JP7448104B1 - Slurry liquid, method for producing slurry liquid, and method for producing negative electrode active material - Google Patents
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Abstract
シリコン粒子を含むスラリー液での分散状態での配向を改善して、分散性を向上させて分散安定化することである。そして、負極活物質を作製し二次電池としたときの容量維持率や初回クーロン効率といった充放電性能を高く維持できるスラリー液、スラリー液の製造方法、及び負極活物質の製造方法を提供することである。本発明のスラリー液は、平均粒子径（Ｄ５０）３０～１０００ｎｍのシリコン粒子と、ポリシロキサン系樹脂と、が１気圧における沸点１００℃以下の有機溶媒に分散している。本発明のスラリー液の製造方法は、平均粒子径（Ｄ５０）１０００ｎｍ以上であるシリコン粒子に、ポリシロキサン－アクリル複合樹脂と、有機溶媒とを加えて湿式粉砕する工程を含む。The objective is to improve the orientation of a slurry liquid containing silicon particles in a dispersed state, thereby improving dispersibility and stabilizing the dispersion. And to provide a slurry liquid, a method for manufacturing a slurry liquid, and a method for manufacturing a negative electrode active material that can maintain high charge/discharge performance such as capacity retention rate and initial coulombic efficiency when a secondary battery is produced by preparing a negative electrode active material. It is. In the slurry liquid of the present invention, silicon particles having an average particle diameter (D50) of 30 to 1000 nm and a polysiloxane resin are dispersed in an organic solvent having a boiling point of 100° C. or less at 1 atmosphere. The method for producing a slurry liquid of the present invention includes the step of adding a polysiloxane-acrylic composite resin and an organic solvent to silicon particles having an average particle diameter (D50) of 1000 nm or more, and wet-pulverizing the silicon particles.
Description
本発明は、シリコン粒子と有機溶媒を含むスラリー液、当該スラリー液の製造方法、及び当該スラリー液の製造方法を含む負極活物質の製造方法に関する。 The present invention relates to a slurry liquid containing silicon particles and an organic solvent, a method for manufacturing the slurry liquid, and a method for manufacturing a negative electrode active material including the method for manufacturing the slurry liquid.
エネルギー需要の環境対応から、電気自動車（ＥＶ）への展開が急速に進んでおり、リチウムイオン電池（ＬＩＢ）の利用範囲が拡大している。ＬＩＢ負極材料の主流である黒鉛では理論容量密度（３７２ｍＡｈ／ｇ）が低く、電池容量向上のため、珪素、錫、ならびに酸化物を用いた高容量活物質の開発が活発に行われている。しかしながら、これらの材料はリチウムイオンの吸蔵、放出に伴って体積膨張および収縮が大きいため充放電の繰り返しによって活物質が微粉化することで充放電特性が悪くなるという課題がある。 The use of electric vehicles (EVs) is rapidly progressing in response to environmental demands for energy, and the scope of use of lithium-ion batteries (LIBs) is expanding. Graphite, which is the mainstream LIB negative electrode material, has a low theoretical capacity density (372 mAh/g), and in order to improve battery capacity, high-capacity active materials using silicon, tin, and oxides are being actively developed. However, these materials have a problem in that their volumetric expansion and contraction are large as they absorb and release lithium ions, and that the active material is pulverized by repeated charging and discharging, resulting in poor charging and discharging characteristics.
特許文献１には、良好な容量維持率及びクーロン効率を得るための活物質として、少なくとも１つのシリコン系微粒子と、Ｓｉ（ケイ素）とＯ（酸素）とＣ（炭素）とを構成元素として含有するＳｉＯＣコート層とを含み、少なくとも１つのシリコン系微粒子は、上記ＳｉＯＣコート層によって被覆されており、体積基準粒度分布による平均粒子径が、１ｎｍ～９９９μｍの範囲にある、ＳｉＯＣ構造体が記載されている。また、特定のシラン化合物を加水分解し、分散剤及びシリコン系微粒子の存在下で重縮合させることにより、シリコン系微粒子／シリコン含有ポリマー複合体を生成することを含む、シリコン系微粒子／シリコン含有ポリマー複合体を製造する方法が記載されている。上記分散剤としては、ポリソルベート類などの非イオン性界面活性剤が記載されており、この分散剤を用いてナノシリコンを分散した後にシリコンモノマーを加えて縮合、反応させている。 Patent Document 1 describes an active material containing at least one silicon-based fine particle and constituent elements of Si (silicon), O (oxygen), and C (carbon) as an active material for obtaining a good capacity retention rate and Coulombic efficiency. An SiOC structure is described in which at least one silicon-based fine particle is covered with the SiOC coating layer, and the average particle diameter according to the volume-based particle size distribution is in the range of 1 nm to 999 μm. ing. In addition, silicone-based fine particles/silicon-containing polymers may be produced by hydrolyzing a specific silane compound and polycondensing it in the presence of a dispersant and silicone-based fine particles to produce silicone-based fine particles/silicon-containing polymer composites. A method of making the composite is described. As the dispersant, nonionic surfactants such as polysorbates are described, and after nanosilicon is dispersed using this dispersant, a silicon monomer is added to cause condensation and reaction.
本発明者らは、上記特許文献１について検討をしたところ、特許文献１に記載のポリソルベート類などの非イオン性界面活性剤を分散剤として用いて分散した後にポリシロキサン系樹脂を投入すると、分散状態ではポリシロキサンがシリコン粒子の一部にしか配向せず、不均一な部分が発生するため分散状態が安定せず、ナノシリコンの粒径（Ｄ５０）の変化率が大きいことが分かった。このため特許文献１では、焼成後にも一部分散剤が炭化した炭素リッチな部分が発生するため、電池性能を低下させることが分かった。 The present inventors studied Patent Document 1 mentioned above and found that if a polysiloxane resin is added after dispersing using a nonionic surfactant such as polysorbates described in Patent Document 1 as a dispersant, It was found that in this state, polysiloxane was oriented only in a part of the silicon particles, and non-uniform parts were generated, so the dispersion state was not stable and the rate of change in the particle size (D50) of nanosilicon was large. For this reason, in Patent Document 1, it was found that even after firing, a carbon-rich portion where a portion of the dispersant is carbonized is generated, which deteriorates the battery performance.
本発明の課題は、上記のようなシリコン粒子を含むスラリー液での分散状態での配向を改善して、分散性を向上させて分散安定化することである。そして、負極活物質を作製し二次電池としたときの容量維持率や初回クーロン効率といった充放電性能を高く維持できるスラリー液、スラリー液の製造方法、及び負極活物質の製造方法を提供することである。 An object of the present invention is to improve the orientation of a slurry liquid containing silicon particles as described above in a dispersed state, thereby improving dispersibility and stabilizing the dispersion. And to provide a slurry liquid, a method for producing a slurry liquid, and a method for producing a negative electrode active material that can maintain high charge/discharge performance such as capacity retention rate and initial coulomb efficiency when a secondary battery is produced by producing a negative electrode active material. It is.
本発明者らは、更に鋭意検討をしたところポリシロキサン－アクリル複合樹脂を用いることで上記課題を解決できることが分かった。これはポリシロキサン－アクリル複合樹脂のポリシロキサン由来のケイ素成分がシリコン粒子の近傍に配位して、分散安定性を向上させるためであると考えられる。そして、この状態で乾燥および焼成を行うと、樹脂の有機成分の多くは除去されるが、ポリシロキサン由来のＳｉが均一にナノシリコンを覆うことができ、これにより高い電池性能が得られる。 The inventors of the present invention further conducted intensive studies and found that the above problems can be solved by using a polysiloxane-acrylic composite resin. This is thought to be because the silicon component derived from the polysiloxane of the polysiloxane-acrylic composite resin coordinates in the vicinity of the silicon particles, improving dispersion stability. When drying and firing are performed in this state, most of the organic components of the resin are removed, but Si derived from polysiloxane can uniformly cover the nanosilicon, thereby providing high battery performance.
本発明は、下記の態様を有する。
［１］ 平均粒子径（Ｄ５０）３０～１０００ｎｍのシリコン粒子と、ポリシロキサン－アクリル複合樹脂と、が１気圧における沸点１００℃以下の有機溶媒に分散しているスラリー液。
［２］ 前記ポリシロキサン－アクリル複合樹脂が、アクリル樹脂構造とポリシロキサン構造の間に化学的な結合を有するポリシロキサン－アクリル複合樹脂である［１］に記載のスラリー液。
［３］ 前記ポリシロキサン－アクリル複合樹脂のポリシロキサン構造とアクリル樹脂構造の重量比が９９／１～３０／７０である［２］に記載のスラリー液。
［４］ 前記ポリシロキサン－アクリル複合樹脂の含有量が、前記シリコン粒子１００重量部に対して１０～５０重量部である［２］または［３］に記載のスラリー液。
［５］ 前記有機溶媒が、ケトン系またはアルコール系のいずれかを含む［１］から［４］のいずれか１つに記載のスラリー液。
［６］ 前記有機溶媒の含有量が、２０～８０重量％である［１］から［５］のいずれか１つに記載のスラリー液。
［７］ 平均粒子径（Ｄ５０）１０００ｎｍ以上であるシリコン粒子に、ポリシロキサン－アクリル複合樹脂と、有機溶媒とを加えて湿式粉砕する工程を含むスラリー液の製造方法。
［８］ 前記の湿式粉砕する工程の前に、水をポリシロキサン-アクリル複合樹脂固形分に対して１～１０重量％投入する工程を有する［７］に記載のスラリー液の製造方法。
［９］ 前記ポリシロキサン－アクリル複合樹脂のポリシロキサン構造とアクリル樹脂構造の重量比が９９／１～３０／７０である［７］または［８］に記載のスラリー液の製造方法。
［１０］ ［７］から［９］のいずれか１つに記載のスラリー液の製造方法で得たスラリー液に、フェノール樹脂を前記シリコン粒子１００重量部に対して２０～５０重量部添加する工程と、前記スラリー液に含まれる有機溶媒を除いた後に乾燥をして焼成する工程を含む負極活物質の製造方法。
The present invention has the following aspects.
[1] A slurry liquid in which silicon particles with an average particle diameter (D50) of 30 to 1000 nm and a polysiloxane-acrylic composite resin are dispersed in an organic solvent with a boiling point of 100° C. or less at 1 atmosphere.
[2] The slurry liquid according to [1], wherein the polysiloxane-acrylic composite resin has a chemical bond between an acrylic resin structure and a polysiloxane structure.
[3] The slurry liquid according to [2], wherein the weight ratio of the polysiloxane structure and the acrylic resin structure of the polysiloxane-acrylic composite resin is 99/1 to 30/70.
[4] The slurry liquid according to [2] or [3], wherein the content of the polysiloxane-acrylic composite resin is 10 to 50 parts by weight based on 100 parts by weight of the silicon particles.
[5] The slurry liquid according to any one of [1] to [4], wherein the organic solvent contains either a ketone type or an alcohol type.
[6] The slurry liquid according to any one of [1] to [5], wherein the content of the organic solvent is 20 to 80% by weight.
[7] A method for producing a slurry liquid, which includes the step of adding a polysiloxane-acrylic composite resin and an organic solvent to silicon particles having an average particle diameter (D50) of 1000 nm or more and wet-pulverizing the silicon particles.
[8] The method for producing a slurry liquid according to [7], which includes a step of adding 1 to 10% by weight of water based on the solid content of the polysiloxane-acrylic composite resin before the wet grinding step.
[9] The method for producing a slurry liquid according to [7] or [8], wherein the weight ratio of the polysiloxane structure to the acrylic resin structure of the polysiloxane-acrylic composite resin is 99/1 to 30/70.
[10] A step of adding 20 to 50 parts by weight of a phenolic resin to 100 parts by weight of the silicon particles to the slurry liquid obtained by the method for producing a slurry liquid according to any one of [7] to [9]. and a method for producing a negative electrode active material, comprising the steps of drying and firing after removing the organic solvent contained in the slurry liquid.
本発明のスラリー液は分散安定性が高く、これを用いて負極活物質を作製した二次電池における容量維持率や初回クーロン効率といった充放電性能を高く維持できる。 The slurry liquid of the present invention has high dispersion stability, and can maintain high charge/discharge performance such as capacity retention rate and initial coulombic efficiency in a secondary battery in which a negative electrode active material is prepared using the slurry liquid.
［スラリー液］
本発明のスラリー液は、平均粒子径（Ｄ５０）３０～１０００ｎｍのシリコン粒子と、ポリシロキサン－アクリル複合樹脂とが１気圧における沸点１００℃以下の有機溶媒に分散している。本発明において「分散している」とは、シリコン粒子が沈降なく安定に存在している状態を示し、スラリー状態で、例えば７２時間静置後のＤ５０の変化率±３％以内となることを指標としている。図２は、本発明ではない（本願比較例１の）スラリー液の乾燥塗膜ＳＥＭ画像であるが、縞状の炭素リッチな成分が凝集しており、不均一となっている。一方、図１は、本発明（本願実施例１）のスラリー液の乾燥塗膜ＳＥＭ画像であるが、縞状の炭素リッチな部分が存在せず、シリコン粒子表面にＳｉが均一に配位している。
[Slurry liquid]
In the slurry liquid of the present invention, silicon particles having an average particle diameter (D50) of 30 to 1000 nm and a polysiloxane-acrylic composite resin are dispersed in an organic solvent having a boiling point of 100° C. or less at 1 atmosphere. In the present invention, "dispersed" refers to a state in which silicon particles exist stably without settling, and in a slurry state, for example, the rate of change in D50 after standing for 72 hours is within ±3%. It is used as an indicator. FIG. 2 is a SEM image of a dry coating film of a slurry liquid that is not of the present invention (Comparative Example 1 of the present application), and the striped carbon-rich components are aggregated and are non-uniform. On the other hand, FIG. 1 is a SEM image of the dry coating film of the slurry liquid of the present invention (Example 1 of the present application), but there are no striped carbon-rich areas and Si is uniformly coordinated on the surface of the silicon particles. ing.
上記ポリシロキサン－アクリル複合樹脂は、アクリル樹脂構造とポリシロキサン構造の間に化学的な結合を有するポリシロキサン－アクリル複合樹脂であることが好ましい。
上記アクリル樹脂構造は、例えばアクリル酸エステルまたはメタクリル酸エステルをモノマー単位とする重合体の構造である。
上記ポリシロキサン構造は、主に珪素元素と炭素元素を含む珪素－炭素骨格の三次元ネットワーク構造または珪素元素と炭素元素と酸素元素を含む珪素－酸素－炭素骨格の三次元ネットワーク構造である。
また、ポリシロキサン－アクリル複合樹脂は、上記のアクリル樹脂構造とポリシロキサン構造が複合的に結合して均一化された構造体である。本発明においてポリシロキサン－アクリル複合樹脂は、シリコン粒子を効果的に分散させ、分散安定化させる働きをする。
The polysiloxane-acrylic composite resin is preferably a polysiloxane-acrylic composite resin having a chemical bond between an acrylic resin structure and a polysiloxane structure.
The above-mentioned acrylic resin structure is, for example, a polymer structure having an acrylic acid ester or a methacrylic acid ester as a monomer unit.
The above-mentioned polysiloxane structure is a three-dimensional network structure of a silicon-carbon skeleton mainly containing a silicon element and a carbon element, or a three-dimensional network structure of a silicon-oxygen-carbon skeleton containing a silicon element, a carbon element, and an oxygen element.
Further, the polysiloxane-acrylic composite resin is a homogeneous structure in which the above-mentioned acrylic resin structure and polysiloxane structure are combined in a composite manner. In the present invention, the polysiloxane-acrylic composite resin functions to effectively disperse silicon particles and stabilize the dispersion.
上記ポリシロキサン－アクリル複合樹脂は、例えば、下記（１）～（３）に示す方法で製造することができる。 The above polysiloxane-acrylic composite resin can be produced, for example, by the methods shown in (1) to (3) below.
（１）アクリル樹脂構造を構成する重合体セグメントの原料として、シラノール基および／または加水分解性シリル基を含有する重合体セグメントを予め調製しておき、この重合体セグメントと、シラノール基および／または加水分解性シリル基、並びにシラン化合物（ポリシロキサン構成物）とを混合し、加水分解縮合反応を行う方法。 (1) As a raw material for the polymer segment constituting the acrylic resin structure, a polymer segment containing a silanol group and/or a hydrolyzable silyl group is prepared in advance, and this polymer segment and a silanol group and/or A method in which a hydrolyzable silyl group and a silane compound (polysiloxane constituent) are mixed and a hydrolytic condensation reaction is performed.
（２）アクリル樹脂構造を構成する重合体セグメントの原料として、シラノール基および／または加水分解性シリル基を含有する重合体セグメントを予め調製する。また、シラノール基および／または加水分解性シリル基、並びにシラン化合物を加水分解縮合反応してポリシロキサンも予め調製しておく。そして、重合体セグメントとポリシロキサン（ポリシロキサン構造）とを混合し、加水分解縮合反応を行う方法。 (2) A polymer segment containing a silanol group and/or a hydrolyzable silyl group is prepared in advance as a raw material for the polymer segment constituting the acrylic resin structure. Further, a polysiloxane is also prepared in advance by subjecting a silanol group and/or a hydrolyzable silyl group and a silane compound to a hydrolytic condensation reaction. A method of mixing a polymer segment and polysiloxane (polysiloxane structure) and performing a hydrolytic condensation reaction.
（３）アクリル樹脂構造を構成する重合体セグメントの原料として、シラノール基および／または加水分解性シリル基を含有する重合体セグメントと、シラノール基および／または加水分解性シリル基、並びに重合性二重結合を併有するシラン化合物（ポリシロキサン構成物）と、ポリシロキサン（ポリシロキサン構造）とを混合し、加水分解縮合反応を行う方法。
この方法によりポリシロキサン系樹脂が得られる。上記ポリシロキサン系樹脂の市販品としては、例えばセラネート（登録商標）シリーズ（有機・無機ハイブリッド型コーティング樹脂；ＤＩＣ株式会社製）やコンポセランＳＱシリーズ（シルセスキオキサン型ハイブリッド；荒川化学工業株式会社製）が挙げられる。
(3) As a raw material for the polymer segment constituting the acrylic resin structure, a polymer segment containing a silanol group and/or a hydrolyzable silyl group, a silanol group and/or a hydrolyzable silyl group, and a polymerizable double A method in which a silane compound (polysiloxane constituent) having a bond and a polysiloxane (polysiloxane structure) are mixed and a hydrolysis condensation reaction is carried out.
A polysiloxane resin can be obtained by this method. Commercially available polysiloxane resins include, for example, the Ceranate (registered trademark) series (organic/inorganic hybrid coating resin; manufactured by DIC Corporation) and the Compoceran SQ series (silsesquioxane hybrid; manufactured by Arakawa Chemical Industries, Ltd.). ).
ポリシロキサン－アクリル複合樹脂のポリシロキサン構造とアクリル樹脂構造の重量比は、例えば９９／１～３０／７０、好ましくは９５／５～４０／６０、より好ましくは９０／１０～５０／５０である。重量比が上記範囲であると、スラリー液とした後に最終的に得られる負極活物質には二次電池における容量維持率や初回クーロン効率といった充放電性能を高く維持できるといった優れた効果を有する。。 The weight ratio of the polysiloxane structure and the acrylic resin structure of the polysiloxane-acrylic composite resin is, for example, 99/1 to 30/70, preferably 95/5 to 40/60, more preferably 90/10 to 50/50. . When the weight ratio is within the above range, the negative electrode active material finally obtained after being made into a slurry liquid has an excellent effect of maintaining high charge/discharge performance such as capacity retention rate and initial Coulombic efficiency in a secondary battery. .
上記ポリシロキサン－アクリル複合樹脂の含有量は、シリコン粒子１００重量部に対して、例えば１０～５０重量部、好ましくは１５～４５重量部である。ポリシロキサン－アクリル複合樹脂の含有量は、スラリー液全量に対して、例えば２～３０重量％、好ましくは４～２０重量％である。また、ポリシロキサン－アクリル複合樹脂の含有量が上記範囲であると、前記スラリー液を用いて最終的に得られる負極活物質には二次電池における容量維持率や初回クーロン効率といった充放電性能を高く維持できるといった優れた効果を有する。。 The content of the polysiloxane-acrylic composite resin is, for example, 10 to 50 parts by weight, preferably 15 to 45 parts by weight, based on 100 parts by weight of silicon particles. The content of the polysiloxane-acrylic composite resin is, for example, 2 to 30% by weight, preferably 4 to 20% by weight, based on the total amount of the slurry liquid. In addition, when the content of the polysiloxane-acrylic composite resin is within the above range, the negative electrode active material finally obtained using the slurry liquid has charge/discharge performance such as capacity retention rate and initial coulombic efficiency in a secondary battery. It has an excellent effect of being able to maintain a high temperature. .
本発明のスラリー液に用いるシリコン粒子の平均粒子径（Ｄ５０）は、３０～１０００ｎｍであるが、好ましくは５０～８００ｎｍ、より好ましくは６０～６００ｎｍである。粒子径（Ｄ５０）が上記範囲であると、二次電池における容量維持率や初回クーロン効率といった充放電性能を高く維持できる。平均粒径（Ｄ５０）は、例えばレーザー回折式粒度分布測定装置を用いて測定することができる。 The average particle diameter (D50) of the silicon particles used in the slurry liquid of the present invention is 30 to 1000 nm, preferably 50 to 800 nm, more preferably 60 to 600 nm. When the particle diameter (D50) is within the above range, high charging and discharging performance such as capacity retention rate and initial coulombic efficiency in the secondary battery can be maintained. The average particle diameter (D50) can be measured using, for example, a laser diffraction particle size distribution analyzer.
上記シリコン粒子の比表面積は、電気容量と初期（クーロン）効率の観点から、１００ｍ２／ｇ～４００ｍ２／ｇが好ましく、１００ｍ２／ｇ～３００ｍ２／ｇがより好ましく、１００ｍ２／ｇ～２３０ｍ２／ｇがさらに好ましい。比表面積は、ＢＥＴ法により求めた値であり、窒素ガス吸着測定により求めることができ、例えば比表面積測定装置を用いて測定することができる。 The specific surface area of the silicon particles is preferably 100 m 2 /g to 400 m 2 /g, more preferably 100 m 2 /g to 300 m 2 /g, and 100 m 2 /g to More preferably 230 m 2 /g. The specific surface area is a value determined by the BET method, and can be determined by nitrogen gas adsorption measurement, for example, using a specific surface area measuring device.
上記シリコン粒子の形状は、粒状、針状、フレーク状のいずれでもよいが、結晶質が好ましい。シリコン粒子が結晶質の場合、Ｘ線回折においてＳｉ（１１１）に帰属される回折ピークから得られる結晶子径が５ｎｍ～１４ｎｍの範囲であれば、初期クーロン効率および容量維持率の観点から好ましい。結晶子径は１２ｎｍ以下が好ましく、１０ｎｍ以下がより好ましい。 The shape of the silicon particles may be granular, acicular, or flaky, but crystalline is preferable. When the silicon particles are crystalline, it is preferable from the viewpoint of initial Coulombic efficiency and capacity retention rate that the crystallite diameter obtained from the diffraction peak attributed to Si (111) in X-ray diffraction is in the range of 5 nm to 14 nm. The crystallite diameter is preferably 12 nm or less, more preferably 10 nm or less.
上記シリコン粒子は、二次電池の負極活物質として用いるときの充放電性能の観点から、長軸方向の長さは３０ｎｍ～３００ｎｍが好ましく、厚みは１ｎｍ～６０ｎｍが好ましい。二次電池の負極活物質として用いるときの充放電性能の観点から、長さに対する厚みの比である、いわゆるアスペクト比が０．５以下である針状またはフレーク状の形状が好ましい。シリコン粒子の形態は、動的光散乱法で平均粒径の測定が可能であるが、透過型電子顕微鏡（ＴＥＭ）や電界放出型走査電子顕微鏡（ＦＥ－ＳＥＭ）の解析手段を用いることで、アスペクト比のサンプルをより容易かつ精密に同定することができる。シリコン粒子の場合は、サンプルを集束イオンビーム（ＦＩＢ）で切断して断面をＦＥ－ＳＥＭ観察することができ、またはサンプルをスライス加工してＴＥＭ観察により状態を同定することができる。なおナノ珪素のアスペクト比は、ＴＥＭ画像に映る視野内のサンプルの主要部分５０粒子をベースにした計算結果である。 The silicon particles preferably have a length in the long axis direction of 30 nm to 300 nm, and a thickness of 1 nm to 60 nm, from the viewpoint of charge/discharge performance when used as a negative electrode active material of a secondary battery. From the viewpoint of charge/discharge performance when used as a negative electrode active material of a secondary battery, a needle-like or flake-like shape having a so-called aspect ratio, which is the ratio of thickness to length, of 0.5 or less is preferable. The average particle size of silicon particles can be measured using dynamic light scattering, but it can be determined by using analysis methods such as transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM). Aspect ratio samples can be identified more easily and precisely. In the case of silicon particles, the sample can be cut with a focused ion beam (FIB) and the cross section can be observed by FE-SEM, or the sample can be sliced and the state can be identified by TEM observation. Note that the aspect ratio of nanosilicon is a calculation result based on 50 particles of the main part of the sample within the field of view reflected in the TEM image.
上記シリコン粒子は、さらに外表面に非晶質酸化膜が存在することが好ましい。非晶質酸化膜とは、アモルファス状態の酸化被膜のことであり、好ましくはシリコン（Ｓｉ）の酸化被膜、特に好ましくはＳｉＯ２膜である。このような非晶質酸化膜が存在すると、シリコン粒子表面に非常に優れた破壊靭性、高温特性、耐熱衝撃性を付与でき、充放電によるＳｉ粒子の崩壊を抑制できる。また、非晶質酸化膜の厚みは、好ましくは８ｎｍ以下、より好ましくは１ｎｍ～７ｎｍ、特に好ましくは２ｎｍ～６ｎｍである。厚みがこの範囲であると、シリコン粒子の充放電性能を阻害することなく、充放電によるＳｉ粒子の崩壊を抑制できる。 Preferably, the silicon particles further include an amorphous oxide film on the outer surface. The amorphous oxide film refers to an oxide film in an amorphous state, preferably a silicon (Si) oxide film, and particularly preferably a SiO 2 film. The presence of such an amorphous oxide film can impart excellent fracture toughness, high-temperature properties, and thermal shock resistance to the silicon particle surface, and can suppress disintegration of the Si particles due to charging and discharging. Further, the thickness of the amorphous oxide film is preferably 8 nm or less, more preferably 1 nm to 7 nm, particularly preferably 2 nm to 6 nm. When the thickness is within this range, the disintegration of the Si particles due to charging and discharging can be suppressed without impairing the charging and discharging performance of the silicon particles.
上記シリコン粒子の含有量は、スラリー液全量に対して、例えば５～４０重量％、好ましくは８～３０重量％、より好ましくは１０～２０重量％である。また、ポリシロキサン－アクリル複合樹脂の含有量が上記範囲であると、二次電池における容量維持率や初回クーロン効率といった充放電性能を高く維持できる。 The content of the silicon particles is, for example, 5 to 40% by weight, preferably 8 to 30% by weight, and more preferably 10 to 20% by weight, based on the total amount of the slurry liquid. Further, when the content of the polysiloxane-acrylic composite resin is within the above range, high charge/discharge performance such as capacity retention rate and initial coulombic efficiency in the secondary battery can be maintained.
本発明のスラリー液における１気圧における沸点が１００℃以下の有機溶媒は、ケトン系またはアルコール系のいずれかを含むことが好ましい。ケトン系有機溶媒としては、アセトン、メチルエチルケトン、メチルイソブチルケトン、ジイソブチルケトンなどが挙げられる。また、アルコール系有機溶媒としては、エタノール、メタノール、ノルマルプロピルアルコール、イソプロピルアルコールなどが挙げられる。１気圧における沸点が１００℃以下であることで、溶媒除去が容易であり、エネルギー削減効果が期待できる。 The organic solvent having a boiling point of 100° C. or less at 1 atm in the slurry liquid of the present invention preferably contains either a ketone type or an alcohol type. Examples of the ketone organic solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, and the like. Further, examples of alcoholic organic solvents include ethanol, methanol, normal propyl alcohol, and isopropyl alcohol. Since the boiling point at 1 atm is 100° C. or less, the solvent can be easily removed and an energy saving effect can be expected.
本発明のスラリー液における有機溶媒の含有量は、スラリー液全量に対して、例えば２０～８０重量％、好ましくは２５～７５重量％、より好ましくは３０～７０重量％である。有機溶媒の含有量が上記範囲であると、均一にシリコン粒子を分散させやすくなる。 The content of the organic solvent in the slurry liquid of the present invention is, for example, 20 to 80% by weight, preferably 25 to 75% by weight, and more preferably 30 to 70% by weight, based on the total amount of the slurry liquid. When the content of the organic solvent is within the above range, it becomes easier to uniformly disperse silicon particles.
本発明のスラリー液は、上記のポリシロキサン系樹脂、シリコン粒子、有機溶媒以外の成分を有していてもよい。このような成分としては、例えばハイドロキノンやブチルヒドロキシトルエンなどの酸化防止剤が挙げられる。このような成分の含有量は、スラリー液全量に対して、例えば１０重量％以下、好ましくは５重量％以下である。 The slurry liquid of the present invention may contain components other than the above-mentioned polysiloxane resin, silicon particles, and organic solvent. Examples of such components include antioxidants such as hydroquinone and butylated hydroxytoluene. The content of such components is, for example, 10% by weight or less, preferably 5% by weight or less, based on the total amount of the slurry liquid.
本発明のスラリー液は、分散安定性が良いという効果を有する。スラリーの作製直後の平均粒子径（Ｄ５０）に対する７２時間静置後の平均粒子径（Ｄ５０）の変化率は、好ましくは５％以下、より好ましくは３％以下である。 The slurry liquid of the present invention has an effect of good dispersion stability. The rate of change in the average particle diameter (D50) after the slurry is left to stand for 72 hours relative to the average particle diameter (D50) immediately after preparation is preferably 5% or less, more preferably 3% or less.
［スラリー液の製造方法］
本発明のスラリー液の製造方法は、平均粒子径（Ｄ５０）１０００ｎｍ以上であるシリコン粒子に、ポリシロキサン－アクリル複合樹脂と、有機溶媒とを加えて湿式粉砕する工程を含む。以下、「平均粒子径（Ｄ５０）１０００ｎｍ以上であるシリコン粒子」を「原料シリコン粒子」と称する。ポリシロキサン－アクリル複合樹脂及び有機溶媒は、上述の本発明のスラリー液にて記載したとおりである。
[Method for producing slurry liquid]
The method for producing a slurry liquid of the present invention includes the step of adding a polysiloxane-acrylic composite resin and an organic solvent to silicon particles having an average particle diameter (D50) of 1000 nm or more, and wet-pulverizing the silicon particles. Hereinafter, "silicon particles having an average particle diameter (D50) of 1000 nm or more" will be referred to as "raw material silicon particles." The polysiloxane-acrylic composite resin and the organic solvent are as described in the slurry liquid of the present invention above.
原料シリコン粒子は、平均粒子径（Ｄ５０）が好ましくは１５００～５０００ｎｍ、より好ましくは２０００～４０００ｎｍである。原料シリコン粒子は、市販品を用いることができる。シリコン粒子の粉砕を促進させるために有機溶媒に上記ポリシロキサン－アクリル複合樹脂を添加する。湿式粉砕装置としてはローラーミル、高速回転粉砕機、容器駆動型ミル、ビーズミルなどが挙げられる。なお、得られたスラリー液におけるシリコン粒子の平均粒径は、上述のとおりである。この湿式粉砕を行うことでシリコン粒子が分散したスラリー液が得られる。 The raw material silicon particles preferably have an average particle diameter (D50) of 1500 to 5000 nm, more preferably 2000 to 4000 nm. Commercially available products can be used as the raw material silicon particles. The above-mentioned polysiloxane-acrylic composite resin is added to an organic solvent in order to accelerate the pulverization of silicon particles. Examples of wet grinding devices include roller mills, high-speed rotary grinders, container-driven mills, and bead mills. Note that the average particle size of silicon particles in the obtained slurry liquid is as described above. By performing this wet pulverization, a slurry liquid in which silicon particles are dispersed is obtained.
上記の湿式粉砕を行う前に、水をポリシロキサン-アクリル複合樹脂固形分に対して、例えば１～１０重量％（好ましくは３～８重量％）投入することが好ましい。すなわち水をポリシロキサン－アクリル複合樹脂固形分１００重量部に対して、例えば１～１０重量部（好ましくは３～８重量部）投入することが好ましい。このように水を加えることでポリシロキサン-アクリル複合樹脂に残存するメトキシ基を加水分解してシラノール基に変換し、シラノール基同士の縮合反応を促進し、シリコン表面近傍で高分子量化して分散を更に良化することができる。 Before performing the above-mentioned wet pulverization, it is preferable to add water, for example, 1 to 10% by weight (preferably 3 to 8% by weight) based on the solid content of the polysiloxane-acrylic composite resin. That is, it is preferable to add, for example, 1 to 10 parts by weight (preferably 3 to 8 parts by weight) of water per 100 parts by weight of the solid content of the polysiloxane-acrylic composite resin. By adding water in this way, the methoxy groups remaining in the polysiloxane-acrylic composite resin are hydrolyzed and converted into silanol groups, promoting the condensation reaction between the silanol groups, increasing the molecular weight near the silicon surface and promoting dispersion. It can be further improved.
ポリシロキサン－アクリル複合樹脂のポリシロキサン構造とアクリル樹脂構造の重量比は９９／１～３０／７０が好ましく、好ましくは９５／５～４０／６０、より好ましくは９０／１０～５０／５０である。重量比が上記範囲であると、二次電池における容量維持率や初回クーロン効率といった充放電性能を高く維持できる。 The weight ratio of the polysiloxane structure and the acrylic resin structure of the polysiloxane-acrylic composite resin is preferably 99/1 to 30/70, preferably 95/5 to 40/60, more preferably 90/10 to 50/50. . When the weight ratio is within the above range, high charging and discharging performance such as capacity retention rate and initial coulombic efficiency in the secondary battery can be maintained.
ポリシロキサン－アクリル複合樹脂以外に、非水系分散剤を併用してもよい。非水系分散剤の種類としては、ポリエーテル系、アルコール系、ポリアルキレンポリアミン系、ポリカルボン酸部分アルキルエステル系などの高分子型、多価アルコールエステル系、アルキルポリアミン系などの低分子型、ポリリン酸塩系などの無機型が挙げられる。 In addition to the polysiloxane-acrylic composite resin, a non-aqueous dispersant may be used in combination. Types of non-aqueous dispersants include polymer types such as polyethers, alcohols, polyalkylene polyamines, and polycarboxylic acid partial alkyl esters, low-molecular types such as polyhydric alcohol esters, and alkyl polyamines, and polyphosphorus. Examples include inorganic types such as acid salts.
［負極活物質の製造方法］
本発明の負極活物質の製造方法は、上述のスラリー液の製造方法で得たスラリー液に、フェノール樹脂をシリコン粒子１００重量部に対して２０～５０重量部（好ましくは２５～４５重量部）添加し混合する工程と、前記スラリー液に含まれる有機溶媒を除く脱溶媒の工程および必要に応じて乾燥工程を経て活物質前駆体を得る工程と前記活物質前駆体を焼成する工程を含む方法である。
また、上述のスラリー液の製造方法でスラリー液を得た後に、前記ポリシロキサン－アクリル複合樹脂を追加で添加する任意の工程を含んでもよい。本発明においては、スラリー液を製造する初期段階からシリコン粒子と、ポリシロキサン－アクリル複合樹脂とを併用することが重要であり、スラリー液を製造する初期段階にポリシロキサン－アクリル複合樹脂を用いない場合（本発明の範囲外）、スラリー液の分散性を向上させて分散安定化することができず、負極活物質を作製し二次電池としたときに容量維持率や初回クーロン効率といった充放電性能を高く維持することができない。
[Method for producing negative electrode active material]
In the method for producing a negative electrode active material of the present invention, 20 to 50 parts by weight (preferably 25 to 45 parts by weight) of a phenol resin is added to the slurry liquid obtained by the above-mentioned method for producing a slurry liquid, based on 100 parts by weight of silicon particles. A method including a step of adding and mixing, a step of desolvation to remove the organic solvent contained in the slurry liquid, a step of obtaining an active material precursor through a drying step if necessary, and a step of firing the active material precursor. It is.
Further, the method may include an optional step of additionally adding the polysiloxane-acrylic composite resin after obtaining the slurry liquid by the above-described slurry liquid manufacturing method. In the present invention, it is important to use silicon particles and polysiloxane-acrylic composite resin together from the initial stage of manufacturing the slurry liquid, and do not use the polysiloxane-acrylic composite resin at the initial stage of manufacturing the slurry liquid. In some cases (outside the scope of the present invention), it is not possible to stabilize the dispersion by improving the dispersibility of the slurry liquid, and when a negative electrode active material is prepared and used as a secondary battery, charging/discharging problems such as capacity retention rate and initial Coulombic efficiency Unable to maintain high performance.
上記フェノール樹脂は、ポリシロキサン－アクリル複合樹脂との混和性が良く、不活性雰囲気中、高温焼成により炭化される成分（炭素源樹脂成分）である。フェノール樹脂としてはクレゾール型とレゾール型があるが、レゾール型が好ましい。フェノール樹脂としては、例えばＳＫレジン（ＨＥ１００Ｃ－３０、エア・ウォーター株式会社製）が挙げられる。クレゾール樹脂としては、例えばＬＣ－１００（リグナイト株式会社製）が挙げられる。フェノール樹脂は、攪拌機などを用いてスラリー液中で均一に混合されることが好ましい。 The above-mentioned phenolic resin is a component (carbon source resin component) that has good miscibility with the polysiloxane-acrylic composite resin and is carbonized by high-temperature firing in an inert atmosphere. There are two types of phenolic resins: cresol type and resol type, with resol type being preferred. Examples of the phenolic resin include SK resin (HE100C-30, manufactured by Air Water Co., Ltd.). Examples of the cresol resin include LC-100 (manufactured by Lignite Co., Ltd.). The phenol resin is preferably mixed uniformly in the slurry using a stirrer or the like.
その後の上記脱溶媒は、濾過など常用の方法で行うことができる。また、上記乾燥は例えば乾燥機、減圧乾燥機、噴霧乾燥機などで行われる。乾燥温度は、例えば８０℃以上、好ましくは１００℃以上である。減圧をしながら乾燥を行ってもよい。 The subsequent solvent removal can be carried out by a conventional method such as filtration. Further, the above-mentioned drying is carried out using, for example, a dryer, a vacuum dryer, a spray dryer, or the like. The drying temperature is, for example, 80°C or higher, preferably 100°C or higher. Drying may be performed under reduced pressure.
そして、乾燥後の活物質前駆体を不活性雰囲気中で焼成する。焼成処理に用いる装置は、流動層反応炉、回転炉、竪型移動層反応炉、トンネル炉、バッチ炉、ロータリーキルン等をその目的に応じ適宜選択することができる。焼成処理は、昇温速度、一定温度での保持時間等により規定されるプログラムに沿って行われる。焼成温度は、例えば、最高到達温度が９００～１２００℃の範囲が好ましい。 Then, the dried active material precursor is fired in an inert atmosphere. The apparatus used for the calcination treatment can be appropriately selected from a fluidized bed reactor, a rotary furnace, a vertical moving bed reactor, a tunnel furnace, a batch furnace, a rotary kiln, etc. depending on the purpose. The firing process is performed according to a program defined by the temperature increase rate, the holding time at a constant temperature, and the like. The firing temperature is preferably in the range of 900 to 1200° C., with the highest temperature reached, for example.
更に、上記焼成物を粉砕し、必要に応じて分級することで所望の粒径の負極活物質が得られる。上記粉砕は、目的とする粒径まで一段で行っても良いし、数段に分けて行っても良い。粉砕物に粗大粒子が含まれる場合は、ジョークラッシャー、ロールクラッシャー等で粗粉砕を行った後、グローミル、ボールミル等で粉砕し、更にビーズミル、ジェットミル等で粉砕してもよい。なお、上記粒径は、体積平均粒径であり、平均粒径（Ｄ５０）の値である。 Furthermore, by pulverizing the above-mentioned fired product and classifying it as necessary, a negative electrode active material having a desired particle size can be obtained. The above-mentioned pulverization may be carried out in one stage until the target particle size is reached, or may be carried out in several stages. If the pulverized product contains coarse particles, they may be coarsely pulverized using a jaw crusher, roll crusher, etc., then pulverized using a glow mill, ball mill, etc., and further pulverized using a bead mill, jet mill, etc. In addition, the said particle diameter is a volume average particle diameter, and is the value of an average particle diameter (D50).
また、粉砕で作製した負極活物質に粗大粒子が含まれる場合は、それを取り除くため、微粉を取り除いて粒度分布を調整する場合は分級を行うのが好ましい。使用する分級機は風力分級機、湿式分級機等目的に応じて使い分けるが、粗大粒子を取り除く場合、篩を通す分級方式が確実に目的を達成できるために好ましい。 Further, if the negative electrode active material produced by pulverization contains coarse particles, it is preferable to perform classification to remove fine particles and adjust the particle size distribution. The classifier used is a wind classifier, a wet classifier, etc. depending on the purpose, but when removing coarse particles, a classification method that passes through a sieve is preferable because it can reliably achieve the purpose.
上記で得られた負極活物質の真密度は、例えば１．６ｇ／ｃｍ３以上２．０ｇ／ｃｍ３以下である。真密度は、得られる二次電池のエネルギー密度を向上させる観点から、１．７５ｇ／ｃｍ３以上が好ましく、１．８０ｇ／ｃｍ３以上がより好ましい。真密度は、真密度測定装置を用いて測定された値である。 The true density of the negative electrode active material obtained above is, for example, 1.6 g/cm 3 or more and 2.0 g/cm 3 or less. The true density is preferably 1.75 g/cm 3 or more, more preferably 1.80 g/cm 3 or more, from the viewpoint of improving the energy density of the obtained secondary battery. True density is a value measured using a true density measuring device.
負極活物質の平均粒径が小さすぎると、比表面積の大幅な上昇につれ、二次電池とした時、充放電時にＳＥＩの生成量が増えることで単位体積当たりの可逆充放電容量が低下することがある。一方、平均粒径が大きすぎると、電極膜作製時に集電体から剥離するおそれがある。よって、負極活物質の体積平均粒径は、２μｍ以上１５μｍ以下が好ましい。負極活物質の体積平均粒径は２．５μｍ以上が好ましく、３．０μｍ以上がより好ましい。また、体積平均粒径は、１２μｍ以下が好ましく、１０μｍ以下がより好ましい。 If the average particle size of the negative electrode active material is too small, as the specific surface area increases significantly, the amount of SEI produced during charging and discharging increases when used as a secondary battery, resulting in a decrease in reversible charge/discharge capacity per unit volume. There is. On the other hand, if the average particle size is too large, there is a risk that the particles will peel off from the current collector during electrode film production. Therefore, the volume average particle size of the negative electrode active material is preferably 2 μm or more and 15 μm or less. The volume average particle size of the negative electrode active material is preferably 2.5 μm or more, more preferably 3.0 μm or more. Further, the volume average particle diameter is preferably 12 μm or less, more preferably 10 μm or less.
負極活物質の比表面積は、０．３ｍ２／ｇ以上１０ｍ２／ｇ以下が好ましい。比表面積は０．５ｍ２／ｇ以上がより好ましく、１ｍ２／ｇ以上が特に好ましい。比表面積が上記範囲であると、電極作製時における溶媒の吸収量を適切に保つことができ、結着性を維持するための結着剤の使用量も適切に保つことができる。なお比表面積は、ＢＥＴ法により求めた値であり、窒素ガス吸着測定により求めることができ、例えば比表面積測定装置を用いて測定することができる。 The specific surface area of the negative electrode active material is preferably 0.3 m 2 /g or more and 10 m 2 /g or less. The specific surface area is more preferably 0.5 m 2 /g or more, particularly preferably 1 m 2 /g or more. When the specific surface area is within the above range, the amount of solvent absorbed during electrode production can be maintained appropriately, and the amount of binder used for maintaining binding properties can also be maintained appropriately. Note that the specific surface area is a value determined by the BET method, and can be determined by nitrogen gas adsorption measurement, for example, by using a specific surface area measuring device.
以下、実施例によって本発明を詳細に説明するが、本発明はこれらに限定されない。本実施例における［％］及び［部］は特段の指定がない限り「重量％」及び「重量部」を表すものとする。なお、ＮＶ（Non－Volatile）は、不揮発分を表す。 EXAMPLES Hereinafter, the present invention will be explained in detail with reference to Examples, but the present invention is not limited thereto. [%] and [parts] in this example represent "% by weight" and "parts by weight" unless otherwise specified. Note that NV (Non-Volatile) represents a non-volatile content.
実施例１
（ナノシリコン含有スラリー液の調製）
ビーズミルに平均粒径（Ｄ５０）３０００ｎｍの原料シリコン粒子１００部、特開２０１５－２２２７３３号公報の合成例１（［００９４］－［００９５］）に記載されている手法と同様の手法で調製したポリシロキサン－アクリル複合樹脂（ポリシロキサン（Ｐｃ）／アクリル（Ａｃ）＝６５／３５）を６７部（ＮＶ３０％のため固形分２０部）、メチルエチルケトン（ＭＥＫ）を４３０部加え、ビーズミルで６時間湿式粉砕、分散し、均一なスラリー液を得た。得られたスラリー液の作製直後の平均粒径（Ｄ５０）は８３ｎｍであり、これを７２時間静置した後に粒子径を測定すると８４ｎｍであり、変化率は１．２％とわずかであった。平均粒径（Ｄ５０）は、レーザー回折式粒度分布測定装置（マルバーン・パナリティカル社製、マスターサイザー３０００）で確認した。 Example 1
(Preparation of nanosilicon-containing slurry liquid)
100 parts of raw silicon particles with an average particle diameter (D50) of 3000 nm were placed in a bead mill, and a polyester prepared by a method similar to that described in Synthesis Example 1 ([0094]-[0095]) of JP-A-2015-222733 was placed in a bead mill. Add 67 parts of siloxane-acrylic composite resin (polysiloxane (Pc)/acrylic (Ac) = 65/35) (solid content 20 parts because NV is 30%) and 430 parts of methyl ethyl ketone (MEK), and wet mill for 6 hours in a bead mill. , to obtain a homogeneous slurry liquid. The average particle size (D50) of the obtained slurry liquid immediately after preparation was 83 nm, and when the particle size was measured after being left to stand for 72 hours, it was 84 nm, and the rate of change was as small as 1.2%. The average particle diameter (D50) was confirmed using a laser diffraction particle size distribution analyzer (Mastersizer 3000, manufactured by Malvern Panalytical).
（負極活物質の作製）
上記で得たスラリー液にフェノール樹脂１００部（スミライトレジン：ＰＲ－５３５７０、住友ベークライト株式会社製、ＮＶ３０％のため固形分３０部）と、上記で加えたポリシロキサン－アクリル複合樹脂（ポリシロキサン（Ｐｃ）／アクリル（Ａｃ）＝６５／３５）３３．５部（ＮＶ３０％のため固形分１０部；後添加）を加え、３０分間攪拌した後にバーコーターで薄膜化し、１０８℃で２時間乾燥させた。得られた乾燥物をある程度粉砕し、１０００℃で８時間焼成し、乳鉢で粉砕し、活物質化した。活物質の表面のＳｉの分布状況をＳＥＭ－ＥＤＸ（ＪＥＬ社製、ＪＳＭ－７８００Ｆ）で確認すると、図１のようにシリコン粒子表面にＳｉが均一に配位していることが観察できた。
(Preparation of negative electrode active material)
To the slurry liquid obtained above, 100 parts of phenol resin (Sumilite Resin: PR-53570, manufactured by Sumitomo Bakelite Co., Ltd., solid content 30 parts because NV is 30%) and the polysiloxane-acrylic composite resin (polysiloxane (Pc)/acrylic (Ac) = 65/35) 33.5 parts (solid content 10 parts for NV 30%; post-addition) was added, stirred for 30 minutes, formed into a thin film using a bar coater, and dried at 108°C for 2 hours. I let it happen. The obtained dried product was pulverized to some extent, baked at 1000° C. for 8 hours, and pulverized in a mortar to form an active material. When the distribution of Si on the surface of the active material was confirmed using SEM-EDX (manufactured by JEL, JSM-7800F), it was observed that Si was uniformly coordinated on the surface of the silicon particles as shown in FIG.
（電池評価）
次に、電池評価のため初期効率とサイクル効率を測定した。初期効率は８３％、３００回充放電後のサイクル効率は７８％と非常に良好な電池性能を示した。
電池評価は、二次電池充放電試験装置（北斗電工社製）を用いて測定した。室温２５℃、カットオフ電圧範囲が０．００５～１．５Ｖに、充放電レートが０．１Ｃ（１～３回）と０．２Ｃ（４サイクル以後）にし、定電流・定電圧式充電／定電流式放電の設定条件下で充放電特性の評価試験を行った。各充放電時の切り替え時には、３０分間、開回路で放置した。初回クーロン効率とサイクル特性（本願では１０サイクル時の容量維持率を指す）は以下のようにして求めた。
・サイクル効率（％）＝初回放電容量（ｍＡｈ／ｇ）／初回充電容量（ｍＡｈ／ｇ）
(Battery evaluation)
Next, initial efficiency and cycle efficiency were measured for battery evaluation. The initial efficiency was 83%, and the cycle efficiency after charging and discharging 300 times was 78%, showing very good battery performance.
Battery evaluation was performed using a secondary battery charge/discharge test device (manufactured by Hokuto Denko Co., Ltd.). The room temperature was 25°C, the cutoff voltage range was 0.005 to 1.5V, the charge/discharge rate was 0.1C (1 to 3 cycles) and 0.2C (after 4 cycles), and constant current/constant voltage charging/ An evaluation test of charging and discharging characteristics was conducted under constant current discharge settings. At each charge/discharge switch, the circuit was left open for 30 minutes. The initial coulombic efficiency and cycle characteristics (in this application, refers to the capacity retention rate at 10 cycles) were determined as follows.
・Cycle efficiency (%) = Initial discharge capacity (mAh/g) / Initial charge capacity (mAh/g)
実施例２－６
上記実施例１と同様の方法でナノシリコン含有スラリー液を調製して負極活物質を作製し、電池評価をした。実施例１からの変更点は下記表１のとおりである。実施例５では、原料シリコン粒子を粉砕処理して使用するのではなく既に粉砕処理後のシリコン粒子（平均粒径５０ｎｍ）をそのまま用いた。スラリー液の作製直後と７２時間静置後のシリコン粒子の平均粒径（Ｄ５０）、その変化率、及び電池評価を表１に示す。 Example 2-6
A nanosilicon-containing slurry liquid was prepared in the same manner as in Example 1, a negative electrode active material was produced, and a battery was evaluated. Changes from Example 1 are shown in Table 1 below. In Example 5, the raw material silicon particles were not used after being pulverized, but the silicon particles (average particle size: 50 nm) that had already been pulverized were used as they were. Table 1 shows the average particle diameter (D50) of the silicon particles, the rate of change thereof, and the battery evaluation immediately after the preparation of the slurry liquid and after standing for 72 hours.
比較例１
（ナノシリコン含有スラリー液の調整）
上記実施例１のポリシロキサン－アクリル樹脂をツイーン８０(＝ポリオキシエチレンソルビタンモノオレアート)３０部に変更した以外は同様にしてスラリー液を得た。
得られたスラリー液作製直後の平均粒径（Ｄ５０）は８０ｎｍであり、これを７２時間静置した後に粒子径を測定すると８５ｎｍであり、変化率は６．２％と大きく変化した。 Comparative example 1
(Adjustment of nanosilicon-containing slurry liquid)
A slurry liquid was obtained in the same manner as in Example 1 except that 30 parts of Tween 80 (=polyoxyethylene sorbitan monooleate) was used instead of the polysiloxane-acrylic resin.
The average particle diameter (D50) immediately after the preparation of the obtained slurry liquid was 80 nm, and when the particle diameter was measured after standing for 72 hours, it was 85 nm, and the rate of change was 6.2%, which was a large change.
（負極活物質の作製）
前記ナノシリコン含有スラリー液にＤＩＣ株式会社製ポリシロキサンアクリル複合樹脂（ポリシロキサン／アクリル＝６５／３５）を６７部（ＮＶ３０％のため固形分２０部）、フェノール樹脂１００部（ＮＶ３０％のため固形分３０部）を加え、３０分間攪拌した後にバーコーターで薄膜化し、１０８℃で２時間乾燥させた。その後、得られた乾燥物をある程度粉砕し、１０００℃で８時間焼成し、乳鉢で粉砕し、活物質化した。活物質の表面をＳＥＭ－ＥＤＸで確認すると、図２のように表面にＳｉは配位しているものの不均一であった。
(Preparation of negative electrode active material)
Into the nanosilicon-containing slurry liquid, 67 parts of polysiloxane acrylic composite resin (polysiloxane/acrylic = 65/35) manufactured by DIC Corporation (solid content 20 parts due to NV 30%) and 100 parts of phenol resin (solid content due to NV 30%) were added. After stirring for 30 minutes, the mixture was formed into a thin film using a bar coater and dried at 108°C for 2 hours. Thereafter, the obtained dried product was pulverized to some extent, baked at 1000° C. for 8 hours, and pulverized in a mortar to form an active material. When the surface of the active material was confirmed by SEM-EDX, it was found that although Si was coordinated on the surface as shown in FIG. 2, it was non-uniform.
（電池評価）
次に、電池評価については初期効率とサイクル効率について比較した。
初期効率は６３％、３００回充放電後のサイクル効率は５５％といずれも低い値を示した。
(Battery evaluation)
Next, regarding battery evaluation, initial efficiency and cycle efficiency were compared.
The initial efficiency was 63%, and the cycle efficiency after 300 charges and discharges was 55%, both of which were low values.
比較例２
上記比較例１との変更点と電池評価の結果は下記表１のとおりである。比較例２では、原料シリコン粒子を粉砕処理して使用するのではなく既に粉砕処理後のシリコン粒子（平均粒径５０ｎｍ）をそのまま用いた。 Comparative example 2
The changes from Comparative Example 1 and the results of battery evaluation are shown in Table 1 below. In Comparative Example 2, the raw material silicon particles were not pulverized and used, but the silicon particles (average particle size 50 nm) that had already been pulverized were used as they were.
上記表１より、実施例１－６では比較例１－２に比べて、Ｄ５０変化率が小さく、分散安定性が高いことが分かる。また、実施例１－６では比較例１－２に比べて、電池評価における初期効率やサイクル効率が高いことが分かる。よって、本発明のスラリー液は、分散安定性が高く、これを用いて負極活物質を作製した二次電池における容量維持率や初回クーロン効率といった充放電性能を高く維持できると言える。 From Table 1 above, it can be seen that Example 1-6 had a smaller D50 change rate and higher dispersion stability than Comparative Example 1-2. Further, it can be seen that the initial efficiency and cycle efficiency in the battery evaluation are higher in Example 1-6 than in Comparative Example 1-2. Therefore, it can be said that the slurry liquid of the present invention has high dispersion stability and can maintain high charge/discharge performance such as capacity retention rate and initial Coulombic efficiency in a secondary battery in which a negative electrode active material is prepared using the slurry liquid.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2015222733A (en) | 2012-12-19 | 2015-12-10 | Dic株式会社 | Active material for non-aqueous secondary battery negative electrodes and non-aqueous secondary battery |
| JP2019057487A (en) | 2017-02-28 | 2019-04-11 | 荒川化学工業株式会社 | Binder aqueous solution for lithium ion battery, slurry for lithium ion battery, manufacturing methods thereof, electrode for lithium ion battery, separator for lithium ion battery, separator/electrode laminate for lithium ion battery, and lithium ion battery |
| JP2021114483A (en) | 2018-12-19 | 2021-08-05 | Dic株式会社 | Silicon nanoparticles, active material for negative electrode of non-aqueous secondary battery including the same, and secondary battery |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2015222733A (en) | 2012-12-19 | 2015-12-10 | Dic株式会社 | Active material for non-aqueous secondary battery negative electrodes and non-aqueous secondary battery |
| JP2019057487A (en) | 2017-02-28 | 2019-04-11 | 荒川化学工業株式会社 | Binder aqueous solution for lithium ion battery, slurry for lithium ion battery, manufacturing methods thereof, electrode for lithium ion battery, separator for lithium ion battery, separator/electrode laminate for lithium ion battery, and lithium ion battery |
| JP2021114483A (en) | 2018-12-19 | 2021-08-05 | Dic株式会社 | Silicon nanoparticles, active material for negative electrode of non-aqueous secondary battery including the same, and secondary battery |
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