JP2015072772A - Lithium ion secondary battery, and method for manufacturing positive electrode active material for lithium ion secondary batteries - Google Patents

Lithium ion secondary battery, and method for manufacturing positive electrode active material for lithium ion secondary batteries Download PDF

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JP2015072772A
JP2015072772A JP2013207298A JP2013207298A JP2015072772A JP 2015072772 A JP2015072772 A JP 2015072772A JP 2013207298 A JP2013207298 A JP 2013207298A JP 2013207298 A JP2013207298 A JP 2013207298A JP 2015072772 A JP2015072772 A JP 2015072772A
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清太郎 伊藤
Seitaro Ito
清太郎 伊藤
相原　雄一
Yuichi Aihara
雄一 相原
町田　信也
Shinya Machida
信也 町田
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Samsung Electronics Co Ltd
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Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery arranged so that the resistance of an interface of a positive electrode active material and a sulfide-based solid electrolyte is reduced.SOLUTION: A lithium ion secondary battery comprises: a positive electrode layer containing a covered positive electrode active material arranged by covering a positive electrode active material with a covering material containing at least one element of Sc, Ti, V, Y, Zr, Nb, Ca, Sr, Ba, Hf, Ta, Cr, Mo and W, lithium and phosphoric acid, and having a lithium ion conductivity; a negative electrode layer; and a solid electrolytic layer including a sulfide-based solid electrolyte. The covering material is preferably amorphous. the concentration of the covering material included in the covered positive electrode active material is preferably 0.01-2.0 mol%. The covering material preferably contains LiZr(PO). The positive electrode active material has a structure of lamellar rock salt structure type, and is preferably a lithium salt of transition metal oxide. The sulfide-based solid electrolyte contains LiS and PS.

Description

本発明は、硫化物系固体電解質を用いるリチウムイオン二次電池に関する。特に被覆材を被覆させた正極活物質を含む正極層を備えるリチウムイオン二次電池に関する。   The present invention relates to a lithium ion secondary battery using a sulfide-based solid electrolyte. In particular, the present invention relates to a lithium ion secondary battery including a positive electrode layer containing a positive electrode active material coated with a coating material.

リチウムイオン二次電池の固体電解質として、リン酸系固体電解質や硫化物系固体電解質が知られる。リン酸系固体電解質を備えるリチウムイオン二次電池の例として、特許文献１がある。特許文献１においては、Ｌｉ１＋ｘＡｌｘＴｉ２−ｘ（ＰＯ３）４（ＬＡＴＰ）やＬｉ１＋ｘＡｌｘＧｅ２−ｘ（ＰＯ３）４（ＬＡＧＰ）等が固体電解質として用いられる。特許文献１に開示される発明は、電極活物質と上記の固体電解質との間にＬｉＺｒ２（ＰＯ４）３を介在させる構造が開示される。この構造により、上記のリチウムイオン二次電池は、リン酸系固体電解質の耐還元性を向上させ、電池の不安定性を解消する。 Known solid electrolytes for lithium ion secondary batteries include phosphoric acid solid electrolytes and sulfide solid electrolytes. There exists patent document 1 as an example of a lithium ion secondary battery provided with a phosphoric acid system solid electrolyte. In Patent Document 1, Li 1 + x Al x Ti 2-x (PO 3) 4 (LATP) and Li 1 + x Al x Ge 2 -x (PO 3) 4 (LAGP) or the like is used as a solid electrolyte. The invention disclosed in Patent Document 1 discloses a structure in which LiZr 2 (PO 4 ) 3 is interposed between an electrode active material and the solid electrolyte. With this structure, the lithium ion secondary battery improves the reduction resistance of the phosphoric acid solid electrolyte and eliminates the instability of the battery.

硫化物系固体電解質を用いたリチウムイオン二次電池は、安定性に優れ、良好な充放電サイクル特性や負荷特性を備える。そのためサイクル劣化が少ないリチウムイオン二次電池を実現するため、硫化物系固体電解質を用いたリチウムイオン二次電池の研究が進んでいる。その一つに電池内の抵抗抑制技術の研究がある。特許文献２には、ａＬｉ２Ｏ-ＺｒＯ２（0.1≦ａ≦2.0）で被覆させた正極活物質を用いることにより、リチウムイオン二次電池のレート特性およびサイクル特性を向上させることが開示される。 A lithium ion secondary battery using a sulfide-based solid electrolyte is excellent in stability and has good charge / discharge cycle characteristics and load characteristics. Therefore, in order to realize a lithium ion secondary battery with little cycle deterioration, research on lithium ion secondary batteries using sulfide-based solid electrolytes is progressing. One of them is research on resistance suppression technology in batteries. Patent Document 2 discloses that the rate characteristics and cycle characteristics of a lithium ion secondary battery are improved by using a positive electrode active material coated with aLi 2 O—ZrO 2 (0.1 ≦ a ≦ 2.0). .

硫化物系固体電解質層と正極層との界面で生じる抵抗は、負極層と硫化物系固体電解質層との界面や、硫化物系固体電解質層内で生じる抵抗と比較して大きい。その理由としてリチウムイオン二次電池の充電時に正極活物質と硫化物系固体電解質との界面で反応が生じ、界面に抵抗成分が生成されることが挙げられる。上記の特許文献２に開示される正極活物質の被覆構造は、正極活物質と硫化物系固体電解質と反応を抑制し、該界面における抵抗成分の生成を防止する。しかし、界面抵抗を抑制させる構造を備えるリチウムイオン二次電池において、さらなる電池性能の向上が望まれる。   The resistance generated at the interface between the sulfide-based solid electrolyte layer and the positive electrode layer is larger than the resistance generated at the interface between the negative-electrode layer and the sulfide-based solid electrolyte layer or in the sulfide-based solid electrolyte layer. The reason is that a reaction occurs at the interface between the positive electrode active material and the sulfide solid electrolyte during charging of the lithium ion secondary battery, and a resistance component is generated at the interface. The covering structure of the positive electrode active material disclosed in Patent Document 2 described above suppresses the reaction between the positive electrode active material and the sulfide-based solid electrolyte and prevents the generation of a resistance component at the interface. However, in a lithium ion secondary battery having a structure that suppresses interface resistance, further improvement in battery performance is desired.

ＷＯ2011-065388号WO2011-065388 特開2011−226161号公報JP 2011-226161

本発明の課題は、電池内の抵抗が抑制され、電池特性に優れる硫化物系固体電解質を備えたリチウムイオン二次電池を提供することである。   The subject of this invention is providing the lithium ion secondary battery provided with the sulfide type solid electrolyte which the resistance in a battery is suppressed and is excellent in a battery characteristic.

本発明は、Ｓｃ、Ｔｉ、Ｖ、Ｙ、Ｚｒ、Ｎｂ、Ｃａ、Ｓｒ、Ｂａ、Ｈｆ、Ｔａ、Ｃｒ、Ｍｏ、Ｗのうちいずれか一種以上の元素と、リチウムと、リン酸とを含有しイオン伝導性を備える被覆材で正極活物質を被覆させた、被覆正極活物質を含有する正極層と、負極層と、硫化物系固体電解質を含有する固体電解質層とを備えるリチウムイオン二次電池である。上記被覆材は非晶質であることが好ましい。被覆正極活物質に含まれる被覆材の正極活物質に対する濃度は0.01ｍｏｌ％以上2.0ｍｏｌ％以下である。該被覆材は、ＬｉＺｒ２（ＰＯ４）3を含有することが好ましい。 The present invention contains one or more elements of Sc, Ti, V, Y, Zr, Nb, Ca, Sr, Ba, Hf, Ta, Cr, Mo, and W, lithium, and phosphoric acid. A lithium ion secondary battery comprising a positive electrode layer containing a coated positive electrode active material, a negative electrode layer, and a solid electrolyte layer containing a sulfide-based solid electrolyte, wherein the positive electrode active material is coated with a coating material having ion conductivity It is. The coating material is preferably amorphous. The density | concentration with respect to the positive electrode active material of the coating material contained in a covering positive electrode active material is 0.01 mol% or more and 2.0 mol% or less. The coating material preferably contains LiZr 2 (PO 4 ) 3 .

本発明に用いられる正極活物質は、層状岩塩型構造を有し、かつ遷移金属酸化物のリチウム塩が好ましい。より好ましくは、層状岩塩型構造を有するＬｉＣｏＯ２、または下記式（１）で表され、かつ層状岩塩型構造を有する３元系金属酸化物である。式（１）において、ＭはＡｌ又はＭｎであり、ｘ、ｙ、ｚは、それぞれ0＜ｘ＜1、0＜ｙ＜1、0＜ｚ＜1、およびｘ＋ｙ＋ｚ＜1を満たす値である。
本発明に用いられる硫化物系固体電解質は、Ｌｉ２ＳとＰ２Ｓ５とを含有するものが好ましい。 The positive electrode active material used in the present invention has a layered rock salt structure and is preferably a lithium salt of a transition metal oxide. More preferably, it is LiCoO 2 having a layered rock salt type structure or a ternary metal oxide represented by the following formula (1) and having a layered rock salt type structure. In Formula (1), M is Al or Mn, and x, y, and z are values that satisfy 0 <x <1, 0 <y <1, 0 <z <1, and x + y + z <1, respectively.
The sulfide-based solid electrolyte used in the present invention preferably contains Li 2 S and P 2 S 5 .

本発明は、正極活物質とリチウムアルコキシドとジルコニウムプロポキシドと酸化リンとを溶媒中で混合し被覆正極活物質材料液を調製する混合工程と、被覆正極活物質材料液に超音波を照射して溶媒を除去し、被覆正極活物質前駆体を得る溶媒除去工程と、酸素ガスもしくは大気雰囲気下、焼成温度300〜750℃で被覆正極活物質前駆体を焼成し、正極活物質をイオン伝導性を有するＬｉＺｒ２（ＰＯ３）４で被覆させた被覆正極活物質を製造する焼成工程とを含む、リチウムイオン二次電池用正極活物質の製造方法を包含する。上記の焼成工程は、酸素ガスもしくは大気雰囲気下、焼成温度300〜400℃の範囲内で被覆正極活物質前駆体を焼成し、イオン電導性を有する非晶質のＬｉＺｒ２（ＰＯ３）４で被覆させた被覆正極活物質を製造する焼成工程を包含する。 The present invention includes a mixing step in which a positive electrode active material, lithium alkoxide, zirconium propoxide, and phosphorus oxide are mixed in a solvent to prepare a coated positive electrode active material material solution; and the coated positive electrode active material material solution is irradiated with ultrasonic waves. Solvent removal step of removing the solvent to obtain a coated positive electrode active material precursor, and firing the coated positive electrode active material precursor at a firing temperature of 300 to 750 ° C. in an oxygen gas or air atmosphere to make the positive electrode active material ion conductive And a firing process for producing a coated positive electrode active material coated with LiZr 2 (PO 3 ) 4 having a method for producing a positive electrode active material for a lithium ion secondary battery. In the firing step, the coated positive electrode active material precursor is fired in an oxygen gas or air atmosphere at a firing temperature of 300 to 400 ° C., and the amorphous LiZr 2 (PO 3 ) 4 having ion conductivity is used. It includes a firing step for producing a coated positive electrode active material.

本発明のリチウムイオン二次電池は、硫化物系固体電解質層と正極層との間の抵抗成分の生成を防止する。これにより上記層の界面抵抗を抑制することができる。その結果本発明は、サイクル特性・負荷特性・放電容量に優れる。   The lithium ion secondary battery of the present invention prevents the generation of a resistance component between the sulfide-based solid electrolyte layer and the positive electrode layer. Thereby, the interface resistance of the said layer can be suppressed. As a result, the present invention is excellent in cycle characteristics, load characteristics, and discharge capacity.

本発明のリチウムイオン二次電池の例を示す概略図である。It is the schematic which shows the example of the lithium ion secondary battery of this invention. 本発明に用いられる被覆正極活物質の例を示す模式図である。It is a schematic diagram which shows the example of the covering positive electrode active material used for this invention.

本発明のリチウムイオン二次電池を図１を用いて説明する。図１は、本発明のリチウムイオン二次電池の例を示す概略図である。図１において、１００はリチウムイオン二次電池、２００は正極層、３００は固体電解質層、４００は負極層、５０１、５０２は集電体である。   The lithium ion secondary battery of this invention is demonstrated using FIG. FIG. 1 is a schematic view showing an example of the lithium ion secondary battery of the present invention. In FIG. 1, 100 is a lithium ion secondary battery, 200 is a positive electrode layer, 300 is a solid electrolyte layer, 400 is a negative electrode layer, and 501 and 502 are current collectors.

放電時、上記のリチウムイオン二次電池１００においては、負極層４００からリチウムイオンと電子とが放出される。放出されたリチウムイオンは、正極層２００と負極層４００と固体電解質層３００とにそれぞれ含有される硫化物系固体電解質を介して正極層２００に到達し、正極層２００でリチウム化合物が生成される。電子は不図示の外部回路を経由して正極層２００に供給される。この外部回路から電気エネルギーが取り出される。   At the time of discharging, in the lithium ion secondary battery 100, lithium ions and electrons are released from the negative electrode layer 400. The released lithium ions reach the positive electrode layer 200 through sulfide-based solid electrolytes respectively contained in the positive electrode layer 200, the negative electrode layer 400, and the solid electrolyte layer 300, and a lithium compound is generated in the positive electrode layer 200. . The electrons are supplied to the positive electrode layer 200 via an external circuit (not shown). Electrical energy is extracted from this external circuit.

リチウムイオン二次電池１００が充電されると、放電時に正極層２００で生成されたリチウム化合物が還元され、リチウムイオンと電子とが生成される。リチウムイオンは正極層２００と硫化物系固体電解質層３００とにそれぞれ含有される硫化物系固体電解質を介して負極層４００に到達する。電子は不図示の外部回路を経由して負極層４００に供給される。負極層４００に到達したリチウムイオンに電子が供給されることで負極層４００にリチウムが吸蔵される。   When the lithium ion secondary battery 100 is charged, the lithium compound generated in the positive electrode layer 200 at the time of discharging is reduced, and lithium ions and electrons are generated. Lithium ions reach the negative electrode layer 400 through the sulfide solid electrolyte contained in the positive electrode layer 200 and the sulfide solid electrolyte layer 300, respectively. The electrons are supplied to the negative electrode layer 400 via an external circuit (not shown). By supplying electrons to the lithium ions that have reached the negative electrode layer 400, lithium is occluded in the negative electrode layer 400.

［正極層］
本発明の正極層は、正極活物質の表面を所定の被覆材で被覆させてなる被覆正極活物質を含有する。図２は、本発明に用いられる被覆正極活物質の例を示す模式図である。図２において、２０１は被覆正極活物質、２０２は正極活物質、２０３は正極活物質２０２の表面を被覆する被覆材、３０１は硫化物固体電解質である。本発明を構成する正極層２００には、上記の被覆正極活物質と硫化物系固体電解質の他、結着剤、導電助剤等が含有される。正極層に硫化物系固体電解質を含有させることにより、被覆正極活物質２０１と硫化物系固体電解質３０１との接触面積を大きくすることができる。これにより被覆正極活物質２０１と硫化物系固体電解質３０１との間のリチウムイオンの授受を効率よく行うことができる。 [Positive electrode layer]
The positive electrode layer of the present invention contains a coated positive electrode active material obtained by coating the surface of the positive electrode active material with a predetermined coating material. FIG. 2 is a schematic view showing an example of a coated positive electrode active material used in the present invention. In FIG. 2, 201 is a coated positive electrode active material, 202 is a positive electrode active material, 203 is a coating material that coats the surface of the positive electrode active material 202, and 301 is a sulfide solid electrolyte. The positive electrode layer 200 constituting the present invention contains, in addition to the above-described coated positive electrode active material and sulfide-based solid electrolyte, a binder, a conductive additive, and the like. By including the sulfide-based solid electrolyte in the positive electrode layer, the contact area between the coated positive electrode active material 201 and the sulfide-based solid electrolyte 301 can be increased. Accordingly, it is possible to efficiently exchange lithium ions between the coated positive electrode active material 201 and the sulfide-based solid electrolyte 301.

本発明の被覆正極活物質２０１は、所定の被覆材２０３で被覆されてなる。そのため正極活物質２０２と硫化物系固体電解質３０１との直接接触が防止される。これにより、正極活物質と硫化物系固体電解質との反応による抵抗成分の生成を抑制できる。上記の被覆材はイオン伝導性を備えるため、被覆材で被覆されない正極活物質を含有する正極層と比較してリチウムイオンの授受効率が著しく低下することがない。   The coated positive electrode active material 201 of the present invention is coated with a predetermined coating material 203. Therefore, direct contact between positive electrode active material 202 and sulfide-based solid electrolyte 301 is prevented. Thereby, the production | generation of the resistance component by reaction with a positive electrode active material and a sulfide type solid electrolyte can be suppressed. Since said coating | covering material is equipped with ion conductivity, compared with the positive electrode layer containing the positive electrode active material which is not coat | covered with coating | covering material, the transfer efficiency of lithium ion does not fall remarkably.

固体電解質層と正極層との間で効率よくリチウムイオンを伝導させるため、正極層内においては、正極活物質が被覆材を介して硫化物系固体電解質と接触する面積が多い方が好ましい。そのような観点から、上記の正極層における被覆正極活物質と硫化物系固体電解質との混合比は、80：20〜40：60が好ましい。上記の好ましい範囲内で、被覆正極活物質や固体電解質の組成、平均粒子径、導電助剤等に応じて、上記混合比を決めることでリチウムイオンの伝導効率を向上させることができる。   In order to efficiently conduct lithium ions between the solid electrolyte layer and the positive electrode layer, it is preferable that the positive electrode active material has a larger area in contact with the sulfide-based solid electrolyte through the coating material in the positive electrode layer. From such a viewpoint, the mixing ratio of the coated positive electrode active material and the sulfide-based solid electrolyte in the positive electrode layer is preferably 80:20 to 40:60. Within the above preferred range, the lithium ion conduction efficiency can be improved by determining the mixing ratio according to the composition of the coated positive electrode active material and the solid electrolyte, the average particle size, the conductive auxiliary agent, and the like.

本発明に用いられる正極活物質としては、リチウムイオンを可逆的に吸蔵し、放出することができるものを制限なく用いることができる。具体的には、コバルト酸リチウム（ＬＣＯ）、ニッケル酸リチウム、ニッケルコバルト酸リチウム、ニッケルコバルトアルミニウム酸リチウム（ＮＣＡ）、ニッケルコバルトマンガン酸リチウム（ＮＣＭ）、リン酸鉄リチウム等が挙げられる。また、層状岩塩型構造を有する遷移金属酸化物のリチウム塩が好ましい。   As the positive electrode active material used in the present invention, those capable of reversibly occluding and releasing lithium ions can be used without limitation. Specific examples include lithium cobaltate (LCO), lithium nickelate, lithium nickel cobaltate, nickel cobalt lithium aluminumate (NCA), nickel cobalt lithium manganate (NCM), and lithium iron phosphate. Moreover, the lithium salt of the transition metal oxide which has a layered rock salt type structure is preferable.

層状岩塩型構造を有する遷移金属酸化物のリチウム塩は、立方晶岩塩型構造の１１１方向に遷移金属とリチウムが規則的に配列して二次元平面を形成する構造を備える。上記の構造においてはリチウム層に遷移金属が、遷移金属層にリチウムが互いに不規則的に配列する。配列の不規則性が少ない方が充放電特性に優れる。   The lithium salt of a transition metal oxide having a layered rock salt structure has a structure in which transition metals and lithium are regularly arranged in the 111 direction of the cubic rock salt structure to form a two-dimensional plane. In the above structure, the transition metal is irregularly arranged in the lithium layer and the lithium is irregularly arranged in the transition metal layer. The smaller the irregularity of the arrangement, the better the charge / discharge characteristics.

好ましい正極活物質として、層状岩塩型構造を有するＬｉＣｏＯ２、または式（１）で表され、かつ層状岩塩型構造を有する３元系金属酸化物が挙げられる。３元系遷移金属酸化物の例としては、ＬｉＮｉ1/3Ｃｏ1/3Ｍｎ1/3Ｏ２、ＬｉＮｉ0.8Ｃｏ0.1Ｍｎ0.1Ｏ2、ＬｉＮｉ0.8Ｃｏ0.15Ａｌ0.05Ｏ2が挙げられる。これらのリチウム塩は、コバルト酸リチウム（ＬＣＯ）を用いる場合と比較してエネルギー密度や充電時の熱安定性が優れるリチウムイオン二次電池を構成することができる。 As a preferable positive electrode active material, LiCoO 2 having a layered rock salt structure or a ternary metal oxide represented by the formula (1) and having a layered rock salt structure can be given. Examples of the ternary transition metal oxide include LiNi 1/3 Co 1/3 Mn 1/3 O 2, LiNi 0.8 Co 0.1 Mn 0.1 O 2 , and LiNi 0.8 Co 0.15 Al 0.05 O 2 . These lithium salts can constitute a lithium ion secondary battery that is superior in energy density and thermal stability during charging compared to the case of using lithium cobalt oxide (LCO).

上記の正極活物質の粒子径は、0.1〜20μｍが好ましく、1〜10μｍがより好ましい。上記の好ましい粒子径を備える正極活物質は比表面積が大きい。   The particle diameter of the positive electrode active material is preferably 0.1 to 20 μm, and more preferably 1 to 10 μm. The positive electrode active material having the above preferable particle diameter has a large specific surface area.

本発明は、上記の正極活物質を、所定の被覆材で被覆させた状態で硫化物系固体電解質と接触させる。被覆材の膜厚は好ましくは、1〜50ｎｍであるため、被覆正極活物質の比表面積は、被覆前の正極活物質の比表面積とほぼ同じである。したがって、被覆正極活物質と硫化物系固体電解質との接触面積が大きく、リチウムイオンの授受経路を大きく確保することができる。これによりリチウムイオン伝導性を良好にすることができる。   In the present invention, the positive electrode active material is brought into contact with a sulfide solid electrolyte in a state where the positive electrode active material is coated with a predetermined coating material. Since the thickness of the coating material is preferably 1 to 50 nm, the specific surface area of the coated positive electrode active material is substantially the same as the specific surface area of the positive electrode active material before coating. Therefore, the contact area between the coated positive electrode active material and the sulfide-based solid electrolyte is large, and a large lithium ion transfer path can be secured. Thereby, lithium ion conductivity can be made favorable.

また上記の被覆材はイオン伝導度が好ましくは10-2〜10-8Ｓ／ｃｍであり、より好ましくは10-2〜10-6Ｓ／ｃｍである。したがって該被覆材を介して、正極活物質と硫化物系固体電解質との間のリチウムイオンの授受を、被覆材を用いない場合と変わらない授受効率で行うことができる。 Further, the above-mentioned coating material preferably has an ionic conductivity of 10 −2 to 10 −8 S / cm, more preferably 10 −2 to 10 −6 S / cm. Therefore, it is possible to exchange lithium ions between the positive electrode active material and the sulfide-based solid electrolyte through the coating material with the same efficiency as when no coating material is used.

本発明においては被覆正極活物質と硫化物系固体電解質とが直接的に接触しない。これにより正極活物質と硫化物系固体電解質との界面における抵抗成分の生成を防止することができる。その結果、本発明は、正極層と固体電解質層との界面で生じる界面抵抗を抑制することができる。   In the present invention, the coated positive electrode active material and the sulfide-based solid electrolyte are not in direct contact. Thereby, the production | generation of the resistance component in the interface of a positive electrode active material and a sulfide type solid electrolyte can be prevented. As a result, the present invention can suppress the interface resistance generated at the interface between the positive electrode layer and the solid electrolyte layer.

また正極層には、本発明の作用効果を損なわない限り、適宜従来公知の導電助剤、結着剤、フィラー、分散剤等を含有させることができる。導電助剤としては、黒鉛、カーボンブラック、アセチレンブラック、ケッチェンブラック、炭素繊維、金属粉等が挙げられる。結着剤としては、ポリテトラフルオロエチレン、ポリフッ化ビニリデン、ポリエチレン等が挙げられる。   In addition, the positive electrode layer may appropriately contain conventionally known conductive assistants, binders, fillers, dispersants and the like as long as the effects of the present invention are not impaired. Examples of the conductive assistant include graphite, carbon black, acetylene black, ketjen black, carbon fiber, and metal powder. Examples of the binder include polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene.

［被覆材］
本発明で用いられる被覆材は、上記の所定の正極活物質の表面を被覆可能でイオン伝導性を備える。該被覆材は、Ｓｃ、Ｔｉ、Ｖ、Ｙ、Ｚｒ、Ｎｂ、Ｃａ、Ｓｒ、Ｂａ、Ｈｆ、Ｔａ、Ｃｒ、Ｍｏ、Ｗのうちいずれか一種以上の元素と、リチウムと、リン酸とを含有する。好ましくは、ＴｉまたはＺｒとの少なくともいずれか一種以上の元素と、リチウムと、リン酸とを包含することが好ましく、具体的には、ＬｉＺｒ２（ＰＯ４）３が特に好ましく用いられる。上記の被覆材は非晶質、結晶体のいずれでもよいが、イオン伝導性を良好にする観点から非晶質であることが好ましい。その場合得られるリチウムイオン二次電池の電池特性をさらに向上させることができる。 [Coating material]
The coating material used in the present invention can coat the surface of the predetermined positive electrode active material and has ion conductivity. The covering material contains one or more elements of Sc, Ti, V, Y, Zr, Nb, Ca, Sr, Ba, Hf, Ta, Cr, Mo, and W, lithium, and phosphoric acid. To do. Preferably, it is preferable to include at least one element of Ti or Zr, lithium, and phosphoric acid, and specifically, LiZr 2 (PO 4 ) 3 is particularly preferably used. The coating material may be either amorphous or crystalline, but is preferably amorphous from the viewpoint of improving ion conductivity. In that case, the battery characteristics of the obtained lithium ion secondary battery can be further improved.

被覆材の種類は、正極活物質の種類に対応して選択される。例えば、Ｓｃ、Ｔｉ、Ｖ、Ｙ、Ｚｒ、Ｎｂ、Ｃａ、Ｓｒ、Ｂａ、Ｈｆ、Ｔａ、Ｃｒ、Ｍｏ、Ｗから選ばれる一種以上の元素が、正極活物質を構成する遷移金属の原子半径より大きい原子半径を有する元素であることが好ましい。そのような元素を含有する被覆材を用いることにより、被覆材が正極活物質の結晶構造内で拡散することを回避し、適切に正極活物質表面を被覆させることができる。   The kind of covering material is selected corresponding to the kind of positive electrode active material. For example, one or more elements selected from Sc, Ti, V, Y, Zr, Nb, Ca, Sr, Ba, Hf, Ta, Cr, Mo, and W are from the atomic radius of the transition metal constituting the positive electrode active material. An element having a large atomic radius is preferred. By using a coating material containing such an element, the coating material can be prevented from diffusing within the crystal structure of the positive electrode active material, and the surface of the positive electrode active material can be appropriately coated.

本発明において「被覆」とは、正極活物質の粒子表面を完全に被覆することを意味する。ただし、被覆材が正極活物質や硫化物系固体電解質と接触することで流動する場合には、正極活物質表面に極めて小さな非被覆領域が存在しうる。そのような非被覆領域を有する正極活物質を含有する正極層と固体電解質層との間の界面抵抗と、完全に被覆された正極活物質を用いた場合の界面抵抗との相違がほとんど認められない場合は、該非被覆領域の存在も許容される。   In the present invention, “coating” means that the particle surface of the positive electrode active material is completely covered. However, when the coating material flows due to contact with the positive electrode active material or the sulfide-based solid electrolyte, an extremely small uncoated region can exist on the surface of the positive electrode active material. There is almost no difference between the interfacial resistance between the positive electrode layer containing the positive electrode active material having such an uncoated region and the solid electrolyte layer, and the interfacial resistance when using a fully coated positive electrode active material. If not, the presence of the uncovered area is allowed.

被覆正極活物質における被覆材の濃度は0.01ｍｏｌ％以上4.0ｍｏｌ％以下が好ましく、0.1ｍｏｌ％以上2.0ｍｏｌ％以下がより好ましい。上記被覆材の濃度が0.01ｍｏｌ％未満の場合、被覆正極活物質において被覆材で被覆されない非被覆領域が大きくなり、界面抵抗が大きくなる。上記濃度が4.0ｍｏｌ％を超える場合、被覆材の膜厚が厚くなりすぎるため硫化物固体電解質との接触面積が小さくなる。被覆材の濃度を上記の好ましい範囲内の濃度にすることにより、本発明は、良好なサイクル特性と初期放電容量とを兼ね備えることができる。   The concentration of the coating material in the coated positive electrode active material is preferably 0.01 mol% or more and 4.0 mol% or less, and more preferably 0.1 mol% or more and 2.0 mol% or less. When the density | concentration of the said coating | covering material is less than 0.01 mol%, the non-coating area | region which is not coat | covered with a coating | covering material in a coating positive electrode active material will become large, and interface resistance will become large. When the concentration exceeds 4.0 mol%, the coating area becomes too thick and the contact area with the sulfide solid electrolyte becomes small. By setting the concentration of the coating material within the above-mentioned preferable range, the present invention can have both good cycle characteristics and initial discharge capacity.

被覆材は正極活物質の粒子表面に均一な膜厚で被覆させることが好ましいが、本発明の作用効果を得られる限り、不均一な膜厚であっても許容される。被覆材の好ましい膜厚は、0.1〜100ｎｍであり、より好ましくは0.5〜50ｎｍである。上記の膜厚で正極活物質を被覆することにより、被覆材自体の抵抗を抑制することができる。   The coating material is preferably coated on the particle surface of the positive electrode active material with a uniform film thickness, but a non-uniform film thickness is acceptable as long as the effects of the present invention can be obtained. The preferred film thickness of the coating material is 0.1 to 100 nm, more preferably 0.5 to 50 nm. By covering the positive electrode active material with the above film thickness, the resistance of the coating material itself can be suppressed.

［硫化物系固体電解質層］
本発明の硫化物系固体電解質層は、硫化物系固体電解質を含有し、その他適宜結着剤、導電助剤等を含有する。本発明に用いられる硫化物系固体電解質は、少なくともＬｉ２ＳとＰ２Ｓ５と含有することが好ましい。 [Sulfide-based solid electrolyte layer]
The sulfide-based solid electrolyte layer of the present invention contains a sulfide-based solid electrolyte, and additionally contains a binder, a conductive aid, and the like as appropriate. The sulfide-based solid electrolyte used in the present invention preferably contains at least Li 2 S and P 2 S 5 .

Ｌｉ２ＳとＰ２Ｓ５との混合比は、60：40〜80：20が好ましく、70：30〜80：20がより好ましい。これによりイオン伝導性に優れる硫化物系固体電解質層を得ることができる。イオン電導度を高めるためにはＬｉ２Ｓの混合量が多い方が好ましいが、過度に混合させた場合、未反応のＬｉ２Ｓが残存する。また、Ｌｉ２Ｓの混合量が少ない場合はリチウムイオン二次電池用途に要するイオン電導度を得られない。そのため上記の所定の範囲内でＬｉ２ＳとＰ２Ｓ５とを混合させることが好ましい。イオン電導度を向上させるため、上記含有成分に加え、ＳｉＳ２、ＧｅＳ２、Ｂ２Ｓ３等を含有させることも好ましい。 The mixing ratio of Li 2 S and P 2 S 5 is preferably 60:40 to 80:20, and more preferably 70:30 to 80:20. Thereby, a sulfide-based solid electrolyte layer having excellent ion conductivity can be obtained. In order to increase the ionic conductivity, it is preferable that the amount of Li 2 S mixed is large, but when it is excessively mixed, unreacted Li 2 S remains. Further, when the mixing amount of the Li 2 S is small not obtain ion conductivity required for the lithium ion secondary battery applications. Therefore, it is preferable to mix Li 2 S and P 2 S 5 within the above predetermined range. In order to improve ionic conductivity, it is also preferable to contain SiS 2 , GeS 2 , B 2 S 3 and the like in addition to the above-described components.

本発明に用いられる硫化物系固体電解質のイオン伝導度は、少なくとも10−４〜10−２Ｓ／ｃｍであることが好ましく、10−3〜10−２Ｓ／ｃｍであることがより好ましい。10−４Ｓ／ｃｍより低い場合は、充放電容量が著しく低下する。Ｌｉ３ＰＳ４のイオン伝導性は、10−２〜10−４Ｓ／ｃｍである。 The ionic conductivity of the sulfide-based solid electrolyte used in the present invention is preferably at least 10 −4 to 10 −2 S / cm, and more preferably 10 −3 to 10 −2 S / cm. When it is lower than 10 −4 S / cm, the charge / discharge capacity is significantly reduced. The ionic conductivity of Li 3 PS 4 is 10 −2 to 10 −4 S / cm.

硫化物系固体電解質の具体例としては、Ｌｉ３ＰＳ４、Ｌｉ４Ｐ２Ｓ７等が挙げられる。硫化物系固体電解質は、非晶質、結晶体、ガラス、ガラスセラミックのいずれでもよいが、非晶質のものがイオン伝導度が高い傾向にあるため好ましく用いられる。 Specific examples of the sulfide-based solid electrolyte include Li 3 PS 4 and Li 4 P 2 S 7 . The sulfide-based solid electrolyte may be amorphous, crystalline, glass, or glass ceramic, but an amorphous one is preferably used because it tends to have high ionic conductivity.

Ｌｉ２ＳとＰ２Ｓ５との混合法は特に限定されないが、好ましくはメカニカルミリング法（ＭＭ法）を適用することができる。ＭＭ法とは、反応器内に上記の出発原料とボールミル等を入れ強撹拌し、出発原料を微粒子化して混合させる方法である。 Li 2 S and mixing method of P 2 S 5 is not particularly limited, preferably can be applied mechanical milling method (MM method). The MM method is a method in which the above starting material and a ball mill are placed in a reactor and vigorously stirred to make the starting material fine particles and mix them.

［負極層］
本発明の負極層は、負極活物質や上記に説明した硫化物系固体電解質を含有する。その他導電助剤等を適宜含有する。本発明で用いられる負極活物質としては、リチウムイオンを吸蔵および放出しうる公知の物質を用いることができる。具体的には、リチウム、インジウム、スズ、アルミ、ケイ素等の金属およびこれらの合金、Ｌｉ４/３Ｔｉ５/３Ｏ４、ＳｎＯ等の遷移金属酸化物を用いることが好ましい。炭素材料としては、黒鉛等リチウムイオンと共に層間化合物を形成するものが好ましい。上記の負極活物質は単独で用いてもよく併用してもよい。 [Negative electrode layer]
The negative electrode layer of the present invention contains a negative electrode active material and the sulfide-based solid electrolyte described above. In addition, it contains conductive aids and the like as appropriate. As the negative electrode active material used in the present invention, a known material that can occlude and release lithium ions can be used. Specifically, lithium, indium, tin, aluminum, metals and alloys such as silicon, the use of Li 4/3 Ti 5/3 O 4 , transition metal oxides of SnO or the like. As a carbon material, what forms an intercalation compound with lithium ions, such as graphite, is preferred. Said negative electrode active material may be used independently, and may be used together.

上記の負極層における負極活物質と硫化物系固体電解質との混合比は、負極活物質と硫化物系固体電解質との接触面積を十分に確保する観点から、60：40が好ましい。これによりリチウムイオン伝導性が良好な負極層を形成することができる。ただし硫化物系固体電解質の混合量は、本発明の作用効果を得られる限り上記の混合比よりも少なくてもよい。   The mixing ratio of the negative electrode active material and the sulfide-based solid electrolyte in the negative electrode layer is preferably 60:40 from the viewpoint of ensuring a sufficient contact area between the negative electrode active material and the sulfide-based solid electrolyte. As a result, a negative electrode layer having good lithium ion conductivity can be formed. However, the mixing amount of the sulfide-based solid electrolyte may be smaller than the above mixing ratio as long as the effects of the present invention can be obtained.

［リチウムイオン二次電池の製造方法］
本発明のリチウムイオン二次電池は、本発明所定の被覆正極活物質を含有する正極合剤を用いて正極層を作製し、負極合剤を用いて負極層を作製し、該正極層と負極層との間に硫化物系固体電解質層を介在させるように各層を積層させて製造することができる。該リチウムイオン電池用正極活物質の製造方法は、出発原料を混合させた被覆正極活物質材料液を調製する混合工程と、被覆正極活物質材料液から溶媒を除去して被覆正極活物質前駆体を得る溶媒除去工程と、被覆正極活物質前駆体を焼成する焼成工程とを含むリチウムイオン二次電池用正極活物質の製造方法を包含する。 [Method for producing lithium ion secondary battery]
In the lithium ion secondary battery of the present invention, a positive electrode layer is prepared using a positive electrode mixture containing the predetermined coated positive electrode active material of the present invention, a negative electrode layer is prepared using a negative electrode mixture, and the positive electrode layer and the negative electrode Each layer can be laminated so that a sulfide-based solid electrolyte layer is interposed between the layers. The method for producing a positive electrode active material for a lithium ion battery includes a mixing step of preparing a coated positive electrode active material material liquid in which starting materials are mixed, and a coated positive electrode active material precursor obtained by removing the solvent from the coated positive electrode active material material liquid. The manufacturing method of the positive electrode active material for lithium ion secondary batteries including the solvent removal process of obtaining, and the baking process of baking a covering positive electrode active material precursor is included.

［硫化物系固体電解質製造工程］
本発明に用いられる硫化物系固体電解質は、溶融急冷法やメカニカルミリング法（ＭＭ法）を用いて製造することができる。ＭＭ法を適用する場合、Ｌｉ２ＳとＰ２Ｓ５とをボールミル等を用いて強撹拌して混合させることで所定の粒子径の硫化物系固体電解質を得ることができる。ＭＭ法を適用する場合、原料成分の熱分解の影響を考慮する必要がないため、簡便に硫化物系固体電解質を得ることができる。Ｌｉ２ＳとＰ２Ｓ５との混合比は、60ｍｏｌ％：40ｍｏｌ％〜80ｍｏｌ％：20ｍｏｌ％が好ましく、70ｍｏｌ％：30ｍｏｌ％〜80ｍｏｌ％：20ｍｏｌ％がより好ましい。上記の好ましい範囲で出発原料を混合させることにより、未反応のＬｉ２Ｓの量を抑制し、かつイオン伝導度の高い硫化物系固体電解質を製造することができる。 [Sulfide-based solid electrolyte production process]
The sulfide-based solid electrolyte used in the present invention can be produced using a melt quench method or a mechanical milling method (MM method). When the MM method is applied, a sulfide-based solid electrolyte having a predetermined particle diameter can be obtained by mixing Li 2 S and P 2 S 5 with strong stirring using a ball mill or the like. When the MM method is applied, it is not necessary to consider the influence of thermal decomposition of the raw material components, so that a sulfide-based solid electrolyte can be easily obtained. The mixing ratio of Li 2 S and P 2 S 5 is preferably 60 mol%: 40 mol% to 80 mol%: 20 mol%, more preferably 70 mol%: 30 mol% to 80 mol%: 20 mol%. By mixing the starting materials in the above preferred range, it is possible to produce a sulfide-based solid electrolyte that suppresses the amount of unreacted Li 2 S and has high ionic conductivity.

溶融急冷法を適用する場合は、Ｌｉ２ＳとＰ２Ｓ５とを好ましい混合比として、60ｍｏｌ％：40ｍｏｌ％〜80ｍｏｌ％：20ｍｏｌ％、より好ましい混合比として70ｍｏｌ％：30ｍｏｌ％〜80ｍｏｌ％：20ｍｏｌ％で混合させてペレット化する。得られたペレットを真空中で反応させた後、急冷することにより、本発明に用いる硫化物系固体電解質を得ることができる。反応温度は、400〜1000℃が好ましく、800〜900℃がより好ましい。反応時間は、0.1時間〜12時間が好ましく、１時間〜12時間がより好ましい。冷却温度は、10℃以下が好ましく、0℃以下がより好ましい。冷却速度は、１〜10000Ｋ／secが好ましく、１〜1000Ｋ／secがより好ましい。 When the melt quenching method is applied, Li 2 S and P 2 S 5 are preferably mixed at a ratio of 60 mol%: 40 mol% to 80 mol%: 20 mol%, and more preferably at a mixing ratio of 70 mol%: 30 mol% to 80 mol%: Mix at 20 mol% and pelletize. By reacting the obtained pellets in a vacuum and then rapidly cooling, the sulfide-based solid electrolyte used in the present invention can be obtained. The reaction temperature is preferably 400 to 1000 ° C, more preferably 800 to 900 ° C. The reaction time is preferably 0.1 hour to 12 hours, and more preferably 1 hour to 12 hours. The cooling temperature is preferably 10 ° C. or lower, and more preferably 0 ° C. or lower. The cooling rate is preferably 1 to 10,000 K / sec, and more preferably 1 to 1000 K / sec.

［正極合剤製造工程］
本発明に用いられる正極合剤は、乳鉢などによって直接混合するか、溶媒中で被覆正極活物質と上記の硫化物系固体電解質とを混合させることにより調製される。他の成分として結着剤や導電助剤等が含有される。被覆正極活物質と硫化物系固体電解質との混合比は、70：30〜40：60が好ましく、60：40がより好ましい。上記の好ましい混合比の範囲内とすることで、該正極活物質の被覆層と硫化物系固体電解質との接触面積を確保でき、リチウムイオンの授受が十分に行われて、所望の充放電容量を得ることができる。 [Positive electrode mixture production process]
The positive electrode mixture used in the present invention is prepared by directly mixing with a mortar or the like, or by mixing the coated positive electrode active material and the sulfide-based solid electrolyte in a solvent. As other components, a binder, a conductive aid and the like are contained. The mixing ratio of the coated positive electrode active material and the sulfide-based solid electrolyte is preferably 70:30 to 40:60, and more preferably 60:40. By making it within the range of the above preferable mixing ratio, the contact area between the coating layer of the positive electrode active material and the sulfide-based solid electrolyte can be ensured, and lithium ions can be sufficiently exchanged to obtain a desired charge / discharge capacity. Can be obtained.

直接混合による場合、被覆正極活物質と、硫化物系固体電解質との粉末を上記の所定の範囲内の混合比で乳鉢に入れ、更に好ましくは結着剤と導電助剤との各粉末を添加し、全ての成分が均質になるまで混合させることで、本発明に用いる正極合剤を得ることができる。得られた正極合剤は、ペレット化して後に説明する積層工程に用いられる。   In the case of direct mixing, the powder of the coated positive electrode active material and the sulfide-based solid electrolyte is put in a mortar at a mixing ratio within the above-mentioned predetermined range, and more preferably each powder of a binder and a conductive aid is added. In addition, the positive electrode mixture used in the present invention can be obtained by mixing until all the components are homogeneous. The obtained positive electrode mixture is pelletized and used in a lamination process described later.

溶媒を用いて正極合剤を調製する場合、正極合剤の溶媒としては、Ｎ−メチル−２−ピロリドン（ＮＭＰ）、Ｎ, Ｎ-ジメチルアセトアミド、Ｎ, Ｎ-ジメチルホルムアミド等を用いることが好ましい。正極合剤100質量部に対し被覆正極活物質70〜40質量部と、硫化物系固体電解質30〜60質量部と、導電助剤1〜10質量部と、結着剤1〜5質量部とになるように添加し、原料成分が均質に分散するまで撹拌させてスラリーを調製する。スラリー中には、分散剤や増粘剤等を適宜添加してもよい。   When preparing a positive electrode mixture using a solvent, it is preferable to use N-methyl-2-pyrrolidone (NMP), N, N-dimethylacetamide, N, N-dimethylformamide or the like as the solvent of the positive electrode mixture. . 70 to 40 parts by mass of the coated positive electrode active material, 30 to 60 parts by mass of the sulfide-based solid electrolyte, 1 to 10 parts by mass of the conductive auxiliary agent, and 1 to 5 parts by mass of the binder with respect to 100 parts by mass of the positive electrode mixture And stirring until the raw material components are uniformly dispersed to prepare a slurry. A dispersant, a thickener, and the like may be appropriately added to the slurry.

得られた正極合剤は、集電体上に塗布後、乾燥させることにより正極層を形成することができる。正極層内の電気抵抗を抑制する観点から、正極層の厚みは、10〜200μmとすることが好ましく、20〜100μmとすることがより好ましい。集電体は、従来公知の材料を用いることができる。具体的には、インジウム、銅、マグネシウム、ステンレス鋼、チタン、鉄、コバルト、ニッケル、亜鉛、アルミニウム、ゲルマニウム、リチウム、又はこれらの合金が挙げられる。上記材料を厚み0.1〜100μｍの板状体または箔状体に成形して用いることが好ましい。   The obtained positive electrode mixture can be applied to a current collector and then dried to form a positive electrode layer. From the viewpoint of suppressing electrical resistance in the positive electrode layer, the thickness of the positive electrode layer is preferably 10 to 200 μm, and more preferably 20 to 100 μm. A conventionally well-known material can be used for a collector. Specifically, indium, copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, lithium, or an alloy thereof can be given. It is preferable to use the above material by forming it into a plate or foil having a thickness of 0.1 to 100 μm.

正極合剤の集電体への塗布は、ダイコーター、ドクターブレード等を用いることができる。集電体上に塗布された正極合剤は、熱処理し、溶媒を除去する。熱処理温度は、80〜200℃が好ましく、熱処理時間は30〜120分間が好ましい。熱処理後の正極合剤を真空乾燥させることにより溶媒が完全に除去され、本発明に用いる正極層を形成することができる。真空乾燥は、好ましくは80〜200℃、より好ましくは80〜120℃で行われる。乾燥後の正極層の厚みは10〜100μｍが好ましい。   A die coater, a doctor blade, or the like can be used to apply the positive electrode mixture to the current collector. The positive electrode mixture applied on the current collector is heat-treated to remove the solvent. The heat treatment temperature is preferably 80 to 200 ° C., and the heat treatment time is preferably 30 to 120 minutes. The positive electrode mixture after the heat treatment is vacuum dried to completely remove the solvent, and the positive electrode layer used in the present invention can be formed. The vacuum drying is preferably performed at 80 to 200 ° C, more preferably 80 to 120 ° C. The thickness of the positive electrode layer after drying is preferably 10 to 100 μm.

［リチウムイオン二次電池用正極活物質の製造方法］
本発明の正極層に含有される被覆正極活物質の製造方法は、被覆正極活物質材料液を調製する混合工程と、溶媒除去工程と、焼成工程とを含む。 [Method for producing positive electrode active material for lithium ion secondary battery]
The method for producing a coated positive electrode active material contained in the positive electrode layer of the present invention includes a mixing step of preparing a coated positive electrode active material material solution, a solvent removing step, and a firing step.

（混合工程）
本発明に用いられる被覆正極活物質材料液は、被覆材原料として、リチウム源となるリチウムアルコキシドと、リン酸と、遷移金属源となる遷移金属アルコキシドを溶媒中で均質に分散するまで混合してゲル溶液を調製し、得られたゲル溶液に正極活物質を混合させることにより得られる。該遷移金属アルコキシドとしては、ジルコニウムプロポキシドが好ましく選択される。 (Mixing process)
The coated positive electrode active material solution used in the present invention is prepared by mixing lithium alkoxide serving as a lithium source, phosphoric acid, and transition metal alkoxide serving as a transition metal source as a coating material raw material until they are uniformly dispersed in a solvent. It is obtained by preparing a gel solution and mixing the positive electrode active material with the obtained gel solution. As the transition metal alkoxide, zirconium propoxide is preferably selected.

上記ゲル溶液の溶媒は、少量の水とアルコールとを混合させたものが好ましい。これにより溶質との相溶性を向上させることができる。アルコールとしては、イソプロパノール、エタノール、メタノールが好ましい。水の添加量は、アルコールに対して1〜6ｍｏｌ％が好ましい。   The solvent of the gel solution is preferably a mixture of a small amount of water and alcohol. Thereby, compatibility with a solute can be improved. As alcohol, isopropanol, ethanol, and methanol are preferable. The amount of water added is preferably 1 to 6 mol% with respect to the alcohol.

リチウムアルコキシドと、リン酸と、遷移金属源としての遷移金属アルコキシドとは、被覆材の所望の組成比に対応させた添加量でゲル溶液に添加される。本発明においては、ゲル溶液に含有される各原料の組成比と、溶媒除去工程と焼成工程とを経て得られる被覆材との組成比がほぼ変わらない。したがって、ゲル溶液調製時の各添加量を調節することで、所望の組成比を備える本発明の被覆材を得ることができる。該被覆材のイオン電導度は、10-2〜10-8Ｓ／ｃｍであり、より好ましくは10-2〜10-6Ｓ／ｃｍである。溶質の分散状態に対応してアセト酢酸エチルを添加しゲル化スピードを調節することも好ましい。 Lithium alkoxide, phosphoric acid, and transition metal alkoxide as a transition metal source are added to the gel solution in an amount corresponding to a desired composition ratio of the coating material. In the present invention, the composition ratio of each raw material contained in the gel solution and the composition ratio of the coating material obtained through the solvent removal step and the firing step are not substantially changed. Therefore, the coating material of this invention provided with a desired composition ratio can be obtained by adjusting each addition amount at the time of gel solution preparation. The ion conductivity of the coating material is 10 −2 to 10 −8 S / cm, and more preferably 10 −2 to 10 −6 S / cm. It is also preferable to adjust the gelation speed by adding ethyl acetoacetate corresponding to the solute dispersion state.

上記のゲル溶液に所定の正極活物質を添加し、正極活物質が均質に分散するまで撹拌し被覆正極活物質材料液を調製する。正極活物質の添加量は、正極活物質添加後のゲル溶液において、被覆材の濃度が正極活物質に対し、好ましくは0.01ｍｏｌ％以上2.0ｍｏｌ％以下になるように調節される。上記の添加量の上限を超えると、被覆材の膜厚が厚くなり電気抵抗が大きくなる。下限より少ない添加量の場合、正極活物質の被覆性が不十分となり、正極活物質と固体電解質とが直接接触して抵抗成分が生成される。上記のゲル溶液にさらに公知の分散剤等を添加してもよい。   A predetermined positive electrode active material is added to the gel solution and stirred until the positive electrode active material is uniformly dispersed to prepare a coated positive electrode active material material solution. The addition amount of the positive electrode active material is adjusted so that the concentration of the coating material is preferably 0.01 mol% or more and 2.0 mol% or less with respect to the positive electrode active material in the gel solution after the addition of the positive electrode active material. When the upper limit of the above addition amount is exceeded, the coating material becomes thick and the electrical resistance increases. When the addition amount is less than the lower limit, the coverage of the positive electrode active material becomes insufficient, and the positive electrode active material and the solid electrolyte are in direct contact with each other to generate a resistance component. You may add a well-known dispersing agent etc. to said gel solution further.

（被覆工程）
上記混合工程で調整された被覆正極活物質材料液を加熱しながら撹拌して溶媒を蒸発させ、乾燥させる。処理温度は、用いられる溶媒を蒸発させることができる温度であればよく、好ましくは40〜100℃であり、より好ましくは40〜60℃である。上記の加熱撹拌は、被覆正極活物質材料液に、超音波を照射しながら行うことが好ましい。これによりゲル状の被覆正極活物質材料液中の微粒子が凝集してできる塊をほぐしながら、溶媒除去を行うことができる。その結果、正極活物質の表面に均一な膜厚で被覆材を担持させた被覆正極活物質前駆体を得ることができる。上記のような均一な被覆層が得られるならば、正極活物質に被覆溶液を噴霧し乾燥するなど、他の方法を採用しても良い。 (Coating process)
The coated positive electrode active material liquid prepared in the mixing step is stirred while heating to evaporate the solvent and dry. The treatment temperature may be any temperature that can evaporate the solvent used, and is preferably 40 to 100 ° C, more preferably 40 to 60 ° C. The heating and stirring is preferably performed while irradiating the coated positive electrode active material material solution with ultrasonic waves. Thus, the solvent can be removed while loosening a lump formed by agglomeration of fine particles in the gel-like coated positive electrode active material liquid. As a result, a coated positive electrode active material precursor in which a coating material is supported on the surface of the positive electrode active material with a uniform film thickness can be obtained. If a uniform coating layer as described above can be obtained, other methods such as spraying a coating solution on the positive electrode active material and drying may be employed.

（焼成工程）
続いて焼成工程により、上記の溶媒除去工程で除去しきれなかった溶媒を除去し、かつ正極活物質の表面に担持される被覆正極活物質前駆体を焼成する。焼成温度は、300〜750℃が好ましく、350〜500℃がより好ましく、350〜400℃がさらに好ましい。焼成温度を350〜500℃の範囲内にすることで、非晶質の被覆材で正極活物質を被覆させることができる。被覆材の膜厚は、好ましくは0.1〜100ｎｍであり、より好ましくは0.5〜20ｎｍになる。 (Baking process)
Subsequently, in the firing step, the solvent that could not be removed in the solvent removal step is removed, and the coated positive electrode active material precursor supported on the surface of the positive electrode active material is fired. The firing temperature is preferably 300 to 750 ° C, more preferably 350 to 500 ° C, and further preferably 350 to 400 ° C. By setting the firing temperature within the range of 350 to 500 ° C., the positive electrode active material can be coated with an amorphous coating material. The film thickness of the coating material is preferably 0.1 to 100 nm, more preferably 0.5 to 20 nm.

焼成温度が上記の好ましい範囲を外れる場合、電池特性が劣化する。焼成時間は60〜120分間が好ましく、40〜80分間がより好ましい。焼成工程においては、酸素ガスを吹き込みながら行ってもよい。その場合、被覆正極活物質材料液に含有される遷移金属の還元を抑制し、充放電容量を維持することができる。   When the firing temperature is outside the above preferred range, the battery characteristics are deteriorated. The firing time is preferably 60 to 120 minutes, more preferably 40 to 80 minutes. The firing step may be performed while blowing oxygen gas. In that case, reduction of the transition metal contained in the coated positive electrode active material liquid can be suppressed, and the charge / discharge capacity can be maintained.

［負極合材製造工程］
負極合剤は、乳鉢などによって直接混合するか、上記の所定の負極活物質と硫化物系固体電解質とを溶媒中で混合させることにより調製される。溶媒としては、Ｎ−メチル−２−ピロリドン（ＮＭＰ）、Ｎ, Ｎ-ジメチルアセトアミド、Ｎ, Ｎ-ジメチルホルムアミド等を用いることが好ましい。適宜溶媒や増粘剤が添加される。これにより、集電体上への塗布時のハンドリング性が良好な負極合剤となる。負極活物質と硫化物系固体電解質との混合比は、質量比にして70：30〜40：60が好ましい。これにより負極活物質と硫化物系固体電解質との接触面積を確保でき、リチウムイオンの伝導性を良好にできる。負極合剤には結着剤や導電助剤が適宜添加される。 [Negative electrode composite production process]
The negative electrode mixture is prepared by directly mixing in a mortar or the like, or by mixing the predetermined negative electrode active material and the sulfide solid electrolyte in a solvent. As the solvent, N-methyl-2-pyrrolidone (NMP), N, N-dimethylacetamide, N, N-dimethylformamide or the like is preferably used. A solvent and a thickener are added as appropriate. Thereby, it becomes a negative mix with favorable handling property at the time of application | coating on a collector. The mixing ratio of the negative electrode active material and the sulfide-based solid electrolyte is preferably 70:30 to 40:60 in terms of mass ratio. Thereby, the contact area of a negative electrode active material and a sulfide type solid electrolyte can be ensured, and the conductivity of lithium ion can be made favorable. A binder and a conductive aid are appropriately added to the negative electrode mixture.

直接混合による場合、被覆負極活物質と、硫化物系固体電解質との粉末を上記の所定の範囲内の混合比で乳鉢に入れ、更に結着剤と導電助剤との各粉末を添加し、全ての成分が均質になるまで混合させることで、本発明に用いる負極合剤を得ることができる。得られた負極合剤は、ペレット化して後に説明する積層工程に用いられる。   In the case of direct mixing, put the powder of the coated negative electrode active material and the sulfide-based solid electrolyte in a mortar at a mixing ratio within the above predetermined range, and further add each powder of a binder and a conductive aid, The negative electrode mixture used in the present invention can be obtained by mixing until all the components are homogeneous. The obtained negative electrode mixture is pelletized and used in a laminating process described later.

溶媒を用いて負極合剤を調製する場合、上記の負極合剤をダイコーター、ドクターブレード等を用いて集電体上に塗布し、乾燥させることにより負極層を形成することができる。負極層の厚みは、0.1〜100μmとすることが好ましく、1〜50μmとすることがより好ましい。集電体は、正極層を形成させる集電体と同じものを用いることができる。   In the case of preparing a negative electrode mixture using a solvent, the negative electrode layer can be formed by applying the above negative electrode mixture onto a current collector using a die coater, a doctor blade or the like and drying it. The thickness of the negative electrode layer is preferably 0.1 to 100 μm, and more preferably 1 to 50 μm. As the current collector, the same current collector as that for forming the positive electrode layer can be used.

集電体上に塗布された負極合剤は、熱処理し、溶媒を除去する。熱処理温度は、80〜200℃が好ましく、熱処理時間は30〜120分間が好ましい。熱処理後の負極合剤を真空乾燥させることにより溶媒が完全に除去され、本発明に用いる負極層を形成することができる。真空乾燥は、好ましくは80〜200℃、より好ましくは100〜120℃で行われる。乾燥後の負極層の厚みは1〜100μmが好ましい。   The negative electrode mixture applied on the current collector is heat-treated to remove the solvent. The heat treatment temperature is preferably 80 to 200 ° C., and the heat treatment time is preferably 30 to 120 minutes. By vacuum drying the negative electrode mixture after the heat treatment, the solvent is completely removed, and the negative electrode layer used in the present invention can be formed. The vacuum drying is preferably performed at 80 to 200 ° C, more preferably 100 to 120 ° C. The thickness of the negative electrode layer after drying is preferably 1 to 100 μm.

［積層工程］
本発明のリチウムイオン二次電池の積層構造の形成においては、まず負極層および正極層は、集電体上に予め積層させ、セル容器の内壁に、負極層を積層させた集電体と正極層を積層させた集電体とを対向させて配置する。さらに負極層と正極層との間に硫化物系固体電解質を充填し、集電体、負極層、硫化物系固体電解質層、正極層、集電体の順に積層された積層体を形成する。該積層体を所定の圧力条件で加圧することにより、本発明のリチウムイオン二次電池を得ることができる。セル容器の形状は特に制限されないが、円筒状が好ましい。加圧後の積層体において、各層の厚みは、負極層が0.1〜50μm、硫化物系固体電解質層が1〜200μm、正極層が1〜200μmが好ましい。 [Lamination process]
In the formation of the laminated structure of the lithium ion secondary battery of the present invention, the negative electrode layer and the positive electrode layer are first laminated in advance on the current collector, and the current collector and the positive electrode obtained by laminating the negative electrode layer on the inner wall of the cell container It arrange | positions facing the electrical power collector which laminated | stacked the layer. Further, a sulfide-based solid electrolyte is filled between the negative electrode layer and the positive electrode layer to form a laminate in which a current collector, a negative electrode layer, a sulfide-based solid electrolyte layer, a positive electrode layer, and a current collector are stacked in this order. By pressing the laminate under a predetermined pressure condition, the lithium ion secondary battery of the present invention can be obtained. The shape of the cell container is not particularly limited, but a cylindrical shape is preferable. In the laminate after pressing, the thickness of each layer is preferably 0.1 to 50 μm for the negative electrode layer, 1 to 200 μm for the sulfide solid electrolyte layer, and 1 to 200 μm for the positive electrode layer.

他の形成方法としては、セル容器の内壁に、ペレット状の負極合剤を厚み0.1〜100μｍで積層する。積層させた負極合剤層上に硫化物系固体電解質を厚み10〜100μｍで積層する。積層させた硫化物系固体電解質の層上にペレット状の正極合剤を厚み0.1〜100μｍで積層する。得られた積層体を圧力3〜6ｔｏｎ／ｃｍ2で加圧することで本発明のリチウムイオン二次電池の積層構造を形成することができる。 As another forming method, a pellet-shaped negative electrode mixture is laminated with a thickness of 0.1 to 100 μm on the inner wall of the cell container. A sulfide-based solid electrolyte is laminated with a thickness of 10 to 100 μm on the laminated negative electrode mixture layer. A pellet-shaped positive electrode mixture is laminated with a thickness of 0.1 to 100 μm on the laminated sulfide-based solid electrolyte layer. The laminated structure of the lithium ion secondary battery of the present invention can be formed by pressurizing the obtained laminated body at a pressure of 3 to 6 ton / cm 2 .

本発明のリチウムイオン二次電池は、正極活物質が所定の被覆材で被覆されるため正極活物質と硫化物固体電解質との反応による抵抗成分の生成を防止する。これにより正極活物質と硫化物系固体電解質との界面抵抗が抑制され、良好な充放電容量とサイクル特性を発揮する。本発明は、携帯情報端末、電気自動車用途に好適である。   In the lithium ion secondary battery of the present invention, since the positive electrode active material is coated with a predetermined coating material, the generation of a resistance component due to the reaction between the positive electrode active material and the sulfide solid electrolyte is prevented. Thereby, the interfacial resistance between the positive electrode active material and the sulfide-based solid electrolyte is suppressed, and good charge / discharge capacity and cycle characteristics are exhibited. The present invention is suitable for portable information terminals and electric vehicle applications.

［実施例１］
Li2SとP2S5とをｍｏｌ％比として80/20の比率でメカニカルミリング処理（ＭＭ処理）により混合させ硫化物系固体電解質を得た。硫化物系固体電解質の平均粒子径は、10μmであった。 [Example 1]
Li 2 S and P 2 S 5 were mixed by mechanical milling (MM treatment) at a molar ratio of 80/20 to obtain a sulfide-based solid electrolyte. The average particle diameter of the sulfide-based solid electrolyte was 10 μm.

１Ｍリチウムメトキシドメタノール溶液0.4質量ｇと、ジルコニウム（ＩＶ）プロポキシド0.34質量ｇと酸化リン（Ｐ2Ｏ5）0.11質量ｇとを、イソプロパノールとアセト酢酸エチルと水の混合溶液中で30分混合した。この混合溶液中に、正極活物質としてのLiNi0.8Co0.15Al0.05O2（以下、「NCA」と記載する。）を5ｇ添加した。 0.4M g of 1M lithium methoxide methanol solution, 0.34 mass g of zirconium (IV) propoxide and 0.11 mass g of phosphorus oxide (P 2 O 5 ) were mixed in a mixed solution of isopropanol, ethyl acetoacetate and water for 30 minutes. did. To this mixed solution, 5 g of LiNi 0.8 Co 0.15 Al 0.05 O 2 (hereinafter referred to as “NCA”) as a positive electrode active material was added.

得られた混合溶液を40℃に加熱して撹拌しながら溶媒を蒸発乾燥させた。上記の乾燥処理は、混合溶液には超音波を照射しながら行った。これにより正極活物質表面にLiZr2(PO4)3の反応前駆体が担持された。さらに、正極活物質表面へ担持されたLiZr2(PO4)3の前駆体を、酸素を吹き込みながら350℃で1時間焼成した。焼成後1.0 ｍｏｌ％のLiZr2(PO4)3が表面に被覆された被覆正極活物質を得た。被覆正極活物質の平均粒子径は、10μmであった。得られた被覆正極活物質と硫化物系固体電解質と導電助剤としての炭素材料とを、混合比（質量％比）として60/35/5の比率で乳鉢を用いて均質になるまで混合し、ハンドプレスによりペレット化させた正極合剤を得た。 The obtained mixed solution was heated to 40 ° C. and the solvent was evaporated to dryness while stirring. The drying process was performed while irradiating the mixed solution with ultrasonic waves. As a result, a reaction precursor of LiZr 2 (PO 4 ) 3 was supported on the surface of the positive electrode active material. Further, the precursor of LiZr 2 (PO 4 ) 3 supported on the surface of the positive electrode active material was fired at 350 ° C. for 1 hour while blowing oxygen. After firing, a coated positive electrode active material having a surface coated with 1.0 mol% LiZr 2 (PO 4 ) 3 was obtained. The average particle diameter of the coated positive electrode active material was 10 μm. The obtained coated positive electrode active material, sulfide-based solid electrolyte, and carbon material as a conductive additive are mixed in a mortar at a mixing ratio (mass% ratio) of 60/35/5 until homogeneous. A positive electrode mixture pelletized by a hand press was obtained.

負極活物質として使用する、平均粒子径10μmのグラファイトと、硫化物系固体電解質と、導電助剤である炭素材料とを質量％比として60/35/5の比率で乳鉢を用いて均質になるまで混合し、ハンドプレスによりペレット化させた負極合剤を得た。   Homogeneous using a mortar at a ratio of 60/35/5 as a mass% ratio of graphite having an average particle diameter of 10 μm, a sulfide-based solid electrolyte, and a carbon material as a conductive aid, used as a negative electrode active material And a negative electrode mixture that was pelletized by a hand press was obtained.

ペレット化された正極合剤と負極合剤とを、それぞれステンレス製集電体上に積層させて正極層と負極層とを作製した。   The pelletized positive electrode mixture and negative electrode mixture were respectively laminated on a stainless steel current collector to produce a positive electrode layer and a negative electrode layer.

セル容器の内壁に、上記負極層を配置した。配置させた負極層上に、硫化物系固体電解質を70ｍｇ積層し、成型機で軽く表面を整えた。さらに非晶質のLiZr2(PO4)3を被覆させた正極活物質を含有する、上記正極層を積層した。得られた積層体を3ｔ／ｃｍ２の圧力で加圧して実施例１のリチウムイオン二次電池を得た。 The negative electrode layer was disposed on the inner wall of the cell container. 70 mg of a sulfide-based solid electrolyte was laminated on the arranged negative electrode layer, and the surface was lightly adjusted with a molding machine. Further, the positive electrode layer containing a positive electrode active material coated with amorphous LiZr 2 (PO 4 ) 3 was laminated. The obtained laminate was pressurized at a pressure of 3 t / cm 2 to obtain a lithium ion secondary battery of Example 1.

［実施例２］
被覆材の出発原料においてジルコニウムピロポキシドから、チタニウムプロポキシドに代えたほかは、実施例１と同様にして、実施例２のリチウムイオン二次電池を得た。 [Example 2]
A lithium ion secondary battery of Example 2 was obtained in the same manner as Example 1 except that zirconium pyropoxide was replaced with titanium propoxide as the starting material for the coating material.

［比較例］
正極活物質としてのＮＣＡと硫化物系固体電解質と導電助剤としての炭素材料とを、混合比（質量％比）として60/35/5の比率で乳鉢を用いて均質になるまで混合し、ハンドプレスによりペレット化させた正極合剤を得た。上記正極合剤には本発明の被覆材原料を添加しなかった。したがって該正極活物質は、所定の被覆材で被覆されなかった。上記の正極合剤を用いた他は、実施例１と同様にして比較例のリチウムイオン二次電池を得た。 [Comparative example]
NCA as a positive electrode active material, sulfide-based solid electrolyte, and carbon material as a conductive additive are mixed using a mortar at a mixing ratio (mass% ratio) of 60/35/5 until homogeneous. A positive electrode mixture pelletized by a hand press was obtained. The coating material of the present invention was not added to the positive electrode mixture. Therefore, the positive electrode active material was not coated with a predetermined coating material. A lithium ion secondary battery of a comparative example was obtained in the same manner as in Example 1 except that the positive electrode mixture was used.

実施例１、実施例２および比較例のリチウムイオン二次電池を、25℃で、0.05Ｃの定電流で、上限電圧4.0Ｖまで充電し、充電状態のインピーダンスを測定した後、放電終止電圧2.5Ｖまで0.05Ｃ放電し初期放電容量を測定した。同様にして0.05 Cの定電流で充電した後、1 Cで放電行い、1 Cの放電容量を0.05 Cの放電容量で除した負荷特性を測定し、当該試験用セルのサイクル特性を評価した。評価結果を表１に示す。   The lithium ion secondary batteries of Example 1, Example 2 and Comparative Example were charged at 25 ° C. with a constant current of 0.05 C to an upper limit voltage of 4.0 V, and the impedance of the charged state was measured. 0.05C was discharged to V and the initial discharge capacity was measured. Similarly, after charging at a constant current of 0.05 C, discharging was performed at 1 C, the load characteristics obtained by dividing the discharge capacity of 1 C by the discharge capacity of 0.05 C were measured, and the cycle characteristics of the test cell were evaluated. The evaluation results are shown in Table 1.

１００ リチウムイオン二次電池
２００ 正極層
２０１ 被覆正極活物質
２０２ 正極活物質
２０３ 被覆材
３００ 固体電解質層
４００ 負極層
５０１、５０２ 集電体
DESCRIPTION OF SYMBOLS 100 Lithium ion secondary battery 200 Positive electrode layer 201 Coated positive electrode active material 202 Positive electrode active material 203 Coating material 300 Solid electrolyte layer 400 Negative electrode layer 501, 502 Current collector

Claims (9)

Ｓｃ、Ｔｉ、Ｖ、Ｙ、Ｚｒ、Ｎｂ、Ｃａ、Ｓｒ、Ｂａ、Ｈｆ、Ｔａ、Ｃｒ、Ｍｏ、Ｗのうちいずれか一種以上の元素と、リチウムと、リン酸とを含有しイオン伝導性を備える被覆材で正極活物質を被覆させた、被覆正極活物質を含有する正極層と、負極層と、硫化物系固体電解質を含有する固体電解質層とを備えるリチウムイオン二次電池。   Sc, Ti, V, Y, Zr, Nb, Ca, Sr, Ba, Hf, Ta, Cr, Mo, and W, containing at least one element, lithium, and phosphoric acid A lithium ion secondary battery comprising a positive electrode layer containing a coated positive electrode active material, a negative electrode layer, and a solid electrolyte layer containing a sulfide-based solid electrolyte, wherein the positive electrode active material is coated with a covering material provided. 被覆材が非晶質である請求項１に記載のリチウムイオン二次電池。   The lithium ion secondary battery according to claim 1, wherein the coating material is amorphous. 被覆正極活物質に含まれる被覆材の濃度が0.01ｍｏｌ％以上2.0ｍｏｌ％以下である請求項１または請求項２に記載のリチウムイオン二次電池。   The lithium ion secondary battery according to claim 1 or 2, wherein the concentration of the coating material contained in the coated positive electrode active material is 0.01 mol% or more and 2.0 mol% or less. ＬｉＺｒ２（ＰＯ４）３を含有する被覆材を用いる請求項１ないし請求項３のいずれかに記載のリチウムイオン二次電池。 The lithium ion secondary battery according to any one of claims 1 to 3, wherein a coating material containing LiZr 2 (PO 4 ) 3 is used. 正極活物質は、層状岩塩型構造を有し、かつ遷移金属酸化物のリチウム塩である、請求項１ないし請求項４のいずれかに記載のリチウムイオン二次電池。   The lithium ion secondary battery according to any one of claims 1 to 4, wherein the positive electrode active material has a layered rock salt structure and is a lithium salt of a transition metal oxide. 正極活物質は、層状岩塩型構造を有するＬｉＣｏＯ２、または下記式（１）で表され、かつ層状岩塩型構造を有する３元系金属酸化物である請求項１ないし請求項４のいずれかに記載のリチウムイオン二次電池。
（上記式（１）において、ＭはＡｌ又はＭｎであり、ｘ、ｙ、ｚは、それぞれ0＜ｘ＜1、0＜ｙ＜1、0＜ｚ＜1、およびｘ＋ｙ＋ｚ＜1を満たす値である。） The positive electrode active material is LiCoO 2 having a layered rock salt type structure, or a ternary metal oxide represented by the following formula (1) and having a layered rock salt type structure. The lithium ion secondary battery as described.
(In the above formula (1), M is Al or Mn, and x, y, z are values satisfying 0 <x <1, 0 <y <1, 0 <z <1, and x + y + z <1, respectively. is there.) Ｌｉ２ＳとＰ２Ｓ５とを含有する硫化物系固体電解質を用いる請求項１ないし請求項６のいずれかに記載のリチウムイオン二次電池。 The lithium ion secondary battery according to any one of claims 1 to 6, wherein a sulfide solid electrolyte containing Li 2 S and P 2 S 5 is used. 正極活物質とリチウムアルコキシドとジルコニウムプロポキシドと酸化リンとを溶媒中で混合し被覆正極活物質材料液を調製する混合工程と、被覆正極活物質前駆体を得る被覆工程と、酸素ガスもしくは大気雰囲気下、焼成温度300〜750℃で被覆正極活物質前駆体を焼成し、正極活物質をイオン伝導性を有するＬｉＺｒ２（ＰＯ３）４で被覆させた被覆正極活物質を製造する焼成工程とを含む、リチウムイオン二次電池用正極活物質の製造方法。 A mixing step of preparing a coated positive electrode active material liquid by mixing a positive electrode active material, lithium alkoxide, zirconium propoxide, and phosphorus oxide in a solvent, a coating step of obtaining a coated positive electrode active material precursor, and oxygen gas or atmospheric atmosphere And firing a coated positive electrode active material precursor at a firing temperature of 300 to 750 ° C. and producing a coated positive electrode active material in which the positive electrode active material is coated with LiZr 2 (PO 3 ) 4 having ion conductivity. A method for producing a positive electrode active material for a lithium ion secondary battery. 酸素ガスもしくは大気雰囲気下、焼成温度300〜400℃の範囲内で被覆正極活物質前駆体を焼成し、イオン電導性を有する非晶質のＬｉＺｒ２（ＰＯ３）４で被覆させた被覆正極活物質を製造する焼成工程を含む、請求項８に記載のリチウムイオン二次電池用正極活物質の製造方法。 A coated positive electrode active in which a coated positive electrode active material precursor is fired in an oxygen gas or air atmosphere at a firing temperature of 300 to 400 ° C. and coated with amorphous LiZr 2 (PO 3 ) 4 having ion conductivity. The manufacturing method of the positive electrode active material for lithium ion secondary batteries of Claim 8 including the baking process which manufactures a substance.
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