JP2009021102A - Lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery in which capacity reduction after repeated charging and discharging under high temperature environments, for example, around 60°C, as well as increase of internal resistance, can be suppressed. <P>SOLUTION: In the lithium ion secondary battery, which is at least equipped with a positive electrode, a negative electrode, and a non-aqueous electrolytic solution composed by dissolving an electrolyte into a non-aqueous solvent, the non-aqueous electrolytic solution contains as the electrolyte a first electrolyte composed of a lithium salt containing fluorine and a second electrolyte expressed by a general formula (1). In the positive electrode, a lithium transition metal complex oxide is contained as a positive electrode active material, while in the negative electrode, metal oxide nano-particulates are contained as a negative electrode active material. In the lithium ion secondary battery before charge and discharge are carried out, the average particulate diameter of the metal oxide nano-particulates is 0.1 to 1 μm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery containing, as an electrolytic solution, a nonaqueous electrolytic solution obtained by dissolving an electrolyte in a nonaqueous solvent such as an organic solvent.

  Lithium ion secondary batteries using non-aqueous electrolytes have high voltage, high energy density, and can be reduced in size and weight. Therefore, in the field of information communication equipment, mainly information terminals such as personal computers and mobile phones. Practical use has progressed and it has become widespread. In other fields, the development of electric vehicles has been urgently promoted due to environmental problems and resource issues, and the use of non-aqueous electrolyte lithium ion secondary batteries as batteries for hybrid vehicles has been studied.

A lithium ion secondary battery mainly includes a positive electrode, a negative electrode, and a non-aqueous electrolyte that moves lithium ions between the positive electrode and the negative electrode. Specifically, for example, for the positive electrode, lithium transition metal composite oxides such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , and derivatives thereof are used as the positive electrode active material, and graphite or coke is used as the negative electrode active material. There are batteries using carbon materials such as. As the electrolytic solution, a nonaqueous electrolytic solution in which a Li salt such as LiPF ₆ is dissolved in an organic mixed solvent of a chain carbonate and a cyclic carbonate is used.

  In recent years, it has been confirmed that nano-particles made of a certain kind of metal oxide can be a suitable material as a negative electrode active material (see Non-Patent Document 1). The nano fine particles have an operating voltage in a range of 0.5 to 1.2 V based on a lithium metal electrode, although it varies depending on the metal species used. This operating voltage itself is located slightly higher than the operating voltage of carbon materials such as graphite, but the charge / discharge capacity when the above-mentioned nanoparticle is used as the negative electrode active material is the same as when graphite is used as the negative electrode active material. It is 600 mAh / g or more corresponding to about twice the charge / discharge capacity. Therefore, it becomes possible to realize a lithium ion secondary battery having a higher energy density by using the nano fine particles as the negative electrode active material.

When considering in-vehicle lithium-ion secondary batteries such as power sources for electric vehicles and hybrid electric vehicles, in addition to high output, it is repeated at a low temperature of about -30 ° C to a high temperature of about 60 ° C. When charging and discharging, it is required that the capacity deterioration is small and the increase in internal resistance of the battery is small.
In constructing a high-power type lithium ion secondary battery, it is becoming an essential condition to use LiPF ₆ having high conductivity as a main component of the electrolyte. However, LiPF ₆ reacts with a small amount of moisture mixed in the electrolyte during the production or use of the lithium ion secondary battery, and generates hydrogen fluoride (HF) (see Non-Patent Document 2). This HF has an adverse effect on the constituent materials in the lithium ion secondary battery, and there is a possibility that battery characteristics such as capacity and output may be deteriorated. In particular, since the adverse effect of HF is increased under a high temperature environment, generation of HF has been a serious problem in a lithium ion secondary battery for in-vehicle use.

P. Poizot et al., “Nature”, 2000, 407, p. 496-p. 499 D. Aurbach et al., “JOURNAL OF POWER SOURCES”, 1997, Vol. 68, p. 91-p. 98

  The present invention has been made in view of such conventional problems, and can suppress a decrease in capacity and an increase in internal resistance when charging and discharging are repeatedly performed in a high temperature environment of, for example, about 60 ° C. The present invention intends to provide a lithium ion secondary battery.

｛但し、Ｍは、遷移金属、周期律表のIII族、IV族、又はV族元素、Ａ^a+は、金属イオン、プロトン、又はオニウムイオン、ａは１〜３、ｂは１〜３、ｐはｂ／ａ、ｍは１〜４、ｎは０〜８、ｑは０又は１をそれぞれ表し、Ｒ¹は、Ｃ₁〜Ｃ₁₀のアルキレン、Ｃ₁〜Ｃ₁₀のハロゲン化アルキレン、Ｃ₆〜Ｃ₂₀のアリーレン、又はＣ₆〜Ｃ₂₀のハロゲン化アリーレン（これらのアルキレン及びアリーレンはその構造中に置換基、ヘテロ原子を持ってもよく、またｍ個存在するＲ¹はそれぞれが結合してもよい。）、Ｒ²は、ハロゲン、Ｃ₁〜Ｃ₁₀のアルキル、Ｃ₁〜Ｃ₁₀のハロゲン化アルキル、Ｃ₆〜Ｃ₂₀のアリール、Ｃ₆〜Ｃ₂₀のハロゲン化アリール、又はＸ³Ｒ³（これらのアルキル及びアリールはその構造中に置換基、ヘテロ原子を持ってもよく、またｎ個存在するＲ²はそれぞれが結合して環を形成してもよい。）、Ｘ¹、Ｘ²、Ｘ³は、Ｏ、Ｓ、又はＮＲ⁴、Ｒ³、Ｒ⁴は、それぞれが独立で、水素、Ｃ₁〜Ｃ₁₀のアルキル、Ｃ₁〜Ｃ₁₀のハロゲン化アルキル、Ｃ₆〜Ｃ₂₀のアリール、Ｃ₆〜Ｃ₂₀のハロゲン化アリールをそれぞれ示す（これらのアルキル及びアリールはその構造中に置換基、ヘテロ原子を持ってもよく、また複数個存在するＲ³、Ｒ⁴はそれぞれが結合して環を形成してもよい。）。｝ The present invention provides a lithium ion secondary battery comprising at least a positive electrode, a negative electrode, and a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent.
The non-aqueous electrolyte contains, as the electrolyte, a first electrolyte made of a lithium salt containing fluorine, and a second electrolyte represented by the following general formula (1),
The positive electrode contains a lithium transition metal composite oxide as a positive electrode active material,
The negative electrode includes, as a negative electrode active material, metal oxide nanoparticles comprising a metal element oxide selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Nb, Pb, or W Containing
In the lithium ion secondary battery before charging / discharging, the average particle diameter of the metal oxide nanoparticles is 0.1 μm to 1 μm.

{However, M is a transition metal, Group III, IV, or V element of the periodic table, A ^{a +} is a metal ion, proton, or onium ion, a is 1 to 3, b is 1 to 3, p the b / a, m is 1 to 4, n is 0 to 8, q represents 0 or 1, respectively, R ¹ represents, C ₁ -C ₁₀ alkylene, a halogenated alkylene of C ₁ -C _10, C ₆ arylene -C _20, or C ₆ -C ₂₀ arylene halide (these alkylene and arylene substituent group in its structure, may have a hetero atom, and R ¹ binds each of the m exist R ² is halogen, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ alkyl halide, C ₆ -C ₂₀ aryl, C ₆ -C ₂₀ aryl halide, or X ³ R ³ (the alkyl and aryl substituents in their structures, even with a heteroatom And the n R ² each may combine with each other to form a ring ^{present.), X 1, X 2} , X 3 is O, S, or NR ^4, R ^3, R ⁴ are each Are independently hydrogen, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ alkyl halide, C ₆ -C ₂₀ aryl, C ₆ -C ₂₀ aryl halide (these alkyl and aryl May have a substituent or a heteroatom in the structure, and a plurality of R ³ and R ⁴ may be bonded to each other to form a ring). }

In the lithium ion secondary battery, the non-aqueous electrolyte contains the second electrolyte represented by the general formula (1) in addition to the first electrolyte. Since the second electrolyte can capture a small amount of water contained in the non-aqueous electrolyte solution, it is possible to avoid problems caused by the presence of water. Specifically, it is possible to prevent hydrogen fluoride (HF) from being generated by the reaction between the first electrolyte made of the above lithium salt containing fluorine such as LiPF ₆ and moisture. Therefore, it is possible to suppress the battery constituent material such as the active material from being corroded by HF, and to suppress a decrease in capacity and an increase in internal resistance when charging and discharging are repeated.

  Further, at least a part of the anion of the second electrolyte is reduced and decomposed when the lithium ion secondary battery is charged, and a stable decomposition film can be formed on the negative electrode. As a result, in the lithium ion secondary battery, even when charging / discharging is repeated, insertion / extraction of lithium ions is performed smoothly, and a decrease in capacity due to repeated charging / discharging can be suppressed. In addition, the decomposition film formed by decomposing the second electrolyte can cause an increase in reaction resistance in a negative electrode active material made of, for example, a carbon-based material. However, as in the lithium ion secondary battery of the present invention. Furthermore, in the negative electrode active material containing the metal oxide nanoparticle having an average particle size of 0.1 μm to 1 μm before charge / discharge, the increase in reaction resistance is small, and the increase in internal resistance can be suppressed.

  Thus, according to the present invention, there is provided a lithium ion secondary battery capable of suppressing a decrease in capacity and an increase in internal resistance when charging and discharging are repeatedly performed in a high temperature environment of about 60 ° C., for example. be able to.

Next, a preferred embodiment of the present invention will be described.
The lithium ion secondary battery includes, for example, the positive electrode and the negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and the non-aqueous electrolyte that moves lithium between the positive electrode and the negative electrode. It can be configured as a main component.

First, the negative electrode of the lithium ion secondary battery will be described.
The negative electrode includes, as a negative electrode active material, metal oxide nanoparticles comprising a metal element oxide selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Nb, Pb, or W Containing.
When the lithium ion secondary battery is charged, the metal oxide nanoparticles (A _m O _n ) are reduced to form a composite in which the metal nanoparticles (A) are dispersed in a Li ₂ O matrix. . Further, during the discharge of the lithium ion secondary battery, this reverse reaction occurs, and the metal nanoparticles (A) are oxidized to form metal oxide nanoparticles (A _m O _n ). These reversible oxidation-reduction reactions are represented by the following reaction formula (a) (where A is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Nb, Pb) , W is a metal element, m is 1 to 3, and n is 1 to 5).
(Reaction Formula a)

The average particle diameter of the metal oxide nanoparticle is 0.1 μm to 1 μm in the lithium ion secondary battery before charging / discharging, but changes depending on the charging / discharging of the lithium ion secondary battery. It is getting smaller.
That is, when the metal oxide nanoparticles are reduced by charging to form metal nanoparticles as described above, the average particle size of the metal nanoparticles can be about 2 to 8 nm. Further, when the metal nanoparticles are oxidized by the discharge to form the metal oxide nanoparticles again, the average particle diameter of the metal oxide nanoparticles can be 5 to 60 nm.

  When the average particle diameter of the metal oxide nanoparticles in a state before charge / discharge of the lithium ion secondary battery exceeds 1 μm, the metal nanoparticles are reduced to form metal nanoparticles. When it is oxidized again, it may be difficult to be oxidized. As a result, the oxidation-reduction reaction of the metal oxide nanoparticles may be difficult to proceed reversibly. In this case, the above-mentioned internal resistance suppression effect by the second electrolyte may be insufficient. On the other hand, the metal oxide nanoparticles having an average particle size of less than 0.1 μm may be difficult to produce. In addition, when the average particle diameter of the metal oxide nanoparticle is less than 0.1 μm, the surface area becomes large, and therefore, the metal oxide nanoparticle may be more likely to be deteriorated when repeated charge / discharge is performed.

  The above-mentioned average particle diameter is obtained by observing fine particles with a transmission electron microscope (TEM), measuring the particle diameter of, for example, 20 fine particles, and determining the average value. The particle size can be defined by the longest particle size of each fine particle.

The metal oxide nanoparticles _{is, TiO 2, Ti 2 O 3} , VO 2, V 2 O 3, V 2 O 5, Cr 2 O 3, MnO, Mn 2 O 3, Mn 3 O 4, MnO 2, FeO Fe ₂ O ₃ , Fe ₃ O ₄ , CoO, Co ₃ O ₄ , NiO, Ni ₂ O ₃ , CuO, Cu ₂ O, ZnO, MoO ₂ , MoO ₃ , NbO, Nb ₂ O ₅ , PbO, PbO ₂ , Pb ₃ O ₄ , WO ₃ , W ₂ O ₅ are preferable.
In this case, the reversible oxidation-reduction reaction represented by the above reaction formula (a) can proceed more stably.

  The negative electrode can be constituted by, for example, a current collector and a negative electrode active material layer formed on the surface thereof. The negative electrode active material layer is a negative electrode in which a binder and a conductive aid such as carbon for improving conductivity are mixed with the negative electrode active material, and an appropriate solvent is added as a dispersing agent to form a paste or slurry. The composite material can be formed by applying to the surface of the current collector, drying, and then compressing.

The negative electrode active material layer preferably contains 50 to 98% by weight of the negative electrode active material, 30 to 1% by weight of the conductive additive, and 20 to 1% by weight of the binder. When the negative electrode active material is less than 50% by weight, battery performance such as capacity may be deteriorated. On the other hand, if it exceeds 98% by weight, the amount of the binder is insufficient, and the particles of the negative electrode active material are not sufficiently bound. Therefore, there is a possibility that the conductivity is lowered. Further, when the conductive auxiliary exceeds 30% by weight, the amount of the negative electrode active material becomes insufficient and the battery performance such as capacity decreases, or the amount of the binder becomes insufficient and the particles of the negative electrode active material become There is a risk of sliding down. On the other hand, when the conductive assistant is less than 1% by weight, the conductivity may be insufficient. If the binder content exceeds 20% by weight, the amount of the negative electrode active material may be insufficient, resulting in a decrease in battery performance such as capacity, or an insufficient amount of conductive aid, resulting in a decrease in conductivity. There is. Further, when the binder is less than 1% by weight, the negative electrode active material particles are not sufficiently bound, and the negative electrode active material layer may slide down. More preferably, the negative electrode active material layer may contain 70 to 96% by weight of the negative electrode active material, 15 to 2% by weight of the conductive additive, and 15 to 2% by weight of the binder.
Moreover, as the negative electrode, a pellet electrode obtained by press-molding the negative electrode mixture can be used.

  The conductive additive is an additive blended to improve the conductivity of the negative electrode. As the conductive aid, for example, carbon powder such as carbon black and graphite can be used.

The binder serves to connect the negative electrode active material particles and to connect the negative electrode active material layer to the current collector, and a polymer material is used. The polymer material is required to have resistance to the non-aqueous solvent used in the non-aqueous electrolyte, stability to potential at which a battery reaction proceeds, heat resistance, and the like. Therefore, as the polymer material of the binder, for example, a fluororesin such as polyvinylidene fluoride, styrene-butadiene rubber, polyacrylonitrile, or the like can be used. These polymer materials can be used alone or in combination of two or more.
Moreover, as a solvent which disperse | distributes the said negative electrode active material, the said conductive support agent, and the said binder, organic solvents, such as N-methyl-2-pyrrolidone, can be used, for example.

  The current collector in the negative electrode is made of a conductive material such as metal. As the conductive material, it is preferable to use a material that does not form an alloy with lithium at the potential at which the battery reaction proceeds. Specifically, for example, copper, nickel, aluminum, titanium, stainless steel or the like can be used. Of these, one type may be used alone, or two or more types may be used in combination. More preferably, the current collector is made of copper or nickel. Further, as the current collector, for example, a metal foil made of the above-described metal or the like can be used.

Next, the positive electrode of the lithium ion secondary battery will be described.
The positive electrode can be constituted by, for example, a current collector and a positive electrode active material layer formed on the surface thereof. The positive electrode active material layer is prepared by mixing a positive electrode active material with a conductive additive or a binder as necessary, adding a suitable solvent as a dispersing agent to form a pellet or slurry, It can be formed by applying to the surface, drying, and then compressing. The positive electrode active material layer contains 50 to 98% by weight of the positive electrode active material, 30 to 1% by weight of the conductive additive, and 20 to 1% by weight of the binder for the same reason as in the case of the negative electrode. Is preferred.
Moreover, as the positive electrode, a pellet electrode obtained by press-molding the positive electrode mixture can be used.

  The positive electrode active material contains a lithium transition metal composite oxide. Specifically, for example, lithium transition metal composite oxides such as lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, and lithium iron phosphate can be used. As the positive electrode active material, only one kind of these compounds may be used, but two or more kinds may be used in combination.

  In addition, as the conductive auxiliary agent and the binder, the same materials as in the case of the negative electrode can be used. In addition, as the solvent for dispersing the positive electrode active material, the conductive additive, and the binder, an organic solvent such as N-methyl-2-pyrrolidone can be used as in the case of the negative electrode.

  As the current collector of the positive electrode, a metal such as aluminum or titanium or an alloy thereof can be used. Preferably, aluminum or an alloy thereof is used. Since aluminum or aluminum alloy is lightweight, in this case, energy density can be improved.

  Next, for example, a porous sheet made of a polyolefin such as polyethylene or polypropylene, a nonwoven fabric, or the like can be used as the separator to be narrowed between the positive electrode and the negative electrode.

Next, the non-aqueous electrolyte will be described.
The non-aqueous electrolyte of the lithium ion secondary battery is obtained by dissolving an electrolyte in a non-aqueous solvent.
As the non-aqueous solvent, an aprotic organic solvent can be used. Specifically, for example, cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), chain carbonates such as diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), γ-butyllactone (GBL), γ -Lactones such as valerolactone (GVL), nitriles such as acetonitrile, esters such as methyl acetate, methyl formate, methyl propionate, ethyl propionate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1, Ethers such as 2-dimethoxyethane and 1,2-diethoxyethane, amides such as dimethylformamide, and the like can be used. These can be used alone, or two or more kinds can be mixed and used.

  The non-aqueous electrolyte contains, as the electrolyte, a first electrolyte made of a lithium salt containing fluorine and a second electrolyte represented by the following general formula (1). The first electrolyte and the second electrolyte are ionized in the non-aqueous electrolyte to form respective cations and anions.

The first _{electrolyte, LiPF 6, LiBF 4, LiAsF} 6, and is preferably made of at least one of the above lithium salt selected from LiSbF ₆ (claim 3).
These electrolytes have relatively high ionic conductivity and are electrochemically stable. Therefore, in this case, the charge / discharge capacity of the lithium ion secondary battery can be further improved. LiPF ₆ is particularly preferable.

上記一般式（１）におけるＡ^a+としては、例えばリチウムイオン、ナトリウムイオン、カリウムイオン、マグネシウムイオン、カルシウムイオン、バリウムイオン、セシウムイオン、銀イオン、亜鉛イオン、銅イオン、コバルトイオン、鉄イオン、ニッケルイオン、マンガンイオン、チタンイオン、鉛イオン、クロムイオン、バナジウムイオン、ルテニウムイオン、イットリウムイオン、ランタノイドイオン、アクチノイドイオン、テトラブチルアンモニウムイオン、テトラエチルアンモニウムイオン、テトラメチルアンモニウムイオン、トリエチルメチルアンモニウムイオン、トリエチルアンモニウムイオン、ピリジニウムイオン、イミダゾリウムイオン、プロトン、テトラエチルホスホニウムイオン、テトラメチルホスホニウムイオン、テトラフェニルホスホニウムイオン、トリフェニルスルホニウムイオン、トリエチルスルホニウムイオン等が挙げられる。
好ましくは、上記一般式（１）におけるＡ^a+としては、リチウムイオン、テトラアルキルアンモニウムイオン、プロトンがよい。 The second electrolyte is a compound represented by the following general formula (1).

As A ^{a +} in the general formula (1), for example, lithium ion, sodium ion, potassium ion, magnesium ion, calcium ion, barium ion, cesium ion, silver ion, zinc ion, copper ion, cobalt ion, iron ion, nickel Ion, manganese ion, titanium ion, lead ion, chromium ion, vanadium ion, ruthenium ion, yttrium ion, lanthanoid ion, actinoid ion, tetrabutylammonium ion, tetraethylammonium ion, tetramethylammonium ion, triethylmethylammonium ion, triethylammonium Ion, pyridinium ion, imidazolium ion, proton, tetraethylphosphonium ion, tetramethylphosphonium ion, Tiger tetraphenylphosphonium ion, triphenylsulfonium ion, triethylsulfonium ion and the like.
Preferably, A ^{a +} in the general formula (1) is a lithium ion, a tetraalkylammonium ion, or a proton.

In the general formula (1), the valence a of A ^{a +} cation is 1-3. When a is larger than 3, the crystal lattice energy of the second electrolyte increases, so that it becomes difficult to dissolve in the organic solvent. Therefore, most preferably a = 1. Such cations A ^{a +} include lithium ions, potassium ions, sodium ions, tetraalkylammonium ions, protons, and the like.
Similarly, the valence b of the anion is 1 to 3, and b = 1 is most preferable.
The constant p representing the ratio of cation to anion is inevitably determined by the valence ratio b / a of both.

The second electrolyte has an ionic metal complex structure, and the central M is selected from a transition metal, a group III, group IV, or group V element of the periodic table.
Preferably, A ^{a +} in the general formula (1) is at least one selected from Li ⁺ , Na ⁺ , K ⁺ , and M is Al, B, V, Ti, Si, Zr, Ge, Sn, Cu. , Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf, or Sb.
In this case, the synthesis of the second electrolyte is facilitated.

  More preferably, M in the general formula (1) is Al, B, or P. In this case, in addition to facilitating the synthesis of the second electrolyte, the toxicity of the second electrolyte can be reduced, and the manufacturing cost can be reduced.

  Next, the ligand part of the second electrolyte (ionic metal complex) will be described. Hereinafter, in the above general formula (1), an organic or inorganic part bonded to M is referred to as a ligand.

R ¹ in general formula (1) is selected from C ₁ -C ₁₀ alkylene, C ₁ -C ₁₀ halogenated alkylene, C ₆ -C ₂₀ arylene, or C ₆ -C ₂₀ halogenated arylene. It consists of things. These alkylene and arylene may have a substituent or a hetero atom in the structure. Specifically, instead of hydrogen on alkylene and arylene, halogen, chain or cyclic alkyl group, aryl group, alkenyl group alkoxy group, aryloxy group, sulfonyl group, amino group, cyano group, carbonyl group, acyl group , An amide group, a hydroxyl group, and a structure in which nitrogen, sulfur, or oxygen is introduced instead of carbon on alkylene and arylene.
Further, when a plurality of R ¹ are present (when q = 1 and m = 2 to 4), each may be bonded, and examples thereof include a ligand such as ethylenediaminetetraacetic acid.

R ² is selected from halogen, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ alkyl halide, C ₆ -C ₂₀ aryl, C ₆ -C ₂₀ aryl halide, or X ³ R ³ It consists of things. Similarly to R ¹ , alkyl and aryl may have a substituent or a heteroatom in the structure, and when there are a plurality of R ² (when n = 2 to 8), each R ² is They may combine to form a ring.
Preferably, R ² is an electron-withdrawing group, particularly fluorine. In this case, it is possible to obtain an effect that the solubility and dissociation degree of the second electrolyte are improved and the ionic conductivity is improved accordingly. Furthermore, in this case, the oxidation resistance is improved, thereby preventing the occurrence of side reactions.

X ¹ , X ² , and X ³ are each independently O, S, or NR ⁴ , and the ligand is bonded to M through these heteroatoms. Here, it is not impossible to combine other than O, S, and N, but it becomes very complicated in synthesis. As a feature of the compound represented by the general formula (1), there is a bond between X ¹ and M by X ² in the same ligand, and these ligands form a chelate structure with M. . The constant q in this ligand is 0 or 1. When q = 0, the chelate ring becomes a five-membered ring, and the complex structure of the second electrolyte is stabilized. Therefore, in this case, the second electrolyte can be prevented from causing side reactions other than the formation of the coating.

R ³ and R ⁴ are each independently hydrogen, C _{1 to} C ₁₀ alkyl, C _{1 to} C ₁₀ alkyl halide, C _{6 to} C ₂₀ aryl, or C _{6 to} C ₂₀ aryl halide. There, the alkyl and aryl substituents in their structures, may have a hetero atom, and if R ^3, R ⁴ is plurally present, may each bind to other to form a ring .

The constants m and n related to the number of ligands described above are determined by the type of M at the center, and m is 1 to 4 and n is 0 to 8. Preferably n = 1-8.
It in ^{R 1, R 2, R 3} , R 4 described above, C ₁ -C ₁₀ indicates 1 to 10 carbon atoms, C ₆ -C ₂₀ is 6 to 20 carbon atoms Indicates.

As the second electrolyte represented by the general formula (1), it is preferable to use at least one compound represented by the following formulas (2) to (5) (Claim 5).

  The compounds represented by the above formulas (2) to (5) can be synthesized relatively easily. In addition, by using the compounds represented by the above formulas (2) to (5) as the second electrolyte, the lithium ion secondary battery has the above-described suppressing effect on the decrease in capacity retention rate and the increase in internal resistance. Can be exhibited more remarkably. More preferably, the second electrolyte is a compound containing P as the element M in the general formula (1) as in the formulas (3) to (5).

Particularly preferably, the second electrolyte is a compound represented by the above formula (4).
In the compound represented by the above formula (4), since the chelate ring in the structure is arranged as a target, the complex structure is stabilized. Therefore, in this case, the charge / discharge efficiency and capacity retention rate of the lithium ion secondary battery can be further improved.

In addition, as a method for synthesizing the second electrolyte, for example, in the case of the compound represented by the above formula (2), after reacting LiBF ₄ and 2 moles of lithium alkoxide in a non-aqueous solvent, oxalic acid is used. There is a method of adding and replacing alkoxide bonded to boron with oxalic acid.

In the non-aqueous electrolyte, the first electrolyte and the second electrolyte may be added in a molar ratio such that the first electrolyte: second electrolyte = 98-20: 2-80. Preferred (claim 7).
When the molar ratio of the second electrolyte to the first electrolyte is less than 2 or when the molar ratio of the first electrolyte to the second electrolyte exceeds 98, when charge and discharge are repeated under high temperature conditions In addition, the capacity of the lithium ion secondary battery may be easily reduced. On the other hand, when the molar ratio of the second electrolyte to the first electrolyte exceeds 80, or when the molar ratio of the first electrolyte to the second electrolyte is less than 20, the initial output of the lithium ion secondary battery is May decrease. More preferably, the first electrolyte is a main component of the electrolyte, and the second electrolyte is a subcomponent. More preferably, 1st electrolyte: 2nd electrolyte = 97-80: 3-20 is good.

  In addition, as the shape of the lithium ion secondary battery, for example, a cylindrical electrode having a sheet-like electrode (positive electrode and negative electrode) and a spiral spiral separator, a cylindrical electrode having an inside-out structure in which a pellet electrode and a separator are combined, a pellet electrode, There are coin types with separators.

Example 1
Next, an embodiment of the present invention will be described with reference to FIG.
In this example, seven types of lithium ion secondary batteries (battery E1 to battery E7) having different types of negative electrode active materials, second electrolytes, and the like are manufactured, and their characteristics are evaluated.

  As shown in FIG. 1, the lithium ion secondary battery 1 of this example has a roll electrode body 7 formed by winding a positive electrode 2 and a negative electrode 3, and the roll electrode body 7 is a 18650 type as a battery case 6. It is a cylindrical battery inserted into a cylindrical case. In the rolled electrode body 7, a separator 4 is sandwiched between the positive electrode 2 and the negative electrode 3, and the separator 4 is wound in a state of being sandwiched between the positive electrode 2 and the negative electrode 3. In addition, a non-aqueous electrolyte is injected into the battery case 6.

In the lithium ion secondary battery 1 of this example, the positive electrode 2 contains lithium nickelate (lithium nickel composite oxide) as a positive electrode active material.
Further, in the lithium ion secondary battery (battery E1 to battery E7) 1 of this example, the negative electrode 3 has CoO (average particle diameter of 1.0 μm), Co ₃ O ₄ (average particle diameter of 1.0 μm) as the negative electrode active material. Or metal oxide nanoparticles comprising Cu ₂ O (average particle size 1.0 μm).
In the lithium ion secondary batteries (battery E1 to battery E7), the non-aqueous electrolyte contains a mixed solvent of ethylene carbonate and diethyl carbonate as the non-aqueous solvent, and the first electrolyte made of LiPF ₆ as the electrolyte. And a second electrolyte of any one of the following formulas (3) to (5).

The manufacturing method of the lithium ion secondary battery (battery E1) 1 of this example will be described.
First, lithium nickelate was prepared as a positive electrode active material, and 85 parts by weight of the positive electrode active material, 10 parts by weight of carbon black as a conductive agent, and 5 parts by weight of polyvinylidene fluoride as a binder were mixed. An appropriate amount of N-methyl-2-pyrrolidone as a dispersant was added to this mixture, and the mixture was dispersed in the dispersant to produce a slurry-like positive electrode mixture.

  This positive electrode mixture was uniformly applied to both sides of an aluminum foil current collector having a thickness of 20 μm and dried by heating. Then, it densified with the roll press and produced the sheet-like positive electrode. The sheet-like positive electrode produced as described above was cut into a size of 52 mm in width and 450 mm in length to obtain a positive electrode 2 for the roll-shaped electrode body 7 (see FIG. 1).

  Next, metal oxide nanoparticles (average particle size 1 μm) made of CoO were prepared as the negative electrode active material. 85 parts by weight of the negative electrode active material, 10 parts by weight of carbon black as a conductive agent, and 5 parts by weight of polyvinylidene fluoride as a binder are mixed, and an appropriate amount of N-methyl-2-pyrrolidone as a dispersant is added. And dispersed to prepare a slurry-like negative electrode mixture. This negative electrode mixture was uniformly applied to both surfaces of a 10 μm thick copper foil current collector and dried by heating. Then, it densified with the roll press and cut out to the magnitude | size of width 54mm x length 500mm, and produced the sheet-like negative electrode 3. FIG.

Next, the non-aqueous electrolyte was prepared as follows.
That is, first, LiPF ₆ as the first electrolyte is added to an organic solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3: 7 so that the concentration becomes 1 mol / L. One electrolyte solution was prepared. In addition, an organic solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3: 7 is mixed with a compound represented by the above formula (4) (LiPF ₂ (C ₂ O ₄ )). ₂ ) was added to a concentration of 1 mol / L to prepare a second electrolyte solution.
Next, the first electrolyte solution and the second electrolyte solution were mixed to prepare a non-aqueous electrolyte. At this time, the 1st electrolyte and the 2nd electrolyte were mixed so that it might become 95: 5 (molar ratio), respectively.

Next, as shown in FIG. 1, a positive electrode current collecting lead 28 and a negative electrode current collecting lead 38 were welded to the sheet-like positive electrode 2 and negative electrode 3 obtained as described above, respectively.
A polyethylene-made separator 4 having a width of 56 mm and a thickness of 25 μm was sandwiched between the positive electrode 2 and the negative electrode 3, and the positive electrode 2, the negative electrode 3, and the separator 4 were wound to produce a spiral roll electrode body 7.

  Subsequently, the roll electrode body 7 was inserted into an 18650-type cylindrical battery case 6 including an outer can 62 and a cap 61. At this time, the positive electrode current collecting lead 28 is connected to the positive electrode current collecting tab 285 disposed on the cap 61 side of the battery case 6 by welding, and the negative electrode current collecting lead 385 is disposed on the negative electrode current collecting tab 385 disposed on the bottom of the outer can 62. 38 were connected by welding.

  Next, the battery case 6 was impregnated with a nonaqueous electrolytic solution. The gasket 5 was disposed inside the cap 61, and the cap 61 was disposed in the opening of the outer can 62. Subsequently, the battery case 6 was hermetically sealed by caulking the cap 61, and the cylindrical lithium ion secondary battery 1 was produced. This is referred to as a battery E1.

Further, in this example, lithium ion secondary batteries (battery E2 to battery E7) that are different from the battery E1 in the type of the negative electrode active material and the type of the second electrolyte were produced.
The battery E2 and the battery E3 are lithium ion secondary batteries manufactured using a second electrolyte different from the battery E1.
That is, the battery E2 was produced in the same manner as the battery E1 except that the compound (LiPF ₄ (C ₂ O ₄ )) represented by the above formula (3) was used as the second electrolyte.
The battery E3 was produced in the same manner as the battery E1, except that the compound (LiP (C ₂ O ₄ ) ₃ ) represented by the above formula (5) was used as the second electrolyte.

The battery E4 is a lithium ion secondary battery manufactured using a negative electrode active material (Co ₃ O ₄ ) different from the battery E1. Battery E4 was produced in the same manner as Battery E1, except that metal oxide nanoparticles having an average particle diameter of 1.0 μm made of Co ₃ O ₄ were used as the negative electrode active material.
The battery E5 is the above battery E1 is a lithium ion secondary battery manufactured using the different negative electrode active material (Co ₃ O ₄₎ and the second electrolyte _{(LiP (C 2 O 4)} 3). Battery E5 uses metal oxide nanoparticles having an average particle diameter of 1.0 μm made of Co ₃ O ₄ as the negative electrode active material and (LiP (C ₂ O ₄ ) ₃ ) as the second electrolyte. Was prepared in the same manner as the battery E1.

The battery E6 is a lithium ion secondary battery manufactured using a negative electrode active material (Cu ₂ O) different from the battery E1. Battery E6 was produced in the same manner as Battery E1, except that metal oxide nanoparticles having an average particle diameter of 1.0 μm made of Cu ₂ O were used as the negative electrode active material.
The battery E7 is a lithium ion secondary battery manufactured using a negative electrode active material (Cu ₂ O) and a second electrolyte (LiP (C ₂ O ₄ ) ₃ ) different from the battery E1. Battery E7 described above except that metal oxide nanoparticles having an average particle diameter of 1.0 μm made of Cu ₂ O were used as the negative electrode active material, and LiP (C ₂ O ₄ ) ₃ was used as the second electrolyte. It was produced in the same manner as the battery E1.

In this example, in order to clarify the excellent characteristics of the batteries E1 to E7, comparative lithium ion secondary batteries (batteries C1 to C8) were produced.
The battery C1 is a lithium ion secondary battery that does not contain the second electrolyte and uses the same negative electrode active material as the batteries E1 to E3. Specifically, the battery C1 uses metal oxide nanoparticles (average particle diameter: 1.0 μm) made of CoO as a negative electrode active material, and the first electrolyte solution, that is, ethylene carbonate (EC) and diethyl carbonate ( DEC) is a lithium ion secondary battery using a solution prepared by adding LiPF ₆ at a concentration of 1 mol / L to an organic solvent mixed with a volume ratio of 3: 7 as a non-aqueous electrolyte. Battery C1 was produced in the same manner as Battery E1, except that the first electrolyte solution was used as the non-aqueous electrolyte.

The battery C2 is a lithium ion secondary battery that does not contain the second electrolyte and uses the same negative electrode active material as the batteries E4 and E5. Specifically, the battery C2 uses metal oxide nanoparticles (average particle size: 1.0 μm) made of Co ₃ O ₄ as a negative electrode active material, and the first electrolyte solution, that is, ethylene carbonate (EC) and diethyl. A lithium ion secondary battery using a solution prepared by adding LiPF ₆ at a concentration of 1 mol / L to an organic solvent mixed with carbonate (DEC) at a volume ratio of 3: 7, as a non-aqueous electrolyte. The battery C2 was the same as the battery E1 except that the first electrolyte solution was used as the non-aqueous electrolyte and metal oxide nanoparticles made of Co ₃ O ₄ were used as the negative electrode active material. Produced.

The battery C3 is a lithium ion secondary battery that does not contain the second electrolyte and uses the same negative electrode active material as the batteries E6 and E7. Specifically, the battery C3 uses metal oxide nanoparticles (average particle size: 1.0 μm) made of Cu ₂ O as the negative electrode active material, and the first electrolyte solution, that is, ethylene carbonate (EC) and diethyl. A lithium ion secondary battery using a solution prepared by adding LiPF ₆ at a concentration of 1 mol / L to an organic solvent mixed with carbonate (DEC) at a volume ratio of 3: 7, as a non-aqueous electrolyte. The battery C3 was prepared in the same manner as the battery E1, except that the first electrolyte solution was used as the non-aqueous electrolyte and metal oxide nanoparticles made of Cu ₂ O were used as the negative electrode active material. did.

Battery C4 is a lithium ion secondary battery that does not contain the second electrolyte in the non-aqueous electrolyte and uses graphite as the negative electrode active material. Specifically, the battery C4 uses graphite as the negative electrode active material, and the first electrolyte solution, that is, ethylene carbonate (EC) and diethyl carbonate (DEC), as the non-aqueous electrolyte, is 3: 7. This is a lithium ion secondary battery using a solution prepared by adding LiPF ₆ to an organic solvent mixed at a volume ratio to a concentration of 1 mol / L. Battery C4 was produced in the same manner as Battery E1, except that the first electrolyte solution was used as the non-aqueous electrolyte and graphite was used as the negative electrode active material.

  The battery C5 is a lithium ion secondary battery containing graphite as a negative electrode active material and containing the same electrolyte solution as the battery E1, the battery E4, and the battery E6 as the non-aqueous electrolyte. Battery C5 was produced in the same manner as Battery E1, except that graphite was used as the negative electrode active material.

The battery C6 is a lithium ion secondary battery using metal oxide nanoparticles having an average particle diameter of 20 μm made of CoO as a negative electrode active material. Battery C6 was produced in the same manner as Battery E1, except that metal oxide nanoparticles having an average particle diameter of 20 μm made of CoO were used as the negative electrode active material.
The battery C7 is a lithium ion secondary battery using metal oxide nanoparticles having an average particle diameter of 30 μm made of Co ₃ O ₄ as a negative electrode active material. Battery C7 was produced in the same manner as Battery E1, except that metal oxide nanoparticles having an average particle diameter of 30 μm made of Co ₃ O ₄ were used as the negative electrode active material.
The battery C8 is a lithium ion secondary battery using metal oxide nanoparticles having an average particle diameter of 50 μm made of Cu ₂ O as a negative electrode active material. Battery C8 was produced in the same manner as Battery E1, except that metal oxide nanoparticles having an average particle diameter of 50 μm made of Cu ₂ O were used as the negative electrode active material.

Next, for the 15 types of lithium ion secondary batteries (battery E1 to battery E7 and battery C1 to battery C8) produced as described above, the following charge / discharge cycle test was performed, and the capacity maintenance rate before and after the test and The resistance increase rate was examined.
"Charge / discharge cycle test"
Each battery (battery E1-battery E7 and battery C1-battery C8) is charged at a constant current density of ² mA / cm ² under a temperature condition of 60 ° C., which is considered to be the upper limit of the actual use temperature range of the battery. was charged to a voltage 4.1 V, then charged and discharged for performing discharge at a constant current of current density of 2 mA / cm ² to a discharge lower limit voltage 1.0V as one cycle was performed the cycle a total of 500 cycles.

"Capacity maintenance rate"
Before and after the charge / discharge cycle test, the discharge current value (mA) of each battery was measured, and the value obtained by multiplying this discharge current value by the time (hr) required for discharge was calculated as the weight of the positive electrode active material in the battery. The discharge capacity was calculated by dividing by (g). When the discharge capacity before the charge / discharge cycle test is capacity A (initial discharge capacity) and the discharge capacity after the charge / discharge cycle test is capacity B, capacity retention rate (%) = capacity B / capacity A × 100 Based on the above, the capacity maintenance rate was calculated. The results are shown in Table 1.

"Resistance increase rate"
Each battery was adjusted to 50% (SOC = 50%) of the battery capacity under a temperature condition of 20 ° C., and a battery voltage after 10 seconds was measured by flowing a current of 0.5A, 1A, 2A, 3A, and 5A. The flowing current and voltage were linearly approximated, and the IV resistance (battery internal resistance) was determined from the slope.
The rate of increase in resistance is: resistance B (%) = (resistance B−resistance A) × 100, where resistance B is the IV resistance after the charge / discharge test and resistance A (initial IV resistance) is the IV resistance before the charge / discharge test. / Calculated based on the resistance A equation. The results are shown in Table 1.

In Table 1, as is known by comparing the batteries E1 to E3 and the battery C1, the battery E4 and the battery E5 and the battery C2, the battery E6 and the batteries E7 and the battery C3, various metal oxide nanoparticles as the negative electrode active material. In this case, by adding the second electrolyte in addition to the first electrolyte (LiPF ₆ ) in the non-aqueous electrolyte, it is possible to improve the capacity retention rate and suppress the resistance increase rate.
Further, as known from the results of the batteries C4 and C5, even when graphite is used as the negative electrode active material, the capacity retention rate can be improved and the resistance increase rate can be suppressed by using the second electrolyte. However, when the metal oxide nanoparticle is used as the negative electrode active material (battery E1 to battery E7), the capacity retention rate improvement effect and resistance by the second electrolyte are higher than when graphite is used (battery C5). The suppression effect of the increase rate was remarkably increased (see Table 1).

Further, as is known from Table 1, in lithium ion secondary batteries (batteries C6 to C8) using metal oxide particles having an average particle size exceeding 1 μm as the negative electrode active material, a metal having an average particle size of 1 μm or less. Compared to lithium ion secondary batteries (battery E1 to battery E7) using oxide particles, the initial discharge capacity and capacity retention rate were significantly reduced, and the resistance increase rate was also greatly increased.
Therefore, in the lithium ion secondary battery, the lithium oxide secondary battery uses a metal oxide nanoparticle having an average particle size of 1 μm or less as a negative electrode active material, and the lithium ion secondary battery has a synergistic effect due to the combined use of the first electrolyte and the second electrolyte. It can be seen that the capacity maintenance rate of the ion secondary battery can be remarkably improved and the resistance increase rate can be remarkably suppressed.

  Further, although not clearly shown in this example, when two or more kinds of materials are used as the negative electrode active material, if the metal oxide nanoparticles are used as at least one of them, the effect of addition is more than Although it may be reduced, it is considered that the same effect as this example can be obtained.

  As described above, according to this example, for example, a lithium ion secondary battery (battery) that can suppress a decrease in capacity and an increase in internal resistance when charging and discharging are repeatedly performed in a high temperature environment of about 60 ° C. E1-battery E7) can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the structure of the lithium ion secondary battery concerning Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 2 Positive electrode 3 Negative electrode 4 Separator 6 Battery case

Claims (7)

In a lithium ion secondary battery comprising at least a positive electrode, a negative electrode, and a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent,
The non-aqueous electrolyte contains, as the electrolyte, a first electrolyte made of a lithium salt containing fluorine, and a second electrolyte represented by the following general formula (1),
The positive electrode contains a lithium transition metal composite oxide as a positive electrode active material,
The negative electrode includes, as a negative electrode active material, metal oxide nanoparticles comprising a metal element oxide selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Nb, Pb, or W Containing
In the lithium ion secondary battery before charge / discharge, the metal oxide nanoparticle has an average particle size of 0.1 μm to 1 μm.

{However, M is a transition metal, Group III, IV, or V element of the periodic table, A ^{a +} is a metal ion, proton, or onium ion, a is 1 to 3, b is 1 to 3, p Is b / a, m is 1 to 4, n is 0 to 8, q is 0 or 1, R ¹ is C _{1 to} C ₁₀ alkylene, C _{1 to} C ₁₀ alkylene halide, C ₆ arylene -C _20, or C ₆ -C ₂₀ arylene halide (these alkylene and arylene substituent group in its structure, may have a hetero atom, and R ¹ binds each of the m exist and may be.), R ² is halogen, C ₁ -C alkyl _10, C ₁ -C ₁₀ halogenated alkyl, aryl C ₆ -C _20, an aryl halide of C ₆ -C _20, or X ³ R ³ (the alkyl and aryl substituents in their structures, even with a heteroatom And the n R ² each may combine with each other to form a ring ^{present.), X 1, X 2} , X 3 is O, S, or NR ^4, R ^3, R ⁴ are each Are independently hydrogen, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ alkyl halide, C ₆ -C ₂₀ aryl, C ₆ -C ₂₀ aryl halide (these alkyl and aryl May have a substituent or a heteroatom in the structure, and a plurality of R ³ and R ⁴ may be bonded to each other to form a ring). } In claim 1, the metal oxide nanoparticles _{is, TiO 2, Ti 2 O 3} , VO 2, V 2 O 3, V 2 O 5, Cr 2 O 3, MnO, Mn 2 O 3, Mn 3 O 4 _{, MnO 2, FeO, Fe 2} O 3, Fe 3 O 4, CoO, Co 3 O 4, NiO, Ni 2 O 3, CuO, Cu 2 O, ZnO, MoO 2, MoO 3, NbO, Nb 2 O 5 , PbO, PbO ₂ , Pb ₃ O ₄ , WO ₃ , W ₂ O ₅ According to claim 1 or 2, the first _{electrolyte, LiPF 6, LiBF 4, LiAsF} 6, and at least one lithium ion secondary battery, characterized by comprising the above lithium salt selected from LiSbF _6. In any one of claims 1 to 3, A ^{a +} is in the above general formula ^{(1), Li +, Na} +, are at least one selected from K ^+, M is, Al, B, V, Ti , A lithium ion secondary battery, which is any one of Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf, or Sb. 5. The at least one compound represented by the following formulas (2) to (5) is used as the second electrolyte represented by the general formula (1) according to claim 1. The lithium ion secondary battery characterized by the above-mentioned.

  6. The lithium ion secondary battery according to claim 5, wherein a compound represented by the formula (4) is used as the second electrolyte.   7. The electrolyte according to claim 1, wherein the first electrolyte and the second electrolyte are in a molar ratio of the first electrolyte: second electrolyte = 98-20: 2 in the non-aqueous electrolyte. A lithium ion secondary battery, wherein the lithium ion secondary battery is added so as to be ˜80.

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