KR101385334B1 - Mixed positive electrode active material for lithium ion secondary battery and lithium ion secondary battery using the same - Google Patents

Abstract

[식 중의 x는 0.1≤x≤0.5를 만족하고, M은 Ni_αCo_βMn_γ(여기서 α, β, γ는 각각 0<α≤0.5, 0≤β≤0.33, 0<γ≤0.5를 만족함)을 나타냄]으로 표시되는 정극 활물질과, 이 정극 활물질의 표면에 존재하고,

(식 중의 y는 0.1<y<0.17을 만족함)으로 표시되는 활물질 조제를 포함한다. 리튬 이온 2차 전지는, 이러한 복합 정극 활물질을 포함하는 정극을 구비한다.It is providing the composite positive electrode active material for lithium secondary batteries which has high discharge capacity and is excellent in cycling characteristics, and the lithium ion secondary battery using the same. The composite positive electrode active material for a lithium ion secondary battery,

[Wherein x satisfies 0.1 ≦ x ≦ 0.5, and M satisfies Ni _α Co _β Mn _γ (where α, β, and γ satisfy 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, and 0 <γ ≦ 0.5, respectively). ) Is present on the surface of the positive electrode active material and the positive electrode active material,

The active material preparation represented by (y in formula satisfies 0.1 <y <0.17) is included. The lithium ion secondary battery is equipped with the positive electrode containing such a composite positive electrode active material.

Description

MIXED POSITIVE ELECTRODE ACTIVE MATERIAL FOR LITHIUM ION SECONDARY BATTERY AND LITHIUM ION SECONDARY BATTERY USING THE SAME}

This invention relates to the positive electrode active material used for the positive electrode of a lithium ion secondary battery, More specifically, it is related with the composite positive electrode active material containing a specific positive electrode active material and active material preparation, and a lithium ion secondary battery using the same.

In recent years, in order to cope with air pollution and global warming, reduction of carbon dioxide emission is desired. In the automobile industry, reduction of carbon dioxide emission by the introduction of an electric vehicle (EV) and a hybrid electric vehicle (HEV) is expected, and development of the motor drive secondary battery which becomes a key when putting these into practical use is actively performed.

In particular, such a motor-driven secondary battery is desired to have high capacity and excellent cycle characteristics, and therefore, a lithium ion secondary battery having a high theoretical energy among various secondary batteries has attracted attention.

In order to improve the energy density in a lithium ion secondary battery, it is necessary to increase the electric charge accumulated per unit mass of a positive electrode and a negative electrode, and solid solution system material attracts attention as a positive electrode material which may satisfy such a requirement. .

And, among these materials are employed system, it is expected to Li ₂ MnO ₃ as a lithium layer over the positive electrode active material (solid solution active material), high-capacity positive electrode material candidate for the parent structure (see, for example, Patent Document 1).

Japanese Patent Application Laid-open No. Hei 9-55211

However, also in the Li excess layered positive electrode active material as mentioned above, there existed a problem that it deteriorated when charge-discharge was performed at high electric potential.

This invention is made | formed in view of the subject which this prior art has, and the objective is to use the composite positive electrode active material for lithium secondary batteries which has high discharge capacity, and was excellent in cycling characteristics, and the lithium ion secondary battery using the same. To provide.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to achieve the said objective, the present inventor discovered that the said objective can be achieved by using together the specific solid solution positive electrode active material and the preparation of the predetermined active material which has ion conductivity, and completed this invention. It came to.

That is, although the composite positive electrode active material for lithium ion secondary batteries of this invention contains a specific solid solution positive electrode active material and active material preparation, specifically,

[Chemical Formula 1]

[Wherein x satisfies 0.1 ≦ x ≦ 0.5, and M satisfies Ni _α Co _β Mn _γ (where α, β, and γ satisfy 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, and 0 <γ ≦ 0.5, respectively). ) Represents a positive electrode active material,

Exists on the surface of this positive electrode active material,

(2)

It is characterized by including the active material preparation represented by (y in formula satisfies 0.1 <y <0.17).

Moreover, the lithium ion secondary battery of this invention is equipped with the positive electrode containing the composite positive electrode active material for lithium secondary batteries as above-mentioned.

According to the present invention, since a specific solid solution positive electrode active material and a predetermined active material preparation having ion conductivity are used in combination, a composite positive electrode active material for a lithium secondary battery having high discharge capacity and excellent cycle characteristics and lithium ion 2 using the same A secondary battery can be provided.

Hereinafter, the composite positive electrode active material for lithium ion secondary batteries of this invention is demonstrated.

The composite positive electrode active material for lithium ion secondary batteries of this invention contains the positive electrode active material represented by General formula (1) shown below, and the active material preparation represented by General formula (2), and this active material preparation exists in the surface of a positive electrode active material.

[Chemical Formula 1]

[Wherein x satisfies 0.1 ≦ x ≦ 0.5, and M satisfies Ni _α Co _β Mn _γ (where α, β, and γ satisfy 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, and 0 <γ ≦ 0.5, respectively). And satisfies α + β + γ = 1).

(2)

(Y in the formula satisfies 0.1 <y <0.17).

Here, the positive electrode active material represented by the formula (1), conventionally with, but referred that such a solid solution positive electrode active material, Li over-layered positive electrode active material, Li ₂ MnO _3-based positive electrode active material, according to the present invention, the composition to satisfy represented by the formula (1).

First, for x, it is necessary to satisfy 0.1≤x≤0.5.

When x exceeds 0.5, the charge / discharge capacity per weight of the positive electrode active material cannot be 200 mAh / g or more higher than the known layered positive electrode active material. Further, in the x is less than 0.1, the composition is closer to Li ₂ MnO _3, there is a case that can not be charged and discharged.

In addition, although M is a component of the nickel-cobalt-manganese system represented by Ni ( _alpha) Co ( _beta) Mn ₍ gamma) as mentioned above, it needs to satisfy 0 <(alpha) <0.5 about (alpha).

When α exceeds 0.5, when the oxidation number of Ni is made bivalent, Ni is not included in the composite positive electrode active material satisfying the composition range of x.

In addition, it is required to satisfy 0≤β≤0.33 for β.

When (beta) exceeds 0.33, cobalt (Co) is not contained in the said composite positive electrode active material in which the oxidation number contains bivalent Ni and satisfy | fills the composition range of x.

In addition, for γ, it is required to satisfy 0 <γ≤0.5.

When gamma exceeds 0.5, when the oxidation number of manganese (Mn) is tetravalent, Mn is not contained in the said composite positive electrode active material which satisfy | fills the composition range of said (alpha), (beta), and x.

Further, for M in the formula (1), the following formula

Ni _α Co _β Mn _γ M ¹ _α

(Α, β, γ, and σ in the formula satisfy 0 <α≤0.5, 0≤β≤0.33, 0 <γ≤0.5, 0≤σ≤0.1, respectively, and also denote α + β + γ + σ = 1. Satisfactory and M ¹ is at least one selected from the group consisting of Al, Fe, Cu, Mg and Ti).

In this case, although the reason for numerical limitation of (alpha), (beta), and (gamma) is similar to the above, it is preferable to satisfy 0 <= <== 0.1 about (sigma).

When sigma exceeds 0.1, the reversible capacity of a positive electrode active material may fall. Further, as the M ^1, among the above-mentioned elements, it can be preferably used for Al and Ti.

In general, nickel (Ni), cobalt (Co), and manganese (Mn) have the viewpoints of improving the purity of the material and improving the electronic conductivity, aluminum (Al), iron (Fe), copper (Cu), and magnesium (Mg). And titanium (Ti) is known to contribute to capacity | capacitance and an output characteristic from a viewpoint of stability improvement of a crystal structure.

On the other hand, the active material preparation represented by the formula (2) is an inorganic solid oxide of ion conductivity, so-called lithium (Li)-lanthanum (La)-titanium (Ti) oxide (hereinafter, abbreviated as "LLT").

In General formula (2), y needs to satisfy 0.1 <y <0.17. If the deviation is within this range, the ionic conductivity of the art, and the compound is less than 10 ⁴ S · cm ^-1 or less, resulting in a factor for inhibiting the movement of lithium ions in the obtained composite positive electrode active material.

As mentioned above, in the composite positive electrode active material of this invention, the active material preparation which is an ion conductive material represented by General formula (2) is arrange | positioned on the surface of the positive electrode active material represented by General formula (1).

Therefore, in the lithium ion secondary battery provided with the positive electrode using this composite positive electrode active material, since electrolyte solution and a positive electrode active material do not directly contact even at the high potential (4.6 V or more in Li standard) at the time of charge, electrolyte solution The decomposition of is suppressed and the cycle characteristics are improved.

That is, by disposing an ion conductive inorganic solid oxide on the surface of the positive electrode active material, since the cracks of particles accompanying the volume change of the positive electrode active material during the charge and discharge process are suppressed, the structure of the positive electrode can be retained, and the cycle characteristics Can be improved.

In the composite positive electrode active material of the present invention, the content ratio with the active material assistant represented by the formula (2) is preferably 1 to 20% by mass.

When the content ratio of the active material preparation is less than 1% by mass, the effect of disposing the above-described active material preparation may not be obtained. When it exceeds 20% by mass, the amount of the positive electrode active material in the composite positive electrode active material is relatively decreased. In some cases, the battery energy density may be reduced.

In the composite positive electrode active material of the present invention, the state of presence of the active material preparation on the surface of the positive electrode active material will be described.

As described above, the active material preparation is present on the surface of the positive electrode active material to suppress the direct contact between the electrolyte solution and the positive electrode active material at the time of charging the lithium ion secondary battery, to achieve a function of suppressing decomposition of the electrolyte solution. Silver is particularly effective at the time of charging at high potential.

From such a viewpoint, it is preferable that the active material preparation is unevenly distributed on the surface side rather than inside of the positive electrode active material, and typically, it is preferable that the active material preparation covers the entire surface of the positive electrode active material with a constant thickness.

The composite positive electrode active material of this invention is comprised by covering the positive electrode active material represented by General formula (1) with the active material preparation represented by General formula (2), Comprising: The said positive electrode active material forms a substantially spherical shape, and the said composite positive electrode active material forms a substantially spherical shape. In the case, between the coating thickness t of the active material preparation and the particle diameter r of the positive electrode active material,

r / (r + t) × 100 = 0.16 to 3.05 (%)

It is preferable that the relationship represented by is established.

In this relation, when it exceeds 3.05%, the function as a positive electrode active material may fall and initial stage capacity may become low.

On the other hand, when it is less than 0.16%, the effect by arrange | positioning said active material preparation may not be acquired.

Moreover, in the composite positive electrode active material of this invention, although it is preferable that an active material preparation has coat | covered the whole surface of a positive electrode active material, it is not limited to this, If a desired effect is acquired (preferably, said relationship is satisfied The active material preparation may partially cover the surface of the positive electrode active material.

Next, the lithium ion secondary battery of this invention is demonstrated.

As mentioned above, the lithium ion secondary battery of this invention has a positive electrode containing the composite positive electrode active material demonstrated above.

Therefore, the lithium ion secondary battery of this invention has high discharge capacity and is excellent in cycling characteristics.

Hereinafter, the member, structure, etc. which are used for the lithium ion secondary battery of this invention are demonstrated.

<Positive electrode active material>

As a positive electrode active material, as mentioned above, although the composite positive electrode active material of this invention is an essential component, it is also possible to use other positive electrode active materials other than this together.

As such a positive electrode active material, a lithium transition metal complex oxide, a lithium transition metal phosphate compound, a lithium transition metal sulfate compound, a ternary system, NiMn system, NiCo system, a spinel Mn system, etc. are mentioned, for example.

Examples of the lithium-transition metal composite oxide include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni, Mn, Co) O ₂ , Li (Li, Ni, Mn, Co) O ₂ , LiFePO ₄ , And some of these transition metals are substituted by other elements.

Examples of the ternary system include nickel cobalt manganese (composite) positive electrode materials. Examples of the spinel Mn system include LiMn ₂ O ₄ and the like. As NiMn-based, LiNi _{0 .5} and the like Mn _{1 .5} O _4. Examples of the NiCo system include Li (NiCo) O ₂ and the like.

Plural types of these positive electrode active materials can also be used together.

In addition, when these positive electrode active materials each express an inherent effect, and the optimum particle size differs, in addition to expressing each unique effect, what is necessary is just to brand the optimum particle sizes, and to use the particle diameter of all active materials. It is not necessary to homogenize.

&Lt; Negative electrode active material &

The negative electrode active material is not particularly limited as long as the negative electrode active material can reversibly occlude and release lithium, and any conventionally known negative electrode active material can be used.

For example, high crystalline carbon graphite (natural graphite, artificial graphite, etc.), low crystalline carbon (soft carbon, hard carbon), carbon black (Ketjen black, acetylene black, channel black, lamp black, oil furnace black, Thermal materials such as thermal black), fullerenes, carbon nanotubes, carbon nanofibers, carbon nanohorns, carbon fibrils; Si, Ge, Sn, Pb, Al, In, Zn, H, Ca, Sr, Ba, Ru , A group of elements alloyed with lithium such as Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te, Cl, and these Oxides containing elements of silicon [SiO, SiO _x (0 <x <2), tin dioxide (SnO ₂ ), SnO _x (0 <x <2), SnSiO ₃ Etc.] and carbides [silicon carbide (SiC) etc.] etc .; Metal materials such as lithium metal; Lithium-transition metal composite oxides such as lithium-titanium composite oxide (lithium titanate: Li ₄ Ti ₅ O ₁₂ ); And other conventionally known negative electrode active materials can be used.

The said negative electrode active material may be used independently or may be used in the form of 2 or more types of mixtures.

<Electrolyte Layer>

The electrolyte layer is a layer containing a nonaqueous electrolyte. The nonaqueous electrolyte (specifically, a lithium salt) contained in the electrolyte layer has a function as a carrier of lithium ions that move between the governmental poles during charging and discharging. The nonaqueous electrolyte is not particularly limited as long as it can exhibit such a function, but a liquid electrolyte or a polymer electrolyte can be used.

The liquid electrolyte has a form in which lithium salt is dissolved in an organic solvent. As an organic solvent, carbonates, such as ethylene carbonate (EC), a propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), can be illustrated, for example.

Examples of lithium salts include Li (CF ₃ SO ₂ ) ₂ N, Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiTaF ₆ , LiClO ₄ , LiCF ₃ SO _3, and the like. Compounds that can be added to the active material layer can likewise be employed.

On the other hand, the polymer electrolyte is classified into a gel polymer electrolyte (gel electrolyte) containing an electrolyte solution and an intrinsic polymer electrolyte containing no electrolyte solution.

The gel polymer electrolyte preferably has a constitution in which the above liquid electrolyte is injected into a matrix polymer (host polymer) composed of an ion conductive polymer. By using the gel polymer electrolyte as the electrolyte, it is excellent in that the fluidity of the electrolyte is lost and it is easy to block the ion conductivity between the layers.

It does not specifically limit as an ion conductive polymer used as a matrix polymer (host polymer). (PVDF-HFP), polyethylene glycol (PEG), polyvinylidene fluoride (PVDF), polyvinylidene fluoride and hexafluoropropylene copolymer, , Polyacrylonitrile (PAN), polymethylmethacrylate (PMMA), and copolymers thereof.

Here, although said ion conductive polymer may be the same as or different from the ion conductive polymer used as electrolyte in an active material layer, the same thing is preferable. The kind of the electrolytic solution (lithium salt and organic solvent) is not particularly limited, and organic solvents such as electrolyte salts such as lithium salts and the carbonates exemplified above can be used.

The intrinsic polymer electrolyte has a structure in which lithium salt is dissolved in the matrix polymer and does not contain an organic solvent. Therefore, there is no fear of liquid leakage from the battery by using the intrinsic polymer electrolyte as the electrolyte, and the reliability of the battery can be improved.

The matrix polymer of the gel polymer electrolyte or the intrinsic polymer electrolyte can express excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, a polymerization initiator such as thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization and the like is applied to a polymeric polymer (for example, PEO or PPO) for forming a polymer electrolyte by using a proper polymerization initiator .

The nonaqueous electrolyte contained in these electrolyte layers may be single 1 type, or 2 or more types may be sufficient as it.

In addition, when an electrolyte layer consists of a liquid electrolyte or a gel polymer electrolyte, a separator is used for an electrolyte layer.

As a specific form of a separator, the microporous film which consists of polyolefins, such as polyethylene and a polypropylene, is mentioned, for example.

In order to reduce the internal resistance, the thickness of the electrolyte layer is preferably as thin as possible. The thickness of the electrolyte layer is usually 1 to 100 占 퐉, preferably 5 to 50 占 퐉.

<Binder>

The binder is added for the purpose of binding the active materials or the active material and the current collector to maintain the electrode structure.

As such a binder, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl acetate, polyimide (PI), polyamide (PA), polyvinyl chloride (PVC), polymethyl acrylate (PMA) ), Polymethyl methacrylate (PMMA), polyethernitrile (PEN), polyethylene (PE), polypropylene (PP) and polyacrylonitrile (PAN), such as thermoplastic resins, epoxy resins, polyurethane resins, and glass Thermosetting resins, such as fish resin, and rubber type materials, such as styrene butadiene rubber (SBR), are mentioned.

<Challenge Preparation>

A conductive aid (also called a conductive agent) refers to an electrically conductive additive blended in order to improve conductivity.

The conductive aid that can be used in the present invention is not particularly limited, and conventionally known ones can be used. For example, carbon materials such as carbon black such as acetylene black, graphite, and carbon fiber can be cited.

When the conductive aid is contained, the electronic network in the inside of the active material layer is effectively formed, which can contribute to the improvement of the output characteristics of the battery and the reliability improvement by the improvement of the liquid retention property of the electrolyte solution.

<Positive electrode>

In the lithium ion secondary battery as described above, the positive electrode includes a positive electrode active material layer on one or both surfaces of a current collector (positive electrode current collector) made of a conductive material such as aluminum foil, copper foil, nickel foil, and stainless steel foil. That is, it has a structure which provided the positive electrode active material layer containing a conductive support agent and a binder as needed with a positive electrode active material.

<Negative electrode>

Similar to the positive electrode, the negative electrode also includes a negative electrode active material layer, ie, a negative electrode active material, on one or both surfaces of the current collector (negative electrode current collector) made of the above conductive material, as necessary, including a conductive aid or a binder as necessary. It has a structure in which an active material layer is formed.

In addition, in the above-described positive electrode and negative electrode (electrode), it is also possible to form the positive electrode active material layer and the negative electrode active material layer on one side and the other side of one current collector, respectively, and such an electrode is a bipolar battery. Applies to

<Structure of battery>

The lithium ion secondary battery has a battery element (electrode structure) in which the positive electrode and the negative electrode as described above are connected through an electrolyte layer, and the battery element is housed in a battery case such as a can member or a laminate container (package). It has a structure.

In addition, a wound battery having a structure in which a battery element is wound around a positive electrode, an electrolyte layer, and a negative electrode, and a positive electrode, an electrolyte layer, and a negative electrode are largely classified into a laminated battery, and the bipolar battery has a stacked structure.

Moreover, depending on the shape and structure of a battery case, it may be called a coin cell, a button battery, a laminated battery, etc.

[Example]

Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.

&Lt; Synthesis of positive electrode active material &

The synthesis | combination of the sample was performed as follows using the composite carbonate method.

A predetermined amount of nickel sulfate, cobalt sulfate, and manganese sulfate was weighed to prepare a mixed solution of these, and ammonia water was added dropwise to pH7, and Na ₂ CO ₃ solution was further added dropwise to mix Ni-Co-Mn. The carbonate was precipitated (while the Na ₂ CO ₃ solution was added dropwise, pH 7 was maintained in ammonia water).

Thereafter, the mixture was suction filtered, washed with water, and dried at 120 ° C for 5 hours. This was calcined at 500 DEG C for 5 hours. Excessive LiOH.H ₂ O was added to this and mixed for 30 minutes by automatic induction.

Then, the then at 900 ℃ 12 sigan firing, cooling rapidly with liquid nitrogen, and Li _{1. 850 [Ni 0 .175 Co 0 .100} Mn 0 .86] O 3 ( hereinafter referred to as "solid solution in the positive electrode active material 1"), _{1 .77} Li [Ni Co _{0 .32 0 .05 0 .86} Mn] O ₃ (Hereinafter, two types of positive electrode active materials (solid solution positive electrode active materials) having the composition of "Soluble Positive Electrode Active Material 2") were obtained.

<Synthesis of Composite Cathode Active Material (Coating Method)>

(2nd comparative example-4th comparative example)

An alkoxide or organic salt (here, tetraethoxysilane, tetraisopropoxide titanium, lanthanum acetate), which is a precursor of the coating, is dissolved in a predetermined amount, ion-exchanged water or lower alcohol to prepare a precursor solution, wherein The solid solution positive electrode active material 1 was immersed.

The mixed solution was stirred at room temperature for 5 hours, and then concentrated to dryness at 80 ° C. The obtained solid was baked at 800 degreeC under air | atmosphere for 8 hours, and the composite positive electrode active material of the 2nd comparative example-the 4th comparative example as shown in Table 1 was obtained.

In addition, the solid solution positive electrode active material 1 (self) which was not coat | covered is shown in Table 1 as a 1st comparative example.

(Examples 1 to 6)

Predetermined amounts of titanium isopropoxide and acetic acid were dissolved in isopropanol, lithium acetate and lanthanum acetate were dissolved in ion-exchanged water, and these two solutions were mixed again, followed by stirring at room temperature for 12 hours.

The solid solution positive electrode active material 1 was immersed in the precursor solution of two kinds of Li _3y La _{2 / 3-y} □ _{1 / 3-2 y} TiO ₃ (see Table 1) thus obtained, and stirred at room temperature for 5 hours. It was concentrated to dryness at ℃. The obtained solid was baked at 800 degreeC under air | atmosphere for 8 hours, and the composite positive electrode active material of Example 1-Example 6 shown in Table 1 was obtained.

(7th Example, 8th Example, 5th Comparative Example)

Except for using the solid solution positive electrode active material 2 in place of the solid solution positive electrode active material 1, the same operation as in the first embodiment was repeated to obtain the composite positive electrode active material of the seventh and eighth embodiments.

In addition, the solid solution positive electrode active material 2 (self) which did not coat | cover was described in Table 2 as a 6th comparative example.

[Performance evaluation]

<Creation of electrode>

The composite positive electrode active material of each Comparative Example and each Example obtained as mentioned above, acetylene black as a conductive support agent, and polyvinylidene fluoride as a binder are mix | blended so that it may become a mass ratio of 80:10:10, and it is N-methylpi Rollidone was added as a solvent and mixed to prepare a positive electrode slurry.

Moreover, the positive electrode using the composite positive electrode active material of each case was produced by using aluminum foil as an electrical power collector, apply | coating so that the said positive electrode slurry so that it might become thickness of 70 micrometers, respectively, and fully drying. The obtained positive electrode was vacuum-dried at 80 degreeC, respectively.

<Charge / Discharge Test of Electrode>

(Production of positive electrode half cell)

The positive electrode produced above and the negative electrode which adhered the metal lithium to the stainless steel disk were made to oppose, and the separator of 20 micrometers in thickness was arrange | positioned between them.

The laminated body of the negative electrode, the separator, and the positive electrode was placed in a coin cell (CR2032) made of stainless steel (SUS316), and injected into the coin cell using 1M LiPF ₆ EC: DEC (1: 1 v / v%) as an electrolyte. Then, it sealed and obtained the lithium ion secondary battery (half cell) of each case.

(Evaluation of cycle characteristics of positive electrode half cell)

The charge / discharge cycle test was done about the lithium ion secondary battery of each case produced by the above, and it investigated about discharge capacity retention rate. That is, under a 30 ° C atmosphere, the battery was charged to 4.8V with a constant voltage method (CC, current: 0.1C), stopped for 10 minutes, discharged to 2V with a constant current (CC, current: 0.1C), and 10 minutes after discharge. This was repeated 30 times with one cycle of stopping and discharging.

The obtained results are written together in Tables 1 and 2.

In addition, the value shown as the retention rate at 30 ^th cycle in a table | surface is a value when the discharge capacity in 1st cycle is made into 100%.

Table 1, as the amount of positive electrode active material Li _{1 .850} kinds of [Ni Co _{0 .175 0 .100 0 .875} Mn] presence or coating (active material preparation) of the coating in the case of using the O _3, coating, on the cycle characteristics The impact is shown. The following can be understood from this table.

(1) La ₂ O _3, TiO _2, before in the example coated with oxides thought that the ion conductivity as SiO ₂ (the second comparative example to the fourth comparative example), the discharge capacity at 1 cycle is coated ( It is falling compared with the 1st comparative example). This is considered to be because Li ion movement in the charge / discharge process was inhibited because the coated species had no ion conductivity.

The retention after 30 cycles is improved as compared with before coating, but it is estimated that the initial capacity is lowered and that decomposition of the electrolyte is suppressed by coating. (2) About each comparative example In each Example, by using LLT which has ion conductivity, the discharge capacity retention rate after 30 cycles is improving, while the discharge capacity of 1st cycle maintains the value of the same level as before coating | coating. .

On the other hand, Table 2, as a positive electrode active material, there is shown a LLT coating effect in the case of using the _{Li 1 .77 [Ni 0 .32 Co} 0 .05 Mn 0 .86] O 3. The following can be understood from this table.

That is, even if the composition of the positive electrode active material to be coated changes, it can be understood that the effect of the LLT coating on the positive electrode characteristics does not change.

As mentioned above, although this invention was demonstrated by some embodiment and an Example, this invention is not limited to these, A various deformation | transformation is possible within the scope of the summary of this invention.

For example, in said embodiment, although coating is performed by putting a positive electrode active material into a coating precursor solution, drying, and baking as a coating method, it is not limited to this, The coating precursor before baking and a positive electrode active material are mechanically mixed. It is also possible to coat by a method such as firing after milling.

Claims (4)

[Chemical Formula 1]

[Wherein x satisfies 0.1 ≦ x ≦ 0.5, and M satisfies Ni _α Co _β Mn _γ (where α, β, and γ satisfy 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, and 0 <γ ≦ 0.5, respectively). ) Represents a positive electrode active material,
Exists on the surface of this positive electrode active material,
(2)

The composite positive electrode active material for lithium ion secondary batteries characterized by including the active material preparation represented by (y in formula satisfies 0.1 <y <0.17). The composite positive electrode active material for lithium ion secondary batteries according to claim 1, wherein the active material preparation is contained at a ratio of 1 to 20 mass%. The coating thickness (t) of the active material preparation is the positive electrode active material according to claim 1 or 2, wherein the composite positive electrode active material has a roughly spherical shape in which the positive electrode active material is coated with the active material preparation. Among the particle diameters (r) of
r / (r + t) × 100 = 0.16 to 3.05 (%)
The composite positive electrode active material for lithium ion secondary batteries characterized by satisfy | filling the relationship shown by.  The lithium ion secondary battery provided with the positive electrode containing the composite positive electrode active material for lithium secondary batteries of Claim 1 or 2.