JP2011165605A - Method for forming active material layer, active material layer formed by the same, and lithium secondary battery including the same formed by the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming an active material layer having a desired inter-layer distance, an active material layer formed by the same, and a lithium secondary battery including the same formed by the method. <P>SOLUTION: The method for forming an active material layer having a rock salt type layered structure includes steps of: preparing an active material raw material having a rock salt type layered structure; preparing a substrate having a predetermined crystal plane; and forming an active material layer containing an active material crystal having a lattice constant different from that of the active material raw material on the crystal plane of the substrate by irradiating the active material raw material with a pulse laser using a pulse laser deposition method. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for forming an active material layer having a desired interlayer distance, an active material layer formed by the method, and a lithium secondary battery including the active material layer formed by the method.

  The secondary battery can convert the decrease in chemical energy associated with the chemical reaction into electrical energy and perform discharge. In addition, the secondary battery converts electrical energy into chemical energy by flowing current in the opposite direction to that during discharge. A battery that can be stored (charged). Among secondary batteries, lithium secondary batteries are widely used as power sources for notebook personal computers, mobile phones, and the like because of their high energy density.

In the lithium secondary battery, when graphite (expressed as C ₆ ) is used as the negative electrode active material, the reaction of the formula (1) proceeds at the negative electrode during discharge.
C ₆ Li → C ₆ + Li ⁺ + e ⁻ (1)
The electrons generated in the formula (1) reach the positive electrode after working with an external load via an external circuit. The lithium ions (Li ⁺ ) generated in the formula (1) move in the electrolyte sandwiched between the negative electrode and the positive electrode by electroosmosis from the negative electrode side to the positive electrode side.

When lithium cobaltate (Li _0.4 CoO ₂ ) is used as the positive electrode active material, the reaction of the formula (2) proceeds at the positive electrode during discharge.
Li _0.4 CoO ₂ + 0.6Li ⁺ + 0.6e ⁻ → LiCoO ₂ (2)
At the time of charging, the reverse reactions of the above formulas (1) and (2) proceed in the negative electrode and the positive electrode, respectively, and in the negative electrode, graphite (C ₆ Li) into which lithium has entered by graphite intercalation is present in the positive electrode. Since lithium cobaltate (Li _0.4 CoO ₂ ) is regenerated, re-discharge is possible.

  As a technique of the lithium secondary battery using the above-described lithium cobalt oxide, Patent Document 1 discloses a lithium secondary battery using a lithium cobalt-based oxide using lithium cobalt oxide as a typical example.

JP 2007-165072 A

In patent document 1, the consideration about the crystalline state of a lithium transition metal oxide is described in the paragraph 26 in a specification. However, the description does not disclose how to control the crystal state of the oxide in order to suppress lithium insertion / extraction resistance.
The present invention has been accomplished in view of the above circumstances, and a method for forming an active material layer having a desired interlayer distance, an active material layer formed by the method, and an active material formed by the method It aims at providing a lithium secondary battery provided with a layer.

  The active material layer forming method of the present invention is a method for forming an active material layer having a rock salt type layered structure, and a step of preparing an active material material having a rock salt type layered structure, and a substrate having a predetermined crystal plane are prepared. And irradiating the active material material with a pulse laser using a pulse laser deposition method, whereby an active material having a lattice constant different from that of the active material material is formed on the crystal plane of the substrate. It has the process of forming the active material layer containing a material crystal | crystallization.

  In the active material layer forming method having such a configuration, the lattice constant of the active material in the active material layer is controlled by utilizing the atomic arrangement in the crystal plane of the substrate, and as a result, the active material layer having a desired interlayer distance is controlled. A material layer can be obtained.

In the active material layer forming method of the present invention, the active material raw material having a rock salt type layered structure is preferably lithium cobaltate (LiCoO ₂ ), and the substrate having the predetermined crystal plane is a Pt {110} substrate. .

  The active material layer forming method having such a configuration can reduce the c-axis value of the active material layer containing lithium cobalt oxide, and as a result, when the active material layer is incorporated into a lithium secondary battery. Thus, charging at a lower potential is possible as compared with a lithium secondary battery having a conventional active material layer.

  The active material layer of the present invention is formed by the above-described active material layer forming method.

  The lithium secondary battery of the present invention is a lithium secondary battery including at least a positive electrode, a negative electrode, and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode includes at least a positive electrode active material layer. The positive electrode active material layer is an active material layer formed by the above active material layer forming method.

  According to the present invention, by utilizing the atomic arrangement in the crystal plane of the substrate, the lattice constant of the active material in the active material layer is controlled, and as a result, an active material layer having a desired interlayer distance can be obtained. it can.

It is the cross-sectional schematic diagram which showed an example of the film forming apparatus which can be used for PLD method, and is the figure which showed the mode in the middle of film forming. It is a cross-sectional schematic diagram which shows an example of the lithium secondary battery of this invention. It is a graph which shows the result of having measured the lithium ion diffusion constant of the active material layer of Example 1 and Example 2. FIG.

1. Active material layer forming method and active material layer formed by the method The active material layer forming method of the present invention is a method for forming an active material layer having a rock salt type layered structure, and has a rock salt type layered structure. The step of preparing an active material raw material, the step of preparing a substrate having a predetermined crystal plane, and the pulsed laser deposition method is used to irradiate the active material raw material with the crystal plane of the substrate. The method further includes the step of forming an active material layer containing an active material crystal having a lattice constant different from that of the active material raw material.

  The pulse laser deposition (hereinafter sometimes referred to as PLD) method used in the present invention is a method in which a pulse laser is irradiated onto a target in a vacuum chamber, which is a thin film material, to form plasma. This is a method for producing a thin film by depositing the liquefied material on a substrate placed on the diagonal of the target. In general, the PLD method has a high film formation speed, and the film surface state can be controlled by adjusting the film formation conditions, and a fine particle film can be manufactured. In addition, the film can be formed in an oxygen atmosphere. It is mainly used for manufacturing oxide films.

In the technical field of single crystal thin films, it is generally known that a semiconductor oxide can be formed relatively easily on an insulator substrate, for example, an alumina (Al ₂ O ₃ ) substrate. In contrast, it is generally a difficult technique to deposit a semiconductor oxide on a conductive metal substrate.
Conventionally, the single crystal thin film manufacturing technique represented by the PLD method described above has been applied to research and production of materials such as transistors and devices for reading signals of hard disks. In order to achieve the object, the transistor, the element, and the like are manufactured mainly by forming a single crystal thin film over a semiconductor substrate. On the other hand, forming a semiconductor oxide film on a conductive metal substrate is a problem peculiar to battery materials, and in particular, production of battery materials by the PLD method has not been performed so far.

  As a result of diligent efforts, the inventors have controlled the lattice constant of the active material in the active material layer by utilizing the surface atomic arrangement in the crystal plane of the substrate, and as a result, the active material layer having a desired interlayer distance. And the present invention has been completed.

  The active material layer forming method of the present invention includes (1) a step of preparing an active material raw material, (2) a step of preparing a substrate, and (3) a step of forming an active material layer using a PLD method. Hereinafter, these steps will be described in order.

1-1. Step of Preparing Active Material Raw Material In this step, an active material raw material having a rock salt type layered structure is prepared. The “rock salt type” structure referred to here is a sodium chloride type structure which is a kind of crystal structure, and the face-centered cubic lattice formed by each of the cation and the anion is 1 / of the ridge of the unit cell. Refers to a structure shifted by two. In addition, the “layered structure” referred to here does not necessarily refer to a layered structure on a macroscopic scale such as a cm scale or mm scale, but also a layered structure on a microscopic scale such as a μm scale or nm scale.

In an active material layer formed from an active material material having a rock salt type layered structure, the interlayer distance of the layered structure is proportional to at least one value of the lattice constant of the active material crystal in the active material layer. That is, when the active material layer is formed such that the value of the lattice constant is larger than the value of the lattice constant of the active material raw material corresponding to the value, the interlayer distance of the layered structure of the formed active material layer is conventionally It becomes longer than the interlayer distance of the layered structure of the active material layer. On the contrary, when the active material layer is formed so that the value of the lattice constant is smaller than the value of the lattice constant of the active material raw material corresponding to the value, the layer structure of the active material layer to be formed The distance is shorter than the interlayer distance of the layered structure of the conventional active material layer.
Thus, an active material layer having a desired interlayer distance can be formed by controlling a value proportional to the interlayer distance of the layered structure among the lattice constants of the active material crystal. Since a lithium ion conductive surface is formed between the active material layers, lithium ion conductivity can be improved by incorporating an active material layer with a controlled interlayer distance into the lithium secondary battery.
A method of controlling the value of the lattice constant of the active material raw material will be described later in the section “1-2.

As the active material raw material having a rock salt type layered structure used in the present invention, specifically, LiCoO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNiPO ₄ , LiMnPO ₄ , LiNiO ₂ , Examples thereof include LiMn ₂ O ₄ , LiCoMnO ₄ , Li ₂ NiMn ₃ O ₈ , Li ₃ Fe ₂ (PO ₄ ) _3, and Li ₃ V ₂ (PO ₄ ) ₃ .
Among these active material materials, LiCoO ₂ is preferably used in the present invention. In the LiCoO ₂ crystal, the lattice constant value parallel to the c-axis (hereinafter referred to as the c-axis value) of the three lattice constants corresponds to the interlayer distance of the layered structure. Therefore, when an active material layer is formed using LiCoO ₂ by the method according to the present invention, the interlayer distance of the active material layer can be adjusted by controlling the c-axis value.

1-2. Step for Preparing Substrate In this step, a substrate having a predetermined crystal plane is prepared. The “substrate having a predetermined crystal plane” as used herein refers to a predetermined area that occupies a ratio of 80 to 100%, preferably 90 to 100%, with respect to the total area of at least one surface of the substrate. Refers to a substrate on which a crystal plane of In the present invention, an active material layer is formed on the predetermined crystal plane.
In the present invention, at least one value of the lattice constant of the active material is determined by the crystal plane of the substrate facing the active material layer. This is because, when the plasma of the ablated active material material reaches the substrate by the PLD method to be described later and an active material layer is formed on the substrate, the interface is substantially the same at the interface between the active material layer and the substrate. This is because the active material layer is formed so that the atomic arrangement of parallel active material molecules substantially matches the atomic arrangement of the substrate substantially parallel to the interface. Here, “atom arrangement matches” means that the atoms of the substrate and the atoms or atomic groups in the active material molecule are arranged in a one-to-one correspondence, or between the atoms of the substrate This means that the gaps and the atoms or atomic groups in the active material molecules are arranged so as to correspond approximately in a one-to-one relationship. Therefore, the active material layer formed according to the present invention corresponds to a state in which the atom of the substrate and the atom or atomic group in the active material molecule are in close contact with each other or the atom or atomic group. It will be in the state fitted in the gap.

  Specific examples of the substrate having a predetermined crystal plane used in the present invention include a Pt {110} substrate, a Pt {111} substrate, a Pt {100} substrate, an Au {100} substrate, and an Au {110} substrate. , Au {111} substrate and the like. Note that in this specification, as a notation of a substrate having a predetermined crystal plane, a chemical formula indicating the chemical composition of the substrate (element symbol in the case of a simple substance) along with the crystal plane is used. For example, a Pt {110} substrate means a platinum substrate having a {110} plane. In this specification, equivalent crystal groups are shown in braces for crystal plane notation. For example, (110) plane, (101) plane, (011) plane, (** 0) plane, (** 0) plane, (0 **) plane (the numbers indicated by asterisks (*) above are “Means“ upper line to 1 ”) and the like are all expressed as {110} planes.

In particular, when LiCoO ₂ is used as the active material raw material and a Pt {110} substrate is used as the substrate having a predetermined crystal plane, the LiCoO ₂ c-axis is substantially parallel to the Pt {110} substrate. A material layer is formed. As described above, since the value of the c-axis of LiCoO ₂ corresponds to the interlayer distance, the lithium ion conductive surface of the obtained active material layer is substantially perpendicular to the Pt {110} substrate.
On the other hand, for example, when LiCoO ₂ is used as the active material material and a Pt {111} substrate or Pt {100} substrate is used as the substrate having a predetermined crystal plane, the c-axis of LiCoO ₂ is substantially omitted from the platinum substrate. The active material layer is formed so as to be vertical, that is, so that the lithium ion conductive surface of the obtained active material layer is substantially parallel to the platinum substrate.
As shown in the examples described later, the c-axis value of the active material crystal in the LiCoO ₂ active material layer when the Pt {110} substrate is used (Example 1) is the case where the Pt {111} substrate is used. It is smaller than both the c-axis value of the active material crystal in the LiCoO ₂ active material layer of Example 2 and the c-axis value of the active material crystal in the conventional LiCoO ₂ active material layer. Thus, from the viewpoint of easier charging at a lower potential as the interlayer distance (the c-axis value of the LiCoO ₂ active material crystal) is smaller when incorporated in a lithium secondary battery, In the invention, it is preferable to use a Pt {110} substrate as the substrate having a predetermined crystal plane.

1-3. Step of forming active material layer using PLD method In this step, the active material material is irradiated onto the above-described crystal surface of the substrate by irradiating the above-mentioned active material material with a pulse laser using the PLD method. This is a step of forming an active material layer containing an active material crystal having a lattice constant different from the lattice constant.
The “active material crystal having a lattice constant different from the lattice constant of the active material raw material” here means that at least one value of the lattice constant of the active material raw material is different from the value of the lattice constant corresponding to the value. It refers to the active material crystal. When the value of the lattice constant of the active material raw material is 100%, the value of the lattice constant of the active material crystal corresponding to the value is preferably 90 to 110%.

FIG. 1 is a schematic cross-sectional view showing an example of a film forming apparatus that can be used in the PLD method, and shows a state during film formation. In addition, the film forming apparatus which can be used for this process is not necessarily limited to the example shown in FIG.
The film forming apparatus 100 includes a vacuum chamber 1, a laser oscillator 2 attached to the vacuum chamber 1, a vacuum pump 3, and an oxygen valve 4.
As the laser oscillator 2, a KrF excimer laser (248 nm) oscillator, an ArF excimer laser (193 nm) oscillator, a XeCl excimer laser (308 nm) oscillator, or the like can be used. Among them, a KrF excimer laser (248 nm) oscillator can be used. preferable. The laser energy is preferably 50 to 250 mJ, and the laser frequency is preferably 0.5 to 20 Hz.

The vacuum pump 3 may be a vacuum pump that can obtain a degree of vacuum of about 10 ⁻⁴ to 10 ⁻⁶ Torr. Specifically, a rotary pump, a turbo molecular pump, or the like that is usually used in a vacuum apparatus may be used. it can. Two or more vacuum pumps can be used in combination.
The oxygen valve 4 is connected to an oxygen supply source (not shown) such as an oxygen cylinder, and is controlled so as to keep the inside of the vacuum chamber 1 at an oxygen partial pressure of about 0.001 to 0.1 Torr.
Before film formation, the vacuum chamber 3 is evacuated by the vacuum pump 3 and then oxygen is introduced from the oxygen valve 4 into the vacuum chamber 1 twice in advance. It is preferable to substitute with.

In the vacuum chamber 1, a target 5, a motor 6 that rotates the target 5, and a substrate 7 are installed.
As the target 5, a solid of an active material material or a stage coated with an active material material is installed. In order to uniformly ablate the entire surface, it is preferable to rotate the target. The target rotation speed is preferably about 10 to 100 rpm, although it depends on the properties of the active material layer to be formed.
As the active material material, the active material material described in the section “1-1. Step of preparing active material material” is used.

The plasma derived from the active material raw material generated in the substantially vertical direction from the target 5 toward the space during laser ablation reaches the substrate 7 and is deposited, and as a result, an active material layer is formed on the substrate. The distance between the target 5 and the substrate 7 may be a distance that allows the ablated active material material to reach the substrate sufficiently, and specifically, about 3 to 15 cm is preferable.
As the substrate 7, the substrate described in the section “1-2.

From the viewpoint of increasing the crystallinity of the active material crystal in the active material layer, it is preferable to heat the substrate. Various methods can be employed for heating the substrate in accordance with the properties of the substrate. As a specific method for heating the substrate, for example, as shown in FIG. 1, there is a method of heating the substrate by connecting a power source 8 to the substrate 7 and passing a current through the substrate. Although the temperature of a board | substrate is based also on the property of the active material layer to form, about -50-350 degreeC is preferable.
In order to form the active material layer uniformly, the substrate itself is preferably rotated. Although the rotation speed of a board | substrate is based also on the property of the active material layer to form, about 10-100 rpm is preferable.

Although depending on the properties of the active material layer to be formed, an active material layer having a thickness of about 0.05 to 2 μm is formed in a film formation time of about 0.5 to 3 hours.
The thickness of the active material layer formed according to the present invention varies depending on the use of the lithium secondary battery in which the active material layer is actually incorporated, but is within the range of 0.5 to 100 μm. It is preferable that it is within a range of 1 to 50 μm, and most preferably within a range of 1 to 30 μm.

  The average particle diameter of the active material crystals in the formed active material layer is, for example, preferably in the range of 1 μm to 50 μm, more preferably in the range of 1 μm to 20 μm, and particularly preferably in the range of 3 μm to 5 μm. If the average particle size of the active material crystal is too small, the handleability may be deteriorated. If the average particle size of the active material crystal is too large, it may be difficult to obtain a flat active material layer. It is. The average particle size of the active material crystal can be determined by measuring and averaging the particle size of the active material carrier observed with, for example, a scanning electron microscope (SEM).

The active material layer of the present invention may contain a conductive material, a binder and the like as necessary.
The conductive material included in the active material layer used in the present invention is not particularly limited as long as the conductivity of the active material layer can be improved. For example, carbon black such as acetylene black and ketjen black is used. Can be mentioned. Moreover, although content of the electrically conductive material in an active material layer changes with kinds of electrically conductive material, it is in the range of 1 mass%-10 mass% normally.

  Examples of the binding material of the active material layer used in the present invention include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Further, the content of the binder in the active material layer may be an amount that can immobilize the active material material and the like, and is preferably smaller. The content of the binder is usually in the range of 1% by mass to 10% by mass.

  The active material layer of the present invention is formed by the above-described active material layer forming method.

2. Lithium secondary battery The lithium secondary battery of the present invention is a lithium secondary battery comprising at least a positive electrode, a negative electrode, and an electrolyte interposed between the positive electrode and the negative electrode. The positive electrode active material layer includes an active material layer formed by the above active material layer forming method.

FIG. 2 is a schematic cross-sectional view showing an example of the lithium secondary battery of the present invention. The battery according to the present invention is not necessarily limited to this example. Although FIG. 2 shows only the stacked battery, a wound battery or the like can also be adopted.
In the lithium secondary battery 200, a positive electrode active material layer 22, an electrolyte 23, and a negative electrode active material layer 24 are sequentially accommodated in a positive electrode can 21 from the bottom of the can, and a negative electrode cap 25 is fitted as a battery lid. ing. The gasket 26 is insulated between the negative electrode active material layer 24 and the positive electrode can 21 and between the negative electrode cap 25 and the positive electrode can 21. In the example shown in FIG. 2, the positive electrode can 21 and the positive electrode active material layer 22 constitute a positive electrode, and the negative electrode cap 25 and the negative electrode active material layer 24 form a negative electrode. The positive electrode can 21 serves both as a positive electrode current collector and a battery case. The negative electrode cap 25 serves both as a negative electrode current collector and a battery case.
In the lithium secondary battery 200 illustrated in FIG. 2, the positive electrode active material layer 22 is an active material layer formed by the above-described active material layer forming method.
Hereinafter, the positive electrode, the negative electrode, the electrolyte, and other components (separator and the like), which are components of the lithium secondary battery according to the present invention, will be described.

(Positive electrode)
The positive electrode of the lithium secondary battery according to the present invention includes a positive electrode active material layer manufactured by the manufacturing method according to the present invention, and is preferably further connected to the positive electrode current collector and the positive electrode current collector. It has a positive electrode lead.

(Positive electrode current collector)
The positive electrode current collector used in the present invention has a function of collecting the positive electrode active material layer. Examples of the material for the positive electrode current collector include aluminum, SUS, nickel, iron, and titanium. Of these, aluminum and SUS are preferable. Examples of the shape of the positive electrode current collector include a foil shape, a plate shape, and a mesh shape, and all or part of the container of the lithium secondary battery can be used as the positive electrode current collector.

(Negative electrode)
The negative electrode of the lithium secondary battery according to the present invention preferably includes a negative electrode current collector and a negative electrode lead directly connected to the negative electrode current collector, and more preferably a negative electrode containing a negative electrode active material An active material layer is provided.
Hereinafter, the negative electrode active material layer and the negative electrode current collector will be described.

(Negative electrode active material layer)
The negative electrode active material used for the negative electrode active material layer is not particularly limited as long as it can occlude / release lithium ions. For example, metal lithium, lithium alloy, metal oxide, metal sulfide, Examples thereof include metal nitrides and carbon materials such as graphite. The negative electrode active material may be in the form of a powder or a thin film.

The negative electrode active material layer may contain a conductive material, a binder, and the like as necessary.
As the binder and the conductive material that can be used in the negative electrode active material layer, those already described in the description of the positive electrode active material layer can be used. Moreover, it is preferable to select the usage-amount of a binder and a electrically conductive material suitably according to the use etc. of a lithium secondary battery. Further, the film thickness of the negative electrode active material layer is not particularly limited, but for example, it is preferably in the range of 10 μm to 100 μm, and more preferably in the range of 10 μm to 50 μm.

(Negative electrode current collector)
As the material for the negative electrode current collector, the same materials as those for the positive electrode current collector described above can be used. Moreover, as a shape of a negative electrode collector, the thing similar to the shape of the positive electrode collector mentioned above is employable.

(Electrolytes)
The electrolyte used in the present invention is not particularly limited as long as it has lithium ion conductivity, and may be solid or liquid. A polymer electrolyte, a gel electrolyte, or the like can also be used.
As the lithium ion conductive solid electrolyte used in the present invention, specifically, an oxide solid electrolyte, a sulfide solid electrolyte, or the like can be used.
Specifically, as the oxide-based solid electrolyte used in the present invention, LiPON (lithium phosphate oxynitride), Li _1.3 Al _0.3 Ti _0.7 (PO ₄ ) ₃ , La _0.51 Li _0.34 TiO _0.74 , Li ₃ PO ₄ , Li ₂ SiO ₂ , Li ₂ SiO ₄ , Li _0.5 La _0.5 TiO ₃ , Li _1.5 Al _0.5 Ge _1.5 (PO _{4 3} ) etc. can be illustrated.
Specific examples of the sulfide-based solid electrolyte used in the present invention include Li ₂ S—P ₂ S ₅ , Li ₂ S—P ₂ S ₃ , Li ₂ S—P ₂ S ₃ —P ₂ S ₅ , _{Li 2 S-SiS 2, LiI} -Li 2 S-P 2 S 5, LiI-Li 2 S-SiS 2 -P 2 S 5, Li 2 S-SiS 2 -Li 4 SiO 4, Li 2 S-SiS 2 _{-Li 3 PO 4, Li 3 PS} 4 -Li 4 GeS 4, Li 3.4 P 0.6 Si 0.4 S 4, Li 3.25 P 0.25 Ge 0.76 S 4, Li 4-x _{Ge 1-x P x S 4} , Li 7 P 3 may be exemplified _{S 11} or the like.

As the lithium ion conductive electrolyte used in the present invention, specifically, an aqueous electrolyte and a non-aqueous electrolyte can be used.
As the aqueous electrolyte solution used for the lithium secondary battery, a solution containing lithium salt in water is usually used. Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiBF ₄ , LiClO _4, and LiAsF ₆ ; and LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ (Li-TFSI), LiN (SO ₂ C ₂ F ₅ ) ₂ , organic lithium salts such as LiC (SO ₂ CF ₃ ) _{3 and the} like.

The type of the non-aqueous electrolyte used in the present invention is preferably selected as appropriate according to the type of the metal ion to be conducted. For example, the non-aqueous electrolyte solution of a lithium secondary battery usually contains the above-described lithium salt and non-aqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl carbonate, butylene carbonate, γ-butyrolactone, sulfolane, Acetonitrile, 1,2-dimethoxymethane, 1,3-dimethoxypropane, diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, and mixtures thereof can be exemplified. The concentration of the lithium salt in the nonaqueous electrolytic solution is, for example, in the range of 0.5 mol / L to 3 mol / L.
In the present invention, the non-aqueous electrolyte may contain a low volatile liquid such as an ionic liquid.

  The polymer electrolyte used in the present invention preferably contains a lithium salt and a polymer. Examples of the lithium salt include the lithium salts described above. The polymer is not particularly limited as long as it forms a complex with a lithium salt, and examples thereof include polyethylene oxide.

The gel electrolyte used in the present invention preferably contains a lithium salt, a polymer, and a nonaqueous solvent.
The lithium salt described above can be used as the lithium salt.
The nonaqueous solvent is not particularly limited as long as it can dissolve the lithium salt. For example, the above-described nonaqueous solvent can be used. The non-aqueous solvent may be used alone or in combination of two or more. Moreover, room temperature molten salt can also be used as a non-aqueous electrolyte.
The polymer is not particularly limited as long as it can be gelled, and examples thereof include polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyvinylidene fluoride (PVDF), polyurethane, polyacrylate, and cellulose. Can be mentioned.

(Other components)
As another component, a separator can be used for the battery of the present invention. The separator is disposed between the positive electrode current collector and the negative electrode current collector described above when a plurality of batteries are stacked and used. Usually, the separator includes a positive electrode active material layer and a negative electrode active material layer. It has a function of preventing contact and holding the electrolyte. Furthermore, examples of the material for the separator include resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Among them, polyethylene and polypropylene are preferable. The separator may have a single layer structure or a multilayer structure. Examples of the separator having a multilayer structure include a separator having a two-layer structure of PE / PP and a separator having a three-layer structure of PP / PE / PP. Furthermore, in the present invention, the separator may be a nonwoven fabric such as a resin nonwoven fabric or a glass fiber nonwoven fabric. Moreover, the film thickness of the said separator is not specifically limited, It is the same as the film thickness of the separator used for a general lithium secondary battery.
Moreover, the battery case which accommodates the battery of this invention can also be used as another component. The shape of the battery case is not particularly limited as long as it can accommodate the above-described positive electrode, negative electrode, electrolyte, and the like, and specific examples include a cylindrical shape, a square shape, a coin shape, a laminate shape, and the like. be able to. As described above, all or part of the battery case may be used as the electrode current collector.

  Specific embodiments of the present invention will be described below in more detail with reference to examples. However, the present invention is not limited to these examples unless it exceeds the gist.

1. Formation of active material layer [Example 1]
First, a φ20 × 5 (mm) LiCoO ₂ sintered body was prepared as an active material raw material having a rock salt type layered structure, and a Pt {110} substrate was prepared as a substrate having a predetermined crystal plane.
Next, the active material layer of Example 1 was formed on the Pt {110} substrate by irradiating the LiCoO ₂ sintered compact target with a pulse laser using the PLD method. Detailed formation conditions of the active material layer are as follows.
Apparatus: Chamber (manufactured by AOV Co., Ltd.), KrF excimer laser (248 nm) (manufactured by Coherent GmbH)
Laser: 150mJ, 10Hz
Film forming time: 1 hour Oxygen partial pressure: 0.025 Torr
Substrate temperature: 600 ° C
Substrate rotation speed: 30 rpm
Target rotation speed: 60rpm
Substrate-target distance: 7.5cm

[Example 2]
The active material layer of Example 2 was formed on the Pt {111} substrate using the same method as in Example 1 except that a Pt {111} substrate was used as the substrate having a predetermined crystal plane.

[Comparative Example 1]
As an active material raw material, powdered LiCoO ₂ (manufactured by Toda Kogyo Co., Ltd.) was prepared and subjected to subsequent structural analysis. In Comparative Example 1, no active material layer was formed.

2. Structural analysis The lattice constants of the active material layers of Example 1 and Example 2 and the active material material of Comparative Example 1 were evaluated by the X-ray diffraction method. X-ray diffraction measurement was performed using an X-ray diffractometer for thin film analysis (manufactured by Rigaku Corporation: ATX-G) using CuKα1 (1.5406 mm) as a light source.

Table 1 below shows values of the a-axis and c-axis of the crystals in the active material layers of Example 1 and Example 2 and the crystals in the active material raw material of Comparative Example 1 obtained by X-ray diffraction measurement. It is the table | surface which compared the value of. Here, the “a-axis value” means a lattice constant value parallel to the a-axis, and the “c-axis value” means a lattice constant value parallel to the c-axis. .
As can be seen from Table 1 below, the difference between the a-axis value according to Comparative Example 1 and the a-axis value according to Example 1, the a-axis value according to Comparative Example 1, and the Example 2 Any difference from the a-axis value is less than 0.05 mm. However, the difference between the c-axis value according to Comparative Example 1 and the c-axis value according to Example 1 is 0.17 mm, and the c-axis value according to Comparative Example 1 and the c-axis value according to Example 2 Since the difference from the value was 0.07 cm, it can be seen that the value of the c-axis of the crystal in the active material changes significantly by using a single crystal substrate.
Also, it can be seen that the c-axis value according to Example 1 is smaller than the c-axis value according to Comparative Example 1, and the c-axis value according to Example 2 is larger than the c-axis value according to Comparative Example 1. .

3. Lithium ion conduction analysis About lithium secondary battery provided with the active material layer of Example 1 or Example 2, using a potentio / galvanostat (manufactured by Solartron: Model 1286), lithium ion diffusion during charging by potential step method Constants were measured.
The detailed configuration of the lithium secondary battery is as follows.
Positive electrode: active material layer of Example 1 or Example 2 Negative electrode: lithium metal (manufactured by Honjo Metal Co., Ltd.)
Electrolyte: 1M LiClO ₄ / EC-DEC (Toyama Pharmaceutical Co., Ltd.)
Separator: Polyolefin porous film (manufactured by Ube Industries, Ltd .: UPORE 2530)

FIG. 3 is a graph showing the results of measuring the lithium ion diffusion constant of the lithium secondary battery including the active material layer of Example 1 or Example 2, and the vertical axis represents the lithium ion diffusion constant D _Li (cm ² s ^{− 1} ) is a graph in which the horizontal axis represents potential E (V).
As can be seen, the graph of Example 1 (black circle plot) has a diffusion constant peak at a potential lower by 0.02 V than the graph of Example 2 (white circle plot).

4). Summary of Experimental Results Considering the results of Table 1 above and the results of FIG. 3 together, the active material layer of Example 1 having a smaller c-axis value of the active material crystal has a c-axis value of the active material crystal. It is considered that charging at a lower potential is easier when incorporated in a lithium secondary battery than in the active material layer of Example 2 having a large. That is, it can be seen that by reducing the value of the c-axis of the active material crystal, the resistance during charging can be reduced when the active material crystal is incorporated in a lithium secondary battery. On the contrary, it can be seen that by increasing the value of the c-axis of the active material crystal, the resistance during charging can be increased when the active material crystal is incorporated in a lithium secondary battery.

DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 Laser oscillator 3 Vacuum pump 4 Oxygen valve 5 Target 6 Motor 7 Board | substrate 8 Power supply 21 Positive electrode can 22 Positive electrode active material layer 23 Electrolyte 24 Negative electrode active material layer 25 Negative electrode cap 26 Gasket 100 Film-forming apparatus 200 Lithium secondary battery

Claims (4)

A method of forming an active material layer having a rock salt type layered structure,
Preparing an active material raw material having a rock salt type layered structure;
Preparing a substrate having a predetermined crystal plane, and
By irradiating the active material raw material with a pulse laser using a pulse laser deposition method, the active material crystal contains an active material crystal having a lattice constant different from the lattice constant of the active material raw material on the crystal surface of the substrate. An active material layer forming method comprising a step of forming an active material layer. _2. The active material layer forming method according to claim 1, wherein the active material material having a rock salt type layered structure is lithium cobaltate (LiCoO ₂ ), and the substrate having the predetermined crystal plane is a Pt {110} substrate.   An active material layer formed by the method for forming an active material layer according to claim 1. A lithium secondary battery comprising at least a positive electrode, a negative electrode, and an electrolyte interposed between the positive electrode and the negative electrode,
The positive electrode includes at least a positive electrode active material layer, and the positive electrode active material layer is an active material layer formed by the active material layer forming method according to claim 1 or 2. Next battery.