KR100811967B1 - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

A positive electrode, a negative electrode, a porous heat-resistant layer interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, the negative electrode includes a negative electrode current collector and a negative electrode mixture layer supported on the surface of the negative electrode current collector, the porous heat resistant layer Supported by the negative electrode, the porous heat resistant layer contains magnesium oxide particles, the average particle diameter of the magnesium oxide particles is 0.5 μm to 2 μm, and the active material density of the negative electrode mixture layer is 1.5 g / ml to 1.8 g / ml. Non-aqueous electrolyte secondary battery.

Description

Non-aqueous electrolyte secondary battery {NON-AQUEOUS ELECTROLYTE SECONDARY BATTERY}

1 is a longitudinal cross-sectional view of a cylindrical lithium ion secondary battery.

The present invention relates to a nonaqueous electrolyte secondary battery including a negative electrode carrying a porous heat resistant layer mainly composed of ceramic particles.

A nonaqueous electrolyte secondary battery such as a lithium ion secondary battery has a separator which electrically insulates a positive electrode and a negative electrode and holds an electrolyte. As for the separator, a porous film made of resin is the mainstream. Polyolefin resin etc. are used for the raw material of a porous film.

The resin porous film deforms at high temperature. Therefore, when an abnormality arises, when a short circuit part is formed in a battery and battery temperature rises, a short circuit part may expand. Therefore, supporting the porous heat resistant layer on the electrode, which is difficult to deform even at high temperatures, has been studied. The porous heat resistant layer is mainly composed of ceramic particles having heat resistance. Therefore, the porous heat resistant layer has a function of suppressing the formation and expansion of the short circuit portion when there is an abnormality.

Aluminum oxide is mainly used for the ceramic particle which comprises a porous heat-resistant layer. Aluminum oxide does not participate in the battery reaction occurring inside the nonaqueous electrolyte secondary battery. Aluminum oxide has high heat resistance and is suitable for controlling the micropore diameter distribution of the porous heat-resistant layer.

It is also proposed to use magnesium oxide for ceramic particles (Japanese Patent Laid-Open No. 2003-142078). Magnesium oxide is also stable and does not participate in the battery reaction occurring inside the nonaqueous electrolyte secondary battery.

The porous heat resistant layer is formed on the electrode using a slurry composed of a mixture of ceramic particles, a binder, and a liquid component. After applying the slurry on the electrode, it is necessary to dry to remove the liquid component. However, the electrode includes a current collector and an electrode mixture layer supported thereon. The liquid component of the slurry penetrates into the electrode mixture layer before being removed by drying. As a result, the thickness of the electrode mixture layer increases.

When the thickness of the electrode mixture layer increases, the active material density decreases. Considering the insertion of the electrode plate group in which the positive electrode and the negative electrode are integrated into a predetermined container (battery case), it is necessary to design the battery in consideration of the increased thickness. Therefore, the energy density of the battery is also reduced. Moreover, even if the battery is carefully designed, difficulties may arise when inserting the electrode plate group into the container.

Therefore, in order to limit the thickness of the final electrode mixture layer, it is also conceivable to roll the electrode mixture layer supported on the current collector with a strong pressure before forming the porous heat resistant layer. However, excessive rolling causes peeling from the collector of the electrode mixture layer. In addition, when the electrode supporting the porous heat resistant layer is rolled, the porosity and the micropore diameter distribution of the porous heat resistant layer change, so that discharge characteristics are impaired. Moreover, since the ceramic particle which comprises a porous heat resistant layer damages the surface of a rolling roll, the lifetime of a manufacturing facility also becomes short.

As described above, when the electrode carrying the porous heat resistant layer is rolled, various problems occur. The present invention makes it possible to avoid such a problem.

The present invention proposes to use magnesium oxide having an average particle diameter of 2 µm or less for ceramic particles.

According to this proposal, it is possible to solve the increase in the thickness of the negative electrode mixture layer without damaging the surface of the rolling roll, and to provide a nonaqueous electrolyte secondary battery having good discharge characteristics.

That is, the present invention includes a positive electrode, a negative electrode, a porous heat resistant layer interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte, and the negative electrode includes a negative electrode current collector and a negative electrode mixture layer supported on the surface of the negative electrode current collector. The porous heat resistant layer is supported on the cathode, the porous heat resistant layer contains magnesium oxide particles, and has an average particle diameter (median diameter D50 based on volume) of magnesium oxide particles of 0.5 µm to 2 µm, A nonaqueous electrolyte secondary battery having an active material density of 1.5 g / ml to 1.8 g / ml in the negative electrode mixture layer is provided.

When a separator is further included between an anode and a cathode, it is preferable that the thickness of a porous heat resistant layer is 1 micrometer-5 micrometers.

When a separator is not included between an anode and a cathode, it is preferable that the thickness of a porous heat resistant layer is 2 micrometers-15 micrometers.

The BET specific surface area of magnesium oxide is preferably 3 m 2 / g to 15 m 2 / g.

It is preferable that a porous heat resistant layer contains 1 weight part-5 weight part binders per 100 weight part of magnesium oxide particles.

The porosity of the porous heat resistant layer is preferably 30% to 70%.

According to the present invention, the energy density of the negative electrode can be increased without damaging the manufacturing equipment. Specifically, the active material density of the negative electrode mixture layer can be controlled to 1.5 g / ml to 1.8 g / ml, and the manufacturing equipment can be extended for a long time. Moreover, according to this invention, the fall of discharge characteristic is also suppressed.

Magnesium oxide hardly damages the surface of a rolling roll. It is thought that magnesium oxide hardly damages the surface of a rolling roll because the hardness of magnesium oxide is low. However, magnesium oxide tends to cause cracking or deformation of the particles by rolling. This means that the change in the porosity and the micropore diameter distribution of the porous heat-resistant layer becomes large.

On the other hand, when using magnesium oxide with a small particle diameter of 2 micrometers or less in average particle diameter, the load by rolling is disperse | distributed to more small particle | grains. Therefore, cracking and deformation of the particles are suppressed. That is, even if the porous heat resistant layer containing magnesium oxide with an average particle diameter of 2 micrometers or less is rolled, it is thought that the change of porosity and micropore diameter distribution is suppressed. Therefore, the fall of discharge characteristic is also suppressed.

The nonaqueous electrolyte secondary battery of the present invention includes a porous heat resistant layer and a nonaqueous electrolyte interposed between a positive electrode, a negative electrode, a positive electrode and a negative electrode. The positive electrode and the nonaqueous electrolyte are not particularly limited. Therefore, various configurations conventionally proposed in the positive electrode and the nonaqueous electrolyte of the nonaqueous electrolyte secondary battery can be applied to the present invention.

The negative electrode is not particularly limited as long as the following requirements are satisfied. Therefore, as long as the following requirements are satisfied, various configurations conventionally proposed in the negative electrode of the nonaqueous electrolyte secondary battery can be applied to the present invention.

The porous heat resistant layer also has a function similar to that of a separator made of a porous film made of resin. However, the structure of the porous heat resistant layer is significantly different from the porous film made of resin obtained by stretching the resin sheet. The porous heat resistant layer has a structure in which ceramic particles are bonded to a binder made of a resin. Therefore, the tensile strength in the surface direction of the porous heat resistant layer is lower than that of the resin porous film. However, the porous heat resistant layer does not heat shrink like a resin porous film even when exposed to high temperature. Therefore, the porous heat resistant layer functions to prevent the expansion of the short circuit portion at the time of the above and to increase the safety of the battery. In addition to the porous heat-resistant layer, the nonaqueous electrolyte secondary battery of the present invention may further include a separator made of a porous film made of resin.

The porous heat resistant layer is supported on at least part of the surface of the cathode. Usually, the area | region of the area | region carrying an active material is larger in a cathode side than an anode. Therefore, it is preferable to carry a porous heat resistant layer on a cathode.

The porous heat resistant layer is, for example, supported on the negative electrode so as to cover the negative electrode mixture layer. Or, in particular, a cathode portion which is likely to cause an internal short circuit is selected, and a porous heat resistant layer is supported thereon. Alternatively, the porous heat resistant layer is partially supported on the surface of the negative electrode mixture layer facing the positive electrode mixture layer in various distribution states. Alternatively, the porous heat resistant layer is supported on the entire surface of the negative electrode mixture layer facing the positive electrode mixture layer.

The negative electrode includes a negative electrode current collector and a negative electrode mixture layer supported on the surface of the negative electrode current collector. The form of the negative electrode current collector and the negative electrode mixture layer is not particularly limited. In a typical form, the negative electrode mixture layer in a thin film state is supported on one or both surfaces of the sheet-like or strip-shaped negative electrode current collector.

The sheet-like or strip-shaped negative electrode current collector is made of, for example, copper or a copper alloy. The negative electrode current collector may be subjected to perforation, mesh processing, lath processing, surface treatment, and the like. As surface treatment, a plating process, an etching process, a film formation, etc. are mentioned.

The negative electrode mixture layer contains a negative electrode active material. As the negative electrode active material, a carbon material, a metal monolith, an alloy, a metal compound, or the like is used. As a carbon material, natural graphite, artificial graphite, non-graphitizable carbon, reverse graphitizable carbon, mesopez carbon, etc. are mentioned, for example. As a metal monolith, silicon, tin, etc. are mentioned, for example. As an alloy, a silicon alloy (Si-Ti alloy, Si-Cu alloy, etc.) is mentioned, for example. Examples of the metal compound include silicon oxide {SiOx (0 <x <2)}, tin oxide (SnO, SnO ₂ ), and the like. These may be used independently and may be used in combination of 2 or more type.

Particularly preferred negative electrode active materials include natural graphite, artificial graphite, non-graphitizable carbon, and reverse graphitizable carbon. It is preferable that they are 5 micrometers-35 micrometers, and, as for these, the average particle diameter (median diameter of a volume basis: D50) is 10 micrometers-25 micrometers still more. In addition, the average particle diameter can be calculated | required from the volume-based particle size distribution measured, for example using the particle size distribution measuring apparatus of a laser diffraction type. In the volume-based particle size distribution, the median diameter: D50 of 50% of the accumulated value corresponds to the average particle diameter. The method for obtaining the average particle diameter is the same for the magnesium oxide particles and the like contained in the porous heat resistant layer.

The negative electrode mixture layer preferably contains 0.5 parts by weight to 5 parts by weight of the binder, and more preferably 0.8 parts by weight to 2 parts by weight of the binder per 100 parts by weight of the negative electrode active material.

Examples of the binder included in the negative electrode mixture layer include fluorine resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), rubber particles, and the like. Among these, rubber particles are particularly preferable.

Examples of the rubber particles include styrene butadiene rubber (SBR), modified styrene butadiene rubber (modified SBR), and the like. Among these, modified SBR is particularly preferable.

The modified SBR preferably includes at least one selected from the group consisting of acrylonitrile units, acrylate units, acrylic acid units, methacrylate units, and methacrylic acid units, and includes acrylonitrile units and acrylate units; Particular preference is given to including acrylic acid units. As the acrylate unit, 2-ethylhexyl acrylate is suitable. As a commercially available preferable binder, Nippon-Xeon Corporation BM-400B etc. are mentioned.

In the case where the modified SBR contains acrylonitrile units, acrylate units and acrylic acid units, in the absorption spectrum obtained by FT-IR measurement, the absorption strength based on C = O stretching vibration is based on the absorption strength based on C≡N stretching vibration. It is preferable that it is 3 to 50 times.

The negative electrode mixture layer may further include 0.5 parts by weight to 3 parts by weight of a thickener per 100 parts by weight of the negative electrode active material. Examples of the thickener include carboxymethyl cellulose (CMC), methyl cellulose (MC), polyvinyl alcohol, polyethylene oxide (PEO), polyacrylic acid (PAN), and the like. Among these, CMC is particularly preferable.

The negative electrode mixture layer may further include a small amount of conductive agent. As the conductive agent, various carbon blacks can be used, for example.

In the manufacturing method of a general negative electrode, first, a negative electrode mixture paste is prepared. The negative electrode mixture paste is prepared by mixing the negative electrode mixture with a liquid component (dispersion medium). A negative electrode mixture contains a negative electrode active material as an essential component, and contains a binder, a electrically conductive agent, a thickener, etc. as an arbitrary component.

The negative electrode mixture paste arrives on one side or both sides of the negative electrode current collector and is dried. At this time, the negative electrode collector is provided with a non-coated portion in which the negative electrode mixture paste has not arrived. The uncoated portion is used for welding the negative electrode lead. The negative electrode mixture in the dry state supported on the negative electrode current collector is rolled by a rolling roll to form a negative electrode mixture layer whose thickness is controlled. At this time, the active material density of the negative electrode mixture layer is 1.5 g / ml-1.8 g / ml. In addition, when the active material density exceeds 1.8 g / ml, there is a fear that peeling of the negative electrode mixture layer from the negative electrode current collector occurs.

The active material density of the negative electrode mixture layer is represented by the weight of the negative electrode active material contained in 1 ml (1 cm 3) of negative electrode mixture layer. Therefore, the active material density can be calculated from the weight ratio of 1 ml of the negative electrode mixture layer and the weight ratio of the negative electrode active material contained in the negative electrode mixture.

The porous heat resistant layer contains magnesium oxide particles. The mean particle diameter (volume-based median diameter: D50) of the magnesium oxide particles is 0.5 µm to 2 µm, and preferably 0.8 µm to 1.5 µm. If the average particle diameter of magnesium oxide particle is less than 0.5 micrometer, the porosity of a porous heat resistant layer will become high too much, and since the mechanical strength of a porous heat resistant layer will fall, safety will fall. On the other hand, when the average particle diameter of magnesium oxide particle | grains exceeds 2 micrometers, when rolling a porous heat resistant layer, a discharge characteristic will fall rapidly.

Even when the average particle diameter of magnesium oxide particle | grains exceeds 2 micrometers, if a porous heat resistant layer is not rolled, discharge characteristics will not fall. On the other hand, when rolling a porous heat resistant layer, it can be considered that a comparatively large magnesium oxide particle produces a crack and a deformation | transformation. As a result, the porosity and the micropore diameter distribution of the porous heat resistant layer change, and the discharge characteristic is lowered. The degree of cracking or deformation of the particles is considered to be remarkable when the average particle diameter of the magnesium oxide particles exceeds 2 µm. This is considered to be because, when the particle diameter of the particles is large, the load due to rolling is difficult to disperse. On the other hand, in the case of magnesium oxide particles having an average particle diameter of 2 µm or less, the load by rolling is dispersed into more particles. Therefore, cracks and deformation are suppressed, and it is estimated that abrupt fall of discharge characteristic is avoided.

When rolling to a porous heat-resistant layer, the tendency for the discharge characteristic to drop rapidly is considered to be a phenomenon peculiar to magnesium oxide particles having an average particle diameter of more than 2 µm. For example, when aluminum oxide particles having an average particle diameter of 2 µm or more are used in place of magnesium oxide, even when rolling the porous heat resistant layer, the discharge characteristics do not rapidly decrease. This difference is considered to be due to the difference in hardness between magnesium oxide and aluminum oxide. Since magnesium oxide is very low in hardness, it can be thought that it is easy to produce a crack and a deformation originally. On the other hand, since aluminum oxide has high hardness, it is thought that cracking and deformation hardly occur regardless of the particle diameter.

It is preferable that it is 3 m <2> / g-15 m <2> / g, and, as for BET specific surface area of magnesium oxide particle, it is still more preferable that it is 3 m <2> / g-12 m <2> / g. In the case of magnesium oxide particles having an average particle diameter of 2 µm or less, it is practically difficult to make the BET specific surface area less than 3 m 2 / g. When BET specific surface area exceeds 15 m <2> / g, the average particle diameter of magnesium oxide particle | grains will become smaller than 0.5 micrometer normally. Therefore, the porosity of a porous heat-resistant layer becomes high and it may become difficult to ensure safety. In addition, when the BET specific surface area becomes too large, the amount of the binder becomes relatively small. Therefore, the strength of the porous heat resistant layer may be lowered in some cases.

The porous heat-resistant layer preferably contains 1 part by weight to 5 parts by weight of a binder, more preferably 2 parts by weight to 4 parts by weight of binder per 100 parts by weight of magnesium oxide particles, and 2.2 parts by weight to 4 parts by weight. It is particularly preferred to include parts by weight binder. When the amount of the binder is less than 1 part by weight per 100 parts by weight of magnesium oxide particles, the strength of the porous heat resistant layer may not be sufficiently obtained. On the other hand, when the quantity of a binder exceeds 5 weight part per 100 weight part of magnesium oxide particles, discharge characteristics may fall. However, the suitable amount of a binder changes with the thickness of a porous heat resistant layer. This is because the thinner the porous heat-resistant layer is, the smaller the influence of the amount of the binder on the discharge characteristics has has on the market.

Although the binder included in the porous heat resistant layer is not specifically limited, For example, the resin material like the above-mentioned binder which can be included in a negative electrode mixture layer can be used. Among them, polyvinylidene fluoride (PVDF), rubber particles and the like are suitable as binders contained in the porous heat-resistant layer.

Rubber particles and PVDF have appropriate elasticity. It is preferable that the binder which has moderate elasticity exists in abundance in a porous heat-resistant layer rather than a negative electrode mixture layer. This is because the negative electrode mixture layer absorbs the stress due to rolling, so that the stress applied to the porous heat resistant layer is reduced. Therefore, changes in the porosity and the micropore diameter distribution of the porous heat resistant layer are significantly suppressed.

In the case where the porous heat resistant layer is supported on the cathode, first, the heat resistant layer slurry is prepared. The heat-resistant layer slurry is prepared by mixing magnesium oxide particles with a liquid component (dispersion medium). As the heat-resistant layer slurry, in addition to magnesium oxide particles, a binder, a thickener, or the like may be included as an optional component. As the liquid component, for example, organic solvents such as N-methyl-2-pyrrolidone and cyclohexanone, water and the like are used, but are not particularly limited.

It is preferable that the apparatus which mixes magnesium oxide particle with a liquid component is a medialess disperser. Since magnesium oxide has low hardness, it is easy to cause cracking or deformation when subjected to shear force, but according to the medialess disperser, cracking and deformation of particles can be suppressed.

The heat resistant layer slurry reaches at least a part of the negative electrode. At this time, the liquid component contained in the heat-resistant layer slurry penetrates into the negative electrode mixture layer, and the thickness of the negative electrode mixture layer increases. Therefore, the active material density of the negative electrode mixture layer immediately after the liquid component is removed by drying decreases from 1.45 g / ml to 1.70 g / ml. The higher the active material density of the negative electrode mixture layer before the thickness increases, the larger the decrease rate of the active material density becomes. However, in the present invention, the negative electrode having an increased thickness of the negative electrode mixture layer can be re-rolled.

The conventional nonaqueous electrolyte secondary battery is produced using the negative electrode of which the thickness increased and the active material density was reduced. This is to avoid changing the porosity and micropore diameter distribution of the porous heat-resistant layer and to avoid damaging the surface of the rolling roll. On the other hand, in the present invention, since magnesium oxide particles having an average particle diameter of 2 µm or less are used, changes in the porosity and the micropore diameter distribution of the porous heat resistant layer are suppressed and the surface of the rolling roll may not be damaged.

In addition, in the case of using ceramic particles other than magnesium oxide particles, for example, aluminum oxide particles, if the negative electrode is re-rolled, the surface of the rolling roll is damaged regardless of the average particle diameter of the particles, and the life of the manufacturing equipment is Shorten.

By re-rolling, the thickness of the negative electrode mixture layer returns to the vicinity of the thickness before the porous heat resistant layer is formed on the negative electrode. At the same time, the active material density of the negative electrode mixture layer is also controlled to 1.5 g / ml to 1.8 g / ml, preferably 1.7 g / ml to 1.8 g / ml, even more preferably 1.75 g / ml to 1.8 g / ml. Therefore, according to this invention, it becomes possible to obtain the battery of a high energy density compared with the conventional battery which has a porous heat resistant layer.

When the nonaqueous electrolyte secondary battery includes a separator made of a porous film made of resin, the thickness of the porous heat resistant layer after re-rolling the negative electrode is preferably 1 μm to 5 μm, and even more preferably 1 μm to 4 μm. Do. When the thickness of a porous heat resistant layer is less than 1 micrometer, the effect which improves safety by a porous heat resistant layer may not fully be acquired. On the other hand, when the thickness of a porous heat resistant layer exceeds 5 micrometers, discharge characteristics may fall comparatively remarkably. This is considered to be because resistance increases by increasing the thickness of the porous heat-resistant layer. Moreover, when the thickness of a porous heat resistant layer is 2 micrometers or less, porosity hardly changes also by re-rolling. It is preferable to measure the thickness of a porous heat resistant layer by the method of measuring the weight of a porous heat resistant layer by fluorescent X-rays, and converting a weight into thickness using a calibration curve.

When the nonaqueous electrolyte secondary battery does not include a separator made of a porous film made of resin, the thickness of the porous heat resistant layer after re-rolling the negative electrode is preferably 2 μm to 15 μm, and preferably 5 μm to 12 μm. Even more preferred. In this case, the porous heat resistant layer also serves as a separator.

From the viewpoint of securing good discharge characteristics, the porosity of the porous heat resistant layer is preferably 30% to 70%, even more preferably 40% to 55%. In the case of using magnesium oxide particles having an average particle diameter of 2 µm or less, it is easy to obtain a porosity of 30% or more even after re-rolling of the cathode, and relatively easy to obtain a porosity of 40% or more. On the other hand, in the case of using magnesium oxide particles having an average particle diameter of more than 2 µm, it is difficult to obtain a porosity of 30% or more after re-rolling of the negative electrode.

The porosity P of the porous heat resistant layer is obtained from the apparent volume V (ie, S × T) obtained from the volume Vt of the porous heat resistant layer supported on the re-rolled cathode and the area S and thickness T of the porous heat resistant layer. Can be calculated {P (%) = 100 (Va-Vt) / Va = 100 (ST-Vt) / ST}. It can also be obtained by mercury porosimetry. When mercury porosity is used, the porosity is calculated using, for example, the difference in the fine pore diameter distribution of the cathode before and after supporting the porous heat resistant layer.

The porous heat resistant layer may contain about 50% by weight or less of ceramic particles other than magnesium oxide particles. However, in order not to impair the effect of this invention largely, 25 weight% or less of the ceramic particle other than magnesium oxide particle is preferable. If the main component of the ceramic particles is magnesium oxide particles, the effect of the present invention is not significantly impaired.

The positive electrode includes, for example, a positive electrode current collector and a positive electrode mixture layer supported on the surface of the positive electrode current collector. The form of the positive electrode current collector and the positive electrode mixture layer is not particularly limited. In a typical form, a positive electrode mixture layer in a thin film state is supported on one or both surfaces of a sheet-like or strip-shaped positive electrode current collector.

The sheet-like or strip-shaped positive electrode current collector is made of, for example, aluminum or an aluminum alloy. The positive electrode current collector may be subjected to perforation, mesh processing, lath processing, surface treatment, and the like. As surface treatment, a plating process, an etching process, a film formation, etc. are mentioned. The thickness of the positive electrode current collector is, for example, 10 µm to 60 µm.

The positive electrode mixture layer contains a positive electrode active material. As the positive electrode active material, for example, a lithium-containing oxide capable of occluding and releasing lithium ions is used. As such a lithium containing oxide, the composite metal oxide of at least 1 sort (s) of transition metal chosen from cobalt, manganese, nickel, chromium, iron, and vanadium, and lithium is mentioned, for example. Especially, it is preferable that a part of transition metal is substituted by Al, Mg, Zn, Ca etc.

Among the composite metal oxides, LixCoO ₂ , LixMnO ₂ , LixNiO ₂ , LixCrO ₂ , αLi _x FeO ₂ , Li _x VO ₂ , Li _x Co _y Ni _1-y O ₂ , Li _x Co _y M _1-y O ₂ , Li _x Ni _1-y M _y O ₂ , Li _x Mn ₂ O ₄ , Li _x Mn _2-y M _y O ₄ (where M = Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, At least one selected from the group consisting of Zn, Al, Cr, Pb, Sb and B, x = 0 to 1.2, y = 0 to 0.9, z = 2 to 2.3), transition metal chalcogenide and vanadium oxide lithium Cargo, lithium oxide of niobium oxide, etc. are preferable. These may be used independently and may be used in combination of 2 or more type. Moreover, said x value increases and decreases by charge and discharge. It is preferable that the average particle diameter of a positive electrode active material is 1 micrometer-30 micrometers.

The positive electrode mixture layer may contain a binder, a conductive agent and the like. As a binder, an electrically conductive agent, etc., the same material as the above-mentioned binder and electrically conductive agent which can be contained in a negative mix layer, for example can be used.

In the general production method of the positive electrode, first, a positive electrode mixture paste is prepared. The positive electrode mixture paste is prepared by mixing the positive electrode mixture with a liquid component (dispersion medium). A positive electrode mixture contains a positive electrode active material as an essential component, and contains a binder, a electrically conductive agent, etc. as an arbitrary component.

The positive electrode mixture paste arrives on one side or both sides of the positive electrode current collector and is dried. At this time, the positive electrode current collector is formed with a non-coated portion which does not reach the positive electrode mixture paste. The uncoated portion is used for welding the positive lead. The positive electrode mixture in a dry state supported on the positive electrode current collector is rolled by a rolling roll to form a positive electrode mixture layer whose thickness is controlled.

As the nonaqueous electrolyte, a nonaqueous solvent in which a lithium salt is dissolved is preferably used. Although the dissolution amount of the lithium salt in a nonaqueous electrolyte is not specifically limited, 0.2-2 mol / L is preferable and, as for lithium salt concentration, 0.5-1.5 mol / L is still more preferable.

Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). ), Chain carbonates such as dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate and ethyl propionate, lactones such as γ-butyrolactone and γ-valerolactone, Chain ethers such as 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), ethoxymethoxyethane (EME), and rings such as tetrahydrofran and 2-methyltetrahydrofran Shape ethers, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monograms, phosphate triesters, trimethoxy Methane, Dioxolane Oil Sieve, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofran derivative, ethyl ether, 1,3-propanesultone , Anisole, N-methyl-2-pyrrolidone can be used. Although these may be used independently, it is preferable to mix and use 2 or more types. Especially, the mixed solvent of cyclic carbonate and chain carbonate, or the mixed solvent of cyclic carbonate, chain carbonate, and aliphatic carboxylic acid ester is preferable.

Examples of the lithium salt dissolved in the nonaqueous solvent include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carbonate, LiBr, LiI, chloroborane lithium, lithium tetraphenylborate, lithium imide salt, and the like. These may be used independently and may be used in combination of 2 or more type. In addition, it is preferable to use at least LiPF _6.

Various additives can be added to the nonaqueous electrolyte in order to improve the charge and discharge characteristics of the battery. As an additive, it is preferable to use at least 1 sort (s) chosen from the group which consists of vinylene carbonate, vinyl ethylene carbonate, and fluorobenzene, for example. In addition, various additives such as triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-lime, pyridine, hexanoic acid triamide, nitrobenzene derivatives, crown ethers, quaternary ammonium salts, Ethylene glycol dialkyl ether and the like can be used.

The separator which consists of a porous film made of resin is polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene chloride, polyacrylonitrile, polyacrylamide, polytetrafluoroethylene, polysulfone, polyether sulfone, polycarbonate, poly It is preferably made of a polymer such as amide, polyimide, polyether (polyethylene oxide or polypropylene oxide), cellulose (carboxymethyl cellulose or hydroxypropyl cellulose), poly (meth) acrylic acid or poly (meth) acrylic acid ester. The multilayer film which laminated | stacked the several porous film is also used preferably. Especially, the single layer or multilayer porous film which consists of polyethylene, a polypropylene, polyvinylidene fluoride, etc. is suitable. As for the thickness of a porous film, 10 micrometers-30 micrometers are preferable.

Next, although this invention is demonstrated concretely based on an Example, this invention is not limited to a following example.

Example 1

(Iii) fabrication of anode

100 parts by weight of lithium cobalt acid (average particle diameter 10 μm) as a positive electrode active material, 4 parts by weight of polyvinylidene fluoride {PVDF: Solid content of # 1320 manufactured by Kureha Chemical Co., Ltd.}, and acetylene black 3 as a conductive agent The parts by weight and the appropriate amount of N-methyl-2-pyrrolidone (NMP) as the dispersion medium were stirred with a twin linker to prepare a positive electrode mixture paste. The positive electrode mixture paste was applied to both surfaces of a strip-shaped positive electrode current collector made of aluminum foil having a thickness of 15 μm. The coated positive electrode mixture paste was dried and rolled with a rolling roll to form a positive electrode mixture layer. The total thickness of the positive electrode current collector and the positive electrode mixture layer supported on both surfaces thereof was 160 μm. The obtained electrode plate was cut to the width that can be inserted into a cylindrical 18650 battery case, thereby obtaining a positive electrode. The active material density of the positive electrode material mixture layer was 3.6 g / ml.

(Ii) preparation of negative electrode

100 parts by weight of artificial graphite (average particle diameter 20 µm) which is a negative electrode active material, 1 part by weight of modified SBR (solid content of BM-400B manufactured by Nihon Xeon Co., Ltd.), which is a binder, and 1 weight of carboxymethyl cellulose (CMC), which is a thickener. The water and the appropriate amount of water, which is a dispersion medium, were stirred with a double-type coalescing machine to prepare a negative electrode mixture paste. The negative electrode mixture paste was applied to both surfaces of a strip-shaped negative electrode current collector made of copper foil having a thickness of 10 μm. The applied negative electrode mixture paste was dried and rolled with a rolling roll to form a negative electrode mixture layer. The total thickness of the negative electrode current collector and the negative electrode mixture layer supported on both surfaces thereof was 180 μm (the thickness of the mixture layer was 85 μm per side). The obtained electrode plate was cut out to the width which can be inserted into the cylindrical 18650 battery case, and the negative electrode was obtained. The active material density of the negative electrode mixture layer was 1.8 g / ml.

(Iii) Formation of porous heat resistant layer

100 parts by weight of magnesium oxide particles (average particle diameter 1.0 μm, BET specific surface area of 11.5 m 2 / g), 3 parts by weight of polyvinylidene fluoride (PVDF) as a binder, and an appropriate amount of NMP as a dispersion medium are medialess dispersers (Emtechnic). Manufactured creamixture), and the heat-resistant layer slurry was prepared. The heat resistant layer slurry was applied to the negative electrode, and the surface of the negative electrode mixture layer was covered with the heat resistant layer slurry. Thereafter, the applied heat-resistant layer slurry was dried to form a porous heat-resistant layer.

In addition, the average particle diameter was measured by micro track HRA (Nikki Sou Co., Ltd.) which is a laser diffraction particle size distribution analyzer. The BET specific surface area was measured by nitrogen adsorption multipoint method using ASAP2010 {Micromeritex, Shimadzu Corporation}.

The thickness of the porous heat resistant layer was measured, which was 3 m. Here, the weight of the porous heat resistant layer was measured with a fluorescent X-ray analyzer {RIGAKU}, and the weight was converted into thickness using a calibration curve.

In addition, the active material density of the negative electrode mixture layer was reduced to 1.7 g / ml by the application of the heat-resistant layer slurry.

(Iii) re-rolling of the cathode

The negative electrode carrying the porous heat resistant layer was again rolled with a rolling roll to adjust the total thickness of the negative electrode current collector and the negative electrode mixture layer supported on both surfaces thereof to 150 μm. Therefore, the active material density of the negative electrode mixture layer returned to 1.8 g / ml. At this time, the thickness of the porous heat resistant layer was 3 micrometers.

A 5 cm x 5 cm sample was cut out from the center of the re-rolled negative electrode and the weight of the sample was measured. From the weight of the sample, the weight of the negative electrode current collector and the negative electrode mixture layer determined in advance was subtracted, and the weight of the porous heat-resistant layer supported on the sample was obtained. On the other hand, the true Vt of the porous heat-resistant layer supported on the sample was calculated from the true density of the magnesium oxide particles and the true density of polyvinylidene fluoride as a binder. In addition, from the size of the sample and the thickness of the porous heat resistant layer, the external appearance volume Va of the porous heat resistant layer supported on the sample was obtained. It was 48% when the porosity P of the porous heat-resistant layer was calculated | required from solid Vt and external volume Va.

{P (%) = 100 (Va-Vt) / Va}.

(Iii) production of batteries

It demonstrates, referring drawings. Here, the cylindrical lithium ion secondary battery shown in FIG. 1 was produced.

First, the positive electrode lead 5a and the negative electrode lead 6a made of nickel were attached to the positive electrode 5 and the negative electrode 6, respectively. The positive electrode 5 and the negative electrode 6 were wound through a separator 7 to obtain a pole plate group. As the separator 7, a polypropylene porous film having a thickness of 20 µm was used. This electrode plate group was inserted in the cylindrical 18650 battery case 1 (18 mm in diameter, metal can with a cylindrical bottom of 65 mm in height). The upper insulating plate 8a was disposed on the upper surface of the electrode plate group, and the lower insulating plate 8b was disposed on the lower surface. Thereafter, the nonaqueous electrolyte was poured into the battery case 1.

As the non-aqueous electrolyte, a compound obtained by dissolving LiPF ₆ at a concentration of 1 mol / liter in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a weight ratio of 1: 3 was used.

After pouring the nonaqueous electrolyte, the opening of the battery case 1 was sealed with a sealing plate 2 in which an insulating gasket 3 was disposed around. Before sealing, the inlet sealing plate 2 and the positive electrode lead 5a were turned on. Thus, a lithium ion secondary battery with a nominal capacity of 2 Ah was completed.

Example 2

A lithium ion secondary battery was produced in the same manner as in Example 1 except that the average particle diameter of the magnesium oxide particles was 0.5 μm (BET specific surface area: 14.8 m 2 / g).

Example 3

A lithium ion secondary battery was produced in the same manner as in Example 1 except that the average particle diameter of the magnesium oxide particles was 1.5 μm (BET specific surface area: 8.6 m 2 / g).

Example 4

A lithium ion secondary battery was produced in the same manner as in Example 1 except that the average particle diameter of the magnesium oxide particles was 2 μm (BET specific surface area: 3.5 m 2 / g).

Comparative Example 1

A lithium ion secondary battery was produced in the same manner as in Example 1 except that the average particle diameter of the magnesium oxide particles was 2.5 μm (BET specific surface area: 2.7 m 2 / g).

Comparative Example 2

A lithium ion secondary battery was produced in the same manner as in Example 1 except that the average particle diameter of the magnesium oxide particles was 3 μm (BET specific surface area: 2.5 m 2 / g).

Comparative Example 3

A lithium ion secondary battery was produced in the same manner as in Example 1, except that the average particle diameter of the magnesium oxide particles was 2.5 μm, and the thickness of the porous heat resistant layer after re-rolling the negative electrode was 7.5 μm.

Comparative Example 4

A lithium ion secondary battery was produced in the same manner as in Example 1 except that the average particle diameter of the magnesium oxide particles was 3 μm and the thickness of the porous heat resistant layer after the negative electrode was re-rolled was 9 μm.

Comparative Example 5

In preparing the heat-resistant layer slurry, a lithium ion secondary battery was produced in the same manner as in Example 1 except that aluminum oxide particles (average particle diameter 1.0 µm, BET specific surface area 5.0 m 2 / g) were used instead of the magnesium oxide particles.

Comparative Example 6

In preparing the heat-resistant layer slurry, a lithium ion secondary battery was produced in the same manner as in Example 1 except that aluminum oxide particles (average particle diameter: 2.5 µm, BET specific surface area: 2.0 m 2 / g) were used instead of the magnesium oxide particles.

Comparative Example 7

In the preparation of the heat-resistant layer slurry, instead of magnesium oxide particles, aluminum oxide particles (average particle diameter 2.5 µm, BET specific surface area 2.0 m 2 / g) were used, and the thickness of the porous heat-resistant layer after re-rolling the negative electrode was 7.5 µm. A lithium ion secondary battery was produced in the same manner as in Example 1 except for the above.

Comparative Example 8

A lithium ion secondary battery was produced in the same manner as in Comparative Example 5 except that the negative electrode having a thick thickness was not re-rolled when forming the porous heat resistant layer.

[evaluation]

The following evaluation was performed about the battery of Examples 1-4 and Comparative Examples 1-8. Table 1 shows the evaluation results simultaneously with the active material density of the negative electrode mixture layer in the negative electrode after re-rolling, the porosity of the porous heat-resistant layer, and the surface state of the rolling roll used for re-rolling of the negative electrode.

<Insertability into battery case>

In the production of batteries except for Comparative Examples 3, 4 and 7, the evaluation was made as to whether or not the electrode plate group could be inserted smoothly when inserted into the battery case.

<2C discharge characteristic>

Each battery was subjected to two practice charges and discharges, and then stored in a 40 ° C environment for two days. Then, each battery was charged and discharged with the following pattern, and 2C discharge capacity in 0 degreeC was calculated | required.

(1) Constant current charge (20 degrees Celsius): 0.7CmA (final voltage 4.2V)

(2) Constant voltage charge (20 degrees Celsius): 4.2V (final current 0.05CmA)

(3) Constant current discharge (0 ° C): 2.0 CmA (final voltage 3 V)

However, the nominal capacity (2Ah) of the battery is 1 CmAh.

Next, each battery was charged and discharged in the following pattern to obtain a 2C discharge capacity at 20 ° C.

(1) Constant current charge (20 degrees Celsius): 0.7CmA (final voltage 4.2V)

(2) Constant voltage charge (20 degrees Celsius): 4.2V (final current 0.05CmA)

(3) Constant current discharge (20 ° C): 2.0 CmA (final voltage 3 V)

The ratio of the 2C discharge capacity at 0 ° C to the 2C discharge capacity at 20 ° C was determined as a percentage.

<Safety>

The following charging was performed about the battery after evaluating charge and discharge characteristic in 20 degreeC environment.

(1) Constant current charge (20 degrees Celsius): 0.7CmA (final voltage 4.25V)

(2) Constant voltage charge (20 degrees Celsius): 4.25V (final current 0.05CmA)

Under a 20 ° C environment, iron round nails with a diameter of 2.7 mm were penetrated at a rate of 5 mm / second from the side of the battery after charging. The arrival temperature after 90 second in the vicinity of the penetration part of a battery was measured.

Table 1

Example 5

A lithium ion secondary battery was produced in the same manner as in Example 2 except that the thickness of the porous heat resistant layer after the negative electrode was rerolled was 0.8 μm.

Example 6

A lithium ion secondary battery was produced in the same manner as in Example 2 except that the thickness of the porous heat resistant layer after the negative electrode was rerolled.

Example 7

A lithium ion secondary battery was produced in the same manner as in Example 2 except that the thickness of the porous heat resistant layer after the negative electrode was rerolled.

Example 8

A lithium ion secondary battery was produced in the same manner as in Example 2 except that the thickness of the porous heat resistant layer after the negative electrode was rerolled was 4 μm.

Example 9

A lithium ion secondary battery was produced in the same manner as in Example 2 except that the thickness of the porous heat resistant layer after the negative electrode was rerolled.

Example 10

A lithium ion secondary battery was produced in the same manner as in Example 2, except that the thickness of the porous heat resistant layer after the negative electrode was rerolled.

With respect to the batteries of Examples 5 to 10, 2C discharge characteristics and safety were evaluated as described above. The results are shown in Table 2.

TABLE 2

Examples 11-12, Comparative Examples 9-10

A lithium ion secondary battery was produced in the same manner as in Example 1 except that the BET specific surface area of the magnesium oxide particles was set to 2.7 m 2 / g, 3.5 m 2 / g, 14.8 m 2 / g or 18.0 m 2 / g.

With respect to the batteries of Examples 11 to 12 and Comparative Examples 9 to 10, 2C discharge characteristics and safety were evaluated in the same manner as above. The results are shown in Table 3.

TABLE 3

Examples 13-18

In the preparation of the heat-resistant layer slurry, lithium ions were prepared in the same manner as in Example 1 except that the amount of the binder per 100 parts by weight of magnesium oxide particles was changed to x parts by weight (x = 0.8, 1, 2, 4, 5 or 6). A secondary battery was produced.

With respect to the batteries of Examples 13 to 18, 2C discharge characteristics and safety were evaluated in the same manner as above. The results are shown in Table 4.

Table 4

Examples 19-25 and Comparative Examples 11-12

By changing the average particle diameter and BET specific surface area and shape of the magnesium oxide particles, the porosity of the porous heat-resistant layer after the re-rolling of the negative electrode was y% (y = 28, 30, 35, 40, 55, 60, 70, 73 Or a lithium ion secondary battery was produced similarly to Example 1 except having changed to 80).

With respect to the batteries of Examples 19 to 25 and Comparative Examples 11 to 12, 2C discharge characteristics and safety were evaluated in the same manner as above. The results are shown in Table 5.

Table 5

[Review]

(Average particle diameter and porosity of magnesium oxide particles)

The safety of the comparative examples 1 and 2 in which the average particle diameter of magnesium oxide particle | grains exceeded 2 micrometers was all favorable. However, in high-rate discharge (2C discharge) at low temperature (0 degreeC), the voltage drop was seen at the beginning of discharge, and discharge was hardly possible. This is considered to be because the load applied to each particle increases at the time of re-rolling because the average particle diameter is large. If the particles do not withstand the load and the fine powder is filled between the particles, the porosity is significantly reduced. This tendency becomes remarkable when the average particle diameter of magnesium oxide particle exceeds 2 micrometers. As the average particle diameter of magnesium oxide particles became smaller, the porosity of the porous heat resistant layer became larger. This improved the 2C discharge characteristics at low temperatures.

When aluminum oxide was used in place of magnesium oxide, relatively good characteristics were obtained, but numerous remarkable damages were formed on the surface of the rolling roll at the time of rerolling. This is because the hardness of aluminum oxide is higher than that of magnesium oxide.

Even when the average particle diameter of magnesium oxide was 0.5 µm, a porous heat-resistant layer having a high porosity was obtained by controlling the particle shape (Examples 24 and 25). In this case, safety could be ensured even at a porosity of 70%, but it was found that at 73%, the attained temperature after the nail penetration increased.

(Thickness of Porous Heat Resistant Layer)

When the thickness of the porous heat resistant layer was 0.8 μm (Example 5), the attained temperature, which is an index of safety, slightly increased. However, abnormal heating did not reach. In addition, since the porous heat resistant layer was thin, the 2C discharge characteristics at low temperatures were good. When the thickness of the porous heat-resistant layer was 6.0 µm (Example 10), the 2C discharge characteristic at low temperature was deteriorated even though the porosity was relatively high. This is because the porous heat resistant layer became a resistance. However, the deterioration of the 2C discharge characteristic is not large, and there is no problem.

(BET specific surface area of magnesium oxide)

The BET specific surface area of magnesium oxide has a correlation with the average particle diameter. When the BET specific surface area was 2.7 m 2 / g (Comparative Example 1), the average particle diameter exceeded 2.0 µm. Therefore, the porosity was lowered and the 2C discharge characteristic at low temperature was unsatisfactory. On the other hand, when BET specific surface area exceeded 15 m <2> / g, average particle diameter became smaller than 0.5 micrometer. Therefore, the porosity became excessively large at 80% and the safety was lowered.

(The amount of binder (PVDF) contained in the porous heat-resistant layer)

When the amount of binders per 100 parts by weight of magnesium oxide was less than 1 part by weight, the attained temperature serving as an index of safety was high and relatively significant heating was observed around 100 ° C. This is considered to be because the porous heat-resistant layer partially peeled from the cathode when forming the electrode plate group because the amount of the binder is small. In particular, near the edge of the cathode, defects in the porous heat resistant layer were likely to occur. When the amount of the binder per 100 parts by weight of magnesium oxide was more than 5 parts by weight, the negative electrode on which the porous heat resistant layer was formed became very hard. Therefore, when constructing the electrode plate group, a myriad of cracks entered into the porous heat resistant layer and peeling occurred.

Examples 26-28

In the preparation of the heat-resistant layer slurry, in place of PVDF, rubber particles {BM400B manufactured by Nihon Xeon Co., Ltd.} were used in an amount of 1 part by weight, 3 parts by weight, or 5 parts by weight per 100 parts by weight of magnesium oxide. Similarly, a lithium ion secondary battery was produced.

With respect to the batteries of Examples 26 to 28, 2C discharge characteristics and safety were evaluated in the same manner as above. The results are shown in Table 6.

Table 6

In Table 6, the evaluation result equivalent to Examples 14-17 is obtained in Examples 26-28. Therefore, it turns out that the effect of this invention is acquired regardless of the kind of binder contained in a porous heat resistant layer.

Example 29

A lithium ion secondary battery was produced in the same manner as in Example 1 except that the thickness of the porous heat resistant layer after the negative electrode was re-rolled was 15 µm and no separator was used.

Example 30

A lithium ion secondary battery was produced in the same manner as in Example 29 except that the average particle diameter of the magnesium oxide particles was 0.5 μm (BET specific surface area: 14.8 m 2 / g).

Example 31

A lithium ion secondary battery was produced in the same manner as in Example 29 except that the average particle diameter of magnesium oxide particles was 1.5 μm (BET specific surface area: 8.6 m 2 / g).

Example 32

A lithium ion secondary battery was produced in the same manner as in Example 29 except that the average particle diameter of magnesium oxide particles was 2 μm (BET specific surface area: 3.5 m 2 / g).

Comparative Example 13

A lithium ion secondary battery was produced in the same manner as in Example 29 except that the average particle diameter of the magnesium oxide particles was 2.5 μm (BET specific surface area: 2.7 m 2 / g).

Comparative Example 14

A lithium ion secondary battery was produced in the same manner as in Example 29 except that the average particle diameter of the magnesium oxide particles was 3 μm (BET specific surface area: 2.5 m 2 / g).

With respect to the batteries of Examples 29 to 32 and Comparative Examples 13 to 14, 2C discharge characteristics and safety were evaluated in the same manner as above. The results are shown in Table 7.

TABLE 7

From Table 7, it can be seen that even when the porous heat-resistant layer formed thick is used in place of the separator, a particularly good result is obtained in the range of the average particle diameter of the magnesium oxide particles in the range of 0.5 to 2 m.

The present invention is particularly useful in nonaqueous electrolyte secondary batteries in which high energy density is required. The present invention is particularly useful in nonaqueous electrolyte secondary batteries that require good discharge characteristics and safety. The present invention is also effective for reducing costs required for manufacturing equipment.

INDUSTRIAL APPLICABILITY The present invention can be applied to various nonaqueous electrolyte secondary batteries, and includes, for example, a nonaqueous electrolyte serving as a power source for driving a consumer electronic device, a portable information terminal, a portable electronic device, and a portable device such as a wireless device. Applicable to secondary batteries. In addition, the present invention can be applied to power sources such as small electric power storage devices, motorcycles, electric vehicles, hybrid electric vehicles, and the like.

The shape of the battery is not particularly limited, and the present invention can be used in any of shapes such as a coin shape, a button shape, a sheet shape, a cylindrical shape, a flat shape, and a square shape. The form of the electrode plate group is not limited, for example, the present invention can be used in any of forms such as a wound type and a laminated type. The size of the battery is not limited, and the present invention can be used for any size, such as small size, medium size, and large size.

Claims (6)

A positive electrode, a negative electrode, a porous heat-resistant layer interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte, wherein the negative electrode includes a negative electrode current collector and a negative electrode mixture layer supported on the surface of the negative electrode current collector; , The porous heat resistant layer is supported on the cathode, The porous heat-resistant layer comprises magnesium oxide particles, The average particle diameter of the said magnesium oxide particle is 0.5 micrometer-2 micrometers, The nonaqueous electrolyte secondary battery whose active material density of the said negative electrode mixture layer is 1.5 g / ml-1.8 g / ml. The nonaqueous electrolyte secondary battery according to claim 1, further comprising a separator between the anode and the cathode, wherein the porous heat resistant layer has a thickness of 1 µm to 5 µm. The nonaqueous electrolyte secondary battery according to claim 1, wherein the porous heat resistant layer has a thickness of 2 µm to 15 µm without a separator between the anode and the cathode. The nonaqueous electrolyte secondary battery according to claim 1, wherein a BET specific surface area of the magnesium oxide particles is 3 m 2 / g to 15 m 2 / g. The nonaqueous electrolyte secondary battery according to claim 1, wherein the porous heat resistant layer contains 1 part by weight to 5 parts by weight of a binder per 100 parts by weight of the magnesium oxide particles. The nonaqueous electrolyte secondary battery according to claim 1, wherein the porous heat resistance layer has a porosity of 30% to 70%.

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