Patent Application
20170222260
1. Field of the Disclosure
The present disclosure relates to solid electrolyte powder, an all-solid-state lithium ion secondary battery in which the solid electrolyte powder is used, and a method of manufacturing solid electrolyte powder.
2. Description of the Related Art
A lithium ion battery is superior because it can obtain a higher energy density than batteries in which other materials are used. However, in lithium ion batteries which have been put into practice, an electrolyte is an organic electrolytic solution. Therefore, it is difficult to reduce the size and thickness of a battery, and liquid leakage or firing may occur.
On the other hand, in a case where a lithium-ion-conductive solid electrolyte is used, the possibility of liquid leakage or firing can be reduced, and a reduction in the size and the thickness of a battery can be realized. Therefore, the energy density per volume can be significantly improved.
For example, in a battery described in Japanese Patent No. 3012211, a lithium-ion-conductive glass ceramic as an ion-conductive solid electrolyte is manufactured according to the following procedure. First, NH4H2PO4, SiO2, TiO2, Al(OH)3, and Li2CO3 are heated and melted in an electrical furnace. Here, the raw materials are decomposed at 700° C. to vaporize CO2, NH3, and H2O components and are further heated to 1450° C. to be further melted. The glass melt prepared as described above is cast on a sheet plate to prepare sheet-shaped glass, and the sheet-shaped glass is annealed at 550° C. to remove distortion. Next, the glass is cut into a predetermined size and polished. Next, a heat treatment is performed on the cut and polished glass at 800° C. for 12 hours and at 1000° C. for 24 hours to prepare a glass ceramic. Crystals deposited by this heat treatment have a structure represented by Li1+X+YAlXTi2−XSiYP3−YO12 and have high conductivity.
However, in the steps of manufacturing a battery described in Japanese Patent No. 3012211, a cooling device is used for cooling high-temperature glass melt to prepare glass. Therefore, there are problems in that introduction costs and an installation space are required for the cooling device.
The present disclosure provides: a solid electrolyte powder with which a small and thin lithium ion battery can be manufactured and a desired conductivity can be realized without introducing a new cooling device; and an all-solid-state lithium ion secondary battery in which the solid electrolyte powder is used.
A solid electrolyte powder according to an aspect of the present invention includes ion-conductive LATP powder that is obtained by heating and melting raw materials at a predetermined temperature to prepare molten LATP mixture, cooling the molten LATP mixture to prepare a crystalline material having a NASICON structure, crushing the crystalline material to prepare crystal powder having a particle size of 1 μm to 10 μm, and performing a heat treatment on the crystal powder in air at a temperature of 800° C. to 1000° C. for a predetermined period of time.
As a result, a small and thin lithium ion battery can be manufactured without introducing a new cooling device. Further, the crystalline material is crushed to prepare crystal powder, and a heat treatment is performed on the crystal powder under predetermined conditions. As a result, LATP powder having a desired conductivity can be obtained.
In the solid electrolyte powder according to the aspect, it is preferable that a crystallite size on a predetermined lattice plane of the LATP powder after the heat treatment is 500 nm or less.
In this case, the predetermined lattice plane refers to, for example, a (134) plane, and by reducing the crystallite size, the ion conductivity of the LATP powder can be increased.
It is preferable that the solid electrolyte powder according to the aspect includes secondary powder having a particle size of 100 nm to 1000 nm that is obtained by crushing the LATP powder.
By reducing the particle size, the ion conductivity can be further increased.
It is preferable that the solid electrolyte powder according to the aspect includes tertiary powder that is obtained by performing a heat treatment again on the secondary powder at a temperature of 300° C. to 700° C. for a predetermined period of time.
By performing the heat treatment again, the ion conductivity can be further increased.
In the solid electrolyte powder according to the aspect, it is preferable that a composition of the LATP powder is represented by Li1+xAlxTi2−x(PO4)3. Here, x satisfies 0<x≦0.5.
In an all-solid-state lithium ion secondary battery according to another aspect of the present invention, any one of the above-described solid electrolyte powders is used.
By using the above-described solid electrolyte powder, a small and thin lithium ion secondary battery having desired performance can be realized.
A method of manufacturing solid electrolyte powder according to still another aspect of the present invention includes: a step of heating and melting raw materials at a predetermined temperature to prepare molten LATP mixture; a step of naturally cooling the molten LATP mixture to prepare a crystalline material having a NASICON structure; a step of crushing the crystalline material to prepare crystal powder having a particle size of 1 μm to 10 μm; and a step of performing a heat treatment on the crystal powder in air at a temperature of 800° C. to 1000° C. for a predetermined period of time to prepare ion-conductive LATP powder.
As a result, a small and thin lithium ion battery can be manufactured without introducing a new cooling device. Further, the crystalline material is crushed to prepare crystal powder, and a heat treatment is performed on the crystal powder under predetermined conditions. As a result, LATP powder having a desired conductivity can be obtained.
Hereinafter, a solid electrolyte powder, an all-solid-state lithium ion secondary battery, and a method of manufacturing solid electrolyte powder according to an embodiment of the present invention will be described with reference to the drawings.
The negative electrode layer 13 has a configuration in which solid electrolyte particles 21 (solid electrolyte powder), an electrode active material 22, and conductive auxiliary agent particles 24 are mixed. The solid electrolyte layer 14 is formed of the solid electrolyte particles 21. The positive electrode layer 15 has a configuration in which the solid electrolyte particles 21, an electrode active material 23, and the conductive auxiliary agent particles 24 are mixed. A mixing ratio between the materials in each of the negative electrode layer 13 and the positive electrode layer 15 can be set based on the specification of the battery and the like.
As a material of the negative electrode current collector 11, for example, copper is used. As a material of the positive electrode current collector 12, for example, aluminum is used. In addition, as the electrode active material 22 of the negative electrode layer 13, for example, graphite, hard carbon, carbon nanotubes, fullerene, or other carbon materials can be used. As the electrode active material 23 of the positive electrode layer 15, for example, lithium nickel oxide, lithium cobalt oxide, or other lithium metal oxides can be used. As a material of the conductive auxiliary agent particle 24, for example, activated carbon, graphite particles, or carbon fibers can be used. The solid electrolyte particles 21 (solid electrolyte powder) will be described below in detail.
The solid electrolyte particle 21 will be described below in the manufacturing step order.
As starting materials, for example, H3PO4, NH4H2PO4, Li2CO3, TiO2, Al(OH)3, or Al2O3 can be used. In addition, from the viewpoint of uniformity of NASICON crystals, it is preferable that the starting materials do not include SiO2.
These raw materials are put into a heating container and are heated and melted at a temperature which are equal to or higher than melting points of the raw materials, for example, at 1500° C. for a predetermined period of time to prepare molten LATP mixture.
The molten LATP mixture prepared in (1) described above is cooled to prepare a crystalline material having a NASICON structure. Regarding the cooling, the molten LATP mixture is naturally cooled, for example, by bringing the heating container into contact with a metal plate (for example, a stainless steel plate) to radiate heat. Here, in general, the NASICON structure refers to a structure of a compound represented by M2(XO4)3 where MO6 octahedra and XO4 tetrahedra sharing vertices are three-dimensionally arranged, M represents a transition metal, and X represents S, P, As, Mo, or W.
The crystalline material prepared in (2) described above is crushed using, for example, a mortar or a pestle to prepare crystal powder. The crushing is performed such that the average particle size of the crystalline material is in a range of 1 μm to 10 μm.
The crystal powder prepared in (3) described above is put into a gas muffle furnace, and a heat treatment (hereinafter, also referred to as “primary heat treatment”) is performed on the crystal powder in air at a predetermined temperature for a predetermined period of time to prepare LATP powder. Due to this heat treatment, highly ion-conductive LATP powder can be obtained in which a crystallite size on a predetermined lattice plane (for example, a (134) plane) or a (300) plane) is 500 nm or less. With this LATP powder, solid electrolyte powder is formed.
Here, preferable conditions of the primary heat treatment are a temperature of higher than 700° C. and lower than 1000° C. and a time of 1 hour to 12 hours. The temperature of the primary heat treatment is more preferably 800° C. or higher.
A composition of the prepared LATP powder is represented by, for example, Li1+xAlxTi2−x(PO4)3, in which x satisfies 0<x<0.5.
The solid electrolyte powder can be prepared through the above-described steps (1) to (4), and it is more preferable that the following steps (5) and (6) are performed from the viewpoint of increasing the ion conductivity.
The LATP powder prepared in (4) described above is crushed using, for example, a mortar or a pestle to prepare secondary powder having an average particle size of 100 nm to 1000 nm.
A heat treatment (hereinafter, also referred to as “secondary heat treatment”) is performed again on the secondary powder prepared in (5) described above to prepare tertiary powder. After putting the secondary powder into, for example, a gas muffle furnace, the heat treatment is performed on the secondary powder in air at a predetermined temperature (for example, 300° C. to 700° C.) for a predetermined period of time (for example, 30 minutes to 12 hours). Due to this heat treatment, the ion conductivity can be further increased.
Hereinafter, Examples will be described. Preparation of Samples
(a) Starting materials of each Example were H3PO4, Li2CO3, TiO2, and Al2O3, and a composition of the respective components present in a mixture of the starting materials is as follows in terms of oxides. Here, “the composition in terms of oxides” represents a composition that represents, assuming that all the starting materials were decomposed and changed into oxides during melting, the contents of the respective components in the molten mixture with respect to 100 mol % of the total amount of all the produced oxides.
(a-1) Example 1
Li2O: 16.2 mol %
Al2O3: 3.8 mol %
TiO2: 42.5 mol %
P2O3: 37.5 mol %
SiO2: 0 mol %
(a-2) Example 2
Li2O: 18.3 mol %
Al2O3: 3.6 mol %
TiO2: 41.5 mol %
P2O3: 36.6 mol %
SiO2: 0 mol %
After the starting materials were mixed with each other using a mortar, a frit was prepared according to the following procedure.
The mixture was heated at 300° C. for 30 minutes and at 700° C. for 30 minutes, was further heated at 1100° C. for 15 minutes, and was extracted and naturally cooled.
For pre-heating, the mixture was heated at 1100° C. for 20 minutes and then was heated at 1300° C. for 10 minutes.
Next, for main heating, the raw materials were heated at 1500° C., as a temperature at which the raw materials were melted, for 5 minutes.
The molten LP mixture of the heating container was cast on a stainless steel plate having a thickness of 20 mm and was naturally cooled.
The crystalline material was crushed using a mortar such that the average particle size of the crystalline material was in a range of 1 μm to 10 μm.
Using a gas muffle furnace HPM-1G (manufactured by Matsuura Manufacture Co., Ltd.), a heat treatment was performed in air for 12 hours. The temperature of the heat treatment was set in a range of 700° C. to 950° C. After the heat treatment, the powder was naturally cooled.
Through the above-described steps, LATP powder according to Example 1 having a configuration represented by Li1.3Al0.3Ti1.7(PO4)3 was obtained, and LATP powder according to Example 2 having a configuration represented by Li1.5Al0.3Ti1.7(PO4)3 was obtained.
After performing the manufacturing steps (a) to (e) on the same starting materials as those in Example 1, the heat treatment of the step (e) was not performed. As a result, a sample according to Comparative Example 1 was prepared. After performing the manufacturing steps (a) to (e) on the same starting materials as those in Example 2, the heat treatment of the step (e) was not performed. As a result, a sample according to Comparative Example 2 was prepared.
Using a focusing diffractometer, X-ray diffraction was performed under the following conditions.
Target: Cu
Tube Voltage: 45 kV
Tube Current: 40 mA
Measurement Range: 10° to 100°
Step Size: 0.016°
T/S: 0.5 s
Incidence Side: FDS
Detector Side: XC
Stage: flat sample
Each of a sample having undergone the heat treatment (primary heat treatment) and a sample not having undergone the heat treatment was crushed using a mortar to prepare a powder pellet, and the powder pellet was interposed between copper plate electrodes to measure an impedance thereof. The measurement was performed in a dry nitrogen atmosphere at 25° C., and the ion conductance was calculated based on a drawing created from a Nyquist plot of the measurement result. Evaluation Results
Regarding (A) to (C) of
As shown in Table 1, the crystallite size of Example 1 was less than that of Comparative Example 1, and the crystallite size of Example 2 was less than that of
Comparative Example 2. In addition, in Examples 1 and 2, the crystallite sizes on the (134) plane were 500 nm or less, which were obviously less than those in Comparative Examples 1 and 2 where the heat treatment was not performed at a heat treatment temperature of higher than 700° C.
Regarding the conductance, as shown in Table 2 and
Regarding the lattice constant, as shown in Table 1, the numerical values of Examples 1 and 2 were substantially the same as those in Comparative Examples 1 and 2, and it can be seen that there were no changes depending on the heat treatment or depending on the temperature of the heat treatment.
The present invention has been described with reference to the above-described embodiment. However, the present invention is not limited to the above-described embodiment, and various improvements or modifications can be made for the purpose of improvements or within the scope of the present invention.
As described above, the solid electrolyte powder according to the present invention is small and thin and is practically useful for realizing a lithium ion battery having no possibility of liquid leakage or firing.
It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims of the equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-213295 | Oct 2014 | JP | national |
This application is a Continuation of International Application No. PCT/JP2015/073483 filed on Aug. 21, 2015, which claims benefit of Japanese Patent Application No. 2014-213295 filed on Oct. 20, 2014. The entire contents of each application noted above are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2015/073483 | Aug 2015 | US |
| Child | 15490986 | US |
