JP7025681B2 - Non-aqueous electrolyte secondary battery - 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 secondary battery using the positive electrode.

In recent years, with the spread of portable electronic devices such as mobile phones and notebook personal computers, there is a strong demand for the development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density. Further, it is strongly desired to develop a high output secondary battery as a battery for electric vehicles such as hybrid vehicles. As a 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. A material that can be separated and inserted is 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 above-mentioned lithium composite oxide for automobile applications, 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.

Further, some of the above-mentioned lithium composite oxides react with moisture and carbon dioxide in the atmosphere to form an inert layer when handled in the atmosphere, causing a decrease in capacity and an increase in resistance. Therefore, it is important to prevent deterioration of these positive electrode active materials.

In Non-Patent Document 1, by forming Li ₂ WO ₄ on LiCoO ₂ using a pulse laser deposition method, Li ₂ WO ₄ acts as a protective film and prevents contact between LiCoO ₂ and the electrolytic solution. It has been reported that the elution of cobalt and the deposition of phosphates are suppressed and the resistance is reduced. That is, in this document, only the effect of reducing the resistance by Li ₂ WO ₄ is mentioned, and no reference is made to the suppression of deterioration of the positive electrode active material during handling in the atmosphere.

In Non-Patent Document ₂ , lithium at the positive electrode / electrolytic solution interface is formed by forming Li2 WO ₄ of the Tetragonal phase having a lithium diffusion path in multiple directions on LiCoO ₂ by using a pulsed laser deposition method. It has been reported to improve diffusion and reduce interfacial resistance. That is, in this document as well, as in Non-Patent Document 1, only the effect of reducing resistance by coating a substance having a large number of lithium diffusion paths is mentioned, and deterioration of the positive electrode active material during handling in the atmosphere is mentioned. No mention is made of suppression.

J. Power Sources 285 (2015) 559 --567 Int. J. Electrochem. Sci., 10 (2015) 8150 --8157

In view of the above problems, the present invention makes it possible to increase the output of the battery when used as the positive electrode of the battery, and when the battery is handled in the atmosphere, the performance of the battery is less deteriorated. It is an object of the present invention to provide a positive electrode for a secondary battery and a positive electrode active material used for the electrode.
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 inventors have 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, tantalum and lithium are on the surface of the lithium metal composite oxide. By forming a coating layer made of a compound containing and, the lithium ion conductivity in the positive electrode, that is, the ease of insertion and desorption of lithium ions on the surface of the positive electrode active material including the layer near the surface, and the solid phase and electrolysis. The surface of the positive electrode active material is improved because the ease of movement of lithium ions at the solid-liquid interface of the liquid is improved and the compound containing tantalum and lithium is less susceptible to deterioration due to moisture and carbon dioxide than the positive electrode active material. It was found that the formation of the resistance layer was suppressed, and the electrolytic solution / positive electrode interfacial resistance of the secondary battery using this positive electrode was significantly reduced to improve the output characteristics of the secondary battery and secondary. The present invention has been completed based on the finding that it is possible to suppress deterioration of battery performance when the next battery is handled in the atmosphere.

In the non-aqueous electrolyte secondary battery of the first invention, a positive electrode composed of a positive electrode active material made of a lithium metal composite oxide and a negative electrode capable of inserting and removing lithium are laminated via a separator to form an electrode body. A non-aqueous electrolyte secondary battery in which the electrode body is impregnated with a non-aqueous electrolyte solution in which a lithium salt as an electrolyte is dissolved in an organic solvent. The surface of the positive electrode has a coating layer formed of a compound containing tantalum and lithium, the compound is a lithium ion conductor, and the thickness of the coating layer is 1 to 500 nm . , The compound is characterized in that it is in an amorphous state .
The non- aqueous electrolyte secondary battery of the second invention is characterized in that, in the first invention, the compound is lithium tantalate.
In the second invention, the non-aqueous electrolyte secondary battery of the third invention is one in which the lithium tantalate is selected from the group consisting of LiTaO ₃ , LiTa ₃ O ₈ , Li ₃ TaO ₄ , and Li ₇ TaO ₆ . It is characterized by containing the compound of.
The non-aqueous electrolyte secondary battery of the fourth invention is characterized in that, in any one of the first to third inventions, the compound is a dielectric.
The non-aqueous electrolyte secondary battery of the fifth invention is characterized in that, in any one of the first to fourth inventions, the positive electrode is a thin film and the coating layer is superimposed on the positive electrode. do.
In the non-aqueous electrolyte secondary battery of the sixth invention, in any one of the first to fourth inventions, the lithium metal composite oxide is in the form of particles, and the coating layer is the particles of the lithium metal composite oxide. It is characterized by being formed on the surface.
In the non-aqueous electrolyte secondary battery of the seventh invention, in the sixth invention, the amount of tantalum contained in the coating layer is 0. It is characterized by having an amount of 05 to 5.0 atomic%.

According to the first invention, the positive electrode for a non-aqueous electrolyte secondary battery is formed of a positive electrode composed of a positive electrode active material made of a lithium metal composite oxide and a compound containing tantalum and lithium on the surface of the positive electrode. By having the coated layer and the compound being a lithium ion conductor, the lithium ion conductivity in the electrode can be improved. Further, since the compound layer containing tantalum and lithium has high weather resistance, the formation of the inert layer on the surface 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 whose high output performance does not easily deteriorate when handled in the atmosphere.
Further, since 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 can be improved and the output characteristics can be improved. Deterioration in the atmosphere can be suppressed, and manufacturing can be easily performed.
In addition, since the compound containing tantalum and lithium is in an amorphous state, the positive electrode interfacial resistance of the positive electrode can be further reduced.
According to the second invention, since the compound forming the coating layer is lithium tantalate, it is stable with respect to the electrolyte used in the non-aqueous electrolyte secondary battery, and the adverse effect on the battery due to the elution of tantalum and the like is reduced. can.
According to the third invention, lithium tantalate contains lithium tantalate by containing any one compound selected from the group consisting of LiTaO ₃ , _LiTa 3O ₈ , Li ₃ TaO ₄ , and Li ₇ TaO ₆ . Can be manufactured stably.
According to the fourth invention, when the compound forming the coating layer is a dielectric, lithium insertion / removal at the interface between the surface coating layer and the positive electrode active material can be further improved. Therefore, by using this electrode, it is possible to provide a positive electrode for a non-aqueous electrolyte secondary battery capable of further increasing the output.
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, it is possible to secure a diffusion path of lithium ions between the thin film positive electrode and the electrolytic solution, and the thin film is formed. The output of the battery using the positive electrode is increased, and it is possible to suppress the deterioration of the output characteristics when the battery is handled in the atmosphere.
According to the sixth invention, 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, so that between the positive electrode active material particles and the electrolytic solution. It is possible to secure a diffusion path for lithium ions, promote the insertion and desorption of lithium between the coating layer and the positive electrode active material particles, and increase the output of the battery using the positive electrode active material particles. It is possible to suppress deterioration of output characteristics when handling particles in the atmosphere.
According to the seventh invention, the amount of tantalum contained in the coating layer is 0.05 to 5.0 atomic% with respect to the total amount of metal elements other than lithium contained in the lithium metal composite oxide. As a result, the diffusion path of lithium ions between the positive electrode active material particles and the electrolytic solution can be more reliably secured, lithium insertion and desorption between the coating layer and the positive electrode active material particles are promoted, and the positive electrode active material particles are used. The output of the battery will be further increased, and it will be possible to further suppress the deterioration of the output characteristics when the battery is handled in the atmosphere.

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.

The positive electrode for a non-aqueous electrolyte secondary battery (hereinafter, simply referred to as “positive electrode”) and the non-aqueous electrolyte secondary battery (hereinafter, simply referred to as “battery”) of the present invention have a tantalum on the surface of a lithium metal composite oxide. It is a battery characterized by being composed of a positive electrode electrode characterized by modifying a compound containing lithium, the positive electrode electrode, a separator, a negative electrode, and an electrolytic solution.

The lithium metal composite oxide material used as a raw material for the lithium metal composite oxide thin film used for the positive electrode has a high voltage of 4 V class, and the diffusion direction of lithium is limited to the a and b plane directions. Any composite oxide may be used, as long as it is a lithium cobalt composite oxide (LiCoO ₂ ), a lithium nickel composite oxide (LiNiO ₂ ), or a lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ). ), Etc., among which LiCoO ₂ , which is relatively easy to synthesize, is preferable, and after the powder of the lithium metal composite oxide material is sintered to prepare a target, Pt / Cr / SiO is used by the PLD method. A lithium metal composite oxide thin film deposited on a conductive substrate such as ₂ or Pt is preferable.

The coating layer made of lithium ion conductive oxide provided on the surface of the lithium metal composite oxide thin film of the positive electrode is formed of a compound containing tantalum and lithium. This compound containing tantalum and lithium has lithium ion diffusion paths in multiple directions, has excellent lithium ion conductivity, and is stable and resistant to deterioration in the atmosphere. As such a substance, lithium tantalate such as LiTaO ₃ , LiTa ₃ O ₈ , Li ₃ TaO ₄ , Li ₇ TaO ₆ and the like is preferable.

Further, the compound containing tantalum and lithium is preferably a dielectric, which promotes the insertion and desorption of lithium between the coating layer and the positive electrode active material particles, and makes it possible to further increase the output of the battery. It is considered that this is because the lithium insertion / desorption at the interface between the dielectric and the active material and the interface between the dielectric and the electrolytic solution is promoted by the polarization effect of the dielectric.

The coating film made of the lithium ion conductive oxide preferably has a thickness of 1 to 500 nm. Since 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 can be improved and the output characteristics of the atmosphere can be improved. Deterioration inside can be suppressed, and further manufacturing can be easily performed. 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.

As the state of lithium tantalate, an amorphous state having a channel structure effective for diffusion of lithium ions is desirable rather than a crystalline state.

In the positive electrode according to the present invention, for example, the powder containing tantalum and lithium is sintered to prepare a target, and then a compound containing tantalum and lithium is deposited on the lithium metal composite oxide thin film by the PLD method. It can be obtained by.

When only the lithium metal composite oxide thin film is used as the positive electrode, when it is handled in the atmosphere, it reacts with water and carbon dioxide contained in the atmosphere and the lithium on the outermost surface of the lithium metal composite oxide is desorbed and deficient, resulting in metal. Is oxidized and inactivated, so that it does not contribute to charging and discharging, resulting in a decrease in capacity and an increase in resistance at the electrolytic solution / positive electrode interface. On the other hand, in the positive electrode electrode in which the surface of the lithium metal composite oxide is modified with a compound containing tantalate and lithium, such as lithium tantalate, which has a poor reaction with atmospheric moisture and carbon dioxide, the compound containing tantalate and lithium is a protective film. Since the lithium metal composite oxide does not come into direct contact with the atmosphere, deterioration is suppressed even when it is handled in the atmosphere. Further, since the protective film is a compound containing tantalum and lithium, lithium ion conduction is maintained. Therefore, it is preferable that the compound containing tantalum and lithium is superimposed on the entire surface of the positive electrode and coated as a thin film. The thickness and crystal state of the compound containing lithium can be controlled to modify the entire surface of the lithium metal composite oxide thin film, which is preferable. Even when the compound containing tantalum and lithium is partially coated, the deterioration of the lithium ion conductivity of the coated portion is suppressed, so that the performance deterioration of the battery can be suppressed. can.

When a battery is assembled using only the lithium metal composite oxide thin film as the positive electrode, the decomposition components of the electrolytic solution such as phosphate adhere to the surface of the positive electrode and contact with the electrolytic solution occurs, which affects the elution of Co from the positive electrode surface. This inhibits the diffusion of lithium ions at the electrolytic solution / positive electrode interface, resulting in an increase in resistance at the electrolytic solution / positive electrode interface. On the other hand, in the positive electrode where the surface of the lithium metal composite oxide thin film is modified with a compound containing tantalum and lithium such as lithium tantalate having good lithium diffusivity, protection of lithium ions having good conductivity that suppresses contact between the positive electrode and the electrolytic solution is good. Since it functions as a film, 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. Therefore, it is preferable that the lithium ion conductive oxide is coated on the entire surface of the positive electrode.

By manufacturing a battery composed of the positive electrode thin film electrode, a separator, a negative electrode capable of inserting and removing lithium, and an electrolytic solution, it is easy to obtain a positive electrode material for a non-aqueous electrolyte secondary battery and a secondary battery capable of achieving high output. It will be possible to provide.
Each configuration of the battery will be described in detail below.

(1) Positive Electrode A positive electrode thin film electrode forming a positive electrode will be described. The material constituting the positive electrode is composed of a positive electrode thin film and a current collector.

The positive electrode active material used as a raw material for the positive electrode thin film may be a layered lithium composite oxide in which a high voltage of 4V class is obtained and the diffusion direction of lithium is limited to the a and b plane directions, and lithium cobalt. Lithium metal composite oxide materials such as composite oxide (LiCoO ₂ ), lithium nickel composite oxide (LiNiO ₂ ), lithium nickel cobalt cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) Used.

For example, after the lithium metal composite oxide powder as a raw material is sintered to prepare a target, a physical film forming method such as a PLD method, a sputter vapor deposition method, or a molecular beam epitaxy method is used to obtain a size suitable for a battery in advance. A lithium metal composite oxide thin film is deposited on a conductive substrate that serves as a current collector such as Pt / Cr / SiO ₂ and Pt cut into a positive electrode to produce a positive electrode.

In the present invention, a lithium ion conductive oxide thin film, preferably a thin film having good dielectric property, is further deposited on the lithium metal composite oxide thin film. Also at this time, it is preferable to use the physical film forming method. In this physical film forming method, the raw material of the compound containing tantalum and lithium that forms the coating layer with the positive electrode may be a target containing tantalum and lithium, but lithium tantalate is preferable.

For example, it is preferable to prepare a target containing the tantalum and lithium by sintering, and then deposit a lithium ion conductive oxide thin film on the surface of the positive electrode thin film electrode by the PLD method to prepare a positive electrode.

FIG. 1 shows a schematic cross-sectional view showing the structure of the positive electrode thin film electrode 1 according to the first embodiment of the present invention. In the positive electrode thin film electrode 1, a positive electrode active material 13 which is a lithium metal composite oxide is deposited in a thin film on a substrate 12 which is a current collector, and a positive electrode active material 13 which is a lithium metal composite oxide is further superimposed to form a good lithium ion such as lithium tantalate. The conductive oxide 14 is formed in the form of a thin film.

FIG. 2 shows an enlarged view of the surface of the positive electrode active material particles 21 according to the second embodiment of the present invention. In the positive electrode active material particles 21, a coating layer made of a thin-film lithium ion conductive oxide 23 is provided on the lithium metal composite oxide 22 which is the primary particles or on the secondary particles made of these primary particles. .. The positive electrode active material particles may be either primary particles, secondary particles in which primary particles are aggregated, or a mixture of primary particles and secondary particles. When it is composed of secondary particles, it is preferable that the coating layer is provided to the inside, but when the coating layer in the form of a thin film is provided on the entire surface of the secondary particles, it is coated to the inside. The layer may not be provided.
The amount of tantalum contained in the coating layer is preferably 0.05 to 5.0 atomic% with respect to the total amount of metal elements other than lithium contained in the lithium metal composite oxide. As a result, a sufficient coating layer can be provided on the positive electrode active material particles 21, a diffusion path of lithium ions between the positive electrode active material particles 21 can be more reliably secured, and the output of the battery using the positive electrode active material particles 21 is further high. Become. Further, since the positive electrode active material particles 21 are sufficiently suppressed from coming into contact with the atmosphere, it is possible to further suppress the deterioration of the output characteristics in the atmosphere.
When the positive electrode active material particles 21 form a positive electrode, the positive electrode active material particles 21 and a conductive material such as carbon powder, a binder, and a solvent are kneaded into a paste in the same manner as the positive electrode of a normal non-aqueous electrolyte secondary battery. , A positive electrode can be obtained by applying the paste on the current collector.

(2) Negative electrode The negative electrode may be made of a material that allows lithium to be inserted and removed as described above, and a powdery carbon substance is placed on the current collector in the same manner as the negative electrode of a normal non-aqueous electrolyte secondary battery. A coated one can be used, and 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 measurement interfering elements.

(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 The positive and negative electrodes are laminated via a separator to form an electrode body, and the electrode body is impregnated with the non-aqueous electrolytic solution. The positive electrode and the negative electrode are connected to external terminals to conduct conduction. A battery is manufactured by putting the above-mentioned structure in a metal container.

(Comparative Example 1)
In this comparative example, a LiCoO ₂ thin film was used as the positive electrode active material.
The LiCoO ₂ thin film was prepared by the PLD method. Li ₂ CO ₃ and Co ₃ O ₄ were mixed so as to have the composition of LiCoO ₂ , and calcined in an oxygen atmosphere at 980 ° C. to prepare LiCoO ₂ powder. Then, LiCoO ₂ powder was sintered at 1000 ° C. to prepare pellets. Using these pellets as a target, a LiCoO ₂ thin film (positive electrode active material 13) is formed on a Pt substrate (substrate 12) in an area of 8 mm × 8 mm to a thickness of about 300 nm under an oxygen atmosphere at 500 ° C., and the positive electrode thin film electrode 1 Was produced.

The evaluation of the positive electrode thin film was carried out by preparing the battery shown in FIG. 3 as shown below and measuring the positive electrode interfacial resistance.
A 2032 type coin-shaped 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.
For the negative electrode 2, metal lithium having a thickness of 0.5 mm punched into a disk shape having a diameter of 13 mm is used, and as the electrolytic solution, ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiPF6 as a supporting electrolyte are used. An equal amount mixed solution (manufactured by Ube Industries, Ltd.) was used. A polyethylene porous membrane having a thin film of 25 μm was used for the separator 3. Further, the coin-type battery 10 has a gasket 4 and a wave washer 5, and the positive electrode can 6 and the negative electrode can 7 are assembled into a coin-shaped 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 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.

(Example 1)
In this example, a LiCoO ₂ thin film was used as the positive electrode active material, and a LiTaO ₃ thin film was formed on the surface thereof as a lithium ion conductive oxide having good dielectric properties.

A LiTaO ₃ thin film (lithium ion conductive oxide 14) was formed on a LiCoO ₂ thin film (positive electrode active material 13) prepared under the same conditions as in Comparative Example 1, to prepare a positive electrode thin film electrode 1. Similar to LiCoO ₂ , the PLD method was used to prepare this thin film. After mixing Li ₂ O and Ta ₂ O ₅ , it was sintered to pelletize and used as a target. Using this target, a LiTaO ₃ thin film was further formed on the LiCoO ₂ thin film obtained above at 25 ° C. and an oxygen partial pressure of 20 Pa to a thickness of about 300 nm to prepare a positive electrode thin film, and LiTaO ₃ was formed by XRD. When the state was confirmed, it was in an amorphous state. 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 it was LiTaO ₃ . Next, the same coin-shaped cell as in Comparative Example 1 was prepared using the prepared amorphous positive electrode thin film, and the battery performance was compared. The results are shown in Table 1.

From Table 1, it was found that the LiCoO ₂ thin film in which the amorphous LiTaO ₃ was deposited was significantly reduced in the positive electrode interfacial resistance and the output characteristics were improved as compared with the LiCoO ₂ thin film in Comparative Example 1. .. As a factor, by modifying lithium tantalate in an amorphous state with excellent lithium ion conductivity and good dielectric property, the lithium diffusivity of the positive electrode is improved, and the resistance of the electric field liquid / positive electrode interface is the LiCoO ₂ thin film. It is probable that it was significantly reduced compared to the above.

(Comparative Example 1a)
In this comparative example, a LiCoO ₂ thin film is used as the positive electrode active material, the positive electrode active material is exposed to a high humidity environment having an ambient temperature of 80 ° C. and a relative humidity of 60% for 24 hours, and then a coin-type battery 10 is manufactured and impedance measurement is performed. Was carried out.

The process is the same as in Comparative Example ₁ up to the point where the LiCoO ₂ thin film is produced. The battery 10 was manufactured and the battery performance was confirmed. The results are shown in Table 2. The positive electrode interfacial resistance was significantly increased as compared with Comparative Example 1 shown in Table 1. As a factor, as a result of exposure to the atmosphere under high humidity conditions, the surface of the LiCoO ₂ thin film reacts with moisture and carbon dioxide in the atmosphere to become inactive Co ₃ O ₄ , which does not contribute to charging and discharging, and interfacial resistance. It is thought that this was a factor in the increase.

(Example 1a)
In this embodiment, a LiCoO ₂ thin film is used as the positive electrode active material, a LiTaO ₃ thin film is formed on the surface of the LiCoO 2 thin film as a lithium ion conductive oxide having good dielectric property, and the positive electrode thin film electrode 1 is manufactured. It is the same as Example 1. Similar to Comparative Example 1a, the produced positive electrode thin film electrode 1 was exposed to a high humidity environment having an ambient temperature of 80 ° C. and a relative humidity of 60% for 24 hours, and then a coin-type battery 10 was produced and impedance measurement was performed.

Table 2 shows the positive electrode interfacial resistance in Example 1a. Compared with the case of Comparative Example 1a, the value of the positive electrode interfacial resistance is small, and the rate of increase from Example 1 is also suppressed. This is because the surface of LiCoO ₂ is coated with LiTaO ₃ , which is very stable in the atmosphere, so that LiTaO ₃ acts as a protective film and suppresses the direct contact of LiCoO ₂ with the atmosphere, thereby suppressing the deterioration of LiCoO ₂ . it is conceivable that. Further, since LiTaO ₃ is very stable in the atmosphere, it is difficult to deteriorate in quality, lithium ion conductivity can be maintained even when exposed to the atmosphere, and it is considered that the increase in the positive electrode interface resistance is small.

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. In addition, this positive electrode material can be applied to various lithium composite oxides and lithium ion conductive oxides without being affected by various properties such as the solubility of the material, and the lithium ion conductive oxide is further applied to the surface of the lithium composite oxide. Since it can be directly deposited, it can be expected to be applied to the development of positive electrode materials for non-aqueous electric field secondary batteries. In addition, it will be useful to elucidate the phenomenon of the interface between lithium composite oxide and lithium ion conduction oxide by performing analysis by combining various analysis methods.

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 22 Lithium metal composite oxide 23 Lithium ion conduction Oxide

Claims (7)

A positive electrode made of a positive electrode active material made of a lithium metal composite oxide and a negative electrode capable of inserting and removing lithium are laminated via a separator to form an electrode body.
A non-aqueous electrolyte secondary battery in which the electrode body is impregnated with a non-aqueous electrolyte solution in which a lithium salt as an electrolyte is dissolved in an organic solvent.
The positive electrode constituting the electrode body is the positive electrode and the positive electrode.
On the surface of the positive electrode, a coating layer formed of a compound containing tantalum and lithium is provided.
The compound is a lithium ion conductor.
The coating layer has a thickness of 1 to 500 nm and has a thickness of 1 to 500 nm.
The compound is in an amorphous state .
A non-aqueous electrolyte secondary battery characterized by this. The compound is lithium tantalate,
The non-aqueous electrolyte secondary battery according to claim 1 . The lithium tantalate is
Includes any one compound selected from the group consisting of LiTaO ₃ , _LiTa 3O ₈ , Li ₃ TaO ₄ , Li ₇ TaO ₆ .
The non-aqueous electrolyte secondary battery according to claim 2 . The compound is a dielectric,
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3 , wherein the non-aqueous electrolyte secondary battery is characterized by the above. The positive electrode is a thin film
The coating layer is formed so as to be superimposed on the positive electrode.
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4 , wherein the non-aqueous electrolyte secondary battery is characterized by the above. 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.
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4 , wherein the non-aqueous electrolyte secondary battery is characterized by the above. The amount of tantalum contained in the coating layer is
It is 0.05 to 5.0 atomic% with respect to the total of metal elements other than lithium contained in the lithium metal composite oxide.
The non-aqueous electrolyte secondary battery according to claim 6 .

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