JP2001085010A - Lithium secondary battery - Google Patents

Lithium secondary battery

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Publication number
JP2001085010A
JP2001085010A JP26139499A JP26139499A JP2001085010A JP 2001085010 A JP2001085010 A JP 2001085010A JP 26139499 A JP26139499 A JP 26139499A JP 26139499 A JP26139499 A JP 26139499A JP 2001085010 A JP2001085010 A JP 2001085010A
Authority
JP
Japan
Prior art keywords
lithium
positive electrode
active material
electrode active
battery
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
JP26139499A
Other languages
Japanese (ja)
Other versions
JP3504195B2 (en
Inventor
Masaya Takahashi
雅也 高橋
Shinichi Tobishima
真一 鳶島
Koji Takei
弘次 武井
Yoji Sakurai
庸司 櫻井
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Telegraph and Telephone Corp
Original Assignee
Nippon Telegraph and Telephone Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nippon Telegraph and Telephone Corp filed Critical Nippon Telegraph and Telephone Corp
Priority to JP26139499A priority Critical patent/JP3504195B2/en
Publication of JP2001085010A publication Critical patent/JP2001085010A/en
Application granted granted Critical
Publication of JP3504195B2 publication Critical patent/JP3504195B2/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • 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

Abstract

PROBLEM TO BE SOLVED: To enhance discharging capacity and cyclic characteristics of a lithium secondary battery is charging and discharging at 4 V or less at which drop in battery lifetime resulting from decomposition of the electrolytic solution is unlikely, compared with non-substituted iron phosphate lithium. SOLUTION: The lithium secondary battery using a positive electrode consisting of lithium iron phosphate series material available at a low cost and capable of charging and discharging at 4 V or less is equipped with an increased discharging capacity with a practical current. The positive electrode active material 5 consists of a substance as phosphoric acid compound of olivin structure expressed by zFe1-yXyPO4(0<z<=1), wherein the element X is stable electrochemically in the potential region 3-4 V with respect to the standard potential of lithium metal in the condition of constituting the phosphate compound, provided that 0<y<=0.3.

Description

【発明の詳細な説明】DETAILED DESCRIPTION OF THE INVENTION

【０００１】[0001]

【産業上の利用分野】本発明はリチウム二次電池に関
し、特に正極活物質の改良に関わり、電池の放電容量の
増加と充放電サイクル特性の向上を目指すものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly to an improvement in a positive electrode active material, which aims at increasing the discharge capacity of the battery and improving the charge / discharge cycle characteristics.

【０００２】[0002]

【従来の技術】リチウム金属、リチウム合金あるいはリ
チウムイオンを吸蔵、放出可能な物質を負極活物質とす
るリチウム二次電池は、高い電圧と優れた可逆性を特徴
としている。特に正極活物質としてリチウムと遷移金属
との複合酸化物を用い、負極活物質として炭素系材料を
用いたリチウムイオン二次電池は、従来の鉛二次電池や
ニッケル−カドミウム二次電池などに比べ軽量で容量も
大きいため携帯電話やノート型パーソナルコンピュータ
ーなどの電子機器に広く用いられている。2. Description of the Related Art A lithium secondary battery using a lithium metal, a lithium alloy or a substance capable of occluding and releasing lithium ions as a negative electrode active material is characterized by high voltage and excellent reversibility. In particular, lithium ion secondary batteries that use a composite oxide of lithium and a transition metal as the positive electrode active material, and that use a carbon-based material as the negative electrode active material have a higher performance than conventional lead secondary batteries and nickel-cadmium secondary batteries Because of its light weight and large capacity, it is widely used in electronic devices such as mobile phones and notebook personal computers.

【０００３】現在一般に用いられているリチウムイオン
二次電池の正極活物質としては主にＬｉＣｏＯ2が用い
られているが、ＬｉＣｏＯ2の原料であるコバルトは埋
蔵量が少なく、しかも限られた地域でしか産出しないた
め、価格の面からも原料の安定供給の面からもリチウム
イオン二次電池の正極活物質として好ましくない。[0003] LiCoO 2 is mainly used as a positive electrode active material of a lithium ion secondary battery generally used at present. Cobalt, which is a raw material of LiCoO 2 , has a small reserve and is used in a limited area. Since it produces only a positive electrode, it is not preferable as a positive electrode active material of a lithium ion secondary battery in terms of price and stable supply of raw materials.

【０００４】これに対して産出量が多く安価な鉄を原料
に用いたＬｉＦｅＰＯ4がリチウム二次電池の正極材料
として動作することが特開平９−１３４７２５号などに
より明らかにされている。またＬｉＦｅＰＯ4の鉄をコ
バルトで置換し電池電圧を制御することが特開平９−１
３４７２４号に示されている。On the other hand, Japanese Patent Application Laid-Open No. Hei 9-134725 discloses that LiFePO 4, which uses a large amount of inexpensive iron as a raw material, operates as a positive electrode material of a lithium secondary battery. Japanese Patent Laid-Open No. 9-1 / 1991 discloses that the iron of LiFePO 4 is replaced with cobalt to control the battery voltage.
No. 34724.

【０００５】[0005]

【発明が解決しようとする課題】しかし、ＬｉＦｅＰＯ
4は電池充放電時のリチウムの挿入脱離反応が遅く、電
池内への正極活物質の充填密度を高めるためにＬｉＦｅ
ＰＯ4粒子のサイズを大きくすると、ごく小さな電流で
しか満足な容量での充放電ができないという問題があ
る。However, LiFePO
4 shows that the lithium insertion / desorption reaction during battery charging / discharging is slow, and LiFe is used to increase the packing density of the positive electrode active material in the battery.
When the size of the PO 4 particles is increased, there is a problem that charging and discharging at a satisfactory capacity can be performed only with a very small current.

【０００６】また、ＬｉＦｅＰＯ4にコバルトを添加し
た場合、コバルトの酸化還元反応はリチウム金属の標準
電位に対して５Ｖ程度の高い電位で起るが、充電電圧が
４．３Ｖを越えると現在のリチウムイオン二次電池に使
用されている電解液では電解液自身の酸化分解が起り、
この様な高い電圧での充放電はサイクル特性を劣化させ
る恐れが強い。高い電圧でも安定な電解液の開発が進め
られているものの、現在のところ実用化されているもの
はなく、必要以上にコバルトを添加することはコストの
点からも電池の寿命の点からも好ましくない。Further, when cobalt is added to LiFePO 4 , the oxidation-reduction reaction of cobalt occurs at a potential as high as about 5 V with respect to the standard potential of lithium metal. The electrolytic solution used in the ion secondary battery undergoes oxidative decomposition of the electrolytic solution itself,
Charge and discharge at such a high voltage have a strong risk of deteriorating cycle characteristics. Although the development of electrolyte solutions that are stable even at high voltages is underway, none has been put into practical use at present, and adding cobalt more than necessary is preferable from the viewpoint of cost and battery life. Absent.

【０００７】従って、本発明は、前述した従来の課題を
解決するためになされたものであり、その目的は、安価
で４Ｖ以下の電圧で充放電が可能なリン酸鉄リチウム系
材料を正極に用いたリチウム二次電池の、実用的な電流
での放電容量を高めることにある。Accordingly, the present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to use a lithium iron phosphate-based material which is inexpensive and can be charged and discharged at a voltage of 4 V or less as a positive electrode. An object of the present invention is to increase the discharge capacity of a used lithium secondary battery at a practical current.

【０００８】[0008]

【課題を解決するための手段】この様な目的を達成する
ために本発明によるリチウム二次電池は、一般式Ｌｉ z
Ｆｅ1-yＸyＰＯ4（０＜ｚ≦１）で与えられるオリビン
構造のリン酸化合物で、元素Ｘは該リン酸化合物を構成
している状態では、リチウム金属の標準電位に対して３
Ｖから４Ｖの電位領域で電気化学的に安定な物質であ
り、なおかつｙが０＜ｙ≦０．３である物質を正極活物
質として含み、リチウム金属、リチウム合金またはリチ
ウムイオンを吸蔵、放出可能な物質を負極活物質とし
て、さらにリチウムイオンが前記正極活物質や前記負極
活物質と電気化学反応をするための移動を行いうる物質
を電解質として含むことを特徴とするものである。Means for Solving the Problems To achieve such an object
Therefore, the lithium secondary battery according to the present invention has the general formula Li z
Fe1-yXyPOFourOlivin given by (0 <z ≦ 1)
Element X is a phosphoric acid compound having the structure
In this state, the standard potential of lithium metal is 3
It is an electrochemically stable substance in the potential range from V to 4V.
And y is 0 <y ≦ 0.3.
Quality, lithium metal, lithium alloy or lithium
A material capable of occluding and releasing calcium ions is used as a negative electrode active material.
And further, lithium ions are added to the positive electrode active material and the negative electrode.
A substance that can move to perform an electrochemical reaction with an active material
As an electrolyte.

【０００９】また、本発明によるリチウム二次電池は、
前述の発明において前記リン酸化合物中の元素Ｘがマグ
ネシウム、コバルト、ニッケル、亜鉛の少なくとも１種
類であることを特徴とするものである。[0009] The lithium secondary battery according to the present invention comprises:
In the above invention, the element X in the phosphoric acid compound is at least one of magnesium, cobalt, nickel, and zinc.

【００１０】本発明をさらに詳しく説明すると、本発明
によるリチウム二次電池の正極活物質は、一般式Ｌｉz
Ｆｅ1-yＸyＰＯ4（０＜ｚ≦１）で与えられるオリビン
構造のリン酸化合物で、元素Ｘは該リン酸化合物を構成
している状態では、リチウム金属の標準電位に対して３
Ｖから４Ｖの電位領域で電気化学的に安定な物質であ
り、なおかつｙが０＜ｙ≦０．３である物質である。More specifically, the positive electrode active material of the lithium secondary battery according to the present invention has a general formula Li z
A phosphate compound having an olivine structure given by Fe 1-y X y PO 4 (0 <z ≦ 1). In a state where the phosphate compound is constituted, the element X is 3 with respect to the standard potential of lithium metal.
It is a substance that is electrochemically stable in a potential range of V to 4 V and y is 0 <y ≦ 0.3.

【００１１】上述の様な一般的にリン酸鉄リチウムと呼
ばれている物質はＬｉＦｅＰＯ4（ｚ＝１）で表され、
構造を保ったままでリチウムをこれ以上挿入することは
できない。この材料を電池の正極として用いた場合、充
電を行うとリチウムが正極から抜けて行き、組成はＦｅ
ＰＯ4に近づき（ｚが小さくなる）、充電した電池を放
電すると、電解液中のリチウムが正極中に挿入され、組
成がＬｉＦｅＰＯ4（ｚ＝１）に戻っていく。電池の放
電容量や作製を考えるとｚ＝１の材料が最も好ましい
が、この様にｚの値は連続的に変化するため、不定比な
組成であるｚ＝０．９などの組成の物質でも、一般的な
定比の組成であるｚ＝１のリン酸鉄リチウムと同等の機
構で動作する電池が作成可能である。このため、上記式
中、ｚは０＜ｚ≦１で示される。A substance generally called lithium iron phosphate as described above is represented by LiFePO 4 (z = 1),
No more lithium can be inserted while maintaining the structure. When this material is used as a positive electrode of a battery, lithium escapes from the positive electrode when charged, and the composition is Fe
When approaching PO 4 (z decreases) and discharging the charged battery, lithium in the electrolyte is inserted into the positive electrode, and the composition returns to LiFePO 4 (z = 1). In consideration of the discharge capacity and fabrication of the battery, a material with z = 1 is most preferable. However, since the value of z changes continuously in this way, even a substance having a non-stoichiometric composition such as z = 0.9 is used. A battery that operates with a mechanism equivalent to that of lithium iron phosphate having a general stoichiometric composition z = 1 can be produced. Therefore, in the above formula, z is represented by 0 <z ≦ 1.

【００１２】ＬｉＦｅＰＯ4を正極材料に用いたリチウ
ム二次電池においては、その充電の際にリチウムが脱離
するとともに鉄イオンが２価から３価に変化する。リチ
ウムが脱離した結果、その部分の結晶構造（オリビン構
造 ）が不安定になり部分的にリチウムの移動経路が塞
がれてしまい、更に内部にあるリチウムが脱離しにくく
なることが、ＬｉＦｅＰＯ4を正極材料に用いたリチウ
ム二次電池において実用的な充放電電流では十分な容量
が得られない原因と考えられる。In a lithium secondary battery using LiFePO 4 as a positive electrode material, lithium is desorbed and the iron ion changes from divalent to trivalent during charging. Results lithium is eliminated, that portion of the crystal structure would be (olivine structure) partially moving path of lithium becomes unstable is blocked, may be difficult further away lithium in the interior are removed, LiFePO 4 It is considered that sufficient capacity cannot be obtained with a practical charge / discharge current in a lithium secondary battery using as a positive electrode material.

【００１３】また、この構造の不安定さが充放電サイク
ルを繰り返すことによる放電容量の減少を引き起こすこ
とが考えられる。これに対して、リン酸化合物を構成し
ている状態でリチウム金属の標準電位に対して３Ｖから
４Ｖの電位領域で電気化学的に安定な亜鉛等の元素で一
部の鉄を置き換えると、充電を行っても亜鉛等の置換し
た元素は２価のままで酸化されず、置換した元素に隣接
するリチウムも脱離せずに結晶内に残る。このため、充
電を行っても置換を行った部分は結晶構造が変化しにく
く、リチウムの移動経路が確保されるために容量が増大
すると共にサイクル安定性を向上させるものと考えられ
る。Further, it is considered that the instability of the structure causes a decrease in discharge capacity due to repeated charge / discharge cycles. On the other hand, when a part of iron is replaced by an element such as zinc which is electrochemically stable in a potential region of 3 V to 4 V with respect to the standard potential of lithium metal in a state where the phosphoric acid compound is formed, the charge The substituted element such as zinc remains divalent and is not oxidized, and lithium adjacent to the substituted element remains in the crystal without elimination. For this reason, it is considered that the crystal structure of the replaced portion is unlikely to change even after charging, and the lithium migration path is secured, thereby increasing the capacity and improving the cycle stability.

【００１４】しかし、脱離しないリチウムは充放電に関
与しないため、この様な置換をあまり多く行うと電池の
容量が減少してしまう。発明者は種々の実験を行い、容
量増加の効果が見られる鉄元素の置換量が３０％（０＜
ｙ≦０．３ ）以下、好ましくは１０％〜３０％（０．
１≦ｙ≦０．３ ）、さらに好ましくは１０〜２０％
（０．１≦ｙ≦０．２） である事を見いだした。However, since lithium which does not desorb does not participate in charge and discharge, if such replacement is performed too much, the capacity of the battery is reduced. The inventor conducted various experiments, and found that the replacement amount of iron element, which shows the effect of increasing the capacity, was 30% (0 <
y ≦ 0.3) or less, preferably 10% to 30% (0.
1 ≦ y ≦ 0.3), more preferably 10 to 20%
(0.1 ≦ y ≦ 0.2).

【００１５】なお、ここで述べたリチウム金属の標準電
位に対して３Ｖから４Ｖの電位領域で電気化学的に安定
な元素とは、まずアルカリ金属やアルカリ土類金属など
のように、リチウム金属の標準電位に対して３Ｖ未満の
電位で酸化還元が起り、それ以上高い電圧では安定な元
素や、あるいはコバルトやニッケルなどのようにリン酸
鉄リチウムの鉄と置換された状態では、リチウム金属の
標準電位に対して３Ｖ未満の電位で２価から金属に還元
され、３Ｖから４Ｖの電位領域では酸化還元が起らず、
４Ｖを越える電位で２価から３価に酸化されるような元
素をさす。The element which is electrochemically stable in the potential range of 3 V to 4 V with respect to the standard potential of lithium metal described above means that lithium metal such as alkali metal or alkaline earth metal is used. Oxidation-reduction occurs at a potential of less than 3 V with respect to the standard potential. At a higher voltage, a stable element or, when replaced with iron of lithium iron phosphate such as cobalt or nickel, a standard of lithium metal is obtained. The metal is reduced from divalent to metal at a potential of less than 3 V, and no oxidation-reduction occurs in a potential region of 3 V to 4 V,
An element that is oxidized from divalent to trivalent at a potential exceeding 4 V.

【００１６】従って、置換する金属は遷移金属に限定さ
れるものではなく、典型金属であってもかまわない。リ
ン酸鉄リチウムのオリビン構造を維持したまま鉄と置換
するためには、３Ｖから４Ｖの電位領域で２価のイオン
であることが望ましく、置換する元素としてはマグネシ
ウム、コバルト、ニッケル、亜鉛などが特に好ましい。Therefore, the metal to be substituted is not limited to a transition metal, but may be a typical metal. In order to substitute iron while maintaining the olivine structure of lithium iron phosphate, it is desirable that the ions be divalent ions in a potential range of 3 V to 4 V. As a replacing element, magnesium, cobalt, nickel, zinc, or the like is used. Particularly preferred.

【００１７】[0017]

【実施例】以下に図面を参照して本発明の実施例をより
詳細に説明する。なお、本発明は以下の実施例のみに限
定されるものではない。Embodiments of the present invention will be described below in detail with reference to the drawings. The present invention is not limited only to the following examples.

【００１８】[0018]

【実施例１】図１は本発明によるリチウム二次電池の一
実施例による構成を示した電池断面図である。図中、１
は封口板、２は金属リチウム負極、３はガスケット、４
はセパレータ、５は正極ペレット、６は正極ケースを示
す。Embodiment 1 FIG. 1 is a sectional view showing a structure of an embodiment of a lithium secondary battery according to the present invention. In the figure, 1
Is a sealing plate, 2 is a metal lithium anode, 3 is a gasket, 4
Denotes a separator, 5 denotes a positive electrode pellet, and 6 denotes a positive electrode case.

【００１９】図１の正極ペレット５に含まれる正極活物
質であるＬｉＦｅ0.7Ｃｏ0.3ＰＯ4は下記の方法で作製
した。LiFe 0.7 Co 0.3 PO 4 as a positive electrode active material contained in the positive electrode pellet 5 of FIG. 1 was prepared by the following method.

【００２０】まず原料である炭酸リチウム（Ｌｉ2Ｃ
Ｏ3）とシュウ酸鉄２水和物（ＦｅＣ2Ｏ4・２Ｈ2Ｏ）と
酢酸コバルト４水和物（Ｃｏ（ＣＨ3ＣＯＯ）2・４Ｈ2
Ｏ）とリン酸水素二アンモニウム（（ＮＨ4）2ＨＰ
Ｏ4）をモル比で０．５：０．７：０．３：１となるよ
うに混合して坩堝に入れ、アルゴン雰囲気下で８００℃
で２４時間焼成することにより作製した。得られた物質
のＸ線回折チャートを図２に示す。First, the raw material lithium carbonate (Li 2 C
O 3 ), iron oxalate dihydrate (FeC 2 O 4 .2H 2 O) and cobalt acetate tetrahydrate (Co (CH 3 COO) 2 .4H 2
O) and diammonium hydrogen phosphate ((NH 4 ) 2 HP
O 4 ) was mixed at a molar ratio of 0.5: 0.7: 0.3: 1 and put into a crucible, and 800 ° C. under an argon atmosphere.
For 24 hours. FIG. 2 shows an X-ray diffraction chart of the obtained substance.

【００２１】報告されているＬｉＦｅＰＯ4のＸ線回折
チャート（ＪＣＰＤＳ １５−０７６０）とほぼ一致し
ており、オリビン構造を維持したまま鉄がコバルトによ
って置換されていることが分かる。この正極活物質７０
重量％と導電剤であるアセチレンブラック２５重量％及
び結着剤であるポリテトラフルオロエチレン５重量％を
混練し、粘土状の塊としたものを２軸ローラーで厚さ
０．６ｍｍ程度に圧延してからポンチで直径１５ｍｍの
円板状に打ち抜いて正極ペレット５を作製した。図３に
ＬｉＦｅＰＯ4のオリビン構造を示す。黒丸がリチウム
原子を、八面体は６個の酸素で囲まれた鉄を、四面体は
４個の酸素で囲まれたリンをそれぞれ示している。The reported X-ray diffraction chart (JCPDS 15-0760) of LiFePO 4 is almost the same as that of the reported LiFePO 4 , indicating that iron was replaced by cobalt while maintaining the olivine structure. This positive electrode active material 70
% By weight, 25% by weight of acetylene black as a conductive agent and 5% by weight of polytetrafluoroethylene as a binder, and a clay-like mass is rolled to a thickness of about 0.6 mm with a biaxial roller. After that, a punch having a diameter of 15 mm was punched out with a punch to produce a positive electrode pellet 5. FIG. 3 shows the olivine structure of LiFePO 4 . The solid circles indicate lithium atoms, the octahedron indicates iron surrounded by six oxygen atoms, and the tetrahedron indicates phosphorus surrounded by four oxygen atoms.

【００２２】次にステンレス製の封口板１上に金属リチ
ウムの負極２を加圧配置したものをポリプロピレン製ガ
スケット３の凹部に挿入し、負極の上にポリプロピレン
製で微孔性のセパレータ４、正極ペレット５をこの順序
に配置し、電解液として、エチレンカーボネートとジメ
チルカーボネートの等積混合溶媒にＬｉＰＦ6を１ｍｏ
ｌ／ｄｍ3濃度に溶解した電解液を適量注入して含浸さ
せた後に、ステンレス製の正極ケース６を被せてかしめ
ることにより、厚さ２ｍｍ、直径２３ｍｍのコイン型電
池を作製した。作製した電池の充放電特性を充電終止電
圧４．０Ｖ、放電終止電圧３．０Ｖ、１ｍＡ定電流とい
う条件で充放電を行って評価した。Next, a metal lithium negative electrode 2 placed under pressure on a stainless steel sealing plate 1 is inserted into a concave portion of a polypropylene gasket 3, and a polypropylene microporous separator 4 and a positive electrode are placed on the negative electrode. The pellets 5 are arranged in this order, and 1 mol of LiPF 6 is used as an electrolytic solution in an equal volume mixed solvent of ethylene carbonate and dimethyl carbonate.
After injecting and impregnating an appropriate amount of an electrolytic solution dissolved at a concentration of l / dm 3 , a stainless-steel positive electrode case 6 was covered and swaged to produce a coin-type battery having a thickness of 2 mm and a diameter of 23 mm. The charge / discharge characteristics of the produced battery were evaluated by performing charge / discharge under the conditions of a charge end voltage of 4.0 V, a discharge end voltage of 3.0 V, and a constant current of 1 mA.

【００２３】図４に１０サイクル目の充放電曲線を示
す。放電電位は、既に知られている置換を行っていない
リン酸鉄リチウムを正極に、リチウム金属を負極に用い
た電池の電圧とほぼ同一であり、鉄イオンの酸化還元に
より充放電が行われていることが分かる。放電容量は１
サイクル目から１０サイクル目にかけていくらか増加し
その後はほぼ一定の容量を示した。FIG. 4 shows a charge / discharge curve at the tenth cycle. The discharge potential is almost the same as the voltage of a battery that uses lithium iron phosphate, which has not been replaced, as a positive electrode and lithium metal as a negative electrode, and is charged and discharged by oxidation and reduction of iron ions. You can see that there is. Discharge capacity is 1
It increased somewhat from the 10th cycle to the 10th cycle, and showed a substantially constant capacity thereafter.

【００２４】また、５０サイクル目の容量は５．６ｍＡ
ｈであった。初期５０サイクルのサイクル回数と放電容
量の関係を図５に示す。また元素Ｘによる鉄の置換量ｙ
と５０サイクル目の放電容量の関係を図６に示す。さら
に電池の正極活物質組成式、置換量ｙと５０サイクル目
の放電容量を表１に示す。The capacity at the 50th cycle is 5.6 mA.
h. FIG. 5 shows the relationship between the number of cycles in the initial 50 cycles and the discharge capacity. The amount of substitution of iron by the element X, y
FIG. 6 shows the relationship between and the discharge capacity at the 50th cycle. Further, Table 1 shows the composition formula of the positive electrode active material of the battery, the replacement amount y, and the discharge capacity at the 50th cycle.

【００２５】[0025]

【比較例１】元素Ｘを含まない正極活物質であるＬｉＦ
ｅＰＯ4を下記の方法で作製した。まず原料である炭酸
リチウム（Ｌｉ2ＣＯ3）とシュウ酸鉄２水和物（ＦｅＣ
2Ｏ4・２Ｈ2Ｏ）とリン酸水素二アンモニウム（（Ｎ
Ｈ4）2ＨＰＯ4）をモル比で０．５：１：１となるよう
に混合して坩堝に入れ、アルゴン雰囲気下で８００℃で
２４時間焼成することにより作製した。Comparative Example 1 LiF which is a positive electrode active material containing no element X
ePO 4 was prepared by the following method. First, the raw materials lithium carbonate (Li 2 CO 3 ) and iron oxalate dihydrate (FeC
2 O 4 · 2H 2 O) and diammonium hydrogenphosphate ((N
H 4 ) 2 HPO 4 ) was mixed in a molar ratio of 0.5: 1: 1, placed in a crucible, and fired at 800 ° C. for 24 hours in an argon atmosphere.

【００２６】得られた正極活物質を用いて実施例１と同
一の方法により正極ペレット及びコイン型電池を作製し
た。実施例１と同一の条件で充放電特性を評価したとこ
ろ、１サイクル目の放電容量は実施例１に示した電池よ
り高かったものの、５サイクル目から放電容量が実施例
１に示した電池に比べて低くなり、５０サイクル目では
実施例１に示した電池の８４％に相当する４．７ｍＡｈ
の容量しか得られなかった。Using the obtained positive electrode active material, a positive electrode pellet and a coin-type battery were produced in the same manner as in Example 1. When the charge / discharge characteristics were evaluated under the same conditions as in Example 1, the discharge capacity at the first cycle was higher than that of the battery shown in Example 1, but the discharge capacity at the fifth cycle was lower than that of the battery shown in Example 1. In the 50th cycle, 4.7 mAh corresponding to 84% of the battery shown in Example 1 was obtained.
Was obtained.

【００２７】初期５０サイクルのサイクル回数と放電容
量の関係を図５に、また元素Ｘによる鉄の置換量ｙと５
０サイクル目の放電容量の関係を図６に、さらに電池の
正極活物質組成式、置換量ｙと５０サイクル目の放電容
量を表１に、それぞれ実施例１の値と併せて示す。FIG. 5 shows the relationship between the number of cycles in the initial 50 cycles and the discharge capacity.
The relationship between the discharge capacity at the 0th cycle is shown in FIG. 6, and the composition formula of the positive electrode active material of the battery, the replacement amount y and the discharge capacity at the 50th cycle are shown in Table 1, together with the values of Example 1.

【００２８】[0028]

【表１】実施例及び比較例に示した電池の正極活物質組
成式、置換量ｙと５０サイクル目の放電容量 TABLE 1 Composition formula of positive electrode active material, substitution amount y and discharge capacity at 50th cycle of batteries shown in Examples and Comparative Examples

【００２９】[0029]

【実施例２】正極ペレットに含まれる正極活物質である
ＬｉＦｅ0.8Ｃｏ0.2ＰＯ4を下記の方法で作製した。ま
ず原料である炭酸リチウム（Ｌｉ2ＣＯ3）とシュウ酸鉄
２水和物（ＦｅＣ2Ｏ4・２Ｈ2Ｏ）と酢酸コバルト４水
和物（Ｃｏ（ＣＨ3ＣＯＯ）2・４Ｈ2Ｏ）とリン酸水素
二アンモニウム（（ＮＨ4）2ＨＰＯ4）をモル比で０．
５：０．８：０．２：１となるように混合して坩堝に入
れ、アルゴン雰囲気下で８００℃で２４時間焼成するこ
とにより作製した。Example 2 LiFe 0.8 Co 0.2 PO 4 as a positive electrode active material contained in a positive electrode pellet was prepared by the following method. First, lithium carbonate (Li 2 CO 3 ), iron oxalate dihydrate (FeC 2 O 4 .2H 2 O) and cobalt acetate tetrahydrate (Co (CH 3 COO) 2 .4H 2 O) which are raw materials And diammonium hydrogen phosphate ((NH 4 ) 2 HPO 4 ) in a molar ratio of 0.1.
The mixture was mixed in a ratio of 5: 0.8: 0.2: 1, put into a crucible, and baked at 800 ° C. for 24 hours in an argon atmosphere.

【００３０】得られた正極活物質を用いて実施例１と同
一の方法により正極ペレット及びコイン型電池を作製し
た。実施例１と同一の条件で充放電特性を評価したとこ
ろ放電容量が２サイクル目から比較例１に示した電池に
比べて高くなり、５０サイクル目では比較例１に示した
電池の１．４３倍にあたる６．７ｍＡｈの容量が得られ
た。Using the obtained positive electrode active material, a positive electrode pellet and a coin-type battery were produced in the same manner as in Example 1. When the charge / discharge characteristics were evaluated under the same conditions as in Example 1, the discharge capacity was higher than that of the battery shown in Comparative Example 1 from the second cycle, and 1.43 of the battery shown in Comparative Example 1 at the 50th cycle. A capacity of 6.7 mAh, which is twice as large, was obtained.

【００３１】初期５０サイクルのサイクル回数と放電容
量の関係を図５に、また元素Ｘによる鉄の置換量ｙと５
０サイクル目の放電容量の関係を図６に、さらに電池の
正極活物質組成式、置換量ｙと５０サイクル目の放電容
量を表１に、それぞれ実施例１及び比較例１の特性と併
せて示す。FIG. 5 shows the relationship between the number of cycles in the initial 50 cycles and the discharge capacity.
FIG. 6 shows the relationship between the discharge capacity at the 0th cycle, and Table 1 shows the composition formula of the positive electrode active material of the battery, the replacement amount y, and the discharge capacity at the 50th cycle, together with the characteristics of Example 1 and Comparative Example 1. Show.

【００３２】[0032]

【実施例３】正極ペレットに含まれる正極活物質である
ＬｉＦｅ0.9Ｃｏ0.1ＰＯ4を下記の方法で作製した。ま
ず原料である炭酸リチウム（Ｌｉ2ＣＯ3）とシュウ酸鉄
２水和物（ＦｅＣ2Ｏ4・２Ｈ2Ｏ）と酢酸コバルト４水
和物（Ｃｏ（ＣＨ3ＣＯＯ）2・４Ｈ2Ｏ）とリン酸水素
二アンモニウム（（ＮＨ4）2ＨＰＯ4）をモル比で０．
５：０．９：０．１：１となるように混合して坩堝に入
れ、アルゴン雰囲気下で８００℃で２４時間焼成するこ
とにより作製した。Example 3 LiFe 0.9 Co 0.1 PO 4 as a positive electrode active material contained in a positive electrode pellet was produced by the following method. First, lithium carbonate (Li 2 CO 3 ), iron oxalate dihydrate (FeC 2 O 4 .2H 2 O) and cobalt acetate tetrahydrate (Co (CH 3 COO) 2 .4H 2 O) which are raw materials And diammonium hydrogen phosphate ((NH 4 ) 2 HPO 4 ) in a molar ratio of 0.1.
The mixture was mixed in a ratio of 5: 0.9: 0.1: 1, put into a crucible, and fired at 800 ° C. for 24 hours in an argon atmosphere.

【００３３】得られた正極活物質を用いて実施例１と同
一の方法によりコイン型電池を作製した。実施例１と同
一の条件で充放電特性を評価したところ放電容量が５サ
イクル目から比較例１に示した電池に比べて高くなり、
５０サイクル目では比較例１に示した電池の１．０４倍
に相当する４．９ｍＡｈの容量が得られた。Using the obtained positive electrode active material, a coin-type battery was manufactured in the same manner as in Example 1. When the charge and discharge characteristics were evaluated under the same conditions as in Example 1, the discharge capacity was higher than that of the battery shown in Comparative Example 1 from the fifth cycle,
At the 50th cycle, a capacity of 4.9 mAh corresponding to 1.04 times that of the battery shown in Comparative Example 1 was obtained.

【００３４】初期５０サイクルのサイクル回数と放電容
量の関係を図５に、また元素Ｘによる鉄の置換量ｙと５
０サイクル目の放電容量の関係を図６に、さらに電池の
正極活物質組成式、置換量ｙと５０サイクル目の放電容
量を表１にそれぞれ実施例１、２及び比較例１の特性と
併せて示す。FIG. 5 shows the relationship between the number of cycles of the initial 50 cycles and the discharge capacity.
The relationship between the discharge capacity at the 0th cycle is shown in FIG. 6, and the composition formula of the positive electrode active material of the battery, the replacement amount y and the discharge capacity at the 50th cycle are shown in Table 1, together with the characteristics of Examples 1 and 2 and Comparative Example 1. Shown.

【００３５】[0035]

【比較例２】正極ペレットに含まれる正極活物質である
ＬｉＦｅ0.6Ｃｏ0.4ＰＯ4を下記の方法で作製した。ま
ず原料である炭酸リチウム（Ｌｉ2ＣＯ3）とシュウ酸鉄
２水和物（ＦｅＣ2Ｏ4・２Ｈ2Ｏ）と酢酸コバルト４水
和物（Ｃｏ（ＣＨ3ＣＯＯ）2・４Ｈ2Ｏ）とリン酸水素
二アンモニウム（（ＮＨ4）2ＨＰＯ4）をモル比で０．
５：０．６：０．４：１となるように混合して坩堝に入
れ、アルゴン雰囲気下で８００℃で２４時間焼成するこ
とにより作製した。Comparative Example 2 LiFe 0.6 Co 0.4 PO 4 as a positive electrode active material contained in a positive electrode pellet was produced by the following method. First, lithium carbonate (Li 2 CO 3 ), iron oxalate dihydrate (FeC 2 O 4 .2H 2 O) and cobalt acetate tetrahydrate (Co (CH 3 COO) 2 .4H 2 O) which are raw materials And diammonium hydrogen phosphate ((NH 4 ) 2 HPO 4 ) in a molar ratio of 0.1.
The mixture was mixed in a ratio of 5: 0.6: 0.4: 1, put in a crucible, and baked at 800 ° C. for 24 hours in an argon atmosphere.

【００３６】得られた正極活物質を用いて実施例１と同
一の方法によりコイン型電池を作製した。実施例１と同
一の条件で充放電特性を評価したところ放電容量が１サ
イクル目から５０サイクル目まで常に比較例１に示した
電池に比べて低くなり、５０サイクル目では比較例１に
示した電池の０．９１倍に当たる４．３ｍＡｈの容量し
か示さなかった。Using the obtained positive electrode active material, a coin-type battery was manufactured in the same manner as in Example 1. When the charge / discharge characteristics were evaluated under the same conditions as in Example 1, the discharge capacity was always lower from the first cycle to the 50th cycle as compared with the battery shown in Comparative Example 1, and was shown in Comparative Example 1 at the 50th cycle. It showed a capacity of only 4.3 mAh, which is 0.91 times that of the battery.

【００３７】初期５０サイクルのサイクル回数と放電容
量の関係を図５に、また元素Ｘによる鉄の置換量ｙと５
０サイグル目の放電容量の関係を図６に、さらに電池の
正極活物質組成式、置換量ｙと５０サイクル目の放電容
量を表１に、それぞれ実施例１から３及び比較例１の特
性と併せて示す。FIG. 5 shows the relationship between the number of cycles in the initial 50 cycles and the discharge capacity.
The relationship between the discharge capacity at the 0th sigle is shown in FIG. 6, the composition formula of the positive electrode active material of the battery, the replacement amount y and the discharge capacity at the 50th cycle are shown in Table 1, and the characteristics of Examples 1 to 3 and Comparative Example 1, respectively. Also shown.

【００３８】[0038]

【実施例４】正極ペレットに含まれる正極活物質である
ＬｉＦｅ0.8Ｚｎ0.2ＰＯ4を下記の方法で作製した。ま
ず原料である水酸化リチウム１水和物（ＬｉＯＨ・Ｈ2
Ｏ）とシュウ酸鉄２水和物（ＦｅＣ2Ｏ4・２Ｈ2Ｏ）と
酢酸亜鉛２水和物（Ｚｎ（ＣＨ3ＣＯＯ）2・２Ｈ2Ｏ）
とリン酸水素二アンモニウム（（ＮＨ4）2ＨＰＯ4）を
モル比で１：０．８：０．２：１となるように混合して
坩堝に入れ、アルゴン雰囲気下で８００℃で２４時間焼
成することにより作製した。Example 4 LiFe 0.8 Zn 0.2 PO 4 as a positive electrode active material contained in a positive electrode pellet was produced by the following method. First, lithium hydroxide monohydrate (LiOH.H 2
O), iron oxalate dihydrate (FeC 2 O 4 .2H 2 O) and zinc acetate dihydrate (Zn (CH 3 COO) 2 .2H 2 O)
And diammonium hydrogen phosphate ((NH 4 ) 2 HPO 4 ) were mixed at a molar ratio of 1: 0.8: 0.2: 1, put into a crucible, and placed in an argon atmosphere at 800 ° C. for 24 hours. It was produced by firing.

【００３９】得られた正極活物質を用いて実施例１と同
一の方法によりコイン型電池を作製した。実施例１と同
一の条件で充放電特性を評価したところ放電容量は１サ
イクル目から比較例１に示した電池に比べて高くなり、
実施例２をやや上回るサイクル回数依存性を示した。ま
た、５０サイクル目では比較例１に示した電池の１．４
９倍に相当する７．０ｍＡｈの容量が得られた。A coin-type battery was manufactured in the same manner as in Example 1 using the obtained positive electrode active material. When the charge / discharge characteristics were evaluated under the same conditions as in Example 1, the discharge capacity was higher than that of the battery shown in Comparative Example 1 from the first cycle,
Cycle number dependency slightly higher than that of Example 2 was shown. Also, at the 50th cycle, 1.4 of the battery shown in Comparative Example 1 was obtained.
A capacity of 7.0 mAh corresponding to 9 times was obtained.

【００４０】初期５０サイクルのサイクル回数と放電容
量の関係を図５に、また、電池の正極活物質組成式、置
換量ｙと５０サイクル目の放電容量を表１に、それぞれ
実施例１から３及び比較例１、２の特性と併せて示す。FIG. 5 shows the relationship between the number of cycles of the initial 50 cycles and the discharge capacity, and Table 1 shows the composition formula of the positive electrode active material of the battery, the replacement amount y, and the discharge capacity at the 50th cycle. The results are shown together with the characteristics of Comparative Examples 1 and 2.

【００４１】[0041]

【実施例５】正極ペレットに含まれる正極活物質である
ＬｉＦｅ0.85Ｍｇ0.15ＰＯ4を下記の方法で作製した。
まず原料である水酸化リチウム１水和物（ＬｉＯＨ・Ｈ
2Ｏ）とシュウ酸鉄２水和物（ＦｅＣ2Ｏ4・２Ｈ2Ｏ）と
酸化マグネシウム（ＭｇＯ）とリン酸水素二アンモニウ
ム（（ＮＨ4）2ＨＰＯ4）をモル比で１：０．８５：
０．１５：１となるように混合して坩堝に入れ、アルゴ
ン雰囲気下で８００℃で２４時間焼成することにより作
製した。Example 5 LiFe 0.85 Mg 0.15 PO 4 as a positive electrode active material contained in a positive electrode pellet was prepared by the following method.
First, lithium hydroxide monohydrate (LiOH.H
2 O), iron oxalate dihydrate (FeC 2 O 4 .2H 2 O), magnesium oxide (MgO), and diammonium hydrogen phosphate ((NH 4 ) 2 HPO 4 ) in a molar ratio of 1: 0. 85:
The mixture was mixed in a ratio of 0.15: 1, put into a crucible, and fired at 800 ° C. for 24 hours in an argon atmosphere.

【００４２】得られた正極活物質を用いて実施例１と同
一の方法によりコイン型電池を作製した。実施例１と同
一の条件で充放電特性を評価したところ放電容量は１サ
イクル目から比較例１に示した電池に比べて高くなり、
実施例２とほぼ同様なサイクル回数依存性を示した。Using the obtained positive electrode active material, a coin-type battery was manufactured in the same manner as in Example 1. When the charge / discharge characteristics were evaluated under the same conditions as in Example 1, the discharge capacity was higher than that of the battery shown in Comparative Example 1 from the first cycle,
The cycle number dependence was almost the same as in Example 2.

【００４３】５０サイクル目では比較例１に示した電池
の１．４５倍に当たる６．８ｍＡｈの容量が得られた。
実施例５に示した電池の正極活物質組成式、置換量ｙと
５０サイクル目の放電容量を表１に、実施例１から４及
び比較例１、２の特性と併せて示す。At the 50th cycle, a capacity of 6.8 mAh, which is 1.45 times that of the battery shown in Comparative Example 1, was obtained.
Table 1 shows the positive electrode active material composition formula, the replacement amount y, and the discharge capacity at the 50th cycle of the battery shown in Example 5, together with the characteristics of Examples 1 to 4 and Comparative Examples 1 and 2.

【００４４】[0044]

【実施例６】正極ペレットに含まれる正極活物質である
ＬｉＦｅ0.8Ｎｉ0.2ＰＯ4を下記の方法で作製した。ま
ず原料である水酸化リチウム１水和物（ＬｉＯＨ・Ｈ2
Ｏ）と酢酸鉄（（ＣＨ3ＣＯＯ）2Ｆｅ）と酸化ニッケル
（ＮｉＯ）とリン酸水素二アンモニウム（（ＮＨ4）2Ｈ
ＰＯ4）をモル比で１：０．８：０．２：１となるよう
に混合して坩堝に入れ、アルゴン雰囲気下で８００℃で
２４時間焼成することにより作製した。Example 6 LiFe 0.8 Ni 0.2 PO 4 as a positive electrode active material contained in a positive electrode pellet was produced by the following method. First, lithium hydroxide monohydrate (LiOH.H 2
O), iron acetate ((CH 3 COO) 2 Fe), nickel oxide (NiO), and diammonium hydrogen phosphate ((NH 4 ) 2 H).
PO 4 ) was mixed in a molar ratio of 1: 0.8: 0.2: 1, placed in a crucible, and fired at 800 ° C. for 24 hours in an argon atmosphere.

【００４５】得られた正極活物質を用いて実施例１と同
一の方法によりコイン型電池を作製した。実施例１と同
一の条件で充放電特性を評価したところ放電容量は１サ
イクル目から比較例１に示した電池に比べて高くなり、
実施例２をやや下回るサイクル回数依存性を示した。ま
た、５０サイクル目では比較例１に示した電池の１．３
８倍に相当する６．５ｍＡｈの容量が得られた。実施例
６に示した電池の正極活物質組成式、置換量ｙと５０サ
イクル目の放電容量を表１に、実施例１から５及び比較
例１、２の特性と併せて示す。Using the obtained positive electrode active material, a coin-type battery was manufactured in the same manner as in Example 1. When the charge / discharge characteristics were evaluated under the same conditions as in Example 1, the discharge capacity was higher than that of the battery shown in Comparative Example 1 from the first cycle,
The cycle number dependency slightly lower than that of Example 2 was shown. At the 50th cycle, 1.3% of the battery shown in Comparative Example 1 was used.
A capacity of 6.5 mAh corresponding to eight times was obtained. Table 1 shows the positive electrode active material composition formula, the replacement amount y, and the discharge capacity at the 50th cycle of the battery shown in Example 6 together with the characteristics of Examples 1 to 5 and Comparative Examples 1 and 2.

【００４６】なお、前述した実施例において、正極とし
てはペレット状に整形したものを用いたが、Ｎ−メチル
−２−ピロリドンの様な溶媒に正極活物質とポリフッ化
ビニリデンの様なバインダを加えてスラリーを作製し、
それを金属箔上に薄く塗布乾燥した塗布電極の様な形状
でも構わない。In the above-described embodiment, the positive electrode was formed into a pellet shape. However, a positive electrode active material and a binder such as polyvinylidene fluoride were added to a solvent such as N-methyl-2-pyrrolidone. To make a slurry,
It may be in the form of a coated electrode which is thinly coated and dried on a metal foil.

【００４７】また、負極材料としてはリチウム金属を用
いたが、他にリチウム合金、黒鉛やコークスなどの炭素
系材料、タングステン酸化物、ニオブ酸化物、バナジウ
ム酸化物、スズ酸化物などの金属酸化物、リチウムマン
ガン窒化物やリチウムコバルト窒化物、リチウム鉄窒化
物などのリチウム遷移金属複合窒化物、硫化鉄や硫化モ
リブデン等の金属カルコゲナイトなどでも構わない。Although lithium metal was used as the negative electrode material, other materials such as lithium alloys, carbon-based materials such as graphite and coke, and metal oxides such as tungsten oxide, niobium oxide, vanadium oxide and tin oxide were also used. Alternatively, lithium transition metal composite nitrides such as lithium manganese nitride, lithium cobalt nitride, and lithium iron nitride, and metal chalcogenites such as iron sulfide and molybdenum sulfide may be used.

【００４８】さらに電解液としてはエチレンカーボネー
トとジメチルカーボネートの等積混合溶媒にＬｉＰＦ6
を１ｍｏｌ／ｄｍ3濃度に溶解した電解液を用いたが、
従来の非水系リチウム二次電池と同様なものも使用可能
である。Further, as the electrolytic solution, LiPF 6 was used in a mixed solvent of equal volume of ethylene carbonate and dimethyl carbonate.
Was dissolved in a concentration of 1 mol / dm 3 ,
A battery similar to a conventional non-aqueous lithium secondary battery can also be used.

【００４９】例えば溶媒としてはジメトキシエタン、２
−メチルテトラヒドロフラン、エチレンカーボネート、
メチルホルメート、ジメチルスルホキシド、プロピレン
カーボネート、アセトニトリル、ジメチルカーボネー
ト、ジエチルカーボネート、メチルエチルカーボネート
などを単独で、あるいは２種類以上を混合して使用する
ことが可能である。For example, dimethoxyethane, 2
-Methyltetrahydrofuran, ethylene carbonate,
Methyl formate, dimethyl sulfoxide, propylene carbonate, acetonitrile, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and the like can be used alone or in combination of two or more.

【００５０】また、溶質としては実施例において用いた
ＬｉＰＦ6以外にも、例えば、ＬｉＣｌＯ4、ＬｉＢ
Ｆ4、ＬｉＡｓＦ6、ＬｉＣＦ3ＳＯ3等でも構わない。更
に、ポリマー電解質、固体電解質、常温溶融塩等も使用
可能である。また、セパレータや電池ケース等の構造材
料等の他の要素についても従来公知の各種材料が使用可
能である。さらに電池形状についても実施例においては
ボタン型としたが、特に制限されるものではなく、円筒
型、角型等の形状でもかまわない。As the solute, other than LiPF 6 used in Examples, for example, LiClO 4 , LiB
F 4 , LiAsF 6 , LiCF 3 SO 3 or the like may be used. Further, a polymer electrolyte, a solid electrolyte, a room temperature molten salt and the like can be used. As for other elements such as a structural material such as a separator and a battery case, various conventionally known materials can be used. Further, the shape of the battery is also a button shape in the embodiment, but is not particularly limited, and may be a cylindrical shape, a square shape, or the like.

【００５１】[0051]

【発明の効果】以上説明したように、本発明によるリチ
ウム二次電池によれば、正極活物質として、リン酸鉄リ
チウム中の鉄を、リン酸化合物を構成している状態では
リチウム金属の標準電位に対して３Ｖから４Ｖの電位領
域で電気化学的に安定な物質により３０％以下の割合で
置き換えた化合物を用いることにより、無置換のリン酸
鉄リチウムに比べて篭解液の分解による電池寿命の低下
が起りにくい４Ｖ以下での充放電において放竃容量やサ
イクル特性を向上させることができた。従って経済的に
優れてなおかつ電池特性の良好なリチウム二次電池の実
現が可能となった。As described above, according to the lithium secondary battery of the present invention, iron in lithium iron phosphate is used as a positive electrode active material, and lithium metal is used as a standard for lithium metal in a state of forming a phosphate compound. By using a compound that is replaced by an electrochemically stable substance at a rate of 30% or less in a potential region of 3 V to 4 V with respect to the potential, the battery is decomposed by decomposition of the lysate compared to unsubstituted lithium iron phosphate. The discharge capacity and cycle characteristics were improved in charging and discharging at 4 V or less where the life is hardly reduced. Therefore, it has become possible to realize a lithium secondary battery which is economically excellent and has good battery characteristics.

【図面の簡単な説明】[Brief description of the drawings]

【図１】本発明によるリチウム二次電池の一実施例によ
る構成を示した断面図。FIG. 1 is a cross-sectional view illustrating a configuration of an embodiment of a lithium secondary battery according to the present invention.

【図２】本発明のリチウム二次電池の実施例１において
正極活物質として用いたＬｉＦｅ0.7Ｃｏ0.3ＰＯ4のＸ
線回折パターンを示した図。FIG. 2 shows X of LiFe 0.7 Co 0.3 PO 4 used as a positive electrode active material in Example 1 of the lithium secondary battery of the present invention.
The figure which showed the line diffraction pattern.

【図３】ＬｉＦｅＰＯ4のオリビン構造を示す図。FIG. 3 is a diagram showing an olivine structure of LiFePO 4 .

【図４】本発明のリチウム二次電池の実施例１における
電池の充放電曲線を示した図。FIG. 4 is a diagram showing a charge / discharge curve of the battery in Example 1 of the lithium secondary battery of the present invention.

【図５】本発明のリチウム二次電池の実施例１〜４にお
けるサイクル回数と放電容量の関係を比較例１、２にお
ける関係と併せて示した図。FIG. 5 is a diagram showing the relationship between the number of cycles and the discharge capacity in Examples 1 to 4 of the lithium secondary battery of the present invention, together with the relationship in Comparative Examples 1 and 2.

【図６】本発明のリチウム二次電池の実施例１〜３にお
ける元素Ｘによる鉄の置換量ｙと放電容量の関係を比較
例１、２における関係と併せて示した図。FIG. 6 is a diagram showing the relationship between the replacement amount y of iron by the element X and the discharge capacity in Examples 1 to 3 of the lithium secondary battery of the present invention, together with the relationship in Comparative Examples 1 and 2.

【符号の説明】[Explanation of symbols]

１ 封口板 ２ 金属リチウム負極 ３ ガスケット ４ セパレータ ５ 正極ペレット ６ 正極ケース DESCRIPTION OF SYMBOLS 1 Sealing plate 2 Metal lithium anode 3 Gasket 4 Separator 5 Positive electrode pellet 6 Positive electrode case

───────────────────────────────────────────────────── フロントページの続き (72)発明者 武井 弘次 東京都千代田区大手町二丁目３番１号 日 本電信電話株式会社内 (72)発明者 櫻井 庸司 東京都千代田区大手町二丁目３番１号 日 本電信電話株式会社内 Ｆターム(参考） 5H003 AA02 AA04 BB01 BB02 BB05 BD00 5H029 AJ03 AJ05 AK03 AL12 AM03 AM05 AM07 BJ03 HJ02  ──────────────────────────────────────────────────続 き Continuing on the front page (72) Koji Takei, Inventor 2-3-1 Otemachi, Chiyoda-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (72) Yoji Sakurai 2-chome, Otemachi 2-chome, Chiyoda-ku, Tokyo No. 1 Nippon Telegraph and Telephone Corporation F term (reference) 5H003 AA02 AA04 BB01 BB02 BB05 BD00 5H029 AJ03 AJ05 AK03 AL12 AM03 AM05 AM07 BJ03 HJ02

Claims (2)

【特許請求の範囲】[Claims] 【請求項１】 一般式ＬｉzＦｅ1-yＸyＰＯ4（０＜ｚ≦
１）で与えられるオリビン構造のリン酸化合物で、元素
Ｘは該リン酸化合物を構成している状態では、リチウム
金属の標準電位に対して３Ｖから４Ｖの電位領域で電気
化学的に安定な物質であり、なおかつｙが０＜ｙ≦０．
３である物質を正極活物質として含み、リチウム金属、
リチウム合金またはリチウムイオンを吸蔵、放出可能な
物質を負極活物質として、さらにリチウムイオンが前記
正極活物質や前記負極活物質と電気化学反応をするため
の移動を行いうる物質を電解質として含むことを特徴と
するリチウム二次電池。1. The method according to claim 1, wherein the general formula Li z Fe 1-y X y PO 4 (0 <z ≦
The phosphoric acid compound having the olivine structure given in 1), wherein the element X is a substance which is electrochemically stable in a potential range of 3 V to 4 V with respect to the standard potential of lithium metal when the phosphoric acid compound is constituted. And y is 0 <y ≦ 0.
3 as a positive electrode active material, lithium metal,
A material capable of occluding and releasing lithium alloys or lithium ions is used as a negative electrode active material, and a material capable of performing lithium ions to perform an electrochemical reaction with the positive electrode active material or the negative electrode active material is included as an electrolyte. Characteristic lithium secondary battery. 【請求項２】 前記リン酸化合物中の元素Ｘがマグネシ
ウム、コバルト、ニッケル、亜鉛の少なくとも１種類で
あることを特徴とする請求項１記載のリチウム二次電
池。2. The lithium secondary battery according to claim 1, wherein the element X in the phosphate compound is at least one of magnesium, cobalt, nickel, and zinc.
JP26139499A 1999-09-16 1999-09-16 Lithium secondary battery positive electrode active material and lithium secondary battery Expired - Lifetime JP3504195B2 (en)

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