JP2015179575A - Negative electrode for non-aqueous electrolyte secondary battery, method for producing the same, and non-aqueous electrolyte secondary battery - Google Patents

Abstract

A negative electrode for a non-aqueous electrolyte secondary battery having a high capacity and a long life is provided. An active material layer composed of a plurality of layers is formed on a current collector (2) as a negative electrode for a nonaqueous electrolyte secondary battery. Here, at least one layer of the first active material layer (3) and the second active material layer (4) are alternately stacked as the active material layer. The first active material layer (3) includes a first active material capable of reversibly occluding and releasing lithium, a conductive auxiliary material, and a binder resin. The second active material layer (4) includes a second active material that can be reversibly alloyed with lithium, a conductive auxiliary material, and a binder resin. The outermost active material layer is the first active material layer (3). A hole portion formed in the second active material layer is filled with the first active material layer, and the first and second active material layers (4) are provided at the interface between the first active material layer (3) and the second active material layer (4). A mixed layer (5) of two active material layers is formed. [Selection] Figure 1

Description

  The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary battery including the same.

  A lithium ion secondary battery has a high energy density, can use a non-aqueous electrolyte, and can obtain a high voltage, and has a smaller memory effect than a secondary battery such as a NiCd (Ni-Cd) battery. There is. For this reason, research and development of lithium-ion secondary batteries for application to power supplies for notebook computers, mobile phones, etc., and next-generation electric industry products such as electric bicycles and electric vehicles are being promoted.

  The reaction of the lithium ion secondary battery is composed of an active material that absorbs and releases lithium in the positive and negative electrodes. Currently, carbon materials such as graphite are used as the negative electrode active material, but the theoretical capacity of graphite is as low as 372 mAh / g, and high capacity is expected. Therefore, Si (about 4200 mAh / g), Sn (about 990 mAh / g), and the like are attracting attention as active materials that can occlude and release more lithium by an alloying reaction with lithium. However, such an active material is alloyed with lithium at the time of charging, so that its volume expands to about 4 times and contracts at the time of discharging. When this charge / discharge cycle is performed over time by use, there is a problem in that a large volume change is repeated, whereby the active material is gradually pulverized and drops off from the electrode to deteriorate characteristics.

  As measures against the above problems, composite active material particles (see Patent Document 1) in which the surface of Si particles is coated with a carbon layer, or composite active material particles in which an organic material or an alloy-based active material layer is coated on graphite particles (Patent Document) 2 and 3) have been proposed. Moreover, the structure which formed the metal thin film layer on the alloy type active material layer is disclosed (refer patent document 4). Further, a structure is disclosed in which a layer containing a conductive agent as a main agent is provided between layers containing Si as an active material (see Patent Document 5).

Japanese Patent Laid-Open No. 2001-283384 Japanese Patent No. 3769647 Japanese Patent No. 3103356 JP 2007-019032 A JP 2006-196247 A

  However, in the countermeasures described in Patent Documents 1, 2, and 3, the coating layer alone does not sufficiently suppress pulverization due to a large volume change of the alloy-based active material particles alone. Further, according to the countermeasure described in Patent Document 4, since the metal thin film layer on the surface is thin and hard, volume change of the lower alloy-based active material layer cannot be buffered. Further, with the countermeasure described in Patent Document 5, since Si is exposed on the surface of the layer, the active material cannot be prevented from falling off from the surface. Further, since the layer mainly composed of the conductive agent of the intermediate layer has no volume change or is small, it is insufficient to relieve the stress generated when the volume of Si changes.

  An object of the present invention is to provide a high-performance and long-life electrode for a non-aqueous electrolyte secondary battery in consideration of the above problems.

  In order to solve the above problems, a negative electrode for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention is a non-aqueous electrolyte secondary battery in which an active material layer including a plurality of layers is formed on a current collector. 1 is a negative electrode for use, and includes a first active material capable of reversibly inserting and extracting lithium, a first active material layer including a conductive auxiliary material and a binder resin, and reversibly alloyable with lithium. The second active material layers including the second active material, the conductive auxiliary material, and the binder resin are alternately stacked at least one layer, and the outermost active material layer is the first active material layer, A hole formed in the second active material layer is filled with a part of the first active material layer, and a mixed layer is formed at the interface between the first and second active material layers. .

The current collector is made of a single metal foil made of one of gold, silver, copper, nickel, stainless steel, titanium, and platinum, or an alloy of two or more kinds of metals among the plurality of metals. It may be configured.
The first active material may be at least one selected from the group consisting of graphite, graphite, carbon black, coke, glassy carbon, carbon fiber, and a fired body thereof.

The second active material may be at least one selected from the group consisting of metal elements and compounds such as aluminum, gallium, indium, silicon, germanium, tin, lead, arsenic, antimony, and bismuth.
A non-aqueous electrolyte secondary battery according to an embodiment of the present invention includes the negative electrode for a non-aqueous electrolyte secondary battery according to the above-described aspect, and the active material layer of the positive electrode and the active material layer of the negative electrode are respectively the same through a separator. It is characterized by being laminated or wound so as to face each other.

  A negative electrode for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention is a method for manufacturing a negative electrode for a non-aqueous electrolyte secondary battery in which an active material layer composed of a plurality of layers is formed on a current collector. A first active material layer containing a first active material capable of reversibly inserting and extracting lithium, a conductive auxiliary material and a binder resin, and a second active material capable of reversibly alloying with lithium And a step of alternately laminating at least one layer of the second active material layer containing the conductive auxiliary material and the binder resin, and forming the first active material layer on the outermost surface of the negative electrode for the nonaqueous electrolyte secondary battery A step of forming an active material layer, a step of forming a hole portion in the second active material layer by producing a second active material layer through a hole making step, and a step of forming a hole portion of the second active material layer Filling one active material layer and forming a mixed layer at the interface between the first active material layer and the second active material layer. And butterflies.

  According to one embodiment of the present invention, even if the second active material reversibly alloyed with lithium undergoes a large volume change accompanying charge / discharge, the first active material has a small volume change accompanying charge / discharge. A layer can buffer well and can prevent destruction of each active material layer. In addition, since the first active material layer is formed on the surface, there is no surface exposure of the second active material to the outside of the layer, so that the second active material can be prevented from falling off. Furthermore, a hole part is formed in the second active material layer by producing the second active material layer through a hole forming step, and the first active material layer is formed in the hole part of the second active material layer. Since it is pushed in and promotes the formation of the mixed layer at the interface between the first and second active material layers, a better buffering action is exhibited and the destruction of the active material layer can be suppressed. Therefore, a negative electrode for a non-aqueous electrolyte secondary battery with a high capacity and a long life can be provided.

It is explanatory drawing which shows typically the principal part cross section of the negative electrode for nonaqueous electrolyte secondary batteries which concerns on embodiment of this invention. It is explanatory drawing which shows typically the principal part cross section of the negative electrode for nonaqueous electrolyte secondary batteries which concerns on embodiment of this invention.

Hereinafter, the present invention will be clarified by describing embodiments of the present invention in detail with reference to the drawings. FIG.1 and FIG.2 is explanatory drawing which shows typically the principal part cross section of the negative electrode for nonaqueous electrolyte secondary batteries which concerns on this embodiment.
As shown in FIGS. 1 and 2, the negative electrode 1 for a non-aqueous electrolyte secondary battery (hereinafter referred to as the negative electrode 1) has a first active material layer 3 and a second active material on a current collector 2. In this structure, the material layers 4 are alternately stacked, and the active material layer on the outermost surface is the first active material layer 3. Further, when a plurality of layers are stacked as shown in FIG. 2, the first active material layers 3 above and below the second active material layer 4 are overlapped to form a bag-like outer periphery, and the second inside the bag-like shape. The active material layer 4 may be inserted and sealed or the like.

The first active material layer 3 is a layer containing a first active material capable of reversibly occluding and releasing lithium without being alloyed with lithium, a conductive auxiliary material, and a binder resin. The second active material layer 4 is a layer containing a second active material that can be reversibly alloyed with lithium, a conductive auxiliary material, and a binder resin.
The first active material layer 3 includes a conductive auxiliary material and a binder resin, and has flexibility because it is an active material with a small volume change due to charge / discharge. Therefore, with such a structure, even if the second active material reversibly alloyed with lithium in the second active material layer 4 undergoes a large volume change with charge / discharge, the second active material layer Effectively buffers the stress and suppresses the destruction of each active material layer. Further, since the active material of the second active material layer 4 is not exposed to the outside of the layer, it is possible to prevent the active material from falling off.

Further, if the structure shown in FIG. 2 is used, since the first active material layer 3 is also formed between the current collector 2 and the second active material layer 4, the active material layer from the current collector is formed. Can be prevented. As a result, the active material continues to react effectively even after repeated cycles, and the cycle characteristics are improved.
Further, the second active material layer 4 is manufactured through a hole forming step, so that a hole portion is formed in the second active material layer 4, and the hole portion of the second active material layer 4 is formed by pressing. The first active material layer 3 is easily pushed in, and the formation of the mixed layer 5 of the first and second active material layers is promoted at the interface between the two layers. As a result, a better buffering action is exhibited, and the destruction of the active material layer can be suppressed. Since the first active material layer 3 is pushed by pressing, the hole portion of the second active material layer 4 may have a shape where the bottom (or the inside) is wider than the opening. Note that the second active material layer 4 has a structure in which the particles are partially bonded to each other by a binder resin. Therefore, the second active material layer 4 has communication holes even in a state where the pore forming process is not used. A hole portion is formed by enlarging this hole by the hole making process. In addition, since the pressing step is an essential step in electrode production, it is assumed that the first active material layer 3 is pushed in by pressing. However, the pressing step is not actually limited to pressing, and a method other than pressing is used. It may be used. Whatever method is used, it is only necessary that the hole formed in the second active material layer 4 is finally filled with a part of the first active material layer 3. Moreover, the hole part of the 2nd active material layer 4 may penetrate. For example, the first active material layers 3 facing each other with the second active material layer 4 interposed therebetween may be connected via a through hole in the hole portion.

  The current collector 2 is preferably made of a highly conductive material. Specifically, it is composed of a metal foil alone such as gold, silver, copper, nickel, stainless steel, titanium, platinum or an alloy containing two or more of these metals. Among these, it is particularly desirable to select copper from the viewpoint of cost and relatively low cost and metal ionization tendency. Furthermore, a rolled foil is preferable. Since the crystals in the rolled foil are arranged in the rolling direction, it is difficult to break even when stress is applied. Therefore, there is an advantage that the formability is high when laminated.

The 1st active material layer 3 and the 2nd active material layer 4 are produced with the slurry (slurry) which contains an active material, a conductive support material, and binder resin, for example, and mixed these with the solvent. Thereby, compared with the case where the active material single-piece | unit with a large volume change is used, there exists a softness | flexibility and the buffering ability with respect to stress is high.
For mixing the slurry, it is preferable to use a kneader capable of imparting high shear. Specific examples of the kneader include a disperser such as a ball mill, a bead mill, a sand mill, and an ultrasonic disperser, and a blade-type stirrer such as a planetary mixer, a kneader, a homogenizer, an ultrasonic homogenizer, and a disperser. Among these, a planetary mixer that can be efficiently dispersed by kneading is particularly preferable. In addition, as for the solid content concentration of the slurry, if the solid content concentration is too high, the solid content is aggregated. It is necessary to adjust appropriately according to the material to be used. Furthermore, examples of the method for drying the slurry include hot air drying, hot air drying, vacuum drying, far infrared drying, and constant temperature and high humidity drying.

  In the pore forming process, a material insoluble in the solvent in the slurry is mixed with the slurry forming the second active material layer 4 in addition to the active material, the conductive auxiliary material, and the binder resin which are solid components forming the active material layer. After the second active material layer 4 is formed on the substrate, the material is removed, and the portion where the material is present is used as a hole. A hole portion is formed in the second active material layer 4 by forming the second active material layer 4 through the hole forming step. The hole making method is not particularly limited as long as the material constituting the second active material layer 4 is not eroded finally. For example, a method in which a foaming agent is mixed and decomposed by heating, a method in which resin particles are mixed and dissolved in a solvent, a method in which a liquid having a boiling point difference from the above solvent is mixed and dried stepwise, and the like can be mentioned. Examples of the foaming agent include azo compounds, nitroso compounds, hydrazine derivatives, and bicarbonates. For example, when the solvent is water and the binder is styrene-butadiene rubber (SBR), the hydrazine derivative foaming agent is mixed and heat-treated at a temperature lower than the heat-resistant temperature of the binder to decompose, and the acrylic particles are mixed to produce alcohol. A method of dissolving in a system solvent can be selected.

As the solvent, it is necessary to appropriately select a material in which the solid content to be used is easily dispersed. Specifically, water, an aqueous solvent obtained by mixing ethanol, N-methylpyrrolidone (NMP) or the like with water, a cyclic amide system such as NMP, a linear chain such as N, N-dimethylformamide, N, N-dimethylacetamide or the like. Examples include upper amides, aromatic hydrocarbons such as toluene and xylene.
The first active material needs to be a material that reacts reversibly with lithium and has a small volume change, that is, a material that can reversibly occlude and release lithium without being alloyed with lithium. Since the volume change is small, the active material does not fall off due to the cycle, and the second active material layer can be favorably retained. In addition, since the actual battery reaction is defined within the limit voltage, it is also important that the material reacts well within the charge / discharge potential of the material selected as the second active material. From the above, the first active material is preferably a carbon-based material, and specific examples include graphite, graphite, carbon black, coke, glassy carbon, carbon fiber, and fired bodies thereof.

The second active material needs to be a high-capacity material, that is, a material that can be reversibly alloyed with lithium. Although the volume change accompanying charging / discharging is large, the effect of the first active material layer can be used without a problem of deterioration of cycle characteristics. Specific examples include metal elements and compounds such as aluminum, gallium, indium, silicon, germanium, tin, lead, arsenic, antimony, and bismuth. Among them, silicon having a higher capacity is desirable, and by using a compound, the capacity is reduced, but the volume change can be reduced and the cycle characteristics can be further improved. Examples of the silicon compound include SiOx (0 <x ≦ 2), or LiSiO, SiB ₄ , SiB ₆ , Mg ₂ Si, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi ₂ . _{2, Cu 5 Si, FeSi 2} , MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O and the like.

  As the conductive auxiliary material, it is necessary to appropriately select a material that can ensure conductivity with the current collector and does not cause a chemical reaction in the charge / discharge reaction. In addition, it is preferable to efficiently conduct electrons in a small amount, but it may be selected as appropriate depending on the familiarity with the active material and the binder resin. Specific examples include carbon black, acetylene black, carbon whisker, carbon fiber, natural graphite, artificial graphite, carbon nanoparticles and nanotubes, metal powder such as titanium oxide, ruthenium oxide, nickel, and fibers, and mixtures thereof.

  As the binder resin, it is necessary to appropriately select a polymer that is stable in the reaction potential window of the solvent, the electrolytic solution, and the electrode. Specifically, resin polymers such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PTFE), aromatic polyamide, rubber polymers such as styrene-butadiene rubber (SBR), ethylene-propylene rubber, poly Examples include acrylic, polyolefin, polyamide, polyimide, polyamideimide, epoxy resin, bakelite, and fluorine-based polymer. Examples of the fluoropolymer include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-ethylene trifluoride chloride (CTFE) copolymer, vinylidene fluoride- Examples thereof include hexafluoropropylene fluororubber, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene fluororubber, vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether fluororubber, and the like. In particular, when used for an active material having a small volume change, a fluorine polymer such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene, or a rubber polymer such as styrene / butadiene rubber (SBR) or ethylene / propylene rubber. It is possible to use an aqueous solvent that can suppress the amount of heat in the processing step. When industrially used, it is more preferable to use SBR having a low melting point because it reduces environmental burden and does not require solvent recovery and can reduce costs. In particular, when used for an active material having a large volume change, a polyimide system having a large binding force is preferably used.

  About the composition ratio of an active material layer, it is necessary to adjust suitably about the material to be used. In the case of using an active material with poor conductivity, it is necessary to increase the conductive auxiliary material and the binder resin in order to supplement the load characteristics, but the cycle characteristics may be deteriorated. Moreover, since the capacity | capacitance per unit mass and volume will fall when there are too many material compounding ratios other than an active material, it is necessary to select a suitable ratio. When a plurality of active material layers are laminated, the composition of each active material layer may not be the same, and may be appropriately selected from the viewpoint of adhesiveness with each interface.

In general, the density of the negative electrode 1 is adjusted by pressing in order to improve the characteristics. However, in the present invention, it is also essential in forming the mixed layer 5 of the first and second active material layers. Examples of the pressing method include a metal roll pressing method, a rubber roll pressing method, and a flat plate pressing method. The bulk density of the active material layer after pressing is preferably 1.0 g / cm ² or more and 3.0 g / cm ² or less. When the bulk density exceeds the above range, there are almost no voids in the active material layer, and the electrolytic solution cannot penetrate into the active material layer, resulting in a decrease in battery performance. Further, if the bulk density is less than the above range, the amount of the binder resin that comes into contact with the current collector is reduced, which causes poor adhesion between the active material layer and the current collector.

  The negative electrode 1 is configured as a battery by being stacked or wound so as to face the positive electrode through a separator for preventing a short circuit that separates the positive electrode and the negative electrode in a cell filled with an electrolytic solution. . The capacities of the positive electrode and the negative electrode need to be approximately equal. When the negative electrode capacity is smaller than the positive electrode capacity, the lithium ions released from the positive electrode active material into the electrolyte during the charging reaction cannot all be occluded in the negative electrode active material layer, and the excess lithium ions are It becomes a metal and deposits on the negative electrode plate in a dendrite shape. This precipitate breaks through the separator that exists between the positive electrode and the negative electrode, short-circuits the positive electrode and the negative electrode, or drops into the electrolyte solution, thereby deteriorating battery performance, or abnormalities due to the rapid reaction of lithium metal There is a risk of heat generation. When the negative electrode capacity is larger than the positive electrode capacity, most of the lithium released from the positive electrode active material during the charge reaction is occluded in an irreversible state by the negative electrode active material, resulting in a decrease in cycle capacity. In addition, since the reaction does not proceed at a portion where the positive electrode active material and the negative electrode active material are not opposed to each other, it is necessary to accurately align both electrodes at the time of stacking.

Similar to the negative electrode, the positive electrode includes a current collector and an active material layer including an active material on the current collector, a conductive auxiliary material, and a binder resin. An active material will not be specifically limited if it is a compound which can occlude and discharge | release lithium ion. The inorganic compound constituting the positive electrode active material, a composition formula, LixMO _2, or, LiyM ₂ O ₄ (where, M is a transition metal, 0 ≦ x ≦ 1,1 ≦ y ≦ 2) composite oxide indicated by An oxide having a hole on the tunnel, a metal chalcogenide having a layered structure, or a chalcogen compound containing lithium ions can be used. _{Specifically, LiCoO, NiO 2, Ni 2} O 3, Mn 2 O 4, LMn 2 O 4, MnO 2, Fe 2 O 3, Fe 3 O 4, FeO 2, V 2 O 5, V 6 O 13 , VOx, Nb ₂ O ₅ , Bi ₂ O ₃ , Sb ₂ O ₃ , etc. Group V metal compounds, CrO ₃ , Cr ₂ O ₃ , MoO ₃ , MoS ₂ , WO ₃ , SeO ₂ , etc. _{compound, TiO 2, TiS 2, SiO} 2, SnO, CuO, CuO 2, Ag 2 O, CuS, CuSO 4, it includes like. Moreover, it is good also as what mixed said transition metal 2 or more types, or the compound containing 2 or more types of transition metals, what is called a binary system and a ternary system. Furthermore, examples of organic compounds constituting the positive electrode active material include conductive polymer compounds such as polypyrrole, polyaniline, polyparaphenylene, polyacetylene, and polyacene materials.

  The separator is not particularly limited as long as it is stable with respect to the electrolytic solution, can sufficiently impregnate the electrolytic solution to express ionic conductivity, and can prevent a short circuit between the positive electrode and the negative electrode. Absent. Specifically, porous materials such as a porous polymer film made of a polyolefin such as polypropylene and polyethylene, a fluororesin, and the like, a glass filter, and a nonwoven fabric can be used.

The electrolytic solution is not particularly limited as long as it has good ionic conductivity and does not decompose at the battery voltage. For example, a solution obtained by dissolving a lithium salt as a supporting electrolyte in an organic solvent, a polymer electrolyte, an inorganic solid electrolyte, and a composite material thereof can be used. As the organic solvent, chain esters, γ-lactones, chain ethers, cyclic ethers, nitriles, and the like can be used. Specifically, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl And carbonate (DPC). As _{the electrolyte, LiBF 4, LiClO 4, LiAlCl} 4, LiPF 6, LiAsF 6, LiSbF 6, LiSCN, LiCl, LiBr, LiI, etc. _{LiCF 3 SO 3, LiC 4 F} 9 SO 3 and the like.

(Effect of this embodiment)
According to this embodiment, there are the following effects.
The negative electrode according to the present embodiment includes, on a current collector, a first active material layer including a first active material capable of reversibly occluding and releasing lithium, a conductive auxiliary material, and a binder resin, lithium And at least one second active material layer containing a second active material reversibly alloyable, a conductive auxiliary material, and a binder resin, and the outermost active material layer is the first active material layer. 1 is an active material layer.

  As a result, even if the second active material reversibly alloyed with lithium undergoes a large volume change along with charge / discharge, the first active material layer with a small volume change associated with charge / discharge can buffer well. The destruction of each active material layer can be suppressed. In addition, since the first active material layer is formed on the outermost surface, there is no surface exposure of the second active material outside the layer, so that the second active material can be prevented from falling off. Furthermore, a hole part is formed in the second active material layer by producing the second active material layer through a hole forming step, and the first active material is formed in the hole part of the second active material layer by pressing. Since the layer is pushed in and the formation of the mixed layer is promoted at the interface between the first and second active material layers, a better buffering action is exhibited and the destruction of the active material layer can be suppressed. Therefore, it is possible to provide a negative electrode for a nonaqueous electrolyte secondary battery having a high capacity and a long life.

Further, in the case where the first active material layer is formed between the current collector and the second active material layer, peeling of the active material layer from the current collector can be suppressed, so that the capacity and lifetime are higher. A negative electrode for a non-aqueous electrolyte secondary battery can be provided.
As mentioned above, although embodiment of this invention was explained in full detail, actually, it is not restricted to said embodiment, Even if there is a change of the range which does not deviate from the summary of this invention, it is included in this invention.

Examples of the present invention will be described below. However, the examples do not limit the present invention.
Example 1
100 parts by mass of Si nanopowder (manufactured by Aldrich) as an active material, 25 parts by mass of vapor grown carbon fiber (“VGCF-H” manufactured by Showa Denko) as a conductive auxiliary material, and acetylene black (“DENKA BLACK HS-100 manufactured by Denki Kagaku Kogyo) ] 25 parts by mass, 1 part by mass of carboxymethylcellulose ammonium salt ("DN-800H" manufactured by Daicel Chemical) as binder resin and 3 parts by mass of styrene-butadiene rubber ("BM-400B" manufactured by Nippon Zeon), pore-forming material As 5 parts by weight of hydrazine derivative-based foaming agent A (4,4′-oxybis (benzenesulfonylhydrazide), foaming temperature 155 ° C.) and 5 parts by weight of urea-based foaming aid (acting to lower the foaming start temperature to 127 ° C.) Then, water as a solvent is added as appropriate so that the solid content is 45 parts by mass, and 120% is added with a planetary mixer. By partially mixing, a slurry for forming the second active material layer was produced.

The slurry is applied to a 12 μm thick copper foil (made by Mitsui Metals), which is a current collector, using a doctor blade type applicator, put in a hot air oven and dried at 80 ° C., and then 130 ° C. Then, the foaming agent was removed, and a second active material layer was formed on the current collector.
Next, 90 parts by mass of natural graphite (“SMG” manufactured by Hitachi Chemical Co., Ltd.) as an active material, 10 parts by mass of artificial graphite (“SFG-6” manufactured by TIMCAL) as a conductive auxiliary material, and carboxymethylcellulose ammonium salt (Daicel) as a binder resin Water as a solvent is appropriately added to 1 part by mass of “DN-800H” manufactured by Chemical Co., Ltd. and 2 parts by mass of styrene-butadiene rubber (“BM-400B” manufactured by Nippon Zeon Co., Ltd.). By mixing with a mixer for 120 minutes, a slurry for forming the first active material layer was prepared.

  The slurry is applied onto the second active material layer using a doctor blade type applicator, put into a hot air oven, dried at 80 ° C., and then pressed by a roll press. Example 1 The negative electrode was made.

(Example 2)
In Example 1, it produced similarly to Example 1 except having formed the 1st active material layer on the electrical power collector beforehand before formation of the 2nd active material layer, and it was set as the negative electrode of Example 2.
(Example 3)
The pore-forming material of Example 1 was prepared in the same manner as in Example 1 except that 7 parts by weight of the azo compound-based foaming agent A (azodicarbonamide, foaming temperature 140 ° C.) and the removal temperature of the foaming agent was 145 ° C. The negative electrode of Example 3 was obtained.
Example 4
In Example 3, a negative electrode of Example 4 was prepared in the same manner as in Example 3 except that the first active material layer was formed on the current collector in advance before forming the second active material layer.

Next, a comparative example for comparison with the embodiment of the present invention will be described.
(Comparative Example 1)
In Example 1, a second active material layer was produced on the current collector in the same manner as in Example 1 except that no pore forming material was used in the slurry for forming the second active material layer. Then, it pressed with the roll press and it was set as the negative electrode of the comparative example 1.

(Comparative Example 2)
After the second active material layer was formed in the same manner as in Comparative Example 1, the first active material layer was formed in the same manner as in Example 1, and then pressed by a roll press to obtain a negative electrode of Comparative Example 2.
(Comparative Example 3)
In Comparative Example 2, a negative electrode of Comparative Example 3 was prepared in the same manner as Comparative Example 2 except that the first active material layer was previously formed on the current collector before the second active material layer was formed.

(Evaluation)
Batteries were prepared using the negative electrodes of the above examples and comparative examples, and charge / discharge evaluation was performed.
First, the positive electrode which becomes a counter electrode of said negative electrode in a battery structure was produced as follows. First, 90 parts by mass of LiMn ₂ O ₄ (“Type-F” manufactured by Mitsui Metals), 5 parts by mass of acetylene black (“Denka Black HS-100” manufactured by Denki Kagaku Kogyo) as a conductive auxiliary material, and PVdF (Kureha Battery as a binder resin) NMP (Mitsubishi Chemical Co., Ltd.) as a solvent is added appropriately to 5 parts by mass of Materials Japan “# 7200”) so as to have a solid content of 65 parts by mass, and mixed for 120 minutes with a planetary mixer. A slurry for forming the material layer was prepared.

Next, the above slurry is applied onto a 15 μm-thick aluminum foil (made in Japan) as a current collector using a doctor blade type applicator, and placed in a hot air oven at 120 ° C. for 30 minutes. The slurry was dried. The coating amount was adjusted to 0.9 times the negative electrode capacity. Then, it pressed with the roll press and was set as the positive electrode. The positive electrode was punched to φ14 mm, the negative electrode was punched to φ15 mm, a φ16 mm separator was sandwiched between the electrodes so as not to be short-circuited, and the electrolyte was filled to prepare a coin cell. A polyolefin resin microporous membrane (“Hypore ND525” manufactured by Asahi Kasei E-Materials) was used as the separator. As the electrolytic solution, a solution in which LiPF ₆ was dissolved in ethylene carbonate: diethyl carbonate = 3: 7 so as to be 1 M and 2 parts by mass of vinylene carbonate was added was used.

  Charging / discharging evaluation was performed using said coin cell. In other words, charging / discharging at a low rate is repeated, and the point at which the increase in discharge capacity is no longer observed is defined as the first cycle (discharge capacity retention rate 100%). went. Table 1 shows the discharge capacity retention rate of each battery at that time.

  As shown in Table 1, when the example of the present invention was adopted, the discharge capacity retention rate was improved as compared with the comparative example of the single layer and the same layer structure. From the above, it was confirmed that a non-aqueous electrolyte secondary battery having a high capacity and a long life could be produced by using the electrode having the configuration of the example.

  A negative electrode for a non-aqueous electrolyte secondary battery according to the present invention includes a first active material layer containing a first active material capable of reversibly occluding and releasing lithium, a conductive auxiliary material, and a binder resin, lithium And at least one second active material layer containing a second active material that can be reversibly alloyed, a conductive auxiliary material, and a binder resin are alternately laminated. The active material layer on the outermost surface is the first active material layer. In addition, the second active material layer is formed through a hole forming step to form a hole portion. Furthermore, the first active material layer is pushed into the hole portion of the second active material layer by pressing, and a mixed layer is formed at the interface between the first and second active material layers. For this reason, it is possible to provide a negative electrode for a non-aqueous electrolyte secondary battery that prevents the active material from falling off due to the charge / discharge cycle and has a high capacity and a long life.

DESCRIPTION OF SYMBOLS 1 ... Negative electrode 2 ... Current collector 3 ... 1st active material layer 4 ... 2nd active material layer 5 ... Mixed layer of 1st active material layer and 2nd active material layer

Claims (6)

A negative electrode for a non-aqueous electrolyte secondary battery in which an active material layer composed of a plurality of layers is formed on a current collector,
The first active material layer and the second active material layer are alternately laminated at least one layer,
The first active material layer includes a first active material capable of reversibly occluding and releasing lithium, a conductive auxiliary material, and a binder resin.
The second active material layer includes a second active material reversibly alloyable with lithium, a conductive auxiliary material, and a binder resin.
The outermost active material layer is the first active material layer, and a part of the first active material layer is filled in a hole formed in the second active material layer, and the first active material layer is filled. A negative electrode for a nonaqueous electrolyte secondary battery, wherein a mixed layer is formed at an interface between the material layer and the second active material layer.   The current collector is composed of a single metal foil made of one of gold, silver, copper, nickel, stainless steel, titanium, and platinum, or an alloy of two or more kinds of metals among the plurality of metals. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1.   The first active material is at least one selected from the group consisting of graphite, graphite, carbon black, coke, glassy carbon, carbon fiber, and a fired body thereof. Item 5. A negative electrode for a non-aqueous electrolyte secondary battery according to Item 2.   The second active material is made of at least one metal element selected from the group consisting of aluminum, gallium, indium, silicon, germanium, tin, lead, arsenic, antimony, bismuth, and a compound. The negative electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3.   5. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the active material layer of the positive electrode and the active material layer of the negative electrode face each other at the same position via a separator. A non-aqueous electrolyte secondary battery, characterized in that it is laminated or wound around. A method for producing a negative electrode for a non-aqueous electrolyte secondary battery in which an active material layer comprising a plurality of layers is formed on a current collector,
A first active material layer containing a first active material capable of reversibly inserting and extracting lithium, a conductive auxiliary material and a binder resin; a second active material capable of reversibly alloying with lithium; and a conductive auxiliary material A step of alternately laminating at least one layer of a second active material layer containing a material and a binder resin;
Forming the first active material layer as an active material layer on the outermost surface of the negative electrode for a non-aqueous electrolyte secondary battery;
Forming a hole in the second active material layer;
Filling a hole portion of the second active material layer with the first active material layer, and forming a mixed layer at an interface between the first active material layer and the second active material layer. The manufacturing method of the negative electrode for nonaqueous electrolyte secondary batteries characterized by the above-mentioned.

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