JP4827117B2 - Nonaqueous battery and manufacturing method thereof - Google Patents

Description

  The present invention relates to a non-aqueous battery, and more particularly to a non-aqueous battery particularly suitable for use as a power source for portable electronic devices, electric vehicles, road leveling and the like.

  Lithium ion batteries, which are a type of non-aqueous battery, are widely used as power sources for portable devices such as mobile phones and notebook personal computers because of their high energy density. As the performance of portable devices increases, the capacity of lithium ion batteries tends to increase further, and ensuring safety is important.

  In the current lithium ion battery, as a separator (separating material) interposed between the positive electrode and the negative electrode, for example, a polyolefin-based porous film having a thickness of about 20 to 30 μm is used. In addition, as a separator material, the constituent resin of the separator is melted below the thermal runaway temperature of the battery to close the pores, thereby increasing the internal resistance of the battery and improving the safety of the battery in the event of a short circuit. In order to secure a so-called shutdown effect that improves, polyethylene having a low melting point may be applied.

  By the way, since the separator of a polyolefin-type porous film is a film | membrane which exists independently, intensity | strength is requested | required to such an extent that it can handle at the time of battery manufacture. In particular, when an electrode is used as a wound body, a tension is applied to the separator at the time of manufacturing (winding), so that the tensile strength needs to be sufficiently high.

  As such a separator, for example, a uniaxially stretched or biaxially stretched film is used to increase the porosity and strength, but the film is distorted by such stretching, and when this is exposed to a high temperature, There is a problem that shrinkage occurs due to residual stress. The shrinkage temperature is very close to the melting point, ie the shutdown temperature. For this reason, when a polyolefin-based porous film separator is used, when the battery temperature reaches the shutdown temperature in the case of abnormal charging, the current must be immediately decreased to prevent the battery temperature from rising. This is because if the pores are not sufficiently closed and the current cannot be reduced immediately, the battery temperature easily rises to the contraction temperature of the separator, and there is a risk of ignition due to an internal short circuit.

  In addition, a composite film is used as a separator instead of a single film having a single layer structure as described above to solve the problem of internal short circuit due to the shrinkage of the separator when the battery becomes hot. Since it is difficult to reduce the thickness of the composite film, there is a problem that the manufacturing process is complicated and the manufacturing cost is increased in addition to an obstacle to improving the load characteristics.

  In view of these circumstances, the tensile strength required for the separator is formed by directly forming the separator on the electrode surface to separate the positive electrode and the negative electrode, instead of using a film that can exist alone as described above. Attempts have been made to solve the above-mentioned problems relating to (tensile strength for ensuring handleability during battery production) and thermal contraction of the separator (Patent Documents 1 to 3). The batteries disclosed in Patent Documents 1 to 3 have a separator formed using various organic fine particles and inorganic fine particles and a binder resin.

Japanese Patent Laid-Open No. 1-167948 WO 98/38688 pamphlet JP 2000-149906 A

  However, the batteries disclosed in Patent Documents 1 to 3 are satisfactory in terms of reliability, for example, an internal short circuit is likely to occur when the temperature inside the battery becomes high, and the above-described shutdown effect cannot be obtained. is not.

  The present invention has been made in view of the above circumstances, and provides a non-aqueous battery that can ensure safety at high temperatures, and in particular, a non-aqueous battery that also realizes improved load characteristics due to a thinner separator, It is an object to provide a method for manufacturing these nonaqueous batteries.

The non-aqueous battery of the present invention capable of ensuring safety at high temperature includes a positive electrode, a negative electrode using a material capable of occluding and releasing lithium, lithium alloy or lithium ion as a negative electrode active material, and the positive electrode and the negative electrode. Having a porous separator in between, the separator is formed on the surface of at least one of a positive electrode and a negative electrode, and organic fine particles (A) having a melting point of 80 to 150 ° C .; At least two kinds of fine particles including a heat resistant fine particle (B) having a heat resistant temperature of 160 ° C. or higher are bound by a binder resin (C), and the heat resistant fine particles ( B) is 4% by mass or more, the binder resin (C) is 1.6% by mass to 13.3% by mass, and the battery is supplied at a rate of 1 ° C./min from 30 ° C. to 150 ° C. When the temperature is raised at 0 ° C., the internal resistance of the battery at 80 ° C. and 130 ° C., when the _{R 30, R 80} and _{R 130, respectively, R} 80 _/ R ₃₀ ≦ 1 _and, to a _R 130 _/ R ₃₀ ≧ 5 It is a nonaqueous battery characterized by.

Furthermore, in the present invention, in producing the nonaqueous battery of the present invention, the organic fine particles (A) having a melting point of 80 to 150 ° C. and a heat resistant temperature of 160 ° C. or higher are formed on the surface of at least one of the positive electrode and the negative electrode. A manufacturing method characterized by forming a porous separator between the positive electrode and the negative electrode by applying and drying a liquid composition containing the heat-resistant fine particles (B) having a binder and the binder resin (C) Is included.

  In the present invention, the separator for interposing between the positive electrode and the negative electrode has a configuration in which the internal resistance clearly changes in a specific temperature range and causes a shutdown, thereby ensuring the safety of the battery at a high temperature. be able to.

  In particular, it is composed of at least two kinds of fine particles of organic fine particles (A) having a melting point of 80 to 150 ° C. and heat resistant fine particles (B) having a heat resistant temperature of 160 ° C. or higher, or on the surface of the heat resistant fine particles (B). Strength (such as tensile strength) of a conventional single membrane separator is required by comprising at least one kind of fine particles including fine particles of a core-shell structure in which a coating layer of a resin having a melting point of 80 to 150 ° C. is formed. Therefore, the thickness of the battery can be reduced to improve the load balance of the battery.

  When the temperature in the battery rises, the surface coating layer of the organic fine particles (A) or the core-shell structured fine particles melts and closes the pores, so that a shutdown function is exhibited, while the presence of the heat-resistant fine particles (B) Since the separator is difficult to shrink, internal short circuit of the battery can be prevented.

  Further, by forming the separator directly on the surface of at least one of the positive electrode and the negative electrode, a further reduction in thickness can be realized.

  The separator according to the nonaqueous battery of the present invention is composed of at least two kinds of fine particles, that is, organic fine particles (A) having a melting point of 80 to 150 ° C. and heat resistant fine particles (B) having a heat resistant temperature of 160 ° C. or higher. . FIG. 1 shows a drawing-substituting photograph (scanning cell micrograph) of the separator according to the present invention, and FIG. 2 shows an enlarged photograph of a part of the separator shown in FIG. 1 and 2, 1 is an organic fine particle (A), 2 is a heat-resistant fine particle (B), 3 is a binder resin (C), 4 is an electrode, and 5 is a separator. As can be seen from FIGS. 1 and 2, in the separator, organic fine particles (A) 1 and heat-resistant fine particles (B) 2 are present in the form of fine particles. As will be described in detail later, the separator shown in FIGS. 1 and 2 is preferably formed using a liquid composition (solution or dispersion) containing organic fine particles (A) and heat-resistant fine particles (B).

  The organic fine particles (A) are fine particles of an organic resin having a melting point of 80 ° C to 150 ° C. The organic fine particles (A) are components for ensuring a shutdown effect such as melting when the temperature in the battery rises, closing the pores of the separator, and increasing the internal resistance of the battery.

  As will be described in detail later, the separator is formed using a liquid composition (solution or dispersion) containing organic fine particles (A) and heat-resistant fine particles (B). Therefore, the organic fine particles (A) are particularly limited as long as the melting point is within the above range, is electrochemically stable, and is stable with respect to the solvent (dispersion medium) used in the electrolytic solution and the liquid composition. For example, polyolefin fine particles are suitable. More specifically, fine particles such as polyethylene, ethylene-vinyl acetate copolymer (vinyl acetate-derived structural unit is less than 15 mol%), or derivatives thereof are preferable. You may mix and use the above. Further, in order to set the shutdown temperature to be somewhat higher than the actual use temperature of the battery, the melting point of the organic fine particles (A) is more preferably 90 ° C. or higher, and a safer temperature range, for example, 130 ° C. or lower. In order to cause shutdown at a temperature of 1, the melting point of the organic fine particles (A) is more preferably 125 ° C. or lower. As such a material, the said material is used suitably. In addition, melting | fusing point of organic fine particle (A) here means the melting temperature measured using a differential scanning calorimeter (DSC) according to the prescription | regulation of JIS-K7121.

  As the size of the organic fine particles (A), it is desirable that the particle size is smaller than the thickness of the separator, but for example, it has an average particle size of 3/4 to 1/100 of the thickness of the separator. More specifically, it is desirable that the number average particle diameter is 0.1 to 20 μm. If the organic fine particles (A) are too small, the gaps between the fine particles are small, so that the ionic conductivity may be reduced and the battery characteristics may be deteriorated. On the other hand, if the organic fine particles (A) are too large, it is difficult to make the separator thin, and this may also cause a decrease in battery characteristics (capacity reduction).

  Moreover, it is preferable that the particle size of the organic fine particles (A) is as uniform as possible. This is because if the particle sizes are not uniform, small particles are likely to enter between the large particles and the porosity tends to decrease. Specifically, the particle diameter is preferably in the range of 0.1 to 20 μm, and the average particle diameter is preferably 0.3 to 15 μm. In addition, the number average particle diameter and the particle size distribution relating to the organic fine particles (A) described in the present specification, the heat-resistant fine particles (B) described later, and the fine particles of the core-shell structure are laser scattering particle size distribution diameters (“LA-” manufactured by HORIBA) 920 ") and measured by dispersing fine particles in toluene.

  The heat-resistant fine particles (B) are fine particles having a heat-resistant temperature of 160 ° C. or higher, for example, fine particles having a heat deformation temperature of 160 ° C. or higher when measured by the JIS-K7191 method or having no heat deformation temperature. It is a component that plays the role of maintaining the shape of the separator at a high temperature and preventing internal short circuit when the temperature in the battery rises. The heat-resistant fine particles (B) do not flow at a temperature lower than 160 ° C., are non-electrically conductive, and are electrochemically stable, and further with respect to the solvent (dispersion medium) used in the electrolytic solution and the liquid composition. There is no particular limitation as long as it is stable. For example, non-electrically conductive inorganic fine particles (inorganic powder), organic fine particles (organic powder) having a melting point of 160 ° C. or higher, and crosslinked polymer fine particles are exemplified. Here, “organic fine particles having a melting point of 160 ° C. or higher” means organic fine particles having a melting temperature measured using DSC of 160 ° C. or higher in accordance with JIS-K7121. .

Examples of non-electrically conductive (electrically insulating) inorganic fine particles include oxide fine particles such as iron oxide, SiO ₂ , Al ₂ O ₃ , TiO ₂ , and BaTiO ₂ ; nitride fine particles such as aluminum nitride and silicon nitride; Insoluble ion crystal fine particles such as calcium fluoride, barium fluoride and barium sulfate; Covalent crystal fine particles such as silicon and diamond; Clay fine particles such as montmorillonite; Further, the surface of conductive fine particles such as metal fine particles; oxide fine particles such as SnO ₂ and tin-indium oxide (ITO); carbon fine particles such as carbon black and graphite; Surface treatment with the above-mentioned materials constituting non-conductive inorganic fine particles, organic fine particles having a melting point of 160 ° C. or higher, and materials constituting cross-linked polymer fine particles, etc. Fine particles may be used.

  Examples of the organic fine particles having a melting point of 160 ° C. or higher include fine particles of polypropylene, polystyrene, polyamide, polyester, etc., and the crosslinked polymer fine particles include crosslinked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, styrene. -Fine particle | grains, such as a divinylbenzene copolymer crosslinked material, a polyimide, a melamine resin, a phenol resin, a benzoguanamine-formaldehyde condensate, can be illustrated. In addition, the organic resin (polymer) constituting these organic fine particles and crosslinked polymer fine particles may be a mixture, modified product, derivative, or copolymer (random copolymer, alternating copolymer, block copolymer) of the materials exemplified above. Polymer, graft copolymer), and crosslinked body (for materials other than the above-mentioned crosslinked polymer).

  As the heat-resistant fine particles (B), the fine particles exemplified above may be used singly or as a mixture of two or more.

  The size of the heat-resistant fine particles (B) is preferably smaller than the thickness of the separator, as with the size of the organic fine particles (A). For example, the number average particle size is preferably 0.001 μm or more. Is 0.1 μm or more, 15 μm or less, more preferably 1 μm or less. If the heat-resistant fine particles (B) are too small, the gaps between the fine particles are small, so that the ionic conductivity is lowered, which may cause deterioration of battery characteristics. On the other hand, if the heat-resistant fine particles (B) are too large, it is difficult to make the separator thin, which may cause a decrease in battery characteristics (capacity reduction).

  Moreover, it is preferable that the heat resistant fine particles (B) have the same particle diameter as possible for the same reason as the organic fine particles (A). Specifically, the particle size is in the range of 0.1 to 20 μm, and the average particle size is more preferably 0.3 to 15 μm.

  As the composition of the organic fine particles (A) and the heat-resistant fine particles (B) constituting the separator, the heat-resistant fine particles (B) are 4% by mass or more, more preferably 10% by mass or more in the total amount of the material of the separator, It is desirable that the content be 74% by mass or less, more preferably 50% by mass or less.

  By containing 4% by mass or more of the heat-resistant fine particles (B), the effect of preventing the occurrence of an internal short circuit when the temperature inside the battery becomes high is enhanced, while the ratio of the heat-resistant fine particles (B) is 74% by mass or less. This is because the shutdown function is easily developed in a shorter time.

In the separator of the present invention, the third component binder resin (C) is used for the purpose of firmly binding the organic fine particles (A) and the heat-resistant fine particles (B). The binder resin (C) is not particularly limited as long as the fine particles can be satisfactorily adhered, is electrochemically stable, and is stable with respect to the solvent (dispersion medium) used in the electrolytic solution and the liquid composition. For example, polyolefin fine particles are suitable as the organic fine particles (A). Therefore, from the viewpoint of improving adhesiveness, a resin having a polyethylene structure (methylene chain) in the molecule is suitable. Specifically, ethylene-vinyl acetate copolymer (the structural unit derived from vinyl acetate is 15 mol% or more, more preferably 30 mol% or less), ethylene-acrylate copolymer (ethylene-methyl acrylate copolymer, Ethylene-ethyl acrylate copolymer, etc.). Fluorine rubber can also be used. These binder resins can be used alone or in admixture of two or more for the binder resin (C).

  Further, the amount of the binder resin (C) is 2% by mass or more, more preferably 5% by mass or more, and 30% by mass or less, more preferably 20% by mass or less, in all materials constituting the separator. It is desirable. By containing 2% by mass or more of the binder resin (C), the binding effect of the fine particles constituting the separator is enhanced. On the other hand, by setting it to 30% by mass or less, the pores of the separator are blocked and the battery characteristics are impaired. Can be prevented from occurring.

As another form of the separator related to the nonaqueous battery, a heat resistance of 160 ° C. or higher is used instead of the organic fine particles (A) and the heat resistant fine particles (B), or together with the organic fine particles (A) or the heat resistant fine particles (B). Fine particles having a core-shell structure in which a resin coating layer having a melting point of 80 to 150 ° C. is formed on the surface of the heat-resistant fine particles (B) having a temperature can also be used.

  As the material constituting the coating layer, the same material as the organic fine particles (A) can be used, and the melting point is preferably 90 ° C. or higher, and preferably 125 ° C. or lower.

  The core-shell structured fine particles are prepared by mixing the heat-resistant fine particles (B) and a resin having a melting point of 80 to 130 ° C. in a solvent capable of dissolving the resin at a temperature equal to or higher than the melting point of the resin, cooling, and spray drying. It can be obtained by removing the solvent.

  Solvents that can dissolve the resin include hydrocarbon-based alkane-based or alkyne-based solvents such as n-hexane, n-pentane, n-heptane, octane, nonane, and decane; ketones such as cyclohexanone; toluene; xylene; Is mentioned.

  The size of the core-shell structured fine particles is preferably smaller than the thickness of the separator, but for example, has an average particle size of 3/4 to 1/100 of the thickness of the separator. More specifically, it is desirable that the number average particle diameter is 0.1 to 20 μm. If the core-shell structured microparticles are too small, the gap between the microparticles becomes small, so that the ionic conductivity may decrease, which may cause a decrease in battery characteristics. On the other hand, if the core-shell structured particles are too large, it is difficult to make the separator thin, and this may also cause a decrease in battery characteristics (capacity reduction).

  Moreover, it is preferable that the particle diameters of the core-shell structured fine particles are as uniform as possible. This is because if the particle sizes are not uniform, small particles are likely to enter between the large particles and the porosity tends to decrease. Specifically, the particle size is in the range of 0.1 to 20 μm, and the average particle size is more preferably 0.3 to 15 μm.

  In the case where the core-shell structured fine particles are used, the separator in the present invention can be constituted only by the core-shell structured fine particles, but may be used together with the organic fine particles (A) or the heat-resistant fine particles (B). The proportion of the core-shell structured fine particles in the total amount of the separator is preferably 4% by mass or more, more preferably 26% by mass or more, and desirably 90% by mass or less. Further, in order to firmly bind the core-shell structured fine particles, the third component binder resin (C) may be used in the same manner as described above.

In a non-aqueous battery, the organic fine particles (A) used as a component of the separator or the resin constituting the coating layer of the core-shell structured fine particles melt at their respective melting points to form pores in the separator. It has a so-called shutdown effect in which the internal resistance of the battery is increased by being blocked.

  Furthermore, since the separator is formed directly on the electrode, heat generated at the electrode in the event of an abnormality is directly conducted to the separator, so that the melting occurs quickly and the shutdown function is manifested in a short time.

In the present invention, the shutdown function can be evaluated by a change in internal resistance corresponding to a change in battery temperature. For example, when the temperature is raised from 20 ° C. to 150 ° C. at a rate of 1 ° C./min, 30 A battery satisfying R ₈₀ / R ₃₀ ≦ 1 and R ₁₃₀ / R ₃₀ ≧ 5 when the internal resistance of the battery at R ° C., 80 ° C. and 130 ° C. is R ₃₀ , R ₈₀ and R ₁₃₀ , respectively, Since the internal resistance does not increase due to shutdown at the actual operating temperature of the battery and the internal resistance increases due to shutdown in the safer temperature range of 130 ° C or lower, the safety of the battery is sufficiently secured. More preferred in the invention. The value of R ₁₃₀ / R ₃₀ is preferably as large as possible, preferably 10 or more, and more preferably 30 or more.

  Also, when measuring changes in the internal resistance of a battery under the above conditions, evaluate the shutdown function from the temperature at which the internal resistance begins to rise and the slope of the internal resistance in the region where the internal resistance increases rapidly. You can also. That is, as shown in FIG. 3 showing a change in internal resistance of the battery of Example 5 to be described later, a “gradual decrease region” in which the internal resistance gradually decreases with the temperature from around room temperature, and then suddenly after the internal resistance starts to increase. When the internal resistance change of the “rising region” that increases is approximated by a straight line, and the intersection is defined as “temperature at which the internal resistance begins to rise”, the temperature is in the range of 80 ° C. to 130 ° C. It is desirable that the slope (unit: Ω / ° C) of the approximate straight line at 1 is 1 or more.

  The temperature at which the internal resistance begins to rise is more preferably 90 ° C. or higher in order to widen the practical temperature range of the battery, while it is 120 ° C. or lower in order to make the shutdown temperature safer. It is more desirable that the temperature is 115 ° C. or lower.

  Further, the slope of the approximate straight line with respect to the temperature in the rising region is more preferably 2 or more, more preferably 3 or more, since the shutdown effect becomes clearer as it becomes steeper.

  In addition, when the melting point of the organic fine particles (A) or the melting point of the resin coating the surface of the core-shell structured fine particles is 110 ° C. or lower, the shutdown function works at a safer temperature of 115 ° C. or lower, which greatly increases the safety of the battery. improves.

Furthermore, it is desirable that the shrinkage of the separator when the battery is held at 150 ° C. for 60 minutes after the temperature rise is suppressed to 5% or less. This makes it difficult for the battery to be short-circuited after the shutdown function has been activated, thereby greatly improving the safety of the battery at high temperatures. In addition, since the separator does not shrink, the internal resistance of the battery is kept high even in the high temperature state after shutdown, so even if the battery is accidentally short-circuited externally, the charged battery gradually discharges. , You can move to a safer state. Of course, even if it discharges intentionally, it can change to a discharge state safely. Here, when the internal resistance of the battery when the temperature is raised to 150 ° C. is R ₁₅₀ , R ₁₅₀ / R ₃₀ is desirably 4 or more, more desirably 8 or more, and desirably 25 or more. Most desirable. Note that the shrinkage rate is a change in the length of the separator. If the shape is a strip, it may be obtained from a change in the length of the long side, and if it is circular, it may be obtained from a change in diameter. In addition, such a shrinkage rate can also be ensured by having the separator described above and below.

  In the present invention, in addition to the separator, a conventionally known separator such as an ion-permeable and electronic insulating microporous film may be used in combination. As such a separator, a microporous film mainly composed of a material selected from polypropylene, polyaramid, polyester, and polyimide is preferably used.

  Further, the separator may contain an electrically insulating fibrous substance that does not substantially deform at 150 ° C. and does not substantially chemically change in the non-aqueous electrolyte. Examples of such fibrous materials include cellulose, cellulose modified material, polypropylene, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyaramid, polyamideimide, polyimide, glass, alumina, silica, and the like. It is preferable to use at least one selected from the above. The term “fibrous” as used herein refers to a substance having an aspect ratio of particles of 4 or more. The diameter of the fibrous substance is desirably equal to or less than the thickness of the separator, but more preferably 0.01 to 5 μm. This is because, by setting the thickness to 0.01 μm or more, the size of the gap of the separator becomes appropriate and the ion permeability is good. By setting the thickness to 5 μm or less, the fibers are entangled with each other, and the strength of the separator is increased. This is because the effect of improvement is increased.

  In addition, the thickness of the separator is desirably determined in view of the surface roughness of the electrode, and it is recommended that the thickness is preferably at least twice the surface roughness of the electrode (the difference between the concave and convex portions). . Specifically, for example, the total thickness (when the separator is formed on both surfaces of the positive electrode and the negative electrode, the total thickness) is 3 μm or more, more preferably 5 μm or more, and 50 μm or less. The thickness is preferably 30 μm or less, more preferably 20 μm or less. If the separator is too thin, it may be difficult to sufficiently cover the convex portions of the electrode, which may cause a short circuit. On the other hand, if the separator is too thick, it may be difficult to increase the energy density of the battery. The thickness of the separator is about 5000 to 10,000 times with a scanning electron microscope for a sample obtained by cutting a section in the thickness direction of the separator and evaporating Au or the like together with the electrode on which the separator is formed. The thickness measured by observation.

Next, other elements constituting the nonaqueous battery of the present invention will be described. The non-aqueous battery of the present invention includes a primary battery and a secondary battery, and the configuration of a secondary battery, which is a main application, will be exemplified below. The positive electrode is not particularly limited as long as it is a positive electrode used in a conventionally known nonaqueous battery. For example, a lithium-containing transition metal oxide having a layered structure represented by Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, etc.) as an active material; LiMn ₂ O ₄ LiMn oxide such as LiMn ₂ O ₄ , LiMn _x M _(1-x) O _{2 in} which part of Mn is substituted with other elements; olivine type LiMPO ₄ (M: Co, Ni, Mn, Fe); LiMn _0.5 Ni _0.5 O ₂ ; Li _{(1 + a)} Mn _x Ni _y Co _(1-xy) O ₂ (−0.1 <a <0.1, 0 <x <0.5, 0 < y <0.5); can be applied to these positive electrode active materials, binders such as known conductive assistants (carbon materials such as carbon black) and polyvinylidene fluoride (PVDF), etc. A positive electrode mixture to which is added as appropriate, with the current collector as the core material What was finished on the body can be used.

Among them, a material containing Mn as a constituent element is suitable for enhancing the safety of the active material itself, and the above Li _{(1 + a)} Mn _x Ni _y Co _{(1-x− )} containing Mn and Ni at about 1: 1. _y) O ₂ (where −0.05 ≦ x−y ≦ 0.05), this compound, a lithium-containing transition metal oxide having a spinel structure such as LiMn ₂ O _4, or a lithium-containing transition having a layered structure such as LiCoNiO ₂ Although a mixture with a metal oxide can be preferably used, sufficiently good results can be obtained by the present invention even with LiCoO ₂ which is generally used in general.

  As the current collector of the positive electrode, a metal foil such as aluminum, a punching metal, a net, an expanded metal, or the like can be used. Usually, an aluminum foil having a thickness of 10 to 30 μm is preferably used.

  The lead portion on the positive electrode side is normally provided by leaving the exposed portion of the current collector without forming the positive electrode mixture layer on a part of the current collector and forming the lead portion at the time of producing the positive electrode. However, the lead portion is not necessarily integrated with the current collector from the beginning, and may be provided by connecting an aluminum foil or the like to the current collector later.

  The negative electrode is not particularly limited as long as it is a negative electrode used in a conventionally known nonaqueous battery. For example, carbon that can occlude and release lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers as active materials One type or a mixture of two or more types of system materials is used. In addition, elements such as Si, Sn, Ge, Bi, Sb, In and their alloys, lithium-containing nitrides, oxides and other compounds that can be charged and discharged at a low voltage close to lithium metal, or lithium metals and lithium / aluminum alloys Can also be used as a negative electrode active material. A negative electrode mixture prepared by appropriately adding a conductive additive (carbon material such as carbon black) or a binder such as PVDF to these negative electrode active materials and using a current collector as a core material is used. In addition, the above-described various alloys and lithium metal foils may be used alone or formed on a current collector.

  When a current collector is used for the negative electrode, a copper or nickel foil, a punching metal, a net, an expanded metal, or the like can be used as the current collector, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is preferably 5 μm.

  As with the lead portion on the positive electrode side, the lead portion on the negative electrode side usually leaves an exposed portion of the current collector without forming a negative electrode mixture layer on a part of the current collector during the preparation of the negative electrode. It is provided by making it a part. However, the negative electrode side lead portion is not necessarily integrated with the current collector from the beginning, and may be provided by connecting a copper foil or the like to the current collector later.

Examples of the electrolyte include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propionate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, ethylene glycol sulfite, 1,2-dimethoxyethane, 1,3- dioxolane, tetrahydrofuran, 2-methyl - tetrahydrofuran, organic solvent consists of only one type, such as diethyl ether or a mixture of two or more solvents, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 _{SO 3, LiCF 3 CO 2,} Li 2 C 2 F 4 (SO 3) 2, LiN (CF 3 SO 2) 2, LiC (CF 3 SO 2) 3, LiC n F 2n + 1 SO 3 (n ≧ 2) LiN (RfOSO _{2) 2} [wherein Rf is a fluoroalkyl group] which was prepared by dissolving at least one selected from lithium salts such as are used. The concentration of the lithium salt in the electrolytic solution is preferably 0.5 to 1.5 mol / l, and more preferably 0.9 to 1.25 mol / l.

  Examples of the form of the non-aqueous battery of the present invention include a rectangular battery and a cylindrical battery using a steel can, an aluminum can or the like as an exterior material, and a soft package battery using a laminated film deposited with a metal as an exterior material. It can also be.

Next, the manufacturing method of the nonaqueous battery of this invention is demonstrated. The separator is formed on the surface of at least one of the positive electrode and the negative electrode (at least one of the surfaces facing each other in the battery). The separator is prepared by preparing a liquid composition containing organic fine particles (A), heat-resistant fine particles (B) and a binder resin (C), and applying or casting the liquid composition on at least one surface of the positive electrode and the negative electrode. It is formed by removing the solvent (dispersion medium) in the composition by drying.

  The liquid composition for forming the separator is a dispersion (slurry) because it contains organic fine particles (A) and heat-resistant fine particles (B) as fine particles. As the solvent (dispersion medium) used in the liquid composition, those capable of uniformly dissolving or dispersing the binder resin (C) are preferable, and for example, toluene, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone and the like are preferable.

  After forming the separator, the positive electrode and the negative electrode are overlapped with each other through the separator to form a laminated electrode body, or the stacked positive electrode and negative electrode are further wound to form a wound electrode body (hereinafter referred to as a laminated electrode body and a wound body). The electrode bodies are collectively referred to as “electrode bodies”). Then, the electrode body is loaded into the exterior material, and after the electrolyte is injected, the exterior material is sealed to obtain a nonaqueous battery.

In the non-aqueous battery thus obtained, before the internal temperature rises to reach the thermal runaway temperature, the coating layer of the organic fine particles (A) or the fine particles of the core shell structure is melted to block the pores of the separator. In addition, combined with the presence of the heat-resistant fine particles (B), a very good shutdown effect can be obtained.

  In the present invention, as described above, the separator is preferably formed directly on the surface of at least one of the positive electrode and the negative electrode. When the electrode and separator are separated, there is a liquid layer of electrolyte between the electrode and separator, so heat generated at the electrode when an abnormality such as a short circuit occurs indirectly passes through the liquid layer to the separator. This is because if the separator is formed directly on the electrode, the heat generated in the electrode is directly transmitted to the separator, so that a battery having excellent shutdown response can be configured.

  In addition, since the separator in the present invention is not stretched like a conventional separator made of a single membrane, it does not easily shrink at high temperatures, and the nonaqueous battery of the present invention is 30 ° C. at a temperature of 150 ° C. Even if held for more than a minute, the state in which the separator remains covering the electrode surface can be maintained. For this reason, an internal short circuit can be sufficiently prevented.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples are not intended to limit the present invention, and all modifications made without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention.

Example 1
<Preparation of positive electrode>
LiCoO _{2 as a} positive electrode active material: 80 parts by mass, acetylene black as a conductive additive: 10 parts by mass, and PVDF as a binder: 5 parts by mass uniformly using N-methyl-2-pyrrolidone (NMP) as a solvent It mixed so that positive electrode mixture containing paste might be prepared. This paste was intermittently applied to both sides of an aluminum foil having a thickness of 15 μm serving as a current collector so that the active material application length was 281 mm on the front surface and 212 mm on the back surface. The thickness of the positive electrode mixture layer was adjusted to 150 μm and cut to a width of 43 mm to produce a positive electrode having a length of 281 mm and a width of 43 mm. Further, the exposed portion of the aluminum foil of the positive electrode was tabbed.

<Production of negative electrode>
A negative electrode mixture-containing paste was prepared by mixing 90 parts by mass of graphite as a negative electrode active material and 5 parts by mass of PVDF as a binder so as to be uniform using NMP as a solvent. This negative electrode mixture-containing paste was intermittently applied on both sides of a 10 μm-thick current collector made of copper foil so that the active material application length was 287 mm on the front surface and 228 mm on the back surface, dried, and then subjected to calendar treatment. The thickness of the negative electrode mixture layer was adjusted so that the total thickness was 142 μm, and the negative electrode mixture layer was cut to have a width of 45 mm to produce a negative electrode having a length of 287 mm and a width of 45 mm. Further, a tab was attached to the exposed portion of the copper foil of the negative electrode.

<Formation of isolation material>
As binder resin (C), ethylene-vinyl acetate copolymer (the structural unit derived from vinyl acetate is 34 mol%, manufactured by Nippon Unicar Co., Ltd.): 100 g and toluene: 6 kg are put in a container and brought to room temperature until evenly dissolved. And stirred. Further, as organic fine particles (A), polyethylene powder [“Flow Beads LE1080 (trade name)” manufactured by Sumitomo Seika Co., Ltd.]: 3 kg was added in 4 portions, and dispersed with stirring with a disper at 2800 rpm for 1 hour. It was. Further, as heat-resistant fine particles (B), alumina (Al ₂ O ₃ ) fine particles [“Sumiko Random AA04 (trade name)” manufactured by Sumitomo Chemical Co., Ltd.]]: 300 g is added, and dispersed by stirring with a disper at 2800 rpm for 3 hours. A uniform slurry was obtained to obtain a liquid composition for forming a separator. The slurry was applied by sliding on the negative electrode with a gap of 50 μm, and then toluene was removed to form a separator with a thickness of 15 μm on the negative electrode surface.

The positive electrode obtained as described above and the negative electrode on which the separator is formed are overlapped with the separator interposed therebetween, loaded inside the Dainippon Printing laminate film exterior material, and an electrolyte solution (ethylene carbonate and ethyl methyl carbonate). A solution in which LiPF ₆ was dissolved at a concentration of 1.2 mol / l) was injected into a solvent mixed at a volume ratio of 1: 2, and vacuum sealing was performed to produce a nonaqueous battery.

Example 2
A non-aqueous battery was produced in the same manner as in Example 1 except that the amount of alumina fine particles to be added was changed to 3 kg, and a liquid composition for forming a separator prepared in the same manner as in Example 1 was used.

Example 3
A liquid composition for forming a separating material prepared in the same manner as in Example 2 except that the amount of polyethylene powder to be added was changed to 1 kg and the binder resin (C) was added to the toluene solution once. A nonaqueous battery was produced in the same manner as in Example 1.

Example 4
Liquid composition for forming a separator prepared in the same manner as in Example 3 except that the heat-resistant fine particles (B) were changed to cross-linked polymethylmethacrylate powder [Sekisui Chemical Co., Ltd. “MBX-5 (trade name)”: 1 kg. A nonaqueous battery was fabricated in the same manner as in Example 1 except that the thickness of the separator formed on the negative electrode surface was changed to 20 μm.

Example 5
Liquid composition for forming a separator prepared in the same manner as in Example 3 except that the heat-resistant fine particles (B) were changed to crosslinked polystyrene fine particles [“SBX-6 (trade name)” manufactured by Sekisui Plastics Co., Ltd.]: 1 kg. A nonaqueous battery was produced in the same manner as in Example 1 except that the thickness of the separator formed on the negative electrode surface was changed to 20 μm.

Example 6
As a binder resin (C), an ethylene-ethyl acrylate copolymer [NUC6570 (trade name) manufactured by Nippon Unicar Co., Ltd.]: 200 g and toluene: 6 kg were placed in a container and stirred at room temperature until evenly dissolved. Further, as the organic fine particles (A), ethylene-vinyl acetate copolymer powder [“Flowback D5020 (trade name)” manufactured by Sumitomo Seika Co., Ltd.]: 1 kg is added and dispersed by stirring for 1 hour with a disper at 2800 rpm. I let you. Further, as fine particles (B), alumina fine particles [“SUMIKORANDAN AA04 (trade name)” manufactured by Sumitomo Chemical Co., Ltd.]: 300 g are added and dispersed with stirring with a disperser at 2800 rpm for 3 hours to form a uniform slurry. A liquid composition for forming a material was obtained. Using this liquid composition, a nonaqueous battery was produced in the same manner as in Example 1 except that the thickness of the separator formed on the negative electrode surface was changed to 20 μm.

Example 7
A liquid composition for forming a separator, prepared in the same manner as in Example 1, except that the amount of polyethylene powder to be added was changed to 1 kg and the binder resin (C) was added to the toluene solution once. A nonaqueous battery was produced in the same manner as in Example 1.

Example 8
A non-aqueous battery was prepared in the same manner as in Example 1, except that the same liquid composition for forming a separator as that used in Example 7 was used, and a separator having a thickness of 15 μm was formed on the surfaces of the positive electrode and the negative electrode. Produced.

Reference Example 9
To 1 kg of toluene, 100 g of polyethylene powder [Sumitomo Seika's “Flowsen UF1.5 (trade name)”]: 100 g and alumina fine particles [Sumitomo Chemical Co., “Sumicorundum AA04 (trade name)]]: 300 g are added, and 100 The polyethylene powder was completely dissolved by heating to ° C. This solution was cooled to near room temperature at once with ice water, and polyethylene resin was deposited on the surface of the alumina fine particles to produce core-shell structured fine particles. 100 g of ethylene-vinyl acetate copolymer (34 mol% vinyl acetate-derived structural unit, manufactured by Nihon Unicar) is added as a binder resin (C) to a toluene solution in which fine particles of a core-shell structure are dispersed and dissolved uniformly. The mixture was stirred at room temperature until a uniform slurry was obtained to obtain a liquid composition for forming a separator. The slurry was applied by sliding on the negative electrode with a gap of 50 μm, and then toluene was removed to form a separator with a thickness of 15 μm on the negative electrode surface.

Comparative Example A nonaqueous battery was produced in the same manner as in Example 1 except that a polyethylene separator having a thickness of 20 μm was used instead of the separator.

  Each of the above batteries was evaluated for the following characteristics.

<Load characteristics>
Each battery was continuously charged at a constant voltage of 4.2 V until it reached 4.2 V at a constant current of 0.2 C. The total time from the start of constant current charge to the end of constant voltage charge was 7.5 hours. About each battery after charge, discharge from 4.2V to 3.0V is performed in the case of 0.2C and 2C, each discharge capacity is measured, and the discharge capacity at 0.2C is measured. The ratio of the discharge capacity at 2C was determined and used as the load characteristics of the battery.

<Shutdown characteristics>
Each battery is placed in an oven, and while measuring the internal resistance of the battery, the temperature is increased from 30 ° C. to 150 ° C. at a rate of 1 ° C./min, and the temperature at which the internal resistance of the battery begins to rise The internal resistances of the batteries at 30 ° C., 80 ° C. and 130 ° C. (hereinafter referred to as R ₃₀ , R ₈₀ and R ₁₃₀ , respectively) were measured to determine R ₈₀ / R ₃₀ and R ₁₃₀ / R ₂₀ . The internal resistance was measured using a contact resistance meter (3560 AC milliohm high tester) manufactured by HIOKI, and the measured value when an alternating current of 1 kHz was applied was defined as the internal resistance of the battery. In the battery of Example 5, the internal resistance of the battery remained high up to 150 ° C., the ratio of the internal resistance (R ₁₅₀ ) and R _{30 at} 150 ° C., and R ₁₅₀ / R ₃₀ was 10. However, in the battery of the comparative example, the internal resistance rapidly decreased with the temperature after the shutdown, and the value of the ratio decreased to 3.

  The changes in internal resistance of the batteries of Example 5 and the comparative example are shown in FIGS. 3 and 4, respectively. From FIG. 3, in the battery of the example, when the temperature is increased from 30 ° C., the internal resistance gradually decreases with the temperature up to about 80 ° C. (this is indicated as “gradual decrease region” in the figure), and then the internal resistance decreases. When the temperature rises and the temperature is further raised, it can be confirmed that the internal resistance increases linearly and abruptly (this is indicated as “rise region” in the figure). In the battery of Example 5, the “temperature at which the internal resistance begins to rise” obtained from the intersection of the approximate straight line of the gradually decreasing region and the rising region is 100 ° C., and the slope of the approximate straight line of the rising region is 4.8 (Ω However, in the battery of the comparative example, it was 136 ° C. and 28 (Ω / ° C.), respectively.

<Safety evaluation>
Subsequent to the evaluation of the shutdown characteristics, the battery was left at a temperature of 150 ° C. for 60 minutes and then taken out and decomposed to examine the change in the size of the separator. That is, for the length of the long side of the separator, the value obtained by dividing the difference between the original length and the length after storage by the original length is obtained as the shrinkage rate (unit:%) of the separator, and the safety Evaluated. When the shrinkage rate of the separator is 5% or less, it means that even if the inside of the battery reaches 150 ° C., an internal short circuit hardly occurs and safety is ensured.

  Tables 1 to 4 show the configuration of the separator for each non-aqueous battery, and Table 5 shows the evaluation results.

In Table 1, “PE” is polyethylene, “EVA” is ethylene-vinyl acetate copolymer, “PMMA” is crosslinked polymethyl methacrylate, “PS” is crosslinked polystyrene, and “EEA” is ethylene-ethyl acrylate copolymer. Each polymer is meant. The same applies to Table 2. Regarding the heat-resistant fine particles (B) used in Examples 1 to 8 and Reference Example 9, the heat deformation temperature when measured by the JIS-K7191 method is 160 ° C. or higher, or there is no heat deformation temperature. Have confirmed.

As can be seen from Table 5, in the non-aqueous batteries of Examples 1 to 8 and Reference Example 9, the temperature at which the internal resistance begins to rise is low, the rate of increase of the internal resistance is high, and the shutdown characteristics are very good. Even when left at 150 ° C. for a long time, the size of the separator (covered state on the electrode surface) does not change, and good safety can be secured. Further, in the batteries of Examples 1 to 7, very good load characteristics can be secured.

  On the other hand, in the battery of the comparative example using the separator having the conventional configuration, the temperature at which the internal resistance rises is high and the response of the shutdown is inferior. A large shrinkage such as shrinkage to 11% of the size (shrinkage rate: 89%) was observed, and a short circuit was likely to occur at a high temperature.

It is a scanning electron micrograph of the separator which concerns on the nonaqueous battery of Example 2 of this invention. It is the photograph which expanded a part of isolation material of FIG. It is a graph which shows the internal resistance change in the shutdown characteristic evaluation of the non-aqueous battery of Example 5. It is a graph which shows the internal resistance change in the shutdown characteristic evaluation of the nonaqueous battery of a comparative example.

Explanation of symbols

1 Organic fine particles (A)
2 Heat-resistant fine particles (B)
3 Binder resin (C)
4 Electrode 5 Separating material

Claims (17)

A non-aqueous battery having a positive electrode, a negative electrode using a negative electrode active material as a material capable of occluding and releasing lithium, a lithium alloy or lithium ions, and a porous separator between the positive electrode and the negative electrode,
The separator is formed of organic fine particles (A) having a melting point of 80 to 150 ° C. and heat resistant fine particles (B) having a heat resistant temperature of 160 ° C. or higher, which are formed on the surface of at least one of the positive electrode and the negative electrode . And containing at least two kinds of fine particles bound by a binder resin (C),
In all the materials constituting the separator, the ratio of the heat-resistant fine particles (B) is 4% by mass or more, and the ratio of the binder resin (C) is 1.6% by mass to 13.3% by mass,
When the battery was heated from 30 ° C. to 150 ° C. at a rate of 1 ° C./min, the internal resistance of the battery at 30 ° C., 80 ° C. and 130 ° C. was R ₃₀ , R ₈₀ and R ₁₃₀ , respectively. Sometimes, R ₈₀ / R ₃₀ ≦ 1 and R ₁₃₀ / R ₃₀ ≧ 5.   When the temperature is increased from 30 ° C. to 150 ° C. at a rate of 1 ° C./min, the temperature at which the internal resistance begins to rise is in the range of 80 ° C. to 130 ° C. The nonaqueous battery according to claim 1, wherein the gradient with respect to temperature is 1 or more. The non-aqueous battery according to claim 1 or 2 melting point of the organic fine particles (A) is 125 ° C. or less. The number average particle diameter of the refractory particles (B) The non-aqueous battery according to any one of claims 1 to 3, at 0.1μm or more 6μm or less. The non-aqueous battery according to any one of claims 1-4 ratio is not more than 74 wt% of the refractory particles in the separation member (B). The organic fine particles (A) is a non-aqueous battery according to any one of claims 1 to 5 which is a polyolefin resin. The organic fine particles (A) are polyethylene or ethylene - what a vinyl acetate copolymer structural unit derived from vinyl acetate of less than 15 mol%, or to any one of claims 1 to 5, which is a derivative thereof The nonaqueous battery as described. The refractory particles (B) is a non-electrically conductive inorganic fine particles, organic fine particles having a 160 ° C. or more melting point or non-aqueous battery according to any one of claims 1 to 7, which is a crosslinked polymer microparticles. The heat-resistant fine particles (B) are iron oxide, SiO ₂ , Al ₂ O ₃ , TiO ₂ , aluminum nitride, silicon nitride, silicon, diamond, barium sulfate, calcium fluoride, barium fluoride, montmorillonite, polyimide, and melamine resin. , phenolic resins, cross-linked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, benzoguanamine - nonaqueous battery according to any one of claims 1 to 7 at least one kind of particles selected from formaldehyde condensate. The refractory particles (B) is not according to any one of claims 1 to 7 heat distortion temperature, as measured by JIS-K7191 method or is 160 ° C. or higher, or one in which heat deformation temperature is not present Water battery. The non-aqueous battery according to any one of claims 1 to 10 , wherein the binder resin (C) is a resin having a methylene chain. Above between the positive electrode and the negative electrode, in addition to the separation member, the non-aqueous battery according to any one of claims 1 to 1 1, ion-permeable insulating microporous membrane is interposed. The number average particle diameter of the organic fine particles (A) The non-aqueous battery according to any one of claims 1 to 1 2 is 0.1μm or more 10μm or less. The non-aqueous battery according to any one of claims 1 to 1 3 shrinkage isolation material when held for 60 minutes at 0.99 ° C. the battery is 5% or less. The thickness of the isolation material is a non-aqueous battery according to any one of claims 1 to 1 4, 3 to 30 .mu.m.   Organic fine particles (A) having a melting point of 80 to 150 ° C. and 160 ° C. or higher on the surface of at least one of the positive electrode and the negative electrode using a material capable of occluding and releasing lithium, lithium alloy or lithium ions as the negative electrode active material The porous separator according to claim 1 is formed by applying and drying a liquid composition comprising heat-resistant fine particles (B) having a heat-resistant temperature and a binder resin (C). A method for producing a non-aqueous battery. After the liquid composition is applied to the surface of at least one of the positive electrode and the negative electrode, the electrodes are laminated before or during drying, and further dried to integrate the positive electrode, the separator, and the negative electrode. The method for manufacturing a non-aqueous battery according to claim 16 .

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