JP2008282619A - Lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium-ion secondary battery with high initial charge/discharge characteristics and excellent in a capacity maintenance ratio. <P>SOLUTION: The lithium-ion secondary battery is at least provided with a cathode, an anode and a nonaqueous electrolyte solution. The anode contains as an anode active material a titanium-based polyanion compound having an oxidation reduction potential exceeding 1.8 V with an oxidation reduction potential of Li as a reference. Further, the nonaqueous electrolyte solution is made by dissolving an electrolyte and an additive consisting of a compound expressed in general formula (1) in a nonaqueous solvent. <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.

  Conventionally, lithium-ion secondary batteries using non-aqueous electrolytes have high voltage, high energy density, and can be reduced in size and weight. Therefore, information communication equipment mainly for information terminals such as personal computers and mobile phones. Practical use has progressed in this field, and it has become widely popular. 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, the positive electrode contains a lithium transition metal composite oxide such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ as a positive electrode active material, and a carbon material such as graphite or coke as the negative electrode active material. The containing battery is used. In addition, polyanionic compounds have been developed as active materials (see Patent Documents 1 to 6). Since this polyanion compound is close to the redox potential of the positive electrode active material, it has been studied to use it as a positive electrode active material. Further, aluminum is generally used for the positive electrode current collector, and copper is generally used for the negative electrode current collector. As the negative electrode, metal Li may be used. 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 such a lithium ion secondary battery, carbonate and Li salt in the electrolytic solution are easily reductively decomposed during the initial charge. As a result, a film called an SEI film is formed on the negative electrode, and a gas mainly containing H ₂ , CO, CO _2, etc. is generated. In the negative electrode, the redox potential of Li metal or carbon material is 0 to 0.5 V (vs Li ⁺ / Li), while the decomposition of the electrolyte is 0.5 to 1.5 V (vs Li ^+). / Li). It is considered that the SEI film produced by the decomposition of the electrolytic solution suppresses further decomposition of the electrolytic solution and enables high charge / discharge efficiency thereafter. However, there was a problem that the initial charge / discharge efficiency deteriorated due to the decomposition of the electrolysis solution. In addition, there is a problem that the pressure in the battery increases due to the generation of gas.

Further, in configuring a high-power type lithium ion secondary battery, it is becoming an essential condition to use a lithium salt such as LiPF ₆ having high conductivity as the main component of the electrolyte. However, LiPF ₆ reacts with a small amount of moisture mixed in the battery at the time of manufacturing a lithium ion secondary battery or at the time of initial charge, and generates hydrogen fluoride (HF) (see Non-Patent Document 1). This HF may adversely affect the constituent materials in the battery and may deteriorate battery characteristics. In particular, when used in a high-temperature environment, there is a problem that side reactions due to HF are accelerated, and the adverse effect on the battery appears remarkably. Such a problem appears remarkably particularly in a battery using aluminum as a positive electrode current collector or a battery exterior material. That is, aluminum is an amphoteric metal and has the property of being easily attacked by acids and alkalis. Therefore, it is easily corroded by HF, and there is a possibility that resistance increases or gas is generated.

In order to solve such a problem, a method of adding an additive composed of a specific complex salt to an electrolytic solution has been developed (see Patent Documents 7 to 11). This additive can trap moisture present in the battery system. Therefore, generation of hydrofluoric acid due to a reaction between moisture and an electrolyte such as LiPF ₆ can be suppressed, and the durability and output of the battery can be improved.

However, the additive has a problem that it is easily reductively decomposed at about 1.8 V (vs. Li ⁺ / Li) at the negative electrode during the first charge. As a result, a decomposition film is formed on the negative electrode, which increases the reaction resistance in the negative electrode. For this reason, the initial charge / discharge efficiency may decrease or the capacity may easily decrease as charge / discharge is repeated. In addition, a relatively large amount of gas is generated by reductive decomposition to increase the internal pressure of the battery, and in the worst case, the battery has a risk of bursting.

Japanese Patent No. 2847663 JP 2000-509193 A JP 2001-266882 A JP 2002-56849 A JP 2002-56848 A Special table 2005-522009 gazette JP 2001-155769 A JP 2002-110235 A JP 2004-146071 A JP 2005-5114 A JP 2005-26203 A D. Aurbach et al., “JOURNAL OF POWER SOURCES”, 1997, Vol. 68, p. 91

  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 having high initial charge / discharge efficiency and excellent capacity retention.

｛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１〜８、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.
The negative electrode contains, as a negative electrode active material, a titanium-based polyanion compound having a redox potential exceeding 1.8 V when the redox potential of Li is used as a reference,
The non-aqueous electrolyte is a lithium ion secondary battery comprising an electrolyte and an additive composed of a compound represented by the following general formula (1) dissolved in a non-aqueous solvent (claim) Item 1).

{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 1 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 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). }

  The lithium ion secondary battery of the present invention contains, as the negative electrode active material, the titanium-based polyanion compound having a redox potential exceeding 1.8 V with respect to the redox potential of Li. Such a titanium-based polyanion compound has a low potential as a positive electrode active material and a high potential as a negative electrode active material when considered from the electrode material of a conventional lithium ion secondary battery. When such a titanium-based polyanion compound is used as the negative electrode active material, the oxidation-reduction potential of the battery can be made higher than the decomposition potential of the electrolytic solution. Therefore, decomposition of the electrolytic solution can be prevented during charging and discharging. Therefore, it is possible to suppress a decrease in charge / discharge efficiency during the first charge / discharge due to the decomposition of the electrolytic solution.

Moreover, the said additive which consists of a compound represented by the said General formula (1) is melt | dissolving in the said non-aqueous electrolyte. Since the additive can capture a small amount of water contained in the non-aqueous electrolyte, it is possible to avoid problems caused by the presence of water. Specifically, for example, it is possible to prevent HF from being generated by the reaction between the electrolyte such as LiPF ₆ and moisture. Therefore, it can suppress that an active material, a collector, etc. are corroded by HF, and can improve durability and output of a battery.

Furthermore, the lithium ion secondary battery contains the titanium-based polyanion compound as a negative electrode active material while containing the additive. Therefore, it is possible to prevent the additive from being decomposed to form a decomposed film on the negative electrode. That is, since the titanium-based polyanion compound having a redox potential exceeding 1.8 V (vs. Li ⁺ / Li) is used as the negative electrode active material, the lithium ion secondary battery is decomposed by the additive during charging and discharging. Does not reach the potential. Therefore, the additive can sufficiently exhibit a function as a trapping agent for moisture without being decomposed to form a film. Therefore, the lithium ion secondary battery is excellent in durability and can exhibit a high capacity retention rate.

  As described above, according to the present invention, it is possible to provide a lithium ion secondary battery having high initial charge / discharge efficiency and excellent capacity retention.

Next, a preferred embodiment of the present invention will be described.
The lithium ion secondary battery of the present invention includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a non-aqueous electrolyte obtained by dissolving an electrolyte and the above-described additive in a non-aqueous solvent.
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 will be described.
The negative electrode can be composed of, 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 mixture of a negative electrode active material mixed with a binder and a conductive assistant such as carbon for improving conductivity, and added with a suitable solvent as a dispersing agent to form a negative electrode mixture. It can be formed by coating on the surface of the current collector, drying, and then compressing.
Moreover, as the negative electrode, a pellet electrode obtained by press-molding the negative electrode mixture can be used.

The negative electrode active material contains a titanium-based polyanion compound having a redox potential exceeding 1.8 V when the redox potential of Li is used as a reference.
A titanium-based polyanion compound is a polyanion compound containing Ti as a cation, and is a compound that can change the valence of Ti during charge and discharge.
When the voltage is 1.8 V (vs. Li ⁺ / Li) or lower, the oxidation-reduction potential of the lithium ion secondary battery may reach the vicinity of the decomposition potential of the electrolytic solution. As a result, the initial charge / discharge efficiency may be reduced, or the capacity retention rate may be reduced.

The oxidation-reduction potential of the titanium-based polyanion compound is preferably 3.0 V or less with respect to Li (claim 2).
When the oxidation-reduction potential of the titanium-based polyanion compound exceeds 3.0 V, the lithium ion secondary battery may not be able to exhibit a practically sufficient battery voltage.

Specific examples of the negative electrode active material include LiTi ₂ (PO ₄ ) ₃ , TiP ₂ O ₇ , (TiO) ₂ P ₂ O ₇ , and Ti ₂ O _1.3 (PO ₄ ) _1.6 . If these titanium-based polyanion compounds are used, the oxidation-reduction potential reliably exceeds 1.8 V, so that the decomposition of the electrolytic solution can be more reliably prevented.

The binder serves to connect the 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.
In addition, as a solvent for dispersing the negative electrode active 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 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.

  The current collector in the negative electrode is made of a conductive material such as metal, for example, and mediates the movement of electrons between the negative electrode active material layer and an external load. 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, 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 aluminum or nickel.

Next, the positive electrode will be described.
A positive electrode can be comprised by the electrical power collector and the positive electrode active material layer formed in the surface, for example. The positive electrode active material layer is prepared by mixing a positive electrode active material with a conductive additive or a binder as necessary, and 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, followed by compression.
Moreover, as the positive electrode, a pellet electrode obtained by press-molding the positive electrode mixture can be used.

The positive electrode active material is a compound that can occlude or release lithium ions.
Examples of the positive electrode active material that can be used 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. . 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 positive electrode active material, a material having an oxidation-reduction potential of 4.5 V (vs. Li ⁺ / Li) or less is preferably used.
When the oxidation-reduction potential of the positive electrode active material exceeds 4.5 V, the additive represented by the general formula (1) may be oxidized and decomposed on the positive electrode. Therefore, it is preferable to use specifically LiCoO ₂ , LiNiO ₂ , Li (Ni, Co, Mn) O ₂ , Li (Ni, Mn) O ₂ , LiFePO ₄ or the like as the positive electrode active material.

The conductive assistant is an additive blended to improve the conductivity of the positive electrode active material layer. As the conductive aid, for example, carbon powder such as carbon black and graphite can be used.
Further, as the binder, a polymer material similar to that of the negative electrode active material layer can be used.

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.
Further, the amount of the positive electrode active material in the positive electrode active material layer in the positive electrode is the same as that of the above-described 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 non-aqueous electrolyte is obtained by dissolving an electrolyte and an additive 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.

In the lithium ion secondary battery, the compound represented by the general formula (1) is added to the non-aqueous electrolyte as the additive.
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 additive 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 additive 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, 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 (Claim 3).
In this case, the additive 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 additive, the toxicity of the additive can be reduced, and the production cost can be reduced.

  Next, the ligand part of the additive (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, the solubility and dissociation degree of the additive 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 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 additive is stabilized. Therefore, in this case, it is possible to prevent the additive from causing a side reaction 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 1 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.

The additive is preferably composed of one or more compounds 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 additive, the lithium ion secondary battery can suppress the above-described suppression of a decrease in initial charge / discharge efficiency and a decrease in capacity retention rate. The effect can be exhibited more remarkably. More preferably, the additive is a compound containing P as the element M in the general formula (1) as in the formulas (3) to (5).

Particularly preferably, the additive is composed of 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.

As a method for synthesizing the additive, for example, in the case of the compound represented by the above formula (2), oxalic acid is added after reacting LiBF ₄ and 2 times mole of lithium alkoxide in a non-aqueous solvent. Then, there is a method of substituting alkoxide bonded to boron with oxalic acid.

Further, an electrolyte is dissolved in the non-aqueous electrolyte.
The electrolyte, LiPF _6, LiBF _4, it is preferable LiAsF _6, or is at least one selected from LiSbF ₆ (claim 4).
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.

Moreover, it is preferable that the said additive is added so that it may become electrolyte: additive = 98-20: 2-80 by molar ratio with the said electrolyte (Claim 7).
When the molar ratio of the additive to the electrolyte is less than 2 or when the molar ratio of the electrolyte to the additive exceeds 98, when the charge / discharge is repeated under high temperature conditions, the lithium ion The capacity of the secondary battery may be easily reduced. On the other hand, if the molar ratio of the additive to the electrolyte exceeds 80, or the molar ratio of the electrolyte to the additive is less than 20, the initial output of the lithium ion secondary battery may be reduced.

  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, examples of the present invention will be described.
In this example, six types of lithium ion secondary batteries (battery E1 to battery E6) having different types of negative electrode active materials, types of additives, and the like are manufactured, and their characteristics are evaluated.

As shown in FIG. 1, the lithium ion secondary battery 1 of this example is a coin-type battery including a positive electrode 2, a negative electrode 3, and a non-aqueous electrolyte.
As shown in the figure, the lithium ion secondary battery 1 has a positive electrode 2 and a negative electrode 3 in a battery case 11 of a 2032 type coin cell, and a separator 4 sandwiched between them. The separator 4 is a porous sheet, and the separator 4 is impregnated with an electrolytic solution. The electrolytic solution is a nonaqueous electrolytic solution obtained by dissolving an electrolyte made of LiPF _{6 in} a nonaqueous solvent. Further, the battery case 11 has a gasket 45 at the end thereof and is sealed by the sealing plate 12.
The positive electrode 2 contains a lithium-containing transition metal oxide having a layered structure represented by LiNi _0.8 Co _0.15 Al _0.05 O ₂ as a positive electrode active material.

In the lithium ion secondary battery 1 (battery E1 to battery E6) according to the present invention, the negative electrode 3 has LiTi ₂ (PO ₄ ) ₃ , TiP ₂ O ₇ , (TiO) ₂ P ₂ O ₇ as a negative electrode active material, or Contains Ti ₂ O _1.3 (PO ₄ ) _1.6 . These negative electrode active materials all have an oxidation-reduction potential exceeding 1.8 V when Li is used as a reference.

In addition, in the lithium ion secondary battery (battery E1 to battery E6), any one of the additives represented by the formulas (3) to (5) is added to the electrolytic solution in addition to the electrolyte.

The manufacturing method of the lithium ion secondary battery (battery E1) 1 of this example will be described.
First, a lithium nickel composite oxide having a layered structure represented by LiNi _0.8 Co _0.15 Al _0.05 O ₂ was prepared as a positive electrode active material. 85 parts by weight of this 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 applied to both sides of an aluminum foil current collector having a thickness of 20 μm and dried. Then, it densified with the roll press and produced the sheet-like positive electrode. In addition, the adhesion amount of the positive electrode active material was about 5.0 mg / cm ² per one side of the current collector. The sheet-like positive electrode produced as described above was punched out with a diameter of 15 mm to obtain a positive electrode 2 for a coin-type battery.

In addition, LiTi ₂ (PO ₄ ) ₃ was prepared as a negative electrode active material. 95 parts by weight of the negative electrode active material and 5 parts by weight of polyvinylidene fluoride as a binder are mixed, and a drop of N-methyl-2-pyrrolidone as a dispersing agent is dropped to disperse the mixture in the dispersing material. A slurry-like negative electrode mixture was prepared. This negative electrode mixture was applied to both sides of an aluminum foil current collector having a thickness of 20 μm and dried. Then, it densified with the roll press and produced the sheet-like negative electrode. In addition, the adhesion amount of the negative electrode active material was about 7.0 mg / cm ² per one side of the current collector. The sheet-like positive electrode produced as described above was punched out with a diameter of 15 mm to obtain a negative electrode 3 for a coin-type battery.

Next, the non-aqueous electrolyte was prepared as follows.
That is, first, an electrolyte solution was prepared by adding LiPF ₆ as an electrolyte to a concentration of 1 mol / L to an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7. . Further, the compound represented by the above formula (4) is added to an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 3: 7 so as to have a concentration of 1 mol / L. An additive solution was prepared.
Next, the electrolyte solution and the additive solution were mixed to prepare a non-aqueous electrolyte. At this time, the electrolyte in the electrolyte solution and the additive in the additive solution were mixed so as to be 95: 5 (molar ratio), respectively.

Next, as shown in FIG. 1, the positive electrode 2 and the negative electrode 3 produced as described above were placed in a SUS coin-type battery case 11 so as to be separated by a separator 4. For the separator 4, a porous polyethylene sheet having a thickness of 25 μm was used. And the gasket 45 was arrange | positioned in the edge part in the battery case 11, and also non-aqueous electrolyte solution was inject | poured and impregnated in the battery case 11 further.
Subsequently, the sealing plate 12 is disposed on the upper part of the battery case 11 and the end of the battery case 11 is crimped to seal the battery case 11 to produce a coin-type battery (lithium ion secondary battery 1). did. This is referred to as a battery E1.

In this example, lithium ion secondary batteries (battery E2 to battery E6) having different types of negative electrode active materials and additives from the battery E1 were produced.
Battery E2 was produced in the same manner as Battery E1, except that TiP ₂ O ₇ was used as the negative electrode active material.
Battery E3 was produced in the same manner as Battery E1, except that (TiO) ₂ P ₂ O ₇ was used as the negative electrode active material.
Battery E4 was produced in the same manner as Battery E1, except that Ti ₂ O _1.3 (PO ₄ ) _1.6 was used as the negative electrode active material.

Battery E5 was produced in the same manner as Battery E1, except that the compound represented by the above formula (3) was used as an additive to be added to the electrolyte together with the electrolyte.
Battery E6 was produced in the same manner as Battery E1, except that the compound represented by the above formula (5) was used as an additive to be added to the electrolytic solution together with the electrolyte.

Furthermore, in this example, two types of lithium ion secondary batteries (battery C1 and battery C2) were produced for comparison with the batteries E1 to E6.
Battery C1 was produced in the same manner as Battery E1, except that graphite was used as the negative electrode active material. Graphite is an active material having a redox potential of 1.8 V or less with respect to Li.
Battery C2 was produced in the same manner as Battery E1, except that no additive was added to the electrolyte.

  About each lithium ion secondary battery (battery E1-battery E6, battery C1, and battery C2) produced in this way, the kind of negative electrode active material, the kind of additive, and the mixture ratio of an electrolyte and an additive are mentioned later. Table 1 shows.

Next, the battery characteristics of the eight types of lithium ion secondary batteries (battery E1 to battery E6, battery C1, and battery C2) produced as described above were examined.
Specifically, the following charge / discharge cycle test was conducted to examine the initial charge / discharge efficiency and capacity retention rate in the charge / discharge cycle.

"Charge / discharge cycle test"
Each battery after fabrication was charged to a battery voltage of 4.1 V at a constant current with a current density of 0.1 mA / cm ² under the condition of a temperature of 20 ° C., and then to a constant current with a current density of 0.1 mA / cm ^2. The battery voltage was discharged to 3.0V. At this time, the capacity at the time of completion of charging (initial charge capacity) and the capacity after completion of discharge (initial discharge capacity) are measured, and the equation of charge / discharge efficiency = initial discharge capacity / initial charge capacity × 100 The charge / discharge efficiency was calculated. The results are shown in Table 1.

Then, under the condition of a temperature of 60 ° C., charging / discharging at 2 C up to a battery voltage of 4.1 V and discharging at 2 C up to a battery voltage of 3.0 V was defined as one cycle, and this cycle was repeated 100 cycles. In each charge / discharge cycle, after charging to 4.1 V and after discharging to 3.0 V, a charging pause time and a discharge pause time were provided for 1 minute each. Then, the discharge capacity (mAh / g) after 100 cycles was measured, and the capacity retention rate (%) at the 100th cycle was calculated. The capacity retention rate was calculated using the formula: capacity retention rate (%) = discharge capacity at the 100th cycle / discharge capacity at the first time of the charge / discharge cycle test × 100. The results are shown in Table 1.
The discharge capacity is a value obtained by measuring the discharge current value (mA) and multiplying this discharge current value by the time (hr) required for the discharge, by the weight (g) of the positive electrode active material in the battery. It was calculated by dividing.

As can be seen from Table 1, the lithium ion secondary batteries of the batteries E1 to E6 have a high initial charge / discharge efficiency and an excellent capacity retention rate.
Moreover, when comparing the battery E1 to the battery E4 using the titanium-based polyanion compound as the negative electrode active material and the battery C1 using the graphite, the battery E1 to the battery E4 have the first charge / discharge efficiency compared to the battery C1. It can be seen that it has improved. This is because in the battery C1, the electrolyte and the additive decompose on the negative electrode containing graphite, but in the batteries E1 to E4, a titanium-based polyanion compound having a high oxidation potential exceeding 1.8 V is used. This is considered to be because the decomposition of the electrolytic solution and the additive can be avoided. In addition, although the capacity | capacitance maintenance factor is a little low compared with the battery E1 and the battery E2, the battery E3 and the battery E4 are considered to originate in the magnitude | size of the irreversible capacity | capacitance of active material itself.

  Moreover, when the battery E1, the battery E5, and the battery E6 containing three different additives are compared with the battery C2 that does not contain the additive, the capacity retention rate is improved by using the additive. You can see that In particular, the capacity maintenance rate of the battery E1 is greatly improved as compared with the battery C2. This is presumably because the compound represented by the above formula (4) sufficiently exhibits the moisture trapping effect without being decomposed during the charge / discharge process.

  As described above, a lithium polyion compound containing a titanium-based polyanion compound having an oxidation-reduction potential exceeding 1.8 V as the reference for the oxidation-reduction potential as the negative electrode active material and containing the above-mentioned additive together with the electrolyte in the electrolytic solution. It can be seen that the secondary batteries (battery E1 to battery E6) have high initial charge / discharge efficiency and can exhibit an excellent capacity retention rate.

(Example 2)
This example is an example of producing a cylindrical battery having a roll electrode body as a lithium ion secondary battery.
As shown in FIG. 2, the lithium ion secondary battery 5 of this example has a roll-shaped electrode body 6 formed by winding a positive electrode 61 and a negative electrode 62, and the roll-shaped electrode body 6 is an 18650 type as a battery case 71. It is a cylindrical battery inserted into a cylindrical case. In the rolled electrode body 6, a separator 63 is sandwiched between the positive electrode 61 and the negative electrode 62, and the separator 63 is wound while being sandwiched between the positive electrode 61 and the negative electrode 62. A nonaqueous electrolytic solution is injected into the battery case 71.

In the lithium ion secondary battery 5 of this example, similarly to the cell E1 in Example 1, the positive electrode 61 as a positive electrode active material contains a compound represented by LiNi _0.8 Co _0.15 Al _0.05 O ₂ The negative electrode 62 contains LiTi ₂ (PO ₄ ) ₃ as a negative electrode active material. In addition, as the nonaqueous electrolytic solution, an electrolytic solution containing the same electrolyte and additive as the battery E1 of Example 1 was used.

Next, the manufacturing method of the lithium ion secondary battery of this example will be described.
First, in the same manner as in Example 1, a lithium nickel composite oxide having a layered structure represented by LiNi _0.8 Co _0.15 Al _0.05 O ₂ was prepared as a positive electrode active material. This positive electrode active material, carbon black as a conductive agent, and polyvinylidene fluoride as a binder are mixed in the same ratio as in Example 1, and an appropriate amount of N-methyl-2-pyrrolidone as a dispersant is added. To prepare a slurry-like positive electrode mixture.
Further, in the same manner as in Example 1, this positive electrode mixture was applied to both sides of an aluminum foil current collector having a thickness of 20 μm, dried, then densified, cut into a shape of 52 mm wide × 450 mm long, and sheet-like A positive electrode was prepared. The adhesion amount of the positive electrode active material was about 5.0 mg / cm ² per one side of the current collector.

Next, LiTi ₂ (PO ₄ ) ₃ was prepared as a negative electrode active material. As in Example 1, 95 parts by weight of this negative electrode active material 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. Thus, a slurry-like negative electrode mixture was produced. This negative electrode mixture was applied to both sides of an aluminum foil current collector having a thickness of 20 μm and dried. Then, it densified with the roll press, cut out into the shape of width 54mm x length 500mm, and produced the sheet-like negative electrode. The adhesion amount of the negative electrode active material was about 7.0 mg / cm ² per one side of the current collector.

  Next, as shown in FIG. 2, a positive electrode current collector lead 613 and a negative electrode current collector lead 623 were welded to the sheet-like positive electrode 61 and negative electrode 62 obtained as described above, respectively. A polyethylene separator 63 having a width of 56 mm and a thickness of 25 μm was sandwiched between the positive electrode 61 and the negative electrode 62, and the positive electrode 61, the negative electrode 62, and the separator 63 were wound to produce a spiral roll electrode body 6.

  Subsequently, the roll electrode body 6 was inserted into an 18650-type cylindrical battery case 7 including an outer can 71 and a cap 72. At this time, the positive electrode current collecting lead 613 is connected to the positive electrode current collecting tab 615 disposed on the cap 72 side of the battery case 7 by welding, and the negative electrode current collecting lead is disposed on the negative electrode current collecting tab 625 disposed on the bottom of the outer can 71. 623 was connected by welding.

Next, in the same manner as the battery E1 of Example 1, an organic solvent obtained by mixing EC and DEC at a volume ratio of 3: 7, LiPF ₆ as an electrolyte, and an additive represented by the above formula (4) A non-aqueous electrolyte solution obtained by dissolving was prepared. The molar ratio of electrolyte to additive in the non-aqueous electrolyte is 95: 5.
Next, the battery case 7 was impregnated with this non-aqueous electrolyte. The gasket 8 was disposed inside the cap 72, and the cap 72 was disposed in the opening of the outer can 71. Subsequently, the battery case 7 was sealed by caulking the cap 72 to produce a cylindrical lithium ion secondary battery 5.

  The cylindrical lithium ion secondary battery thus obtained also has the same high initial charge / discharge efficiency as the battery E1 of Example 1 (see Table 1) and can exhibit excellent charge / discharge efficiency. It was confirmed.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the structure of the coin-type battery as a lithium ion secondary battery concerning Example 1. FIG. FIG. 5 is an explanatory diagram showing a configuration of a cylindrical battery as a lithium ion secondary battery according to Example 2.

Explanation of symbols

1 Lithium ion secondary battery 2 Positive electrode 3 Negative electrode

Claims (7)

In a lithium ion secondary battery comprising at least a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The negative electrode contains, as a negative electrode active material, a titanium-based polyanion compound having a redox potential exceeding 1.8 V when the redox potential of Li is used as a reference,
The lithium ion secondary battery, wherein the nonaqueous electrolytic solution is obtained by dissolving an electrolyte and an additive composed of a compound represented by the following general formula (1) in a nonaqueous solvent.

{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 1 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 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). }   2. The lithium ion secondary battery according to claim 1, wherein an oxidation-reduction potential of the titanium-based polyanion compound is 3.0 V or less when Li is used as a reference.   In Claim 1 or 2, M in the said 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, a lithium ion secondary battery. In any one of claims 1 to 3, the _{electrolyte, LiPF 6, LiBF 4, LiAsF} 6 , lithium-ion secondary battery which is characterized in that at least one selected from LiSbF _6,. 5. The lithium ion secondary battery according to claim 1, wherein the additive comprises any one or more of compounds represented by the following formulas (2) to (5). .

  6. The lithium ion secondary battery according to claim 5, wherein the additive comprises a compound represented by the formula (4).   7. The additive according to claim 1, wherein the additive is added in a molar ratio with the electrolyte such that electrolyte: additive = 98-20: 2-80. Lithium ion secondary battery.

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