JP2005032716A - Lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery that is excellent in discharging and charging cycle property under elevated temperature conditions, and which can be easily manufactured at a low cost. <P>SOLUTION: The lithium ion secondary battery has: (a) a positive pole including an oxide containing lithium and a transition metal or a polyanionic compound as a base component of a positive pole active material; (b) a negative pole containing a carbon material as a negative pole active material; and (c) a nonaqueous electrolyte dissolving an electrolyte in an organic solvent. The nonaqueous electrolyte contains an additive represented by the general formula (1) (wherein, M represents a transition metal, or an element selected from III-group elements, IV-group elements and V-group elements in the periodic table; A<SP>a+</SP>represents a metal ion, proton, or onium ion; a represents a numeral from 1 to 3; b represents a numeral from 1 to 3; p represents a ratio of b/a; m represents a numeral from 1 to 4; n represents a numeral from 1 to 8; q represents a numeral of 0 or 1). The nonaqueous electrolyte contains water at a ratio of 100 to 10,000 ppm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a lithium ion secondary battery using insertion / extraction of lithium ions.

  Conventionally, lithium ion secondary batteries that use lithium ion storage / release have high voltage and high energy density. Therefore, in the field of information equipment and communication equipment, mainly personal information terminals such as personal computers and mobile phones. Practical use has progressed and it has become widely popular. In other fields, the development of electric vehicles is urgently required due to environmental problems and resource issues, and the use of lithium ion secondary batteries as power sources for electric vehicles is being 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.
The non-aqueous electrolyte is made of, for example, an organic solvent in which an electrolyte is dissolved. Examples of the electrolyte include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) _2, and LiCF ₃ SO _3. is there.

Among lithium ion secondary batteries having such an electrolyte, a lithium ion secondary battery having LiPF ₆ as an electrolyte is particularly put into practical use (see Patent Document 1).
Lithium ion secondary batteries containing LiPF ₆ as an electrolyte are less explosive and toxic than other electrolytes and are excellent in safety. In addition, since LiPFO ₄ hardly elutes metal such as aluminum from the current collector, such a lithium ion secondary battery has an advantage that capacity deterioration is small when charging and discharging are repeated. ing.

However, the lithium ion secondary battery using the electrolyte as described above has a problem of low thermal stability.
That is, when such a lithium ion secondary battery is repeatedly used under high temperature conditions, the electrolyte may be decomposed to form a high resistance film on the negative electrode. As a result, there are problems that the charge / discharge capacity is reduced and the internal resistance of the battery is increased to lower the output voltage.

The electrolyte decomposes by reacting with water and corrodes a metal such as aluminum contained in the current collector, causing a decrease in battery capacity and an increase in internal resistance.
Therefore, when producing a lithium ion secondary battery using the non-aqueous electrolyte solution having the electrolyte, it is necessary to prevent water from entering the battery system as much as possible in the manufacturing process.

Specifically, in manufacturing such a lithium ion secondary battery, in order to prevent water from being mixed into the non-aqueous electrolyte, a process for preparing the non-aqueous electrolyte, a non-aqueous electrolyte, The process of injecting into the battery was performed using an Ar atmosphere glove box or the like. In addition, in order to bring the amount of moisture in the battery system as close to zero as possible, the process of vacuum drying the electrode and the process of winding the electrode were also performed in a dry room, and measures were taken to thoroughly remove moisture. .
However, as a result, facilities such as a glove box and a dry room are required, resulting in high manufacturing costs and complicated production of the lithium ion secondary battery.

JP 2001-307768 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 has excellent charge / discharge cycle characteristics under high temperature conditions and can be easily manufactured at low cost.

｛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 comprises a positive electrode containing an oxide or polyanionic compound containing lithium and a transition metal as a main component of a positive electrode active material, a negative electrode containing a carbon material as a negative electrode active material, and an electrolyte dissolved in an organic solvent. In a lithium ion secondary battery having a nonaqueous electrolyte solution,
In the non-aqueous electrolyte, a compound represented by the following general formula (1) is added as an additive,
The non-aqueous electrolyte is in a lithium ion secondary battery characterized by containing water at a concentration of 100 ppm to 10000 ppm.

{Where 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 halogenated alkylene, C ₆ ~ C ₂₀ arylene or C ₆ -C ₂₀ halogenated arylene (These alkylenes and arylenes may have a substituent or a heteroatom in the structure, and m R ^{1 s} are bonded to each other. R ² may be 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 independent and represent hydrogen, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ alkyl halide, C ₆ -C ₂₀ aryl, C ₆ -C ₂₀ aryl halide, respectively (these alkyl and aryl May have a substituent or a hetero atom in the structure, and a plurality of R ³ and R ⁴ may be bonded to each other to form a ring). }

In the lithium ion secondary battery of the present invention, a compound represented by the above general formula is added as an additive together with the electrolyte in the non-aqueous electrolyte.
Therefore, when the lithium ion secondary battery is charged one or more times, all or part of the additive is decomposed, and the surface of the positive electrode or / and the negative electrode, the positive electrode active material, and / or the negative electrode active material. A coating covering these is formed on the surface.

The coating is low in resistance and stable, and covers the surface of the positive electrode or / and the negative electrode and the surface of the positive electrode active material or / and the negative electrode active material as described above.
Therefore, in the lithium ion secondary battery, the insertion and extraction of lithium ions is performed smoothly, and the interface between the surface of the positive electrode or / and the negative electrode, the surface of the positive electrode active material or / and the negative electrode active material, and the electrolytic solution. The resistance is reduced and the initial output of the battery can be improved over a wide temperature range. In particular, since the resistance of the electrolytic solution increases at low temperatures, the improvement in output becomes more remarkable.
In addition, the coating can suppress the formation of a high-resistance film on the negative electrode, which occurs due to decomposition of the electrolyte in the nonaqueous electrolytic solution.

Moreover, the formation of the high-resistance film described above is particularly likely to occur when the lithium ion secondary battery is used in a high temperature environment of, for example, 60 ° C., and reduces the output voltage, the discharge capacity, and the like.
In the lithium ion secondary battery of the present invention, the coating can prevent the formation of a high-resistance film on the negative electrode. Therefore, even when used in a high temperature environment of 60 ° C., for example, an excellent discharge capacity and output voltage can be exhibited.
For example, when an electrolytic solution using LiPF ₆ that has already been put into practical use as a supporting salt is used, HF may be generated by hydrolysis. This HF may corrode a current collector made of, for example, Al in an environment of, for example, 60 ° C. and 4.1 V. As a result, the resistance increases and the battery characteristics may be deteriorated.
On the other hand, in the lithium ion secondary battery, since the compound represented by the above general formula is added to the non-aqueous electrolyte, HF is not generated even when hydrolyzed. Therefore, the lithium ion secondary battery can exhibit excellent durability.

Moreover, in the said lithium ion secondary battery, in addition to the said electrolyte and the said additive being added in the said nonaqueous electrolyte solution, it contains water in the ratio of 100 ppm-10000 ppm.
Therefore, the lithium ion secondary battery does not require a special device or facility for preventing moisture from entering the battery as in the prior art. Therefore, the lithium ion secondary battery of the present invention can be easily manufactured at low cost. In addition, since the above-mentioned additive is added to the non-aqueous electrolyte in the lithium ion secondary battery, even if it contains moisture in the above-mentioned concentration range, the current collector is hardly corroded, and the temperature is high. Excellent cycle characteristics under conditions. That is, even if charging / discharging is repeatedly performed under high temperature conditions, a decrease in charge / discharge capacity and an increase in internal resistance can be suppressed.

  Thus, according to the present invention, it is possible to provide a lithium ion secondary battery that has high output, excellent charge / discharge cycle characteristics under high temperature conditions, and can be easily manufactured at low cost.

In the lithium ion secondary battery of the present invention (Claim 1), the compound represented by the general formula (1) is added to the non-aqueous electrolyte as the additive.
Specific examples of such additives are shown below.

In the above example, A ^{a +} in the general formula (1) is ^a lithium ion, but as a cation other than lithium ion, for example, 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 Tetraethyl phosphonium ion, tetramethyl phosphonium ion, 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, tetraalkylammonium ions, and protons.
Similarly, the valence b of the anion is 1 to 3, and b = 1 is most preferable.
In addition, 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, It may be either Hf or Sb (Claim 2).
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, it is possible to obtain effects that the toxicity of the additive is reduced and the manufacturing cost is 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 the general formula (1) is selected from C _{1 to} C ₁₀ alkylene, C _{1 to} C ₁₀ halogenated alkylene, C _{6 to} C ₂₀ arylene, or C _{6 to} 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 in place of carbon on alkylene and arylene.
Further, when a plurality of R ¹ are present (when q = 1, 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 preferably an electron-withdrawing group, particularly fluorine. In this case, the solubility and dissociation degree of the additive can be improved, and the ion conductivity can be improved accordingly. Furthermore, in this case, the oxidation resistance is improved, thereby preventing the occurrence of side reactions.

X ¹ , X ² , and X ³ are each independently O, S, or NR ⁴ , and the ligand is bonded to M through these heteroatoms. Here, it is not impossible to combine other than O, S, and N, but it becomes very complicated in synthesis. As a feature of the compound represented by the general formula (1), there is binding to M by X ¹ and X ² in the same in the ligand, these ligands form a M and chelate structure . 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 -C ₁₀ alkyl, C ₁ -C ₁₀ alkyl halide, C ₆ -C ₂₀ aryl, C ₆ -C ₂₀ aryl halide. Yes, 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, they may combine 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, where m is 1 to 4 and n is 1 to 8.
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 a method for synthesizing the additive, for example, in the case of a compound represented by the following chemical formula (2), oxalic acid is added after reacting LiBF ₄ with 2 moles of lithium alkoxide in a non-aqueous solvent. Thus, there is a method of replacing alkoxide bonded to boron with oxalic acid.

  Next, in the lithium ion secondary battery of the present invention, as described above, all or part of the additive is decomposed by charging the lithium ion secondary battery at least once, so that the positive electrode or The surface of the negative electrode and / or the surface of the positive electrode active material or / and the negative electrode active material is coated to form a coating.

  The coating can be detected by, for example, X-ray photoelectron spectroscopy (XPS) or IR analysis.

  The lithium ion secondary battery contains water in the nonaqueous electrolyte at a concentration of 100 ppm to 10000 ppm.

When the concentration of water in the non-aqueous electrolyte is less than 100 ppm, special equipment and operation are required to produce a low-concentration lithium ion secondary battery having a moisture content of less than 100 ppm. Therefore, the manufacturing cost of the lithium ion secondary battery is increased, and the manufacturing process may be complicated.
On the other hand, when the concentration of water in the non-aqueous electrolyte exceeds 10,000 ppm, the charge / discharge capacity of the lithium ion secondary battery is easily deteriorated and the internal resistance is increased by repeatedly performing charge / discharge under high temperature conditions. Tends to rise.
In addition, the lithium ion secondary battery may contain moisture in portions other than the non-aqueous electrolyte such as the positive electrode, the negative electrode, and the inner wall of the battery case.

  Next, the lithium ion secondary battery includes the positive electrode and the negative electrode, a separator that is sandwiched between the positive electrode and the negative electrode, the non-aqueous electrolyte that moves lithium between the positive electrode and the negative electrode, and the like. Can be configured as main components.

  For example, the positive electrode is made by mixing a conductive material and a binder with the above positive electrode active material and adding a suitable solvent to form a paste-like positive electrode mixture on the surface of a metal foil current collector such as aluminum or stainless steel. It can be applied and dried, and compressed to increase the electrode density as necessary.

  The positive electrode active material is mainly composed of an oxide or polyanionic compound containing lithium and a transition metal M.

Examples of the oxide containing lithium and the transition metal M include, for example, LiMO ₂ having a layered rock salt structure, LiM ₂ O ₄ having a spinel structure, and these Li or transition metal M with other metal elements. Some have been partially replaced.

Examples of the polyanionic compound containing lithium and the transition metal M include Li ₃ M ₂ (SO ₄ ) ₃ , Li ₃ M ₂ (WO ₄ ) ₃ , Li ₃ M ₂ (MoO ₄ ) ₃ , In addition, there are olivine-structured phosphorus oxides such as LiMPO ₄ , and other examples include Li ₃ M ₂ (PO ₄ ) ₃ .

The positive electrode active material preferably contains at least one selected from Ni, Co, Mn, Fe, and Ti as the transition metal M.
In this case, the effect that the potential and charge / discharge capacity of the lithium ion secondary battery are increased can be obtained.

Moreover, the oxide and polyanionic compound which are the main components of the positive electrode active material may contain, for example, Al, Mg and the like in addition to the lithium and the transition metal.
In this case, the effect that the charge / discharge capacity of the lithium ion secondary battery is further improved can be obtained.

Specific examples of oxides and polyanionic compounds containing Al and Mg include, for example, Li (Ni, Co, Al, Mg) O ₂ having a layered rock salt structure.

  The conductive material is for ensuring the electrical conductivity of the positive electrode. For example, one or more carbon powder powders such as carbon black, acetylene black, natural graphite, artificial graphite, and cokes are used. Can be used.

The binder serves to bind the active material particles and the conductive material particles. For example, a fluorine-containing resin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene. Etc. can be used. In addition, an aqueous dispersion of cellulose or styrene butadiene rubber which is an aqueous binder can be used.
For example, an organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent for dispersing the active material, the conductive material, and the binder.

  Next, the negative electrode is prepared by mixing a binder with the carbon material, which is the negative electrode active material, and applying a suitable solvent to form a paste of the negative electrode mixture on the surface of a metal foil current collector such as copper. It can be dried and then formed by pressing. Similarly to the positive electrode, a fluorine-containing resin such as polyvinylidene fluoride can be used as the binder to be mixed with the negative electrode active material, and an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent.

  Examples of the carbon material of the negative electrode active material include natural or artificial graphite, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers and mixed materials thereof, vapor-grown carbonized fibers, and organic compound fired bodies such as phenol resins. , Cokes, carbon black, pyrolytic carbons, carbon fibers and the like. These carbon materials can be used alone or in combination of two or more.

The carbon material as the negative electrode active material preferably has a specific surface area of 0.8 to ⁵ m ² / g.
In this case, when the lithium ion secondary battery is charged, the additive is decomposed to easily form a low resistance and stable coating on the negative electrode or / and the negative electrode active material. An increase in internal resistance can be further suppressed.
When the specific surface area is less than 0.8 m ² / g or more than 5 m ² / g, the coating is not sufficiently formed, and the increase in the internal resistance may not be sufficiently suppressed.

  The separator to be narrowly attached to the positive electrode and the negative electrode separates the positive electrode and the negative electrode and holds the non-aqueous electrolyte. For example, a thin microporous film such as polyethylene or polypropylene can be used.

  Next, as the non-aqueous electrolyte, a solution obtained by dissolving the additive and the electrolyte in an organic solvent can be used.

The electrolyte may be A ^{a +} (PF ₆ ⁻ ) _a , A ^{a +} (ClO ₄ ⁻ ) _a , A ^{a +} (BF ₄ ⁻ ) _a , A ^{a +} (AsF ₆ ⁻ ) _a , or A ^{a +} (SbF ₆ ⁻ ) _a , (However, A ^{a +} is a metal ion, a proton, or an onium ion, and a is 1 to 3).

  In this case, it is possible to obtain an effect that the ion conductivity is relatively high and electrochemically stable. In this case, the lithium ion secondary battery can be manufactured at a low cost.

In the non-aqueous electrolyte, the additive is made of a compound in which A ^{a +} in the general formula (1) is Li ⁺ , and the electrolyte is LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , or One or more selected from LiSbF ₆ is preferred (claim 4).
In this case, it is possible to obtain an effect that the ion conductivity is relatively high and electrochemically stable, and further, an effect that the lithium ion of the additive can also contribute to the charge / discharge reaction of the battery. be able to. In this case, the lithium ion secondary battery can be produced at low cost.

  As the organic solvent for dissolving the additive and the electrolyte, an aprotic organic solvent can be used. As such an organic solvent, for example, a mixed solvent composed of one kind or two or more kinds selected from cyclic carbonate, chain carbonate, cyclic ester, cyclic ether, chain ether and the like can be used.

  Here, examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate. Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Examples of the cyclic ester carbonate include gamma butyrolactone and gamma valerolactone. Examples of the cyclic ether include tetrahydrofuran and 2-methyltetrahydrofuran. Examples of the chain ether include dimethoxyethane and ethylene glycol dimethyl ether. As the organic solvent, any one of these may be used alone, or two or more kinds may be mixed and used.

Moreover, it is preferable that the said additive is added in the said non-aqueous electrolyte so that it may become electrolyte: additive = 99.9-5: 0.1-95 by molar ratio with the said electrolyte ( Claim 5).
When the molar ratio between the electrolyte and the additive is out of the above range, repeated charging / discharging increases the internal resistance (IV resistance) of the lithium ion secondary battery and obtains a sufficient output. There is a risk that it will not be possible.

When it is desired to further improve the charge / discharge capacity of the lithium ion secondary battery, it is particularly preferable that electrolyte: additive = 95-20: 5-80. More preferably, electrolyte: additive = 90-20: 10-80.
Moreover, when it is desired to further suppress the IV resistance increase rate of the lithium ion secondary battery, it is particularly preferable that electrolyte: additive = 99.9-20: 0.1-80. More preferably, electrolyte: additive = 95-50: 5-50.
Moreover, when it is desired to improve the initial output of the lithium ion secondary battery, it is particularly preferable that electrolyte: additive = 99.9 to 90: 0.1 to 10. More preferably, electrolyte: additive = 99 to 93: 1 to 7 is preferable.
Therefore, the mixing ratio of the electrolyte and the additive can be appropriately determined according to battery characteristics required according to the use of the lithium ion secondary battery.

(Example 1)
Next, an embodiment of the lithium ion secondary battery of the present invention will be described with reference to FIGS.
As shown in FIGS. 1 and 2, the lithium ion secondary battery 1 of this example includes a positive electrode 2 containing an oxide or polyanionic compound containing lithium and a transition metal as a main component of the positive electrode active material 25, carbon It has the negative electrode 3 which contains a material as the negative electrode active material 35, and the nonaqueous electrolyte solution formed by melt | dissolving the electrolyte 51 in an organic solvent.

In the non-aqueous electrolyte, a compound represented by the following formula (6) is added as an additive 53.
The non-aqueous electrolyte contains water at a concentration of 100 ppm to 10000 ppm.

Hereinafter, the lithium ion secondary battery 1 of this example will be described in detail with reference to FIGS.
As shown in FIG. 1, the lithium ion secondary battery 1 of this example 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 an 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.
Further, 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.

As shown in FIGS. 1 and 2, the positive electrode 2 contains LiNi _0.75 Co _0.15 Al _0.10 O ₂ as the positive electrode active material 25, and the negative electrode 3 contains a carbon material as the negative electrode active material 35.
The positive electrode 2 and the negative electrode 3 are respectively provided with a positive electrode current collecting lead 23 and a negative electrode current collecting lead 33 by welding. The positive electrode current collecting lead 23 is connected by welding to a positive electrode current collecting tab 235 disposed on the cap 63 side. Further, the negative electrode current collecting lead 33 is connected to the negative electrode current collecting tab 335 disposed on the bottom of the outer can 65 by welding.

In addition, the nonaqueous electrolytic solution is obtained by dissolving LiPF ₆ as the electrolyte 51 in an organic solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 30:70 as shown in FIG. Has been injected into. This non-aqueous electrolyte contains water at a concentration of 100 ppm to 10000 ppm. In addition, a compound represented by the above formula (6) (hereinafter appropriately referred to as LPFO) is added as an additive 53 to the non-aqueous electrolyte. The additive 53 is decomposed by charging the lithium ion secondary battery 1 one or more times, covering the positive electrode 2 or / and the negative electrode 3, the positive electrode active material 25 or / and the negative electrode active material 35, and covering 55. Form. FIG. 2 shows a state in which the covering 55 is formed on the surface of the negative electrode 3.

Next, the manufacturing method of the lithium ion secondary battery of this example will be described with reference to FIGS.
First, the non-aqueous electrolyte was prepared as follows.
That is, first, an electrolyte solution was prepared by adding LiPF ₆ as an electrolyte to an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7 to a final concentration of 1M. . In addition, the final concentration of the compound (LPFO) represented by the above formula (6) is 1M in an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 3: 7. In addition to the above, an additive solution was prepared.

Next, the electrolyte solution and the additive solution were mixed, and water was further added at a concentration of about 1000 ppm to prepare a non-aqueous electrolyte. At this time, the electrolyte solution and the additive solution are such that the electrolyte (LiPF ₆ ) and the additive (LPFO) in the non-aqueous electrolyte have an electrolyte: additive = 95: 5 molar ratio. Mixed.

Next, a positive electrode and a negative electrode were prepared as follows.
In the positive electrode, LiNi _0.75 Co _0.15 Al _0.10 O ₂ is first prepared as a positive electrode active material, the positive electrode active material, carbon black (TB5500, manufactured by Tokai Carbon Co., Ltd.) as a conductive material, and polyfluoride as a binder. Vinylidene chloride (Kureha Chemical Industries, Ltd., KF polymer) was mixed, an appropriate amount of n-methyl-2-pyrrolidone was added as a dispersant, and kneaded to obtain a paste-like positive electrode mixture. 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 and dried. Thereafter, the sheet was densified with a roll press and cut into a shape having a width of 52 mm and a length of 450 mm to produce a sheet-like positive electrode. The amount of positive electrode active material deposited was about 7 mg / cm ² per side.

  On the other hand, in the negative electrode, fibrous graphite is prepared as a negative electrode active material, and the negative electrode active material and polyvinylidene fluoride (a KF polymer, manufactured by Kureha Chemical Industry Co., Ltd.) are mixed as a dispersant. An appropriate amount of n-methyl-2-pyrrolidone was added and kneaded to obtain a paste-like negative electrode mixture. The mixing ratio of the negative electrode active material and the binder was a weight ratio of negative electrode active material: binder = 95: 5.

Next, the negative electrode mixture obtained as described above was applied to both sides of a 10 μm thick copper foil current collector and dried. Thereafter, the sheet was densified with a roll press and cut into a shape having a width of 54 mm and a length of 500 mm to produce a sheet-like negative electrode. In addition, the adhesion amount of the negative electrode active material was about 5 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 with a polyethylene separator 4 (manufactured by Tonen Tarpis Co., Ltd.) having a width of 56 mm and a thickness of 25 μm sandwiched between them, to produce a spiral wound electrode.

  Subsequently, the wound electrode 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 25 is connected to the positive electrode current collecting tab 235 disposed on the cap 63 side of the battery case 6 by welding, and the negative electrode current collecting lead is disposed on the negative electrode current collecting tab 335 disposed on the bottom of the outer can 6. 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 hermetically sealed by caulking the cap 63, and the lithium ion secondary battery 1 was manufactured. This was designated as Sample E1.

Further, in this example, the sample E1 is the same as the sample E1 in 11 types of lithium ion secondary batteries having different mixing ratios and moisture contents of the electrolyte and the additive in the non-aqueous electrolyte. These were made Sample E2 to Sample E12. The lithium ion secondary batteries of Sample E2 to Sample E12 were produced in the same manner as Sample E1, except that the mixing ratio and the amount of water of the electrolyte and the additive in the non-aqueous electrolyte were changed. did.
In Sample E1 to Sample E12, the molar ratio between the electrolyte and the additive and the amount of water contained in the nonaqueous electrolytic solution are shown in Table 1 described later.

  In the lithium ion secondary batteries of Sample E1 to Sample E12 produced in this example, as shown in FIG. 2, an additive 53 is added to the non-aqueous electrolyte. Therefore, in the lithium ion secondary battery 1 of each sample, when it is charged once or more, all or a part of the additive 53 is decomposed, and the surface of the negative electrode 3 and / or the negative electrode active material 35 is covered with the coating 55. Form.

  Moreover, the lithium ion secondary batteries of Sample E1 to Sample E12 of this example contain water in the nonaqueous electrolytic solution. Therefore, there is no need to prevent water from entering the battery as in the prior art, and the battery can be easily manufactured without using a special device or operation.

(Comparative example)
In this example, in order to clarify the excellent characteristics of the lithium ion secondary batteries (samples E1 to E12) produced in Example 1, a comparative lithium ion secondary battery was produced. Specifically, for comparison, three types of lithium ion secondary batteries (sample C1 to sample C3) in which the non-aqueous electrolyte did not contain the additive were prepared.

Specifically, first, an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 3: 7 is prepared, and LiPF ₆ as an electrolyte is added to the organic solvent at a final concentration of 1M. In addition, non-aqueous electrolyte was prepared by adding water at a concentration of about 1000 ppm.
Subsequently, in the same manner as in Example 1 above, a positive electrode and a negative electrode were prepared, and the positive electrode, the negative electrode, and the non-aqueous electrolyte were placed in a battery case to produce a lithium ion secondary battery. This was designated as Sample C1.
Sample C1 is the same as Sample E1 to Sample E4 except that the additive (LPFO) is not added to the nonaqueous electrolytic solution.

  In addition, a non-aqueous electrolyte having a different amount of water in the non-aqueous electrolyte from that of the sample C1 is prepared, and using this non-aqueous electrolyte, two types of lithium ion secondary batteries ( Samples C2 and C3) were prepared.

  Among these, sample C2 contains water at a concentration of about 1500 ppm in the non-aqueous electrolyte, and the additive (LPFO) is not added to the non-aqueous electrolyte. That is, Sample C2 is the same as Sample E5 to Sample E8 except that the additive is not added.

On the other hand, Sample C3 contains water at a concentration of about 100 ppm in the non-aqueous electrolyte and the additive (LPFO) is not added to the non-aqueous electrolyte. That is, sample C3 is the same as sample E9 to sample E12 except that the additive is not added.
In Sample C1 to Sample C3, the amount of water contained in the non-aqueous electrolyte is shown in Table 1 described later.

(Experimental example 1)
Next, in this example, the following charge / discharge cycle test was performed using the samples E1 to E12 prepared in Example 1 and the samples C1 to C3 prepared in the comparative example, and the capacity maintenance rate and The resistance increase rate was measured.

"Charge / discharge cycle test"
The sample E1 to sample E12 and the sample C1 to sample C3 were charged at a constant current of 2.0 mA / cm ^{2 at} a constant current density of 4 mA under a temperature condition of 60 ° C., which is regarded as the upper limit of the actual use temperature range of the battery. Charging / discharging in which the battery was charged to ² V and then discharged to a discharge lower limit voltage of 3 V at a constant current of 2.0 mA / cm ² was defined as one cycle, and this cycle was performed for a total of 100 cycles.

"Capacity maintenance rate"
When the discharge capacity before the charge / discharge cycle test was capacity A (initial discharge capacity) and the discharge capacity after the charge / discharge cycle test was capacity B, it was calculated by the following equation (a).
Capacity maintenance rate (%) = capacity B / capacity A × 100 (a)

  In calculating the capacity retention rate, the discharge capacity before and after the charge / discharge cycle test was measured for each sample, and the capacity retention rate was calculated from the above equation (a). The results are shown in Table 1.

In addition, the resistance increase rate before and after the charge / discharge cycle test was calculated as follows.
"Evaluation of resistance increase rate"
Each sample was adjusted to 50% of the battery capacity (SOC = 50%), and 0.12A, 0.4A, 1.2A, 2.4A, 4.8A current was passed and the battery voltage after 10 seconds was measured. did. The applied current and voltage were linearly approximated, and IV resistance was obtained from the slope.
The rate of increase in resistance can be calculated by the following equation (b), where IV resistance after the charge / discharge test is resistance A (initial IV resistance) and IV resistance before the charge / discharge test is resistance B.
Resistance increase rate (%) = (resistance B−resistance A) × 100 / resistance A (b)

  In the calculation of the resistance increase rate, the IV resistance before and after the charge / discharge cycle test was measured for each sample, and the resistance increase rate was calculated from the above formula (b). The results are shown in Table 1.

  As can be seen from Table 1, when samples E1 to E4 containing 1000 ppm of water in the non-aqueous electrolyte were compared with sample C1 containing the same amount of water, sample E1 to which an additive was added was used. -Sample E4 showed a higher capacity retention rate after a cycle test under a high temperature condition of 60 ° C. than Sample C1. In addition, it can be seen that Sample E1 to Sample E4 have a smaller IV resistance increase rate than Sample C1, and the increase in internal resistance is suppressed.

  Similarly, when sample E5 to sample E8 and sample C2, and sample E9 to sample E12 and sample C3 are respectively compared, sample E5 to sample E8 and sample E9 to sample E12 each contain substantially the same amount of moisture. Compared to Sample C2 and Sample C3, the capacity retention rate was high and the rate of increase in internal resistance was low.

As described above, in a lithium ion secondary battery containing water in the range of 100 to 1000 ppm in the non-aqueous electrolyte, the additive is added to the non-aqueous electric field, so that a high temperature condition of about 60 ° C. It can be seen that the cycle characteristics below can be improved.
Further, although not clearly shown in this example, it has been confirmed that the same result as described above can be obtained even in a lithium ion secondary battery containing a maximum amount of 10000 ppm of water in a non-aqueous electrolyte. .

  Further, as is known from Table 1, when electrolyte and additive are added in a non-aqueous electrolyte at a molar ratio of electrolyte: additive = 95-50: 5-50, It can be seen that the cycle characteristics in can be significantly improved. Although not shown in the table, when the molar ratio of the electrolyte added to the non-aqueous electrolyte and the additive is electrolyte: additive = 95-5: 5-95, It has been confirmed that the cycle characteristics of the secondary battery can be sufficiently improved.

  The reason why the lithium ion secondary batteries of Samples E1 to E12 are excellent in charge / discharge cycle characteristics at a high temperature of about 60 ° C. as described above is that these lithium ion secondary batteries are as shown in FIG. 1 (sample E1 to sample E12) is considered to be because the non-aqueous electrolytic solution contains water and the electrolyte 51 and the additive 53 are added.

  As shown in the figure, at least a part of the additive 53 in the non-aqueous electrolyte is decomposed during the first charge, and the surface of the negative electrode active material 35 and / or the negative electrode 3 has a low resistance and a stable coating 55. This is considered to prevent the electrolyte 51 from being decomposed to form a high-resistance film on the negative electrode.

Further, when the voltage-charge capacity curves at the time of initial charge of the samples E1 to E12 and the samples C1 to C3 are examined, in the samples E1 to E12 in which the additive is added together with the electrolyte to the non-aqueous electrolyte, A capacity component that was considered to decompose the additive to form a coating on the negative electrode was observed in the vicinity of 1.8V.
On the other hand, in Sample C1 to Sample C3 to which no additive is added, there is no capacity component in the vicinity of 1.8 V as described above, and it is considered that no coating is formed on the negative electrode.

(Example 2)
In this example, a lithium ion secondary battery used for an initial output test performed in Experimental Example 2 described later is manufactured.
In this example, the sample E1 in Example 1 is the same as the sample E1 in three types of lithium ion secondary batteries having different mixing ratios of the electrolyte and the additive in the non-aqueous electrolyte. Made. These were designated as Sample E13 to Sample E15, respectively. The lithium ion secondary batteries of Sample E13 to Sample E15 are the same as Sample E1 of Example 1 except that the mixing ratio of the electrolyte and the additive in the non-aqueous electrolyte is changed. It was produced.

Specifically, in the sample E13, the electrolyte (LiPF ₆ ) and the additive (LPFO) in the non-aqueous electrolyte are in a molar ratio of LPFO (mol) / (LiPF ₆ (mol) + LPFO (mol). )) = 0.03, that is, electrolyte (mol): additive (mol) = 97: 3, the electrolyte solution and the additive solution are mixed, and water is added at a concentration of about 1000 ppm. A non-aqueous electrolyte was prepared and used. In Sample E13, as the organic solvent in the nonaqueous electrolytic solution, a mixed solvent in which EC and DEC were mixed at a volume ratio of 3: 7 was used as in Example 1.
That is, the sample E13 is the same as the sample E1 of Example 1 except that the electrolyte and the additive are added in a ratio of electrolyte: additive = 97: 3 in the nonaqueous electrolytic solution. It is.

Sample E14 has a molar ratio of the electrolyte (LiPF ₆ ) and the additive (LPFO) in the non-aqueous electrolyte, LPFO (mol) / (LiPF ₆ (mol) + LPFO (mol)) = The electrolyte solution and the additive solution are mixed so that 0.07, that is, electrolyte (mole): additive (mole) = 93: 7, and water is added at a concentration of about 1000 ppm to perform non-aqueous electrolysis. A liquid was prepared and used. In sample E14, as the organic solvent in the non-aqueous electrolyte, a mixed solvent in which EC and DEC were mixed at a volume ratio of 3: 7 was used as in Example 1.
That is, the sample E14 is the same as the sample E1 of Example 1 except that the electrolyte and the additive are added in a ratio of electrolyte: additive = 93: 7 in the nonaqueous electrolytic solution. It is.

Sample E15 has a molar ratio of the electrolyte (LiPF ₆ ) and the additive (LPFO) in the non-aqueous electrolyte, LPFO (mol) / (LiPF ₆ (mol) + LPFO (mol)) = 0.15, that is, electrolyte (mole): additive (mole) = 85: 15 The above electrolyte solution and the additive solution are mixed, and water is further added at a concentration of about 1000 ppm to perform non-aqueous electrolysis. A liquid was prepared and used. In sample E15, as the organic solvent in the non-aqueous electrolyte, a mixed solvent in which EC and DEC were mixed at a volume ratio of 3: 7 was used as in Example 1.
That is, the sample E15 is the same as the sample E1 of Example 1 except that the electrolyte and the additive are added in a ratio of electrolyte: additive = 85: 15 in the nonaqueous electrolytic solution. It is.

  In this example, the sample E1 in Example 1 is different from the sample E1 in six types in which the mixing ratio of the electrolyte and the additive in the non-aqueous electrolyte and the organic solvent in the non-aqueous electrolyte are different. A lithium ion secondary battery was produced in the same manner as Sample E1. These were designated as Sample E16 to Sample E21, respectively. The lithium ion secondary batteries of Sample E16 to Sample E21 are obtained by changing the mixing ratio of the electrolyte and the additive in the non-aqueous electrolyte, and using ethylene carbonate (EC) and dimethyl carbonate as organic solvents of the non-aqueous electrolyte. The sample was prepared in the same manner as the sample E1 in Example 1 except that a solvent in which (DMC) and ethylmethyl carbonate (EMC) were mixed at a volume ratio of 3: 3: 4 was used.

Specifically, the sample E16 is a non-aqueous electrolyte solution in an organic solvent obtained by mixing EC, DMC, and EMC at a volume ratio of 3: 3: 4, and the electrolyte (LiPF ₆ ) and the additive ( LPFO) and the molar ratio of LPFO (mol) / (LiPF ₆ (mol) + LPFO (mol)) = 0.05, that is, electrolyte (mol): additive (mol) = 95: 5 It was produced using what was added as such. Further, water was added at a concentration of about 1000 ppm to the non-aqueous electrolysis solution of sample E16.
That is, the sample E16 is the sample of Example 1 except that a mixed solvent obtained by mixing EC, DMC, and EMC at a volume ratio of 3: 3: 4 is used as the organic solvent of the nonaqueous electrolytic solution. It is the same as E1.

Sample E17 was prepared as a nonaqueous electrolyte solution in an organic solvent obtained by mixing EC, DMC, and EMC at a volume ratio of 3: 3: 4, the electrolyte (LiPF ₆ ), the additive (LPFO), and Is added at a molar ratio of LPFO (mol) / (LiPF ₆ (mol) + LPFO (mol)) = 0.10, that is, electrolyte (mol): additive (mol) = 90: 10 It was produced using. In addition, water was added at a concentration of about 1000 ppm to the non-aqueous electrolytic solution of sample E17.
That is, the sample E17 is the sample of Example 1 except that a mixed solvent obtained by mixing EC, DMC, and EMC at a volume ratio of 3: 3: 4 is used as the organic solvent of the nonaqueous electrolytic solution. It is the same as E2.

Sample E18 is a non-aqueous electrolyte, in which an electrolyte (LiPF ₆ ) and the additive (LPFO) are mixed in an organic solvent obtained by mixing EC, DMC, and EMC at a volume ratio of 3: 3: 4. Use is made so that the molar ratio is LPFO (mol) / (LiPF ₆ (mol) + LPFO (mol)) = 0.20, that is, electrolyte (mol): additive (mol) = 80: 20. It was produced. In addition, water was added at a concentration of about 1000 ppm to the non-aqueous electrolytic solution of sample E18.
That is, the sample E18 is the sample of Example 1 except that a mixed solvent obtained by mixing EC, DMC, and EMC in a volume ratio of 3: 3: 4 is used as the organic solvent of the nonaqueous electrolyte. It is the same as E3.

Sample E19 is a non-aqueous electrolyte, in which an electrolyte (LiPF ₆ ) and the additive (LPFO) are mixed in an organic solvent obtained by mixing EC, DMC, and EMC at a volume ratio of 3: 3: 4. Use is made so that LPFO (mol) / (LiPF ₆ (mol) + LPFO (mol)) = 0.03, that is, electrolyte (mol): additive (mol) = 97: 3 in molar ratio. It was produced. In addition, water was added at a concentration of about 1000 ppm to the non-aqueous electrolytic solution of sample E19.
That is, the sample E19 is the same as the sample E13 except that a mixed solvent obtained by mixing EC, DMC, and EMC at a volume ratio of 3: 3: 4 is used as the organic solvent of the nonaqueous electrolytic solution. belongs to.

Sample E20 is a non-aqueous electrolyte, in which an electrolyte (LiPF ₆ ) and the additive (LPFO) are mixed in an organic solvent obtained by mixing EC, DMC, and EMC at a volume ratio of 3: 3: 4. In a molar ratio, LPFO (mol) / (LiPF ₆ (mol) + LPFO (mol)) = 0.07, ie, electrolyte (mol): additive (mol) = 93: 7 It was produced. Further, water was added at a concentration of about 1000 ppm to the non-aqueous electrolysis solution of sample E20.
That is, the sample E20 is the same as the sample E14 except that a mixed solvent obtained by mixing EC, DMC, and EMC at a volume ratio of 3: 3: 4 is used as the organic solvent of the nonaqueous electrolytic solution. belongs to.

Sample E21 is a non-aqueous electrolyte, in which an electrolyte (LiPF ₆ ) and the additive (LPFO) are mixed in an organic solvent obtained by mixing EC, DMC, and EMC at a volume ratio of 3: 3: 4. In a molar ratio, LPFO (mol) / (LiPF ₆ (mol) + LPFO (mol)) = 0.15, ie, electrolyte (mol): additive (mol) = 85: 15 It was produced. In addition, water was added at a concentration of about 1000 ppm to the non-aqueous electrolytic solution of sample E21.
That is, the sample E21 is the same as the sample E15 except that a mixed solvent obtained by mixing EC, DMC, and EMC at a volume ratio of 3: 3: 4 is used as the organic solvent of the nonaqueous electrolytic solution. belongs to.

Further, in this example, comparative lithium secondary batteries for the samples E16 to E21 were produced. This is designated as Sample C4.
Sample C4 was added as a non-aqueous electrolyte to an organic solvent obtained by mixing EC, DMC, and EMC at a volume ratio of 3: 3: 4, and LiPF ₆ as an electrolyte was added to a final concentration of 1M. It was prepared using an electrolytic solution to which water was added at a concentration of about 1000 ppm. The additive (LPFO) is not added to the non-aqueous electrolyte of sample C4.
That is, the sample C4 is the same as the sample C1 of the comparative example except that a solvent obtained by mixing EC, DMC, and EMC at a volume ratio of 3: 3: 4 is used as the organic solvent. is there.

(Experimental example 2)
Next, in this example, the samples E13 to E21 and the sample C4 prepared in the above Example 2, the samples E1 to E3 prepared in the above Example 1, and the sample C1 prepared in the comparative example are low temperature ( The initial output at −30 ° C. was measured. The measurement was performed by the following initial output test.
Samples E1 to E3, samples E13 to E21, and samples C1 and C4 are lithium ion secondary batteries in which the molar ratio between the electrolyte and the additive contained in the non-aqueous electrolyte and the type of organic solvent are different. Table 2 below shows the molar ratio of the electrolyte to the additive and the organic solvent in the electrolyte solution of each sample.

"Initial output test"
Each sample (Samples E1 to E3, Samples E13 to E21, Samples C1 and C4) was kept at −30 ° C. After that, the battery capacity is adjusted to 50% (SOC = 50%), 0.12A, 0.4A, 1.2A, 2.4A, 4.8A current is applied and the battery voltage after 10 seconds is measured. The output value was calculated. The measurement was performed by preparing three samples similar to each sample, and obtaining the average.
The output value of each sample was expressed as a relative value when the value of the sample C1 was 1, that is, a value normalized based on the value of the sample C1. The result is shown in FIG.

  As shown in FIG. 3, in the samples E1 to E3 and the samples E13 to E15 using a mixed solvent of EC and DEC as the organic solvent in the electrolytic solution, the sample E1 is the highest at a low temperature of −30 ° C. The initial output value was shown, and the output was 1.3 to 1.4 times larger than that of the sample C1. Sample E13 and sample E14 showed 1.2 to 1.3 times larger output than sample C1, and sample E2 also showed the same output as sample C1. On the other hand, the sample E15 and the sample E3 showed a smaller output than the sample C1.

  When a mixed solvent of EC, DMC, and EMC was used as the organic solvent in the electrolytic solution, the sample C4 containing no additive showed a larger output than the sample C1. In Samples E16 to E21, Sample E16 showed the highest initial output value under a low temperature condition of −30 ° C. The sample E16 showed a large output of about 1.7 times that of the sample C1, and the output was remarkably improved compared to the sample C4. Sample E19 and sample E20 also showed an output 1.5 to 1.6 times larger than that of sample C1, and the output was greatly improved as compared with sample C4. The sample E17 was larger than the sample C1 and showed the same output as the sample C4. On the other hand, the sample E18 and the sample E21 showed a smaller output than the sample C4.

  That is, as is known from FIG. 3, there is an optimum ratio of the mixing ratio of the electrolyte and the additive for improving the output at low temperature. In this example, 0 <{additive (mole) / (electrolyte ( It can be seen that if the mixing ratio is such that (mol) + additive (mol)) <0.1, a good initial output can be obtained. Further, considering the balance with durability, it is more preferable that 0.03 ≦ {additive (mole) / (electrolyte (mole) + additive (mole)) ≦ 0.07.

Thus, it can be seen that the output performance at a low temperature is remarkably improved by adding an appropriate amount of the additive (LPFO). This is because at least a part of the additive (LiPF ₂ (C ₂ O ₄ ) ₂ ) is decomposed during the initial charge, and a stable film is formed on the surface of the positive electrode or / and the negative electrode, the positive electrode active material or / and the negative electrode active material. It is thought that it is because of forming. This film activates the interface between the active material and the electrolyte (the interface between the electrode and the electrolyte), so that lithium ions can be smoothly inserted and desorbed. As a result, the resistance at the interface is reduced. It is thought that the initial output of the battery could be improved.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the structure of the lithium ion secondary battery concerning Example 1. FIG. The elements on larger scale of the positive electrode of the lithium ion secondary battery concerning Example 1, and a negative electrode. The diagram which shows the initial output in the low temperature about the lithium ion secondary battery of the sample E1-sample E3, the sample E13-sample E21, the sample C1, and the sample C4 concerning the experiment example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 2 Positive electrode 25 Positive electrode active material 3 Negative electrode 35 Negative electrode active material 51 Electrolyte 53 Additive 55 Covering material

Claims (5)

A non-aqueous solution comprising a positive electrode containing an oxide or polyanionic compound containing lithium and a transition metal as a main component of a positive electrode active material, a negative electrode containing a carbon material as a negative electrode active material, and an electrolyte dissolved in an organic solvent In a lithium ion secondary battery having an electrolyte solution,
In the non-aqueous electrolyte, a compound represented by the following general formula (1) is added as an additive,
The non-aqueous electrolyte contains water at a concentration of 100 ppm to 10,000 ppm.

{Where 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 halogenated alkylene, C ₆ ~ C ₂₀ arylene or C ₆ -C ₂₀ halogenated arylene (These alkylenes and arylenes may have a substituent or a heteroatom in the structure, and m R ^{1 s} are bonded to each other. R ² may be 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 independent and represent hydrogen, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ alkyl halide, C ₆ -C ₂₀ aryl, C ₆ -C ₂₀ aryl halide, respectively (these alkyl and aryl May have a substituent or a hetero atom in the structure, and a plurality of R ³ and R ⁴ may be bonded to each other to form a ring). }   In claim 1, M in the general formula (1) is Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, A lithium ion secondary battery, which is any one of Sc, Hf, and Sb. 3. The electrolyte according to claim 1, wherein the electrolyte includes A ^{a +} (PF ₆ ⁻ ) _a , A ^{a +} (ClO ₄ ⁻ ) _a , A ^{a +} (BF ₄ ⁻ ) _a , A ^{a +} (AsF ₆ ⁻ ) _a , or A ^{a +.} A lithium ion secondary battery characterized by being one or more selected from (SbF ₆ ⁻ ) _a , wherein A ^{a +} is a metal ion, proton, or onium ion, and a is 1 to 3. _4. The additive according to claim 1, wherein the additive comprises a compound in which A ^{a +} in the general formula (1) is Li ⁺ , and the electrolyte is LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF. ₆ or a lithium ion secondary battery characterized by being at least one selected from LiSbF ₆ . 5. The non-aqueous electrolyte solution according to claim 1, wherein the additive has a molar ratio with the electrolyte of electrolyte: additive = 99.9-5: 0.1-95. A lithium ion secondary battery characterized by being added in the inside.
It is characterized by being.

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