KR102172381B1 - A cathode active material, method of preparing the same, and lithium secondary battery comprising a cathode comprising the cathode active material - Google Patents

Abstract

The present invention relates to a cathode active material comprising a compound represented by Li _1-x Na _x P _α MO ₂ , a method for preparing the same, and a lithium secondary battery including a cathode comprising the same.

Description

A cathode active material, method of preparing the same, and lithium secondary battery comprising a cathode comprising the cathode active material

It relates to a positive electrode active material, a method for manufacturing the same, and a lithium secondary battery including a positive electrode including the positive electrode active material.

Since the lithium secondary battery was commercialized by Sony in 1991, demand has been rapidly increasing in various fields ranging from small home appliances such as mobile IT products to medium and large electric vehicles and energy storage systems. In particular, low-cost, high-energy cathode materials are essential for mid- to large-sized electric vehicles and energy storage systems. Cobalt, the main raw material of single crystal LiCoO ₂ (LCO), which is a cathode active material currently commercially available, is expensive.

So, LiNi _x Co _y Mn _z O ₂ (NCM, x+y+z=1) and LiNi _x Co _y Al _z O, in which a part of Co is substituted with another transition metal instead of LCO as a cathode active material for a mid- to large-sized secondary battery. ₂ (NCA, x+y+z=1), a Ni-based cathode active material is used, and these NCM and NCA-based cathode active materials have the advantage that the price of nickel as a raw material is low and has a high reversible capacity. The Ni-based cathode active material is prepared by mixing a transition metal compound precursor synthesized by a coprecipitation method with a lithium source and then synthesizing it in a solid state. However, the Ni-based cathode material synthesized in this way exists in the form of secondary particles in which small primary particles are agglomerated, and there is a problem that micro-crack occurs inside the secondary particles during a long-term charging/discharging process. The microcracks cause a side reaction between the new interface of the positive electrode active material and the electrolyte, and as a result, deterioration of battery performance such as degradation of stability due to gas generation and degradation of battery performance due to depletion of the electrolyte is caused. In addition, an increase in electrode density (>3.3g/cc) is required to realize a high energy density, which causes the collapse of secondary particles, causing electrolyte depletion due to side reactions with the electrolyte, causing a sharp decline in initial lifespan. Consequently, it means that the Ni-based cathode active material in the form of secondary particles synthesized by the conventional co-precipitation method cannot realize high energy density.

In order to solve the problems of the above-described secondary particle type Ni-based positive electrode active material, the development of a single-particle type Ni-based positive electrode active material has been recently made. The single crystal type Ni-based positive electrode active material does not cause particle collapse when the electrode density is increased (> 3.3g/cc) to realize high energy density, so it can realize excellent electrochemical performance. However, regardless of the shape of the particles, the Ni-based positive electrode active material may deteriorate battery stability due to structural and/or thermal instability due to unstable Ni ³⁺ and Ni ⁴⁺ ions during electrochemical evaluation. Therefore, in order to develop a high-energy lithium secondary battery, it is necessary to stabilize unstable Ni ions of the positive electrode active material together with the development of a single crystal Ni-based positive electrode active material.

According to one aspect, by providing a lithium transition metal oxide in which a part of the transition metal is substituted with boron (B) among lithium transition metal oxides, it stabilizes unstable Ni ions in the positive electrode active material particles to increase capacity per volume and improve life stability. It is aimed at.

According to one aspect, a positive electrode active material represented by the following Chemical Formula 1 is provided.

<Formula 1>

Li _x P _α M _1-β B _β O ₂

In Formula 1,

M is one or more transition metals,

0.98≤x≤1.02, 0<α≤0.007, 0<β≤0.1.

A mixing step of mixing a lithium precursor, a transition metal precursor, a phosphorus precursor, and a boron precursor to obtain a precursor mixture; And

There is provided a method of manufacturing a positive electrode active material comprising a heat treatment step of heat-treating the precursor mixture to obtain the positive electrode active material represented by Chemical Formula 1.

According to another aspect, a positive electrode including a positive electrode active material represented by Formula 1; cathode; And there is provided a lithium secondary battery including an electrolyte.

According to one aspect, the cathode active material in which a part of the transition metal is substituted with B ions in the lithium transition metal compound represented by Formula 1 stabilizes unstable Ni ions in the active material particles, so that the lithium secondary battery including the same has high capacity and long life characteristics. I can.

1 is a SEM (Verios 460, FEI) photograph of the positive electrode active material obtained in Examples 1 to 3 and Comparative Example 1.
2 is a particle size distribution curve obtained by measuring the average particle size (Cilas1090, Scinco) of the positive electrode active materials obtained in Examples 1 to 3 and Comparative Example 1.
3 is an XRD spectrum of the positive electrode active material obtained in Examples 1 to 3 and Comparative Example 1.
4 is a high resolution transmission electron microscope (high resolution transmission electron microscopy (HR-TEM)) photograph and energy dispersive X-ray spectroscopy (EDX) analysis results of the positive electrode active material obtained in Example 3 to be.
5 is a graph showing capacity retention rates for 50 charge/discharge cycles of half cells prepared in Examples 4 to 6 and Comparative Example 2. FIG.
6 is a schematic diagram of a lithium battery according to an exemplary 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

The present inventive concept described below may apply various transformations and may have various embodiments. Specific embodiments are illustrated in the drawings and will be described in detail in the detailed description. However, this is not intended to limit the present creative idea to a specific embodiment, it is to be understood as including all transformations, equivalents or substitutes included in the technical scope of the present creative idea.

The terms used below are only used to describe specific embodiments, and are not intended to limit the present inventive idea. Singular expressions include plural expressions unless the context clearly indicates otherwise. Hereinafter, terms such as "comprises" or "have" are intended to indicate the existence of features, numbers, steps, actions, components, parts, components, materials, or a combination thereof described in the specification. It is to be understood that the above other features, or the possibility of the presence or addition of numbers, steps, actions, components, parts, components, materials, or combinations thereof, are not excluded in advance. "/" used below may be interpreted as "and" or "or" depending on the situation.

In the drawings, the thickness is enlarged or reduced in order to clearly express various layers and regions. The same reference numerals are assigned to similar parts throughout the specification. Throughout the specification, when a part such as a layer, film, region, plate, etc. is said to be "on" or "on" another part, this includes not only the case directly above the other part, but also the case where there is another part in the middle. . Throughout the specification, terms such as first and second may be used to describe various components, but the components should not be limited by terms. The terms are used only for the purpose of distinguishing one component from another.

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

The positive electrode active material according to an embodiment may include a compound represented by Formula 1 below.

<Formula 1>

Li _x P _α M _1-β B _β O ₂

In Formula 1,

M is one or more transition metals,

0.98≤x≤1.02, 0<α≤0.007, 0<β≤0.1.

As a positive electrode active material for a high-energy lithium secondary battery, a Ni-based positive electrode active material containing a high concentration of Ni ("high-nickel-based positive electrode active material") is attracting attention. High-nickel-based cathode active material has a higher capacity as the content of nickel among the transition metals constituting the cathode active material is higher than that of other transition metals, but structural instability due to unstable Ni ³⁺ and Ni ⁴⁺ ions on the surface of the cathode active material There is a limitation of having Therefore, there is still a problem for stabilizing unstable Ni ions present in particles of a high-nickel-based positive electrode active material having a high capacity.

In this regard, the inventor of the present invention has completed the present invention in view of stabilizing unstable Ni ions by substituting part of the transition metal with B ions in the high-nickel lithium transition metal oxide. In addition, even if a small amount of transition metal among the transition metals is replaced with B ions, the size of the crystals and particles of lithium transition metal oxide is maintained, thereby maintaining the high energy density and long life characteristics of the existing single crystal active material, while at the same time preventing unstable Ni ions. Further improvement of the life characteristics of the active material can be expected through stabilization.

The M may include at least one transition metal selected from Ni, Co, Mn, Al, Mg, V, and Ti.

For example, the M may include one or more transition metals selected from Ni, Co, Mn, and Al, but is not limited thereto.

Formula 1 may be a compound represented by the following Formula 2:

<Formula 2>

Li _x P _α Ni _1-β-γ M1 _γ B _β O ₂

In Formula 2,

M1 is one or more transition metals selected from Co, Mn, Al, Mg, V, and Ti,

0.98≤x≤1.02, 0<α≤0.007, 0<β≤0.1, 0<γ<1, and 0<β+γ<1.

In Formula 2, y may be 0<y<0.5.

The positive electrode active material represented by Chemical Formula 2 does not replace other elements in the crystal structure of the nickel-based single crystal single-particle positive electrode active material, but has a structure in which a P element is doped in an empty tetrahedral position. Therefore, doping of the P element does not affect the stoichiometric value of Li or transition metals such as Ni and Co. As a result, the single crystal nickel-based positive electrode active material represented by Chemical Formula 2 may have a composition that deviates stoichiometrically through the introduction of the P element.

According to one embodiment, the P element may be located at a tetrahedral site in a layered structure of a single crystal. The tetrahedral site may be an empty site in the layered structure of the single crystal. Since the P element is located in the empty tetrahedron site, the amount of residual lithium is reduced. Without being bound by theory, it is possible to reduce the residual lithium by suppressing the release of Li due to the formation of oxygen defects in the crystal structure in the first heat treatment step at high temperature by partially replacing P in the empty tetrahedron site in the crystal structure. . The released Li may react with CO ₂ and moisture in the air at high temperature to form a residual lithium compound. However, P present in the empty tetrahedron in the structure stabilizes the oxygen framework in the anode structure, thereby reducing the residual lithium by suppressing the formation of oxygen defects at high temperatures.

According to one embodiment, the P element may exist inside a single crystal. For example, the P element is not present on the surface of the single crystal positive electrode active material, but may exist inside the single crystal positive electrode active material.

Since the P element is located at a tetrahedral site inside the single crystal, phase transition is alleviated during intercalation/deintercalation of lithium ions due to charge and discharge, thereby contributing to the phase stability of the positive electrode active material.

Formula 1 may be a compound represented by the following Formula 3:

<Formula 3>

Li _x P _α Ni _1-β-γ-δ M1 _γ M2 _δ B _β O ₂

In Formula 3,

M1 and M2 are each independently at least one transition metal selected from Co, Mn, Al, Mg, V, and Ti,

M1 and M2 are different from each other,

0.98≤x≤1.02, 0<α≤0.007, 0<β≤0.1, 0<γ<1, 0<δ<1 and 0<β+γ+δ<1.

In Formula 3, γ and δ may be 0<γ<0.4, and 0<δ<0.4.

In Formula 3, M1 is Co, and M2 may be at least one element selected from Mn, Mg, V, and Ti, but is not limited thereto.

Formula 1 may be a compound represented by any one of the following Formulas 4 to 6:

<Formula 4>

_{Li x 'P α' Ni 1} -β'-γ'-δ 'Co γ' Mn δ 'B β' O 2

<Formula 5>

Li _x'' P _α'' Ni _{1-β''-γ''-δ''} Co _γ'' Al _δ'' B _β'' O ₂

<Formula 6>

Li _x''' P _α''' Ni _{1-β'''-γ'''-δ'''} Co _γ''' B _β''' O ₂

In Formulas 4 to 6,

0.98≤x'≤1.02, 0<α'≤0.007, 0<β'≤0.01, 0<γ'≤0.3, and 0<δ'≤0.3,

0.98≤x''≤1.02, 0<α''≤0.007, 0<β''≤0.01, 0<γ''≤0.3, and 0<δ''≤0.05,

0.98≤x'''≤1.02, 0<α'''≤0.007, 0<β'''≤0.01 and 0<γ'''≤0.2.

The average particle diameter (D50) of the positive electrode active material is 0.1 μm to 20 μm. The average particle diameter of the positive electrode active material is not limited to the above range, and includes arbitrary values selected from the above range. When the average particle diameter of the positive electrode active material falls within the above range, a desired energy density per volume may be achieved.

When the average particle diameter of the positive electrode active material exceeds 20 μm, the charge/discharge capacity rapidly decreases, and when it is less than 0.1 μm, it is difficult to obtain a desired energy density per volume.

The compound represented by Formula 1 is a single crystal. Here, a single crystal has a concept that is distinct from a single particle. A single particle refers to a particle formed of one particle regardless of the type and number of crystals therein, and a single crystal means that a single crystal is included in the particle. Since the core has a single crystal, the structural stability is very high. In addition, lithium ion conduction is easier than that of polycrystalline, and high-speed charging characteristics are superior to that of polycrystalline active material.

The compound represented by Formula 1 is a single particle. Here, a single particle is a concept that is distinguished from a secondary particle that is an aggregate of a plurality of single particles. Since the positive electrode active material has a single particle shape, it is possible to prevent the particles from being broken even at a high electrode density. Accordingly, it is possible to realize a high energy density of the positive electrode active material. Since the core is a single particle, it is possible to achieve high energy density by preventing breakage during rolling, and it is possible to prevent deterioration in life due to breakage of the particles.

The compound represented by Formula 1 according to the present invention is a single crystal and a single particle. By being formed of a single crystal and a single particle, structurally stable and high-density electrodes can be implemented, and a lithium secondary battery including the same can have improved lifespan characteristics and high energy density at the same time.

The cathode active material according to an embodiment of the present invention may have a main peak at least in the (003) plane and a minor peak in the (104) plane in an X-ray diffraction spectrum obtained by XRD analysis using CuKα rays. According to an embodiment, the main peak may be 2θ = 19.00±0.50° and the minor peak may be a peak at a position of 2θ = 44.50±0.50°.

The cathode active material according to an embodiment of the present invention has an X-ray diffraction spectrum obtained by XRD analysis using CuKα rays, 2θ=18.5±0.50°, 2θ=36.5±0.50°, 2θ=38.0±0.50°, 2θ=44.5± It may have a peak at the positions of 0.50°, 2θ=48.5±0.50°, 2θ=58.5±0.50°, 2θ=64.5±0.50°, and 2θ=68.0±0.50°.

In the case of the positive electrode active material according to an embodiment of the present invention, in the X-ray diffraction spectrum obtained by XRD analysis, when the maximum intensity of the peak on the (003) plane is IA and the maximum intensity of the peak on the (104) plane is IB, The IA/IB value may be 1.2 or higher. The IA/IB value indicates the degree of structural alignment, and the larger the IA/IB value, the higher the structural stability, and the IA/IB value of 1.2 or more means that the structural alignment degree is considerably high, which is one of the present invention. This means that the positive electrode active material according to the embodiment has a well-developed layered structure.

Hereinafter, a method of manufacturing a cathode active material according to an aspect will be described in detail.

A method of preparing a positive electrode active material according to an embodiment includes a mixing step of obtaining a precursor mixture by mixing a lithium precursor, a transition metal precursor, a phosphorus precursor, and a boron precursor; And

A heat treatment step of heat-treating the precursor mixture to obtain a positive electrode active material represented by the following Formula 1; may include:

<Formula 1>

Li _x P _α M _1-β B _β O ₂

In Formula 1,

M is one or more transition metals,

0.98≤x≤1.02, 0<α≤0.007, 0<β≤0.1.

For a detailed description of Chemical Formula 1, refer to the foregoing.

The mixing step includes mechanical mixing the precursor. The mechanical mixing is carried out dry. The mechanical mixing is to form a uniform mixture by pulverizing and mixing substances to be mixed by applying a mechanical force. Mechanical mixing is a mixing device such as a ball mill, a planetary mill, a stirred ball mill, a vibrating mill, etc. using chemically inert beads. It can be done using At this time, in order to maximize the mixing effect, alcohol such as ethanol and higher fatty acids such as stearic acid may be selectively added in small amounts.

The mechanical mixing is carried out in an oxidizing atmosphere, which is to prevent reduction of the transition metal in a transition metal source (eg, Ni compound), thereby realizing structural stability of the active material.

The lithium precursor may include lithium hydroxide, oxide, nitride, carbonate, or a combination thereof, but is not limited thereto. For example, the lithium precursor may be LiOH or Li ₂ CO ₃ .

The transition metal precursor may include a transition metal hydroxide, oxide, nitride, carbonate or a combination thereof, but is not limited thereto. For _{example, NiO, NiCO 3, MnO,} MnCO 3, CoO, CoCO 3, may be an AlO, AlCO _3, or a combination thereof.

The phosphorus precursor includes all phosphorus-containing compounds capable of providing the P element. For example, the phosphorus precursor may be NH ₄ HPO ₄ .

The boron precursor may include boron hydroxide, oxide, nitride, carbonate, or a combination thereof, but is not limited thereto. The sodium precursor may be BOH or H ₃ BO ₃ .

After the mixing step, it may include a step of heat treatment. The heat treatment step may include a first heat treatment step and a second heat treatment step. The first heat treatment step and the second heat treatment step may be performed continuously or may have a rest period after the first heat treatment step. In addition, the first heat treatment step and the second heat treatment step may be performed in the same chamber or may be performed in different chambers.

The heat treatment temperature in the first heat treatment step may be higher than the heat treatment temperature in the second heat treatment step.

The first heat treatment step may be performed at a heat treatment temperature of 800°C to 1200°C. The heat treatment temperature may be, for example, 850°C to 1200°C, 860°C to 1200°C, 870°C to 1200°C, 880°C to 1200°C, 890°C to 1200°C, or 900°C to 1200°C, but limited thereto It does not, and includes all the ranges configured by selecting any two points within the range.

In the second heat treatment step, the heat treatment temperature may be performed at 700°C to 800°C. The heat treatment temperature is 710 ℃ to 800 ℃, 720 ℃ to 800 ℃, 730 ℃ to 800 ℃, 740 ℃ to 800 ℃, 750 ℃ to 800 ℃, 700 ℃ to 780 ℃, 700 ℃ to 760 ℃, 700 ℃ to 750 ℃, or 700 ℃ to 730 ℃ may be, but is not limited thereto, and includes all ranges configured by selecting any two points within the above range.

According to an embodiment, the heat treatment time in the first heat treatment step may be shorter than the heat treatment time in the second heat treatment step.

For example, the heat treatment time in the first heat treatment step may be 3 hours to 5 hours, 4 hours to 5 hours, or 3 hours to 4 hours, but is not limited thereto, and any two points within the above range are selected. It includes all the ranges constructed by this.

For example, the heat treatment time in the second heat treatment step may be 10 hours to 20 hours, 10 hours to 15 hours, but is not limited thereto, and includes all ranges configured by selecting any two points within the range. .

The first heat treatment step may include performing heat treatment at a heat treatment temperature of 800°C to 1200°C for 3 to 5 hours.

The second heat treatment step may include performing heat treatment at a heat treatment temperature of 700°C to 800°C for 10 to 20 hours.

In the first heat treatment step, the lithium transition metal oxide forms the positive electrode active material having a layered structure and at the same time causes the growth of particles, thereby forming a single crystal shape. In the first heat treatment step, the primary particles in the lithium transition metal oxide in the form of secondary particles rapidly grow and are fused to each other while revealing the inside of the primary particles as they cannot withstand the stress between the particles, so that the single crystal positive active material for secondary batteries is It is thought to be formed. The second heat treatment step increases the crystallinity of the layered structure generated in the first heat treatment step by performing heat treatment at a lower temperature in the first heat treatment step for a long time. Through the first and second heat treatment steps, a single phase, single crystal, and single particle nickel-based positive electrode active material may be obtained.

According to one embodiment, the lithium transition metal oxide manufactured by the above manufacturing method is a single crystal or a single particle, and the single crystal may have a layered structure. In addition, the average particle diameter of the lithium transition metal oxide may be 0.1㎛ to 20㎛.

In addition, in the positive electrode active material manufactured by the method of manufacturing the positive electrode active material, P is partially located in the place of the empty tetrahedron in the single crystal structure, thereby securing the stability of the battery and achieving a long life by suppressing the phase transition during charging/discharging.

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

According to another aspect, the anode; cathode; And there is provided a lithium secondary battery comprising; an electrolyte. The lithium secondary battery has a capacity retention rate (%) after 50 times of charging and discharging of 90% or more of the capacity after initial charging and discharging. In contrast, the capacity retention rate of a lithium secondary battery including a positive electrode active material in which some of the transition metals are not substituted with B is less than 90% after charging and discharging 50 times.

The positive electrode and a lithium secondary battery including the same may be manufactured by the following method.

First, the anode is prepared.

For example, a cathode active material composition in which the above-described cathode active material, conductive material, binder, and solvent are mixed is prepared. The positive electrode active material composition is directly coated on a metal current collector to prepare a positive electrode plate. Alternatively, the positive electrode active material composition may be cast on a separate support, and then a film peeled from the support may be laminated on a metal current collector to prepare a positive electrode plate. The anode is not limited to the shapes listed above, but may be in a shape other than the above shape.

Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon black; Conductive tubes such as carbon nanotubes; Conductive whiskers such as fluorocarbon, zinc oxide, and potassium titanate; Conductive metal oxides such as titanium oxide; And the like 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 the binder, vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, mixtures thereof, metal salts, or styrene butadiene Rubber-based polymers and the like may be used, but are not limited thereto, and any one that can be used as a binder in the art may be used. As another example of the binder, lithium salt, sodium salt, calcium salt, or Na salt of the above-described polymer may be used.

As the solvent, N-methylpyrrolidone, acetone, or water may be used, but are not limited thereto, and any solvent that can be used in the art may be used.

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

Next, the cathode is prepared.

For example, an anode active material composition is prepared by mixing an anode active material, a conductive material, a binder, and a solvent. The negative electrode active material composition is directly coated and dried on a metal current collector having a thickness of 3 μm to 500 μm to prepare a negative electrode plate. Alternatively, after the negative active material composition is cast on a separate support, a film peeled from the support may be laminated on a metal current collector to prepare a negative electrode plate.

The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes to the battery, and for example, copper, nickel, or copper surface-treated with carbon may be used.

The anode active material may be any material that can be used as an anode 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, 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, or Te.

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.

In the negative active material composition, the conductive material, the binder, and the solvent may be the same as those of the positive active material composition.

The contents of the negative electrode active material, the conductive material, the binder, and the solvent are generally used in lithium batteries. One or more of the conductive material, the binder, and the solvent may be omitted depending on the use and configuration of the lithium battery.

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. The separator may be a single film or a multilayer film, for example, as selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), or a combination thereof. , It may be in the form of non-woven fabric or woven fabric. Further, a mixed multilayer film such as a polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, a polypropylene/polyethylene/polypropylene three-layer separator, and the like may be used. 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, 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. Cyclic carbonates, such as propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, and vinylene carbonate, for example; Chain carbonates such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate and dibutyl carbonate; Esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone; Ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, and 2-methyltetrahydrofuran; Nitriles such as acetonitrile; And amides such as dimethylformamide. These can be used alone or in combination of a plurality of them. For example, a solvent in which a cyclic carbonate and a chain carbonate are mixed can be used.

In addition, a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide and polyacrylonitrile with an electrolyte solution, or LiI, Li ₃ N, Li _x Ge _y P _z S _α , Li _x Ge _y P _z S _α X _δ ( Inorganic solid electrolytes such as X=F, Cl, Br) can be used.

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. 6, 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 5 may be a cylindrical shape, a square shape, a pouch type, a coin type, or a thin film type. For example, the lithium battery 1 may be a thin film type battery. The lithium battery 1 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, power storage systems, and the like.

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

[Example]

(Manufacture of positive electrode active material)

Example 1

100 g of Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and 40.0 g of Li ₂ CO ₃ and 0.2 g of (NH ₄ ) ₂ HPO ₄ and 0.03 g of H ₃ BO ₃ after mechanical mixing, 950 ^o C 6 hours and A single crystal LiP _0.007 Ni _0.8 Co _0.1 Mn _0.1 B _0.0005 O ₂ compound was synthesized through firing at 850 ^o C for 10 hours.

Example 2

100 g of Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and 40.0 g of Li ₂ CO ₃ and 0.2 g of (NH ₄ ) ₂ HPO ₄ and 0.18 g of H ₃ BO ₃ after mechanical mixing, 950 ^o C 6 hours and A single crystal LiP _0.007 Ni _0.8 Co _0.1 Mn _0.1 B _0.003 O ₂ compound was synthesized through firing at 850 ^o C for 10 hours.

Example 3

100 g of Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and 40.0 g of Li ₂ CO ₃ and 0.2 g of (NH ₄ ) ₂ HPO ₄ and 0.60 g of H ₃ BO ₃ after mechanical mixing, 950 ^o C 6 hours and A single crystal LiP _0.007 Ni _0.8 Co _0.1 Mn _0.1 B _0.01 O ₂ compound was synthesized through firing at 850 ^o C for 10 hours.

Comparative Example 1

100 g of Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and 40.0 g of Li ₂ CO ₃ and 0.2 g of (NH ₄ ) ₂ HPO ₄ were mechanically mixed, followed by firing at 950 ^o C for 6 hours and 850 ^o C for 10 hours. Single crystal LiP _0.007 Ni _0.8 Co _0.1 Mn _0.1 O ₂ compound was synthesized.

(Creation of Coin Cell)

Example 4

The cathode active material obtained in Example 1: the conductive material: the binder was mixed in a weight ratio of 94:3:3 to prepare a slurry. Here, carbon black was used as the conductive material, and polyvinylidene fluoride (PVdF) was dissolved in an N-methyl-2-pyrrolidone solvent and used as the binder.

The slurry was uniformly coated on an Al current collector and dried at 110° C. for 2 hours to prepare a positive electrode. The loading level of the electrode plate was 11.0 mg/cm ² and the electrode density was 3.6 g/cc.

Using the positive electrode thus prepared as a working electrode, a lithium foil used as a counter electrode, and the EC / EMC / DEC as a lithium salt in a mixed solvent in a volume ratio of 3/4/3 to the concentration of 1.3M LiPF ₆ A CR2032 half cell was fabricated according to a commonly known process using a liquid electrolyte added as possible.

Examples 5 to 6

A half cell was manufactured in the same manner as in Example 4, except that the positive electrode active materials obtained in Examples 2 to 3 were used, respectively, instead of the positive electrode active material obtained in Example 1.

Comparative Example 2

A half cell was manufactured in the same manner as in Example 4, except that the positive electrode active material obtained in Comparative Example 1 was used instead of the positive electrode active material obtained in Example 1.

Evaluation Example 1: Elemental evaluation of positive electrode active material

Inductively coupled plasma (ICP) analysis was performed on the positive electrode active materials obtained in Examples 1 to 3 and Comparative Example 1, and the results are shown in Table 1 below.

Li Ni Co Mn B P Comparative Example 1 1.00 79.5 10.3 10.2 0 0.007 Example 1 1.00 79.6995 10.1 10.2 0.0005 0.007 Example 2 1.00 79.197 10.6 10.2 0.003 0.007 Example 3 1.00 79.49 10.4 10.0 0.01 0.007

As shown in Table 1, considering that the molar ratio of B increased as the molar ratio of the transition metal (Ni, Co, Mn) decreased, it can be seen that the transition metal was substituted with B. In addition, considering that the molar ratio of P is constant independent of transition metals (Ni, Co, Mn) and lithium, it is considered that P independently exists in empty spaces in the crystal.

Evaluation Example 2: Evaluation of particle size of positive electrode active material

SEM (Verios 460, FEI) photos were taken for the positive electrode active materials obtained in Examples 1 to 3 and Comparative Example 1, and the average particle size was measured (Cilas1090, Scinco), and the results are shown in FIGS. 1 and 2. In addition, the size of the particle size is shown in Table 2 below.

D _min (㎛) D ₁₀ (㎛) D ₅₀ (㎛) D ₉₀ (㎛) D _max (㎛) Example 1 0.4 2.9 6.5 11.0 18.0 Example 2 0.4 2.8 6.3 10.8 18.0 Example 3 0.3 2.6 6.5 10.7 18.0 Comparative Example 1 0.4 2.4 6.4 10.8 18.0

Referring to FIG. 2, although B was additionally introduced into the lithium transition metal oxide of Comparative Example 1, it can be seen that there is no significant change in the average particle diameter of the particles.

Evaluation Example 3: Crystal evaluation of positive electrode active material

For the positive electrode active materials obtained in Examples 1 to 3 and Comparative Example 1, XRD analysis using CuKα rays was performed, and the X-ray spectrum is shown in FIG. 3.

3, Examples 1 to 3 and Comparative Example 1 all showed the same XRD pattern. In other words, in the positive electrode active materials of Examples 1 to 3 in which B ions were introduced into the positive electrode active material of Comparative Example 1, B ions did not form a bond with other elements on the surface, form a new phase, or cause a phase transition. Can be seen.

In addition, the positive electrode active material obtained in Example 3 was photographed using a high resolution transmission electron microscopy (HR-TEM), and energy dispersive X-ray spectroscopy ( EDX)) analysis was carried out. The results are shown in FIG. 4.

Referring to FIG. 4, it can be seen that B ions are included in the crystal structure.

In the end, considering the results of elemental evaluation of the positive electrode active material and the contents of the crystal evaluation, the molar ratio of B ions increased as the reduced molar ratio of transition metal ions, and the introduced B ions formed a new compound without changing the crystal structure of the positive electrode active material. It was not done, and it was confirmed that B ions were present in the positive electrode active material, which proves that some of the transition metals in the crystal structures of the positive electrode active materials obtained in Examples 1 to 3 had a crystal structure in which B ions were replaced.

Evaluation Example 4: Room temperature life evaluation

For the half-cells produced in Examples 4 to 6 and Comparative Example 2, charge in CC mode to 4.3V at 0.5C at room temperature (25°C), and then proceed in CV mode to a current corresponding to 0.05C I did. Next, discharge was performed in CC mode to 3.0V at 1C, and this process was repeated a total of 50 times.

The capacity retention rate after 50 times of charging and discharging was calculated for the initial capacity, and the results are shown in Table 3 below. In addition, a graph showing the capacity retention rate according to the cycle is shown in FIG. 5.

After 50 charging/discharging
Capacity retention rate (%) Example 4 90.4 Example 5 91.3 Example 6 95.8 Comparative Example 2 89.3

Referring to Table 3 and FIG. 5, the capacity retention rate after 50 charging/discharging is in Comparative Example 2 in which Examples 4 to 6 employing positive electrodes including the positive electrode active materials of Examples 1 to 3 doped with Na were not. Compared to that, it showed about 2-6% higher capacity retention rate.

In the above, preferred embodiments according to the present invention have been described with reference to the drawings and embodiments, but these are only exemplary, and various modifications and other equivalent embodiments are possible from those of ordinary skill in the art. You will be able to understand. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims (19)

Including a compound represented by the following formula (1),
The compound is a single crystal, and the P element is present in the single crystal, the cathode active material:
<Formula 1>
Li _x P _α M _1-β B _β O ₂
In Formula 1,
M is one or more transition metals,
0.98≤x≤1.02, 0<α≤0.007, 0<β≤0.1. The method of claim 1,
The M is Ni, Co, Mn, Al, Mg, V, and including one or more transition metals selected from Ti, the positive electrode active material. The method of claim 1,
Formula 1 is represented by the following Formula 2, a positive electrode active material:
<Formula 2>
Li _x P _α Ni _1-β-γ M1 _γ B _β O ₂
In Formula 2,
M1 is at least one transition metal selected from Co, Mn, Al, Mg, V, and Ti,
0.98≤x≤1.02, 0<α≤0.007, 0<β≤0.1, 0<γ<1, and 0<β+γ<1. The method of claim 1,
Formula 1 is represented by the following Formula 3, a positive electrode active material:
<Formula 3>
Li _x P _α Ni _1-β-γ-δ M1 _γ M2 _δ B _β O ₂
In Formula 3,
M1 and M2 are each independently at least one transition metal selected from Co, Mn, Al, Mg, V, and Ti,
M1 and M2 are different from each other,
0.98≤x≤1.02, 0<α≤0.007, 0<β≤0.1, 0<γ<1, 0<δ<1 and 0<β+γ+δ<1. The method of claim 4,
0<γ<0.4, and 0<δ<0.4, the positive electrode active material. The method of claim 4,
M1 is Co,
M2 is at least one element selected from Mn, Mg, V, and Ti, the cathode active material. The method of claim 1,
Formula 1 is a cathode active material represented by any one of the following Formulas 4 to 6:
<Formula 4>
_{Li x 'P α' Ni 1} -β'-γ'-δ 'Co γ' Mn δ 'B β' O 2
<Formula 5>
Li _x'' P _α'' Ni _{1-β''-γ''-δ''} Co _γ'' Al _δ'' B _β'' O ₂
<Formula 6>
Li _x''' P _α''' Ni _{1-β'''-γ'''-δ'''} Co _γ''' B _β''' O ₂
In Formulas 4 to 6,
0.98≤x'≤1.02, 0<α'≤0.007, 0<β'≤0.01, 0<γ'≤0.3, and 0<δ'≤0.3,
0.98≤x''≤1.02, 0<α''≤0.007, 0<β''≤0.01, 0<γ''≤0.3, and 0<δ''≤0.05,
0.98≤x'''≤1.02, 0<α'''≤0.007, 0<β'''≤0.01 and 0<γ'''≤0.2. The method of claim 1,
The positive electrode active material has an average particle diameter (D50) of 0.1 μm to 20 μm. delete The method of claim 1,
The compound is a single particle, a positive electrode active material. The method of claim 1,
The positive electrode active material has an X-ray diffraction spectrum obtained by XRD analysis using CuKα rays has a main peak at least in the (003) plane and a negative peak in the (104) plane. The method of claim 11,
When the maximum intensity of the main peak on the (003) plane is set to IA and the maximum strength of the minor peak on the (104) plane is set to IB, the positive electrode active material has an IA/IB value of 1.2 or more. A mixing step of mixing a lithium precursor, a transition metal precursor, a phosphorus precursor, and a boron precursor to obtain a precursor mixture; And
Including; a heat treatment step of heat-treating the precursor mixture to obtain a positive electrode active material represented by the following formula (1),
The compound is a single crystal, and the P element is a method for preparing a cathode active material present in the single crystal:
<Formula 1>
Li _x P _α M _1-β B _β O ₂
In Formula 1,
M is one or more transition metals,
0.98≤x≤1.02, 0<α≤0.007, 0<β≤0.1. The method of claim 13,
The mixing step comprises mechanically mixing the precursor, a method for producing a positive electrode active material. The method of claim 13,
The heat treatment step includes a first heat treatment step and a second heat treatment step. The method of claim 15,
The heat treatment temperature in the first heat treatment step is higher than the heat treatment temperature in the second heat treatment step. The method of claim 15,
The heat treatment time in the first heat treatment step is shorter than the heat treatment time in the second heat treatment step. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 8 and 10 to 12;
cathode; And
Electrolytes;
Lithium secondary battery comprising a. The method of claim 18,
The lithium secondary battery has a capacity retention rate (%) after 50 charging and discharging times of 90% or more with respect to the capacity after initial charging and discharging.

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