JP4207510B2 - Positive electrode material, positive electrode, and battery - Google Patents

Description

【００５２】
続いて、この正極活物質混合粉末と、バインダであるポリフッ化ビニリデン（ＰＶｄＦ）と、導電材であるカーボンブラックとを、質量比で焼成物：ＰＶｄＦ：カーボンブラック＝９４：３：３となるように混合して正極合剤を調製し、Ｎ−メチル−２−ピロリドン（ＮＭＰ）に分散させて正極合剤スラリーとした。そののち、この正極合剤スラリーを厚み２０μｍのアルミニウム箔よりなる正極集電体１２Ａに塗布し、乾燥・圧縮成型して厚み５０μｍの正極合剤層１２Ｂを形成し、正極１２を作製した。
【００５３】
また、負極活物質である人造黒鉛と、バインダであるＰＶｄＦとを、質量比で人造黒鉛：ＰＶｄＦ＝９０：１０になるように混合して負極合剤を調製し、ＮＭＰに分散させて負極合剤スラリーとした。次いで、この負極合剤スラリーを厚み２０μｍの銅箔よりなる負極集電体１４Ａに塗布し、乾燥・圧縮成型して厚み５０μｍの負極合剤層１４Ｂを形成し、負極１４を作製した。
【００５４】
正極１２および負極１４を作製したのち、正極１２を直径１５ｍｍに打ち抜くと共に、負極１４を直径１６ｍｍに打ち抜き、外装カップ１３，負極１４およびセパレータ１５をこの順に積層し、電解液１６を注いで正極１２を入れた外装缶１１を被せ、ガスケット１７を介してかしめた。電解液１６には、エチレンカーボネートとジメチルカーボネートとを１：１の体積比で混合した溶媒に、六フッ化リン酸リチウムを１ｍｏｌ／ｌの濃度で溶解させたものを使用した。これにより実施例１−１〜１−５の二次電池を得た。
【００５５】
得られた実施例１−１〜１−５の二次電池について、１．５ｍＡ、４．２Ｖの低電流低電圧方式により終止電流を０．０６ｍＡとして充電し、１．５ｍＡ低電流方式により終止電圧２Ｖとして放電する充放電サイクル試験を行った。その初回の充電容量および放電容量を表１に示す。
【００５６】
本実施例に対する比較例として、正極活物質として、ＮＡＳＩＣＯＮ型のリチウムとチタンとのリン酸化合物を混合せず、リン酸リチウム鉄のみを用いたことを除き、本実施例と同様にして二次電池を作製した。比較例についても、本実施例と同様にして充放電サイクル試験を行った。その初回の充電容量および放電容量を表１に合わせて示す。
【００５７】
表１からわかるように、ＮＡＳＩＣＯＮ型のリチウムとチタンとのリン酸化合物を混合した本実施例によれば、混合していない比較例よりも、大きな放電容量が得られた。すなわち、低酸化還元電位化合物を含むようにすれば、容量を向上させることができることが分かった。
【００５８】
また、ＮＡＳＩＣＯＮ型のリチウムとチタンとのリン酸化合物の含有量を多くすると、放電容量は大きくなり、極大値を示したのち小さくなる傾向がみられた。すなわち、低酸化還元電位化合物の含有量は、リチウム含有リン酸化合物との質量比で、１：０＜リチウム含有リン酸化合物：低酸化還元電位化合物≦８：２程度の範囲内が好ましいことが分かった。
【００５９】
（実施例２−１〜２−３）
低酸化還元電位化合物として、表２に示した他のＮＡＳＩＣＯＮ型化合物を用いたことを除き、実施例１−２と同様にして二次電池を作製した。なお、低酸化還元電位化合物として、実施例２−１ではＮＡＳＩＣＯＮ型のリチウムと鉄とのリン酸化合物（Ｌｉ₃ Ｆｅ₂ （ＰＯ₄ ）₃ ）を用い、実施例第２−２ではＮＡＳＩＣＯＮ型の鉄の硫酸化合物（Ｆｅ₂ （ＳＯ₄ ）₃ ）を用い、実施例２−３ではＮＡＳＩＣＯＮ型のバナジウムの硫酸化合物（Ｖ₂ （ＳＯ₄ ）₃ ）を用いた。実施例２−１〜２−３についても、実施例１−２と同様にして充放電サイクル試験を行った。その初回の充電容量および放電容量を、実施例１−２および比較例の結果と共に表２に示す。
【００６０】
【表２】

【００６１】
表２からわかるように、他のＮＡＳＩＣＯＮ型化合物を用いた実施例２−１〜２−３についても、実施例１−２と同様に、比較例よりも大きな放電容量を得ることができた。すなわち、低酸化還元電位化合物として、ＮＡＳＩＣＯＮ型化合物を用いるようにすれば、容量を向上させることができることが分かった。
【００６２】
また、これらの中でも、ＮＡＳＩＣＯＮ型のリチウムとチタンとのリン酸化合物を用いた実施例１−２において、特に大きな放電容量が得られた。すなわち、低酸化還元電位化合物として、ＮＡＳＩＣＯＮ型のリチウムとチタンとのリン酸化合物を用いるようにすれば、特に好ましいことが分かった。
【００６３】
（実施例３−１〜３−８）
低酸化還元電位化合物として、ＮＡＳＩＣＯＮ型のリチウムとチタンとのリン酸化合物（Ｌｉ_1+x Ｔｉ₂ （ＰＯ₄ ）₃ ）を用い、表３に示したように、実施例３−１〜３−８でリチウムの組成、すなわちｘの値を変化させたことを除き、実施例１−３と同様にして二次電池を作製した。なお、実施例３−１は実施例１−３と同一組成のものを用いている。実施例３−１〜３−８についても、実施例１−３と同様にして充放電サイクル試験を行った。その初回容量および１０サイクル目の容量を表３に示すと共に、図４にｘ値と１０サイクル目の容量との関係を示す。
【００６４】
【表３】

【００６５】
また、本実施例に対する参照例３−１〜３−８として、ＮＡＳＩＣＯＮ型のリチウムとチタンとのリン酸化合物（Ｌｉ_1+x Ｔｉ₂ （ＰＯ₄ ）₃ ）のみを正極活物質として用い、対極にリチウム金属板を用いたことを除き、本実施例と同様にして評価セルを作製した。その際、参照例３−１〜３−８で、実施例３−１〜３−８と同様に、表４に示したようにリチウムの組成、すなわちｘの値を変化させた。参照例３−１〜３−８の評価セルについても、本実施例と同様にして充放電サイクル試験を行った。その初回容量および１５サイクル目の容量を表４に示す。
【００６６】
【表４】

【００６７】
表３からわかるように、ＬｉＴｉ₂ （ＰＯ₄ ）₃ を用いた実施例３−１では１０サイクル目の容量劣化が激しいが、リチウムを過剰とした実施例３−２〜３−８では１０サイクル目の容量劣化が改善されている。これは、表４の参照例３−１〜３−８の結果とも一致しており、サイクル劣化はＬｉ_1+x Ｔｉ₂ （ＰＯ₄ ）₃ の容量劣化によるものと考えられる。すなわち、Ｌｉ_1+x Ｔｉ₂ （ＰＯ₄ ）₃ において、ｘが充放電前において１．０以上２．０以下の範囲内のものを用いるようにすれば、サイクル特性を改善できることが分かった。
【００６８】
なお、上記実施例では、リチウム含有リン酸化合物としてリン酸リチウム鉄を用いる場合を具体的に挙げて説明したが、他のリチウム含有リン酸化合物を用いる場合についても、同様の結果を得ることができる。また、上記実施例では、低酸化還元電位化合物として用いるＮＡＳＩＣＯＮ型化合物についていくつかの具体例を挙げて説明したが、他のＮＡＳＩＣＯＮ型化合物を用いる場合、または他の低酸化還元電位化合物を用いる場合についても、同様の結果を得ることができる。
【００６９】
更に、上記実施例では、負極活物質および電解質について一例を挙げて説明したが、本発明は正極１２の材料による充放電特性に関するものであり、負極活物質および電解質の種類に依存するものではなく、他の材料を用いても同様の結果を得ることができる。
【００７０】
以上、実施の形態および実施例を挙げて本発明を説明したが、本発明は上記実施の形態および実施例に限定されるものではなく、種々変形可能である。例えば、上記実施の形態および実施例では、液状の電解質である電解液を用いる場合について説明したが、他の電解質を用いるようにしてもよい。他の電解質としては、例えば、電解液を高分子化合物に保持させたゲル状電解質、イオン伝導性を有する高分子化合物に電解質塩を分散させた高分子電解質、イオン伝導性セラミックス，イオン伝導性ガラスあるいはイオン性結晶などよりなる無機固体電解質、溶融塩電解質、またはこれらを混合したものが挙げられる。
【００７１】
また、上記実施の形態および実施例では、正極１２および負極１４の構造について一例を挙げて具体的に説明したが、集電体を有していなくてもよく、また、合剤層に代えて、活物質よりなる活物質層を有していてもよい。
【００７２】
更に、上記実施の形態および実施例では、コイン型の二次電池を具体的に挙げて説明したが、本発明は他の構造を有する円筒型や、ボタン型あるいは角型など他の形状を有する二次電池、または巻回構造などの他の構造を有する二次電池についても同様に適用することができる。更に、一次電池などの他の電池についても同様に適用することができる。
【００７３】
【発明の効果】
以上説明したように請求項１ないし請求項３のいずれか１項に記載の正極材料、または請求項４ないし請求項６のいずれか１項に記載の正極、または請求項７ないし請求項９のいずれか１項に記載の電池によれば、リチウム含有リン酸化合物よりも低い酸化還元電位においてリチウムを吸蔵および放出することが可能であると共に充放電前にリチウム吸蔵可能な状態にある低酸化還元電位化合物を含むようにしたので、リチウム含有リン酸化合物の内部インピーダンスが高い領域において低酸化還元電位化合物を利用することにより、リチウム含有リン酸化合物の容量ロス分を低酸化還元電位化合物で補充することができ、容量を向上させることができる。また、低酸化還元電位化合物として、ＮＡＳＩＣＯＮ型化合物を含むようにしたので、リチウム含有リン酸化合物と結晶的に親和性が高く、容易に製造することができる。さらに、低酸化還元電位化合物として、中心金属元素がチタン，バナジウムおよび鉄からなる群のうちの少なくとも１種よりなるものを含むようにしたので、より高い容量を得ることができる。
【００７６】
更に、請求項２記載の正極材料、または請求項５記載の正極、または請求項８記載の電池によれば、低酸化還元電位化合物として、ＮＡＳＩＣＯＮ型のリチウムとチタンとのリン酸化合物であり、チタンに対するリチウムの組成比（Ｌｉ／Ｔｉ）が充放電前において２／２以上３／２以下の範囲内のものを含むようにしたので、サイクル特性を向上させることができ、より高い効果を得ることができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係る二次電池の構成を表す断面図である。
【図２】図１に示した二次電池における正極の初回充放電曲線を表す特性図である。
【図３】図１に示した二次電池における正極の他の初回充放電曲線を表す特性図である。
【図４】本発明の実施例におけるＬｉ_1+x Ｔｉ₂ （ＰＯ₄ ）₃ のｘ値と１０サイクル目の容量との関係を表す特性図である。
【符号の説明】
１１…外装缶、１２…正極、１２Ａ…正極集電体、１２Ｂ…正極合剤層、１３…外装カップ、１４…負極、１４Ａ…負極集電体、１４Ｂ…負極合剤層、１５…セパレータ、１６…電解液、１７…ガスケット。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode material containing a lithium-containing phosphate compound, a positive electrode, and a battery using the same.
[0002]
[Prior art]
The development and progress of portable electronic devices in recent years have been remarkable, and the demand for batteries used therefor has been increasing rapidly. For example, recent small portable electronic devices have a relatively high driving voltage of 3 V to 4 V and consume a large current, so a high-output power source is required. Since it is carried at the same time, it is desired that its weight is light. Furthermore, there are many demands for a battery having a large capacity from the viewpoint of extending the driving time.
[0003]
As a power source used for such a portable electronic device, that is, a small secondary battery, for example, there are a nickel metal hydride battery and a lithium ion secondary battery. Among these, a lithium ion secondary battery has a higher voltage, is lighter, and has a larger active capacity than nickel metal hydride, and is therefore optimal as a power source for small portable electronic devices.
[0004]
A conventional general lithium ion secondary battery uses, for example, a lithium-cobalt composite oxide for a positive electrode, graphite for a negative electrode, and a lithium salt such as lithium hexafluorophosphate or lithium tetrafluoroborate as an electrolyte. Is dissolved in a solvent such as ethylene carbonate or dimethyl carbonate.
[0005]
However, this lithium ion secondary battery has insufficient reliability and stability, and improvement is desired. One of the causes is considered to be thermal stability of the positive electrode, and various positive electrode active materials replacing lithium-cobalt composite oxide have been studied. Among them, the lithium-containing phosphate compound having a strong three-dimensional framework structure is Jay. Bye. It has been proposed by J.B. Goodenough et al. (See Non-Patent Document 1), and high thermal stability of this material is expected.
[0006]
[Non-Patent Document 1]
Kay. S. Outside Nanjandaswamy (K.S.Nanjundaswamy),
“Solid State Ionics”,
Elsevier Science Publishers BV, Netherlands
(ELSEVIER SCINENCE PUBLISHERS BV),
1996, 92, p. 1-10
[Non-Patent Document 2]
A. S. Andersson,
Jay. Oh. Thomas (J.O.Thomas),
“Journal of Power Source”,
Elsevier Science Publishers BV, Netherlands
(ELSEVIER SCINENCE PUBLISHERS BV),
2001, No. 498, p. 97-98
[0007]
[Problems to be solved by the invention]
However, this lithium-containing phosphate compound has a problem that the internal impedance rapidly increases at the end of charge and at the end of discharge, and only about 50% to 80% of the contained capacity can be used (Non-patent Document 2). reference).
[0008]
The present invention has been made in view of such problems, and an object thereof is to provide a positive electrode material capable of outputting a capacity close to the theoretical capacity, a positive electrode, and a battery using the same.
[0009]
[Means for Solving the Problems]
  The positive electrode material according to the present invention is capable of inserting and extracting lithium at a lithium-containing phosphate compound and a lower oxidation-reduction potential than the lithium-containing phosphate compound.AsLow oxidation-reduction potential compounds that can occlude lithium before charge and discharge.Lithium-containing phosphate compound is Li _a MI _b PO _Four (In the formula, MI represents at least one selected from the group consisting of iron (Fe), cobalt (Co), manganese (Mn), and nickel (Ni). The ranges of a and b are 0 ≦ a ≦ 1 respectively) .1, 0.85 ≦ b ≦ 1.15)), and the low redox potential compound is (Li) _c [M II ₂ (XO _Four ) _Three (Where c is a value within the range of 0 ≦ c ≦ 3, and M II Represents at least one selected from the group consisting of vanadium (V), titanium (Ti) and iron (Fe), and X represents phosphorus (P) or sulfur (S). ) NASICON type compound represented byIs.
[0010]
  The positive electrode according to the present invention is capable of occluding and releasing lithium at a lithium-containing phosphate compound and a lower oxidation-reduction potential than the lithium-containing phosphate compound.AsLow oxidation-reduction potential compounds that can occlude lithium before charge and discharge.Lithium-containing phosphate compound is Li _a MI _b PO _Four (In the formula, MI represents at least one selected from the group consisting of iron, cobalt, manganese and nickel. The ranges of a and b are 0 ≦ a ≦ 1.1 and 0.85 ≦ b ≦ 1.15, respectively. And the low redox potential compound is (Li) _c [M II ₂ (XO _Four ) _Three (Where c is a value within the range of 0 ≦ c ≦ 3, and M II Represents at least one member selected from the group consisting of vanadium, titanium and iron, and X represents phosphorus or sulfur. ) NASICON type compound represented byIs.
[0011]
  The battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, and the positive electrode can store and release lithium at a lithium-containing phosphate compound and a lower redox potential than the lithium-containing phosphate compound. Is possibleAsLow oxidation-reduction potential compounds that can occlude lithium before charge and discharge.Lithium-containing phosphate compound is Li _a MI _b PO _Four (In the formula, MI represents at least one selected from the group consisting of iron, cobalt, manganese and nickel. The ranges of a and b are 0 ≦ a ≦ 1.1 and 0.85 ≦ b ≦ 1.15, respectively. And the low redox potential compound is (Li) _c [M II ₂ (XO _Four ) _Three (Where c is a value within the range of 0 ≦ c ≦ 3, and M II Represents at least one member selected from the group consisting of vanadium, titanium and iron, and X represents phosphorus or sulfur. ) NASICON type compound represented byIs.
[0012]
In the positive electrode material, the positive electrode, and the battery according to the present invention, the low oxidation-reduction potential compound is used in a region where the internal impedance of the lithium-containing phosphate compound is high, and the capacity is improved.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0014]
FIG. 1 shows a cross-sectional structure of a secondary battery using a positive electrode material and a positive electrode according to an embodiment of the present invention. This secondary battery is a so-called coin-type battery. A disc-shaped positive electrode 12 accommodated in the outer can 11 and a disc-shaped negative electrode 14 accommodated in the outer cup 13 are interposed via a separator 15. Are stacked. The interiors of the outer can 11 and the outer cup 13 are filled with an electrolytic solution 16 that is a liquid electrolyte, and the peripheral portions of the outer can 11 and the outer cup 13 are sealed by caulking through an insulating gasket 17. The outer can 11 and the outer cup 13 are made of, for example, a metal such as stainless steel or aluminum (Al).
[0015]
The positive electrode 12 includes, for example, a positive electrode current collector 12A and a positive electrode mixture layer 12B provided on the positive electrode current collector 12A. The positive electrode current collector 12A is made of, for example, a metal foil such as an aluminum foil, a nickel (Ni) foil, or a stainless steel foil. The positive electrode mixture layer 12B includes, for example, a positive electrode material capable of inserting and extracting lithium as a positive electrode active material, and is configured with a conductive agent such as carbon black or graphite and a binder such as polyvinylidene fluoride as necessary. Has been.
[0016]
This positive electrode material is capable of occluding and releasing lithium at a lithium-containing phosphate compound and a redox potential lower than that of the lithium-containing phosphate compound, and is in a state in which lithium can be occluded before charge and discharge. And a redox potential compound.
[0017]
The lithium-containing phosphoric acid compound has an olivine structure, and for example, those typically represented by Chemical Formula 1 are preferable.
[0018]
[Chemical 1]
Li_aMI_bPO_Four
In the formula, MI represents chromium (Cr), vanadium (V), molybdenum (Mo), aluminum, gallium (Ga), boron (B), niobium (Nb), copper (Cu), titanium (Ti), zinc (Zn ), Magnesium (Mg), iron (Fe), cobalt (Co), manganese (Mn), and nickel. In the case of a stoichiometric composition, a and b are each 1, but it may not be a stoichiometric composition. The preferred ranges of a and b are 0 ≦ a ≦ 1.1 and 0.85 ≦ b ≦ 1.15, respectively. This is because it is difficult to synthesize a lithium-containing phosphate compound having an ordered olivine structure within a range outside this range. Further, the composition of oxygen is set to “4” of the stoichiometric composition, but may deviate from the stoichiometric composition.
[0019]
Specific examples of such lithium-containing phosphate compounds include, for example, LiFePO_Four, LiCoPO_Four, Li (MnFe) PO_Four, LiNiPO_FourIs mentioned.
[0020]
The low oxidation-reduction potential compound replaces the lithium-containing phosphate compound in a region where the internal impedance of the lithium-containing phosphate compound is high, and improves the capacity. “Lithium can be occluded before charging / discharging” means that it does not contain lithium that can be released before charging or discharging, or the content of lithium that can be occluded / released even if it contains it. Means less than the amount. In order to obtain a higher capacity, it is preferable that lithium which can be released before charging / discharging is contained or the content thereof is 20% or less of the theoretical amount. The smaller the amount of lithium that can be released before charging / discharging, and the larger the amount of lithium that can be occluded, the capacity loss of the lithium-containing phosphate compound that occurs due to the sudden increase in internal impedance can be replenished instead. Because. The amount of releasable lithium contained before charging / discharging is determined from the discharge capacity.
[0021]
As the low redox potential compound, a NASICON type compound having a high crystallinity with the lithium-containing phosphate compound is preferable. In this specification, the NASICON type compound is referred to as Jay. Bye. Based on the proposal of JB Goodenough, and is represented by the chemical formula 2 (for example, “AK Journal”, “Journal Electrochemical Society”) , USA, Electrochemical Society, Inc., 1997, 144, p. 160, or non-patent document 1).
[0022]
[Chemical formula 2]
(Li)_c[MII₂(XO_Four)_Three]
In the formula, c is a value in the range of 0 ≦ c ≦ 3, and MII is from chromium, vanadium, molybdenum, aluminum, gallium, boron, niobium, copper, titanium, zinc, magnesium, iron, cobalt, manganese and nickel. X represents phosphorus (P), arsenic (As), molybdenum, tungsten (W), or sulfur (S). Chemical formula 2 is expressed in stoichiometric composition and may deviate from the stoichiometric composition.
[0023]
This NASICON type compound is a type of sodium ion conductor, NASICON (NA Super Ionic CONductor) (Klaus-Dieter Kreuer), “High Conductivity Solid Ionic Conductors Recent Trends and Applications (Takehiko Takahashi) (HIGH CONDUCTIVITY SOLID IONIC CONDUCTORS-RECENT TRENDS AND APPLICATIONS (Ed. Takehiko Takahashi)) ", Singapore, World Scientific Publishing (World Scientific Publishing Co. Pte. Ltd., 1989, p.242) MIIO₆Octahedron and XO_FourIt has a polyanion skeleton composed of point shares with a tetrahedron. In this NASICON type compound, the lithium cation balances the valence, the MII valence changes, and the lithium cation number changes, whereby lithium is absorbed and released. The crystal structure includes a monoclinic type and a rhombohedral type.
[0024]
Among these, those in which the central metal element MII is at least one selected from the group consisting of titanium, vanadium and iron are preferred. This is because a higher capacity can be obtained. In particular, it is a NASICON type phosphoric acid compound of lithium and titanium, in which the composition ratio of lithium to titanium (Li / Ti) is 2/2 or more before charge / discharge. Ti tetravalent stoichiometric composition (LiTi₂(PO_Four)_ThreeThis is because the cycle characteristics can be improved by using lithium in excess of (). However, if the composition ratio of lithium to titanium is larger than 3/2, a by-product is generated, and therefore, it is preferably 3/2 or less before charging / discharging. This NASICON type compound is represented by the chemical formula 3.
[0025]
[Chemical 3]
Li_{1 + x}Ti₂(PO_Four)_Three
In the formula, x is a value within a range of 1.0 or more and 2.0 or less before charge / discharge.
[0026]
The content of the low oxidation-reduction potential compound is preferably in the range of 1: 0 <lithium-containing phosphate compound: low oxidation-reduction potential compound ≦ 8: 2, for example, by mass ratio with the lithium-containing phosphate compound. This is because if there are more low redox potential compounds than this, the characteristics of the lithium-containing phosphate compound cannot be sufficiently obtained, and the capacity decreases.
[0027]
The positive electrode material may contain a plurality of types of lithium-containing phosphate compounds, and may contain a plurality of types of low redox potential compounds. In addition to the lithium-containing phosphate compound and the low redox potential compound, other materials may be included. Examples of other positive electrode materials include sulfuric acid compounds, vanadic acid compounds, lithium cobalt composite oxides, lithium nickel composite oxides, lithium manganese composite oxides, and other lithium oxides, lithium sulfides, or polymer materials. Can be mentioned.
[0028]
The negative electrode 14 includes, for example, a negative electrode current collector 14A and a negative electrode mixture layer 14B provided on the negative electrode current collector 14A. The negative electrode current collector 14A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. The negative electrode mixture layer 14B contains, for example, lithium metal, a lithium alloy, or any one or more of negative electrode materials capable of inserting and extracting lithium as a negative electrode active material. Depending on the case, it is configured with a conductive agent and a binder.
[0029]
Examples of the negative electrode material capable of inserting and extracting lithium include carbonaceous materials, oxides, sulfides, alloys (such as intermetallic compounds), silicon (Si), silicon compounds, or conductive polymers. Any one or two or more of these may be used in combination. Among these, examples of the carbonaceous material include graphite, non-graphitizable carbon, and graphitizable carbon. As the oxide, for example, a lithium titanium composite oxide having a spinel structure (Li_FourTi_FiveO₁₂), Tungsten oxide (WO₂), Niobium oxide (Nb)₂O_Five) Or tin oxide (SnO). Examples of the alloy include a tin-antimony alloy (Sn—Sb), an aluminum-antimony alloy (Al—Sb), a gallium-antimony alloy (Ga—Sb), and a copper-tin alloy (Cu—Sn). Examples of the conductive polymer include polyacetylene and polypyrrole.
[0030]
Among them, it is preferable to use a material having a low potential with respect to lithium metal such as a carbonaceous material because the battery voltage can be increased. In addition, it is preferable to use an alloy, silicon, silicon compound, or the like because the capacity can be increased.
[0031]
The separator 15 separates the positive electrode 12 and the negative electrode 14 and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. The separator 15 is made of, for example, a porous film made of a synthetic resin made of polytetrafluoroethylene, polypropylene, polyethylene, or the like, or a porous film made of an inorganic material such as a ceramic nonwoven fabric. The porous film may be laminated.
[0032]
The electrolytic solution 16 is obtained by dissolving a lithium salt as an electrolyte salt in a solvent, and exhibits ion conductivity when the lithium salt is ionized. Examples of lithium salts include lithium hexafluorophosphate (LiPF).₆), Lithium perchlorate (LiClO)_Four), Lithium hexafluoroarsenate (LiAsF)₆), Lithium boron tetrafluoride (LiBF)_Four), Lithium trifluoromethanesulfonate (LiCF)_ThreeSO_Three) Or bis (trifluoromethanesulfonyl) imidolithium (LiN (CF_ThreeSO₂)₂Etc.) are suitable, and any one or two or more of these may be used in combination.
[0033]
Examples of the solvent include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, sulfolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 2-methyltetrahydrofuran, 3-methyl-1,3- Non-aqueous solvents such as dioxolane, methyl propionate, methyl butyrate, dimethyl carbonate, diethyl carbonate or dipropyl carbonate are preferred, and any one or two or more of these may be used in combination.
[0034]
The secondary battery having such a configuration can be manufactured, for example, as follows.
[0035]
First, for example, a positive electrode active material containing a lithium-containing phosphate compound and a low redox potential compound and, if necessary, a conductive agent and a binder are mixed to prepare a positive electrode mixture, such as N-methyl-2-pyrrolidone After being dispersed in the above solvent to obtain a paste-like positive electrode mixture slurry, the mixture is applied to the positive electrode current collector 12A, dried, and compression molded by a roll press or the like to form the positive electrode mixture layer 12B. 12
[0036]
Next, for example, a negative electrode active material and, if necessary, a conductive agent and a binder are mixed to prepare a negative electrode mixture, which is dispersed in a solvent such as N-methyl-2-pyrrolidone and pasted into a negative electrode mixture slurry. Then, it is applied to the negative electrode current collector 14A, the solvent is dried, and compression molding is performed by a roll press machine or the like to form the negative electrode mixture layer 14B.
[0037]
Subsequently, the negative electrode 14 and the separator 15 are placed in this order at the center of the outer cup 13, the electrolyte solution 16 is poured from above the separator 15, and the outer can 11 containing the positive electrode 12 is covered and caulked through the gasket 17. Thereby, the secondary battery shown in FIG. 1 is formed.
[0038]
This secondary battery operates as follows.
[0039]
2 and 3 are typical representations of the initial charge / discharge curve of the positive electrode 12. FIG. 2 shows a case where the low redox potential compound does not contain lithium that can be released before charge / discharge, and FIG. This is the case where the reduction potential compound contains lithium that can be released before charge and discharge. In the secondary battery, when charged, for example, lithium ions are released from the positive electrode 12 and inserted in the negative electrode 14 through the electrolytic solution 16. When discharging is performed, for example, lithium ions are extracted from the negative electrode 14 and inserted into the positive electrode 12 through the electrolytic solution 16.
[0040]
For example, when the low redox potential compound does not contain lithium that can be released before charging / discharging, as shown in FIG. 2, at the time of initial charge, lithium is not released from the low redox potential compound at the positive electrode 12, Lithium is released from the lithium-containing phosphate compound, and the potential of the positive electrode 12 increases accordingly. In the first discharge, lithium is first occluded in the lithium-containing phosphate compound in the positive electrode 12. Along with this, the potential of the positive electrode 12 decreases, and the internal impedance rapidly increases at the end of discharge, so that the potential of the positive electrode 12 rapidly decreases before reaching the theoretical capacity. Thereafter, in region A where the internal impedance of the lithium-containing phosphate compound is high, lithium is occluded in the low redox potential compound having a lower oxidation-reduction potential than the lithium-containing phosphate compound. That is, the capacity loss of the lithium-containing phosphate compound is supplemented by the low redox potential compound.
[0041]
Further, for example, when the low redox potential compound contains lithium that can be released before charging and discharging, as shown in FIG. 3, at the time of initial charge, lithium is first released from the low redox potential compound at the positive electrode 12, Lithium is then released from the lithium-containing phosphate compound. At the time of the first discharge, lithium is first occluded in the lithium-containing phosphate compound in the positive electrode 12, and then in the region A where the internal impedance of the lithium-containing phosphate compound is high, lithium is occluded in the low redox potential compound. That is, the capacity loss of the lithium-containing phosphate compound is supplemented by the low redox potential compound. However, the replenishment amount is reduced by the amount of releasable lithium contained in the low oxidation-reduction potential compound before charging and discharging compared to the case of FIG.
[0042]
From the second time onward, in both cases, after lithium is released from the low redox potential compound in charging, lithium is released from the lithium-containing phosphate compound, and after discharging, lithium is occluded in the lithium-containing phosphate compound. Lithium is occluded in the low redox potential compound.
[0043]
As described above, according to the present embodiment, the positive electrode 12 can occlude and release lithium at a lower redox potential than the lithium-containing phosphate compound, and is in a state in which lithium can be occluded before charge and discharge. Since the low redox potential compound is included, the capacity loss of the lithium containing phosphate compound is reduced by using the low redox potential compound in the region A where the internal impedance of the lithium containing phosphate compound is high. Can be replenished with compounds and can increase capacity.
[0044]
In particular, if a NASICON type compound is included as the low redox potential compound, it has a high crystal affinity with the lithium-containing phosphate compound and can be easily produced.
[0045]
Further, when the low oxidation-reduction potential compound includes at least one member selected from the group consisting of titanium, vanadium and iron as the central metal element, a higher effect can be obtained.
[0046]
Further, as a low redox potential compound, Li_{1 + x}Ti₂(PO_Four)_Three(X is a value within the range of 1.0 or more and 2.0 or less before charging / discharging), the cycle characteristics can be improved and higher effects can be obtained. Obtainable.
[0047]
【Example】
Further, specific embodiments of the present invention will be described in detail.
[0048]
(Examples 1-1 to 1-5)
First, lithium phosphate (Li_ThreePO_Four) And iron phosphate octahydrate (Fe_Three(PO_Four)₂・ 8H₂O) and mixed so that the molar ratio of lithium to iron is Li / Fe = 1.000 / 1.075, and further, acetylene black powder, which is an amorphous carbon material, is added to 10% of the entire fired product. It added so that it might become mass%, and it was set as the mixture. Next, this mixture and an aluminum oxide ball having a diameter of 10 mm are put into an aluminum oxide pot having a diameter of 100 mm as a mixture: aluminum oxide ball = 1: 2 in a mass ratio, and milled into the mixture using a planetary ball mill. Was given. The planetary ball mill has an experimental planetary rotating pot mill “LA-PO”._FourThe revolution radius was 200 mm, the revolution speed was 250 rpm, the rotation speed was 250 rpm, and the operation time was 15 hours.
[0049]
Next, the milled mixture is put into a ceramic crucible and baked at a temperature of 600 ° C. for 5 hours in an electric furnace in a nitrogen atmosphere, so that lithium iron phosphate (LiFePO 4) as a lithium-containing phosphate compound is obtained._Four) And acetylene black were obtained.
[0050]
Further, as a low redox potential compound, in accordance with Non-Patent Document 1, a NASICON type lithium phosphate compound (LiTi)₂(PO_Four)_Three) Was produced. Next, as shown in Table 1, the fired product containing the lithium iron phosphate obtained and the phosphate compound of NASICON type lithium and titanium were used in Examples 1-1 to 1-5 as LiFePO 4._Four: LiTi₂(PO_Four)_ThreeThe positive electrode active material mixed powder was prepared by changing the mass ratio.
[0051]
[Table 1]

[0052]
Subsequently, the positive electrode active material mixed powder, polyvinylidene fluoride (PVdF) as a binder, and carbon black as a conductive material are calcined: PVdF: carbon black = 94: 3: 3 by mass ratio. To prepare a positive electrode mixture, and dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode mixture slurry. Thereafter, this positive electrode mixture slurry was applied to a positive electrode current collector 12A made of an aluminum foil having a thickness of 20 μm, dried and compression molded to form a positive electrode mixture layer 12B having a thickness of 50 μm, and the positive electrode 12 was produced.
[0053]
Further, artificial graphite as a negative electrode active material and PVdF as a binder are mixed at a mass ratio so as to be artificial graphite: PVdF = 90: 10 to prepare a negative electrode mixture, which is dispersed in NMP and mixed with the negative electrode. An agent slurry was obtained. Next, this negative electrode mixture slurry was applied to a negative electrode current collector 14A made of a copper foil having a thickness of 20 μm, dried and compression molded to form a negative electrode mixture layer 14B having a thickness of 50 μm, and the negative electrode 14 was produced.
[0054]
After the positive electrode 12 and the negative electrode 14 are manufactured, the positive electrode 12 is punched to a diameter of 15 mm, the negative electrode 14 is punched to a diameter of 16 mm, the outer cup 13, the negative electrode 14, and the separator 15 are laminated in this order, and the electrolyte solution 16 is poured into the positive electrode 12 Covered with an outer can 11 filled with water and caulked through a gasket 17. As the electrolytic solution 16, a solution in which lithium hexafluorophosphate was dissolved at a concentration of 1 mol / l in a solvent in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 1 was used. This obtained the secondary battery of Examples 1-1 to 1-5.
[0055]
For the obtained secondary batteries of Examples 1-1 to 1-5, the termination current was charged as 0.06 mA by the low current low voltage method of 1.5 mA, 4.2 V, and the termination was performed by the 1.5 mA low current method. A charge / discharge cycle test was performed in which the battery was discharged at a voltage of 2V. The initial charge capacity and discharge capacity are shown in Table 1.
[0056]
As a comparative example with respect to the present example, as a positive electrode active material, a secondary compound was obtained in the same manner as in the present example except that only a lithium iron phosphate was used without mixing a phosphate compound of NASICON type lithium and titanium. A battery was produced. For the comparative example, the charge / discharge cycle test was conducted in the same manner as in this example. The initial charge capacity and discharge capacity are shown in Table 1.
[0057]
As can be seen from Table 1, according to this example in which a phosphate compound of NASICON type lithium and titanium was mixed, a larger discharge capacity was obtained than in the comparative example in which no mixing was performed. That is, it was found that the capacity can be improved by including a low redox potential compound.
[0058]
Further, when the content of the NASICON-type phosphoric acid compound of lithium and titanium was increased, the discharge capacity was increased, and after reaching the maximum value, it tended to decrease. That is, the content of the low redox potential compound is preferably in the range of 1: 0 <lithium-containing phosphate compound: low redox potential compound ≦ 8: 2 in terms of mass ratio with the lithium-containing phosphate compound. I understood.
[0059]
(Examples 2-1 to 2-3)
A secondary battery was fabricated in the same manner as in Example 1-2, except that other NASICON type compounds shown in Table 2 were used as the low redox potential compound. In addition, as a low redox potential compound, in Example 2-1, a NASICON type lithium phosphate compound (Li_ThreeFe₂(PO_Four)_ThreeIn Example 2-2, NASICON-type iron sulfate compound (Fe)₂(SO_Four)_ThreeIn Example 2-3, the NASICON type vanadium sulfate compound (V₂(SO_Four)_Three) Was used. Examples 2-1 to 2-3 were also subjected to the charge / discharge cycle test in the same manner as in Example 1-2. The initial charge capacity and discharge capacity are shown in Table 2 together with the results of Example 1-2 and the comparative example.
[0060]
[Table 2]

[0061]
As can be seen from Table 2, also in Examples 2-1 to 2-3 using other NASICON type compounds, a discharge capacity larger than that of the comparative example could be obtained as in Example 1-2. That is, it was found that the capacity can be improved by using a NASICON type compound as the low redox potential compound.
[0062]
Among these, in Example 1-2 using a NASICON type phosphoric acid compound of lithium and titanium, a particularly large discharge capacity was obtained. That is, it has been found that it is particularly preferable to use a NASICON-type phosphate compound of lithium and titanium as the low redox potential compound.
[0063]
(Examples 3-1 to 3-8)
As a low redox potential compound, a NASICON type lithium phosphate compound (Li_{1 + x}Ti₂(PO_Four)_ThreeAs shown in Table 3, a secondary battery was obtained in the same manner as in Example 1-3 except that the composition of lithium, that is, the value of x was changed in Examples 3-1 to 3-8. Was made. In addition, Example 3-1 uses the same composition as Example 1-3. Examples 3-1 to 3-8 were also subjected to the charge / discharge cycle test in the same manner as in Example 1-3. The initial capacity and the capacity at the 10th cycle are shown in Table 3, and FIG. 4 shows the relationship between the x value and the capacity at the 10th cycle.
[0064]
[Table 3]

[0065]
In addition, as Reference Examples 3-1 to 3-8 for this example, a NASICON type lithium phosphate compound (Li_{1 + x}Ti₂(PO_Four)_Three) Was used as the positive electrode active material, and an evaluation cell was prepared in the same manner as in this example, except that a lithium metal plate was used as the counter electrode. At that time, in Reference Examples 3-1 to 3-8, the composition of lithium, that is, the value of x was changed as shown in Table 4, as in Examples 3-1 to 3-8. For the evaluation cells of Reference Examples 3-1 to 3-8, a charge / discharge cycle test was performed in the same manner as in this example. The initial capacity and the capacity at the 15th cycle are shown in Table 4.
[0066]
[Table 4]

[0067]
As can be seen from Table 3, LiTi₂(PO_Four)_ThreeIn Example 3-1, which uses NO, the capacity deterioration at the 10th cycle is severe, but in Examples 3-2 to 3-8 in which lithium is excessive, the capacity deterioration at the 10th cycle is improved. This is consistent with the results of Reference Examples 3-1 to 3-8 in Table 4, and the cycle deterioration is Li._{1 + x}Ti₂(PO_Four)_ThreeThis is thought to be due to the deterioration of the capacity. That is, Li_{1 + x}Ti₂(PO_Four)_ThreeThus, it was found that the cycle characteristics can be improved by using x in the range of 1.0 to 2.0 before charge / discharge.
[0068]
In the above examples, the case where lithium iron phosphate is used as the lithium-containing phosphate compound has been specifically described, but the same result can be obtained when other lithium-containing phosphate compounds are used. it can. Further, in the above embodiment, the NASICON type compound used as the low redox potential compound has been described with some specific examples. However, when other NASICON type compounds are used, or when other low redox potential compounds are used. Similar results can be obtained for.
[0069]
Furthermore, in the above-described embodiments, the negative electrode active material and the electrolyte have been described by way of examples. However, the present invention relates to charge / discharge characteristics depending on the material of the positive electrode 12, and does not depend on the types of the negative electrode active material and the electrolyte. Similar results can be obtained using other materials.
[0070]
Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, the case where an electrolytic solution that is a liquid electrolyte is used has been described, but another electrolyte may be used. Other electrolytes include, for example, a gel electrolyte in which an electrolytic solution is held in a polymer compound, a polymer electrolyte in which an electrolyte salt is dispersed in a polymer compound having ion conductivity, ion conductive ceramics, and ion conductive glass Or the inorganic solid electrolyte which consists of an ionic crystal etc., molten salt electrolyte, or what mixed these is mentioned.
[0071]
In the above embodiment and examples, the structure of the positive electrode 12 and the negative electrode 14 has been specifically described with an example. However, the current collector may not be provided, and instead of the mixture layer. And an active material layer made of an active material.
[0072]
Furthermore, in the above-described embodiments and examples, the coin-type secondary battery has been specifically described, but the present invention has other shapes such as a cylindrical shape having another structure, a button shape, or a square shape. The present invention can be similarly applied to a secondary battery or a secondary battery having another structure such as a winding structure. Furthermore, the present invention can be similarly applied to other batteries such as a primary battery.
[0073]
【The invention's effect】
  As described above, claims 1 to3The positive electrode material according to claim 1, or the claim4Or claims6The positive electrode according to claim 1, or the claim7Or claims9According to the battery described in any one of the above, it is possible to occlude and release lithium at a lower oxidation-reduction potential than the lithium-containing phosphate compound.AsSince the low oxidation-reduction potential compound in a state in which lithium can be occluded before charging and discharging is included, by using the low oxidation-reduction potential compound in a region where the internal impedance of the lithium-containing phosphate compound is high, the lithium-containing phosphoric acid The capacity loss of the compound can be supplemented with the low redox potential compound, and the capacity can be improved.In addition, since the NASICON compound is included as the low redox potential compound, it has a high crystal affinity with the lithium-containing phosphate compound and can be easily produced. Furthermore, as the low redox potential compound, the central metal element includes at least one selected from the group consisting of titanium, vanadium and iron, so that a higher capacity can be obtained.
[0076]
  Furthermore, the claim2Claimed positive electrode material or claim5Claimed positive electrode or claim8According to the battery described, the low redox potential compound is a NASICON type phosphate compound of lithium and titanium, and the composition ratio of lithium to titanium (Li / Ti) is 2/2 or more 3 / Since it included within the range of 2 or less, cycling characteristics can be improved and a higher effect can be acquired.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of a secondary battery according to an embodiment of the invention.
2 is a characteristic diagram showing an initial charge / discharge curve of a positive electrode in the secondary battery shown in FIG. 1. FIG.
FIG. 3 is a characteristic diagram showing another initial charge / discharge curve of the positive electrode in the secondary battery shown in FIG. 1;
FIG. 4 shows Li in an embodiment of the present invention._{1 + x}Ti₂(PO_Four)_ThreeIt is a characteristic view showing the relationship between x value of and the capacity | capacitance of the 10th cycle.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Exterior can, 12 ... Positive electrode, 12A ... Positive electrode collector, 12B ... Positive electrode mixture layer, 13 ... Exterior cup, 14 ... Negative electrode, 14A ... Negative electrode collector, 14B ... Negative electrode mixture layer, 15 ... Separator, 16 ... electrolyte, 17 ... gasket.

Claims (9)

A lithium-containing phosphate compound;
Look containing lithium certain lithium before can der Rutotomoni discharge of occluding and releasing the occluded ready low redox potential compound at low redox potential than the lithium-containing phosphate compound,
The lithium-containing phosphate compound is Li _a MI _b PO ₄ (wherein MI represents at least one selected from the group consisting of iron (Fe), cobalt (Co), manganese (Mn), and nickel (Ni)). The ranges of a and b are 0 ≦ a ≦ 1.1 and 0.85 ≦ b ≦ 1.15, respectively.
The low redox potential compound is (Li) _c [M II ₂ (XO ₄ ) ₃ ] (where c is a value in the range of 0 ≦ c ≦ 3, and M II is vanadium (V), titanium. (Ti represents at least one selected from the group consisting of Ti and iron (Fe), and X represents phosphorus (P) or sulfur (S)) . As the low redox potential compound, the M II is titanium and the X is phosphorus, and the composition ratio of lithium to titanium (Li / Ti) is in the range of 2/2 or more and 3/2 or less before charge / discharge. including the NASICON type compound
The positive electrode material of 請 Motomeko 1, wherein the. The content of the low redox potential compound is in the range of 1: 0 <lithium-containing phosphate compound: low redox potential compound ≦ 8: 2 in terms of mass ratio with the lithium-containing phosphate compound.
The positive electrode material according to claim 1. A lithium-containing phosphate compound;
Look containing lithium certain lithium before can der Rutotomoni discharge of occluding and releasing the occluded ready low redox potential compound at low redox potential than the lithium-containing phosphate compound,
The lithium-containing phosphate compound is Li _a MI _b PO ₄ (wherein MI represents at least one member selected from the group consisting of iron, cobalt, manganese and nickel. The ranges of a and b are each 0 ≦ a ≦ 1.1, 0.85 ≦ b ≦ 1.15))
The low redox potential compound is (Li) _c [M II ₂ (XO ₄ ) ₃ ] (wherein c is a value in the range of 0 ≦ c ≦ 3, and M II is composed of vanadium, titanium and iron. A positive electrode which is a NASICON type compound represented by the formula: at least one member selected from the group consisting of X and X representing phosphorus or sulfur . As the low redox potential compound, the M II is titanium and the X is phosphorus, and the composition ratio of lithium to titanium (Li / Ti) is in the range of 2/2 or more and 3/2 or less before charge / discharge. including the NASICON type compound
請 Motomeko 4 positive electrode described. The content of the low redox potential compound is in the range of 1: 0 <lithium-containing phosphate compound: low redox potential compound ≦ 8: 2 in terms of mass ratio with the lithium-containing phosphate compound.
The positive electrode according to claim 4. A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The positive electrode, a lithium-containing phosphate compound, a low is lithium before can der Rutotomoni charging and discharging to the inserting and extracting lithium at low redox potential than the lithium-containing phosphate compound to storable state only it contains an oxidation-reduction potential compound,
The lithium-containing phosphate compound is Li _a MI _b PO ₄ (wherein MI represents at least one member selected from the group consisting of iron, cobalt, manganese and nickel. The ranges of a and b are each 0 ≦ a ≦ 1.1,0.85 a ≦ b ≦ 1.15.) is a compound represented by,
The low redox potential compound is (Li) _c [M II ₂ (XO ₄ ) ₃ ] (wherein c is a value in the range of 0 ≦ c ≦ 3, and M II is composed of vanadium, titanium and iron. A battery that is a NASICON-type compound represented by: X represents phosphorus or sulfur . As the low redox potential compound, the M II is titanium and the X is phosphorus, and the composition ratio of lithium to titanium (Li / Ti) is in the range of 2/2 or more and 3/2 or less before charge / discharge. battery of NASICON-type compound including claim 7. The content of the low redox potential compound is in the range of 1: 0 <lithium-containing phosphate compound: low redox potential compound ≦ 8: 2 in terms of mass ratio with the lithium-containing phosphate compound.
The battery according to claim 7.

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