JP2015069711A - Negative electrode for nonaqueous electrolyte secondary battery, method for manufacturing the same, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for a high-capacity and long-life nonaqueous electrolyte secondary battery.SOLUTION: A negative electrode for a nonaqueous electrolyte secondary battery comprises a first active material layer (3) on a collector (2) and a second active material layer (4) covering the first active material layer (3). The first active material layer (3) includes a first active material which can be reversibly alloyed with lithium, a conductive auxiliary material, and a binder resin. The second active material layer (4) includes a second active material which is not alloyed with lithium and can reversibly occlude and discharge lithium, a conductive auxiliary material, and a binder resin.

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 is characterized by a high energy density, a high voltage can be obtained because of the use of a non-aqueous electrolyte, and a smaller memory effect than a secondary battery such as a nickel cadmium battery. For this reason, research and development of lithium-ion secondary batteries for application to power supplies such as notebook computers and mobile phones, 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 made up of an active material that occludes 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 charging / discharging cycle is performed over time by use, there is a problem that the active material gradually becomes fine powder due to repeated large volume changes and drops from the electrode, which may deteriorate the characteristics.

  As a countermeasure for the above problem, composite active material particles (Patent Document 1) in which the surface of Si particles is coated with a carbon layer, or composite active material particles (Patent Document 2, which covers an organic material or an alloy-based active material layer on graphite particles). 3) has been proposed. Moreover, the structure which formed the metal thin film layer on the alloy type active material layer is disclosed (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 (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, the countermeasures described in Patent Documents 1 to 3 do not sufficiently suppress pulverization due to a large volume change of the alloy-based active material particles alone with the coating layer 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. Furthermore, since the layer mainly composed of the conductive agent of the intermediate layer has no volume change, it is insufficient to suppress the stress of the volume change of Si.
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 problems in the background art.

  In order to solve the above problems, a negative electrode for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention covers a first active material layer formed on a current collector and the first active material layer The first active material layer is a layer including a first active material reversibly alloyable with lithium, a conductive auxiliary material, and a binder resin. The active material layer is a layer containing a second active material capable of reversibly occluding and releasing lithium without being alloyed with lithium, a conductive auxiliary material, and a binder resin.

A mixed layer formed by mixing a part of the components of the first active material layer in the second active material layer may be formed between the first active material layer and the second active material layer. good.
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 metals of the plurality of metals. May be.

The first active material may be at least one selected from the group consisting of metal elements and compounds such as Al, Ga, In, Si, Ge, Sn, Pb, As, Sb, and Bi.
The second 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 method for producing a negative electrode for a non-aqueous electrolyte secondary battery, which is an aspect of the present invention, includes a first step of applying and drying a slurry for forming the first active material layer on a current collector, and the first step. A second step of applying and drying a slurry for forming the second active material layer on the active material layer, wherein the binder resin of the first active material layer is formed by the second step. The mixed layer is formed by dissolving in a solvent of a slurry forming the second active material layer, and the second active material layer contains the component of the first active material layer.

  Another method for producing a negative electrode for a non-aqueous electrolyte secondary battery, which is an aspect of the present invention, includes a step of applying and drying a slurry for forming the first active material layer on a current collector, and the first step. A step of applying and drying a slurry for forming the second active material layer on the active material layer; and a step of simultaneously pressing the negative electrode on which the first and second active material layers are formed. The mixed layer in which the component of the first active material layer is included in the second active material layer is formed.

  A nonaqueous electrolyte secondary battery according to an aspect of the present invention includes the negative electrode for a nonaqueous electrolyte secondary battery according to the above aspect, and the positive electrode active material layer and the negative electrode active material layer are located at the same position via a separator. It is characterized by being laminated or wound so as to face each other.

  According to the aspect of the present invention, in the negative electrode, a first active material layer including a first active material that can be reversibly alloyed with lithium, a conductive auxiliary material, and a binder resin is formed on a current collector. In addition, a second active material layer that covers the first active material layer and includes a second active material capable of reversibly occluding and releasing lithium without being alloyed with lithium, a conductive auxiliary material, and a binder resin is formed. It has a structured. As a result, even if the first active material reversibly alloyed with lithium undergoes a large volume change due to charge / discharge, the second active material layer having a small volume change accompanying charge / discharge is well buffered. In addition, since there is no surface exposure outside the first active material layer, it is possible to prevent the first active material from falling off, and to provide a negative electrode for a non-aqueous electrolyte secondary battery having a high capacity and a long life. It is.

  Here, the step of dissolving the binder resin of the first active material layer in the solvent of the slurry forming the second active material layer or simultaneously pressing the negative electrode on which the first and second active material layers are formed In the case where a mixed layer of both layers is provided at the interface between the first and second active material layers, the adhesion at the interface between the two layers is improved, and the non-aqueous electrolysis has a higher capacity and a longer life. A negative electrode for a liquid secondary battery 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 are examples of explanatory views schematically showing a cross-section of the main part of a negative electrode for a non-aqueous electrolyte secondary battery according to the present invention.
As shown in FIG. 1, the negative electrode 1 for a nonaqueous electrolyte secondary battery (hereinafter sometimes simply referred to as the negative electrode 1) has a first active material layer 3 formed on a current collector 2. The second active material layer 4 that covers the first active material layer 3 is formed. The first active material layer 3 is a layer containing a first active material that can be reversibly 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 capable of reversibly occluding and releasing lithium without being alloyed with lithium, a conductive auxiliary material, and a binder resin.

  With such a structure, the first active material layer covers the second active material layer 4 even if the first active material reversibly alloyed with lithium undergoes a large volume change due to charge / discharge. Therefore, the first active material is not exposed to the outside of the layer, so that the first active material can be prevented from falling off. In addition, since the second active material layer 4 includes a conductive auxiliary material and a binder resin and has a small volume change due to charge and discharge, the second active material layer 4 has flexibility, and thus the first active material layer 3 It is possible to satisfactorily buffer the stress of the entire volume change, and to prevent the first active material from falling off without breaking the second active material layer 4. As a result, the first active material continues to react effectively even after repeated cycles, and the cycle characteristics are improved.

Further, as shown in FIG. 2, a part of the components of the first active material layer is mixed in the second active material layer between the first active material layer 3 and the second active material layer 4. A mixed layer 5 may be formed. Thereby, the interface adhesiveness of both layers improves, the said effect of a 2nd active material layer is accelerated | stimulated, and cycling characteristics improve more.
For example, the negative electrode 1 in which the binder resin of the first active material layer 3 is dissolved in the solvent of the slurry that forms the second active material layer 4 or the first and second active material layers 3 and 4 are formed. By selecting the step of simultaneously pressing, the mixed layer 5 of both layers is formed at the interface between the first and second active material layers 3 and 4.

  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 and 2nd active material layers 3 and 4 are produced with the slurry which mixed the active material, the electrically conductive auxiliary material, and binder resin with these. 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. Therefore, it is possible to prevent the first active material from falling off without destroying the second active material layer 4.
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. As for the solid content concentration of the slurry, if the solid content concentration is too high, the solid content aggregates, and if it is too low, it precipitates during drying, resulting in non-uniform material dispersion in the active material layer and reduced battery performance. It is necessary to adjust appropriately according to the material to be used. 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.

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 high-capacity material, that is, a material that can be reversibly alloyed with lithium. Although the volume change accompanying charging / discharging is large, the second active material layer 4 can be used without any problem of deterioration of cycle characteristics by preventing the falling off by the second active material layer 4. Specific examples include metal elements and compounds such as Al, Ga, In, Si, Ge, Sn, Pb, As, Sb, and Bi. Among these, higher capacity Si 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 Si compound include SiOx (0 <x ≦ 2), LiSiO, SiB ₄ , SiB ₆ , Mg ₂ Si, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi. _{2, Cu 5 Si, FeSi 2} , MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, etc. _{Si 3 N 4, Si 2 N} 2 O and the like.

  The second 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, there is no loss of the active material due to the cycle, and the first active material layer 3 can be held well. 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 first active material. From the above, the second active material is preferably a carbon-based material, specifically, graphite, graphite, carbon black, coke, glassy carbon, carbon fiber, and a fired body thereof.

  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 appropriately selected depending on the familiarity with the active material and the binder resin. Specifically, carbon powder, acetylene black, carbon whisker, carbon fiber, natural graphite, artificial graphite, carbon nanoparticles and nanotubes, titanium oxide, ruthenium oxide, aluminum, nickel and other metal powders and fibers, and mixtures thereof It is done.

  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 preferable to use a water-based solvent that can suppress the amount of heat in the processing step, and when used industrially, it has a low melting point because it reduces the environmental burden and eliminates the need for solvent recovery and cost reduction. It is more preferable to use SBR. 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 solid content compounding 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 an appropriate ratio.

In order to improve the characteristics, the density of the negative electrode 1 is generally adjusted by pressing. 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 stacking the negative electrode 1 so as to face the positive electrode through a separator for preventing a short circuit 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, 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 and the like. Moreover, it is good also as what mixed the 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 the organic compound constituting the positive electrode active material include conductive polymer compounds such as polypyrrole, polyaniline, polyparaphenylene, polyacetylene, and polyacene materials. The current collector, the conductive auxiliary material, and the binder resin can be the same material as the negative electrode.

  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. Specific examples include porous materials such as a porous polymer film made of polyolefin such as polypropylene and polyethylene and a fluororesin, a glass filter, and a non-woven fabric.

The electrolytic solution has good ionic conductivity and is not particularly limited as long as there is no decomposition at the battery voltage. A solution in which a lithium salt as a supporting electrolyte is dissolved in an organic solvent, a polymer electrolyte, an inorganic solid electrolyte, And their composites 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 A carbonate (DPC) is mentioned. As _{the electrolyte, LiBF 4, LiClO 4, LiAlCl} 4, LiPF 6, LiAsF 6, LiSbF 6, LiSCN, LiCl, LiBr, LiI, and the like _{LiCFSO 3, LiC 4 F 9 SO} 3.

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 (made by Aldrich) as an active material, 25 parts by mass of vapor grown carbon fiber (VGCF-H made by Showa Denko) and 25 parts by mass of acetylene black (Denka Black HS-100 made by Denki Kagaku Kogyo) as a conductive auxiliary material NMP (manufactured by Mitsubishi Chemical) as a solvent is added to 25 parts by mass of a polyamidoimide resin (Hitachi Chemical HPC-9000) as a binder resin, and added to a solid content of 30 parts by mass, and 120 minutes with a planetary mixer. By mixing, a slurry for forming the first 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 into a hot air oven and treated at 120 ° C. for 30 minutes to dry the slurry. Thus, a first active material layer was formed on the current collector.
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, 25 parts by mass of polyamideimide resin (HPC-9000 manufactured by Hitachi Chemical Co., Ltd.) as a binder resin In addition, NMP (manufactured by Mitsubishi Chemical) as a solvent was appropriately added so as to have a solid content of 40 parts by mass, and mixed with a planetary mixer for 120 minutes to prepare a slurry for forming the second active material layer. .

  The slurry was applied onto the first active material layer using a doctor blade type applicator, put into a hot air oven and treated at 120 ° C. for 30 minutes to dry the slurry, and then fired at 200 ° C. for 3 hours. . Then, it pressed with the roll press and it was set as the negative electrode of Example 1.

(Example 2)
A negative electrode of Example 2 was prepared in the same manner as in Example 1 except that the first active material in Example 1 was changed to 100 parts by mass of SiO powder (manufactured by Aldrich).
(Example 3)
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 from Showa Denko) and 30 parts by mass of acetylene black (Denka Black HS-100, manufactured by Denki Kagaku Kogyo) as a conductive auxiliary material Parts, 1 part by mass of carboxymethylcellulose ammonium salt (DN-800H manufactured by Daicel Chemical Industries) as a binder resin and 3 parts by mass of styrene-butadiene rubber (BM-400B manufactured by Nippon Zeon), and water as a solvent to 45 parts by mass The slurry for forming a 1st active material layer was produced by adding suitably so that it might become, and mixing for 120 minutes with a planetary mixer.

The slurry is applied to a 12 μm thick copper foil (Mitsui Metals), which is a current collector, using a doctor blade type applicator, put into a hot air oven and treated at 80 ° C. for 30 minutes to dry the slurry. A first active material layer was formed on the current collector.
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, carboxymethylcellulose ammonium salt (DN-800H manufactured by Daicel Chemical Industries) 1 as a binder resin By properly adding water as a solvent to 2 parts by mass and styrene-butadiene rubber (BM-400B manufactured by Nippon Zeon) so that the solid content is 45 parts by mass and mixing with a planetary mixer for 120 minutes, the second A slurry for forming an active material layer was prepared.
The slurry was applied onto the first active material layer using a doctor blade type applicator, put into a hot air oven and treated at 80 ° C. for 30 minutes to dry the slurry. Then, it pressed with the roll press and it was set as the negative electrode of Example 3.

Example 4
A negative electrode of Example 4 was prepared in the same manner as in Example 3 except that the first active material in Example 3 was changed to 100 parts by mass of SiO powder (manufactured by Aldrich).
(Example 5)
100 parts by mass of SiO powder (manufactured by Aldrich) as an active material, 10 parts by mass of vapor grown carbon fiber (VGCF-H, manufactured by Showa Denko) and 10 parts by mass of acetylene black (Denka Black HS-100, manufactured by Denki Kagaku Kogyo) as a conductive auxiliary material In addition, NMP (manufactured by Mitsubishi Chemical) as a solvent is appropriately added to 10 parts by mass of PVdF (# 7200 manufactured by Kureha Battery Materials Japan) as a binder resin, and mixed for 120 minutes with a planetary mixer. Thus, a slurry for forming the first 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 into a hot air oven and treated at 120 ° C. for 30 minutes to dry the slurry. Thus, a first active material layer was formed on the current collector.
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, 10 parts by mass of PVdF (# 7200 manufactured by Kureha Battery Japan) as a binder resin, solvent NMP (manufactured by Mitsubishi Chemical) was added as appropriate so as to have a solid content of 55 parts by mass, and mixed with a planetary mixer for 120 minutes to prepare a slurry for forming the second active material layer.
The slurry was applied onto the first active material layer using a doctor blade type applicator, put into a hot air oven and treated at 120 ° C. for 30 minutes to dry the slurry. Then, it pressed with the roll press and it was set as the negative electrode of Example 5.

(Example 6)
A negative electrode of Example 6 was prepared in the same manner as in Example 5 except that the first active material in Example 5 was changed to 100 parts by mass of SiO powder (manufactured by Aldrich).
(Comparative Example 1)
As in Example 1, after forming the first active material layer on the current collector, it was put into a hot air oven and baked at 200 ° C. for 3 hours, and then pressed by a roll press under the same conditions as in Example 1. Thus, an electrode of Comparative Example 1 was obtained.

(Comparative Example 2)
As in Example 2, a first active material layer was formed on a current collector, then placed in a hot air oven and baked at 200 ° C. for 3 hours, and then pressed by a roll press under the same conditions as in Example 2. Thus, an electrode of Comparative Example 2 was obtained.
(Comparative Example 3)
Similarly to Example 3, a first active material layer was formed on the current collector, and then pressed by a roll press under the same conditions as Example 3 to obtain an electrode of Comparative Example 3.
(Comparative Example 4)
In the same manner as in Example 4, a first active material layer was formed on the current collector, and then pressed by a roll press under the same conditions as in Example 4 to obtain an electrode of Comparative Example 4.

(Comparative Example 5)
Similarly to Example 5, a first active material layer was formed on the current collector, and then pressed by a roll press under the same conditions as Example 5 to obtain an electrode of Comparative Example 4.
(Comparative Example 6)
In the same manner as in Example 5, a first active material layer was formed on the current collector, and then pressed by a roll press under the same conditions as in Example 5 to obtain an electrode of Comparative Example 5.
(Evaluation)
Batteries were produced using the negative electrodes of the examples and comparative examples, and charge / discharge evaluation was performed.

In the battery configuration, the positive electrode serving as the counter electrode of the negative electrode was produced as follows. First, 90 parts by mass of LiMn ₂ O ₄ (Mitsui Metals Type-F), 5 parts by mass of acetylene black (Denka Black HS-100 manufactured by Denki Kagaku Kogyo) as a conductive auxiliary material, and PVDF (manufactured by Kureha # 7200) 5 as a binder resin A slurry for forming an active material layer of the positive electrode is prepared by appropriately adding NMP (made by Mitsubishi Chemical) as a solvent to mass parts so as to have a solid content of 65 parts by mass and mixing with a planetary mixer for 120 minutes. did.

Next, the slurry was applied onto a 15 μm-thick aluminum foil (made in Japan) as a current collector using a doctor blade type applicator, placed in a hot air oven, treated 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 two 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 the coin cell. The charge / discharge at a low rate was repeated, and the place where the increase in the discharge capacity was not observed was regarded as the first cycle (discharge capacity retention rate 100%), and thereafter 100 cycles of charge / discharge were performed with charge 0.2C and discharge 1C. . The discharge capacity retention rate at this time is shown in Table 1.

表１に示すように、各種活物質およびバインダー樹脂を使用した実施例において、比較例より放電容量維持率が向上したことが分かる。以上のことから、実施例の構成の電極により、高容量かつ高寿命な非水電解液二次電池が作製可能であることを確認した。

As shown in Table 1, in the examples using various active materials and binder resins, it can be seen that the discharge capacity retention rate was improved from the comparative example. 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.

  The negative electrode for a non-aqueous electrolyte secondary battery according to the present invention has a first active material layer that includes a first active material that can be reversibly alloyed with lithium, a conductive auxiliary material, and a binder resin on a current collector. And a second active material layer containing a second active material capable of reversibly occluding and releasing lithium, a conductive auxiliary material and a binder resin. Therefore, 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 and 2nd active material layer

Claims (8)

A first active material layer formed on the current collector, and a second active material layer covering the first active material layer,
The first active material layer is a layer containing a first active material reversibly alloyable with lithium, a conductive auxiliary material, and a binder resin.
The second active material layer is a layer containing a second active material capable of reversibly occluding and releasing lithium without being alloyed with lithium, a conductive auxiliary material, and a binder resin. Negative electrode for liquid secondary battery.   Between the first active material layer and the second active material layer, a mixed layer in which a part of the components of the first active material layer is mixed in the second active material layer is formed. The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1.   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 metals of the plurality of metals. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1 or 2.   The first active material is at least one selected from the group consisting of metal elements and compounds such as Al, Ga, In, Si, Ge, Sn, Pb, As, Sb, and Bi. The negative electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3.   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. The negative electrode for a non-aqueous electrolyte secondary battery according to any one of Items 4. A method for producing a negative electrode for a nonaqueous electrolyte secondary battery according to claim 2,
A first step of applying and drying a slurry for forming the first active material layer on a current collector;
And a second step of applying and drying a slurry for forming the second active material layer on the first active material layer,
In the second step, the binder resin of the first active material layer is dissolved in the solvent of the slurry that forms the second active material layer, and the first active material layer is added to the second active material layer. And the mixed layer is formed to produce a negative electrode for a non-aqueous electrolyte secondary battery. A method for producing a negative electrode for a nonaqueous electrolyte secondary battery according to claim 2,
Applying and drying a slurry for forming the first active material layer on a current collector;
Applying and drying a slurry for forming the second active material layer on the first active material layer;
Simultaneously pressing the negative electrode on which the first and second active material layers are formed,
The method for producing a negative electrode for a non-aqueous electrolyte secondary battery, wherein the mixed layer containing the component of the first active material layer is formed in the second active material layer by the pressing.   A negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the positive electrode active material layer and the negative electrode active material layer are opposed to each other at the same position via a separator. A non-aqueous electrolyte secondary battery, characterized in that it is laminated or wound around.

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