JP5811857B2 - Negative electrode active material for lithium ion secondary battery, lithium ion secondary battery using the negative electrode active material, and method for producing negative electrode active material for lithium ion secondary battery - Google Patents

Negative electrode active material for lithium ion secondary battery, lithium ion secondary battery using the negative electrode active material, and method for producing negative electrode active material for lithium ion secondary battery Download PDF

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JP5811857B2
JP5811857B2 JP2012005744A JP2012005744A JP5811857B2 JP 5811857 B2 JP5811857 B2 JP 5811857B2 JP 2012005744 A JP2012005744 A JP 2012005744A JP 2012005744 A JP2012005744 A JP 2012005744A JP 5811857 B2 JP5811857 B2 JP 5811857B2
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宇野　貴博
貴博 宇野
久芳　完治
完治 久芳
樋上　晃裕
晃裕 樋上
広太郎 岩田
広太郎 岩田
幸俊 上原
幸俊 上原
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Mitsubishi Materials Corp
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Description

本発明は、高容量かつサイクル特性に優れた負極活物質と、この負極活物質を用いたリチウムイオン二次電池と、上記負極活物質を製造する方法に関するものである。   The present invention relates to a negative electrode active material having a high capacity and excellent cycle characteristics, a lithium ion secondary battery using the negative electrode active material, and a method for producing the negative electrode active material.

近年、携帯電話やノート型パソコン等のポータブル電子機器の発達や、電気自動車の実用化等に伴い、小型軽量でかつ高容量の二次電池が必要とされるようになってきた。現在、この要求に応える高容量二次電池として、正極材料にＬｉＣｏＯ2等の含リチウム複合酸化物を用い、負極活物質に炭素系材料を用いたリチウムイオン電池が商品化されている。この炭素系材料を負極に使用した場合、その理論容量は３７２ｍＡｈ／ｇと金属リチウムの約１／１０の容量しかなく、また理論密度が２．２ｇ／ｃｃと低く、実際に負極シートとした場合には、更に密度が低下する。そのため、体積当たりでより高容量な材料を負極として利用することが電池の高容量化の面から望まれている。 In recent years, along with the development of portable electronic devices such as mobile phones and laptop computers, and the practical application of electric vehicles, secondary batteries with small size and light weight and high capacity have been required. Currently, lithium ion batteries using a lithium-containing composite oxide such as LiCoO 2 as a positive electrode material and a carbon-based material as a negative electrode active material are commercialized as high-capacity secondary batteries that meet this requirement. When this carbon material is used for the negative electrode, its theoretical capacity is 372 mAh / g, which is only about 1/10 the capacity of metallic lithium, and its theoretical density is as low as 2.2 g / cc. In addition, the density further decreases. For this reason, it is desired to use a material having a higher capacity per volume as the negative electrode from the viewpoint of increasing the capacity of the battery.

一方、Ａｌ、Ｇｅ、Ｓｉ、Ｓｎ、Ｚｎ、Ｐｂ等の金属又は半金属は、リチウムと合金化することが知られており、これらの金属又は半金属を負極活物質に用いた二次電池が検討されている。これらの材料は、高容量かつ高エネルギー密度であり、炭素系材料を用いた負極よりも多くのリチウムイオンを吸蔵、脱離できるため、これらの材料を使用することで高容量、高エネルギー密度な電池を作製することができると考えられている。例えば、純粋なスズは９９３ｍＡｈ／ｇの高い理論容量を示すことが知られている。   On the other hand, metals or metalloids such as Al, Ge, Si, Sn, Zn, and Pb are known to be alloyed with lithium, and secondary batteries using these metals or metalloids as negative electrode active materials are known. It is being considered. These materials have a high capacity and a high energy density, and can absorb and desorb more lithium ions than a negative electrode using a carbon-based material. Therefore, by using these materials, a high capacity and a high energy density can be obtained. It is believed that a battery can be made. For example, pure tin is known to exhibit a high theoretical capacity of 993 mAh / g.

しかし、炭素系材料に比べてサイクル特性に劣るため未だ実用化には至っていない。その理由としては、スズをそのままリチウムイオン二次電池の負極活物質に用いると、充放電に伴う大きな体積変化により微粉化し、集電板から剥離したり、導電助剤との接触が失われたりするため、十分なサイクル特性を得ることができないという問題が生じる。   However, since the cycle characteristics are inferior to those of carbon-based materials, it has not yet been put into practical use. The reason for this is that if tin is used as a negative electrode active material for a lithium ion secondary battery as it is, it will be pulverized due to a large volume change associated with charge and discharge, and may be peeled off from the current collector plate or lost contact with the conductive auxiliary agent. Therefore, there arises a problem that sufficient cycle characteristics cannot be obtained.

このような上記問題点を解決する技術として、シリコンやスズ等の無機質の粒子に他の物質を添加させることで、体積変化の少ない負極材料が研究、開発されている。具体的には、リチウムと合金化する金属としてスズを、リチウムと合金化しない金属としてコバルトを使用し、これらの合金薄膜を負極活物質層とした技術が研究、開発されている（例えば、特許文献１，２参照。）。特許文献１では、湿式メッキにより集電体上にＳｎ−Ｃｏ合金層を設け、このＳｎ−Ｃｏ合金層を非晶質にすることで、サイクル特性の改善を目指している。また、特許文献２では、電解メッキや無電解メッキ等の電気化学的な方法を用いて、Ｓｎ−Ｃｏ合金薄膜を集電板上に生成させることで、サイクル特性の向上を図っている。   As a technique for solving such a problem, a negative electrode material having a small volume change has been researched and developed by adding other substances to inorganic particles such as silicon and tin. Specifically, a technique in which tin is used as a metal alloying with lithium and cobalt is used as a metal not alloying with lithium and these alloy thin films are used as a negative electrode active material layer has been researched and developed (for example, patents). References 1 and 2). In Patent Document 1, an Sn—Co alloy layer is provided on a current collector by wet plating, and the Sn—Co alloy layer is made amorphous so as to improve cycle characteristics. In Patent Document 2, cycle characteristics are improved by generating an Sn—Co alloy thin film on a current collector plate using an electrochemical method such as electrolytic plating or electroless plating.

特開２００９−２４５７９４号公報（段落［００４２］、段落［００４３］）JP 2009-245794 A (paragraph [0042], paragraph [0043]) 特開２００２−３７３６４７号公報（請求項１、請求項１５、段落［０００６］、段落［００１１］）JP 2002-373647 A (Claim 1, claim 15, paragraph [0006], paragraph [0011])

しかし、上記従来の特許文献１及び２に示される負極では、リチウムと合金化しないコバルトをスズと合金化することで、サイクル特性の劣化を抑制してきたけれども、これらはほぼ均一組成であり、容量及びサイクル特性ともに十分とはいえなかった。   However, in the negative electrodes shown in the above-mentioned conventional patent documents 1 and 2, although deterioration of cycle characteristics has been suppressed by alloying cobalt, which is not alloyed with lithium, with tin, they have a substantially uniform composition and a capacity. In addition, the cycle characteristics were not sufficient.

本発明の目的は、リチウムイオン二次電池を形成する際に負極活物質として用いられる複合粒子であって、コバルトが負極活物質を構成する複合粒子の外面及びポアの内面に偏在することで充放電時の体積膨張・収縮による応力を緩和できるとともに導電性を確保でき、また複合粒子内に複数のポアが存在することで充電時の体積膨張を緩和でき、高容量でサイクル特性及び出力特性に優れた長寿命のリチウムイオン二次電池を製造できる負極活物質及びその製造方法を提供することにある。本発明の別の目的は、高容量であり、かつサイクル特性に優れた長寿命のリチウムイオン二次電池を提供することにある。   An object of the present invention is a composite particle used as a negative electrode active material when forming a lithium ion secondary battery, wherein cobalt is unevenly distributed on the outer surface of the composite particle constituting the negative electrode active material and the inner surface of the pore. It can relieve stress due to volume expansion and contraction during discharge and ensure conductivity, and the presence of multiple pores in the composite particle can relieve volume expansion during charging, resulting in high capacity and cycle characteristics and output characteristics. An object of the present invention is to provide a negative electrode active material capable of producing an excellent long-life lithium ion secondary battery and a method for producing the same. Another object of the present invention is to provide a long-life lithium ion secondary battery having a high capacity and excellent cycle characteristics.

本発明の第１の観点は、スズ（Ｓｎ）とコバルト（Ｃｏ）の合計量に対するコバルト（Ｃｏ）の割合が５〜４０原子％である複合粒子からなり、複合粒子が切断面において複合粒子の表面に連通する複数のポアを有し、コバルト（Ｃｏ）が複合粒子の外面及びポアの内面に偏在し、かつ複合粒子の比表面積が１．０〜６．０ｍ2／ｇであるリチウムイオン二次電池用負極活物質である。 A first aspect of the present invention is composed of composite particles in which the ratio of cobalt (Co) to the total amount of tin (Sn) and cobalt (Co) is 5 to 40 atomic%, and the composite particles are Lithium ions having a plurality of pores communicating with the surface, cobalt (Co) is unevenly distributed on the outer surface of the composite particle and the inner surface of the pore, and the specific surface area of the composite particle is 1.0 to 6.0 m 2 / g. It is a negative electrode active material for secondary batteries.

本発明の第２の観点は、第１の観点に基づく発明であって、更に複合粒子の平均粒径が０．１〜２０μｍであることを特徴とする。   A second aspect of the present invention is an invention based on the first aspect, wherein the average particle size of the composite particles is 0.1 to 20 μm.

本発明の第３の観点は、第１又は第２の観点に基づく発明であって、更に構成元素として、クロム（Ｃｒ）及び亜鉛（Ｚｎ）のうち少なくとも１種を更に含むことを特徴とする。   A third aspect of the present invention is the invention based on the first or second aspect, and further includes at least one of chromium (Cr) and zinc (Zn) as a constituent element. .

本発明の第４の観点は、第３の観点に基づく発明であって、更にクロム（Ｃｒ）の含有量が質量比で０．００５〜１％であり、亜鉛（Ｚｎ）の含有量が質量比で５〜５０ｐｐｍであることを特徴とする。   A fourth aspect of the present invention is an invention based on the third aspect, wherein the chromium (Cr) content is 0.005 to 1% by mass, and the zinc (Zn) content is mass. The ratio is 5 to 50 ppm.

本発明の第５の観点は、第１ないし第４の観点に基づく発明であって、更にポリアクリル酸、水溶性セルロース及びポリビニルピロリドンからなる群より選ばれた少なくとも１種を更に含むことを特徴とする。   A fifth aspect of the present invention is an invention based on the first to fourth aspects, further comprising at least one selected from the group consisting of polyacrylic acid, water-soluble cellulose and polyvinylpyrrolidone. And

本発明の第６の観点は、負極活物質を有する負極と、正極活物質を有する正極と、非水電解質とを備えたリチウムイオン二次電池において、負極活物質が、スズ（Ｓｎ）とコバルト（Ｃｏ）の合計量に対するコバルト（Ｃｏ）の割合が５〜４０原子％である複合粒子からなり、複合粒子が切断面において複合粒子の表面に連通する複数のポアを有し、コバルト（Ｃｏ）が複合粒子の外面及びポアの内面に偏在し、かつ複合粒子の比表面積が１．０〜６．０ｍ2／ｇであることを特徴とする。 According to a sixth aspect of the present invention, in a lithium ion secondary battery including a negative electrode having a negative electrode active material, a positive electrode having a positive electrode active material, and a non-aqueous electrolyte, the negative electrode active material includes tin (Sn) and cobalt. Cobalt (Co) is a composite particle having a ratio of cobalt (Co) to the total amount of (Co) of 5 to 40 atomic%, and the composite particle has a plurality of pores communicating with the surface of the composite particle at the cut surface. Is unevenly distributed on the outer surface of the composite particle and the inner surface of the pore, and the specific surface area of the composite particle is 1.0 to 6.0 m 2 / g.

本発明の第７の観点は、第６の観点に基づく発明であって、更に複合粒子の平均粒径が０．１〜２０μｍであることを特徴とする。   A seventh aspect of the present invention is an invention based on the sixth aspect, and is characterized in that the composite particles have an average particle size of 0.1 to 20 μm.

本発明の第８の観点は、第６又は第７の観点に基づく発明であって、更に負極活物質の構成元素として、クロム（Ｃｒ）及び亜鉛（Ｚｎ）のうち少なくとも１種を更に含むことを特徴とする。   An eighth aspect of the present invention is the invention based on the sixth or seventh aspect, and further includes at least one of chromium (Cr) and zinc (Zn) as a constituent element of the negative electrode active material. It is characterized by.

本発明の第９の観点は、第８の観点に基づく発明であって、更にクロム（Ｃｒ）の含有量が質量比で０．００５〜１％であり、亜鉛（Ｚｎ）の含有量が質量比で５〜５０ｐｐｍであることを特徴とする。   A ninth aspect of the present invention is an invention based on the eighth aspect, wherein the chromium (Cr) content is 0.005 to 1% by mass and the zinc (Zn) content is mass. The ratio is 5 to 50 ppm.

本発明の第１０の観点は、第６ないし第９の観点に基づく発明であって、更に負極活物質にポリアクリル酸、水溶性セルロース及びポリビニルピロリドンからなる群より選ばれた少なくとも１種を更に含むことを特徴とする。   A tenth aspect of the present invention is an invention based on the sixth to ninth aspects, and further comprises at least one selected from the group consisting of polyacrylic acid, water-soluble cellulose and polyvinylpyrrolidone as the negative electrode active material. It is characterized by including.

本発明の第１１の観点は、スズイオン及びコバルトイオンを含む水溶液と２価クロムイオンを含む還元剤水溶液とを混合し、この混合液の温度、ｐＨ、処理時間又は撹拌速度の少なくとも１つの条件を調整することにより、混合液中でスズイオン及びコバルトイオンを還元させて複合粒子を合成するとともに、この複合粒子内部のスズ（Ｓｎ）を溶出させて複合粒子の比表面積を制御し、第１の観点に記載のリチウムイオン二次電池用負極活物質を製造する方法である。   In an eleventh aspect of the present invention, an aqueous solution containing tin ions and cobalt ions and a reducing agent aqueous solution containing divalent chromium ions are mixed, and at least one condition of temperature, pH, treatment time or stirring speed of the mixed solution is set. By adjusting, the composite particles are synthesized by reducing tin ions and cobalt ions in the mixed solution, and the specific surface area of the composite particles is controlled by eluting the tin (Sn) inside the composite particles. Is a method for producing a negative electrode active material for a lithium ion secondary battery.

本発明の第１２の観点は、第１１の観点に基づく発明であって、更に混合液中にポリアクリル酸、水溶性セルロース及びポリビニルピロリドンからなる群より選ばれた少なくとも１種の分散剤を更に含むことを特徴とする。   A twelfth aspect of the present invention is the invention based on the eleventh aspect, further comprising at least one dispersant selected from the group consisting of polyacrylic acid, water-soluble cellulose and polyvinylpyrrolidone in the mixed solution. It is characterized by including.

本発明の第１の観点の負極活物質では、スズとコバルトの合計量に対するコバルトの割合が５〜４０原子％である負極活物質を構成する複合粒子が切断面において複合粒子の表面に連通する複数のポアを有するので、この負極活物質を用いたリチウムイオン二次電池が充放電を繰り返したときに、複合粒子内のポアが充電時の複合粒子の体積膨張を吸収して緩和できる。またコバルトが複合粒子の外面及びポアの内面に偏在するので、即ち複数のポアを有する母材でありかつ硬度及び導電率の比較的低いスズの外面又はポア内面に、硬度及び導電率の比較的高いコバルトの偏在したスズ層が形成されるので、充放電時の体積膨張・収縮による応力を緩和できるとともに導電性を確保できる。更に複合粒子の比表面積が１．０〜６．０ｍ2／ｇと比較的大きいので、スズのリチウムとの反応面積が比較的広くなる。この結果、スズがリチウムと効率良く反応するというスズ本来の性能を引き出すことができる。従って、リチウムと合金化しないコバルトをスズとほぼ均一組成で合金化して負極を作製したため、十分な容量及びサイクル特性が得られなかった従来のリチウムイオン二次電池と比較して、本発明の負極活物質を用いたリチウムイオン二次電池は、サイクル特性及び出力特性に優れ、寿命が長くなり、かつ容量が高くなる。 In the negative electrode active material according to the first aspect of the present invention, the composite particles constituting the negative electrode active material in which the ratio of cobalt to the total amount of tin and cobalt is 5 to 40 atomic% communicate with the surface of the composite particles at the cut surface. Since it has a plurality of pores, when the lithium ion secondary battery using this negative electrode active material is repeatedly charged and discharged, the pores in the composite particles can absorb and relax the volume expansion of the composite particles during charging. In addition, since cobalt is unevenly distributed on the outer surface of the composite particle and the inner surface of the pore, that is, a base material having a plurality of pores and a relatively low hardness and conductivity of tin or the inner surface of the pore, Since a high cobalt unevenly distributed tin layer is formed, stress due to volume expansion / contraction during charge / discharge can be relieved and conductivity can be ensured. Furthermore, since the specific surface area of the composite particles is relatively large at 1.0 to 6.0 m 2 / g, the reaction area of tin with lithium is relatively wide. As a result, the original performance of tin that tin reacts efficiently with lithium can be brought out. Therefore, the negative electrode of the present invention is compared with a conventional lithium ion secondary battery in which sufficient capacity and cycle characteristics are not obtained because cobalt which is not alloyed with lithium is alloyed with tin with a substantially uniform composition to produce a negative electrode. A lithium ion secondary battery using an active material is excellent in cycle characteristics and output characteristics, has a long life, and has a high capacity.

本発明の第２又は第７の観点の負極活物質又はリチウムイオン二次電池では、複合粒子の平均粒径が０．１〜２０μｍであるので、負極活物質として粒径制御された粉末が用いられる。この結果、負極活物質をスラリー化して負極集電板に塗工することができるので、従来と同様のリチウムイオン二次電池の製造プロセスを適用できる。   In the negative electrode active material or the lithium ion secondary battery of the second or seventh aspect of the present invention, since the average particle size of the composite particles is 0.1 to 20 μm, the particle size controlled powder is used as the negative electrode active material. It is done. As a result, since the negative electrode active material can be made into a slurry and applied to the negative electrode current collector plate, the same manufacturing process for a lithium ion secondary battery as that in the past can be applied.

本発明の第１１の観点の負極活物質の製造方法では、スズイオン及びコバルトイオンを含む水溶液と２価クロムイオンを含む還元剤水溶液とを混合する湿式法により負極活物質を合成するので、イニシャルコスト（初期投資費用）が多大に掛かる特殊な装置類を用いずに済み、製造コストを抑制できる。   In the method for producing a negative electrode active material according to the eleventh aspect of the present invention, the negative electrode active material is synthesized by a wet method in which an aqueous solution containing tin ions and cobalt ions and a reducing agent aqueous solution containing divalent chromium ions are mixed. It is not necessary to use special devices that require a large (initial investment cost), and the manufacturing cost can be suppressed.

本発明実施形態の複合粒子の表面からの深さの変化に対するスズ濃度及びコバルト濃度の変化をそれぞれ示す図である。It is a figure which shows the change of the tin concentration with respect to the change of the depth from the surface of the composite particle of this invention embodiment, and a cobalt concentration, respectively. 実施例１〜４のスズイオン及びコバルトイオンを含む水溶液と還元剤水溶液とを所定の割合で混合した混合液の撹拌保持時間の相対的な相違を示した図である。It is the figure which showed the relative difference of the stirring holding time of the liquid mixture which mixed the aqueous solution containing the tin ion and cobalt ion of Examples 1-4 and the reducing agent aqueous solution in a predetermined ratio. 実施例１の複合粒子を切断した面の電子顕微鏡写真図である。FIG. 3 is an electron micrograph of a surface obtained by cutting composite particles of Example 1.

次に本発明を実施するための形態を説明する。本発明のリチウムイオン二次電池用負極活物質は、スズ（Ｓｎ）とコバルト（Ｃｏ）の合計量に対するコバルト（Ｃｏ）の割合が５〜４０原子％、好ましくは１０〜３０原子％である複合粒子からなる。ここで、複合粒子中のコバルトの割合を上記範囲に限定したのは、コバルトの割合が５原子％を下回ると、硬度の比較的低いスズの外面又はポア内面に形成された硬度の比較的高いコバルトの偏在したスズ層が薄くなって、この負極活物質を用いた二次電池の充放電時の体積膨張・収縮による応力を緩和できず、二次電池のサイクル特性が低下する不具合が生じるためであり、コバルトの割合が４０原子％を上回っても、この負極活物質を用いた二次電池のサイクル特性は良好であるけれども、コバルト量が増大し、相対的にリチウムと反応するスズ量が減少してしまい、初回放電容量が小さくなる不具合が生じるためである。   Next, the form for implementing this invention is demonstrated. The negative electrode active material for a lithium ion secondary battery of the present invention is a composite in which the ratio of cobalt (Co) to the total amount of tin (Sn) and cobalt (Co) is 5 to 40 atomic%, preferably 10 to 30 atomic%. Consists of particles. Here, the proportion of cobalt in the composite particles is limited to the above range because when the proportion of cobalt is less than 5 atomic%, the hardness formed on the outer surface of the tin or the inner surface of the pore having a relatively low hardness is relatively high. Because the tin layer with uneven distribution of cobalt becomes thin, stress due to volume expansion / contraction during charging / discharging of the secondary battery using this negative electrode active material cannot be relieved, resulting in a problem that the cycle characteristics of the secondary battery deteriorate. Even if the proportion of cobalt exceeds 40 atomic%, the cycle characteristics of the secondary battery using this negative electrode active material are good, but the amount of cobalt increases and the amount of tin that reacts relatively with lithium increases. This is because the first discharge capacity decreases due to the decrease.

上記複合粒子は切断面において複合粒子の表面に連通する複数のポアを有する。またコバルト（Ｃｏ）は複合粒子の外面及びポアの内面に偏在し、かつ複合粒子の比表面積は１．０〜６．０ｍ2／ｇ、好ましくは２．０〜５．０ｍ2／ｇである。これにより本発明の負極活物質は、従来より知られているような、粒子の中心部と外周部とでスズ−コバルトの組成の偏りがない、略均一に合金化した形態はとらない。ここで、複合粒子の比表面積を上記範囲に限定したのは、比表面積が１．０ｍ2／ｇを下回ると、本発明の負極活物質を用いたリチウムイオン二次電池のサイクル特性が低下してしまい、比表面積が６．０ｍ2／ｇを上回ると、サイクル特性は良好であるけれども、スズの量が少なくなって初回放電容量が小さくなる不具合が生じるためである。なお、複合粒子の比表面積の測定方法としては、複合粒子の外面及びポアの内面に吸着占有面積の分かった分子を液体窒素温度で吸着させ、その量から複合粒子の比表面積を求めるＢＥＴ吸着測定方法が用いられる。 The composite particle has a plurality of pores communicating with the surface of the composite particle at the cut surface. Cobalt (Co) is unevenly distributed on the outer surface of the composite particle and the inner surface of the pore, and the specific surface area of the composite particle is 1.0 to 6.0 m 2 / g, preferably 2.0 to 5.0 m 2 / g. . As a result, the negative electrode active material of the present invention does not take an almost uniform alloyed form in which there is no bias in the composition of tin-cobalt between the central part and the outer peripheral part of the particles as conventionally known. Here, the specific surface area of the composite particles was limited to the above range because, when the specific surface area was less than 1.0 m 2 / g, the cycle characteristics of the lithium ion secondary battery using the negative electrode active material of the present invention deteriorated. If the specific surface area exceeds 6.0 m 2 / g, the cycle characteristics are good, but the amount of tin decreases and the initial discharge capacity decreases. As a method for measuring the specific surface area of the composite particles, BET adsorption measurement is performed by adsorbing molecules having a known adsorption area on the outer surface of the composite particles and the inner surface of the pores at the liquid nitrogen temperature, and determining the specific surface area of the composite particles from the amount. The method is used.

このように構成された負極活物質では、複合粒子が切断面において複合粒子の表面に連通する複数のポアを有するので、この負極活物質を用いたリチウムイオン二次電池が充放電を繰り返したときに、複合粒子内のポアが充電時の複合粒子の体積膨張を吸収して緩和できる。またコバルトが複合粒子の外面及びポアの内面に偏在するので、即ち複数のポアを有する母材でありかつ硬度及び導電率の比較的低いスズの外面又はポア内面に、硬度及び導電率の比較的高いコバルトの偏在したスズ層が形成されるので、充放電時の体積膨張・収縮による応力を緩和できるとともに導電性を確保できる。更に複合粒子の比表面積が比較的大きいので、スズのリチウムとの反応面積が比較的広くなる。この結果、スズがリチウムと効率良く反応するというスズ本来の性能を引き出すことができる。従って、本発明の負極活物質を用いたリチウムイオン二次電池は、サイクル特性及び出力特性に優れ、寿命が長くなり、かつ容量が高くなる。   In the negative electrode active material configured in this manner, the composite particle has a plurality of pores communicating with the surface of the composite particle at the cut surface, and therefore when a lithium ion secondary battery using this negative electrode active material is repeatedly charged and discharged Further, the pores in the composite particles can absorb and relax the volume expansion of the composite particles during charging. In addition, since cobalt is unevenly distributed on the outer surface of the composite particle and the inner surface of the pore, that is, a base material having a plurality of pores and a relatively low hardness and conductivity of tin or the inner surface of the pore, Since a high cobalt unevenly distributed tin layer is formed, stress due to volume expansion / contraction during charge / discharge can be relieved and conductivity can be ensured. Furthermore, since the specific surface area of the composite particles is relatively large, the reaction area of tin with lithium is relatively wide. As a result, the original performance of tin that tin reacts efficiently with lithium can be brought out. Therefore, the lithium ion secondary battery using the negative electrode active material of the present invention is excellent in cycle characteristics and output characteristics, has a long life, and has a high capacity.

本発明の負極活物質を構成する複合粒子は、平均粒径が０．１〜２０μｍ、好ましくは０．５〜１０μｍの範囲に粒径制御されることがその取り扱い易さから好ましい。このように粒径制御された複数の複合粒子からなる粉末は、スラリー化して負極集電体に塗工することができ、従来からのリチウムイオン二次電池製造プロセスを適用できる。ここで、複合粒子の平均粒径を上記範囲に限定したのは、平均粒径が０．１μｍ未満ではスラリー化が困難となり、既存のリチウムイオン二次電池製造プロセスに適用できない不具合があり、２０μｍを越えるとコバルトの偏在したスズ層による膨張抑制効果が不十分となり、サイクル特性が低下する不具合があるからである。なお、複合粒子の平均粒径は、粒度分布測定装置（堀場製作所製ＬＡ−９５０）を用いて測定し、体積基準平均粒径を平均粒径とした。   The composite particles constituting the negative electrode active material of the present invention preferably have an average particle diameter of 0.1 to 20 μm, preferably 0.5 to 10 μm in view of ease of handling. The powder composed of a plurality of composite particles whose particle diameters are controlled in this way can be slurried and applied to the negative electrode current collector, and a conventional lithium ion secondary battery manufacturing process can be applied. Here, the average particle size of the composite particles is limited to the above range because when the average particle size is less than 0.1 μm, it becomes difficult to form a slurry, and there is a problem that it cannot be applied to an existing lithium ion secondary battery manufacturing process. This is because the expansion suppression effect by the tin layer in which cobalt is unevenly distributed becomes insufficient and the cycle characteristics deteriorate. The average particle size of the composite particles was measured using a particle size distribution measuring device (LA-950 manufactured by Horiba, Ltd.), and the volume-based average particle size was defined as the average particle size.

また、負極活物質は、構成元素として、クロム（Ｃｒ）及び亜鉛（Ｚｎ）のうち少なくとも１種を更に含むことが好適である。クロムや亜鉛を含ませることで、初回放電容量を増大させることができる。この理由の詳細は不明であるが、クロムや亜鉛を含有することで、粒子中心部まで速やかにリチウムが拡散することができるのではないかと推察される。クロムの含有量は質量比で０．００５〜１％、好ましくは０．１〜０．９％であり、亜鉛の含有量は質量比で５〜５０ｐｐｍ、好ましくは１０〜３０ｐｐｍの範囲である。ここで、クロム及び亜鉛の含有量を上記範囲に限定したのは、クロムの含有量が０．００５％以上又は亜鉛の含有量が５ｐｐｍ以上でないと初回放電容量の増大効果が発現せず、クロムの含有量が１％又は亜鉛の含有量が５０ｐｐｍを上回ると、コバルトの偏在したスズ層の強度が低下し保護効果が低下し、サイクル特性が低下してしまう不具合を生じるからである。なお、本発明の負極活物質を構成する複合粒子中のスズ、コバルト、クロム、亜鉛の各含有量はＩＣＰ（誘導結合プラズマ）を用いた定量分析により求めることができる。   The negative electrode active material preferably further includes at least one of chromium (Cr) and zinc (Zn) as a constituent element. By including chromium or zinc, the initial discharge capacity can be increased. Although the details of this reason are unknown, it is presumed that lithium can be rapidly diffused to the particle center by containing chromium or zinc. The chromium content is 0.005 to 1% by mass, preferably 0.1 to 0.9%, and the zinc content is 5 to 50 ppm, preferably 10 to 30 ppm by mass. Here, the chromium and zinc contents are limited to the above range because the effect of increasing the initial discharge capacity is not exhibited unless the chromium content is 0.005% or more or the zinc content is 5 ppm or more. If the content of 1% or the content of zinc exceeds 50 ppm, the strength of the tin layer in which cobalt is unevenly distributed is lowered, the protective effect is lowered, and the cycle characteristics are deteriorated. In addition, each content of tin, cobalt, chromium, and zinc in the composite particles constituting the negative electrode active material of the present invention can be obtained by quantitative analysis using ICP (inductively coupled plasma).

また、負極活物質は、ポリアクリル酸、水溶性セルロース及びポリビニルピロリドンからなる群より選ばれた少なくとも１種の分散剤を更に含むことが好適である。上記種類の分散剤を含ませることで、分散剤が粒子を覆うことになり、コバルトの偏在したスズ層による膨張収縮抑制効果を増強し、サイクル特性を向上させることができる。更に、負極活物質には、カーボンナノファイバー（ＣＮＦ）からなる導電性助剤を添加することが好適である。この導電性助剤を添加することで、導電性助剤が粒子を覆うことになり、負極全体に網目状に導電性パスを形成することができるので、サイクル特性を更に向上させることができる。   The negative electrode active material preferably further includes at least one dispersant selected from the group consisting of polyacrylic acid, water-soluble cellulose, and polyvinylpyrrolidone. By including the above type of dispersant, the dispersant covers the particles, thereby enhancing the expansion and contraction suppressing effect by the tin layer in which cobalt is unevenly distributed, and improving the cycle characteristics. Furthermore, it is preferable to add a conductive auxiliary agent made of carbon nanofiber (CNF) to the negative electrode active material. By adding this conductive auxiliary agent, the conductive auxiliary agent covers the particles, and a conductive path can be formed in a network form on the entire negative electrode, so that the cycle characteristics can be further improved.

次に、上記リチウムイオン二次電池用負極活物質の製造方法を説明する。本発明のリチウムイオン二次電池用負極活物質は、スズイオン及びコバルトイオンを含む水溶液と２価クロムイオンを含む還元剤水溶液とを混合し、この混合液の温度、ｐＨ、処理時間又は撹拌速度の少なくとも１つの条件を調整することにより製造される。具体的には、上記スズイオン及びコバルトイオンを含む水溶液と２価クロムイオンを含む還元剤水溶液とを混合することにより、この混合液中でスズイオン及びコバルトイオンを還元させて複合粒子を合成し、上記混合液の温度、ｐＨ、処理時間又は撹拌速度の少なくとも１つの条件を調整することにより、複合粒子内部のスズ（Ｓｎ）を溶出させて複合粒子の比表面積を制御する。これにより、スズとコバルトの合計量に対するコバルトの割合が５〜４０原子％である複合粒子からなり、複合粒子が切断面において複合粒子の表面に連通する複数のポアを有し、コバルトが複合粒子の外面及びポアの内面に偏在し、かつ複合粒子の比表面積が１．０〜６．０ｍ2／ｇである負極活物質が製造される。 Next, the manufacturing method of the said negative electrode active material for lithium ion secondary batteries is demonstrated. The negative electrode active material for a lithium ion secondary battery of the present invention is a mixture of an aqueous solution containing tin ions and cobalt ions and an aqueous reducing agent solution containing divalent chromium ions, and the temperature, pH, treatment time or stirring speed of the mixed solution. Manufactured by adjusting at least one condition. Specifically, by mixing the aqueous solution containing tin ions and cobalt ions and the reducing agent aqueous solution containing divalent chromium ions, the composite particles are synthesized by reducing tin ions and cobalt ions in the mixed solution, By adjusting at least one of the temperature, pH, treatment time or stirring speed of the mixed solution, tin (Sn) in the composite particles is eluted to control the specific surface area of the composite particles. Accordingly, the composite particles are composed of composite particles in which the ratio of cobalt to the total amount of tin and cobalt is 5 to 40 atomic%, the composite particles have a plurality of pores communicating with the surface of the composite particles at the cut surface, and the cobalt is composite particles. A negative electrode active material is produced that is unevenly distributed on the outer surface and the inner surface of the pores, and the specific surface area of the composite particles is 1.0 to 6.0 m 2 / g.

上記混合液中で還元反応させると、先ず、スズイオンが還元して均一なスズ粒子が生じ、このスズ粒子が一定の粒径まで成長する。続いて、コバルトイオンが還元し、一定の粒径にまで成長したスズ粒子を母材として、この母材の周囲に上記コバルトが進入し、スズ粒子の外面にコバルトが偏在した複合粒子となる。上記混合液の温度、ｐＨ、処理時間又は撹拌速度の少なくとも１つの条件を調整すると、上記複合粒子にこの粒子の表面に連通する複数のポアが形成されるとともに、コバルトが複合粒子の外面及びポアの内面に偏在して、複合粒子の外面及びポアの内面にコバルトの偏在したスズ層が形成される。このコバルトの偏在したスズ層におけるコバルト濃度は複合粒子の外面及びポアの内面からスズ母材内方に向うに従って次第に低くなり、スズ濃度は複合粒子の外面及びポアの内面からスズ母材内方に向うに従って次第に高くなるように形成される（図１）。なお、上記複合粒子に複数のポアが形成されるのは次の理由によると推察される。スズの水素過電圧は高いため、スズの溶解反応は起こり難い。一方、コバルトの水素過電圧はスズの水素過電圧より低いため、スズとコバルトが接することによってコバルト側から水素が発生する。この結果、複合粒子内部のスズが非常に溶け易くなるので、複合粒子に複数のポアが形成される。   When the reduction reaction is performed in the mixed solution, first, tin ions are reduced to produce uniform tin particles, and the tin particles grow to a certain particle size. Subsequently, cobalt ions are reduced and tin particles grown to a certain particle size are used as a base material, and the cobalt enters the periphery of the base material, resulting in composite particles in which cobalt is unevenly distributed on the outer surface of the tin particles. When adjusting at least one of the temperature, pH, treatment time or stirring speed of the mixed solution, a plurality of pores communicating with the surface of the composite particles are formed in the composite particles, and cobalt is formed on the outer surface and the pores of the composite particles. A tin layer in which cobalt is unevenly distributed is formed on the outer surface of the composite particle and the inner surface of the pore. The cobalt concentration in this unevenly distributed tin layer gradually decreases from the outer surface of the composite particle and the inner surface of the pore toward the inner side of the tin base material, and the tin concentration decreases from the outer surface of the composite particle and the inner surface of the pore to the inner side of the tin base material. It is formed so as to gradually become higher as it goes (FIG. 1). In addition, it is guessed that a several pore is formed in the said composite particle for the following reason. Since the hydrogen overvoltage of tin is high, the dissolution reaction of tin hardly occurs. On the other hand, since the hydrogen overvoltage of cobalt is lower than that of tin, hydrogen is generated from the cobalt side when tin and cobalt come into contact with each other. As a result, tin inside the composite particle is very easily dissolved, and a plurality of pores are formed in the composite particle.

スズイオン及びコバルトイオンを含む水溶液には、得られる複合粒子の凝集を抑制する分散剤を含ませることが好ましい。分散剤としては、ポリアクリル酸、水溶性セルロース及びポリビニルピロリドンから選ばれた少なくとも１種が挙げられる。   The aqueous solution containing tin ions and cobalt ions preferably contains a dispersant that suppresses aggregation of the resulting composite particles. Examples of the dispersant include at least one selected from polyacrylic acid, water-soluble cellulose, and polyvinyl pyrrolidone.

還元剤水溶液に含まれる２価クロムイオンは、還元剤としての機能を有する。この２価クロムイオンは不安定であるため、還元剤水溶液はスズイオン及びコバルトイオンを含む水溶液と混合する際にその都度調製することが好ましい。具体的には、例えば、塩化第２クロム溶液を非酸化性雰囲気下、好ましくは窒素ガス雰囲気下で金属亜鉛に接触させるか、或いは電気化学的にクロムを還元し、塩化第１クロム溶液としたものを用いるとよい。塩化第２クロム溶液はｐＨ０〜２に調整することが好ましい。それはｐＨが上限値を越えると、３価クロムイオンが水酸化物として沈殿するという不具合が生じ易いからである。   The divalent chromium ion contained in the reducing agent aqueous solution has a function as a reducing agent. Since the divalent chromium ions are unstable, the reducing agent aqueous solution is preferably prepared each time when it is mixed with an aqueous solution containing tin ions and cobalt ions. Specifically, for example, the second chromium chloride solution is brought into contact with metallic zinc in a non-oxidizing atmosphere, preferably a nitrogen gas atmosphere, or the chromium is electrochemically reduced to obtain a first chromium chloride solution. Use a good one. The second chromium chloride solution is preferably adjusted to pH 0-2. This is because when the pH exceeds the upper limit value, a problem that trivalent chromium ions precipitate as hydroxides easily occurs.

スズイオン及びコバルトイオンを含む水溶液と２価クロムイオンを含む還元剤水溶液とを混合した混合液の温度は１５〜５０℃、好ましくは２５〜４０℃に設定され、混合液のｐＨは０〜４、好ましくは０〜２に設定される。また上記混合液の処理時間は１〜４０時間、好ましくは３〜３０時間に設定され、混合液の撹拌速度は０．２〜１．５ｍ／秒、好ましくは０．４〜１．０ｍ／秒に設定される。上記混合液の処理時間は、混合液の撹拌保持時間をいう。また上記混合液の撹拌速度は、撹拌羽根の回転により混合液が流動したときの混合液の平均流速をいう。ここで、混合液の温度を上記範囲に限定したのは、１５℃未満では、スズが溶け難くなり、複合粒子に複数のポアが形成され難くなるため、充電時の複合粒子の体積膨張を吸収して緩和する効果が低下してしまい、５０℃を越えると、スズの溶出が促進され、サイクル特性は良好であるけれども、スズの量が少なくなって初回放電容量が小さくなってしまうからである。また、混合液のｐＨを上記範囲に限定したのは、ｐＨが０未満では、スズの溶出が促進されて、サイクル特性が良好であるけれども、スズの量が少なくなって初回放電容量が小さくなってしまい、ｐＨが４を越えると、スズとコバルトが接することによるコバルト側からの水素発生が生じ難くなって、複合粒子内部のスズが溶け難くなるので、複合粒子に複数のポアが形成され難くなり、これにより充電時の複合粒子の体積膨張を吸収して緩和する効果が低下してしまうからである。また、混合液の処理時間を上記範囲に限定したのは、１時間未満では、複合粒子に形成されるポアの数が少なくなるため、充電時の複合粒子の体積膨張を吸収して緩和する効果が低下してしまい、４０時間を越えると、目的の負極活物質を得るための時間が掛かり過ぎ、これにより製造コストが増大し、生産効率が低下してしまうからである。更に混合液の撹拌速度を上記範囲に限定したのは、０．２ｍ／秒未満では、混合液の組成を均一に保つことができなくなって、所望の負極活物質を得ることができず、１．５ｍ／秒を越えると、所望の負極活物質を得るために過剰のエネルギーを投入することになり、エネルギーコストの無駄が発生してしまうからである。なお、混合液の温度は高くなるに従って複合粒子の比表面積が大きくなり、混合液のｐＨは小さくなるに従って複合粒子の比表面積が大きくなる傾向にある。また、混合液の処理時間は長くなるに従って複合粒子の比表面積が大きくなり、混合液の撹拌速度は速くなるに従って複合粒子の比表面積が大きくなる傾向にある。   The temperature of the mixed solution obtained by mixing the aqueous solution containing tin ions and cobalt ions and the reducing agent aqueous solution containing divalent chromium ions is set to 15 to 50 ° C, preferably 25 to 40 ° C, and the pH of the mixed solution is 0 to 4, Preferably it is set to 0-2. The processing time of the above mixed solution is set to 1 to 40 hours, preferably 3 to 30 hours, and the stirring speed of the mixed solution is 0.2 to 1.5 m / second, preferably 0.4 to 1.0 m / second. Set to The processing time of the mixed solution refers to the stirring and holding time of the mixed solution. Moreover, the stirring speed of the said liquid mixture says the average flow velocity of a liquid mixture when a liquid mixture flows by rotation of a stirring blade. Here, the temperature of the mixed solution is limited to the above range. If the temperature is lower than 15 ° C., tin hardly dissolves and a plurality of pores are hardly formed in the composite particle, so that the volume expansion of the composite particle during charging is absorbed. When the temperature exceeds 50 ° C., elution of tin is promoted and the cycle characteristics are good, but the amount of tin is reduced and the initial discharge capacity is reduced. . In addition, the pH of the mixed solution was limited to the above range. If the pH is less than 0, elution of tin is promoted and the cycle characteristics are good, but the amount of tin is reduced and the initial discharge capacity is reduced. If the pH exceeds 4, the generation of hydrogen from the cobalt side due to the contact between tin and cobalt is difficult to occur, and the tin inside the composite particle is difficult to dissolve, so that it is difficult to form a plurality of pores in the composite particle. This is because the effect of absorbing and relaxing the volume expansion of the composite particles during charging is reduced. In addition, the treatment time of the mixed solution is limited to the above range because the number of pores formed in the composite particle is reduced if it is less than 1 hour, and therefore the effect of absorbing and relaxing the volume expansion of the composite particle during charging. This is because, if it exceeds 40 hours, it takes too much time to obtain the target negative electrode active material, which increases the manufacturing cost and decreases the production efficiency. Furthermore, the stirring speed of the mixed solution is limited to the above range because if it is less than 0.2 m / second, the composition of the mixed solution cannot be kept uniform, and a desired negative electrode active material cannot be obtained. If it exceeds 0.5 m / sec, excessive energy will be input to obtain the desired negative electrode active material, resulting in wasted energy costs. Note that the specific surface area of the composite particles increases as the temperature of the mixed solution increases, and the specific surface area of the composite particles tends to increase as the pH of the mixed solution decreases. In addition, the specific surface area of the composite particles increases as the treatment time of the mixed solution increases, and the specific surface area of the composite particles tends to increase as the stirring speed of the mixed solution increases.

このように本発明の製造方法は湿式法であり、水溶液調製や還元反応がともに室温程度の温度で実施可能であるため、イニシャルコストが多大にかかる特殊な装置類も不要となり、製造コストを抑制できる。   As described above, the manufacturing method of the present invention is a wet method, and both the aqueous solution preparation and the reduction reaction can be performed at a temperature of about room temperature. Therefore, special equipment that requires a large initial cost is not required, and the manufacturing cost is suppressed. it can.

なお、製造する負極活物質の構成元素として、クロム（Ｃｒ）及び亜鉛（Ｚｎ）のうち少なくとも１種を更に含ませる場合には、スズイオン及びコバルトイオンを含む水溶液と還元剤水溶液との混合割合を増減させる、還元剤水溶液を調製する際に使用する金属亜鉛量を増減させる、塩化亜鉛をスズイオン及びコバルトイオンを含む水溶液や還元剤水溶液に加えるなどの手法により、クロムや亜鉛の含有量を制御することができる。   In addition, when further including at least one of chromium (Cr) and zinc (Zn) as a constituent element of the negative electrode active material to be manufactured, the mixing ratio of the aqueous solution containing tin ions and cobalt ions and the reducing agent aqueous solution is Control chromium and zinc contents by increasing or decreasing, increasing or decreasing the amount of metallic zinc used in preparing the reducing agent aqueous solution, adding zinc chloride to an aqueous solution containing tin ions and cobalt ions, or an aqueous reducing agent solution. be able to.

次に上記負極活物質と導電助剤と結着剤とを所定の割合で混合した後、この混合物に所定の割合（例えば、負極活物質、導電助剤及び結着剤の合計量１００質量％に対して３５〜６０質量％）で溶媒を混合することにより、負極用組成物のスラリーを調製する。次に上記負極用組成物のスラリーを負極集電体上に、ドクターブレード法などの手法により塗布した後に乾燥して負極を作製する。   Next, after mixing the negative electrode active material, the conductive additive, and the binder in a predetermined ratio, the mixture is mixed with a predetermined ratio (for example, the total amount of the negative electrode active material, the conductive auxiliary, and the binder is 100% by mass). The slurry of the composition for negative electrodes is prepared by mixing a solvent in 35-60 mass%). Next, the slurry of the negative electrode composition is applied onto the negative electrode current collector by a technique such as a doctor blade method, and then dried to produce a negative electrode.

なお、負極の作製に使用した導電助剤、結着剤、溶媒及び負極集電体は、特に限定されるものではなく、従来より一般的に用いられるものを使用することができる。例えば、導電助剤としてはアセチレンブラック、ケッチェンブラックなどのカーボンブラック、ＶＧＣＦ或いは銅やチタン等のリチウムと合金化し難い金属粉末などが挙げられる。そして導電助剤は、複合粒子の外面、又は複合粒子の外面及びポアの内面に網目状に付着するように構成される。また、結着剤としてはポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶｄＦ）、エチレン−プロピレン−ジエン共重合体（ＥＰＤＭ）、スチレン−ブタジエンゴム（ＳＢＲ）などが挙げられる。溶媒としてはＮ−メチルピロリドン、水などが挙げられる。負極集電体としては銅箔、ステンレス箔、ニッケル箔などが挙げられる。   In addition, the conductive support agent, the binder, the solvent, and the negative electrode current collector used for the production of the negative electrode are not particularly limited, and those generally used conventionally can be used. For example, examples of the conductive assistant include carbon black such as acetylene black and ketjen black, VGCF, or metal powder that is difficult to alloy with lithium such as copper and titanium. The conductive additive is configured to adhere to the outer surface of the composite particle, or the outer surface of the composite particle and the inner surface of the pore in a mesh shape. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), and styrene-butadiene rubber (SBR). Examples of the solvent include N-methylpyrrolidone and water. Examples of the negative electrode current collector include copper foil, stainless steel foil, and nickel foil.

このようにして得られた負極を用いてリチウムイオン二次電池を作製する。正極活物質をバインダ及び導電助剤と所定の割合で混合して正極用組成物のスラリーを調製する。次に、上記正極用組成物のスラリーを正極集電体上に、ドクターブレード法などの手法により塗布した後に乾燥して正極を作製する。   A lithium ion secondary battery is produced using the negative electrode thus obtained. A positive electrode active material is mixed with a binder and a conductive additive at a predetermined ratio to prepare a slurry of the positive electrode composition. Next, the slurry for the positive electrode composition is applied onto the positive electrode current collector by a technique such as a doctor blade method, and then dried to produce a positive electrode.

なお、正極の作製に使用した正極活物質、バインダ、導電助剤及び正極集電体は、特に限定されるものではなく、従来より一般的に用いられるものを使用することができる。例えば、正極活物質としては、ＬｉＣｏＯ2、ＬｉＮｉＯ2、ＬｉＭｎ2Ｏ4、ＬｉＭｎＯ2、ＬｉＦｅＰＯ4などが挙げられる。導電助剤としては、アセチレンブラック、ケッチェンブラックなどのカーボンブラック、ＶＧＣＦ、黒鉛等が挙げられる。また、バインダとしては、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶｄＦ）、エチレン−プロピレン−ジエン共重合体（ＥＰＤＭ）、スチレン−ブタジエンゴム（ＳＢＲ）等が挙げられる。正極集電体としては、アルミニウム箔、ステンレス鋼箔、ニッケル箔等が挙げられる。 In addition, the positive electrode active material, the binder, the conductive auxiliary agent, and the positive electrode current collector used for the production of the positive electrode are not particularly limited, and those conventionally used can be used. For example, examples of the positive electrode active material include LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , LiMnO 2 , and LiFePO 4 . Examples of the conductive assistant include carbon black such as acetylene black and ketjen black, VGCF, graphite and the like. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), and styrene-butadiene rubber (SBR). Examples of the positive electrode current collector include aluminum foil, stainless steel foil, and nickel foil.

次に、負極集電体上に負極活物質層を形成して得られた負極と、セパレータと、正極集電体上に正極活物質層を形成して得られた正極とを、正極と負極の活物質面をそれぞれ対向させた状態で積層し、積層体を形成する。セパレータは合成樹脂製不織布、ポリエチレン多孔質フィルム、ポリプロピレン多孔質フィルム等から形成される。   Next, the negative electrode obtained by forming the negative electrode active material layer on the negative electrode current collector, the separator, and the positive electrode obtained by forming the positive electrode active material layer on the positive electrode current collector are combined with the positive electrode and the negative electrode. The active material surfaces are stacked in a state of facing each other to form a stacked body. The separator is formed from a synthetic resin nonwoven fabric, a polyethylene porous film, a polypropylene porous film, or the like.

そして、上記積層体の正極側裏面及び負極側裏面にそれぞれメッシュ材の一端を接続し、袋状に作製したアルミラミネート材にメッシュ材の他端がはみ出るように積層体を装填する。次に、ラミネート材の開口部から非水電解液を加え、真空引きしながら、ラミネート材の開口部を熱融着させることより、リチウムイオン二次電池が得られる。   Then, one end of the mesh material is connected to each of the positive electrode-side back surface and the negative electrode-side back surface of the laminate, and the laminate is loaded so that the other end of the mesh material protrudes into the bag-shaped aluminum laminate material. Next, a lithium ion secondary battery is obtained by adding a non-aqueous electrolyte from the opening of the laminate and heat-sealing the opening of the laminate while evacuating.

正極側裏面に接続したメッシュ材としてはアルミメッシュ材が、負極側裏面に接続したメッシュ材としてはニッケルメッシュ材が使用される。   An aluminum mesh material is used as the mesh material connected to the back surface on the positive electrode side, and a nickel mesh material is used as the mesh material connected to the back surface on the negative electrode side.

また、非水電解液には、非水溶媒に電解質を溶解させた溶媒が使用される。非水溶媒としては、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）等の環状カーボネート、ジメチルカーボネート（ＤＭＣ）、メチルエチルカーボネート（ＭＥＣ）、ジエチルカーボネート（ＤＥＣ）等の鎖状カーボネート、ジメトキシエタン、ジエトキシエタン、エトキシメトキシエタン等の鎖状エーテルや、テトラヒドロフラン、２−メチルテトラヒドロフラン等の環状エーテル、クラウンエーテル、γ−ブチロラクトン等の脂肪酸エステル、アセトニトリル等の窒素化合物、スルホラン、ジメチルスルホキシド等の硫化物等が例示される。上記非水電解液は単独で使用しても、２種以上混合した混合溶媒として使用してもよい。電解質としては、過塩素酸リチウム（ＬｉＣｌＯ4）、六フッ化リン酸リチウム（ＬｉＰＦ6）、ほうフッ化リチウム（ＬｉＢＦ4）、六フッ化ヒ素リチウム（ＬｉＡｓＦ6）、トリフルオロメタスルホン酸リチウム（ＬｉＣＦ3ＳＯ3）、ビストリフルオロメチルスルフォニルイミドリチウム［ＬｉＮ（ＣＦ3ＳＯ2）2］等のリチウム塩が例示される。 For the non-aqueous electrolyte, a solvent in which an electrolyte is dissolved in a non-aqueous solvent is used. Non-aqueous solvents include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), chain carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC), dimethoxyethane, Chain ethers such as ethoxyethane and ethoxymethoxyethane, cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, fatty acid esters such as crown ether and γ-butyrolactone, nitrogen compounds such as acetonitrile, sulfides such as sulfolane and dimethyl sulfoxide, etc. Is exemplified. The non-aqueous electrolyte may be used alone or as a mixed solvent in which two or more kinds are mixed. Examples of the electrolyte include lithium perchlorate (LiClO 4 ), lithium hexafluorophosphate (LiPF 6 ), lithium borofluoride (LiBF 4 ), lithium arsenic hexafluoride (LiAsF 6 ), lithium trifluorometasulfonate ( Examples thereof include lithium salts such as LiCF 3 SO 3 ) and bistrifluoromethylsulfonylimide lithium [LiN (CF 3 SO 2 ) 2 ].

このように製造されたリチウムイオン二次電池では、複合粒子が切断面において複合粒子の表面に連通する複数のポアを有するので、リチウムイオン二次電池が充放電を繰り返したときに、複合粒子内のポアが充電時の複合粒子の体積膨張を吸収して緩和でき、またコバルトが複合粒子の外面及びポアの内面に偏在するので、充放電時の体積膨張・収縮による応力を緩和できるとともに導電性を確保でき、更に複合粒子の比表面積が比較的大きいので、スズのリチウムとの反応面積が比較的広くなる。この結果、スズがリチウムと効率良く反応するというスズ本来の性能を引き出すことができるので、本発明のリチウムイオン二次電池は、サイクル特性及び出力特性に優れ、寿命が長くなり、かつ容量が高くなる。また、負極活物質にカーボンナノファイバー（ＣＮＦ）からなる導電性助剤を添加すると、この導電性助剤が粒子を覆うことになり、負極全体に網目状に導電性パスを形成することができるので、活物質当りの初回放電容量及びサイクル特性を更に向上させることができる。   In the lithium ion secondary battery manufactured in this way, since the composite particle has a plurality of pores communicating with the surface of the composite particle at the cut surface, when the lithium ion secondary battery is repeatedly charged and discharged, The pores can absorb and relax the volume expansion of the composite particles during charging, and cobalt is unevenly distributed on the outer surface of the composite particles and the inner surface of the pores. Furthermore, since the specific surface area of the composite particles is relatively large, the reaction area of tin with lithium is relatively wide. As a result, the original performance of tin that tin reacts efficiently with lithium can be brought out, so the lithium ion secondary battery of the present invention has excellent cycle characteristics and output characteristics, has a long life, and has a high capacity. Become. In addition, when a conductive auxiliary agent made of carbon nanofiber (CNF) is added to the negative electrode active material, the conductive auxiliary agent covers the particles, and a conductive path can be formed in a net shape throughout the negative electrode. Therefore, the initial discharge capacity and cycle characteristics per active material can be further improved.

次に本発明の実施例を比較例とともに詳しく説明する。   Next, examples of the present invention will be described in detail together with comparative examples.

＜実施例１＞
先ず、イオン交換水に分散剤、塩化スズ（II）及び塩化コバルト（II）を、合成して得られる複合粒子のスズとコバルトの合計に対するコバルト割合が２０原子％となるような割合で加え、撹拌溶解し、塩酸を更に加えてｐＨを０．７に調整した。分散剤にはポリアクリル酸を用いた。 <Example 1>
First, a dispersant, tin (II) chloride and cobalt (II) chloride are added to ion-exchanged water at a ratio such that the cobalt ratio with respect to the total of tin and cobalt in the composite particles obtained by synthesis is 20 atomic%. The mixture was dissolved with stirring, and hydrochloric acid was further added to adjust the pH to 0.7. Polyacrylic acid was used as the dispersant.

一方、イオン交換水に塩化クロム（III）を加えて撹拌溶解し、これに金属亜鉛（Ｚｎ）を投入することでクロムイオンを３価から２価に還元し、全クロムイオン中の２価のクロム比が７０％以上となるように調製した。これを還元剤水溶液とした。   On the other hand, chromium (III) chloride is added to ion-exchanged water and dissolved by stirring. By adding metal zinc (Zn) to this, chromium ions are reduced from trivalent to divalent, and divalent in all chromium ions. The chromium ratio was adjusted to 70% or more. This was designated as a reducing agent aqueous solution.

次に、スズイオン及びコバルトイオンを含む水溶液と還元剤水溶液とを所定の割合で混合し、撹拌保持時間を１．０[a.u.]（arbitrary units：任意単位）（図２）としてスズイオンとコバルトイオンを還元反応させた。この混合液の温度は２５℃であり、ｐＨは０．８であり、撹拌速度は０．５ｍ／秒であった。   Next, an aqueous solution containing tin ions and cobalt ions and a reducing agent aqueous solution are mixed at a predetermined ratio, and stirring and holding time is set to 1.0 [au] (arbitrary units: arbitrary units) (FIG. 2). A reduction reaction was performed. The temperature of this liquid mixture was 25 degreeC, pH was 0.8, and the stirring speed was 0.5 m / sec.

その後、撹拌混合した液を静置し、合成した粒子を沈降させ、上澄み液を除去した。続いて、沈降物にイオン交換水を加えて撹拌洗浄、静置沈降及び上澄み液除去の操作を数回繰り返し、最後にエタノールで撹拌洗浄、静置沈降及び上澄み液除去を行った。得られた沈降物を真空乾燥することで、スズとコバルトの合計量に対するコバルトの割合が２０原子％である複合粒子からなり、この複合粒子が切断面において複合粒子の表面に連通する複数のポアを有し（図３）、コバルトが複合粒子の外面及びポアの内面に偏在し、更に複合粒子の比表面積が１．０ｍ2／ｇである負極活物質を得た。 Then, the liquid which was stirred and mixed was left still, the synthesized particle | grains were settled, and the supernatant liquid was removed. Subsequently, ion-exchanged water was added to the precipitate, and the operations of stirring and washing, standing sedimentation and supernatant removal were repeated several times, and finally stirring and washing with ethanol, standing sedimentation and supernatant removal were performed. The obtained precipitate is vacuum-dried to form composite particles in which the ratio of cobalt to the total amount of tin and cobalt is 20 atomic%, and the composite particles communicate with the surface of the composite particles at the cut surface. (FIG. 3), cobalt was unevenly distributed on the outer surface of the composite particle and the inner surface of the pore, and a negative electrode active material having a specific surface area of 1.0 m 2 / g of the composite particle was obtained.

＜実施例２＞
スズイオン及びコバルトイオンを含む水溶液と還元剤水溶液とを所定の割合で混合し、撹拌保持時間を１．５[a.u.]（図２）としてスズイオンとコバルトイオンを還元反応させたこと以外は実施例１と同様にして負極活物質を得た。この負極活物質の複合粒子の比表面積は２．０ｍ2／ｇであった。 <Example 2>
Example 1 except that an aqueous solution containing tin ions and cobalt ions and an aqueous reducing agent solution were mixed at a predetermined ratio, and the stirring and holding time was 1.5 [au] (FIG. 2) to cause the tin ions and cobalt ions to undergo a reduction reaction. In the same manner, a negative electrode active material was obtained. The specific surface area of the composite particles of the negative electrode active material was 2.0 m 2 / g.

＜実施例３＞
スズイオン及びコバルトイオンを含む水溶液と還元剤水溶液とを所定の割合で混合し、撹拌保持時間を２．０[a.u.]（図２）としてスズイオンとコバルトイオンを還元反応させたこと以外は実施例１と同様にして負極活物質を得た。この負極活物質の複合粒子の比表面積は３．０ｍ2／ｇであった。 <Example 3>
Example 1 except that an aqueous solution containing tin ions and cobalt ions and an aqueous reducing agent solution were mixed at a predetermined ratio, and the stirring and holding time was set to 2.0 [au] (FIG. 2) to cause the tin ions and cobalt ions to undergo a reduction reaction. In the same manner, a negative electrode active material was obtained. The specific surface area of the composite particles of the negative electrode active material was 3.0 m 2 / g.

＜実施例４＞
スズイオン及びコバルトイオンを含む水溶液と還元剤水溶液とを所定の割合で混合し、撹拌保持時間を２．５[a.u.]（図２）としてスズイオンとコバルトイオンを還元反応させたこと以外は実施例１と同様にして負極活物質を得た。この負極活物質の複合粒子の比表面積は４．０ｍ2／ｇであった。 <Example 4>
Example 1 except that an aqueous solution containing tin ions and cobalt ions and an aqueous reducing agent solution were mixed at a predetermined ratio, and the stirring and holding time was 2.5 [au] (FIG. 2) to cause the tin ions and cobalt ions to undergo a reduction reaction. In the same manner, a negative electrode active material was obtained. The specific surface area of the composite particles of the negative electrode active material was 4.0 m 2 / g.

＜実施例５＞
スズイオン及びコバルトイオンを含む水溶液と還元剤水溶液とを所定の割合で混合し、撹拌保持時間を３．０[a.u.]（図２）としてスズイオンとコバルトイオンを還元反応させたこと以外は実施例１と同様にして負極活物質を得た。この負極活物質の複合粒子の比表面積は５．０ｍ2／ｇであった。 <Example 5>
Example 1 except that an aqueous solution containing tin ions and cobalt ions and an aqueous reducing agent solution were mixed at a predetermined ratio, and the stirring and holding time was 3.0 [au] (FIG. 2) to cause the tin ions and cobalt ions to undergo a reduction reaction. In the same manner, a negative electrode active material was obtained. The specific surface area of the composite particles of the negative electrode active material was 5.0 m 2 / g.

＜実施例６＞
スズイオン及びコバルトイオンを含む水溶液と還元剤水溶液とを所定の割合で混合し、撹拌保持時間を３．５[a.u.]（図２）としてスズイオンとコバルトイオンを還元反応させたこと以外は実施例１と同様にして負極活物質を得た。この負極活物質の複合粒子の比表面積は６．０ｍ2／ｇであった。 <Example 6>
Example 1 except that an aqueous solution containing tin ions and cobalt ions and an aqueous reducing agent solution were mixed at a predetermined ratio, and the stirring and holding time was 3.5 [au] (FIG. 2) to cause the tin ions and cobalt ions to undergo a reduction reaction. In the same manner, a negative electrode active material was obtained. The specific surface area of the composite particles of the negative electrode active material was 6.0 m 2 / g.

＜比較例１＞
スズイオン及びコバルトイオンを含む水溶液と還元剤水溶液とを所定の割合で混合し、撹拌保持時間を０．２[a.u.]（図２）としてスズイオンとコバルトイオンを還元反応させたこと以外は実施例１と同様にして負極活物質を得た。この負極活物質の複合粒子の比表面積は０．８ｍ2／ｇであった。 <Comparative Example 1>
Example 1 except that an aqueous solution containing tin ions and cobalt ions and an aqueous reducing agent solution were mixed at a predetermined ratio, and the stirring and holding time was 0.2 [au] (FIG. 2) to cause the tin ions and cobalt ions to undergo a reduction reaction. In the same manner, a negative electrode active material was obtained. The specific surface area of the composite particles of the negative electrode active material was 0.8 m 2 / g.

＜比較例２＞
スズイオン及びコバルトイオンを含む水溶液と還元剤水溶液とを所定の割合で混合し、撹拌保持時間を４．０[a.u.]（図２）としてスズイオンとコバルトイオンを還元反応させたこと以外は実施例１と同様にして負極活物質を得た。この負極活物質の複合粒子の比表面積は６．５ｍ2／ｇであった。 <Comparative Example 2>
Example 1 except that an aqueous solution containing tin ions and cobalt ions and an aqueous reducing agent solution were mixed at a predetermined ratio, and the stirring and holding time was 4.0 [au] (FIG. 2) to cause the tin ions and cobalt ions to undergo a reduction reaction. In the same manner, a negative electrode active material was obtained. The specific surface area of the composite particles of the negative electrode active material was 6.5 m 2 / g.

＜比較試験１及び評価＞
実施例１〜６と比較例１及び２の負極活物質について、ＩＣＰ定量分析を行い、複合粒子中のスズ、コバルト、クロム、亜鉛の各含有量を求めた。得られた結果を次の表１に示す。なお、表１中の「＜０．００１」及び「＜２」は、ＩＣＰの検出限界以下の測定値であったことを示す。また、表１の「負極活物質の構造」の「ポア」において、「有」は負極活物質の複合粒子が複数のポアを有することを示し、「負極活物質の構造」の「Ｃｏ位置」において、「偏在」はコバルトが複合粒子の外面及びポアの内面に偏在することを示す。上記複数のポアの存在やコバルトの偏在は、負極活物質の電子顕微鏡写真や、この負極活物質の断面における電子顕微鏡写真により確認した。 <Comparative test 1 and evaluation>
ICP quantitative analysis was performed about the negative electrode active material of Examples 1-6 and Comparative Examples 1 and 2, and each content of tin, cobalt, chromium, and zinc in a composite particle was calculated | required. The obtained results are shown in Table 1 below. In Table 1, “<0.001” and “<2” indicate that the measured values were below the ICP detection limit. Further, in “pore” of “structure of negative electrode active material” in Table 1, “present” indicates that the composite particles of the negative electrode active material have a plurality of pores, and “Co position” of “structure of negative electrode active material”. In the graph, “uneven distribution” indicates that cobalt is unevenly distributed on the outer surface of the composite particle and the inner surface of the pore. The presence of the plurality of pores and the uneven distribution of cobalt were confirmed by an electron micrograph of the negative electrode active material and an electron micrograph of a cross section of the negative electrode active material.

また実施例１〜６と比較例１及び２の負極活物質を用い、負極活物質粉末を導電助剤、結着剤、溶媒と混合しスラリーをそれぞれ調製した。即ち、合成した負極活物質粉末、アセチレンブラック、カーボンナノファイバー（ＣＮＦ）、ポリフッ化ビニリデン（ＰＶｄＦ）及びｎ−メチルピロリジノン（ＮＭＰ）を質量比で８０：５：５：１０：１００の割合となるように秤量し、混練機を用いて混練することでスラリーを作製した。   Moreover, using the negative electrode active materials of Examples 1 to 6 and Comparative Examples 1 and 2, the negative electrode active material powder was mixed with a conductive additive, a binder, and a solvent to prepare slurries. That is, the synthesized negative electrode active material powder, acetylene black, carbon nanofiber (CNF), polyvinylidene fluoride (PVdF) and n-methylpyrrolidinone (NMP) have a mass ratio of 80: 5: 5: 10: 100. Thus, the slurry was prepared by weighing and kneading using a kneader.

次に、得られたスラリーをアプリケータを用いて銅箔上に活物質密度が５ｍｇ／ｃｍ2となるように塗布し、乾燥、圧延し、幅３ｃｍ長さ３ｃｍに切断することで負極電極を作製した。 Next, the obtained slurry was applied on a copper foil using an applicator so that the active material density was 5 mg / cm 2 , dried, rolled, and cut into a width of 3 cm and a length of 3 cm to form a negative electrode. Produced.

上記作製した負極を用いて半電池を組み、充放電サイクル試験を行った。対極及び参照極にはリチウム金属を用い、電解液には１Ｍ濃度で六フッ化リン酸リチウム（ＬｉＰＦ6）を溶解した炭酸エチレン（ＥＣ）と炭酸ジエチル（ＤＥＣ）の等体積溶媒を用いた。充電は電圧が５ｍＶとなるまで０．５ｍＡ／ｃｍ2の定電流条件で実施し、その後、電流が０．０１ｍＡ／ｃｍ2になるまで５ｍＶの定電圧条件で実施した。 A half battery was assembled using the produced negative electrode, and a charge / discharge cycle test was conducted. Lithium metal was used for the counter electrode and the reference electrode, and equal volume solvents of ethylene carbonate (EC) and diethyl carbonate (DEC) in which lithium hexafluorophosphate (LiPF 6 ) was dissolved at a concentration of 1 M were used for the electrolyte. Charging was performed under a constant current condition of 0.5 mA / cm 2 until the voltage reached 5 mV, and then under a constant voltage condition of 5 mV until the current reached 0.01 mA / cm 2 .

放電は電圧が１Ｖになるまで０．５ｍＡ／ｃｍ2の定電流条件で実施した。充電と放電を各１回実施した状態を１サイクルとし、１００サイクルまでの充放電試験を行い、初回の活物質重量あたりの放電容量と、１００サイクル目の放電容量の初回放電容量に対する割合を寿命特性として性能評価した。得られた評価結果を次の表１に示す。 The discharge was carried out under a constant current condition of 0.5 mA / cm 2 until the voltage reached 1V. The state in which charging and discharging are performed once is regarded as one cycle, a charge / discharge test up to 100 cycles is performed, and the discharge capacity per active material weight for the first time and the ratio of the discharge capacity at the 100th cycle to the initial discharge capacity are lifetimes. Performance was evaluated as a characteristic. The obtained evaluation results are shown in Table 1 below.

表１から明らかなように、複合粒子の比表面積が６．５ｍ2／ｇである比較例２では、初回放電容量が４９２ｍＡｈ／ｇと低くなったのに対し、複合粒子の比表面積が０．８〜６．０ｍ2／ｇの範囲内である実施例１〜６及び比較例１では、初回放電容量が６４５〜７９０ｍＡｈ／ｇと大きくなった。これらの結果から、複合粒子の比表面積には初回放電容量を高めるのに最適な範囲が存在することが確認された。なお、比較例２では、リチウムと反応するスズの量が少な過ぎたため、初回放電容量が低くなったのに対し、実施例１〜６及び比較例１では、リチウムとの反応面積が広く、かつリチウムと反応するスズの量が比較的多かったため、初回放電容量が高くなったものと推察される。 As is clear from Table 1, in Comparative Example 2 where the specific surface area of the composite particles was 6.5 m 2 / g, the initial discharge capacity was as low as 492 mAh / g, whereas the specific surface area of the composite particles was 0.00. In Examples 1 to 6 and Comparative Example 1 in the range of 8 to 6.0 m 2 / g, the initial discharge capacity increased to 645 to 790 mAh / g. From these results, it was confirmed that the specific surface area of the composite particles had an optimum range for increasing the initial discharge capacity. In Comparative Example 2, since the amount of tin that reacts with lithium was too small, the initial discharge capacity was low, whereas in Examples 1 to 6 and Comparative Example 1, the reaction area with lithium was wide, and Since the amount of tin that reacts with lithium was relatively large, it is assumed that the initial discharge capacity was increased.

また、複合粒子の比表面積が０．８ｍ2／ｇである比較例１では、寿命特性が８９．１％と低かったのに対し、複合粒子の比表面積が１．０〜６．５ｍ2／ｇの範囲内である実施例１〜６及び比較例２では、寿命特性が９４．５〜９８．８％と高くなった。これは、比較例１では、複合粒子がこの粒子表面に連通するポアを有せず、電池充電時の複合粒子の体積膨張を吸収できなかったため、寿命特性が低くなったのに対し、実施例１〜６及び比較例２では、複合粒子がこの粒子表面に連通する複数のポアを有し、電池充電時の複合粒子の体積膨張を複数のポアが吸収して緩和できたため、寿命特性が高くなったものと推察される。 In Comparative Example 1 the specific surface area of the composite particles is 0.8 m 2 / g, whereas the life characteristics was as low as 89.1%, the specific surface area of the composite particles 1.0~6.5m 2 / In Examples 1 to 6 and Comparative Example 2 within the range of g, the life characteristics were as high as 94.5 to 98.8%. In Comparative Example 1, the composite particles did not have pores communicating with the particle surface, and the volume expansion of the composite particles during battery charging could not be absorbed. In 1 to 6 and Comparative Example 2, the composite particles have a plurality of pores communicating with the particle surface, and the volume expansion of the composite particles at the time of battery charging was absorbed by the plurality of pores so that the life characteristics were high. It is presumed that

＜実施例７＞
合成して得られる複合粒子のスズとコバルトの合計に対するコバルト割合が５原子％となるような割合で塩化スズ（II）及び塩化コバルト（II）を加えてスズイオン及びコバルトイオンを含む水溶液を調製したこと以外は実施例４と同様にして負極活物質を得た。 <Example 7>
An aqueous solution containing tin ions and cobalt ions was prepared by adding tin (II) chloride and cobalt (II) chloride in such a ratio that the cobalt ratio of the composite particles obtained by synthesis was 5 atomic% with respect to the total of tin and cobalt. A negative electrode active material was obtained in the same manner as in Example 4 except that.

＜実施例８＞
合成して得られる複合粒子のスズとコバルトの合計に対するコバルト割合が１０原子％となるような割合で塩化スズ（II）及び塩化コバルト（II）を加えてスズイオン及びコバルトイオンを含む水溶液を調製したこと以外は実施例４と同様にして負極活物質を得た。 <Example 8>
An aqueous solution containing tin ions and cobalt ions was prepared by adding tin (II) chloride and cobalt (II) chloride in such a ratio that the cobalt ratio in the composite particles obtained by synthesis was 10 atomic% with respect to the total of tin and cobalt. A negative electrode active material was obtained in the same manner as in Example 4 except that.

＜実施例９＞
実施例４と同様に、合成して得られる複合粒子のスズとコバルトの合計に対するコバルト割合が２０原子％となるような割合で塩化スズ（II）及び塩化コバルト（II）を加えてスズイオン及びコバルトイオンを含む水溶液を調製して負極活物質を得た。 <Example 9>
In the same manner as in Example 4, tin ions and cobalt were added by adding tin (II) chloride and cobalt (II) chloride in such a ratio that the ratio of cobalt to the total of tin and cobalt in the composite particles obtained by synthesis was 20 atomic%. An aqueous solution containing ions was prepared to obtain a negative electrode active material.

＜実施例１０＞
合成して得られる複合粒子のスズとコバルトの合計に対するコバルト割合が３０原子％となるような割合で塩化スズ（II）及び塩化コバルト（II）を加えてスズイオン及びコバルトイオンを含む水溶液を調製したこと以外は実施例４と同様にして負極活物質を得た。 <Example 10>
An aqueous solution containing tin ions and cobalt ions was prepared by adding tin (II) chloride and cobalt (II) chloride at a ratio such that the cobalt ratio in the composite particles obtained by synthesis was 30 atomic% with respect to the total of tin and cobalt. A negative electrode active material was obtained in the same manner as in Example 4 except that.

＜実施例１１＞
合成して得られる複合粒子のスズとコバルトの合計に対するコバルト割合が４０原子％となるような割合で塩化スズ（II）及び塩化コバルト（II）を加えてスズイオン及びコバルトイオンを含む水溶液を調製したこと以外は実施例４と同様にして負極活物質を得た。 <Example 11>
An aqueous solution containing tin ions and cobalt ions was prepared by adding tin (II) chloride and cobalt (II) chloride in such a ratio that the cobalt ratio in the composite particles obtained by synthesis was 40 atomic% with respect to the total of tin and cobalt. A negative electrode active material was obtained in the same manner as in Example 4 except that.

＜比較例３＞
合成して得られる複合粒子のスズとコバルトの合計に対するコバルト割合が３原子％となるような割合で塩化スズ（II）及び塩化コバルト（II）を加えてスズイオン及びコバルトイオンを含む水溶液を調製したこと以外は実施例４と同様にして負極活物質を得た。 <Comparative Example 3>
An aqueous solution containing tin ions and cobalt ions was prepared by adding tin (II) chloride and cobalt (II) chloride in such a ratio that the cobalt ratio in the composite particles obtained by synthesis was 3 atomic% with respect to the total of tin and cobalt. A negative electrode active material was obtained in the same manner as in Example 4 except that.

＜比較例４＞
合成して得られる複合粒子のスズとコバルトの合計に対するコバルト割合が４５原子％となるような割合で塩化スズ（II）及び塩化コバルト（II）を加えてスズイオン及びコバルトイオンを含む水溶液を調製したこと以外は実施例４と同様にして負極活物質を得た。 <Comparative Example 4>
An aqueous solution containing tin ions and cobalt ions was prepared by adding tin (II) chloride and cobalt (II) chloride in such a ratio that the cobalt ratio in the composite particles obtained by synthesis was 45 atomic% with respect to the total of tin and cobalt. A negative electrode active material was obtained in the same manner as in Example 4 except that.

＜比較例５＞
スズとコバルトの合計に対するコバルト割合が２０原子％であり、中心部と外周部での組成の偏りがなく粒子が略均一組成物となっているスズ−コバルト粉を負極活物質とした。 <Comparative Example 5>
The negative electrode active material was a tin-cobalt powder having a cobalt ratio of 20 atomic% with respect to the total of tin and cobalt, having no compositional deviation in the center portion and the outer peripheral portion, and having a substantially uniform composition.

＜比較試験２及び評価＞
実施例７〜１１及び比較例３〜５の負極活物質について、上記比較試験１と同様に、ＩＣＰ定量分析を行い、複合粒子中のスズ、コバルト、クロム、亜鉛の各含有量を求めた。得られた結果を次の表２に示す。なお、表２中の「＜０．００１」及び「＜２」は、ＩＣＰの検出限界以下の測定値であったことを示す。また、表２の「負極活物質の構造」の「ポア」において、「有」は負極活物質の複合粒子が複数のポアを有することを示し、「負極活物質の構造」の「Ｃｏ位置」において、「偏在」はコバルトが複合粒子の外面及びポアの内面に偏在することを示す。上記複数のポアの存在やコバルトの偏在は、負極活物質の電子顕微鏡写真や、この負極活物質の断面における電子顕微鏡写真により確認した。 <Comparative test 2 and evaluation>
About the negative electrode active material of Examples 7-11 and Comparative Examples 3-5, similarly to the said comparative test 1, ICP quantitative analysis was performed and each content of tin in the composite particle, cobalt, chromium, and zinc was calculated | required. The obtained results are shown in Table 2 below. In Table 2, “<0.001” and “<2” indicate that the measured values were below the ICP detection limit. In addition, in the “pore” of “Negative electrode active material structure” in Table 2, “Yes” indicates that the composite particles of the negative electrode active material have a plurality of pores, and “Co position” of “Negative electrode active material structure”. In the graph, “uneven distribution” indicates that cobalt is unevenly distributed on the outer surface of the composite particle and the inner surface of the pore. The presence of the plurality of pores and the uneven distribution of cobalt were confirmed by an electron micrograph of the negative electrode active material and an electron micrograph of a cross section of the negative electrode active material.

実施例７〜１１及び比較例３〜５の負極活物質を用い、上記比較試験１と同様に、負極電極を作製した。またこの負極電極を用い、上記比較試験１と同様に、半電池を組み、充放電サイクル試験を行い、初回の活物質重量あたりの放電容量と、１００サイクル目の放電容量の初回放電容量に対する割合を寿命特性として性能評価した。得られた評価結果を次の表２に示す。   Using the negative electrode active materials of Examples 7 to 11 and Comparative Examples 3 to 5, negative electrodes were produced in the same manner as in Comparative Test 1 above. In addition, using this negative electrode, as in Comparative Test 1 above, a half-cell was assembled and a charge / discharge cycle test was performed. Was evaluated as a life characteristic. The obtained evaluation results are shown in Table 2 below.

表２から明らかなように、複合粒子が切断面において複合粒子の表面に連通する複数のポアを有し、コバルトが複合粒子の外面及びポアの内面に偏在する構造である実施例７〜１１と比較例３及び４では、いずれも高い寿命特性を示したのに対し、粒子中のコバルトとスズとを略均一とした比較例５では、寿命特性が４０．１％と非常に低い結果であった。この結果から、複合粒子が切断面において複合粒子の表面に連通する複数のポアを有し、コバルトが複合粒子の外面及びポアの内面に偏在した構造をとる複合粒子は非常に高いサイクル特性が得られることが確認された。 As apparent from Table 2, the composite particles have a plurality of pores communicating with the surface of the composite particles at the cut surface, and cobalt is unevenly distributed on the outer surface of the composite particles and the inner surface of the pores. In Comparative Examples 3 and 4, both showed high life characteristics, whereas in Comparative Example 5 in which cobalt and tin in the particles were substantially uniform, the life characteristics were very low at 40.1%. It was. From this result, composite particles having a structure in which the composite particle has a plurality of pores communicating with the surface of the composite particle at the cut surface and cobalt is unevenly distributed on the outer surface of the composite particle and the inner surface of the pore have very high cycle characteristics. It was confirmed that

また、複合粒子が切断面において複合粒子の表面に連通する複数のポアを有し、コバルトが複合粒子の外面及びポアの内面に偏在した構造とし、コバルト割合を変動させた実施例７〜１１と比較例３及び４を比較すると、実施例７〜１１のコバルト割合が５〜４０原子％の範囲では、高い初回放電容量が得られ、かつ寿命特性も高い結果になったのに対し、比較例３の３原子％のようにコバルト割合が低くなると、寿命特性が低下し、比較例４の４５原子％のようにコバルト割合が高くなると、初回放電容量が低くなる傾向が見られた。これらの結果から、粒子中のコバルト割合には適切な範囲が存在することが確認された。   In addition, the composite particles had a plurality of pores communicating with the surface of the composite particles at the cut surface, and the cobalt was unevenly distributed on the outer surface of the composite particles and the inner surface of the pores, and Examples 7 to 11 in which the cobalt ratio was varied Comparing Comparative Examples 3 and 4, when the cobalt ratio of Examples 7 to 11 was in the range of 5 to 40 atomic%, a high initial discharge capacity was obtained, and the life characteristics were also high. When the cobalt ratio was low as in 3 atom% of 3, the life characteristics were lowered, and when the cobalt ratio was high as in 45 atom% of Comparative Example 4, the initial discharge capacity tended to be low. From these results, it was confirmed that an appropriate range exists for the cobalt ratio in the particles.

＜実施例１２＞
合成して得られる複合粒子に質量比で０．００５％のクロムが更に含まれるように、スズイオン及びコバルトイオンを含む水溶液と還元剤水溶液との混合割合を調節したこと以外は実施例４と同様にして負極活物質を得た。 <Example 12>
The same as in Example 4 except that the mixing ratio of the aqueous solution containing tin ions and cobalt ions and the reducing agent aqueous solution was adjusted so that the composite particles obtained by synthesis further contained 0.005% chromium by mass. Thus, a negative electrode active material was obtained.

＜実施例１３＞
合成して得られる複合粒子に質量比で０．１％のクロムが更に含まれるように、スズイオン及びコバルトイオンを含む水溶液と還元剤水溶液との混合割合を調節したこと以外は実施例４と同様にして負極活物質を得た。 <Example 13>
The same as in Example 4 except that the mixing ratio of the aqueous solution containing tin ions and cobalt ions and the reducing agent aqueous solution was adjusted so that the composite particles obtained by synthesis further contained 0.1% chromium by mass. Thus, a negative electrode active material was obtained.

＜実施例１４＞
合成して得られる複合粒子に質量比で１％のクロムが更に含まれるように、スズイオン及びコバルトイオンを含む水溶液と還元剤水溶液との混合割合を調節したこと以外は実施例４と同様にして負極活物質を得た。 <Example 14>
Except that the mixing ratio of the aqueous solution containing tin ions and cobalt ions and the reducing agent aqueous solution was adjusted so that the composite particles obtained by synthesis further contained 1% chromium by mass ratio, the same as in Example 4. A negative electrode active material was obtained.

＜実施例１５＞
合成して得られる複合粒子に質量比で５ｐｐｍの亜鉛が更に含まれるように、還元剤水溶液を調製する際の金属亜鉛投入量を調節したこと以外は実施例４と同様にして負極活物質を得た。 <Example 15>
The negative electrode active material was prepared in the same manner as in Example 4 except that the amount of zinc metal in preparing the reducing agent aqueous solution was adjusted so that the composite particles obtained by synthesis further contained 5 ppm of zinc by mass ratio. Obtained.

＜実施例１６＞
合成して得られる複合粒子に質量比で２５ｐｐｍの亜鉛が更に含まれるように、還元剤水溶液を調製する際の金属亜鉛投入量を調節したこと以外は実施例４と同様にして負極活物質を得た。 <Example 16>
The negative electrode active material was prepared in the same manner as in Example 4 except that the amount of metal zinc input when preparing the reducing agent aqueous solution was adjusted so that the composite particles obtained by synthesis further contained 25 ppm of zinc by mass. Obtained.

＜実施例１７＞
合成して得られる複合粒子に質量比で５０ｐｐｍの亜鉛が更に含まれるように、還元剤水溶液を調製する際の金属亜鉛投入量を調節したこと以外は実施例４と同様にして負極活物質を得た。 <Example 17>
The negative electrode active material was prepared in the same manner as in Example 4 except that the amount of metal zinc input in preparing the reducing agent aqueous solution was adjusted so that the composite particles obtained by synthesis further contained 50 ppm of zinc by mass. Obtained.

＜実施例１８＞
合成して得られる複合粒子に質量比で１．５％のクロムが更に含まれるように、スズイオン及びコバルトイオンを含む水溶液と還元剤水溶液との混合割合を調節したこと以外は実施例４と同様にして負極活物質を得た。 <Example 18>
The same as in Example 4 except that the mixing ratio of the aqueous solution containing tin ions and cobalt ions and the reducing agent aqueous solution was adjusted so that 1.5% by mass of chromium was further contained in the composite particles obtained by synthesis. Thus, a negative electrode active material was obtained.

＜実施例１９＞
合成して得られる複合粒子に質量比で７５ｐｐｍの亜鉛が更に含まれるように、還元剤水溶液を調節する際の金属亜鉛投入量を調整したこと以外は実施例４と同様にして負極活物質を得た。 <Example 19>
The negative electrode active material was prepared in the same manner as in Example 4 except that the amount of metal zinc added when adjusting the reducing agent aqueous solution was adjusted so that the composite particles obtained by synthesis further contained 75 ppm of zinc by mass. Obtained.

＜比較試験３及び評価＞
実施例１２〜１９の負極活物質について、上記比較試験１と同様に、ＩＣＰ定量分析を行い、複合粒子中のスズ、コバルト、クロム、亜鉛の各含有量を求めた。得られた結果を次の表３に示す。なお、表３中の「＜０．００１」及び「＜２」は、ＩＣＰの検出限界以下の測定値であったことを示す。また、表３の「負極活物質の構造」の「ポア」において、「有」は負極活物質の複合粒子が複数のポアを有することを示し、「負極活物質の構造」の「Ｃｏ位置」において、「偏在」はコバルトが複合粒子の外面及びポアの内面に偏在することを示す。上記複数のポアの存在やコバルトの偏在は、負極活物質の電子顕微鏡写真や、この負極活物質の断面における電子顕微鏡写真により確認した。 <Comparative test 3 and evaluation>
About the negative electrode active material of Examples 12-19, similarly to the said comparative test 1, ICP quantitative analysis was performed and each content of tin, cobalt, chromium, and zinc in a composite particle was calculated | required. The results obtained are shown in Table 3 below. In Table 3, “<0.001” and “<2” indicate that the measured values were below the detection limit of ICP. In “Pore” of “Structure of negative electrode active material” in Table 3, “Yes” indicates that the composite particle of the negative electrode active material has a plurality of pores, and “Co position” of “Structure of negative electrode active material”. In the graph, “uneven distribution” indicates that cobalt is unevenly distributed on the outer surface of the composite particle and the inner surface of the pore. The presence of the plurality of pores and the uneven distribution of cobalt were confirmed by an electron micrograph of the negative electrode active material and an electron micrograph of a cross section of the negative electrode active material.

実施例１２〜１９の負極活物質を用い、上記比較試験１と同様に、負極電極を作製した。またこの負極電極を用い、上記比較試験１と同様に、半電池を組み、充放電サイクル試験を行い、初回の活物質重量あたりの放電容量と、１００サイクル目の放電容量の初回放電容量に対する割合を寿命特性として性能評価した。得られた評価結果を次の表３に示す。   Using the negative electrode active materials of Examples 12 to 19, negative electrodes were produced in the same manner as in Comparative Test 1 above. In addition, using this negative electrode, as in Comparative Test 1 above, a half-cell was assembled, a charge / discharge cycle test was performed, and the discharge capacity per active material weight for the first time and the ratio of the discharge capacity at the 100th cycle to the initial discharge capacity Was evaluated as a life characteristic. The obtained evaluation results are shown in Table 3 below.

表３から明らかなように、クロムを０．００５〜１％又は亜鉛を５〜５０ｐｐｍ更に含有させた実施例１２〜１７では、クロムの含有量が０．００１％未満及び亜鉛の含有量が２ｐｐｍ未満と低い実施例４の結果に比べ、高い初回放電容量が得られた。一方、クロムの含有量が１．５％と高い実施例１８及び亜鉛の含有量が７５ｐｐｍと高い実施例１９では、実施例４の結果と同程度の高い初回放電容量が得られているが、寿命特性が低い結果となった。これらの結果から、クロムや亜鉛を所定量含有することで初回放電容量値を高めることができる一方、クロムや亜鉛を含有し過ぎると、その特性が低下してしまうことから、クロムと亜鉛の含有量には適切な範囲が存在することが確認された。 As is apparent from Table 3, in Examples 12 to 17 in which chromium was further contained in 0.005 to 1% or zinc in 5 to 50 ppm, the chromium content was less than 0.001% and the zinc content was 2 ppm. A high initial discharge capacity was obtained as compared with the result of Example 4 which is less than the lower value. On the other hand, in Example 18 with a high chromium content of 1.5% and Example 19 with a high zinc content of 75 ppm, a high initial discharge capacity similar to the result of Example 4 was obtained. The life characteristics were low. From these results, it is possible to increase the initial discharge capacity value by containing a predetermined amount of chromium and zinc. On the other hand, if too much chromium and zinc are contained, the characteristics will deteriorate, so the inclusion of chromium and zinc. It was confirmed that there was an appropriate range for the amount.

Claims (12)

スズ（Ｓｎ）とコバルト（Ｃｏ）の合計量に対するコバルト（Ｃｏ）の割合が５〜４０原子％である複合粒子からなり、前記複合粒子が切断面において前記複合粒子の表面に連通する複数のポアを有し、前記コバルト（Ｃｏ）が前記複合粒子の外面及び前記ポアの内面に偏在し、かつ前記複合粒子の比表面積が１．０〜６．０ｍ2／ｇであるリチウムイオン二次電池用負極活物質。 A plurality of pores comprising composite particles in which the ratio of cobalt (Co) to the total amount of tin (Sn) and cobalt (Co) is 5 to 40 atomic%, wherein the composite particles communicate with the surface of the composite particles at the cut surface. A lithium ion secondary battery in which the cobalt (Co) is unevenly distributed on the outer surface of the composite particle and the inner surface of the pore, and the specific surface area of the composite particle is 1.0 to 6.0 m 2 / g Negative electrode active material. 前記複合粒子の平均粒径が０．１〜２０μｍである請求項１記載の負極活物質。   The negative electrode active material according to claim 1, wherein the composite particles have an average particle size of 0.1 to 20 μm. 構成元素として、クロム（Ｃｒ）及び亜鉛（Ｚｎ）のうち少なくとも１種を更に含む請求項１又は２記載の負極活物質。   The negative electrode active material according to claim 1, further comprising at least one of chromium (Cr) and zinc (Zn) as a constituent element. 前記クロム（Ｃｒ）の含有量が質量比で０．００５〜１％であり、前記亜鉛（Ｚｎ）の含有量が質量比で５〜５０ｐｐｍである請求項３記載の負極活物質。   4. The negative electrode active material according to claim 3, wherein a content of the chromium (Cr) is 0.005 to 1% by mass and a content of the zinc (Zn) is 5 to 50 ppm by mass. ポリアクリル酸、水溶性セルロース及びポリビニルピロリドンからなる群より選ばれた少なくとも１種を更に含む請求項１ないし４いずれか１項に記載の負極活物質。   The negative electrode active material according to any one of claims 1 to 4, further comprising at least one selected from the group consisting of polyacrylic acid, water-soluble cellulose, and polyvinylpyrrolidone. 負極活物質を有する負極と、正極活物質を有する正極と、非水電解質とを備えたリチウムイオン二次電池において、
前記負極活物質が、スズ（Ｓｎ）とコバルト（Ｃｏ）の合計量に対するコバルト（Ｃｏ）の割合が５〜４０原子％である複合粒子からなり、前記複合粒子が切断面において前記複合粒子の表面に連通する複数のポアを有し、前記コバルト（Ｃｏ）が前記複合粒子の外面及び前記ポアの内面に偏在し、かつ前記複合粒子の比表面積が１．０〜６．０ｍ2／ｇであることを特徴とするリチウムイオン二次電池。 In a lithium ion secondary battery comprising a negative electrode having a negative electrode active material, a positive electrode having a positive electrode active material, and a non-aqueous electrolyte,
The negative electrode active material is composed of composite particles in which the ratio of cobalt (Co) to the total amount of tin (Sn) and cobalt (Co) is 5 to 40 atomic%, and the composite particles are cut at the surface of the composite particles. The cobalt (Co) is unevenly distributed on the outer surface of the composite particle and the inner surface of the pore, and the specific surface area of the composite particle is 1.0 to 6.0 m 2 / g. The lithium ion secondary battery characterized by the above-mentioned. 前記複合粒子の平均粒径が０．１〜２０μｍである請求項６記載のリチウムイオン二次電池。   The lithium ion secondary battery according to claim 6, wherein the composite particles have an average particle size of 0.1 to 20 μm. 前記負極活物質の構成元素として、クロム（Ｃｒ）及び亜鉛（Ｚｎ）のうち少なくとも１種を更に含む請求項６又は７記載のリチウムイオン二次電池。   The lithium ion secondary battery according to claim 6 or 7, further comprising at least one of chromium (Cr) and zinc (Zn) as a constituent element of the negative electrode active material. 前記クロム（Ｃｒ）の含有量が質量比で０．００５〜１％であり、前記亜鉛（Ｚｎ）の含有量が質量比で５〜５０ｐｐｍである請求項８記載のリチウムイオン二次電池。   The lithium ion secondary battery according to claim 8, wherein a content of the chromium (Cr) is 0.005 to 1% by mass ratio, and a content of the zinc (Zn) is 5 to 50 ppm by mass ratio. 前記負極活物質にポリアクリル酸、水溶性セルロース及びポリビニルピロリドンからなる群より選ばれた少なくとも１種を更に含む請求項６ないし９いずれか１項に記載のリチウムイオン二次電池。   The lithium ion secondary battery according to any one of claims 6 to 9, further comprising at least one selected from the group consisting of polyacrylic acid, water-soluble cellulose, and polyvinylpyrrolidone in the negative electrode active material. スズイオン及びコバルトイオンを含む水溶液と２価クロムイオンを含む還元剤水溶液とを混合し、この混合液の温度、ｐＨ、処理時間又は撹拌速度の少なくとも１つの条件を調整することにより、前記混合液中で前記スズイオン及びコバルトイオンを還元させて複合粒子を合成するとともに、前記複合粒子内部のスズ（Ｓｎ）を溶出させて前記複合粒子の比表面積を制御し、請求項１に記載のリチウムイオン二次電池用負極活物質を製造する方法。   By mixing an aqueous solution containing tin ions and cobalt ions with an aqueous reducing agent solution containing divalent chromium ions, and adjusting at least one of the temperature, pH, treatment time or stirring speed of the mixed solution, The lithium ion secondary according to claim 1, wherein the tin ions and cobalt ions are reduced to synthesize composite particles and tin (Sn) in the composite particles is eluted to control the specific surface area of the composite particles. A method for producing a negative electrode active material for a battery. 前記混合液中にポリアクリル酸、水溶性セルロース及びポリビニルピロリドンからなる群より選ばれた少なくとも１種の分散剤を更に含む請求項１１記載の負極活物質の製造方法。   The method for producing a negative electrode active material according to claim 11, further comprising at least one dispersant selected from the group consisting of polyacrylic acid, water-soluble cellulose, and polyvinylpyrrolidone in the mixed solution.
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