JP2021136198A - Positive electrode layer used for lithium ion secondary battery, and lithium ion secondary battery - Google Patents
Positive electrode layer used for lithium ion secondary battery, and lithium ion secondary battery Download PDFInfo
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 79
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 79
- 239000002245 particle Substances 0.000 claims abstract description 251
- 239000007784 solid electrolyte Substances 0.000 claims abstract description 102
- 239000007774 positive electrode material Substances 0.000 claims abstract description 73
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 claims description 60
- 229910052731 fluorine Inorganic materials 0.000 claims description 60
- 239000011737 fluorine Substances 0.000 claims description 60
- QLOAVXSYZAJECW-UHFFFAOYSA-N methane;molecular fluorine Chemical compound C.FF QLOAVXSYZAJECW-UHFFFAOYSA-N 0.000 claims description 8
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 claims description 7
- 239000002482 conductive additive Substances 0.000 claims description 2
- 239000007789 gas Substances 0.000 description 50
- 238000000034 method Methods 0.000 description 44
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 29
- 239000000463 material Substances 0.000 description 19
- 229910052799 carbon Inorganic materials 0.000 description 16
- 239000012752 auxiliary agent Substances 0.000 description 15
- 238000003682 fluorination reaction Methods 0.000 description 13
- 239000000843 powder Substances 0.000 description 13
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- 229910020731 Li0.35La0.55TiO3 Inorganic materials 0.000 description 10
- 229910052751 metal Inorganic materials 0.000 description 10
- 229910012851 LiCoO 2 Inorganic materials 0.000 description 9
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 9
- 229910052744 lithium Inorganic materials 0.000 description 9
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- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 229910018133 Li 2 S-SiS 2 Inorganic materials 0.000 description 2
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- 229910000625 lithium cobalt oxide Inorganic materials 0.000 description 2
- HSZCZNFXUDYRKD-UHFFFAOYSA-M lithium iodide Chemical compound [Li+].[I-] HSZCZNFXUDYRKD-UHFFFAOYSA-M 0.000 description 2
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 description 2
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical compound [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 description 2
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- 229910052715 tantalum Inorganic materials 0.000 description 2
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- 229910052720 vanadium Inorganic materials 0.000 description 2
- 229910052727 yttrium Inorganic materials 0.000 description 2
- AIFLGMNWQFPTAJ-UHFFFAOYSA-J 2-hydroxypropanoate;titanium(4+) Chemical compound [Ti+4].CC(O)C([O-])=O.CC(O)C([O-])=O.CC(O)C([O-])=O.CC(O)C([O-])=O AIFLGMNWQFPTAJ-UHFFFAOYSA-J 0.000 description 1
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- 239000005279 LLTO - Lithium Lanthanum Titanium Oxide Substances 0.000 description 1
- 241001175904 Labeo bata Species 0.000 description 1
- 229910014689 LiMnO Inorganic materials 0.000 description 1
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- OPLYJBURBHOMOC-UHFFFAOYSA-N acetic acid;lanthanum Chemical compound [La].CC(O)=O OPLYJBURBHOMOC-UHFFFAOYSA-N 0.000 description 1
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- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 description 1
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- 229910052738 indium Inorganic materials 0.000 description 1
- AMGQUBHHOARCQH-UHFFFAOYSA-N indium;oxotin Chemical compound [In].[Sn]=O AMGQUBHHOARCQH-UHFFFAOYSA-N 0.000 description 1
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- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 1
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- 229910000664 lithium aluminum titanium phosphates (LATP) Inorganic materials 0.000 description 1
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 description 1
- FRMOHNDAXZZWQI-UHFFFAOYSA-N lithium manganese(2+) nickel(2+) oxygen(2-) Chemical compound [O-2].[Mn+2].[Ni+2].[Li+] FRMOHNDAXZZWQI-UHFFFAOYSA-N 0.000 description 1
- IDBFBDSKYCUNPW-UHFFFAOYSA-N lithium nitride Chemical compound [Li]N([Li])[Li] IDBFBDSKYCUNPW-UHFFFAOYSA-N 0.000 description 1
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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
Abstract
Description
本発明はリチウムイオン二次電池に用いられる正極層及びリチウムイオン二次電池に関する。 The present invention relates to a positive electrode layer and a lithium ion secondary battery used in a lithium ion secondary battery.
リチウムイオン二次電池は、携帯電話やノート型パソコン等の携帯型電子機器や自動車等に広く用いられている。
近年、このような携帯型電子機器や車載用のリチウムイオン二次電池として小型化・軽量化が求められ、単位質量あたりの放電容量、サイクル特性、レート特性、及び電池としての安定性等の更なる性能向上が望まれている。
Lithium-ion secondary batteries are widely used in portable electronic devices such as mobile phones and notebook computers, automobiles, and the like.
In recent years, miniaturization and weight reduction have been required for such portable electronic devices and lithium-ion secondary batteries for automobiles, and the discharge capacity per unit mass, cycle characteristics, rate characteristics, stability as a battery, etc. have been improved. Performance improvement is desired.
従来、リチウムイオン二次電池においては液体の電解質が使用されてきたが、安全性の向上や高速充放電が期待できる点から、固体電解質をリチウムイオン二次電池の電解質として用いる全固体型リチウムイオン二次電池が注目されている。 Conventionally, liquid electrolytes have been used in lithium-ion secondary batteries, but all-solid-state lithium ions that use solid electrolytes as electrolytes in lithium-ion secondary batteries can be expected to improve safety and charge / discharge at high speed. Secondary batteries are attracting attention.
全固体型リチウムイオン二次電池用の正極層としては、例えば正極活物質、固体電解質及び導電助剤等を含有し、シート状等に加工された正極層を使用できる。 As the positive electrode layer for the all-solid-state lithium ion secondary battery, for example, a positive electrode layer containing a positive electrode active material, a solid electrolyte, a conductive auxiliary agent, or the like and processed into a sheet shape or the like can be used.
例えば、特許文献１においては、少なくとも正極活物質を含有する層であり、必要に応じて、固体電解質材料、導電化材および結着材の少なくとも一つを含有する正極層について記載されている。 For example, Patent Document 1 describes a positive electrode layer that is a layer containing at least a positive electrode active material and, if necessary, contains at least one of a solid electrolyte material, a conductive material, and a binder.
しかしながら、このような正極層を用いた全固体型リチウムイオン二次電池においては、液体の電解質を用いる場合に比べ、正極層中の粒子同士の界面における抵抗により、リチウムイオン伝導が抑制されやすいという課題がある。これは、正極層中の粒子間に浸透する液体電解質を用いる場合と比較して、正極層が含有する粒子同士の接触界面が小さくなりやすいためと考えられる。このような粒子同士の界面の抵抗により、正極層のリチウムイオン伝導度が低下し、リチウムイオン二次電池の特性を低下させてしまうという問題がある。 However, in an all-solid-state lithium-ion secondary battery using such a positive electrode layer, lithium ion conduction is more likely to be suppressed due to resistance at the interface between particles in the positive electrode layer, as compared with the case of using a liquid electrolyte. There are challenges. It is considered that this is because the contact interface between the particles contained in the positive electrode layer tends to be smaller than that in the case of using the liquid electrolyte that permeates between the particles in the positive electrode layer. Due to the resistance at the interface between the particles, there is a problem that the lithium ion conductivity of the positive electrode layer is lowered and the characteristics of the lithium ion secondary battery are lowered.
そこで本発明は、電池特性が向上するリチウムイオン二次電池用の正極層を提供することを目的とする。具体的には、正極層中の粒子同士のリチウムイオンの伝導経路を確保し、リチウムイオン伝導性を向上することを目的とする。 Therefore, an object of the present invention is to provide a positive electrode layer for a lithium ion secondary battery having improved battery characteristics. Specifically, it is an object of securing a conduction path of lithium ions between particles in the positive electrode layer and improving lithium ion conductivity.
本発明者らは、鋭意検討を重ねた結果、正極層が、表面がフッ素化された正極活物質粒子又は表面がフッ素化された固体電解質粒子を含むことにより、上記課題を解決できることを見出し、本発明を完成させた。 As a result of diligent studies, the present inventors have found that the above problems can be solved by including positive electrode active material particles having a fluorinated surface or solid electrolyte particles having a fluorinated surface. The present invention has been completed.
すなわち、本発明は、下記［１］〜［６］に関するものである。
［１］正極活物質粒子、固体電解質粒子、及び導電助剤を含む正極層であって、
前記正極活物質粒子および前記固体電解質粒子の少なくとも一方が表面にフッ素化された層を有する、
リチウムイオン二次電池用正極層。
［２］前記固体電解質粒子が表面にフッ素化された層を有し、前記フッ素化された層の最表面におけるフッ素の含有量が９５質量％以上である、［１］に記載のリチウムイオン二次電池用正極層。
［３］前記固体電解質粒子が、硫化物系固体電解質粒子及び酸化物系固体電解質粒子の少なくとも一方を含む、［１］または［２］に記載のリチウムイオン二次電池用正極層。
［４］前記固体電解質粒子の平均粒径が０．０１〜３０μｍである、［１］〜［３］のいずれか１に記載のリチウムイオン二次電池用正極層。
［５］前記正極活物質粒子が表面にフッ素化された層を有し、前記正極活物質粒子における前記フッ素化された層がフッ素化されたカーボン粒子からなる、［１］〜［４］のいずれか１に記載のリチウムイオン二次電池用正極層。
［６］［１］〜［５］のいずれか１に記載の正極層を含む正極と、固体電解質層と、負極と、を含む、リチウムイオン二次電池。
That is, the present invention relates to the following [1] to [6].
[1] A positive electrode layer containing positive electrode active material particles, solid electrolyte particles, and a conductive additive.
At least one of the positive electrode active material particles and the solid electrolyte particles has a fluorinated layer on the surface.
Positive electrode layer for lithium ion secondary batteries.
[2] The lithium ion rechargeable battery according to [1], wherein the solid electrolyte particles have a fluorinated layer on the surface, and the fluorine content on the outermost surface of the fluorinated layer is 95% by mass or more. Positive electrode layer for next battery.
[3] The positive electrode layer for a lithium ion secondary battery according to [1] or [2], wherein the solid electrolyte particles contain at least one of a sulfide-based solid electrolyte particle and an oxide-based solid electrolyte particle.
[4] The positive electrode layer for a lithium ion secondary battery according to any one of [1] to [3], wherein the solid electrolyte particles have an average particle size of 0.01 to 30 μm.
[5] Of [1] to [4], wherein the positive electrode active material particles have a fluorinated layer on the surface, and the fluorinated layer in the positive electrode active material particles is composed of fluorinated carbon particles. The positive electrode layer for a lithium ion secondary battery according to any one.
[6] A lithium ion secondary battery including a positive electrode including the positive electrode layer according to any one of [1] to [5], a solid electrolyte layer, and a negative electrode.
本発明に係る正極層によれば、当該正極層に含まれる正極活物質粒子および固体電解質粒子の少なくとも一方の表面がフッ素化されていることにより、正極層のイオン伝導性を向上でき、リチウムイオン二次電池における電池特性を向上できる。 According to the positive electrode layer according to the present invention, since at least one surface of the positive electrode active material particles and the solid electrolyte particles contained in the positive electrode layer is fluorinated, the ionic conductivity of the positive electrode layer can be improved, and lithium ions can be obtained. The battery characteristics of the secondary battery can be improved.
以下、本発明を詳細に説明するが、本発明は以下の実施形態に限定されるものではなく、本発明の要旨を逸脱しない範囲において、任意に変形して実施できる。また、数値範囲を示す「〜」とは、その前後に記載された数値を下限値及び上限値として含む意味で使用される。 Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following embodiments, and can be arbitrarily modified and carried out without departing from the gist of the present invention. Further, "~" indicating a numerical range is used to mean that the numerical values described before and after the numerical range are included as the lower limit value and the upper limit value.
＜正極層＞
本実施形態に係る正極層は、リチウムイオン二次電池に用いられる。本実施形態に係る正極層は正極活物質粒子、固体電解質粒子、及び導電助剤を含み、正極活物質粒子および固体電解質粒子の少なくとも一方が表面にフッ素化された層を有する。
<Positive layer>
The positive electrode layer according to this embodiment is used for a lithium ion secondary battery. The positive electrode layer according to the present embodiment includes positive electrode active material particles, solid electrolyte particles, and a conductive auxiliary agent, and has a layer in which at least one of the positive electrode active material particles and the solid electrolyte particles is fluorinated on the surface.
（正極活物質粒子）
正極活物質粒子は、リチウムイオンの吸蔵及び放出、言い換えるとリチウムイオンの脱離及び挿入（インターカレーション）、又は、該リチウムイオンとそのカウンターアニオン（例えば、ＰＦ６−）のドープ及び脱ドープを可逆的に進行できる正極活物質を含む粒子であればよい。正極活物質としては特に限定されず、公知の正極活物質を使用できる。
(Positive electrode active material particles)
The positive electrode active material particles are occluded and released of lithium ions, in other words, desorption and insertion (intercalation) of lithium ions, or doping and dedoping of the lithium ions and their counter anions (for example, PF 6-). Any particles containing a positive electrode active material that can proceed reversibly may be used. The positive electrode active material is not particularly limited, and a known positive electrode active material can be used.
正極活物質としては、例えば、コバルト酸リチウム（ＬｉＣｏＯ２）、ニッケル酸リチウム（ＬｉＮｉＯ２）、マンガン酸リチウム（ＬｉＭｎＯ２）、ニッケルマンガン酸リチウム、Ｌｉ（ＮｉｘＣｏｙＭｎｚＭａ）Ｏ２（ｘ＋ｙ＋ｚ＋ａ＝１、０≦ｘ≦１、０≦ｙ≦１、０≦ｚ≦１、０≦ａ≦１であり、ＭはＡｌ、Ｍｇ、Ｎｂ、Ｔｉ、Ｃｕ、Ｚｎ、Ｃｒから選択される少なくとも一種）で表される複合金属酸化物、ＬｉａＭｂ（ＰＯ４）ｃ（１≦ａ≦４、１≦ｂ≦２、１≦ｃ≦３であり、ＭはＦｅ、Ｖ、Ｃｏ、Ｍｎ、Ｎｉ、ＶＯから選択される少なくとも一種）で表されるポリアニオンオリビン型正極、ポリアセチレン、ポリアニリン、ポリピロール、ポリチオフェン、及びポリアセン等が挙げられる。これらは単独で用いてもよいし、複数種を組み合わせて用いてもよい。 As the positive electrode active material, for example, lithium cobalt oxide (LiCoO 2), lithium nickelate (LiNiO 2), lithium manganate (LiMnO 2), lithium nickel manganese oxide, Li (Ni x Co y Mn z M a) O 2 (X + y + z + a = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ a ≦ 1, and M is selected from Al, Mg, Nb, Ti, Cu, Zn, and Cr. A composite metal oxide represented by (at least one kind), Li a M b (PO 4 ) c (1 ≦ a ≦ 4, 1 ≦ b ≦ 2, 1 ≦ c ≦ 3, where M is Fe, V, Co, Examples thereof include a polyanion olivine type positive electrode represented by (at least one selected from Mn, Ni, and VO), polyacetylene, polyaniline, polypyrrole, polythiophene, and polyacene. These may be used alone or in combination of a plurality of types.
正極活物質粒子の平均粒径は、正極層中におけるリチウムイオン伝導性と電子伝導性を確保する観点から０．０１μｍ以上が好ましく、０．０２μｍ以上がより好ましく、０．０５μｍ以上がさらに好ましい。また、正極活物質粒子の平均粒径は正極層中の形成しやすさの観点から３０μｍ以下が好ましく、２０μｍ以下がより好ましく、１０μｍ以下がさらに好ましい。 The average particle size of the positive electrode active material particles is preferably 0.01 μm or more, more preferably 0.02 μm or more, still more preferably 0.05 μm or more, from the viewpoint of ensuring lithium ion conductivity and electron conductivity in the positive electrode layer. The average particle size of the positive electrode active material particles is preferably 30 μm or less, more preferably 20 μm or less, still more preferably 10 μm or less, from the viewpoint of ease of formation in the positive electrode layer.
正極活物質粒子の平均粒径は、例えば、粒径分布測定装置により求められる。なお、後述するように正極活物質粒子がフッ素化された層を有する場合は、フッ素化された層の厚みも含む径を粒径として測定する。粒子の平均粒径としては、通常、Ｄ５０平均粒径（メジアン径：頻度の累積が５０％になる粒子径）を採用できる。 The average particle size of the positive electrode active material particles is determined by, for example, a particle size distribution measuring device. When the positive electrode active material particles have a fluorinated layer as described later, the diameter including the thickness of the fluorinated layer is measured as the particle size. As the average particle size of the particles, a D50 average particle size (median diameter: particle size at which the cumulative frequency becomes 50%) can be usually adopted.
具体的には、粒子を水中または有機溶剤中に超音波処理によって充分に分散させ、レーザ回折／散乱式粒子径分布測定装置にて粒子の測定を行う。頻度分布および累積体積分布曲線を得ることで体積基準の粒度分布を得、累積体積分布曲線において５０％となる点の粒子径をＤ５０平均粒径と定義する。
また、正極層を形成した後に、正極層を割断しその断面におけるＳＥＭ観察から、正極活物質の粒径を測定することもできる。
Specifically, the particles are sufficiently dispersed in water or an organic solvent by ultrasonic treatment, and the particles are measured by a laser diffraction / scattering type particle size distribution measuring device. A volume-based particle size distribution is obtained by obtaining a frequency distribution and a cumulative volume distribution curve, and the particle size at a point of 50% in the cumulative volume distribution curve is defined as the D50 average particle size.
Further, after forming the positive electrode layer, the positive electrode layer can be cut and the particle size of the positive electrode active material can be measured from the SEM observation in the cross section thereof.
本実施形態に係る正極層において、正極活物質粒子の含有量は、充放電容量を高める観点から５０質量％以上が好ましく、６０質量％以上がより好ましく、７０質量％以上がさらに好ましい。また、正極活物質粒子の含有量は、正極層におけるリチウムイオン伝導性、電子伝導性確保の観点から９９質量％以下が好ましく、９７質量％以下がより好ましく、９５質量％以下がさらに好ましい。
本実施形態に係る正極層において、正極活物質粒子の含有量は、例えば、正極層形成前の正極層形成のスラリー調製時の正極活物質配合比率により測定できる。具体的には、正極活物質粒子の重量測定を行う。また、正極層形成後における正極活物質粒子の含有量については、正極層を割断し、その断面からＳＥＭ／ＥＤＸ分析で元素分析を行うことで一定の定量性をもって正極活物質粒子の含有量を測定できる。
In the positive electrode layer according to the present embodiment, the content of the positive electrode active material particles is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, from the viewpoint of increasing the charge / discharge capacity. The content of the positive electrode active material particles is preferably 99% by mass or less, more preferably 97% by mass or less, still more preferably 95% by mass or less, from the viewpoint of ensuring lithium ion conductivity and electron conductivity in the positive electrode layer.
In the positive electrode layer according to the present embodiment, the content of the positive electrode active material particles can be measured by, for example, the mixing ratio of the positive electrode active material at the time of preparing the slurry for forming the positive electrode layer before forming the positive electrode layer. Specifically, the weight of the positive electrode active material particles is measured. Regarding the content of the positive electrode active material particles after the formation of the positive electrode layer, the content of the positive electrode active material particles is determined with a certain quantitativeness by dividing the positive electrode layer and performing elemental analysis by SEM / EDX analysis from the cross section thereof. Can be measured.
（固体電解質粒子）
本実施形態に係る正極層は固体電解質粒子を含む。本実施形態に係る正極層を用いたリチウムイオン二次電池において、正極活物質粒子が吸蔵及び放出するリチウムイオンは、正極層が含む固体電解質粒子を介して正極層中および正極層と固体電解質層との間を移動できる。
(Solid electrolyte particles)
The positive electrode layer according to this embodiment contains solid electrolyte particles. In the lithium ion secondary battery using the positive electrode layer according to the present embodiment, the lithium ions stored and released by the positive electrode active material particles are contained in the positive electrode layer and in the positive electrode layer and the solid electrolyte layer via the solid electrolyte particles contained in the positive electrode layer. You can move between.
固体電解質粒子は、リチウムイオン伝導性を有する固体電解質を含む粒子であれば特に限定されず、公知の固体電解質を使用できる。固体電解質としては、例えば、硫化物系固体電解質、酸化物系固体電解質、窒化リチウム、及びヨウ化リチウム等の無機固体電解質等が挙げられる。これらの固体電解質は単独で用いてもよいし、複数種を組み合わせて用いてもよい。なかでも、リチウムイオン伝導性の観点から、リチウムイオン伝導性に優れる硫化物系固体電解質及び酸化物系固体電解質の少なくとも一方を好ましく使用できる。 The solid electrolyte particles are not particularly limited as long as they are particles containing a solid electrolyte having lithium ion conductivity, and known solid electrolytes can be used. Examples of the solid electrolyte include sulfide-based solid electrolytes, oxide-based solid electrolytes, lithium nitride, and inorganic solid electrolytes such as lithium iodide. These solid electrolytes may be used alone or in combination of two or more. Among them, at least one of a sulfide-based solid electrolyte and an oxide-based solid electrolyte having excellent lithium ion conductivity can be preferably used from the viewpoint of lithium ion conductivity.
硫化物系固体電解質は、硫化物系であれば特に限定されず、硫黄（Ｓ）を含有し、かつリチウムイオン伝導性を有するものを好適に使用できる。硫化物系固体電解質としては、例えば、Ｌｉ２Ｓ−ＳｉＳ２系固体電解質が挙げられる。Ｌｉ２Ｓ−ＳｉＳ２系固体電解質は一般に、１０−４Ｓ／ｃｍオーダーのリチウムイオン伝導率を有する。硫化物系固体電解質としては、他にもＰ２Ｓ５−Ｌｉ２Ｓ系、Ｂ２Ｓ３−Ｌｉ２Ｓ系、Ｂ２Ｓ３−Ｌｉ２Ｓ系、ＧｅＳ２−Ｌｉ２Ｓ系などが挙げられる。これらは単独で用いてもよいし、複数種を組み合わせて用いてもよい。 The sulfide-based solid electrolyte is not particularly limited as long as it is a sulfide-based electrolyte, and those containing sulfur (S) and having lithium ion conductivity can be preferably used. The sulfide-based solid electrolyte, for example, Li 2 S-SiS 2 system solid electrolyte. Li 2 S-SiS 2 system solid electrolyte generally has a lithium ion conductivity of 10 -4 S / cm order. Other sulfide-based solid electrolytes include P 2 S 5- Li 2 S series, B 2 S 3- Li 2 S series, B 2 S 3- Li 2 S series, and GeS 2- Li 2 S series. Can be mentioned. These may be used alone or in combination of a plurality of types.
酸化物系固体電解質は、酸化物系であれば特に限定されず、酸素（Ｏ）を含有し、かつリチウムイオン伝導性を有するものを好適に使用できる。例えば、リチウムを含むペロブスカイト型酸化物、リチウムを含むガーネット型酸化物、リン酸リチウム（Ｌｉ３ＰＯ４）、ニオブ酸リチウム（ＬｉＮｂＯ３）、ＮＡＳＩＣＯＮ構造のＬＡＧＰ（Ｌｉ１＋ｘＡｌｘＧｅ２−ｘ（ＰＯ４）３（０≦ｘ≦１））、ＮＡＳＩＣＯＮ構造のＬＡＴＰ（Ｌｉ１＋ｘＡｌｘＴｉ２−ｘ（ＰＯ４）３（０≦ｘ≦１））、ＮＡＳＩＣＯＮ構造のＬＺＰ（Ｌｉ１＋４ｘＺｒ２−ｘ（ＰＯ４）３（０≦ｘ≦０．４、ＬＺＰの一部の金属元素が別の金属元素で置き換わっていてもよく、別の金属元素をドーピングしていてもよい。別の金属元素としては、Ｎａ、Ｓｒ、Ｃａ、Ｍｇ、Ｌａ、Ｙ、Ｓｃ、Ｃｅ、Ｉｎ、Ａｌ、Ｇｅ、Ｔｉ、Ｖなどが挙げられる。）等が挙げられる。これらは単独で用いてもよいし、複数種を組み合わせて用いてもよい。 The oxide-based solid electrolyte is not particularly limited as long as it is an oxide-based solid electrolyte, and those containing oxygen (O) and having lithium ion conductivity can be preferably used. For example, perovskite-type oxide containing lithium, garnet-type oxide containing lithium, lithium phosphate (Li 3 PO 4 ), lithium niobate (LiNbO 3 ), LAGP (Li 1 + x Al x Ge 2-x ) having a NASICON structure ( PO 4 ) 3 (0 ≦ x ≦ 1)), LATP with NASICON structure (Li 1 + x Al x Ti 2-x (PO 4 ) 3 (0 ≦ x ≦ 1)), LZP with NASICON structure (Li 1 + 4 x Zr 2-) x (PO 4 ) 3 (0 ≦ x ≦ 0.4, some metal elements of LZP may be replaced with another metal element, or another metal element may be doped. Another metal element. Examples thereof include Na, Sr, Ca, Mg, La, Y, Sc, Ce, In, Al, Ge, Ti, V and the like.) These may be used alone or in plurality. Seeds may be used in combination.
リチウムを含むペロブスカイト型酸化物は、ペロブスカイト型結晶構造を持つＡＢＯ３で表される酸化物であり、Ａサイトが、Ｌａ、Ｓｒ、Ｂａ、Ｎａ、Ｃａ及びＮｄよりなる群から選択される少なくとも１種の元素と、Ｌｉを含み、Ｂサイトが、Ｔｉ、Ｔａ、Ｃｒ、Ｆｅ、Ｃｏ、Ｇａ及びＮｂよりなる群から選択される少なくとも１種の元素を含むことが好ましい。具体的には、ペロブスカイト型酸化物として、チタン酸リチウムランタンＬｉ３ｘＬａ２／３−ｘＴｉＯ３（０≦ｘ≦１／６、ＬＬＴＯとも呼ばれる）、ニオブ酸リチウムランタン（ＬｉｘＬａ（１−ｘ）／３ＮｂＯ３）（０≦ｘ≦１）、等が挙げられる。なお、チタン酸リチウムランタンを構成する元素の一部が別の元素に置き換わっていてもよく、別の元素をドーピングしていてもよい。別の元素としては、Ｎａ、Ｋ、Ｒｂ、Ａｇ、Ｔｌ、Ｍｇ、Ｓｒ、Ｃａ、Ｂａ、Ｎｂ、Ｔａ、Ｗ、Ｒｕ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ａｌ、Ｇａ、Ｓｉ、Ｇｅ、Ｚｒ、Ｈｆ、Ｐｒ、Ｎｄ、Ｓｍ、Ｇｄ、Ｄｙ、Ｙ、Ｅｕ、Ｔｂ等が挙げられ、具体的には、Ｌａ（２／３）−ｘＳｒｘＬｉｘＴｉＯ３、ＬｉｘＬａ２／３Ｔｉ１−ｘＡｌｘＯ３等が挙げられる。 The perovskite-type oxide containing lithium is an oxide represented by ABO 3 having a perovskite-type crystal structure, and the A site is at least one selected from the group consisting of La, Sr, Ba, Na, Ca and Nd. It is preferable that the element of the seed and Li are contained, and the B site contains at least one element selected from the group consisting of Ti, Ta, Cr, Fe, Co, Ga and Nb. Specifically, as perovskite-type oxides, lithium titanate Li 3 x La 2 / 3-x TiO 3 (0 ≦ x ≦ 1/6, also called LLTO), lithium niobate lantern (Li x La (1-)). x) / 3 NbO 3 ) (0 ≦ x ≦ 1), and the like. A part of the elements constituting lithium titanate lanthanum may be replaced with another element, or another element may be doped. Other elements include Na, K, Rb, Ag, Tl, Mg, Sr, Ca, Ba, Nb, Ta, W, Ru, Cr, Mn, Fe, Co, Al, Ga, Si, Ge, Zr, Examples thereof include Hf, Pr, Nd, Sm, Gd, Dy, Y, Eu, Tb, etc. Specifically, La (2/3) -x Sr x Li x TiO 3 , Li x La 2/3 Ti 1 -X Al x O 3 and the like can be mentioned.
ガーネット型酸化物としては、例えば、Ｌｉ７Ｌａ３Ｚｒ２Ｏ１２、Ｌｉ５Ｌａ３Ｎｂ２Ｏ１２、Ｌｉ５Ｌａ３Ｔａ２Ｏ１２、及びＬｉ６Ｌａ２ＢａＴａ２Ｏ１２等が挙げられる。 Examples of the garnet-type oxide include Li 7 La 3 Zr 2 O 12 , Li 5 La 3 Nb 2 O 12 , Li 5 La 3 Ta 2 O 12 , and Li 6 La 2 BaTa 2 O 12 .
なお、酸化物系固体電解質は結晶材料に限定されず、アモルファスの材料であってもよい。例えば、酸化物系固体電解質はアモルファス材料としてＬｉ４ＳｉＯ４、Ｌｉ３ＰＯ４、Ｌｉ３ＢＯ３、ＳｉＯ２、Ｂ２Ｏ３等と複合化されていてもよい。 The oxide-based solid electrolyte is not limited to the crystalline material, and may be an amorphous material. For example, the oxide-based solid electrolyte may be composited with Li 4 SiO 4 , Li 3 PO 4 , Li 3 BO 3 , SiO 2 , B 2 O 3, etc. as an amorphous material.
固体電解質粒子の平均粒径は、０．０１μｍ以上が好ましく、０．０２μｍ以上がより好ましく、０．０３μｍ以上がさらに好ましい。また、固体電解質粒子の平均粒径は３０μｍ以下が好ましく、２０μｍ以下がより好ましく、１０μｍ以下がさらに好ましい。固体電解質粒子の平均粒径が上記範囲であると、固体電解質粒子の粒径が正極活物質粒子の粒径に対して適度に小さいため、固体電解質粒子が正極活物質粒子の周囲をより密着して覆いやすくなる。これにより、正極活物質粒子の周囲において、正極活物質粒子と固体電解質粒子との間のリチウムイオン伝導経路を確保しやすくなる。固体電解質粒子の平均粒径は、上述した正極活物質粒子の場合と同様の方法で測定できる。 The average particle size of the solid electrolyte particles is preferably 0.01 μm or more, more preferably 0.02 μm or more, still more preferably 0.03 μm or more. The average particle size of the solid electrolyte particles is preferably 30 μm or less, more preferably 20 μm or less, still more preferably 10 μm or less. When the average particle size of the solid electrolyte particles is in the above range, the particle size of the solid electrolyte particles is appropriately smaller than the particle size of the positive electrode active material particles, so that the solid electrolyte particles are more closely attached to the periphery of the positive electrode active material particles. It becomes easy to cover. This makes it easier to secure a lithium ion conduction path between the positive electrode active material particles and the solid electrolyte particles around the positive electrode active material particles. The average particle size of the solid electrolyte particles can be measured by the same method as in the case of the positive electrode active material particles described above.
本実施形態に係る正極層において、固体電解質粒子の含有量は、正極層にリチウムイオン伝導性を付与し優れた充放電容量を得るため、１質量％以上が好ましく、２質量％以上がより好ましく、３質量％以上がさらに好ましい。また、固体電解質粒子の含有量は、正極層において正極活物質を多く用いて高容量とするため３０質量％以下が好ましく、２５質量％以下がより好ましく、２０質量％以下がさらに好ましい。固体電解質粒子の含有量は、上述した正極活物質粒子の場合と同様の方法で測定できる。 In the positive electrode layer according to the present embodiment, the content of the solid electrolyte particles is preferably 1% by mass or more, more preferably 2% by mass or more, in order to impart lithium ion conductivity to the positive electrode layer and obtain an excellent charge / discharge capacity. 3, 3% by mass or more is more preferable. The content of the solid electrolyte particles is preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass or less, because a large amount of the positive electrode active material is used in the positive electrode layer to increase the capacity. The content of the solid electrolyte particles can be measured by the same method as in the case of the positive electrode active material particles described above.
（フッ素化された層）
本実施形態に係る正極層は、正極活物質粒子および固体電解質粒子の少なくとも一方が表面にフッ素化された層を有する。ここで、上記少なくとも一方の粒子について、正極層中の該粒子の全てがフッ素化された層を有してもよいし、フッ素化された層を有しない粒子が含まれていてもよい。また、正極活物質粒子および固体電解質粒子の両方が、表面にフッ素化された層を有していてもよい。
(Fluorinated layer)
The positive electrode layer according to the present embodiment has a layer in which at least one of the positive electrode active material particles and the solid electrolyte particles is fluorinated on the surface. Here, for at least one of the above particles, all of the particles in the positive electrode layer may have a fluorinated layer, or may include particles that do not have a fluorinated layer. Further, both the positive electrode active material particles and the solid electrolyte particles may have a fluorinated layer on the surface.
正極層に含まれる正極活物質粒子および固体電解質粒子の少なくとも一方の表面がフッ素化されていることにより、これらの粒子同士の界面の抵抗（以下、粒界抵抗ともいう）を低減できる。その結果、正極層が含む粒子同士の界面におけるリチウムイオンの伝導経路を確保でき、正極層のリチウムイオン伝導性を向上できる。 Since at least one surface of the positive electrode active material particles and the solid electrolyte particles contained in the positive electrode layer is fluorinated, the resistance at the interface between these particles (hereinafter, also referred to as grain boundary resistance) can be reduced. As a result, the conduction path of lithium ions at the interface between the particles contained in the positive electrode layer can be secured, and the lithium ion conductivity of the positive electrode layer can be improved.
正極活物質粒子および固体電解質粒子の少なくとも一方の表面がフッ素化されていることにより、粒界抵抗を低減できる理由については明らかではないが、以下のように推測される。
すなわち、かかる粒子の表面がフッ素化されることにより、粒子表面は低融点化される。これらの粒子を含む材料に対して熱処理を行い、シート状の正極層を形成する際に、フッ素化された層を有する粒子の表面が容易に溶解することで、フッ素化された層を有する粒子と、それと隣り合う粒子との粒子界面において、粒子同士の密着性が良好となる。その結果、正極層中の粒子同士の粒界抵抗が低減されリチウムイオン伝導性が向上するものと推察される。
あるいは、フッ素化により粒子表面が安定化されつつ、電気陰性度の大きなフッ素の存在に伴って粒子表面が分極し、リチウムイオンとの相互作用により、フッ素化された層を有する粒子と周囲の粒子との界面における粒界抵抗が小さくなる。これにより、良好なリチウムイオン伝導経路が形成される可能性も考えられる。
また、正極活物質粒子の表面においては、正極活物質を構成する酸素原子が欠け、格子欠陥が生じている場合がある。このとき、フッ素化された層が含有するフッ素原子により格子欠陥が埋められると、正極活物質のリチウムイオンに対する拘束力が弱まり、リチウムイオンが移動しやすくなることも考えられる。
It is not clear why the grain boundary resistance can be reduced by fluorinating at least one surface of the positive electrode active material particles and the solid electrolyte particles, but it is presumed as follows.
That is, the surface of the particles is fluorinated, so that the melting point of the particles is lowered. When the material containing these particles is heat-treated to form a sheet-like positive electrode layer, the surface of the particles having the fluorinated layer is easily dissolved, so that the particles having the fluorinated layer are formed. And, at the particle interface between the particles adjacent to it, the adhesion between the particles becomes good. As a result, it is presumed that the grain boundary resistance between the particles in the positive electrode layer is reduced and the lithium ion conductivity is improved.
Alternatively, while the particle surface is stabilized by fluorination, the particle surface is polarized due to the presence of fluorine having a high electronegativity, and the particles having a fluorinated layer and surrounding particles due to the interaction with lithium ions. The grain boundary resistance at the interface with is reduced. As a result, it is possible that a good lithium ion conduction path is formed.
Further, on the surface of the positive electrode active material particles, oxygen atoms constituting the positive electrode active material may be missing, resulting in lattice defects. At this time, if the lattice defects are filled with the fluorine atoms contained in the fluorinated layer, the binding force of the positive electrode active material on the lithium ions is weakened, and it is considered that the lithium ions are easily moved.
さらに、正極活物質粒子の表面においては、上記格子欠陥がフッ化物イオンにより埋められることで、正極活物質が含有する遷移金属元素が格子欠陥を介して拡散してしまうことも抑制できる。遷移金属元素の拡散を抑制することにより、リチウムイオン二次電池が充放電を繰り返した場合においても電池特性が低下しにくくなる。 Further, by filling the lattice defects on the surface of the positive electrode active material particles with fluoride ions, it is possible to prevent the transition metal elements contained in the positive electrode active material from diffusing through the lattice defects. By suppressing the diffusion of transition metal elements, the battery characteristics are less likely to deteriorate even when the lithium ion secondary battery is repeatedly charged and discharged.
また、正極活物質粒子および固体電解質粒子の少なくとも一方の表面がフッ素化されていることにより、粒子および該粒子を含む正極層の加水分解耐性も向上する。この理由は、フッ素化により粒子表面が安定化されるためと考えられる。これにより、かかる粒子や該粒子を含む正極層が空気中の水分等と反応してしまうことを抑制でき、粒子そのものや正極層のハンドリング性が向上する。 Further, since at least one surface of the positive electrode active material particles and the solid electrolyte particles is fluorinated, the hydrolysis resistance of the particles and the positive electrode layer containing the particles is also improved. The reason for this is considered to be that the particle surface is stabilized by fluorination. As a result, it is possible to prevent the particles and the positive electrode layer containing the particles from reacting with moisture in the air, and the handleability of the particles themselves and the positive electrode layer is improved.
正極活物質粒子および固体電解質粒子の形状は、一次粒子であってもよいし、一次粒子が凝集してなる二次粒子であってもよいし、または一次粒子及び二次粒子の組み合わせであってもよい。粒子形状が一次粒子である場合は、その一次粒子の表面がフッ素化されていてもよく、粒子形状が二次粒子である場合は、一次粒子が凝集して形成される二次粒子の表面がフッ素化されていてもよい。本実施形態に係る正極層は、二次粒子の表面がフッ素化された正極活物質粒子または固体電解質粒子を含むことが、本発明の効果の観点から好ましい。 The shape of the positive electrode active material particles and the solid electrolyte particles may be primary particles, secondary particles formed by aggregating primary particles, or a combination of primary particles and secondary particles. May be good. When the particle shape is a primary particle, the surface of the primary particle may be fluorinated, and when the particle shape is a secondary particle, the surface of the secondary particle formed by agglomeration of the primary particles is It may be fluorinated. From the viewpoint of the effect of the present invention, it is preferable that the positive electrode layer according to the present embodiment contains positive electrode active material particles or solid electrolyte particles in which the surface of the secondary particles is fluorinated.
以上のように、正極活物質粒子または固体電解質粒子の少なくとも一方が表面にフッ素化された層を有することにより、正極層中におけるリチウムイオンの伝導経路の形成によるリチウムイオン伝導性の向上が図られる。これにより、リチウムイオン二次電池の電池特性が改善されて良好なものとなる。 As described above, by having at least one of the positive electrode active material particles or the solid electrolyte particles having a fluorinated layer on the surface, the lithium ion conductivity can be improved by forming the lithium ion conduction path in the positive electrode layer. .. As a result, the battery characteristics of the lithium ion secondary battery are improved and become good.
正極活物質粒子または固体電解質粒子が表面にフッ素化された層を有する場合、該フッ素化された層は、フッ素化された層の最表面におけるフッ素の含有量が９５質量％以上であることが好ましい。最表面のフッ素の含有量が９５質量％以上であることにより、粒子表面が高濃度にフッ素化されることになり、リチウムイオン伝導性がより向上しやすくなるため、本発明における所望の効果を得ることができる。最表面のフッ素の含有量は９７質量％以上がより好ましく、最表面のフッ素の含有量は９８質量％以上がさらに好ましい。 When the positive electrode active material particles or the solid electrolyte particles have a fluorinated layer on the surface, the fluorinated layer may have a fluorine content of 95% by mass or more on the outermost surface of the fluorinated layer. preferable. When the content of fluorine on the outermost surface is 95% by mass or more, the surface of the particles is fluorinated to a high concentration, and the lithium ion conductivity is more likely to be improved. Therefore, the desired effect in the present invention can be obtained. Obtainable. The content of fluorine on the outermost surface is more preferably 97% by mass or more, and the content of fluorine on the outermost surface is further preferably 98% by mass or more.
ここで「フッ素化された層の最表面におけるフッ素の含有量」とは、フッ素化された層の表面から２ｎｍの深さにおける粒子構成成分（上述した粒子を構成する成分）を除いたフッ素の含有割合をいう。「粒子構成成分を除く」とは、粒子からフッ素化された層への拡散または移動される粒子構成成分を除く意味である。 Here, the "fluorine content on the outermost surface of the fluorinated layer" refers to the fluorine obtained by excluding the particle constituents (components constituting the above-mentioned particles) at a depth of 2 nm from the surface of the fluorinated layer. The content ratio. "Excluding particle constituents" means excluding particle constituents that are diffused or transferred from the particles to the fluorinated layer.
フッ素化された層の最表面におけるフッ素の含有量は、以下の方法で測定する。すなわち、透過型電子顕微鏡（ＴＥＭ）による元素マッピング、またはＥＳＣＡ（Ｘ線光電子分光法）による粒子表面から粒内方向への深度元素プロファイル分析により、フッ素化された層の表面から２ｎｍの深さにおける、粒子構成成分を除いたフッ素の含有割合を測定する。 The fluorine content on the outermost surface of the fluorinated layer is measured by the following method. That is, at a depth of 2 nm from the surface of the fluorinated layer by elemental mapping with a transmission electron microscope (TEM) or depth element profile analysis from the particle surface to the inside of the grain by ESCA (X-ray photoelectron spectroscopy). , Measure the content of fluorine excluding the particle constituents.
なお、フッ素化された層が後述するフッ化水素ガス（ＨＦガス）により形成される場合は、フッ素化された層の最表面に微量の水素が存在することになる。このとき、フッ素化された層の最表面における水素の含有量は０．１〜５質量％であることが好ましく、０．１〜３質量％であることがより好ましい。上記範囲であることによって、フッ素化された層の最表面における微量の水素による影響を最小限に抑えられる。
フッ素化された層の最表面の水素の含有量は、上記フッ素含有量と同様の方法にて測定できる。
When the fluorinated layer is formed by hydrogen fluoride gas (HF gas) described later, a trace amount of hydrogen is present on the outermost surface of the fluorinated layer. At this time, the content of hydrogen on the outermost surface of the fluorinated layer is preferably 0.1 to 5% by mass, more preferably 0.1 to 3% by mass. Within the above range, the influence of a trace amount of hydrogen on the outermost surface of the fluorinated layer can be minimized.
The hydrogen content on the outermost surface of the fluorinated layer can be measured by the same method as the above-mentioned fluorine content.
固体電解質粒子または正極活物質粒子が表面にフッ素化された層を有する場合、正極層中の固体電解質粒子全体または正極活物質粒子全体におけるフッ素含有量は、１０質量％以下であることが好ましい。フッ素化された層の最表面におけるフッ素の含有量を上述の好ましい範囲としながら、固体電解質粒子全体または正極活物質粒子全体におけるフッ素含有量を１０質量％以下とすることにより、粒子内部に存在するフッ素含有量が少なくなり、結晶性の悪化や低イオン伝導性成分の過剰に起因するリチウムイオン伝導性の低下を軽減できる。また、絶縁性であるＬｉＦによる導電性の低下も抑制できる。固体電解質粒子全体または正極活物質粒子全体におけるフッ素含有量は、９質量％以下がより好ましく、８質量％以下がさらに好ましい。また、フッ素含有量の合計は０．１質量％以上であることが、粒子の表面にフッ素化された層を形成する上で好ましく、１質量％以上がより好ましく、２質量％以上がさらに好ましい。 When the solid electrolyte particles or the positive electrode active material particles have a fluorinated layer on the surface, the fluorine content in the entire solid electrolyte particles or the entire positive electrode active material particles in the positive electrode layer is preferably 10% by mass or less. It exists inside the particles by setting the fluorine content on the outermost surface of the fluorinated layer to the above-mentioned preferable range and setting the fluorine content in the entire solid electrolyte particles or the entire positive electrode active material particles to 10% by mass or less. The fluorine content is reduced, and the decrease in lithium ion conductivity due to deterioration of crystallinity and excess of low ion conductive components can be reduced. In addition, it is possible to suppress a decrease in conductivity due to LiF, which is an insulating property. The fluorine content in the entire solid electrolyte particles or the entire positive electrode active material particles is more preferably 9% by mass or less, further preferably 8% by mass or less. Further, the total fluorine content is preferably 0.1% by mass or more in order to form a fluorinated layer on the surface of the particles, more preferably 1% by mass or more, still more preferably 2% by mass or more. ..
なお、固体電解質粒子全体または正極活物質粒子全体におけるフッ素含有量は、燃焼法による元素分析の結果から求められる。あるいは、かかるフッ素含有量は、フッ素化された固体電解質粒子全体または正極活物質を水中に浸漬し遊離してくるＦ−を、フッ素イオン電極を用いて定量分析することによっても測定できる。 The fluorine content in the whole solid electrolyte particles or the whole positive electrode active material particles can be obtained from the result of elemental analysis by the combustion method. Alternatively, the fluorine content can also be measured by quantitatively analyzing F − released by immersing the entire fluorinated solid electrolyte particles or the positive electrode active material in water using a fluorine ion electrode.
正極活物質粒子表面または固体電解質粒子表面におけるフッ素化された層の厚みは、本発明の効果がより得られる観点から１ｎｍ以上が好ましく、１．２５ｎｍ以上がより好ましく、１．５ｎｍ以上がさらに好ましく、２ｎｍ以上がよりさらに好ましい。また、フッ素化された層の厚みは、導電性の低下を抑制する点から、５０ｎｍ以下が好ましく、２０ｎｍ以下がより好ましく、１０ｎｍ以下がさらに好ましい。
特に、フッ素化された層を有する粒子が二次粒子を含む場合において、二次粒子におけるフッ素化された層の厚みは１ｎｍ以上が好ましく、１．２５ｎｍ以上がより好ましく、１．５ｎｍ以上がさらに好ましく、２ｎｍ以上がよりさらに好ましい。また、フッ素化された層の厚みは、５０ｎｍ以下が好ましく、２０ｎｍ以下がより好ましく、１０ｎｍ以下がさらに好ましい。
フッ素化された層が、後述する、粒子表面をフッ素化された別の粒子により覆うことで形成された層である場合、フッ素化された層の厚みは、本発明の効果がより得られる点から０．１μｍ以上が好ましく、また、１μｍ以下が好ましい。
なお、フッ素化された層の厚みはＸ線光電子分光法や粒子断面からの元素マッピング等の分析により求められる。
The thickness of the fluorinated layer on the surface of the positive electrode active material particles or the surface of the solid electrolyte particles is preferably 1 nm or more, more preferably 1.25 nm or more, still more preferably 1.5 nm or more from the viewpoint of further obtaining the effects of the present invention. 2 nm or more is even more preferable. The thickness of the fluorinated layer is preferably 50 nm or less, more preferably 20 nm or less, still more preferably 10 nm or less, from the viewpoint of suppressing a decrease in conductivity.
In particular, when the particles having the fluorinated layer include secondary particles, the thickness of the fluorinated layer in the secondary particles is preferably 1 nm or more, more preferably 1.25 nm or more, and further 1.5 nm or more. Preferably, 2 nm or more is even more preferable. The thickness of the fluorinated layer is preferably 50 nm or less, more preferably 20 nm or less, and even more preferably 10 nm or less.
When the fluorinated layer is a layer formed by covering the particle surface with another fluorinated particle, which will be described later, the thickness of the fluorinated layer is a point in which the effect of the present invention can be further obtained. From 0.1 μm to 0.1 μm or more, and 1 μm or less is preferable.
The thickness of the fluorinated layer can be obtained by analysis such as X-ray photoelectron spectroscopy and element mapping from a particle cross section.
（フッ素化された層の形成方法）
フッ素化された層の形成方法は特に限定されず、フッ素化された層とは、例えば、正極活物質粒子または固体電解質粒子の、粒子そのものの表面がフッ素化された層であってもよい。あるいは、正極活物質粒子または固体電解質粒子の粒子表面をフッ素化された別の粒子により覆うことで形成された層であってもよい。
(Method of forming fluorinated layer)
The method for forming the fluorinated layer is not particularly limited, and the fluorinated layer may be, for example, a layer of positive electrode active material particles or solid electrolyte particles whose surface is fluorinated. Alternatively, it may be a layer formed by covering the particle surface of the positive electrode active material particles or the solid electrolyte particles with another fluorinated particles.
粒子そのものの表面がフッ素化された層を有する場合、その形成方法としては、例えば、粒子をフッ素化可能な気体と接触させる方法が挙げられる。かかる方法によれば、粒子の表面を選択的に高濃度にフッ素化でき、粒子内部に存在するフッ素含有量の増加を抑制できる。すなわち、粒子内部におけるイオン伝導性の低いＬｉＦの形成を抑制でき、ひいては正極層そのもののイオン伝導性の低下を抑制できる。また、フッ素化された層の形成過程において熱や応力による材料の劣化を防ぐ観点からも、粒子をフッ素化可能な気体と接触させる方法を好ましく適用できる。 When the surface of the particles themselves has a fluorinated layer, examples of the method for forming the particles include a method of contacting the particles with a fluorinated gas. According to such a method, the surface of the particles can be selectively fluorinated to a high concentration, and an increase in the fluorine content existing inside the particles can be suppressed. That is, the formation of LiF having low ionic conductivity inside the particles can be suppressed, and thus the decrease in ionic conductivity of the positive electrode layer itself can be suppressed. Further, from the viewpoint of preventing deterioration of the material due to heat or stress in the process of forming the fluorinated layer, a method of contacting the particles with a fluorinated gas can be preferably applied.
粒子をフッ素化可能な気体と接触させる方法の一例を以下に説明する。粒子をフッ素化可能な気体と接触させる方法でフッ素化された層が形成された場合、粒子表面のフッ素含有量は、粒子内部のフッ素含有量よりも多くなる。 An example of a method of contacting particles with a fluorinated gas will be described below. When the fluorinated layer is formed by contacting the particles with a fluorinated gas, the fluorine content on the surface of the particles is higher than the fluorine content inside the particles.
フッ素化可能な気体とは、フッ素元素を含む気体であり、フッ素ガス（Ｆ２ガス）、フッ化水素ガス（ＨＦガス）、ＢＦ３ガス、ＮＦ３ガス、ＰＦ５ガス、ＳｉＦ４ガス、ＳＦ６ガス等が挙げられる。これらフッ素元素を含む気体は単独で用いても、窒素ガスやアルゴンガス等の不活性ガスとの混合ガスを用いてもよい。 The fluorinated gas is a gas containing a fluorine element, and is fluorine gas (F 2 gas), hydrogen fluoride gas (HF gas), BF 3 gas, NF 3 gas, PF 5 gas, SiF 4 gas, SF. 6 Gas and the like can be mentioned. The gas containing these fluorine elements may be used alone or may be a mixed gas with an inert gas such as nitrogen gas or argon gas.
これらの中でも、純粋にフッ素のみを反応させるという意味において他の元素を含まないので、フッ素ガス（Ｆ２ガス）、フッ化水素ガス（ＨＦガス）、またはこれらと不活性ガスとの混合ガスが好ましい。粒子とＦ２ガス又はＨＦガスとの接触によりフッ素化された層が形成された場合、正極活物質中または固体電解質粒子には、フッ素原子または水素原子のみしか含有されないので、かかるガスの接触によりフッ素化された層が形成されたと判断できる。 Among these, since it does not contain other elements in the sense that it reacts purely with fluorine, fluorine gas (F 2 gas), hydrogen fluoride gas (HF gas), or a mixed gas of these and an inert gas is used. preferable. When a fluorinated layer is formed by contact between the particles and F 2 gas or HF gas, the positive electrode active material or the solid electrolyte particles contain only fluorine atoms or hydrogen atoms, and thus the contact with the gas causes the fluorinated layer to be formed. It can be determined that the fluorinated layer was formed.
混合ガスを用いる場合、フッ素元素を含む気体の濃度は、反応の制御のしやすさ及び経済的な観点から、混合ガス全体に対して０．０１体積％以上が好ましく、０．１体積％以上がより好ましい。また、フッ素元素を含む気体の濃度は、５０体積％以下が好ましく、３５体積％以下がより好ましく、２０体積％以下がさらに好ましい。 When a mixed gas is used, the concentration of the gas containing a fluorine element is preferably 0.01% by volume or more, preferably 0.1% by volume or more, based on the total mixed gas from the viewpoint of ease of control of the reaction and economic viewpoint. Is more preferable. The concentration of the gas containing a fluorine element is preferably 50% by volume or less, more preferably 35% by volume or less, and further preferably 20% by volume or less.
粒子とフッ素元素を含む気体とを接触させる時間は、１０秒以上が好ましく、１分以上がより好ましく、また、１２０分以下が好ましく、１０分以下がより好ましい。かかる範囲にすることで、粒子の表面に濃度を制御したフッ素化された層を精度よく形成でき、ひいてはサイクル特性や充放電特性に優れた正極層を形成できる。 The time for contacting the particles with the gas containing the fluorine element is preferably 10 seconds or more, more preferably 1 minute or more, preferably 120 minutes or less, and more preferably 10 minutes or less. Within such a range, a fluorinated layer having a controlled concentration can be formed on the surface of the particles with high accuracy, and a positive electrode layer having excellent cycle characteristics and charge / discharge characteristics can be formed.
粒子とフッ素元素を含む気体とを接触させる温度は、１０〜１５０℃の範囲で温度制御しながら行うことが好ましい。粒子表面におけるフッ素濃度を高めたい場合には、温度を上げることで粒子表面とフッ素との反応性が上がり高濃度で所望のフッ素を含む層を形成することもできる。これにより、効率よくフッ素化された層を形成できる。
フッ素元素を含む気体との接触は、加圧しながら行ってもよい。その圧力は、安全性を高める観点及び過剰なフッ素化を抑制する観点から、０．６ＭＰａ（ゲージ圧）以下が好ましく、０．３ＭＰａ以下がより好ましい。
The temperature at which the particles are brought into contact with the gas containing the fluorine element is preferably controlled in the range of 10 to 150 ° C. When it is desired to increase the fluorine concentration on the particle surface, the reactivity between the particle surface and fluorine is increased by raising the temperature, and a layer containing desired fluorine can be formed at a high concentration. This makes it possible to efficiently form a fluorinated layer.
Contact with a gas containing a fluorine element may be performed while pressurizing. The pressure is preferably 0.6 MPa (gauge pressure) or less, more preferably 0.3 MPa or less, from the viewpoint of enhancing safety and suppressing excessive fluorination.
フッ素元素を含む気体との接触は、流通式又はバッチ式が好ましい。
流通式の場合は、反応容器内に粒子を静置した状態で入れ、所定の濃度のフッ素を含む気体を開放型の反応容器内に連続的に供給して、粒子とフッ素を含む気体とを接触させる方法が好ましい。
バッチ式の場合は、所定の濃度とされたフッ素元素を含む気体雰囲気の密閉された反応容器内に粒子を収容して、粒子とフッ素元素を含む気体とを接触させる方法が好ましい。
The contact with the gas containing a fluorine element is preferably a flow type or a batch type.
In the case of the circulation type, the particles are placed in the reaction vessel in a stationary state, and the gas containing fluorine at a predetermined concentration is continuously supplied into the open type reaction vessel to separate the particles and the gas containing fluorine. The contact method is preferred.
In the case of the batch type, a method of accommodating the particles in a closed reaction vessel having a gas atmosphere containing a fluorine element having a predetermined concentration and bringing the particles into contact with the gas containing the fluorine element is preferable.
流通式で行う場合、粒子に対して均一にフッ素元素を含む気体を接触させる観点から、反応容器として粒子を置き流動させる流動床を備えるものや、管状炉などのキルンを用いることも可能である。流動床を備える場合には、フッ素化する処理時間の短縮化および過剰なフッ素化を抑制し、より均一なフッ素化を実現できるので特に好ましい。
バッチ式で行う場合、粒子に対して均一にフッ素元素を含む気体を接触させるために、粒子を撹拌混合しながら行うことも可能である。
In the case of the distribution method, from the viewpoint of uniformly contacting the particles with a gas containing a fluorine element, it is also possible to use a reaction vessel provided with a fluidized bed in which the particles are placed and flowed, or a kiln such as a tube furnace. .. When a fluidized bed is provided, it is particularly preferable because the treatment time for fluorination can be shortened, excessive fluorination can be suppressed, and more uniform fluorination can be achieved.
In the case of the batch method, it is also possible to carry out while stirring and mixing the particles in order to uniformly contact the gas containing the fluorine element with the particles.
フッ素化された層が、粒子表面をフッ素化された別の粒子により覆うことで形成された層である場合、その形成方法としては、例えば、粒子の表面をフッ素化されたカーボン粒子で覆う方法や、粒子の表面をフッ素化された酸化物粒子で覆う方法等が挙げられる。なかでも、フッ素化されたカーボンの粒子で覆う方法は、高電位における安定性や大きな比表面積をもったカーボン粒子を用いることでフッ素濃度を高めることも可能となり、フッ素化による効果が十分に得られるので好ましい。このような方法でフッ素化された層が形成された場合、粒子表面のフッ素含有量は、粒子内部のフッ素含有量よりも多くなる。 When the fluorinated layer is a layer formed by covering the surface of the particles with another fluorinated particle, the forming method thereof is, for example, a method of covering the surface of the particles with fluorinated carbon particles. Alternatively, a method of covering the surface of the particles with fluorinated oxide particles and the like can be mentioned. Among them, the method of covering with fluorinated carbon particles makes it possible to increase the fluorine concentration by using carbon particles having stability at a high potential and a large specific surface area, and the effect of fluorination is sufficiently obtained. It is preferable because it can be used. When the fluorinated layer is formed by such a method, the fluorine content on the particle surface becomes higher than the fluorine content inside the particle.
カーボンの粒子は粒子状に限られず、繊維状のカーボンでもよい。いずれの場合にも、カーボンの表面にフッ素が化学吸着もしくは化学結合しているものを作製できる。
粒子状のカーボンとしては、ケッチェンブラック、アセチレンブラック、サーマルブラック、ファーネスブラック、チャンネルブラック等のカーボンブラック、活性炭、黒鉛、Ｃ６０、Ｃ７０、Ｃ８４等のフラーレン類、ダイヤモンド等が挙げられる。
繊維状のカーボンとしては、カーボンファイバー、カーボンナノチューブ等が挙げられる。
The carbon particles are not limited to particles, and may be fibrous carbon. In either case, it is possible to produce a carbon having fluorine chemically adsorbed or chemically bonded to the surface of the carbon.
Examples of the particulate carbon include carbon black such as Ketjen black, acetylene black, thermal black, furnace black and channel black, activated carbon, graphite, fullerenes such as C 60 , C 70 and C 84 , and diamond.
Examples of the fibrous carbon include carbon fibers and carbon nanotubes.
上記の中でも、サイクル特性およびエネルギー密度が充分に高くなる点から、粒子状のカーボンが好ましく、高比表面積をもったケッチェンブラック又は活性炭がより好ましい。なお、カーボンは１種を単独で用いてもよく、２種以上を併用してもよい。 Among the above, particulate carbon is preferable, and Ketjen black or activated carbon having a high specific surface area is more preferable from the viewpoint of sufficiently high cycle characteristics and energy density. One type of carbon may be used alone, or two or more types may be used in combination.
フッ素化された層が、粒子表面をフッ素化された別の粒子で覆うことで形成される場合、フッ素化された層の厚みは０．１〜１μｍが好ましいことから、フッ素化されたカーボンの粒子の粒径も１μｍ以下が好ましい。 When the fluorinated layer is formed by covering the surface of the particles with another fluorinated particle, the thickness of the fluorinated layer is preferably 0.1 to 1 μm. The particle size of the particles is also preferably 1 μm or less.
フッ素化された層がフッ素化されたカーボンの粒子から形成される場合、フッ素化された層におけるカーボンの含有量は、正極活物質粒子表面または固体電解質粒子表面を隙間なくコートでき、粒子表面の界面抵抗の増大を抑制する必要性から５０質量％以上が好ましい。また、フッ素化における効果を得るために、カーボンの含有量は９９質量％以下が好ましく、９５質量％以下がより好ましい。一方、フッ素化された層におけるフッ素の含有量は１質量％以上が好ましく、５質量％以上がより好ましく、また、５０質量％以下が好ましい。
フッ素化された層におけるフッ素及びカーボンの含有量は、燃焼法による元素分析により求められる。
When the fluorinated layer is formed from fluorinated carbon particles, the carbon content in the fluorinated layer can coat the surface of the positive electrode active material particles or the surface of the solid electrolyte particles without gaps, and the surface of the particles can be coated. From the necessity of suppressing an increase in interfacial resistance, 50% by mass or more is preferable. Further, in order to obtain the effect in fluorination, the carbon content is preferably 99% by mass or less, more preferably 95% by mass or less. On the other hand, the content of fluorine in the fluorinated layer is preferably 1% by mass or more, more preferably 5% by mass or more, and preferably 50% by mass or less.
The content of fluorine and carbon in the fluorinated layer is determined by elemental analysis by the combustion method.
粒子の表面をフッ素化された別の粒子によって覆う方法におけるフッ素化された別の粒子が、カーボンである場合、カーボンとフッ素化合物とを混合接触させることにより、フッ素化されたカーボンを製造できる。 When the other fluorinated particles in the method of covering the surface of the particles with another fluorinated particles are carbon, the fluorinated carbon can be produced by mixing and contacting the carbon and the fluorinated compound.
フッ素化に用いるフッ素化合物としては、フッ素ガス、フッ化水素ガス、ＣｌＦ３、及びＩＦ５等のフッ化ハロゲン、ＢＦ３、ＮＦ３、ＰＦ５、ＳｉＦ４、ＳＦ６等のガス状フッ化物、ＬｉＦ、及びＮｉＦ２等の金属フッ化物等が挙げられる。 Examples of the fluorine compound used for fluorination include fluorine gas, hydrogen fluoride gas, halogen fluorides such as ClF 3 , and IF 5 , and gaseous fluorides such as BF 3 , NF 3 , PF 5 , SiF 4 , and SF 6 . Examples thereof include metal fluorides such as LiF and NiF 2.
これらのうち、取り扱いの容易性および、得られるフッ素化されたカーボンに含まれる不純物を少なくする点から、ガス状フッ化物を使用することが好ましく、Ｆ２、ＣｌＦ３、及びＮＦ３がより好ましく、Ｆ２が特に好ましい。
ガス状フッ化物を用いる場合には、フッ素化処理を制御し易くするためＮ２等の不活性ガスで希釈して用いてもよい。
Of these, it is preferable to use gaseous fluoride, and F 2 , ClF 3 , and NF 3 are more preferable, from the viewpoint of ease of handling and reduction of impurities contained in the obtained fluorinated carbon. , F 2 is particularly preferable.
When gaseous fluoride is used, it may be diluted with an inert gas such as N 2 in order to facilitate control of the fluorination treatment.
カーボンをフッ素化する際の温度は、−２０℃以上が、カーボン表面にフッ素が化学吸着もしくは化学結合の形成を可能とするため好ましい。また、かかる温度は、極度のフッ素化反応を抑制するため、３５０℃以下が好ましい。 The temperature at which carbon is fluorinated is preferably −20 ° C. or higher because fluorine enables chemical adsorption or formation of chemical bonds on the carbon surface. Further, the temperature is preferably 350 ° C. or lower in order to suppress an extreme fluorination reaction.
上記で得たフッ素化されたカーボンを粒子と混合することで、フッ素化された層を有する粒子が得られる。
混合方法は、乾式法又は湿式法が挙げられる。乾式法は、分散媒を用いずに混合する方式であるが、混合後の乾燥が不要であること、及び、湿式法に必要な分散液の調製が不要であること等の理由から、乾式法が簡便であり好ましい。
By mixing the fluorinated carbon obtained above with the particles, particles having a fluorinated layer can be obtained.
Examples of the mixing method include a dry method and a wet method. The dry method is a method of mixing without using a dispersion medium, but the dry method does not require drying after mixing and preparation of a dispersion liquid required for the wet method. Is simple and preferable.
乾式法において混合に用いる機器としては、各種ディスパ、ボールミル、スーパーミキサ、ヘンシェルミキサ、アトマイザ、Ｖ型混合機、ペイントシェーカ、コニカルブレンダ、ナウターミキサ、ＳＶミキサ、ドラムミキサ、シェーカーミキサ、プロシェアーミキサ、万能ミキサ、リボン型混合機、リボンミキサ、及びコンテナミキサ等が挙げられる。小スケールで混合を行う場合には、自転・公転ミキサを用いてもよい。 The equipment used for mixing in the dry method includes various dispas, ball mills, super mixers, Henschel mixers, atomizers, V-type mixers, paint shakers, conical blenders, nower mixers, SV mixers, drum mixers, shaker mixers, pro-share mixers, and universal mixers. , Ribbon type mixer, ribbon mixer, container mixer and the like. When mixing on a small scale, a rotation / revolution mixer may be used.
乾式法の混合時間は、生産性の点から１〜６０分間が好ましく、１〜３０分間がより好ましい。また、混合温度は２０〜３０℃が好ましい。 The mixing time of the dry method is preferably 1 to 60 minutes, more preferably 1 to 30 minutes from the viewpoint of productivity. The mixing temperature is preferably 20 to 30 ° C.
（導電助剤）
本実施形態に係る正極層は、導電助剤を含む。正極層が導電助剤を含むことで、リチウムイオン二次電池用として好適な電子伝導性を有する正極層が得られる。導電助剤としては特に限定されず、公知の正極用導電助剤を使用できる。正極用導電助剤としては、例えば、黒鉛、カーボンブラック、アセチレンブラック等の炭素系材料や、銅、ニッケル、ステンレス、鉄等の金属、酸化インジウムスズ（ＩＴＯ）等の導電性酸化物が挙げられる。導電助剤としては、電子伝導性に優れ、粒径の小さい炭素系材料は、正極層中で細かく分散することにより、電子伝導性を高めることができるため、好ましく使用できる。これら導電助剤は単独で用いてもよいし、複数種を組み合わせて用いてもよい。
(Conductive aid)
The positive electrode layer according to the present embodiment contains a conductive auxiliary agent. When the positive electrode layer contains a conductive auxiliary agent, a positive electrode layer having electron conductivity suitable for a lithium ion secondary battery can be obtained. The conductive auxiliary agent is not particularly limited, and a known conductive auxiliary agent for a positive electrode can be used. Examples of the conductive auxiliary agent for the positive electrode include carbon-based materials such as graphite, carbon black and acetylene black, metals such as copper, nickel, stainless steel and iron, and conductive oxides such as indium tin oxide (ITO). .. As the conductive auxiliary agent, a carbon-based material having excellent electron conductivity and a small particle size can be preferably used because the electron conductivity can be enhanced by finely dispersing in the positive electrode layer. These conductive auxiliaries may be used alone or in combination of two or more.
本実施形態に係る正極層において、導電助剤の含有量は、正極層における伝導性付与の観点から１質量％以上が好ましく、２質量％以上がより好ましく、３質量％以上がさらに好ましい。また、導電助剤の含有量は正極層中に正極活物質を多く用いて高容量化する観点から２０質量％以下が好ましく、１５質量％以下がより好ましく、１０質量％以下がさらに好ましい。 In the positive electrode layer according to the present embodiment, the content of the conductive auxiliary agent is preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 3% by mass or more, from the viewpoint of imparting conductivity in the positive electrode layer. Further, the content of the conductive auxiliary agent is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less, from the viewpoint of increasing the volume by using a large amount of the positive electrode active material in the positive electrode layer.
（その他添加剤）
本実施形態に係る正極層は、上記成分の他、正極層自体の構造を保持するため、適宜バインダー、を含んでいてもよい。バインダーとしては従来公知のものを使用でき、例えば、ブタジエンゴム（ＢＲ）、アクリレートブタジエンゴム（ＡＢＲ）、スチレンブタジエンゴム（ＳＢＲ）、ポリフッ化ビニリデン（ＰＶｄＦ）、及びポリテトラフルオロエチレン（ＰＴＦＥ）等を使用できる。
(Other additives)
In addition to the above components, the positive electrode layer according to the present embodiment may appropriately contain a binder in order to retain the structure of the positive electrode layer itself. Conventionally known binders can be used, for example, butadiene rubber (BR), acrylate butadiene rubber (ABR), styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), and the like. Can be used.
また、正極層は、フッ素化された無機化合物の粒子等を含んでいてもよい。フッ素化された無機化合物の粒子を含むことで、固体電解質粒子の電気化学的な安定性や大気雰囲気下での安定性を向上できる。無機化合物の粒子としては、ＴｉＯ２、ＳｉＯ２、ＺｒＯ２などの酸化物粒子やＴｉＮ、ＳｉＮ、ＺｒＮなどの窒化物粒子などが挙げられる。無機化合物をフッ素化する方法としては特に限定されないが、例えば、無機化合物にフッ素含有ガスを接触させる方法や、液相法、固相法等が挙げられる。 Further, the positive electrode layer may contain particles of a fluorinated inorganic compound or the like. By including the particles of the fluorinated inorganic compound, the electrochemical stability of the solid electrolyte particles and the stability in the air atmosphere can be improved. Examples of the particles of the inorganic compound include oxide particles such as TiO 2 , SiO 2 , and ZrO 2, and nitride particles such as TiN, SiN, and ZrN. The method for fluorinating the inorganic compound is not particularly limited, and examples thereof include a method in which a fluorine-containing gas is brought into contact with the inorganic compound, a liquid phase method, and a solid phase method.
（正極層の製造方法）
本実施形態に係る正極層を形成する方法は特に限定されないが、例えば、上記した正極層を構成する成分を溶媒に分散あるいは溶解させてスラリーとし、層状（シート状）に塗工し、乾燥させ、任意にプレスする方法が挙げられる。必要に応じて、熱をかけて脱バインダー処理を行ってもよい。当該スラリーの塗工量等を調整することで、正極層の厚みを容易に調整できる。
なお、上記したような湿式成形ではなく、正極層を形成する対象（正極集電体、固体電解質層等）の表面において、正極層を構成する成分を含む材料等を乾式でプレス成形することによって正極層を形成してもよい。あるいは、他の基材に正極層を形成し、これを、正極層を形成する対象の表面に転写してもよい。正極層を形成する対象の表面に強固な正極層を工業的に安定して形成可能である観点から、溶媒を用いた湿式成形によって、対象の表面に正極層を形成することが好ましい。
(Manufacturing method of positive electrode layer)
The method for forming the positive electrode layer according to the present embodiment is not particularly limited, but for example, the above-mentioned components constituting the positive electrode layer are dispersed or dissolved in a solvent to form a slurry, which is coated in a layered form (sheet form) and dried. , The method of pressing arbitrarily can be mentioned. If necessary, heat may be applied to perform the debinder treatment. The thickness of the positive electrode layer can be easily adjusted by adjusting the coating amount of the slurry.
In addition, instead of the wet molding as described above, by dry-press molding a material containing the components constituting the positive electrode layer on the surface of the object (positive electrode current collector, solid electrolyte layer, etc.) on which the positive electrode layer is formed. A positive electrode layer may be formed. Alternatively, the positive electrode layer may be formed on another substrate and transferred to the surface of the object on which the positive electrode layer is formed. From the viewpoint that a strong positive electrode layer can be industrially and stably formed on the surface of the target on which the positive electrode layer is formed, it is preferable to form the positive electrode layer on the surface of the target by wet molding using a solvent.
正極層の厚みは特に限定されず、目的とする電池の性能に応じて適宜決定すればよい。正極層の厚みは、例えば、高容量化の観点からは、１０μｍ以上が好ましく、２０μｍ以上がより好ましく、３０μｍ以上がさらに好ましい。また、正極層の厚みは、厚み方向におけるリチウムイオン伝導性や電子伝導性を確保する観点から５００μｍ以下が好ましく、３００μｍ以下がより好ましい。 The thickness of the positive electrode layer is not particularly limited, and may be appropriately determined according to the performance of the target battery. The thickness of the positive electrode layer is preferably 10 μm or more, more preferably 20 μm or more, still more preferably 30 μm or more, for example, from the viewpoint of increasing the capacity. The thickness of the positive electrode layer is preferably 500 μm or less, more preferably 300 μm or less, from the viewpoint of ensuring lithium ion conductivity and electron conductivity in the thickness direction.
＜リチウムイオン二次電池＞
本実施形態に係るリチウムイオン二次電池は、上述の正極層を含む正極と、固体電解質層と、負極と、を含むものである。固体電解質層及び負極は従来公知の物が用いられる。以下に具体例を示すが、これらに限定されるものではない。
<Lithium-ion secondary battery>
The lithium ion secondary battery according to the present embodiment includes a positive electrode including the above-mentioned positive electrode layer, a solid electrolyte layer, and a negative electrode. Conventionally known solid electrolyte layers and negative electrodes are used. Specific examples are shown below, but the present invention is not limited thereto.
（正極）
正極は、少なくとも上述の正極層と、正極集電体とを含有する。
(Positive electrode)
The positive electrode contains at least the above-mentioned positive electrode layer and a positive electrode current collector.
正極集電体は、導電性を有する材料であればよく、例えば、アルミニウム又はそれらの合金、ステンレス等の金属薄板（金属箔）やスパッタ材等を使用できる。これらは、耐酸化性に優れており好ましい。 The positive electrode current collector may be any material having conductivity, and for example, aluminum or an alloy thereof, a thin metal plate (metal foil) such as stainless steel, a sputter material, or the like can be used. These are preferable because they have excellent oxidation resistance.
正極を作製する方法は特に限定されず、例えば、あらかじめ上述の方法等で形成した正極層と正極集電体とを積層する方法や、正極集電体上に直接正極層を形成する方法が挙げられる。 The method for producing the positive electrode is not particularly limited, and examples thereof include a method of laminating a positive electrode layer and a positive electrode current collector formed in advance by the above method and the like, and a method of forming a positive electrode layer directly on the positive electrode current collector. Be done.
（固体電解質層）
固体電解質層は、リチウムイオン伝導性を有する固体電解質を含み、正極と負極との短絡を防止でき、かつ、正極と負極との間におけるリチウムイオンの移動を可能とするものであればよい。固体電解質の種類としては特に限定されないが、上述の正極層が含有する固体電解質粒子に使用できるものとして例示した固体電解質と同様の固体電解質を好適に使用できる。また、固体電解質層は必要に応じてバインダー等の添加剤を適宜含んでいてもよい。固体電解質層の形状や厚み、形成方法等も特に限定されず、目的とする電池の性能に応じて適宜決定すればよい。
(Solid electrolyte layer)
The solid electrolyte layer may contain a solid electrolyte having lithium ion conductivity, can prevent a short circuit between the positive electrode and the negative electrode, and can move lithium ions between the positive electrode and the negative electrode. The type of the solid electrolyte is not particularly limited, but a solid electrolyte similar to the solid electrolyte exemplified as the one that can be used for the solid electrolyte particles contained in the positive electrode layer described above can be preferably used. Further, the solid electrolyte layer may appropriately contain an additive such as a binder, if necessary. The shape and thickness of the solid electrolyte layer, the forming method, and the like are not particularly limited, and may be appropriately determined according to the performance of the target battery.
（負極）
負極は、少なくとも負極集電体および負極活物質を含有する。
(Negative electrode)
The negative electrode contains at least a negative electrode current collector and a negative electrode active material.
負極集電体は、導電性を有する材料であればよく、例えば、銅やアルミニウム等の金属薄板（金属箔）やスパッタ材等を使用できる。これらは、耐酸化性に優れており好ましい。 The negative electrode current collector may be any material having conductivity, and for example, a thin metal plate (metal foil) such as copper or aluminum, a sputter material, or the like can be used. These are preferable because they have excellent oxidation resistance.
負極活物質としては、リチウムイオンの吸蔵及び放出、言い換えるとリチウムイオンの脱離及び挿入（インターカレーション）、又は、該リチウムイオンとそのカウンターアニオン（例えば、ＰＦ６−）のドープ及び脱ドープを可逆的に進行できれば特に限定されず、公知の負極活物質を使用できる。上記負極活物質としては、例えば、黒鉛、ハードカーボン、ソフトカーボン等の炭素系材料、アルミニウム、シリコン、スズ等のリチウムと合金を形成することが出来る金属、酸化シリコン、酸化スズ等の非晶質の酸化物、及びチタン酸リチウム（Ｌｉ４Ｔｉ５Ｏ１２）等が挙げられる。 As the negative electrode active material, occlusion and release of lithium ions, in other words, desorption and insertion (intercalation) of lithium ions, or doping and dedoping of the lithium ions and their counter anions (for example, PF 6- ) are performed. As long as it can proceed reversibly, the present invention is not particularly limited, and a known negative electrode active material can be used. Examples of the negative electrode active material include carbon-based materials such as graphite, hard carbon and soft carbon, metals capable of forming alloys with lithium such as aluminum, silicon and tin, and amorphous materials such as silicon oxide and tin oxide. Oxide, lithium titanate (Li 4 Ti 5 O 12 ) and the like.
その他、負極は、負極活物質同士を結合すると共に、負極活物質と負極集電体とを結合するバインダーを有してもよい。バインダーは従来公知のものを使用できる。
また、負極は、公知の負極用導電助剤を有してもよく、上記正極用導電助剤と同様のものを使用できる。
上記の他、負極は、リチウムイオン伝導性の観点から、上記負極活物質の他に、固体電解質粒子等を含んでもよい。
In addition, the negative electrode may have a binder that binds the negative electrode active materials to each other and also binds the negative electrode active material and the negative electrode current collector. Conventionally known binders can be used.
Further, the negative electrode may have a known conductive auxiliary agent for a negative electrode, and the same one as the above-mentioned conductive auxiliary agent for a positive electrode can be used.
In addition to the above, the negative electrode may contain solid electrolyte particles and the like in addition to the above negative electrode active material from the viewpoint of lithium ion conductivity.
上記固体電解質層、正極及び負極等のリチウムイオン二次電池を構成するものは、電池外装体に格納される。電池外装体の材料も、従来公知のものを使用できるが、具体的には、ニッケルメッキを施した鉄、ステンレス、アルミニウムまたはその合金、ニッケル、チタン、樹脂材料、フィルム材料等が挙げられる。 Those constituting the lithium ion secondary battery such as the solid electrolyte layer, the positive electrode and the negative electrode are stored in the battery exterior. As the material of the battery exterior, conventionally known materials can be used, and specific examples thereof include nickel-plated iron, stainless steel, aluminum or an alloy thereof, nickel, titanium, a resin material, and a film material.
リチウムイオン二次電池の形状としては、コイン型、シート状（フィルム状）、折り畳み状、巻回型有底円筒型、ボタン型等が挙げられ、用途に応じて適宜選択できる。 Examples of the shape of the lithium ion secondary battery include a coin type, a sheet type (film type), a fold type, a winding type bottomed cylindrical type, a button type, and the like, which can be appropriately selected depending on the intended use.
本実施形態に係るリチウムイオン二次電池は、良好なリチウムイオン伝導性を実現し得る。 The lithium ion secondary battery according to the present embodiment can realize good lithium ion conductivity.
以下に実施例を挙げ、本発明を具体的に説明するが、本発明はこれらに限定されない。 Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.
＜フッ素化ＬｉＣｏＯ２の作製＞
コバルト酸リチウムＬｉＣｏＯ２（ＡＧＣセイミケミカル社製、平均粒径：１３μｍ、比表面積：０．２ｍ２／ｇ）を単独で正極活物質粒子として用いる。
（フッ素化処理）
内容積０．３Ｌのハステロイ製反応器内に上記ＬｉＣｏＯ２の粉末を３．３ｇ入れて、Ｆ２ガスを２０体積％含むＮ２ガスを用いて、圧力０．５６ＫＰａ、室温で２時間フッ素化処理を行い、表面にフッ素化された層を有する正極活物質粒子として、フッ素化ＬｉＣｏＯ２粉末を得る。ＥＳＣＡ分析（Ｘ線光電子分光法）として、アルバック・ファイ社製、ＥＳＣＡ５５００（商品名）を用いてフッ素化ＬｉＣｏＯ２粉末粒子の最表面のフッ素含有量を測定する。また、フッ素化された層の最表面におけるフッ素の含有量が９５質量％以上である。
自動試料燃焼装置（三菱ケミカルアナリテック（ダイヤインスツルメンツ）社製、ＡＱＦ−１００）とイオンクロマトグラフィー（ダイオネクス製、ＤＸ１２０）とを用いて、フッ素含有量を定量分析する。
<Preparation of fluorinated LiCoO 2>
Lithium cobalt oxide LiCoO 2 (manufactured by AGC Seimi Chemical Co., Ltd., average particle size: 13 μm, specific surface area: 0.2 m 2 / g) is used alone as positive electrode active material particles.
(Fluorination treatment)
3.3 g of the above LiCoO 2 powder is placed in a Hastelloy reactor having an internal volume of 0.3 L, and fluorinated at a pressure of 0.56 KPa at room temperature for 2 hours using N 2 gas containing 20% by volume of F 2 gas. The treatment is performed to obtain fluorinated LiCoO 2 powder as positive electrode active material particles having a fluorinated layer on the surface. As an ESCA analysis (X-ray photoelectron spectroscopy), the fluorine content on the outermost surface of the fluorinated LiCoO 2 powder particles is measured using ESCA5500 (trade name) manufactured by ULVAC-PHI. Further, the content of fluorine on the outermost surface of the fluorinated layer is 95% by mass or more.
Quantitative analysis of fluorine content is performed using an automatic sample combustion device (AQF-100 manufactured by Mitsubishi Chemical Analytech (Dia Instruments)) and ion chromatography (DX120 manufactured by Dionex).
＜フッ素化Ｌｉ０．３５Ｌａ０．５５ＴｉＯ３の作製＞
（Ｌｉ０．３５Ｌａ０．５５ＴｉＯ３粉末の合成）
炭酸リチウム（Ｌｉ２ＣＯ３）３．８７ｇと酢酸ランタン（Ｌａ（ＣＨ３ＣＯＯ）３・１．５Ｈ２Ｏ）０．２７ｇを２３．８８ｇの水に撹拌しながら溶かし、ここに乳酸チタン水溶液（マツモトファインケミカル社製、オルガチックスＴＣ−３１５、Ｔｉ含量８．３％）１１．９８ｇをゆっくりと加えた。得られた水分散液を８０℃で２４時間乾燥後、メノウ乳鉢を使い粉砕した。その後、アルミナ容器に入れて、７００℃で４時間熱処理し、７５μｍメッシュを通して粉末を合成した。得られた粉末のＸ線回折装置（Ｒｉｇａｋｕ社、Ｓｍａｒｔ Ｌａｂ）による測定により、Ｌｉ０．３５Ｌａ０．５５ＴｉＯ３が形成していることを確認し、これを固体電解質粒子とした。
（フッ素化処理）
内容積０．３Ｌのハステロイ製反応器内に上記にて合成したＬｉ０．３５Ｌａ０．５５ＴｉＯ３粉末を３ｇ入れて、Ｆ２ガスを２０体積％含むＮ２ガスを用いて、圧力２．５ＫＰａ、温度１４０℃で２時間、Ｌｉ０．３５Ｌａ０．５５ＴｉＯ３粉末のフッ素化処理を行うことで、粒子表面にフッ素化された層を有する固体電解質粒子としてＬｉ０．３５Ｌａ０．５５ＴｉＯ３粉末を得た。
<Preparation of Fluorinated Li 0.35 La 0.55 TiO 3>
(Synthesis of Li 0.35 La 0.55 TiO 3 powder)
Dissolved with stirring lithium carbonate (Li 2 CO 3) 3.87g and acetic acid lanthanum (La (CH 3 COO) 3 · 1.5H 2 O) 0.27g of water 23.88 g, titanium lactate aqueous solution here ( 11.98 g of Organtics TC-315, Ti content 8.3%) manufactured by Matsumoto Fine Chemicals Co., Ltd. was slowly added. The obtained aqueous dispersion was dried at 80 ° C. for 24 hours and then pulverized using an agate mortar. Then, it was placed in an alumina container and heat-treated at 700 ° C. for 4 hours to synthesize a powder through a 75 μm mesh. By measuring the obtained powder with an X-ray diffractometer (Smart Lab, Rigaku Co., Ltd.), it was confirmed that Li 0.35 La 0.55 TiO 3 was formed, and this was used as a solid electrolyte particle.
(Fluorination treatment)
3 g of Li 0.35 La 0.55 TiO 3 powder synthesized above was placed in a Hasteloy reactor having an internal volume of 0.3 L, and pressure was 2 using N 2 gas containing 20% by volume of F 2 gas. By fluorinating Li 0.35 La 0.55 TiO 3 powder at .5 KPa and temperature 140 ° C. for 2 hours, Li 0.35 La 0 as solid electrolyte particles having a fluorinated layer on the particle surface. .55 TiO 3 powder was obtained.
（最表面のフッ素含有量）
ＥＳＣＡ分析（Ｘ線光電子分光法）として、アルバック・ファイ社製ＥＳＣＡ５５００を用いて測定し、フッ素化された層の最表面におけるフッ素の含有量は１００質量％であった。
（粉末中のフッ素含有量）
自動試料燃焼装置（三菱ケミカルアナリテック（ダイヤインスツルメンツ）社製、ＡＱＦ−１００）とイオンクロマトグラフィー（ダイオネクス社製、ＤＸ１２０）とを用いて、フッ素含有量を定量分析したところ、フッ素化された層を有するＬｉ０．３５Ｌａ０．５５ＴｉＯ３粉末全体中のフッ素の含有量は９質量％であった。
（平均粒径）
レーザ回折・散乱式粒子径分布測定装置（日機装社製、製品名ＭＴ−３３００ＥＸ）を用いて上記粉末の平均粒径を測定したところ、３μｍであった。
(Fluorine content on the outermost surface)
As an ESCA analysis (X-ray photoelectron spectroscopy), the measurement was performed using an ESCA5500 manufactured by ULVAC-PHI, Inc., and the fluorine content on the outermost surface of the fluorinated layer was 100% by mass.
(Fluorine content in powder)
Quantitative analysis of the fluorine content using an automatic sample combustion device (Mitsubishi Chemical Analytech (Dia Instruments), AQF-100) and ion chromatography (Dionex, DX120) revealed that the fluorinated layer. The content of fluorine in the whole Li 0.35 La 0.55 TiO 3 powder having was 9% by mass.
(Average particle size)
The average particle size of the powder was measured using a laser diffraction / scattering type particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., product name MT-3300EX) and found to be 3 μm.
（正極層および正極の作製）
次に、以下の手順により正極集電体上に正極層が形成されたリチウムイオン二次電池用正極を作製する。
［例１（実施例）］
上記で作製した正極活物質として、フッ素化ＬｉＣｏＯ２を０．７ｇ、固体電解質材料として、Ｌｉ０．３５Ｌａ０．５５ＴｉＯ３を０．２０ｇ、導電助剤として、デンカブラック（電気化学工業社製）０．０５ｇを秤量し自転・公転ミキサ（ＴＨＩＮＫＹ社製、あわとり練太郎、ＡＲＥ−３１０）を用いて、２０００ｒｐｍ、１０分間粉体混合する。得られる混合粉体を成型加工することで正極層（厚み１００μｍ）を形成する。
［例２（実施例）］
また、同様にＬｉＣｏＯ２を０．７ｇ、固体電解質材料として、フッ素化Ｌｉ０．３５Ｌａ０．５５ＴｉＯ３を０．２０ｇ、導電助剤としてデンカブラック（電気化学工業社製）０．０５ｇを秤量し使用すること以外は、例１の正極層と同様の手順にて正極層（厚み１００μｍ）を形成する。
［例３（比較例）］
また、同様にＬｉＣｏＯ２を０．７ｇ、固体電解質材料として、Ｌｉ０．３５Ｌａ０．５５ＴｉＯ３を０．２０ｇ、導電助剤としてデンカブラック（電気化学工業社製）０．０５ｇを秤量し使用すること以外は、例１の正極層と同様の手順にて正極層（厚み１００μｍ）を形成する。
(Preparation of positive electrode layer and positive electrode)
Next, a positive electrode for a lithium ion secondary battery in which a positive electrode layer is formed on a positive electrode current collector is produced by the following procedure.
[Example 1 (Example)]
0.7 g of fluorinated LiCoO 2 as the positive electrode active material prepared above, 0.20 g of Li 0.35 La 0.55 TiO 3 as the solid electrolyte material, and Denka Black (Electrochemical Industry Co., Ltd.) as the conductive auxiliary agent. ) Weigh 0.05 g and mix the powder at 2000 rpm for 10 minutes using a rotating / revolving mixer (manufactured by THINKY, Awatori Rentaro, ARE-310). A positive electrode layer (thickness 100 μm) is formed by molding the obtained mixed powder.
[Example 2 (Example)]
Similarly, 0.7 g of LiCoO 2 , 0.20 g of fluorinated Li 0.35 La 0.55 TiO 3 as a solid electrolyte material, and 0.05 g of Denka Black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive auxiliary agent. A positive electrode layer (thickness 100 μm) is formed in the same procedure as the positive electrode layer of Example 1 except that it is weighed and used.
[Example 3 (Comparative example)]
Similarly, 0.7 g of LiCoO 2 , 0.20 g of Li 0.35 La 0.55 TiO 3 as a solid electrolyte material, and 0.05 g of Denka Black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive auxiliary agent are weighed. A positive electrode layer (thickness 100 μm) is formed in the same procedure as the positive electrode layer of Example 1 except that it is used.
（リチウムイオン二次電池用評価セルの作製）
上記手順で作製した例１〜例３の正極層について、固体電解質層として厚さ１００μｍのＬｉ０．３５Ｌａ０．５５ＴｉＯ３からなる固体電解質を用い、負極としてはリチウムを用いて充放電特性を評価する。
アルゴンガスグローブボックス内でステンレス製簡易密閉セルに上記の正極層、固体電解質層、負極を入れ、リチウムイオン二次電池用評価セルを組み立てる。
(Preparation of evaluation cell for lithium ion secondary battery)
Regarding the positive electrode layers of Examples 1 to 3 produced by the above procedure, a solid electrolyte composed of Li 0.35 La 0.55 TiO 3 having a thickness of 100 μm was used as the solid electrolyte layer, and lithium was used as the negative electrode for charge / discharge characteristics. To evaluate.
The above positive electrode layer, solid electrolyte layer, and negative electrode are placed in a simple sealed cell made of stainless steel in an argon gas glove box, and an evaluation cell for a lithium ion secondary battery is assembled.
（電池特性）
リチウムイオン二次電池用評価セルを用いて、以下の充放電特性評価を実施する。
Ｃ−レート０．０５Ｃで電圧４．２Ｖまで定電流充電する。また、充電完了後に同じＣ−レート０．０５Ｃで電圧２Ｖまで定電流放電する。表１に、例１〜例３における正極層の構成材料と充放電特性を示す。充電は４．２Ｖ時、放電は２Ｖ時における正極活物質単位ｇ当たりの容量を示す。
(Battery characteristics)
The following charge / discharge characteristic evaluation is carried out using the evaluation cell for the lithium ion secondary battery.
It is charged with a constant current up to a voltage of 4.2 V at a C-rate of 0.05 C. Further, after charging is completed, a constant current discharge is performed up to a voltage of 2 V at the same C-rate of 0.05 C. Table 1 shows the constituent materials and charge / discharge characteristics of the positive electrode layer in Examples 1 to 3. The charge shows the capacity per unit g of the positive electrode active material at 4.2 V and the discharge shows the capacity at 2 V.
上記の結果から、本発明の実施形態における正極活物質粒子および固体電解質粒子の少なくとも一方が、表面にフッ素化された層を有することで優れた電池特性を示すことが確認される。 From the above results, it is confirmed that at least one of the positive electrode active material particles and the solid electrolyte particles in the embodiment of the present invention exhibits excellent battery characteristics by having a fluorinated layer on the surface.
Claims (6)
前記正極活物質粒子および前記固体電解質粒子の少なくとも一方が表面にフッ素化された層を有する、
リチウムイオン二次電池用正極層。 A positive electrode layer containing positive electrode active material particles, solid electrolyte particles, and a conductive additive.
At least one of the positive electrode active material particles and the solid electrolyte particles has a fluorinated layer on the surface.
Positive electrode layer for lithium ion secondary batteries.
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| JP2019179758A (en) * | 2017-06-26 | 2019-10-17 | 株式会社半導体エネルギー研究所 | Method for manufacturing positive electrode active material |
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