TW201709593A - Negative electrode active material for nonaqueous electrolyte secondary batteries, nonaqueous electrolyte secondary battery, and method for producing negative electrode material for nonaqueous electrolyte secondary batteries - Google Patents

Abstract

The present invention is a negative electrode active material for nonaqueous electrolyte secondary batteries, which comprises negative electrode active material particles that contain a silicon compound (SiOx, wherein 0.5 ≤ x ≤ 1.6) containing an Li compound, and which is characterized in that: each negative electrode active material particle has a cyclic carbonate layer on the surface, said cyclic carbonate layer containing a cyclic carbonate; and the cyclic carbonate layer additionally contains an Li salt. Consequently, the present invention provides a negative electrode active material for nonaqueous electrolyte secondary batteries, which is highly stable with respect to an aqueous slurry, while having high capacity, good cycle characteristics and good initial efficiency.

Description

Negative electrode active material for nonaqueous electrolyte secondary battery, nonaqueous electrolyte secondary battery, and method for producing negative electrode material for nonaqueous electrolyte secondary battery

The present invention relates to a negative electrode active material for a nonaqueous electrolyte secondary battery. Further, the present invention relates to a nonaqueous electrolyte secondary battery comprising the negative electrode active material. Further, the present invention relates to a method of producing a negative electrode material for a nonaqueous electrolyte secondary battery.

In recent years, small electronic devices such as mobile terminals have been widely used, and further miniaturization, weight reduction, and longevity have been strongly demanded. In response to such market demands, development of a secondary battery which is particularly small and lightweight and capable of achieving high energy density has been advanced. The application of the secondary battery is not limited to a small electronic device, and the application of a large-scale electronic device represented by an automobile or the like, and a power storage system represented by a house or the like is also under study.

Among them, lithium ion secondary batteries are expected to be smaller in size and higher in capacity, and are expected to have higher energy density than lead batteries and nickel cadmium batteries.

The lithium ion secondary battery includes a positive electrode and a negative electrode, a separator, and an electrolytic solution, and the negative electrode includes a negative electrode active material related to a charge and discharge reaction.

As the negative electrode active material, a carbon material is widely used, and on the other hand, recent market demands further increase in battery capacity. In order to increase the battery capacity, helium is being studied as a material for the negative electrode active material. The reason is that the theoretical capacity of ruthenium (4199 mAh/g) is more than 10 times larger than the theoretical capacity of graphite (372 mAh/g), so it is expected to greatly increase the battery capacity. The development of a ruthenium material as a material of the negative electrode active material is not only studied for ruthenium monomers, but also for compounds represented by alloys and oxides. Further, the shape of the active material is being studied from a standard coating type by a carbon material to an integral type directly deposited on a current collector.

However, when ruthenium is used as the main raw material of the negative electrode active material, the negative electrode active material expands and contracts at the time of charge and discharge, and thus it is likely to be mainly broken in the vicinity of the surface layer of the negative electrode active material. Further, an ionic substance is formed inside the active material, and the negative electrode active material is easily broken. If the surface layer of the negative electrode active material is broken, a new surface is generated, and the reaction area of the active material is increased. At this time, the decomposition reaction of the electrolytic solution occurs on the newly formed surface, and the decomposition product of the electrolytic solution, that is, the coating film, is formed on the newly formed surface, so that the electrolytic solution is consumed. Therefore, the cycle characteristics are easily reduced.

Heretofore, in order to improve the initial efficiency of the battery, the cycle characteristics, and the like, various studies have been made on the negative electrode material and electrode composition of a lithium ion secondary battery using a ruthenium material as a main material.

Specifically, in order to obtain good cycle characteristics and high safety, a vapor phase method is used to simultaneously deposit tantalum and amorphous ceria (see, for example, Patent Document 1). Moreover, in order to obtain high battery capacity and safety, a carbon material (conductive material) is provided on the surface layer of the cerium oxide particles (see, for example, Patent Document 2). Further, in order to improve the cycle characteristics and obtain high input/output characteristics, an active material containing cerium and oxygen is produced, and an active material layer having a high oxygen ratio is formed in the vicinity of the current collector (see, for example, Patent Document 3). Moreover, in order to improve the cycle characteristics, oxygen is contained in the ruthenium active material, and it is formed in the following manner: the average oxygen content is 40 at% or less, and the oxygen content in the vicinity of the current collector is large (refer to, for example, Patent Document 4) ).

Moreover, in order to improve the initial charge and discharge efficiency, a nanocomposite containing a cerium (Si) phase, SiO ₂ or a _My O metal oxide is used (see, for example, Patent Document 5). Further, in order to improve the cycle characteristics, SiO _x (0.8 ≦ x ≦ 1.5, particle size range = 1 μm to 50 μm) is mixed with a carbon material and calcined at a high temperature (see, for example, Patent Document 6). Further, in order to improve the cycle characteristics, the molar ratio of oxygen in the negative electrode active material to ruthenium is set to 0.1 to 1.2, and the active material is controlled to the maximum and minimum molar ratio of the active material in the vicinity of the interface of the current collector. The difference between the values is in the range of 0.4 or less (see, for example, Patent Document 7). Moreover, in order to improve battery load characteristics, a metal oxide containing lithium is used (see, for example, Patent Document 8). Moreover, in order to improve the cycle characteristics, a water-repellent layer such as a decane compound is formed on the surface layer of the ruthenium material (see, for example, Patent Document 9).

In addition, in order to improve the cycle characteristics, a ruthenium oxide is used, and a graphite film is formed on the surface layer to impart conductivity (see, for example, Patent Document 10). In Patent Document 10, with respect to the displacement value obtained by the Raman spectrum associated with the graphite film, broad peaks appear at 1330 cm ^-1 and 1580 cm ^-1 , and the intensity ratios of the I ₁₃₃₀ / I ₁₅₈₀ is 1.5 < I ₁₃₃₀ / I ₁₅₈₀ <3. Further, in order to increase the battery capacity and improve the cycle characteristics, a type of particles having a ruthenium crystal phase dispersed in ruthenium dioxide are used (see, for example, Patent Document 11). In addition, in order to improve the overcharge and overdischarge characteristics, a ruthenium oxide having an atomic ratio of ruthenium to oxygen of 1: y (0 < y < 2) is used (see, for example, Patent Document 12). In addition, a mixed electrode of tantalum and carbon is produced in order to increase the battery capacity and improve the cycle characteristics, and the niobium ratio is designed to be 5 wt% or more and 13 wt% or less (see, for example, Patent Document 13). [Previous Technical Literature] (Patent Literature)

Patent Document 1: Japanese Laid-Open Patent Publication No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. Japanese Patent Laid-Open Publication No. JP-A-2008- No. PCT Publication No. 2008- No. JP-A-2007-234255, JP-A-2009-212074, JP-A-2009-212950, JP-A-2009-205950, JP-A-2009-205950, JP-A No. 2009-205950, Patent Document 12: Japanese Patent No. 2997741 Bulletin No. -092830

[Problems to be Solved by the Invention] As described above, in recent years, high-performance and multi-functionalization of small electronic devices represented by mobile terminals and the like have been progressing, and the main power source of the lithium ion secondary battery is required to increase the battery. capacity. As one of methods for solving this problem, it is desired to develop a lithium ion secondary battery composed of a negative electrode using a ruthenium material as a main material.

Further, it is desirable that the battery characteristics of a lithium ion secondary battery using a ruthenium material are similar to those of a lithium ion secondary battery using a carbon material. Therefore, as the negative electrode active material, the cerium oxide which has been modified by the insertion or detachment of lithium (Li) is used, thereby improving the cycle retention rate and the primary efficiency of the battery. However, the modified niobium oxide is modified with lithium, so the water resistance is low. Therefore, the stabilization of the slurry containing the above-described modified cerium oxide produced at the time of producing the negative electrode is insufficient, and there is a problem that it is impossible to use or is difficult to use, which is generally used when coating a carbon-based active material in the past. Device. As a result, when the ruthenium oxide which improves the initial efficiency and the cycle retention ratio by using the modification of lithium is used, the stability of the slurry containing water is insufficient, and therefore, a nonaqueous electrolyte 2 has not been proposed yet. A negative electrode active material for a secondary battery, which is advantageous in industrial production of a secondary battery.

The present invention has been made in view of the above problems, and an object of the invention is to provide a negative electrode active material for a nonaqueous electrolyte secondary battery, which has high stability to an aqueous slurry and high capacity. And the cycle characteristics and initial efficiency are good.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a negative electrode active material for a nonaqueous electrolyte secondary battery, which has negative electrode active material particles, and the negative electrode active material particles contain a ruthenium compound SiO _x containing a lithium compound. In the negative electrode active material for a non-aqueous electrolyte secondary battery, the negative electrode active material particle has a cyclic carbonate layer containing a cyclic carbonate on the surface, and the cyclic carbonate layer is 0.5 ≦ x ≦ 1.6. Further comprising a lithium salt.

In the negative electrode active material of the present invention, the negative electrode active material particles (hereinafter also referred to as lanthanum active material particles) containing a ruthenium compound have a cyclic carbonate layer composed of a cyclic carbonate and containing a lithium salt on the surface thereof. The water resistance is higher than that of the aqueous slurry. Further, in the past, an aqueous slurry containing a modified cerium oxide by insertion and detachment of lithium tends to be alkaline. Therefore, a thickener (adhesive) which is relatively weak to a base, that is, carboxymethylcellulose or a sodium salt thereof, cannot be stably used, and thus the slurry is liable to be unstable. However, in the present invention, the lanthanide-based active material particles have a cyclic carbonate layer containing a lithium salt as described above, whereby the pH of the slurry is not easily biased to be alkaline, and in particular, the thickener is not easily deteriorated, and thus it is possible to obtain Stable coating film and sufficient adhesion. Therefore, when the negative electrode active material of the present invention is used, it is possible to industrially produce a nonaqueous electrolyte secondary battery which utilizes the original cerium oxide which has been modified by using lithium. Features, and high battery capacity and good cycle retention.

In this case, it is preferred that the lithium salt contained in the cyclic carbonate layer contains LiPF ₆ , LiBF ₄ , LiClO ₄ , LiBOB (lithium bis(oxalate)borate), LiFSA (lithium bis(fluorosulfonyl)amine), One or more of LiTFSA (lithium trifluoromethanesulfonamide) and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide)

Specific examples of the lithium salt contained in the cyclic carbonate layer include lithium salts as described above. Among them, in particular, by including LiPF ₆ , LiBF ₄ , and LiClO ₄ as a lithium salt in the cyclic carbonate layer, the slurry can be made more stable.

Further, in this case, it is preferred that the cyclic carbonate contained in the cyclic carbonate layer contains ethyl carbonate, propyl carbonate, fluoroacetate, difluoroacetate, and ethylene carbonate. More than one of the esters.

Since the cyclic carbonate as described above is a solid at normal temperature, a cyclic carbonate layer containing these cyclic carbonates can be a more stable water-resistant layer. Among them, when ethyl carbonate or ethyl fluorocarbonate is contained, particularly stable battery characteristics can be obtained.

In this case, it is preferred that the mass of the cyclic carbonate layer is 15% by mass or less based on the mass of the ruthenium compound.

When the cyclic carbonate layer is formed in the above ratio, the cyclic carbonate layer is not excessively thick, and therefore the negative electrode active material can have high conductivity. Further, since the ratio of the cyclic carbonate layer in the negative electrode active material is within an appropriate range, the negative electrode active material can contain a sufficient amount of the ruthenium compound and can have a high battery capacity.

Further, in this case, it is preferred that the cyclic carbonate layer further contains a chain carbonate.

By including a chain carbonate in the cyclic carbonate layer, the pH of the slurry can be made less alkaline.

In this case, the negative electrode active material particles preferably contain one or more of lithium carbonate and lithium fluoride between the ruthenium compound and the cyclic carbonate layer.

As a result, by forming lithium carbonate or lithium fluoride in at least a portion between the ruthenium compound and the cyclic carbonate layer in advance, the amount of lithium consumed in charging the battery can be reduced.

Moreover, in this case, it is preferable that one or more of Li ₂ SiO ₃ and Li ₄ SiO ₄ are present as the lithium compound contained in the ruthenium compound.

Lithium niobate such as Li ₂ SiO ₃ and Li ₄ SiO _{4 is} relatively stable as a lithium compound, so that more excellent battery characteristics can be obtained.

In this case, it is preferred that the negative electrode active material particles have a carbon coating on the surface of the ruthenium compound.

By having a carbon film, the conductivity of the negative electrode active material particles can be improved, so that more excellent battery characteristics can be obtained.

Further, in this case, the ruthenium compound is preferably obtained by chemically inserting lithium or detaching lithium.

In the case of an electrochemical method, the potential of the ruthenium compound can be easily controlled by using an external potential and a reference electrode, etc., and lithium inserted into an unnecessary region can be removed by using a discharge process. Therefore, the ruthenium compound which is modified in this way can have desired characteristics.

In this case, it is preferred that the above-mentioned cerium compound has a half-value width (2θ) of a diffraction peak due to a Si (111) crystal plane obtained by X-ray diffraction and is 1.2 or more, and is crystallized therefrom. The crystallite size caused by the surface is below 7.5 nm.

The ruthenium-based active material having such a half-value width and a crystallite size has a low crystallinity and a small amount of ruthenium crystals, so that battery characteristics can be improved.

Further, in this case, it is preferred that the median diameter of the ruthenium compound is 0.5 μm or more and 20 μm or less.

When the median diameter is 0.5 μm or more, the area where the side reaction occurs on the surface of the ruthenium compound is small, so that lithium is not additionally consumed, and the cycle retention rate of the battery can be maintained high. Further, when the median diameter is 20 μm or less, the expansion when lithium is inserted is small, the crack is not easily broken, and cracking is less likely to occur. Further, since the swelling of the cerium compound is small, for example, the negative electrode active material layer or the like obtained by mixing the carbon active material in the lanthanoid active material which is generally used is not easily broken.

In order to achieve the above object, the present invention provides a nonaqueous electrolyte secondary battery comprising the negative electrode active material for any of the above nonaqueous electrolyte secondary batteries.

Such a secondary battery can have a high cycle retention rate and primary efficiency, and can be industrially advantageously manufactured.

In order to achieve the above object, the present invention provides a method for producing a negative electrode material for a nonaqueous electrolyte secondary battery, which is a method for producing a negative electrode material for a nonaqueous electrolyte secondary battery comprising negative electrode active material particles, which is characterized in that a step of preparing cerium oxide particles represented by the general formula SiO _x and 0.5 ≦ x ≦ 1.6; a step of modifying the cerium oxide particles by inserting the cerium oxide particles Lithium or lithium is removed to modify the cerium oxide particles; and a step of forming a cyclic carbonate layer, which forms a lithium salt and is composed of a cyclic carbonate on the surface of the modified cerium oxide particles The cyclic carbonate layer is used, and the ruthenium oxide particles in which the cyclic carbonate layer is formed are used as the negative electrode active material particles to produce a negative electrode material for a nonaqueous electrolyte secondary battery.

According to the method for producing a negative electrode material for a nonaqueous electrolyte secondary battery, it is possible to obtain a nonaqueous negative electrode material which utilizes the original characteristics of cerium oxide which is modified by using lithium, and has a high Battery capacity and good cycle retention. Further, since the negative electrode material produced in this manner contains the lanthanum-based active material particles having the cyclic carbonate layer as described above, the slurry produced at the time of producing the negative electrode is stabilized. That is, it is possible to obtain a negative electrode material which is industrially advantageous in producing a secondary battery.

In this case, it is preferred that in the step of forming the cyclic carbonate layer, the modified cerium oxide particles are washed with a solution containing a cyclic carbonate and a lithium salt, and then the washed cerium oxide particles are dried. Thus, a cyclic carbonate layer composed of a cyclic carbonate and containing a lithium salt is formed on the surface of the modified cerium oxide particles.

Specifically, a cyclic carbonate layer containing a lithium salt can be formed by such a method. [Effect of the invention]

The negative electrode active material of the present invention can improve the stability of the slurry produced when the secondary battery is produced, and if the slurry is used, an industrially usable coating film can be formed, so that the battery capacity can be substantially achieved. , cycle characteristics and initial charge and discharge characteristics improved. Moreover, the secondary battery of the present invention containing the negative electrode active material can be industrially advantageous, and the battery capacity, cycle characteristics, and initial charge and discharge characteristics are good. Further, even in an electronic device, an electric power tool, an electric vehicle, a power storage system, or the like using the secondary battery of the present invention, the same effects can be obtained.

Moreover, in the method for producing a negative electrode material of the present invention, it is possible to manufacture a negative electrode material capable of improving the stability of a slurry produced in the production of a secondary battery, and capable of making battery capacity, cycle characteristics, and initial charge and discharge. Feature enhancements.

Hereinafter, the embodiment of the present invention will be described, but the present invention is not limited to the following description.

As described above, as one of methods for increasing the battery capacity of a lithium ion secondary battery, a method of using a negative electrode containing a lanthanoid active material as a main material as a negative electrode of a lithium ion secondary battery has been studied. For a lithium ion secondary battery using a lanthanum-based active material as a main material, it is desirable that the cycle characteristics and initial efficiency are similar to those of a lithium ion secondary battery using a carbon material, but in order to obtain and use a lithium ion of a carbon material When the secondary battery has similar cycle characteristics and initial efficiency, and the lanthanum-based active material obtained by upgrading with lithium, it is difficult to produce a stable slurry, and it is difficult to produce a good-quality negative electrode.

Therefore, the inventors have repeatedly studied intensively in order to obtain a negative electrode active material which can easily produce a nonaqueous electrolyte secondary battery which has high battery capacity, and has cycle characteristics and initial efficiency. Good, thus completing the present invention.

The negative electrode active material of the present invention has negative electrode active material particles, and the negative electrode active material particles are a lanthanum active material particle containing a cerium compound containing a lithium compound (general SiO _x : 0.5 ≦ x ≦ 1.6) ). Further, the negative electrode active material particles have a cyclic carbonate layer containing a cyclic carbonate on the surface. Moreover, the cyclic carbonate layer further contains a lithium salt.

The negative electrode active material contains a lanthanum-based active material particle in which a cyclic carbonate layer containing a lithium salt is formed on at least a part of the surface. Therefore, when a negative electrode is produced, a water-based slurry is produced. At the time, the pH of the slurry is not easily alkaline. Therefore, it is possible to reduce the adverse effect on the thickener (adhesive) which is weak to the base. Further, the cyclic carbonate layer is excellent in water resistance. Further, by including a lithium salt in the inside of the cyclic carbonate layer, it is possible to facilitate the smooth transfer and reception of lithium ions during charging and discharging of the secondary battery. According to these effects, the negative electrode active material is a negative electrode active material which can produce a stable aqueous slurry and is easy to be industrialized even when a lanthanum-based active material particle obtained by upgrading with lithium is used. A secondary battery with high capacity and good cycleability and first-time efficiency is mass-produced.

[Configuration of Negative Electrode] Next, the configuration of the negative electrode of the secondary battery including the negative electrode active material of the present invention will be described.

Fig. 1 is a cross-sectional view showing a negative electrode including the negative electrode active material of the present invention. As shown in FIG. 1, the negative electrode 10 has a negative electrode active material layer 12 on the negative electrode current collector 11. The negative electrode active material layer 12 may be provided on both surfaces of the negative electrode current collector 11 or may be provided only on one surface of the negative electrode current collector 11 . Further, in the negative electrode of the nonaqueous electrolyte secondary battery of the present invention, the negative electrode current collector 11 may not be provided.

[Negative Electrode Current Collector] The negative electrode current collector 11 is an excellent conductive material and is composed of a material having excellent mechanical strength. Examples of the conductive material that can be used for the anode current collector 11 include copper (Cu) and nickel (Ni). The conductive material is preferably a material which does not form an intermetallic compound with lithium (Li).

The anode current collector 11 preferably contains carbon (C) and sulfur (S) in addition to the main element. The reason is that the physical strength of the anode current collector can be improved. In particular, when the active material layer which swells during charging is provided, when the current collector contains the above elements, the effect of suppressing deformation of the electrode including the current collector is obtained. The content of the above-mentioned element is not particularly limited, and among them, it is preferably 100 ppm or less. The reason is that a higher deformation suppression effect can be obtained.

The surface of the anode current collector 11 may be roughened or not roughened. The roughened negative electrode current collector is, for example, a metal foil subjected to electrolytic treatment, embossing treatment, or chemical etching treatment. The negative electrode current collector that is not roughened is, for example, a rolled metal foil or the like.

[Negative Electrode Active Material Layer] The negative electrode active material layer 12 may contain a plurality of negative electrode active materials such as a carbon-based active material in addition to the lanthanum-based active material particles. Further, other materials such as a thickener (also referred to as "adhesive", "adhesive") or a conductive auxiliary agent may be included in the design of the battery. Further, the shape of the negative electrode active material may be in the form of particles.

As described above, the negative electrode of the secondary battery of the present invention contains lanthanum active material particles composed of SiO _x (0.5 ≦ x ≦ 1.6) as the lanthanoid active material. The lanthanum active material particles are cerium oxide materials (SiO _x : 0.5 ≦ x ≦ 1.6), and as a composition thereof, x is preferably close to 1. The reason is that high cycle characteristics can be obtained. Further, the composition of the cerium oxide material in the present invention does not necessarily mean that the purity is 100%, and may contain a trace amount of an impurity element.

Further, in the present invention, the lower the crystallinity of the ruthenium compound contained in the negative electrode, the better. Specifically, it is preferable that the half value width (2θ) of the diffraction peak caused by the (111) crystal plane obtained by X-ray diffraction of the lanthanoid active material is 1.2° or more, and the crystal face thereof is The resulting crystallite size is below 7.5 nm. As a result, in particular, the crystallinity is low and the amount of the ruthenium crystal is small, whereby not only the battery characteristics can be improved, but also a stable lithium compound can be produced.

Further, the median diameter of the ruthenium compound is not particularly limited, and is preferably 0.5 μm or more and 20 μm or less. The reason is that, within this range, lithium ions can be easily released and released during charge and discharge, and the lanthanide-based active material particles are less likely to be broken. When the median diameter is 0.5 μm or more, the surface area is not excessively large, so that side reactions are less likely to occur during charge and discharge, and the irreversible capacity of the battery can be reduced. On the other hand, when the median diameter is 20 μm or less, the ruthenium-based active material particles are less likely to be broken and a new surface is less likely to occur, which is preferable.

Further, in the present invention, the lanthanoid active material is preferably one or more of Li ₂ SiO ₃ and Li ₄ SiO ₄ as a lithium compound contained in the ruthenium compound. Lithium niobate such as Li ₂ SiO ₃ and Li ₄ SiO ₄ is relatively more stable than other lithium compounds, and thus the lanthanide-based active material containing these lithium compounds can obtain more stable battery characteristics. These lithium compounds can be obtained by selectively changing a part of the SiO ₂ component formed inside the ruthenium compound into a lithium compound.

In particular, such an antimony compound is preferably obtained by electrochemically inserting lithium or liberating lithium. In the electrochemical method, a lithium compound can be selectively produced by changing the conditions by performing potential adjustment, current adjustment, or the like on the lithium counter electrode. Further, in the case of an electrochemical method, the potential of the ruthenium compound can be easily controlled by using an external potential and a reference electrode, and lithium inserted into the unnecessary region can be removed by using a discharge process. Therefore, the ruthenium compound which is modified by this method can have desired characteristics.

The lithium compound in the active material can be quantified by NMR (nuclear magnetic resonance) and XPS (X-ray photoelectron spectroscopy). The measurement of XPS and NMR can be carried out, for example, by the following conditions. XPS ‧ device: X-ray photoelectron spectroscopy device; ‧ X-ray source: monochromatic Al Kα ray; ‧ X-ray spot diameter: 100 μm; ‧ Ar ion gun sputtering conditions: 0.5 kV 2 mm × 2 mm ²⁹ Si MAS NMR (Magic Angle Spinning Nuclear Magnetic Resonance) ‧ Device: 700 NMR nuclear magnetic resonance spectrum analyzer manufactured by Bruker; ‧ Probe: 50 μL of 4 mm HR-MAS rotor; ‧ Sample rotation speed: 10 kHz; ‧ Measurement ambient temperature: 25 ° C.

By using such a modified (bulk internal modification) method to produce a negative electrode active material, it is possible to reduce or avoid lithium compounding in the ruthenium region, and in the atmosphere, or in an aqueous slurry, a solvent slurry. It becomes a stable substance in the material. Further, by performing the modification by an electrochemical method, it is possible to produce a more stable substance with respect to the thermally modified (thermal doping method) which is compounded at random.

By having at least one of Li ₄ SiO ₄ and Li ₂ SiO ₃ which are formed inside the bulk of the lanthanoid active material, it is possible to improve the characteristics, and to further improve the characteristics, these two kinds of coexisting states.

Further, it is preferable that the lanthanum-based active material particles have a carbon coating on the surface of the ruthenium compound. The reason is that conductivity is easily obtained.

Further, when the oxime compound is modified by the electrochemical method as described above, it is preferred to form a carbon film on the surface of the ruthenium compound before the modification. The reason is that when the in-block reforming treatment by the electrochemical method is performed, the potential distribution can be reduced and the generated lithium compound can be more uniformly controlled by allowing the carbon film to exist on the surface of the ruthenium compound.

Furthermore, in the present invention, the negative electrode active material particles preferably contain one or more of lithium carbonate and lithium fluoride between the ruthenium compound and the cyclic carbonate layer. By forming lithium carbonate, lithium fluoride, or the like in at least a portion between the ruthenium compound and the cyclic carbonate layer in advance, it is possible to reduce the amount of lithium released from the positive electrode side in the negative electrode when the battery is initially charged. Therefore, the initial efficiency of the battery can be improved. Further, lithium carbonate and lithium fluoride can be formed on the surface of the ruthenium compound as a solid-electrolyte interface (SEI) when the anode active material particles are electrochemically modified, and can be combined with the above-mentioned ruthenium Lithium acid is produced at the same time.

Further, as described above, when a carbon film is formed in advance before the modification of the ruthenium compound, one or more layers including lithium carbonate and lithium fluoride are formed on the surface of the carbon film.

When the lanthanum active material particles have a carbon film, a layer containing one or more of lithium carbonate and lithium fluoride, and a cyclic carbonate layer, it is preferred to laminate the layers in the following order: carbon film, coated carbon film The upper lithium carbonate and/or lithium fluoride layer and the water-repellent layer covering the outermost layer are also a cyclic carbonate layer. Further, as described above, the cyclic carbonate layer contains a lithium salt. When such a laminated negative electrode active material is provided, the slurry can be kept stable, and a coating film of good quality can be obtained, thereby improving battery characteristics.

Further, in the present invention, it is preferred that the cyclic carbonate contained in the cyclic carbonate layer comprises ethyl carbonate, propyl carbonate, fluoroacetate, difluoroacetate, and ethylene carbonate. More than one of them. Since the cyclic carbonate as described above is a solid at normal temperature, a cyclic carbonate layer containing these cyclic carbonates can be a more stable water-resistant layer. Among them, when ethyl carbonate or ethyl fluorocarbonate is contained, particularly stable battery characteristics can be obtained.

Moreover, it is preferable that the lithium salt contained in the cyclic carbonate layer contains one or more of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiBOB, LiFSA, LiTFSA, and LiTFSI. Specific examples of the lithium salt contained in the cyclic carbonate layer include lithium salts as described above. Among them, in particular, as the lithium salt, LiPF ₆ , LiBF ₄ , and LiClO ₄ are contained in the cyclic carbonate layer, whereby the slurry is more stable. Further, the lithium salt existing inside the cyclic carbonate layer can be confirmed by XPS. The conditions for XPS can be the same as those for the measurement of the lithium compound in the above-mentioned ruthenium active material.

Further, in the invention, it is preferred that the mass of the cyclic carbonate layer is 15% by mass or less based on the mass of the ruthenium compound. When the cyclic carbonate layer is formed so that the ratio is 15% by mass or less, it is possible to prevent the conductivity from deteriorating. Further, since a sufficient amount of the ruthenium compound is present, a high battery capacity can be obtained. Further, in order to make the cyclic carbonate layer as thin as possible, the amount of the cyclic carbonate layer to be coated is preferably the minimum amount, but it is preferably carried out in a desired amount depending on the method of holding the slurry. Even if the cyclic carbonate layer is in a thinner state, the above effects can be exhibited.

Further, in this case, it is preferred that the cyclic carbonate layer further contains a chain carbonate. When the cyclic carbonate layer is made of a chain carbonate, when the negative electrode is produced, the pH of the slurry can be made less alkaline, so that the slurry is more stable.

[Manufacturing Method of Negative Electrode] Next, an example of a method for producing a negative electrode of the nonaqueous electrolyte secondary battery of the present invention will be described.

First, a method of manufacturing the negative electrode material contained in the negative electrode will be described. First, cerium oxide particles represented by SiO _x (0.5 ≦ x ≦ 1.6) were produced. Then, the cerium oxide particles are modified by inserting lithium or detaching lithium from the cerium oxide particles. At this time, a lithium compound can be formed inside and on the surface of the cerium oxide particles. Further, on the surface of the modified cerium oxide particles, a cyclic carbonate layer containing a lithium salt and composed of a cyclic carbonate is formed. Further, such a cerium oxide particle can be used as a negative electrode active material particle and mixed with a conductive agent or a binder to produce a negative electrode material.

More specifically, the negative electrode material is produced by, for example, the following procedure.

First, a raw material for generating cerium oxide gas is heated in the presence of an inert gas or under reduced pressure in a temperature range of 900 ° C to 1600 ° C to generate cerium oxide gas. At this time, the raw material is a mixture of metal cerium powder and cerium oxide powder, and in consideration of the surface oxygen of the metal cerium powder and the presence of trace oxygen in the reaction furnace, it is preferable that the mixed molar ratio is 0.8 < metal cerium powder / two The cerium oxide powder is in the range of <1.3. The ruthenium crystallites in the particles are controlled by the change of the feed range, the vaporization temperature, or the heat treatment after the formation. The generated gas is deposited on the adsorption plate. The sediment is taken out in a state where the temperature in the reactor is lowered to 100 ° C or lower, and pulverization and powdering are carried out using a ball mill, a jet mill, or the like.

Then, a carbon film can be formed on the surface of the obtained powder material, but this step is not necessary. However, it is effective for improving battery characteristics.

As a method of forming a carbon film on the surface layer of the obtained powder material, pyrolysis chemical vapor deposition (thermal cracking CVD) is preferred. In thermal cracking CVD, cerium oxide powder is charged into a furnace, and the hydrocarbon gas is filled in the furnace, and then the temperature in the furnace is raised. The decomposition temperature is not particularly limited, and particularly preferably 1200 ° C or lower. More preferably, it is 950 ° C or less, and it is possible to suppress undesired unevenness of niobium oxide. The hydrocarbon gas is not particularly limited, and is preferably 3≧n in the composition of C _n H _m . The reason is that the manufacturing cost is low, and the physical properties of the decomposition product are preferable.

In vivo reformation of the block is preferably carried out using a device capable of electrochemically inserting lithium or detaching lithium. The device structure is not particularly limited, and the in-vivo modification can be performed using, for example, the in-vivo reforming device 20 as shown in Fig. 2 . The in-body reforming device 20 has a bath 27 filled with an organic solvent 23, a positive electrode (lithium source, modified source) 21 disposed in the bath 27 and connected to one of the power sources 26, and a powder containing container 25, The other is disposed in the bath 27 and connected to the other side of the power source 26; and the partition plate 24 is disposed between the positive electrode 21 and the powder containing container 25. In the powder containing container 25, the powder 22 of cerium oxide is accommodated. Further, cerium oxide particles are contained in the powder accommodating container, and a voltage is applied to the powder accommodating container containing the cerium oxide particles and the positive electrode (lithium source) by a power source. Thereby, lithium can be inserted into the cerium oxide particles or lithium can be removed, so that the powder 22 of cerium oxide can be modified.

Further, lithium niobate is formed inside the powder 22 of cerium oxide by reforming, and can also be formed simultaneously on the surface of the powder 22 of cerium oxide containing lithium carbonate (Li ₂ CO ₃ ) and lithium fluoride (LiF). More than one layer. When a carbon film is formed on the surface of the active material particles before the reforming, as described above, a layer containing the above-described lithium carbonate or the like is formed on the carbon film.

Further, as described above, formation of a carbon film is not necessary. However, since the carbon film is present on the surface of the ruthenium compound, the potential distribution can be reduced, and the generated lithium compound can be more evenly controlled. Therefore, it is preferable to form carbon on the surface of the yttrium oxide powder 22 before the modification. Membrane.

As the organic solvent 23 in the bath 27, ethyl carbonate, propyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluoromethyl methyl carbonate, difluoromethyl methyl carbonate can be used. Wait. Further, as the electrolyte salt contained in the organic solvent 23, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), or the like can be used.

A lithium foil can be used for the positive electrode 21, and a lithium-containing compound can also be used. Examples of the lithium-containing compound include lithium carbonate, lithium oxide, lithium cobaltate, olivine-type iron lithium, lithium nickelate, and lithium vanadium phosphate.

Then, on the surface of the modified cerium oxide particles, a cyclic carbonate layer containing a lithium salt and composed of a cyclic carbonate is formed. The cyclic carbonate layer can be formed using, for example, a procedure as described below.

First, the modified cerium oxide particles are washed with a solution containing a cyclic carbonate and a lithium salt. For example, it is washed with a solution obtained by mixing ethyl carbonate (cyclic carbonate), diethyl carbonate (chain carbonate), and LiBF ₄ (lithium salt) for about 30 minutes. At this time, the amount of coating of the cyclic carbonate layer can be controlled by controlling the kind or ratio of the cyclic carbonate and the chain carbonate. For example, when the amount of coating of the cyclic carbonate layer is reduced in order to secure conductivity or battery capacity, if dimethyl carbonate is used as the chain carbonate, the amount of ethyl carbonate which is coated on the surface can be greatly reduced. Further, the concentration of the lithium salt in the solution can be, for example, about 1 mol/kg. Further, when propylene carbonate or ethyl carbonate is used as the cyclic carbonate, the coating efficiency can be further improved. Further, the cyclic carbonate layer can be formed by drying the washed cerium oxide particles.

Then, the lanthanum-based active material contains cerium oxide particles having the above-described cyclic carbonate layer, and the lanthanum-based active material is optionally mixed with a carbon-based active material, and these negative electrode active materials are bonded to a binder and a conductive auxiliary agent. The other materials are mixed to form a negative electrode mixture, and then an organic solvent, water or the like is added to prepare a slurry.

Then, the slurry of the negative electrode mixture is applied onto the surface of the negative electrode current collector 11 and dried to form the negative electrode active material layer 12 as shown in Fig. 1 . At this time, hot pressing or the like may be performed as needed. The negative electrode of the nonaqueous electrolyte secondary battery of the present invention can be produced in the above manner.

<Lithium Ion Secondary Battery> A laminated thin film type lithium ion secondary battery will be described as a specific example of the above-described nonaqueous electrolyte secondary battery of the present invention.

[Structure of the laminated film type secondary battery] The laminated film type secondary battery 30 shown in Fig. 3 mainly houses the wound electrode body 31 in the inside of the sheet-shaped exterior member 35. The wound electrode body 31 is formed by winding a separator between a positive electrode and a negative electrode. Further, there is a case where a separator is provided between the positive electrode and the negative electrode, and a laminate is accommodated. In any of the electrode bodies, a positive electrode lead 32 is mounted on the positive electrode, and a negative electrode lead 33 is mounted on the negative electrode. The outermost peripheral portion of the electrode body is protected by a protective tape.

The positive and negative electrode leads 32 and 33 are led out in one direction from the inside to the outside of the exterior member 35, for example. The positive electrode lead 32 is formed of a conductive material such as aluminum, and the negative electrode lead 33 is formed of a conductive material such as nickel or copper.

The exterior member 35 is, for example, a laminated film in which a fusion layer, a metal layer, and a surface protective layer are sequentially laminated, and the laminated film is a fusion layer of the two layers of the film in such a manner that the fusion layer faces the electrode body 31. The outer peripheral portions of the middle portions are fused to each other or bonded by a binder or the like. The fusion portion is, for example, a film of polyethylene or polypropylene, and the metal layer is aluminum foil or the like. The protective layer is, for example, nylon or the like.

An adhesive film 34 is interposed between the exterior member 35 and the positive and negative electrode leads to prevent intrusion of outside air. This material is, for example, polyethylene, polypropylene, polyolefin resin.

[Positive Electrode] The positive electrode has a positive electrode active material layer on both surfaces or one surface of the positive electrode current collector, for example, similarly to the negative electrode 10 of FIG. 1 .

The positive electrode current collector is formed of a conductive material such as aluminum.

The positive electrode active material layer contains at least one or two or more kinds of positive electrode materials capable of occluding and releasing lithium ions, and may contain other materials such as a positive electrode adhesive, a positive electrode conductive auxiliary agent, and a dispersant depending on the design. In this case, detailed information on the positive electrode binder and the conductive auxiliary agent is the same as, for example, the negative electrode adhesive and the negative electrode conductive auxiliary agent described.

As the positive electrode material, a lithium-containing compound is preferred. Examples of the lithium-containing compound include a composite oxide composed of lithium and a transition metal element, or a phosphoric acid compound having lithium and a transition metal element. Among these positive electrode materials, at least one or more compounds having nickel, iron, manganese, and cobalt are preferred. The chemical formula of these positive electrode materials is represented by, for example, Li _x M ₁ O ₂ or Li _y M ₂ PO ₄ . In the above formula, M ₁ and M ₂ represent at least one or more transition metal elements. The values of x and y indicate different values depending on the state of charge and discharge of the battery, and are generally expressed by 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

Examples of the composite oxide having a lithium and a transition metal element include a lithium cobalt composite oxide (Li _x CoO ₂ ), a lithium nickel composite oxide (Li _x NiO ₂ ), and a lithium nickel cobalt composite oxide. The lithium nickel cobalt composite oxide may, for example, be a lithium nickel cobalt aluminum composite oxide (NCA) or a lithium nickel cobalt manganese composite oxide (NCM).

Examples of the phosphoric acid compound having a lithium and a transition metal element include a lithium iron phosphate compound (LiFePO ₄ ) or a lithium iron manganese phosphate compound (LiFe _1-u Mn _u PO ₄ (0<u<1)). When these positive electrode materials are used, high battery capacity can be obtained, and excellent cycle characteristics can also be obtained.

[Negative Electrode] The negative electrode has the same configuration as the negative electrode 10 for a lithium ion secondary battery of Fig. 1 described above, and has, for example, a negative electrode active material layer on both surfaces of the current collector. The negative electrode preferably has a larger negative electrode charging capacity with respect to the electric capacity obtained from the positive electrode active material agent (as a charging capacity of the battery). Thereby, precipitation of lithium metal on the negative electrode can be suppressed.

The positive electrode active material layer is provided on a part of both surfaces of the positive electrode current collector, and similarly, the negative electrode active material layer is also provided on a part of both surfaces of the negative electrode current collector. At this time, for example, the negative electrode active material layer provided on the negative electrode current collector is provided with a region where the opposing positive electrode active material layer does not exist. The reason is to implement a stable battery design.

In the region where the negative electrode active material layer and the positive electrode active material layer do not face each other, the charge and discharge are hardly affected. Therefore, the state of the negative electrode active material layer can be maintained at all times after the formation, and the composition and the like of the negative electrode active material can be accurately and accurately investigated without depending on the presence or absence of charge and discharge.

[Separator] A separator that isolates the positive electrode from the negative electrode to prevent short-circuiting of current caused by contact between the two electrodes and to allow lithium ions to pass. The separator is formed of a porous film made of, for example, a synthetic resin or a ceramic, and may have a laminated structure in which two or more kinds of porous films are laminated. Examples of the synthetic resin include polytetrafluoroethylene, polypropylene, and polyethylene.

[Electrolyte] At least a part of the active material layer or the separator is impregnated with a liquid electrolyte (electrolyte). This electrolyte dissolves an electrolyte salt in a solvent, and may contain other materials such as an additive.

As the solvent, for example, a nonaqueous solvent can be used. Examples of the nonaqueous solvent include ethyl carbonate, propyl carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, and 1,2-dimethyl Oxyethane, tetrahydrofuran, and the like. Among them, at least one of ethyl carbonate, propyl carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate is preferably used. The reason is that better characteristics can be obtained. Further, in this case, by combining a high-viscosity solvent such as ethyl carbonate or propylene carbonate with a low-viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate or diethyl carbonate, more advantageous characteristics can be obtained. The reason is that the dissociation property and ion mobility of the electrolyte salt can be improved.

Preferably, as a solvent additive, an unsaturated carbon bond cyclic carbonate is contained. The reason is that a stable film is formed on the surface of the negative electrode during charge and discharge, and the decomposition reaction of the electrolytic solution can be suppressed. The unsaturated carbon bond cyclic carbonate may, for example, be a vinyl carbonate or a vinyl carbonate.

Further, it is preferred to include a sultone (cyclic sulfonate) as a solvent additive. The reason is that the chemical stability of the battery can be improved. Examples of the sultone include propane sultone and propylene sultone.

Further, the solvent preferably contains an acid anhydride. The reason is that the chemical stability of the electrolyte can be improved. The acid anhydride may, for example, be propane disulfonic acid anhydride.

The electrolyte salt may contain any one or more of light metal salts such as a lithium salt. Examples of the lithium salt include lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ).

The content of the electrolyte salt is preferably 0.5 mol/kg or more and 2.5 mol/kg or less with respect to the solvent. The reason is that high ion conductivity can be obtained.

[Manufacturing Method of Laminated Film Type Secondary Battery]

The positive electrode was fabricated using the above positive electrode material. First, the positive electrode active material is mixed with a positive electrode binder, a positive electrode conductive auxiliary agent, or the like as needed to prepare a positive electrode mixture, and then dispersed in an organic solvent to prepare a positive electrode mixture slurry. Then, the mixture slurry is applied onto the positive electrode current collector by a coating device such as a die coater having a knife roll or a die, and hot air drying is performed to obtain a positive electrode active material layer. . Finally, the positive electrode active material layer is compression-molded by a roll press or the like. At this time, heating can be performed, and the compression can be repeated a plurality of times.

Then, using the same operation procedure as in the case of producing the negative electrode 10 for a lithium ion secondary battery described above, a negative electrode active material layer was formed on the negative electrode current collector to prepare a negative electrode.

When the positive electrode and the negative electrode are produced, each active material layer is formed on both surfaces of the positive electrode and the negative electrode current collector. At this time, in any of the electrodes, the active material coating length of the double-sided portion may not coincide (see Fig. 1).

Then, an electrolytic solution was prepared. Then, the positive electrode lead 32 is attached to the positive electrode current collector by ultrasonic welding or the like, and the negative electrode lead 33 is attached to the negative electrode current collector. Then, the wound electrode body 31 is produced by laminating or winding the positive electrode and the negative electrode through a separator, and a protective tape is adhered to the outermost peripheral portion thereof. Then, the wound body is molded in a flat shape. Then, the wound electrode body is sandwiched between the folded film-shaped exterior members 35, and then the insulating portions of the exterior member are bonded by heat fusion, and the wound electrode body is opened only in one direction. Enclosed. Then, an adhesive film is inserted between the positive electrode lead and the negative electrode lead and the exterior member. Then, a predetermined amount of the above-prepared electrolytic solution was supplied from the open portion, and vacuum impregnation was carried out. After impregnation, the open portion is bonded by vacuum heat fusion. In the above manner, the laminated film type secondary battery 30 can be manufactured.

In the nonaqueous electrolyte secondary battery of the present invention, which is produced by the above-described laminated thin film type secondary battery 30, it is preferable that the negative electrode utilization rate at the time of charge and discharge is 93% or more and 99% or less. When the negative electrode utilization rate is set to be in the range of 93% or more, the initial charging efficiency is not lowered, and the battery capacity can be greatly increased. Moreover, when the negative electrode utilization rate is set to 99% or less, safety can be ensured when lithium is not deposited. [Examples]

Hereinafter, the present invention will be more specifically described by showing examples and comparative examples of the invention, but the invention is not limited thereto.

(Example 1-1) A laminated thin film type lithium secondary battery 30 as shown in Fig. 3 was produced by the following procedure.

Start by making the positive electrode. The positive electrode active material is a mixture of 95 parts by mass of lithium cobalt aluminum composite oxide (LiNi _0.7 Co _0.25 Al _0.05 O), 2.5 parts by mass of a positive electrode conductive auxiliary agent (acetylene black), and 2.5 parts by mass of a positive electrode adhesive (polyfluorinated fluorine) Ethylene, PVDF) was used as a positive electrode mixture. Then, the positive electrode mixture was dispersed in an organic solvent (N-methyl-2-pyrrolidone: NMP) to prepare a paste-like slurry. Then, the slurry was applied to both sides of the positive electrode current collector by a coating device having a die, and dried by a hot air drying device. At this time, the positive electrode current collector was a positive electrode current collector having a thickness of 15 μm. Finally, compression molding is carried out by using a roll press.

Then, a negative electrode was produced. First, a lanthanide active material was produced in the following manner. The raw material obtained by mixing the metal ruthenium and the ruthenium dioxide was placed in a reaction furnace, vaporized in an environment of a vacuum of 10 Pa, and then deposited on an adsorption plate, and sufficiently cooled, and then the deposit was taken out and pulverized by a ball mill. After the particle diameter is adjusted, the carbon film is coated by performing thermal cracking CVD. The powder thus produced was subjected to electrochemical modification to carry out in-block reforming in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3:7 (containing an electrolyte salt of a concentration of 1.3 mol/kg). Then, the modified cerium oxide particles were washed with a mixed solution of ethyl carbonate (EC), diethyl carbonate (DEC), and LiBF ₄ , and then filtered and dried to remove DEC. Thereby, a cyclic carbonate layer containing ethyl carbonate and LiBF ₄ was formed.

The ruthenium-based active material produced in the above manner and the carbon-based active material were blended at a mass ratio of 1:9 to prepare a negative electrode active material. Here, as the carbon-based active material, a carbon-based active material obtained by mixing natural graphite and artificial graphite coated with an asphalt layer at a mass ratio of 5:5 is used. Further, the median diameter of the carbon-based active material was 20 μm.

Then, the negative electrode active material, the conductive auxiliary agent 1 (carbon nanotubes, CNT), the conductive auxiliary agent 2 (carbon fine particles having a median diameter of about 50 μm), and the styrene butadiene rubber (styrene butadiene copolymer) (hereinafter referred to as SBR), carboxymethyl cellulose (hereinafter referred to as CMC), mixed at a dry weight ratio of 92.5:1:1:2.5:3, and then diluted with pure water to prepare a negative electrode mixture slurry . Further, the above SBR and CMC are negative electrode binders (negative electrode adhesives). Here, the pH of the negative electrode mixture slurry was measured to evaluate the stability of the slurry. Further, the pH of the negative electrode mixture slurry was measured after one hour from the preparation of the negative electrode mixture slurry.

Further, as the negative electrode current collector, an electrolytic copper foil (thickness: 15 μm) was used. Finally, the negative electrode mixture slurry was coated on the negative electrode current collector, and dried at 100 ° C for 1 hour in a vacuum atmosphere. After drying, the deposition amount (also referred to as area density) per unit area of the negative electrode active material layer on one side of the negative electrode was 5 mg/cm ² .

Then, as a solvent, fluorine-containing ethyl ester (FEC), ethyl carbonate (EC), and diethyl carbonate (DEC) were mixed, and then an electrolyte salt (lithium hexafluorophosphate: LiPF ₆ ) was dissolved to prepare an electrolytic solution. At this time, the composition of the solvent was set to FEC:EC:DEC=1:2:7 by volume ratio, and the content of the electrolyte salt was set to 1.0 mol/kg with respect to the solvent. Further, 1.5% by mass of a vinyl carbonate (VC) was added to the obtained electrolytic solution.

Then, the secondary battery was assembled in the following manner. Initially, the aluminum lead is ultrasonically welded to one end of the positive electrode current collector, and the nickel lead is welded to the negative electrode current collector. Then, the positive electrode, the separator, the negative electrode, and the separator were sequentially laminated, and then wound longitudinally to obtain a wound electrode body. The winding end portion is fixed with PET protective tape. In the separator, a laminate film of 12 μm is used, and the laminate film is formed by a film containing porous polypropylene as a main component and sandwiched between a film containing porous polyethylene as a main component. Then, the electrode body is sandwiched between the exterior members, and then the outer peripheral portions are thermally fused to each other except for one side, and the electrode body is housed inside. The exterior member is an aluminum laminate film formed by laminating a nylon film, an aluminum foil, and a polypropylene film. Then, the prepared electrolytic solution was injected from the opening and impregnated in a vacuum atmosphere, followed by thermal fusion to seal.

The cycle characteristics and initial charge and discharge characteristics of the secondary battery produced in the above manner were evaluated.

For the cycle characteristics, the investigation was conducted in the following manner. Initially, in order to stabilize the battery, the battery was charged and discharged twice at 0.2 C in an environment of 25 ° C, and the discharge capacity of the second cycle was measured. Then, charging and discharging were performed until the total number of cycles became 499 cycles, and each discharge capacity was measured. Finally, the capacity retention rate of the 500th cycle obtained by charging and discharging at 0.2 C was divided by the discharge capacity of the second cycle, and the capacity retention ratio (hereinafter also referred to simply as the maintenance ratio) was calculated. In general, the cycle is performed from the third cycle to the 499th cycle, and charging and discharging are performed by charging 0.7 C and discharging 0.5 C.

When the initial charge and discharge characteristics are investigated, the initial efficiency (hereinafter sometimes referred to as initial efficiency) is calculated. The initial efficiency is calculated by a formula expressed by the following formula: initial efficiency (%) = (primary discharge capacity / initial charge capacity) × 100. The ambient temperature is set to be the same as when the cycle characteristics are investigated.

The stability (pH value) of the negative electrode mixture slurry of Example 1-1 and Examples 1-2 to 1-9 and Comparative Examples 1-1 to 1-4 to be described later, and the cycle characteristics of the secondary battery (maintained) After the initial charge and discharge characteristics (initial efficiency %), the results shown in Table 1 were obtained.

(Examples 1-2 to 1-9) The ratio of the mass of the cyclic carbonate layer to the mass of the ruthenium compound was changed as shown in Table 1, and basically, it was carried out in the same manner as in Example 1-1. Make a secondary battery. The adjustment of the amount of coating of the cyclic carbonate layer can be adjusted by changing the ratio of EC to DEC. For example, when the cyclic carbonate layer is coated so that the ratio of the mass is 2% by mass, the ratio of EC:DEC=5:95 is adjusted.

Further, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge and discharge characteristics were evaluated in the same manner as in Example 1-1.

(Comparative Example 1-1) A secondary battery was produced in the same manner as in Example 1-1 except that no lithium compound was formed in the ruthenium compound and a cyclic carbonate layer was not formed. Further, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge and discharge characteristics were evaluated in the same manner as in Example 1-1.

(Comparative Examples 1-2 to 1-3) A secondary battery was produced in the same manner as in Example 1-1 except that the cyclic carbonate layer was not formed. Further, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge and discharge characteristics were evaluated in the same manner as in Example 1-1. Further, in Comparative Example 1-3, although a cyclic carbonate layer was not formed, a layer containing LiBF _{4 was} formed on the surface of the ruthenium compound, and the layer was 0.1% by mass based on the mass of the ruthenium compound. The way to form.

(Comparative Example 1-4) A secondary battery was produced in the same manner as in Example 1-1 except that the cyclic carbonate layer was not formed and the lithium salt was not contained. Further, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge and discharge characteristics were evaluated in the same manner as in Example 1-1.

At this time, the lanthanum active material particles of Examples 1-1 to 1-9 and Comparative Examples 1-1 to 1-4 had the following properties. Whether or not the cyclic carbonate layer, the amount of coating, the type of cyclic carbonate, the presence or absence of a lithium salt, the type of lithium salt, the lithium compound contained in the ruthenium compound, and the presence or absence of one or more layers including lithium carbonate and lithium fluoride, Table 1 is described.

The lanthanum active material particles have an x value of 1.0 in the cerium compound represented by SiO _x and a median diameter D ₅₀ of the cerium compound 4 μm. Further, the half value width (2θ) of the diffraction peak due to Si (111) obtained by X-ray is 2.593°, and the crystallite size caused by the crystal face Si (111) is 3.29 nm. Moreover, the coating amount of the carbon film was 5% by mass based on the total amount of the ruthenium compound and the carbon film.

[Table 1] SiO _x : X = 1, D ₅₀ = 4 μm; graphite (natural graphite: artificial graphite = 5:5): D ₅₀ = 20 μm; half value width 2θ = 2.593 °; Si (111) crystallite 3.29 nm ; positive NCA; carbon film: 5 mass%; SiO _x ratio: 10% by mass

If the pH of the slurry exceeds 10, the alkalinity is strong and the binder is adversely affected, so that it is difficult to obtain a stable coating film at the time of electrode coating. As shown in Table 1, in Examples 1-1 to 1-9, it was confirmed that the pH of the slurry was all less than 10, and a stable coating film was obtained. On the other hand, the ruthenium compounds of Comparative Examples 1-2 and 1-3 contained a lithium compound inside and did not form a cyclic carbonate layer, and in Comparative Examples 1-2 and 1-3, the pH of the slurry exceeded 10 . Further, Comparative Example 1-4 did not contain a lithium salt in the cyclic carbonate layer, and in Comparative Example 1-4, the pH value also exceeded 10, and was largely alkaline. Further, in Comparative Example 1-1, no lithium compound was formed in the ruthenium compound, and in Comparative Example 1-1, the cycle retention ratio and the initial efficiency were lowered. When the lithium compound is not formed in the ruthenium compound as in Comparative 1-1, the initial efficiency is particularly low, and the irreversible capacity is large, so that it is difficult to increase the battery capacity.

Further, in particular, the mass of the cyclic carbonate layer of Examples 1-1 to 1-8 was 15% by mass or less based on the mass of the ruthenium compound, and particularly excellent in Examples 1-1 to 1-8. Cycle maintenance rate. Further, the ratio of the mass of the cyclic carbonate layer to the mass of the cerium compound is such that after coating the cyclic carbonate layer, the powder of the cerium compound is heat-treated at 200 ° C for 4 hours under vacuum, and then heat-treated. The mass change before and after is calculated.

(Example 2-1 to Example 2-6) The type of the lithium salt contained in the cyclic carbonate layer was changed as shown in Table 2, and basically, it was produced in the same manner as in Example 1-4. Secondary battery. Further, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge and discharge characteristics were evaluated in the same manner as in Example 1-4. The results are shown in Table 2.

[Table 2] SiO _x : X = 1, D ₅₀ = 4 μm; graphite (natural graphite: artificial graphite = 5:5): D ₅₀ = 20 μm; half value width 2θ = 2.593 °; Si (111) crystallite 3.29 nm ; positive electrode NCA; carbon film: 5 mass%; SiO _x ratio: 10 mass% (active material ratio); cyclic carbonate layer: EC 2 mass%; lithium niobate; lithium carbonate, lithium fluoride

As shown in Table 2, in Examples 2-1 to 2-6, the pH was 10 or less, and a good cycle maintenance ratio and initial efficiency were obtained. In particular, when LiPF ₆ or LiClO ₄ is contained in the cyclic carbonate layer, the pH can be further lowered as in the case of containing LiBF ₄ .

(Example 3-1 to Example 3-6) The type of the cyclic carbonate layer was changed to that shown in Table 3, and a secondary battery was produced in substantially the same manner as in Example 1-4. Further, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge and discharge characteristics were evaluated in the same manner as in Example 1-4. The results are shown in Table 3. Further, in Table 3, FEC means fluoroethyl carbonate, PC means propylene carbonate, DFEC means difluoroacetate, and VC means carbonic acid extending vinyl ester. The mixing ratio of each of the cyclic carbonates in Examples 3-1 and 3-6 was 50:50 (volume ratio).

[Table 3] SiO _x : X = 1, D ₅₀ = 4 μm; graphite (natural graphite: artificial graphite = 5:5): D ₅₀ = 20 μm; half value width 2θ = 2.593 °; Si (111) crystallite 3.29 nm ; positive electrode NCA; carbon film: 5 mass%; SiO _x ratio: 10 mass% (active material ratio); cyclic carbonate layer: 2% by mass; lithium salt: LiBF4: lithium niobate; lithium carbonate, fluorination lithium

As shown in Table 3, in Examples 3-1 to 3-6, the pH was 10 or less, and a good cycle maintenance ratio and initial efficiency were obtained. In particular, when FEC is contained as the cyclic carbonate, a particularly good cycle maintenance ratio and primary efficiency can be obtained.

(Examples 4-1, 4-2, Comparative Examples 4-1 and 4-2) The amount of oxygen was adjusted for the ruthenium compound represented by SiO _x , and was basically carried out in the same manner as in Example 1-4. Make a secondary battery. Further, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge and discharge characteristics were evaluated in the same manner as in Example 1-4. The results are shown in Table 4.

[Table 4] SiO _x : D ₅₀ = 4 μm; graphite (natural graphite: artificial graphite = 5:5): D ₅₀ = 20 μm; half value width 2θ = 2.593 °; Si (111) crystallite 3.29 nm; positive electrode NCA; Carbon film: 5% by mass; SiO _x ratio: 10% by mass (active material ratio); cyclic carbonate layer: EC/LiBF ₄ 2% by mass; lithium niobate; lithium carbonate, lithium fluoride

If the amount of oxygen in the ruthenium compound is reduced, that is, if x < 0.5, it becomes Si-rich, and the cycle retention rate is drastically lowered. Further, when O-rich is obtained, that is, when x>1.6, the electric resistance of the niobium oxide becomes high, and the cycle maintenance ratio is largely lowered.

(Example 5-1) A carbon film was not formed on the surface of the ruthenium compound, and a secondary battery was produced in substantially the same manner as in Example 1-4. Further, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge and discharge characteristics were evaluated in the same manner as in Example 1-4. The results are shown in Table 5.

[Table 5] SiO _x : X = 1, D ₅₀ = 4 μm; graphite (natural graphite: artificial graphite = 5:5): D ₅₀ = 20 μm; half value width 2θ = 2.593 °; Si (111) crystallite 3.29 nm ; positive NCA; SiO _x ratio: 10% by mass (active material ratio); cyclic carbonate layer: EC / LiBF ₄ 2% by mass; lithium niobate; lithium carbonate, lithium fluoride

As shown in Table 5, when the ruthenium compound has a carbon film, the cycle characteristics are greatly improved.

(Examples 6-1 to 6-9) A secondary battery was produced by basically changing the crystallinity of the ruthenium compound in the same manner as in Example 1-4. Further, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge and discharge characteristics were evaluated in the same manner as in Example 1-4. Further, the change in crystallinity can be controlled by heat treatment in a non-atmospheric environment. The half value width of the diffraction peak due to the (111) crystal plane obtained by X-rays of the lanthanoid active material is 2θ (°), which is shown in Table 6. Further, in Example 6-9, although the half value width was calculated to be 20 or more, this was a result of fitting using the analytical software, and substantially no peak was obtained. Therefore, the hydrazine compound of Examples 6-9 is substantially amorphous.

[Table 6] SiO _x : X = 1, D ₅₀ = 4 μm; graphite (natural graphite: artificial graphite = 5:5): D ₅₀ = 20 μm; carbon film: 5 mass%; positive electrode NCA; SiO _x ratio: 10 mass % (active material ratio); cyclic carbonate layer: EC / LiBF ₄ 2% by mass; lithium niobate; lithium carbonate, lithium fluoride

As shown in Table 6, in particular, a low crystalline material having a half-value width (2θ) of 1.2° or more and a crystallite size of 7.5 nm or less caused by the Si (111) plane can achieve a high capacity retention ratio and Stable slurry characteristics.

(Examples 7-1 to 7-6) The secondary battery was produced in the same manner as in Example 1-4 except that the median diameter of the lanthanoid compound was changed as shown in Table 7. Further, the stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge and discharge characteristics were evaluated in the same manner as in Example 1-4. The results are shown in Table 7.

[Table 7] SiO _x : X = 1; half value width 2θ = 2.593 °; Si (111) crystallite 3.29 nm; graphite (natural graphite: artificial graphite = 5:5): D ₅₀ = 20 μm; carbon film: 5 Mass %; positive NCA; SiO _x ratio: 10% by mass (active material ratio); cyclic carbonate layer: EC/LiBF ₄₂ 2% by mass; lithium niobate; lithium carbonate, lithium fluoride

As shown in Table 7, when the median diameter of the ruthenium compound is 0.5 μm or more, the maintenance ratio can be increased and the pH of the slurry can be lowered. The reason is presumed to be that the surface area of the ruthenium compound is not excessively large, and the area causing side reactions can be reduced. On the other hand, when the median diameter is 20 μm or less, the particles are less likely to be broken during charging, and the water resistance of the surface is not lowered. Further, when the median diameter is 20 μm or less, it is difficult to form a new surface on the surface of the particles, and it is difficult to generate SEI due to the newly formed surface during charge and discharge, so that loss of reversible lithium can be suppressed.

(Example 8-1 to Example 8-3, Comparative Example 8-1) The mass ratio of the lanthanoid active material to the carbon ruthenium active material in the negative electrode active material was changed, and basically, in the same manner as in Example 1-4 It is carried out to manufacture a secondary battery. Further, when the amount of the lanthanide active material was increased, the amounts of the conductive auxiliary agent and the binder were set to be the same as those of Example 1-4, and only the ratio of the carbon-based active material was changed. The stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge and discharge characteristics were evaluated in the same manner as in Example 1-4. The results are shown in Table 8.

[Table 8] SiO _x : X = 1; D ₅₀ = 4 μm; half value width 2θ = 2.593 °; Si (111) crystallite 3.29 nm; graphite (natural graphite: artificial graphite = 5: 5): D ₅₀ = 20 μm Carbon film: 5% by mass; positive electrode NCA; cyclic carbonate layer: EC/LiBF ₄ 2% by mass

Although the higher the battery capacity can be obtained as the ratio of the lanthanoid active material in the negative electrode active material is increased, as shown in Table 8, the maintenance ratio and the initial efficiency are lowered. Further, even if the ratio of the lanthanoid active material obtained by upgrading with lithium is increased, the pH of the slurry is still less than 10. On the other hand, as is clear from Table 8, the slurry resistance of the unmodified ruthenium compound was high, but the initial efficiency was extremely low, so that it was difficult to estimate the increase in capacity.

(Example 9-1 to Example 9-3) The cyclic carbonate layer was contained in the chain carbonate as shown in Table 9, and was basically produced in the same manner as in Example 1-4. battery. When the ruthenium compound is washed, the filtration is carried out violently, that is, the time taken for the filtration is shortened, whereby a small amount of the chain carbonate can be enclosed in a part of the cyclic carbonate layer. Moreover, it is only necessary to change the kind of the chain carbonate to be contained in the mixed solution used for washing, in order to change the type of the chain carbonate to be sealed.

The stability of the slurry, the cycle characteristics of the produced secondary battery, and the initial charge and discharge characteristics were evaluated in the same manner as in Example 1-4. The results are shown in Table 9. Further, in Table 9, DMC represents dimethyl carbonate, and EMC represents ethyl methyl carbonate.

[Table 9] SiO _x : X = 1; D ₅₀ = 4 μm; half value width 2θ = 2.593 °; Si (111) crystallite 3.29 nm; graphite (natural graphite: artificial graphite = 5: 5): D ₅₀ = 20 μm Carbon film: 5% by mass; positive electrode NCA; SiO _x ratio: 10% by mass (active material ratio); cyclic carbonate layer: EC/LiBF ₄ 2% by mass

As is clear from Table 9, when the cyclic carbonate layer contains a chain carbonate, the pH can be lowered to further improve the stability of the slurry.

Furthermore, the present invention is not limited to the above embodiment. The above-described embodiment is exemplified, and any one having substantially the same configuration as the technical idea described in the patent application scope of the present invention and exhibiting the same effects is included in the technical scope of the present invention.

All symbols are single paragraph numbers
10‧‧‧negative
11‧‧‧Negative current collector
12‧‧‧Negative active material layer
20‧‧‧Block internal modification device
21‧‧‧ positive
22‧‧‧Oxide powder
23‧‧‧Organic solvents
24‧‧ ‧ partition
25‧‧‧Powder container
26‧‧‧Power supply
27‧‧‧ bath
30‧‧‧Laminated film type secondary battery
31‧‧‧Wound electrode body
32‧‧‧positive lead
33‧‧‧Negative lead
34‧‧‧Blinded film
35‧‧‧ Exterior components

Fig. 1 is a cross-sectional view showing the structure of a negative electrode including the negative electrode active material of the present invention. Fig. 2 is a block in vivo reforming apparatus used in the production of the negative electrode active material of the present invention. Fig. 3 is a view showing a configuration example of a lithium secondary battery including the negative electrode active material of the present invention (laminate film type).

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10‧‧‧negative

11‧‧‧Negative current collector

12‧‧‧Negative active material layer

Claims (14)

A negative electrode active material for a non-aqueous electrolyte secondary battery, comprising a negative electrode active material particle, wherein the negative electrode active material particle contains a cerium compound SiO _x containing a lithium compound, and 0.5 ≦ x ≦ 1.6, the negative electrode for a nonaqueous electrolyte secondary battery The active material is characterized in that the negative electrode active material particles have a cyclic carbonate layer containing a cyclic carbonate on the surface, and the cyclic carbonate layer further contains a lithium salt. The negative electrode active material for a nonaqueous electrolyte secondary battery according to claim 1, wherein the lithium salt contained in the cyclic carbonate layer contains LiPF ₆ , LiBF ₄ , LiClO ₄ , LiBOB, LiFSA, LiTFSA, and LiTFSI. More than one. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the cyclic carbonate contained in the cyclic carbonate layer contains ethyl carbonate, propyl carbonate, and fluoroethyl carbonate. And one or more of difluoroacetic acid ethyl ester and carbonic acid extending vinyl ester. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the mass of the cyclic carbonate layer is 15% by mass or less based on the mass of the ruthenium compound. The negative electrode active material for a nonaqueous electrolyte secondary battery according to claim 1, wherein the cyclic carbonate layer further contains a chain carbonate. The negative electrode active material for a nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material particle contains one of lithium carbonate and lithium fluoride between the ruthenium compound and the cyclic carbonate layer. the above. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein one or more of Li ₂ SiO ₃ and Li ₄ SiO ₄ are present as the lithium compound contained in the ruthenium compound. The negative electrode active material for a nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material particle has a carbon film on the surface of the ruthenium compound. The negative electrode active material for a nonaqueous electrolyte secondary battery according to claim 1, wherein the ruthenium compound is obtained by chemically inserting lithium or detaching lithium. The negative electrode active material for a nonaqueous electrolyte secondary battery according to claim 1, wherein the ruthenium compound has a half value width of a diffraction peak caused by a Si (111) crystal plane obtained by X-ray diffraction. (2θ) is 1.2° or more, and the crystallite size caused by the crystal face thereof is 7.5 nm or less. The negative electrode active material for a nonaqueous electrolyte secondary battery according to claim 1, wherein the ruthenium compound has a median diameter of 0.5 μm or more and 20 μm or less. A non-aqueous electrolyte secondary battery according to any one of claims 1 to 11, comprising the negative electrode active material for a non-aqueous electrolyte secondary battery. A method for producing a negative electrode material for a nonaqueous electrolyte secondary battery, which is a method for producing a negative electrode material for a nonaqueous electrolyte secondary battery comprising negative electrode active material particles, the production method comprising the steps of: producing cerium oxide particles step, the silicon oxide particles is represented by the general formula SiO _x, and 0.5 ≦ x ≦ 1.6; the step of the modified silicon oxide particles, silicon oxide particles by the insertion of lithium from lithium or to the modified a cerium oxide particle; and a step of forming a cyclic carbonate layer, forming a cyclic carbonate layer comprising a lithium salt and comprising a cyclic carbonate on the surface of the modified cerium oxide particle; The cerium oxide particles in which the cyclic carbonate layer is formed are used as the negative electrode active material particles to produce a negative electrode material for a nonaqueous electrolyte secondary battery. The method for producing a negative electrode material for a nonaqueous electrolyte secondary battery according to claim 13, wherein in the step of forming a cyclic carbonate layer, the modification is performed by a solution containing a cyclic carbonate and a lithium salt. After the cerium oxide particles are dried, the washed cerium oxide particles are dried to form a cyclic carbonate layer containing the lithium salt and composed of a cyclic carbonate on the surface of the modified cerium oxide particles. .