JP6745782B2 - Negative electrode for lithium-ion secondary battery and lithium-ion secondary battery - Google Patents

Description

The present invention relates to a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery.

Conventionally, a lithium ion secondary battery has been known as a secondary battery used as a power source for portable electronic devices and the like.

The use of tin, which has a larger theoretical capacity than that of a carbon material, as the negative electrode active material of the lithium ion secondary battery has been studied. For example, one having a tin film with a thickness of 10 to 300 μm formed on the surface of a current collector may be used. It is known to be used as a negative electrode of the lithium ion secondary battery (see, for example, Patent Document 1).

However, the tin film has extremely large volume expansion when occluding lithium ions, and peels from the surface of the current collector when the charge/discharge reaction is repeated, so that the charge/discharge cycle performance of the lithium ion secondary battery deteriorates. There is a problem. Therefore, in order to solve the above problem, a negative electrode for a lithium ion secondary battery in which a cross-shaped mesh made of copper thin wires is used as a current collector and the current collector is plated with tin is known (for example, Patent Document 1). 2).

JP 2001-68094 A JP, 2008-91035, A

However, even if a cross-shaped mesh made of thin copper wires is used as a current collector, the tin film is peeled from the surface of the current collector when the charge/discharge reaction is repeated due to large volume expansion when the lithium ions are absorbed. It is the same, and improvement is desired.

In view of such circumstances, the present invention does not peel off the tin film formed on the surface of the current collector even when the charge/discharge reaction is repeated, and can suppress deterioration of charge/discharge cycle performance, and It is an object of the present invention to provide a negative electrode for a lithium-ion secondary battery that can secure a required energy capacity.

Moreover, the objective of this invention is also providing the lithium ion secondary battery provided with the said negative electrode for lithium ion secondary batteries.

In order to achieve such an object, the negative electrode for a lithium ion secondary battery of the present invention comprises a flat plate current collector and a first flat plate current collector having a thickness in the range of 100 to 1200 nm. A first negative electrode member having a tin coating, a mesh-shaped current collector having electrical conductivity, and a second tin coating having a thickness in the range of 100 to 1200 nm that covers the surface of the mesh-shaped current collector. And a second negative electrode member having a space surrounded by the second tin film, wherein at least one second negative electrode member is laminated on the first tin film of the first negative electrode member. It is characterized by being.

In the negative electrode for a lithium ion secondary battery of the present invention, the first negative electrode member includes a plate-shaped current collector and a first tin film that covers the surface of the plate-shaped current collector. Here, since the first tin film has a thickness in the range of 100 to 1200 nm, volume expansion can be suppressed when lithium ions are occluded, and even when charging and discharging are repeated in a lithium ion battery. It is possible to prevent peeling from the current collector and suppress deterioration of charge/discharge cycle performance.

When the thickness of the first tin film is less than 100 nm, the action of occluding lithium ions as a negative electrode active material becomes too small, and when the thickness exceeds 1200 nm, volume expansion cannot be suppressed when occluding lithium ions. ..

On the other hand, in the lithium-ion secondary battery negative electrode of the present invention, it is difficult to secure the required energy capacity only with the first tin film having a thickness within the above range. Therefore, in the negative electrode for a lithium ion secondary battery of the present invention, at least one second negative electrode member is laminated on the first tin film of the first negative electrode member.

The second negative electrode member includes a mesh-shaped current collector having electrical conductivity, and a second tin film having a thickness in the range of 100 to 1200 nm that covers the surface of the mesh-shaped current collector. .. In addition, the second negative electrode member has a space surrounded by the second tin film by coating the surface of the mesh-shaped current collector with the second tin film.

As a result, when the second negative electrode member is laminated on the first tin film of the first negative electrode member, the electrolyte solution fills the space surrounded by the second tin film in the lithium ion battery. Will be satisfied. Therefore, both the first tin film and the second tin film can make good contact with lithium ions through the electrolytic solution, and a required energy capacity can be secured.

In the lithium ion secondary battery negative electrode of the present invention, at least one second negative electrode member may be laminated on the first negative electrode member, and the energy of the lithium ion secondary battery negative electrode depends on the number thereof. The capacity can be adjusted.

The reason why the thickness of the second tin film is set in the range of 100 to 1200 nm is the same as in the case of the first tin film.

In the negative electrode for a lithium ion secondary battery of the present invention, the first tin film and the second tin film may be formed by electroless plating, but are preferably formed by electroplating. According to electroplating, the tin film has good adhesion to the current collector, and a large-area tin film can be easily and inexpensively formed.

Further, the lithium ion secondary battery of the present invention may include the negative electrode for the lithium ion secondary battery, a positive electrode arranged to face the second negative electrode member, and an electrolytic solution.

The typical sectional view showing one example of composition of the negative electrode for lithium ion secondary batteries of the present invention. The top view of the 2nd negative electrode member shown in FIG. FIG. 3 is a schematic cross-sectional view showing a configuration example of the lithium-ion secondary battery of the present invention. The graph which shows the relationship between the thickness of the 1st tin film in a 1st negative electrode member, and charge/discharge cycle performance. FIG. 3 is a plan view showing a configuration of a main part of the expanded metal used for the mesh current collector. FIG. 6 is an assembly diagram showing another configuration example of the lithium-ion secondary battery of the present invention. The graph which shows the charging/discharging cycle performance of the lithium ion secondary battery of this invention.

Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

As shown in FIG. 1, the lithium-ion secondary battery negative electrode 1 of the present embodiment includes a first negative electrode member 2 and a second negative electrode member 3. The first negative electrode member 2 includes a plate-shaped current collector 21 and a first tin film 22 that covers at least one surface of the plate-shaped current collector 21. In addition, the second negative electrode member 3 is laminated on the first tin film 22, and the mesh-shaped current collector 32 made of the thin wire 31 having electrical conductivity and the second tin film coating the surface of the thin wire 31. And 33.

The plate-shaped current collector 21 is not particularly limited as long as it is a material having electric conductivity, but, for example, one made of aluminum, copper, steel, titanium or the like can be used. It is also possible to use tin as the material of the flat plate current collector 21. In this case, the plate-shaped current collector 21 also serves as the first tin film 22. The thickness of the flat plate-shaped current collector 21 is preferably thin in order to improve the energy density of the battery, but if it is too thin, it is difficult to handle and productivity is reduced, so the thickness should be in the range of 5 to 50 μm. preferable. In addition, the flat plate current collector 21 may be cut or melted on the surface to form irregularities.

The first tin coating 22 has a thickness in the range of 100 to 1200 nm. The first tin film 22 can be formed by electroplating or electroless plating, but the first tin film 22 has good adhesion to the plate-shaped current collector 21, and a large-area film can be formed easily and inexpensively. It is preferably formed by plating.

When the first tin film 22 is formed by electroplating, the flat plate current collector 21 is immersed in an acid such as nitric acid, hydrochloric acid or sulfuric acid, or washed with water to remove dust and oxide film on the surface. Alternatively, it can be carried out by immersing in a plating bath in which a tin salt such as tin chloride is dissolved in an acid such as sulfuric acid, and energizing at a predetermined temperature. At this time, β-naphthol, gelatin, and cresol sulfonic acid may be dissolved in appropriate amounts in order to form a more uniform first tin film 22. The plating bath may be one in which a tin salt such as tin chloride is dissolved in an alkaline solution such as sodium hydroxide instead of sulfuric acid. The thickness of the first tin film 22 can be controlled by the energization time.

The thin wire 31 forming the mesh-shaped current collector 32 is not particularly limited as long as it is a material having electrical conductivity, and for example, one made of aluminum, copper, steel, titanium, or the like can be used. .. It is also possible to use tin as the material of the thin wire 31. In this case, the thin wire 31 also serves as the second tin film 33. The material of the thin wire 31 may be the same as or different from that of the flat plate-shaped current collector 21.

The thickness of the mesh-shaped current collector 32 is preferably thin in order to improve the energy density of the battery, but if it is too thin, it is difficult to handle and productivity is reduced, so the thickness may be in the range of 3 to 500 μm. preferable.

The second tin film 33 has a thickness in the range of 100 to 1200 nm and can be formed by the same method as the first tin film 22. At this time, as shown in FIG. 2, since the second tin film 33 is formed on the surface of the thin wire 31, the second negative electrode member 3 has the space 34 surrounded by the second tin film 33. ..

In addition, in the second negative electrode member 3, the mesh-shaped current collector 32 may be a fine wire 31 knitted in the vertical and horizontal directions, and holes formed uniformly in a foil made of a material having electric conductivity like punching metal. It may be Further, the mesh-shaped current collector 32 may be an expanded metal that is formed into a rhombic shape or a hexagonal shape by forming a flat plate made of a material having electrical conductivity, such as a metal plate, in a zigzag shape while expanding the zigzag shape. In the case of a cross-shaped mesh formed by knitting fine wires, the gap between the thin wires opens or closes when bent or stretched, so that the distance between the gaps is not constant, and the second negative electrode member 3 is manufactured. At times, even if a slight force is applied, it is deformed, and it becomes difficult to manufacture the second negative electrode member 3. On the other hand, punching metal and expanded metal have some hardness when bent or bent, as compared to a cloth mesh made by knitting fine wires, so the shape is easily fixed, and even if it expands or shrinks a little, Does not open or close. Therefore, in a cell in which the second negative electrode member 3 is bent in the cell, such as a cylindrical cell or a wound type, punching metal or expanded metal is more preferable than a cross mesh formed by knitting fine wires. Further, since punching metal and expanded metal can be bent, they can be applied to a battery having a flexible shape.

When the mesh-shaped current collector 32 is formed by knitting the fine wires 31 in the vertical and horizontal directions, the interval (opening) of the fine wires 31 is in the range of 1 to 50 μm, for example. When the mesh current collector 32 is made of expanded metal, for example, the strand width is 0.001 to 10 mm, the opening short side dimension is 0.01 to 10 mm, and the opening long side dimension is 0.05 to 50 mm. Has become.

The diameter of the space 34 in the second negative electrode member 3 is set such that the mesh-shaped current collector 32 has a diameter such that the electrolytic solution is easily infiltrated when the lithium ion secondary battery 4 described below is formed and the resistance does not increase. When the fine wire 31 is knitted in the longitudinal and lateral directions, it is preferably in the range of 0.001 to 48 μm, and more preferably in the range of 1 to 40 μm. Further, the diameter of the space 34 in the second negative electrode member 3 is preferably in the range of 0.001 μm to 10 mm when the mesh current collector 32 is made of expanded metal, and is in the range of 1 to 500 μm. More preferably. The porosity of the second negative electrode member 3 is 1% or more in both cases where the mesh-shaped current collector 32 is formed by knitting the fine wire 31 in the longitudinal and lateral directions and in the case where it is made of expanded metal. Preferably.

In the present embodiment, as an example of the negative electrode 1 for a lithium ion secondary battery, one in which one second negative electrode member 3 is laminated on the first negative electrode member 2 is shown. However, the negative electrode 1 for a lithium-ion secondary battery only needs to have at least one second negative electrode member 3 laminated on the first negative electrode member 2, and more negative electrode members 3 may be further laminated. Good. The number of the second negative electrode member 3 is not particularly limited, but is preferably in the range of 1 to 5 in order to facilitate manufacturing.

Further, since the first negative electrode member 2 has conductivity and also functions as a current collector, a mixture containing a negative electrode active material is provided between the first negative electrode member 2 and the second negative electrode member 3. Layers may be provided. Examples of the negative electrode active material include artificial graphite, natural graphite, hard carbon, soft carbon, silicon, silicon oxide, tin, silver, aluminum, zinc, lead, germanium, lithium and the like, or alloys thereof. .. The mixture layer containing the negative electrode active material is prepared by adding a binder, a conductive auxiliary agent or the like to the negative electrode active material to prepare a slurry, and applying the slurry on the first negative electrode member 2. Of course, a foil made of the negative electrode active material may be arranged on the first negative electrode member 2. Then, the second negative electrode member 3 is arranged on the above-mentioned mixture layer.

The lithium-ion secondary battery negative electrode 1 of the present embodiment can be used, for example, in the lithium-ion secondary battery 4 shown in FIG.

The lithium-ion secondary battery 4 is configured by arranging a lithium-ion secondary battery negative electrode 1, a separator 6 impregnated with an electrolytic solution, and a positive electrode 7 inside a cell 5. In the lithium-ion secondary battery 4, the lithium-ion secondary battery negative electrode 1 is arranged so that the second negative electrode member 2 faces the positive electrode 7 with the separator 6 interposed therebetween. The positive electrode 7 includes a positive electrode current collector 71 and a positive electrode mixture layer 72, and is arranged so that the positive electrode mixture layer 72 faces the separator 6. Further, the negative electrode lead 8 is connected to the flat plate-shaped current collector 21 and the mesh current collector 32 of the negative electrode 1 for the lithium ion secondary battery, and the positive electrode lead 9 is connected to the positive electrode current collector 71 of the positive electrode 7. Has been done.

In the lithium-ion secondary battery 4, the separator 6 may be made of synthetic resin such as polyethylene. Further, as the electrolytic solution with which the separator 6 is impregnated, it is possible to use a solution obtained by dissolving a lithium salt as a supporting salt in the solvent using a phosphoric acid ester represented by the following general formula (1) as a solvent.

In the general formula (1), R ¹ , R ² , and R ³ are linear hydrocarbon groups such as alkyl groups, alkenyl groups, and alkynyl groups, or groups in which some of the hydrogen atoms are replaced with fluorine, and It may be the same or different. Further, since the viscosity of the straight-chain hydrocarbon group becomes too high when the number of carbon atoms is large and the handling becomes difficult, the number of carbon atoms is preferably 7 or less, and more preferably 3 or less.

The phosphoric acid ester is preferably, for example, trimethyl phosphate, triethyl phosphate, tristrifluoroethyl phosphate, or the like, because it has an appropriate viscosity and a high solubility in a lithium salt that is a supporting salt.

Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , Li ₂ SO ₄ , Li ₃ PO ₄ , Li ₂ HPO ₄ , LiH ₂ PO ₄ , LiCF ₃ SO ₃ , and LiC. _{4 F 9 SO 3, LiN (} FSO 2) consisting of an imide anion _{2, LiN (CF 3 SO 2} ) 2, LiN (C 2 F 5 SO 2) 2, LiN (CF 3 SO 2) (C 2 F 5 SO _{2), LiN (CF 3 SO} 2) (C 4 F 9 SO 2), LiN containing a five-membered ring structure _{(CF 2 SO 2) 2 (} CF 2), LiN having a six-membered ring structure _(CF 2 SO ₂ ) ₂ (CF ₂ ) _{2 and the} like. Furthermore, as the lithium salt, LiPF _{5 (CF 3)} to at least one fluorine atom substituted with the fluoroalkyl group _{LiPF 6, LiPF 5 (C 2} F 5), LiPF 5 (C 3 F 7), LiPF 4 _{(CF 3) 2, LiPF 4} (CF 3) (C 2 F 5), may also be mentioned LiPF _{3 (CF 3)} 3 and the like. In this case, the pH of the electrolytic solution is preferably in the range of 4-10.

If the pH of the electrolytic solution is 4 to 10, an additive amount of 60% by volume or less may be added. As the additive, vinylene carbonate (VC), vinyl ethylene carbonate (VEC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), ether Group-containing dimethoxyethane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, (anhydrous) succinic acid, (anhydrous) maleic acid, γ-butyrolactone, γ-valerolactone, ethylene sulfite, sulfolane, ionic liquid, borohydride Examples thereof include acid ester, acetonitrile, phosphazene, and the like, or those obtained by fluorinating a part of hydrogen groups thereof.

In addition, by repeating charge and discharge, tin repeatedly expands and contracts, becomes fine particles and peels from the current collector, and in order to prevent diffusion into the liquid, a polymerization initiator or a polymer is added to the above-mentioned electrolytic solution, You may make it. As the polymerization initiator and the polymer, polyvinylidene fluoride/hexafluoropropylene (PVDF-HFP), (poly)acrylonitrile, (poly)acrylic acid, polymethylmethacrylate, etc. can be used, but are not limited thereto. Do not mean. Moreover, you may add a crosslinking agent to these. In order to gel the electrolytic solution, after preparing a battery, the battery can be warmed together with the battery, and the electrolytic solution can be thermally polymerized to be used. May be.

A solid electrolyte can also be used as a method for preventing the diffusion of tin fine particles into the liquid. The solid as the electrolyte, _Li 3 PO ₄ and _{Li 7 La 3 Zr 2 O 12} , La 2/3-x Li x TiO 3, Li 0.33 La 0.55 TiO 3, Li 1.3 Al 0.7 An oxide solid electrolyte such as Ti _1.3 (PO ₄ ) ₃ , Li _a Ge _x P _y S _z , (a, x, y are arbitrary values), LiSiPSCl, LS S PS (Li _10.35 [Sn _{0 .27} Si _1.08 ]P _1.65 S ₁₂ (Li _3.45 [Sn _0.09 Si _0.36 ]P _0.55 S ₄ )) or a sulfur-based solid obtained by adding a halogen element thereto. An electrolyte, polyethylene oxide (PEO), polyethylene oxide-LiTFSI, lithium phosphate oxynitride (LiPON), or the like can be used. Since these materials do not volatilize, they are considered to contribute to the improvement of safety as compared with liquid electrolytes.

The concentration of the supporting salt in the electrolytic solution is preferably in the range of 0.1 to 3 mol/L, more preferably 0.6 to 1.5 mol/L.

The current collector 71 in the positive electrode 7 is not particularly limited as long as it is a material having electrical conductivity, and, for example, one made of aluminum, copper, steel, titanium or the like can be used. The thickness of the current collector 71 is preferably thin in order to improve the energy density of the battery, but if it is too thin, it is difficult to handle and productivity is reduced, so the thickness is preferably in the range of 5 to 50 μm.

The positive electrode mixture layer 72 in the positive electrode 7 is prepared by mixing an appropriate amount of a positive electrode active material and a binder such as polyvinylidene fluoride (PVDF), and diluting the slurry with N-methylpyrrolidone to prepare a doctor blade method or the like. It can be formed by applying and applying to the current collector 71. The positive electrode mixture layer 72 preferably has a high content rate of the positive electrode active material with respect to the total amount, and for example, the content rate is preferably 85% by mass or more. Further, the positive electrode mixture layer 72 may include a conductive auxiliary agent in addition to the positive electrode active material and the binder.

As the positive electrode active material, a layered structure such as LiMnO ₂ , Li _x Mn ₂ O ₄ (0<x<2), Li ₂ MnO ₃ , and LixMn _1.5 Ni _0.5 O ₄ (0<x<2) is used. Lithium manganate provided or lithium manganate provided with a spinel structure, LiCo ₂ O ₂ , LiNiO ₂ or a compound obtained by substituting a part of the transition metal with another metal, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ Lithium transition metal oxides in which a specific transition metal such as does not exceed half of the total, compounds in which Li is in excess of stoichiometric composition in these lithium transition metal oxides, compounds having an olivine structure such as LiFePO ₄ Etc. can be mentioned.

Further, as the positive electrode active material, a part of the metal of these metal oxides is Al, Fe, P, Ti, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te. Materials substituted with Zn, La, or the like can also be used. In particular, Li _α Ni _β Co _γ Al _δ O ₂ (1≦α≦2, β+γ+δ=1, β≧0.7, γ≦0.2) or Li _α Ni _β Co _γ Mn _δ O ₂ (1≦α ≦1.2, β+γ+δ=1, β≧0.1, γ≦0.2) are preferable.

As the positive electrode active material, one of the above compounds may be used alone, or two or more thereof may be used in combination.

In the positive electrode 7, iron sulfide, iron disulfide, sulfur, polysulfide, Li ₃ VO _4, or the like can be used as the positive electrode active material instead of the positive electrode mixture layer 72. Further, a radical material such as a nitroxyl compound having a nitroxyl radical partial structure can also be used. In the case of these positive electrode active materials, since there is no lithium source in the battery, it is desirable to dope the negative electrode with lithium in advance by short-circuiting with the lithium source, vapor deposition, or the like.

Next, examples and comparative examples of the present invention will be shown.

[Reference Examples 1 to 4 and Comparative Reference Example 1]
In this reference example, first, a copper foil (50 mm×50 mm) having a thickness of 20 μm was used as a flat plate current collector 21, the surface thereof was washed with sulfuric acid, one surface thereof was masked with an epoxy tape, and heated to 50° C. It was immersed in a warm electroless plating bath to form a first tin film 22 on the unmasked surface. Next, the flat plate-shaped current collector 21 on which the first tin film 22 was formed was cut into a size of 26 mm×44 mm to form the first negative electrode member 2. At this time, the immersion time was adjusted, and five types of first negative electrode members 2 each having the first tin film 22 having a thickness of 230 nm, 440 nm, 770 nm, 1200 nm, and 2000 nm were produced.

Next, LiCoO ₂ as a positive electrode active material, a conductive auxiliary agent, and polyvinylidene fluoride (PVDF) as a binder were mixed at a mass ratio of 92:4:4 to prepare a slurry, and the obtained slurry was obtained. Was applied to a 15 μm thick aluminum foil (50 mm×50 mm) by the doctor blade method to form a positive electrode mixture layer. The aluminum foil having the positive electrode mixture layer formed thereon was cut into a size of 25 mm×44 mm to obtain a positive electrode.

Next, a polyethylene separator (30 mm×50 mm) having a thickness of 25 μm is arranged between each first negative electrode member 2 and the positive electrode, and the polyethylene separator impregnated with the electrolytic solution is vacuumed in a laminate cell. Five types of lithium-ion secondary batteries were produced by sealing and using the first negative electrode member 2 shown in FIG. 1 as a negative electrode. The electrolytic solution contains LiPF ₆ at a concentration of 1.0 mol/L in a triethyl phosphate solvent.

Next, the lithium-ion secondary battery was charged to a maximum potential of 4.05 V with a charging current of 0.1 mA in an environment of 25° C., and after 10 minutes of rest, discharged to 2.5 V as one cycle. The operation was performed 10 cycles, the discharge capacity (mAh) after each cycle was measured, and the charge/discharge cycle performance of the first negative electrode member 2 was evaluated.

The case where the thickness of the first tin film 22 is 230 nm is Reference Example 1, the case of 440 nm is Reference Example 2, the case of 770 nm is Reference Example 3, the case of 1200 nm is Reference Example 4, and the case of 2000 nm is Comparative Reference Example 1 The results are shown in FIG.

From FIG. 4, in the case of Comparative Reference Example 1 in which the thickness of the first tin film 22 is 2000 nm, the discharge capacity decreases as the cycle is repeated, while the thickness of the first tin film 22 decreases. In the case of Reference Examples 1 to 4 having a wavelength of 230 to 1200 nm, the initial discharge capacity is maintained even after repeated cycles, and it is clear that excellent charge/discharge cycle performance is provided.

From this, a lithium ion secondary battery using the negative electrode 1 for a lithium ion secondary battery in which the second negative electrode member 3 is laminated on the first negative electrode member 2 having the first tin film 22 having a thickness of 100 to 1200 nm. According to this, it is expected that the deterioration of the charge/discharge cycle performance can be suppressed and that the required energy capacity can be secured.

[Example 1]
In this example, first, except that a 10 μm-thick copper foil was used as the plate-shaped current collector 21, the same as in Reference Examples 1 to 4, one surface of which had a thickness of 400 nm by electroless plating. The first tin film 22 was formed. Next, the flat plate-shaped current collector 21 on which the first tin film 22 was formed was punched out into a disk shape having a diameter of 14 mm to obtain the first negative electrode member 2.

Next, an unmasked portion is the same as the first negative electrode member 2 except that both the front and back surfaces of one end of the copper expanded metal 34 (manufactured by Cosmo Co., Ltd.) shown in FIG. 5 are masked with epoxy tape. A second tin film (not shown) having a thickness of 400 nm was formed by electroless plating. The expanded metal 34 has a thickness of 26 μm, and as shown in FIG. 5, a mesh-shaped collection having a strand width W of 0.14 mm, an opening short side dimension SW of 0.64 mm, and an opening long side dimension LW of 1.3 mm. It is an electric body.

Next, the portion of the expanded metal 34 on which the second tin film is formed is punched out into a disk shape having a diameter of 14 mm to form the second negative electrode member 3, while the second portion of the expanded metal 34 connected to the second negative electrode member 3 is punched out. The portion where the tin film was not formed (the portion which was masked) was punched out into a semi-disc shape having a diameter of 14 mm to form the lead portion 35.

Next, as shown in FIG. 6, on a stainless steel lower lid 11 having a diameter of 20 mm and a thickness of 2 mm, a spacer 12 made of stainless steel having a diameter of 15 mm and a thickness of 1 mm, a first negative electrode member 2, and a second negative electrode. A member 3, a separator 13 made of polyethylene having a diameter of 19 mm and a thickness of 20 μm, a lithium foil 14 having a diameter of 16 mm as a counter electrode and a thickness of 100 μm, which are laminated and impregnated with an electrolytic solution, have an outer diameter of 1.8 mm, A coin cell (half cell) 16 as a lithium ion secondary battery was produced by sealing with a stainless steel upper lid 15 having a bottomed cylindrical body having a depth of 2 mm. At this time, the first negative electrode member 2 is arranged such that the first tin film 22 is on the second negative electrode member 3 side. Further, the lead member 35 has a function of promoting current collection from the second negative electrode member 3 by being bent and inserted between the lower lid 11 and the spacer 12 as shown by a dashed line in FIG. doing.

The electrolyte solution contains LiPF ₆ in a concentration of 1.0 mol/L in a triethyl phosphate/dimethyl carbonate (DEC)/fluoroethylene carbonate (FEC) (8/1/1=vol%) solvent. The coin cell 16 has the lower lid 11 as one electrode plate and the upper lid 15 as a counter electrode plate, and a packing (not shown) made of an insulator is provided between the lower lid 11 and the upper lid 15. Has been done. The spacer 12 has a function of bringing the first negative electrode member 2, the second negative electrode member 3, the separator 13, and the lithium foil 14 as the counter electrode sandwiched between the lower lid 11 and the upper lid 15 into close contact with the adjacent members. Have

Next, the coin cell 16 obtained in this example was repeatedly charged and discharged with a current amount of 1 C for 15 cycles at a voltage in the range of 0.1 to 2 V. After 15 cycles, the initial charge capacity was 0.4 mAh. The maintenance rate was 111%. The results are shown in Fig. 7.

In the coin cell 16 obtained in this example, the reason why the charge capacity increased during repeated cycles was that the electrolytic solution was formed from the holes (openings) of the expanded metal 34 as the mesh-shaped current collector to the second negative electrode member. It is considered that the reaction area increased because it soaked into the inner part of No. 3 gradually.

[Example 2]
In this example, a coin cell 16 as a lithium ion secondary battery was produced in exactly the same manner as in Example 1 except that two second negative electrode members 3 were laminated on the first negative electrode member 2.

Next, the coin cell 16 obtained in this example was repeatedly charged and discharged for 15 cycles with a current amount of 1 C at a voltage in the range of 0.1 to 2 V. After 15 cycles, the initial charge capacity was 0.63 mAh. Was maintained at 100%. The results are shown in Fig. 7.

[Example 3]
In this example, triethyl phosphate/dimethyl carbonate (DMC)/FEC (80/1/1=vol%) was mixed with 8 wt% of PVDF-HFP in the electrolytic solution, and further 1.0 mol of LiPF ₆ was added. A coin cell 16 was produced in exactly the same manner as in Example 1 except that the one dissolved in /L was used.

Next, the coin cell 16 obtained in this example was warmed at 60° C. for 1 hour to gelate the electrolytic solution, and then charged and discharged with a current amount of 1 C at a voltage in the range of 0.1 to 2V. When 15 cycles were repeated, the retention rate after 15 cycles was 99% with respect to the initial charge capacity of 0.36 mAh. The results are shown in Fig. 7.

The coin cell 16 of the present embodiment in which the electrolytic solution is gelled exhibits a capacity retention ratio that is substantially the same as that of the coin cell 16 of the embodiment 1 in which the electrolytic solution is a liquid, shows a constant capacity maintenance ratio from the initial stage, and has high reliability. Can be said to be a high battery.

[Comparative Example 1]
In this comparative example, a coin cell 16 as a lithium ion secondary battery was produced in exactly the same manner as in Example 1 except that the second negative electrode member 3 was not laminated at all on the first negative electrode member 2.

Next, the coin cell 16 obtained in this comparative example was repeatedly charged and discharged with a current amount of 1 C at a voltage in the range of 0.1 to 2 V for 15 cycles, and after 15 cycles for an initial charge capacity of 0.14 mAh. The maintenance rate was 91%. The results are shown in Fig. 7.

From FIG. 7, according to the lithium-ion secondary batteries (coin cell 16) of Examples 1 and 2 including the second negative electrode member 3, it is possible to suppress the deterioration of the charge/discharge cycle performance and to obtain the required energy capacity. It is clear that they can be secured. Further, according to the lithium-ion secondary battery of Example 2, it is clear that a larger energy capacity can be secured by increasing the number of the second negative electrode members 3 as compared with the lithium-ion secondary battery of Example 1. Is.

On the other hand, according to the lithium ion secondary battery of Comparative Example 1 that does not include the second negative electrode member 3 at all, sufficient energy capacity cannot be secured as compared with the lithium ion secondary batteries of Examples 1 and 2. In addition, it is apparent that the lithium ion secondary batteries of Examples 1 and 2 are inferior to the lithium ion secondary batteries in terms of suppressing deterioration of charge/discharge cycle performance.

DESCRIPTION OF SYMBOLS 1... Negative electrode for lithium ion secondary batteries, 2... 1st negative electrode member, 3... 2nd negative electrode member, 4, 16... Lithium ion secondary battery, 21... Flat-plate collector, 22... 1st tin Film, 31... Fine wire, 32, 34... Mesh current collector, 33... Second tin film.

Claims (3)

A lithium-ion secondary battery negative electrode used in a lithium-ion secondary battery, which comprises a negative electrode for a lithium-ion secondary battery, a separator impregnated with an electrolytic solution, and a positive electrode arranged inside a cell. There
A plate-shaped current collector, and a first negative electrode member including a first tin film having a thickness in the range of 100 to 1200 nm that covers the surface of the plate-shaped current collector,
A mesh-shaped current collector having electrical conductivity and a second tin film having a thickness in the range of 100 to 1200 nm that covers the surface of the mesh-shaped current collector are provided, and the second tin film is surrounded by the second tin film. A second negative electrode member having a space,
A negative electrode for a lithium ion secondary battery, wherein at least one second negative electrode member is laminated on the first tin film of the first negative electrode member. The negative electrode for a lithium ion secondary battery according to claim 1, wherein the first tin film or the second tin film is formed by plating. A plate-shaped current collector, a first negative electrode member having a first tin film with a thickness in the range of 100 to 1200 nm that covers one surface of the plate-shaped current collector, and a mesh shape having electrical conductivity A second negative electrode including a current collector and a second tin film having a thickness in the range of 100 to 1200 nm that covers the surface of the mesh current collector, and having a space surrounded by the second tin film. A negative electrode in which the second negative electrode member is laminated on the first tin film of the first negative electrode member,
A positive electrode arranged to face the second negative electrode member,
A lithium ion secondary battery comprising an electrolytic solution.