KR102220906B1 - Composite cathode active material, preparation method thereof, and cathode and lithium battery containing the material - Google Patents

Abstract

A core capable of storing and discharging lithium; And a coating layer formed on at least a portion of the core, wherein the coating layer includes a lithium metal oxide, which is an inert lithium ion conductor, and the metal of the lithium metal oxide has an atomic weight of 27 or more and is in the group consisting of groups 3 to 14 of the periodic table. A composite positive electrode active material, which is one selected element, a method of manufacturing the same, and a positive electrode and lithium battery employing the same are presented.

Description

Composite cathode active material, preparation method thereof, and cathode and lithium battery containing the material

It relates to a composite positive electrode active material, a method of manufacturing the same, and a positive electrode and lithium battery employing the same.

In order to meet the miniaturization and high performance of various devices, high energy density in addition to miniaturization and weight reduction of lithium batteries is becoming important. In other words, high voltage and high capacity lithium batteries are becoming more important.

In order to implement a lithium battery suitable for the above use, high voltage and high capacity positive electrode active materials are being studied.

The conventional high voltage and high capacity positive electrode active material causes side reactions with the electrolyte during the charging and discharging process, and by-products such as transition metals and gases eluted from the positive electrode active material are generated. The performance of the battery is deteriorated by the side reaction of the cathode active material and by-products generated from the cathode active material.

Therefore, there is a need for a method capable of preventing deterioration in performance of a battery including a high voltage and high capacity positive electrode active material.

One aspect is to provide a new composite cathode active material capable of preventing deterioration of battery performance under high temperature and high voltage.

Another aspect is to provide a positive electrode including the composite positive electrode active material.

Another aspect is to provide a lithium battery employing the positive electrode.

Another aspect is to provide a method of manufacturing the composite positive electrode active material.

According to one side

A core capable of storing and discharging lithium; And

It includes a coating layer formed on at least a portion of the core,

The coating layer includes a lithium metal oxide which is an inert lithium ion conductor,

The lithium metal oxide has an atomic weight of 27 or more, and a composite cathode active material is provided, which is one element selected from the group consisting of groups 3 to 14 of the periodic table.

According to another aspect, a positive electrode including the composite positive electrode active material is provided.

According to another aspect, a lithium battery including the positive electrode is provided.

According to another aspect

A method for preparing a composite cathode active material comprising a; forming a coating layer including lithium metal oxide, which is an inert lithium ion conductor, on core particles capable of intercalating and discharging lithium is provided.

According to one aspect, the initial charge/discharge efficiency, high rate characteristics, and life characteristics of a lithium battery may be improved by coating the core capable of storing and discharging lithium with lithium metal oxide, which is inert to electrode reactions and is a lithium ion conductor.

1A is an XRD (X-ray diffraction) spectrum for _{Li 4} SiO ₄ prepared in Preparation Example 1. FIG.
1B is an XRD (X-ray diffraction) spectrum of _{Li 4} TiO ₄ prepared in Preparation Example 2. FIG.
1C is an X-ray diffraction (XRD) spectrum for _{Li 4} GeO ₄ prepared in Preparation Example 3. FIG.
2A is a scanning cell microscope (SEM) image of the composite cathode active material prepared in Example 1. FIG.
2B is a scanning cell microscope (SEM) image of the composite cathode active material prepared in Example 2.
2C is a scanning cell microscope (SEM) image of the composite positive electrode active material prepared in Example 3. FIG.
2D is a scanning cell microscope (SEM) image of the positive electrode active material prepared in Comparative Example 1.
3 is a result of a life characteristic test for lithium batteries of Examples 13, 17 to 18, and Comparative Example 9.
4 is a schematic diagram of a lithium battery according to an embodiment.
<Explanation of symbols for major parts of drawings>
1: lithium battery 2: negative electrode
3: anode 4: separator
5: battery case 6: cap assembly

Hereinafter, a composite positive electrode active material according to exemplary embodiments, a method of manufacturing the same, and a positive electrode and a lithium battery including the same will be described in more detail.

The composite cathode active material according to an embodiment includes a core capable of storing and discharging lithium; And a coating layer formed on at least a portion of the core, wherein the coating layer includes a lithium metal oxide, which is an inert lithium ion conductor, and the metal of the lithium metal oxide has an atomic weight of 27 or more and is in the group consisting of groups 3 to 14 of the periodic table. It is one selected element. For example, the core may include one or more compounds selected from the group consisting of overlithiated or non-overlithiated layered compounds, spinel compounds, and olivine compounds.

Since the coating layer formed on the core is inert to electrode reactions and contains lithium metal oxide, which is a lithium ion conductor, side reactions due to electron transfer between the core and the electrolyte may be suppressed. For example, since the lithium metal oxide is not involved in battery capacity by not storing and discharging lithium, the coating layer including the lithium metal oxide may serve as a protective layer of the core. Therefore, the coating layer can suppress side reactions such as decomposition of the electrolyte. In addition, the coating layer may serve to prevent the transition metal from eluting from the core capable of occluding and discharging the lithium.

In particular, since the lithium metal oxide has conductivity to lithium ions, unlike a conventional insulator, the lithium ion conductivity of the composite cathode active material may not be lowered. Accordingly, charging/discharging efficiency, high rate characteristics, and high temperature life characteristics of a lithium battery including the composite positive electrode active material may be improved.

In the following specification, the lithium metal oxide is a lithium ion conductor that is inert to electrode reactions unless otherwise described.

The lithium metal oxide may be highly crystalline. That is, a lithium-free oxide having a spinel structure and having a high crystallinity may exhibit a sharp diffraction peak compared to a lithium metal oxide having a low crystallinity in an X-ray diffraction spectrum using a Cu-Kα ray. Since the lithium metal oxide has high crystallinity, the stability of the electrode active material at a high voltage may be improved. For example, XRD spectra of the lithium metal oxide are shown in FIGS. 1A to 1C.

For example, the lithium metal oxide may be represented by the following Formula 1:

<Formula 1>

Li _x MO _y

In the above formula, 4≤x≤6, 4≤y≤6, and M is Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, It is one element selected from the group consisting of Os, Co, Rh, Ir, Ni, CU, Zn, Ga, In, Tl, Si, Ge, Sn, and Pb.

For example, the lithium metal oxide may be represented by the following Formula 2:

<Formula 2>

Li ₄ MO ₄

In the above formula, M is Si, Ge, Ti, Mo, Zn, V, Cr, Mn, Fe, Co, Ni, Cu, Ga, Zr, Nb, Tc, Ru, Rh, Pd, Ag, Cd, Sn, W And Hf is one selected from the group consisting of.

Specifically, the lithium metal oxide may be at least one selected from the group consisting _{of Li 4} SiO ₄ , Li ₄ TiO ₄ , and Li ₄ GeO _4.

In the composite cathode active material, the ionic conductivity of the lithium metal oxide ^{may be greater than 0 to 10 -6} S/cm at 100°C. When the ionic conductivity of lithium metal oxide exceeds 0, it means that it has ionic conductivity for lithium ions. It means that it has ionic conductivity. For example, the ionic conductivity of _{Li 4} SiO ₄ and Li ₄ GeO ₄ ^{is 10 -7} S/cm or less at 100°C. Since the lithium metal oxide has a higher ionic conductivity than an insulator without lithium ion conductivity, a high rate characteristic of a lithium battery including the lithium metal oxide may be improved.

In the composite positive electrode active material, the content of lithium metal oxide included in the coating layer may be 5% by weight or less based on the total weight of the composite positive electrode active material. For example, the content of lithium metal oxide included in the coating layer may be greater than 0 to 4% by weight. For example, the content of lithium metal oxide included in the coating layer may be greater than 0 to 3% by weight. For example, the content of lithium metal oxide contained in the coating layer may be greater than 0 to 2% by weight. For example, the content of lithium metal oxide included in the coating layer may be greater than 0 to 1% by weight based on the total weight of the composite positive electrode active material. Further improved battery characteristics can be obtained in the above content range.

In the composite positive electrode active material, in the X-ray photoelectric spectrum of the surface of the composite positive electrode active material, the content of the metal contained in the lithium metal oxide may be 8 atomic% or less with respect to the total composition of the composite positive electrode active material surface. For example, the content of the metal contained in the lithium metal oxide in the X-ray photoelectric spectrum may be greater than 0 to 7.8 atomic%. For example, the content of the metal contained in the lithium metal oxide in the X-ray photoelectric spectrum may be greater than 0 to 5 atomic% or less. For example, the content of the metal contained in the lithium metal oxide in the X-ray photoelectric spectrum may be greater than 0 to 3 atomic% or less. Further improved battery characteristics can be obtained in the above content range.

In the composite cathode active material, the core may include one compound selected from the group consisting of an overlithiated layered compound, a spinel compound, and an olivine compound.

For example, the core may include a compound represented by Formula 3:

<Formula 3>

pLi ₂ MO ₃ -(1-p)LiMeO ₂

In the above formula, 0<p≤0.8, and M is Ru, Rh, Pd, Os, Ir, Pt, Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Ni , Mn, Cr, Fe, Mg, Sr, V, and one or more metals selected from the group consisting of rare earth elements, wherein Me is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Mg, Zr And at least one metal selected from the group consisting of B.

For example, the core may include a compound represented by Formula 4:

<Formula 4>

Li[Li _x Me _y ]O _2+d

In the above formula, x+y=1, 0<x<1, 0≤d≤0.1, and Me is Mn, V, Cr, Fe, Co, Ni, Zr, Re, Al, B, Ge, Ru, Sn , Ti, Nb, Mo, and one or more metals selected from the group consisting of Pt.

For example, the core may include a compound represented by Formula 5:

<Formula 5>

Li[Li _x Ni _a Co _b Mn _c ]O _2+d

In the above formula, x+a+b+c=1; 0<x<1, 0<a<1, 0<b<1, 0<c<1; 0≤d≤0.1.

In addition, some or all of Ni, Co, and Mn in Formula 5 may be substituted with Al.

For example, the core may include a compound represented by Formula 6:

<Formula 6>

pLi ₂ MnO _{3 --} (1-p)LiNi _a Co _b Mn _c O ₂

In the above formula, 0<p<1, 0<a<1, 0<b<1, 0<c<1, a+b+c=1.

For example, the core may include a compound represented by Formula 7:

<Formula 7>

_{xLi 2 MO 3 -yLiMeO 2 -zLi 1} + d M '2 - d O 4

In the above formula, x+y+z=1; 0<x<1, 0<y<1, 0<z<1; 0≤d≤0.33, wherein M is Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Ni, Mn, Cr, Fe, Mg, Sr, V or rare earth elements It is at least one metal selected from the group consisting of, and Me is at least one metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Mg, Zr, and B, and the M'is at least one metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Mg, Zr and B.

For example, the core may include a compound represented by Formulas 8 to 12 below:

<Formula 8>

Li _x Co _{1 - y} M _y O _{2 -α} X _α

<Formula 9>

Li _x Co _{1 -y- z} Ni _y M _z O _{2 -α} X _α

<Formula 10>

Li _x Mn _{2 - y} M _y O _{4 -α} X _α

<Formula 11>

Li _x Co _{2 - y} M _y O _{4 -α} X _α

<Formula 12>

Li _x Me _y M _z PO _{4 -α} X _α

In the above formulas, 0.90≤x≤1.1, 0≤y≤0.9, 0≤z≤0.5, 1-yz>0, 0≤α≤2, and Me is Ti, V, Cr, Mn, Fe, Co, One or more metals selected from the group consisting of Ni, Cu, Al, Mg, Zr and B, and M is Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Ni, Mn , Cr, Fe, Mg, Sr, V, or at least one element selected from the group consisting of rare earth elements, and X is an element selected from the group consisting of O, F, S, and P.

For example, the core may include an olivine compound represented by Formula 13:

<Formula 13>

Li _x M _{y M'z} P0 _{4 - d} X _d

In the above formula, 0.9≦x≦1.1, 0<y≦1, 0≦z≦1, 1.9≦x+y+z≦2.1, 0≦d≦0.2; M is at least one selected from the group consisting of Fe, Mn, Ni and Co; M'is at least one selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, and Si; X is at least one selected from the group consisting of S and F.

For example, the core may include _{LiCoO 2, LiFePO 4, LiFe 1} -a Mn a PO 4 (0 <a <1) and at least one selected from the group consisting of LiMnPO _4.

In the composite cathode active material, the thickness of the coating layer may be 1 Å to 1 μm. For example, the thickness of the coating layer may be 1nm to 1㎛. For example, the thickness of the coating layer may be 1nm to 100nm. For example, the thickness of the coating layer may be 1nm to 30nm. For example, the thickness of the coating layer may be 5nm to 15nm. A lithium battery having improved physical properties in the thickness of the coating layer may be provided.

In the composite cathode active material, the core may be particles having an average particle diameter of 10 nm to 500 μm. For example, the average particle diameter of the core may be 10nm to 100㎛. For example, the average particle diameter of the core may be 10 nm to 50 μm. For example, the average particle diameter of the core may be 1 μm to 30 μm. A lithium battery having improved physical properties in the core average particle diameter may be provided.

The positive electrode according to another exemplary embodiment may include the above-described composite positive electrode active material.

The positive electrode is prepared by mixing the above-described composite positive electrode active material, a conductive agent, a binder, and a solvent to prepare a positive electrode active material composition. The positive electrode active material composition may be directly coated and dried on an aluminum current collector to prepare a positive electrode plate having a positive electrode active material layer formed thereon. Alternatively, the positive electrode active material composition may be cast on a separate support, and then a film obtained by peeling from the support may be laminated on the aluminum current collector to prepare a positive electrode plate having a positive electrode active material layer.

Conductive agents include carbon black, graphite fine particles, natural graphite, artificial graphite, acetylene black, Ketjen black, carbon fiber; Carbon nanotubes; Metal powders such as copper, nickel, aluminum, silver, or metal fibers or metal tubes; Conductive polymers such as polyphenylene derivatives may be used, but are not limited thereto, and any material that can be used as a conductive material in the art may be used.

As a binder, vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene (PTFE), a mixture of the aforementioned polymers, styrene butadiene rubber type A polymer or the like may be used, and as a solvent, N-methylpyrrolidone (NMP), acetone, water, and the like may be used, but are not necessarily limited thereto, and any solvent that can be used in the art may be used.

In some cases, it is also possible to form pores inside the electrode plate by adding a plasticizer to the positive electrode active material composition.

The contents of the composite positive electrode active material, the conductive agent, the binder, and the solvent are the levels commonly used in lithium batteries. Depending on the use and configuration of the lithium battery, one or more of the conductive material, the binder, and the solvent may be omitted.

In addition, the positive electrode may additionally include a general positive electrode active material other than the above-described composite positive electrode active material.

The general positive electrode active material is a lithium-containing metal oxide and may be used without limitation as long as it is commonly used in the art. For example, one or more of a complex oxide of a metal and lithium selected from cobalt, manganese, nickel, and combinations thereof may be used, and specific examples thereof include Li _a A _{1 - b} B _b D ₂ (the Where 0.90≦a≦1, and 0≦b≦0.5); _{Li a E 1 - b B b} O 2 - ( in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05) c D c; _{LiE 2 - b B b O 4} - ( in the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05) c D c; Li _a Ni _{1 -b- c} Co _b B _c D _α (in the above formula, 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 (in the above formula, 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 (in the above formula, 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 (in the above formula, 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 (in the above formula, 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 (wherein, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _b E _c G _d O ₂ (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 (wherein, 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 (in the above formula, 0.90≦a≦1, 0.001≦b≦0.1); Li _a CoG _b O ₂ (in the above formula, 0.90≦a≦1, 0.001≦b≦0.1); Li _a MnG _b O ₂ (in the above formula, 0.90≦a≦1, 0.001≦b≦0.1); Li _a Mn ₂ G _b O ₄ (In the above formula, 0.90≦a≦1, 0.001≦b≦0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0≦f≦2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0≦f≦2); A compound 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 a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

For example, LiCoO ₂ , LiMn _x O _2x (x=1, 2), LiNi _{1 -x} Mn _x O _2x (0<x<1), LiNi _{1 -x- y} 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 be used, or a mixture of the compound and a compound having a coating layer may be used. The coating layer may contain a coating element compound of oxide, hydroxide, oxyhydroxide of coating element, oxycarbonate of coating element, or hydroxycarbonate of coating element. The compound 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 may be used. The coating layer formation process may be any coating method as long as the compound can be coated by a method that does not adversely affect the physical properties of the positive electrode active material by using these elements (e.g. spray coating, dipping method, etc.). Since the content can be well understood by those engaged in the relevant field, detailed description will be omitted.

A lithium battery according to another embodiment employs a positive electrode including the composite positive electrode active material. The lithium battery may be manufactured by the following method.

First, a positive electrode is manufactured according to the positive electrode manufacturing method described above.

Next, the negative electrode can be manufactured as follows. The negative electrode may be manufactured in the same manner as the positive electrode, except that the negative electrode active material is used instead of the composite positive electrode active material. In addition, in the negative electrode active material composition, the same conductive agent, binder, and solvent as in the case of the positive electrode may be used.

For example, a negative electrode active material composition may be prepared by mixing a negative electrode active material, a conductive agent, a binder, and a solvent, and the negative electrode plate may be manufactured by directly coating this on a copper current collector. Alternatively, a negative electrode plate may be manufactured by casting the negative active material composition on a separate support and laminating a negative electrode active material film peeled from the support on a copper current collector.

In addition, the negative active material may be any material that can be used as a negative active material for lithium batteries in the art. For example, it may include at least one 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 (wherein 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 Si), Sn-Y alloy (the Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element, or a combination element thereof, but not Sn ), etc. The element Y is 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 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 graphite such as amorphous, plate-shaped, flake, spherical or fibrous natural graphite or artificial graphite, and the amorphous carbon is soft carbon (low temperature calcined carbon) or hard carbon (hard carbon). carbon), mesophase pitch carbide, calcined coke, or the like.

The contents of the negative electrode active material, the conductive agent, the binder, and the solvent are the levels commonly used in lithium batteries.

Next, a separator to be inserted between the positive and negative electrodes is prepared. Any of the separators can be used as long as they are commonly used in lithium batteries. Those having low resistance to ion migration of the electrolyte and excellent in the ability to impregnate the electrolyte may be used. For example, as selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, it may be a non-woven fabric or a woven fabric. For example, a woundable separator such as polyethylene or polypropylene may be used for a lithium ion battery, and a separator having excellent organic electrolyte impregnation ability may be used for a lithium ion polymer battery. For example, the separator may be manufactured according to the following method.

A polymer resin, a filler, and a solvent are mixed to prepare a separator composition. The separator composition may be directly coated and dried on an electrode to form a separator. Alternatively, after the separator composition is cast and dried on a support, a separator film peeled off from the support may be laminated on an electrode to form a separator.

The polymer resin used for manufacturing the separator is not particularly limited, and all materials used for the bonding material of the electrode plate may be used. For example, vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or mixtures thereof may be used.

Next, the electrolyte is prepared.

For example, the electrolyte may be an organic electrolyte. In addition, the electrolyte may be a solid. For example, boron oxide, lithium oxynitride, etc. may be used, but the present invention is not limited thereto, and any solid electrolyte may be used as long as it can be used as a solid electrolyte in the art. The solid electrolyte may be formed on the negative electrode by a method such as sputtering.

For example, an organic electrolyte may be prepared. The organic electrolyte may be prepared by dissolving a lithium salt in an organic solvent.

The organic solvent may be used as long as it can be used as an organic solvent in the art. For example, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate , Benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide, dimethylsulfoxide , Dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, or mixtures thereof.

The lithium salt may also be used as long as it can be used as a lithium salt in the art. For example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (where x,y are natural numbers), LiCl, LiI, or a mixture thereof.

As shown in FIG. 4, the lithium battery 1 includes a positive electrode 3, a negative electrode 2, and a separator 4. The positive electrode 3, the negative electrode 2 and the separator 4 described above are wound or folded to be accommodated in the battery case 5. Subsequently, an organic electrolyte is injected into the battery case 5 and sealed with a cap assembly 6 to complete the lithium battery 1. The battery case may have a cylindrical shape, a square shape, or a thin film shape. For example, the lithium battery may be a large thin film type battery. The lithium battery may be a lithium ion battery.

A separator may be disposed between the positive electrode and the negative electrode to form a battery structure. After the battery structure is stacked in a bi-cell structure, it is impregnated with an organic electrolyte, and the resulting product is accommodated in a pouch and sealed to complete a lithium ion polymer battery.

In addition, a plurality of battery structures are stacked to form a battery pack, and the battery pack can be used in all devices requiring high capacity and high output. For example, it can be used for laptop computers, smart phones, electric vehicles, and the like.

In addition, since the lithium battery has excellent life characteristics and high rate characteristics, it can be used in an electric vehicle (EV). For example, it can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). In addition, it can be used in a field requiring a large amount of power storage. For example, it can be used for electric bicycles, power tools, and the like.

A method of manufacturing a composite cathode active material according to another embodiment includes forming a coating layer including lithium metal oxide, which is an inert lithium ion conductor, on core particles capable of intercalating and discharging lithium.

For example, the formation of the coating layer may be performed by a dry method.

When the coating layer is formed by a dry method, the manufacturing method includes mixing a core containing an electrode active material capable of storing and discharging lithium and lithium metal oxide particles, which are inert lithium ion conductors; And forming a surface treatment layer containing a lithium??-free oxide on the core by a dry method.

The dry method includes all methods of forming a surface treatment layer by applying mechanical energy without using a solvent to a mixture of core particles including an electrode active material and lithium metal oxide particles.

The dry method is: a) a coating material, for example lithium metal oxide spinel powder, is brought into contact with the surface of the core particle with a low-rotation ball mill, so that the coating material particles adhere to the core particle surface, and the attached coating material particles are aggregated with each other to form a coating layer. B) The coating material particles are constrained to the surface of the core particles by the movement of the pulverizing medium or the rotor inside the device to bind the core and the coating material particles, and at the same time, the coating material particles on the core particles are mechanically bonded to each other by the stress accompanying the coating material particles. A method of bonding these particles by softening or melting the coating layer of the coating material particles on the core particle by heat generated from the bonding or stress, and the coating layer by heat treatment of the coated core with the coating formed by the a) and/or b) method. And a method of melting a part or all of the core and then cooling it again, but is not limited thereto, and any dry method that can be used in the art may be used.

For example, the dry method may be one method selected from the group consisting of a planetary ball mill method, a low speed ball mill method, a high speed ball mill method, a hybridization method, and a mechanofusion method. For example, a mechanofusion method can be used.

The mechanofusion method is a method of injecting the mixture into a rotating container, fixing the mixture to the inner wall of the container by centrifugal force, and then compressing the mixture into a gap between the inner wall of the container and an arm head that is close at a slight distance. The mechanofusion method corresponds to the method b) above.

After the step of forming the surface treatment layer by the dry method, a step of heat-treating the resultant surface treatment layer may be additionally included. Through the heat treatment, the surface treatment layer may be more solid. The heat treatment conditions may be any condition capable of melting part or all of the surface treatment layer.

In the manufacturing method, the content of the lithium metal oxide may be 5% by weight or less of the total weight of the core and the lithium-free oxide. For example, the content of the lithium metal oxide may be greater than 0 to 4% by weight of the total weight of the core and the lithium metal oxide. For example, the content may be more than 0 to 3% by weight. For example, the content may be greater than 0 to 3% by weight.

Alternatively, in the manufacturing method, the formation of the penile coating layer may be formed by a wet method.

When the coating layer is formed by a wet method, the manufacturing method may include mixing a core containing an electrode active material and a precursor of a lithium-free oxide having a spinel structure; And forming a surface treatment layer including a lithium-free oxide on the core by a wet method.

The wet method may include, for example, reducing the precursor in a solution to form a lithium metal oxide on the core.

The present invention will be described in more detail through the following examples and comparative examples. However, the examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

(Manufacture of lithium metal oxide)

Manufacturing Example 1

After mixing Li ₂ CO ₃ and H ₂ SiO ₃ in a composition ratio of 2:1, the mixture was calcined at 850° C. for 6 hours in an air atmosphere to prepare _{Li 4} SiO _{4, which is an inert lithium ion conductor.} Subsequently, the Li ₄ SiO ₄ was pulverized with a ball mill for 24 hours _{to prepare Li 4} SiO ₄ particles having a particle diameter of about 250 nm.

Manufacturing Example 2

After mixing Li ₂ CO ₃ and TiO ₂ (anatase) in a composition ratio of 2:1, the mixture was calcined at 1000° C. for 4 hours in a nitrogen atmosphere containing 2% by weight of hydrogen to produce Li, an inert lithium ion conductor. ₄ TiO ₄ was prepared. Subsequently, the Li ₄ TiO ₄ was pulverized with a ball mill for 24 hours _{to prepare Li 4} TiO ₄ particles having a particle diameter of about 500 nm.

Manufacturing Example 3

After mixing Li ₂ CO ₃ and GeO ₂ in a composition ratio of 2:1, the mixture was calcined at 700° C. for 20 hours in an air atmosphere to prepare _{Li 4} GeO _{4, which is an inert lithium ion conductor.} Subsequently, the Li ₄ GeO ₄ was pulverized in a ball mill for 24 hours _{to prepare Li 4} GeO ₄ particles having a particle diameter of about 2000 nm.

Manufacturing Example 4

After mixing Li ₂ CO ₃ and MoO ₃ in a composition ratio of 2:1, the mixture was calcined at 700° C. for 20 hours in an air atmosphere to prepare _{Li 4} GeO _{4, which is an inert lithium ion conductor.} Subsequently, the Li ₄ MoO ₄ was pulverized in a ball mill for 24 hours _{to prepare Li 4} MoO ₄ particles having a particle diameter of about 2000 nm.

(Production of composite cathode active material)

Example 1

_{0.5 parts by weight of Li 4} SiO ₄ particles prepared in Preparation Example 1 and 100 parts by weight _{of Li 1.18} Ni _0.17 Co _0.1 Mn _0.56 O ₄ powder having an average particle diameter of 10 μm were mixed. The mixture was put in a dry surface treatment device (Hosokawa Micron Corporation, Japan, Mechanofusion device, Nobilta-mini) and treated at 3000 rpm for 20 minutes, followed by Li _{1 .18} Ni _{0 .17} Co _{0 .1} Mn _{0 .56} O ₄ A composite positive electrode active material was prepared in which a coating layer containing _{Li 4} SiO _{4 was formed on the core.} The prepared composite cathode active material is shown in FIG. 2A.

Example 2

A composite positive electrode active material was prepared in the same manner as in Example 1, except that the amount of _{Li 4} SiO _{4 particles was changed to 1.0 part by weight.}

The prepared composite cathode active material is shown in FIG. 2B.

Example 3

A composite positive electrode active material was prepared in the same manner as in Example 1, except that the amount of _{Li 4} SiO _{4 particles was changed to 3.0 parts by weight.}

The prepared positive electrode active material is shown in FIG. 2C.

Example 4

A composite cathode active material was prepared in the same manner as in Example 1, except that the amount of _{Li 4} SiO _{4 particles was changed to 5.0 parts by weight.}

Example 5

A composite cathode active material was prepared in the same manner as in Example 1, except that _{the Li 4} TiO ₄ particles prepared in Preparation Example 2 were used instead of the _{Li 4} SiO _{4 particles.}

Example 6

A composite cathode active material was prepared in the same manner as in Example 1, except that _{the Li 4} GeO ₄ particles prepared in Preparation Example 2 were used instead of the _{Li 4} SiO _{4 particles.}

Comparative Example 1

_{Li 1.18} Ni _0.17 Co _0.1 Mn _0.56 O ₄ powder having an average particle diameter of 10 μm was used as a positive electrode active material as it was without the process of preparing the surface treatment layer.

The prepared positive electrode active material is shown in FIG. 2D.

Comparative Example 2

_{0.2 parts by weight of alumina (Al 2} O ₃ ) particles having an average particle diameter of 300 nm and 100 parts by weight _{of Li 1.18} Ni _0.17 Co _0.1 Mn _0.56 O ₄ powder having an average particle diameter of 10 μm were mixed. The mixture was put in a dry surface treatment device (Hosokawa Micron Corporation, Japan, Mechanofusion device, Nobilta-mini) and treated at 3000 rpm for 20 minutes, followed by Li _{1 .18} Ni _{0 .17} Co _{0 .1} Mn _{0 .56} O ₄ A composite cathode active material in which a coating layer containing _{Al 2} O _{3 was formed on the core was prepared.}

Comparative Example 3

A composite cathode active material was prepared in the same manner as in Comparative Example 2, except that the addition amount of the alumina particles was changed to 1.0 part by weight.

Comparative Example 4

A composite cathode active material was prepared in the same manner as in Comparative Example 2, except that the addition amount of the alumina particles was changed to 1.7 parts by weight.

(Manufacture of anode)

Example 7

The composite cathode active material prepared in Example 1, a carbon conductive agent (Denka Black), and a mixture of polyvinylidene fluoride (PVdF) in a weight ratio of 94:3:2 was mixed with N-methylpyrrolidone (NMP). A slurry was prepared by mixing together in an agate mortar. A positive electrode plate with a positive electrode active material layer formed by applying the slurry to a thickness of about 40 μm using a doctor blade on a 15 μm-thick aluminum current collector, drying at room temperature, drying again under vacuum and 120° C., rolling and punching Was prepared.

Examples 8-12

A positive electrode plate was manufactured in the same manner as in Example 6, except that the composite positive electrode active materials of Examples 2 to 6 were used, respectively.

Comparative Examples 5 to 8

A positive electrode plate was manufactured in the same manner as in Example 6, except that the positive electrode active materials of Comparative Examples 1 to 4 were used, respectively.

(Manufacture of lithium battery)

Example 13

Using the positive electrode plate prepared in Example 7, lithium metal was used as a counter electrode, and a PTFE separator and 1.3M LiPF ₆ were EC (ethylene carbonate) + DEC (diethyl carbonate) + EMC (ethyl methyl carbonate). A coin cell was manufactured using a solution dissolved in (3:5:2 by volume) as an electrolyte.

Examples 14-18

It was prepared in the same manner as in Example 11, except that the positive electrodes prepared in Examples 8 to 12 were used respectively.

Comparative Examples 9-12

It was prepared in the same manner as in Example 11, except that the positive electrodes prepared in Comparative Examples 5 to 8 were used respectively.

Evaluation Example 1: XRD experiment

XRD (X-ray diffraction) experiments were performed on each of the _{Li 4} SiO ₄ , Li ₄ TiO _4, and Li ₄ GeO ₄ particles prepared in Preparation Examples 1 to 3, and the results are shown in FIGS. 1A to 1C. XRD was measured using a Cu-Kα ray.

As shown in FIGS. 1A to 1C, the lithium metal oxides showed sharp peaks indicating high formation properties.

Evaluation Example 2: XPS experiment

Some of the results obtained by performing X-ray Photoelelctron Spectroscopy on the surface of the positive electrode active material prepared in Examples 1 to 6 are shown in Table 1 below. _{Table 1 is for Li 4} SiO ₄ prepared in Examples 1 to 3.

C is
[atom%] O 1s
[atom%] Si 2p
[atom%] Mn 2p
[atom%] Example 3 12.94 69.20 7.72 10.15 Example 2 12.78 69.69 7.71 9.83 Example 1 26.69 58.37 0.97 13.97

As shown in Table 1, the content of Si on the surface of the composite cathode active material of Examples 1 to 3 was 8 atomic% or less.

Evaluation Example 3: Evaluation of battery characteristics

The coin cells prepared in Examples 13 to 18 and Comparative Examples 9 to 12 were charged with a constant current to 4.7 V at a rate of 0.1 C in the 1st cycle, and discharged at a constant current to 3.0 V at a rate of 0.1 C.

2 ^nd cycle was constant voltage charging until the constant current charging to 4.6V at a rate of 0.5C, and subsequently kept at 4.6V current is a constant current discharge at a rate of 0.2C was 0.05C to 3.0 V.

3 ^rd cycle was kept at the constant current charging and then 4.6V at a rate of 0.5C to 4.6V constant voltage charge until the current is a constant current discharge at a rate of 1.0C was 0.05C to 3.0 V.

4th The cycle was charged at a constant current to 4.6V at a rate of 0.5C, and then charged at a constant voltage until the current reached 0.05C while maintaining at 4.6V, and a constant current discharge was performed to 3.0V at a rate of 2.0C.

5th The cycle was charged with a constant current to 4.6V at a rate of 1C, and then charged at a constant voltage until the current reached 0.05C while maintaining at 4.6V, and a constant current discharge was performed to 3.0V at a rate of 1C.

Some of the charging and discharging results are shown in Table 2 below. Initial Coulomb efficiency and high rate characteristics are defined by Equations 1 and 2, respectively.

<Equation 1>

Initial coulomb efficiency [%] = [discharge capacity at ^{1 st cycle / charge capacity at 1 th} cycle] × 100

<Equation 2>

2C capacity retention rate [%] = [Discharge capacity at 4th cycle / Discharge capacity at 2nd cycle] × 100

Initial charge/discharge efficiency
[%] 2C capacity retention rate
[%] Example 13 88.0 75.2 Example 14 87.6 74.7 Example 17 87.4 71.5 Example 18 87.4 73.2 Comparative Example 9 86.0 67.6 Comparative Example 10 84.1 64.7 Comparative Example 11 85.0 61.4 Comparative Example 12 76.2 59.5

As shown in Table 2, the lithium batteries of Examples 13, 14, 17, and 18 have improved initial charge/discharge efficiency and high rate characteristics compared to the lithium batteries of Comparative Example.

Evaluation Example 7: Evaluation of high temperature life characteristics

The coin cells prepared in Examples 13, 17, 18 and Comparative Example 9 were charged and discharged 70 times at a constant current of 1C rate in a voltage range of 3.0 to 4.6V compared to lithium metal at a high temperature of 45°C. The capacity retention rate in the 70th cycle is expressed by Equation 2 below. The initial coulomb efficiency is represented by Equation 3 below. The capacity retention rate in the 70th cycle is shown in Table 3 and FIG. 3 below.

<Equation 3>

70 ^th capacity retention ratio in the cycle (%) = [discharge capacity at a discharge capacity / 1 ^st cycle at 70th cycle] × 100

Capacity retention rate at 70 ^{th cycle}
[%] Example 13 82.5 Example 17 81.9 Example 18 84.1 Comparative Example 9 56.8

As shown in Table 3 and FIG. 3, the lithium batteries of Examples 13, 17, and 18 exhibit improved high-temperature life characteristics compared to the lithium batteries of Comparative Example 9.

Claims (19)

A core capable of storing and discharging lithium; And
It includes a coating layer formed on at least a portion of the core,
The core comprises a layered compound or an olivine compound,
The coating layer includes a lithium metal oxide which is an inert lithium ion conductor,
The metal of the lithium metal oxide has an atomic weight of 27 or more and is one element selected from the group consisting of groups 3 to 14 of the periodic table,
The lithium metal oxide is represented by the following formula (1),
The lithium metal oxide has crystallinity, a composite cathode active material:
<Formula 1>
Li _x MO _y
In the above formula, 4≤x≤6, 4≤y≤6,
M is Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, CU, Zn, Ga, It is one element selected from the group consisting of In, Tl, Ge, Sn and Pb. The composite cathode active material of claim 1, wherein the lithium metal oxide is represented by the following Formula 2:
<Formula 2>
Li ₄ MO ₄
In the above formula, M is Ge, Ti, Mo, Zn, V, Cr, Mn, Fe, Co, Ni, Cu, Ga, Zr, Nb, Tc, Ru, Rh, Pd, Ag, Cd, Sn, W and Hf It is one selected from the group consisting of. The composite cathode active material of claim 1, wherein the lithium metal oxide is at least one selected from the group consisting _{of Li 4} TiO ₄ and Li ₄ GeO _4. The composite cathode active material according to claim 1, wherein the lithium metal oxide has an ionic conductivity of greater than 0 to 10 ^{-6 S/cm at 100°C.} The composite positive electrode active material according to claim 1, wherein the content of the lithium metal oxide contained in the coating layer is 5% by weight or less based on the total weight of the composite positive electrode active material. The composite positive electrode active material according to claim 1, wherein the content of the metal contained in the lithium metal oxide is 8 atomic% or less with respect to the total composition of the composite positive electrode active material surface in the X-ray photoelectric spectrum of the surface of the composite positive electrode active material. The composite cathode active material of claim 1, wherein the core comprises a compound represented by the following formula (3):
<Formula 3>
pLi ₂ MO ₃ -(1-p)LiMeO ₂
In the above formula, 0<p≤0.8,
The M is Ru, Rh, Pd, Os, Ir, Pt, Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Ni, Mn, Cr, Fe, Mg, Sr , V and one or more metals selected from the group consisting of rare earth elements, and
The Me is at least one metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Mg, Zr and B. The composite cathode active material according to claim 1, wherein the core comprises a compound represented by the following formula (4).
<Formula 4>
Li[Li _x Me _y ]O _2+d
In the above formula, x+y=1, 0<x<1, 0≤d≤0.1,
Me is one or more metals selected from the group consisting of Mn, V, Cr, Fe, Co, Ni, Zr, Re, Al, B, Ge, Ru, Sn, Ti, Nb, Mo, and Pt. The composite cathode active material of claim 1, wherein the core comprises a compound represented by the following formula (5):
<Formula 5>
Li[Li _x Ni _a Co _b Mn _c ]O _2+d
In the above formula, x+a+b+c=1; 0<x<1, 0<a<1, 0<b<1, 0<c<1; 0≤d≤0.1. The composite cathode active material of claim 1, wherein the core comprises a compound represented by the following formula (6):
<Formula 6>
pLi ₂ MnO ₃ -(1-p)LiNi _a Co _b Mn _c O ₂
In the above formula,
0<p<1, 0<a<1, 0<b<1, 0<c<1, a+b+c=1. The composite cathode active material of claim 1, wherein the core comprises a compound represented by the following formula (7):
<Formula 7>
_{xLi 2 MO 3 -yLiMeO 2 -zLi 1} + d M '2 - d O 4
In the above formula, x+y+z=1; 0<x<1, 0<y<1, 0<z<1; 0≤d≤0.33,
The M is at least selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Ni, Mn, Cr, Fe, Mg, Sr, V or rare earth elements Is a single metal
The Me is at least one metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Mg, Zr and B,
The M'is at least one metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Mg, Zr and B. The composite cathode active material of claim 1, wherein the core comprises a compound represented by Formulas 8, 9 and 12:
<Formula 8>
Li _x Co _1-y M _y O _2-α X _α
<Formula 9>
Li _x Co _1-yz Ni _y M _z O _2-α X _α
<Formula 12>
Li _x Me _y M _z PO _4-α X _α
In the above equations, 0.90≤x≤1.1, 0≤y≤0.9, 0≤z≤0.5, 1-yz>0, 0≤α≤2,
Me is at least one metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Mg, Zr and B,
M is at least one selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Ni, Mn, Cr, Fe, Mg, Sr, V, or rare earth elements Is an element of
X is an element selected from the group consisting of O, F, S and P. The composite cathode active material of claim 1, wherein the core comprises a compound represented by the following formula (13):
<Formula 13>
Li _x M _{y M'z} P0 _{4 - d} X _d
In the above formula, 0.9≦x≦1.1, 0<y≦1, 0≦z≦1, 1.9≦x+y+z≦2.1, 0≦d≦0.2;
M is at least one selected from the group consisting of Fe, Mn, Ni and Co;
M'is at least one selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, and Si;
X is at least one selected from the group consisting of S and F. A positive electrode comprising the composite positive electrode active material according to any one of claims 1 to 13. A lithium battery comprising the positive electrode according to claim 14. As a method for producing a composite cathode active material according to any one of claims 1 to 13,
Forming a coating layer including lithium metal oxide, which is an inert lithium ion conductor, on core particles capable of storing and discharging lithium. The method of claim 16, wherein the coating layer is formed by a dry method. The method of claim 17, wherein the dry method is one selected from the group consisting of a planetary ball mill method, a low speed ball mill method, a high speed ball mill method, a hybridization method, and a mechanofusion method. Manufacturing method. The method of claim 16, wherein the coating layer is formed by a wet method.

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