JP2016039114A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the interface resistance between a negative electrode active material (base material) and a non-aqueous electrolyte by optimizing the existence form of a dielectric material (child material) with respect to a negative electrode active material (base material), and particularly Provided is a non-aqueous electrolyte secondary battery such as a lithium-ion secondary battery that achieves high output under low temperature conditions. A non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode including a positive electrode active material layer containing a positive electrode active material, a negative electrode including a negative electrode active material layer containing a negative electrode active material, and a non-aqueous electrolyte. Equipped with. Further, the negative electrode active material layer contains, as a negative electrode active material, a dielectric material composite negative electrode active material in which a dielectric material having a relative dielectric constant higher than that of the negative electrode active material and the non-aqueous electrolyte is carried on the surface of the negative electrode active material particles as a base material. To do. Here, the particle diameter ratio of the average particle diameter of the dielectric material supported on the dielectric material composite negative electrode active material to the average particle diameter of the negative electrode active material is 0.005 to 0.1. [Selection diagram] None

Description

  The present invention relates to a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery.

  One of the non-aqueous electrolyte secondary batteries is a lithium ion secondary battery. The lithium ion secondary battery includes positive and negative electrodes capable of reversibly occluding and releasing lithium ions, and a separator interposed between these two electrodes. In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been used in motor drives or auxiliary power supplies for electric vehicles, hybrid electric vehicles, and fuel cell vehicles. Therefore, further higher output is required.

In a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, in order to achieve higher output, the conductivity of charge carriers such as lithium ions in the non-aqueous electrolyte is one of the important items. is there. As a means for improving the conductivity, there is a method of reducing the interface resistance between the active material and the electrolyte. In particular, when the charge carrier in the electrolytic solution (in the case of a lithium ion battery: Li ⁺ ) reacts with the active material to perform insertion / desorption, there is a large activation barrier when Li ⁺ is desolvated (the activation energy is Therefore, the interface resistance on the negative electrode active material surface is large. Therefore, there is a method of reducing the interface resistance between the negative electrode active material and the electrolyte. For example, Patent Document 1 describes a nonaqueous electrolyte battery in which an anode active material layer contains an inorganic compound having a relative dielectric constant of 12 or more.

  Patent Document 2 discloses a high relative dielectric constant between the positive electrode active material or the negative electrode active material and the electrolyte material in order to reduce the interface resistance between the positive electrode active material or the negative electrode active material and the electrolyte. A secondary battery in which a high dielectric material (eg, barium titanate) is disposed is described.

Japanese Patent Laid-Open No. 2001-283863 JP 2012-142268 A

The techniques described in Patent Documents 1 and 2 can reduce the interfacial resistance between the positive electrode active material or the negative electrode active material and the electrolyte material, and can contribute to higher output of the nonaqueous electrolyte secondary battery. However, depending on the form of the dielectric material (hereinafter also simply referred to as “dielectric material”) with respect to the negative electrode active material, the effect of suppressing the interface resistance may not be sufficiently obtained.
Specifically, simply adding a dielectric material to the negative electrode active material layer tends to increase the distance between the surface of the negative electrode active material, which is a reaction field for charge carriers, and the dielectric material, and the effect of suppressing interface resistance is sufficient. There is a possibility that it cannot be obtained. Even if the dielectric material is supported on the surface of the negative electrode active material, if the particle size ratio of the dielectric material to the negative electrode active material is large, the distance between the surface of the negative electrode active material and the dielectric material is increased, so the interface resistance is suppressed. There is a possibility that the above effect cannot be sufficiently obtained. On the other hand, when the particle size ratio is small, the dielectric material covers the negative electrode active material, the reaction field is reduced, and the effect of suppressing the interface resistance may not be sufficiently obtained.
In particular, since the interface resistance increases under low temperature conditions such as 0 ° C. or lower, there is still room for improvement when output improvement is desired at low temperatures.

  Accordingly, the present invention has been created in view of the above problems, and in a non-aqueous electrolyte secondary battery, by optimizing the existence form of the dielectric material with respect to the negative electrode active material, the present invention is provided between the negative electrode active material and the non-aqueous electrolyte. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery in which the interfacial resistance of the lithium ion secondary battery is reduced and the high output is achieved particularly under low temperature conditions.

In order to solve the above problems, a nonaqueous electrolyte secondary battery according to the present invention includes a positive electrode including a positive electrode active material layer containing a positive electrode active material, a negative electrode including a negative electrode active material layer containing a negative electrode active material, A non-aqueous electrolyte. Further, the negative electrode active material layer contains a negative electrode active material having a dielectric material composite negative electrode active material in which a negative electrode active material and a dielectric material having a relative dielectric constant higher than that of the nonaqueous electrolyte are supported on the surface of the negative electrode active material particles as a base material To do. Here, the particle diameter ratio of the average particle diameter of the dielectric material supported on the dielectric material composite negative electrode active material to the average particle diameter of the negative electrode active material is 0.005 to 0.1. The particle size here is a particle size obtained by a general laser diffraction type particle size distribution measuring apparatus. The relative dielectric constant here is a measured value measured by a method based on JIS-C2565, for example.
According to the said structure, the dielectric material which is a child material is carry | supported by the negative electrode active material surface which is a base material, and the ratio of the particle diameter with respect to a negative electrode active material is optimized with 0.005-0.1. Therefore, the distance between the surface of the negative electrode active material, which is a reaction field for charge carriers, and the dielectric material is optimally controlled, and the dielectric material covers the negative electrode active material, thereby suppressing the reaction field from decreasing. . Therefore, a non-aqueous electrolyte secondary battery that sufficiently reduces the interfacial resistance between the negative electrode active material and the electrolyte, improves the conductivity of the charge carrier in the electrolyte even at low temperatures, and realizes a high output. Can be provided.

In a preferable aspect of the nonaqueous electrolyte secondary battery disclosed herein, the dielectric constant of the dielectric material is 10 times or more higher than that of the negative electrode active material.
According to the above configuration, since the relative permittivity of the dielectric material is sufficiently high, the interface resistance between the negative electrode active material and the electrolyte is further reduced, and the conductivity of the charge carrier in the electrolyte is improved. Therefore, it is possible to provide a non-aqueous electrolyte secondary battery that achieves higher output.

In a particularly preferable aspect of the nonaqueous electrolyte secondary battery disclosed herein, the dielectric material is preferably an inorganic oxide.
According to the said structure, it can become a dielectric material stable in air | atmosphere by being an inorganic oxide. That is, according to the above configuration, it is possible to stably reduce the interface resistance between the negative electrode active material and the electrolyte without being affected by the inclusion of the dielectric material.

Furthermore, the dielectric material is preferably an inorganic oxide having a perovskite structure. A suitable example of such a perovskite oxide is barium titanate (BaTiO ₃ ).
An inorganic oxide (barium titanate) having a perovskite structure has a very high relative permittivity, so that the interfacial resistance between the negative electrode active material and the electrolyte can be further reduced, and charge carrier conduction in the electrolyte can be further reduced. Improves. Therefore, it is possible to provide a non-aqueous electrolyte secondary battery that achieves high output even at low temperatures.

1 is a perspective view schematically showing an outer shape of a nonaqueous electrolyte secondary battery (lithium ion secondary battery) according to an embodiment of the present invention. It is a longitudinal cross-sectional view which shows typically the cross-sectional structure which follows the II-II line | wire in FIG. It is a graph showing the relationship between a particle size ratio (child material: dielectric material / base material: negative electrode active material) and resistance reduction rate.

Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.
In the following drawings, members / parts having the same action are described with the same reference numerals, and overlapping descriptions may be omitted or simplified. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

  Hereinafter, as a type of the nonaqueous electrolyte secondary battery 100 in which the present invention can be preferably carried out, a preferred embodiment will be described taking a lithium ion secondary battery 100 (hereinafter simply referred to as “battery” in some cases) as an example. . However, the lithium ion secondary battery 100 is an example, and the technical idea of the present invention is also applied to other nonaqueous electrolyte secondary batteries (for example, sodium ion secondary batteries) including other charge carriers (for example, sodium ions). Is done.

  FIG. 1 is a view showing an appearance of a battery (cell) 100 according to the present embodiment. Moreover, FIG. 2 is sectional drawing which shows typically the internal structure of the battery case 30 concerning this embodiment.

  As shown in FIGS. 1 and 2, the lithium ion secondary battery 100 according to the present embodiment is roughly a flat corner between a flat wound electrode body 20 and a nonaqueous electrolyte (not shown). This is a so-called prismatic battery 100 configured to be accommodated in a battery case (that is, an outer container) 30 of a type. The battery case 30 has a box-shaped (that is, bottomed rectangular parallelepiped) case body 32 having an opening at one end (corresponding to an upper end in a normal use state of the battery), and an opening of the case body 32. And a lid 34 to be sealed. As a material of the battery case 30, for example, a light metal material having a good thermal conductivity such as aluminum, stainless steel, or nickel-plated steel can be preferably used.

  Also, as shown in FIGS. 1 and 2, the lid 34 is opened so that the internal pressure is released when the internal pressure of the battery case 30 rises above a predetermined level. And a thin safety valve 36 set to 1 and an injection port (not shown) for injecting a non-aqueous electrolyte (non-aqueous electrolyte). Note that the battery case 30 of the lithium ion secondary battery 100 is not limited to a rectangular (box) shape as illustrated, but may be other known shapes. For example, other shapes include a cylindrical shape, a coin shape, a laminate shape, and the like, and a case shape can be selected as appropriate.

  As shown in FIG. 2, the wound electrode body 20 accommodated in the battery case 30 includes a positive electrode active material layer along the longitudinal direction on one side or both sides (here, both sides) of a long positive electrode current collector 52. The negative electrode 60 in which the negative electrode active material layer 64 is formed along the longitudinal direction on one side or both sides (here, both sides) of the long negative electrode current collector 62. The laminated body laminated | stacked through the elongate separator 70 is wound by the elongate direction, and is shape | molded by the flat shape. Such a wound electrode body 20 is formed into a flat shape by, for example, crushing and lagging the wound body obtained by winding the laminated body from the side surface direction. The positive electrode current collector 52 constituting the positive electrode 50 is made of an aluminum foil or the like. On the other hand, the negative electrode current collector 62 constituting the negative electrode 60 is made of copper foil or the like.

  As shown in FIG. 2, a wound core portion (that is, a positive electrode active material layer 54 of the positive electrode 50 and a negative electrode active material layer 64 of the negative electrode 60; A laminated structure in which the separator 70 is laminated) is formed. In addition, at both ends in the winding axis direction of the wound electrode body 20, the positive electrode active material layer non-formed portion 52a and the negative electrode active material layer non-formed portion 62a partially protrude outward from the wound core portion. Yes. The positive electrode side protruding portion (positive electrode active material layer non-forming portion 52a) and the negative electrode side protruding portion (negative electrode active material layer non-forming portion 62a) are respectively provided with a positive electrode current collecting plate 42a and a negative electrode current collecting plate 44a. The terminal 42 and the negative terminal 44 are electrically connected to each other.

The positive electrode active material layer 54 according to the present embodiment contains a positive electrode active material that is a main component. Such a positive electrode active material is not particularly limited in composition and shape, and one or more materials conventionally used in the lithium ion secondary battery 100 can be used without any particular limitation. For example, an oxide containing lithium and a transition metal element as constituent metals, such as lithium nickel composite oxide (LiNiO ₂ etc.), lithium cobalt composite oxide (LiCoO ₂ etc.), lithium manganese composite oxide (LiMn ₂ O ₄ etc.) And a phosphate containing lithium and a transition metal element as constituent metal elements such as lithium oxide (lithium transition metal composite oxide), lithium manganese phosphate (LiMnPO ₄ ), and lithium iron phosphate (LiFePO ₄ ).
Furthermore, as a so-called spinel-type positive electrode active material having a spinel structure, for example, a lithium manganese composite oxide having a spinel structure represented by a general formula: Li _p Mn _{2 -q} M _q O _{4 + α} can be given as a preferred example. Where p is 0.9 ≦ p ≦ 1.2; q is 0 ≦ q <2, typically 0 ≦ q ≦ 1 (eg 0.2 ≦ q ≦ 0.6). Α is a value determined so as to satisfy the charge neutrality condition with −0.2 ≦ α ≦ 0.2. When q is larger than 0 (0 <q), M may be one or more selected from any metal element or nonmetal element other than Mn. More specifically, Na, Mg, Ca, Sr, Ti, Zr, V, Nb, Cr, Mo, Fe, Co, Rh, Ni, Pd, Pt, Cu, Zn, B, Al, Ga, In, It can be Sn, La, W, Ce or the like. Especially, at least 1 sort (s) of transition metal elements, such as Fe, Co, and Ni, can be employ | adopted preferably. Specific examples include LiMn ₂ O ₄ and LiCrMnO ₄ .
Among these, a spinel positive electrode active material having Li, Ni, and Mn as essential elements is preferable. More specifically, the general _formula: lithium-nickel-manganese composite oxide of _{Li x (Ni y Mn 2-} y-z M1 z) spinel structure represented by _{O 4 + beta} and the like. Here, M1 is not present, or is any transition metal element or typical metal element other than Ni and Mn (for example, one or more selected from Fe, Co, Cu, Cr, Zn, and Al). possible. Especially, it is preferable that M1 contains at least one of trivalent Fe and Co. Alternatively, it may be a metalloid element (for example, one or more selected from B, Si and Ge) and a nonmetallic element. And x is 0.9 ≦ x ≦ 1.2; y is 0 <y; z is 0 ≦ z; y + z <2 (typically y + z ≦ 1); β can be the same as α described above. In a preferred embodiment, y is 0.2 ≦ y ≦ 1.0 (more preferably 0.4 ≦ y ≦ 0.6, such as 0.45 ≦ y ≦ 0.55); z is 0 ≦ z <1.0 (for example, 0 ≦ z ≦ 0.3). A particularly preferred specific example is LiNi _0.5 Mn _1.5 O ₄ .
A spinel-based positive electrode active material (LiNi _0.5 Mn _1.5 O ₄ or the like) can be preferably used from the viewpoint of battery performance and durability because it has high thermal stability and high electrical conductivity.

  As the positive electrode active material, for example, a lithium transition metal composite oxide powder prepared by a conventionally known method can be used as it is. Although not particularly limited, for example, a lithium transition substantially composed of secondary particles having a particle size (median diameter) in the range of 1 μm to 25 μm (typically 2 μm to 10 μm, for example, 6 μm to 10 μm). Metal composite oxide powder can be preferably used as the positive electrode active material. In the present specification, “particle diameter (particle diameter)” refers to a median diameter in a volume-based particle size distribution obtained by a general laser diffraction particle size distribution measuring apparatus unless otherwise specified.

  The positive electrode active material layer 54 may include components other than the positive electrode active material which is the main component described above, such as a conductive material and a binder (binder). As the conductive material, carbon black such as acetylene black (AB) and other (such as graphite) carbon materials can be suitably used. As the binder, polyvinylidene fluoride (PVdF) or the like can be used.

Such a positive electrode active material layer 54 can be produced as follows, for example. First, a positive electrode active material as described above (for example, LiNi _0.5 Mn _1.5 O ₄ which is a high potential positive electrode active material) and other materials (binder, conductive material, etc.) used as necessary are appropriately used. In a suitable solvent (N-methyl-2-pyrrolidone (NMP) is preferred when PVdF is used as a binder), and a paste-like composition (a slurry-like composition and an ink-like composition are included in the paste-like composition). The same shall apply hereinafter). Next, an appropriate amount of the composition is applied to the surface of the positive electrode current collector 52, and then the positive electrode active material layer 54 having a desired property is formed on the positive electrode current collector 52 by removing the solvent by drying. Can do. In addition, the properties of the positive electrode active material layer 54 (for example, average thickness, active material density, porosity of the active material layer, etc.) can be adjusted by performing an appropriate press treatment as necessary.

The negative electrode active material layer 64 is mainly used as a negative electrode active material capable of occluding and releasing Li ^{+ serving} as a charge carrier. A dielectric material composite negative electrode active material carrying a dielectric material (child material) having a high dielectric constant is contained. Such a negative electrode active material (base material) is not particularly limited in composition and shape, and one or more materials conventionally used in lithium ion secondary batteries can be used. Although not particularly limited, for example, the average particle diameter may be about 1 to 40 μm (typically 5 to 30 μm, for example, 7 to 25 μm).
Examples of the negative electrode active material (base material) as described above include carbon materials generally used in lithium ion secondary batteries. Representative examples of the carbon material include graphite, hard carbon, and soft carbon. Preferably, a particulate carbon material (carbon particles) including a graphite structure (layered structure) at least partially is used. In addition, as the negative electrode active material, it is also possible to use oxides such as lithium titanate, simple substances such as silicon materials and tin materials, alloys, compounds, and composite materials using the above materials in combination. Among them, it is particularly preferable to use a negative electrode active material (matrix) having a reduction potential (vs. Li ^/ Li ⁺ ) of about 0.5 V or less (typically 0.2 V or less, for example, 0.1 V or less). . By using the negative electrode active material (base material) having the reduction potential, higher output can be realized. Examples of the material that can be at such a low potential include graphite-based carbon materials (typically graphite particles).
The proportion of the negative electrode active material (base material) in the negative electrode active material layer 64 exceeds approximately 50 wt%, and is approximately 90 wt% to 99 wt% (typically 95 wt% to 99 wt%, for example, 97 wt% to 99 wt%). Is preferred.

The dielectric material (child material) has a relative dielectric constant higher than that of the negative electrode active material (base material) and the non-aqueous electrolyte. Since the dielectric material (child material) has the above-described relative permittivity, the activation barrier when Li ^{+ as the} charge carrier is desolvated (dissociated) is reduced (interfacial resistance is reduced), and the charge in the electrolyte is reduced. The conductivity of the carrier is improved. The dielectric material (child material) is not particularly limited. For example, the average particle size is 0.01 μm to 1.5 μm (typically 0.01 μm to 1 μm, for example, 0.1 μm to 1 μm). It can be. Furthermore, the ratio of the particle diameter to the negative electrode active material particles (base material) is 0.005 to 0.1. More preferably, it is 0.01-0.07. When the ratio of the particle diameter to the negative electrode active material (base material) is larger than 0.1, the distance between the reaction field on the negative electrode active material and the dielectric material is large, and the effect of reducing the interface resistance may not be sufficiently obtained. . On the other hand, when the ratio of the particle diameter is smaller than 0.005, the dielectric material (child material) covers the negative electrode active material (base material), the reaction field is reduced, and the effect of reducing the interface resistance is sufficiently obtained. It may not be possible.

Here, the dielectric material (child material) is not particularly limited, but is preferably a ferroelectric material that is 10 times or more higher than the relative dielectric constant of the negative electrode active material (base material). Ferroelectrics have a high relative dielectric constant, and can relax the electric field at the interface by utilizing spontaneous polarization even when no external voltage is applied. Therefore, the effect of smooth movement of Li ^{+ as} the charge carrier can be obtained not only in the vicinity of the dielectric material but also in a remote location, and the interface resistance can be efficiently reduced even with a small amount of dielectric material (child material). it can. The dielectric material (child material) is preferably, for example, a solid, but may be a gel as long as the shape and size can be maintained on the surface of the negative electrode active material (base material). It is preferably a solid having an insolubility or solubility of less than 100 mg / L in 1 L of non-aqueous electrolyte. Since the solid has extremely low fluidity, the dielectric material (child material) can be more reliably disposed (supported) at the interface between the negative electrode active material (base material) and the electrolyte without moving. Examples of the solid dielectric material (child material) include oxides, sulfides, nitrides, and polymers. Among these, an oxide is preferable. The oxide is stable in the air, and the interface resistance can be stably reduced efficiently. Examples of the oxide include Rochelle salt (potassium sodium tartrate), an oxide having a perovskite structure, and potassium phosphate (K ₃ PO ₄ ). Among them, an oxide having a perovskite structure is preferable. Specific examples include barium titanate (BaTiO ₃ ), strontium titanate (SrTiO ₃ ), lithium diobate (LiNbO ₃ ), lead zirconate titanate ( PZT), lead titanate (PbTiO ₃ ), lead zirconate (PbZrO ₃ ), and the like are preferable, and barium titanate (BaTiO ₃ ) is more preferable. Barium titanate is preferable because it has a very high relative dielectric constant and has oxidation resistance in a non-aqueous electrolyte.
The content of the dielectric material (child material) in the negative electrode active material layer is approximately 30 wt% (for example, 20 wt% to 40 wt%, typically 25 wt% to 35 wt%), where the negative electrode active material (base material) content is 100. %).

  The negative electrode active material layer 64 may include components other than the above-described dielectric material composite negative electrode active material, such as a thickener and a binder (binder). As the binder, styrene butadiene rubber (SBR) or the like can be used. As the thickener, for example, various polymer materials such as carboxymethyl cellulose (CMC) can be employed. The ratio of these additives in the negative electrode active material layer 64 is not particularly limited, but is preferably about 0.8 to 10 wt% (typically 1 to 5 wt%, for example 1 to 3 wt%).

Such a negative electrode active material layer 64 can be produced, for example, as follows. First, a composite material comprising a negative electrode active material (for example, graphite) as a base material and a dielectric material (for example, barium titanate) as a base material is combined to carry a dielectric material on the surface of the negative electrode active material. A negative electrode active material is produced. An example of the compounding process is mechanofusion.
The dielectric composite negative electrode active material and other materials (binder, thickener, etc.) used as necessary are dispersed in an appropriate solvent (ion exchange water is preferred when SBR is used as the binder), A paste-like composition is prepared. Next, it can be formed by applying an appropriate amount of the composition to the surface of the negative electrode current collector 62 and then removing the solvent by drying. In addition, the properties (for example, average thickness, active material density, porosity of the active material layer, etc.) of the negative electrode active material layer 64 can be adjusted by performing an appropriate press treatment as necessary. The basis weight per unit area of the negative electrode active material layer 64 to the negative electrode current collector 62 (the coating amount in terms of solid content of the paste-like composition) is not particularly limited, but a sufficient conductive path (conduction) 2 mg / cm ² or more per side of the negative electrode current collector 62 (typically 3 mg / cm ² or more, for example, 4 mg / cm ² or more) and 40 mg / cm ² or less (typical) Is preferably 25 mg / cm ² or less, for example, 10 mg / cm ² or less.

  Examples of the separator 70 include a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Such a porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PE layers are laminated on both sides of a PP layer).

  As the non-aqueous electrolyte, typically, an organic solvent (non-aqueous solvent) containing a predetermined supporting salt and an additive can be used.

As the non-aqueous solvent, organic solvents such as various carbonates, ethers, esters, nitriles, sulfones, and lactones used for the electrolyte of the general lithium ion secondary battery 100 are used without particular limitation. Can do. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and the like. Such a non-aqueous solvent can be used individually by 1 type or in combination of 2 or more types as appropriate.
Alternatively, fluorine-based compounds such as fluorinated carbonates such as fluoroethylene carbonate (FEC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), trifluorodimethyl carbonate (TFDMC), and methyltrifluoroethyl carbonate (MTFEC) A solvent can be preferably used. For example, a mixed solvent containing FEC and MTFEC in a volume ratio of 1: 2 to 2: 1 (for example, 1: 1) has high oxidation resistance and can be suitably used in combination with a high potential electrode.

As the supporting salt, for example, a lithium salt such as LiPF ₆ , LiBF ₄ , or LiClO ₄ can be suitably used. Particularly preferred support salt include LiPF _6. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less, particularly preferably about 1.0 mol / L.

  The non-aqueous electrolyte may further contain components other than the above-described non-aqueous solvent and supporting salt as long as the effects of the present invention are not significantly impaired. Such optional components are used for one or more purposes such as, for example, improvement of battery output performance, improvement of storage stability (suppression of capacity reduction during storage, etc.), improvement of initial charge / discharge efficiency, and the like. obtain. Examples of such optional components include gas generating agents such as biphenyl (BP) and cyclohexylbenzene (CHB); oxalato complex compounds containing boron and / or phosphorus atoms, vinylene carbonate (VC), fluoroethylene carbonate ( Various additives such as film forming agents such as FEC), dispersants, thickeners and the like.

  The non-aqueous electrolyte secondary battery 100 such as a lithium ion secondary battery disclosed herein can be used for various applications. For example, a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), an electric vehicle (EV), etc. It can be suitably used as a driving power source mounted on the vehicle.

  Hereinafter, although the test example regarding this invention is demonstrated, it is not intending to limit the technical scope of this invention to what was demonstrated by this test example.

<Example 1>
As a positive electrode mixture, a spinel-based positive electrode active material, acetylene black (conductive material), and PVdF (binder) are mixed so that the weight ratio thereof is 87: 10: 3, and the solvent is pasted as NMP. A composition was prepared. The spinel positive electrode active material used here is LiNi _0.5 Mn _1.5 O ₄ and has an average particle diameter of 13 μm. This positive electrode mixture was applied to an aluminum foil (positive electrode current collector) having a thickness of 15 μm, and then dried to form a positive electrode active material layer, which was roll pressed to produce a positive electrode. The positive electrode was cut into a square with a band-shaped portion protruding from one corner so that the design capacity of the battery was 13.4 mAh, the active material layer was removed from the band-shaped portion, and the aluminum foil was exposed to form a terminal portion. The positive electrode with a terminal part was obtained.

  As a negative electrode mixture, graphite (negative electrode active material = base material: average particle diameter 7.5 μm, graphitization degree ≧ 0.9) and barium titanate (dielectric material = child material: average particle diameter 1.0 μm, negative electrode active The compound = particle size ratio of the base material to the base material: 0.13) was subjected to a composite treatment using a composite apparatus Nobilta (Hosokawa Micron) for 30 minutes at 2000 rpm. Here, the content of the dielectric material (child material) in the negative electrode mixture is 30 wt%, where the content of the negative electrode active material (base material) is 100. The dielectric material composite negative electrode active material obtained by the composite treatment, CMC (thickener), and SBR (binder) are mixed so that the weight ratio thereof becomes 98: 1: 1, and the solvent is added. A paste-like composition was prepared as water. This negative electrode mixture was applied to a copper foil (negative electrode current collector) having a thickness of 10 μm and then dried to form a negative electrode active material layer, which was roll pressed to produce a negative electrode. This negative electrode was processed into the same area and shape as the positive electrode with a terminal part to obtain a negative electrode with a terminal part.

A non-aqueous electrolyte was prepared by dissolving LiPF ₆ in a mixed solvent containing FEC and MTFEC at a volume ratio of 1: 1 to a concentration of 1 mol / L.

  The positive electrode with terminal part and the negative electrode with terminal part are overlapped with each other through a separator (porous PE / PP / PE three-layer sheet) cut into an appropriate size and impregnated with the non-aqueous electrolyte, and laminated film Covered with. The non-aqueous electrolyte was further injected here, and the film was sealed to construct a laminated cell type battery.

<Example 2>
As the negative electrode mixture, graphite (negative electrode active material = base material: average particle diameter 10 μm, graphitization degree ≧ 0.9) and barium titanate (dielectric material = child material: average particle diameter 1.0 μm, negative electrode active material = A laminated cell type battery was constructed in the same manner as in Example 1 except that the particle size ratio with the base material was 0.1).

<Example 3>
As the negative electrode mixture, graphite (negative electrode active material = base material: average particle diameter 15 μm, graphitization degree ≧ 0.9) and barium titanate (dielectric material = child material: average particle diameter 1.0 μm, negative electrode active material = A laminated cell type battery was constructed in the same manner as in Example 1 except that the particle size ratio with respect to the base material was 0.067).

<Example 4>
As the negative electrode mixture, graphite (negative electrode active material = base material: average particle diameter 20 μm, graphitization degree ≧ 0.9) and barium titanate (dielectric material = child material: average particle diameter 1.0 μm, negative electrode active material = A laminated cell type battery was constructed in the same manner as in Example 1 except that the particle size ratio with respect to the base material was 0.05).

<Example 5>
As the negative electrode mixture, graphite (negative electrode active material = base material: average particle size 20 μm, graphitization degree ≧ 0.9) and barium titanate (dielectric material = child material: average particle size 0.5 μm, negative electrode active material = A laminated cell type battery was constructed in the same manner as in Example 1 except that the particle size ratio with respect to the base material was 0.025).

<Example 6>
As the negative electrode mixture, graphite (negative electrode active material = base material: average particle diameter 20 μm, graphitization degree ≧ 0.9) and barium titanate (dielectric material = child material: average particle diameter 0.1 μm, negative electrode active material = A laminated cell type battery was constructed in the same manner as in Example 1 except that the particle size ratio with respect to the base material was 0.005).

<Example 7>
As the negative electrode mixture, graphite (negative electrode active material = base material: average particle diameter 10 μm, graphitization degree ≧ 0.9) and barium titanate (dielectric material = child material: average particle diameter 0.01 μm, negative electrode active material = A laminated cell type battery was constructed in the same manner as in Example 1 except that the particle size ratio with respect to the base material was 0.001).

[Conditioning processing]
Each battery cell according to Examples 1 to 7 described above was sandwiched between two plates and restrained in a state where a load of 350 kgf (350 kg / 25 cm ² ) was applied. Each restrained battery cell was charged at a constant current of up to 4.9 V at a temperature of 25 ° C. and at a rate of 1/5 C, and rested for 10 minutes. The operation of discharging a constant current to 3.5 V at a rate of / 5 C and resting for 10 minutes was repeated three times. The following measurements and the like were performed on battery cells in a 25 ° C. environment and restrained unless otherwise specified.

[Initial capacity calculation]
After the conditioning process, the battery cells in each example were charged with a constant current up to 4.9 V at a rate of 1/5 C, and were charged with a constant voltage until the current value at the time of constant current charging was 1/50 C. did. Thereafter, the capacity at the time of constant current discharge to 3.5 V at a rate of 1/5 C was defined as the initial capacity.

〔Resistance measurement〕
After confirming the initial capacity, the battery in a state of constant current discharge to SOC 0% at a rate of 1/5 C was charged at a constant current to SOC 60% (capacity 60% of the initial discharge capacity) at a rate of 1/5 C, then Impedance was measured in an environment of 10 ° C., and the reduction rate of the interface resistance was calculated.

  Table 1 shows the initial capacities of the obtained cells before and after the composite treatment.

As shown in Table 1, regarding the initial capacity, it was confirmed that there was no effect even when the composite treatment of barium titanate (BaTiO ₃ ) was performed. This is because the dielectric material (child material) barium titanate (BaTiO ₃ ) is an insoluble or hardly soluble oxide having a solubility in non-aqueous electrolyte 1 L of less than 100 mg / L. This is considered to be because it did not react with the electrode.

  Next, the reduction ratio of the interface resistance in each cell obtained is shown in Table 2, and the relationship between the particle size ratio (child material / base material) of each cell and the reduction ratio of the interface resistance is shown in FIG.

As shown in Table 2 and FIG. 3, the ratio of the particle diameter of the dielectric material (child material) to the negative electrode active material (base material) is 0.005 to 0.1 (Examples 2 to 6), and the interface resistance is reduced. A reduction was observed. This is because the reaction field on the negative electrode active material can be sufficiently secured and the distance between the reaction field and the dielectric material (child material) is suitable, so that Li ^{+ as the} charge carrier is desolvated (dissociated). This is considered to be because the activation barrier during the process can be made sufficiently small.

  On the other hand, in Example 1, since the ratio of the particle diameter of the dielectric material (child material) to the negative electrode active material (matrix) is large, the surface of the negative electrode active material that is the reaction field of the charge carrier and the dielectric material (child material) It is thought that the distance was increased and the interface resistance reduction effect was not sufficiently obtained. On the other hand, in Example 7, since the ratio of the particle diameter is small, the surface of the negative electrode active material (base material) is covered with a dielectric material (child material), the reaction field is reduced, and the effect of reducing the interface resistance is sufficient. It is thought that it was not obtained.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here.

20 Winding electrode body 30 Battery case 32 Battery case body 34 Cover body 36 Safety valve 42 Positive electrode terminal 42a Positive electrode current collector plate 44 Negative electrode terminal 44a Negative electrode current collector plate 50 Positive electrode 52 Positive electrode current collector 52a Positive electrode active material layer non-formed part 54 Positive electrode Active material layer 60 Negative electrode 62 Negative electrode current collector 62a Negative electrode active material layer non-formed portion 64 Negative electrode active material layer 70 Separator 100 Nonaqueous electrolyte secondary battery (lithium ion secondary battery)

Claims (5)

A positive electrode comprising a positive electrode active material layer containing a positive electrode active material;
A negative electrode comprising a negative electrode active material layer containing a negative electrode active material;
A non-aqueous electrolyte,
A non-aqueous electrolyte secondary battery comprising:
The negative electrode active material layer is a dielectric material composite in which a negative electrode active material base material and a dielectric material having a relative dielectric constant higher than that of the non-aqueous electrolyte are supported on the surface of negative electrode active material particles as a base material. Contains a negative electrode active material,
Here, the particle size ratio of the average particle diameter of the dielectric material supported on the dielectric material composite negative electrode active material to the average particle diameter of the negative electrode active material base material is 0.005 to 0.1. Non-aqueous electrolyte secondary battery.   The nonaqueous electrolyte secondary battery according to claim 1, wherein a relative dielectric constant of the dielectric material is 10 times or more higher than a relative dielectric constant of the negative electrode active material base material.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the dielectric material is an inorganic oxide.   The non-aqueous electrolyte secondary battery according to claim 3, wherein the dielectric material is an inorganic oxide having a perovskite structure.   The non-aqueous electrolyte secondary battery according to claim 4, wherein the dielectric material is barium titanate.

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