JP2005174616A - Positive electrode active material for secondary battery, positive electrode for secondary battery using it, and secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for improving a cycle characteristic in a secondary battery. <P>SOLUTION: This application provides this secondary battery provided with: a power generation element equipped with this positive electrode for a secondary battery, an electrolyte, a separator, and a negative electrode disposed oppositely to the positive electrode for a secondary battery through the electrolyte and the separator; and an armoring body for housing the power generation element. In this case, the positive electrode for a secondary battery contains a positive electrode active material for a secondary battery having base substance particles containing a lithium-manganese composite oxide, and a lanthanoid element-containing compound adhering to at least a part of surfaces of the base substance particles. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a positive electrode active material for a secondary battery including a lithium manganese composite oxide, a positive electrode for a secondary battery using the same, and a secondary battery.

  Lithium secondary batteries have the feature of being small and have a large capacity, and are widely used as power sources for mobile phones, notebook computers and the like. The lithium secondary battery described here is a battery that operates by moving lithium ions in the electrolyte solution, in which a positive electrode active material capable of occluding and releasing lithium exists in the positive electrode and the negative electrode, respectively. In addition to materials that occlude and release lithium ions for carbon materials and the like, the materials include those that use metal materials that form alloys with Li, such as Li and Al.

  In particular, in a non-aqueous electrolyte secondary battery using lithium metal or a lithium compound as a negative electrode, when lithium cobaltate is used as a positive electrode active material, an electromotive force exceeding 4 V can be obtained, and research has been conducted energetically. Lithium cobalt oxide is widely used as a positive electrode active material in today's lithium ion secondary batteries because it exhibits good characteristics such as potential flatness, capacity, discharge potential, and cycle characteristics.

However, cobalt is an expensive material with a small recoverable reserve. In addition, since lithium cobaltate has a layered rock salt structure (α-NaFeO ₂ structure), an oxygen layer having a large electronegativity is adjacent due to lithium desorption during charging. Therefore, it is necessary to limit the amount of lithium extracted during actual use.If the amount of lithium extracted is excessive, such as in an overcharged state, the structure will change due to electrostatic repulsion between the oxygen layers and heat will be generated. There is much room for improvement and alternative materials are sought.

  As a positive electrode active material of a 4V class non-aqueous electrolyte secondary battery other than lithium cobaltate, lithium nickelate, spinel type lithium manganese composite oxide, etc. are considered.

Although lithium nickelate has a capacity greater than that of lithium cobaltate, the crystal structure is the same layered structure as lithium cobaltate, which is due to the instability of Ni ⁴⁺ during charging, resulting in oxygen desorption from lithium cobaltate. The temperature is low and safety is more difficult to secure. Furthermore, considering that the discharge potential is lower than that of lithium cobaltate and the environmental load of Ni is high, it is not attractive as an alternative material for lithium cobaltate.

  On the other hand, spinel-type lithium-manganese composite oxide is made of inexpensive manganese, is a stable spinel-type crystal, contains almost no excess lithium used only during overcharge, and lithium cobaltate. Compared with high safety, it is a highly anticipated material and has already been put into practical use in part. In particular, it is advantageous compared to cobalt and nickel in terms of resource supply and environmental load. Therefore, it has the high potential as a power storage for road leveling and a power source for future electric vehicles, taking into account the above-mentioned advantages of low price. Yes.

  However, lithium secondary batteries using lithium-manganese composite oxides for the positive electrode actually tend to have capacity degradation that gradually decreases with repeated charge and discharge, which is a significant improvement in their practical application. There was room for.

  In view of this, various methods have been studied in order to improve the cycle characteristics of organic electrolyte secondary batteries using lithium manganese composite oxide as the positive electrode. For example, characteristics improvement by improving reactivity during synthesis, characteristics improvement by controlling particle size, characteristics improvement by removing impurities, etc., all of which still have room for improvement in improving cycle characteristics Is leaving.

  Apart from the above, attempts have been made to improve the cycle characteristics by making the composition ratio of Li sufficiently excessive with respect to the stoichiometric ratio (see, for example, Patent Document 1). The improvement of cycle characteristics by this method can be clearly confirmed experimentally.

Further, as an effect similar to the Li excess composition, the Mn spinel material LiMn ₂ O ₄ and the Li-Mn composite oxide Li ₂ Mn ₂ O ₄ , LiMnO ₂ , Li ₂ MnO that are Li richer than this material are used. _A technique of mixing ₃ etc. and using it as a positive electrode active material has also been developed.

  However, when Li is added excessively or mixed with another Li-rich compound, the cycle characteristics are improved, while the charge / discharge capacity value / charge / discharge energy value decreases. There is room for further improvement because it is difficult to balance the lifetime. In contrast, attempts have been made to increase the specific surface area with the aim of improving the energy density and high rate (the current during charging / discharging is large relative to the capacity) and improving the charge / discharge characteristics and the completeness of the reaction. Since achieving a high cycle life was difficult, there was room for improvement as well.

  On the other hand, studies have been made to improve characteristics by adding another element to the three-component compound of Li—Mn—O. For example, addition / doping of Co, Ni, Fe, Cr, Al, or the like (see, for example, Patent Document 2 or Patent Document 3). The addition of these metal elements tends to be accompanied by a reduction in charge / discharge capacity, and further ingenuity is required to satisfy the total performance.

  Among other element additions, boron addition is expected to improve other characteristics, such as cycle characteristics and self-discharge characteristics, with little reduction in charge / discharge capacity (see, for example, Patent Document 4). . In either case, manganese dioxide or lithium manganese composite oxide is mixed with a boron compound (for example, boric acid) in solid phase or immersed in an aqueous solution of boron compound, and heat treatment is performed to synthesize a composite oxide of lithium, manganese, and boron. Yes. It was expected that the composite particle powder of these boron compounds and manganese oxides had a reduced surface activity, so that the reaction with the electrolyte was suppressed and the capacity storage characteristics were improved.

  However, simply adding boron tends to cause grain growth, a reduction in tap density, and the like, and there is still much room for improvement in increasing the capacity of a battery. In addition, depending on the synthesis conditions, capacity reduction in the effective potential range when combined with the carbon negative electrode may be observed, such as insufficient reaction suppression with the electrolyte, which is not necessarily effective in improving storage characteristics There wasn't.

  On the other hand, the spinel type lithium manganese composite oxide is an oxide of at least one element selected from La, Nd, and Sm in the battery, or a composite oxidation of manganese with at least one element selected from La, Nd, and Sm. Inclusion of an object can improve the charge / discharge cycle characteristics, storage characteristics, and safety of the battery (see, for example, Patent Document 5).

  However, although the technique disclosed in Patent Document 5 has a certain effect, there is some room for improvement as described below.

  There is also room for improvement in terms of battery external swelling. This cause seems to be due to the presence state of the element disclosed in Patent Document 5 existing inside the battery. The reason seems to be that partial reaction products at or near the surface have some effect.

Furthermore, there is room for improvement of various characteristics related to resistance. This is because the oxide disclosed in Patent Document 5 is almost an insulator at room temperature.
Subsequently, a non-aqueous electrolyte secondary battery using a film-shaped outer package will be described.

  Recently, a power generation element is enclosed in a film-like exterior body such as an aluminum laminate film in which a heat-fusible resin film is laminated on an aluminum foil, and a metal lead for current extraction passes through the fusion part of the film-like exterior body. Development of non-aqueous electrolyte batteries having a configuration in which they are taken out from the inside to the outside has been actively conducted.

  In recent years, the development of thinner and lighter electronic devices and the development of power storage devices for automobiles are progressing, and there is a strong demand for thinner and lighter and lower resistance batteries for these applications. The film-clad battery is more advantageous than a battery in which a hard metal can is used as the outer package and the current extraction terminal has a complicated shape.

  As mentioned above, spinel-type lithium manganese composite oxide is a material that has advantages in various aspects of cost, safety, stable supply of resources, and environmental impact, and it is thin, lightweight, low resistance, etc. Combining a film-clad battery, which is a battery that shows superiority in terms of power, is highly anticipated as a power storage or power source for electric vehicles, and is being developed.

  However, the conventional film exterior type batteries using lithium manganese composite oxide for the positive electrode are caused by decomposition of the electrolyte when stored in a charged state at a high temperature, such as repeated charge / discharge cycles. As a result, there is a room for improvement in safety because the generated gas tends to swell the outer shape of the battery. In the case of a film-clad battery, the outer shape of the battery easily swells when gas is generated inside the battery. Therefore, an unnecessary problem occurs when a metal can is used as the outer package. In other words, there is a problem that when it is mounted on an electric device, the surrounding size is exceeded and the surrounding area is compressed.

  As a technique for solving the room for improvement, in the case where the electrolyte contains a composition that can generate hydrogen ions by reacting with water, a hydrogen ion scavenger is disposed at a place in contact with the electrolyte in the battery. It is known that a film-covered non-aqueous electrolyte secondary battery excellent in discharge cycle characteristics, storage characteristics, safety, and battery outer shape swelling suppression characteristics can be produced (for example, see Patent Document 6). This technique can also be confirmed by experiments.

  However, although the technique disclosed in Patent Document 6 has a certain effect, further improvement is required, and various characteristics relating to resistance are required to be improved as described below.

  In other words, in addition to improving the room for improvement that has been pointed out in the past, such as charge / discharge cycle life and capacity storage characteristics, further improvement of the battery outer shape swelling suppression characteristics, and newly emerged low resistance characteristics and low resistance increase characteristics Such improvement of factors relating to long-term reliability is an important issue in using a film-encased nonaqueous electrolyte secondary battery as a power storage or power source for an electric vehicle.

With the above technologies, the cycle characteristics, storage characteristics, and safety were improved temporarily. However, in recent years, the importance of the problem of the battery outer shape swelling characteristic peculiar to a film exterior type battery has increased more than before. In addition, the combination of spinel-type lithium manganese composite oxide and film-clad batteries is considered to produce a significant advantage. New issues such as the realization of low resistance increase rate characteristics have emerged, and further innovation is required.
JP 7-282798 A (page 4-7, Table 2) JP-A-4-282560 (page 3-6, Table 1 to Table 3) Japanese Patent Laid-Open No. 4-28962 (page 2-3, Table 1) JP-A-9-115515 (Page 4-5, Table 1) JP 2000-311689 A (Page 4-5, Table 1) JP 2001-176546 A (Page 13, Table 7 to Table 8)

  This invention is made | formed in view of the said subject, and it aims at providing the technique which implement | achieves the improvement of cycling characteristics in a secondary battery.

  According to the present invention, there is provided a positive electrode active material for a secondary battery comprising a base particle containing a lithium manganese composite oxide and a lanthanoid element-containing compound attached to at least a part of the surface of the base particle. Is done.

  According to the present invention, since the lanthanoid element-containing compound has a configuration in which the lanthanoid element-containing compound exists on or near the surface of the lithium manganese composite oxide, the elution of Mn from the lithium manganese composite oxide is reduced. There is an effect that the cycle characteristics of the secondary battery are improved.

  In addition, according to the present invention, there is also provided a positive electrode for a secondary battery characterized by including the above-described positive electrode active material for a secondary battery, and has the same effect as the above. Further, a hydrogen ion scavenger may be further included.

  When this secondary battery positive electrode further contains a hydrogen ion scavenger, the elution of Mn from the lithium manganese composite oxide is further reduced as compared with the case where no hydrogen ion scavenger is contained. This is because the effect can be remarkably exhibited.

  According to the present invention, the power generation element and the exterior body that stores the power generation element are provided. The power generation element includes the positive electrode for the secondary battery, the electrolyte, the separator, the electrolyte, and the separator. There is also provided a secondary battery characterized in that it is a power generation element comprising a positive electrode for the secondary battery and a negative electrode disposed opposite to the positive electrode for the secondary battery. It may be a sealed film-shaped exterior body.

  When this outer package is a film-shaped outer package sealed with a sealing material, the battery outer shape tends to swell compared with the case where a can-shaped outer package is adopted. It is because generation | occurrence | production of gas, carbon monoxide gas, carbon dioxide gas etc. is suppressed, and as a result, the battery external form swelling which is easy to occur in a film-like exterior body can be suppressed.

  As mentioned above, although the structure of this invention was demonstrated, what combined these structures arbitrarily is effective as an aspect of this invention. Moreover, what converted the expression of this invention into the other category is also effective as an aspect of this invention.

  For example, according to the present invention, an electric device equipped with the secondary battery is provided. Examples of the electric device include a mobile phone, a notebook computer, a PDA (Personal Digital Assistant), various cameras, a navigation system, an automobile, a non-stop power supply, and a portable music device.

  As described above, according to the present invention, a positive electrode for a secondary battery containing a positive electrode active material for a secondary battery having a configuration in which the lanthanoid element-containing compound is present on or near the surface of the lithium manganese composite oxide is used. Thus, the cycle characteristics of the secondary battery can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.
<Positive electrode active material for secondary battery>
Hereinafter, embodiments of a positive electrode active material for a secondary battery provided by the present invention will be described.

  The positive electrode active material for a secondary battery used in the present embodiment includes a base particle containing a lithium manganese composite oxide and a compound containing a lanthanoid element attached to at least a part of the surface of the base particle or in the vicinity of the surface as a constituent element ( In the present specification, a positive electrode active material for a secondary battery comprising a lanthanoid element-containing compound containing a lanthanoid element compound).

  That is, in the secondary battery used in the present embodiment, the lanthanoid element-containing compound is not limited to anywhere in the secondary battery, but it is effective that the lanthanoid element-containing compound exists on or near the surface of the spinel type lithium manganese composite oxide. .

The lithium manganese composite oxide is a composite oxide composed of lithium, manganese, and oxygen, and will be described in detail later. For example, spinels such as LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ , and LiMnO ₂ are used. It may be a lithium manganese composite oxide having a structure.

  Here, the lanthanoid element-containing compound is obtained by firing a raw material mixture obtained by mixing a first raw material powder containing a lithium manganese composite oxide and a second raw material powder containing a compound containing a lanthanoid element as a constituent element. The substance produced | generated by (1) may be sufficient.

Wherein the first raw material powders described above, although the details will be described later, for _{example, LiMn 2 O 4, Li 2} Mn 2 O 4, and LiMnO may include lithium-manganese composite oxide having a spinel structure _2. Moreover, although this 1st raw material powder is mentioned later in detail, for example, you may classify as needed and may arrange | equalize a particle size.

  The second raw material powder may be an oxide or carbonate of one or more elements selected from the group consisting of La, Nd, and Sm. Further, the average particle diameter of the second raw material powder may be within a specific range described below (for example, 1 μm or less).

Here, the oxide or carbonate will be described in detail later. For example, La ₂ O ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ , La ₂ (CO ₃ ) ₃ , Nd ₂ (CO ₃ ) ₃ and a compound having a composition such as Sm ₂ (CO ₃ ) ₃ .

  And when the content of the lithium manganese composite oxide in the raw material mixture is a part by mass and the content of the compound containing the lanthanoid element as a constituent element in the raw material mixture is b part by mass, These a and b may have a value of b / (a + b) within a specific range described later (for example, 0.005 or more and 0.05 or less).

  Thus, since the elution of Mn ions from the lithium manganese composite oxide is suppressed by including the compound of the lanthanoid element on or near the surface of the lithium manganese composite oxide contained in the positive electrode active material, the secondary battery It is possible to improve the cycle life and capacity storage characteristics at high temperatures of the battery, the battery outer shape swelling suppression characteristics, the low resistance characteristics, and the low resistance increase rate characteristics.

  The lanthanoid element-containing compound may be a substance produced by firing under a specific temperature condition (for example, a temperature condition of 550 ° C. or higher and a decomposition reaction temperature of the lithium manganese composite oxide) described later. .

  As described above, in order to allow the lanthanoid element-containing compound to be present on the surface of the spinel type lithium manganese composite oxide or in the vicinity of the surface, the lanthanoid element containing compound was separated from the spinel type lithium manganese composite oxide under the condition of pulverizing to submicron scale. It is effective to sinter a raw material mixture obtained by mixing a lanthanoid element-containing compound with an appropriate composition under an appropriate temperature condition (for example, 550 ° C. or higher and lower than the decomposition reaction temperature of the lithium manganese composite oxide). is there.

  The positive electrode active material for a secondary battery may have a structure in which the lanthanoid element-containing compound is distributed substantially uniformly on the surface of the base particle.

  In the present specification, the structure that is distributed substantially uniformly on the surface of the base particle means a structure in which the abundance of the lanthanoid element-containing compound per unit area on the surface of the base particle is substantially uniform. For example, although not particularly limited, a layered structure including a lanthanoid element-containing compound formed on the surface of a base particle, a layered structure formed by aggregation of particles including a lanthanoid element-containing compound, or a particle including a lanthanoid element-containing compound A structure in which dots are scattered is conceivable.

  The lanthanoid element-containing compound contained in the positive electrode active material obtained by firing the above raw material mixture is distributed substantially uniformly on the surface of the base particles containing the lithium manganese composite oxide. The positive electrode active material for secondary batteries having such a structure has been confirmed from the experimental results obtained by the XRD measurement method and the EDX measurement method, and the elution of Mn ions from the lithium manganese composite oxide is suppressed. This is because it has been confirmed by experiments to be described later that it is possible to improve the cycle life and capacity storage characteristics of the secondary battery at high temperatures, the battery external swelling suppression characteristics, the low resistance characteristics, the low resistance increase rate characteristics, and the like.

  However, the experimental results by the XRD measurement method and the EDX measurement method shown in FIGS. 3 and 4 to be described later have denied that very few lanthanoid elements are dissolved in the base particles containing the lithium manganese composite oxide. Therefore, for example, in the above positive electrode active material for a secondary battery, the lanthanoid element-containing compound adheres to the surface of the base particle through an intermediate layer in which the lanthanoid element is dissolved in a lithium manganese composite oxide. You may have a structure.

  Also in this case, according to the experimental results by the XRD measurement method shown in FIG. 5, FIG. 6 and FIG. 7 described later, most of the lanthanoid elements are an oxide of a lanthanoid element and a composite oxide of a lanthanoid element and Mn. This is because it is considered that the same effect as described above can be obtained because it is present as a lanthanoid element-containing compound containing.

In the present specification, the intermediate layer in which the lanthanoid element is dissolved in the lithium manganese composite oxide is not particularly limited, for example, but is a compound having a composition such as LaMnO ₃ , NdMnO ₃ , or SmMnO ₃ . A layered structure containing s is considered.

  The lanthanoid element-containing compound may be a substance including a lanthanoid oxide and a lanthanoid manganese composite oxide composed of a lanthanoid element and Mn composite oxide. The lanthanoid element may be one or more elements selected from the group consisting of La, Nd, and Sm.

Here, although the details of the lanthanoid oxide will be described later, for example, the lanthanoid oxide may have a composition such as La ₂ O ₃ , Nd ₂ O ₃ , and Sm ₂ O ₃ . Further, the lanthanoid manganese composite oxide will be described in detail later, but may have a composition such as LaMnO ₃ , NdMnO ₃ , and SmMnO ₃ , for example.

The XRD measurement shown in FIGS. 5, 6, and 7 to be described later is a positive electrode active material obtained by firing the above raw material mixture under the condition that at least one element selected from La, Nd, and Sm is used as the lanthanoid element. As a result of the investigation, an oxide of at least one element selected from La, Nd, and Sm and at least one selected from La, Nd, and Sm are formed on or near the surface of the base particle containing the spinel type lithium manganese composite oxide. This is because it has been confirmed that a lanthanoid element-containing compound containing a complex oxide of the above element and Mn exists.
<Positive electrode for secondary battery>
Hereinafter, embodiments of the positive electrode for a secondary battery provided by the present invention will be described.

  The positive electrode for a secondary battery used in the present embodiment is a positive electrode for a secondary battery including the positive electrode active material for a secondary battery having the above-described configuration.

  Here, as will be described in detail later, the secondary battery positive electrode generally contains a conductivity imparting material, a binder and the like in addition to the secondary battery positive electrode active material.

Further, the positive electrode for a secondary battery will be described in detail later, but may further contain a hydrogen ion scavenger such as a lithium nickel composite oxide. The lithium nickel composite oxide, which will be described in detail later, may be, for example, LiNi _0.8 Co _0.2 O ₂ .

The hydrogen ion scavenger is not limited to the lithium nickel composite oxide, and is particularly suitable as long as it has a function of reducing the hydrogen ion concentration by reacting with hydrogen ions (H ⁺ ) present in the organic electrolyte. Without limitation, any hydrogen ion scavenger can be used. Moreover, if it can function also as an electrode material, it can mix with said positive electrode active material, and can comprise the electrode excellent in electroconductivity.

  This hydrogen ion scavenger may be either an inorganic compound or an organic compound. For example, lithium nickel composite oxide, hydrogen storage alloy, carbon capable of storing hydrogen, and the like can be given. These can be used in powder form.

  As described above, the technology disclosed in Patent Document 1 that can improve the characteristics by sufficiently increasing the Li composition ratio relative to the stoichiometric ratio, as disclosed in Patent Document 6, and the electrolyte If the composition contains a composition that can react with water to generate hydrogen ions, the characteristics can be improved even when combined with a technology that can improve the characteristics by placing a hydrogen ion scavenger in the place where it contacts the electrolyte in the battery. The effect is obtained synergistically.

  This is because the presence of a hydrogen ion scavenger causes various actions such as reducing the concentration of hydrogen ions in the secondary battery, which suppresses the decomposition and deterioration of the electrolyte. As a result, the cycle life of the secondary battery at high temperatures This is because it is possible to improve capacity storage characteristics, battery external expansion suppression characteristics, low resistance characteristics, and low resistance increase rate characteristics.

  Moreover, in said positive electrode for secondary batteries, let said content of said lithium manganese complex oxide in this positive electrode for secondary batteries be (100-a) mass part, and said said in said positive electrode for secondary batteries In the case where the content of the lithium nickel composite oxide is a part by mass, a will be described in detail later, but it may satisfy a specific relationship (for example, an inequality represented by 3 <a ≦ 45). Good.

Thus, if the composition ratio of the lithium manganese composite oxide and the lithium nickel composite oxide in the positive electrode for the secondary battery is within an appropriate range, the effect of stabilizing the characteristics of the secondary battery can be obtained. .
<Structure of secondary battery>
Hereinafter, embodiments of the secondary battery provided by the present invention will be described.

  The secondary battery used in the present embodiment includes a power generation element and an exterior body that houses the power generation element. The power generation element includes the above-described positive electrode for a secondary battery, an electrolyte, a separator, the electrolyte, and the separator. A secondary battery characterized by being a power generation element comprising a positive electrode for a secondary battery and a negative electrode disposed opposite to each other via a negative electrode.

Since this secondary battery includes the positive electrode for the secondary battery described above, elution of Mn ions from the lithium manganese composite oxide contained in the positive electrode for the secondary battery is suppressed, so that the cycle life and capacity storage characteristics at high temperatures are achieved. In addition, the battery external swelling suppression characteristic, the low resistance characteristic, the low resistance increase rate characteristic, etc. are remarkably improved.
Here, the outer package may be a film-shaped package sealed with a sealing material.

  As described above, when the film-shaped outer package is used, the battery outer shape swells more easily than when the can-shaped outer package is employed. However, since the secondary battery includes the positive electrode for the secondary battery described above, the progress of the characteristic deterioration mechanism accompanying the decomposition of the electrolyte and the supporting salt can be delayed, so that oxygen gas, carbon monoxide gas, carbon dioxide gas It is because generation | occurrence | production of these etc. is suppressed and the battery external form swelling which is easy to occur in a film-like exterior body can be suppressed as a result.

The electrolyte may be a non-aqueous electrolyte containing a supporting salt containing LiPF ₆ or LiBF ₄ and an organic solvent.

As described above, when the supporting salt containing LiPF ₆ or LiBF ₄ is used, the elution of Mn ions into the electrolyte is particularly large, and the acidity of the electrolyte is increased, which is considered to result from the decomposition of the electrolyte. Oxygen gas, carbon monoxide gas, carbon dioxide gas, etc. are generated and the battery outer shape tends to swell. However, since the secondary battery includes the positive electrode for the secondary battery described above, the progress of the characteristic deterioration mechanism accompanying the decomposition of the electrolyte and the supporting salt can be delayed, so that oxygen gas, carbon monoxide gas, carbon dioxide gas It is because generation | occurrence | production of these etc. is suppressed and the battery external form swelling which is easy to occur in a film-like exterior body can be suppressed as a result.

  The secondary battery used in the present embodiment is structurally composed of, for example, a positive electrode using a lithium-containing metal composite oxide as a positive electrode active material and a negative electrode having a negative electrode active material capable of occluding and releasing lithium. A separator that does not cause electrical connection is sandwiched between the positive electrode and the negative electrode, and the positive electrode and the negative electrode are immersed in a lithium ion conductive electrolyte (generally an electrolyte containing a supporting salt in an organic solvent). These are in a state of being sealed in the battery case. When a voltage is applied to the positive electrode and the negative electrode, lithium ions are released from the positive electrode active material, and the lithium ions are occluded in the negative electrode active material, resulting in a charged state. In addition, by causing electrical contact between the positive electrode and the negative electrode outside the battery, lithium ions are released from the negative electrode active material, and lithium ions are occluded in the positive electrode active material, which is opposite to that during charging. .

  FIG. 1 is a schematic view showing an embodiment of a film-encased nonaqueous electrolyte secondary battery provided by the present invention. Moreover, FIG. 2 is sectional drawing which shows one Embodiment of the film-clad type nonaqueous electrolyte secondary battery provided by this invention. That is, FIG. 2 schematically shows a cross section taken along A-A ′ of the secondary battery of FIG. 1.

  For example, as shown in FIG. 1 or FIG. 2, the secondary battery used in the present embodiment includes a wound power generation element 2 that includes a heat-fusible resin film 11, a metal foil 12, and a heat-resistant resin film 13. It is enclosed with a laminate film 1. Two laminated films 1 face each other so that the heat-fusible resin film 11 faces the inside of the secondary battery, and the four sides around the power generating element 2 are heat-sealed. One side of the laminate film 1 is heat-sealed so that the positive electrode lead 31 and the negative electrode lead 32 are pulled out from the power generation element 2 so as to be sandwiched therebetween.

  Here, the laminate film 1 is molded so as to have a bottom surface portion and a side surface portion in accordance with the shape of the power generation element 2 on both sides. The power generation element 2 is impregnated with a non-aqueous electrolyte. The power generation element 2 includes a positive electrode, a negative electrode, an electrolyte, and a separator (not shown). In general, an electrolyte is generally a substance that can react with water to generate hydrogen ions.

  In the above embodiment, the film-like outer package is a film obtained by laminating the above heat-fusible resin film directly or via an adhesive on a heat-resistant resin film such as polyethylene terephthalate, or heat-fusible It can also be composed of a resin film alone film or the like. This is because even with these film-like exterior bodies, the power generation element can be suitably enclosed inside.

  Among these, an aluminum laminate film in which a heat-resistant resin film is laminated on one surface of an aluminum foil and a heat-fusible resin film is laminated on the other surface is particularly preferable as a film-shaped outer package. As a material of the heat resistant resin film, polyester, nylon or the like can be used. Examples of the material of the heat-fusible resin film include ionomers, polyethylene, polypropylene, those obtained by graft polymerization of acidic groups such as maleic anhydride, or those obtained by copolymerizing acidic groups such as maleic anhydride. Can be used.

In the above embodiment, the internal structure of the secondary battery is not limited, and can take the form of a winding type, a laminated type, a single layer type having a positive electrode and a negative electrode facing each other with a separator interposed therebetween. is there. As the external shape of the secondary battery, various shapes such as a square shape, a paper shape, a stacked shape, a cylindrical shape, and a coin shape can be employed.
<Method for producing positive electrode active material for secondary battery>
Hereinafter, an embodiment of a method for producing a positive electrode active material for a secondary battery provided by the present invention will be described.

  First, a method for producing a lithium manganese composite oxide contained in the positive electrode active material for a secondary battery will be described.

This lithium manganese composite oxide is an oxide composed of lithium, manganese and oxygen, and examples include a lithium manganese composite oxide having a spinel structure such as LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ , and LiMnO _2. it can.

Among these, a lithium manganese composite oxide having a spinel structure such as LiMn ₂ O ₄ is preferable. If the spinel structure is used, the [Li] / [Mn] ratio does not need to be strictly 0.50, but rather Li-rich. It may be a ratio. This is because the spinel structure is stabilized and the elution of Mn is suppressed when the ratio is Li-rich.

  This [Li] / [Mn] ratio is usually 0.50 or more, may be 0.51 or more, and may be 0.53 or more. The [Li] / [Mn] ratio is usually 0.7 or less, 0.65 or less, and further 0.625 or less.

  This is because when the [Li] / [Mn] ratio is within these ranges, an effect of stabilizing the characteristics of the secondary battery can be obtained.

  Similarly, if the lithium manganese composite oxide is a spinel structure, the [Li + Mn] / [O] ratio need not be 0.75. This is because if the lithium manganese composite oxide has a spinel structure, the effect of stabilizing the characteristics of the secondary battery can be obtained.

  In consideration of the ease of slurry formation in preparing the positive electrode and the uniformity of the battery reaction, the particle size of the lithium manganese composite oxide is a quantity average particle size, usually 3 μm or more and 30 μm or less. Also good. Such a lithium manganese composite oxide can be manufactured as follows.

As the Li raw material, for example, lithium compounds such as lithium carbonate, lithium oxide, lithium nitrate, and lithium hydroxide can be used. Examples of the Mn raw material include various manganese oxides such as electrolytic manganese dioxide (EMD), Mn ₂ O ₃ , Mn ₃ O ₄ , and chemical manganese dioxide (CMD), and manganese salts such as manganese carbonate and manganese oxalate. Manganese compounds can be used. However, taking into account the ease of securing the composition ratio of Li and Mn, the ease of securing the target particle size, the ease of processes and handling when mass-producing industrially, the presence or absence of generation of harmful substances, the cost, etc. A combination of electrolytic manganese dioxide and lithium carbonate can be used.

  As a pre-stage for mixing the starting materials, it is preferable to pulverize the lithium material and the manganese material as necessary to obtain an appropriate particle size. The particle size of the Mn raw material is usually 1 μm or more, and may be 3 μm or more. Further, the particle size of the Mn raw material is usually 70 μm or less, and may be 30 μm or less. The particle size of the Li raw material is usually 10 μm or less, may be 5 μm or less, and may be 3 μm or less.

Since the reaction of the lithium manganese composite oxide proceeds on the solid surface, if the mixing of the Li raw material and the Mn raw material is insufficient or the particle size is too coarse, the lithium manganese having the desired composition and structure A composite oxide may not be obtained. For example, when producing a lithium manganese composite oxide having a spinel structure, if mixing of the Li raw material and the Mn raw material is insufficient or the particle size is too large, Mn ₂ O ₃ , Mn ₃ O ₄ , Li ₂ Oxide phases other than the spinel structure such as MnO ₃ , Li ₂ Mn ₄ O ₉ , Li ₄ Mn ₅ O ₁₂ may be generated, and the battery voltage is lower than the lithium manganese composite oxide of the spinel structure, The energy density may decrease.

  Therefore, in order to obtain a lithium manganese composite oxide having a desired composition and structure, it is possible to increase the contact area of the Li raw material and the Mn raw material by using the raw material having the particle diameter as described above, thereby improving the uniformity of the reaction. it can. Therefore, particle size control or granulation of mixed powder may be performed. Further, when the particle size of the raw material is controlled, a lithium manganese composite oxide having a target particle size can be easily obtained.

  Next, the raw materials are weighed and mixed sufficiently so that the molar ratio of Li / Mn matches the target composition ratio of the lithium manganese composite oxide, and then fired in an oxygen atmosphere. For the firing atmosphere, pure oxygen may be used, or a mixed gas of an inert gas such as nitrogen or argon and oxygen may be used. The oxygen partial pressure at this time may be not less than 50 torr and not more than 760 torr.

The firing temperature is appropriately selected so that a desired phase is obtained. For example, when producing a lithium manganese composite oxide having a spinel structure, if the firing temperature is too high, unintended phases such as Mn ₂ O ₃ and Li ₂ MnO ₃ are generated and mixed, and the battery voltage and energy density are not sufficient. There is a case. On the other hand, if the firing temperature is too low, oxygen may be excessively increased or the powder density may be reduced, which may not be preferable for realizing a high capacity. Therefore, when producing a lithium manganese composite oxide having a spinel structure, the firing temperature is usually 400 ° C. or higher, 600 ° C. or lower, and 700 ° C. or lower. Moreover, although this baking temperature is 1000 degrees C or less normally, 900 degrees C or less may be sufficient and also 850 degrees C or less may be sufficient.

  Although baking time can be adjusted suitably, it is 6 hours or more normally, and 12 hours or more may be sufficient as it. Moreover, this baking time is 100 hours or less normally, and 48 hours or less may be sufficient as it. The cooling rate can be adjusted as appropriate, but it is better not to cool rapidly during the final baking treatment, and for example, the cooling rate can be about 100 ° C./h or less.

  Furthermore, it is desirable to classify the lithium manganese composite oxide powder obtained in this way as necessary to make the particle sizes uniform.

  Next, a technique for causing a compound of at least one element selected from La, Nd, and Sm to exist on the surface of the spinel type lithium manganese composite oxide or in the vicinity of the surface will be described.

With respect to the lithium manganese composite oxide obtained as described above, a compound raw material of at least one element selected from La, Nd, and Sm, such as La ₂ O ₃ , in terms of mass ratio (La ₂ O ₃ , Nd _{The value of} at least one selected from ₂ O ₃ and Sm ₂ O ₃ ) / (lithium manganese composite oxide + [at least one selected from La ₂ O ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ )] is 0.005. The positive electrode active material for a secondary battery provided by the present invention can be obtained by mixing, baking, and classifying so as to be 0.05 or less.

  This is because when this value is within this range, an effect of increasing the production stability of the positive electrode active material for the secondary battery can be obtained.

  In this case, examples of the compound raw material include oxides and carbonates of at least one element selected from La, Nd, and Sm, and oxides are preferable.

  Moreover, it is preferable that the compound raw material is sufficiently fine as a pretreatment in order to improve the characteristics. The raw material ground to submicron scale has a large surface area. Therefore, it is easy to partially react with the spinel type lithium manganese composite oxide. Specifically, it is desirable that the average particle size is 1 μm or less and the maximum particle size is 3 μm or less.

In addition, it is necessary to optimize the firing temperature. If the firing temperature is too low, partial reaction in the vicinity of the surface of the lithium manganese composite oxide does not proceed, and the mixture of the lithium manganese composite oxide and a compound raw material containing at least one element selected from La, Nd, and Sm Tend to remain. On the other hand, if the firing temperature is too high, the decomposition reaction of the lithium manganese composite oxide proceeds and Li ₂ MnO ₃ is generated. Li ₂ MnO ₃ does not contribute to charging / discharging and may be very unpreferable. Therefore, the reaction temperature can be set to 550 ° C. or higher and not higher than the decomposition reaction temperature of the lithium manganese composite oxide.

  Although the decomposition reaction temperature varies depending on the molar ratio of Li / Mn, for example, when the value of Li / Mn is 0.5, it varies depending on the production method, but is generally 820 ° C. to 850 ° C., When the value of Li / Mn is 0.625, it is about 620 ° C. Within the above range, the decomposition reaction temperature tends to decrease as the Li / Mn ratio increases.

As in the above method, the compound of at least one element selected from La, Nd, and Sm is present on or near the surface of the spinel type lithium manganese composite oxide at an appropriate firing temperature using an appropriate raw material. The spinel-type lithium manganese composite oxide thus obtained is also abbreviated as “surface-treated spinel” in the present specification.
This surface treatment spinel has the following characteristics.

  FIG. 3 is a graph showing measurement results of the positive electrode active material for secondary batteries provided by the present invention by the XRD measurement method.

  Here, the XRD measurement method is generally described as an X-ray diffraction method, and means an analysis method for obtaining information on the arrangement of atoms such as crystals. This XRD method can know the structure of a substance whose structure is unknown. For example, when the composition is clear and a single crystal is obtained, the atomic position in the compound can be known from the measurement result of the X-ray diffraction intensity. it can. Even in the case of a powder sample, the structure may be known by performing Rietveld analysis. This XRD method can also identify unknown substances, and in the case of a crystalline substance that can be predicted in advance, compare it with the X-ray diffraction pattern of the known substance or measure several surface spacing values. And can be identified by comparison with known ones. If the crystallinity is good, each can be identified even in a mixed sample of two or more compounds.

  As shown in FIG. 3, the lattice constants of surface-treated spinels of A-La, A-Nd, and A-Sm obtained in Examples described later were obtained from a general XRD measurement method and Rietveld analysis. Almost no change in lattice constant was observed. That is, it is strongly suggested that elements such as La, Nd, and Sm hardly enter the lattice (does not form a solid solution).

  FIG. 4 is a photograph showing the measurement results of the positive electrode active material for secondary battery provided by the present invention by the EDX measurement method and the SEM measurement method.

  Moreover, when the distribution state of the element on the surface of the surface treatment spinel of A-La, A-Nd, and A-Sm obtained in the examples described later was observed by a general EDX measurement method and SEM measurement method, Each element did not exist locally and was distributed almost uniformly. FIG. 4 shows the A-Nd-based EDX measurement result that was most clearly confirmed. Although not shown, almost the same results were obtained with other elements.

  Here, the EDX measurement method generally means an energy dispersive X-ray fluorescence analysis method. Since each atom that constitutes a substance has its own shell electron level, when such a substance is irradiated with X-rays, γ-rays, electron beams, etc., X-rays (characteristic X-rays) that have properties peculiar to atoms from the substance. ) Occurs. These X-rays are collectively referred to as fluorescent X-rays, and their energy (wavelength) is equal to the inner-shell electron level difference of the atoms, that is, the intrinsic intershell transition energy. Therefore, the type and amount of atoms present in the substance can be analyzed using this fluorescent X-ray.

  In addition, the SEM measurement method generally means scanning electron microscopy. In general, a focused electron beam is scanned on the surface of a sample, electrons emitted from each scanning point are received by a detector, amplified, and displayed as an image on a cathode ray tube in synchronization with the scanning. There is an advantage that a minute surface shape of a sample can be analyzed three-dimensionally.

  As described above, judging from two points, it was presumed that the compound of at least one element selected from La, Nd, and Sm exists on or near the surface of the spinel type lithium manganese composite oxide.

  However, the experimental results by the XRD measurement method and the EDX measurement method shown in FIGS. 3 and 4 do not deny that a very small amount of the lanthanoid element is dissolved in the base particle containing the lithium manganese composite oxide. For example, the above-described positive electrode active material for a secondary battery includes an intermediate layer in which a compound of at least one lanthanoid element selected from La, Nd, and Sm is dissolved in a spinel type lithium manganese composite oxide. And may have a structure attached to the surface of the spinel type lithium manganese composite oxide.

  Also in this case, according to the experimental results by the XRD measurement method shown in FIG. 5, FIG. 6 and FIG. 7 described later, most of the lanthanoid elements are an oxide of a lanthanoid element and a composite oxide of a lanthanoid element and Mn. This is because it is considered that the same effect as described above can be obtained because it is present as a lanthanoid element-containing compound containing.

  5, 6 and 7 are graphs showing measurement results of the positive electrode active material for secondary batteries provided by the present invention by the XRD measurement method. These figures consist of FIG. 5 using La as the lanthanoid element, FIG. 6 using Nd, and FIG. 7 using Sm.

  5, 6, and 7, in the surface-treated spinel of A-La, A-Nd, and A-Sm obtained in Examples described later, in addition to the spinel-type lithium manganese composite oxide, La The peak of the oxide of at least one element selected from Nd, Sm was observed. At the same time, a peak of a complex oxide of at least one element selected from La, Nd, and Sm and Mn was observed. Therefore, the surface-treated spinel is a composite oxide of Mn at least one element selected from La, Nd, Sm and an oxide of at least one element selected from La, Nd, Sm on or near the surface. It was found to have a multiphase mixture.

  Here, “a multiphase mixture of an oxide of at least one element selected from La, Nd, and Sm and a complex oxide of at least one element selected from La, Nd, and Sm and Mn” will be described in detail. .

When producing a surface-treated spinel, when heat treatment is applied at a temperature of 550 ° C. or higher and a decomposition reaction temperature or lower, a compound raw material of at least one element selected from La, Nd, and Sm, such as La ₂ O ₃ , and a spinel type Lithium manganese composite oxide partially reacts. As a result of partial reaction, an oxide of at least one element selected from La, Nd, and Sm that is a raw material, and a composite oxidation of Mn with at least one element selected from La, Nd, and Sm generated as a result of the reaction Since things are present at the same time, the state is called “multiphase mixture” for convenience. This “multiphase mixture” is slightly different from a general “mixture” that can be separated by mechanical operation or the like. As a result of XRD measurement, a state in which two or more single phases exist simultaneously can be confirmed, and the multiphase mixed state is simply called “multiphase mixture”.

  Furthermore, the present inventor has also investigated whether the calcination reaction is not partial, but complete calcination, that is, until the oxide containing the lanthanoid element as a raw material is exhausted. Since the proper temperature range has been determined and the firing temperature cannot be raised, the firing time has been made extremely long. As a result, the peak intensity of the raw material oxide in the XRD measurement surely decreased. However, it has been difficult to completely eliminate the peak of the raw material oxide. In addition, there was no significant difference in characteristics due to the difference in firing time. Therefore, for the time being, it has been determined that it is not necessary to proceed the firing reaction completely in order to obtain the desired characteristics.

Although it is difficult to measure the conductivity of the complex oxide of Mn and at least one element selected from La, Nd, and Sm formed on the surface of the lithium manganese composite oxide or in the vicinity thereof, LaMnO ₃ It is known that a compound derived from, for example, SrO-added LaMnO ₃ (for example, see Ceramics, 38 (2003), No. 11, p899, for reference) is not an insulator. Therefore, there seems to be a possibility that this complex oxide is not an insulator.
<Method for producing positive electrode for secondary battery>
Hereinafter, an embodiment of a method for producing a positive electrode for a secondary battery provided by the present invention will be described.

  The positive electrode used for the nonaqueous electrolyte secondary battery provided by the present invention contains the above-described positive electrode active material for a secondary battery containing such surface-treated spinel. In addition, the positive electrode further contains a hydrogen ion scavenger in some cases.

  The method for producing the positive electrode for the secondary battery is not particularly limited. For example, only the surface-treated spinel powder or the surface-treated spinel powder and the lithium nickel composite oxide powder are imparted with conductivity. The material and binder (binder) are mixed with an appropriate dispersion medium that can dissolve the binder (often by a slurry method) and then applied onto a current collector made of a metal thin film such as aluminum foil. Then, after the solvent is dried, the film is compressed by a press or the like to form a film.

  In addition, there is no restriction | limiting in particular as an electroconductivity imparting material, In addition to carbon materials, such as carbon black, acetylene black, natural graphite, artificial graphite, and carbon fiber, metal materials, such as Al, powders of conductive oxide, etc. are usually used. Can be used. Moreover, as a binder, what is normally used, such as a polytetrafluoroethylene (PTFE) and a polyvinylidene fluoride (PVDF), can be used.

  The addition amount of the conductivity imparting material is preferably 0.5% by mass or more and 10% by mass or less with respect to the total amount of the positive electrode active material, the conductivity imparting material, and the binder. The amount of the binder added is also preferably 1% by mass or more and 10% by mass or less with respect to the total amount of the positive electrode active material and the binder. This is because if the ratio between the conductivity-imparting material and the binder is small, the electron conductivity tends to be inferior or the electrode tends to peel off. Moreover, it is because the capacity | capacitance per secondary battery mass will become small when the ratio of an electroconductivity imparting material and a binder is large.

The proportion of the positive electrode active material is, for example, usually 70% by mass or more and 88% by mass or more with respect to the total amount of the positive electrode active material, the conductivity imparting material, and the binder. Moreover, this ratio is 99 mass% or less normally, and may be 97 mass% or less. This is because if the proportion of the positive electrode active material is too small, the energy density of the secondary battery tends to be disadvantageous. In addition, if the proportion of the positive electrode active material is too large, the proportion per mass of the conductivity-imparting material and the binder becomes low, and the electronic conductivity tends to be inferior or the electrode tends to peel off. .
<Method for producing secondary battery>
Hereinafter, an embodiment of a manufacturing method for a secondary battery provided by the present invention will be described.

  First, the electrolyte used in this embodiment will be described. The electrolyte used in the present invention is obtained by dissolving a supporting salt in a non-aqueous solvent. The solvent is commonly used as a solvent for nonaqueous electrolytes. For example, carbonates, chlorinated hydrocarbons, ethers, ketones, nitriles, and the like can be used.

  Preferably, at least one kind from ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), etc. as the high dielectric constant solvent, and diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl as the low viscosity solvent At least one kind selected from carbonate (EMC), esters and the like, and a mixed solution thereof is used. Combinations such as EC + DEC, PC + DMC, PC + EMC, PC + EC + EMC, or PC + EC + DEC can be used.

As the supporting salt, at least one kind of LiClO ₄ , LiI, LiPF ₆ , LiAlCl ₄ , LiBF ₄ , CF ₃ SO ₃ Li and the like can be used. Here, in general, it is difficult for the non-aqueous solvent to completely remove moisture, and it is easy to absorb moisture during the production of the battery. Therefore, the supporting salt often reacts with this trace amount of water to generate hydrogen ions.

According to the study by the present inventor, it has been confirmed that particularly LiPF ₆ or LiBF ₄ has a remarkable production of hydrogen ions, and the electrolyte tends to become acidic. LiPF ₆ or LiBF ₄ is excellent in that the electrical conductivity is reasonably high, the stability and safety are high, and the price is not so expensive. However, LiPF ₆ or LiBF ₄ has a drawback that it easily generates hydrogen ions. It was. Since the positive electrode for a secondary battery provided by the present invention is most effective when applied to a battery system using an electrolyte that easily generates hydrogen ions, LiPF ₆ or LiBF ₄ is a suitable supporting salt for the present invention. .

The concentration of the supporting salt in the electrolyte is usually 0.8M or higher. The concentration of the supporting salt is usually 1.5M or less and may be 1.1M or less. When the concentration of the supporting salt exceeds 1.1M, the density and viscosity of the electrolyte increase, which tends to be undesirable in the manufacturing process of the secondary battery. When the concentration is less than 0.8M, the electrolyte This is because the electrical conductivity of the secondary battery tends to decrease and the electromotive force of the secondary battery tends to decrease.
Next, the negative electrode used in this embodiment will be described.

  Further, as the negative electrode active material, a material capable of inserting and extracting lithium is used, and a material containing carbon material such as graphite or amorphous carbon, lithium metal, lithium alloy, Si, Sn, Al, SiO, SnO, or the like. Can be used alone or in combination.

  A negative electrode can be formed by forming a negative electrode active material on a current collector with a conductivity-imparting material and a binder. As an example of the conductivity imparting material, a conductive oxide powder or the like can be used in addition to the carbon material. As the binder, polyvinylidene fluoride or the like can be used. As the current collector, a metal thin film mainly composed of Cu or the like can be used.

  Although the material of a separator is not specifically limited, A woven fabric, glass fiber, a porous synthetic resin film | membrane etc. can be used. For example, a polypropylene or polyethylene-based porous film is suitable in terms of a thin film and a large area, film strength and film resistance.

  The negative electrode and the positive electrode obtained by the above procedure are laminated via a separator in a dry air or inert gas atmosphere, or after being wound, the laminated one is accommodated in a battery can, or a synthetic resin and a metal foil The secondary battery according to this embodiment can be manufactured by sealing with a flexible film or the like made of the laminated body.

The non-aqueous electrolyte secondary battery obtained by such a procedure is a non-aqueous electrolyte having excellent characteristics with improved characteristics such as charge / discharge cycle life at high temperature, capacity retention characteristics, or resistance increase after storage. It becomes a secondary battery.
<Other embodiments>

  As mentioned above, although the structure of this invention was demonstrated, what combined these structures arbitrarily is effective as an aspect of this invention. Moreover, what converted the expression of this invention into the other category is also effective as an aspect of this invention.

For example, in the above embodiment, in addition to the positive electrode active material mainly composed of surface-treated spinel, a compound generally known as a positive electrode active material such as LiCoO ₂ can also be mixed and used. Further, for safety and the like, a commonly used additive substance such as Li ₂ CO ₃ can be further added.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not limited to these.

In this example, a film-encased non-aqueous electrolyte secondary battery having the configuration shown in FIGS. 1 and 2 was produced and evaluated. Prior to the production of this secondary battery, a surface-treated spinel used for the positive electrode active material was produced and evaluated as follows.
<Synthesis of surface treatment spinel>

As a spinel-type lithium manganese composite oxide, attention was focused on Li _{1 + x} Mn _2−x O _4, and experiments on compounds having this composition were conducted mainly.

Li ₂ CO ₃ and electrolytic manganese dioxide (EMD) were used as starting materials for the synthesis of Li _{1 + x} Mn _2−x O ₄ .

As a previous step of mixing the above starting materials, Li ₂ CO ₃ pulverization and EMD classification are performed for the purpose of obtaining Li _{1 + x} Mn _2-x O ₄ having a desired particle size and improving reactivity. went. When Li _{1 + x} Mn _2−x O ₄ is used as the positive electrode active material of a battery, it has an average particle diameter of 5 mm or more and 30 mm or less in view of ensuring uniformity of charge / discharge reaction, ease of slurry preparation, safety, etc. Since it is preferable, the particle diameter of EMD is also set to 5 mm or more and 30 mm or less, which is the same as the target particle diameter of Li _{1 + x} Mn _2−x O ₄ .

On the other hand, Li ₂ CO ₃ preferably has a particle size of 5 mm or less in order to ensure a uniform reaction, and thus was pulverized so that the D ₅₀ particle size was 1.4 mm.

Thus, EMD and Li ₂ CO ₃ having a predetermined particle diameter were mixed so that the value of x was a predetermined ratio in a range satisfying the expression of 0.00 ≦ x ≦ 0.20.

  This mixed powder was first baked at 600 ° C. or higher and 800 ° C. or lower in an atmosphere of dry air flow, and then secondary baked again at 600 ° C. or higher and 800 ° C. or lower in an atmosphere of dry air flow.

Next, fine particles having a particle size of 1 mm or less in the obtained Li _{1 + x} Mn _2-x O ₄ particles were removed by an air classifier. At this time, the specific surface area of the obtained Li _{1 + x} Mn _2−x O ₄ was 0.6 m ² / g or more and 0.9 m ² / g or less.

Moreover, the tap density of the obtained _{Li 1 + x Mn 2-x} O 4 particles 2.14 g / cm ³ or more and 2.22 g / cm ³ or less, the true density was 3.98 g / cm ³ or more and 4.13g / Cm ³ or less, and D ₅₀ particle size was 11 mm or more and 16 mm or less.
Subsequently, a treatment for using the obtained Li _{1 + x} Mn _2-x O ₄ as a surface treatment spinel was performed.

First, the raw material was pulverized. In a wet ball mill using zirconia balls, La ₂ O ₃ , Nd ₂ O ₃ , and Sm ₂ O ₃ as raw materials were separately ground for 6 hours using ethanol as a solvent. The D ₅₀ particle size after pulverization was 0.75 μm, 0.51 μm, and 0.61 μm, respectively, as evaluated by a particle size analyzer “FRA” manufactured by MicroTrack.

Subsequently, the produced Li _{1 + x} Mn _2−x O ₄ and the pulverized raw material are in a mass ratio (a kind selected from La ₂ O ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ ) / ((lithium manganese The composite oxide) + (at least one selected from La ₂ O ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ )) was mixed so that the value was 0.02.

  After mixing, the temperature was raised to 600 ° C. at a temperature rising rate of 100 ° C./h, held at 600 ° C. for 2 hours, and then cooled to room temperature at a temperature lowering rate of 100 ° C./h.

Incidentally, a resulting surface treated spinel _{(Li 1 + x Mn 2-} x O 4), corresponding to the excess Li content x values (calculated from the charged composition ratio) and was subjected to a surface treatment atoms, x = 0.154 (that is, 2Li / Mn = 1.25). Samples satisfying the formula: La surface-treated spinel, Nd surface-treated spinel, and Sm surface-treated spinel. Hereinafter, the above three types will be referred to as group A.

  As a comparative example, a sample having the same composition that has not been surface-treated and satisfying the equation x = 0.154 (that is, 2Li / Mn = 1.25) is denoted as B.

Based on the technology disclosed in Patent Document 6, LiNi _0.8 Co _0.2 O ₂ having a specific surface area of 1.7 m ² / g was prepared as the lithium nickel composite oxide. Hereinafter, this LiNi _0.8 Co _0.2 O ₂ is expressed as Z.
<Evaluation Test Example 1>

As a comparative example, 5 g of B was weighed separately as a comparative example, and an electrolyte of a mixed solvent of propylene carbonate (PC) and dimethyl carbonate (DMC) (50:50 (volume%)) containing LiPF ₆ (concentration 1 M). 10 cm ³ was placed in a sealed container.

  These sealed containers were heated to 80 ° C. and left for 20 days. Thereafter, the electrolyte was extracted, and the Mn ion concentration in the electrolyte was subjected to composition analysis by ICP emission spectroscopy. The results are shown in Table 1.

この結果から、表面処理スピネルの場合では、電解質中に溶出するＭｎが少なくなっており、水素イオンの捕捉効果が高いことがわかる。このように、表面処理スピネルは、特許文献５で開示されている技術と同様に、高温で使用しても、正極活物質の安定性が増加することが予想される。
＜評価試験例２＞

From this result, it can be seen that in the case of the surface-treated spinel, the amount of Mn eluted in the electrolyte is small and the effect of capturing hydrogen ions is high. As described above, the surface-treated spinel is expected to increase the stability of the positive electrode active material even when used at a high temperature, as in the technique disclosed in Patent Document 5.
<Evaluation Test Example 2>

  As a spinel type lithium manganese complex oxide, A group, A group + Z, B and B + Z were used as comparative examples, and an aluminum-laminated film was used as an exterior body, and a film exterior type battery was manufactured as a prototype.

Further, as a comparison with Patent Document 5, Comparative Example 1 was used, La ₂ O ₃ , SrCO ₃ , Nd ₂ O ₃ , and Sm ₂ O ₃ were included in the positive electrode, and an aluminum laminate film was used as the outer package. A film exterior type non-aqueous electrolyte secondary battery was fabricated.

Below, the trial production method of this film exterior type nonaqueous electrolyte secondary battery is described. First, each of the spinel type lithium manganese oxide, or B and La ₂ O ₃ , B and SrCO ₃ , B and Nd ₂ O ₃ , B and Sm ₂ O ₃ , and the conductivity imparting material is dry mixed, A slurry was prepared by uniformly dispersing in N-methyl-2-pyrrolidone (NMP) in which PVDF as a binder was dissolved. Carbon black was used as the conductivity imparting material.

  The slurry was applied on an aluminum metal foil having a thickness of 25 μm, and NMP was evaporated to obtain a positive electrode sheet. The solid content ratio in the positive electrode was a mixing ratio of “spinel-type lithium manganese composite oxide and the like: conductivity imparting material: PVDF = 80: 10: 10” by mass ratio.

When mixing Z, the ratio of the above “spinel-type lithium manganese composite oxide etc.” was mixed so that the group A or B and Z were in a mass ratio of 80:20. However, when any of La ₂ O ₃ , SrCO ₃ , Nd ₂ O ₃ , and Sm ₂ O ₃ is mixed with B, the mass ratio between B and “spinel-type lithium manganese composite oxide” is B: (A mixture of La ₂ O ₃ , SrCO ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ ) = 98: 2 was mixed.

  On the other hand, the negative electrode sheet was prepared by mixing in a ratio of carbon: PVDF = 90: 10 (mass%), dispersing in NMP, and coating on a copper foil having a thickness of 20 μm.

  The positive and negative electrode sheets produced as described above were wound up using an elliptical core through a 25 μm thick polyethylene porous membrane separator, and further subjected to hot pressing to obtain a thin elliptical electrode winding body. .

  On the other hand, two laminated films having a structure in which polypropylene resin (sealing layer, thickness 70 μm), polyethylene terephthalate (thickness 20 μm), aluminum (thickness 50 μm), and polyethylene terephthalate (thickness 20 μm) are laminated in this order are cut out to a predetermined size. Then, a recess having a bottom surface portion and a side surface portion matching the size of the electrode winding body was formed in a part thereof.

The above-mentioned electrode winding body was wrapped with these facing each other, and the periphery was heat-sealed to produce a film-clad battery having a shape as schematically shown in FIGS. The electrode winding body was impregnated with the electrolyte before heat sealing the last side. The electrode winding body impregnated with the electrolyte corresponds to the power generation element 2 in FIG. The electrolyte was 1M LiPF ₆ as a supporting salt, and a mixed solvent of propylene carbonate (PC) and diethyl carbonate (DEC) (50:50 (volume%)) was used as a solvent.

  First, the rated capacity was measured using the produced film-clad battery. Each of the fabricated batteries was charged to 4.2 V at 700 mA, and then subjected to constant voltage charging for 1.5 hours. Subsequently, constant current discharge was performed up to 2.5 V at 70 mA, and the capacity obtained at this time was defined as the rated capacity of each battery.

  Thereafter, as so-called aging treatment, the battery was charged under the same conditions as described above, left at 25 ° C. for one week, and discharged to 2.5 V at 70 mA. Each battery subjected to the above series of treatments was charged again under the same conditions. The battery after charging is equivalent to 0.2C of each battery (current value at which the rated capacity is discharged in 5 hours. 140 mA if the rated capacity is 700 mA). Depth of discharge (DOD) up to 50% After discharging, the voltage when discharged at a current of 1 C for 10 seconds was measured.

After standing for 10 minutes, the voltage when charged for 10 seconds at a current of 1 C rate was measured. Further, the voltage was measured when the battery was discharged for 10 seconds at 3C after being left for 10 minutes, and the voltage when charged for 10 seconds at the 3C rate after being left again for 10 minutes was measured. Thereafter, the same charge and discharge rate was set to 5C and 7C while a 10-minute leaving interval was provided, and the V-I straight line was obtained. The slope of this straight line was defined as the initial internal DC resistance.
<Capacity recovery after storage and internal DC resistance>

  Each battery whose initial internal DC resistance was measured was adjusted to a DOD of 50% with a current value corresponding to 0.2 C of each battery, and then stored in a thermostat at 55 ° C. for 4 weeks. After storage, the battery was discharged at a constant current of 70 mA to 2.5 V, charged at 700 mA to 4.2 V, and then charged at a constant voltage for 1.5 hours.

  Subsequently, constant current discharge was performed to 2.5 V at 70 mA, the capacity obtained at this time was defined as the recovery capacity of each battery, and the capacity recovery rate (%) = recovery capacity / rated capacity × 100 was calculated. The calculated capacity recovery rate results are shown in Table 2.

また、初期内部直流抵抗の測定と同様の方法でＶ−Ｉ直線を求め、その傾きを保存後の内部直流抵抗とした。すなわち、抵抗上昇倍率＝（保存後の内部直流抵抗）／（初期内部直流抵抗）の式で求められる値である。算出した結果を表３に示した。

Further, the VI straight line was obtained by the same method as the measurement of the initial internal DC resistance, and the slope was taken as the internal DC resistance after storage. That is, the resistance increase magnification = (the internal DC resistance after storage) / (the initial internal DC resistance). The calculated results are shown in Table 3.

容量回復率は、Ｂを用いた比較例よりも、特許文献５の技術による例(Ｂ＋Ｌａ₂Ｏ₃、ＳｒＣＯ₃、Ｎｄ₂Ｏ₃、Ｓｍ₂Ｏ₃)が優れており、特許文献５の技術による例（Ｂ＋Ｌａ₂Ｏ₃、ＳｒＣＯ₃、Ｎｄ₂Ｏ₃、Ｓｍ₂Ｏ₃)よりも、本発明による実施例(Ａ群)の方が顕著に優れていた。なお、本発明による技術と、特許文献６の技術との組合せ(Ａ群＋Ｚ)で、更に相乗的に特性改善が見られていることも分かる。

As for the capacity recovery rate, the example (B + La ₂ O ₃ , SrCO ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ ) according to the technique of Patent Document 5 is superior to the comparative example using B. The example according to the present invention (group A) was significantly superior to the example according to (B + La ₂ O ₃ , SrCO ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ ). It can also be seen that the characteristic improvement is further seen synergistically by the combination of the technique according to the present invention and the technique of Patent Document 6 (Group A + Z).

Further, in the resistance increase magnification, the comparative example and the example of the technique of Patent Document 5 showed almost the same result, but the embodiment according to the present invention showed a significant improvement. Moreover, it turns out that the Example by this invention is very excellent in the characteristic regarding resistance compared with the example by the technique of patent document 5. FIG.
<Evaluation Test Example 3>

  Using the film-clad batteries of Examples and Comparative Examples produced in Evaluation Test Example 2, the initial thickness of the battery immediately after production and the thickness of the battery after 100 charge / discharge cycle tests at 55 ° C. were measured. did. Charging was performed at 350 mA up to 4.2 V, and discharging was performed at 700 mA up to 3.0 V. The results are shown in Table 4.

比較例や、特許文献５の例に比べ、本発明による実施例の方が、充放電サイクルによる電池外形膨れが抑制されていることが分かる。特に、特許文献５の例によるＢ＋ＳｒＣＯ₃の例では、電池外形膨れがむしろ悪化していることが顕著である。なお、本発明による技術と、特許文献６の技術との組合せで、更に相乗的に特性改善が見られていることも分かる。
＜評価試験例４＞

Compared with the comparative example and the example of Patent Document 5, it can be seen that the embodiment according to the present invention suppresses the expansion of the battery outer shape due to the charge / discharge cycle. In particular, in the case of B + SrCO ₃ according to the example of Patent Document 5, it is remarkable that the battery outer shape swelling is rather deteriorated. It can also be seen that the combination of the technique according to the present invention and the technique of Patent Document 6 shows a further synergistic improvement in characteristics.
<Evaluation Test Example 4>

  Using the film-clad batteries of Examples and Comparative Examples prepared in Evaluation Test Example 3, the amount of battery external swelling when stored at 60 ° C. was evaluated. First, the initial thickness of the battery was measured, and then charged at a constant current of 350 mA to 4.2 V, and then charged at a constant voltage of 4.2 V for 2 hours. Then, after leaving at 60 degreeC for 28 days, the thickness of the battery was measured again. The results are shown in Table 5.

比較例や、特許文献５の例よりも、本発明による実施例の方が、充放電サイクルによる電池外形膨れが抑制されていることが分かる。特に、特許文献５の例によるＢ＋ＳｒＣＯ₃の例では、充放電サイクルによる電池外形膨れがむしろ悪化していることが顕著である。なお、本発明による技術と、特許文献６の技術との組合せで、更に相乗的に特性改善が見られていることも分かる。
＜評価試験例５＞

It turns out that the battery external shape swelling by the charging / discharging cycle is suppressed by the Example by this invention rather than the example of a comparative example and patent document 5. FIG. In particular, in the case of B + SrCO ₃ according to the example of Patent Document 5, it is remarkable that the battery external swelling due to the charge / discharge cycle is rather deteriorated. It can also be seen that the combination of the technique according to the present invention and the technique of Patent Document 6 shows a further synergistic improvement in characteristics.
<Evaluation Test Example 5>

The film-clad battery of the present invention produced in Evaluation Test Example 2 using Group A, and as a comparative example, when producing Group A, grains of La ₂ O ₃ , Nd ₂ O ₃ and Sm ₂ O ₃ as raw materials Using film-clad batteries produced in the same manner as in Evaluation Test Example 3 with diameters of 2.10 μm, 1.63 μm, and 1.30 μm, respectively, the initial thickness of the battery immediately after production and the charge at 55 ° C. The battery thickness after 100 cycles of the discharge cycle test was measured. Charging was performed at 350 mA up to 4.2 V, and discharging was performed at 700 mA up to 3.0 V. The results are shown in Table 6.

比較例に比べ、原料をサブミクロンスケールまで粉砕し、表面処理スピネルを作製した実施例の方が、充放電サイクルによる電池外形膨れが抑制されていることが分かる。
＜評価試験例６＞

Compared with the comparative example, it can be seen that the example in which the raw material was pulverized to a submicron scale and the surface-treated spinel was produced suppressed the expansion of the battery outer shape due to the charge / discharge cycle.
<Evaluation Test Example 6>

  As the film-clad battery of the present invention produced in Evaluation Test Example 2 using Group A and as a comparative example, the firing temperature was set to 550 ° C., 600 ° C., and 800 ° C. when Group A was produced. First, the positive electrode active material capacity per mass was calculated at the time of cell preparation. The results are shown in Table 7.

焼成温度を８００℃としたものは、正極容量の劣化が著しいことが分かる。続いて、評価試験例２の手法で作製したフィルム外装型電池を用いて、作製直後の電池の初期厚さと、５５℃における充放電サイクル試験を１００サイクル行った後の電池の厚さを測定した。充電は３５０ｍＡで４．２Ｖまで、放電は７００ｍＡで３．０Ｖまで行った。その結果を表７に示す。比較例に比べ、焼成温度を６００℃としたものが、最も充放電サイクルによる電池外形膨れが抑制されていることが分かる。

It can be seen that when the firing temperature is 800 ° C., the cathode capacity is significantly deteriorated. Subsequently, using the film-clad battery produced by the method of Evaluation Test Example 2, the initial thickness of the battery immediately after production and the thickness of the battery after 100 charge / discharge cycle tests at 55 ° C. were measured. . Charging was performed at 350 mA up to 4.2 V, and discharging was performed at 700 mA up to 3.0 V. The results are shown in Table 7. Compared with the comparative example, it can be seen that when the firing temperature is 600 ° C., the expansion of the battery outer shape due to the charge / discharge cycle is most suppressed.

  In the above, this invention was demonstrated based on the Example. It is to be understood by those skilled in the art that this embodiment is merely an example, and that various modifications are possible and that such modifications are within the scope of the present invention.

It is a schematic diagram which shows one Embodiment of the film exterior type nonaqueous electrolyte secondary battery provided by this invention. It is sectional drawing which shows one Embodiment of the film exterior type nonaqueous electrolyte secondary battery provided by this invention. It is a graph showing the measurement result by the XRD measuring method of the positive electrode active material for secondary batteries provided by this invention. It is a photograph figure showing the measurement result by the EDX measuring method and SEM measuring method of the positive electrode active material for secondary batteries provided by this invention. It is a graph showing the measurement result by the XRD measuring method of the positive electrode active material for secondary batteries provided by this invention. It is a graph showing the measurement result by the XRD measuring method of the positive electrode active material for secondary batteries provided by this invention. It is a graph showing the measurement result by the XRD measuring method of the positive electrode active material for secondary batteries provided by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laminate film 2 Power generation element 3 Electrode lead 11 Heat-fusion resin film 12 Metal foil 13 Heat-resistant resin film 31 Positive electrode lead 32 Negative electrode lead

Claims (12)

  A positive electrode active material for a secondary battery, comprising: base particles containing lithium manganese composite oxide; and a lanthanoid element-containing compound attached to at least a part of the surface of the base particles.   2. The positive electrode active material for a secondary battery according to claim 1, wherein the lanthanoid element-containing compound is attached to at least a part of the surface of the base particle by firing. 3. .   3. The positive electrode active material for a secondary battery according to claim 1, wherein the lanthanoid element-containing compound has a structure in which the lanthanoid element-containing compound is distributed substantially uniformly on the surface of the substrate particles. 4.   4. The positive electrode active material for a secondary battery according to claim 1, wherein the lanthanoid element-containing compound includes a lanthanoid oxide and a lanthanoid manganese composite oxide composed of a composite oxide of a lanthanoid element and Mn. 5. A positive electrode active material for a secondary battery.   5. The secondary battery positive electrode active material according to claim 1, wherein the lanthanoid element is one or more elements selected from the group consisting of La, Nd, and Sm. Positive electrode active material.   A positive electrode for a secondary battery comprising the positive electrode active material for a secondary battery according to claim 1.   The positive electrode for a secondary battery according to claim 6, further comprising a hydrogen ion scavenger.   The positive electrode for a secondary battery according to claim 7, wherein the hydrogen ion scavenger is a lithium nickel composite oxide. The positive electrode for a secondary battery according to claim 8, wherein the content of the lithium manganese composite oxide in the positive electrode for the secondary battery is (100-a) parts by mass, and the lithium in the positive electrode for the secondary battery When the content of the nickel composite oxide is a part by mass,
3 <a ≦ 45
The positive electrode for secondary batteries characterized by satisfy | filling.   A power generation element and an exterior body that houses the power generation element, the power generation element including the positive electrode for a secondary battery according to any one of claims 6 to 9, an electrolyte, a separator, the electrolyte, and the separator. A secondary battery comprising a power generation element comprising the positive electrode for a secondary battery and a negative electrode disposed oppositely.   11. The secondary battery according to claim 10, wherein the outer package is a film-shaped outer package sealed with a sealing material. 12. The secondary battery according to claim 10, wherein the electrolyte is a non-aqueous electrolyte containing a supporting salt containing LiPF ₆ or LiBF ₄ and an organic solvent.

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