JP7067037B2 - Positive electrode for non-aqueous electrolyte secondary battery, positive electrode active material used for this, and non-aqueous electrolyte secondary battery using this - Google Patents

Description

The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery, a positive electrode active material used therein, and a secondary battery using the positive electrode. More specifically, the present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery used in electronic devices and automobiles, a positive electrode active material used therein, and a non-aqueous electrolyte secondary battery using the same.

In recent years, with the widespread use of portable electronic devices such as mobile phones and notebook computers, the development of small and lightweight secondary batteries having a high energy density is strongly desired. Further, it is strongly desired to develop a high output secondary battery as a battery for a hybrid vehicle or an electric vehicle. As a non-aqueous electrolyte secondary battery satisfying such a requirement, there is a lithium ion secondary battery.

The lithium ion secondary battery is composed of a positive electrode whose main component is a positive electrode active material, a negative electrode whose main component is a negative electrode active material, and a non-aqueous electrolyte solution. Materials that can be used are used.
Such lithium-ion secondary batteries are currently being actively researched and developed, and lithium-ion secondary batteries using a layered lithium metal composite oxide as a positive electrode material can obtain a high voltage of 4V class. Therefore, it is being put into practical use as a battery having a high energy density.

The positive electrode materials proposed so far include lithium cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ) using nickel, which is cheaper than cobalt, and lithium nickel cobalt. Manganese composite oxides (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and the like can be mentioned.

In order to develop the lithium composite oxide as an automobile battery, it is important to improve the positive electrode material to obtain a higher output than the current state, that is, to reduce the resistance of the positive electrode material.
In addition, some of the above-mentioned lithium composite oxides react with moisture and carbon dioxide in the atmosphere to cause surface denaturation when handled in the atmosphere, resulting in a decrease in capacity and an increase in resistance. Therefore, it is important to prevent deterioration of these positive electrode active materials.

In Patent Document 1, Li compounds such as Li ₃ PO ₄ , LiPON (lithium oxynitride phosphate), and Li ₂ S-SiS ₂ -Li ₃ PO ₄ are attached to the surface of particles made of lithium nickel cobalt manganese oxide. It has been reported that the increase in internal resistance is suppressed after storage for one week.

Patent Document 2 describes a lithium ion secondary battery having excellent cycle characteristics and rate characteristics by coating the surface of a lithium-containing composite oxide powder containing a Li element and a transition metal element with Li ₃ PO ₄ . It has been reported that a positive electrode active material that can be provided can be obtained.

Patent Document 3 reports that it is possible to reduce the positive electrode resistance of a battery and improve the output characteristics by mixing lithium metal composite oxide powder and lithium tungstate.

However, when it is coated with a compound containing lithium and phosphorus as in Patent Documents 1 and 2, or when a compound containing lithium and tungsten is simply mixed as in Patent Document 3, deterioration of battery performance can be prevented or an electrolytic solution can be prevented. / The effect of reducing the positive electrode interface resistance and obtaining high output was not sufficient.

Japanese Patent No. 4923397 International release WO2012 / 176903 Japanese Unexamined Patent Publication No. 2013-17178

In view of the above problems, the present invention provides a positive electrode for a non-aqueous electrolyte secondary battery, which enables high output of the battery when used as a positive electrode of the battery and hardly deteriorates the performance of the battery, and the electrode. It is an object of the present invention to provide a positive electrode active material to be used.
Another object of the present invention is to provide a non-aqueous electrolyte secondary battery which can obtain high output and hardly deteriorate the performance of the battery.

In order to solve the above problems, the present inventor has investigated various characteristics of the lithium metal composite oxide used as a positive electrode active material for a non-aqueous electrolyte secondary battery, and as a result, the surface of the lithium metal composite oxide is composed of niobium . It was found that by forming a coating layer composed of a compound containing a metal element, tungsten and lithium, the lithium ion conductivity on the surface of the lithium metal composite oxide in the positive electrode can be improved in more detail. Obtained. Further, by using this positive electrode, it is possible to significantly reduce the electrolytic solution / positive electrode interfacial resistance of the secondary battery, improve the output characteristics of the secondary battery, and suppress the deterioration of the battery performance. The present invention was completed based on the above findings.

The positive electrode for a non-aqueous electrolyte secondary battery of the first invention comprises a positive electrode made of a positive electrode active material made of a lithium metal composite oxide, and a metal element made of niob and tungsten formed on the surface of the positive electrode. It is composed of a coating layer made of a lithium ion conductive oxide containing lithium, and is characterized in that the lithium ion conductive oxide is a compound composed of Li ₂ WO ₄ and LiNbO ₃ .
In the positive electrode for a non-aqueous electrolyte secondary battery of the second invention, in the first invention, the molar ratio of Nb to W of the lithium ion conductive oxide composed of Li ₂ WO ₄ and LiNbO ₃ exceeds 0.5. It is characterized by being less than 4.
In the positive electrode for a non-aqueous electrolyte secondary battery of the third invention, in the first or second invention, the total molar amount of tungsten and niobium contained in the coating layer is the lithium metal composite oxide. It is characterized in that it is 0.05 to 5.0% with respect to the total molar amount of metal elements other than lithium contained.
In the first , second or third invention, the positive electrode for a non-aqueous electrolyte secondary battery of the fourth invention is a lithium ion conductive oxide containing the metal element composed of niobium , tungsten and lithium. Is characterized by being in an amorphous state.
In the first , second, third or fourth aspect of the invention, the positive electrode for a non-aqueous electrolyte secondary battery of the fifth invention has the positive electrode being a thin film, and the coating layer is layered on the positive electrode. It is characterized by being formed in.
In the positive electrode for a non-aqueous electrolyte secondary battery of the sixth invention, in the first , second, third or fourth invention, the lithium metal composite oxide is in the form of particles, and the coating layer is the lithium. It is characterized in that it is formed on the surface of particles of a metal composite oxide.
The positive electrode for a non-aqueous electrolyte secondary battery of the seventh invention is characterized in that, in the fifth or sixth invention, the thickness of the coating layer is 1 to 500 nm.
The positive electrode active material for a non-aqueous electrolyte secondary battery of the eighth invention is a positive electrode active material used for the positive electrode for a non-aqueous electrolyte secondary battery according to claim 5 or 6 , and is used in the lithium metal composite oxide . It is characterized in that a coating layer made of a lithium ion conductive oxide containing a metal element made of niob and tungsten and lithium is formed.
The non-aqueous electrolyte secondary battery of the ninth invention is characterized in that a positive electrode using the positive electrode active material according to claim 8 is used.

According to the first invention, the positive electrode for a non-aqueous electrolyte _secondary battery is a lithium ion conductive oxide forming a coating layer on the surface of a positive electrode composed of a positive electrode active material made of a lithium metal composite oxide. Since it is a compound composed of ₄ and LiNbO ₃ , the lithium ion conductivity in the electrode can be improved , it is stable with respect to the electrolyte, and the adverse effect on the battery due to the elution of tungsten or niobium can be reduced . Therefore, by using this electrode, it is possible to realize high output, and it is possible to provide a positive electrode for a non-aqueous electrolyte secondary battery in which high output performance is not easily deteriorated .
According to the second invention, the molar ratio of Nb to W of the lithium ion conductive oxide composed of Li ₂ WO ₄ and LiNbO ₃ forming the coating layer is more than 0.5 and less than 4, so that the lithium of the coating layer is lithium. The ionic conductivity can be further improved, and the output characteristics of the battery can be improved.
According to the third invention, the total molar amount of tungsten and niobium contained in the coating layer is 0.05 to 5.0 with respect to the total amount of metal elements other than lithium contained in the lithium metal composite oxide. When it is%, the diffusion path of lithium ions between the positive electrode active material particles and the electrolytic solution can be more reliably secured, and the output of the battery using the positive electrode active material particles can be increased.
According to the fourth invention, when the lithium ion conductive oxide containing a metal element composed of niobium , tungsten and lithium is in an amorphous state, the positive electrode interfacial resistance of the positive electrode can be further reduced.
According to the fifth invention, since the positive electrode is a thin film and the coating layer is formed so as to be superimposed on the positive electrode, deterioration of the surface of the positive electrode active material is suppressed and lithium ions are generated between the thin film positive electrode and the electrolytic solution. It is possible to secure a diffusion path and increase the output of a battery using a thin film positive electrode.
According to the sixth invention, since the lithium metal composite oxide is in the form of particles and the coating layer is formed on the surface of the particles of the lithium metal composite oxide, deterioration of the surface of the positive electrode active material is suppressed and the positive electrode is formed. It is possible to secure a diffusion path of lithium ions between the active material particles and the electrolytic solution, and it is possible to increase the output of the battery using the positive electrode active material particles.
According to the seventh invention, when the thickness of the coating layer is 1 to 500 nm, a coating layer having lithium ion conductivity and weather resistance can be sufficiently secured, so that the output characteristics of the battery are improved. be able to.
According to the eighth invention, a coating layer made of a lithium ion conductive oxide containing a metal element made of niobium , tungsten and lithium is formed on the surface of particles of a lithium metal composite oxide which is a positive electrode active material. Therefore, the lithium ion conductivity of the positive electrode active material can be improved, and the deterioration of this performance can be suppressed.
According to the ninth invention, it is possible to increase the output of the secondary battery and suppress the deterioration of the performance of the high output.

It is the schematic of the cross section which shows the structure of the positive electrode thin film electrode which concerns on 1st Embodiment of this invention. It is an enlarged view of the surface of the positive electrode active material particle which concerns on 2nd Embodiment of this invention. It is a schematic explanatory drawing of the battery which used the positive electrode which concerns on 1st Embodiment of this invention. It is a graph of the measurement result of the impedance spectrum of the positive electrode which concerns on 1st Embodiment of this invention. It is explanatory drawing of the equivalent circuit used for analysis.

(Basic Concept of the Present Invention)
The positive electrode for a non-aqueous electrolyte secondary battery of the present invention (hereinafter, simply referred to as “positive electrode”) is a lithium composed of a metal element composed of niobium , a compound containing tungsten and lithium on the surface of a lithium metal composite oxide. It is a positive electrode coated with an ionic conduction oxide. Further, the non-aqueous electrolyte secondary battery (hereinafter, simply referred to as “battery”) is a battery composed of a separator, a negative electrode, and an electrolytic solution in addition to the positive electrode.

The positive electrode of the present invention has a coating layer formed of a lithium ion conductive oxide composed of a metal element composed of niobium and a compound containing tungsten and lithium, whereby the lithium ion conductivity of the electrode can be improved and the lithium ion conductivity can be improved. Deterioration of the positive electrode active material can be suppressed. Therefore, by using this electrode, it is possible to realize high output, and it is possible to provide a positive electrode for a non-aqueous electrolyte secondary battery in which high output performance is not easily deteriorated.

(Positive electrode active material)
The lithium metal composite oxide material used as a raw material for the thin film and particles used for the positive electrode can obtain a high voltage of 4V class, and the layered lithium composite oxidation in which the diffusion direction of lithium is limited to the a and b plane directions. Anything is fine. Examples of such lithium composite oxides include lithium cobalt composite oxide (LiCoO ₂ ), lithium nickel composite oxide (LiNiO ₂ ), and lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 ). Materials such as O ₂ ) are mentioned, and they are used properly according to the target battery characteristics. Among them, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is widely used as a positive electrode active material in which charge / discharge capacity and battery safety are well-balanced.

The thin-film positive electrode is made by sintering the powder of the lithium metal composite oxide material to prepare a target, and then by the PLD method (pulse laser deposition method, the same applies hereinafter) to conduct conductivity such as Pt / Cr / SiO ₂ and Pt. It is obtained by depositing a lithium metal composite oxide on a sex substrate.
For the positive electrode using the particulate lithium metal composite oxide, the powder of the lithium metal composite oxide material is mixed with a conductive auxiliary agent and a binder, and if necessary, a solvent for adjusting the viscosity is added. These are kneaded to prepare a positive electrode mixture paste, which is then applied to the surface of a current collector made of, for example, an aluminum foil and dried. If necessary, pressurization may be performed by a roll press or the like in order to increase the electrode density.

(Lithium ion conductive oxide)
The coating layer made of lithium ion conductive oxide provided on the surface of the lithium metal composite oxide serving as the positive electrode is formed of a metal element made of niobium and a compound containing tungsten and lithium. The lithium ion conductive oxide containing the metal element composed of niobium , tungsten and lithium has diffusion paths of lithium ions in multiple directions, has excellent lithium ion conductivity, and is stable and resistant to deterioration in the atmosphere. There is a feature.

Lithium ion conductive oxides include those containing niobium , tungsten and lithium .
Examples of this substance include a composite oxide of Li ₂ WO ₄ and LiNbO ₃ and a composite oxide of Li ₄ WO ₅ and LiNbO ₃ . In addition, a composite oxide of Li ₆ W ₂ O ₉ and Li NbO ₃ , a composite oxide of Li ₂ WO ₄ and Li ₃ NbO ₄ , a composite oxide of Li ₄ WO ₅ and Li ₃ NbO ₄ , Li ₆ W ₂ O ₉ And Li ₃ NbO ₄ complex oxides and the like.

In the present invention, by using a compound containing a metal element composed of niobium , tungsten and lithium for coating, (a) a compound containing two elements of lithium and phosphorus and (b) two elements of lithium and tungsten are used. The following effects, which cannot be achieved when a compound containing (c) or a compound containing two elements of lithium and niob, are used for coating, can be obtained.

That is, compared to the case of forming a compound consisting of (a) phosphorus and lithium only, (b) tungsten and lithium only, or (c) niobium and lithium only, a metal element composed of niobium , tungsten and lithium are used. By including it in an appropriate proportion, the proportion of non-crosslinked oxygen that is thought to trap lithium can be reduced. The non-crosslinked oxygen referred to here is oxygen that forms a bond with only one metal element among the oxygen in the lithium metal composite oxide, and if there is a large amount of non-crosslinked oxygen, lithium is contained in the positive electrode active material. When moving, the phenomenon of being trapped by oxygen atoms and hindering the movement is likely to occur, which lowers the lithium ion conductivity.
In the present invention, since there are many W —O and Nb—O bonds, the ionic bond tendency becomes higher than the covalent bond tendency, and the amount of non-crosslinked oxygen decreases. Therefore, the lithium ion conductivity can be made higher than in the above cases (a), (b) and (c).

As the above-mentioned lithium ion conductive oxide, a compound composed of Li ₂ WO ₄ and LiNbO ₃ is particularly preferable.
Since the compound is a compound composed of Li ₂ WO ₄ and LiNbO ₃ , the coating layer is stable with respect to the electrolyte used for the non-aqueous electrolyte secondary battery, and the elution of tungsten, phosphorus, niobium, etc. causes the coating layer to the battery. Adverse effects, such as increased resistance, can be reduced. The presence of Li ₂ WO ₄ and LiNbO ₃ in a complex manner makes it possible to mutually suppress tungsten elution from Li ₂ WO ₄ and niobium elution from Li NbO ₃ as compared with the case of each alone. This is because it is considered.

The molar ratio of Nb to W of the lithium ion conductive oxide composed of Li ₂ WO ₄ and LiNbO ₃ is preferably more than 0.5 and less than 4.
When the molar ratio of Nb to W of the compound composed of Li ₂ WO ₄ and LiNbO ₃ is more than 0.5 and less than 4, the lithium ion conductivity of the coating layer can be further improved, and the output characteristics of the battery can be improved. Can be improved. When the molar ratio of Nb to W is 0.5 or less, or 4 or more, the ratio of the above-mentioned non-crosslinked oxygen that traps lithium increases, and it becomes difficult to improve the lithium ion conductivity, which is not preferable.

The total molar amount of tungsten and niobium contained in the coating layer may be 0.05 to 5.0% with respect to the total molar amount of metal elements other than lithium contained in the lithium metal composite oxide. preferable.
In this case, the diffusion path of lithium ions between the positive electrode active material particles and the electrolytic solution can be more reliably secured, and the output of the battery using the positive electrode active material particles can be increased.
On the contrary, if it is less than 0.05%, a sufficient coating layer cannot be provided on the positive electrode active material particles 21, and a diffusion path of lithium ions with the electrolytic solution cannot be secured. On the other hand, if it exceeds 5.0%, the coating layer becomes too thick, the proportion of the effective lithium metal composite oxide in the positive electrode is reduced, and the charge / discharge capacity of the battery is lowered.

As the state of the compound containing the metal element composed of niobium , tungsten and lithium, an amorphous state is preferable to a crystalline state. This is because the amorphous state has a channel structure that is more effective in diffusing lithium ions. This is because the diffusion path of lithium is limited to the direction plane perpendicular to the c-axis in the layered compound with well-organized crystals, whereas in the amorphous state, the lithium diffusion path exists in the three-dimensional direction due to the disorder of the crystal. be.

(Positive electrode: Form of coating layer)
The coating layer in the present invention may be superimposed on the positive electrode and coated (see FIG. 1), or may be coated on the positive electrode active material particles constituting the positive electrode (see FIG. 2).

An embodiment of a thin-film positive electrode will be described with reference to FIG.
The positive electrode shown in the figure is a thin film type, and the positive electrode active material 13 is formed in a layer on the upper surface of the substrate 12 which is a current collector, and the lithium ion conductive oxide 14 is formed in a layer on the upper surface of the positive electrode active material 13. There is. The layer of the lithium ion conductive oxide 14 is a coating layer within the scope of the claims.

For the thin-film positive electrode 1 as described above, for example, the powder containing tungsten and lithium and the powder containing phosphorus and lithium are sintered to prepare a positive electrode active material 13 made of a lithium metal composite oxide. Then, it is obtained by depositing a compound containing a metal element composed of niobium , tungsten and lithium on the lithium metal composite oxide thin film by the PLD method to form a lithium ion conductive oxide 14.

When a battery is assembled using only the lithium metal composite oxide thin film as the positive electrode, decomposition components of the electrolytic solution such as phosphate adhere to the surface of the positive electrode, surface deterioration due to contact with the electrolytic solution, elution of Co from the positive electrode surface, etc. Due to the influence of the above, diffusion of lithium ions at the electrolytic solution / positive electrode interface is inhibited, which causes an increase in resistance at the electrolytic solution / positive electrode interface.
On the other hand, in the positive electrode, the surface of the lithium metal composite oxide thin film is coated with a metal element composed of niobium such as a compound composed of Li ₂ WO ₄ and LiNbO ₃ having good lithium diffusivity, and a compound containing tungsten and lithium. Since this coating layer suppresses contact between the positive electrode and the electrolytic solution and functions as a protective film having good permeability of lithium ions, adhesion of decomposition components of the electrolytic solution, surface deterioration of the surface of the positive electrode active material, and Co from the surface of the positive electrode It is possible to prevent phenomena such as elution.

Therefore, the resistance at the electric field liquid / positive electrode interface is significantly reduced as compared with the case where only the lithium metal composite oxide thin film is used as the positive electrode, and the output characteristics of the battery can be improved.
In order to take advantage of this effect, it is preferable that the lithium ion conductive oxide is coated on the entire surface of the positive electrode.

The coating layer made of the lithium ion conductive oxide preferably has a thickness of 1 to 500 nm. This layer thickness is applied to both the coating layer 14 (see FIG. 1) superimposed and coated on the positive electrode and the coating layer 23 (see FIG. 2) coated with the positive electrode active material particles constituting the positive electrode.
When the thickness of the coating layer is 1 to 500 nm, lithium ion conductivity can be exhibited and the output characteristics of the battery can be improved. That is, if the thickness of the coating film is less than 1 nm, the diffusion path of lithium ions may not work effectively, and if it exceeds 500 nm, the diffusion path becomes too long, and the charge / discharge capacity and output characteristics are improved. It may not be enough.

An embodiment of a positive electrode using positive electrode active material particles will be described with reference to FIG. 2. FIG. 2 is an enlarged view of the surface of the positive electrode active material particles 21 constituting the positive electrode active material 12.
The positive electrode active material 21 is formed by aggregating a plurality of primary particles 22. The positive electrode active material particles 21 are made of lithium ion conductive oxide on the lithium metal composite oxide 22 which is the primary particles or on the secondary particles (that is, the active material particles 21) composed of these primary particles 22. A coating layer 23 is provided. The positive electrode active material particles 21 may be either primary particles 22, secondary particles 21 in which the primary particles 22 are aggregated, or a mixture of the primary particles 22 and the secondary particles 21.

When the positive electrode active material 21 is composed of the secondary particles 21, it is preferable that the coating layer 23 is provided to the inside (that is, on the surface of the primary particles 22), but the surface of the secondary particles 21. When the thin film-shaped coating layer 23 is provided as a whole, the coating layer may not be provided to the inside.
Since the coating layer 23 is formed on the surface of the particles of the lithium metal composite oxide, it is possible to secure a diffusion path of lithium ions between the positive electrode active material particles and the electrolytic solution, and the positive electrode active material particles can be obtained. It is possible to increase the output of the used battery.

(Non-hydrogen electrolyte secondary battery)
In addition to the above positive electrode thin film electrode, by manufacturing a battery consisting of a separator, a negative electrode into which lithium can be inserted and removed, and an electrolytic solution, a positive electrode material for a non-aqueous electrolyte secondary battery and a secondary battery capable of achieving high output can be produced. It can be easily provided.

Each configuration of the battery will be described in detail below.
(1) Positive Electrode When the positive electrode thin film electrode 1 shown in FIG. 1 is configured, the positive electrode active material 13 which is a lithium metal composite oxide is deposited in a thin film on the substrate 12 which is a current collector, and is further superimposed . The lithium ion conductive oxide 14 is formed in the form of a thin film.

As shown in FIG. 2, when the positive electrode is formed by the positive electrode active material particles 21, the positive electrode active material particles 21 and the conductive material such as carbon powder, the binder, and the solvent are formed in the same manner as the positive electrode of a normal non-aqueous electrolyte secondary battery. Can be kneaded to form a paste, and the paste on the current collector is applied to obtain a positive electrode.

(2) Negative electrode The negative electrode may be made of a material that allows lithium to be inserted and removed, and is coated with a powdered carbon substance on the current collector, similar to the negative electrode of a normal non-aqueous electrolyte secondary battery. In the case of a coin cell, metallic lithium or a lithium alloy is preferably used. The thickness of the metallic lithium or lithium alloy constituting the negative electrode is preferably in the range of 0.5 to 2.0 mm so that the coin cell does not swell. It is necessary to hollow out the negative electrode to an area of about a diameter (5 to 15 mm) so that it fits in the coin cell, and the negative electrode preferably has a larger area than the positive electrode.

(3) Separator A separator is sandwiched between the positive electrode and the negative electrode. The separator has functions such as insulation between the positive electrode and the negative electrode and also holds an electrolytic solution, and a separator used in a general non-aqueous electrolyte secondary battery can be used. For example, polyethylene (PE), polypropylene (PP), glass (SiO ₂ ), or a porous film such as a laminated product thereof may be used as long as it has the necessary functions, and is used in a general non-aqueous electrolyte secondary battery. The separator is not particularly limited as long as it does not contain a measurement interfering element.

(4) Non-aqueous electrolyte solution The non-aqueous electrolyte solution is obtained by dissolving a lithium salt as an electrolyte in an organic solvent. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate, and moreover, tetrahydrofuran and 2-. One selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethyl sulfone and butane sulton, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. is used alone or in combination of two or more. be able to.

As the electrolyte, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , etc., and a composite salt thereof can be used. Further, the non-aqueous electrolyte solution may contain a radical catching agent, a surfactant, a flame retardant and the like.

(5) Battery Configuration As shown in FIG. 3, the positive electrode 1 and the negative electrode 2 described in (1) to (4) above are laminated via a separator 3 to form an electrode body, and non-aqueous electrolysis is performed on the electrode body. Impregnate with liquid. The positive electrode 1 and the negative electrode 2 are connected to external terminals to conduct conduction. A battery is manufactured by putting the above-mentioned structure in a metal container.

(Example 1)
In this embodiment, a LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film is used as the positive electrode active material 13, and the surface thereof is composed of Li ₂ WO ₄ and Li ₃ PO ₄ as the lithium ion conductive oxide 14. A compound thin film was formed.

(1) Positive electrode active material 13
The LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film was prepared by the PLD method. LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is mixed with Li ₂ CO ₃ and NiO, Co ₃ O ₄ and MnO ₂ and fired in an oxygen atmosphere at 980 ° C. LiNi _1/3 . Co _1/3 Mn _1/3 O ₂ powder was prepared. Then, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder was pressure-molded into pellets and sintered in an oxygen atmosphere at 1000 ° C. to obtain LiNi _1/3 Co _1/3 Mn _1/3 O ₂ pellets. Made. Targeting these pellets, under an oxygen atmosphere at 500 ° C., only a LiNi _1/3 Co _1/3 Mn _{1/3 O2} thin film (positive electrode active material 13) is placed on a Pt substrate (substrate 12) with an area of 8 mm × 8 mm. It was formed to a thickness of about 300 nm.
(2) Lithium ion conductive oxide 14
The PLD method was used to prepare the compound thin film composed of Li ₂ WO ₄ and Li ₃ PO ₄ , as in the case of the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film. The raw material powder was mixed so as to have the composition of Li ₂ WO ₄ , and then sintered to be pelletized and used as a target. Further, the raw material powder was mixed so as to have the composition of Li ₃ PO ₄ , and then sintered to be pelletized and used as a target.
(3) Positive electrode thin film electrode 1
Using the above target, on the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film which is the positive electrode active material 13 and further from Li ₂ WO ₄ and Li ₃ PO ₄ which are lithium ion conductive oxides 14. A compound thin film was formed. The forming procedure was to form the electrode at 25 ° C. and an oxygen partial pressure of 20 Pa to a thickness of about 300 nm, and the positive electrode thin film electrode 1 was produced in this way.
When the state of the compound consisting of Li ₂ WO ₄ and Li ₃ PO ₄ was confirmed by XRD, it was in an amorphous state, and the ratio of W to P in the compound consisting of Li ₂ WO ₄ and Li ₃ PO ₄ was determined by XPS. Upon confirmation, it was 1: 1. Further, when the positive electrode thin film was heat-treated at 600 ° C. for 2.5 hours and XRD measurement was performed, it was confirmed that the compound was composed of Li ₂ WO ₄ and Li ₃ PO ₄ .

(4) Evaluation The evaluation of the positive electrode thin film was performed by preparing the battery shown in FIG. 3 as shown below and measuring the positive electrode interfacial resistance.
A 2032 type coin-type battery 10 was produced using the positive electrode thin film electrode 1 (evaluation electrode) in a glove box having an Ar atmosphere with a dew point controlled at −80 ° C.
The negative electrode 2 is made of lithium metal having a thickness of 0.5 mm punched into a disk shape having a diameter of 13 mm, and the electrolytic solution is ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiPF ₆ as a supporting electrolyte. (Made by Ube Kosan Co., Ltd.) was used. A polyethylene porous membrane having a thin film of 25 μm was used for the separator 3. Further, in the coin-type battery 10, a container is formed by combining a positive electrode can 6 and a negative electrode can 7 with a gasket 4, and a positive electrode 1 and a negative electrode 2 etc. placed inside the container are fixed by a wave washer 5 to form a coin. Assembled into batteries.
For the positive surface resistance, the coin-type battery 10 was charged to a charging potential of 4.0 V, and AC impedance was measured using a frequency response analyzer and a potentiogalvanostat to obtain the impedance spectrum shown in FIG. In the obtained impedance spectrum, two semicircles are observed in the high frequency region and the intermediate frequency region, and a straight line is observed in the low frequency region. Was analyzed. Here, Rs is a bulk resistance, R1 is a positive electrode coating resistance, Rct is an electrolytic solution / positive electrode interface resistance (Li ⁺ transfer resistance at the interface), W is a wobble component, and CPE1 and CPE2 are constant phase elements. Next, the battery performance was compared using the prepared amorphous positive electrode thin film. The results are shown in Table 1.

(Example 2)
A compound consisting of Li ₂ WO ₄ and Li ₃ PO ₄ , which are lithium ion conductive oxides 14, is placed on a LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film, which is the positive electrode active material 13, of W and P. A coin-type battery was produced using the positive electrode material for a non-aqueous electrolyte secondary battery produced in the same manner as in Example 1 except that the film was formed with a ratio of 1: 2, and the battery was evaluated.

(Example 3)
A compound consisting of Li ₂ WO ₄ and Li ₃ PO ₄ , which are lithium ion conductive oxides 14, is placed on a LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film, which is the positive electrode active material 13, of W and P. A coin-type battery was produced using the positive electrode material for a non-aqueous electrolyte secondary battery produced in the same manner as in Example 1 except that the film was formed with a ratio of 1: 4, and the battery was evaluated.

(Example 4)
A compound consisting of Li ₂ WO ₄ and Li ₃ PO ₄ , which are lithium ion conductive oxides 14, is placed on a LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film, which is the positive electrode active material 13, of W and P. A coin-type battery was produced using the positive electrode material for a non-aqueous electrolyte secondary battery produced in the same manner as in Example 1 except that the film was formed with a ratio of 1: 0.5, and the battery was evaluated.

(Example 5)
In this embodiment, a LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film is used as the positive electrode active material 13, and a compound thin film composed of Li ₂ WO ₄ and LiNbO ₃ as the lithium ion conductive oxide 14 on the surface thereof. Formed.

(1) Positive electrode active material 13
It was produced in the same manner as in Example 1.
(2) Lithium ion conductive oxide 14
The PLD method was used to prepare the compound thin film composed of Li ₂ WO ₄ and LiNbO ₃ in the same manner as the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film. The raw material powder was mixed so as to have the composition of Li ₂ WO ₄ , and then sintered to be pelletized and used as a target. Further, the raw material powder was mixed so as to have a composition of Li ₃ NbO ₄ , and then sintered to be pelletized and used as a target.
(3) Positive electrode thin film electrode 1
Using the above target, a compound consisting of _Li2 WO ₄ and LiNbO ₃ which are lithium ion conductive oxides 14 is further formed on a LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film which is a positive electrode active material 13. A thin film was formed. The forming procedure was to form the electrode at 25 ° C. and an oxygen partial pressure of 20 Pa to a thickness of about 300 nm, and the positive electrode thin film electrode 1 was produced in this way.
When the state of the compound composed of Li ₂ WO ₄ and LiNbO ₃ was confirmed by XRD, it was in an amorphous state, and when the ratio of W and Nb in the compound composed of Li ₂ WO ₄ and LiNbO ₃ was confirmed by XPS, it was confirmed. It was 1: 1. Further, when the positive electrode thin film was heat-treated at 600 ° C. for 2.5 hours and XRD measurement was performed, it was confirmed that the compound was composed of Li ₂ WO ₄ and Li NbO ₃ .

(4) Evaluation The same procedure as in Example 1 was carried out.

(Example 6)
The ratio of W to Nb in the compound consisting of Li ₂ WO ₄ and LiNbO ₃ as the lithium ion conductive oxide 14 on the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film which becomes the positive electrode active material 13 is 1. A coin-type battery was produced using the positive electrode material for a non-aqueous electrolyte secondary battery produced in the same manner as in Example 5 except that the film was formed as: 2, and the battery was evaluated.

(Example 7)
The ratio of W to Nb in the compound consisting of Li ₂ WO ₄ and LiNbO ₃ as the lithium ion conductive oxide 14 on the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film which becomes the positive electrode active material 13 is 1. A coin-type battery was produced using the positive electrode material for a non-aqueous electrolyte secondary battery produced in the same manner as in Example 5 except that the film was formed as: 4, and the battery was evaluated.

(Example 8)
The ratio of W to Nb in the compound consisting of Li ₂ WO ₄ and LiNbO ₃ as the lithium ion conductive oxide 14 on the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film which becomes the positive electrode active material 13 is 1. A coin-type battery was produced using the positive electrode material for a non-aqueous electrolyte secondary battery produced in the same manner as in Example 5 except that the film was formed as 0.5, and the battery was evaluated.

(Comparative Example 1)
In Comparative Example 1, a LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film was used as the positive electrode active material.
The LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film was prepared in the same manner as in Example 1. Targeting the obtained LiNi _1/3 Co _1/3 Mn _1/3 O ₂ pellet, LiNi _1/3 Co _{1 /} on an area of 8 mm × 8 mm on a Pt substrate (substrate 12) under an oxygen atmosphere at 500 ° C. ₃ Only a Mn _1/3 O ₂ thin film (positive electrode active material 13) was formed to a thickness of about 300 nm to prepare a positive electrode thin film electrode 1. A coating layer made of lithium ion conductive oxide is not formed.
The evaluation of the positive electrode thin film was carried out by producing the battery shown in FIG. 3 and measuring the interface resistance of the positive electrode in the same manner as in Examples 1 to 4.

(Comparative Example 2)
Positive electrode for non-aqueous electrolyte secondary battery produced in the same manner as in Example 1 except that Li ₂ WO ₄ was formed on the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film, which is the positive electrode active material. A coin-type battery was manufactured using the material, and the battery was evaluated. Li ₂ WO ₄ is the composition described in Patent Document 3.

(Comparative Example 3)
Positive electrode for non-aqueous electrolyte secondary battery produced in the same manner as in Example 1 except that Li ₃ PO ₄ was formed on a thin film of Li Ni _1/3 Co _1/3 Mn _1/3 O ₂ which is a positive electrode active material. A coin-type battery was manufactured using the material, and the battery was evaluated. Li ₃ PO ₄ is a composition contained in lithium phosphate described in Patent Document 1, and is a composition described in Patent Document 2.

(Comparative Example 4)
A positive electrode material for a non-aqueous electrolyte secondary battery produced in the same manner as in Example 1 except that LiNbO ₃ was formed on a LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film as a positive electrode active material. A coin-type battery was manufactured using the battery, and the battery was evaluated.

From Table 1, the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film having a coating layer made of a lithium ion conductive oxide composed of Li ₂ WO ₄ and Li ₃ PO ₄ of Examples 1 to 4 was formed. Compared with the uncoated LiNi _1/3 Co _1/3 Mn _{1/3 O2} thin film of Comparative Example 1, the positive interfacial resistance is significantly reduced (about 1/4 to 1/5) and the output characteristics are improved. I found out how it was. As a factor, by coating a compound consisting of Li ₂ WO ₄ and Li ₃ PO ₄ in an amorphous state with excellent lithium ion conductivity, LiNi _1/3 Co _1/3 Mn _1/3 , which is a positive electrode active material, is used. Since the O ₂ thin film no longer comes into direct contact with the electrolytic solution, deterioration is suppressed, the lithium diffusivity of the positive electrode is further improved, and the resistance at the electric field solution / positive electrode interface is LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film. This is probably because it was significantly reduced in comparison.

Further, Examples 1 to 4 are a LiNi _1/3 Co _1/3 Mn _{1/3 O2} thin film and Comparative Example 3 in which only Li ₂ WO ₄ of Comparative Example 2 (corresponding to the prior art of Patent Document 3) is deposited. Compared with the LiNi _1/3 Co _1/3 Mn _{1/3 O2} thin film in which only Li ₃ PO ₄ deposited (corresponding to the prior art of Patent Documents 1 and 2) is compared, the positive interfacial resistance is reduced and the output is reduced. It was found that the characteristics were improved. As a factor, by mixing Li ₂ WO ₄ and Li ₃ PO ₄ , which have excellent lithium ion conductivity, the compound consisting of Li ₂ WO ₄ and Li ₃ PO ₄ has more lithium ion conductivity than a single substance, respectively. It is considered that this is because the lithium diffusivity of the positive electrode has improved.

Further, when Examples 1 to 4 are compared with each other, Example 3 in which W: P is 1: 4 and Example 4 in which W: P is 1: 0.5 have positive electrode interface resistance as compared with Comparative Examples 1 to 3. However, the positive electrode interface resistance may be slightly larger than that of Examples 1 and 2. Therefore, it can be seen that it is more effective that W: P exceeds 1: 0.5 and is smaller than 1: 4.

From Table 2, the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film having a coating layer made of a lithium ion conductive oxide composed of Li ₂ WO ₄ and LiNbO ₃ of Examples 5 to 8 is a comparative example. Compared with the uncoated LiNi _1/3 Co _1/3 Mn _{1/3 O2} thin film of 1, the positive interfacial resistance is significantly reduced (about 1/4 to 1/5), and the output characteristics are improved. I understood the situation. As a factor, by coating a compound consisting of Li ₂ WO ₄ and LiNbO ₃ in an amorphous state with excellent lithium ion conductivity, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ which is a positive electrode active material is used. Deterioration is suppressed because the thin film no longer comes into direct contact with the electrolytic solution, the lithium diffusivity of the positive electrode is further improved, and the resistance at the electric field solution / positive electrode interface is higher than that of the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film. This is probably because it was significantly reduced.

Further, Examples 5 to 8 are a LiNi _1/3 Co _1/3 Mn _{1/3 O2} thin film and Comparative Example 4 in which only Li ₂ WO ₄ of Comparative Example 2 (corresponding to the prior art of Patent Document 3) is deposited. It was found that the positive interfacial resistance was reduced and the output characteristics were improved as compared with the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film in which only LiNbO ₃ was deposited. As a factor, by mixing Li ₂ WO ₄ and LiNbO ₃ which are excellent in lithium ion conductivity, the compound composed of Li ₂ WO ₄ and LiNbO ₃ further improves the lithium ion conductivity and the positive electrode, respectively, than the simple substance. This is probably because the lithium diffusivity has improved.

Further, when Examples 5 to 8 are compared with each other, Example 7 having W: Nb of 1: 4 and Example 8 having W: Nb of 1: 0.5 have a positive electrode as compared with Comparative Examples 1, 2 and 4. Although the interfacial resistance is reduced, the positive electrode interfacial resistance may be slightly larger than that of Examples 5 and 6. Therefore, it can be seen that it is more effective that W: Nb exceeds 1: 0.5 and is smaller than 1: 4.

The positive electrode material for a non-aqueous electrolyte secondary battery and the secondary battery of the present invention are suitable for batteries for electric vehicles and hybrid vehicles that require high output. Further, this positive electrode material can be applied to various lithium metal composite oxides and lithium ion conductive oxides without being influenced by various properties such as solubility of the material.

1 Positive electrode thin film electrode 2 Negative electrode 3 Separator 4 Gasket 5 Wave washer 6 Positive electrode can 7 Negative electrode can 10 Coin-type battery 12 Substrate 13 Positive electrode active material 14 Lithium ion conduction oxide 21 Positive electrode active material particles (secondary particles)
22 Lithium metal composite oxide (primary particles)
23 Lithium-ion conductive oxide

Claims (9)

A positive electrode composed of a positive electrode active material made of a lithium metal composite oxide, and a positive electrode
It is composed of a coating layer made of a metal element made of niobium and a lithium ion conductive oxide containing tungsten and lithium, which is formed on the surface of the positive electrode .
The lithium ion conductive oxide is a compound composed of Li ₂ WO ₄ and LiNbO ₃ .
A positive electrode for a non-aqueous electrolyte secondary battery . The non-aqueous electrolyte secondary battery according to claim 1 , wherein the molar ratio of Nb to W of the lithium ion conductive oxide composed of Li ₂ WO ₄ and LiNbO ₃ is more than 0.5 and less than 4. For positive electrode. The total molar amount of tungsten and niobium contained in the coating layer is 0.05 to 5.0% with respect to the total molar amount of metal elements other than lithium contained in the lithium metal composite oxide. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1 or 2 , wherein the positive electrode is characterized. The non-aqueous electrolyte secondary battery according to claim 1 , 2 or 3, wherein the lithium ion conductive oxide containing the metal element composed of niobium , tungsten and lithium is in an amorphous state. Positive electrode. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1 , 2, 3 or 4, wherein the positive electrode is a thin film, and the coating layer is superimposed on the positive electrode to form a layer. The non-aqueous system according to claim 1 , 2, 3 or 4, wherein the lithium metal composite oxide is in the form of particles, and the coating layer is formed on the surface of the particles of the lithium metal composite oxide. Positive electrode for electrolyte secondary batteries. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 5 or 6 , wherein the coating layer has a thickness of 1 to 500 nm. A positive electrode active material used for the positive electrode for a non-aqueous electrolyte secondary battery according to claim 5 or 6 , wherein the lithium metal composite oxide contains a metal element composed of niobium , tungsten, and lithium. A positive electrode active material for a non-aqueous electrolyte secondary battery, characterized in that a coating layer made of an oxide is formed. A non-aqueous electrolyte secondary battery according to claim 8, wherein a positive electrode using the positive electrode active material is used .

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