JP2009283315A - Negative electrode for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode for a nonaqueous electrolyte secondary battery with a fiber sheet hardly peeling off a nonwoven fabric from the surface of an active material layer and for preventing coming off of an active material from the active material layer. <P>SOLUTION: The negative electrode 100 for the nonaqueous electrolyte secondary battery with the fiber sheet includes a current collector 11 and an active material layer 12 formed on at least one surface. The negative electrode 100 for the nonaqueous electrolyte secondary battery with the fiber sheet is formed on the surface of the active material layer 12 by integrally fusing a fiber sheet 14 containing fibers containing resin having a melting point of 200-380°C and having autohesion property. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a negative electrode of a non-aqueous electrolyte secondary battery such as a lithium secondary battery. The present invention also relates to a non-aqueous electrolyte secondary battery using the negative electrode.

  In general, graphite is used as a negative electrode active material of a lithium secondary battery. However, with the recent increase in functionality of electronic devices, their power consumption has increased remarkably, and the need for large-capacity secondary batteries is increasing. It is difficult to meet. Therefore, development of a negative electrode active material made of an alloy-based material such as a Sn-based material or a Si-based material, which has a higher capacity than graphite, has been actively conducted.

  When manufacturing a battery using a negative electrode including a negative electrode active material made of Sn-based material, Si-based material, or the like, for example, when manufacturing a rectangular battery, the negative electrode is used together with a positive electrode and a separator to form a wound body. The wound body is flatly pressed and then accommodated in a battery can. In this pressing step, the largest strain is applied to the portion of the pressed wound body having the largest curvature, and the active material may fall off from the negative electrode active material layer due to the strain. In addition, the separator may be damaged due to the dropout, and the battery may be short-circuited.

  By the way, the present applicant has previously proposed a negative electrode for a non-aqueous electrolyte secondary battery in which a metal material having a low lithium compound forming ability is infiltrated between particles of a silicon-based material (see Patent Document 1). ). According to this negative electrode, since the active material can contribute uniformly to the electrode reaction over the entire thickness direction of the active material layer, the secondary battery equipped with the negative electrode has the advantage of improved charge / discharge cycle characteristics. . However, when the negative electrode is wound as described above, the active material may fall off from the active material layer.

  A technique for preventing the active material from falling off from the negative electrode active material layer is proposed in Patent Document 2 and Patent Document 3, although it is different from the falling off due to the press of the wound body. This technique is intended to prevent the active material from falling off due to the active material layer coming into contact with the guide roller or the like when the electrode is conveyed in the battery manufacturing process. In order to prevent the active material from falling off, in Patent Document 2, a porous protective layer containing fine particles made of alumina or the like and a binder made of polyvinylidene fluoride or the like is formed on the surface of the negative electrode active material layer. In Patent Document 3, in order to prevent the active material from falling off the surface of the positive electrode, a non-woven fabric is provided so as to cover the surface coated with the active material, and the non-woven fabric is closely integrated by a roller press.

  Compared with the force applied to the active material layer during conveyance of the negative electrode, the force applied to the active material layer by the press of the wound body is overwhelmingly large. From the description of Patent Document 2, the thickness of the binder portion in the porous protective layer is unknown, but from the description of the Examples of the same document, it is estimated that the thickness of the binder portion is extremely thin. Therefore, the porous protective layer described in the document cannot prevent the active material from falling off due to the pressing of the wound body. Furthermore, the alumina particles may fall off.

  In the positive electrode described in Patent Document 3, since the non-woven fabric is simply adhered to the surface by a roller press, the non-woven fabric is easily peeled off from the surface of the positive electrode, and the active material cannot be prevented from falling off. Moreover, in order to prevent peeling of the nonwoven fabric described in Patent Document 3, when the roller press is applied with heat, the nonwoven fabric may be formed into a film, which may hinder free passage of the electrolyte. In addition, the elasticity of the nonwoven fabric is lost due to the roller press, and the expansion of the negative electrode during occlusion of lithium cannot be absorbed, which may cause the electrode to rupture. Moreover, in order to prevent peeling of the nonwoven fabric described in Patent Document 3, when an adhesive is used, there is a possibility of causing a side reaction with passing ions.

International Publication No. 2007/046327 Pamphlet Japanese Patent Laid-Open No. 7-220759 JP-A-2-33861

  Therefore, the object of the present invention is for a non-aqueous electrolyte secondary battery with a fiber sheet that prevents the nonwoven fabric from peeling off from the surface of the active material layer of the negative electrode, prevents the active material from falling off the active material layer, and prevents internal short circuit. The object is to provide a negative electrode and a non-aqueous electrolyte secondary battery.

The present invention includes a current collector and an active material layer formed on at least one surface thereof, and a fiber sheet containing self-bonding fibers is fused and integrated on the surface of the active material layer. A negative electrode for a non-aqueous electrolyte secondary battery with a fiber sheet is provided.
The present invention also provides a non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a separator interposed between the positive electrode, the negative electrode and a current collector formed on at least one surface thereof. A fiber sheet including a fiber having self-bonding property is disposed between the negative electrode and the separator, and the fiber sheet and the active material layer of the negative electrode are fused and integrated. The present invention provides a non-aqueous electrolyte secondary battery.

  According to the negative electrode for a non-aqueous electrolyte secondary battery with a fiber sheet of the present invention, it is difficult for the nonwoven fabric to peel off from the surface of the negative electrode without hindering the flow of the electrolytic solution, thereby preventing the active material from falling off the active material layer. Can do. Further, according to the non-aqueous electrolyte secondary battery using the negative electrode for the non-aqueous electrolyte secondary battery with a fiber sheet of the present invention, the active material is difficult to fall off from the negative electrode active material layer. The battery can be prevented from being damaged, and a short circuit of the battery can be prevented.

  The present invention will be described below based on preferred embodiments with reference to the drawings. FIG. 1 shows the structure of an embodiment of the negative electrode for a non-aqueous electrolyte secondary battery with a fiber sheet (hereinafter also simply referred to as “negative electrode with a fiber sheet”) of the present invention. The negative electrode 100 with a fiber sheet of the present embodiment includes a current collector 11, a negative electrode body 10 including an active material layer 12 formed on at least one surface thereof, and a fiber sheet 14. 1 shows a state in which the active material layer 12 is formed only on one side of the current collector 11 for convenience, the active material layer may be formed on both sides of the current collector. .

  The negative electrode 100 with a fiber sheet of this embodiment is characterized by the fiber sheet 14 being fused and integrated with the surface of the active material layer 12. By providing the fiber sheet 14, the negative electrode 100 with a fiber sheet of the present embodiment is used together with the positive electrode and the separator to form a wound body, and even if the wound body is pressed flat, the active material layer 12 can be activated. It is possible to effectively prevent the material from falling off. Further, due to the voids of the fiber sheet 14, when an active material such as Sn or Si that significantly expands during charging is used as the negative electrode, the expansion can be absorbed and stress can be relaxed to prevent the electrode plate from collapsing. Furthermore, the fiber sheet 14 has electrolyte solution retention, and even if the cycle is repeated, the entire electrode plate reacts uniformly and has an effect of improving the cycle life.

  The fiber sheet 14 covers the outermost surface of the active material layer 12 substantially continuously over the entire area. Therefore, the outermost surface of the active material layer 12 is not exposed to the outside. That is, the outermost surface of the negative electrode 100 is the fiber sheet 14. Fusion integration of the fiber sheet 14 may be partial, preferably linear, and more preferably by a surface. From the viewpoint of more effectively preventing the active material from falling off the active material layer 12, it is preferable that the fusion integration be performed by a surface. Here, “in terms of surface” does not mean that there is no non-fused portion between the fiber sheet 14 and the active material layer 12 and is unavoidable due to fluctuations in manufacturing conditions and the like. This is to allow a slight non-fused portion to occur.

  The fiber sheet 14 has a structure in which gaps are formed between the constituent fibers and a non-aqueous electrolyte can flow through the gaps. The fibers constituting the fiber sheet 14 have self-bonding properties. Here, “self-bonding property” means that the fiber form before heating can be maintained in a temperature range above the softening point and below the melting point, and the surface of the fiber softens in this temperature range, thereby making contact. It is not limited to the narrow sense of the property that fibers bind to each other without using a binder, but the broad sense of the property that fibers bind to other materials (active material layer or surface layer in the present invention) without using a binder. Should be interpreted. By using such a fiber as a constituent fiber, when the fiber sheet 14 is fused to the surface of the active material layer 12, a gap between the fibers is maintained, and the fiber sheet 14 can be prevented from being formed into a film. Become. Specifically, the fiber having self-bonding property is not easily formed into a film because the fiber has high shape retention even if it is softened by applying heat. In particular, by using a fiber whose melting point is preferably in the range described later, fine unevenness in which a part of the fiber exists on the surface of the active material layer 12 due to the softening of the fiber at the time of heat-sealing. Get inside. As a result, the fibers are locked to the irregularities on the surface of the active material layer 12 by an anchor effect, and the fiber sheet 14 is difficult to peel off from the surface of the active material layer 12.

  The fiber having self-bonding property is composed of, for example, a single thermoplastic resin having self-bonding property. In a range that does not impair the self-bonding property of the fiber, a fiber having self-bonding property may be constituted from a mixture obtained by mixing another thermoplastic resin with a thermoplastic resin having self-bonding property. In addition, as a fiber having self-bonding property, a composite fiber made of two or more kinds of thermoplastic resins having different melting points (this resin may not have self-bonding property), for example, core-sheath type composite A fiber and a side-by-side type composite fiber can also be used. The fiber having self-bonding property that is particularly preferably used is a fiber made of a single thermoplastic resin having self-bonding property.

  When the fiber is formed from the above-described thermoplastic resin having self-bonding property, the resin preferably has a melting point of 200 to 380 ° C, particularly 240 to 380 ° C. When the melting point is in this range, the fiber sheet 14 can be firmly bonded to the surface of the active material layer 12 while preventing the fiber sheet 14 from being formed into a film during fusion integration.

  A typical example of the above-mentioned thermoplastic resin having self-bonding property is a thermoplastic liquid crystal polymer. A liquid crystal polymer is a polymer compound that exhibits liquid crystal-like properties in a molten state. In the present invention, a conventionally known liquid crystal polymer can be used without particular limitation. Examples thereof include polyester liquid crystal polymers such as thermotropic liquid crystal polyester and thermotropic liquid crystal polyester amide, and polyacrylate liquid crystal polymers. By forming the fiber from the liquid crystal polymer and forming the fiber sheet 14 from the fiber, the structure of the battery can be stabilized by absorbing the expansion of the negative electrode during the occlusion of lithium, and electrolysis can be performed by the liquid retaining property of the fiber. An effective effect that the liquid can be held in the reaction system of the positive electrode and the negative electrode is exhibited.

  The fiber sheet 14 is a sheet-like material made of fibers. The fiber sheet 14 may be composed of only the fibers having the above-described self-bonding property, or may be mixed with other types of fibers as long as the self-bonding property of the fiber is not impaired. Examples of the fiber sheet 14 include a nonwoven fabric, a woven fabric, a knitted fabric, or a composite material combining these. In view of ease of production and ease of distribution of the non-aqueous electrolyte, it is preferable to use a non-woven fabric as the fiber sheet 14. As a nonwoven fabric, what was manufactured by conventionally well-known methods, such as a melt blown nonwoven fabric, a spun bond nonwoven fabric, a spun lace nonwoven fabric, an air through nonwoven fabric, a needle punch nonwoven fabric, a resin bond nonwoven fabric, can be used, for example. In particular, it is preferable to use a binderless nonwoven fabric from the viewpoint of preventing inconvenience due to the use of the binder. From the viewpoint of preventing the fibers from falling off or fluffing in the battery, it is preferable to use a long-fiber nonwoven fabric. When these viewpoints are put together, it is particularly preferable to use a meltblown nonwoven fabric which is a binderless long fiber nonwoven fabric.

When using a non-woven fabric as the fiber sheet 14, the basis weight is 3 to 40 g / m ² , and particularly 5 to 20 g / m ² , which effectively removes the active material while ensuring a smooth flow of the non-aqueous electrolyte. It is preferable from the point of preventing it.

  The active material layer 12 to which the fiber sheet 14 is fused includes active material particles 12a. Due to the presence of the particles 12 a, fine irregularities are formed on the surface of the active material layer 12. As the active material, a material containing Si or Sn and capable of occluding and releasing lithium ions is used. As an example of the negative electrode active material containing Si, silicon alone, an alloy of silicon and metal, silicon oxide, silicon nitride, silicon boride and the like can be used. These materials can be used alone or in combination. Examples of the metal used in the alloy include one or more elements selected from the group consisting of Cu, Ni, Co, Cr, Fe, Ti, Pt, W, Mo, and Au. Among these metals, Cu, Ni, and Co are preferable, and Cu and Ni are preferably used from the viewpoint of excellent electronic conductivity and a low ability to form a lithium compound. Further, lithium may be occluded in the negative electrode active material containing Si before or after the negative electrode is incorporated in the battery. A particularly preferable negative electrode active material containing Si is silicon alone or silicon oxide from the viewpoint of high lithium storage capacity.

  On the other hand, as an example of the negative electrode active material containing Sn, tin alone, an alloy of tin and metal, or the like can be used. These materials can be used alone or in combination. Examples of the metal that forms an alloy with tin include one or more elements selected from the group consisting of Cu, Ni, Co, Cr, Fe, Ti, Pt, W, Mo, and Au. Of these metals, Cu, Ni, and Co are preferable. An example of the alloy is a Sn—Co—C alloy. An alloy containing Sn, Co, C, and at least one of Ni and Cr is also preferably used.

  The active material layer 12 may be a coating layer formed by coating a mixture obtained by mixing the above-described particles 12 a together with a binder, a solvent, and the like on the surface of the current collector 11. Preferably, as shown in FIG. 1, the active material layer 12 is covered with at least a part of the surface of the particle 12 with a metal material 13 having a low lithium compound forming ability and with the metal material 13. A structure in which voids are formed between the particles is preferable.

  The metal material 13 covering at least a part of the surface of the active material particle 12a is a material different from the constituent material of the particle 12a. Gaps are formed between the particles 12 a covered with the metal material 13. That is, the metal material 13 covers the surfaces of the particles 12a in a state where a gap is secured so that the non-aqueous electrolyte containing lithium ions can reach the particles 12a. In FIG. 1, the metal material 13 is conveniently represented as a thick line surrounding the periphery of the particle 12a. This figure is a schematic diagram showing the cross-sectional structure of the active material layer 12 two-dimensionally. Actually, the active material particles 12 a are in direct contact with other particles 12 a or through the metal material 13. Here, “low ability to form a lithium compound” means that lithium does not form an intermetallic compound or solid solution, or even if formed, the amount of lithium is very small or very unstable. .

  The metal material 13 has conductivity, and examples thereof include copper, nickel, iron, cobalt, and alloys of these metals. In particular, the metal material 13 is preferably a highly ductile material in which even if the active material particles 12a expand and contract, the coating on the surface of the particles 12a is not easily broken. It is preferable to use copper as such a material.

  The metal material 13 is preferably present on the surface of the active material particles 12 a over 90% or more of the thickness direction of the active material layer 12, particularly over the entire region. The particles 12 a are preferably present in the matrix of the metal material 13. As a result, even if the particles 12a are pulverized due to expansion and contraction due to charge / discharge, it is difficult for the particles 12a to fall off. In addition, since the electronic conductivity of the entire active material layer 12 is ensured through the metal material 13, the electrically isolated particles 12 a are generated, and in particular, the electrically isolated particles 12 a are generated in the deep part of the active material layer 12. Is effectively prevented. This is particularly advantageous when a material that is a semiconductor and has poor electron conductivity, such as a material containing Si, is used as the active material. The presence of the metal material 13 on the surface of the particle 12a over the entire thickness direction of the active material layer 12 can be confirmed by electron microscope mapping using the metal material 13 as a measurement target.

  The metal material 13 covers the surface of the active material particles 12a continuously or discontinuously. When the metal material 13 continuously covers the surfaces of the particles 12a, it is preferable to form fine voids in the coating of the metal material 13 that allow the non-aqueous electrolyte to flow. When the metal material 13 discontinuously coats the surface of the particle 12a, the non-aqueous electrolyte is supplied to the particle 12a through a portion of the surface of the particle 12a that is not covered with the metal material 13.

  The average thickness of the metal material 13 covering the surface of the active material particles 12a is preferably 0.05 to 2 μm, more preferably 0.1 to 0.25 μm. That is, the metal material 13 covers the surface of the particle 12a with a minimum thickness. As a result, while the energy density is increased, the particles 12a are prevented from falling off due to expansion / contraction and pulverization due to charge / discharge. The “average thickness” referred to here is a value calculated based on a portion of the surface of the particle 12 a that is actually covered with the metal material 13. Therefore, the portion of the surface of the particle 12a that is not covered with the metal material 13 is not used as a basis for calculating the average value.

  The voids formed between the active material particles 12a coated with the metal material 13 serve as a flow path for the non-aqueous electrolyte containing lithium ions. Since the non-aqueous electrolyte smoothly flows in the thickness direction of the active material layer 12 due to the presence of the voids, cycle characteristics can be improved. Further, the voids formed between the particles 12a also have a function as a space for relieving stress caused by the volume change of the active material particles 12a due to charge and discharge. The increase in the volume of the active material particles 12a whose volume has been increased by charging is absorbed by the voids. As a result, the pulverization of the particles 12a is difficult to occur, and significant deformation of the negative electrode body 10 and the negative electrode 100 with the fiber sheet is effectively prevented.

  When the present inventors examined the voids formed in the active material layer 12, the porosity of the active material layer 12 is preferably 15 to 45%, more preferably 20 to 40%, and still more preferably 25 to 35%. It was found that the flow of the non-aqueous electrolyte in the active material layer 12 was extremely good, and it was extremely effective for stress relaxation associated with expansion and contraction of the active material particles 12a. In particular, setting the upper limit to 35% is extremely effective in improving the conductivity and maintaining the strength in the active material layer, and setting the lower limit to 25% can widen the range of selection of the electrolyte. By using the negative electrode main body 10 and the negative electrode 100 with a fiber sheet having such a high porosity active material layer, a high-viscosity non-aqueous electrolyte that has been considered difficult to use in the past is used. Is possible.

  The void amount of the active material layer 12 is measured by a mercury intrusion method (JIS R 1655). The mercury intrusion method is a method for obtaining information on the physical shape of a solid by measuring the size and volume of pores in the solid. The principle of the mercury intrusion method is to apply a pressure to mercury to inject it into the pores of the object to be measured, and measure the relationship between the pressure applied at that time and the volume of mercury that has been pushed in (intruded). In this case, mercury enters sequentially from the large voids present in the active material layer 12. The measurement is performed on the negative electrode body 10 obtained by peeling the fiber sheet 14 from the negative electrode 100 with fiber sheet.

  In the present invention, the void amount measured at a pressure of 90 MPa is regarded as the entire void amount. In the present invention, the porosity (%) of the active material layer 12 is obtained by dividing the void amount per unit area measured by the above-mentioned method by the apparent volume of the active material layer 12 per unit area, and dividing it by 100. Find by multiplying.

The active material layer 12 is preferably formed by subjecting a coating obtained by applying a slurry containing particles 12a and a binder onto a current collector and drying it, and performing electrolytic plating using a predetermined plating bath. It is formed by depositing a metal material 13 between 12a. The degree of precipitation of the metal material 13 affects the value of the porosity of the active material layer 12. In order to achieve a desired porosity, it is necessary that a space in which the plating solution can permeate is formed in the coating film. As a result of the examination by the present inventors, it was found that the particle size distribution of the active material particles 12a is a large factor in order to form a space in which the plating solution can penetrate into the coating film as necessary and sufficient. . Specifically, by adopting particles having a particle size distribution represented by D ₁₀ / D ₉₀ of preferably 0.05 to 0.5, more preferably 0.1 to 0.3, as the active material particles 12a. It was found that a desired degree of space was formed in the coating film and the plating solution was sufficiently permeated. It was also found that the coating film can be effectively prevented from peeling off during electrolytic plating. It can be seen that the closer the D ₁₀ / D ₉₀ is to 1, the closer the particle size of the particles 12a is to monodisperse, so that the particle size distribution in the above range is sharp. That is, in the present embodiment, it is preferable to use the particles 12a having a sharp particle size distribution. By using the particles 12a having a sharp particle size distribution, the voids between the particles can be increased when the particles 12a are packed at a high density. On the other hand, when particles having a broad particle size distribution are used, it is easy for small particles to enter between large particles, and it is not easy to increase the voids between the particles. Further, the use of the particles 12a having a sharp particle size distribution has an advantage that variations in reaction are less likely to occur.

In order to obtain a negative electrode having excellent cycle characteristics, in addition to the particle size distribution of the active material particles 12a being within the above range, the particle size of the particles 12a itself is also important. When the particle size of the active material particles 12a is excessively large, the particles 12a are likely to be finely powdered by repeating expansion and contraction, thereby frequently generating electrically isolated particles 12a. If the particle size of the active material particles 12a is too small, the gaps between the particles 12a may be too small, and the gaps may be filled by penetration plating described later. This has a negative effect on the improvement of cycle characteristics. Therefore, in this embodiment, it is preferable that the average particle diameter of the active material particles 12a is 0.1 to 5 μm, particularly 0.2 to 3 μm, expressed as D ₅₀ .

The values of the particle size distribution D ₁₀ / D ₉₀ and the average particle size D ₅₀ of the active material particles 12a are measured by laser diffraction scattering type particle size distribution measurement or electron microscope observation (SEM observation).

  In order to set the porosity of the active material layer 12 within the above range, it is preferable that the plating solution is sufficiently permeated into the coating film. In addition to this, it is preferable to make conditions suitable for depositing the metal material 13 by electrolytic plating using the plating solution. The plating conditions include the composition of the plating bath, the pH of the plating bath, and the current density of electrolysis. Regarding the pH of the plating bath, it is preferable to adjust it to more than 7 and 11 or less, particularly 7.1 or more and 11 or less. By controlling the pH within this range, the dissolution of the active material particles 12a is suppressed, the surface of the particles 12a is cleaned, and plating on the particle surface is promoted. Is formed. The value of pH is measured at the temperature at the time of plating.

When using copper as the metal material 13 for plating, it is preferable to use a copper pyrophosphate bath. When nickel is used as the metal material, for example, an alkaline nickel bath is preferably used. In particular, it is preferable to use a copper pyrophosphate bath, even if the active material layer 12 is thick, because the voids can be easily formed over the entire thickness direction of the layer. Further, since the metal material 13 is deposited on the surface of the active material particles 12a and the metal material 13 is less likely to be deposited between the particles 12a, the voids between the particles 12a are also successfully formed. preferable. When using a copper pyrophosphate bath, the bath composition, electrolysis conditions and pH are preferably as follows.
Copper pyrophosphate trihydrate: 85-120 g / l
-Potassium pyrophosphate: 300-600 g / l
-Potassium nitrate: 15-65 g / l
-Bath temperature: 45-60 ° C
・ Current density: 1 to 7 A / dm ²
PH: Ammonia water and polyphosphoric acid are added to adjust the pH to 7.1 to 9.5.

In particular, when a copper pyrophosphate bath is used, it is preferable to use a P ratio defined by the ratio of the weight of P ₂ O _{7 to} the weight of Cu (P ₂ O ₇ / Cu) of 5 to 12. . When the P ratio is less than 5, the metal material 13 covering the active material particles 12a tends to be thick, and it may be difficult to form desired voids between the particles 12a. Further, when a P ratio exceeding 12 is used, current efficiency is deteriorated, and gas generation is likely to occur, so that production stability may be lowered. When a copper pyrophosphate bath having a P ratio of 6.5 to 10.5 is used as a more preferable copper pyrophosphate bath, the size and number of voids formed between the active material particles 12a may be reduced. This is very advantageous for the flow of the water electrolyte.

When an alkaline nickel bath is used, the bath composition, electrolysis conditions and pH are preferably as follows.
Nickel sulfate: 100 to 250 g / l
Ammonium chloride: 15-30 g / l
・ Boric acid: 15-45 g / l
-Bath temperature: 45-60 ° C
・ Current density: 1 to 7 A / dm ²
-PH: 25% by weight ammonia water: Adjust to pH 8-11 within the range of 100-300 g / l.
When this alkaline nickel bath and the above-described copper pyrophosphate bath are compared, there is a tendency that moderate voids are formed in the active material layer 12 when the copper pyrophosphate bath is used, and the life of the negative electrode is increased. It is preferable because it is easy to achieve.

  The characteristics of the metal material 13 can be appropriately adjusted by adding various additives used in the electrolytic solution for producing copper foil such as protein, active sulfur compound, and cellulose to the above various plating baths.

  In the negative electrode body 10 of the present embodiment, the porosity calculated from the void amount of the active material layer 12 measured by the mercury intrusion method is within the above range, and is measured by the mercury intrusion method at 10 MPa. The porosity calculated from the amount of voids in the active material layer 12 is preferably 10 to 40%. Moreover, it is preferable that the porosity calculated from the void amount of the active material layer 12 measured by the mercury intrusion method at 1 MPa is 0.5 to 15%. Furthermore, it is preferable that the porosity calculated from the void amount of the active material layer 12 measured by the mercury intrusion method at 5 MPa is 1 to 35%. As described above, in the mercury intrusion measurement, the mercury intrusion conditions are gradually increased. Under low pressure conditions, mercury is pressed into large gaps, and under high pressure conditions, mercury is pressed into small gaps. Therefore, the porosity measured at a pressure of 1 MPa is mainly derived from large voids. On the other hand, the porosity measured at a pressure of 10 MPa reflects the presence of small voids. These measurements are performed on the negative electrode body 10 obtained by peeling the fiber sheet 14 from the negative electrode 100 with fiber sheet.

  As described above, the active material layer 12 is preferably subjected to electrolytic plating using a predetermined plating bath on a coating film obtained by applying and drying a slurry containing particles 12a and a binder, It is formed by depositing a metal material 13 between the particles 12a. Therefore, the above-mentioned large voids are mainly derived from the spaces between the particles 12a, while the small voids described above are mainly derived from the spaces between the crystal grains of the metal material 13 deposited on the surface of the particles 12a. It is thought that. The large void mainly serves as a space for relieving stress caused by the expansion and contraction of the particles 12a. On the other hand, the small voids mainly serve as a path for supplying the nonaqueous electrolytic solution to the particles 12a. By balancing the abundance of these large voids and small voids, the cycle characteristics are further improved.

  If the amount of the active material relative to the whole negative electrode is too small, it is difficult to sufficiently improve the energy density of the battery. Conversely, if the amount is too large, the strength decreases and the active material tends to fall off. Considering these, the thickness of the active material layer 12 is preferably 10 to 40 μm, more preferably 15 to 30 μm, and still more preferably 18 to 25 μm.

  In the negative electrode main body 10 of the negative electrode 100 with a fiber sheet, a thin surface layer (not shown) may be formed on the surface of the active material layer 12. The negative electrode main body 10 may not have such a surface layer. The thickness of the surface layer is 0.25 μm or less, preferably 0.1 μm or less. There is no restriction | limiting in the lower limit of the thickness of a surface layer. By forming the surface layer, the pulverized active material particles 12a can be further prevented from falling off. However, in the present embodiment, by setting the porosity of the active material layer 12 within the above-described range, the active material particles 12a pulverized with charge / discharge can be sufficiently dropped without using a surface layer. It is possible to prevent.

  When the negative electrode main body 10 has the thin surface layer or does not have the surface layer, an overvoltage when the secondary battery is assembled using the negative electrode 100 with the fiber sheet and the battery is initially charged. Can be lowered. This means that lithium can be prevented from being reduced on the surface of the active material layer 12 when the secondary battery is charged. The reduction of lithium leads to the generation of dendrites that cause a short circuit between the two electrodes.

  When the negative electrode main body 10 has a surface layer, the surface layer covers the surface of the active material layer 12 continuously or discontinuously. When the surface layer continuously covers the surface of the active material layer 12, the surface layer has a large number of microscopic voids (not shown) that are open at the surface and communicate with the active material layer 12. It is preferable. The fine voids are preferably present in the surface layer so as to extend in the thickness direction of the surface layer. The fine voids allow the non-aqueous electrolyte to flow. The role of the fine voids is to supply a non-aqueous electrolyte into the active material layer 12. When the surface of the negative electrode main body 10 is viewed in plan by electron microscope observation, the fine voids have a ratio of the area covered with the metal material 13, that is, the coverage is 95% or less, particularly 80% or less, particularly 60% or less. Such a size is preferable. When the coverage exceeds 95%, it is difficult for the non-aqueous electrolyte having high viscosity to enter, and the range of selection of the non-aqueous electrolyte may be narrowed.

  The surface layer is made of a metal material having a low lithium compound forming ability. This metal material may be the same as or different from the metal material 13 present in the active material layer 12. The surface layer may have a structure of two or more layers made of two or more different metal materials. Considering the ease of production of the negative electrode main body 10, the metal material 13 present in the active material layer 12 and the metal material constituting the surface layer are preferably the same type.

  As the current collector 11 in the negative electrode main body 10 and the negative electrode 100 with the fiber sheet, the same current collector as that conventionally used as the negative electrode current collector for a non-aqueous electrolyte secondary battery can be used. The current collector 11 is preferably made of a metal material having a low lithium compound forming ability as described above. Examples of such metal materials are as already described. In particular, it is preferably made of copper, nickel, stainless steel or the like. Also, it is possible to use a copper alloy foil represented by a Corson alloy foil. The thickness of the current collector 11 is preferably 9 to 35 μm, considering the balance between maintaining the strength of the negative electrode body 10 and the negative electrode 100 with fiber sheet and improving the energy density. In addition, when using copper foil as the electrical power collector 11, it is preferable to give the rust prevention process using organic compounds, such as a chromate process and a triazole type compound and an imidazole type compound.

  Next, the preferable manufacturing method of the negative electrode 100 with a fiber sheet of this embodiment is demonstrated, referring FIG. In the figure, steps for manufacturing the negative electrode body 10 are sequentially shown. In this production method, a coating film is formed on the current collector 11 using a slurry containing particles of the active material and a binder, and then the coating is electroplated to form an active material layer.

  First, a current collector 11 is prepared as shown in FIG. Then, a slurry containing active material particles 12 a is applied onto the current collector 11 to form a coating film 15. The surface roughness of the coating film forming surface of the current collector 11 is preferably 0.5 to 4 μm at the maximum height of the contour curve. If the maximum height exceeds 4 μm, the formation accuracy of the coating film 15 is lowered and current concentration of the permeation plating tends to occur on the convex portions. When the maximum height is less than 0.5 μm, the adhesion of the active material layer 12 tends to be lowered. As the active material particles 12a, those having the above-described particle size distribution and average particle size are preferably used.

  The slurry contains a binder and a diluting solvent in addition to the active material particles. The slurry may contain a small amount of conductive carbon material particles such as acetylene black and graphite. In particular, when the active material particles 12a are made of a silicon-based material, the conductive carbon material is preferably contained in an amount of 1 to 3% by weight based on the weight of the active material particles 12a. When the content of the conductive carbon material is less than 1% by weight, the viscosity of the slurry is lowered and the sedimentation of the active material particles 12a is promoted, so that it is difficult to form a good coating film 15 and uniform voids. . On the other hand, if the content of the conductive carbon material exceeds 3% by weight, plating nuclei concentrate on the surface of the conductive carbon material, and it becomes difficult to form a good coating.

  As the binder, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyethylene (PE), ethylene propylene diene monomer (EPDM), or the like is used. As a diluting solvent, N-methylpyrrolidone, cyclohexane or the like is used. The amount of the active material particles 12a in the slurry is preferably about 30 to 70% by weight. The amount of the binder is preferably about 0.4 to 4% by weight. A dilution solvent is added to these to form a slurry.

  The formed coating film 15 has a large number of minute spaces between the particles 12a. The current collector 11 on which the coating film 15 is formed is immersed in a plating bath containing a metal material having a low lithium compound forming ability. By immersion in the plating bath, the plating solution enters the minute space in the coating film 15 and reaches the interface between the coating film 15 and the current collector 11. Under this condition, electrolytic plating is performed to deposit plating metal species on the surfaces of the particles 12a (hereinafter, this plating is also referred to as permeation plating). The osmotic plating is performed by using the current collector 11 as a cathode, immersing a counter electrode as an anode in a plating bath, and connecting both electrodes to a power source.

  The deposition of the metal material by the osmotic plating is preferably progressed from one side of the coating film 15 to the other side. Specifically, as shown in FIGS. 2B to 2D, electrolytic plating is performed so that the deposition of the metal material 13 proceeds from the interface between the coating film 15 and the current collector 11 toward the surface of the coating film. I do. By precipitating the metal material 13 in this way, the surface of the active material particles 12a can be successfully coated with the metal material 13, and a void is successfully formed between the particles 12a coated with the metal material 13. be able to. In addition, it becomes easy to set the void ratio of the voids to the above-described preferable range.

  As described above, the conditions of the infiltration plating for depositing the metal material 13 include the composition of the plating bath, the pH of the plating bath, the current density of electrolysis, and the like. Such conditions are as already described.

  As shown in FIGS. 2B to 2D, when plating is performed such that the deposition of the metal material 13 proceeds from the interface between the coating film 15 and the current collector 11 toward the surface of the coating film. In the forefront portion of the precipitation reaction, fine particles 13a made of plating nuclei of the metal material 13 are present in layers with a substantially constant thickness. As the deposition of the metal material 13 proceeds, adjacent microparticles 13a combine to form larger particles, and when the deposition proceeds further, the particles combine to continuously cover the surface of the active material particles 12a. It becomes like this.

  The permeation plating is terminated when the metal material 13 is deposited on the entire thickness direction of the coating film 15. By adjusting the end point of plating, a surface layer (not shown) can be formed on the upper surface of the active material layer 12. When the metal material 13 covering the surface of the active material particles 12a is different from the material constituting the surface layer, once the metal material 13 is deposited in the entire thickness direction of the coating film 15, the permeation plating is temporarily stopped. To do. Then, osmotic plating is performed again using a plating solution containing a metal material different from the metal material 13 to form a surface layer. In this way, the target active material layer 12 is obtained as shown in FIG.

  When the negative electrode main body 10 is obtained in this way, the fiber sheet 14 is fused and integrated with the surface of the active material layer 12. The surface of the active material layer 12 before the fiber sheet 14 is fused and integrated (if a surface layer is present, the surface thereof) has a surface roughness Ra measured according to JIS B0601 of 0.1 to 0.1. It is preferably 5 μm, particularly 0.3 to 3 μm. By forming the fiber sheet 14 on the surface of the active material layer 12 having a surface roughness Ra of 5 μm or less, good adhesion between the fiber sheet 14 and the active material layer 12 can be ensured. Further, by forming the fiber sheet 14 on the surface of the active material layer 12 having a surface roughness Ra of 0.1 μm or more, the anchor effect can be sufficiently exhibited.

  For the fusion integration of the fiber sheet 14, for example, a roll press method using a pair of smooth rolls can be used. The press temperature is preferably mp-50 ° C. or higher based on the melting point (mp) of the resin constituting the fiber in order to maintain the fiber shape. When the fiber sheet 14 is comprised from the fiber containing a liquid crystal polymer, the plane press method can also be used besides a roll press method. In this case, the flat pressing temperature is preferably equal to or higher than the softening point of the liquid crystal polymer. In particular, it is preferable to perform pressing in a temperature range that is higher than the softening point of the liquid crystal polymer and higher than or equal to mp-120 ° C. from the viewpoint of reliable fusion. Although depending on the pressurization time, the upper limit of the heating temperature is preferably less than the melting point from the viewpoint of preventing the fiber from forming into a film. Whether or not the constituent fibers of the fiber sheet 14 are made of a liquid crystal polymer in order to allow the resin to enter the void formed between the active material particles 12a and 12a coated with the metal material 13 for the purpose of anchoring. The press is preferably performed at a pressure of 100 kPa to 3000 kPa, more preferably 500 kPa to 1500 kPa.

  FIG. 3 schematically shows a flat press device suitably used for fusing and integrating the fiber sheet 14 made of fibers containing a liquid crystal polymer to the negative electrode body 10. The figure shows a state in which the fiber sheet 14 is fused and integrated with the negative electrode body 10 in which the active material layer is formed only on one surface of the current collector. A flat press apparatus 200 shown in the figure includes a pair of rectangular hot plates 201 and 202 arranged to face each other. The hot plates 201 and 202 can be heated to a predetermined temperature. The fiber sheet 14 and the negative electrode main body 10 are disposed between the hot plates 201 and 202 and pressed under heating. In this case, both members are arranged so that the fiber sheet 14 and the active material layer of the negative electrode body 10 face each other. By the pressing under heating, the constituent fibers of the fiber sheet 14 are softened and enter the fine irregularities formed on the surface of the active material layer of the negative electrode body 10. Thereby, the fiber sheet 14 and the negative electrode main body 10 are integrated, and the negative electrode 100 with a fiber sheet is formed. In addition, when using what the active material layer was formed in both surfaces of the collector as the negative electrode main body 10, in FIG. 3, arrangement | positioning structure between the hot plate 201 and the negative electrode main body 10 is set to the hot plate 202 and the negative electrode. What is necessary is just to employ | adopt also between the main bodies 10.

  In order to fuse and integrate the fiber sheet 14 and the negative electrode body 10 with a uniform pressure, the surface facing the fiber sheet 14 is mirror-finished between the hot plate 201 and the fiber sheet 14. It is preferable to arrange the end plate 203 made of a good heat transfer material such as metal. For the same purpose, it is preferable to dispose a mirror plate 204 made of a good heat transfer material such as metal and having a mirror-finished surface facing the negative electrode body 10 between the hot plate 202 and the negative electrode body 10. The degree of the mirror surface may be a normal buffing degree.

  From the viewpoint of bringing the fiber sheet 14 and the negative electrode body 10 into closer contact and efficiently conducting the heat of the hot plate 201 to the fiber sheet 14, when pressing with the flat press device 200, between the end plate 203 and the fiber sheet 14. The metal foil 205 is preferably disposed. For the same purpose, it is preferable to dispose a metal foil 206 of the same kind or different kind from the metal foil 205 between the end plate 204 and the negative electrode body 10. Examples of the metal foils 205 and 206 include copper and aluminum.

  It is also preferable to interpose a sheet material 207 having heat resistance and releasability between the metal foil 205 and the fiber sheet 14 for the purpose of smoothly peeling the metal foil 205 and the fiber sheet 14 after completion of pressing. . Examples of such a sheet material 207 include a polyimide film. In addition, when fusing and integrating the two fiber sheets 14 and 14 to the negative electrode body 10 in which the active material layers are formed on both surfaces of the current collector, a sheet material similar to the above-described sheet material 207 is used. It is preferable to interpose between the metal foil 206 and the fiber sheet 14.

  The negative electrode 100 with a fiber sheet thus obtained is used together with a known positive electrode, separator and nonaqueous electrolyte, and constitutes a nonaqueous electrolyte secondary battery. The form of the secondary battery is not particularly limited, but from the viewpoint of preventing the active material layer from falling off the negative electrode when the negative electrode, the separator, and the rolled body of the positive electrode are pressed, a stacked type or a cylindrical type is preferable. A secondary battery is preferred. However, there is no problem even if the shape is a square shape or a coin shape.

  As a positive electrode in a secondary battery, for example, lithium transition metal composite oxide particles are suspended in a suitable solvent together with a conductive agent such as acetylene black and a binder such as polyvinylidene fluoride to prepare a positive electrode mixture. Is applied to at least one surface of a current collector made of aluminum foil or the like, dried, then rolled and pressed.

  As the separator, a synthetic resin nonwoven fabric, a polyolefin such as polyethylene or polypropylene, or a polytetrafluoroethylene porous film is preferably used.

The nonaqueous electrolytic solution is a solution in which a lithium salt as a supporting electrolyte is dissolved in an organic solvent. The lithium _{salt, CF 3 SO 3 Li, (} CF 3 SO 2) 2 NLi, (C 2 F 5 SO 2) 2 NLi, LiClO 4, LiA1Cl 4, LiPF 6, LiAsF 6, LiSbF 6, LiCl, LiBr, Examples include LiI, LiC ₄ F ₉ SO _{3 and the} like. These can be used alone or in combination of two or more.

  As mentioned above, although this invention was demonstrated based on the preferable embodiment, this invention is not restrict | limited to the said embodiment. For example, in the above-described embodiment, the secondary battery is configured by combining the negative electrode 100 with the fiber sheet with the positive electrode and the separator, but instead, the negative electrode body 10, the fiber sheet 14, the positive electrode, and the separator are prepared, Prior to constituting the secondary battery, the negative electrode body 10 and the fiber sheet 14 may be fused and integrated, and then the secondary battery may be assembled using the positive electrode and the separator.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” means “% by weight”.

[Example 1]
A current collector made of an electrolytic copper foil having a thickness of 18 μm was acid washed at room temperature for 30 seconds. After the treatment, it was washed with pure water for 15 seconds. A slurry containing particles made of Si was applied to both surfaces of the current collector so as to have a film thickness of 15 μm to form a coating film. The composition of the slurry was particles: styrene butadiene rubber (binder): acetylene black = 100: 1.7: 2 (weight ratio). The average particle diameter D ₅₀ of the particles was 2 [mu] m. The average particle diameter D ₅₀ was measured using a Microtrac particle size distribution measuring device (No. 9320-X100) manufactured by Nikkiso Co., Ltd.

The current collector on which the coating film was formed was immersed in a copper pyrophosphate bath having the following bath composition, and copper was plated on the coating film by electrolysis to form an active material layer. The electrolysis conditions were as follows. DSE was used for the anode. A DC power source was used as the power source. The electrolytic plating was terminated when copper was deposited over the entire thickness direction of the coating film. In this way, an active material layer was formed. The surface roughness Ra of the active material layer measured according to JIS B0601 was 2.4 μm. The porosity of the entire active material layer measured by the above method was 24.8%.
Copper pyrophosphate trihydrate: 105 g / l
-Potassium pyrophosphate: 450 g / l
・ Potassium nitrate: 30 g / l
・ Bath temperature: 50 ° C
・ Current density: 3 A / dm ²
-PH: Ammonia water and polyphosphoric acid were added to adjust to pH 8.2.

A non-woven fabric obtained from Kuraray Co., Ltd. (trade name “Vecruz: MBBK” per unit area 8.5 g / m ² , melting point 350 ° C.) was used. This nonwoven fabric is composed of fibers made of a liquid crystal polymer. Two sheets of this nonwoven fabric are prepared, and the nonwoven fabric is fused to each of the surface of the current collector and the active material layer formed on the back surface by a flat press device (heating and cooling molding machine PY-30EA manufactured by Kodaira Seisakusho Co., Ltd.) Integrated. When pressing with a flat press device equipped with a pair of hot plates, a buffed end plate is placed between the one hot plate and the non-woven fabric on the surface side of the current collector, and the end plate and non-woven fabric A 35 μm thick copper foil was placed between them, and a 25 μm thick polyimide film was placed between the copper foil and the nonwoven fabric. Similar to the current collector surface side, a buffed end plate is disposed between the other hot plate and the nonwoven fabric on the back side of the current collector, and a 35 μm thick copper is placed between the end plate and the nonwoven fabric. A foil was disposed, and a polyimide film having a thickness of 25 μm was disposed between the copper foil and the nonwoven fabric. The conditions of the flat pressing apparatus were a temperature of 250 ° C., a press pressure of 1200 kPa, and a pressurization time of 3 minutes. Thus, the negative electrode with a fiber sheet which fused and integrated the fiber sheet to the active material layers on both sides of the current collector was obtained.

[Comparative Example 1]
In Example 1, a negative electrode was obtained in the same manner as in Example 1 except that the fiber sheet was not fused and integrated with the active material layer on the current collector.

[Evaluation]
Non-aqueous electrolyte secondary batteries were prepared using the negative electrodes obtained in the examples and comparative examples, and the performance of each negative electrode was evaluated. A secondary battery was produced by the following procedure. Li _1.03 Mn _0.06 Co _0.91 O ₂ was used as the positive electrode active material. This was suspended in N-methylpyrrolidone as a solvent together with acetylene black and polyvinylidene fluoride to obtain a positive electrode mixture. The weight ratio of the blending was positive electrode active material: acetylene black: polyvinylidene fluoride = 88: 6: 6. This positive electrode mixture was applied to a current collector made of an aluminum foil (thickness 20 μm) using an applicator, dried at 120 ° C., and then roll-pressed with a load of 0.5 ton / cm to obtain a positive electrode. As the electrolytic solution, a solution obtained by adding 2% by volume of vinylene carbonate to a solution of 1 mol / l LiPF ₆ dissolved in a 1: 1 volume ratio mixed solvent of ethylene carbonate and diethyl carbonate was used. A polypropylene porous film was used as the separator. The negative electrodes obtained in Examples and Comparative Examples are used together with the above-described positive electrode and the above-described separator to form a cylindrical wound body, and after the rolled body is pressed flat, in an aluminum laminate battery can The prismatic secondary battery was manufactured by accommodating 10 pieces each. These were charged / discharged. The initial charge curves are shown in FIGS. As shown in FIG. 3, in the secondary battery of the example, there was no short-circuited battery among the 10 batteries, whereas in the secondary battery of the comparative example, 2 batteries out of 10 as shown in FIG. Battery shorted.

It is a schematic diagram which shows the cross-section of one Embodiment of the negative electrode with a fiber sheet of this invention. It is process drawing which shows the manufacturing method of a negative electrode main body. It is a schematic diagram of a plane press apparatus. 2 is an initial charge curve of a battery using the negative electrode of Example 1. 2 is an initial charge curve of a battery using the negative electrode of Comparative Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Negative electrode 10 with a non-aqueous electrolyte secondary battery fiber sheet Negative electrode main body 11 Current collector 12 Active material layer 12a Active material particle 13 Metal material 14 Fiber sheet 200 Planar press apparatus 201, 202 Hot plate 203, 204 End plate 205, 206 Metal foil 207 Sheet material

Claims (7)

  It has a current collector and an active material layer formed on at least one surface thereof, and a fiber sheet containing fibers having self-bonding properties is fused and integrated on the surface of the active material layer. Negative electrode for non-aqueous electrolyte secondary battery with fiber sheet.   The negative electrode for a non-aqueous electrolyte secondary battery with a fiber sheet according to claim 1, wherein the fibers are made of a resin having a melting point of 200 ° C to 380 ° C.   The negative electrode for a non-aqueous electrolyte secondary battery with a fiber sheet according to claim 1 or 2, wherein the fusion integration is performed by a surface.   The active material layer contains particles of an active material containing Si or Sn, and at least a part of the surface of the particles is covered with a metal material having a low lithium compound forming ability and is covered with the metal material. The negative electrode for a non-aqueous electrolyte secondary battery with a fiber sheet according to any one of claims 1 to 3, wherein voids are formed between the particles.   The negative electrode for a non-aqueous electrolyte secondary battery with a fiber sheet according to any one of claims 2 to 4, wherein the fibers contain a thermoplastic liquid crystal polymer.   A non-aqueous electrolyte secondary battery comprising the negative electrode for a non-aqueous electrolyte secondary battery according to claim 1. In a non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a separator interposed between the two,
The negative electrode has a current collector and an active material layer formed on at least one surface thereof,
A fiber sheet containing self-bonding fibers is disposed between the negative electrode and the separator, and the fiber sheet and the active material layer of the negative electrode are fused and integrated. Water electrolyte secondary battery.

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