JP2010140703A - Nonaqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery capable of alleviating local dendrite growth of metal Li in its anode, whatever material is used for an anode active material. <P>SOLUTION: The lithium secondary battery is provided with an anode, a cathode, and nonaqueous electrolyte located between the anode and the cathode, with a metal thin film formed on a face of the anode at an opposite side of the nonaqueous electrolyte. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nonaqueous electrolyte battery, and more specifically to a lithium secondary battery including a metal thin film.

  In lithium secondary batteries, lithium ions from the positive electrode via the solid electrolyte are deposited as metal lithium and deposited on the negative electrode during charging, and metal lithium is ionized during discharge and deposited on the positive electrode from the negative electrode via the solid electrolyte. Is done. When charging with a large current, the lithium metal deposition reaction on the negative electrode is less likely to occur uniformly on the inner surface side of the negative electrode (the solid electrolyte side or the side where the electrochemical reaction occurs), and metal lithium dendrites grow where the current is concentrated. There is a problem. Dendrites are dendritic and, when grown, penetrate the solid electrolyte and reach the positive electrode, causing a short circuit.

In order to prevent this, a lithium secondary battery using a substance having an ion site capable of taking in and out lithium ions (that is, graphite, transition metal sulfide, etc.) in the negative electrode has been proposed (Patent Document 1). This reduces dendritic growth of metallic lithium.
JP-A-6-338345

  (1) However, materials having lithium ion sites as described above are limited, and when such a material, for example, graphite or the like is used for the negative electrode, there is a disadvantage that the battery capacity density is reduced. Therefore, there is a problem that the dendrite growth of metallic lithium needs to be reduced without depending on the selection of the material constituting the negative electrode.

(2) Further, the inventors of the present application indicate that the cause of dendritic growth of metallic lithium targeted by the present invention is a variation in electrical resistance distribution caused by the pressure of contact between the negative electrode and the negative electrode current collector. discovered. That is, as shown in FIG. 2, the negative electrode 103 and the negative electrode current collector 112 are in close contact with each other by pressing, but when the pressing is not sufficient, the contact pressure between the negative electrode 103 and the negative electrode current collector 112 varies. Produce.
Specifically, the electrical resistance is small and a large current flows at a location where the contact pressure is large, whereas the electrical resistance is large and the current does not easily flow at a location where the contact pressure is small. And in the place where a contact pressure is small, precipitation of metallic lithium preferentially arises at the time of charge.

  In order to suppress dendrite growth of metallic lithium caused by such a fact, a means for uniformly increasing the pressure between the negative electrode and the negative electrode current collector can be considered. This is because if the pressing is performed uniformly, the variation can be easily reduced. However, (i) a solid electrolyte, which is often made of a relatively fragile material, (ii) a positive electrode made of a sintered compact of lithium composite oxide having a low mechanical strength, or (iii) a vapor deposition method, a sputtering method or a pulsed laser device. It is difficult to apply a strong pressing force to a lithium secondary battery including a thin-film positive electrode having a low mechanical strength that is formed by a vapor phase method such as a position method. As a result, the inventors of the present invention have clarified the problem that the contact pressure between the negative electrode and the negative electrode current collector remains uneven in such a lithium secondary battery.

An object of this invention is to reduce the local dendritic growth of the metal Li in the negative electrode of a nonaqueous electrolyte battery. It is another object of the present invention to reduce dendritic growth of metallic lithium without pressing the nonaqueous electrolyte battery.

  (1) The nonaqueous electrolyte battery of the present invention comprises a negative electrode, a positive electrode, and a nonaqueous electrolyte positioned between the negative electrode and the positive electrode, and a metal thin film is provided on the surface of the negative electrode opposite to the nonaqueous electrolyte side. It is formed.

In the present invention described above, one of the major causes of current concentration on the inner surface of the negative electrode of the lithium secondary battery is the non-uniform distribution of electrical resistance at the interface between the negative electrode and the negative electrode current collector, that is, the outer surface of the negative electrode. Based on the discovery that there is. If the above structure is adopted, the outer surface of the negative electrode becomes an electron conductive layer by the metal thin film, the variation in the electrical resistance distribution on the inner surface side of the negative electrode is alleviated, and the negative electrode active material constituting the negative electrode and the metal thin film There is always a reliable contact between them. Therefore, the non-uniformity of the electrical resistance distribution is reduced and dendritic growth of metallic lithium is reduced.

  Furthermore, in the case of a lithium secondary battery as disclosed in the prior art, a strong force is used so that the negative electrode current collector and the negative electrode are more closely attached in order to prevent variation in the distribution of electric resistance. Although pressing has been performed, the configuration of the present invention eliminates the need for pressing with a strong force. As a result, such pressing is not required even for thin lithium secondary batteries that are weak in mechanical strength.

The present invention will be described more specifically with reference to FIG. In the present invention, as shown in FIG. 3, a metal thin film 5 is formed on the negative electrode 3 by vapor deposition or the like. The electrically conductive medium (carrier) in the metal thin film 5 is an electron e ⁻ . Electrons move faster than lithium ions and move quickly with a velocity component in the in-plane direction of the metal thin film, so it is easy to automatically eliminate variations in current density. Therefore, even if the contact pressure varies between the metal thin film and the negative electrode current collector 12, current concentration does not occur at the interface between the metal thin film 5 and the negative electrode 3.

  Note that the negative electrode active material of the lithium secondary battery does not need to be a specific material. For this reason, for example, metallic lithium can be used for the negative electrode active material, and a sufficiently high battery capacity density can be secured.

(2) The metal thin film in the present invention can be formed by vapor deposition, sputtering, or pulsed laser deposition.
Such a method is generally called a gas phase method. According to these methods, the metal thin film can be densely provided on the negative electrode active material. Therefore, the electrical resistance between the negative electrode active material and the metal thin film can be extremely reduced.

(3) In the present invention, the thickness of the metal thin film is preferably 0.1 μm or more and 5 μm or less.
When the thickness of the metal thin film is less than 0.1 μm, the movement distance of the electrons in the metal thin film along the in-plane direction of the thin film is insufficient, and the degree of equalization of the uneven distribution of electrical resistance becomes insufficient. On the other hand, if the metal thin film exceeds 5 μm, the film formation time such as vapor deposition becomes long and the manufacturing time is prolonged.

(4) The nonaqueous electrolyte battery of the present invention further includes a negative electrode current collector, and the negative electrode current collector is disposed on a metal thin film.
According to such a configuration, the distribution of electrical resistance between the negative electrode and the negative electrode current collector is small. Therefore, when the non-aqueous electrolyte battery is charged, the current distribution is reduced, so that dendritic growth of metallic lithium is reduced.

(5) In the nonaqueous electrolyte battery of the present invention, the nonaqueous electrolyte can be composed of a solid electrolyte.
When the nonaqueous electrolyte is composed of a solid electrolyte, the mechanical strength is weak. Therefore, in a nonaqueous electrolyte battery provided with such a solid electrolyte, it is not possible to press with a strong force in order to secure current collection between the negative electrode current collector and the negative electrode. However, in the case where the metal thin film of the present invention is provided, there is almost no need for pressing to secure current collection. Therefore, in a non-aqueous electrolyte battery using a non-aqueous electrolyte as a solid electrolyte, The effect is particularly remarkable.

  (6) In the nonaqueous electrolyte battery of the present invention, the positive electrode can be composed of a sintered body of a lithium composite oxide. Alternatively, in the nonaqueous electrolyte battery of the present invention, the positive electrode can be constituted by a thin film type positive electrode formed by a vapor deposition method, a sputtering method, or a pulse laser deposition method.

  When the positive electrode is composed of a lithium composite oxide sintered body or a thin film positive electrode as described above, the mechanical strength of the positive electrode is extremely weak. Therefore, in a nonaqueous electrolyte battery equipped with such a positive electrode, it is difficult to press with a strong force in order to secure current collection between the negative electrode current collector and the negative electrode. However, in the case where the metal thin film of the present invention is provided, almost no pressing is required to secure current collection, and thus the effect of the present invention can be obtained particularly remarkably in such a nonaqueous electrolyte battery.

  According to the present invention, since the current collecting property between the negative electrode and the negative electrode current collector is good, it is not necessary to press the nonaqueous electrolyte battery. In the nonaqueous electrolyte battery of the present invention, local dendrite growth of metallic lithium in the negative electrode can be reduced.

(1) FIG. 1 shows the structure of an all solid-state lithium secondary battery in an embodiment of the present invention. The positive electrode active material 1 is positioned on the positive electrode current collector 11. A solid electrolyte 2 is positioned on the positive electrode active material 1. A negative electrode active material 3 is located on the solid electrolyte 2. Then, a metal thin film 5 is formed on the negative electrode active material 3. A negative electrode current collector 12 is disposed on the metal thin film 5.

  Next, each part of the lithium secondary battery 10 shown in FIG. 1 will be described.

[Positive electrode current collector]
Copper, aluminum, nickel, alloys of these metals, foils such as SUS (stainless steel), or plate-like bodies can be used. The thickness is preferably about 3 μm to 40 μm, but may be a thickness outside this range.

[Positive electrode active material]
A thin film of a lithium composite oxide such as LiCoO ₂ , LiMn ₂ O ₄ , or LiNiO ₂ can be used. As a forming method, a thin film forming process such as vapor deposition, sputtering, or PLD (pulsed laser deposition) can be used. Moreover, it can also be set as the sintered compact formed using the screen printing method etc. instead of a thin film. In both the case of the thin film and the case of the sintered body, the thickness is preferably 0.5 μm to 100 μm.

[Solid electrolyte]
Li ₂ S—P ₂ S ₅ , LiLaTiO, LiLaZrO, or the like can be used. In addition, although partially overlapping, an Li—P—S—O amorphous film or a polycrystalline film may be used, or an Li—P—O—N amorphous film or a polycrystalline film may be used. As a forming method, a thin film forming process such as vapor deposition, sputtering, or PLD can be used. The thickness of the solid electrolyte is preferably about 1 μm to 20 μm.

[Negative electrode active material]
A thin film of Li metal, Li alloy, Si, Sn, In, or Ag can be used. The thickness is preferably 0.5 μm to 75 μm. As a forming method, a thin film forming process such as vapor deposition, sputtering, or PLD can be used.

[Metal thin film]
The material of the metal thin film 5 is preferably a metal such as copper, aluminum, nickel, or an alloy of these metals. The thickness is preferably in the range of 0.1 μm to 5 μm.
As a method for forming the metal thin film 5, a thin film formation process (vapor phase method) such as an evaporation method, a sputtering method, or a PLD can be used.

[Negative electrode current collector]
When the negative electrode current collector is used, copper, aluminum, nickel, an alloy of these metals, a foil body such as SUS (stainless steel), or a plate body can be used. The thickness is preferably about 3 μm to 40 μm, but may be a thickness outside this range.
When the negative electrode active material is also used as the current collector without using the negative electrode current collector, the connection terminal is connected to the negative electrode active material by a conductive adhesive or the like.

(2) Next, a method for manufacturing a lithium secondary battery will be described.

[When forming the positive electrode as a thin film]
When forming the positive electrode 1 with a thin film, it manufactures according to the flowchart shown in FIG. First, a thin film of the positive electrode 1 is formed on the positive electrode current collector 11. As described above, the thin film is formed by vacuum deposition, PLD, sputtering, or the like. The film thickness is preferably about 0.5 to 30 μm.
Subsequently, solid electrolyte 2 / negative electrode active material 3 is formed in order. Then, a metal thin film 5 is formed on the negative electrode 3. Thereafter, when the negative electrode current collector is used as a separate body, the negative electrode current collector is disposed. When the negative electrode 3 / metal thin film 5 is also used as a negative electrode current collector, the current collecting terminal is connected to the metal thin film 5 using a conductive adhesive or the like.

  In the case of a single lithium secondary battery, it is packaged as it is, and the inside of the package is evacuated and decompressed. However, usually, it is often a laminated battery in which a plurality of batteries are laminated. In the case of a laminated battery, as shown in FIG. 5, a single laminated structure of (positive electrode 1 / solid electrolyte 2 / negative electrode 3 / metal thin film 5) is not limited to one surface of the positive electrode current collector 11, Form on both sides. For this reason, after forming a single laminated structure on one surface of the positive electrode current collector 11, the positive electrode current collector 1 is turned upside down, and the other surface has a single laminated structure (positive electrode 1 / Solid electrolyte 2 / negative electrode 3 / metal thin film 5) are formed. As a result, a single laminated structure is formed with mirror symmetry about the positive electrode current collector 11. That is, a total of two single batteries are formed one above the other around the positive electrode current collector 11. By stacking and assembling the mirror-symmetric batteries and collecting current from each of the negative electrode current collector and the positive electrode current collector, a stacked battery in which all the batteries are connected in parallel can be obtained. As a result, a large capacity or large current power source can be obtained in a small volume.

  The single battery or the assembled laminated battery is finally packaged, and the inside of the package is evacuated to reduce the pressure. This pressing of the package by the reduced pressure becomes a pressure for pressing the negative electrode current collector against the metal thin film 5.

[When forming the positive electrode with a sintered body]
When a single battery is formed using a sintered body for the positive electrode 1, a sintered material is coated on the positive electrode current collector 11 using a screen printing method or the like and sintered. Thereafter, the thin film of the solid electrolyte 2 / the thin film of the negative electrode 3 / the metal thin film 5 are sequentially formed. These thin film forming processes are the same as those shown in FIG.

  When forming a laminated battery using a sintered body for the positive electrode 1, as described above, after forming the laminated body on the surface side of the positive electrode current collector 11, use a manufacturing method that repeats the same process upside down. Can do.

  Further, when a laminated battery is formed using a sintered body for the positive electrode 1, the positive electrode 1 can be placed above and below the conductive paste 25 so as to sandwich the conductive paste 25 and sintered (FIG. 6). reference). After that, as shown in FIG. 7, (the thin film of the solid electrolyte 2 / the thin film of the negative electrode 3 / the metal thin film 5) is sequentially formed on the positive electrode 1 on one surface side by the thin film formation process. Then, the same thin film forming process is performed on the positive electrode 1 on the other surface side upside down. As a result, two batteries are formed at mirror-symmetric positions with the conductive paste 25 as the center. As described above, this mirror-symmetric battery is stacked and collected to form a large-capacity power source. At that time, the positive electrode current collection can be performed from the end face of the positive electrode 1 / conductive paste 25 / positive electrode 1.

(3) Next, a modified example will be described.

[Modification 1]
FIG. 8 is a diagram illustrating a first modification of the all solid-state lithium secondary battery illustrated in FIG. 1. FIG. 8 is characterized in that an intermediate layer 16 is inserted between the positive electrode 1 and the solid electrolyte 2. The intermediate layer 16 is formed of an oxide material containing Li, such as LiNbO ₃ . The intermediate layer 16 is also called a buffer layer. The reason why the intermediate layer 16 is inserted between the positive electrode 1 and the solid electrolyte 2 is to reduce the electrical resistance at the interface between the positive electrode 1 and the solid electrolyte 2.

  Since the material of the intermediate layer 16 has a flat surface, it is easy to obtain a flat surface of the negative electrode 3 and the metal thin film 5 by vapor deposition or the like. For this reason, when the separate negative electrode current collector 12 is used, the metal thin film 5 can be contacted with a uniform contact surface pressure.

  As described above, even if the contact pressure between the metal thin film 5 and the separate negative electrode current collector 12 varies, local dendrite growth of metallic lithium does not immediately occur. Due to the electronic conductivity of the metal thin film 5, current concentration in the negative electrode active material and the solid electrolyte is reduced. However, uniform contact between the metal thin film 5 and the negative electrode current collector 12 with no variation over the entire surface is preferable in order to sufficiently exhibit battery performance.

[Modification 2]
FIG. 9 is a diagram illustrating a second modification of the all solid-state lithium secondary battery illustrated in FIG. 1. FIG. 9 is characterized in that a current collecting terminal 22 is connected to the metal thin film 5 by a conductive paste 25 and a separate negative electrode current collector is not used. You may connect the current collection terminal 22 by the electrically conductive paste 25 to the end surface of the laminated part of (the negative electrode 3 / metal thin film 5). Thereby, the stacking height can be reduced, and the battery capacity density can be improved.

  Next, the lithium secondary battery of the present invention will be described with reference to examples. Lithium secondary battery elements of Invention Example A1 and Comparative Example B1 were produced. The manufacturing method is based on the method described above.

[Invention Sample A1]
The structure of Example A1 of the present invention is as shown in FIG.
Positive electrode current collector copper foil (thickness 15 μm) / positive electrode active material LiCoO ₂ (thickness 10 μm) / intermediate layer LiNbO ₃ (thickness 0.02 μm) / solid electrolyte Li ₂ S—P ₂ S ₅ (thickness 3 μm) / Li metal of negative electrode active material (thickness 5 μm) / Cu thin film of metal thin film (thickness 2 μm) / Stainless steel of negative electrode current collector (thickness 20 μm)

[Comparative Example B1]
The structure of Comparative Example B1 is a structure obtained by removing only the metal thin film from the lithium secondary battery element of Invention Example A1.
(Copper foil (thickness 15 μm) of positive electrode current collector / LiCoO ₂ (thickness 10 μm) of positive electrode active material / LiNbO ₃ (thickness 0.02 μm) of intermediate layer / Li ₂ S—P ₂ S ₅ (thickness 3 μm) ) / Li metal of negative electrode active material (thickness 5 μm) / stainless steel of negative electrode current collector (thickness 20 μm)

[Evaluation 1]
Before the lithium secondary battery elements of Invention Example A1 and Comparative Example B1 were housed in an aluminum laminate film package and decompressed by evacuation, the resistance of the lithium secondary battery was measured.
As a result, the resistance of Invention Example A1 was smaller than that of Comparative Example B1.
In Comparative Example B1, the resistance between the negative electrode and the negative electrode current collector is distributed, and the resistance is generally increased. On the other hand, the present invention example A1 includes a metal thin film, and thus the negative electrode and the negative electrode current collector. It seems that the variation in electrical resistance between the two is suppressed, the current collecting property is improved, and the resistance is reduced.

[Evaluation 2]
Subsequently, the lithium secondary battery elements of Invention Example A1 and Comparative Example B1 were housed in an aluminum laminate film package, and the pressure was reduced by evacuation to complete the lithium secondary battery.
As a result, the resistance of Comparative Example B1 approached a value almost equivalent to that of Invention Example A1. It can be seen that the effect of reducing the internal resistance obtained by pressing in Comparative Example B1 is obtained without pressing in Invention Example A2.

[Evaluation 3]
Finally, the lithium secondary batteries of Invention Example A1 and Comparative Example B1 were charged and discharged.
As a result, the voltage of the lithium secondary battery of Comparative Example B1 decreased. It seems that dendrites of metallic lithium grew from the negative electrode and reached the positive electrode. On the other hand, in the lithium secondary battery of Invention Example A1, no voltage drop was observed even when charging and discharging were repeated. No internal short circuit due to dendrite growth appears to have occurred.

  Although the embodiments and examples of the present invention have been described above, the embodiments and examples of the present invention disclosed above are merely examples, and the scope of the present invention is the implementation of these inventions. It is not limited to the form. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  According to the lithium secondary battery of the present invention, local dendrite growth of metallic lithium can be reduced. INDUSTRIAL APPLICABILITY The present invention can be used for a nonaqueous electrolyte secondary battery mounted on a portable device or an electric vehicle.

It is a figure which shows the lithium secondary battery in Embodiment 1 of this invention. It is a figure for demonstrating the problem in the conventional lithium secondary battery. It is a figure for demonstrating the effect | action of the metal thin film contained in the lithium secondary battery of this invention. 3 is a flowchart illustrating one method for manufacturing a lithium secondary battery in an embodiment of the present invention. It is a figure which shows the laminated battery which has two battery elements located in mirror symmetry. It is a figure which illustrates one form of the lithium secondary battery of this invention when forming a positive electrode with a sintered compact. It is a flowchart which illustrates one of the manufacturing methods when manufacturing the positive electrode of the lithium secondary battery of this invention by sintering. It is a lithium secondary battery of this invention, Comprising: It is a figure which shows the modification 1 of FIG. It is a lithium secondary battery of this invention, Comprising: It is a figure which shows the modification 2 of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 2,102 Solid electrolyte 3,103 Negative electrode 5 Metal thin film 10 Nonaqueous electrolyte battery (lithium secondary battery)
DESCRIPTION OF SYMBOLS 11 Positive electrode collector 12, 112 Negative electrode collector 16 Intermediate | middle layer 22 Current collection terminal 25 Conductive paste

Claims (5)

A nonaqueous electrolyte battery comprising a negative electrode, a positive electrode, and a nonaqueous electrolyte located between the negative electrode and the positive electrode,
A non-aqueous electrolyte battery, wherein a metal thin film is formed on a surface of the negative electrode opposite to the non-aqueous electrolyte side. The nonaqueous electrolyte battery according to claim 1,
A non-aqueous electrolyte battery, wherein the metal thin film is formed by a vapor deposition method, a sputtering method, or a pulse laser deposition method.   The thickness of the said metal thin film is 0.1 micrometer or more and 5 micrometers or less, The nonaqueous electrolyte battery described in Claim 1 or 2 characterized by the above-mentioned. The nonaqueous electrolyte battery according to claim 1, 2 or 3,
The non-aqueous electrolyte battery further includes a negative electrode current collector,
The non-aqueous electrolyte battery, wherein the negative electrode current collector is disposed on the metal thin film. The non-aqueous electrolyte battery according to claim 1, 2, 3 or 4,
A non-aqueous electrolyte battery, wherein the non-aqueous electrolyte is a solid electrolyte.

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