JP6654667B2 - 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 into practical use as batteries for vehicles including hybrid vehicles and electric vehicles. A lithium ion secondary battery is used as such a battery for a vehicle-mounted power supply. Lithium ion secondary batteries are required to have various characteristics such as output characteristics, energy density, capacity, life, and high temperature stability. In particular, various improvements have been made to electrolytes to improve battery life (cycle characteristics and storage characteristics).

For example, Patent Literature 1 discloses an electrolytic solution containing propylene carbonate and vinylene carbonate for the purpose of preventing the crystal structure of a lithium-manganese-based composite oxide, which is a positive electrode active material, from being destroyed under high-temperature storage of a battery. It has been proposed to use liquids. In the example of Patent Document 1, a lithium / manganese-based composite oxide was used as a positive electrode active material, and a non-aqueous electrolyte composed of propylene carbonate (or ethylene carbonate), vinylene carbonate, and diethyl carbonate was used as an electrolyte. It has been disclosed.
Further, from the viewpoint of improving the cycle life, it has been attempted to use a lithium / nickel-based composite oxide as the positive electrode active material.

JP-A-11-283667

However, when an electrolyte containing a cyclic carbonate having an unsaturated bond such as vinylene carbonate is used as an additive in a battery using a lithium / nickel-based composite oxide as a positive electrode active material, carbon dioxide (CO ₂ ) is mainly used. There is a problem that a gas containing is generated. This is due to the fact that alkaline substances such as lithium carbonate (Li ₂ CO ₃ ) and lithium hydroxide (LiOH) remaining in the lithium-nickel composite oxide due to the production method react with the additive. Conceivable. When gas is generated in the battery, the performance of the battery may be reduced, such as swelling of the battery and a reduction in the capacity maintenance rate of the battery.
Therefore, the present invention prevents the generation of gas derived from the electrolyte in a lithium ion secondary battery using a lithium-nickel composite oxide as a positive electrode active material, and maintains the discharge capacity of the battery (cycle characteristics and storage life). The purpose is to improve.

The lithium ion secondary battery according to the embodiment of the present invention includes a positive electrode in which a positive electrode active material layer including a lithium-nickel based composite oxide as a positive electrode active material is disposed on a positive electrode current collector, and a negative electrode active material layer in which a negative electrode current collector is used. A lithium ion secondary battery including a power generation element including a negative electrode, a separator, and an electrolyte disposed in a body inside a package. Here, the positive electrode contains a residual alkali component of less than 1% based on the weight of the lithium-nickel-based composite oxide contained as the positive electrode active material. Further, the electrolytic solution contains an additive, and the molar ratio of the cyclic carbonate additive having an unsaturated bond is 44.1 to 62.2% when the total molar amount of the additive is 100. I do.

  In the lithium ion secondary battery of the present invention, generation of gas derived from the electrolyte is significantly reduced, and the discharge capacity retention rate of the battery is improved.

FIG. 1 is a schematic sectional view showing a lithium ion secondary battery according to one embodiment of the present invention.

  An embodiment of the present invention will be described below. In the embodiment, the positive electrode is a thin plate-like material in which a mixture of a positive electrode active material, a binder, and a conductive additive, if necessary, is coated or rolled and dried on a positive electrode current collector such as a metal foil to form a positive electrode active material layer. Or it is a sheet-shaped battery member. The negative electrode is a thin or sheet-like battery member in which a mixture of a negative electrode active material, a binder, and, if necessary, a conductive additive is applied to a negative electrode current collector to form a negative electrode active material layer. The separator is a film-shaped battery member for separating the positive electrode and the negative electrode and securing the conductivity of lithium ions between the negative electrode and the positive electrode. The electrolytic solution is an electrically conductive solution obtained by dissolving an ionic substance in a solvent. In the present embodiment, a nonaqueous electrolytic solution can be used. The power generating element including the positive electrode, the negative electrode, the separator, and the electrolytic solution is one unit of a main constituent member of the battery. Usually, the positive electrode and the negative electrode are stacked (laminated) with the separator interposed therebetween. Are immersed in the electrolyte.

  The lithium ion secondary battery of the embodiment includes the power generation element inside the exterior body, and preferably, the power generation element is sealed inside the exterior body. Being sealed means that the power generating element is wrapped in an exterior body material so as not to contact 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-based composite oxide as the positive electrode active material. The lithium-nickel-based composite oxide is represented by 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, And at least one metal selected from the group consisting of Mg and Pb.) And a transition metal composite oxide containing lithium and nickel.

In the embodiment, the positive electrode active material layer includes, as a positive electrode active material, a lithium nickel manganese cobalt-based composite oxide having a layered crystal structure represented by a general formula Li _x Ni _y Co _z Mn _(1-yz) O _2. Is preferred. Here, x in the general formula is 1 ≦ x ≦ 1.2, y and z are positive numbers satisfying 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, and therefore it is preferable to satisfy 1−yz ≦ 0.4. Further, when the proportion of cobalt increases, the cost increases and the capacity decreases, so z <y and z <1-yz are desirable. In order to obtain a high-capacity battery, it is particularly preferable that y> 1-yz and y> z.

Here, the positive electrode contains a residual alkali component of less than 1% based on the weight of the lithium-nickel-based composite oxide contained as the positive electrode active material. Here, the residual alkali component refers to an alkaline substance that can be contained in a lithium-nickel-based composite oxide included as a positive electrode active material from the production of the positive electrode active material. Examples of the alkali component include a metal hydroxide and a metal carbonate. LiOH for example, raw materials used in manufacturing the lithium nickel composite _{oxide, LiOH · H 2 O, Li} 2 CO 3, Ni (OH) 2, NiCo 3, lithium-nickel-cobalt-manganese composite oxide Co (OH) ₂ , CoCO ₃ , Mn (OH) ₂ , MnCO _3, etc., which are raw materials used in the production of These alkali components are raw materials of the transition metal composite oxide which is the positive electrode active material, and cannot be avoided from remaining in the positive electrode active material. For example, the firing temperature, the firing time, the adjustment of the firing atmosphere, the alkali component The residual amount can be reduced by adjusting the amount of used, selecting the kind of raw material, adjusting the Li / Me (metal) ratio, adding an impurity removing step, and the like. In this way, it is preferable to include less than 1% of the residual alkali component based on the weight of the lithium-nickel-based composite oxide contained as the positive electrode active material. It is more preferable to include 0.2% or less of a residual alkali component based on the weight of the lithium-nickel-based composite oxide contained as the positive electrode active material.

The electrolytic solution used in the embodiment is a non-aqueous electrolytic solution, which is dimethyl carbonate (hereinafter, referred to as “DMC”), diethyl carbonate (hereinafter, referred to as “DEC”), di-n-propyl carbonate, di-t. Chain carbonates such as -propyl carbonate, di-n-butyl carbonate, di-isobutyl carbonate or di-t-butyl carbonate; propylene carbonate (hereinafter referred to as "PC"); ethylene carbonate (hereinafter referred to as "EC"). ) Is preferable. The electrolyte is obtained by dissolving lithium carbonate such as lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), and lithium perchlorate (LiClO ₄ ) in such a carbonate mixture.

  The electrolyte solution may contain additives in addition to the above components. In the embodiment, additives that can be added to the electrolytic solution include an additive containing sulfur, a cyclic carbonate additive having an unsaturated bond, a cyclic carbonate additive having a halogen, and the like. The additive containing sulfur is capable of electrochemically decomposing during the charging and discharging of the battery and forming a film on the surface of the electrode used in all the embodiments described below to stabilize the electrode structure. It is. Examples of such additives include cyclic disulfonic acid esters (for example, methylene methane disulfonic acid ester (hereinafter, referred to as “MMDS”), ethylene methane disulfonic acid ester, propylene methane disulfonic acid ester), and cyclic sulfonic acid esters (for example, Sultone), and chain sulfonic acid esters (for example, methylenebisbenzenesulfonic acid ester, methylenebisphenylmethanesulfonic acid ester, and methylenebisethanesulfonic acid ester).

  The cyclic carbonate additive having an unsaturated bond is an additive that forms a protective film of the positive electrode and the negative electrode in the charge and discharge process of the battery. It is an additive that can prevent attacks on the contained positive electrode active material. Such additives include vinylene carbonate, vinyl ethylene carbonate, propylene methacrylate carbonate, propylene acrylate carbonate, and the like. Vinylene carbonate (hereinafter referred to as “VC”) is particularly preferred as a cyclic carbonate additive having an unsaturated bond.

  The cyclic carbonate additive having a halogen is an additive that forms a protective film of the positive electrode and the negative electrode during the charge / discharge process of the battery. In particular, the additive containing a lithium-nickel-based composite oxide due to the additive containing sulfur described above is contained. It is an additive that can prevent attack on the positive electrode active material. Examples of such additives include fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, and trichloroethylene carbonate. Fluoroethylene carbonate is particularly preferred as the halogenated cyclic carbonate additive.

  The additive is added in an amount of 20% by weight or less, preferably 15% by weight or less, more preferably 10% by weight or less, based on the total weight of the electrolytic solution when the electrolytic solution is charged. In the embodiment, when the total molar amount of the additives is 100, the molar ratio of the cyclic carbonate additive having an unsaturated bond is preferably 78% or less. When the total molar amount of the additives is 100, the molar ratio of the cyclic carbonate additive having an unsaturated bond is preferably 63% or less, particularly preferably 44.1 to 62.2%.

  The negative electrode that can be used in all embodiments includes a negative electrode in which a negative electrode active material layer including 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 on a negative electrode current collector made of a metal foil such as a copper foil, and drying. ing. In each embodiment, it is preferable that the negative electrode active material includes graphite particles and / or amorphous carbon particles. When a mixed carbon material containing both graphite particles and amorphous carbon particles is used, the regenerative performance of the battery is improved.

  Graphite is a carbon material of hexagonal hexagonal plate-like crystals, and is sometimes called graphite, graphite, or the like. The graphite is preferably in the form of particles. Amorphous carbon refers to a carbon material that is amorphous as a whole, and may have a structure in which microcrystals are randomly networked, which may have a structure partially similar to graphite. I do. Examples of amorphous carbon include carbon black, coke, activated carbon, carbon fiber, hard carbon, soft carbon, mesoporous carbon, and the like. The amorphous carbon is preferably in the form of particles.

  Examples of the conductive auxiliary used in the negative electrode active material layer include carbon fibers such as carbon nanofibers, carbon black such as acetylene black and Ketjen black, activated carbon, mesoporous carbon, fullerenes, and carbon materials such as carbon nanotubes. Can be In addition, additives generally used for forming an electrode, such as a thickener, a dispersant, and a stabilizer, can be appropriately used for the negative electrode active material layer.

  As the binder used for the negative electrode active material layer, conductive resins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and fluororesin such as polyvinyl fluoride (PVF); polyanilines, polythiophenes, polyacetylenes, and polypyrroles Synthetic polymers 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 the positive electrode active material layer including the positive electrode active material described above is disposed on the 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, in some cases, a conductive auxiliary on a positive electrode current collector made of a metal foil such as an aluminum foil, and drying. ing.

  As a conductive additive optionally used in the positive electrode active material layer, carbon materials such as carbon fibers such as carbon nanofibers, carbon black such as acetylene black and Ketjen black, activated carbon, graphite, mesoporous carbon, fullerenes, and carbon materials such as carbon nanotubes Is mentioned. In addition, additives generally used for forming an electrode, such as a thickener, a dispersant, and a stabilizer, can be appropriately used for the positive electrode active material layer.

  As a binder used for the positive electrode active material layer, conductive resins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororesin such as polyvinyl fluoride (PVF), polyanilines, polythiophenes, polyacetylenes, and polypyrroles Synthetic polymers 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 content of water relative to the weight of the lithium-nickel composite oxide in the positive electrode active material is preferably 400 ppm or less, particularly preferably 295 ppm or more and 385 ppm or less. Since water that may be contained in the positive electrode active material may promote gas generation from the electrolyte additive, it is desirable to reduce the water as much as possible. While handling the positive electrode active material or manufacturing the positive electrode, it is not possible to completely prevent water from entering the positive electrode active material due to unforeseen circumstances. If it is about 400 ppm, especially 295 ppm or more and 385 ppm or less, it is possible to suppress the gas generation promoting effect.

  The separator used in all embodiments is composed of an olefin-based resin layer. The olefin-based resin layer is a layer composed of a polyolefin obtained by polymerizing or copolymerizing an α-olefin such as ethylene, propylene, butene, pentene, and hexene. In the embodiment, a structure having pores closed when the battery temperature rises, that is, a layer composed of a porous or microporous polyolefin is preferable. Since the olefin-based resin layer has such a structure, even if the battery temperature rises, the separator is closed (shut down) and the ion flow can be cut off. In order to exhibit a shutdown effect, it is very preferable to use a porous polyethylene film. The separator may optionally have a layer of heat-resistant fine particles. At this time, the heat-resistant fine particle layer provided to prevent abnormal heat generation of the battery has heat resistance of 150 ° C. or higher and is made of inorganic fine particles stable to an 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, and zirconium oxide; boehmite, zeolite, apatite, kaolin, Minerals such as spinel, mica, and mullite can be mentioned. Thus, a separator having a heat-resistant resin layer is generally called a “ceramic separator”.

  Here, a configuration example of the lithium ion secondary battery according to the embodiment will be described with reference to the drawings. FIG. 1 illustrates 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 layers 13 are provided on both surfaces of the negative electrode current collector 11 and the positive electrode active material layers 15 are provided on both surfaces of the positive electrode current collector 12, but only on one surface 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 (in the figure, a unit cell 19). A plurality of such unit cells 19 are stacked via the separator 17. The extension extending from each negative electrode current collector 11 is collectively joined on the negative electrode lead 25, and the extension extending from each positive electrode current collector 12 is jointly joined on the positive electrode lead 27. Note that an aluminum plate is preferably used as the positive electrode lead and a copper plate is preferably used as the negative electrode lead, and may have a partial coating with another metal (for example, nickel, tin, solder) or a polymer material in some cases. The positive and negative leads are welded to the positive and negative electrodes, respectively. A battery formed by stacking a plurality of unit cells in this manner is packaged by an outer package 29 in a form in which the welded negative electrode lead 25 and positive electrode lead 27 are pulled out. An electrolytic solution 31 is injected into the exterior body 29. The exterior body 29 has a shape in which two laminates are overlapped and the peripheral edge is thermally fused.

<Preparation of Negative Electrode: Examples and Comparative Examples>
As the negative electrode active material, a 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 having a BET specific surface area of 62 m ² / g (hereinafter, referred to as “CB”) as a conductive additive, carboxymethyl cellulose (hereinafter, referred to as “CMC”) as a binder resin, and styrene butadiene. A copolymer latex (hereinafter referred to as "SBR") was mixed at a solid content 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 on 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. Further, the negative electrode active material layer was pressed to produce a negative electrode in which the negative electrode active material layer was applied on one surface of the negative electrode current collector.

<Preparation of Positive Electrode: Reference Example 1, Examples 2, 3, Comparative Examples 1 to 6, and Comparative Example 8>
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 such 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. This lithium / nickel-based composite oxide is pulverized to obtain a lithium / nickel-based composite oxide (nickel / cobalt / lithium manganate (NCM523, that is, nickel: cobalt: manganese = 5: 2: 3, lithium: / Metal ratio = 1.04, BET specific surface area 22 m ² / g)).
A mixed oxide obtained by mixing the lithium nickel composite oxide thus obtained and lithium manganese oxide (LiMn ₂ O ₄ ) at a weight ratio of 70:30, and a BET specific surface area as a conductive additive and CB of 62m ² / g, and graphite powder having a BET specific surface area of ^22m 2 / g (GR), and polyvinylidene fluoride as a binder resin (PVDF), a solid content mass ratio of CB: GR: PVDF is 3: 1: It was added to a solvent, N-methylpyrrolidone (hereinafter, referred to as “NMP”) at a ratio of 3. Further, 0.03 parts by mass of oxalic anhydride (molecular weight 90) as an organic water scavenger was added to the mixture with respect to 100 parts by mass of the solid content excluding NMP from the mixture, and the mixture was subjected to planetary dispersion mixing. By carrying out for 30 minutes, these materials were uniformly dispersed to prepare a slurry. The obtained slurry was applied on a 20-μm-thick aluminum foil serving as a positive electrode current collector. Next, the positive electrode active material layer was formed by heating the electrode at 125 ° C. for 10 minutes and evaporating NMP. Further, by pressing the positive electrode active material layer, a positive electrode in which the positive electrode active material layer was applied on one surface of the positive electrode current collector was produced.

<Preparation of positive electrode: Example 4 and Comparative Example 7>
A positive electrode having a further reduced alkali component than the positive electrode used in Reference Example 1 was produced. That is, lithium carbonate (Li ₂ CO ₃ ), nickel hydroxide (Ni (OH) ₂ ), and hydroxide are so reduced that the amount of LiOH and the amount of Li ₂ CO ₃ after firing are reduced to 0.05% by weight or less. A positive electrode active material was prepared by adjusting the molar ratio of cobalt (Co (OH) ₂ ) to manganese hydroxide (Mn (OH) ₂ ) and changing the firing conditions. The method for producing the positive electrode was the same as in Reference Example 1 and the like.

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

<Electrolyte>
As non-aqueous electrolytes, 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. : EMC = dissolved in a non-aqueous solvent mixed at a ratio of 30:60:10 (volume ratio) so that the concentration of lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt was 0.9 mol / L. On the other hand, a cyclic disulfonate (methylene methanedisulfonate (MMDS) and vinylene carbonate (VC) dissolved therein) was used as an additive.

<Production of lithium ion secondary battery>
Each of the negative electrode and the positive electrode produced as described above was cut into a rectangle of a predetermined size. Among these, the positive electrode lead terminal made of aluminum was ultrasonically welded to the 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 the polypropylene porous separator such that the two active material layers overlap with the separator interposed therebetween, to obtain an electrode plate laminate. Except for one of the long sides of the two aluminum laminated films, three sides were bonded by heat fusion to produce a bag-shaped laminated outer package. The above-mentioned electrode laminate was inserted into the laminate outer package. After the electrolyte was injected and impregnated in vacuum, the opening was sealed by heat sealing under reduced pressure to obtain a stacked lithium ion battery. High-temperature aging was performed several times on the stacked lithium-ion battery to obtain a stacked lithium-ion battery having a battery capacity of 5 Ah.

<Initial charge / discharge>
The battery is charged at a constant current and a constant voltage of 0% to 100%, at an ambient temperature of 25 ° C., at a constant current of 1 C and an upper limit voltage of 4.15 V, and then reaches a SOC of 0% from 0% to 100%. Until then, constant current discharge at 1 C current was performed.

<Measurement of residual amount of additive VC>
After the initial charge / discharge of the lithium ion secondary battery, the battery was disassembled, and the amount of each additive remaining in the electrolyte was measured by nuclear magnetic resonance (NMR). The molar ratio of VC to the total number of moles of the additives was as shown in Table 1.

<Measurement of alkali content>
The amount of the alkali component contained in the positive electrode active material was measured by a titration method.

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

<Battery resistance>
The battery resistance was obtained by preparing a battery having a remaining capacity (SOC) of 50%, performing constant current discharge at 10 A at 25 ° C. for 10 seconds, and measuring the voltage at the end of discharge. The volume of the battery was measured according to JIS Z 8807 "Method for measuring density and specific gravity of solid-method for measuring density and specific gravity by liquid weighing method".

<Storage characteristics test>
After measuring the amount of each additive remaining in the electrolytic solution, the battery was sealed again in the same procedure as above. The prepared battery was charged at a constant current and a constant voltage with a current of 1 C and an upper limit voltage of 4.15 V to make the SOC 100%, stored in a thermostat at 45 ° C., and subjected to a storage test.
The discharge capacity and DC resistance before and after storage were measured, and the 1C discharge capacity maintenance rate and the cell DC resistance rise rate were calculated.

<Measurement of gas generation>
The volume of the battery after the initial charge / discharge and the volume of the battery after the storage test in which the battery with the SOC of 100% is stored at 45 ° C. for 20 weeks were measured according to JIS Z 8807 “Method for measuring the density and specific gravity of a solid—weighing in liquid”. Measurement Method of Density and Specific Gravity ”. The amount of gas generated was measured by the following formula: (volume of battery after storage test)-(volume of battery after initial charge and discharge).

  By keeping the ratio of VC in the electrolyte additive low and reducing the amount of alkali component remaining in the positive electrode active material, generation of gas derived from oxidative decomposition of the electrolyte additive is almost completely prevented. It could be suppressed (Examples 2 to 4). These batteries have a high rate of maintenance of the discharge capacity after the storage test and a low rate of increase in the battery resistance. That is, it is found that by considering the balance between the ratio of the additive and the amount of the alkaline component remaining in the positive electrode active material, the amount of gas generated from the electrolyte can be suppressed, and the life of the battery can be improved. The mechanism by which such an effect occurs is to suppress the oxidative decomposition reaction of the positive electrode interface product by adjusting the amount of the additive and the alkali component remaining in the positive electrode active material within a predetermined range, and This is probably because the oxidative decomposition reaction and the chemical decomposition reaction of cyclic carbonate such as VC accelerated in the presence of moisture are effectively suppressed. It is considered that the amount of gas generated due to the additive and the remaining alkaline component is significantly reduced while maintaining a high discharge capacity maintenance rate and a low battery resistance increase rate. In particular, in Examples 2 to 4, the amount of generated gas was almost equal to that of the remaining Examples, despite the fact that the remaining alkaline component was not different from those of the other Examples or Comparative Examples and the additive VC remained. 0CC ', which indicates that the effect of the present invention is remarkable.

  As mentioned above, although the Example of this invention was described, the said Example only showed an example of embodiment of this invention, and does not limit the technical scope of this invention to a specific embodiment or a specific structure. Absent.

Reference Signs List 10 lithium ion secondary battery 11 negative electrode current collector 12 positive electrode current 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 (6)

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,
An electrolyte,
A lithium ion secondary battery including a power generation element including inside the exterior body,
The positive electrode active material layer includes a lithium nickel-based composite oxide as a positive electrode active material,
The positive electrode contains less than 1% of a residual alkali component based on the weight of the lithium-nickel composite oxide contained as the positive electrode active material;
The negative electrode active material layer includes graphite particles and / or amorphous carbon particles as a negative electrode active material,
Electrolyte solution is ethylene carbonate, and contains diethyl carbonate and ethyl methyl carbonate, electrolytic solution containing the additive, electrolytic solution, as a first additive, including Mutotomoni a cyclic carbonate additive having an unsaturated bond Including , as a second additive, an additive containing sulfur ,
After the initial charge / discharge of the lithium ion secondary battery, the molar ratio of the cyclic carbonate additive having an unsaturated bond is 44.1 to 62.2% when the total molar amount of the additive is 100. The lithium ion secondary battery described above. 2. The lithium ion secondary battery according to claim 1, wherein the positive electrode contains 0.2% or less of a residual alkali component based on the weight of the lithium-nickel composite oxide contained as the positive electrode active material. 3.   3. The lithium ion secondary battery according to claim 1, wherein the cyclic carbonate additive having an unsaturated bond is vinylene carbonate. The positive electrode active material layer has a general formula Li _x Ni _y Co _z Mn _(1-yz) O ₂ (where x is 1 ≦ x ≦ 1.2, and y and z satisfy y + z <1). The positive electrode active material according to any one of claims 1 to 3, wherein the positive electrode active material comprises a lithium nickel manganese cobalt composite oxide having a layered crystal structure represented by a positive number and the value of y is 0.5 or less. The lithium ion secondary battery according to the above.   5. The lithium ion secondary battery according to claim 1, wherein the positive electrode contains 295 ppm or more and 385 ppm or less of water based on the weight of the lithium-nickel composite oxide serving as the positive electrode active material. The lithium ion secondary battery according to any one of claims 1 to 5 , wherein the second additive containing sulfur is methylene methane disulfonic acid ester .

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