JP4248190B2 - Cathode active material and non-aqueous electrolyte battery - Google Patents

Description

【００８２】
【表２】

【００８３】
【表３】

【００８４】
表１〜表３の結果から、以下のことが明らかになった。粒子Ａと粒子Ｂの配合比Ｗ_Ａ：Ｗ_Ｂが一定である場合、粒子Ａのメジアン径Ｄ_Ａまたは粒子Ｂのメジアン径Ｄ_Ｂが大きくなるにつれ、３Ｃ放電維持率が低下している。また、粒子Ａと粒子Ｂの配合比Ｗ_Ａ：Ｗ_Ｂが一定である場合、粒子Ａのメジアン径Ｄ_Ａまたは粒子Ｂのメジアン径Ｄ_Ｂが小さくなるにつれ、発煙または発火に至る確率が高くなっている。
【００８５】
一方、粒子Ａの配合量Ｗ_Ａを８０重量％にすると、メジアン径が小さい場合には釘刺し試験時に発煙または発火を生じた。そこで、発煙及び発火を防止するためにメジアン径を大きくすると、３Ｃ放電維持率が著しく低くなった。
【００８６】
これらの結果から、粒子Ａの配合量Ｗ_Ａは７７．８重量％未満が好ましく、また、放電負荷特性を向上させる観点からは、粒子Ａのメジアン径Ｄ_Ａについては、直線Ｄ_Ａ＝−０．０９Ｗ_Ａ＋１５で算出されるメジアン径と等しいか、または小さい領域、一方、粒子Ｂのメジアン径Ｄ_Ｂについては、直線Ｄ_Ｂ＝−０．０６Ｗ_Ａ＋２０で算出されるメジアン径と等しいか、または小さい領域を選択することが好ましいことがわかる。さらに、安全性を向上させる観点からは、粒子Ａのメジアン径Ｄ_Ａについては、直線Ｄ_Ａ＝０．０９Ｗ_Ａ＋１で算出されるメジアン径と等しいか、または大きい領域、一方、粒子Ｂのメジアン径Ｄ_Ｂについては、直線Ｄ_Ｂ＝０．０４Ｗ_Ａ＋１で算出されるメジアン径と等しいか、または大きい領域を選択することが好ましいことがわかる。
【００８７】
よって、粒子Ａの配合量Ｗ_Ａ（重量％）と粒子Ｂの配合量Ｗ_Ｂが０＜Ｗ_Ａ＜７７．８、Ｗ_Ｂ＝１００−Ｗ_Ａである際に、粒子Ａのメジアン径Ｄ_Ａ（μｍ）が、直線Ｄ_Ａ＝０．０９Ｗ_Ａ＋１と直線Ｄ_Ａ＝−０．０９Ｗ_Ａ＋１５で囲まれる領域に含まれ、かつ粒子Ｂのメジアン径Ｄ_Ｂ（μｍ）が、直線Ｄ_Ｂ＝０．０４Ｗ_Ａ＋１と直線Ｄ_Ｂ＝−０．０６Ｗ_Ｂ＋２０で囲まれる領域に含まれる正極活物質を用いることで、良好な放電負荷特性と、優れた安全性とを両立した電池を得ることができる。
【００８８】
（参考例１７）
粒子Ａとして、組成がＬｉＮｉ_0.8Ｃｏ_0.2Ｓｎ_0.01Ｏ₂（ＬｉＮｉ_0.8Ｃｏ_0.2Ｏ₂１モルに対してＬｉ₂ＳｎＯ₃が０．０１モルの割合で混合された混合物）で表わされるメジアン径Ｄ_Ａが２μｍの粒子を用意した。また、粒子Ｂとして、組成がＬｉＣｏＯ₂で表わされるメジアン径Ｄ_Ｂが２μｍの粒子を用意した。粒子ＡのＣｏとＮｉのモル比（ｙ／ｚ）は、４である。一方、粒子ＢのＣｏとＮｉのモル比（ｙ／ｚ）は、０である。
【００８９】
粒子Ａの組成分析は、試料を塩酸に溶解し、セイコーインスツルメンツ社製 ＩＣＰ１２００Ａ を用いて、ＩＣＰ発光分析によって定量を行った。
【００９０】
粒子Ａと粒子Ｂとを重量比Ｗ_Ａ：Ｗ_Ｂが２０：８０で混合し、正極活物質とした。
【００９１】
この正極活物質１００重量部に対し、導電助剤としてアセチレンブラック６重量部、バインダーとしてポリテトラフルオロエチレン３重量部を添加し、これらを乳鉢で混合してシート状に成型し、これを１ｃｍ角に切出してＳＵＳメッシュに貼りつけ、正極を得た。
【００９２】
対極および参照極としてＬｉ金属を用いた。対極と参照極は、セパレータを介して正極と対向させた。これら電極を電解セル中にて非水電解液に浸漬させて模擬電池セルを作製した。なお、非水電解液としては、エチレンカーボネート（ＥＣ）とγ−ブチロラクトン（ＧＢＬ）が体積比率１：２で混合された非水溶媒に四フッ化ホウ酸リチウム（ＬｉＢＦ₄ ）をその濃度が１．５ｍｏｌ／Ｌになるように溶解させたものを用いた。
【００９３】
（参考例１８）
粒子Ａの組成をＬｉＮｉ_0.8Ｃｏ_0.2Ｓｎ_0.002Ｏ₂（ＬｉＮｉ_0.8Ｃｏ_0.2Ｏ₂１モルに対してＬｉ₂ＳｎＯ₃が０．００２モルの割合で混合された混合物）に変更すること以外は、前述した参考例１７と同様にして模擬電池セルを組み立てた。
【００９４】
（参考例１９）
粒子Ａの組成をＬｉＮｉ_0.8Ｃｏ_0.2Ｓｎ_0.1Ｏ₂（ＬｉＮｉ_0.8Ｃｏ_0.2Ｏ₂１モルに対してＬｉ₂ＳｎＯ₃が０．１モルの割合で混合された混合物）に変更すること以外は、前述した参考例１７と同様にして模擬電池セルを組み立てた。
【００９５】
（参考例２０）
粒子Ａとして、組成がＬｉＮｉ_0.8Ｃｏ_0.2Ｏ₂で表わされるメジアン径Ｄ_Ａが２μｍの粒子を用意した。また、粒子Ｂとして、組成がＬｉＣｏＳｎ_0.04Ｏ₂（ＬｉＣｏＯ₂１モルに対してＬｉ₂ＳｎＯ₃が０．０４モルの割合で混合された混合物）で表わされるメジアン径Ｄ_Ｂが２μｍの粒子を用意した。粒子ＡのＣｏとＮｉのモル比（ｙ／ｚ）は、４である。一方、粒子ＢのＣｏとＮｉのモル比（ｙ／ｚ）は、０である。
【００９６】
粒子Ａと粒子Ｂとを重量比Ｗ_Ａ：Ｗ_Ｂが２０：８０で混合し、正極活物質とした。
【００９７】
このような正極活物質を用いること以外は、前述した参考例１７と同様にして模擬電池セルを組み立てた。
【００９８】
（参考例１−２）
前述した参考例１で説明したのと同様な正極活物質を用いること以外は、前述した参考例１７と同様にして模擬電池セルを組み立てた。
【００９９】
得られた参考例１７〜２０および参考例１−２の模擬セルを、均一な電極の含浸状態とするために３．０Ｖ〜４．２Ｖ，３ｍＡで２サイクル充放電を行った後、２０℃，３ｍＡ，４．２Ｖの充電状態として交流インピーダンス測定を実施した後、４５℃で一定時間保存し、再度交流インピーダンス測定を実施して、インピーダンス上昇の様子を調べた。その結果を図３，４に示す。図３の縦軸は、電池の交流インピーダンスの虚数成分を示し、横軸は実数成分を示す。
【０１００】
図４は、図３の要部を拡大した図である。
【０１０１】
図３及び図４から明らかなように、粒子Ａまたは粒子ＢにＳｎが含有されている参考例１７〜参考例２０の電池によると、Ｓｎが無添加の参考例１−２と比較して、４５℃の高温で貯蔵した際のインピーダンスの上昇が緩やかであった。参考例１８のように粒子中のＳｎ含有量がごく少量でも、Ｓｎ無添加の参考例１−２に比べて１／３以下と、十分な効果が見られる。また、Ｓｎの添加量を多くする、あるいは、同一添加量であっても参考例２０のように粒子ＢにＳｎを含有させると、一層効果が大きくなる。
【０１０２】
なお、前述した実施例においては、粒子Ａと粒子Ｂの２種類からなる正極活物質に適用した例を説明したが、正極活物質としては、放電負荷特性と安全性の双方を満足できる限り、粒子Ａ，ＢにＬｉＮｉＯ₂のような他の種類の粒子を混合させた３種類以上の粒子からなるものを用いることができる。
【０１０３】
また、前述した実施例においては、円筒形非水電解質二次電池に適用した例を説明したが、角形非水電解質二次電池、薄型非水電解質二次電池、コイン型非水電解質二次電池にも同様に適用することができる。また、前述した実施例においては、電極群を収納する容器として金属製容器を用いたが、金属層と樹脂層を含有するラミネートフィルム製の容器を備えた電池にも同様に適用することができる。
【０１０４】
【発明の効果】
以上詳述したように本発明によれば、釘刺し試験時の発煙及び発火の抑制と放電負荷特性の向上との双方を達成することが可能な正極活物質と、この正極活物質を備える非水電解質電池を提供することができる。
【図面の簡単な説明】
【図１】 本発明に係る正極活物質に含まれる粒子Ａと粒子Ｂについての配合量と粒径との関係を示す特性図。
【図２】 本発明に係る非水電解質電池の一例である円筒形非水電解質二次電池を示す部分切欠斜視図。
【図３】 参考例１７〜２０と参考例１−２の模擬セルについての高温保管による内部インピーダンス変化を示す特性図。
【図４】 図３の要部を示す拡大図。
【符号の説明】
１…容器、
３…電極群、
４…正極、
６…負極、
５…セパレータ、
７…ＰＴＣ素子、
８…安全弁、
９…正極端子、
１０…絶縁ガスケット。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte battery including a positive electrode active material and a positive electrode including the positive electrode active material.
[0002]
[Prior art]
Currently, as a positive electrode active material of a lithium ion secondary battery which is an example of a non-aqueous electrolyte battery, mainly LiCoO₂Is used. In this non-aqueous electrolyte battery, the demand for higher capacity has been increasing year by year as the functionality of mobile phones, notebook computers, PDAs, etc. has increased.₂As a positive electrode active material capable of obtaining a higher capacity than LiNiO₂LiNiO₂A lithium nickel cobalt composite oxide in which a part of Ni is replaced with Co is being developed for practical use.
[0003]
However, LiNiO₂And lithium nickel cobalt composite oxide are both LiCoO₂Therefore, secondary batteries manufactured using these oxides tend to emit smoke or ignite during the nail penetration test. In addition, such secondary batteries have a problem that the discharge load characteristics are not sufficient.
[0004]
[Problems to be solved by the invention]
The present invention provides a positive electrode active material capable of achieving both suppression of smoke and ignition during a nail penetration test and improvement of discharge load characteristics, and a nonaqueous electrolyte battery including the positive electrode active material. Objective.
[0005]
[Means for Solving the Problems]
  The positive electrode active material according to the present invention has a general formula Li_xNi_yCo_zSn_wO₂(However, the molar ratios x, y, z, and w are 0.95 ≦ x ≦ 1.05, 0.85 ≦ y + z ≦ 1, 0 ≦ w ≦ 0.1, and satisfy x + y + z + w = 2). The particles A and B having the composition described above are included, and the ratio (y / z) of Ni and Co in the particles A isMore than 7/3, andRatio of Ni and Co in the particle B (y / z)Is 3/7 or less (including 0),
  Median diameter D of particle A_A(Μm) satisfies the following formula (1), and the median diameter D of the particle B_B(Μm) satisfies the following formula (2)And
  The median diameter D _A And the median diameter D _B Is more than 5μmIt is characterized by that.
[0006]
0.09W_A+ 1 ≦ D_A≦ −0.09W_A+15 (1)
0.04W_A+ 1 ≦ D_B≦ −0.06W_A+20 (2)
However, W_AIs a blending amount (% by weight) of the particles A, and 0 <W_A<77.8 is satisfied.
[0007]
  The nonaqueous electrolyte battery according to the present invention is a nonaqueous electrolyte battery comprising a positive electrode containing a positive electrode active material, a negative electrode, and a nonaqueous electrolyte,
  The positive electrode active material has the general formula Li_xNi_yCo_zSn_wO₂(However, the molar ratios x, y, z, and w are 0.95 ≦ x ≦ 1.05, 0.85 ≦ y + z ≦ 1, 0 ≦ w ≦ 0.1, and satisfy x + y + z + w = 2). The particles A and B having the composition described above are included, and the ratio (y / z) of Ni and Co in the particles A isMore than 7/3, andRatio of Ni and Co in the particle B (y / z)Is 3/7 or less (including 0),
  Median diameter D of particle A_A(Μm) satisfies the following formula (1), and the median diameter D of the particle B_B(Μm) satisfies the following formula (2)And
  The median diameter D _A And the median diameter D _B Is more than 5μmIt is characterized by that.
[0008]
0.09W_A+ 1 ≦ D_A≦ −0.09W_A+15 (1)
0.04W_A+ 1 ≦ D_B≦ −0.06W_A+20 (2)
However, W_AIs a blending amount (% by weight) of the particles A, and 0 <W_A<77.8 is satisfied.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The positive electrode active material according to the present invention has a general formula Li_xNi_yCo_zSn_wO₂(However, the molar ratios x, y, z, and w are 0.95 ≦ x ≦ 1.05, 0.85 ≦ y + z ≦ 1, 0 ≦ w ≦ 0.1, and satisfy x + y + z + w = 2). Two types of particles A and B having the composition described above are included. The ratio of Ni and Co (y / z) in the particle A is larger than the ratio of Ni and Co (y / z) in the particle B.
[0010]
Further, the median diameter D of the particle A_A(Μm) satisfies the following formula (1), and the median diameter D of the particle B_B(Μm) satisfies the following formula (2).
[0011]
0.09W_A+ 1 ≦ D_A≦ −0.09W_A+15 (1)
0.04W_A+ 1 ≦ D_B≦ −0.06W_A+20 (2)
However, W_AIs the blending amount (% by weight) of the particles A. The amount (% by weight) of the particle B is W_BW_AAnd W_BIs 0 <W_A<77.8, W_B= 100-W_AMeet.
[0012]
First, the composition of particles A and particles B will be described.
[0013]
(Li)
The reason why the molar ratio x of lithium is defined within the above range will be described. When the molar ratio x of lithium is less than 0.95, the lithium ions that are applied to the battery reaction are insufficient, and a high capacity cannot be obtained. On the other hand, when the molar ratio x of lithium exceeds 1.05, the alkali content on the active material surface increases, and when the binder is added and kneaded into a paste at the time of electrode preparation, the alkali content of the binder is reduced. There arises a problem that a cross-linking reaction is caused to produce a large number of lumps of about 1 mm to 2 mm in the paste, thereby preventing uniform application of the paste. A more preferable range of the molar ratio x is 0.99 to 1.03.
[0014]
(Ni, Co)
The reason why the total of the molar ratio y of nickel and the molar ratio z of cobalt is defined within the above range will be described. If the total molar ratio (y + z) is less than 0.85, the composition has a relatively large amount of lithium or tin. If the amount of lithium is large, the alkali content on the surface of the active material becomes high, making it difficult to apply the paste. When there is a lot of tin, the lattice points where lithium ions enter the battery reaction decrease, so that a high capacity cannot be obtained. On the other hand, when the total molar ratio (y + z) exceeds 1, the lithium ion that is applied to the battery reaction is insufficient, and a high capacity cannot be obtained, and the effect of tin described later is also reduced.
[0015]
A more preferable range of the total molar ratio (y + z) is 0.92 to 0.98.
[0016]
As the ratio of nickel to cobalt (y / z) is increased, the charge / discharge capacity of the secondary battery is increased. On the other hand, as (y / z) is decreased, the thermal stability of the positive electrode active material and the secondary battery are increased. There is a tendency that the discharge load characteristic of the is high.
[0017]
The particles A having (y / z) of 7/3 or more have a high effect of improving the charge / discharge capacity of the secondary battery, but are slightly inferior in thermal stability and discharge load characteristics. In the particle A, (y / z) is preferably in the range of 7/3 or more and 9/1 or less.
[0018]
When the (y / z) of the particle A is 9/1 or more, the thermal stability tends to be remarkably lowered.
[0019]
Particles B whose (y / z) is 3/7 or less (including the case where (y / z) is 0) have high thermal stability and discharge load characteristics, but it is difficult to obtain a sufficient charge / discharge capacity. Among the particles B, the general formula Li_xCo_zSn_wO₂(However, the molar ratios x, z and w are 0.95 ≦ x ≦ 1.05, 0.85 ≦ z ≦ 1, 0 ≦ w ≦ 0.1) It is desirable because of its excellent thermal stability and discharge load characteristics.
[0020]
(Sn)
Sn serves to suppress the side reaction between the non-aqueous electrolyte (particularly, containing γ-butyrolactone) and the positive electrode active material in a high temperature environment, but the charge / discharge capacity decreases as the Sn ratio in the active material increases. There is a fear. Therefore, the Sn molar ratio w is desirably 0.1 or less. Within this range, it is possible to suppress a side reaction in a high temperature environment and suppress an increase in impedance while ensuring a high charge / discharge capacity. In particular, when Sn is contained in the particle B, an increase in impedance when stored in a high temperature environment can be significantly suppressed.
[0021]
A more preferable range of the molar ratio w is 0.01 to 0.05.
[0022]
Median diameter D of particles A and B_A(Μm), median diameter D_B(Μm) will be described. Here, the median diameter is a particle size distribution (50% cumulative frequency particle size) of particles having a particle size distribution measured by the microtrack method and adding up the volume from particles having a small particle size to 50%.
[0023]
The particle size distribution is measured by the method described below. That is, the particle size distribution is measured by using a laser light scattering type particle size distribution analyzer (for example, MICROTRAC II PATICLE-SIZE ANALYZER manufactured by LEEDS & NORTH UP). This utilizes the light scattering phenomenon that occurs when a particle is irradiated with laser light as a measurement principle. Since the intensity and angle of scattered light largely depend on the size of the particle, the particle size distribution of the granules can be obtained by measuring the intensity and angle of the scattered light with an optical detector and processing it with a computer. .
[0024]
In measuring the median diameter, a laser light scattering particle size distribution meter capable of measuring a wet sample can be suitably used. Specifically, it is preferable to perform measurement after suspending the active material in an appropriate solvent to prepare a slurry and sufficiently dispersing the slurry with ultrasonic waves. The type of the ultrasonic device is preferably a structure in which a metal chip connected by an ultrasonic oscillator is directly immersed in the slurry. This structure is advantageous in that since ultrasonic waves are directly transmitted to the slurry, it can be efficiently dispersed and the reproducibility of dispersion is excellent.
[0025]
The ultrasonic output is desirably 100 W or more. If it is less than 100 W, even if it takes time to irradiate ultrasonic waves, the mechanical energy is insufficient, and it is difficult to destroy the aggregation between the fine structures. On the other hand, when energy of 200 W or more is input, the slurry temperature rises rapidly, and it is difficult to obtain reproducibility of the dispersed state.
[0026]
The vibration frequency of the ultrasonic vibrator is about 20 kHz. In particular, it is preferable to have a control system capable of tracking the frequency.
[0027]
The slurry concentration is desirably in the range of 0.001 to 1% by mass. If the concentration is higher than this, the association probability between the particles becomes high, and the crushed fine particles are re-agglomerated and it is difficult to grasp the exact crushing state. Further, when the slurry concentration is less than 0.001% by mass, the absorption efficiency of the ultrasonic energy by the particles is lowered, and the S / N ratio is lowered due to the restriction of the measuring device that detects light by scattering, and the noise is increased.
[0028]
The ultrasonic irradiation time is preferably within 5 minutes. Irradiation beyond this raises the slurry temperature and changes the amplitude of the ultrasonic wave, so the reproducibility becomes poor.
[0029]
Compounding amount W of particle A_AAnd particle B content W_BWhen the total amount is 100% by weight, the compounding amount W of the particles A_AIs set within a range of less than 77.8% by weight. Compounding amount W of particle A_AIs 77.8 wt% or more, the median diameter D of the particles A_AAnd median diameter D of particle B_BRegardless of the value, it becomes difficult to achieve both excellent discharge load characteristics and high safety. Compounding amount W of particle A_AThe more preferable range is 20 to 40% by weight.
[0030]
Median diameter D of particle A_AThe range of (μm) is defined by the above equation (1), and the median diameter D of the particle B_BThe reason why (μm) is defined in the above equation (2) will be described with reference to FIG. FIG. 1 is a characteristic diagram showing the relationship between the blending amount and particle size of particles A and B. The horizontal axis of FIG._A(% By weight). 1 represents the median diameter D of the particle A._A(Μm) and median diameter D of particle B_B(Μm).
[0031]
Median diameter D of particle A_AThe reason why (μm) is limited within the range of the formula (1) will be described. The blending amount (weight%) of the particles A is 0 <W_A<Median diameter D of particle A when it is within the range of <77.8_AStraight line D_A= 0.09W_AIf it is smaller than the value calculated from +1 (D_A<0.09W_A+1) Since the thermal stability of the positive electrode active material decreases due to an increase in the specific surface area of the particles A, the probability of causing smoke or ignition in the nail penetration test is increased. On the other hand, the blending amount (weight%) of the particles A is 0 <W_A<Median diameter D of particle A when it is within the range of <77.8_AStraight line D_A= -0.09W_AIf it is larger than the value calculated from +15 (D_A> −0.09W_A+15) Since the reactivity of the positive electrode active material is reduced due to the reduction in the specific surface area of the particles A, the discharge load characteristics of the secondary battery are reduced.
[0032]
Median diameter D of particle B_BThe reason why (μm) is limited within the range of the formula (2) will be described. The blending amount (weight%) of the particles A is 0 <W_AWhen it is within the range of <77.8, the median diameter D of the particles B_BStraight line D_B= 0.04W_AIf it is smaller than the value calculated from +1 (D_B<0.04W_A+1) Since the thermal stability of the positive electrode active material decreases due to an increase in the specific surface area of the particles B, the probability of causing smoke or ignition in the nail penetration test increases. On the other hand, the blending amount (weight%) of the particles A is 0 <W_AWhen it is within the range of <77.8, the median diameter D of the particles B_BStraight line D_B= -0.06W_AWhen larger than the value calculated from +20 (D_B> −0.06W_A+20) Since the reactivity of the positive electrode active material decreases due to the decrease in the specific surface area of the particles B, it becomes difficult to improve the discharge load characteristics of the secondary battery.
[0033]
As in the present invention, the blending amount W of the particles A_A(Wt%) 0 <W_A<77.8 and median diameter D of particle A_A(Μm) is within the range of the formula (1), and the median diameter D of the particle B_BBy making (μm) within the range of the above formula (2), the relationship between the mixing ratio of the particles A and B and the median diameter can be optimized, so the discharge load characteristics of the non-aqueous electrolyte secondary battery can be reduced. Can be improved. At the same time, smoke and fire in the nail penetration test can be suppressed, and the safety of the nonaqueous electrolyte secondary battery can be improved.
[0034]
Further, by adding a small amount of Sn to the particle A, the particle B, or both of the particles A and B, a side reaction between the positive electrode active material and the nonaqueous electrolyte in a high temperature environment (particularly, the positive electrode active material and γ-butyrolactone) Therefore, the positive electrode active material having excellent discharge load characteristics, safety and high temperature storage characteristics can be realized. In particular, when the particles B contain a small amount of Sn, the high-temperature storage characteristics can be further enhanced.
[0035]
Hereinafter, the nonaqueous electrolyte battery according to the present invention will be described.
[0036]
The nonaqueous electrolyte battery according to the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte layer disposed between the positive electrode and the negative electrode.
[0037]
1) Positive electrode
The positive electrode includes a current collector and a positive electrode active material-containing layer that is formed on one or both sides of the current collector and contains a positive electrode active material.
[0038]
This positive electrode is produced, for example, by suspending a positive electrode active material, a conductive agent and a binder in an appropriate solvent, applying the obtained suspension to the surface of the current collector, drying, and pressing. .
[0039]
As the positive electrode active material, the above-described positive electrode active material according to the present invention can be used.
[0040]
Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine-based rubber.
[0041]
Examples of the conductive agent include acetylene black, carbon black, and graphite.
[0042]
The compounding ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 to 95 wt% of the positive electrode active material, 3 to 20 wt% of the conductive agent, and 2 to 7 wt% of the binder.
[0043]
The current collector can be used without particular limitation as long as it is a conductive material, but as the current collector for the positive electrode, it is preferable to use a material that is not easily oxidized during battery reaction, for example, aluminum, stainless steel, Titanium or the like can be used.
[0044]
2) Negative electrode
The negative electrode includes a current collector and a negative electrode layer formed on one side or both sides of the current collector.
[0045]
The negative electrode is produced, for example, by kneading a negative electrode material powder and a binder in the presence of an organic solvent, applying the obtained suspension to a current collector, drying, and pressing.
[0046]
Examples of the negative electrode material include carbonaceous materials that occlude and release lithium ions, metals such as aluminum, magnesium, tin, and silicon, metal oxides, metal sulfides, metal nitrides, and lithium alloys.
[0047]
Examples of the carbonaceous material include graphite or carbonaceous materials such as graphite, coke, carbon fiber, and spherical carbon, thermosetting resin, isotropic pitch, mesophase pitch, mesophase pitch-based carbon fiber, mesophase microspheres, etc. And a mesophase pitch-based carbon fiber is preferable because of its high capacity and charge / discharge cycle characteristics), and a graphite material or a carbonaceous material obtained by heat treatment at 500 to 3000 ° C. In particular, the heat treatment temperature is 2000 ° C. or higher, and the (002) plane spacing d is obtained.₀₀₂It is preferable to use a graphite material having a graphite crystal having a thickness of 0.34 nm or less. A nonaqueous electrolyte secondary battery including a negative electrode containing such a graphite material as a carbonaceous material can greatly improve battery capacity and large current discharge characteristics. The surface spacing d₀₀₂Is more preferably 0.336 nm or less.
[0048]
Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like. Can be used.
[0049]
The mixing ratio of the negative electrode material and the binder is preferably in the range of 90 to 98% by weight of the negative electrode material and 1 to 10% by weight of the binder.
[0050]
As the current collector, any conductive material can be used without any particular limitation. Among them, foil, mesh, punched metal, lath metal, or the like made of copper, stainless steel, or nickel can be used.
[0051]
3) Nonaqueous electrolyte layer
The nonaqueous electrolyte layer can impart ionic conductivity between the positive electrode and the negative electrode.
[0052]
Examples of the non-aqueous electrolyte layer include a separator holding a non-aqueous electrolyte, a gel-like non-aqueous electrolyte layer, a separator holding a gel-like non-aqueous electrolyte, a solid polymer electrolyte layer, and an inorganic solid electrolyte layer. Can be mentioned.
[0053]
As the separator, for example, a porous material can be used. Examples of such a separator include a synthetic resin nonwoven fabric, a polyethylene porous film, and a polypropylene porous film.
[0054]
The nonaqueous electrolytic solution is prepared, for example, by dissolving an electrolyte in a nonaqueous solvent.
[0055]
As the non-aqueous solvent, for example, a non-aqueous solvent mainly composed of a cyclic carbonate such as ethylene carbonate (EC) or propylene carbonate (PC), or a mixed solvent of these cyclic carbonate and a non-aqueous solvent having a viscosity lower than that of the cyclic carbonate. Can be used. Examples of the low-viscosity non-aqueous solvent include linear carbonates (eg, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate), γ-butyrolactone, acetonitrile, methyl propionate, ethyl propionate, cyclic ether (eg, tetrahydrofuran). , 2-methyltetrahydrofuran), and chain ethers (for example, dimethoxyethane, diethoxyethane, etc.). In particular, when a container made of a laminate film including a metal layer and a resin layer is used to reduce the weight and thickness of a secondary battery, or a non-aqueous electrolyte containing γ-butyrolactone is used. And the swelling of the container due to gas generation can be suppressed.
[0056]
A lithium salt is used as the electrolyte. Specifically, lithium hexafluorophosphate (LiPF₆), Lithium borofluoride (LiBF)_Four), Lithium arsenic hexafluoride (LiAsF)₆), Lithium perchlorate (LiClO)_Four), Lithium trifluorometasulfonate (LiCF)_ThreeSO_Three) And the like. In particular, lithium hexafluorophosphate (LiPF₆), Lithium borofluoride (LiBF)_Four) Is a preferred example.
[0057]
The amount of electrolyte dissolved in the non-aqueous solvent is preferably 0.5 to 2 mol / L.
[0058]
The gel-like nonaqueous electrolyte is obtained, for example, by combining a nonaqueous electrolyte and a polymer material. Examples of the polymer material include polymers of monomers such as polyacrylonitrile, polyacrylate, polyvinylidene fluoride (PVdF), polyethylene oxide (PECO), and copolymers with other monomers.
[0059]
The solid polymer electrolyte layer can be obtained, for example, by dissolving an electrolyte in a polymer material and solidifying it. Examples of such a polymer material include polymers of monomers such as polyacrylonitrile, polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), and copolymers with other monomers.
[0060]
Examples of the inorganic solid electrolyte include a ceramic material containing lithium._ThreeN, Li_ThreePO_Four-Li₂S-SiS₂, LiI-Li₂S-SiS₂Glass etc. are mentioned.
[0061]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0062]
  (referenceExample 1)
  Ni of various median diameters_0.8Co_0.2(OH)₂1.00 mol and LiOH.H₂O1.00 mol is uniformly mixed in a mortar and reacted in an oxygen stream at 700 ° C. for 5 hours._0.8Co_0.2O₂The particle | grains A represented by these were obtained. The molar ratio (y / z) of Co and Ni in this particle A is 4.
[0063]
On the other hand, Co with various median diameters₃O₄1.00 mol, Li₂CO₃1.00 mol is uniformly mixed and reacted in the atmosphere at 850 ° C. for 5 hours, and the composition is LiCoO.₂The particle | grains B represented by these were obtained. The molar ratio (y / z) of Co and Ni in this particle B is zero.
[0064]
Among the obtained particles A and particles B, the median diameter D_A, Median diameter D_BWere selected to be 2 μm each. The median diameter D of the particle A_AAnd the median diameter D of the particle B_BIs measured by the method described below.
[0065]
After stirring 0.5 g of the sample in 100 ml of water, ultrasonic dispersion was performed under the condition of 100 W-3 min. Thereafter, the median diameter (50% cumulative frequency particle diameter) was measured using a MICROTRAC II PATICLE-ANALYZER TYPE 7997-10 manufactured by LEEDS & NORTHRUP.
[0066]
Median diameter D_AIs 2 μm particle A and median diameter D_BIs a weight ratio W of particles B of 2 μm_A: W_BWere mixed at 20:80 to obtain a positive electrode active material.
[0067]
A mixture of 90% by weight of the positive electrode active material, 6% by weight of the conductive material, and 4% by weight of the binder is dispersed in a suitable solvent to form a slurry, which is applied to an Al foil, dried, and roller The positive electrode was obtained by compression molding with a press machine and cutting into a predetermined size.
[0068]
Further, N-methyl-2-pyrrolidone in which 6% by weight of polyvinylidene fluoride was dissolved was added to 94% by weight of mesophase pitch-based carbon fiber heat-treated at 3000 ° C. to prepare a mixture slurry. This mixture slurry was applied to a copper foil, dried, and heated and roll pressed to produce a negative electrode.
[0069]
On the other hand, ethylene carbonate (EC) and γ-butyrolactone (GBL) were mixed at a volume ratio of 1: 2. Lithium tetrafluoroborate (LiBF) was added to the obtained mixed solvent._Four) Was dissolved to a concentration of 1.5 mol / L to prepare a non-aqueous electrolyte.
[0070]
An electrode group was prepared by winding a separator made of a polyethylene porous film between the positive electrode and the negative electrode in a spiral shape.
[0071]
After this electrode group was housed in a bottomed cylindrical container, a nonaqueous electrolyte solution was injected and fixed by caulking to assemble a cylindrical nonaqueous electrolyte secondary battery having the structure shown in FIG.
[0072]
That is, as shown in FIG. 2, the bottomed cylindrical container 1 made of, for example, stainless steel has an insulator 2 disposed at the bottom. The electrode group 3 is accommodated in the container 1. The electrode group 3 has a structure in which a belt-like material in which the positive electrode 4, the separator 5, and the negative electrode 6 are laminated in this order is wound in a spiral shape.
[0073]
A non-aqueous electrolyte is accommodated in the container 1. In the upper opening of the container 1, a PTC element 7 having a hole in the center, a safety valve 8 for venting gas, and a hat-shaped positive terminal 9 are arranged. These are caulked and fixed to the upper opening of the container 1 via an insulating gasket 10. One end of the positive electrode lead 11 is connected to the positive electrode 4, and the other end is connected to the PTC element 7. The negative electrode 6 is connected to the container 1 serving as a negative electrode terminal through a negative electrode lead (not shown).
[0074]
  (Example 24,6-9,11-16Reference examples 1, 5, 10And Comparative Examples 1 to 28)
  Compounding amount W of particles A and B_A, W_B, Median diameter D_A, D_BIs set as described in Tables 2 to 3 below, as described above.referenceA cylindrical non-aqueous electrolyte secondary battery having the same configuration as described in Example 1 was assembled.
[0075]
  Example 2 obtained4,6-9,11-16Reference examples 1, 5, 10And about the secondary battery of Comparative Examples 1-28, the discharge load characteristic and the nail penetration test were implemented by the method demonstrated below, and the result is shown in following Table 1-Table 3. FIG.
[0076]
(Discharge load characteristics)
The discharge load characteristic test was performed according to the following procedure.
[0077]
The current value at which the designed capacity of 4.2V to 3.0V of each of the produced secondary batteries was completely discharged in 1 hour was defined as 1C, and the capacity when 1C was discharged was measured. Next, the capacity at the time of discharging at 3 times the current value of 3C was measured, the capacity at the time of 1C discharge was taken as 100%, and the capacity retention rate at the time of 3C discharge was evaluated.
[0078]
(Nail penetration test)
In the nail penetration test, the prepared secondary battery is charged to 4.4 V, fixed to a test device with a 2.5 mmφ nail attached to a hydraulic press machine, and the nail is lowered at a speed of 70 mm / sec. A nail was stabbed into the body and the behavior at that time was investigated.
[0079]
In the table, A to E of the nail penetration test results are as follows: A: All are only leaked, B: Less than half are safety valve operation and leakage, C: More than half are safety valve operation and leakage, D: Less than half of the valves operate as a safety valve, and after leakage, smoke or fire, E: More than half of the valves operate as a safety valve, and after leakage, smoke or fire.
[0080]
Tables 1 to 3 also show each compounding amount W of the particles A._AMedian diameter D_ATolerance (0.09W_A+ 1 ≦ D_A≦ −0.09W_A+15) and each compounding amount W of particle B_BMedian diameter D_BTolerance (0.04W_A+ 1 ≦ D_B≦ −0.06W_A+20).
[0081]
[Table 1]

[0082]
[Table 2]

[0083]
[Table 3]

[0084]
From the results of Tables 1 to 3, the following became clear. Mixing ratio W of particle A and particle B_A: W_BIs constant, the median diameter D of the particle A_AOr median diameter D of particle B_BAs the value increases, the 3C discharge maintenance ratio decreases. Also, the mixing ratio W of the particles A and the particles B_A: W_BIs constant, the median diameter D of the particle A_AOr median diameter D of particle B_BAs becomes smaller, there is a higher probability of smoke or fire.
[0085]
On the other hand, the blending amount W of the particles A_AWhen the median diameter was small, smoke or ignition occurred during the nail penetration test. Therefore, when the median diameter was increased in order to prevent smoke and ignition, the 3C discharge maintenance ratio was significantly lowered.
[0086]
From these results, the compounding amount W of the particles A_AIs preferably less than 77.8 wt%, and from the viewpoint of improving the discharge load characteristics, the median diameter D of the particles A_AFor the straight line D_A= -0.09W_AAn area equal to or smaller than the median diameter calculated by +15, while the median diameter D of the particle B_BFor the straight line D_B= -0.06W_AIt can be seen that it is preferable to select a region equal to or smaller than the median diameter calculated by +20. Furthermore, from the viewpoint of improving safety, the median diameter D of the particles A_AFor the straight line D_A= 0.09W_AA region equal to or larger than the median diameter calculated by +1, while the median diameter D of the particle B_BFor the straight line D_B= 0.04W_AIt can be seen that it is preferable to select a region equal to or larger than the median diameter calculated by +1.
[0087]
  Therefore, the blending amount W of the particles A_A(Wt%) and the amount W of particles B_BIs 0 <W_A<77.8, W_B= 100-W_AThe median diameter D of the particles A_A(Μm) is straight line D_A= 0.09W_A+1 and straight line D_A= -0.09W_AMedian diameter D of particles B included in the region surrounded by +15_B(Μm) is straight line D_B= 0.04W_A+1 and straight line D_B= -0.06W_BBy using the positive electrode active material contained in the region surrounded by +20, it is possible to obtain a battery having both good discharge load characteristics and excellent safety..
[0088]
  (referenceExample 17)
  As particles A, the composition is LiNi_0.8Co_0.2Sn_0.01O₂(LiNi_0.8Co_0.2O₂Li to 1 mol₂SnO_ThreeIs a median diameter D represented by the following formula:_A2 μm particles were prepared. Further, as the particle B, the composition is LiCoO.₂The median diameter D expressed by_B2 μm particles were prepared. The molar ratio (y / z) of Co and Ni in the particle A is 4. On the other hand, the molar ratio (y / z) of Co and Ni in the particle B is zero.
[0089]
In the composition analysis of the particles A, the sample was dissolved in hydrochloric acid and quantified by ICP emission analysis using ICP1200A manufactured by Seiko Instruments Inc.
[0090]
Weight ratio W of particles A and B_A: W_BWere mixed at 20:80 to obtain a positive electrode active material.
[0091]
6 parts by weight of acetylene black as a conductive additive and 3 parts by weight of polytetrafluoroethylene as a binder are added to 100 parts by weight of this positive electrode active material, and these are mixed in a mortar and molded into a sheet shape. And was attached to a SUS mesh to obtain a positive electrode.
[0092]
Li metal was used as a counter electrode and a reference electrode. The counter electrode and the reference electrode were opposed to the positive electrode through a separator. These electrodes were immersed in a nonaqueous electrolytic solution in an electrolytic cell to produce a simulated battery cell. As the non-aqueous electrolyte, lithium tetrafluoroborate (LiBF) was mixed with a non-aqueous solvent in which ethylene carbonate (EC) and γ-butyrolactone (GBL) were mixed at a volume ratio of 1: 2._Four) Was used so that its concentration was 1.5 mol / L.
[0093]
  (referenceExample 18)
  The composition of the particle A is LiNi_0.8Co_0.2Sn_0.002O₂(LiNi_0.8Co_0.2O₂Li to 1 mol₂SnO_Three, Except that the mixture is changed to 0.002 mole ratio).referenceA simulated battery cell was assembled in the same manner as in Example 17.
[0094]
  (referenceExample 19)
  The composition of the particle A is LiNi_0.8Co_0.2Sn_0.1O₂(LiNi_0.8Co_0.2O₂Li to 1 mol₂SnO_Three, Except that the mixture is changed to 0.1)referenceA simulated battery cell was assembled in the same manner as in Example 17.
[0095]
  (referenceExample 20)
  As particles A, the composition is LiNi_0.8Co_0.2O₂The median diameter D expressed by_A2 μm particles were prepared. Further, as the particle B, the composition is LiCoSn._0.04O₂(LiCoO₂Li to 1 mol₂SnO_ThreeIs a median diameter D expressed by the following formula:_B2 μm particles were prepared. The molar ratio (y / z) of Co and Ni in the particle A is 4. On the other hand, the molar ratio (y / z) of Co and Ni in the particle B is zero.
[0096]
Weight ratio W of particles A and B_A: W_BWere mixed at 20:80 to obtain a positive electrode active material.
[0097]
  Except for using such a positive electrode active material, as described above.referenceA simulated battery cell was assembled in the same manner as in Example 17.
[0098]
  (referenceExample 1-2)
  Mentioned abovereferenceAs described above, except that a positive electrode active material similar to that described in Example 1 is used.referenceA simulated battery cell was assembled in the same manner as in Example 17.
[0099]
  ObtainedreferenceExamples 17-20 andreferenceIn order to make the simulated cell of Example 1-2 in a uniform electrode impregnation state, charge and discharge was performed at 3.0 V to 4.2 V and 3 mA for 2 cycles, and then charged at 20 ° C., 3 mA and 4.2 V. After carrying out AC impedance measurement, it was stored at 45 ° C. for a certain period of time, and AC impedance measurement was carried out again to examine the state of impedance rise. The results are shown in FIGS. The vertical axis in FIG. 3 indicates the imaginary component of the AC impedance of the battery, and the horizontal axis indicates the real component.
[0100]
FIG. 4 is an enlarged view of a main part of FIG.
[0101]
  As apparent from FIGS. 3 and 4, Sn is contained in the particles A or B.referenceExample 17 ~referenceAccording to the battery of Example 20, Sn was not added.referenceCompared to Example 1-2, the increase in impedance when stored at a high temperature of 45 ° C. was moderate.referenceEven if the Sn content in the particles is very small as in Example 18, no Sn was added.referenceA sufficient effect of 1/3 or less compared to Example 1-2 is observed. Moreover, even if the addition amount of Sn is increased or the same addition amountreferenceWhen Sn is contained in the particle B as in Example 20, the effect is further increased.
[0102]
In the above-described embodiment, the example applied to the positive electrode active material composed of the two types of particles A and B has been described. As the positive electrode active material, as long as both discharge load characteristics and safety can be satisfied, LiNiO on particles A and B₂Those composed of three or more kinds of particles in which other kinds of particles are mixed can be used.
[0103]
Further, in the above-described embodiments, the example applied to the cylindrical nonaqueous electrolyte secondary battery has been described. However, the prismatic nonaqueous electrolyte secondary battery, the thin nonaqueous electrolyte secondary battery, and the coin type nonaqueous electrolyte secondary battery are described. It can be similarly applied to. In the above-described embodiments, a metal container is used as a container for storing an electrode group. However, the present invention can be similarly applied to a battery including a laminate film container containing a metal layer and a resin layer. .
[0104]
【The invention's effect】
  As described above in detail, according to the present invention, a positive electrode active material capable of achieving both smoke suppression and ignition suppression during the nail penetration test and an improvement in discharge load characteristics, and a non-positive electrode provided with the positive electrode active material are provided. A water electrolyte battery can be provided.
[Brief description of the drawings]
FIG. 1 is a characteristic diagram showing the relationship between the blending amount and particle size of particles A and B contained in a positive electrode active material according to the present invention.
FIG. 2 is a partially cutaway perspective view showing a cylindrical nonaqueous electrolyte secondary battery which is an example of a nonaqueous electrolyte battery according to the present invention.
[Fig. 3]referenceExamples 17-20 andreferenceThe characteristic view which shows the internal impedance change by the high temperature storage about the simulation cell of Example 1-2.
4 is an enlarged view showing a main part of FIG. 3. FIG.
[Explanation of symbols]
  1 ... container,
  3 ... Electrode group,
  4 ... positive electrode,
  6 ... negative electrode,
  5 ... separator,
  7: PTC element,
  8 ... Safety valve,
  9: Positive terminal,
  10: Insulating gasket.

Claims (6)

Formula _{Li x Ni y Co z Sn w} O 2 ( where the molar ratio x, y, z and w, 0.95 ≦ x ≦ 1.05,0.85 ≦ y + z ≦ 1,0 ≦ w ≦ 0. 1 and satisfying x + y + z + w = 2), the ratio of Ni to Co in the particle A (y / z) is 7/3 or more, and in the particle B The ratio of Ni to Co (y / z) is 3/7 or less (including 0),
The median diameter D _A (μm) of the particle A satisfies the following formula (1), and the median diameter D _B (μm) of the particle B satisfies the following formula (2) :
The positive electrode active material wherein the median diameter D _A and the median diameter D _B is characterized der Rukoto than 5 [mu] m.
0.09W _A + 1 ≦ D _A ≦ −0.09 W _A +15 (1)
0.04W _A + 1 ≦ D _B ≦ −0.06 W _A +20 (2)
However, the _{W A,} the amount of particles A _(weight%), satisfy 0 <W A <77.8. The positive electrode active material according to claim 1, wherein the (y / z) of the particle A is 7/3 or more and 9/1 or less . 3. The positive electrode active according to claim 1, wherein the Sn molar ratio w of the particles A is 0 and the Sn molar ratio w of the particles B is in a range of 0 <w ≦ 0.1. material. The positive electrode active material according to claim 3 , wherein the molar ratio w of the particles B is 0.01 ≦ w ≦ 0.05 . The positive electrode active material according to claim 1, wherein the molar ratio x of the particles A and the particles B is 0.99 ≦ x ≦ 1.03. A nonaqueous electrolyte battery comprising a positive electrode containing the positive electrode active material according to claim 1, a negative electrode, and a nonaqueous electrolyte.

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