WO2016088837A1 - Lithium secondary battery - Google Patents

Abstract

Provided is a lithium secondary battery having excellent high-temperature cycle characteristics, which comprises a positive electrode that is capable of absorbing and desorbing lithium, a negative electrode, and an electrolyte solution that contains a nonaqueous electrolyte solvent. This lithium secondary battery is characterized in that: a negative electrode active material contains a compound containing elemental silicon; and the surface of the negative electrode contains a phosphorus compound having a cyclic phosphoric acid ester structure wherein -O-P-O- constitutes a part of the ring structure.

Description

Lithium secondary battery

The present invention relates to a lithium secondary battery, a vehicle, and a storage battery.

Lithium secondary batteries are characterized by their small size and large capacity, and are widely used as power sources for electronic devices such as mobile phones and laptop computers, and have contributed to improving the convenience of portable IT devices. In recent years, the use in a larger application such as a power source for driving a motorcycle or an automobile or a storage battery for a smart grid has attracted attention. As the demand for lithium secondary batteries rises and is used in various fields, the battery has higher energy density, life characteristics that can withstand long-term use, and can be used in a wide range of temperature conditions. The characteristics are required.

When charging / discharging a lithium secondary battery, the electrolyte surface is brought into a very strong reducing or oxidizing environment on the negative electrode surface and the positive electrode surface. Therefore, the electrolytic solution is reduced or oxidized on the electrode surface. Inevitably, the electrolyte solution decomposes by causing a side reaction with the material constituting the electrode (electrode active material). Therefore, when charging / discharging of the lithium secondary battery is repeated over a long period of time, there is a problem that the capacity of the battery is deteriorated. In particular, these problems have remarkably appear in a lithium ion battery using a high-voltage positive electrode that has attracted attention in recent years in increasing energy density.

In the past, research has been conducted to improve the battery capacity degradation by forming a stable coating on the electrode surface. Since the electrode coating has a close relationship with the battery characteristics, it is necessary to optimize the structure and composition of the coating in order to improve the battery characteristics.

It has been proposed that a coating containing a phosphorus compound is formed on the surface of the positive electrode to suppress decomposition of the electrolytic solution on the surface of the positive electrode, to suppress an increase in resistance, and to extend the life. As an example of analyzing the positive electrode surface coating, phosphorus-derived photoelectrons on the positive electrode surface by X-ray absorption fine structure (XAFS) analysis method (Patent Document 1) and X-ray photoelectron spectroscopy (XPS analysis method) (Patent Document 2) What defines the spectral intensity is shown. In these documents, it is shown that the presence of an appropriate amount of phosphorus element in the film can be expected to increase the life, but the structure of the phosphorus compound forming the film is specified. It has not been.

Patent Document 3 shows an example in which the peak intensity ratio of lithium phosphate ion, lithium borate ion and lithium arsenate ion component on the negative electrode or positive electrode surface is defined by time-of-flight secondary ion mass spectrometry (TOF-SIMS). Are listed. Patent Document 4 discloses an example in which a battery having a protective film mainly composed of at least one of a phosphate derived from a phosphorus compound having a P—OH structure and a metal salt thereof is formed on the surface of the positive electrode. Has been. In these documents, the film component has a structure such as PO, so that the stability of the film is improved, the effect of suppressing the resistance increase due to the decomposition of the electrolytic solution, and the effect of improving the cycle characteristics are shown. However, the effect on the high-temperature cycle characteristics of a high energy density battery using a positive electrode operating at a high potential and a high capacity Si-based negative electrode has not been sufficient. Moreover, the example regarding a cyclic phosphate structure was not shown as a structure of the phosphorus compound which forms a film.

Japanese Patent No. 5277686 Japanese Patent No. 5357517 JP2013-62026A JP2013-152825A

In Patent Documents 1 to 4 described above, the effect of suppressing resistance increase due to the decomposition of the electrolytic solution and the effect of improving cycle characteristics are shown. However, when a positive electrode active material that operates at a high potential is used, a decomposition reaction of the electrolyte occurs at the contact portion between the positive electrode and the electrolyte, and the decomposition product decomposed on the positive electrode side is further reduced at the negative electrode. There are problems such as gas generation and deterioration of charge / discharge cycle characteristics. In particular, in a lithium secondary battery using a positive electrode active material exhibiting a high potential of 4.5 V or more, a decomposition product of the electrolytic solution is likely to be generated on the positive electrode side. The cycle characteristics at a high temperature such as 45 ° C. or higher were not sufficient.

An object of the present invention is to provide a lithium secondary battery that is under high voltage and high temperature conditions, effectively suppresses decomposition of the electrolytic solution even with a Si-based negative electrode, and has excellent long-term cycle characteristics.

The present invention is a secondary battery having a positive electrode capable of inserting and extracting lithium, a negative electrode, and an electrolyte containing a nonaqueous electrolytic solvent, wherein the negative electrode active material includes a compound containing silicon element. The present invention relates to a lithium secondary battery comprising a phosphorus compound having a cyclic phosphate structure in which —O—P—O— is part of the ring structure on the surface of the positive electrode or the negative electrode.

According to the present invention, it is possible to provide a lithium secondary battery that is under high voltage and high temperature conditions, effectively suppresses the decomposition of the electrolytic solution even with a Si-based negative electrode, and has excellent long-term cycle characteristics.

It is sectional drawing of one Embodiment of the lithium secondary battery of this invention. It is a disassembled perspective view which shows the basic structure of a film-clad battery. It is sectional drawing which shows the cross section of the battery of FIG. 2 typically.

As a result of studying suitable film components in order to suppress deterioration under a high-temperature cycle, the present inventors formed a film during a high-temperature cycle (especially when using a positive electrode operating at a high potential). It has been found that by having a compound having a cyclic phosphate structure having —O—P—O— as part of the ring structure as a component, decomposition of the electrolytic solution on the electrode surface can be suppressed.

Hereinafter, an example of the lithium secondary battery of the present invention will be described for each component, but the present invention is not limited to the specific contents thereof.

The secondary battery of this embodiment is a secondary battery having a positive electrode capable of inserting and extracting lithium, a negative electrode, and an electrolytic solution containing a nonaqueous electrolytic solvent, wherein the negative electrode active material is silicon element And a phosphorus compound having a cyclic phosphate structure in which —O—P—O— is part of the ring structure on the surface of the positive electrode or the negative electrode.

[Positive electrode]
In this embodiment, a positive electrode active material will not be specifically limited if a lithium ion can be inserted at the time of charge, and can be desorbed at the time of discharge, A well-known thing can be used.

Examples of the positive electrode active material include lithium manganate having a layered structure such as LiMnO ₂ and Li _x Mn ₂ O ₄ (0 <x <2) or lithium manganate having a spinel structure; LiCoO ₂ , LiNiO _2, or these Some transition metals replaced with other metals; LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and other specific transition metals such as lithium transition metal oxides; LiFePO ₄ and other olivines Those having a structure; in these lithium transition metal oxides, those having an excess of Li rather than the stoichiometric composition can be mentioned. In particular, Li _α Ni _β Co _γ Al _δ O ₂ (1 ≦ α ≦ 1.2, α + β + γ + δ = 2, β ≧ 0.7, γ ≦ 0.2) or Li _α Ni _β Co _γ Mn _δ O ₂ (1 ≦ α ≦ 1.2, α + β + γ + δ = 2, β ≧ 0.6, γ ≦ 0.2) are preferable. These materials can be used individually by 1 type or in combination of 2 or more types.

In the present embodiment, it is preferable that the positive electrode has a charge / discharge region of 4.4 V or higher with respect to lithium. The effect of the present embodiment can be more exerted by the effect of suppressing the decomposition of the electrolytic solution under a high voltage.

As the positive electrode active material that operates at a potential of 4.4 V or higher, for example, a lithium manganese composite oxide represented by the following formula (1) can be used.

Li _a (M _x Mn _2-xy Y _y ) (O _4-w Z _w ) (1)
(In the formula (1), 0.4 ≦ x ≦ 1.2, 0 ≦ y, x + y <2, 0 ≦ a ≦ 1.2, 0 ≦ w ≦ 1, M is Co, Ni, Fe, Cr And Y is at least one selected from the group consisting of Li, B, Na, Mg, Al, Ti, Si, K, and Ca, and Z is F or Cl. At least one kind.)

Specifically, as the lithium manganese composite oxide represented by the formula (1), for example, LiNi _0.5 Mn _1.5 O ₄ , LiCrMnO ₄ , LiFeMnO ₄ , LiCoMnO ₄ , LiCu _0.5 Mn _1.5 Preferred examples include O ₄ . These positive electrode active materials have a high capacity.

The positive electrode active material operating at a potential of 4.4 V or higher is more preferably a lithium manganese composite oxide represented by the following formula (1-1) from the viewpoint of obtaining sufficient capacity and extending the life. .

LiNi _x Mn _2-xy A _y O ₄ (1-1)
(In the formula (1-1), 0.4 <x <0.6, 0 ≦ y <0.3, A is at least selected from the group consisting of Li, B, Na, Mg, Al, Ti and Si. It is a kind.)

In addition, examples of the olivine-type positive electrode active material include those represented by the following formula (2).

LiMPO ₄ (2)
(In Formula (2), M is at least one selected from the group consisting of Co and Ni.)

Among the olivine type positive electrode active materials, LiCoPO ₄ , LiNiPO _{4 and the} like are preferable.

Examples of the positive electrode active material that operates at a potential of 4.4 V or higher include those having a layered structure. Examples of the positive electrode active material having such a layered structure are represented by the following formula (3). And the like.

_{Li (Li x M 1-x} -z Mn z) O 2 (3)
(In Formula (3), 0 ≦ x <0.3, 0.3 ≦ z ≦ 0.7, and M is at least one selected from the group consisting of Co, Ni, and Fe.)

Also, examples of the positive electrode active material that operates at a potential of 4.4 V or higher include Si composite oxides, and examples include those represented by the following formula (4).

Li ₂ MSiO ₄ (4)
(In formula (4), M is at least one selected from the group consisting of Mn, Fe and Co.)

The positive electrode active material can be selected from several viewpoints. From the viewpoint of increasing the energy density, it is preferable to include a high-capacity compound. Examples of the high-capacity compound include nickel-lithium oxide (LiNiO ₂ ) or lithium-nickel composite oxide obtained by substituting a part of nickel in nickel-lithium oxide with another metal element. The layered structure represented by the following formula (A) Lithium nickel composite oxide is preferred.

Li _y Ni _(1-x) M _x O ₂ (A)
(However, 0 ≦ x <1, 0 <y ≦ 1.2, and M is at least one element selected from the group consisting of Co, Al, Mn, Fe, Ti, and B.)

From the viewpoint of high capacity, the Ni content is high, that is, in the formula (A), x is preferably less than 0.5, and more preferably 0.4 or less. Examples of such a compound include Li _α Ni _β Co _γ Mn _δ O ₂ (0 <α ≦ 1.2, preferably 1 ≦ α ≦ 1.2, β + γ + δ = 1, β ≧ 0.7, γ ≦ 0. .2), Li _α Ni _β Co _γ Al _δ O ₂ (0 <α ≦ 1.2, preferably 1 ≦ α ≦ 1.2, β + γ + δ = 1, β ≧ 0.6, preferably β ≧ 0.7, γ ≦ 0.2), etc., especially LiNi _β Co _γ Mn _δ O ₂ (0.75 ≦ β ≦ 0.85, 0.05 ≦ γ ≦ 0.15, 0.10 ≦ δ ≦ 0.20). ). More specifically, for example, LiNi _0.8 Co _0.05 Mn _0.15 O ₂ , LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O _{2, LiNi} 0.8 _Co 0.1 _Al can be preferably used 0.1 _{O 2} or the like.

From the viewpoint of thermal stability, it is also preferable that the Ni content does not exceed 0.5, that is, in the formula (A), x is 0.5 or more. It is also preferred that the number of specific transition metals does not exceed half. Such compounds include Li _α Ni _β Co _γ Mn _δ O ₂ (0 <α ≦ 1.2, preferably 1 ≦ α ≦ 1.2, β + γ + δ = 1, 0.2 ≦ β ≦ 0.5, 0 0.1 ≦ γ ≦ 0.4, 0.1 ≦ δ ≦ 0.4). More specifically, LiNi _0.4 Co _0.3 Mn _0.3 O ₂ (abbreviated as NCM433), LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (abbreviated as NCM523), LiNi _0.5 Co _0.3 Mn _0.2 O ₂ (abbreviated as NCM532), etc. (however, the content of each transition metal in these compounds varies by about 10%) Can also be included).

In addition, two or more compounds represented by the formula (A) may be used as a mixture. For example, NCM532 or NCM523 and NCM433 range from 9: 1 to 1: 9 (typically 2 It is also preferable to use a mixture in 1). Furthermore, in the formula (A), a material having a high Ni content (x is 0.4 or less) and a material having a Ni content not exceeding 0.5 (x is 0.5 or more, for example, NCM433) are mixed. As a result, a battery having a high capacity and high thermal stability can be formed.

The positive electrode can be formed, for example, by applying a positive electrode slurry prepared by mixing a positive electrode active material, a positive electrode binder, and, if necessary, a conductivity-imparting agent onto a current collector.

Examples of the conductivity-imparting agent include carbon materials such as acetylene black, carbon black, fibrous carbon and graphite, metal substances such as Al, and conductive oxide powders.

The positive electrode binder is not particularly limited. For example, polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene. Copolymer rubber, polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamideimide and the like can be used.

The content of the conductivity-imparting agent in the positive electrode can be, for example, 1 to 10% by mass. The content of the binder in the positive electrode can be, for example, 1 to 10% by mass. If it exists in such a range, it will be easy to ensure the ratio of the amount of active materials in an electrode, and it will become easy to obtain sufficient capacity | capacitance per unit mass.

The positive electrode current collector is not particularly limited, but aluminum, nickel, copper, silver, and alloys thereof are preferable from the viewpoint of electrochemical stability. Examples of the shape include foil, flat plate, and mesh.

[Negative electrode]
In the present embodiment, the negative electrode includes a compound containing a silicon element as a negative electrode active material. By using such a material, the capacity of the negative electrode can be increased, and the energy density of the battery can be increased.

As a negative electrode active material containing silicon,
Si oxide represented by SiO _x (0 <x ≦ 2) such as SiO and SiO ₂ ;
M1 _y Si _1-y (M1 is a metal element and is composed of Li, B, Mg, Na, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Sn. A silicon alloy represented by 0 <y <1 including at least one selected from the group;
M2 _z Si _1-z O _w (M2 is a metal element, Li, B, Mg, Na, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and Sn A silicon composite oxide represented by 0 <z <1, 0 <w <2, including at least one selected from the group consisting of:
Si simple substance; and silicon nitride. The negative electrode active material may include a compound containing silicon alone or two or more kinds.

In the silicon alloy M1 _y Si _1-y , M1 is Li, B, Mg, Na, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Sn. The metal element selected from the group consisting of preferably 80% or more, more preferably 90% or more, and 100% of the composition ratio y of M1.

Further, the _M2 z _{Si 1-z O w} is the silicon composite oxide, M2 is Li, B, Mg, Na, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu , Zn and Sn may be contained in the composition ratio z, preferably 80% or more, more preferably 90% or more, and 100%.

M1 and M2 may contain two or more metals. For example, examples of silicon alloys including two types include Si—B—Al, Si—B—Fe, Si—B—Ni, Si—B—Cu, Si—B—Ti, Si—B—Sn, and Si—. B—Zn, Si—Ti—Al, Si—Ti—Ge, Si—Ti—Fe, Si—Ti—Ni, Si—Ti—Cu, Si—Ti—Zn, Si—Ti—Sn, Si—Cu— Al, Si-Cu-Fe, Si-Cu-Ni, Si-Cu-Zn, Si-Cu-Sn, Si-Fe-Al, Si-Fe-Ni, Si-Fe-Zn, Si-Fe-Sn, Si—Zn—Al, Si—Zn—V, Si—Zn—Sn, Si—Sn—Al, and Si—Sn—V are applicable.

In the present embodiment, the content of the compound containing silicon with respect to the total amount of the negative electrode active material is preferably 30% by mass or more, more preferably 50% by mass or more, and further preferably 80% by mass or more. Preferably, it may be 100% by mass.

The negative electrode active material may contain another negative electrode active material in addition to the silicon-based material. Examples thereof include a carbon material (a) that can occlude and release lithium ions, a metal (b) that can be alloyed with lithium, or a metal oxide (c) that can occlude and release lithium ions.

As the carbon material (a), graphite, amorphous carbon, diamond-like carbon, carbon nanotube, or a composite thereof can be used. Here, graphite with high crystallinity has high electrical conductivity, and is excellent in adhesiveness and voltage flatness with a positive electrode current collector made of a metal such as copper. On the other hand, since amorphous carbon having low crystallinity has a relatively small volume expansion, it has a high effect of relaxing the volume expansion of the entire negative electrode, and deterioration due to non-uniformity such as crystal grain boundaries and defects hardly occurs. The carbon material (a) is preferably 0% by mass or more and 80% by mass or less, more preferably 2% by mass or more and 80% by mass or less in the negative electrode active material, and 2% by mass or more and 30% by mass or less. The following range is more preferable. Moreover, the carbon material (a) may coat the surface of the compound containing silicon.

As the metal (b), a metal mainly composed of Al, Pb, Sn, Zn, Cd, Sb, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, La, or the like, or these two kinds The above alloys, or an alloy of these metals or alloys and lithium can be used. The metal (b) is preferably 0% by mass to 90% by mass in the negative electrode active material, more preferably 5% by mass to 90% by mass, and more preferably 20% by mass to 50% by mass. More preferably, it is the range.

Examples of the metal oxide (c) include aluminum oxide, tin oxide such as SnO and SnO ₂ , indium oxide, zinc oxide, lithium oxide, or a composite thereof, LiFe ₂ O ₃ , WO ₂ , MoO ₂ , CuO, and Nb. ₃ O ₅ , Li _x Ti _2-x O ₄ (1 ≦ x ≦ 4/3), PbO ₂ , Pb ₂ O _{5 and the} like can be used. In addition, one or more elements selected from nitrogen, boron and sulfur may be added to the metal oxide (c), for example, 0.1 to 5% by mass. By carrying out like this, the electrical conductivity of a metal oxide (c) can be improved. The metal oxide (c) is preferably 0% by mass to 90% by mass in the negative electrode active material, preferably in the range of 5% by mass to 90% by mass, and 40% by mass to 70% by mass. The following range is more preferable.

Other examples of the negative electrode active material include metal sulfide (d) that can occlude and release lithium ions. Metal sulfide as (d) are, for example, SnS and FeS ₂ or the like. Other examples of the negative electrode active material include metal lithium or lithium alloy, polyacene or polythiophene, or Li ₅ (Li ₃ N), Li ₇ MnN ₄ , Li ₃ FeN ₂ , Li _2.5 Co _0. Examples thereof include lithium nitride such as ₅ N or Li ₃ CoN.

In addition to the compound containing silicon, the negative electrode active material may contain the carbon material (a), the metal (b), the metal oxide (c), the metal sulfide (d), or the like alone or in combination. .

In addition, the shape of the negative electrode active material such as a silicon-based negative electrode active material, carbon material (a), metal (b), metal oxide (c), and metal sulfide (d) is not particularly limited, Particulate materials can be used.

The specific surface areas of the negative electrode active material is, for example, 0.01 ~ ^20m 2 / g, preferably 0.05 ~ ^15m 2 / g, more preferably ^{0.1 ~ 10m 2 / g, 0.15} ~ 8m ² / g is more preferable. By setting the specific surface area in such a range, the contact area with the electrolytic solution can be adjusted to an appropriate range. That is, when the specific surface area is 0.01 m ² / g or more, lithium ions can be easily inserted and desorbed smoothly, and the resistance can be further reduced. Moreover, it becomes easy to suppress that decomposition | disassembly of electrolyte solution accelerates | stimulates and the constituent element of an active material elutes by making a specific surface area into 20 m < ² > / g or less.

The central particle size of the negative electrode active material is preferably 0.01 to 50 μm, more preferably 0.02 to 40 μm. By setting the particle size to 0.02 μm or more, elution of constituent elements of the positive electrode material can be further suppressed, and deterioration due to contact with the electrolytic solution can be further suppressed. In addition, when the particle size is 50 μm or less, lithium ions can be easily inserted and desorbed smoothly, and the resistance can be further reduced. The particle size can be measured by a laser diffraction / scattering particle size distribution measuring apparatus.

The binder for the negative electrode is not particularly limited, but polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene copolymer. Polymerized rubber, polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamideimide and the like can be mentioned.

The content of the negative electrode binder is preferably in the range of 1 to 40% by mass, more preferably 1.5 to 30% by mass with respect to the total amount of the negative electrode active material and the negative electrode binder. By setting the content to 1% by mass or more, the adhesion between the active materials or between the active material and the current collector is improved, and the cycle characteristics are improved. Moreover, by setting it as 30 mass% or less, an active material ratio can improve and a negative electrode capacity | capacitance can be improved.

The negative electrode current collector is not particularly limited, but aluminum, nickel, copper, silver, iron, chromium, molybdenum and alloys thereof are preferable from the viewpoint of electrochemical stability. Examples of the shape include a foil shape, a flat plate shape, and a mesh shape.

The negative electrode can be produced by forming a negative electrode active material layer containing a negative electrode active material and a negative electrode binder on a negative electrode current collector. Examples of the method for forming the negative electrode active material layer include a doctor blade method, a die coater method, a CVD method, and a sputtering method. After forming a negative electrode active material layer in advance, a thin film of aluminum, nickel, or an alloy thereof may be formed by a method such as vapor deposition or sputtering to form a negative electrode current collector.

In the present invention, the surface of the negative electrode after charge / discharge contains a phosphorus compound having a cyclic phosphate structure in which —O—P—O— is part of the ring structure. The phosphorus compound having a cyclic phosphate structure can reduce the reactivity at the negative electrode by forming a film on the negative electrode surface. For this reason, long-term cycle characteristics can be achieved even with a Si-based negative electrode having high voltage and high temperature conditions in which electrolyte decomposition products are likely to be generated and having high reactivity with the electrolyte decomposition products.

As a method for detecting the coating component, for example, there is a time-of-flight secondary ion mass spectrometry (TOF-SIMS) method. In the TOF-SIMS method, pulsed ions (primary ions) are irradiated onto the sample surface in an ultra-high vacuum, and the ions (secondary ions) emitted from the sample surface fly with a certain kinetic energy. Guided to a time-type mass spectrometer. Each secondary ion accelerated with the same energy passes through the analyzer at a speed corresponding to the mass, but since the distance to the detector is constant, the time to reach it (time of flight) is By measuring this time-of-flight distribution precisely, a mass distribution of secondary ions, that is, a mass spectrum can be obtained. By analyzing from the mass spectrum and the components of the electrolytic solution, organic substances and inorganic substances existing on the sample surface can be identified, and knowledge about the abundance can be obtained from the peak intensity. Further, since the detection depth in the TOF-SIMS method is several nm or less, it is suitable as a method for analyzing the negative electrode surface coating.

When the surface of the negative electrode active material is irradiated with primary ions by the TOF-SIMS method, and secondary ions released from the surface of the negative electrode are measured with a mass spectrometer, cyclic phosphate ester ions are detected. Many other types of components are detected as surface coating components of the negative electrode, but the cycle characteristics at high temperatures can be improved by having a certain amount or more of the cyclic phosphate ion count ratio. . The peak intensity ratio of the cyclic phosphate ester ion (the ion count ratio of the peak intensity derived from the cyclic phosphate ion to the total peak intensity derived from all negative electrode surface detection components) is 0.0001 or higher. It is preferably 0.1 or less, more preferably 0.001 or more and 0.05 or less. Moreover, cyclic phosphate ester ions can be detected even in a cell that has been sufficiently cycled. For example, it is preferable that the peak intensity ratio of cyclic phosphate ion after 200 cycles at 45 ° C. is 0.001 or more.

The structure of the cyclic phosphate ester is not particularly limited, but preferably has a cyclic phosphate structure represented by the following formula (5).

(R ₁ represents a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms.)

The cyclic phosphate ion is more preferably an ethylene phosphate ion represented by the following formula (6). The ethylene phosphate ion represented by the formula (6) is observed around a mass number of 122.98 in the TOF-SIMS mass spectrum.

Peak intensity ratio of ethylene phosphate ion represented by formula (6) (peak intensity ratio derived from ethylene phosphate ion represented by formula (6) with respect to the total peak intensity derived from all negative electrode surface detection components) The peak intensity ratio is preferably 0.0001 or more and 0.1 or less, and more preferably 0.001 or more and 0.05 or less. Further, the cyclic phosphate ion can be detected even in a cell that has been sufficiently cycled. For example, the peak intensity ratio of the cyclic phosphate ions after 200 cycles at 45 ° C. is preferably 0.001 or more.

The initial charge / discharge is the first charge / discharge performed on a cell in which a predetermined electrolytic solution is sealed after the secondary battery is assembled, and is generally called a conditioning process. The number of times of charging / discharging as initial charging / discharging should just be 1 time or more, and it is preferable that they are 2 times or more and 5 times or less. In order to form a negative electrode film containing a phosphorus compound having the cyclic phosphate structure, it is preferable that the temperature during initial charge / discharge be 20 ° C. or higher and 70 ° C. or lower. More preferably, it is 35 degreeC or more and 55 degrees C or less. The negative electrode surface coating is mainly formed by the decomposition reaction of the electrolytic solution on the negative electrode surface. However, if the temperature is too low, the decomposition reaction of the electrolytic solution is not promoted, and the coating component is difficult to be formed. Becomes worse. If the temperature is too high, the electrolytic solution is excessively decomposed, which causes solvent alteration, gas generation, and resistance increase.

The surface of the positive electrode active material preferably also contains a phosphorus compound having a cyclic phosphate structure in which —O—P—O— is part of the ring structure. The above compound can be detected by analysis such as TOF-SIMS as in the negative electrode. The peak intensity ratio of cyclic phosphate ester ions by the TOF-SIMS method (the ion count ratio of the peak intensity derived from cyclic phosphate ester ions to the total peak intensity derived from all positive electrode surface detection components) is the peak intensity ratio. Is preferably 0.0001 or more and 0.1 or less, and more preferably 0.001 or more and 0.05 or less. Moreover, cyclic phosphate ester ions can be detected even in a cell that has been sufficiently cycled. For example, it is preferable that the peak intensity ratio of cyclic phosphate ion after 200 cycles at 45 ° C. is 0.001 or more.

The structure of the cyclic phosphate ester ion is not particularly limited, but preferably has a cyclic phosphate structure represented by the following formula (7).

(R ₁ represents a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms.)

The structure of the cyclic phosphate ester ion is more preferably an ethylene phosphate ion represented by the following formula (8). The ethylene phosphate ion represented by the formula (8) is observed around a mass number of 122.98 in the TOF-SIMS mass spectrum.

Peak intensity ratio of ethylene phosphate ion represented by formula (8) (the ion count of the peak intensity of ethylene phosphate ion represented by formula (8) with respect to the total peak intensity derived from all positive electrode surface detection components) Ratio) is preferably 0.0001 or more and 0.1 or less, and more preferably 0.001 or more and 0.05 or less. By containing a certain amount or more of a phosphorus compound having a cyclic phosphate structure in the positive electrode surface coating, reductive decomposition of the electrolytic solution can be suppressed, and cycle characteristics during high-temperature cycling are improved.

In order to form a positive electrode film containing a phosphorus compound having the cyclic phosphate structure, it is preferable to set the temperature during initial charge / discharge to 20 ° C. or higher and 70 ° C. or lower. More preferably, it is 35 degreeC or more and 55 degrees C or less. Similarly to the negative electrode film, the positive electrode surface film is also formed by a decomposition reaction of the electrolytic solution on the positive electrode surface. If the temperature is too low, the decomposition reaction of the electrolytic solution is not promoted, the film component is difficult to be formed, the cycle characteristics are deteriorated, and if the temperature is too high, the electrolytic solution is excessively decomposed and the solvent changes, It causes gas generation and resistance increase.

[Electrolyte]
The electrolytic solution in the present embodiment includes a lithium salt and a non-aqueous solvent.

The lithium salt preferably contains lithium hexafluorophosphate. It is considered that a part of lithium hexafluorophosphate containing phosphorus reacts on the electrode surface in order to form a good film component. The concentration of the lithium salt in the electrolytic solution is preferably 0.5 to 1.5 mol / l. More preferably, it is 0.8 to 1.2 mol / l. If the lithium salt concentration is too low, the coating component is difficult to form and sufficient cycle characteristics cannot be obtained. If the lithium salt concentration is too high, the battery characteristics deteriorate due to an increase in viscosity or excessive film formation.

As the lithium salt, in addition to lithium hexafluorophosphate, LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ CO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, lithium chloroborane, lithium tetraphenylborate, LiCl, LiBr, LiI, LiSCN, etc. Can be used. In addition to lithium hexafluorophosphate, these can be used alone or in combination.

It is preferable to contain a carbonate compound represented by the following formula (9) as the non-aqueous solvent.

(In Formula (9), R ₂ and R ₃ each independently represents a substituted or unsubstituted alkyl group. The carbon atom of R _{2 and} the carbon atom of R ₃ are bonded through a single bond or a double bond. And a cyclic structure may be formed, and a part of hydrogen of R ₂ and R ₃ may be substituted with fluorine.)

Since the carbonate compound has an action of forming a film on the positive electrode, the negative electrode, or both of them, the inclusion of these compounds can improve the cycle characteristics of the lithium secondary battery. A carbonate compound can be used individually by 1 type or in mixture of 2 or more types.

The carbonic acid ester compound is selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and a compound having a cyclic carbonic acid ester structure in which some or all of the hydrogen atoms contained therein are substituted with fluorine atoms. It is preferable that there is at least one. Since the compound having a cyclic carbonate structure has a high dielectric constant, the ion dissociation property of the electrolytic solution is improved, and the viscosity of the electrolytic solution is lowered. Therefore, in addition to the film forming effect, ion mobility can be improved.

The electrolytic solution in the present embodiment preferably further contains a fluorinated ether compound represented by the following formula (10) as a nonaqueous electrolytic solvent.

(In the formula, R ₄ and R ₅ each independently represents an alkyl group or a fluorinated alkyl group, provided that at least one of R ₄ and R ₅ is a fluorinated alkyl group.)

By containing the fluorinated ether, it is possible to reduce the viscosity of the electrolytic solution and improve the conductivity of the electrolytic solution while maintaining the oxidation resistance of the electrolytic solution.

In the formula (10), it is preferred carbon number _{n 2} with carbon number _n 1, _{R 5} of _{R 4} are each _{1 ≦ n 1 ≦ 8,1 ≦ n} 2 ≦ 8. Further, the total number of carbon atoms of R ₄ and R ₅ is more preferably 10 or less.

The fluorinated alkyl group is preferably a fluorinated alkyl group in which 50% or more, more preferably 60% or more, of the hydrogen atoms of the corresponding unsubstituted alkyl group are substituted with fluorine atoms. When the fluorine atom content is large, the voltage resistance is further improved, and even when a positive electrode active material that operates at a high potential is used, it is possible to more effectively reduce the deterioration of the battery capacity after the cycle.

Of the fluorinated ether compounds, a fluorinated ether compound represented by the following formula (10-1) is more preferable.

X ^1- (CX ² X ³ ) _n -O- (CX ⁴ X ⁵ ) _m -X ⁶ (10-1)
(In the formula (10-1), n and m are each independently 1 to 8. X ¹ to X ⁶ are each independently a fluorine atom or a hydrogen atom, provided that at least ^one of X ¹ to X ³ One is a fluorine atom, and at least one of X ⁴ to X ⁶ is a fluorine atom, and when n is 2 or more, a plurality of X ² and X ³ are each independent of each other; When m is 2 or more, a plurality of X ⁴ and X ⁵ are independent of each other.)

The fluorinated ether compound is more preferably a compound represented by the following formula (10-2) from the viewpoint of voltage resistance and compatibility with other electrolytes.

X ^1- (CX ² X ³ ) _n -CH ₂ O-CX ⁴ X ⁵ -CX ⁶ X ⁷ -X ⁸ (10-2)
(In the formula (10-2), n is 1 to 7, and X ¹ to X ⁸ are each independently a fluorine atom or a hydrogen atom, provided that at least one of X ¹ to X ³ is a fluorine atom. And at least one of X ⁴ to X ⁸ is a fluorine atom.)

In the formula (10-2), when n is 2 or more, a plurality of X ² may be the same or different, and a plurality of X ³ are the same or different from each other. Also good.

Furthermore, from the viewpoint of voltage resistance and compatibility with other electrolytes, the fluorinated ether compound is more preferably represented by the following formula (10-3).

H- (CY ¹ Y ² -CY ³ Y ⁴ ) _n -CH ₂ O-CY ⁵ Y ⁶ -CY ⁷ Y ⁸ -H (10-3)

In the formula (10-3), n is 1, 2, 3 or 4. Y ¹ to Y ⁸ are each independently a fluorine atom or a hydrogen atom. However, at least one of Y ¹ to Y ⁴ is a fluorine atom, and at least one of Y ⁵ to Y ⁸ is a fluorine atom.

In formula (10-3), when n is 2 or more, the plurality of Y ¹ to Y ⁴ may be the same or different from each other.

Examples of the fluorinated ether compound include CF ₃ OCH ₃ , CF ₃ OC ₂ H ₅ , F (CF ₂ ) ₂ OCH ₃ , F (CF ₂ ) ₂ OC ₂ H ₅ , and CF ₃ (CF ₂ ) CH ₂ O. (CF ₂ ) CF ₃ , F (CF ₂ ) ₃ OCH ₃ , F (CF ₂ ) ₃ OC ₂ H ₅ , F (CF ₂ ) ₄ OCH ₃ , F (CF ₂ ) ₄ OC ₂ H ₅ , F (CF ₂ ) ₅ OCH ₃ , F (CF ₂ ) ₅ OC ₂ H ₅ , F (CF ₂ ) ₈ OCH ₃ , F (CF ₂ ) ₈ OC ₂ H ₅ , F (CF ₂ ) ₉ OCH ₃ , CF ₃ CH ₂ OCH ₃ , CF ₃ CH ₂ OCHF ₂ , CF ₃ CF ₂ CH ₂ OCH ₃ , CF ₃ CF ₂ CH ₂ OCHF ₂ , CF ₃ CF ₂ CH ₂ O (CF ₂ ) ₂ H, CF ₃ CF ₂ CH ₂ O ( CF _{2) 2} F, HC _{2 CH 2 OCH 3, (CF} 3) (CF 2) CH 2 O (CF 2) 2 H, H (CF 2) 2 OCH 2 CH 3, H (CF 2) 2 OCH 2 CF 3, H (CF 2 ) ₂ CH ₂ OCHF ₂ , H (CF ₂ ) ₂ CH ₂ O (CF ₂ ) ₂ H, H (CF ₂ ) ₂ CH ₂ O (CF ₂ ) ₃ H, H (CF ₂ ) ₃ CH ₂ O (CF _{2) 2 H, H (CHF} ) 2 CH 2 O (CF 2) 2 H, (CF 3) 2 CHOCH 3, (CF 3) 2 CHCF 2 OCH 3, CF 3 CHFCF 2 OCH 3, CF 3 CHFCF 2 OCH ₂ CH ₃ , CF ₃ CHFCF ₂ CH ₂ OCHF ₂ , CF ₃ CHFCF ₂ OCH ₂ (CF ₂ ) ₂ F, CF ₃ CHFCF ₂ OCH ₂ CF ₂ CF ₂ H, H (CF ₂ ) ₄ CH ₂ O (C F ₂ ) ₂ H, CH ₃ CH ₂ O (CF ₂ ) ₄ F, F (CF ₂ ) ₄ CH ₂ O (CF ₂ ) ₂ H, H (CF ₂ ) ₂ CH ₂ OCF ₂ CHFCF ₃ , F (CF _{2) 2 CH 2 OCF 2 CHFCF} 3, H (CF 2) 4 CH 2 O (CF 2) H, CF 3 OCH 2 (CF 2) 2 F, CF 3 CHFCF 2 OCH 2 (CF 2) 3 F, CH ₃ CF ₂ OCH ₂ (CF ₂ ) ₂ F, CH ₃ CF ₂ OCH ₂ (CF ₂ ) ₃ F, CH ₃ O (CF ₂ ) ₅ F, F (CF ₂ ) ₃ CH ₂ OCH ₂ (CF ₂ ) _{3 F, F (CF 2) 2} CH 2 OCH 2 (CF 2) 2 F, H (CF 2) 2 CH 2 OCH 2 (CF 2) 2 H, CH 3 CF 2 OCH 2 (CF 2) such as ₂ H is Can be mentioned.

In addition, the fluorinated ether compound represented by the formula (10) may be used alone or in combination of two or more.

In the present embodiment, the non-aqueous solvent may include a fluorinated phosphate ester represented by the following formula (11).

(In the formula (11), R ₆ , R ₇ and R ₈ each independently represents a substituted or unsubstituted alkyl group, and at least one of R ₆ , R ₇ and R ₈ is a fluorine-substituted alkyl. The carbon atom of R _{6 and} the carbon atom of R ₇ may be bonded via a single bond or a double bond to form a cyclic structure.)

In the formula (11), it is preferable that R ₆ , R ₇ and R ₈ each independently have 1 to 3 carbon atoms. At least one of R ₆ , R ₇ and R ₈ is preferably a fluorine-substituted alkyl group in which 50% or more of the hydrogen atoms of the corresponding unsubstituted alkyl group are substituted with fluorine atoms. Moreover, all of R ₆ , R ₇ and R ₈ are fluorine-substituted alkyl groups, and 50% or more of the hydrogen atoms of the corresponding unsubstituted alkyl groups represented by R ₆ , R ₇ and R ₈ are substituted with fluorine atoms. More preferred is a fluorine-substituted alkyl group. This is because when the fluorine atom content is high, the voltage resistance is further improved, and even when a positive electrode active material that operates at a high potential is used, deterioration of the battery capacity after cycling can be further reduced.

The fluorinated phosphate ester is not particularly limited. For example, phosphoric acid tris (trifluoromethyl), phosphoric acid tris (pentafluoroethyl), phosphoric acid tris (2,2,2-trifluoroethyl), phosphoric acid Tris (2,2,3,3-tetrafluoropropyl), Tris phosphate (3,3,3-trifluoropropyl), Tris phosphate (2,2,3,3,3-pentafluoropropyl), etc. A fluorinated alkyl phosphate compound may be mentioned. Among these, as the fluorinated phosphate compound, tris (2,2,2-trifluoroethyl) phosphate is preferable. Fluorinated phosphates can be used alone or in combination of two or more.

In this embodiment, a sulfone compound represented by the following formula (12) may be included as the non-aqueous solvent.

(In Formula (12), R ₉ and R ₁₀ each independently represents a substituted or unsubstituted alkyl group. The carbon atom of R _{9 and} the carbon atom of R ₁₀ are bonded via a single bond or a double bond. And a ring structure may be formed.)

Preferred examples of the cyclic sulfone compound represented by the formula (12) include tetramethylene sulfone (sulfolane), pentamethylene sulfone, hexamethylene sulfone and the like. Preferred examples of the cyclic sulfone compound having a substituent include 3-methylsulfolane and 2,4-dimethylsulfolane. Since these materials are excellent in oxidation resistance, they can suppress the decomposition of the electrolytic solution under a high voltage, and have a relatively high dielectric constant, so that they have an advantage of excellent dissolution / dissociation action of lithium salt.

The sulfone compound may be a chain sulfone compound. Examples of the chain sulfone compound include ethyl methyl sulfone, ethyl isopropyl sulfone, ethyl isobutyl sulfone, dimethyl sulfone, and diethyl sulfone. Of these, dimethyl sulfone, ethyl methyl sulfone, ethyl isopropyl sulfone, and ethyl isobutyl sulfone are preferable. Since these materials are excellent in oxidation resistance, they can suppress the decomposition of the electrolytic solution under a high voltage, and have a relatively high dielectric constant, so that they have an advantage of excellent dissolution / dissociation action of lithium salt.

The sulfone compounds can be used alone or in combination of two or more.

In this embodiment, the nonaqueous solvent may include a carboxylic acid ester represented by the following formula (13).

(In Formula (13), R ₁₁ and R ₁₂ each independently represents a substituted or unsubstituted alkyl group. The carbon atom of R _{11 and} the carbon atom of R ₁₂ are bonded via a single bond or a double bond. And a cyclic structure may be formed, and a part of hydrogen of R ₁₁ and R ₁₂ may be substituted with fluorine.)

The carboxylate ester is not particularly limited, and examples thereof include ethyl acetate, methyl propionate, ethyl formate, ethyl propionate, methyl butyrate, ethyl butyrate, methyl acetate, and methyl formate. In order to improve the voltage resistance, a compound in which a hydrogen atom is substituted with a fluorine atom is preferable. For example, ethyl pentafluoropropionate, ethyl 3,3,3-trifluoropropionate, methyl 2,2,3,3-tetrafluoropropionate, 2,2-difluoroethyl acetate, methyl heptafluoroisobutyrate, 2, Methyl 3,3,3-tetrafluoropropionate, methyl pentafluoropropionate, methyl 2- (trifluoromethyl) -3,3,3-trifluoropropionate, ethyl heptafluorobutyrate, 3,3,3-tri Methyl fluoropropionate, 2,2,2-trifluoroethyl acetate, isopropyl trifluoroacetate, tert-butyl trifluoroacetate, ethyl 4,4,4-trifluorobutyrate, methyl 4,4,4-trifluorobutyrate, 2,2-difluoroacetic acid butyl, ethyl difluoroacetate, trifluoroacetic acid n- Chill, acetic acid 2,2,3,3-tetrafluoropropyl, ethyl 3- (trifluoromethyl) butyrate, methyl tetrafluoro-2- (methoxy) propionate, 3,3,3- trifluoropropionic acid 3,3 , 3 trifluoropropyl, methyl difluoroacetate, 2,2,3,3-tetrafluoropropyl trifluoroacetate, 1H, 1H-heptafluorobutyl acetate, methyl heptafluorobutyrate, ethyl trifluoroacetate and the like. Of these, methyl 2,2,3,3-tetrafluoropropionate, 2,2,3,3-tetrafluoropropyl trifluoroacetate and the like are preferable from the viewpoint of withstand voltage and boiling point.

The chain carboxylic acid ester has a feature that the viscosity is low when the carbon number is short, but the boiling point tends to be low. If the boiling point is low, the battery may vaporize during high temperature operation. If the number of carbon atoms is too large, the viscosity may increase and the conductivity may decrease. For these reasons, the carboxylic acid ester preferably has 3 to 12 carbon atoms. Moreover, oxidation resistance can be improved by substituting with fluorine. If the amount of fluorine substitution is small, it may react with the positive electrode at a high potential, resulting in a decrease in capacity retention rate or generation of gas. On the other hand, if the fluorine substitution amount is too large, it may be difficult to dissolve in the electrolytic solution or the boiling point may be lowered. For these reasons, the substitution amount of fluorine in the hydrogen atoms is preferably 1% or more and 90% or less, more preferably 10% or more and 85% or less, and 20% or more and 80% or less. More preferably.

As the solvent, in addition to the above, for example, γ-lactones such as γ-butyrolactone, chain ethers such as 1,2-ethoxyethane (DEE) and ethoxymethoxyethane (EME), tetrahydrofuran, 2-methyltetrahydrofuran Cyclic ethers such as dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, 1,3 -Dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolide And aprotic organic solvents such as These can be used alone or in combination of two or more.

By using a mixture of a plurality of types of solvents, the surface of the negative electrode can be coated with more phosphorus compounds having a cyclic phosphate structure, and good cycle characteristics may be achieved. Preferred solvent type combinations include carbonic acid ester / fluorinated ether / fluorinated phosphate ester, carbonic acid ester / fluorinated ether / sulfone compound, fluorinated ether / sulfone compound and carbonic acid ester / fluorinated ether / carboxylic acid ester. It is also possible to add other kinds of solvents to these mixed solvents.

[Separator]
The separator is not particularly limited, and a known separator can be used. Specifically, as the separator, for example, a polyolefin microporous film such as polyethylene or polypropylene, or one containing cellulose or glass fiber can be used.

[Exterior body]
As an exterior body, as long as it is stable to an electrolytic solution and has a sufficient water vapor barrier property, it can be appropriately selected and used. For example, in the case of a laminated laminate type secondary battery, a laminate film made of aluminum, silica-coated polypropylene, polyethylene, or the like can be used as the outer package.

[Secondary battery]
A secondary battery includes, for example, a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, a separator as an insulator sandwiched between the positive electrode and the negative electrode, and an electrolyte having lithium ion conductivity. It can take the form sealed in the exterior body. By applying a voltage to the positive electrode and the negative electrode, the positive electrode active material releases lithium ions, the negative electrode active material occludes lithium ions, and the battery is charged. In the discharged state, the state is opposite to the charged state.

Examples of the shape of the battery include a cylindrical shape, a square shape, a coin shape, a button shape, and a laminate shape. Examples of the battery outer package include stainless steel, iron, aluminum, titanium, two or more alloys thereof, or a plated product thereof. As the plating, for example, nickel plating can be used.

A secondary battery is, for example, a battery in which a negative electrode and a positive electrode are laminated via a separator in a dry air or inert gas atmosphere, or a laminate of the laminate is accommodated in an outer container such as a can case. And it can manufacture by inject | pouring electrolyte solution and sealing with the flexible film etc. which consist of a laminated body etc. of a synthetic resin and metal foil.

The form of the secondary battery is not particularly limited, and for example, it is possible to take a form such as a positive electrode opposed to a separator, a winding type in which a negative electrode is wound, and a laminated type in which these are stacked.

FIG. 1 shows a laminate type secondary battery as an example of the secondary battery. A separator 5 is sandwiched between a positive electrode composed of a positive electrode active material layer 1 containing a positive electrode active material and a positive electrode current collector 3, and a negative electrode composed of a negative electrode active material layer 2 and a negative electrode current collector 4. The positive electrode current collector 3 is connected to the positive electrode lead terminal 8, and the negative electrode current collector 4 is connected to the negative electrode lead terminal 7. An exterior laminate 6 is used for the exterior body, and the inside of the secondary battery is filled with an electrolytic solution.

As another aspect, a secondary battery having a structure as shown in FIGS. 2 and 3 may be used. The secondary battery includes a battery element 20, a film outer package 10 that houses the battery element 20 together with an electrolyte, and a positive electrode tab 51 and a negative electrode tab 52 (hereinafter also simply referred to as “electrode tabs”). .

As shown in FIG. 3, the battery element 20 is formed by alternately laminating a plurality of positive electrodes 30 and a plurality of negative electrodes 40 with a separator 25 interposed therebetween. In the positive electrode 30, the electrode material 32 is applied to both surfaces of the metal foil 31. Similarly, in the negative electrode 40, the electrode material 42 is applied to both surfaces of the metal foil 41.

The secondary battery in FIG. 1 has electrode tabs drawn out on both sides of the outer package. However, in the secondary battery to which the present invention can be applied, the electrode tab is drawn out on one side of the outer package as shown in FIG. It may be a configuration. Although detailed illustration is omitted, each of the positive and negative metal foils has an extension on a part of the outer periphery. The extensions of the negative electrode metal foil are collected together and connected to the negative electrode tab 52, and the extensions of the positive electrode metal foil are collected together and connected to the positive electrode tab 51 (see FIG. 3). The portions gathered together in the stacking direction between the extension portions in this way are also called “current collecting portions”.

The film outer package 10 is composed of two films 10-1 and 10-2 in this example. The films 10-1 and 10-2 are heat sealed to each other at the periphery of the battery element 20 and sealed. In FIG. 3, the positive electrode tab 51 and the negative electrode tab 52 are drawn out in the same direction from one short side of the film outer package 10 sealed in this way.

Of course, electrode tabs may be drawn from two different sides. As for the film configuration, FIGS. 2 and 3 show examples in which a cup portion is formed on one film 10-1 and a cup portion is not formed on the other film 10-2. In addition, a configuration in which a cup portion is formed on both films (not shown) or a configuration in which neither cup portion is formed (not shown) may be employed.

Examples of the laminate resin film used for the laminate mold include aluminum, an aluminum alloy, and a titanium foil. Examples of the material of the heat-welded portion of the metal laminate resin film include thermoplastic polymer materials such as polyethylene, polypropylene, and polyethylene terephthalate. Further, the metal laminate resin layer and the metal foil layer are not limited to one layer, and may be two or more layers.

[vehicle]
The secondary battery according to the present embodiment can be used for a vehicle. Vehicles according to the present embodiment include hybrid vehicles, fuel cell vehicles, and electric vehicles (all include four-wheeled vehicles (passenger cars, commercial vehicles such as trucks and buses, light vehicles, etc.), two-wheeled vehicles (motorcycles), and three-wheeled vehicles. ). Since these vehicles include the secondary battery according to the present embodiment, safety is high. The vehicle according to the present embodiment is not limited to an automobile, and may be various power sources for other vehicles, for example, a moving body such as a train.

[Power storage device]
Further, the secondary battery according to the present embodiment can be used for a power storage device. As the power storage device according to the present embodiment, for example, a power source connected to a commercial power source supplied to a general household and a load such as a home appliance, and used as a backup power source or auxiliary power at the time of a power failure, Examples include photovoltaic power generation, which is also used for large-scale power storage for stabilizing power output with large time fluctuation due to renewable energy.

Hereinafter, examples of the present embodiment will be described in detail. However, the present embodiment is not limited to the following examples.

[Example 1]
(Preparation of positive electrode)
First, powders of MnO ₂ , NiO, Li ₂ CO ₃ , and TiO ₂ were weighed so as to have a target composition ratio, and pulverized and mixed. Thereafter, the mixed powder was fired at 750 ° C. for 8 hours to produce LiNi _0.5 Mn _1.37 Ti _0.13 O ₄ . This positive electrode active material was confirmed to have a substantially single-phase spinel structure. The produced positive electrode active material and carbon black as a conductivity imparting agent were mixed, and this mixture was dispersed in a solution in which polyvinylidene fluoride (PVDF) as a binder was dissolved in N-methylpyrrolidone to prepare a positive electrode slurry. . The mass ratio of the positive electrode active material, the conductivity-imparting agent, and the positive electrode binder was 93/3/4. The positive electrode slurry was uniformly applied to both surfaces of a current collector made of Al. Then, it was made to dry in vacuum for 12 hours, and the positive electrode was produced by compression molding with a roll press. In addition, the weight of the positive electrode active material layer per unit area after drying was set to 0.040 g / cm ² .

(Preparation of negative electrode)
As the negative electrode active material, a material obtained by coating the surface of SiO with carbon was used. The mass ratio of SiO to carbon was 95/5. SiO shown below is a composite material in which 5% by mass of carbon is surface-treated. SiO was dispersed in a solution in which a polyimide binder was dissolved in N-methylpyrrolidone to prepare a negative electrode slurry. The mass ratio of the negative electrode active material to the binder material was 85/15. This negative electrode slurry was uniformly coated on a 10 μm thick Cu current collector. Then, it was dried in vacuum for 12 hours to produce a negative electrode. The weight of the negative electrode active material layer per unit area after drying was 0.0025 g / cm ² .

(Nonaqueous electrolyte)
A fluorinated ether (FE1) represented by ethylene carbonate (EC), sulfolane (SL) and H (CF ₂ ) ₂ CH ₂ O (CF ₂ ) ₂ H was converted into EC: SL: FE1 = 30: 20: 50 ( A non-aqueous solvent mixed at a volume ratio) was prepared. A non-aqueous electrolyte solution in which LiPF ₆ was dissolved at a concentration of 1.2 mol / L as an electrolyte was prepared.

(Production of laminated battery)
The positive electrode and the negative electrode were cut into 1.5 cm × 3 cm. Five layers of the obtained positive electrode and six layers of the negative electrode were alternately stacked while sandwiching a polypropylene porous film as a separator. The ends of the positive electrode current collector not covered with the positive electrode active material and the negative electrode current collector not covered with the negative electrode active material are welded respectively, and further, the positive electrode terminal made of aluminum and the negative electrode terminal made of nickel are connected to the welded portion. Each was welded to obtain an electrode element having a planar laminated structure. The electrode element was wrapped with an aluminum laminate film as an outer package, and an electrolyte solution was injected therein, and then sealed while reducing the pressure to produce a secondary battery.

(conditioning)
Initial charge / discharge (conditioning) was performed on the fabricated secondary battery. At 45 ° C, the initial charge is performed so that the total charge time is 10 hours up to 4.75V with constant current constant voltage (CCCV) charge of 0.2C, and constant current (CC) discharge is 3V at 0.2C. Went up. The second charge was performed in the same manner, and the battery was stored for 2 days while being discharged to a discharge depth of 80%, and then discharged to 3V.

(TOF-SIMS analysis of negative electrode surface)
The above-conditioned cell was opened under an argon atmosphere, and the negative electrode was taken out. In mass spectrometry by the TOF-SIMS method, TOF. SIM5 (trade name) was used. The analysis conditions are: primary ion species: Bi ^{3 ++} , primary ion energy: 30 keV, pulse width: 3.1 ns, secondary ion polarity: negative, measured mass range (m / z): 0 to 1500, measurement area: 200 μm × 200 μm, latter stage acceleration 10 kV, measurement vacuum (before sample introduction): 4 × 10 ⁻⁷ Pa or less. Than the mass analysis, near 122.98m / z ^- Table 1 shows the one expressed in the ratio of the sum of all the peak intensities of the peak intensity of the _{(C 2} H ₄ PO 4 peaks can be estimated as the peak of the origin) .

(High temperature cycle test)
A cycle test was performed at 45 ° C. on a cell that had been subjected to conditioning under the same conditions as the cell used in the TOF-SIMS analysis. After charging to 4.75 V at 1 C, a constant voltage charge was performed for 2.5 hours in total, and then a constant current discharge to 3.0 V at 1 C was repeated 200 times at 45 ° C. As a capacity retention rate, the ratio of the discharge capacity after 200 cycles to the initial discharge capacity was determined. The capacity retention rate after 200 cycles is shown in Table 1.

[Example 2]
A secondary battery was made in the same manner as Example 1 except that the lithium salt concentration of the non-aqueous electrolyte was 1.0M.

[Example 3]
The solvent composition of the nonaqueous electrolytic solution is fluorinated ether (FE2) represented by ethylene carbonate (EC), sulfolane (SL), H (CF ₂ ) ₂ CH ₂ OCF ₂ CHFCF ₃ , EC: SL: FE2 = A secondary battery was fabricated in the same manner as in Example 1 except that the ratio was 30:20:50 (volume ratio) and the lithium salt concentration was 1.0 M.

[Example 4]
The solvent composition of the non-aqueous electrolyte is ethylene carbonate (EC), sulfolane (SL), fluorinated ether (FE3) represented by H (CF ₂ ) ₄ CH ₂ O (CF ₂ ) H, EC: SL: A secondary battery was fabricated in the same manner as in Example 1, except that the ratio of FE3 was set to 30:20:50 (volume ratio) and the lithium salt concentration was 1.0 M.

[Example 5]
A secondary battery was fabricated in the same manner as in Example 1 except that the lithium salt concentration of the nonaqueous electrolytic solution was 0.8M.

[Example 6]
The solvent composition of the non-aqueous electrolyte is ethylene carbonate (EC), fluorinated ether (FE1) represented by H (CF ₂ ) ₂ CH ₂ O (CF ₂ ) ₂ H, tris phosphate (2,2,2- (Trifluoroethyl) (PTTFE) was changed to EC: FE1: PTTFE = 30: 50: 20 (volume ratio), and the lithium salt concentration was changed to 1.0 M. Was made.

[Example 7]
The solvent composition of the nonaqueous electrolytic solution is ethylene carbonate (EC), propylene carbonate (PC), fluorinated ether (FE1) represented by H (CF ₂ ) ₂ CH ₂ O (CF ₂ ) ₂ H, tris phosphate ( 2,2,2-trifluoroethyl) (PTTFE) except that the ratio of EC: PC: FE1: PTTFE = 20: 10: 40: 30 (volume ratio) and the lithium salt concentration was 0.8M. A secondary battery was fabricated in the same manner as in Example 1.

[Example 8]
The solvent composition of the non-aqueous electrolyte is sulfolane (SL), fluorinated ether (FE1) represented by H (CF ₂ ) ₂ CH ₂ O (CF ₂ ) ₂ H, SL: FE1 = 70: 30 (volume ratio) ) And the lithium salt concentration was 1.0 M, and a secondary battery was fabricated in the same manner as in Example 1.

[Example 9]
The solvent composition of the non-aqueous electrolyte is fluorinated ether (FE1) represented by propylene carbonate (PC), H (CF ₂ ) ₂ CH ₂ O (CF ₂ ) ₂ H, 2,2,3,3-tetrafluoro A secondary battery was prepared in the same manner as in Example 1 except that methyl propionate (TFMP) was changed to a ratio of PC: FE1: TFMP = 30: 40: 30 (volume ratio) and the lithium salt concentration was 1.0 M. Produced.

[Comparative Example 1]
A secondary battery was fabricated in the same manner as in Example 1 except that LiBF ₄ was used as the lithium salt and the lithium salt concentration was 1.0 M.

[Comparative Example 2]
The solvent composition of the non-aqueous electrolyte is ethylene carbonate (EC), fluorinated ether (FE1) represented by H (CF ₂ ) ₂ CH ₂ O (CF ₂ ) ₂ H, tris phosphate (2,2,2- Trifluoroethyl) (PTTFE) was set to the ratio of EC: FE1: PTTFE = 30: 50: 20 (volume ratio), LiBF ₄ was used as the lithium salt, and the concentration was 1.0 M. Similarly, a secondary battery was produced.

Table 1, Examples 1 to 9 and Comparative solvent composition of Examples 1 and 2, in the TOF-SIMS analysis of the negative electrode surface after conditioning _C 2 _{H 4} PO 4 ^- peak intensity ratio of from, after 45 ° C. 200 cycles Indicates the capacity maintenance rate.

In Examples 1 to 9, an ethylene phosphate ion component was detected as a coating component on the negative electrode surface. These 45 ° C. cycle characteristics were better than those of Comparative Examples 1 and 2, which were not detected. The presence of the cyclic phosphate ester compound derived from ethylene phosphate ions as a negative electrode coating component suppresses the reactivity between the silicon negative electrode and the electrolytic solution, and the effect of improving the cycle characteristics at high temperatures is obtained. As further shown in Examples _{1 ~ 5, C 2 H 4} PO 4 - If the peak intensity ratio of the components is 0.01 or more, it was found that improvement of more cycle characteristics is large. When the electrolyte solution contained a sulfone compound, a carbonate ester, and a fluorinated ether, particularly a large amount of ethylene phosphate ions was detected, and the capacity retention rate after cycling was also high. By setting it as such electrolyte solution, it is thought that the favorable film | membrane was formed on the silicon negative electrode, and cycling characteristics improved.

As described above, according to this embodiment, it is possible to obtain a battery with improved life characteristics.

This embodiment can be used in, for example, all industrial fields that require a power source and industrial fields related to the transport, storage, and supply of electrical energy. Specifically, power supplies for mobile devices such as mobile phones and notebook computers; power supplies for transportation and transportation media such as trains, satellites, and submarines, including electric vehicles such as electric cars, hybrid cars, electric bikes, and electric assist bicycles A backup power source such as a UPS; a power storage facility for storing power generated by solar power generation, wind power generation, etc .;

DESCRIPTION OF SYMBOLS 1 Positive electrode active material layer 2 Negative electrode active material layer 3 Positive electrode collector 4 Negative electrode collector 5 Separator 6 Exterior laminate 7 Negative electrode lead terminal 8 Positive electrode lead terminal 10 Film exterior body 20 Battery element 25 Separator 30 Positive electrode 40 Negative electrode

Claims (19)

1. A secondary battery having a positive electrode capable of inserting and extracting lithium, a negative electrode, and an electrolyte solution containing a nonaqueous electrolytic solvent, wherein the negative electrode active material contains a compound containing silicon element, and the negative electrode surface A lithium secondary battery comprising a phosphorus compound having a cyclic phosphate structure in which —O—P—O— is part of the ring structure.
2. The lithium secondary battery according to claim 1, wherein the phosphorus compound has a cyclic phosphate structure represented by the following formula (1).
   

   

   (R ₁ represents a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms.)
3. 2. A cyclic phosphate ion is included in a component detected when the negative electrode surface after charge / discharge is irradiated with primary ions by time-of-flight secondary ion mass spectrometry (TOF-SIMS). Or the lithium secondary battery of 2.
4. The lithium secondary battery according to claim 3, wherein the cyclic phosphate ion has a structure represented by the following formula (2).
   

   
5. The ion count ratio of the peak intensity derived from the cyclic phosphate ion to the total peak intensity derived from all negative electrode surface detection components is 0.0001 or more and 0.1 or less, or 4. The lithium secondary battery according to 4.
6. The lithium secondary battery according to any one of claims 1 to 5, wherein the electrolytic solution contains lithium hexafluorophosphate.
7. 7. The lithium secondary battery according to claim 1, wherein the electrolytic solution contains a carbonate ester compound represented by the following formula (3).
   

   

   (In Formula (3), R ₂ and R ₃ each independently represents a substituted or unsubstituted alkyl group. The carbon atom of R _{2 and} the carbon atom of R ₃ are bonded through a single bond or a double bond. And a ring structure may be formed.)
8. The carbonate compound is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and a compound having a cyclic carbonate structure in which some or all of the hydrogen atoms contained therein are substituted with fluorine atoms. The lithium secondary battery according to claim 7, which is a seed.
9. The lithium secondary battery according to any one of claims 1 to 8, wherein the electrolytic solution contains a fluorinated ether compound represented by the following formula (4).
   (In formula (4), R ₄ and R ₅ each independently represents an alkyl group or a fluorinated alkyl group, provided that at least one of R ₄ and R ₅ is a fluorinated alkyl group.)
10. The lithium secondary battery according to any one of claims 1 to 9, wherein the electrolytic solution contains a sulfone compound represented by the following formula (5).
    

    

    (In Formula (5), R ₆ and R ₇ each independently represents a substituted or unsubstituted alkyl group. The carbon atom of R _{6 and} the carbon atom of R ₇ are bonded through a single bond or a double bond. And a ring structure may be formed.)
11. The electrolytic solution is a carbonic acid ester compound represented by formula (3) according to claim 7, a fluorinated ether compound represented by formula (4) according to claim 9, and The lithium secondary battery according to any one of claims 1 to 10, comprising a sulfone compound represented by the formula (5).
12. A compound containing silicon element contained in the negative electrode active material,
    Si oxide represented by SiO _x (0 <x ≦ 2),
    M1 _y Si _1-y (M1 is a metal element and is composed of Li, B, Mg, Na, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Sn. A silicon alloy represented by 0 <y <1 including at least one selected from the group,
    M2 _z Si _1-z O _w (M2 is a metal element, Li, B, Mg, Na, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and Sn A silicon composite oxide represented by 0 <z <1, 0 <w <2, including at least one selected from the group consisting of:
    The lithium secondary battery according to any one of claims 1 to 11, wherein the lithium secondary battery is at least one selected from the group consisting of Si alone and silicon nitride.
13. The lithium secondary battery according to any one of claims 1 to 12, wherein the positive electrode has a charge / discharge region of 4.4 V or higher with respect to lithium.
14. The lithium secondary battery according to any one of claims 1 to 13, wherein the positive electrode active material contains a lithium manganese composite oxide represented by the following formula (6).
    Li _a (M _x Mn _2-xy Y _y ) (O _4-w Z _w ) (6)
    (In formula (6), 0.4 ≦ x ≦ 1.2, 0 ≦ y, x + y <2, 0 ≦ a ≦ 1.2, 0 ≦ w ≦ 1, and M is Co, Ni, Fe, Cr And Y is at least one selected from the group consisting of Li, B, Na, Mg, Al, Ti, Si, K, and Ca, and Z is F or Cl. At least one kind.)
15. The positive electrode active material is a lithium metal composite oxide represented by the following formula (7), a lithium metal composite oxide represented by the following formula (8), or an Si composite oxide represented by the following formula (9). The lithium secondary battery according to any one of claims 1 to 14, further comprising:
    LiMPO ₄ (7)
    (In Formula (7), M is at least one selected from the group consisting of Co and Ni.)
    _{Li (Li x M 1-x} -z Mn z) O 2 (8)
    (In formula (8), 0 ≦ x <0.3, 0.3 ≦ z ≦ 0.7, and M is at least one selected from the group consisting of Co, Ni, and Fe.)
    Li ₂ MSiO ₄ (9)
    (In formula (9), M is at least one selected from the group consisting of Mn, Fe and Co.)
16. In the lithium secondary battery, by performing initial charge and discharge at a temperature of 20 ° C. or higher and 70 ° C. or lower, a phosphorus compound having a cyclic phosphate structure in which OP—O— is part of the ring structure is formed on the negative electrode. The lithium secondary battery according to any one of claims 1 to 15, wherein a film having the same is formed.
17. A vehicle comprising the lithium secondary battery according to any one of claims 1 to 16.
18. A power storage device using the lithium secondary battery according to any one of claims 1 to 16.
19. A method for manufacturing a lithium secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium, the positive electrode and a negative electrode containing a compound containing a silicon element as a negative electrode active material arranged opposite to each other to form an electrode element And a step of enclosing the electrode element and the electrolytic solution in an outer package, and charging and discharging at a temperature of 20 ° C. or higher and 70 ° C. or lower to form —O—P—O— in the ring structure on the negative electrode. A method for producing a lithium secondary battery, comprising forming a film having a phosphorus compound having a cyclic phosphate structure as a part.

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