JP6657671B2 - Stabilized lithium powder, negative electrode for lithium ion secondary battery and lithium ion secondary battery using the same - Google Patents
Stabilized lithium powder, negative electrode for lithium ion secondary battery and lithium ion secondary battery using the same Download PDFInfo
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- 229910052744 lithium Inorganic materials 0.000 title claims description 130
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- 239000000843 powder Substances 0.000 title claims description 82
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims description 27
- 229910001416 lithium ion Inorganic materials 0.000 title claims description 27
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Description
本発明は、安定化リチウム粉末、それを用いたリチウムイオン二次電池用負極およびリチウムイオン二次電池に関する。 The present invention relates to a stabilized lithium powder, a negative electrode for a lithium ion secondary battery using the same, and a lithium ion secondary battery.
正極にコバルト酸リチウムに代表されるリチウム含有遷移金属酸化物、負極にリチウムをドープ・脱ドープ可能な炭素材料を用いたリチウムイオン二次電池を代表とする電気化学デバイスは、高エネルギー密度を有するという特徴から携帯電話に代表される携帯電子機器の電源として重要なものであり、これら携帯電子機器の急速な普及に伴いその需要は高まる一方である。 Electrochemical devices such as lithium ion secondary batteries using a lithium-containing transition metal oxide typified by lithium cobalt oxide for the positive electrode and a lithium-doped / dedopable carbon material for the negative electrode have a high energy density Therefore, it is important as a power source for portable electronic devices represented by portable telephones, and the demand for these portable electronic devices is increasing with the rapid spread.
また、ハイブリッド自動車など、環境対応を意識した自動車が数多く開発されているが、搭載される電源の一つとして、高エネルギー密度を有するリチウムイオン二次電池が大きく注目されている。 In addition, a number of environmentally conscious vehicles such as hybrid vehicles have been developed, and lithium-ion secondary batteries having high energy density have attracted much attention as one of the power supplies to be mounted.
リチウムイオン二次電池の容量は主に電極の活物質に依存する。負極活物質には、一般に黒鉛が利用されているが、上記の要求に対応するためにはより高容量な負極活物質を用いることが必要である。そのため、黒鉛の理論容量（３７２ｍＡｈ／ｇ）に比べてはるかに大きな理論容量（４２１０ｍＡｈ／ｇ）をもつ金属シリコン（Ｓｉ）が注目されている。 The capacity of the lithium ion secondary battery mainly depends on the active material of the electrode. Although graphite is generally used as the negative electrode active material, it is necessary to use a higher capacity negative electrode active material in order to meet the above requirements. For this reason, metallic silicon (Si) having a much larger theoretical capacity (4210 mAh / g) than the theoretical capacity of graphite (372 mAh / g) has attracted attention.
このようなリチウムイオン二次電池の性能向上化手段の一つとして、リチウムオン蓄電デバイスの主に負極に対して予めリチウムイオンをドープすることによりリチウムイオン蓄電デバイス内の電極の不可逆容量を抑制するプレドープ技術が知られている。 As one of the means for improving the performance of such a lithium ion secondary battery, the irreversible capacity of the electrode in the lithium ion storage device is suppressed by doping lithium ions in advance mainly to the negative electrode of the lithium-on storage device. Pre-doping techniques are known.
例えば、集電体に貫通孔のある孔開き箔を使用した垂直プレドープ法が特許文献１に記載されている。垂直プレドープ法では、正極、負極の他に、正極や負極にリチウムイオンを供給するための第３極を用いる。
For example,
この垂直プレドープ法は、通常のリチウムイオン蓄電デバイスよりも製造工程が複雑になり時間とコストが必要となる。 The vertical pre-doping method requires a more complicated manufacturing process and requires more time and cost than a normal lithium ion storage device.
また、正極合材層や負極合材層全体にリチウム箔を用いて導入する手法も存在するが、リチウムは柔らかいため均等に貼り付けるのが非常に困難である。また、この作業そのもののハンドリング性が低いことから、量産時の生産性に影響が出る可能性がある。 There is also a method of introducing the whole of the positive electrode mixture layer and the negative electrode mixture layer using lithium foil, but it is very difficult to apply evenly because lithium is soft. In addition, since the workability of the work itself is low, productivity in mass production may be affected.
これらを解決する手段として、リチウム粉末を利用し、その粉末を溶液塗布してプレドープを行う方法が提案されている（特許文献２参照）。 As means for solving these problems, a method has been proposed in which lithium powder is used, and the powder is applied as a solution to perform pre-doping (see Patent Document 2).
このようなリチウム粉末を利用したプレドープ方法は、リチウム粉末の安定性の悪さから、安定化処理したものも開発されている。リチウム粉末の安定化処理方法としては、金属リチウム粉末の表面に安定性の高い物質、例えば、ＮＢＲ（ニトリルブタジエンゴム）、ＳＢＲ（スチレンブタジエンゴム）等の有機ゴム、ＥＶＡ（エチレンビニルアルコール共重合樹脂）、ＰＶＤＦ（ポリフッ化ビニリデン）、ＰＥＯ（ポリエーテル）等の有機樹脂や、金属化合物等の無機化合物で金属リチウム粒子を被覆した安定化リチウム粒子を使用する方法が挙げられる。 As such a pre-doping method using lithium powder, a method of stabilizing lithium powder has been developed because of the poor stability of the lithium powder. As a method for stabilizing lithium powder, substances having high stability on the surface of lithium metal powder, for example, organic rubbers such as NBR (nitrile butadiene rubber) and SBR (styrene butadiene rubber), and EVA (ethylene vinyl alcohol copolymer resin) ), PVDF (polyvinylidene fluoride), PEO (polyether) or the like, or a method using stabilized lithium particles coated with metal lithium particles with an inorganic compound such as a metal compound.
これらの安定化リチウム粒子を用いることで、大気中やトルエン、キシレン等の溶媒中でも安定化し、また露点がマイナス４０℃程度のドライルームにおいてもリチウムの変質を防止できる。またプレドープ時に、リチウムと負極活物質との間の過度な反応が抑制されるため、この反応により生じる発熱量を低減できる。 By using these stabilized lithium particles, it is possible to stabilize even in the air or a solvent such as toluene or xylene, and to prevent the deterioration of lithium even in a dry room having a dew point of about −40 ° C. In addition, during pre-doping, an excessive reaction between lithium and the negative electrode active material is suppressed, so that the amount of heat generated by this reaction can be reduced.
しかしながら、被覆部として有機系高分子を使用した場合、電池中において電解液にさらされることで、被覆部が溶出し電池性能の低下を招く恐れがある。特に高温環境下や高電位下では、溶出や反応性が増すことでその影響が顕著になる。一方、リチウム炭酸塩や酸化リチウム等の無機化合物等でリチウム金属を被覆したものは、安全性や安定性としては未だ不十分である。 However, when an organic polymer is used as the coating portion, the coating portion is eluted by exposure to the electrolytic solution in the battery, which may cause a decrease in battery performance. In particular, under a high temperature environment or a high potential, the effect becomes remarkable because elution and reactivity increase. On the other hand, those coated with lithium metal with inorganic compounds such as lithium carbonate and lithium oxide are still insufficient in safety and stability.
本発明の目的は、上記課外に鑑み電池性能を維持しつつ、電極製造時の安全性及び生産性を向上させた安定化リチウム粒子を提供することにある。 SUMMARY OF THE INVENTION An object of the present invention is to provide stabilized lithium particles that have improved safety and productivity during electrode production while maintaining battery performance in view of the above extracurrencies.
本発明者らは、電池性能を維持しつつ、電極製造時の安全性を高めることで生産性を向上させるべく鋭意検討を重ねた結果、安定化リチウム粉末の製造時または製造後の副生成物として水酸化リチウムが生成することを発見した。
この水酸化リチウムは高い親水性を持ち、また熱的に不安定であるため、例えば熱により酸化リチウムを生成する過程で水を放出する。この水は金属リチウムと反応が生じることで急な温度上昇を生じる可能性があり好ましくない。さらに水酸化リチウムが水和物となった場合には、更に親水性が高まり、より急な温度上昇を生じてしまう。また、水酸化リチウムは塩基性が高いためリチウムイオン二次電池内で予想もしない反応が起こる可能性や腐食性が原因で電池としての製法の低下が懸念される。このようなことから水酸化リチウムの量を制御することは安全性及び生産性に優れた電池を提供する上で非常に重要であることがわかった。
The present inventors have conducted intensive studies to improve productivity by increasing safety during electrode production while maintaining battery performance, and as a result, by-products during or after production of stabilized lithium powder. To form lithium hydroxide.
Since lithium hydroxide has high hydrophilicity and is thermally unstable, it releases water in the process of producing lithium oxide by heat, for example. This water is not preferred because it may cause a rapid temperature rise due to the reaction with lithium metal. Further, when lithium hydroxide becomes a hydrate, the hydrophilicity is further increased, and a more rapid temperature rise occurs. In addition, since lithium hydroxide has a high basicity, there is a possibility that an unexpected reaction may occur in a lithium ion secondary battery or that the production method as a battery may be deteriorated due to corrosiveness. Thus, it has been found that controlling the amount of lithium hydroxide is very important in providing a battery excellent in safety and productivity.
本発明にかかる安定化リチウム粉末は、リチウム粒子を含み、そのリチウム粒子はその表面に無機化合物を有し、前記無機化合物中の水酸化リチウム含有量は、前記安定化リチウム粉末全体に対し２．０重量％以下であることを特徴とする。かかる安定化リチウム粉末により、電極製造時の安全性及び生産性を向上させることができる。 The stabilized lithium powder according to the present invention includes lithium particles , and the lithium particles have an inorganic compound on the surface thereof. The content of the lithium hydroxide in the inorganic compound is set to 2.% with respect to the entire stabilized lithium powder. 0% by weight or less. With such a stabilized lithium powder , it is possible to improve safety and productivity in manufacturing an electrode.
また、前記無機化合物は、酸化リチウムを含有することが好ましい。酸化リチウムは水酸化リチウムに比べて親水性が低く、さらにリチウム粒子の安定化に寄与する。 Further, it is preferable that the inorganic compound contains lithium oxide. Lithium oxide has lower hydrophilicity than lithium hydroxide, and further contributes to stabilization of lithium particles.
上記安定化リチウム粉末を用いリチウムのドーピングが施された負極であれば、高い安全性と生産性を持ち、優れた電池特性を生じる電極を提供することが可能となる。 A negative electrode doped with lithium using the stabilized lithium powder can provide an electrode having high safety and productivity, and having excellent battery characteristics.
また、上記安定化リチウム粉末を用いリチウムのドーピングが施された負極と、正極と、電解質と、を有するリチウムイオン二次電池においては、十分なドーピング効果により優れた電池特性を持った電池を提供できる。 In addition, a lithium ion secondary battery having a lithium-doped negative electrode using the above stabilized lithium powder , a positive electrode, and an electrolyte provides a battery having excellent battery characteristics due to a sufficient doping effect. it can.
本発明によれば、電極製造時の安全性及び生産性を向上させた安定化リチウム粉末およびそれを用いたリチウムイオン二次電池を作製することが可能となる。 ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to manufacture the stabilized lithium powder which improved safety and productivity at the time of electrode manufacture, and a lithium ion secondary battery using the same.
以下、本発明について本発明の好適な実施形態について説明する。なお、本発明は以下の実施形態に限定されるものではない。 Hereinafter, preferred embodiments of the present invention will be described. Note that the present invention is not limited to the following embodiments.
（安定化リチウム粉末）
本実施形態に係る安定化リチウム粉末は、リチウム粒子２の表面に無機化合物を有している。その無機化合物は、図１に示すように安定化層１として膜状に形成してもよいし島状に形成されていてもよいが、完全にリチウム粒子２を被覆していることが好ましい。
さらにリチウム粒子は、平均粒径が１〜２００μｍであることが好ましい。
なお、測定方法としては、不活性ガスまたは炭化水素油中等の不活性雰囲気下での光学顕微鏡、電子顕微鏡、粒度分布計等により安定した測定が可能である。
(Stabilized lithium powder)
The stabilized lithium powder according to the present embodiment has an inorganic compound on the surface of the
Further, the lithium particles preferably have an average particle size of 1 to 200 μm.
In addition, as a measuring method, stable measurement can be performed by an optical microscope, an electron microscope, a particle size distribution meter, or the like under an inert atmosphere such as in an inert gas or hydrocarbon oil.
リチウム粒子の表面に有する無機化合物は、酸化リチウムをさらに含有することが好ましい。 The inorganic compound on the surface of the lithium particles preferably further contains lithium oxide.
この安定化リチウム粉末によれば、取り扱い性に優れ、露点マイナス４０℃程度のドライルームで取り扱うことが可能である。 According to this stabilized lithium powder, it is excellent in handleability and can be handled in a dry room having a dew point of about minus 40 ° C.
前記安定化リチウム粉末の安定化層となる酸化リチウムは、リチウム粒子が被覆されている量があれば問題はないが、安定化リチウム粉末全体の重量に対し１重量％以上１０重量％以下であることが好ましい。より好ましくは１．０重量％以上５．０重量％以下である。この範囲において、負極作製時の発熱による負極の損失を減らせ、安全性および生産性を向上させた電極の作製が可能となる。 The lithium oxide serving as the stabilizing layer of the stabilized lithium powder is not problematic as long as the amount of the lithium particles coated is 1% to 10% by weight based on the total weight of the stabilized lithium powder. Is preferred. More preferably, the content is 1.0% by weight or more and 5.0% by weight or less. Within this range, it is possible to reduce the loss of the negative electrode due to heat generated during the preparation of the negative electrode, and to manufacture an electrode with improved safety and productivity.
また、前記水酸化リチウムと前記酸化リチウムの含有量の比（水酸化リチウム／酸化リチウム）は、０．３以上２以下が好ましい。かかる構成によれば、より優れた初期充放電効率を得ることができる。 Further, the ratio of the content of the lithium hydroxide to the content of the lithium oxide (lithium hydroxide / lithium oxide) is preferably 0.3 or more and 2 or less. According to such a configuration, more excellent initial charge / discharge efficiency can be obtained.
前記安定化リチウム粉末の安定化層は、酸化リチウム以外の化合物が混在していても良い。例えば炭酸リチウム、塩化リチウム、酢酸リチウム、臭化リチウム、硝酸リチウム、硫化リチウム、硫酸リチウム、炭化リチウム等である。これらは安定化層に積層されていても、点在していても良い。 The stabilizing layer of the stabilized lithium powder may contain a compound other than lithium oxide. For example, lithium carbonate, lithium chloride, lithium acetate, lithium bromide, lithium nitrate, lithium sulfide, lithium sulfate, lithium carbide and the like. These may be laminated on the stabilizing layer or may be scattered.
またその安定化層は遷移金属を含有していることが好ましい。特にＮｉ、Ｆｅ、Ｃｒ、Ｍｎ、Ｚｒ、Ｔｉ、Ａｌが好ましい。かかる金属は水酸化物イオンが仮に生じたとしても化合物を生成し安定化させる働きがあり、安定化リチウム粉末として信頼性が向上するため好ましい。
この遷移金属は金属単体であっても、化合物として存在していてもよい。特に酸素を含有する化合物が安定しているため好ましい。例えば酸化物が挙げられる。またこの遷移金属は安定化リチウム粉末全体に対し、金属換算で１．０×１０−３質量％以上１０．０×１０−３質量％含有することが好ましい。なお、遷移金属の含有量はＩＣＰ（発光分光分析法）により求めることができる。
The stabilizing layer preferably contains a transition metal. Particularly, Ni, Fe, Cr, Mn, Zr, Ti, and Al are preferable. Such a metal has a function of generating and stabilizing a compound even if hydroxide ions are generated, and is preferable because reliability is improved as a stabilized lithium powder .
The transition metal may be a simple metal or may be present as a compound. Particularly, a compound containing oxygen is preferable because it is stable. For example, an oxide is used. Further, it is preferable that the transition metal is contained in an amount of 1.0 × 10 −3 mass% or more and 10.0 × 10 −3 mass% in terms of metal with respect to the entire stabilized lithium powder . The content of the transition metal can be determined by ICP (emission spectroscopy).
前記安定化リチウム粉末の安定化層は電池特性に影響が出ない範囲であれば、層厚に制限はない。また、層の厚みが一定である必要もない。 The thickness of the stabilizing layer of the stabilized lithium powder is not limited as long as it does not affect battery characteristics. Further, the thickness of the layer does not need to be constant.
また、前記安定化リチウム粉末の形状は図１に示す球形でも、様々な形態でもよいが、球形ではない歪な形状であることが好ましい。 The shape of the stabilized lithium powder may be the spherical shape shown in FIG. 1 or various shapes, but it is preferable that the shape is not spherical but a distorted shape.
なお、安定化リチウム粉末の組成に関しては公知の固体ＬｉＮＭＲでの定量や、Ｘ線光電子分光分析やＸ線回折等を利用しても定量化することが可能である。固体ＬｉＮＭＲでは、微量の分析をするためにも高分解能の固体ＮＭＲが望ましく、たとえばＢｒｕｋｅｒ社製の固体核磁気共鳴装置ＤＳＸ４００等を使用すればよい。 It should be noted that the composition of the stabilized lithium powder can be quantified by using known solid-state LiNMR, X-ray photoelectron spectroscopy, X-ray diffraction, or the like. In solid-state LiNMR, high-resolution solid-state NMR is desirable even in order to perform trace analysis. For example, a solid state nuclear magnetic resonance apparatus DSX400 manufactured by Bruker may be used.
さらに上記安定化リチウム粉末を用い負極にリチウムをドーピングした負極であれば、負極作製時の発熱による負極の損失を減らせ、安全性および生産性が向上させることが可能となる。さらにこの電極は、優れた電池特性を生じる電極を提供することが可能となる。 Furthermore, if the negative electrode is doped with lithium using the above-mentioned stabilized lithium powder , loss of the negative electrode due to heat generation during the preparation of the negative electrode can be reduced, and safety and productivity can be improved. Further, this electrode can provide an electrode that produces excellent battery characteristics.
（安定化リチウム粉末の製造方法）
本実施形態の安定化リチウム粉末は、リチウム金属を炭化水素油中でその融点以上の温度まで加熱し、溶融リチウムを高速撹拌し、その後、特定の条件下において高純度炭酸ガスと反応溶液よりも高い温度を有する炭化水素油と乾燥剤を入れることによりリチウム粉末と水分との接触を防ぎ、水酸化リチウムを意図的に消失させ、水酸化物をほとんど有さない安定化リチウム粉末が製造される。本発明を用いれば他のアルカリ金属、例えばナトリウム及びカリウムも同様に製造できる。
(Method for producing stabilized lithium powder)
The stabilized lithium powder of the present embodiment is obtained by heating lithium metal in a hydrocarbon oil to a temperature equal to or higher than its melting point, stirring the molten lithium at a high speed, and then, under specific conditions, a higher purity carbon dioxide gas than the reaction solution. By adding a hydrocarbon oil having a high temperature and a desiccant, contact between the lithium powder and moisture is prevented, lithium hydroxide is intentionally eliminated, and a stabilized lithium powder having almost no hydroxide is produced. . Using the present invention, other alkali metals, such as sodium and potassium, can be produced as well.
本発明の安定化リチウム粉末を作製する際の原料となる金属リチウムとしてはリチウムイオン二次電池の使用に支障のない範囲のリチウムであれば、特に限定されず、角状、粒状、粉末状、箔状等の金属リチウムを用いることができる。 Metallic lithium as a raw material at the time of producing the stabilized lithium powder of the present invention is not particularly limited as long as it is lithium in a range that does not hinder use of the lithium ion secondary battery, and is rectangular, granular, powdery, Metallic lithium, such as a foil, can be used.
本発明の安定化リチウム粉末を作製するために必要な炭化水素油は、多様な炭化水素油を使用することができる。本明細書中で使用される炭化水素油とは、主に炭化水素混合物からなる種々の油性液体を含み、鉱油、即ち油と認識される粘度制限を有する鉱物起源の液体産物を含み、従って、石油、ケツ岩油、パラフィン油等を含むが、これらに限定はされない。典型的な炭化水素油は、例えば、三光化学工業社製の流動パラフィン、Ｓタイプ、工業用タイプ、ＭＯＲＥＳＣＯ社の商品名：モレスコホワイトＰ−４０、Ｐ−５５、Ｐ−６０、Ｐ−７０、Ｐ−８０、Ｐ−１００、Ｐ−１２０、Ｐ−１５０、Ｐ−２００、Ｐ−２６０、Ｐ−３５０Ｐや、カネダ社製のハイコールＭシリーズ（ハイコールＭ−５２、ハイコールＭ−７２、ハイコールＭ−１７２、ハイコールＭ−３５２、Ｋシリーズ（ハイコールＫ−１４０Ｎ、ハイコールＫ−１６０、ハイコールＫ−２３０、ハイコールＫ−２９０、ハイコールＫ−３５０、およびハイコールＥ−７ のような炭化水素油である。これらに限らずリチウム又はナトリウム金属の融点以上で沸騰する精製炭化水素溶媒であれば使用できる。 Various hydrocarbon oils can be used as the hydrocarbon oil required for preparing the stabilized lithium powder of the present invention. Hydrocarbon oils as used herein include various oily liquids consisting primarily of hydrocarbon mixtures and include mineral oils, i.e., liquid products of mineral origin having a viscosity limit recognized as oils, Includes, but is not limited to, petroleum, ashes oil, paraffin oil and the like. Typical hydrocarbon oils include, for example, liquid paraffin manufactured by Sanko Chemical Industry Co., Ltd., S type, industrial type, and trade names of MORESCO Corporation: Moresco White P-40, P-55, P-60, P-70. , P-80, P-100, P-120, P-150, P-200, P-260, P-350P, and the Hi-Coll M series manufactured by Kaneda Corporation (Hi-Cho M-52, Hi-Cho M-72, Hi-Cho M) Hydrocarbon oils such as -172, Hicoll M-352, K Series (Hicoll K-140N, Hicoll K-160, Hicoll K-230, Hicoll K-290, Hicoll K-350, and Hicoll E-7. Not limited to these, any purified hydrocarbon solvent that boils above the melting point of lithium or sodium metal can be used.
上記炭化水素油は、リチウムインゴットを１重量部としたとき、溶融後の均一分散性の観点から１〜３０重量部であることが好ましく、２〜１５重量部であることがより好ましい。 The amount of the hydrocarbon oil is preferably 1 to 30 parts by weight, and more preferably 2 to 15 parts by weight, when lithium ingot is 1 part by weight, from the viewpoint of uniform dispersibility after melting.
上記分散液の冷却後の温度は１００℃以下が好ましく、５０℃以下がより好ましい。また、上記分散液は１時間以上かけて徐々に冷却することが好ましい。 The temperature of the dispersion after cooling is preferably 100 ° C. or lower, more preferably 50 ° C. or lower. Further, it is preferable that the dispersion liquid is gradually cooled over 1 hour or more.
上記二酸化炭素は、リチウムインゴットを１重量部としたとき、０．１〜１０重量部がこの分散混合物に加えられることが好ましく、１〜３重量部であることがより好ましい。二酸化炭素はこの混合物の表面下に導入されることが好ましく、分散液を製造するために必要な激しい攪拌条件は、分散混合物上に導入される二酸化炭素と分散された金属との接触をもたらするために十分であるべきである。 With respect to the carbon dioxide, when the lithium ingot is 1 part by weight, 0.1 to 10 parts by weight is preferably added to the dispersion mixture, and more preferably 1 to 3 parts by weight. The carbon dioxide is preferably introduced below the surface of the mixture, and the vigorous stirring conditions required to produce the dispersion result in contact between the carbon dioxide introduced over the dispersion mixture and the dispersed metal. Should be enough to
本発明の安定化リチウム粉末を作製するために必要な乾燥剤は、リチウムと反応しないものに限られる。好ましくはモレキュラーシーブ３Ａ、モレキュラーシーブ４Ａ、モレキュラーシーブ５Ａ、酸化アルミニウム、シリカゲル、酸化マグネシウムなどが利用可能であり、これらに限らずリチウム又はナトリウムのようなアルカリ金属と反応しにくい乾燥剤であれば使用できる。 The desiccant required to produce the stabilized lithium powder of the present invention is limited to those that do not react with lithium. Preferably, molecular sieve 3A, molecular sieve 4A, molecular sieve 5A, aluminum oxide, silica gel, magnesium oxide and the like can be used, but not limited thereto, and any desiccant which does not easily react with an alkali metal such as lithium or sodium can be used. it can.
本発明の安定化リチウム粉末を作製するために必要な温度は、リチウム金属が溶融する温度以上であることが好ましい。具体的には、１９０℃〜２５０℃、好ましくは１９５℃〜２４０℃、より好ましくは２００℃〜２２０℃である。低すぎるとリチウムが固体化しリチウムの粉末の製造が困難となり、温度が高すぎると炭化水素油の種類によっては気化が起こり、製造上扱いにくくなるためである。 The temperature required to produce the stabilized lithium powder of the present invention is preferably equal to or higher than the temperature at which lithium metal melts. Specifically, it is 190 ° C to 250 ° C, preferably 195 ° C to 240 ° C, and more preferably 200 ° C to 220 ° C. If the temperature is too low, lithium is solidified and it becomes difficult to produce lithium powder, and if the temperature is too high, vaporization occurs depending on the type of hydrocarbon oil, which makes the production difficult to handle.
本発明の安定化リチウム粉末を作製するために必要な撹拌能力は、その容器サイズや処理量にもよるが、所望の粒径が得られる撹拌方法であれば、撹拌装置を限定する必要はなく、様々な撹拌、分散機での微粒子化が可能である。 The stirring capacity required to produce the stabilized lithium powder of the present invention depends on the container size and processing amount, but it is not necessary to limit the stirring device as long as the stirring method can obtain a desired particle size. Fine particles can be formed by various stirring and dispersing machines.
本発明の安定化リチウム粉末を作製するために必要な炭酸ガスは、高純度であることが好ましい。濃度としては９８％以上が好ましい。リチウム金属との反応であるため、水分が多いことは好ましくない。また、純度が低いとリチウム金属が不純物と反応する恐れがあるため好ましくない。 The carbon dioxide gas required to produce the stabilized lithium powder of the present invention is preferably of high purity. The concentration is preferably 98% or more. Since it is a reaction with lithium metal, it is not preferable that the amount of water is large. On the other hand, a low purity is not preferred because lithium metal may react with impurities.
（リチウムイオン二次電池）
上述のように説明した安定化リチウム粉末を負極集電体２２に形成した負極活物質層２４上に塗布することでリチウムを負極にドーピングできる。
(Lithium ion secondary battery)
The negative electrode can be doped with lithium by applying the stabilized lithium powder described above on the negative electrode
このようにしてドーピングした負極２０と、正極１０と、電解質を含浸させたセパレータ１８とを図２のように作製することでリチウムイオン二次電池１００を作製することができる。
ここで、正極１０は、正極集電体１２上に正極活物質層１４を形成することで作製することができる。
なお、図面中６０と６２は、それぞれ正極と負極の引出し電極を示す。
なお、本発明の安定化リチウム粉はリチウムイオン二次電池用途に限定されるものではなく、リチムイオンキャパシタ、ＥＤＬＣ（電気二重層キャパシタ）などの電気化学デバイスにも適用可能である。
The lithium ion
Here, the
In the drawings,
The stabilized lithium powder of the present invention is not limited to lithium ion secondary battery applications, but can be applied to electrochemical devices such as lithium ion capacitors and EDLCs (electric double layer capacitors).
以下、実施例及び比較例に基づいて本発明をより具体的に説明するが、本発明は以下の実施例に限定されるものではない。 Hereinafter, the present invention will be described more specifically based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.
［実施例１］
市販されているリチウム金属１０ｇを乾燥アルゴンの雰囲気下中、室温で、ステンレススチール製フラスコ反応器に装入した。反応器をオイルバスにより熱制御が可能になるように設置した。反応器内に流動パラフィンハイコールＫ−２９０（カネダ社製）を５０ｇを添加した。次に、ホットスターラーを用いて反応器を約２００℃まで加熱し、攪拌機を用いて目視において金属が溶融したのを確認した。次いで、攪拌機を用いて激しく撹拌することでリチウム粉末を微粒子化させ、その後、高純度炭酸ガスを高速撹拌中に１００ｍｌ／ｍｉｎの量でさらに２０℃程加温させながら１分間導入撹拌した。ガスを導入した後、撹拌、加熱を止め反応溶液よりも３０℃高く加熱しておいたハイコールＫ−２９０を１０ｇと市販のモレキュラ―シーブ３Ａを５ｇを反応容器に入れた後、混合物が約４５℃に冷却するまで緩やかに撹拌した。次いで、分散液の上部に浮いたリチウムとハイコールＫ−２９０の混合物をビーカーに移した。更に、そのビーカーに移した混合物ををヘキサンで３度濾過洗浄し、炭化水素油媒体を除去した。ろ物をアルゴン雰囲気化のオーブンで乾燥させ、微量の溶媒を除去し、生じた自由流動性の粉末を貯蔵瓶に移して安定化リチウム粉末を作製した。
[Example 1]
10 g of commercially available lithium metal was charged to a stainless steel flask reactor at room temperature under an atmosphere of dry argon. The reactor was installed such that heat control was possible with an oil bath. 50 g of liquid paraffin high coal K-290 (manufactured by Kaneda) was added into the reactor. Next, the reactor was heated to about 200 ° C. using a hot stirrer, and visually confirmed that the metal was melted using a stirrer. Next, the lithium powder was finely divided by vigorous stirring using a stirrer, and then high-purity carbon dioxide gas was introduced and stirred at a rate of 100 ml / min for about 1 minute while further heating at about 20 ° C. during high-speed stirring. After the gas was introduced, stirring and heating were stopped, 10 g of Hicoll K-290, which had been heated 30 ° C. higher than the reaction solution, and 5 g of commercially available molecular sieve 3A were placed in the reaction vessel. Stirred gently until cooled to ° C. Next, the mixture of lithium and Hi-Kol K-290 floating on the top of the dispersion was transferred to a beaker. Further, the mixture transferred to the beaker was filtered and washed three times with hexane to remove the hydrocarbon oil medium. The filtrate was dried in an oven under an argon atmosphere to remove a trace amount of solvent, and the resulting free-flowing powder was transferred to a storage bottle to produce a stabilized lithium powder.
この安定化リチウム粉末の成分比を測定した結果、Ｘ線回折およびＬｉ固体ＮＭＲにより、水酸化リチウムは安定化リチウム粉末全体に対し２．０重量％であることがわかった。また酸化リチウムが１．０重量％、リチウム金属が９６．０重量％とその他１．０重量％であることが判明した。 As a result of measuring the component ratio of this stabilized lithium powder, X-ray diffraction and Li solid NMR revealed that lithium hydroxide was 2.0% by weight based on the whole stabilized lithium powder. It was also found that lithium oxide was 1.0% by weight, lithium metal was 96.0% by weight, and 1.0% by weight.
＜リチウムドープ活物質の作製＞
この安定化リチウムパウダーを用い、リチウムドープ活物質の作製を、露点マイナス５０℃〜マイナス４０℃のドライルーム中において、以下の手順で行った。電解液として、１ＭのＬｉＰＦ６溶液（溶媒：エチレンカーボネート／ジエチルカーボネート＝３／７（体積比））を調製した。この電解液５０質量部中に、負極活物質（ＳｉＯ）１００質量部と、上記安定化リチウムパウダー７質量部とを加え、混合物を得た。得られた混合物をマグネチックスターラーで室温にて２４時間攪拌することで、負極活物質と上記安定化リチウムパウダーとを電気的に接触させ、負極活物質にリチウムをドープした（ドーピング工程）。その後、得られた活物質をジエチルカーボネートで洗浄し、真空乾燥してリチウムドープ活物質を得た。
<Preparation of lithium-doped active material>
Using the stabilized lithium powder, a lithium-doped active material was produced in a dry room having a dew point of −50 ° C. to −40 ° C. in the following procedure. As an electrolytic solution, a 1 M LiPF 6 solution (solvent: ethylene carbonate / diethyl carbonate = 3/7 (volume ratio)) was prepared. 100 parts by mass of the negative electrode active material (SiO) and 7 parts by mass of the above-mentioned stabilized lithium powder were added to 50 parts by mass of the electrolytic solution to obtain a mixture. The resulting mixture was stirred with a magnetic stirrer at room temperature for 24 hours to bring the negative electrode active material into electrical contact with the stabilized lithium powder, thereby doping lithium into the negative electrode active material (doping step). Thereafter, the obtained active material was washed with diethyl carbonate and dried in vacuum to obtain a lithium-doped active material.
＜負極の作製＞
上記の方法で作製したリチウムドープ活物質８３質量部、導電助剤としてアセチレンブラック２質量部、バインダとしてポリアミドイミド１５質量部、及び溶剤としてＮ−メチルピロリドン８２質量部を混合し、活物質層形成用のスラリーを調製した。このスラリーを、集電体として厚さ１４μｍの銅箔の一面に、リチウムドープ活物質の塗布量が２．０ｍｇ／ｃｍ２となるように塗布し、１００℃で乾燥することで負極活物質層を形成した。その後、ローラープレスにより集電体上に形成した負極活物質層を加圧成形し、真空中、３５０℃で３時間熱処理することで、活物質層の厚さが２２μｍである負極を得た。
<Preparation of negative electrode>
83 parts by mass of the lithium-doped active material prepared by the above method, 2 parts by mass of acetylene black as a conductive aid, 15 parts by mass of polyamideimide as a binder, and 82 parts by mass of N-methylpyrrolidone as a solvent were mixed to form an active material layer. Slurry was prepared. This slurry was applied to one surface of a copper foil having a thickness of 14 μm as a current collector so that the application amount of the lithium-doped active material was 2.0 mg / cm 2, and dried at 100 ° C. to form a negative electrode active material layer. Was formed. Thereafter, the negative electrode active material layer formed on the current collector was formed by pressure using a roller press, and heat-treated at 350 ° C. for 3 hours in a vacuum to obtain a negative electrode having a thickness of the active material layer of 22 μm.
＜生産性確認試験＞
上記＜負極の作製＞の方法で負極を３０枚作製を試み、作業中に１００℃／秒以上の急激な温度上昇が生じ電極が損失したものの電極枚数を表１に示す。
＜評価用リチウムイオン二次電池の作製＞
上記で作製した負極と、正極として銅箔にリチウム金属箔を貼り付けた対極とを、それらの間にポリエチレン微多孔膜からなるセパレータを挟んでアルミラミネートパックに入れ、このアルミラミネートパックに、電解液として１ＭのＬｉＰＦ６溶液（溶媒：エチレンカーボネート／ジエチルカーボネート＝３／７（体積比））を注入した後、真空シールし、評価用のリチウムイオン二次電池を作製した。
<Productivity confirmation test>
An attempt was made to produce 30 negative electrodes by the method of <Preparation of Negative Electrode>, and Table 1 shows the number of electrodes where a rapid temperature rise of 100 ° C./sec or more occurred and the electrodes were lost during the operation.
<Production of lithium ion secondary battery for evaluation>
The negative electrode prepared above and a counter electrode obtained by attaching a lithium metal foil to a copper foil as a positive electrode are put in an aluminum laminate pack with a separator made of a microporous polyethylene film interposed therebetween. After injecting a 1M LiPF 6 solution (solvent: ethylene carbonate / diethyl carbonate = 3/7 (volume ratio)) as a liquid, vacuum sealing was performed to prepare a lithium ion secondary battery for evaluation.
＜初期充放電効率の測定＞
実施例及び比較例で作製した評価用リチウムイオン二次電池について、二次電池充放電試験装置（北斗電工株式会社製）を用い、電圧範囲を０．００５Ｖから２．５Ｖまでとし、１Ｃ＝１６００ｍＡｈ／ｇとしたときの０．０５Ｃでの電流値で充放電を行った。これにより、初期充電容量、初期放電容量及び初期効率を求めた。なお、初期効率（％）は、初期充電容量に対する初期放電容量の割合（１００×初期放電容量／初期充電容量）である。この初期効率が高いほど、不可逆容量が低減されており、優れたドーピング効率が得られていることを意味する。結果を表１に示す。
<Measurement of initial charge / discharge efficiency>
Regarding the lithium ion secondary batteries for evaluation produced in Examples and Comparative Examples, using a secondary battery charge / discharge tester (manufactured by Hokuto Denko Corporation), the voltage range was from 0.005 V to 2.5 V, and 1C = 1600 mAh. The charge / discharge was performed at a current value of 0.05 C / g. Thereby, the initial charge capacity, the initial discharge capacity, and the initial efficiency were obtained. The initial efficiency (%) is a ratio of the initial discharge capacity to the initial charge capacity (100 × initial discharge capacity / initial charge capacity). The higher the initial efficiency is, the lower the irreversible capacity is, which means that an excellent doping efficiency is obtained. Table 1 shows the results.
［実施例２］
モレキュラ―シーブ３Ａの量を７ｇに変更した以外は実施例１と同様の方法にて、表１の実施例２に記載した成分を含む安定化リチウム粉末を作製した。この安定化リチウム粉末を用いて行った生産性確認試験、初期充放電効率においても良好であることがわかった。この安定化リチウム粉末の成分比を測定した結果、Ｘ線回折およびＬｉ固体ＮＭＲにより、水酸化リチウムは安定化リチウム粉末全体に対し１．０重量％であることがわかった。また酸化リチウムが１．０重量％、リチウム金属が９８．０重量％であることが判明した。
[Example 2]
A stabilized lithium powder containing the components described in Example 2 of Table 1 was produced in the same manner as in Example 1 except that the amount of Molecular Sieve 3A was changed to 7 g. It was found that the productivity confirmation test performed using the stabilized lithium powder and the initial charge / discharge efficiency were also good. As a result of measuring the component ratio of the stabilized lithium powder, X-ray diffraction and Li solid NMR revealed that lithium hydroxide was 1.0% by weight based on the whole stabilized lithium powder. It was also found that lithium oxide was 1.0% by weight and lithium metal was 98.0% by weight.
［実施例３］
高純度炭酸ガスを導入する時間を１．４倍にし、モレキュラ―シーブ３Ａを７ｇ添加した以外は実施例１と同様の方法にて、表１の実施例３に記載した成分を含む安定化リチウム粉末を作製した。この安定化リチウム粉末を用いて行った生産性確認試験、初期充放電効率においても良好であることがわかった。この安定化リチウム粉末の成分比を測定した結果、Ｘ線回折およびＬｉ固体ＮＭＲにより、水酸化リチウムは安定化リチウム粉末全体に対し１．０重量％であることがわかった。また酸化リチウムが２．０重量％、リチウム金属が９７．０重量％であることが判明した。
[Example 3]
Stabilized lithium containing the components described in Example 3 of Table 1 in the same manner as in Example 1 except that the time for introducing high-purity carbon dioxide gas was 1.4 times and 7 g of Molecular Sieve 3A was added. A powder was made. It was found that the productivity confirmation test performed using the stabilized lithium powder and the initial charge / discharge efficiency were also good. As a result of measuring the component ratio of the stabilized lithium powder, X-ray diffraction and Li solid NMR revealed that lithium hydroxide was 1.0% by weight based on the whole stabilized lithium powder. It was also found that lithium oxide was 2.0% by weight and lithium metal was 97.0% by weight.
［実施例４］
高純度炭酸ガスを導入する時間を２倍にし、反応溶液よりも３０℃高く加熱しておいたハイコールＫ−２９０を１５ｇとモレキュラ―シーブ３Ａを８ｇ添加した以外は実施例１と同様の方法において、表の実施例２に記載した成分を含む安定化リチウム粉末を作製した。生産性確認試験、初期充放電効率においても良好であることがわかった。この安定化リチウム粉末の成分比を測定した結果、Ｘ線回折およびＬｉ固体ＮＭＲにより、水酸化リチウムは安定化リチウム粉末全体に対し１．０重量％であることがわかった。また酸化リチウムが３．０重量％、リチウム金属が９６．０重量％であることが判明した。
[Example 4]
A method similar to that of Example 1 was repeated except that the time for introducing high-purity carbon dioxide was doubled, and 15 g of Hicoll K-290 and 8 g of Molecular Sieve 3A which had been heated 30 ° C. higher than the reaction solution were added. A stabilized lithium powder containing the components described in Example 2 in the table was produced. It was found that the productivity confirmation test and the initial charge / discharge efficiency were also good. As a result of measuring the component ratio of the stabilized lithium powder, X-ray diffraction and Li solid NMR revealed that lithium hydroxide was 1.0% by weight based on the whole stabilized lithium powder. It was also found that lithium oxide was 3.0% by weight and lithium metal was 96.0% by weight.
［実施例５］
高純度炭酸ガスを導入する時間を２．５倍にし、反応溶液よりも３０℃高く加熱しておいたハイコールＫ−２９０を１８ｇとモレキュラ―シーブ３Ａを１０ｇ添加した以外は実施例１と同様の方法において、表の実施例３の成分を含む安定化リチウム粉末を作製した。生産性確認試験、初期充放電効率においても良好であることがわかった。この安定化リチウム粉末の成分比を実施例１と同様に測定した結果、水酸化リチウムは検出されず安定化リチウム粉末全体に対し検出限界以下の１．０重量％未満であることがわかった。
［実施例６］
高純度炭酸ガスを導入する時間を３．５倍にし、反応溶液よりも３０℃高く加熱しておいたハイコールＫ−２９０を２０ｇとモレキュラ―シーブ３Ａを１２ｇ添加した以外は実施例１と同様の方法において、表の実施例４の成分を含む安定化リチウム粉末を作製した。生産性確認試験、初期充放電効率においても良好であることがわかった。この安定化リチウム粉末の成分比を実施例１と同様に測定した結果、水酸化リチウムは検出されず安定化リチウム粉末全体に対し検出限界以下の１．０重量％未満であることがわかった。
[Example 5]
The same as Example 1 except that the time for introducing high-purity carbon dioxide gas was increased by 2.5 times, and 18 g of Hicoll K-290 and 10 g of Molecular Sieve 3A which had been heated 30 ° C. higher than the reaction solution were added. In the method, a stabilized lithium powder containing the components of Example 3 in the table was prepared. It was found that the productivity confirmation test and the initial charge / discharge efficiency were also good. As a result of measuring the component ratio of the stabilized lithium powder in the same manner as in Example 1, no lithium hydroxide was detected, and it was found that the content was less than the detection limit of less than 1.0% by weight based on the entire stabilized lithium powder.
[Example 6]
The same procedure as in Example 1 was performed except that the time for introducing high-purity carbon dioxide gas was 3.5 times, and 20 g of Hicoll K-290 and 12 g of Molecular Sieve 3A which had been heated 30 ° C. higher than the reaction solution were added. In the method, a stabilized lithium powder containing the components of Example 4 in the table was prepared. It was found that the productivity confirmation test and the initial charge / discharge efficiency were also good. As a result of measuring the component ratio of the stabilized lithium powder in the same manner as in Example 1, no lithium hydroxide was detected, and it was found that the content was less than the detection limit of less than 1.0% by weight based on the entire stabilized lithium powder.
［実施例７〜９］
安定化リチウム粉の製造条件を、二酸化炭素の供給と同時に、市販のＦｅの粉末を表２の濃度になるように添加した以外は実施例１と同様として、実施例７〜９の安定化リチウム粉を得た。また、得られた安定化リチウム粉に対し実施例１と同様の方法にて負極を３０枚作製し、加速試験として５０℃条件下での安定性を確認した。その際、作業中に１００℃／秒以上の急激な温度上昇が生じた電極の枚数を表２に示す。併せて実施例１と同様の方法で初期充放電効率も測定した。その結果を表２に併記した。
[Examples 7 to 9]
The production conditions of the stabilized lithium powder were the same as those in Example 1 except that the commercially available Fe powder was added to the concentration shown in Table 2 simultaneously with the supply of carbon dioxide. Powder was obtained. In addition, 30 negative electrodes were prepared from the obtained stabilized lithium powder in the same manner as in Example 1, and the stability at 50 ° C. was confirmed as an acceleration test. At this time, Table 2 shows the number of electrodes where a rapid temperature rise of 100 ° C./sec or more occurred during the operation. In addition, the initial charge / discharge efficiency was measured in the same manner as in Example 1. The results are shown in Table 2.
その結果、実施例７〜９の試料はいずれも優れた安定性、すなわち優れた生産性を有する安定化リチウム粉であることが確認できた。 As a result, it was confirmed that all of the samples of Examples 7 to 9 were stabilized lithium powder having excellent stability, that is, excellent productivity.
［比較例１］
日本国特許公報第２６９９０２６号中に記載されている実施例１のプロセスと同様にリチウム金属３００ｇをアルゴンの存在下、乾燥雰囲気空間中でステンレス容器中に２ｇのナトリウム金属と９０％のペネテック炭化水素オイルを加え、２００℃で加熱しながら１００００ｒｐｍの高速度撹拌を行った。その際二酸化炭素を導入しながら５分間の撹拌を行った。その後６５℃まで冷却し、そのリチウム分散液を濾過し、グラスウールのろ過装置にてろ過し、ヘキサンで洗浄し従来のプロセスで作製した安定化リチウム粉末を得た。この安定化リチウム粉末を用いて、生産性確認試験を行った結果、５枚の電極がプレス後の発熱により電極が損失し一部の電池作製が行えなかった。
[Comparative Example 1]
Similar to the process of Example 1 described in Japanese Patent Publication No. 2699026, 300 g of lithium metal was put in a stainless steel container in a dry atmosphere space in a stainless steel container in the presence of argon in the presence of 2 g of sodium metal and 90% penetec hydrocarbon. Oil was added, and high-speed stirring at 10,000 rpm was performed while heating at 200 ° C. At that time, stirring was performed for 5 minutes while introducing carbon dioxide. After cooling to 65 ° C., the lithium dispersion was filtered, filtered through a glass wool filter, and washed with hexane to obtain a stabilized lithium powder produced by a conventional process. As a result of conducting a productivity confirmation test using the stabilized lithium powder, as a result, the electrodes of the five electrodes were lost due to heat generation after pressing, and some of the batteries could not be manufactured.
［比較例２］
市販されているリチウム粒子の表面に無機化合物の安定化層が施されていないリチウム粉末を用いて、生産性確認試験を行った結果、全ての電極がプレス後の発熱により電極が損失しこれらの電池作製が行えなかった。
[Comparative Example 2]
As a result of conducting a productivity confirmation test using lithium powder on the surface of a commercially available lithium particle on which a stabilizing layer of an inorganic compound has not been applied, all electrodes were lost due to heat generation after pressing, and these electrodes were lost. Battery fabrication failed.
［比較例３］
高純度炭酸ガスを導入する際の時間を０．５倍、温度を１９０℃にした以外は実施例１と同様の方法において、表の比較例３の成分を含む安定化リチウム粉末を作製した。生産性確認試験を行った結果、３枚の電極がプレス後の発熱により電極が損失し一部の電池作製が行えなかった。
A stabilized lithium powder containing the components of Comparative Example 3 in the table was prepared in the same manner as in Example 1, except that the time for introducing high-purity carbon dioxide gas was 0.5 times and the temperature was 190 ° C. As a result of the productivity confirmation test, the three electrodes lost heat due to heat generation after pressing, and some batteries could not be manufactured.
１…安定化層、２…リチウム粒子、１０…正極、１２…正極集電体、１４…正極活物質層、１８…セパレータ、２０…負極、２２…負極集電体、２４…負極活物質層、３０…積層体、５０…外装体、６２…正極リード、６０…負極リード、１００…リチウムイオン二次電池
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| JPH11135153A (en) * | 1997-10-31 | 1999-05-21 | Denso Corp | Nonaqueous electrolyte secondary battery |
| JP2003168431A (en) * | 2001-11-30 | 2003-06-13 | Toyota Central Res & Dev Lab Inc | Positive electrode active material for lithium secondary battery, its manufacturing method and lithium secondary battery using the same |
| JP2008300178A (en) * | 2007-05-31 | 2008-12-11 | Samsung Sdi Co Ltd | Nonaqueous secondary battery |
| US20090061321A1 (en) * | 2007-08-31 | 2009-03-05 | Fmc Corporation, Lithium Division | Stabilized lithium metal powder for li-ion application, composition and process |
| JP2013089321A (en) * | 2011-10-13 | 2013-05-13 | Samsung Yokohama Research Institute Co Ltd | Lithium ion secondary battery and method for producing positive electrode active material for lithium ion secondary battery |
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2015
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