JP2015056215A - All-solid state battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an all-solid state battery with a sufficient amount of discharge capacity.SOLUTION: The all-solid state battery includes: a cathode active material layer containing cathode active material; an anode active material layer containing anode active material; and a solid electrolyte layer which is positioned between the cathode active material layer and the anode active material layer and which contains solid electrolyte. The cathode active material is a chemical compound expressed by the following formula: LiNiMnO, where 0.65<x<0.8), and the solid electrolyte contains lithium phosphorous oxynitride (LiPON).

Description

  The present invention relates to an all solid state battery in which interfacial resistance is suppressed by suppressing formation of a resistance layer on the surface of a positive electrode.

  With the miniaturization of personal computers, video cameras, mobile phones, etc., in the fields of information-related equipment and communication equipment, lithium secondary batteries have been put into practical use because of their high energy density as the power source used for these equipment. It has become widespread. On the other hand, in the field of automobiles, development of electric vehicles and hybrid vehicles is urgently caused by environmental problems and resource issues. Lithium secondary batteries are also being considered as power sources for electric vehicles and hybrid vehicles. Yes.

  Currently, lithium secondary batteries use organic electrolytes that use flammable organic solvents as solvents, and in terms of structure and materials to prevent the installation of safety devices that prevent temperature rise during short circuits and to prevent short circuits. Improvement is needed. In order to solve such problems, in recent years, all-solid batteries in which the liquid electrolyte is changed to a solid electrolyte have been proposed. Since this all-solid-state battery does not use a flammable organic solvent in the battery, the safety device can be simplified, and it is considered that the production cost and productivity are excellent.

  Such an all-solid battery includes a positive electrode and a negative electrode, and an electrolyte disposed therebetween, and the electrolyte is made of a solid. In general, the positive electrode and the negative electrode include an electrode active material, an active material layer containing a conductive material, a solid electrolyte, a binder, and the like, and a current collector, if necessary. The solid electrolyte layer includes, in addition to the solid electrolyte, a binder for imparting flexibility to the solid electrolyte layer as necessary.

  The active material layer can be formed, for example, by pressure-forming an active material material obtained by adding and mixing a solid electrolyte, a conductive material, or the like to the electrode active material as necessary, by a powder molding method. In addition, the solid electrolyte layer can be formed by pressure-molding an electrolyte material obtained by adding and mixing a binder or the like to a solid electrolyte as necessary by a powder molding method. In general, an all-solid battery is manufactured by laminating an active material layer and a solid electrolyte layer that have been pressure-molded as described above, and further pressing them.

  The conventional all solid state battery has a problem that the interface resistance between the positive electrode active material layer and the solid electrolyte layer is large. Therefore, when charging / discharging in a room temperature environment, a capacity | capacitance will fall remarkably. In order to solve such a problem, Patent Document 1 proposes to dispose a modifier having a high relative dielectric constant between the positive electrode active material layer and the solid electrolyte layer.

JP 2013-062133 A

  In all solid state batteries, the interfacial resistance between the positive electrode active material layer and the solid electrolyte layer is significant when a high voltage material is used as the positive electrode active material. In addition, there is a problem that the discharge capacity is not sufficient even if the modifying material is arranged.

In order to solve the above problems, according to the present invention, a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and between the positive electrode active material layer and the negative electrode active material layer And a solid electrolyte layer containing a solid electrolyte, wherein the positive electrode active material has the following formula Li _x Ni _0.5 Mn _1.5 O ₄
(In the above formula, 0.65 <x <0.8)
The solid electrolyte contains lithium phosphate oxynitride (LiPON).

In the all solid state battery of the present invention, by making the amount of Li of the positive electrode active material smaller than the positive ratio, the generation of the resistance layer due to the Li excessive composition such as Li ₂ MnO ₃ formed on the surface of the positive electrode active material layer is suppressed. The For this reason, charging / discharging becomes possible, without providing a modifier layer between a positive electrode active material and a solid electrolyte material.

It is a schematic sectional drawing of the all-solid-state battery of this invention. It is sectional drawing in the AA part of FIG. 1 is a schematic diagram showing a manufacturing process of an all solid state battery of the present invention. 1 is a schematic diagram showing a manufacturing process of an all solid state battery of the present invention. 1 is a schematic diagram showing the form of an all solid state battery of the present invention.

  FIG. 1 is a schematic cross-sectional view showing an example of the all solid state battery 1 of the present invention. As shown in FIG. 1, the all solid state battery of the present invention includes a positive electrode active material layer 3 containing a positive electrode active material, a negative electrode active material layer 5 containing a negative electrode active material, and the positive electrode active material on a substrate 2. A solid electrolyte layer 4 containing a solid electrolyte disposed between the layer 3 and the negative electrode active material layer 5 is disposed. Although not shown, a positive electrode current collector that collects current from the positive electrode active material layer and a negative electrode current collector that collects current from the negative electrode active material layer are disposed in each layer. The all solid state battery of the present invention is not particularly limited as long as it has the configuration shown in FIG. 1, and examples thereof include a thin film type, a powder type, and a sintered type.

In the present invention, the positive electrode active material contained in the positive electrode active material layer has the following formula: Li _x Ni _0.5 Mn _1.5 O ₄
(In the above formula, 0.65 <x <0.8)
It is a compound represented by these. Examples of the shape of the positive electrode active material include a particle shape such as a true sphere and an oval sphere, and a thin film shape. Moreover, when a positive electrode active material is a particle shape, it is preferable that the average particle diameter exists in the range of 0.1 micrometer-50 micrometers, for example. Further, the content of the positive electrode active material in the positive electrode active material layer is preferably in the range of 10 wt% to 99 wt%, for example, and more preferably in the range of 20 wt% to 90 wt%.

  The positive electrode active material layer in the present invention may contain other materials as necessary in addition to the above-described positive electrode active material, and examples thereof include a solid electrolyte material. The solid electrolyte material is not particularly limited as long as it is used for a general all-solid battery, and a solid electrolyte material described later can be suitably used. The content of the solid electrolyte material in the positive electrode active material layer is, for example, preferably in the range of 1% by weight to 90% by weight, and more preferably in the range of 10% by weight to 80% by weight.

  Furthermore, the positive electrode active material layer may contain a conductive agent from the viewpoint of improving the conductivity of the positive electrode active material layer in addition to the solid electrolyte material described above. Examples of the conductive material include acetylene black, ketjen black, and carbon fiber. Moreover, the positive electrode active material may contain a binder. Examples of such a binder include fluorine-containing binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

  The thickness of the positive electrode active material layer varies depending on the type of the all-solid battery intended, but is preferably in the range of 0.1 μm to 1000 μm, for example. Further, the method for forming the positive electrode active material layer is not particularly limited as long as it can form the target positive electrode active material layer.

The solid electrolyte layer in the all solid state battery of the present invention is formed between the positive electrode active material layer and the negative electrode active material layer, and contains a solid electrolyte material containing at least lithium phosphate oxynitride (LiPON). For example, Li _2.9 PO _3.3 N _0.45 can be used as LiPON. Moreover, oxide solid electrolyte materials other than LiPON and sulfide solid electrolyte materials may also be included in the solid electrolyte layer.

Examples of other oxide solid electrolyte materials used in the present invention include LiLaTiO (for example, Li _0.34 La _0.51 TiO ₃ ), LiLaZrO (for example, Li ₇ La ₃ Zr ₂ O ₁₂ ), and the like. Can do. Still another example of the oxide solid electrolyte material includes a compound having a NASICON type structure. As an example of a compound having a NASICON type structure, a compound represented by the general formula Li _{1 + x} Al _x Ge _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 2) can be given. In the above general formula, the range of x may be 0 or more, more preferably greater than 0, and more preferably 0.3 or more. On the other hand, the range of x should just be 2 or less, and it is preferable that it is 1.7 or less especially, and it is more preferable that it is 1 or less. Above all, in the present invention, the oxide solid electrolyte _{material, Li 1.5 Al 0.5 Ge 1.5 (} PO 4) is preferably _3. Another example of the compound having a NASICON structure is a compound represented by the general formula Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 2). In the above general formula, the range of x may be 0 or more, more preferably greater than 0, and more preferably 0.3 or more. On the other hand, the range of x should just be 2 or less, and it is preferable that it is 1.7 or less especially, and it is more preferable that it is 1 or less. Above all, in the present invention, the oxide solid electrolyte _{material, Li 1.3 Al 0.3 Ti 1.7 (} PO 4) is preferably _3.

Examples of the sulfide solid electrolyte material used in the present invention include Li ₂ S—P ₂ S ₅ , Li ₂ S—P ₂ S ₅ —LiI, Li ₂ S—P ₂ S ₅ —Li ₂ O, _{Li 2 S-P 2 S 5} -Li 2 O-LiI, Li 2 S-SiS 2, Li 2 S-SiS 2 -LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li _{2 S-SiS 2 -B 2 S} 3 -LiI, Li 2 S-SiS 2 -P 2 S 5 -LiI, Li 2 S-B 2 S 3, Li 2 S-P 2 S 5 -Z m S n ( However, m and n are positive numbers. Z is any one of Ge, Zn, and Ga.), Li ₂ S—GeS ₂ , Li ₂ S—SiS ₂ —Li ₃ PO ₄ , Li ₂ S—SiS ₂ —. Li _x MO _y (where, x, y is the number of positive .M is, P, Si, e, B, Al, Ga, either an In.) and the like. The description of “Li ₂ S—P ₂ S ₅ ” means a sulfide solid electrolyte material using a raw material composition containing Li ₂ S and P ₂ S _5, and the same applies to other descriptions. is there. More specifically, for example, Li ₇ P ₃ S ₁₁ , Li _3.25 P _0.95 S ₄ , Li _3.25 Ge _0.25 P _0.75 S _{4 and the} like can be mentioned.

  Examples of the shape of the solid electrolyte material include particle shapes such as true spheres and ellipsoids, and thin film shapes. Moreover, when a solid electrolyte material is a particle shape, it is preferable that the average particle diameter exists in the range of 50 nm-5 micrometers, for example, and it is more preferable that it exists in the range of 100 nm-3 micrometers.

  The solid electrolyte layer is preferably composed only of the solid electrolyte material described above, but may contain a binder as necessary. The binder used for the solid electrolyte layer is the same as in the positive electrode active material layer described above.

  The thickness of the solid electrolyte layer varies greatly depending on the type of the solid electrolyte material and the configuration of the all-solid battery, but is preferably in the range of 0.1 μm to 1000 μm, for example, 0.1 μm to 300 μm. More preferably within the range. The method for forming the solid electrolyte layer is not particularly limited as long as it is a method capable of forming the target solid electrolyte layer.

The negative electrode active material layer in the all solid state battery of the present invention is a layer containing at least a negative electrode active material, and may contain at least one of a solid electrolyte material and a conductive agent as necessary. When the all-solid battery of the present invention is an all-solid lithium battery, the negative electrode active material is not particularly limited as long as it can occlude and release Li ions, which are conductive ions. For example, a carbon active material And a metal active material. Examples of the carbon active material include graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. On the other hand, examples of the metal active material include alloy materials such as Li alloy and Sn—Co—C, In, Al, Si, and Sn. In addition, examples of other negative electrode active materials include oxide materials such as Li ₄ TiO ₅ .

  Note that the solid electrolyte material and the conductive agent used in the negative electrode active material layer are the same as those in the solid electrolyte layer and the positive electrode active material layer described above, respectively. The thickness of the negative electrode active material layer is, for example, in the range of 0.1 μm to 1000 μm. The method for forming the negative electrode active material layer is not particularly limited as long as it can form the target negative electrode active material layer.

  The all solid state battery of the present invention has at least the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer described above. Furthermore, it usually has a positive electrode current collector for collecting current of the positive electrode active material layer and a negative electrode current collector for collecting current of the negative electrode active material layer. Examples of the material for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. Among them, SUS is preferable. On the other hand, examples of the material for the negative electrode current collector include SUS, copper, nickel, and carbon. Among them, SUS is preferable. In addition, the thickness and shape of the positive electrode current collector and the negative electrode current collector are preferably appropriately selected according to the use of the all solid state battery. Moreover, the battery case used for a general all-solid-state battery can be used for the battery case used for this invention, For example, the battery case made from SUS etc. can be mentioned. Further, the all solid state battery of the present invention may be one in which the power generating element is formed inside the insulating ring.

  In the all solid state battery of the present invention, since the amount of Li in the positive electrode active material is small, it is possible to suppress the formation of a resistive layer having an excessive Li composition on the surface of the positive electrode bond, and charge / discharge is possible. Examples of the shape of the all solid state battery of the present invention include a coin type, a laminate type, a cylindrical type, and a square type.

  The method for producing an all-solid battery of the present invention is not particularly limited as long as it is a method capable of obtaining the above-described all-solid battery, and a method similar to a general method for producing an all-solid battery may be used. it can. For example, when the all-solid-state battery is in the form of a thin film, the positive electrode active material layer is formed on the substrate, the above-described modifier layer is formed on the positive electrode active material layer, and then the solid electrolyte layer and the negative electrode active material layer are sequentially formed. And a method of laminating.

Example 1
Preparation of positive electrode active material layer A Pt (300 nm) / Cr (20 nm) / SiO / Si substrate was used as a substrate, and a Li _x Ni _0.5 Mn _1.5 O ₄ film (LNM film) was formed on this substrate by high-frequency sputtering (RF sputtering). ) Was formed. Each condition of the RF sputtering method is as follows.
Target composition: Li _1.0 Ni _0.5 Mn _1.5 O ₄
・ Output: 500W
-Chamber atmosphere: 2.0 Pa, Ar 100%
-Substrate temperature: 300 ° C
-Film formation time: 2 hours The LNM film | membrane after film-forming was baked in the air at 700 degreeC in the muffle furnace for 5 hours, and the LNM thin film was crystallized.

Preparation of solid electrolyte layer A LiPON film was formed on the LNM thin film by RF sputtering. Each condition of this RF sputtering method is as follows.
-Target composition: Li ₃ PO ₄
・ Output: 300W
-Chamber atmosphere: 1.0 Pa, N ₂ 100%
-Substrate temperature: room temperature-Deposition time: 30 hours

Preparation of negative electrode active material layer A metal Li film was formed on the LiPON film by a heating vacuum deposition method.

Example 2
It was produced in the same manner as in Example 1 except that in the positive electrode active material layer production process of Example 1, the firing temperature of the LNM film after film formation was 650 ° C.

Comparative Example 1
It was produced in the same manner as in Example 1 except that Li _1.1 Ni _0.5 Mn _1.5 O ₄ was used as a target in the positive electrode active material layer production process of Example 1.

Comparative Example 2
In the positive electrode active material layer preparation step of Example 1, the positive electrode active material layer was prepared in the same manner as in Example 1 except that the substrate temperature during film formation was 500 ° C.

  The all solid state battery produced as described above was evaluated for composition analysis, interface resistance, and cyclic voltammetry of the LNM thin film. In the composition analysis, the amount of Li was measured by atomic absorption spectrometry, and the amounts of Ni and Mn were measured by ICP emission spectroscopy. The interface resistance was evaluated by the AC impedance method (measurement frequency: 1 MHz to 0.01 Hz, potential amplitude: 10 mV, battery potential: 4.7 V). Cyclic voltammetry was measured in a potential range of 3.5 to 5 V and a sweep rate of 0.1 mV / sec.

The measurement results of the composition analysis of the LNM thin film are shown in Table 1 below. The value x of Li _x Ni _0.5 Mn _1.5 O ₄ is in the range of 0.65 <x <0.8 in Examples 1 and 2, and is larger than this range in Comparative Example 1 and smaller in Comparative Example 2. Yes.

  The measurement result of cyclic voltammetry is shown in FIG. In Examples 1 and 2, a charge / discharge peak around 4.7 V was observed, and a discharge capacity of about 100 mAh / g was obtained. On the other hand, in the comparative example, a peak of 4.7 V was not observed, and the battery was only slightly discharged at a low potential.

The measurement result of AC impedance is shown in FIG. The arc on the low frequency side corresponds to the interface resistance at 4.7V. In Examples 1 and 2, a low resistance of about 3500 Ω · cm ² was exhibited. Comparative Examples 1 and 2 showed such a large value that the interfacial resistance could not be measured, and due to this large interfacial resistance, no CV charge / discharge peak was observed near 4.7V. The reason why the interfacial resistance of Comparative Example 1 is large is considered to be that a Li-excess composition such as Li ₂ MnO ₃ formed on the resurface of the LNM layer decomposes at a high potential to become a resistance layer. The reason why the interface resistance of Comparative Example 2 is large is considered to be that an oxide made of Ni—Mn—O having no Li conductivity was formed on the outermost surface of the LNM layer.

  FIG. 4 shows the relationship between the Li amount of the LNM thin film and the discharge capacity, and FIG. 5 shows the relationship between the Li amount and the interface resistance. The interface resistance decreased in the Li composition region where 0.65 <x <0.8, and discharge was possible in the 5V region, indicating a high capacity.

DESCRIPTION OF SYMBOLS 1 All-solid-state battery 2 Board | substrate 3 Positive electrode active material layer 4 Solid electrolyte layer 5 Negative electrode active material layer

Claims (2)

A positive electrode active material layer containing a positive electrode active material; a negative electrode active material layer containing a negative electrode active material; and a solid electrolyte layer containing a solid electrolyte disposed between the positive electrode active material layer and the negative electrode active material layer; The positive electrode active material has the following formula: Li _x Ni _0.5 Mn _1.5 O ₄
(In the above formula, 0.65 <x <0.8)
An all-solid battery in which the solid electrolyte contains lithium phosphate oxynitride (LiPON).   The all-solid-state battery of Claim 1 whose thickness of the said positive electrode active material layer is 100 nm-10 micrometers.

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