JP6311445B2 - All solid lithium ion secondary battery - Google Patents

Description

  The present invention relates to an all solid lithium ion secondary battery.

In recent years, the reliability of lithium ion secondary batteries using organic electrolytes has been regarded as a problem. To solve this problem, research on all-solid-state lithium ion secondary batteries in which the electrolyte is made of ceramics has been actively conducted. The all-solid lithium secondary battery is composed of a solid battery consisting of a positive electrode, a negative electrode, and an electrolyte. Therefore, compared to a lithium secondary battery using an organic electrolyte, the electrochemical resistance increases and the output The current tends to be small.
In order to increase the output current of the all-solid lithium secondary battery, it is desirable that the electrolyte has a high ion conductivity, and lithium silicic acid phosphate or a sulfide-based solid electrolyte is used.

  However, a battery using a solid electrolyte material mainly composed of lithium silicate and sulfide is easily affected by moisture contained in the atmosphere and easily deteriorates due to generation of hydrogen. As a method for suppressing the deterioration of the solid electrolyte material due to such a reaction with moisture, for example, Patent Document 1 discloses a manufacturing method for assembling a solid battery in a regenerated argon gas atmosphere dehydrated and / or deoxygenated. Yes. However, even in the case of a system solid battery obtained by such a method, the reaction between the solid electrolyte material and moisture in the outside air such as the atmosphere is suppressed when used in an environment where moisture exists in the atmosphere or the like. There was a problem that could not.

  Further, such an all solid lithium secondary battery is a sintered ceramic and has a problem that it is easily broken when subjected to an impact. In order to solve the above-described problem, Patent Document 2 discloses cutting a plurality of all-solid-state secondary batteries in which a plurality of battery elements each having a positive electrode, a solid electrolyte, and a negative electrode are sequentially stacked on a current collector. However, there is a problem that the impact cannot be completely suppressed although the influence of the impact or the like is dispersed.

JP-A-8-167425 JP 2001-15153 A

  Provided is a highly reliable, all-solid-state battery that can withstand impacts and has improved water resistance.

To achieve the above object, an all-solid lithium ion secondary battery having a battery body having an electrolyte layer between a positive electrode layer and a negative electrode layer, and an electrode at the end of the battery body, In the ion secondary battery, the battery body is covered with a waterproof layer having a water contact angle of 60 ° or more, and the waterproof layer is an elastic layer having an elastic modulus of 1 × 10 ⁻⁴ Pa to 9 × 10 ⁻⁴ Pa. The electrode is formed so as to cover the end faces of the waterproof layer and the elastic layer. Thereby, it is possible to provide a highly reliable, surface-mountable all solid state battery which is strong against impact and has improved water resistance of the battery body and the end.

  The elastic layer is preferably made of a resin material, and exhibits stable elasticity even when the battery generates heat, so that it can absorb impacts over a wide temperature range.

  The waterproof layer is preferably made of a material containing an inorganic compound as a main component, and the waterproof layer can suppress reaction with moisture.

  It is possible to provide a highly reliable, surface-mountable all solid state battery that is strong against impact and has improved water resistance.

It is sectional drawing which shows the conceptual structure of an all-solid-state lithium ion secondary battery. It is a result of the moisture absorption weight change with respect to time of the lithium ion secondary battery which has a waterproof layer.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be appropriately combined.

<Lithium ion secondary battery>
The lithium ion secondary battery of the present embodiment is an all solid-state lithium ion secondary battery composed of a sintered body in which positive electrode layers and negative electrode layers are alternately stacked via a solid electrolyte layer. It has a solid electrolyte layer.

(Structure of lithium ion secondary battery)
FIG. 1 is a cross-sectional view showing a conceptual structure of a lithium ion secondary battery 10 according to an example of the present embodiment. In the lithium ion secondary battery 11 shown in FIG. 1, a positive electrode layer 1 and a negative electrode layer 2 are laminated via a solid electrolyte layer 3, and the positive electrode layer 1 has a positive electrode active material 4 and a current collector layer 5. The negative electrode layer 2 has a negative electrode active material 6 and a current collector layer 5, and has a solid electrolyte layer 3. Furthermore, it is composed of a positive electrode layer, an electrode 7 connected to the negative electrode layer, a waterproof layer 9 and an elastic layer 10.

(Positive electrode active material and negative electrode active material)
As the positive electrode active material 4 and the negative electrode active material 6 constituting the positive electrode layer 1 and the negative electrode layer 2 of the lithium ion secondary battery 11 of this embodiment, it is preferable to use a material that efficiently releases and adsorbs lithium ions. For example, it is preferable to use a transition metal oxide or a transition metal composite oxide. Specifically, the lithium manganese composite oxide _{Li 2 Mn x3 Ma 1-x3} O 3 (0.8 ≦ x3 ≦ 1, Ma = Co, Ni), lithium cobaltate (LiCoO _2), lithium nickelate (LiNiO ₂ ), Lithium manganese spinel (LiMn ₂ O ₄ ), and a general formula: LiNi _x4 Co _y4 Mn _z4 O ₂ (x4 + y4 + z4 = 1, 0 ≦ x4 ≦ 1, 0 ≦ y4 ≦ 1, 0 ≦ z4 ≦ 1) Composite metal oxide, lithium vanadium compound (LiV ₂ O ₅ ), olivine type LiMbPO ₄ (where Mb is one or more selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr) Element), lithium vanadium phosphate (Li ₃ V ₂ (PO ₄ ) ₃ or LiVOPO ₄ ), Li-rich solid solution positive electrode Li ₂ MnO ₃ -L iMcO ₂ (Mc = Mn, Co, Ni), lithium titanate (Li ₄ Ti ₅ O ₁₂ ), Li _a Ni _x5 Co _y5 Al _z5 O ₂ (0.9 <a <1.3, 0.9 <x5 + y5 + z5) It is preferably any of the composite metal oxides represented by <1.1).

  Here, the active material constituting the positive electrode layer 1 or the negative electrode layer 2 is not clearly distinguished, and the potentials of two kinds of compounds are compared, and a compound showing a more noble potential is used as the positive electrode active material 4. A compound exhibiting a base potential can be used as the negative electrode active material 6.

(Method for producing lithium ion secondary battery)
In the lithium ion secondary battery 11 of the present embodiment, each material of the positive electrode layer 1, the solid electrolyte layer 3, and the negative electrode layer 2 is pasted, applied and dried to produce a green sheet, and the green sheet is laminated, Manufactured by co-firing the produced laminate.

  The method for forming the paste is not particularly limited, and for example, a paste can be obtained by mixing the powder of each of the above materials in a vehicle. Here, the vehicle is a general term for the medium in the liquid phase. The vehicle includes a solvent and a binder. By this method, a paste for the positive electrode layer 1, a paste for the solid electrolyte layer 3, and a paste for the negative electrode layer 2 are prepared.

The prepared paste is applied in a desired order on a substrate such as PET and dried as necessary, and then the substrate is peeled off to produce a green sheet. The paste application method is not particularly limited, and a known method such as screen printing, application, transfer, doctor blade, or the like can be employed.

  The produced green sheets for the positive electrode layer 1, the solid electrolyte layer 3, and the negative electrode layer 2 are stacked in a desired order and the number of layers, and alignment, cutting, and the like are performed as necessary to produce a laminate. In the case of manufacturing a parallel type or series-parallel type battery, it is preferable to align and stack the end surfaces of the positive electrode layer and the negative electrode layer so that they do not coincide with each other.

  The produced laminate is pressed together. The pressure bonding is performed while heating, and the heating temperature is, for example, 40 to 90 ° C.

  The pressure-bonded laminated body is heated and fired, for example, in an air atmosphere. In the manufacture of the lithium ion secondary battery 10 of the present embodiment, the firing temperature is preferably in the range of 600 to 1200 ° C. If the temperature is lower than 600 ° C., the firing does not proceed sufficiently, and if it exceeds 1200 ° C., problems such as melting of the solid electrolyte 7 and changes in the structures of the positive electrode active material 4 and the negative electrode active material 6 occur. Furthermore, it is more preferable to set it as the range of 700-1100 degreeC. A range of 700 to 1100 ° C. is more suitable for promoting firing and reducing manufacturing costs. The firing time is, for example, 1 to 3 hours.

(Preparation of waterproof layer)
The waterproof layer 9 according to the present invention has a water contact angle of 60 ° or more. When the contact angle of water is 60 ° or more, the reaction between the electrolyte and water can be suppressed. As the inorganic material having a water contact angle of 60 ° or more, for example, an oxide film or a nitride film of silicon, hafnium, aluminum, tantalum, strontium, titanium, zirconium, or barium is preferably used. Two or more kinds may be used in combination. As a method for forming the waterproof layer 9, for example, a CVD method, a coating method, a sputtering method, or various printing methods are used to form a film only on the battery body.

(Production of elastic layer)
The elastic layer 10 according to the present invention has an elastic modulus of 1 × 10 ⁻⁴ Pa to 9 × 10 ⁻⁴ Pa. When the elastic modulus is within the above range, impact from the outside can be suppressed. When the resin material having the above elastic modulus includes, for example, a thermoplastic elastomer or a rubber-based resin, the elastic layer can have rubber elasticity. Examples of rubber resins include butyl rubber resin, urethane rubber, butadiene rubber, styrene butadiene rubber, polysulfide rubber, nitrile rubber, fluorine rubber, silicone rubber, ethylene propylene rubber, chloroprene rubber, acrylic rubber, natural rubber, epichlorohydrin rubber, etc. Can be used. The elastic modulus of the resin component exhibiting rubber elasticity is generally 1 × 10 ⁻⁴ Pa or more and 9 × 10 ⁻⁴ Pa or less. The elastic layer 10 can be produced, for example, as follows.
A dispersion containing the above-mentioned resin, which is a constituent component of the elastic layer, is dropped on the all-solid-state lithium ion battery on the surface excluding the electrode surface so as to have a predetermined thickness using, for example, a spin coater. Dry it. In this manner, the elastic layer 10 can be formed on the all solid lithium ion battery covered with the waterproof layer 12.

(Production of electrodes)
The electrode 7 is for taking out the electricity from the all-solid-state lithium ion secondary battery 11 to the outside, and is electrically connected to the positive electrode layer and the negative electrode layer. Platinum, gold, silver, copper, aluminum, zinc, nickel, titanium Known metal species such as bismuth, and alloys thereof are preferred. As an electrode manufacturing method, an existing method such as an evaporation method, a printing method, an ink jet method, a spin coating method, a CVD method, or a paste can be used.

(Example 1-1)
EXAMPLES The present invention will be described in detail below using examples, but the present invention is not limited to these examples. In addition, unless otherwise indicated, a part display is a weight part.

(Production of active material)
Li ₂ MnO ₃ produced by the following method was used as the active material. Li ₂ CO ₃ and MnCO ₃ were used as starting materials, these were weighed so as to have a molar ratio of 2: 1, wet-mixed in a ball mill for 16 hours using water as a solvent, and then dehydrated and dried. The obtained powder was calcined in air at 800 ° C. for 2 hours. The calcined product was coarsely pulverized, wet pulverized with a ball mill for 16 hours using water as a solvent, and then dehydrated and dried to obtain an active material powder. The average particle size of this powder was 0.40 μm. It was confirmed using an X-ray diffractometer that the composition of the produced powder was Li ₂ MnO ₃ .

(Production of active material paste)
The active material paste comprises 100 parts of this active material powder, 0.37 mol% to 1.69 mol% of H ₃ BO ₃ powder and 2.19 mol% to 17.79 mol% of Li ₂ CO ₃ powder, 15 parts of ethyl cellulose as a binder, 65 parts of dihydroterpineol was added as a solvent, and kneaded and dispersed with a three roll to prepare an active material paste.

(Preparation of solid electrolyte sheet)
As a solid electrolyte, Li _3.5 Si _0.5 P _0.5 O ₄ produced by the following method was used. Using Li ₂ CO ₃ , SiO ₂ and Li ₃ PO ₄ as starting materials, these were weighed to a molar ratio of 2: 1: 1, wet mixed with a ball mill for 16 hours using water as a solvent, and then dehydrated and dried. did. The obtained powder was calcined in air at 950 ° C. for 2 hours. The calcined product was coarsely pulverized, wet-ground with a ball mill for 16 hours using water as a solvent, and then dehydrated and dried to obtain a solid electrolyte powder. The average particle size of this powder was 0.49 μm. It was confirmed using an X-ray diffractometer that the composition of the produced powder was Li _3.5 Si _0.5 P _0.5 O ₄ .

Next, 100 parts of this powder was mixed with 0.37 mol% to 1.69 mol% of H ₃ BO ₃ powder and 2.19 mol% to 17.79 mol% of Li ₂ CO ₃ powder, 100 parts of ethanol as a solvent, and 200 parts of toluene by a ball mill. In addition, wet mixing was performed. Thereafter, 16 parts of polyvinyl butyral binder and 4.8 parts of benzylbutyl phthalate were further added and mixed to prepare a solid electrolyte paste. This solid electrolyte paste was formed into a sheet using a PET film as a base material by a doctor blade method to obtain a solid electrolyte sheet having a thickness of 9 μm.

(Preparation of current collector paste)
After mixing Ag / Pd with a weight ratio of 70/30 and Li ₂ MnO ₃ as a current collector in a volume ratio of 60:40, Examples 1-1 to 1 in Table 1 with respect to Li ₂ MnO ₃ were made. amount become as _H 3 BO ₃ powder 0.37 mol% of 1-20 ~1.69mol% and _Li 2 CO ₃ powder 2.19mol% ~17.79mol%, and ethyl cellulose 10 parts as binder, dihydro as solvent A collector paste was prepared by adding 50 parts of terpineol and kneading and dispersing with three rolls. Here, Ag / Pd having a weight ratio of 70/30 was a mixture of Ag powder (average particle size 0.3 μm) and Pd powder (average particle size 1.0 μm).

(Preparation of terminal electrode paste)
Silver powder, epoxy resin, and solvent were kneaded and dispersed with three rolls to produce a thermosetting conductive paste.

Using these pastes, lithium ion secondary batteries were produced as follows.

(Production of active material unit)
On the solid electrolyte sheet, an active material paste was printed with a thickness of 7 μm by screen printing. Next, the printed active material paste was dried at 80 to 100 ° C. for 5 to 10 minutes, and the current collector paste was printed thereon with a thickness of 5 μm by screen printing. Next, the printed current collector paste was dried at 80 to 100 ° C. for 5 to 10 minutes, and the active material paste was printed thereon again by screen printing to a thickness of 7 μm. The printed active material paste was dried at 80 to 100 ° C. for 5 to 10 minutes, and then the PET film was peeled off. In this way, an active material unit sheet in which the active material paste, the current collector paste, and the active material paste were printed and dried in this order on the solid electrolyte sheet was obtained.

(Production of laminate)
Two active material units were stacked with a solid electrolyte interposed therebetween. At this time, the current collector paste layer of the first active material unit extends only to one end surface, and the current collector paste layer of the second active material unit extends only to the other surface, Each unit was staggered and stacked. A solid electrolyte sheet was stacked on both surfaces of the stacked unit so as to have a thickness of 500 μm, and then this was molded at a temperature of 80 ° C. and a pressure of 1000 kgf / cm ² [98 MPa], and then cut to prepare a laminated block. . Thereafter, the laminated block was simultaneously fired to obtain a laminated body. In the simultaneous firing, the temperature was raised to 800 ° C. at a rate of temperature rise of 200 ° C./hour in the air, kept at that temperature for 2 hours, and naturally cooled after firing. The external appearance size of the battery after simultaneous firing was 3.7 mm × 3.2 mm × 0.35 mm.

(External electrode formation process)
A terminal electrode paste was applied to the end faces of the laminate, waterproof layer, and elastic layer, and thermosetting was performed at 150 ° C. for 30 minutes to form a pair of terminal electrodes 7 to obtain a lithium ion secondary battery.

(Preparation of waterproof layer)
A silicon oxynitride thin film having a thickness of 50 nm was formed by reactive sputtering using a Si target. The contact angle of water with the silicon oxynitride thin film was 60 °.

(Production of elastic layer)
A liquid uncured silicone rubber composition was used as the resin component, and was applied to a thickness of 50 μm on an all-solid battery coated with a waterproof layer using a spin coater (100 rpm). Then, it dried at 60 degreeC for 1 hour, and formed the elastic layer on the solid battery. The heat resistant temperature of the elastic layer is 200 ° C., and the elastic layer does not deform even if the electrode paste is heat-cured at 150 ° C. The elastic modulus of the silicone rubber was 6.6 × 10 ⁻⁴ Pa.

(Example 1-2)
Instead of liquid uncured silicone rubber as a resin component, a fluororesin was applied to a thickness of 50 μm on the all-solid-state battery coated with a waterproof layer using a spin coater (100 rpm). Then, it dried at 60 degreeC for 1 hour, and formed the elastic layer on the solid battery. Except for the elastic layer, it was produced in the same manner as Example 1. The elastic modulus of the fluororesin was 6.6 × 10 ⁻⁴ Pa.

(Comparative Example 1)
A structure prepared in the same manner as in Example 1-1 and having no waterproof layer and no elastic layer was used as Comparative Example 1.

(Drop test)
In this example, it was allowed to fall freely from a height of 1 m in accordance with JISC 60068-2-31. The obtained results are shown in Table 1.

  As shown in Table 1, Comparative Example 1 without an elastic layer was damaged in a drop test, while Examples 1-1 and 1-2 with an elastic layer were not damaged. From this result, it can be seen that Examples 1-1 and 1-2 are excellent in external impact.

  In this example, the weight change was measured under the conditions of a temperature of 20 ° C. and a humidity of 60%. The obtained results are shown in FIG.

  As shown in FIG. 2, the weight of Comparative Example 1 without a waterproof layer increased with the passage of time, while the example with a waterproof layer had no change in weight. From this result, it can be seen that Example 1-1 is superior to moisture absorption.

  As described above, the all-solid-state lithium ion secondary battery according to the present invention is effective in waterproofness and impact resistance from the outside, and can be surface-mounted on a substrate. Providing such a highly reliable battery contributes greatly, particularly in the field of electronics.

DESCRIPTION OF SYMBOLS 1 Positive electrode layer 2 Negative electrode layer 3 Solid electrolyte layer 4 Positive electrode active material 5 Current collector layer 6 Negative electrode active material 7 Electrode 9 Waterproof layer 10 Elastic layer 11 Lithium ion secondary battery

Claims (3)

An all-solid lithium ion secondary battery having a battery element having an electrolyte layer between a positive electrode layer and a negative electrode layer, and an electrode at an end of the battery element,
In the all solid lithium ion secondary battery, the battery body is covered with a waterproof layer having a water contact angle of 60 ° or more,
Furthermore, the waterproof layer is covered with an elastic layer having an elastic modulus of 1 × 10 ⁻⁴ Pa to 9 × 10 ⁻⁴ Pa,
The all-solid-state lithium ion secondary battery, wherein the electrode is formed so as to cover end faces of the waterproof layer and the elastic layer.   The all-solid-state lithium ion secondary battery of Claim 1 with which the said elastic layer is comprised with the resin material.   The all-solid-state lithium ion secondary battery according to claim 1, wherein the waterproof layer is made of a material mainly composed of an inorganic compound.

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