JPH09274918A - Positive electrode material for lithium secondary battery - Google Patents
Positive electrode material for lithium secondary batteryInfo
- Publication number
- JPH09274918A JPH09274918A JP8104579A JP10457996A JPH09274918A JP H09274918 A JPH09274918 A JP H09274918A JP 8104579 A JP8104579 A JP 8104579A JP 10457996 A JP10457996 A JP 10457996A JP H09274918 A JPH09274918 A JP H09274918A
- Authority
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- Japan
- Prior art keywords
- secondary battery
- lithium secondary
- positive electrode
- sample
- electrode material
- Prior art date
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Classifications
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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)
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、高い放電電圧，耐
久性及び良好な低温性能を併有するリチウム２次電池用
正極材料、好ましくは、室温でスピネル構造を有するリ
チウム２次電池用正極材料に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode material for a lithium secondary battery having a high discharge voltage, durability and good low-temperature performance, preferably a positive electrode material for a lithium secondary battery having a spinel structure at room temperature. It is a thing.
【０００２】[0002]
【従来の技術】種々の電子機器の電源用として、高エネ
ルギー密度を有する２次電池への強い要望がある。特に
最近、充放電電圧が高く且つ充放電容量も大きいという
特長のため、リチウム２次電池が注目されている。従
来、リチウム２次電池の正極材料としては、規則配列し
た層状の岩塩構造を有するＬｉＣｏＯ2 が用いられてき
た。しかしＬｉＣｏＯ2 には高価なコバルト（Ｃｏ）が
使用されるので、コバルトの資源量や価格の点から、２
次電池の正極材料としての地位を、スピネル構造のＬｉ
Ｍｎ2 Ｏ4 に置き換わられつつある。2. Description of the Related Art There is a strong demand for a secondary battery having a high energy density as a power source for various electronic devices. In particular, recently, a lithium secondary battery has been drawing attention because of its high charge / discharge voltage and large charge / discharge capacity. Conventionally, LiCoO 2 having a regularly arranged layered rock salt structure has been used as a positive electrode material of a lithium secondary battery. However, since expensive cobalt (Co) is used for LiCoO 2 , in terms of the amount of cobalt resources and the price, 2
Positioned as a positive electrode material for secondary batteries, Li with spinel structure
It is being replaced by Mn 2 O 4 .
【０００３】[0003]
【発明が解決しようとする課題】スピネル構造のＬｉＭ
ｎ2 Ｏ4 には２つの問題点がある。第１の問題点は耐久
性である。つまりリチウム２次電池の放電に伴い、リチ
ウムイオンが正極に挿入される。この結果、リチウム量
の変動を加味した組成式Ｌｉx Ｍｎ2 Ｏ4 において、ｘ
＝１で結晶構造が立方晶から正方晶へと変化し、格子体
積も約５％膨張する。以下、この現象をリチウム量によ
る構造相転移と呼ぶ。LiM having a spinel structure
There are two problems with n 2 O 4 . The first problem is durability. That is, lithium ions are inserted into the positive electrode as the lithium secondary battery discharges. As a result, in the composition formula Li x Mn 2 O 4 in which the fluctuation of the amount of lithium is taken into consideration, x
= 1, the crystal structure changes from cubic to tetragonal and the lattice volume expands by about 5%. Hereinafter, this phenomenon is called a structural phase transition depending on the amount of lithium.
【０００４】リチウム量による構造相転移に伴い、ｘ＝
１で放電電圧も階段状に約１Ｖ低下する。充放電の度に
リチウム量による構造相転移が繰り返されるので、正極
は徐々に崩壊し、結果として容量も低下する。リチウム
２次電池の正極材料としてスピネル構造のＬｉＭｎ2 Ｏ
4 を使用する場合、Ｍｎイオンの価数（リチウム量の変
動によって変動する）はリチウム２次電池の特性に大き
く影響する。例えば、リチウム２次電池において正極材
料としてスピネル構造のＬｉＭｎ2 Ｏ4 を使用した場合
の、Ｍｎイオンの平均価数の変化による特性変化を図７
に示す。図７から、Ｍｎイオンの平均価数を最適に選択
すべきであることが分かる。With the structural phase transition depending on the amount of lithium, x =
At 1, the discharge voltage also decreases stepwise by about 1V. Since the structural phase transition due to the amount of lithium is repeated each time charging and discharging, the positive electrode gradually collapses, and as a result, the capacity also decreases. LiMn 2 O having a spinel structure as a positive electrode material for lithium secondary batteries
When 4 is used, the valence of Mn ions (which varies depending on the variation of the amount of lithium) greatly affects the characteristics of the lithium secondary battery. For example, FIG. 7 shows changes in characteristics due to changes in the average valence of Mn ions when LiMn 2 O 4 having a spinel structure is used as a positive electrode material in a lithium secondary battery.
Shown in From FIG. 7, it can be seen that the average valence of Mn ions should be optimally selected.
【０００５】リチウム量による構造相転移を緩和又は回
避するために、従来、ＬｉＭｎ2 Ｏ4 のＬｉ，Ｍｎ，Ｏ
の一部を他のイオンで置換する方法が提案されている。
しかし、この方法により得られた正極材料を用いたリチ
ウム２次電池では、その容量が大幅に低下する。これは
置換により充放電に関与できるリチウムイオンの総数が
減少したり、又は結晶構造が立方晶スピネル構造でなく
なるためであるIn order to alleviate or avoid the structural phase transition due to the amount of lithium, Li, Mn, O of LiMn 2 O 4 has hitherto been used.
There has been proposed a method of substituting a part of the ions with other ions.
However, the capacity of the lithium secondary battery using the positive electrode material obtained by this method is significantly reduced. This is because the substitution reduces the total number of lithium ions that can participate in charge and discharge, or the crystal structure is not a cubic spinel structure.
【０００６】第２の問題点は低温での性能劣化である。
これはＬｉx Ｍｎ2 Ｏ4 の結晶構造が温度によって変化
することに起因する。すなわち室温以上の高温から温度
を下げていくと、室温より僅かに低温で結晶構造が立方
晶から正方晶へ変化する。以下、この現象を温度による
構造相転移と呼び、その温度を転移温度と呼ぶ。The second problem is performance deterioration at low temperatures.
This is because the crystal structure of Li x Mn 2 O 4 changes with temperature. That is, as the temperature is lowered from a high temperature above room temperature, the crystal structure changes from cubic to tetragonal at a temperature slightly lower than room temperature. Hereinafter, this phenomenon is called a structural phase transition due to temperature, and that temperature is called a transition temperature.
【０００７】温度による構造相転移に伴い、リチウムイ
オンの正極内での拡散係数や引き抜き電圧が変化するの
で、結果として、転移温度以下では放電電圧，容量とも
に低下する。温度による構造相転移を回避するために
は、リチウム２次電池を常に室温以上に加熱して使用す
ることが考えられる。しかし、室温以上に加熱して使用
する場合には加熱用のヒーターが必要となり、又、加熱
にエネルギーを要するので、高エネルギー密度であると
いうリチウム２次電池の特長が損なわれる。Since the diffusion coefficient and the extraction voltage of lithium ions in the positive electrode change with the structural phase transition due to temperature, as a result, both the discharge voltage and the capacity decrease below the transition temperature. In order to avoid structural phase transition due to temperature, it is considered that the lithium secondary battery is always heated to room temperature or higher before use. However, when it is used after being heated to room temperature or higher, a heater for heating is required, and since energy is required for heating, the feature of the lithium secondary battery having high energy density is impaired.
【０００８】本発明者らは、上述の如き従来技術の問題
点を解決すべく鋭意研究した結果、本発明を成すに至っ
た。しかして、本発明の目的は、高い放電電圧，耐久性
及び良好な低温性能を併有するリチウム２次電池用正極
材料を提供することにある。The present inventors have completed the present invention as a result of intensive studies to solve the above-mentioned problems of the prior art. Therefore, an object of the present invention is to provide a positive electrode material for a lithium secondary battery, which has a high discharge voltage, durability and good low temperature performance.
【０００９】[0009]
【課題を解決するための手段】すなわち本発明のリチウ
ム２次電池用正極材料は、組成式Ｌｉx Ｍｎ2 Ｏ
4-d（ここで０＜ｘ≦２、０．０１≦ｄ≦０．０７）で
表されることを特徴とする。That is, the positive electrode material for a lithium secondary battery of the present invention has a composition formula Li x Mn 2 O.
4-d (where 0 <x ≦ 2, 0.01 ≦ d ≦ 0.07).
【００１０】本発明の作用につき以下に説明する。本発
明のリチウム２次電池用正極材料は、Ｌｉx Ｍｎ2 Ｏ4
中に存在する酸素を僅かに欠損させた正極材料である。
このため金属イオンの総数は、酸素欠損のない試料と比
べて変化しない。つまり充放電に関与するリチウムイオ
ンの総数が酸素欠損のない試料と同等なので、例えば、
酸素を欠損させた試料と正規組成の試料をそれぞれ用い
て作製したリチウム２次電池の容量はほぼ等しい。よっ
て本発明にかかるリチウム２次電池用正極材料は、従来
品と同様に高容量である。The operation of the present invention will be described below. The positive electrode material for a lithium secondary battery according to the present invention is Li x Mn 2 O 4
It is a positive electrode material in which oxygen existing therein is slightly deficient.
Therefore, the total number of metal ions does not change as compared with the sample having no oxygen deficiency. That is, since the total number of lithium ions involved in charging and discharging is equivalent to that of a sample without oxygen deficiency,
The capacities of the lithium secondary batteries manufactured by using the oxygen deficient sample and the sample of the normal composition are almost equal. Therefore, the positive electrode material for a lithium secondary battery according to the present invention has a high capacity like the conventional product.
【００１１】又、本発明のリチウム２次電池用正極材料
においては、酸素の一部が欠損していることにより、酸
素を介したＭｎイオン間の長距離相互作用は著しく弱め
られている。前述のリチウム量による構造相転移と温度
による構造相転移の両方とも、その主因はＭｎイオン間
の長距離相互作用である。したがって、本発明のリチウ
ム２次電池用正極材料においては、酸素欠損により、ど
ちらの構造相転移も生じ難くなる。Further, in the positive electrode material for a lithium secondary battery of the present invention, the long-range interaction between Mn ions via oxygen is significantly weakened because a part of oxygen is deficient. Both of the above-described structural phase transition due to the amount of lithium and the structural phase transition due to temperature are mainly caused by long-range interaction between Mn ions. Therefore, in the positive electrode material for a lithium secondary battery of the present invention, neither structural phase transition is likely to occur due to oxygen deficiency.
【００１２】このため、本発明のリチウム２次電池用正
極材料（酸素欠損のある正極材料）を用いたリチウム２
次電池では、充放電を繰り返してもリチウム量による構
造相転移が高容量側へシフトしつつ抑制されるので、充
放電の繰り返しによる容量低下を防止することができ
る。更に温度による構造相転移も低温側へシフトするの
で、本発明のリチウム２次電池用正極材料を用いたリチ
ウム２次電池は、低温においても性能劣化も起こさな
い。すなわち、高い放電電圧，耐久性及び良好な低温性
能を併有するリチウム２次電池用正極材料を提供するこ
とができる。Therefore, lithium 2 using the positive electrode material for a lithium secondary battery (positive electrode material having oxygen deficiency) of the present invention is used.
In the secondary battery, the structural phase transition due to the amount of lithium is suppressed while shifting to the high capacity side even if charging and discharging are repeated, so that it is possible to prevent the capacity from decreasing due to repeating charging and discharging. Furthermore, since the structural phase transition due to temperature shifts to the low temperature side, the lithium secondary battery using the positive electrode material for a lithium secondary battery of the present invention does not cause performance deterioration even at low temperatures. That is, it is possible to provide a positive electrode material for a lithium secondary battery, which has both high discharge voltage, durability and good low-temperature performance.
【００１３】[0013]
【発明の実施の形態】前記組成式Ｌｉx Ｍｎ2 Ｏ4-d に
おいては、０＜ｘ≦２である。２＜ｘでは、前記組成式
で表される物質に可逆的にリチウムイオンが出入りでき
なくなるおそれがある。又、０．０１≦ｄ≦０．０７で
ある。ｄ＜０．０１では、酸素欠損量が少なすぎて所望
の効果が得られない。又、０．０７＜ｄでは、試料の一
部が分解してしまい、容量が大幅に低下するおそれがあ
る。BEST MODE FOR CARRYING OUT THE INVENTION In the composition formula Li x Mn 2 O 4-d , 0 <x ≦ 2. When 2 <x, there is a possibility that lithium ions cannot reversibly enter and leave the substance represented by the composition formula. Also, 0.01 ≦ d ≦ 0.07. When d <0.01, the desired effect cannot be obtained because the amount of oxygen vacancies is too small. On the other hand, when 0.07 <d, a part of the sample is decomposed, and the capacity may be significantly reduced.
【００１４】前記組成式Ｌｉx Ｍｎ2 Ｏ4-d でｘが１を
表す場合の組成式ＬｉＭｎ2 Ｏ4-dの結晶構造は、室温
で立方晶スピネル構造であることが望ましい。何故なら
ば、酸素欠損量ｄを増加させると、ｄ＝０．０７近傍で
結晶構造が正方晶に変化するが、正極材料中にこの正方
晶相が出現すると充放電電圧が低下するので、酸素欠損
を導入しても立方晶スピネル構造を保つことが望まし
い。The crystal structure of the composition formula LiMn 2 O 4-d when x represents 1 in the composition formula Li x Mn 2 O 4-d is preferably a cubic spinel structure at room temperature. This is because when the oxygen deficiency amount d is increased, the crystal structure changes to tetragonal in the vicinity of d = 0.07, but when this tetragonal phase appears in the positive electrode material, the charge / discharge voltage decreases, so It is desirable to maintain the cubic spinel structure even if defects are introduced.
【００１５】[0015]
【実施例】以下の実施例及び比較例において、本発明を
更に詳細に説明する。実施例１〜２及び比較例１〜２ 以下の如く、炭酸リチウム（Ｌｉ2 ＣＯ3 ）の粉末と二
酸化マンガン（ＭｎＯ2 ）の粉末とを用いてＬｉＭｎ2
Ｏ4-d を合成した。３．５０５ｇのＬｉ2 ＣＯ3 と１
６．４９５ｇのＭｎＯ2 とを、エタノールを溶媒とし
て、遊星ボールミル中で混合した。混合粉末を乾燥後、
ペレット状にプレス成形して、８００℃、８時間、静止
大気中で３回仮焼した。このペレットを充分に粉砕した
粉末について、酸素欠損量を０にするために、以下のよ
うな条件で熱処理して標準試料Ｓ１を得た。 熱処理条件：６００℃，２４時間，２０％Ｏ2 −Ａｒ気
流中 冷却条件：０℃に急冷The present invention will be described in more detail in the following examples and comparative examples. Examples 1-2 and Comparative Examples 1-2 As described below, LiMn 2 was prepared using lithium carbonate (Li 2 CO 3 ) powder and manganese dioxide (MnO 2 ) powder.
O 4-d was synthesized. 3.505 g of Li 2 CO 3 and 1
6.495 g of MnO 2 was mixed in a planetary ball mill with ethanol as the solvent. After drying the mixed powder,
The mixture was press-formed into pellets and calcined at 800 ° C. for 8 hours in still air three times. The powder obtained by sufficiently pulverizing the pellets was heat-treated under the following conditions in order to reduce the amount of oxygen deficiency to obtain a standard sample S1. Heat treatment condition: 600 ° C., 24 hours, in a 20% O 2 —Ar stream Cooling condition: Quenching to 0 ° C.
【００１６】標準試料Ｓ１の組成は、誘導結合プラズマ
分析とＫＭｎＯ4 を用いた化学滴定により求めた。次い
で、標準試料Ｓ１を以下のような条件で熱処理して、酸
素欠損量の異なる４つの試料（試料１〜４）を合成し
た。結果を下記表１に示す。The composition of the standard sample S1 was determined by inductively coupled plasma analysis and chemical titration using KMnO 4 . Next, the standard sample S1 was heat-treated under the following conditions to synthesize four samples (Samples 1 to 4) having different oxygen deficiency amounts. The results are shown in Table 1 below.
【表１】 [Table 1]
【００１７】試料１〜４の組成は、標準試料Ｓ１を基準
とした重量分析により求めた。標準試料Ｓ１及び試料１
〜４の組成を下記表２に示す。The compositions of Samples 1 to 4 were determined by gravimetric analysis based on the standard sample S1. Standard sample S1 and sample 1
The compositions of ~ 4 are shown in Table 2 below.
【表２】 [Table 2]
【００１８】標準試料Ｓ１及び試料１〜４のＸ線回折パ
ターンを図１に示す。試料１〜３（ｄ≦０．０７９）で
は立方晶スピネル構造に由来する回折ピークのみが観測
された。つまりＬｉＭｎ2 Ｏ4-d （ｄ≦０．０７９）試
料はスピネル構造の単一相である。これに対して、ｄ＝
０．１の試料４のＸ線回折パターンには、立方晶スピネ
ル構造に由来する回折ピークの他に、正方晶スピネル構
造に由来する回折ピーク（矢印で示す）も観測された。
すなわちｄ＝０．１近傍で、立方晶スピネル構造の試料
の一部が正方晶に転移することが示された。酸素欠損を
導入した試料でも試料全体の電荷中性は保たれなければ
ならない。このためＭｎイオンの平均価数はｄの増加と
ともに減少する。この結果Ｍｎ3+の濃度が増加して部分
的に正方晶が出現すると考えられる。The X-ray diffraction patterns of the standard sample S1 and samples 1 to 4 are shown in FIG. In Samples 1 to 3 (d ≦ 0.079), only diffraction peaks derived from the cubic spinel structure were observed. That is, the LiMn 2 O 4-d (d ≦ 0.079) sample is a single phase having a spinel structure. On the other hand, d =
In the X-ray diffraction pattern of Sample 4 of 0.1, in addition to the diffraction peak derived from the cubic spinel structure, a diffraction peak derived from the tetragonal spinel structure (indicated by an arrow) was also observed.
That is, in the vicinity of d = 0.1, it was shown that a part of the sample having the cubic spinel structure was transformed into the tetragonal system. Even in a sample in which oxygen deficiency is introduced, the charge neutrality of the entire sample must be maintained. Therefore, the average valence of Mn ions decreases as d increases. As a result, it is considered that the Mn 3+ concentration increases and a tetragonal crystal partially appears.
【００１９】示差走査熱量分析（ＤＳＣ）により、標準
試料Ｓ１及び試料１〜４を−１５０℃から昇温しながら
測定した結果を図２に示す。標準試料Ｓ１では−２５℃
近傍に吸熱ピーク（矢印で示す）が観測された。このピ
ークは温度による低温正方晶から高温立方晶への構造相
転移に付随している。酸素欠損量を増やすと、試料１，
２（ｄ≦０．０６６）までは（すなわち、実施例１，２
の試料では）、このピークは低温側にシフトし、次いで
試料３，４（すなわち、比較例１，２の試料では）で
は、高温側にシフトした。特に、試料４（ｄ＝０．１）
では、このピークは約２０℃に観測された。FIG. 2 shows the results of measurement of the standard sample S1 and the samples 1 to 4 while raising the temperature from -150 ° C. by differential scanning calorimetry (DSC). -25 ° C for standard sample S1
An endothermic peak (indicated by an arrow) was observed in the vicinity. This peak is associated with a structural phase transition from low temperature tetragonal to high temperature cubic with temperature. When the amount of oxygen deficiency is increased, sample 1,
Up to 2 (d ≦ 0.066) (that is, Embodiments 1 and 2)
Of the sample), this peak was shifted to the low temperature side, and then of Samples 3 and 4 (that is, the samples of Comparative Examples 1 and 2) to the high temperature side. In particular, sample 4 (d = 0.1)
Then, this peak was observed at about 20 ° C.
【００２０】図３に、ＤＳＣから求めた正方晶と立方晶
の転移温度（Ｔc ）とｄとの関係を示す。明らかにｄ＝
０．０５付近でＴc が最小となることが分かる。ｄ＝
０．０５付近の試料１，２のＴc は標準試料Ｓ１のＴc
より５〜１０℃低い。FIG. 3 shows the relationship between the tetragonal and cubic transition temperatures (T c ) determined by DSC and d. Clearly d =
It can be seen that T c becomes the minimum near 0.05. d =
T c of the samples 1 and 2 in the vicinity of 0.05 T c of the standard sample S1
5-10 ° C lower.
【００２１】このようなＴc とｄの関係は、以下のと
の２つの効果が拮抗して発現すると考えられる。 −ｄが増加すると酸素が失われるので、酸素を介した
Ｍｎイオン間の長距離相互作用が弱まる。これは協同現
象である構造相転移を起こり難くするので、Ｔcを下げ
る効果がある。 −ｄが増加するとＭｎイオンの平均価数が下がる。こ
の結果Ｍｎ3+の濃度が増加して正方晶歪みが増大する。
これはＴc を上げる効果がある。Such a relationship between T c and d is considered to be manifested by the following two effects antagonizing each other. Oxygen is lost as -d increases, so long-range interactions between Mn ions via oxygen are weakened. This makes it difficult to cause a structural phase transition, which is a cooperative phenomenon, and thus has an effect of lowering T c . As -d increases, the average valence of Mn ions decreases. As a result, the concentration of Mn 3+ increases and tetragonal strain increases.
This has the effect of increasing T c .
【００２２】低いＴc は温度以外の種々の擾乱に対して
も、立方晶相が安定であることを示唆している。例えば
電池の放電反応に伴い、Ｌｉx Ｍｎ2 Ｏ4 中のリチウム
量ｘが増加する。Ｌｉx Ｍｎ2 Ｏ4 はｘ≦１では立方晶
であるが、１＜ｘでは正方晶相が出現する。正方晶相の
出現に伴い、放電電圧は階段状に約１Ｖ低下する。ここ
で低いＴc のＬｉx Ｍｎ2 Ｏ4-d 試料は、リチウム量が
変化しても立方晶相が安定なので、放電電圧の階段状の
低下も抑制されるか又は高容量側へシフトすることが予
想される。The low T c indicates that the cubic phase is stable against various disturbances other than temperature. For example, the amount of lithium x in Li x Mn 2 O 4 increases with the discharge reaction of the battery. Li x Mn 2 O 4 is a cubic crystal when x ≦ 1, but a tetragonal phase appears when 1 <x. With the appearance of the tetragonal phase, the discharge voltage decreases stepwise by about 1V. In the Li x Mn 2 O 4-d sample having a low T c, the cubic phase is stable even when the amount of lithium changes, so that the stepwise decrease of the discharge voltage is suppressed or shifted to the high capacity side. It is expected that.
【００２３】＜リチウム２次電池の性能評価＞次に正極
材料として前記試料１〜４及び標準試料Ｓ１をそれぞれ
用いたリチウム２次電池を試験用セルを用いて組み立
て、その特性を評価した。まず前記リチウム２次電池の
構成につき説明する。前記リチウム２次電池の正極は、
前記試料１〜４又は標準試料Ｓ１が５０ｗｔ％、導電性
結着剤が５０ｗｔ％からなる。又、前記リチウム２次電
池の負極には厚さ０．４ｍｍの金属Ｌｉ箔を１枚用い
た。前記正極と負極との間に設けたセパレーターにはポ
リプロピレン不織布を用いた。更に、前記リチウム２次
電池における電解液は１規定のＬｉＰＦ6 溶液で、その
溶媒はポリカーボネートとジメトキシエタンの１：１混
合液である。<Evaluation of Performance of Lithium Secondary Battery> Next, a lithium secondary battery using each of Samples 1 to 4 and Standard Sample S1 as positive electrode materials was assembled using a test cell, and its characteristics were evaluated. First, the structure of the lithium secondary battery will be described. The positive electrode of the lithium secondary battery is
The samples 1 to 4 or the standard sample S1 are 50 wt% and the conductive binder is 50 wt%. In addition, one metal Li foil having a thickness of 0.4 mm was used as the negative electrode of the lithium secondary battery. A polypropylene non-woven fabric was used for the separator provided between the positive electrode and the negative electrode. Further, the electrolyte in the lithium secondary battery is a 1N LiPF 6 solution, and the solvent is a 1: 1 mixture of polycarbonate and dimethoxyethane.
【００２４】前記リチウム２次電池の、初期放電特性と
サイクル特性測定における充放電条件について説明す
る。まず各リチウム２次電池を、４．５Ｖまで１ｍＡ／
ｃｍ2の定電流で充電した。その後電圧が４．５Ｖに到
達後は、この電圧で定電圧充電を行った。なお以上の充
電時間の合計は２時間であった。次いで充電完了直後に
放電を開始した。放電条件は１ｍＡ／ｃｍ2 の定電流で
放電を行い、３．５Ｖに到達したら放電を終了した。
又、放電が終了した直後に再度充電を開始した。以上を
１サイクルとした。Charging / discharging conditions for measuring the initial discharge characteristics and the cycle characteristics of the lithium secondary battery will be described. First, each lithium secondary battery, 1mA / 4.5V up to
It was charged with a constant current of cm 2 . After that, after the voltage reached 4.5 V, constant voltage charging was performed at this voltage. The total of the above charging times was 2 hours. Then, the discharge was started immediately after the completion of charging. The discharge conditions were constant current of 1 mA / cm 2 and discharge when 3.5 V was reached.
In addition, immediately after the discharging was completed, the charging was started again. The above was regarded as one cycle.
【００２５】図４に、試料１〜４又は標準試料Ｓ１を正
極としたリチウム２次電池の初期放電特性を示す。ここ
で各試料のデータを見やすくするために、標準試料Ｓ１
に対して、試料１のデータは０．２Ｖ、試料２のデータ
は０．４Ｖ、試料３のデータは０．６Ｖ、試料４のデー
タは０．８Ｖだけ縦軸を上方（高放電電圧側）にずらし
てある。標準試料Ｓ１と比較すると、試料１（実施例
１）と試料２（実施例２）を用いたリチウム２次電池で
は、放電電圧の低下が高容量側（右側）にシフトしてい
ることが分かる。つまりリチウム量による構造相転移が
抑制された結果、高電圧（４Ｖ）部分の放電容量が増加
した。これに対して、試料３（比較例１）と試料４（比
較例２）では、標準試料Ｓ１より低容量側で放電電圧が
低下した。つまり高電圧（４Ｖ）部分の放電容量が減少
した。これは酸素欠損量が多すぎて、正方晶相が出現し
やすくなったためと考えられる。FIG. 4 shows the initial discharge characteristics of a lithium secondary battery having Samples 1 to 4 or standard sample S1 as a positive electrode. Here, in order to make the data of each sample easy to see, the standard sample S1
On the other hand, the data of the sample 1 is 0.2V, the data of the sample 2 is 0.4V, the data of the sample 3 is 0.6V, and the data of the sample 4 is 0.8V, the vertical axis is upward (high discharge voltage side). It is shifted. As compared with the standard sample S1, in the lithium secondary batteries using the sample 1 (Example 1) and the sample 2 (Example 2), it can be seen that the decrease in discharge voltage is shifted to the high capacity side (right side). . That is, as a result of suppressing the structural phase transition due to the amount of lithium, the discharge capacity in the high voltage (4V) portion increased. On the other hand, in Sample 3 (Comparative Example 1) and Sample 4 (Comparative Example 2), the discharge voltage decreased on the lower capacity side than the standard sample S1. That is, the discharge capacity in the high voltage (4V) part was reduced. It is considered that this is because the amount of oxygen deficiency was too large and the tetragonal phase was likely to appear.
【００２６】図５に、試料１〜４又は標準試料Ｓ１を正
極としたリチウム２次電池のサイクル特性を示す。図５
の縦軸は、図４に示した初期放電容量を１とした場合の
相対放電容量である。又、図５の横軸は、繰り返した回
数、すなわちサイクル数である。標準試料Ｓ１と比較す
ると、試料１（実施例１）と試料２（実施例２）を用い
たリチウム２次電池では、充放電の繰り返しによる放電
容量の低下が少ないことが分かる。一方試料３（比較例
１）と試料４（比較例２）では、標準試料Ｓ１より充放
電の繰り返しによる放電容量の低下が急激である。FIG. 5 shows the cycle characteristics of a lithium secondary battery using Samples 1 to 4 or standard sample S1 as a positive electrode. FIG.
The vertical axis of is the relative discharge capacity when the initial discharge capacity shown in FIG. 4 is 1. Further, the horizontal axis of FIG. 5 represents the number of repetitions, that is, the number of cycles. As compared with the standard sample S1, it can be seen that the lithium secondary batteries using the sample 1 (Example 1) and the sample 2 (Example 2) show less decrease in discharge capacity due to repeated charging and discharging. On the other hand, in Sample 3 (Comparative Example 1) and Sample 4 (Comparative Example 2), the decrease in discharge capacity due to repeated charging / discharging is more rapid than in the standard sample S1.
【００２７】図６に、試料２（実施例２）又は標準試料
Ｓ１を正極としたリチウム２次電池の充放電特性の温度
依存性を示す。図６の縦軸は２５℃の初期放電容量を１
とした場合の相対放電容量である。標準試料Ｓ１と比較
すると、試料２（実施例２）を用いたリチウム２次電池
では、低温での容量低下が抑えられていることが理解で
きる。FIG. 6 shows the temperature dependence of the charge / discharge characteristics of the lithium secondary battery using the sample 2 (Example 2) or the standard sample S1 as the positive electrode. The vertical axis of FIG. 6 is the initial discharge capacity at 25 ° C. of 1
Is the relative discharge capacity. As compared with the standard sample S1, it can be understood that the lithium secondary battery using the sample 2 (Example 2) suppresses the capacity decrease at low temperatures.
【００２８】[0028]
【発明の効果】本発明のリチウム２次電池用正極材料を
使用することにより、従来のリチウム２次電池に比べて
より高い放電容量と高い耐久性、並びに良好な低温性能
を併有するリチウム２次電池が得られる。本発明のリチ
ウム２次電池用正極材料において、組成式ＬｉＭｎ2 Ｏ
4-d （ここで０．０１≦ｄ≦０．０７）を有し、且つ室
温で立方晶スピネル構造であるものは特に有用である。EFFECTS OF THE INVENTION By using the positive electrode material for a lithium secondary battery of the present invention, a lithium secondary battery having higher discharge capacity, higher durability and good low-temperature performance than those of conventional lithium secondary batteries. A battery is obtained. In the positive electrode material for lithium secondary batteries of the present invention, the composition formula LiMn 2 O
Those having 4-d (where 0.01 ≦ d ≦ 0.07) and having a cubic spinel structure at room temperature are particularly useful.
【図１】試料１〜４及び標準試料Ｓ１の粉末Ｘ線回折パ
ターンを示す図である。FIG. 1 is a view showing powder X-ray diffraction patterns of samples 1 to 4 and standard sample S1.
【図２】試料１〜４及び標準試料Ｓ１の示差走査熱量分
析の測定結果を示す図である。FIG. 2 is a diagram showing measurement results of differential scanning calorimetry of samples 1 to 4 and standard sample S1.
【図３】試料１〜４及び標準試料Ｓ１の転移温度と酸素
欠損量との関係を示す図である。FIG. 3 is a diagram showing the relationship between the transition temperature and the amount of oxygen deficiency of Samples 1 to 4 and standard sample S1.
【図４】試料１〜４及び標準試料Ｓ１を正極材料として
用いたリチウム２次電池の初期放電特性を示す図であ
る。FIG. 4 is a diagram showing initial discharge characteristics of a lithium secondary battery using samples 1 to 4 and standard sample S1 as positive electrode materials.
【図５】試料１〜４及び標準試料Ｓ１を正極材料として
用いたリチウム２次電池のサイクル特性を示す図であ
る。FIG. 5 is a diagram showing cycle characteristics of a lithium secondary battery using samples 1 to 4 and standard sample S1 as positive electrode materials.
【図６】試料２及び標準試料Ｓ１を正極材料として用い
たリチウム２次電池の充放電容量の温度依存性を示す図
である。FIG. 6 is a diagram showing temperature dependence of charge / discharge capacity of a lithium secondary battery using Sample 2 and standard sample S1 as positive electrode materials.
【図７】正極材料としてＬｉＭｎ2 Ｏ4 を用いたリチウ
ム２次電池の、Ｍｎイオンの平均価数の変化による特性
変化を示す図である。FIG. 7 is a diagram showing a characteristic change of a lithium secondary battery using LiMn 2 O 4 as a positive electrode material due to a change in average valence of Mn ions.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 畑中 達也 愛知県愛知郡長久手町大字長湫字横道41番 地の１ 株式会社豊田中央研究所内 (72)発明者 伊藤 忠 愛知県愛知郡長久手町大字長湫字横道41番 地の１ 株式会社豊田中央研究所内 (72)発明者 日置 辰視 愛知県愛知郡長久手町大字長湫字横道41番 地の１ 株式会社豊田中央研究所内 (72)発明者 亀頭 直樹 愛知県豊橋市北山町字東浦高師住宅５− 402 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuya Hatanaka, Nagakute-cho, Aichi-gun, Aichi Prefecture, Nagakage 1 41, Yokochi, Toyota Central Research Institute Co., Ltd. 1 in 41 Central Road, Toyota Central Research Institute Co., Ltd. (72) Inventor Tatsumi Hioki 1 in 41 Central Road, Nagakute-cho, Aichi-gun, Aichi Prefecture 1 in Toyota Central Research Center Co., Ltd. (72) Inventor Naoki Kamez Aichi 5-402 Higashiura Takashi Housing, Kitayama-cho, Toyohashi-shi, Japan
Claims (2)
ｘ≦２、０．０１≦ｄ≦０．０７）で表されることを特
徴とするリチウム２次電池用正極材料。1. A composition formula of Li x Mn 2 O 4-d (where 0 <
x ≦ 2, 0.01 ≦ d ≦ 0.07), which is a positive electrode material for a lithium secondary battery.
方晶スピネル構造であることを特徴とする請求項１記載
のリチウム２次電池用正極材料。2. The positive electrode material for a lithium secondary battery according to claim 1, wherein x represents 1 in the composition formula and has a cubic spinel structure at room temperature.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8104579A JPH09274918A (en) | 1996-04-02 | 1996-04-02 | Positive electrode material for lithium secondary battery |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8104579A JPH09274918A (en) | 1996-04-02 | 1996-04-02 | Positive electrode material for lithium secondary battery |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH09274918A true JPH09274918A (en) | 1997-10-21 |
Family
ID=14384354
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP8104579A Pending JPH09274918A (en) | 1996-04-02 | 1996-04-02 | Positive electrode material for lithium secondary battery |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH09274918A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2000251894A (en) * | 1998-12-29 | 2000-09-14 | Hitachi Maxell Ltd | Nonaqueous secondary battery, and usage thereof |
| JP2015179634A (en) * | 2014-03-19 | 2015-10-08 | 旭化成株式会社 | Lithium-containing complex oxide, manufacturing method thereof, positive electrode active material including complex oxide, and nonaqueous lithium ion secondary battery |
-
1996
- 1996-04-02 JP JP8104579A patent/JPH09274918A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2000251894A (en) * | 1998-12-29 | 2000-09-14 | Hitachi Maxell Ltd | Nonaqueous secondary battery, and usage thereof |
| JP2015179634A (en) * | 2014-03-19 | 2015-10-08 | 旭化成株式会社 | Lithium-containing complex oxide, manufacturing method thereof, positive electrode active material including complex oxide, and nonaqueous lithium ion secondary battery |
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