JP6757505B2 - Power storage element - Google Patents

Description

The present invention relates to a power storage element such as a non-aqueous electrolyte secondary battery.

Conventionally, a non-aqueous electrolyte secondary battery containing a positive electrode, a negative electrode, and an electrolytic solution, and the electrolytic solution contains a specific cyclic disulfonic acid ester is known (for example, Patent Document 1). In the battery described in Patent Document 1, a sulfur-containing compound is generated on the surface of the negative electrode by reducing the cyclic disulfonic acid ester. Such a sulfur-containing compound is detected as a compound having a peak at 162.9 to 164.0 eV when the surface of the negative electrode is analyzed by XPS.

However, in the battery described in Patent Document 1, the capacity and output may decrease after being left for a long period of time.

Japanese Patent No. 4844718

An object of the present invention is to provide a power storage element in which a decrease in capacity and output is suppressed after being left for a long period of time.

Electric storage element of the present invention includes a positive electrode, a negative electrode, if the surface of the positive electrode is XPS analysis, the concentration of sulfur S1, is calculated by the peak based on the SO ₄ ^2-is 0.3 atomic% or more It is 1.0 atomic% or less, and the concentration of sulfur S2 calculated by the peaks based on SS and SC is 0 atomic% or more and 1.0 atomic% or less (concentration of sulfur S2) /. (Concentration of sulfur S1) is 0 or more and 2 or less. According to the power storage element having such a configuration, it is possible to suppress a decrease in capacity and output after being left for a long period of time.

In the above-mentioned power storage element, (concentration of sulfur S2) / (concentration of sulfur S1) may increase with the passage of time. With such a configuration, it is possible to more reliably suppress a decrease in the capacity and output of the power storage element after being left for a long period of time.

In the above power storage element, when the surface of the negative electrode is analyzed by XPS,
The concentration of sulfur S3 calculated by the peak of 163 eV or more and 170 eV or less based on the sulfur component may be 0.5 atomic% or more and 5.0 atomic% or less. As a result, it is possible to more reliably suppress a decrease in the capacity and output of the power storage element after being left for a long period of time.

In the above electricity storage device, the positive electrode comprises an active material, active _{material, Li v Ni w Mn x Co} y O z lithium-metal composite oxide represented by the chemical composition (but, 0 <v ≦ 1. Even if it is 3, w + x + y = 1, 0 <w <1, 0 <x <1, 0 <y <1, and 1.7 ≦ z ≦ 2.3). Good. With such a configuration, it is possible to more reliably suppress a decrease in the capacity and output of the power storage element after being left for a long period of time.

In the above-mentioned power storage element, the negative electrode contains an active material, and the active material may be non-graphitized carbon. With such a configuration, it is possible to more reliably suppress a decrease in the capacity and output of the power storage element after being left for a long period of time.

According to the present invention, it is possible to suppress a decrease in capacity and output after being left for a long period of time.

FIG. 1 is a perspective view of a power storage element according to the present embodiment. FIG. 2 is a front view of the power storage element according to the same embodiment. FIG. 3 is a cross-sectional view taken along the line III-III of FIG. FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. FIG. 5 is a perspective view of a part of the power storage element according to the same embodiment, which is a perspective view of a state in which the liquid injection plug, the electrode body, the current collector, and the external terminal are assembled to the lid plate. is there. FIG. 6 is a diagram for explaining the configuration of the electrode body of the power storage element according to the embodiment. FIG. 7 is a cross-sectional view (VII-VII cross section of FIG. 6) of the superposed positive electrode, negative electrode, and separator. FIG. 8 is a perspective view of a power storage device including a power storage element according to the same embodiment. FIG. 9 is a graph showing the maintenance rate of the battery capacity. FIG. 10 is a graph showing the maintenance rate of the assist output performance at 25 ° C. FIG. 11 is a graph showing the maintenance rate of the assist output performance at −10 ° C.

Hereinafter, an embodiment of the power storage element according to the present invention will be described with reference to FIGS. 1 to 7. The power storage element includes a secondary battery, a capacitor, and the like. In the present embodiment, a rechargeable secondary battery will be described as an example of the power storage element. The name of each component (each component) of the present embodiment is that of the present embodiment, and may be different from the name of each component (each component) in the background technology.

The power storage element 1 of the present embodiment is a non-aqueous electrolyte secondary battery. More specifically, the power storage element 1 is a lithium ion secondary battery that utilizes electron transfer generated by the movement of lithium ions. This type of power storage element 1 supplies electrical energy. The power storage element 1 is used alone or in a plurality. Specifically, the power storage element 1 is used alone when the required output and the required voltage are small. On the other hand, when at least one of the required output and the required voltage is large, the power storage element 1 is used in the power storage device 100 in combination with the other power storage element 1. In the power storage device 100, the power storage element 1 used in the power storage device 100 supplies electrical energy.

As shown in FIGS. 1 to 7, the power storage element 1 includes an electrode body 2 including a positive electrode 11 and a negative electrode 12, a case 3 accommodating the electrode body 2, and an external terminal 7 arranged outside the case 3. It contains an external terminal 7 that is conductive to the electrode body 2 and an electrolytic solution injected into the case 3. Further, the power storage element 1 further includes a current collector 5 or the like for conducting the electrode body 2 and the external terminal 7.

The electrode body 2 is formed by winding a laminated body 22 in which a positive electrode 11 and a negative electrode 12 are laminated in a state of being insulated from each other by a separator 4.

The positive electrode 11 has a metal foil 111 (positive electrode base material 111) and a positive electrode active material layer 112 that is arranged so as to overlap the metal foil 111 and contains an active material. The positive electrode active material layer 112 is laminated on both sides of the metal foil 111, respectively. For example, the surface of the positive electrode 11 to be analyzed by XPS (described later) is one surface of the positive electrode active material layer 112, which is the surface opposite to the surface overlapping the metal foil 111.

The metal foil 111 is strip-shaped. The thickness of the metal foil 111 is usually 10 μm or more and 20 μm or less. The metal foil 111 of the positive electrode 11 of the present embodiment is, for example, an aluminum foil. The positive electrode 11 has an exposed portion 105 in which the positive electrode active material layer 112 is not formed and the metal foil 111 is exposed at one edge portion in the width direction, which is the lateral direction of the band shape.

The positive electrode active material layer 112 is arranged so as to face the negative electrode 12 via the separator 4. If the surface of the positive electrode active material layer 112 facing the negative electrode 12 (the surface opposite to the surface which overlaps with the metal foil 111) is XPS analysis, the concentration of sulfur S1, it is calculated by the peak based on the _SO ^{4 2-is} 0 .3 atomic% or more and 1.0 atomic% or less. The concentration of sulfur S2 calculated from the peaks based on SS and SC is 0 atomic% or more and 1.0 atomic% or less. Further, (concentration of sulfur S2) / (concentration of sulfur S1) is 0 or more and 2 or less. In addition, XPS is X-ray Photoelectron Spectroscopy. SO ₄ ^{2-, S-S,} calculation of the concentration by the peak based on the respective S-C is performed by peak splitting the photoelectron spectrum obtained by the XPS analysis. The details of the analysis conditions of the XPS analysis and the method of calculating the concentration of each sulfur by peak division will be described in detail in Examples described later.

The positive electrode active material layer 112 of the positive electrode 11 has a compound containing at least sulfur S1 among sulfur S1 and sulfur S2 on the surface. The above-mentioned compound containing at least sulfur S1 is a positive electrode active material due to decomposition of an additive described later contained in the electrolytic solution or application of a compound containing sulfur S1 or sulfur S2 to the positive electrode active material layer 112. It occurs on the surface of layer 112. In the present embodiment, on the surface of the positive electrode active material layer 112, a compound produced by decomposition of an additive described later contained in the electrolytic solution and containing at least sulfur S1 is generated.

Sulfur S1 is in photoelectron spectrum obtained by XPS analysis, are represented by the peak based on the _SO ^{4 2-.} The _{photoelectrons SO} ^{4 2-S-element} is released with respect to the soft X-rays irradiated in XPS analysis, a peak based on the _SO ^{4 2-is} obtained. Peaks based on SO ₄ ^2-manifests itself in less than 168 eV 170 eV. The compound containing sulfur S1 is considered to be, for example, a sulfonic acid compound. The compound containing sulfur S1 may be an impurity of the positive electrode active material. The concentration of sulfur S1 may be 0.3 atomic% or more and 0.7 atomic% or less.

The concentration of sulfur S1 can be increased, for example, by increasing the amount of unsaturated sultone compound added to the electrolytic solution. On the other hand, the concentration of sulfur S1 can be reduced, for example, by reducing the amount of the cyclic sulfone compound added to the electrolytic solution.

Sulfur S2 is represented by peaks based on SS and SC in the photoelectron spectrum obtained by XPS analysis. Photoelectrons emitted by the S element of the SS bond and the SC bond with respect to the irradiated soft X-rays in the XPS analysis provide peaks based on SS and SC. Peaks based on SS and SC appear above 163 eV and below 165 eV. The compound containing sulfur S2 is considered to be, for example, a disulfide compound. In the present embodiment, the positive electrode active material layer 112 of the positive electrode 11 may have a compound containing sulfur S2 on its surface.

The above (concentration of sulfur S2) / (concentration of sulfur S1) may be 0.8 or more and 1.6 or less.

In XPS analysis, the surface of a sample is irradiated with soft X-rays in a vacuum, and photoelectrons emitted from the surface are detected by an analyzer. Since the length (mean free path) at which photoelectrons can travel through a substance is several nm, the detection depth on the surface is several nm. In XPS analysis, it is possible to know the element to be used as a material on the surface based on the binding energy value of the bound electron in the substance. From the energy shift of each peak in the photoelectron spectrum, the valence and bonding state of the element can be known. Quantitative analysis of elements such as sulfur elements can be performed based on the ratio of peak areas. Details such as measurement conditions for XPS analysis will be described in Examples.

(Concentration of sulfur S2) / (concentration of sulfur S1) increases with the passage of time. Usually, the above (concentration of sulfur S2) / (concentration of sulfur S1) is a numerical value of the concentration of sulfur S1, the concentration of sulfur S2, and (concentration of sulfur S2) / (concentration of sulfur S1) shown above. Within the range, it grows over time. The above-mentioned (concentration of sulfur S2) / (concentration of sulfur S1) increases with the passage of time when the battery is allowed to stand in an environment of 65 ° C. for 30 days, and the (sulfur) in the battery before standing. It means that (concentration of sulfur S2) / (concentration of sulfur S1) in the battery after standing is at least 1.1 times or more with respect to (concentration of S2) / (concentration of sulfur S1).

In the power storage element 1, (concentration of sulfur S2) / (concentration of sulfur S1) increases with the passage of time by being left at a high temperature such as 65 ° C.

The positive electrode active material layer 112 contains an active material and a binder. Specifically, the positive electrode active material layer 112 contains 80% by mass or more and 98% by mass or less of the active material, and 0.1% by mass or more and 10% by mass or less of the binder.

The active material of the positive electrode 11 is a compound that can occlude and release lithium ions. The active material of the positive electrode 11 is in the form of particles. The active material of the positive electrode 11 is, for example, a lithium metal oxide. Specifically, the active material of the positive electrode 11 is, for example, a composite oxide represented by Li _v Me _{w + x + y} O _z (Me represents one or more transition metals) (L _v Co _y O ₂ , Li _{v). Ni w O 2, Li v Mn} x O 4, Li v Ni w Co y Mn x O 2 , _{etc.), Li a Me b (XO} c) d (Me represents one or more transition metals, X is For example, a polyanionic compound represented by (representing P, Si, B, V) (Li _a Fe _b PO ₄ , Li _a Mn _b PO ₄ , Li _a Mn _b SiO ₄ , Li _a Co _b PO ₄ F, etc.). ..

In this embodiment, the active material of the positive electrode _{11, Li v Ni w Mn x Co} y O z lithium-metal composite oxide represented by the chemical composition (provided that at 0 <v ≦ 1.3, w + x + y = 1 , 0 <w <1, 0 <x <1, 0 <y <1, and 1.7 ≦ z ≦ 2.3).

In the above such _{Li v Ni w Mn x Co y} O lithium-metal composite oxide represented by the chemical composition of _z, a 0 <v <1.3, | a <0.03, | w-x 0.33 ≦ y <1 may be satisfied. The lithium metal composite oxide is, for example, LiNi _1/6 Co _2/3 Mn _1/6 O ₂ or LiNi _1/3 Co _1/3 Mn _1/3 O ₂ .

Additional such _{Li v Ni w Mn x Co y} O lithium-metal composite oxide represented by the chemical composition of _z has alpha-NaFeO ₂ type crystal structure (layered rock-salt structure). The α-NaFeO type ₂ crystal structure is confirmed by powder X-ray diffraction according to a conventional method.

The binder used for the positive electrode active material layer 112 is, for example, polyvinylidene fluoride (PVdF), a copolymer of ethylene and vinyl alcohol, polymethylmethacrylate, polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic. Acid, styrene-butadiene rubber (SBR). The binder of this embodiment is polyvinylidene fluoride.

The positive electrode active material layer 112 may further have a conductive auxiliary agent such as Ketjen Black (registered trademark), acetylene black, and graphite. The positive electrode active material layer 112 of the present embodiment has acetylene black as a conductive auxiliary agent.

The negative electrode 12 is arranged so as to face the positive electrode 11. The negative electrode 12 has a metal foil 121 (negative electrode base material 121) and a negative electrode active material layer 122 that is arranged so as to overlap the metal foil 121 and contains an active material. The negative electrode active material layer 122 is laminated on both sides of the metal foil 121, respectively. The metal foil 121 is strip-shaped. The metal foil 121 of the negative electrode 12 of the present embodiment is, for example, a copper foil. The negative electrode 12 has an exposed portion 105 in which the negative electrode active material layer 122 is not formed and the metal foil 121 is exposed at one edge portion in the width direction, which is the lateral direction of the band shape.

The negative electrode active material layer 122 has an active material and a binder. The negative electrode active material layer 122 is arranged so as to face the positive electrode 11 via the separator 4. When the surface of the negative electrode active material layer 122 facing the positive electrode 11 (the surface opposite to the surface overlapping the metal foil 121) is subjected to peak division of the photoelectron spectrum obtained by XPS analysis, 163 eV based on the sulfur component is performed. The concentration of sulfur S3 calculated from the peak of 170 eV or less is 0.5 atomic% or more and 5.0 atomic% or less. The concentration of sulfur S3 may be 0.5 atomic% or more and 3.0 atomic% or less. The XPS analysis of the surface of the negative electrode 12 (the surface of the negative electrode active material layer 122) is performed in the same manner as the XPS analysis of the surface of the positive electrode 11 (the surface of the positive electrode active material layer 112) described above.

Sulfur S3 is the photoelectron spectrum obtained by the XPS analysis, S-S, S-C , SO 4 2-, and is represented by the peak based on the sulfur components such _SO ^{3 2-.} Peaks based on these sulfur components appear at 163 eV or more and 170 eV or less, respectively.

The negative electrode active material layer 122 has a compound containing sulfur S3 on its surface. The compound containing sulfur S3 is formed on the surface of the negative electrode active material layer 122 by decomposing the additive described later contained in the electrolytic solution or by applying the compound containing sulfur S3 to the negative electrode active material layer 122. It is happening. In the present embodiment, on the surface of the negative electrode active material layer 122, a compound containing sulfur S3 produced by decomposition of an additive described later contained in the electrolytic solution is generated.

The active material of the negative electrode 12 can contribute to the electrode reaction of the charge reaction and the discharge reaction in the negative electrode 12. The active material of the negative electrode 12 is in the form of particles. The active material of the negative electrode 12 is, for example, a carbon material such as graphite, non-graphitized carbon, and easily graphitized carbon, or a material that undergoes an alloying reaction with lithium ions such as silicon (Si) and tin (Sn). .. The active material of the negative electrode 12 of this embodiment is non-graphitized carbon.

The binder used for the negative electrode active material layer 122 is the same as the binder used for the positive electrode active material layer 112. The binder of this embodiment is polyvinylidene fluoride.

The negative electrode active material layer 122 may further have a conductive auxiliary agent such as Ketjen Black (registered trademark), acetylene black, and graphite. The negative electrode active material layer 122 of the present embodiment does not have a conductive auxiliary agent.

The separator 4 is a member having an insulating property. The separator 4 has a strip shape. The separator 4 is arranged between the positive electrode 11 and the negative electrode 12. As a result, in the electrode body 2 (specifically, the laminated body 22), the positive electrode 11 and the negative electrode 12 are insulated from each other. Further, the separator 4 holds the electrolytic solution in the case 3. As a result, when the power storage element 1 is charged and discharged, lithium ions move between the positive electrode 11 and the negative electrode 12 which are alternately laminated with the separator 4 in between.

The separator 4 is made porous by, for example, a woven fabric, a non-woven fabric, or a porous membrane. Examples of the material of the separator 4 include polymer compounds, glass, and ceramics. Examples of the polymer compound include polyesters such as polyacrylonitrile (PAN), polyamide (PA) and polyethylene terephthalate (PET), polyolefins (PP) such as polypropylene (PP) and polyethylene (PE), and cellulose. ..

The width of the separator 4 (dimension of the strip shape in the lateral direction) is slightly larger than the width of the negative electrode active material layer 122. The separator 4 is arranged between the positive electrode 11 and the negative electrode 12 in which the positive electrode active material layer 112 and the negative electrode active material layer 122 are overlapped with each other in a state of being displaced in the width direction so as to overlap each other.

In the electrode body 2 of the present embodiment, the positive electrode 11 and the negative electrode 12 configured as described above are wound in a state of being insulated by the separator 4. That is, in the electrode body 2 of the present embodiment, the laminated body 22 of the positive electrode 11, the negative electrode 12, and the separator 4 is wound.

In a state where the positive electrode 11 and the negative electrode 12 are laminated, as shown in FIG. 6, the exposed portion 105 of the positive electrode 11 and the exposed portion 105 of the negative electrode 12 do not overlap. That is, the exposed portion 105 of the positive electrode 11 protrudes in the width direction from the region where the positive electrode 11 and the negative electrode 12 overlap, and the exposed portion 105 of the negative electrode 12 extends in the width direction (positive electrode 11) from the region where the positive electrode 11 and the negative electrode 12 overlap. (In the direction opposite to the protruding direction of the exposed portion 105). The electrode body 2 is formed by winding the positive electrode 11, the negative electrode 12, and the separator 4, that is, the laminated body 22, in a laminated state. The exposed laminated portion 26 in the electrode body 2 is formed by the portion where only the exposed portion 105 of the positive electrode 11 or the exposed portion 105 of the negative electrode 12 is laminated.

The exposed laminated portion 26 is a portion of the electrode body 2 that is electrically connected to the current collector 5. The exposed laminated portion 26 has two portions (divided exposed laminated portion) 261 sandwiching the hollow portion 27 (see FIG. 6) in the winding center direction of the wound positive electrode 11, negative electrode 12, and separator 4. It is divided into.

The exposed laminated portion 26 configured as described above is provided at each pole of the electrode body 2. That is, the exposed laminated portion 26 in which only the exposed portion 105 of the positive electrode 11 is laminated constitutes the exposed laminated portion of the positive electrode 11 in the electrode body 2, and the exposed laminated portion 26 in which only the exposed portion 105 of the negative electrode 12 is laminated constitutes the electrode body. The exposed laminated portion of the negative electrode 12 in No. 2 is formed.

The case 3 has a case main body 31 having an opening, and a lid plate 32 that closes (closes) the opening of the case main body 31. In the case 3, the electrolytic solution is housed in the internal space together with the electrode body 2 and the current collector 5. Case 3 is formed of a metal that is resistant to electrolytes. The case 3 is formed of, for example, an aluminum-based metal material such as aluminum or an aluminum alloy. The case 3 may be formed of a metal material such as stainless steel and nickel, or a composite material in which a resin such as nylon is adhered to aluminum.

The electrolytic solution is a non-aqueous electrolyte solution. The electrolytic solution is obtained by dissolving the electrolyte salt in an organic solvent. The organic solvent is, for example, cyclic carbonates such as propylene carbonate and ethylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Electrolyte salts are LiClO ₄ , LiBF ₄ , LiPF ₆ , and the like.

The electrolytic solution contains, for example, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. The electrolytic solution is, for example, a solution in which 0.5 to 1.5 mol / L of LiPF ₆ is dissolved in a mixed solvent in which these organic solvents are mixed at a predetermined volume ratio.

The electrolytic solution may contain an additive having sulfur (S) in the molecule in an amount of 0.1% by mass or more and 5.0% by mass or less, or may contain an additive of 1.0% by mass or more and 5.0% by mass or less. .. The additive is dissolved in the electrolyte. Examples of the additive include at least one selected from the group consisting of 1,2-pentanediol sulfate ester, 1,3-propene sultone, 1,4-butane sultone and the like. The electrolyte does not contain glycolsulfite.

Additives decompose over time. Additives are also decomposed by the charge / discharge reaction of the battery. The compound produced by the decomposition adheres to the positive electrode active material layer 112 or the negative electrode active material layer 122.

The case 3 is formed by joining the opening peripheral edge of the case body 31 and the peripheral edge of the rectangular lid plate 32 in a superposed state. Further, the case 3 has an internal space defined by the case main body 31 and the lid plate 32. In the present embodiment, the peripheral edge of the opening of the case body 31 and the peripheral edge of the lid plate 32 are joined by welding.

In the following, as shown in FIG. 1, the long side direction of the lid plate 32 is the X-axis direction, the short side direction of the lid plate 32 is the Y-axis direction, and the normal direction of the lid plate 32 is the Z-axis direction.

The case body 31 has a square tube shape (that is, a bottomed square tube shape) in which one end in the opening direction (Z-axis direction) is closed.

The lid plate 32 is a plate-shaped member that closes the opening of the case body 31. Specifically, the lid plate 32 comes into contact with the case body 31 so as to close the opening of the case body 31. More specifically, the peripheral edge of the lid plate 32 is overlapped with the peripheral edge of the opening of the case body 31 so that the lid plate 32 closes the opening. The boundary portion between the lid plate 32 and the case body 31 is welded in a state where the opening peripheral edge portion and the lid plate 32 are overlapped with each other. As a result, the case 3 is configured.

The lid plate 32 has a contour shape corresponding to the opening peripheral edge of the case body 31 in the Z-axis direction. That is, the lid plate 32 is a rectangular plate material long in the X-axis direction in the Z-axis direction. The four corners of the lid plate 32 are arcuate.

The lid plate 32 has a gas discharge valve 321 capable of discharging the gas in the case 3 to the outside. The gas discharge valve 321 discharges gas from the inside of the case 3 to the outside when the internal pressure of the case 3 rises to a predetermined pressure. The gas discharge valve 321 is provided at the center of the lid plate 32 in the X-axis direction.

The case 3 is provided with a liquid injection hole for injecting an electrolytic solution. The liquid injection hole communicates the inside and the outside of the case 3. The liquid injection hole is provided in the lid plate 32.

The injection hole is sealed (closed) by the injection plug 326. The liquid injection plug 326 is fixed to the case 3 (lid plate 32 in the example of this embodiment) by welding.

The external terminal 7 is a portion electrically connected to the external terminal 7 of another power storage element 1 or an external device or the like. The external terminal 7 is formed of a conductive member. For example, the external terminal 7 is formed of a highly weldable metal material such as an aluminum-based metal material such as aluminum or an aluminum alloy, or a copper-based metal material such as copper or a copper alloy.

The external terminal 7 has a surface 71 to which a bus bar or the like can be welded. The surface 71 is a flat surface. The external terminal 7 has a plate shape that extends along the lid plate 32. Specifically, the external terminal 7 has a rectangular plate shape in the Z-axis direction.

The current collector 5 is arranged in the case 3 and is directly or indirectly connected to the electrode body 2 so as to be energized. The current collector 5 of the present embodiment is electrically connected to the electrode body 2 via the clip member 50. That is, the power storage element 1 includes a clip member 50 that connects the electrode body 2 and the current collector 5 so as to be energized.

The current collector 5 is formed of a conductive member. As shown in FIG. 3, the current collector 5 is arranged along the inner surface of the case 3.

The current collector 5 is arranged on the positive electrode 11 and the negative electrode 12 of the power storage element 1, respectively. In the power storage element 1 of the present embodiment, the storage element 1 is arranged in the exposed laminated portion 26 of the positive electrode 11 of the electrode body 2 and the exposed laminated portion 26 of the negative electrode 12 in the case 3, respectively.

The current collector 5 of the positive electrode 11 and the current collector 5 of the negative electrode 12 are formed of different materials. Specifically, the current collector 5 of the positive electrode 11 is formed of, for example, aluminum or an aluminum alloy, and the current collector 5 of the negative electrode 12 is formed of, for example, copper or a copper alloy.

In the power storage element 1 of the present embodiment, the electrode body 2 (specifically, the electrode body 2 and the current collector 5) in a state of being housed in a bag-shaped insulating cover 6 that insulates the electrode body 2 and the case 3 is the case 3. It is housed inside.

Next, a method of manufacturing the power storage element of the above embodiment will be described.

In the method for manufacturing the power storage element 1, a mixture containing an active material is applied to a metal foil (electrode base material) to form an active material layer, and electrodes (positive electrode 11 and negative electrode 12) are produced. Next, the positive electrode 11, the separator 4, and the negative electrode 12 are superposed and wound to form the electrode body 2. Subsequently, the electrode body 2 is put into the case 3, and the electrolytic solution is put into the case 3 to assemble the power storage element 1.

In the production of the electrode (positive electrode 11), the positive electrode active material layer 112 is formed by applying a mixture containing an active material, a binder, and a solvent to both surfaces of the metal foil 111. As a coating method for forming the positive electrode active material layer 112, a general method is adopted. The negative electrode 12 is also manufactured in the same manner.

In the formation of the electrode body 2, the laminated body 22 having the separator 4 sandwiched between the positive electrode 11 and the negative electrode 12 is wound around. Specifically, the positive electrode 11, the separator 4, and the negative electrode 12 are superposed to form a laminated body 22 so that the positive electrode active material layer 112 and the negative electrode active material layer 122 face each other via the separator 4. Subsequently, the laminated body 22 is wound to form the electrode body 2.

In assembling the power storage element 1, the electrode body 2 is put into the case body 31 of the case 3, the opening of the case body 31 is closed with the lid plate 32, and the electrolytic solution is injected into the case 3. When closing the opening of the case body 31 with the lid plate 32, the electrode body 2 is inserted inside the case body 31, the positive electrode 11 and one external terminal 7 are made conductive, and the negative electrode 12 and the other external terminal 7 are connected. The opening of the case body 31 is closed with the lid plate 32 in a conductive state. When the electrolytic solution is injected into the case 3, the electrolytic solution is injected into the case 3 through the injection hole of the lid plate 32 of the case 3.

In the electricity storage device 1 of the present embodiment configured as described above, when the surface of the positive electrode 11 (the surface of the positive electrode active material layer 112) is XPS analysis, sulfur calculated by the peak based on the SO ₄ ^2- The concentration of S1 is 0.3 atomic% or more (for example, more than 0.35 atomic%) and 1.0 atomic% or less, and the concentration of sulfur S2 calculated by the peaks based on SS and SC is , 0 atomic% or more and 1.0 atomic% or less, and (concentration of sulfur S2) / (concentration of sulfur S1) is 0 or more and 2 or less. As a result, it is possible to suppress a decrease in capacity and output after being left for a long period of time.

In the above-mentioned power storage element 1, (concentration of sulfur S2) / (concentration of sulfur S1) increases with the passage of time. With such a configuration, it is possible to more reliably suppress a decrease in the capacity and output of the power storage element after being left for a long period of time.

In the above power storage element, when the surface of the negative electrode 12 (the surface of the negative electrode active material layer 122) is analyzed by XPS,
The concentration of sulfur S3 calculated by the peak of 163 eV or more and 170 eV or less based on the sulfur component is 0.5 atomic% or more and 5.0 atomic% or less. With such a configuration, it is possible to more reliably suppress a decrease in the capacity and output of the power storage element after being left for a long period of time.

In the above-mentioned power storage element, the electrolytic solution contains the above-mentioned additive having sulfur (S) in the molecule. Additives are decomposed over time, charged at least once, etc. to become sulfur-containing compounds. Such a sulfur-containing compound adheres to the surfaces of the active material layers of the positive electrode 11 and the negative electrode 12. Such a compound containing sulfur has good ionic conductivity and is a relatively stable compound. Such compounds containing sulfur, when obtaining the photoelectron spectrum by XPS analysis, a peak based on the SO ₄ ^2-, or is represented by the peak based on the S-S and S-C. It is considered that such a sulfur-containing compound is stably present on the surface of the active material layer of the positive electrode 11 and the negative electrode 12, and stably suppresses the decarbonization reaction on the surface of the active material layer. It is considered that this makes it possible to more reliably suppress the decrease in the capacity and output of the power storage element after being left for a long period of time.

In the above power storage element, the active material of the positive electrode 11 is a lithium metal composite oxide represented by the chemical composition of Li _v Ni _w Mn _x Co _{y Oz} (however, 0 <v ≦ 1.3 and w + x + y = 1; 0 <w <1, 0 <x <1, 0 <y <1, 1.7≤z≤2.3). With such a configuration, it is possible to more reliably suppress a decrease in the capacity and output of the power storage element after being left for a long period of time.

In the above-mentioned power storage element, the active material of the negative electrode 12 is non-graphitized carbon. With such a configuration, it is possible to more reliably suppress a decrease in the capacity and output of the power storage element after being left for a long period of time.

The power storage element of the present invention is not limited to the above embodiment, and it goes without saying that various modifications can be made without departing from the gist of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment. In addition, some of the configurations of certain embodiments can be deleted.

In the above embodiment, the power storage element 1 having the positive electrode active material layer 112 and the negative electrode active material layer 122 on the surface of the compound generated by the decomposition of the additive having sulfur (S) in the molecule and containing sulfur is described in detail. explained. However, in the present invention, the concentration of sulfur S1, the concentration of sulfur S2, and sulfur S3 are formed by applying a sulfur-containing compound to the positive electrode active material layer 112 and the negative electrode active material layer 122 before assembling the power storage element. The concentration of may be in the above-mentioned numerical range.

In the above embodiment, the concentration of sulfur S1 and the sulfur S2 when the surface of the positive electrode 11 (the surface of the positive electrode active material layer 112) and the surface of the negative electrode 12 (the surface of the negative electrode active material layer 122) are analyzed by XPS. The concentration was explained in detail. However, in the present invention, the site to be analyzed by XPS is not limited to these.

In the above embodiment, the electrodes (positive electrode 11 and negative electrode 12) in which the active material layer is in direct contact with the metal foil have been described in detail, but in the present invention, in at least one of the positive electrode and the negative electrode, a binder and a conductive auxiliary agent are used. An intermediate layer containing the above may be arranged between the metal foil and the active material layer.

In the above embodiment, the electrodes in which the active material layer is arranged on both side surfaces of the metal leaf of each electrode have been described, but in the power storage element of the present invention, the positive electrode 11 or the negative electrode 12 has the active material layer on one side of the metal leaf. It may be provided only on the side.

In the above embodiment, the power storage element 1 including the electrode body 2 in which the laminated body 22 is wound has been described in detail, but the power storage element of the present invention may include the laminated body 22 which is not wound. Specifically, the power storage element may include an electrode body in which a positive electrode, a separator, a negative electrode, and a separator each formed in a rectangular shape are stacked a plurality of times in this order.

In the above embodiment, the case where the power storage element 1 is used as a chargeable / dischargeable non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) has been described, but the type and size (capacity) of the power storage element 1 are arbitrary. is there. Further, in the above embodiment, the lithium ion secondary battery has been described as an example of the power storage element 1, but the present invention is not limited to this. For example, the present invention can be applied to various secondary batteries and other storage elements of capacitors such as electric double layer capacitors.

The power storage element 1 (for example, a battery) may be used in a power storage device 100 (a battery module when the power storage element is a battery) as shown in FIG. The power storage device 100 includes at least two power storage elements 1 and a bus bar member 91 that electrically connects two (different) power storage elements 1 to each other. In this case, the technique of the present invention may be applied to at least one power storage element.

A non-aqueous electrolyte secondary battery (lithium ion secondary battery) was manufactured as shown below.

(Example 1)
(1) Preparation of positive electrode N-methyl-2-pyrrolidone (NMP) as solvent, conductive additive (acetylene black), binder (PVdF), and active material (LiNi _1/6 Co _2/3 Mn _1/6) The particles of O ₂ ) were mixed and kneaded to prepare a mixture for the positive electrode. The blending amounts of the conductive auxiliary agent, the binder, and the active material were 4.5% by mass, 4.5% by mass, and 91% by mass, respectively. The prepared mixture for the positive electrode was applied to both sides of the aluminum foil so that the coating amount (basis weight) after drying was 1.00 g / m ² . After drying, a roll press was performed. Then, it was vacuum dried to remove water.

(2) Preparation of Negative Electrode As the active material, particulate non-graphitizable carbon having an average particle size D50 of 10 μm was used. Moreover, PVdF was used as a binder. The mixture for the negative electrode was prepared by mixing and kneading NMP as a solvent, a binder, and an active material. The binder was blended so as to be 7% by mass, and the active material was blended so as to be 93% by mass. The prepared mixture for the negative electrode was applied to both sides of the copper foil so that the coating amount (basis weight) after drying was 0.46 g / m ² . After drying, a roll press was performed and vacuum dried to remove water.

(3) Separator A polyethylene microporous membrane was used as the separator.

(4) Preparation of electrolytic solution As the electrolytic solution, the one prepared by the following method was used. As the non-aqueous solvent, a solvent obtained by mixing 1 part by volume of propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate was used, and the electrolyte salt (LiPF ₆ ) was added to the non-aqueous solvent so as to have a concentration of 1 mol / L. It was dissolved and an electrolytic solution was prepared. 1,2-Pentanediol sulfate ester was added to the electrolytic solution so as to be 1% by mass.

(5) Arrangement of Electrode Body in Case Using the above positive electrode, the above negative electrode, the above electrolytic solution, the separator, and the case, a battery was manufactured by a general method.
First, a sheet-like material in which a separator was arranged between the positive electrode and the negative electrode and laminated was wound. Next, the wound electrode body was placed in the case body of the aluminum square battery case as a case. Subsequently, the positive electrode and the negative electrode were electrically connected to each of the two external terminals. Furthermore, a lid plate was attached to the case body. The above electrolytic solution was injected into the case through a liquid injection port formed on the lid plate of the case. Finally, the case was sealed by sealing the injection port of the case.

(Example 2)
Lithium ion in the same manner as in Example 1 except that LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was used as the active material instead of LiNi _1/6 Co _2/3 Mn _1/6 O _2. Manufactured a secondary battery.

(Example 3)
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was used as the active material instead of LiNi _1/6 Co _2/3 Mn _1/6 O ₂ , and 1,2-pentanediol sulfate ester was used. A lithium ion secondary battery was produced in the same manner as in Example 1 except that 1,3-propene sultone was added to the electrolytic solution so as to be 0.5% by mass and 0.5% by mass. did.

(Comparative Example 1)
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was used as the active material instead of LiNi _1/6 Co _2/3 Mn _1/6 O ₂ , and 1,2-pentanediol sulfate ester was used. A lithium ion secondary battery was produced in the same manner as in Example 1 except that 1,3-propene sultone was added to the electrolytic solution in an amount of 0.5% by mass instead.

(Comparative Example 2)
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was used as the active material instead of LiNi _1/6 Co _2/3 Mn _1/6 O ₂ , and 1,2-pentanediol sulfate ester was used. A lithium ion secondary battery was produced in the same manner as in Example 1 except that glycol sulfite was added to the electrolytic solution so as to be 1.0% by mass instead.

<XPS analysis>
XPS analysis (X-ray photoelectron spectroscopy, also referred to as ESCA) was performed using "Quantera SXM" manufactured by PHI. The induced X-rays were single crystal spectroscopic AlKα _{1 and 2} lines (1486.6 eV). The X-ray spot was a circle of 200 μm. The output was 10 kV, 22 mA. The analyzer mode is described in Constant Analyzer Energy (CAE) Mode, Pass Energy Wide Scan: Res. 4 = 150eV Now scan: Res. It was 2 = 50 eV. The photoelectron escape angle (inclination of the detector with respect to the sample surface) was 45 °. In the XPS analysis of the negative electrode surface, the horizontal axis correction was performed by setting the main peak of the neutral carbon C1s to 284.6 eV. On the other hand, in the XPS analysis of the positive electrode surface, the horizontal axis correction was not performed. Spectral smoothing was performed by 9-point smoothing. Data processing in peak division was performed using smoothing 3points, peak area measurement, backglond subtraction, and peak synthesis. The atomic% of each component was calculated by peak division.
Prior to the measurement, the batteries were pretreated. In the pretreatment, the battery was discharged to 2.5 V at 0.1 C (a battery having a predetermined capacity is discharged with a constant current, and when the discharge is completed in 1 hour, the current is referred to as 1 C). When removing the positive electrode or the negative electrode from the pretreated battery, the battery was disassembled in a glove box filled with argon gas. The removed positive electrode or negative electrode was stored in a state where it was not exposed to the atmosphere.
Even after the battery was left for a predetermined number of days under the conditions of 65 ° C. and 80% SOC (4.0 V), XPS analysis was performed in the same manner.

The results of the XPS analysis are shown in Tables 1 to 4. Table 1 shows the concentration (atomic%) of sulfur S1 calculated based on the peak of 168 eV or more and 170 eV or less from the photoelectron spectrum of the XPS analysis of the positive electrode. Table 2 shows the concentration (atomic%) of sulfur S2 calculated based on the peak of 163 eV or more and 165 eV or less from the photoelectron spectrum of the XPS analysis of the positive electrode. Table 3 shows the concentration of sulfur S2 / the concentration of sulfur S1. Table 4 shows the atomic% of sulfur S3 of the sulfur component calculated based on the peak of 163 eV or more and 170 eV or less from the photoelectron spectrum of the XPS analysis of the negative electrode.

As can be seen from the above results, the value of (concentration of sulfur S2) / (concentration of sulfur S1) increased with the passage of time in the positive electrode.

<Evaluation of battery capacity>
Immediately after production, and after leaving the battery for a predetermined number of days under the conditions of 65 ° C. and 80% SOC (4.0 V), the battery capacity was measured according to a conventional method.

<Evaluation of assist output performance>
Immediately after production, and after leaving the battery for a predetermined number of days under the conditions of 65 ° C. and 80% SOC (4.0 V), the assist output was measured at 25 ° C. and −10 ° C., respectively. The evaluation result is shown by the output value after a predetermined number of days with respect to the initial value.

For each of the above evaluation results, graphs showing the measured values after a predetermined number of days as relative values to the initial measured values are shown in FIGS. 9 to 11. FIG. 9 shows the evaluation result of the battery capacity after being left unattended. FIG. 10 shows the evaluation result of the assist output performance at 25 ° C. FIG. 11 shows the evaluation result of the assist output performance at −10 ° C.

As can be seen from the above results, the battery of the example was able to suppress a decrease in capacity and output after being left for a long period of time as compared with the battery of the comparative example. The battery of the example was able to suppress a decrease in output particularly at a low temperature of -10 ° C.

1: Power storage element (non-aqueous electrolyte secondary battery),
2: Electrode body,
26: Exposed laminated part,
3: Case, 31: Case body, 32: Lid plate,
4: Separator,
5: Current collector, 50: Clip member,
6: Insulation cover,
7: External terminal, 71: Surface,
11: Positive electrode,
111: Metal leaf of positive electrode (positive electrode base material), 112: Positive electrode active material layer,
12: Negative electrode,
121: Metal foil of negative electrode (negative electrode base material), 122: Negative electrode active material layer,
91: Bus bar member,
100: Power storage device.

Claims (3)

It has a positive electrode and a negative electrode,
Day 0, and, 65 ° C., after a lapse 360 days under the conditions of SOC 80%, either when the positive electrode surface are respectively XPS analysis,
The concentration of sulfur S1, is calculated by the peak based on the SO ₄ ^2-is 1.0 atomic% or less 0.3 atomic% or more,
The concentration of sulfur S2 calculated from the peaks based on SS and SC is 0 atomic% or more and 0.36 atomic% or less.
(Concentration of sulfur S2) / (concentration of sulfur S1) is 0 or more and 2 or less.
The positive electrode includes a positive electrode active material and the binder, the positive electrode active _{material, Li v Ni w Mn x Co} y O z lithium-metal composite oxide represented by the chemical composition (but, 0 <v ≦ 1. 3, w + x + y = 1, 0 <w <1, 0 <x <1, 0 <y ≦ 1/3, 1.7 ≦ z ≦ 2.3). ,
The binder is at least one selected from the group consisting of polyvinylidene fluoride, a copolymer of ethylene and vinyl alcohol, and polymethylmethacrylate.
The negative electrode contains a negative electrode active material, and the negative electrode active material is a graphitized carbon, which is a power storage element. The power storage element according to claim 1, wherein the (concentration of sulfur S2) / (concentration of sulfur S1) increases with the passage of time. Day 0, and, 65 ° C., after a lapse 360 days under the conditions of SOC 80%, either when the surface of the negative electrode is respectively XPS analysis,
The power storage device according to claim 1 or 2, wherein the concentration of sulfur S3 calculated by a peak of 163 eV or more and 170 eV or less based on the sulfur component is 0.5 atomic% or more and 5.0 atomic% or less.