JPH04286864A - Secondary battery - Google Patents

Abstract

PURPOSE:To obtain a nonaqueous secondary battery of a high-performance high-energy density, and provide practical and good-workability techniques which are applicable to mass-production by composing alkaline metal electrodes of lithium, sodium, etc., to be long-life electrodes capable of discharging a large current. CONSTITUTION:Adouble-structure electrode is composed of an active metal to be negative pole active material, and a metal capable of forming an alloy with the active metal wherein both metals serve as a combination to form the alloy electrochemcally. The metal capable of electrochemically forming the alloy with the active metal for the negative material is of a structure of grid, mesh, expanded metal, bored plate, etc., or a porous body such as sintered plate, foam metal, powder-painted plate, mat, or felt.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to secondary batteries, and in particular,
This invention relates to a secondary battery that uses an alkali metal such as lithium as the active component of the negative electrode.

0002

2. Description of the Related Art With the rapid spread of various small cordless devices, the demand for batteries as power sources is also rapidly increasing. There are two types of small batteries used: primary batteries and secondary batteries, but secondary batteries are generally used as power sources for applications that have moving parts, heavy loads, and are frequently used, mainly for economical reasons. .

[0003] As demand for these secondary batteries increases, demands for higher capacity, rapid charging and discharging, etc. are increasing from the viewpoint of ease of use. Among these, there is a deep-rooted consumer demand for higher capacity devices that can be used for a longer time with a single charge, and technological development in this regard has continued unremittingly.

[0004] Along with increasing the capacity of existing batteries, new types of batteries have been actively developed. Among them, non-aqueous electrolyte secondary batteries that use alkali metals such as lithium as negative electrode active materials have a high battery voltage of 2 to 3 V, and have a power consumption of 100 Wh.
Since it is possible to achieve a high energy density of more than /kg, it has been highly evaluated as a future high-performance battery and has been the subject of extensive research.

However, since these batteries use a non-aqueous electrolyte, the internal resistance of the battery is high, and the charging and discharging reaction rate of the alkali metal negative electrode active material such as lithium is slow.
Furthermore, due to dendrite precipitation and inactivation due to reaction with the electrolyte, there remained problems in charging and discharging large currents and lifespan, and it could not be said to be sufficient compared to existing secondary batteries. Therefore, it is possible to make the electrode thinner and increase the electrode area to enable charging and discharging of large currents without increasing the current density, or to modify the properties of negative electrode active materials such as lithium by alloying them with other metals. Things have been tried. (For example, JP-A-48-33812, JP-A-5
Examples include No. 3-75437 and Japanese Unexamined Patent Publication No. 59-228370. ) However, regarding the former, the properties of the metal of the negative electrode active material itself have not changed, so the problems of dendrite precipitation and inactivation have not been solved. In the latter case, the hardening of lithium due to alloying made it difficult to uniformly produce thin electrodes with a large area, making it extremely difficult to turn this into a practical industrial technology. Therefore, this technology is only applied to coin-shaped lithium secondary batteries.
It could not be applied to cylindrical secondary batteries, which have a structure for extracting large currents.

[0006]

[Problem to be solved by the invention] For this reason, lithium,
Maintaining the plasticity of single alkali metals such as sodium to make electrodes thinner and larger in area, as well as alloying lithium and other metals with other metals to modify their properties, resulting in dendrite precipitation and inactivation through reaction with electrolytes. We must develop technology that satisfies the contradictory conditions of suppressing such problems.

An object of the present invention is to enable high current charging and discharging of alkali metal electrodes such as lithium and sodium, and
The object of the present invention is to provide a long-life, practical and workable technology suitable for mass production, and to obtain a high-performance, high-energy-density non-aqueous secondary battery.

[0008]

[Means for Solving the Problems] In order to solve the above-mentioned problems of the prior art, the present invention is characterized by providing a dual-layer structure consisting of an active metal that can be an electrode active material and a metal that can form an alloy with the active metal. In addition, the active metal that can serve as the electrode active material and the metal that can form an alloy with the active metal are in a combination that can electrochemically form an alloy. Here, the above-mentioned double structure does not simply mean that two types of flat metal plates are laminated, but it refers to the distribution of active metals on an inert metal structure. It is important that the boundary between the two has a complex shape. With this combination, it is possible to maintain the plasticity of single alkali metals such as lithium and sodium, make the electrode thinner, increase the electrode area, and form a battery using techniques such as winding. By modifying the properties, it is possible to suppress dendrite precipitation, inactivation due to reaction with electrolyte, etc. Furthermore, since the reaction surface area for the alloying reaction is large and the interface thereof has a complicated shape, mechanical deterioration such as collapse and falling off due to volume changes due to charging and discharging can be prevented.

[0009] To form a double-structured electrode, two types of metal structures can be stacked and pressed together, two types of metal structures can be stacked and then hot pressed, or a metal with a higher melting point can be formed. Methods include depositing a melt of a metal with a lower melting point on the structure, and forming a layer of active metal powder on an inert metal structure. In the above method, it is important to take structural measures to ensure sufficient strength of the double-structure bond formed by the two types of metal plates and to cause the active materials of the electrodes to react effectively. For example, if the metal that can form an alloy with the electrode active material metal has a planar structure such as a lattice shape, a wire mesh shape, an expanded metal shape, or a perforated plate shape,
The metal that can form an alloy with the electrode active material metal on which the active metal layer is formed is a porous body such as a sintered plate, foamed metal, powder coated plate, mat, or felt. An example is forming. In addition, in the present invention,
Since the metal that can form an alloy with the active metal is a portion that does not dissolve and disappear during the charging and discharging process, a structure in which this portion is disposed on the electrode current collection side is preferable.

Active metals that can be used as electrode active materials include alkali metals such as lithium and sodium, as well as zinc, lead,
These include cadmium and magnesium. Metals that can form an alloy with the electrode active material metal include magnesium, aluminum, gallium, indium, tin, lead, bismuth, zinc, and cadmium.

[0011] The compounding ratio of the electrode active material metal and the metal that can form an alloy with the active metal changes depending on what kind of intermetallic compound or solid solution is formed by each alloy combination. . Naturally, it also changes depending on the shape of the double arrangement. However, since the metal that can form an alloy with the active metal is an inactive portion that does not directly contribute to the discharge capacity, it is preferable to have a smaller amount as long as the effect is not reduced.

0012

[Operation] The gist of the present invention is the electrochemical deposition of the alloy. Since the dual structure electrodes are an electrochemically alloyable combination, the active metal components released during the first discharge will form an alloy when deposited during the subsequent charge. This is repeated in subsequent charge/discharge cycles. Therefore, when an electrode is incorporated into a battery, even if it does not form an alloy, when it is involved in charging and discharging within the battery, it functions in the same way as an electrode that forms an alloy. Therefore, it is necessary to maintain the plasticity of the active metal, make the electrode thinner, increase the electrode area, and form a battery using techniques such as winding, and modify the properties of the active metal through alloying to cause dendrite precipitation and interaction with the electrolyte. This makes it possible to simultaneously suppress inactivation caused by reactions.

[0013] In order to smoothly proceed with the formation of the alloy, it is necessary that a sufficient surface area be secured for the deposition of the active metal component released during discharge upon subsequent charging. Therefore, the metal that can form an alloy with the electrode active material metal is arranged in a lattice shape.
Shapes such as wire mesh, expanded metal, perforated plate, etc.
Alternatively, it is effective to increase the surface area by using a porous material such as a sintered plate, foamed metal, powder coated plate, mat, or felt. In addition, it is important to ensure that the bonding strength of the double structure consisting of the active metal and another metal is sufficient.
active material) to react effectively. To do this, two types of metal plates are stacked and pressed together, two types of metal plates are stacked and then hot pressed, and a molten metal with a lower melting point is placed on top of a molded body of the metal with a higher melting point. Methods such as depositing active metal powder or forming a layer of active metal powder on a molded body of metal capable of forming an alloy with the active metal are applied.

[0014]

[Example] The present invention will be explained in more detail with reference to an example in which the present invention is applied to a negative electrode of a cylindrical lithium secondary battery.

Example 1 The negative electrode for a lithium secondary battery used to carry out the present invention was made of lithium and aluminum. Metal lithium foil with a thickness of 0.5 mm has a porosity of 9
5%, was pressed onto foamed aluminum with a thickness of 1.5 mm, and further molded with a roller press to a thickness of 0.3 mm to obtain a negative electrode. The positive electrode uses a powder obtained by firing a mixture of manganese dioxide and lithium hydroxide at 400°C as an active material,
Carbon black powder as a conductive agent was mixed with this, and the mixture was bound with polytetrafluoroethylene. These electrodes were wound together with a separator interposed in between, and filled with an electrolyte into a battery container to assemble an AA-sized sealed lithium secondary battery. The separator consists of a 0.025 mm thick microporous polytetrafluoroethylene film and a 0.2 mm thick microporous polytetrafluoroethylene film.
mm 2 polypropylene nonwoven fabric, and the electrolytic solution is one in which 1 mol/l of lithium hexafluorophosphate is dissolved in a mixed solvent mainly composed of propylene carbonate. All operations were performed in an argon atmosphere. The water content in the electrolyte was kept at 10 ppm or less. The capacity of the obtained battery was 600mAh. This battery was subjected to charge/discharge cycle evaluation at room temperature. Charging was carried out for up to 6 hours at a charging current of 100 mA and an upper limit voltage of 4.0 V. Discharge was carried out to a final voltage of 2.0 V at a discharge current of 200 mA. The results thus obtained are shown in FIG. 1A.

For comparison, FIG. 1B shows the results of a similar evaluation of a battery manufactured in the same manner using a metal lithium foil as the negative electrode. Furthermore, C in FIG. 1 shows the results of similarly evaluating a battery prepared in the same manner using a negative electrode prepared by laminating and press-bonding a metal lithium foil and a metal aluminum foil.

From FIG. 1, it can be seen that the battery A of the present invention is a high-performance, long-life battery that can maintain a larger discharge capacity over a longer cycle than the conventional comparative examples B and C.

Example 2 A sealed AA-type lithium secondary battery was assembled using a negative electrode formed by impregnating a porous lead plate with molten metal lithium. The porous lead plate was formed by coating fine lead powder with an average particle size of 0.008 mm bound with 3 wt % polytetrafluoroethylene fine powder on expanded nickel metal. This is 5
After pressurizing it at a pressure of 0 kg/cm2, it was immersed in a molten bath of metallic lithium to form a negative electrode. The obtained battery was used in Example 1.
It was evaluated in the same way. The results are shown in FIG. 2D.

For comparison, lithium-lead alloy (Li7
A battery was prepared and evaluated in the same manner using a negative electrode prepared in the same manner using Pb2) powder as the active material and bound by 3 wt % polytetrafluoroethylene fine powder, and the results are shown in FIG. 1E.

It can be seen from FIG. 1 that the battery D of the present invention is a high-performance, long-life battery that can maintain a larger discharge capacity over a longer cycle than the comparative example E of the prior art.

[0021]

[Effects of the Invention] According to the present invention, an alkali metal electrode such as lithium or sodium can be made into an electrode that can be charged and discharged at a large current and has a long life. I was able to get the next battery. On top of that,
The negative electrode is flexible and easy to wind, making it a practical and workable technology suitable for mass production. Furthermore, since the negative electrode alloy is formed electrochemically within the battery, it does not require a high-temperature heat treatment process that is required for normal alloy production.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the results of a charge/discharge cycle test at room temperature of an AA-type sealed lithium secondary battery according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing test results at room temperature of an AA-type sealed lithium secondary battery according to a second embodiment of the present invention.

[Explanation of symbols]

A...Charge/discharge cycle characteristics of the AA sealed lithium secondary battery of the present invention, B...Charge/discharge cycle characteristics of the AA sealed lithium secondary battery of the prior art, C...Charge/discharge cycle characteristics of the AA sealed lithium secondary battery of the prior art Charge/discharge cycle characteristics of sealed lithium secondary battery, D...
Charge/discharge cycle characteristics of the AA sealed lithium secondary battery of the present invention, E...Charge/discharge cycle characteristics of the AA sealed lithium secondary battery of the prior art.

Claims (5)

[Claims] 1. A double-structured electrode comprising a rechargeable positive electrode, an electrolyte, and a combination of an active metal that can be an electrode active material and a metal that can form an alloy with the active metal, the electrode comprising: A secondary battery comprising a negative electrode in which a structure formed of a metal capable of forming the alloy is filled with the active metal. 2. According to claim 1, the active metal that can become the electrode active material and the metal that can form an alloy have a planar structure such as a lattice shape, a wire mesh shape, an expanded metal shape, or a perforated plate shape. battery. 3. In claim 1, the metal capable of forming an alloy with the active metal capable of becoming the electrode active material is a porous body such as a sintered plate, foamed metal, powder coated plate, mat, or felt. Next battery. 4. The secondary battery according to claim 1, wherein the active metal that can serve as the electrode active material is an alkali metal such as lithium or sodium. 5. In claim 1, 2, 3 or 4, the metal capable of forming an alloy with the active metal capable of becoming the electrode active material is magnesium, aluminum, gallium, indium, tin, lead, bismuth, zinc, Secondary batteries are single metals such as cadmium and silver, or alloys containing them.