KR102094991B1 - lithium secondary battery - Google Patents

Abstract

anode; cathode; And a sulfide-based solid electrolyte interposed between the positive electrode and the negative electrode, wherein the positive electrode includes positive electrode active material particles formed on the surface with a coating film containing oxides including lithium (Li) and zirconium (Zr), and the coating film. A lithium secondary battery having an average secondary particle diameter (D50) of 5 μm or less is provided.

Description

Lithium secondary battery

It relates to a lithium secondary battery.

With the recent development of electronic technology, miniaturization, light weight and light weight of portable electronic devices, etc. are dazzling. In addition, demands for high performance and high reliability for power cells supporting such electronic devices are also increasing. As a battery technology capable of meeting these demands, a solid-state lithium secondary battery using a solid battery instead of an electrolyte solution is excellent in terms of liquid leakage and safety, and is highly reliable. In addition, since it is a battery using lithium, it can be charged and discharged at a high voltage and a high energy density, and thus, it is attracting attention in practicality.

The solid-state lithium secondary battery basically includes a positive electrode, a solid electrolyte, and a negative electrode. As the solid electrolyte, a sulfide-based solid electrolyte is used.

In the case of using a sulfide-based solid electrolyte, a reaction occurs at the interface between the positive electrode active material and the solid electrolyte during charging, thereby generating a resistance component at the interface, whereby the resistance when lithium ions move between the positive electrode active material and the solid electrolyte (hereinafter, “ Interface resistance ”). Since the lithium ion conductivity is lowered by the increase in the interface resistance, the output of the lithium secondary battery is lowered. Therefore, there is a high need to develop a method for reducing the interface resistance between the positive electrode active material and the solid electrolyte.

One aspect is to provide a lithium secondary battery with improved cycle characteristics, capacity and rate characteristics.

According to one aspect,

anode; cathode; And a sulfide-based solid electrolyte interposed between the positive electrode and the negative electrode,

The positive electrode includes positive electrode active material particles on which a coating film containing an oxide containing lithium (Li) and zirconium (Zr) is formed on the surface,

A lithium secondary battery having an average secondary particle diameter (D50) of 5 μm or less is provided in the positive electrode active material particles on which the coating film is formed.

The lithium secondary battery according to an embodiment of the present invention can increase the specific surface area of the positive electrode active material and reduce the effect of the resistance component, thereby increasing the conductivity of lithium ions, reducing overvoltage during charging and discharging, and improving rate and cycle characteristics. Can be realized.

1 is a view schematically showing the configuration of a lithium secondary battery according to an embodiment.
2 shows the structure of a lithium secondary battery according to an embodiment.

Hereinafter, a lithium secondary battery according to an exemplary embodiment will be described in more detail.

Explain.

Anode containing cathode active material particles; cathode; And a sulfide-based solid electrolyte interposed between the positive electrode and the negative electrode, wherein the positive electrode active material particle is coated with a coating film containing oxides including lithium (Li) and zirconium (Zr) on its surface, and the coating film is formed. A lithium secondary battery having an average secondary particle diameter (D50) of positive electrode active material particles of 5 μm or less is provided.

 [Formula 1]

aLi ₂ O-ZrO ₂

In Formula 1, 0.1≤a≤2.0.

The compound of Formula 1 is a complex oxide of Li ₂ O and ZrO ₂ .

When positive electrode active material particles having an average particle diameter of 5 μm or less are adopted as positive electrode active material particles in the production of a positive electrode for a lithium secondary battery, the specific surface area of the positive electrode active material is increased, thereby minimizing the effect of the lithium resistance layer to reduce interfacial resistance.

However, as the area of the interface is increased by using the positive electrode active material particles having a small particle size, the charge and discharge reaction of the lithium secondary battery is promoted and the generation of the interface resistance layer is also promoted. As a result, the interface resistance is significantly increased by repeated charge and discharge, and battery characteristics Can degrade.

However, in the lithium secondary battery according to an embodiment, when a coating film including the compound represented by Chemical Formula 1 is formed on the surface of the positive electrode active material, reaction at the interface between the positive electrode active material and the solid electrolyte can be significantly suppressed and the interface resistance layer By being able to effectively suppress the formation of, it is possible to fully utilize the advantage of using a positive electrode active material having a small particle size.

As a result, the lithium secondary battery can not only improve the interfacial resistance during charging and discharging, thereby improving the discharge capacity, but also significantly improve the rate and cycle characteristics.

In Formula 1, when a is within the above range, a lithium secondary battery having a positive electrode using such a positive electrode active material not only has improved cycle characteristics and impedance characteristics, but also has an increased initial discharge capacity and excellent lithium ion conductivity.

According to one embodiment, in Formula 1, a is 1.

The compound represented by Chemical Formula 1 may be obtained through a process of heating Li ₂ O and ZrO ₂ to a temperature above which they are dissolved and dissolving and mixing at a predetermined ratio, maintaining a predetermined time, and rapidly cooling.

According to one embodiment, the average particle diameter of the positive electrode active material coated with an oxide containing lithium (Li) and zirconium (Zr) is 5 μm or less, specifically 0.1 to 5 μm.

The average particle diameter (D10) of the positive electrode active material is 2.0 to 3.5 μm, for example, 2.5 to 3.0 μm. In addition, the particle diameter (D50) of the positive electrode active material is 3.0 to 5.0 μm, for example, 3.3 to 4.5 μm, and the particle diameter (D90) of the positive electrode active material is 3.5 to 5.0 μm, for example, 4.5 to 5.0 μm.

The terms “D50”, “D10”, and “D90” refer to particle diameters representing 50% by volume, 10% by volume, and 90% by volume, respectively, in the cumulative distribution curve.

According to one embodiment, the sulfide-based solid electrolyte includes lithium sulfide (Li ₂ S) and phosphorus pentasulfide (P ₂ S ₅ ).

Hereinafter, a method of forming a coating film including an oxide including lithium (Li) and zirconium (Zr) on the surface of the positive electrode active material will be described.

First, the positive electrode active material is obtained by collecting particles having an average particle diameter of 5 μm or less into a fine powder of the positive electrode active material.

An automatic sieve machine can be used to obtain the positive electrode active material fine powder.

Mixing a lithium alkoxide and zirconium alkoxide in a solvent to prepare a stirred solution of the alcohol _{aLi 2 O-ZrO 2 (aLi} 2 O-ZrO 2 coating the coating liquid).

As the solvent, alcohols such as methanol and ethanol are used. It is also possible to use water as a gelling accelerator and add acetoacetate as a gelling inhibitor.

Lithium alkoxide can be obtained, for example, by reacting organic lithium with alcohol.

The time for stirring and mixing the lithium alkoxide and zirconium alkoxide is not particularly limited, but may be, for example, about 30 minutes. In addition, compounds having a structure of CH ₃ -CO-CH ₂ -CO-OR such as ethyl acetoacetate (R is an alkyl group of C1-C10, for example, methyl, ethyl, propyl, etc.) are in the structure. Since the two carbonyl groups have the effect of stabilizing unstable metals by acting as a chelating agent, they act as stabilizers for zirconium alkoxides.

Next, the prepared coating liquid for coating aLi ₂ O-ZrO ₂ is mixed with the above-mentioned positive electrode active material fine powder, and the mixed solution is heated while stirring to evaporate the solvent such as alcohol to be evaporated to dryness. At this time, ultrasonic waves are irradiated to the mixed solution. Thereby, the precursor of aLi ₂ O-ZrO ₂ can be uniformly supported on the surface of the particles of the positive electrode active material micropowder.

The drying is 30 to 80 ° C, for example about 40 ° C. When performing the drying process, a vacuum pump or a rotary evaporator can be used.

In addition, the precursor of aLi ₂ O-ZrO ₂ supported on the particle surface of the positive electrode active material is heat-treated at high temperature. At this time, the heat treatment temperature is set to 350 ° C to 750 ° C, for example, about 350 ° C.

The heat treatment time is not particularly limited, but may be, for example, about 1 to 3 hours, specifically about 2 hours.

The heat treatment is performed under an oxygen gas atmosphere. When oxygen gas is supplied, the reduction of nickel in the anode material including nickel can be suppressed to maintain the capacity.

By going through the above-described manufacturing process, it is possible to obtain a positive electrode active material on which aLi ₂ O-ZrO ₂ coating film is formed.

The content of Li ₂ O-ZrO ₂ in the coating film is 0.01 to 2 mol%, for example, 0.01 to 0.95 mol%, based on the total weight of the positive electrode active material particles and Li ₂ O-ZrO ₂ . When the Li ₂ O-ZrO ₂ content is within the above range, high initial discharge capacity and excellent cycle characteristics can be obtained.

The obtained coated positive electrode active material micropowder is mixed with a solid electrolyte and a conductive agent to obtain a positive electrode composition, which is applied to obtain a positive electrode.

The conductive agent may include carbon black, graphite, acetylene black, ketjen black, carbon fiber, and the like.

The positive electrode composition may further include a binder or the like.

Examples of the binder include polytetrafluoroethylene, polyvinylidene fluoride, SBS (styrene-butadiene block copolymer), NBR (nitrile rubber), CR (chloroprene rubber), and partial hydrides thereof, or complete hydrides , Copolymer of polyacrylic acid ester, VDF-HFP (vinylidene fluoride-hexafluoropropylene copolymer), and their carboxylic acid modified products, CM (polyethylene chloride), polymethacrylic acid ester, polyvinyl Styrene thermoplastic elastomers such as alcohol, ethylene-vinyl alcohol copolymer, polyimide, polyamide, polyamideimide, SEBS (styrene-ethylene-butadiene-styrene block copolymer), styrene-styrene-butadiene-styrene block copolymer, etc. , SBR (styrene-butadiene rubber), BR (butadiene rubber), NR (natural rubber), IR (isoprene rubber), EPDM (ethylene-propylene-diene terpolymer), and partial hydrides thereof, humps There is a completely hydride can be exemplified. In addition, polystyrene, polyolefin (polyolefin), olefin-based thermoplastic elastomer, polycycloolefin, silicone resin, etc. may be exemplified, but is not limited to them, and any non-polar resin that can be used as a binder in the art can be used. Do.

Specifically, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or the like can be used as the binder. In addition, all of the materials commonly used in manufacturing a cathode for a lithium secondary battery, such as fillers, dispersants, and ionic electric conductors, can be added to the cathode composition.

The negative electrode can be manufactured according to the same method as the positive electrode, except that the negative electrode active material is used instead of the positive electrode active material.

The negative electrode active material is not limited as long as it is capable of alloying with lithium or a material capable of reversibly storing and releasing lithium, for example, metals such as lithium, indium, tin, aluminum, silicon, and these alloys, or Li4 / Transition metal oxide such as 3Ti5 / 3O4, SnO, artificial graphite, graphite carbon fiber, resin-fired carbon, pyrolysis vapor-grown carbon, coke, mesocarbon microbeads (MCMB), perfuryl alcohol resin fired carbon, polyacene, pitch system And carbon materials such as carbon fiber, vapor-grown carbon fiber, and natural graphite.

A lithium secondary battery is manufactured by stacking the positive electrode, the solid electrolyte, and the negative electrode obtained according to the above process.

The solid electrolyte uses, for example, a sulfide-based solid electrolyte including lithium sulfide (Li ₂ S) and phosphorus pentasulfide (P ₂ S ₅ ). The solid electrolyte may further include sulfides such as SiS ₂ , GeS ₂ and B ₂ S _{3 in} addition to lithium sulfide (Li ₂ S) and phosphorus pentasulfide (P ₂ S ₅ ).

The sulfide-based solid electrolyte including lithium sulfide (Li ₂ S) and phosphorus pentasulfide (P ₂ S ₅ ) is a sulfide containing lithium sulfide (Li ₂ S) and phosphorus pentasulfide (P ₂ S ₅ ). ₂ S) and phosphorus pentasulfide (P ₂ S ₅ ) It can be obtained by heating to a range above the dissolution temperature, dissolving and mixing both at a predetermined ratio, and keeping the mixture for a predetermined time, followed by rapid cooling. Here, the mixing ratio of lithium sulfide (Li ₂ S) and phosphorous pentasulfide (P ₂ S ₅ ) is a molar ratio of 50:50 to 80:20, for example, 60:40 to 75:25.

Or a sulfide-based solid electrolyte containing a sulfide, lithium (Li ₂ S) and ohhwang tetroxide in (P ₂ S ₅₎ are sulfides including sulfide, lithium (Li ₂ S) and ohhwang tetroxide in (P ₂ S ₅₎ is a mechanical milling method Can be obtained by treatment.

<Configuration of lithium secondary battery>

First, the configuration of a solid-state lithium secondary battery that is one of the lithium secondary batteries according to an embodiment will be described with reference to FIG. 1.

The solid-state lithium secondary battery includes a positive electrode 11, a negative electrode 13, and a solid electrolyte interposed between the positive electrode 11 and the negative electrode 13. In addition, the positive electrode 11 is composed of a coated positive electrode active material and a solid electrolyte, and the positive electrode active material having a small particle diameter has a large interface area in contact with more solid electrolyte.

[Battery material]

(Material of positive electrode active material)

The positive electrode active material is not limited as long as it is a material capable of reversibly storing and releasing lithium ions, for example, lithium cobaltate (LCO), lithium nickel oxide, lithium nickel cobaltate, lithium nickel cobalt aluminum, and nickel cobalt manganese Lithium acid, lithium manganate, lithium iron phosphate, nickel sulfide, copper sulfide, sulfur, iron oxide, vanadium oxide, and the like can be exemplified. These positive electrode active materials may be used alone or in combination of two or more.

For example, the positive electrode active material is a lithium-containing metal oxide, and can be used without limitation as long as it is commonly used in the art. For example, cobalt, manganese, nickel, and metals selected from a combination thereof and one or more of a complex oxide of lithium may be used, and specific examples thereof include Li _a A _{1 - b} B _b D ₂ (above In the formula, 0.90 ≤ a ≤ 1, and 0 ≤ b ≤ 0.5); Li _a E _{1 - b} B _b O _{2 - c} D _c (where 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE _{2 - b} B _b O _{4 -c} D _c (where 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a Ni _{1 -b- c} Co _b B _c D _α (where 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α ≤ 2); Li _a Ni _{1 -b - c} Co _b B _c O _{2 -α} F _α (wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _{1 -b - c} Co _b B _c O _{2 -α} F ₂ (where 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _{1 -b- c} Mn _b B _c D _α (where 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α ≤ 2); Li _a Ni _{1 -b- c} Mn _b B _c O _{2 -α} F _α (where 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _{1 -b- c} Mn _b B _c O _{2 -α} F ₂ (where 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _b E _c G _d O ₂ (In the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1.); Li _a Ni _b Co _c Mn _d GeO ₂ (where 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (where 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li _a CoG _b O ₂ (where 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li _a MnG _b O ₂ (in the above formula, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (where 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); Compounds represented by any one of the formulas of LiFePO ₄ can be used:

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

For example, LiCoO ₂ , LiMn _x O _2x (x = 1 or 2), LiNi _{1 -x} Mn _x O _2x (0 <x <1), LiNi _{1 -xy} Co _x Mn _y O ₂ (0≤x≤ 0.5, 0≤y≤0.5), FePO _4, and the like.

Of course, one having a coating layer on the surface of the compound may also be used, or a compound having a coating layer and the compound may be mixed and used. The coating layer may include a coating element oxide, a hydroxide, a coating element oxyhydroxide, a coating element oxycarbonate, or a coating element hydroxycarbonate coating element compound. The compounds constituting these coating layers may be amorphous or crystalline. As a coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof can be used. In the coating layer forming process, any coating method may be used as long as the compound can be coated with a method that does not adversely affect the physical properties of the positive electrode active material using these elements (for example, spray coating, immersion method, etc.). Since it can be well understood by people in the field, detailed description will be omitted.

The positive electrode active material may be a lithium salt of a transition metal oxide having a layered rock salt type structure, among the positive electrode active materials exemplified above. In the present specification, “layered” refers to a thin sheet-like shape, and “rock salt type” is a sodium chloride type structure that is one type of crystal structure, and the face-centered cubic lattices formed by cations and anions, respectively, are unit grids. It means a structure that is only 1/2 of the corner. As a lithium salt of a transition metal oxide having such a layered rock salt structure, for example, Li _1-xyz Ni _x Co _y Al _z O ₂ (NCA) (0 <x <1, 0 <y <1, 0 <z <1, x + y + z = 1) or Li _1-xyz Ni _x Co _y Mn _z O ₂ (NCM) (0 <x <1, 0 <y <1, 0 <z <1, x + y + The lithium salt of the ternary transition metal oxide represented by z = 1) can be illustrated.

(Material of cathode)

The negative electrode active material may be any material that can be used as a negative electrode active material in a lithium secondary battery in the art.

The negative electrode active material may include, for example, one or more selected from the group consisting of lithium metal, a metal alloyable with lithium, a transition metal oxide, a non-transition metal oxide, and a carbon-based material.

For example, the metal alloyable with lithium is Si, Sn, Al, Ge, Pb, Bi, Sb Si-Y alloy (where Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth) Element or a combination thereof, not Si), Sn-Y alloy (where Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element, or a combination element thereof, not Sn) ). The elements Y are 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, Se, Te, Po, or a combination thereof.

For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, or the like.

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

The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be amorphous, plate-like, flake-like, graphite such as spherical or fibrous natural graphite or artificial graphite, and the amorphous carbon is soft carbon (low-temperature calcined carbon) or hard carbon (hard) carbon), mesophase pitch carbide, calcined coke, and the like.

Particularly, examples of the negative electrode active material include graphite-based active materials, for example, artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, and the like. Further, as the negative electrode active material, tin (Sn) or silicon (Si) materials can be used instead of graphite.

(Material of solid electrolyte)

The solid electrolyte includes a sulfide-based solid electrolyte, specifically lithium sulfide, and is synthesized from at least one compound selected from the group consisting of silicon sulfide, phosphorus sulfide and boron sulfide as the second component, for example Li ₂ SP ₂ S ₅ can be.

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

Specifically, the solid electrolyte is _{Li 2 SP 2 S 5, Li} 2 -SiS 2, Li 3 .25 P 0 .25 Ge 0 .76 S 4, Li 4 - x Ge 1 -x P x S 4 (0 <x < 1), Li ₇ P ₃ S ₁₁ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ Glass and the like. Among them, Li ₂ SP ₂ S ₅ is used.

The lithium secondary battery includes all of the lithium secondary battery, a lithium ion secondary battery, and a solid-state lithium secondary battery.

A plurality of lithium secondary batteries are stacked to form a battery pack, and such a battery pack can be used in all devices requiring high capacity and high output. For example, it can be used for laptops, smartphones, electric vehicles, and the like.

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

Example  One

The positive electrode active material _{LiNi 1/3 Mn 1/3} Co 1/3 O 2 (NCM) , the automated external particles of less than about 5㎛ to (auto sieving machine) (D10: 2.5㎛, D50: 3.3㎛, D90: 4.5㎛ ) Were collected to obtain a fine powder of positive electrode active material. Lithium methoxide, zirconium propoxide, ethanol and ethyl acetoacetate, stirred and mixed for 30 minutes in an alcohol solution of aLi ₂ O-ZrO ₂ (a = 1) (aLi ₂ O-ZrO ₂ coating) Solution). Here, the content of lithium methoxide and zirconium propoxide was adjusted so that the content of aLi ₂ O-ZrO ₂ (a = 1) coated on the surface of the positive electrode active material was 0.5 mol%.

Next, the coating solution for coating aLi ₂ O-ZrO ₂ was mixed with the above-mentioned positive electrode active material fine powder, and the mixture was heated to about 40 ° C. while stirring to evaporate the solvent such as alcohol to be evaporated to dryness. At this time, ultrasonic waves were irradiated to the mixed solution.

By performing the above process, a precursor of aLi ₂ O-ZrO ₂ could be supported on the particle surface of the positive electrode active material micropowder.

In addition, the precursor of aLi ₂ O-ZrO ₂ (a = 1) supported on the particle surface of the positive electrode active material was heat-treated under an oxygen atmosphere at about 350 ° C. for 1 hour. It is a precursor of _{aLi 2 O-ZrO 2 (a} = 1) existing in the positive electrode active material in the upper heat treatment was changed to _{aLi 2 O-ZrO 2 (a} = 1).

According to the above-described manufacturing process, it is possible to obtain a positive electrode active material coated on the surface of aLi ₂ O-ZrO ₂ .

Subsequently, the powder obtained by mixing the obtained positive electrode active material micropowder and the solid electrolyte 80:20 molar ratio of lithium sulfide (Li ₂ S) -phosphorus sulfide (P ₂ S ₅ ) and carbon as a conductive agent in a hand press Pressed at a pressure of 4.5 ton / cm 2 was used to obtain a pellet-shaped positive electrode compact. The obtained positive electrode compact body 21, the solid electrolyte compact body 22, and the negative electrode compact body 23 were stacked to produce a solid-state lithium secondary battery 20 in FIG.

The solid electrolyte compact was obtained by performing mechanical milling of Li2S-P2S5 (80-20 mol%). In addition, an indium thin film (thickness: about 0.05 mm) was used as the negative electrode compact.

<Comparative Example 1>

The positive electrode active material _{LiNi 1/3 Mn 1/3} Co 1/3 O 2 , the automated external (auto mathine sieving) of the particles of less than about 5㎛ gather (D10: 4.5㎛ 2.5㎛, D50: : 3.3㎛, D90) It was obtained as a positive electrode active material fine powder.

The positive electrode active material fine powder, a powder mixed with 80:20 molar ratio of lithium sulfide (Li ₂ S) -phosphorus sulphide (P ₂ S ₅ ) as a solid electrolyte and carbon, which is a conductive agent, is caused by hand pressing at 4.5ton / cm 2 It was press-pressed to obtain a pellet-shaped anode compact. The obtained positive electrode compact body 21, the solid electrolyte compact body 22, and the negative electrode compact body 23 were stacked to produce a solid-state lithium secondary battery 20 in FIG.

The solid electrolyte compact was obtained by performing mechanical milling of Li2S-P2S5 (80-20 mol%). In addition, an indium thin film (thickness: about 0.05 mm) was used as the negative electrode compact.

<Comparative Example 2>

The positive electrode active material _{LiNi 1/3 Mn 1/3} Co 1/3 O 2 , the automated external (auto mathine sieving) of the particles of less than about 5㎛ gather (D10: 9.1㎛ 4.6㎛, D50: : 6.4㎛, D90) It was obtained as a positive electrode active material fine powder.

The positive electrode active material fine powder, a powder mixed with 80:20 molar ratio of lithium sulfide (Li ₂ S) -phosphorus sulphide (P ₂ S ₅ ) as a solid electrolyte and carbon, which is a conductive agent, is caused by hand pressing at 4.5ton / cm 2 It was press-pressed to obtain a pellet-shaped anode compact.

The obtained positive electrode compact body 21, the solid electrolyte compact body 22, and the negative electrode compact body 23 were stacked to produce a solid-state lithium secondary battery 20 in FIG.

The solid electrolyte compact was obtained by performing mechanical milling of Li ₂ SP ₂ S ₅ (80-20 mol%). In addition, an indium thin film (thickness: about 0.05 mm) was used as the negative electrode compact.

<Comparative Example 3>

Particle diameter (D10) of the positive electrode active material particles as a positive electrode active material is 4.6㎛, the average particle diameter (D50) of 6.4㎛, particle diameter (D90) is 9.1㎛ cathode active material _{LiNi 1/3 Mn 1/3} Co 1/3 O 2 with A lithium secondary battery was manufactured in the same manner as in Example 1, except for the above.

Evaluation example  1: battery characteristics

After charging the lithium secondary battery according to Example 1 and Comparative Examples 1-3 at 25 ° C., with a constant current of 0.05 C, until the upper limit voltage of 4.3 V is measured, the initial discharge capacity is measured, and the discharge end voltage is 2.5 V. 0.1 C discharge was performed until it reached. Subsequently, 20 cycles of charging and discharging were repeated in the same current and voltage section. The capacity retention of the initial capacity after 20 cycles was measured to evaluate the cycle characteristics of the lithium secondary battery.

Separately, the lithium secondary battery according to Example 1 and Comparative Example 1-3 was charged at 25 ° C. with a constant current of 1 C until the upper limit voltage of 4.3 V was measured, and the initial discharge capacity was measured, and the discharge end voltage was 2.5. 0.1 C discharge was performed until V was reached.

Rate characteristics were evaluated by measuring the ratio of the discharge capacity at 1C to the discharge capacity at 0.05C after one cycle.

The results of evaluation of the battery characteristics are shown in Table 1 below.

division Anode composition Discharge capacity
(mAh / g) Rate characteristic (%)
(1C rate / 0.05
C rate) Cycle characteristics (%)
(Capacity after 20 cycles
Retention rate) Example 1 Small particle positive electrode active material + aLi ₂ O-ZrO ₂ coating film 114 58 80 Comparative Example 1 Small particle positive electrode active material 101 36 - Comparative Example 2 Large-diameter positive electrode active material 94 23 74 Comparative Example 3 Large-diameter positive electrode active material + coating film 110 23 -

Referring to Table 1, the lithium secondary battery of Example 1 had excellent discharge capacity and rate characteristics as well as excellent cycle characteristics compared to those of Comparative Examples 1-3.

Evaluation example  2: Impedance characteristics

The lithium secondary battery according to Example 1 and Comparative Examples 1-3 was charged at 25 ° C., at a constant current of 0.05 C, until the upper limit voltage of 4.3 V was measured, and after measuring the initial discharge capacity, the discharge end voltage was 2.5 V. Until this, 0.1 C discharge was performed. Subsequently, 100 cycles of charging and discharging were repeated in the same current and voltage section. The impedances after 1 cycle repeated and after 100 cycles repeated were measured and are shown in Table 2 below.

The impedance was measured by the alternating current impedance method after the initial charging and after 100 cycles.

Anode composition Average particle diameter of positive electrode active material (D50) (㎛) Impedance after 1st cycle
(Ω) Example 1 Small particle positive electrode active material + aLi ₂ O-ZrO ₂ Coating film 3.3 89 Comparative Example 1 Small particle positive electrode active material 3.3 181 Comparative Example 2 Large-diameter positive electrode active material 6.4 Comparative Example 3 Large-diameter positive electrode active material + coating film 6.4 190

Referring to Table 2, in the case of Comparative Example 1 using a small-diameter positive electrode active material, the impedance was somewhat smaller than that of Comparative Example 2-3, but the impedance was larger after 100 cycles.

On the other hand, in Example 1, aLi ₂ O-ZrO ₂ was applied to the surface of the small-diameter positive electrode active material. It was found that after forming the coating film, the impedance after the first cycle and 100 cycles was significantly reduced compared to the case of Comparative Examples 1-3, thereby improving lithium conductivity.

Above, exemplary embodiments of one aspect have been described in detail with reference to the accompanying drawings, but one aspect is not limited to the disclosed embodiments. It is clear that a person having ordinary knowledge in the field of the technology is within the scope of the technical spirit described in the claims, and various modifications can be derived in the modified examples, and these are also naturally disclosed. It belongs to the technical scope of the inventive concept. For example, in the embodiment of the technology, although the solid electrolyte is described as being included in the positive electrode and the negative electrode, even if the negative electrode does not contain the solid electrolyte, the effect of the invention can be achieved.

11, 21: anode 12, 22: electrolyte
13, 23: cathode

Claims (14)

anode; cathode; And a sulfide-based solid electrolyte interposed between the positive electrode and the negative electrode,
The positive electrode includes positive electrode active material particles on which a coating film containing an oxide containing lithium (Li) and zirconium (Zr) is formed on the surface,
The average secondary particle diameter (D50) of the positive electrode active material particles on which the coating film is formed is 5 μm or less, and the oxide including lithium (Li) and zirconium (Zr) is a compound represented by Formula 1 below, and the sulfide-based solid electrolyte is sulfide Lithium (Li ₂ S) and phosphorus pentasulfide (P ₂ S ₅ ), the content of the compound represented by Formula 1 is 0.01 to 2 mol% based on the total weight of the positive electrode active material particles and the compound represented by Formula 1 , The lithium secondary battery having a particle diameter (D10) of 2.0 to 3.5 μm, an average particle diameter (D50) of 3.0 to 5.0 μm, and a particle diameter (D90) of 3.5 to 5.0 μm of the positive electrode active material particles:
[Formula 1]
aLi ₂ O-ZrO ₂
In Formula 1, 0.1≤a≤2.0. delete According to claim 1,
In Formula 1, a is a lithium secondary battery. According to claim 1,
The compound represented by Chemical Formula 1 is Li ₂ O-ZrO ₂ , and the Li ₂ O-ZrO ₂ content is 0.01 to 2 mol% of the lithium secondary battery based on the total weight of the positive electrode active material particles and Li ₂ O-ZrO ₂ . According to claim 1,
The compound represented by Chemical Formula 1 is Li ₂ O-ZrO ₂ , and the Li ₂ O-ZrO ₂ content is 0.01 to 0.95 mol% of lithium secondary battery based on the total weight of the positive electrode active material particles and Li ₂ O-ZrO ₂ . According to claim 1,
The positive electrode active material is Li _1-xyz Ni _x Co _y Al _z O ₂ (NCA) (0 <x <1, 0 <y <1, 0 <z <1, x + y + z = 1) or Li _1- Lithium secondary battery with _xyz Ni _x Co _y Mn _z O ₂ (NCM) (0 <x <1, 0 <y <1, 0 <z <1, x + y + z = 1). delete According to claim 1,
The lithium secondary battery having a mixing ratio of lithium sulfide (Li ₂ S) and phosphorus pentasulfide (P ₂ S ₅ ) is 50:50 to 80:20 molar ratio. delete According to claim 1,
The lithium secondary battery having a particle diameter (D10) of 2.5 μm, an average particle diameter (D50) of 3.3 μm, and a particle diameter (D90) of 4.5 μm of the positive electrode active material particles. The lithium secondary battery according to claim 1, wherein an average secondary particle diameter (D50) of the positive electrode active material particles on which the coating film is formed is 0.1 to 5 μm. The lithium secondary battery according to claim 1, wherein the positive electrode active material particles have a particle diameter (D10) of 2.5 to 3.0 μm, an average particle diameter (D50) of 3.3 to 4.5 μm, and a particle diameter (D90) of 4.5 to 5.0 μm. The method of claim 1, wherein the compound of Formula 1 is Li ₂ O-ZrO ₂ , the Li ₂ O-ZrO ₂ content is 0.01 to 2 mol% relative to the total weight of the positive electrode active material particles and Li ₂ O-ZrO ₂ , The positive electrode active material particles are Li _1-xyz Ni _x Co _y Al _z O ₂ (NCA) (0 <x <1, 0 <y <1, 0 <z <1, x + y + z = 1) or Li _{1 A} lithium secondary battery having _-xyz Ni _x Co _y Mn _z O ₂ (NCM) (0 <x <1, 0 <y <1, 0 <z <1, x + y + z = 1). The lithium secondary battery according to claim 1, wherein the positive electrode active material has a layered rock salt structure.

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