JP2000200621A - All-solid-state secondary battery and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the density and extend the life of an inorganic solid electrolyte, to improve the reliability against failure and ignition, and to make it simple without forming a thin film of the inorganic solid electrolyte on a positive electrode active material. Can be formed. SOLUTION: An all-solid-state secondary battery 1 including a positive electrode 2 made of a positive electrode active material, a negative electrode 3 made of a negative electrode active material, and an inorganic solid electrolyte 4 interposed between the positive electrode 2 and the negative electrode 3 has an inorganic solid state. The electrolyte 4 is obtained by sintering a powder of the constituent material of the inorganic solid electrolyte 4 by applying a DC pulse current under pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an all-solid-state secondary battery using a solid electrolyte as an electrolyte as well as a positive electrode and a negative electrode, and a method of manufacturing the same. More specifically, the present invention provides:
The present invention relates to an inorganic solid electrolyte of an all-solid-state secondary battery using an inorganic solid electrolyte as a solid electrolyte, and to its bonding to an electrode member.

[0002]

2. Description of the Related Art Secondary batteries used for power storage and power supply of mobile equipment are used for a long time (high energy density) by one charge, and increase in the number of rechargeable charging / discharging (long life). ) And high reliability against failure and ignition. A conventional secondary battery often uses a liquid as an electrolyte, and thus has an outer tank for preventing liquid leakage and a separator for preventing an internal short circuit between positive and negative electrodes.

However, in a secondary battery using an electrolytic solution,
Since it is necessary to uniformly retain the electrolyte between the positive and negative electrodes so that the electrolyte can be used without bias, the shape of the secondary battery is limited. In order to increase the energy density, it is indispensable to reduce the ratio of the outer tank to the weight and volume of the battery, but this is not easy in relation to the liquid retention. Furthermore, it has been pointed out that decomposition of the electrolyte solution contributes to a decrease in the number of charge / discharge cycles. 66, No. 3 (1998), p.
314-320). In order to extend the life of the secondary battery, it is necessary to suppress the reaction between the electrolytic solution and each electrode.

As described above, there are various inconveniences in using an electrolyte for a secondary battery. Therefore, as an alternative to a secondary battery using an electrolyte, a solid polymer or inorganic material such as an electrolyte is used as an electrolyte. An all-solid-state secondary battery using a solid has been developed. At present, as an all-solid-state secondary battery aiming at upsizing, a battery mainly using a polymer solid electrolyte is being studied. However, the solid polymer electrolyte is 60-80 ° C.
Therefore, when heated by use of a secondary battery, there is a possibility that the solid polymer electrolyte is crushed by the external pressure and the positive and negative electrodes are short-circuited. Further, if the secondary battery is heated to a temperature higher than the melting point of the solid polymer electrolyte, the battery is easily deformed or the like, thereby lowering reliability. Therefore, a system for preventing heating and maintaining reliability is required.

On the other hand, an all-solid-state secondary battery using an inorganic material as an electrolyte can be expected to have high reliability against failure and ignition due to the fact that the electrolyte is nonflammable. Among them, LiTi ₂ (PO ₄ ) _{3, which} is abbreviated as LTP, is promising as an inorganic solid electrolyte. However, for example, in a normal sintering method in which pressure is applied while simply heating such as a solid phase reaction method, There is a problem that the density is low and the conductivity is insufficient as an electrolyte of the all-solid-state secondary battery. Therefore, as this conventional all-solid-state secondary battery, there is an all-solid-state secondary battery formed by joining an inorganic solid electrolyte to a positive electrode by forming a thin film by vacuum deposition or the like.

[0006]

However, in the above-mentioned all-solid-state secondary battery, since the inorganic solid electrolyte is formed into a thin film on the positive electrode by vacuum deposition or the like, it is difficult to increase the area of the secondary battery. In addition, the yield is poor due to the occurrence of pinholes and the like, and the manufacturing cost is increased. For this reason, so-called on-board type thin film batteries (for example,
K. Kanehoriet al. , Solid St
ate Ionics, vol. 9/10 (198
3), p. 1445), it is difficult to apply to secondary batteries, and applications are limited.

Therefore, the present invention aims to increase the density and extend the life of the inorganic solid electrolyte, improve the reliability against failure and ignition, and to simplify the inorganic solid electrolyte without forming a thin film on the polar active material. It is an object of the present invention to provide an all-solid-state secondary battery that can be formed in a battery and a method for manufacturing the same.

[0008]

As a result of repeated studies by the present inventor to achieve such an object, LiTi is regarded as a promising inorganic solid electrolyte for an all-solid-state lithium secondary battery.
It has been found that by conducting discharge pulse sintering of the powder of ₂ (PO ₄ ) ₃ under pressure to produce a sintered body, it is possible to obtain conductivity suitable as an inorganic solid electrolyte as shown in FIGS. 9 and 10. did. Thereby, a conductive inorganic solid electrolyte such as LiT which can be used as an electrolyte of an all-solid-state secondary battery
It has become possible to obtain a sintered body of i ₂ (PO ₄ ) ₃ .

Therefore, the present invention provides an all-solid-state secondary battery including a positive electrode made of an active material, a negative electrode made of an active material, and an inorganic solid electrolyte interposed between the positive electrode and the negative electrode. The solid electrolyte is made by sintering a powder of the constituent material by applying a DC pulse current under pressure.

Therefore, since the powder is sintered under pressure during the production of the inorganic solid electrolyte, Joule heat, which is self-heating of the green compact due to the pressure, can be directly used for sintering. The thermal efficiency can be improved as compared with other sintering methods using induction heating or radiant heating. In addition, since the plastic deformation force is generated by the pressurization, the joining between the powders is facilitated.

Further, since a pulsed voltage and a current are applied while applying pressure, a discharge phenomenon can be caused in a gap between powder particles, and sintering and joining are promoted by a local high temperature accompanying the discharge. Can be. In addition, a discharge activating action occurs on the particle surface due to discharge plasma or discharge impact pressure. In addition, an electrolytic diffusion effect in the electric field also occurs. For these reasons, it is possible to produce a dense body by forming a neck between particles, so that a desired joined body can be produced at a lower temperature and in a shorter time than other sintering methods using an electric furnace or the like. become.

For this reason, the powder is sufficiently heated and sintered even without externally heating as compared with the solid-state reaction method to produce the inorganic solid electrolyte, so that the production time can be reduced to a short time. . In addition, since the inorganic solid electrolyte is made of a sintered body, it is easy to increase the area of the secondary battery, and it is possible to eliminate poor yield due to the occurrence of pinholes and the like, and the degree of freedom in shape becomes relatively large. It can be applied to various secondary batteries. Furthermore, since the density of the inorganic solid electrolyte after fabrication can be increased, the conductivity and strength can be improved.

According to a second aspect of the present invention, there is provided an all-solid-state secondary battery including a positive electrode made of an active material, a negative electrode made of the active material, and an inorganic solid electrolyte interposed between the positive electrode and the negative electrode. Or at least one of the negative electrode and the inorganic solid electrolyte, the active material powder and the inorganic solid electrolyte powder forming the pole are laminated, and a DC pulse current is applied to the laminated powder under pressure. It is sintered.

Therefore, since at least one of the positive electrode and the negative electrode is joined to the inorganic solid electrolyte by sintering, the conductivity and the joining strength between the two can be improved.

According to a third aspect of the present invention, there is provided a method for manufacturing an all-solid-state secondary battery, comprising laminating a powder of an active material and a powder of an inorganic solid electrolyte forming one of a positive electrode and a negative electrode in two layers. Then, a direct current pulse current is applied to the laminated powder under pressure, and one of the electrodes and the inorganic solid electrolyte are integrally formed by sintering, and a pole member made of an active material forming the other pole is attached to the inorganic solid electrolyte. To form an all-solid-state secondary battery.

Therefore, the powder is sufficiently heated and sintered even without externally heating as in the solid-state reaction method for manufacturing the inorganic solid electrolyte and the electrode member. The time can be reduced to a short time.

According to a fourth aspect of the present invention, there is provided a method of manufacturing an all-solid-state secondary battery, comprising: laminating an active material powder and an inorganic solid electrolyte powder for forming a positive electrode and a negative electrode into three layers; A direct current pulse current is applied under pressure to form each electrode and the inorganic solid electrolyte integrally by sintering to form an all-solid-state secondary battery.

Therefore, the powder is sufficiently heated and sintered without externally heating as in the solid-state reaction method in order to manufacture the inorganic solid electrolyte and the electrode member. The time can be reduced to a short time. Moreover,
Since the positive and negative electrodes and the inorganic solid electrolyte are sintered at the same time, the manufacturing time of the all-solid-state secondary battery can be further reduced.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail based on an example of an embodiment shown in the drawings. FIG. 1 shows an example of a general form of the all-solid-state secondary battery 1. The all-solid-state secondary battery 1 includes a positive electrode 2 made of an active material, a negative electrode 3 made of an active material, and an inorganic solid electrolyte 4 interposed between the positive electrode 2 and the negative electrode 3. The all-solid-state secondary battery 1 here may be used as a single unit, or may be used as a secondary battery cell connected in multiple stages.

The positive electrode 2 and the inorganic solid electrolyte 4 are
It is composed of a joined body 5 obtained by laminating powders of the respective materials, applying a DC pulse current to the laminated powder under pressure, and sintering. For this reason, at the time of producing the joined body 5, a discharge phenomenon occurs in the gap between the powder particles, and the cleaning and activation of the particle surface by discharge plasma, discharge impact pressure, and the like,
And sintering is promoted by an electrolytic diffusion effect generated in an electric field, a thermal diffusion effect by Joule heat, and a plastic deformation force by pressurization. The body is sufficiently heated and sintered to reduce the fabrication time. In addition, since the density of the joined body 5 after fabrication can be increased, the positive electrode 2
In addition, it is possible to improve the conductivity, strength and bonding property between the inorganic solid electrolyte 4 itself and the inorganic solid electrolyte 4 itself. The negative electrode 3
Is attached to the inorganic solid electrolyte 4.

As the inorganic solid electrolyte 4, for example, LiT
i ₂ (PO ₄ ) ₃ , LiZr ₂ (PO ₄ ) ₃ , LiGe ₂ (P
O ₄ ) ₃ , LiLaTiO ₃ , Li ₃ N, Li ₃ PO ₄ , Li
BPO _{4 and the} like can be mentioned, and among them, use of LiTi ₂ (PO ₄ ) ₃ which is a lithium ion conductor is preferable. The method for preparing the LiTi ₂ (PO ₄ ) ₃ powder, which is the raw material of the inorganic solid electrolyte 4, is not particularly limited in terms of the raw material, conditions, and the like. For example, a hydrothermal synthesis method (Kazua)
ki Ado, Yuria Saito, Takash
i Asai, Hiroyuki Kageyama
a, and Osamu Nakamura, Chem
itry Express, vol. 7 (1992)
p245) or a solid-phase reaction method or the like, but can be prepared using LiOH.H ₂ O, H ₂ TiO ₃ , H ₂
It is preferable to use LiTi ₂ (PO ₄ ) ₃ powder obtained by a hydrothermal synthesis method or a solid-phase reaction method using ₃ PO ₄ as a starting material.

As the active material of the positive electrode, for example, Li
CoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , Li ₄ Mn
₅ O ₁₂ , LiFeO ₂ , LiTi ₂ O ₄ , Li ₄ Ti ₅
O _{12 and the} like can be mentioned, and among them, use of LiCoO ₂ which is a positive electrode active material of a lithium ion battery is preferable. The method of preparing the powder of LiCoO ₂ , which is the raw material of the positive electrode active material, is not particularly limited in terms of the raw material and conditions, and is prepared by a synthesis method such as a hydrothermal synthesis method or a solid phase reaction method. LiOH.H ₂ O, CoOO
It is preferable to use LiCoO ₂ powder obtained by a hydrothermal synthesis method or a solid-phase reaction method using H as a starting material. Further, as the active material of the negative electrode, for example, Li, LiC ₆ , L
Examples thereof include an i-Al alloy, a Li-In alloy, and a Li-Sn alloy. Among them, Li is preferably used.

On the other hand, discharge plasma sintering of the positive electrode active material and the inorganic solid electrolyte 4 is performed by an existing discharge plasma sintering apparatus 6 as shown in FIG. As the discharge plasma sintering device 6, a device capable of heating, cooling and pressurizing the laminated powder and applying a current sufficient to generate a discharge is used. The discharge plasma sintering apparatus 6 includes a molding die 8 into which a powder 7 is loaded, and a pair of upper and lower compression energizing punches 9 and 10. The punches 9 and 10 are energized and pressed punch electrodes 1
1 and 12, the current-carrying punch electrode 1
The pressing force P is applied to the powder 7 loaded in the die 8 via
While supplying a pulse current.

The die 8 and the punches 9 and 10 are formed of a conductive material such as graphite, and are formed in a shape corresponding to the shape of the joined body 5 to be sintered. In the present embodiment, the punches 9 and 10 are formed in a cylindrical shape, and the die 8 is
It has a cylindrical shape that fits into zero. Therefore, the joined body 5
As a result, a cylindrical pellet-shaped sintered body is obtained. Further, in the present embodiment, the die 8 and the punches 9 and 10 are formed of conductive graphite. However, the present invention is not limited to this, and any other materials having conductivity, heat resistance, and strength capable of withstanding pressure can be used. It may be formed of an alloy, a conductive ceramic, or the like.

The energizing and pressing punch electrodes 11 and 12 are driven by a pressing mechanism 13 to
Press. The energizing and pressing punch electrodes 11 and 12 are
The punches 9 and 10 and the sintering power supply 14 are connected by a power supply path (not shown) provided inside. A pulse current is generated by the sintering power supply 14 and supplied to the powder 7 via the die 8 and the punches 9 and 10. further,
The current-pressing punch electrodes 11 and 12 have a cooling water passage 15 built therein.

The tips of the die 8, the punches 9, 10 and the energizing and pressing punch electrodes 11, 12 are housed in a water-cooled vacuum chamber 16. The inside of the water-cooled vacuum chamber 16 is maintained at a predetermined degree of vacuum by an atmosphere control mechanism 17, or is an inert gas atmosphere such as an argon gas or an air atmosphere depending on the type of the joined body 5.

Further, the control unit 18 of the discharge plasma sintering apparatus 6 includes a pressurizing mechanism 13, a power source 14 for sintering, a position measuring mechanism 19 for measuring the positions of the punches 9 and 10, and an atmosphere control mechanism 17 Then, a water cooling mechanism 20 for flowing the cooling water channel 15 to cool the energized pressurized punch electrodes 11 and 12 and a temperature measuring mechanism 21 for measuring the temperature of the powder 7 are drive-controlled. The control unit 18 drives the pressure mechanism 13 to
The punches 9 and 10 are controlled to compress the powder 7 at a predetermined compression pressure. The temperature of the compressed powder 7 is detected by a temperature measuring mechanism 21 such as a thermocouple or a radiation thermometer (not shown) attached to the die 8. This detected value is stored in the control unit 1
The sintering power supply 14 is driven based on a predetermined control program to apply a pulse current to the powder 7. For this reason, the ON-O such as discharge plasma sintering, discharge sintering, pulse current sintering, and current sintering is performed by the discharge plasma sintering device 6.
Using a sintering method by FF pulse conduction, the powder 7 can be compression-sintered and joined while controlling the material temperature by controlling the peak current and the pulse width.

The controller 18 adjusts the current and voltage values so that the detected temperature value of the powder 7 coincides with a preset temperature rising curve. Water is supplied to the cooling water passage 15 as necessary to cool the energized pressurized punch electrodes 11 and 12.

The procedure for manufacturing the above-described all-solid-state secondary battery 1 will be described below.

Each powder 7 of the inorganic solid electrolyte 4 and the positive electrode active material is prepared in advance. Li as the inorganic solid electrolyte 4
When Ti ₂ (PO ₄ ) ₃ is prepared by a hydrothermal synthesis method,
For example, as starting materials, LiOH.H ₂ O, H ₂ Ti
O ₃ and H ₃ PO ₄ are mixed and stirred in an aqueous solvent to form a solution. This LiOH.H ₂ O, H ₂ TiO ₃ , H ₃
The concentration of the PO ₄ solution was 0.05 to 5.0 M in each case,
More preferably, it is in the range of 0.1 to 1M. The solution is subjected to hydrothermal treatment at, for example, 380 ° C. for 5 hours, and the obtained white precipitate is washed with distilled water, filtered and dried to obtain LiTi ₂ (PO ₄ ) ₃ powder.

When LiCoO ₂ is prepared as a positive electrode active material by hydrothermal synthesis, for example, LiOH · H ₂ O and CoOOH are mixed and stirred in a water solvent as a starting material to form a solution. The concentration of this LiOH.H ₂ O is in the range of 1 to 20 g, more preferably ₂ to 5 g per 100 ml of H ₂ O, and the concentration of the CoOOH solution is in the range of 0.1 to 20 M, more preferably 5 to 20 g. Ｍ15M. The solution is subjected to hydrothermal treatment at, for example, 220 ° C. for 10 hours, and the obtained precipitate is washed with distilled water, filtered, and dried to obtain a LiCoO ₂ powder.

The die 8 of the spark plasma sintering apparatus 6
The powder 7 of the positive electrode active material and the powder 7 of the inorganic solid electrolyte 4 are layered and charged, and a pulse current is supplied while being pressed by the punches 9 and 10.

For this reason, the powder 7 becomes a green compact by pressurization, and a pulse current is given to this green compact,
The powder 7 is compression-sintered and joined to form the joined body 5. Here, the powder is 5 to 60 MPa, preferably 10 to 50 M
A pressure of Pa is applied. If the pressure is less than 5 MPa, sintering becomes insufficient. If the pressure exceeds 60 MPa, an excessive load acts on the die 8 or the like, which is not preferable.
It seems that a sufficient sintered body can be obtained at a pressure of about MPa.

The heating temperature required for sintering varies depending on the type of the raw material powder, but is usually 300 to 1200 ° C., preferably about 400 to 900 ° C. In contrast, 300
If the temperature is lower than ℃, it is difficult to obtain heat required for sintering,
If it exceeds 0 ° C., it is not preferable from the viewpoint of current supply.

Further, the current application time is preferably as short as about 3 to 5 minutes. Thereby, only the surface of the powder 7 can be melted to effectively perform sintering.

Therefore, in order to obtain such a heating temperature, in the present embodiment, a DC pulse current of, for example, 400
９００900A is preferable. The frequency of the pulse current is preferably in the range of 300 Hz to 30 kHz, and is preferably a low frequency using a low frequency power supply from the viewpoint of power supply price.

On the other hand, after the formation of the joined body 5, the negative electrode 3 is pressed against the inorganic solid electrolyte 4 and is sandwiched by applying pressure from the outside. Thereby, the secondary battery 1 is formed.

In the present embodiment, graphite is used for the die 8 and the punches 9 and 10, so the vicinity of the surface of the joined body 5 obtained contains graphite as an impurity. Such an impurity is obtained by polishing the surface. Can be removed.

As described above, according to the secondary battery 1 of the present embodiment, LiTi ₂ (PO ₄ ) _{3 is used} as the inorganic solid electrolyte 4.
Since the sintered body is produced by spark plasma sintering under pressure using, the density of the sintered body can be increased and the conductivity can be improved as shown in FIGS. Moreover, since the sintered body is manufactured by spark plasma sintering under pressure using LiCoO ₂ as the positive electrode active material, the density of the sintered body can be increased as shown in FIG. For these reasons, the performance of the secondary battery 1 can be improved.

Although the above embodiment is an example of a preferred embodiment of the present invention, the present invention is not limited to this embodiment, and various modifications can be made without departing from the gist of the present invention. For example, in the above-described embodiment, the powder 7 of the positive electrode 2 and the inorganic solid electrolyte 4 is laminated and joined by discharge plasma sintering under pressure, but the invention is not limited thereto. Any sintered body obtained by spark plasma sintering may be used. In this case, the secondary battery 1 can be formed by attaching the positive electrode 2 and the negative electrode 3 to both sides of the inorganic solid electrolyte 4. Even in this case, since the density of the inorganic solid electrolyte 4 after the production can be increased, the conductivity and the strength can be improved.
In addition, a discharge phenomenon occurs in the gap between the powder particles when the inorganic solid electrolyte 4 is manufactured, and the manufacturing time can be suppressed to a short time.

In the above-described embodiment, the powder 7 of the positive electrode 2 and the inorganic solid electrolyte 4 is laminated and joined by discharge plasma sintering under pressure. However, the present invention is not limited to this.
And the powder 7 of the inorganic solid electrolyte 4 may be laminated and joined by discharge plasma sintering under pressure. In this case, the production time of the negative electrode 3 and the inorganic solid electrolyte 4 can be reduced, and the conductivity, strength, and bonding properties of the negative electrode 3 and the inorganic solid electrolyte 4 after the production can be improved.

Further, in the above-described embodiment, the powder 7 of one of the pole members and the inorganic solid electrolyte 4 is laminated and joined. However, the present invention is not limited to this. Powder 7 may be laminated, and three layers may be simultaneously sintered and joined. In this case, the secondary battery 1 can be manufactured more quickly.

In the above-described embodiment, the all-solid-state secondary battery uses LiTi ₂ (PO ₄ ) ₃ as the inorganic solid electrolyte 4, uses LiCoO ₂ as the positive electrode active material, and uses lithium as the negative electrode active material. However, the present invention is not limited to this, and may be an all-solid-state secondary battery 1 using other materials as the inorganic solid electrolyte 4, the positive electrode active material, and the negative electrode active material. Furthermore, the present invention is not limited to the lithium secondary battery 1 but can be applied to other all solid-state secondary batteries 1 such as sodium and silver batteries. In any case, the all-solid-state secondary battery 1 having both high energy density and high reliability can be easily manufactured as compared with the conventional all-solid-state secondary battery 1 using a polymer electrolyte or the like.

[0044]

EXAMPLES (Comparative Example 1) 0.5 M LiO weighed to obtain a stoichiometric ratio in order to obtain LiTi ₂ (PO ₄ ) ₃
The respective aqueous solutions of H, H ₂ TiO ₃ and H ₃ PO ₄ were mixed and stirred, and the mixture was placed in a silver test tube and placed in an autoclave.
Hydrothermal treatment was performed at 0 ° C. for 5 hours. After the reaction, the obtained white precipitate was washed with distilled water, filtered and dried at 100 ° C. overnight to obtain LiTi ₂ (PO ₄ ) ₃ powder.

The obtained powder was observed by a scanning electron microscope (SEM), X-ray analysis (XRD), and thermogravimetric analysis / differential thermal analysis (TG / DTA).

FIG. 3 shows the result of observation by SEM. As shown in the figure, the LiTi ₂ (PO ₄ ) ₃ powder was a granular material having an average diameter of about 2 μm. FIG. 7 shows the results of XRD. Further, the result of TG / DTA is shown in FIG. As shown in the figure, no endothermic peak near 800 ° C. during heating with DTA and no exothermic peak near 785 ° C. during cooling with DTA were observed.

(Comparative Example 2) 4% of 1M Co (OH) ₂
5M NaOH was added dropwise to obtain a Co (OH) ₂ precipitate. It is oxidized by blowing air into it, and
OH was obtained. 2.7 g of the obtained CoOOH and commercially available L
50 g of iOH.H ₂ O was placed in 100 ml of distilled water, thoroughly mixed and stirred in a Teflon beaker, and subjected to hydrothermal treatment in an autoclave at 220 ° C. for 10 hours. After the reaction, the obtained precipitate was washed with distilled water, filtered, and dried at 100 ° C. for about several hours to obtain a LiCoO ₂ powder.

The obtained powder was observed by a scanning electron microscope (SEM) and subjected to X-ray analysis (XRD).
FIG. 11 shows the results of observation by SEM. As shown in the figure, the LiCoO ₂ powder was an elliptical spherical particle having a total length of about 0.2 μm. FIG. 15 shows the result of XRD.

(Comparative Example 3) A pressure of 190 MPa was applied to a LiTi ₂ (PO ₄ ) ₃ powder, and then 1100 ° C. in air.
For 3 hours. Thus, a sintered body was obtained.

The sintered body was observed by a scanning electron microscope (SEM) and subjected to X-ray analysis (XRD).

FIG. 6 shows the result of observation by SEM. As shown in the figure, this sintered body is LiTi ₂ (P
It was a porous body composed of granules having an average diameter of about 2 μm equivalent to O ₄ ) ₃ powder. FIG. 7 shows the result of XRD of this sintered body. As shown in the figure, no impurities of TiP ₂ O ₇ were observed. This density is 1.6 g / cm ³ , 5
4%.

FIG. 9 shows the temperature dependence of the conductivity of the sintered body. The conductivity of this sintered body is about 10 at 50 ° C.
^-8 S / cm.

FIG. 10 shows the relationship between the conductivity and the density of the sintered body.

Comparative Example 4 Lithium Carbonate (Li ₂ CO ₃ )
And titanium oxide (TiO ₂ ) and ammonium phosphate ((N
H ₄ ) ₂ HPO ₄ ) and LiTi
₂ (PO ₄ ) ₃ was prepared. The density of the conjugate obtained by cold-pressing this LiTi ₂ (PO ₄ ) ₃ was 2.3 g.
/ Cm ^-3 . FIG. 22 shows the temperature dependence of the conductivity of this combined body.

Comparative Example 5 A sintered body was obtained by laminating LiTi ₂ (PO ₄ ) ₃ powder and LiCoO ₂ powder. This sintered body was broken at the boundary between both materials. This is presumably because both powders were weakly bonded and could not absorb different thermal expansions of each material.

(Example 1) As a discharge plasma sintering device 6, a discharge plasma sintering machine SPS- manufactured by Sumitomo Coal Mining Co., Ltd. was used.
515S was used. The die 8 is made of graphite and has an inner diameter of 1.
A 5 cm cylindrical shape was used. This die 8 has LiTi
₂ (PO ₄ ) ₃ powder is charged, a DC pulse current of 800 to 1300 A is applied while applying a pressure P = 39 MPa (discharge plasma sintering method, hereinafter referred to as SPS), and the applied current is made different to obtain a die 8. Temperature of 600, 80
150 ℃ / m up to 0,950,1100,1200 ℃
in. When each temperature was reached, it was maintained for 3-10 minutes, the current application and compression were stopped, and the sample was cooled to room temperature. This cooling takes 1200 minutes to 600 ° C in about 1 minute.
It was performed at a rate that reduced it. The sintered body taken out in this state is black with graphite graphite as an impurity on the surface, but if sintered at 800 ° C or lower, the graphite is removed by polishing and sintered at 950 ° C or higher. If so, graphite was removed by annealing at 800 ° C. for 2 hours in the air. Thereby, a 1.5 cm diameter LiTi
₂ (PO ₄ ) ₃ sintered body was obtained.

Then, the obtained sintered body was observed by a scanning electron microscope (SEM) and analyzed by X-ray analysis (XR
D), energy dispersive X-ray analysis (EDX), thermogravimetric analysis / differential thermal analysis (TG / DTA), and infrared spectroscopy (IR).

The results of observation by SEM are shown in FIGS. As shown in these figures, in this sintered body, the original was 2
A few μm to 10 μm particles are closely bonded to each other
The size was about μm. For this reason, it was found that the sintered body obtained by spark plasma sintering obtained in Example 1 had a higher bonding property of the granular material than the sintered body obtained in Comparative Example 3 and could be densified.

FIG. 7 shows the result of XRD of this sintered body. As shown in the figure, some TiP ₂ O ₇ and other impurities were observed. Moreover, the higher the sintering temperature, the higher the TiP ₂
O ₇ was more. On the other hand, since TiP ₂ O ₇ was not observed in the sintered body obtained in Comparative Example 3 as described above, TiP ₂ O ₇
It is thought that Li was formed from i ₂ (PO ₄ ) ₃ by elimination. Then, the sintered body of LiTi ₂ (PO ₄ ) ₃
The lattice parameters of were consistent with those of the powder before sintering. Also, 1
The density of the product obtained by spark plasma sintering at 200 ° C. for 10 minutes was 2.4 g / cm ³ , 81%. Therefore, it was found that the sintered body obtained by the spark plasma sintering obtained in Example 1 could have a higher density than the sintered body obtained in Comparative Example 3.

FIG. 8 shows the result of TG / DTA of the sintered body obtained by the discharge plasma sintering at 1200 ° C. for 10 minutes.
The DTA results shown in FIG.
Endothermic peak that partially melts at
An exothermic peak at which all solidified at 80 to 790 ° C was observed. In addition, according to the TG results shown in the figure, the weight loss up to 1200 ° C. was less than 1%. By the way, LiTi ₂
In a synthetic electrolyte composed of (PO ₄ ) ₃ and LiNO ₃ , it is known that Li ₄ P ₂ O ₇ increases the density of the synthetic electrolyte. Therefore, it is considered that a similar phenomenon occurs during spark plasma sintering in the sintered body of this embodiment.
That is, some T is contained in the sintered body LiTi ₂ (PO ₄ ) _3.
Due to the inclusion of iP ₂ O ₇ and other impurities,
It is considered that partial melting and solidification occurred at around 00 ° C., thereby increasing the density of the sintered body and improving the ionic conductivity.

FIG. 9 shows the temperature dependence of the conductivity of each sintered body. Among them, the conductivity of the sintered body obtained by the discharge plasma sintering at 1200 ° C. for 10 minutes is about 10 ⁻⁶ S / c at 50 ° C.
m. Therefore, the conductivity of the sintered body obtained in Comparative Example 3 was improved by two orders of magnitude. For this reason, it turned out that the sintered compact by discharge plasma sintering has conductivity applicable as an inorganic solid electrolyte of an all solid-state secondary battery. In addition, 1
The DC conductivity of the sintered body obtained by discharge plasma sintering at 200 ° C. for 3 minutes is less than about 10 ⁻⁹ S / cm at room temperature, which is lower than the AC conductivity (6.9 × 10 ⁻⁷ S / cm). Less than about 0.1%. Therefore, it was found that the contribution due to electron conduction was negligible.

FIG. 10 shows the relationship between the conductivity and the density of the sintered body. As shown in the figure, the conductivity increased as the density increased. Therefore, it was found that by forming the sintered body by spark plasma sintering, it was possible to achieve high density and high conductivity.

An IR analysis was performed on a sintered body obtained by spark plasma sintering at 1200 ° C. for 3 minutes.
The cm ^-1 band did not clearly appear, indicating that OH was scarcely present. Therefore, OH ^-1 and H ⁺
It has been found that the contribution of at least one of the ions to conduction is negligible.

(Embodiment 2) As in Embodiment 1 described above,
Using a spark plasma sintering apparatus 6, LiT
A sintered body was prepared using LiCoO ₂ powder instead of i ₂ (PO ₄ ) ₃ powder. The production method was the same as that in Example 1 except that the raw materials were different.

Then, the obtained sintered body was observed by a scanning electron microscope (SEM), and X-ray analysis (XR
D) was performed.

The results of observation by SEM are shown in FIGS. As shown in these figures, in this sintered body, the granular body grew into a rectangular rod shape. In particular, in a high temperature range exceeding 800 ° C., LiCoO ₂ grew in the c-axis direction.

FIG. 15 shows the results of XRD of this sintered body.
Shown in As shown in the figure, some Co ₃ O ₄ and CoO
And other impurities were found. These impurities are LiCoO
₂ , which is obtained by decomposition at 800 ° C.
Especially when it exceeded. Then, it was found that the (006) peak and the (009) peak grew when the temperature exceeded 800 ° C., which coincided with the growth of LiCoO _{2 in} the c-axis direction shown in FIG. Furthermore, the sintered body LiCoO
The lattice parameters of ₂ corresponded to the powder before sintering. Also,
The density of the sintered body obtained by discharge plasma sintering at 600 ° C. for 5 minutes is 3.1 g / cm ³ , 61%, and the density of the sintered body obtained by discharge plasma sintering at 800 ° C. for 5 minutes is 3.3 g / cm 3.
^3, it was 65%. Therefore, it was determined that it is preferable to use a sintered body obtained by discharge plasma sintering at 600 ° C. or 800 ° C. for 5 minutes as the positive electrode of the all-solid-state secondary battery.

(Embodiment 3) As in Embodiments 1 and 2 described above, a discharge plasma
About 0.4 g of iTi ₂ (PO ₄ ) ₃ powder and about 0.5 g of LiCoO ₂ powder were added in this order, and the sintering temperature was set to 800 ° C., followed by sintering to produce a joined body 5. The production method was the same as in Examples 1 and 2, except that the raw materials and the sintering temperatures were different.

Then, the obtained joined body 5 was observed with a scanning electron microscope (SEM), and X-ray analysis (XR
D) and energy dispersive X-ray characteristic analysis (EDX).

FIG. 16 shows the result of observation by SEM. As shown in the figure, the boundary between two layers of the inorganic solid electrolyte (LiTi ₂ (PO ₄ ) ₃ ) 4 and the positive electrode active material (LiCoO ₂ ) is clearly observed at the center of the side surface of the joined body 5. Was done.
Although the third phase 22 considered to be generated by the reaction exists between the two layers 2 and 4, it is determined that the effect on the conductivity is small since the third phase 22 is thin.

Further, A- of the interface of the joined body 5 shown in FIG.
FIG. 17 shows the result of element distribution measurement by EDX on the B line. As shown in the figure, it can be seen that the element distributions of Ti, Co, and P change rapidly at the interface. This indicates that a sharp joint surface could be formed by the spark plasma sintering method.

Further, the LiTi ₂ (PO ₄ ) ₃ and Li
XR of sintered body obtained by spark plasma sintering of CoO ₂ mixed powder
The result of D is shown in FIG. As shown in FIG.
Impurities such as O ₃ , Co ₂ TiO ₄ and LiCoPO ₄ were found. For this reason, the third phase 22 is composed of these CoTiO ₃
And at least one of Co ₂ TiO ₄ and LiCoPO ₄ .

(Embodiment 4) As in Embodiment 3 described above,
Using a discharge plasma sintering apparatus 6, LiTi
About 0.4 g of ₂ (PO ₄ ) ₃ powder and about 0.5 g of LiCoO ₂ powder are put in this order, and a DC pulse current of 600 A is applied while applying a pressure P = 39 MPa, and the temperature of the die 8 is reduced to 600 ° C. Up to 100 ° C./min. When the temperature reached 600 ° C., the temperature was maintained for 3 minutes, the application of current and the compression were stopped, and the sample was cooled to room temperature. The surface of the sintered body taken out in this state was polished to obtain a joined body 5 having a diameter of 1.5 cm.

Then, the obtained sintered body was observed by a scanning electron microscope (SEM), and X-ray analysis (XR
D) and energy dispersive X-ray characteristic analysis (EDX).

FIG. 19 shows the result of observation by SEM. As shown in the figure, a boundary between two layers of the inorganic solid electrolyte 4 and the positive electrode active material was clearly observed at the center of the side surface of the joined body 5. In the middle of the two layers 2 and 4, there is a third phase 22, which is considered to have been formed by the reaction.
Since No. 2 is thin, it is determined that the influence on conductivity is small.

Further, A- at the interface of the joined body 5 shown in FIG.
FIG. 20 shows the results of element distribution measurement by EDX on the B line. As shown in the figure, it can be seen that the element distributions of Ti, Co, and P change rapidly at the interface. This indicates that a sharp joint surface could be formed by the spark plasma sintering method.

Further, the LiTi ₂ (PO ₄ ) ₃ and Li
XR of sintered body obtained by spark plasma sintering of CoO ₂ mixed powder
The result of D is shown in FIG. As shown in the figure, Co ₃ O
₄ and impurities such as CoO were observed. Therefore, the third phase 2
2 is considered to be at least one of Co ₃ O ₄ and CoO.

(Embodiment 5) Joint 5 prepared in Embodiment 4
To the LiTi ₂ (PO ₄ ) ₃ side in a glove box (dew point -90 ° C.) to attach a negative electrode 3 made of a negative electrode active material made of metallic lithium to produce an all-solid-state secondary battery 1. .

This all-solid-state secondary battery 1 was subjected to a charge / discharge test at a charge / discharge current density of 1.3 nA / cm ² and a constant current of 4.3 V / 3.0 V voltage regulation. The result is shown in FIG.
Shown in As shown in the figure, when the battery was charged with a constant current value, the battery voltage increased (reference numeral 23 in the figure), and the open circuit voltage after charging showed a higher value than before charging. On the other hand, when the battery was discharged, the battery voltage decreased (reference numeral 24 in the figure), and the open circuit voltage after the discharge showed a lower value than before the discharge. Further, the voltage value indicated by the appearing plateau (indicated by reference numeral 25 in the figure) matched the value estimated from each of the materials of the positive electrode 2 and the negative electrode 3 used, and a similar curve was obtained in several cycle tests. Thus, it was confirmed that the solid-state secondary battery 1 suitably functions.

Example 6 Lithium carbonate (Li ₂ CO ₃ )
And titanium oxide (TiO ₂ ) and ammonium phosphate ((N
H ₄ ) ₂ HPO ₄ ) and LiTi
₂ (PO ₄ ) ₃ was prepared. This LiTi ₂ (PO ₄ ) ₃ was subjected to spark plasma sintering to produce a sintered body. The density of this sintered body was 2.7 g / cm ^-3 , which was 92% of the theoretical X-ray density. This was higher than the density of the conjugate obtained by cold pressing in Comparative Example 4 of 2.3 g / cm ^-3 .

As shown in FIG. 22, the ionic conductivity of the sintered body obtained by the discharge plasma sintering obtained in Example 6 was improved by one digit or more than the sintered body obtained in Comparative Example 4. .

[0082]

As is clear from the above description, according to the all-solid-state secondary battery according to the first aspect, the density of the inorganic solid electrolyte can be increased after fabrication, so that the conductivity and the strength can be improved. And the service life of the inorganic solid electrolyte can be extended. In addition, the powder is sufficiently heated and sintered without external heating for preparing the inorganic solid electrolyte, so that the preparation time can be reduced to a short time.

Further, since the inorganic solid electrolyte is made of a sintered body, it is easy to increase the area of the secondary battery, and it is possible to eliminate poor yield due to the generation of pinholes and the like, and the degree of freedom in shape is relatively high. It becomes large and can be applied to various secondary batteries.

According to the all-solid-state secondary battery of the second aspect, since the pole member and the inorganic solid electrolyte are joined by sintering, the conductivity and the joining strength between the two can be improved. Can be.

Further, according to the method of manufacturing an all-solid-state secondary battery according to the third aspect, the powder is sufficiently heated without much external heating for manufacturing the inorganic solid electrolyte and the electrode member. Since the sintering is performed, the manufacturing time of the all-solid-state secondary battery can be reduced to a short time.

According to the method of manufacturing an all-solid-state secondary battery according to the fourth aspect, since the positive electrode, the negative electrode, and the inorganic solid electrolyte are simultaneously sintered, the manufacturing time of the all-solid-state secondary battery can be further reduced. You can save time.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an entire solid-state secondary battery of the present invention.

FIG. 2 is a block diagram showing a discharge plasma sintering apparatus for producing an all-solid-state secondary battery.

FIG. 3 is an electron micrograph showing a powder of LiTi ₂ (PO ₄ ) ₃ obtained in Comparative Example 1 before sintering.

FIG. 4 is an electron micrograph showing a sintered body of LiTi ₂ (PO ₄ ) ₃ obtained by spark plasma sintering (1100 ° C., 10 minutes).

FIG. 5 is an electron micrograph showing a sintered body of LiTi ₂ (PO ₄ ) ₃ obtained by spark plasma sintering (1200 ° C., 10 minutes).

FIG. 6 is an electron micrograph showing a sintered body of LiTi ₂ (PO ₄ ) ₃ obtained in Comparative Example 3.

FIG. 7 is a view showing a result of XRD of each sintered body obtained in Example 1.

FIG. 8 shows a comparative example 1 and 1200 by a discharge plasma sintering method.
It is a figure which shows the result of TG / DTA of the sintered compact sintered at 10 degreeC and 10 minutes.

FIG. 9 is a diagram showing the temperature dependence of conductivity of each sintered body obtained by the spark plasma sintering method and the sintered body obtained in Comparative Example 3.

FIG. 10 is a diagram showing the relationship between the density and conductivity of each sintered body obtained by the spark plasma sintering method and the sintered body obtained in Comparative Example 3.

FIG. 11 is an electron micrograph showing a powder of LiCoO ₂ obtained in Comparative Example 2 before sintering.

FIG. 12 is an electron micrograph showing a sintered body of LiCoO ₂ obtained by a spark plasma sintering method (600 ° C., 5 minutes).

FIG. 13 is an electron micrograph showing a sintered body of LiCoO ₂ obtained by a discharge plasma sintering method (800 ° C., 5 minutes).

FIG. 14 is an electron micrograph showing a LiCoO ₂ sintered body obtained by a discharge plasma sintering method (1000 ° C., 5 minutes).

FIG. 15 is a view showing the results of XRD of each sintered body obtained by the spark plasma sintering method and the sintered body obtained in Comparative Example 2.

FIG. 16 is an electron micrograph showing an interface portion of a joined body of LiTi ₂ (PO ₄ ) ₃ and LiCoO ₂ .

FIG. 17 is a graph showing T by EDX along the line AB in FIG. 16;
It is a figure which shows the distribution measurement result of i, Co, and P element.

FIG. 18 is a view showing an XRD result of a sintered body obtained by spark plasma sintering a mixed powder of each of LiTi ₂ (PO ₄ ) ₃ and LiCoO ₂ .

FIG. 19 is an electron micrograph showing an interface portion of a joined body of LiTi ₂ (PO ₄ ) ₃ and LiCoO ₂ .

FIG. 20 is a graph showing T by EDX along the line AB in FIG. 19;
It is a figure which shows the distribution measurement result of i, Co, and P element.

FIG. 21 is a view showing the charging / discharging results of the all-solid-state secondary battery obtained in Example 5.

FIG. 22 is a graph showing the temperature dependence of the conductivity of the sintered body obtained in Example 6 and the sintered body obtained in Comparative Example 4.

[Explanation of symbols]

 1 All-solid secondary battery 2 Positive electrode 3 Negative electrode 4 Inorganic solid electrolyte

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tomonari Takeuchi 1-8-31 Midorioka, Ikeda-shi, Osaka Prefecture Inside the Industrial Technology Research Institute, Osaka Institute of Technology (72) Inventor Mitsuharu Tabuchi 1-8-8 Midorioka, Ikeda-shi, Osaka No. 31 Industrial Technology Institute Osaka Institute of Industrial Technology (72) Inventor Kazuaki Ado 1-38 Midorioka Ikeda City, Osaka Prefecture Industrial Technology Institute Osaka Institute of Industrial Technology Research Institute (72) Inventor Hiroyuki Kageyama Osaka 1-8-31 Midorigaoka, Ikeda-shi F-term in Osaka Institute of Technology (reference) 5H029 AJ05 AJ06 AJ11 AJ14 AK03 AL12 AM11 AM12 BJ03 CJ02 CJ03 DJ09

Claims (4)

[Claims] 1. An all-solid-state secondary battery comprising a positive electrode made of an active material, a negative electrode made of an active material, and an inorganic solid electrolyte interposed between the positive electrode and the negative electrode. An all-solid-state secondary battery characterized by being sintered by applying a direct-current pulse current to the powder under pressure. 2. An all-solid-state secondary battery comprising a positive electrode made of an active material, a negative electrode made of an active material, and an inorganic solid electrolyte interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is used. One of the electrodes and the inorganic solid electrolyte were formed by laminating a powder of the active material forming the pole and a powder of the inorganic solid electrolyte, and sintering by applying a DC pulse current under pressure to the laminated powder. An all-solid-state secondary battery characterized in that: 3. An active material powder and an inorganic solid electrolyte powder forming one of the positive electrode and the negative electrode are laminated in two layers, and a DC pulse current is applied to the laminated powder under pressure. The one-pole and the inorganic solid electrolyte are integrally formed by sintering, and a pole member made of an active material forming the other pole is attached to the inorganic solid electrolyte to form an all-solid-state secondary battery. For producing an all-solid-state secondary battery. 4. A method in which a powder of an active material and a powder of an inorganic solid electrolyte which form a positive electrode and a negative electrode are laminated in three layers, and a DC pulse current is applied to the laminated powder under pressure so that each electrode and the inorganic solid A method for producing an all-solid-state secondary battery, comprising forming an all-solid-state secondary battery by integrally forming an electrolyte and sintering.