JP6487139B2 - Electricity storage element - Google Patents

Description

  The present invention relates to an energy storage device including an electrode body having a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode.

  The shift from gasoline cars to electric cars has become important as a global environmental problem. For this reason, use of electrical storage elements such as nonaqueous electrolyte secondary batteries as a power source for electric vehicles has been studied.

  Such a power storage element includes an electrode body having a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The separator separates the positive electrode active material layer and the negative electrode active material layer facing each other through the separator to prevent a short circuit and ensure ion permeability. A separator made of a polyolefin-based resin has been proposed as a separator having the short-circuit prevention function and the ion permeation function and also having a shutdown function at a high temperature (see, for example, Patent Documents 1 and 2).

JP 2008-140551 A JP 2011-138762 A

  However, in the electricity storage device having the separator using the polyolefin resin, for example, the pores of the separator using the polyolefin resin are crushed by the pressure due to the expansion of the negative electrode active material, and the pores are clogged due to oxidation. As a result, the ion permeability decreases. As a result, output performance such as cycle characteristics decreases. On the other hand, in order to improve the ion permeability, a manufacturing cost increases in order to reduce the thickness and increase the porosity of a separator using a polyolefin resin.

  The present invention has been made to solve the above-described problem, and an object thereof is to provide a power storage device with improved output performance while reducing manufacturing cost.

In order to achieve the above object, a power storage device according to one embodiment of the present invention is a power storage device including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte. Te, the negative electrode has a negative electrode active material containing at least carbon, the separator is viewed contains cellulosic fibers, wherein the positive electrode and at least one surface of the negative electrode, the protective layer is formed, the protective layer The film thickness is thicker than 10 μm.

  According to this, the energy density can be improved as compared with a power storage device using a titanium-based oxide, tungsten oxide, or the like having a lithium ion occlusion potential more noble than a carbon-based material as a negative electrode active material. . In addition, since the separator has a higher porosity as compared with a separator using a conventionally used polyolefin-based resin, it has excellent ion permeability and can reduce the cell internal resistance. Therefore, the output performance as a secondary battery improves. Furthermore, since the separator has a fiber structure that promotes capillary action, the separator is excellent in impregnation and liquid injection properties, and the process of injecting the nonaqueous electrolyte into the container of the electricity storage element can be shortened. Therefore, it is possible to improve the output performance while reducing the manufacturing cost.

  Further, a protective layer may be formed on at least one surface of the positive electrode and the negative electrode.

  According to this, the growth of dendrites segregating on the negative electrode surface in the positive electrode direction and the dissolution of metal foreign matter on the positive electrode surface and the precipitation on the negative electrode surface are suppressed, so the occurrence rate of micro short-circuits between the electrodes is suppressed. On the other hand, high output performance reflecting a separator having excellent ion permeability and a negative electrode having a low lithium ion storage potential is realized.

  The protective layer may be made of an insulating ceramic.

  According to this, since at least one of the negative electrode surface and the positive electrode surface is insulated, it is possible to prevent both electrodes from being short-circuited even through a separator having a high porosity. Moreover, it becomes easy to infiltrate nonaqueous electrolyte between ceramic particles, and contributes to shortening of the injection time of a nonaqueous electrolyte with the separator using a highly invasive cellulose fiber.

  Moreover, the film thickness of the protective layer formed on the surface of the negative electrode may be 5 μm or more.

  According to this, even if a high porosity of the separator is ensured, the occurrence of a minute short-circuit can be reduced by insulating at least one of the positive electrode surface and the negative electrode surface, and the separator and lithium ion occlusion having excellent ion permeability. High output performance reflecting negative electrode with low potential is realized.

  Moreover, the film thickness of the protective layer formed on the surface of the positive electrode may be 5 μm or more.

  According to this, even if the high porosity of the separator is ensured, the incidence of minute short-circuits can be reduced by the insulation property of the positive electrode surface, reflecting the separator having excellent ion permeability and the negative electrode having a low lithium ion storage potential. High output performance is realized.

  The average particle size of the ceramic constituting the protective layer may be 0.03 μm or more and 3 μm or less.

  According to this, since the nonaqueous electrolyte easily infiltrates between the ceramic particles constituting the protective layer, it can contribute to shortening the time for injecting the nonaqueous electrolyte together with the separator using the highly invasive cellulose fiber. . In addition, the internal resistance of the cell can be lowered, and high ion permeability is ensured. Moreover, since it is excellent in slurrying manufacturability from the viewpoint of uniform dispersion of the protective layer, production cost can be reduced.

  The positive electrode has a positive electrode base material layer made of a conductive member and a positive electrode mixture layer formed on the surface of the positive electrode base material layer containing a positive electrode active material, and the negative electrode is made of a conductive member. And a negative electrode mixture layer formed on the surface of the negative electrode substrate layer containing a negative electrode active material, and at least one of the positive electrode mixture layer and the negative electrode mixture layer is water-based bonded. The protective layer formed on at least one surface of the positive electrode mixture layer and the negative electrode mixture layer includes one of an adhesive and a solvent-based binder, and the other of the water-based binder and the solvent-based binder. May be included.

  According to this, when the protective layer is formed on the surface of the composite material layer, the composite material layer and the protective layer contain different types of binders. Do not mix with each other. Therefore, it can prevent that the withstand voltage of a protective layer falls because an active material melt | dissolves in a protective layer. In addition, since the composite material layer and the protective layer are prevented from melting, the coating accuracy of the protective layer is improved, and a dense and thin film-like protective layer is obtained.

  In addition, at least one of the positive electrode mixture layer and the negative electrode mixture layer includes the aqueous binder, and the protective layer formed on at least one surface of the positive electrode mixture layer and the negative electrode mixture layer is The solvent-based binder may be included.

  A layer containing a solvent-based binder has a feature that it is superior in coating property than a layer containing a water-based binder. By using this solvent-based binder as a protective layer instead of a composite layer that is allowed to be porous and has defects, the insulating property of the protective layer is ensured, and a dense and thin film quality can be obtained.

  The non-aqueous electrolyte may contain an additive that makes the non-aqueous electrolyte flame-retardant.

  According to this, since the possibility of ignition at a high temperature can be eliminated, safety is improved.

  The additive may be a fluorine compound.

  According to this, since the non-aqueous electrolyte to which the flame retardant that is a fluorine compound is added has a high viscosity, by adding the flame retardant, the internal resistance of the cell is relatively increased, and The liquid time also becomes longer. However, by using a cellulose fiber membrane as a separator, it is possible to suppress an increase in cell internal resistance and a prolonged liquid injection time. Therefore, even when the flame retardant is added to the non-aqueous electrolyte, the manufacturing cost is reduced, and the safety at high temperatures can be ensured while suppressing the occurrence of minute short circuits.

  Further, the positive electrode may have a positive electrode active material including at least one of a compound group represented by a polyanion compound.

  Whereas lithium cobaltate, lithium nickelate, and lithium manganate, which are conventionally used as positive electrodes for nonaqueous electrolyte secondary batteries, tend to release oxygen at high temperatures, polyanion compounds contain phosphorus and oxygen. Since it is covalently bonded, it has the property of suppressing oxygen release at high temperatures. Accordingly, it is possible to prevent ignition from the electrode body itself composed of the positive electrode, the negative electrode, and the separator at a high temperature, and safety is improved.

  According to the electricity storage device of the present invention, the energy density can be improved while ensuring high liquid injection property of the nonaqueous electrolyte from the combination of the negative electrode containing carbon as a negative electrode active material and the separator containing cellulose fiber. . Therefore, it is possible to improve the output performance while reducing the manufacturing cost.

It is a perspective view which shows typically the external appearance of the electrical storage element which concerns on embodiment of this invention. It is a perspective view which shows the external appearance of the electrode body which concerns on embodiment of this invention. It is sectional drawing which shows the structure of the electrode body which concerns on embodiment of this invention. It is sectional drawing which shows the structure of the electrode body which concerns on the 1st modification of embodiment of this invention. It is a figure explaining the dendrite precipitation phenomenon assumed in the electrode body in which the protective layer is not formed. It is a figure explaining the dendrite precipitation phenomenon assumed in the electrode body in which the protective layer was formed. It is sectional drawing which shows the structure of the electrode body which concerns on the 2nd modification of embodiment of this invention. It is a figure explaining the metal foreign material precipitation phenomenon assumed in the electrode body in which the protective layer is not formed. It is a figure explaining that a contact with a metal foreign material and a positive electrode is prevented by a protective layer. It is a figure explaining that the short circuit through Li dendrite is prevented by a protective layer. It is a graph showing the relationship between the thickness of a protective layer, and a micro short circuit incidence. It is a graph showing the relationship between the film thickness of a protective layer, and the surface resistance of a negative electrode. It is a graph showing the relationship between the alumina average particle diameter of a protective layer, cell internal resistance, and liquid injection time.

  Hereinafter, a power storage device according to an embodiment of the present invention will be described with reference to the drawings. Each of the embodiments described below shows a preferred specific example of the present invention. Numerical values, shapes, materials, constituent elements, arrangement positions and connection forms of constituent elements, and the like shown in the following embodiments are merely examples, and are not intended to limit the present invention. In addition, among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims indicating the highest concept of the present invention are described as optional constituent elements that constitute a more preferable embodiment.

(Embodiment)
First, the configuration of the power storage element 10 will be described.

  FIG. 1 is a perspective view schematically showing an external appearance of a power storage device 10 according to an embodiment of the present invention. In addition, the figure is a figure which saw through the container inside. FIG. 2 is a perspective view showing an appearance of the electrode body 400 according to the embodiment of the present invention.

The power storage element 10 is a secondary battery that can charge electricity and discharge electricity, and more specifically, is a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. For example, the electric storage element 10 is a hybrid electric vehicle (Hybrid) that charges and discharges at a high rate cycle.
It is a secondary battery used for Electric Vehicle (HEV). In addition, the electrical storage element 10 is not limited to a nonaqueous electrolyte secondary battery, A secondary battery other than a nonaqueous electrolyte secondary battery may be sufficient, and a capacitor may be sufficient as it.

  As shown in FIG. 1, the storage element 10 includes a container 100, a positive electrode terminal 200, a negative electrode terminal 300, a positive electrode current collector 120 accommodated inside the container 100, a negative electrode current collector 130, and an electrode body. 400. The container 100 includes a lid plate 110 that is an upper wall. Note that a liquid such as an electrolytic solution (nonaqueous electrolyte) is sealed in the container 100 of the power storage element 10, but the liquid is not shown.

  The container 100 includes a casing body having a rectangular cylindrical shape made of metal and having a bottom, and a metal lid plate 110 that closes an opening of the casing body. In addition, the container 100 can be hermetically sealed by welding the lid plate 110 and the housing body after the electrode body 400 and the like are accommodated therein. Examples of the material of the container 100 include aluminum, stainless steel, a laminate of aluminum and stainless steel, and polypropylene resin.

  The electrode body 400 includes a positive electrode, a negative electrode, and a separator, and is a member that can store electricity. Specifically, as shown in FIG. 2, the electrode body 400 is wound in a layered manner so that the separator is sandwiched between the negative electrode and the positive electrode so that the whole becomes an oval shape. Is formed. In the drawing, the shape of the electrode body 400 is oval, but it may be circular or elliptical. The shape of the electrode body 400 is not limited to a wound type, and may be a shape in which flat plate plates are stacked. The detailed configuration of the electrode body 400 will be described later.

  Returning to FIG. 1, the positive electrode terminal 200 is an electrode terminal electrically connected to the positive electrode of the electrode body 400, and the negative electrode terminal 300 is an electrode terminal electrically connected to the negative electrode of the electrode body 400. That is, the positive electrode terminal 200 and the negative electrode terminal 300 lead the electricity stored in the electrode body 400 to the external space of the power storage element 10, and in order to store the electricity in the electrode body 400, It is an electrode terminal made of metal for introducing. Further, the positive electrode terminal 200 and the negative electrode terminal 300 are attached to a lid plate 110 disposed above the electrode body 400.

  The positive electrode current collector 120 is disposed between the positive electrode of the electrode body 400 and the side wall of the container 100, and is a member having conductivity and rigidity that is electrically connected to the positive electrode terminal 200 and the positive electrode of the electrode body 400. It is. The positive electrode current collector 120 is formed of aluminum or an aluminum alloy, like the positive electrode base material layer of the electrode body 400.

  The negative electrode current collector 130 is disposed between the negative electrode of the electrode body 400 and the side wall of the container 100, and is a member having conductivity and rigidity that is electrically connected to the negative electrode terminal 300 and the negative electrode of the electrode body 400. It is. The negative electrode current collector 130 is formed of copper or a copper alloy, like the negative electrode base material layer of the electrode body 400.

  Specifically, the positive electrode current collector 120 and the negative electrode current collector 130 are metal plates arranged in a bent state along the side wall and the cover plate 110 from the side wall of the main body of the container 100 to the cover plate 110. It is a shaped member. The positive electrode current collector 120 and the negative electrode current collector 130 are fixedly connected to the cover plate 110, and are fixedly connected to the positive electrode and the negative electrode of the electrode body 400 by welding or the like. Accordingly, the electrode body 400 is held in a state of being suspended from the lid plate 110 by the positive electrode current collector 120 and the negative electrode current collector 130 inside the container 100.

  Next, the configuration of the electrode body 400 will be described in detail.

  FIG. 3 is a cross-sectional view showing the configuration of the electrode assembly 400 according to the embodiment of the present invention. Specifically, FIG. 2 is a view showing a cross section when the portion where the wound state of the electrode body 400 shown in FIG. 2 is developed is cut along the AA cross section. As shown in the figure, the electrode body 400 is formed by laminating a positive electrode 410, a negative electrode 420, and two separators 430.

(Positive electrode)
The positive electrode 410 includes a positive electrode base material layer 411 and a positive electrode mixture layer 412 that includes a positive electrode active material and is formed on the surface of the positive electrode base material layer 411. The negative electrode 420 includes a negative electrode base material layer 421 and a negative electrode mixture layer 422 that includes a negative electrode active material and is formed on the surface of the negative electrode base material layer 421.

  The positive electrode base material layer 411 is a long belt-shaped conductive current collector foil made of aluminum or an aluminum alloy. The negative electrode base material layer 421 is a long belt-shaped conductive current collector foil made of copper or a copper alloy. Note that as the current collector foil, a known material such as nickel, iron, stainless steel, titanium, baked carbon, a conductive polymer, conductive glass, or an Al—Cd alloy can be used as appropriate.

  The positive electrode mixture layer 412 is an active material layer formed on the positive electrode 410 and disposed on both the outer and inner surfaces (the Z-axis plus side and minus side surfaces in FIG. 3) of the positive electrode base material layer 411. The positive electrode mixture layer 412 includes a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

As a positive electrode active material used for the electrical storage element 10, a well-known material can be used suitably if it is a positive electrode active material which can occlude-release lithium ion. For example, a composite oxide represented by Li _x MO _y (M represents at least one transition metal) (Li _x CoO ₂ , Li _x NiO ₂ , Li _x Mn ₂ O ₄ , Li _x MnO ₃ , Li _x Ni _{y Co (1-y) O} 2, Li x Ni y Mn z Co , etc. _{(1-y-z) O} 2, Li x Ni y Mn (2-y) O 4), _or, Li _w Me x (XO _{y) z} (Me represents at least one transition metal, X is for example P, Si, B, polyanionic compound represented by _{V) (LiFePO 4, LiMnPO 4} , LiNiPO 4, LiCoPO 4, Li 3 V 2 (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F, etc.). The elements or polyanions in these compounds may be partially substituted with other elements or anion species, and the surface is coated with a metal oxide such as ZrO ₂ , WO ₂ , MgO, Al ₂ O ₃ or carbon. May be. Furthermore, conductive polymer compounds such as disulfide, polypyrrole, polyaniline, polyparastyrene, polyacetylene, and polyacene materials, pseudographite-structured carbonaceous materials, and the like are included, but the invention is not limited thereto. Moreover, these compounds may be used independently and may mix and use 2 or more types.

A particularly preferable positive electrode active material is a polyanionic compound lithium iron phosphate (LiFePO ₄ ). Lithium cobaltate (Li _x CoO ₂ ), lithium nickelate (Li _x NiO ₂ ), and lithium manganate (Li _x Mn ₂ O ₄ ) easily release oxygen at high temperatures, whereas polyanion compounds Since phosphorus and oxygen are covalently bonded, they have the property of suppressing oxygen release at high temperatures. Therefore, by using lithium iron phosphate, which is a polyanion compound, as a positive electrode active material, it is possible to prevent ignition from the electrode body 400 itself composed of the positive electrode, the negative electrode, and the separator at a high temperature, thereby improving safety.

  In addition, in power storage element 10 according to the present embodiment, it is more preferable to use lithium iron phosphate as the positive electrode active material in response to using separator 430 formed of cellulose fibers. The separator 430 formed of cellulose fiber has a high heat resistance, and thus has a property of not being deformed or melted at a high temperature. For this reason, the separator 430 does not have a so-called shutdown function in which a separator using a polyolefin resin contracts around 80 ° C. and melts around 120 ° C. to prevent ignition. However, as described above, by using lithium iron phosphate as the positive electrode active material, it is possible to prevent ignition from the electrode body 400 itself even if the separator 430 itself does not have a shutdown function.

  In the present embodiment and examples, the high temperature indicates a temperature range of 80 ° C. or higher.

  Examples of the positive electrode conductive agent include acetylene black, carbon black, coke, carbon fiber, and graphite.

  Examples of the positive electrode binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), styrene-butadiene rubber (SBR), polyethylene oxide (PEO), and the like. .

  Here, there are two types of positive electrode binders, water-based and solvent-based. The water-based binder is a binder in which polymer fine particles, a rubber material, and the like are dispersed in water, and a known material can be appropriately used. Examples of the water-based binder include the above-mentioned PTFE and SBR. On the other hand, the solvent-based binder is a binder dispersed in an organic solvent, and a known material can be used as appropriate. Examples of the solvent-based binder include PVDF described above.

  For example, the positive electrode 410 is prepared by mixing a mixture of lithium iron phosphate powder (active material), acetylene black (conductive agent), and polyvinylidene fluoride (binder) solution and then forming the positive electrode mixture layer 412. It is applied on an aluminum foil to be the base material layer 411 and dried.

(Negative electrode)
The negative electrode mixture layer 422 is an active material layer formed on the negative electrode 420 that is disposed on both the outer and inner surfaces of the negative electrode base material layer 421 (the Z-axis positive side and negative side surfaces in FIG. 3). The negative electrode mixture layer 422 includes a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent.

  Examples of the negative electrode active material used for the electricity storage element 10 include graphite, amorphous carbon, coke, and those containing a tin alloy, silicon, or silicon oxide in these carbon materials. That is, the negative electrode 420 is formed of the negative electrode base material layer 421 and the negative electrode mixture layer 422 containing at least carbon.

  Compared with a power storage element using a titanium-based oxide or a tungsten oxide having a lithium ion occlusion potential more noble than the carbon-based material as a negative electrode active material, the present embodiment using the carbon-based material as a negative electrode active material The energy storage device 10 according to the embodiment can improve the energy density.

  Examples of the negative electrode conductive agent include acetylene black, carbon black, coke, carbon fiber, and graphite.

  Examples of the negative electrode binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), styrene-butadiene rubber (SBR), polyethylene oxide (PEO), and the like. .

  Here, there are two types of negative electrode binders, water-based and solvent-based. The water-based binder is a binder in which polymer fine particles, a rubber material, and the like are dispersed in water, and a known material can be appropriately used. Examples of the water-based binder include the above-mentioned PTFE and SBR. On the other hand, the solvent-based binder is a binder dispersed in an organic solvent, and a known material can be used as appropriate. Examples of the solvent-based binder include PVDF described above.

  For example, the negative electrode 420 is obtained by mixing a graphite powder (active material and conductive agent) and a polyvinylidene fluoride (binder) solution, and then mixing the mixture that becomes the negative electrode mixture layer 422 on the copper foil that becomes the negative electrode base material layer 421. It is prepared by applying to and drying.

(Separator)
Separator 430 is a long strip separator disposed between positive electrode 410 and negative electrode 420. The separator 430 is wound in the longitudinal direction (Y-axis direction) together with the positive electrode 410 and the negative electrode 420 and laminated in a plurality of layers, whereby the electrode body 400 is formed.

  Separator 430 is a porous body formed of cellulose fibers. The porous body comprised with the said cellulose fiber is implement | achieved in the state of a nonwoven fabric or paper, for example. By forming the porous body with cellulose fibers, the heat resistance of the separator 430 can be improved.

  Since the separator 430 formed of cellulose fiber has a higher porosity than a separator using a polyolefin resin that has been conventionally used, it has excellent ion permeability and can reduce the cell internal resistance. Therefore, the output performance as a secondary battery improves. Furthermore, since the separator 430 has a fiber structure that promotes capillary action, the separator 430 is excellent in impregnation and liquid injection properties, and the process of injecting the electrolyte into the container 100 can be shortened.

  Here, it is preferable to use an electrolyte solution having high flame retardance for the purpose of preventing ignition phenomenon at high temperature, but the flame retardant electrolyte solution has high viscosity. Even when the flame-retardant electrolyte solution having a high viscosity is used, the injection efficiency is not lowered by using cellulose fibers as the separator 430. Furthermore, since the cellulose fiber as a paper or a nonwoven fabric is cheap compared with a polyolefin film | membrane, manufacturing cost can be reduced.

  Here, the thickness of the separator 430 (the thickness in the Z-axis direction in the figure) is preferably in the range of 10 to 30 μm, for example.

[First Modification]
As described above, the positive electrode 410, the negative electrode 420, and the separator 430 are configured. From the viewpoint of improving the performance of the storage element 10 as a secondary battery, protection is provided on at least one surface of the positive electrode 410, the negative electrode 420, and the separator 430. A layer may be formed.

  FIG. 4 is a cross-sectional view showing a configuration of an electrode body according to a first modification of the embodiment of the present invention. The laminated sectional view shown in the figure is a sectional view corresponding to the region B in FIG. The negative electrode according to this modification is different from the negative electrode 420 illustrated in FIG. 3 in that a protective layer 423 is formed on the surface of the negative electrode mixture layer 422.

The protective layer 423 is a protective layer for suppressing the precipitation of dendrites on the surface of the negative electrode 420, and is preferably made of an insulating ceramic. Examples of the main material of the protective layer 423 include alumina (Al ₂ O ₃ ) particles and titania (TiO ₂ ) particles. A protective layer 423 is formed by mixing the main material with a protective layer binder. Examples of the protective layer binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), styrene-butadiene rubber (SBR), polyethylene oxide (PEO), and the like.

  Here, when the same kind of binder is used for the binder contained in the negative electrode mixture layer 422 and the binder contained in the negative electrode protective layer, the protective layer 423 is formed on the surface of the negative electrode mixture layer. The component of the negative electrode mixture layer 422 and the component of the protective layer 423 are mixed with each other. Thereby, for example, the negative electrode active material is dissolved in the protective layer 423, the insulating property of the protective layer 423 is lowered, and the withstand voltage is lowered. Further, the negative electrode composite material layer 422 and the protective layer 423 are melted together, so that the coating accuracy of the protective layer 423 is lowered. Therefore, it is preferable that different types of binders be used for the binder contained in the negative electrode mixture layer 422 and the binder contained in the protective layer 423.

  Furthermore, the layer containing the solvent-based binder has a feature that it is superior in coating property than the layer containing the water-based binder. Therefore, in order to form a uniform and dense protective thin film on the porous composite material layer, it is desirable to use a solvent-based binder for the protective layer 423. In other words, the binder contained in the negative electrode mixture layer 422 is preferably a water-based binder, and the binder contained in the protective layer 423 is preferably a solvent-based binder. The water-based binder used as the binder included in the negative electrode mixture layer 422 is, for example, SBR, and the solvent-based binder used as the binder included in the protective layer 423 is, for example, , PVDF.

  Here, the role of the protective layer 423 will be described with reference to FIGS. 5A and 5B.

  FIG. 5A is a diagram for explaining a dendrite precipitation phenomenon assumed in an electrode body in which a protective layer is not formed, and FIG. 5B is a diagram for explaining a dendrite precipitation phenomenon assumed in an electrode body in which a protection layer is formed. It is. Note that in FIGS. 5A and 5B, the separator 430, the positive electrode mixture layer 412, and the negative electrode mixture layer 422 are shown not in contact with each other. This is an enlargement of the boundary in order to explain the precipitation state of Li dendrite at the boundary between the separator 430 and the adjacent composite layer, and each layer is actually in contact as shown in FIG. 3 or FIG. .

  As shown in FIG. 5A, it is assumed that Li dendrite is segregated on the negative electrode surface in the electrode body in which the protective layer is not provided. This is a phenomenon that occurs because the potential of the negative electrode 420 containing carbon is base, and Li dendrite is selectively deposited on the negative electrode surface facing the pinholes of the separator 430. As the segregation of this Li dendrite proceeds, the probability that a micro short circuit will occur between the positive electrode and the negative electrode increases.

  On the other hand, as shown in FIG. 5B, by forming a protective layer 423 on the surface of the negative electrode mixture layer 422, Li dendrite in the direction of the separator 430 and the positive electrode 410 (Z direction in FIG. 4). Growth can be suppressed and precipitation of Li dendrite can be flattened. As a result, the power storage device according to the present modification can ensure high energy density output performance while preventing a short circuit between the electrodes.

  Note that the protective layer may be formed on the surface of the positive electrode 410 or the surface of the separator 430 instead of being formed on the negative electrode. These modes can also prevent a short circuit between the electrodes.

[Second Modification]
FIG. 6 is a cross-sectional view showing a configuration of an electrode body according to a second modification of the embodiment of the present invention. The laminated sectional view shown in the figure is a sectional view corresponding to the region C in FIG. The positive electrode according to this modification is different from the positive electrode 410 illustrated in FIG. 3 in that a protective layer 413 is formed on the surface of the positive electrode mixture layer 412.

The protective layer 413 prevents the metal foreign matter from dissolving on the surface of the positive electrode 410, and the metal foreign matter and Li dendrite deposited on the surface of the negative electrode 420 come into contact with the surface of the positive electrode 410, thereby causing a short circuit between the positive electrode 410 and the negative electrode 420. It is preferable that the protective layer is made of an insulating ceramic. Examples of the main material of the protective layer 413 include alumina (Al ₂ O ₃ ) particles and titania (TiO ₂ ) particles. The protective layer 413 is formed by mixing the main material with a protective layer binder. Examples of the protective layer binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), styrene-butadiene rubber (SBR), polyethylene oxide (PEO), and the like.

  Here, when the same kind of binder is used for the binder contained in the positive electrode mixture layer 412 and the binder contained in the positive electrode protective layer, the protective layer 413 is formed on the surface of the positive electrode mixture layer 412. At this time, the component of the positive electrode 410 and the component of the protective layer 413 are mixed with each other. Thereby, for example, the positive electrode active material is dissolved in the protective layer 413, the insulating property of the protective layer 413 is lowered, and the withstand voltage is lowered. Further, the positive electrode mixture layer 412 and the protective layer 413 are melted together, so that the coating accuracy of the protective layer 413 is lowered. Therefore, it is preferable that different types of binders are used for the binder contained in the positive electrode mixture layer 412 and the binder contained in the protective layer 413.

  Furthermore, the layer containing the solvent-based binder has a feature that it is superior in coating property than the layer containing the water-based binder. Therefore, in order to form a uniform and dense protective thin film on the porous composite material layer, it is desirable to use a solvent-based binder for the protective layer 423. That is, the binder contained in the positive electrode mixture layer 412 is preferably a water-based binder, and the binder contained in the protective layer 413 is preferably a solvent-based binder. The water-based binder used as the binder contained in the positive electrode mixture layer 412 is, for example, SBR, and the solvent-based binder used as the binder contained in the protective layer 413 is, for example, , PVDF.

  Here, the role of the protective layer 413 will be described with reference to FIGS. 7A to 7C.

  FIG. 7A is a diagram illustrating a metal foreign matter precipitation phenomenon assumed in an electrode body in which a protective layer is not formed, and FIG. 7B illustrates that the contact between the metal foreign matter and the positive electrode is prevented by the protective layer. FIG. 7C is a diagram for explaining that a short circuit through the Li dendrite is prevented by the protective layer. 7A to 7C, the separator 430, the positive electrode mixture layer 412, and the negative electrode mixture layer 422 are shown not in contact with each other. This is an enlargement of the boundary in order to explain the precipitation state of the metallic foreign matter and Li dendrite at the boundary between the separator 430 and the adjacent composite material layer. Actually, each layer is as shown in FIG. 3 or FIG. Touching.

  As shown in FIG. 7A, in the electrode body in which the protective layer is not provided, first, when the metal foreign matter is mixed into the positive electrode surface, the metal foreign matter is dissolved by the positive electrode potential. Next, the dissolved metal foreign matter is deposited by the negative electrode potential. The deposited metallic foreign matter grows in the positive electrode direction through the separator 430, and the positive electrode and the negative electrode are short-circuited through the grown metallic foreign matter. The above is the generation mechanism of the micro short-circuit when the protective layer is not provided on the positive electrode.

  On the other hand, when foreign metal is mixed in after the formation of the protective layer 413, as shown in FIG. 7B, the protective layer 413 is formed on the surface of the positive electrode mixture layer 412, so that the foreign metal becomes positive electrode 410. The metal foreign matter does not dissolve because it does not come into contact with. Therefore, a minute short circuit between the positive electrode and the negative electrode does not occur.

  On the other hand, when the metal foreign matter is mixed between the protective layer 413 and the positive electrode mixture layer 412, as shown in FIG. 7C, the metal foreign matter dissolved by the positive electrode potential is deposited by the negative electrode potential, and the separator 430 and the positive electrode There is a possibility of growing as Li dendrite in the direction of 410. Even in this case, for example, the contact between the Li dendrite and the positive electrode 410 is prevented by the hard protective layer 413 made of ceramic.

  As described above, the power storage device according to this modification in which the protective layer 413 is formed on the surface of the positive electrode mixture layer 412 can ensure high energy density output performance while preventing a short circuit between the electrodes. .

(Nonaqueous electrolyte)
Next, the nonaqueous electrolyte will be described.

  Various non-aqueous electrolytes (electrolytic solutions) sealed in the container 100 can be selected. For example, as a non-aqueous electrolyte organic solvent, ethylene carbonate (EC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), propylene carbonate (PC), butylene carbonate, trifluoropropylene carbonate, γ-butyrolactone, γ-valero Lactone, sulfolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 2-methyl-1,3-dioxolane, dioxolane, fluoroethyl methyl ether, ethylene glycol diacetate, propylene glycol Diacetate, ethylene glycol dipropionate, propylene glycol dipropionate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, prop Ethyl lopionate, propyl propionate, dimethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, methyl isopropyl carbonate, ethyl isopropyl carbonate, diisopropyl carbonate, dibutyl carbonate, acetonitrile, fluoroacetonitrile, ethoxypentafluorocyclotriphosphazene, di Alkoxy and halogen-substituted cyclic phosphazenes or chain phosphazenes such as ethoxytetrafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, phosphate esters such as triethyl phosphate, trimethyl phosphate, trioctyl phosphate, triethyl borate, Boric acid esters such as tributyl borate, N-methyloxazo Jin Won include nonaqueous solvents, such as N- ethyl-oxazolidinone. When a solid electrolyte is used, a porous polymer solid electrolyte membrane may be used as the polymer solid electrolyte, and an electrolyte solution may be further contained in the polymer solid electrolyte. Moreover, when using a gel-like polymer solid electrolyte, the electrolyte solution which comprises gel and the electrolyte solution contained in the pore etc. may differ. However, when high output is required as in HEV applications, it is more preferable to use a non-aqueous electrolyte alone than to use a solid electrolyte or a polymer solid electrolyte.

As the electrolyte salt contained in the nonaqueous electrolyte is not particularly _{limited, LiClO 4, LiBF 4, LiPF} 6, LiBOB, LiAsF 6, LiCF 3 SO 3, LiN (SO 2 CF 3) 2, LiN (SO 2 _{C 2 F 5) 2, LiN} (SO 2 CF 3) (SO 2 C 4 F 9), LiSCN, LiBr, LiI, Li 2 SO 4, Li 2 B 10 Cl 10, NaClO 4, NaI, NaSCN, NaBr, Examples thereof include ionic compounds such as KClO ₄ and KSCN, and mixtures of two or more thereof.

  In the electrical storage element 10, these organic solvents and electrolyte salt are combined and used as a nonaqueous electrolyte. Among these nonaqueous electrolytes, it is preferable to use a mixture of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate because the lithium ion conductivity is maximized.

  Here, the non-aqueous electrolyte preferably has flame retardancy. Thereby, it becomes possible to prevent the ignition by the external fire type even if the above-mentioned electrode body itself does not ignite. As a configuration for the non-aqueous electrolyte to have flame retardancy, for example, a fluorine compound is added to the non-aqueous electrolyte. Examples of the fluorine compound additive for flame retardancy include fluorinated phosphate ester or fluorinated carbonate ester.

[Example]
First, the manufacturing method of the electrical storage element 10 is demonstrated. Specifically, batteries as power storage elements in Examples 1 to 16 and Comparative Examples 1 to 7, which will be described later, were produced as follows. Examples 1 to 16 all relate to power storage element 10 according to the above-described embodiment.

(1-1) Production of positive electrode LiFePO ₄ was used as a positive electrode active material.

  In Examples 1 to 16 and Comparative Examples 1 to 7, acetylene black was used as the conductive agent, PVDF as a solvent-based binder was used as the binder, the positive electrode active material was 90% by mass, and the conductive agent was It was blended so that 5% by mass and the binder were 5% by mass. In addition, an aluminum foil having a thickness of 20 μm is used as the foil, N-methyl-2-pyrrolidone (NMP) is added to the positive electrode active material, the conductive agent, and the binder, kneaded, applied in a foil shape, dried, and then pressed. It was.

  In Examples 17 to 21, acetylene black was used as the conductive agent, SBR, which is a water-based binder, was used as the binder, the positive electrode active material was 90% by mass, the conductive agent was 5% by mass, and the binder. Of 5% by mass. Also, an aluminum foil having a thickness of 20 μm was used as the foil, purified water was added to the positive electrode active material, the conductive agent, and the binder, kneaded, applied into a foil shape, dried, and then pressed.

  In Examples 18 to 21, alumina particles, PVDF, sodium carboxymethylcellulose, NMP, and a surfactant were mixed so that the ratio of alumina particles to PVDF was 97: 3 to prepare a coating agent. And the protective layer 413 was formed by coating the said coating agent on the positive electrode compound material layer 412 by the gravure method, and drying at 80 degreeC after coating.

(1-2) Production of negative electrode Graphite was used as a negative electrode active material.

  Moreover, in Examples 1-21 and Comparative Examples 1-7, PVDF which is a solvent-based binder is used as the binder, so that the negative electrode active material is 95% by mass and the binder is 5% by mass. Blended into Further, a copper foil having a thickness of 15 μm was used as the foil, and NMP was added to the negative electrode active material and the binder, kneaded, applied in a foil shape, dried, and then pressed.

  In Examples 22 to 26, SBR, which is a water-based binder, was used as the binder, and the negative electrode active material was mixed at 95 mass% and the binder was 5 mass%. Further, a copper foil having a thickness of 15 μm was used as the foil, purified water was added to the negative electrode active material and the binder, kneaded, applied into a foil shape, dried, and then pressed.

  In Examples 2 to 16 and Comparative Examples 2 to 7, alumina particles, SBR, sodium carboxymethylcellulose, ion-exchanged water, and a surfactant were mixed so that the ratio of alumina particles to SBR was 97: 3. A coating agent was prepared. And the protective layer 423 was formed by coating the said coating agent on the negative mix layer 422 by the gravure method, and drying at 80 degreeC after coating.

  In Examples 23 to 26, alumina particles, PVDF, sodium carboxymethylcellulose, NMP and a surfactant were mixed so that the ratio of alumina particles to PVDF was 97: 3 to prepare a coating agent. And the protective layer 423 was formed by coating the said coating agent on the negative mix layer 422 by the gravure method, and drying at 80 degreeC after coating.

(1-3) Production of Separator As the separator 430, in Examples 1 to 21, a cellulose fiber membrane having a thickness of 20 μm and a porosity of 60% was used. In Comparative Examples 1 to 7, a polyolefin microporous film having a thickness of 25 μm and a porosity of 20% was used as the base material layer.

(1-4) Generation of Nonaqueous Electrolyte To the nonaqueous electrolyte, LiPF ₆ was added as an electrolyte salt to a mixed solvent of EC and dimethyl carbonate. Moreover, in Example 16 and Comparative Example 7, 25 mass% of fluorinated phosphates were mixed as a fluorine compound additive.

(1-5) Production of Battery The positive electrode 410, the negative electrode 420, and the separator 430 were laminated and wound, and then inserted into the container 100, and a nonaqueous electrolyte was injected and sealed. Next, the following battery evaluation test was performed.

(2-1) Micro short-circuit occurrence rate When the battery is charged to 20% of the rated battery capacity and stored at 25 ° C. for 20 days, the difference between the battery voltage before storage and the battery voltage after storage (battery voltage) The ratio (%) of the batteries in which (decrease) was 0.1 V or more is defined as the minute short-circuit occurrence rate. In this example, a constant voltage of 3.1 V was charged for 3 hours, then the voltage was measured from 5 minutes to 12 hours, and the voltage was measured again after being stored at 25 ° C. for 20 days. The difference was defined as a battery voltage drop. And the test of 50 cells per 1 level was done, the said ratio was calculated, and it was set as the micro short circuit occurrence rate.

(2-2) Cell internal resistance When the thickness of the protective layer 423 is 10 μm, the alumina average particle diameter is 0.5 μm, and the cellulosic fiber membrane is used as the separator 430, the cell internal resistance is normalized to 100. The cell internal resistance measured for each comparative example was normalized.

(2-3) Manufacturability evaluation The pouring time, which is the time required for pouring the nonaqueous electrolyte into the container 100 from the pouring port, the slurrying manufacturability of the protective layer, and the manufacturability of the protective layer are evaluated. did.

(2-4) Surface Resistance In the negative electrode 420 using graphite as the negative electrode active material, the surface resistance of the negative electrode 420 when the protective layer 423 is not formed on the surface is normalized to 1, and the protective layer thickness is changed. The surface resistance was evaluated.

  First, Table 1 below shows the micro short-circuit occurrence rate of the battery obtained as described above. Specifically, in Table 1, for Examples 1 to 5 and Comparative Examples 1 to 5, when the protective layer 423 is formed on the surface of the negative electrode 420, the battery microscopicity when the thickness of the protective layer 423 is changed is shown. The short-circuit occurrence rate is compared. Moreover, about Example 17-21, when the protective layer 413 is formed in the surface of the positive electrode 410, the micro short circuit incidence rate of the battery when the thickness of the protective layer 413 is changed is compared.

  FIG. 8 is a graph showing the relationship between the thickness of the protective layer and the minute short-circuit occurrence rate. Specifically, this figure is a graph with the “protective layer thickness” in Table 1 as the horizontal axis and the “small short-circuit occurrence rate” as the vertical axis.

  As shown in Table 1 and FIG. 8 described above, in Comparative Examples 1 to 5 (polyolefin microporous membrane separator), the micro short-circuit occurrence rate is 3% or less. On the other hand, in Examples 1 to 5 (cellulose fiber separator), as the protective layer 423 is thicker, the micro short-circuit occurrence rate decreases. This is considered due to the fact that the protective layer 423 suppresses the growth of Li dendrite deposited on the negative electrode surface in the positive electrode direction. From Table 1 and FIG. 8, in order to make the micro short-circuit occurrence rate of the electricity storage device 10 according to the present invention equal to or less than that of the electricity storage device (Comparative Examples 1 to 5) using the conventional polyolefin separator, In the embodiment, the thickness of the protective layer 423 is preferably 5 μm or more. Thereby, the high output performance reflecting the separator 430 having excellent ion permeability and the negative electrode 420 having a low lithium ion occlusion potential while maintaining the short-circuit occurrence rate low is ensured.

  In Examples 17 to 21 (cellulose fiber separator), as the protective layer 413 is thicker, the occurrence rate of micro short-circuits decreases. This is because the protective layer 413 prevents the contact between the metal foreign matter and the positive electrode 410, and that the Li dendrite deposited on the negative electrode surface grows and contacts the positive electrode 410. This is thought to be due to the prevention. From Table 1 and FIG. 8, in order to make the micro short-circuit occurrence rate of the electricity storage device 10 according to the present invention a practical level, in this embodiment, the thickness of the protective layer 413 is preferably 5 μm or more. . Further, preferably, in order to make the occurrence rate of micro short-circuit of the electricity storage device 10 according to the present invention equal to or less than that of the electricity storage device (Comparative Examples 1 to 5) using the conventional polyolefin separator, the present embodiment Then, it is preferable that the thickness of the protective layer 413 is 10 μm or more. Thereby, the high output performance reflecting the separator 430 having excellent ion permeability and the negative electrode 420 having a low lithium ion occlusion potential while maintaining the short-circuit occurrence rate low is ensured.

  Next, for Examples 1 to 5 and Examples 22 to 26, the surface resistance of the electrodes when the thickness of the protective layer is changed is shown in Table 2 below.

  FIG. 9 is a graph showing the relationship between the thickness of the protective layer and the surface resistance of the negative electrode. Specifically, FIG. 2 is a graph with “protective layer thickness” in Table 2 as the horizontal axis and “surface resistance” as the vertical axis. Note that the surface resistance shown in Table 2 and FIG. 9 is a normalized value with the surface resistance of the negative electrode 420 when the protective layer is not formed on the surface of the negative electrode 420 being 1.

  As shown in Table 2 and FIG. 9, in Examples 1 to 5 and Examples 22 to 26, the surface resistance of the negative electrode 420 increases as the thickness of the protective layer 423 increases. This indicates that the withstand voltage on the surface of the negative electrode 420 increases as the protective layer thickness increases.

  Furthermore, in Examples 2 to 5 and Examples 23 to 26, when the same protective layer film thickness is compared, Examples 23 to 26 have higher surface resistance. That is, the binder contained in the negative electrode mixture layer 422 is more than the examples 2 to 5 in which a solvent system is used as the binder contained in the negative electrode mixture layer 422 and an aqueous system is used as the binder contained in the protective layer 423. In Examples 23 to 26, in which a water-based material is used as the adhesive and a solvent-based material is used as the binder contained in the protective layer 423, the dielectric strength voltage is higher.

  This is because the binder material included in the negative electrode mixture layer 422 and the binder material included in the protective layer 423 are different from each other in order to avoid mixing the components of the negative electrode mixture layer 422 and the components of the protective layer 423. In Examples 23 to 26, a solvent-based binder having excellent coatability was used for the protective layer 423 while using a system binder. That is, it is desirable to use a solvent-based binder for the protective layer 423 in order to form a uniform and dense protective thin film on the porous composite material layer. Thereby, it is possible to prevent a short circuit between the electrodes.

  Next, for Examples 6 to 14, the cell internal resistance, liquid injection time, slurrying manufacturability, and protective layer manufacturability when the particle size of the protective layer is changed are shown in Table 3 below.

  FIG. 10 is a graph showing the relationship between the alumina average particle diameter of the protective layer, the cell internal resistance, and the injection time. Specifically, the graph is graphed with “alumina average particle size” in Table 3 as the horizontal axis, “cell internal resistance” as the vertical axis (left), and “injection time” as the vertical axis (right). It is a thing.

  As shown in Table 3 and FIG. 10, in Examples 6 to 14, the larger the average alumina particle size of the protective layer 423, the shorter the nonaqueous electrolyte injection time. This indicates that the larger the average alumina particle size on the surface of the protective layer 423, the easier the electrolyte solution infiltrates between the alumina particles. Therefore, the larger the average alumina particle size, the easier it is to infiltrate the non-aqueous electrolyte between the ceramic particles, and together with the separator 430 using the highly invasive cellulose fiber, it can contribute to shortening the time for injecting the non-aqueous electrolyte. .

  On the other hand, as shown in Table 3 and FIG. 10, the cell internal resistance decreases as the average alumina particle size increases. However, when the thickness of the protective layer 423 is 10 μm, the cell internal resistance tends to increase when the average particle diameter of the alumina is 5 μm or more. This indicates that the larger the average alumina particle size on the surface of the protective layer 423, the higher the ion permeability. However, if the protective layer 423 is thick and the particle size becomes too large, the ion permeability is alienated. Suggests that

  Furthermore, in both cases where the protective layer 423 has a thickness of 5 μm and 10 μm, when the alumina average particle size is 0.01 μm, it takes time to uniformly disperse the protective layer 423, and the alumina average particle size is 0.03 μm or more. Compared with the case, slurrying productivity is inferior.

  Further, when the protective layer 423 has a thickness of 5 μm and the alumina average particle diameter is 3 μm, and when the protective layer 423 has a thickness of 10 μm and the alumina average particle diameter is 5 μm, the formed protective layer 423 has defects and coating. Chips are seen.

  As mentioned above, in this Embodiment, it is preferable that it is 0.03 micrometer or more and 3 micrometers or less as a range of an alumina average particle diameter.

  Next, for Examples 15 to 16 and Comparative Examples 6 to 7, the cell internal resistance and the injection time depending on whether or not a flame retardant is added to the electrolyte are shown in Table 4 below.

  As shown in Table 4 above, in Example 15, when the flame retardant is not added to the electrolyte, the cell internal resistance is low and the injection time is also short. Therefore, when the predetermined protective layer 423 is formed on the surface of the negative electrode 420 and the flame retardant is not added to the electrolyte, the ion permeability is improved and the number of manufacturing steps is shortened. Therefore, according to the present embodiment, the manufacturing cost is reduced, and the output performance can be improved while suppressing the occurrence of a short circuit.

  In Example 16 and Comparative Example 7, the addition of a flame retardant to the electrolyte increases the cell internal resistance and also increases the time for injecting the liquid. This is considered due to the fact that the nonaqueous electrolyte to which the flame retardant, which is a fluorine compound, is added has a high viscosity. However, even when the cellulose fiber membrane is used for the separator and the flame retardant is added (Example 16), the polyolefin microporous membrane is used for the separator and the flame retardant is not added (Comparative Example 6). Cell internal resistance and liquid injection time are secured. Therefore, according to this Embodiment, even if it is a case where a flame retardant is added to electrolyte, manufacturing cost can be reduced and the safety | security at high temperature can be improved, suppressing short circuit generation | occurrence | production.

  In addition, even if it is the structure by which the protective layer is arrange | positioned at the positive electrode instead of the negative electrode protective layer, the relative relationship of the cell internal resistance shown in Table 4 is materialized. That is, when the flame retardant is not added to the electrolyte, the cell internal resistance is low and the injection time is short. Therefore, when the predetermined protective layer 413 is formed on the surface of the positive electrode 410 and the flame retardant is not added to the electrolyte, the ion permeability is improved and the number of manufacturing steps is shortened. Therefore, according to the present embodiment, the manufacturing cost is reduced, and the output performance can be improved while suppressing the occurrence of a short circuit. Moreover, even when a cellulose fiber membrane is used as a separator and the flame retardant is added, the cell internal resistance and liquid injection are the same as when a polyolefin microporous membrane is used as a separator and the flame retardant is not added. Time is secured. Therefore, in the configuration in which the protective layer 413 is formed on the positive electrode 410, even when a flame retardant is added to the electrolyte, the manufacturing cost is reduced, and the occurrence of a short circuit is suppressed, and the safety at high temperature is improved. Can be made.

  As described above, according to power storage device 10 according to the embodiment of the present invention, negative electrode 420 has a negative electrode active material containing at least carbon, and separator 430 contains cellulose fibers. Thereby, the energy storage device 10 using a carbon-based material having a low lithium ion storage potential as the negative electrode active material can improve the energy density. Moreover, since the separator 430 has a high porosity as compared with a separator using a conventionally used polyolefin resin, it has excellent ion permeability and can reduce the internal resistance of the cell. Therefore, the output performance as a secondary battery improves. Furthermore, since the separator 430 has a fiber structure that promotes capillary action, the separator 430 is excellent in impregnation and liquid injection properties, and the process of injecting the electrolyte into the container 100 can be shortened. Therefore, it is possible to improve the output performance while reducing the manufacturing cost.

  Further, as an aspect according to the embodiment of the present invention, in the power storage element 10, a protective layer is formed on at least one of the positive electrode 410, the negative electrode 420, and the separator 430. Among these, it is preferable that a protective layer 423 for suppressing the precipitation of dendrites is formed on the surface of the negative electrode 420. In addition, a protective layer 413 is preferably formed on the surface of the positive electrode 410 in order to suppress deposition of metal foreign substances. Accordingly, high output performance reflecting the separator 430 having excellent ion permeability and the negative electrode 420 having a low lithium ion occlusion potential while maintaining a small short-circuit occurrence rate between the electrodes is realized.

  Here, the protective layers 413 and 423 are preferably made of an insulating ceramic. Thereby, it can prevent that both electrodes short-circuit through the separator 430 with a high porosity. Moreover, it becomes easy to infiltrate electrolyte solution between ceramic particles, and the effect which used the separator 430 as the highly invasive cellulose fiber becomes remarkable.

  Further, as one aspect according to an embodiment of the present invention, the protective layers 413 and 423 have a thickness of 5 μm or more. Furthermore, the thickness of the protective layer 413 is preferably 10 μm or more. As a result, the micro-short-circuit occurrence rate can be reduced while maintaining the high porosity of the separator 430, and high output performance reflecting the separator 430 having excellent ion permeability and the negative electrode 420 having a low lithium ion storage potential is realized. .

  Moreover, as one aspect according to the embodiment of the present invention, the electricity storage device 10 further includes a flame-retardant non-aqueous electrolyte. In particular, the non-aqueous electrolyte exhibits flame retardancy by adding a fluorine compound. Since the nonaqueous electrolyte to which the flame retardant that is a fluorine compound is added has high viscosity, the cell internal resistance is relatively increased, and the injection time is also prolonged. However, by using a cellulose fiber membrane for the separator 430, it is possible to prevent an increase in cell internal resistance and a prolonged liquid injection time. Therefore, even when the flame retardant is added to the non-aqueous electrolyte, the manufacturing cost is reduced, and safety at high temperatures can be improved while suppressing occurrence of short circuits.

  Further, as one aspect according to an embodiment of the present invention, the positive electrode 410 includes a positive electrode active material containing lithium iron phosphate. Lithium cobaltate, lithium nickelate, and lithium manganate, which are conventionally used as positive electrodes for nonaqueous electrolyte secondary batteries, easily release oxygen at high temperatures, whereas lithium iron phosphate having an olivine structure Since phosphorus and oxygen are covalently bonded, they have the property of suppressing oxygen release at high temperatures. Thereby, it can prevent that it ignites from the electrode body 400 itself at high temperature.

  Although the power storage device according to the embodiment of the present invention and the modification thereof has been described above, the present invention is not limited to the above-described embodiment and the modification. In other words, it should be considered that the embodiment and its modification disclosed this time are illustrative and not restrictive in all respects. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  Moreover, the form constructed | assembled combining the said embodiment and the said modification arbitrarily is also contained in the scope of the present invention.

  The present invention can be applied to power storage elements such as lithium ion secondary batteries having high output performance while reducing manufacturing costs.

DESCRIPTION OF SYMBOLS 10 Storage element 100 Container 110 Cover plate 120 Positive electrode collector 130 Negative electrode collector 200 Positive electrode terminal 300 Negative electrode terminal 400 Electrode body 410 Positive electrode 411 Positive electrode base material layer 412 Positive electrode mixture layer 413, 423 Protective layer 420 Negative electrode 421 Negative electrode base material Layer 422 Negative electrode composite material layer 430 Separator

Claims (9)

A power storage device including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte,
The negative electrode has a negative electrode active material containing at least carbon,
The separator includes cellulose fibers,
On the surface of at least one of the positive electrode and the negative electrode, a protective layer for suppressing a minute short circuit between the electrodes is formed,
The protective layer has a thickness greater than 10 μm. The electric storage element according to claim 1, wherein the protective layer has a thickness greater than 10 μm and not greater than 15 μm. The protective layer, electric storage device according to claim 1 comprising a ceramic having an insulating property. The electrical storage element according to claim 3, wherein an average particle diameter of the ceramic constituting the protective layer is 0.03 μm or more and 3 μm or less. The positive electrode has a positive electrode base material layer made of a conductive member, and a positive electrode mixture layer formed on the surface of the positive electrode base material layer containing a positive electrode active material,
The negative electrode has a negative electrode substrate layer made of a conductive member, and a negative electrode mixture layer formed on the surface of the negative electrode substrate layer containing a negative electrode active material,
At least one of the positive electrode mixture layer and the negative electrode mixture layer includes one of a water-based binder and a solvent-based binder,
The power storage device according to claim 1, wherein the protective layer formed on at least one surface of the positive electrode mixture layer and the negative electrode mixture layer includes the other of a water-based binder and a solvent-based binder. At least one of the positive electrode composite material layer and the negative electrode composite material layer includes the aqueous binder.
The power storage device according to claim 5, wherein the protective layer formed on at least one surface of the positive electrode mixture layer and the negative electrode mixture layer includes the solvent-based binder. The power storage device according to claim 1, wherein the non-aqueous electrolyte includes an additive that makes the non-aqueous electrolyte flame-retardant. The electricity storage device according to claim 7, wherein the additive is a fluorine compound. The power storage element according to claim 1, wherein the positive electrode has a positive electrode active material including at least one of a compound group represented by a polyanion compound.

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