JP2013058313A - Production method of negative electrode material and lithium titanate compound for lithium secondary battery - Google Patents
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Abstract
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本発明は、結晶化度が調整されたチタン酸リチウム化合物の製造方法及びチタン酸リチウム化合物を用いたリチウム二次電池用負極材に関する。 The present invention relates to a method for producing a lithium titanate compound having an adjusted crystallinity and a negative electrode material for a lithium secondary battery using the lithium titanate compound.
リチウム二次電池は、電解質中のリチウムイオンが電気導電を担う二次電池であって、エネルギー密度が高く、携帯電話やノートパソコン等に広く使用されている。また、ハイブリッド自動車、電気自動車、電動スクーター、電動自転車などの分野への展開も期待されている。 Lithium secondary batteries are secondary batteries in which lithium ions in an electrolyte are responsible for electrical conduction, have a high energy density, and are widely used in mobile phones, laptop computers, and the like. It is also expected to be deployed in fields such as hybrid vehicles, electric vehicles, electric scooters, and electric bicycles.
リチウム二次電池の正極材には、コバルト酸リチウムなどのリチウム遷移金属複合酸化物が用いられている。また、負極材としては、グラファイトカーボン、ハードカーボン等の炭素系材料や、特許文献１に記載されるように、チタン酸リチウムなどのリチウムチタン複合酸化物が用いられている。 Lithium transition metal composite oxides such as lithium cobalt oxide are used for the positive electrode material of the lithium secondary battery. Further, as the negative electrode material, carbon-based materials such as graphite carbon and hard carbon, and lithium titanium composite oxides such as lithium titanate as described in Patent Document 1 are used.
炭素系材料を負極材に用いたリチウム二次電池は、破裂や発火の恐れがあり、安全性に問題があった。これに対し、チタン酸リチウムを負極材に用いたリチウム二次電池は、安全性に優れるものの、放電容量及びサイクル特性において要求特性を両立しない問題があった。 A lithium secondary battery using a carbon-based material as a negative electrode material has a problem in safety because it may rupture or ignite. On the other hand, a lithium secondary battery using lithium titanate as a negative electrode material is excellent in safety, but has a problem of not satisfying required characteristics in terms of discharge capacity and cycle characteristics.
よって、本発明の目的は、安全性に優れ、サイクル特性に優れたリチウム二次電池を得ることができるリチウム二次電池用負極材及びチタン酸リチウム化合物の製造方法を提供することにある。 Therefore, the objective of this invention is providing the manufacturing method of the negative electrode material for lithium secondary batteries which can be excellent in safety | security, and can obtain the lithium secondary battery excellent in cycling characteristics, and a lithium titanate compound.
本発明者らは、種々検討の結果、チタン化合物とリチウム化合物とを反応させ、１５０〜３００℃の温度で熱処理してチタン酸リチウム化合物を合成する際に、ＴｉとＬｉとのモル比を調整してチタン化合物とリチウム化合物を反応させることにより、得られるチタン酸リチウム化合物の結晶化度を調整できることを見出した。そして、結晶化度を特定の範囲に調整したチタン酸リチウムを、リチウム二次電池用負極材として用いることで、サイクル特性に優れたリチウム二次電池とすることができること見出した。 As a result of various studies, the present inventors have reacted the titanium compound with the lithium compound and adjusted the molar ratio of Ti and Li when synthesizing the lithium titanate compound by heat treatment at a temperature of 150 to 300 ° C. Then, it was found that the crystallinity of the resulting lithium titanate compound can be adjusted by reacting the titanium compound with the lithium compound. And it discovered that it could be set as the lithium secondary battery excellent in cycling characteristics by using the lithium titanate which adjusted the crystallinity in the specific range as a negative electrode material for lithium secondary batteries.
すなわち、本発明のリチウム二次電池用負極材は、下記方法で求められる結晶化度が２５〜８５％のチタン酸リチウム化合物を含有することを特徴とする。 That is, the negative electrode material for a lithium secondary battery of the present invention is characterized by containing a lithium titanate compound having a crystallinity of 25 to 85% obtained by the following method.
結晶化度の測定方法：チタニウムイソプロポキシドと、水酸化リチウムとを、モル比でＴｉ：Ｌｉ＝１００：８７２となるように水溶液中で混合し、６０℃で２０時間反応させて１５０℃で乾燥させて得られるチタン酸リチウム化合物の結晶化度を１００％とみなし、該チタン酸リチウム化合物のＣｕＫα線によるＸ線回折の回折角２θ＝４４．６°のピーク強度と、測定すべきチタン酸リチウム化合物のＣｕＫα線によるＸ線回折の回折角２θ＝４４．６°のピーク強度との比から、測定すべきチタン酸リチウム化合物の結晶化度を算出する。 Method for measuring crystallinity: Titanium isopropoxide and lithium hydroxide are mixed in an aqueous solution so that the molar ratio is Ti: Li = 100: 872, and reacted at 60 ° C. for 20 hours at 150 ° C. The degree of crystallinity of the lithium titanate compound obtained by drying is regarded as 100%, the peak intensity at the diffraction angle 2θ = 44.6 ° of the X-ray diffraction by CuKα ray of the lithium titanate compound, and the titanic acid to be measured The crystallinity of the lithium titanate compound to be measured is calculated from the ratio of the diffraction intensity 2θ = 44.6 ° of the X-ray diffraction of the lithium compound by CuKα ray to the peak intensity.
本発明のリチウム二次電池用負極材によれば、結晶化度が２５〜８５％のチタン酸リチウム化合物を含有するので、サイクル特性に優れたリチウム二次電池とすることができる。また、結晶化度が上記範囲内であれば、充放電効率は比較的良好であるが、特に充放電電流量密度が小さい場合は、チタン酸リチウム化合物の結晶化度を上記範囲内で大きくすることで、充放電効率が大きくなる傾向にある。また、チタン酸リチウム化合物の結晶化度を上記範囲内で小さくすることで、放電容量が大きくなる傾向にある。このため、例えば、サイクル特性と充放電効率とを両立させたい場合は、チタン酸リチウム化合物の結晶化度を上記範囲内で大きくすればよく、サイクル特性と放電容量とを両立させたい場合は、チタン酸リチウム化合物の結晶化度を上記範囲内で小さくすればよい。このように、チタン酸リチウム化合物の結晶化度を上記範囲内で適宜調整することで、要求特性に適したリチウム二次電池を得ることができる。 According to the negative electrode material for a lithium secondary battery of the present invention, since the lithium titanate compound having a crystallinity of 25 to 85% is contained, a lithium secondary battery excellent in cycle characteristics can be obtained. Moreover, if the crystallinity is within the above range, the charge / discharge efficiency is relatively good, but particularly when the charge / discharge current amount density is small, the crystallinity of the lithium titanate compound is increased within the above range. Thus, the charge / discharge efficiency tends to increase. Further, the discharge capacity tends to be increased by reducing the crystallinity of the lithium titanate compound within the above range. For this reason, for example, when it is desired to achieve both cycle characteristics and charge / discharge efficiency, the crystallinity of the lithium titanate compound may be increased within the above range, and when it is desired to achieve both cycle characteristics and discharge capacity, The crystallinity of the lithium titanate compound may be reduced within the above range. Thus, the lithium secondary battery suitable for a required characteristic can be obtained by adjusting the crystallinity degree of a lithium titanate compound suitably within the said range.
本発明のリチウム二次電池用負極材の前記チタン酸リチウム化合物は、ＣｕＫα線によるＸ線回折において、回折角２θ＝４４．６°±０．５°及び回折角２θ＝６４．６°±０．５°に回折ピークを有することが好ましい。 The lithium titanate compound of the negative electrode material for a lithium secondary battery of the present invention has a diffraction angle 2θ = 44.6 ° ± 0.5 ° and a diffraction angle 2θ = 64.6 ° ± 0 in X-ray diffraction by CuKα ray. It preferably has a diffraction peak at 5 °.
また、本発明のチタン酸リチウム化合物の製造方法は、チタン化合物とリチウム化合物とを反応させ、１５０〜３００℃の温度で熱処理してチタン酸リチウム化合物を合成する際に、得られるチタン酸リチウム化合物の結晶化度（前記測定方法で求められる結晶化度）が所望の値になるように、ＴｉとＬｉとのモル比を調整して前記チタン化合物と前記リチウム化合物を反応させることを特徴とする。 Moreover, the manufacturing method of the lithium titanate compound of this invention makes a titanium compound and a lithium compound react, and when it heat-processes at the temperature of 150-300 degreeC, and synthesize | combines a lithium titanate compound, the lithium titanate compound obtained The titanium compound and the lithium compound are reacted by adjusting the molar ratio of Ti and Li so that the crystallinity (the crystallinity obtained by the above-described measurement method) becomes a desired value. .
本発明のチタン酸リチウム化合物の製造方法によれば、ＴｉとＬｉとのモル比を調整してチタン化合物とリチウム化合物を反応させることにより、チタン酸リチウム化合物の結晶化度を所望の範囲に調整できる。 According to the method for producing a lithium titanate compound of the present invention, the crystallinity of the lithium titanate compound is adjusted to a desired range by adjusting the molar ratio of Ti and Li to react the titanium compound and the lithium compound. it can.
本発明のチタン酸リチウム化合物の製造方法は、ＴｉとＬｉとのモル比を、Ｔｉ：Ｌｉ＝１００：６０〜２００の範囲で選択し、上記方法で求められる結晶化度が２５〜８５％のチタン酸リチウム化合物を得ることが好ましい。 In the method for producing a lithium titanate compound of the present invention, the molar ratio of Ti and Li is selected in the range of Ti: Li = 100: 60 to 200, and the crystallinity required by the above method is 25 to 85%. It is preferable to obtain a lithium titanate compound.
本発明のチタン酸リチウム化合物の製造方法は、前記チタン化合物が、チタニウムアルコキシドであることが好ましい。また、前記リチウム化合物が、水酸化リチウムであることが好ましい。 In the method for producing a lithium titanate compound of the present invention, the titanium compound is preferably a titanium alkoxide. The lithium compound is preferably lithium hydroxide.
本発明のリチウム二次電池用負極材を用いることで、安全性に優れ、サイクル特性に優れたリチウム二次電池とすることができる。 By using the negative electrode material for a lithium secondary battery of the present invention, a lithium secondary battery having excellent safety and cycle characteristics can be obtained.
本発明のリチウム二次電池用負極材は、チタン酸リチウム化合物を含有する。 The negative electrode material for a lithium secondary battery of the present invention contains a lithium titanate compound.
チタン酸リチウム化合物の結晶化度は、２５〜８５％であることが必要である。結晶化度が上記範囲内であれば、リチウム二次電池のサイクル特性を良好にできる。結晶化度が２５％未満であったり、８５％を超えると、リチウム二次電池のサイクル特性が低下する。 The crystallinity of the lithium titanate compound needs to be 25 to 85%. When the crystallinity is within the above range, the cycle characteristics of the lithium secondary battery can be improved. When the degree of crystallinity is less than 25% or exceeds 85%, the cycle characteristics of the lithium secondary battery deteriorate.
また、チタン酸リチウム化合物の結晶化度が、上記範囲内であれば、充放電効率は比較的良好であるが、特に充放電流量密度が小さい場合においては、チタン酸リチウム化合物の結晶化度を大きくすることで、充放電効率が大きくなる傾向にある。このため、充放電流量密度が１ｍＡ／ｃｍ２以上の場合において、サイクル特性と充放電効率とを両立させたい場合は、チタン酸リチウム化合物の結晶化度は、２５〜８５％が好ましい。また、充放電流量密度が１ｍＡ／ｃｍ２未満の場合において、サイクル特性と充放電効率とを両立させたい場合は、チタン酸リチウム化合物の結晶化度を４０〜８５％とすることが好ましく、５０〜８５％がより好ましい。 In addition, if the crystallinity of the lithium titanate compound is within the above range, the charge / discharge efficiency is relatively good, but particularly when the charge / discharge flow density is small, the crystallinity of the lithium titanate compound is reduced. Increasing the charge tends to increase charge / discharge efficiency. For this reason, when the charge / discharge flow density is 1 mA / cm 2 or more, when it is desired to achieve both cycle characteristics and charge / discharge efficiency, the crystallinity of the lithium titanate compound is preferably 25 to 85%. Further, when the charge / discharge flow density is less than 1 mA / cm 2 , the crystallinity of the lithium titanate compound is preferably set to 40 to 85% in order to achieve both cycle characteristics and charge / discharge efficiency. -85% is more preferable.
また、チタン酸リチウム化合物の結晶化度を上記範囲内で小さくすることで、放電容量が大きくなる傾向にある。このため、例えば、サイクル特性と放電容量とを両立させたい場合は、チタン酸リチウム化合物の結晶化度を２５〜７０％とすることが好ましく、３０〜６０％がより好ましい。 Further, the discharge capacity tends to be increased by reducing the crystallinity of the lithium titanate compound within the above range. For this reason, for example, when it is desired to achieve both cycle characteristics and discharge capacity, the crystallinity of the lithium titanate compound is preferably 25 to 70%, more preferably 30 to 60%.
このように、本発明によれば、チタン酸リチウム化合物の結晶化度を上記範囲内で適宜調整して、リチウム二次電池用負極材として用いることで、要求特性に適したリチウム二次電池を得ることができる。 Thus, according to the present invention, a lithium secondary battery suitable for required characteristics can be obtained by appropriately adjusting the crystallinity of the lithium titanate compound within the above range and using it as a negative electrode material for a lithium secondary battery. Can be obtained.
なお、本発明では、チタニウムイソプロポキシドと、水酸化リチウムとを、モル比でＴｉ：Ｌｉ＝１００：８７２となるように水溶液中で混合し、６０℃で２０時間反応させて１５０℃で乾燥させて得られるチタン酸リチウム化合物の結晶化度を１００％とみなし、該チタン酸リチウム化合物のＣｕＫα線によるＸ線回折の回折角２θ＝４４．６°のピーク強度と、測定すべきチタン酸リチウム化合物のＣｕＫα線によるＸ線回折の回折角２θ＝４４．６°のピーク強度との比から、測定すべきチタン酸リチウム化合物の結晶化度を算出した。なお、回折角２θ＝４４．６°は、類似のパターンを示すカードデータ（ＬｉＴｉＯ２）においての最強ピークであることから利用した。 In the present invention, titanium isopropoxide and lithium hydroxide are mixed in an aqueous solution so that the molar ratio is Ti: Li = 100: 872, and reacted at 60 ° C. for 20 hours and dried at 150 ° C. The crystallinity of the obtained lithium titanate compound is regarded as 100%, the peak intensity at the diffraction angle 2θ = 44.6 ° of the X-ray diffraction by CuKα ray of the lithium titanate compound, and the lithium titanate to be measured The crystallinity of the lithium titanate compound to be measured was calculated from the ratio to the peak intensity at the diffraction angle 2θ = 44.6 ° of the X-ray diffraction of the compound by CuKα ray. The diffraction angle 2θ = 44.6 ° was used because it is the strongest peak in card data (LiTiO 2 ) showing a similar pattern.
本発明において、チタン化合物としては、特に限定は無い。チタニウムテトラメトキシド、チタニウムテトラエトキシド、チタニウムテトラ−ｎ−プロポキシド、チタニウムテトライソプロポキシド、チタニウムテトラ−ｎ−ブトキシド等のチタニウムアルコキシド、酸化チタン等を用いることができる。 In the present invention, the titanium compound is not particularly limited. Titanium alkoxides such as titanium tetramethoxide, titanium tetraethoxide, titanium tetra-n-propoxide, titanium tetraisopropoxide, titanium tetra-n-butoxide, titanium oxide, and the like can be used.
次に、本発明のチタン酸リチウム化合物の製造方法について説明する。 Next, the manufacturing method of the lithium titanate compound of this invention is demonstrated.
本発明では、チタン化合物とリチウム化合物とを反応させ、１５０〜３００℃の温度で熱処理してチタン酸リチウム化合物を合成する。その際、得られるチタン酸リチウム化合物の結晶化度が所望の値になるように、ＴｉとＬｉとのモル比を調整してチタン化合物とリチウム化合物を反応させることを特徴とする。 In the present invention, a titanium compound and a lithium compound are reacted and heat-treated at a temperature of 150 to 300 ° C. to synthesize a lithium titanate compound. At that time, the molar ratio of Ti and Li is adjusted to cause the titanium compound and the lithium compound to react so that the crystallinity of the obtained lithium titanate compound becomes a desired value.
従来より、チタン酸リチウムの製造工程において、チタン化合物とリチウム化合物とを、目的とするチタン酸リチウムの化学量論比から外れる割合で合成しても、得られる生成物は、チタン酸リチウムと、未反応のチタン化合物又はリチウム化合物との混合物になると考えられていた。このため、原料の無駄を少なくし、目的とするチタン酸リチウムの収率を高めるため、従来は、目的とするチタン酸リチウムの化学量論比となる割合で、各原料を反応させていた。 Conventionally, in the production process of lithium titanate, even if the titanium compound and the lithium compound are synthesized at a ratio that deviates from the stoichiometric ratio of the target lithium titanate, the resulting product is lithium titanate, It was thought to be a mixture with an unreacted titanium compound or lithium compound. For this reason, in order to reduce the waste of the raw material and increase the yield of the target lithium titanate, each of the raw materials has been conventionally reacted at a ratio corresponding to the stoichiometric ratio of the target lithium titanate.
しかしながら、本発明者らによれば、チタン化合物とリチウム化合物との混合比を変化させて反応させることにより、結晶化度の異なるチタン酸リチウムが得られることを見出した。詳細な理由は定かではないが、チタン化合物とリチウム化合物との混合比を変えて反応させることにより、３価のＴｉと、４価のＴｉとの割合が異なったチタン酸リチウムが得られるためであると考えられる。 However, according to the present inventors, it has been found that lithium titanate having a different crystallinity can be obtained by changing the mixing ratio of the titanium compound and the lithium compound to cause the reaction. The detailed reason is not clear, but by changing the mixing ratio of the titanium compound and the lithium compound and reacting them, lithium titanate with different ratios of trivalent Ti and tetravalent Ti can be obtained. It is believed that there is.
本発明において、チタン化合物とリチウム化合物との反応は、水中で行うことが好ましい。水中で反応させることで容易に反応進行し、更には、製造プロセスを簡略化できる。 In the present invention, the reaction between the titanium compound and the lithium compound is preferably performed in water. The reaction proceeds easily by reacting in water, and the production process can be simplified.
チタン化合物とリチウム化合物との反応割合は、目的とするチタン酸リチウム化合物の結晶化度により異なる。ＴｉとＬｉとのモル比を、Ｔｉ：Ｌｉ＝１００：６０〜２００の範囲で選択することで、結晶化度が２５〜８５％のチタン酸リチウム化合物を得ることができる。Ｌｉのモル比が６０未満であると、上記条件で反応させた場合、得られるチタン酸リチウムの結晶化度が２５％未満になる傾向にある。２００よりも大きいと、上記条件で反応させた場合、得られるチタン酸リチウムの結晶化度が８５％よりも大きくなる傾向にある。 The reaction ratio between the titanium compound and the lithium compound varies depending on the crystallinity of the target lithium titanate compound. By selecting the molar ratio of Ti and Li in the range of Ti: Li = 100: 60 to 200, a lithium titanate compound having a crystallinity of 25 to 85% can be obtained. When the molar ratio of Li is less than 60, when the reaction is carried out under the above conditions, the crystallinity of the resulting lithium titanate tends to be less than 25%. If it is greater than 200, the crystallinity of the resulting lithium titanate tends to be greater than 85% when reacted under the above conditions.
本発明において、リチウム化合物としては、特に限定は無く、水酸化リチウム、硝酸リチウム、硫酸リチウム等を用いることができる。 In the present invention, the lithium compound is not particularly limited, and lithium hydroxide, lithium nitrate, lithium sulfate and the like can be used.
本発明において、チタン化合物とリチウム化合物との反応温度は、５〜１００℃が好ましく、２０〜９０℃がより好ましく、５０〜７０℃が特に好ましい。５℃未満であると、反応性が劣り、結晶化度が小さくなり易く、目的の結晶化度のチタン酸リチウムを得るのに時間を要する傾向にある。１００℃を超えると、安全性や材料への熱履歴の観点から好ましくないことがある。 In the present invention, the reaction temperature between the titanium compound and the lithium compound is preferably 5 to 100 ° C, more preferably 20 to 90 ° C, and particularly preferably 50 to 70 ° C. When the temperature is less than 5 ° C., the reactivity is inferior, the crystallization degree tends to be small, and it takes time to obtain lithium titanate having the desired crystallization degree. If it exceeds 100 ° C., it may be unfavorable from the viewpoint of safety and thermal history of the material.
本発明において、チタン化合物とリチウム化合物との反応時間は、３〜５０時間が好ましく、５〜３０時間がより好ましく、１０〜２５時間が特に好ましい。３時間未満であると、結晶化度が小さくなり易い。５０時間を超えると、生産性に支障が生じる。また、反応が進みすぎて、結晶化度が高くなることがある。 In the present invention, the reaction time between the titanium compound and the lithium compound is preferably 3 to 50 hours, more preferably 5 to 30 hours, and particularly preferably 10 to 25 hours. If it is less than 3 hours, the crystallinity tends to be small. If it exceeds 50 hours, productivity will be hindered. In addition, the reaction may proceed too much and the crystallinity may increase.
本発明において、チタン化合物とリチウム化合物との反応物の熱処理は、１５０〜３００℃の温度で行う。熱処理温度は、２００〜３００℃が好ましく、２５０〜３００℃がより好ましい。上記温度範囲にて熱処理を行うことで、ＣｕＫα線によるＸ線回折において、回折角２θ＝４４．６°±０．５°及び回折角２θ＝６４．６°±０．５°に回折ピークを有するチタン酸リチウム化合物が得られる。熱処理温度が１５０℃未満であると、水分除去が不十分あるいは必要以上に時間を必要とする場合がある。３００℃を超えると、上記回折ピークを有するチタン酸リチウム化合物が得られない。また、熱処理時間は、３〜５０時間が好ましく、１０〜２５時間がより好ましい。熱処理時間が３時間未満であると、水分除去が不十分であり、５０時間を超えると製造コスト面で不利になる。 In the present invention, the heat treatment of the reaction product of the titanium compound and the lithium compound is performed at a temperature of 150 to 300 ° C. The heat treatment temperature is preferably 200 to 300 ° C, more preferably 250 to 300 ° C. By performing heat treatment in the above temperature range, diffraction peaks appear at diffraction angles 2θ = 44.6 ° ± 0.5 ° and diffraction angles 2θ = 64.6 ° ± 0.5 ° in X-ray diffraction using CuKα rays. The lithium titanate compound is obtained. If the heat treatment temperature is less than 150 ° C., moisture removal may be insufficient or more time may be required. If it exceeds 300 ° C., the lithium titanate compound having the diffraction peak cannot be obtained. The heat treatment time is preferably 3 to 50 hours, more preferably 10 to 25 hours. If the heat treatment time is less than 3 hours, moisture removal is insufficient, and if it exceeds 50 hours, the manufacturing cost is disadvantageous.
以下、チタン化合物としてチタニウムイソプロポキシドを用い、リチウム化合物として水酸化リチウムを用いた場合を例に挙げて、チタン酸リチウム化合物の製造方法のより好ましい具体例を説明する。 Hereinafter, a more preferable specific example of the method for producing a lithium titanate compound will be described by taking as an example the case where titanium isopropoxide is used as the titanium compound and lithium hydroxide is used as the lithium compound.
ＴｉとＬｉとのモル比を、Ｔｉ：Ｌｉ＝１００：６０〜２００の範囲で選択して、水酸化リチウムと、チタニウムイソプロポキシドとを水中で混合し、５５〜６５℃で、１８〜２２時間反応させる。 The molar ratio of Ti and Li is selected in the range of Ti: Li = 100: 60 to 200, lithium hydroxide and titanium isopropoxide are mixed in water, and the temperature is 55 to 65 ° C. and 18 to 22 Let react for hours.
次に、チタニウムイソプロポキシドとリチウム化合物との反応物を洗浄し、１５０〜３００℃に加熱して熱処理することで、本発明のチタン酸リチウム化合物が得られる。 Next, the reaction product of titanium isopropoxide and a lithium compound is washed, and heated to 150 to 300 ° C. to perform heat treatment, whereby the lithium titanate compound of the present invention is obtained.
このチタン酸リチウム化合物は、ＣｕＫα線によるＸ線回折において、回折角２θ＝４４．６°±０．５°及び回折角２θ＝６４．６°±０．５°に回折ピークを有しており、また、その結晶化度は、２５〜８５％の範囲にある。 This lithium titanate compound has diffraction peaks at a diffraction angle 2θ = 44.6 ° ± 0.5 ° and a diffraction angle 2θ = 64.6 ° ± 0.5 ° in X-ray diffraction by CuKα ray. The crystallinity is in the range of 25 to 85%.
このようにして得られるチタン酸リチウムを必要に応じて粉砕処理し、テトラフルオロエチレン系バインダー、アセチレンブラック等のその他の助剤を混合し、所定の形状に成形して８０〜１５０℃熱乾燥処理することで、本発明のリチウム二次電池用負極材が得られる。 The lithium titanate thus obtained is pulverized as necessary, mixed with other auxiliary agents such as a tetrafluoroethylene binder and acetylene black, molded into a predetermined shape, and heat-dried at 80 to 150 ° C. By doing so, the negative electrode material for a lithium secondary battery of the present invention is obtained.
チタニウムイソプロポキシドと水酸化リチウム水溶液とを、ＴｉとＬｉとのモル比が、表１に示す割合となるように混合し、６０℃のオイルバス中で２０時間撹拌した。得られた沈殿物に蒸留水を加え遠心分離機を用いて沈殿を水洗した。上澄み溶液が中性になるまでこの操作を繰り返した。洗浄した沈殿物を１５０℃の乾燥機で２時間乾燥（熱処理）させて、製造例１〜４のチタン酸リチウム化合物を得た。 Titanium isopropoxide and an aqueous lithium hydroxide solution were mixed so that the molar ratio of Ti and Li was as shown in Table 1, and stirred in an oil bath at 60 ° C. for 20 hours. Distilled water was added to the resulting precipitate, and the precipitate was washed with a centrifuge. This operation was repeated until the supernatant solution became neutral. The washed precipitate was dried (heat treated) with a dryer at 150 ° C. for 2 hours to obtain lithium titanate compounds of Production Examples 1 to 4.
得られた各チタン酸リチウム化合物について、Ｘ線回折法（ＸＲＤ）によりピーク強度を検出した。結果を図１に示す。また、粉末Ｘ線回折データベースのＬｉＴｉＯ２（ｃａｒｄ１６−０２２３）のピーク強度を併せて記す。 About each obtained lithium titanate compound, peak intensity | strength was detected by the X ray diffraction method (XRD). The results are shown in FIG. The peak intensity of LiTiO 2 (card16-0223) in the powder X-ray diffraction database is also shown.
図１に示されるように、製造例１〜４のチタン酸リチウム化合物は、ＣｕＫα線によるＸ線回折において、回折角２θ＝４４．６°±０．５°及び回折角２θ＝６４．６°±０．５°に回折ピークを有し、ＬｉＴｉＯ２（アナターゼ型）に類似した結晶構造を有するものであることが分かる。 As shown in FIG. 1, the lithium titanate compounds of Production Examples 1 to 4 have a diffraction angle 2θ = 44.6 ° ± 0.5 ° and a diffraction angle 2θ = 64.6 ° in X-ray diffraction using CuKα rays. It can be seen that it has a diffraction peak at ± 0.5 ° and a crystal structure similar to LiTiO 2 (anatase type).
また、製造例４のチタン酸リチウム化合物の結晶化度を便宜上１００％とみなし、製造例１〜３のチタン酸リチウム化合物の結晶化度を、製造例４のチタン酸リチウム化合物のＣｕＫα線によるＸ線回折の回折角２θ＝４４．６°のピーク強度と、各チタン酸リチウム化合物のＸ線回折の回折角２θ＝４４．６°のピーク強度との比から算出した。結果を表１に記す。 Further, the crystallinity of the lithium titanate compound of Production Example 4 is regarded as 100% for convenience, and the crystallinity of the lithium titanate compound of Production Examples 1 to 3 is determined by X It was calculated from the ratio of the peak intensity at the diffraction angle 2θ = 44.6 ° of the line diffraction and the peak intensity at the diffraction angle 2θ = 44.6 ° of the X-ray diffraction of each lithium titanate compound. The results are shown in Table 1.
次に、各チタン酸リチウム化合物を粉砕処理し、テトラフルオロエチレン系バインダー、アセチレンブラックを混合し、所定の形状にプレス成形し、１２０〜１５０℃熱乾燥処理して、実施例１〜３、比較例１の負極材を得た。
対極・参照極に金属リチウムを用い、作用極に上記で得られた各負極材を用い、電解液として１ｍｏｌ・ｄｍ−３ ＬｉＣｌＯ４／ＰＣを用いて評価用のリチウム二次電池を製造し、充放電試験を行い、１サイクル目の放電容量及び充放電効率と、サイクル試験後の容量保持率を評価した。なお、測定には充放電装置を使用した。作用極にリチウムイオンを電気化学的に挿入する過程を放電、リチウムイオンが作用極から脱離して金属リチウムへ析出する過程を充電と定義した。また、定電流充放電測定は、放電から開始した。
測定条件は、充放電電流密度５．０ｍＡ・ｃｍ−２又は０．５ｍＡ・ｃｍ−２、電位範囲１．０〜４．０Ｖ ｖｓ．Ｌｉ／Ｌｉ＋、測定温度は室温とした。容量は用いた電極中の活物質の重量で規格化して評価した。充放電電流密度０．５ｍＡ・ｃｍ−２の試験結果を表２に、充放電電流密度５ｍＡ・ｃｍ−２の試験結果を表３に記す。
Next, each lithium titanate compound is pulverized, mixed with a tetrafluoroethylene-based binder and acetylene black, press-formed into a predetermined shape, and heat-dried at 120 to 150 ° C. The negative electrode material of Example 1 was obtained.
Lithium secondary battery for evaluation was manufactured using 1 mol · dm −3 LiClO 4 / PC as an electrolytic solution, using metallic lithium for the counter electrode and the reference electrode, each negative electrode material obtained above for the working electrode, A charge / discharge test was conducted, and the discharge capacity and charge / discharge efficiency of the first cycle and the capacity retention after the cycle test were evaluated. In addition, the charging / discharging apparatus was used for the measurement. The process of electrochemically inserting lithium ions into the working electrode was defined as discharging, and the process of lithium ions being desorbed from the working electrode and deposited on metallic lithium was defined as charging. Moreover, the constant current charge / discharge measurement was started from discharge.
Measurement conditions, charging and discharging current density 5.0 mA · cm -2 or 0.5 mA · cm -2, the potential range 1.0～4.0V vs. Li / Li + , the measurement temperature was room temperature. The capacity was standardized and evaluated by the weight of the active material in the electrode used. Table 2 shows the test results with a charge / discharge current density of 0.5 mA · cm −2 , and Table 3 shows the test results with a charge / discharge current density of 5 mA · cm −2 .
上記結果より、結晶化度が１００％のチタン酸リチウム化合物を負極材として用いた、比較例１は、サイクル試験後の充放電容量保持率（％）が低く、サイクル特性が著しく劣るものであった。 From the above results, Comparative Example 1 using a lithium titanate compound having a crystallinity of 100% as the negative electrode material has a low charge / discharge capacity retention (%) after the cycle test, and the cycle characteristics are extremely inferior. It was.
これに対し、結晶化度が２５〜８５％のチタン酸リチウム化合物を負極材として用いた、実施例１〜３は、サイクル試験後の充放電容量保持率（％）が高く、サイクル特性に優れるものであった。
また、充放電電流密度が低い場合は、チタン酸リチウム化合物の結晶化度が大きくなるに伴い、充放電効率が大きくなる傾向にあった。
また、放電容量については、結晶化度が２５〜８５％の範囲において、結晶化度が小さい製造例１，２の方が、製造例３よりも高かった。特に製造例２のチタン酸リチウム化合物（結晶化度５６％）を用いた場合、充放電電流密度の高い低いによらず、放電容量が最も高い値を示した。
On the other hand, Examples 1 to 3 using a lithium titanate compound having a crystallinity of 25 to 85% as a negative electrode material have a high charge / discharge capacity retention rate (%) after the cycle test and excellent cycle characteristics. It was a thing.
When the charge / discharge current density is low, the charge / discharge efficiency tends to increase as the crystallinity of the lithium titanate compound increases.
Further, regarding the discharge capacity, in the range of 25 to 85% of the crystallinity, Production Examples 1 and 2 having a low crystallinity were higher than Production Example 3. In particular, when the lithium titanate compound of Production Example 2 (crystallinity 56%) was used, the discharge capacity showed the highest value regardless of whether the charge / discharge current density was high or low.
Claims (6)
結晶化度の測定方法：チタニウムイソプロポキシドと、水酸化リチウムとを、モル比でＴｉ：Ｌｉ＝１００：８７２となるように水溶液中で混合し、６０℃で２０時間反応させて１５０℃で乾燥させて得られるチタン酸リチウム化合物の結晶化度を１００％とみなし、該チタン酸リチウム化合物のＣｕＫα線によるＸ線回折の回折角２θ＝４４．６°のピーク強度と、測定すべきチタン酸リチウム化合物のＣｕＫα線によるＸ線回折の回折角２θ＝４４．６°のピーク強度との比から、測定すべきチタン酸リチウム化合物の結晶化度を算出する。 A negative electrode material for a lithium secondary battery, comprising a lithium titanate compound having a crystallinity of 25 to 85% obtained by the following method.
Method for measuring crystallinity: Titanium isopropoxide and lithium hydroxide are mixed in an aqueous solution so that the molar ratio is Ti: Li = 100: 872, and reacted at 60 ° C. for 20 hours at 150 ° C. The degree of crystallinity of the lithium titanate compound obtained by drying is regarded as 100%, the peak intensity at the diffraction angle 2θ = 44.6 ° of the X-ray diffraction by CuKα ray of the lithium titanate compound, and the titanic acid to be measured The crystallinity of the lithium titanate compound to be measured is calculated from the ratio of the diffraction intensity 2θ = 44.6 ° of the X-ray diffraction of the lithium compound by CuKα ray to the peak intensity.
結晶化度の測定方法：チタニウムイソプロポキシドと、水酸化リチウムとを、モル比でＴｉ：Ｌｉ＝１００：８７２となるように水溶液中で混合し、６０℃で２０時間反応させて１５０℃で乾燥させて得られるチタン酸リチウム化合物の結晶化度を１００％とみなし、該チタン酸リチウム化合物のＣｕＫα線によるＸ線回折の回折角２θ＝４４．６°のピーク強度と、測定すべきチタン酸リチウム化合物のＣｕＫα線によるＸ線回折の回折角２θ＝４４．６°のピーク強度との比から、測定すべきチタン酸リチウム化合物の結晶化度を算出する。 The molar ratio of Ti and Li is selected in the range of Ti: Li = 100: 60-200, and the lithium titanate compound whose crystallinity calculated | required by the following method is 25-85% is obtained. A method for producing a lithium titanate compound.
Method for measuring crystallinity: Titanium isopropoxide and lithium hydroxide are mixed in an aqueous solution so that the molar ratio is Ti: Li = 100: 872, and reacted at 60 ° C. for 20 hours at 150 ° C. The degree of crystallinity of the lithium titanate compound obtained by drying is regarded as 100%, the peak intensity at the diffraction angle 2θ = 44.6 ° of the X-ray diffraction by CuKα ray of the lithium titanate compound, and the titanic acid to be measured The crystallinity of the lithium titanate compound to be measured is calculated from the ratio of the diffraction intensity 2θ = 44.6 ° of the X-ray diffraction of the lithium compound by CuKα ray to the peak intensity.
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| US10847793B2 (en) | 2015-05-19 | 2020-11-24 | Samsung Sdi Co., Ltd. | Negative active material for rechargeable lithium battery and rechargeable lithium battery comprising same |
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| US10847793B2 (en) | 2015-05-19 | 2020-11-24 | Samsung Sdi Co., Ltd. | Negative active material for rechargeable lithium battery and rechargeable lithium battery comprising same |
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