WO2015015894A1

WO2015015894A1 - Positive electrode for use in non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery using the same

Info

Publication number: WO2015015894A1
Application number: PCT/JP2014/064630
Authority: WO
Inventors: 智裕蕪木; 山本　伸司
Original assignee: 日産自動車株式会社
Priority date: 2013-07-31
Filing date: 2014-06-02
Publication date: 2015-02-05
Also published as: JP2016173875A

Abstract

The present invention provides a positive electrode for use in a non-aqueous electrolyte secondary battery capable of realizing high initial discharge capacity and capacity retention rate, and a non-aqueous electrolyte secondary battery using the same. This positive electrode for use in a non-aqueous electrolyte secondary battery contains a positive electrode active material and an auxiliary conduction agent. The positive electrode active material comprises a solid solution of transition metal oxide containing lithium, represented by the chemical formula: Li_1.5[Ni_aCo_bMn_c[Li]_d]O₃ (where Li represents lithium, Ni represents nickel, Co represents cobalt, Mn represents manganese and O represents oxygen; a, b, c and d satisfy the relationships: 0 < a < 1.4, 0 ≤ b < 1.4, 0 < c < 1.4, 0.1 < d ≤ 0.4, a + b + c + d = 1.5, and 1.1 ≤ a + b + c < 1.4). Then, the auxiliary conduction agent contains a carbon material, the BET specific surface area of the carbon material being 30 to 200 m²/g.

Description

Positive electrode for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery using the same

The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the same.

In recent years, in order to cope with air pollution and global warming, reduction of carbon dioxide emissions has been strongly desired. In the automobile industry, there are high expectations for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV). For this reason, electric devices such as secondary batteries for driving motors, which are the key to practical use, are being actively developed.

As a secondary battery for driving a motor, a lithium ion secondary battery having a high theoretical energy is attracting attention, and is currently being developed rapidly. Generally, a lithium ion secondary battery has a configuration in which a positive electrode, a negative electrode, and an electrolyte positioned therebetween are housed in a battery case. The positive electrode is formed by applying a positive electrode slurry containing a positive electrode active material to the surface of the current collector, and the negative electrode is formed by applying a negative electrode slurry containing a negative electrode active material to the surface of the negative electrode current collector.

And selection of each active material is extremely important for improving capacity characteristics and output characteristics of the lithium ion secondary battery.

Conventionally, a cathode composition for a lithium ion battery having the formula (a) Li _y [M ¹ _(1-b) Mn _b ] O ₂ or (b) Li _x [M ¹ _(1-b) Mn _b ] O _{1.5 + c} The thing is proposed (refer patent document 1). In the formula, 0 ≦ y <1, 0 <b <1, and 0 <c <0.5, and M ¹ represents one or more metal elements. However, in the case of (a), M ¹ is a metal element other than chromium. The composition has a single-phase form having an O3 crystal structure that does not cause a phase transition to a spinel crystal structure when a predetermined full charge / discharge cycle operation is performed.

JP-T-2004-538610

However, as a result of investigations by the present inventors, there was a problem that even a lithium ion battery using the cathode composition of Patent Document 1 could not realize a high discharge capacity and capacity retention rate. .

The present invention has been made in view of such problems of the conventional technology. And the objective is to provide the positive electrode for nonaqueous electrolyte secondary batteries which can implement | achieve a high discharge capacity and a capacity | capacitance maintenance factor, and a nonaqueous electrolyte secondary battery using the same.

The positive electrode for nonaqueous electrolyte secondary batteries according to an aspect of the present invention includes a positive electrode active material and a conductive additive. The positive electrode active material has the chemical formula:
Li _1.5 [Ni _a Co _b Mn _c [Li] _d ] O ₃ (1)
(In the formula, Li represents lithium, Ni represents nickel, Co represents cobalt, Mn represents manganese, O represents oxygen, and a, b, c and d are 0 <a <1.4 and 0 ≦ b <1.4. , 0 <c <1.4, 0.1 <d ≦ 0.4, a + b + c + d = 1.5, 1.1 ≦ a + b + c <1.4) Contains products. The conductive auxiliary agent contains a carbon material, and the carbon material has a BET specific surface area of 30 to 200 m ² / g.

FIG. 1 is a schematic cross-sectional view showing a lithium ion secondary battery according to an embodiment of the present invention. FIG. 2 is a graph illustrating the definition of the spinel structure change rate.

According to the present invention, by using the solid solution represented by the chemical formula (1) as the positive electrode active material, a high discharge capacity and capacity retention rate can be realized. Furthermore, when using the above solid solution, a positive electrode for a non-aqueous electrolyte secondary battery capable of exhibiting high rate characteristics by using a carbon material having a BET specific surface area of 30 to 200 m ² / g as a conductive auxiliary agent, and A non-aqueous electrolyte secondary battery using the same can be provided.

Hereinafter, the positive electrode for a nonaqueous electrolyte secondary battery and the nonaqueous electrolyte secondary battery of the present invention will be described in detail, but the present invention is not limited to the following embodiments. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from actual ratios.

A positive electrode for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention includes a lithium-containing transition metal oxide (hereinafter, lithium-containing transition metal oxide) having a solid solution form represented by the above chemical formula (1) in a positive electrode active material layer. Is also simply referred to as “transition metal oxide”). By using the lithium-containing transition metal oxide as a positive electrode active material in a nonaqueous electrolyte secondary battery, a high initial discharge capacity and capacity retention rate can be realized. In this specification, among lithium-containing transition metal oxides having a predetermined composition, those having a solid solution form are particularly “solid solution lithium-containing transition metal oxides”, or simply “solid solution transition metal oxides” or “solid solutions”. Is also referred to.

On the other hand, according to the study by the present inventors, the solid solution represented by the chemical formula (1) has a characteristic that the reaction resistance as an active material is larger than that of a conventional lithium-containing transition metal oxide. There was found. When the reaction resistance of the active material is high, sufficient capacity cannot be taken out (ie, high rate characteristics are not sufficient) under the high output conditions required for motor-driven secondary batteries such as EV and HEV A new problem can arise. Accordingly, it has been required to provide means capable of exhibiting sufficiently high rate characteristics when the solid solution represented by the chemical formula (1) is used as the positive electrode active material.

The present inventors have intensively studied on this new problem. As a result, when the solid solution represented by the above chemical formula (1) is used as the positive electrode active material, the problem can be solved by using a carbon material having a BET specific surface area of 30 to 200 m ² / g as a conductive auxiliary. The inventors have found that the present invention can be solved, and have completed the above-described present invention. According to the present invention, in addition to high initial discharge capacity and capacity retention rate, it is possible to realize high rate characteristics even under high output conditions. Hereinafter, the positive electrode for a non-aqueous electrolyte secondary battery and the non-aqueous electrolyte secondary battery according to the present invention will be described taking the positive electrode for a lithium ion secondary battery and the lithium ion secondary battery as examples.

<Lithium ion secondary battery>
FIG. 1 shows an example of a lithium ion secondary battery according to an embodiment of the present invention. Such a lithium ion secondary battery is called a laminated lithium ion secondary battery.

As shown in FIG. 1, the lithium ion secondary battery 1 of the present embodiment has a configuration in which a battery element 10 to which a positive electrode lead 21 and a negative electrode lead 22 are attached is enclosed in an exterior body 30 formed of a laminate film. have. In the present embodiment, the positive electrode lead 21 and the negative electrode lead 22 are led out in the opposite direction from the inside of the exterior body 30 to the outside. Although not shown, the positive electrode lead and the negative electrode lead may be led out in the same direction from the inside of the exterior body toward the outside. Moreover, such a positive electrode lead and a negative electrode lead can be attached to a positive electrode current collector and a negative electrode current collector described later by, for example, ultrasonic welding or resistance welding.

<Positive electrode lead and negative electrode lead>
The positive electrode lead 21 and the negative electrode lead 22 are made of, for example, a metal material such as aluminum (Al), copper (Cu), titanium (Ti), nickel (Ni), alloys thereof, and stainless steel (SUS). However, the material is not limited thereto, and a conventionally known material used as a lead for a lithium ion secondary battery can be used. The positive electrode lead and the negative electrode lead may be made of the same material or different materials.

Further, as in the present embodiment, a separately prepared lead may be connected to a positive electrode current collector and a negative electrode current collector described later, and each positive electrode current collector and each negative electrode current collector described later are extended. The lead may be formed by this. Although not shown, the positive lead and the negative lead taken out from the exterior body do not affect products (for example, automobile parts, especially electronic devices) by contacting with peripheral devices or wiring and causing electric leakage. Thus, it is preferable to coat with a heat-resistant insulating heat-shrinkable tube or the like.

Although not shown, a current collecting plate may be used for the purpose of taking out current outside the battery. The current collector plate is electrically connected to a current collector or a lead, and is taken out of a laminate film that is an exterior material of the battery. The material which comprises a current collector plate is not specifically limited, The well-known highly electroconductive material conventionally used as a current collector plate for lithium ion secondary batteries can be used. As a constituent material of the current collector plate, for example, metal materials such as aluminum (Al), copper (Cu), titanium (Ti), nickel (Ni), alloys thereof, and stainless steel (SUS) are preferable, and light weight and corrosion resistance. From the viewpoint of high conductivity, aluminum (Al), copper (Cu), and the like are more preferable. Note that the same material may be used for the positive electrode current collector plate and the negative electrode current collector plate, or different materials may be used.

<Exterior body>
For example, the exterior body 30 is preferably formed of a film-shaped exterior material from the viewpoint of size reduction and weight reduction. However, an exterior body is not limited to this, The conventionally well-known material used for the exterior body for lithium ion secondary batteries can be used. That is, a metal can case can also be applied.

From the viewpoint of high output and cooling performance, and suitable for use in large equipment batteries of electric vehicles and hybrid electric vehicles, the exterior body has a polymer-metal composite with excellent thermal conductivity. A laminate film can be mentioned. More specifically, an exterior body formed of a three-layer laminate film in which polypropylene as a thermocompression bonding layer, aluminum as a metal layer, and nylon as an external protective layer are laminated in this order is preferably used. it can.

Note that the exterior body may be constituted by another structure, for example, a laminate film having no metal material, a polymer film such as polypropylene, or a metal film, instead of the above-described laminate film.

Here, the general structure of the exterior body can be represented by a laminated structure of an external protective layer / metal layer / thermocompression bonding layer. However, the external protective layer and the thermocompression bonding layer may be composed of a plurality of layers. It is sufficient that the metal layer functions as a moisture-permeable barrier film, and not only aluminum foil but also stainless steel foil, nickel foil, plated iron foil, and the like can be used. However, as the metal layer, an aluminum foil that is thin and lightweight and excellent in workability can be suitably used.

The structures that can be used as the exterior body are listed in the form of (external protective layer / metal layer / thermocompression layer). Polyethylene terephthalate / nylon / aluminum / non-stretched polypropylene, polyethylene terephthalate / nylon / aluminum / nylon / non-stretched polypropylene, polyethylene terephthalate / nylon / aluminum / nylon / polyethylene, nylon / polyethylene / aluminum / linear Low density polyethylene, polyethylene terephthalate, polyethylene / aluminum / polyethylene terephthalate Low density polyethylene, and a polyethylene terephthalate, nylon / aluminum / low-density polyethylene cast polypropylene.

<Battery element>
As shown in FIG. 1, the battery element 10 includes both a positive electrode 11 having a positive electrode active material layer 11B formed on both main surfaces of the positive electrode current collector 11A, an electrolyte layer 13, and a negative electrode current collector 12A. A plurality of negative electrodes 12 each having a negative electrode active material layer 12 </ b> B formed on the main surface are stacked. At this time, the positive electrode active material layer 11B formed on one main surface of the positive electrode current collector 11A in one positive electrode 11 and the one main surface of the negative electrode current collector 12A in the negative electrode 12 adjacent to the one positive electrode 11 The negative electrode active material layer 12 </ b> B formed on the surface of the substrate faces the electrolyte layer 13. In this way, a plurality of layers are laminated in the order of the positive electrode, the electrolyte layer, and the negative electrode.

Thus, the adjacent positive electrode active material layer 11B, electrolyte layer 13 and negative electrode active material layer 12B constitute one unit cell layer 14. Therefore, the lithium ion secondary battery 1 according to the present embodiment has a configuration in which a plurality of single battery layers 14 are stacked and electrically connected in parallel. In addition, the positive electrode and the negative electrode may have each active material layer formed only on one main surface of each current collector. In the present embodiment, for example, the negative electrode current collector 12a located in the outermost layer of the battery element 10 has the negative electrode active material layer 12B formed only on one side.

Although not shown, an insulating layer for insulating between the adjacent positive electrode current collector and negative electrode current collector may be provided on the outer periphery of the unit cell layer. Such an insulating layer is preferably formed of a material that holds the electrolyte contained in the electrolyte layer and the like and prevents electrolyte leakage from the outer periphery of the unit cell layer. Specifically, general-purpose plastics such as polypropylene (PP), polyethylene (PE), polyurethane (PUR), polyamide resin (PA), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polystyrene (PS), etc. Or thermoplastic olefin rubber can be used. Silicone rubber can also be used.

<Positive electrode current collector and negative electrode current collector>
The positive electrode current collector 11A and the negative electrode current collector 12A are made of a conductive material. The size of the current collector can be determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used. There is no particular limitation on the thickness of the current collector. The thickness of the current collector is usually about 1 to 100 μm. The shape of the current collector is not particularly limited. In the battery element 10 shown in FIG. 1, in addition to the current collector foil, a mesh shape (such as an expanded grid) can be used. In addition, when forming the thin film alloy which is an example of a negative electrode active material directly on the negative electrode collector 12A by sputtering method etc., it is desirable to use a current collection foil.

There are no particular restrictions on the materials that make up the current collector. For example, a metal or a resin in which a conductive filler is added to a conductive polymer material or a non-conductive polymer material can be employed. Specifically, examples of the metal include aluminum (Al), nickel (Ni), iron (Fe), stainless steel (SUS), titanium (Ti), copper (Cu), and the like. In addition to these, it is preferable to use a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material combining these metals. Moreover, the foil by which the metal surface was coat | covered with aluminum may be sufficient. Among these, aluminum, stainless steel, copper, and nickel are preferable from the viewpoints of electronic conductivity, battery operating potential, and the like.

Examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Since such a conductive polymer material has sufficient conductivity without adding a conductive filler, it is advantageous in terms of facilitating the manufacturing process or reducing the weight of the current collector.

Non-conductive polymer materials include, for example, polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polystyrene (PS), and the like. Such a non-conductive polymer material has excellent potential resistance or solvent resistance.

A conductive filler can be added to the conductive polymer material or non-conductive polymer material as necessary. In particular, when the resin used as the base material of the current collector is made of only a non-conductive polymer, a conductive filler is inevitably necessary to impart conductivity to the resin. The conductive filler can be used without particular limitation as long as it is a substance having conductivity. For example, a metal, conductive carbon, etc. are mentioned as a material excellent in electroconductivity, electric potential resistance, or lithium ion interruption | blocking property.

Examples of the metal used as the conductive filler include nickel (Ni), titanium (Ti), aluminum (Al), copper (Cu), platinum (Pt), iron (Fe), chromium (Cr), tin (Sn), Mention may be made of at least one metal selected from the group consisting of zinc (Zn), indium (In), antimony (Sb) and potassium (K). Further, alloys or metal oxides containing these metals can also be mentioned as suitable examples.

Examples of the conductive carbon include at least one selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. it can. The amount of the conductive filler added is not particularly limited as long as it is an amount capable of imparting sufficient conductivity to the current collector, and is generally about 5 to 35% by mass. However, the material is not limited to these, and a conventionally known material used as a current collector for a lithium ion secondary battery can be used.

<Positive electrode active material layer>
The positive electrode active material layer 11B essentially includes a predetermined solid solution lithium-containing transition metal oxide and a conductive additive as a positive electrode active material. And other additives, such as a binder, may be included as needed.

The positive electrode active material layer according to this embodiment contains a lithium-containing transition metal oxide represented by the following chemical formula (1) as a positive electrode active material.

Li _1.5 [Ni _a Co _b Mn _c [Li] _d ] O ₃ (1)
In the formula, Li represents lithium, Ni represents nickel, Co represents cobalt, Mn represents manganese, and O represents oxygen. A, b, c, and d are 0 <a <1.4, 0 ≦ b <1.4, 0 <c <1.4, 0.1 <d ≦ 0.4, a + b + c + d = 1.5. 1.1 ≦ a + b + c <1.4 is satisfied.

The lithium-containing transition metal oxide has a layered structure portion and a portion (a layered structure Li ₂ MnO ₃ ) that changes to a spinel structure by charging or charging / discharging in a predetermined potential range.

Furthermore, Li ₂ MnO ₃ having a layered structure in the lithium-containing transition metal oxide is changed to LiMn ₂ O ₄ having a spinel structure. When the ratio when the layered structure Li ₂ MnO ₃ is all changed to the spinel structure LiMn ₂ O ₄ is 1, the spinel structure change ratio of the lithium-containing transition metal oxide is 0.25 or more and 1.0. It is preferable that it is less than.

When such a solid solution lithium-containing transition metal oxide is used as a positive electrode active material of a lithium ion secondary battery, it can realize a high discharge capacity and capacity retention rate. It is suitably used for secondary batteries. As a result, it can be suitably used as a lithium-ion secondary battery for vehicle drive power or auxiliary power. In addition to this, the present invention can be sufficiently applied to lithium ion secondary batteries for home use and portable devices.

In the lithium-containing transition metal oxide according to the present embodiment, in the chemical formula (1), a, b, c, and d are 0 <a <1.4, 0 ≦ b <1.4, 0 <c <1.4, It is necessary to satisfy the relationship of 0.1 <d ≦ 0.4, a + b + c + d = 1.5, 1.1 ≦ a + b + c <1.4. If this mathematical formula is not satisfied, the crystal structure of the lithium-containing transition metal oxide may not be stabilized.

Here, in the present specification, the “spinel structure change ratio” means that when charging or charging / discharging in a predetermined potential range is performed, Li ₂ MnO ₃ having a layered structure in the lithium-containing transition metal oxide is LiMn having a spinel structure. _The ratio of change to ₂ O ₄ is specified. That is, the lithium-containing transition metal oxide in this embodiment includes a layered structure Li ₂ MnO ₃ that changes to a spinel structure by charging or charging / discharging in a predetermined potential range, and a layered structure part (LiMO that does not change to a spinel structure). ₂ ). The spinel structure change ratio when the Li ₂ MnO ₃ having a layered structure in the lithium-containing transition metal oxide is all changed to LiMn ₂ O ₄ having a spinel structure is set to 1. The “predetermined potential range” can be set to 4.3 to 4.8 V, for example. Specifically, the spinel structure change ratio is defined by the following mathematical formula 1.

The definition of “spinel structure change ratio” will be described by taking the case shown in FIG. 2 as an example. FIG. 2 is a graph showing the relationship between potential and capacity for a battery assembled using a positive electrode using a lithium-containing transition metal oxide as a positive electrode active material. A state in which the battery is charged from an initial state A before starting charging to 4.5 V is referred to as a charged state B. Further, a state in which the state is charged from the state of charge B to 4.8 V through the plateau region is referred to as an overcharge state C, and a state of being discharged to 2.0 V is referred to as a discharge state D. The “measured capacity of the plateau region” in Equation 1 above may be the measured capacity of the lithium-containing transition metal oxide in the plateau region of FIG. The plateau region is specifically a region from 4.5 V to 4.8 V, and is a region resulting from a change in crystal structure. Therefore, the measured capacity V _BC of the battery in the region BC from the charged state B to the overcharged state C corresponds to the measured capacity in the plateau region.

Actually, in the transition metal oxide of the chemical formula (1), the measured capacity V _{AB in} the region AB from the initial state A to the charged state B charged to 4.5 V is LiMO _{2 having a} layered structure that does not change to the spinel structure. This corresponds to the product of the composition ratio (y) of LiMO _{2 and} the theoretical capacity (V _L ) of LiMO ₂ . The measured capacity V _{BC in} the region BC in the overcharged state C charged from the charged state B charged to 4.5 V to the 4.8 V is expressed by the composition ratio (x) of Li ₂ MnO ₃ that is the spinel structure part. This corresponds to the product of the theoretical capacity (V _S ) of Li ₂ MnO ₃ . Therefore, when the measured capacity (V _T ) measured from the initial state A to a predetermined plateau region is (V _T = V _AB + V _BC ), V _AB = y × (V _L ), V _BC = xx × (V _{Since S 1} ) × K, the spinel structure change ratio can also be calculated using Equation 2 below. Note that M in the above-described chemical formula LiMO ₂ represents at least one selected from the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn).

The “composition ratio of Li ₂ MnO _{3 in} the lithium-containing transition metal oxide” can be calculated from the chemical formula (1) of the lithium-containing transition metal oxide. Specifically, the positive electrode active material 7 (Li _1.5 [Ni _0.2 Co _0.2 Mn _0.8 [Li] _0.3 ] O ₃ (a + b + c + d = 1.5) described later in Example 1-7. , D = 0.3, a + b + c = 1.2)), the composition ratio of Li ₂ MnO ₃ is 0.6 according to the chemical formula (1). The composition ratio of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (= Li _1.5 Ni _0.5 Mn _0.5 Co _0.5 O ₃ ) is 0.4.

In the lithium-containing transition metal oxide, the presence or absence of a lamellar structure site (LiMO ₂ ) and a spinel structure site (Li ₂ MnO ₃ ) that do not change to a spinel structure is specific to the lamellar structure site and spinel structure by X-ray diffraction analysis (XRD). It can be determined by the presence of a simple peak. Further, the ratio of the layered structure part and the spinel structure part can be determined from the measurement / calculation of the capacity as described above.

In the lithium-containing transition metal oxide, the spinel structure change ratio does not become 1.0. That is, the Li ₂ MnO ₃ having a layered structure in the lithium-containing transition metal oxide is not completely changed to LiMn ₂ O ₄ having a spinel structure. Further, when the spinel structure change ratio is less than 0.25, only a solid solution lithium-containing transition metal oxide capable of realizing a discharge capacity and a capacity retention rate similar to those of the conventional one can be obtained.

In the present specification, “charging” refers to an operation of increasing the potential difference between the electrodes continuously or stepwise. In addition, “charging / discharging” refers to an operation of decreasing a potential difference between electrodes continuously or stepwise, or an operation of repeating this appropriately, after an operation of increasing the potential difference between electrodes continuously or stepwise. Say.

In the chemical formula (1), a, b, c and d are 0 <a <1.35, 0 ≦ b <1.35, 0 <c <1.35, 0.15 <d ≦ 0.35, a + b + c + d = 1.5, 1.15 ≦ a + b + c <1.35 is preferably satisfied. Furthermore, when charge or charge / discharge in a predetermined potential range is performed, it is preferable that the spinel structure change ratio of the lithium-containing transition metal oxide is 0.4 or more and less than 0.9. When such a solid solution lithium-containing transition metal oxide is used for the positive electrode active material, higher discharge capacity and capacity retention rate can be obtained.

Furthermore, in the chemical formula (1), a, b, c and d are 0 <a <1.3, 0 ≦ b <1.3, 0 <c <1.3, 0.15 <d ≦ 0.35. A + b + c + d = 1.5 and 1.2 ≦ a + b + c <1.3 are more preferable. In addition, when charging or charging / discharging in a predetermined potential range is performed, it is more preferable that the spinel structure change ratio of the lithium-containing transition metal oxide is 0.6 or more and 0.8 or less. Such a solid solution lithium-containing transition metal oxide can achieve higher discharge capacity and capacity retention when used as a positive electrode active material of a lithium ion secondary battery. It is suitably used for a secondary battery.

Another preferable embodiment of the lithium-containing transition metal oxide has a BET specific surface area of 1 m ² / g or more and 8.0 m ² / g or less. Hereinafter, the preferable form is referred to as a second form. When the BET specific surface area is in this range, the lithium ion diffusibility in the lithium-containing transition metal oxide is improved, and the discharge capacity can be improved in charge / discharge at a high rate. The BET specific surface area of the lithium-containing transition metal oxide can be measured based on Japanese Industrial Standard JIS Z8830.

In the second embodiment, the pore volume measured with nitrogen in the lithium-containing transition metal oxide is 0.025 cm ³ / g or less when the relative pressure is 0.98 to 0.99. When the pore volume is 0.025 cm ³ / g or less, it is possible to obtain a solid solution lithium-containing transition metal oxide capable of realizing a higher discharge capacity and capacity retention than conventional ones. The pore volume can be measured based on Japanese Industrial Standard JIS Z8831-2.

In the second embodiment, the lithium-containing transition metal oxide preferably has a 50% passing particle diameter (median diameter, D50) of less than 15 μm. Further, the lithium-containing transition metal oxide preferably has particles having a particle size of less than 1 μm. By using the lithium-containing transition metal oxide having such a particle size, the porosity of the positive electrode active material layer can be easily controlled, and the permeability of the non-aqueous electrolyte can be improved. And since the permeability of the nonaqueous electrolytic solution is improved, the direct current resistance of the positive electrode active material layer can be reduced. The 50% passing particle size can be determined from the particle size distribution measured by the dynamic light scattering method.

In the second embodiment, the lithium-containing transition metal oxide preferably has an N-methyl-2-pyrrolidone liquid absorption of 0.5 cm ³ / g or less. When the lithium-containing transition metal oxide has a BET specific surface area of 1 m ² / g or more and 8.0 m ² / g or less and a pore volume of 0.025 cm ³ / g or less, N-methyl-2- The liquid absorption amount of pyrrolidone tends to be 0.5 cm ³ / g or less. In this case, since the permeability of the nonaqueous electrolytic solution and the lithium ion diffusibility in the lithium-containing transition metal oxide are improved, the discharge capacity and the capacity retention rate can be further improved.

In the second embodiment, the lithium-containing transition metal oxide preferably has a true density of 4.1 g / cm ³ or more and 4.6 g / cm ³ or less. When the true density is 4.1 g / cm ³ or more, the weight (filling amount) per unit volume of the lithium-containing transition metal oxide is increased, and the discharge capacity can be improved. In addition, when the true density is 4.6 g / cm ³ or less, the amount of voids in the positive electrode active material layer increases, and the permeability of the non-aqueous electrolyte and the lithium ion diffusibility can be improved. The true density can be determined by a liquid phase replacement method (pycnometer method).

Furthermore, according to another preferable embodiment of the lithium-containing transition metal oxide, the BET specific surface area is 1 m ² / g or more and 9 m ² / g or less. Hereinafter, the preferable form which concerns on the said lithium containing transition metal oxide is called a 3rd form. When the BET specific surface area is within this range, the lithium ion diffusibility in the lithium-containing transition metal oxide is improved, and a high discharge capacity can be obtained. The BET specific surface area can be measured based on Japanese Industrial Standard JIS Z8830 as in the second embodiment.

Among the third forms, in the chemical formula (1), a, b, c and d are 0 <a <1.35, 0 ≦ b <1.35, 0 <c <1.35, 0.15. <D ≦ 0.35, a + b + c + d = 1.5, 1.15 ≦ a + b + c <1.35 are preferably satisfied. Furthermore, when charging or charging / discharging in a predetermined potential range is performed, the spinel structure change ratio of the lithium-containing transition metal oxide is preferably 0.4 or more and less than 0.9. In addition, the BET specific surface area of the lithium-containing transition metal oxide is preferably ² m ² / g or more and 8 m ² / g or less.

Further, in the third form, in the chemical formula (1), a, b, c and d are 0 <a <1.3, 0 ≦ b <1.3, 0 <c <1.3, 0. It is preferable that 15 <d ≦ 0.35, a + b + c + d = 1.5, and 1.2 ≦ a + b + c <1.3 are satisfied. Moreover, it is more preferable that the spinel structure change ratio of the lithium-containing transition metal oxide is 0.6 or more and 0.8 or less. In addition, the BET specific surface area of the lithium-containing transition metal oxide is more preferably 3 m ² / g or more and 6 m ² / g or less. Such a lithium-containing transition metal oxide can realize a higher discharge capacity and capacity retention when used as a positive electrode active material of a lithium ion secondary battery. The secondary battery is preferably used.

Furthermore, according to another preferable embodiment of the lithium-containing transition metal oxide, the lithium-containing transition metal oxide contains the first lithium-containing transition metal oxide and the second lithium-containing transition metal oxide represented by the chemical formula (1). Then, BET specific surface area of the first transition metal oxide containing lithium is not more than 1.0 m ² / g or more 4.0m ² / g, BET specific surface area of the second lithium-containing transition metal oxide is 4.0 m ² / More than g and not more than 8.0 m ² / g. Hereinafter, the preferable form which concerns on the said lithium containing transition metal oxide is called a 4th form. Thus, by containing two types of lithium-containing transition metal oxides having different BET specific surface areas, the lithium ion diffusibility in the solid solution lithium-containing transition metal oxide is improved, and in charge / discharge at a high rate, the discharge capacity Can be increased. This is because the first lithium-containing transition metal oxide is effective for improving the discharge capacity, and the second lithium-containing transition metal oxide is effective for improving the rate characteristics.

In the fourth embodiment, the first lithium-containing transition metal oxide and the second lithium-containing transition metal oxide may have the same composition or different compositions. That is, the solid solution lithium-containing transition metal oxide of this embodiment contains at least two types of lithium-containing transition metal oxides having different BET specific surface areas.

Such a solid solution lithium-containing transition metal oxide, when used as a positive electrode active material of a lithium ion secondary battery, has a high discharge capacity and capacity maintenance rate in charge and discharge at a high rate such as 1.0 C and 2.5 C. Can be realized. Therefore, it is suitably used for a positive electrode for lithium ion secondary batteries and a lithium ion secondary battery. As a result, it can be suitably used as a lithium-ion secondary battery for vehicle drive power or auxiliary power. In addition to this, the present invention can be sufficiently applied to lithium ion secondary batteries for home use and portable devices.

In the fourth form, in the chemical formula (1), a, b, c and d are 0 <a <1.35, 0 ≦ b <1.35, 0 <c <1.35, 0. It is preferable that the following relationships are satisfied: 15 <d ≦ 0.35, a + b + c + d = 1.5, 1.15 ≦ a + b + c <1.35. Furthermore, when charging or charging / discharging in a predetermined potential range is performed, the spinel structure change ratio of the first and second lithium-containing transition metal oxides is preferably 0.4 or more and less than 0.9. .

Further, in the fourth form, in the chemical formula (1), a, b, c and d are 0 <a <1.3, 0 ≦ b <1.3, 0 <c <1.3, 0. It is preferable that 15 <d ≦ 0.35, a + b + c + d = 1.5, and 1.2 ≦ a + b + c <1.3 are satisfied. Moreover, it is more preferable that the spinel structure change ratio of the first and second lithium-containing transition metal oxides is 0.6 or more and 0.8 or less.

In the fourth embodiment, the solid solution lithium-containing transition metal oxide has a pore volume measured with nitrogen of 0.025 cm ³ / g or less when the relative pressure is 0.98 to 0.99. It is preferred to contain first and second lithium-containing transition metal oxides. When the pore volume is 0.025 cm ³ / g or less, it is possible to obtain a solid solution lithium-containing transition metal oxide capable of realizing a higher discharge capacity and capacity retention than conventional ones. The pore volume can be measured based on Japanese Industrial Standard JIS Z8831-2, as in the second embodiment.

Furthermore, in the fourth embodiment, the first lithium-containing transition metal oxide has a 50% passing particle size (median diameter, D50) of less than 15 μm, and the second lithium-containing transition metal oxide has a 50% passing particle size. Is preferably less than 10 μm. Furthermore, it is preferable that the solid solution lithium-containing transition metal oxide includes particles having a particle size of less than 1 μm. That is, at least one of the first and second lithium-containing transition metal oxides preferably includes particles having a particle size of less than 1 μm. By using the lithium-containing transition metal oxide having such a particle size, the porosity of the positive electrode active material layer can be easily controlled, and the permeability of the non-aqueous electrolyte can be improved. And since the permeability of the nonaqueous electrolytic solution is improved, the direct current resistance of the positive electrode active material layer can be reduced. The 50% passing particle diameter can be determined from the particle size distribution measured by the dynamic light scattering method, as in the second embodiment.

In the fourth embodiment, the first lithium-containing transition metal oxide and the second lithium-containing transition metal oxide have an N-methyl-2-pyrrolidone liquid absorption of 0.5 cm ³ / g or less. Is preferred. In this case, since the permeability of the nonaqueous electrolytic solution and the lithium ion diffusibility in the lithium-containing transition metal oxide are improved, the discharge capacity and the capacity retention rate can be further improved.

Furthermore, in the fourth embodiment, the true density of the first lithium-containing transition metal oxide and the second lithium-containing transition metal oxide is preferably 4.1 g / cm ³ or more and 4.6 g / cm ³ or less. It is. When the true density is 4.1 g / cm ³ or more, the weight (filling amount) per unit volume of the lithium-containing transition metal oxide is increased, and the discharge capacity can be improved. In addition, when the true density is 4.6 g / cm ³ or less, the amount of voids in the positive electrode active material layer increases, and the permeability of the non-aqueous electrolyte and the lithium ion diffusibility can be improved. The true density can be obtained by a liquid phase replacement method (pycnometer method) as in the second embodiment.

In this embodiment, as long as the positive electrode active material includes the solid solution represented by the chemical formula (1), other conventionally known positive electrode active material materials may be used in combination. However, in order to realize a high initial discharge capacity and capacity retention rate, the content ratio of the solid solution in the positive electrode active material is preferably 80% by mass or more, more preferably 90% by mass, and 95% by mass. % Or more, more preferably 98% by mass or more, and most preferably 100% by mass.

Next, a method for producing a solid solution lithium-containing transition metal oxide (lithium-containing transition metal oxide) according to this embodiment will be described.

First, as a precursor of a lithium-containing transition metal oxide, raw materials containing lithium compounds such as sulfates and nitrates, nickel compounds, cobalt compounds and manganese compounds are mixed to prepare a mixture. At this time, in the method for producing a solid solution lithium-containing transition metal oxide having a predetermined BET specific surface area in the second to fourth embodiments, the crystallite size of the mixture is preferably 10 nm or more and 100 nm or less. Next, the obtained mixture is calcined at 800 to 1000 ° C. for 6 to 24 hours in an inert gas atmosphere. Thereby, a lithium containing transition metal oxide can be prepared. Note that nitrogen or argon is preferably used as the inert gas.

As another manufacturing method, first, as a precursor of a lithium-containing transition metal oxide, raw materials containing lithium compounds such as sulfates and nitrates, nickel compounds, cobalt compounds, and manganese compounds are mixed to prepare a mixture. . At this time, in the method for producing a solid solution lithium-containing transition metal oxide having a predetermined BET specific surface area in the second to fourth embodiments, the crystallite size of the mixture is preferably 10 nm or more and 100 nm or less. Next, the obtained mixture is baked at 800 to 1000 ° C. for 6 to 24 hours to obtain a baked product. Thereafter, the fired product obtained is heat-treated at 600 to 800 ° C. in an inert gas atmosphere. Thereby, a lithium containing transition metal oxide can be prepared.

In order to obtain a desired spinel structure change ratio, the following treatment is preferably performed. Although details will be described later, in the lithium ion secondary battery using the solid solution lithium-containing transition metal oxide as a positive electrode, the maximum potential of the positive electrode in a predetermined potential range is 4.3 V or more in terms of a lithium metal counter electrode. Charging or charging / discharging which is less than 8V is performed (electrochemical pretreatment). Thereby, the solid solution lithium containing transition metal oxide whose spinel structure change ratio is 0.25 or more and less than 1.0 can be obtained.

The method for producing the solid solution lithium-containing transition metal oxide according to this embodiment will be described in more detail.

A carbonate method (composite carbonate method) can be applied to the method for producing the precursor of the lithium-containing transition metal oxide. Specifically, first, nickel, cobalt, manganese sulfates, nitrates, and the like are prepared as starting materials. After weighing a predetermined amount of these, a mixed aqueous solution is prepared.

Next, aqueous ammonia is added dropwise to the mixed aqueous solution until pH 7 is reached, and an aqueous sodium carbonate (Na ₂ CO ₃ ) solution is further added dropwise to precipitate Ni—Co—Mn complex carbonate. Incidentally, while dropping the aqueous solution of Na ₂ CO ₃ is the pH of the mixed aqueous solution kept at 7 with aqueous ammonia.

Then, the precipitated composite carbonate is suction filtered, washed with water, dried, and pre-baked. The drying conditions may be drying in an inert gas atmosphere at 100 to 150 ° C. for about 2 to 10 hours (eg, 120 ° C. for 5 hours), but are not limited to this range. Pre-baking conditions may be pre-baking in an inert gas atmosphere at 360 to 600 ° C. for 3 to 10 hours (for example, 500 ° C. for 5 hours), but are not limited to this range.

Further, a small excess of lithium hydroxide (LiOH.H ₂ O) is added to the temporarily fired powder and mixed. At this time, in the method for producing a solid solution lithium-containing transition metal oxide having a predetermined BET specific surface area in the second to fourth embodiments, the crystallite size of the mixture is preferably 10 nm or more and 100 nm or less. Then, the precursor of a lithium containing transition metal oxide can be produced by carrying out this baking. As the main firing condition, for example, it may be performed in an inert gas atmosphere at 800 to 1000 ° C. (for example, 800 to 900 ° C.) for about 6 to 24 hours (for example, 12 hours). Preferably, after the main calcination, rapid cooling is performed using liquid nitrogen. This is because quenching with liquid nitrogen or the like after the main baking is preferable for reactivity and cycle stability.

And the solid solution lithium containing transition metal oxide which concerns on this form can be obtained by oxidizing the said precursor. Examples of the oxidation treatment include (1) charging or charging / discharging in a predetermined potential range (electrochemical pretreatment, charge / discharge pretreatment), (2) oxidation with an oxidizing agent corresponding to charging, and (3) redox mediator. Oxidation using can be mentioned. Here, (1) charging or charging / discharging in a predetermined potential range is specifically charging or charging / discharging from a low potential region that does not cause a significant change in the crystal structure of the lithium-containing transition metal oxide from the beginning. Say. Moreover, (2) As an oxidizing agent corresponding to charge, halogens, such as a bromine and chlorine, can be mentioned, for example.

Here, a relatively simple method among the oxidation treatments (1) to (3) is the oxidation treatment method (1). Then, as the oxidation treatment of (1), after making a battery using the lithium-containing transition metal oxide precursor obtained as described above, charging or charging is performed so as not to exceed a predetermined maximum potential. Charging / discharging, that is, electrochemical pretreatment with regulated potential is effective. In addition, after creating a positive electrode or a structure corresponding to the positive electrode using the lithium-containing transition metal oxide precursor obtained as described above, charging or charging / discharging is performed so as not to exceed a predetermined maximum potential. You may go. Thereby, the positive electrode active material which implement | achieved high discharge capacity and a capacity | capacitance maintenance factor can be obtained.

As the electrochemical pretreatment method in which the potential is regulated, the maximum potential in the predetermined potential range with respect to lithium metal as a counter electrode (the upper limit potential of charge / discharge converted to lithium metal) is 4.3 V or more and 4.8 V or less. Therefore, it is desirable to perform charging and discharging for 1 to 30 cycles. More preferably, it is desirable to perform charging and discharging for 1 to 30 cycles under the condition of 4.4 V or more and 4.6 V or less. By performing the oxidation treatment by charging / discharging within this potential range, a high discharge capacity and capacity retention rate can be realized. Note that the potential converted to the lithium metal corresponds to a potential based on the potential exhibited by the lithium metal in the electrolytic solution in which 1 mol / L of lithium ions are dissolved.

In addition, it is desirable to further increase the maximum potential in the predetermined potential range in charge and discharge stepwise after 1 to 30 cycles of charging and discharging in the predetermined potential range with respect to the lithium metal as the counter electrode. In particular, 4.7V, 4.8Vvs. In the case of using up to a high potential capacity of Li, the durability of the electrode can be improved even in a short time oxidation treatment by gradually increasing the maximum potential of the charge / discharge potential in the oxidation treatment.

When increasing the maximum potential (upper limit potential) for charging / discharging step by step, the number of cycles required for charging / discharging at each step is effectively in the range of 1 to 10 times. In addition, the total number of charge / discharge cycles when increasing the maximum potential of charge / discharge stepwise, that is, the total number of cycles required for charge / discharge of each step is effectively in the range of 4 to 20 times. It is.

Also. When raising the maximum potential of charging / discharging step by step, 0.05 to 0.1V is effective as a potential increase range (raising allowance) at each step.

Furthermore, when raising the maximum potential of charge / discharge stepwise, it is effective that the final maximum potential (end maximum potential) is 4.6V to 4.9V. However, the pretreatment is not limited to the above range, and the electrochemical pretreatment may be performed up to a higher terminal maximum potential as long as the above effects can be achieved.

The minimum potential in a predetermined potential range in charge / discharge is 2 V or more and less than 3.5 V, more preferably 2 V or more and less than 3 V with respect to lithium metal as a counter electrode. By performing oxidation treatment by charging or charging / discharging within the above range, a high discharge capacity and capacity retention rate can be realized. The charge / discharge potential (V) refers to a potential per unit cell.

The temperature of the electrode that is charged and discharged as the oxidation treatment can be arbitrarily set as long as it does not impair the effects of the present invention. From the viewpoint of economy, it is desirable to carry out at room temperature (25 ° C.) that does not require special heating and cooling. On the other hand, it is desirable to carry out at a temperature higher than room temperature from the viewpoint that a larger capacity can be expressed and the capacity retention rate is improved by a short charge / discharge treatment.

The step of applying the oxidation treatment (electrochemical pretreatment) is not particularly limited. For example, such an oxidation treatment can be performed in a state in which a battery is configured or a configuration corresponding to a positive electrode or a positive electrode as described above. That is, any of application in the state of positive electrode active material powder, application in the state of positive electrode, and application after assembling a battery together with the negative electrode may be used. In application to a battery, it is preferable to determine the oxidation treatment conditions in consideration of the potential profile of the capacitance of the negative electrode to be combined.

Here, in the case where the battery is configured, it is superior in that oxidation treatment of a large number of positive electrodes can be performed at a time, rather than the individual positive electrodes or configurations corresponding to the positive electrodes. On the other hand, when it is performed for each positive electrode or for each configuration corresponding to the positive electrode, it is easier to control conditions such as the oxidation potential than the state in which the battery is configured. In addition, the method performed for each individual positive electrode is excellent in that variations in the degree of oxidation of the individual positive electrodes hardly occur.

In addition, as the oxidizing agent used in the oxidation method of (2) above, for example, halogen such as bromine and chlorine can be used. These oxidizing agents may be used alone or in combination of two or more. Oxidation with an oxidizing agent may be performed by, for example, dispersing lithium-containing transition metal oxide fine particles in a solvent in which the lithium-containing transition metal oxide is not dissolved, and blowing the oxidant into the dispersion to dissolve it and gradually oxidizing it. it can.

The conductive auxiliary agent is blended to improve the conductivity of the positive electrode active material layer. As a conductive support agent, carbon materials, such as carbon black, such as acetylene black, a graphite, a vapor growth carbon fiber, can be mentioned, for example. Among these, it is preferable to use acetylene black and vapor grown carbon fiber. However, it is not limited only to these carbon materials, and conventionally known materials that are used as conductive assistants for lithium ion secondary batteries can be used. However, in order to exhibit a sufficiently high rate characteristic, the content of the carbon material in the conductive assistant is preferably 80% by mass or more, more preferably 90% by mass, and 95% by mass or more. More preferably, it is more preferably 98% by mass or more, and most preferably 100% by mass. These conductive assistants may be used alone or in combination of two or more.

In this embodiment, even when the solid solution represented by the chemical formula (1) having a large reaction resistance is used as the positive electrode active material, the BET specific surface area of the carbon material can be exhibited so that a sufficiently high rate characteristic can be exhibited. Is in the following range. Specifically, the BET specific surface area of the carbon material is 30 to 200 m ² / g, preferably 50 to 180 m ² / g. When the BET specific surface area is less than 30 m ² / g, the primary particle size is increased, and the contact area with the active material can be reduced. On the other hand, when the BET specific surface area exceeds 200 m ² / g, the primary particle diameter becomes small, and the crystallinity of the carbon material itself may be lowered. Therefore, when the BET specific surface area of the carbon material is out of the range of 30 to 200 m ² / g, a sufficiently high rate characteristic is exhibited when the solid solution represented by the chemical formula (1) is used as the positive electrode active material. May not be possible. In addition, in this specification, the value obtained by the method as described in the below-mentioned Example is employ | adopted for the BET specific surface area of a carbon material.

The carbon material preferably has a D band peak intensity ratio (D value / G value) of 1.18 or less, preferably 1.15 or less, as measured by Raman spectroscopy. It is preferable. The G band of carbon observed by Raman spectroscopy is a peak derived from in-plane vibration of graphene, while the D band is a peak derived from amorphous carbon. Therefore, the smaller the intensity ratio (D value / G value) of the peak of the D band to the G band, the higher the crystallinity of the carbon material. The lower limit value of the D value / G value is not particularly limited, and is most preferably 0. When the D value / G value is 1.18 or less, the carbon material has high crystallinity, and when the solid solution represented by the above chemical formula (1) is used as the positive electrode active material, more excellent high rate characteristics are exhibited. Can do. In this specification, the value obtained by the method described in the examples described later is adopted as the D value / G value.

In this embodiment, the content of the conductive additive in the positive electrode active material layer is not particularly limited, but 2 to 10 with respect to the weight of the positive electrode active material layer from the viewpoint of exhibiting a desired discharge capacity and high rate characteristics. The mass is preferably 2, and more preferably 2 to 6 mass%.

Further, the ratio of the average particle diameter (average secondary particle diameter) of the conductive additive to the average particle diameter of the positive electrode active material (conductive auxiliary agent particle diameter / active material particle diameter) is from the viewpoint of exhibiting sufficiently high rate characteristics. 1/40 to 10 is preferable, and 0.07 to 2.5 is more preferable.

The binder (binder) is not particularly limited, and examples thereof include the following materials. For example, polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile (PAN), polyimide (PI), polyamide (PA), cellulose, carboxymethyl cellulose (CMC), ethylene -Vinyl acetate copolymer, polyvinyl chloride (PVC), styrene-butadiene rubber (SBR), isoprene rubber, butadiene rubber, ethylene-propylene rubber, ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer Examples thereof include thermoplastic polymers such as a polymer and a hydrogenated product thereof, a styrene-isoprene-styrene block copolymer and a hydrogenated product thereof. Polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoro Examples thereof include fluorine resins such as ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF). Furthermore, vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based fluororubber), vinylidene fluoride- Pentafluoropropylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethylvinylether-tetra Fluoroethylene-based fluororubber (VDF-PFMVE-TFE-based fluororubber), vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber) ) And vinylidene fluoride-based fluorine rubbers such as, epoxy resins. Among these, polyvinylidene fluoride, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable. These suitable binders are excellent in heat resistance, have a very wide potential window, are stable at both the positive electrode potential and the negative electrode potential, and can be used for the positive electrode active material layer and the negative electrode active material layer. Moreover, you may use the conductive binder which has the function of the said conductive support agent and a binder as a binder. As the conductive binder, for example, commercially available TAB-2 manufactured by Hosen Co., Ltd. can be used. However, the material is not limited to these, and a known material conventionally used as a binder for a lithium ion secondary battery can be used. These binders may be used alone or in combination of two or more.

The amount of the binder contained in the positive electrode active material layer is not particularly limited as long as it is an amount capable of binding the positive electrode active material. However, the binder amount is preferably 0.5 to 15% by mass, and more preferably 1 to 10% by mass with respect to the positive electrode active material layer.

Furthermore, the density of the positive electrode active material layer is preferably 2.5 g / cm ³ or more and 3.0 g / cm ³ or less. When the density of the positive electrode active material layer is 2.5 g / cm ³ or more, the weight (filling amount) per unit volume increases, and the discharge capacity can be improved. Moreover, when the density of the positive electrode active material layer is 3.0 g / cm ³ or less, it is possible to prevent a decrease in the void amount of the positive electrode active material layer and improve the permeability of the non-aqueous electrolyte and the lithium ion diffusibility. Can do.

<Negative electrode active material layer>
The negative electrode active material layer 12B contains a negative electrode material capable of occluding and releasing lithium as a negative electrode active material, and may contain a binder and a conductive additive as necessary. In addition, the above-mentioned thing can be used for a binder and a conductive support agent.

Examples of the negative electrode material capable of inserting and extracting lithium include graphite (natural graphite, artificial graphite, etc.), which is highly crystalline carbon, low crystalline carbon (soft carbon, hard carbon), carbon black (Ketjen) Black, acetylene black, channel black, lamp black, oil furnace black, thermal black, etc.), carbon materials such as fullerene, carbon nanotube, carbon nanofiber, carbon nanohorn, and carbon fibril. In addition, the said carbon material contains what contains 10 mass% or less silicon nanoparticles. Also, silicon (Si), germanium (Ge), tin (Sn), lead (Pb), aluminum (Al), indium (In), zinc (Zn), hydrogen (H), calcium (Ca), strontium (Sr ), Barium (Ba), ruthenium (Ru), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), silver (Ag), gold (Au), cadmium (Cd), mercury (Hg) ), Gallium (Ga), thallium (Tl), carbon (C), nitrogen (N), antimony (Sb), bismuth (Bi), oxygen (O), sulfur (S), selenium (Se), tellurium (Te) ), Elemental elements that form an alloy with lithium such as chlorine (Cl), and oxides containing these elements (silicon monoxide (SiO), SiO _x (0 <x <2), tin dioxide (SnO ₂ ), SnO _x 0 <x <2), etc. SnSiO ₃₎ and the like carbides (silicon carbide (SiC)), and the like. Further examples include metal materials such as lithium metal and lithium-transition metal composite oxides such as lithium-titanium composite oxide (lithium titanate: Li ₄ Ti ₅ O ₁₂ ). However, it is not limited to these, The conventionally well-known material used as a negative electrode active material for lithium ion secondary batteries can be used. These negative electrode active materials may be used alone or in combination of two or more.

In this embodiment, the carbon material is preferably made of a graphite material that is covered with an amorphous carbon layer and is not scaly. The carbon material preferably has a BET specific surface area of 0.8 m ² / g or more and 1.5 m ² / g or less and a tap density of 0.9 g / cm ³ or more and 1.2 g / cm ³ or less. It is. A carbon material made of a graphite material that is coated with an amorphous carbon layer and that is not scale-like is preferable because of its high lithium ion diffusibility into the graphite layered structure. Further, when the BET specific surface area of such a carbon material is 0.8 m ² / g or more and 1.5 m ² / g or less, the capacity retention rate can be further improved. Furthermore, when the tap density of such a carbon material is 0.9 g / cm ³ or more and 1.2 g / cm ³ or less, the weight (filling amount) per unit volume can be improved, and the discharge capacity is improved. be able to.

Furthermore, in this embodiment, it is preferable that the negative electrode active material layer containing at least the carbon material and the binder has a BET specific surface area of 2.0 m ² / g or more and 3.0 m ² / g or less. When the BET specific surface area of the negative electrode active material layer is 2.0 m ² / g or more and 3.0 m ² / g or less, the permeability of the non-aqueous electrolyte can be improved, and the capacity retention rate is further improved. Gas generation due to decomposition of the non-aqueous electrolyte can be suppressed.

In this embodiment, the negative electrode active material layer containing at least a carbon material and a binder preferably has a BET specific surface area after pressure molding of 2.01 m ² / g or more and 3.5 m ² / g or less. is there. By setting the BET specific surface area of the negative electrode active material layer after pressure molding to 2.01 m ² / g or more and 3.5 m ² / g or less, the permeability of the non-aqueous electrolyte can be improved and the capacity can be maintained. The rate can be improved and gas generation due to decomposition of the non-aqueous electrolyte can be suppressed.

Furthermore, in this embodiment, the increase in the BET specific surface area of the negative electrode active material layer containing at least the carbon material and the binder before and after pressure press molding is 0.01 m ² / g or more and 0.5 m ² / g or less. It is preferable that Thereby, since the BET specific surface area after the pressure forming of the negative electrode active material layer can be 2.01 m ² / g or more and 3.5 m ² / g or less, the permeability of the non-aqueous electrolyte can be improved. In addition, the capacity retention rate can be further improved, and gas generation due to decomposition of the non-aqueous electrolyte can be suppressed.

Also, the thickness of each active material layer (active material layer on one side of the current collector) is not particularly limited, and conventionally known knowledge about the battery can be referred to as appropriate. As an example, the thickness of each active material layer is usually about 1 to 500 μm, preferably 2 to 100 μm, taking into consideration the intended use of the battery (emphasis on output, energy, etc.) and ion conductivity.

Furthermore, when the optimum particle diameter is different for expressing the unique effect of each active material, the optimum particle diameters may be mixed and used for expressing each unique effect. Therefore, it is not necessary to make the particle sizes of all the active materials uniform. For example, in the case of using a particle-form positive electrode active material comprising a solid solution lithium-containing transition metal oxide, the average particle diameter is approximately the same as the average particle diameter of the positive electrode active material contained in the existing positive electrode active material layer Well, not particularly limited. From the viewpoint of increasing the output, it is preferably in the range of 0.5 to 20 μm. More preferably, it may be in the range of 0.7 to 10 μm. Note that the “particle diameter” is any two points on the contour line of the active material particle (observation surface) observed using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). This means the maximum distance among the distances. As the value of “average particle size”, a value calculated as the average value of the particle size of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope or a transmission electron microscope is adopted. It shall be. The particle diameters and average particle diameters of other components can be defined in the same manner.

However, the average particle diameter is not limited to such a range, and may be outside this range as long as the effects of the present embodiment can be effectively expressed.

<Electrolyte layer>
Examples of the electrolyte layer 13 include an electrolyte solution, a polymer gel electrolyte, a solid polymer electrolyte formed in a separator described later, and a layer structure formed using a solid polymer electrolyte, and further a polymer gel electrolyte and a solid polymer electrolyte. Examples thereof include those having a laminated structure formed thereon.

For example, the electrolyte solution is preferably one that is usually used in a lithium ion secondary battery, and specifically has a form in which a supporting salt (lithium salt) is dissolved in an organic solvent. Examples of the lithium salt include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), six lithium fluoride tantalate (LiTaF _6), four lithium aluminum chloride acid (LiAlCl _4), at least one selected from inorganic acid anion salts such as lithium deca chloro deca boronic acid _(Li ₂ B _{10 Cl} 10) A lithium salt etc. can be mentioned. Further, lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bis (trifluoromethanesulfonyl) imide (Li (CF ₃ SO ₂ ) ₂ N), lithium bis (pentafluoroethanesulfonyl) imide (Li (C ₂ F ₅₎ Examples include at least one lithium salt selected from organic acid anion salts such as SO ₂ ) ₂ N). Among these, lithium hexafluorophosphate (LiPF ₆ ) is preferable. Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC); chain carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC). Ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-dibutoxyethane; lactones such as γ-butyrolactone; nitriles such as acetonitrile; methyl propionate Esters such as amides; amides such as dimethylformamide; at least one selected from methyl acetate and methyl formate can be used. Examples of the separator include a microporous film made of polyolefin such as polyethylene (PE) and polypropylene (PP), a porous flat plate, and a nonwoven fabric.

The polymer gel electrolyte is a solid polymer electrolyte having ion conductivity containing the above-described electrolytic solution usually used in a lithium ion secondary battery. However, the present invention is not limited to this, and includes a structure in which a similar electrolyte solution is held in a polymer skeleton having no lithium ion conductivity. For example, polyvinylidene fluoride (PVdF), polyvinyl chloride (PVC), polyacrylonitrile (PAN), or polymethyl methacrylate (PMMA) is used as a polymer having no lithium ion conductivity used in the polymer gel electrolyte. it can. However, it is not necessarily limited to these. Note that polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and the like are in a class having almost no ionic conductivity, and thus can be a polymer having the ionic conductivity. However, here, polyacrylonitrile and polymethyl methacrylate are exemplified as polymers having no lithium ion conductivity.

Examples of the solid polymer electrolyte include a structure in which the lithium salt is dissolved in polyethylene oxide (PEO), polypropylene oxide (PPO), and the like, and does not contain an organic solvent. Therefore, when the electrolyte layer is composed of a solid polymer electrolyte, there is no fear of liquid leakage from the battery, and the battery reliability can be improved.

The thickness of the electrolyte layer is preferably thinner from the viewpoint of reducing internal resistance. The thickness of the electrolyte layer is usually 1 to 100 μm, preferably 5 to 50 μm.

In addition, the matrix polymer of the polymer gel electrolyte or the solid polymer electrolyte can express excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, a polymerization process such as thermal polymerization, ultraviolet polymerization, radiation polymerization, or electron beam polymerization may be performed on a polymerizable polymer for forming a polymer electrolyte using an appropriate polymerization initiator. Examples of the polymerizable polymer include polyethylene oxide and polypropylene oxide.

<Method for producing lithium ion secondary battery>
Next, an example of a manufacturing method of the lithium ion secondary battery according to this embodiment described above will be described.

First, a positive electrode is produced. For example, when a granular positive electrode active material is used, the solid solution lithium-containing transition metal oxide, the conductive additive, and optionally a binder and a viscosity adjusting solvent are mixed to prepare a positive electrode slurry. Next, this positive electrode slurry is applied to a positive electrode current collector, dried, and compression molded to form a positive electrode active material layer.

Also, make a negative electrode. For example, when a granular negative electrode active material is used, a negative electrode active material and, if necessary, a conductive additive, a binder, and a viscosity adjusting solvent are mixed to prepare a negative electrode slurry. Thereafter, the negative electrode slurry is applied to a negative electrode current collector, dried, and compression molded to form a negative electrode active material layer.

Next, the positive electrode lead is attached to the positive electrode, the negative electrode lead is attached to the negative electrode, and then the positive electrode, the separator, and the negative electrode are laminated. Further, the laminated product is sandwiched between polymer-metal composite laminate sheets, and the outer peripheral edge except for one side is heat-sealed to form a bag-like outer package. Thereafter, the electrolytic solution is prepared and injected into the interior from the opening of the exterior body, and the opening of the exterior body is thermally fused and sealed. Thereby, a laminate-type lithium ion secondary battery is completed.

Furthermore, another example of a method for manufacturing a lithium ion secondary battery will be described. First, a positive electrode and a negative electrode are prepared in the same manner as described above. Next, the positive electrode lead is attached to the positive electrode and the negative electrode lead is attached to the negative electrode, and then the positive electrode, the separator, and the negative electrode are laminated. Further, the laminated product is sandwiched between polymer-metal composite laminate sheets, and the outer peripheral edge except for one side is heat-sealed to form a bag-like outer package.

After this, the above electrolyte is prepared and injected into the inside from the opening of the exterior body, and the opening of the exterior body is heat-sealed and sealed. Further, the electrochemical pretreatment described above is performed. Thereby, a laminate-type lithium ion secondary battery is completed.

As described above, the laminate type battery and the coin type battery are exemplified as the lithium ion secondary battery, but the present invention is not limited to this. That is, a conventionally known form / structure such as a button-type battery or a can-type battery having a square shape or a cylindrical shape can be applied.

Further, the present invention can be applied not only to the above-described stacked type (flat type) battery but also to a conventionally known form / structure such as a wound type (cylindrical) battery.

Furthermore, the present invention is not only the above-described normal type (internal parallel connection type) battery but also a bipolar type (internal series connection type) when viewed in terms of electrical connection form (electrode structure) in the lithium ion secondary battery. Conventionally known forms and structures such as batteries can also be applied. A battery element in a bipolar battery generally has a bipolar electrode in which a negative electrode active material layer is formed on one surface of a current collector and a positive electrode active material layer is formed on the other surface, and an electrolyte layer. A plurality of layers.

The positive electrode for a non-aqueous electrolyte secondary battery and the non-aqueous electrolyte secondary battery according to the present invention can realize a high discharge capacity and a capacity retention ratio by having the above-described configuration, and also have a high rate characteristic even under high output conditions. Can demonstrate. Therefore, the positive electrode for nonaqueous electrolyte secondary batteries and the nonaqueous electrolyte secondary battery of the present invention can be preferably applied to driving power supplies and auxiliary power supplies for motors of electric vehicles, fuel cell vehicles, and hybrid electric vehicles.

Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples. In the following, a laminate type lithium ion secondary battery is manufactured using the solid solution of this embodiment as the positive electrode active material and acetylene black having various physical properties (BET specific surface area, D value / G value) as the conductive auxiliary agent. The performance was evaluated.

<Synthesis of lithium-containing transition metal oxide>
A lithium-containing transition metal oxide represented by the following chemical formula (2) was synthesized using a composite carbonate method. Three kinds of sulfates of Ni, Co, and Mn were used as starting materials, and these were dissolved in ion-exchanged water so as to have a ratio of the following chemical formula (2) to obtain a 2M mixed aqueous solution. Next, a 1M sodium carbonate aqueous solution was dropped into the aqueous solution to obtain a composite carbonate of nickel cobalt manganese. The obtained composite carbonate was recovered by filtration, dried, and fired at a firing temperature of 700 ° C. for 4 hours to obtain a composite oxide. The obtained composite oxide and lithium hydroxide were mixed so as to have a ratio of the following chemical formula (2), and fired at 900 ° C. in the air to obtain a target sample. The composition was confirmed using XRD.

Chemical formula: Li _1.5 [Ni _0.45 Co ₀ Mn _0.855 [Li] _0.195 ] O ₃ (2)
<Production of electrode>
A negative electrode active material slurry was prepared by mixing 93 parts by mass of graphite as a negative electrode active material, 7 parts by mass of PVdF as a binder, and an appropriate amount of NMP as a slurry viscosity adjusting solvent. A stainless steel mesh of φ16 mm is prepared as a negative electrode current collector, and a negative electrode active material slurry is applied to the surface and dried. A negative electrode active material layer (size 3 × 4 cm square, active material amount per unit volume) : 9 mg / cm ² , thickness: 60 μm) was produced.

On the other hand, 92 parts by mass of the lithium-containing transition metal oxide synthesized above as the positive electrode active material, 4 parts by mass of acetylene black shown in Table 2 below as the conductive auxiliary agent, 4 parts by mass of PVdF as the binder, and N as the slurry viscosity adjusting solvent A suitable amount of methyl-2-pyrrolidone (NMP) was mixed to prepare a positive electrode active material slurry. A positive electrode active material slurry was applied to an Al foil as a positive electrode current collector and dried for 4 hours with a dryer at 120 ° C., and a positive electrode active material layer (size 3 × 4 cm square, active per unit volume) was formed on the current collector surface. A positive electrode having a substance amount of 8 mg / cm ² and a thickness of 30 μm was formed.

In addition, the BET specific surface area of acetylene black in the following Table 2 was measured by gas adsorption with nitrogen by the BET method (sample 1 g).

The D value / G value of acetylene black (powder) in Table 2 below was determined by performing peak fitting on the Raman spectrum measured under the following conditions. When acetylene black in the positive electrode active material layer after producing the positive electrode was measured in the same manner, it was confirmed that the D value / G value was the same as that of acetylene black (powder).

Device name: Bruker Optics Microscopic Laser Raman SENTERRA
Excitation wavelength: 532 nm
Exposure time: 30 seconds Integration count: 5 times.

<Production of lithium ion secondary battery>
As an electrolytic solution, a solution in which LiPF ₆ as a lithium salt was dissolved at a concentration of 1.0 mol / liter in a mixed solvent of ethylene carbonate (EC): diethyl carbonate (DEC) = 3: 7 (volume ratio) was prepared. . An electrolyte solution was formed by impregnating a separator (thickness 20 μm, polyethylene porous membrane) with the electrolytic solution.

The negative electrode, the electrolyte layer, and the positive electrode prepared above were sequentially laminated, and the obtained laminate was sealed and molded using an aluminum laminate film to complete a laminated lithium ion secondary battery.

<Electrochemical pretreatment and rate characteristics evaluation>
The said lithium ion secondary battery was connected to the charging / discharging apparatus, and it charged / discharged on the conditions as shown below. By performing the treatment by gradually increasing the charging voltage, the activation state of the electrode is stabilized and the cycle durability is improved. In addition, it defined as 1C = 200mA / g (positive electrode active material weight). Further, energy density in cycle 8 / energy density in cycle 5 × 100 (%) was calculated, and rate characteristics were evaluated.

The results are shown in the table below.

From the above results, Examples 1 to 4 using a carbon material having a BET specific surface area of 30 to 200 m ² / g as a conductive aid exhibit high rate characteristics even under high output conditions (2.5 C). Was shown. Moreover, it was shown that the high rate characteristics are further improved by setting the D value / G value to 1.18 or less. This is to effectively reduce the reaction resistance of the solid solution represented by the chemical formula (2) by setting the BET specific surface area and the D value / G value of the carbon material used as the conductive auxiliary agent within a predetermined range. It was thought that this was because

This application is based on Japanese Patent Application No. 2013-159502 filed on July 31, 2013, the disclosure of which is incorporated by reference in its entirety.

1 Lithium ion secondary battery,
10 battery elements,
11 positive electrode,
11A positive electrode current collector,
11B positive electrode active material layer,
12 negative electrode,
12A negative electrode current collector,
12B negative electrode active material layer,
13 electrolyte layer,
14 cell layer,
21 positive lead,
22 negative lead,
30 Exterior body.

Claims

Including a positive electrode active material and a conductive additive,
The positive electrode active material is
Chemical formula:
Li 1.5 [Ni a Co b Mn c [Li] d ] O 3 (1)
(In the formula, Li represents lithium, Ni represents nickel, Co represents cobalt, Mn represents manganese, O represents oxygen, and a, b, c and d are 0 <a <1.4 and 0 ≦ b <1.4. , 0 <c <1.4, 0.1 <d ≦ 0.4, a + b + c + d = 1.5, 1.1 ≦ a + b + c <1.4) Containing
The conductive auxiliary agent contains a carbon material,
The positive electrode for a non-aqueous electrolyte secondary battery, wherein the carbon material has a BET specific surface area of 30 to 200 m 2 / g.
2. The nonaqueous electrolyte secondary battery according to claim 1, wherein an intensity ratio (D value / G value) of a peak of a D band to a G band of carbon measured by Raman spectroscopy of the carbon material is 1.18 or less. Positive electrode.
The positive electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the carbon material has a BET specific surface area of 50 to 180 m 2 / g.
The intensity ratio (D value / G value) of the peak of the D band to the G band of the carbon measured by Raman spectroscopy of the carbon material is 1.15 or less, according to any one of claims 1 to 3. Positive electrode for non-aqueous electrolyte secondary battery.
A positive electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4,
A negative electrode,
A non-aqueous electrolyte secondary battery comprising: