JP2008010183A - Lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery which has both high output and output durability in a high level. <P>SOLUTION: The lithium ion secondary battery includes at least a cathode, an anode 3, and a nonaqueous electrolyte obtained by dissolving an electrolyte in a nonaqueous solvent. The anode 3 has a current collector 31 composed mainly of a metal, and an anode active material layer 35 disposed thereon. The anode active material layer 35 contains an anode active material 32 composed of a carbonaceous material which can occlude or release lithium ions, a conductive material 36, and a binder 34. The anode active material layer 35 contains hard carbon as the carbonaceous material, carbon black as the conductive material 36, and a polymer containing a nitrogen atom or an oxygen atom as the binder 34. <P>COPYRIGHT: (C)2008,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.

  In general, a negative electrode of a lithium ion secondary battery includes a current collector and a negative electrode active material layer containing a negative electrode active material disposed on the current collector. Conventionally, a graphite-based carbon material has been used as the negative electrode active material of the lithium ion secondary battery. However, while the graphite-based carbon material has a high volumetric energy density, it has the following problems.

  That is, first, the graphite-based carbon material is in the form of a plate or scale having a laminated structure, so that the conductivity in the direction of the laminated surface is excellent, but the conductivity in the direction perpendicular to the laminated surface is poor. There was a problem. In addition, the graphite-based carbon material has a large volume change during charging and discharging, and a volume change of about 10% occurs. Therefore, the electrode may be destroyed by this volume change. Furthermore, when the graphite-based carbon material comes into contact with an organic solvent such as propylene carbonate, which is widely used as an electrolyte for lithium ion secondary batteries, delamination may occur in the laminated structure, which may reduce battery performance. .

  Therefore, a technique using hard carbon as a negative electrode active material of a lithium ion secondary battery has been proposed (see Patent Document 1). When hard carbon is used as the negative electrode active material, the above-described problems caused by using a graphite-based carbon material can be solved. Therefore, by using hard carbon as the negative electrode active material, battery characteristics such as charge / discharge cycle characteristics of the lithium ion secondary battery can be improved as compared with the case of using a graphite-based carbon material.

  Incidentally, in recent years, lithium ion secondary batteries are expected as power sources for automobiles such as electric vehicles (EV) and hybrid vehicles (HEV). Therefore, further higher output is required for the lithium ion secondary battery. Further, as a power source for automobiles, it is desired that the battery can be used for a long period of time, and a lithium secondary battery excellent in output durability is demanded so that the output is not easily lowered even after repeated charge and discharge.

  Therefore, reduction of electric resistance has been studied even in a negative electrode using hard carbon. Specifically, a technique for adding scaly graphite to the negative electrode active material layer of the negative electrode has been proposed (see Patent Document 2). Further, a technique for adding polyvinylidene fluoride and carbon black to the negative electrode active material layer of the negative electrode has been proposed (Patent Document 3).

However, scaly graphite has the same problem as the above-mentioned graphite-based carbon material, and when scaly graphite is used, there is a possibility that the output of the lithium ion secondary battery cannot be sufficiently improved. there were.
Further, according to the technique of adding the above-mentioned polyvinylidene fluoride and carbon black, the output density can be improved, but the adhesion of the negative electrode active material layer is lowered, so that sufficient output durability cannot be obtained. There was a problem. There is also a method of increasing the amount of polyvinylidene fluoride in order to ensure adhesion, but in this case, the electrical resistance of the negative electrode increases and battery characteristics such as capacity may be deteriorated.

JP 2001-126760 A International Publication No. 98/05083 JP 2005-317469 A

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a lithium ion secondary battery that combines high output and excellent output durability at a high level.

The present invention relates to 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 negative electrode has a current collector mainly composed of a metal, and a negative electrode active material layer disposed on the current collector.
The negative electrode active material layer contains a negative electrode active material made of a carbon material capable of occluding or releasing lithium ions, a conductive material, and a binder.
The negative electrode active material layer contains hard carbon as the carbon material, carbon black as the conductive material, and a polymer containing a nitrogen atom or an oxygen atom as the binder. It exists in a secondary battery (Claim 1).

  In the lithium ion secondary battery of the present invention, the negative electrode active material layer contains the hard carbon having excellent conductivity as the negative electrode active material, and contains carbon black as the conductive material. Therefore, the resistance of the negative electrode can be reduced, and the conductivity of the negative electrode can be improved. Therefore, the lithium ion secondary battery can exhibit high output.

  The negative electrode active material layer contains the polymer containing a nitrogen atom or an oxygen atom as the binder. Therefore, the adhesion of the negative electrode active material layer to the current collector can be improved, and the negative electrode active material layer can be held on the current collector for a long period of time with excellent adhesion. Therefore, the lithium ion secondary battery is not easily deteriorated in output even when used for a long time, and the output durability is improved.

  Moreover, since the said binder can adhere the said negative electrode active material layer to the said electrical power collector with the outstanding adhesiveness, it is not necessary to increase the amount of binders more than necessary. That is, the adhesiveness of the negative electrode active material layer to the current collector can be improved without substantially impairing the conductivity of the negative electrode. Therefore, the lithium ion secondary battery can have high output and excellent output durability at a high level.

The reason why the above polymer of nitrogen atom and / or oxygen atom can hold the negative electrode active material layer on the current collector with excellent adhesion is considered as follows.
That is, since the current collector contains metal as a main component, it is considered that a metal oxide is formed on at least a part of the surface by natural oxidation. Since this metal oxide and the nitrogen atom and / or oxygen atom in the polymer exhibit high affinity, the polymer is considered to exhibit excellent adhesion as described above.

  Thus, according to the present invention, it is possible to provide a lithium ion secondary battery that combines high output and excellent output durability at a high level.

Next, a preferred embodiment of the present invention will be described.
The lithium ion secondary battery of the present invention has a positive electrode, a negative electrode, and a nonaqueous electrolytic solution obtained by dissolving an electrolyte in a nonaqueous solvent. Specifically, 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-transferring lithium between the positive electrode and the negative electrode. A water electrolyte or the like can be configured as a main component.

First, the negative electrode will be described.
The negative electrode can be constituted by the current collector containing metal as a main component and the negative electrode active material layer formed on the surface thereof. The negative electrode active material layer is, for example, applied to the surface of the current collector by mixing the binder and the conductive material into the negative electrode active material, adding a suitable solvent as a dispersing agent to form a slurry, It can be formed by drying and subsequent compression. As the negative electrode, a pellet electrode obtained by press-molding the negative electrode mixture can be used.

Hard carbon is used as the negative electrode active material (carbon material). Hard carbon is a carbon material whose stacking order hardly changes even when heat-treated at a high temperature of 2000 ° C. or higher, and is also called non-graphitizable carbon.
The average particle diameter of hard carbon is preferably 0.1 to 20 μm. When the average particle diameter of the hard carbon is less than 0.1 μm, the contact resistance between the hard carbon particles increases, which may increase the resistance of the entire negative electrode. On the other hand, if it exceeds 20 μm, the surface area of the hard carbon particles exposed to the electrolyte solution on the negative electrode surface decreases, and the contact area between the electrolyte solution and the hard carbon particles decreases, which may increase the electrode reaction resistance. is there. Furthermore, since the lithium ion conduction path inside the hard carbon particles becomes long and lithium ions occluded inside the particles are difficult to desorb, the reaction efficiency may be lowered. More preferably, the average particle size of the hard carbon is 1 to 15 μm.

Further, carbon black is used as the conductive material. Carbon black is a carbon material produced by thermally decomposing liquid or gaseous hydrocarbons. As said carbon black, 1 or more types chosen from acetylene black, Ketjen black, channel black, furnace black, thermal black etc. can be used, for example.
Preferably, acetylene black is used as the carbon black. In general, acetylene black having a structure in which primary particles are connected is excellent in conductivity, and can further improve the conductivity of the negative electrode active material layer. Therefore, the output characteristics of the lithium secondary battery can be further improved.

  As the binder, a polymer containing a nitrogen atom and / or an oxygen atom is used. The binder serves to connect the hard carbon particles and to connect the negative electrode active material layer to the current collector. Moreover, as said binder, the polymer provided with the tolerance with respect to the said nonaqueous solvent used for the said nonaqueous electrolyte, the stability with respect to the electric potential which a battery reaction advances, heat resistance, etc. is preferable.

  Specific examples of the polymer used as the binder include a modified fluororesin in which a fluororesin such as polyvinylidene fluoride is modified with a functional group containing an oxygen atom such as a carboxyl group. Further, as the polymer, acrylic resin such as polyacrylonitrile and polyamide containing nitrogen atom, polymethyl methacrylate containing oxygen atom, and the like can be used. These polymers can be used alone or in combination of two or more.

  In addition, as a solvent for dispersing the negative electrode active material, the conductive material, and the binder, for example, an organic solvent such as N-methyl-2-pyrrolidone can be used.

The negative electrode active material layer preferably contains 50 to 95% by weight of the negative electrode active material, 1 to 20% by weight of the conductive material, and 4 to 30% 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. Moreover, when the said electrically conductive material is less than 1 weight%, there exists a possibility that it may become difficult to fully improve the output performance of the said lithium secondary battery. Moreover, when the said binder is less than 4 weight%, there exists a possibility that it may become difficult to fully improve the adhesiveness with respect to the said collector of the said negative electrode active material layer. In addition, when the negative electrode active material exceeds 95% by weight, the amount of the conductive material or the binder decreases, and thus it may be difficult to improve the output performance and adhesion described above. In addition, when the conductive material exceeds 20% by weight, the amount of the negative electrode active material or the binder decreases, so that it is difficult to reduce battery performance such as capacity or to improve the above-described adhesion. There is a risk. Further, when the binder exceeds 30% by weight, the amount of the negative electrode active material or the conductive material is reduced, so that battery performance such as capacity is lowered or it is difficult to improve the output performance described above. There is a risk. More preferably, the negative electrode active material layer preferably contains 60 to 90% by weight of the negative electrode active material, 3 to 20% by weight of the conductive material, and 7 to 20% by weight of the binder.

Moreover, it is preferable that the density of the active material in the said negative electrode active material layer is 0.6-1.0 g / cm < ³ >. When the density is less than 0.6 g / cm ³ , the contact resistance on the surface of the hard carbon particles increases, and the electrical resistance on the negative electrode may increase. On the other hand, if it exceeds 1.0 g / cm ³ , the electrolyte may not sufficiently permeate between the hard carbon particles, and the lithium ion conduction resistance may increase. As a result, the electrical resistance at the negative electrode may increase. More preferably, the density of the active material is 0.7 to 0.9 g / cm ³ . The density of the active material in the negative electrode active material layer is the weight of the negative electrode active material (hard carbon) contained per unit volume of the negative electrode active material layer. The density of the active material in the negative electrode active material layer can be adjusted by pressing the negative electrode to adjust the thickness of the negative electrode active material layer.

Moreover, it is preferable that the thickness of the said negative electrode active material layer is 5-100 micrometers.
If the thickness is less than 5 μm, the battery capacity may be insufficient. On the other hand, when it exceeds 100 μm, the ionic conductivity in the negative electrode active material layer may be lowered, and the charge / discharge characteristics under high output may be insufficient. More preferably, the thickness of the negative electrode active material layer is 10 to 70 μm.

  In addition, the current collector in the negative electrode contains metal as a main component and mediates the movement of electrons between the negative electrode active material layer and an external load. As the metal that is the main component of the current collector, it is preferable to use a metal that does not form an alloy with lithium at the potential at which the battery reaction proceeds. Specifically, for example, copper, nickel, 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.

  The thickness of the current collector is preferably 1 to 50 μm. When the thickness is less than 1 μm, the current collector cannot withstand the stress when the negative electrode active material layer is formed on the current collector surface, and the current collector may be cut or cracked. On the other hand, when the thickness exceeds 50 μm, the manufacturing cost increases and the battery may be increased in size. More preferably, the thickness of the current collector is 5 to 20 μm.

Next, the positive electrode will be described.
The positive electrode can be constituted by, for example, a current collector and a positive electrode active material layer containing a positive electrode active material formed on the surface thereof, similarly to the negative electrode. The positive electrode active material layer is prepared by mixing a positive electrode active material with a conductive material or a binder as necessary, adding a suitable solvent as a dispersing agent to form a slurry, and coating the surface of the current collector. It can be formed by drying and subsequent compression. Moreover, as the positive electrode, a pellet electrode obtained by press-molding the positive electrode mixture can be used.

  As the positive electrode active material, a compound capable of inserting or extracting lithium ions can be used. Specifically, examples of the positive electrode active material include lithium transition metal composite oxides such as lithium manganese oxide, lithium cobalt oxide, and lithium nickel oxide, and lithium transition metal phosphate compounds such as 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.

The said electrically conductive material used for the said positive electrode is an additive mix | blended in order to improve the electroconductivity of a positive electrode active material layer, For example, carbon powder, such as carbon black and a graphite, can be used.
Moreover, as said binder used for the said positive electrode, polymeric materials, such as fluorine resins, such as a polyvinylidene fluoride, a styrene-butadiene type rubber, a polyacrylonitrile, can be used, for example. A binder similar to that of the negative electrode can also be used. These polymer materials can be used alone or in combination of two or more.

  As the current collector of the positive electrode, for example, 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.

  Moreover, about the compounding ratio of the positive electrode active material in the positive electrode active material layer in a positive electrode, a electrically conductive material, and a binder, the thickness of an electrical power collector, and the density of an active material, it is the same as that of the above-mentioned negative electrode.

  Moreover, as said separator narrowly provided between a positive electrode and a negative electrode, the porous sheet | seat which uses polyolefin, such as polyethylene and a polypropylene, for example, or a nonwoven fabric can be used.

Next, the nonaqueous electrolytic solution is obtained by dissolving an electrolyte in a nonaqueous 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.

｛但し、Ｍは、遷移金属、周期律表のIII族、IV族、又はV族元素、ｂは１〜３、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。）。｝ Moreover, it is preferable that the said non-aqueous electrolyte contains the anion compound represented by following General formula (1) (Claim 3).

{However, M is a transition metal, a group III, IV or V element of the periodic table, b is 1 to 3, m is 1 to 4, n is 0 to 8, q is 0 or 1 respectively. , R ¹ is C ₁ -C ₁₀ alkylene, C ₁ -C ₁₀ halogenated alkylene, C ₆ -C ₂₀ arylene, or C ₆ -C ₂₀ halogenated arylene (the alkylene and arylene have the structure) And R ¹ may be bonded to each other.), R ² is halogen, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ Alkyl halides, C ₆ -C ₂₀ aryls, C ₆ -C ₂₀ aryl halides, or X ³ R ³ (these alkyls and aryls may have substituents, heteroatoms in their structures, the n number R ² each may combine with each other to form a ring present.), X ^{1, 2,} X ³ is O, S, or NR ^4, R ^3, R ⁴ are, each independently, hydrogen, alkyl of C ₁ -C _10, alkyl halide C ₁ ~C _10, C ₆ ~C ₂₀ aryls and C ₆ -C ₂₀ aryl halides are shown respectively. (These alkyls and aryls may have a substituent or a hetero atom in the structure, and a plurality of R ³ and R ⁴ are respectively present. May combine to form a ring. }

When the anionic compound is contained, it is possible to suppress a decrease in the output of the lithium ion secondary battery when charging and discharging are repeated. That is, the output durability of the lithium ion secondary battery can be further improved.
The reason is considered as follows.
That is, the anionic compound represented by the general formula (1) can form a coating such as an electrochemically stable coating on the active material surface. By forming the coating, it is considered that in the lithium ion secondary battery, even when charging and discharging are repeatedly performed, lithium ions are smoothly inserted and extracted, and a decrease in output can be suppressed.

In the said General formula (1), the valence b of an anion is 1-3. When b is larger than 3, the crystal lattice energy of the salt of the anionic compound is increased, so that it is difficult to form the anionic compound by dissolving the salt of the anionic compound in the non-aqueous solvent. Therefore, b = 1 is most preferable.
For the same reason, the valence of the cation constituting the salt of the anionic compound is preferably 1 to 3, and most preferably the valence of the cation is 1. Examples of such cations include lithium ions, sodium ions, rubidium ions, cesium ions, potassium ions, tetraalkylammonium ions, and protons.

  In addition, the anion compound represented by the general formula (1) has an ionic metal complex structure, and M as the center is a transition metal, a group III, group IV, or group V element of the periodic table. Chosen from.

In the non-aqueous electrolyte, the electrolyte compound composed of the anion compound and the cation represented by the general formula (1) is ionized, and M in the general formula (1) is Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf, or Sb, and the cation is at least Li ⁺ or Na + One is preferable (claim 4).
In this case, the nonaqueous electrolytic solution containing the anionic compound can be easily prepared by dissolving the electrolyte compound, that is, the salt of the anionic compound in the nonaqueous solvent. In this case, the anion compound or the electrolyte compound can be easily synthesized.

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

In addition to the electrolyte compound composed of the anion compound and the cation represented by the general formula (1), another electrolyte is added to the non-aqueous electrolyte as the electrolyte. Is preferably 2 to 80% by weight based on the total electrolytic mass (Claim 5).
When the amount of the electrolyte compound added is less than 2% by weight, the effect of improving the output durability may not be sufficiently obtained. The reason for this is considered that a coating such as a film formed on the surface of the active material by the anionic compound is not sufficiently formed. On the other hand, when the amount of the electrolyte compound added exceeds 80% by weight, the resistance increases, and the capacity of the lithium ion secondary battery may be reduced. This is probably because the thickness of the coating formed on the surface of the active material becomes larger than necessary.

The aforementioned non-aqueous electrolyte solution, as other electrolytes other than the above electrolyte _{compounds, LiPF 6, LiBF 4, LiAsF} 6, LiSbF 6, LiClO 4, Li (C 2 F 5 SO 2) 2 N, LiN (SO _{2 CF 3) 2, Li (} SO 3 C 2 F 5), it is preferable that at least one member selected from lithium Bisuo Kisara oxalatoborate (LiBOB) is added (claim 6).
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.

Next, the ligand part of the anionic compound will be described.
Hereinafter, in the present specification, an organic or inorganic part bonded to M in the general formula (1) 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 Examples thereof include a 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.
Furthermore, 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 or 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, the solubility and dissociation degree of the salt of the anionic compound can be improved, and the effect of improving the ionic conductivity can be obtained. 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 the synthesis becomes very complicated. 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 anionic compound is stabilized. Therefore, in this case, the anionic compound 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. These alkyls and aryls may have a substituent or a heteroatom in the structure, and when a plurality of R ³ and R ⁴ are present, each may be bonded 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.
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 said anion compound represented by the said General formula (1), 1 or more types represented, for example by following formula (2)-(5) can be used.
In this case, the solubility and dissociation degree of the salt of the anionic compound can be improved, and the ionic conductivity of the non-aqueous electrolyte can be improved. Furthermore, in this case, oxidation resistance can be improved.

Preferably, as the anion compound, a compound represented by the above formula (4) (LiPF ₂ (C ₂ O ₄ ) ₂ ) may be used.
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 output durability of the lithium ion secondary battery can be further improved.

  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 FIGS.
In this example, six types of lithium ion secondary batteries (Sample E1 to Sample E4, Sample C1, and Sample C2) having different types and blending ratios of binders in the negative electrode are prepared, and their output characteristics are compared.

First, the lithium ion secondary battery of sample E1 will be described.
As shown in FIG. 1, the sample E <b> 1 is a cylindrical lithium secondary battery 1. The lithium ion secondary battery 1 includes a positive electrode 2, a negative electrode 3, a separator 4, a gasket 59, a battery case 6, and the like. The battery case 6 is a 18650-type cylindrical battery case, and includes a cap 63 and an outer can 65. In the battery case 6, a sheet-like positive electrode 2 and a negative electrode 3 are arranged in a wound state together with a separator 4 sandwiched between the positive electrode 2 and the negative electrode 3.

A gasket 59 is disposed inside the cap 63 of the battery case 6, and a non-aqueous electrolyte is injected into the battery case 6.
The positive electrode 2 includes a current collector made of an aluminum foil and a positive electrode active material layer disposed on the current collector. The positive electrode active material layer contains 85 wt% of lithium nickelate (LiNiO ₂ ) as the positive electrode active material, 10 wt% of carbon black as the conductive material, and 5 wt% of polyvinylidene fluoride as the binder.
As shown in FIG. 2, the negative electrode 3 includes a current collector 31 made of copper foil, and a negative electrode active material layer 35 disposed on the current collector 31. The negative electrode active material layer 35 contains 85 wt% of hard carbon as the negative electrode active material 32, 10 wt% of acetylene black as the conductive material 36, and 5 wt% of polyacrylonitrile as the binder 34. Polyacrylonitrile is a polymer having a nitrogen atom.

  As shown in FIG. 1, a positive electrode current collector lead 23 and a negative electrode current collector lead 33 are provided on the positive electrode 2 and the negative electrode 3, respectively, by welding. The positive electrode current collector lead 23 is connected to the positive electrode current collector tab 235 disposed on the cap 63 side by welding. Further, the negative electrode current collecting lead 33 is connected by welding to a negative electrode current collecting tab 335 disposed on the bottom of the outer can 65.

The nonaqueous electrolytic solution is obtained by dissolving 1 M of LiPF ₆ in a nonaqueous solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) at 30:70 (volume ratio). This non-aqueous electrolyte is injected into the battery case 6.

Hereinafter, the manufacturing method of the lithium ion secondary battery (sample E1) of this example will be described.
First, the nonaqueous electrolyte solution was prepared as follows.
That is, first, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 30:70 to prepare a non-aqueous solvent. Next, as an electrolyte, LiPF ₆ was dissolved in a non-aqueous solvent so as to have a concentration of 1 M to prepare a non-aqueous electrolyte.

Next, the positive electrode 2 and the negative electrode 3 were produced as follows.
In preparing the positive electrode 2, first, LiNiO ₂ (lithium nickelate) having a discharge capacity of 190 mAh / g was prepared as a positive electrode active material. This positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride as a binder are mixed, and an appropriate amount of N-methyl-2-pyrrolidone as a dispersing agent is added and dispersed to form a slurry-like positive electrode mixture. Was made. The mixing ratio of the positive electrode active material, the conductive material, and the binder was a weight ratio of positive electrode active material: conductive material: binder = 85: 10: 5.

Next, the positive electrode mixture obtained as described above was applied to both surfaces of an aluminum foil current collector having a thickness of 20 μm by a coater and dried. Then, it densified with the roll press, cut out in the shape of 52 mm width x 450 mm length, and produced the sheet-like positive electrode 2. The amount of positive electrode active material deposited was about 7.0 mg / cm ² per side.

  On the other hand, in producing the negative electrode 3, first, hard carbon having a discharge capacity of 340 mAh / g was prepared as the negative electrode active material 32. This negative electrode active material 32, acetylene black as the conductive material 36, and polyacrylonitrile as the binder 34 are mixed, and an appropriate amount of N-methyl-2-pyrrolidone is added as a dispersing agent, and dispersed to form a slurry-like negative electrode composite. The material was obtained. The mixing ratio of the negative electrode active material, the conductive material, and the binder was a weight ratio of negative electrode active material: conductive material: binder = 85: 10: 5. The amount of the dispersing material was adjusted so that the negative electrode active material, the conductive material, and the binder were sufficiently dispersed while adjusting the viscosity of the slurry.

Next, the negative electrode mixture obtained as described above was applied to both surfaces of a copper foil current collector 31 having a thickness of 10 μm by a coater and dried. Then, it densified with the roll press and cut out into the shape of 54 mm width x 500 mm length. Thereby, a sheet-like negative electrode 3 in which the negative electrode active material layer 35 was disposed on the current collector 31 was produced. The adhesion amount of the negative electrode active material 32 was about 4.4 mg / cm ² per side.

  Next, as shown in FIG. 1, a positive electrode current collecting lead 23 and a negative electrode current collecting lead 33 were welded to the sheet-like positive electrode 2 and negative electrode 3 obtained as described above, respectively. The positive electrode 2 and the negative electrode 3 were wound in a state where a polyethylene separator 4 having a width of 56 mm and a thickness of 25 μm was sandwiched between them, and a roll-shaped electrode body was produced.

  Subsequently, the roll-shaped electrode body was inserted into an 18650-type cylindrical battery case 6 including an outer can 65 and a cap 63. At this time, the positive electrode current collecting lead 23 is connected to the positive electrode current collecting tab 235 arranged on the cap 63 side of the battery case 6 by welding, and the negative electrode current collecting lead is arranged on the negative electrode current collecting tab 335 arranged on the bottom of the outer can 65. 33 was connected by welding.

  Next, the battery case 6 was impregnated with the non-aqueous electrolyte prepared as described above. A gasket 59 is disposed inside the cap 63, and the cap 63 is disposed in the opening of the outer can 65. Subsequently, the battery case 6 was sealed by caulking the cap 63, and the lithium ion secondary battery 1 was produced. This was designated as Sample E1.

Further, in this example, five types of lithium ion secondary batteries (sample E2 to sample E4, sample C1, and sample C2), which are different from the sample E1 in the type and blending ratio of the binder in the negative electrode, were prepared.
Sample E2 was prepared in the same manner as Sample E1 except that an acrylic resin was used as the negative electrode binder. The acrylic resin is a polymer having oxygen atoms.

Sample E3 was prepared in the same manner as Sample E1 except that modified polyvinylidene fluoride was used as the negative electrode binder. The modified polyvinylidene fluoride used in this example is a polymer obtained by adding a carboxyl group to polyvinylidene fluoride and has an oxygen atom.
In sample E4, the negative electrode active material: conductive material: binder = 81: 9.5: 9.5 was mixed at the weight ratio of the negative electrode active material, the conductive material, and the binder when the negative electrode mixture was produced. The sample was prepared in the same manner as the sample E1 except for.

Sample C1 was prepared in the same manner as Sample E1, except that unmodified polyvinylidene fluoride was used as the binder for the negative electrode.
Sample C2 uses modified polyvinylidene fluoride as the negative electrode binder, and the negative electrode active material: conductive material: binder in the weight ratio of the mixing ratio of the negative electrode active material, the conductive material, and the binder during the preparation of the negative electrode mixture. = 81: 9.5: A sample was produced in the same manner as the sample E1 except that it was set to 9.5.

  Next, the following output test is performed on the six types of lithium ion secondary batteries (sample E1 to sample E4, sample C1, and sample C2) manufactured as described above, and the output (initial output) of each battery is calculated. It was measured.

"Output test"
First, each sample was adjusted to 50% of the battery capacity (SOC = 50%). Next, discharging was performed by flowing an output current for 10 seconds at arbitrary 5 to 6 points in the range of 0.25 to 10 mA / cm ² . And the voltage when discharging for 10 second by each output current value was measured. The measurement was performed at a temperature of 20 ° C. From the obtained voltage value and output current value, the current value at the battery lower limit voltage of 2.0 V was calculated. The output (initial output; W) was calculated from the current value at the lower limit voltage of 2.0 V. The results are shown in Table 1. In Table 1, the initial output of each sample is shown as a relative value when the initial output of the sample E1 is 100.

Moreover, the following charging / discharging cycle test was done about each sample.
"Charge / discharge cycle test"
Charge the lithium ion secondary battery of each sample to a maximum charge voltage of 4.1 V at a constant current density of 2.0 mA / cm ² under a temperature condition of 60 ° C, which is considered to be the upper limit of the actual operating temperature range of the battery. Then, charging / discharging for discharging to a discharge lower limit voltage of 2.5 V at a constant current of a current density of 2.0 mA / cm ^{2 was} defined as one cycle, and this cycle was performed for a total of 500 cycles.

Next, the output test was performed on each sample after the charge / discharge cycle test. Thereby, the output after the charge / discharge cycle test was calculated. Then, when the output before the charge / discharge cycle test (initial output) was output A and the output after the charge / discharge cycle test was output B, the output retention rate (%) was calculated by the following equation (a). The results are shown in Table 1.
Output maintenance ratio = Output B / Output A × 100 (a)

  In Table 1, as is known by comparing Sample E1 to Sample E3 and Sample C1 and Sample E4 and Sample C2, in the negative electrode containing hard carbon as the negative electrode active material and carbon black as the conductive material, As described above, it is understood that a high output and an output maintaining ratio can be exhibited by using a polymer having a nitrogen atom and / or an oxygen atom such as polyacrylonitrile, an acrylic resin, and modified polyvinylidene fluoride.

The reason is considered as follows.
When carbon black is added as a conductive material to the negative electrode active material layer using hard carbon as the negative electrode active material, conductivity can be improved and output can be improved. However, the adhesion between the negative electrode active material layer and the current collector is improved. It tends to decrease and cannot show a sufficient output retention rate (output durability) (see Sample C1 and Sample C2 in Table 1). That is, since carbon black has a small particle size and a large surface area, a relatively large amount of solvent is required when producing the slurry-like negative electrode mixture containing carbon black. Therefore, when the negative electrode mixture is applied to the current collector and dried, the amount of solvent that evaporates increases, and the shrinkage of the negative electrode mixture on the current collector increases. As a result, it is difficult to ensure sufficient adhesion of the negative electrode active material layer to the current collector, and it is considered that the output maintenance ratio becomes insufficient.

  On the other hand, in the samples E1 to E4, a metal oxide formed by natural oxidation or the like on at least a part of the surface of the current collector 31, and nitrogen in a polymer such as polyacrylonitrile used as the binder 34 Atoms and / or oxygen atoms show a high affinity (see FIG. 2). Therefore, the binder 34 can bind the negative electrode current collector layer 35 to the current collector 31 with excellent adhesion. As a result, it is considered that the output maintenance ratio, that is, the output durability can be improved.

(Example 2)
This example is in the non-aqueous electrolyte solution of a lithium ion secondary battery fabricated in Example 1 (Sample E1), formula (4) anion compound represented by the Li ⁺ and an electrolyte compound consisting of (LiPF ₂ (C _{In this example, 2} O ₄ ) ₂ ) is added and the effect on the output retention rate is examined.

Specifically, in the lithium ion secondary battery of this example, LiPF ₆ and an electrolyte compound (non-aqueous solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 30:70 are used. LiPF ₂ (C ₂ O ₄ ) ₂ ) is dissolved in a total of 1 M to have a non-aqueous electrolyte. In the non-aqueous electrolyte, at least a part of the electrolyte compound is ionized to Li ⁺ with the anion compound represented by the above formula (4), so the non-aqueous electrolyte contains the anion compound. The lithium ion secondary battery of this example is the same battery as the sample E1 of Example 1 except that it has a nonaqueous electrolytic solution containing an anionic compound.

In this example, five types of lithium ion secondary batteries (sample E5 to sample E9) containing LiPF ₂ (C ₂ O ₄ ) ₂ in non-aqueous electrolyte at different concentrations were prepared.
In preparing the sample E5, first, a nonaqueous solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) at a ratio of 30:70 (volume ratio) was prepared. Next, a mixed support salt in which LiPF ₆ and LiPF ₂ (C ₂ O ₄ ) ₂ were mixed at a weight ratio of 98: 2 was prepared as an electrolyte. This mixed support salt was dissolved in a non-aqueous solvent to a concentration of 1M to prepare a non-aqueous electrolyte. Using this non-aqueous electrolyte, a lithium ion secondary battery was fabricated in the same manner as in the sample E1 of Example 1. This is designated as Sample E5.

In preparing the sample E6, first, except that a mixed support salt in which LiPF ₆ and LiPF ₂ (C ₂ O ₄ ) ₂ were mixed at a weight ratio of 80:20 was used, Similarly, a non-aqueous electrolyte was prepared. Next, using this non-aqueous electrolyte, a lithium ion secondary battery (sample E6) was produced in the same manner as the sample E1 of Example 1.
Sample E7 was prepared in the same manner as Sample E5 except that a mixed support salt in which LiPF ₆ and LiPF ₂ (C ₂ O ₄ ) ₂ were mixed at a weight ratio of 20:80 was used. Thus, a non-aqueous electrolyte was prepared. Next, using this non-aqueous electrolyte, a lithium ion secondary battery (sample E7) was produced in the same manner as the sample E1 of Example 1.

In preparing the sample E8, first, except that a mixed support salt in which LiPF ₆ and LiPF ₂ (C ₂ O ₄ ) ₂ were mixed at a weight ratio of 99: 1 was used, Similarly, a non-aqueous electrolyte was prepared. Next, using this non-aqueous electrolyte, a lithium ion secondary battery (sample E8) was produced in the same manner as the sample E1 of Example 1.
Sample E9 was prepared in the same manner as Sample E5 except that a mixed support salt in which LiPF ₆ and LiPF ₂ (C ₂ O ₄ ) ₂ were mixed at a weight ratio of 15:85 was used. Thus, a non-aqueous electrolyte was prepared. Next, using this non-aqueous electrolyte, a lithium ion secondary battery (sample E9) was produced in the same manner as the sample E1 of Example 1.

Each sample (sample E5 to sample E9) contains 5 wt% of polyacrylonitrile as a binder in the negative electrode active material layer of the negative electrode.
The concentration (wt%) of the electrolyte compound (LiPF ₂ (C ₂ O ₄ ) ₂ ) in the total electrolyte contained in each sample is shown in Table 2 described later.

  Moreover, about each sample, the output test and the charging / discharging cycle test were done like Example 1, and the output (initial output) and the output maintenance factor were measured. The results are shown in Table 2 below. In Table 2, the results of the sample E1 are also shown for comparison, and the output of each sample is expressed as a relative value when the output of the sample E1 of Example 1 is 100.

  As is known from Table 2, the output maintenance ratio of Samples E5 to E9 containing the electrolyte compound in the electrolytic solution was further improved as compared with Sample E1 not containing the electrolyte compound. Therefore, in the electrolyte solution of the lithium ion secondary battery having a negative electrode containing hard carbon as a negative electrode active material, carbon black as a conductive material, and a polymer containing nitrogen atoms and / or oxygen atoms as a binder, an electrolyte compound It can be seen that the output retention ratio can be further improved by adding.

  Further, in the sample E8 in which the electrolyte compound is 1% by weight, the output retention rate is increased by less than about 1% compared to the sample E1. On the other hand, in the sample E5 in which the electrolyte compound was 2% by weight, the maintenance ratio was improved by about 7% compared to the sample E1. Therefore, it can be seen that the amount of the electrolyte compound in the total electrolytic mass is preferably 2% by weight or more.

  In addition, in sample E9 in which the electrolyte compound was 85% by weight, the initial output was lower than that of sample E1. On the other hand, sample E7 in which the electrolyte compound was 80% by weight showed an initial output substantially equivalent to that of sample E1. Therefore, it can be seen that the electrolyte compound in the total electrolytic mass is preferably 80% by weight or less.

  Thus, according to this example, it is found that the lithium ion secondary battery of this example preferably contains an anionic compound, which can further improve the output retention rate, that is, the output durability. Moreover, it turns out that it is preferable that the addition amount of the said electrolyte compound is 2 to 80 weight% in the total electrolytic mass.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the structure of the negative electrode 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 31 Current collector 32 Negative electrode active material 33 Conductive material 34 Binder 35 Negative electrode active material layer 4 Separator 6 Battery case

Claims (6)

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 negative electrode has a current collector mainly composed of a metal, and a negative electrode active material layer disposed on the current collector.
The negative electrode active material layer contains a negative electrode active material made of a carbon material capable of occluding or releasing lithium ions, a conductive material, and a binder.
The negative electrode active material layer contains hard carbon as the carbon material, contains carbon black as the conductive material, and contains a polymer containing nitrogen atoms and / or oxygen atoms as the binder. Ion secondary battery.   2. The lithium active material layer according to claim 1, wherein the negative electrode active material layer contains 50 to 95 wt% of the negative electrode active material, 1 to 20 wt% of the conductive material, and 4 to 30 wt% of the binder. Ion secondary battery. 3. The lithium ion secondary battery according to claim 1, wherein the non-aqueous electrolyte contains an anion compound represented by the following general formula (1).

{However, M is a transition metal, a group III, IV or V element of the periodic table, b is 1 to 3, m is 1 to 4, n is 0 to 8, q is 0 or 1 respectively. , R ¹ is C ₁ -C ₁₀ alkylene, C ₁ -C ₁₀ halogenated alkylene, C ₆ -C ₂₀ arylene, or C ₆ -C ₂₀ halogenated arylene (the alkylene and arylene have the structure) And R ¹ may be bonded to each other.), R ² is halogen, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ Alkyl halides, C ₆ -C ₂₀ aryls, C ₆ -C ₂₀ aryl halides, or X ³ R ³ (these alkyls and aryls may have substituents, heteroatoms in their structures, the n number R ² each may combine with each other to form a ring present.), X ^{1, 2,} X ³ is O, S, or NR ^4, R ^3, R ⁴ are, each independently, hydrogen, alkyl of C ₁ -C _10, alkyl halide C ₁ ~C _10, C ₆ ~C ₂₀ aryls and C ₆ -C ₂₀ aryl halides are shown respectively. (These alkyls and aryls may have a substituent or a hetero atom in the structure, and a plurality of R ³ and R ⁴ are respectively present. May combine to form a ring. } In any one of Claims 1-3, in the said non-aqueous electrolyte, the electrolyte compound which consists of the said anion compound represented by the said General formula (1) and a cation is ionizing, The said general formula ( M in 1) is any of Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf, or Sb. A lithium ion secondary battery, wherein the cation is at least one of Li ^{+ and} Na +.   In any 1 item | term of Claims 1-4, in the said non-aqueous electrolyte, in addition to the electrolyte compound which consists of the said anion compound and cation represented by the said General formula (1) as said electrolyte, other An electrolyte is added, and the addition amount of the electrolyte compound is 2% by weight to 80% by weight in the total electrolytic mass. In claim 5, the non-aqueous electrolyte solution, as other electrolytes other than the above electrolyte _{compounds, LiPF 6, LiBF 4, LiAsF} 6, LiSbF 6, LiClO 4, Li (C 2 F 5 SO 2) 2 N, A lithium ion secondary battery, wherein at least one selected from LiN (SO ₂ CF ₃ ) ₂ , Li (SO ₃ C ₂ F ₅ ), and lithium bisoxalatoborate (LiBOB) is added.

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