any electronically conductive material can be used as long as it does not cause chemical change. Examples include natural graphite, artificial graphite, carbon black, acetylene black, and Ketjen. Carbon-based materials such as black and carbon fiber; Metallic substances such as metal powders such as copper, nickel, aluminum, and silver, or metal fibers; Conductive polymer materials such as polyphenylene derivatives; Alternatively, a conductive material containing a mixture thereof may be used.

The current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, conductive metal-coated polymer substrate, and combinations thereof.

The negative electrode and positive electrode are manufactured by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and applying this composition to a current collector. Since this electrode manufacturing method is widely known in the field, detailed description will be omitted in this specification. The solvent may be N-methylpyrrolidone, but is not limited thereto.

Depending on the type of lithium secondary battery, a separator may exist between the positive and negative electrodes. Such separators may be polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof, such as polyethylene/polypropylene two-layer separator, polyethylene/polypropylene/polyethylene three-layer separator, polypropylene/polyethylene/poly. Of course, mixed multilayer films such as propylene three-layer separator can be used.

Hereinafter, embodiments of the present invention will be described in more detail through examples. However, the following example is only a preferred example of the present invention, and the present invention is not limited by the following example.

Example 1: Li _6.01 P.S. _4.96 Cl _0.99 O _0.09 Preparation of solid electrolyte

_The reactants Li ₂ S _{, P 2} S _{5 , LiCl} and After quantifying Li ₂ SO ₄ , the mixture was mixed at 300 rpm for about 8 hours using a planetary mill to form a mixture.

Next, a pressure of 300 Mpa was applied to the mixture to form pellets.

Next, the pellet was heat-treated at 550°C in an argon (Ar) atmosphere to prepare a Li _6.01 PS _4.96 Cl _0.99 O _0.09 solid electrolyte.

Example 2: Li _6.03 P.S. _4.98 Cl _0.97 O _0.18 Preparation of solid electrolyte

_The reactants Li ₂ S _, P _{2 S 5 , LiCl} and Li _6.03 PS _4.98 Cl _0.97 O _0.18 solid electrolyte was prepared in the same manner as in Example ₁ , except that Li ₂ SO 4 was quantified.

Example 3: Li _6.05 P.S. _5.00 Cl _0.95 O _0.26 Preparation of solid electrolyte

_The reactants Li ₂ S _{, P 2} S _{5 , LiCl} and Li _6.05 PS _5.00 Cl _0.95 O _0.26 solid electrolyte was prepared in the same manner as in Example 1, except that Li ₂ SO ₄ was quantified.

Example 4: Li _6.11 P.S. _5.06 Cl _0.89 O _0.50 Preparation of solid electrolyte

_The reactants Li ₂ S _{, P 2} S _{5 , LiCl} and Li _6.11 PS _5.06 Cl _0.89 O _0.50 solid electrolyte was prepared in the same manner as in Example 1, except that Li ₂ SO ₄ was quantified.

Example 5: Li _6.25 P.S. _5.19 Cl _0.75 O _1.06 Preparation of solid electrolyte

_The reactants Li ₂ S _{, P 2} S _{5 , LiCl} and Li _6.25 PS _5.19 Cl _0.75 O _1.06 solid electrolyte was prepared in the same manner as in Example 1, except that Li ₂ SO ₄ was quantified.

Example 6: Li _6.43 P.S. _5.36 Cl _0.57 O _1.79 Preparation of solid electrolyte

_The reactants Li ₂ S _{, P 2} S _{5 , LiCl} and A Li _6.43 PS _5.36 Cl _0.57 O _1.79 solid electrolyte was prepared in the same manner as in Example 1, except that Li ₂ SO ₄ was quantified.

Comparative Example 1: Li ₆ P.S. ₅ Preparation of Cl solid electrolyte

Li ₂ S, P ₂ S ₅ and LiCl were mixed at 300 rpm for about 8 hours using a planetary mill to form a mixture.

Next, a pressure of 300 Mpa was applied to the mixture to form pellets.

Next, the pellet was heat-treated at 550°C in an argon (Ar) atmosphere to prepare Li ₆ PS ₅ Cl solid electrolyte.

Table 1 below summarizes the composition and mole ratio between component atoms of the solid electrolytes prepared according to Examples 1 to 6 and Comparative Example 1.

Furtherance [Li]/[P] [S]/[P] [Cl]/[P] [O]/[S] Comparative Example 1 Li ₆ PS ₅ Cl 6 5 One 0 Example 1 Li _6.01 PS _4.96 Cl _0.99 O _0.09 6.01 4.96 0.99 0.02 Example 2 Li _6.03 PS _4.98 Cl _0.97 O _0.18 6.03 4.98 0.97 0.04 Example 3 Li _6.05 PS _5.00 Cl _0.95 O _0.26 6.05 5.00 0.95 0.05 Example 4 Li _6.11 PS _5.06 Cl _0.89 O _0.50 6.11 5.06 0.89 0.10 Example 5 Li _6.25 PS _5.19 Cl _0.75 O _1.06 6.25 5.19 0.75 0.20 Example 6 Li _6.43 PS _5.36 Cl _0.57 O _1.79 6.43 5.36 0.57 0.33

Experimental Example 1: Moisture stability evaluation

An experiment was conducted to evaluate the moisture stability of the solid electrolytes prepared according to Examples 1 to 6 and Comparative Example 1, and the results are shown in Table 2 below. The specific experimental method is as follows.

(1) Evaluation of ionic conductivity before exposure to air

After pulverizing the solid electrolyte, it was manufactured into pellet form under 300 Mpa pressure. Afterwards, a cell was manufactured at a pressure of 700 Mpa using SUS as a working electrode. Afterwards, the impedance was measured by applying a voltage of 10 mV at 25°C.

(2) Evaluation of ionic conductivity after exposure to air

In a dry room with a dew point of about -40°C, 2 g of solid electrolyte in powder form was left for about 12 hours, then it was recovered and the impedance was measured.

(3) Retention rate evaluation

The retention rate was derived by converting the ionic conductivity after air exposure to the ionic conductivity before air exposure derived above into a percentage (%).

Furtherance Before atmospheric exposure
Ion conductivity
(mS/cm) After atmospheric exposure
Ion conductivity
(mS/cm) retention rate
(%) Comparative Example 1 Li ₆ PS ₅ Cl 3.1 1.61 52% Example 1 Li _6.01 PS _4.96 Cl _0.99 O _0.09 2.7 1.9 70% Example 2 Li _6.03 PS _4.98 Cl _0.97 O _0.18 2.5 1.8 72% Example 3 Li _6.05 PS _5.00 Cl _0.95 O _0.26 2.1 1.7 81% Example 4 Li _6.11 PS _5.06 Cl _0.89 O _0.50 1.5 1.1 73% Example 5 Li _6.25 PS _5.19 Cl _0.75 O _1.06 0.8 0.5 63% Example 6 Li _6.43 PS _5.36 Cl _0.57 O _1.79 0.3 0.2 67%

As can be seen from Table 2, it was confirmed that the ionic conductivity before exposure to air decreased as the oxygen doping amount increased compared to Li ₆ PS ₅ Cl, which is the basic azyrodite structure. This can be interpreted as the fact that as the doping amount of oxygen increases, the crystal structure of ajirodite is greatly deformed, making lithium ion movement less smooth, and ultimately reducing ionic conductivity.

However, looking at the retention rate, the oxygen doping amount (proportional to the x value), [Li]/[P], [S]/[P], [Cl]/[P] and [O]/[S] values are appropriate. It was confirmed that the well-adjusted solid electrolytes according to Examples 1 to 6 had significantly superior retention rates compared to Comparative Example 1, which had a basic azyrodite structure. In particular, it was confirmed that all solid electrolytes according to Examples 1 to 6 had a retention rate of 60% or more.

In particular, looking at the ionic conductivity after atmospheric exposure, the oxygen doping amount (proportional to the x value), [Li]/[P], [S]/[P], [Cl]/[P], and [O]/[S ] It was confirmed that the solid electrolytes according to Examples 1 to 3, whose values were more appropriately adjusted, not only had superior retention rates compared to Comparative Example 1, but also excellent ionic conductivity after exposure to air. This means that Comparative Example 1 had high ionic conductivity before exposure to the air, but when exposed to the air, the ionic conductivity was significantly lowered due to a side reaction with moisture. On the other hand, in Examples 1 to 3, the ionic conductivity reduction rate was relatively low due to high moisture stability. It can be interpreted as a result that occurred.

Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and can be implemented with various modifications within the scope of the patent claims, detailed description of the invention, and the accompanying drawings, and this can also be done in various ways. It is natural that it falls within the scope of the invention.

Accordingly, the actual scope of rights of the present invention will be defined by the attached patent claims and their equivalents.

Claims (8)

A sulfide-based solid electrolyte having an argyrodite-based crystal structure, at least a portion of the crystal structure being doped with oxygen, and represented by the following formula (1):
[Formula 1]
Li _(6-5x) P _(1-x) S _(4.95-4x) A _1-2x O _4x+0.05
In Formula 1, A is F, Cl, Br, I, or a combination thereof, and 0 < x < 0.5.
According to paragraph 1,
The solid electrolyte is a sulfide-based solid electrolyte that satisfies the following formula 1:
<Equation 1>
6.005 ≤ [Li]/[P] ≤ 6.5
In Equation 1, [Li] and [P] mean at% of Li and P, respectively.
According to paragraph 1,
The solid electrolyte is a sulfide-based solid electrolyte that satisfies the following equation 2:
<Equation 2>
4.9 ≤ [S]/[P] ≤ 5.4
In Equation 2 above, [S] and [P] mean at% of S and P, respectively.
According to paragraph 1,
The solid electrolyte is a sulfide-based solid electrolyte that satisfies the following formula 3:
<Equation 3>
0.5 ≤ [A]/[P] ≤ 0.995
In Equation 3 above, [A] and [P] mean at% of A and P, respectively.
According to paragraph 1,
The solid electrolyte is a sulfide-based solid electrolyte that satisfies the following equation 4:
<Equation 4>
0.01 ≤ [O]/[S] ≤ 0.4
In Equation 4 above, [O] and [S] mean at% of O and S, respectively.
According to paragraph 1,
When measuring an X-ray diffraction (XRD) pattern, the solid electrolyte
A sulfide-based solid electrolyte in which impurity peaks do not appear at the positions of 16.0˚ < 2θ < 17.5˚ and 18.5˚ < 2θ < 24.5˚.
According to paragraph 1,
A sulfide-based solid electrolyte in which the ionic conductivity of the solid electrolyte after exposure to the atmosphere is maintained in the range of 60 to 83% of the ionic conductivity before exposure to the atmosphere.
anode; cathode; And a solid electrolyte layer located between the anode and the cathode,
A lithium secondary battery, wherein at least one of the positive electrode, negative electrode, and solid electrolyte layer includes the solid electrolyte according to claim 1.