JP6441778B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte battery, particularly a lithium ion secondary battery.

  Nonaqueous electrolyte batteries have been put to practical use as automobile batteries including hybrid cars and electric cars. Lithium ion secondary batteries are used as such on-vehicle power supply batteries. Lithium ion secondary batteries are required to have various characteristics such as output characteristics, energy density, capacity, lifetime, and high temperature stability. In order to improve battery life (cycle characteristics and storage characteristics) in particular, various improvements have been made to the electrolyte.

  For example, Patent Document 1 proposes to use an electrolyte containing a cyclic disulfonic acid ester as a non-aqueous electrolyte having excellent rate characteristics after high-temperature storage of a battery. Cyclic disulfonic acid esters are known to decompose on the surface of an electrode (particularly the negative electrode) to form a film, and the formed film can improve the cycle characteristics of the battery. Among these, methylene methyl disulfonate (hereinafter referred to as “MMDS”) is known to have a high negative electrode protection effect. From the viewpoint of improving the cycle life of the battery, it has been attempted to use a lithium / nickel composite oxide as the positive electrode active material.

JP 2012-94454 A

However, when an electrolyte containing a disulfonic acid ester such as methylenemethane disulfonic acid ester is used as an additive in a battery using a lithium / nickel composite oxide as a positive electrode active material, the capacity of the battery tends to decrease. It is known. The disulfonic acid ester compound reacts with water that can be contained in a small amount in the battery material to generate a decomposition product (disulfonic acid compound). This disulfonic acid is adsorbed on the surface of the positive electrode to form a positive electrode protective film. However, if the amount of the adsorbed disulfonic acid is too large, it may attack the lithium / nickel composite oxide, which may cause an increase in battery resistance and a decrease in output.
Therefore, an object of the present invention is to suppress an increase in resistance of a lithium ion secondary battery using a lithium / nickel composite oxide as a positive electrode active material.

A lithium ion secondary battery according to an embodiment of the present invention includes a positive electrode in which a positive electrode active material layer is disposed on a positive electrode current collector, a negative electrode in which a negative electrode active material layer is disposed on a negative electrode current collector, a separator, and an electrolyte solution Is a lithium ion secondary battery including a power generation element including the inside of the exterior body. Here, the positive electrode active material layer includes a lithium / nickel composite oxide as a positive electrode active material, and the electrolytic solution contains a cyclic carbonate compound having an unsaturated bond and / or a decomposition product of a cyclic carbonate compound having a halogen. The lithium ion secondary battery of the embodiment, the amount of decomposition product of a cyclic carbonate compound having a cyclic carbonate compound and / or halogen having the unsaturated bond to the surface area of the lithium-nickel composite oxide is 0.2 to 3. 5 g / m ² or less.

  In the lithium ion secondary battery of the present invention, an increase in the resistance of the battery after a charge / discharge cycle or after long-term storage is suppressed.

FIG. 1 is a schematic cross-sectional view showing a lithium ion secondary battery according to an embodiment of the present invention. FIG. 2 is a graph showing the relationship between the amount of unsaturated carbonate compound (VC and FEC , both decomposed products) with respect to the surface area of the positive electrode active material, and the direct current resistance value of the battery after storage. FIG. 3 is a graph showing the relationship between the amount of the unsaturated carbonate compound (VC and FEC) and their decomposition products with respect to the surface area of the positive electrode active material, and the DC resistance value of the battery after cycle charge / discharge.

  Embodiments of the present invention will be described below. In the embodiment, the positive electrode is a thin plate in which a positive electrode active material layer is formed by applying or rolling and drying a mixture of a positive electrode active material, a binder, and, if necessary, a conductive additive on a positive electrode current collector such as a metal foil. Or it is a sheet-like battery member. The negative electrode is a thin plate-like or sheet-like battery member in which a negative electrode active material layer is formed by applying a mixture of a negative electrode active material, a binder, and, if necessary, a conductive additive to a negative electrode current collector. The separator is a film-like battery member for separating the positive electrode and the negative electrode and ensuring the conductivity of lithium ions between the negative electrode and the positive electrode. The electrolytic solution is an electrically conductive solution in which an ionic substance is dissolved in a solvent. In this embodiment, a nonaqueous electrolytic solution can be used in particular. The power generation element including the positive electrode, the negative electrode, the separator, and the electrolytic solution is a unit of the main constituent member of the battery. Usually, the positive electrode and the negative electrode are laminated via the separator, and this laminate is immersed in the electrolytic solution. Has been.

  The lithium ion secondary battery of the embodiment is configured such that the power generation element is included in the exterior body, and preferably the power generation element is sealed inside the exterior body. The term “sealed” means that the power generation element is encased in an exterior body material so as not to touch the outside air. That is, the exterior body has a bag shape capable of sealing the power generation element therein.

Here, the positive electrode active material layer preferably contains a lithium / nickel composite oxide as the positive electrode active material. The lithium-nickel based composite oxide is a general formula Li _x Ni _y Me _(1-y) O ₂ (where Me is Al, Mn, Na, Fe, Co, Cr, Cu, Zn, Ca, K, It is a transition metal composite oxide containing lithium and nickel, represented by at least one metal selected from the group consisting of Mg and Pb.

The positive electrode active material layer can further contain a lithium / manganese composite oxide as a positive electrode active material. Examples of the lithium / manganese composite oxide include a zigzag layered structure lithium manganate (LiMnO ₂ ) and spinel type lithium manganate (LiMn ₂ O ₄ ). By using a lithium-manganese composite oxide in combination, the positive electrode can be produced at a lower cost. In particular, it is preferable to use spinel type lithium manganate (LiMn ₂ O ₄ ) which is excellent in terms of stability of the crystal structure in an overcharged state.

The electrolyte used in all the embodiments of the present specification is a non-aqueous electrolyte, which is dimethyl carbonate (hereinafter referred to as “DMC”), diethyl carbonate (hereinafter referred to as “DEC”), di-n-. Chain carbonates such as propyl carbonate, di-t-propyl carbonate, di-n-butyl carbonate, di-isobutyl carbonate, or di-t-butyl carbonate, propylene carbonate (hereinafter referred to as “PC”), and ethylene carbonate. A mixture containing a cyclic carbonate such as (hereinafter referred to as “EC”) is preferred. The electrolytic solution is obtained by dissolving a lithium salt such as lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), or lithium perchlorate (LiClO ₄ ) in such a carbonate mixture.

In the embodiment, the electrolytic solution may contain an additive. Examples of the additive that can be added to the electrolytic solution include a cyclic carbonate compound having an unsaturated bond. The cyclic carbonate compound having an unsaturated bond is electrochemically decomposed during the charging and discharging of the battery, and a film is formed on the electrode surface used in all embodiments described later to stabilize the electrode structure. Functions as an additive. Examples of the cyclic carbonate compound having an unsaturated bond include vinylene carbonate, vinyl ethylene carbonate, methacrylic acid propylene carbonate, and acrylic acid propylene carbonate. Vinylene carbonate (hereinafter referred to as “VC”) is particularly preferably used as the cyclic carbonate compound having an unsaturated bond. The amount of the cyclic carbonate compound is preferably 0.2 to 3.5 g / m ² of the decomposition product of the cyclic carbonate compound having an unsaturated bond with respect to the surface area of the lithium-nickel composite oxide described above. . Here, the “surface area of the lithium / nickel composite oxide” refers to the surface area of the lithium / nickel composite oxide particles. That is, the specific surface area that can be measured by the usual method for measuring the specific surface area of particles such as the BET method and the surface area calculated from the weight of the lithium-nickel composite oxide, and the area of the positive electrode plate Does not mean. Usually, the carbonate compound having an unsaturated bond is adsorbed not only on the surface of the positive electrode but also inside the positive electrode active material, that is, between the positive electrode active material particles and the voids of the positive electrode active material crystal to form a film. Therefore, in this embodiment , the abundance of the decomposition product of the carbonate compound having an unsaturated bond with respect to the surface area of the lithium / nickel composite oxide is defined.

In addition to this, the electrolytic solution may contain a cyclic carbonate compound having a halogen. The cyclic carbonate compound having a halogen is also a compound that is electrochemically decomposed during the charge and discharge process of the battery to form a protective film for the positive electrode and the negative electrode. In particular, it is a compound that can prevent attack on the positive electrode active material containing a lithium / nickel composite oxide by a sulfur-containing compound such as the above-described disulfonic acid compound or disulfonic acid ester compound. Examples of the cyclic carbonate compound having halogen include fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, and trichloroethylene carbonate. Fluoroethylene carbonate, which is a cyclic carbonate compound having a halogen and an unsaturated bond, is particularly preferably used.

  Moreover, it is preferable that electrolyte solution further contains a disulfonic acid compound. The disulfonic acid compound is a compound having two sulfo groups in one molecule, and includes a disulfonate compound in which the sulfo group forms a salt with a metal ion, or a disulfonate compound in which the sulfo group forms an ester. .

  The disulfonic acid compound that can be included in the electrolytic solution has the following formula:

（式中、Ｒ_１１は、アルキレン基、アリーレン基、またはアルキレン基とアリーレン基の組み合わせである。）で表される。

(Wherein R ₁₁ is an alkylene group, an arylene group, or a combination of an alkylene group and an arylene group).

  One or two of the sulfo groups of the disulfonic acid compound may form a salt with the metal ion or may be in an anionic state. Examples of disulfonic acid compounds include methanedisulfonic acid, 1,2-ethanedisulfonic acid, 1,3-propanedisulfonic acid, 1,4-butanedisulfonic acid, benzenedisulfonic acid, naphthalenedisulfonic acid, biphenyldisulfonic acid, and these And salts (lithium methanedisulfonate, lithium 1,3-ethanedisulfonate, etc.) and anions thereof (methanedisulfonate anion, 1,3-ethanedisulfonate anion, etc.).

  The disulfonic acid compound can be added to the electrolytic solution when the battery of the embodiment is manufactured. Alternatively, a disulfonic acid ester compound in which a sulfo group forms an ester can be added to the electrolytic solution at the time of battery production. The disulfonic acid ester compound may react with water that may be present in a minute amount in the battery, whereby the ester may be hydrolyzed to form a disulfonic acid compound. Here, the disulfonic acid ester compound that can be added to the electrolytic solution during the production of the battery is a compound having one or two sulfonic acid ester groups in one molecule, and is a kind of disulfonic acid compound. The disulfonic acid ester compound has the following formula:

（式中、Ｒ_１１は、アルキレン基、アリーレン基、またはアルキレン基とアリーレン基の組み合わせであり、Ｒ_１２は、アルキル基、またはアリール基であり、Ｒ_１３は、アルキル基、またはアリール基である。）で表される鎖状化合物か、または、以下の式：

Wherein R ₁₁ is an alkylene group, an arylene group, or a combination of an alkylene group and an arylene group, R ₁₂ is an alkyl group or an aryl group, and R ₁₃ is an alkyl group or an aryl group. Or a chain compound represented by the following formula:

（式中、Ｒ_１は、アルキレン基、アリーレン基、またはアルキレン基とアリーレン基の組み合わせであり、Ｒ_２は、アルキレン基、アリーレン基、またはアルキレン基とアリーレン基の組み合わせである。）で表される環状化合物を含む。

(Wherein R ₁ is an alkylene group, an arylene group, or a combination of an alkylene group and an arylene group, and R ₂ is an alkylene group, an arylene group, or a combination of an alkylene group and an arylene group). Cyclic compounds.

  As disulfonic acid ester compounds, methanedisulfonic acid, 1,2-ethanedisulfonic acid, 1,3-propanedisulfonic acid, 1,4-butanedisulfonic acid, benzenedisulfonic acid, naphthalenedisulfonic acid, or biphenyldisulfonic acid alkyl diester or And chain disulfonic acid esters such as aryl diesters; and cyclic disulfonic acid esters such as methylene methane disulfonic acid esters, ethylene methane disulfonic acid esters, and propylene methane disulfonic acid esters. Methylenemethane disulfonate (hereinafter referred to as “MMDS”) is particularly preferably used.

  In the case where a cyclic disulfonic acid ester compound is added to the electrolytic solution during battery production, a scheme will be described in which the cyclic disulfonic acid ester compound reacts with water that may be present inside the battery to produce a disulfonic acid compound. In the following formula, the cyclic disulfonic acid ester compound (1) reacts with water to produce the disulfonic acid compound (2). The acidic disulfonic acid compound (2) is adsorbed on an alkaline positive electrode surface containing a lithium / nickel composite oxide as a positive electrode active material to form a positive electrode film (3). When a film is appropriately formed on the surface of the positive electrode, it is very preferable because the outflow of elements such as manganese in the positive electrode active material can be suppressed.

（式中、Ｒ_１は、アルキレン基、アリーレン基、またはアルキレン基とアリーレン基の組み合わせであり、Ｒ_２は、アルキレン基、アリーレン基、またはアルキレン基とアリーレン基の組み合わせである。）

(Wherein R ₁ is an alkylene group, an arylene group, or a combination of an alkylene group and an arylene group, and R ₂ is an alkylene group, an arylene group, or a combination of an alkylene group and an arylene group.)

If too much (3) in the formula is present on the surface of the positive electrode, it will attack the lithium / nickel composite oxide itself, which may lead to an increase in the internal resistance of the positive electrode and a resulting decrease in capacity. Therefore, the amount of the disulfonic acid compound relative to the surface area of the lithium-nickel composite oxide described above is preferably small (for example, 1.0 g / m ² or less).

The positive electrode active material layer preferably contains a lithium nickel manganese cobalt composite oxide having a layered crystal structure represented by the general formula Li _x Ni _y Co _z Mn _(1-yz) O ₂ as a positive electrode active material. Here, x in the general formula is 1 ≦ x ≦ 1.2, y and z are positive numbers that satisfy y + z <1, and the value of y is 0.5 or less. Note that when the proportion of manganese increases, it becomes difficult to synthesize a single-phase composite oxide, so 1-yz ≦ 0.4 is desirable. Further, since the cost increases and the capacity decreases when the proportion of cobalt increases, it is desirable to satisfy z <y and z <1-yz. In order to obtain a high capacity battery, it is particularly preferable to satisfy y> 1-yz and y> z.

When the positive electrode active material layer further contains a lithium / manganese composite oxide as the positive electrode active material , the amount of the decomposition product of the carbonate compound having an unsaturated bond with respect to the surface area of the lithium / manganese composite oxide is 0. It is preferable that it is 8-5.5 g / m < ² >. The decomposition product of the carbonate compound having an unsaturated bond present in the positive electrode active material depends on the compound containing sulfur, particularly when the electrolytic solution contains a compound containing sulfur such as the above-described disulfonic acid compound or disulfonic acid ester compound. Further, attack on the positive electrode active material containing the lithium / nickel composite oxide can be prevented. Therefore, it is highly preferable to keep the amount of the decomposition product of the carbonate compound having an unsaturated bond with respect to the surface area of the lithium-manganese composite oxide. Here, the “surface area of the lithium / manganese composite oxide” refers to the surface area of the lithium / manganese composite oxide particles. That is, the specific surface area that can be measured by the usual method of measuring the specific surface area of particles such as the BET method and the surface area calculated from the weight of the lithium-manganese composite oxide, and the area of the positive electrode plate Does not mean. Usually, the carbonate compound having an unsaturated bond is adsorbed not only on the surface of the positive electrode but also inside the positive electrode active material, that is, between the positive electrode active material particles and the voids of the positive electrode active material crystal to form a film. Therefore, in this embodiment , the abundance of the decomposition product of the carbonate compound having an unsaturated bond with respect to the surface area of the lithium-manganese composite oxide is defined.

In another embodiment, the positive electrode active material layer may contain only the lithium / manganese composite oxide as the positive electrode active material. Even when the positive electrode active material layer contains only a lithium-manganese composite oxide as the positive electrode active material, for example, a zigzag layered lithium manganate (LiMnO ₂ ), spinel type lithium manganate (LiMn ₂ O ₄ ), etc. Can be used. In particular, it is preferable to use spinel type lithium manganate (LiMn ₂ O ₄ ) alone. As explained above, the disulfonic acid compound derived from the charge liquid present in the positive electrode active material can suppress the outflow of elements such as manganese from the positive electrode, and can prevent an increase in internal resistance and a decrease in capacity. When a lithium / manganese composite oxide is used as the positive electrode active material, it is very preferable to keep the amount of the disulfonic acid compound relative to the surface area appropriate. The amount of the disulfonic acid compound relative to the surface area of the lithium / manganese composite oxide is preferably 0.04 to 0.6 to g / m ² .

  Additives to electrolytes selected from sulfur-containing compounds such as disulfonic acid or disulfonic acid compound ester compounds, cyclic carbonate compounds having unsaturated bonds, cyclic carbonate compounds having halogens, and mixtures thereof include: At the time of preparation, it is added at a ratio of 15% by weight or less, preferably 10% by weight or less, more preferably 5% by weight or less with respect to the weight of the whole electrolyte solution.

  The negative electrode that can be used in all embodiments includes a negative electrode in which a negative electrode active material layer containing a negative electrode active material is disposed on a negative electrode current collector. Preferably, the negative electrode has a negative electrode active material layer obtained by applying or rolling a mixture of a negative electrode active material, a binder, and optionally a conductive additive to a negative electrode current collector made of a metal foil such as copper foil, and drying. ing. In each embodiment, the negative electrode active material preferably includes graphite particles and / or amorphous carbon particles. When a mixed carbon material containing both graphite particles and amorphous carbon particles is used, battery regeneration performance is improved.

  Graphite is a carbon material of hexagonal hexagonal plate crystal, and is sometimes referred to as graphite or graphite. The graphite is preferably in the form of particles. Amorphous carbon means a carbon material that may have a structure that partially resembles graphite, or a structure in which microcrystals are randomly networked, and is amorphous as a whole. To do. Examples of the amorphous carbon include carbon black, coke, activated carbon, carbon fiber, hard carbon, soft carbon, and mesoporous carbon. The amorphous carbon is preferably in the form of particles.

  Examples of conductive auxiliary agents used in the negative electrode active material layer include carbon fibers such as carbon nanofibers, carbon blacks such as acetylene black and ketjen black, carbon materials such as activated carbon, mesoporous carbon, fullerenes, and carbon nanotubes. It is done. In addition, electrode additives generally used for electrode formation, such as a thickener, a dispersant, and a stabilizer, can be appropriately used for the negative electrode active material layer.

As a binder used for the negative electrode active material layer, fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinyl fluoride (PVF), and conductive materials such as polyanilines, polythiophenes, polyacetylenes, and polypyrroles. Polymer, synthetic rubber such as styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), acrylonitrile butadiene rubber (NBR), or carboxymethyl cellulose (CMC), xanthan gum, guar gum, Polysaccharides such as pectin can be used.

  The positive electrode that can be used in all embodiments includes a positive electrode in which a positive electrode active material layer including the positive electrode active material described above is disposed on a positive electrode current collector. Preferably, the positive electrode has a positive electrode active material layer obtained by applying or rolling a mixture of a positive electrode active material, a binder, and optionally a conductive additive to a positive electrode current collector made of a metal foil such as an aluminum foil, and drying. ing.

  Carbon fibers such as carbon nanofibers, carbon blacks such as acetylene black and ketjen black, activated carbon, graphite, mesoporous carbon, fullerenes, carbon nanotubes and other carbon materials as conductive aids optionally used in the positive electrode active material layer Is mentioned. In addition, electrode additives generally used for electrode formation, such as thickeners, dispersants, and stabilizers, can be appropriately used for the positive electrode active material layer.

As a binder used for the positive electrode active material layer, fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinyl fluoride (PVF), and conductive materials such as polyanilines, polythiophenes, polyacetylenes, and polypyrroles. Polymer, synthetic rubber such as styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), acrylonitrile butadiene rubber (NBR), or carboxymethyl cellulose (CMC), xanthan gum, guar gum, Polysaccharides such as pectin can be used.

  In the embodiment, the water content relative to the weight of the lithium / nickel composite oxide in the positive electrode active material is preferably as low as possible, for example, 400 ppm or less. As described above, the water that can be contained in the positive electrode active material promotes the decomposition of the additive into the electrolytic solution to form a film on the positive electrode. is not. However, if too much water is present, gas generation from the electrolyte solution additive may be promoted. Therefore, it is desirable to reduce the amount as much as possible and prepare an appropriate amount. It is not possible to completely prevent water from entering the cathode active material due to unforeseen circumstances during the handling of the cathode active material or the manufacturing process of the cathode, but the water content is less than the weight of the lithium-nickel composite oxide. If it is about 400 ppm, it is possible to suppress the gas generation promotion effect.

  The separator used in all the embodiments is composed of an olefin resin layer. The olefin resin layer is a layer composed of polyolefin obtained by polymerizing or copolymerizing α-olefin such as ethylene, propylene, butene, pentene, hexene and the like. In the embodiment, a structure having pores that are closed when the battery temperature rises, that is, a layer composed of a porous or microporous polyolefin is preferable. Since the olefin resin layer has such a structure, even if the battery temperature rises, the separator is closed (shuts down), and the ion flow can be cut off. In order to exert a shutdown effect, it is very preferable to use a porous polyethylene film. The separator may optionally have a heat-resistant fine particle layer. At this time, the heat-resistant fine particle layer provided for preventing abnormal heat generation of the battery is composed of inorganic fine particles having a heat-resistant temperature of 150 ° C. or more and stable in electrochemical reaction. Examples of such inorganic fine particles include inorganic oxides such as silica, alumina (α-alumina, β-alumina, θ-alumina), iron oxide, titanium oxide, barium titanate, zirconium oxide; boehmite, zeolite, apatite, kaolin, Mention may be made of minerals such as spinel, mica and mullite. Thus, a separator having a heat resistant resin layer is generally referred to as a “ceramic separator”.

  Here, the structural example of the lithium ion secondary battery concerning embodiment is demonstrated using drawing. FIG. 1 shows an example of a cross-sectional view of a lithium ion secondary battery. The lithium ion secondary battery 10 includes a negative electrode current collector 11, a negative electrode active material layer 13, a separator 17, a positive electrode current collector 12, and a positive electrode active material layer 15 as main components. In FIG. 1, the negative electrode active material layer 13 is provided on both surfaces of the negative electrode current collector 11 and the positive electrode active material layer 15 is provided on both surfaces of the positive electrode current collector 12, but only on one side of each current collector. An active material layer can also be formed. The negative electrode current collector 11, the positive electrode current collector 12, the negative electrode active material layer 13, the positive electrode active material layer 15, and the separator 17 are constituent units of one battery, that is, a power generation element (unit cell 19 in the figure). A plurality of such unit cells 19 are stacked via the separator 17. The extending portion extending from each negative electrode current collector 11 is collectively bonded onto the negative electrode lead 25, and the extending portion extending from each positive electrode current collector 12 is collectively bonded to the positive electrode lead 27. An aluminum plate is preferably used as the positive electrode lead, and a copper plate is preferably used as the negative electrode lead, and in some cases, it may have a partial coating with another metal (for example, nickel, tin, solder) or a polymer material. The positive electrode lead and the negative electrode lead are welded to the positive electrode and the negative electrode, respectively. A battery formed by laminating a plurality of single cells in this manner is packaged by an outer package 29 so that the welded negative electrode lead 25 and positive electrode lead 27 are drawn out to the outside. An electrolytic solution 31 is injected into the exterior body 29. The exterior body 29 has a shape in which two laminated bodies are overlapped and the peripheral portion is heat-sealed.

  The capacity of the lithium ion secondary battery according to the embodiment is preferably 5 Ah or more and 70 Ah or less, and more preferably 30 to 60 Ah. A lithium ion battery having a capacity in such a range is particularly conveniently used as a vehicle-mounted battery or a stationary battery. Such a battery is required to have a high capacity retention rate, and it is particularly useful to apply the battery of this embodiment to the above-described application.

<Production of negative electrode: Examples and Comparative Examples>
As the negative electrode active material, graphite powder having a BET specific surface area of 3.4 m ² / g was used as the negative electrode active material. This graphite powder, carbon black powder (hereinafter referred to as “CB”) having a BET specific surface area of 62 m ² / g as a conductive auxiliary agent, carboxymethyl cellulose (hereinafter referred to as “CMC”) and styrene butadiene as a binder resin. A copolymer latex (hereinafter referred to as “SBR”) is mixed at a solid mass ratio of CB: CMC: SBR = 0.3: 1.0: 2.0 and added to ion-exchanged water. Then, these materials were uniformly dispersed in water to prepare a slurry. The obtained slurry was applied onto a 10 μm thick copper foil serving as a negative electrode current collector. Next, the electrode was heated at 125 ° C. for 10 minutes to evaporate water, thereby forming a negative electrode active material layer. Furthermore, the negative electrode which apply | coated the negative electrode active material layer on the single side | surface of the negative electrode collector was produced by pressing a negative electrode active material layer.

LiOH after calcination of lithium carbonate (Li ₂ CO ₃ ), nickel hydroxide (Ni (OH) ₂ ), cobalt hydroxide (Co (OH) ₂ ) and manganese hydroxide (Mn (OH) ₂ ) The mixture was mixed at a predetermined molar ratio so that the amount of Li ₂ CO ₃ was 1.0% by weight or less, and baked at 750 ° C. for 20 hours in a dry atmosphere. The lithium / nickel composite oxide was pulverized to obtain a lithium / nickel composite oxide having a mean particle size of 9 μm (nickel / cobalt / lithium manganate (NCM523, ie, nickel: cobalt: manganese = 5: 2: 3, lithium / Metal ratio = 1.04, BET specific surface area 22 m ² / g)). And the lithium-nickel composite oxide, a CB of lithium-manganese oxide (LiMn ₂ O ₄₎ using a mixed mixed oxide and, BET specific as a conductive additive surface area ^62m 2 / g, BET specific surface area 22 m ² / g graphite powder (GR) and polyvinylidene fluoride (PVDF) as a binder resin are solvents so that the ratio of CB: GR: PVDF is 3: 1: 3 in terms of solid content mass ratio. Added to NMP. Further, oxalic anhydride (molecular weight 90) as an organic moisture scavenger was added to this mixture in an amount of 0.03 parts by mass with respect to 100 parts by mass of the solid content obtained by removing NMP from the above mixture, followed by planetary dispersion mixing. By carrying out for 30 minutes, these materials were disperse | distributed uniformly and the slurry was produced. The obtained slurry was applied onto an aluminum foil having a thickness of 20 μm to be a positive electrode current collector. Next, the electrode was heated at 125 ° C. for 10 minutes to evaporate NMP, thereby forming a positive electrode active material layer. Furthermore, the positive electrode which applied the positive electrode active material layer on the single side | surface of the positive electrode collector was produced by pressing a positive electrode active material layer.

<Separator>
A ceramic separator composed of a heat-resistant fine particle layer using alumina as the heat-resistant fine particles and an olefin resin layer made of polypropylene and having a thickness of 25 μm was used.

<Electrolyte>
As the non-aqueous electrolyte, ethylene carbonate (hereinafter referred to as “EC”), diethyl carbonate (hereinafter referred to as “DEC”), and ethyl methyl carbonate (hereinafter referred to as “EMC”) are EC: DEC. : In a non-aqueous solvent mixed at a ratio of EMC = 30: 60: 10 (volume ratio), lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt is dissolved so as to have a concentration of 0.9 mol / L. In contrast, methylenemethane disulfonate (MMDS) and / or vinylene carbonate (VC) dissolved therein were used as additives. The addition amounts of MMDS and VC were adjusted so that after the initial charge / discharge of the battery, the remaining amount of VC on the positive electrode became the value shown in Table 1.

<Production of lithium ion secondary battery>
Each negative electrode and positive electrode produced as described above were cut into rectangles of a predetermined size. Among these, an aluminum positive electrode lead terminal was ultrasonically welded to an uncoated portion for connecting the terminal. Similarly, a nickel negative electrode lead terminal having the same size as the positive electrode lead terminal was ultrasonically welded to an uncoated portion of the negative electrode plate. The negative electrode plate and the positive electrode plate were arranged on both surfaces of a polypropylene porous separator so that both active material layers overlapped with the separator interposed therebetween to obtain an electrode plate laminate. A bag-like laminate outer package was prepared by bonding one side of the two aluminum laminate films except for one of the long sides by heat fusion. The electrode laminate was inserted into the laminate outer package. After the electrolytic solution was injected and vacuum impregnated, the opening portion was sealed by thermal fusion under reduced pressure to obtain a stacked lithium ion battery. The laminated lithium ion battery was subjected to high temperature aging several times to obtain a laminated lithium ion battery.

<Initial charge / discharge>
The remaining capacity of the battery (hereinafter referred to as “SOC”) is charged from 0% to 100% at an ambient temperature of 25 ° C., with a constant current and constant voltage charge at a 1 C current and an upper limit voltage of 4.15 V, and then the SOC becomes 0%. The constant current discharge at 1 C current was performed.

<Measurement of amount of disulfonic acid compound (MMDS) remaining on positive electrode>
After initial charge / discharge of the lithium ion secondary battery, the battery was disassembled, and the amount of the disulfonic acid compound adsorbed on the positive electrode was measured by a nuclear magnetic resonance method (NMR). Table 1 shows the amount of MMDS relative to the surface area of the lithium / nickel composite oxide and the amount of MMDS relative to the surface area of the lithium / manganese composite oxide.

<Measurement of Cyclic Carbonate Compound (VC) Having Unsaturated Bond Remaining in Positive Electrode and Cyclic Carbonate Compound (FEC) Having Halogen (both Decomposed Products) >
After initial charge and discharge of the lithium ion secondary battery, the battery was disassembled, and the amount of the decomposition product of the cyclic carbonate compound having an unsaturated bond and the halogenated cyclic carbonate compound adsorbed on the positive electrode was determined by nuclear magnetic resonance. Measured by the method (NMR). The amount of the amount of VC and FEC to the surface area of the lithium-nickel composite oxide (both degradation product), and VC and FEC to the surface area of the lithium-manganese-based composite oxide (both degradation product) is a shown in Table 1 there were.

<Measurement of specific surface area of positive electrode and negative electrode active material>
The specific surface areas of the positive electrode and the negative electrode active material were measured by the N ₂ gas adsorption method by the BET method.

<Calculation of surface area of positive electrode lithium / nickel composite oxide>
The surface area of the positive electrode lithium / nickel composite oxide was calculated as follows.
[Equation 1]
Surface area (m ² ) of positive electrode lithium / nickel composite oxide =
Specific surface area of positive electrode active material lithium / nickel composite oxide (m ² / g) × weight of lithium / nickel composite oxide of positive electrode (g)

<Calculation of surface area of positive electrode lithium / manganese composite oxide>
The surface area of the positive electrode lithium / manganese composite oxide was calculated as follows.
[Equation 2]
Surface area (m ² ) of positive electrode lithium-manganese composite oxide =
Specific surface area of positive electrode active material lithium / manganese composite oxide (m ² / g) × weight of lithium / manganese composite oxide of positive electrode (g)

<Measurement of water content>
The amount of water contained in the positive electrode active material was measured by the Karl Fischer method.

<Cycle characteristic test>
The battery manufactured as described above is charged under a temperature of 45 ° C., charging: 1 C current, constant current constant voltage charging at an upper limit voltage of 4.15 V, discharging: constant current discharging at the end of 1 C current, lower limit voltage of 2.5 V The discharge cycle was repeated 500 times. After the cycle test, the DC resistance value of the battery was measured by the following method.

<Storage test>
The battery produced as described above was stored for 2 weeks in an environment at a temperature of 45 ° C. After the storage test, the DC resistance value of the battery was measured by the following method.

<Battery resistance>
The battery resistance is determined by preparing a battery with a remaining battery capacity (SOC) of 50%, performing a constant current discharge at 10 A at 25 ° C. for 10 seconds, and measuring the voltage at the end of the discharge to determine the direct current resistance value (DCR of the battery). ) The volume of the battery was measured in accordance with JIS Z 8807 “Method for measuring density and specific gravity of solids—Method for measuring density and specific gravity by submerged weighing method”.

The abundance of each electrolyte additive and the direct current resistance value of the battery after the storage test and the direct current resistance value of the battery after cycle charge / discharge were plotted against the surface area of the lithium / nickel composite oxide as the positive electrode active material (see FIG. 2, FIG. 3). As shown in Table 1, the amount of each additive with respect to the surface area of the positive electrode active material can be changed by adjusting the amount of the additive charged into the electric liquid. 2 and 3, the amount of the carbonate compound (decomposed product) or the disulfonic acid compound relative to the surface area of the lithium / nickel composite oxide and the lithium / manganese composite oxide is adjusted to an appropriate value. It can be seen that an increase in DC resistance can be suppressed. As can be seen from FIG. 2 and FIG. 3, the coating on the positive electrode active material by the electrolytic solution additive may not be formed too much or too little, and it can be said that there is an appropriate range in the amount of coating formed. By making the formation of a film on the positive electrode active material with an electrolyte additive within a suitable range, an increase in resistance after storage or cycle charge / discharge is suppressed, that is, a battery having high cycle characteristics and a long shelf life is obtained. Can do.

  As mentioned above, although the Example of this invention was described, the said Example was only an example of Embodiment of this invention, and in the meaning which limits the technical scope of this invention to specific embodiment or a specific structure. Absent.

DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery 11 Negative electrode collector 12 Positive electrode collector 13 Negative electrode active material layer 15 Positive electrode active material layer 17 Separator 25 Negative electrode lead 27 Positive electrode lead 29 Exterior body 31 Electrolyte

Claims (9)

A positive electrode having a positive electrode active material layer disposed on a positive electrode current collector;
A negative electrode having a negative electrode active material layer disposed on a negative electrode current collector;
A separator;
An electrolyte,
A lithium ion secondary battery including a power generation element including
The positive electrode active material layer includes a lithium / nickel composite oxide as a positive electrode active material,
The electrolytic solution contains a decomposition product of a cyclic carbonate compound having an unsaturated bond and / or a decomposition product of a cyclic carbonate compound having a halogen,
The total amount of the decomposition product of the cyclic carbonate compound having an unsaturated bond and the decomposition product of the cyclic carbonate compound having a halogen with respect to the surface area of the lithium / nickel composite oxide is 0.2 to 3.5 g / m ^2. The lithium ion secondary battery is characterized by the above. The positive electrode active material layer further includes a lithium-manganese composite oxide as a positive electrode active material,
The electrolytic solution contains a decomposition product of a cyclic carbonate compound having an unsaturated bond and / or a decomposition product of a cyclic carbonate compound having a halogen, and the unsaturated bond present per surface area of the lithium-manganese composite oxide. ^2. The lithium ion secondary battery according to claim 1, wherein the total amount of the decomposition product of the cyclic carbonate compound having halogen and the decomposition product of the cyclic carbonate compound having halogen is 0.8 to 5.5 g / m ² . The positive electrode active material layer further contains a lithium / manganese composite oxide as a positive electrode active material, the electrolyte further contains a disulfonic acid compound, and the disulfonic acid compound relative to the surface area of the lithium / manganese composite oxide The lithium ion secondary battery of Claim 1 whose quantity is 0.04-0.6g / m < ² >. The lithium-nickel-based composite oxide has the general formula Li _x Ni _y Co _z Me _(1-yz) O ₂ (where Me is Al, Mn, Na, Fe, Cr, Cu, Zn, Ca, 4. The lithium nickel cobalt composite oxide having a layered crystal structure represented by K, Mg, and Pb and including a layered crystal structure is included as a positive electrode active material. Lithium ion secondary battery. The lithium-nickel composite oxide includes a lithium nickel cobalt manganese composite oxide having a layered crystal structure represented by the general formula Li _x Ni _y Co _z Mn _(1-yz) O ₂ as a positive electrode active material. The lithium ion secondary battery in any one of Claims 1-3. The lithium ion secondary battery according to claim 2, wherein the lithium-manganese composite oxide is LiMn ₂ O ₄ .   The lithium ion secondary battery according to any one of claims 1 to 6, wherein the negative electrode active material layer includes a carbon-based negative electrode material as a negative electrode active material.   The lithium ion secondary battery according to any one of claims 1 to 7, wherein the cyclic carbonate compound having an unsaturated bond is vinylene carbonate, and the cyclic carbonate compound having a halogen is fluoroethylene carbonate.   The lithium ion secondary battery according to any one of claims 1 to 8, wherein the capacity of the lithium ion secondary battery is 5 Ah or more and 70 Ah or less.

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