JP4465756B2 - Non-aqueous electrolyte secondary battery, alloy for the battery, and manufacturing method thereof - Google Patents

Description

【００９７】
表１からわかるように、合金を酸水溶液に浸漬処理せずに、そのまま電極を作製した場合には、Liの充放電効率が75％と低かった。即ち、吸蔵されたLiのうち25％は放出されない不可逆的な吸蔵であった。
【００９８】
一方、本発明に従って酸水溶液で浸漬処理を行うと、放電容量を低下させずに (場合によりやや増大する) 、充放電効率が85％以上に増大した。充放電効率は、酸水溶液の濃度が0.2 ％以上であれば90％以上になった。特に、酸水溶液の濃度が２重量％以上になると、95〜97％という非常に高い充放電効率を得ることができ、Liのほとんどが放出可能な可逆的な吸蔵となった。
【００９９】
【実施例２】
本実施例では、本発明に係るZn基合金を製造し、この合金のLi放出効率を評価するために、この合金を用いて作製した電極の充放電容量を３極式セルで試験した。
【０１００】
合金組成を10％Mg−90％Zn (以下、Mg90Znと表記する) に、Arガスアトマイズ後の熱処理温度を300 ℃に、それぞれ変更して、実施例１と同様に合金粉末を調製し、分級し、熱処理した。
【０１０１】
熱処理後の合金粉末の断面をエッチング後にＳＥＭで観察して合金組織を調べたところ、マトリックスはMgZn₁₁相であり、その中にZn相が散在して析出していた。従って、この合金は、Zn相をコアとし、その周囲がMgZn₁₁相で包囲された組織を有する。Zn相の平均粒径は約５μｍであった。なお、MgZn₁₁の固相線温度は364 ℃であるので、熱処理温度(300℃) はこの固相線温度より低い。
【０１０２】
熱処理したガスアトマイズ法Zn基合金粉末について、酸水溶液としてHCl またはHNO₃の水溶液を用いた以外は実施例１と同様に酸水溶液による浸漬処理を行った。この合金粉末を用いて、実施例１と同様に電極の作製と３極式セル試験を実施し、放電容量と充放電効率を求めた。
【０１０３】
別に、ガスアトマイズ法合金粉末と同組成のZn基合金を構成する原料を用いて、実施例１で説明したのと同様の要領でプラズマ回転電極法によるZn基合金粉末を調製し、分級した。この時の凝固速度は100 ℃/secであった。分級した合金粉末にガスアトマイズ法と同様の熱処理を施して、合金を調べたところ、ガスアトマイズ法合金粉末と同様の構成の組織であり、Zn相の平均粒径は約24μｍであった。
【０１０４】
この合金粉末をHCl 濃度10wt％の酸水溶液に５分間浸漬した後、真空中60℃で乾燥し、室温まで放冷してから大気中に取り出し、60時間経過後に、実施例１に記載したようにして電極を作製し、Li放出能力を評価した。
これらの試験結果を、酸水溶液への浸漬処理を行わなかった場合の結果と一緒に表２に示す。
【０１０５】
【表２】

【０１０６】
表２からわかるように、Zn基合金の場合も、試験結果は実施例１のSi基合金と同様の傾向を示した。即ち、酸水溶液による浸漬処理を行わないと、充放電効率は80％より低く、不芳であったのに対し、この浸漬処理を施すことにより、放電容量を維持したまま、充放電効率が80％以上に増大し、酸水溶液の濃度が0.5 重量％以上では90％以上の高い充放電効率が得られた。また、酸を塩酸から硝酸に変えても、同様の充放電効率の改善が得られた。
【０１０７】
【実施例３】
表３に示す合金組成となる原料を用いて、実施例１と同様にArガスアトマイズ法により合金粉末を作製し、分級した後、表３に示す温度で熱処理し、酸水溶液での浸漬処理を行った。酸水溶液の浸漬条件は、No.1〜18のSi含有合金では２％HF水溶液中に15分間であり、No. 19〜24のSiを含有しない合金では５％HCl 水溶液中に15分間の条件とした。
【０１０８】
熱処理後の合金粉末の組織を調べたところ、いずれもコアのＡ相がマトリックスのＢ相で包囲されている合金であり、Ａ相はNo.1〜18のSi含有合金ではSi相、No. 19〜24の合金ではZn相であった。このコア相の平均粒径は、いずれの合金についても30μｍ以下と微細であった。Ｂ相を構成する主要な金属間化合物または固溶体とその固相線温度を表３に示す。表３からわかるように、熱処理温度はいずれもこの固相線温度より10℃以上低い温度であった。
【０１０９】
これらの各合金粉末を用いて、実施例１と同様に電極の作製と３極式セル試験を実施し、放電容量と充放電効率を求めた。試験結果を、酸水溶液への浸漬処理を行わなかった場合の結果と一緒に表３に示す。
【０１１０】
【表３】

【０１１１】
表３に示すように、いずれの合金系についても、酸水溶液での浸漬処理を行うことにより、放電容量を全く或いはほとんど低下させず、充放電効率を著しく向上させることができた。
【０１１２】
【実施例４】
本実施例では、表１の試験記号Ｅ、表２の試験記号Ｄ、および表３に示した合金の一部 (いずれもArガスアトマイズ法で得た粉末を分級し、熱処理と酸水溶液での浸漬処理を施した本発明に係る合金の粉末；Si含有合金は２％HF水溶液で15分の浸漬処理、Siを含有しない合金は１％HCl 水溶液で15分の浸漬処理) を用いて電極を作製し、これを負極とする非水電解質リチウム二次電池の性能を、次に述べるようにして評価した。
【０１１３】
別に、酸水溶液に浸漬しなかった合金粉末を用いて同様に電池を作製して性能を評価した。
図１に本実施例で作製した円筒型電池の縦断面図を示す。
【０１１４】
この電池では、正極板５および負極板６がセパレータ７を介して複数回渦巻状に巻回されて電池ケース１内に収納されている。そして、上記正極板５からは正極リード5aが引き出されて封口板２に接続され、負極板６からは負極リード6aが引き出されて、電池ケース１の底部に接続されている。８は絶縁リングで、極板群４の上下部にそれぞれ設けられている。３は絶縁パッキンである。
【０１１５】
電池ケースやリード板は、非水電解液に耐性のある電子伝導性の金属または合金を用いることができる。例えば、鉄、ニッケル、チタン、クロム、モリブデン、銅、アルミニウム等の金属またはそれらの合金が使用できる。電池ケースにはステンレス鋼板、Al−Mn合金板が適しており、正極リードはアルミニウム、負極リードはニッケルが最適である。
【０１１６】
電池ケースに電解液を注入し、封口板でケースを密閉すると電池缶が完成する。このとき、封口板には図示のように安全弁を設置したり、安全素子を設けることができる。安全素子の例は、ヒューズ、バイメタル、ＰＴＣ素子などの過電流防止素子である。また、電池ケースの内圧上昇の対策として、安全弁の他に、電池ケースに切込みを入れる、ガスケットもしくは封口板に亀裂を入れる、リード板との切断、といった手段を講ずることもできる。さらに、充電器に過充電や過放電対策を組み込んだ保護回路を備えるか、独立に接続させてもよい。過充電対策として、電池内圧の上昇により電流を遮断する方式も利用できる。このとき、内圧を挙げる化合物を電極合剤または電解質中に含有させてもよい。内圧を挙げる化合物としては、Li₂CO₃、LiHCO₃、Na₂CO₃、NaHCO₃、CaCO₃ 、MgCO₃ 等の炭酸塩が挙げられる。電池ケース、封口板、リード板の溶接には、電気溶接、レーザー溶接、超音波溶接等が利用できる。封口用シール剤として、アスファルト等のシール剤を使用できる。
【０１１７】
負極板は次のようにして作製した。表４に示す合金組成の本発明の合金粉末75％、導電剤のアセチレンブラック20％、結着剤のポリフッ化ビニリデン(PVDF)５％の混合物を脱水N-メチルピロリドン(NMP) 中で攪拌して、スラリーを調製した。このスラリーを、集電体となる厚さ0.015 mmの銅箔の表面の塗着し、乾燥後、ロール圧延し、切断して、厚さ0.2 mm、幅37mm、長さ300 mmの負極板を得た。この負極板中の合金の充填量は約３〜10ｇの範囲であった。
【０１１８】
一方、正極板は、コバルト酸リチウム(LiCoO₂)の粉末85％、導電剤のアセチレンブラック10％、結着剤のPVDF５％の混合物から、上記の負極板と同様にして作製した。但し、正極板の集電体としては負極用の銅箔と同じ厚みのアルミニウム箔を用いた。
【０１１９】
電解液としては、エチレンカーボネートとエチルメチルカーボネートとの体積比１：１の混合溶媒に、LiPF₆ を1.5 Ｍ濃度で溶解した溶液を使用した。作製した電池は、直径18 mm 、高さ650 mmの円筒型電池であった。
【０１２０】
これらの電池を、100 mAの定電流で4.2 Ｖまで充電した後、100 mAの定電流で３Ｖまで放電し、放電容量と充放電効率 (放電容量／充電容量×100)を求めた。また、同様に作製した別の電池を用いて、100 mAの定電流で電圧4.2 Ｖ、放電終止電圧25Ｖで充放電サイクル試験を行い、１サイクル目の充放電容量を測定するとともに、500 サイクル後の放電容量を測定し、１サイクル目の放電容量に対する500 サイクル目の放電容量の割合(%) をサイクル寿命として求めた。測定は全て25℃で行った。これらの試験結果を表４に示す。
【０１２１】
【表４】

【０１２２】
表４からわかるように、本発明のSiまたはZn基前記合金を負極材料とする非水電解質リチウム二次電池は、放電容量、充放電効率、サイクル寿命の全てが良好であった。
【０１２３】
【発明の効果】
ガスアトマイズ法といった急冷凝固法により製造され、最後に酸水溶液による浸漬処理を施した、本発明の非水電解質二次電池用のSiまたはZn基前記合金は、コア相のSi相やZn相のLi吸蔵能力が高く、かつ不可逆的なLi吸蔵の原因となる表面酸化膜が除去されているため、多量のLiを吸蔵して、吸蔵されたLiのほとんどを放出することができる。また、コア相の周囲が拘束されているため、Li吸蔵・放出に基づく体積変化が抑制され、Li吸蔵・放出を繰り返しても、微粉化しにくく、Li吸蔵能力を長期間保持できる。
【０１２４】
そのため、この合金をリチウム二次電池のような非水電解質二次電池の負極材料として使用すると、放電容量が高く、かつ充放電効率が85％以上、好ましくは90％以上という二次電池を作製することができる。充放電効率が高いと、充電に要する電気量が低減し、エネルギー効率の高い電池となる。また、この非水電解質二次電池は、充放電繰り返し寿命にも優れている。従って、本発明によりリチウム二次電池で代表される非水電解質二次電池の性能が著しく向上し、その用途拡大につながるものと期待される。
【図面の簡単な説明】
【図１】実施例で作製したリチウム二次電池の構造を示す略式縦断面図である。
【符号の説明】
１：電池ケース、２：封口板、３：絶縁パッキン、４：極板群、５：正極板、６：負極板、７：セパレータ、８：絶縁リング。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an alloy for a non-aqueous electrolyte secondary battery capable of occluding and releasing a large amount of an alkali metal such as Li, and more specifically, a discharge capacity using an alloy containing at least one of Si and Zn. The present invention relates to an alloy for a non-aqueous electrolyte secondary battery that can produce a non-aqueous electrolyte secondary battery that is high, has excellent charge / discharge cycle life, and high charge / discharge efficiency. The present invention also relates to a method for producing the alloy and a non-aqueous electrolyte secondary battery using the alloy.
[0002]
[Prior art]
With the spread of portable small electric / electronic devices, non-aqueous electrolyte secondary batteries using Li as an active material, which are small and high-capacity secondary batteries, are being actively developed.
[0003]
Since Li shows the lowest potential among metals, secondary batteries using Li as the negative electrode active material have higher voltage and higher energy density than other secondary batteries such as Ni-hydrogen batteries. It becomes. However, when metal Li is used as the negative electrode active material, the metal Li grows from the negative electrode in a dendrite shape due to repeated charge and discharge, and penetrates through the separator, which is an insulator, and is short-circuited with the positive electrode. There were problems with discharge cycle life and safety.
[0004]
In order to cope with this problem, instead of metallic Li, a material containing Li ions is used for the electrode, and a carbonaceous material capable of occluding and releasing Li ions is used for the negative electrode. It was put into practical use. In this battery, the positive electrode Li-containing compound (e.g., LiCoO₂) Li ions dissolved from) are intercalated between the carbonaceous material layers of the negative electrode, and LiC₆By forming this compound, Li ions are occluded in the carbonaceous material of the negative electrode. During discharge, the negative electrode LiC₆Li ions are released from and return to the positive electrode. That is, Li ions only reciprocate between the positive electrode and the negative electrode during charging and discharging (so this type of battery has come to be called a lithium ion secondary battery), and Li does not precipitate as a metal at the negative electrode. The above problems due to dendrite growth can be avoided.
[0005]
Of the carbonaceous materials used in the negative electrodes of practical lithium secondary batteries, graphite materials have a theoretical discharge capacity of 372 mAh / g (about 1/10 of Li), which is the upper limit of capacity. There is a problem that it is low. The non-graphite material also has a lower discharge capacity than the graphite material when it is put into practical use. Non-graphite materials have been reported to have a high discharge capacity of, for example, 600 mAh / g or more.However, the irreversible capacity is large, and a large loss may occur at the battery design stage. Since a significant portion is not discharged, there is a disadvantage that the charge / discharge efficiency (ratio of discharge capacity to charge capacity) is poor. If the charge / discharge efficiency is poor, an extra amount of electricity is required for charging, and the energy efficiency of the battery deteriorates.
[0006]
For this reason, intermetallic compound materials have been developed as an alternative to carbonaceous materials with the aim of increasing capacity, extending life and increasing efficiency. For example, the Mg-Ge alloy disclosed in JP-A-9-63651 is known to function as a host material capable of inserting and extracting Li into the crystal lattice, much like a carbonaceous material. ing. A lithium secondary battery using an intermetallic compound of Si and Ni or Fe as a negative electrode has been proposed in JP-A-5-159780, JP-A-7-240201, and JP-A-9-63651.
[0007]
[Problems to be solved by the invention]
Among the intermetallic compounds disclosed in JP-A-9-63651 is Mg.₂Ge, Mg₂Some batteries have very high charge capacity, such as Pb and AlSb, but the discharge capacity is low and the charge / discharge efficiency is poor. Therefore, it is not always possible to obtain non-aqueous electrolyte secondary batteries with high discharge capacity. In addition, a large amount of energy is required for charging, resulting in poor energy efficiency.
[0008]
Batteries using an intermetallic compound of Si and Ni or Fe proposed in JP-A-5-159780, JP-A-7-240201, and JP-A-9-63651 have a high charge / discharge efficiency. The capacity itself is not high enough.
[0009]
An object of the present invention is to provide an alloy that has an unprecedented large storage / release capacity of Li and excellent discharge efficiency, which is the ratio of released hydrogen to absorbed hydrogen. A non-aqueous electrolyte secondary battery using such an alloy as a negative electrode material should be able to have a large discharge capacity and excellent charge / discharge efficiency, which has never been seen before.
[0010]
The present inventors have reversibly recombined Si with Li (intermetallic compound (Li_{twenty two}Si_FiveThe theoretical charge / discharge capacity of the non-aqueous electrolyte secondary battery is 4199 mAh / g. Focusing on the fact that it is much larger than the 372 mAh / g carbonaceous material, the non-aqueous electrolyte is composed of an alloy powder having Si phase particles as a core and surrounded by an intermetallic compound containing Si or a solid solution. A negative electrode material for a secondary battery and a method for producing the same were previously proposed (Japanese Patent Application No. 10-253981).
[0011]
Also, like Si, Zn is a compound that reversibly forms and decomposes with Li._{twenty two}Zn_FiveAnd the charge / discharge capacity is 1800 mAh / g, which is theoretically larger than that of carbonaceous materials, and a battery using an alloy powder surrounded by an intermetallic compound containing Zn or a solid solution with a Zn phase as a core is not known in the art. The capacity is larger than that of the water electrolyte secondary battery.
[0012]
These negative electrode materials have unprecedented discharge capacity and excellent charge / discharge cycle life, but charge / discharge efficiency (measured as the ratio of discharge capacity to charge capacity at the same current value, It was found that the ratio of the amount of discharged electricity to the amount of electricity, also called Coulomb efficiency and ampere-hour efficiency, was insufficient.
[0013]
The present invention aims to solve the above-mentioned problems by improving the charge / discharge efficiency of the negative electrode material previously proposed by the present inventors.
[0014]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have studied the factors that reduce the charge / discharge efficiency, and as a result, have obtained the following knowledge.
[0015]
The above-mentioned powder material of the alloy having the Si phase or Zn phase as the core uses a rapid solidification method such as gas atomization, roll quenching method, rotating electrode method, etc., in order to obtain a large Li storage / release capacity. Manufactured. Therefore, the obtained alloy has a quenching strain, which may adversely affect the charge / discharge cycle life. Therefore, the solidified alloy is usually heat-treated for the purpose of removing the quenching strain.
[0016]
The rapid solidification and heat treatment are performed in a vacuum or in an inert gas atmosphere. However, in an industrial production facility, it is inevitable that the surface of the alloy powder is covered with an oxide film to some extent.
[0017]
In an attempt, the present inventors made lithium secondary batteries using powders having different degrees of surface oxidation with respect to the alloy having a Si phase as a core, and investigated the charge and discharge efficiency of each. As a result, the sample with more surface oxidation (thick oxide film) showed a smaller discharge capacity value for the same charge capacity.
[0018]
The reason why the surface oxide film lowers the charge / discharge efficiency is estimated as follows:
For example, the surface of the alloy powder is Si oxide.₂If it is covered with₂Is reduced to Si, and the reduced Si reacts with Li to form an intermetallic compound of Li and Si. SiO₂The amount of electricity required to reduce the amount of Si to Si becomes an irreversible charge capacity and does not contribute to the discharge capacity, so the charge / discharge efficiency deteriorates. Moreover, when a surface oxide exists, the contact resistance between powders becomes large. This contact resistance is also considered to be involved in the decrease in charge / discharge efficiency.
[0019]
Therefore, it is necessary to remove the oxide film formed on the surface of the alloy powder. As a result of further investigation on this point, it was found that immersion in an acid aqueous solution is effective for removing the surface oxide film. In addition, when the alloy from which the surface oxide film has been removed is used for a non-aqueous electrolyte secondary battery, it has been confirmed that the battery has excellent charge / discharge efficiency, and the present invention has been achieved.
[0020]
  Here, the present inventionIt is a manufacturing method of the alloy for nonaqueous electrolyte secondary batteries characterized by including the following processes. Ie, Si or Zn, and an alloy composed of an A phase having a particle size of 0.01 to 40 μm and a B phase surrounding at least a part of the periphery of the A phase, wherein the B phase is Si constituting the A phase. Or between Zn and at least one element selected from Group IIA, IIIA to IIB transition elements, Group IIIB, Group IVB excluding C, and Group VB elements of the Long Periodic Periodic Table In compound or solid solutionA step of forming an alloy by a method including solidifying a molten alloy material having a predetermined composition at a solidification rate of 100 ° C./sec or more, before immersing the solidified alloy in an acid aqueous solution, A step of heat-treating at a temperature 10 ° C. lower than the line temperature, and a step of immersing the obtained alloy in an acid aqueous solution.
[0022]
  This manufacturing method is,alloyContains Si and the aqueous acid solution is an HF aqueous solution or the alloy contains Zn and the aqueous acid solution is HCl or HNO._ThreeThe aqueous solution is preferably. In this case, the acid aqueous solution is an aqueous HF solution having a concentration of 0.05 to 15% by weight, or HCl or HNO having a concentration of 0.05 to 10% by weight, respectively._ThreeAn aqueous solution is preferred.
[0023]
The alloy according to the present invention can reversibly absorb and release alkali metals such as Li, and is useful as a negative electrode material for non-aqueous electrolyte secondary batteries such as lithium secondary batteries. According to the present invention, a nonaqueous electrolyte secondary battery using this alloy as a negative electrode material is also provided.
[0024]
The nonaqueous electrolyte secondary battery referred to in the present invention includes both a secondary battery using a nonaqueous electrolyte in which a supporting electrolyte is dissolved in an organic solvent and a secondary battery using a nonaqueous electrolyte such as a polymer electrolyte or a gel electrolyte. Is included.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
The alloy for a non-aqueous electrolyte secondary battery of the present invention is an alloy composed of an A phase containing at least one element of Si and Zn and a B phase surrounding at least a part of the periphery of the A phase. The B phase is an intermetallic compound or solid solution containing at least one element of Si and Zn.
[0026]
As described above, the phase A of the core containing Si or Zn is Li._{twenty two}Si_FiveOr Li_{twenty two}Zn_FiveLi can be reversibly absorbed and released through the formation of intermetallic compounds such as That is, it combines with Li to form the above compound during charging, and dissociates to release Li during discharging. As can be seen from the above chemical formula of the intermetallic compound, Si and Zn can occlude and release a very large amount of Li, and the theoretical charge / discharge capacity of a non-aqueous electrolyte secondary battery becomes very high.
[0027]
The phase A is preferably substantially composed of only Si and / or Zn capable of inserting and extracting a large amount of Li, but may further contain other metals and / or nonmetallic elements. However, the proportion of other elements is preferably as small as possible.
[0028]
Along with the absorption and release of Li by the A phase, the volume of the A phase expands and contracts. When the A phase is cracked due to this volume change and the A phase is pulverized, Li occlusion / release is inhibited, so that the charge / discharge capacity of the battery is reduced, leading to a reduction in the charge / discharge cycle life.
[0029]
By enclosing the periphery of the A phase with the B phase, the A phase is restrained against the volume change, the cracking and pulverization are suppressed, and the charge / discharge cycle life is improved. Even if the A phase of the core is completely surrounded by the B phase, the Li ion has a very small ionic radius and easily passes between the lattices of the B phase and reaches the A phase of the core and is occluded. It is released from the core to the electrolyte. That is, the B phase can constrain the A phase against volume changes without substantially obstructing the passage of Li.
[0030]
The B phase only needs to at least partially surround the A phase particles. Even in a partial siege, the purpose of siege is achieved if the above constraint is effective. In particular, in industrial production, it may be difficult to produce a product in which all A-phase particles are completely surrounded by a B-phase, and confirmation thereof is also difficult.
[0031]
The B phase is composed of one or more of an intermetallic compound containing Si or Zn or a solid solution. When the B phase is composed of two or more substances, the structure is not particularly limited. For example, a structure in which a certain substance forms a matrix and other substances are dispersed in the matrix may be used, or a structure in which all substances are finely mixed may be used.
[0032]
Since the purpose of surrounding the periphery of the A phase of the core with the B phase is to restrain the volume change of the A phase, in principle, the B phase does not need to contain Si or Zn. However, if the adhesiveness between the A phase and the B phase is low, the surrounding B phase is detached and the purpose of restraining the A phase cannot be achieved. In consideration of adhesion, the B phase contains the same Si or Zn as contained in the A phase. Thereby, the adhesion between the A phase and the B phase is improved through mutual diffusion of the same atoms.
[0033]
Elements that form an intermetallic compound or a solid solution with Si or Zn are not particularly limited, but generally are transition elements from Group IIA (alkaline earths), Group IIIA to Group IIB of the Long Periodic Periodic Table, One or more elements selected from the group consisting of Group IIIB, Group IVB excluding C, and Group VB. This element includes Mg and Ca of group IIa, Y of transition element and rare earth element, Ti, V, Nb, Cr, W, Mn, Fe, Co, Ni, Cu and Cd, Al of group IIIB element, and IVB group element And one or more elements selected from VB group element P are preferable. Particularly preferred are Mn, Cu, Ti, Fe, Co, and Ni.
[0034]
The ratio of the A phase and the B phase of the alloy of the present invention is not particularly limited, but the A phase preferably occupies 5 to 99 wt%, particularly 8 to 95 wt%. When the ratio of the A phase is too large, the B phase is too small and the above restraint is hardly effective. If there is too little A phase that occludes / releases Li, the amount of Li occlusion / release, and hence the charge / discharge capacity of the battery, will decrease.
[0035]
The powder particle size of the alloy of the present invention is preferably 100 μm or less. If a powder having a particle size exceeding 100 μm is used for a negative electrode for a nonaqueous electrolyte secondary battery, the thickness of the negative electrode becomes too large. The particle size is more preferably in the range of 5 to 50 μm.
[0036]
In each particle of this powder, only one A phase of the core may be present or two or more may be present. The particle size of the A phase of the core is not particularly limited, but is preferably 0.01 to 40 μm, particularly preferably 1 to 35 μm. If the A phase is too large, the restraint by the B phase is difficult to be effective, and if it is too small, the proportion of the B phase is generally too large, the surface oxidation becomes severe, and the proportion of the material lost by removing the oxide film cannot be ignored.
[0037]
As described above, the alloy of the present invention can be produced by immersing an alloy produced by a rapid solidification method in an acid aqueous solution to remove the surface oxide film. Hereinafter, this method will be described.
[0038]
The raw material is a mixture of elements constituting an alloy composed of an A phase and a B phase. That is, it is a mixture of Si and / or Zn and other elements. When the raw material adjusted to be an alloy having a predetermined composition is melted and the obtained molten metal is rapidly cooled, an alloy in which the B phase is surrounded around the core of the A phase is obtained by the peritectic reaction.
[0039]
For example, when the alloy contains Si, since Si has a higher solidification temperature than other metals, the Si phase first precipitates to become the A phase of the core, and an intermetallic compound or solid solution containing Si precipitates around it. , B phase surrounding the core. Therefore, the alloy composition of the raw material is Si-rich with respect to the solid solution or intermetallic compound phase that becomes the B phase. In the case of Zn, conversely, the freezing point is lower than that of other metals, but the intermetallic compound or solid solution containing Zn has a lower freezing point than Zn alone. Therefore, if the Zn phase is richer than the B phase containing Zn, the Zn phase first precipitates to become the A phase of the core, and then the intermetallic compound or solid solution phase containing Zn having a lower freezing point is the A phase. Precipitate around. In any case, the ratio of Si or Zn in the raw material to other elements (that is, how much Si or Zn is excessive with respect to the chemical composition of the intermetallic compound or solid solution of the B phase) The ratio between the phase and the surrounding B phase is determined.
[0040]
The particle size of the A phase depends on the solidification rate. When the solidification rate is less than 100 ° C./sec, the particle size of the A phase becomes too large, and the restriction on the volume change by the B phase becomes difficult to be effective. When the solidification rate is 100 ° C./sec or more, the particle size of the A phase becomes small, and an alloy having an A phase with an average particle size of 40 μm or less can be easily produced even if heat treatment described below is performed under appropriate conditions. be able to. The upper limit of the solidification rate is not particularly limited, but 10⁶C / sec is considered the upper limit in terms of cost and completeness as a mass production technology.
[0041]
As a cooling method in which the solidification rate is 100 ° C./sec or more, any one of an atomizing method, a roll quenching method, and a rotating electrode method is preferable in consideration of the perfection of manufacturing technology, mass productivity, cost, and the like. As the atomizing method, either a gas atomizing method or a liquid atomizing method can be used, but the gas atomizing method is preferred because it can obtain particles having a nearly spherical shape. In any case, in order to prevent oxidation of the alloy, it is preferable to maintain the melting and solidification environment in a non-oxidizing atmosphere (for example, in a vacuum or an inert gas atmosphere).
[0042]
In the gas atomization method, a raw material having a predetermined composition is usually melted in a high-frequency induction melting furnace in a vacuum or an inert atmosphere. Melted melt (molten metal) is dropped into the atomizing tank through a hot water supply pipe. The inside of the tank is normally maintained in an inert gas atmosphere so as to prevent the generated atomized powder from being oxidized. A gas atomizing nozzle is disposed in the vicinity of the hot water supply pipe, and an atomizing gas is ejected from the nozzle hole or slit toward the molten metal being dropped. The molten metal is divided into four by the energy of the jet gas, solidifies and turns into powder. The produced powdered alloy is guided to the powder storage device from the lower part of the atomizing tank and stored.
[0043]
The particle size of the powder produced by the gas atomizing method usually decreases as the energy of the jet gas applied to the molten metal being dropped increases. The energy of the ejected gas can be adjusted by, for example, the pressure of the gas, the size or arrangement of the nozzle holes or slits. If the energy of the jet gas is the same, the particle size of the powder is usually smaller as the amount of molten metal dropped per unit time is smaller. The dropping amount of the molten metal can be adjusted by the inner diameter of the hot water supply pipe or the pressure applied to the molten metal in the hot water supply pipe.
[0044]
The roll quenching method is a method in which a raw material melt having a predetermined composition is thinly poured on the outer periphery of a rotating roll that has been cooled, and is rapidly cooled by removing heat from the roll. Either a single roll or a twin roll can be used. The molten metal is usually stored in a tundish and injected from the bottom nozzle in a controlled amount. The solidification rate of the alloy by the roll quenching method can be controlled by the rotation speed of the roll, the amount of molten metal injected, and the like.
[0045]
In the case of the single roll quenching method, the rotational speed of the roll is 1 × 10 at the outer peripheral speed.^-2~ 6 × 10²Often in the m / second range. A roll having a diameter of 100 to 600 mm is relatively often used. From a practical standpoint, the roll diameter is 400-600mm and the roll peripheral speed is 6 × 10.^-2~ 1.3 x10²m / sec is preferred.
[0046]
The alloy that has been rapidly cooled and solidified by the roll is often dropped from the roll in the form of foil strips and / or pieces, and this is collected in a suitable storage device. The resulting alloy is generally very thin and can be easily powdered by mechanical grinding means (eg, ball mill, jet mill, etc.). Including this pulverization, the roll quenching method is preferably performed in an inert gas atmosphere.
[0047]
In the plasma rotating electrode method that is usually used in the rotating electrode method, 10^-1~Ten^-2The inside of a closed chamber whose pressure is reduced to about torr is used. In this chamber, a cathode made of an alloy having a desired composition and an anode for generating plasma are arranged to face each other, and are usually connected to a driving device via connecting shafts so that they can rotate in opposite directions. . The cathode is often cylindrical, and its diameter is usually about 30 to 120 mm. The anode is usually composed of an electrode portion made of tungsten and a copper nozzle that houses the electrode portion, and each is cooled with water so as to withstand the high temperature during plasma generation.
[0048]
An inert gas such as Ar or He for generating plasma is supplied to the electrode portion, and an electric field is formed by applying a voltage between the anode and the cathode to generate plasma. The cathode is sequentially dissolved by the plasma, scattered around by the rotation, and solidified into a powder. The number of rotations of the anode and the cathode is often about 1000 to 5000 rpm, but may be higher than this. The particle size of the powder is generally determined by the number of rotations and the diameter of the cathode, and the number of rotations is large. The scattered and solidified powder is collected from the lower part of the chamber.
[0049]
An alloy formed through rapid solidification with a solidification rate of 100 ° C./sec or more is easily pulverized during use because of distortion due to rapid cooling. Therefore, it is preferable to perform heat treatment to remove this rapid cooling distortion. When the alloy is pulverized, the heat treatment may be performed either before pulverization or after pulverization. The heat treatment atmosphere is preferably performed in a non-oxidizing atmosphere such as a vacuum or an inert gas atmosphere in order to prevent oxidation of the negative electrode material during the heat treatment.
[0050]
The heat treatment temperature is 10 ° C. or more lower than the solidus temperature of the intermetallic compound or solid solution constituting the B phase that is the envelope layer. When the B phase is composed of two or more materials, the solidus temperature is 10 ° C or higher than the solidus temperature of the intermetallic compound or solid solution (usually the phase that forms the B phase matrix) having the lowest solidus temperature. Heat treatment is performed at a low temperature. A preferable heat treatment temperature is 20 ° C. or more lower than the solidus temperature.
[0051]
  In addition to eliminating the quenching distortion, the heat treatment produces a diffusion effect and improves the adhesion between the A phase and the B phase. This diffusion effect usually increases the particle size of the A phase of the core. When the heat treatment temperature is higher than the solidus temperature, the particle size of the A phase of the core isToo bigIn some cases, sintering of the powder occurs. The lower limit of the heat treatment temperature is not limited as long as the quenching strain is removed, but is preferably 300 ° C. or higher, more preferably 500 ° C. or higher.
[0052]
When the B phase is composed of two or more substances, some of the substances may disappear due to diffusion, and the structure of the B phase may change. Although the heat treatment time is not particularly limited, it is usually preferably 1 hour or longer, particularly 2 hours or longer.
[0053]
As described above, even if each process of alloy production such as rapid solidification, pulverization, and heat treatment is carried out in a non-oxidizing atmosphere, it is impossible to completely prevent surface oxidation of the alloy in industrial operation. Thus, an alloy covered with a surface oxide film is obtained, and the charge / discharge efficiency of the nonaqueous electrolyte secondary battery is lowered by this oxide film.
[0054]
According to the present invention, it is possible to avoid a decrease in charge / discharge efficiency by immersing the alloy in an acid aqueous solution to remove the surface oxide film. This acid treatment is preferably performed after all of the pulverization and heat treatment are completed. When pulverization is performed after dipping in an acid aqueous solution, an oxide film is formed during the pulverization, and it may be necessary to immerse in the acid aqueous solution again.
[0055]
The acid of the acid aqueous solution in which the alloy is immersed is not particularly limited, and an organic acid can also be used. However, in order to achieve the object in a relatively short time, it is preferable to use a strong acid, particularly an inorganic strong acid. . Preferred acids include HF, HCl, HNO_ThreeIs mentioned. When the alloy contains Si, a preferable aqueous acid solution is an aqueous HF solution. Preferred aqueous acid solutions when the alloy contains Zn are HCl or HNO_ThreeIt is an aqueous solution.
[0056]
The preferred concentration of these acid aqueous solutions is 0.05 to 15% by weight, more preferably 0.5 to 3% by weight in HF aqueous solution, HCl and HNO._ThreeIn aqueous solution, it is 0.05-10 weight%, respectively, More preferably, it is 1-5 weight%. If the acid concentration is too low, it takes a long time to remove the surface oxide film, which is not practical. Conversely, if the acid concentration is too high, the A phase exposed after removal of the oxide film reacts with the acid, and the amount of the A phase may decrease as hydrogen gas is generated.
[0057]
To the aqueous acid solution, if desired, other acids selected from the above preferred acids, or H₂SO_Four, H₂O₂One kind or two or more kinds of other acid or oxidizing solutions such as may be mixed. In order to control the reaction, it is also effective to mix glycerin or the like with the acid aqueous solution.
[0058]
The weight ratio of the acid aqueous solution: alloy used for the dipping treatment is preferably in the range of 2: 1 to 10: 1, particularly 3: 1 to 6: 1. If the weight ratio of the aqueous acid solution to the alloy is less than 2, the concentration of eluted ions in the aqueous acid solution becomes too high and the effect of immersion is reduced. If the weight ratio of the acid aqueous solution is too high, the reaction for removing the oxide film proceeds smoothly, but the productivity is lowered.
[0059]
The temperature of the acid aqueous solution is not particularly limited, but if the temperature is too high, the reaction for removing the oxide film proceeds excessively and the amount of the exposed A phase may be reduced. On the other hand, if it is too low, the reaction will not proceed easily. The temperature of the preferred aqueous acid solution is 20 ° C or higher and 50 ° C or lower. The immersion time is set so that the surface oxide film is substantially completely removed from the alloy. The required immersion time varies greatly depending on the type, concentration, temperature, and other conditions of the aqueous acid solution, and a few minutes may be sufficient. From an industrial viewpoint, it is preferable that the immersion time is within 10 hours, particularly within 1 hour.
[0060]
The alloy immersed in the acid aqueous solution is dried and stored. If drying is performed at a low temperature of 100 ° C. or lower, it may be performed in air or, of course, in a non-oxidizing atmosphere such as an inert gas. Similarly, the storage may be either an air atmosphere or a non-oxidizing atmosphere. Even if it is left in the atmosphere at room temperature, the formation of the surface oxide film is not so remarkable. When storage takes a long time, it is preferable to store in a non-oxidizing atmosphere.
[0061]
From the alloy having a core containing Si or Zn immersed in an acid aqueous solution according to the present invention, an electrode is produced according to a method for producing an electrode well known to those skilled in the art, and this is used as a negative electrode for a nonaqueous electrolyte secondary battery A negative electrode can be manufactured.
[0062]
To produce an electrode, the alloy powder of the present invention is mixed with an appropriate binder, and if necessary, an appropriate conductive agent for improving conductivity, and a solvent for dissolving the binder, A paste-like or slurry-like electrode mixture is prepared. One or more of fillers, dispersants, pressure enhancers and other various additives may be added to the electrode mixture. The electrode mixture is applied to one or both sides of an electrode substrate to be a current collector, dried, then consolidated by roll rolling, pressing, etc., cut to a predetermined size, punched, etc. Is made.
[0063]
As the binder, either a thermoplastic resin or a thermosetting resin can be used. Examples of binders include polyolefins such as polyethylene and polypropylene; polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene, vinylidene fluoride or chlorotri Fluorinated polymers such as copolymers of fluoroethylene and other fluorinated or non-fluorinated monomers; Styrene butadiene rubber; Copolymerization of ethylene with acrylate monomers such as acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate Or (Na of this copolymer)⁺) Ionic cross-linked product (ionomer), and the like. Water-soluble resins such as carboxymethyl cellulose and polyvinyl alcohol can also be used as binders or thickeners.
[0064]
Of these, styrene-butadiene rubber, PVDF, ethylene-acrylate monomer copolymer or its (Na⁺) An ionic cross-linked product.
[0065]
The solvent is selected according to the binder so that the binder dissolves. For example, an organic solvent such as N-methylpyrrolidone (NMP) or dimethylformamide (DMF), or water is used.
[0066]
It is not always necessary to add a conductive agent, but the larger current characteristics are better when added. The conductive agent is not particularly limited as long as it is an electron conductive material. Examples thereof include carbonaceous materials such as graphite, carbon black, and carbon fibers, metal powders such as Cu and Ni, metal fibers, and organic conductive materials such as polyphenylene derivatives. A preferred conductive agent is a carbonaceous material. This is because the carbonaceous material can occlude Li ions between the layers, so that it can contribute to the capacity of the negative electrode in addition to the conductivity, and also has excellent liquid retention. Among these, artificial graphite, acetylene black, and carbon fiber are preferable. The addition amount of the conductive agent is preferably 1 to 50% by weight, particularly 1 to 30% by weight, based on the alloy.
[0067]
The current collector is not particularly limited as long as it is an electronic conductor that does not cause a chemical change in the environment of the nonaqueous electrolyte secondary battery. For example, stainless steel, nickel, copper, titanium, carbon, conductive resin, or a material obtained by coating carbon, nickel, or titanium on the surface of copper or stainless steel can be used. Preference is given to copper and copper alloys which are good conductors. The form of the current collector may be a foil, a film, a sheet, a net, a perforated plate, a porous body, a foam, a fiber aggregate, and the like. The thickness is not particularly limited, but is usually 1 to 500 μm.
[0068]
A nonaqueous electrolyte secondary battery is produced using the electrode thus produced as a negative electrode. A typical example of the nonaqueous electrolyte secondary battery is a lithium secondary battery, and the alloy according to the present invention is suitable as a negative electrode material for the lithium secondary battery.
[0069]
The non-aqueous electrolyte secondary battery includes a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte as a basic structure. The negative electrode is manufactured according to the present invention as described above, but the other positive electrode, separator, and electrolyte are not particularly limited, and conventionally known for non-aqueous electrolyte secondary batteries such as lithium secondary batteries, Or the material developed from now on should just be used appropriately.
[0070]
In the case of a lithium secondary battery, the positive electrode preferably uses a Li-containing transition metal compound as a positive electrode active material. Examples of Li-containing transition metal compounds are LiM_1-XM '_XO₂  Or LiM_2yM '_yO_Four (In the formula, 0 ≦ X, Y ≦ 1, M and M ′ are at least one of Ba, Co, Ni, Mn, Cr, Ti, V, Fe, Zn, Al, In, Sn, Sc, and Y, respectively) It is a compound shown by these. However, transition metal chalcogenides; vanadium oxide and lithium compounds thereof; niobium oxide and lithium compounds thereof; conjugated polymers using organic conductive materials; other compounds containing or not containing Li such as chevrel phase compounds It is also possible to use a positive electrode material. The average particle size of the positive electrode active material is not particularly limited, but is preferably in the range of 1 to 30 μm.
[0071]
Similarly to the electrode using the alloy of the present invention for the negative electrode described above, the electrode material is prepared by pasting or slurrying the active material powder together with the binder and the conductive agent. Usually, it is manufactured by a method of applying to an electric body, compacting and cutting. As the binder, the conductive agent, and the current collector, basically, the same materials as described above for the negative electrode can be used.
[0072]
Among the binders, PVDF and PTFE are particularly preferable for the positive electrode. Particularly preferred conductive agents for the positive electrode are artificial graphite and acetylene black. The blending amount of the conductive agent is basically the same as described above, but in the case of a carbonaceous material, the range of 2 to 15% by weight is preferable. Preferred current collector materials for the positive electrode are aluminum and aluminum alloys.
[0073]
In the case of a lithium secondary battery, a general nonaqueous electrolyte is a solution in which a lithium salt as a supporting electrolyte is dissolved in an organic solvent. Examples of lithium salts include LiClO._Four, LiBF_Four, LiAlCl_Four, LiPF₆, LiAsF₆, LiSbF₆, LiSCN, LiCl, LiBr, LiI, LiCF_ThreeSO_Three, LiC_FourF₉SO_Three, LiCH_ThreeSO_Three, Li (CF_ThreeSO₂)₂N, Li (CF₂SO₂)₂, LiB (C₆H_Five), LiB_TenCl_Ten, Lower aliphatic lithium carboxylates, lithium chloroborane, lithium tetraphenylborate, imides and the like, and one kind or two or more kinds can be used. Especially LiPF₆An electrolyte containing is preferred.
[0074]
Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; aliphatic carboxylic acids such as methyl formate, ethyl acetate, and methyl propionate. Esters; γ-lactones such as γ-butyrolactone; chain ethers such as 1,2-dimethoxyethane; cyclic ethers such as tetrahydrofuran; other dimethyl sulfoxide, dioxolanes, amides, nitriles, sulfolanes, etc. It is preferable to use one or more of various aprotic solvents. Particularly preferred solvents are a mixed system of a cyclic carbonate and a chain carbonate, and a system in which an aliphatic carboxylic acid ester is further mixed. Of these, a mixed solvent of ethylene carbonate and ethyl methyl carbonate is preferable.
[0075]
The concentration of the supporting electrolyte in the solvent is not particularly limited, but is usually in the range of 0.2 to 2M, particularly preferably in the range of 0.5 to 1.5M.
[0076]
The non-aqueous electrolyte may be a solid rather than a liquid (solution). Solid electrolytes for nonaqueous electrolyte secondary batteries are roughly classified into inorganic solid electrolytes and organic solid electrolytes. Known inorganic solid electrolytes include Li nitrides, halides, oxyacid salts, and the like. Among them, Li_FourSiO_Four, Li_FourSiO_Four-LiI-LiOH, xLi_ThreePO_Four-_(1-x)Li_FourSiO_Four, Li₂SiS_Three, Li_ThreePO_Four-Li₂S-SiS₂, Phosphorus sulfide compounds are effective. Examples of organic solid electrolytes include polymer materials such as polyethylene oxide, polypropylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride, polyhexafluoropropylene, and derivatives, mixtures, and composites thereof. It is valid.
[0077]
Other compounds can be added to the non-aqueous electrolyte for the purpose of improving the charge / discharge characteristics. Examples of such compounds include triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, pyridine, hexaphosphoric acid triamide, nitrobenzene derivatives, crown ethers, quaternary ammonium salts, ethylene glycol dialkyl ether, and the like.
[0078]
The separator serves as an insulating film that electrically insulates the positive electrode from the negative electrode, and also contributes to the retention of the nonaqueous electrolyte. As the separator, an insulating microporous thin film having large ion permeability and appropriate mechanical strength is used. In order to increase the safety of the battery, it is preferable to have a function of increasing the resistance by closing the pores when the temperature exceeds a certain temperature.
[0079]
In consideration of organic solvent resistance and hydrophobicity, a separator is often made of a microporous sheet, a nonwoven fabric, a woven fabric or the like made of a polyolefin polymer or glass fiber. The pore diameter of the separator is preferably about 0.01 to 1 μm so that the material detached from the electrode does not permeate. The thickness of the separator is generally about 10 to 300 μm. The porosity is usually preferably in the range of 30 to 80%.
[0080]
As a type of lithium secondary battery, a polymer material that absorbs and retains a non-aqueous electrolyte (a solution in which a lithium salt is dissolved in a non-aqueous solvent) is included in the positive electrode mixture and the negative electrode mixture, There is also a battery constructed by absorbing and holding the same non-aqueous electrolyte. In this case, the polymer material for absorbing and retaining the organic electrolyte is particularly preferably a copolymer of vinylidene fluoride and hexafluoropropylene.
[0081]
The shape of the nonaqueous electrolyte secondary battery is not particularly limited, and may be any of a cylindrical shape, a square shape, a coin shape, a button shape, a sheet shape, a laminated shape, a flat shape, a large size for an electric vehicle, and the like. The nonaqueous electrolyte secondary battery of the present invention can be used for portable information terminals, portable electronic devices, small household power storage devices, motorcycles, electric vehicles, hybrid electric vehicles, etc. is not.
[0082]
The non-aqueous electrolyte secondary battery of the present invention uses a powder material of the alloy having a core phase with a high theoretical capacity as a negative electrode material, and the volume change at the time of insertion and extraction of Li can be suppressed. High and excellent cycle life for repeated charge and discharge. In addition, since the oxide film on the alloy surface that lowers the charge / discharge efficiency is removed, the charge / discharge efficiency is also very high, so that excellent performance can be exhibited when used for any of the above applications. .
[0083]
【Example】
The present invention will be specifically described with reference to the following examples, but these are illustrative and do not limit the present invention. In the examples, unless otherwise specified,% is% by weight.
[0084]
[Example 1]
In this example, a Si-based alloy according to the present invention was produced, and in order to evaluate the Li release efficiency of this alloy, the charge / discharge capacity of an electrode produced using this alloy was tested in a tripolar cell.
[0085]
<Manufacture of alloys>
48% Ni-52% Si (hereinafter referred to as Ni52Si) The raw materials were blended so as to constitute an alloy, which was melted in an Ar atmosphere using a high frequency induction melting furnace, and then alloyed from the molten metal by an Ar gas atomization method. A powder was prepared.
[0086]
The solidification rate of this Ar gas atomization method is confirmed by a well-known method of measuring the distance between the dendrite secondary arms of the Cu-Al alloy powder prepared by the Ar gas atomization method using the same conditions as the above alloy powder. did. The result is 10^Three~Ten^FiveThe temperature was 100 ° C./sec.
[0087]
Ni52Si alloy powder produced by Ar gas atomization was classified and adjusted to an average particle size of 30 μm and a maximum particle size of 100 μm. NiSi with the lowest solidus temperature among the Ni-Si intermetallic compounds in the Ar atmosphere in the classified alloy powder₂Heat treatment was performed at 900 ° C. lower than the solidus temperature of the phase (966 ° C.) for 4 hours. When the cross section of the alloy powder after the heat treatment was etched and observed by SEM, the alloy structure was examined. The matrix was NiSi.₂The Si phase was interspersed therein, and the NiSi phase was also deposited around the Si phase. Therefore, this alloy has the Si phase as the core, and the surroundings are NiSi phase and NiSi.₂It has a tissue surrounded by a phase. The average particle size of the Si phase (average value of the particle size of 100 Si phases randomly selected in the SEM photograph) was about 12 μm.
[0088]
The heat-treated alloy powder was subjected to an acid aqueous solution immersion treatment using an HF aqueous solution under various conditions shown in Table 1. The temperature of the HF aqueous solution was constant at 30 ° C. The acid-treated alloy powder was dried at 60 ° C. in a vacuum. After allowing to cool to room temperature, it was taken out into the atmosphere, and after 60 hours, an electrode was prepared using this alloy powder as described below, and the Li releasing ability was evaluated.
[0089]
Separately, the raw materials constituting the alloy having the same composition as the gas atomized alloy powder were similarly melted and cast into a mold in an Ar atmosphere to obtain an ingot having a diameter of 30 mm and a length of 60 mm. Using this ingot as a cathode, an alloy powder was prepared by a plasma rotating electrode method. Using a Cu—Al alloy obtained under the same conditions as above, the solidification rate was measured and found to be 100 ° C./sec.
[0090]
The alloy powder produced by this plasma rotating electrode method was classified to adjust the average particle size to 30 μm and the maximum particle size to 100 μm. The classified alloy powder was subjected to the same heat treatment as described above, and the alloy was examined in the same manner. The structure was the same as that of the gas atomized alloy powder, and the average particle size of the Si phase was about 24 μm.
[0091]
This alloy powder is immersed in an acid aqueous solution with a HF concentration of 15 wt% for 5 minutes, dried in vacuum at 60 ° C., allowed to cool to room temperature, taken out into the atmosphere, and after 60 hours, as described below. Electrodes were prepared and evaluated for Li release capability.
[0092]
<Tripolar cell test>
After 10% acetylene black and 10% PVDF (polyvinylidene fluoride) were added to the alloy powder, NMP (N-methylpyrrolidone) was added as appropriate and mixed and stirred to prepare a slurry.
[0093]
This slurry was applied to a 30 μm-thick electrolytic copper foil using a doctor blade, and after drying, punched out to a diameter of 13 mm and pressed to produce an electrode. The thickness of the electrode mixture on the copper foil of this electrode was about 100 μm. The alloy weight contained in this mixture was calculated from the mixture volume, mixture composition and specific gravity of the alloy obtained by Archimedes method.
[0094]
Using this electrode, Li metal was placed on the counter electrode and the reference electrode, respectively, to produce a non-aqueous electrolyte tripolar cell. The electrolyte used was LiPF as the supporting electrolyte in a 1: 1 mixed solvent of ethylene carbonate and dimethoxyethane in a volume ratio.₆A non-aqueous solution in which 1 was dissolved at 1 M concentration was used. The measurement was carried out at 25 ° C. in an apparatus capable of maintaining an inert atmosphere such as a glove box while maintaining the atmospheric dew point at about −70 ° C.
[0095]
First, with 1/10 charge (current value that becomes fully charged in 10 hours), the battery is charged until it reaches 0 V with reference to Li, and then discharged until the voltage reaches 2 V with the same current value. The discharge capacity at the first cycle and the charge / discharge efficiency calculated by discharge capacity / charge capacity × 100 were obtained. The results are shown in Table 1 together with the results of the samples not subjected to the immersion treatment in the acid aqueous solution.
[0096]
[Table 1]

[0097]
As can be seen from Table 1, when the electrode was produced as it was without immersing the alloy in an acid aqueous solution, the charge / discharge efficiency of Li was as low as 75%. That is, 25% of the stored Li was irreversible storage that was not released.
[0098]
On the other hand, when the immersion treatment was performed with the acid aqueous solution according to the present invention, the charge / discharge efficiency was increased to 85% or more without decreasing the discharge capacity (in some cases, slightly increasing). The charge / discharge efficiency was 90% or more when the concentration of the acid aqueous solution was 0.2% or more. In particular, when the concentration of the acid aqueous solution was 2% by weight or more, a very high charge / discharge efficiency of 95 to 97% could be obtained, and reversible occlusion was possible in which most of Li could be released.
[0099]
[Example 2]
In this example, a Zn-based alloy according to the present invention was manufactured, and in order to evaluate the Li release efficiency of this alloy, the charge / discharge capacity of an electrode produced using this alloy was tested in a three-electrode cell.
[0100]
The alloy composition was changed to 10% Mg-90% Zn (hereinafter referred to as Mg90Zn) and the heat treatment temperature after Ar gas atomization was changed to 300 ° C., and the alloy powder was prepared and classified as in Example 1. Heat-treated.
[0101]
When the cross-section of the alloy powder after heat treatment was etched and observed by SEM, the alloy structure was examined. The matrix was MgZn.₁₁In this phase, Zn phases were scattered and precipitated. Therefore, this alloy has a Zn phase as the core and the surrounding area is MgZn.₁₁It has a tissue surrounded by a phase. The average particle size of the Zn phase was about 5 μm. MgZn₁₁Since the solidus temperature is 364 ° C., the heat treatment temperature (300 ° C.) is lower than the solidus temperature.
[0102]
For heat-treated gas atomized Zn-based alloy powder, HCl or HNO as the aqueous acid solution_ThreeAn immersion treatment with an aqueous acid solution was performed in the same manner as in Example 1 except that the aqueous solution was used. Using this alloy powder, an electrode was prepared and a three-electrode cell test was conducted in the same manner as in Example 1 to determine the discharge capacity and charge / discharge efficiency.
[0103]
Separately, a Zn-based alloy powder by the plasma rotating electrode method was prepared and classified in the same manner as described in Example 1 using raw materials constituting a Zn-based alloy having the same composition as the gas atomized alloy powder. The solidification rate at this time was 100 ° C./sec. The classified alloy powder was subjected to the same heat treatment as in the gas atomizing method, and the alloy was examined. The alloy had a structure similar to that of the gas atomized method alloy powder, and the average particle size of the Zn phase was about 24 μm.
[0104]
This alloy powder was immersed in an acid aqueous solution having an HCl concentration of 10 wt% for 5 minutes, dried in a vacuum at 60 ° C., allowed to cool to room temperature, and then taken out into the atmosphere. After 60 hours had passed, as described in Example 1 Then, an electrode was prepared and the Li release ability was evaluated.
These test results are shown in Table 2 together with the results when the immersion treatment in the acid aqueous solution was not performed.
[0105]
[Table 2]

[0106]
As can be seen from Table 2, in the case of the Zn-based alloy, the test results showed the same tendency as that of the Si-based alloy of Example 1. That is, when the immersion treatment with the acid aqueous solution was not performed, the charge / discharge efficiency was lower than 80%, which was unsatisfactory, whereas by performing this immersion treatment, the charge / discharge efficiency was 80 with maintaining the discharge capacity. When the concentration of the acid aqueous solution was 0.5% by weight or more, a high charge / discharge efficiency of 90% or more was obtained. Further, even when the acid was changed from hydrochloric acid to nitric acid, the same improvement in charge / discharge efficiency was obtained.
[0107]
[Example 3]
Using the raw materials having the alloy composition shown in Table 3, alloy powders were prepared and classified by the Ar gas atomization method in the same manner as in Example 1, and then heat-treated at the temperatures shown in Table 3, followed by immersion treatment with an acid aqueous solution. It was. The immersion conditions for the acid aqueous solution are 15 minutes in a 2% HF aqueous solution for No. 1-18 Si-containing alloys, and 15 minutes in a 5% HCl aqueous solution for No. 19-24 Si-free alloys. It was.
[0108]
When the microstructure of the alloy powder after heat treatment was examined, all of them were alloys in which the A phase of the core was surrounded by the B phase of the matrix, and the A phase was the Si phase in the No. 1-18 Si-containing alloys. In the alloys of 19-24, it was Zn phase. The average particle size of the core phase was as fine as 30 μm or less for any alloy. Table 3 shows the main intermetallic compounds or solid solutions constituting the B phase and their solidus temperatures. As can be seen from Table 3, the heat treatment temperature was 10 ° C. or more lower than the solidus temperature.
[0109]
Using each of these alloy powders, an electrode was prepared and a tripolar cell test was conducted in the same manner as in Example 1 to determine the discharge capacity and charge / discharge efficiency. The test results are shown in Table 3 together with the results when the immersion treatment in the acid aqueous solution was not performed.
[0110]
[Table 3]

[0111]
As shown in Table 3, for any of the alloy systems, the charge / discharge efficiency could be remarkably improved by performing immersion treatment with an acid aqueous solution with little or no decrease in discharge capacity.
[0112]
[Example 4]
In this example, test symbol E in Table 1, test symbol D in Table 2, and some of the alloys shown in Table 3 (all classified powder obtained by Ar gas atomization method, heat treatment and immersion in acid aqueous solution The electrode of the alloy according to the present invention was processed; the Si-containing alloy was immersed in a 2% HF solution for 15 minutes, and the Si-free alloy was immersed in a 1% HCl aqueous solution for 15 minutes. The performance of the nonaqueous electrolyte lithium secondary battery using this as a negative electrode was evaluated as described below.
[0113]
Separately, a battery was similarly produced using an alloy powder that was not immersed in an acid aqueous solution, and performance was evaluated.
FIG. 1 shows a longitudinal sectional view of a cylindrical battery produced in this example.
[0114]
In this battery, the positive electrode plate 5 and the negative electrode plate 6 are spirally wound a plurality of times via a separator 7 and stored in the battery case 1. A positive electrode lead 5 a is drawn from the positive electrode plate 5 and connected to the sealing plate 2, and a negative electrode lead 6 a is drawn from the negative electrode plate 6 and connected to the bottom of the battery case 1. Insulating rings 8 are provided on the upper and lower portions of the electrode plate group 4, respectively. Reference numeral 3 denotes an insulating packing.
[0115]
For the battery case and the lead plate, an electron conductive metal or alloy resistant to a non-aqueous electrolyte can be used. For example, metals such as iron, nickel, titanium, chromium, molybdenum, copper, and aluminum, or alloys thereof can be used. A stainless steel plate or an Al-Mn alloy plate is suitable for the battery case, and aluminum is the most suitable for the positive electrode lead and nickel is the most suitable for the negative electrode lead.
[0116]
A battery can is completed by injecting an electrolyte into the battery case and sealing the case with a sealing plate. At this time, the sealing plate can be provided with a safety valve or a safety element as shown. Examples of safety elements are overcurrent prevention elements such as fuses, bimetals, and PTC elements. In addition to the safety valve, measures such as cutting the battery case, cracking the gasket or the sealing plate, and cutting the lead plate can also be taken as measures against the increase in internal pressure of the battery case. Further, the charger may be provided with a protection circuit incorporating measures against overcharge and overdischarge, or may be connected independently. As a measure against overcharge, a method of cutting off current by increasing the battery internal pressure can be used. At this time, a compound that increases the internal pressure may be contained in the electrode mixture or the electrolyte. As compounds that increase the internal pressure, Li₂CO_Three, LiHCO_Three, Na₂CO_Three, NaHCO_Three, CaCO_Three, MgCO_ThreeAnd carbonates such as Electric welding, laser welding, ultrasonic welding, etc. can be used for welding the battery case, sealing plate, and lead plate. As the sealing agent for sealing, a sealing agent such as asphalt can be used.
[0117]
The negative electrode plate was produced as follows. A mixture of 75% of the alloy powder of the present invention having an alloy composition shown in Table 4, 20% of acetylene black as a conductive agent, and 5% of polyvinylidene fluoride (PVDF) as a binder was stirred in dehydrated N-methylpyrrolidone (NMP). A slurry was prepared. This slurry was applied to the surface of a copper foil having a thickness of 0.015 mm as a current collector, dried, roll-rolled and cut to obtain a negative electrode plate having a thickness of 0.2 mm, a width of 37 mm, and a length of 300 mm. Obtained. The filling amount of the alloy in the negative electrode plate was in the range of about 3 to 10 g.
[0118]
On the other hand, the positive electrode plate is made of lithium cobalt oxide (LiCoO₂) Powder 85%, conductive agent acetylene black 10%, and binder PVDF 5%. However, as the current collector for the positive electrode plate, an aluminum foil having the same thickness as the copper foil for the negative electrode was used.
[0119]
As an electrolytic solution, a mixed solvent of ethylene carbonate and ethyl methyl carbonate having a volume ratio of 1: 1 is mixed with LiPF.₆Was used at a concentration of 1.5 M. The produced battery was a cylindrical battery having a diameter of 18 mm and a height of 650 mm.
[0120]
These batteries were charged to 4.2 V at a constant current of 100 mA, and then discharged to 3 V at a constant current of 100 mA to determine the discharge capacity and charge / discharge efficiency (discharge capacity / charge capacity × 100). Also, using another battery prepared in the same manner, a charge / discharge cycle test was conducted at a constant current of 100 mA at a voltage of 4.2 V and a discharge end voltage of 25 V, and the charge / discharge capacity at the first cycle was measured, and after 500 cycles The discharge capacity was measured, and the ratio (%) of the discharge capacity at the 500th cycle to the discharge capacity at the first cycle was determined as the cycle life. All measurements were performed at 25 ° C. These test results are shown in Table 4.
[0121]
[Table 4]

[0122]
As can be seen from Table 4, the non-aqueous electrolyte lithium secondary battery using the Si or Zn-based alloy of the present invention as the negative electrode material had good discharge capacity, charge / discharge efficiency, and cycle life.
[0123]
【The invention's effect】
Si or Zn-based alloy for non-aqueous electrolyte secondary battery of the present invention, which is manufactured by a rapid solidification method such as gas atomizing method, and finally immersed in an acid aqueous solution, is an Si phase of a core phase or a Li phase of a Zn phase. Since the surface oxide film that has a high occlusion capability and causes irreversible Li occlusion is removed, a large amount of Li can be occluded and most of the occluded Li can be released. In addition, since the periphery of the core phase is constrained, volume change based on Li occlusion / release is suppressed, and even when Li occlusion / release is repeated, it is difficult to pulverize and the Li occlusion ability can be maintained for a long time.
[0124]
Therefore, when this alloy is used as a negative electrode material for a non-aqueous electrolyte secondary battery such as a lithium secondary battery, a secondary battery having a high discharge capacity and a charge / discharge efficiency of 85% or more, preferably 90% or more is produced. can do. When the charge / discharge efficiency is high, the amount of electricity required for charging is reduced, resulting in a battery with high energy efficiency. Moreover, this non-aqueous electrolyte secondary battery is also excellent in charge / discharge repeated life. Therefore, it is expected that the performance of the non-aqueous electrolyte secondary battery represented by the lithium secondary battery will be remarkably improved by the present invention, and that its application will be expanded.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view showing the structure of a lithium secondary battery produced in an example.
[Explanation of symbols]
1: battery case, 2: sealing plate, 3: insulating packing, 4: electrode plate group, 5: positive electrode plate, 6: negative electrode plate, 7: separator, 8: insulating ring.

Claims (3)

A method for producing an alloy for a nonaqueous electrolyte secondary battery, comprising the following steps:
An alloy composed of Si or Zn and having an A phase with a particle size of 0.01 to 40 μm and a B phase surrounding at least a part of the periphery of the A phase, the B phase constituting the A phase Metal of Si or Zn and at least one element selected from Group IIA, Group IIIA to IIB transition elements, Group IIIB, Group IVB excluding C, and Group VB of the long-period periodic table Forming an alloy that is an intermetallic compound or a solid solution by a method including solidifying a molten alloy raw material having a predetermined composition at a solidification rate of 100 ° C./sec or more, before immersing the solidified alloy in an acid aqueous solution, A step of heat-treating at a temperature 10 ° C. or more lower than the B-phase solidus temperature , and a step of immersing the obtained alloy in an acid aqueous solution 2. The alloy for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the alloy contains Si and the acid aqueous solution is an HF aqueous solution, or the alloy contains Zn, and the acid aqueous solution is an aqueous solution of HCl or HNO ₃ . Production method. It said aqueous acid solution, HF aqueous solution of 0.05 to 15 wt% concentration or method of manufacturing a nonaqueous electrolyte secondary battery alloy, respectively claim 2, wherein the HCl or HNO ₃ solution of 0.05 to 10 wt% concentration.

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