JP2018198193A - Cathode electrode for nonaqueous electrolyte secondary battery, cathode active material used therefor, and nonaqueous electrolyte secondary battery utilizing the same - Google Patents

Abstract

To provide a cathode electrode for a nonaqueous electrolyte secondary battery which reduces deterioration in performance of a battery by improving output of the battery, a cathode active material and the secondary battery.SOLUTION: The present invention relates to a nonaqueous battery in which a cathode electrode for a nonaqueous electrolyte secondary battery consists of: a cathode 1 formed from a cathode active material 13 consisting of a lithium metal composite oxide; and a coating layer consisting of a lithium ion conduction oxide 14 using a compound containing at least one or more metal elements selected from phosphor and niobium, tungsten and lithium. The lithium ion conduction oxide 14 is a compound consisting of LiWOand LiPOor a compound consisting of LiWOand LiNbO. In the cathode electrode for the nonaqueous electrolyte secondary battery, lithium ion conductivity in the cathode electrode 1 can be improved by the lithium ion conduction oxide, deterioration of the cathode active material can be suppressed, high output can be implemented and output performance hardly deteriorates.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery, a positive electrode active material used therefor, and a secondary battery using the same. 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 therefor, 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 laptop computers, development of small and lightweight secondary batteries having high energy density is strongly desired. In addition, development of a high output secondary battery is strongly desired as a battery for hybrid vehicles and electric vehicles. There is a lithium ion secondary battery as a non-aqueous electrolyte secondary battery that satisfies such requirements.

A lithium ion secondary battery is composed of a positive electrode having a positive electrode active material as a main component, a negative electrode having a negative electrode active material as a main component, and a non-aqueous electrolyte, and the negative electrode and the positive electrode desorb and insert lithium. 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 have a high voltage of 4V. Therefore, practical use is progressing as a battery having a high energy density.

Examples of positive electrode materials that have been 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 oxide (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 a battery for automobiles, it is important to improve the positive electrode material that can obtain higher output than the current state, that is, to lower the resistance of the positive electrode material.
In addition, some of the above lithium composite oxides react with moisture and carbon dioxide in the atmosphere when handled in the atmosphere, causing surface modification, causing 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 phosphate oxynitride), 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 after storage for 1 week is suppressed.

Patent Document 2 discloses a lithium ion secondary battery excellent in cycle characteristics and rate characteristics by covering the surface of a lithium-containing composite oxide powder containing 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 is obtained.

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

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

Japanese Patent No. 4923397 International Publication WO2012 / 176903 JP 2013-171785 A

In view of the above problems, the present invention provides a positive electrode for a non-aqueous electrolyte secondary battery that can increase the output of the battery when used as the positive electrode of the battery and has little deterioration in the performance of the battery. It aims at providing the positive electrode active material used.
It is another object of the present invention to provide a non-aqueous electrolyte secondary battery that can obtain high output and has little deterioration in battery performance.

  In order to solve the above problems, the present inventor has examined various properties of a lithium metal composite oxide used as a positive electrode active material for a non-aqueous electrolyte secondary battery. As a result, the surface of the lithium metal composite oxide was formed from phosphorus or niobium. By forming a coating layer composed of a compound containing at least one selected metal element and tungsten and lithium, the lithium ion conductivity on the positive electrode electrode, more specifically on the lithium metal composite oxide surface, is improved. The knowledge that it can be made was acquired. In addition, by using this positive electrode, it is possible to greatly reduce the electrolyte / positive electrode interface resistance of the secondary battery, improve the output characteristics of the secondary battery, and suppress the deterioration of the battery performance. As a result, the present invention was completed.

The positive electrode for a non-aqueous electrolyte secondary battery of the first invention is a positive electrode composed of a positive electrode active material made of a lithium metal composite oxide, and at least one selected from phosphorus or niobium formed on the surface of the positive electrode. And a coating layer made of a lithium ion conductive oxide containing at least one kind of metal element, tungsten, and lithium.
The positive electrode for a non-aqueous electrolyte secondary battery of the second invention is characterized in that, in the first invention, the lithium ion conductive oxide is a compound composed of Li ₂ WO ₄ and Li ₃ PO ₄ .
The positive electrode for a non-aqueous electrolyte secondary battery according to a third aspect of the invention is the positive electrode for the nonaqueous electrolyte secondary battery according to the second aspect, wherein the molar ratio of P to W of the lithium ion conductive oxide composed of Li ₂ WO ₄ and Li ₃ PO ₄ is 0.5. It is characterized by being more than 4 and less than 4.
The positive electrode for a nonaqueous electrolyte secondary battery according to a fourth aspect of the present invention is the positive electrode for the nonaqueous electrolyte secondary battery according to any one of the first to third aspects, wherein the total molar amount of tungsten and phosphorus contained in the coating layer is the lithium metal composite oxide. It is 0.05 to 5.0% with respect to the total molar amount of metal elements other than lithium contained in the metal.
The positive electrode for a non-aqueous electrolyte secondary battery according to a fifth aspect of the present invention is characterized in that, in the first aspect, the lithium ion conductive oxide is a compound composed of Li ₂ WO ₄ and LiNbO ₃ .
The positive electrode for a non-aqueous electrolyte secondary battery according to a sixth aspect of the present invention is the fifth aspect of the invention, wherein 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.
A positive electrode for a non-aqueous electrolyte secondary battery according to a seventh aspect of the present invention is the positive electrode for the non-aqueous electrolyte secondary battery according to any one of the first, fifth and sixth aspects, wherein the total molar amount of tungsten and niobium contained in the coating layer is It is 0.05 to 5.0% with respect to the total molar amount of metal elements other than lithium contained in the metal composite oxide.
A positive electrode for a non-aqueous electrolyte secondary battery according to an eighth aspect of the present invention is the lithium electrode according to any one of the first to seventh aspects, comprising at least one metal element selected from phosphorus or niobium, tungsten and lithium. The ion conductive oxide is in an amorphous state.
The positive electrode for a non-aqueous electrolyte secondary battery according to a ninth aspect of the present invention is the positive electrode according to any one of the first to eighth aspects, wherein the positive electrode is a thin film, and the coating layer is formed in a layered manner overlapping the positive electrode. It is characterized by that.
The positive electrode for a non-aqueous electrolyte secondary battery according to a tenth aspect of the present invention is the positive electrode according to any one of the first to eighth aspects, wherein the lithium metal composite oxide is particulate, and the coating layer is made of the lithium metal composite oxide. It is formed on the surface of particles.
The positive electrode for a nonaqueous electrolyte secondary battery according to an eleventh aspect of the invention is characterized in that, in the ninth aspect or the tenth aspect, the coating layer has a thickness of 1 to 500 nm.
A positive electrode active material for a non-aqueous electrolyte secondary battery according to a twelfth aspect of the invention is a positive electrode active material used for the positive electrode for a non-aqueous electrolyte secondary battery according to the ninth or tenth aspect of the invention. A coating layer made of a lithium ion conductive oxide containing at least one metal element selected from phosphorus or niobium, tungsten, and lithium is formed.
A non-aqueous electrolyte secondary battery according to a thirteenth aspect is characterized in that the positive electrode according to any one of the first to eleventh aspects is used.

According to the first invention, the positive electrode for a non-aqueous electrolyte secondary battery has at least one metal selected from phosphorus or niobium on the surface of the positive electrode composed of a positive electrode active material made of a lithium metal composite oxide. By having a coating layer formed of a compound containing an element, tungsten, and lithium, lithium ion conductivity in the electrode can be improved and deterioration of the positive electrode active material can be suppressed. Therefore, by using this electrode, a high output can be realized, and a positive electrode for a non-aqueous electrolyte secondary battery in which high output performance is hardly deteriorated can be provided.
According to the second invention, since the lithium ion conductive oxide forming the coating layer is a compound composed of Li ₂ WO ₄ and Li ₃ PO ₄ , the coating layer can be used for the electrolyte used in the non-aqueous electrolyte secondary battery. It is stable and can reduce adverse effects on the battery due to elution of tungsten and phosphorus.
According to the third invention, the coating layer is formed by having a molar ratio of P to W of the lithium ion conductive oxide comprising Li ₂ WO ₄ and Li ₃ PO ₄ forming the coating layer exceeding 0.5 and less than 4. The lithium ion conductivity of the battery can be further improved, and the output characteristics of the battery can be improved.
According to the fourth invention, the total molar amount of tungsten and phosphorus contained in the coating layer is 0.05 to 5.0 with respect to the total of metal elements other than lithium contained in the lithium metal composite oxide. %, The lithium ion diffusion path between the positive electrode active material particles and the electrolytic solution can be ensured more reliably, and the output of the battery using the positive electrode active material particles can be increased.
According to the fifth invention, since the lithium ion conductive oxide forming the coating layer is a compound composed of Li ₂ WO ₄ and LiNbO ₃ , the coating layer is stable with respect to the electrolyte used in the non-aqueous electrolyte secondary battery. Thus, adverse effects on the battery due to elution of tungsten or niobium can be reduced.
According to the sixth invention, the lithium ion conductive oxide comprising Li ₂ WO ₄ and LiNbO ₃ forming the coating layer has a molar ratio of Nb to W of more than 0.5 and less than 4, so that the lithium of the coating layer The ion conductivity can be further improved, and the output characteristics of the battery can be improved.
According to the seventh 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 of metal elements other than lithium contained in the lithium metal composite oxide. %, The lithium ion diffusion path between the positive electrode active material particles and the electrolytic solution can be ensured more reliably, and the output of the battery using the positive electrode active material particles can be increased.
According to the eighth invention, the lithium ion conductive oxide containing at least one metal element selected from phosphorus or niobium, tungsten and lithium is in an amorphous state, whereby the positive electrode interface resistance of the positive electrode is reduced. Further reduction can be achieved.
According to the ninth invention, since the positive electrode is a thin film and the coating layer is formed so as to overlap the positive electrode, the deterioration of the surface of the positive electrode active material is suppressed, and lithium ion ions are interposed between the thin film positive electrode and the electrolyte. A diffusion path can be secured, and a battery using a thin film positive electrode can have a high output.
According to the tenth invention, the lithium metal composite oxide is in the form of particles and the coating layer is formed on the surfaces of the lithium metal composite oxide particles, so that the deterioration of the surface of the positive electrode active material is suppressed and the positive electrode A lithium ion diffusion path can be secured between the active material particles and the electrolytic solution, and the output of the battery using the positive electrode active material particles can be increased.
According to the eleventh aspect of the invention, since the covering layer has a thickness of 1 to 500 nm, a sufficient covering layer having lithium ion conductivity and weather resistance can be secured, thereby improving the output characteristics of the battery. be able to.
According to the twelfth invention, the surface of the lithium metal composite oxide particles as the positive electrode active material comprises a lithium ion conductive oxide containing at least one metal element selected from phosphorus or niobium, tungsten and lithium. By forming the coating layer, it is possible to improve the lithium ion conductivity of the positive electrode active material and to suppress the deterioration of the performance.
According to the thirteenth aspect of the invention, the non-aqueous electrolyte secondary battery using the positive electrode of the first to eleventh aspects of the invention makes it possible to increase the output of the secondary battery and increase the output. It is possible to suppress the deterioration of the performance.

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 using 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 the 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”) has at least one metal element selected from phosphorus or niobium on the surface of a lithium metal composite oxide and tungsten. It is a positive electrode coated with a lithium ion conductive oxide made of a compound containing lithium. A non-aqueous electrolyte secondary battery (hereinafter simply referred to as “battery”) is a battery including 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 compound containing at least one metal element selected from phosphorus or niobium and tungsten and lithium, so that the lithium in the electrode Ion conductivity can be improved and deterioration of the positive electrode active material can be suppressed. Therefore, by using this electrode, it is possible to provide a positive electrode for a non-aqueous electrolyte secondary battery that can achieve high output and is less likely to deteriorate high output performance.

(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 is a layered type lithium composite oxide in which a high voltage of 4V is obtained and the diffusion direction of lithium is limited to the a and b plane directions. If it is a thing. As such a lithium composite oxide, lithium cobalt composite oxide (LiCoO ₂ ), lithium nickel composite oxide (LiNiO ₂ ), lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3) Examples thereof include materials such as O ₂ ), which are properly used according to the intended battery characteristics. Among them, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is widely used as a positive electrode active material that balances charge / discharge capacity and battery safety.

The thin-film positive electrode is made of a conductive material such as Pt / Cr / SiO ₂ or Pt by a PLD method (pulse laser deposition method, the same applies hereinafter) after sintering the powder of the lithium metal composite oxide material and producing a target. It is obtained by depositing a lithium metal composite oxide on a conductive substrate.
The positive electrode using the particulate lithium metal composite oxide is a mixture of the powder of the lithium metal composite oxide material, a conductive additive and a binder, and if necessary, a solvent for viscosity adjustment is added, These are kneaded to prepare a positive electrode mixture paste, and then applied to the surface of a current collector made of aluminum foil, for example, and dried. If necessary, pressure may be applied by a roll press or the like 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 compound containing at least one metal element selected from phosphorus or niobium, tungsten, and lithium. ing. This lithium ion conductive oxide containing at least one metal element selected from phosphorus or niobium, tungsten and lithium has a lithium ion diffusion path in multiple directions, has excellent lithium ion conductivity, and is in the atmosphere. It is characterized by being stable and resistant to alteration.

There are two types of lithium ion conductive oxides: those containing phosphorus, tungsten and lithium, and those containing niobium, tungsten and lithium.
The former substance includes a composite compound of Li ₂ WO ₄ and Li ₃ PO _4, a composite compound of Li ₄ WO ₅ and Li ₃ PO _{4, and} a composite compound of Li ₆ W ₂ O ₉ and Li ₃ PO ₄ .
Examples of the latter 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 . Further, a composite oxide of Li ₆ W ₂ O ₉ and LiNbO _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 composite oxide.

  In the present invention, a compound containing at least one metal element selected from phosphorus or niobium and tungsten and lithium is used for coating, so that (a) a compound containing two elements lithium and phosphorus; The following effects can be obtained that cannot be achieved by using a compound containing two elements of lithium and tungsten or (c) a compound containing two elements of lithium and niobium for coating.

That is, at least one or more selected from phosphorus or niobium is formed as compared with the case where (a) phosphorus and lithium only, (b) tungsten and lithium only, or (c) niobium and lithium only. By including the metal element, tungsten, and lithium in an appropriate ratio, the ratio of non-bridging oxygen that is thought to trap lithium can be reduced. Non-bridging oxygen as used herein refers to oxygen that forms a bond with only one metal element among the oxygen in the lithium metal composite oxide. When is moved, a phenomenon that is trapped by oxygen atoms and hinders the movement is likely to occur, and the lithium ion conductivity is lowered.
In the present invention, since there are many P—O, W—O, and Nb—O bonds, the ionic bond tendency becomes higher than the covalent bond tendency, and non-bridging oxygen decreases. For this reason, lithium ion conductivity can be made higher than the case of said (a), (b), and (c).

As the above-described lithium ion conductive oxide, a compound composed of Li ₂ WO ₄ and Li ₃ PO ₄ or 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 Li ₃ PO ₄ , or a compound composed of Li ₂ WO ₄ and LiNbO ₃ , the coating layer is stable with respect to the electrolyte used in the non-aqueous electrolyte secondary battery. It is possible to reduce adverse effects on the battery due to elution of tungsten, phosphorus, niobium, etc., for example, an increase in resistance. Compared to the case of each of them alone, Li ₂ WO ₄ and Li ₃ PO ₄ , or Li ₂ WO ₄ and LiNbO ₃ are present in a composite, so that tungsten elution from Li ₂ WO ₄ and Li ₃ PO ₄ This is because it is considered that phosphorus elution and niobium elution from LiNbO ₃ can be mutually suppressed.

The molar ratio of P to W in the lithium ion conductive oxide composed of Li ₂ WO ₄ and Li ₃ PO ₄ is preferably more than 0.5 and less than 4.
When the molar ratio of P to W of the compound consisting of Li ₂ WO ₄ and Li ₃ PO ₄ is more than 0.5 and less than 4, the lithium ion conductivity of the coating layer can be further improved, and the output of the battery Characteristics can be improved. If the molar ratio of P to W is 0.5 or less, or 4 or more, the proportion of non-bridging oxygen that traps lithium described above increases, and it becomes difficult to improve lithium ion conductivity.

The total molar amount of tungsten and phosphorus 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. preferable.
In this case, a lithium ion diffusion path between the positive electrode active material particles and the electrolytic solution can be ensured more reliably, and the battery using the positive electrode active material particles can have high output.
On the other hand, 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 between the electrolyte and the electrolytic solution is not ensured. On the other hand, if it exceeds 5.0%, the coating layer becomes too thick and the ratio of the effective lithium metal composite oxide in the positive electrode is reduced, so that the charge / discharge capacity as a battery is lowered.

The lithium ion conductive oxide composed of Li ₂ WO ₄ and LiNbO ₃ preferably has a molar ratio of Nb to W of more than 0.5 and less than 4.
When the molar ratio of Nb to W of the compound consisting 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. If the molar ratio of Nb to W is 0.5 or less, or 4 or more, the proportion of non-bridging oxygen that traps lithium described above increases, making it difficult to improve lithium ion conductivity, which is not preferable.

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. preferable.
In this case, a lithium ion diffusion path between the positive electrode active material particles and the electrolytic solution can be ensured more reliably, and the battery using the positive electrode active material particles can have high output.
On the other hand, 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 between the electrolyte and the electrolytic solution is not ensured. On the other hand, if it exceeds 5.0%, the coating layer becomes too thick and the ratio of the effective lithium metal composite oxide in the positive electrode is reduced, so that the charge / discharge capacity as a battery is lowered.

  The state of the compound containing at least one metal element selected from phosphorus or niobium, tungsten, and lithium is preferably an amorphous state rather than a crystalline state. This is because the amorphous state has a more effective channel structure for lithium ion diffusion. This is because the lithium diffusion path is limited to the direction plane perpendicular to the c-axis in a layered compound with an aligned crystal, whereas in the amorphous state, there is a lithium diffusion path in a three-dimensional direction from the disorder of the crystal. is there.

(Positive electrode: form of coating layer)
The coating layer in the present invention may be coated so as to overlap the positive electrode (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 illustrated positive electrode has a thin film shape. A positive electrode active material 13 is formed in a layer on the upper surface of a substrate 12 as a current collector, and a lithium ion conductive oxide 14 is formed in a layer on the upper surface of the positive electrode active material 13. Yes. This layer of lithium ion conductive oxide 14 is a coating layer referred to in the claims.

  The thin film positive electrode 1 as described above, for example, sinters the powder containing tungsten and lithium and the powder containing phosphorus and lithium to produce the positive electrode active material 13 made of a lithium metal composite oxide. Thereafter, a lithium ion conductive oxide 14 is formed by depositing a compound containing at least one metal element selected from phosphorus or niobium, tungsten, and lithium on the lithium metal composite oxide thin film by a PLD method. can get.

When a battery is assembled using only the lithium metal composite oxide thin film as a positive electrode, the decomposition component of the electrolyte solution such as phosphate adheres to the positive electrode surface, surface deterioration due to contact with the electrolyte solution, Co elution from the positive electrode surface, etc. As a result, the diffusion of lithium ions at the electrolyte / positive electrode interface is hindered, leading to an increase in resistance at the electrolyte / positive electrode interface.
On the other hand, at least one selected from phosphorus or niobium such as a compound composed of Li ₂ WO ₄ and Li ₃ PO ₄ having good lithium diffusibility or a compound composed of Li ₂ WO ₄ and LiNbO _{3 on the} surface of the lithium metal composite oxide thin film. In a positive electrode coated with a compound containing more than one metal element, tungsten and lithium, this coating layer suppresses the contact between the positive electrode and the electrolyte and functions as a protective film having good lithium ion permeability. Phenomena such as adhesion of decomposition components, surface deterioration of the surface of the positive electrode active material, and elution of Co from the surface of the positive electrode can be prevented.

For this reason, the resistance at the interface between the electrolytic solution and the positive electrode is greatly 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, the lithium ion conductive oxide is preferably 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) that is covered with the positive electrode and the coating layer 23 (see FIG. 2) that is coated with the positive electrode active material particles constituting the positive electrode.
When the thickness of the coating layer is 1 to 500 nm, the lithium ion conductivity can be exhibited and the output characteristics of the battery can be improved. That is, when the thickness of the coating film is less than 1 nm, the lithium ion diffusion path may not work effectively. When the thickness exceeds 500 nm, the diffusion path becomes too long, and the charge / discharge capacity and output characteristics are improved. You may not get enough.

An embodiment of the positive electrode using the positive electrode active material particles will be described based on FIG. 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. And in the positive electrode active material particle 21, it consists of lithium ion conductive oxide on the lithium metal complex oxide 22 which is primary particles, or the secondary particle (namely, active material particle 21) which consists of these primary particles 22. A covering layer 23 is provided. The positive electrode active material particles 21 may be either the primary particles 22, the 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 up to the inside (that is, on the surface of the primary particles 22). When the thin film-like coating layer 23 is provided as a whole, the coating layer may not be provided up to the inside.
Since the coating layer 23 is formed on the surface of the lithium metal composite oxide particles, a diffusion path of lithium ions can be secured between the positive electrode active material particles and the electrolytic solution, The output of the used battery can be increased.

(Non-hydrogen electrolyte secondary battery)
In addition to the positive electrode thin film electrode, a positive electrode material for a non-aqueous electrolyte secondary battery and a secondary battery that can realize high output by producing a battery composed of a separator, a negative electrode capable of inserting and extracting lithium, and an electrolytic solution. It can be provided easily.

Below, each structure of a battery is demonstrated in detail.
(1) Positive electrode When the positive electrode thin film electrode 1 shown in FIG. 1 is configured, a positive electrode active material 13 that is a lithium metal composite oxide is deposited in a thin film form on a substrate 12 that is a current collector, and further superimposed. A lithium ion conductive oxide 14 such as a compound made of Li ₂ WO ₄ and Li ₃ PO ₄ is formed in 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 a conductive material such as carbon powder, a binder, and a solvent are used similarly to the positive electrode of a normal non-aqueous electrolyte secondary battery. A positive electrode can be obtained by kneading and pasting and applying the paste on the current collector.

(2) Negative electrode The negative electrode may be made of any material capable of inserting and extracting lithium. Similar to the negative electrode of a normal non-aqueous electrolyte secondary battery, a carbon material powder is coated on the current collector. In the case of a coin cell, metallic lithium or a lithium alloy is preferably used. The thickness of the metal 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 cut out the negative electrode in an area of a diameter (5 to 15 mm) so as to be accommodated in the coin cell, and the negative electrode preferably has a larger area than the positive electrode.

(3) Separator A separator is interposed 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 those used in general nonaqueous electrolyte secondary batteries can be used. For example, a porous film such as polyethylene (PE), polypropylene (PP), glass (SiO ₂ ), or a laminate thereof may be used as long as it has the necessary functions, and is used in a general non-aqueous electrolyte secondary battery. As long as the separator does not contain a measurement interfering element, the separator is not particularly limited.

(4) Non-aqueous electrolyte The non-aqueous electrolyte 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, ethyl methyl carbonate, and dipropyl carbonate; and tetrahydrofuran, 2- One kind selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. are used alone or in admixture of two or more. be able to.

As the electrolyte, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and complex salts thereof can be used. Furthermore, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.

(5) Configuration of Battery As shown in FIG. 3, the positive electrode 1 and the negative electrode 2 described in the above (1) to (4) are laminated via a separator 3 to form an electrode body, and this electrode body is subjected to nonaqueous electrolysis. Impregnate with liquid. Each of the positive electrode 1 and the negative electrode 2 is connected to an external terminal to be conducted. A battery is fabricated by placing the above 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 made 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 produced by the PLD method. Li ₂ CO ₃ and NiO, Co ₃ O ₄ , and MnO ₂ are mixed so as to have a composition of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and fired in an oxygen atmosphere at 980 ° C. to form LiNi _1/3. Co _1/3 Mn _1/3 O ₂ powder was prepared. Thereafter, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder is pressure-molded into pellets, sintered in an oxygen atmosphere at 1000 ° C., and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ pellets are formed. Produced. Using this pellet as a target, only a LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film (positive electrode active material 13) having an area of 8 mm × 8 mm on a Pt substrate (substrate 12) in an oxygen atmosphere at 500 ° C. The film was formed to a thickness of about 300 nm.
(2) Lithium ion conductive oxide 14
For the production of a compound thin film composed of Li ₂ WO ₄ and Li ₃ PO ₄ , the PLD method was used 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 a composition of Li ₂ WO ₄ and then sintered to form a pellet as a target. Further, after the raw material powder was mixed to a composition of Li ₃ PO _4, it was targeted into pellets and sintered.
(3) Positive electrode thin film electrode 1
Using the above target, Li ₂ WO ₄ and Li ₃ PO ₄ that are lithium ion conductive oxides 14 are further formed on the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film that is the positive electrode active material 13. A compound thin film was formed. The formation procedure was to form a film having a thickness of about 300 nm at 25 ° C. and an oxygen partial pressure of 20 Pa. Thus, the positive electrode thin film electrode 1 was produced.
When the state of the compound composed 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 and P in the compound composed of Li ₂ WO ₄ and Li ₃ PO ₄ was determined by XPS. When confirmed, it was 1: 1. When it was XRD measurement was heat-treated for 2.5 hours the cathode thin film 600 ° C., it was confirmed that the compound consisting of _Li 2 WO ₄ and _Li 3 PO _4.

(4) Evaluation The positive electrode thin film was evaluated by preparing the battery shown in FIG. 3 as follows and measuring the positive electrode interface resistance.
Using the positive electrode thin film electrode 1 (evaluation electrode), a 2032 type coin-type battery 10 was produced in a glove box in an Ar atmosphere in which the dew point was controlled at −80 ° C.
The negative electrode 2 was made of metal lithium having a thickness of 0.5 mm punched into a disk shape having a diameter of 13 mm, and the electrolyte was ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiPF ₆ as a supporting electrolyte. The equivalent liquid mixture (made by Ube Industries, Ltd.) was used. The separator 3 was a polyethylene porous film having a thin film thickness of 25 μm. In addition, the coin-type battery 10 is configured by combining a positive electrode can 6 and a negative electrode can 7 with a gasket 4, and fixing the positive electrode 1, the negative electrode 2, and the like contained therein with a wave washer 5. Assembled into a battery.
For the positive electrode interface 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 potentio galvanostat to obtain an 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. Therefore, an equivalent circuit model shown in FIG. Was analyzed. Here, Rs is a bulk resistance, R1 is a positive electrode film resistance, Rct is an electrolyte / positive electrode interface resistance (Li ⁺ movement resistance at the interface), W is a Warburg component, and CPE1 and CPE2 are constant phase elements. Next, the battery performance was compared using the produced positive electrode thin film in an amorphous state. The results are shown in Table 1.

(Example 2)
On the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film serving as the positive electrode active material 13, a compound composed of Li ₂ WO ₄ and Li ₃ PO _{4 serving} as the lithium ion conductive oxide 14 is formed. 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 at a ratio of 1: 2, and the battery was evaluated.

Example 3
On the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film serving as the positive electrode active material 13, a compound composed of Li ₂ WO ₄ and Li ₃ PO _{4 serving} as the lithium ion conductive oxide 14 is formed. A coin-type battery was produced using the positive electrode material for a nonaqueous electrolyte secondary battery produced in the same manner as in Example 1 except that the film was formed at a ratio of 1: 4, and the battery was evaluated.

(Example 4)
On the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film serving as the positive electrode active material 13, a compound composed of Li ₂ WO ₄ and Li ₃ PO _{4 serving} as the lithium ion conductive oxide 14 is formed. 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 at a ratio of 1: 0.5, and the battery was evaluated.

(Example 5)
In this example, 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 made of Li ₂ WO ₄ and LiNbO ₃ is used as the lithium ion conductive oxide 14 on the surface. Formed.

(1) Positive electrode active material 13
It was produced in the same manner as in Example 1.
(2) Lithium ion conductive oxide 14
For the production of a compound thin film composed of Li ₂ WO ₄ and LiNbO ₃ , the PLD method was used 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 a composition of Li ₂ WO ₄ and then sintered to form a pellet as a target. Further, after the raw material powder was mixed to a composition of Li ₃ NbO _4, it was targeted into pellets and sintered.
(3) Positive electrode thin film electrode 1
A compound comprising Li ₂ WO ₄ and LiNbO ₃ which are lithium ion conductive oxides 14 on the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film which is the positive electrode active material 13 using the above target. A thin film was formed. The formation procedure was to form a film having a thickness of about 300 nm at 25 ° C. and an oxygen partial pressure of 20 Pa. Thus, the positive electrode thin film electrode 1 was produced.
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, 1: 1. When it was XRD measurement was heat-treated for 2.5 hours the cathode thin film 600 ° C., it was confirmed that the compound consisting of _Li 2 WO ₄ and LiNbO _3.

(4) Evaluation It carried out similarly to Example 1.

(Example 6)
The ratio of W and Nb in the compound made of Li ₂ WO ₄ and LiNbO ₃ to be the lithium ion conductive oxide 14 on the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film to be the positive electrode active material 13 is set to 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 and Nb in the compound made of Li ₂ WO ₄ and LiNbO ₃ to be the lithium ion conductive oxide 14 on the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film to be the positive electrode active material 13 is set to 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 and Nb in the compound made of Li ₂ WO ₄ and LiNbO ₃ to be the lithium ion conductive oxide 14 on the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film to be the positive electrode active material 13 is set to 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 produced in the same manner as in Example 1. The resulting _LiNi 1/3 _Co 1/3 _Mn 1/3 _{O 2} pellets as a target, under 500 ° C. oxygen atmosphere, _LiNi an area of 8 mm × 8 mm on a Pt substrate (substrate 12) 1/3 _{Co 1 /} Only the ₃ Mn _1/3 O ₂ thin film (positive electrode active material 13) was formed to a thickness of about 300 nm to produce the positive electrode thin film electrode 1. A coating layer made of lithium ion conductive oxide is not formed.
For the evaluation of the positive electrode thin film, the battery shown in FIG. 3 was prepared and the positive electrode interface resistance was measured in the same manner as in Examples 1 to 4.

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

(Comparative Example 3)
A positive electrode for a non-aqueous electrolyte secondary battery produced in the same manner as in Example 1 except that Li ₃ PO ₄ was formed on a LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film serving as a positive electrode active material. A coin-type battery was produced 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 nonaqueous 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 serving as a positive electrode active material. A coin-type battery was produced 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 in which the coating layer made of the lithium ion conductive oxide composed of Li ₂ WO ₄ and Li ₃ PO _{4 of} Examples 1 to 4 is formed, Compared with the uncoated LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film of Comparative Example 1, the positive electrode interface resistance is greatly reduced (about 1/4 to 1/5), and the output characteristics are improved. I found out. As a factor, LiNi _1/3 Co _1/3 Mn _1/3 which is a positive electrode active material is obtained by coating a compound composed of Li ₂ WO ₄ and Li ₃ PO _{4 in} an amorphous state excellent in lithium ion conductivity. Since the O ₂ thin film is no longer in direct contact with the electrolytic solution, the deterioration is suppressed, the lithium diffusibility of the positive electrode is further improved, and the resistance at the interface between the electrolytic solution and the positive electrode is LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film This is thought to be due to a significant reduction in comparison.

In addition, Examples 1 to 4 are LiNi _1/3 Co _1/3 Mn _1/3 O ₂ 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 O ₂ thin film on which only Li ₃ PO ₄ is deposited (corresponding to the prior art of Patent Documents 1 and 2), the positive electrode interface 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 excellent in lithium ion conductivity, a compound composed of Li ₂ WO ₄ and Li ₃ PO ₄ has a higher lithium ion conductivity than a single substance, respectively. This is thought to be because the lithium diffusibility of the positive electrode was improved.

  Further, comparing Examples 1 to 4, Example 3 in which W: P is 1: 4 and Example 4 in which W: P is 1: 0.5 are more positive electrode interface resistances than Comparative Examples 1 to 3. However, the positive electrode interface resistance may be slightly higher than in 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 in which the coating layer made of the lithium ion conductive oxide composed of Li ₂ WO ₄ and LiNbO _{3 of} Examples 5 to 8 is a comparative example. Compared with 1 uncoated LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film, the positive electrode interface resistance is greatly reduced (about 1/4 to 1/5), and the output characteristics are improved. I understood the situation. As a factor, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ which is a positive electrode active material is obtained by coating a compound composed of Li ₂ WO ₄ and LiNbO _{3 in} an amorphous state excellent in lithium ion conductivity. Deterioration is suppressed because the thin film is no longer in direct contact with the electrolyte, and the lithium diffusivity of the positive electrode is further improved. The resistance at the interface between the electrolytic solution and the positive electrode is compared with the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film This is thought to be due to a significant reduction.

In Examples 5 to 8, the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film in which only Li ₂ WO ₄ was deposited in Comparative Example 2 (corresponding to the prior art of Patent Document 3) and Comparative Example 4 were used. Compared with the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ thin film in which only LiNbO ₃ was deposited, it was found that the positive electrode interface resistance was reduced and the output characteristics were improved. By Factors of mixing _Li 2 WO ₄ and LiNbO ₃ having excellent lithium ion conductivity, it is more of a positive electrode improves lithium ion conductive compound consisting of _Li 2 WO ₄ and LiNbO ₃ than alone respectively This is thought to be due to improved lithium diffusibility.

  Further, when Examples 5 to 8 are compared, Example 7 in which W: Nb is 1: 4 and Example 8 in which W: Nb is 1: 0.5 are more positive than Comparative Examples 1, 2, and 4. Although the interfacial resistance is reduced, the positive electrode interfacial resistance may be slightly higher than in 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 an electric vehicle and a hybrid vehicle battery that require high output. Further, the present 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.

DESCRIPTION OF SYMBOLS 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 Board | substrate 13 Positive electrode active material 14 Lithium ion conductive oxide 21 Positive electrode active material particle (secondary particle)
22 Lithium metal composite oxide (primary particles)
23 Lithium ion conductive oxide

Claims (13)

A positive electrode composed of a positive electrode active material comprising a lithium metal composite oxide;
A coating layer formed on the surface of the positive electrode and made of a lithium ion conductive oxide containing at least one metal element selected from phosphorus or niobium, tungsten and lithium;
A positive electrode for a non-aqueous electrolyte secondary battery, comprising: The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium ion conductive oxide is a compound composed of Li ₂ WO ₄ and Li ₃ PO ₄ . _3. The non-aqueous electrolyte 2 according to claim 2, wherein a molar ratio of P to W in the lithium ion conductive oxide composed of Li ₂ WO ₄ and Li ₃ PO ₄ is more than 0.5 and less than 4. 4. Positive electrode for secondary battery. The total molar amount of tungsten and phosphorus 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 any one of claims 1 to 3, wherein the positive electrode is a non-aqueous electrolyte secondary battery. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium ion conductive oxide is a compound composed of Li ₂ WO ₄ and LiNbO ₃ . The non-aqueous electrolyte secondary battery according to claim 6, wherein a molar ratio of Nb to W in the lithium ion conductive oxide composed of Li ₂ WO ₄ and LiNbO ₃ is more than 0.5 and less than 4. 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 nonaqueous electrolyte secondary battery according to any one of claims 1, 5, and 6. The lithium ion conductive oxide containing at least one or more metal elements selected from phosphorus or niobium, tungsten, and lithium is in an amorphous state. A positive electrode for a non-aqueous electrolyte secondary battery according to Item. 9. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode is a thin film, and the coating layer is formed in a layered manner so as to overlap with the positive electrode. Positive electrode. The lithium metal composite oxide is in the form of particles, and the coating layer is formed on the surfaces of the particles of the lithium metal composite oxide. The positive electrode for non-aqueous electrolyte secondary batteries. The thickness of the said coating layer is 1-500 nm, The positive electrode for nonaqueous electrolyte secondary batteries of Claim 9 or 10 characterized by the above-mentioned. The positive electrode active material used for the positive electrode for a non-aqueous electrolyte secondary battery according to claim 9 or 10, wherein the lithium metal composite oxide is at least one metal element selected from phosphorus or niobium. A cathode active material for a non-aqueous electrolyte secondary battery, characterized in that a coating layer made of a lithium ion conductive oxide containing aluminum, tungsten and lithium is formed. A non-aqueous electrolyte secondary battery using the positive electrode according to any one of claims 1 to 11.