JP2018022656A - Nonaqueous secondary battery - Google Patents
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Abstract
Description
本発明は、非水系二次電池に関する。 The present invention relates to a non-aqueous secondary battery.
リチウムイオン二次電池等の非水系二次電池では、更なる電池性能の向上が検討されている。例えば特許文献１には、非水電解液に対して難溶なポリマーを添着させた鱗片状黒鉛質粒子と、アスペクト比が１〜４である炭素質粒子と、を含んだ負極を備える非水系二次電池が開示されている。特許文献１には、上記構成によって電池の安定性や充放電レート特性等の諸特性を向上し得る旨が記載されている。 In non-aqueous secondary batteries such as lithium ion secondary batteries, further improvements in battery performance are being studied. For example, Patent Document 1 discloses a non-aqueous system including a negative electrode including scaly graphite particles impregnated with a polymer that is hardly soluble in a non-aqueous electrolyte and carbonaceous particles having an aspect ratio of 1 to 4. A secondary battery is disclosed. Patent Document 1 describes that the above-described configuration can improve various characteristics such as battery stability and charge / discharge rate characteristics.
ところで、非水系二次電池のなかには、例えば２Ｃ（特には５Ｃ）以上のハイレートで充放電を繰り返す態様で使用されるものがある。その典型が、車両搭載用の高出力電源として用いられる電池である。このような電池は、例えば特許文献１に記載されるような電池に比べて、充放電サイクルに伴う負荷が大きい。つまり、ハイレート充放電時には、活物質の膨張収縮に伴うポンプ効果や非水電解液の体積膨張等の影響で、非水電解液が電極体から過剰に押し出されることがある。かかる態様での使用を繰り返すと、非水電解液中の電荷担体の濃度にムラが生じたり、電極で液枯れを生じたりすることがある。その結果、電荷担体の移動に伴う負荷が増大して、電池の内部抵抗が上昇することがある。 By the way, some non-aqueous secondary batteries are used in such a manner that charge and discharge are repeated at a high rate of, for example, 2C (particularly 5C) or more. A typical example is a battery used as a high-output power source mounted on a vehicle. Such a battery has a larger load associated with a charge / discharge cycle than a battery described in Patent Document 1, for example. That is, at the time of high-rate charge / discharge, the non-aqueous electrolyte solution may be excessively pushed out of the electrode body due to the pump effect accompanying the expansion and contraction of the active material, the volume expansion of the non-aqueous electrolyte solution, or the like. If the use in such a mode is repeated, the concentration of the charge carrier in the non-aqueous electrolyte may be uneven, or the electrode may be drained. As a result, the load accompanying the movement of the charge carriers increases, and the internal resistance of the battery may increase.
本発明者が、負極から非水電解液が過剰に押し出されてしまう現象について種々検討を行ったところ、この現象には負極に加わる応力が関係していることが判明した。すなわち、ハイレート充放電時には、活物質や非水電解液等の膨張によって電池ケース内の圧力が高まり、負極に応力が負荷される。このため、ハイレート充放電を繰り返すと、負極活物質層が徐々に潰れて、非水電解液の保持機能が低下してしまう。したがって、応力の負荷に対して潰れが生じ難い（形状保持性の高い）負極を備えた非水系二次電池の創出が求められている。 The inventor conducted various studies on the phenomenon in which the non-aqueous electrolyte is excessively extruded from the negative electrode, and it has been found that this phenomenon is related to the stress applied to the negative electrode. That is, at the time of high rate charge / discharge, the pressure in the battery case increases due to expansion of the active material, the non-aqueous electrolyte, etc., and stress is applied to the negative electrode. For this reason, when high-rate charge / discharge is repeated, the negative electrode active material layer is gradually crushed and the retention function of the non-aqueous electrolyte is degraded. Therefore, the creation of a non-aqueous secondary battery including a negative electrode that is less likely to be crushed by stress load (high shape retention) is demanded.
本発明はかかる点に鑑みてなされたものであり、その目的は、負極の形状保持性を向上して、ハイレートサイクル特性に優れた非水系二次電池を提供することにある。 This invention is made | formed in view of this point, The objective is to improve the shape retainability of a negative electrode and to provide the non-aqueous secondary battery excellent in the high rate cycle characteristic.
本発明により、正極と負極と非水電解液とを備える非水系二次電池が提供される。上記負極は、負極活物質粉末を含む負極活物質層を備える。上記負極活物質粉末は、第１の負極活物質と、上記第１の負極活物質よりも平均粒径の大きな第２の負極活物質とを含む。上記第２の負極活物質は、人造黒鉛、ハードカーボンおよびソフトカーボンのうちの１つ以上である。上記負極活物質粉末の体積基準の粒度頻度分布曲線において、頻度の最大値をＡとし、上記負極活物質層の平均厚みの９０％に相当する大きさの粒径の頻度をＢとしたときに、上記Ａと上記Ｂとが、次の式（１）：０．０７５≦（Ｂ／Ａ）≦０．１０９；を満たす。 According to the present invention, a non-aqueous secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte is provided. The negative electrode includes a negative electrode active material layer containing a negative electrode active material powder. The negative electrode active material powder includes a first negative electrode active material and a second negative electrode active material having an average particle size larger than that of the first negative electrode active material. The second negative electrode active material is one or more of artificial graphite, hard carbon, and soft carbon. In the volume-based particle size frequency distribution curve of the negative electrode active material powder, when the maximum value of frequency is A and the frequency of particle diameters corresponding to 90% of the average thickness of the negative electrode active material layer is B A and B satisfy the following formula (1): 0.075 ≦ (B / A) ≦ 0.109;
負極活物質粉末の粒度頻度分布曲線が上記式を満たすことで、負極活物質層が潰れ難くなる。これにより、負極の形状保持性を向上することができ、非水電解液の保持機能を安定的に発揮することができる。したがって、ハイレート充放電を繰り返しても抵抗が増大し難く、ハイレートサイクル特性に優れた非水系二次電池を実現することができる。 When the particle size frequency distribution curve of the negative electrode active material powder satisfies the above formula, the negative electrode active material layer is hardly crushed. Thereby, the shape maintenance property of a negative electrode can be improved and the holding | maintenance function of a non-aqueous electrolyte can be exhibited stably. Accordingly, it is possible to realize a non-aqueous secondary battery that does not easily increase in resistance even after repeated high-rate charge / discharge and has excellent high-rate cycle characteristics.
本発明の好適な一態様において、上記負極活物質粉末の平均アスペクト比が１．０以上１．５以下である。これにより、上記式（１）を好適に満たすことができる。また、負極活物質粉末の形状を略球状とすることで、負極活物質粉末を構成する粒子の長軸方向が負極集電体に対して平行に配向することを抑えることができる。したがって、本発明の効果を高いレベルで奏することができる。 In a preferred aspect of the present invention, the negative electrode active material powder has an average aspect ratio of 1.0 or more and 1.5 or less. Thereby, the said Formula (1) can be satisfy | filled suitably. Moreover, it can suppress that the major axis direction of the particle | grains which comprise negative electrode active material powder orientates in parallel with a negative electrode collector by making the shape of negative electrode active material powder into a substantially spherical shape. Therefore, the effect of the present invention can be achieved at a high level.
なお、活物質の粒度頻度分布に関する先行技術文献として、特許文献２が挙げられる。
以下、本発明の好適な実施形態を説明する。なお、本明細書において特に言及している事項（例えば、負極活物質層の構成）以外の事柄であって本発明の実施に必要な事柄（例えば、本発明を特徴付けない電池の構成要素や一般的な製造プロセス）は、当該分野における従来技術に基づく当業者の設計事項として把握され得る。本発明は、本明細書に開示されている内容と当該分野における技術常識とに基づいて実施することができる。なお、本明細書において「Ａ〜Ｂ（ただし、Ａ，Ｂが任意の値）」という表現は、特に断らない限りＡ，Ｂの値（上限値および下限値）を包含するものとする。 Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification (for example, the structure of the negative electrode active material layer) and matters necessary for the implementation of the present invention (for example, battery components not characterizing the present invention) The general manufacturing process) can be understood as a design matter of a person skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In the present specification, the expression “A to B (where A and B are arbitrary values)” includes values of A and B (upper limit value and lower limit value) unless otherwise specified.
ここに開示される非水系二次電池は、正極と負極と非水電解液とを備える。以下、各構成要素について順に説明する。 The non-aqueous secondary battery disclosed herein includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. Hereinafter, each component will be described in order.
正極は、典型的には、正極集電体と、該正極集電体上に固着された正極活物質層とを備える。正極集電体としては、導電性の良好な金属（例えばアルミニウム）からなる導電性部材を好適に採用し得る。正極活物質層は、少なくとも正極活物質粉末を含み、さらに他の任意成分（例えばバインダや導電材粉末等）を含み得る。正極活物質粉末としては、例えば、リチウム元素と遷移金属元素とを含むリチウム遷移金属複合酸化物粉末を採用し得る。バインダとしては、例えば、ポリフッ化ビニリデン（ＰＶｄＦ）等のハロゲン化ビニル樹脂を採用し得る。導電材粉末としては、例えば、アセチレンブラックやケッチェンブラック等の炭素材料を採用し得る。 The positive electrode typically includes a positive electrode current collector and a positive electrode active material layer fixed on the positive electrode current collector. As the positive electrode current collector, a conductive member made of a metal having good conductivity (for example, aluminum) can be suitably employed. The positive electrode active material layer includes at least a positive electrode active material powder, and may further include other optional components (such as a binder and a conductive material powder). As the positive electrode active material powder, for example, a lithium transition metal composite oxide powder containing a lithium element and a transition metal element can be employed. As the binder, for example, a vinyl halide resin such as polyvinylidene fluoride (PVdF) can be adopted. As the conductive material powder, for example, a carbon material such as acetylene black or ketjen black can be employed.
負極は、典型的には、負極集電体と、該負極集電体上に固着された負極活物質層とを備える。負極集電体としては、導電性の良好な金属（例えば銅）からなる導電性部材を好適に採用し得る。負極活物質層は、少なくとも負極活物質粉末を含み、さらに他の任意成分（例えばバインダや増粘剤等）を含み得る。バインダとしては、例えば、スチレンブタジエンゴム（ＳＢＲ）等を採用し得る。増粘剤としては、例えば、カルボキシメチルセルロース（ＣＭＣ）等を採用し得る。 The negative electrode typically includes a negative electrode current collector and a negative electrode active material layer fixed on the negative electrode current collector. As the negative electrode current collector, a conductive member made of a metal having good conductivity (for example, copper) can be suitably used. The negative electrode active material layer includes at least a negative electrode active material powder, and may further include other optional components (for example, a binder, a thickener, and the like). As the binder, for example, styrene butadiene rubber (SBR) or the like can be adopted. As the thickener, for example, carboxymethylcellulose (CMC) can be employed.
負極活物質粉末としては、炭素材料、例えば、天然黒鉛や人造黒鉛等の黒鉛（グラファイト）材料、難黒鉛化非晶質炭素（ハードカーボン）や易黒鉛化非晶質炭素（ソフトカーボン）等の非晶質炭素材料、それらの複合材料等を採用し得る。これらの材料は１種を単独で、または２種以上を適宜組みあわせて用いることができる。なかでも負極活物質粉末がハードカーボンを含むことが好ましい。これにより、充電時の負極の膨張を小さく抑えることができる。また、負極活物質層の形状を長期にわたってより良く安定的に維持することができる。 Examples of the negative electrode active material powder include carbon materials such as graphite materials such as natural graphite and artificial graphite, non-graphitizable amorphous carbon (hard carbon), and easily graphitized amorphous carbon (soft carbon). An amorphous carbon material, a composite material thereof, or the like can be adopted. These materials can be used singly or in appropriate combination of two or more. Especially, it is preferable that negative electrode active material powder contains a hard carbon. Thereby, the expansion | swelling of the negative electrode at the time of charge can be suppressed small. In addition, the shape of the negative electrode active material layer can be maintained more stably over a long period of time.
負極活物質粉末の形状は、略球状であるとよい。言い換えれば、負極活物質粉末の平均アスペクト比（粒子に外接する最小の長方形において、短軸方向の長さに対する長軸方向の長さの比）が、概ね１〜１．５、例えば１．１〜１．５であるとよい。２種類以上の負極活物質材料を組みあわせて用いる場合は、各材料の平均アスペクト比が上記範囲であるとよい。これにより、粒度頻度分布曲線が式（１）の範囲を好適に満たし得る。また、負極活物質粉末のアスペクト比が大きいと、負極活物質粒子の長軸方向が負極集電体に対して平行に配向され易くなる。負極活物質粉末の形状を略球状とすることで、このような配向を抑制して、ここに開示される技術の効果を高いレベルで奏することができる。 The shape of the negative electrode active material powder is preferably substantially spherical. In other words, the average aspect ratio of the negative electrode active material powder (ratio of the length in the major axis direction to the length in the minor axis direction in the smallest rectangle circumscribing the particles) is approximately 1 to 1.5, for example 1.1. It is good to be -1.5. When two or more types of negative electrode active material are used in combination, the average aspect ratio of each material is preferably in the above range. Thereby, a particle size frequency distribution curve can satisfy the range of a formula (1) suitably. Moreover, when the aspect ratio of the negative electrode active material powder is large, the major axis direction of the negative electrode active material particles is easily aligned in parallel to the negative electrode current collector. By making the shape of the negative electrode active material powder substantially spherical, such an orientation can be suppressed, and the effects of the technique disclosed herein can be achieved at a high level.
負極活物質粉末の面間隔（ｄ００２）は、概ね３．５Å以上、例えば３．７Å以上であるとよい。２種類以上の負極活物質材料を組みあわせて用いる場合は、少なくとも一つ（好ましくは２つ以上）の材料の面間隔が上記範囲であるとよい。このような負極活物質粉末は、リチウムを挿入した場合の面間隔（ｄ００２）以上の結晶構造を最初から有する。面間隔が上記範囲の負極活物質粉末を用いることで、充放電時の負極の膨張・収縮を小さく抑えることができる。 The inter-surface spacing (d002) of the negative electrode active material powder is preferably about 3.5 mm or more, for example, 3.7 mm or more. In the case where two or more types of negative electrode active material are used in combination, the interplanar spacing of at least one (preferably two or more) materials is preferably in the above range. Such a negative electrode active material powder has a crystal structure from the beginning having a face spacing (d002) or more when lithium is inserted. By using the negative electrode active material powder having a surface spacing within the above range, expansion / contraction of the negative electrode during charging / discharging can be suppressed to a low level.
負極活物質粉末は、体積基準の粒度頻度分布曲線において、頻度の最大値をＡとし、負極活物質層の平均厚みの９０％に相当する大きさの粒径の頻度をＢとしたときに、上記Ａと上記Ｂとが、次の式（１）：０．０７５≦（Ｂ／Ａ）≦０．１０９；を満たす。なお、Ｂ／Ａは、負極活物質粉末中の大きな粒子の存在割合を指標化したものである。高温保存特性の観点からは、Ｂ／Ａが０．０９５以下であるとよい。粒度頻度分布曲線において、頻度の最大値Ａにおける粒径は、負極活物質層の平均厚みの概ね７０％以下、例えば１０〜５０％に相当する大きさであってもよい。 In the volume-based particle size frequency distribution curve, the negative electrode active material powder has a maximum value of A, and a particle size frequency corresponding to 90% of the average thickness of the negative electrode active material layer is B. The above A and B satisfy the following formula (1): 0.075 ≦ (B / A) ≦ 0.109; B / A is an index of the ratio of large particles present in the negative electrode active material powder. From the viewpoint of high temperature storage characteristics, B / A is preferably 0.095 or less. In the particle size frequency distribution curve, the particle size at the maximum frequency A may be approximately 70% or less, for example, 10 to 50% of the average thickness of the negative electrode active material layer.
図１は、一実施形態に係る負極１０の模式的な断面図である。負極１０は、負極集電体１２と、負極集電体１２上に固着された負極活物質層１４とを備える。負極活物質層１４の平均厚みＴは、概ね２０〜２００μｍ、例えば３０〜１００μｍであってもよい。負極活物質層１４は、第１の負極活物質１６と、第１の負極活物質１６よりも平均粒径の大きな第２の負極活物質１８とを含んでいる。
第１の負極活物質１６は、質量基準で、負極活物質粉末全体の５０質量％以上を占めるメインの負極活物質材料である。第１の負極活物質１６は、高容量の観点から、黒鉛系材料（例えば非晶質コート天然黒鉛）であるとよい。第１の負極活物質１６は、高容量の観点から、質量基準で、負極活物質層１４全体の５０質量％以上、例えば８０％以上であるとよい。第２の負極活物質１８は、高硬度の観点から、人造黒鉛、ハードカーボン、ソフトカーボンのうちの１つ以上であるとよい。第２の負極活物質１８は、質量基準で、負極活物質粉末全体の５〜１０％程度であるとよい。第２の負極活物質１８は、質量基準で、負極活物質層１４全体の５〜１０％程度であるとよい。
FIG. 1 is a schematic cross-sectional view of a
The first negative electrode
非水電解液は、典型的には、支持塩と非水溶媒とを含んでいる。支持塩としては、例えばＬｉＰＦ６、ＬｉＢＦ４等のリチウム塩を採用し得る。非水溶媒としては、例えば、カーボネート類、エステル類、エーテル類等の非プロトン性溶媒を採用し得る。非水電解液は、さらに各種添加剤等の任意成分（例えば皮膜形成剤やガス発生剤等）を含み得る。 A non-aqueous electrolyte typically includes a supporting salt and a non-aqueous solvent. As the supporting salt, for example, a lithium salt such as LiPF 6 or LiBF 4 can be adopted. As the non-aqueous solvent, for example, aprotic solvents such as carbonates, esters, ethers and the like can be adopted. The non-aqueous electrolyte may further contain optional components such as various additives (for example, a film forming agent and a gas generating agent).
ここに開示される非水系二次電池は、従来品に比べてハイレートサイクル特性に優れたものである。したがって、ハイレート充放電を繰り返すような用途で好適に採用することができる。例えば、プラグインハイブリッド自動車、ハイブリッド自動車、電気自動車等の動力源（駆動用電源）として好適に用いることができる。 The non-aqueous secondary battery disclosed herein is superior in high-rate cycle characteristics compared to conventional products. Therefore, it can employ | adopt suitably by the use which repeats high-rate charging / discharging. For example, it can be suitably used as a power source (drive power source) for plug-in hybrid vehicles, hybrid vehicles, electric vehicles, and the like.
以下、本発明に関するいくつかの実施例を説明するが、本発明をかかる具体例に示すものに限定することを意図したものではない。 Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to the specific examples.
≪試験例Ｉ≫
正極活物質材料としてのＬｉＮｉ１／３Ｃｏ１／３Ｍｎ１／３Ｏ２と、導電材と、バインダとしてのポリフッ化ビニリデン（ＰＶｄＦ）とを、アルミニウム箔（正極集電体）に固着させ、正極集電体上に正極活物質層を備えた正極シートを作製した。
≪Test Example I≫
LiNi 1/3 Co 1/3 Mn 1/3 O 2 as a positive electrode active material, a conductive material, and polyvinylidene fluoride (PVdF) as a binder are fixed to an aluminum foil (positive electrode current collector), A positive electrode sheet having a positive electrode active material layer on a positive electrode current collector was produced.
次に、負極活物質材料として、非晶質コート球形化天然黒鉛（第１の負極活物質）と、平均アスペクト比が異なる４種類のハードカーボン（第２の負極活物質）とを用意した。次に、各例につき、第１の負極活物質と第２の負極活物質とを混合して、負極活物質粉末を調製し、体積基準の粒度頻度分布曲線を測定した。図２には、一例として比較例１の粒度頻度分布曲線を示している。
次に、この負極活物質粉末と、バインダとしてのスチレン−ブタジエン共重合体（ＳＢＲ）と、増粘剤としてのカルボキシメチルセルロース（ＣＭＣ）とを混練して、スラリーを調製した。このスラリーを銅箔（負極集電体）に固着させ、負極集電体上に平均厚みが凡そ３５μｍの負極活物質層を備えた負極シートを作製した。負極活物質層に占める第２の負極活物質の割合を表１に示す。また、負極活物質粉末の粒度頻度分布曲線から、Ａ，Ｂの値を読み取り、Ｂ／Ａを算出した。
Next, amorphous coated spheroidized natural graphite (first negative electrode active material) and four types of hard carbon (second negative electrode active material) having different average aspect ratios were prepared as negative electrode active material materials. Next, for each example, the first negative electrode active material and the second negative electrode active material were mixed to prepare a negative electrode active material powder, and a volume-based particle size frequency distribution curve was measured. FIG. 2 shows a particle size frequency distribution curve of Comparative Example 1 as an example.
Next, this negative electrode active material powder, a styrene-butadiene copolymer (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were kneaded to prepare a slurry. This slurry was fixed to a copper foil (negative electrode current collector), and a negative electrode sheet provided with a negative electrode active material layer having an average thickness of about 35 μm on the negative electrode current collector was produced. Table 1 shows the ratio of the second negative electrode active material in the negative electrode active material layer. Moreover, the values of A and B were read from the particle size frequency distribution curve of the negative electrode active material powder, and B / A was calculated.
次に、上記作製した正極シートと負極シートとを、セパレータシートを介して積層、捲回して捲回電極体を作製した。この捲回電極体を円筒形状の電池ケースに収容した後、非水電解液を注液した。非水電解液としては、エチレンカーボネートとエチルメチルカーボネートとジメチルカーボネートとを、体積比率が３０：４０：３０となるように混合した混合溶媒に、支持塩としてのＬｉＰＦ６を１．１ｍｏｌ／Ｌの濃度で溶解させたものを使用した。このようにして、円筒型のリチウムイオン二次電池（実施例１〜７、比較例１〜４、設計容量：０．５Ａｈ）を構築した。 Next, the produced positive electrode sheet and negative electrode sheet were laminated and wound through a separator sheet to produce a wound electrode body. After this wound electrode body was accommodated in a cylindrical battery case, a non-aqueous electrolyte was injected. As a non-aqueous electrolyte, 1.1 mol / L of LiPF 6 as a supporting salt was mixed in a mixed solvent in which ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were mixed so that the volume ratio was 30:40:30. What was dissolved in the concentration was used. In this way, cylindrical lithium ion secondary batteries (Examples 1 to 7, Comparative Examples 1 to 4, design capacity: 0.5 Ah) were constructed.
＜初期特性＞ ２５℃の環境下において、初期容量と初期抵抗を測定した。具体的には、上記構築した電池を電圧が４．１Ｖとなるまで１／３Ｃのレートで定電流充電した後、電流値が０．０２Ｃとなるまで定電圧充電した。次に、電圧が３Ｖとなるまで１／３Ｃのレートで定電流放電し、このときのＣＣ放電容量を初期容量とした。次に、上記電池をＳＯＣ６０％の状態に調整した。この電池について、１０Ｃのレートで１０秒間の定電流放電を行い、電圧降下量を測定した。そして、電圧降下量の値を対応する電流値で除すことにより、初期抵抗を算出した。
<Initial characteristics> Initial capacity and initial resistance were measured in an environment of 25 ° C. Specifically, the battery thus constructed was charged with a constant current at a rate of 1/3 C until the voltage reached 4.1 V, and then charged with a constant voltage until the current value reached 0.02 C. Next, constant current discharge was performed at a rate of 1/3 C until the voltage reached 3 V, and the CC discharge capacity at this time was defined as the initial capacity. Next, the battery was adjusted to
＜ハイレートサイクル特性＞ ２５℃の環境下において、上記電池に対しハイレート充放電を３０００サイクル繰り返した。充放電条件は、２０Ｃのレートで４０秒間定電流充電した後、８Ｃのレートで１００秒間定電流放電するものとした。そして、ハイレートサイクル試験終了後の電池について、初期抵抗と同様に抵抗を求め、ハイレートサイクル試験前後の抵抗の比較から、ハイレート抵抗増加率（％）を算出した。結果を表１に示す。 <High Rate Cycle Characteristics> In the environment at 25 ° C., high rate charge / discharge was repeated 3000 cycles for the battery. The charging / discharging conditions were such that constant current charging was performed at a rate of 20 C for 40 seconds and then constant current discharging was performed at a rate of 8 C for 100 seconds. And about the battery after completion | finish of a high rate cycle test, resistance was calculated | required similarly to initial stage resistance, and the high rate resistance increase rate (%) was computed from the comparison of the resistance before and behind a high rate cycle test. The results are shown in Table 1.
＜高温保存特性＞ 上記電池をＳＯＣ８０％の状態に調整した後、６０℃の環境下で６０日間保存した。そして、高温保存試験終了後の電池について、初期容量と同様に電池容量を求め、高温保存試験前後の電池容量の比較から、保存後容量維持率（％）を算出した。結果を表１に示す。 <High temperature storage characteristic> After adjusting the said battery to the state of SOC80%, it preserve | saved for 60 days in a 60 degreeC environment. And about the battery after completion | finish of a high temperature storage test, battery capacity was calculated | required similarly to the initial capacity, and the capacity retention rate (%) after storage was calculated from the comparison of the battery capacity before and after the high temperature storage test. The results are shown in Table 1.
表１に示すように、Ｂ／Ａが０．０７５未満の比較例１，２では、ハイレート抵抗増加率が高かった。これは、ハイレート充放電時に負極に加わる応力によって負極活物質層が潰れてしまい、負極の非水電解液保持機能が低下したためと考えられる。また、Ｂ／Ａが０．１０９を超える比較例３でも、ハイレート抵抗増加率が高かった。これは、第２の負極活物質のアスペクト比が大きいために、負極活物質が負極集電体に対して平行に配向し易くなり、ここに開示される技術の効果が低下したためと考えられる。また、比較例４では、ハイレート抵抗増加率は抑えられていたものの、高温保存特性が大きく低下した。これは、第２の負極活物質の含有量が多いために、セパレータと干渉して自己放電が起こり易くなったためと考えられる。 As shown in Table 1, in Comparative Examples 1 and 2 where B / A was less than 0.075, the high rate resistance increase rate was high. This is presumably because the negative electrode active material layer was crushed by the stress applied to the negative electrode during high-rate charge / discharge, and the nonaqueous electrolyte holding function of the negative electrode was reduced. In Comparative Example 3 where B / A exceeded 0.109, the high rate resistance increase rate was high. This is probably because the negative electrode active material is easily oriented in parallel to the negative electrode current collector because the aspect ratio of the second negative electrode active material is large, and the effect of the technique disclosed herein is reduced. In Comparative Example 4, the high-rate resistance increase rate was suppressed, but the high-temperature storage characteristics were greatly deteriorated. This is presumably because the content of the second negative electrode active material is large, so that self-discharge easily occurs due to interference with the separator.
これら比較例に対して、Ｂ／Ａが０．０７５〜０．１０９である実施例１〜７では、ハイレート抵抗増加率が低く抑えられていた。また、高温保存特性が大きく低下することもなかった。かかる結果は、ここに開示される技術の意義を示している。 Compared to these comparative examples, in Examples 1 to 7 where B / A is 0.075 to 0.109, the high rate resistance increase rate was kept low. Further, the high temperature storage characteristics were not greatly deteriorated. Such a result indicates the significance of the technology disclosed herein.
≪試験例ＩＩ≫
第２の負極活物質を表２のように変更したこと以外は、上記実施例５と同様にリチウムイオン二次電池（実施例８，９、比較例５）を構築し、評価した。結果を表２に示す。
≪Test Example II≫
A lithium ion secondary battery (Examples 8 and 9 and Comparative Example 5) was constructed and evaluated in the same manner as in Example 5 except that the second negative electrode active material was changed as shown in Table 2. The results are shown in Table 2.
表２に示すように、第２の負極活物質として球形化天然黒鉛を用いた比較例５では、ハイレート抵抗増加率が高かった。これは、球形化天然黒鉛が柔らかいために、ハイレート充放電時に負極に加わる応力によって負極活物質層が潰れてしまい、負極の非水電解液保持機能が低下したためと考えられる。これに対して、第２の負極活物質として人造黒鉛やソフトカーボンを用いた実施例８，９では、第２の負極活物質としてハードカーボンを用いた上記実施例５と同等の効果が得られていた。 As shown in Table 2, in Comparative Example 5 in which spheroidized natural graphite was used as the second negative electrode active material, the high rate resistance increase rate was high. This is presumably because the spheroidized natural graphite is soft, so that the negative electrode active material layer is crushed by the stress applied to the negative electrode during high-rate charge / discharge, and the nonaqueous electrolyte holding function of the negative electrode is reduced. On the other hand, in Examples 8 and 9 using artificial graphite or soft carbon as the second negative electrode active material, the same effect as in Example 5 using hard carbon as the second negative electrode active material is obtained. It was.
以上、本発明を詳細に説明したが、上記実施形態および実施例は例示にすぎず、ここに開示される発明には上述の具体例を様々に変形、変更したものが含まれる。 As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and modified the above-mentioned specific example is included in the invention disclosed here.
１０ 負極
１２ 負極集電体
１４ 負極活物質層
１６，１８ 負極活物質
DESCRIPTION OF
Claims (2)
前記負極は、負極活物質粉末を含む負極活物質層を備え、
前記負極活物質粉末は、第１の負極活物質と、前記第１の負極活物質よりも平均粒径の大きな第２の負極活物質とを含み、
前記第２の負極活物質は、人造黒鉛、ハードカーボンおよびソフトカーボンのうちの１つ以上であり、
前記負極活物質粉末の体積基準の粒度頻度分布曲線において、頻度の最大値をＡとし、前記負極活物質層の平均厚みの９０％に相当する大きさの粒径の頻度をＢとしたときに、前記Ａと前記Ｂとが、次の式（１）：
０．０７５≦（Ｂ／Ａ）≦０．１０９ （１）；を満たす、非水系二次電池。 A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The negative electrode includes a negative electrode active material layer containing a negative electrode active material powder,
The negative electrode active material powder includes a first negative electrode active material and a second negative electrode active material having an average particle size larger than that of the first negative electrode active material,
The second negative electrode active material is one or more of artificial graphite, hard carbon, and soft carbon,
In the volume-based particle size frequency distribution curve of the negative electrode active material powder, when the maximum value of frequency is A and the frequency of particle diameters corresponding to 90% of the average thickness of the negative electrode active material layer is B , A and B are represented by the following formula (1):
A nonaqueous secondary battery satisfying 0.075 ≦ (B / A) ≦ 0.109 (1);
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| WO2022099457A1 (en) * | 2020-11-10 | 2022-05-19 | 宁德新能源科技有限公司 | Negative electrode active material, electrochemical apparatus using same, and electronic device |
| CN115461896A (en) * | 2021-03-19 | 2022-12-09 | 积水化学工业株式会社 | Positive electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery, battery module, and battery system using same |
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| WO2022099457A1 (en) * | 2020-11-10 | 2022-05-19 | 宁德新能源科技有限公司 | Negative electrode active material, electrochemical apparatus using same, and electronic device |
| CN115461896A (en) * | 2021-03-19 | 2022-12-09 | 积水化学工业株式会社 | Positive electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery, battery module, and battery system using same |
| US11811062B2 (en) | 2021-03-19 | 2023-11-07 | Sekisui Chemical Co., Ltd. | Positive electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery, battery module and battery system using the same |
| US11862798B2 (en) | 2021-03-19 | 2024-01-02 | Sekisui Chemical Co., Ltd. | Positive electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery, battery module and battery system using the same |
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