JP6431707B2 - Electrode layer for all solid state battery and all solid state battery - Google Patents

Description

  The present invention relates to an electrode layer for an all solid state battery and an all solid state battery, and more particularly to an electrode layer for an all solid state battery in which lithium ions are responsible for electrical conduction and an all solid state battery.

  In recent years, the demand for lithium ion secondary batteries has increased in applications such as portable information terminals, portable electronic devices, electric vehicles, hybrid electric vehicles, and stationary power storage systems. However, the current lithium ion secondary battery uses a flammable organic solvent as an electrolyte, and requires a strong exterior so that the organic solvent does not leak. In addition, in a portable personal computer or the like, there are restrictions on the structure of the device, such as the need to take a structure in preparation for the risk that the electrolyte should leak.

  Furthermore, the use is extended to mobile bodies such as automobiles and airplanes, and a large capacity is required for stationary lithium ion secondary batteries. Under such circumstances, safety tends to be more important than before, and efforts are being made to develop all-solid lithium ion secondary batteries that do not use harmful substances such as organic solvents.

  The use of oxides, phosphate compounds, organic polymers, sulfides and the like as solid electrolytes in all solid-state lithium ion secondary batteries has been studied. However, oxides and phosphoric acid compounds have low resistance to oxidation and reduction, and it is difficult to stably exist in lithium ion secondary batteries. Moreover, when materials, such as metallic lithium, low crystalline carbon, and graphite, are used as a negative electrode, it also has the fault that a solid electrolyte and a negative electrode will react (patent document 1).

  Furthermore, oxides and phosphoric acid compounds have the property that their particles are hard. Therefore, in order to form a solid electrolyte layer using these materials, it is generally necessary to sinter at a high temperature of 600 ° C. or more, which is troublesome. Furthermore, when an oxide or a phosphoric acid compound is used as the material for the solid electrolyte layer, there is a disadvantage that the interfacial resistance with the electrode active material is increased. The organic polymer has a drawback that the lithium ion conductivity at room temperature is low and the conductivity rapidly decreases as the temperature decreases.

On the other hand, sulfide has high lithium ion conductivity of 1.0 × 10 ⁻³ S / cm or more (Patent Document 2) and 0.2 × 10 ⁻³ S / cm or more (Patent Document 3) at room temperature. It has been known. Furthermore, since the particles are soft, it is possible to produce a solid electrolyte layer by a cold press and to easily bring the contact interface into a good state. However, when materials containing Ge or Si are used as the sulfide solid electrolyte material (Patent Document 2 and Patent Document 4), these materials have a problem that they are easily reduced. Further, when a battery is formed using a negative electrode active material having an electrode potential of about 0 V (Li standard) typified by lithium metal or a carbon-based active material capable of securing a high voltage in a single cell (Patent Document 4), a sulfide solid There is also a problem that a reduction reaction of the electrolyte occurs.

In order to prevent the above problems, a method of providing a film on the surface of the negative electrode active material (Patent Document 5), a method of devising the composition of the solid electrolyte (Patent Documents 6 to 10), and the like have been proposed. In particular, in Patent Document 10, a solid electrolyte containing P ₂ S ₅ is used, but even when such a sulfide solid electrolyte is used, there remains a concern about the reaction with the negative electrode active material (non-patent). Reference 1). Further, the stability of the negative electrode is easily changed by a small amount of impurities in the solid electrolyte layer, and its control is not easy. For this reason, a solid electrolyte that has high lithium ion conductivity, does not adversely affect the stability of the electrode active material, and can form a good interface with an adjacent material is desired.

Regarding the new lithium ion conductive solid electrolyte, it was reported in 2007 that the high temperature phase of LiBH ₄ has a high lithium ion conductivity (Non-patent Document 2), and in 2009 it can be achieved by adding LiI to LiBH _4. It was reported that the solid solution can maintain a high-temperature phase even at room temperature (Non-patent Document 3 and Patent Document 11; hereinafter, an ion conductor containing a complex hydride such as LiBH ₄ is also referred to as a complex hydride solid electrolyte. ). LiBH ₄ has a low density, and when these are used as a solid electrolyte, a light battery can be produced. Further, it is stable up to 200 ° C., and a heat-resistant battery can be produced. It has been studied to construct a battery using this complex hydride solid electrolyte, and it is disclosed that the effect is exhibited particularly when metallic lithium is used for the negative electrode (Patent Documents 12 and 13).

However, the solid electrolyte containing LiBH ₄ has a drawback of reducing an oxide, for example, LiCoO _2, which is a commonly used positive electrode active material. As a technique for preventing this, a charge / discharge cycle at 120 ° C. can be achieved by coating about 10 nm of Li ₃ PO ₄ on a 100 nm LiCoO ₂ layer formed by pulsed laser deposition (PLD; Pulse Laser Deposition). It has been reported that this is possible (Non-Patent Document 4). However, since this is a thin film battery manufactured using vapor phase film deposition instead of the bulk type, it has a drawback that the capacity per cell cannot be secured as in the bulk type and the productivity is not good.

  Although a method for avoiding reduction by complex hydride by using a specific positive electrode active material has been found, usable positive electrode active materials are extremely limited (for example, polycyclic aroma having a polyacene skeleton structure). Group hydrocarbons, perovskite-type fluorides, etc.) (Patent Document 12). Moreover, these positive electrode active materials are not the oxide type positive electrode active materials generally used for the lithium ion secondary battery currently marketed, and there is no track record regarding long-term stability. Patent Document 12 also states that an oxide-type positive electrode active material coated with a specific ion conductor or carbon is difficult to reduce, but the data shown in the examples shows the reducing action during charging. It does not necessarily describe the effect when charging and discharging are repeated.

Non-Patent Document 4 shows that reduction of LiCoO ₂ by LiBH ₄ occurs during charging. 1 clearly shows that the battery resistance increases with repeated charge and discharge cycles. From this, it can be said that there is a demand for an effective means that not only suppresses the reduction of the positive electrode active material by the complex hydride in the short term but also suppresses the increase in battery resistance even after repeated charge and discharge.

JP 2000-223156 A International Publication No. 2011/118801 JP 2012-43646 A JP 2006-277797 A JP 2011-150942 A Japanese Patent No. 3149524 Japanese Patent No. 3163374 Japanese Patent No. 3343934 Japanese Patent No. 4165536 JP 2003-68361 A Japanese Patent No. 5187703 JP2012-209106A JP2012-209104A

SEI Technical Review, September 2005, No. 167, p. 54-60 Applied PhysiCS Letters (2007) 91, p. 224103 JOURNAL OF THE AMERICA CHEMICAL SOCIETY (2009), 131, p. 894-895 Journal of Power Sources (2013), 226, p. 61-64

The inventors diligently studied an electrode layer composed of a complex hydride solid electrolyte and an active material. As a result, it has been newly found that an electrode layer containing a complex hydride solid electrolyte undergoes degradation due to decomposition of the complex hydride due to side reactions when the voltage during charging and discharging is high.
In order to solve the above problems, the present invention has an object to provide an electrode layer for obtaining an all-solid battery having high ion conductivity and excellent stability, and an all-solid battery including such an electrode layer. And

The present inventors have found that it is effective to combine a complex hydride solid electrolyte and a specific active material having a relatively low electrode potential as a configuration of an electrode layer that can solve the above-described problems. Therefore, the present invention is as follows, for example.
[1] An electrode layer comprising an active material and a complex hydride solid electrolyte, wherein the active material comprises lithium titanate.
[2] The electrode layer according to [1], wherein the lithium titanate is selected from the group consisting of LiTi ₂ O ₄ , Li ₄ Ti ₅ O ₁₂ and Li ₂ Ti ₃ O ₇ .
[3] The electrode layer according to [2], wherein the lithium titanate is Li ₄ Ti ₅ O ₁₂ .
[4] The electrode layer according to any one of [1] to [3], wherein the complex hydride solid electrolyte is a mixture of LiBH ₄ or LiBH ₄ and an alkali metal compound represented by the following formula (1). :
MX (1)
[In formula (1), M represents an alkali metal atom selected from the group consisting of lithium atom, rubidium atom and cesium atom, X represents a halogen atom or an NH ₂ group. ].
[5] The electrode layer according to [4], wherein the alkali metal compound is selected from the group consisting of rubidium halide, lithium halide, cesium halide, and lithium amide.
[6] The electrode layer is a positive electrode layer, the complex hydride solid electrolyte is LiBH ₄ , and 90% by weight or more of the total active material contained in the positive electrode layer is 1.20 V to 1.80 V based on lithium. The electrode layer according to any one of [1] to [5], which is an active material having an electrode potential of
[7] The electrode layer is a positive electrode layer, the complex hydride solid electrolyte is 3LiBH ₄ -LiI, and 90% by weight or more of the total active material contained in the positive electrode layer is 1.20 V to 2 on a lithium basis. The electrode layer according to any one of [1] to [5], which is an active material having an electrode potential of 70V.
[8] A positive electrode layer, a negative electrode layer, and a solid electrolyte layer having lithium ion conductivity disposed between the positive electrode layer and the negative electrode layer,
Either the said positive electrode layer or the said negative electrode layer is an all-solid-state battery which is an electrode layer in any one of [1]-[7].
[9] The all solid state battery according to [8], wherein the negative electrode layer is the electrode layer according to any one of [1] to [5].
[10] The all solid state battery according to [8], wherein the positive electrode layer is the electrode layer according to any one of [1] to [7].
[11] The complex hydride solid electrolyte contained in the positive electrode layer is LiBH _4, the upper limit charge voltage applied to the positive electrode layer is 1.55V~1.80V based on lithium, total solids according to [10] battery.
[12] The complex hydride solid electrolyte contained in the positive electrode layer is 3LiBH ₄ -LiI, and the upper limit charging voltage applied to the positive electrode layer is 1.55 V to 2.70 V based on lithium, All solid battery.

  According to the present invention, it is possible to provide an electrode layer for obtaining an all-solid battery having high ion conductivity and excellent stability, and an all-solid battery including such an electrode layer.

Sectional drawing of the all-solid-state battery which concerns on embodiment of this invention. The figure which shows transition of the charge capacity of the all-solid-state battery produced in Example 1, and coulomb efficiency. The figure which shows transition of the charge capacity of the all-solid-state battery produced in Example 2, and coulomb efficiency. The figure which shows the charge-and-discharge curve of 1, 2 and 20th cycle about the all-solid-state battery produced in Example 1 (charge-discharge test 1). The figure which shows the charging / discharging curve of 1st and 2nd cycles about the all-solid-state battery produced in Example 1 (charging / discharging test 2). The figure which shows the charging / discharging curve of 1, 2 and 20th cycle about the all-solid-state battery produced in Example 2. FIG. The figure which shows the charging / discharging curve of the 1st cycle about the all-solid-state battery produced by the comparative example 1. FIG. The figure which shows the charging / discharging curve of the 1st cycle about the all-solid-state battery produced by the comparative example 2. FIG.

  Embodiments of the present invention will be described below. The materials, configurations, and the like described below do not limit the present invention and can be variously modified within the scope of the gist of the present invention.

1. Electrode Layer According to one embodiment of the present invention, there is provided an electrode layer comprising an active material and a complex hydride solid electrolyte, wherein the active material comprises lithium titanate. This electrode layer is preferably an electrode layer used in an all-solid battery, and more preferably an electrode layer used in an all-solid lithium ion secondary battery. The electrode layer of the present invention can be used for both the negative electrode layer and the positive electrode layer, and may further contain a conductive additive, a binder, and the like as necessary. Hereinafter, lithium titanate, complex hydride solid electrolyte, and other materials that can be used for the electrode layer are also collectively referred to as “electrode material”.

Hereinafter, the electrode material will be described in detail.
(1) Lithium titanate The electrode layer of the present invention contains lithium titanate as an active material. As lithium titanate, spinel-type LiTi ₂ O ₄ , spinel-type Li ₄ Ti ₅ O ₁₂ , ramsdellite-type Li ₂ Ti ₃ O _7, etc. can be used, and preferably spinel-type Li ₄ Ti _5. O is _12. Li ₄ Ti ₅ O ₁₂ may be expressed as Li _4/3 Ti _5/3 O ₄ or Li [Li _1/6 Ti _5/6 ] ₂ O ₄ , and the space group is Fd-3mE. When lithium ions are inserted into this, the structure changes to a rock salt type structure.

  There are various methods for producing an active material made of an oxide containing lithium and titanium, such as lithium titanate, and any method such as a liquid phase method or a solid phase method may be used.

  The particle size of lithium titanate is preferably in the range of 0.05 to 200 μm, more preferably 0.1 to 100 μm, when observed with an electron microscope. When it is desired to produce an output type electrode, it is better to use an electrode having a small particle size.

  As described above, the inventors have found that an electrode layer containing a complex hydride solid electrolyte is deteriorated by decomposition of the complex hydride due to a side reaction when the voltage during charging and discharging is high. In the present invention, by using lithium titanate having a relatively low electrode potential as an active material, it is possible to suppress an increase in voltage during charging and discharging, and therefore it is possible to prevent decomposition due to side reaction of the complex hydride. . Therefore, lithium titanate having an electrode potential (based on lithium) of 1.0 to 1.8 V as shown in the above specific example is preferable. Further, as described above, when the complex hydride is used as a solid electrolyte, there is a concern about reduction of the positive electrode active material. However, lithium titanate is less susceptible to reduction by complex hydrides. Therefore, by using lithium titanate as a positive electrode active material, a complex hydride having high lithium ion conductivity can be used as a solid electrolyte without concern about reduction of the positive electrode active material by the complex hydride. Thus, by using an electrode layer containing lithium titanate and a complex hydride solid electrolyte as an electrode layer of an all-solid battery, decomposition due to side reaction of the complex hydride is suppressed, and the electrode layer is used as a positive electrode layer. When used, the reduction of the positive electrode active material can also be prevented. As a result, it is possible to provide an all solid state battery that operates stably over a long period of time even when the charge / discharge cycle is repeated.

The electrode layer of the present invention may contain an active material other than lithium titanate. As active materials other than lithium titanate, α-Fe ₂ O ₃ , LiCoO ₂ , LiCo ₂ O ₄ , LiMnO ₂ , LiMn ₂ O ₄ , Li ₂ Mn ₂ O _4, LiMnCoO ₄ , Li ₂ MnCoO ₄ , LiNi _{0 .8} Co _0.15 Al _0.05 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , Li ₂ NiMn ₃ O ₈ , LiVO ₂ , V ₂ O ₃ , LiV ₃ O ₃ , LiCrO ₂ , LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ , LiVOPO ₄ , LiNiO ₂ , LiNi ₂ O ₄ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , LiFeBO _3, etc. it can.

  The ratio of lithium titanate to the total amount of the active material contained in the electrode layer is preferably 90% by weight or more, more preferably 95% by weight, and further preferably 98% by weight or more.

  In the electrode layer of the present invention, it is preferable that the active material (may be plural types) and the complex hydride solid electrolyte exist in a bulk type. On the other hand, it is known that lithium titanate can be used as a coating layer that covers the surface of an active material other than lithium titanate. When used in such an embodiment, in view of the necessity of limiting the voltage during charge and discharge described above, as an active material other than lithium titanate, an electrode potential higher than the voltage causing a side reaction of the complex hydride is used. It is not preferable to use an active material. The use of an active material having an electrode potential higher than the voltage causing the side reaction of the complex hydride charges and discharges at a voltage lower than the voltage causing the side reaction of the complex hydride, and the capacity of the lithium titanate of the coating layer However, it is not impossible if the battery is operated using only the electrode, but the capacity density of the entire electrode is lowered.

  Particularly, in the positive electrode layer, coating of the positive electrode active material with an ion conductor such as lithium titanate is well known for all solid state batteries using a sulfide-based solid electrolyte. When the positive electrode active material and the sulfide-based solid electrolyte are in direct contact, element diffusion in the range of about 50 nm from the contact interface (the transition metal in the active material is on the solid electrolyte side, the constituent elements of the solid electrolyte are on the active material side, respectively (For example, “Development and manufacturing technology of an all-solid-state lithium ion secondary battery”, Science & Technology Publishing, p149-p151). That is, when the coating layer containing lithium titanate has a thickness within a range where element diffusion occurs, lithium titanate does not exist in a pure state, and the electrode potential shifts with respect to pure lithium titanate. It is thought that it has occurred. It is also known that such a coating layer becomes a resistance layer when the thickness is increased ("Development and manufacturing technology of an all-solid-state lithium ion secondary battery", p62 to p68). These phenomena are considered to occur not only when using sulfide solid electrolytes but also when using complex hydride solid electrolytes ("Development and manufacturing technology of all-solid lithium ion secondary batteries"). ", P62).

  Using the technology of coating the positive electrode active material as described above with lithium titanate, the potential applied to the complex hydride solid electrolyte, which is one of the objects of the present invention, is suppressed to prevent the occurrence of side reactions. Various problems can arise when trying to achieve. For example, when lithium titanate is coated on a known active material having a high electrode potential, in order to prevent decomposition of the complex hydride solid electrolyte due to side reactions, charging and discharging is performed at a low voltage using only the lithium titanate capacity. There is a need to do. Therefore, it is necessary to increase the thickness of the coating layer containing lithium titanate, and it is necessary to secure a film thickness of 50 nm or more that is hardly affected by element diffusion. The film thickness of the coating layer needs to be, for example, 100 nm or more, preferably 500 nm or more, more preferably 1000 nm or more, and particularly preferably 2000 nm or more. As described above, the resistance layer can be formed by increasing the thickness of the coating layer. Therefore, in the known method of coating the positive electrode active material with lithium titanate, it is not assumed that the film thickness of the coating layer is set in the large range as described above, and there is no such necessity. As described above, it can be said that the known method of coating the positive electrode active material with lithium titanate is not supposed to suppress the decomposition of the solid electrolyte.

(2) Complex hydride solid electrolyte The complex hydride solid electrolyte is not particularly limited as long as it is a material containing a complex hydride having lithium ion conductivity. For example, the complex hydride solid electrolyte is LiBH ₄ or a mixture of LiBH ₄ and an alkali metal compound represented by the following formula (1):
MX (1)
[In formula (1), M represents an alkali metal atom selected from the group consisting of lithium atom, rubidium atom and cesium atom, X represents a halogen atom or an NH ₂ group. ].
The halogen atom as X in the formula (1) may be an iodine atom, a bromine atom, a fluorine atom, a chlorine atom or the like. X is preferably an iodine atom, a bromine atom or an NH ₂ group, and more preferably an iodine atom or an NH ₂ group.

Specifically, the alkali metal compound includes lithium halide (eg, LiI, LiBr, LiF or LiCl), rubidium halide (eg, RbI, RbBr, RbF or RbCl), cesium halide (eg, CsI, CsBr, CsF or CsCl) or lithium amide (LiNH ₂ ) is preferable, and LiI, RbI, CsI, or LiNH ₂ is more preferable. An alkali metal compound may be used individually by 1 type, and may be used in combination of 2 or more type. A preferred combination includes a combination of LiI and RbI.

As LiBH ₄ and the alkali metal compound, known compounds can be used respectively. Further, the purity of these compounds is preferably 80% or more, and more preferably 90% or more. This is because a compound having a purity within the above range has high performance as a solid electrolyte.

The molar ratio of LiBH ₄ to the alkali metal compound is preferably 1: 1 to 20: 1, and more preferably 2: 1 to 7: 1. By setting the molar ratio within the above range, a sufficient amount of LiBH _{4 in} the electrode layer can be ensured, and high ion conductivity can be obtained. On the other hand, if the amount of LiBH ₄ is too large, the transition temperature of the high-temperature phase (high ion conduction phase) is difficult to decrease, and sufficient ion conductivity cannot be obtained at a temperature lower than the transition temperature (115 ° C.) of the high-temperature phase of LiBH _4. There is a tendency.

  When using 2 or more types of alkali metal compounds together, the mixing ratio is not particularly limited. For example, when LiI and another alkali metal compound (preferably RbI or CsI) are used in combination, the molar ratio between LiI and the other alkali metal compound is preferably 1: 1 to 20: 1. : More preferably, it is 1-20: 1. This is because such a mixture ratio preferably acts as a solid electrolyte when the material remains after lithium doping.

The complex hydride solid electrolyte has at least 2θ = 24.0 ± 1.0 deg, 25.6 ± 1.2 deg, 27.3 ± 1.2 deg, 35 in X-ray diffraction (CuKα: λ = 1.5405４０). It is preferable to have diffraction peaks at 4 ± 1.5 deg and 42.2 ± 2.0 deg. It is more preferable to have diffraction peaks at 2θ = 23.7 ± 0.7 deg, 25.2 ± 0.8 deg, 26.9 ± 0.8 deg, 35.0 ± 1.0 deg, and 41.3 ± 1.0 deg. Preferably, it has a diffraction peak at 2θ = 23.6 ± 0.5 deg, 24.9 ± 0.5 deg, 26.7 ± 0.5 deg, 34.6 ± 0.5 deg, and 40.9 ± 0.5 deg. Is particularly preferred. Further, it has diffraction peaks at least at 2θ = 23.6 ± 0.3 deg, 24.9 ± 0.3 deg, 26.7 ± 0.3 deg, 34.6 ± 0.3 deg, and 40.9 ± 0.3 deg. Is more preferable. The diffraction peaks in these five regions correspond to the diffraction peaks of the high temperature phase of LiBH ₄ . Even when the temperature is lower than the transition temperature of the high temperature phase of LiBH _4, the material having the diffraction peak in the five regions as described above tends to exhibit high ionic conductivity even when the temperature is lower than the transition temperature.

  The method for producing the complex hydride solid electrolyte is not particularly limited, but it is preferably produced by mechanical milling or melt mixing described in Japanese Patent No. 5187703.

(3) Conductive auxiliary agent The conductive auxiliary agent used for the electrode layer is not particularly limited as long as it has a desired conductivity, and examples thereof include a conductive auxiliary agent made of a carbon material. Specific examples include carbon black, acetylene black, ketjen black, and carbon fiber.

  The content of the conductive additive in the electrode layer is preferably smaller as long as desired electronic conductivity can be secured. Content of the conductive support agent with respect to electrode material is 0.1 mass%-40 mass%, for example, and it is preferable that they are 1 mass%-20 mass%.

(4) Binder As the binder used for the electrode layer, any binder generally used for a positive electrode layer of a lithium ion secondary battery can be used. For example, polysiloxane, polyalkylene glycol, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), ethylene-vinyl alcohol copolymer (EVOH), or the like can be used. If necessary, a thickener such as carboxymethylcellulose (CMC) can also be used.

  Further, as the binder, an electron conductive conductive polymer or an ion conductive conductive polymer may be used. Examples of the electron conductive conductive polymer include polyacetylene. In this case, since the binding agent also functions as a conductive assistant, it is not necessary to add a conductive assistant.

  Although content of a binder is not specifically limited, It is preferable that it is 0.1-10 mass% on the basis of the sum of the mass of an active material, a conductive support agent, and a binder, 0.1-4 mass % Is more preferable. If the amount of the binder is excessive, the ratio of the active material in the electrode layer is reduced and the energy density is lowered. Therefore, the amount of the binder is set to a minimum amount that can sufficiently maintain the molding strength of the electrode layer. It is preferable. Note that the lithium-containing complex hydride and the sulfur-based electrode active material have a considerable function as a binder, and therefore when these materials are used as electrode materials, no binder is used. It is also possible to produce an electrode layer.

Next, a method for manufacturing the electrode layer will be described.
First, an electrode material containing lithium titanate and a complex hydride solid electrolyte is mixed. The mixing is preferably performed in an inert gas atmosphere such as argon or helium. The mixing method is not particularly limited, and examples thereof include a method using a reika machine, a ball mill, a planetary ball mill, a bead mill, a rotation / revolution mixer, a high-speed stirring type mixing apparatus, a tumbler mixer, and the like. However, using a method that gives large energy during mixing, such as mixing using a planetary ball mill, there is a possibility that not only mixing but lithium titanate and complex hydride will react, and mild mixing will occur. It is preferable to use a reiki machine, a tumbler mixer, a rotation / revolution mixer, and the like. When done on a small scale, manual mortar mixing is preferred. The mixing is preferably carried out dry, but it can also be carried out in a solvent having reduction resistance. When a solvent is used, an aprotic non-aqueous solvent is preferable, and more specific examples include ether solvents such as tetrahydrofuran and diethyl ether, N, N-dimethylformamide, N, N-dimethylacetamide and the like. it can.

  The proportion of lithium titanate and complex hydride solid electrolyte in the electrode layer is preferably higher if the shape of the electrode layer can be maintained and the necessary ion conductivity can be ensured. . For example, the lithium titanate: complex hydride solid electrolyte in a weight ratio is preferably in the range of 9: 1 to 1: 9, and more preferably 8: 2 to 2: 8.

  The electrode layer can be produced by a commonly used method. For example, it can manufacture by apply | coating the electrode material mixed as mentioned above on a collector, and removing the solvent in the coating material apply | coated on the collector.

  The current collector that can be used is not particularly limited, and materials conventionally used as current collectors for lithium ion secondary batteries, such as thin plates and meshes of aluminum, stainless steel, copper, nickel, or alloys thereof, can be used. Can be used. Moreover, a carbon nonwoven fabric, a carbon woven fabric, etc. can be used as a collector.

  Examples of the solvent used when applying the electrode material on the current collector include ether solvents such as tetrahydrofuran and diethyl ether, and aprotic such as N-methyl-2-pyrrolidone and N, N-dimethylformamide. Non-aqueous solvents can be used.

  There is no restriction | limiting in particular as a coating method, The method employ | adopted when producing an electrode layer normally can be used. Examples thereof include a slit die coating method and a doctor blade method.

  The method for removing the solvent in the paint applied on the current collector is not particularly limited, and the current collector applied with the paint may be dried, for example, in an atmosphere of 80 to 150 ° C.

  And what is necessary is just to press-process the electrode layer produced in this way with a roll press apparatus etc. as needed. The linear pressure of the roll press can be, for example, 10 to 50 kgf / cm.

  In addition, without using a solvent, a method of forming a mixed powder of an electrode material with a press, a method of applying vibration after placing the mixed powder on a current collector, or pressing an electrode material with a spatula, etc. It is also possible to produce the electrode layer by a method of filling the porous portion. Alternatively, the electrode material can be molded in advance and then bonded to the current collector, or the electrode material can be integrally molded with the solid electrolyte layer or the other electrode layer and then bonded to the current collector.

  Although the thickness of an electrode layer is not specifically limited as long as it functions as an electrode, it is preferable that they are 1 micrometer-1000 micrometers, and it is more preferable that they are 10 micrometers-200 micrometers.

2. All-solid-state battery The electrode layer of this invention can be used for either the positive electrode layer or the negative electrode layer of an all-solid-state battery. Therefore, according to one embodiment of the present invention, an all-solid battery including the electrode layer is provided.
That is, the all solid state battery of the present invention comprises a positive electrode layer, a negative electrode layer, and a solid electrolyte layer having lithium ion conductivity disposed between the positive electrode layer and the negative electrode layer. Either one is an electrode layer containing the above-described lithium titanate and a complex hydride solid electrolyte.

Hereinafter, the case where the electrode layer of the present invention is used as a positive electrode layer will be described as a “first embodiment”, and the case where the electrode layer of the present invention is used as a negative electrode layer will be described in detail as a “second embodiment”.
(First embodiment)
According to one embodiment of the present invention, a positive electrode layer, a negative electrode layer, and a solid electrolyte layer having lithium ion conductivity disposed between the positive electrode layer and the negative electrode layer are provided. An all solid state battery is provided that is an electrode layer comprising lithium titanate and a complex hydride solid electrolyte. The configuration of the all solid state battery will be described with reference to FIG.

FIG. 1 is a cross-sectional view of an all solid state battery of the present invention.
The all solid state battery 10 in the present invention is, for example, an all solid state lithium ion secondary battery, and can be used in various devices such as a mobile phone, a personal computer, and an automobile. The all solid state battery 10 has a structure in which a solid electrolyte layer 2 is disposed between a positive electrode layer 1 and a negative electrode layer 3. In the first embodiment, as the positive electrode layer 1, an electrode layer containing both the above-described lithium titanate and a complex hydride solid electrolyte is used.

(1) Positive electrode layer About the structure and preparation method of the positive electrode layer 1, it is as having demonstrated by the item of the said "1. electrode layer." In addition, if the electrode potential of the active material contained in the positive electrode layer 1 is lower than the potential at which a side reaction of the complex hydride solid electrolyte used in the positive electrode layer 1 occurs, the higher the energy density of the battery is improved. Therefore, it is preferable.

Specifically, when the complex hydride solid electrolyte used for the positive electrode layer 1 is LiBH ₄ , 90% by weight or more of the total active material contained in the positive electrode layer 1 is 1.20 V to 1.80 V based on lithium. It is preferable that the active material has an electrode potential of 95% by weight or more, more preferably 98% by weight or more.
When the complex hydride solid electrolyte contained in the positive electrode layer 1 is 3LiBH ₄ -LiI, 90% by weight or more of the total active material contained in the positive electrode layer 1 has an electrode potential of 1.20 V to 2.70 V based on lithium. An active material is preferable, and an active material having an electrode potential in the above range is more preferably 95% by weight or more, and further preferably 98% by weight or more.

(2) Solid electrolyte layer The solid electrolyte layer 2 is a layer having lithium ion conductivity disposed between the positive electrode layer 1 and the negative electrode layer 3, and is formed from a solid electrolyte having lithium ion conductivity. As the solid electrolyte, a complex hydride solid electrolyte, an oxide-based material, a sulfide-based material, a polymer-based material, Li ₃ N, or the like can be used. More specifically, Li ₃ PO ₄ —Li ₄ SiO ₄ and Li ₃ BO ₄ —Li ₄ SiO ₄ which are oxide glasses; La _0.5 Li _0.5 TiO ₃ which is a perovskite oxide; NASICON type Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ and Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ which are oxides; Li ₁₄ Zn which is a LISICON type oxide ( GeO ₄ ) ₄ , Li ₃ PO ₄ and Li ₄ SiO ₄ ; Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₅ La ₃ Ta ₂ O ₁₂ and Li ₅ La ₃ Nb ₂ O ₁₂ which are garnet-type oxides; sulfide glass or sulfide glass _{ceramics, Li 2 S-P 2 S} 5, 80Li 2 S-20P 2 S 5, 70Li 2 S-27P 2 S 5 -3P 2 ₅ and _{Li 2 S-SiS 2; thio} -LISICON type material in which _{Li 3.25 Ge 0.25 P 0.75 S 4} , Li 4 SiS 4, Li 4 GeS 4 and _Li 3 PS _4; high lithium ion conductivity Li ₁₀ GeP ₂ S ₁₂ ; Li _3.3 PO _3.8 N _0.22 and Li _2.9 PO _3.3 N ₀ , which are materials called LIPON obtained by partially nitriding Li ₃ PO _{4 .46} ; polymer materials such as polyethylene oxide, polyacrylonitrile, poly (cyanoethoxyvinyl) derivatives (CPVA) and the like. Among these, a complex hydride solid electrolyte is preferable because the interface state with the positive electrode layer 1 is good. As the complex hydride solid electrolyte, the same materials as those described above in “1. Electrode layer, (2) Complex hydride solid electrolyte” can be used.

  The solid electrolyte layer 2 may contain materials other than those described above as necessary. For example, it is possible to use a solid electrolyte layer formed into a sheet shape using a binder. Moreover, in order to adapt to the electrode material used in the positive electrode layer 1 and the negative electrode layer 3, the solid electrolyte layer 2 can also be made into two or more layers.

  The thickness of the solid electrolyte layer 2 is preferably thinner. Specifically, it is preferably in the range of 0.05 μm to 1000 μm, and more preferably in the range of 0.1 μm to 200 μm.

(3) Negative electrode layer The negative electrode layer 3 is a layer containing at least a negative electrode active material, and may contain a solid electrolyte, a conductive additive, a binder, and the like as necessary.

  As the negative electrode active material, for example, a metal active material and a carbon active material can be used. Examples of the metal active material include Li, In, Al, Si, and Sn. Examples of the carbon active material include mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Especially, since the energy density of a battery improves and operating voltage increases, it is preferable to use the active material from which the electrode potential as a negative electrode becomes lower. Examples of such a negative electrode active material include Li, a carbon active material, and Si.

  The solid electrolyte used for the negative electrode layer 3 is not particularly limited as long as it has lithium ion conductivity and is stable with the negative electrode active material. For example, a complex hydride solid electrolyte may be used. it can. Since the complex hydride solid electrolyte is relatively soft, it can form a favorable interface with a negative electrode active material such as graphite and is preferable because it is stable against reduction. The negative electrode layer 3 is preferably a bulk type containing both the negative electrode active material and the solid electrolyte. As the complex hydride solid electrolyte contained in the negative electrode layer 3, the same materials as those described above in “1. Electrode layer, (2) Complex hydride solid electrolyte” can be used. In particular, the negative electrode layer 3 and the solid electrolyte layer 2 preferably contain the same complex hydride solid electrolyte. When layers containing solid electrolytes with different compositions come into contact, it is highly possible that the solid electrolytes will react with each other or that the constituent elements of the solid electrolyte will diffuse between the layers, which may reduce lithium ion conductivity. It is.

  The ratio of the negative electrode active material to the solid electrolyte is preferably higher as long as the shape of the negative electrode layer 3 can be maintained and the necessary ion conductivity can be ensured. For example, the weight ratio of negative electrode active material: solid electrolyte is preferably in the range of 9: 1 to 1: 9, more preferably 8: 2 to 2: 8.

  As the conductive additive used for the negative electrode layer 3, the same conductive additive as the positive electrode layer 1 can be used. Content of the conductive support agent with respect to a negative electrode layer forming material is 0.1 mass%-20 mass%, for example, and it is preferable that they are 3 mass%-15 mass%.

  As a binder used for the negative electrode layer 3, if it is generally used for the negative electrode layer of a lithium ion secondary battery, it can be used. Examples thereof include polysiloxane, polyalkylene glycol, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and polyacrylic acid. If necessary, a thickener such as carboxymethylcellulose (CMC) can also be used.

  Although the thickness of the negative electrode layer 3 is not limited as long as it functions as a negative electrode layer, it is preferably 0.05 μm to 1000 μm, and more preferably 0.1 μm to 200 μm.

(Second Embodiment)
According to one embodiment of the present invention, a positive electrode layer, a negative electrode layer, and a solid electrolyte layer having lithium ion conductivity disposed between the positive electrode layer and the negative electrode layer are provided. An all solid state battery is provided that is an electrode layer comprising lithium titanate and a complex hydride solid electrolyte. Since the configuration of the all-solid-state battery is the same as that of the first embodiment, it will be described with reference to FIG. 1 again. In the second embodiment, as the negative electrode layer 3, an electrode layer containing both the above-described lithium titanate and a complex hydride solid electrolyte is used.

(1) Positive electrode layer The positive electrode layer 1 is a layer containing at least a positive electrode active material. The positive electrode layer 1 may contain a solid electrolyte, a conductive additive, a binder, and the like as necessary.

Any positive electrode active material can be used as long as it can release lithium ions during charging and occlude lithium ions during discharge. For example, a metal oxide having a transition metal, a sulfur-based positive electrode active material, organic Examples of the positive electrode active material include FeF ₃ and VF ₃ using a conversion reaction.

As the metal oxide having a transition metal, particles or a thin film of metal oxide containing at least one of transition metals Mn, Co, Ni, Fe, Cr, and V and lithium can be used. Specifically, α-Fe ₂ O ₃ , LiCoO ₂ , LiCo ₂ O ₄ , LiMnO ₂ , LiMn ₂ O ₄ , Li ₂ Mn ₂ O _4, LiMnCoO ₄ , Li ₂ MnCoO ₄ , LiNi _0.8 Co _{0. 15} Al _0.05 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , Li ₂ NiMn ₃ O ₈ , LiVO ₂ , V ₂ O ₃ , LiV ₃ O ₃ , LiCrO ₂ , LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ , LiVOPO ₄ , LiNiO ₂ , LiNi ₂ O ₄ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , LiFeBO _{3 and the} like. Among them, LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , Li ₂ NiMn ₃ O ₈ , LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ , LiVOPO ₄ , LiNiO ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ are preferred.

Sulfur-based positive electrode active materials include S, TiS ₂ , TiS ₃ , TiS ₄ , NiS, NiS ₂ , CuS, FeS ₂ , Li ₂ S, MoS ₃ , sulfur-modified polyacrylonitrile, rubeanic acid (dithiooxamide), disulfide compound Etc. Among them, TiS ₂ , TiS ₃ , TiS ₄ , NiS, NiS ₂ , FeS ₂ , Li ₂ S, MoS ₃ , sulfur-modified polyacrylonitrile, and rubeanic acid (dithiooxamide) are preferable.

  Examples of organic positive electrode active materials include radical compounds represented by 2,2,6,6-tetramethylpiperidinoxyl-4-yl methacrylate and polytetramethylpiperidinoxyvinyl ether, quinone compounds, radialene compounds, tetra Examples thereof include cyanquinodimethane and phenane dioxide. Among them, radical compounds and quinone compounds are preferable because they have a large theoretical capacity and can maintain a relatively good discharge capacity.

  The solid electrolyte used for the positive electrode layer 1 is not particularly limited as long as it has lithium ion conductivity and is stable with the positive electrode active material. For example, a complex hydride solid electrolyte, an oxide solid electrolyte, a phosphoric acid compound solid electrolyte, a sulfide solid electrolyte, and a mixed system thereof, such as an oxysulfide solid electrolyte, can be mentioned. Therefore, an appropriate solid electrolyte may be used. For example, in the case of using a complex hydride solid electrolyte, since there is a concern about the reduction of the positive electrode active material by the complex hydride as described above, a positive electrode active material that is easily reduced is not suitable. In addition, when using a complex hydride solid electrolyte, if the voltage during charging and discharging is high, the complex hydride may decompose due to side reactions and change in quality. Active materials are also unsuitable. Unless there is a restriction by the active material, it is preferable to use a complex hydride solid electrolyte or a sulfide solid electrolyte. Since the complex hydride solid electrolyte and the sulfide solid electrolyte are relatively soft, a good interface can be formed even between the solid transition metal oxide positive electrode active material. The positive electrode layer 1 is preferably a bulk type containing both a positive electrode active material and a solid electrolyte.

  The details of each solid electrolyte used for the positive electrode layer 1 are the same as those described in “(2) Solid electrolyte layer” of the first embodiment.

  The ratio of the positive electrode active material to the solid electrolyte in the positive electrode layer 1 is preferably as high as possible if the shape of the positive electrode can be maintained and the necessary ionic conductivity can be ensured. For example, the weight ratio of positive electrode active material: solid electrolyte is preferably in the range of 9: 1 to 2: 8, and more preferably 8: 2 to 4: 6.

  The conductive aid used for the positive electrode layer 1 is not particularly limited as long as it has desired conductivity, and examples thereof include a conductive aid made of a carbon material. Specific examples include carbon black, acetylene black, ketjen black, and carbon fiber.

  The content of the conductive auxiliary in the positive electrode layer 1 is preferably smaller as long as desired electronic conductivity can be secured. The ratio of the conductive additive to the positive electrode layer forming material is, for example, 0.1% by mass to 20% by mass, and preferably 3% by mass to 15% by mass.

  As the binder used for the positive electrode layer 1, any binder generally used for the positive electrode layer of a lithium secondary battery can be used. For example, polysiloxane, polyalkylene glycol, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), ethylene-vinyl alcohol copolymer (EVOH), or the like can be used. If necessary, a thickener such as carboxymethylcellulose (CMC) can also be used.

In order to improve the interface state between the positive electrode active material and the solid electrolyte, conductive additive or current collector, a coating layer can be provided on the particles or thin film of the positive electrode active material. Specific methods include those described in the following patent documents. For example, as an effective coating layer when a sulfide solid electrolyte is used, Japanese Patent Laid-Open No. 2012-054151 uses LiNbO ₃ for controlling a depletion layer generated at the interface between different types of ionic conductors. Japanese Patent Application Laid-Open No. 2011-159639 discloses that the interface resistance is reduced by providing a coating layer of LiNbO ₃ or Li ₄ Ti ₅ O _{12 on} the positive electrode active material. Furthermore, Japanese Patent Application Laid-Open No. 2008-103280 discloses that rate characteristics are improved by coating the positive electrode. Examples of the coating material include titanate spinel, tantalum oxide, niobium oxide, and the like. Specifically, Li ₄ Ti ₅ O ₁₂ , LiTaO ₃ , LiNbO ₃ , LiAlO ₂ , Li ₂ ZrO. ₃ , Li ₂ WO ₄ , Li ₂ TiO ₃ , Li ₂ B ₄ O ₇ , Li ₃ PO ₄ , Li ₂ MoO ₄ and LiBO ₂ .

In addition, when using an active material having an olivine type structure typified by LiFePO ₄ or LiCoPO ₄ having a low electron conductivity, the active material is coated with carbon in order to facilitate a charge transfer reaction. However, this technique is also effective in the present invention.

  The thickness of the positive electrode layer 1 is not particularly limited as long as it functions as a positive electrode layer, but is preferably 0.05 μm to 1000 μm, and more preferably 0.1 μm to 200 μm.

(2) Solid Electrolyte Layer The configuration and manufacturing method of the solid electrolyte layer 2 are as described in the item “(2) Solid electrolyte layer” in the first embodiment.

(3) Negative Electrode Layer The configuration and production method of the negative electrode layer 3 are as described in the above item “1. Electrode layer”.

3. Production method of all solid state battery Each layer described above is produced and laminated to produce an all solid state battery. However, the production method and lamination method of each layer are not particularly limited. For example, a method in which a solid electrolyte or electrode active material is dispersed in a solvent to form a slurry, and is applied by a doctor blade, spin coating, etc., and rolled to form a film; a vacuum deposition method, an ion plating method, There are a vapor phase method in which a film is formed and laminated using a sputtering method, a laser ablation method, etc .; a press method in which powder is formed by hot pressing or cold pressing without applying temperature, and then laminated. In the case of using a relatively soft complex hydride solid electrolyte or sulfide solid electrolyte, it is particularly preferable to produce a battery by molding and laminating each layer by pressing. As a pressing method, there are a hot press that is heated and a cold press that is not heated. An appropriate method may be selected depending on the combination of the solid electrolyte and the active material. Each layer is preferably integrally formed by pressing, and the pressure at that time is preferably 50 to 800 MPa, and more preferably 114 to 500 MPa. By pressing at a pressure in the above range, a layer having few voids between particles and good adhesion can be obtained, which is preferable from the viewpoint of ion conductivity. Increasing the pressure more than necessary is not practical because it is necessary to use a pressure device or a molded container made of an expensive material and the useful life thereof is shortened.

4). Voltage Conditions During Charge / Discharge As described above, when the voltage during charge / discharge is high, the electrode layer containing the complex hydride solid electrolyte may be deteriorated due to decomposition of the complex hydride due to side reactions. The voltage that causes decomposition varies depending on the complex hydride solid electrolyte to be used. For example, when LiBH ₄ is used, charging is preferably performed at a voltage of 1.80 V or less on the basis of lithium, and the upper limit charging voltage is 1.55 V. More preferably, it is set to ˜1.80V. Also, when using 3LiBH ₄ -LiI is preferably charged by 2.70V or less of the voltage based on lithium, it is more preferable that the upper limit charge voltage and 1.55V～2.70V. By charging at a voltage in the above range, decomposition due to side reaction of the complex hydride solid electrolyte can be prevented. In addition, by using lithium titanate as an electrode active material as in the present invention, it is possible to charge at a voltage in the above range.

Therefore, according to one embodiment of the present invention, the electrode layer is a positive electrode layer, the complex hydride solid electrolyte in the positive electrode layer is LiBH ₄ , and the upper limit charging voltage applied to the positive electrode layer is 1.55 V to An all-solid battery that is 1.80V is provided.
According to another embodiment of the present invention, the electrode layer is a positive electrode layer, the complex hydride solid electrolyte in the positive electrode layer is 3LiBH ₄ -LiI, and the upper limit charging voltage applied to the positive electrode layer is 1. An all solid state battery is provided that is between 55V and 2.70V.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, the content of this invention is not limited by this.

<Example 1>
(Preparation of complex hydride solid electrolyte)
In a glove box under an argon atmosphere, LiBH ₄ (manufactured by Sigma-Aldrich, purity 90%) was weighed and ground in an agate mortar to obtain a complex hydride solid electrolyte (LiBH ₄ ).

(Preparation of positive electrode layer powder)
Active material Li ₄ Ti ₅ O ₁₂ (manufactured by Toho Titanium Co.): complex hydride solid electrolyte (LiBH ₄ ): carbon black (manufactured by Sigma-Aldrich, purity 99.9%) = 38: 55: 7 (weight ratio) The powder was measured in a glove box and mixed in a mortar to obtain a positive electrode layer powder. The electrode potential (lithium reference) of the active material Li ₄ Ti ₅ O ₁₂ is 1.5V.

(Production of all-solid battery)
The powder of the complex hydride solid electrolyte prepared above was put into a powder tablet molding machine having a diameter of 8 mm, and press-molded into a disk shape at a pressure of 143 MPa (formation of complex hydride solid electrolyte layer). Without removing the molded product, the positive electrode layer powder prepared above was put into a tablet molding machine and integrally molded at a pressure of 285 MPa. In this way, a disk-shaped pellet in which the positive electrode layer (75 μm) and the complex hydride solid electrolyte layer (600 μm) were laminated was obtained. A lithium metal foil (made by Honjo Metal Co., Ltd.) with a thickness of 200 μm and φ8 mm is pasted on the opposite side of the positive electrode layer of this pellet to form a Li negative electrode layer, put into a battery test cell made of SUS304, and an all-solid secondary battery did.

(Charge / discharge test 1)
For the all-solid-state battery produced as described above, a potentiostat / galvanostat (Bio-Logic VMP3) was used under the conditions of a test temperature of 120 ° C., a cutoff voltage of 1.4 to 1.7 V, and a 0.1 C rate. The battery was charged and discharged from a discharge at a constant current to obtain a charge / discharge capacity. In addition, the rest for 3 minutes was provided after charge and discharge, respectively. The open circuit voltage immediately before the start of the second cycle discharge was 1.67V. Moreover, (Capacity of Li ₄ Ti ₅ O ₁₂ ) / (Theoretical capacity of Li ₄ Ti ₅ O ₁₂ = 175) at this time is 96.6%, which is a potential slightly higher than the electrode potential which is a theoretical value. It can be seen that the capacity of lithium titanate can be fully extracted.

(Charge / discharge test 2)
The charge / discharge is performed in the same manner as in the charge / discharge test 1 except that the cut-off voltage at the first cycle is 1.1 to 2.0 V and the cut-off voltage is 1.4 to 1.7 V after the second cycle. The charge / discharge capacity was determined. A large irreversible capacity was generated from the time when the voltage was slightly higher than 1.8 V during charging. This is presumed to be due to LiBH ₄ being decomposed by side reactions. That is, when a voltage of 1.8 V or more is applied to LiBH ₄ on the basis of lithium, a large irreversible capacity is caused due to the decomposition of LiBH ₄ by a side reaction at the beginning of the cycle test, and the solid electrolyte is deteriorated. It is thought to get. If such a solid electrolyte is repeatedly altered by repeating a charge / discharge cycle at a high voltage, it may adversely affect a long-term cycle test. Therefore, in order to stably use the battery having the configuration as in Example 1 over a long period of time, it can be said that it is preferable not to apply a voltage exceeding 1.8 V on the basis of lithium during charging. The open circuit voltages immediately before the start of discharge in the first and second cycles were 1.83 V and 1.67 V, respectively.

<Example 2>
(Preparation of complex hydride solid electrolyte)
In a glove box under an argon atmosphere, LiBH ₄ (manufactured by Sigma-Aldrich, purity 90%) and LiI (manufactured by Sigma-Aldrich, purity 99.999%) are mixed with a mole of LiBH ₄ : LiI = 3: 1. It mixed in the agate mortar so that it might become ratio. Next, the mixed starting materials were charged into a 45 mL SUJ-2 pot, and SUJ-2 balls (φ7 mm, 20 pieces) were further charged to completely seal the pot. This pot was attached to a planetary ball mill (P7 manufactured by Frichche), and mechanical milling was performed at a rotation speed of 400 rpm for 5 hours to obtain a complex hydride solid electrolyte (3LiBH ₄ -LiI).

(Preparation of positive electrode layer powder)
Active material Li ₄ Ti ₅ O ₁₂ (manufactured by Toho Titanium): Complex hydride solid electrolyte (3LiBH ₄ -LiI): Carbon black (manufactured by Sigma-Aldrich, purity 99.9%) = 27: 64: 9 (weight) The powder was weighed in a glove box and mixed in a mortar to obtain a positive electrode layer powder. The electrode potential (lithium reference) of the active material Li ₄ Ti ₅ O ₁₂ is 1.5V.

(Production of all-solid battery)
An all-solid battery was produced in the same manner as in Example 1 except that the solid electrolyte and positive electrode layer powder prepared above were used.

(Charge / discharge test)
Using a potentiostat / galvanostat (Bio-Logic VMP3), the battery was charged and discharged from discharge at a constant current under conditions of a test temperature of 25 ° C., a cut-off voltage of 1.1 to 2.1 V, and a 0.1 C rate. The charge / discharge capacity was determined. In addition, the rest for 3 minutes was provided after charge and discharge, respectively. The open circuit voltage immediately before the start of discharge in the second cycle was 1.76V.

<Comparative Example 1>
(Preparation of positive electrode layer powder)
Cathode active material LiCoO ₂ (manufactured by Nippon Chemical Industry, cell seed C-5H): complex hydride solid electrolyte (LiBH ₄ ): carbon black (manufactured by Sigma-Aldrich, purity 99.9%) = 40:60: 6 (weight ratio) was weighed in a glove box and mixed in a mortar to obtain a positive electrode layer powder. The electrode potential (lithium reference) of the active material LiCoO ₂ is 3.95V.
An all-solid battery was produced in the same manner as in Example 1 except that the above positive electrode layer powder was used. The charge / discharge test was performed in the same manner as in Example 1 except that the test was started from charging and the cut-off voltage was set to 3.2 to 4.2V. During charging, a large irreversible capacity occurred from around 1.8V. The open circuit voltage immediately before the start of discharge in the first cycle was 3.43V.

<Comparative Example 2>
(Preparation of positive electrode layer powder)
Cathode active material LiCoO ₂ (manufactured by Nippon Chemical Industry, cell seed C-5H): complex hydride solid electrolyte (3LiBH ₄ -LiI): carbon black (manufactured by Sigma-Aldrich, purity 99.9%) = 40: The powder made into 60: 6 (weight ratio) was measured in the glove box, and it mixed in the mortar, and was set as the positive electrode layer powder. The electrode potential (lithium reference) of the active material LiCoO ₂ is 3.95V.
An all-solid battery was produced in the same manner as in Example 1 except that the above positive electrode layer powder was used. The charge / discharge test was performed in the same manner as in Example 2 except that the test was started from charging and the cut-off voltage was set to 3.2 to 4.2V. A large irreversible capacity was generated from a voltage near 2.70 V during charging. The open circuit voltage immediately before the start of discharge in the first cycle was 3.86V.

<Comparative Example 3>
(Preparation of positive electrode layer powder)
Positive electrode active material LiFePO ₄ (SLFP-ES01): Complex hydride solid electrolyte (LiBH ₄ ): Carbon black (manufactured by Sigma-Aldrich, purity 99.9%) = 40: 60: 6 (weight ratio) Weighed in a glove box and mixed in a mortar to obtain a positive electrode layer powder. The electrode potential (lithium reference) of the active material LiFePO ₄ is 3.4V.
An all-solid battery was produced in the same manner as in Example 1 except that the above positive electrode layer powder was used. The charge / discharge test was performed in the same manner as in Example 1 except that the test was started from charging and the cut-off voltage was set to 2.5 to 3.8V.

FIG. 2 shows the transition of the charging capacity of the battery manufactured in Example 1, and FIG. 3 shows the transition of the charging capacity of the battery manufactured in Example 2. The charge / discharge curves of Examples 1 and 2 are shown in FIG. 4 (Charge / Discharge Test 1 of Example 1; 1st, 2nd and 20th cycles) and FIG. 5 (Charge / Discharge Test 2 of Example 1; 1st and 2nd cycles, respectively). ) And FIG. 6 (Example 2; 1, 2 and 20th cycles). The charge / discharge curves in the first cycle of Comparative Examples 1 and 2 are shown in FIGS. 7 and 8, respectively. Table 1 below shows battery resistance, coulomb efficiency, and charge capacity in the second and twentieth cycles for the batteries produced in Examples 1-2 and Comparative Examples 1-3. In addition, the charge capacity was calculated as the value per 1 g of the positive electrode active material, based on the charge capacity obtained with the tested battery. The battery resistance was calculated from the IR drop immediately after the start of discharge. Coulomb efficiency was calculated from charge capacity / discharge capacity. “No discharge capacity is obtained” means that the discharge capacity per 1 g of the active material is less than 5 mAh.

About Comparative Examples 1-3, the discharge capacity was not obtained (the discharge capacity per 1g of active material was less than 5 mAh), and it did not function as a battery. In Comparative Examples 1 to 3, the complex hydride solid electrolyte was decomposed by a side reaction because the cathode active material was reduced by the complex hydride solid electrolyte and the cathode active material having a relatively high electrode potential was used. It is thought that it originates in having done.
On the other hand, it can be seen that the all solid state battery of the present invention can avoid a large irreversible capacity at the time of charging, and the battery resistance is hardly increased even when the charge / discharge cycle is repeated, and the discharge capacity is not easily lowered accordingly. Therefore, it can be said that the all solid state battery of the present invention can operate stably over a long period of time. Moreover, it turned out that the all-solid-state battery of this invention also has the advantage that coulomb efficiency does not fall easily even after repeating a charging / discharging cycle. From these results, it can be said that in the present invention, the reduction of lithium titanate by the complex hydride hardly occurs, and the decomposition by the side reaction of the complex hydride solid electrolyte due to the voltage load at the time of charging and discharging can be avoided.

Specifically, when the solid electrolyte mixed in the positive electrode layer is LiBH ₄ , the charge voltage applied to the positive electrode layer is 1.8 V or less (lithium reference), and in the case of 3LiBH ₄ -LiI, the charge applied to the positive electrode layer. It has been found that a large irreversible capacity can be avoided by setting the voltage to 2.70 V or lower (lithium reference).
Furthermore, as described above, according to the present invention, a complex hydride having high lithium ion conductivity can be used as the solid electrolyte without concern about reduction of the positive electrode active material by the complex hydride. Moreover, as a result of forming a good interface between the active material and the solid electrolyte, the interface resistance is lowered, and the lithium ion conductivity of the entire battery can be improved.

  DESCRIPTION OF SYMBOLS 1 ... Positive electrode layer, 2 ... Solid electrolyte layer, 3 ... Negative electrode layer, 10 ... All-solid-state battery.

Claims (5)

A positive electrode layer containing an active material and a complex hydride solid electrolyte, the active material is seen containing a lithium titanate, the complex hydrides solid electrolyte is LiBH _4, of Zenkatsu material contained in the positive electrode layer 90 wt% or more, the positive electrode layer as an active material having an electrode potential of 1.20V~1.80V based on lithium. The lithium _{titanate, LiTi 2 O 4, Li 4} Ti 5 O positive layer according to claim 1, from ₁₂ and _Li 2 the group consisting of _Ti 3 _{O 7} is selected. The lithium _titanate, the cathode layer of claim 2 wherein the Li ₄ Ti _{5 O 12.} Comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer having lithium ion conductivity disposed between the positive electrode layer and the negative electrode layer;
The positive electrode layer, all-solid-state battery is a positive electrode layer according to any one of claims 1-3. The upper limit charge voltage according to the prior SL positive electrode layer is 1.55V~1.80V based on lithium, all-solid-state battery according to claim 4.