JP2021190314A - Nonaqueous secondary battery - Google Patents

Abstract

To provide a nonaqueous secondary battery capable of suppressing various types of deterioration in a positive electrode active material when being charged/discharged under a high temperature environment, even in a nonaqueous secondary battery in which a positive electrode active material with a high nickel ratio is used.SOLUTION: A nonaqueous secondary battery includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator and a nonaqueous electrolyte. The nonaqueous electrolyte has a content of FSO3 anions of 100 ppm or less, and the positive electrode contains a lithium-containing metal oxide represented by the following general formula: LiNixCoyMnzO2. When c1 represents the lattice constant of a c axis when a non-energized positive electrode before the nonaqueous secondary battery is assembled is analyzed by powder X-ray diffraction using a Cu-Kα ray, and c2 represents the lattice constant of a c axis when a positive electrode after the nonaqueous secondary battery is energized in a specific condition is analyzed by powder X-ray diffraction using a Cu-Kα ray, the change rate from c1 to c2 is 1% or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a non-aqueous secondary battery.

Non-aqueous secondary batteries such as lithium-ion batteries are characterized by their light weight, high energy, and long life, and are widely used as power sources for various portable electronic devices. In recent years, a lithium-containing metal oxide having a high nickel ratio has been used as a positive electrode active material for the purpose of increasing the capacity. However, although the non-aqueous secondary battery can have a high capacity, there remains a problem that the long-term durability performance is inferior.

According to Patent Document 1, the crystallite size of the positive electrode active material is controlled, and by adding fluoroethylene carbonate to the non-aqueous electrolyte solution, the increase in the positive electrode resistance during charging and discharging is controlled, and the cycle characteristics are improved. It has been reported.

According to Patent Document 2, it is reported that by defining the c / a axis ratio of the positive electrode within a predetermined range, expansion and contraction during charging and discharging can be suppressed, and cycle characteristics under high voltage can be improved.

According to Patent Documents 3 and 4, it is reported that by defining the crystal size and the specific surface area of the positive electrode within a predetermined range, the cycle characteristics and the rate characteristics are excellent and the energy density is high.

International Publication No. 2015/129187 International Publication No. 2011/135953 Japanese Unexamined Patent Publication No. 2018-98174 Japanese Patent No. 6619562

As a deterioration factor of non-aqueous secondary batteries using a positive electrode active material in which the ratio of Ni in the lithium-containing metal oxide exceeds 0.7, the primary particles of the positive electrode active material due to expansion and contraction of the positive electrode active material due to charging and discharging. It is known that cracks occur at the interface and cause various deteriorations. If the deterioration further progresses, spinel transition occurs, the crystal structure cannot be maintained, and the cycle performance is significantly deteriorated. However, even if the crystallite size, specific surface area, or c / a axis ratio as described in Patent Documents 1 to 4 is within a predetermined range, cracks occur in the positive electrode active material having a high Ni ratio, which is good. The cycle performance was not sufficient. Further, Patent Documents 1 to 4 specify the physical property values of the positive electrode active material before charging and discharging, but do not show the physical property values of the positive electrode active material after charging and discharging.

The present invention has been made in view of the above problems, and even in a non-aqueous secondary battery using a positive electrode active material having a high nickel ratio, various deteriorations of the positive electrode active material when charged and discharged in a high temperature environment. It is an object of the present invention to provide a non-aqueous secondary battery capable of suppressing.

The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they have found that the above problems can be solved by using a non-aqueous secondary battery having the following configuration, and have completed the present invention. That is, the present invention is as follows.
[1]
A non-aqueous secondary battery having a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, a separator, and a non-aqueous electrolyte solution.
The non-aqueous electrolyte solution has an FSO ₃ anion content of 100 ppm or less.
The positive electrode contains a lithium-containing metal oxide and has a lithium-containing metal oxide.
The lithium-containing metal oxide has the following general formula:
LiNi _x Co _y Mn _z O ₂
In the formula, 0.7 <x <0.9, 0 <y <0.2, 0 <z <0.2.
The c-axis lattice constant of the positive electrode active material when the unenergized positive electrode before assembling the non-aqueous secondary battery is analyzed by powder X-ray diffraction with Cu-Kα rays is set to c1 and the non-aqueous secondary battery is used. Assuming that the c-axis lattice constant of the positive electrode active material is c2 when the positive electrode after energization is analyzed by powder X-ray diffraction with Cu-Kα rays under the following conditions, the following equation 1:
{(C2 / c1) -1} × 100 ・ ・ ・ Equation 1
The rate of change represented by is 1% or less,
The conditions for energization are that the non-aqueous secondary battery is charged at a constant current in a 25 ° C environment until the battery voltage reaches 4.2 V, and then charged at a constant current until the current value reaches 0.025 C. The process of discharging to 3 V with current is performed for 2 cycles, then the above non-aqueous secondary battery is charged at a constant current in a 50 ° C environment until the battery voltage reaches 4.2 V, and until the current value reaches 0.05 C. A non-aqueous secondary battery that performs 1000 cycles of charging at a constant voltage and discharging to 3V at a constant current.
[2]
The non-aqueous secondary battery according to item 1, wherein the lattice constant c2 of the c-axis of the positive electrode active material in the positive electrode after energization is 14.35 Å or less.
[3]
The non-aqueous secondary battery according to item 1 or 2, wherein the crystallite size of the positive electrode active material in the positive electrode after energization is 600 Å or more.
[4]
The non-aqueous secondary battery according to any one of Items 1 to 3, wherein the non-aqueous electrolyte solution contains an imide salt and LiPF _6, and the molar concentration of the imide salt> _{the molar concentration of LiPF 6.}

According to the present invention, even in a non-aqueous secondary battery using a positive electrode active material having a high nickel ratio, it is possible to suppress cracking of the positive electrode active material during a charge / discharge cycle in a high temperature environment. , Various deterioration phenomena in a high temperature environment can be suppressed.

FIG. 1 is a plan view schematically showing a non-aqueous secondary battery. FIG. 2 is a cross-sectional view taken along the line AA of FIG.

Hereinafter, embodiments for carrying out the present invention (hereinafter, simply referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiments, and various modifications can be made without departing from the gist thereof. The numerical range described by using "~" in the present specification includes the numerical values described before and after it.

<< Non-water-based secondary battery >>
The non-aqueous secondary battery of the present embodiment has a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, a separator, and a non-aqueous electrolyte solution. Further, although not limited, the non-aqueous secondary battery of the present embodiment includes a positive electrode containing a positive electrode material capable of storing and releasing lithium ions as a positive electrode active material, and lithium as a negative electrode active material. Examples thereof include a lithium ion battery including a negative electrode material capable of storing and releasing ions and / or a negative electrode containing metallic lithium.

Specifically, the non-aqueous secondary battery of the present embodiment may be the non-aqueous secondary battery shown in FIGS. 1 and 2. Here, FIG. 1 is a plan view schematically showing a non-aqueous secondary battery, and FIG. 2 is a sectional view taken along line AA of FIG. The non-aqueous secondary battery 100 shown in FIGS. 1 and 2 is composed of a pouch-type cell. The non-aqueous secondary battery 100 includes a laminated electrode body composed of a positive electrode 150 and a negative electrode 160 laminated via a separator 170 in a space 120 of a battery exterior 110 composed of two aluminum laminated films, and a non-aqueous secondary battery 100. Contains an electrolytic solution (not shown). The outer peripheral portion of the battery exterior 110 is sealed by heat-sealing the upper and lower aluminum laminated films. The laminate in which the positive electrode 150, the separator 170, and the negative electrode 160 are laminated in this order is impregnated with the non-aqueous electrolytic solution. However, in FIG. 2, in order to avoid complicating the drawings, the layers constituting the battery exterior 110 and the layers of the positive electrode 150 and the negative electrode 160 are not shown separately. The aluminum laminate film constituting the battery exterior 110 is preferably made by coating both sides of the aluminum foil with a polyolefin-based resin.

The positive electrode 150 is connected to the positive electrode lead body 130 in the non-aqueous secondary battery 100. Although not shown, the negative electrode 160 is also connected to the negative electrode lead body 140 in the non-aqueous secondary battery 100. One end of each of the positive electrode lead body 130 and the negative electrode lead body 140 is pulled out to the outside of the battery exterior 110 so that they can be connected to an external device or the like, and their ionomer portions are 1 of the battery exterior 110. It is heat-sealed together with the sides.

In the non-aqueous secondary battery 100 shown in FIGS. 1 and 2, the positive electrode 150 and the negative electrode 160 each have one laminated electrode body, but the number of laminated positive electrodes 150 and 160 is determined by the capacity design. It can be increased as appropriate. In the case of a laminated electrode body having a plurality of positive electrodes 150 and 160 negative electrodes, tabs of the same electrode may be joined to one lead body by welding or the like and then taken out of the battery. As the tab of the same pole, a mode composed of an exposed portion of the current collector, a mode configured by welding a metal piece to the exposed portion of the current collector, and the like are possible.

The positive electrode 150 is composed of a positive electrode active material layer made from a positive electrode mixture and a positive electrode current collector. The negative electrode 160 is composed of a negative electrode active material layer made from a negative electrode mixture and a negative electrode current collector. The positive electrode 150 and the negative electrode 160 are arranged so that the positive electrode active material layer and the negative electrode active material layer face each other via the separator 170.

As each of these members, a material provided in a conventional lithium ion battery can be used as long as each requirement in the present embodiment is satisfied. Hereinafter, each member of the non-aqueous secondary battery will be described in more detail.

[Positive electrode]
In the non-aqueous secondary battery according to the present embodiment, the positive electrode has a positive electrode active material layer on one side or both sides of the positive electrode current collector.

<Positive electrode active material layer>
The positive electrode active material layer preferably contains a positive electrode active material, and if necessary, further contains a conductive auxiliary agent and a binder.

(Positive electrode active material)
The positive electrode active material layer preferably contains, as the positive electrode active material, a material capable of occluding and releasing lithium ions. When such a material is used, it is preferable because a high voltage and a high energy density tend to be obtained.

Examples of the positive electrode active material include a positive electrode active material containing Ni and at least one transition metal element selected from the group consisting of Mn and Co, and the following general formula (a):
Li _p Ni _q Co _r Mn _s M _t O _u ... (a)
{In the formula, M is at least one metal selected from the group consisting of Al, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, Zr, Sr, and Ba, and 0 <p. <1.3, 0.7 <q <0.9, 0≤r <0.2, 0≤s <0.2, 0≤t <0.3, 0.7≤q + r + s + t≤1.2, 1 It is in the range of .8 <u <2.2, and p is a value determined by the charge / discharge state of the battery. }
At least one Li-containing metal oxide selected from the Li-containing metal oxides represented by is preferable.

Examples of the positive electrode active material include lithium cobalt oxide represented by _{LiCoO 2} ; lithium manganese oxide represented by _{LiMnO 2} , LiMn ₂ O ₄ and Li ₂ Mn ₂ O _{4 ; LiNiO 2.} Lithium nickel oxide; represented by LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , and LiNi _0.8 Co _0.2 O _2. Li _z MO ₂ (M contains at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and two or more selected from the group consisting of Ni, Mn, Co, Al, and Mg. Indicates the metal element of, z indicates a number of more than 0.9 and less than 1.2.) Examples thereof include lithium-containing composite metal oxides represented by.

In particular, when the Ni content ratio q of the Li-containing metal oxide represented by the general formula (a) is 0.7 <q <0.9, the amount of Co, which is a rare metal, can be reduced and high energy can be obtained. It is preferable because both densification is achieved. On the other hand, as the Ni content ratio increases, the cycle tends to deteriorate in a high temperature environment. As a Li-containing metal oxide having 0.7 <q <0.9, more specifically, the following general formula:
LiNi _x Co _y Mn _z O ₂
{In the formula, 0.7 <x <0.9, 0 <y <0.2, 0 <z <0.2}
Examples thereof include Li-containing metal oxides represented by.

The present inventor has a positive electrode before assembling a battery (hereinafter, also referred to as “non-energized positive electrode”) and a positive electrode after 1000 cycles of charge / discharge under a predetermined high temperature environment (hereinafter, “positive electrode after energization”). The positive electrode active material in) is analyzed by powder X-ray diffraction, and the c-axis lattice constant c2 of the positive electrode active material in the positive electrode after energization is compared with the c-axis lattice constant c1 of the positive electrode active material in the unenergized positive electrode. It has been found that the deterioration of the positive electrode is reduced by setting the rate of change (hereinafter, also referred to as “rate of change of lattice constant”) to 1% or less. The rate of change of the lattice constant is preferably 0.8% or less, more preferably 0.6% or less. The conditions for energization are that the non-aqueous secondary battery is charged at a constant current in a 25 ° C environment until the battery voltage reaches 4.2 V, and then charged at a constant current until the current value reaches 0.025 C. The process of discharging to 3V and the non-aqueous secondary battery are charged at a constant current in a 50 ° C environment until the battery voltage reaches 4.2V, and then charged at a constant current until the current value reaches 0.025C. The above two steps, that is, the step of discharging up to 3 V, are regarded as one cycle, and 1000 cycles are performed. When the rate of change of the lattice constant is 1% or less, it is considered that the deterioration of the charge / discharge capacity of the battery is reduced because the progress of cracking of the positive electrode active material can be suppressed. In order to control the rate of change of the lattice constant to 1% or less, in order to reduce the ratio of the crystal interface, the lattice constant and crystallite size of the positive electrode active material are controlled within a certain range, and the internal resistance of the battery is reduced during the cycle. It is preferable to apply a non-aqueous electrolyte solution that does not contain an increasing component.

The lattice constant c2 is preferably 14.35 Å or less, more preferably 14.33 Å or less, still more preferably 14.31 Å or less. When the lattice constant c2 is 14.35 Å or less, lithium ions are sufficiently packed in the lattice, which is preferable.

When the positive electrode after energization is observed by SEM in cross section, a large number of cracks tend to be confirmed between the primary particles. These cause an oxidative decomposition reaction of the electrolytic solution, an increase in internal resistance, and elution of transition metals, resulting in a decrease in cycle performance. It is considered that the cracking of the positive electrode active material due to these charges and discharges is caused by the stress at the crystal interface caused by the expansion and contraction of the crystal. The positive electrode active material with a large crystallite size has a smaller proportion of the interface between the crystallites than the positive electrode active material with a small crystallite size. Deterioration can be suppressed. Therefore, the crystallite size of the positive electrode active material is preferably 500 Å or more, and more preferably 600 Å or more.

The positive electrode active material may contain other lithium-containing compounds in addition to the Li-containing metal oxide represented by the formula (a), and is not particularly limited as long as it is a lithium-containing compound. Examples of such a lithium-containing compound include a composite oxide containing lithium and a transition metal element, a metal chalcogen product having lithium, a phosphate metal compound containing lithium and a transition metal element, and lithium and a transition metal element. Examples include metal silicate compounds containing. From the viewpoint of obtaining a higher voltage, the lithium-containing compound is at least one transition metal element selected from the group consisting of lithium, Co, Ni, Mn, Fe, Cu, Zn, Cr, V, and Ti. And, a metal phosphate compound containing is preferable.

More specifically, as other lithium-containing compounds, the following formula (Xa):
Li _v MI _u D ₂ (Xa)
{In the formula, D indicates a chalcogen element, MI indicates one or more transition metal elements including at least one transition metal element, and the value of v is determined by the charge / discharge state of the battery and is 0.05 to 1. .10 indicates a number, and u indicates a number 0-2. },
The following formula (Xb):
Li _w MII _u PO ₄ (Xb)
{In the formula, D represents a chalcogen element, MII represents one or more transition metal elements including at least one transition metal element, and the value of w is determined by the charge / discharge state of the battery and is 0.05 to 1. .10 indicates a number, and u indicates a number 0-2. } And the following formula (Xc):
_{Li t MIII u SiO 4 (Xc} )
{In the formula, D represents a chalcogen element, MIII represents one or more transition metal elements including at least one transition metal element, and the value of t is determined by the charge / discharge state of the battery and is 0.05 to 1. .10 indicates a number, and u indicates a number 0-2. }, Examples thereof include compounds represented by each of.

The lithium-containing compound represented by the above formula (Xa) has a layered structure, and the compounds represented by the above formulas (Xb) and (Xc) have an olivine structure. These lithium-containing compounds are those in which a part of the transition metal element is replaced with Al, Mg, or other transition metal elements for the purpose of stabilizing the structure, and these metal elements are included in the grain boundaries. , A substance in which a part of an oxygen atom is replaced with a fluorine atom or the like, a substance in which at least a part of the surface of the positive electrode active material is coated with another positive electrode active material, or the like may be used.

As the positive electrode active material in the present embodiment, the lithium-containing compound as described above may be used, or another positive electrode active material may be used in combination with the lithium-containing compound. Examples of such other positive electrode active materials include metal oxides or metal chalcogenides having a tunnel structure and a layered structure; sulfur; conductive polymers and the like. Metal oxides or metal chalcogenides having a tunnel structure and a layered structure include, for example, MnO ₂ , FeO ₂ , FeS ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , TiS ₂ , MoS ₂ , and NbSe. Examples thereof include oxides, sulfides, selenium compounds and the like of metals other than lithium represented by _2. Examples of the conductive polymer include conductive polymers typified by polyaniline, polythiophene, polyacetylene, and polypyrrole.

The above-mentioned other positive electrode active materials may be used alone or in combination of two or more, and are not particularly limited. However, since lithium ions can be reversibly and stably occluded and released, and high energy density can be achieved, the positive electrode active material layer is at least one transition metal element selected from Ni, Mn, and Co. Is preferably contained. When a lithium-containing compound and another positive electrode active material are used in combination as the positive electrode active material, the usage ratio of both is preferably 80% by mass or more, preferably 85% by mass, as the usage ratio of the lithium-containing compound to the total positive electrode active material. % Or more is more preferable.

(Conductive aid)
Examples of the conductive auxiliary agent include graphite, acetylene black, carbon black typified by Ketjen black, and carbon fiber. The content ratio of the conductive auxiliary agent is preferably 10 parts by mass or less, and more preferably 1 to 5 parts by mass with respect to 100 parts by mass of the positive electrode active material.

(binder)
Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene-butadiene rubber, and fluororubber. The content ratio of the binder is preferably 6 parts by mass or less, and more preferably 0.5 to 4 parts by mass with respect to 100 parts by mass of the positive electrode active material.

<Positive current collector>
The positive electrode current collector is composed of, for example, a metal foil such as an aluminum foil, a nickel foil, and a stainless steel foil. The surface of the positive electrode current collector may be coated with carbon or may be processed into a mesh shape. The thickness of the positive electrode current collector is preferably 5 to 40 μm, more preferably 7 to 35 μm, and even more preferably 9 to 30 μm.

<Formation of positive electrode active material layer>
For the positive electrode active material layer, a positive electrode mixture-containing slurry in which a positive electrode mixture obtained by mixing a positive electrode active material and, if necessary, a conductive auxiliary agent and a binder is dispersed in a solvent is applied to a positive electrode current collector and dried (solvent removal). ) And can be formed by pressing as needed. The solvent is not particularly limited, and conventionally known solvents can be used. For example, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, water and the like can be mentioned.

[Negative electrode]
The negative electrode is generally composed of a negative electrode active material layer made from a negative electrode mixture and a negative electrode current collector. The negative electrode can act as the negative electrode of the non-aqueous secondary battery.

The negative electrode active material layer preferably contains a negative electrode active material and, if necessary, a conductive auxiliary agent and a binder.

Examples of the negative electrode active material include amorphous carbon (hard carbon), artificial graphite, natural graphite, graphite, thermally decomposed carbon, coke, glassy carbon, calcined body of organic polymer compound, mesocarbon microbeads, carbon fiber, and activated carbon. , Graphite, carbon colloid, and carbon materials such as carbon black, as well as metallic lithium, metal oxides, metal nitrides, lithium alloys, tin alloys, silicon alloys, intermetal compounds, organic compounds, inorganic compounds, and metal complexes. , Organic polymer compounds and the like. The negative electrode active material may be used alone or in combination of two or more.

The negative electrode active material layer contains lithium ions of 0.4 V vs. as the negative electrode active material from the viewpoint of increasing the battery voltage. It is preferable to contain a material that can be occluded at a lower potential than Li / Li ^+.

Examples of the conductive auxiliary agent include graphite, acetylene black, carbon black typified by Ketjen black, and carbon fiber. The content ratio of the conductive auxiliary agent is preferably 20 parts by mass or less, and more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material.

Examples of the binder include carboxymethyl cellulose, PVDF, PTFE, polyacrylic acid, and fluororubber. Further, a diene-based rubber, for example, styrene-butadiene rubber and the like can also be mentioned. The content ratio of the binder is preferably 10 parts by mass or less, and more preferably 0.5 to 6 parts by mass with respect to 100 parts by mass of the negative electrode active material.

For the negative electrode active material layer, a negative electrode mixture-containing slurry in which a negative electrode mixture obtained by mixing a negative electrode active material and, if necessary, a conductive auxiliary agent and a binder is dispersed in a solvent is applied to a negative electrode current collector and dried (solvent removal). It is formed by pressing as needed. The solvent is not particularly limited, and conventionally known solvents can be used. For example, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, water and the like can be mentioned.

The negative electrode current collector is composed of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. Further, the negative electrode current collector may be coated with carbon on the surface or may be processed into a mesh shape. The thickness of the negative electrode current collector is preferably 5 to 40 μm, more preferably 6 to 35 μm, and even more preferably 7 to 30 μm.

[Non-aqueous electrolyte solution]
In the present specification, the "non-aqueous electrolyte solution" (hereinafter, also simply referred to as "electrolyte solution") refers to an electrolytic solution in which water is 1% by mass or less based on the total amount of the electrolytic solution.

In the present embodiment, the electrolytic solution preferably contains as little water as possible, but may contain a very small amount of water as long as it does not hinder the solution of the problem of the present invention. The content of such water is preferably 300% by mass or less, more preferably 200% by mass or less, based on the total amount of the non-aqueous electrolyte solution. As for the non-aqueous electrolyte solution, as long as it has a configuration for achieving the solution to the problem of the present invention, as for other components, the constituent materials in the known non-aqueous electrolyte solution used for the lithium ion battery may be appropriately used. Can be selected and applied.

In the present embodiment, the electrolytic solution can contain a non-aqueous solvent, a lithium salt, an electrode protection additive, and an FSO ₃ anion. In order to suppress the rate of change in the lattice constant, the electrolytic solution is unlikely to undergo a decomposition reaction at the positive and negative electrodes even when charged and discharged in a high temperature environment, and suppresses the elution of transition metals from the positive electrode active material. It is preferable to use a solvent having a low polar solvent, and as a result, the increase in internal resistance is small and the deterioration of the positive electrode active material can be prevented, so that good cycle performance can be obtained.

<Non-aqueous solvent>
Here, a non-aqueous solvent will be described. The "non-aqueous solvent" as used in the present embodiment means a component other than the lithium salt and various additives among the components contained in the electrolytic solution. However, when the electrolytic solution contains an electrode protection additive, the electrode protection additive that plays a role as a solvent for dissolving the lithium salt is also treated as a “non-aqueous solvent”. Examples of the non-aqueous solvent include alcohols such as methanol and ethanol; aprotic solvents and the like. Of these, aprotic solvents are preferred. The non-aqueous solvent may contain a solvent other than the aprotic solvent as long as the effect of the present invention is not impaired.

For example, the non-aqueous solvent related to the non-aqueous electrolyte solution can contain acetonitrile as an aprotic solvent. Since the non-aqueous solvent contains acetonitrile, the ionic conductivity of the non-aqueous electrolyte solution is improved, so that the diffusivity of lithium ions in the battery can be enhanced. Therefore, when the non-aqueous electrolyte solution contains acetonitrile, lithium ions are difficult to reach even in a positive electrode in which the positive electrode active material layer is thickened to increase the filling amount of the positive electrode active material, especially when discharging under a high load. Lithium ions can be well diffused to the nearby region. Therefore, it is possible to draw out a sufficient capacity even at the time of high load discharge, and it is possible to obtain a non-aqueous secondary battery having excellent load characteristics.
Further, since the non-aqueous solvent contains acetonitrile, the quick charging characteristics of the non-aqueous secondary battery can be enhanced. In constant current (CC) -constant voltage (CV) charging of a non-aqueous secondary battery, the capacity per unit time in the CC charging period is larger than the charging capacity per unit time in the CV charging period. When acetonitrile is used as the non-aqueous solvent of the non-aqueous electrolyte solution, the CC charging area can be increased (CC charging time can be lengthened) and the charging current can be increased. Therefore, from the start of charging the non-aqueous secondary battery. The time required to fully charge the battery can be significantly reduced.
Acetonitrile is easily electrochemically reduced and decomposed. Therefore, when acetonitrile is used, an electrode protection additive for forming a protective film on the electrode may be used in combination with acetonitrile as a non-aqueous solvent (for example, an aprotic solvent other than acetonitrile). It is preferable to add.

The content of acetonitrile is preferably 5 to 95% by volume as the amount per total amount of the non-aqueous solvent. The content of acetonitrile is more preferably 20% by volume or more or 30% by volume or more, and further preferably 40% by volume or more, as the amount per total amount of the non-aqueous solvent. This value is more preferably 85% by volume or less, and further preferably 66% by volume or less. When the content of acetonitrile is 5% by volume or more as the amount per total amount of the non-aqueous solvent, the ionic conductivity tends to increase and high output characteristics tend to be exhibited, and further, the dissolution of the lithium salt is promoted. Can be done. Since the additive forming the electrode protective film described later suppresses the increase in the internal resistance of the battery, when the content of acetonitrile in the non-aqueous solvent is within the above range, the excellent performance of acetonitrile is maintained. There is a tendency for the high temperature cycle characteristics and other battery characteristics to be further improved.

Examples of the aprotic solvent other than acetonitrile include cyclic carbonates, fluoroethylene carbonates, lactones, organic compounds other than the general formula (1) having a sulfur atom, chain fluorinated carbonates, cyclic ethers, and mononitriles other than acetonitrile. Examples thereof include alkoxy group-substituted nitriles, dinitriles, cyclic nitriles, short-chain fatty acid esters, chain ethers, fluorinated ethers, ketones, and compounds in which some or all of the H atoms of the aprotonic solvent are substituted with halogen atoms.

Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentylene carbonate, trans-2, Examples thereof include 3-pentylene carbonate, cis-2,3-pentylene carbonate, vinylene carbonate, 4,5-dimethylvinylene carbonate, and vinylethylene carbonate.

Examples of the fluoroethylene carbonate include 4-fluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, and cis-4,5-difluoro-1,3-. Dioxolan-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, 4,4,5,5 -Tetrafluoro-1,3-dioxolan-2-one and 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one can be mentioned.

Examples of the lactone include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone.

Examples of the organic compound having a sulfur atom other than the general formula (1) include ethylene sulphite, propylene sulphite, butylene sulphite, pentensulfite, sulfolane, 3-sulfolene, 3-methylsulfolane, and 1,3-propane. Examples thereof include sultone, 1,4-butane sultone, 1-propene 1,3-sultone, dimethylsulfoxide, tetramethylenesulfoxide, and ethylene glycol sulfide.

Examples of the chain carbonate include ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate and ethyl propyl carbonate.

Examples of the cyclic ether include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane.

Examples of mononitriles other than acetonitrile include propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile.

Examples of the alkoxy group-substituted nitrile include methoxyacetonitrile and 3-methoxypropionitrile.

Examples of the dinitrile include malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, and 2,6-. Dicyanoheptane, 1,8-dicyanooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononene, 1,10-dicyanodecane, 1,6-dicyanodecane, and 2,4-dimethylglue. Talonitrile may be mentioned.

Examples of the cyclic nitrile include benzonitrile.

Examples of short-chain fatty acid esters include methyl acetate, methyl propionate, methyl isobutyrate, methyl butyrate, methyl isovalerate, methyl valerate, methyl pivalate, methyl hydroangelica, methyl caproate, ethyl acetate, and propionic acid. Ethyl, ethyl isobutyrate, ethyl butyrate, ethyl isovalerate, ethyl valerate, ethyl pivalate, ethyl hydroangelica, ethyl caproate, propyl acetate, propyl propionate, propyl isobutyrate, propyl butyrate, propyl isovalerate, Propyl valerate, propyl pivalate, propyl hydroangelica, propyl caproate, isopropyl acetate, isopropyl propionate, isopropyl isobutyrate, isopropyl butyrate, isopropyl isovalerate, isopropyl valerate, isopropyl pivalate, isopropyl hydroangelica, capron Isopropyl acid, butyl acetate, butyl propionate, butyl isobutyrate, butyl butyrate, butyl isovalerate, butyl valerate, butyl pivalate, butyl hydroangelica, butyl caproate, isobutyl acetate, isobutyl propionate, isobutyl isobutyrate, Isobutyl butyrate, isobutyl isovalerate, isobutyl valerate, isobutyl pivalate, isobutyl hydroangelica, isobutyl caproate, tert-butyl acetate, tert-butyl propionate, tert-butyl isobutyrate, tert-butyl butyrate, isovaleric acid Examples thereof include tert-butyl, tert-butyl valerate, tert-butyl pivalate, tert-butyl hydroangelica, and tert-butyl caproate.

Examples of the chain ether include dimethoxyethane, diethyl ether, 1,3-dioxolane, diglime, triglime, and tetraglime.

Examples of the fluorinated ether include Rf ^20- OR ²¹ (Rf ²⁰ is an alkyl group containing a fluorine atom, and R ²¹ is an organic group containing a fluorine atom).

Examples of the ketone include acetone, methyl ethyl ketone, and methyl isobutyl ketone.

Examples of the compound in which a part or all of the H atom of the aprotic solvent is replaced with a halogen atom include a compound in which the halogen atom is fluorine.

Examples of the fluorinated product of the chain carbonate include methyl trifluoroethyl carbonate, trifluorodimethyl carbonate, trifluorodiethyl carbonate, trifluoroethyl methyl carbonate, methyl 2,2-difluoroethyl carbonate, and methyl 2,2,2-tri. Examples thereof include fluoroethyl carbonate and methyl 2,2,3,3-tetrafluoropropyl carbonate. The above fluorinated chain carbonate has the following general formula:
R ^29- OC (O) O-R ³⁰
(In the formula, R ²⁹ and R ³⁰ are at least one selected from the group consisting of _{CH 3} , CH ₂ CH ₃ , CH ₂ CH ₂ CH ₃ , CH (CH ₃ ) 2, and CH ₂ Rf ^31. , Rf ³¹ is an alkyl group having 1-3 carbon atoms in which a hydrogen atom is substituted with at least one fluorine atom, and R ²⁹ and / or R ³⁰ contains at least one fluorine atom). be able to.

Examples of the fluorinated product of the short-chain fatty acid ester include fluorinated shorts represented by 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate and 2,2,3,3-tetrafluoropropyl acetate. Examples include chain fatty acid esters. The fluorinated short-chain fatty acid ester has the following general formula:
R ^32- C (O) O-R ³³
(In the formula, R ³² is CH ₃ , CH ₂ CH ₃ , CH ₂ CH ₂ CH ₃ , CH (CH ₃ ) ₂ , CF ₃ CF ₂ H, CFH ₂ , CF ₂ Rf ³⁴ , CFHRf ³⁴ , and CH _2. At least one selected from the group consisting of ^{Rf 35 , where R 33} is _{from the group consisting of CH 3} , CH ₂ CH ₃ , CH ₂ CH ₂ CH ₃ , CH (CH ₃ ) ₂ , and CH ₂ Rf ^35. At least one selected, Rf ³⁴ is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom may be substituted with ^{at least one fluorine atom, and Rf 35} is at least one fluorine atom having a hydrogen atom. R ³³ is not CH ₃ if it is a substituted alkyl group with 1-3 carbon atoms and R ³² and / or R ³³ contains at least one hydrogen atom and R ³² is CF _{2 H.} It can be represented by.).

As the aprotic solvent other than acetonitrile in the present embodiment, one kind may be used alone, or two or more kinds may be used in combination.

<Lithium salt>
In this embodiment, the lithium salt is not particularly limited. For example, in this embodiment, the lithium salt _{may contain LiPF 6} or an imide salt. From the viewpoint of high temperature durability, it is preferable that _{the imide salt and LiPF 6} are contained, and the molar concentration of the imide salt> the molar concentration of LiPF _6.

The imide _{salt, LiN (SO 2 C m F} 2m + 1) is 2 {m is an integer of 0-8. }, More preferably, it contains at least one of _{LiN (SO 2} F) ₂ and LiN (SO ₂ CF ₃ ) _2. Only one of these imide salts may be contained or both may be contained. The imide salt may contain an imide salt other than these imide salts.

When acetonitrile is contained in the non-aqueous solvent, the saturation concentration of the imide salt with respect to acetonitrile is higher than _{the saturation concentration of LiPF 6 , so that the imide salt is contained at a molar concentration of LiPF 6} ≤ imide salt, that is, lithium at a low temperature. It is preferable because it can suppress the association and precipitation of salt and acetonitrile. Further, it is preferable that the content of the imide salt is 0.5 mol or more and 3 mol or less with respect to 1 L of the non-aqueous solvent from the viewpoint of the amount of ion supply. According to the acetonitrile-containing non-aqueous electrolyte solution containing at least one of LiN (SO ₂ F) ₂ and LiN (SO ₂ CF ₃ ) ₂ , ion conduction in a low temperature range such as -10 ° C or -30 ° C. The reduction of the rate can be effectively suppressed, and excellent low temperature characteristics can be obtained. By limiting the content of the imide salt in this way, it is possible to more effectively suppress the increase in resistance during high-temperature heating.

The lithium salt may contain a fluorine-containing inorganic lithium salt other than _{LiPF 6 , for example, LiBF 4} , LiAsF ₆ , Li ₂ SiF ₆ , LiSbF ₆ , Li ₂ B ₁₂ F _b H _12-b {b is 0 to 3 Is an integer of. }, Etc., may contain a fluorine-containing inorganic lithium salt. The "inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom in an anion and is soluble in acetonitrile. Further, the "fluorine-containing inorganic lithium salt" refers to a lithium salt which does not contain a carbon atom in an anion but contains a fluorine atom in an anion and is soluble in acetonitrile. The fluorine-containing inorganic lithium salt is excellent in that it forms a passivation film on the surface of the metal foil which is the positive electrode current collector and suppresses corrosion of the positive electrode current collector. These fluorine-containing inorganic lithium salts may be used alone or in combination of two or more. As the fluorine-containing inorganic lithium salt, a compound which is a double salt of LiF and Lewis acid is desirable, and among them, a fluorine-containing inorganic lithium salt having a phosphorus atom is more preferable because it facilitates the release of free fluorine atoms. A typical fluorine-containing inorganic lithium salt is _{LiPF 6} which dissolves and releases a _{PF 6 anion.} When a fluorine-containing inorganic lithium salt having a boron atom is used as the fluorine-containing inorganic lithium salt, it is preferable because it is easy to capture an excess free acid component that may cause deterioration of the battery, and from such a viewpoint. LiBF ₄ is particularly preferred.

The content of the fluorine-containing inorganic lithium salt in the non-aqueous electrolyte solution of the present embodiment is not particularly limited, but is preferably 0.01 mol or more, preferably 0.1 mol or more with respect to 1 L of the non-aqueous solvent. Is more preferable, and 0.25 mol or more is further preferable. When the content of the fluorine-containing inorganic lithium salt is within the above range, the ionic conductivity tends to increase and high output characteristics tend to be exhibited. Further, it is preferably less than 2.8 mol, more preferably less than 1.5 mol, and further preferably less than 1 mol with respect to 1 L of the non-aqueous solvent. When the content of the fluorine-containing inorganic lithium salt is within the above range, the ionic conductivity tends to increase and high output characteristics can be exhibited, and the decrease in ionic conductivity due to the increase in viscosity at low temperature tends to be suppressed. There is a tendency for the high temperature cycle characteristics and other battery characteristics to be further improved while maintaining the excellent performance of the non-aqueous electrolyte solution.

The non-aqueous electrolyte solution of the present embodiment may further contain an organolithium salt. The "organolithium salt" is a lithium salt containing a carbon atom in an anion and soluble in acetonitrile. Examples of the organolithium salt include an organolithium salt having an oxalic acid group. Specific examples of the organic lithium salt having an oxalate group include, for example, LiB (C ₂ O ₄ ) ₂ , LiBF ₂ (C ₂ O ₄ ), LiPF ₄ (C ₂ O ₄ ), and LiPF ₂ (C ₂ O). ₄ ) Organic lithium salts represented by each of ₂ can be mentioned, and at least one lithium salt selected from lithium salts represented by _{LiB (C 2} O ₄ ) ₂ and LiBF ₂ (C ₂ O _4). Is preferable. Further, it is more preferable to use one or more of these with a fluorine-containing inorganic lithium salt. This organic lithium salt having an oxalic acid group may be added to the non-aqueous electrolyte solution or may be contained in the negative electrode (negative electrode active material layer).

The amount of the organic lithium salt having a oxalic acid group added to the non-aqueous electrolyte solution is 0.005 mol per 1 L of the non-aqueous electrolyte solution from the viewpoint of ensuring the better effect of its use. The above is preferable, 0.02 mol or more is more preferable, and 0.05 mol or more is further preferable. However, if the amount of the organolithium salt having an oxalic acid group in the non-aqueous electrolyte solution is too large, it may precipitate. Therefore, the amount of the organic lithium salt having a oxalic acid group added to the non-aqueous electrolyte solution is preferably less than 1.0 mol per 1 L of the non-aqueous electrolyte solution, preferably 0.5 mol. It is more preferably less than, and even more preferably less than 0.2 mol.

Organolithium salts having an oxalic acid group are known to be sparingly soluble in less polar organic solvents, especially chain carbonates. The organic lithium salt having an oxalic acid group may contain a trace amount of lithium oxalate, and further reacts with a trace amount of water contained in other raw materials when mixed in a non-aqueous electrolyte solution. Therefore, a new white precipitate of lithium oxalate may be generated. Therefore, the content of lithium oxalate in the non-aqueous electrolyte solution of the present embodiment is not particularly limited, but is preferably 0 to 500 ppm.

In addition to the above, as the lithium salt in the present embodiment, a lithium salt generally used for non-aqueous secondary batteries may be supplementarily added. Specific examples of other lithium salts include, for example, LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiB ₁₀ Cl ₁₀ , and chloroborane Li, which are inorganic lithium salts containing no fluorine atom in an anion; LiCF ₃ SO ₃ , LiCF ₃ CO _2. , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{(2n + 1)} SO ₃ (n ≧ 2), lower aliphatic carboxylic acid Li, tetraphenylborate Li, LiB ( C ₃ O ₄ H ₂ ) Organic lithium salt such as _{2 ; LiPF n} (C _p F _{2p + 1} ) _6-n such as _{LiPF 5} (CF ₃ ) [n is an integer of 1 to 5, p is an integer of 1 to 8] Organic lithium salt represented by; LiBF _q (C _s F _{2s + 1} ) _4-q [q is an integer of 1 to 3 and s is an integer of 1 to 8] such as _{LiBF 3} (CF _3). Salt; Lithium salt bonded to polyvalent anion; Formula (a) below:
LiC (SO ₂ R ^A ) (SO ₂ R ^B ) (SO ₂ R ^C ) (a)
^{Wherein, R A, ^{R B,} and ^{R C} may be the being the same or different, show a perfluoroalkyl group having 1 to 8 carbon atoms. },
The following formula (b)
LiN (SO ₂ OR ^D ) (SO ₂ OR ^E ) (b)
{In the formula, ^RD and ^RE may be the same or different from each other and represent a perfluoroalkyl group having 1 to 8 carbon atoms. } And the following formula (c)
^{_{LiN (SO 2 R F) (}} SO 2 OR G) (c)
{Wherein, R ^F, and R ^G may be the being the same or different, show a perfluoroalkyl group having 1 to 8 carbon atoms. }
Examples thereof include organic lithium salts represented by each of the above, and one or more of these can be used together with a fluorine-containing inorganic lithium salt.

<Additive for electrode protection>
The electrolytic solution in the present embodiment may contain an additive that protects the electrodes. The electrode protection additive is not particularly limited as long as it does not hinder the solution of the problem according to the present invention. It may substantially overlap with a substance (ie, the non-aqueous solvent described above) that serves as a solvent for dissolving the lithium salt. The electrode protection additive, which is liquid and contains about 10% by volume or more in the non-aqueous electrolyte solution, also serves as a solvent for dissolving the lithium salt. The electrode protection additive is preferably a substance that contributes to improving the performance of the electrolytic solution and the non-aqueous secondary battery in the present embodiment, but also includes a substance that is not directly involved in the electrochemical reaction.

Specific examples of the electrode protection additive include 4-fluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, and cis-4,5-difluoro. -1,3-dioxolan-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, 4, Fluoroethylene carbonate typified by 4,5,5-tetrafluoro-1,3-dioxolan-2-one and 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one; Anhydride bond-containing cyclic carbonate typified by vinylene carbonate, 4,5-dimethylvinylene carbonate, and vinylethylene carbonate; γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε -Lactone typified by caprolactone; cyclic ether typified by 1,4-dioxane; ethylene sulphite, propylene sulphite, butylene sulphite, pentence sulphite, sulforane, 3-sulfolene, 3-methyl sulfolane, 1,3 -Cyclic sulfur compounds typified by propane sulton, 1,4-butane sulton, 1-propen 1,3-sulton, and tetramethylene sulfoxide; chain acid anhydrides typified by acetic anhydride, propionic anhydride, and benzoic anhydride. Malonic acid anhydride, succinic anhydride, glutaric anhydride, maleic anhydride, phthalic anhydride, 1,2-cyclohexanedicarboxylic acid anhydride, 2,3-naphthalenedicarboxylic acid anhydride, or naphthalene-1,4 , 5,8-Cyclic acid anhydride typified by tetracarboxylic acid dianhydride; a mixed acid anhydride having a structure in which two different types of carboxylic acids or different types of acids such as carboxylic acid and sulfonic acid are dehydrated and condensed. Can be mentioned. These may be used alone or in combination of two or more.

The content of the electrode protection additive in the electrolytic solution in the present embodiment is not particularly limited, but the content of the electrode protection additive with respect to the total amount in the non-aqueous electrolyte solution is 0.1 to 30% by volume. It is preferably 0.3 to 15% by volume, more preferably 0.5 to 10% by volume.

In the present embodiment, the larger the content of the electrode protection additive, the more the deterioration of the electrolytic solution can be suppressed. However, the smaller the content of the electrode protection additive, the better the high output characteristics of the non-aqueous secondary battery in a low temperature environment. Therefore, by adjusting the content of the electrode protection additive within the above range, excellent performance based on the high ionic conductivity of the electrolytic solution can be obtained without impairing the basic function as a non-aqueous secondary battery. It tends to be able to be maximized. By preparing the electrolytic solution with such a composition, the cycle performance of the non-aqueous secondary battery, the high output performance in a low temperature environment, and other battery characteristics all tend to be further improved.

Since acetonitrile, which is a component of the non-aqueous solvent, is easily reductively decomposed by electrochemical reduction, the non-aqueous solvent containing acetonitrile is a cyclic aprotic polarity as an electrode protection additive for forming a protective film on the negative electrode. It is preferable to contain one or more kinds of solvents, and it is more preferable to contain one or more kinds of unsaturated bond-containing cyclic carbonates.

The unsaturated bond-containing cyclic carbonate is preferably vinylene carbonate, and the content of vinylene carbonate is preferably 0.1% by volume or more and 4% by volume or less, and 0.2% by volume or more and 3 volumes by volume in the non-aqueous electrolyte solution. It is more preferably less than%, and even more preferably 0.5% by volume or more and less than 2.5% by volume. As a result, the low temperature durability can be improved more effectively, and it becomes possible to provide a secondary battery having excellent low temperature performance.

Vinylene carbonate as an electrode protection additive suppresses the reductive decomposition reaction of acetonitrile on the surface of the negative electrode, so it is often indispensable, and if it is insufficient, the battery performance may deteriorate sharply. On the other hand, excessive film formation causes deterioration of low temperature performance. Therefore, by adjusting the amount of vinylene carbonate added within the above range, the interface (coating) resistance can be suppressed to a low level, and cycle deterioration at low temperatures can be suppressed.

<FSO ₃ anion>
In the present embodiment, _{if the content of the FSO 3} anion contained in the electrolytic solution is too large, the reduction decomposition reaction proceeds on the surface of the negative electrode, and the deposited decomposition product increases the interface (coating) resistance and the output performance. It causes a decline. On the other hand, since a small amount of FSO ₃ anion acts to strengthen the negative electrode protective film, _{the content of FSO 3} anion is preferably in the range of 0.01 ppm or more and 100 ppm or less, and 0.1 ppm or more and 70 ppm with respect to the electrolytic solution. The range is more preferably 1 ppm or more and 50 ppm or less.

<Other optional additives>
In the present embodiment, for the purpose of improving the charge / discharge cycle characteristics of the non-aqueous secondary battery, improving the high temperature storage property, improving the safety (for example, preventing overcharging, etc.), the non-aqueous electrolytic solution is used, for example, a sulfonic acid ester. , Diphenyldisulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, phosphate esters, nitrogen-containing cyclic compounds with no steric hindrance around unshared electron pairs, and optional additions selected from derivatives of these compounds. The agent may be appropriately contained. Phosphate esters include ethyldiethylphosphonoacetate (EDPA): (C ₂ H ₅ O) ₂ (P = O) -CH ₂ (C = O) OC ₂ H ₅ , tris phosphate (trifluoroethyl) ( TFEP) :( CF ₃ CH ₂ O) ₃ P = O, Triphenyl Phosphate (TPP): (C ₆ H ₅ O) ₃ P = O, and Triallyl Phosphate: (CH ₂ = CHCH ₂ O) ₃ P = O and the like can be mentioned. Examples of the nitrogen-containing cyclic compound having no steric hindrance around the unshared electron pair include pyridine, 1-methyl-1H-benzotriazole, 1-methylpyrazole and the like. Phosphoric acid esters are particularly effective because they have the effect of suppressing side reactions during storage.

The content of the other optional additives in the present embodiment is calculated as a mass percentage with respect to the total mass of all the components constituting the non-aqueous electrolyte solution. The content of other optional additives is not particularly limited, but is preferably in the range of 0.01% by mass or more and 10% by mass or less, and 0.02% by mass or more, based on the total amount of the non-aqueous electrolyte solution. It is more preferably 5% by mass or less, and further preferably 0.05 to 3% by mass. By adjusting the content of other optional additives within the above range, it tends to be possible to add even better battery characteristics without impairing the basic functions of a non-aqueous secondary battery. be.

[Separator]
The non-aqueous secondary battery in the present embodiment preferably has a separator between the positive electrode and the negative electrode from the viewpoint of preventing short circuits between the positive electrode and the negative electrode and imparting safety such as shutdown. The separator is not limited, but may be the same as that provided in a known non-aqueous secondary battery, and an insulating thin film having high ion permeability and excellent mechanical strength is preferable. .. Examples of the separator include woven fabrics, non-woven fabrics, and microporous membranes made of synthetic resin. Among these, microporous synthetic resin membranes are preferable.

As the synthetic resin microporous membrane, for example, a polyolefin-based microporous membrane such as a microporous membrane containing polyethylene or polypropylene as a main component or a microporous membrane containing both of these polyolefins is preferably used. Examples of the non-woven fabric include a porous film made of a heat-resistant resin such as glass, ceramic, polyolefin, polyester, polyamide, liquid crystal polyester, and aramid.

The separator may have a structure in which one type of microporous membrane is laminated in a single layer or a plurality of types, or may be a structure in which two or more types of microporous membranes are laminated. The separator may have a structure in which two or more kinds of resin materials are melt-kneaded and laminated in a single layer or a plurality of layers using a mixed resin material.

Inorganic particles may be present on the surface layer or inside of the separator for the purpose of imparting a function, and other organic layers may be further coated or laminated. Further, it may include a crosslinked structure. In order to improve the safety performance of the non-aqueous secondary battery, these methods may be combined as necessary. By using such a separator, it is possible to realize good input / output characteristics and low self-discharge characteristics particularly required for the above-mentioned lithium ion secondary battery for high output applications.

The film thickness of the microporous membrane is not particularly limited, but is preferably 1 μm or more from the viewpoint of film strength, and is preferably 500 μm or less from the viewpoint of permeability. 5 μm or more and 30 μm from the viewpoint of being used for high output applications such as safety tests where the calorific value is relatively high and self-discharge characteristics higher than before are required, and from the viewpoint of winding performance with a large battery winding machine. It is preferably 10 μm or more, and more preferably 25 μm or less. When both short-circuit resistance and output performance are emphasized, it is more preferably 15 μm or more and 25 μm or less, but when both high energy density and output performance are emphasized, it is 10 μm or more and less than 15 μm. It is more preferable to have.

The porosity is preferably 30% or more and 90% or less, more preferably 35% or more and 80% or less, still more preferably 40% or more and 70% or less, from the viewpoint of following the rapid movement of lithium ions at the time of high output. When priority is given to improving output performance while ensuring safety, 50% or more and 70% or less is particularly preferable, and when both short-circuit resistance and output performance are emphasized, 40% or more and 50%. Less than% is particularly preferable.

From the viewpoint of the balance between the film thickness and the porosity, the air permeability is preferably 1 second / 100 cm ³ or more and 400 seconds / 100 cm ³ or less, and more preferably 100 seconds / 100 cm ³ or more and 350/100 cm ³ or less. When it is important to achieve both short-circuit resistance and output performance, 150 seconds / 100 cm ³ or more and 350 seconds / 100 cm ³ or less is particularly preferable, and when improvement of output performance is prioritized while ensuring safety. Is particularly preferably ^{100/100 cm 3} seconds or more and less than 150 seconds / 100 cm ^3.

On the other hand, when a non-aqueous electrolyte solution having low ionic conductivity and a separator within the above range are combined, the moving speed of lithium ions is not the structure of the separator, but the high ionic conductivity of the electrolytic solution is the rate-determining factor, which is expected. There is a tendency that such input / output characteristics cannot be obtained. Therefore, the ionic conductivity of the non-aqueous electrolytic solution is preferably 10 mS / cm or more, more preferably 15 mS / cm, and even more preferably 20 mS / cm. However, the film thickness, air permeability and porosity of the separator, and the ionic conductivity of the non-aqueous electrolyte solution are not limited to the above examples.

[Battery exterior]
The configuration of the battery exterior of the non-aqueous secondary battery in the present embodiment is not particularly limited, and for example, any battery exterior of a battery can and a laminated film exterior can be used. As the battery can, for example, a metal can such as a square type, a square cylinder type, a cylindrical type, an elliptical type, a flat type, a coin type, or a button type made of steel, stainless steel, aluminum, clad material, or the like can be used. .. As the laminated film exterior body, for example, a laminated film having a three-layer structure of a heat-melted resin / metal film / resin can be used.

The laminated film exterior is in a state where two sheets are stacked with the heat-melted resin side facing inward, or bent so that the heat-melted resin side faces inward, and the end is sealed by a heat seal. Can be used as an exterior body. When using the laminated film exterior body, connect the positive electrode lead body (or the lead tab connected to the positive electrode terminal and the positive electrode terminal) to the positive electrode current collector, and connect the negative electrode lead body (or the negative electrode terminal and the negative electrode terminal) to the negative electrode current collector. A lead tab) may be connected. In this case, the laminated film exterior body may be sealed with the ends of the positive electrode lead body and the negative electrode lead body (or the lead tabs connected to the positive electrode terminal and the negative electrode terminal respectively) pulled out to the outside of the exterior body. ..

<< Manufacturing method of non-aqueous secondary battery >>
The non-aqueous secondary battery in the present embodiment uses the above-mentioned non-aqueous electrolyte solution, a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a separator, and if necessary, a battery exterior, by a known method. Can be made.

First, a laminate composed of a positive electrode, a negative electrode, and a separator can be formed. For example, a method of producing a laminated body in which a long positive electrode and a negative electrode are interposed between a positive electrode and a negative electrode and the long separator is interposed, and winding this to form a laminated body having a wound structure; a positive electrode. A method of forming a laminated body having a laminated structure in which a positive electrode sheet and a negative electrode sheet obtained by cutting a negative electrode into a plurality of sheets having a certain area and shape are alternately laminated via a separator sheet. A method of forming a laminated body having a laminated structure in which the positive electrode body sheet and the negative electrode body sheet are alternately inserted between the zigzag-folded separators is possible.

Next, the above-mentioned laminate is housed in the battery exterior (battery case), the electrolytic solution is injected into the battery case, and the laminate is immersed in the electrolytic solution to seal the non-aqueous system in the present embodiment. A secondary battery can be manufactured. Alternatively, a gel-like electrolyte film is prepared in advance by impregnating a base material made of a polymer material with an electrolytic solution, and a laminated structure is laminated using a sheet-shaped positive electrode, negative electrode, and electrolyte film, and a separator. After forming the body, it can be housed in the battery exterior to produce a non-aqueous secondary battery.

It should be noted that the arrangement of the electrodes is such that there is a portion where the outer peripheral edge of the negative electrode active material layer and the outer peripheral edge of the positive electrode active material layer overlap, or there is a portion where the width is too small in the non-opposing portion of the negative electrode active material layer. If it is designed as such, the charge / discharge cycle characteristics of the non-aqueous secondary battery may deteriorate due to the displacement of the electrodes during battery assembly. Therefore, in the electrode body used for the non-aqueous secondary battery, it is preferable to fix the position of the electrode in advance with a tape such as a polyimide tape, a polyphenylene sulfide tape, a PP tape, an adhesive or the like.

In the present embodiment, when a non-aqueous electrolyte solution using acetonitrile is used, the lithium ions released from the positive electrode during the initial charging of the non-aqueous secondary battery diffuse to the entire negative electrode due to its high ionic conductivity. There is a possibility that it will be done. In a non-aqueous secondary battery, the area of the negative electrode active material layer is generally larger than that of the positive electrode active material layer. However, if lithium ions are diffused and occluded to a portion of the negative electrode active material layer that does not face the positive electrode active material layer, the lithium ions are not released at the time of initial discharge and remain in the negative electrode. Therefore, the contribution of the unreleased lithium ion becomes an irreversible capacity. For this reason, a non-aqueous secondary battery using a non-aqueous electrolyte solution containing acetonitrile may have a low initial charge / discharge efficiency. On the other hand, when the area of the positive electrode active material layer is larger than that of the negative electrode active material layer, or when both are the same, current is likely to be concentrated at the edge portion of the negative electrode active material layer during charging, and lithium dendrite is generated. It will be easier.

There is no particular limitation on the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other, but for the above reason, it is larger than 1.0 and less than 1.1. It is more preferably greater than 1.002 and less than 1.09, more preferably greater than 1.005 and less than 1.08, and particularly greater than 1.01 and less than 1.08. preferable. In a non-aqueous secondary battery using a non-aqueous electrolyte solution containing acetonitrile, the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other is reduced. The initial charge / discharge efficiency can be improved.

Reducing the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other means that the negative electrode active material layer does not face the positive electrode active material layer. It means limiting the proportion of the area of the part. As a result, of the lithium ions released from the positive electrode during the initial charge, the amount of lithium ions occluded in the portion of the negative electrode active material layer not facing the positive electrode active material layer (that is, released from the negative electrode during the initial discharge). It is possible to reduce the amount of lithium ions, which becomes an irreversible capacity) as much as possible. Therefore, by designing the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other within the above range, the load characteristics of the battery can be improved by using acetonitrile. It is possible to improve the initial charge / discharge efficiency of the battery and further suppress the generation of lithium dendrite.

The non-aqueous secondary battery in the present embodiment can function as a battery by the first charge, but is stabilized by a part of the electrolytic solution being decomposed at the first charge. The method of initial charging is not particularly limited, but the initial charging is preferably performed at 0.001 to 0.3C, more preferably 0.002 to 0.25C, and 0.003 to 0.2C. It is more preferable to be carried out in. It is also preferable that the initial charging is performed via constant voltage charging on the way. The constant current that discharges the design capacity in 1 hour is 1C. By setting a long voltage range in which the lithium salt is involved in the electrochemical reaction, a stable and strong SEI is formed on the electrode surface, which has the effect of suppressing an increase in internal resistance, and the reaction product is a negative electrode. It is not firmly fixed only to the 160, but somehow gives a good effect to members other than the negative electrode 160, such as the positive electrode 150 and the separator 170. Therefore, it is very effective to perform the initial charging in consideration of the electrochemical reaction of the lithium salt dissolved in the non-aqueous electrolyte solution.

The non-aqueous secondary battery in the present embodiment can also be used as a battery pack in which a plurality of non-aqueous secondary batteries are connected in series or in parallel. From the viewpoint of controlling the charge / discharge state of the battery pack, the working voltage range per battery pack is preferably 2 to 5 V, more preferably 2.5 to 5 V, and more preferably 2.75 V to 5 V. Especially preferable.

Although the embodiment for carrying out the present invention has been described above, the present invention is not limited to the above-described embodiment. The present invention can be modified in various ways without departing from the gist thereof.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

(1) Preparation of non-aqueous electrolyte solution Under an inert atmosphere, various non-aqueous solvents, various acid anhydrides, and various additives are mixed so as to have a predetermined concentration, and further, various lithium salts are added to each predetermined concentration. The non-aqueous electrolyte solutions (S1) and (S2) were prepared by adding them to a concentration. The composition of these non-aqueous electrolyte solutions is shown in Table 1.

The abbreviations for non-aqueous solvents, lithium salts, and additives in Table 1 have the following meanings. Further, the mass% of the additive in Table 1 indicates the mass% with respect to the total amount of the non-aqueous electrolyte solution.
(Non-aqueous solvent)
EMC: Ethyl Methyl Carbonate GBL: γ-Butyrolactone EC: Ethylene Carbonate VC: Vinylene Carbonate (Lithium Salt)
LiPF ₆ : Lithium hexafluorophosphate LiFSI: Lithium bis (fluorosulfonyl) imide (LiN (SO ₂ F) ₂ )

(2) Fabrication of coin-type non-aqueous secondary battery (2-1) Fabrication of positive electrode (A) Composite oxide of lithium, nickel, manganese, and cobalt as positive electrode active material (LiNi _0.8 Mn _0.1 Co _{0) .1} O ₂ ), (B) acetylene black powder as a conductive auxiliary agent, and polyvinylidene fluoride (PVDF) as a binder were mixed at a mass ratio of 94: 3: 3 to obtain a positive electrode mixture. .. N-Methyl-2-pyrrolidone as a solvent was added to the obtained positive electrode mixture so as to have a solid content of 68% by mass and further mixed to prepare a slurry containing a positive electrode mixture. Applying width 240 to 250 mm, coating length 125 mm, uncoated length 20 mm while adjusting the basis weight of this positive electrode mixture-containing slurry on one side of an aluminum foil with a thickness of 15 μm and a width of 280 mm, which is a positive electrode current collector. The coating was applied using a 3-roll transfer coater so as to have the coating pattern of, and the solvent was dried and removed in a hot air drying oven. Both sides of the obtained electrode roll were trimmed and cut, and dried under reduced pressure at 130 ° C. for 8 hours. Then, by rolling with a roll press so that the density of the positive electrode active material layer was 2.9 g / cm ³ , a positive electrode composed of the positive electrode active material layer and the positive electrode current collector was obtained. The basis weight excluding the positive electrode current collector was 16.6 mg / cm ² .

(2-2) Preparation of negative electrode (a) Graphite powder as a negative electrode active material, (b) acetylene black powder as a conductive auxiliary agent, and polyvinylidene fluoride (PVDF) as a binder, 90.0: 3. The mixture was mixed at a mass ratio of 0.0: 7.0 to obtain a negative electrode mixture. Water was added to the obtained negative electrode mixture as a solvent so as to have a solid content of 45% by mass, and the mixture was further mixed to prepare a slurry containing the negative electrode mixture. While adjusting the basis weight of this negative electrode mixture-containing slurry on one side of a copper foil with a thickness of 8 μm and a width of 280 mm, which is a negative electrode current collector, the coating width is 240 to 250 mm, the coating length is 125 mm, and the coating length is 20 mm. The coating was applied using a 3-roll transfer coater so as to have the coating pattern of, and the solvent was dried and removed in a hot air drying furnace. Both sides of the obtained electrode roll were trimmed and cut, and dried under reduced pressure at 80 ° C. for 12 hours. Then, it was rolled by a roll press so that the density of the negative electrode active material layer was 1.4 g / cm ³ , and a negative electrode composed of the negative electrode active material layer and the negative electrode current collector was obtained. The basis weight excluding the negative electrode current collector was 10.3 mg / cm ² .

(2-3) Assembly of coin-type non-aqueous secondary battery A polypropylene gasket is set in a CR2032 type battery case (SUS304 / Al clad), and the positive electrode obtained as described above is placed in the center thereof with a diameter of 15.958 mm. The one punched out in the shape of a disk was set with the positive electrode active material layer facing up. A glass fiber filter paper (GA-100 manufactured by Advantech) punched out in a disk shape having a diameter of 16.156 mm was set from above, and 150 μL of a non-aqueous electrolyte solution was injected, and then obtained as described above. The negative electrode was punched into a disk shape having a diameter of 16.156 mm and set with the negative electrode active material layer facing down. After setting the spacer and spring, the battery cap was fitted and crimped with a caulking machine. The overflowing electrolyte was wiped clean with a waste cloth. The battery was kept at 25 ° C. for 12 hours, and the non-aqueous electrolyte solution was sufficiently blended into the laminate to obtain a coin-type non-aqueous secondary battery.

(3) Evaluation of coin-type non-aqueous secondary battery For the coin-type non-aqueous secondary battery obtained as described above, first, the initial charging process and the initial charge / discharge capacity measurement are performed according to the procedure of (3-1) below. gone. Next, each coin-type non-aqueous secondary battery was evaluated according to the procedure of (3-2). Charging / discharging was performed using a charging / discharging device ACD-M01A (trade name) manufactured by Asuka Electronics Co., Ltd. and a program constant temperature bath IN804 (trade name) manufactured by Yamato Scientific Co., Ltd. Here, 1C means a current value that is expected to end the discharge in 1 hour by discharging the fully charged battery with a constant current. It means a current value that is expected to be discharged at a constant current from a fully charged state and to be completed in 1 hour.

(3-1) Initial charge / discharge treatment of a coin-type non-aqueous secondary battery Set the ambient temperature of the coin-type non-aqueous secondary battery to 25 ° C, and charge it with a constant current of 0.15 mA, which corresponds to 0.025 C. After reaching 3.1V, it is charged with a constant current of 0.3mA corresponding to 0.05C, and after reaching 4.2V, it is charged with a constant voltage of 4.2V until the current is attenuated to 0.025C. gone. Then, it was discharged to 3.0V with a constant current of 0.9mA corresponding to 0.15C. Next, after reaching 4.2 V with a constant current of 1.2 mA corresponding to 0.2 C, charging was performed with a constant voltage of 4.2 V until the current attenuated to 0.025 C. Then, it was discharged to 3V with a current value of 1.2mA corresponding to 0.2C. Then, the same charge / discharge as above was performed for another cycle.

(3-2) Cycle test For a coin-type non-aqueous secondary battery that was initially charged and discharged by the method described in (3-1) above, the ambient temperature was set to 50 ° C and 9 mA equivalent to 1.5 C. After reaching 4.2 V with a constant current of 4.2 V, charging was performed with a constant voltage of 4.2 V until the current attenuated to 0.025 C. After that, it was discharged to 3 V with a current value of 9 mA corresponding to 1.5 C. Then, in the same manner as described above, 1000 cycles were performed with one charge / discharge at 50 ° C. as one cycle. The charge capacity of the 1000th cycle in the cycle test when the discharge capacity of the second cycle in the first charge / discharge treatment was set to 100% was calculated as the capacity retention rate.

(3-3) Powder X-ray diffraction of positive electrode After the cycle test is completed, the coin-type non-aqueous secondary battery is disassembled in an argon atmosphere, the positive electrode is taken out, washed with diethyl carbonate, dried, and subjected to a powder X-ray diffractometer. Measurements were made. In addition, the positive electrode before assembling the coin-type non-aqueous secondary battery was also measured by a powder X-ray diffractometer. The measuring device used was Ultima-IV manufactured by Rigaku. X-ray source is Cu-Kα, excitation voltage is 40kV, current is 40mA, optical system is centralized optical system, Cu-Kβ ray filter is Ni foil, detector is Dtex (high sensitivity detector), measurement method is θ / 2θ method, DS = 1 ° for slit, SS = release, RS = release, vertical slit = 10 mm, 2θ / θ scan is 2θ = 5 to 90 ° (0.02 ° / step, 0.5 ° / min) did.

Rigaku's software (PDXL) was used to calculate the lattice constant and crystallite size. Si was used as an external standard for evaluation of crystallite size. The following Scherrer equation was used to calculate the crystallite size. The lattice constant was refined by the least squares method using all the observed peaks. The lattice was hexagonal, and the space group was R-3m (a = b, α = β = 90 °, γ = 120 °).
Scherrer's equation D = K × λ / (β × cos θ)
D: Crystallite size (crystallite size was calculated from the diffraction peak (110) of 2θ = 64.5 to 66.0 °)
K: Scherrer constant (0.94)
λ: Wavelength (1.5418), β: Full width at half maximum (rad)
θ: Bragg angle β = B · γ
^{γ = 0.9991-0.01905 (b / B)} -2.8205 (b / B) 2 +2.878 (b / B) 3 -1.0366 (b / B) 4
Here, b is the half-value width of Si, and B is the half-value width of the sample.
Let c1 be the lattice constant of the c-axis of the positive electrode active material in the positive electrode before assembling the coin-type non-aqueous secondary battery, and c2 be the lattice constant of the c-axis of the positive electrode active material in the positive electrode after the cycle test.

[Example 1 and Comparative Example 1]
Using the positive electrode, the negative electrode, and the non-aqueous electrolyte solution shown in Table 1, a coin-type non-aqueous secondary battery was produced according to the method described in (2) above. Next, each coin-type non-aqueous secondary battery was evaluated according to the above-mentioned procedures (3-1) to (3-3). The test results are shown in Tables 2 and 3.

As shown in Tables 2 and 3, in Example 1, the capacity retention rate in the cycle test was 80% or more, the rate of change in the lattice constant was 0.9% or less, and the crystallite size was 630 Å or more. On the other hand, in Comparative Example 1, the capacity retention rate in the cycle test was 76% or less, the rate of change of the lattice constant was 1.2% or more, and the crystallite size was less than 600 Å. As shown by this result, it is clear that the non-aqueous secondary battery of the present invention having a change rate of the lattice constant of 1% or less has a high capacity retention rate in a cycle test and can improve the cycle performance in a high temperature environment. became.

The non-aqueous secondary battery of the present invention is, for example, a rechargeable battery for portable devices such as mobile phones, portable audio devices, personal computers, and IC (Integrated Circuit) tags; automobiles such as hybrid vehicles, plug-in hybrid vehicles, and electric vehicles. Rechargeable batteries; low-voltage power sources such as 12V class power supplies, 24V class power supplies, and 48V class power supplies; Expected to be used as residential power storage systems, IoT devices, and the like. Further, the non-aqueous secondary battery of the present invention can be applied to applications in cold regions, outdoor applications in summer, and the like.

100 Non-aqueous secondary battery 110 Battery exterior 120 Space 130 Positive electrode lead body 140 Negative electrode lead body 150 Positive electrode 160 Negative electrode 170 Separator

Claims (4)

A non-aqueous secondary battery having a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, a separator, and a non-aqueous electrolyte solution.
The non-aqueous electrolyte solution has an FSO ₃ anion content of 100 ppm or less.
The positive electrode contains a lithium-containing metal oxide and has a lithium-containing metal oxide.
The lithium-containing metal oxide has the following general formula:
LiNi _x Co _y Mn _z O ₂
In the formula, 0.7 <x <0.9, 0 <y <0.2, 0 <z <0.2.
The c-axis lattice constant of the positive electrode active material when the unenergized positive electrode before assembling the non-aqueous secondary battery is analyzed by powder X-ray diffraction with Cu—Kα rays is set to c1 and the non-aqueous secondary battery is used. Assuming that the c-axis lattice constant of the positive electrode active material is c2 when the positive electrode after energization is analyzed by powder X-ray diffraction with Cu-Kα rays under the following conditions, the following equation 1:
{(C2 / c1) -1} × 100 ・ ・ ・ Equation 1
The rate of change represented by is 1% or less,
The energization condition is that the non-aqueous secondary battery is charged at a constant current in a 25 ° C environment until the battery voltage reaches 4.2 V, and then charged at a constant current until the current value reaches 0.025 C. Two cycles of discharging to 3V with current, then the non-aqueous secondary battery is charged at a constant current in a 50 ° C environment until the battery voltage reaches 4.2V, until the current value reaches 0.025C. A non-aqueous secondary battery that performs 1000 cycles of charging at a constant voltage and discharging to 3V at a constant current. The non-aqueous secondary battery according to claim 1, wherein the lattice constant c2 of the c-axis of the positive electrode active material in the positive electrode after energization is 14.35 Å or less. The non-aqueous secondary battery according to claim 1 or 2, wherein the crystallite size of the positive electrode active material in the positive electrode after energization is 600 Å or more. The non-aqueous secondary battery according to any one of claims 1 to 3, wherein the non-aqueous electrolyte solution contains an imide salt and LiPF _6, and the molar concentration of the imide salt> _{the molar concentration of the LiPF 6.} ..

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