JP2017054783A - Positive electrode active material particle, lithium ion secondary battery arranged by use thereof, and method for manufacturing positive electrode active material particles - Google Patents

Positive electrode active material particle, lithium ion secondary battery arranged by use thereof, and method for manufacturing positive electrode active material particles Download PDF

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JP2017054783A
JP2017054783A JP2015179886A JP2015179886A JP2017054783A JP 2017054783 A JP2017054783 A JP 2017054783A JP 2015179886 A JP2015179886 A JP 2015179886A JP 2015179886 A JP2015179886 A JP 2015179886A JP 2017054783 A JP2017054783 A JP 2017054783A
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positive electrode
active material
electrode active
material particles
lithium
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JP6724271B2 (en
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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
本間　格
Itaru Honma
格 本間
ムルカナハリ デバラジャ
Murukanahari Debaraja
ムルカナハリ デバラジャ
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Tohoku Techno Arch Co Ltd
Samsung R&D Institute Japan Co Ltd
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Tohoku Techno Arch Co Ltd
Samsung R&D Institute Japan Co Ltd
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    • 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
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    • Y02E60/10—Energy storage using batteries

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Abstract

PROBLEM TO BE SOLVED: To provide a lithium cobalt-based positive electrode active material improved in discharge capacity, a lithium ion secondary battery having a positive electrode produced by use of the positive electrode active material, etc.SOLUTION: A lithium secondary ion battery 1 comprises: a positive electrode 3 having positive electrode active material particles; an electrolyte 9; and a negative electrode 5. At least part of the positive electrode active material particles has a spinel type crystal structure in a plate form in which a (111) plane makes at least one principal face. The positive electrode active material particles have an element composition expressed by: LiCoNiO(where 0<x<2).SELECTED DRAWING: Figure 1

Description

本明細書に開示された技術は、リチウムイオン二次電池及び正極活物質の製造方法に関する。   The technology disclosed in the present specification relates to a method of manufacturing a lithium ion secondary battery and a positive electrode active material.

リチウムイオン二次電池用の正極活物質として、スピネル構造を有する材料が知られているが、実用的な容量を示すのはマンガンを有する材料もしくはその一部置換体に限られている。   As a positive electrode active material for a lithium ion secondary battery, a material having a spinel structure is known, but a material having a practical capacity is limited to a material containing manganese or a partially substituted material thereof.

例えば、特許文献１には、リチウムマンガン複合酸化物（LiMn2O4等）が正極活物質として用いられ、炭素質微粒子が負極活物質として用いられたリチウムイオン二次電池が記載されている。 For example, Patent Document 1 describes a lithium ion secondary battery in which lithium manganese composite oxide (LiMn 2 O 4 or the like) is used as a positive electrode active material and carbonaceous fine particles are used as a negative electrode active material.

また、特許文献２には、LiMn2O4等からなる正極活物質の製造方法が記載されている。 Patent Document 2 describes a method for producing a positive electrode active material made of LiMn 2 O 4 or the like.

特開２０１２−１９９０２５号公報JP 2012-199025 A 特開２０１１−８１９２６号公報JP 2011-81926 A

上述の材料のうち電池に用いた場合に実用的な容量を示すスピネル材料は、現在のところマンガンを有する材料とその一部置換体に限られている。   Among the above materials, spinel materials that exhibit a practical capacity when used in batteries are currently limited to materials containing manganese and partially substituted products thereof.

本発明の目的は、放電容量が改善されたリチウムコバルト系のスピネル型正極活物質と、当該正極活物質を用いて作製された正極を有するリチウムイオン二次電池等とを提供することを目的とする。   An object of the present invention is to provide a lithium cobalt-based spinel positive electrode active material with improved discharge capacity, a lithium ion secondary battery having a positive electrode produced using the positive electrode active material, and the like. To do.

本発明の発明者らは、上記課題を解決すべく鋭意検討した結果、リチウムコバルト系の正極活物質粒子の（１１１）面が少なくとも一方の主面となるプレート状で且つスピネル型の結晶構造を有していることによって、上記課題を解決することが可能であることを見出し、本発明を完成するに至った。   The inventors of the present invention have intensively studied to solve the above problems, and as a result, have a plate-like and spinel-type crystal structure in which the (111) plane of the lithium cobalt-based positive electrode active material particles is at least one main surface. It has been found that the above-mentioned problems can be solved by having the present invention, and the present invention has been completed.

すなわち、本明細書に開示された正極活物質粒子は、（１１１）面が少なくとも一方の主面となるプレート状で且つスピネル型の結晶構造を有しており、組成式LiCo2-xNixO4（ただし、０＜ｘ＜２）で表される元素組成からなる。また、本明細書に開示されたリチウムイオン二次電池は、上述の正極活物質粒子を有する正極と、電解質と、負極を備えている。 That is, the positive electrode active material particles disclosed in the present specification have a plate-like and spinel-type crystal structure in which the (111) plane is at least one main surface, and the composition formula LiCo 2-x Ni x It consists of an element composition represented by O 4 (where 0 <x <2). Moreover, the lithium ion secondary battery disclosed in this specification includes a positive electrode having the above-described positive electrode active material particles, an electrolyte, and a negative electrode.

本明細書に開示された正極活物質粒子を正極に用いれば、リチウムイオン二次電池の放電容量を大きく改善することができる。   If the positive electrode active material particles disclosed in the present specification are used for the positive electrode, the discharge capacity of the lithium ion secondary battery can be greatly improved.

図１は、本明細書に開示された実施形態に係るリチウムイオン二次電池を模式的に示す断面図である。FIG. 1 is a cross-sectional view schematically showing a lithium ion secondary battery according to an embodiment disclosed in the present specification. 図２は、本明細書に開示された実施例と参考例とに係る正極活物質粒子について、Ｘ線回折（ＸＲＤ）法による測定結果を示す図である。FIG. 2 is a diagram showing measurement results by an X-ray diffraction (XRD) method for positive electrode active material particles according to Examples and Reference Examples disclosed in the present specification. 図３は、参考例１に係るリチウムコバルト複合酸化物の透過型電子顕微鏡（ＴＥＭ）による写真を示す図である。FIG. 3 is a view showing a photograph of a lithium cobalt composite oxide according to Reference Example 1 using a transmission electron microscope (TEM). 図４は、実施例５に係るリチウムコバルトニッケル複合酸化物のＴＥＭによる写真を示す図である。4 is a TEM photograph of the lithium cobalt nickel composite oxide according to Example 5. FIG. 図５は、実施例４、５及び参考例１に係る正極活物質の放電特性を示す図である。FIG. 5 is a graph showing the discharge characteristics of the positive electrode active materials according to Examples 4 and 5 and Reference Example 1.

−正極活物質粒子及びリチウムイオン二次電池の構成−
図１は、本明細書に開示された実施形態に係るリチウムイオン二次電池を模式的に示す断面図である。なお、図１に示すのは本実施形態のリチウムイオン二次電池の一例であって、実際の電池構成はこれに限定されない。 -Configuration of positive electrode active material particles and lithium ion secondary battery-
FIG. 1 is a cross-sectional view schematically showing a lithium ion secondary battery according to an embodiment disclosed in the present specification. FIG. 1 shows an example of the lithium ion secondary battery of the present embodiment, and the actual battery configuration is not limited to this.

図１に示すように、本明細書に開示されたリチウムイオン二次電池１は、正極活物質粒子を有する正極３と、負極５と、正極３と負極５との間に満たされた電解質９と、正極３と負極５との間に設置され、電解質９を仕切るセパレータ７と、正極３、負極５、セパレータ７及び電解質９を収容する容器１１とを備えている。   As shown in FIG. 1, a lithium ion secondary battery 1 disclosed in the present specification includes a positive electrode 3 having positive electrode active material particles, a negative electrode 5, and an electrolyte 9 filled between the positive electrode 3 and the negative electrode 5. And a separator 7 that is installed between the positive electrode 3 and the negative electrode 5 and partitions the electrolyte 9, and a container 11 that houses the positive electrode 3, the negative electrode 5, the separator 7, and the electrolyte 9.

電解質９はリチウムイオンが溶出できる材料であればよく、液体であっても、ゲル状であってもよい。リチウムイオン二次電池１が全固体型の電池である場合には電解質９は固体であってもよい。電解質９の構成材料として、例えば液体ではリチウム塩が溶解したエチレンカーボネート(EC)、プロピレンカーボネート(PC)が挙げられ、固体ではNASICON型酸化物LixAlyTiz(PO4)3、ペロブスカイト型酸化物LaxLiyTiO3、硫化物Li10GeP2S12、Li2S-P2S5を主原料とした硫化物固体電解質(Li3PS4, Li7P3S11, Li6PS5Cl, Li10GeP2S12等)が挙げられる。 The electrolyte 9 may be any material that can elute lithium ions, and may be liquid or gelled. When the lithium ion secondary battery 1 is an all-solid battery, the electrolyte 9 may be solid. As the constituent material of the electrolyte 9, for example, ethylene carbonate lithium salt is dissolved in a liquid (EC), propylene carbonate (PC) can be mentioned, NASICON type oxide in solid Li x Al y Ti z (PO 4) 3, perovskite Oxide La x Li y TiO 3 , sulfide Li 10 GeP 2 S 12 , sulfide solid electrolyte made mainly of Li 2 SP 2 S 5 (Li 3 PS 4 , Li 7 P 3 S 11 , Li 6 PS 5 Cl, Li 10 GeP 2 S 12 etc.).

セパレータ７は電子を通さず、リチウムイオンを通す材料で構成されている。セパレータ７の材料としては、ポリエチレンやポリプロピレンからなる微多孔膜等の公知の材料を用いることができる。   The separator 7 is made of a material that does not pass electrons but allows lithium ions to pass. As a material of the separator 7, a known material such as a microporous film made of polyethylene or polypropylene can be used.

負極５は、例えば銅箔等からなる集電体と、集電体に塗布された負極活物質とバインダーとの混合物とを有している。負極活物質としては、黒鉛やハードカーボン等の公知の材料を用いることができる。   The negative electrode 5 has a current collector made of, for example, copper foil, and a mixture of a negative electrode active material and a binder applied to the current collector. As the negative electrode active material, known materials such as graphite and hard carbon can be used.

正極３は、粒子状の正極活物質を有している。具体的に、正極３は、アルミ箔等の集電体と、集電体に塗布された、正極活物質粒子と公知のバインダーとの混合物とを有している。   The positive electrode 3 has a particulate positive electrode active material. Specifically, the positive electrode 3 has a current collector such as an aluminum foil, and a mixture of positive electrode active material particles and a known binder applied to the current collector.

本実施形態の正極活物質粒子は、（１１１）面が少なくとも一方の主面となるプレート状の結晶構造であり且つスピネル型の結晶構造を有している。ここで、本明細書において主面とは、プレート状の結晶において、厚さ方向と直交し、表裏で対向する２つの広い板面のことを指すものとする。正極活物質の結晶構造の主面形状は六角形となっている。   The positive electrode active material particles of the present embodiment have a plate-like crystal structure in which the (111) plane is at least one main surface, and a spinel crystal structure. Here, in this specification, the main surface refers to two wide plate surfaces that are orthogonal to the thickness direction and face each other on the front and back sides in a plate-like crystal. The main surface shape of the crystal structure of the positive electrode active material is a hexagon.

正極活物質粒子の元素組成はLiCo2-xNixO4（ただし、０＜ｘ＜２）で表される。つまり、本実施形態の正極活物質粒子はLiCo2O4のコバルトの一部がニッケルによって置換された材料で構成されている。 Elemental composition of the positive electrode active material particles LiCo 2-x Ni x O 4 ( provided that, 0 <x <2) is represented by. That is, the positive electrode active material particles of the present embodiment are made of a material in which a part of cobalt of LiCo 2 O 4 is replaced by nickel.

本実施形態の正極活物質粒子において、コバルトの一部をニッケルに置き換えていることで、理論上の充放電電位を高くすることができ、理論容量を大きくすることができるため、高容量・小型化が求められる電池用に好適である。ところで、コバルトの一部をニッケルに置換した系は、立方体型の結晶構造を有し、リチウムイオンの挿入脱離を行う（１１１）面が特異的に露出しているわけではない。そのため十分な容量を得にくく、負荷特性も低いものとなる。これに対し、本実施形態の正極活物質粒子では、上述の結晶構造を有していることにより、リチウムイオンの放出及び挿入が行われる（１１１）面の露出面積が、立方体型の結晶構造を持つLiCo2O4に比べて広くなっている。このため、本実施形態の正極活物質を用いることで、LiCo2O4を正極活物質として用いる場合に比べてリチウムイオン二次電池の放電容量を大きくすることができる。また、本実施形態の正極活物質を用いることで充放電速度の向上も期待できる。 In the positive electrode active material particles of this embodiment, by replacing a part of cobalt with nickel, the theoretical charge / discharge potential can be increased and the theoretical capacity can be increased. It is suitable for a battery that needs to be made. By the way, a system in which a part of cobalt is substituted with nickel has a cubic crystal structure, and the (111) plane where lithium ions are inserted and desorbed is not specifically exposed. Therefore, it is difficult to obtain a sufficient capacity, and load characteristics are low. In contrast, the positive electrode active material particles of the present embodiment have the above-described crystal structure, so that the exposed area of the (111) plane where lithium ions are released and inserted has a cubic crystal structure. It is wider than LiCo 2 O 4 . For this reason, by using the positive electrode active material of the present embodiment, the discharge capacity of the lithium ion secondary battery can be increased as compared with the case where LiCo 2 O 4 is used as the positive electrode active material. Moreover, the improvement of charging / discharging speed | velocity can also be anticipated by using the positive electrode active material of this embodiment.

正極活物質粒子の元素組成（LiCo2-xNixO4）において、ｘが０＜ｘ＜２の範囲であれば電池の放電容量を改善することができるが、ｘが０．８以上１．２未満であればより充放電電位を高くするとともに放電容量を十分に大きくすることができるので好ましい。ｘ＝１であれば、放電容量を大きく上昇させることができるので、より好ましい。 In elemental composition of the positive electrode active material particles (LiCo 2-x Ni x O 4), can improve the discharge capacity of the battery so long as x is 0 <x <a 2, x is 0.8 or more 1 Less than .2 is preferable because the charge / discharge potential can be increased and the discharge capacity can be sufficiently increased. If x = 1, the discharge capacity can be greatly increased, which is more preferable.

これは、ｘが０．８未満の場合にはｘが小さくなるにつれて正極活物質粒子の結晶中で立方体構造をとる割合が高く（すなわち、プレート状構造をとる割合が低く）なり、ｘが１．２以上の場合にはｘが大きくなるにつれてプレート状で且つスピネル型の結晶構造が崩れてゆくためである。ｘ＝１の場合に放電容量を大きく上昇させることができるのは、この場合にほぼ全ての正極活物質粒子の結晶構造がプレート型になるためである。   This is because, when x is less than 0.8, the proportion of the positive electrode active material particles having a cubic structure increases as x decreases (that is, the proportion of the plate-like structure decreases), and x is 1 This is because in the case of 2 or more, the plate-like and spinel crystal structure collapses as x increases. The reason why the discharge capacity can be greatly increased in the case of x = 1 is that in this case, the crystal structure of almost all the positive electrode active material particles becomes a plate type.

また、正極活物質粒子の平均粒子径は特に限定されないが、１０００ｎｍ以下であれば好ましい。正極活物質粒子の平均粒子径が１０００ｎｍ以下である場合、平均粒子径が１０００ｎｍを超える場合に比べて正極活物質粒子と液体の電解質９との接触面積を大きくすることができるとともに、リチウムイオンが粒子内部の電極材料に移動する際の移動距離を小さくすることができる。このため、正極活物質粒子を備えたリチウムイオン二次電池の放電容量をより向上させることができる。   The average particle size of the positive electrode active material particles is not particularly limited, but is preferably 1000 nm or less. When the average particle diameter of the positive electrode active material particles is 1000 nm or less, the contact area between the positive electrode active material particles and the liquid electrolyte 9 can be increased as compared with the case where the average particle diameter exceeds 1000 nm, and lithium ions The movement distance when moving to the electrode material inside the particles can be reduced. For this reason, the discharge capacity of the lithium ion secondary battery provided with the positive electrode active material particles can be further improved.

さらに、正極活物質粒子の平均粒子径が５００ｎｍ以下であれば、正極活物質粒子と液体の電解質９との接触面積をより大きくできるので、好ましい。なお、平均粒子径の測定は、粒度分布測定装置を用いて行う。具体的には、ＴＥＭを用いた観察により粒径を直接解析することができる。正極活物質粒子がプレート状である場合、面方向と厚さ方向とで粒径が大きく異なることになるが、本実施形態の正極活物質の場合、面方向のサイズで粒径を判定する。   Furthermore, if the average particle diameter of the positive electrode active material particles is 500 nm or less, the contact area between the positive electrode active material particles and the liquid electrolyte 9 can be increased, which is preferable. The average particle size is measured using a particle size distribution measuring device. Specifically, the particle size can be directly analyzed by observation using a TEM. When the positive electrode active material particles are plate-shaped, the particle size is greatly different between the surface direction and the thickness direction. In the case of the positive electrode active material of this embodiment, the particle size is determined by the size in the surface direction.

また、正極に含まれる正極活物質粒子の粒子径が均一であれば電池特性のばらつきを小さくできる。さらに、集電体上には正極活物質が均一に分散されて塗布されていることが好ましい。   Moreover, if the particle diameter of the positive electrode active material particles contained in the positive electrode is uniform, variation in battery characteristics can be reduced. Furthermore, it is preferable that the positive electrode active material is uniformly dispersed on the current collector.

本実施形態の正極活物質粒子を用いた正極は、リチウムイオン二次電池の正極として用いることができる。   The positive electrode using the positive electrode active material particles of the present embodiment can be used as a positive electrode of a lithium ion secondary battery.

本実施形態の正極活物質粒子の製造方法は、上述の結晶構造を実現できる方法であれば特に限定されないが、例えば超臨界流体を用いる方法であってもよい。   Although the manufacturing method of the positive electrode active material particle of this embodiment will not be specifically limited if it is a method which can implement | achieve the above-mentioned crystal structure, For example, the method using a supercritical fluid may be used.

超臨界流体を用いる方法は、コバルトを含む材料、ニッケルを含む材料及びリチウムを含む材料を超臨界流体中で反応させてリチウム、コバルト、ニッケルを含む金属複合酸化物を生成させるステップと、当該金属複合酸化物とリチウムを含む材料とを混合して反応させることにより、（１１１）面が少なくとも一方の主面となるプレート状で且つスピネル型の結晶構造を有しており、元素組成がLiCo2-xNixO4（ただし、０＜ｘ＜２）で表される正極活物質粒子を製造するステップとを備えている。 A method using a supercritical fluid includes a step of reacting a material containing cobalt, a material containing nickel, and a material containing lithium in a supercritical fluid to form a metal composite oxide containing lithium, cobalt, and nickel; By mixing and reacting the composite oxide and a material containing lithium, the (111) plane has a plate-like and spinel crystal structure with at least one main surface, and the element composition is LiCo 2. and -x Ni x O 4 (where 0 <x <2).

金属複合酸化物をリチウムを含む材料と反応させるステップでは、例えば２５０℃〜４５０℃程度の熱処理を１時間程度行ってもよい。また、コバルトを含む材料としては、例えば硝酸コバルトの水和物（Co(NO3)2・6H2O）等が用いられ、ニッケルを含む材料としては硝酸ニッケルの水和物（Ni(NO3)2・6H2O）等が用いられる。リチウムを含む材料としては例えば水酸化リチウムの水和物（LiOH・H2O）等が用いられる。 In the step of reacting the metal composite oxide with a material containing lithium, for example, heat treatment at about 250 ° C. to 450 ° C. may be performed for about 1 hour. As the material containing cobalt, for example, cobalt nitrate hydrate (Co (NO 3 ) 2 · 6H 2 O) or the like is used, and as the material containing nickel, nickel nitrate hydrate (Ni (NO 3) 2 · 6H 2 O) etc. are used. As a material containing lithium, for example, a hydrate of lithium hydroxide (LiOH.H 2 O) or the like is used.

上述の超臨界状態は、超臨界流体用の装置を用い、反応容器内を２５０℃〜５００℃、２０ＭＰａ〜５０ＭＰａ程度の高温・高圧条件にすることで作り出される。   The above-mentioned supercritical state is created by using a device for a supercritical fluid and setting the inside of the reaction vessel to high temperature and high pressure conditions of about 250 ° C. to 500 ° C. and about 20 MPa to 50 MPa.

この方法によれば、均一なナノサイズの正極活物質粒子を作製することができる。   According to this method, uniform nano-sized positive electrode active material particles can be produced.

−正極活物質粒子の作製−
まず、固体水和物であるCo(NO3)2・6H2O、Ni(NO3)2・6H2O及びLiOH・H2Oを所定の濃度になるようにエタノールに溶解し、５０℃で攪拌及び混合した。エタノール中の硝酸コバルト濃度は０．５Ｍ、硝酸ニッケル濃度は０．５Ｍ、水酸化リチウム濃度は３Ｍとした。 -Production of positive electrode active material particles-
First, Co (NO 3 ) 2 · 6H 2 O, Ni (NO 3 ) 2 · 6H 2 O and LiOH · H 2 O, which are solid hydrates, are dissolved in ethanol to a predetermined concentration, and 50 ° C. Stir and mix with. The concentration of cobalt nitrate in ethanol was 0.5M, the concentration of nickel nitrate was 0.5M, and the concentration of lithium hydroxide was 3M.

次に、この混合溶液を超臨界合成用装置（ＡＫＩＣＯ社製）の容器内に封入し、３００℃、１０ＭＰａの条件下で４０分間上述の金属化合物同士を反応させた。この条件下では、溶媒であるエタノールは超臨界流体となっている。   Next, this mixed solution was sealed in a container of a supercritical synthesis apparatus (manufactured by AKICO), and the above metal compounds were reacted with each other at 300 ° C. and 10 MPa for 40 minutes. Under these conditions, the solvent ethanol is a supercritical fluid.

ここで、上記混合液中のコバルト：ニッケルのモル比を９：１にしたものを実施例１、４：１にしたものを実施例２、７：３にしたものを実施例３、３：２にしたものを実施例４、１：１にしたものを実施例５、２：３にしたものを実施例６とした。   Here, what made the molar ratio of cobalt: nickel in the said liquid mixture 9: 1 into Example 1, 4: 1 changed into Example 2, and 7: 3 changed into Example 3, 3: Example 2 was obtained by changing Example 2 into Example 4, and Example 5 and Example 5 and 2: 3.

次いで、溶媒を留去して得られた粉末をLiOH・H2Oと混合した後、６５０℃、５時間の条件で熱処理を行い、目的とする正極活物質粒子を得た。正極活物質粒子の組成をLiCo2-xNixO4と表すと、実施例１ではｘ＝０．２、実施例２ではｘ＝０．４、実施例３ではｘ＝０．６、実施例４ではｘ＝０．８、実施例５ではｘ＝１．０、実施例６ではｘ＝１．２となった。 Next, after the solvent was distilled off and the powder obtained was mixed with LiOH.H 2 O, heat treatment was performed at 650 ° C. for 5 hours to obtain the desired positive electrode active material particles. When the composition of the positive electrode active material particles is expressed as LiCo 2-x Ni x O 4 , x = 0.2 in Example 1, x = 0.4 in Example 2, x = 0.6 in Example 3, In Example 4, x = 0.8, in Example 5, x = 1.0, and in Example 6, x = 1.2.

また、最初の工程で、硝酸ニッケル溶液を加えずに硝酸コバルト溶液と水酸化リチウム溶液とを混合して超臨界流体中で反応させた後、実施例１〜６と同様の方法で熱処理することで、LiCo2O4の組成を有する正極活物質粒子を作製し、これを参考例１とした。 In the first step, a cobalt nitrate solution and a lithium hydroxide solution are mixed and reacted in a supercritical fluid without adding a nickel nitrate solution, and then heat-treated in the same manner as in Examples 1 to 6. Thus, positive electrode active material particles having a composition of LiCo 2 O 4 were prepared.

以上のようにして得られた実施例１〜６及び参考例１に係る正極活物質粒子の結晶構造を確認するために、ＸＲＤ法による解析を行った。また、上記組成式においてｘ＝０の場合（参考例１；LiCo2O4）とｘ＝１の場合（実施例５；LiCo1.0Ni1.0O4）の正極活物質粒子をそれぞれＴＥＭを用いて撮影し、粒子の外観を確認した。 In order to confirm the crystal structures of the positive electrode active material particles according to Examples 1 to 6 and Reference Example 1 obtained as described above, analysis by the XRD method was performed. Further, in the above composition formula, positive electrode active material particles in the case of x = 0 (Reference Example 1; LiCo 2 O 4 ) and x = 1 (Example 5; LiCo 1.0 Ni 1.0 O 4 ) are respectively used by TEM. Images were taken and the appearance of the particles was confirmed.

−電池の電気化学評価−
先の工程で得られた正極活物質粒子のうち、参考例１及び実施例４、５に係る正極活物質粒子を用いた正極を有する評価セルを作製し、当該評価セルの電気化学評価を行った。具体的には、正極活物質粒子、アセチレンブラック及びポリテトラフルオロエチレン（PTFE）を８０：１０：１０の重量比で乳鉢を用いて混合し、得られた材料を正極材料とした。 -Electrochemical evaluation of batteries-
Of the positive electrode active material particles obtained in the previous step, an evaluation cell having a positive electrode using the positive electrode active material particles according to Reference Example 1 and Examples 4 and 5 was prepared, and electrochemical evaluation of the evaluation cell was performed. It was. Specifically, positive electrode active material particles, acetylene black and polytetrafluoroethylene (PTFE) were mixed at a weight ratio of 80:10:10 using a mortar, and the obtained material was used as a positive electrode material.

負極材料としてはリチウム金属箔を用いた。評価セル中では正極材料及び負極材料を金属メッシュにそれぞれ固定し、電解液（1M LiClO4 in EC:DEC(1:1 volume)）を容器中に封入した。この評価セルを用いて、４．７Ｖから２．７Ｖのカットオフ電圧まで、０．１Ｃの電流密度で充放電試験を行った。 Lithium metal foil was used as the negative electrode material. In the evaluation cell, each of the positive electrode material and the negative electrode material was fixed to a metal mesh, and an electrolytic solution (1M LiClO 4 in EC: DEC (1: 1 volume)) was sealed in a container. Using this evaluation cell, a charge / discharge test was performed at a current density of 0.1 C from a cutoff voltage of 4.7 V to 2.7 V.

−測定結果−
図２は、実施例１〜６及び参考例１に係る正極活物質粒子のＸＲＤ法による測定結果を示す図である。同図に示すように、組成式LiCo2-xNixO4のｘが０〜１．２の範囲で共通する回折角度（図２の横軸）において強度のピークが見られ、ｘが０〜１．２の範囲で正極活物質粒子はスピネル型の結晶構造を有していることが確認できた。ただし、LiCo0.8Ni1.2O4では回折角度が２０°付近の強度のピークが著しく大きくなっており、ｘが１．２未満の場合とは結晶構造が異なっていることが示唆された。 -Measurement results-
FIG. 2 is a diagram illustrating measurement results of positive electrode active material particles according to Examples 1 to 6 and Reference Example 1 by an XRD method. As shown in the figure, an intensity peak is observed at a common diffraction angle (horizontal axis in FIG. 2) when x of the composition formula LiCo 2-x Ni x O 4 is in the range of 0 to 1.2, and x is 0. It was confirmed that the positive electrode active material particles had a spinel type crystal structure in the range of -1.2. However, in LiCo 0.8 Ni 1.2 O 4 , the intensity peak near a diffraction angle of 20 ° is remarkably large, suggesting that the crystal structure is different from the case where x is less than 1.2.

図３は、参考例に係るリチウムコバルト複合酸化物の透過型電子顕微鏡（ＴＥＭ）による写真を示す図であり、図４は、実施例５に係るリチウムコバルトニッケル複合酸化物のＴＥＭによる写真を示す図である。   3 is a view showing a photograph of a lithium cobalt composite oxide according to a reference example by a transmission electron microscope (TEM), and FIG. 4 is a photograph of the lithium cobalt nickel composite oxide according to Example 5 taken by a TEM. FIG.

図３に示す顕微鏡写真から、組成がLiCo2O4である正極活物質粒子の多くは符号Ａで示すような立方体状の結晶構造を有していることが確認できた。これに対し、図４に示すように、組成がLiCo1.0Ni1.0O4である正極活物質粒子の多くは符号Ｂで示すような六角形のプレート状であることが確認できた。立方体状からプレート状への結晶構造の変化は、ニッケルの添加によって生じたと考えられる。 From the micrograph shown in FIG. 3, it was confirmed that many of the positive electrode active material particles having a composition of LiCo 2 O 4 had a cubic crystal structure as indicated by the symbol A. On the other hand, as shown in FIG. 4, it was confirmed that most of the positive electrode active material particles having a composition of LiCo 1.0 Ni 1.0 O 4 have a hexagonal plate shape as indicated by symbol B. The change in the crystal structure from the cubic shape to the plate shape is considered to be caused by the addition of nickel.

図５は、実施例４、５及び参考例１に係る正極活物質の放電特性を示す図である。同図に示す結果から、正極活物質粒子の組成がLiCo0.8Ni1.2O4である場合には正極活物質粒子の組成がLiCo2O4である場合に比べて放電電位が高く、電池の放電容量も大きくできることが確認できた。正極活物質粒子の組成がLiCo1.0Ni1.0O4である場合には、正極活物質粒子の組成がLiCo0.8Ni1.2O4である場合よりもさらに放電容量が大きくできることも確認できた。 FIG. 5 is a graph showing the discharge characteristics of the positive electrode active materials according to Examples 4 and 5 and Reference Example 1. From the results shown in the figure, when the composition of the positive electrode active material particles is LiCo 0.8 Ni 1.2 O 4 , the discharge potential is higher than when the composition of the positive electrode active material particles is LiCo 2 O 4. It was confirmed that the capacity could be increased. It was also confirmed that when the composition of the positive electrode active material particles is LiCo 1.0 Ni 1.0 O 4 , the discharge capacity can be further increased than when the composition of the positive electrode active material particles is LiCo 0.8 Ni 1.2 O 4 .

以上で説明したように、本開示の一例に係る正極活物質粒子は、リチウムイオン二次電池の正極やリチウムイオンキャパシタ等の電極に適用されうる。   As described above, the positive electrode active material particles according to an example of the present disclosure can be applied to electrodes such as a positive electrode of a lithium ion secondary battery and a lithium ion capacitor.

１ リチウムイオン二次電池
３ 正極
５ 負極
７ セパレータ
９ 電解質
１１ 容器 DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 3 Positive electrode 5 Negative electrode 7 Separator 9 Electrolyte 11 Container

Claims (8)

（１１１）面が少なくとも一方の主面となるプレート状で且つスピネル型の結晶構造を有しており、
組成式LiCo2-xNixO4（ただし、０＜ｘ＜２）で表される元素組成からなる、正極活物質粒子。 It has a plate-like and spinel-type crystal structure in which the (111) plane is at least one main surface,
Formula LiCo 2-x Ni x O 4 ( provided that, 0 <x <2) consisting of elemental composition represented by the positive electrode active material particle. 前記正極活物質粒子の元素組成を表す前記組成式中のｘは０．８以上１．２未満である、請求項１に記載の正極活物質粒子。   The positive electrode active material particle according to claim 1, wherein x in the composition formula representing the elemental composition of the positive electrode active material particle is 0.8 or more and less than 1.2. 前記正極活物質粒子の元素組成を表す前記組成式中のｘは１である、請求項１又は２に記載の正極活物質粒子。   3. The positive electrode active material particle according to claim 1, wherein x in the composition formula representing the elemental composition of the positive electrode active material particle is 1. 前記正極活物質粒子の平均粒子径は１０００ｎｍ以下である、請求項１〜３のうちいずれか１つに記載の正極活物質粒子。   The positive electrode active material particles according to claim 1, wherein the positive electrode active material particles have an average particle size of 1000 nm or less. 前記正極活物質粒子の平均粒子径は５００ｎｍ以下である、請求項１〜４のうちいずれか１つに記載の正極活物質粒子。   The positive electrode active material particles according to claim 1, wherein an average particle diameter of the positive electrode active material particles is 500 nm or less. 前記正極活物質粒子は単結晶構造を有している、請求項１〜５のうちいずれか１つに記載の正極活物質粒子。   The positive electrode active material particles according to claim 1, wherein the positive electrode active material particles have a single crystal structure. 正極活物質粒子を有する正極と、電解質と、負極とを備えた、リチウムイオン二次電池であって、
前記正極活物質粒子は、請求項１〜６のいずれか１つに記載の正極活物質粒子である、リチウムイオン二次電池。 A lithium ion secondary battery comprising a positive electrode having positive electrode active material particles, an electrolyte, and a negative electrode,
The said positive electrode active material particle is a lithium ion secondary battery which is a positive electrode active material particle as described in any one of Claims 1-6. コバルトを含む材料、ニッケルを含む材料及びリチウムを含む材料とを超臨界流体中で反応させてコバルト、ニッケル及びリチウムを含む金属複合酸化物を生成させるステップと、
前記金属複合酸化物とリチウムを含む材料とを混合して反応させることにより、（１１１）面が少なくとも一方の主面となるプレート状で且つスピネル型の結晶構造を有しており、元素組成がLiCo2-xNixO4（ただし、０＜ｘ＜２）で表される正極活物質粒子を製造するステップとを備えている正極活物質粒子の製造方法。 Reacting a material containing cobalt, a material containing nickel and a material containing lithium in a supercritical fluid to produce a metal composite oxide containing cobalt, nickel and lithium;
By mixing and reacting the metal composite oxide and a material containing lithium, the (111) plane has a plate-like and spinel crystal structure with at least one main surface, and the elemental composition is LiCo 2-x Ni x O 4 ( provided that, 0 <x <2) the production method of the positive electrode active material particles and a step of producing a positive electrode active material particles represented by.
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