JP2019071194A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

To rapidly suppress a short-circuit current after a short-circuit.SOLUTION: An nonaqueous electrolyte secondary battery at least includes a positive electrode 110, a negative electrode 120, an electrolyte, and coated particles 10. The coated particles 10 are dispersed in the electrolyte. The coated particles 10 each include core particles 11 and a shell layer 12. The core particles 11 each contain a ferromagnetic material. The shell layer 12 covers the surface of each of the core particles 11. The shell layer 12 contains an insulator. The ratio of the coated particles 10 to a sum of the electrolyte and the coated particles 10 ranges from 3 to 15 vol.%. The core particles 11 each have an average particle diameter ranging from 50 to 2000 nm.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a non-aqueous electrolyte secondary battery.

  Unexamined-Japanese-Patent No. 2000-123866 (patent document 1) is disclosing the electrolyte solution containing a thermosetting resin composition.

Unexamined-Japanese-Patent No. 2000-123866

  When the electrolytic solution contains a thermosetting resin composition, the thermosetting resin composition may be polymerized by Joule heat due to a short circuit current when a short circuit occurs. This may inhibit the diffusion of lithium ions. That is, suppression of the short circuit current is expected.

  However, since the trigger of the polymerization is heat, the short circuit state may be sustained to some extent, so that the suppression effect of the short circuit current may not be obtained unless the temperature of the electrolyte is increased by Joule heat.

  An object of the present disclosure is to suppress a short circuit current promptly after the occurrence of a short circuit.

  Hereinafter, technical configurations and effects of the present disclosure will be described. However, the mechanism of action of the present disclosure includes presumption. The scope of the claims should not be limited by the correctness of the mechanism of action.

  The non-aqueous electrolyte secondary battery includes at least a positive electrode, a negative electrode, an electrolyte and coated particles. The coated particles are dispersed in the electrolyte. The coated particles comprise core particles and a shell layer. The core particle comprises a ferromagnetic material. The shell layer covers the surface of the core particle. The shell layer comprises an insulator. The ratio of the coated particles to the total of the electrolytic solution and the coated particles is 3% by volume or more and 15% by volume or less. The core particles have an average particle size of 50 nm or more and 2000 nm or less.

FIG. 1 is a conceptual diagram for explaining the action mechanism of the present disclosure.
For example, it is conceivable that the conductive foreign matter 20 such as a nail shorts the positive electrode 110 and the negative electrode 120. A short circuit current (I) is thereby generated. It is considered that a magnetic field (H) is generated due to the short circuit current (I) simultaneously with the generation of the short circuit current (I). The magnetic field (H) is considered to be generated in the form of a vortex around the short circuit current (I) according to Ampere's law.

  The coated particles 10 are dispersed in the electrolytic solution. The coated particle 10 penetrates into the void inside the positive electrode 110 and the negative electrode 120 together with the electrolytic solution. The coated particle 10 has a core-shell structure. That is, the coated particle 10 includes the core particle 11 and the shell layer 12. The core particle 11 contains a ferromagnetic material. It is believed that the coated particles 10 respond to the swirling magnetic field and collect around the short circuit current. As a result, it is expected that the coated particle 10 adheres to the short circuit site (i.e., the conductive foreign matter 20). The shell layer 12 includes an insulator. Therefore, when the covering particle 10 adheres to the conductive foreign matter 20, the surface of the conductive foreign matter 20 is covered with the insulator. This can inhibit the flow of current through the conductive foreign material 20. That is, suppression of the short circuit current is expected.

  The trigger for starting the movement of the coated particle 10 is a magnetic field. As mentioned above, the magnetic field is considered to occur simultaneously with the occurrence of the short circuit current. Therefore, in the non-aqueous electrolyte secondary battery of the present disclosure, it is expected that the short circuit current will be suppressed immediately after the occurrence of the short circuit.

  However, the ratio of the coated particles 10 to the total of the electrolytic solution and the coated particles 10 is 3% by volume or more and 15% by volume or less. If the ratio is less than 3% by volume, the effect of suppressing the short circuit current tends to be small. It is considered that the surface of the conductive foreign matter 20 can not be sufficiently covered because the amount of the covering particles 10 is small. Even if the ratio exceeds 15% by volume, the effect of suppressing the short circuit current tends to be small. It is considered that the response of the coated particle 10 to the magnetic field is slowed down because the flowability of the electrolytic solution and the entire coated particle 10 is reduced. When the ratio exceeds 15% by volume, the increase in resistance tends to be large.

  Furthermore, the core particle 11 has an average particle diameter of 50 nm or more and 2000 nm or less. If the average particle size is less than 50 nm, the effect of suppressing the short circuit current tends to be small. It is considered that the surface of the conductive foreign matter 20 can not be sufficiently covered because the coated particle 10 is excessively small. Even if the average particle size exceeds 2000 nm, the effect of suppressing the short circuit current tends to be small. It is considered that the response to the magnetic field is slowed down because the coated particle 10 is excessively large.

FIG. 1 is a conceptual diagram for explaining the action mechanism of the present disclosure. FIG. 2 is a schematic view showing an example of the configuration of the non-aqueous electrolyte secondary battery of the present embodiment. FIG. 3 is a schematic view showing an example of the configuration of the electrode group of the present embodiment. FIG. 4 is a schematic view showing an example of the configuration of the positive electrode of the present embodiment. FIG. 5 is a schematic view showing an example of the configuration of the negative electrode of the present embodiment.

  Hereinafter, embodiments of the present disclosure (referred to herein as “the embodiments”) will be described. However, the following description does not limit the scope of the claims. For example, in the present embodiment, a “lithium ion secondary battery” is described as an example of the non-aqueous electrolyte secondary battery. However, the non-aqueous electrolyte secondary battery should not be limited to the lithium ion secondary battery. The non-aqueous electrolyte secondary battery of the present embodiment may be, for example, a "sodium ion secondary battery" or the like. Hereinafter, "non-aqueous electrolyte secondary battery" may be abbreviated as "battery".

<Non-aqueous electrolyte secondary battery>
FIG. 2 is a schematic view showing an example of the configuration of the non-aqueous electrolyte secondary battery of the present embodiment.
Battery 100 includes case 190. Case 190 is square (flat rectangular parallelepiped). Of course, the case may be cylindrical. The case 190 includes a container 191 and a lid 192. The lid 192 is joined to the container 191, for example, by laser welding. Case 190 is sealed. Case 190 may be made of, for example, an aluminum (Al) alloy. The case may be, for example, a pouch made of an Al laminated film, as long as the case can be sealed. That is, the battery may be a laminate type battery.

  The lid 192 is provided with an external terminal 193. The lid 192 may be provided with, for example, a liquid injection hole, a current shutoff mechanism (CID), a gas discharge valve, and the like.

  The case 190 accommodates the electrode group 150 and the electrolytic solution. The dashed-dotted line in FIG. 2 has shown the liquid level of electrolyte solution. The electrolytic solution is also present in the air gap in the electrode assembly 150. The coated particles 10 (FIG. 1) are dispersed in the electrolytic solution. In the present embodiment, when the short circuit occurs, it is expected that the short circuit current is suppressed by the covering particle 10 responding to the magnetic field.

<< Electrolyte solution >>
The electrolyte is a non-aqueous electrolyte. That is, the electrolyte contains an aprotic solvent and a support salt. The aprotic solvent should not be particularly limited. Aprotic solvents may, for example, comprise cyclic carbonates and linear carbonates. The mixing ratio of the cyclic carbonate and the linear carbonate may be, for example, “cyclic carbonate / linear carbonate = 1/9 to 5/5 (volume ratio)”.

  The cyclic carbonate may be, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC) or the like. One cyclic carbonate may be used alone. Two or more cyclic carbonates may be used in combination.

  The linear carbonate may be, for example, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) or the like. One type of linear carbonate may be used alone. Two or more linear carbonates may be used in combination.

  Aprotic solvents may include, for example, lactones, cyclic ethers, linear ethers, carboxylic esters, and the like. The lactone may be, for example, γ-butyrolactone (GBL), δ-valerolactone or the like. The cyclic ether may be, for example, tetrahydrofuran (THF), 1,3-dioxolane, 1,4-dioxane and the like. The chain ether may be 1,2-dimethoxyethane (DME) or the like. The carboxylic acid ester may be, for example, methyl formate (MF), methyl acetate (MA), methyl propionate (MP) and the like.

The electrolytic solution may contain, for example, a supporting salt of 0.5 mol / l or more and 2 mol / l or less. The supporting salt may be, for example, LiPF ₆ , LiBF ₄ , Li [N (FSO ₂ ) ₂ ], Li [N (CF ₃ SO ₂ ) ₂ ] or the like. One type of supporting salt may be used alone. Two or more types of supporting salts may be used in combination.

The electrolyte may further include various functional additives in addition to the aprotic solvent and the support salt. The electrolytic solution may contain, for example, 1% by mass or more and 5% by mass or less of the functional additive. Examples of the functional additive include gas generating agents (so-called overcharge additives), solid electrolyte interface (SEI) film forming agents, and the like. The gas generating agent may be, for example, cyclohexylbenzene (CHB), biphenyl (BP) or the like. Examples of SEI film forming agents include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), Li [B (C ₂ O ₄ ) ₂ ], LiPO ₂ F ₂ , propanesultone (PS), ethylene sulfite (ES) Or the like. One functional additive may be used alone. Two or more functional additives may be used in combination.

<< Coated particle >>
The coated particle 10 comprises a core particle 11 and a shell layer 12 (FIG. 1). The coated particles 10 are dispersed in the electrolytic solution. The coated particles 10 can penetrate into the voids in the positive electrode 110 and the negative electrode 120 together with the electrolytic solution. Therefore, it is expected that the suppression effect of the short circuit current can be obtained even if the amount of the coated particles 10 is small.

  The ratio of the coated particles 10 to the total of the electrolytic solution and the coated particles 10 is 3% by volume or more and 15% by volume or less. If the ratio is less than 3% by volume, the effect of suppressing the short circuit current tends to be small. It is considered that the surface of the conductive foreign matter 20 can not be sufficiently covered because the amount of the covering particles 10 is small. Even if the ratio exceeds 15% by volume, the effect of suppressing the short circuit current tends to be small. It is considered that the response of the coated particle 10 to the magnetic field is slowed down because the flowability of the electrolytic solution and the entire coated particle 10 is reduced. When the ratio exceeds 15% by volume, the increase in resistance tends to be large. The same ratio may be, for example, 5% by volume or more. The same ratio may be, for example, 10% by volume or less. It is expected that the suppression effect of the short circuit current is large in the range.

(Core particle)
The core particle 11 imparts magnetism to the coated particle 10. That is, the core particle 11 contains a ferromagnetic material. The core particle 11 may be formed substantially only of a ferromagnetic material. "Ferromagnetic" refers to a substance in which free atoms of magnetic atoms or metals form spontaneous magnetization by aligning magnetic moments in parallel by positive exchange interaction. Ferromagnets are attracted to the magnetic field. Therefore, in the present embodiment, when a short circuit occurs, it is considered that the coated particle 10 is attracted to the short circuit site and adheres to the short circuit site. In the present embodiment, for example, it is expected that the coated particle 10 adheres to the short circuit site in about several milliseconds.

  The ferromagnetic material may be, for example, iron, magnetite, ferrite, iron nitride or the like. One ferromagnetic substance may be used alone. Two or more ferromagnetic substances may be used in combination. That is, the ferromagnetic material may be, for example, at least one selected from the group consisting of iron, magnetite, ferrite and iron nitride. The ferromagnetic material may be, for example, at least one selected from the group consisting of iron and magnetite.

  The core particle 11 has an average particle diameter of 50 nm or more and 2000 nm or less. "Average particle size" indicates a harmonic mean particle size (diameter) according to the scattered light intensity standard. If the average particle size is less than 50 nm, the effect of suppressing the short circuit current tends to be small. It is considered that the surface of the conductive foreign matter 20 can not be sufficiently covered because the coated particle 10 is excessively small. Even if the average particle size exceeds 2000 nm, the effect of suppressing the short circuit current tends to be small. It is considered that the response to the magnetic field is slowed down because the coated particle 10 is excessively large. The core particle 11 may have an average particle size of, for example, 100 nm or more. The core particles 11 may have an average particle size of, for example, 1000 nm or less. In this range, it is expected that the suppression effect of the short circuit current is large.

(Shell layer)
The shell layer 12 covers the surface of the core particle 11. The shell layer 12 provides insulation to the coated particles 10. That is, the shell layer 12 contains an insulator. The shell layer 12 may be formed only of an insulator. Since the shell layer 12 includes an insulator, the coating particle 10 adheres to the shorting site, whereby the resistance of the shorting site can be increased.

  The shell layer 12 preferably covers the entire surface of the core particle 11. However, as long as the short circuit site can be made to have a high resistance, a part of the surface of the core particle 11 may not be covered by the shell layer 12.

The insulator of the present embodiment may have, for example, a resistivity of 10 ⁶ Ω · m or more. The insulator may have a resistivity of, for example, 10 ¹⁰ Ω · m or more and 10 ²⁰ Ω · m or less. The insulator may be organic. The shell layer 12 may be formed, for example, by surface treatment of the core particle 11 with a silane coupling agent, surfactant or the like. That is, the shell layer 12 may contain a silyl compound. The silyl compound indicates a compound having a silyl group.

  The insulator may be inorganic. The shell layer 12 may be formed, for example, by attaching ceramic particles to the surface of the core particle 11. The ceramic particles may be, for example, silica, titania, alumina or the like. The shell layer 12 may have a thickness of, for example, 1 nm or more and 10 nm or less.

<< Electrode group >>
FIG. 3 is a schematic view showing an example of the configuration of the electrode group of the present embodiment.
The electrode group 150 is a wound type. That is, the electrode group 150 is formed by stacking the positive electrode 110, the separator 130, the negative electrode 120, and the separator 130 in this order and further winding them in a spiral. Of course, the electrode group may be of a stacked type. The stack-type electrode group can be formed by alternately laminating the positive electrode and the negative electrode. A separator is disposed between each of the electrodes.

<< positive electrode >>
FIG. 4 is a schematic view showing an example of the configuration of the positive electrode of the present embodiment.
The positive electrode 110 of the present embodiment is a belt-like sheet. The positive electrode 110 includes a positive electrode current collector 111 and a positive electrode mixture layer 112. The positive electrode current collector 111 may be, for example, an Al foil or the like. The positive electrode current collector 111 may have a thickness of, for example, 5 μm to 50 μm.

  In the present embodiment, the thickness of each component can be measured, for example, by a micrometer or the like. The thickness of each component may be measured in a cross-sectional microscope image or the like of each component. Thickness can be measured in at least three places. An arithmetic mean of three thicknesses may be taken as the measurement result. It is desirable that the intervals between measurement points be approximately equal.

  The positive electrode mixture layer 112 is formed on the surface of the positive electrode current collector 111. The positive electrode mixture layer 112 may be formed on both the front and back sides of the positive electrode current collector 111. Positive electrode mixture layer 112 may have a thickness of, for example, 10 μm or more and 200 μm or less. A portion where the positive electrode current collector 111 protrudes outside the positive electrode mixture layer 112 in the x-axis direction of FIG. 4 can be used for connection with the external terminal 193.

The positive electrode mixture layer 112 contains at least a positive electrode active material. The positive electrode mixture layer 112 may contain, for example, a positive electrode active material, a conductive material, and a binder. The positive electrode active material should not be particularly limited. The positive electrode active material is, for example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni, Co, Mn) O ₂ (eg LiNi _1/3 Co _1/3 Mn _1/3 O ₂ etc.), It may be Li (Ni, Co, Al) O ₂ (eg LiNi _0.82 Co _0.15 Al _0.03 O ₂ etc.), LiFePO ₄ etc. One type of positive electrode active material may be used alone. Two or more positive electrode active materials may be used in combination.

  The conductive material may be, for example, 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. The conductive material should not be particularly limited. The conductive material may be, for example, acetylene black (AB) or the like. The binder may be, for example, 0.5 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. The binder should not be particularly limited. The binder may be, for example, polyvinylidene fluoride (PVdF) or the like.

<< negative electrode >>
FIG. 5 is a schematic view showing an example of the configuration of the negative electrode of the present embodiment.
The negative electrode 120 of the present embodiment is a belt-like sheet. The negative electrode 120 includes a negative electrode current collector 121 and a negative electrode mixture layer 122. The negative electrode current collector 121 may be, for example, a copper (Cu) foil or the like. The negative electrode current collector 121 may have a thickness of, for example, 5 μm or more and 50 μm or less. The negative electrode mixture layer 122 is formed on the surface of the negative electrode current collector 121. The negative electrode mixture layer 122 may be formed on both the front and back sides of the negative electrode current collector 121. Negative electrode mixture layer 122 may have a thickness of, for example, 10 μm or more and 50 μm or less. A portion where the negative electrode current collector 121 protrudes outward beyond the negative electrode mixture layer 122 in the x-axis direction of FIG. 5 can be used for connection with the external terminal 193.

  The negative electrode mixture layer 122 contains at least a negative electrode active material. The negative electrode mixture layer 122 may contain, for example, a negative electrode active material and a binder. The negative electrode active material should not be particularly limited. The negative electrode active material may be, for example, graphite, graphitizable carbon, non-graphitizable carbon, silicon, silicon oxide, silicon-based alloy, tin, tin oxide, tin-based alloy and the like. One type of negative electrode active material may be used alone. Two or more negative electrode active materials may be used in combination. The binder may be, for example, 0.5 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the negative electrode active material. The binder should not be particularly limited. The binder may be, for example, carboxymethylcellulose (CMC) and styrene butadiene rubber (SBR).

«Separator»
The separator 130 of the present embodiment is a belt-like sheet. Separator 130 may have a thickness of, for example, 5 μm or more and 50 μm or less. The separator 130 is porous. The separator 130 is an insulator. The separator 130 may be made of, for example, polyethylene (PE) or polypropylene (PP).

  The separator 130 may have, for example, a single layer structure. The separator 130 may be formed only of a porous sheet made of, for example, PE. The separator 130 may have, for example, a multilayer structure. The separator 130 may be formed, for example, by laminating a porous sheet made of PP, a porous sheet made of PE, and a porous sheet made of PP in this order.

  A heat resistant layer may be formed on the surface of the separator 130. The heat-resistant layer may have a thickness of, for example, 1 μm to 8 μm. The heat resistant layer contains a heat resistant material. The heat-resistant material may be, for example, alumina or the like.

  Hereinafter, examples of the present disclosure will be described. However, the following description does not limit the scope of the claims.

Example 1
<< Preparation of coated particles >>
Iron particles (average particle size 100 nm) were prepared. The iron particle is a core particle 11 substantially formed only of iron (ferromagnetic material). The iron particles were surface-treated with a silane coupling agent. Thereby, the shell layer 12 which coats the core particle 11 (iron particle) was formed. That is, coated particles 10 were formed. The shell layer 12 is considered to contain a silyl compound.

<< Preparation of electrolyte solution >>
An electrolyte was prepared containing the following aprotic solvent and a Li salt.
Li salt: LiPF ₆ (1 mol / l)
Aprotic solvent: [EC / DMC / EMC = 3/4/3 (volume ratio)]

  The electrolyte and the coated particles 10 were mixed. Thereby, the coated particles 10 were dispersed in the electrolytic solution. The ratio of the coated particles 10 to the total of the electrolytic solution and the coated particles 10 is 10% by volume.

<< Manufacturing of positive electrode >>
The following materials were prepared.
Positive electrode active material: Li (Ni, Co, Mn) O ₂
Conductive material: AB
Binder: PVdF
Solvent: N-methyl-2-pyrrolidone (NMP)
Positive current collector: Al foil (20 μm thick)

  The paste was prepared by mixing the positive electrode active material, the conductive material, the binder, and the solvent. The mixing ratio of the solid content is “positive electrode active material / conductive material / binder = 100/8/2 (mass ratio)”. The paste was applied to the surfaces (both front and back sides) of the positive electrode current collector 111 and dried to form the positive electrode mixture layer 112. The positive electrode mixture layer 112 was rolled. The positive electrode mixture layer 112 and the positive electrode current collector 111 were cut. Thus, the positive electrode 110 was manufactured. The positive electrode 110 has the following external dimensions.

Thickness dimension of the positive electrode 110 (dimension in the y-axis direction in FIG. 4): 70 μm
Length dimension of the positive electrode 110 (dimension in the z-axis direction in FIG. 4): 3000 mm
Width dimension of the positive electrode 110 (dimension in the x-axis direction in FIG. 4): 114 mm
Width dimension of the positive electrode mixture layer 112 (dimension in the x-axis direction in FIG. 4): 94 mm

<< Manufacturing of negative electrode >>
The following materials were prepared.
Negative electrode active material: Graphite Binder: CMC and SBR
Solvent: water Negative electrode current collector: Cu foil (10 μm thick)

  The paste was prepared by mixing the negative electrode active material, the binder and water. The mixing ratio of the solid content is “negative electrode active material / binder = 100/2”. CMC and SBR are equivalent. The paste was applied to the surfaces (both front and back sides) of the negative electrode current collector 121 and dried to form a negative electrode mixture layer 122. The negative electrode mixture layer 122 was rolled. The negative electrode mixture layer 122 and the negative electrode current collector 121 were cut. Thus, the negative electrode 120 was manufactured. Negative electrode 120 has the following external dimensions.

Thickness dimension of the negative electrode 120 (dimension in the y-axis direction in FIG. 5): 80 μm
Length dimension of the negative electrode 120 (dimension in the z-axis direction in FIG. 5): 3300 mm
Width dimension of negative electrode 120 (dimension in the x-axis direction in FIG. 5): 120 mm
Width dimension of the negative electrode mixture layer 122 (dimension in the x-axis direction in FIG. 5): 100 mm

"assembly"
A separator 130 was prepared. The separator 130 has a thickness of 20 μm. The separator 130 is formed by laminating a porous sheet made of PP, a porous sheet made of PE, and a porous sheet made of PP in this order.

  A paste was prepared by mixing alumina, an acrylic binder and a solvent. The paste was applied to the surface (one side) of the separator 130 and dried to form a heat resistant layer.

  The positive electrode 110, the separator 130, the negative electrode 120, and the separator 130 were stacked in this order, and further wound in a spiral shape to form an electrode group 150. The separator 130 was disposed such that the heat-resistant layer faced the negative electrode 120. The electrode group 150 was formed into a flat shape. Case 190 was prepared. The electrode group 150 was housed in the case 190.

  The electrolyte in which the coated particles 10 were dispersed was injected into the case 190. The case 190 was sealed. Thus, the battery 100 (lithium ion secondary battery) was manufactured. Battery 100 is designed to have a rated capacity of 4 Ah in a voltage range of 3 to 4.1V.

  The battery 100 was charged to 4.1 V with a current of 4A. The battery 100 was discharged to 3 V by the current of 4A. Thus, the battery 100 was in the initial state.

Examples 2 to 5
A battery 100 was manufactured in the same manner as in Example 1 except that iron particles having the average particle diameter in Table 1 below were used, and the battery 100 was in an initial state.

Examples 6 to 8
A battery 100 was manufactured in the same manner as in Example 1 except that the electrolytic solution and the coated particles 10 were mixed so as to obtain the ratios in Table 1 below, and the battery 100 was in an initial state.

Example 9
A battery 100 was manufactured in the same manner as in Example 1 except that magnetite particles were used instead of iron particles, and the battery 100 was in an initial state.

Example 10
A battery 100 was manufactured in the same manner as in Example 7 except that magnetite particles were used instead of iron particles, and the battery 100 was in an initial state.

Comparative Example 1
A battery 100 was manufactured in the same manner as in Example 1 except that the coated particles 10 were not used, and the battery 100 was in an initial state.

Comparative Examples 2 and 3
A battery 100 was manufactured in the same manner as in Example 1 except that iron particles having the average particle diameter in Table 1 below were used, and the battery 100 was in an initial state.

Comparative Examples 4 and 5
A battery 100 was manufactured in the same manner as in Example 1 except that the electrolytic solution and the coated particles 10 were mixed so as to obtain the ratios in Table 1 below, and the battery 100 was in an initial state.

Comparative Example 6
A battery 100 was manufactured in the same manner as in Example 9 except that magnetite particles having the average particle diameter in Table 1 below were used, and the battery 100 was in an initial state.

<Evaluation>
"Peeling test"
The battery 4 was charged to 4.1 V by the current of 4A. A nail was prepared. The nail has a torso diameter of 3 mm. A nail was inserted into the battery 100 at a speed of 1 mm / sec. The amount of voltage drop one second after the nail was inserted into the battery 100 was measured. The results are shown in Table 1 below. As the voltage drop amount is smaller, it is considered that the suppression effect of the short circuit current is obtained at an early stage after the occurrence of the short circuit.

Initial resistance
The voltage of the battery 100 was adjusted to 3.7V. In a temperature environment of 25 ° C., the battery 100 was discharged by a current of 40 A. The amount of voltage drop 10 seconds after the start of discharge was measured. The resistance was calculated by dividing the amount of voltage drop by the current. The results are shown in Table 1 below.

<Result>
As shown in Table 1 above, the dispersion of the coated particles 10 in the electrolytic solution tends to suppress the short circuit current. The coated particles 10 respond to the magnetic field due to the short circuit current, and the coated particles 10 adhere to the surface of the nail (conductive foreign body 20), which is considered to rapidly insulate the nail.

  The comparative example 2 has a small effect of suppressing the short circuit current. It is considered that the response to the magnetic field is slowed down because the coated particle 10 (core particle 11) is excessively large.

  The comparative example 3 has a small effect of suppressing the short circuit current. It is considered that the surface of the nail can not be covered sufficiently because the coated particles 10 are excessively small.

  The comparative example 4 has a small effect of suppressing the short circuit current. It is considered that the surface of the nail can not be sufficiently covered because the amount of the covering particles 10 is small.

  The comparative example 5 has a small effect of suppressing the short circuit current. It is considered that the response to the magnetic field is weakened by the decrease in the fluidity of the electrolytic solution and the entire coated particle 10 because the coated particle 10 is excessively large. Further, in Comparative Example 5, the increase in initial resistance with the addition of the coated particles 10 is large.

  From the results of Examples 1, 7, 9, and 10, it is considered that the effect of suppressing the short circuit current can be obtained regardless of the type of ferromagnetic material.

  The embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The technical scope determined by the description of the claims includes all the modifications within the meaning and scope equivalent to the claims.

  DESCRIPTION OF REFERENCE NUMERALS 10 coated particle, 11 core particle, 12 shell layer, 20 conductive foreign matter, 100 battery (non-aqueous electrolyte secondary battery), 110 positive electrode, 111 positive electrode current collector, 112 positive electrode mixture layer, 120 negative electrode, 121 negative electrode collection A collector, 122 negative electrode mixture layers, 130 separators, 150 electrode groups, 190 cases, 191 containers, 192 lids, 193 external terminals.

Claims (1)

At least a positive electrode, a negative electrode, an electrolytic solution and coated particles,
The coated particles are dispersed in the electrolyte solution,
The coated particle comprises a core particle and a shell layer,
The core particle comprises a ferromagnetic material,
The shell layer covers the surface of the core particle,
The shell layer comprises an insulator,
The ratio of the coated particles to the total of the electrolytic solution and the coated particles is 3% by volume or more and 15% by volume or less,
The core particles have an average particle size of 50 nm to 2000 nm,
Nonaqueous electrolyte secondary battery.

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