JPH07282800A - Negative electrode, manufacture thereof, and lithium secondary battery - Google Patents

Abstract

PURPOSE:To obtain an Li battery negative electrode excellent in performance by providing a diffusion barrier layer of a conductor hard to react to a liquid Li alloy onto a collector tape, thereon the wet promoting material layer to the liquid Li alloy and an affinity conductor, and thereon a melting plating quick cooling layer having thinner than specified and composed of the Li alloy. CONSTITUTION:The diffusion barrier layer 2 of a conductor hard to react to liquid Li alloy is provided on a collector tape 1. A wet promoting material layer 3 composed of the liquid Li alloy and an affinity conductor is provided on this layer 2 to promote the wet of the liquid Li alloy at the time of melting plating. A melting plating quick cooling layer 4, composed of the Li alloy and thinner than 59mum, is provided on the layer 3. That is, the quick cooling layer 4 can be formed and a negative electrode can be manufactured by a method, wherein the collector tape 1 thereon the diffusion barrier layer 2 and the wet promoting material layer 3 are provided is introduced into the melting plating bath of the Li alloy to quickly treat the coating layer of the plating, and the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Li secondary battery excellent in charge / discharge capacity, energy density, charge / discharge cycle life, and the like, and a lithium alloy-based negative electrode and a manufacturing method thereof.

[0002]

2. Description of the Related Art Tape-like electrodes have been proposed in Li secondary batteries using non-aqueous electrolytes because large-area electrodes are advantageous in terms of charge / discharge capacity and energy density. Such a tape-shaped electrode is used for forming a battery, for example, as a positive and negative electrode wound product via a separator.

Conventionally, as the above-mentioned tape-shaped negative electrode, a current collector tape in which a powder of a lithium alloy such as Li-Al is dispersed in a binder resin and applied, Li-Ag
It has been known that a solid solution type lithium alloy plate such as Li-Mg or the like is rolled into a tape shape, and a lithium tape is pressure-bonded with a Sn-Cd alloy plated Ni expanded metal rolling tape.

However, L can be obtained in any case due to defects due to variations in quality in the length direction, deformation such as unevenness, and dropping of the active material and the like during winding.
There is a problem in that the secondary battery has poor charge / discharge capacity, energy density, and charge / discharge cycle life, and the advantages of increasing the area of the negative electrode cannot be fully exerted.

[0005]

The present invention can form a Li secondary battery having excellent charge / discharge capacity, energy density, and charge / discharge cycle life even when used as a large-area body such as a tape-like material. Therefore, it is an object to develop a lithium alloy-based negative electrode that can take full advantage of the large area of the electrode.

[0006]

According to the present invention, a diffusion barrier layer made of a conductor that does not easily react with a liquid lithium alloy is provided on a current collector tape, and the diffusion barrier layer is compatible with the liquid lithium alloy. Negative electrode for a Li secondary battery, which has a wetting promoting material layer made of a conductive conductor, and a hot-dip quenching layer made of a lithium alloy and having a thickness of 50 μm or less formed on the wetting promoting material layer, and a liquid. With a current collector tape covering the surface of a diffusion barrier layer made of a conductor that does not easily react with a lithium alloy, and a wetting promoting material layer made of a conductor having an affinity for the liquid lithium alloy provided on one or both sides of the diffusion barrier layer. A lithium alloy coating layer is introduced into a lithium alloy hot-dip bath to form a lithium alloy coating layer having a thickness of 50 μm or less on the wetting promoter layer, and then the coating layer is rapidly cooled. A method for producing a negative electrode for a Li secondary battery, and L comprising the above negative electrode
It provides a secondary battery.

[0007]

Examples of Embodiments The current collector tape is made of copper, aluminum or silver, the diffusion barrier layer is made of nickel, cobalt or iron, and the wetting promoter layer is made of silver, copper, zinc, magnesium, aluminum or calcium. It is made of barium, bismuth, indium, lead, platinum, palladium or tin, and the hot-dip quenching layer is quenched at a cooling rate of 300 ° C./sec or more. Each thickness of the diffusion barrier layer and the wetting promoter layer Is 0.01 to 5 μm, and the thickness of the current collector tape and the hot-dip quenching layer is 10 to 30
and a lithium content of 10 to 50 μm, and the lithium content of the lithium alloy forming the hot-dip quenching layer is 80% or more based on the atomic ratio.

[0008]

The present inventors have conducted extensive research to overcome the above-mentioned problems, but in order to simultaneously achieve high energy density, high charge / discharge capacity, and long cycle life of charge / discharge, the area of the electrode must be increased. It was clarified that it is the most effective measure to further proceed with, and decided to try to make the negative electrode active material layer thinner.

That is, by thinning the negative electrode active material layer, the area of the electrode can be increased without increasing the amount of the negative electrode active material in the battery, and thus the energy density and the charge / discharge capacity can be increased with the increase of the electrode area. The current density can be suppressed to a low level, the lithium precipitate during charging has a dense structure, and a long cycle life of charge / discharge can be achieved. The reason is that the thinner layer can reduce bending strain applied to the negative electrode active material layer in the winding step, and can eliminate peeling and deformation of the active material layer.

However, regarding the thinning of the active material layer of the negative electrode according to the above-mentioned conventional technique, in the case of the coating layer of the binder dispersion paste, it is difficult to form the target thin layer with good uniformity even by the doctor blade method. In the case of solid solution type lithium alloy and lithium, the mechanical strength was low and it was difficult to roll to a thin tape.

Therefore, the inventors of the present invention have further conducted intensive studies and found that under a lithium-rich condition, the object can be achieved even if the thickness of the active material layer is thin, or even about 10 to 50 μm. It was That is, as in the present invention described above, by forming the active material layer as a hot-dip layer made of a lithium alloy and having a thickness of 50 μm or less, it is possible to easily form a large area negative electrode such as a tape and improve the charge / discharge capacity. be able to. In addition, Li, which is excellent in charge / discharge capacity and energy density, exhibits good conductivity without variations in quality in the length direction, deformation such as unevenness, and detachment of the active material layer during winding, which are drawbacks of the prior art. Can form a secondary battery,
This makes it possible to obtain a negative electrode that can take full advantage of the large area of the electrode.

Further, by quenching the hot-dip plated layer to form a quenched layer, the crystal grains can be made finer and the space factor of the grain boundaries can be increased, and the lattice defect concentration can be increased so that the atomic vacancies can be formed. Will increase. The absorption / desorption associated with charge / discharge of lithium proceeds due to the diffusion of lithium in the alloy, and the diffusion is fast at the crystal grain boundaries, and the faster the number of atomic vacancies in the crystal grains, the faster the grain boundary by the quenching treatment. The increase of the space factor and the number of atomic vacancies can promote the diffusion of lithium, thereby facilitating the absorption and release of lithium and improving the cycle life of charge and discharge of the Li secondary battery. The long-term sustainability of such characteristics is that the crystal grains have the same structure as the previous crystal structure that becomes the deposition base for lithium that is deposited during charging, and the atomic vacancies are new due to ionization and elution of lithium during discharging. Since atomic vacancies are formed in the cell, even if the amount of lithium is reduced by lithium deposition during charging (lithium intrusion into the vacancies), it will continue to exist for a long time as a whole, and will be diffusion-leveled based on the concentration gradient of atomic vacancies. It is considered that this is due to the property of being evenly dispersed in the hot-dip quenching layer.

[0013]

EXAMPLES A negative electrode of the present invention has a diffusion barrier layer made of a conductor that does not easily react with a liquid lithium alloy on a current collector tape, and a conductor having an affinity for the liquid lithium alloy on the diffusion barrier layer. And a hot-dip quenching layer having a thickness of 50 μm or less made of a lithium alloy on the wetting promoting material layer, which is used for forming a Li secondary battery.

The negative electrode of the present invention is illustrated in FIGS. 1 and 2. 1
Is a current collector tape, 2 is a diffusion barrier layer, 3 is a wetting accelerator layer, and 4 is a hot-dip quenching layer made of a lithium alloy. As is clear from FIGS. 1 and 2, the hot-dip quenching layer and the like may be provided on both sides of the current collector tape or may be provided on one side.

In the present invention, as the current collector tape, one having excellent conductivity such as copper, aluminum or silver is used. The thickness of the current collector tape is appropriately determined according to the purpose of use of the electrode and the like, and is generally 100 μm or less, and in particular, 5 to 50 μm, particularly 10 to 30 μm from the viewpoint of thinning.

The diffusion barrier layer provided on the current collector tape functions to prevent the current collector tape from being eroded by the liquid lithium alloy such as lithium or its components during hot dipping. In the absence of the diffusion barrier layer, the current collector material described above reacts rapidly with the liquid lithium alloy into a semi-molten state, and the current collector tape easily breaks in a short time.
Further, the lithium alloy component such as lithium in the hot-dip quenching layer gradually penetrates to increase the electric resistance of the current collector tape and increase the internal resistance of the battery.

Therefore, for the formation of the diffusion barrier layer, for example, a liquid lithium alloy such as nickel, cobalt, or iron, or an appropriate conductor which does not easily react with its components can be used. The formation can be performed by an appropriate method such as an electroplating method, an electroless plating method, and a physical or chemical vapor deposition method. The thickness of the diffusion barrier layer is 0.01 to
5 μm, preferably 0.05 to 1 μm. If the thickness is less than 0.01 μm, defects such as voids and pinholes are likely to occur, and if it exceeds 5 μm, the electrical resistance of the current collector tape tends to increase.

The wetting promoting material layer provided on the diffusion barrier layer aims to promote wetting of the liquid lithium alloy during hot dipping and facilitate formation of a flat negative electrode active material layer having a uniform thickness. . Therefore, for the formation of the wetting promoting material layer, a conductor having an appropriate affinity with the liquid lithium alloy or its component, preferably a liquid lithium alloy or its component that easily reacts and has an excellent chemical affinity can be used. Examples thereof include silver, copper, zinc, magnesium, aluminum, calcium, barium, bismuth, indium, lead, platinum, palladium and tin.

When the wetting promoting material layer is not provided, the coating by hot dipping becomes impossible, or the lithium alloy coating layer having a uniform thickness is difficult to be formed, and the surface property of the electrode is easily deteriorated due to unevenness, and the thickness is 50 μm. It becomes difficult to form a thin layer having a thickness equal to or less than that. The wetting promoting material layer can be formed by an appropriate method such as an electroplating method or a physical or chemical vapor deposition method, and has a thickness of 0.01 to
5 μm, preferably 0.1 to 1 μm. When the thickness of the wetting promoter layer is less than 0.01 μm, the wetting promoting effect of the liquid lithium alloy is poor, and when it exceeds 5 μm, it may act as an impurity of the negative electrode active material layer to reduce charge / discharge capacity and electromotive force. .

The hot-dip quenching layer provided on the wetting promoting material layer is formed of a lithium alloy and serves as the active material layer of the negative electrode. In the present invention, the thickness is 50 μm or less, especially 5
.About.25 .mu.m, especially 10 to 20 .mu.m.

The formation of the quenching layer for hot dip plating, and thus the production of the negative electrode of the present invention, is carried out by, for example, introducing a current collector tape provided with a diffusion barrier layer and a wetting promoter layer into a hot dip bath of a lithium alloy to form the coating layer. After forming, the coating layer can be subjected to a quenching treatment or the like. At that time, as shown in FIGS. 3 and 4, a continuous method in which a long current collector tape 5 having a diffusion barrier layer and a wetting promoting material layer is continuously introduced into the hot dip plating bath 6 and passed through, or a predetermined length is used. Appropriate manufacturing methods such as a batch method in which the current collector tape 10 is soaked in the hot dip plating bath 6 and taken out can be adopted. In addition, 7 in FIG. 3 or FIG.
Is a coating thickness adjusting means, 9 is a cooling gas nozzle, 11
Is a weight.

Quenching of the hot dip layer is performed on the coating layer having a predetermined thickness. For the rapid cooling treatment, an appropriate method such as a method of spraying a cooling inert gas such as argon gas or helium gas onto the coating layer having a predetermined thickness can be used. In that case, it is preferable to perform rapid cooling at a rate of 300 ° C./sec or more from the viewpoint of improving the negative electrode characteristics by making the crystal grains finer. Such rapid cooling can be easily achieved by controlling the temperature and supply amount of the cooling gas or the like. Also, the solidification time of the hot-dip layer at room temperature is usually 2 or 3
From the viewpoint of achieving a quenching treatment of 300 ° C./sec or more, it is preferable to perform a quenching treatment within 1 second after setting a predetermined coating thickness through the thickness adjusting means, if necessary. .

In the above, when the quenching treatment atmosphere such as cooling gas reaches the coating thickness adjusting means, the current collector tape is fixed to the means to cause wire breakage, or the coating layer is cooled before the thickness becomes a predetermined thickness. It is desirable to prevent the quenching treatment atmosphere from reaching the coating layer before the predetermined thickness, as illustrated in FIGS. Such a purpose can be easily achieved by a method of controlling the supply direction of the cooling gas or the like and sucking and removing the gas that has finished its role.

As the lithium alloy used for forming the hot-dip quenching layer (coating layer), Li and, for example, Al,
Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, P
Examples thereof include alloys of binary or ternary or more with metals such as t, Sr and Te, to which Si, Cd, Zn, La and the like are added, if necessary, and any known material can be used. Incidentally, as specific examples of the lithium alloy, for example, Al,
Li alloy composed of an intermetallic compound such as Bi, Sn or In and Li and Li, an alloy of Li and Pb with La added to improve mechanical properties, or Ag, Al, Mg, Z
Li containing an X component consisting of at least one of n and Ca
Examples include -X-Te based alloys.

The content of the components other than lithium in the lithium alloy is 40% or less based on the atomic ratio, especially 5 to 3
0%, especially 10 to 20% is preferable. Its content is 40
If it exceeds 20%, the energy density of the negative electrode active material may significantly decrease, and if it exceeds 20%, the electromotive force may decrease. If it is less than 5%, the effect of improving the properties due to alloying may be poor. Li-Ag is a lithium alloy that can be particularly preferably used in terms of charge / discharge cycle life, high electromotive force, high discharge capacity, high energy density, and the like.
-The atomic ratio of Li: Ag: Te composed of a Te-based alloy is 80.
.About.150: 1 to 20: 0.001 to 30 and the like, and contains 80 atomic% or more of Li.

The negative electrode of the present invention is for forming a Li secondary battery, but the Li secondary battery to be formed is not particularly limited except that such a negative electrode is used, and an electrolyte and a positive electrode are used. Can be performed according to conventional methods. Therefore, the form of the Li secondary battery can be appropriately determined according to the purpose of use and the like. For example, like a coin type, a button type, or a wound type, a positive electrode is provided through a porous insulating film containing an electrolyte. A suitable form such as a form in which the negative electrode and the negative electrode are arranged can be adopted. Incidentally, the coin type is illustrated in FIG. Reference numerals 12 and 18 are battery cans, 13 and 17 are current collecting nickel plates, 14 is a negative electrode, 15 is an electrolyte layer (a separator made of a porous insulating film), 16 is a positive electrode, and 19 is an insulating sealing material.

As the electrolyte, it is possible to use an appropriate electrolyte capable of moving Li ions. Examples thereof include polymer electrolytes such as those obtained by mixing a lithium salt with a salt-electrolytic polymer, inorganic Li solid electrolytes, or solid electrolytes such as those obtained by dispersing it in a resin,
Examples include non-aqueous electrolyte-based electrolytes prepared by dissolving a lithium salt in an organic solvent such as ester or ether. Typical examples of the above salt-electrolytic polymers include polyethylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, their derivatives, mixtures and complexes. In the case of a solid electrolyte, it is
It has the advantage that it can also serve as a separator between the negative electrodes.

Typical examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane, dimethylsulfoxide, sulfolane, γ-butyrolactone and 1,2-dimethoxyethane. , Diethyl ether, 1,3-dioxolane, methyl formate, methyl acetate,
Examples thereof include N, N-dimethylformamide, acetonitrile, a mixture thereof and the like.

Typical examples of lithium salts include LiI and Li
CF ₃ SO ₃ , Li (CF ₂ SO ₂ ) ₂ , LiBF ₄ , LiClO
₄ , LiAlCl ₄ , LiPF ₄ , LiPF ₆ , LiAsF ₃ , Li
AsF _{6 and the} like. The concentration of lithium salt in the electrolytic solution is generally 0.1 to 3 mol / liter, but is not limited to this. In the formation of the above-mentioned non-aqueous electrolyte solution, 2-methylfuran, thiophene, pyrrole, crown ether, Li complex ions are added as necessary for the purpose of improving battery characteristics such as life, discharge capacity and electromotive force. It is also possible to add organic additives such as forming agents (such as macrocyclic compounds).

As the positive electrode, an appropriate one such as carbon or metal type, or organic conductive substance type such as conjugated polymer can be used. Examples of the metal-based positive electrode include Li, Ti, Mo, Cu, Nb,
Examples thereof include complex oxides of metals such as V, Mn, Cr, Ni, Co and P, sulfides and selenides, and typical examples thereof include MnO ₂ , LiCoO ₂ , Li _w Co _1-xy M.
_x P _y O _{2 + z} (where M is one or more transition metals, w is 0 <w ≦ 2, x is 0 ≦ x <1, y is 0 <y <
1 and z are −1 ≦ z ≦ 4. ), Or a phosphate containing Li to Li · Co and / or an oxide of Co to Li · Co and containing 0.1 mol or more of Co and 0.2 mol or more of P per 1 mol of Li. The active material is, for example.

The sheet-shaped positive electrode is formed, for example, by using an active material, if necessary, a conductive material such as acetylene black or Ketjen black, and polytetrafluoroethylene, polyethylene, polyvinylidene fluoride, ethylene / propylene / diene. It can be performed by a method such as casting with a binder such as a polymer, a compression molding method, a roll molding method, a doctor blade method, various vapor deposition methods, rolling methods, hot extrusion methods and the like. . The positive electrode sheet can also be obtained as a reinforced form obtained by adhering the positive electrode material to the current collector sheet by an appropriate method such as coating and adhering with a binder resin.

On the other hand, as the porous insulating film (separator) interposed between the positive electrode and the negative electrode, an appropriate porous material such as a porous polymer film made of polypropylene or the like, a glass filter, a non-woven fabric or the like can be used. . The electrolyte-containing porous insulating film may be formed by an appropriate method such as a method of impregnating or filling the porous insulating film with an electrolyte or an electrolytic solution, or a method of filling the battery can with the electrolytic solution or the like. it can.

The Li secondary battery can be charged by a method of continuously supplying a constant current, or a method of supplying a pulse current by using an appropriate pulse power source. The charging method using a pulse current has the advantage that dendrites are less likely to grow because the concentration change of the electrolyte is suppressed because energization / stopping is repeated.

Example 1 A current collector formed by electroplating nickel with a thickness of 1 μm on both surfaces of a long copper tape having a width of 41 mm and a thickness of 10 μm, and then electroplating silver with a thickness of 0.8 μm thereon. Body tape in a high-purity argon atmosphere with a Li: Ag: Te atomic ratio of 9
It was continuously introduced into a 5-10: 0.1 Li-Ag-Te alloy hot-dip bath (350 ° C) at a speed of 2 m / min and passed through, and the coating thickness on both sides was 15 μm with a drawing jig. Then, argon gas was blown through the liquid cylinder to rapidly cool it at a rate of 300 ° C./sec or more (FIG. 3) to continuously obtain a negative electrode tape.

On the other hand, lithium carbonate, basic cobalt carbonate and an aqueous phosphoric acid solution having a phosphoric acid content of 85% are used as Li: Co: P =
It was mixed in an atomic ratio of 2: 1.5: 0.5, put in an alumina crucible and heat-treated at 900 ° C. for 24 hours to obtain lithium phosphate, lithium cobalt phosphate and cobalt oxide. Was formed into a mixture (active material) and was pulverized with a ball mill to obtain a powder having a particle size of 20 μm or less. Next, 46 parts by weight of the powder, 4 parts by weight of acetylene black, 2 parts by weight of polyvinylidene fluoride, and 50 parts by weight of N-methylpyrrolidone are mixed, and the mixture is 38 mm wide, 400 mm long,
It was coated on an aluminum tape having a thickness of 20 μm and vacuum dried to form a coating layer (positive electrode layer) having a thickness of 200 μm to obtain a positive electrode tape.

Next, the negative electrode tape and the positive electrode tape having a length of 400 mm described above are wound with a porous polypropylene film (separator) having a thickness of 25 μm interposed therebetween, and the resulting product is housed in a battery can and 3 ml of an electrolytic solution is put therein. It was injected to form an AA type secondary battery. The cross-sectional area of the wound material was about 90% of the cross-sectional area inside the battery can, and the electrolyte used was 1 liter of propylene carbonate in which 1 mol of LiClO ₄ was dissolved.

With respect to the above secondary battery, 4.2 V (charge) to 2.75 V at a charging current and a discharging current of 100 mA.
3 charge / discharge cycles between (Discharge: 1 hour after charging)
When the discharge capacity retention rate (hereinafter the same) after repeating 00 times was examined, it was 94%. The discharge capacity in the first cycle was 410 mAh.

Example 2 A negative electrode tape was obtained in the same manner as in Example 1 except that the hot-dip plating rate, that is, the production rate was 20 m / min.
i got a secondary battery. The discharge capacity of the first cycle is 46
At 0 mAh, the discharge capacity retention rate after charging / discharging cycle 300 times was 97%.

Comparative Example The hot dip plated layer was solidified at room temperature without quenching treatment (2 to
3 seconds) A negative electrode tape was obtained, and L was used according to Example 1
i got a secondary battery. The discharge capacity of the first cycle is 35
At 0 mAh, the discharge capacity retention rate after 300 charge / discharge cycles was 82%.

[0040]

EFFECTS OF THE INVENTION According to the present invention, the thickness is uniform, the surface is flat, and the properties are uniform, the active material does not easily fall off, the quality is stable, and the strength is excellent, which is advantageous for winding treatment. To obtain a highly reliable Li secondary battery that can easily obtain a large area negative electrode such as a tape with a current collector tape, has a large charge / discharge capacity and energy density, and has an excellent charge / discharge cycle life. You can

[Brief description of drawings]

FIG. 1 is a sectional view of an example.

FIG. 2 is a sectional view of another embodiment.

FIG. 3 is an explanatory diagram of a manufacturing example.

FIG. 4 is an explanatory view of another manufacturing example.

FIG. 5 is an explanatory diagram of a battery example.

[Explanation of symbols]

1, 5, 10: Current collector tape 2: Diffusion barrier layer
3: Wetting promoter layer 4: Hot-dip quenching layer 6: Hot-dip bath
9: Cooling gas nozzle 14: Negative electrode 15: Electrolyte layer (separator made of porous insulating film) 16: Positive electrode

Claims (3)

[Claims] 1. A wetting promoting material comprising, on a current collector tape, a diffusion barrier layer made of a conductor which does not easily react with a liquid lithium alloy, and on the diffusion barrier layer being made of a conductor having an affinity with the liquid lithium alloy. A negative electrode for a Li secondary battery, which has a layer and a hot-dip quenching layer made of a lithium alloy and having a thickness of 50 μm or less on the wetting promoter layer. 2. A current collector tape, the surface of which is covered with a diffusion barrier layer made of a conductor that does not easily react with a liquid lithium alloy, and a wetting promoting material made of a conductor having affinity with the liquid lithium alloy on one or both sides of the diffusion barrier layer. In a state where the layer is provided, it is introduced into a lithium alloy hot-dip plating bath to form a lithium alloy coating layer with a thickness of 50 μm or less on the wetting promoter layer, and then the coating layer is rapidly cooled. And a method for producing a negative electrode for a Li secondary battery. 3. A Li secondary battery comprising the negative electrode according to claim 1.