JP7148873B2 - Manufacturing method of negative electrode active material - Google Patents
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Description
本発明は、リチウムイオン二次電池に用いられる負極活物質材料の製造方法に関する。詳しくは、リチウムイオンを吸蔵および放出可能な炭素粒子（負極活物質）の表面にチタン化合物からなる被覆物が形成された負極活物質材料の形成方法に関する。 The present invention relates to a method for producing a negative electrode active material used in lithium ion secondary batteries. Specifically, the present invention relates to a method of forming a negative electrode active material in which a coating made of a titanium compound is formed on the surface of carbon particles (negative electrode active material) capable of intercalating and deintercalating lithium ions.
リチウムイオン二次電池は、既存の電池に比べて軽量かつエネルギー密度が高いことから、近年、パソコンや携帯端末等のいわゆるポータブル電源さらには車両駆動用電源として好ましく用いられている。リチウムイオン二次電池は、特に、電気自動車（ＥＶ）、ハイブリッド自動車（ＨＶ）、プラグインハイブリッド自動車（ＰＨＶ）等の車両の駆動用高出力電源として、益々の普及が期待されている。 Lithium ion secondary batteries are lighter in weight and have higher energy density than existing batteries, and thus, in recent years, they have been favorably used as so-called portable power sources for personal computers, portable terminals, and the like, as well as power sources for driving vehicles. Lithium-ion secondary batteries are expected to become increasingly popular as high-output power sources for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV).
この種のリチウムイオン二次電池では、構造的に安定でありリチウムイオンの吸蔵／放出も比較的良好なことから、負極活物質として黒鉛等の炭素粒子がよく用いられている。さらに、かかる黒鉛等からなる炭素粒子のリチウムイオン拡散経路を増大させ、抵抗を低減するために当該炭素粒子の表面を他の化合物で被覆することが行われている。例えば、以下の特許文献１には、炭素粒子の表面をチタン酸リチウム（ＬＴＯ）で被覆する技術が開示されている。 In this type of lithium ion secondary battery, carbon particles such as graphite are often used as the negative electrode active material because they are structurally stable and exhibit relatively good lithium ion absorption/desorption. Furthermore, in order to increase the lithium ion diffusion path of such carbon particles made of graphite or the like and to reduce the resistance, the surfaces of the carbon particles are coated with other compounds. For example, Patent Document 1 below discloses a technique of coating the surface of carbon particles with lithium titanate (LTO).
ところで、負極活物質たる炭素粒子の表面に存在するチタン酸リチウム（ＬＴＯ）は、上述したリチウムイオン拡散経路の増大やそれに伴う抵抗の低減に加えて、内部短絡や釘刺し試験等において瞬間的に大電流が負極側に流れた際の安全性を向上させ得るという効果を奏する。即ち、チタン酸リチウムは、放電状態（即ち、リチウムイオンがＬＴＯから放出された酸化状態）では絶縁体となり導電性を示さなくなるため、短絡電流を抑制することができる。
しかしながら、特許文献１に記載されるＬＴＯ被膜付き負極活物質は、内部短絡や釘刺し試験等の異常時においての電池反応の進行を抑制するという観点からは、まだまだ改善の余地があった。
そこで、本発明はかかる課題を解決すべく創出されたものであり、その目的とするところは、チタン酸リチウムが表面に存在する炭素粒子からなる負極活物質材料であって、抵抗の低減に加えて内部短絡や釘刺し試験等の異常時のジュール熱発生を抑制する負極活物質材料およびその製造方法を提供することである。また、当該負極活物質材料を用いることによって、より高い安全性と信頼性を実現したリチウムイオン二次電池の提供を他の目的とする。
By the way, lithium titanate (LTO) present on the surface of the carbon particles, which is the negative electrode active material, increases the lithium ion diffusion path described above and reduces the resistance associated therewith, and in addition to the above-mentioned increase in lithium ion diffusion path, it is instantaneously affected by internal short circuit, nail penetration test, etc. This has the effect of improving safety when a large current flows to the negative electrode side. That is, lithium titanate becomes an insulator and does not exhibit conductivity in a discharged state (that is, in an oxidized state in which lithium ions are released from LTO), so that short-circuit current can be suppressed.
However, the LTO-coated negative electrode active material described in Patent Literature 1 still has room for improvement from the viewpoint of suppressing the progress of the battery reaction during an abnormality such as an internal short circuit or a nail penetration test.
Therefore, the present invention was created to solve such problems, and an object of the present invention is to provide a negative electrode active material composed of carbon particles having lithium titanate present on the surface thereof, and to reduce the resistance. An object of the present invention is to provide a negative electrode active material that suppresses Joule heat generation during an internal short circuit or an abnormality such as a nail penetration test, and a method for producing the same. Another object of the present invention is to provide a lithium ion secondary battery that achieves higher safety and reliability by using the negative electrode active material.
本発明者は、炭素材料にＬＴＯを被覆物として形成させる際、所定の温度域で焼成を行うことによって、該炭素材料表面にリチウムイオン導電性を有する物質（ＬＴＯ）とともにリチウムイオン導電性を有さない物質（二酸化チタン；ＴｉＯ２）とを含む被覆物が形成されて両物質の界面においてＬＴＯからのリチウムイオンの放出が顕著に促進されることを見出した。そして、これを備えたリチウムイオン二次電池においては、内部短絡時のジュール熱発生が顕著に抑制されることを見出し、本発明を完成するに至った。 The present inventors found that when LTO is formed as a coating on a carbon material, the surface of the carbon material has lithium ion conductivity together with a substance having lithium ion conductivity (LTO) by firing in a predetermined temperature range. It has been found that a coating containing a substance (titanium dioxide; TiO 2 ) that does not form a layer is formed to significantly promote the release of lithium ions from LTO at the interface between the two substances. Then, in a lithium ion secondary battery equipped with this, it was found that the generation of Joule heat during an internal short circuit was remarkably suppressed, and the present invention was completed.
即ち、上記目的を実現するべく、本発明は、リチウムイオンを吸蔵および放出可能な炭素材料と該炭素材料の表面に形成された被覆物とから構成される負極活物質材料を製造する方法を提供する。上記炭素材料と、チタンアルコキシドと、リチウム塩と、溶媒とを含む混合物を調製すること、および、上記混合物から上記溶媒を除去した後に５５０～６００℃の温度域で焼成することを特徴とする。 That is, in order to achieve the above object, the present invention provides a method for producing a negative electrode active material composed of a carbon material capable of intercalating and deintercalating lithium ions and a coating formed on the surface of the carbon material. do. A mixture containing the carbon material, a titanium alkoxide, a lithium salt, and a solvent is prepared, and the mixture is fired at a temperature range of 550 to 600 ° C. after removing the solvent.
かかる構成の製造方法は、上記混合物を５５０～６００℃の温度域で焼成することによって、炭素材料の表面にリチウムイオン伝導性を有するＬＴＯと、リチウムイオン伝導性を有さないＴｉＯ２の両方を含む被覆物を形成することができる。これら２つの物質の界面におけるＬＴＯからのリチウム放出が促進されることによって、抵抗の低減に加えて、内部短絡や釘刺し試験などの異常時のジュール熱発生を抑制する負極活物質材料、および、安全性および信頼性の高いリチウムイオン二次電池を提供することができる。 In the manufacturing method having such a configuration, both LTO having lithium ion conductivity and TiO 2 having no lithium ion conductivity are formed on the surface of the carbon material by firing the above mixture in a temperature range of 550 to 600 ° C. A coating can be formed comprising: A negative electrode active material that suppresses Joule heat generation during abnormalities such as internal short circuits and nail penetration tests in addition to reducing resistance by promoting lithium release from LTO at the interface between these two substances, and A highly safe and reliable lithium ion secondary battery can be provided.
以下、図面を参照しながら、本発明による一実施形態を説明する。なお、以下に説明する図面において、同じ作用を奏する部材、部位には同じ符号を付し、重複する説明は省略または簡略化することがある。また、各図における寸法関係（長さ、幅、厚さ等）は実際の寸法関係を反映するものではない。また、本明細書において特に言及している事項以外の事柄であって本発明の実施に必要な事柄は、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。
なお、本明細書において数値範囲：Ａ～Ｂ（ここでＡとＢは、Ａ＜Ｂの関係にある任意の数値）と記載している場合は、Ａ以上Ｂ以下を意味しており、Ａを上回る場合（Ａを含まずにそれ以上の場合）、Ｂを下回る場合（Ｂを含まずにそれ以下の場合）も包含される数値範囲である。
An embodiment according to the present invention will be described below with reference to the drawings. In the drawings described below, members and portions having the same function are denoted by the same reference numerals, and redundant description may be omitted or simplified. Also, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships. Matters other than those specifically mentioned in this specification, which are necessary for carrying out the present invention, can be grasped as design matters by those skilled in the art based on the prior art in the relevant field.
It should be noted that, in the present specification, the numerical range: A to B (where A and B are arbitrary numerical values in the relationship of A<B) means A or more and B or less, and A (not including A) and below B (not including B).
本明細書において「二次電池」とは、繰り返し充放電可能な蓄電デバイス一般をいい、リチウムイオン二次電池、ニッケル水素電池、ニッケルカドミウム電池等のいわゆる蓄電池（すなわち化学電池）のほか、電気二重層キャパシタ等のキャパシタ（すなわち物理電池）を包含する。また、「負極活物質」とは、リチウムイオン二次電池において電荷担体となる化学種（即ち、リチウムイオン）を化学的に吸蔵および放出（典型的には挿入および脱離）可能な物質（負極活物質）をいう。 As used herein, the term "secondary battery" generally refers to an electricity storage device that can be repeatedly charged and discharged. It includes capacitors (ie physical batteries) such as multilayer capacitors. In addition, the "negative electrode active material" is a substance (negative electrode active material).
図１には、一実施形態に係る製造方法のフローが模式的に示されている。図１に示されるように、混合物調製工程Ｓ１０においては、出発物質である、炭素材料と、チタンアルコキシド（ＲＯＴｉ）と、リチウム塩と、溶媒とを準備し、これらを含む混合物を調製する。これらの混合の際には、必要に応じて撹拌処理を行ってもよく、市販のミキサー等の適当な撹拌手段によって行うことができる。
炭素材料としては、リチウムイオンを吸蔵および放出可能な炭素材料を好ましく用いることができ、例えば、天然黒鉛および人造黒鉛等の黒鉛材料が挙げられる。
FIG. 1 schematically shows the flow of the manufacturing method according to one embodiment. As shown in FIG. 1, in the mixture preparation step S10, a carbon material, a titanium alkoxide (ROTi), a lithium salt, and a solvent, which are starting materials, are prepared, and a mixture containing them is prepared. At the time of mixing these, a stirring treatment may be performed as necessary, and it can be performed by a suitable stirring means such as a commercially available mixer.
As the carbon material, a carbon material capable of intercalating and deintercalating lithium ions can be preferably used, and examples thereof include graphite materials such as natural graphite and artificial graphite.
黒鉛材料として、これを一般的な加工プロセス（粉砕プロセス、球状成形プロセス）によって球状に加工したものを使用することができる。黒鉛材料の粒子サイズは、通常、リチウムイオン二次電池の負極活物質として使用される黒鉛材料と同程度のものであればよく、平均粒径は、レーザー散乱・回折法に基づく粒度分布測定装置に基づいて測定した粒度分布から導き出されるメジアン径（平均粒径Ｄ５０：５０％体積平均粒径）においておよそ１μｍ～３０μｍ（典型的には５μｍ～２５μｍ）であることが好ましい。 As a graphite material, it is possible to use a material processed into a spherical shape by a general processing process (crushing process, spherical forming process). The particle size of the graphite material should be about the same as the graphite material normally used as the negative electrode active material of lithium ion secondary batteries, and the average particle size is measured by a particle size distribution measuring apparatus based on the laser scattering/diffraction method. The median diameter (average particle diameter D 50 : 50% volume average particle diameter) derived from the particle size distribution measured based on the above is preferably about 1 μm to 30 μm (typically 5 μm to 25 μm).
ＲＯＴｉとしては、特に限定されないが、例えば、オルトチタン酸テトライソプロピル、チタン酸テトラ－ｎ－ブチル、チタン酸テトラエチル等であってよい。１種のＲＯＴｉが単独で使用されてもよいし、２種類以上のＲＯＴｉを組み合わせて使用してもよい。
リチウム塩としては、例えば、硝酸リチウム等が挙げられる。
また、溶媒としては、例えば、低級アルコール（典型的には、エタノール等）を好適に用いることができる。
ROTi is not particularly limited, but may be, for example, tetraisopropyl orthotitanate, tetra-n-butyl titanate, tetraethyl titanate, or the like. One type of ROTi may be used alone, or two or more types of ROTi may be used in combination.
Lithium salts include, for example, lithium nitrate.
Moreover, as a solvent, for example, a lower alcohol (typically ethanol or the like) can be suitably used.
ＲＯＴｉおよびリチウム塩の混合物の質量％は、炭素材料１００質量％に対して、０．０５質量％～１０質量％程度であることが好ましく、０．１質量％～５質量％程度、あるいは、０．５質量％～３質量％程度であることがさらに好ましい。 The mass% of the mixture of ROTi and lithium salt is preferably about 0.05% by mass to 10% by mass with respect to 100% by mass of the carbon material, and is about 0.1% by mass to 5% by mass. More preferably, it is about 5% by mass to 3% by mass.
焼成工程Ｓ２０においては、まず、前処理として、混合物調製工程Ｓ１０で得た混合物から、溶媒を、例えば乾燥させることにより除去する。そして、溶媒を除去した後に、当該混合物を所定の条件で焼成する。
具体的には、例えば、溶媒を除去した混合物を不活性雰囲気（例えば、アルゴン雰囲気、または窒素雰囲気等）において、５５０～６００℃の温度域で焼成する。ここで、焼成時間は、例えば、２～１５時間程度（または、４～１０時間程度）であってよい。
In the baking step S20, first, as a pretreatment, the solvent is removed from the mixture obtained in the mixture preparation step S10, for example, by drying. After removing the solvent, the mixture is baked under predetermined conditions.
Specifically, for example, the mixture from which the solvent has been removed is fired in an inert atmosphere (eg, an argon atmosphere, a nitrogen atmosphere, or the like) at a temperature range of 550 to 600°C. Here, the firing time may be, for example, about 2 to 15 hours (or about 4 to 10 hours).
上述したような手法によって、炭素材料の表面に被覆物が形成された負極活物質材料を製造することができる。ここで、図２に、一実施形態に係る製造方法によって製造される負極活物質材料を示す。図２に示されるように、チタン酸リチウム（ＬＴＯ）３０および二酸化チタン（ＴｉＯ２）４０を含む被覆物が、炭素材料２０の表面に形成された負極活物質材料１０が製造される。
炭素材料２０表面に形成されたチタン酸リチウム（ＬＴＯ）３０および二酸化チタン（ＴｉＯ２）４０は、市販のＸ線回折装置または分光分析装置等により解析することができる。
また、エネルギー分散型Ｘ線分析法に基づく分析機器を用いた負極活物質材料１０の断面構造観察により、以下の式に基づいて被覆率を算出することができる。
被覆率＝（被覆物厚み）／（炭素材料全周）×１００ （１）
A negative electrode active material in which a coating is formed on the surface of a carbon material can be manufactured by the method described above. Here, FIG. 2 shows the negative electrode active material manufactured by the manufacturing method according to one embodiment. As shown in FIG. 2, negative electrode
Lithium titanate (LTO) 30 and titanium dioxide (TiO 2 ) 40 formed on the surface of
In addition, the coverage can be calculated based on the following formula by observing the cross-sectional structure of the negative electrode
Coverage = (thickness of coating) / (perimeter of carbon material) x 100 (1)
本発明においては、焼成を５５０～６００℃の温度域で行うことにより、炭素材料２０の表面に、被覆物としてリチウムイオン導電性を有する物質（チタン酸リチウム（ＬＴＯ）３０）とともにリチウムイオン導電性を有さない物質（二酸化チタン（ＴｉＯ２）４０）とを含む被覆物が形成される。これらの物質の界面においては、チタン酸リチウム（ＬＴＯ）３０からのリチウムイオンの放出が顕著に促進される。この性質により、負極活物質材料１０を使用することによって、リチウムイオン二次電池における内部短絡や釘刺し試験等の異常時のジュール熱発生を抑制することができる。そのため、より高い安全性と信頼性を実現したリチウムイオン二次電池が提供される。
In the present invention, by performing firing in a temperature range of 550 to 600° C., the surface of the
以下、本発明に関するいくつかの試験例を説明するが、本発明をかかる試験例に示すものに限定することを意図したものではない。 Some test examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in such test examples.
［負極活物質材料の製造］
以下に説明するプロセスにより、実施例１、実施例２、比較例１～６に係る負極活物質材料を製造した。
＜実施例１＞
リチウムイオン二次電池に一般的に用いられる黒鉛材料（平均粒径２０μｍ）を炭素材料として使用し、以下の処理を施して実施例１の負極活物質材料を製造した。
即ち、まず、オルトチタン酸テトライソプロピルおよび硝酸リチウムを、これらから生成されるＬＴＯおよびＴｉＯ２の配合比が表１に示される値になるように混合する。これを、黒鉛材料を１００質量％としたときに１質量％の割合で混合した混合物を調製し、溶媒としてのエタノール中で撹拌した。撹拌処理後、該混合物から溶媒を乾燥させることにより除去した。その後、混合物に対してアルゴン雰囲気下６００℃で８時間の焼成を実施し、実施例１に係る負極活物質材料を作製した。
＜実施例２＞
ＬＴＯおよびＴｉＯ２の配合比を表１に記載されるものとし、焼成温度を５５０℃にしたこと以外は実施例１と同じ条件で実施例２に係る負極活物質材料を作製した。
＜比較例１＞
ＬＴＯおよびＴｉＯ２の配合比を表１に記載されるものとし、焼成温度を６３０℃にしたこと以外は実施例１と同じ条件で比較例１に係る負極活物質材料を作製した。
＜比較例２＞
ＬＴＯおよびＴｉＯ２の配合比を表１に記載されるものとし、焼成温度を５００℃にしたこと以外は実施例１と同じ条件で比較例２に係る負極活物質材料を作製した。
＜比較例３＞
被覆物形成反応を行わない黒鉛材料を、比較例３に係る負極活物質材料とした。
＜比較例４＞
黒鉛材料１００質量％に対して１質量％のＴｉＯ２粉末（粒子径５０ｎｍ）を添加して混合し、比較例４に係る負極活物質材料を作製した。
＜比較例５＞
黒鉛材料１００質量％に対して１質量％のＬＴＯ粉末（粒子径５０ｎｍ）を添加して混合し、比較例５に係る負極活物質材料を作製した。
＜比較例６＞
黒鉛材料１００質量％に対して１質量％のＬＴＯおよびＴｉＯ２粉末（混合比８：２）を添加して混合し、比較例６に係る負極活物質材料を作製した。
[Production of negative electrode active material]
Negative electrode active materials according to Examples 1, 2, and Comparative Examples 1 to 6 were produced by the process described below.
<Example 1>
A graphite material (average particle size: 20 μm) generally used in lithium ion secondary batteries was used as the carbon material, and the negative electrode active material of Example 1 was produced by performing the following treatment.
That is, first, tetraisopropyl orthotitanate and lithium nitrate are mixed so that the compounding ratio of LTO and TiO 2 generated from these is the value shown in Table 1. A mixture was prepared by mixing this at a ratio of 1% by mass when the graphite material was 100% by mass, and stirred in ethanol as a solvent. After stirring, the solvent was removed from the mixture by drying. After that, the mixture was baked at 600° C. for 8 hours in an argon atmosphere to prepare a negative electrode active material according to Example 1.
<Example 2>
A negative electrode active material according to Example 2 was produced under the same conditions as in Example 1, except that the blending ratio of LTO and TiO 2 was as shown in Table 1 and the firing temperature was 550°C.
<Comparative Example 1>
A negative electrode active material according to Comparative Example 1 was produced under the same conditions as in Example 1, except that the blending ratio of LTO and TiO 2 was as shown in Table 1 and the firing temperature was 630°C.
<Comparative Example 2>
A negative electrode active material according to Comparative Example 2 was produced under the same conditions as in Example 1, except that the blending ratio of LTO and TiO 2 was as shown in Table 1 and the firing temperature was 500°C.
<Comparative Example 3>
A graphite material that does not undergo a coating-forming reaction was used as a negative electrode active material according to Comparative Example 3.
<Comparative Example 4>
A negative electrode active material according to Comparative Example 4 was prepared by adding 1% by mass of TiO 2 powder (particle size: 50 nm) to 100% by mass of graphite material and mixing.
<Comparative Example 5>
1% by mass of LTO powder (particle diameter: 50 nm) was added to 100% by mass of the graphite material and mixed to prepare a negative electrode active material according to Comparative Example 5.
<Comparative Example 6>
1% by mass of LTO and TiO 2 powder (mixing ratio 8:2) was added to 100% by mass of the graphite material and mixed to prepare a negative electrode active material according to Comparative Example 6.
［サンプル電池の作製］
＜正極の作製＞
正極活物質としてのリチウムニッケルコバルトマンガン複合酸化物と、導電材としてのアセチレンブラックと、バインダとしてのポリフッ化ビニリデンとを、質量比１００：１０：３となるように秤量し、これらをＮＭＰに分散させて正極ペーストを調製した。
該正極ペーストを厚み２０μｍのアルミニウム製正極集電体上に塗布し、真空乾燥させ、所定の寸法に加工した後にプレス機で圧延処理を施して正極シートを作製した。加工寸法については、正極板厚みは７０μｍ、正極板長さ３０００ｍｍ、正極活物質層幅９５ｍｍ、正極集電体未塗工部幅２０ｍｍとした。
＜負極の作製＞
上記作製した各々の負極活物質材料と、増粘剤としてのカルボキシメチルセルロースと、バインダとしてのスチレンブタジエンラバーとを、質量比１００：１：１となるように秤量し、これらを水に分散させて負極ペーストを調製した。
該負極ペーストを厚み１０μｍの銅製負極集電体上に塗布し、真空乾燥させ、所定の寸法に加工した後にプレス機で圧延処理を施して負極シートを作製した。加工寸法については、負極板厚みは８０μｍ、負極板長さ３３００ｍｍ、正極活物質層幅１００ｍｍ、負極集電体未塗工部幅２０ｍｍとした。
＜電池の構築＞
各正負極シートを、耐熱層を形成した厚み２０μｍのセパレータ（ポリプロピレン／ポリエチレン／ポリプロピレン）を介在させつつ捲回し、扁平形状の捲回電極体を得た。なお、この時、耐熱層は負極に対向させた。そして、当該捲回電極体を角型の電池ケースに収容し、５Ａｈのサンプル電池を構築した。当該電池の電解液としては、エチレンカーボネートと、ジメチルカーボネートと、エチルメチルカーボネートとを体積比１：１：１で混合して調製した非水溶媒に１ＭのＬｉＰＦ６を溶解した非水電解液を使用した。
［活性化処理（初期充電）］
上記サンプル電池の活性化処理（初期充電）を行った。
具体的には、２５℃の温度条件下において、１／３Ｃの電流で電池電圧が４．１Ｖになるまで定電流（ＣＣ）充電を行った後、電流値が１／５０Ｃになるまで定電圧（ＣＶ）充電を行い、満充電状態とした。その後、１／３Ｃの電流で電池電圧が３．０ＶになるまでＣＣ放電を行い、この時の容量を初期容量とした。
[Preparation of sample battery]
<Preparation of positive electrode>
A lithium-nickel-cobalt-manganese composite oxide as a positive electrode active material, acetylene black as a conductive material, and polyvinylidene fluoride as a binder were weighed so that the mass ratio was 100:10:3, and dispersed in NMP. to prepare a positive electrode paste.
The positive electrode paste was applied onto an aluminum positive electrode current collector having a thickness of 20 μm, vacuum-dried, processed into a predetermined size, and then subjected to rolling treatment with a press to prepare a positive electrode sheet. As for processing dimensions, the positive electrode plate thickness was 70 μm, the positive electrode plate length was 3000 mm, the positive electrode active material layer width was 95 mm, and the positive electrode current collector uncoated portion width was 20 mm.
<Production of negative electrode>
Each negative electrode active material prepared above, carboxymethyl cellulose as a thickener, and styrene-butadiene rubber as a binder were weighed so that the mass ratio was 100: 1: 1, and these were dispersed in water. A negative electrode paste was prepared.
The negative electrode paste was applied onto a copper negative electrode current collector having a thickness of 10 μm, vacuum-dried, processed into a predetermined size, and then rolled with a press to prepare a negative electrode sheet. As for processing dimensions, the thickness of the negative electrode plate was 80 μm, the length of the negative electrode plate was 3300 mm, the width of the positive electrode active material layer was 100 mm, and the width of the uncoated portion of the negative electrode current collector was 20 mm.
<Battery construction>
Each of the positive and negative electrode sheets was wound while interposing a separator (polypropylene/polyethylene/polypropylene) having a thickness of 20 μm with a heat-resistant layer formed therebetween to obtain a flat wound electrode assembly. At this time, the heat-resistant layer was opposed to the negative electrode. Then, the wound electrode assembly was housed in a rectangular battery case to construct a 5 Ah sample battery. The electrolyte of the battery is a non-aqueous electrolyte prepared by mixing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1 and dissolving 1M LiPF 6 in a non-aqueous solvent. used.
[Activation process (initial charge)]
An activation process (initial charge) was performed on the sample battery.
Specifically, under a temperature condition of 25 ° C., constant current (CC) charging is performed at a current of 1/3 C until the battery voltage reaches 4.1 V, and then constant voltage until the current value reaches 1/50 C. (CV) Charging was performed to obtain a fully charged state. Thereafter, CC discharge was performed at a current of ⅓ C until the battery voltage reached 3.0 V, and the capacity at this time was taken as the initial capacity.
［釘刺し試験］
上記各サンプル電池をＳＯＣ１００％に調整した。そして、２５℃の試験後で、充電後のサンプル電池に直径３ｍｍ、長さ５０ｍｍ、先端角度３０°の四角錐形状の釘を１０ｍｍ／秒の速度で貫通させた。この際、各サンプル電池における発煙の有無を確認した。
結果を表１に示す。ここで、表１中、発煙がなかったサンプルを〇印で表し、発煙があったサンプルを△印で表す。
[Nail penetration test]
Each of the above sample batteries was adjusted to have an SOC of 100%. After the test at 25° C., a quadrangular pyramid-shaped nail having a diameter of 3 mm, a length of 50 mm, and a tip angle of 30° was pierced through the charged sample battery at a rate of 10 mm/sec. At this time, the presence or absence of smoke generation in each sample battery was checked.
Table 1 shows the results. Here, in Table 1, the samples that did not emit smoke are indicated by ◯, and the samples that emitted smoke are indicated by Δ.
表１から明らかなように、実施例１および実施例２に係るサンプル電池においては、釘刺しによる発煙は確認されなかった。これに対し、比較例１～６ではいずれも発煙が確認された。即ち、炭素材料の表面にＬＴＯおよびＴｉＯ２がヘテロの状態で被覆物として形成されたことにより、内部短絡時に速やかにＬＴＯからリチウムイオンが放出されて絶縁状態が形成され、内部短絡時の温度上昇（発煙）を抑制し得ることが確認された。 As is clear from Table 1, in the sample batteries according to Examples 1 and 2, no smoke due to nail penetration was confirmed. On the other hand, smoking was confirmed in all of Comparative Examples 1 to 6. That is, since LTO and TiO 2 are formed as a coating in a hetero state on the surface of the carbon material, lithium ions are quickly released from LTO when an internal short circuit occurs, forming an insulating state and increasing the temperature during an internal short circuit. (fuming) can be suppressed.
［電池抵抗および出力特性の測定］
あらかじめ電圧を３．７０Ｖ（ＳＯＣ５６％）に調整した各電池について、２５℃の温度条件下でＣＣ充電を行って、端子間電圧を３．０Ｖに調整した。そして、５秒間のＣＣ放電を行い、電池抵抗（ＩＶ抵抗）および出力値を求めた。
結果を表１に示す。
[Measurement of battery resistance and output characteristics]
Each battery whose voltage had been previously adjusted to 3.70V (SOC 56%) was CC-charged at a temperature of 25°C to adjust the terminal voltage to 3.0V. Then, CC discharge was performed for 5 seconds, and the battery resistance (IV resistance) and output value were obtained.
Table 1 shows the results.
表１から明らかなように、ＬＴＯを含む被覆物が炭素材料に形成されているサンプル電池においては、放電後の電池容量が維持され、電池抵抗は低下していた。そして、実施例１および実施例２に係るサンプル電池の電池抵抗は比較例と比べて、顕著に低下することが確認された。これにより、負極活物質材料を５５０～６００℃の温度域で焼成して作製することにより、電池抵抗が低下することが確認された。
このように、本発明によれば、優れた電池特性を維持しつつ内部短絡時の温度上昇を抑制し得る負極活物質材料の製造方法を提供することができる。
As is clear from Table 1, in the sample battery in which the coating containing LTO was formed on the carbon material, the battery capacity after discharge was maintained and the battery resistance decreased. It was also confirmed that the battery resistances of the sample batteries according to Examples 1 and 2 were significantly lower than those of the comparative example. From this, it was confirmed that the battery resistance was lowered by baking the negative electrode active material in the temperature range of 550 to 600°C.
As described above, according to the present invention, it is possible to provide a method for producing a negative electrode active material capable of suppressing temperature rise during an internal short circuit while maintaining excellent battery characteristics.
１０ 負極活物質材料
２０ 炭素材料
３０ ＬＴＯ
４０ ＴｉＯ２
10 negative electrode
40TiO2
Claims (1)
以下の工程：
前記炭素材料と、チタンアルコキシドと、硝酸リチウムであるリチウム塩と、低級アルコールである溶媒とから構成された混合物であって、該炭素材料１００質量％に対して、該チタンアルコキシドと該リチウム塩とが合計で０．５質量％～３質量％以下である混合物を調製する混合物調製工程；および、
前記混合物調製工程の後、前記混合物から前記溶媒を除去して、 前記溶媒が除去された後の該混合物を、不活性雰囲気にて５５０～６００℃の温度域で４～１０時間焼成する焼成工程；を包含し、
前記混合物調製工程では、前記チタンアルコキシドと前記リチウム塩とから生成されるチタン酸リチウムと二酸化チタンとの配合比（チタン酸リチウム：二酸化チタン）が９：１～８：２になるように、該チタンアルコキシドと該リチウム塩とを混合する 、製造方法。
A method for producing a negative electrode active material composed of a carbon material capable of intercalating and deintercalating lithium ions and a coating formed on the surface of the carbon material, comprising:
The following steps:
the carbon material, titanium alkoxide,is lithium nitratea lithium salt;is a lower alcoholsolvent andwherein the total amount of the titanium alkoxide and the lithium salt is 0.5% by mass to 3% by mass or less with respect to 100% by mass of the carbon materialprepare the mixturemixture preparation step;and,
After the mixture preparation step, removing the solvent from the mixture, the solventButRemovalIn an inert atmosphere, the mixture afterin the temperature range of 550-600°C4-10 hoursbakefiring process;ofembrace,
In the mixture preparation step, the compounding ratio (lithium titanate:titanium dioxide) of lithium titanate and titanium dioxide produced from the titanium alkoxide and the lithium salt is 9:1 to 8:2. Mixing the titanium alkoxide and the lithium salt ,Production method.
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