JP2009004250A - Negative electrode active material and all solid polymer battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode active material which is effective in reduction of internal resistance and increase of battery capacity when used for a battery, in particular, an all solid polymer battery and in which superior cycle characteristics are obtained when used for a secondary battery, and the all solid polymer battery containing the negative electrode material. <P>SOLUTION: A lithium system active material 1 contains crystal grains 2 and crystal boundaries 3 and at least a part of the crystal boundaries 3 is exposed on the surface. The exposed area of the crystal boundaries 3 is made 0.02-0.5 cm<SP>2</SP>per the surface 1 cm<SP>2</SP>of the lithium system active material 1. A negative electrode, and as a result, a battery are manufactured using this lithium system active material 1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a negative electrode active material and an all solid-state polymer battery.

  Nonaqueous electrolyte batteries can be broadly classified into electrolyte type batteries and solid type batteries. In the electrolytic solution type battery, an electrolytic solution is interposed between the positive electrode and the negative electrode. Although the electrolyte type battery has a high battery capacity, a precise structure is required to prevent the occurrence of so-called liquid leakage in which the electrolyte leaks out of the battery. In a solid battery, a solid electrolyte is interposed between the positive electrode and the negative electrode. A solid battery has the advantages of high safety and reliability as a battery since there is no risk of liquid leakage, and that the battery can be thinned or stacked.

  In solid-state batteries, various inorganic materials and organic materials are used for the solid electrolyte. Among these, the solid electrolyte made of an inorganic material has high ionic conductivity, but it is difficult to process into a flexible film because of its high brittleness. On the other hand, as a solid electrolyte made of an organic material, for example, a polymer electrolyte made of an organic polymer compound is known. The polymer electrolyte is flexible and can form a thin film, and thus is expected as a thin solid electrolyte material having a high energy density. A solid state battery including a polymer electrolyte is generally called an all solid state polymer battery.

Examples of the polymer electrolyte include a polymer electrolyte formed by combining polyethylene oxide and an alkali metal salt such as a lithium salt or a sodium salt. However, this polymer electrolyte has a low ion conductivity of 10 ⁻⁴ to 10 ⁻⁷ S / cm at room temperature. Therefore, the solid battery containing the polymer electrolyte has a problem that the battery capacity obtained under a high load is low. Further, there has been proposed a polymer electrolyte including a comb polymer in which a relatively short ethylene oxide chain as a side chain is bonded to polyethylene oxide as a main chain (see, for example, Non-Patent Document 1). Since the polymer electrolyte of Non-Patent Document 1 contains a comb polymer whose crystallization is suppressed by making the molecular arrangement amorphous, it exhibits a conductivity of 10 ⁻⁴ S / cm or more at room temperature. However, even in the solid battery including the polymer electrolyte of Non-Patent Document 1, the problem that the battery capacity under a high load is low as compared with the electrolyte battery has not been sufficiently solved.

By the way, in order to improve the charge / discharge efficiency of the electrolyte type non-aqueous electrolyte secondary battery, it has been proposed to use a negative electrode containing an alkali metal crystal having an average crystal grain size of 20 μm ² or more (for example, Patent Document 1). reference). When this negative electrode is used, the alkali metal precipitates in a spherical or thick line shape on the surface of the alkali metal crystal during charging. And since most of the deposited alkali metals are eluted at the time of discharge, the charge / discharge efficiency is improved. Similarly, the charge / discharge efficiency of a nonaqueous electrolyte secondary battery can also be improved by using a negative electrode containing an alkali metal crystal having an average crystal grain size of 1 μm ³ or more (see, for example, Patent Document 2).

  The negative electrodes of Patent Documents 1 and 2 are effective for an electrolyte type battery, but when used for an all solid-state polymer battery, the internal resistance before and after charge / discharge increases, and sufficiently prevents a decrease in battery capacity. I can't. In addition, when the all solid-state polymer battery including the negative electrode of Patent Document 1 or 2 is converted into a secondary battery, the cycle characteristics are insufficient.

The latest polymer battery technology II, supervised by Seiji Kanamura, p113, CM Publishing JP-A 63-143747 JP-A-63-146355

  The object of the present invention is effective in reducing internal resistance and increasing battery capacity, particularly when used in all solid-state polymer batteries, and provides excellent cycle characteristics even when all-solid polymer batteries are made secondary batteries. An anode active material that can be produced, and an all solid-state polymer battery including the anode active material.

The inventors of the present invention have intensively studied to solve the above problems. In the research process, attention was paid to the contact area between the negative electrode active material and the electrolyte (hereinafter simply referred to as “contact area”) at the interface between the negative electrode and the electrolyte (hereinafter referred to as “negative electrode interface”).
In a negative electrode containing lithium or a lithium alloy (hereinafter referred to as “lithium-based active material”), which is an alkali metal, as the negative electrode active material, the volume of the lithium-based active material varies greatly with the charge / discharge reaction. At this time, if the electrolyte is a liquid electrolyte as in the electrolyte type battery, it is easy to maintain a large contact area at the negative electrode interface even if the volume of the lithium-based active material varies. Therefore, if the negative electrode of patent documents 1 and 2 is used for an electrolyte type battery, the improvement effect of charging / discharging efficiency will be acquired.

On the other hand, the polymer electrolyte used in all solid-state polymer batteries is solid and has poor fluidity compared to liquid electrolytes and gel polymer electrolytes. Therefore, if the volume of the lithium-based active material varies, the contact area at the negative electrode interface Is almost constant, and the contact area is remarkably reduced. As a result, the resistance at the negative electrode interface (hereinafter referred to as “interface resistance”) increases. As a result, the battery capacity is reduced, and the cycle characteristics are deteriorated when the secondary battery is formed.
As a result of further research based on such knowledge, the inventors have succeeded in obtaining a lithium-based active material capable of reducing the interface resistance even when the contact area at the negative electrode interface is small, and completed the present invention. did.

That is, the present invention is lithium or a lithium alloy that includes crystal grains and crystal grain boundaries, and the crystal grain boundaries are exposed on the surface. The exposed area of the crystal grain boundaries is 1 cm ^{2 on} the surface of the lithium or lithium alloy. Provided is a negative electrode active material that is 0.02 to 0.5 cm ² per unit.
In the negative electrode active material of the present invention, it is preferable that the crystal grain boundary contains lithium oxide and the lithium oxide exists on the exposed surface of the crystal grain boundary.
In the negative electrode active material of the present invention, it is preferable that the crystal grain boundary contains lithium oxide, and the lithium oxide is present in a region from 100 to 1000 nm in the direction perpendicular to the exposed surface from the exposed surface of the crystal grain boundary. .
In the negative electrode active material of the present invention, the crystal grain size is preferably 100 to 1000 nm.
Moreover, this invention provides the all-solid-state polymer battery containing the negative electrode active material of this invention.

The negative electrode active material of the present invention is a lithium-based active material that can suppress an increase in interface resistance and reduce interface resistance even when the contact area at the negative electrode interface decreases. Therefore, the negative electrode active material of the present invention can be suitably used in various batteries, and is particularly effective as a negative electrode active material for all solid-state polymer batteries.
The all-solid-state polymer battery of the present invention has a low resistance at the negative electrode interface, a high battery capacity, and a high battery capacity even under a high load, despite using the same polymer electrolyte as the conventional electrolyte. it can. Moreover, when the all solid-state polymer battery of the present invention is converted to a secondary battery, the secondary battery has a high battery capacity and excellent cycle characteristics.

[Negative electrode active material]
The negative electrode active material of the present invention is lithium or a lithium alloy that includes crystal grains and crystal grain boundaries in the crystal structure, and at least part of the crystal grain boundaries are exposed on the surface. FIG. 1 is a longitudinal sectional view schematically showing an example of the crystal structure of the negative electrode active material 1 according to the first embodiment of the present invention. The negative electrode active material 1 is lithium (lithium alone) or a lithium alloy. Here, as a lithium alloy, what is commonly used as an electrode active material in the battery field can be used. For example, a Li—Si alloy, a Li—Sn alloy, a Li—Al alloy, a Li—Ga alloy, a Li—Mg alloy, Li-In alloy etc. are mentioned. The negative electrode active material 1 includes crystal grains 2 and crystal grain boundaries 3 in the crystal structure. The crystal grain boundary 3 exists, for example, between adjacent crystal grains 2, and at least a part is exposed on the surface 1 a of the negative electrode active material 1.

The surface 1a of the negative electrode active material 1, the area of the exposed surface of the crystal grain boundary 3 is 1 cm ² per 0.02～0.5Cm ² of the surface 1a. Since the crystal grain boundary 3 has higher ionic conductivity than the crystal grain 2, it becomes an ion conduction path at the negative electrode interface during charging and discharging. Therefore, by exposing the crystal grain boundary 3 at the above ratio on the surface 1a of the negative electrode active material 1, even if the contact area at the negative electrode interface is reduced, ion conduction is ensured, and the interface resistance at the negative electrode interface is reduced. it can. If the exposed area is less than 0.02 cm ² , the effect of reducing the interfacial resistance at the negative electrode interface may be insufficient. On the other hand, if the exposed area exceeds 0.5 cm ² , the active material capacity may be reduced. That is, since the crystal grain boundary 3 is not a part directly involved in the charge / discharge reaction, when the exposed area of the crystal grain boundary 3 is increased, the part involved in the charge / discharge reaction is reduced accordingly, and the active material capacity may be reduced. is there.

  In the negative electrode active material 1, it is preferable that the crystal grain boundary 3 contains lithium oxide. Lithium oxide has a particularly high ion conductivity and provides a good ion conduction path at the negative electrode interface. Since the crystal grain boundary 3 is an active site, it reacts with oxygen in the atmosphere and lithium oxide is easily generated. In addition, the crystal grain boundary 3 may react with water and carbon dioxide in the atmosphere, and may generate lithium hydroxide and lithium carbonate having lower ion conductivity than lithium oxide. Since lithium hydroxide and lithium carbonate become an insulating layer at the time of charging / discharging, it is not preferable that they are present at the surface 1a of the negative electrode active material 1 and at the negative electrode interface. Therefore, when manufacturing the negative electrode active material 1, it is preferable to select the conditions that make it easy for lithium oxide to be produced and hardly produce lithium hydroxide and lithium carbonate. In addition, the manufacturing method of the negative electrode active material 1 is explained in full detail later.

Further, the lithium oxide ranges from 100 to 1000 nm from the exposed surface of the crystal grain boundary 3 on the surface 1a of the negative electrode active material 1 toward the inside of the negative electrode active material 1a in a direction perpendicular to the exposed surface. It is preferable that it exists in. The presence of lithium oxide up to the inside of the negative electrode active material 1 increases the contact area between the crystal grains 2 and the crystal grain boundaries 3, and the ionic conductivity in the negative electrode active material 1 is further improved. During charging / discharging, ions are inserted and desorbed from the crystal grains 2 in contact with the lithium oxide. When the existing range of lithium oxide exceeds 1000 nm, the active material capacity of the negative electrode active material 1 may be reduced.
The presence of lithium oxide can be confirmed by, for example, XPS (X-ray Photoelectron Spectroscopy, X-ray photoelectron spectroscopy) or AES (Auger Electron Spectroscopy, Auger Electron Spectroscopy). Specifically, in the analysis by XPS or AES, the presence or absence of a Li—O bond can be confirmed by confirming the peak of O (1s).

  The particle size of the crystal grains 2 of the negative electrode active material 1 is not particularly limited, but the average particle size is preferably 10 to 1000 nm. In the negative electrode active material 1 including the crystal grains 2 having an average particle diameter in this range, the contact area of the crystal grains 2 with respect to the crystal grain boundaries 3 can be further increased, so that the interface resistance at the negative electrode interface can be further reduced. If the average particle size is less than 10 nm, the active material capacity of the negative electrode active material 1 may be reduced. On the other hand, if the average particle size exceeds 1000 nm, the effect of reducing the interface resistance may be insufficient. The crystal grain boundaries, crystal grain size (including average grain size), and area can be obtained by image processing of images observed with a scanning electron microscope (SEM).

  At least one selected from the inside of the crystal grain 2 of the negative electrode active material 1, the exposed surface of the crystal grain 2, the inside of the crystal grain boundary 3, the exposed surface of the crystal grain boundary 3, and the contact surface between the crystal 2 and the crystal grain boundary 3. In addition to lithium oxide, inevitable impurities may be present. Inevitable impurities may be present within a range that does not impair the preferable characteristics of the negative electrode active material 1. Specific examples of the inevitable impurities include lithium hydroxide, lithium carbonate, lithium nitride, lithium alkoxide, lithium alkyl carbonate, and the like.

  The negative electrode active material 1 can be manufactured, for example, by controlling the structure of the lithium-based active material. A metal material including a lithium-based active material is generally an aggregate of many crystals (crystal grains). And metal structure control is performed by utilizing the phase transformation, precipitation phenomenon, etc. which occur by heating, cooling or heating and cooling the metal. Since the negative electrode active material 1 is used to form a negative electrode active material layer in the negative electrode of the battery, when forming the negative electrode active material layer on the surface of the negative electrode current collector using a lithium-based active material (lithium or lithium alloy), By appropriately selecting various conditions, the production of the negative electrode and the synthesis of the negative electrode active material 1 can be performed simultaneously in parallel, which is industrially advantageous. More specifically, for example, a molten lithium-based active material is placed on the surface of the negative electrode current collector and cooled, the lithium-based active material solidified by cooling is rolled, and further post-treatment such as heating is performed. When forming the lithium-based active material layer, the negative electrode active material 1 is manufactured by appropriately selecting the composition of the lithium-based active material, the cooling rate, the heating time after rolling, and the like. Here, the cooling rate is a rate at which the molten lithium-based active material is placed on the surface of the negative electrode current collector and cooled.

For example, when the lithium-based active material is simple lithium, the cooling rate is about 1.5 to 2.5 ° C./minute, the post-treatment heating temperature is about 140 to 160 ° C., and the post-treatment heating time is 20 to The negative electrode active material 1 is obtained by setting the time to about 40 minutes or about 4.5 to 5.5 hours. When the lithium-based active material is a lithium-aluminum alloy, the aluminum content in the alloy is 0.1 to 15% by weight, preferably 0.2 to 10% by weight, and the cooling rate is 0.001 to 2%. The negative electrode active material 1 is obtained by setting the heating temperature for post-treatment to about 140 ° C. to 160 ° C. and the heating time after the post-treatment to about 5 minutes to 5.5 hours. Thus, also in other alloys, the negative electrode active material 1 can be produced by appropriately adjusting the composition, cooling rate, heating time, heating temperature, and the like.
The negative electrode active material 1 thus obtained can be used as a negative electrode active material in various batteries, and is particularly useful as a negative electrode active material for an all solid polymer battery.

[All-solid polymer battery]
The all-solid-state polymer battery of the present invention has the same configuration as that of a conventional all-solid-state polymer battery except that it includes a negative electrode including the negative electrode active material 1 of the present invention. FIG. 2 is a longitudinal sectional view schematically showing a configuration of an all solid-state polymer battery 10 according to another embodiment of the present invention. The all solid-state polymer battery 10 includes a negative electrode 11, a positive electrode 12, a polymer electrolyte layer 13, and a sealing material 14.

The negative electrode 11 includes a negative electrode active material layer 20 and a negative electrode current collector 21. The negative electrode active material layer 20 is provided on at least one surface in the thickness direction of the negative electrode current collector 21. The negative electrode active material layer 20 includes the negative electrode active material 1 of the present invention. Furthermore, the negative electrode active material layer 20 may contain various negative electrode active materials that are commonly used in this field as long as the preferable characteristics of the negative electrode active material 1 of the present invention are not impaired. As the negative electrode current collector 21, a porous or non-porous conductive substrate can be used. Examples of the porous conductive substrate include a mesh body, a porous body, and a nonwoven fabric. Examples of the non-porous conductive substrate include a metal foil and a metal plate. Examples of the material for the conductive substrate include copper, nickel, silver, and stainless steel.
The negative electrode 11 is formed by, for example, melting a metal sheet made of a lithium-based active material, placing it on one surface in the thickness direction of the heated negative electrode current collector 21, cooling it, and solidifying the lithium-based active material in a predetermined manner. It can produce by rolling to the dimension of this, and performing a heat processing succeedingly. At this time, as described above, the negative electrode active material layer 20 containing the negative electrode active material of the present invention can be obtained by appropriately selecting the composition of the lithium-based active material, the cooling rate, the heat treatment conditions after rolling, and the like. It is as follows.

The positive electrode 12 includes a positive electrode active material layer 22 and a positive electrode current collector 23. The positive electrode active material layer 22 is provided on at least one surface in the thickness direction of the positive electrode current collector 23. The positive electrode active material layer 22 includes a positive electrode active material, and may include a conductive agent, a binder, and the like as necessary.
As the positive electrode active material, those commonly used in the battery field can be used. Specific examples of the positive electrode active material include, for example, (CF) _n , (C ₂ F) _n , MnO ₂ , TiS ₂ , MoS ₂ , FeS ₂ , Li _xa CoO ₂ , Li _xa NiO ₂ , Li _xa MnO ₂ , _{Li xa Co y Ni 1-y} O 2, Li xa Co y M 1-y O z, Li xa Ni 1-y M y O z, Li xb Mn 2 O 4, Li xb Mn 2-y M y O 4 (In the above formulas, M represents at least one element selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb and B. Xa = 0-1.2, xb = 0-2.0, y = 0-0.9, z = 2.0-2.3), vanadium oxide and its lithium compound, niobium oxide And its lithium compounds, conjugated polymers that are organic conductive materials, chevrel phase compounds, olivine compounds Etc., and the like. The values of xa and xb are values before the start of charging / discharging, and increase / decrease due to charging / discharging. A positive electrode active material can be used individually by 1 type, or can be used in combination of 2 or more type.

  Examples of the conductive agent include graphites such as natural graphite and artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, and conductive properties such as carbon fiber and metal fiber. Examples thereof include fibers, metal powders such as aluminum powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and organic conductive materials such as phenylene derivatives. A conductive agent can be used individually by 1 type, or can be used in combination of 2 or more type as needed.

  Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, and polyacrylic acid. Ethyl, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene butadiene rubber, carboxy Examples include methyl cellulose. Moreover, you may use the polymer electrolyte demonstrated in detail later as a binder. It is preferable to use a polymer electrolyte as the binder because ions can easily reach from the surface of the positive electrode 12 to the deep part. A binder can be used individually by 1 type, or can be used in combination of 2 or more type as needed.

  As the positive electrode current collector 23, a porous or non-porous conductive substrate can be used. Examples of the porous conductive substrate include a mesh body, a porous body, and a nonwoven fabric. Examples of the non-porous conductive substrate include a metal foil and a metal plate. Examples of the material for the conductive substrate include stainless steel, aluminum, and titanium.

  The positive electrode 12 can be manufactured, for example, by preparing a positive electrode mixture containing a positive electrode active material and, if necessary, a conductive agent, a binder, and the like, and pressing the positive electrode mixture to the positive electrode current collector 23. Further, the positive electrode 12 is prepared by dissolving or dispersing the positive electrode mixture in a liquid medium to prepare a positive electrode mixture slurry, applying the positive electrode mixture slurry to the surface of the positive electrode current collector 23 and drying, and rolling as necessary. Can also be manufactured. Here, examples of the liquid medium include organic solvents such as N-methyl-2-pyrrolidone, water, and mixed solvents thereof.

  As the polymer electrolyte 13, those commonly used in the battery field can be used. For example, polymers containing oxygen atoms having a large electronegativity such as ether oxygen and ester oxygen (hereinafter referred to as “oxygen-containing polymer”). And a lithium salt complex is preferable. Lithium ions are coordinated to oxygen atoms having a high electronegativity in the polymer, so that a lithium salt is dissolved in the polymer and exhibits ion conductivity while being a solid electrolyte. Thus, the presence of relatively negatively charged ether oxygen or ester oxygen in the polymer is a condition for exhibiting high conductivity.

  As the oxygen-containing polymer, for example, a polymer having an ethylene oxide unit and / or a propylene oxide unit such as polyethylene oxide, polypropylene oxide, a copolymer of ethylene oxide and propylene oxide is preferably used. Among these, the use of a polymer having ether oxygen in the polymer side chain and a shortened chain length is particularly preferable because efficient lithium ion migration at the negative electrode interface becomes possible.

Examples of the lithium salt complexed with the oxygen-containing polymer include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiAsF ₆ , lower aliphatic lithium carboxylate, LiCl, LiBr, Examples include LiI, lithium chloroborane, lithium tetraphenylborate, LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ . A lithium salt can be used individually by 1 type, or can be used in combination of 2 or more type as needed.

  The compounding of the oxygen-containing polymer and the lithium salt can be performed according to a known method. For example, an oxygen-containing polymer may be dissolved in an organic solvent, and the obtained polymer solution and a lithium salt may be mixed. At this time, the use ratio of the oxygen-containing polymer and the lithium salt is not particularly limited, and may be appropriately selected according to the form, type, performance, application, etc. of the battery to be manufactured. For example, the molar ratio between oxygen in the oxygen-containing portion of the oxygen-containing polymer and lithium ions contained in the lithium salt may be adjusted as appropriate. The polymer electrolyte solution obtained by mixing the polymer solution and the lithium salt is applied to the surface of the negative electrode active material layer 20 and dried, for example, so that the polymer electrolyte 13 is provided on the surface of the negative electrode active material layer 20, and the negative electrode 11 And the polymer electrolyte 13 can be laminated.

As the sealing material 14, a material commonly used in the battery field can be used. For example, the sealing material which consists of synthetic resin materials is mentioned.
The all solid-state polymer battery 10 is manufactured as follows, for example. First, the polymer electrolyte 13 is laminated on the surface of the negative electrode 11 on the negative electrode active material layer 20 side. This laminate and the positive electrode 12 are overlapped. At this time, the stacking is performed so that the polymer electrolyte 13 of the laminate and the positive electrode active material layer 22 of the positive electrode 12 face each other. Next, the all-solid-state polymer battery 20 is obtained by sealing the periphery of the negative electrode 11 and the positive electrode 12 with the sealing material 14.

  The all solid-state polymer battery 10 is not limited in its configuration and form, and can take the structure and form known in the battery field. Specific examples of the configuration include a stacked type, a wound type, and a bipolar type. Specific examples of the form include a flat shape, a coin shape, a cylindrical shape, a square shape, and a laminate shape. The all solid-state polymer battery 10 can be configured as either a primary battery or a secondary battery.

Hereinafter, the present invention will be described in detail with reference to Examples, Comparative Examples and Test Examples. In addition, each operation in an Example and a comparative example was implemented in the atmosphere by which dew point management was all -30 degrees C or less.
(Example 1 and Comparative Example 1)
(1) Production of negative electrode active material and production of negative electrodes 1 to 14 and comparative negative electrodes 1 to 3 In an argon atmosphere, a lithium-based active material foil having a thickness of 300 μm was produced by an extrusion molding machine and heated to 200 ° C. to melt. I let you. The lithium-based active material in a molten state was placed on a heated copper foil having a thickness of 20 μm, and the copper foil was cooled to room temperature at the cooling rate shown in Table 1. Subsequently, after placing a guide (diameter 10 mm) of a predetermined size on the surface of the copper foil on which the lithium-based active material is installed, the lithium-based active material is pressed and rolled to a thickness of about 100 μm and the same size as the guide. Then, it was pressure-bonded onto a copper foil to be a negative electrode current collector. The lithium-based active material foil obtained by rolling was heated to 150 ° C. to remove the rolling distortion, and the production of the negative electrode active material and the production of the negative electrodes 1 to 14 and the comparative negative electrodes 1 to 3 were simultaneously performed. The heating time was as shown in Table 1.

The obtained negative electrodes 1 to 14 and comparative negative electrodes 1 to 3 were each punched into a circle having a diameter of 10 mm so that the lithium-based active material layer did not protrude from the copper foil, thereby preparing samples. The surface of this sample was subjected to SEM observation, XPS analysis, and AES analysis, and the area of the crystal grain boundary, the location of lithium oxide existing at the crystal grain boundary, and the grain size of the crystal grain were measured. The results are shown in Table 1. The depth of lithium oxide is measured with respect to the negative electrode (or negative electrode active material) surface, and “0” means that lithium oxide is exposed on the negative electrode surface.
[SEM observation]
SEM observation (magnification: 10000 times, acceleration voltage: 3.0 kV) was performed using a scanning electron microscope (trade name: S-4500, manufactured by Hitachi High-Technologies Corporation), and negative electrodes 1 to 14 and comparative negative electrodes 1 to 1 were used. An SEM photograph of the surface of No. 3 was taken. Image processing was performed on 10 arbitrary positions of the photographed SEM photograph, and the exposed area of the grain boundary on the negative electrode surface was determined. For the image processing, an image analysis type particle size distribution system (trade name: Macview ver3.5, Mountec Co., Ltd.) was used.
Exposed area of grain boundaries per surface 1 cm ² in the anode 1 to 14 were confirmed to be 0.02~0.5cm ^2. On the other hand, the exposed area of the crystal grain boundaries per surface 1 cm ² in the comparative negative electrode 1 and 3 is 0.01 cm ^2, the exposed area of the crystal grain boundaries per surface 1 cm ² in the comparative negative electrode 2 also is a 0.7 cm ² It was confirmed.

[XPS analysis]
For the XPS analysis, an X-ray photoelectron spectrometer (trade name: XPS-7000, manufactured by Rigaku Corporation) was used. The measurement conditions are as follows. X-ray source: Mg-Kα, voltage: 10 kV, current: 10 mA, X-ray spot size: about 9 mm. Charging correction is used for 1s electron binding energy of hydrocarbon or ion etching (ion etching up to 2000 nm, acceleration voltage: 500 V, angle: 90 degrees, ion current density: 32 μA / cm ² , etching rate: 1 nm / min) This was performed based on the binding energy of 2p electrons of argon. Further, the XPS analysis when the ion etching was performed was similarly performed.

[AES analysis]
For the AES analysis, an Auger electron spectroscopy analyzer (trade name: SAM670xi, manufactured by ULVAC-PHI Co., Ltd.) was used. The measurement conditions are as follows. Acceleration voltage: 3 kV, sample current: 10 nA, beam diameter: about 75 nm. In addition, AES analysis was performed in the same manner when ion etching up to 2000 nm was performed under the conditions of an acceleration voltage of the ion gun of 3 kV, an etching rate of 10 nm / min, and a sample inclination of 30 degrees.

(2) Production of negative electrode plate Negative electrodes 1 to 14 and comparative negative electrodes 1 to 3 shown in Table 1 were cut out into circles each having a diameter of 14 mm to produce negative electrode plates. Note that the lithium-based active material and the copper foil had a center at the same position. Therefore, the peripheral part of the lithium-based active material of the negative electrode plate was in a state where the copper foil was exposed.
(3) Production of polymer electrolyte layer 1 g of polyethylene oxide (viscosity average molecular weight 100,000, manufactured by Sigma-Aldrich) was dissolved in 10 g of acetonitrile to prepare an acetonitrile solution of polyethylene oxide. LiN (CF ₃ SO ₂ ) ₂ as a lithium salt is added to this acetonitrile solution, and the molar ratio [Li] / [EO of the ether oxygen concentration [EO] of the ethylene oxide part in the polymer to the lithium ion concentration [Li] in the lithium salt. ] To be 1/50 to prepare a polymer electrolyte solution.

  The obtained polymer electrolyte solution was apply | coated by the spin coat method on the negative electrodes 1-14 and the comparative negative electrodes 1-3. Then, vacuum drying is performed at 80 ° C. for 48 hours to completely remove the solvent component, thereby forming a circular polymer electrolyte layer having a thickness of 30 μm and a diameter of 10 mm on the negative electrode plate, and laminating the negative electrode plate and the polymer electrolyte layer. A body (hereinafter simply referred to as “laminated body”) was produced. Note that the negative electrode plate and the polymer electrolyte layer had a center at the same position. Therefore, the peripheral portion of the surface of the negative electrode plate on the side where the polymer electrolyte layer was formed was in a state where the polymer electrolyte layer was not formed and the copper foil was exposed.

(4) Production of all solid-state polymer primary battery Electrolytic manganese dioxide (MnO ₂ , positive electrode active material) heat-treated at 400 ° C., acetylene black (conductive agent), polyethylene oxide having an average molecular weight of 100,000 (viscosity average) A molecular weight of 100,000, Sigma-Aldrich) and LiN (CF ₃ SO ₂ ) ₂ were dissolved or dispersed in acetonitrile and kneaded to prepare a paste-like positive electrode mixture. Here, MnO _2: acetylene black: polymer electrolyte = 70 wt%: 20 wt%: was blended so that a 10 wt%. In addition, the mass of the polymer electrolyte was a mass in terms of solid content.

  The obtained paste-like positive electrode mixture was applied to one side of an aluminum foil (positive electrode current collector) having a thickness of 20 μm, dried at 120 ° C. for 24 hours, and then rolled by a roll press, whereby a positive electrode active material having a thickness of 10 μm. A layer was formed to produce a film electrode. The obtained film-like electrode was cut out into a circle having a diameter of 14 mm, and then peeled off so that the positive electrode active material layer had a diameter of 10 mm, thereby producing a positive electrode plate in which the peripheral aluminum foil was exposed. In addition, the positive electrode active material layer and the aluminum foil had a center at the same position.

Next, the laminate of the negative electrode plate and the polymer electrolyte layer obtained above and the positive electrode plate were overlapped so that the polymer electrolyte layer and the positive electrode active material layer faced each other. Next, a window frame-shaped sealing material made of an insulating resin film is disposed between the exposed portion of the peripheral edge portion of the negative electrode plate and the peripheral edge portion of the positive electrode plate, and the sealing material is welded to bond the positive electrode plate and the negative electrode plate. The gap was sealed. Thereby, a flat type all solid polymer primary battery was produced.
The flat all solid polymer primary batteries including the negative plates obtained from the negative electrodes 1 to 14 are referred to as batteries 1 to 14, respectively. Moreover, let the flat type all-solid-type polymer primary battery containing the negative electrode plate obtained from the comparison negative electrodes 1-3 be the comparison batteries 1-3, respectively.

(Test Example 1)
The batteries 1 to 14 and the comparative batteries 1 to 3 were subjected to a discharge test at room temperature under conditions of a constant current of 10 μA and a discharge end voltage of 2.0 V, and the battery capacity was measured. Moreover, the alternating current impedance measurement of the battery before and behind the said discharge test was performed using the Solartron 1255WB type electrochemical measurement system. As a result, an arc was confirmed from the Nyqist plot in the frequency range of 0.01 Hz to 1 MHz. The real axis intercept on the high frequency side of this arc was considered as the electrolyte resistance, the real axis intercept on the low frequency side was considered as the sum of the electrolyte resistance and the interface resistance, and the interface resistance value was calculated from the values of these intercepts. The results are shown in Table 2. In Table 2, “Crystal Grain Interface Area”, “Position of Lithium Oxide” and “Crystal Grain Size” shown in Table 1 are shown again.

In Table 2, from the comparison between the batteries 1 to 4 and the comparative batteries 1 and ² , the discharge test was performed when the exposed area of the crystal grain boundary per 1 cm ^{2 of} the lithium-based active material surface was 0.02 to 0.5 cm ^2. It can be seen that the interfacial resistance value before and after can be reduced and the capacity of the all solid-state lithium primary battery can be increased. This is presumably because the crystal grain boundary with high ion conductivity serves as an ion conduction path at the negative electrode interface during discharge and contributes to improvement in battery characteristics.
Further, from comparison between the batteries 1 and 5 and the comparative battery 3, the presence of lithium oxide on at least the outermost surface of the lithium-based active material reduces the interfacial resistance value before and after the discharge test. As a result, all-solid lithium primary It can be seen that the capacity of the battery can be increased. This is thought to be because lithium oxide existing at the crystal grain boundary has high lithium ion conductivity, so that the negative electrode interface can be a good ion conduction path by the presence of lithium oxide on the outermost surface serving as the negative electrode interface. .

Moreover, it is understood from the comparison between the battery 2 and the batteries 6 to 10 that it is more preferable that the lithium oxide existing at the crystal grain boundary exists in the region of 100 to 1000 nm from the lithium-based active material surface toward the inside. It can be seen that the presence of lithium oxide in the above range reduces the interface resistance value before and after the discharge test, and as a result, the capacity of the all-solid-state lithium primary battery can be increased. This is presumably because the area where the crystal grains of the lithium-based active material are in contact with the crystal grain boundary is increased and the area of the portion serving as the ion conduction path can be increased by the presence of lithium oxide further inside the active material.
Further, from comparison between the battery 2 and the batteries 11 to 14, the crystal grain size of the lithium-based active material, that is, the average crystal grain size of 100 to 1000 nm reduces the interface resistance value before and after the discharge test. It can be seen that the capacity of the all solid-state lithium primary battery can be increased. This is presumably because, even when the proportion of the crystal grain boundary on the negative electrode active material surface is the same, the crystal grain area in contact with the crystal grain boundary increases as the crystal grain becomes smaller.

(Example 2)
[Preparation of all-solid-state polymer secondary battery]
A paste-like positive electrode mixture was prepared in the same manner as in Example 1 except that spinel-type lithium manganate (LiMn ₂ O ₄ ) was used as the positive electrode active material instead of electrolytic manganese dioxide. Using the obtained paste-like positive electrode mixture and a 20 μm thick aluminum foil (positive electrode current collector), a film-like electrode including a positive electrode active material layer having a thickness of 10 μm was prepared in the same manner as in Example 1. A positive electrode plate was prepared by cutting out a disk having a diameter of 10 mm.
A flat all solid polymer secondary battery was produced in the same manner as in Example 1 except that the positive electrode plate obtained above was used. The flat all solid-state polymer secondary batteries including the negative plates obtained from the negative electrodes 1 to 14 are referred to as batteries 15 to 28, respectively. Moreover, let the flat type all-solid-state polymer secondary battery containing the negative electrode plate obtained from the comparison negative electrodes 1-3 be the comparison batteries 4-6, respectively.

(Test Example 2)
The batteries 15 to 28 and the comparative batteries 4 to 6 were subjected to a 30-cycle charge / discharge test under the conditions of a constant current of 10 μA and a discharge end voltage of 3.5 V at room temperature, and capacity retention rates were obtained. The capacity retention ratio was calculated as a percentage of the discharge capacity at the 30th cycle with respect to the discharge capacity at the 2nd cycle (%, [discharge capacity at the 30th cycle / discharge capacity at the 2nd cycle] × 100). Moreover, the alternating current impedance measurement of the battery before and behind the said charge / discharge test was performed using the 1255WB type electrochemical measurement system by Solartron. As a result, an arc was confirmed from the Nyqist plot in the frequency range of 0.01 Hz to 1 MHz. The real axis intercept on the high frequency side of this arc was considered as the electrolyte resistance, the real axis intercept on the low frequency side was considered as the sum of the electrolyte resistance and the interface resistance, and the interface resistance value was calculated from the value of this intercept. The results are shown in Table 3. In Table 3, “Crystal Grain Interface Area”, “Position of Lithium Oxide” and “Crystal Grain Size” shown in Table 1 are listed again.

In Table 3, the comparison with the comparative batteries 4 and 5 and the battery 15 to 18, by the exposed area of the lithium-based active material surface 1cm per ² crystal grain boundary is 0.02～0.5Cm ^2, the charge and discharge It can be seen that the increase in interface resistance due to repeated cycles can be suppressed and the capacity retention rate can be improved. This is presumably because the crystal grain boundaries with high ion conductivity serve as ion conduction paths at the negative electrode interface during charge and discharge, contributing to improved battery characteristics.
Further, from the comparison between the batteries 15 and 19 and the comparative battery 6, the presence of lithium oxide on at least the surface of the lithium-based active material suppresses an increase in interface resistance due to repeated charge / discharge cycles, resulting in a capacity retention rate. It can be seen that can be improved. This is presumably because lithium oxide existing at the crystal grain boundary has high lithium ion conductivity, and therefore, the lithium oxide is exposed on the surface serving as the negative electrode interface, so that the negative electrode interface becomes a good ion conduction path.

Further, from the comparison between the battery 16 and the batteries 20 to 24, the lithium oxide contained in the crystal grain boundary is present in the region from 100 to 1000 nm from the surface of the negative electrode active material toward the inside, thereby repeating the charge / discharge cycle. It can be seen that the increase in the interfacial resistance due to can be suppressed, and as a result, the capacity retention rate can be improved. This is because the contact area between the crystal grains of the lithium-based active material and the crystal grain boundary increases due to the presence of lithium oxide to the inside of the negative electrode active material, and the area of the portion serving as the ion conduction path increases. Conceivable.
Further, from the comparison between the battery 16 and the batteries 25 to 28, the crystal grain size of the lithium-based active material, that is, the average crystal grain size is 100 to 1000 nm, thereby suppressing an increase in interface resistance due to repeated charge / discharge cycles. As a result, it can be seen that the capacity retention rate can be improved. This is presumably because, even when the proportion of the crystal grain boundary on the active material surface is the same, the crystal grain area in contact with the crystal grain boundary increases as the crystal grain becomes smaller.

  According to the present invention, it is possible to reduce the interface resistance between the negative electrode active material and the polymer electrolyte, and as a result, it is possible to provide an all solid-state polymer battery having high battery capacity and excellent cycle characteristics when it is made a secondary battery. It is possible to provide a thin and flexible all-solid-state polymer battery that is safe without the risk of leakage and takes advantage of the free shape of the polymer electrolyte, and can be used for portable information terminals, portable electronic devices, and medical devices. All-solid-state polymer batteries can be used as power sources for devices that are thin and require high reliability.

It is a longitudinal cross-sectional view which shows roughly an example of the crystal structure of the negative electrode active material which is 1st Embodiment of this invention. It is a longitudinal cross-sectional view which shows schematically the structure of the all-solid-state polymer battery which is the other form of implementation of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lithium type active material 2 Crystal grain 3 Grain boundary 10 All solid-state polymer battery 11 Negative electrode 12 Positive electrode 13 Polymer electrolyte layer 14 Sealing material 20 Lithium type active material layer 21 Negative electrode current collector 22 Positive electrode active material layer 23 Positive electrode current collector

Claims (5)

Lithium or a lithium alloy that includes crystal grains and crystal grain boundaries, and at least a part of the crystal grain boundaries are exposed on the surface, and the area of the exposed surface of the crystal grain boundaries is 0.000 per 1 cm ² of the surface of the lithium or lithium alloy. The negative electrode active material which is 02-0.5 cm < ² >.   The negative electrode active material according to claim 1, wherein the crystal grain boundary contains lithium oxide, and the lithium oxide is present on the exposed surface of the crystal grain boundary.   The negative electrode active material according to claim 1 or 2, wherein the crystal grain boundary contains lithium oxide, and the lithium oxide is present in a region from 100 to 1000 nm in a direction perpendicular to the exposed surface from the exposed surface of the crystal grain boundary.   The negative electrode active material according to claim 1, wherein the crystal grains have a particle size of 100 to 1000 nm.   The all-solid-state polymer battery containing the negative electrode active material as described in any one of Claims 1-4.

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