JP7244366B2 - Electrode materials for secondary batteries - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electrode material for secondary batteries. Specifically, it relates to an electrode material in which a dielectric is arranged on the surface of active material particles.

BACKGROUND ART Secondary batteries such as lithium-ion secondary batteries and nickel-metal hydride batteries are lightweight and have high energy density, and in recent years, they are preferably used as so-called portable power sources for personal computers, portable terminals, and the like, as well as power sources for driving vehicles. Among them, lithium-ion secondary batteries have high current density and high battery capacity per unit mass, so they are particularly suitable for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). As a high-output power source, it is expected to spread more and more.

For example, as one form of electrode material contained in secondary batteries such as lithium ion secondary batteries and sodium ion secondary batteries, a substance different from the active material is arranged on the surface of the active material as a core particle. electrode materials.
Various types of such substances have been studied according to purposes, and one example thereof is a dielectric substance. For example, Patent Literature 1 discloses a lithium ion secondary battery including a positive electrode material in which ferroelectric barium titanate is present on the surface of the positive electrode active material. Patent document 1 describes that the interfacial resistance of the lithium-ion secondary battery disclosed in Patent Document 1 is lowered due to the presence of barium titanate on the surface of the positive electrode active material.
Although Patent Document 2 discloses an example of a conventional method for producing barium titanate particles, the technical idea disclosed in this document has no relevance to the field of batteries.

JP 2014-116129 A JP 2016-155748 A

By the way, when a dielectric is placed on the surface of the active material, the dielectric can be dielectrically polarized. Specifically, for example, when a dielectric is placed on the surface of the positive electrode active material, the surface in contact with the electrolyte (electrolytic solution or solid electrolyte) can be positively dielectric, and the surface in contact with the positive electrode active material can be negatively dielectric. It is believed that this causes the charge carriers in the electrolyte (for example, lithium ions in the case of a lithium ion secondary battery) to be attracted to the positive electrode active material, allowing a smooth battery reaction to proceed at the interface of the positive electrode active material.
On the other hand, since the dielectric itself has insulating properties, for example, when the abundance ratio of the dielectric on the surface of the active material increases, the free movement of electrons is hindered in the active material layer containing such an active material. . If so, there is a risk that the battery reaction on the surface of the active material will rather be hindered. In order to solve such problems, it is conceivable to reduce the size (for example, grain size) of the dielectric.

However, typical dielectrics (eg, barium titanate, etc.) become less crystalline as the grain size is reduced, and accordingly the dielectric properties of the dielectric are reduced. Then, for example, when a dielectric with a small particle size is arranged on the surface of the active material, the effect of reducing the interfacial resistance in a secondary battery (for example, a lithium ion secondary battery) cannot be sufficiently obtained, and good battery performance cannot be obtained. There is a possibility that it cannot be realized.

Accordingly, the present invention has been created to solve the above problems, and an object of the present invention is to provide a dielectric having good dielectric properties even when the particle size is set small on the surface of the active material. An object of the present invention is to provide a secondary battery having excellent battery performance by arranging the

The inventors of the present invention found that the battery resistance of a secondary battery can be significantly reduced by disposing a generally rectangular parallelepiped dielectric on the surface of a positive electrode active material or a negative electrode active material. was completed.
That is, in order to achieve the above object, the electrode material for a secondary battery disclosed herein contains a positive electrode active material or a negative electrode active material, and a dielectric disposed on the surface of the active material.
The above dielectrics are XYO ₃ type, X ₂ Y ₂ O ₇ type, and XX′ ₃ Y ₄ O ₁₂ type (where X is an alkali metal element, an alkaline earth metal element, a rare earth metal element, Cu, Pb and Bi). X′ is one or two or more elements of the transition metal elements, Y is one or two of the transition metal elements and Sn It is a composite oxide having a crystal structure of any of the following elements:
Here, the dielectric is formed in a substantially rectangular parallelepiped shape as a whole.
When the dielectric disposed on the surface of the active material is observed under a scanning transmission electron microscope (STEM), the dielectric has a substantially rectangular peripheral edge consisting of four straight sides and four rounded corners. On one surface, the major axis of the rectangular surface is L1 (nm), and the length of the shorter one of the two straight sides substantially parallel to the major axis out of the four right sides is L2 (nm), the average ratio of L2 to L1 under STEM observation satisfies 0.5≦L2/L1≦1.0.

A secondary battery electrode material having such a configuration provides a secondary battery electrode material in which a dielectric having excellent dielectric properties is arranged because the dielectric is a composite oxide having the above-described crystal structure. be able to.
The entire dielectric is formed in a substantially rectangular parallelepiped shape, and when the dielectric placed on the surface of the active material is observed under a STEM, the peripheral edge of the dielectric extends from the four straight sides and the four corner R portions. The average ratio of L2 to L1 under STEM observation on one surface of the substantially rectangular shape is within a predetermined range, so that good dielectric properties are realized even when the grain size of the dielectric is set small. be able to. Moreover, by using the dielectric, the interfacial resistance on the surface of the active material can be significantly reduced.
By adopting the secondary battery electrode material disclosed herein, a secondary battery having excellent battery performance can be provided.

1 is a schematic diagram of an electrode material disclosed herein; FIG. 2 is a diagram schematically showing the shape of a dielectric in the electrode material of FIG. 1; FIG. 1 is a cross-sectional view schematically showing a secondary battery including an electrode material according to one embodiment; FIG. 4 is an image obtained by observing the electrode (positive electrode) material according to Example 1 in a state in which the dielectric is arranged on the surface of the active material. (A) is an image observed under STEM at a magnification of 250K. (B) is an observation image under STEM at a magnification of 1500K. (C) is an image visualized by EDS analysis of the presence of Ba element in the same observation range as (B). (D) is an image visualized by EDS analysis of the presence of Co element in the same observation range as (B). (E) is an image visualized by EDS analysis of the presence of O element in the same observation range as (B). (F) is an image visualized by EDS analysis of the presence of Ti element in the same observation range as (B).

Preferred embodiments of the present invention will now be described with reference to the drawings as appropriate. Matters other than the matters specifically mentioned in the present specification (for example, the composition and properties of the electrode material) and necessary for the implementation of the present invention (for example, other battery components that do not characterize the present invention, general battery manufacturing process, etc.) can be grasped as design matters for those skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and common general technical knowledge in the field. Further, in the present specification, when a numerical range is described as A to B (where A and B are arbitrary numerical values), it means A or more and B or less. The range from A to B includes the range above A and the range below B.

As used herein, the term “secondary battery” generally refers to an electricity storage device that can be repeatedly charged and discharged. For example, lithium-ion secondary batteries, sodium-ion secondary batteries, and the like in which alkali metal ions in the electrolyte are responsible for charge transfer are typical examples included in the secondary battery referred to here.
In addition, the "active material" is a chemical species (for example, lithium ion) that can be used as a charge carrier in a secondary battery such as a lithium ion secondary battery. A material (active material). The term "dielectric" refers to a substance that has better dielectric properties than electrical conductivity and can be said to be an insulator against a DC voltage. Typically, it refers to a substance having a volume resistivity (ρ _v ) of 1×10 ⁵ Ω·m or more at 20° C., which is a value unique to the substance. A particularly preferable dielectric constant (20° C., 1 MHz) is 8 or more.
Hereinafter, as an embodiment of the secondary battery electrode material (hereinafter also simply referred to as "electrode material") disclosed herein, a lithium ion secondary battery (hereinafter also simply referred to as "secondary battery") The present invention will be described in detail by taking the case of application as an example. However, it is not intended to limit the present invention to those described in such embodiments.

<Electrode material>
First, the electrode material disclosed herein will be described with reference to FIG. FIG. 1 is a diagram schematically showing the electrode material disclosed herein.
The electrode material 10 disclosed herein includes a positive electrode active material or a negative electrode active material (indicated by reference numeral 12 in FIG. 1) and the active material (hereinafter, when no distinction is made between positive and negative, simply " and a dielectric 14 disposed on the surface of the active material. Here, "arranged" refers to the fact that the dielectric is attached to a part of the surface of the active material (particle), and the attached dielectric and the active material (particle) are bonded The form is not limited.

<Positive electrode active material>
When the active material 12 is a positive electrode active material, any material typically used as a positive electrode active material for lithium ion secondary batteries can be used without particular limitation. For example, lithium-transition metal composite oxides having various crystal structures such as layered rock salt structure, rock salt structure, spinel structure, and perovskite structure can be employed.
The positive electrode active material is preferably a lithium transition metal composite oxide having a layered rock salt structure or a spinel structure, and preferably contains one or more of Ni, Co, and Mn as a transition element. For example, specific examples of the lithium-transition metal composite oxide having a layered rock salt structure include lithium-nickel composite oxide, lithium-cobalt composite oxide, lithium-manganese composite oxide, or ternary lithium such as lithium-nickel-cobalt-manganese composite oxide. containing complex oxides. In addition, lithium transition metal composite oxides containing transition metal elements other than Ni, Co, and Mn, typical metal elements, etc., may be used as in the conventional ones. Examples thereof include lithium transition metal composite oxides represented by the formula: Li _1+x Ni _y Co _z Mn _(1-yz) M _α O _2-β A _β . where 0≤x≤0.7, 0.1<y<0.9, 0.1<z<0.4, 0≤α≤0.1, 0≤β≤0.5 and obtain. M may be one or more elements selected from Zr, Mo, W, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn and Al. Also, A may be one or more elements selected from F, Cl, and Br.
Further, for example, as a composite oxide having a spinel structure, for example, the formula: Li _1+x Mn _2-y M _y O ₄ (where M does not exist or is one selected from Al, Mg, Co, Fe, Ni and Zn Composite oxides represented by the above metal elements, 0≦x<1, 0≦y<2) can be mentioned.

In addition, a polyanionic compound represented by a general formula such as LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ (wherein M is at least one element selected from Co, Ni, Mn and Fe) is used as a positive electrode active material. You may use it as a substance.

<Negative electrode active material>
When the active material 12 is a negative electrode active material, any material typically used as a negative electrode active material for lithium ion secondary batteries can be used without particular limitation. For example, carbon materials such as graphite (natural graphite and artificial graphite), hard carbon and soft carbon can be preferably used.

<Dielectric>
Next, the dielectric will be described in detail with reference to FIGS. 1 and 2. FIG. FIG. 2 is a diagram schematically showing the shape of the dielectric in the electrode material of FIG.
－Dielectric shape－
-Overall Shape The dielectric 14 is formed in, for example, a substantially rectangular parallelepiped shape as a whole. The term "substantially rectangular parallelepiped" is not limited to the case where the overall shape of the dielectric 14 is a perfect rectangular parallelepiped. It also includes the case where it looks almost like a rectangular parallelepiped at first glance. For example, the surfaces and sides forming the dielectric 14 may have minute unevenness. It is also permissible, for example, if the vertex portion has a rounded shape.

- Planar View In a plan view, the dielectric 14 can be observed as a substantially rectangular shape as illustrated. The term “substantially rectangular” is not limited to the case where the dielectric 14 is perfectly rectangular in plan view. It also includes the case where it looks almost rectangular at first glance. Specifically, for example, when the electrode material 10 is observed under a scanning transmission electron microscope (STEM), for example, the dielectric 14 has four straight sides (146a, 146b, 146c, 146d) and four corners R It can be seen as a substantially rectangular surface 142 consisting of a portion 148 . In the substantially rectangular surface 142, the major axis of the substantially rectangular surface 142 is L1 (nm), and the shorter one of the two straight sides (146a and 146c) substantially parallel to the major axis out of the four straight sides is Let L2 (nm) be the length of the straight side. At this time, the average ratio of L2 to L1 under STEM observation preferably satisfies 0.5≦L2/L1≦1.0. Since the dielectric 14 has a predetermined shape, good dielectric properties can be achieved even when the average grain size is set small. Also, the interfacial resistance on the surface of the active material 12 can be significantly reduced.
Here, "substantially parallel" with the major axis and the two straight sides (146a and 146c) is not limited to being completely parallel. A case where they are almost parallel at first glance is also included. For example, the two straight sides (146a and 146c) are not limited to perfectly straight lines, but may have minute irregularities. Also, the two straight sides (146a and 146c) can be tilted within a range of ±10° with respect to the major axis. Further, the average L2/L1 ratio is specifically calculated by, for example, performing STEM observation of the electrode material 10 and measuring L1 and L2 of about 100 dielectrics 14 .

-nature-
By arranging the dielectric 14 on the surface of the active material 12, the interfacial resistance on the surface of the active material can be significantly reduced by the following mechanism during charging and discharging.
1. The dielectric polarization of the dielectric 14 attracts lithium ions in the electrolyte to the vicinity of the active material 12 (specifically, for example, dielectrically polarized sites in the dielectric 14), and the active material 12 absorbs and releases lithium ions. promote
2. Desolvation of the lithium ions is then facilitated by lowering the solvation energy of the attracted lithium ions (ie, the binding energy between the lithium ions and the electrolyte).
3. It increases the movement speed of lithium ions entering from lattice defects in the active material 12 .

－Crystal Structure of Dielectrics－
Preferred examples of the dielectric 14 include composite oxides having a crystal structure of one of XYO ₃ type, X ₂ Y ₂ O ₇ type, and XX' ₃ Y ₄ O ₁₂ type.
X is an alkali metal element (specifically, for example, Group 1 elements such as Na, K, Rb, Cs), an alkaline earth metal element (specifically, for example, Group 2 elements such as Ca, Sr, Ba elements), rare earth metal elements (specifically, La, Ce, Nd, Sm, Gd, Yb, etc.), Cu, Pb and Bi, or one or more elements. X′ is, for example, one or more elements among transition metal elements (details will be described later), and is an element different from X.
Y is one or more elements selected from transition metal elements and Sn. Transition metal elements are, for example, elements belonging to Groups 3-11 of the IUPAC classification. Specifically, for example, Group 4 elements (eg Ti, Zr, Hf, etc.), Group 5 elements (eg, V, Nb, Ta, etc.), Group 6 elements (Cr, Mo, W, etc.), Group 7 elements (Mn , Tc, etc.), Group 8 elements (Fe, Ru, Os, etc.), Group 9 elements (Co, Rh, Ir, etc.), Group 10 elements (Ni, Pd, Pt, etc.), Group 11 elements (Cu, Ag, Au etc.) and rare earth metal elements (La, Ce, Sm, etc.).
Moreover, Y preferably contains an element different from X, and more preferably consists of an element different from X. For example, BaTiO ₃ and SrTiO ₃ are preferred. The crystal structure of the dielectric 14 can be confirmed by XRD measurement using CuKα rays.

－Dielectric Constant－
The relative permittivity of the dielectric 14 is 8 to 500 (preferably 50 or higher, more preferably 100 or higher, still more preferably 200 or higher) or higher. In addition, the volume resistivity at normal temperature (20° C.) is 1×10 ⁵ Ω·m or more (preferably 1×10 ⁶ Ω·m or more, more preferably 1×10 ¹⁰ Ω·m or more). As a result, it is possible to promote the intercalation and deintercalation of lithium ions on the surface of the active material 12 and reduce the interfacial resistance.
-Average particle size of dielectric material-
The average grain size of the dielectric 14 is approximately 1000 nm or less, but typically 3 to 100 nm is preferred. If the average grain size is less than 3 nm, the stability of the crystal structure of the dielectric 14 may deteriorate. However, good dielectric properties can be achieved. On the other hand, if the average particle size is larger than 100 nm, the insulating properties of the dielectric 14 may hinder the progress of the battery reaction on the surface of the active material 12 .
Note that the average particle diameter of the dielectric may be, for example, the average major axis (ie, L1) when the electrode material is observed under STEM. For example, the STEM observation of the electrode material 10 is performed, L1 of about 100 dielectrics 14 is measured, and the average grain size is calculated.

-Manufacturing method of dielectric-
A method for manufacturing the dielectric 14 is not particularly limited as long as the dielectric 14 is formed into the desired shape as described above, and various conventionally known methods can be employed. In one example, a hydrothermal method, such as that described in US Pat. Specific materials, procedures, reaction conditions, etc. in the present invention are described in each example described later. The method includes hydrothermal treatment using an autoclave. Dielectrics 14 with different shapes, average L2/L1 ratios, and grain sizes can be produced by changing the pH, temperature conditions, and processing time of the material mixture during the hydrothermal treatment as needed. can be manufactured.

<Method for producing electrode material>
The method of attaching the dielectric to the surface of the active material is not particularly limited. For example, an active material and a dielectric can be prepared in advance, and the dielectric can be placed on the surface of the active material by a conventional method (for example, a conventional method such as forming a coating on the active material).
As an example of the conventional method, a mechanochemical treatment using various mechanochemical apparatuses is particularly preferable. For example, by using a pulverizing and mixing device such as a ball mill, planetary mill, bead mill, etc., desired mechanochemical reactions can be caused to produce the electrode material.
Specifically, for example, first, an active material (powder material) and dielectric particles (powder material) are put into a predetermined mechanochemical device (ball mill or the like). Next, kinetic energy is applied for a predetermined period of time at a predetermined number of revolutions. This allows the dielectric to adhere to the surface of the active material. After the mechanochemical treatment, the dielectric can be sintered on the surface of the active material by firing at a temperature of approximately 200 to 1000° C. (eg, 300 to 800° C.).

For example, when an electrode material is produced by such mechanochemical treatment, the ratio between the amount of active material and the amount of dielectric material may vary depending on the composition, shape, etc. of the active material and dielectric material. Therefore, the ratio is not particularly limited, but generally the amount of dielectric material is preferably in the range of 0.05 to 20 mol%, particularly in the range of 0.1 to 10 mol%, with respect to the amount of active material. preferable. If the ratio of the dielectric amount is less than 0.05 mol %, it may be difficult to dispose the dielectric on the surface of the active material to the extent that the effects of the present invention are realized. In addition, if the ratio of the dielectric amount is more than 20 mol %, the progress of the battery reaction on the surface of the active material may be hindered by the insulating properties of the dielectric.

<Detection Means>
The presence of the dielectric placed on the surface of the active material can be detected (observed) by various detection means.
For example, electron microscopes such as scanning cell microscopes (SEM), transmission electron microscopes (TEM), and STEM can be used.
In addition, scanning electron microscope-energy dispersive X-ray spectrometer (STEM-EDS, STEM-EDX), secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), fluorescence Techniques such as X-ray analysis (XRF) can be employed to qualitatively and quantitatively analyze elemental composition, crystallinity, and the like.

<Action and effect: reduction of interfacial resistance>
The electrode material disclosed herein achieves excellent dielectric properties because the dielectric is a composite oxide having a predetermined crystal structure. In addition, the entire dielectric is formed in a substantially rectangular parallelepiped shape, and the dielectric has a predetermined shape when observed under an STEM. can be realized. Then, the interfacial resistance on the surface of the active material can be significantly reduced.

<Provision of secondary batteries>
Since the electrode material disclosed herein can reduce the interfacial resistance on the surface of the active material as described above, it is suitably used for the configuration of the electrode (that is, the positive electrode and / or the negative electrode) of the secondary battery. be able to. That is, the secondary battery can use the electrode material disclosed herein for the configuration of at least one of the positive electrode and the negative electrode. This makes it possible to provide a secondary battery with good battery performance.

<Example of secondary battery>
There are no restrictions on the method of constructing the secondary battery, the various materials used, the form of the battery, etc., except that the electrodes are provided with the electrode material disclosed herein, and may be the same as conventional ones.
For example, a non-aqueous electrolyte secondary battery (e.g. non-aqueous electrolyte lithium ion secondary battery) having a non-aqueous electrolyte as an electrolyte, an all-solid battery having a solid electrolyte as an electrolyte (e.g. all-solid lithium ion secondary battery), Various forms of secondary batteries can be provided, such as a secondary battery (for example, a lithium ion polymer secondary battery) including a gel polymer as an electrolyte.

Next, a secondary battery that can contain the electrode material disclosed herein will be described with reference to FIG. FIG. 3 is a cross-sectional view schematically showing a secondary battery including an electrode material according to one embodiment.
As shown, the secondary battery 100 includes a flat wound electrode assembly 20, a battery case 30, and an electrolyte (non-aqueous electrolyte) not shown.
The battery case 30 is composed of a bottomed rectangular parallelepiped case main body 32 having an opening at the upper end, and a lid 34 attached to the opening to close the opening. The battery case 30 is made of aluminum, for example. A positive electrode terminal 42 for external connection, a negative electrode terminal 44 and a safety valve 36 are formed on the lid 34 .
The wound electrode body 20 is configured by stacking long sheet-like positive electrodes 50, negative electrodes 60, and separators (70, 72) and winding them in the longitudinal direction.

The positive electrode 50 is formed by adding a positive electrode active material or an electrode material disclosed herein (positive electrode material) to one or both surfaces of a positive electrode current collector 52 made of a sheet-shaped aluminum foil or the like, and adding a conductive material, a binder, or the like. The positive electrode active material layer 54 is formed by adhering a composition (for example, a paste (slurry)) supply material prepared by adding a non-aqueous solvent to a predetermined thickness. The positive electrode current collector 52 has an uncoated portion 52a where the positive electrode active material layer 54 is not coated, to which the tip portion 42a of the positive electrode terminal 42 is joined.
In the negative electrode 60, a negative electrode active material or an electrode material (negative electrode material) disclosed herein is applied to one surface or both surfaces of a negative electrode current collector 62 made of a sheet-like copper foil or the like as a binder, a thickener, or the like. The negative electrode active material layer 64 is formed by depositing a composition prepared by mixing with additives (for example, a paste (slurry) supply material prepared by adding a non-aqueous solvent to a predetermined thickness). Further, the negative electrode current collector 62 is provided with an uncoated portion 62a where the negative electrode active material layer 64 is not coated, to which the tip portion 44a of the negative electrode terminal 44 is joined.
As the separators (70, 72), for example, a separator having a single layer structure or a separator having a laminated structure made of a porous polyolefin resin such as polypropylene (PP) or polyethylene (PE) can be used.

The above description of the structure of the secondary battery, construction materials, etc. is general and does not particularly characterize the present invention, so further detailed description and illustrations will be omitted. Other than using the electrode materials disclosed herein, those skilled in the art can readily fabricate lithium ion secondary batteries and other secondary batteries of various shapes and sizes by employing conventional materials and manufacturing processes. can be built to

Several test examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the test examples.

<<Test Example 1. Examination of the shape of the dielectric material>>
-Example 1-
[Fabrication of dielectric]
First, predetermined amounts of barium hydroxide octahydrate, titanium bis(ammonium lactate) dihydroxide, sodium hydroxide, tert-butylamine, and oleic acid were mixed in pure water. Then, the pH of the mixture was appropriately adjusted, and a hydrothermal treatment was performed in an autoclave for a predetermined treatment time under predetermined temperature conditions.
After the hydrothermal treatment, the mixture was filtered, and the obtained dielectric (BaTiO ₃ ) was washed with water and dried.
[Preparation of positive electrode material]
A lithium-nickel-cobalt-manganese composite oxide (specifically, LiNiCoMnO ₂ ) having a layered rock salt structure was prepared as a positive electrode active material. Next, the positive electrode active material and the above BaTiO ₃ were put into a ball mill and subjected to mechanochemical treatment, followed by firing treatment in an air atmosphere at a temperature of 300°C. A positive electrode material in which the body (BaTiO ₃ ) was arranged was obtained.

[Observation and elemental composition analysis of positive electrode material]
Regarding the positive electrode material obtained above, confirm that BaTiO ₃ is arranged on the surface of the positive electrode active material, and the elemental composition of the positive electrode material (specifically, each element of Ba, Co, O, and Ti). Therefore, STEM-EDS was performed. The results are shown in FIGS. 4(A) to 4(F). FIG. 4 is an image obtained by observing the electrode (positive electrode) material according to Example 1 in a state in which the dielectric is arranged on the surface of the active material. (A) is an image observed under STEM at a magnification of 250K. (B) is an observation image under STEM at a magnification of 1500K. (C) to (F) are images visualized by EDS analysis of the presence of elements Ba, Co, O, and Ti in the same observation range as (B).
As shown in the figure, it was confirmed that a substantially rectangular dielectric was arranged on the surface of the positive electrode active material. Also, according to STEM-EDS, Ba element and Ti element were detected in the substantially rectangular dielectric portion. On the other hand, Co element and O element were detected in the positive electrode active material portion.
-Comparative Example 1-
A positive electrode material (dielectric: BaTiO ₃ ) according to Comparative Example 1 was produced in the same manner as in Example 1, except that the hydrothermal treatment using an autoclave was not performed.

[Calculation of average L2/L1 ratio of dielectric]
The average L2/L1 ratio of the dielectric was calculated for a total of two positive electrode materials of Example 1 and Comparative Example 1. Specifically, STEM observation was performed for each of the two kinds of positive electrode materials, L1 and L2 of 100 observed dielectrics were measured, and an average L2/L1 ratio was calculated. As a result, the average L2/L1 ratio in Example 1 was within the range of 0.5≦L2/L1≦1.0. On the other hand, the average L2/L1 ratio in Comparative Example 1 was outside the range. Table 1 shows specific numerical values.

[Construction of secondary battery]
A secondary battery was constructed using the above two kinds of positive electrode materials.
Specifically, first, the positive electrode material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are mixed in a mass ratio of positive electrode active material: AB:PVdF=94:3. :3 and mixed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry. This positive electrode slurry was applied along the longitudinal direction of a strip-shaped aluminum foil (positive electrode current collector, 15 μm) and dried at 120°C. Then, the dried positive electrode slurry was pressed together with an aluminum foil. Thus, a strip-shaped positive electrode sheet having a positive electrode active material layer on the positive electrode current collector was produced.

Next, on a copper foil (negative electrode current collector, 10 μm), natural graphite (negative electrode active material), carboxymethyl cellulose (CMC) as a thickener, and styrene-butadiene rubber (SBR) or PVdF as a binder are applied. , The mass ratio was negative electrode active material:CMC:SBR or PVdF=98:1:1, and mixed in water or NMP to prepare a negative electrode slurry. Using this, a strip-shaped negative electrode sheet provided with a negative electrode active material layer was prepared by the method described above. Next, the positive electrode sheet and the negative electrode sheet prepared above are opposed to each other with a strip-shaped separator sheet (20 μm-thick PP/PE/PP structure separator) interposed therebetween, and wound in the longitudinal direction to obtain a wound electrode. made the body. Then, the positive electrode current collecting member was welded to the positive electrode sheet, and the negative electrode current collecting member was welded to the negative electrode sheet.
Next, as a non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a volume ratio of EC:DMC:EMC = 3:4:3, A 1.0M solution of LiPF ₆ as a supporting salt was prepared.
Then, the wound electrode body and the non-aqueous electrolytic solution prepared above were housed in a battery case to construct a secondary battery (Example 1 and Comparative Example 1). The battery capacity of the secondary battery was 5 Ah.

[IV resistance measurement]
The above secondary battery activated under predetermined conditions was adjusted to SOC 50%, and discharged at a current value of 100 Ah for 10 seconds. The voltage drop amount ΔV at this time was acquired, and the battery resistance was calculated using the current value and ΔV. Taking the resistance of the secondary battery of Comparative Example 1 as 100%, the resistance ratio of the secondary battery of the example was obtained. Table 1 shows the results.

As shown in Table 1, it was confirmed that the average L2/L1 ratio of the dielectric according to Example 1 satisfies a predetermined range. It was also confirmed that the IV resistance of the secondary battery was lowered by arranging such a dielectric on the surface of the positive electrode active material.

<<Test Example 2. Investigation of particle size of dielectric material>>
In this test example, the particle size of the dielectric material was appropriately varied to prepare positive electrode materials, and the secondary batteries constructed using the positive electrode materials were evaluated in the same manner as in test example 1.
-Example 2-
A positive electrode material according to Example 2 was produced using the same materials and processes as in Example 1, except that the pH of the mixture before the hydrothermal treatment and the hydrothermal treatment conditions (e.g., temperature conditions and treatment time) were changed as appropriate. The positive electrode material was observed under STEM, and the average L2/L1 ratio was calculated in the same manner as in Test Example 1. Also, a secondary battery was constructed in the same manner as in Test Example 1, and the same characteristics were evaluated. The results are shown in the corresponding columns of Table 2. Note that "average particle size (nm)" in Table 2 indicates the value corresponding to L1 (nm) measured in the observation under the STEM.

As shown in Table 2, it was confirmed that the average L2/L1 ratio of the dielectric according to Example 2 satisfies a predetermined range. Moreover, it was confirmed that the IV resistance of the secondary battery was lowered even when the average particle diameter was set small by arranging such a dielectric on the surface of the positive electrode active material.

<<Test Example 3. Examination of the amount of dielectric added>>
In this test example, positive electrode materials were produced by appropriately varying the amount (mol %) of the dielectric added, and secondary batteries constructed using the positive electrode materials were evaluated in the same manner as in test example 1.
- Examples 3 to 7 -
In the mechanochemical treatment, the dielectric according to Example 2 was used, and the secondary battery was produced using the same materials and processes as in Example 1, except that the amount (mol%) of the dielectric added to the positive electrode active material was changed as appropriate. built. Then, the same characteristic evaluation as in Test Example 1 was performed. The results are shown in the corresponding columns of Table 3.

As shown in Table 3, it was confirmed that the IV resistance of the secondary battery was lowered by disposing the dielectrics according to Examples 2 to 7 on the surface of the positive electrode active material. The addition amount of the dielectric in the mechanochemical treatment was preferably 0.05 to 20 mol %, more preferably 0.1 to 10 mol %.

<<Test Example 4. Examination of the type of active material≫
In this test example, electrode materials (i.e., positive electrode material and negative electrode material) were produced by appropriately changing the type of active material, and the same evaluation as in test example 1 was performed on the secondary battery constructed using the electrode material. gone.
-Example 8-
In the mechanochemical treatment, except that the dielectric according to Example 2 was used, the spinel structure positive electrode active material was used as the positive electrode active material, and the amount of the dielectric added to the positive electrode active material was 1 mol%. A secondary battery was constructed using the same materials and processes as in Example 1.
-Example 9-
Example 1 except that a negative electrode active material in which the dielectric according to Example 2 was added in an amount of 1 mol% and placed on the surface of natural graphite was used as a negative electrode active material, and a positive electrode active material in which no dielectric was placed on the surface was used. A secondary battery was constructed using the same materials and processes as
-Comparative Example 2-
In the mechanochemical treatment, the dielectric according to Comparative Example 1 was used, the spinel structure positive electrode active material was used as the positive electrode active material, and the amount of the dielectric added to the positive electrode active material was 1 mol%. A secondary battery was constructed using the same materials and processes as in Example 1.
-Comparative Example 3-
Example 1 except that a negative electrode active material in which the dielectric according to Comparative Example 1 was added in an amount of 1 mol% and placed on the surface of natural graphite was used as a negative electrode active material, and a positive electrode active material in which no dielectric was placed on the surface was used. A secondary battery was constructed using the same materials and processes as
Then, in the same manner as in the test example, the characteristics of the four types of secondary batteries were evaluated. Table 4 shows the results.

As shown in Table 4, it was confirmed that the IV resistance of the secondary battery was lowered by arranging a predetermined dielectric on the surface of the active material, regardless of the type of active material.

Although the present invention has been described in detail above, the above-described embodiments and test examples are merely examples, and the invention disclosed herein includes various modifications and alterations of the above-described specific examples. For example, although a lithium ion secondary battery is illustrated here as an example of a secondary battery, similar effects can be achieved even when applied to a sodium ion secondary battery and a magnesium ion secondary battery.

10 Electrode material 12 Active material 14 Dielectric 142 Surface 146a Straight side 146b Straight side 146c Straight side 146d Straight side 148 Corner R 20 Wound electrode body 30 Battery case 32 Case main body 34 Lid 36 Safety valve 42 Positive electrode terminal 42a Tip portion 44 Negative electrode terminal 44a Tip portion 50 Positive electrode 52 Positive electrode current collector 52a Uncoated portion 54 Positive electrode active material layer 60 Negative electrode 62 Negative electrode current collector 62a Uncoated portion 64 Negative electrode active material layers 70, 72 Separator 100 Lithium ion Secondary battery L1 Long diameter L2 Length

Claims (4)

An electrode material for a secondary battery containing a positive electrode active material or a negative electrode active material and a dielectric disposed on the surface of the active material,
The dielectrics are XYO ₃ type, X ₂ Y ₂ O ₇ type, and XX′ ₃ Y ₄ O ₁₂ (where X is an alkali metal element, alkaline earth metal element, rare earth metal element, Cu, Pb and Bi). X′ is one or two or more elements of the transition metal elements, Y is one or two of the transition metal elements and Sn are the above elements.) A composite oxide having a crystal structure of any one of
Here, the dielectric is formed in a substantially rectangular parallelepiped shape as a whole,
When the dielectric disposed on the surface of the active material is observed under a scanning transmission electron microscope (STEM), the dielectric has a substantially rectangular peripheral edge consisting of four straight sides and four rounded corners. In one surface, L1 (nm) is the major axis of the substantially rectangular surface, and the length of the shorter one of the four right side parts substantially parallel to the major axis When the height is L2 (nm), the average ratio of L2 to L1 under the STEM observation satisfies 0.5 ≤ L2 / L1 ≤ 1.0,
An electrode material for a secondary battery, characterized by: Said XYO ₃ In a dielectric having a crystal structure of the type
X is an alkaline earth metal element, Pb, or Bi;
2. The electrode material for a secondary battery according to claim 1, wherein Y is a Group 4 element. 3. The electrode material for a secondary battery according to claim 1, wherein said dielectric has an average particle size of 3 nm or more and 100 nm or less. 4. The electrode material for a secondary battery according to claim 1, wherein the dielectric has a dielectric constant of 8 or more and 500 or less.

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