JP6738865B2 - Lithium ion secondary battery - Google Patents

Description

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

Non-aqueous electrolyte batteries have been put to practical use as batteries for automobiles including hybrid cars and electric cars. A lithium ion secondary battery is used as such an on-vehicle power supply battery. Lithium-ion secondary batteries are becoming higher in capacity as the development progresses, and accordingly, ensuring safety is essential.

As a separator used for a power generation element of a lithium ion secondary battery, a porous film or a microporous film of polyolefin such as polyethylene or polypropylene is used. In particular, porous polyethylene membranes having a so-called shutdown effect, in which resistance increases due to blockage of pores at high temperature, are widely used.

When the separator shuts down, the flow of ions stops (that is, the separator resistance increases). However, even if the flow of ions is stopped, in a battery in which the reaction between the electrode and the electrolyte is activated and the temperature rises, an internal short circuit condition will occur and ions will start to flow again, causing an abnormal heat generation state. .. In order to prevent such an internal short circuit secondary to the battery temperature rise, there is always a demand for a separator having not only a shutdown effect but also high heat resistance.

Patent Document 1 proposes a battery separator composed of a multilayer porous film having a resin porous film mainly composed of a resin that secures a shutdown function and a heat-resistant porous layer mainly composed of heat-resistant fine particles having high heat resistance. Has been done. The separator proposed in Patent Document 1 can form a battery with improved safety while suppressing deterioration of battery characteristics.

JP-A-2009-283273

On the other hand, when an additive for the purpose of forming a stable film on the surface of the electrode is mixed with the non-aqueous electrolyte, the additive is not optimally used for forming the electrode film, resulting in the formation of the electrode film. There is a possibility that the capacity retention rate of the battery may be reduced due to insufficient performance.
The present invention provides a lithium ion battery capable of maintaining a capacity retention rate while improving battery safety.

The lithium ion secondary battery in the embodiment of the present invention is a positive electrode in which a positive electrode active material layer is arranged on a positive electrode current collector, a negative electrode in which a negative electrode active material layer is arranged on a negative electrode current collector, a separator, and a sulfur-containing material. A lithium ion secondary battery including a power generation element including an electrolyte solution containing an additive inside an exterior body. Here, the positive electrode active material layer has a general formula Li _x Ni _y Co _z Mn _(1-yz) O ₂ (where x in the formula is 1≦x≦1.2, and y and z are y+z). A positive number satisfying <1 and the value of y is 0.5 or less.) The initial charge/discharge of a lithium-ion secondary battery containing a lithium nickel cobalt manganese composite oxide having a layered crystal structure represented by Is carried out, 0.02 to 0.11% by weight of sulfur is adsorbed on the separator, and the sulfur additive is a cyclic disulfonic acid ester.

In the lithium ion secondary battery of the present invention, a part of the additive (decomposed product) is less likely to be adsorbed on the separator surface, and the film can be efficiently formed by the additive on the electrode surface. Therefore, it is possible to maintain the capacity retention rate while improving the safety of the battery.

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

Embodiments of the present invention will be described below. In the present embodiment, the positive electrode is a thin plate having a positive electrode active material layer formed by applying or rolling a mixture of a positive electrode active material, a binder, and a conductive auxiliary agent on a positive electrode current collector such as a metal foil, and drying the mixture. -Shaped or sheet-shaped battery member. The negative electrode is a thin plate-shaped or sheet-shaped 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 a conductive additive, if necessary, to a negative electrode current collector. The separator is a film-shaped battery member for isolating 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, and a non-aqueous electrolytic solution can be particularly used in the present embodiment. The power generation 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, and usually, the positive electrode and the negative electrode are stacked (laminated) via the separator to form a laminate. Is immersed in the electrolyte.

In the lithium ion secondary battery of the embodiment, the power generation element is included inside 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 wrapped with an outer casing material so as not to be exposed to the outside air. That is, the exterior body has a bag shape capable of sealing the power generating element inside.

Here, the separator contains 0.02 to 0.11% by weight of sulfur with respect to the weight of the separator. Here, the sulfur component contained in the separator is derived from the additive contained in the electrolytic solution described later. It was found that when the sulfur component contained in the separator was 0.02 to 0.11% by weight based on the weight of the separator, the cycle characteristics of the battery were improved.

The negative electrode that can be used in all the embodiments includes a negative electrode in which a negative electrode active material layer containing a negative electrode active material is arranged 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 a copper foil, and drying. ing. In each embodiment, the negative electrode active material preferably contains graphite particles and/or amorphous carbon particles. When the 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 crystal, and is sometimes called graphite, graphite, or the like. The graphite is preferably in the form of particles. Amorphous carbon means a carbon material that may have a structure partially similar to graphite, has 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 shape of particles.

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

As a binder used for the negative electrode active material layer, fluororesin such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), etc., conductivity of polyaniline, polythiophene, polyacetylene, polypyrrole, etc. Polymer, styrene-butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), acrylonitrile butadiene rubber (NBR), or synthetic rubber, or carboxymethyl cellulose (CMC), xanthan gum, guar gum, Polysaccharides such as pectin can be used.

The positive electrode that can be used in all the embodiments includes a positive electrode in which a positive electrode active material layer containing a positive electrode active material is arranged 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 metal foil such as aluminum foil, and drying. ing. As the positive electrode active material, a lithium transition metal oxide can be used. For example, a lithium-nickel-based oxide (for example, LiNiO ₂ ), a lithium-cobalt-based oxide (for example, LiCoO ₂ ), a lithium-manganese-based oxide (for example, LiMn _{2 ).} Preference is given to using O ₄ ) and mixtures thereof. Also be as a positive electrode active material, using the general formula _{Li x Ni y Co z Mn (} 1-y-z) lithium-nickel-cobalt-manganese composite oxide represented by _{O 2.} 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. It should be noted that 1-y z ≤ 0.4 is desirable because it becomes difficult to synthesize a single-phase composite oxide when the proportion of manganese increases. Further, when the proportion of cobalt increases, the cost increases and the capacity also decreases. Therefore, it is desirable that z<y and z<1-yz. In order to obtain a high capacity battery, y>1-yz and y>z are particularly preferable. The lithium nickel cobalt manganese composite oxide preferably has a layered crystal structure.

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

As a binder used in the positive electrode active material layer, a fluororesin such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), etc., a conductive material such as polyaniline, polythiophene, polyacetylene, polypyrrole, etc. Polymer, styrene-butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), acrylonitrile butadiene rubber (NBR), or synthetic rubber, or carboxymethyl cellulose (CMC), xanthan gum, guar gum, Polysaccharides such as pectin can be used.

Electrolytes that can be used in all embodiments are non-aqueous electrolytes, such as dimethyl carbonate (hereinafter "DMC"), diethyl carbonate (hereinafter "DEC"), di-n-propyl. A chain carbonate such as carbonate, di-t-propyl carbonate, di-n-butyl carbonate, di-isobutyl carbonate, or di-t-butyl carbonate, propylene carbonate (hereinafter referred to as "PC"), ethylene carbonate ( Hereinafter, a mixture containing a cyclic carbonate such as "EC") is preferable. The electrolytic solution is obtained by dissolving a lithium salt such as lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium perchlorate (LiClO ₄ ) in such a carbonate mixture.

The electrolytic solution may contain additives in addition to the above components. The additive that can be added to the electrolytic solution is preferably a substance that can be electrochemically decomposed to form a film on the electrode or the like in the process of charging and discharging the battery. Above all, it is particularly desirable to use an additive capable of stabilizing the negative electrode structure on the negative electrode surface. As such an additive, a cyclic disulfonic acid ester (for example, methylene methane disulfonic acid ester, ethylene methane disulfonic acid ester, propylene methane disulfonic acid ester), a cyclic sulfonic acid ester (for example, sultone), a chain sulfonic acid ester (for example, , Methylene bisbenzene sulfonate, methylene bis phenyl methane sulfonate, methylene bis ethane sulfonate, etc., and additives containing a compound containing sulfur in the molecule (hereinafter referred to as “sulfur-containing additive”). ) Can be mentioned. In addition, vinylene carbonate, vinyl ethylene carbonate, propylene carbonate methacrylate, propylene carbonate acrylate, and the like can be added as an additive capable of forming a protective film for the positive electrode and the negative electrode during the charging/discharging process of the battery. Further, other additives that form protective films for the positive electrode and the negative electrode in the charge/discharge process of the battery include fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, trichloroethylene carbonate, and the like. .. These additives are additives that can prevent the sulfur-containing additive from attacking the positive electrode active material containing the lithium-nickel composite oxide. The additive is contained in a proportion of 20% by weight or less, preferably 15% by weight or less, and more preferably 10% by weight or less, based on the total weight of the electrolytic solution.

In the embodiment, the separator is composed of an olefin resin layer. Here, the olefin resin layer is a layer composed of a polyolefin obtained by polymerizing or copolymerizing α-olefins such as ethylene, propylene, butene, pentene, and hexene. In the embodiment, it is preferable that the layer has pores that are closed when the battery temperature rises, that is, a layer composed of a porous or microporous polyolefin. Since the olefin resin layer has such a structure, even if the battery temperature rises, the separator will be blocked (shut down) and the ion flow can be cut off. In order to exert the shutdown effect, it is highly preferable to use a porous polyethylene membrane.

On the other hand, in another embodiment, the separator preferably has an olefin resin layer and a heat resistant fine particle layer. The heat resistant fine particle layer is provided to prevent abnormal heat generation of the battery. As the heat-resistant fine particles, it is possible to use inorganic fine particles having a heat resistance temperature of 150° C. or higher and stable in electrochemical reaction. As such inorganic fine particles, inorganic oxides such as silica, alumina (α-alumina, β-alumina, θ-alumina), iron oxide, titanium oxide, barium titanate, zirconium oxide; boehmite, zeolite, apatite, kaolin, Minerals such as spinel, mica and mullite can be mentioned. As described above, the separator including the olefin resin layer and the heat resistant resin layer may be referred to as “ceramic separator” in the present specification.

A separator having an olefin resin layer, and optionally a heat-resistant fine particle layer, and a predetermined amount of each electrolytic solution component are mixed to assemble a battery together with a non-aqueous electrolytic solution, a positive electrode, a negative electrode, a separator and an outer casing, and then charged. By performing a predetermined operation such as discharging, the battery is ready for shipping (before shipping). In the process of charging/discharging the battery, the above additives are decomposed by an electrochemical reaction or a chemical reaction, respectively, and consumed to form a film on the electrode surface. As a result, the amount of additive in the electrolytic solution is reduced. When the battery is put into a pre-shipment state, part of the additive (decomposed product) may be adsorbed on the separator surface. Adsorption of some of these additives on the surface of the separator does not immediately adversely affect the battery performance. However, the sulfur-containing additive, which is originally added for the purpose of forming a film on the electrode surface, is adsorbed on the surface of the separator, which is problematic in that the additive that plays a desired role is reduced. As described above, the sulfur-containing additive is added to stabilize the negative electrode by forming a film on the surface of the negative electrode (particularly graphite negative electrode), but a part of the additive is adsorbed on the surface of the separator. This means that the amount of coating film formed on the negative electrode is reduced by the amount. As a result, the cycle life of the battery can be shortened and the capacity retention rate can be reduced.

The separator in the lithium ion secondary battery of the embodiment contains 0.02 to 0.11% by weight of sulfur with respect to the weight of the separator. This means that adsorption of part of the sulfur-containing additive (sulfur component) on the separator surface is unlikely to occur, and the sulfur-containing additive is used for its original purpose of forming a film on the electrode surface. To do. Examples of such a separator include a separator composed of a porous or microporous olefin resin layer. Other examples include a ceramic separator having an olefin resin layer and a heat resistant fine particle layer. At this time, when the heat-resistant fine particles are alumina (α-alumina, β-alumina, γ-alumina, θ-alumina, etc.) or boehmite, the thermal stability is good and the sulfur-containing additive decomposes on the separator. It turned out that can be effectively prevented.

In the embodiment, when a ceramic separator having an olefin resin layer and a heat-resistant fine particle layer is used, a relatively small amount of the sulfur-containing additive is decomposed, and the sulfur component produced by the decomposition mainly forms the heat-resistant fine particle layer. Adsorbed. Particularly when alumina or boehmite is used as the heat-resistant fine particles, almost all of 0.02 to 0.11% by weight of sulfur contained in the separator is adsorbed in the heat-resistant fine particle layer.

The ceramic separator having the olefin resin layer and the heat resistant fine particle layer has a form in which the heat resistant fine particle layer is laminated on the surface of the olefin resin film. The heat-resistant fine particle layer can be provided only on one side of the olefin resin film, or can be provided on both sides. The ratio of the total thickness of the heat-resistant fine particle layer is preferably about 1/10 to 1/2, preferably about 1/8 to 1/3 of the thickness of the olefin resin layer. If the thickness of the heat-resistant fine particle layer is too thick, decomposition products of the sulfur-containing additive contained in the electrolytic solution may increase, and if it is too thin, the effect of improving the heat resistance of the separator cannot be expected.

Here, a configuration example of the lithium ion secondary battery according to the present embodiment will be described with reference to the drawings. 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 constituent elements. 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. It is also possible to form an active material layer. 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 a constituent unit of one battery, that is, a power generation element (in the figure, a cell 19). The separator 17 may be composed of a heat resistant fine particle layer and an olefin resin film (both not shown). A plurality of such unit cells 19 are stacked with the separator 17 interposed therebetween. The extending portions extending from each negative electrode current collector 11 are collectively joined on the negative electrode lead 25, and the extending portions extending from each positive electrode current collector 12 are collectively joined on 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 may have a partial coating of another metal (for example, nickel, tin, solder) or a polymer material in some cases. The positive electrode lead and the negative electrode lead are welded to the positive electrode and the negative electrode, respectively. The battery formed by stacking a plurality of unit cells in this way is packaged by the outer package 29 in such a manner that the welded negative electrode lead 25 and positive electrode lead 27 are drawn to the outside. An electrolytic solution 31 is injected into the exterior body 29. The outer package 29 has a shape in which two laminated bodies are stacked and the peripheral edge portion is heat-sealed.

<Production of negative electrode>
As the negative electrode active material, surface-coated natural graphite powder, carbon black powder as a conduction aid, styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as a binder resin, and the solid content mass ratio was 93:3:2:2. These materials were added in a proportion to ion-exchanged water and stirred, and these materials were uniformly dispersed in water to prepare a slurry. The obtained slurry was applied onto a copper foil having a thickness of 10 μm which serves as a negative electrode current collector. Next, the negative electrode active material layer was formed by heating the electrode at 125° C. for 10 minutes and evaporating the water. Further, the negative electrode active material layer was pressed to prepare a negative electrode in which the negative electrode active material layer was coated on one surface of the negative electrode current collector.

<Production of positive electrode>
As the positive electrode active material, nickel-cobalt-lithium manganate (NCM811, that is, nickel:cobalt:manganese=8:1:1) and lithium manganese oxide (LiMn ₂ O ₄ ) were mixed at 25:75 (weight ratio). The mixed oxides mixed, carbon black powder as a conduction aid, and polyvinylidene fluoride as a binder resin were added to NMP as a solvent at a solid content mass ratio of 90:5:5. Further, by adding 0.03 parts by mass of oxalic anhydride (molecular weight 90) as an organic moisture scavenger to the mixture with respect to 100 parts by mass of the solid content excluding NMP from the mixture, and stirring the mixture, The above materials were uniformly dispersed to prepare a slurry. The obtained slurry was applied onto an aluminum foil having a thickness of 20 μm which serves as a positive electrode current collector. Then, the positive electrode active material layer was formed by heating the electrode at 125° C. for 10 minutes to evaporate NMP. Further, the positive electrode active material layer was pressed to prepare a positive electrode in which a positive electrode active material layer having a basis weight of 20 mg/cm ² and a density of 3.0 g/cm ³ was applied on one surface of the positive electrode current collector.

<Separator>
A ceramic separator composed of a heat-resistant fine particle layer having a thickness of 5 μm using alumina as the heat-resistant fine particles and an olefin resin layer having a thickness of 20 μm made of polypropylene was used. A plurality of ceramic separators having different amounts of θ-alumina contained in the heat resistant fine particle layer were used. Table 1 shows the types of separators used. In Example 3, a 25 μm thick polypropylene single layer separator was used.

<Electrolyte>
A non-aqueous solvent prepared by mixing ethylene carbonate (hereinafter, referred to as “EC”) and DEC in a ratio of EC:DEC=30:70 (volume ratio) is used as an electrolyte salt of lithium hexafluorophosphate (LiPF). ₆ ) was dissolved to a concentration of 1.0 mol/L, and cyclic disulfonic acid ester (methylene methane disulfonate (MMDS) and vinylene carbonate (VC) were added at a concentration of 1 weight each as an additive. What was melt|dissolved so that it might become% was used.

<Preparation of lithium-ion secondary battery>
Each of the negative electrode plate and the positive electrode plate manufactured as described above was cut into a rectangle 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 above-mentioned negative electrode plate and positive electrode plate were arranged on both surfaces of the separator so that both active material layers were overlapped with the separator interposed therebetween to obtain an electrode plate laminate. Two sides of the aluminum laminate film except one of the long sides were bonded by heat fusion on the three sides to produce a bag-shaped laminate exterior body. The above electrode laminate was inserted into the laminate exterior body. After pouring the electrolyte solution and impregnating it under vacuum, the opening was sealed by heat fusion under reduced pressure to obtain a laminated lithium ion battery. After performing initial charge/discharge for this laminated lithium ion battery, high temperature aging was performed to obtain a laminated lithium ion battery having a battery capacity of 5 Ah.

<Initial charge/discharge>
Initial charge/discharge was performed from 0% to 100% of the remaining capacity of the battery (hereinafter referred to as “SOC”) at an ambient temperature of 55° C. The conditions of charge and discharge are as follows: constant current charge (CC charge) up to 4.1V at 0.1C current, then constant voltage charge (CV charge) at 4.1V, and then at 0.1C current. Constant current discharge (CC discharge) is performed up to 2.5V.

<Sulfur content of separator>
After the initial charge and discharge of the lithium ion secondary battery, the battery was disassembled, and the sulfur content of the separator was measured by high frequency inductively coupled plasma emission spectroscopy (ICP emission spectroscopy).

<Cycle characteristic test>
A cycle test was conducted on the prepared battery under the following conditions. Under the environment of 55°C, constant current constant voltage charge (CCCV charge) at 1C current, 4.15V and constant current discharge (CC discharge) at 1C current between SOC 0% and 100% of the manufactured battery were performed. Repeated 300 times. The capacity retention rate by this was calculated by a calculation formula of (battery capacity after 300 cycles)/(initial battery capacity).

The batteries (Example 1, Example 2 and Example 3) having a low sulfur content in the separator after the initial charge/discharge have a high battery capacity retention rate after the cycle characteristic test. It is considered that this is because the sulfur component of the sulfur-containing additive was not adsorbed on the surface of the separator during the initial charging/discharging, and the coating film was effectively formed on the surface of the electrode. It was found that when alumina was used as the heat resistant fine particles, the content of the sulfur component changed depending on the content rate of θ-alumina. The higher the content of θ-alumina, the greater the amount of sulfur components adsorbed on the separator. Therefore, when using alumina as the heat-resistant fine particles, α-, β-, or γ-alumina is used instead of θ-alumina. Is considered good to use.

Although the examples of the present invention have been described above, the above examples merely show one example of the embodiment of the present invention, and are intended to limit the technical scope of the present invention to a particular embodiment or a specific configuration. Absent.

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 Outer Package 31 Electrolyte

Claims (1)

A positive electrode in which the positive electrode active material layer is arranged on the positive electrode current collector,
A negative electrode in which the negative electrode active material layer is arranged on the negative electrode current collector,
A separator,
An electrolytic solution containing a sulfur-containing additive at a concentration of 1% by weight ;
A lithium-ion secondary battery including a power generation element including:
The positive electrode active material layer has a general formula Li _x Ni _y Co _z Mn _(1-yz) O ₂ (where x in the formula is 1≦x≦1.2, and y and z are y+z<1. Which is a positive number that satisfies y, and the value of y is 0.5 or less.), including a lithium nickel cobalt manganese composite oxide having a layered crystal structure represented by
The separator has an olefin-based resin layer and a heat-resistant fine particle layer, and the heat-resistant fine particle layer is selected from the group consisting of α-alumina, β-alumina, γ-alumina, and boehmite. 0.02 to 0.11 weight relative to the weight of the separator after the initial charge and discharge of the secondary battery at a temperature of 55° C. at a current of 0.1 C and then discharging at a current of 0.1 C % Sulfur is adsorbed on the separator, the sulfur is contained in the heat-resistant fine particle layer of the separator,
The lithium ion secondary battery, wherein the sulfur-containing additive is methylene methane disulfonic acid ester.

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