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
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- 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 |
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Publication Number | Publication Date |
---|---|
JPH09274918A true JPH09274918A (en) | 1997-10-21 |
Family
ID=14384354
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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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