JP2016081855A - Positive electrode material for nonaqueous electrolyte lithium ion secondary batteries, and nonaqueous electrolyte lithium ion secondary battery arranged by use thereof - Google Patents
Positive electrode material for nonaqueous electrolyte lithium ion secondary batteries, and nonaqueous electrolyte lithium ion secondary battery arranged by use thereof Download PDFInfo
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本発明は、金属酸化物の被覆層を形成した非水電解質リチウムイオン二次電池用正極材料、及び、その正極材料を用いた非水電解質リチウムイオン二次電池用正極、及び、その正極を用いた非水電解質リチウムイオン二次電池に関する。 The present invention uses a positive electrode material for a non-aqueous electrolyte lithium ion secondary battery having a metal oxide coating layer formed thereon, a positive electrode for a non-aqueous electrolyte lithium ion secondary battery using the positive electrode material, and the positive electrode. The present invention relates to a non-aqueous electrolyte lithium ion secondary battery.
従来、長時間、経済的に使用できる電池として、再充電可能な二次電池の研究が継続して行なわれており、特にリチウムイオン電池は、４Ｖ級の高い電圧が得られ、高エネルギー密度であり、パソコンや携帯端末の電源などで広く普及するに至っている。車両搭載用電源も含め、今後益々の需要増大が見込まれている。これらの用途においては、電池の小型化・軽量化、高容量が求められており、電池のエネルギー密度を高めることや高いサイクル安定性が要求されている。 Conventionally, as a battery that can be used economically for a long time, research on a rechargeable secondary battery has been continuously carried out. In particular, a lithium ion battery has a high voltage of 4V and has a high energy density. Yes, it has become widespread in PCs and mobile terminals. Increasing demand is expected in the future, including on-board power supplies. In these applications, battery size and weight reduction and high capacity are required, and it is required to increase the energy density of the battery and to have high cycle stability.
リチウムイオン二次電池用の正極活物質には、ＬｉＣｏＯ２、ＬｉＮｉＯ２、ＬｉＮｉ０．８Ｃｏ０．２Ｏ２、ＬｉＭｎ２Ｏ４、ＬｉＮｉ０．３３Ｃｏ０．３３Ｍｎ０．３３Ｏ２等のリチウムと遷移金属等との複合酸化物が用いられており、リチウムに対し４Ｖ以上の電位を示し、正極活物質として用いると高いエネルギー密度を有する二次電池が実現できる。しかし、この電位が高い状態での繰り返し使用により、電解液を形成する有機成分が酸化分解するなど、電池の充放電特性に悪影響を与え、電池特性が劣化する課題がある。 Examples of the positive electrode active material for the lithium ion secondary battery include LiCoO 2 , LiNiO 2 , LiNi 0.8 Co 0.2 O 2 , LiMn 2 O 4 , LiNi 0.33 Co 0.33 Mn 0.33 O 2 and the like. A composite oxide of lithium and a transition metal or the like is used, and a secondary battery having a high energy density can be realized when it exhibits a potential of 4 V or more with respect to lithium and is used as a positive electrode active material. However, repeated use in a state where the potential is high has a problem that the battery components are deteriorated by adversely affecting the charge / discharge characteristics of the battery, such as oxidative decomposition of the organic components forming the electrolyte solution.
これらを解決するために、化学的に安定で、電気化学的に不活性な材料で、正極活物質表面を被覆して改良することが試みられており、表面を被覆することによりサイクル特性の向上、レート特性の向上、高温保存特性による影響の抑制の効果があることが分かっている。しかし、表面を被覆することで電池の内部抵抗が上昇するため、電池容量は低下してしまう問題がある。特許文献１では、Ｍｎを含有する正極活物質表面に金属酸化物を被覆したものを用いた正極の抵抗を測定し、被覆することにより抵抗が小さくなり電池内で発生したフッ酸による劣化が抑制されたことを述べている。 In order to solve these problems, attempts have been made to coat and improve the surface of the positive electrode active material with a chemically stable and electrochemically inert material, and the cycle characteristics are improved by coating the surface. It has been found that there is an effect of improving the rate characteristics and suppressing the influence due to the high temperature storage characteristics. However, since the internal resistance of the battery increases by covering the surface, there is a problem that the battery capacity decreases. In Patent Document 1, the resistance of a positive electrode using a surface of a positive electrode active material containing Mn coated with a metal oxide is measured, and the resistance is reduced by the coating, so that deterioration due to hydrofluoric acid generated in the battery is suppressed. States that it was.
しかしながら、特許文献１では正極活物質に対応して４．８Ｖという、実電池では使用しない領域の高電圧が必要であり、実際、そのような高電圧では、電解液の酸化分解を抑える技術は見いだされていないのが現状である。 However, Patent Document 1 requires a high voltage of 4.8 V corresponding to the positive electrode active material, which is not used in an actual battery. In fact, a technique for suppressing oxidative decomposition of an electrolyte solution at such a high voltage is not disclosed. The current situation is not found.
本発明は、二次電池の内部抵抗を低減し、高容量を維持でき、高温環境下も含めた充放電サイクル特性が優れた非水電解質リチウムイオン二次電池用正極材料とその正極材料を用いた正極及びこの正極を用いて構成された非水電解質リチウムイオン二次電池を提供することを課題とする。 The present invention uses a positive electrode material for a non-aqueous electrolyte lithium ion secondary battery that can reduce internal resistance of a secondary battery, maintain high capacity, and has excellent charge / discharge cycle characteristics including high temperature environments, and the positive electrode material. It is an object of the present invention to provide a positive electrode and a non-aqueous electrolyte lithium ion secondary battery configured using the positive electrode.
本発明者らは、上記目的を達成すべく検討を行い、その結果、リチウム含有複合酸化物の表面に、金属酸化物層（金属はＴｉ、Ｖ、Ｚｒ、Ｎｂ、Ｔａのいずれか一種）が均一に前記リチウム含有複合酸化物粉末の表面を覆っており、かつ、該金属酸化物被覆層内にリチウムが存在している正極材料を得ることができることを見出した。そして、この正極材料を正極活物質とした正極を用いて構成された非水電解質リチウムイオン二次電池の内部抵抗が、金属酸化物被覆を施さない正極材料を含む正極を用いて構成された非水電解質リチウムイオン二次電池に対して低くなることを見出し、本発明を完成するに至った。 The present inventors have studied to achieve the above object, and as a result, a metal oxide layer (metal is any one of Ti, V, Zr, Nb, and Ta) is formed on the surface of the lithium-containing composite oxide. It was found that a positive electrode material that uniformly covers the surface of the lithium-containing composite oxide powder and in which lithium is present in the metal oxide coating layer can be obtained. And the internal resistance of the non-aqueous electrolyte lithium ion secondary battery configured using a positive electrode using the positive electrode material as a positive electrode active material is a non-configured using a positive electrode including a positive electrode material that is not coated with a metal oxide. It has been found that it is lower than that of the water electrolyte lithium ion secondary battery, and the present invention has been completed.
すなわち、本発明は、以下の発明を提供する。
（１） リチウム含有複合酸化物を活物質とする非水電解質リチウムイオン二次電池用正極材料において、リチウム含有複合酸化物の表面に、金属酸化物（金属はＴｉ、Ｖ、Ｚｒ、Ｎｂ、Ｔａのいずれか一種）の被覆層を形成し、前記金属酸化物被覆層が均一に前記リチウム含有複合酸化物粉末の表面を覆っており、かつ、前記金属酸化物被覆層内にリチウムが存在していることを特徴とする非水電解質リチウムイオン二次電池用正極材料。
（２） 上記（１）に記載のリチウム含有複合酸化物が、一般式ＬｉｘＭＯｙ（式中のＭは、Ｃｏ、Ｎｉ、Ｍｎ、Ａｌ、Ｍｇの少なくとも一種を含む。また、式中のｘは０．９〜１．２、式中のｙは２又は４である。）であることを特徴とする非水電解質リチウムイオン二次電池用正極材料。
（３） 上記（１）又は上記（２）に記載の正極材料を含むことを特徴とする非水電解質リチウムイオン二次電池用正極。
（４） 上記（３）に記載の正極を用いて構成されたことを特徴とする非水電解質リチウムイオン二次電池。
（５） 上記（４）の非水電解質リチウムイオン二次電池の抵抗が、金属酸化物被覆を施さないリチウム含有複合酸化物を含む正極を用いて構成された非水電解質リチウムイオン二次電池に対して低いことを特徴とする上記（４）に記載の非水電解質リチウムイオン二次電池。
That is, the present invention provides the following inventions.
(1) In a positive electrode material for a non-aqueous electrolyte lithium ion secondary battery using a lithium-containing composite oxide as an active material, a metal oxide (metal is Ti, V, Zr, Nb, Ta) on the surface of the lithium-containing composite oxide. Any one kind of coating layer), the metal oxide coating layer uniformly covers the surface of the lithium-containing composite oxide powder, and lithium is present in the metal oxide coating layer. A positive electrode material for a non-aqueous electrolyte lithium ion secondary battery.
(2) The lithium-containing composite oxide according to (1) above has a general formula LixMOy (wherein M includes at least one of Co, Ni, Mn, Al, and Mg. X in the formula is 0) .9 to 1.2, and y in the formula is 2 or 4.) A positive electrode material for a non-aqueous electrolyte lithium ion secondary battery.
(3) A positive electrode for a nonaqueous electrolyte lithium ion secondary battery comprising the positive electrode material according to (1) or (2).
(4) A nonaqueous electrolyte lithium ion secondary battery comprising the positive electrode according to (3).
(5) A non-aqueous electrolyte lithium ion secondary battery in which the resistance of the non-aqueous electrolyte lithium ion secondary battery of (4) is configured using a positive electrode including a lithium-containing composite oxide that is not coated with a metal oxide. The nonaqueous electrolyte lithium ion secondary battery according to (4) above, which is low.
本発明に係わる非水電解質リチウムイオン二次電池用正極材料は、金属酸化物層が均一にリチウム含有複合酸化物粉末の表面を覆い、かつ、該金属酸化物被覆層内にリチウムが存在しているため、本発明に係わる非水電解質リチウムイオン二次電池用正極材料を正極活物質として用いて製造された二次電池は、電池量を維持し、高温環境下も含めた充放電サイクル特性に優れる。したがって、エネルギー密度が要求される非水電解質二次電池、すなわち多機能の小型携帯機器用、自動車用、電動工具用等の非水電解質二次電池に有用であり、本発明は、工業的に極めて有用である。 In the positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to the present invention, the metal oxide layer uniformly covers the surface of the lithium-containing composite oxide powder, and lithium is present in the metal oxide coating layer. Therefore, the secondary battery manufactured using the positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to the present invention as a positive electrode active material maintains the battery amount and has charge / discharge cycle characteristics including a high temperature environment. Excellent. Therefore, it is useful for non-aqueous electrolyte secondary batteries that require energy density, that is, non-aqueous electrolyte secondary batteries for multifunctional small portable devices, automobiles, power tools, etc. Very useful.
本発明に係わる母材となる活物質のリチウム含有複合酸化物は、一般式ＬｉｘＭＯｙで表され、式中のＭは、Ｃｏ、Ｎｉ、Ｍｎ、Ａｌ、Ｍｇの少なくとも一種を含む。また、式中のｘは０．９〜１．２、式中のｙは２又は４であり、好ましくは、ｘは０．９５〜１．１である。また、この式において、金属Ｍは、Ｃｏ、Ｎｉ、Ｍｎ、Ａｌ、Ｍｇの少なくとも一種以上の元素を含む金属である。そして、金属Ｍが複数の元素からなる場合、金属Ｍは、実用性の観点から、少なくともＣｏ、Ｎｉ、Ｍｎを含む場合が好ましく、さらにＡｌ、ＭｇはＣｏ、Ｎｉ、Ｍｎを含む状態で同時に含むことが好ましい。 The active material lithium-containing composite oxide as a base material according to the present invention is represented by the general formula LixMOy, and M in the formula includes at least one of Co, Ni, Mn, Al, and Mg. Moreover, x in the formula is 0.9 to 1.2, and y in the formula is 2 or 4, and preferably x is 0.95 to 1.1. Further, in this formula, the metal M is a metal containing at least one element of Co, Ni, Mn, Al, and Mg. When the metal M is composed of a plurality of elements, the metal M preferably contains at least Co, Ni, and Mn from the viewpoint of practicality. Further, Al and Mg are simultaneously contained in a state containing Co, Ni, and Mn. It is preferable.
リチウム含有複合酸化物は、例えば、ＬｉＣｏＯ２、ＬｉＮｉＯ２、ＬｉＮｉ０．８Ｃｏ０．２Ｏ２、ＬｉＭｎ２Ｏ４、ＬｉＮｉ０．３３Ｃｏ０．３３Ｍｎ０．３３Ｏ２などを用いることができる。 As the lithium-containing composite oxide, for example, LiCoO 2 , LiNiO 2 , LiNi 0.8 Co 0.2 O 2 , LiMn 2 O 4 , LiNi 0.33 Co 0.33 Mn 0.33 O 2, or the like is used. it can.
本発明に係る表面被覆したリチウム含有複合酸化物粒子は、リチウム含有複合酸化物の表面に、金属酸化物層（金属はＴｉ、Ｖ、Ｚｒ、Ｎｂ、Ｔａのいずれか一種）が均一に前記リチウム含有複合酸化物粉末の表面を覆っており、かつ、該金属酸化物被覆層内にリチウムが存在していることで本発明の効果が達成される。金属酸化物の金属元素はＴｉ、Ｖ、Ｚｒ、Ｎｂ、Ｔａのいずれか一種を含む。これはこれら金属元素を含む原料を用いて被覆処理製造を行うことで本発明の効果が現れる。 The surface-coated lithium-containing composite oxide particles according to the present invention have a metal oxide layer (metal is any one of Ti, V, Zr, Nb, and Ta) uniformly on the surface of the lithium-containing composite oxide. The effect of the present invention is achieved by covering the surface of the composite oxide powder and the presence of lithium in the metal oxide coating layer. The metal element of the metal oxide includes any one of Ti, V, Zr, Nb, and Ta. This is because the effect of the present invention is manifested by carrying out coating treatment production using raw materials containing these metal elements.
本発明の表面被覆したリチウム含有複合酸化物の製造方法について以下説明する。本発明は、被覆させる成分を、液相反応法を用いて、母材粒子表面に被覆させる。具体的には、金属を含有する化合物の原料をエタノール、２−プロパノール、ｎ−ブタノール、２−ブタノール等の有機溶媒に溶解させ、その中に母材粒子を投入し、超音波照射処理を行って母材表面全域に渡って金属を含有する化合物溶解液が接触する状態とする。引き続き所定温度で有機溶媒が揮発しないように還流管を繋げた状態で加熱反応処理を行い、反応後溶媒を減圧下除去し、残留物を乾燥した後、大気中あるいは酸素雰囲気中で加熱処理を行うことにより表面被覆処理した粒子を得る。 The method for producing the surface-coated lithium-containing composite oxide of the present invention will be described below. In the present invention, the base material particle surface is coated with the component to be coated using a liquid phase reaction method. Specifically, the raw material of the metal-containing compound is dissolved in an organic solvent such as ethanol, 2-propanol, n-butanol, 2-butanol, etc., and the base material particles are put therein, followed by ultrasonic irradiation treatment. Thus, the compound solution containing the metal is brought into contact over the entire surface of the base material. Subsequently, heat treatment is performed with the reflux tube connected so that the organic solvent does not volatilize at a predetermined temperature. After the reaction, the solvent is removed under reduced pressure, the residue is dried, and then heat treatment is performed in air or in an oxygen atmosphere. By performing, surface-treated particles are obtained.
好ましくは、被覆させる金属を含有する化合物の原料として、金属アルコキシドを用いる。金属アルコキシドは水による加水分解反応を起こし、引き続き重合反応を起こすことにより前駆体物を形成するが、加水分解時の水分量をコントロールすることにより前駆体物状態を調整し易いため原料として用いる。Ｔｉ、Ｖ、Ｚｒ、Ｎｂ、Ｔａは金属アルコキシドの原料として用いることができ、かつ、前駆体形成およびその後の加熱処理により母材表面に均一に金属酸化物層を形成することが可能である。 Preferably, a metal alkoxide is used as a raw material of the compound containing the metal to be coated. The metal alkoxide undergoes a hydrolysis reaction with water and subsequently forms a precursor by causing a polymerization reaction, but is used as a raw material because the precursor state can be easily adjusted by controlling the amount of water during hydrolysis. Ti, V, Zr, Nb, and Ta can be used as raw materials for the metal alkoxide, and a metal oxide layer can be uniformly formed on the surface of the base material by precursor formation and subsequent heat treatment.
加水分解時の水分量は、極少量であるのが好ましい。この場合、新たに外部より水を添加するのではなく、大気中に含まれる程度の水分量が好適である。Ｔｉ、Ｖ、Ｚｒ、Ｎｂ、Ｔａの金属アルコキシドは、水との接触により反応が速く進行するため、水量が多くなると重合反応が速く進み重合度が増して粒子成長が促進された状態となる。その結果、金属酸化物の前駆体粒子が大きくなること、および、前駆体粒子同士が凝集した二次付着物状態となりやすく、母材表面に均一に被覆することが出来なくなる。 It is preferable that the amount of water during hydrolysis is extremely small. In this case, the amount of water contained in the atmosphere is suitable instead of newly adding water from the outside. The reaction of metal alkoxides of Ti, V, Zr, Nb, and Ta proceeds rapidly by contact with water. Therefore, when the amount of water increases, the polymerization reaction proceeds faster, the degree of polymerization increases, and particle growth is promoted. As a result, the precursor particles of the metal oxide become large, and the precursor particles tend to be in a secondary adhering state in which the precursor particles are aggregated, so that the surface of the base material cannot be uniformly coated.
前記の水分量で加熱した状態での加水分解反応、引き続く緩やかな重合反応により、適度な重合状態まで進行した状態で金属酸化物の前駆体物が形成される。反応させるための加熱温度は有機溶媒の沸点未満であれば、好適な金属酸化物の前駆体物が得られる。反応終了後、例えば、実験室的にはロータリーエバポレーター装置を用いて減圧下で有機溶媒を徐々に除去して残留物を回収し、その残留物を乾燥処理することにより母材表面に前駆体物が覆われた状態の固形粉末が得られる。 A precursor of metal oxide is formed in a state of proceeding to an appropriate polymerization state by the hydrolysis reaction in the state heated with the water content and the subsequent slow polymerization reaction. If the heating temperature for the reaction is less than the boiling point of the organic solvent, a suitable metal oxide precursor can be obtained. After the reaction is completed, for example, in the laboratory, the organic solvent is gradually removed under reduced pressure using a rotary evaporator apparatus, and the residue is recovered. A solid powder in a state of being covered with is obtained.
得られた粉末を大気中あるいは酸素雰囲気中で加熱焼成することで金属酸化物が得られる。本発明では、ＴｉＯ２、Ｖ２Ｏ５、ＺｒＯ２、Ｎｂ２Ｏ５、Ｔａ２Ｏ５が得られる。焼成温度は、３００〜７００℃が好ましい。３００℃未満では、出発原料に含まれる有機成分が残留することがあり、安定した電池性能を引き出せなくなる。一方、７００℃を超えると、金属酸化物の結晶生成が促進されて結晶性が高くなり過ぎることおよび金属酸化物層内にリチウムが過多に拡散移動してきて電気化学的に不活性な金属酸化物とは異なる組成の被覆層と成ってしまうため、電解液劣化の抑制効果が低くなってしまうため好ましくない。焼成温度は、さらには、特に４５０℃〜５５０℃がより好ましく、この温度領域では、金属酸化物が形成されるとともに、母材よりリチウム成分が金属酸化物層内に拡散移動するようになり、母材と金属酸化物の界面付近の金属酸化物層にリチウムが多く存在する被覆層が形成されるようになる。このような被覆層となることで、被覆層のリチウムイオン伝導性が高まり、二次電池の充放電作動時に、正極粒子でのリチウムイオンの挿脱入が促進されたものと発明者らは推定している。 The obtained powder is heated and fired in the air or in an oxygen atmosphere to obtain a metal oxide. In the present invention, TiO 2, V 2 O 5 , ZrO 2, Nb 2 O 5, Ta 2 O 5 is obtained. The firing temperature is preferably 300 to 700 ° C. If it is less than 300 degreeC, the organic component contained in a starting material may remain, and it becomes impossible to draw out stable battery performance. On the other hand, if the temperature exceeds 700 ° C., the crystal formation of the metal oxide is promoted and the crystallinity becomes too high, and lithium is diffused and moved excessively in the metal oxide layer, which is electrochemically inactive. Since the coating layer has a composition different from that of the liquid crystal, the effect of suppressing the deterioration of the electrolytic solution is lowered, which is not preferable. The firing temperature is more preferably 450 ° C. to 550 ° C., and in this temperature range, a metal oxide is formed and a lithium component diffuses and moves from the base material into the metal oxide layer. A coating layer containing a large amount of lithium is formed on the metal oxide layer near the interface between the base material and the metal oxide. The inventors estimate that the lithium ion conductivity of the coating layer is increased and the insertion / extraction of lithium ions in the positive electrode particles is promoted during the charging / discharging operation of the secondary battery by using such a coating layer. doing.
本発明の金属酸化物はリチウム含有複合酸化物粉末全質量に対して０．１０〜０．７５質量％で均一に被覆させるのが好ましい。０．１０質量％未満では、活物質粒子表面を完全に被覆することが出来ず、特に電解液と活物質の界面反応を抑制する効果が不十分となる。一方、０．７５質量％を超えると、被覆厚みが厚くなり過ぎて被覆層内にリチウムが存在しない電気化学的に不活性な金属酸化物層の割合が増えていき、リチウムイオンの挿脱入が阻害されてしまうため得られる電池容量が低下してしまい好ましくない。 The metal oxide of the present invention is preferably uniformly coated at 0.10 to 0.75% by mass with respect to the total mass of the lithium-containing composite oxide powder. If it is less than 0.10% by mass, the surface of the active material particles cannot be completely covered, and in particular, the effect of suppressing the interface reaction between the electrolytic solution and the active material becomes insufficient. On the other hand, if it exceeds 0.75 mass%, the coating thickness becomes too thick and the proportion of the electrochemically inactive metal oxide layer in which lithium is not present in the coating layer increases, and lithium ion insertion / extraction occurs. Is not preferable because the obtained battery capacity decreases.
本発明で製造した表面被覆したリチウム含有複合酸化物粒子は、金属酸化物が均一に母材のリチウム含有複合酸化物粒子表面に被覆している。これは走査型電子顕微鏡による粒子表面状態の観察、エネルギー分散型Ｘ線分光法による被覆粒子全体にわたる被覆金属元素の存在の分布状態、およびＸ線光電子分光法による被覆層の各元素の存在比の併せた分析により確認することができる。走査型電子顕微鏡による数万倍の像拡大により母材表面に被覆した状態を観察できる。例えば、粒子が凝集した二次付着物となれば、母材表面に不均一に粒子形状の付着した状態で存在することが確認できる。一方、本発明では個々の被覆粒子の存在が観えないほど小さく連続的な皮膜状として均一に被覆しているため、母材との差異を認識することが難しい状態で存在する。エネルギー分散型Ｘ線分光法では、走査型電子顕微鏡より低い倍率の視野で被覆金属元素の存在の分布状態を確認できる。本発明の均一に被覆している粒子では金属酸化物の被覆金属元素が均一に分布した状態で存在し、比較対象とした不均一被覆粒子では不均一な分布状態で被覆金属元素が存在しているため、均一か不均一かの被覆状態の差異を確かめられる。Ｘ線光電子分光法では、表面近傍の各元素の存在比を確認することができる。Ｘ線光電子分光法は、光源として試料表面に特性Ｘ線を照射し、励起された試料表面から放出される光電子をエネルギー分光器にて検出する手法であり、光電子の脱出深さがおよそ数ｎｍ程度であり、測定試料の最表面近傍の情報を検出するのに有効な手段である。母材粒子中の金属元素とリチウム元素の存在比率で表したとき、被覆処理していない母材粒子中のリチウム元素比率に対して本発明の被覆粒子のリチウム元素比率が低く認められる。また被覆処理しても母材がむき出しの不均一な粒子では被覆処理していない母材粒子のみとそれほど差異がないリチウム元素比率で存在していた。このことは、本発明の被覆粒子は被覆層で均一に覆われているために、母材がむき出しの不均一な事象とは異なることを仄めかしており、本発明の被覆粒子が均一に被覆した状態であることを走査型電子顕微鏡とエネルギー分散型Ｘ線分光法の分析結果とともに照らし合わせることで類推することが出来る。 In the surface-coated lithium-containing composite oxide particles produced according to the present invention, the metal oxide is uniformly coated on the surface of the base lithium-containing composite oxide particles. This is because of the observation of the surface state of the particles with a scanning electron microscope, the distribution of the presence of the coated metal elements over the entire coated particles by energy dispersive X-ray spectroscopy, and the abundance ratio of each element in the coating layer by X-ray photoelectron spectroscopy. This can be confirmed by combined analysis. The surface of the base material can be observed by magnifying the image several tens of thousands times with a scanning electron microscope. For example, if it becomes a secondary adhering substance in which particles are aggregated, it can be confirmed that the particles are non-uniformly adhered to the surface of the base material. On the other hand, in the present invention, since it is uniformly coated as a continuous film that is so small that the presence of individual coated particles cannot be seen, it is difficult to recognize the difference from the base material. In the energy dispersive X-ray spectroscopy, the distribution state of the presence of the coating metal element can be confirmed with a field of view lower than that of the scanning electron microscope. In the uniformly coated particles of the present invention, the coated metal element of the metal oxide is present in a uniformly distributed state, and in the non-uniformly coated particles used for comparison, the coated metal element is present in a non-uniformly distributed state. Therefore, the difference in coating state between uniform and non-uniform can be confirmed. In X-ray photoelectron spectroscopy, the abundance ratio of each element in the vicinity of the surface can be confirmed. X-ray photoelectron spectroscopy is a technique in which a sample surface is irradiated with characteristic X-rays as a light source, and photoelectrons emitted from the excited sample surface are detected by an energy spectrometer, and the escape depth of photoelectrons is approximately several nm. This is an effective means for detecting information near the outermost surface of the measurement sample. When represented by the abundance ratio of the metal element and lithium element in the base material particles, the lithium element ratio of the coated particles of the present invention is recognized to be lower than the lithium element ratio in the base material particles not coated. Further, even if the coating treatment was performed, the non-uniform exposed base material particles were present in a lithium element ratio that was not so different from only the non-coated base material particles. This suggests that the coated particles of the present invention are uniformly covered with a coating layer, which is different from the phenomenon in which the base material is not exposed, and the coated particles of the present invention are uniformly coated. It can be analogized by comparing the state with the analysis results of a scanning electron microscope and energy dispersive X-ray spectroscopy.
前記したように本発明で製造した表面被覆したリチウム含有複合酸化物粒子は、金属酸化物被覆層内にリチウムが存在しており、その存在はＸ線光電子分光法による表面からの層内部にＸ線を浸入させた深さ方向の測定分析による被覆層および母材粒子の成分の所定元素の相対的比率より類推することができる。本発明の粒子では被覆成分の金属元素の存在に対するリチウム元素の存在比率が、表面付近では緩やかにリチウム比率が増加していくが、さらに内部まで測定していくにしたがい所定の深さよりリチウムの存在比率が急激に増加していくことが認められた。このことは、被覆層内で徐々に深さ方向でリチウム量が多くなり、所定の深さ以降はリチウムが元々存在する母材成分のみになっていることが推測されるものである。 As described above, in the surface-coated lithium-containing composite oxide particles produced in the present invention, lithium is present in the metal oxide coating layer, and the presence of X exists in the layer from the surface by X-ray photoelectron spectroscopy. It can be inferred from the relative ratio of the predetermined elements of the components of the coating layer and the base material particles by the measurement analysis in the depth direction into which the line has entered. In the particles of the present invention, the abundance ratio of the lithium element to the presence of the metal element of the coating component gradually increases in the vicinity of the surface, but the presence of lithium from a predetermined depth as it is further measured to the inside. It was observed that the ratio increased rapidly. This is presumed that the amount of lithium gradually increases in the depth direction in the coating layer, and only the base material component in which lithium originally exists after a predetermined depth.
本発明のリチウム二次電池を構成するための他の部材（材料）としては、従来公知の種々の材料を用いることができる。 As other members (materials) for constituting the lithium secondary battery of the present invention, various conventionally known materials can be used.
本発明に用いる負極活物質としては、リチウム系の負極材料であれば、特に限定されず、
リチウムドープ及び脱ドープ可能な材料であることが、安全性、サイクル寿命などの信頼性が向上するため好ましい。リチウムドープ及び脱ドープ可能な材料としては、公知のリチウム系二次電池用負極材料として使用されている黒鉛系物質、炭素系物質、錫酸化物系、ケイ素系酸化物などの金属酸化物、ケイ素、錫系合金などが挙げられる。
The negative electrode active material used in the present invention is not particularly limited as long as it is a lithium-based negative electrode material.
A lithium-doped and dedopeable material is preferable because reliability such as safety and cycle life is improved. Examples of materials that can be lithium-doped and dedope include graphite-based materials, carbon-based materials, tin oxide-based, silicon-based oxides and the like, which are used as known negative electrode materials for lithium secondary batteries, silicon And tin-based alloys.
本発明の正極活物質及び負極活物質を電極に形成する方法は、所望の非水系二次電池の特性などに応じて公知の手法から適宜選択することが出来る。例えば、正極活物質（又は負極活物質）とバインダー、必要に応じてＮ−メチル−２−ピロリドン（ＮＭＰ）などの溶媒とを混合し、スラリーを得た後、これを集電体に塗布し、乾燥後、圧縮して成形される塗布法や、活物質、ポリ四フッ化エチレンの混合物を混練し、圧延ロールを用いてシート化するシート法などが挙げられる。 The method for forming the positive electrode active material and the negative electrode active material of the present invention on the electrode can be appropriately selected from known methods according to the desired characteristics of the nonaqueous secondary battery. For example, a positive electrode active material (or negative electrode active material), a binder, and optionally a solvent such as N-methyl-2-pyrrolidone (NMP) are mixed to obtain a slurry, which is then applied to a current collector. Examples thereof include a coating method in which the mixture is dried and then compressed and a sheet method in which a mixture of an active material and polytetrafluoroethylene is kneaded and formed into a sheet using a rolling roll.
本発明の非水系二次電池に用いる正極及び負極を成形する場合、必要に応じ、導電材、バインダーを用いる。バインダーの種類は、特に限定されるものではないが、ポリフッ化ビニリデン、ポリ四フッ化エチレンなどのフッ素系樹脂類、フッ素系ゴム、ＳＢＲ、アクリル樹脂、ポリエチレン、ポリプロピレンなどのポリオレフィン類などが例示される。バインダー量はバインダーの種類、目的とする電極強度を勘案し、適宜決定することができる。 When forming the positive electrode and the negative electrode used in the non-aqueous secondary battery of the present invention, a conductive material and a binder are used as necessary. The type of the binder is not particularly limited, and examples thereof include fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene, fluorine rubber, SBR, acrylic resin, polyolefins such as polyethylene and polypropylene, and the like. The The amount of the binder can be appropriately determined in consideration of the type of binder and the intended electrode strength.
また、導電材の種類は、特に限定されるものではないが、カーボンブラック、アセチレンブラック、気相成長炭素繊維などが例示される。導電材量は、電極において、充分な電子伝導性を確保できれば、特に限定されるものではない。 The type of the conductive material is not particularly limited, and examples thereof include carbon black, acetylene black, and vapor grown carbon fiber. The amount of the conductive material is not particularly limited as long as sufficient electronic conductivity can be secured in the electrode.
正極、負極を集電体上に形成する場合、集電体の材質は材質の耐電圧性を考慮した上で選択することができ、銅箔、ステンレス鋼箔、チタン箔、アルミニウム箔などが例示される。 When the positive electrode and the negative electrode are formed on the current collector, the material of the current collector can be selected in consideration of the voltage resistance of the material, such as copper foil, stainless steel foil, titanium foil, and aluminum foil. Is done.
上記セルにおいて、正極、負極の間に絶縁、電解液保持の目的でセパレータが配置される場合、このセパレータは、特に限定されるものではなく、ポリエチレン微多孔膜、ポリプロピレン微多孔膜、あるいはポリエチレンとポリプロピレンの積層膜、セルロース抄紙、ガラス繊維、アラミド繊維、ポリアクリルニトリル繊維などからなる織布、あるいは不織布などがあり、その目的と状況に応じ、適宜決定することが可能である。 In the above cell, when a separator is disposed between the positive electrode and the negative electrode for the purpose of insulation and electrolyte solution retention, the separator is not particularly limited, and is a polyethylene microporous film, a polypropylene microporous film, or polyethylene. There are polypropylene laminated film, cellulose paper, woven fabric or nonwoven fabric made of glass fiber, aramid fiber, polyacrylonitrile fiber, etc., which can be appropriately determined according to the purpose and situation.
本発明の非水系二次電池は、例えば、電解質として非水系電解液、ゲル電解質、固体電解質を用いることができる。非水系電解液としては、リチウム塩を含む非水系電解液を用いることが可能であり、正極材料の種類、負極材料の性状、充電電圧などの使用条件などに対応して、適宜決定される。リチウム塩を含む非水系電解液としては、例えば、ＬｉＰＦ６
、ＬｉＢＦ４、ＬｉＣｌＯ４、リチウムビス（オキサラト）ボレート（ＬｉＢＯＢ）等のリチウム塩をプロピレンカーボネート、エチレンカーボネート、ジエチルカーボネート、ジメチルカーボネート、メチルエチルカーボネート、ジメトキシエタン、γ−ブチロラクトン、酢酸メチル、蟻酸メチルなどの１種又は２種以上からなる有機溶媒に溶解したものを用いることができる。また、電解液濃度は、特に限定されるものではないが、一般的に０．５〜２ｍｏｌ／ｌ程度が実用的である。電解液は、当然のことながら、水分が１００ｐｐｍ以下のものを用いることが好ましい。
In the non-aqueous secondary battery of the present invention, for example, a non-aqueous electrolyte solution, a gel electrolyte, or a solid electrolyte can be used as an electrolyte. As the non-aqueous electrolyte, a non-aqueous electrolyte containing a lithium salt can be used, and is appropriately determined according to the use conditions such as the type of the positive electrode material, the properties of the negative electrode material, and the charging voltage. As a non-aqueous electrolyte solution containing a lithium salt, for example, LiPF 6
LiBF 4 , LiClO 4 , lithium salts such as lithium bis (oxalato) borate (LiBOB), propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dimethoxyethane, γ-butyrolactone, methyl acetate, methyl formate, etc. Those dissolved in an organic solvent composed of one or more of the above can be used. Further, the concentration of the electrolytic solution is not particularly limited, but generally about 0.5 to 2 mol / l is practical. As a matter of course, it is preferable to use an electrolytic solution having a water content of 100 ppm or less.
本発明の非水系二次電池は、上記で説明した一般式ＬｉｘＭＯｙ（式中のＭは、Ｃｏ、Ｎｉ、Ｍｎ、Ａｌ、Ｍｇの少なくとも一種を含む。また、式中のｘは０．９〜１．２、式中のｙは２又は４である。）で表されるリチウム含有複合酸化物の表面に、金属酸化物（金属はＴｉ、Ｖ、Ｚｒ、Ｎｂ、Ｔａのいずれか一種）の被覆層を形成した非水電解質リチウムイオン二次電池用正極材料を用いた正極、負極、セパレータ、電解質などを電池容器内に収容した構成となる。 The nonaqueous secondary battery of the present invention has the general formula LixMOy described above (wherein M includes at least one of Co, Ni, Mn, Al, and Mg. Further, x in the formula is 0.9 to 0.9). 1.2, y in the formula is 2 or 4.) On the surface of the lithium-containing composite oxide represented by (1), a metal oxide (metal is any one of Ti, V, Zr, Nb, Ta). A positive electrode, a negative electrode, a separator, an electrolyte, and the like using a positive electrode material for a non-aqueous electrolyte lithium ion secondary battery in which a coating layer is formed are configured to be accommodated in a battery container.
本発明の非水系二次電池の形状は、特に限定されるものではなく、コイン型、円筒型、角型、フィルム型など、その目的に応じ、適宜決定することが可能である。 The shape of the non-aqueous secondary battery of the present invention is not particularly limited, and can be appropriately determined according to the purpose, such as a coin type, a cylindrical type, a square type, and a film type.
次に実施例を比較例と比較して本発明をさらに具体的に説明するが、これは単に例示であって本発明を制限するものではない。 Next, the present invention will be described more specifically by comparing examples with comparative examples. However, this is merely illustrative and does not limit the present invention.
〔被覆処理正極粒子の調製〕
（実施例）
母材であるリチウム含有複合酸化物としてＬｉＮｉ０．３３Ｃｏ０．３３Ｍｎ０．３３Ｏ２粒子（平均粒径１０μｍ）を用意した。開放系の環境で、ｎ−ブタノールを攪拌している中にジルコニウムブトキシド（Ｚｒ（ＯＣ４Ｈ９）４）を投入して溶解させた。その溶液に母材粒子を溶液中のジルコニウム量が母材粒子に対して０．５質量％になるように投入し、超音波照射を１０分間施した。引き続き９０℃で１時間処理を行い、室温放冷後、減圧下ｎ−ブタノールを除去し、残留物を１１０℃加熱乾燥して粉末を得た。この粉末を、電気炉を用いて５００℃で１時間の焼成処理を行い、室温まで放冷して被覆処理した正極粒子を得た。
[Preparation of coated cathode particles]
(Example)
LiNi 0.33 Co 0.33 Mn 0.33 O 2 particles (average particle size 10 μm) were prepared as a lithium-containing composite oxide as a base material. In an open system environment, zirconium butoxide (Zr (OC 4 H 9 ) 4 ) was added and dissolved while stirring n-butanol. Base material particles were added to the solution so that the amount of zirconium in the solution was 0.5 mass% with respect to the base material particles, and ultrasonic irradiation was performed for 10 minutes. Subsequently, the mixture was treated at 90 ° C for 1 hour, allowed to cool to room temperature, n-butanol was removed under reduced pressure, and the residue was heated and dried at 110 ° C to obtain a powder. This powder was fired at 500 ° C. for 1 hour using an electric furnace, allowed to cool to room temperature, and coated positive electrode particles were obtained.
（比較例１）
水に硝酸アルミニウム九水和物（Ａｌ（ＮＯ３）３・９Ｈ２Ｏ）を溶解させたものと、水にリン酸二水素アンモニウム（ＮＨ４Ｈ２ＰＯ４）を溶解したものを混合した水溶液を調製した。次に、希釈したアンモニア水をｐＨ＝７になるまで添加した。添加後徐々に白濁した。その溶液に実施例と同じ母材粒子を溶液中のアルミニウム＋リン酸量が母材粒子に対して０．５質量％になるように投入し、超音波照射を１０分間施した。引き続き９０℃で１時間処理を行い、室温放冷後、固液ろ過し、固形分を１１０℃加熱乾燥して粉末を得た。この粉末を、電気炉を用いて５００℃で１時間の焼成処理を行い、室温まで放冷して被覆処理した正極粒子を得た。
(Comparative Example 1)
Aluminum nitrate nonahydrate in water (Al (NO 3) 3 · 9H 2 O) and those obtained by dissolving an aqueous solution obtained by mixing a solution obtained by dissolving ammonium dihydrogen phosphate (NH 4 H 2 PO 4) in water Was prepared. Next, diluted aqueous ammonia was added until pH = 7. It became cloudy gradually after the addition. Into the solution, the same base material particles as in the example were added so that the amount of aluminum + phosphoric acid in the solution was 0.5 mass% with respect to the base material particles, and ultrasonic irradiation was performed for 10 minutes. Subsequently, the mixture was treated at 90 ° C. for 1 hour, allowed to cool to room temperature, filtered through solid-liquid, and the solid content was heated and dried at 110 ° C. to obtain a powder. This powder was fired at 500 ° C. for 1 hour using an electric furnace, allowed to cool to room temperature, and coated positive electrode particles were obtained.
（比較例２）
被覆用原料として、酢酸亜鉛二水和物（Ｚｎ（ＣＨ３ＣＯＯ）２・２Ｈ２Ｏ）を用いた以外は実施例と同様に実施した。
(Comparative Example 2)
As coating material, except for using zinc acetate dihydrate (Zn (CH 3 COO) 2 · 2H 2 O) was carried out analogously to Example.
実施例、比較例１、比較例２で得られた粒子を未被覆の母材粒子（比較例３）とともに走査型電子顕微鏡で粒子表面を観察した。図１に実施例で得られた粒子、図２に比較例１で得られた粒子、図３に比較例２で得られた粒子、図４に母材粒子の走査型電子顕微鏡写真を示す。実施例で得られた粒子表面は母材粒子（比較例３）と似たように観える。一方、比較例１では微粒形状物が母材表面に付着した箇所と付着していない箇所が観られ、比較例２も比較例１とは異なった微粒物が母材表面に付着した箇所と付着していない箇所が観られ、いずれも不均一に被覆した状態であること分かる。エネルギー分散型Ｘ線分光分析により粒子表面の被覆金属元素の分布状態を分析すると実施例ではジルコニウムが均一分散して観られ、比較例１ではアルミニウムおよびリンの分布に偏りが観られ，比較例２では亜鉛の分布に偏りが観られた。 The particle surfaces of the particles obtained in Examples, Comparative Examples 1 and 2 were observed with a scanning electron microscope together with uncoated base material particles (Comparative Example 3). FIG. 1 shows particles obtained in Examples, FIG. 2 shows particles obtained in Comparative Example 1, FIG. 3 shows particles obtained in Comparative Example 2, and FIG. 4 shows scanning electron micrographs of base material particles. The surface of the particles obtained in the examples looks similar to the base material particles (Comparative Example 3). On the other hand, in Comparative Example 1, a part where the fine-shaped object adhered to the surface of the base material and a part where it did not adhere were observed. The part which is not done is seen and it turns out that all are the states coat | covered unevenly. When the distribution state of the coated metal element on the particle surface is analyzed by energy dispersive X-ray spectroscopic analysis, zirconium is uniformly dispersed in the example, and in the comparative example 1, the distribution of aluminum and phosphorus is biased. Then there was a bias in the zinc distribution.
実施例の粒子、比較例１の粒子、母材粒子（比較例３）、について、Ｘ線光電子分光分析を実施し、母材粒子中の金属元素とリチウム元素の存在比率に対して、被膜処理粒子中のリチウム／母材のみのリチウムで表すと、実施例では８６％、比較例１では１０３％であり、比較例１は母材のみ粒子とほぼ同等レベルであった。また、深さ方向の測定分析（ＳｉＯ２換算での浸入深さ）では、被覆成分の金属元素の存在に対するリチウム元素の存在比率が、実施例（リチウム／ジルコニウム存在比率）では、表面から１０ｎｍ程度まではＬｉ／Ｚｒ比が３．９→４．４の緩やかにリチウム比率が増加していくが、さらに倍の深さまで測定していくにしたがい４．４→７．６となり、リチウムの存在比率が急激に増加していくことが確認でき、比較例１（リチウム／アルミニウムあるいはリン存在比率）では、そのような傾向は無かった。表面からの緩やかなリチウム比率の増加はジルコニア層が存在し、母材側に向かってリチウム量が増えていくと考えられ、さらにリチウムの存在比率が急激に増加するのが母材のみの割合が増えていくことに因るものと考えられる。以上のことより、走査型電子顕微鏡写真による粒子表面状態、エネルギー分散型Ｘ線分光分析による粒子表面の被覆金属元素の分布状態の結果と併せて解析すると、実施例では被覆層（ジルコニア）が母材表面に均一に被覆していると言え、その被覆層内に母材側よりリチウムが拡散してきていることが類推される。 X-ray photoelectron spectroscopic analysis was performed on the particles of Examples, the particles of Comparative Example 1, and the base material particles (Comparative Example 3), and the coating treatment was performed on the abundance ratio of the metal element and the lithium element in the base material particles. In terms of lithium in the particles / lithium only in the base material, it was 86% in the example and 103% in the comparative example 1, and in the comparative example 1, only the base material was almost the same level as the particle. Further, in the measurement analysis in the depth direction (penetration depth in terms of SiO 2 ), the abundance ratio of the lithium element to the presence of the metal element of the coating component is about 10 nm from the surface in the example (lithium / zirconium abundance ratio). Until then, the Li / Zr ratio gradually increases from 3.9 to 4.4, but as the depth is further increased from 4.4 to 7.6, the abundance ratio of lithium In Comparative Example 1 (lithium / aluminum or phosphorus existing ratio), there was no such tendency. The gradual increase in the lithium ratio from the surface is due to the presence of the zirconia layer, and the amount of lithium is expected to increase toward the base metal side. This is thought to be due to the increase. From the above, when analyzed together with the results of the particle surface state by scanning electron micrographs and the distribution state of the coating metal element on the particle surface by energy dispersive X-ray spectroscopic analysis, the coating layer (zirconia) is the mother layer in the examples. It can be said that the material surface is uniformly coated, and it can be inferred that lithium has diffused from the base material side into the coating layer.
［リチウム二次電池用正極活物質の電気化学評価］
上記実施例及び比較例のリチウム二次電池用正極活物質を用いて以下の手順で評価セルを作製し、初期充放電特性、交流抵抗、高温サイクル特性を評価した。
[Electrochemical evaluation of cathode active material for lithium secondary battery]
An evaluation cell was prepared according to the following procedure using the positive electrode active materials for lithium secondary batteries of the above Examples and Comparative Examples, and initial charge / discharge characteristics, AC resistance, and high temperature cycle characteristics were evaluated.
実施例及び比較例１〜３で作製した正極活物質を用い、導電材にアセチレンブラック、バインダーにポリテトラフルオロエチレン（ＰＴＦＥ）を使用し、活物質：８５重量部、導電材：１０重量部、バインダー：５重量部で混合し、電極シートを作製した。作製した電極シートを１４ｍｍ×２０ｍｍサイズに打ち抜いた後、導電ペーストを用いて２０μｍのＡｌ箔に接着し、１７０℃１０時間真空乾燥し、電池特性評価用の正極電極とした。作製した電極物性を表１に示す。
負極材にはメソカーボンマイクロビーズを用い、導電材にアセチレンブラック、バインダーにポリビニリデンフルオライド（ＰＶｄＦ）を使用し、活物質：９３重量部、導電材：２重量部、バインダー：５重量部で混合し、電極重量が約１２．０ｍｇ／ｃｍ２となるように１０μｍのＣｕ箔に塗工し電極を作製した。作製した電極を１５ｍｍ×２１ｍｍ角に打ち抜いた後、１７０℃１０時間真空乾燥し、電池特性評価用の負極電極とした。 Mesocarbon microbeads are used for the negative electrode material, acetylene black is used for the conductive material, polyvinylidene fluoride (PVdF) is used for the binder, active material: 93 parts by weight, conductive material: 2 parts by weight, binder: 5 parts by weight The electrodes were mixed and coated on a 10 μm Cu foil so that the electrode weight was about 12.0 mg / cm 2 . The produced electrode was punched into a 15 mm × 21 mm square and then vacuum-dried at 170 ° C. for 10 hours to obtain a negative electrode for battery characteristic evaluation.
上記作製電極を正極、負極とし、電解液には、１ｍｏｌ／ｌでＬｉＰＦ６をエチレンカーボネートとエチルメチルカーボネート（体積比３０：７０）に溶解したもの、セパレータにはポリエチレン微多孔膜（厚み２０μｍ）とを重ね合わせたものを用いて評価セルを作製した。 The prepared electrode is a positive electrode and a negative electrode, the electrolyte is 1 mol / l of LiPF 6 dissolved in ethylene carbonate and ethyl methyl carbonate (volume ratio 30:70), and the separator is a polyethylene microporous film (thickness 20 μm). An evaluation cell was produced using a superposition of and.
実施例１、及び比較例１〜３において、初期充放電容量・交流抵抗・高温サイクル特性は、以下に記載する方法で評価を行った。 In Example 1 and Comparative Examples 1 to 3, the initial charge / discharge capacity, AC resistance, and high-temperature cycle characteristics were evaluated by the methods described below.
［初期放電容量］
２５℃環境下で、充電電流０．２ＣＡ、充電電圧４．４０Ｖの定電流定電圧充電を行い、電流値がＣ／２０に達したら充電を終了した。充電終了後、放電電流０．２ＣＡ、終止電圧２．７Ｖの条件で放電を行なった。その放電容量を初期放電容量とした。
[Initial discharge capacity]
Under a 25 ° C. environment, a constant current / constant voltage charge with a charge current of 0.2 CA and a charge voltage of 4.40 V was performed, and the charge was terminated when the current value reached C / 20. After the completion of charging, discharging was performed under the conditions of a discharge current of 0.2 CA and a final voltage of 2.7 V. The discharge capacity was defined as the initial discharge capacity.
［交流抵抗］
前記初期放電容量測定後、２５℃環境下で、充電電流０．２ＣＡ、充電電圧４．４０Ｖの定電流定電圧充電を行い、電流値がＣ／２０に達したら充電を終了した。充電終了後、２５℃環境下で充電後電池の交流抵抗を評価した。
交流抵抗評価条件は、周波数範囲１，０００ｋＨｚ〜０．１Ｈｚ、振幅１０ｍＶの条件にて測定を行った。上記周波数範囲で順次走査しながら測定し、周波数０．１Ｈｚの交流抵抗値を比較した。この値は電池抵抗の指標となる。
[AC resistance]
After measurement of the initial discharge capacity, constant current and constant voltage charging with a charging current of 0.2 CA and a charging voltage of 4.40 V were performed in an environment of 25 ° C., and the charging was terminated when the current value reached C / 20. After completion of charging, the AC resistance of the battery after charging was evaluated in a 25 ° C. environment.
The AC resistance evaluation conditions were measured under conditions of a frequency range of 1,000 kHz to 0.1 Hz and an amplitude of 10 mV. Measurements were made while sequentially scanning in the above frequency range, and AC resistance values at a frequency of 0.1 Hz were compared. This value is an indicator of battery resistance.
［高温サイクル試験］
前記交流抵抗測定後、２５℃環境下で放電電流０．２ＣＡ、終止電圧２．７Ｖの条件で放電を行なった後、高温サイクル特性を評価した。
高温サイクル特性評価条件は、５０℃環境下で、充電電流０．５ＣＡ、充電電圧４．４０Ｖの定電流定電圧充電を行い、電流値がＣ／２０に達したら充電を終了した。充電終了後、放電電流０．２ＣＡ、終止電圧２．７Ｖの条件で放電を行なった。
上記充放電を１０回繰り返し、２サイクル目の放電容量（ｍＡｈ）と１０サイクル目の放電容量（ｍＡｈ）から下記の数式（※）により容量維持率を算出した。
容量維持率（％）＝（１０サイクル目の放電容量）×１００／（２サイクル目の放電容量）…数式（※）
[High-temperature cycle test]
After the AC resistance measurement, the battery was discharged under the conditions of a discharge current of 0.2 CA and a final voltage of 2.7 V in a 25 ° C. environment, and then the high-temperature cycle characteristics were evaluated.
The conditions for evaluating the high-temperature cycle characteristics were a constant current and constant voltage charge with a charge current of 0.5 CA and a charge voltage of 4.40 V in a 50 ° C. environment, and the charge was terminated when the current value reached C / 20. After the completion of charging, discharging was performed under the conditions of a discharge current of 0.2 CA and a final voltage of 2.7 V.
The above charge / discharge was repeated 10 times, and the capacity retention rate was calculated from the discharge capacity (mAh) at the second cycle and the discharge capacity (mAh) at the 10th cycle by the following formula (*).
Capacity maintenance ratio (%) = (discharge capacity at the 10th cycle) × 100 / (discharge capacity at the second cycle)... (*)
初期放電容量・交流抵抗・高温サイクル試験の結果を表２にまとめる。
実施例１は、比較例１〜３と比較して、初期放電容量、高温サイクル特性共に高く、交流抵抗も低くなっていることが分かる。
It can be seen that Example 1 has higher initial discharge capacity and high temperature cycle characteristics and lower AC resistance than Comparative Examples 1 to 3.
以上のように、本発明の実施例の正極粒子を比較例とともに、リチウム二次電池用正極活物質の電気化学評価をした結果，初期放電容量、高温サイクル特性共に高く、交流抵抗も低くなっていることが明らかになった。この材料を用いることで，二次電池の内部抵抗を低減し、高容量を維持でき、高温環境下も含めた充放電サイクル特性が優れた次世代型非水電解質リチウムイオン電池開発の実現可能性が高まると考えられる。 As described above, the positive electrode particles of the examples of the present invention were subjected to electrochemical evaluation of the positive electrode active material for the lithium secondary battery together with the comparative example. As a result, both the initial discharge capacity and the high temperature cycle characteristics were high, and the AC resistance was also low. It became clear that By using this material, it is possible to reduce the internal resistance of secondary batteries, maintain high capacity, and to develop next-generation non-aqueous electrolyte lithium ion batteries with excellent charge / discharge cycle characteristics including high temperature environments. Is expected to increase.
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