JP7669033B2 - Solid electrolyte, powder for producing solid electrolyte, and method for producing solid electrolyte - Google Patents
Solid electrolyte, powder for producing solid electrolyte, and method for producing solid electrolyte Download PDFInfo
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- 239000007784 solid electrolyte Substances 0.000 title claims description 109
- 239000000843 powder Substances 0.000 title claims description 36
- 238000004519 manufacturing process Methods 0.000 title claims description 29
- 229910000664 lithium aluminum titanium phosphates (LATP) Inorganic materials 0.000 claims description 63
- 238000005245 sintering Methods 0.000 claims description 60
- 239000000463 material Substances 0.000 claims description 48
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 20
- 239000011248 coating agent Substances 0.000 claims description 20
- 238000000576 coating method Methods 0.000 claims description 20
- 239000010941 cobalt Substances 0.000 claims description 19
- 229910017052 cobalt Inorganic materials 0.000 claims description 19
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 19
- 239000002904 solvent Substances 0.000 claims description 19
- 150000001868 cobalt Chemical class 0.000 claims description 14
- 239000002228 NASICON Substances 0.000 claims description 13
- UFMZWBIQTDUYBN-UHFFFAOYSA-N cobalt dinitrate Chemical compound [Co+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O UFMZWBIQTDUYBN-UHFFFAOYSA-N 0.000 claims description 11
- 229910001981 cobalt nitrate Inorganic materials 0.000 claims description 11
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 9
- 239000006185 dispersion Substances 0.000 claims description 9
- QGUAJWGNOXCYJF-UHFFFAOYSA-N cobalt dinitrate hexahydrate Chemical group O.O.O.O.O.O.[Co+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O QGUAJWGNOXCYJF-UHFFFAOYSA-N 0.000 claims description 8
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 7
- 239000003792 electrolyte Substances 0.000 claims description 7
- 229910052760 oxygen Inorganic materials 0.000 claims description 7
- 239000001301 oxygen Substances 0.000 claims description 7
- 239000007787 solid Substances 0.000 claims description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 6
- 229910000428 cobalt oxide Inorganic materials 0.000 claims description 5
- IVMYJDGYRUAWML-UHFFFAOYSA-N cobalt(ii) oxide Chemical compound [Co]=O IVMYJDGYRUAWML-UHFFFAOYSA-N 0.000 claims description 5
- 238000001035 drying Methods 0.000 claims description 5
- 238000000465 moulding Methods 0.000 claims description 5
- 229910001429 cobalt ion Inorganic materials 0.000 claims description 4
- XLJKHNWPARRRJB-UHFFFAOYSA-N cobalt(2+) Chemical compound [Co+2] XLJKHNWPARRRJB-UHFFFAOYSA-N 0.000 claims description 4
- 239000002002 slurry Substances 0.000 claims description 4
- 150000002500 ions Chemical class 0.000 claims description 3
- BDERNNFJNOPAEC-UHFFFAOYSA-N propan-1-ol Chemical compound CCCO BDERNNFJNOPAEC-UHFFFAOYSA-N 0.000 claims description 3
- 238000010298 pulverizing process Methods 0.000 claims description 2
- 239000011343 solid material Substances 0.000 claims description 2
- 238000010586 diagram Methods 0.000 description 7
- 238000000034 method Methods 0.000 description 7
- 238000009792 diffusion process Methods 0.000 description 6
- 239000012535 impurity Substances 0.000 description 6
- 210000003739 neck Anatomy 0.000 description 6
- 239000007789 gas Substances 0.000 description 5
- NHNBFGGVMKEFGY-UHFFFAOYSA-N nitrate group Chemical group [N+](=O)([O-])[O-] NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 5
- 239000007774 positive electrode material Substances 0.000 description 5
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 4
- 230000006872 improvement Effects 0.000 description 4
- 239000007788 liquid Substances 0.000 description 4
- 229910001416 lithium ion Inorganic materials 0.000 description 4
- 239000002245 particle Substances 0.000 description 4
- 229910002651 NO3 Inorganic materials 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 238000004090 dissolution Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- -1 Co( NO3 ) 2.6H2O Chemical compound 0.000 description 2
- 229910009178 Li1.3Al0.3Ti1.7(PO4)3 Inorganic materials 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- XZXAIFLKPKVPLO-UHFFFAOYSA-N cobalt(2+);dinitrate;hydrate Chemical compound O.[Co+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O XZXAIFLKPKVPLO-UHFFFAOYSA-N 0.000 description 2
- 238000009694 cold isostatic pressing Methods 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 239000010408 film Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000004570 mortar (masonry) Substances 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- 239000010409 thin film Substances 0.000 description 2
- 239000010936 titanium Substances 0.000 description 2
- 229910052723 transition metal Inorganic materials 0.000 description 2
- 150000003624 transition metals Chemical class 0.000 description 2
- QTBSBXVTEAMEQO-UHFFFAOYSA-M Acetate Chemical compound CC([O-])=O QTBSBXVTEAMEQO-UHFFFAOYSA-M 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- 208000005156 Dehydration Diseases 0.000 description 1
- 229910006210 Li1+xAlxTi2-x(PO4)3 Inorganic materials 0.000 description 1
- 229910006212 Li1+xAlxTi2−x(PO4)3 Inorganic materials 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 239000011149 active material Substances 0.000 description 1
- 230000003466 anti-cipated effect Effects 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- SAXCKUIOAKKRAS-UHFFFAOYSA-N cobalt;hydrate Chemical compound O.[Co] SAXCKUIOAKKRAS-UHFFFAOYSA-N 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000018044 dehydration Effects 0.000 description 1
- 238000006297 dehydration reaction Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 229910052732 germanium Inorganic materials 0.000 description 1
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical group [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- FGHSTPNOXKDLKU-UHFFFAOYSA-N nitric acid;hydrate Chemical compound O.O[N+]([O-])=O FGHSTPNOXKDLKU-UHFFFAOYSA-N 0.000 description 1
- 239000010450 olivine Substances 0.000 description 1
- 229910052609 olivine Inorganic materials 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 239000013535 sea water Substances 0.000 description 1
- 238000003746 solid phase reaction Methods 0.000 description 1
- 238000010671 solid-state reaction Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 238000001291 vacuum drying Methods 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
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- Conductive Materials (AREA)
Description
本発明は、固体電解質、固体電解質製造用の粉末および固体電解質の製造方法に関するものである。 The present invention relates to a solid electrolyte, a powder for producing a solid electrolyte, and a method for producing a solid electrolyte.
次世代の充電池として、全固体二次電池が強く期待されている。
全固体二次電池は、正極および負極の電極と固体電解質が主要構成材であるが、特に現在注目を集めているリチウムイオン全固体二次電池では、固体電解質として電気伝導度、機械的強度、化学的安定性などが優れた特性を有するＮＡＳＩＣＯＮ型のＬＴＰ系固体電解質、特に性能が優れているＬｉ１．３Ａｌ０．３Ｔｉ１．７（ＰＯ４）３などのＬＡＴＰ固体電解質が主に検討されている。
All-solid-state secondary batteries are highly anticipated as the next generation of rechargeable batteries.
The main components of an all-solid-state secondary battery are positive and negative electrodes and a solid electrolyte. In particular, for lithium-ion all-solid-state secondary batteries, which are currently attracting attention, NASICON-type LTP solid electrolytes, which have excellent properties such as electrical conductivity, mechanical strength, and chemical stability, and LATP solid electrolytes such as Li1.3Al0.3Ti1.7 ( PO4 ) 3 , which have particularly excellent performance , are being mainly studied.
全固体二次電池を生産性高く低コストで効率的に生産するためには、電極とＬＴＰやＬＡＴＰ固体電解質を一体焼結法で作製するのが好ましい。
ＬＴＰやＬＡＴＰ固体電解質は一般的に焼結法によって作製されるが、その焼結温度は１０００℃以上である。一方、橄欖石型（オリビン型）の正極活物質の一般的な焼結温度は、電極との拡散を抑制するため、約８００℃である。
このため、一体焼結を行う場合、焼結温度は、正極活物質のそれがボトルネックになって、ＬＴＰやＬＡＴＰ固体電解質よりも低い８００℃に制限される。ちなみに、１０００℃で焼結すると、電極とＬＴＰやＬＡＴＰ固体電解質間で拡散が起こり、固相反応による高抵抗相の生成などの電気特性が優れなくなるという問題が起こる。
In order to efficiently produce all-solid-state secondary batteries with high productivity and low cost, it is preferable to prepare the electrodes and the LTP or LATP solid electrolyte by a co-sintering method.
LTP and LATP solid electrolytes are generally produced by a sintering method, and the sintering temperature is 1000° C. or higher. On the other hand, the general sintering temperature for olivine-type positive electrode active materials is about 800° C. in order to suppress diffusion with the electrode.
For this reason, when sintering together, the sintering temperature of the positive electrode active material becomes a bottleneck and is limited to 800° C., which is lower than that of the LTP or LATP solid electrolyte. Incidentally, if sintering is performed at 1000° C., diffusion occurs between the electrode and the LTP or LATP solid electrolyte, causing problems such as poor electrical properties due to the generation of a high resistance phase caused by a solid-state reaction.
焼結温度を約８００℃とした場合、焼結助剤無添加ＬＴＰやＬＡＴＰの相対密度は、１０００℃で焼結させた場合の約８０％に対して、約６０％と大変低く、電気伝導度も低いものになる。 When the sintering temperature is about 800°C, the relative density of LTP and LATP without added sintering aids is very low at about 60%, compared to about 80% when sintered at 1000°C, and the electrical conductivity is also low.
そこで、焼結温度が８００℃以下で、高密度化が可能であり、高い機械的強度と電気伝導度に優れた易焼結性のＬＴＰ固体電解質、その固体電解質を製造する上で欠かせない固体電解質製造用粉末、およびそれらの製造方法が嘱望されていた。 Therefore, there was a demand for an easily sinterable LTP solid electrolyte that can be sintered at a sintering temperature of 800°C or less, can be made dense, and has excellent mechanical strength and electrical conductivity, as well as a powder for producing the solid electrolyte, which is essential for producing the solid electrolyte, and a method for producing the same.
特許文献１には、オリビン型正極活物質とＮＡＳＩＣＯＮ型固体電解質を同時焼成する際に、正極活物質から固体電解質へのＬｉ金属元素(Ｍｎ、Ｃｏ、Ｎｉ)の拡散を抑制し、充放電時への影響を抑制する全固体二次電池および製造方法が開示されている。そこでは、電解質層に拡散する遷移金属を添加するが、それにより反応が抑制され、焼結性を向上させている。ここで、遷移金属の添加は、電解質の合成時もしくは合成した電解質に対して、酸化物、炭酸塩もしくは酢酸塩により行われる。なお、酸化物により添加される方法は、粒径や粒子の分散性に起因した不均一性が局所構造に生じるため、焼結助剤が多く取り残された構造や不純物相を形成しやすく、粉末粒子の分散制御に課題がある。 Patent Document 1 discloses an all-solid-state secondary battery and a manufacturing method thereof that suppresses the diffusion of Li metal elements (Mn, Co, Ni) from the positive electrode active material to the solid electrolyte when sintering an olivine type positive electrode active material and a NASICON type solid electrolyte simultaneously, thereby suppressing the effects on charging and discharging. In this case, a transition metal that diffuses into the electrolyte layer is added, which suppresses the reaction and improves sinterability. The transition metal is added by oxide, carbonate, or acetate during the synthesis of the electrolyte or to the synthesized electrolyte. Note that the method of adding by oxide creates nonuniformity in the local structure due to the particle size and particle dispersibility, so it is easy to form a structure in which a large amount of sintering aid is left behind or an impurity phase, and there is a problem with controlling the dispersion of the powder particles.
本発明は、上記の背景技術で説明した従来の問題点を解消するためになされたものであり、密度が高く電気伝導度に優れた易焼結性のＮＡＳＩＣＯＮ型ＬＴＰやＬＡＴＰ固体電解質およびその固体電解質の製造に好適な焼結用粉末を提供することを目的とする。
また、焼結温度が８００℃以下で、密度が高く電気伝導度に優れた易焼結性のＮＡＳＩＣＯＮ型ＬＴＰやＬＡＴＰ固体電解質の製造方法を提供することを目的とする。
The present invention has been made to solve the conventional problems described in the background art above, and aims to provide a NASICON type LTP or LATP solid electrolyte that has high density and excellent electrical conductivity and is easily sinterable, and a powder for sintering that is suitable for producing the solid electrolyte.
Another object of the present invention is to provide a method for producing a NASICON type LTP or LATP solid electrolyte which is easily sintered at a sintering temperature of 800° C. or less, has high density and excellent electrical conductivity.
本発明の構成を下記に示す。
（構成１）
バルク部がＮＡＳＩＣＯＮ型ＬＴＰからなり、
ネック部には酸化コバルトが存在する焼結体からなる、固体電解質。
（構成２）
バルク部がＮＡＳＩＣＯＮ型ＬＡＴＰおよびＮＡＳＩＣＯＮ型ＬＡＧＰからなる群より選ばれる１種類以上の電解質からなる、構成１記載の固体電解質。
（構成３）
バルク部がＮＡＳＩＣＯＮ型ＬＡＴＰからなる、構成１記載の固体電解質。
（構成４）
固体電解質母材と前記固体電解質母材の表面を覆う被覆材からなる粉末であって、
前記固体電解質母材はＮＡＳＩＣＯＮ型ＬＴＰからなり、
前記被覆材はコバルト（Ｃｏ）イオンを含み、
前記被覆材の厚さが原子層オーダーである、固体電解質製造用の粉末。
（構成５）
前記固体電解質母材は、ＮＡＳＩＣＯＮ型ＬＡＴＰおよびＮＡＳＩＣＯＮ型ＬＡＧＰからなる群より選ばれる１以上からなる、構成４記載の粉末。
（構成６）
前記固体電解質母材は、ＮＡＳＩＣＯＮ型ＬＡＴＰからなる、構成５記載の粉末。
（構成７）
コバルトイオンは、前記被覆材にのみ含まれる、構成４から６の何れか１項記載の粉末。
（構成８）
前記被覆材は、コバルト硝酸塩を含む、構成４から７の何れか１項記載の粉末。
（構成９）
コバルト塩を、水と共沸させることが可能な溶媒に溶解させて溶液を作製することと、
ＮＡＳＩＣＯＮ型ＬＴＰからなる固体電解質母材を前記溶液に投入、分散させた分散液（スラリー）を作製することと、
前記分散液を乾燥させて固形物を得ることと、
前記固形物を解砕してコバルトイオンを含有する粉体を得ることと、
前記粉体を成型して成型体を得ることと、
前記成型体を酸素が存在する環境下で焼結する、固体電解質の製造方法。
（構成１０）
前記固体電解質母材は、ＮＡＳＩＣＯＮ型ＬＡＴＰおよびＮＡＳＩＣＯＮ型ＬＡＧＰからなる群より選ばれる１以上からなる、構成９記載の固体電解質の製造方法。
（構成１１）
前記固体電解質母材は、ＮＡＳＩＣＯＮ型ＬＡＴＰである、構成９記載の固体電解質の製造方法。
（構成１２）
前記コバルト塩は、コバルト硝酸塩である、構成９から１１の何れか１項記載の固体電解質の製造方法。
（構成１３）
前記コバルト硝酸塩は、Ｃｏ（ＮＯ３）２・６Ｈ２Ｏである、構成１２記載の固体電解質の製造方法。
（構成１４）
前記溶媒は、メタノール、エタノールおよびプロパノールからなる群より選ばれる１以上を含む、構成９から１３の何れか１項記載の固体電解質の製造方法。
（構成１５）
前記溶媒は、エタノールである、構成１４記載の固体電解質の製造方法。
（構成１６）
前記焼結は、大気環境で行われる、構成９から１５の何れか１項記載の固体電解質の製造方法。
（構成１７）
前記焼結の温度は、６００℃以上８００℃以下である、構成９から１６の何れか１項記載の固体電解質の製造方法。
（構成１８）
前記固体電解質母材のモル量Ａに対する前記コバルト塩のモル量Ｂの比率Ｂ／Ａは、０．００１以上０．１以下である、構成９から１７の何れか１項記載の固体電解質の製造方法。
The configuration of the present invention is shown below.
(Configuration 1)
The bulk part is made of NASICON type LTP,
A solid electrolyte consisting of a sintered body with cobalt oxide present in the neck portion.
(Configuration 2)
2. The solid electrolyte according to claim 1, wherein the bulk portion comprises one or more electrolytes selected from the group consisting of NASICON-type LATP and NASICON-type LAGP.
(Configuration 3)
2. The solid electrolyte according to claim 1, wherein the bulk portion is made of NASICON-type LATP.
(Configuration 4)
A powder comprising a solid electrolyte base material and a coating material covering a surface of the solid electrolyte base material,
The solid electrolyte base material is made of NASICON type LTP,
the coating material includes cobalt (Co) ions;
The powder for producing a solid electrolyte, wherein the coating material has a thickness on the order of an atomic layer.
(Configuration 5)
5. The powder according to claim 4, wherein the solid electrolyte base material is one or more selected from the group consisting of NASICON-type LATP and NASICON-type LAGP.
(Configuration 6)
6. The powder of claim 5, wherein the solid electrolyte base material comprises NASICON type LATP.
(Configuration 7)
7. The powder of any one of claims 4 to 6, wherein cobalt ions are contained only in the coating material.
(Configuration 8)
8. The powder of any one of claims 4 to 7, wherein the coating material comprises cobalt nitrate.
(Configuration 9)
dissolving a cobalt salt in a solvent capable of forming an azeotrope with water to form a solution;
A solid electrolyte base material made of NASICON type LTP is put into the solution and dispersed to prepare a dispersion (slurry);
drying the dispersion to obtain a solid;
pulverizing the solid material to obtain a powder containing cobalt ions;
Molding the powder to obtain a molded body;
The molded body is sintered in an environment in which oxygen is present.
(Configuration 10)
10. The method for producing a solid electrolyte according to claim 9, wherein the solid electrolyte base material is one or more selected from the group consisting of NASICON-type LATP and NASICON-type LAGP.
(Configuration 11)
10. The method for producing a solid electrolyte according to claim 9, wherein the solid electrolyte base material is a NASICON-type LATP.
(Configuration 12)
12. The method for producing a solid electrolyte according to any one of claims 9 to 11, wherein the cobalt salt is cobalt nitrate.
(Configuration 13)
13. The method for producing a solid electrolyte according to claim 12, wherein the cobalt nitrate is Co(NO 3 ) 2.6H 2 O.
(Configuration 14)
14. The method for producing a solid electrolyte according to any one of claims 9 to 13, wherein the solvent includes at least one selected from the group consisting of methanol, ethanol, and propanol.
(Configuration 15)
15. The method for producing a solid electrolyte according to claim 14, wherein the solvent is ethanol.
(Configuration 16)
16. The method for producing a solid electrolyte according to any one of claims 9 to 15, wherein the sintering is performed in an air environment.
(Configuration 17)
17. The method for producing a solid electrolyte according to any one of claims 9 to 16, wherein the sintering temperature is 600°C or higher and 800°C or lower.
(Configuration 18)
18. The method for producing a solid electrolyte according to any one of claims 9 to 17, wherein a ratio B/A of a molar amount B of the cobalt salt to a molar amount A of the solid electrolyte base material is 0.001 or more and 0.1 or less.
本発明によれば、密度が高く電気伝導度に優れた易焼結性のＮＡＳＩＣＯＮ型ＬＴＰ固体電解質およびその固体電解質の製造に好適な焼結用粉末が提供される。また、焼結温度が８００℃以下で、密度が高く電気伝導度に優れた易焼結性のＮＡＳＩＣＯＮ型ＬＴＰ固体電解質の製造方法が提供される。 According to the present invention, a NASICON-type LTP solid electrolyte having high density and excellent electrical conductivity and a powder for sintering suitable for producing the solid electrolyte is provided. Also provided is a method for producing a NASICON-type LTP solid electrolyte having high density and excellent electrical conductivity and a sintering temperature of 800°C or less.
以下、本発明について詳細に説明する。以下に記載する本発明の詳細な説明は、代表的な態様、実施形態、および実施例に基づいてなされることがあるが、これらは例示であり、本発明はそのような態様、実施形態、及び実施例に限定されるものではない。
なお、「Ａ～Ｂ」は、Ａ以上Ｂ以下を示す。
The present invention will be described in detail below. The detailed description of the present invention described below may be based on representative aspects, embodiments, and examples, but these are merely examples, and the present invention is not limited to such aspects, embodiments, and examples.
In addition, "A to B" indicates A or more and B or less.
（実施の形態１）
実施の形態１では、本発明のＮＡＳＩＣＯＮ型ＬＴＰ易焼結性リチウムイオン固体電解質の製造方法を説明する。
(Embodiment 1)
In the first embodiment, a method for producing a NASICON type LTP sinterable lithium ion solid electrolyte of the present invention will be described.
本発明は、溶解、析出反応により電解質粒子表面に極少量の焼結助剤となる元素（コバルト（Ｃｏ））のイオンを均一かつ簡便にコーティングさせて固体電解質の焼結性を向上させるものである。その結果、固体電解質に接して配置される電極およびその電極を構成する活物質との反応や拡散が抑制される８００℃というような比較的低温の焼結で固体電解質としての必要十分な高い電気伝導度や高い相対密度が得られる。ここで、相対密度が高いと、一般に、高い機械強度が得られる。
以下、その詳細を下記に示す。
The present invention improves the sinterability of a solid electrolyte by uniformly and simply coating the surface of electrolyte particles with a very small amount of ions of an element (cobalt (Co)) that acts as a sintering aid through a dissolution and precipitation reaction. As a result, a high electrical conductivity and a high relative density necessary and sufficient for a solid electrolyte can be obtained by sintering at a relatively low temperature of, for example, 800°C, at which reaction and diffusion between the electrodes arranged in contact with the solid electrolyte and the active materials that compose the electrodes are suppressed. Here, a high relative density generally results in high mechanical strength.
The details are given below.
実施の形態１による全固体電解質の製造工程を図２に示す。
最初に、コバルト塩を溶媒に溶解させる（工程Ｓ０１）。
本発明では、固体電解質用粉末は、その表面がコバルトを含んだ被覆材で覆われていることを特徴とするが、そのコバルトを含んだ被覆材の仕込みとしてコバルト塩を用いる。
ここで、コバルト塩としては、コバルト硝酸塩を好んで挙げることができ、コバルト硝酸塩六水和物（Ｃｏ（ＮＯ３）２・６Ｈ２Ｏ）を特に好んで用いることができる。コバルト硝酸塩は、焼結の際に硝酸基が揮発してコバルトのみが残るため、不純物の残存を極力抑えることが可能になる。さらに、コバルト硝酸塩の水和物、特にＣｏ（ＮＯ３）２・６Ｈ２Ｏにすることにより、溶媒によく溶け、少量のコバルトが極めて均一に含有された被覆材を得ることが可能になる。
FIG. 2 shows a process for producing the all-solid-state electrolyte according to the first embodiment.
First, a cobalt salt is dissolved in a solvent (step S01).
In the present invention, the powder for solid electrolyte is characterized in that its surface is covered with a coating material containing cobalt, and a cobalt salt is used as the feed for the coating material containing cobalt.
Here, as the cobalt salt, cobalt nitrate can be preferably used, and cobalt nitrate hexahydrate (Co( NO3 ) 2.6H2O ) can be particularly preferably used. When using cobalt nitrate, the nitrate group volatilizes during sintering, leaving only cobalt, making it possible to minimize the amount of remaining impurities. Furthermore, by using a cobalt nitrate hydrate, particularly Co( NO3 ) 2.6H2O , it is possible to obtain a coating material that dissolves well in a solvent and contains a small amount of cobalt very uniformly.
溶媒は、水と共沸させることが可能な溶媒であり、例えばメタノール、エタノール、プロパノールからなる群より選ばれる１以上を含む溶媒、特に好んではエタノールを挙げることができる。ここで、例えばエタノールを含む溶媒としては、エタノールに水が添加された溶媒を挙げることができる。
なお、この溶解には、スターラー攪拌や超音波印加を伴って行うことが好ましい。温度は室温が、取り扱いが容易で、低コストなため好ましい。
The solvent is a solvent capable of forming an azeotrope with water, and may be, for example, a solvent containing one or more selected from the group consisting of methanol, ethanol, and propanol, and is particularly preferably ethanol. Here, for example, an example of a solvent containing ethanol is a solvent in which water is added to ethanol.
The dissolution is preferably carried out with stirring using a stirrer or application of ultrasonic waves. Room temperature is preferred because it is easy to handle and low cost.
次に、ＮＡＳＩＣＯＮ型ＬＴＰ固体電解質母材を前記溶媒に投入、分散させた分散液を作製する（工程Ｓ０２）。
ここで、ＬＴＰは、ＬＡＴＰおよびＮＡＳＩＣＯＮ型ＬＡＧＰからなる群より選ばれる１以上とすることがより好ましい。ＬＡＴＰおよび／またはＬＡＧＰにするとより性能の高い固体電解質を得ることが容易になる。
ここで、本発明におけるＬＡＴＰは、それを構成するＡｌの原子数比率ｘ（Ｌi１＋xＡｌｘＴｉ２－ｘ（ＰＯ４）３のｘ）が０以上１以下であるリチウム－アルミニウム－チタン－リン酸化合物のことをいう。この中でも、Ｌｉ１．３Ａｌ０．３Ｔｉ１．７（ＰＯ４）３が、汎用に用いられているため、好んで用いることができる。
さらに、ＬＡＴＰは、ＬＡＴＰのチタン（Ｔｉ）をゲルマニウム（Ｇｅ）に置換したＬＡＧＰより固体電解質に接触して配置される電極との反応性が低いので、ＬＡＴＰを特に好んで用いることができる。
なお、この混合、分散には、スターラー攪拌や超音波印加を伴うことが好ましく、温度は室温が、取り扱いが容易で、低コストなため好ましい。
Next, the NASICON type LTP solid electrolyte base material is put into the solvent and dispersed to prepare a dispersion liquid (step S02).
Here, it is more preferable that LTP is at least one selected from the group consisting of LATP and NASICON-type LAGP. By using LATP and/or LAGP, it becomes easier to obtain a solid electrolyte with higher performance.
Here, LATP in the present invention refers to a lithium-aluminum-titanium-phosphate compound in which the ratio of the number of Al atoms constituting it ( x in Li1 + xAlxTi2 -x ( PO4 ) 3 ) is 0 to 1. Among these, Li1.3Al0.3Ti1.7 ( PO4 ) 3 is preferably used because it is widely used.
Furthermore, LATP has a lower reactivity with the electrodes placed in contact with the solid electrolyte than LAGP, which is obtained by substituting germanium (Ge) for titanium (Ti) in LATP, and therefore LATP can be used with particular preference.
It is preferable that this mixing and dispersion is accompanied by stirring with a stirrer or application of ultrasonic waves, and the temperature is preferably room temperature because of ease of handling and low cost.
発明者は、長年の研究により、ＣｏがＬＡＴＰの焼結助剤として優れていることを見出していた。すなわち、ＣｏがＬＡＴＰ粉間の界面に介在していると、低温でも十分な焼結が行えて、焼結材の相対密度が高くなり、また電気伝導度も向上することを見出していた。
その検討の中で、多量の焼結助剤は、ＬＡＴＰの固体電解質としての性能低下、例えば電気伝導度や相対密度の低下をもたらすことも見出していた。
そこで、どうやったら少量のＣｏをＬＡＴＰ粉に均一にコーティングできるかを鋭意検討してきた。
その結果、コバルトを塩の形で、水と共沸させることが可能な溶媒に溶解させた溶液を用いればよいこと、さらにはコバルト塩を、焼結の際に硝酸基が揮発してコバルトのみが残るコバルト硝酸塩とすればさらによいこと、コバルト硝酸塩としてコバルト硝酸塩水和物、特にＣｏ（ＮＯ３）２・６Ｈ２Ｏを用いるとさらにいっそう少量のＣｏをＬＡＴＰ紛に均一にコーティングできることを多大な試行錯誤の結果導き出した。これは、この溶媒が硝酸塩の水和物をよく溶解させることと、表面張力が小さく、かつＬＡＴＰとの界面張力も小さいことから、ＬＡＴＰの表面によく馴染んで均一な液膜が形成され、その液膜の乾燥時もムラなく溶液が引いていくことによると考えている。
Through many years of research, the inventors have found that Co is an excellent sintering aid for LATP. In other words, when Co is present at the interface between LATP powders, sufficient sintering can be performed even at low temperatures, the relative density of the sintered material increases, and the electrical conductivity is also improved.
In the course of this investigation, it was also found that a large amount of sintering aid reduces the performance of LATP as a solid electrolyte, for example reducing the electrical conductivity and relative density.
Therefore, we have been actively studying how to coat the LATP powder uniformly with a small amount of Co.
As a result, after much trial and error, we found that it would be better to use a solution in which cobalt is dissolved in the form of a salt in a solvent that can form an azeotrope with water, and that it would be even better to use cobalt nitrate, in which the nitrate group volatilizes during sintering and only cobalt remains, and that if cobalt nitrate hydrate, especially Co(NO 3 ) 2.6H 2 O, is used as the cobalt nitrate, an even smaller amount of Co can be uniformly coated on the LATP powder. We believe that this is because this solvent dissolves nitrate hydrate well, has low surface tension, and also has low interfacial tension with LATP, so it blends well with the surface of LATP to form a uniform liquid film, and the solution is removed evenly when the liquid film dries.
固体電解質母材とコバルト塩の添加量に関しては、固体電解質母材のモル量Ａに対するコバルト塩のモル量Ｂの比率Ｂ／Ａを０．００１以上０．１以下とすることが好ましい。添加量をこの範囲にすることにより、高い相対密度および高い電気伝導度の焼結体を得ることができる。 Regarding the amount of solid electrolyte base material and cobalt salt added, it is preferable that the ratio B/A of the molar amount B of the cobalt salt to the molar amount A of the solid electrolyte base material is 0.001 or more and 0.1 or less. By setting the amount added within this range, a sintered body with high relative density and high electrical conductivity can be obtained.
しかる後、分散液を乾燥させて固形物を得る（工程Ｓ０３）。乾燥方法としては、加熱乾燥、真空乾燥を挙げることができる。 Then, the dispersion is dried to obtain a solid (step S03). Drying methods include heat drying and vacuum drying.
次に、固形物の凝集体を解砕して粉体を得て、その後粉体を加圧成型する（工程Ｓ０４）。ここで、解砕の方法としては、乳棒・乳鉢による方法、ボールミルを挙げることができる。成型には、例えば一軸加圧成型、ＣＩＰ（Ｃｏｌｄ Ｉｓｏｓｔａｔｉｃ Ｐｒｅｓｓｉｎｇ）、シート成型などを用いることができ、圧力としては、例えば２０ＭＰａ以上３５０ＭＰａ以下とすることができる。加圧の雰囲気は大気、Ａrガス、Ｎ２ガス、Ｏ２ガスとすることができるが、大気が取り扱い容易でコストも低いので好んで用いることができる。 Next, the solid aggregates are crushed to obtain a powder, which is then pressure molded (step S04). Here, examples of the crushing method include a method using a pestle and mortar, and a ball mill. For molding, for example, uniaxial pressure molding, CIP (Cold Isostatic Pressing), sheet molding, etc. can be used, and the pressure can be, for example, 20 MPa or more and 350 MPa or less. The atmosphere for pressurization can be air, Ar gas, N2 gas, or O2 gas, but air is preferably used because it is easy to handle and has low costs.
このようにしてできた粉体１の構造を図３に示す。
粉体１は、ＬＴＰ、ＬＡＴＰやＬＡＧＰなどからなる固体電解質母材１１がコバルト塩からなる被覆材１２で覆われた構造である。ここで、被覆材は均一な厚さで切れ目や欠損の少ない緻密なものになる。被覆材の厚さは、原子層オーダーの制御が好ましい。具体的には、１原子層以上１０原子層以下が好ましく、より好ましくは１原子層以上４原子層以下、さらに好ましくは１原子層以上２原子層以下がよい。この厚さの制御は、コバルト塩の仕込み量、すなわち固体電解質母材のモル量Ａに対するコバルト塩のモル量Ｂの比率Ｂ／Ａにより制御できる。特に、コバルト硝酸塩および水と共沸させることが可能な溶媒を用いることにより、コバルトの分布ムラが生じにくくなって、原子層オーダーで制御された極薄膜をムラを抑えて形成することが可能になる。
被覆材がこのような薄い膜であると、焼結助剤の量を減らしながら稠密で十分な焼結を行うことができるので、焼結温度が低くても、高い相対密度や高い電気伝導度などの固体電解質として求められる十分な性能を得ることができる。
The structure of the powder 1 thus obtained is shown in FIG.
The powder 1 has a structure in which a solid electrolyte base material 11 made of LTP, LATP, LAGP, etc. is covered with a coating material 12 made of a cobalt salt. Here, the coating material is dense with a uniform thickness and few breaks or defects. The thickness of the coating material is preferably controlled on the order of atomic layers. Specifically, it is preferably 1 to 10 atomic layers, more preferably 1 to 4 atomic layers, and even more preferably 1 to 2 atomic layers. This thickness can be controlled by the amount of cobalt salt charged, that is, the ratio B/A of the molar amount B of the cobalt salt to the molar amount A of the solid electrolyte base material. In particular, by using a solvent that can be azeotroped with cobalt nitrate and water, uneven distribution of cobalt is less likely to occur, making it possible to form an ultra-thin film controlled on the order of atomic layers with reduced unevenness.
When the coating material is such a thin film, dense and sufficient sintering can be achieved while reducing the amount of sintering aid used. This makes it possible to obtain sufficient performance required of a solid electrolyte, such as high relative density and high electrical conductivity, even at a low sintering temperature.
この粉体中のコバルトは、粉体形成までは固体電解質母材内に拡散するほどの高温処理が行われていないので、固体電解質母材１１内には入り込まず、被覆材１２にのみ存在する。このことにより、コバルトの量を固体電解質の緻密性を上げる焼結助剤として機能するに必要な極小量にすることができ、高い性能をもつ固体電解質を製造することが可能になる。 Because the cobalt in this powder has not been subjected to high-temperature treatment that would cause it to diffuse into the solid electrolyte base material before the powder is formed, it does not penetrate into the solid electrolyte base material 11 and exists only in the coating material 12. This allows the amount of cobalt to be kept to the minimum necessary to function as a sintering aid that increases the density of the solid electrolyte, making it possible to produce a solid electrolyte with high performance.
なお、コバルトが存在するとは、成分として含むことを意味し、存在しないとは成分として含まないことを意味する。ここでは、不純物として意図せず混入したものは含まないものとして取り扱う。コバルトは、固体電解質母材１１内に不純物としても含まないことが好ましいが、そのために精製純度を上げることは、コストパフォーマンスを鑑みて判断することが好ましい。 The presence of cobalt means that it is included as a component, and the absence of cobalt means that it is not included as a component. Here, cobalt that is unintentionally mixed in as an impurity is treated as not being included. It is preferable that cobalt is not included as an impurity in the solid electrolyte base material 11, but it is preferable to consider cost performance when deciding whether to increase the purification purity for this purpose.
しかる後、大気など酸素が存在する環境下で焼結を行う（工程Ｓ０５）。
焼結温度は、６００℃以上８００℃以下が好ましく、８００℃がより一層好ましい。この上限温度の維持時間は、例えば１Ｈｒ以上１０Ｈｒ以下とすることができ、昇温および降温の速度（レート）は、例えば１００℃／Ｈｒ以上３００℃／Ｈｒとすることができる。このような焼結条件では、固体電解質に接して配置される電極との間で拡散などが起きにくく、この固体電解質を用いて作製された二次電池は高い性能をもつものになる。
酸素が関与してコバルトが酸化し、効率の高い焼結助剤となるので、８００℃というような低い焼結温度でも二次電池などに求められる高い相対密度や高い電気伝導度などを備えた固体電解質が供給される。なお、焼結を大気下で行うことは、取り扱いが容易でコストメリットもあることから好ましい。
Thereafter, sintering is carried out in an environment in which oxygen is present, such as the air (step S05).
The sintering temperature is preferably 600° C. to 800° C., more preferably 800° C. The time for which this upper limit temperature is maintained can be, for example, 1 Hr to 10 Hr, and the rate of temperature increase and decrease can be, for example, 100° C./Hr to 300° C./Hr. Under such sintering conditions, diffusion is unlikely to occur between the solid electrolyte and the electrodes arranged in contact with it, and a secondary battery produced using this solid electrolyte has high performance.
Oxygen is involved in the oxidation of cobalt, which becomes a highly efficient sintering aid, and therefore a solid electrolyte having high relative density and high electrical conductivity required for secondary batteries can be provided even at a low sintering temperature of 800° C. Note that sintering in the atmosphere is preferable because it is easy to handle and has cost advantages.
このようにして形成された焼結体１０１は、図１に示すように、バルク部２１がＮＡＳＩＣＯＮ型ＬＴＰからなり、ネック部２２には酸化コバルトが存在する焼結体からなる固体電解質になる。ネック部２２はＮＡＳＩＣＯＮ型ＬＴＰ以外の酸化コバルトを含むが少量なので、酸化コバルトの存在による電気特性の低下は僅かなものとなる。一方で、ネック部２２でバルク部２１同士が十分に密着し、高い相対密度の焼結体１０１になる。 As shown in FIG. 1, the sintered body 101 thus formed is a solid electrolyte consisting of a sintered body in which the bulk portion 21 is made of NASICON-type LTP and cobalt oxide is present in the neck portion 22. The neck portion 22 contains cobalt oxide other than NASICON-type LTP, but in small amounts, so that the presence of cobalt oxide causes only a slight decrease in electrical properties. On the other hand, the bulk portions 21 are sufficiently adhered to each other in the neck portion 22, resulting in a sintered body 101 with a high relative density.
なお、本発明は、上記実施形態に限定されるものではなく、上記実施形態は、本発明を説明するための例示であり、本発明の特許請求の範囲に記載された技術的思想と実質的に同一な構成を有し、同様な作用効果を奏するものは、いかなるものであっても本発明の技術的範囲に包含される。
また、上記説明では、全固体二次電池用の固体電解質を念頭に述べてきたが、この固体電解質の適用は全固体二次電池に限るものではなく、例えば、セパレーター、ＣＯ２センサー、キャパシタ、電気化学的デバイス、海水中のリチウムイオン回収などにも適用が可能である。
It should be noted that the present invention is not limited to the above-described embodiments, which are merely examples for explaining the present invention. Anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included within the technical scope of the present invention.
In addition, the above explanation has been given with a solid electrolyte for an all-solid-state secondary battery in mind, but the application of this solid electrolyte is not limited to all-solid-state secondary batteries, and it can also be applied to, for example, separators, CO2 sensors, capacitors, electrochemical devices, and the recovery of lithium ions from seawater.
以下、実施例を用いて本発明をさらに詳細に説明するが、本発明は、必ずしも下記の実施例に限定されるものではない。 The present invention will be described in more detail below using examples, but the present invention is not necessarily limited to the following examples.
（実施例１）
最初に、焼結助剤になる硝酸塩を作製するために硝酸コバルト・六水和物（Ｗａｋｏ）を準備し、それを特に脱水処理のされていない市販のエタノールからなる溶媒に溶解させて、硝酸塩溶液を作製した（図２の工程Ｓ０１）。ここで、この溶解は大気下の室温で行った。
次に、固体電解質母材としてＮＡＳＩＣＯＮ型構造をもつ市販のＬＡＴＰ粉（豊島製作所）を用意し、それを超音波印加下で硝酸塩溶液に分散、攪拌させて分散液（スラリー）を作製した（工程Ｓ０２）。その環境は大気圧、室温である。ここで、ＬＡＴＰの量は、エタノール溶媒に対して固形分濃度が１５ｖｏｌ％になる量とし、硝酸コバルト・六水和物の量は、ＬＡＴＰの重量に対してＣｏの重量比が０．１～２．０ｗｔ％（ＬＡＴＰに対するＣｏのモル比は０．００６５０６～０．１３０１２３）になるように電子天秤を用いて秤量した。
Example 1
First, cobalt nitrate hexahydrate (Wako) was prepared to prepare a nitrate to be used as a sintering aid, and was dissolved in a solvent made of commercially available ethanol that had not been subjected to any particular dehydration treatment to prepare a nitrate solution (step S01 in FIG. 2). Here, this dissolution was carried out at room temperature in the air.
Next, a commercially available LATP powder (TOSHIMA) having a NASICON structure was prepared as a solid electrolyte base material, and dispersed and stirred in a nitrate solution under ultrasonic application to prepare a dispersion liquid (slurry) (step S02). The environment was atmospheric pressure and room temperature. Here, the amount of LATP was set to an amount that would result in a solid content concentration of 15 vol% relative to the ethanol solvent, and the amount of cobalt nitrate hexahydrate was weighed using an electronic balance so that the weight ratio of Co to the weight of LATP was 0.1 to 2.0 wt% (the molar ratio of Co to LATP was 0.006506 to 0.130123).
その後、得られたスラリーをディスポーサブル容器中に平坦、均一になるように拡げ、５０℃のオーブン中大気圧下で１時間の乾燥処理を行った（工程Ｓ０３）。乾燥試料はメノウ乳鉢で力をかけずにすり潰し、乾燥処理により生じた粗大固形物の解砕を行った。
しかる後、得られた解砕物であるＣｏが添加されたＬＡＴＰ(Ｃｏ－ＬＡＴＰ)を金型に充填し、プレスして、成型体を得た（工程Ｓ０４）。そのときの圧力は１００ＭＰａとし、３分大気圧下で圧力を印加した。
最後に、得られた成型体を大気圧の各温度（８００℃、１０００℃）で焼成して、焼結体を得た（工程Ｓ０５）。このとき、昇温速度１００℃／Ｈｒ、最大温度維持時間１０Ｈｒ、そして降温速度は１００℃／Ｈｒとした。
The obtained slurry was then spread evenly and flatly in a disposable container, and dried for 1 hour under atmospheric pressure in an oven at 50° C. (Step S03). The dried sample was ground in an agate mortar without applying force, and coarse solids generated by the drying process were crushed.
Thereafter, the resulting crushed LATP (Co-LATP) was filled into a metal mold and pressed to obtain a molded body (step S04). The pressure was set to 100 MPa, and pressure was applied for 3 minutes under atmospheric pressure.
Finally, the obtained molded body was sintered at various temperatures (800° C., 1000° C.) under atmospheric pressure to obtain a sintered body (step S05). At this time, the temperature increase rate was 100° C./Hr, the maximum temperature was maintained for 10 Hr, and the temperature decrease rate was 100° C./Hr.
パラメータをＣｏ添加量、焼結温度を８００℃と１０００℃の２水準としたときのＣｏ－ＬＡＴＰの相対密度の焼結温度依存性を図４に示す。ここで、相対密度の測定は、嵩密度(体積/重量)とした。なお、同図には焼結を行う前の相対密度も併せて示している（このデータは２５℃のところに表示している）。
８００℃の焼結温度において、Ｃｏを添加した全てのＬＡＴＰ焼結体は未添加のＬＡＴＰよりも高い相対密度になっており、Ｃｏの添加が相対密度改善に寄与していることがわかる。
The sintering temperature dependence of the relative density of Co-LATP is shown in Figure 4, where the parameter is the amount of Co added and the sintering temperature is set to two levels, 800°C and 1000°C. Here, the relative density was measured as bulk density (volume/weight). The figure also shows the relative density before sintering (this data is displayed at 25°C).
At a sintering temperature of 800° C., all of the LATP sintered bodies to which Co was added had a higher relative density than LATP to which no Co was added, indicating that the addition of Co contributed to improving the relative density.
図５は、焼結温度を８００℃として大気下で以上の工程により作製した焼結体(Ｃｏ－ＬＡＴＰ)の相対密度およびＣｏ添加量依存性を示す。Ｃｏを０．１ｗｔ％（ＬＡＴＰに対するモル比は０．００６５０６）添加することにより相対密度はＣｏを添加しない場合の約５９％より約２割向上して約７１％になり、Ｃｏを０．２ｗｔ％～２．０ｗｔ％（ＬＡＴＰに対するモル比０．０１３０１２～０．１３０１２３）添加することにより相対密度は７５％を超え、Ｃｏを０．３ｗｔ％（ＬＡＴＰに対するモル比０．０１９５１８）添加したときに相対密度が極大の約８０％になることがわかる。なお、Ｃｏを１０ｗｔ％（ＬＡＴＰに対するモル比０．６５０６１７）添加したときの相対密度は５４．５４％、焼結収縮率は－１０．２３％になった。Ｃｏを添加しないときの相対密度は５８．６３％、焼結収縮率は－６．８４％であり、１０ｗｔ％というような量が多いＣｏ添加は相対密度改善に有意な効果を生まなかった。 Figure 5 shows the relative density and the dependence of Co on the amount of added Co of the sintered body (Co-LATP) produced by the above process in air at a sintering temperature of 800°C. By adding 0.1 wt% Co (molar ratio to LATP: 0.006506), the relative density increases by about 20% from about 59% without Co to about 71%, and by adding 0.2 wt% to 2.0 wt% Co (molar ratio to LATP: 0.013012 to 0.130123), the relative density exceeds 75%, and when 0.3 wt% Co is added (molar ratio to LATP: 0.019518), the relative density reaches a maximum of about 80%. When 10 wt% Co is added (molar ratio to LATP: 0.650617), the relative density is 54.54% and the sintering shrinkage is -10.23%. When no Co was added, the relative density was 58.63% and the sintering shrinkage rate was -6.84%, and adding a large amount of Co, such as 10 wt%, did not have a significant effect on improving the relative density.
図６は、焼結の雰囲気が大気からＡｒガスに変わった以外は図５と同じ条件で作製した試料の相対密度とＣｏ添加量依存性を示す。酸素が介在しない焼結条件では、酸素が存在する焼結とは異なり、Ｃｏ添加による相対密度の向上は僅かなものにとどまっている。これは、相対密度向上のメカニズムにＣｏの酸化が大いに寄与していることを示している。焼結の環境として酸素が存在することが好ましいことがこの結果からわかる。 Figure 6 shows the relative density and the dependence on the amount of Co added for samples prepared under the same conditions as in Figure 5, except that the sintering atmosphere was changed from air to Ar gas. Under sintering conditions without oxygen, the improvement in relative density due to the addition of Co is only slight, unlike sintering in which oxygen is present. This shows that the oxidation of Co contributes greatly to the mechanism of the improvement in relative density. This result shows that the presence of oxygen is preferable as a sintering environment.
図７は、大気下８００℃で焼結したＣｏ未添加ＬＡＴＰの破断面組織のＳＥＭ写真であり、図８はＣｏを添加した以外同じ条件で焼結作成したＣｏ－ＬＡＴＰの破断面組織のＳＥＭ写真である。図７の（ａ）と（ｂ）は倍率が異なり、（ａ）は（ｂ）の１０倍の倍率で、図７（ａ）と図８は同じ倍率になっている。
この結果から、Ｃｏ未添加ＬＡＴＰよりもＣｏ添加ＬＡＴＰの粒子成長は促進されておらず、Ｃｏ添加により各粒子間のネック部の形成が認められた。
Figure 7 is an SEM photograph of the fracture surface structure of Co-free LATP sintered at 800°C in air, and Figure 8 is an SEM photograph of the fracture surface structure of Co-LATP sintered under the same conditions except for the addition of Co. Figures 7(a) and (b) are at different magnifications, with (a) being 10 times that of (b), and Figures 7(a) and 8 being at the same magnification.
From these results, it was found that the grain growth of the Co-added LATP was not promoted as much as that of the Co-free LATP, and the addition of Co caused the formation of necks between the grains.
図９は、大気下１０００℃で焼結したＣｏ－ＬＡＴＰの破断面組織ＳＥＭ写真である。図８に示した８００℃で焼結したＣｏ－ＬＡＴＰよりも焼結が進行し、緻密化している組織が観察された。 Figure 9 shows an SEM photograph of the fracture surface structure of Co-LATP sintered at 1000°C in air. Sintering has progressed more than in the Co-LATP sintered at 800°C shown in Figure 8, and a denser structure was observed.
図１０に大気下８００℃で焼結したＣｏ－ＬＡＴＰの電気伝導率測定結果を示す。
Ｃｏ添加量０．５ｗｔ％（ＬＡＴＰに対するモル比０．０３２５３１）までは添加量の増加に伴い電気伝導率が向上した。Ｃｏ添加量が１．０ｗｔ％（ＬＡＴＰに対するモル比０．０６５０６２）以上から電気伝導率は低下するが、Ｃｏ未添加の電気伝導率と同等かそれ以上の値であった。
Ｃｏ添加量が０．５ｗｔ％までは主に密度の向上が電気伝導率の向上に寄与しているものと考えられる。Ｃｏ添加量が１．０ｗｔ％以上では、不純物相の影響が顕著になるため、電気伝導率が減少に転じたものと考えられる。
FIG. 10 shows the results of measuring the electrical conductivity of Co-LATP sintered at 800° C. in air.
The electrical conductivity improved with increasing Co content up to 0.5 wt% (molar ratio to LATP: 0.032531). The electrical conductivity decreased when the Co content was 1.0 wt% or more (molar ratio to LATP: 0.065062), but was equal to or higher than the electrical conductivity without Co.
It is considered that the improvement in density mainly contributes to the improvement in electrical conductivity up to the Co content of 0.5 wt%. When the Co content is 1.0 wt% or more, the influence of the impurity phase becomes significant, and the electrical conductivity starts to decrease.
図１１に大気下１０００℃で焼結したＣｏ－ＬＡＴＰの電気伝導率測定結果を示す。
Ｃｏ添加量の増加に伴い電気伝導率は減少した。１０００℃ではＣｏ未添加のＬＡＴＰが十分に焼結する温度であり、全ての試料において、密度の差異よりＣｏ添加による不純物相の生成量の差異が電気伝導率に反映されていると考えられる。
FIG. 11 shows the results of measuring the electrical conductivity of Co-LATP sintered at 1000° C. in air.
The electrical conductivity decreased with an increase in the amount of Co added. At 1000°C, LATP without Co added is sufficiently sintered, and it is considered that the difference in the amount of impurity phase generated by the addition of Co is reflected in the electrical conductivity in all samples due to the difference in density.
本発明により、密度が高く電気伝導度に優れたＮＡＳＩＣＯＮ型ＬＴＰ固体電解質、その製造に好適な易焼結性の粉末、および正極活物質の拡散が十分抑えられる８００℃以下の焼結で、密度が高く電気伝導度に優れた易焼結性のＮＡＳＩＣＯＮ型ＬＴＰ固体電解質の製造方法が提供される。この固体電解質、その固体電解質製造用粉末および固体電解質の製造方法を用いれば、機械特性および電気特性が優れるリチウムイオン全固体二次電池を生産性良く低コストで供給できるため、民生、産業用途を問わず、産業に寄与すると考えられる。 The present invention provides a NASICON-type LTP solid electrolyte with high density and excellent electrical conductivity, an easily sinterable powder suitable for its production, and a method for producing an easily sinterable NASICON-type LTP solid electrolyte with high density and excellent electrical conductivity, which is sintered at 800°C or less, at which diffusion of the positive electrode active material is sufficiently suppressed. By using this solid electrolyte, the powder for producing the solid electrolyte, and the method for producing the solid electrolyte, lithium-ion all-solid-state secondary batteries with excellent mechanical and electrical properties can be supplied with good productivity and low cost, which is believed to contribute to industry regardless of whether it is for consumer or industrial use.
１：粉体
１１：固体電解質母材（ＬＡＴＰ）
１２：コバルト含有被覆材
２１：バルク部
２２：ネック部
１０１：焼結体
1: Powder 11: Solid electrolyte base material (LATP)
12: Cobalt-containing coating material 21: Bulk portion 22: Neck portion 101: Sintered body
Claims (18)
ネック部には酸化コバルトが存在する焼結体からなる、固体電解質であり、
前記ＮＡＳＩＣＯＮ型ＬＴＰに対するコバルト（Ｃｏ）の重量パーセント濃度は、０．１ｗｔ％以上０．５ｗｔ％以下である、固体電解質。 The bulk part is made of NASICON type LTP,
The neck portion is a solid electrolyte made of a sintered body containing cobalt oxide.
A solid electrolyte, wherein the weight percent concentration of cobalt (Co) relative to the NASICON-type LTP is 0.1 wt % or more and 0.5 wt % or less.
前記固体電解質母材はＮＡＳＩＣＯＮ型ＬＴＰからなり、
前記被覆材はコバルト（Ｃｏ）イオンを含み、
前記被覆材の厚さが原子層オーダーである、固体電解質製造用の粉末。 A powder comprising a solid electrolyte base material and a coating material covering a surface of the solid electrolyte base material,
The solid electrolyte base material is made of NASICON type LTP,
the coating material includes cobalt (Co) ions;
The powder for producing a solid electrolyte, wherein the coating material has a thickness on the order of an atomic layer.
ＮＡＳＩＣＯＮ型ＬＴＰからなる固体電解質母材を前記溶液に投入、分散させた分散液（スラリー）を作製することと、
前記分散液を乾燥させて固形物を得ることと、
前記固形物を解砕してコバルトイオンを含有する粉体を得ることと、
前記粉体を成型して成型体を得ることと、
前記成型体を酸素が存在する環境下で焼結する、固体電解質の製造方法。 dissolving a cobalt salt in a solvent capable of forming an azeotrope with water to form a solution;
A solid electrolyte base material made of NASICON type LTP is put into the solution and dispersed to prepare a dispersion (slurry);
drying the dispersion to obtain a solid;
pulverizing the solid material to obtain a powder containing cobalt ions;
Molding the powder to obtain a molded body;
The molded body is sintered in an environment in which oxygen is present.
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