JP6353714B2 - Positive electrode active material for sodium secondary battery and sodium secondary battery - Google Patents
Positive electrode active material for sodium secondary battery and sodium secondary battery Download PDFInfo
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- 239000011734 sodium Substances 0.000 title claims description 109
- 229910052708 sodium Inorganic materials 0.000 title claims description 58
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 title claims description 57
- 239000007774 positive electrode material Substances 0.000 title claims description 36
- 239000003792 electrolyte Substances 0.000 claims description 6
- 239000007864 aqueous solution Substances 0.000 claims description 2
- 239000004020 conductor Substances 0.000 claims description 2
- 239000003960 organic solvent Substances 0.000 claims description 2
- 239000007784 solid electrolyte Substances 0.000 claims description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 25
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 20
- 229910052744 lithium Inorganic materials 0.000 description 13
- 239000000126 substance Substances 0.000 description 13
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 11
- 239000011572 manganese Substances 0.000 description 11
- 229910012851 LiCoO 2 Inorganic materials 0.000 description 10
- 229910015643 LiMn 2 O 4 Inorganic materials 0.000 description 7
- 238000006479 redox reaction Methods 0.000 description 6
- 239000013078 crystal Substances 0.000 description 5
- 229910052742 iron Inorganic materials 0.000 description 4
- 239000005486 organic electrolyte Substances 0.000 description 4
- 238000006864 oxidative decomposition reaction Methods 0.000 description 4
- KEAYESYHFKHZAL-UHFFFAOYSA-N Sodium Chemical compound [Na] KEAYESYHFKHZAL-UHFFFAOYSA-N 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 229910052723 transition metal Inorganic materials 0.000 description 3
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 2
- FKNQFGJONOIPTF-UHFFFAOYSA-N Sodium cation Chemical compound [Na+] FKNQFGJONOIPTF-UHFFFAOYSA-N 0.000 description 2
- 239000011149 active material Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 239000007772 electrode material Substances 0.000 description 2
- 229910001416 lithium ion Inorganic materials 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 229910001415 sodium ion Inorganic materials 0.000 description 2
- 150000003624 transition metals Chemical class 0.000 description 2
- 238000012795 verification Methods 0.000 description 2
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000006182 cathode active material Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 239000013535 sea water Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
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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
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- Secondary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
Description
本発明は、ナトリウム二次電池用正極活物質、及びナトリウム二次電池に関する。 The present invention relates to a positive electrode active material for a sodium secondary battery and a sodium secondary battery.
電気自動車、携帯情報端末、定置型蓄電設備などでは、高容量の二次電池が利用される。現在、二次電池の主流はリチウム二次電池であるが、その正極活物質としてはＬｉＣｏＯ2、ＬｉＭｎ2Ｏ4などが知られている。 High capacity secondary batteries are used in electric vehicles, portable information terminals, stationary power storage facilities, and the like. At present, the mainstream of secondary batteries is lithium secondary batteries, and LiCoO 2 , LiMn 2 O 4 and the like are known as positive electrode active materials.
しかしこれらの物質の主要な組成であるリチウムは、地球上における存在量としては豊富であるが、その多くは海水中に存在しており、しかもリチウムの採取が産業として経済的に成り立つ地域は、リチウムを多く含んだ塩湖が存在する、政治的に不安定な南米の一部の地域に集中しており、今後の電池の世界的な需要拡大に伴い供給不安や価格高騰が懸念されている。 However, lithium, which is the main composition of these substances, is abundant as abundance on the earth, but most of it exists in seawater, and the region where the extraction of lithium is economically viable as an industry is Concentrated in some politically unstable parts of South America where there are salt lakes rich in lithium, and there are concerns about supply insecurity and price increases as global battery demand grows in the future .
こうした背景の下、近年、電極活物質としてナトリウムを用いたナトリウム二次電池が注目されており、活発に研究開発が行われている。ナトリウム二次電池は、負極集電体としてレアメタルを用いるリチウム二次電池と異なり、正極と同じアルミニウムを使用することができるため、電池の軽量化や低コスト化も期待されている。 Against this background, in recent years, sodium secondary batteries using sodium as an electrode active material have attracted attention and are actively researched and developed. Unlike a lithium secondary battery that uses a rare metal as a negative electrode current collector, a sodium secondary battery can use the same aluminum as the positive electrode, and therefore, it is expected to reduce the weight and cost of the battery.
ナトリウム二次電池に関し、例えば、特許文献１には、ナトリウム二次電池の放電容量の向上等を目的として、電極活物質を、ＮａおよびＭ1（ここで、Ｍ1は遷移金属元素からなる群より選ばれる１種以上の元素を表す。）をＮａ：Ｍ1のモル比でｘ：１（ここで、ｘは２以上５以下の範囲の値である。）となるように含む原料が焼成されてなる金属酸化物を含有する構成とすることが記載されている。
With respect to sodium secondary batteries, for example,
現状、リチウム二次電池といえどもエネルギー密度は十分ではなく、スマートフォン等の小型モバイル用から電気自動車等の大型機器に至るまで、様々な分野において二次電池の高容量化が切望されている。また既存の正極活物質と同等以上の容量を有する二次電池を実現するには、正極活物質を４Ｖ以上の電圧で作動させる必要があるが、その場合、有機電解液等の分解に伴うサイクル性能の劣化を防ぐことが課題となる。 At present, even with lithium secondary batteries, the energy density is not sufficient, and high capacity of secondary batteries is desired in various fields ranging from small mobile devices such as smartphones to large devices such as electric vehicles. Moreover, in order to realize a secondary battery having a capacity equal to or greater than that of an existing positive electrode active material, it is necessary to operate the positive electrode active material at a voltage of 4 V or more. Preventing performance degradation is an issue.
本発明は、高容量のナトリウム二次電池を実現するための正極活物質、及びこれを用いたナトリウム二次電池を提供することを目的としている。 An object of this invention is to provide the positive electrode active material for implement | achieving a high capacity | capacitance sodium secondary battery, and a sodium secondary battery using the same.
上記目的を達成するための本発明のうちの一つは、上記ナトリウム二次電池用正極活物質であって、前記一般式がＮａ2Ｎｉ(1-x)ＦｅxＯ2（０≦ｘ≦０．６）であることとする。
One of the present invention for achieving the above object, a cathode active material for a sodium secondary battery, the general formula Na 2 Ni (1-x) Fe x O 2 (0 ≦ x ≦ 0.6).
本発明のうちの他の一つは、上記ナトリウム二次電池用正極活物質であって、前記一般式がＮａ2Ｎｉ(1-x)ＭｎxＯ2 （０≦ｘ≦０．２）であることとする。 Another aspect of the present invention is the positive electrode active material for a sodium secondary battery, wherein the general formula is Na 2 Ni (1-x) Mn x O 2 (0 ≦ x ≦ 0.2). Suppose that there is.
本発明のうちの他の一つは、上記ナトリウム二次電池用正極活物質を備えたナトリウム二次電池であることとする。 Another one of the present invention is a sodium secondary battery including the positive electrode active material for a sodium secondary battery.
上記ナトリウム二次電池は、例えば、有機溶媒を電解質として構成される。 The sodium secondary battery is composed of, for example, an organic solvent as an electrolyte.
また、上記ナトリウム二次電池は、例えば、水溶液を電解質として構成される。 Moreover, the said sodium secondary battery is comprised by using aqueous solution as electrolyte, for example.
また、上記ナトリウム二次電池は、例えば、ナトリウム伝導体である固体電解質を電解質として構成される。 Moreover, the said sodium secondary battery is comprised as an electrolyte the solid electrolyte which is a sodium conductor, for example.
その他、本願が開示する課題、及びその解決方法は、発明を実施するための形態の欄、及び図面により明らかにされる。 In addition, the subject which this application discloses, and its solution method are clarified by the column of the form for inventing, and drawing.
本発明によれば、高容量のナトリウム二次電池を実現することができる。 According to the present invention, a high-capacity sodium secondary battery can be realized.
以下、本発明の一実施形態について、図面を参照しつつ詳細に説明する。 Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
現状のリチウム二次電池の性能を凌駕するナトリウム二次電池を実現可能な正極活物質を見出すべく、本発明者らは、候補として選出した複数の正極活物質（Ｎａ2ＮｉＯ2、Ｎａ2Ｎｉ0.5Ｆｅ0.5Ｏ2、及びＮａ2Ｎｉ0.5Ｍｎ0.5Ｏ2）について、夫々を正極活物質として用いた場合におけるナトリウム二次電池の容量と起電力との関係を第一原理計算により求めた。具体的には、第一原理計算により得られる主要な結果の一つである、計算対象とした系の全エネルギーを利用することにより、次の方法でナトリウム二次電池の容量と起電力との関係を求めた。 In order to find a positive electrode active material capable of realizing a sodium secondary battery that surpasses the performance of current lithium secondary batteries, the present inventors have selected a plurality of positive electrode active materials (Na 2 NiO 2 , Na 2 Ni) selected as candidates. For 0.5 Fe 0.5 O 2 and Na 2 Ni 0.5 Mn 0.5 O 2 ), the relationship between the capacity of the sodium secondary battery and the electromotive force when each was used as the positive electrode active material was determined by first-principles calculation. Specifically, by using the total energy of the system to be calculated, which is one of the main results obtained from the first-principles calculation, the capacity and electromotive force of the sodium secondary battery can be calculated by the following method. Sought a relationship.
まず二次電池の起電力は、充電状態と放電状態との間のギブス自由エネルギー差であるため、エントロピーを無視する近似の範囲で起電力を第一原理計算により評価することができる。例えば、リチウムイオン二次電池の起電力Ｖ（負極にリチウム金属を使用した場合）は、文献（G. Ceder et al., Electrochimica Acta 45 (1999) 131-150）によれば、
ナトリウムイオン二次電池の場合もリチウムイオン二次電池の場合と同様であり、ナトリウムイオン二次電池の正極活物質のＮａ／Ｎａ+電位に対する起電力Ｖ（負極にナトリウム金属を使用した場合）は、
尚、本実施形態では、第一原理計算における解析プログラムとして、全エネルギーの計算において信頼性が確認されている、文献（A. Kato et al., J. Cond. Matt. 21 (2009)205801）に記載されているプログラムを用いた。 In this embodiment, as an analysis program in the first-principles calculation, reliability has been confirmed in the calculation of total energy (A. Kato et al., J. Cond. Matt. 21 (2009) 205801). The program described in is used.
＜第一原理計算の信頼性の検証＞
まずＬｉＭｎ2Ｏ4を正極活物質として用いたリチウム二次電池について第一原理計算を行い、容量［ｍＡｈ／ｇ］と起電力［Ｖ］との関係（容量発現時の電位（ｖｓ Ｎａ／Ｎａ+）））を求め、第一原理計算の信頼性を検証した。
<Verification of the reliability of first-principles calculations>
First, a first-principles calculation was performed on a lithium secondary battery using LiMn 2 O 4 as a positive electrode active material, and the relationship between the capacity [mAh / g] and the electromotive force [V] (the potential at the time of capacity development (vs Na / Na + )))) Was obtained and the reliability of the first principle calculation was verified.
図１にＬｉＭｎ2Ｏ4を正極活物質とするリチウム二次電池について行った第一原理計算の結果を示す。同図に示すように、有機電解液の酸化分解が懸念される電位である４Ｖ（ｖｓ Ｌｉ／Ｌｉ+）以下において約１００［ｍＡｈ／ｇ］の容量が得られている。ここでＬｉＭｎ2Ｏ4は、平均作動電位（３．８［Ｖ］）において容量が１１０［ｍＡｈ／ｇ］であることが知られているが、これは上記第一原理計算の結果とほぼ一致しており、第一原理計算の信頼性が十分に高いことが検証された。 FIG. 1 shows the results of a first principle calculation performed on a lithium secondary battery using LiMn 2 O 4 as a positive electrode active material. As shown in the figure, a capacity of about 100 [mAh / g] is obtained at 4 V (vs Li / Li + ) or less, which is a potential for oxidative decomposition of the organic electrolyte. Here, LiMn 2 O 4 is known to have a capacity of 110 [mAh / g] at an average operating potential (3.8 [V]), which is almost the same as the result of the first principle calculation. It was verified that the reliability of the first-principles calculation was sufficiently high.
＜ナトリウム二次電池用正極活物質の候補の検証＞
続いて、候補として選出した３つの正極活物質（Ｎａ2ＮｉＯ2、Ｎａ2Ｎｉ0.5Ｆｅ0.5Ｏ2、及びＮａ2Ｎｉ0.5Ｍｎ0.5Ｏ2）の夫々について、夫々を用いて構成したナトリウム二次電池の特性（容量［ｍＡｈ／ｇ］と起電力［Ｖ］との関係（容量発現時の電位（ｖｓ Ｎａ／Ｎａ+）））を第一原理計算により求めた。以下、各正極活物質について順に説明する。
<Verification of candidate positive electrode active materials for sodium secondary batteries>
Subsequently, for each of the three positive electrode active materials (Na 2 NiO 2 , Na 2 Ni 0.5 Fe 0.5 O 2 , and Na 2 Ni 0.5 Mn 0.5 O 2 ) selected as candidates, a sodium secondary composed using each of them. The characteristics of the battery (relationship between capacity [mAh / g] and electromotive force [V] (potential at the time of capacity development (vs Na / Na + ))) were determined by first-principles calculation. Hereinafter, each positive electrode active material will be described in order.
（１）Ｎａ2ＮｉＯ2
図２はＮａ2ＮｉＯ2を正極活物質とするナトリウム二次電池について行った第一原理計算の結果である。ここでリチウム二次電池の正極活物質として用いた場合に比較的高い容量を示すことが知られているＬｉＣｏＯ2は、平均作動電位３．７Ｖ（ｖｓ Ｌｉ／Ｌｉ＋）において約１５０［ｍＡｈ／ｇ］の容量を示す。このため、このエネルギー密度（５６０［ｍＷｈ／ｇ］）を凌駕するには、Ｎａ2ＮｉＯ2（分子量１３６．７）の平均作動電位を３．５Ｖ（ｖｓ Ｎａ／Ｎａ＋（０．３Ｖ ｖｓ Ｌｉ／Ｌｉ＋））とした場合、例えば、１６０［ｍＡｈ／ｇ］の容量を実現できればよく、Ｎａ2ＮｉＯ2の化学式あたり０．８個のナトリウムが容量として寄与すればよいことになる。
(1) Na 2 NiO 2
FIG. 2 shows the results of first-principles calculations performed on a sodium secondary battery using Na 2 NiO 2 as a positive electrode active material. Here, LiCoO 2 known to exhibit a relatively high capacity when used as a positive electrode active material of a lithium secondary battery is about 150 [mAh / g at an average operating potential of 3.7 V (vs Li / Li +). ] Capacity. Therefore, in order to surpass this energy density (560 [mWh / g]), the average operating potential of Na 2 NiO 2 (molecular weight 136.7) is set to 3.5 V (vs Na / Na + (0.3 V vs Li / In the case of Li +)), for example, a capacity of 160 [mAh / g] may be realized, and 0.8 sodium per chemical formula of Na 2 NiO 2 may contribute as a capacity.
同図に示すように、有機電解液の酸化分解の懸念の少ない４［Ｖ］以下（平均作動電位は３．５Ｖ程度）において約２００［ｍＡｈ／ｇ］程度の容量が得られており、Ｎａ2ＮｉＯ2は、正極活物質として、ＬｉＣｏＯ2やＮａＣｒＯ2（容量１１０［ｍＡｈ／ｇ］）等の既存の正極活物質の性能を十分に凌駕する性能を有していることがわかる。また化学式（Ｎａ2ＮｉＯ2）当たり１個のナトリウムが寄与するとした場合の理論容量は１９６［ｍＡｈ／ｇ］であるので、化学式当たりほぼ１個のナトリウムがレドックス反応に寄与していることがわかる。 As shown in the figure, a capacity of about 200 [mAh / g] is obtained at 4 [V] or less (average operating potential is about 3.5 V) with little concern about oxidative decomposition of the organic electrolyte. It can be seen that 2 NiO 2 has a performance sufficiently surpassing that of existing positive electrode active materials such as LiCoO 2 and NaCrO 2 (capacity 110 [mAh / g]) as the positive electrode active material. Further, the theoretical capacity in the case where one sodium contributes per chemical formula (Na 2 NiO 2 ) is 196 [mAh / g], so that it is understood that almost one sodium per chemical formula contributes to the redox reaction. .
また１個のナトリウムが充電時にＮａ2ＮｉＯ2の結晶から脱離する際は同等量のナトリウム（１化学式あたり１個のナトリウム）が結晶中に残存するので、Ｎａ2ＮｉＯ2は、ＬｉＣｏＯ2と同様、優れた結晶安定性を示し、サイクル特性の向上にも貢献すると考えられる。ちなみにＬｉＣｏＯ2などの層状化合物では、理論容量の６割程度の容量しか発現しない。これはリチウムをレドックス反応に用いると、結晶構造の骨格自体が変化してしまうことが原因と考えられる。 Further, when one sodium is detached from the Na 2 NiO 2 crystal during charging, an equivalent amount of sodium (one sodium per chemical formula) remains in the crystal, so that Na 2 NiO 2 is composed of LiCoO 2 and Similarly, it exhibits excellent crystal stability and is thought to contribute to the improvement of cycle characteristics. Incidentally, a layered compound such as LiCoO 2 exhibits only a capacity of about 60% of the theoretical capacity. This is thought to be because the skeleton of the crystal structure itself changes when lithium is used for the redox reaction.
（２）Ｎａ2Ｎｉ0.5Ｆｅ0.5Ｏ2
図３はＮａ2Ｎｉ0.5Ｆｅ0.5Ｏ2を正極活物質とするナトリウム二次電池の第一原理計算の結果である。同図に示すように、有機電解液の酸化分解の懸念の少ない４［Ｖ］以下において約２００［ｍＡｈ／ｇ］程度の容量が得られており、Ｎａ2Ｎｉ0.5Ｆｅ0.5Ｏ2は、正極活物質として、ＬｉＣｏＯ2等の既存の正極活物質の性能を十分に凌駕する性能を有していることがわかる。またＮａ2ＮｉＯ2と同様に、化学式（Ｎａ2Ｎｉ0.5Ｆｅ0.5Ｏ2）当たりほぼ１個のナトリウムがレドックス反応に寄与していることがわかる。
(2) Na 2 Ni 0.5 Fe 0.5 O 2
FIG. 3 shows the result of first-principles calculation of a sodium secondary battery using Na 2 Ni 0.5 Fe 0.5 O 2 as a positive electrode active material. As shown in the figure, a capacity of about 200 [mAh / g] is obtained at 4 [V] or less with little concern about oxidative decomposition of the organic electrolyte, and Na 2 Ni 0.5 Fe 0.5 O 2 is a positive electrode. It can be seen that the active material has a performance sufficiently surpassing that of existing positive electrode active materials such as LiCoO 2 . In addition, as with Na 2 NiO 2 , it can be seen that almost one sodium per chemical formula (Na 2 Ni 0.5 Fe 0.5 O 2 ) contributes to the redox reaction.
尚、一般式Ｎａ2Ｎｉ(1-x)ＦｅxＯ2で表される物質において、鉄は通常、＋２価で存在し、また＋４価にはなりにくいので、＋２価⇔＋３価の１電子レドックス反応を示すが、鉄の価数変化による作動電位が２．４Ｖ（ｖｓ Ｎａ／Ｎａ＋）であるためエネルギー密度は低下する（同図において、充電初期の電位が平均で２．４Ｖ程度となっているが、これは鉄の＋２価⇔＋３価の反応によるものであると考えられる。）。ここで一般式Ｎａ2Ｎｉ(1-x)ＦｅxＯ2で表される活物質におけるエネルギー密度は、化学式当たり１個のナトリウムがレドックス反応に寄与するとすれば、１９６×（２．４×ｘ＋３．５×（１−ｘ））［ｍＷｈ／ｇ］となる。上式から、既存のＬｉＣｏＯ2のエネルギー密度である５６０［ｍＷｈ／ｇ］を凌駕するには０≦ｘ≦０．６が条件となることがわかる。
Incidentally, in the general formula Na 2 Ni (1-x)
（３）Ｎａ2Ｎｉ0.5Ｍｎ0.5Ｏ2
図４はＮａ2Ｎｉ0.5Ｍｎ0.5Ｏ2を正極活物質とするナトリウム二次電池の第一原理計算の結果である。同図に示すように、有機電解液の酸化分解の懸念の少ない４［Ｖ］以下において約１００［ｍＡｈ／ｇ］程度の容量となっている。これは化学式当たり０．５個分（９８［ｍＡｈ／ｇ］）のナトリウムしか容量に寄与していないことを示しており、Ｎａ2Ｎｉ0.5Ｆｅ0.5Ｏ2と比べてマンガンがレドックス反応において不活性であることがわかる。ここで一般式Ｎａ2Ｎｉ(1-x)ＭｎxＯ2で表される正極活物質のエネルギー密度は、１９６×３．５×（１−ｘ）［ｍＷｈ／ｇ］となる。上式から、既存のＬｉＣｏＯ2のエネルギー密度である５６０［ｍＷｈ／ｇ］を凌駕するには０≦ｘ≦０．２が条件となることがわかる。
(3) Na 2 Ni 0.5 Mn 0.5 O 2
FIG. 4 shows the result of first-principles calculation of a sodium secondary battery using Na 2 Ni 0.5 Mn 0.5 O 2 as a positive electrode active material. As shown in the figure, the capacity is about 100 [mAh / g] at 4 [V] or less where there is little concern about oxidative decomposition of the organic electrolyte. This indicates that only 0.5 (98 [mAh / g]) sodium per chemical formula contributes to the capacity, and manganese is inactive in the redox reaction compared to Na 2 Ni 0.5 Fe 0.5 O 2. It can be seen that it is. Here, the energy density of the positive electrode active material represented by the general formula Na 2 Ni (1-x) Mn x O 2 is 196 × 3.5 × (1-x) [mWh / g]. From the above equation, it can be seen that 0 ≦ x ≦ 0.2 is a condition for surpassing 560 [mWh / g] which is the energy density of the existing LiCoO 2 .
＜総括＞
以上のように、Ｎａ2ＮｉＯ2を正極活物質とすることで、既存の正極活物質を十分に凌駕する性能を有するナトリウム二次電池を実現できることがわかった。またＮａ2ＮｉＯ2を正極活物質とすることで、ＬｉＣｏＯ2と同様に優れた結晶安定性が得られ、サイクル特性の向上を期待できることがわかった。
<Summary>
As described above, it was found that by using Na 2 NiO 2 as the positive electrode active material, a sodium secondary battery having a performance sufficiently surpassing that of the existing positive electrode active material can be realized. It was also found that by using Na 2 NiO 2 as the positive electrode active material, excellent crystal stability was obtained in the same manner as LiCoO 2 and an improvement in cycle characteristics could be expected.
尚、Ｎａ2ＮｉＯ2は、遷移金属とキャリアイオンの比が、ＬｉＣｏＯ2と比較して２倍、ＬｉＭｎ2Ｏ4と比較して４倍であるので理論的にも高容量化が期待できる。 Since Na 2 NiO 2 has a ratio of transition metal to carrier ions that is twice that of LiCoO 2 and four times that of LiMn 2 O 4 , a high capacity can be expected theoretically.
また遷移金属としてニッケルのように複数の価数状態をとることが可能な（多電子反応が可能な）元素を選択することにより、複数のナトリウムを寄与させてナトリウム二次電池のさらなる高容量化を期待することができる。 In addition, by selecting an element that can take multiple valence states (capable of multi-electron reaction), such as nickel, as the transition metal, the sodium secondary battery can be further increased in capacity by contributing multiple sodium. Can be expected.
また一般式がＮａ2Ｎｉ(1-x)ＸxＯ2（Ｘは、Ｆｅ、及びＭｎのうちの少なくともいずれか）で表される物質や、Ｎａ2Ｎｉ(1-x)ＦｅxＯ2（０≦ｘ≦０．６）で表される物質、或いは一般式がＮａ2Ｎｉ(1-x)ＭｎxＯ2（０≦ｘ≦０．２）で表される物質を正極活物質として用いることにより、高容量のナトリウム二次電池を実現可能であることを確認することができた。 The general formula Na 2 Ni (1-x) X x O 2 (X is, Fe, and at least one of Mn) represented material and is at, Na 2 Ni (1-x ) Fe x O 2 A material represented by (0 ≦ x ≦ 0.6) or a material represented by the general formula Na 2 Ni (1-x) Mn x O 2 (0 ≦ x ≦ 0.2) is used as the positive electrode active material. It was confirmed that a high-capacity sodium secondary battery could be realized by using it.
ところで、以上の説明は本発明の理解を容易にするためのものであり、本発明を限定するものではない。本発明はその趣旨を逸脱することなく、変更、改良され得ると共に本発明にはその等価物が含まれることは勿論である。 By the way, the above description is for facilitating the understanding of the present invention, and does not limit the present invention. It goes without saying that the present invention can be changed and improved without departing from the gist thereof, and that the present invention includes equivalents thereof.
１０１ ＬｉＭｎ2Ｏ4の容量−電位特性グラフ、
１０２ Ｎａ2ＮｉＯ2の容量−電位特性グラフ、
１０３ Ｎａ2Ｎｉ0.5Ｆｅ0.5Ｏ2の容量−電位特性グラフ、
１０４ Ｎａ2Ｎｉ0.5Ｍｎ0.5Ｏ2の容量−電位特性グラフ、
101 LiMn 2 O 4 capacitance-potential characteristic graph,
102 Capacitance-potential characteristic graph of 102 Na 2 NiO 2 ,
103 capacitance-potential characteristic graph of 103 Na 2 Ni 0.5 Fe 0.5 O 2 ,
104 Na 2 Ni 0.5 Mn 0.5 O 2 capacitance-potential characteristic graph,
Claims (6)
ことを特徴とするナトリウム二次電池用正極活物質。 Positive electrode active material for sodium secondary batteries which general formula is characterized in that it is a Na 2 Ni (1-x) Fe x O 2 (0 ≦ x ≦ 0.6).
ことを特徴とするナトリウム二次電池用正極活物質。 A positive electrode active material for a sodium secondary battery, wherein the general formula is Na 2 Ni (1-x) Mn x O 2 (0 ≦ x ≦ 0.2) .
有機溶媒を電解質として構成されることを特徴とするナトリウム二次電池。 The sodium secondary battery according to claim 3 ,
A sodium secondary battery comprising an organic solvent as an electrolyte.
水溶液を電解質として構成されることを特徴とするナトリウム二次電池。 The sodium secondary battery according to claim 3 ,
A sodium secondary battery comprising an aqueous solution as an electrolyte.
ナトリウム伝導体である固体電解質を電解質として構成されることを特徴とするナトリウム二次電池。 The sodium secondary battery according to claim 3 ,
A sodium secondary battery comprising a solid electrolyte as a sodium conductor as an electrolyte.
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