JP2019050098A - Cathode for nonaqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery - Google Patents
Cathode for nonaqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery Download PDFInfo
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Abstract
Description
本開示は、非水電解質二次電池用正極、及び非水電解質二次電池に関する。 The present disclosure relates to a positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.
正極活物質として、層状リチウム金属複合酸化物を用いた非水電解質二次電池が広く知られている。例えば、特許文献1には、表面増強ラマン分光スペクトルにおいて、800cm−1以上、1000cm−1以下にピークを有するリチウム金属複合酸化物を正極活物質とする非水電解質二次電池が開示されている。また、特許文献1には、正極の導電材として、窒素吸着比表面積が70m2/g以上、300m2/g以下、かつ平均粒径が10nm以上、35nm以下であるカーボンブラックを用いることが開示されている。 A nonaqueous electrolyte secondary battery using a layered lithium metal composite oxide is widely known as a positive electrode active material. For example, Patent Document 1 discloses a surface enhanced Raman spectrum, 800 cm -1 or more, the lithium metal composite oxide is non-aqueous electrolyte secondary battery that the cathode active material is disclosed having a peak at 1000 cm -1 or less . Patent Document 1 discloses that carbon black having a nitrogen adsorption specific surface area of 70 m 2 / g or more and 300 m 2 / g or less and an average particle diameter of 10 nm or more and 35 nm or less is used as a conductive material of the positive electrode. Has been.
ところで、層状リチウム金属複合酸化物を用いた非水電解質二次電池において、正極の合剤層の充填密度が低い場合、合剤層内の空隙に電解液が十分に含浸されるため、容量確保は可能であるが、活物質の粒子間距離が長くなり、放電時の抵抗が大きくなり易い。一方、合剤層の充填密度が高い場合、抵抗は小さくなるが、合剤層中の電解液の量が不足して、容量が低下する虞があった。 By the way, in a non-aqueous electrolyte secondary battery using a layered lithium metal composite oxide, if the packing density of the mixture layer of the positive electrode is low, the space in the mixture layer is sufficiently impregnated with the electrolyte solution, ensuring the capacity. However, the distance between the particles of the active material becomes long, and the resistance during discharge tends to increase. On the other hand, when the packing density of the mixture layer is high, the resistance decreases, but the amount of the electrolyte in the mixture layer is insufficient, and the capacity may be reduced.
本開示の目的は、電池容量を十分に確保でき、かつ内部抵抗が低く、良好なハイレート特性を有する非水電解質二次電池を実現可能な正極を提供することである。 The objective of this indication is providing the positive electrode which can implement | achieve the nonaqueous electrolyte secondary battery which can fully ensure battery capacity, has low internal resistance, and has a favorable high-rate characteristic.
本開示に係る非水電解質二次電池用正極は、層状のリチウム金属複合酸化物と、導電材とを含む正極合剤層を有し、前記正極合剤層の単位体積当たりに含まれる前記導電材の比表面積の合計が20m2/cm3以上であり、かつ前記正極合剤層の充填密度が2.2g/cm3以上であることを特徴とする。 The positive electrode for a non-aqueous electrolyte secondary battery according to the present disclosure has a positive electrode mixture layer including a layered lithium metal composite oxide and a conductive material, and the conductive material included per unit volume of the positive electrode mixture layer. The total specific surface area of the material is 20 m 2 / cm 3 or more, and the packing density of the positive electrode mixture layer is 2.2 g / cm 3 or more.
本開示に係る非水電解質二次電池は、上記正極と、負極合剤層を有する負極と、前記正極と前記負極との間に介在するセパレータとで構成される電極体と、非水電解質とを備えることを特徴とする。 A nonaqueous electrolyte secondary battery according to the present disclosure includes an electrode body including the positive electrode, a negative electrode having a negative electrode mixture layer, a separator interposed between the positive electrode and the negative electrode, a nonaqueous electrolyte, It is characterized by providing.
本開示に係る非水電解質二次電池用正極によれば、合剤層の充填密度が低い場合でも、通電経路を確保でき、抵抗を低く抑えることができる。このため、電池容量が高く、内部抵抗の低い非水電解質二次電池を提供できる。また、合剤層の充填密度が高い場合でも、導電材の表面により多くの電解液を保持することができる。そのため、導電材を介して極板内の電解液を優先的に活物質の表面に導くことができる。そのため、活物質近傍における電解液の不足を抑制することができ、容量低下を抑えることができる。高容量、低抵抗を両立した非水電解質二次電池が得られる。 According to the positive electrode for a nonaqueous electrolyte secondary battery according to the present disclosure, even when the packing density of the mixture layer is low, an energization path can be secured and the resistance can be suppressed low. For this reason, a nonaqueous electrolyte secondary battery having a high battery capacity and a low internal resistance can be provided. Further, even when the packing density of the mixture layer is high, more electrolytic solution can be held on the surface of the conductive material. Therefore, the electrolytic solution in the electrode plate can be preferentially guided to the surface of the active material through the conductive material. Therefore, the shortage of the electrolytic solution in the vicinity of the active material can be suppressed, and a decrease in capacity can be suppressed. A non-aqueous electrolyte secondary battery having both high capacity and low resistance can be obtained.
上述のように、従来の非水電解質二次電池用正極では、合剤層の充填密度が低い場合、活物質粒子間の空間が広いので、合剤層内の保液性が良好である。そのため、電池容量を十分に確保できる。しかし、活物質の粒子間距離が長く、通電経路が少ないので、抵抗が高い。一方で、合剤層の充填密度が高い場合は、通電経路は確保できるものの、合剤層内の電解液量が少ない、そのため十分な容量を確保できない。つまり、両方の場合において、容量確保と低抵抗の両立は困難である。 As described above, in the conventional positive electrode for a nonaqueous electrolyte secondary battery, when the packing density of the mixture layer is low, the space between the active material particles is wide, so that the liquid retention in the mixture layer is good. Therefore, a sufficient battery capacity can be secured. However, the resistance is high because the distance between the particles of the active material is long and there are few energization paths. On the other hand, when the packing density of the mixture layer is high, an energization path can be secured, but the amount of the electrolyte in the mixture layer is small, so that a sufficient capacity cannot be secured. That is, in both cases, it is difficult to ensure both capacitance and low resistance.
これに対して、本開示に係る非水電解質二次電池用正極(以下、正極とも記載する)を用いた非水電解質二次電池は、電池容量を十分に確保でき、かつ内部抵抗が低い。そのため、良好なハイレート特性を有する。本開示に係る正極では、正極合剤層内の単位体積当りの導電材の比表面積の合計が20m2/cm3以上と高いため、導電材どうし、又は導電材と活物質粒子との接触面積が大きくなり易い。このため、合剤層の充填密度が低くても通電経路を確保でき、抵抗を低減することが可能になると考えられる。また、合剤層の充填密度が高い場合も、正極合剤層内の導電材の比表面積の合計を20m2/cm3以上とすることで、電解液を活物質の粒子表面に導くことが可能となり、容量低下を抑えることができると考えられる。なお、この導電材の比表面積の合計(m2/cm3)は、導電材の比表面積(m2/g)と、合剤層の充填密度(g/cm3)と、合剤層における導電材の添加量(質量%)から算出される。なお、上記導電材の添加量は、活物質に対する導電材の質量比率(a質量%)から算出する場合、活物質に対する結着材(バインダ)の添加量(b質量%)を用いて、活物質と導電材と結着材との配合比(100:a:b)を算出し、a/(100+a+b)として算出することができる。 In contrast, a non-aqueous electrolyte secondary battery using a positive electrode for a non-aqueous electrolyte secondary battery according to the present disclosure (hereinafter also referred to as a positive electrode) can sufficiently ensure battery capacity and has low internal resistance. Therefore, it has a good high rate characteristic. In the positive electrode according to the present disclosure, since the total specific surface area of the conductive material per unit volume in the positive electrode mixture layer is as high as 20 m 2 / cm 3 or more, the contact area between the conductive materials or between the conductive material and the active material particles Tends to be large. For this reason, even if the packing density of the mixture layer is low, it is considered that the energization path can be secured and the resistance can be reduced. Moreover, even when the packing density of the mixture layer is high, the electrolyte solution can be guided to the particle surface of the active material by setting the total specific surface area of the conductive material in the positive electrode mixture layer to 20 m 2 / cm 3 or more. It is possible to suppress the decrease in capacity. The total specific surface area (m 2 / cm 3 ) of the conductive material is the specific surface area (m 2 / g) of the conductive material, the packing density (g / cm 3 ) of the mixture layer, and the mixture layer. It is calculated from the added amount (% by mass) of the conductive material. In addition, when the addition amount of the conductive material is calculated from the mass ratio (a mass%) of the conductive material to the active material, the addition amount (b mass%) of the binder (binder) to the active material is used. The compounding ratio (100: a: b) of the substance, the conductive material and the binder can be calculated and calculated as a / (100 + a + b).
なお、正極の合剤層の充填密度が高くなると、合剤の塗布部と非塗布部で圧延時の伸び率の違いに起因してシワが生じ、このシワが集電体の表面上の凹凸になる虞がある。そして、このシワによって、合剤層と集電体との間における集電性を低下させる虞がある。その影響度合いは、圧延ロールの径や圧延手法により様々である。このため、充填密度の上限値は圧延の手法等により異なる。充填密度の上限の一例は、3.8g/cm3である。また、正極合剤層の充填密度が2.2g/cm3より低い場合、特に抵抗が著しく増大し、本開示における導電材の効果も得られにくくなる。さらに、充填密度が2.2g/cm3より低い場合、充填密度の変化に対する抵抗の変動が大きくなることから、同一の電池を連続的に作製しようとしても、各電池において、少しの充填密度の違いで電池の特性が変動してしまう虞がある。上記のことから、本開示の正極では、合剤層の2.2g/cm3以上であることが好ましい。 In addition, when the packing density of the mixture layer of the positive electrode is increased, wrinkles occur due to the difference in elongation at rolling between the coated portion and the non-coated portion of the mixture, and the wrinkles are uneven on the surface of the current collector. There is a risk of becoming. And this wrinkle may reduce the current collecting property between the mixture layer and the current collector. The degree of influence varies depending on the diameter of the rolling roll and the rolling technique. For this reason, the upper limit value of the packing density varies depending on the rolling method and the like. An example of the upper limit of the packing density is 3.8 g / cm 3 . In addition, when the packing density of the positive electrode mixture layer is lower than 2.2 g / cm 3 , the resistance is particularly increased, and the effect of the conductive material in the present disclosure is hardly obtained. Further, when the packing density is lower than 2.2 g / cm 3 , the resistance variation with respect to the change in the packing density becomes large. Therefore, even if the same battery is continuously manufactured, each battery has a small packing density. There is a possibility that the characteristics of the battery may fluctuate due to the difference. From the above, in the positive electrode of the present disclosure, it is preferably 2.2 g / cm 3 or more of the mixture layer.
本実施形態に係る非水電解質二次電池において、負極活物質は特に限定されないが、好適な一例は、チタン酸リチウムに代表されるリチウムチタン複合酸化物である。負極にリチウムチタン複合酸化物を用いた場合、リチウムイオンが出入する際の障害となり得る表面被膜(SEI被膜)が形成されなくなるため、電池のハイレート特性が向上する。また、リチウムチタン複合酸化物は、充放電に伴う体積変化が小さいため、電池のサイクル特性が向上する。ゆえに、抵抗増大等の電池性能の劣化は、正極材料の劣化の影響を受け易くなる。本開示に係る正極は、導電性及び保液性に優れるため、正極材料が劣化し難いという特徴がある。即ち、本開示に係る正極と、リチウムチタン複合酸化物を用いた負極との組み合わせは、電池の容量、ハイレート特性、及び耐久性の向上に大きく寄与する。 In the nonaqueous electrolyte secondary battery according to this embodiment, the negative electrode active material is not particularly limited, but a suitable example is a lithium titanium composite oxide typified by lithium titanate. When a lithium-titanium composite oxide is used for the negative electrode, a surface coating (SEI coating) that can be an obstacle when lithium ions enter and exit is not formed, so that the high-rate characteristics of the battery are improved. Moreover, since the lithium titanium complex oxide has a small volume change accompanying charging / discharging, the cycle characteristics of the battery are improved. Therefore, deterioration of battery performance such as increased resistance is easily affected by deterioration of the positive electrode material. Since the positive electrode according to the present disclosure is excellent in conductivity and liquid retention, the positive electrode material is not easily deteriorated. That is, the combination of the positive electrode according to the present disclosure and the negative electrode using the lithium-titanium composite oxide greatly contributes to improvement of battery capacity, high rate characteristics, and durability.
図1は、実施形態の一例である非水電解質二次電池10を示す図である。図1では、角形の電池ケース11を備えた角形電池である非水電解質二次電池10を示している。但し、本開示に係る非水電解質二次電池は、角形電池に限定されず、円筒形、コイン形等の金属製ケースを備えた円筒形電池、コイン形電池等であってもよく、樹脂フィルムによって構成される樹脂製ケースを備えた所謂ラミネート電池であってもよい。また、図1では、電極体は帯状の正極と帯状の負極がセパレータを介して渦巻き状に捲回されてなる捲回式の電極体14を例示するが、複数の正極と複数の負極とをセパレータを介して積層した積層型の電極体であってもよい。 FIG. 1 is a diagram illustrating a nonaqueous electrolyte secondary battery 10 which is an example of an embodiment. FIG. 1 shows a non-aqueous electrolyte secondary battery 10 that is a square battery including a square battery case 11. However, the non-aqueous electrolyte secondary battery according to the present disclosure is not limited to a rectangular battery, and may be a cylindrical battery, a coin-shaped battery, or the like provided with a metal case such as a cylindrical shape or a coin shape. A so-called laminate battery provided with a resin case constituted by: In FIG. 1, the electrode body exemplifies a wound electrode body 14 in which a strip-shaped positive electrode and a strip-shaped negative electrode are spirally wound via a separator, but a plurality of positive electrodes and a plurality of negative electrodes are combined. A laminated electrode body laminated via a separator may also be used.
図1に例示するように、非水電解質二次電池10は、電池ケース11と、当該ケース内に収容された電極体14とを備える。また、電池ケース11内には、非水電解質(図示せず)が充填されている。電池ケース11は、有底筒状のケース本体12と、当該本体の開口部を塞ぐ封口板13とで構成される角形の金属製ケースである。電極体14は、正極15と、負極16と、正極15と負極16との間に介在するセパレータ17とで構成される。図1に例示する電極体14は、帯状の正極15と、帯状の負極16がセパレータ17を介して交互に積層された積層構造を有する。 As illustrated in FIG. 1, the nonaqueous electrolyte secondary battery 10 includes a battery case 11 and an electrode body 14 accommodated in the case. Further, the battery case 11 is filled with a non-aqueous electrolyte (not shown). The battery case 11 is a rectangular metal case including a bottomed cylindrical case main body 12 and a sealing plate 13 that closes an opening of the main body. The electrode body 14 includes a positive electrode 15, a negative electrode 16, and a separator 17 interposed between the positive electrode 15 and the negative electrode 16. The electrode body 14 illustrated in FIG. 1 has a stacked structure in which strip-shaped positive electrodes 15 and strip-shaped negative electrodes 16 are alternately stacked via separators 17.
非水電解質二次電池10は、正極15と電気的に接続された正極端子18と、負極16と電気的に接続された負極端子19とを備える。図1に示す例では、正極端子18が封口板13で構成される電池ケース11の上面部の長手方向一端側に設けられ、負極端子19が当該上面部の長手方向他端側に設けられている。なお、非水電解質二次電池10には、電極と端子とを接続する導電性部材が設けられていてもよい。 The nonaqueous electrolyte secondary battery 10 includes a positive electrode terminal 18 that is electrically connected to the positive electrode 15 and a negative electrode terminal 19 that is electrically connected to the negative electrode 16. In the example shown in FIG. 1, the positive electrode terminal 18 is provided on one end side in the longitudinal direction of the upper surface portion of the battery case 11 constituted by the sealing plate 13, and the negative electrode terminal 19 is provided on the other end side in the longitudinal direction of the upper surface portion. Yes. The nonaqueous electrolyte secondary battery 10 may be provided with a conductive member that connects the electrode and the terminal.
以下、非水電解質二次電池10の各構成要素について詳説する。 Hereinafter, each component of the nonaqueous electrolyte secondary battery 10 will be described in detail.
[正極]
図2は、正極11の断面の一部を示す図であって、(a)は正極合剤層21の充填密度が低い場合を、(b)は正極合剤層21の充填密度が高い場合をそれぞれ示す。図2に例示するように、正極11は、帯状の正極集電体20と、当該集電体上に形成された正極合剤層21とを有する。正極集電体20には、アルミニウムなどの正極11の電位範囲で安定な金属の箔、当該金属を表層に配置したフィルム等を用いることができる。
[Positive electrode]
FIG. 2 is a diagram illustrating a part of the cross section of the positive electrode 11, where (a) shows a case where the packing density of the positive electrode mixture layer 21 is low, and (b) shows a case where the packing density of the positive electrode mixture layer 21 is high. Respectively. As illustrated in FIG. 2, the positive electrode 11 includes a strip-shaped positive electrode current collector 20 and a positive electrode mixture layer 21 formed on the current collector. For the positive electrode current collector 20, a metal foil that is stable in the potential range of the positive electrode 11 such as aluminum, a film in which the metal is disposed on the surface layer, or the like can be used.
正極合剤層21は、リチウム金属複合酸化物22と、導電材23とを含み、正極集電体20の両面に形成される。また、正極合剤層21は、リチウム金属複合酸化物22及び導電材23を結着して層を形成する結着材を含む。リチウム金属複合酸化物22は、正極活物質として機能する。正極11は、正極集電体20上に正極活物質、導電材23、結着材等を含む正極合剤スラリーを塗布し、塗膜を乾燥させた後、圧延して正極合剤層21を正極集電体20の両面に形成することにより作製できる。 The positive electrode mixture layer 21 includes a lithium metal composite oxide 22 and a conductive material 23, and is formed on both surfaces of the positive electrode current collector 20. The positive electrode mixture layer 21 includes a binder that binds the lithium metal composite oxide 22 and the conductive material 23 to form a layer. The lithium metal composite oxide 22 functions as a positive electrode active material. In the positive electrode 11, a positive electrode mixture slurry containing a positive electrode active material, a conductive material 23, a binder, and the like is applied onto the positive electrode current collector 20, the coating film is dried, and then rolled to form a positive electrode mixture layer 21. It can be produced by forming on both surfaces of the positive electrode current collector 20.
リチウム金属複合酸化物22は、例えば、一般式Li1+xMaO2+b(式中、x+a=1、−0.2<x≦0.2、−0.1≦b≦0.1であり、MはNi、Co、Mn、及びAlから選択される少なくとも1種を含む)で表される複合酸化物である。正極活物質として、他のリチウム金属複合酸化物等が少量含まれていてもよいが、上記一般式で表されるリチウム金属複合酸化物22を主成分とすることが好ましい。 The lithium metal composite oxide 22 is, for example, a general formula Li 1 + x M a O 2 + b (where, x + a = 1, −0.2 <x ≦ 0.2, −0.1 ≦ b ≦ 0.1, M is a composite oxide represented by (including at least one selected from Ni, Co, Mn, and Al). The positive electrode active material may contain a small amount of other lithium metal composite oxides and the like, but it is preferable that the main component is lithium metal composite oxide 22 represented by the above general formula.
リチウム金属複合酸化物22は、Ni、Co、Mn、及びAl以外の他の元素を含んでいてもよい。他の元素としては、例えばLi以外のアルカリ金属元素、Ni、Co、Mn以外の遷移金属元素、アルカリ土類金属元素、第12族元素、Al以外の第13族元素、並びに第14族元素が挙げられる。具体的には、Zr、B、Mg、Ti、Fe、Cu、Zn、Sn、Na、K、Ba、Sr、Ca、W、Mo、Nb、Si等が例示できる。 The lithium metal composite oxide 22 may contain elements other than Ni, Co, Mn, and Al. Examples of other elements include alkali metal elements other than Li, transition metal elements other than Ni, Co, and Mn, alkaline earth metal elements, Group 12 elements, Group 13 elements other than Al, and Group 14 elements. Can be mentioned. Specific examples include Zr, B, Mg, Ti, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Si, and the like.
リチウム金属複合酸化物22の粒径は、特に限定されないが、例えば平均粒径が2μm以上30μm未満であることが好ましい。平均粒径が2μm未満である場合、正極合剤層21内の導電材23による通電を阻害して抵抗増加する場合がある。一方、平均粒径が30μm以上である場合、反応面積の低下により、負荷特性が低下する場合がある。平均粒径とは、レーザ回折法によって測定される体積平均粒径であって、粒子径分布において体積積算値が50%となるメジアン径を意味する。平均粒径は、例えば、レーザ回折散乱式粒度分布測定装置(株式会社堀場製作所製)を用いて測定できる。正極活物質の比表面積は、0.1m2/g以上、7m2/g以下であることが好ましい。比表面積が0.1m2/gより低くなると抵抗が高く、比表面積が7m2/gを超えると、スラリーの流動性が低下するためである。 The particle size of the lithium metal composite oxide 22 is not particularly limited, but for example, the average particle size is preferably 2 μm or more and less than 30 μm. When the average particle size is less than 2 μm, there is a case where resistance increases due to obstruction of energization by the conductive material 23 in the positive electrode mixture layer 21. On the other hand, when the average particle size is 30 μm or more, the load characteristics may be reduced due to a reduction in the reaction area. The average particle diameter is a volume average particle diameter measured by a laser diffraction method, and means a median diameter at which the volume integrated value is 50% in the particle diameter distribution. The average particle diameter can be measured using, for example, a laser diffraction / scattering particle size distribution measuring apparatus (manufactured by Horiba, Ltd.). The specific surface area of the positive electrode active material is preferably 0.1 m 2 / g or more and 7 m 2 / g or less. When the specific surface area is lower than 0.1 m 2 / g, the resistance is high, and when the specific surface area exceeds 7 m 2 / g, the fluidity of the slurry is lowered.
導電材23として、例えばカーボンブラック、アセチレンブラック、ケッチェンブラック、黒鉛等の炭素材料を用いることができる。これらは、単独で用いてもよく、2種類以上を組み合わせて用いてもよい。導電材23の電気伝導率は、0.1Ω・cm以上、0.3Ω・cm以下であることが好ましい。導電材23の電気伝導率が0.1Ω・cmより低い場合、十分に正極合剤層内の抵抗を低減できず、導電材23の電気伝導率が0.3Ω・cmを超えた場合、正極合剤層内における抵抗低減効果は飽和するからである。 As the conductive material 23, for example, a carbon material such as carbon black, acetylene black, ketjen black, or graphite can be used. These may be used alone or in combination of two or more. The electrical conductivity of the conductive material 23 is preferably 0.1 Ω · cm or more and 0.3 Ω · cm or less. When the electrical conductivity of the conductive material 23 is lower than 0.1 Ω · cm, the resistance in the positive electrode mixture layer cannot be sufficiently reduced, and when the electrical conductivity of the conductive material 23 exceeds 0.3 Ω · cm, This is because the resistance reduction effect in the mixture layer is saturated.
導電材23の好適な一例は、比表面積が30〜140m2/gの炭素材料である。導電材23の比表面積が30m2/gより低い場合、導電材23の添加量を多くする必要があり、正極合剤スラリー中での分散性が低下する。この場合、正極合剤層21に反応斑が生じ、電池性能が低下する可能性がある。一方、比表面積が140m2/gを超える場合、正極合剤スラリーの粘度が高くなって塗工性が低下し、均質な正極合剤層21を形成することが難しくなる。また、導電材23の平均一次粒子径は、例えば10nm以上、50nm以下である。 A suitable example of the conductive material 23 is a carbon material having a specific surface area of 30 to 140 m 2 / g. When the specific surface area of the conductive material 23 is lower than 30 m 2 / g, it is necessary to increase the amount of the conductive material 23 added, and the dispersibility in the positive electrode mixture slurry is lowered. In this case, reaction spots are generated in the positive electrode mixture layer 21, and the battery performance may be deteriorated. On the other hand, when the specific surface area exceeds 140 m 2 / g, the viscosity of the positive electrode mixture slurry is increased, the coating property is lowered, and it becomes difficult to form the homogeneous positive electrode mixture layer 21. Moreover, the average primary particle diameter of the electrically conductive material 23 is 10 nm or more and 50 nm or less, for example.
なお、導電材23の配合比率は、活物質の質量に対して3質量%以上、15質量%以下であることが好ましい。これは、導電材23の配合比率が3質量%を下回ると正極合剤層内の抵抗が増加し、導電材の配合比率が15質量%を超えるとスラリー性状が安定しないためである。 In addition, it is preferable that the mixture ratio of the electrically conductive material 23 is 3 mass% or more and 15 mass% or less with respect to the mass of an active material. This is because when the blending ratio of the conductive material 23 is less than 3% by mass, the resistance in the positive electrode mixture layer increases, and when the blending ratio of the conductive material exceeds 15% by mass, the slurry properties are not stable.
正極11では、正極合剤層21の単位体積当たりに含まれる導電材23の比表面積の合計が20m2/cm3以上であり、かつ正極合剤層21の充填密度が2.2m2/cm3以上である。この条件を満たすことで、電池容量を十分に確保でき、かつ内部抵抗が低く、良好なハイレート特性を有する非水電解質二次電池10が得られる。ここで、正極合剤層21の単位体積当たりに含まれる導電材23の比表面積の合計は、導電材23の比表面積、及び導電材23の含有量から算出できる。導電材23の比表面積は、窒素吸脱着によるBET比表面積測定装置を用いてBET法により測定できる。また、正極合剤層21の充填密度は、測定された電極合剤層の厚さ及び集電体の厚さとそれらの質量から見積もられる。 In the positive electrode 11, the total specific surface area of the conductive material 23 contained per unit volume of the positive electrode mixture layer 21 is 20 m 2 / cm 3 or more, and the packing density of the positive electrode mixture layer 21 is 2.2 m 2 / cm. 3 or more. By satisfying this condition, it is possible to obtain the nonaqueous electrolyte secondary battery 10 having a sufficient battery capacity, low internal resistance, and good high rate characteristics. Here, the total specific surface area of the conductive material 23 contained per unit volume of the positive electrode mixture layer 21 can be calculated from the specific surface area of the conductive material 23 and the content of the conductive material 23. The specific surface area of the conductive material 23 can be measured by the BET method using a BET specific surface area measuring device by nitrogen adsorption / desorption. The packing density of the positive electrode mixture layer 21 is estimated from the measured thickness of the electrode mixture layer, the thickness of the current collector, and their mass.
正極合剤層21の充填密度の上限は、特に限定されないが、好適な一例としては3.8g/cm3である。正極合剤層21の充填密度は、例えば2.2g/cm3以上、3.8g/cm3の範囲に設定される。上述のように、正極合剤層21の充填密度が3.8g/cm3より高くなると、正極合剤の塗布部と非塗布部で圧延時の伸び率の違いに起因してシワが生じ易くなる。このシワが集電体の表面上の凹凸になる虞がある。そして、このシワによって、合剤層と集電体との間における集電性を低下させる虞がある。一方、正極合剤層21の充電密度が2.2g/cm3より低い場合、正極活物質の粒子間の距離が長すぎて導電パスを十分に確保できないことによる影響が大きくなり、本開示の導電材の影響が小さい。そのため、充填密度が2.2g/cm3より低い正極合剤層は、抵抗が著しく増大する。 The upper limit of the packing density of the positive electrode mixture layer 21 is not particularly limited, but a suitable example is 3.8 g / cm 3 . Packing density of the positive electrode mixture layer 21, for example 2.2 g / cm 3 or more, is set in the range of 3.8 g / cm 3. As described above, when the packing density of the positive electrode mixture layer 21 is higher than 3.8 g / cm 3 , wrinkles are likely to occur due to the difference in elongation at rolling between the coated portion and the non-coated portion of the positive electrode mixture. Become. The wrinkles may become uneven on the surface of the current collector. And this wrinkle may reduce the current collecting property between the mixture layer and the current collector. On the other hand, when the charge density of the positive electrode mixture layer 21 is lower than 2.2 g / cm 3, the influence due to the fact that the distance between the particles of the positive electrode active material is too long and a sufficient conductive path cannot be secured increases. The effect of conductive material is small. Therefore, the resistance of the positive electrode mixture layer having a packing density lower than 2.2 g / cm 3 is remarkably increased.
図2(a)に例示するように、正極合剤層21の充填密度が低い場合(但し、2.2g/cm3以上)であっても、正極合剤層21の単位体積当たりの導電材23の比表面積の合計を20m2/cm3以上とすることで、通電経路を十分に確保できる。これにより、正極11の抵抗を低く抑えることができる。他方、図2(b)に例示するように、正極合剤層21の充填密度が高い場合であっても、正極合剤層21の単位体積当たりの導電材23の比表面積の合計を20m2/cm3以上とすることで、導電材21の内部又は近傍により多くの電解液を保持することができる。そのため、導電材21を介して電解液を正極活物質(リチウム金属複合酸化物22)の粒子表面に導くことができ、容量低下を抑えることができる。 As illustrated in FIG. 2A, the conductive material per unit volume of the positive electrode mixture layer 21 even when the packing density of the positive electrode mixture layer 21 is low (however, 2.2 g / cm 3 or more). By setting the total of the specific surface areas of 23 to 20 m 2 / cm 3 or more, a current-carrying path can be sufficiently secured. Thereby, the resistance of the positive electrode 11 can be kept low. On the other hand, as illustrated in FIG. 2B, even if the packing density of the positive electrode mixture layer 21 is high, the total specific surface area of the conductive material 23 per unit volume of the positive electrode mixture layer 21 is 20 m 2. By setting it to / cm 3 or more, more electrolytic solution can be held in or near the conductive material 21. Therefore, the electrolytic solution can be guided to the particle surface of the positive electrode active material (lithium metal composite oxide 22) through the conductive material 21, and the capacity reduction can be suppressed.
正極合剤層21の単位体積当たりに含まれる導電材23の比表面積の合計の上限は、特に限定されないが、好適な一例としては40m2/cm3である。正極合剤層21における導電材23の比表面積の合計は、例えば20〜40m2/cm3に設定される。なお、導電材23の比表面積の合計が当該範囲内にあればよく、使用する導電材23の比表面積は、上述のように特に限定されない。導電材23の比表面積の合計は、主に、使用する導電材23の比表面積と、その添加量により調製される。 Although the upper limit of the total specific surface area of the conductive material 23 included per unit volume of the positive electrode mixture layer 21 is not particularly limited, a suitable example is 40 m 2 / cm 3 . The total specific surface area of the conductive material 23 in the positive electrode mixture layer 21 is set to 20 to 40 m 2 / cm 3 , for example. In addition, the total of the specific surface area of the electrically conductive material 23 should just be in the said range, and the specific surface area of the electrically conductive material 23 to be used is not specifically limited as mentioned above. The total specific surface area of the conductive material 23 is prepared mainly by the specific surface area of the conductive material 23 to be used and its addition amount.
正極合剤層21に含まれる結着材としては、ポリテトラフルオロエチレン(PTFE)、ポリフッ化ビニリデン(PVdF)等のフッ素樹脂、ポリアクリロニトリル(PAN)、ポリイミド、アクリル樹脂、ポリオレフィン等が例示できる。また、これらの樹脂と、カルボキシメチルセルロース(CMC)又はその塩、ポリエチレンオキシド(PEO)等が併用されてもよい。これらは、単独で用いてもよく、2種類以上を組み合わせて用いてもよい。 Examples of the binder contained in the positive electrode mixture layer 21 include fluorine resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resin, and polyolefin. These resins may be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like. These may be used alone or in combination of two or more.
なお、正極合剤層21に含まれる結着材の配合比率は、正極活物質の質量に対して、1質量%以上、5質量%以下であることが好ましい。この配合比率が1質量%より低い場合、極板から活物質が脱落し易くなる。この配合比率が5質量%を超える場合、正極合剤層内の抵抗又は正極合剤層と集電体との間の抵抗が増加する虞がある。 In addition, it is preferable that the mixture ratio of the binder contained in the positive mix layer 21 is 1 mass% or more and 5 mass% or less with respect to the mass of a positive electrode active material. When this blending ratio is lower than 1% by mass, the active material easily falls off from the electrode plate. When this compounding ratio exceeds 5 mass%, there exists a possibility that the resistance in a positive mix layer or the resistance between a positive mix layer and a collector may increase.
[負極]
負極16は、帯状の負極集電体と、当該集電体上に形成された負極合剤層とを有する。負極集電体には、銅などの負極の電位範囲で安定な金属の箔、当該金属を表層に配置したフィルム等を用いることができる。負極合剤層は、負極活物質、及び結着材を含み、負極集電体の両面に形成される。負極は、負極集電体上に負極活物質、結着材等を含む負極合剤スラリーを塗布し、塗膜を乾燥させた後、圧延して負極合剤層を負極集電体の両面に形成することにより作製できる。
[Negative electrode]
The negative electrode 16 has a strip-shaped negative electrode current collector and a negative electrode mixture layer formed on the current collector. As the negative electrode current collector, a metal foil that is stable in the potential range of a negative electrode such as copper, a film in which the metal is disposed on the surface layer, or the like can be used. The negative electrode mixture layer includes a negative electrode active material and a binder, and is formed on both surfaces of the negative electrode current collector. The negative electrode is prepared by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, etc. on the negative electrode current collector, drying the coating film, and rolling the negative electrode mixture layer on both sides of the negative electrode current collector. It can be manufactured by forming.
負極活物質としては、リチウムイオンを可逆的に吸蔵、放出できるものであれば特に限定されず、例えば天然黒鉛、人造黒鉛等の炭素材料、ケイ素(Si)、錫(Sn)等のLiと合金化する金属、又はSi、Sn等の金属元素を含む酸化物などを用いることができる。また、負極合剤層は、リチウムチタン複合酸化物を含んでいてもよい。リチウムチタン複合酸化物は、負極活物質として機能する。 The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium ions. For example, carbon materials such as natural graphite and artificial graphite, and Li and alloys such as silicon (Si) and tin (Sn) Or an oxide containing a metal element such as Si or Sn can be used. The negative electrode mixture layer may contain a lithium titanium composite oxide. The lithium titanium composite oxide functions as a negative electrode active material.
リチウムチタン複合酸化物は、例えば、一般式Li4+yTi5O12(式中、yは0以上1以下である)で表されるチタン酸リチウムであって、スピネル型の結晶構造を有する。なお、リチウムチタン複合酸化物は、Mg、Al、Ca、Ba、Bi、Ga、V、Nb、W、Mo、Ta、Cr、Fe、Ni、Co、Mn等の金属元素を含有していてもよい。負極活物質にリチウムチタン複合酸化物を用いることで、上述のように、電池のハイレート特性、サイクル特性が向上する。非水電解質二次電池10では、上述の構成を備えた正極11と、リチウムチタン複合酸化物を用いた負極との組み合わせが好適である。 The lithium titanium composite oxide is, for example, lithium titanate represented by a general formula Li 4 + y Ti 5 O 12 (wherein y is 0 or more and 1 or less), and has a spinel crystal structure. The lithium titanium composite oxide may contain a metal element such as Mg, Al, Ca, Ba, Bi, Ga, V, Nb, W, Mo, Ta, Cr, Fe, Ni, Co, and Mn. Good. By using the lithium titanium composite oxide as the negative electrode active material, the high rate characteristics and cycle characteristics of the battery are improved as described above. In the nonaqueous electrolyte secondary battery 10, a combination of the positive electrode 11 having the above-described configuration and a negative electrode using a lithium titanium composite oxide is preferable.
リチウムチタン複合酸化物は、層状リチウム金属複合酸化物の合成方法(後述の実施例1参照)に準じた方法で合成できる。例えば、水酸化リチウム等のリチウム含有化合物と、二酸化チタン、水酸化チタン等のチタン含有化合物とを、目的とする混合比率で混合し、当該混合物を焼成することにより、上記一般式で表されるリチウムチタン複合酸化物を合成できる。この合成法で得られるリチウムチタン複合酸化物は、一次粒子が凝集してなる二次粒子である。混合物の焼成は、一般的に、大気中(又は酸素気流中)、焼成温度500〜1100℃程度、焼成時間1〜30時間程度の条件で行われる。 The lithium titanium composite oxide can be synthesized by a method according to the method for synthesizing the layered lithium metal composite oxide (see Example 1 described later). For example, a lithium-containing compound such as lithium hydroxide and a titanium-containing compound such as titanium dioxide and titanium hydroxide are mixed at a target mixing ratio, and the mixture is baked to be expressed by the above general formula. Lithium titanium composite oxide can be synthesized. The lithium titanium composite oxide obtained by this synthesis method is a secondary particle formed by agglomerating primary particles. The mixture is generally fired in the atmosphere (or in an oxygen stream) under conditions of a firing temperature of about 500 to 1100 ° C. and a firing time of about 1 to 30 hours.
リチウムチタン複合酸化物の比表面積は3m2/g以上、7m2/g以下であることが好ましい。リチウムチタン複合酸化物の比表面積が3m2/gより低い場合、反応活性点が少なくなり抵抗が増加し、リチウムチタン複合酸化物の比表面積が7m2/gより高い場合、抵抗低減効果は飽和し、かつスラリー性状は低下するためである。 The specific surface area of the lithium titanium composite oxide is preferably 3 m 2 / g or more and 7 m 2 / g or less. When the specific surface area of the lithium-titanium composite oxide is lower than 3 m 2 / g, the reaction active sites decrease and the resistance increases, and when the specific surface area of the lithium-titanium composite oxide is higher than 7 m 2 / g, the resistance reduction effect is saturated. In addition, the slurry properties are lowered.
リチウムチタン複合酸化物を用いる場合、負極合剤層は導電材を含むことが好ましい。導電材としては、カーボンブラック、アセチレンブラック、ケッチェンブラック、黒鉛等の炭素材料が例示できる。これらは、単独で用いてもよく、2種類以上を組み合わせて用いてもよい。また、チタン酸リチウムを用いる場合、合剤層の充填密度は1.6g/cm3以上、2.2g/cm3以下であることが好ましい。なお、負極合剤層の充填密度が1.6g/cm3より低い場合、活物質粒子間の負極内導電性が低下する。一方、負極合剤層の充填密度が2.2g/cm3より高い場合、負極合剤の塗布部と非塗布部との間で圧延時の集電体の伸び率の違いに起因してシワが生じ易くなる。そして、シワが集電体の表面の凹凸となることにより、集電体と負極合剤層の間の集電性が低下して抵抗増加を招く。 When using a lithium titanium composite oxide, the negative electrode mixture layer preferably contains a conductive material. Examples of the conductive material include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. These may be used alone or in combination of two or more. Moreover, when using lithium titanate, it is preferable that the packing density of a mixture layer is 1.6 g / cm < 3 > or more and 2.2 g / cm < 3 > or less. In addition, when the packing density of a negative mix layer is lower than 1.6 g / cm < 3 >, the electroconductivity in the negative electrode between active material particles falls. On the other hand, when the packing density of the negative electrode mixture layer is higher than 2.2 g / cm 3 , wrinkles are caused by the difference in elongation rate of the current collector during rolling between the coated portion and the non-coated portion of the negative electrode mixture. Is likely to occur. And since wrinkles become the unevenness | corrugation of the surface of a collector, the current collection property between a collector and a negative mix layer will fall, and it will cause resistance increase.
なお、負極合剤層に含まれる導電材の配合比率は、負極活物質の質量に対して3質量%以上、15質量%以下の範囲であることが好ましい。負極合剤層内の導電材の配合比率が3質量%より低い場合、負極合剤層内の抵抗が増加する。負極合剤層内の導電材の配合比率が15質量%より大きい場合、スラリー性状が安定しない。なお、負極合剤層に含まれる導電材の平均1次粒子径は、例えば10nm以上、50nm以下である。 In addition, it is preferable that the mixture ratio of the electrically conductive material contained in a negative mix layer is the range of 3 mass% or more and 15 mass% or less with respect to the mass of a negative electrode active material. When the blending ratio of the conductive material in the negative electrode mixture layer is lower than 3% by mass, the resistance in the negative electrode mixture layer increases. When the blending ratio of the conductive material in the negative electrode mixture layer is greater than 15% by mass, the slurry properties are not stable. In addition, the average primary particle diameter of the electrically conductive material contained in the negative electrode mixture layer is, for example, 10 nm or more and 50 nm or less.
負極合剤層に含まれる結着材には、公知の結着材を用いることができ、正極20の場合と同様に、PTFE、PVdF等のフッ素樹脂、PAN、ポリイミド系樹脂、アクリル系樹脂、並びに、ポリオレフィン系樹脂等を用いることができる。また、水系溶媒を用いて負極合剤スラリーを調製する場合に用いられる結着材としては、CMC又はその塩、スチレン−ブタジエンゴム(SBR)、ポリアクリル酸(PAA)又はその塩、ポリビニルアルコール(PVA)等が例示できる。 As the binder contained in the negative electrode mixture layer, a known binder can be used. Similarly to the case of the positive electrode 20, a fluororesin such as PTFE and PVdF, PAN, a polyimide resin, an acrylic resin, In addition, a polyolefin-based resin or the like can be used. Moreover, as a binder used when preparing a negative electrode mixture slurry using an aqueous solvent, CMC or a salt thereof, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol ( PVA) etc. can be illustrated.
なお、負極合剤層に含まれる結着材の配合比率は、負極活物質の質量に対して1質量%以上、5質量%以下であることが好ましい。これは、負極合剤層中の結着材の配合比率が1質量%より低い場合、極板から活物質が脱落し易くなり、結着材の配合比率が5質量%を超えると、負極合剤層内の抵抗あるいは負極合剤層と集電体との間の抵抗が増加する虞があるためである。 In addition, it is preferable that the mixture ratio of the binder contained in a negative mix layer is 1 mass% or more and 5 mass% or less with respect to the mass of a negative electrode active material. This is because when the blending ratio of the binder in the negative electrode mixture layer is lower than 1% by mass, the active material tends to fall off from the electrode plate, and when the blending ratio of the binder exceeds 5% by mass, This is because the resistance in the agent layer or the resistance between the negative electrode mixture layer and the current collector may increase.
[セパレータ]
セパレータには、イオン透過性及び絶縁性を有する多孔性シートが用いられる。多孔性シートの具体例としては、微多孔薄膜、織布、不織布等が挙げられる。セパレータの材質としては、ポリエチレン、ポリプロピレン等のオレフィン系樹脂、セルロース等が好適である。セパレータは、セルロース繊維層及びオレフィン系樹脂等の熱可塑性樹脂繊維層を有する積層体であってもよい。また、ポリエチレン層及びポリプロピレン層を含む多層セパレータであってもよく、セパレータの表面にアラミド系樹脂等の樹脂、又はアルミナ、チタニア等の無機微粒子が塗布されたものを用いることもできる。
[Separator]
As the separator, a porous sheet having ion permeability and insulating properties is used. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. As the material of the separator, olefinic resins such as polyethylene and polypropylene, cellulose and the like are suitable. The separator may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. In addition, a multilayer separator including a polyethylene layer and a polypropylene layer may be used, and a separator whose surface is coated with a resin such as an aramid resin or inorganic fine particles such as alumina or titania can also be used.
[非水電解質]
非水電解質は、非水溶媒と、非水溶媒に溶解した電解質塩とを含む。非水溶媒には、例えばエステル類、エーテル類、アセトニトリル等のニトリル類、ジメチルホルムアミド等のアミド類、及びこれらの2種以上の混合溶媒等を用いることができる。非水溶媒は、これら溶媒の水素の少なくとも一部をフッ素等のハロゲン原子で置換したハロゲン置換体を含有していてもよい。また、非水電解質は液体電解質(非水電解液)に限定されず、ゲル状ポリマー等を用いた固体電解質であってもよい。
[Nonaqueous electrolyte]
The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and a mixed solvent of two or more of these can be used. The non-aqueous solvent may contain a halogen-substituted product in which at least a part of hydrogen in these solvents is substituted with a halogen atom such as fluorine. The non-aqueous electrolyte is not limited to a liquid electrolyte (non-aqueous electrolyte), and may be a solid electrolyte using a gel polymer or the like.
上記エステル類の例としては、エチレンカーボネート(EC)、プロピレンカーボネート(PC)、ブチレンカーボネート等の環状炭酸エステル、ジメチルカーボネート(DMC)、メチルエチルカーボネート(MEC)、ジエチルカーボネート(DEC)、メチルプロピルカーボネート、エチルプロピルカーボネート、メチルイソプロピルカーボネート等の鎖状炭酸エステル、γ−ブチロラクトン(GBL)、γ−バレロラクトン(GVL)等の環状カルボン酸エステル、酢酸メチル、酢酸エチル、酢酸プロピル、プロピオン酸メチル(MP)、プロピオン酸エチル等の鎖状カルボン酸エステルなどが挙げられる。 Examples of the esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), and methyl propyl carbonate. Chain carbonates such as ethyl propyl carbonate and methyl isopropyl carbonate, cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone (GVL), methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP ) And chain carboxylic acid esters such as ethyl propionate.
上記エーテル類の例としては、1,3−ジオキソラン、4−メチル−1,3−ジオキソラン、テトラヒドロフラン、2−メチルテトラヒドロフラン、プロピレンオキシド、1,2−ブチレンオキシド、1,3−ジオキサン、1,4−ジオキサン、1,3,5−トリオキサン、フラン、2−メチルフラン、1,8−シネオール、クラウンエーテル等の環状エーテル、1,2−ジメトキシエタン、ジエチルエーテル、ジプロピルエーテル、ジイソプロピルエーテル、ジブチルエーテル、ジヘキシルエーテル、エチルビニルエーテル、ブチルビニルエーテル、メチルフェニルエーテル、エチルフェニルエーテル、ブチルフェニルエーテル、ペンチルフェニルエーテル、メトキシトルエン、ベンジルエチルエーテル、ジフェニルエーテル、ジベンジルエーテル、o−ジメトキシベンゼン、1,2−ジエトキシエタン、1,2−ジブトキシエタン、ジエチレングリコールジメチルエーテル、ジエチレングリコールジエチルエーテル、ジエチレングリコールジブチルエーテル、1,1−ジメトキシメタン、1,1−ジエトキシエタン、トリエチレングリコールジメチルエーテル、テトラエチレングリコールジメチル等の鎖状エーテル類などが挙げられる。 Examples of the ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4 -Cyclic ethers such as dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineol, crown ether, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether , Dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxy toluene, benzyl ethyl ether, diphenyl ether, dibenzyl Ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, tri Examples thereof include chain ethers such as ethylene glycol dimethyl ether and tetraethylene glycol dimethyl.
上記ハロゲン置換体としては、フルオロエチレンカーボネート(FEC)等のフッ素化環状炭酸エステル、フッ素化鎖状炭酸エステル、フルオロプロピオン酸メチル(FMP)等のフッ素化鎖状カルボン酸エステル等を用いることが好ましい。 As the halogen-substituted product, it is preferable to use a fluorinated cyclic carbonate such as fluoroethylene carbonate (FEC), a fluorinated chain carbonate, a fluorinated chain carboxylate such as methyl fluoropropionate (FMP), or the like. .
電解質塩は、リチウム塩であることが好ましい。リチウム塩の例としては、LiBF4、LiClO4、LiPF6、LiAsF6、LiSbF6、LiAlCl4、LiSCN、LiCF3SO3、LiCF3CO2、Li(P(C2O4)F4)、LiPF6−x(CnF2n+1)x(1<x<6,nは1又は2)、LiB10Cl10、LiCl、LiBr、LiI、クロロボランリチウム、低級脂肪族カルボン酸リチウム、Li2B4O7、Li(B(C2O4)F2)等のホウ酸塩類、LiN(SO2CF3)2、LiN(ClF2l+1SO2)(CmF2m+1SO2){l,mは1以上の整数}等のイミド塩類などが挙げられる。リチウム塩は、これらを1種単独で用いてもよいし、複数種を混合して用いてもよい。これらのうち、イオン伝導性、電気化学的安定性等の観点から、LiPF6を用いることが好ましい。リチウム塩の濃度は、非水溶媒1L当り0.8〜1.8molとすることが好ましい。 The electrolyte salt is preferably a lithium salt. Examples of the lithium salt, LiBF 4, LiClO 4, LiPF 6, LiAsF 6, LiSbF 6, LiAlCl 4, LiSCN, LiCF 3 SO 3, LiCF 3 CO 2, Li (P (C 2 O 4) F 4), LiPF 6-x (C n F 2n + 1 ) x (1 <x <6, n is 1 or 2), LiB 10 Cl 10 , LiCl, LiBr, LiI, lithium chloroborane, lithium lower aliphatic carboxylate, Li 2 B 4 O 7, Li (B ( C 2 O 4) F 2) boric acid salts such as, LiN (SO 2 CF 3) 2, LiN (C l F 2l + 1 SO 2) (C m F 2m + 1 SO 2) {l , M is an integer greater than or equal to 1} and the like. These lithium salts may be used alone or in combination of two or more. Of these, LiPF 6 is preferably used from the viewpoints of ion conductivity, electrochemical stability, and the like. The concentration of the lithium salt is preferably 0.8 to 1.8 mol per liter of the nonaqueous solvent.
以下、実施例により本開示をさらに説明するが、本開示はこれらの実施例に限定されるものではない。 Hereinafter, although this indication is further explained by an example, this indication is not limited to these examples.
<実施例1>
[正極の作製]
リチウム含有化合物と、Ni、Co、Mnを含有する複合酸化物と、酸化ジルコニウムとを、目的とする混合比率で混合し、当該混合物を焼成することにより、組成式Li1.050Ni0.189Co0.567Mn0.189Zr0.005O2で表される層状リチウム金属複合酸化物を得た。正極活物質として、当該リチウム金属複合酸化物を用いる。当該リチウム金属複合酸化物は、一次粒子が凝集してなる二次粒子である。なお、正極活物質及び後述する負極活物質の組成は、ICP発光分光分析装置(Thermo Fisher Scientific社製iCAP6300)を用いて測定した。
<Example 1>
[Production of positive electrode]
A lithium-containing compound, a composite oxide containing Ni, Co, and Mn, and zirconium oxide are mixed at a target mixing ratio, and the mixture is fired to obtain a composition formula Li 1.050 Ni 0.189. A layered lithium metal composite oxide represented by Co 0.567 Mn 0.189 Zr 0.005 O 2 was obtained. The lithium metal composite oxide is used as the positive electrode active material. The lithium metal composite oxide is a secondary particle obtained by agglomerating primary particles. The composition of the positive electrode active material and the negative electrode active material described later was measured using an ICP emission spectroscopic analyzer (Thermo Fisher Scientific iCAP6300).
上記正極活物質と、活物質に対して7質量%のカーボンブラックと、活物質に対して2質量%のポリフッ化ビニリデン(PVdF)とを混合し、当該混合物に分散媒としてN−メチル−2−ピロリドン(NMP)を加え、混合機(プライミクス株式会社製、T.K.ハイビスミックス)を用いて攪拌し、正極合剤スラリーを調製した。次に、正極集電体であるアルミニウム箔上に正極合剤スラリーを塗布し、塗膜(正極合剤層)を乾燥させた後、正極合剤層の充填密度が2.2g/cm3となるように、正極合剤層を圧延ロールにより圧延して、アルミニウム箔の両面に正極合剤層が形成された正極を作製した。 The positive electrode active material, 7% by mass of carbon black with respect to the active material, and 2% by mass of polyvinylidene fluoride (PVdF) with respect to the active material are mixed, and N-methyl-2 is used as a dispersion medium in the mixture. -Pyrrolidone (NMP) was added and stirred using a mixer (Primix Co., Ltd., TK Hibismix) to prepare a positive electrode mixture slurry. Next, after applying the positive electrode mixture slurry on the aluminum foil as the positive electrode current collector and drying the coating film (positive electrode mixture layer), the packing density of the positive electrode mixture layer was 2.2 g / cm 3 . Thus, the positive electrode mixture layer was rolled with a rolling roll to produce a positive electrode in which the positive electrode mixture layer was formed on both surfaces of the aluminum foil.
正極の作製において、導電材として使用したカーボンブラックの比表面積、その添加量、及び圧延条件を調整して、正極合剤層の単位体積当りに含まれるカーボンブラックの比表面積の合計を20.5m2/cm3とした。 In the production of the positive electrode, the specific surface area of carbon black used as the conductive material, the amount of addition thereof, and the rolling conditions were adjusted, and the total specific surface area of carbon black contained per unit volume of the positive electrode mixture layer was 20.5 m. 2 / cm 3 .
[負極の作製]
組成式Li4Ti5O12で表されるリチウムチタン複合酸化物と、カーボンブラックと、ポリフッ化ビニリデン(PVdF)とを、90:8:2の質量比で混合した。当該混合物にNMPを加え、混合機(プライミクス株式会社製、T.K.ハイビスミックス)を用いて攪拌し、負極合剤スラリーを調製した。次に、負極集電体であるアルミニウム箔上に負極合剤スラリーを塗布し、塗膜を乾燥させた後、塗膜を圧延ローラにより圧延して、アルミニウム箔の両面に負極合剤層が形成された負極を作製した。
[Production of negative electrode]
A lithium titanium composite oxide represented by the composition formula Li 4 Ti 5 O 12 , carbon black, and polyvinylidene fluoride (PVdF) were mixed at a mass ratio of 90: 8: 2. NMP was added to the mixture, and the mixture was stirred using a mixer (manufactured by PRIMIX Corporation, TK Hibismix) to prepare a negative electrode mixture slurry. Next, after applying the negative electrode mixture slurry on the aluminum foil as the negative electrode current collector and drying the coating film, the coating film is rolled with a rolling roller to form a negative electrode mixture layer on both surfaces of the aluminum foil. A negative electrode was prepared.
[非水電解質の調製]
プロピレンカーボネート(PC)と、エチルメチルカーボネート(EMC)と、ジメチルカーボネート(DMC)とを、25:35:40の体積比で混合した。当該混合溶媒に対して、LiPF6を1.2モル/Lの濃度となるように溶解させて、非水電解質を調製した。
[Preparation of non-aqueous electrolyte]
Propylene carbonate (PC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 25:35:40. LiPF 6 was dissolved in the mixed solvent to a concentration of 1.2 mol / L to prepare a nonaqueous electrolyte.
[電池の作製]
上記正極と上記負極を、ポリプロピレン製の微多孔膜からなるセパレータを介して渦巻き状に巻回した後、プレス成形して電極体を作製した。この電極体から突出した正負極の各非塗工部に封口体の集電体部を溶接して、電極体をアルミニウム製の電池ケースに収容し、電池ケース内に上記非水電解質を注入した。その後、電池ケースの開口部を封口して、図1に示す角形の非水電解質二次電池(定格容量10Ah)を作製した。
[Production of battery]
The positive electrode and the negative electrode were spirally wound through a separator made of a polypropylene microporous film, and then press-molded to produce an electrode body. The current collector part of the sealing body was welded to each non-coated part of the positive and negative electrodes protruding from the electrode body, the electrode body was accommodated in an aluminum battery case, and the nonaqueous electrolyte was injected into the battery case. . Then, the opening part of the battery case was sealed, and the square nonaqueous electrolyte secondary battery (rated capacity 10Ah) shown in FIG. 1 was produced.
<実施例2>
正極の作製において、正極合剤層の充填密度が2.4g/cm3、単位体積当りに含まれる導電材の比表面積の合計が22.3m2/cm3(活物質に対して7質量%のカーボンブラックを添加)となるように、正極合剤層を形成したこと以外は、実施例1と同様にして電池を作製した。
<Example 2>
In the production of the positive electrode, the packing density of the positive electrode mixture layer was 2.4 g / cm 3 , and the total specific surface area of the conductive material contained per unit volume was 22.3 m 2 / cm 3 (7% by mass with respect to the active material) A battery was fabricated in the same manner as in Example 1 except that the positive electrode mixture layer was formed so that the carbon black was added.
<実施例3>
正極の作製において、正極合剤層の充填密度が3.0g/cm3、単位体積当りに含まれる導電材の比表面積の合計が39.9m2/cm3(活物質に対して10質量%のカーボンブラックを添加)となるように、正極合剤層を形成したこと以外は、実施例1と同様にして電池を作製した。
<Example 3>
In the production of the positive electrode, the packing density of the positive electrode mixture layer is 3.0 g / cm 3 , and the total specific surface area of the conductive material contained per unit volume is 39.9 m 2 / cm 3 (10% by mass with respect to the active material) A battery was fabricated in the same manner as in Example 1 except that the positive electrode mixture layer was formed so that the carbon black was added.
<比較例1>
正極の作製において、正極合剤層の充填密度が2.2g/cm3、単位体積当りに含まれる導電材の比表面積の合計が2.6m2/cm3となるように、正極合剤層を形成したこと以外は、実施例1と同様にして電池を作製した。
<Comparative Example 1>
In the production of the positive electrode, the positive electrode mixture layer has a packing density of 2.2 g / cm 3 and a total specific surface area of the conductive material contained per unit volume of 2.6 m 2 / cm 3. A battery was fabricated in the same manner as in Example 1 except that was formed.
<比較例2>
正極の作製において、正極合剤層の充填密度が2.4g/cm3、単位体積当りに含まれる導電材の比表面積の合計が4.9m2/cm3となるように、正極合剤層を形成したこと以外は、実施例1と同様にして電池を作製した。
<Comparative example 2>
In the production of the positive electrode, the positive electrode mixture layer has a packing density of the positive electrode mixture layer of 2.4 g / cm 3 and a total specific surface area of the conductive material contained per unit volume of 4.9 m 2 / cm 3. A battery was fabricated in the same manner as in Example 1 except that was formed.
<比較例3>
正極の作製において、正極合剤層の充填密度が2.4g/cm3、単位体積当りに含まれる導電材の比表面積の合計が8.2m2/cm3となるように、正極合剤層を形成したこと以外は、実施例1と同様にして電池を作製した。
<Comparative Example 3>
In the production of the positive electrode, the positive electrode mixture layer has a packing density of the positive electrode mixture layer of 2.4 g / cm 3 and a total specific surface area of the conductive material contained per unit volume of 8.2 m 2 / cm 3. A battery was fabricated in the same manner as in Example 1 except that was formed.
<比較例4>
正極の作製において、正極合剤層の充填密度が3.0g/cm3、単位体積当りに含まれる導電材の比表面積の合計が14.3m2/cm3となるように、正極合剤層を形成したこと以外は、実施例1と同様にして電池を作製した。
<Comparative example 4>
In the production of the positive electrode, the positive electrode mixture layer has a packing density of the positive electrode mixture layer of 3.0 g / cm 3 and a total specific surface area of the conductive material contained per unit volume of 14.3 m 2 / cm 3. A battery was fabricated in the same manner as in Example 1 except that was formed.
実施例及び比較例の各電池について、以下の方法で性能評価試験を実施した。評価結果は、表1に示した。 About each battery of an Example and a comparative example, the performance evaluation test was implemented with the following method. The evaluation results are shown in Table 1.
[電池容量測定試験]
25℃の温度雰囲気で、各電池を、電流値10Aで電池電圧が2.65Vになるまで定電流充電した。15分間の休止後、電流値1100mAで電池電圧が1.5Vになるまで定電流放電を行い、このときの放電容量を電池容量とし、比較例1の値を基準(100)とする相対値として表1に示した。
[Battery capacity measurement test]
In a temperature atmosphere of 25 ° C., each battery was charged with a constant current at a current value of 10 A until the battery voltage reached 2.65V. After a pause of 15 minutes, constant current discharge is performed until the battery voltage reaches 1.5 V at a current value of 1100 mA, the discharge capacity at this time is defined as the battery capacity, and the relative value with the value of Comparative Example 1 as the reference (100) It is shown in Table 1.
[ハイレート特性試験]
25℃の温度雰囲気で、各電池を、1Cの充電電流でSOC(充電深度)50%まで充電した。その後、5C放電→5C充電→10C放電→10C充電→15C放電→15C充電→20C放電→20C充電→25C放電→25C充電の順で充放電電流を増加させた。このとき、各ステップの間に15分間の休止期間を設け、30秒間の放電→15分間休止→30秒間充電→15分間休止の順で充放電を行った。そして、この放電が10秒経過した時点における電池電圧を放電電流に対してプロットし、最小二乗法にて求めた直線が1.5Vに達したときの電流値を出力値として算出した。その際の抵抗値を、比較例1の値を基準(100)とする相対値として表1に示した。
[High rate characteristics test]
In a temperature atmosphere of 25 ° C., each battery was charged to a SOC (charge depth) of 50% with a charging current of 1 C. Thereafter, the charge / discharge current was increased in the order of 5C discharge → 5C charge → 10C discharge → 10C charge → 15C discharge → 15C charge → 20C discharge → 20C charge → 25C discharge → 25C charge. At this time, a pause period of 15 minutes was provided between each step, and charging / discharging was performed in the order of discharge for 30 seconds → pause for 15 minutes → charge for 30 seconds → pause for 15 minutes. The battery voltage at the time when 10 seconds had elapsed from this discharge was plotted against the discharge current, and the current value when the straight line obtained by the least square method reached 1.5 V was calculated as the output value. The resistance values at that time are shown in Table 1 as relative values based on the value of Comparative Example 1 as a reference (100).
表1に示すように、実施例の電池はいずれも、比較例1,2の電池と比べて放電抵抗が低く、また比較例3,4の電池と比べて高容量であった。つまり、実施例の電池によれば、比較例の電池では実現困難な高容量と低抵抗を両立することができる。 As shown in Table 1, each of the batteries of the examples had a lower discharge resistance than the batteries of Comparative Examples 1 and 2, and had a higher capacity than the batteries of Comparative Examples 3 and 4. In other words, according to the battery of the example, it is possible to achieve both high capacity and low resistance, which are difficult to realize with the battery of the comparative example.
実施例1の電池では、正極合剤層の充填密度が低いにも関わらず、ハイレート放電抵抗が低く、電池容量とハイレート特性が両立されている。これは、合剤層における導電材比表面積の大幅増加により、活物質粒子間の通電経路が形成されたためと考えられる。実施例2の電池は、実施例1の場合より正極合剤層の充填密度が高くなっているにも関わらず、電池容量が低下しておらず、電池容量とハイレート特性が両立されている。これは、合剤層における導電材比表面積の大幅増加により、活物質粒子間の通電経路が形成されると共に、活物質粒子の表面近傍に電解液が導かれたためと考えられる。実施例3の電池では、実施例2の場合と同様に、電池容量とハイレート特性が両立されている。一方、実施例3の電池特性が実施例2の場合より良化しないのは、導電材の比表面積に起因する通電経路の形成効果、電解液の導入経路の形成効果が飽和する領域にあるためと考えられる。 In the battery of Example 1, although the packing density of the positive electrode mixture layer is low, the high-rate discharge resistance is low and the battery capacity and the high-rate characteristics are compatible. This is presumably because an energization path between the active material particles was formed due to a significant increase in the specific surface area of the conductive material in the mixture layer. In the battery of Example 2, although the packing density of the positive electrode mixture layer is higher than that of Example 1, the battery capacity is not reduced, and the battery capacity and the high rate characteristics are compatible. This is presumably because the energization path between the active material particles was formed due to a large increase in the specific surface area of the conductive material in the mixture layer, and the electrolyte was led near the surface of the active material particles. In the battery of Example 3, as in the case of Example 2, the battery capacity and the high rate characteristics are compatible. On the other hand, the reason why the battery characteristics of Example 3 are not improved as compared with Example 2 is because the formation effect of the energization path due to the specific surface area of the conductive material and the formation effect of the introduction path of the electrolyte solution are saturated. it is conceivable that.
また、実施例1〜3を用いて、正極合剤層の充填密度の変化と、抵抗の変化の関係を見ると、実施例1〜3の電池では、いずれも、抵抗値の差が小さく安定していることがわかる。そして、正極合剤層の充填密度が2.2g/cm3である実施例1の電池と比べて、充填密度が2.4g/cm3以上である、実施例2、3の電池の抵抗値は、低抵抗でありながら、物性はほぼ同等である。そのため、実施例2、3の電池間における抵抗値の変動が極めて小さいと言える。このことから、充填密度が2.2g/cm3以上である合剤層のうち、充填密度が2.4g/cm3以上である正極合剤層は、電池間で多少の充填密度に差が生じたとしても、本開示の正極に用いられる合剤層として、特に優れた出力特性を安定的に発現できることがわかる。 In addition, when the relationship between the change in the packing density of the positive electrode mixture layer and the change in resistance is observed using Examples 1 to 3, the batteries of Examples 1 to 3 each have a small difference in resistance value and are stable. You can see that Then, as compared filling density of the positive electrode mixture layer and the battery of Example 1 is 2.2 g / cm 3, the packing density is the 2.4 g / cm 3 or more, the resistance value of the battery of Example 2 and 3 Although the resistance is low, the physical properties are almost the same. Therefore, it can be said that the variation of the resistance value between the batteries of Examples 2 and 3 is extremely small. Therefore, among the mixture layers having a packing density of 2.2 g / cm 3 or more, the positive electrode mixture layer having a packing density of 2.4 g / cm 3 or more has a slight difference in packing density between batteries. Even if it occurs, it can be seen that particularly excellent output characteristics can be stably exhibited as a mixture layer used in the positive electrode of the present disclosure.
なお、比較例1,2の電池は、ハイレート放電時の抵抗が高い。これは、正極合剤層の充填密度が2.2及び2.4g/cm3と低く、導電材の比表面積も2.6及び4.9m2/cm3と低いため、活物質粒子間距離が離れて通電経路を確保できないためと考えられる。充填密度を2.4及び3.0g/cm3、導電材の比表面積を8.2及び14.3m2/cm3とした正極を備える比較例3,4の電池は、比較例1,2の場合よりも単位体積当りの導電材比表面積が増加することで、ハイレート放電時の抵抗低減は僅かに確認されるが、一方で、電池容量が低下している。これは、正極合剤層の充填密度が高くなることで、合剤層に導入される電解液量が減少したためと考えられる。 Note that the batteries of Comparative Examples 1 and 2 have high resistance during high-rate discharge. This is because the packing density of the positive electrode mixture layer is as low as 2.2 and 2.4 g / cm 3 and the specific surface area of the conductive material is as low as 2.6 and 4.9 m 2 / cm 3. This is thought to be because the energization path cannot be secured due to separation. The batteries of Comparative Examples 3 and 4 having positive electrodes with a packing density of 2.4 and 3.0 g / cm 3 and a specific surface area of the conductive material of 8.2 and 14.3 m 2 / cm 3 are Comparative Examples 1 and 2, respectively. As the conductive material specific surface area per unit volume is increased as compared with the above, a decrease in resistance during high-rate discharge is slightly confirmed, but on the other hand, the battery capacity is reduced. This is presumably because the amount of the electrolyte introduced into the mixture layer was reduced by increasing the packing density of the positive electrode mixture layer.
10 非水電解質二次電池、11 電池ケース、12 ケース本体、13 封口板、14 電極体、15 正極、16 負極、17 セパレータ、18 正極端子、19 負極端子、20 正極集電体、21 正極合剤層、22 リチウム金属複合酸化物、23 導電材 DESCRIPTION OF SYMBOLS 10 Nonaqueous electrolyte secondary battery, 11 Battery case, 12 Case main body, 13 Sealing plate, 14 Electrode body, 15 Positive electrode, 16 Negative electrode, 17 Separator, 18 Positive electrode terminal, 19 Negative electrode terminal, 20 Positive electrode collector, 21 Positive electrode combination Agent layer, 22 lithium metal composite oxide, 23 conductive material
Claims (7)
前記正極合剤層の単位体積当たりに含まれる前記導電材の比表面積の合計が20m2/cm3以上である、
非水電解質二次電池用正極。 It has a positive electrode mixture layer containing a layered lithium metal composite oxide and a conductive material,
The total specific surface area of the conductive material contained per unit volume of the positive electrode mixture layer is 20 m 2 / cm 3 or more,
Positive electrode for non-aqueous electrolyte secondary battery.
請求項1に記載の非水電解質二次電池用正極。 The packing density of the positive electrode mixture layer is 2.2 g / cm 3 or more,
The positive electrode for nonaqueous electrolyte secondary batteries according to claim 1.
請求項1に記載の非水電解質二次電池用正極。 The lithium metal composite oxide has a general formula Li 1 + x M a O 2 + b (wherein x + a = 1, −0.2 <x ≦ 0.2, −0.1 ≦ b ≦ 0.1, and M is And at least one selected from Ni, Co, Mn, and Al).
The positive electrode for nonaqueous electrolyte secondary batteries according to claim 1.
請求項1又は2に記載の非水電解質二次電池用正極。 The specific surface area of the conductive material is 30 m 2 / g or more and 140 m 2 / g or less.
The positive electrode for nonaqueous electrolyte secondary batteries of Claim 1 or 2.
請求項1〜3のうちいずれか一つに記載の非水電解質二次電池用正極。 The electrical conductivity of the conductive material is 0.1Ω · cm or more and 0.3Ω · cm or less,
The positive electrode for nonaqueous electrolyte secondary batteries as described in any one of Claims 1-3.
非水電解質と、
を備えた、
非水電解質二次電池。 It is comprised with the positive electrode for nonaqueous electrolyte secondary batteries as described in any one of Claims 1-4, the negative electrode which has a negative mix layer, and the separator interposed between the said positive electrode and the said negative electrode. An electrode body;
A non-aqueous electrolyte,
With
Non-aqueous electrolyte secondary battery.
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JP2005317509A (en) * | 2004-03-30 | 2005-11-10 | Sanyo Electric Co Ltd | Nonaqueous electrolyte secondary battery |
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JP2012221684A (en) * | 2011-04-07 | 2012-11-12 | Denki Kagaku Kogyo Kk | Carbon black for nonaqueous secondary battery, electrode and nonaqueous secondary battery |
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JP2005317509A (en) * | 2004-03-30 | 2005-11-10 | Sanyo Electric Co Ltd | Nonaqueous electrolyte secondary battery |
JP2006210007A (en) * | 2005-01-25 | 2006-08-10 | Mitsubishi Chemicals Corp | Electrode for electrochemistry element, and lithium secondary battery using the same |
JP2012221684A (en) * | 2011-04-07 | 2012-11-12 | Denki Kagaku Kogyo Kk | Carbon black for nonaqueous secondary battery, electrode and nonaqueous secondary battery |
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