JP5145494B2 - Metal negative electrode for lithium ion secondary battery, method for producing the same and lithium ion secondary battery using the same - Google Patents

Description

  The present invention relates to a metal negative electrode for a lithium ion secondary battery, a method for producing the same, and a lithium ion secondary battery using the metal negative electrode. More specifically, when used as a lithium secondary battery negative electrode, The present invention relates to a novel metal negative electrode for lithium battery that can be a lithium secondary battery having excellent charge / discharge cycle characteristics, an industrially efficient production method thereof, and a high-performance lithium secondary battery using the same.

In recent years, lithium secondary batteries have been actively researched and developed as power sources for driving electronic devices. In this lithium secondary battery, battery characteristics such as charge / discharge voltage, charge / discharge cycle life characteristics, and storage characteristics are greatly affected by the electrode active material used.
By the way, in general, as a negative electrode active material of a lithium ion secondary battery, a graphite material composed of a powdery body of a carbon substance such as natural graphite, artificial graphite, an organic compound fired body such as a phenol resin, or a coke is mainly used. there were. However, the graphite material has, for example, a theoretical capacity per unit mass of 372 mAh / g 2 and a specific gravity as small as 2.25 g / cm ³ , so that the capacity per unit volume is as small as 837 mAh / cm ^3. There was a problem that capacity was difficult.

For this reason, it is intended to improve battery characteristics by improving the negative electrode active material. For example, by using metallic lithium (Li) as the negative electrode active material, a battery with a high energy density can be configured both by weight and by volume. However, when the battery is charged, there is a problem that lithium precipitates in a dendrite state and causes an internal short circuit.
As a solution, a lithium secondary battery using aluminum, silicon, tin or the like electrochemically alloyed with lithium as a negative electrode material during charging has been reported (for example, see Non-Patent Document 1). Among these, in particular, silicon is promising as a negative electrode for a battery having a large theoretical capacity and a high capacity, and various secondary batteries using this as a negative electrode active material have been proposed (for example, Patent Document 1, Non-Patent Document). Reference 2). However, in these alloy negative electrodes, the alloy itself as the electrode active material undergoes a large volume change due to charge and discharge, causing cracks in the active material particles, poor contact between the pulverized active material and the current collector, and the like. For this reason, there is a problem that sufficient cycle characteristics cannot be obtained because current collection characteristics deteriorate.

On the other hand, as an alternative negative electrode material, many studies have been made on the use of an oxide negative electrode material having the ability to occlude and release lithium. For example, as a metal oxide capable of inserting and extracting lithium, an oxide mainly composed of tin (see, for example, Patent Documents 2 and 3) and an oxide mainly composed of silicon (for example, refer to Patent Document 4). Alternatively, a lithium titanium spinel oxide represented by LiTi ₂ O ₄ or Li _4/3 Ti _5/3 O ₄ (for example, see Non-Patent Document 3) has been proposed. However, in the negative electrode made of an oxide mainly composed of tin or silicon, the cycle characteristics are not sufficient. On the other hand, in the negative electrode made of lithium titanium spinel oxide, the cycle characteristics are relatively good, but the potential is high. There is a problem that the voltage cannot be increased when the battery is used.

As another alternative negative electrode material, some transition metal oxides have been found to undergo redox reaction with lithium. Among these, it has been reported that lithium occlusion of ruthenium oxide (RuO ₂ ) exhibits good reversibility (see, for example, Non-Patent Document 4). However, ruthenium oxide (RuO ₂ ) has a problem that the cycle characteristics are extremely low, for example, the active material is peeled off from the current collector in 4 cycles.

Moreover, oxide-based negative electrode materials usually have a problem of irreversible capacity because stable lithium oxide (Li ₂ O) is formed in the first charge / discharge cycle.
From the above situation, when used as a negative electrode for a lithium secondary battery, a novel metal active material constituting a negative electrode capable of achieving a lithium secondary battery having high charge / discharge capacity and excellent charge / discharge cycle characteristics. Is required.

JP-A-10-255768 (first page, second page) JP-A-7-201318 (first page, second page) JP-A-7-288123 (first page, second page) JP-A-6-325765 (first page, second page) Solid State Ionics, 1998, 113-115, p. 57 Koichi Yamamoto et al., Proceedings of the 45th Battery Conference, 2004, p. 288 Journal of Electrochemical Society, 1995, 142, No. 5, p. 1431 Advanced Functional Materials, 2003, Vol. 13, No. 8, p. 621

  An object of the present invention is to provide a lithium secondary battery having a high charge / discharge capacity and excellent charge / discharge cycle characteristics when used as a negative electrode for a lithium secondary battery in view of the above-mentioned problems of the prior art. An object of the present invention is to provide a novel metal negative electrode for a lithium battery, an industrially efficient production method thereof, and a high-performance lithium secondary battery using the same.

  In order to achieve the above object, the present inventors have made extensive studies on a metal negative electrode for a lithium ion secondary battery, and as a result, formed a metal negative electrode for a lithium ion secondary battery using metal ruthenium as a negative electrode active material. As a result, a lithium secondary battery having a high charge / discharge capacity and excellent charge / discharge cycle characteristics can be obtained, and the metal negative electrode can be obtained industrially efficiently by a production method using a gas deposition method. As a result, the present invention has been completed.

That is, according to the first aspect of the present invention, the negative electrode active material is made of metal ruthenium deposited and formed on a current collector by a gas deposition method . A metal negative electrode is provided.

According to the second invention of the present invention, in the first invention, the gas deposition method includes forming an electrode on a current collector substrate whose surface has been cleaned, and from a nozzle, from nitrogen gas or a rare gas. There is provided a method for producing a metal negative electrode for a lithium ion secondary battery, characterized in that a metal ruthenium powder is discharged together with a carrier gas.

According to a third aspect of the present invention, the metal negative electrode for a lithium ion secondary battery according to the first aspect of the present invention, a positive electrode made of an oxide capable of occluding lithium, and a non-aqueous electrolyte are provided. A lithium ion secondary battery is provided.

  The metal negative electrode for a lithium ion secondary battery according to the present invention is formed by using ruthenium metal as a negative electrode active material. Using this, a lithium secondary battery having a high charge / discharge capacity and excellent charge / discharge cycle characteristics is obtained. Since it can be obtained and the manufacturing method is industrially efficient, its industrial value is extremely high.

Hereinafter, the metal negative electrode for lithium ion secondary batteries of this invention, its manufacturing method, and a lithium ion secondary battery using the same are demonstrated in detail.
The metal negative electrode for a lithium ion secondary battery of the present invention is characterized by using metal ruthenium deposited and formed on a current collector by a gas deposition method as a novel negative electrode active material.

In the present invention, it is important to use metal ruthenium as the negative electrode active material of the negative electrode for a lithium ion secondary battery. Thereby, the lithium ion secondary battery which shows a high capacity | capacitance of 400 mAh / g or more is obtained using the said metal negative electrode for lithium ion secondary batteries. Moreover, since ruthenium (Ru) has a specific gravity of 12.4 g / cm ³ and is much larger than that of graphite material, lithium as a negative electrode having a high capacity of several times that when graphite material is used is used as a negative electrode. An ion secondary battery can be constituted.

Furthermore, good cycle characteristics can be obtained using the metal negative electrode for a lithium ion secondary battery. That is, as described above, when an oxide-based negative electrode material such as ruthenium oxide (RuO ₂ ) is used, there is a problem that lithium oxide (Li ₂ O) is formed prior to the lithium occlusion reaction. In contrast, ruthenium metal does not have the oxygen source required for this reaction. Therefore, as seen in ruthenium oxide (RuO ₂ ), the decomposition and re-formation of RuO ₂ into Li ₂ O and Ru during charging / discharging does not occur, and the load applied to the electrode during charging / discharging is less, so cycle characteristics Will be excellent.
In addition, unlike ruthenium and oxide-based negative electrode materials, metal ruthenium has ductility, so it is considered to be tough against volume changes associated with insertion and extraction of lithium, thereby providing good cycle characteristics. can get.

Moreover, metal ruthenium has higher conductivity than silicon, oxide-based negative electrode materials, etc. that have been proposed in the past, so that the internal resistance of the electrode can be reduced.
As is clear from the above, the metal negative electrode for a lithium ion secondary battery is suitable as a lithium reaction electrode of a lithium secondary battery in terms of various characteristics such as capacity per unit volume, cycle characteristics, and internal resistance of the electrode. A lithium ion secondary battery having a very high volume capacity density can be formed.

  The ruthenium metal used for the lithium ion secondary battery metal negative electrode is usually of a purity that does not contain an impurity element to the extent that it affects the electrode reaction, but other elements may be used depending on other purposes. It is possible to use a ruthenium alloy that has been alloyed by adding.

  The form of metal ruthenium constituting the metal negative electrode for lithium ion secondary batteries is not particularly limited, and can be used in various forms depending on the method for producing the metal negative electrode.

  The method for producing a metal negative electrode for a lithium ion secondary battery of the present invention is not particularly limited, and a conventional method for producing a metal negative electrode for a lithium ion secondary battery, for example, a desired proportion of metals. After ruthenium powder is mixed with a desired proportion of conductive auxiliary material and a desired proportion of binder, a sheet electrode is formed by rolling, or a suitable solvent is added to form a paste, and a metal foil current collector such as copper is collected. A method of forming an electrode in which metal ruthenium powder is deposited on a current collector by a gas deposition method, etc., applied to the surface of the body, dried, and compressed to increase the electrode density as necessary. Among these, an electrode formation method by a gas deposition method is particularly preferable.

  As the conductive auxiliary material used in the electrode using the sheet electrode or paste, graphite, carbon black, acetylene black, carbon fiber, metal powder, metal fiber, and other conductive polymers are used. As the binder used in the electrode using the sheet electrode or the paste, polyvinylidene fluoride, polytetrafluoroethylene, ethylene propylene diene rubber, fluorine rubber, styrene butadiene, cellulose resin, polyacrylic acid, or the like can be used. Moreover, it plays a role of holding the active material particles, and for example, fluorine-containing resins such as polytetrafluoroethylene, polyvinylidene fluoride, and fluorine rubber, and thermoplastic resins such as polypropylene and polyethylene can be used.

  In the electrode forming method by the gas deposition method, for example, the metal ruthenium powder is sprayed on the current collector at a high speed, and the metal ruthenium powder is deposited on the current collector to form the electrode. The gas deposition method is not particularly limited, and a general metal powder spraying method is used. Among these, for example, a surface mounted in a chamber is cleaned on a current collector substrate. A method of discharging a metal ruthenium powder together with a carrier gas made of nitrogen gas or rare gas from a nozzle set with a metal mask, forming a circular electrode and set at a predetermined distance is preferable. Here, as the current collector, a commonly used copper-based material such as a copper foil such as a rolled copper foil can be used. However, if necessary, nickel, stainless steel, molybdenum, tungsten, and tantalum. Other current collector materials can be used.

  In the electrode formation method by the gas deposition method, metal ruthenium powders are bonded to each other, so that a strong electrode can be formed without using a conductive auxiliary material, a binder, etc. Has an appropriate space between the particles, and therefore has an advantage that good lithium reactivity can be maintained.

  The lithium ion secondary battery of this invention is comprised from the said metal negative electrode for lithium ion secondary batteries, the positive electrode which consists of an oxide which can occlude lithium, and a non-aqueous electrolyte. Thereby, a lithium ion secondary battery having a high capacity and good cycle characteristics can be obtained.

The positive electrode composed of the above-described lithium occlusion oxide is not particularly limited, and lithium cobalt composite oxide (LiCoO ₂ ), lithium manganese composite oxide (LiMn ₂ O ₄ ), or lithium nickel composite oxide (LiNiO). ₂ ) Further, those obtained by substituting these Co and Ni with other additive elements are used.

As the non-aqueous electrolyte, a solution obtained by dissolving a lithium salt as a supporting salt in an organic solvent is used. As said organic solvent, a cyclic carbonate, a chain carbonate, an ether compound etc. can be used, for example. Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and complex salts thereof.

Hereinafter, the present invention will be described in more detail by way of examples and comparative examples of the present invention, but the present invention is not limited to these examples. In addition, the evaluation method of the charging / discharging characteristic used by the Example and the comparative example is as follows.
[Evaluation method of charge / discharge characteristics]
Using a tripolar beaker cell, metal lithium plate (made by Rare Metallic Co., Ltd., thickness 1 mm, purity 99.9%) as a counter electrode and a reference electrode, propylene carbonate (1M LiClO ₄ supported salt as an electrolyte) ( PC) solution (manufactured by Kishida Chemical Co., Ltd.) was used. In addition, with a charge / discharge measuring device (manufactured by Instrument Center Co., Ltd., BS2506), a current value of 0.05 mA and 0.005 to 3.4 Vvs. Charging / discharging was repeated with the potential width of Li / Li ⁺ , and cycle characteristics up to 1000 times were evaluated.

Example 1
First, a negative electrode was prepared using metal ruthenium powder (manufactured by Sumitomo Metal Mining Co., Ltd., purity 99.9%, average particle size 20 μm) by the following [Method for producing negative electrode by gas deposition method].
[Production method of electrode by gas deposition method]
As the current collector substrate, a rolled copper foil (manufactured by Nilaco, thickness 20 μm, purity 99%) was degreased with acetone, then pickled with nitric acid, washed with water, and then ultrasonically washed again with acetone. . The current collector substrate was mounted in a chamber, a metal mask was placed on the current collector substrate, and a 6 mmφ circular electrode was formed. In the gas deposition, the substrate / nozzle distance was set to 10 mm, the nozzle diameter was set to 0.8 mm, and about 50 mg of metal ruthenium powder was discharged using argon gas as the carrier gas (0.6 MPa).
Subsequently, the charge / discharge characteristics of the obtained negative electrode were evaluated by the above procedure. The results are shown in FIG. FIG. 1 is a diagram showing the cycle dependency of the discharge capacity.

(Comparative Example 1)
A negative electrode was formed in the same manner as in Example 1 except that a ruthenium oxide negative electrode was produced using ruthenium oxide powder (purity 99.9%, average particle size 10 μm) instead of metal ruthenium powder. The charge / discharge characteristics of the obtained negative electrode were evaluated. The results are shown in FIG.

(Comparative Example 2)
A negative electrode was prepared in the same manner as in Example 1 except that a metal tin negative electrode was produced using tin powder (manufactured by Ametallic, purity 99.99%, average particle size 45 μm) instead of metal ruthenium powder. The charge / discharge characteristics of the formed negative electrode were evaluated. The results are shown in FIG.

  From FIG. 1, it can be seen that in Example 1, metal ruthenium was used as the negative electrode active material and the process was performed according to the present invention, so that high charge / discharge capacity and excellent cycle characteristics were obtained. That is, at the initial stage of charging / discharging, the discharge capacity has a value of about 200 mAh / g, but the capacity rapidly increases by 20 cycles and becomes a high capacity of about 400 mAh / g. This seems to indicate that the active material is activated and the discharge capacity is increased. Thereafter, even if the cycle is repeated, the discharge capacity does not decrease, shows a stable capacity up to 1000 cycles, and exhibits good cycle characteristics.

In contrast, in Comparative Example 1 or 2, it can be seen that the negative electrode active material does not meet these conditions, so that satisfactory results cannot be obtained.
That is, the negative electrode made of ruthenium oxide powder shows a very high capacity of 780 to 1000 mAh / g at the very initial stage as reported in the past, but shows a large capacity reduction by several to 10 cycles. In addition, peeling of the electrode active material from the substrate was already observed at the time of charging in the first cycle, and it is considered that the discharge capacity was reduced due to this. Further, after several tens of cycles, the discharge capacity continuously decreases, and after several hundred cycles, the capacity decreases to 80 to 200 mAh / g. This is the same as the separation of the active material from the substrate was observed in the first cycle, the decomposition and re-formation of RuO ₂ into Li ₂ O and Ru during charging and discharging, and the insertion of Li into the metal ruthenium and It seems that due to the load of desorption, the contact between the substrate and the negative electrode active material or between the negative electrode active materials continuously deteriorates with the cycle.
In addition, the negative electrode made of metallic tin exhibits a discharge capacity of about 250 mAh / g, which is equivalent to that of metal ruthenium, at the initial stage of charge and discharge, but the discharge capacity rapidly decreases to several tens of mAh / g in several cycles. In addition, when the state of the negative electrode was observed, peeling of tin was observed, and it was considered that the cycle characteristics were thereby lowered.

  As is clear from the above, the metal negative electrode for lithium ion secondary batteries of the present invention is particularly suitable as a lithium reaction electrode for lithium secondary batteries in terms of various properties such as capacity per unit volume, cycle characteristics, and internal resistance of the electrodes. In place of conventional materials such as graphite materials, they are suitably used as negative electrodes for lithium ion secondary batteries. In particular, in terms of various characteristics such as capacity per unit volume, cycle characteristics, internal resistance of the electrode, etc., it is suitable as a lithium reaction electrode of a lithium secondary battery, and in particular, constitutes a lithium ion secondary battery having a very high volume capacity density. Can do.

It is a figure showing cycle characteristic evaluation of the charging / discharging capacity | capacitance at the time of using the negative electrode as described in Example 1 and Comparative Examples 1 and 2 of this invention.

Claims (3)

A metal negative electrode for a lithium ion secondary battery, comprising metal ruthenium deposited and formed on a current collector by a gas deposition method as a negative electrode active material. The gas deposition method, an electrode is formed on the current collector substrate cleaning the surface from the nozzle, thereby discharging the metal ruthenium powder with a carrier gas consisting of nitrogen gas or rare gas to claim 1, wherein The manufacturing method of the metal negative electrode for lithium ion secondary batteries of description.   A lithium ion secondary battery comprising the metal negative electrode for a lithium ion secondary battery according to claim 1, a positive electrode made of an oxide capable of occluding lithium, and a non-aqueous electrolyte.

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