JP2015041474A - Negative electrode, power storage device, and vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a negative electrode which enables the suppression of delamination of an active material layer and a metal foil; and to provide a power storage device and a vehicle.SOLUTION: A negative electrode sheet 22 comprises: a metal foil 26; and an active material layer 27 including active material particles 27a and formed on a surface 26c of the metal foil 26. In a formation region where the active material layer 27 is formed, concave portions 26d are formed in the surface 26c of the metal foil 26. The active material particles 27a are partially located in the concave portions 26d. Of the active material particles 27a, which are partially located in the concave portions 26d, the average distance between centers C1 and C2 of the adjacent active material particles 27a is 70-98% of the average particle diameter.

Description

  The present invention relates to a negative electrode, a power storage device including the negative electrode, and a vehicle equipped with the power storage device.

  Conventionally, lithium-ion secondary batteries and nickel-hydrogen secondary batteries are well known as power storage devices mounted on vehicles and the like. For example, in a lithium ion secondary battery, an electrode assembly (electrode) in which an active material layer containing active material particles is formed on the surface of a metal foil is stacked or wound, and the electrode assembly is housed in a case. .

  In such a lithium ion secondary battery, a paste containing active material particles (active material mixture) is applied to a metal foil, dried and then pressed, and the peel strength of the active material layer on the metal foil The thing which improved (adhesion intensity | strength) is proposed (for example, patent document 1). In Patent Document 1, in the drying process, high temperature steam of a solvent is supplied to promote melting of the binder contained in the paste, thereby strengthening the binding between the active material layer and the metal foil by the binder and improving the peel strength. I am letting.

JP 2008-103098 A

  By the way, a power storage device such as a secondary battery is repeatedly applied with vibration by being mounted on a vehicle or the active material layer is repeatedly expanded and contracted with charge / discharge. May peel from the metal foil. If the active material layer and the metal foil are peeled off, it may cause a decline in the performance as a power storage device, such as a decrease in electric capacity, and further suppress the peeling of the active material layer and the metal foil. Is expected to be.

  The present invention has been made paying attention to the problems existing in the above-described prior art, and its purpose is to provide a negative electrode, a power storage device, and a vehicle that can suppress the separation of the active material layer and the metal foil. There is to do.

  A negative electrode that solves the above problem is a negative electrode in which an active material layer containing active material particles for a negative electrode is formed on a surface of a metal foil, and the surface of the metal foil in a formation region where the active material layer is formed Is formed with a recess, at least a part of the active material particles is present in the recess, and among the active material particles having at least a part of the recess, an average distance between centers of adjacent active material particles is an average. The gist is that it is 70% or more and 98% or less of the particle diameter.

  According to this configuration, a recess is formed on the surface of the metal foil, and at least a part of the active material particles is present in the recess, so that the active material layer can be prevented from peeling from the metal foil. And among the active material particles in which at least a part is present in the recess, the average distance between the centers of the adjacent active material particles is 70% or more of the average particle diameter, so that it is less than 70%. In addition, the active material particles can be prevented from interfering with each other due to the expansion caused by charging, and the generation of stress, and the active material layer can be prevented from peeling from the metal foil. Moreover, since the average distance between the centers of the adjacent active material particles is 98% or less of the average particle diameter, the distance between the active material particles having at least a part of the recesses as compared with the case where it exceeds 98%. The adhesion between the active material layer and the metal foil can be improved by reducing the thickness of the active material layer, thereby preventing the active material layer from being peeled off from the metal foil along with charge / discharge. Therefore, it can suppress that an active material layer and metal foil peel.

  Regarding the negative electrode, among the active material particles having at least a portion in the concave portion, the active material particles having a particle diameter equal to or larger than the average particle diameter are up to a depth of 50% or less of the particle diameter of the active material particles. It is preferable to be indented into the recess.

  When the active material particles having a particle diameter equal to or larger than the average particle diameter are present in the recess exceeding 50% of the particle diameter, wrinkles and the like are generated due to deformation of the metal foil. However, according to this configuration, the active material particles having a particle diameter equal to or larger than the average particle diameter are present in the concave portion to a depth of 50% or less of the particle diameter of the active material particles. It can suppress suitably that etc. arise.

  About the said negative electrode, it is preferable that the auxiliary | assistant metal foil which consists of the same metal as the said metal foil is joined to the non-formation area | region in which the said active material layer is not formed in the surface of the said metal foil.

  According to this configuration, since the auxiliary metal foil is bonded to the non-formation region where the active material layer is not formed, the formation region of the active material layer is pressurized by, for example, pressing, so that the concave portion is formed. When at least a part of the active material particles is present in the concave portion, it is possible to suppress the formation of wrinkles or the like in the metal foil.

In the negative electrode, the metal foil is preferably made of copper. According to this structure, it can suppress that an active material layer peels from the metal foil which consists of copper in a negative electrode.
A power storage device that solves the above-mentioned problem is obtained by laminating or winding an electrode in which an active material layer containing active material particles is formed on the surface of a metal foil with a sheet-like separator interposed therebetween, In a power storage device having an electrode assembly having a layered structure, the electrode includes the negative electrode.

  According to this configuration, it is possible to prevent the active material layer from peeling from the metal foil of the negative electrode constituting the electrode assembly. As a result, it is possible to improve the durability of the power storage device having the electrode assembly.

  The gist of a vehicle for solving the above problems is that the power storage device is mounted. According to this structure, it can suppress that an active material layer peels from the metal foil of a negative electrode, and can improve the durability as an electrical storage apparatus. Therefore, it is possible to suppress a reduction in the replacement cycle of the power storage device in the vehicle.

  According to this invention, it can suppress that an active material layer and metal foil peel.

The perspective view which shows a secondary battery typically. The perspective view which shows typically the decomposed | disassembled electrode assembly. The schematic diagram which shows the state which observed the cross section of the negative electrode sheet with the scanning electron microscope. The graph which shows the relationship between the distance between average particle | grains, and peeling strength. The graph which shows the relationship between the distance between average particle | grains, and the cycle number of charging / discharging until a discharge capacity maintenance factor will be 80%. The schematic diagram of the electrode sheet in another embodiment. The perspective view which shows typically the secondary battery in another embodiment. The perspective view which shows typically the electrode assembly which decomposed | disassembled in another embodiment.

Hereinafter, an embodiment of a negative electrode and a secondary battery will be described with reference to FIGS.
As shown in FIG. 1, for example, a secondary battery 10 serving as a power storage device mounted on a vehicle such as an industrial vehicle or a passenger vehicle has a case 11 having a substantially rectangular parallelepiped shape as a whole. The case 11 has a bottomed cylindrical main body member 12 and a flat lid member 13 that seals the opening 12 a of the main body member 12. Both the main body member 12 and the lid member 13 are made of metal such as stainless steel or aluminum. A positive electrode terminal 15 and a negative electrode terminal 16 are fixed to the lid member 13 and protrude outward.

The case 11 is filled with an electrolyte according to the type of the secondary battery 10 such as a lithium ion secondary battery or a nickel hydride secondary battery. As the electrolytic solution, for example, one or more nonaqueous electrolytic solutions selected from propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), and the like can be used. As the electrolyte to be dissolved, an alkali metal salt that is soluble in an organic solvent such as LiPF ₆ , LiBF ₄ , and LiAsF ₆ can be used.

  The case 11 houses an electrode assembly 25 covered with an insulating bag (not shown). The electrode assembly 25 includes a positive electrode sheet 21 as a positive electrode, a negative electrode sheet 22 as a negative electrode, and a separator 23 that insulates between the positive electrode sheet 21 and the negative electrode sheet 22. The electrode assembly 25 is a stacked electrode assembly in which the positive electrode sheet 21 and the negative electrode sheet 22 are stacked so as to alternately overlap each other with a separator 23 interposed therebetween. The separator 23 is made of an insulating resin material such as polyethylene or polypropylene, and is a rectangular porous sheet having a fine pore structure.

  Further, as shown in FIG. 2, the positive electrode sheet 21 and the negative electrode sheet 22 include a rectangular sheet-like metal foil 26. The thickness of the metal foil 26 is, for example, 10 μm or more and 50 μm or less, and preferably 15 μm or more and 25 μm or less. The metal foil 26 is made of metal according to the type of the secondary battery 10 such as a lithium ion secondary battery or a nickel hydride secondary battery. The metal used for the metal foil 26 is different between the positive electrode sheet 21 and the negative electrode sheet 22. In the present embodiment, the metal foil 26 of the positive electrode sheet 21 is made of aluminum, and the metal foil 26 of the negative electrode sheet 22 is made of copper.

  On the surface 26 c of each metal foil 26, an active material layer 27 is formed on the entire surface except for the non-formation region 26 b extending along the edge 26 a of each metal foil 26. The non-formation region 26b is a region where the active material layer 27 is not formed. The active material layer 27 will be described in detail later.

  A positive electrode current collecting tab 21 a that is a part of the non-formation region 26 b protrudes from the edge portion 26 a of each positive electrode sheet 21. Moreover, the negative electrode current collection tab 22a which is a part of the non-formation area | region 26b protrudes in the edge part 26a of each negative electrode sheet 22. FIG.

  As shown in FIG. 1, a positive electrode current collecting tab group 28 in which a plurality of positive electrode current collecting tabs 21 a are layered is projected from an edge portion 25 a of the electrode assembly 25. In addition, a negative electrode current collection tab group 29 in which a plurality of negative electrode current collection tabs 22 a overlap each other is formed on the edge 25 a of the electrode assembly 25 at a portion different from the positive electrode current collection tab group 28. And the positive electrode current collection tab group 28 (positive electrode current collection tab 21a) and the positive electrode terminal 15 mentioned above are electrically connected. Moreover, the negative electrode current collection tab group 29 (negative electrode current collection tab 22a) and the negative electrode terminal 16 are electrically connected.

  Next, the active material layer 27 formed on the surface 26c of the metal foil 26 in the positive electrode sheet 21 and the negative electrode sheet 22 will be described in detail. The active material layer 27 formed on the surface 26c of each metal foil 26 includes active material particles, a binder, and a conductive agent (conductive aid). The conductive agent is dispersed in the binder.

Examples of the positive electrode active material used for the active material layer 27 of the positive electrode sheet 21 include LiCoO ₂ , Li ₂ MnO ₂ , and LiNi _1/3 Mn _1/3 Co _1/3 O ₂ . The binder used for the active material layer 27 of the positive electrode sheet 21 is, for example, polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE). The conductive agent used for the active material layer 27 of the positive electrode sheet 21 is, for example, acetylene black (AC) or ketjen black (KB).

Moreover, the active material for negative electrodes used for the active material layer 27 of the negative electrode sheet 22 is, for example, silicon oxide represented by a composition formula of SiO _n (0.1 ≦ n ≦ 2), such as SiO ₂ (silicon dioxide) or , SiO (silicon monoxide) and the like. The binder used for the active material layer 27 of the negative electrode sheet 22 is, for example, PVDF or PTFE. The conductive agent used for the active material layer 27 of the negative electrode sheet 22 is, for example, AC or KB.

Next, the active material layer 27 of the negative electrode sheet 22 will be described in detail with reference to FIG.
In the active material layer 27 formed on the surface 26c of the metal foil 26 of the negative electrode sheet 22, the active material particles 27a are bound to each other by a binder 27b. The average particle diameter of the active material particles 27a is, for example, 2 μm or more and 10 μm or less, and preferably 4 μm or more and 8 μm or less. The “average particle size” in this specification means the particle size at an integrated value of 50% in the particle size distribution obtained by the laser diffraction / scattering method. Further, each “particle diameter” in the active material particles 27a means a particle diameter observed with a scanning electron microscope (SEM).

  In the formation region 27 c of the active material layer 27 of the negative electrode sheet 22, some of the active material particles 27 a exist in the recesses 26 d on the surface 26 c of the metal foil 26. That is, in the formation region 27c of the active material layer 27, a part of the particles of the active material particles 27a adjacent to the surface 26c of the metal foil 26 is buried so as to exist in the recess 26d of the surface 26c. In other words, at least a part of the active material particles 27 a is embedded (embedded) in the surface portion including the surface 26 c in the metal foil 26, and the other part of the active material particles 27 a is the metal foil 26. It protrudes from the surface 26c. Then, the surface of the active material particles 27a embedded in the metal foil 26 is in contact with or close to the side surface and the bottom surface of the recess 26d.

  Of the active material particles 27a partially present in the recesses 26d of the metal foil 26, the average of the distances L (the average distance between the centers) from the center C1 to the center C2 of the adjacent active material particles 27a is the active material. When the average particle diameter of the active material particles 27a contained in the layer 27 is 100%, the distance is preferably 70% or more and 98% or less, more preferably 72% or more and 95% or less.

  In the following description, the ratio of the average of the distance L from the center C1 to the center C2 (average distance between centers) with respect to the average particle diameter is simply indicated as “average interparticle distance”. Further, in this specification, “the center of the active material particle 27a” means a direction along the surface direction of the metal foil 26 and a direction orthogonal to the surface direction of the metal foil 26 when observed with a scanning electron microscope. Means the center of

The density (electrode density) of the negative electrode sheet 22 is, for example, 1.07 g / cm ³ when the average interparticle distance is 98%, and is, for example, 1.08 g / cm ³ when the average interparticle distance is 70%. The density (electrode density) of the negative electrode sheet 22 is, for example, 1.25 g / cm ³ when the average interparticle distance is 72%, and is, for example, 1.09 g / cm ³ when the average interparticle distance is 95%. Become. In the active material layer 27 of the negative electrode sheet 22, the active material particles 27 a having a particle diameter equal to or larger than the average particle diameter among the active material particles 27 a partially present in the recesses 26 d of the surface 26 c of the metal foil 26. Is present in the recess 26d of the metal foil 26 to a depth of 50% or less of the particle diameter of the active material particles 27a. That is, the active material particles 27a having a particle diameter equal to or larger than the average particle diameter do not exceed 50% of the particle diameter and are not embedded in the metal foil 26. In the positive electrode sheet 21 of the present embodiment, the active material particles 27 a are not recessed into the surface 26 c of the metal foil 26 in the formation region 27 c of the active material layer 27.

Next, a method for manufacturing the secondary battery 10 including the positive electrode sheet 21 and the negative electrode sheet 22 will be described.
First, active material particles 27a, a conductive agent, a binder 27b, and N-methylpyrrolidone (NMP) as a solvent are mixed to prepare a paste-like active material mixture. Next, the paste-like active material mixture obtained in the preparation step is applied to the surface (both sides) 26c of the strip-like (long sheet-like) metal foil 26 obtained in a step different from the preparation step. And applying a uniform thickness (for example, 70 μm or more and 80 μm or less including a copper foil having a thickness of 18 μm) to form an active material layer 27. In the coating step, a non-formation region 26b is formed on one side (edge) in the width direction of the metal foil 26 where the active material mixture is not applied with a constant width over the entire length direction.

  Subsequently, the metal foil 26 on which the active material layer 27 is formed is passed through a drier (drying furnace), and a drying process for removing the solvent contained in the active material layer 27 is performed. Next, by pressing the dried metal foil 26 through a roll press, the active material layer 27 is compressed, and a pressing step for densifying and smoothing is performed. The roll press machine passes the metal foil 26 having the active material layer 27 formed on the surface 26c through a gap formed between a pair of cylindrical rollers arranged in parallel to each other, whereby the active material layer 27 Is compressed (pressed).

  In the case of manufacturing the positive electrode sheet 21, in this pressing step, the active material particles 27 a included in the active material layer 27 do not sink into the surface 26 c of the metal foil 26 due to the linear pressure applied between the rollers of the roll press machine. This is done by setting the linear pressure. Through this pressing step, a belt-like (long sheet-like) positive electrode sheet 21 is obtained.

  On the other hand, when the negative electrode sheet 22 is manufactured, in the pressing process, the active material particles 27a included in the active material layer 27 are applied to the surface 26c (surface portion) of the metal foil 26 by the linear pressure applied between the rollers of the roll press machine. This is done by setting the line pressure to sink. In the pressing step, the average particle distance is a line that is preferably 70% to 98%, more preferably 72% to 95% of the average particle diameter of the active material particles 27a included in the active material layer 27. Set to pressure. Further, in the pressing step, the active material layer 27 of the negative electrode sheet 22 has an active material particle 27a partially existing in the recess 26d of the surface 26c of the metal foil 26, and the active material particle 27a has an active particle size equal to or larger than the average particle size. The material particle 27a is set to a linear pressure that sinks into the metal foil 26 to a depth of 50% or less of the particle diameter of the active material particle 27a. That is, the active material particles 27a of the negative electrode sheet 22 are formed so that a concave portion 26d is formed on the surface of the metal foil 26, and further (simultaneously) the concave portion 26d is partly present. Then, through this pressing step, a strip-like (long sheet-like) negative electrode sheet 22 is obtained.

  Next, the rectangular (substantially rectangular) positive electrode sheet 21 and the negative electrode sheet 22 are formed by stamping the belt-like (long sheet-like) positive electrode sheet 21 and the negative electrode sheet 22 respectively. Next, the electrode assembly 25 is formed by laminating the positive electrode sheet 21 and the negative electrode sheet 22 with the separator 23 interposed therebetween. Thereby, the electrode assembly 25 is completed.

Subsequently, the positive electrode current collecting tab group 28 (positive electrode current collecting tab 21a) of the electrode assembly 25 and the positive electrode terminal 15 are joined and electrically connected, and the negative electrode current collecting tab group 29 (negative electrode current collecting tab 22a). ) And the negative electrode terminal 16 are joined and electrically connected. Subsequently, the electrode assembly 25 is housed in the main body member 12 while being covered with the insulating bag, and the lid member 13 is assembled to the main body member 12 while the positive electrode terminal 15 and the negative electrode terminal 16 protrude from the upper surface. . Then, the secondary battery 10 is completed by finally filling the electrolyte (electrolytic solution).
<Example>
Examples are given below to describe the above embodiments more specifically, but the present invention is not limited to these examples.
(Production of negative electrode sheet)
SiO powder (manufactured by Sigma-Aldrich Japan, average particle size = 5 μm, tap density = 3.2 g / cm ³ ), KB, polyamideimide resin (solvent composition: NMP / xylene = 4), which are commercially available active material particles / 1, Cured residue 30.0%, Silica in cured residue: 2% (all ratios are weight ratios, viscosity 8700 mPa · s / 25 ° C.) and NMP are mixed, and paste-like active material mixture Got. The compounding ratio of the active material particles, KB, and binder (solid content) was 80.75: 4.25: 15 in terms of mass ratio.

Next, the obtained paste-like active material mixture was applied to the surface (both sides) of the strip-shaped copper foil and shaped, and the basis weight of the active material mixture was 7 mg / cm ² (thickness 18 μm copper) The thickness including the foil was 76 μm).

Next, the copper foil coated with the active material mixture was passed through a dryer to remove the solvent and dry. Subsequently, the dried copper foil was passed through a roll press, the dried active material layer was compressed, and the thickness of the active material layer was 15 μm. At this time, negative electrode sheets with different average inter-particle distances were obtained by adjusting the linear pressure applied between the rollers of the roll press machine.
(Observation with a scanning electron microscope)
The obtained negative electrode sheet was cut with a focused ion beam processing and observation apparatus (JEM-9310FIB, manufactured by JEOL Ltd.), and the cross section was observed with a scanning electron microscope (Hitachi High Technology Co., Ltd., S-4800). As a result, for all the produced negative electrode sheets, the active material particles are indented on the surface of the copper foil (recesses are formed on the surface of the copper foil, and at least part of the active material particles are present in the recesses). Was observed.
(Visual observation)
Moreover, about all the manufactured negative electrode sheets, whether the copper foil is wrinkled and cracked in the boundary part of the formation area (formation area | region 27c) of an active material layer, and a non-formation area | region (non-formation area | region 26b). Was observed.

  As a result, among the active material particles embedded in the surface of the copper foil, the active material particles having a particle diameter equal to or larger than the average particle diameter are embedded in the copper foil to a depth of 50% or less of the particle diameter of the active material particles. For the samples (existing in the recesses formed in the copper foil), no wrinkles or cracks occurred in the copper foil at the boundary.

  On the other hand, among the active material particles embedded in the surface of the copper foil, the active material particles having a particle diameter equal to or larger than the average particle diameter are embedded in the copper foil to a depth exceeding 50% of the particle diameter of the active material particles. About the sample (it exists in the recessed part formed in copper foil), the wrinkle etc. had arisen in copper foil in the said boundary part.

  In the case where the active material particles are sunk to a depth exceeding 50% of the particle diameter of the active material particles, the non-formation region of the active material layer that weakly contacts the roller of the roll press machine, and the non-formation region It is considered that wrinkles and the like occur in the copper foil at the boundary portion as a result of the difference in the amount of copper foil stretched between the active material layer forming region that is in contact with the roller more strongly.

Therefore, among the active material particles embedded in the surface of the copper foil in the active material layer of the negative electrode sheet, for the active material particles having a particle size equal to or larger than the average particle size, 50% of the particle size of the active material particles is reduced. It was confirmed that it was preferable to squeeze into the copper foil to a depth not exceeding.
(Measurement of peel strength)
The peel strength was measured using an adhesive tape / adhesive sheet test method. First, the manufactured strip-shaped negative electrode sheets were each punched to prepare strip-shaped samples each having a length of 80 mm and a width of 25 mm. Also, in the peel strength measurement method, a commercially available strong double-sided tape (3M, YHB Y-4945) is used on a rectangular test table supported so as to be slidable, and the longitudinal direction of the test table matches the sample. In this state, the sample is affixed, and the end of the sample in the longitudinal direction is fixed to a fixture that is supported so as to be movable in a direction perpendicular to the sample affixing surface on the test bench.

  And, when moving the load measuring instrument (Minebibear, LTS-200N-S20) connected to the fixture at a constant speed of 20 mm / min in a direction away from the sample, the sample is peeled off from the test table. Measure the load. And the average value of the load per 1 cm in width between 10 mm-30 mm from the position where peeling started among the measured loads was made into peeling strength.

  Table 1 and the graph of FIG. 4 show the measurement results of peel strength for each sample of the negative electrode sheet with different average interparticle distances.

As shown in Table 1 and FIG. 4, when the average interparticle distance was less than 60%, it was confirmed that the peel strength was reduced as compared with the case where the average interparticle distance was 60% or more. . This is presumably because the amount of the binder existing between the active material particles is small, and the strength of bonding the active material particles and the copper foil is lowered instead. It was also confirmed that good peel strength was exhibited when the average interparticle distance was 60% or more and 98% or less.

From the above, when the average interparticle distance is 60% or more and 98% or less, the peel strength between the active material layer and the copper foil is increased by the adhesion by the binder and the anchor effect of the active material particles to the copper foil. It was confirmed that it can be suitably improved. In consideration of mounting the secondary battery 10 on an industrial vehicle such as a forklift, it is preferable that the average interparticle distance is 75% or more and a peel strength of 2.67 N / cm is secured.
(Production of lithium ion secondary battery)
A lithium ion secondary battery (half cell) was produced using each negative electrode sheet produced by the above procedure as an evaluation electrode. The counter electrode was a metal lithium foil (thickness 500 μm). The counter electrode was punched to φ13 mm, the evaluation electrode was punched to φ11 mm, and a separator (Hoechst Celanese glass filter and celgard 2400) was sandwiched between them to form an electrode assembly. This electrode assembly was accommodated in a battery case (manufactured by Hosen Co., Ltd., CR2032 coin cell). In addition, a non-aqueous electrolyte in which LiPF ₆ was dissolved at a concentration of 1 M was injected into the battery case in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a ratio of 1: 1 (volume ratio). And the battery case was sealed, and each sample of the lithium secondary battery was obtained.
(Evaluation of cycle characteristics)
In order to evaluate the cycle characteristics, a charge / discharge test was performed on each sample. In the charge / discharge test, under a temperature environment of 25 ° C., the battery was first charged with a constant current of 0.05 mA to a discharge end voltage of 0.01 V on the basis of metal Li, and then a constant current of 0.05 mA to a charge end voltage of 2 V. A discharge was performed. The first charge / discharge test after the first charge / discharge test was taken as the first cycle, and the same charge / discharge was repeated until the fifth cycle. Subsequently, charging / discharging was repeatedly performed at 0.1 mA for the 6th to 10th cycles, 0.2 mA for the 11th to 15th cycles and 0.05 mA for the 16th and subsequent cycles. The end voltage of charge / discharge was 0.01 to 2 V in any cycle.

  In each cycle, the discharge capacity and the charge capacity per unit mass of the active material with respect to the voltage were measured. And the discharge capacity maintenance factor in each cycle was computed. The discharge capacity retention ratio is a value obtained by dividing the N-th cycle discharge capacity by the initial discharge capacity ((N-cycle discharge capacity) / (first-cycle discharge capacity) × 100). (N is an integer value).

  FIG. 5 shows the results of measuring the number of cycles until the discharge capacity retention rate reaches 80% for each sample of the lithium ion secondary battery manufactured using negative electrode sheets with different average interparticle distances.

  As shown in FIG. 5, it was confirmed that excellent cycle characteristics were exhibited when the average interparticle distance was 70% or more and 98% or less. Further, it was confirmed that particularly excellent cycle characteristics were exhibited when the average interparticle distance was 72% or more and 95% or less.

  Here, when the average inter-particle distance is less than 70%, the active material particles partially existing in the recesses interfere with each other due to the expansion of the active material particles due to charging, and stress is generated. It is considered that the cycle characteristics deteriorate due to the peeling of copper from the copper foil.

  On the other hand, when the average inter-particle distance exceeds 98%, the distance between the active material particles partially existing in the recesses is larger than that in the case where the average particle distance is 98% or less. Since the number of active material particles to be reduced is small, the active material layer is easily peeled off from the copper foil with charge and discharge, and it is considered that the cycle characteristics are deteriorated due to this.

  Further, when the average interparticle distance is less than 70%, the active material particles are close to each other, so that it takes time to impregnate the active material layer with the electrolyte. Therefore, from the viewpoint of shortening the manufacturing time of the secondary battery 10, it can be said that the average interparticle distance in the positive electrode sheet is preferably 70% or more.

Therefore, according to the present embodiment, the following effects can be obtained.
(1) In the negative electrode sheet 22, a part of the active material particles 27 a exists in the recesses 26 d of the metal foil 26, so that the active material layer 27 is made of the metal foil by the anchor effect of the active material particles 27 a with respect to the metal foil 26. It can suppress that it peels from 26. And among the active material particles 27a partially present in the recesses 26d, when the average inter-particle distance between the adjacent active material particles 27a is 70% or more, it is less than 70%. Further, it is possible to suppress the active material particles 27a from interfering with each other due to expansion caused by charging, and to prevent the active material layer 27 from peeling from the metal foil 26. Further, when the average interparticle distance of the active material particles 27a is 98% or less, compared with the case where it exceeds 98%, the distance between the active material particles 27a is reduced to enhance the anchor effect, thereby charging and discharging. Accordingly, the active material layer 27 can be prevented from peeling from the metal foil 26. Therefore, it can suppress that the active material layer 27 and the metal foil 26 peel.

  (2) When the active material particles 27 a having a particle diameter equal to or larger than the average particle diameter are present in the concave portion 26 d of the metal foil 26 exceeding 50% of the particle diameter, wrinkles or the like are caused by deformation of the metal foil 26. Occurs. However, according to the present embodiment, the active material particles 27a having a particle diameter equal to or larger than the average particle diameter are present in the recess 26d to a depth of 50% or less of the particle diameter of the active material particles 27a. It can suppress suitably that a wrinkle etc. arise in foil 26.

(3) When the metal foil 26 of the negative electrode sheet 22 is a copper foil, the active material layer 27 can be prevented from peeling from the copper metal foil 26.
(4) In the electrode assembly 25, the positive electrode sheet 21 and the negative electrode sheet 22 are laminated with the separator 23 interposed therebetween, and the positive electrode sheet 21 and the negative electrode sheet 22 are layered. For this reason, in the electrode assembly 25 in which the positive electrode sheet 21 and the negative electrode sheet 22 have a layered structure, it is possible to suppress the active material layer 27 from being separated from the metal foil 26 of the negative electrode sheet 22.

  (5) As a result of preventing the active material layer 27 from peeling from the metal foil 26 of the negative electrode sheet 22 constituting the electrode assembly 25, the durability of the secondary battery 10 having the electrode assembly 25 is improved. be able to.

  (6) In the negative electrode sheet 22, among the active material particles 27 a partially existing in the recess 26 d, the average inter-particle distance between the adjacent active material particles 27 a is set to 72% or more, thereby further increasing the secondary battery 10. As a result, the cycle characteristics can be improved.

  (7) In the negative electrode sheet 22, among the active material particles 27 a partially present in the recesses 26 d, the average inter-particle distance between the adjacent active material particles 27 a is set to 95% or less to further increase the secondary battery 10. As a result, the cycle characteristics can be improved.

  (8) In the negative electrode sheet 22, among the active material particles 27a partially present in the recesses 26d, the average inter-particle distance between the adjacent active material particles 27a is 75% or more, so that the active material layer 27 It can suppress that time required to impregnate electrolyte (electrolyte solution) becomes long.

  (9) In the negative electrode sheet 22, among the active material particles 27a partially present in the recesses 26d, the average distance between adjacent active material particles 27a is 75% or more, so that the negative electrode sheet 22 is mounted on an industrial vehicle. It is possible to prevent the active material layer 27 from being peeled off from the metal foil 26 even under conditions in which large vibrations are applied to the secondary battery 10 such as at times.

The embodiment is not limited as described above, and may be embodied as follows, for example.
As shown in FIG. 6, the auxiliary metal foil 35, which is the same metal as the metal foil 26, is joined to the non-formation region 26 b where the active material layer 27 is not formed on the surface 26 c of the metal foil 26 in the negative electrode sheet 22. It may be. The metal foil 26 and the auxiliary metal foil 35 may be joined by, for example, seam welding, which is a type of resistance welding. In this case, the auxiliary metal foil 35 may be formed to have the same thickness (substantially the same thickness) as that of the active material layer 27. According to this, since the auxiliary metal foil 35 is joined to the non-formation region 26b where the active material layer 27 is not formed, the depression 26d is formed by pressurizing the formation region 27c of the active material layer 27 by, for example, pressing. In the case where at least a part (a part) of the active material particles 27a is present in the concave portion 26d while forming the metal foil 26, it is possible to suppress wrinkles and the like from being generated in the metal foil 26.

  As shown by a two-dot chain line in FIG. 6, the auxiliary metal foil 35 and the metal foil 26 sandwich a sheet 35 a made of a metal having a higher electric resistance than the metal forming the auxiliary metal foil 35 and the metal foil 26. It may be joined in a state. According to this, resistance welding of the auxiliary metal foil 35 and the metal foil 26 can be facilitated.

As shown in FIG. 6, the active material layer 27 may be formed only on one side of the metal foil 26.
As shown in FIG. 7 and FIG. 8, the electrode assembly 25 is a state in which the positive electrode sheet 21, the negative electrode sheet 22, and the separator 23 are formed in a strip shape (long sheet shape) and the separator 23 is sandwiched therebetween. Thus, the positive electrode sheet 21 and the negative electrode sheet 22 may be wound in a spiral shape so that the positive electrode sheet 21 and the negative electrode sheet 22 have a layered structure (laminated structure). In this case, the non-formation area | region 26b extended along the length direction of the positive electrode sheet 21 is formed in one edge part of the width direction in the positive electrode sheet 21, The said non-formation area | region 26b is used as the positive electrode current collection tab 21a. On the other hand, a non-formation region 26b extending along the length direction of the negative electrode sheet 22 is formed at the other edge in the width direction of the negative electrode sheet 22, and the non-formation region 26b is used as the negative electrode current collecting tab 22a. . Then, by winding the positive electrode sheet 21 and the negative electrode sheet 22, the positive electrode current collecting tab group 28 in which the positive electrode current collecting tab 21a has a layered structure is formed on one edge of the electrode assembly 25, while the electrode A negative electrode current collecting tab group 29 in which the negative electrode current collecting tab 22a forms a layered structure may be formed on the other edge of the assembly 25.

The shape of the positive electrode sheet 21 and the negative electrode sheet 22 may be changed.
In the active material layer 27 of the positive electrode sheet 21, the active material particles 27 a may partially exist in the recesses 26 d of the metal foil 26.

The electrode assembly 25 may be laminated by folding the positive electrode sheet 21 and the negative electrode sheet 22 into a bellows shape with the separator 23 interposed therebetween.
(Circle) the metal foil 26 used for the positive electrode sheet 21 may be formed from different metals, such as nickel and stainless steel. Similarly, for the negative electrode sheet 22, the metal of the metal foil 26 may be changed.

  ○ Of the active material particles 27a existing in the recesses 26d on the surface 26c of the metal foil 26, the active material particles 27a having a particle diameter equal to or larger than the average particle diameter are 50% or more of the particle diameter of the active material particles 27a. It may be present in the recess 26d to the depth (it may be embedded in the metal foil 26). However, from the viewpoint of suppressing generation of wrinkles and the like of the metal foil 26, it is preferable to configure as in the above embodiment.

  The number of the positive electrode sheets 21 and the negative electrode sheets 22 constituting the electrode assembly 25 may be changed as appropriate. For example, the electrode assembly 25 may include one positive electrode sheet 21 and one negative electrode sheet 22.

The shape of the case 11 may be formed in a columnar shape or an elliptical column shape that is flat in the left-right direction.
○ The secondary battery 10 of the above embodiment is mounted on a vehicle (for example, an industrial vehicle or a passenger vehicle), and is charged by a generator installed in the vehicle. Alternatively, an electric motor for driving the wheels or an electrical component such as a car navigation system may be driven. According to this, it can suppress that the active material layer 27 peels from the metal foil 26, and can improve the durability as the secondary battery 10. Therefore, it can suppress that the replacement cycle of the secondary battery 10 becomes short in a vehicle.

  The present invention may be embodied in an electric double layer capacitor as a power storage device.

  C1 ... center, C2 ... center, 10 ... secondary battery (power storage device), 21 ... positive electrode sheet, 22 ... negative electrode sheet (negative electrode), 23 ... separator, 25 ... electrode assembly, 26 ... metal foil, 26b ... non Formation region, 26c ... surface, 26d ... recess, 27 ... active material layer, 27a ... active material particles, 27b ... binder, 27c ... formation region, 35 ... auxiliary metal foil.

A negative electrode that solves the above problem is a negative electrode for a lithium ion secondary battery in which an active material layer containing active material particles for a negative electrode is formed on the surface of a metal foil, wherein the active material particles are SiO _n (0 .1 ≦ n ≦ 2) is a particle of silicon oxide represented by a composition formula of, wherein the surface of the metal foil in a region where the active material layer is formed, that at least partially sinks in the active material particles Thus, a recess defined by the surface of the recessed active material particle is formed , and among the active material particles at least part of which is present in the recess, the average distance between the centers of adjacent active material particles is the average particle diameter. 70% 98% less der is, the non-formation region in which the no active material layer is formed on the surface of the metal foil, the gist that the auxiliary metal foil made of the metal foil of the same metal are joined When That.

According to this configuration, a recess is formed on the surface of the metal foil, and at least a part of the active material particles is present in the recess, so that the active material layer can be prevented from peeling from the metal foil. And among the active material particles in which at least a part is present in the recess, the average distance between the centers of the adjacent active material particles is 70% or more of the average particle diameter, so that it is less than 70%. In addition, the active material particles can be prevented from interfering with each other due to the expansion caused by charging, and the generation of stress, and the active material layer can be prevented from peeling from the metal foil. Moreover, since the average distance between the centers of the adjacent active material particles is 98% or less of the average particle diameter, the distance between the active material particles having at least a part of the recesses as compared with the case where it exceeds 98%. The adhesion between the active material layer and the metal foil can be improved by reducing the thickness of the active material layer, thereby preventing the active material layer from being peeled off from the metal foil along with charge / discharge. Therefore, it can suppress that an active material layer and metal foil peel.
In addition, since the auxiliary metal foil is joined to the non-formation region where the active material layer is not formed, the active material is formed in the depression while forming the depression by, for example, pressing the formation region of the active material layer with a press. When at least a part of the particles is present, wrinkles and the like can be prevented from occurring in the metal foil.

Claims (6)

A negative electrode in which an active material layer containing active material particles for a negative electrode is formed on the surface of a metal foil,
In the formation region where the active material layer is formed, a recess is formed on the surface of the metal foil, and at least a part of the active material particles is present in the recess,
Of the active material particles having at least a part in the recess, an average distance between centers of adjacent active material particles is 70% or more and 98% or less of an average particle diameter.   Of the active material particles having at least a portion in the recess, the active material particles having a particle diameter equal to or larger than the average particle diameter are embedded in the recess to a depth of 50% or less of the particle diameter of the active material particle. The negative electrode according to claim 1.   3. The negative electrode according to claim 1, wherein an auxiliary metal foil made of the same metal as the metal foil is bonded to a non-formation region where the active material layer is not formed on the surface of the metal foil.   The negative electrode according to claim 1, wherein the metal foil is made of copper. An electrode assembly in which an electrode having an active material layer containing active material particles formed on the surface of a metal foil is laminated or wound with a sheet-like separator interposed therebetween, and the electrode has a layered structure. In a power storage device having
The power storage device according to claim 4, wherein the electrode includes the negative electrode according to claim 4.   A vehicle comprising the power storage device according to claim 5.