JP2017004635A - Nonaqueous electrolyte secondary battery, and cathode active material for nonaqueous electrolyte secondary battery - Google Patents
Nonaqueous electrolyte secondary battery, and cathode active material for nonaqueous electrolyte secondary battery Download PDFInfo
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Abstract
Description
本発明は、非水電解液二次電池と、その正極活物質とに関する。 The present invention relates to a non-aqueous electrolyte secondary battery and a positive electrode active material thereof.
リチウムイオン二次電池等の非水電解液二次電池において、中空構造を有する正極活物質を用いるものは、電池の充電状態であるＳＯＣ（State Of Charge）が低い状態でも高い出力が得られることが知られている（例えば、特許文献１参照）。 A non-aqueous electrolyte secondary battery such as a lithium ion secondary battery that uses a positive electrode active material having a hollow structure can obtain a high output even when the state of charge (SOC) of the battery is low. Is known (see, for example, Patent Document 1).
特許文献１に開示された正極活物質は、殻部とその内部に形成された中空部（空洞部）とを有する中空構造の粒子形態をなし、殻部は、上記中空部と粒子外部とを連通させる貫通孔を有する。この貫通孔が殻部に形成されることによって、中空部と外部との間で電解液が行き来しやすくなり、殻部を構成する粒子と電解液とが効率よく接触するため、電池の出力特性を高めることができる。また、特許文献１には、貫通孔の開口幅の平均は、概ね０．０１μｍ以上２．０μｍ以下であると、電解液の流通路として貫通孔をより有効に機能させ得ることも開示されている。 The positive electrode active material disclosed in Patent Document 1 has a hollow particle form having a shell part and a hollow part (hollow part) formed therein, and the shell part includes the hollow part and the particle outside. It has a through hole for communication. By forming this through-hole in the shell, the electrolyte easily flows between the hollow part and the outside, and the particles that make up the shell and the electrolyte efficiently contact each other. Can be increased. Patent Document 1 also discloses that when the average opening width of the through holes is approximately 0.01 μm or more and 2.0 μm or less, the through holes can function more effectively as a flow path for the electrolyte solution. Yes.
しかし、発明者の実験等を通じて、貫通孔の開口幅の平均が上記範囲内であっても、電池の出力特性が良好にならない場合があることが判明した。そのため、貫通孔の適切な開口幅などについては、改善が求められていた。 However, it has been found through experimentation by the inventors that the output characteristics of the battery may not be good even if the average opening width of the through holes is within the above range. For this reason, there has been a demand for improvement of the appropriate opening width of the through holes.
本発明は、上記実情を鑑みてなされたものであり、その目的は、出力特性を良好にすることができる非水電解液二次電池、およびその正極活物質を提供することにある。 This invention is made | formed in view of the said situation, The objective is to provide the nonaqueous electrolyte secondary battery which can make output characteristics favorable, and its positive electrode active material.
以下、上記課題を解決するための手段及びその作用効果について記載する。
上記課題を解決する非水電解液二次電池は、複数の一次粒子からなり中空構造を有する二次粒子を正極活物質に含有する非水電解液二次電池であって、前記二次粒子は、前記一次粒子からなる殻部と、前記殻部の内側に形成された中空部とを有し、前記殻部には、当該殻部の外側と当該殻部の中空部とを連通する貫通孔が設けられるとともに、前記貫通孔の直径は、１μｍ以下であって、水銀圧入法による細孔容積分布測定によって得られるモード径が０．１μｍ以上０．６μｍ以下であって、水銀圧入法による細孔容積分布測定によって得られる細孔容積であって０．１μｍ以上０．６μｍ以下の直径を有する全ての貫通孔の総容積を示す部分細孔容積が、０．０４５ｍｌ／ｇ以上であり、水銀圧入法による細孔容積分布測定によって得られる細孔容積であって１μｍ以下の直径を有する全ての貫通孔の総容積を示す全細孔容積に対する前記部分細孔容積の百分率が、７５％以上であることを要旨とする。
Hereinafter, means for solving the above-described problems and the effects thereof will be described.
A non-aqueous electrolyte secondary battery that solves the above problems is a non-aqueous electrolyte secondary battery that contains secondary particles having a hollow structure made of a plurality of primary particles in a positive electrode active material, wherein the secondary particles are A through-hole that has a shell part made of the primary particles and a hollow part formed inside the shell part, and communicates the outside of the shell part with the hollow part of the shell part. And the diameter of the through hole is 1 μm or less, and the mode diameter obtained by the pore volume distribution measurement by the mercury intrusion method is 0.1 μm or more and 0.6 μm or less. The pore volume obtained by pore volume distribution measurement, the partial pore volume indicating the total volume of all the through-holes having a diameter of 0.1 μm or more and 0.6 μm or less is 0.045 ml / g or more, mercury Obtained by measuring pore volume distribution by press-fitting method The gist is that the percentage of the partial pore volume with respect to the total pore volume indicating the total volume of all through-holes having a diameter of 1 μm or less is 75% or more.
上記課題を解決する非水電解液二次電池の正極活物質は、非水電解液二次電池に備えられ、複数の一次粒子からなり中空構造を有する二次粒子を含有する正極活物質であって、前記二次粒子は、前記一次粒子からなる殻部と、前記殻部の内側に形成された中空部とを有し、前記殻部には、当該殻部の外側と当該殻部の中空部とを連通する貫通孔が設けられるとともに、前記貫通孔の直径は、１μｍ以下であって、水銀圧入法による細孔容積分布測定によって得られるモード径が０．１μｍ以上０．６μｍ以下であって、水銀圧入法による細孔容積分布測定によって得られる細孔容積であって０．１μｍ以上０．６μｍ以下の直径を有する全ての貫通孔の総容積を示す部分細孔容積が、０．０４５ｍｌ／ｇ以上であり、水銀圧入法による細孔容積分布測定によって得られる細孔容積であって１μｍ以下の直径を有する全ての貫通孔の総容積を示す全細孔容積に対する前記部分細孔容積の百分率が、７５％以上であることを要旨とする。 A positive electrode active material for a non-aqueous electrolyte secondary battery that solves the above problems is a positive electrode active material that is provided in a non-aqueous electrolyte secondary battery and contains secondary particles that are composed of a plurality of primary particles and have a hollow structure. The secondary particles have a shell portion made of the primary particles and a hollow portion formed inside the shell portion. The shell portion includes an outer portion of the shell portion and a hollow portion of the shell portion. And a diameter of the through hole is 1 μm or less, and a mode diameter obtained by a pore volume distribution measurement by a mercury intrusion method is 0.1 μm or more and 0.6 μm or less. The pore volume obtained by measuring the pore volume distribution by the mercury intrusion method, and the partial pore volume indicating the total volume of all the through holes having a diameter of 0.1 μm or more and 0.6 μm or less is 0.045 ml. / G or more, pore volume by mercury porosimetry The gist of the invention is that the percentage of the partial pore volume with respect to the total pore volume, which is the pore volume obtained by the cloth measurement and indicates the total volume of all the through-holes having a diameter of 1 μm or less, is 75% or more. .
上記各構成では、二次粒子の殻部に設けられる貫通孔は、その最頻値であるモード径が、０．１μｍ以上０．６以下であって、且つ全細孔容積に対する部分細孔容積の百分率が、７５％以上である。このため、貫通孔を介した電解液の中空部への流入、及び中空部から貫通孔を介した電解液の流出が円滑に行われるようになるため、良好な電池の出力特性を得ることができる。 In each of the above configurations, the through hole provided in the shell of the secondary particle has a mode diameter which is the mode value of 0.1 μm or more and 0.6 or less, and a partial pore volume with respect to the total pore volume. % Is 75% or more. For this reason, since the inflow of the electrolyte solution through the through hole into the hollow portion and the outflow of the electrolyte solution from the hollow portion through the through hole are smoothly performed, it is possible to obtain good battery output characteristics. it can.
上記非水電解液二次電池について、前記全細孔容積に対する前記部分細孔容積の百分率が９０％以上であることが好ましい。
上記構成では、全細孔容積に対する部分細孔容積の百分率が、９０％以上である。このため、貫通孔を介した電解液の中空部への流入、及び中空部から貫通孔を介した電解液の流出が円滑に行われるようになるため、良好な電池の出力特性を得ることができる。
About the said nonaqueous electrolyte secondary battery, it is preferable that the percentage of the said partial pore volume with respect to the said total pore volume is 90% or more.
In the above configuration, the percentage of the partial pore volume with respect to the total pore volume is 90% or more. For this reason, since the inflow of the electrolyte solution through the through hole into the hollow portion and the outflow of the electrolyte solution from the hollow portion through the through hole are smoothly performed, it is possible to obtain good battery output characteristics. it can.
上記非水電解液二次電池について、前記細孔容積分布測定によって得られる細孔容積分布であって、前記貫通孔の直径が０．６μｍ以下の範囲の細孔容積分布が一峰性の分布であることが好ましい。 The nonaqueous electrolyte secondary battery is a pore volume distribution obtained by the pore volume distribution measurement, and the pore volume distribution in the range where the diameter of the through hole is 0.6 μm or less is a unimodal distribution. Preferably there is.
モード径が０．１μｍ以上０．６μｍ以下である二次粒子は、０．１μｍ以上０．６μｍ以下の範囲にピークを有する。上記構成では、０．６μｍ以下の範囲の対数微分細孔容積分布は一峰性の分布であるため、０．１μｍ以上０．６μｍ以下の範囲に一つのピークを有し、それ以外のピークを有さない。すなわち、二次粒子の貫通孔の直径は、その多くが０．１μｍ以上０．６μｍ以下の範囲に含まれ、その範囲よりも小さい範囲の直径を有する貫通孔は少ない。そのため、貫通孔を介した電解液の中空部への流入、及び中空部から貫通孔を介した電解液の流出が円滑に行われるようになるため、良好な電池の出力特性を得ることができる。 Secondary particles having a mode diameter of 0.1 μm or more and 0.6 μm or less have a peak in the range of 0.1 μm or more and 0.6 μm or less. In the above configuration, since the logarithmic differential pore volume distribution in the range of 0.6 μm or less is a unimodal distribution, it has one peak in the range of 0.1 μm to 0.6 μm and other peaks. No. That is, most of the diameters of the through holes of the secondary particles are included in the range of 0.1 μm or more and 0.6 μm or less, and there are few through holes having a diameter in a range smaller than the range. Therefore, since the inflow of the electrolyte solution through the through hole into the hollow portion and the outflow of the electrolyte solution from the hollow portion through the through hole can be performed smoothly, good output characteristics of the battery can be obtained. .
本発明の非水電解液二次電池およびその正極活物質によれば、電池の出力特性を良好にすることができる。 According to the nonaqueous electrolyte secondary battery and the positive electrode active material of the present invention, the output characteristics of the battery can be improved.
以下、非水電解液二次電池と、その正極活物質とについて、その一実施形態を説明する。本実施形態では、非水電解液二次電池を、リチウムイオン二次電池に具体化して説明する。リチウムイオン二次電池は、リチウムイオンを、正極と負極との間で移動させることによって充放電を行う電池である。 Hereinafter, an embodiment of the non-aqueous electrolyte secondary battery and the positive electrode active material will be described. In the present embodiment, the non-aqueous electrolyte secondary battery is described as a lithium ion secondary battery. A lithium ion secondary battery is a battery that charges and discharges by moving lithium ions between a positive electrode and a negative electrode.
まずリチウムイオン二次電池の構成について説明する。
図１に示すように、リチウムイオン二次電池は、ケース１１と、ケース１１の開口を封止する蓋体１２とを備える。蓋体１２には、正極端子１３と、負極端子１４とが設けられている。ケース１１内には、電極体１５が、非水電解液とともに収容されている。
First, the configuration of the lithium ion secondary battery will be described.
As shown in FIG. 1, the lithium ion secondary battery includes a case 11 and a lid 12 that seals the opening of the case 11. The lid 12 is provided with a positive electrode terminal 13 and a negative electrode terminal 14. In the case 11, the electrode body 15 is accommodated together with the non-aqueous electrolyte.
図２を参照して、電極体１５の構成について説明する。電極体１５は、正極である正極シート２０と、負極である負極シート３０とが、セパレータ４０，４１を介して巻回された積層体である。正極シート２０は、長尺状に形成され、シート状の正極集電体２１と、正極集電体２１の両面に設けられた正極合材層２２とを備える。負極シート３０は、長尺状に形成され、シート状の負極集電体３１と、負極集電体３１の両面に設けられた負極合材層３２とを備える。巻回前の積層体は、正極シート２０、セパレータ４０、負極シート３０、セパレータ４１の順に積層されている。 The configuration of the electrode body 15 will be described with reference to FIG. The electrode body 15 is a laminate in which a positive electrode sheet 20 that is a positive electrode and a negative electrode sheet 30 that is a negative electrode are wound through separators 40 and 41. The positive electrode sheet 20 is formed in a long shape, and includes a sheet-like positive electrode current collector 21 and a positive electrode mixture layer 22 provided on both surfaces of the positive electrode current collector 21. The negative electrode sheet 30 is formed in a long shape, and includes a sheet-like negative electrode current collector 31 and a negative electrode mixture layer 32 provided on both surfaces of the negative electrode current collector 31. The laminated body before winding is laminated | stacked in order of the positive electrode sheet 20, the separator 40, the negative electrode sheet 30, and the separator 41. FIG.
積層体は、その長尺方向に巻回されることによって巻回体とされ、巻回体をその周面から押圧することによって扁平形状に成形されている。成形後の電極体１５であって、その径方向の中央部には、正極合材層２２と負極合材層３２とが密に積層された部分が形成されている。 The laminated body is formed into a wound body by being wound in the longitudinal direction, and is formed into a flat shape by pressing the wound body from its peripheral surface. In the molded electrode body 15, a portion in which the positive electrode mixture layer 22 and the negative electrode mixture layer 32 are densely laminated is formed in the central portion in the radial direction.
また、正極シート２０の長尺方向に沿って延びる一方の端部には、正極合材層２２が形成されずに正極集電体２１が露出した正極端部２３が設けられている。この正極端部２３は、負極シート３０及びセパレータ４０，４１からはみ出た状態となっている。この正極端部２３は、ケース１１内の内部正極端子等を介して、正極端子１３に電気的に接続されている。 Further, a positive electrode end portion 23 where the positive electrode current collector 21 is exposed without forming the positive electrode mixture layer 22 is provided at one end portion extending in the longitudinal direction of the positive electrode sheet 20. The positive electrode end portion 23 protrudes from the negative electrode sheet 30 and the separators 40 and 41. The positive electrode end portion 23 is electrically connected to the positive electrode terminal 13 via an internal positive electrode terminal or the like in the case 11.
また、負極シート３０の長尺方向に沿って延びる一方の端部にも、負極合材層３２が形成されずに負極集電体３１が露出した負極端部３３が設けられている。この負極端部３３は、正極シート２０及びセパレータ４０，４１からはみ出た状態となっている。この負極端部３３は、ケース１１内の内部負極端子等を介して、負極端子１４に電気的に接続されている。 In addition, a negative electrode end portion 33 in which the negative electrode current collector 31 is exposed without forming the negative electrode mixture layer 32 is provided at one end portion extending in the longitudinal direction of the negative electrode sheet 30. The negative electrode end 33 protrudes from the positive electrode sheet 20 and the separators 40 and 41. The negative electrode end portion 33 is electrically connected to the negative electrode terminal 14 via an internal negative electrode terminal or the like in the case 11.
（正極）
次に、正極について詳述する。まず、正極シート２０を構成する正極集電体２１は、従来の二次電池の構成要素と同様の構成要素を用いることができる。例えば、正極集電体２１の材料として、導電性の良好な金属からなる導電性材料が好ましく用いられる。例えば、導電性材料としては、アルミニウムを含む材料、アルミニウム合金を含む材料を用いることができる。
(Positive electrode)
Next, the positive electrode will be described in detail. First, the positive electrode current collector 21 constituting the positive electrode sheet 20 can use the same components as those of a conventional secondary battery. For example, as the material of the positive electrode current collector 21, a conductive material made of a metal having good conductivity is preferably used. For example, as the conductive material, a material containing aluminum or a material containing an aluminum alloy can be used.
正極合材層２２に含まれる正極活物質は、層状の結晶構造を有するリチウム遷移金属酸化物を含有する。リチウム遷移金属酸化物は、Ｌｉ以外に、１乃至複数の所定の遷移金属元素を含む。リチウム遷移金属酸化物に含有される遷移金属元素は、Ｎｉ，Ｃｏ，Ｍｎの少なくとも一つであることが好ましい。 The positive electrode active material contained in the positive electrode mixture layer 22 contains a lithium transition metal oxide having a layered crystal structure. The lithium transition metal oxide contains one or more predetermined transition metal elements in addition to Li. The transition metal element contained in the lithium transition metal oxide is preferably at least one of Ni, Co, and Mn.
上記リチウム遷移金属酸化物の好適な一例として、Ｎｉ，ＣｏおよびＭｎの全てを含むリチウム遷移金属酸化物（以下「ＬＮＣＭ酸化物」と表記することもある。）が挙げられる。 A preferable example of the lithium transition metal oxide is a lithium transition metal oxide containing all of Ni, Co, and Mn (hereinafter sometimes referred to as “LNCM oxide”).
正極活物質は、遷移金属元素（すなわち、Ｎｉ，ＣｏおよびＭｎの少なくとも１種）の他に、付加的に、１種または複数種の元素を含有し得る。付加的な元素としては、周期表の１族（ナトリウム等のアルカリ金属）、２族（マグネシウム、カルシウム等のアルカリ土類金属）、４族（チタン、ジルコニウム等の遷移金属）、６族（クロム、タングステン等の遷移金属）、８族（鉄等の遷移金属）、１３族（半金属元素であるホウ素、もしくはアルミニウムのような金属）および１７族（フッ素のようなハロゲン）に属するいずれかの元素を含むことができる。 In addition to the transition metal element (that is, at least one of Ni, Co, and Mn), the positive electrode active material can additionally contain one or more elements. Additional elements include Group 1 (alkali metals such as sodium), Group 2 (alkaline earth metals such as magnesium and calcium), Group 4 (transition metals such as titanium and zirconium), Group 6 (chromium). , Transition metals such as tungsten), group 8 (transition metals such as iron), group 13 (metals such as boron, which is a semimetal element) and group 17 (halogens such as fluorine) Elements can be included.
好ましい一態様において、正極活物質は、下記一般式（１）で表される組成（平均組成）を有し得る。
Ｌｉ１＋ｘＮｉｙＣｏｚＭｎ（１−ｙ−ｚ）ＭＡαＭＢβＯ２ …（１）
上記式（１）において、ｘは、０≦ｘ≦０．２を満たす実数であり得る。ｙは、０．１＜ｙ＜０．６を満たす実数であり得る。ｚは、０．１＜ｚ＜０．６を満たす実数であり得る。ＭＡは、Ｗ，ＣｒおよびＭｏから選択される少なくとも１種の金属元素であり、αは０＜α≦０．０１（典型的には０．０００５≦α≦０．０１、例えば０．００１≦α≦０．０１）を満たす実数である。ＭＢは、Ｚｒ，Ｍｇ，Ｃａ，Ｎａ，Ｆｅ，Ｚｎ，Ｓｉ，Ｓｎ，Ａｌ，ＢおよびＦからなる群から選択される１種または２種以上の元素であり、βは０≦β≦０．０１を満たす実数であり得る。βが実質的に０（すなわち、ＭＢを実質的に含有しない酸化物）であってもよい。なお、層状構造のリチウム遷移金属酸化物を示す化学式では、便宜上、Ｏ（酸素）の組成比を２として示しているが、この数値は厳密に解釈されるべきではなく、多少の組成の変動（典型的には１．９５以上２．０５以下の範囲に包含される）を許容し得るものである。
In a preferred embodiment, the positive electrode active material may have a composition (average composition) represented by the following general formula (1).
Li 1 + x Ni y Co z Mn (1-yz) MA α MB β O 2 (1)
In the above formula (1), x may be a real number that satisfies 0 ≦ x ≦ 0.2. y may be a real number that satisfies 0.1 <y <0.6. z may be a real number that satisfies 0.1 <z <0.6. MA is at least one metal element selected from W, Cr and Mo, and α is 0 <α ≦ 0.01 (typically 0.0005 ≦ α ≦ 0.01, for example 0.001 ≦ It is a real number satisfying α ≦ 0.01). MB is one or more elements selected from the group consisting of Zr, Mg, Ca, Na, Fe, Zn, Si, Sn, Al, B, and F, and β is 0 ≦ β ≦ 0. It can be a real number satisfying 01. β may be substantially 0 (that is, an oxide containing substantially no MB). Note that in the chemical formula showing the lithium transition metal oxide having a layered structure, the composition ratio of O (oxygen) is shown as 2 for convenience, but this numerical value should not be interpreted strictly, and some composition variation ( (Typically included in the range of 1.95 to 2.05).
（正極活物質の中空構造）
次に図３を参照して、正極活物質の中空構造について説明する。正極活物質は、典型的には、殻部１０１と、その内部に形成された中空部１０２（空洞部）とを有する中空構造の粒子形態をなす。この正極活物質粒子１００は、典型的には、概ね球形、やや歪んだ球形等であり得る。正極活物質粒子１００の殻部１０１は、中空部１０２と粒子外部とを連通させる貫通孔１１０を有する。
(Hollow structure of positive electrode active material)
Next, the hollow structure of the positive electrode active material will be described with reference to FIG. The positive electrode active material typically takes the form of a hollow-structured particle having a shell portion 101 and a hollow portion 102 (hollow portion) formed therein. Typically, the positive electrode active material particles 100 may have a generally spherical shape, a slightly distorted spherical shape, or the like. The shell portion 101 of the positive electrode active material particle 100 has a through hole 110 that allows the hollow portion 102 to communicate with the outside of the particle.
殻部１０１は、リチウム遷移金属酸化物の一次粒子１１１が球殻状に集まって形成されたものである。即ち、正極活物質粒子１００は、一次粒子１１１が集まった二次粒子１１２である。ここで「一次粒子」とは、外見上の幾何学的形態から判断して単位粒子(ultimate particle)と考えられる粒子を指す。ここに開示される正極活物質において、一次粒子１１１は、典型的にはリチウム遷移金属酸化物の結晶子の集合物である。正極活物質の形状観察はＳＥＭ（Scanning Electron Microscope）画像により行うことができる。中空部１０２は、隣接する二次粒子１１２の間に存在する隙間より大きい空間である。 The shell portion 101 is formed by collecting primary particles 111 of a lithium transition metal oxide in a spherical shell shape. That is, the positive electrode active material particles 100 are secondary particles 112 in which primary particles 111 are collected. Here, the “primary particle” refers to a particle that is considered to be a unit particle (ultimate particle) based on an apparent geometric form. In the positive electrode active material disclosed herein, the primary particles 111 are typically a collection of crystallites of a lithium transition metal oxide. The shape of the positive electrode active material can be observed with a SEM (Scanning Electron Microscope) image. The hollow portion 102 is a space larger than a gap existing between adjacent secondary particles 112.
一次粒子１１１は、その長径Ｌ１が、０．１μｍ以上１．０μｍ以下であり得る。長径Ｌ１が小さすぎると、電池の容量維持性が低下傾向となることがあり得る。そのような観点から、長径Ｌ１は０．２μｍ以上であることが好ましく、０．３μｍ以上であることがより好ましく、０．４μｍ以上であることがさらに好ましい。なお、長径Ｌ１は、正極活物質粒子表面のＳＥＭ画像において、概ね最も長い長径Ｌ１を有する一次粒子１１１を選択し、当該選択された一次粒子１１１において最も長い径を長径Ｌ１とするとよい。 The primary particle 111 may have a major axis L1 of 0.1 μm or more and 1.0 μm or less. If the long diameter L1 is too small, the capacity maintenance of the battery may tend to decrease. From such a viewpoint, the major axis L1 is preferably 0.2 μm or more, more preferably 0.3 μm or more, and further preferably 0.4 μm or more. For the long diameter L1, it is preferable to select the primary particle 111 having the longest long diameter L1 in the SEM image of the surface of the positive electrode active material particle, and set the longest diameter in the selected primary particle 111 as the long diameter L1.
一方、長径Ｌ１が大きすぎると、結晶の表面から内部（Ｌ１の中央部）までの距離（Ｌｉイオンの拡散距離）が長くなるため、結晶内部へのイオン拡散が遅くなり、出力特性（特に、低ＳＯＣ域における出力特性）が低くなりがちである。そのような観点から、長径Ｌ１は０．８μｍ以下であることが好ましい。好ましい一態様では、一次粒子の長径Ｌ１は０．２μｍ以上０．８μｍ以下である。一次粒子１１１の長径Ｌ１は、例えば、正極活物質粒子１００の粒子表面のＳＥＭ画像に基づいて測定することができる。 On the other hand, if the major axis L1 is too large, the distance (Li ion diffusion distance) from the surface of the crystal to the inside (the center portion of L1) becomes long, so that the ion diffusion into the crystal becomes slow, and the output characteristics (particularly, The output characteristics in the low SOC range tend to be low. From such a viewpoint, the major axis L1 is preferably 0.8 μm or less. In a preferred embodiment, the major particle L1 of the primary particles is 0.2 μm or more and 0.8 μm or less. The major axis L1 of the primary particle 111 can be measured based on, for example, an SEM image of the particle surface of the positive electrode active material particle 100.
正極活物質粒子１００の平均粒径（二次粒径）は、例えば、およそ２μｍ以上であることが好ましく、３μｍ以上であることがより好ましい。正極活物質粒子１００の平均粒径が小さすぎると、中空部１０２の容積も小さくなるため、中空部１０２に蓄えられる電解液の量も少なくなる。また、正極活物質の生産性の観点からは、正極活物質粒子１００の平均粒径は２５μｍ以下であることが好ましく、１５μｍ以下であることがより好ましい。好ましい一態様では、正極活物質の平均粒径は、３μｍ以上１０μｍ以下である。上記正極活物質粒子の平均粒径は、当該分野で公知の方法、例えばレーザ回折散乱法に基づく測定による体積基準のメジアン径（Ｄ５０：５０％体積平均粒径）として求めることができる。 The average particle diameter (secondary particle diameter) of the positive electrode active material particles 100 is, for example, preferably about 2 μm or more, and more preferably 3 μm or more. When the average particle diameter of the positive electrode active material particles 100 is too small, the volume of the hollow portion 102 is also small, and the amount of the electrolyte solution stored in the hollow portion 102 is also small. Further, from the viewpoint of productivity of the positive electrode active material, the average particle diameter of the positive electrode active material particles 100 is preferably 25 μm or less, and more preferably 15 μm or less. In a preferred embodiment, the positive electrode active material has an average particle size of 3 μm or more and 10 μm or less. The average particle diameter of the positive electrode active material particles can be determined as a volume-based median diameter (D 50 : 50% volume average particle diameter) measured by a method known in the art, for example, a laser diffraction scattering method.
正極活物質粒子１００は、粒子空孔率が５％以上の中空構造を有することが好ましい。ここで、「粒子空孔率」とは、正極合材層２２をランダムな位置で切断した断面の平均において、該活物質の見かけの断面積のうち中空部１０２が占める割合をいう。この割合は、例えば、正極合材層２２の断面におけるＳＥＭ画像を通じて把握することができる。 The positive electrode active material particles 100 preferably have a hollow structure with a particle porosity of 5% or more. Here, the “particle porosity” refers to the ratio of the hollow portion 102 in the apparent cross-sectional area of the active material in the average of the cross sections obtained by cutting the positive electrode mixture layer 22 at random positions. This ratio can be grasped through an SEM image in the cross section of the positive electrode mixture layer 22, for example.
粒子空孔率は、１０％以上であることがより好ましく、１５％以上であることがさらに好ましい。粒子空孔率の上限は特に限定されないが、中空構造の耐久性や製造容易性等の点から、通常は９５％以下とすることが適当である。 The particle porosity is more preferably 10% or more, and further preferably 15% or more. The upper limit of the particle porosity is not particularly limited, but it is usually suitably 95% or less from the viewpoint of the durability of the hollow structure and the ease of production.
次に、殻部１０１の構成について説明する。好ましい一態様では、殻部１０１は、一次粒子１１１が環状（数珠状）に連なった形態を有する。一次粒子１１１は、殻部１０１の厚み方向において、単層であってもよく、多層であってもよい。 Next, the configuration of the shell 101 will be described. In a preferred embodiment, the shell portion 101 has a form in which the primary particles 111 are arranged in a ring shape (beaded). The primary particles 111 may be a single layer or multiple layers in the thickness direction of the shell portion 101.
好ましい一態様に係る正極活物質粒子１００は、殻部１０１の全体に亘って、一次粒子１１１が実質的に単層で連なった形態に構成されている。また、殻部１０１が多層構造である場合、一次粒子１１１の積層数は、およそ５個以下（例えば２〜５個）であることが好ましく、およそ３個以下（例えば２〜３個）であることがより好ましい。なお、図３に示す正極活物質粒子１００は、その構成の一例を示すものであり、殻部１０１の層数、中空部１０２の形状、殻部１０１の厚みと中空部１０２の幅との比率、貫通孔１１０の数や大きさ等は、図３に示す正極活物質粒子１００に限定されるものではない。 The positive electrode active material particles 100 according to a preferred embodiment are configured in such a manner that the primary particles 111 are substantially continuous in a single layer over the entire shell portion 101. When the shell 101 has a multilayer structure, the number of the primary particles 111 stacked is preferably about 5 or less (for example, 2 to 5), and about 3 or less (for example, 2 to 3). It is more preferable. Note that the positive electrode active material particle 100 shown in FIG. 3 shows an example of the configuration, and the number of layers of the shell portion 101, the shape of the hollow portion 102, the ratio of the thickness of the shell portion 101 and the width of the hollow portion 102. The number and size of the through holes 110 are not limited to the positive electrode active material particles 100 shown in FIG.
また、殻部１０１は、貫通孔１１０以外の部分では、少なくとも一般的な電解液を通過させない程度に緻密に焼結している。この構造の正極活物質粒子１００によると、正極活物質粒子１００の外部と中空部１０２との間で電解液が流通し得る箇所が、貫通孔１１０のある箇所に制限される。 Further, the shell 101 is densely sintered at a portion other than the through-hole 110 so as not to allow at least a general electrolytic solution to pass therethrough. According to the positive electrode active material particles 100 having this structure, the locations where the electrolytic solution can flow between the outside of the positive electrode active material particles 100 and the hollow portion 102 are limited to the locations where the through holes 110 are present.
殻部１０１の厚さは、好ましくは３．０μｍ以下であり、より好ましくは２．５μｍ以下、さらに好ましくは２．０μｍ以下である。殻部１０１の厚さが小さいほど、充電時には殻部１０１の内部（厚さの中央部）からもＬｉイオンが放出されやすく、放電時にはＬｉイオンが殻部１０１の内部まで吸収されやすくなる。 The thickness of the shell portion 101 is preferably 3.0 μm or less, more preferably 2.5 μm or less, and still more preferably 2.0 μm or less. The smaller the thickness of the shell portion 101, the easier it is to release Li ions from the inside of the shell portion 101 (the central portion of the thickness) during charging, and it becomes easier for Li ions to be absorbed up to the inside of the shell portion 101 during discharging.
殻部１０１の厚さの下限値は特に限定されないが、通常は、概ね０．１μｍ以上であることが好ましい。殻部の厚さを０．１μｍ以上とすることにより、電池の製造時または使用時に加わり得る応力や、充放電に伴う正極活物質の膨張収縮等に対して、高い耐久性を保持することができる。内部抵抗低減効果と耐久性とを両立させる観点からは、殻部の厚さはおよそ０．１μｍ以上２．２μｍ以下であることが好ましく、０．２μｍ以上２．０μｍ以下であることがより好ましく、０．５μｍ以上１．５μｍ以下であることが特に好ましい。 Although the lower limit value of the thickness of the shell portion 101 is not particularly limited, it is generally preferable that the thickness is generally 0.1 μm or more. By setting the thickness of the shell portion to 0.1 μm or more, high durability can be maintained against stress that can be applied during the manufacture or use of the battery, expansion / contraction of the positive electrode active material accompanying charge / discharge, and the like. it can. From the viewpoint of achieving both an internal resistance reduction effect and durability, the thickness of the shell is preferably about 0.1 μm to 2.2 μm, more preferably 0.2 μm to 2.0 μm. It is particularly preferably 0.5 μm or more and 1.5 μm or less.
次に、貫通孔１１０について詳述する。殻部１０１の貫通孔１１０は、中空部１０２と、正極活物質粒子１００の外部とで電解液を行き来させる。貫通孔１１０は、殻部１０１を構成する複数の一次粒子１１１の間に設けられた隙間によって構成される。殻部１０１に貫通孔１１０が設けられることで、外部の電解液が貫通孔１１０を介して中空部１０２に流入しやすくなるとともに、中空部１０２内の電解液が貫通孔１１０を介して外部に流出しやすくなる。その結果、中空部１０２内の電解液が適当に入れ替わる。 Next, the through hole 110 will be described in detail. The through hole 110 of the shell part 101 allows the electrolyte solution to pass back and forth between the hollow part 102 and the outside of the positive electrode active material particles 100. The through hole 110 is constituted by a gap provided between the plurality of primary particles 111 constituting the shell portion 101. By providing the through-hole 110 in the shell portion 101, it is easy for an external electrolyte to flow into the hollow portion 102 through the through-hole 110, and the electrolyte in the hollow portion 102 is exposed to the outside via the through-hole 110. It becomes easy to leak. As a result, the electrolytic solution in the hollow portion 102 is appropriately replaced.
また、中空部１０２には電解液が蓄えられるため、正極合材層２２で電解液が不足する、液枯れも生じにくくなる。リチウムイオン二次電池は、リチウムイオンの移動により充放電を行うため、中空部１０２と外部との間で電解液を行き来しやすくすることで、中空部１０２に面する一次粒子１１１がより活発に充放電に活用され得る。 Moreover, since electrolyte solution is stored in the hollow part 102, electrolyte solution runs short in the positive electrode mixture layer 22, and it becomes difficult to produce liquid withering. Since the lithium ion secondary battery charges and discharges by movement of lithium ions, the primary particles 111 facing the hollow portion 102 are more actively activated by facilitating the transfer of the electrolyte between the hollow portion 102 and the outside. It can be utilized for charging and discharging.
また、リチウムイオン二次電池の内部抵抗は、活物質と電解液との界面の電荷移動抵抗、正極活物質内のＬｉイオンの拡散移動抵抗、電解液の溶液抵抗等の複数の抵抗成分から構成される。中空構造の正極活物質粒子１００の場合、貫通孔１１０の数や直径等も、Ｌｉイオンの拡散に影響を与えるため、リチウムイオン二次電池の内部抵抗に寄与すると考えられる。 The internal resistance of the lithium ion secondary battery is composed of a plurality of resistance components such as charge transfer resistance at the interface between the active material and the electrolyte, diffusion transfer resistance of Li ions in the positive electrode active material, and solution resistance of the electrolyte. Is done. In the case of the positive electrode active material particles 100 having a hollow structure, the number and diameter of the through-holes 110 also affect the diffusion of Li ions, and thus are considered to contribute to the internal resistance of the lithium ion secondary battery.
正極活物質粒子１００が有する貫通孔１１０の数は、正極活物質粒子１００の一粒子当たりの平均として、およそ１〜１０個程度（例えば１〜５個）であることが好ましい。上記平均貫通孔数が多すぎると、中空形状を維持しにくくなることがある。また、平均貫通孔数は多いほど電解液が行き来しやすくなるが、平均貫通孔数を多くすると単位体積あたりの正極活物質量が少なくなるため、エネルギー密度が低下する。このため、貫通孔１１０の数は、必要最小限とすることが好ましい。 The number of through-holes 110 included in the positive electrode active material particles 100 is preferably about 1 to 10 (for example, 1 to 5) as an average per particle of the positive electrode active material particles 100. If the average number of through holes is too large, it may be difficult to maintain the hollow shape. Further, the larger the average number of through-holes, the easier the electrolyte goes back and forth. However, when the average number of through-holes is increased, the amount of the positive electrode active material per unit volume decreases, and the energy density decreases. For this reason, it is preferable that the number of through-holes 110 be the minimum necessary.
また、一つの正極活物質粒子１００に設けられる複数の貫通孔１１０の直径Ｄは、１μｍ以下におけるモード径が、０．１μｍ以上０．６μｍ以下である。貫通孔１１０の直径Ｄは、貫通孔１１０を円形状の孔にモデル化したときの直径であり、必ずしも貫通孔１１０の開口幅の最大値を示すものではない。 The diameter D of the plurality of through holes 110 provided in one positive electrode active material particle 100 has a mode diameter of 0.1 μm or more and 0.6 μm or less at 1 μm or less. The diameter D of the through hole 110 is a diameter when the through hole 110 is modeled as a circular hole, and does not necessarily indicate the maximum value of the opening width of the through hole 110.
貫通孔１１０の直径Ｄのモード径が、０．１μｍ以上であると、電解液の流通路として貫通孔１１０をより有効に機能させ得る。貫通孔１１０の直径Ｄが０．６μｍよりも大きいと、殻部１０１の全体に対する空孔率が大きくなるため、殻部１０１の強度が低下する可能性がある。なお、直径が１μｍ超の細孔は、二次粒子１１２である正極活物質粒子１００の隙間の大きさに相当するため、貫通孔１１０とみなさない。 When the mode diameter of the diameter D of the through hole 110 is 0.1 μm or more, the through hole 110 can function more effectively as a flow path for the electrolytic solution. If the diameter D of the through hole 110 is larger than 0.6 μm, the porosity of the entire shell portion 101 is increased, and thus the strength of the shell portion 101 may be reduced. Note that pores having a diameter of more than 1 μm correspond to the size of the gap between the positive electrode active material particles 100 that are the secondary particles 112, and thus are not regarded as the through holes 110.
正極活物質粒子１００における貫通孔１１０のモード径は、水銀圧入法により測定される細孔容積分布から求められる。一般的に、細孔容積分布は、細孔の直径と、同じ直径（又は同じ直径範囲）を有する複数の細孔の総容積との関係を示すものであり、モード径は、細孔容積が最大となるときの直径である。 The mode diameter of the through hole 110 in the positive electrode active material particle 100 is obtained from the pore volume distribution measured by a mercury intrusion method. In general, the pore volume distribution indicates the relationship between the pore diameter and the total volume of a plurality of pores having the same diameter (or the same diameter range). This is the maximum diameter.
水銀圧入法は、水銀と固体試料との接触角が大きいことを利用した測定法である。細孔を含む固体試料と水銀とが接触しただけでは、直径が小さい細孔には水銀は浸入しない。このため、水銀を加圧することによって固体試料の細孔に水銀を浸入させ、細孔の直径と容積とを算出する。水銀に加える圧力が大きくなるほど、直径が小さい細孔に水銀が浸入する。また、細孔に圧入された水銀量から、細孔容積が算出される。 The mercury intrusion method is a measurement method that utilizes the large contact angle between mercury and a solid sample. Mercury does not penetrate into pores with a small diameter simply by contacting a solid sample containing pores with mercury. For this reason, mercury is intruded into the pores of the solid sample by pressurizing mercury, and the diameter and volume of the pores are calculated. As the pressure applied to mercury increases, mercury penetrates into pores with a small diameter. Further, the pore volume is calculated from the amount of mercury press-fitted into the pores.
図４を参照して、水銀に加えられる圧力と、一般的な細孔の直径Ｄとの関係について説明する。細孔２００は、底部を有する円形状の孔であると仮定する。圧力Ｐが加えられた水銀２０１が、直径Ｄの細孔２００に浸入しうるとき、下記数式１に従って、圧力Ｐと、水銀の接触角θと、水銀の表面張力σとから、細孔２００の直径Ｄが求められる。即ち、水銀２０１に圧力Ｐが加えられたとき、下記数式１で求められる直径Ｄ以上の細孔２００に水銀２０１が浸入するとみなすことができる。なお、接触角θ及び表面張力σは、定数を用いることが多い。 With reference to FIG. 4, the relationship between the pressure applied to mercury and the diameter D of a general pore is demonstrated. The pore 200 is assumed to be a circular hole having a bottom. When the mercury 201 to which the pressure P is applied can enter the pore 200 having the diameter D, the pressure P, the contact angle θ of mercury, and the surface tension σ of mercury are determined according to the following formula 1. A diameter D is determined. That is, when the pressure P is applied to the mercury 201, it can be considered that the mercury 201 enters the pores 200 having a diameter D or more obtained by the following formula 1. In many cases, constants are used for the contact angle θ and the surface tension σ.
−４σｃｏｓθ＝ＰＤ ・・・（数式１）
正極活物質粒子１００の細孔容積を測定する方法の一例について説明する。装置として、水銀ポロシメータが用いられる。また、正極活物質の試料をセルに入れて、セル内を真空排気する。さらに真空排気したセル内に水銀を注入し、水銀に圧力を加える。このとき、圧力を、例えば１４ｋＰａ〜４１４ＭＰａまで変化させる。なお、測定圧力「１４ｋＰａ」では、直径Ｄが９０μｍ相当からそれ以上の大きさの細孔に水銀を浸入させることができる。測定圧力「４１４ＭＰａ」では、直径Ｄが０．００３μｍ相当からそれ以上の大きさの細孔に水銀を浸入させることができる。
−4σ cos θ = PD (Formula 1)
An example of a method for measuring the pore volume of the positive electrode active material particles 100 will be described. A mercury porosimeter is used as the device. Further, a sample of the positive electrode active material is put in the cell, and the inside of the cell is evacuated. Further, mercury is injected into the evacuated cell and pressure is applied to the mercury. At this time, the pressure is changed, for example, from 14 kPa to 414 MPa. Note that at a measurement pressure of “14 kPa”, mercury can be introduced into pores having a diameter D corresponding to 90 μm or more and larger. At a measurement pressure of “414 MPa”, mercury can be infiltrated into pores having a diameter D equivalent to 0.003 μm or more.
なお、正極活物質粒子１００を試料としたとき、殻部１０１に形成された貫通孔１１０は、中空部１０２と連通しているため、水銀圧入法によって測定される細孔容積分布に基づき得られた細孔容積は、実質的に中空部１０２の容積も含む。 When the positive electrode active material particle 100 is used as a sample, the through-hole 110 formed in the shell portion 101 communicates with the hollow portion 102 and is thus obtained based on the pore volume distribution measured by the mercury intrusion method. The pore volume substantially includes the volume of the hollow portion 102.
また、モード径を測定するにあたり、水銀の密度は、１３．５２ｇ／ｍｌ以上１３．５４ｇ／ｍｌ以下であればよく、接触角θは、１３０°以上１４０°以下であればよく、表面張力σは、４８０ｄｙｎｓ／ｃｍ以上４８５ｄｙｎｓ／ｃｍ以下であればよい。 Further, in measuring the mode diameter, the mercury density may be 13.52 g / ml or more and 13.54 g / ml or less, the contact angle θ may be 130 ° or more and 140 ° or less, and the surface tension σ May be 480 dyns / cm or more and 485 dyns / cm or less.
ここで、水銀圧入法によって得られる細孔容積であって１μｍ以下の径を有する貫通孔１１０の全容積を全細孔容積Ｖａとし、０．１μｍ以上０．６μｍ以下の径を有する貫通孔１１０の全容積を部分細孔容積Ｖｂとすると、全細孔容積Ｖａに対する部分細孔容積Ｖｂの百分率である容積比率Ｒｔ（Ｒｔ＝（Ｖｂ／Ｖａ）・１００）が、７５％以上である。容積比率Ｒｔが、７５％以上であると、０．１μｍ以上０．６μｍ以下の径を有する貫通孔１１０の割合を十分に多くすることができる。当該貫通孔１１０は、電解液の流通路として有効に機能する孔であるため、リチウムイオン二次電池において内部抵抗を低下させることができる。 Here, the total volume of the through holes 110 having a diameter of 1 μm or less, which is a pore volume obtained by the mercury intrusion method, is defined as a total pore volume Va, and the through holes 110 having a diameter of 0.1 μm or more and 0.6 μm or less. Is the partial pore volume Vb, the volume ratio Rt (Rt = (Vb / Va) · 100), which is a percentage of the partial pore volume Vb to the total pore volume Va, is 75% or more. When the volume ratio Rt is 75% or more, the ratio of the through holes 110 having a diameter of 0.1 μm or more and 0.6 μm or less can be sufficiently increased. Since the through-hole 110 is a hole that effectively functions as a flow path for the electrolytic solution, the internal resistance can be reduced in the lithium ion secondary battery.
また、部分細孔容積Ｖｂは、０．０４５ｍｌ／ｇ以上である。部分細孔容積Ｖｂが、０．０４５ｍｌ／ｇ以上であって、且つ容積比率Ｒｔが７５％以上であると、０．１μｍ以上０．６μｍ以下の径を有する貫通孔１１０を通じて、正極活物質粒子１００の中空部内に十分な量の電解液が蓄えられ、リチウムイオン二次電池の内部抵抗を低下させることができる。また、十分な量の電解液が蓄えられることにより、大電流放電にも対応可能であるため、電気自動車（ハイブリッド自動車を含む）にも好適に利用可能である。なお、部分細孔容積Ｖｂが０．０４５ｍｌ／ｇ未満であると、０．１μｍ以上０．６μｍ以下の径を有する貫通孔１１０を有していても、当該貫通孔１１０を介して正極活物質粒子１００内に十分な量の電解液が入り込まない。そのため、リチウムイオン二次電池の内部抵抗が高くなってしまい、大電流にも対応できない。また、容積比率Ｒｔを９０％以上とすると、内部抵抗をさらに低下させることができる。 The partial pore volume Vb is 0.045 ml / g or more. When the partial pore volume Vb is 0.045 ml / g or more and the volume ratio Rt is 75% or more, the positive electrode active material particles pass through the through holes 110 having a diameter of 0.1 μm or more and 0.6 μm or less. A sufficient amount of electrolyte is stored in the hollow portion of 100, and the internal resistance of the lithium ion secondary battery can be reduced. In addition, since a sufficient amount of electrolyte can be stored, it is possible to cope with a large current discharge, and therefore it can be suitably used for electric vehicles (including hybrid vehicles). When the partial pore volume Vb is less than 0.045 ml / g, the positive electrode active material can be provided through the through-hole 110 even if the through-hole 110 has a diameter of 0.1 μm or more and 0.6 μm or less. A sufficient amount of electrolyte does not enter the particles 100. For this reason, the internal resistance of the lithium ion secondary battery becomes high, and it cannot cope with a large current. Further, when the volume ratio Rt is 90% or more, the internal resistance can be further reduced.
なお、正極は、正極活物質として、上述した中空構造の正極活物質のほかに、従来公知の他の正極活物質（例えば中実構造の正極活物質）を含んでもよい。但し、他の正極活物質の割合は、正極活物質全体の５０質量％以下、好ましくは３０質量％以下、より好ましくは１０質量％以下とすることが望ましい。 The positive electrode may include other positive electrode active materials known in the art (for example, a positive electrode active material having a solid structure) in addition to the above-described positive electrode active material having a hollow structure as a positive electrode active material. However, the proportion of the other positive electrode active material is 50% by mass or less, preferably 30% by mass or less, more preferably 10% by mass or less of the entire positive electrode active material.
次に、中空構造の正極活物質粒子１００の作用について説明する。この正極活物質粒子１００と対比されるものとしては、一般的な多孔質構造の粒子が挙げられる。ここで多孔質構造とは、実体のある部分と空隙部分とが粒子全体にわたって混在している構造（スポンジ状構造）を指す。多孔質構造を有する正極活物質粒子の代表例として、いわゆる噴霧焼成法（スプレードライ製法と称されることもある。）により得られた正極活物質粒子が挙げられる。本実施形態における中空構造の正極活物質粒子は、実体のある部分が殻部１０１に偏っており、中空部１０２に明確にまとまった空間が形成されているという点で、上記多孔質構造の正極活物質粒子とは、構造上、明らかに区別されるものである。 Next, the effect | action of the positive electrode active material particle 100 of a hollow structure is demonstrated. Examples of contrast with the positive electrode active material particles 100 include particles having a general porous structure. Here, the porous structure refers to a structure (sponge-like structure) in which a substantial part and a void part are mixed over the entire particle. As a typical example of the positive electrode active material particles having a porous structure, positive electrode active material particles obtained by a so-called spray firing method (sometimes referred to as a spray dry production method) can be given. The positive electrode active material particles having a hollow structure according to the present embodiment are such that the substantial portion is biased toward the shell portion 101, and a space is clearly formed in the hollow portion 102. The active material particles are clearly distinguished from each other in structure.
上記の中空構造を有する正極活物質粒子１００は、内部に空洞のない緻密構造の正極活物質粒子に比べて、一次粒子１１１の凝集が少ない。そのため、該粒子内の粒界が少なく、粒子内部へのＬｉイオンの拡散が速い。このような粒界の少ない正極活物質粒子１００によると、正極活物質粒子１００を有するリチウムイオン二次電池の出力特性を向上させることができる。 The positive electrode active material particles 100 having the hollow structure described above have less aggregation of the primary particles 111 than the positive electrode active material particles having a dense structure without a cavity inside. Therefore, there are few grain boundaries in the particles, and Li ions diffuse quickly into the particles. According to the positive electrode active material particles 100 with few grain boundaries, the output characteristics of the lithium ion secondary battery having the positive electrode active material particles 100 can be improved.
例えば、低ＳＯＣ域の電池出力では、正極活物質のＬｉ固体内拡散性が律速であり、Ｌｉ固体内拡散性にはＬｉ拡散距離が影響する。このため、正極活物質粒子１００を、貫通孔１１０を有する中空構造とし、且つ貫通孔１１０のモード径と容積比率Ｒｔとを好ましい範囲とすることで、貫通孔１１０を介して殻部１０１のＬｉイオンと電解液とを効率よく接触させることが可能となる。これにより、Ｌｉイオンの固体内拡散性が高められ、リチウムイオン二次電池の内部抵抗が低下するので、低ＳＯＣ域の出力特性を向上することができる。 For example, at the battery output in the low SOC range, the Li solid diffusivity of the positive electrode active material is rate limiting, and the Li diffusion distance affects the Li solid diffusivity. For this reason, the positive electrode active material particles 100 have a hollow structure having the through-holes 110, and the mode diameter and volume ratio Rt of the through-holes 110 are in a preferable range, so that the Li of the shell portion 101 is interposed through the through-holes 110. It becomes possible to make an ion and electrolyte solution contact efficiently. Thereby, the in-solid diffusibility of Li ions is enhanced, and the internal resistance of the lithium ion secondary battery is lowered, so that the output characteristics in the low SOC region can be improved.
（負極）
次に、負極について説明する。負極集電体３１としては、従来のリチウムイオン二次電池と同様に、導電性の良好な金属からなる導電性部材が好ましく用いられる。そのような導電性部材としては、例えば銅または銅を主成分とする合金を用いることができる。
(Negative electrode)
Next, the negative electrode will be described. As the negative electrode current collector 31, a conductive member made of a metal having good conductivity is preferably used as in the case of a conventional lithium ion secondary battery. As such a conductive member, for example, copper or an alloy containing copper as a main component can be used.
負極合材層には、電荷担体となるＬｉイオンを吸蔵および放出可能な負極活物質が含まれる。負極活物質の組成や形状に特に制限はなく、従来からリチウムイオン二次電池に用いられる物質の１種または２種以上を使用することができる。そのような負極活物質としては、例えばリチウムイオン二次電池で一般的に用いられる炭素材料が挙げられる。上記炭素材料の代表例としては、グラファイトカーボン（黒鉛）、アモルファスカーボン等が挙げられる。少なくとも一部にグラファイト構造（層状構造）を含む粒子状の炭素材料（カーボン粒子）が好ましく用いられる。その他、負極活物質として、チタン酸リチウム等の酸化物、ケイ素材料、スズ材料等の単体、合金、化合物、上記材料を併用した複合材料を用いることも可能である。 The negative electrode mixture layer includes a negative electrode active material that can occlude and release Li ions serving as charge carriers. There is no restriction | limiting in particular in a composition and a shape of a negative electrode active material, The 1 type (s) or 2 or more types of the material conventionally used for a lithium ion secondary battery can be used. As such a negative electrode active material, for example, a carbon material generally used in lithium ion secondary batteries can be cited. Representative examples of the carbon material include graphite carbon (graphite) and amorphous carbon. A particulate carbon material (carbon particles) containing a graphite structure (layered structure) at least partially is preferably used. In addition, as the negative electrode active material, it is also possible to use oxides such as lithium titanate, simple substances such as silicon materials and tin materials, alloys, compounds, and composite materials using the above materials in combination.
なお、非水電解液、及びセパレータは、従来からリチウムイオン二次電池に用いられるものを用いることができる。電解液としては、リチウム塩（例えばＬｉＣｌＯ４、ＬｉＰＦ６、ＬｉＡｓＦ６、ＬｉＢＦ４、ＬｉＳＯ３ＣＦ３等）を、有機溶媒に溶解したものが挙げられる。有機溶媒としては、例えば、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、トリフルオロプロピレンカーボネート等の環状カーボネート、ジエチルカーボネート、ジメチルカーボネート、エチルメチルカーボネート、ジプロピルカーボネート等の鎖状カーボネート、テトラヒドロフラン、２‐メチルテトラヒドロフラン、ジメトキシエタン等のエーテル化合物、エチルメチルスルホン、ブタンスルトン等の硫黄化合物、又はリン酸トリエチル、リン酸トリオクチル等のリン化合物等が挙げられ、これらを１乃至複数混合して用いることができる。 In addition, what is conventionally used for a lithium ion secondary battery can be used for a non-aqueous electrolyte and a separator. Examples of the electrolytic solution include a lithium salt (for example, LiClO 4 , LiPF 6 , LiAsF 6 , LiBF 4 , LiSO 3 CF 3, etc.) dissolved in an organic solvent. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, and dipropyl carbonate, tetrahydrofuran, and 2-methyltetrahydrofuran. And ether compounds such as dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate.
（正極活物質の製造方法）
次に、正極活物質の製造方法について説明する。正極活物質の製造方法は、例えば、原料水酸化物生成工程と、混合工程と、焼成工程とを含む。
(Method for producing positive electrode active material)
Next, the manufacturing method of a positive electrode active material is demonstrated. The manufacturing method of a positive electrode active material includes a raw material hydroxide production | generation process, a mixing process, and a baking process, for example.
原料水酸化物生成工程は、遷移金属化合物の水溶液にアンモニウムイオン（ＮＨ４ ＋）を供給して、遷移金属水酸化物の粒子を水溶液から析出させる工程である。ここで、水溶液は、リチウム遷移金属酸化物を構成する遷移金属元素の少なくとも１種を含む。 The raw material hydroxide generation step is a step of supplying ammonium ions (NH 4 + ) to the aqueous solution of the transition metal compound to precipitate the transition metal hydroxide particles from the aqueous solution. Here, the aqueous solution contains at least one transition metal element constituting the lithium transition metal oxide.
原料水酸化物生成工程は、水溶液から遷移金属水酸化物を析出させる核生成段階と、核生成段階よりも水溶液のｐＨを減少させた状態で遷移金属水酸化物を成長させる粒子成長段階とを含むことが好ましい。粒子成長段階では、ｐＨ及びアンモニウムイオン濃度を変更することにより、遷移金属水酸化物の析出速度を調整することで、正極活物質粒子１００の構造を変化させることができる。反応液中のアンモニウムイオン濃度を低くし、析出速度を高めると、貫通孔１１０を有する中空構造の正極活物質粒子１００を生成しやすくなる。また、粒子成長時間を調整することによっても、粒子空孔率等を調整することができる。 The raw material hydroxide generation step includes a nucleation stage in which the transition metal hydroxide is precipitated from the aqueous solution, and a particle growth stage in which the transition metal hydroxide is grown in a state in which the pH of the aqueous solution is reduced as compared with the nucleation stage. It is preferable to include. In the particle growth stage, the structure of the positive electrode active material particle 100 can be changed by adjusting the deposition rate of the transition metal hydroxide by changing the pH and ammonium ion concentration. If the ammonium ion concentration in the reaction solution is decreased and the deposition rate is increased, the positive electrode active material particles 100 having a hollow structure having the through-holes 110 are easily generated. Also, the particle porosity and the like can be adjusted by adjusting the particle growth time.
混合工程は、洗浄、濾過、乾燥して得られた遷移金属水酸化物とリチウム化合物とを混合して未焼成の混合物を調製する工程である。所定の割合でできるだけ均一に混合すると良い。 The mixing step is a step of preparing an unfired mixture by mixing a transition metal hydroxide obtained by washing, filtering and drying and a lithium compound. It is better to mix as uniformly as possible at a predetermined ratio.
焼成工程は、混合物を焼成して正極活物質を得る工程である。焼成工程は、例えば酸化性雰囲気中（例えば大気雰囲気中）で行われる。焼成温度は、例えば７００℃以上１１００℃以下である。また、焼成工程は、異なる温度範囲で焼成する複数の工程を含んでいてもよい。さらに、好適には、焼成後に焼成物を解砕し、篩分けを行なうとよい。 A baking process is a process of baking a mixture and obtaining a positive electrode active material. The firing step is performed, for example, in an oxidizing atmosphere (for example, in an air atmosphere). The firing temperature is, for example, 700 ° C. or higher and 1100 ° C. or lower. Moreover, the baking process may include a plurality of processes for baking at different temperature ranges. More preferably, the fired product is crushed and sieved after firing.
正極合材層には、正極活物質の他、必要に応じて導電材、結着材（バインダ）等の添加材が含有され得る。導電材としては、カーボン粉末やカーボンファイバー等の導電性粉末を含むことが好ましい。結着材としては各種のポリマー材料が挙げられる。 In addition to the positive electrode active material, the positive electrode mixture layer may contain additives such as a conductive material and a binder (binder) as necessary. The conductive material preferably contains conductive powder such as carbon powder or carbon fiber. Examples of the binder include various polymer materials.
正極合材層２２に占める正極活物質の割合は、５０質量％超であることが好ましい。７０質量％以上９７質量％以下であることがより好ましく、特に７５質量％以上９５質量％以下であるとよい。 The proportion of the positive electrode active material in the positive electrode mixture layer 22 is preferably more than 50% by mass. It is more preferably 70% by mass or more and 97% by mass or less, and particularly preferably 75% by mass or more and 95% by mass or less.
上述した正極活物質粒子を用いた正極の作製方法は特に限定されず、従来の方法を適宜採用することができる。例えば以下の方法によって作製することができる。まず、正極活物質、必要に応じて導電材、結着材等を適当な溶媒（水系溶媒、非水系溶媒またはこれらの混合溶媒）で混合してペースト状またはスラリー状の正極合材層形成用組成物を調製する。 The method for producing the positive electrode using the positive electrode active material particles described above is not particularly limited, and a conventional method can be appropriately employed. For example, it can be produced by the following method. First, a positive electrode active material, if necessary, a conductive material, a binder, etc. are mixed with an appropriate solvent (aqueous solvent, non-aqueous solvent or a mixed solvent thereof) to form a paste-like or slurry-like positive electrode mixture layer A composition is prepared.
上記組成物を正極集電体に塗付し、乾燥により溶媒を揮発させた後、圧縮（プレス）する。
正極集電体２１上への正極合材層２２の単位面積当たりの塗布量は、特に限定されるものではないが、充分な導電経路（伝導パス）を確保する観点から、正極集電体２１の片面当たり３ｍｇ／ｃｍ２以上が好ましく、５ｍｇ／ｃｍ２以上がより好ましく、特に６ｍｇ／ｃｍ２以上であるとよい。なお、塗布量は、正極合材層形成用組成物の固形分換算の塗付量である。
The above composition is applied to the positive electrode current collector, and the solvent is volatilized by drying, followed by compression (pressing).
The coating amount per unit area of the positive electrode mixture layer 22 on the positive electrode current collector 21 is not particularly limited. However, from the viewpoint of securing a sufficient conductive path (conductive path), the positive electrode current collector 21. It is preferably 3 mg / cm 2 or more per side, more preferably 5 mg / cm 2 or more, and particularly preferably 6 mg / cm 2 or more. The coating amount is a coating amount in terms of solid content of the composition for forming a positive electrode mixture layer.
また、正極集電体２１の片面当たりの塗布量は、４５ｍｇ／ｃｍ２以下が好ましく、２８ｍｇ／ｃｍ２以下がより好ましく、特に１５ｍｇ／ｃｍ２以下が好ましい。正極合材層の密度も、特に限定されないが、１．０ｇ／ｃｍ３以上３．８ｇ／ｃｍ３以下であることが好ましく、１．５ｇ／ｃｍ３以上３．０ｇ／ｃｍ３以下がより好ましく、特に１．８ｇ／ｃｍ３以上２．４ｇ／ｃｍ３以下とすることが好ましい。 In addition, the coating amount per side of the positive electrode current collector 21 is preferably 45 mg / cm 2 or less, more preferably 28 mg / cm 2 or less, and particularly preferably 15 mg / cm 2 or less. The density of the positive-electrode mixture layer is also not particularly limited, is preferably not more than 1.0 g / cm 3 or more 3.8 g / cm 3, more preferably 1.5 g / cm 3 or more 3.0 g / cm 3 or less In particular, it is preferably 1.8 g / cm 3 or more and 2.4 g / cm 3 or less.
以下、実施例１〜３、比較例１〜２について説明する。なお、実施例は本発明を限定するものではない。
（実施例１）
正極活物質は、Ｌｉ１．１４Ｎｉ０．３４Ｃｏ０．３３Ｍｎ０．３３Ｚｒ０．００２Ｗ０．００５Ｏ２で表される平均組成を有するものを準備した。この正極活物質について、以下の測定条件でモード径の測定及び容積比率Ｒｔの測定を行い、図５中、「実施例１」として表す細孔容積分布を得た。なお、細孔容積分布は、細孔容積を直径Ｄの対数（ｌｏｇＤ）で微分したＬｏｇ微分細孔容積分布で表している。即ち、グラフの縦軸は、細孔容積Ｖを直径Ｄの対数（ｌｏｇＤ）で微分した値（ｄＶ／ｄ（ｌｏｇＤ））であり、横軸は、直径Ｄである。
Hereinafter, Examples 1-3 and Comparative Examples 1-2 will be described. In addition, an Example does not limit this invention.
Example 1
A positive electrode active material having an average composition represented by Li 1.14 Ni 0.34 Co 0.33 Mn 0.33 Zr 0.002 W 0.005 O 2 was prepared. With respect to this positive electrode active material, the mode diameter was measured and the volume ratio Rt was measured under the following measurement conditions, and a pore volume distribution represented as “Example 1” in FIG. 5 was obtained. The pore volume distribution is represented by a Log differential pore volume distribution obtained by differentiating the pore volume by the logarithm (log D) of the diameter D. That is, the vertical axis of the graph is a value (dV / d (logD)) obtained by differentiating the pore volume V by the logarithm (logD) of the diameter D, and the horizontal axis is the diameter D.
測定装置：マイクロメリテックス細孔分布測定装置 オートポア ９５２０形 島津製作所製
水銀密度：１３．５３ｇ／ｍｌ
接触角：１３０°
表面張力：４８５ｄｙｎｓ／ｃｍ
細孔容積分布のピークの頂点に対応する直径は、およそ０．２５μｍであって、０．１μｍ以上０．６μｍ以下の範囲に含まれた。また図７の表に示すように、貫通孔のモード径が０．６μｍ以下の部分細孔容積は、０．０６６ｍｌ／ｇであり、容積比率Ｒｔは、９２％であった。
Measuring device: Micromeritex pore distribution measuring device Autopore 9520 model, manufactured by Shimadzu Corporation Mercury density: 13.53 g / ml
Contact angle: 130 °
Surface tension: 485 dynes / cm
The diameter corresponding to the peak apex of the pore volume distribution was approximately 0.25 μm, and was included in the range of 0.1 μm to 0.6 μm. Further, as shown in the table of FIG. 7, the partial pore volume having a through-hole mode diameter of 0.6 μm or less was 0.066 ml / g, and the volume ratio Rt was 92%.
（実施例２）
実施例１と同様な材料からなる正極活物質について、実施例１と同じ条件で、モード径の測定及び容積比率Ｒｔの測定を行い、図５中、「実施例２」として表す細孔容積分布を得た。細孔容積分布のピークの頂点に対応する直径は、およそ０．２５μｍであって、０．１μｍ以上０．６μｍ以下の範囲に含まれた。また図７の表に示すように、貫通孔のモード径が０．６μｍ以下の細孔容積は、０．０４８ｍｌ／ｇであり、容積比率Ｒｔは、９３％であった。
(Example 2)
For the positive electrode active material made of the same material as in Example 1, the mode diameter and volume ratio Rt were measured under the same conditions as in Example 1, and the pore volume distribution represented as “Example 2” in FIG. Got. The diameter corresponding to the peak apex of the pore volume distribution was approximately 0.25 μm, and was included in the range of 0.1 μm to 0.6 μm. Further, as shown in the table of FIG. 7, the pore volume having a through-hole mode diameter of 0.6 μm or less was 0.048 ml / g, and the volume ratio Rt was 93%.
（実施例３）
実施例１と同様な材料からなる正極活物質について、実施例１と同じ条件で、モード径の測定及び容積比率Ｒｔの測定を行い、図５中、「実施例３」として表す細孔容積分布を得た。直径０．６μｍ以下の範囲の細孔容積分布は、２つのピークを有する二峰性であった。そのうち部分細孔容積が高いピークの頂点に対応する直径は、およそ０．２５μｍであって、０．１μｍ以上０．６μｍ以下の範囲に含まれた。他方のピークの頂点に対応する直径は、０．０４μｍ付近であって、他方のピークは、高さが小さいものであった。また図７の表に示すように、貫通孔のモード径が０．６μｍ以下の細孔容積は、０．０４８ｍｌ／ｇであり、容積比率Ｒｔは、７６％であった。
(Example 3)
For the positive electrode active material made of the same material as in Example 1, the mode diameter and volume ratio Rt were measured under the same conditions as in Example 1, and the pore volume distribution represented as “Example 3” in FIG. Got. The pore volume distribution in the range of 0.6 μm or less in diameter was bimodal with two peaks. Among them, the diameter corresponding to the apex of the peak having a high partial pore volume was approximately 0.25 μm, and was included in the range of 0.1 μm to 0.6 μm. The diameter corresponding to the apex of the other peak was around 0.04 μm, and the other peak had a small height. Further, as shown in the table of FIG. 7, the pore volume having a through-hole mode diameter of 0.6 μm or less was 0.048 ml / g, and the volume ratio Rt was 76%.
（比較例１）
実施例１と同様な材料からなる正極活物質について、実施例１と同じ条件で、モード径の測定及び容積比率Ｒｔの測定を行い、図５中、「比較例１」として表す細孔容積分布を得た。直径０．６μｍ以下の範囲の細孔容積分布は、２つのピークを有する二峰性であった。そのうち部分細孔容積が高いピークの頂点に対応する直径は、およそ０．２５μｍであって、０．１μｍ以上０．６μｍ以下の範囲に含まれた。他方のピークは、直径０．０７μｍ付近にあり、幅が広いブロードなピークであった。また図７の表に示すように、貫通孔のモード径が０．６μｍ以下の細孔容積は、０．０６９ｍｌ／ｇであり、容積比率Ｒｔは、６７％であった。
(Comparative Example 1)
For the positive electrode active material made of the same material as in Example 1, the mode diameter and volume ratio Rt were measured under the same conditions as in Example 1, and the pore volume distribution represented as “Comparative Example 1” in FIG. Got. The pore volume distribution in the range of 0.6 μm or less in diameter was bimodal with two peaks. Among them, the diameter corresponding to the apex of the peak having a high partial pore volume was approximately 0.25 μm, and was included in the range of 0.1 μm to 0.6 μm. The other peak was in the vicinity of 0.07 μm in diameter and was a broad and broad peak. Further, as shown in the table of FIG. 7, the pore volume having a through-hole mode diameter of 0.6 μm or less was 0.069 ml / g, and the volume ratio Rt was 67%.
（比較例２）
実施例１と同様な材料からなる正極活物質について、実施例１と同じ条件で、モード径の測定及び容積比率Ｒｔの測定を行い、図５中、「比較例２」として表す細孔容積分布を得た。直径０．６μｍ以下の範囲の細孔容積分布は、２つのピークを有する二峰性であった。そのうち部分細孔容積が高いピークの頂点に対応する直径は、およそ０．２μｍであって、０．１μｍ以上０．６μｍ以下の範囲に含まれた。他方のピークは、直径０．０２μｍ付近にみられた。また図７の表に示すように、貫通孔のモード径が０．６μｍ以下の細孔容積は、０．０５８ｍｌ／ｇであり、容積比率Ｒｔは、５３％であった。
(Comparative Example 2)
For the positive electrode active material made of the same material as in Example 1, the mode diameter and volume ratio Rt were measured under the same conditions as in Example 1, and the pore volume distribution represented as “Comparative Example 2” in FIG. Got. The pore volume distribution in the range of 0.6 μm or less in diameter was bimodal with two peaks. Among them, the diameter corresponding to the apex of the peak having a high partial pore volume was approximately 0.2 μm, and was included in the range of 0.1 μm to 0.6 μm. The other peak was seen near a diameter of 0.02 μm. Further, as shown in the table of FIG. 7, the pore volume having a through-hole mode diameter of 0.6 μm or less was 0.058 ml / g, and the volume ratio Rt was 53%.
（評価）
次に、実施例１〜３、比較例１〜２の正極活物質を用いて、リチウムイオン二次電池を作成した。負極は、非晶質炭素にてコートされた球形化天然黒鉛に、カルボキシメチルセルロース（ＣＭＣ）とスチレンブタジエンコポリマー（ＳＢＲ）を混合して作成した。電解液の組成は、エチレンカーボネート、ジメチルカーボネート、エチルメチルカーボネートを同量ずつ混合し、ＬｉＰＦ６を溶解したものとした。そして、このリチウムイオン二次電池を放電回路に接続し、内部抵抗を測定した。電池のＳＯＣは６０％、温度は２０℃とした。
(Evaluation)
Next, lithium ion secondary batteries were created using the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 and 2. The negative electrode was prepared by mixing carboxymethyl cellulose (CMC) and styrene butadiene copolymer (SBR) with spheroidized natural graphite coated with amorphous carbon. The composition of the electrolytic solution was such that ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed in equal amounts to dissolve LiPF 6 . And this lithium ion secondary battery was connected to the discharge circuit, and internal resistance was measured. The SOC of the battery was 60% and the temperature was 20 ° C.
図６に示すグラフは、横軸が容積比率Ｒｔを示し、縦軸が内部抵抗Ｒｓを示す。実施例１のリチウムイオン二次電池の内部抵抗は「２．８８６ｍΩ」、実施例２のリチウムイオン二次電池の内部抵抗は「２．８８１ｍΩ」と良好な値となり、両者の値はほぼ同じであった。また、実施例３のリチウムイオン二次電池の内部抵抗は「２．８８９」と２．９ｍΩ以下であり、これも良好な値となった。 In the graph shown in FIG. 6, the horizontal axis represents the volume ratio Rt, and the vertical axis represents the internal resistance Rs. The internal resistance of the lithium ion secondary battery of Example 1 was “2.886 mΩ”, and the internal resistance of the lithium ion secondary battery of Example 2 was “2.881 mΩ”, both values being substantially the same. there were. In addition, the internal resistance of the lithium ion secondary battery of Example 3 was “2.889”, which was 2.9 mΩ or less, which was also a good value.
一方、比較例１のリチウムイオン二次電池及び比較例２のリチウムイオン二次電池は、部分細孔容積が０．０４５ｍｌ／ｇ以上であるにも関らず、容積比率Ｒｔも７０％未満であり、内部抵抗も２．９ｍΩよりも大きくなった。また、実施例２の容積比率Ｒｔと実施例３の容積比率Ｒｔとの差は１７％である。一方、比較例１の容積比率Ｒｔと実施例３の容積比率Ｒｔとの差は９％と実施例２と実施例３との容積比率Ｒｔの差よりも小さいが、それらの内部抵抗の差は、実施例２と実施例３との内部抵抗の差よりも大きい。 On the other hand, although the lithium ion secondary battery of Comparative Example 1 and the lithium ion secondary battery of Comparative Example 2 have a partial pore volume of 0.045 ml / g or more, the volume ratio Rt is also less than 70%. In addition, the internal resistance was larger than 2.9 mΩ. Further, the difference between the volume ratio Rt of Example 2 and the volume ratio Rt of Example 3 is 17%. On the other hand, the difference between the volume ratio Rt of Comparative Example 1 and the volume ratio Rt of Example 3 is 9% and smaller than the difference of the volume ratio Rt between Example 2 and Example 3, but the difference in their internal resistance is The difference in internal resistance between Example 2 and Example 3 is larger.
したがって、比較例１のリチウムイオン二次電池及び比較例２のリチウムイオン二次電池は、直径が小さい貫通孔１１０が多く形成され、貫通孔１１０を介した電解液の中空部への流入、及び中空部から貫通孔を介した電解液の流出が円滑に行われていないと考えられる。実施例１〜３のリチウムイオン二次電池は、直径の大きい貫通孔１１０が多く形成されていると推定され、貫通孔１１０を介した電解液の中空部への流入、及び中空部から貫通孔を介した電解液の流出が円滑に行われていると考えられる。なお、電気自動車の場合、多くの数（例えば５０以上）のリチウムイオン二次電池からなる組電池が用いられ、大電流放電が行われるため、内部抵抗の差が小さくても組電池全体としては大きく影響する。 Therefore, the lithium ion secondary battery of Comparative Example 1 and the lithium ion secondary battery of Comparative Example 2 are formed with a large number of through holes 110 having a small diameter, and the inflow of the electrolyte solution through the through holes 110 into the hollow portion, and It is considered that the electrolyte does not smoothly flow out from the hollow portion through the through hole. In the lithium ion secondary batteries of Examples 1 to 3, it is presumed that many through holes 110 having a large diameter are formed, and the inflow of the electrolytic solution to the hollow portion through the through holes 110 and the through holes from the hollow portions to the through holes 110 are performed. It is considered that the outflow of the electrolyte solution through the slab is carried out smoothly. In the case of an electric vehicle, an assembled battery made up of a large number (for example, 50 or more) of lithium ion secondary batteries is used and large current discharge is performed. Therefore, even if the difference in internal resistance is small, A big influence.
以上説明したように、上記実施形態によれば、以下に列挙する効果が得られるようになる。
（１）二次粒子である正極活物質粒子１００の殻部１０１に設けられる貫通孔１１０は、その最頻値であるモード径が、０．１μｍ以上０．６μｍ以下であって、且つ全細孔容積に対する部分細孔容積の百分率である容積比率Ｒｔが、７５％以上であり、さらに好ましくは９０％以上である。このため、貫通孔１１０を介した電解液の中空部への流入、及び中空部から貫通孔を介した電解液の流出が円滑に行われるようになるため、良好な電池の出力特性を得ることができる。
As described above, according to the embodiment, the effects listed below can be obtained.
(1) The through-hole 110 provided in the shell part 101 of the positive electrode active material particle 100 which is a secondary particle has a mode diameter which is the mode value of 0.1 μm to 0.6 μm and is fine. The volume ratio Rt, which is the percentage of the partial pore volume with respect to the pore volume, is 75% or more, more preferably 90% or more. For this reason, since the inflow of the electrolyte solution through the through hole 110 into the hollow portion and the outflow of the electrolyte solution from the hollow portion through the through hole can be performed smoothly, good battery output characteristics can be obtained. Can do.
（２）モード径が０．１μｍ以上０．６μｍ以下である正極活物質粒子１００の０．６μｍ以下の範囲の細孔容積分布（図５における対数微分細孔容積分布）は一峰性の分布であるとき、０．１μｍ以上０．６μｍ以下の範囲に一つのピークを有し、それ以外のピークを有さない。すなわち、正極活物質粒子１００の貫通孔１１０の直径は、その多くが０．１μｍ以上０．６μｍ以下の範囲に含まれ、その範囲よりも小さい範囲の直径を有する貫通孔１１０は少ない。そのため、このような正極活物質粒子１００では、貫通孔１１０を介した電解液の中空部１０２への流入、及び中空部１０２から貫通孔１１０を介した電解液の流出が円滑に行われるようになるため、良好な電池の出力特性を得ることができる。 (2) The pore volume distribution (logarithmic differential pore volume distribution in FIG. 5) in the range of 0.6 μm or less of the positive electrode active material particle 100 having a mode diameter of 0.1 μm or more and 0.6 μm or less is a unimodal distribution. In some cases, it has one peak in the range of 0.1 μm to 0.6 μm and no other peaks. That is, most of the diameters of the through holes 110 of the positive electrode active material particles 100 are included in the range of 0.1 μm or more and 0.6 μm or less, and there are few through holes 110 having a diameter in a range smaller than that range. Therefore, in such positive electrode active material particles 100, the electrolyte solution can smoothly flow into the hollow portion 102 through the through hole 110, and the electrolyte solution can flow out from the hollow portion 102 through the through hole 110 smoothly. Therefore, good battery output characteristics can be obtained.
（他の実施例）
なお、上記各実施形態は、以下のように適宜変更して実施することもできる。
・正極合材層２２は、正極集電体２１の少なくとも一方の面に設けられていればよく、片面に設けられていてもよい。また、負極合材層３２は、負極集電体３１の少なくとも一方の面に設けられていればよく、片面に設けられていてもよい。
(Other examples)
In addition, each said embodiment can also be suitably changed and implemented as follows.
-The positive electrode mixture layer 22 should just be provided in the at least one surface of the positive electrode electrical power collector 21, and may be provided in the single side | surface. Moreover, the negative electrode composite material layer 32 should just be provided in the at least one surface of the negative electrode collector 31, and may be provided in the single side | surface.
・電解液と正極との間でナトリウムイオンが移動するナトリウムイオン二次電池であってもよい。
・電極体１５は、正極シート２０及び負極シート３０を、セパレータ４０，４１を介して巻回した電極構造に限定されず、電池の形状や使用目的に応じて適宜変更してもよい。例えば、正極シート２０及び負極シート３０を、セパレータ４０，４１を介して積層した巻回しないタイプの電極構造であってもよい。
A sodium ion secondary battery in which sodium ions move between the electrolytic solution and the positive electrode may be used.
-The electrode body 15 is not limited to the electrode structure which wound the positive electrode sheet 20 and the negative electrode sheet 30 via the separators 40 and 41, You may change suitably according to the shape and intended purpose of a battery. For example, a non-winding type electrode structure in which the positive electrode sheet 20 and the negative electrode sheet 30 are stacked via separators 40 and 41 may be used.
１１…ケース、１２…蓋体、１３…正極端子、１４…負極端子、１５…電極体、２０…正極シート、３０…負極シート、１００…正極活物質粒子、１０１…殻部、１０２…中空部、１１０…貫通孔、１１１…一次粒子、１１２…二次粒子。 DESCRIPTION OF SYMBOLS 11 ... Case, 12 ... Lid body, 13 ... Positive electrode terminal, 14 ... Negative electrode terminal, 15 ... Electrode body, 20 ... Positive electrode sheet, 30 ... Negative electrode sheet, 100 ... Positive electrode active material particle, 101 ... Shell part, 102 ... Hollow part 110 through-holes 111 primary particles 112 secondary particles
Claims (4)
前記二次粒子は、前記一次粒子からなる殻部と、前記殻部の内側に形成された中空部とを有し、前記殻部には、当該殻部の外側と当該殻部の中空部とを連通する貫通孔が設けられるとともに、
前記貫通孔の直径は、１μｍ以下であって、水銀圧入法による細孔容積分布測定によって得られるモード径が０．１μｍ以上０．６μｍ以下であって、
水銀圧入法による細孔容積分布測定によって得られる細孔容積であって０．１μｍ以上０．６μｍ以下の直径を有する全ての貫通孔の総容積を示す部分細孔容積が、０．０４５ｍｌ／ｇ以上であり、
水銀圧入法による細孔容積分布測定によって得られる細孔容積であって１μｍ以下の直径を有する全ての貫通孔の総容積を示す全細孔容積に対する前記部分細孔容積の百分率が、７５％以上である
ことを特徴とする非水電解液二次電池。 A non-aqueous electrolyte secondary battery containing secondary particles composed of a plurality of primary particles and having a hollow structure in a positive electrode active material,
The secondary particles have a shell part made of the primary particles and a hollow part formed inside the shell part, and the shell part includes an outer side of the shell part and a hollow part of the shell part. A through-hole communicating with the
The diameter of the through hole is 1 μm or less, and the mode diameter obtained by the pore volume distribution measurement by the mercury intrusion method is 0.1 μm or more and 0.6 μm or less,
A partial pore volume obtained by measuring the pore volume distribution by the mercury intrusion method and indicating the total volume of all through-holes having a diameter of 0.1 μm or more and 0.6 μm or less is 0.045 ml / g. That's it,
The percentage of the partial pore volume with respect to the total pore volume, which is the pore volume obtained by the pore volume distribution measurement by the mercury intrusion method and indicates the total volume of all through-holes having a diameter of 1 μm or less, is 75% or more. A non-aqueous electrolyte secondary battery, characterized in that
請求項１に記載の非水電解液二次電池。 The nonaqueous electrolyte secondary battery according to claim 1, wherein a percentage of the partial pore volume with respect to the total pore volume is 90% or more.
請求項１又は２に記載の非水電解液二次電池。 The pore volume distribution obtained by the pore volume distribution measurement, wherein the pore volume distribution in a range where the diameter of the through-hole is 0.6 μm or less is a unimodal distribution. Water electrolyte secondary battery.
前記二次粒子は、前記一次粒子からなる殻部と、前記殻部の内側に形成された中空部とを有し、前記殻部には、当該殻部の外側と当該殻部の中空部とを連通する貫通孔が設けられるとともに、
前記貫通孔の直径は、１μｍ以下であって、水銀圧入法による細孔容積分布測定によって得られるモード径が０．１μｍ以上０．６μｍ以下であって、
水銀圧入法による細孔容積分布測定によって得られる細孔容積であって０．１μｍ以上０．６μｍ以下の直径を有する全ての貫通孔の総容積を示す部分細孔容積が、０．０４５ｍｌ／ｇ以上であり、
水銀圧入法による細孔容積分布測定によって得られる細孔容積であって１μｍ以下の直径を有する全ての貫通孔の総容積を示す全細孔容積に対する前記部分細孔容積の百分率が、７５％以上である
ことを特徴とする非水電解液二次電池の正極活物質。 A positive electrode active material provided in a non-aqueous electrolyte secondary battery, containing secondary particles having a hollow structure consisting of a plurality of primary particles,
The secondary particles have a shell part made of the primary particles and a hollow part formed inside the shell part, and the shell part includes an outer side of the shell part and a hollow part of the shell part. A through-hole communicating with the
The diameter of the through hole is 1 μm or less, and the mode diameter obtained by the pore volume distribution measurement by the mercury intrusion method is 0.1 μm or more and 0.6 μm or less,
A partial pore volume obtained by measuring the pore volume distribution by the mercury intrusion method and indicating the total volume of all through-holes having a diameter of 0.1 μm or more and 0.6 μm or less is 0.045 ml / g. That's it,
The percentage of the partial pore volume with respect to the total pore volume, which is the pore volume obtained by the pore volume distribution measurement by the mercury intrusion method and indicates the total volume of all through-holes having a diameter of 1 μm or less, is 75% or more. A positive electrode active material for a non-aqueous electrolyte secondary battery.
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