JP5832729B2 - Secondary battery electrode and non-aqueous electrolyte battery - Google Patents

Description

  The present invention relates to an electrode for a secondary battery and a non-aqueous electrolyte battery.

  In the field of secondary batteries, there is an increasing demand for the development of batteries having a high energy density. Non-aqueous electrolyte batteries, particularly lithium secondary batteries (lithium ion secondary batteries) have been developed as secondary batteries that satisfy this requirement. Lithium secondary batteries have the advantages of higher voltage, higher energy density and lighter weight than nickel cadmium batteries, lead livestock batteries, and nickel metal hydride batteries.

  A lithium secondary battery is a battery having an active material that absorbs and releases lithium ions in both positive and negative electrodes. As a negative electrode active material of a lithium secondary battery, metallic lithium, lithium alloy, carbon, and graphite are widely known.

  Although metallic lithium achieves the highest energy density, there is a problem in terms of battery life and safety because lithium dendrites on the negative electrode surface, internal short circuit with the positive electrode, and high reaction activity to the electrolyte. Lithium alloys such as Li-Pb and Li-Al greatly improve these problems, but there is a problem of particle collapse and pulverization associated with charge / discharge cycles, and sufficient battery life has not been obtained. .

  Carbon or graphite is currently used as a negative electrode material for lithium secondary batteries because there is no or little lithium dendrite precipitation and there is no or little particle collapse associated with charge / discharge cycles. However, although many efforts have been made to increase the discharge capacity of these materials, there is a problem that the discharge capacity of these materials is significantly lower than that of metal materials at present.

  Secondary batteries capable of realizing a high energy density for such problems have been developed and disclosed in, for example, Patent Documents 1 to 6.

  Patent Document 1 includes metal-carbon composite particles in which metal particles are embedded in a plurality of phases of carbon, and the carbon includes graphite and amorphous carbon, and includes graphite particles and metal particles in which the metal particles are embedded. Metal-carbon composite particles having a structure in which no graphite particles are integrated through amorphous carbon are disclosed.

  In the cited document 2, a non-aqueous electrolyte secondary battery having a composite negative electrode plate in which a porous metal substrate filled with a carbon material and a porous metal substrate filled with silicon are superposed and the metal substrates are joined together. Is disclosed.

  Reference 3 discloses a non-aqueous electrolyte secondary battery using a negative electrode in which the surface of a foam metal that is not alloyed with lithium is coated with a material that forms an alloy with lithium and can absorb and release lithium ions. ing.

  Cited Document 4 discloses a battery in which a porous metal having a metal alloying with lithium serves as a negative electrode active material and a negative electrode current collector.

  In the cited document 5, an electrode active material thin film layer is formed on a porous metal current collector, and carbon is disposed between the porous metal current collector and the electrode active material thin film layer. Is disclosed.

  Cited Document 6 discloses at least one element selected from the group consisting of a conductive material having a diameter smaller than the average pore size of the porous conductive substrate, and a metal element and a semimetal element capable of reversibly occluding and releasing lithium. A non-aqueous electrolyte secondary battery including a simple substance, an alloy, or a compound containing as an active material is disclosed.

  However, when the alloy particles having a large volume expansion and the carbon having a small volume expansion are present in the same layer as the particles described in the cited document 1, if the expansion and contraction due to charge and discharge is repeated, the carbon and the alloy are There is a problem in that a gap is generated and the conductive network is torn, so that the capacity is reduced (or a large amount of conductive auxiliary material is required and sufficient capacity cannot be obtained).

  In the secondary battery described in the cited document 2, the volume occupied by the porous metal substrate in the negative electrode is large, and the filling amount of the active material amount cannot be increased (particularly, the carbon side does not need to suppress expansion, It is necessary to use a porous metal for the silicon side). Furthermore, in manufacturing the negative electrode, it is necessary to fill the metal substrate with each material and then perform welding, which not only complicates the process, but also requires a welding operation for the number of negative electrodes to be stacked, resulting in a large cost. There was a problem that it took. In addition, it is necessary to optimize the positive electrode for each of the carbon material side and the silicon side of the negative electrode, and there is a problem that a lot of cost is required (on the alloy side where deterioration is fast and on the carbon side where deterioration is low) The cathodes facing each other are deteriorated unevenly, and the carbon electrode may be overcharged after the alloy is deteriorated).

  The negative electrode of the secondary battery described in the cited document 3 has a problem that the volume energy density is low because the voids in the pores of the foam metal do not contribute to the increase in battery capacity. Further, when the pore diameter is reduced, there is a problem that it is difficult to form a uniform coating (plating coating) in the depth direction. In addition, the structure cannot relax the stress accompanying the volume change at the time of volume expansion, and there is a possibility that an active material that does not contribute to charge / discharge may be generated in the long term because cracks and peeling occur.

  In the battery described in Cited Document 4, the porous metal forms a negative electrode, and although this negative electrode has a porous structure, the skeleton itself is an active material, so that it expands and contracts greatly, thus causing a problem in cycle characteristics. . In addition, the negative electrode described in the cited document 4 has a problem that the porous metal itself does not have mechanical strength and is porous, and breaks when the battery is assembled, when it is wound, or when the porous structure is broken. there were.

  Although the electrode described in the cited document 5 has a configuration suitable for high-speed input / output, there is a problem that the battery capacity and cycle characteristics cannot be greatly improved.

In the secondary battery described in the cited document 6, it is shown that the cycle characteristics are improved, but this effect is achieved by using a conductive material having high conductivity. Specifically, it is disclosed that higher cycle characteristics can be obtained when carbon nanotubes (CNT) and carbon nanofibers (CNF) having high conductivity are used. However, although CNT and CNF have high conductivity, they have almost no binding force, and there is no effect on “a crack occurs between alloy particles and carbon due to volume change”, which is the cause of capacity reduction in the first place. (Because CNT itself has no functional group, it is unlikely that it is in spontaneous contact with the alloy particles, and it is even less likely to continue to follow the volume change of the alloy particles). Thus, as reported in the Examples of the cited document 6, the alloy 90 weight parts per (specific gravity 6-8 g / cm ^3), it is necessary to add CNT5 parts by weight (specific gravity 1.4 g / cm ³⁾ It is necessary to increase the ratio of CNT that is a conductive material agent. In addition, CNT is expensive, and there is a problem that the cost of the secondary battery is greatly increased.

Japanese Patent No. 4281099 Japanese Patent No. 4162510 JP 2003-257420 A JP 2005-294013 A JP 2006-59641 A JP 2007-335283 A

  This invention is made | formed in view of the said actual condition, and makes it a subject to provide the electrode and nonaqueous electrolyte battery which can obtain the battery provided with the high capacity | capacitance and the outstanding cycling characteristics.

  In order to solve the above-mentioned problems, the present inventors have made studies on the structure of the electrode, and as a result, have reached the present invention.

That is, the electrode for a secondary battery of the present invention includes a porous current collector formed of a conductive material, and reversibly occludes / releases lithium disposed in the pores of the porous current collector. A first active material layer having a possible first active material, and a second active material layer having a second active material made of a carbon material disposed on the surface of the porous current collector. The first active material layer is in a state of being disposed up to the surface of the porous current collector in the pores of the porous current collector, and the first active material has an average particle diameter of 0.5 to 30 nm. It is formed from particles.

The nonaqueous electrolyte battery according to the present invention is characterized by using the secondary battery electrode according to any one of claims 1 to 8 .

  In the secondary battery electrode of the present invention, the first active material layer is disposed in the pores of the porous current collector, and the second active material layer is disposed on the surface of the current collector. By providing the first active material layer in the pores of the porous current collector, the first active material layer in the first active material layer is suppressed from causing volume expansion, and the first active material layer It is possible to suppress the formation of a gap in the conductive network. That is, the stable conductive network of the first active material layer is not hindered by repeated charge and discharge, and can be used stably in a high capacity state.

  A second active material layer is provided on the surface of the current collector. By providing the second active material layer on the surface of the current collector, when the secondary battery is formed, the second active material layer forms an opposing surface with the opposing electrode. Reacts uniformly. That is, when the second active material undergoes an electrode reaction, unevenness in the reaction amount does not occur in the electrode, and a high battery capacity is ensured.

  The non-aqueous electrolyte battery of the present invention uses the electrode having the above effects and exhibits the above effects.

(Electrode for secondary battery)
The electrode for a secondary battery of the present invention is a porous current collector formed of a conductive material, and can reversibly occlude / release lithium disposed in the pores of the porous current collector. A first active material layer having a first active material; and a second active material layer having a second active material made of a carbon material disposed on the surface of the porous current collector. And in the state where the first active material layer is arranged up to the surface of the porous current collector in the pores of the porous current collector , the second active material layer is on the surface of the porous current collector, It is formed by applying a slurry having a second active material.

  The porous current collector is a current collector formed of a conductive material. The porous current collector is not limited except that a porous current collector is formed.

  As the conductive material for forming the porous current collector, a material used as a current collector in a conventional secondary battery can be used. Examples of such a material include nickel, copper, titanium, stainless steel, and carbon. That is, the porous current collector is preferably made of at least one selected from the group consisting of nickel, copper, titanium, stainless steel, and carbon.

  As long as the porous current collector has a structure in which the first active material layer has pores disposed therein, the structure is not limited, and the porous current collector in the conventional secondary battery is not limited. It can be set as the structure which forms. That is, the porous current collector is preferably made of any one of a foam, a sintered body, a punching plate, and a nonwoven fabric.

  The pores of the porous current collector are not particularly limited as long as the first active material layer can be formed inside.

  The porous current collector preferably has a porosity of 30 to 70%. When the porosity is less than 30%, the amount of the first active material filled in the pores decreases, and the battery capacity cannot be sufficiently obtained. When the porosity exceeds 70%, the ratio of the conductive material in the current collector becomes too small, and it becomes difficult to maintain the shape of the current collector itself.

  The pore diameter (average pore diameter) of the porous current collector is not limited as long as the particles of the first active material layer can be arranged in the pores. If the pore size (average pore size) of the porous current collector becomes too large, the first active material of the first active material layer arranged in the pores will peel off (peel off) as the volume changes. This is likely to occur (the cycle characteristics of the secondary battery are likely to deteriorate). If the pore diameter is too small, it becomes difficult to arrange a sufficient amount of the first active material in the pores (the effect of improving battery capacity cannot be sufficiently obtained). The porous current collector preferably has an average pore diameter of 5 μm to 25 μm.

  The first active material layer has a first active material disposed in the pores of the porous current collector and capable of reversibly inserting and extracting lithium.

  Since the first active material layer is disposed in the pores of the porous current collector, electricity generated in the first active material contained in the first active material layer can be taken out. In addition, by arranging the first active material layer in the pores of the porous current collector, it is possible to suppress an excessive volume change (expansion) of the active material layer (particles) in the pores. . Furthermore, even if cracking or peeling occurs in the active material layer (particles) in the pores, contact with the peeled active material layer (particles) can be maintained, and a reduction in battery capacity can be suppressed.

  Since the first active material is made of an active material capable of reversibly occluding and releasing lithium, electricity can be generated by occluding and releasing lithium. The type of the first active material is not limited as long as it is an active material capable of reversibly occluding and releasing lithium. That is, a material that is used as an active material in a battery that uses lithium (lithium ion) as an electrolyte, such as a conventional lithium battery or lithium ion battery, can be used.

  Since the secondary battery electrode of the present invention can suppress volume change (expansion) by arranging the first active material layer in the pores of the current collector, the first active material has a volume It is preferable to use a material having a large change. That is, the first active material preferably contains at least one selected from the group consisting of Mg, Al, Si, Zn, Ge, Bi, and Sn. Since a larger battery capacity can be obtained with these elements, it is more preferable that the first active material contains Si.

  In addition to the first active material, the first active material layer can use additives and the like used for electrodes in conventional secondary batteries. Examples of the additive include a conductive additive and a binder. The conductive additive conducts electricity generated in the first active material in the active material layer. Examples of the conductive aid include carbonaceous materials such as graphite, carbon black, acetylene black, thermal black, channel black, vapor grown carbon fiber (VGCF), metal powder, and the like.

  The ratio of the first active material and the conductive additive to be included in the first active material layer is generally determined because it varies depending on the type of battery manufactured and the characteristics of the current collector (material, porosity, pore diameter, etc.). It is not something. For example, when the mass of the entire first active material layer is 100, the mass of the first active material is preferably 85 to 95 parts by mass, and the ratio of the conductive additive is preferably 5 to 15 parts by mass.

  The first active material is preferably formed from particles having an average particle size of 0.5 to 30 nm, for example. If the average particle diameter is less than 0.5 nm, the particles are too small, and the amount of binder used for arranging in the pores increases, and the proportion of the first active material in the first active material layer decreases. Battery capacity cannot be obtained sufficiently. Moreover, when the average particle diameter is less than 0.5 nm, the particles are too small, and peeling due to a volume change of the active material is likely to occur. When the average particle diameter exceeds 30 nm, the amount of expansion of the active material becomes too large. Furthermore, when the particle diameter becomes too large, it becomes difficult to arrange in the pores.

  When the first active material layer contains an additive such as a conductive additive, these particle sizes are not particularly limited, and are preferably the same size as the first active material.

  The second active material layer has a second active material made of a carbon material disposed on the surface of the porous current collector. By disposing the second active material layer on the surface of the porous current collector, the first active material layer can be prevented from being detached from the pores of the current collector. Further, the surface layer of the secondary battery electrode of the present invention is constituted by the second active material layer, and the opposite electrode (electrode facing the electrode of the present invention, positive electrode when the electrode of the present invention is a negative electrode) Can react uniformly. Furthermore, the second active material layer constitutes the surface layer of the secondary battery electrode according to the present invention, so that even if the conductive auxiliary agent contained in the first active material layer inside the porous metal is reduced, it is prevented from falling off. Can do.

  The second active material layer is disposed on the surface of the current collector, and is more preferably disposed on both surfaces of the current collector. When the second active material layer is disposed on both sides of the current collector, in particular, the opposite electrode (the electrode facing the electrode of the present invention, the positive electrode when the electrode of the present invention is a negative electrode), and the current collector Can react uniformly on both sides.

  The second active material is made of a carbon material. The carbon material constituting the second active material layer can reversibly store and release lithium. The first active material filled in the current collector also functions as a conductive material for causing an electrical reaction. As long as the carbon material functions in this way, the specific material is not limited. That is, the carbon material preferably contains at least one selected from the group consisting of graphite, graphite, carbon black, coke, glassy carbon, carbon fiber, and a fired body thereof.

  In addition to the second active material, the second active material layer can use an additive used for an electrode of a conventional secondary battery using a carbon material as an active material. Examples of the additive include a conductive additive and a binder.

  The ratios of the second active material and the conductive additive to be included in the second active material layer are not generally determined because they vary depending on the type of battery to be manufactured and the characteristics of the first active material layer. For example, when the mass of the entire second active material layer is 100, the mass of the second active material is preferably 80 to 95 parts by mass, and the proportion of the conductive additive is preferably 5 to 20 parts by mass.

  The second active material preferably has an average particle size of 1 to 30 nm. That is, the second active material layer is preferably formed from carbon material particles having an average particle diameter of 1 to 30 nm. If the average particle size is less than 1 nm, the particles are too small, the amount of binder used to bind the second active material particles increases, and the proportion of the second active material in the second active material layer decreases. Battery capacity cannot be obtained sufficiently. When the average particle diameter exceeds 30 nm, the amount of expansion of the active material becomes too large.

  When the second active material layer contains an additive such as a conductive additive, these particle sizes are not particularly limited, and are preferably the same size as the second active material.

  The thickness of the second active material layer on the current collector surface is preferably 5 μm to 300 μm. If the thickness of the second active material layer is less than 5 μm, the effect of forming the second active material layer cannot be obtained. When the thickness of the second active material layer exceeds 300 μm, the thickness of the second active material layer becomes too thick, and the reaction amount of the electrode reaction in the first active material layer cannot be sufficiently obtained.

  The secondary battery electrode of the present invention is preferably a negative electrode for a non-aqueous electrolyte secondary battery. The electrode for a secondary battery of the present invention is an electrode capable of obtaining a secondary battery having excellent cycle characteristics and a long life. Among such secondary batteries, a non-aqueous electrolyte secondary battery is more preferable.

(Nonaqueous electrolyte battery)
The non-aqueous electrolyte battery of the present invention uses the secondary battery electrode according to any one of claims 1 to 9. As described above, the secondary battery electrode according to any one of claims 1 to 9 is an electrode capable of obtaining a high battery capacity and excellent cycle characteristics. Since the nonaqueous electrolyte battery of the present invention uses this secondary battery electrode, a high battery capacity and excellent cycle characteristics can be obtained. The nonaqueous electrolyte battery of the present invention is more preferably a lithium ion secondary battery.

  The non-aqueous electrolyte battery of the present invention can have the same configuration as a conventionally known non-aqueous electrolyte battery (secondary battery) except that the secondary battery electrode is used.

  The non-aqueous electrolyte battery of the present invention is preferably a non-aqueous electrolyte battery having a positive electrode, a negative electrode, and an electrolyte, and the above-described secondary battery electrode is used as a negative electrode, but a lithium ion secondary battery It is more preferable that

  In the non-aqueous electrolyte battery of the present invention, the positive electrode has an electrode mixture layer in which an additive selected from active materials, binders, conductive materials and other materials as necessary is mixed on the surface of the current collector. It is preferable to form it.

An example of such a compound is a lithium-containing transition metal oxide that is a positive electrode active material of a lithium ion secondary battery. The lithium-containing transition metal oxide is a material capable of removing and inserting Li ions (Li ⁺ ), and can include a lithium-metal composite oxide having a layered structure or a spinel structure. Specific examples include metal oxide materials such as Li _1-Z NiO ₂ , Li _1-Z MnO ₂ , Li _1-Z Mn ₂ O ₄ , and Li _1-Z CoO ₂ . Furthermore, examples of Li _1-Z βPO ₄ include LiFePO _4, and examples thereof include compounds containing one or more of them. Z represents a number from 0 to 1. In addition, each metal oxide-based material may be Li, Mg, Al, or a material in which a transition metal such as Co, Ti, Nb, or Cr is added or substituted. Furthermore, these lithium-metal composite oxides may be used alone or in combination.

  The binder is desirably formed of a polymer material, and is desirably a material that is chemically and physically stable in the atmosphere in the secondary battery. Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene (PTFE), and carboxymethyl cellulose (CMC).

  Examples of the conductive material include ketjen black, acetylene black, carbon black, graphite, carbon nanotube, and amorphous carbon. Further, conductive polymer polyaniline, polypyrrole, polythiophene, polyacetylene, polyacene and the like can be mentioned.

  As a method of forming an electrode mixture layer on the surface of the current collector, an electrode mixture having an active material, a binder, and a conductive material is dispersed or dissolved in an appropriate dispersion medium, and then the surface of the current collector The method of applying and drying can be mentioned.

  The electrolytic solution is not particularly limited, and an electrolytic solution in which a supporting salt is dissolved in a solvent such as an organic solvent, an ionic liquid that is liquid itself, or a supporting salt that is further dissolved in the ionic liquid. I can give you.

  As an organic solvent, the organic solvent used for the electrolyte solution of a normal lithium ion secondary battery can be mention | raise | lifted. Examples thereof include carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolane compounds and the like. In particular, it is preferable to use propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, or a mixed solvent thereof. Among these organic solvents, in particular, one or more non-aqueous solvents selected from the group consisting of carbonates and ethers are excellent in the solubility, dielectric constant and viscosity of the supporting salt, and the charge / discharge efficiency of the battery is also high. Therefore, it is preferable.

An ionic liquid will not be specifically limited if it is an ionic liquid normally used for the electrolyte solution of a lithium secondary battery. For example, as the cation component of the ionic liquid, or N- methyl -N- propyl piperidinium, and dimethyl ethyl methoxy ammonium cations like, and an anionic _{component, BF 4 -, N (SO} 2 CF 3) ₂ etc. can be mentioned.

In the lithium ion secondary battery, the supporting salt used in the electrolytic solution is not particularly limited. For example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , Examples of the salt compound include LiC (CF ₃ SO ₂ ) ₃ , LiSbF ₆ , LiSCN, LiClO ₄ , LiAlCl ₄ , NaClO ₄ , NaBF ₄ , NaI, and derivatives thereof. Among these, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiN (FSO ₂ ) ₂ , LiN (CF ₃ One or more selected from the group consisting of a derivative of SO ₂ ) (C ₄ F ₉ SO ₂ ), a derivative of LiCF ₃ SO _3, a derivative of LiN (CF ₃ SO ₂ ) _{2 and} a derivative of LiC (CF ₃ SO ₂ ) ₃ It is preferable to use a salt from the viewpoint of electrical characteristics.

  In a lithium ion secondary battery, it is preferable to interpose a separator, which is a member that achieves both electrical insulation and ion conduction, between the positive electrode and the negative electrode. When the supporting electrolyte is liquid, the separator also serves to hold the liquid supporting electrolyte. Examples of the separator include a porous synthetic resin film, particularly a porous film of polyolefin polymer (polyethylene, polypropylene). Furthermore, it is preferable that the separator has a larger size than the positive electrode and the negative electrode for the purpose of ensuring the insulation between the positive electrode and the negative electrode.

  The non-aqueous electrolyte battery of the present invention preferably comprises other elements as needed in addition to the above elements.

  Hereinafter, the secondary battery electrode and the nonaqueous electrolyte battery of the present invention will be described with reference to examples. In addition, this invention is not limited to the following Example.

  As an example of the present invention, a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery (evaluation cell) were manufactured.

(Example)
(Manufacture of negative electrode)
Prepare 90 parts by mass of silicon (negative electrode active material, first active material) having an average particle diameter of 7 nm , 5 parts by mass of ketjen black (conductive aid), and 5 parts by mass of SBR (binder), and disperse them in NMP. A first negative electrode mixture slurry was prepared.

  The prepared first negative electrode mixture slurry was filled in a nickel porous body (porous current collector, porosity: 50%) having an average pore diameter of 20 μm, and dried at 60 ° C. until the tackiness disappeared. After drying, the mixture layer adhering to the surface (both sides) of the porous current collector was scraped with a rod-shaped member (φ10 mm) subjected to fluororesin processing. The negative electrode precursor was manufactured by the above.

  Next, 90 parts by mass of graphite (negative electrode active material, second active material) having an average particle diameter of 15 nm, 5 parts by mass of ketjen black (conductive agent), and 5 parts by mass of PVDF (binder) are prepared. A second negative electrode mixture slurry was prepared by dispersing.

  After the prepared second negative electrode mixture slurry was applied to both sides of the negative electrode precursor, it was press-dried and extracted with a φ14 mm circular punch and vacuum-dried at 120 ° C. to produce the negative electrode of this example. .

(Manufacture of positive electrode)
80 parts by mass of LiFePO ₄ (positive electrode active material), 10 parts by mass of acetylene black (conductive aid), and 10 parts by mass of PVDF (binder) were prepared and dispersed in N-methylpyrrolidone to prepare a positive electrode mixture slurry.

  The prepared positive electrode mixture slurry was applied to both sides of a 15 μm-thick aluminum foil (current collector) so as to be 5.0 mg / φ14 mm, then press-dried and extracted with a φ14 mm circular punch. Vacuum drying was performed to manufacture the positive electrode of this example.

(Manufacture of non-aqueous electrolyte)
LiPF ₆ was dissolved in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 so as to be 1 mol / liter, thereby producing a nonaqueous electrolytic solution of this example.

(Manufacture of batteries)
A separator made of a polyethylene film having micropores was interposed between the positive electrode and the negative electrode described above to form a laminated electrode body.

  After the manufactured laminated electrode body was housed in a battery case, the above-described non-aqueous electrolyte was injected, covered and sealed, and a coin-type non-aqueous electrolyte battery was produced.

(Comparative Example 1)
The first negative electrode mixture slurry and the second negative electrode mixture slurry prepared in the examples were mixed at a volume ratio of 1: 1 to prepare a third negative electrode mixture slurry.

  The prepared third negative electrode mixture slurry was applied to both surfaces of a 20 μm thick nickel foil (current collector, foil shape without holes) and press-dried to obtain a negative electrode of this comparative example.

  The battery of this comparative example was configured in the same manner as in Example 1 except that the above negative electrode was used.

(Comparative Example 2)
The first negative electrode mixture slurry prepared in the example was placed on one surface of a 20 μm thick nickel foil (current collector, foil shape without holes), and the second negative electrode mixture slurry was placed on the other surface of the current collector. It apply | coated to the surface and press-dried to make the negative electrode of this comparative example. In the negative electrode of this comparative example, active material layers made of different materials are formed on both surfaces of the current collector.

  The battery of this comparative example was configured in the same manner as in Example 1 except that the above negative electrode was used.

(Comparative Example 3)
The third negative electrode mixture slurry prepared in Comparative Example 1 was filled in the pores of the current collector made of the nickel foil used in the Examples, and dried at 60 ° C. until the tackiness disappeared. After drying, the mixture layer adhering to the surface (both sides) of the porous current collector was scraped with a rod-shaped member (φ10 mm) subjected to fluororesin processing. Thus, the negative electrode of this comparative example was manufactured.

  The battery of this comparative example was configured in the same manner as in Example 1 except that the above negative electrode was used.

(Evaluation)
As the evaluation of the batteries of the above Examples and Comparative Examples, initial discharge capacity and cycle characteristics (capacity maintenance ratio) were measured.

Initial discharge capacity, first, a constant current charging at a charging current 0.10mA / cm ² to 0.01 V, was constant current discharging at a discharging current 0.10mA / cm ² to 1.0 V. The discharge capacity at this time was defined as the initial discharge capacity.

  The capacity maintenance rate is measured by first measuring the discharge capacity when 30 cycles of charge / discharge performed at the time of measuring the initial discharge capacity are repeated. Then, [(discharge capacity at 30th cycle) / (discharge capacity at 1st cycle)] × 100 = capacity maintenance ratio (%).

  Table 1 shows the measurement results of the initial discharge capacity and the capacity retention rate.

  As shown in Table 1, the batteries of the examples had excellent initial discharge capacity and cycle characteristics (capacity maintenance ratio).

  On the other hand, the batteries of Comparative Examples 1 and 2 had the same initial capacity as that of the battery of the example, but the capacity retention rate was greatly reduced. Further, the battery of Comparative Example 3 had a capacity retention rate equivalent to that of the battery of the example, but the initial capacity was greatly reduced.

  Specifically, as can be seen from Comparative Examples 1 to 3 in Table 1, Comparative Examples 1 and 2 in which a negative electrode active material was formed on the surface of a foil-like current collector without pores provided a large initial capacity, In Comparative Example 3 in which the negative electrode active material is filled in the pores of the porous current collector, a high capacity retention rate is obtained. However, the capacity retention rates of Comparative Examples 1 and 2 are greatly reduced. This means that when a negative electrode active material layer is formed on the surface of a foil-like current collector and charging and discharging are repeated, the negative electrode active material peels off and falls off due to volume change, and electricity can be taken out by the current collector. By disappearing. In Comparative Example 3 in which the negative electrode active material layer is formed in the pores of the porous current collector, a high capacity retention ratio can be obtained by suppressing the volume change of the negative electrode active material that occurs in Comparative Examples 1 and 2. However, since the negative electrode active material is filled in the pores of the porous current collector, the reaction amount of the electrode reaction of the negative electrode active material is suppressed. As a result, in Comparative Example 3, the initial capacity is insufficient.

  On the other hand, in the battery of the example, Si (first active material) capable of obtaining a large battery capacity is filled in the pores of the porous current collector, and graphite (first material) is formed on the surface of the porous current collector. A negative electrode having a structure in which a second active material is arranged is used.

  The battery of the present embodiment obtains a large battery capacity by using Si (first active material) that can obtain a large battery capacity. And the volume change is suppressed by filling the 1st active material in the pore of a porous electrical power collector. And the surface of a negative electrode is formed with a 2nd active material by arranging graphite (2nd active material) on the surface of a porous electrical power collector. Then, the second active material disposed on the surface of the porous current collector suppresses the first active material layer from being detached from the pores of the current collector. In addition, the capacity retention rate is increased by the second active material uniformly reacting with the positive electrode.

  As described above, the battery of the example is composed of the negative electrode having the first active material filled in the pores of the porous current collector and the second active material arranged on the surface of the porous current collector. Both the initial discharge capacity and the cycle characteristics (capacity maintenance ratio) were excellent.

Claims (9)

A porous current collector formed of a conductive material;
A first active material layer having a first active material disposed in the pores of the porous current collector and capable of reversibly occluding and releasing lithium;
A second active material layer having a second active material made of a carbon material disposed on the surface of the porous current collector,
The first active material layer is disposed in the pores of the porous current collector up to the surface of the porous current collector;
The electrode for a secondary battery, wherein the first active material is formed of particles having an average particle diameter of 0.5 to 30 nm.   2. The secondary battery electrode according to claim 1, wherein the first active material includes at least one selected from the group consisting of Mg, Al, Si, Zn, Ge, Bi, and Sn.   3. The secondary battery according to claim 1, wherein the carbon material includes at least one selected from the group consisting of graphite, graphite, carbon black, coke, glassy carbon, carbon fiber, and a fired body thereof. electrode.   The secondary battery electrode according to claim 1, wherein the second active material has an average particle diameter of 1 to 30 nm.   5. The electrode for a secondary battery according to claim 1, wherein the porous current collector is made of at least one selected from the group consisting of nickel, copper, titanium, stainless steel, and carbon.   The secondary battery electrode according to claim 1, wherein the porous current collector is formed of any one of a foam, a sintered body, a punching plate, and a nonwoven fabric.   The electrode for a secondary battery according to any one of claims 1 to 6, wherein the porous current collector has a porosity of 30 to 70%.   It is a negative electrode for nonaqueous electrolyte secondary batteries, The electrode for secondary batteries in any one of Claims 1-7. A non-aqueous electrolyte battery comprising the secondary battery electrode according to claim 1.