JP2015141864A - lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent metal from being precipitated on a negative electrode, thereby suppressing an increase in battery resistance.SOLUTION: A lithium ion battery includes a lamination unit 100 including a positive electrode 101 and a negative electrode 102 disposed to face each other via a conductive porous body 104. The lithium ion battery has a separator 103 provided between the positive electrode 101 and the conductive porous body 104 and between the negative electrode 102 and the conductive porous body 104. The conductive porous body 104 is electrically connected to the negative electrode 102.

Description

  The present invention relates to a lithium ion battery.

  Japanese Patent Laid-Open No. 2000-311716 (Patent Document 1) discloses an average particle diameter of an amorphous carbon material in a lithium secondary battery using an amorphous carbon material as a negative electrode active material and lithium manganate as a positive electrode active material. Is 10 μm or less.

JP 2000-311716 A

  The lithium ion battery has a problem that metal eluted from the positive electrode is deposited on the negative electrode. When metal deposits on the negative electrode, the reaction area available for electrode reaction decreases, and the battery resistance increases. The technique disclosed in Patent Document 1 is a technique in which the negative electrode active material is made into small-diameter particles, thereby increasing the surface area of the negative electrode, that is, the reaction area, and relatively reducing the influence even if metal is deposited on the negative electrode. It is. However, this technique does not fundamentally solve the problem of metal deposition on the negative electrode.

  The present invention has been made in view of the above problems, and an object thereof is to prevent metal deposition on the negative electrode and suppress an increase in battery resistance.

  The lithium ion battery includes a laminated unit in which a positive electrode and a negative electrode are arranged to face each other through a conductive porous body, and between the positive electrode and the conductive porous body and between the negative electrode and the conductive porous body. A separator is provided between the conductive porous body and the negative electrode, and the conductive porous body is electrically connected to the negative electrode.

  In this lithium ion battery, a conductive porous body (for example, a metal mesh) is interposed between the positive electrode and the negative electrode. The conductive porous body is electrically connected to the negative electrode. Therefore, the conductive porous body and the negative electrode are equipotential. As a result, when metal elution occurs in the positive electrode and the metal ions move to the negative electrode side by electrophoresis, the metal ions receive electrons in the conductive porous body before reaching the negative electrode, and the conductive porous body It precipitates in. Accordingly, it is possible to prevent the metal from being deposited on the negative electrode, thereby suppressing an increase in battery resistance.

  According to the lithium ion battery of the present invention, an increase in battery resistance can be suppressed.

It is a schematic diagram which shows an example of a structure of the lamination | stacking unit of the lithium ion battery which concerns on one Embodiment of this invention. FIG. 2 is a schematic diagram illustrating a metal precipitation phenomenon in the stacked unit shown in FIG. 1. It is a schematic diagram illustrating the metal precipitation phenomenon in the lamination | stacking unit of the lithium ion battery which concerns on a reference example. It is a schematic diagram illustrating the reduction of the reaction area accompanying metal deposition. It is a graph which shows an example of the relationship between the metal precipitation amount on a negative electrode, and battery resistance. It is a graph which shows the relationship between the structure of the lithium ion battery concerning one Embodiment of this invention, a resistance increase rate, and the metal deposition amount on a negative electrode.

  Hereinafter, an embodiment of the present invention (hereinafter, also referred to as “this embodiment”) will be described in detail, but the present embodiment is not limited thereto.

<Lithium ion battery>
(Reference example)
First, using a reference example, the mechanism by which the battery performance decreases as the metal is eluted from the positive electrode will be described.

  FIG. 3 is a schematic diagram illustrating the configuration of the stack unit and the metal deposition phenomenon in the lithium ion battery of the reference example. The battery of the reference example shown in FIG. 3 has a stacked unit 200 in which a positive electrode 201, a separator 203, and a negative electrode 202 are stacked in this order.

In the stacked unit 200, when metal ions (M ⁺ ) are eluted from the positive electrode 201, the metal ions (M ⁺ ) pass through the separator 203, receive electrons on the negative electrode 202, and deposit as metal (M). .

Referring to FIG. 4, when metal (M) is deposited on negative electrode 202, the reaction area with lithium ions (Li ⁺ ) decreases, causing an increase in battery resistance and a decrease in battery capacity. FIG. 5 is a graph showing the relationship between the amount of metal deposited on the negative electrode 202 and the battery resistance. From FIG. 5, it can be confirmed that the battery resistance increases as the amount of deposited metal on the negative electrode increases.

Next, the lithium ion battery of this embodiment will be described.
(Embodiment)
FIG. 1 is a schematic diagram illustrating an example of a configuration of a stack unit in the present embodiment. Referring to FIG. 1, the lithium ion battery includes a laminated unit 100 in which a positive electrode 101 and a negative electrode 102 are arranged to face each other with a conductive porous body 104 interposed therebetween.

  The stacked unit 100 includes a separator 103 between the positive electrode 101 and the conductive porous body 104. The laminated unit 100 also has a separator 103 between the negative electrode 102 and the conductive porous body 104.

  The conductive porous body 104 is electrically connected to the negative electrode 102. As a result, the conductive porous body 104 and the negative electrode 102 are equipotential.

FIG. 2 is a schematic diagram illustrating the precipitation phenomenon when metal ions (M ⁺ ) are eluted from the positive electrode 101 in the stacked unit 100. As shown in FIG. 2, the metal ions (M ⁺ ) eluted from the positive electrode 101 move to the negative electrode 102 side by electrophoresis. However, since the conductive porous body 104 is equipotential with the negative electrode 102, the metal ions (M ⁺ ) cannot reach the negative electrode 102, receive electrons in the conductive porous body 104, and the metal (M) To be deposited. Therefore, a reduction in the reaction area in the negative electrode 102 is prevented.

Since Li ⁺ in the electrolytic solution has a large ionization tendency, it is considered that it does not precipitate on the conductive porous body 104. In the present embodiment, the shape of the battery is not particularly limited, and can have any conventionally known outer shape such as a cylindrical shape, a square shape, a pouch shape (also referred to as a laminate type), a sheet shape, and a coin shape.

Hereinafter, each part which comprises the lithium ion battery of this embodiment is demonstrated.
(Lamination unit)
The laminated unit 100 includes a positive electrode 101, a negative electrode 102, and a conductive porous body 104. In the stacked unit 100, the positive electrode 101 and the negative electrode 102 are disposed to face each other with the conductive porous body 104 interposed therebetween.

  The lithium ion battery of this embodiment can also include two or more stacking units 100. Moreover, the lamination | stacking unit 100 may be wound. Furthermore, the stack unit 100 may be partially configured in a stacked or wound electrode group.

(Conductive porous material)
The conductive porous body 104 may have any configuration as long as it has conductivity and has a communication hole through which the electrolytic solution can permeate and permeate. Examples of the conductive porous body include metal mesh, punching metal, expanded metal, metal foam, metal sintered body, metal fiber aggregate (woven fabric, knitted fabric, etc.), and the like. The material of the porous body is not limited to metal, but may be, for example, a material obtained by depositing metal on a porous body made of resin (PP, PE, etc.) to impart conductivity. Examples of the metal that can form the conductive porous body include Cu, Ag, Ni, Pt, Au, and the like.

  The means for electrically connecting the conductive porous body and the negative electrode is not particularly limited. For example, it may be directly connected by ultrasonic welding or resistance welding, or may be connected by a separate conduction path such as a lead tab.

(Positive electrode)
The positive electrode 101 includes a positive electrode active material and a current collector. The configuration of the positive electrode 101 is not particularly limited. For example, a positive electrode mixture layer containing a positive electrode active material may be coated on a metal foil (current collector), or the positive electrode active material may be included. The positive electrode mixture (granulated product) may be formed into a pellet shape or a sheet shape.

The positive electrode active material may be any material that can act as a positive electrode of a lithium ion battery. For example, LiCoO ₂ , LiNiO ₂ , LiNi _a Co _b O ₂ (a + b = 1, 0 <a <1, 0 <b <1) _{, LiMnO 2, LiMn 2 O 4} , LiNi a Co b Mn c O 2 (a + b + c = 1,0 <a <1,0 <b <1,0 <c <1), it is possible to use LiFePO _4, or the like.

  As a typical configuration of the positive electrode 101, a positive electrode mixture layer including a positive electrode active material, a conductive additive [(acetylene black (AB), etc.), and a binder (polyvinylidene fluoride (PVdF), etc.) is an Al foil. Examples of the composition of each component in the positive electrode mixture include, for example, a positive electrode active material (about 80 to 98% by mass), a conductive additive (1 to 10% by mass). Degree) and a binder (about 1 to 10% by mass).

(Negative electrode)
The negative electrode 102 includes a negative electrode active material and a current collector. The configuration of the negative electrode 102 is not particularly limited. For example, a negative electrode mixture layer containing a negative electrode active material may be coated on a metal foil (current collector), or the negative electrode active material may be included. The negative electrode mixture (granulated product) may be formed into a pellet shape or a sheet shape.

  The negative electrode active material only needs to be capable of acting as a negative electrode of a lithium ion battery, for example, a carbon-based negative electrode active material such as natural graphite or artificial graphite, an alloy-based negative electrode active material such as silicon or tin, or Li metal, A Li—Al alloy or the like can be used.

  As a typical configuration of the negative electrode 102, a negative electrode mixture layer including a negative electrode active material, a thickening material [carboxymethyl cellulose (CMC) or the like] and a binder (styrene butadiene rubber (SBR) or the like) is formed of Cu foil or the like. The thing fixed on the electrical power collector can be illustrated. The composition of each component in the negative electrode mixture is, for example, a negative electrode active material (about 90 to 99% by mass), a thickener and a binder (about 1 to 10% by mass).

(Separator)
The separator 103 holds the electrolytic solution and prevents electrical contact between the positive electrode 101 and the conductive porous body 104 and electrical contact between the negative electrode 102 and the conductive porous body 104. As the separator 103, for example, a microporous film or a nonwoven fabric made of a polyolefin-based material such as polyethylene (PE) or polypropylene (PP) can be used.

(Electrolyte)
In the present embodiment, the composition of the electrolytic solution is not particularly limited. Examples of the electrolyte include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone (GBL) and vinylene carbonate (VC), dimethyl carbonate (DMC), ethyl For example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO ₃ are mixed in a mixed solvent composed of chain carbonates such as methyl carbonate (EMC) and diethyl carbonate (DEC). What dissolved Li salts, such as, can be used. A solid or gel electrolyte can also be used instead of the electrolyte.

  Hereinafter, although this embodiment is described in detail using an example, this embodiment is not limited to these.

  A laminated battery of a high voltage type (upper limit voltage 4.2V) is manufactured as follows, and an endurance test (high temperature charge storage test) is performed to evaluate the amount of metal deposited on the negative electrode and the resistance increase rate of the battery. did.

<Example>
(Preparation of positive electrode)
A ternary positive electrode active material containing Ni, Co and Mn, AB (conducting aid), PVdF (binder), and N-methyl-2-pyrrolidone (solvent) are mixed and kneaded to mix the positive electrodes. A material slurry was obtained, and the positive electrode mixture slurry was coated on an Al foil (current collector) and dried to form a positive electrode mixture layer on the Al foil. And the positive electrode 101 was obtained by rolling a positive mix layer.

(Preparation of negative electrode)
Graphite powder (negative electrode active material), CMC (thickening material), and SBR (binder) are kneaded in water to obtain a negative electrode mixture slurry, and the negative electrode mixture slurry is made of Cu foil (current collector). It was coated and dried on top to form a negative electrode mixture layer on the Cu foil. And the negative electrode 102 was obtained by rolling a negative electrode compound-material layer.

(Preparation of electrolyte)
EC, DMC, and EMC were mixed so that EC: DMC: EMC = 3: 4: 3 (volume ratio) to obtain a mixed solvent. Next, an electrolytic solution was prepared by dissolving LiPF ₆ (1.0 mol / L) in the mixed solvent.

(assembly)
An electrode group composed of the laminate unit 100 shown in FIG. 1 was prepared, and the electrode group was inserted into a battery outer package composed of a laminate sheet. Furthermore, the lithium ion battery which concerns on an Example was obtained by injecting electrolyte solution to a battery exterior body, and sealing the periphery of a battery exterior body by heat welding.

<Comparative example>
A lithium ion battery according to a comparative example was manufactured using the same material and the same conditions as in the example except that the electrode group including the stacked unit 200 shown in FIG. 3 was manufactured.

<Evaluation>
First, the state of charge (SOC) of each battery was adjusted to 80%, and the initial battery resistance was measured. Next, each battery was stored in a thermostat set at 60 ° C. for 20 days, and the battery resistance after storage was measured. The resistance increase rate was calculated by dividing the battery resistance after storage by the initial battery resistance.

  Furthermore, each battery was disassembled to collect the negative electrode, and the amount of metal (Ni, Co and Mn) deposited on the negative electrode was measured by an inductively coupled plasma emission spectrometer (ICP-AES). The measurement results are shown in FIG.

  As shown in FIG. 6, a laminate unit in which a positive electrode and a negative electrode are arranged to face each other with a conductive porous body interposed therebetween, between the positive electrode and the conductive porous body, and between the negative electrode and the conductive material. The lithium ion battery of the example which has a separator between the porous body and the conductive porous body is electrically connected to the negative electrode does not satisfy the above conditions. In comparison with, the amount of metal deposited on the negative electrode after the durability test was small, and the resistance increase rate was low.

  From this result, it is considered that in the lithium ion battery of the example, metal deposition on the negative electrode could be suppressed by metal deposition on the conductive porous body.

  Although the present embodiment and examples have been described as described above, it should be considered that the embodiments and examples disclosed this time are illustrative and not restrictive in all respects. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  100,200 Laminating unit, 101,201 positive electrode, 102,202 negative electrode, 103,203 separator, 104 conductive porous body.

Claims (1)

A laminate unit in which a positive electrode and a negative electrode are arranged to face each other through a conductive porous body,
Having a separator between the positive electrode and the conductive porous body, and between the negative electrode and the conductive porous body;
The conductive porous body is a lithium ion battery that is electrically connected to the negative electrode.

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