JP2017216126A - Active material for battery negative electrode, battery, and method for manufacturing active material for battery negative electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active material for a battery negative electrode, which can materialize a safe, inexpensive, high-energy density battery using an electrolyte solution of an alkali aqueous solution by improving charge and discharge behaviors in the case using iron or an iron compound for an active material for a negative electrode and solving the problem of passivation of the iron or iron compound.SOLUTION: An active material for a battery negative electrode comprises: iron; and one or more kinds of metal elements other than iron, provided that of the metal elements other than iron, at least one kind of metal elements are metal elements which never cause a redox reaction in a battery in action; and an inorganic/organic hybrid compound resulting from a chemical reaction of a metal oxide or a metal oxide derivative including at least one kind of the metal elements which never cause a redox reaction in a battery in action, and an organic polymer having a hydroxyl group.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a battery negative electrode active material, a battery including a negative electrode containing a battery negative electrode active material, and a method for producing a battery negative electrode active material. The present invention is particularly applied to a battery using an alkaline aqueous solution as an electrolytic solution.

  A battery is generally composed of both positive and negative electrodes, a separator separating them, and an electrolytic solution that has spread throughout the battery. The negative electrode active material has a property of wanting to pass electrons to the positive electrode active material, and at the time of discharging, current flows as electrons move from the negative electrode active material to the positive electrode active material through an external circuit. That is, during discharge, the negative electrode active material is oxidized and the positive electrode active material is reduced. However, if electrons move only between the positive and negative electrodes through an external circuit, the same type of charge continues to accumulate on both the positive and negative electrodes, and current does not flow immediately. For this reason, when the electrolyte conducts ions between the positive and negative electrodes, the accumulated electric charge is released at any time, and a steady current can be obtained. The separator is for preventing so-called short-circuiting, in which both positive and negative active materials come into contact to directly exchange electrons, and current cannot be taken out to the outside. When the secondary battery is charged, a voltage is applied from the outside to cause the opposite electron movement. That is, in the rechargeable battery, the negative electrode active material is reduced and the positive electrode active material is oxidized.

  As seen in the recent spread of portable devices, the spread of hybrid vehicles against the backdrop of environmental and energy issues, and the development of stationary large-sized batteries for electric vehicles and surplus power storage, batteries, especially secondary batteries The role played and the expectations for it are growing. However, in portable devices such as smartphones and tablet terminals that have been used for a long time on a large screen, power consumption has increased, and a shortage of stored energy in the power source has become a problem. Large batteries for in-vehicle use and surplus power storage require not only storage energy density but also low price and extremely high safety, but there are currently no batteries that satisfy these conditions. It is.

At present, the lithium ion battery has the highest storage energy density, and the lithium ion battery is widely used in portable devices, hybrid vehicles, electric vehicles, and the like. Lithium ion batteries use carbon for the negative electrode, metal oxide for the positive electrode, and an organic solvent in which a lithium salt is dissolved as the electrolyte. The negative electrode is charged as shown in the following formulas (1) and (2). Sometimes electrochemical reduction of lithium ions in the electrolyte and intercalation between carbon layers occurs, and conversely, lithium is electrochemically oxidized and released into the electrolyte.
[Charging] Li ⁺ + C _X + e ⁻ → LiC _X (1)
[Discharge] LiC _X → Li ⁺ + C _X + e ⁻ (2)
Since such lithium oxidation-reduction occurs at a very low potential, the lithium ion battery can obtain a very high voltage, which is a factor of the high storage energy density of the lithium ion battery. However, a low oxidation-reduction potential indicates that oxidation is very easy, and the amount of heat generated when oxidation occurs is large and the degree of danger is high. Further, since the oxidation-reduction potential is base, lithium is also oxidized by contact with water, and the water is decomposed to generate hydrogen gas. Therefore, water-based electrolytes cannot be used, and organic solvent-based electrolytes must be used. However, generally used organic solvent-based electrolytes are flammable and are incompatible with lithium reactivity. It is a cause that increases the danger. Furthermore, since this organic solvent electrolyte has low ionic conductivity, it is necessary to make the electrode and separator thinner and increase the facing area to compensate for the low electrical conductivity. This is one factor that increases the risk.

  When a solid is precipitated from a solution as in the above charging reaction (1), a needle-like precipitate called a dendrite is likely to be formed, which is likely to cause a short circuit. In a lithium ion battery, reduced lithium is interposed between carbon layers. The generation of dendrites is avoided by intercalating. However, when the intercalation speed is not in time due to charging with a large current, dendrites are deposited on the carbon surface. Therefore, in a lithium ion battery, it is necessary to avoid charging with a large current, and it is necessary to perform extremely slow charging, particularly at the end of charging. As a result, the lithium ion battery cannot be fully charged rapidly, and it takes time to charge, resulting in problems such as poor usability of the electric vehicle and shortening the cruising distance. In addition, since the battery is inherently high risk, it is necessary to carefully perform charge control, temperature detection, and so on. However, the high merit has also faded. In addition to the necessity of expensive materials from the beginning, there is also a situation that it is difficult to reduce the price due to the necessity of consideration for safety including the auxiliary machine. In a large battery for storing surplus power, it is indispensable to be inexpensive and safe because it is particularly large in scale, making it difficult to apply a lithium ion battery.

  On the other hand, with portable devices, as the power consumption increases, even with the use of lithium ion batteries with the highest storage energy density, the power source energy is insufficient. There have been problems with the cruising range of electric vehicles, and so far, attempts have been made to further increase the energy density of lithium-ion batteries, but the technology is quite saturated and no further significant improvement can be expected.

A typical secondary battery other than the lithium ion battery is a nickel metal hydride battery. The nickel-metal hydride battery uses a hydrogen storage alloy for the negative electrode, nickel hydroxide for the positive electrode, and an alkaline aqueous electrolyte as the electrolyte. The negative electrode is charged as shown in the following formulas (3) and (4). Occasionally, the electrochemical reduction of hydrogen in water molecules and the occlusion of hydrogen into the hydrogen storage alloy occur, and the reverse is the electrochemical oxidation and release of the stored hydrogen during discharge.
[Charging] H ₂ O + e ⁻ → H (Occlusion) + OH ⁻ (3)
[Discharge] H (Occlusion) + OH ⁻ → H ₂ O + e ⁻ (4)
As the hydrogen storage alloy, those mainly composed of an alloy of rare earth and nickel are mainly used.

  Since the oxidation-reduction potential of the hydrogen storage alloy electrode (hydrogen oxidation-reduction potential) is considerably noble compared to the lithium electrode, non-flammable aqueous electrolytes can be used, thereby making nickel-metal hydride batteries highly safe Sexuality can be secured. Furthermore, since the aqueous electrolyte has high ion conductivity, it is not necessary to make the electrodes and separators thin and long, so that short-circuiting does not easily occur. In the first place, the hydrogen itself of the negative electrode active material is not a metal, so short-circuiting hardly occurs. Further, even if the battery is charged relatively quickly with a constant current, the electrolysis of water in the electrolytic solution is automatically replaced when the battery is fully charged, thereby suppressing an increase in voltage. Thus, the nickel-metal hydride battery is a safe battery that is easy to control charging, and is cheaper than a lithium ion battery. Currently, nickel metal hydride batteries are widely used as batteries for hybrid vehicles.

  As described above, the safety of the hydrogen storage alloy is mainly due to the fact that the redox potential (hydrogen redox potential) of the hydrogen storage alloy electrode, which is the negative electrode, is significantly more noble than the lithium electrode. This means that the battery voltage is lowered. Therefore, the nickel-metal hydride battery has a considerably lower storage energy density than the lithium ion battery. Therefore, even if safety is low, the situation becomes even more severe with respect to the problem of shortage of power source energy such as portable devices and electric vehicles. In addition, the hydrogen storage alloy used in the negative electrode contains rare earth elements, and its production volume is small and the country of origin is limited. Therefore, there are concerns about the procurement of raw materials such as stable supply of resources and price stability. is there.

  By the way, although not directly related to the above problem, the present inventors have used an alkaline battery based on an inorganic / organic hybrid compound in which a zirconic acid compound and polyvinyl alcohol are chemically bonded. It is disclosed that it has a hydroxide ion conductivity and can serve as an electrolytic solution while being solid, and can be provided with various other functions (Patent Documents 1 and 2). 3). For example, by applying these inorganic / organic hybrid compounds, it is possible to contribute to a reduction in the amount of electrolyte solution of a nickel metal hydride battery, or to reduce the thickness of the separator by a short circuit prevention function. Moreover, the dendrite production | generation suppression effect etc. of the zinc electrode in a nickel zinc battery are also disclosed. According to Patent Documents 1 and 2, it is also disclosed that these inorganic / organic hybrid compounds can obtain high hydroxide ion conductivity by performing a treatment of immersing in an alkaline aqueous solution, that is, a treatment of absorbing the alkaline aqueous solution. ing.

  According to Patent Documents 1 and 2, the inorganic / organic hybrid compound in which the zirconate compound and polyvinyl alcohol are chemically bonded neutralizes the zirconium salt or oxyzirconium salt in a solution in which polyvinyl alcohol coexists, and the solvent is used. It can be obtained by removing. In Patent Documents 3 and 4, a solid in which a zirconium salt or oxyzirconium salt and polyvinyl alcohol coexist is formed in advance, and the solid is contacted with an alkali to neutralize the zirconium salt or oxyzirconium salt. A method is disclosed.

Japanese Patent No. 3848882 Japanese Patent No. 4081343 Japanese Patent No. 5095249 Japanese Patent No. 4871225

As described above, existing secondary batteries such as lithium ion batteries and nickel metal hydride batteries have any of the following problems: safety, price, storage energy density, and raw material supply. Many of these problems are attributed to the properties of the negative electrode material.
In the case of a lithium ion battery, as can be seen from reaction formulas (1) and (2), one lithium atom can exchange only one electron, and carbon for absorbing lithium atoms is also necessary. Therefore, the electrode capacity is small. In other words, the lithium ion battery has a small capacity, but has a high energy density because the energy (voltage) per electron is high. However, as described above, for this reason, the negative electrode potential becomes extremely low, which causes the safety to be impaired.
A nickel-metal hydride battery is safe because its voltage is low, but as shown in reaction formulas (3) and (4), one hydrogen atom can exchange only one electron like lithium, and Since the voltage is low, the stored energy density is low.

  From this point of view, in order to achieve both safety and high storage energy density, an element that has a relatively noble redox potential, such as hydrogen, and one atom can exchange a plurality of electrons is used as the negative electrode. It is considered preferable to apply as an active material. That is, using such a negative electrode active material, it is desirable to constitute a battery of a type that gains energy density by having a large capacity but a low battery voltage. Alternatively, it is desirable that safety is ensured by having a relatively noble oxidation-reduction potential even if the capacity is not large, the material is inexpensive, and the raw material can be supplied stably. One type of negative electrode active material is iron.

The reaction formulas when iron is used are shown in the following formulas (5) and (6).
[Charging] FeOOH + H ₂ O + 3e ⁻ → Fe + 3OH ⁻ (5)
[Discharge] Fe + 3OH ⁻ → FeOOH + H ₂ O + 3e ⁻ (6)
Iron is an inexpensive material, an abundant resource that exists everywhere on the earth, and is an extremely ideal electrode active material in that there is no problem of raw material supply. The iron electrode exhibits an oxidation-reduction potential that is relatively close to that of the hydrogen storage alloy electrode, and an aqueous electrolyte solution of an alkaline aqueous solution can be used in the same manner as the nickel metal hydride battery. Iron oxides have extremely low solubility in an alkaline aqueous solution and maintain stability in the battery in that they do not dissolve in the electrolyte. As seen in reaction formulas (5) and (6), iron has three electrons that can be taken in and out per atom and has a potentially large theoretical capacity. That is, there is a potential condition that can be an ideal negative electrode material with a high capacity but not high voltage.
However, in reality, batteries using iron or an iron compound as an electrode have a problem that the electrode becomes passivated and become inactive with respect to a charge / discharge reaction. . As described above, since iron oxide has low solubility in an alkaline aqueous solution, protons, hydroxide ions, oxygen ions are required for the reactions such as reaction formulas (5) and (6) to proceed at the iron electrode. One of the water molecules needs to move in the iron oxide solid, but if it has a stable and dense structure, the movement speed of the substance in the solid is slowed and the electrode activity is greatly impaired. Cause passivity. This problem is an essential problem derived from the structure of iron oxides, so it is difficult to solve the fundamental problem as long as it remains in the normal iron or iron oxide state, and essential improvements are required. However, no effective method has been obtained at present.

  Even if the passivation problem is solved, the iron electrode has an essential problem in charge / discharge characteristics. Charging / discharging of the iron electrode in the alkaline electrolyte occurs stepwise from +3 to +2 and from +2 to 0. Here, the electrode equilibrium potential (redox potential) of the iron electrode in the alkaline electrolyte is schematically shown in FIG. 1A. As shown in FIG. 1A, since the electrode equilibrium potential (oxidation-reduction potential) curve has two stages, the charge / discharge potential curve also has two stages, and charging / discharging is performed at a greatly different potential at each stage. The equilibrium potential where the +2 valence and the 0 valence coexist is slightly lower than the oxidation-reduction potential of hydrogen, and charging is a competitive reaction with hydrogen generation, so that it is difficult to be fully charged. On the other hand, the equilibrium potential at which +3 valence and +2 valence coexist is larger than the oxidation-reduction potential of hydrogen and is on the noble side, deviating from the ideal charge / discharge potential and considerably lowering the discharge voltage of the battery. In other words, whichever region is used for charging / discharging, it is out of the practical suitable potential range. However, this oxidation-reduction potential is unique to the substance and cannot be changed as long as it uses an aqueous electrolyte (alkaline aqueous solution) and uses iron or an iron compound in a normal state that is stable in the environment.

  If the equilibrium potential where +2 and 0 valence coexist can be shifted slightly to the noble side, charging will be easier, or if the equilibrium potential where +3 and +2 valence coexist can be shifted slightly to the base side. There is a possibility that a high-voltage discharge can be performed, good charge / discharge can be performed, and a safe battery can be configured that is inexpensive and does not have a problem of raw material supply. Furthermore, if the potentials of these two regions can be leveled and an average charge / discharge curve is shown, three electrons per atom are fully used, and a large capacity charge / discharge is achieved. There is a possibility of being able to do it. However, if the type of metal element is determined to be iron, the equilibrium potential curve in the alkaline electrolyte is determined, and there is no known method for changing it as intended. It is possible to change the potential curve by changing the type of electrolyte, but it is necessary to be aqueous from the viewpoint of battery safety. From the stability of iron compounds or other peripheral members, it is almost equivalent to alkaline aqueous electrolyte. Limited.

  In order to improve the negative electrode active material of iron or iron compounds and solve the problems of conventional secondary batteries, some properties unique to iron or iron compounds such as redox potential or structural factors that cause passivation There is a need for a method that can be controlled and adjusted. In a normal state of a metal or a compound, it is a large aggregate including a certain number of atoms, and these atoms are regularly arranged to form a specific stable crystal structure. The oxidation-reduction potential is determined by the chemical potential of the compound, but in the normal state, the chemical potential is a chemical in a state in which a metal atom whose valence changes is surrounded by many other atoms having a specific arrangement. Potential. That is, as long as the metal or compound is a large aggregate containing a certain number of atoms, the surrounding environment is always the same when focusing on the metal atoms therein, and thus shows the same potential. Therefore, if iron or an iron compound is in a normal state, it cannot always take its own oxidation-reduction potential and move the potential.

  If the crystal structure of iron or an iron compound can be changed, the environment surrounding the iron atom can be changed, and the potential can also be changed. However, iron or an iron compound tends to have a thermodynamically stable structure in the manufacturing process, and thus it is inherently difficult to have a crystal structure different from a normal state. In addition, even if it is possible to have a crystal structure different from the normal state, when used in a battery, charge and discharge are repeated, and the electrode active material repeatedly undergoes a large structural change. Will return to a thermodynamically stable crystal structure.

  As described above, although it is difficult to control the potential in terms of the crystal structure, as another method, it is conceivable that another metal element is dissolved in iron or an iron compound. In this case, the presence of a different solid solution metal atom around the iron atom can change the oxidation-reduction potential under the influence thereof. In this case, it is necessary for the different solid solution metal elements to be mixed at the atomic level, and each of the iron or iron compound and the metal or metal compound of the different metal element contains only the same type of metal or compound. By simply coexisting in the state of forming a large aggregate containing atoms, the redox potential cannot be essentially changed. In that case, the potential of each metal or compound is independently developed, and only a stepwise charge / discharge curve having a plurality of stages is obtained. However, in many cases, in crystals, it is thermodynamically stable to form a crystal phase with the same kind of metal or compound, and it is difficult to dissolve a large amount of different atoms therein. Even if it is possible, charging and discharging are repeated when used in the battery, and the electrode active material repeatedly undergoes large material changes, and in this process, phase separation is achieved in a thermodynamically stable state. Wake up. Therefore, it is difficult to stably maintain a solid solution at the atomic level.

  As another method for changing the potential, there is a method of making the aggregate of metals or compounds containing iron extremely small, ideally at a level of several nanometers. When the aggregate is extremely small, the number of atoms surrounding the valence-changing metal atom is extremely smaller than that in the normal state, so that the potential changes as the surrounding environment changes. In this case, since the number of atoms is not so large as to take a specific regular crystal structure, a specific structure cannot be obtained, and the electric potential also changes due to structural factors. In addition, since it is difficult to obtain a specific stable crystal phase, a large phase structure transition does not occur, and charging / discharging proceeds only when the average valence of iron atoms changes continuously. Therefore, in the case of nanoparticles or amorphous, it is expected that the electrode equilibrium potential (redox potential) is not a stepped curve, but a curve that is leveled as a whole as shown in FIG. 1B. . If the potential curve is leveled as a whole as described above, the potential curve enters an ideal potential region.

  Furthermore, when the size of a metal or compound unit is at the nano level, it is difficult to obtain a specific stable crystal phase from the beginning, so it is easy to dissolve a large amount of different elements. In a fine particle unit such as a nanoparticle, a stable structure peculiar to each element cannot be obtained from the beginning, so the effect of mixing entropy is dominant as in the case of liquid mixing. This makes it possible for different atoms to be dissolved in a solid state and to stabilize in that state. As described above, if a large amount of different elements can be dissolved in a mixed state at the atomic level, the potential is also affected, so that the potential can be controlled to an appropriate level.

  As described above, when the size of the metal or compound unit is at the nano level, it is difficult to obtain a specific dense crystal structure, and thus passivation is less likely to occur. Even if it has a dense structure, the size of the particles is extremely small, and most of the particles are on the surface, so that protons, hydroxide ions, oxygen ions, water molecules, etc. are in the solid phase during the charge / discharge reaction. Is not required to move over a long distance, and from this point of view, passivation is unlikely to occur. Furthermore, since it becomes possible to dissolve a large amount of different elements, it becomes possible to prevent passivation by essentially modifying the properties inherent to iron or its compounds by such a method. .

  As described above, by making iron or iron compounds as fine particles as nanoparticles, we can move away from their inherent properties such as redox potential and passivation, and improve them into electrode active materials suitable for practical use. It turns out that is possible. However, since a fine aggregate such as a nanoparticle itself is thermodynamically unstable, it is difficult to form a fine aggregate state itself. Even if a fine aggregate state can be formed, aggregation and growth occur in the process of repeated large changes in the electrode active material by charging and discharging in the battery, and it is difficult to maintain the nano level.

The present invention has been made to solve the above-described conventional problems.
The active material for battery negative electrode of the present invention is an active material for battery negative electrode used for a battery using an alkaline aqueous electrolyte, contains iron and one or more kinds of metal elements other than iron, and is made of a metal other than iron. At least one of the elements is a metal element that does not cause a redox reaction during battery operation, and a metal oxide or metal oxide containing at least one of the metal elements that do not cause a redox reaction during battery operation. It includes an inorganic / organic hybrid compound in which a derivative is chemically bonded to an organic polymer having a hydroxyl group.
In the above-described active material for battery negative electrode of the present invention, more preferably, the diffraction peak of any diffraction peak of iron or a compound containing iron has a half width of 1 (2θ °) or more.

  In the above-described negative electrode active material of the present invention, preferably, zirconium or nickel is contained as a metal element other than iron, polyvinyl alcohol is contained as an organic polymer having a hydroxyl group, and the inorganic / organic hybrid compound is at least a zirconate compound and polyvinyl alcohol. And a chemical bond.

  The battery of the present invention includes at least a positive electrode, a negative electrode, and an electrolytic solution, an alkaline aqueous electrolyte is used as the electrolytic solution, and the negative electrode includes the battery negative electrode active material of the present invention. The battery of the present invention can be configured as, for example, a nickel-iron battery or an air-iron battery.

The method for producing an active material for a battery negative electrode of the present invention is a method for producing the above-described active material for a battery negative electrode of the present invention, wherein an iron salt and a salt of a metal element other than iron are each an organic polymer having a hydroxyl group. In the state of coexistence, it is neutralized with an alkali, and through a process of forming an inorganic / organic hybrid compound in which a metal oxide or metal oxide derivative containing the metal element is chemically bonded to an organic polymer having a hydroxyl group, An active material for a battery negative electrode is produced.
Then, in the process of forming the inorganic / organic hybrid compound, an iron salt, a salt of a metal element other than each iron, and an organic polymer having a hydroxyl group are mixed in a solvent to prepare a mixed solution. The solid can be formed by removing solids, and the solid is brought into contact with an alkali to neutralize the iron salt and the salt of a metal element other than each iron in the solid.

According to the configuration of the battery negative electrode active material of the present invention, the battery negative electrode active material contains iron and a metal element other than iron, and is in the state of fine particles such as amorphous or nanoparticles. In this state, the iron or iron compound does not form a thermodynamically stable unique crystal structure, and the redox potential of the iron or iron compound changes from the intrinsic one, and the charge / discharge is leveled out as a whole. It is possible to take a potential curve. In addition, since it does not have a crystal structure, it is possible to dissolve a large amount of metal elements other than iron, and as a result, many atoms of metal elements other than iron exist in the vicinity of iron atoms, and oxidation is also affected by the influence. Since the reduction potential is changed, it is possible to adjust the reduction potential so as to be better. In addition, by dissolving different kinds of metal elements other than iron, properties unique to iron or iron compounds can be modified, so that the problem of passivation can be solved.
According to the configuration of the battery negative electrode active material of the present invention, an inorganic / organic hybrid compound in which iron or an oxide other than iron or an oxide derivative is chemically bonded to an organic polymer having a hydroxyl group is formed. Instead of a regular crystal structure in a normal state, the state becomes a fine particle state such as an amorphous or nanoparticle containing the above-described plurality of metal elements, and the state is stably maintained. That is, it is possible to provide a negative electrode active material having practical performance including iron.

  In this way, in the present invention, since it is possible to provide a negative electrode active material having practical performance including iron, a safe aqueous electrolyte is used, and the raw material is lower in price, higher in storage energy density, and more raw material. A battery that can be stably supplied can be provided.

  According to the method for producing an active material for a battery negative electrode of the present invention, the iron or iron compound does not have a regular crystal structure in a normal state, but includes a plurality of metal elements as described above, such as amorphous or nano particles. It becomes possible to easily produce a negative electrode active material in the form of fine particles.

A It is the figure which represented typically the electrode equilibrium potential of the normal iron electrode in alkaline electrolyte. B is a diagram schematically showing an electrode equilibrium potential expected when a metal or compound containing iron is made into nanoparticles or amorphous. 1 is a system diagram schematically showing a representative embodiment of a process for producing a battery negative electrode active material according to the present invention. A is a diffraction intensity-diffraction angle diagram obtained by a powder X-ray diffraction method of a normal iron compound (commercially available Fe ₂ O ₃ ). B is a diffraction intensity-diffraction diagram obtained by the powder X-ray diffraction method of the battery negative electrode active material of the present invention. A and B are charge / discharge potential curves of an electrode using a normal iron compound battery negative electrode active material. A, B It is a charging / discharging electric potential curve of the electrode using the active material for battery negative electrodes of this invention.

Embodiments of the present invention will be described below.
The battery negative electrode active material of the present invention is a negative electrode active material for a battery using an alkaline aqueous electrolyte, contains one or more metal elements other than iron and iron, and is at least of metal elements other than iron. One type is a metal element that does not cause a redox reaction during battery operation, and an organic polymer having a metal oxide or a metal oxide derivative containing at least one of the metal elements that do not cause a redox reaction during battery operation and a hydroxyl group Is based on containing an inorganic / organic hybrid compound chemically bonded.

  The method for producing an active material for a battery negative electrode according to the present invention comprises neutralizing an iron salt and a salt of a metal element other than each iron with an alkali in the presence of an organic polymer having a hydroxyl group, and a metal oxide containing the metal element. An active material for a battery negative electrode is produced by a process in which an inorganic compound or metal oxide derivative forms an inorganic / organic hybrid compound chemically bonded to an organic polymer having a hydroxyl group.

The present invention relates to a negative electrode active material used in a battery using an alkaline aqueous electrolyte. The alkaline aqueous electrolyte here is obtained by dissolving an alkaline electrolyte such as potassium hydroxide, sodium hydroxide, or lithium hydroxide in a solvent containing water as a main component.
Because water itself is nonflammable and extinguishable, water based electrolytes are much safer than flammable organic solvent based electrolytes. The risk of is significantly reduced.
If the main component of the solvent is water, it is possible to obtain a safety feature, so that a small amount of other solvents are allowed to be mixed. The negative electrode active material of the present invention is used in batteries using an alkaline aqueous electrolyte solution, including such an electrolyte solution.

In the present invention, the battery negative electrode active material contains iron.
The active material for battery negative electrode of the present invention is applied to a battery using an alkaline aqueous electrolyte, and in the alkaline aqueous electrolyte, iron exists in the form of a metal, an oxide or a hydroxide.
The battery negative electrode active material of the present invention also contains one or more metal elements other than iron, and at least one of the metal elements other than iron is a metal element that does not cause a redox reaction during battery operation. These metal elements also exist as metals, oxides or oxide derivatives, mainly hydroxides, in the alkaline aqueous electrolyte.
Iron and metallic elements other than iron take the form of metals, oxides or oxide derivatives, but they may form one phase or may coexist as a plurality of phases. However, in a phase containing at least iron, it is desirable that an iron atom and a metal atom other than iron coexist (solve) in one phase.

In the active material for battery negative electrode of the present invention, preferably, in a diffraction intensity-diffraction angle diagram obtained by a powder X-ray diffraction method using Cu-α-ray, any diffraction peak of iron or a compound containing iron has a half width. 1 (2θ °) or more. Here, the negative electrode active material is limited to only the materials that directly control the oxidation-reduction potential (equilibrium potential) in the equilibrium state among the electrode constituent materials. The electrode base material, current collecting member, conductive agent Various additives having auxiliary roles such as binders and binders are not included in the negative electrode active material.
The diffraction intensity-diffraction angle diagram is generally obtained as a result of powder X-ray diffraction, and shows the relationship of the number of X-ray counts to the diffraction angle 2θ. When the material is crystalline, the X-ray diffraction phenomenon occurs due to the regular stacking of crystal planes, the X-ray count is significantly increased at a certain diffraction angle corresponding to the plane spacing of the crystal planes, and the diffraction intensity -A sharp peak is obtained at the diffraction angle position in the diffraction angle diagram. If the regularity of the crystal plane stacking is broken, or if the particles are small and the number of crystal plane stacking is not large, the peak is broad and broad, so the half-width (diffraction peak) The peak width at the half height of the apex is expressed in 2θ angle units 2θ °). In addition, in the case of fine particles such as nanoparticles that are completely amorphous or so small that a substance cannot form a crystal, no diffraction peak appears even at a diffraction angle at which a peak should occur when the substance is originally a crystal. That is, the half width is infinite. Therefore, the full width at half maximum can be regarded as a measure representing the degree of fine particles such as low crystallinity, amorphous or nanoparticles of the substance, and the larger the half width, the lower the crystallinity and the more amorphous or fine particles. It is shown that.
In the diffraction intensity-diffraction angle diagram, any diffraction peak of iron or a compound containing the same has a half-value width of 1 (2θ °) or more, so that the negative electrode active material is low crystalline, amorphous, or nanoparticle-like. The state of fine particles.

The battery negative electrode active material of the present invention is a metal element that does not cause a redox reaction during battery operation, and at least one of the metal elements other than iron is at least one of the metal elements that does not cause a redox reaction during battery operation. Inorganic / organic hybrid compounds in which one type of metal oxide or metal oxide derivative and an organic polymer having a hydroxyl group are chemically bonded are included.
In the present invention, the “metal oxide derivative” includes a metal oxide represented by the chemical formula of MOx (M: metal element) as a basic unit. Indicates all compounds with atoms, molecules, ions, etc. added. For example, hydroxides and hydrates added with H ₂ O (MOx · yH ₂ O) are also based on MOx. Further, derivatives that are partially substituted with another element within a range in which the characteristics are not impaired, those that deviate from the stoichiometric composition, or those that are added with additives are also included in the derivatives.

When producing the active material for battery negative electrode of the present invention, both iron and oxides of metal elements other than iron or oxide derivatives chemically bond with organic polymers to form inorganic / organic hybrid compounds. Thus, aggregation / growth or crystallization of fine particles is inhibited. At this time, the hydroxyl group of the organic polymer functions as a bonding hand when chemically bonding to the oxide or the oxide derivative.
Since iron oxides or oxide derivatives cause an oxidation-reduction reaction during battery operation, the bond with the organic polymer may be eliminated. However, since the battery negative electrode active material of the present invention contains a metal element that does not cause a redox reaction during battery operation, an oxide or oxide derivative of the metal element forms an inorganic / organic hybrid compound. The entire inorganic / organic hybrid compound is stably maintained. Therefore, iron-containing metals, metal oxides or metal oxide derivatives continue to be hindered by the aggregation / growth or crystallization of fine particles in this inorganic / organic hybrid compound. Can exist stably in the form of fine particles.

Since the battery negative electrode active material of the present invention is used in a battery using an alkaline electrolyte, it is required to have alkali resistance enough to withstand strong alkali. For this purpose, a metal that forms an inorganic / organic hybrid compound High alkali resistance is also required for oxides or metal oxide derivatives.
From these conditions, a zirconic acid compound is suitable as a metal oxide or a metal oxide derivative of a metal element other than iron that forms an inorganic / organic hybrid compound.
Here, zirconic acid is a compound containing ZrO ₂ as a basic unit and containing H ₂ O, and can be represented by the general formula ZrO ₂ .xH ₂ O. It is an acid and a derivative of zirconic acid or a compound mainly composed of zirconic acid. Therefore, it may be one in which another element is substituted as long as the characteristics of zirconic acid are not impaired, one deviating from the stoichiometric composition, or one having an additive added. For example, zirconic acid salts and hydroxides are also based on ZrO ₂ , and derivatives based on salts or hydroxides or compounds based on them are also included in the zirconic acid compounds. That is, in the present invention, it is desirable to include zirconium as a metal element other than iron.

  Moreover, in this invention, it is desirable to contain nickel as another metal element other than iron. The coexistence of nickel can prevent the passive state of the negative electrode active material containing iron of the present invention (a phenomenon that becomes inactive with respect to the charge / discharge reaction). In this case, nickel is not necessarily introduced in order to form an inorganic / organic hybrid compound such as zirconium, and to suppress particle growth and crystal growth of iron or an iron compound. It is not always necessary to chemically bond with an organic polymer having a hydroxyl group, and an oxidation-reduction reaction may occur during battery operation. In addition to nickel and zirconium, magnesium, aluminum, calcium, titanium, manganese, cobalt, copper, zinc, strontium, yttrium, silver, and the like can be introduced as metal elements other than iron.

  The organic polymer component having a hydroxyl group of the inorganic / organic hybrid compound contained in the active material for battery negative electrode of the present invention may be basically any one. The most typical organic polymer used in the present invention is polyvinyl alcohol, which binds to an inorganic substance via its hydroxyl group. When the organic polymer component of the inorganic / organic hybrid compound is polyvinyl alcohol, the polyvinyl alcohol does not need to be complete, and any substance that essentially functions as polyvinyl alcohol can be used. For example, those in which some hydroxyl groups are substituted with other groups and those in which other polymers are partially copolymerized can function as polyvinyl alcohol. Moreover, since the same effect is acquired if it passes through polyvinyl alcohol in the reaction process of this invention, the polyvinyl acetate etc. which are the raw materials of polyvinyl alcohol can be used as a starting material.

  In an inorganic / organic hybrid compound, a metal oxide or a metal oxide derivative that does not cause a redox reaction during battery operation and an organic polymer having a hydroxyl group are chemically bonded. That is, both are intertwined with each other at the molecular level and at the nano level, and are firmly connected by dehydration condensation via the hydroxyl group of the organic polymer. A hybrid compound is a compound and is distinguished from a mixture obtained by physical mixing of a metal oxide or a derivative of a metal oxide and an organic polymer. That is, unlike a mixture, in a hybrid compound, the chemical properties of each component are not necessarily retained after hybridization. For example, in the present invention, when the component of the hybrid compound is polyvinyl alcohol, polyvinyl alcohol alone is water-soluble (hot water soluble), but for example, after formation of the hybrid compound with a zirconate compound, Basically does not dissolve. Thus, it can be said that these are hybrid compounds different from the mixture by physical mixing by the chemical property changing after hybridization.

  In the inorganic / organic hybrid compound, if the amount of the inorganic substance with respect to the organic polymer having a hydroxyl group is too small, sufficient water resistance and alkali resistance cannot be obtained, and the electrode capacity is reduced. On the other hand, when there are too many inorganic substances, the effect of inhibiting aggregation / growth or crystallization of fine particles of inorganic substances cannot be sufficiently obtained. Therefore, it is preferable to control the hybrid compound so that the weight ratio of the weight of the metal oxide or metal oxide derivative that does not cause a redox reaction to the weight of the organic polymer is 0.1-1.

Next, the manufacturing method of the active material for battery negative electrodes of this invention is demonstrated.
In the method for producing an active material for a battery negative electrode of the present invention, an iron salt and a salt of a metal element other than each iron are neutralized with an alkali in the presence of an organic polymer having a hydroxyl group, and the metal oxidation containing the metal element is performed. An active material for a battery negative electrode is obtained through a process of forming an inorganic / organic hybrid compound in which a product or a metal oxide derivative is chemically bonded to an organic polymer having a hydroxyl group.

  Iron salts produce oxides or hydroxides when neutralized with alkali. However, since an organic polymer having a hydroxyl group coexists here, the iron oxide or hydroxide is also linked to the organic polymer through the hydroxyl group at the time of formation. That is, small oxides or hydroxides that have just been formed by neutralization are unstable and try to be stabilized in combination with something. At this time, if there are only iron oxides or hydroxides, the newly born iron oxides or hydroxides are connected, aggregated, and grown, but if there is a polymer having a hydroxyl group in the vicinity, Also associated with the polymer. Therefore, the growth of iron oxide or hydroxide is suppressed and remains as fine particles such as nanoparticles. In the present invention, fine particles such as iron oxide or hydroxide nanoparticles can be produced in this manner. In the case of bonding with an organic polymer at the molecular level or nano level, crystallization is also inhibited.

  Thus, in the production of the battery negative electrode active material of the present invention, the compound such as iron oxide or hydroxide is combined with the organic polymer having a hydroxyl group to form fine particles such as nanoparticles. When a salt of a metal element other than iron that does not cause an oxidation-reduction reaction at the time of battery operation is allowed to coexist, the salt is also neutralized by an alkali, and the neutralized product is also linked to an organic polymer having a hydroxyl group. A hybrid compound is formed. As described above, unlike iron compounds, oxides or oxide derivatives of metal elements other than iron do not cause an oxidation-reduction reaction during battery operation, so that the inorganic / organic hybrid compound is stable even during battery operation. Is maintained, thereby continuing to suppress the growth of iron or iron compounds.

The iron salt may be of any type as long as it dissolves in the solvent used, and iron sulfate, iron nitrate, iron chloride, or hydrates thereof can be used. It can be anything.
The metal oxide or metal oxide derivative that does not cause an oxidation-reduction reaction during battery operation is preferably a zirconate compound, but as a salt of zirconium, a zirconate compound is produced by neutralization with an alkali, Any material can be used as long as it produces a stable inorganic / organic hybrid compound of a zirconate compound and an organic polymer having a hydroxyl group. Zirconium salts and oxyzirconium salts can be used, and zirconium oxychloride, zirconium acetate, zirconium nitrate or hydrates thereof can be used.
Furthermore, it is preferable to include nickel as a metal element other than iron. In this case, nickel sulfate, nickel nitrate, nickel chloride, nickel acetate, or the like can be used as a nickel salt.

  In one embodiment of the method for producing an active material for battery negative electrode of the present invention, the process of forming the inorganic / organic hybrid compound includes an iron salt and a salt of each metal element other than iron, an organic polymer having a hydroxyl group, Are mixed in a solvent to prepare a mixed solution, and a solid is formed by removing the solvent from the mixed solution. The solid is contacted with an alkali to remove the iron salt in the solid and each iron other than the iron. This is done by neutralizing the metal element salt.

Here, FIG. 2 shows a system diagram schematically showing an embodiment of the manufacturing method described above.
As shown in FIG. 2, first, as a raw material, a solvent in Step 1, an iron salt in Step 2, a salt containing a metal element other than iron in Step 3, and an organic polymer having a hydroxyl group in Step 4, respectively. prepare.
Next, in Step 5, these raw materials are mixed to obtain a raw material solution in which an iron salt and a salt containing a metal element other than iron and an organic polymer having a hydroxyl group coexist. At this time, any solvent may be used as long as it can dissolve an iron salt, a salt containing a metal element other than each iron, and an organic polymer having a hydroxyl group. As described above, a typical example of the organic polymer is polyvinyl alcohol. In this case, the optimum solvent is water.

Next, in step 6, the solvent is removed from the raw material solution in which the salt of iron and a salt containing a metal element other than iron and the organic polymer having a hydroxyl group coexist, and in step 7, a solid is obtained.
Thereafter, in step 8, the solid is brought into contact with an alkali to neutralize iron or a salt containing a metal element other than iron, and in step 9, a metal oxide or metal oxide containing a metal element other than iron and iron. An active material for a battery negative electrode containing an inorganic / organic hybrid compound in which the derivative is chemically bonded to an organic polymer having a hydroxyl group is obtained. In this case, the generated metal oxide or metal oxide derivative particles containing iron are bonded to the organic polymer, or the metal oxide or metal oxide derivative containing the metal element other than the adjacent iron and the organic polymer. In the diffraction intensity-diffraction angle diagram obtained by the powder X-ray diffraction method, the half-value width of the diffraction peak intensity corresponding to the 001 plane is 1 (2θ °) or higher or no diffraction peak.

In Step 7, the solids containing the iron salt, the salt containing a metal element other than iron, and the organic polymer having a hydroxyl group may be in any form, and may be in the form of a film, thread, powder, or the like. is there.
In the case of a film-like material, it can be formed by casting a raw material solution on a flat surface and then removing the solvent by heating.
In the case of a filamentous material, it can be formed by, for example, ejecting the raw material liquid from a nozzle having a narrow mouth and simultaneously removing the solvent by heating. It is also possible to use an electrospinning method in which an electric field is applied to the raw material liquid so that the material liquid jumps out.
In the case of powder, it can be molded by spray drying, in which the raw material liquid is sprayed and heated to remove the solvent. When forming into a powder form or a granular form, a method of immersing in an alkali in a droplet state without removing the solvent is also possible.

  In the neutralization step with alkali in Step 8, in order to efficiently perform neutralization in a short time, it is desirable that the solid has a large specific surface area. If so, the yarn diameter is preferably 1 mm or less, and even in powder form, the diameter is preferably 1 mm or less. From the viewpoint of easy handling, a film shape is desirable.

  In Step 8, the alkali to be contacted after the solvent removal may be any alkali as long as these can be neutralized, and potassium hydroxide, sodium hydroxide, lithium hydroxide and the like can be used. These may be used alone or in a mixed state. When using an alkaline solution, the alkali concentration may be basically any, but shortening the time of the neutralization process, suppressing changes in the solution concentration during the neutralization reaction, or from solids From the standpoint of carrying out a neutralization reaction before each of the components is eluted, the alkaline solution preferably has a higher concentration. As a method of contacting with an alkali, there are a method of immersing in an alkali solution, applying or spraying an alkali solution onto a composite compound, or exposing to an alkali vapor.

  Specific examples of the battery negative electrode active material according to the present invention will be described below. In addition, this invention is not limited to the content of description of these Examples.

The battery negative electrode active material according to the present invention was actually produced, and the characteristics of the battery negative electrode active material were examined.
This example shows a case where two types of elements other than iron, zirconium and nickel, are included.
A solution of 6 g of ferrous chloride tetrahydrate, 2 g of zirconium oxychloride octahydrate and 9 g of nickel nitrate hexahydrate in 27 cc of water was added to polyvinyl alcohol (degree of polymerization 3,100-3,900, saponification). The mixture was mixed with 10 g of a 10% by weight aqueous solution having a degree of 86 to 90%) to prepare a raw material mixed solution.
Next, this raw material mixed solution was laid on a smooth pedestal of a coating apparatus (K Control Coater 202 manufactured by RK Print Coat Instruments Ltd.) equipped with a blade capable of adjusting the gap with the pedestal using a micrometer. The film was cast on a polyester film. At this time, heating was performed while controlling the pedestal to be 65 ° C. After casting the raw material solution on the pedestal, a blade whose gap was adjusted to 0.5 mm was immediately swept over the raw material solution at a constant speed to obtain a constant thickness. Furthermore, the moisture was blown away by leaving it to stand while heating. By this operation, a film-like solid in which an iron salt, an oxyzirconium salt, a nickel salt and polyvinyl alcohol were mixed was produced.

  Next, the produced membranous solid was peeled off from the pedestal, immersed in a 10 wt% sodium hydroxide solution, and allowed to stand overnight. After standing, the film-like material was pulled up from the sodium hydroxide solution, washed with water, dried, coarsely pulverized with a mixer, and then heated in an oven at 130 ° C. for 30 minutes. Then, it grind | pulverized further finely using the ball mill, and it was set as the active material for battery negative electrodes.

About the obtained active material, the powder X-ray-diffraction measurement (X'Part Pro by a panalical company, Cu (alpha) ray use) was performed. The obtained diffraction intensity-diffraction angle diagram is shown in FIG. 3B. Further, FIG. 3A shows a diffraction intensity-diffraction angle diagram of ordinary commercially available Fe ₂ O ₃ (Wako Pure Chemical Industries, Ltd.) under the same conditions.
As shown in FIG. 3A, in a normal commercially available Fe ₂ O ₃ , a sharp diffraction peak due to the crystal structure is clearly seen. On the other hand, as shown in FIG. 3B, no sharp peak was observed in the battery negative electrode active material of this example. While the full width at half maximum of the diffraction peak of ordinary Fe ₂ O ₃ is smaller than 1 (2θ °), the diffraction peak is very broad and low in the active material for battery negative electrode of this example. The value ranges were all 1 (2θ °) or more.
Further, in the diffraction intensity-diffraction angle diagram of the battery negative electrode active material of this example, no peaks of the compound containing zirconium and nickel other than the introduced iron were observed. That is, it can be seen that zirconium and nickel do not form a crystalline phase independently but are dissolved at the atomic level or at least at the level of fine particles such as nanoparticles.

Next, the electrode was produced using the active material for battery negative electrodes of this invention, and the characteristic of the electrode was evaluated.
The active material powder and copper powder prepared in Example 1 were mixed in the same weight, and 0.35 g of this mixture was mixed with 0.03 g of a polytetrafluoroethylene dispersion (solid content 60 wt%, Aldrich) to make a 2 cm square. The cut copper sponge (Fushimi Pharmaceutical Co., Ltd.) was filled and pressed at a pressure of 10 MPa to obtain an electrode. The electrode was immersed in a beaker filled with 30% by weight aqueous potassium hydroxide after the lead was attached.
The electrode was charged and discharged using a hydrogen storage alloy electrode (denoted as MH (1 atm)), which can be regarded as being almost in equilibrium with 1 atm adsorbed hydrogen overnight after full charge, with a nickel plate as a counter electrode. . Initially, when all the iron compounds in the active material were Fe ₂ O ₃ , charging / discharging was repeatedly performed at a current of 50 mA (50 mAg ⁻¹ ) per 1 g of Fe ₂ O ₃ .
Further, as a control, also produced in the same manner the electrodes for a typical commercial Fe ₂ O _3, were charged and discharged under the same conditions.

4A and 4B show charge / discharge curves of a normal commercially available Fe ₂ O ₃ electrode, and FIGS. 5A and 5B show charge / discharge curves of an electrode using the battery negative electrode active material prepared in this example. Show.
4A and 5A show curves during discharging, and FIGS. 4B and 5B show curves during charging. Moreover, the code | symbol in FIG. 4A-FIG. 5B has shown the cycle number of repeated charging / discharging.

From FIG. 4A and FIG. 4B, the electrode using a normal iron compound has a two-stage charge / discharge curve as described above, and the charge / discharge capacity drastically decreases with the number of charge / discharge repetitions, and is rendered passive. Is happening.
On the other hand, from FIG. 5A and FIG. 5B, unlike the normal iron compound, the electrode of this example is not a two-stage with a clear charge / discharge potential curve, and is expected in the case of nanoparticles or amorphous. As shown in FIG. 1B, a potential curve in which the two-stage charge / discharge potential of a normal iron compound is leveled is shown. That is, it was shown that the redox potential of the iron compound can be changed (controlled) by the method of the present invention. Furthermore, it was shown that the capacity of the active material of the present invention hardly decreases even when charging and discharging are repeated, and passivation does not occur.

In addition, since these results are results obtained by evaluating the electrode alone using the active material of the present invention, they are generated only from the active material of the present invention. It is a nature to be. Therefore, the same effect can be obtained for all batteries using the negative electrode active material of the present invention, such as nickel-iron batteries and air-iron batteries.
In addition, examples of inorganic / organic hybrid compounds using polyvinyl alcohol are given in the examples, but polyvinyl alcohol has only a hydroxyl group in a hydrocarbon chain, and is the simplest of organic polymers having a hydroxyl group. It has a simple structure. Therefore, the effect of the present invention obtained by using polyvinyl alcohol as in this example means that the same effect can be obtained for the whole organic polymer having a hydroxyl group.

  The active material for a battery negative electrode of the present invention is obtained by forming an inorganic / organic hybrid compound, whereby iron or an iron compound is obtained in a state of fine particles such as low crystallinity, amorphous or nanoparticles, and stably Can be maintained. This makes it possible to control the charge / discharge potential more practically different from normal iron or iron compounds, and to solve specific problems such as passivation. As a result, it is possible to provide a battery that is made of a resource-rich electrode material that is safe, inexpensive, and has a high energy density.

Claims (10)

A battery negative electrode active material used in a battery using an alkaline aqueous electrolyte,
Containing iron and one or more kinds of metal elements other than iron,
Among the metal elements other than iron, at least one kind is a metal element that does not cause a redox reaction during battery operation,
A battery comprising an inorganic / organic hybrid compound in which a metal oxide or a metal oxide derivative containing at least one of the metal elements that do not cause an oxidation-reduction reaction when the battery is operated is chemically bonded to an organic polymer having a hydroxyl group. Active material for negative electrode.   2. A diffraction intensity-diffraction angle diagram obtained by a powder X-ray diffraction method using Cu-α-rays, wherein the half-value width of any diffraction peak of iron or a compound containing iron is 1 (2θ °) or more. Active material for battery negative electrode.   The battery negative electrode active material according to claim 1, comprising zirconium as a metal element other than iron.   The active material for battery negative electrodes of Claim 1 which contains nickel as metal elements other than the said iron.   The battery negative electrode active material according to claim 1, wherein the organic polymer having a hydroxyl group is polyvinyl alcohol.   2. The battery according to claim 1, comprising zirconium as a metal element other than iron, polyvinyl alcohol as the organic polymer having a hydroxyl group, and the inorganic / organic hybrid compound including at least a chemical bond between a zirconate compound and polyvinyl alcohol. Active material for negative electrode. A battery comprising at least a positive electrode, a negative electrode, and an electrolyte solution,
An alkaline aqueous electrolyte is used as the electrolyte.
A battery comprising the negative electrode active material according to claim 1.   The battery according to claim 7, which is either a nickel-iron battery or an air-iron battery. A method for producing the battery negative electrode active material according to claim 1,
An iron salt and a salt of each metal element other than iron are neutralized with an alkali in the presence of an organic polymer having a hydroxyl group, and the metal oxide or metal oxide derivative containing the metal element is used to form the hydroxyl group. A method for producing an active material for a battery negative electrode, wherein a process of forming an inorganic / organic hybrid compound chemically bonded to an organic polymer is formed.   In the process of forming the inorganic / organic hybrid compound, an iron salt, a salt of each metal element other than the iron, and an organic polymer having a hydroxyl group are mixed in a solvent to prepare a mixed solution. Forming a solid by removing the solvent, contacting the solid with an alkali, and neutralizing the salt of the iron and the metal element other than each iron in the solid Item 10. A method for producing an active material for battery negative electrode according to Item 9.

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