JP2003331912A - Lithium ion conductive solid electrolyte composite body, and lithium cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion conductive solid electrolyte composite body with excellent lithium ion movability and forming property, and to provide a totally solid lithium cell using the composite body having low internal impedance and high energy density. <P>SOLUTION: The lithium ion conductive solid electrolyte composite body contains lithium ion conductive inorganic solid electrolyte and polymer. The polymer has lithium ion permeation property with a transference number of not less than 0.7, and the volume percentage of the polymer to the total volume of the lithium ion conductive solid electrolyte composite body is not less than 2 volume % and not more than 20 volume %. The lithium cell uses the composite body. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lithium ion conductive solid electrolyte composite in which a mobile ion species is lithium ion, and a lithium battery using the same.

[0002]

2. Description of the Related Art In recent years, with the development of portable devices such as personal computers and mobile phones, the demand for batteries as a power source thereof has become very large. In particular, a lithium battery is a substance that has a small atomic weight of lithium and a large ionization energy, and thus has been actively researched as a battery that can obtain a high energy density, and is now widely used as a power source for portable devices. Has been. On the other hand, with the generalization of lithium batteries, the increase in internal energy due to the increase in the amount of active material contained and the increase in the content of organic solvent, which is a combustible substance used in the electrolyte, may cause the danger of ignition of the battery. Interest in sex has been highlighted in recent years.

As a method for ensuring the safety of lithium batteries, it is extremely effective to use a solid electrolyte, which is a nonflammable substance, instead of the organic solvent electrolyte, and various lithium ion conductive inorganic solid electrolyte powders are used. The development of all-solid-state lithium batteries with high safety is progressing by applying the. In the development of lithium ion conductive inorganic solid electrolytes, it has been done mainly to increase the lithium ion conductivity in the inorganic solid electrolytes, but when applied to devices such as batteries, high lithium ion conductivity It is important to have excellent workability. By thinning the solid electrolyte layer, not only the internal impedance can be reduced and the output characteristics can be improved, but the volume ratio of the solid electrolyte layer in the battery is reduced, and the energy density of the battery is also improved. . However, when an inorganic solid electrolyte is generally applied to a battery, a polycrystalline powder or an amorphous powder is used by pressure molding, but the resulting molded body is hard and brittle, so it has poor workability and a thin shape. Was difficult to convert.

Therefore, a "polymer insol" (polymer) comprising a high-concentration inorganic salt having a lithium ion conductivity and a rubber-like polymer in order to impart processability thereto.
In recent years, a proposal of a new solid electrolyte named as "insult) type" has been made [C. A. Angel, C.I. Liu, and E. Sanchez, "Nature", No.632
Vol., P. 137 (1993) {C. A. Angell, C. Liu, an
d E. Sanchez, Nature, Vol. 632 (1993) 137}] However, its lithium ion conductivity is not sufficient.

As an alternative to the above, a lithium ion conductive solid electrolyte composite prepared by mixing a non-rubber polymer has been proposed (Taro Inada, Kazunori Takada, Ryohisa Kajiyama, Masaru Takaguchi, Kondo). Shigeo, Watanabe, 26th Annual Meeting of Solid State Ionics Forum, p114). In this method, the lithium ion conductive solid electrolyte composite compounded mainly by dry mixing without using a solvent shows good conductivity. However, when considering mass productivity such as application to all-solid-state lithium batteries, thin film / large-area electrolyte layer can be simply and continuously produced, such as the doctor blade method or screen printing method. It is desirable to adopt the wet method. When a lithium ion conductive solid electrolyte and a polymer are compounded by a wet method, a lithium ion conductive inorganic solid electrolyte is dispersed in a solution obtained by dissolving the polymer in a solvent to prepare a slurry. Since it is done by coating, there are the following concerns. That is, after the solvent is volatilized and removed after coating, the polymer is deposited on the particle surface of the lithium ion conductive inorganic solid electrolyte and coats the particles, so that diffusion of lithium ions in the obtained composite is inhibited. However, there is a problem that ionic conductivity is reduced. It is presumed that this is because the polymer is generally insulating by itself against ionic conduction.

In order to suppress the decrease in ionic conductivity, a liquid macromonomer as a polymer is added to a lithium ion conductive inorganic solid electrolyte, and the liquid is processed in a state in which the surface of the solid electrolyte particles is covered with a film. The method of doing so was invented (Taro Inada, Kazunori Takada, Ryohisa Kajiyama, Hideki Sasaki, Shigeo Kondo, Tsutomu Watanabe, 27th Annual Meeting of the Solid State Ionics Forum, p250). In the present invention, the desired final molded body is produced under pressure, and the high deformability suggested by the solid electrolyte exhibiting a high molding density of more than 90% is utilized to make the liquid a gap between the solid electrolyte particles. To form a domain structure. Thereby, the solid electrolyte particles are sufficiently in contact with each other, and good ionic conduction is obtained, and further, by heating the molded body in a pressurized state, the macromonomer is polymerized into a rubber-like state,
The purpose is to develop binder properties. However, in this case, the binder property of the polymer may not be sufficiently obtained in the final product. In particular, since the electrolyte particles are in contact with each other, for example, the sheet-shaped molded body becomes hard, and thus there is a problem that it is difficult to use it for the uneven portion and the curved portion in the device when applied as a battery. .

An invention that attempts to improve the ion insulating property of a polymer is disclosed in Japanese Patent Application Laid-Open No. 10-3818. According to the above-mentioned publication, a polymer having a structure in which sulfuric anhydride is added to a carbon-carbon double bond contained on a side chain is combined with a lithium ion conductive inorganic solid electrolyte, so that at a contact interface between both materials. Only, it is suggested that ionic conductivity due to the formation of SO ₃ -Li ion pair appears. Therefore, it is estimated that lithium ion conduction may be promoted on the surface of the inorganic solid electrolyte particles. However, based on the above mechanism, when the polymer covers the inorganic solid electrolyte particles, it is impossible for the lithium ions to diffuse inside the polymer matrix to which the inorganic solid electrolyte cannot contact. However, this polymer does not show ion permeability, and a sufficient effect cannot be obtained.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium ion conductive solid electrolyte composite which is rich in lithium ion mobility and excellent in moldability, and finally has a low internal impedance and energy. The object is to provide an all-solid-state lithium battery with high density.

[0009]

SUMMARY OF THE INVENTION The present invention will be summarized as follows. (1) A lithium ion conductive solid electrolyte composite containing a lithium ion conductive inorganic solid electrolyte and a polymer, wherein the polymer exhibits lithium ion permeability, and the lithium ion transport number is 0.7. The lithium ion conductive solid electrolyte composite is at least 2% by volume and at most 20% by volume with respect to the entire solid electrolyte composite. (2) The lithium ion conductive solid electrolyte composite, wherein the polymer contains lithium ions, or the polymer does not contain an inorganic electrolyte salt as an additive. The lithium ion conductive solid electrolyte composite, preferably, the lithium ion conductive inorganic solid electrolyte is a lithium-containing sulfide, wherein the lithium ion conductive solid electrolyte composite. (3) The lithium ion conductive solid electrolyte composite is placed between a pair of positive and negative electrodes made of an active material capable of inserting and extracting lithium ions, and the composite is added to at least one of the positive and negative electrodes. A lithium battery characterized by the following.

As a result of various investigations in view of the above-mentioned state of the art, the present inventors have found that when a specific polymer is adopted as a binder, the surface of particles of the lithium ion conductive inorganic solid electrolyte is coated with the polymer. Even if
The present invention has been accomplished on the basis of the finding that a lithium ion conductive solid electrolyte composite having excellent processability without significantly impairing the excellent ion conductivity of the inorganic solid electrolyte can be obtained.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. The present inventors have conducted various experimental studies to achieve the object of the present invention. As a result, a polymer having a lithium ion transport number of 0.7 or more is added to the lithium ion conductive inorganic solid electrolyte. When 2% by volume or more and 20% by volume or less is added to the whole solid electrolyte composite,
The inventors have found that the object of the present invention can be achieved, and arrived at the present invention. If the addition amount is less than 2% by volume, the lithium ion conductive solid electrolyte composite obtained has insufficient moldability and it is difficult to obtain a thin film-shaped molded product, and if it exceeds 20% by volume, the lithium ion conductivity decreases. It is difficult to achieve the object of the invention.

The process by which the present inventors arrived at the present invention will be described below. That is, the following points are expected as the properties that the polymer used in the lithium ion conductive solid electrolyte composite for the all solid lithium battery should have. First, good binder performance by the polymer, that is, a wet process is adopted to uniformly coat the surface of the electrolyte particles with the polymer.
Therefore, it is necessary that the polymer is soluble in the solvent. Secondly, electrochemical stability up to about 0.5 to 5 V is required for practical lithium batteries. Thirdly, it is necessary that the polymer has ion permeability and has high lithium ion selectivity in its ion conduction. The above points will be described below.

Regarding the solubility of the polymer in a solvent, a dissolution test can be conducted in any solvent. That is, it is possible to visually judge the state in which a uniform solution is obtained.
On the other hand, as a case where the polymer does not dissolve, a state in which the polymer is separated in the solvent or a state in which the polymer is swollen is observed, so that it can be easily determined. Electrochemical stability is also called the potential window.
The electrochemical stability can be evaluated by, for example, cyclic voltammetry by assembling a cell in which a composite molded body of a lithium ion conductive inorganic solid electrolyte and a polymer is sandwiched between stainless steel and lithium foil.

The ion permeability of the polymer can be judged by examining the ionic conductivity of a sample obtained by forming the polymer into a film by a casting method or the like. The ionic conductivity can be evaluated by measuring the electric conductivity by the AC impedance method or the like and confirming that the electron conduction does not appear by the DC polarization method.

It has previously been stated that polymers by themselves are generally insulating against ionic conduction. A group of substances known as ion-conducting polymers is known, but ion permeability is narrower than ion conductivity. JP-A-10-381 mentioned above.
The polymer disclosed in Japanese Patent No. 8 has ion conductivity limited to the contact interface with the inorganic solid electrolyte, and has ion conductivity only at the interface. However, this polymer is not ion-permeable because ions do not flow inside the polymer membrane that is not in contact with the inorganic solid electrolyte.

On the other hand, the polymer can be made ion-permeable by adding a specific auxiliary agent to the polymer which is not ion-permeable. That is, it is possible to obtain high lithium ion conductivity by adding a lithium salt that dissociates and mixes uniformly in a matrix of the polymer to a polymer having a specific structure such as polyethers. Known and widely studied [eg A. Nishimoto, M.A. Watanabe, Y. Ikeda and S.I. Kojiya, "Electro Shimica Actor", Volume 43, Volume 1
Page 17 (1998) {A. Nishimoto, M. Watanabe, Y. I
keda, and S. Kohjiya, Electrochim. Acta, 43, (199
8) 117.} etc.].

The lithium salt is also called a supporting electrolyte.
[Hashimoto, latest technology of new secondary battery materials, supervised by Kumi,
-MC (1997), page 152], for example,
Nion is ClO_Four ^-, BF_Four ^-, PF₆ ^-, AsF₆ ^-, SbF₆ ^-, CF₃SO₃ ^-,
(CF₃SO₂) N^-, Or (C₂F_FiveSO₂) N ^-And lithium cation
It does not show ionic conduction by itself, but it is a polymer
When a complex polymer film is formed by being compatible with
Generated lithium ions inside the polymer film, and
Since the molecular membrane serves as a pathway for ion transport,
The child membrane shows ion permeability.

The lithium salt is an inorganic lithium compound, but it is clearly distinguished from the lithium ion conductive inorganic solid electrolyte used in the present invention. That is, as described above, the former does not show ionic conductivity in a single state without ionic dissociation, whereas the latter shows ionic conductivity alone. This is because the latter simultaneously has a lithium ion and a matrix through which the lithium ion flows, and so to speak to ion conduction, it has the functions of both the lithium salt and the polymer membrane in the former complex of lithium salt and polymer. It is estimated that

The ion-permeable polymer requires the presence of lithium ions inside the polymer, and as one method therefor, a method of dissociating a lithium salt into the polymer has been described.
However, in such a system, in addition to the lithium ions, the counter anions derived from the lithium salt as described above may move in the matrix of the polymer, and in this case, the substantial lithium ion transport number may be increased. Will fall.

On the other hand, in the lithium ion conductive inorganic solid electrolyte, only lithium ions can be selectively conducted. Such a conductive property is generally called a single ion conductivity, and the expression that the lithium ion transport number is 1 is used. Therefore, the polymer used in the present invention is required to have not only high ionic conductivity but also high lithium ion transport number. Generally, for ionic conductivity, an alternating current is applied to measure the impedance,
Calculate from that value. Therefore, even if the ionic conductivity shows a high value, if ions other than lithium, especially anions, are mixed in the species responsible for the ionic conductivity, the battery reaction is a direct current reaction, causing polarization and increasing internal resistance. Can be. That is, when charging the battery,
Lithium ions move from the electrolyte particles on the positive electrode side to the electrolyte particles adjacent to the negative electrode side via the binder made of a polymer. At this time, if the lithium ion transport number of the binder is low, the anions move in the direction of the positive electrode and the binder matrix is polarized. As a result, resistance is increased because the ion insulating layer is formed in the binder matrix. It is feared that the influence of such polarization on the battery reaction will be more remarkable as the charge / discharge speed of the battery is higher. If a polymer having a low lithium-ion transport number is used, not only polarization may occur in the binder matrix for the above-mentioned reason, but also the presence of anionic species may induce side reactions, which both reduce the charge / discharge performance of the battery. I'm afraid to let it happen.

As a means for improving the lithium ion transport number of the polymer, suppressing the movement of anion species is the most effective means. If it is evenly distributed in the polymer matrix, the lithium ion flowing from the positive electrode side proceeds in the direct current cell reaction without delay by using the vicinity of the anion as a conduction path.

Specific methods for suppressing the movement of anions include a method of chemically capturing the anions with an additive,
A method of introducing an anion site on the polymer chain can be mentioned. Regarding the former, for example, M.K. A. Mesa, T. Fujinami, S. Inouye, K. Matsushita, T.M. Miwa, and T.W. Inoue, "Electro Shimica Actor", No. 45
Volume, 1175 (2000) [MA Metha, T. Fujina
mi, S. Inoue, K. Matsushita, T. Miwa, and T. Inou
e, Electrochim. Acta, 45 (2000) 1175] and the like are known. Regarding the latter, a method of obtaining a polymer from a lithium compound as a raw material [eg T. Fujinami, K. Sugie,
K. Mori and M.M. A. Mesa, "Chemistry Letters," page 619 (1998), W.M. Sue, M. D. Williams, and C.I. A Angel, "Chemistry
Of Materials, Vol. 14, p. 401 (200
2), M.M. Watanabe, Y. Suzuki, and A. Nishimoto,
"Electro Shimica Actor", Vol. 45, No. 1187
Page (2000) {T. Fujinami, K. Sugie, K. Mori, and
MA Metha, Chem. Lett., (1998) 619., W. Xu, M.
D. Williams, and CA Angell, Chem. Mater., 14 (2
002) 401., M. Watanabe, Y. Suzuki, and A. Nishimot
O, Electrochim. Acta, 45 (2000) 1187} etc.]. Methods for reductive lithiation of polymers [eg Sugai, Matsumi, Ohno, Proc. 50th Symposium on Polymers, 50 (12) (2001) 299
1. etc.) are known. For the latter, not only those having an anion site in the molecule with lithium as a counter cation, but also those having an ionic polarization in the molecular structure (for example, mesoionic structure) may be used.

When a polymer is added to a lithium ion conductive inorganic solid electrolyte to obtain a solid electrolyte composite, even if the surface of the inorganic solid electrolyte particles is coated with the polymer, the lithium transport selectivity of the polymer is high. Therefore, good charge / discharge characteristics can be obtained in the battery using the solid electrolyte composite obtained by adding the lithium ion conductive inorganic solid electrolyte.

The polymer used in the present invention is not limited to those exemplified above. Polymers exhibiting high lithium-ion transport selectivity are a field that has been vigorously researched in recent years, and how to improve the lithium-ion transport number of ion-conducting polymers, and further improve the ion conductivity. The focus of the research is on the issue of "Uruka". Further, various proposals regarding the molecular design have been reported [eg, J. F. Snyder, M.A. A. Ratner, and D.L.
F. Shriver, "Journal of Electrochemical Society", Volume 148, A858 (20)
01), (J. F. Snyder, MA Ratner, and DF S
hriver, J. Electrochem. Soc., 148 (2001) A858} etc.].

As the polymer used in the present invention, a solvent used in a wet process, that is, a solvent that dissolves or disperses a high lithium ion transport number polymer, does not deteriorate the solid electrolyte, and the polymer is the above-mentioned polymer. Any of those which meet the electrochemical stability described as the second condition can be used as the additive for the binder of the inorganic solid electrolyte. The polymer used in the present invention may be used alone or in combination as long as it has a high lithium ion transport number, and further, a polymer such as polyethylene oxide or poly (propylene oxide-ethylene oxide) may be used. You may add and use an ether polymer. By adding these, the strength of the high lithium ion transport number polymer is increased, and in particular, when the polymer is an oil, it is possible to prevent the polymer from bleeding out of the molded body of the composite solid electrolyte. Also plays the role of doing.

As the solvent which hardly deteriorates the inorganic solid electrolyte, a non-polar aprotic solvent represented by a hydrocarbon solvent such as hexane, heptane, octane, nonane, decane, decalin, toluene and xylene is most preferable.
They can also be used for the sulfide-based lithium ion conductor, which is the most unstable inorganic solid electrolyte. However, even in that case, the water content of the solvent is reduced to 10 ppm or less, preferably 1 ppm or less by a known method [for example, Organic Chemistry Experiment Guide 1, Chapter 5 (Chemical Doujinshi)], and the slurry preparation and coating operation are performed. It is desirable to use an environment in which the water content is controlled, such as an argon substitution glove box.

In general, a polymer having a high lithium ion transport number is not soluble in a non-polar solvent. Therefore, when these solvents are used, the polymer is homogeneously dispersed in an emulsion state. Then, it may be mixed with the inorganic solid electrolyte. The protic solvent is not preferable because it decomposes when a sulfide-based inorganic solid electrolyte is used. Further, in the case of an aprotic solvent or a polar solvent,
Although the polymer with a high lithium-ion transport number can be dissolved well, it has a great advantage in the composite manufacturing process.
For example, dimethyl sulfoxide or the like is not preferable because it may react with the sulfide-based inorganic solid electrolyte and decompose the inorganic solid electrolyte. If it is acetone or acetonitrile, decomposition of the sulfide-based inorganic solid electrolyte is small and it can be used.

Further, when selecting a highly viscous oily substance among the high ionic transport number polymers, after performing a dry mixing with the inorganic solid electrolyte, a molding process is performed with the aprotic nonpolar solvent. Is also possible and preferred. Further, in consideration of a practical manufacturing process, JP-A-6-2
Reference may be made to known techniques for obtaining a desired atmosphere, such as JP-A-79050, JP-A-6-279049, and JP-A-8-167425.

The present inventors have further obtained the lithium ion conductive solid electrolyte composite and arranged it between a pair of positive and negative electrodes made of an active material capable of inserting and extracting lithium ions, and further, the composite. It was found that a lithium battery having excellent charge-discharge characteristics can be obtained by adding at least one of the positive and negative electrodes to the present invention.

The lithium battery of the present invention will be described below, including the manufacturing method thereof. In the following description, the polymer represented by the chemical formula (I) will be exemplified, but it goes without saying that the present invention is not limited thereto.

[0031]

[Chemical 1]

In the present invention, a polymer having a high lithium ion transport number as described above is added to a lithium ion conductive inorganic solid electrolyte and processed into a lithium ion conductive solid electrolyte composite (hereinafter referred to as a composite electrolyte sheet). Then, by examining the processability, by charging and discharging the battery obtained by providing electrodes on both main surfaces of the composite electrolyte sheet, the composite solid electrolyte of the present invention, it is possible to bring out excellent battery characteristics. I found it.

First, the production of the composite electrolyte sheet will be described. 1 to 1 lithium ion conductive inorganic solid electrolyte
Grind to 5 μm. Examples of the inorganic solid electrolyte,
There are various types such as oxide type and sulfide type. Of these, the sulfide-based inorganic solid electrolyte has a higher conductivity than that of an oxide-based solid electrolyte, and is therefore preferable in designing a practical battery. Examples of the sulfide-based lithium ion conductive inorganic solid electrolyte include sulfide glass and sulfide crystals. As an example of sulfide glass, 0.01
_{Li 3 PO 4 · 0.63Li 2 S} · 0.36SiS 2 [N.
Aothani, K.K. Iwamoto, K. Takada, and S.I. Kondo, "Solid State Ionics", Volume 68,
Page 35 (1994), {N. Aotani, K. Iwamoto, K.
Takada, and S. Kondo, Solid State Ionics, 68, (199
4) 35.}], 0.45LiI · 0.55 (0.69Li
₂ S ・ 0.31P ₂ S ₅ ) [R. Mercia, J. P. Margani, B.I. Phase, and G. Robert, "Solid
State Ionics ", Vol. 5, p. 663 (198)
1), {R. Mercier, JP Malugani, B. Fahys, and
G. Robert, Solid State Ionics, 5, (1981) 663.
}], Or 0.45LiI · 0.55 (0.69Li ₂
S · 0.31B ₂ S ₃₎ [H. Wada, M.A. Menetria,
L. Levasol, and P. Hagend Müller, "Material Research Bulletin", Volume 18, 18
Page 9 (1983) {H. Wada, M. Menetrier, A. Levass
eur, and P. Hagentmuller, Mat. Res. Bull, 18 (198
3) 189.}] and the like. As the sulfide crystal, lithium germanium thio-phosphate having a composition such as Li _3.25 Ge _0.25 P _0.75 S ₄ (Masayama Murayama, Ryuji Sugano, Yoji Kawamoto, Takashi Kamiyama, IEICE 68th).
The conference proceedings abstracts, p183), etc. These are particularly preferable in practical use because they have a particularly high ionic conductivity and have a wide electrochemically stable potential region. These lithium ion conductive inorganic solid electrolytes may be used alone or in combination.

Examples of the method for pulverizing the electrolyte include a vibration mill and a planetary ball mill. In the present invention, the particle size was visually observed by SEM observation, but it can be evaluated by a method of classifying with an electroform sieve or a mesh sieve, or an optical method such as laser scattering.

Next, the polymer is dissolved in a solvent to obtain a solution. The pulverized inorganic solid electrolyte is added to this solution to prepare a slurry. A sheet can be obtained by applying the obtained slurry. Examples of the coating method include a screen printing method, a doctor blade method, a spraying method and a dipping method. Among them, the screen printing method is most preferable because it is possible to uniformly produce a thin sheet having a thickness of 10 to 20 μm. The reason for this thickness is that the above-mentioned thickness is rational when it is assumed to replace the conventional liquid battery separator, and when the thickness increases, the proportion of the electrolyte layer in the battery increases, and the energy density of the battery decreases. Because. However, the all-solid-state battery does not require the safety circuit required for the liquid-type battery, so that the filling amount of the electrode material can be increased correspondingly. Therefore, the thickness is not necessarily limited to the above thickness. Further, the reason for uniforming is to avoid an internal short circuit due to penetration of electrolyte particles in a thin sheet. In this coating process, the material to be coated is an electrode sheet or a core material.

The electrode to be coated may be either a positive electrode, a negative electrode, or both. Examples of the material for the positive electrode include oxides such as lithium cobalt oxide, lithium nickel oxide, and lithium manganate, or those obtained by partially replacing the transition metal with other metals, or layered sulfides such as titanium sulfide. Examples include a mixture of a lithium ion conductive inorganic solid electrolyte. Examples of the negative electrode include indium, gallium, lithium or an alloy thereof, a graphite film formed on a negative electrode current collector, or carbon powder or the alloy powder mixed with a lithium ion conductive inorganic solid electrolyte. .

The core material described later is used to improve the mechanical properties of the molded body, and an electrically insulating structure can also be used. As an electrically insulating structure,
For example, a polymer mesh can be used. Examples of the polymer mesh include those woven from polyester or polyarylate. By coating the polymer mesh with the slurry, a molded body made of a lithium ion conductive solid electrolyte composite having excellent mechanical strength and the like can be obtained.

Next, the workability of the sheet will be described. When coating by the screen printing method as described above, the mesh passability is the first criterion. Further, assuming that the battery is assembled, the second criterion is to endure the transfer to the next step and to endure the operation in the next step. Here, examples of the next step include a process of coating another slurry on the obtained composite electrolyte sheet, or a process of laminating the above-mentioned sheet and another electrode sheet which is separately prepared. Further, a process of cutting the sheet as required is also envisioned. As described above, the workability is diverse, and the process generally differs depending on the actual battery form. Therefore, in the present invention, typically, a process of obtaining an electrolyte sheet without a core material by a screen printing method is assumed, and the workability is evaluated by the screen passing property which is the first criterion.

In general, the inorganic solid electrolyte powder has a large difference in specific gravity from the slurry solvent and tends to exist as a sedimentary additive rather than uniformly dispersing and acting as a structural viscosity agent.
Therefore, when a slurry is prepared using an organic solvent, it is difficult to obtain a homogeneous slurry by simply dispersing the inorganic solid electrolyte. Such a slurry generally has poor mesh permeability and cannot be applied. By adding the polymer, the viscosity of the solution can be increased and a homogeneous slurry can be obtained. When the high molecular weight to be added is small, the effect of increasing the solution viscosity is weakened and the coating becomes difficult. As measures against this, methods such as (1) increasing the mesh opening, (2) using a polymer having a high molecular weight, and (3) using a solvent having a high viscosity can be considered. However, with the measure (1), it is difficult to obtain a coating film having a uniform thickness, and with the measure (2), the solubility of the polymer in the solvent decreases and the amount of the solvent increases, so that the solution viscosity does not increase. Further, in the measure (3), if the high viscosity oily liquid is used to prepare the slurry, it is difficult to remove the liquid. Therefore, in order to improve the mesh passability of the slurry, it is considered that there is a lower limit of the amount of polymer added. Based on the results of studies by the present inventors, the lower limit addition amount was 2% by volume with respect to the entire composite electrolyte. If the high molecular weight is lower than this, coating is extremely difficult.

On the other hand, if the amount of polymer added is increased,
Although the above-mentioned workability is remarkably increased, it is difficult to obtain a suitable coating film if it is too much. Therefore, for coating, there is an appropriate polymer addition amount range with a certain upper limit. However, in reality, the upper limit of the amount of the polymer added is determined by the ionic conductivity of the composite rather than the coating performance. Based on the experimental results of the present inventors, when the polymer volume ratio in the composite exceeds 20%, the ionic conductivity of the composite at room temperature is lower than 10 ⁻⁴ S / cm, which is sufficient for the battery. It doesn't work.

Next, the relationship between the battery characteristics and the lithium ion transport number of the polymer will be described. As described above, it is considered that the high and low transport numbers of the polymer greatly appear in the DC characteristics such as charge and discharge. The charge and discharge characteristics are also affected by the conductivity of the electrolyte when the charge and discharge rate is fast, but in the charge and discharge rate region where this does not appear, the effect of the transport number is affected even if polymers with different conductivity are used. It is possible to argue. The method of measuring the transport number is described in, for example, the literature [K. M. Abraham, Z. Iang, and B. Carroll, "Chemistry of Materials," Volume 9, 1978 (199
7) {KM Abraham, Z. Jiang, and B. Carroll, Che
m. Mater., 9, 1978 (1997)}].

As an embodiment, a low molecular weight Li salt is made compatible with a polymer in a solvent to prepare a uniform solution, and an inorganic solid electrolyte is added to this to prepare a composite solid electrolyte powder having different transport numbers. Obtain a slurry. At this time, in order to improve the compatibility of the Li salt, a polymer and a polyether such as polyethylene oxide or poly (propylene oxide-ethylene oxide) may be added. Addition of polyether does not change the transport number. The solvent is distilled off from the obtained composite to form a molded body, and a positive electrode, a negative electrode, and a current collector are provided on both surfaces of the molded body to prepare a battery. Charge and discharge the battery,
The characteristics were evaluated by comparing the capacities. In addition, in order to investigate the effectiveness of the ion-permeable polymer, a composite using ion-insulating silicone was prepared and the charge-discharge characteristics were investigated.

The lithium battery of the present invention contains a lithium ion conductive solid electrolyte composite having excellent lithium ion mobility and excellent workability as a constituent element.
It has excellent charge-discharge characteristics and a high capacity retention rate.

[0044]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to these examples.

Examples 1 to 5 and Comparative Examples 1 to 3 In an argon-substituted glove box, the polymer represented by the above chemical formula (I) having the composition shown in Table 1 was placed in an evaporation dish, and dehydrated acetone was added. To obtain a solution. In addition, the polymer is described in the literature [T. Fujinami, K. Sugie, K.K. Mori, and M.M. A. Mesa, "Chemistry Letters", page 619 (1998)]. That is, magnetic stirring was performed under an argon stream having a purity of 99.998% or more, a dropping funnel and a Liebig cooling tube were provided.
3-neck round bottom flask polyethylene grease monomethyl ether _CH 3 in _{(OCH 2 CH 2) n OH} ( number average molecular weight of about 350, the value of n which is calculated from the molecular weight of about 7.
4.2 g (12 mmol) of 2) was added, and the mixture was cooled to -78 ° C with a dry ice / methanol bath. A lithium aluminum hydride / THF solution (containing 6 mmol of lithium aluminum hydride) is dropped from the dropping funnel over 10 minutes. After the dropping, the mixture was stirred at room temperature for 1 hour and then at -78 ° C.
Then, a THF solution of 732 mg (6 mmol) of phenylboric acid is added dropwise over 10 minutes. Stir at room temperature for 1 hour and then at 70 ° C. for 12 hours. The solvent is distilled off under reduced pressure to obtain a viscous oily substance. In the polymer acetone solution,
Reference [N. Aothani, K.K. Iwamoto, K. Takada, and S.I. Kondo "Solid State Ionics", Vol. 68, No. 35 pp (1994)] synthesized in accordance with, 5 to 10 [mu] m to sulfide glass _{0.01Li 3 PO 4 · 0.63Li 2 S} · was ground by a vibration mill 0.36Si
The S ₂ was charged to obtain an electrolyte composite slurry.

The density of the polymer used for calculating the volume fraction is 1.36 g / cm ³ , and the density of the sulfide glass is 1.84 g.
/ Cm ³ . The density was measured by using a Shibata Scientific Hubbard pycnometer for the polymer and decalin as the additive liquid for weighing. For sulfide glass, Shimadzu dry type automatic densimeter Accupic 1330 was used.

30 m of the obtained electrolyte composite slurry was added.
The indium foil was coated using a 200-mesh stainless screen equipped with an m × 30 mm mask. As a result, when the amount of the polymer added is less than 2% of the total amount of the composite electrolyte, the slurry does not pass through the screen mesh even if the printing pressure and the printing speed are changed, and coating cannot be performed.

Further, after the solvent was distilled off from the composite slurry under reduced pressure, the composite powder obtained was put into a mold of 10φ and pressurized at 125 MPa, and the obtained molded body was not released from the mold. A LiTiS ₂ layer was provided as an electrode material on both main surfaces, and the electrical conductivity of the molded body pressed at 500 MPa was measured by the AC impedance method. At this time, it was confirmed by conducting another direct current polarization measurement that the composite did not show electronic conductivity, and it was found that the electric conductivity in the previous period shows ionic conductivity. As a result, when the polymer volume ratio in the composite exceeds 20%, the ionic conductivity of the composite at room temperature falls below 10 ⁻⁴ S / cm.

[0049]

[Table 1]

Examples 6 to 7 and Comparative Example 4 An acetone solution of the above polymer was prepared in an argon displacement glove box, and trifluoromethanesulfonic acid lithium salt (LiTrf) having the composition shown in Table 2 was placed in an evaporation dish. , Add dehydrated acetone and stir. The resulting solution had a composition of 0.01Li ₃ PO ₄ .0.63Li ₂ S
Add 0.36SiS ₂ sulfide glass to obtain a composite solid electrolyte slurry. After removing the solvent by evaporation,
The obtained powder is 125 MPa using a 10 mmφ mold.
Press molding with. Without releasing the obtained pellet,
The positive electrode material powder and the negative electrode material powder are respectively charged on both main surfaces, and pressure molding is further performed at 500 MPa. Lithium cobalt oxide was used for the positive electrode, and indium foil was used for the negative electrode.
In addition, Example 6 has the same composition as the composite body of Example 3.

After joining the terminals to both electrodes, the upper limit voltage is set to 3.5 V and 1/100 CμA (14 μA / cm
After charging in ² ), set the lower limit voltage to 1.5V and 1 /
The discharge was performed at 10 CμA (140 μA / cm ² ). As a result, as shown in Table 2, the lithium ion transport number was 0.
When it was 6 or less, the capacity retention ratio was lowered, and when the discharge capacity was 100 when the transport number was 1, it was lowered to 91.

Comparative Example 5 In order to show the effectiveness of the composite of the present invention containing an ion-permeable polymer, a composite using silicone which is an ion-insulating polymer was prepared and ion-permeable polymer was prepared. The comparison was made with a composite using a hydrophilic polymer. As the silicone, an addition polymerization type liquid silicone rubber CY52-005 (Toray Dow Corning Silicone) was used. The preparation of the complex was based on: That is, the composition is 0.01 Li ₃ PO ₄ .0.63 Li
₂ S · 0.36 SiS ₂ sulfide glass was added with dehydrated acetone and stirred, and then acetone was distilled off under reduced pressure. Next, the liquid silicone rubber is put into an evaporation dish, and the sulfide glass is put into a solution to which dehydrated heptane is added to prepare an electrolyte composite slurry. The solvent was distilled off from the obtained electrolyte composite slurry under reduced pressure, a battery was prepared in the same manner as in Example 6, and heated to 150 ° C. to cure the silicone. As a result of examining the charge / discharge characteristics of the battery gradually cooled to room temperature under the same conditions as in Example 6, as shown in Table 2, the capacity retention rate is remarkably smaller than that in Example 6.

[0053]

[Table 2]

[0054]

EFFECT OF THE INVENTION The lithium ion conductive inorganic solid electrolyte composite of the present invention is a lithium ion conductive inorganic solid having a lithium ion permeability and a specific polymer having a lithium ion transport number of 0.7 or more. It has a composition in which a specific amount is mixed with the electrolyte, and as a result, it has excellent workability, can easily achieve a thin film, and has excellent ionic conductivity. It can be applied to various high-reliability electrochemical devices including the first and is extremely useful industrially. Further, since the lithium battery of the present invention uses the lithium ion conductive inorganic solid electrolyte composite, it has the property of maintaining a high capacity retention rate, reflecting the above characteristics, and is extremely industrially It is useful.

   ─────────────────────────────────────────────────── ─── Continued front page    (71) Applicant 000003296             Denki Kagaku Kogyo Co., Ltd.             1-4-1 Yurakucho, Chiyoda-ku, Tokyo (72) Inventor Taro Inada             3-5-1, Asahi-cho, Machida-shi, Tokyo Electrification             Gakkou Central Research Institute (72) Inventor Kazunori Takada             1-2-1 Sengen, Tsukuba-shi, Ibaraki Independent             National Institute for Materials Science (72) Inventor Shigeo Kondo             1-2-1 Sengen, Tsukuba-shi, Ibaraki Independent             National Institute for Materials Science (72) Inventor Watanabe             1-2-1 Sengen, Tsukuba-shi, Ibaraki Independent             National Institute for Materials Science (72) Inventor Takayoshi Sasaki             1-2-1 Sengen, Tsukuba-shi, Ibaraki Independent             National Institute for Materials Science (72) Inventor Tatsuo Fujinami             1-2-1 Sengen, Tsukuba-shi, Ibaraki Independent             National Institute for Materials Science (72) Inventor Ryuji Kanno             1-2-1 Sengen, Tsukuba-shi, Ibaraki Independent             National Institute for Materials Science (72) Inventor Ryohisa Kajiyama             1-1-1 Shinoki, Onoda City, Yamaguchi Prefecture             Industry Co., Ltd. Creative Headquarters (72) Inventor Hideki Sasaki             Kyoto Prefecture Kyoto City Minami-ku Kichijoin Nishinosho Inono Babacho             No. 1 Research & Development Division, Nippon Battery Co., Ltd. F-term (reference) 5G301 CA30 CD01                 5H029 AJ03 AJ06 AJ14 AK03 AL11                       AM12 AM16 CJ06 CJ08 DJ09                       DJ16 EJ06 EJ12 HJ00

Claims (5)

[Claims] 1. A lithium ion conductive solid electrolyte composite comprising a lithium ion conductive inorganic solid electrolyte and a polymer, wherein the polymer exhibits lithium ion permeability and has a lithium ion transport number of 0. 0.7 or more, and the proportion of the polymer added is 2% by volume or more and 20% by volume or less with respect to the entire lithium ion conductive solid electrolyte complex. body. 2. The lithium ion conductive solid electrolyte composite according to claim 1, wherein the polymer contains lithium ions. 3. The lithium ion conductive solid electrolyte composite according to claim 1, wherein the polymer does not contain an inorganic electrolyte salt as an additive. 4. The lithium-ion conductive inorganic solid electrolyte is a lithium-containing sulfide.
4. The lithium ion conductive solid electrolyte composite according to any one of 3 above. 5. The lithium ion conductive solid electrolyte composite according to claim 1, is placed between a pair of positive and negative electrodes made of an active material capable of inserting and extracting lithium ions, and A lithium battery, wherein a composite is added to at least one of the positive and negative electrodes.