JP2017183048A - Positive electrode active material, positive electrode arranged by use thereof, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery superior in cycle characteristic.SOLUTION: A positive electrode active material comprises: a first compound represented by the chemical formula, Li(NiMa)O(where 0.95≤x≤1.05, 0.3≤y≤0.9, and Ma represents at least one element selected from Co, Mn, V, Ti, Fe, Zr, Nb, Mo, Al and W); and a second compound represented by the chemical formula, LiMbVO(where 0.80≤z≤1.05, and Mb represents at least one element selected from Ni and Co). The content of the second compound 0.1-10 wt% to that of the first compound.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode active material, a positive electrode using the same, and a lithium ion secondary battery.

In recent years, layered compounds such as ternary Li (Ni, Co, Mn) O ₂ and Li (Ni, Co, Al) O ₂ have attracted attention as active materials for positive electrode materials of lithium ion secondary batteries. These layered compounds are known to exhibit a higher discharge capacity and higher energy density than conventional active materials. However, a lithium ion secondary battery using the above layered compound has a problem that cycle characteristics due to repeated charge and discharge are low. For this reason, attempts have been made to improve cycle characteristics by repeated charge and discharge by coating the particle surface of the compound with an inorganic substance and maintaining the particle structure. For example, Patent Document 1 reports that the surface of a lithium-containing composite powder is coated with ZrO ₂ . Patent Document 2 reports that cycle deterioration is improved by using secondary particles made of transition metal oxide primary particles coated with ZrO ₂ . Nevertheless, sufficient cycle characteristics are not obtained only by the techniques described in Patent Documents 1 and 2, and further improvement is required.

JP 2006-156032 A JP2013-235666A

  The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide a positive electrode active material having excellent cycle characteristics, a positive electrode using the positive electrode material, and a lithium ion secondary battery.

In order to achieve the above object, the positive electrode active material according to the present invention has a chemical formula Li _x (Ni _y Ma _1-y ) O ₂ (0.95 ≦ x ≦ 1.05, 0.3 ≦ y ≦ 0.9). , Ma is at least one element selected from Co, Mn, V, Ti, Fe, Zr, Nb, Mo, Al, and W), and a chemical formula Li _z MbVO ₄ (0.80 ≦ z ≦ 1.05, Mb is a second compound represented by at least one element selected from Ni and Co), and the second compound is 0 with respect to the first compound. .1 to 10 wt%.

When the positive electrode active material according to the present invention is configured as described above, the cycle characteristics can be improved as compared with the case where conventional Li _x (Ni _y Ma _1-y ) O ₂ is used.

In the positive electrode active material of this configuration, Ni or Co eluted from the first compound by repetition of charge and discharge is supplemented by Ni or Co contained in Li _z MbVO ₄ , so that the crystal structure of the first compound is deteriorated. As a result, it is presumed that high capacity and excellent cycle characteristics can be exhibited. The reason why the above-described effects can be obtained in the Li _z MbVO ₄ type compound is considered that these compounds themselves contain two or more transition metals. Even when Ni or Co is used for complementation and the charge balance of the compound is lost, it is presumed that the charge balance of the Li _z MbVO ₄ type compound is maintained by changing the valence of the remaining V component. As a result, it is considered that the structure degradation of the Li _z MbVO ₄ type compound itself is suppressed, and Ni or Co can be complemented over a long period of time.

  It is preferable that at least a part of the surface of the primary particles of the first compound according to the present invention is coated with the second compound to form a coating layer.

  When the coating layer of the second compound is formed on the surface of the first compound, Ni or Co is quickly complemented by the first compound, so that high capacity and excellent cycle characteristics can be exhibited.

  The coating layer thickness of the second compound according to the present invention is preferably in the range of 10 nm to 500 nm.

  When the thickness of the coating layer of the second compound satisfies the above range, an excellent discharge capacity can be exhibited by effectively suppressing a decrease in capacity of the first compound while exhibiting high cycle characteristics.

  The primary particles of the first compound according to the present invention are preferably aggregated to form secondary particles.

  When the first compound forms secondary particles, an excellent discharge capacity can be exhibited while exhibiting high cycle characteristics.

  The particle size of the secondary particles of the first compound according to the present invention is preferably in the range of 5 μm to 40 μm.

  When the secondary particle diameter of said 1st compound satisfy | fills the said range, the outstanding discharge capacity can be exhibited, showing a high cycle characteristic.

  The positive electrode according to the present invention includes the first compound and the second compound.

  When the said positive electrode contains a 1st 1st compound and a 2nd compound, the outstanding discharge capacity can be exhibited, showing a high cycle characteristic.

  The lithium ion secondary battery according to the present invention preferably includes the positive electrode, an electrolyte, and a negative electrode.

  When the lithium ion secondary battery includes the positive electrode, the electrolyte, and the negative electrode, excellent discharge capacity can be exhibited while exhibiting high cycle characteristics.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode active material excellent in cycling characteristics, the positive electrode using the same, and a lithium ion secondary battery can be provided.

It is a schematic cross section of a lithium ion secondary battery provided with the positive electrode and negative electrode which concern on one Embodiment of this invention.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be appropriately combined.

(Lithium ion secondary battery)
FIG. 1 is a schematic cross-sectional view showing a lithium ion secondary battery according to this embodiment. As shown in FIG. 1, the lithium ion secondary battery 100 mainly includes a laminate 30, a case 50 that accommodates the laminate 30 in a sealed state, and a pair of leads 60 and 62 connected to the laminate 30. ing.

  The laminated body 30 is configured such that a pair of a positive electrode 10 and a negative electrode 20 are disposed to face each other with a separator 18 interposed therebetween. The positive electrode 10 is obtained by providing a positive electrode active material layer 14 on a plate-like (film-like) positive electrode current collector 12. The negative electrode 20 is obtained by providing a negative electrode active material layer 24 on a plate-like (film-like) negative electrode current collector 22. The main surface of the positive electrode active material layer 14 and the main surface of the negative electrode active material layer 24 are in contact with the main surface of the separator 18. Leads 62 and 60 are connected to the end portions of the positive electrode current collector 12 and the negative electrode current collector 22, respectively, and the end portions of the leads 60 and 62 extend to the outside of the case 50.

(Positive electrode active material)
The positive electrode active material of this embodiment has the chemical formula Li _x (Ni _y Ma _1-y ) O ₂ (0.95 ≦ x ≦ 1.05, 0.3 ≦ y ≦ 0.9, Ma is Co, Mn, V , Ti, Fe, Zr, Nb, Mo, Al, W, and a first compound represented by the chemical formula Li _z MbVO ₄ (0.80 ≦ z ≦ 1.05, Mb) Is a second compound represented by at least one element selected from Ni and Co), and the second compound is contained in an amount of 0.1 to 10 wt% with respect to the first compound. It is characterized by.

In the positive electrode active material of this configuration, Ni or Co eluted from the first compound by repetition of charge and discharge is supplemented by Ni or Co contained in Li _z MbVO ₄ , so that the crystal structure of the first compound is deteriorated. As a result, it is presumed that high capacity and excellent cycle characteristics can be exhibited. The reason why the above-described effects can be obtained in the Li _z MbVO ₄ type compound is considered that these compounds themselves contain two or more transition metals. Even when Ni or Co is used for complementation and the charge balance of the compound is lost, it is presumed that the charge balance of the Li _z MbVO ₄ type compound is maintained by changing the valence of the remaining V component. As a result, it is considered that the structure degradation of the Li _z MbVO ₄ type compound itself is suppressed, and Ni or Co can be complemented over a long period of time.

  The second compound is more preferably 2.5 to 10.0 wt%. This further improves cycle characteristics. Furthermore, it is more preferable that it is 5.0-10.0 wt%. This further improves cycle characteristics.

  Even if a part of Mb is missing in the second compound in the present embodiment. Thereby, Mb becomes a mixed valence, and the cycle characteristics are further improved by improving the electronic conductivity of the second compound.

  In the second compound in this embodiment, about 1 to 10 wt% of Mb may be substituted with a transition metal other than Ni and Co.

  Thereby, even when Ni and Co are supplemented with the first compound, the charge balance can be easily maintained, so that the cycle characteristics are further improved.

  Thereby, Mb becomes a mixed valence, and the cycle characteristics are further improved by improving the electronic conductivity of the second compound.

  It is preferable that at least a part of the surface of the primary particles of the first compound of the present embodiment is coated with the second compound to form a coating layer.

  The coverage of the coating layer is preferably 25 to 100%. This improves the cycle characteristics. Furthermore, it is more preferable that it is 50 to 100%. This further improves cycle characteristics.

  The coverage in the present embodiment is defined as follows. First, the particle cross section of the first compound coated with the second compound is observed by SEM or the like, and the perimeter of the first compound particle and the coating length of the second compound with respect to the first compound are measured. Next, the coverage was calculated by dividing the coating length of the second compound by the circumference of the first compound particles. This was performed on about 500 particles, and the average value was defined as the coverage. In addition, the particle cross-section sample of the first compound is prepared by a cross section polisher (CP), ion milling (IM), or the like, so that an image near the center, not the end of the particle, can be obtained in order to increase the accuracy. Adjusted accordingly.

  When the coating layer of the second compound is formed on the surface of the first compound, Ni or Co is quickly complemented by the first compound, so that high capacity and excellent cycle characteristics can be exhibited.

  The thickness of the coating layer of the second compound of the present embodiment is preferably in the range of 10 nm to 500 nm. Further, the thickness of the coating layer is more preferably 100 to 500 nm, still more preferably 250 to 500 nm. This further improves cycle characteristics.

  The coating layer thickness in the present embodiment is defined as follows. The particle cross section of the first compound coated with the second compound is observed with an SEM or the like, and the coating layer thickness of the second compound is measured. This was performed on 500 particles, and the average value was defined as the thickness of the coating layer of the second compound. In addition, the particle cross-section sample of the first compound is prepared by a cross section polisher (CP), ion milling (IM) or the like, so that an image around the center portion, not the end portion of the particles, can be obtained in order to increase the accuracy. Adjusted accordingly.

  When the thickness of the coating layer of the second compound satisfies the above range, an excellent discharge capacity can be exhibited by effectively suppressing a decrease in capacity of the first compound while exhibiting high cycle characteristics.

As a method for coating the surface of the first compound Li _x (Ni _y Ma _1-y ) O ₂ with the second compound Li _z MbVO ₄ , dry mixing using a pot mill containing zirconia balls or alumina balls is possible. Examples thereof include dry mixing using a machine, coating with a fluidized bed apparatus, and particle combination by mechanofusion. The second compound can also be coated by adding a material containing a vanadium element such as V ₂ O ₅ or LiVOPO ₄ to the first compound and appropriately heat-treating it.

  The primary particles of the first compound of the present embodiment are preferably aggregated to form secondary particles.

  When the first compound forms secondary particles, an excellent discharge capacity can be exhibited while exhibiting high cycle characteristics.

  The particle diameter of the secondary particles of the first compound of the present embodiment is preferably in the range of 5 μm to 40 μm. More preferably, the particle diameter of the secondary particles of the first compound is preferably 10 to 30 μm.

  When the secondary particle diameter of said 1st compound satisfy | fills the said range, the outstanding discharge capacity can be exhibited, showing a high cycle characteristic.

(Positive electrode current collector)
The positive electrode current collector 12 may be a conductive plate material, and for example, a metal thin plate (metal foil) such as aluminum, an alloy thereof, or stainless steel can be used.

(Positive electrode active material layer)
The positive electrode active material layer 14 is mainly composed of a positive electrode active material, a binder, and a conductive auxiliary agent in an amount as necessary.

(Positive electrode binder)
The binder is not particularly limited as long as the positive electrode active material and the conductive material can be bound to the current collector 12, and a known binder can be used. Examples thereof include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and vinylidene fluoride-hexafluoropropylene copolymer.

(Positive electrode conductive aid)
The positive electrode conductive auxiliary agent is not particularly limited as long as it improves the conductivity of the positive electrode active material layer 14, and a known conductive auxiliary agent can be used. Examples thereof include carbon-based materials such as graphite and carbon black, metal fine powders such as copper, nickel, stainless steel, and iron, a mixture of carbon materials and metal fine powders, and conductive oxides such as ITO.

(Negative electrode active material)
As the negative electrode active material, for example, carbon materials such as graphite capable of inserting and extracting lithium ions, non-graphitizable carbon, graphitizable carbon, low-temperature calcined carbon, and lithium such as Al, Si, Sn, etc. Examples thereof include a metal, an amorphous compound mainly composed of an oxide such as SiO, SiO ₂ , SnO ₂ , and Fe ₂ O _3, and particles containing Li ₄ Ti ₅ O _{12 and the} like.

(Negative electrode current collector)
The negative electrode current collector 22 may be any conductive plate material, and for example, a metal thin plate (metal foil) of copper, nickel, stainless steel, or an alloy thereof can be used.

(Negative electrode active material layer)
The negative electrode active material layer 24 is mainly composed of graphite as a negative electrode active material, a binder, and a conductive auxiliary agent in an amount as required.

(Negative electrode binder)
In addition to the above-described materials exemplified as the positive electrode binder, cellulose, styrene / butadiene rubber, ethylene / propylene rubber, polyimide resin, polyamideimide resin, polyacrylic acid, or the like may be used as the binder.

(Negative conductive auxiliary)
A negative electrode conductive support agent is not specifically limited, A well-known conductive support agent can be used. Examples thereof include carbon materials such as pyrolytic carbon such as carbon black, cokes, glassy carbons, organic polymer compound fired materials, carbon fibers, and activated carbon. Moreover, you may add negative electrode active material materials, such as non-graphitizable carbon, easily graphitizable carbon, and graphite, changing a shape.

  With the components described above, the electrodes 10 and 20 can be produced by a commonly used method. For example, a paint containing an active material (a positive electrode active material or a negative electrode active material), a binder (a positive electrode binder or a negative electrode binder), a solvent, and a conductive additive (a positive electrode conductive additive or a negative electrode conductive aid) is placed on the current collector. It can manufacture by apply | coating and removing the solvent in the coating material apply | coated on the electrical power collector.

  As the solvent, for example, N methyl-2-pyrrolidone, N, N-dimethylformamide, water or the like can be used.

  There is no restriction | limiting in particular as an application | coating method, The method employ | adopted when producing an electrode normally can be used. Examples thereof include a slit die coating method and a doctor blade method.

  The method for removing the solvent in the paint applied on the current collectors 12 and 22 is not particularly limited, and the current collectors 12 and 22 applied with the paint are dried, for example, in an atmosphere of 80 ° C. to 150 ° C. Just do it.

  Then, the electrodes on which the active material layers 14 and 24 are formed in this way may then be pressed by a roll press device or the like as necessary. The linear pressure of the roll press can be, for example, 100 to 2,000 kgf / cm.

  Next, other components of the lithium ion secondary battery 100 will be described.

(Separator)
The separator 18 only needs to be formed of an electrically insulating porous structure, for example, a single layer of a film made of polyethylene, polypropylene or polyolefin, a stretched film of a laminate or a mixture of the above resins, or cellulose, polyester And a fiber nonwoven fabric made of at least one constituent material selected from the group consisting of polypropylene.

(Electrolytes)
The electrolyte is contained in the positive electrode active material layer 14, the negative electrode active material layer 24, and the separator 18. The electrolyte is not particularly limited. For example, in the present embodiment, an electrolyte containing a lithium salt can be used. However, the electrolyte aqueous solution is preferably an electrolyte that uses an organic solvent because the electrochemical decomposition voltage is low and the withstand voltage during charging is limited to be low. As the electrolyte, a lithium salt dissolved in an organic solvent is preferably used. Examples of the lithium salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiCF ₃ , CF ₂ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , A salt such as LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (CF ₃ CF ₂ CO) ₂ , or LiBOB can be used. In addition, these salts may be used individually by 1 type, and may use 2 or more types together.

  Moreover, as an organic solvent, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate etc. are mentioned preferably, for example. These may be used alone or in combination of two or more at any ratio.

  In the present embodiment, an example of the electrolyte has been described, but a gel electrolyte to which a gelling agent is added may be used. Moreover, it can replace with these electrolytes and can also use a solid electrolyte.

(Case)
The case 50 seals the laminated body 30 and the electrolyte therein. The case 50 is not particularly limited as long as it can prevent leakage of the electrolyte to the outside and entry of moisture and the like into the lithium ion secondary battery 100 from the outside. For example, as the case 50, as shown in FIG. 1, a metal laminate film in which a metal foil 52 is coated with a polymer film 54 from both sides can be used. As the metal foil 52, for example, an aluminum foil can be used, and as the synthetic resin film 54, a film such as polypropylene can be used. For example, the material of the outer polymer film 54 is preferably a polymer having a high melting point such as polyethylene terephthalate (PET) or polyamide, and the material of the inner polymer film 54 is preferably polyethylene or polypropylene.

(Lead)
The leads 60 and 62 are made of a conductive material such as aluminum. Then, the leads 62 and 60 are respectively welded to the positive electrode current collector 12 and the negative electrode current collector 22 by a known method, and a separator is provided between the positive electrode active material layer 14 of the positive electrode 10 and the negative electrode active material layer 24 of the negative electrode 20. 18 may be inserted into the case 50 together with the electrolytic solution with the 18 interposed therebetween, and the entrance of the case 50 may be sealed.

  The lithium ion secondary battery of this embodiment preferably includes the positive electrode, an electrolyte, and a negative electrode.

  When the lithium ion secondary battery includes the positive electrode, the electrolyte, and the negative electrode, excellent discharge capacity can be exhibited while exhibiting high cycle characteristics.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. For example, the lithium ion secondary battery is not limited to the shape shown in FIG. It may be a type or the like.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
(Preparation of positive electrode active material)
After adding 2.5% by weight of LiNiVO ₄ as the second compound to 100 g of Li _1.00 (Ni _0.85 Co _0.10 Al _0.05 ) O ₂ as the first compound, ₂ mmφ zirconia balls Was mixed in a pot mill containing 50 rpm for 2 hours to obtain a positive electrode active material of Example 1.

(Preparation of positive electrode)
A mixture of the positive electrode active material of Example 1, polyvinylidene fluoride (PVDF) as a binder, and acetylene black was dispersed in N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a slurry. Note that the slurry was prepared so that the weight ratio of the positive electrode active material, acetylene black, and PVDF was 92: 3: 5 in the slurry. This slurry was applied on an aluminum foil as a positive electrode current collector, dried, and then rolled to obtain a positive electrode on which an active material layer containing a positive electrode active material was formed.

(Preparation of negative electrode)
A mixture of graphite as a negative electrode active material, styrene / butadiene rubber and cellulose as a binder, and carbon black as a conductive additive was dispersed in pure water as a solvent to prepare a slurry. This slurry was applied on a copper foil as a negative electrode current collector, dried, and then rolled to obtain a negative electrode on which an active material layer containing a negative electrode active material was formed.

(Production of evaluation cell)
The positive electrode and negative electrode prepared as described above and a separator made of a polyethylene porous film are cut into predetermined dimensions, and laminated in such a sequence as negative electrode, separator, positive electrode, separator, and negative electrode to form four negative electrodes and three positive electrodes. did. This laminate was put in an aluminum laminate pack, an electrolyte solution was injected, and then vacuum-sealed to produce a lithium ion secondary battery using the positive electrode active material of Example 1. As the electrolyte solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1 M (1 mol / L) in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) was used. The volume ratio of EC to DEC in the mixed solvent was EC: DEC = 30: 70.

(Example 2)
An evaluation cell was produced in the same manner as in Example 1 except that the amount of the second compound added was changed to 0.1% by weight.

(Example 3)
An evaluation cell was produced in the same manner as in Example 1 except that the amount of the second compound added was changed to 5.0% by weight.

Example 4
An evaluation cell was produced in the same manner as in Example 1 except that the amount of the second compound added was changed to 10.0% by weight.

(Example 5)
An evaluation cell was produced in the same manner as in Example 1 except that the second compound was changed to LiCoVO ₄ .

(Example 6)
An evaluation cell was produced in the same manner as in Example 1 except that the second compound was changed to LiCoVO ₄ and the addition amount was changed to 0.1% by weight.

(Example 7)
An evaluation cell was produced in the same manner as in Example 1 except that the second compound was changed to LiCoVO ₄ and the addition amount was changed to 5.0% by weight.

(Example 8)
An evaluation cell was produced in the same manner as in Example 1 except that the second compound was changed to LiCoVO ₄ and the addition amount was changed to 10.0% by weight.

Example 9
An evaluation cell was produced in the same manner as in Example 1 except that the first compound was changed to Li _1.00 (Ni _0.34 Co _0.33 Mn _0.33 ) O ₂ .

(Example 10)
Except that the first compound was changed to _{Li 1.00 (Ni 0.34 Co 0.33 Mn} 0.33) O 2, change the Li z MbVO ₄ to LiCoVO _4, the same method as in Example 1 A cell for evaluation was produced.

(Comparative Example 1)
An evaluation cell was produced in the same manner as in Example 1 except that the second compound was not added.

(Comparative Example 2)
An evaluation cell was produced in the same manner as in Example 1 except that the amount of the second compound added was changed to 15.0% by weight.

(Comparative Example 3)
An evaluation cell was produced in the same manner as in Example 1 except that the second compound was changed to LiCoVO ₄ and the addition amount was changed to 15.0% by weight.

(Comparative Example 4)
In the same manner as in Example 1 except that the first compound was changed to Li _1.00 (Ni _0.34 Co _0.33 Mn _0.33 ) O ₂ and the second compound was not added. An evaluation cell was produced.

(Comparative Example 5)
Implementation was performed except that the first compound was changed to Li _1.00 (Ni _0.34 Co _0.33 Mn _0.33 ) O ₂ and the addition amount of the second compound was changed to 15.0% by weight. An evaluation cell was produced in the same manner as in Example 1.

(Measurement of 0.1C discharge capacity)
About the lithium ion secondary battery for evaluation produced in the Example and the comparative example, the discharge rate was 0.1 C (constant current discharge was performed at 25 degreeC) using the secondary battery charge / discharge test apparatus (made by Hokuto Denko Co., Ltd.). The discharge capacity (unit: mAh / g) was measured when the current value was reached when discharge was completed in 10 hours.

(Evaluation method of cycle characteristics)
About the lithium ion secondary battery for evaluation produced by the Example and the comparative example, the cycle characteristic was measured in the environment of 25 degreeC using the secondary battery charging / discharging test apparatus (made by Hokuto Denko Co., Ltd.). Charge / discharge cycle of constant current and constant voltage charge to 4.2V at 0.5C, constant current discharge to 2.8V at 1C, repeat capacity cycle after 100 cycles, measure capacity retention after 100 cycles, cycle characteristics as cycle retention ratio As evaluated.

(Measurement of content of second compound)
The second compound content in the positive electrode active material of the present invention can be measured using a fluorescent X-ray analyzer. First, using a fluorescent X-ray analyzer (manufactured by RIGAKU), a plurality of samples prepared in advance with known contents of the second compound are measured, and a calibration curve is created. Thereafter, the positive electrode active material of the present invention is set in a fluorescent X-ray analyzer and analyzed, and the second compound content is calculated from the calibration curve.

(Judgment of results)
When the 0.1C discharge capacity is 150 mAh / g or more and the capacity maintenance rate after 100 cycles is 90% or more, it is defined as “good”, and the 0.1C discharge capacity is less than 150 mAh / g, or the capacity maintenance rate after 100 cycles is Those with less than 90% were judged as “bad”.

  Table 1 shows the first compound, the second compound and the amount added, 0.1 C discharge capacity, and cycle retention. In addition, it confirmed from the content measurement of the 2nd compound that the addition amount of the 2nd compound shown in an Example did not change with content with respect to the 1st compound finally obtained, and was the same content.

  As shown in Table 1, since the lithium ion secondary batteries of Examples 1 to 10 had an appropriate first compound composition range and an appropriate addition amount of the second compound, 0.1C discharge capacity and 100 The effect of the present invention, such as excellent capacity retention after cycling, was confirmed. On the other hand, in Comparative Examples 1 to 5, the second compound was not added, or the addition amount was out of the range of the present invention, so that desired characteristics could not be obtained.

  DESCRIPTION OF SYMBOLS 10 ... Positive electrode, 12 ... Positive electrode collector, 14 ... Positive electrode active material layer, 18 ... Separator, 20 ... Negative electrode, 22 ... Negative electrode collector, 24 ... Negative electrode Active material layer, 30 ... laminate, 50 ... case, 52 ... metal foil, 54 ... polymer film, 60, 62 ... lead, 100 ... lithium ion secondary battery.

Claims (7)

Chemical formula Li _x (Ni _y Ma _1-y ) O ₂ (0.95 ≦ x ≦ 1.05, 0.3 ≦ y ≦ 0.9, Ma is Co, Mn, V, Ti, Fe, Zr, Nb, A first compound represented by at least one element selected from Mo, Al, and W) and a chemical formula Li _z MbVO ₄ (0.80 ≦ z ≦ 1.05, where Mb is at least one selected from Ni and Co). A second compound represented by a seed element), wherein the second compound is contained in an amount of 0.1 to 10 wt% with respect to the first compound.   The positive electrode active material according to claim 1, wherein at least a part of the surface of the primary particles of the first compound is coated with the second compound to form a coating layer.   The positive electrode active material according to claim 2, wherein the coating layer has a thickness of 10 nm to 500 nm.   4. The positive electrode active material according to claim 1, wherein primary particles of the first compound are aggregated to form secondary particles. 5.   The positive electrode active material according to claim 4, wherein the secondary particles have a particle size in a range of 5 μm to 40 μm.   The positive electrode containing the positive electrode active material as described in any one of Claims 1 thru | or 5. A lithium ion secondary battery comprising: the positive electrode according to claim 6; a negative electrode having a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; and a nonaqueous electrolyte.

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