JP6124784B2 - Negative electrode active material, method for producing the negative electrode active material, and lithium ion secondary battery using the negative electrode active material - Google Patents

Description

  The present invention relates to a negative electrode active material capable of occluding and releasing lithium, having a high reversible capacity and a reduced initial irreversible capacity. The present invention also relates to a method for producing the negative electrode active material and a lithium ion secondary battery using the negative electrode active material.

  Lithium ion secondary batteries that use non-aqueous electrolytes with high energy density are widely used as the power source for information devices such as mobile phones and laptop computers. The performance of these information devices and the amount of information handled In order to cope with the increase in power consumption accompanying the increase in the battery capacity, it is desired to increase the discharge capacity of the lithium ion secondary battery. In addition, from the viewpoints of reducing oil consumption, mitigating air pollution, and reducing emissions of carbon dioxide, which causes global warming, we are working on low-emission vehicles such as electric vehicles and hybrid vehicles that replace gasoline and teal vehicles. Expectations are increasing, and it is desired to develop a large-sized lithium ion secondary battery having high energy density and high output density and thus high capacity density as a motor drive power source for these low-pollution vehicles.

Current lithium ion secondary batteries using non-aqueous electrolytes use lithium layered compounds such as lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, graphite that absorbs and releases lithium as a negative electrode active material, and hexafluoride. The mainstream is a solution obtained by dissolving a lithium salt such as lithium phosphate (LiPF ₆ ) in a non-aqueous solvent such as ethylene carbonate or propylene carbonate. In order to increase the capacity of such a lithium ion secondary battery, it is necessary to increase the amount of lithium stored and released in the negative electrode active material. However, the theoretical capacity of graphite calculated from LiC ₆ that occludes the maximum amount of lithium is 372 mAhg ⁻¹ , and the current secondary battery has already obtained a capacity close to the theoretical capacity. In order to increase the capacity, it is essential to use a negative electrode active material instead of graphite. In addition, the substitute must exhibit stable characteristics with respect to the charge / discharge cycle experience.

As an alternative having a high capacity instead of graphite, there is a metal that forms an alloy with lithium, such as aluminum, zinc, and tin. In particular, tin is suitable because the theoretical capacity calculated from Li _4.4 Sn is as high as 994 mAhg- ¹ . However, there is a problem that the volume expansion accompanying the lithium occlusion of tin is extremely large. When the volume of Sn is 100%, the volume of Li _4.4 Sn reaches 358%. For this reason, repeated charge / discharge cycles in a battery using tin as the negative electrode active material cause cracks in the negative electrode due to an excessively large volume change that accompanies the insertion and extraction of lithium, destroying the electron conduction path essential for the charge / discharge reaction. In addition, the discharge capacity is rapidly reduced even when only a few charge / discharge cycles are repeated.

  In order to solve this problem, a method has been proposed in which tin is dispersed in a matrix of a carbon material or an oxide to relieve stress due to a volume change of tin. The conductive carbon material as a matrix not only relieves stress due to the volume change of tin, but also plays a role of securing an electron conduction path even if the negative electrode active material is mechanically damaged by the volume change of tin.

  As a negative electrode active material in which tin is dispersed in a carbon material matrix, Patent Document 1 (Japanese Patent Laid-Open No. 2000-90916) mixes tin dioxide as a tin source and a heat treated coal tar pitch as a carbonaceous material source. Thus, the powdered powder is heat treated at 900 ° C. to show a negative electrode active material in which tin metal fine particles coated in a carbonaceous material matrix are highly dispersed. However, the discharge capacity of the half-cell using this negative electrode active material and having the counter electrode as lithium deteriorated to 60% or 91% after only four charge / discharge cycle tests, and good cycle characteristics were obtained. Not.

One method for dispersing tin in an oxide matrix is to use tin dioxide as an active material. Tin dioxide occludes lithium by the reactions of the following formulas (I) and (II). The reaction in which reduction of tin dioxide of formula (I) and generation of lithium oxide occur is referred to as “conversion reaction”, and the reaction in which an alloy of tin and lithium of formula (II) is generated is referred to as “alloying reaction”. It is considered that lithium oxide generated by the conversion reaction acts as a matrix of tin, relieves stress caused by tin volume change in the alloying reaction region, and suppresses aggregation of tin in the alloying reaction region.

Regarding the negative electrode active material composed of tin dioxide, Non-Patent Document 1 (Journal of Power Sources 159 (2006) 345-348) has a particle size of 0.5 to 1 μm and internal pores formed by spray pyrolysis. Disclosed is a negative electrode active material comprising porous tin dioxide particles. The tin dioxide particles have primary particles composed of crystals having an average of about 5 nm, and stress due to tin volume change in the alloying reaction region is suppressed not only by the lithium oxide matrix but also by vacancies inside the tin dioxide particles. . About the half cell which used this negative electrode active material and made the counter electrode lithium, it was made to experience the charging / discharging cycle of the range of 0.05-1.35V with respect to a Li / Li ⁺ electrode with the current density of 100 mAg < ^-1 >. An initial irreversible capacity of 328 mAhg ⁻¹ is observed. Moreover, the capacity retention rate after experiencing 50 charge / discharge cycles is only 68% of the initial capacity (601 mAhg ⁻¹ ), and good cycle characteristics are not obtained.

Non-Patent Document 2 (CARBON 46 (2008) 35-40) discloses a negative electrode active material in which a carbon film is formed by thermal decomposition of malic acid on the surface of tin dioxide particles of several tens to 300 nm. . A half cell using this negative electrode active material and having the counter electrode as lithium was subjected to a charge / discharge cycle in the range of 0.05 to 1.5 V with respect to the Li / Li ⁺ electrode at a current density of 100 mAg ^−1. An initial irreversible capacity of 732 mAhg ⁻¹ is observed. In addition, this negative electrode active material has a capacity of about 600 mAhg ⁻¹ at the start of the charge / discharge cycle test, but the capacity has decreased to about 400 mAhg ⁻¹ after experiencing 30 charge / discharge cycles. The maintenance rate is not satisfactory in practice.

If the negative electrode active material made of tin dioxide can be used for the entire conversion reaction of the above formula (I) and the alloying reaction of the formula (II), it is theoretically about 0V to about 2V with respect to the Li / Li ⁺ electrode. The theoretical capacity of the conversion reaction is 711 mAhg ⁻¹ , the theoretical capacity of the alloying reaction is 783 mAhg ⁻¹ , and the total theoretical capacity reaches 1494 mAhg ⁻¹ . However, conventionally, since lithium oxide is thermodynamically stable, it has been said that the conversion reaction represented by the above formula (I) is an irreversible reaction. Therefore, in the lithium ion secondary battery using tin dioxide as the negative electrode active material, only the alloying reaction region (range of 0V to about 1V with respect to the Li / Li ⁺ electrode) that is a reversible reaction region is used. Therefore, a high discharge capacity has not been obtained. Further, when charge / discharge was performed by expanding the potential range to the potential including the conversion reaction region, a large initial irreversible capacity due to the irreversibility of the conversion reaction was recognized. The initial irreversible capacity observed in the negative electrode active materials of Non-Patent Document 1 and Non-Patent Document 2 also seems to be due to the irreversibility of the conversion reaction.

  Therefore, the conventional negative electrode active material made of tin dioxide has not been satisfactory in terms of capacity and cycle characteristics. In response to this problem, the applicant reversibly proceeds with the conversion reaction that was previously considered to be an irreversible reaction in WO2011 / 040022 published after the filing date of the application on which the priority claim of the present application is based. A negative electrode active material was proposed.

  The negative electrode active material shown in WO2011 / 040022 is a negative electrode active material containing tin oxide powder and nano-sized conductive carbon powder in a highly dispersed state. When this negative electrode active material is used, the conversion reaction, which has been considered to be an irreversible reaction in the past, has progressed reversibly, and therefore alloyed for the insertion and extraction of lithium. Not only the reaction area but also the conversion reaction area can be used.

The reason why the conversion reaction has progressed reversibly is not clear at the present time, but is considered as follows. The conductive carbon powder having a nanosize contains abundant oxygen atoms (oxygen of surface functional groups such as carbonyl group and hydroxyl group, adsorbed oxygen). Therefore, Sn—O— mediated by this abundant oxygen is contained. It is thought that C bond is likely to occur. The lithium oxide produced by the conversion reaction is considered to exist in a metastable state as shown in the following formula (III), and a state in which lithium is easily detached from this metastable lithium oxide is formed. Therefore, it is considered that the formation of tin oxide is likely to occur along with the elimination of lithium, and the conversion reaction occurs reversibly. When nano-sized conductive carbon powder and tin oxide powder are present in a highly dispersed state, the number of contact points between the carbon powder and tin oxide powder increases, so that Sn—O—C bonds are formed at many sites. Therefore, after the conversion reaction, the metastable state of formula (III) is formed at many sites. As a result, a charge / discharge cycle in the range of 0 V to about 2 V can be realized with respect to the Li / Li ⁺ electrode, and the discharge capacity can be greatly increased.

JP 2000-90916 A

Journal of Power Sources 159 (2006) 345-348 CARBON 46 (2008) 35-40

  The negative electrode active material containing the above tin oxide powder and nano-sized conductive carbon powder in a highly dispersed state uses not only the alloying reaction region but also the conversion reaction region for lithium storage and release. As a result of further investigation, the following detailed description will be made using a comparative example. The initial irreversible capacity, which is thought to be caused by the electrochemical decomposition of the electrolyte on the surface of the conductive carbon powder. It was found that is recognized. This initial irreversible capacity leads to the need for more positive electrode active material when the negative electrode active material is combined with the positive electrode active material to form a lithium ion secondary battery. This is not preferable because the amount of the split negative electrode active material is reduced and the capacity per cell is reduced.

  Accordingly, an object of the present invention is to reversibly convert the negative electrode active material based on the negative electrode active material containing the above-described tin oxide powder and nano-sized conductive carbon powder in a highly dispersed state. It is to provide a negative electrode active material in which the initial irreversible capacity is further reduced while maintaining a high reversible capacity by maintaining the progress.

  As a result of intensive studies, the inventors of the present invention have found that in the negative electrode active material containing the above-described tin oxide powder and nano-sized conductive carbon powder in a highly dispersed state, tin oxide out of the surface of the conductive carbon powder. When a metal oxide other than tin oxide is supported on a portion that is not in contact with tin, or a portion of the surface of the conductive carbon powder that is not in contact with tin oxide is coated with a low-conductivity amorphous carbon film. This is probably because the active sites on the surface of the conductive carbon powder that catalyze the electrochemical decomposition of the electrolyte solution are covered with the metal oxide and / or the amorphous carbon film, but the initial irreversible capacity is reduced. And it discovered that the reversible progress of the conversion reaction was maintained as it was.

  Therefore, the present invention is a negative electrode active material capable of occluding and releasing lithium, in which a conductive carbon powder having a nanosize and a tin oxide powder are contained in a highly dispersed state. The present invention further relates to a first negative electrode active material, further comprising a metal oxide, wherein the tin oxide powder and the metal oxide are in contact with the surface of the conductive carbon powder.

  In the present specification, the range of “metal oxide” includes oxides of typical metals, transition metals and metalloids, but excludes tin oxide. Further, the shape of the “powder” is not limited and is not limited to spherical particles, and needles, tubes, or strings are also included in the “powder” range. And, “having nanosize” means that when the powder is a spherical particle, the average particle diameter is 1 to 500 nm, preferably 1 to 50 nm, and the powder is needle-like, tubular or string-like The mean diameter is 1 to 500 nm, preferably 1 to 50 nm. The “highly dispersed state” is generally 30% by mass or more, preferably 85% by mass or more, more preferably 95% by mass or more, and particularly preferably primary particles of the conductive carbon powder and tin oxide powder. It means that 98 mass% or more is not aggregated. Here, the non-aggregation rate of the powder is a value calculated from the result of observing the state of the powder with a transmission electron microscope (TEM) photograph. Furthermore, the term “supported” means that an object to be supported (such as tin oxide) having an average size smaller than the support (conductive carbon powder) is in contact with the surface of the support. The “low conductivity amorphous carbon film” is 1/100 or less, preferably 1/1000 or less, particularly preferably 1/10000 or less of the electrical conductivity of the conductive carbon powder contained in the composite. An amorphous carbon film having an electrical conductivity of

In the first negative electrode active material of the present invention, the nano-sized conductive carbon powder and tin oxide powder that are present in a highly dispersed state are likely to generate Sn—O—C bonds, and therefore, after the conversion reaction, the above formula (III) As a result, the charge / discharge cycle in the range of 0V to about 2V can be realized with respect to the Li / Li ⁺ electrode, and the discharge capacity can be greatly increased. Can do. In addition, the active sites on the surface of the conductive carbon powder that catalyze the electrochemical decomposition of the electrolytic solution are covered with metal oxide, which seems to inhibit the electrochemical decomposition of the electrolytic solution, but the initial irreversible Capacity is reduced. Therefore, the first negative electrode active material of the present invention is a negative electrode active material having a high reversible capacity and a reduced initial irreversible capacity.

  In the first negative electrode active material of the present invention, the nano-sized conductive carbon powder is preferably nano-sized spherical particles and may have conductivity, but preferably has a smaller particle size. Particular preference is given to spherical particles having an average particle diameter of ˜50 nm. A carbon powder with a small particle size and a large specific surface area has abundant oxygen (oxygen of surface functional groups, adsorbed oxygen), and therefore Sn-O—C bonds are more likely to occur, and the above metastable state is further formed. This is because the dispersion state of the tin oxide powder is further improved.

The tin oxide powder also preferably has a nanosize, and particularly preferably spherical particles having a nanosize, particularly fine spherical particles having an average particle diameter of 1 to 10 nm. When such a tin oxide powder is supported on the conductive carbon powder, the surface area of the tin oxide increases, so that a Sn—O—C bond is more likely to occur, and the metastable state is more easily formed. Because. The conductive carbon powder having nano-size and supporting the metal oxide on the surface, preferably spherical particles, and the tin oxide powder having nano-size supported thereon, preferably spherical particles It has reversible capacity, reduced initial irreversible capacity, and in addition, the cycle characteristics are small in discharge capacity even in the charge / discharge cycle test in the range of 0V to about 2V with respect to the Li / Li ⁺ electrode. A very good negative electrode active material can be obtained.

  Conventionally, structural changes such as volume expansion and aggregation of the negative electrode active material in which tin oxide and carbon are combined have been considered only in the alloying reaction region, and have not been considered in the conversion reaction region. This is because the conversion reaction is considered to be an irreversible reaction, and only the alloying reaction region, which is a reversible reaction region, has been used. However, the adoption of a negative electrode active material that contains nano-sized conductive carbon powder and tin oxide powder in a highly dispersed state enables charge / discharge cycle tests in the potential range including the conversion region, and conversion reaction. Consideration in the area became possible. As a result, in order to obtain a negative electrode active material having good cycle characteristics in the potential range including the conversion reaction region in the negative electrode active material of tin oxide and carbon, only suppression of stress due to volume change in the alloying reaction region is required. It was also found that it is important to suppress aggregation of the negative electrode active material occurring in the conversion reaction region (see WO2011 / 040022 published after the filing date of the application on which the priority of the present application is based).

In order to suppress this aggregation, it is effective to use a nano-sized conductive carbon powder having a large surface area, and it is important that the carbon powder and the tin oxide powder are present in a highly dispersed state. It is preferable that the porous carbon powder has voids and the tin oxide powder is substantially present in the voids. This is because it has been found that the aggregation of the negative electrode active material is particularly induced by the tin oxide powder supported on the outer surface of the conductive carbon powder. In addition to the pores of porous carbon powder, “voids” include internal pores of Ketjen Black (registered trademark: hereinafter simply referred to as “Ketjen Black”) , carbon nanotubes and carbon nanotube tubes. Voids and intertube gaps are also included. The term “tin oxide is substantially present in the void” means that 95% by mass or more, preferably 98% by mass or more, particularly preferably 99% by mass or more of the entire tin oxide is present in the void. Means that

  Among them, as the conductive carbon powder, it is preferable to use ketjen black having a hollow shell structure and having open cells connecting the inner surface and the outer surface of the shell. Ketjen Black has a large surface area and a large amount of oxygen (surface functional group oxygen, adsorbed oxygen) on the inner and outer surfaces and the edge surface, so abundant formation of Sn-O-C bonds and the above metastable states Is done. In addition, since nano-sized tin oxide powder can be preferentially supported in the internal pores of the ketjen black, aggregation of the negative electrode active material occurring in the conversion reaction region is suppressed, and the alloying reaction region is The volume expansion of tin is effectively suppressed.

  The first negative electrode active material of the present invention can further include a low-conductivity amorphous carbon film covering the surface of the conductive carbon powder. Of the active points on the surface of the conductive carbon powder that catalyze the electrochemical decomposition of the electrolytic solution, the active points that are not covered with the metal oxide are effectively covered with the low-conductivity amorphous carbon film, and the electrolytic solution This is thought to be due to the effective inhibition of the electrochemical decomposition of the metal, but the initial irreversible capacity of the negative electrode active material is greatly reduced by the synergistic effect of the metal oxide and the low-conductivity amorphous carbon film, In addition, the reversible progress of the conversion reaction is maintained as it is. The surface state of the amorphous carbon film is the same as the surface state of the conductive carbon powder. However, since the amorphous carbon film has low conductivity, electrons necessary for the electrochemical decomposition of the electrolytic solution are not generated. It is difficult to be supplied to the surface of the amorphous carbon film, and therefore, electrochemical decomposition of the electrolytic solution on the surface of the amorphous carbon film is suppressed.

  The low-conductivity amorphous carbon film is preferably a film obtained by incomplete combustion of glutamic acid. A dense film is obtained by incomplete combustion of glutamic acid. And it seems that among the active sites on the surface of the conductive carbon powder, the active sites not covered with the metal oxide are covered with this dense film, but the initial irreversible capacity of the negative electrode active material is remarkable. To reduce.

  The present invention further relates to a negative electrode active material capable of occluding and releasing lithium in which a conductive carbon powder having nanosize and a tin oxide powder are contained in a highly dispersed state. The present invention relates to a second negative electrode active material, further comprising a low-conductivity amorphous carbon film that is in contact with the tin oxide powder and covers the surface of the conductive carbon powder.

In the second negative electrode active material of the present invention, Sn—O—C bonds are likely to occur due to the nano-sized conductive carbon powder and tin oxide powder that are present in a highly dispersed state, and therefore the above formula (III) after the conversion reaction. As a result, the charge / discharge cycle in the range of 0V to about 2V can be realized with respect to the Li / Li ⁺ electrode, and the discharge capacity can be greatly increased. Can do. Also, it seems that the active sites on the surface of the conductive carbon powder that catalyze the electrochemical decomposition of the electrolyte solution are covered with a low-conductivity amorphous carbon film, which inhibits the electrochemical decomposition of the electrolyte solution. However, the initial irreversible capacity is reduced. As described above, the surface state of the amorphous carbon film is the same as the surface state of the conductive carbon powder. However, because the amorphous carbon film has low conductivity, the electrolyte solution is electrochemically decomposed. Therefore, the electrons necessary for this are difficult to be supplied to the surface of the amorphous carbon film, and thus the electrochemical decomposition of the electrolytic solution on the surface of the amorphous carbon film is suppressed. Therefore, the second negative electrode active material of the present invention is a negative electrode active material having a high reversible capacity and a reduced initial irreversible capacity.

In the second negative electrode active material as well as the first negative electrode active material of the present invention, the low-conductivity amorphous carbon film is preferably a film obtained by incompletely burning glutamic acid. In addition, the nano-sized conductive carbon powder is preferably a nano-sized spherical particle, and may be conductive, but a smaller particle size is preferable, and a spherical particle having an average particle size of 10 to 50 nm. Particular preference is given to particles. The tin oxide powder also preferably has a nanosize, and particularly preferably spherical particles having a nanosize, particularly fine spherical particles having an average particle diameter of 1 to 10 nm. Conductive carbon powder having nano-sized and low-conductivity amorphous carbon coating on the surface, preferably spherical particles, and tin oxide powder having nano-size supported thereon, preferably spherical particles. It has reversible capacity, reduced initial irreversible capacity, and in addition, the cycle characteristics are small in discharge capacity even in the charge / discharge cycle test in the range of 0V to about 2V with respect to the Li / Li ⁺ electrode. A very good negative electrode active material can be obtained.

  Further, in the second negative electrode active material of the present invention as well as the first negative electrode active material of the present invention, the conductive carbon powder has voids, and the tin oxide powder is substantially present in the voids. In particular, it is preferable to use ketjen black having a hollow shell structure and having open cells connecting the inner surface and the outer surface of the shell as the conductive carbon powder.

  Of the first negative electrode active material and the second negative electrode active material of the present invention, the negative electrode active material in a form in which the tin oxide powder is a spherical particle having a nanosize and is supported on the conductive carbon powder, By utilizing the sol-gel reaction and dispersion in a centrifugal field, it can be suitably produced.

  Therefore, the present invention also provides a reaction solution in which a conductive carbon powder having nanosize is added to a solution in which a metal oxide precursor other than a tin oxide precursor and a tin oxide precursor is dissolved in a swirlable reactor. And the reaction of the hydrolysis and polycondensation reaction of the tin oxide precursor and the metal oxide precursor while applying shear stress and centrifugal force to the reaction solution by turning the reactor. It is related with the manufacturing method of the 1st negative electrode active material characterized by including the process of carrying | supporting the obtained reaction product on the conductive carbon powder which has the said nano size in a highly dispersed state simultaneously with performing.

  In the present specification, the “tin oxide precursor” means a compound that changes to tin oxide through the production process of the negative electrode active material. The “metal oxide precursor” means a compound that changes to a metal oxide through the production process of the negative electrode active material, and excludes a tin oxide precursor. Furthermore, the term “amorphous carbon precursor” to be described later means a compound that is thermally decomposed (incomplete combustion) and changes to amorphous carbon by heat treatment, and excludes a compound that volatilizes before thermal decomposition. Further, in this specification, four types of negative electrode active materials, that is, a negative electrode active material containing a nanosized conductive carbon powder and a tin oxide powder in a highly dispersed state, and a nanosized conductive carbon powder. And a tin oxide powder are included in a highly dispersed state, and a negative active material further including a metal oxide, a nano-sized conductive carbon powder and a tin oxide powder are included in a highly dispersed state, and low conductivity Negative electrode active material further comprising a conductive amorphous carbon film, and a conductive carbon powder and a tin oxide powder having nano-size are contained in a highly dispersed state, and a metal oxide and a low-conductivity amorphous carbon film A negative electrode active material further comprising: Among these, the negative electrode active material in which the conductive carbon powder and the tin oxide powder having nano size are included in a highly dispersed state, and the conductive carbon powder and the tin oxide powder having a nano size are included in a highly dispersed state. The negative electrode active material further including a metal oxide is often referred to as a “composite”.

  In this production method, it is considered that mechanical energy of both shear stress and centrifugal force is simultaneously applied to the reaction solution, and this mechanical energy is converted to chemical energy. The hydrolysis reaction and polycondensation reaction of the tin oxide precursor and the metal oxide precursor can be performed, and the reaction product obtained at the same time can be supported on the conductive carbon powder in a highly dispersed state. As a result, spherical particles of nano-sized tin oxide are supported on the conductive carbon powder in a highly dispersed state, and the metal oxide is at least on the surface of the conductive carbon powder that is not in contact with the tin oxide. A supported negative electrode active material is obtained.

  In particular, when ketjen black is used as the conductive carbon powder, spherical particles of nano-sized tin oxide in the inner pores of the ketjen black, preferably spherical particles having an average particle diameter of 1 to 10 nm, particularly preferably 1 Since spherical particles having an average particle diameter of ˜2 nm can be effectively supported, aggregation of the negative electrode active material generated in the conversion reaction region is suppressed, and further, the volume expansion of tin in the alloying reaction region is effective by the shell. Therefore, it is extremely preferable.

In the manufacturing method, when a thin film containing the tin oxide precursor and the metal oxide precursor is generated in the swirling reactor and shear stress and centrifugal force are applied to the thin film, the tin oxide in the thin film is formed. A large shear stress and centrifugal force are applied to the precursor and the metal oxide precursor, and further hydrolysis and polycondensation reactions can be promoted. For the above reaction, it is preferable to use a reactor that is composed of a concentric cylinder of an outer cylinder and an inner cylinder, a through-hole is provided on the side surface of the inner cylinder, and a slat is arranged at the opening of the outer cylinder. it can. Then, the reaction liquid in the inner cylinder is moved to the inner wall surface of the outer cylinder through the through-hole of the inner cylinder by centrifugal force due to the turning of the inner cylinder, and the tin oxide precursor and the metal oxide precursor are transferred to the inner wall surface of the outer cylinder. In addition to generating a thin film containing a body, hydrolysis and polycondensation reaction of the tin oxide precursor and the metal oxide precursor are promoted while applying shear stress and centrifugal force to the thin film. Here, by setting the thickness of the thin film to 5 mm or less, and setting the centrifugal force applied to the reaction liquid in the inner cylinder of the reactor to 1500 kgms ⁻² or more, the spherical particles of tin oxide and the metal oxide The effect of making fine particles and increasing the dispersion can be enhanced.

  In addition, the nano-sized tin oxide spherical particles and the metal oxide are supported on the conductive carbon powder, and further includes a low-conductivity amorphous carbon film covering the surface of the conductive carbon powder. A very preferable first negative electrode active material is a kneaded product of a negative electrode active material (composite) and an amorphous carbon precursor obtained by the production method using the sol-gel reaction and dispersion in the ultracentrifugal force field described above. And a process of thermally decomposing the amorphous carbon precursor to form a low-conductivity amorphous carbon film by heat-treating the kneaded product. It can be obtained by a method. As the amorphous carbon precursor, a compound that is thermally decomposed (incompletely burned) by heat treatment and changes to amorphous carbon having low conductivity can be used without any particular limitation. Examples include monosaccharides, oligosaccharides, polysaccharides, hydroxy acids, fatty acids, polyols, amino acids, and derivatives thereof. Glutamic acid can be particularly preferably used as the amorphous carbon precursor.

  By kneading the composite and the amorphous carbon precursor, an amorphous carbon precursor layer is formed on at least a portion of the surface of the conductive carbon powder that is not in contact with tin oxide and metal oxide. Is done. Furthermore, when the kneaded material is heat-treated and the amorphous carbon precursor is pyrolyzed to be converted into amorphous carbon having low conductivity, it contacts at least tin oxide and metal oxide on the surface of the conductive carbon powder. A low-conductivity amorphous carbon film is formed on the unexposed portion. By this method, a negative electrode active material in which the initial irreversible capacity is significantly reduced by the synergistic effect of the metal oxide and the low-conductivity amorphous carbon film can be obtained. In general, the amorphous carbon precursor penetrates into gaps formed between adjacent grains of the composite during kneading, and is a low-conductivity, which is a thermal decomposition product of the amorphous carbon precursor during thermal decomposition. Since the amorphous carbon layer is formed also in this gap portion, the specific surface area of the finally obtained negative electrode active material is lower than the specific surface area of the composite. This is also considered to contribute to a decrease in the initial irreversible capacity.

  The present invention also includes a step of introducing a reaction solution in which a conductive carbon powder having nanosize is added to a solution in which a tin oxide precursor is dissolved in a swirlable reactor, swirling the reactor, and The tin oxide precursor is hydrolyzed and polycondensed while applying shear stress and centrifugal force to the reaction solution, and at the same time, the resulting reaction product is highly dispersed in the conductive carbon powder having the nanosize. A step of supporting the amorphous carbon precursor by heat-treating the kneaded product, a step of obtaining a kneaded product of the conductive carbon powder carrying the reaction product and an amorphous carbon precursor, The present invention relates to a method for producing a second negative electrode active material comprising a step of thermally decomposing to form a low-conductivity amorphous carbon film.

  In this manufacturing method, mechanical energy of both shear stress and centrifugal force is applied to the reaction solution at the same time, and this mechanical energy is considered to be converted into chemical energy. A hydrolysis reaction and a polycondensation reaction of the tin precursor can be performed, and at the same time, the obtained reaction product can be supported on the conductive carbon powder in a highly dispersed state. Then, when the conductive carbon powder carrying the obtained reaction product is dried as necessary, nano-sized conductive carbon powder and nano-sized tin oxide spherical particles are contained in a highly dispersed state. Negative electrode active material (composite) is obtained. Subsequently, by kneading the composite and the amorphous carbon precursor, an amorphous carbon precursor layer is formed at least on the surface of the conductive carbon powder that is not in contact with tin oxide. Is done. Furthermore, when the kneaded material is heat-treated and the amorphous carbon precursor is thermally decomposed to change to amorphous carbon having low conductivity, at least a portion of the surface of the conductive carbon powder that is not in contact with tin oxide is applied. A low conductivity amorphous carbon film is formed. Also in this production method, generally, the amorphous carbon precursor penetrates into a gap formed between adjacent grains of the composite during kneading, and is a pyrolysis product of the amorphous carbon precursor during thermal decomposition. Since a certain low-conductivity amorphous carbon layer is formed also in this gap portion, the specific surface area of the finally obtained negative electrode active material is lower than the specific surface area of the composite. This is also considered to contribute to a decrease in the initial irreversible capacity. Also in this production method, it is preferable to use ketjen black as the conductive carbon powder, and it is preferable to use glutamic acid as the amorphous carbon precursor.

In this production method, when a thin film containing the tin oxide precursor is generated in the swirling reactor and shear stress and centrifugal force are applied to the thin film, a large shear stress is applied to the tin oxide precursor in the thin film. Centrifugal force is applied, and further hydrolysis reaction and polycondensation reaction can be promoted. Also in this manufacturing method, for the above reaction, a reactor comprising a concentric cylinder of an outer cylinder and an inner cylinder, a through hole provided in the side surface of the inner cylinder, and a slat plate disposed at the opening of the outer cylinder is preferable. Can be used for Then, the reaction liquid in the inner cylinder is moved to the inner wall surface of the outer cylinder through the through hole of the inner cylinder by the centrifugal force generated by the rotation of the inner cylinder, and a thin film containing the tin oxide precursor is generated on the inner wall surface of the outer cylinder. At the same time, hydrolysis and polycondensation reaction of the tin oxide precursor are promoted while applying shear stress and centrifugal force to the thin film. Here, by setting the thickness of the thin film to 5 mm or less, and setting the centrifugal force applied to the reaction liquid in the inner cylinder of the reactor to 1500 kgms ⁻² or more, the spherical particles of tin oxide can be made fine particles. The effect of high dispersion can be enhanced.

  Since the first negative electrode active material and the second negative electrode active material of the present invention have a high reversible capacity and a reduced initial irreversible capacity, they are suitable for lithium ion secondary batteries. Therefore, the present invention further provides a lithium ion secondary battery comprising a negative electrode containing these negative electrode active materials, a positive electrode, and a separator holding a non-aqueous electrolyte disposed between the negative electrode and the positive electrode. . In addition, the negative electrode active material of the present invention can also be suitably used to form a hybrid capacitor in combination with a positive electrode active material such as activated carbon.

  In the present invention, a negative electrode active material capable of occluding and releasing lithium containing nano-sized conductive carbon powder and tin oxide powder in a highly dispersed state, further comprising a metal oxide other than tin oxide In addition, the tin oxide powder and the metal oxide are in contact with the surface of the conductive carbon powder, or the tin oxide powder is in contact with the surface of the conductive carbon powder. The negative electrode active material further comprising a low-conductivity amorphous carbon film covering the surface of the conductive carbon powder has a high reversible capacity and a reduced initial irreversible capacity. Have. In particular, the negative electrode active material including the conductive carbon powder having both the metal oxide and the amorphous carbon film on the surface has a large initial irreversible capacity due to the synergistic effect of the metal oxide and the amorphous carbon film. To reduce. Therefore, the negative electrode active material of the present invention is extremely promising as a negative electrode active material that can replace graphite in lithium ion secondary batteries and hybrid capacitors.

It is an X-ray powder diffractogram of a negative electrode active material, (A)-(C) are diffractograms about a negative electrode active material of an example, and (D) is a diffractogram about a negative electrode active material of a comparative example. It is the figure which showed the relationship between the electric potential in the charging / discharging of the 1st time in the electric potential area | region containing the conversion reaction area | region about the negative electrode active material of a comparative example, and the primary differentiation of charging / discharging capacity | capacitance. It is the figure which showed the relationship between the electric potential in the 2nd charging / discharging in the electric potential area | region containing the conversion reaction area | region about the negative electrode active material of a comparative example, and the primary differentiation of charging / discharging capacity | capacitance. It is the figure which showed the relationship between the electric potential in the charging / discharging of the 1st time in the electric potential area | region containing the conversion reaction area | region about the negative electrode active material of an Example, and the primary differentiation of charging / discharging capacity | capacitance. It is the figure which showed the relationship between the electric potential in the charging / discharging of the 1st time in the electric potential area | region containing the conversion reaction area | region about the negative electrode active material of an Example, and the primary differentiation of charging / discharging capacity | capacitance. It is the figure which showed the relationship between the electric potential in the charging / discharging of the 1st time in the electric potential area | region containing the conversion reaction area | region about the negative electrode active material of an Example, and the primary differentiation of charging / discharging capacity | capacitance. It is the figure which showed the relationship between the electric potential in the 1st discharge about Ketjen Black, and the first derivative of discharge capacity. It is the figure which showed the change of the discharge capacity in the charging / discharging cycle test in the electric potential area | region containing a conversion reaction area | region. It is the figure which showed the capacity | capacitance maintenance factor in the charging / discharging cycle test in the electric potential area | region containing a conversion reaction area | region. It is an X-ray powder diffractogram of a negative electrode active material.

(1) 1st negative electrode active material The 1st negative electrode active material of this invention can occlude and discharge | release lithium containing the electroconductive carbon powder and tin oxide powder which have nanosize in a highly dispersed state The negative electrode active material further includes a metal oxide other than tin oxide, and the tin oxide powder and the metal oxide are in contact with the surface of the conductive carbon powder. It seems that the active sites on the surface of the conductive carbon powder that catalyzes the electrochemical decomposition of the electrolyte solution of the lithium ion secondary battery are covered with the metal oxide, but the initial irreversible capacity is reduced, and The reversible progression of the conversion reaction is maintained as it is.

The tin oxide powder contained in the negative electrode active material can be tin dioxide or a mixture of tin dioxide and tin monoxide. The tin oxide powder does not need to have a nano size, but if the tin oxide powder has a nano size, the surface area of the tin oxide increases and the contact point with the carbon powder having the nano size increases. Therefore, the Sn—O—C bond is formed at more sites, and therefore, the metastable state shown in the above formula (III) is easily formed after the conversion reaction, which is preferable. In addition, if the average particle size of the tin oxide powder is small, fine tin will be dispersed in the lithium oxide matrix after the conversion reaction, and a large volume change of tin accompanying lithium occlusion and release in the reversible alloying reaction Is suppressed, the reaction site of the tin oxide powder is increased, and the diffusion distance in the tin oxide powder is shortened. As nano-sized tin oxide, nano-sized spherical particles as well as nanowires and nanotubes can be used, but spherical particles, preferably spherical particles having an average particle diameter of 1 to 10 nm, particularly preferably 1 to 2 nm. It is preferable to use spherical particles having an average particle size of Conductive carbon powder having nanosize, preferably spherical particles, and tin oxide powder having nanosize supported thereon, preferably spherical particles, have high reversible capacity and reduced initial irreversible capacity In addition, in the charge / discharge cycle test in the range of 0 V to about 2 V with respect to the Li / Li ⁺ electrode, a negative electrode active material having a very good cycle characteristic can be obtained with little decrease in discharge capacity.

  Nano-sized conductive carbon powder includes nano-sized carbon black such as ketjen black, acetylene black, channel black, fullerene, carbon nanotube, carbon nanofiber, amorphous carbon, carbon fiber, natural graphite, artificial graphite , Graphitized ketjen black, activated carbon, mesoporous carbon and the like. Also, vapor grown carbon fiber can be used. These carbon powders may be used alone or in combination of two or more.

It is considered that the conversion reaction proceeds reversibly due to the formation of Sn—O—C bonds via oxygen in the conductive carbon powder. It is preferable that oxygen atoms are contained abundantly. Therefore, a carbon powder having a large surface area is preferable, a surface area per 1 g of the carbon powder is particularly preferably 1000 m ² or more, a fine carbon powder is preferable, and spherical particles having an average particle diameter of 10 to 50 nm are used. It is particularly preferred to use it. In terms of the amount of oxygen in the carbon powder, the amount of oxygen per gram of carbon powder is preferably 5.0 mmol or more. Here, “the amount of oxygen per 1 g of carbon powder” is a TG measurement of the carbon powder used for the negative electrode active material at a temperature rising rate of 1 ° C./min in the range of 30 to 1000 ° C. in a nitrogen atmosphere. The oxygen amount calculated on the assumption that all the weight loss in the range of 150 to 1000 ° C. was desorbed as CO ₂ . For example, if the weight loss amount in the range of 150 to 1000 ° C. of 1 g of carbon powder is 22 mg, the oxygen amount per 1 g of carbon powder is calculated as 1 mmol. Examples of such carbon powder include nano-sized spherical carbon black, preferably ketjen black.

  In order to obtain a negative electrode active material having good cycle characteristics in the potential range including the conversion reaction region, not only the stress due to volume change in the alloying reaction region but also the aggregation of the negative electrode active material occurring in the conversion reaction region is suppressed. I know it is important to do. In order to suppress this aggregation, it is effective to use nano-sized conductive carbon powder having a large surface area, and it is important that this carbon powder and tin oxide are present in a highly dispersed state. It is preferable that the conductive carbon powder has voids such as ketjen black, carbon nanotube, carbon nanofiber, and porous carbon, and the tin oxide powder is substantially present in the voids. This is because it has been found that the aggregation of the negative electrode active material is particularly induced by tin oxide supported on the outer surface of the conductive carbon powder.

  Therefore, it is preferable to use ketjen black having a hollow shell structure as the conductive carbon powder. Ketjen Black has a large surface area and a large amount of oxygen (surface functional group oxygen, adsorbed oxygen) on the inner and outer surfaces and the edge surface, so that Sn—O—C bonds are abundantly formed. The metastable state shown in (III) is abundantly formed. In addition, since the nano-sized tin oxide powder can be preferentially supported in the internal pores of the ketjen black, the aggregation of the negative electrode active material occurring in the conversion reaction region is suppressed, and the shell is further in the alloying reaction region. This is preferable because volume expansion of tin is suppressed.

  The metal oxide that is in contact with at least the portion of the surface of the conductive carbon powder that is not in contact with tin oxide is amorphous or nano-sized microcrystals. There are no particular limitations on the metal constituting the metal oxide, Fe, Co, Ni, Cu, Zn, Al, Si, Ti, Zr, La, V, Cr, Mo, W, Mn, Re, Ru, Rh, Pd, Pt, Ag, Sb, Pb, Bi etc. can be illustrated. The above-mentioned metal oxide is any oxide in the case where there are a plurality of oxides containing the same kind of metal such as diiron trioxide, triiron tetroxide, and iron monoxide but having different valences. It may be a composite oxide containing two or more metals. The metal oxide may be a single compound or a mixture of two or more compounds. In particular, iron oxide is preferable because it is easy to make fine particles.

  The first negative electrode active material preferably includes a low-conductivity amorphous carbon film that covers at least a portion of the surface of the conductive carbon powder that is not in contact with tin oxide and metal oxide. Of the active points on the surface of the conductive carbon powder that catalyze the electrochemical decomposition of the electrolytic solution, the active points that are not covered with the metal oxide are effectively covered with the low-conductivity amorphous carbon film, and the electrolytic solution This is thought to be due to the effective inhibition of the electrochemical decomposition of the metal, but the initial irreversible capacity of the negative electrode active material is greatly reduced by the synergistic effect of the metal oxide and the low-conductivity amorphous carbon film.

  In the method for producing the first negative electrode active material that does not include the low-conductivity amorphous carbon film that covers the surface of the conductive carbon powder, a highly dispersed state of the tin oxide powder and the conductive carbon powder is realized. The method is not particularly limited. For example, after the conductive carbon powder is mixed with the tin oxide precursor and the metal oxide precursor in the dispersion medium, and the tin oxide precursor and the metal oxide precursor are reacted with the surface functional groups of the conductive carbon powder, By performing the heat treatment, the tin oxide precursor and the metal oxide precursor can be changed into tin oxide and a metal oxide. Conductive carbon powder is mixed with a tin oxide precursor in a dispersion medium, and the tin oxide precursor and the surface functional group of the conductive carbon powder are reacted and heat-treated to change the tin oxide precursor to tin oxide. After that, the obtained product and the metal oxide precursor are mixed in a dispersion medium, and the surface functional group of the product and the metal oxide precursor are reacted and heat-treated to obtain a metal oxide precursor. The body can also be changed to a metal oxide. In addition, the conductive carbon powder is mixed with the metal oxide precursor in the dispersion medium, and the metal oxide precursor and the surface functional group of the conductive carbon powder are reacted and heat-treated to thereby convert the metal oxide precursor. After changing to a metal oxide, the obtained product and a tin oxide precursor are mixed in a dispersion medium, and the surface functional group of the product and the tin oxide precursor are reacted and heat-treated, It is also possible to change the tin oxide precursor to tin oxide.

  Examples of the tin oxide precursor include inorganic metal compounds such as tin dichloride, tin tetrachloride, tin nitrate, and tin carbonate; organometallic compounds such as tin acetate, tin lactate, tetramethoxytin, tetraethoxytin, and tetraisopropoxytin; Alternatively, a mixture of these can be used. Examples of the metal oxide precursor include inorganic metal compounds such as chlorides, nitrates, and carbonates of various metals, organic metal compounds such as acetates, lactates, tetraethoxides, tetraisopropoxides, tetrabutoxides, or the like. Mixtures can be used. When a medium that can dissolve the tin oxide precursor and the metal oxide precursor and does not adversely affect the reaction is used as the dispersion medium, it is preferable because the tin oxide and the metal oxide in the negative electrode active material to be obtained become fine particles.

  The first negative electrode active material that does not include the low-conductivity amorphous carbon film that covers the surface of the conductive carbon powder is manufactured by a method in which the sol-gel method and the dispersion are simultaneously performed in the ultracentrifugal field shown below. Is very preferred. By this reaction, conductive carbon powder having a nanosize, preferably spherical particles having a particle size of 10 to 50 nm, particularly preferably Ketjen Black, tin oxide spherical particles having a nanosize, preferably 1 to 10 nm. Spherical particles having an average particle diameter, particularly preferably spherical particles having an average particle diameter of 1 to 2 nm can be supported in a highly dispersed state, and Sn—O—C bonds can be formed at more sites. At the same time, the amorphous or nano-sized microcrystalline metal oxide can be supported on at least a portion of the surface of the conductive carbon powder that is not in contact with the tin oxide. In particular, when Ketjen Black is used as the conductive carbon powder, spherical particles of nano-sized tin oxide are formed in the inner pores of Ketjen Black by the method of simultaneously performing the sol-gel method and dispersion in the following ultracentrifugal force field. It can be carried effectively.

  In the ultracentrifugal force field, the sol-gel method and dispersion are simultaneously performed by adding nano-sized conductive carbon powder to a solution in which a tin oxide precursor and a metal oxide precursor are dissolved in a swirlable reactor. A step of introducing the reaction solution, and a reaction of hydrolysis and polycondensation reaction of the tin oxide precursor and the metal oxide precursor while rotating the reactor and applying shear stress and centrifugal force to the reaction solution. And simultaneously carrying the obtained reaction product on the conductive carbon powder having the nano size in a highly dispersed state. By this method, mechanical energy of both shear stress and centrifugal force can be applied to the reaction solution at the same time, which is thought to be due to the conversion of this mechanical energy into chemical energy. The hydrolysis reaction and polycondensation reaction of the precursor and the metal oxide precursor can be performed, and the reaction product obtained at the same time can be supported on the conductive carbon powder in a highly dispersed state. A method of simultaneously performing the sol-gel method and dispersion in this ultracentrifugal force field is disclosed in Japanese Patent Application Laid-Open No. 2007-160151 by the applicant by an example in which titanium oxide and ruthenium oxide are supported on carbon powder with high dispersion. However, the description of the swirlable reactor and the description of the sol-gel reaction using this reactor in this publication are incorporated herein by reference in their entirety. It is very preferable not to add a reaction inhibitor for the hydrolysis reaction and polycondensation reaction to the reaction solution containing the tin oxide precursor and metal oxide precursor and the conductive carbon powder.

  A method of simultaneously performing the sol-gel method and dispersion in an ultracentrifugal force field includes a concentric cylinder of an outer cylinder and an inner cylinder, as shown in FIG. 1 of Japanese Patent Application Laid-Open No. 2007-160151. Can be carried out using a reactor in which a plate is arranged at the opening of the outer cylinder.

In this reaction, examples of the tin oxide precursor include inorganic metal compounds such as tin dichloride, tin tetrachloride, tin nitrate, and tin carbonate, tin acetate, tin lactate, tetramethoxytin, tetraethoxytin, and tetraisopropoxytin. Organometallic compounds or mixtures thereof can be used. Examples of the metal oxide precursor include inorganic metal compounds such as chlorides, nitrates, and carbonates of various metals, organic metal compounds such as acetates, lactates, tetraethoxides, tetraisopropoxides, tetrabutoxides, or the like. Mixtures can be used. As a solvent for dissolving these precursors, any solvent can be used without particular limitation as long as it can dissolve these precursors and does not adversely affect the reaction. Water, methanol, ethanol, isopropyl alcohol Etc. can be used suitably. For hydrolysis, a solution in which NaOH, KOH, Na ₂ CO ₃ , NaHCO ₃ , NH ₄ OH, or the like is dissolved in the above-described solvent can be used. Water can also be used for hydrolysis of the tin oxide precursor and the metal oxide precursor.

  And the solution which melt | dissolved the tin oxide precursor and the metal oxide precursor and the conductive carbon powder mentioned above are introduce | transduced into the inner cylinder of the said reactor, a tin oxide precursor and a metal oxide are rotated by rotating an inner cylinder The precursor and conductive carbon powder are mixed and dispersed. Further, an alkaline solution for hydrolysis of the tin oxide precursor and the metal oxide precursor is added, and the inner cylinder is swung again. A thin film containing a tin oxide precursor and a metal oxide precursor on the inner wall surface of the outer cylinder by the reaction liquid in the inner cylinder moving to the inner wall surface of the outer cylinder through the through hole of the inner cylinder by the centrifugal force generated by the rotation of the inner cylinder This thin film rises to the upper part of the inner wall of the outer cylinder. As a result, it seems that shear stress and centrifugal force are applied to this thin film, and this mechanical energy is converted to chemical energy necessary for the reaction, so-called activation energy, but tin oxide precursor and metal oxide precursor. The hydrolysis and polycondensation reaction proceed in a short time.

  In the above reaction, the mechanical energy applied increases as the thickness of the thin film decreases. The thickness of the thin film is generally 5 mm or less, preferably 2.5 mm or less, and particularly preferably 1.0 mm or less. The thickness of the thin film can be set by the width of the reactor plate and the amount of the reaction liquid introduced into the reactor.

The reaction is considered to be realized by the mechanical energy of shear stress and centrifugal force applied to the reaction solution, and this shear stress and centrifugal force are generated by the centrifugal force applied to the reaction solution by the rotation of the inner cylinder. The centrifugal force applied to the reaction solution in the inner cylinder is generally 1500 kgms ⁻² or more, preferably 70000 kgms ⁻² or more, particularly preferably 270000 kgms ⁻² or more.

  After the reaction is complete, the inner cylinder stops turning, and the conductive carbon powder is recovered and dried, so that nanosized tin oxide spherical particles are supported in a highly dispersed state on the surface of the conductive carbon powder. A negative electrode active material in which an amorphous or nano-sized microcrystalline metal oxide is supported on at least a portion of the surface of the conductive carbon powder that is not in contact with tin oxide can be obtained.

  In the sol-gel method in the ultracentrifugal field using this reactor, depending on the type of conductive carbon powder used, spherical particles of tin dioxide and nanoparticle of tin monoxide supported on the conductive carbon powder The ratio of changes. When a carbon powder having a large surface area and a nanosize containing abundant oxygen atoms (surface functional group oxygen, adsorbed oxygen) is used, the proportion of spherical particles of tin dioxide increases. When ketjen black suitable as conductive carbon powder is used, tin oxide is only tin dioxide as long as it is judged from the X-ray powder diffraction pattern even if a divalent tin salt is used as a raw material. Consists of. Further, according to the TEM photograph, the spherical particles of tin dioxide are preferentially carried in the internal holes of the ketjen black.

  Furthermore, in the method of simultaneously performing the sol-gel method and the dispersion described above, polyvinyl alcohol can be used in combination with the tin oxide precursor and the metal oxide precursor. Here, the term “polyvinyl alcohol” does not mean that polyvinyl acetate has a saponification degree of 100%, but a saponification degree of 80% or more. In this form, the hydrolysis reaction and polycondensation reaction of the tin oxide precursor and the metal oxide precursor can be performed, and the reaction product of the nano-sized spherical tin oxide precursor and metal oxide precursor is obtained. At the same time, the reaction product of the tin oxide precursor and the metal oxide precursor can be supported in a highly dispersed state on the conductive carbon powder. At the same time, the strong interaction between the tin oxide precursor and / or the reaction product of the tin oxide precursor and the hydroxyl group of the polyvinyl alcohol and / or the oxygen ion from which the hydroxyl group is dissociated causes polyvinyl alcohol to react with the tin oxide precursor. It can be attached to the surface of the reaction product. Moreover, the particle size of the reaction product of the tin oxide precursor is made finer than that of the reaction product obtained from the reaction solution that does not use polyvinyl alcohol. Next, the obtained product is dried, and polyvinyl alcohol is subjected to thermal decomposition (incomplete combustion) under a non-oxidizing atmosphere, preferably in an inert atmosphere such as nitrogen or argon, at a temperature of about 500 ° C. or lower. A spherical particle of tin oxide having a size, preferably a spherical particle having an average particle diameter of 1 to 10 nm, particularly preferably a surface of the conductive carbon powder among the surfaces of spherical particles having an average particle diameter of 1 to 2 nm; The non-contact portion is covered with an amorphous carbon thin film derived from polyvinyl alcohol. Thermal decomposition (incomplete combustion) in a non-oxidizing atmosphere can be performed simultaneously with thermal decomposition of the amorphous carbon precursor in the production of the following negative electrode active material. Since the amorphous carbon film derived from this polyvinyl alcohol suppresses the aggregation of the negative electrode active material in the charge / discharge cycle experience, even if the tin oxide powder is present on the outer surface of the conductive carbon powder, this form is good. Cycle characteristics can be obtained. When a suitable ketjen black is used as the conductive carbon powder, the composite can contain more tin oxide than can be accommodated in the inner cavities of the ketjen black, and a swivelable reactor. Even if the mass of the tin oxide precursor in the reaction solution introduced into the quaternary is increased to a range of 1.5 to 4 times the mass of ketjen black in terms of tin dioxide, good cycle characteristics can be obtained. “Tin dioxide conversion” means that the mass is calculated on the assumption that all of the tin contained in the tin oxide precursor has changed to tin dioxide.

  The negative electrode active material further comprising a low-conductivity amorphous carbon film covering a portion of the surface of the conductive carbon powder that is not in contact with tin oxide and metal oxide is a sol-gel in the ultracentrifugal field described above. A kneading step of kneading a negative electrode active material (composite) and an amorphous carbon precursor obtained by the method of simultaneously performing the process and dispersion to obtain a kneaded product, and heat treating the kneaded product Can be suitably obtained by carrying out a heat treatment step of thermally decomposing the amorphous carbon precursor to form a low-conductivity amorphous carbon film. By this production method, a negative electrode active material in which the initial irreversible capacity is significantly reduced by the synergistic effect of the metal oxide and the low-conductivity amorphous carbon can be obtained.

  Amorphous carbon precursors include amino acids such as glutamic acid and aspartic acid, monosaccharides such as glucose and mannose, oligosaccharides such as lactose and maltotriose, polysaccharides such as starch, cellulose and dextrin, malic acid, tartaric acid and citramalic acid Hydroxy acids such as, fatty acids such as palmitic acid, stearic acid, oleic acid, linoleic acid, polyols such as ethylene glycol, glycerin, erythritol, arabinitol, polyethylene glycol, polyvinyl alcohol, and derivatives thereof such as carboxymethyl cellulose, hydroxypropyl Examples thereof include cellulose, oleodistearin, oleodipalmitin and the like. Glutamic acid can be particularly preferably used as the amorphous carbon precursor. A dense amorphous carbon film is obtained from glutamic acid by the heat treatment step. And, it seems that the active points that are not covered with the metal oxide among the active points on the surface of the conductive carbon powder that catalyze the electrochemical decomposition of the electrolytic solution are covered with this dense film. The initial irreversible capacity of the negative electrode active material is significantly reduced.

  In the kneading process, a composite, an amorphous carbon precursor, and an appropriate amount of a dispersion medium are combined, and a kneaded product is obtained by kneading while evaporating the dispersion medium as necessary. As a dispersion medium for kneading, any medium that does not adversely affect the composite can be used without particular limitation, and water, methanol, ethanol, isopropyl alcohol, and the like can be preferably used. Use of a dispersion medium capable of dissolving the amorphous carbon precursor is preferable because a uniform amorphous carbon film is easily formed, and an acidic dispersion or an alkaline dispersion can be used as necessary. The ratio of the composite to the amorphous carbon precursor is generally in the range of 3: 1 to 1: 3, preferably in the range of 1.5: 1 to 1: 1.5, by mass ratio. By this kneading step, an amorphous carbon precursor layer is formed at least on the surface of the conductive carbon powder that is not in contact with the tin oxide and the metal oxide. In general, the amorphous carbon precursor also enters a gap formed between adjacent grains of the composite. Next, in the heat treatment step, the kneaded product obtained is dried as necessary and then heat treated, and preferably heat treatment at about 500 ° C. or less in an inert atmosphere such as nitrogen or argon, or about 200 in vacuum. The amorphous carbon precursor is thermally decomposed (incomplete combustion) and converted into amorphous carbon having a low conductivity by performing a heat treatment at a temperature not higher than ° C. By this heat treatment step, a low-conductivity amorphous carbon film is formed on at least a portion of the surface of the conductive carbon powder that is not in contact with tin oxide and metal oxide. In general, a low-conductivity amorphous carbon layer is also formed in a gap formed between adjacent grains of the composite. Accordingly, the specific surface area of the finally obtained negative electrode active material is generally lower than the specific surface area of the composite. This is also considered to contribute to a decrease in the initial irreversible capacity.

(2) Second negative electrode active material The second negative electrode active material of the present invention is capable of occluding and releasing lithium containing a conductive carbon powder having a nanosize and a tin oxide powder in a highly dispersed state. A further negative electrode active material, wherein the tin oxide powder is in contact with the surface of the conductive carbon powder, and further includes a low conductive amorphous carbon film covering the surface of the conductive carbon powder It is. This is probably because the active sites on the surface of the conductive carbon powder that catalyze the electrochemical decomposition of the electrolyte solution of the lithium ion secondary battery are covered with a low-conductivity amorphous carbon film. And the reversible progress of the conversion reaction is maintained as it is.

  The tin oxide powder contained in the negative electrode active material can be tin dioxide or a mixture of tin dioxide and tin monoxide. Regarding the tin oxide powder in the second negative electrode active material and its preferred form, the description of the tin oxide powder in the first negative electrode active material and its preferred form also applies in this case. Omitted.

  Nano-sized conductive carbon powder includes nano-sized carbon black such as ketjen black, acetylene black, channel black, fullerene, carbon nanotube, carbon nanofiber, amorphous carbon, carbon fiber, natural graphite, artificial graphite , Graphitized ketjen black, activated carbon, mesoporous carbon and the like. Also, vapor grown carbon fiber can be used. These carbon powders may be used alone or in combination of two or more. Regarding the conductive carbon powder in the second negative electrode active material and preferred forms thereof, the description of the conductive carbon powder in the first negative electrode active material and preferred forms thereof also applies to this case. Description is omitted.

  The method for producing the second negative electrode active material is not particularly limited as long as it is a method that realizes a highly dispersed state of tin oxide powder and conductive carbon powder. For example, a conductive carbon powder is mixed with a tin oxide precursor in a dispersion medium, the tin oxide precursor is reacted with a surface functional group of the conductive carbon powder, and then heat-treated to convert the tin oxide precursor into tin oxide. Can be converted to Examples of the tin oxide precursor include inorganic metal compounds such as tin dichloride, tin tetrachloride, tin nitrate, and tin carbonate; organometallic compounds such as tin acetate, tin lactate, tetramethoxytin, tetraethoxytin, and tetraisopropoxytin; Alternatively, a mixture of these can be used. When a medium that can dissolve the tin oxide precursor and does not adversely affect the reaction is used as the dispersion medium, it is preferable because the tin oxide in the obtained negative electrode active material becomes fine particles.

  The second negative electrode active material is very preferably produced by a method in which the sol-gel method and the dispersion are simultaneously performed in the following ultracentrifugal force field. By conducting the sol-gel method and dispersion simultaneously in an ultracentrifugal force field, nano-sized conductive carbon powder, preferably spherical particles having a particle size of 10 to 50 nm, particularly preferably Ketjen Black, has nano-size Tin particles of tin oxide, preferably spherical particles having an average particle diameter of 1 to 10 nm, particularly preferably spherical particles having an average particle diameter of 1 to 2 nm can be supported in a highly dispersed state, and Sn—O—C Bonds can be formed at more sites. In particular, when ketjen black is used as the conductive carbon powder, spherical particles of nano-sized tin oxide can be effectively supported in the inner pores of the ketjen black by the method of simultaneously performing the sol-gel method and the dispersion. Can do. Then, by performing the subsequent kneading and heat treatment, at least a portion of the surface of the conductive carbon powder that is not in contact with tin oxide can be covered with the low-conductivity amorphous carbon film.

  Regarding the method of simultaneously performing the sol-gel method and the dispersion in the ultracentrifugal force field, a manufacturing method of a suitable form of the first negative electrode active material, that is, a nanosized carbon powder having high nanoparticle size tin oxide spherical particles. The above description of the method of supporting the metal oxide in a dispersed state and simultaneously supporting the metal oxide on at least a portion of the surface of the conductive carbon powder that is not in contact with the tin oxide indicates that the tin oxide precursor and the metal oxide precursor are Since this is also true except that only the tin oxide precursor is used instead of using both, further explanation is omitted. As for the method of kneading and heat treatment, a suitable first negative electrode active material including a low-conductivity amorphous carbon film covering the surface of the conductive carbon powder is obtained by the kneading step and the heat treatment step. Since the above description of the method is also applicable in this case except that the powder combined with the amorphous carbon precursor in the kneading process is a conductive carbon powder supporting only spherical particles of tin oxide, no more Description is omitted.

(3) Use of negative electrode active material The first negative electrode active material and the second negative electrode active material of the present invention are suitable for a lithium ion secondary battery. Therefore, the present invention also provides a negative electrode including the first negative electrode active material or the second negative electrode active material of the present invention, a positive electrode, and a separator holding a non-aqueous electrolyte disposed between the negative electrode and the positive electrode. A lithium ion secondary battery comprising:

  The negative electrode in the lithium ion secondary battery of the present invention can be formed by providing an active material layer containing the first negative electrode active material or the second negative electrode active material of the present invention on a current collector.

  As the current collector, a conductive material such as platinum, gold, nickel, aluminum, titanium, steel, or carbon can be used. As the shape of the current collector, any shape such as a film shape, a foil shape, a plate shape, a net shape, an expanded metal shape, and a cylindrical shape can be adopted.

  The active material layer is formed using a mixed material in which a binder, a conductive material, or the like is added to the first negative electrode active material or the second negative electrode active material of the present invention as necessary.

  As the binder, known binders such as polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinyl fluoride, and carboxymethyl cellulose are used. The content of the binder is preferably 1 to 30% by mass with respect to the total amount of the mixed material. If it is 1% by mass or less, the strength of the active material layer is not sufficient, and if it is 30% by mass or more, disadvantages such as a decrease in the discharge capacity of the negative electrode and an excessive internal resistance occur. As the conductive material, carbon powder such as carbon black, natural graphite, and artificial graphite can be used.

  The negative electrode using the above mixed material is obtained by dispersing the first negative electrode active material or the second negative electrode active material of the present invention and, if necessary, other additives in a solvent in which a binder is dissolved. It can be prepared by coating on a current collector by a doctor blade method or the like and drying. Moreover, a solvent may be added to the obtained mixed material as necessary to form into a predetermined shape, and may be pressure-bonded on the current collector.

  As the separator, for example, a polyolefin fiber nonwoven fabric or a glass fiber nonwoven fabric is preferably used. As the electrolytic solution retained in the separator, an electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent is used, and a known non-aqueous electrolytic solution can be used without any particular limitation.

  As the solvent for the non-aqueous electrolyte, electrochemically stable ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, sulfolane, 3-methyl sulfolane, γ-butyrolactone, acetonitrile and dimethoxyethane, N-methyl-2-pyrrolidone, dimethylformamide or a mixture thereof can be preferably used.

As a solute of the nonaqueous electrolytic solution, a salt that generates lithium ions when dissolved in an organic electrolytic solution can be used without any particular limitation. For _{example, LiPF 6, LiBF 4, LiClO} 4, LiN (CF 3 SO 2) 2, LiCF 3 SO 3, LiC (SO 2 CF 3) 3, LiN (SO 2 C 2 F 5) 2, LiAsF 6, LiSbF 6 Or a mixture thereof can be preferably used. Further, a quaternary ammonium salt or a quaternary phosphonium salt having a quaternary ammonium cation or a quaternary phosphonium cation can be used as a solute of the nonaqueous electrolytic solution. For example, a cation represented by R ¹ R ² R ³ R ⁴ N ⁺ or R ¹ R ² R ³ R ⁴ P ⁺ (where R ¹ , R ² , R ³ and R ⁴ are alkyl having 1 to 6 carbon atoms) Group), PF ₆ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , N (CF ₃ SO ₃ ) ₂ ⁻ , CF ₃ SO ₃ ⁻ , C (SO ₂ CF ₃ ) ₃ ⁻ , N (SO ₂ C ₂ A salt composed of an anion composed of F ₅ ) ₂ ⁻ , AsF ₆ ^— or SbF ₆ ^— , or a mixture thereof can be suitably used.

As a positive electrode active material for constituting the positive electrode, a known positive electrode active material capable of occluding and releasing lithium can be used without particular limitation. For example, composite oxides of lithium and transition metals such as LiMn ₂ O ₄ , LiMnO ₂ , LiV ₃ O ₅ , LiNiO ₂ and LiCoO ₂ , sulfides such as TiS ₂ and MoS ₂ , selenides such as NbSe ₃ , Cr Transition metal oxides such as ₃ O ₈ , V ₂ O ₅ , V ₅ O ₁₃ , VO ₂ , Cr ₂ O ₅ , MnO ₂ , TiO ₂ , MoV ₂ O ₈ , polyfluorene, polythiophene, polyaniline, polyparaphenylene Conductive polymers such as can be used.

  The active material layer for the positive electrode can be formed using a mixed material in which the binder, the conductive material, and the like exemplified for the negative electrode are added to the positive electrode active material as necessary. In the positive electrode using this mixed material, the positive electrode active material and other additives as necessary are dispersed in a solvent in which a binder is dissolved, and the obtained dispersion is applied to the negative electrode by a doctor blade method or the like. It can be made by coating and drying. Moreover, a solvent may be added to the obtained mixed material as necessary to form into a predetermined shape, and may be pressure-bonded on the current collector.

The first negative electrode active material and the second negative electrode active material of the present invention are suitable not only as a lithium ion secondary battery but also as a negative electrode active material for a hybrid capacitor. In the hybrid capacitor, activated carbon, carbon nanotube, mesoporous carbon, etc. are used as the positive electrode active material, and lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ are dissolved in non-aqueous solvents such as ethylene carbonate, dimethyl carbonate, diethyl carbonate and the like. The electrolyte is used.

  The present invention will be described with reference to the following examples, but the present invention is not limited to the following examples.

1: Effect of metal oxide and low-conductivity amorphous carbon film a. Production of negative electrode active material Example 1
As shown in FIG. 1 of Japanese Patent Application Laid-Open No. 2007-160151, it is composed of a concentric cylinder of an outer cylinder and an inner cylinder, a through hole is provided in the side surface of the inner cylinder, and a skirting plate is disposed at the opening of the outer cylinder. 10.8 g SnCl ₂ .2H ₂ O and 0.870 g Fe (CH ₃ COO) ₂ dissolved in 120 mL water are introduced into the inner cylinder of the reactor, and 0.6 mL hydrochloric acid having a concentration of 6M is further introduced. And 4.80 g of ketjen black (trade name ketjen black EC600J, manufactured by ketjen black international, primary particle size 34 nm, pore size 4 nm, specific surface area 1520 m ² / g, oxygen content 6.1 mmol / g) introduced, the inner cylinder is pivoted for 300 seconds as the centrifugal force of 70000Kgms ^-2 is applied to the reaction _{solution, SnCl 2 · 2H 2 O,} Fe (CH 3 COO) 2 and ketch The down black was dispersed. The turning of the inner cylinder was once stopped, 8.3 mL of a 12M NaOH aqueous solution was added to the inner cylinder, and the inner cylinder was turned for 300 seconds so that a centrifugal force of 70000 kgms- ² was applied to the reaction solution again. During this time, a thin film was formed on the inner wall of the outer cylinder, shear stress and centrifugal force were applied to the thin film, and hydrolysis and polycondensation reaction of SnCl ₂ and Fe (CH ₃ COO) ₂ proceeded. After the inner cylinder stopped rotating, the ketjen black was recovered by filtration, dried in vacuum at 180 ° C. for 12 hours, and further dried in nitrogen at 500 ° C. for 1 hour to obtain a negative electrode active material.

When the obtained negative electrode active material was confirmed by X-ray powder diffraction (see FIG. 1A), tin dioxide and a small amount of tin were produced. The diffraction peak of iron oxide was not confirmed, and amorphous or nano-sized microcrystalline iron oxide was generated. In addition, TG-DTA measurement was performed in an air atmosphere at a heating rate of 1 ° C./min, and the composition ratio between tin dioxide and carbon was calculated using a weight loss of 200 ° C. or more as the carbon content. A value substantially coincided with the charged amount (SnO ₂ : ketjen black = 60: 40 in mass ratio) was obtained. Further, according to the TEM photograph, tin dioxide spherical particles having a particle diameter of 1 to 2 nm are substantially present in the inner pores of the ketjen black, and 96% by mass of the primary particles are present in a non-aggregated state. It was confirmed that Further, the obtained negative electrode active material was immersed in an aqueous nitric acid solution having a concentration of 5% by mass, and Fe dissolved in the aqueous solution was confirmed by ICP spectroscopic analysis. As a result, the charged amount during the reaction (Mn ratio: Sn: Fe = 1: A value approximately in agreement with 0.1) was obtained.

Example 2:
A solution prepared by dissolving 10.8 g of SnCl ₂ .2H ₂ O in 120 mL of water was introduced into the inner cylinder of the reactor used in Example 1, and 0.6 mL of 6M hydrochloric acid and 4.80 g of ketjen were further introduced. Black (trade name Ketjen Black EC600J, manufactured by Ketjen Black International Co., Ltd., primary particle size 34 nm, pore size 4 nm, specific surface area 1520 m ² / g, oxygen content 6.1 mmol / g) was introduced, and 70000 kgms ⁻² The inner cylinder was swirled for 300 seconds so that the centrifugal force was applied to the reaction solution, and SnCl ₂ .2H ₂ O and ketjen black were dispersed. The turning of the inner cylinder was once stopped, 8.3 mL of a 12M NaOH aqueous solution was added to the inner cylinder, and the inner cylinder was turned for 300 seconds so that a centrifugal force of 70000 kgms- ² was applied to the reaction solution again. During this time, a thin film was formed on the inner wall of the outer cylinder, and shear stress and centrifugal force were applied to the thin film, and SnCl ₂ hydrolysis and polycondensation reaction proceeded. After the inner cylinder stopped rotating, the ketjen black was collected by filtration and dried in vacuum at 180 ° C. for 12 hours. Next, the dried ketjen black, water, and glucose were mixed at a mass ratio of 1: 0.5: 1 and kneaded to obtain a kneaded product. After evaporating water from the kneaded product, the glucose is thermally decomposed by heat treatment in nitrogen at 500 ° C. for 1 hour, and the surface of the ketjen black is a pyrolytic product of glucose (a low conductivity amorphous carbon film). A coated negative electrode active material was obtained.

When the obtained negative electrode active material was confirmed by X-ray powder diffraction (see FIG. 1B), a small amount of tin monoxide and tin were produced in addition to tin dioxide. The diffraction peak of the pyrolysis product of glucose was not confirmed, and an amorphous carbon film was formed. Moreover, when the composition ratio of tin dioxide and carbon was calculated by the method similar to the method in Example 1, a value substantially coinciding with the charged amount at the time of reaction (SnO ₂ : Ketjen Black = 60: 40 in mass ratio) was obtained. Obtained. Further, according to the TEM photograph, tin dioxide spherical particles having a particle diameter of 1 to 2 nm are substantially present in the inner pores of the ketjen black, and 96% by mass of the primary particles are present in a non-aggregated state. It was confirmed that

Example 3:
A solution prepared by dissolving 10.8 g of SnCl ₂ .2H ₂ O and 0.870 g of Fe (CH ₃ COO) ₂ in 120 mL of water was introduced into the inner cylinder of the reactor used in Example 1, and the concentration was 6M. 0.6 mL of hydrochloric acid and 4.80 g of ketjen black (trade name ketjen black EC600J, manufactured by Ketjenblack International Co., Ltd., primary particle size 34 nm, pore size 4 nm, specific surface area 1520 m ² / g, oxygen content 6.1 The inner cylinder was swirled for 300 seconds so that a centrifugal force of 70000 kgms ⁻² was applied to the reaction solution, and SnCl ₂ .2H ₂ O, Fe (CH ₃ COO) ₂ and Ketjen Black Was dispersed. The turning of the inner cylinder was once stopped, 8.3 mL of a 12M NaOH aqueous solution was added to the inner cylinder, and the inner cylinder was turned for 300 seconds so that a centrifugal force of 70000 kgms- ² was applied to the reaction solution again. During this time, a thin film was formed on the inner wall of the outer cylinder, shear stress and centrifugal force were applied to the thin film, and hydrolysis and polycondensation reaction of SnCl ₂ and Fe (CH ₃ COO) ₂ proceeded. After the inner cylinder stopped rotating, the ketjen black was collected by filtration and dried in vacuum at 180 ° C. for 12 hours. Next, the dried ketjen black, water, and glucose were mixed at a mass ratio of 1: 0.5: 1 and kneaded to obtain a kneaded product. After evaporating water from the kneaded product, the glucose is thermally decomposed by heat treatment in nitrogen at 500 ° C. for 1 hour, and the surface of the ketjen black is a pyrolytic product of glucose (a low conductivity amorphous carbon film). A coated negative electrode active material was obtained.

When the obtained negative electrode active material was confirmed by X-ray powder diffraction (see FIG. 1C), a small amount of tin monoxide and tin were generated in addition to tin dioxide. The diffraction peaks of the pyrolyzate of iron oxide and glucose were not confirmed, and an amorphous or nano-sized microcrystalline iron oxide and amorphous carbon film was formed. Moreover, when the composition ratio of tin dioxide and carbon was calculated by the method similar to the method in Example 1, a value substantially coinciding with the charged amount at the time of reaction (SnO ₂ : Ketjen Black = 60: 40 in mass ratio) was obtained. Obtained. Further, according to the TEM photograph, tin dioxide spherical particles having a particle diameter of 1 to 2 nm are substantially present in the inner pores of the ketjen black, and 96% by mass of the primary particles are present in a non-aggregated state. It was confirmed that Further, the obtained negative electrode active material was immersed in an aqueous nitric acid solution having a concentration of 5% by mass, and Fe dissolved in the aqueous solution was confirmed by ICP spectroscopic analysis. As a result, the charged amount during the reaction (Mn ratio: Sn: Fe = 1: A value approximately in agreement with 0.1) was obtained.

Comparative Example 1
A solution prepared by dissolving 10.8 g of SnCl ₂ .2H ₂ O in 120 mL of water was introduced into the inner cylinder of the reactor used in Example 1, and 0.6 mL of 6M hydrochloric acid and 4.80 g of ketjen were further introduced. Black (trade name Ketjen Black EC600J, manufactured by Ketjen Black International Co., Ltd., primary particle size 34 nm, pore size 4 nm, specific surface area 1520 m ² / g, oxygen content 6.1 mmol / g) was introduced, and 70000 kgms ⁻² The inner cylinder was swirled for 300 seconds so that the centrifugal force was applied to the reaction solution, and SnCl ₂ .2H ₂ O and ketjen black were dispersed. The turning of the inner cylinder was once stopped, 8.3 mL of a 12M NaOH aqueous solution was added to the inner cylinder, and the inner cylinder was turned for 300 seconds so that a centrifugal force of 70000 kgms- ² was applied to the reaction solution again. During this time, a thin film was formed on the inner wall of the outer cylinder, and shear stress and centrifugal force were applied to the thin film, and SnCl ₂ hydrolysis and polycondensation reaction proceeded. After the inner cylinder stopped rotating, the ketjen black was recovered by filtration, dried in vacuum at 180 ° C. for 12 hours, and further dried in nitrogen at 500 ° C. for 1 hour to obtain a negative electrode active material.

When the obtained negative electrode active material was confirmed by X-ray powder diffraction (see FIG. 1D), tin dioxide was produced. Moreover, when the composition ratio of tin dioxide and carbon was calculated by the method similar to the method in Example 1, a value substantially coinciding with the charged amount at the time of reaction (SnO ₂ : Ketjen Black = 60: 40 in mass ratio) was obtained. Obtained. Further, according to the TEM photograph, tin dioxide spherical particles having a particle diameter of 1 to 2 nm are substantially present in the inner pores of the ketjen black, and 96% by mass of the primary particles are present in a non-aggregated state. It was confirmed that

b. Preparation of Half Battery 1M LiPF ₆ ethylene carbonate / diethyl carbonate obtained by adding 30% by mass of polyvinylidene fluoride to 0.7 mg of each of the negative electrode active materials of Examples 1 to 3 and Comparative Example 1 to form a negative electrode A half-cell was prepared using the 1: 1 solution as the electrolyte and the counter electrode as lithium.

c. Charge / Discharge Characteristics About half-cells using the negative electrode active materials of Examples 1 to 3 and Comparative Example 1, a potential range of 0 to 2 V (including a conversion reaction region) under constant current conditions at a rate of 0.2 C (298 mAg ⁻¹ ). The range was evaluated for charge / discharge characteristics. Although this evaluation is an evaluation as a half battery, the same effect can be expected in all batteries using the positive electrode.

  First, with respect to the half battery using the negative electrode active material of Comparative Example 1, the first charge / discharge was compared with the second charge / discharge. FIG. 2 is a diagram showing a relationship (dQ / dE plot) between the potential in the first charge / discharge in the potential region of 0 to 2 V including the conversion reaction region and the first derivative of the charge / discharge capacity, and FIG. It is the figure which showed the relationship (dQ / dE plot) with the electric potential in the charging / discharging of the 2nd time, and the first derivative of charging / discharging capacity | capacitance.

  From the comparison between FIG. 2 and FIG. 3, it can be seen that in the first discharge, three irreversible capacity peaks having maximum values at potentials of about 1.2 V, about 0.8 V and about 0.2 V are recognized. Hereinafter, the irreversible capacity recognized in the range of potential 1.0 to 1.4 V is the irreversible capacity of region I, the irreversible capacity recognized in the range of potential 0.6 to 1.0 V is the irreversible capacity of region II, potential 0 to 0 The irreversible capacity recognized in the range of 6V is represented as the irreversible capacity of region III.

  FIG. 4 shows the relationship between the potential in the first charge / discharge in the potential region of 0 to 2 V including the conversion reaction region and the first derivative of the charge / discharge capacity for the half cell using the negative electrode active material of Example 1 ( dQ / dE plot), FIG. 5 is a corresponding diagram for a half cell using the negative electrode active material of Example 2, and FIG. 6 is a half cell using the negative electrode active material of Example 3. FIG.

  FIG. 7 shows the relationship (dQ / dE plot) between the potential in the first discharge and the first derivative of the discharge capacity when a charge / discharge test was performed on a half cell using only ketjen black as the negative electrode active material. FIG. It can be seen that two peaks with maximum values at potentials of about 0.8V and about 0.2V are observed. The potential range in which these two peaks are recognized substantially matches the potential range in which the irreversible capacities in the regions II and III in FIGS. 2 and 4 to 6 are recognized. With reference to this result, the irreversible capacity of region I in FIGS. 2 and 4 to 6 is the irreversible capacity due to the irreversible conversion reaction that remains very slightly, and the irreversible capacity of region II is that of Ketjen Black. The irreversible capacity due to the electrochemical decomposition reaction of the electrolyte solution on the surface, the irreversible capacity of region III, the erosion capacity of the electrolyte solution on the surface of the ketjen black and the tin surface generated after the conversion reaction, etc. The irreversible capacity due to the factors was judged. Moreover, it turned out that the production | generation of a trace amount tin and tin monoxide in the negative electrode active material of Examples 1-3 does not affect an irreversible capacity | capacitance from the comparison of FIG.

Table 1 shows the irreversible capacity and the reversible capacity in the first charge / discharge of the half cells using the negative electrode active materials of Examples 1 to 3 and Comparative Example 1.

From Table 1, the negative electrode active material carrying iron oxide on the ketjen black surface of Example 1 and the negative electrode active material having the ketjen black surface of Example 2 coated with a low conductivity amorphous carbon film are also comparative examples. Compared with the negative electrode active material of No. 1, the reduction amount of the irreversible capacity is larger than the reduction amount of the reversible capacity. You can see that Furthermore, the negative electrode active material having iron oxide and a low-conductivity amorphous carbon film on the surface of the ketjen black of Example 3 has a slightly larger reversible capacity than the negative electrode active material of Example 2, and The amount of decrease in irreversible capacity (1377-670 mAhg ⁻¹ ) based on the negative electrode active material of Example ¹ is the same as the amount of decrease in the negative electrode active material of Example 2 (1377-1077 mAhg ⁻¹ ) and the amount of negative electrode active material of Example 3. It was larger than the total amount with the decrease amount (1377-1010 mAhg ⁻¹ ). Therefore, it can be seen that, in the negative electrode active material of Example 3, a significant reduction in irreversible capacity was achieved due to the synergistic effect of the iron oxide on the surface of ketjen black and the amorphous carbon film having low conductivity.

Table 2 summarizes the irreversible capacities in each region for the half cells using the negative electrode active materials of Examples 1 to 3 and Comparative Example 1.

  From Table 2, although the irreversible capacity | capacitance of the negative electrode active material of Examples 1-3 is increasing slightly in the area | region I compared with the negative electrode active material of the comparative example 1, it is large in the area | region II and the area | region III. It can be seen that the number has decreased.

  As described above, the irreversible capacity in the region II is irreversible due to the electrochemical decomposition reaction of the electrolyte on the surface of the ketjen black, and the irreversible capacity in the region III is generated on the surface of the ketjen black or after the conversion reaction. Although it is thought that it is an irreversible capacity | capacitance resulting from several factors, such as the electrochemical decomposition reaction of the electrolyte solution in the surface of tin, in the negative electrode active material of Examples 1-3, the reduction | decrease in an irreversible capacity | capacitance in the area | region II and the area | region III In particular, since the reduction rate of the irreversible capacity in region II is remarkable, the active sites that catalyze the electrochemical decomposition reaction of the electrolyte present on the surface of the ketjen black are not oxidized by iron oxide and / or low conductivity. It was judged that the coating with a regular carbon film and, therefore, the inhibition of the electrochemical decomposition reaction of the electrolyte led to a reduction in the overall irreversible capacity. It was. In particular, the negative electrode active material of Example 3 has an increase in irreversible capacity in region I that is less than that in the negative electrode active materials of Examples 1 and 2, and the irreversible capacity in region II and region III is remarkably reduced, which is extremely good. Met.

For the half-cells using the negative electrode active materials of Examples 1 to 3 and Comparative Example 1, a charge / discharge cycle test in a potential range of 0 to 2 V (a range including a conversion reaction region) under a constant current condition of a rate of 0.5 C. Went. FIG. 8 is a diagram showing a change in discharge capacity in the charge / discharge cycle experience, and FIG. 9 is a diagram showing a capacity retention rate. Each negative electrode active material showed a reversible capacity significantly increased from the theoretical capacity of 372 mAhg ⁻¹ of conventional graphite, and furthermore, after the discharge capacity was stabilized, almost no decrease in the discharge capacity was observed. Cycling was shown. Therefore, the negative electrode active materials of Examples 1 to 3 were negative electrode active materials having high reversible capacity, reduced initial irreversible capacity, and excellent cycle characteristics.

2. Effect of amorphous carbon precursor a. Production of negative electrode active material Example 4:
A solution prepared by dissolving 10.8 g of SnCl ₂ .2H ₂ O and 0.870 g of Fe (CH ₃ COO) ₂ in 120 mL of water was introduced into the inner cylinder of the reactor used in Example 1, and the concentration was 6M. 0.6 mL of hydrochloric acid and 4.80 g of ketjen black (trade name ketjen black EC600J, manufactured by Ketjenblack International Co., Ltd., primary particle size 34 nm, pore size 4 nm, specific surface area 1520 m ² / g, oxygen content 6.1 The inner cylinder was swirled for 300 seconds so that a centrifugal force of 70000 kgms ⁻² was applied to the reaction solution, and SnCl ₂ .2H ₂ O, Fe (CH ₃ COO) ₂ and Ketjen Black Was dispersed. The turning of the inner cylinder was once stopped, 8.3 mL of a 12M NaOH aqueous solution was added to the inner cylinder, and the inner cylinder was turned for 300 seconds so that a centrifugal force of 70000 kgms- ² was applied to the reaction solution again. During this time, a thin film was formed on the inner wall of the outer cylinder, shear stress and centrifugal force were applied to the thin film, and hydrolysis and polycondensation reaction of SnCl ₂ and Fe (CH ₃ COO) ₂ proceeded. After the inner cylinder stopped rotating, the ketjen black was collected by filtration and dried in vacuum at 180 ° C. for 12 hours. Next, the dried ketjen black, water, and glutamic acid were mixed at a mass ratio of 1: 0.5: 1 and kneaded to obtain a kneaded product. After evaporating water from the kneaded product, the glutamic acid is thermally decomposed by heat treatment in nitrogen at 500 ° C. for 1 hour, and the surface of the ketjen black is a thermal decomposition product of glutamic acid (a low conductivity amorphous carbon film). A coated negative electrode active material was obtained.

When the obtained negative electrode active material was confirmed by X-ray powder diffraction, a small amount of tin monoxide and tin were produced in addition to tin dioxide. Diffraction peaks of thermal decomposition products of iron oxide and glutamic acid were not confirmed, and amorphous or nano-sized microcrystalline iron oxide and amorphous carbon films were formed. Moreover, when the composition ratio of tin dioxide and carbon was calculated by the method similar to the method in Example 1, a value substantially coinciding with the charged amount at the time of reaction (SnO ₂ : Ketjen Black = 60: 40 in mass ratio) was obtained. Obtained. Further, according to the TEM photograph, tin dioxide spherical particles having a particle diameter of 1 to 2 nm are substantially present in the inner pores of the ketjen black, and 96% by mass of the primary particles are present in a non-aggregated state. It was confirmed that Further, the obtained negative electrode active material was immersed in an aqueous nitric acid solution having a concentration of 5% by mass, and Fe dissolved in the aqueous solution was confirmed by ICP spectroscopic analysis. As a result, the charged amount during the reaction (Mn ratio: Sn: Fe = 1: A value approximately in agreement with 0.1) was obtained.

Example 5:
A solution prepared by dissolving 5.64 g of SnCl ₂ .2H ₂ O and 0.56 g of polyvinyl alcohol in 120 mL of water was introduced into the inner cylinder of the reactor used in Example 1, and further 3.2 mL of hydrochloric acid having a concentration of 2 M was introduced. And 1.62 g of ketjen black (trade name ketjen black EC600J, manufactured by ketjen black international, primary particle size 34 nm, pore size 4 nm, specific surface area 1520 m ² / g, oxygen content 6.1 mmol / g) The inner cylinder was swirled for 300 seconds so that a centrifugal force of 70000 kgms- ² was applied to the reaction solution, and SnCl ₂ .2H ₂ O, polyvinyl alcohol and ketjen black were dispersed. The turning of the inner cylinder was once stopped, 56.4 mL of 1 M NaOH aqueous solution was added into the inner cylinder, and the inner cylinder was turned for 300 seconds so that a centrifugal force of 70000 kgms- ² was applied to the reaction solution again. During this time, a thin film was formed on the inner wall of the outer cylinder, and shear stress and centrifugal force were applied to the thin film, and SnCl ₂ hydrolysis and polycondensation reaction proceeded. After the inner cylinder stopped rotating, the ketjen black was collected by filtration and dried in vacuum at 180 ° C. for 12 hours. Next, the dried ketjen black, water, and glutamic acid were mixed at a mass ratio of 1: 0.5: 1 and kneaded to obtain a kneaded product. After evaporating water from the kneaded product, the polyvinyl alcohol and glutamic acid are thermally decomposed by heat treatment at 500 ° C. for 1 hour in nitrogen, and the surface of the tin oxide particles and the surface of the ketjen black are thermally decomposed products of polyvinyl alcohol, respectively. And the negative electrode active material coat | covered with the thermal decomposition product (low conductivity amorphous carbon film) of glutamic acid was obtained.

When the obtained negative electrode active material was confirmed by X-ray powder diffraction, a small amount of tin was generated in addition to tin dioxide. A diffraction peak of thermal decomposition products of polyvinyl alcohol and glutamic acid was not confirmed, and an amorphous carbon film was formed. In addition, TG-DTA measurement was performed in an air atmosphere at a heating rate of 1 ° C./min, and the composition ratio between tin dioxide and carbon was calculated using a weight loss of 200 ° C. or more as the carbon content. A value substantially coincided with the charged amount (SnO ₂ : Ketjen black = 70: 30 in mass ratio) was obtained. Furthermore, according to a TEM photograph, spherical particles of tin dioxide having a particle diameter of 1 to 2 nm are supported on the inner and outer surfaces of Ketjen Black, and 96% by mass of the primary particles are present in a non-aggregated state. confirmed.

Example 6:
A solution prepared by dissolving 5.64 g of SnCl ₂ .2H ₂ O, 0.43 g of Fe (CH ₃ COO) ₂ and 0.56 g of polyvinyl alcohol in 120 mL of water in the inner cylinder of the reactor used in Example 1. Further, 3.2 mL of 2M hydrochloric acid and 1.62 g of Ketjen black (trade name Ketjen Black EC600J, manufactured by Ketjen Black International Co., Ltd., primary particle size 34 nm, pore size 4 nm, specific surface area 1520 m ² / g, oxygen amount 6.1 mmol / g), and the inner cylinder was swirled for 300 seconds so that a centrifugal force of 70000 kgms- ² was applied to the reaction solution, and SnCl ₂ .2H ₂ O, Fe (CH ₃ COO) ₂ , polyvinyl alcohol and ketjen black were dispersed. The turning of the inner cylinder was once stopped, 56.4 mL of 1 M NaOH aqueous solution was added into the inner cylinder, and the inner cylinder was turned for 300 seconds so that a centrifugal force of 70000 kgms- ² was applied to the reaction solution again. During this time, a thin film was formed on the inner wall of the outer cylinder, shear stress and centrifugal force were applied to the thin film, and hydrolysis and polycondensation reaction of SnCl ₂ and Fe (CH ₃ COO) ₂ proceeded. After the inner cylinder stopped rotating, the ketjen black was collected by filtration and dried in vacuum at 180 ° C. for 12 hours. Next, the dried ketjen black, water, and glutamic acid were mixed at a mass ratio of 1: 0.5: 1 and kneaded to obtain a kneaded product. After evaporating water from the kneaded product, the polyvinyl alcohol and glutamic acid are thermally decomposed by heat treatment at 500 ° C. for 1 hour in nitrogen, and the surface of the tin oxide particles and the surface of the ketjen black are thermally decomposed products of polyvinyl alcohol, respectively. And the negative electrode active material coat | covered with the thermal decomposition product (low conductivity amorphous carbon film) of glutamic acid was obtained.

When the obtained negative electrode active material was confirmed by X-ray powder diffraction, a small amount of tin was generated in addition to tin dioxide. Diffraction peaks of thermal decomposition products of iron oxide, polyvinyl alcohol and glutamic acid were not confirmed, and amorphous or nanosized microcrystalline iron oxide and amorphous carbon films were formed. Moreover, when the composition ratio of tin dioxide and carbon was calculated by the method similar to the method in Example 1, the value substantially coincided with the charged amount at the time of reaction (SnO ₂ : Ketjen Black = 70: 30 in mass ratio). Obtained. Furthermore, according to a TEM photograph, spherical particles of tin dioxide having a particle diameter of 1 to 2 nm are supported on the inner and outer surfaces of Ketjen Black, and 96% by mass of the primary particles are present in a non-aggregated state. confirmed. Further, the obtained negative electrode active material was immersed in an aqueous nitric acid solution having a concentration of 5% by mass, and Fe dissolved in the aqueous solution was confirmed by ICP spectroscopic analysis. As a result, the charged amount during the reaction (Mn ratio: Sn: Fe = 1: A value approximately in agreement with 0.1) was obtained.

Example 7:
A solution prepared by dissolving 5.64 g of SnCl ₂ .2H ₂ O, 0.43 g of Fe (CH ₃ COO) ₂ and 0.56 g of polyvinyl alcohol in 120 mL of water in the inner cylinder of the reactor used in Example 1. Further, 3.2 mL of hydrochloric acid having a concentration of 2 M and 1.62 g of Ketjen Black (trade name Ketjen Black EC600J, manufactured by Ketjen Black International Co., Ltd., primary particle size 34 nm, pore size 4 nm, specific surface area 1520 m ² / g, oxygen amount 6.1 mmol / g), and the inner cylinder was swirled for 300 seconds so that a centrifugal force of 70000 kgms- ² was applied to the reaction solution, and SnCl ₂ .2H ₂ O, Fe (CH ₃ COO) ₂ , polyvinyl alcohol and ketjen black were dispersed. The turning of the inner cylinder was once stopped, 56.4 mL of 1 M NaOH aqueous solution was added into the inner cylinder, and the inner cylinder was turned for 300 seconds so that a centrifugal force of 70000 kgms- ² was applied to the reaction solution again. During this time, a thin film was formed on the inner wall of the outer cylinder, shear stress and centrifugal force were applied to the thin film, and hydrolysis and polycondensation reaction of SnCl ₂ and Fe (CH ₃ COO) ₂ proceeded. After the inner cylinder stopped rotating, the ketjen black was collected by filtration and dried in vacuum at 180 ° C. for 12 hours. Next, the dried ketjen black, water, and glucose were mixed at a mass ratio of 1: 0.5: 1 and kneaded to obtain a kneaded product. After evaporating water from the kneaded product, the polyvinyl alcohol and glucose are thermally decomposed by heat treatment at 500 ° C. for 1 hour in nitrogen, and the surface of the tin oxide particles and the surface of the ketjen black are the pyrolyzed product of polyvinyl alcohol and A negative electrode active material coated with a pyrolyzate of glucose (low conductivity amorphous carbon film) was obtained.

When the obtained negative electrode active material was confirmed by X-ray powder diffraction, tin monoxide and tin were produced in addition to tin dioxide. Diffraction peaks of thermal decomposition products of iron oxide, polyvinyl alcohol and glucose were not confirmed, and amorphous or nano-sized microcrystalline iron oxide and amorphous carbon films were formed. Moreover, when the composition ratio of tin dioxide and carbon was calculated by the method similar to the method in Example 1, the value substantially coincided with the charged amount at the time of reaction (SnO ₂ : Ketjen Black = 70: 30 in mass ratio). Obtained. Furthermore, according to a TEM photograph, spherical particles of tin dioxide having a particle diameter of 1 to 2 nm are supported on the inner and outer surfaces of Ketjen Black, and 96% by mass of the primary particles are present in a non-aggregated state. confirmed. Further, the obtained negative electrode active material was immersed in an aqueous nitric acid solution having a concentration of 5% by mass, and Fe dissolved in the aqueous solution was confirmed by ICP spectroscopic analysis. As a result, the charged amount during the reaction (Mn ratio: Sn: Fe = 1: A value approximately in agreement with 0.1) was obtained.

Comparative Example 2:
A solution prepared by dissolving 5.64 g of SnCl ₂ .2H ₂ O and 0.56 g of polyvinyl alcohol in 120 mL of water was introduced into the inner cylinder of the reactor used in Example 1, and further 3.2 mL of hydrochloric acid having a concentration of 2 M was introduced. And 1.62 g of ketjen black (trade name ketjen black EC600J, manufactured by ketjen black international, primary particle size 34 nm, pore size 4 nm, specific surface area 1520 m ² / g, oxygen content 6.1 mmol / g) The inner cylinder was swirled for 300 seconds so that a centrifugal force of 70000 kgms- ² was applied to the reaction solution, and SnCl ₂ .2H ₂ O, polyvinyl alcohol and ketjen black were dispersed. The turning of the inner cylinder was once stopped, 56.4 mL of 1 M NaOH aqueous solution was added into the inner cylinder, and the inner cylinder was turned for 300 seconds so that a centrifugal force of 70000 kgms- ² was applied to the reaction solution again. During this time, a thin film was formed on the inner wall of the outer cylinder, and shear stress and centrifugal force were applied to the thin film, and SnCl ₂ hydrolysis and polycondensation reaction proceeded. After stopping the swiveling of the inner cylinder, the ketjen black is recovered by filtration, dried in vacuum at 180 ° C. for 12 hours, and further dried in nitrogen at 500 ° C. for 1 hour, so that the surface of the tin oxide particles becomes the heat of polyvinyl alcohol. A negative electrode active material coated with a decomposition product was obtained. Furthermore, according to a TEM photograph, spherical particles of tin dioxide having a particle diameter of 1 to 2 nm are supported on the inner and outer surfaces of Ketjen Black, and 96% by mass of the primary particles are present in a non-aggregated state. confirmed.

When the obtained negative electrode active material was confirmed by X-ray powder diffraction, tin dioxide was produced. Moreover, when the composition ratio of tin dioxide and carbon was calculated by the method similar to the method in Example 1, the value substantially coincided with the charged amount at the time of reaction (SnO ₂ : Ketjen Black = 70: 30 in mass ratio). Obtained. Furthermore, according to a TEM photograph, tin dioxide particles having a particle diameter of 1 to 2 nm are substantially present in the internal pores of the ketjen black, and 96% by mass of the primary particles are present in a non-aggregated state. Was confirmed.

  The negative electrode active material of Example 6 produced a small amount of tin in addition to tin dioxide, and the negative electrode active material of Example 7 produced tin monoxide and tin in addition to tin dioxide (see FIG. 10). However, the following test was conducted to investigate the cause. Glutamic acid or glucose was introduced into the annular furnace, the temperature of the annular furnace was increased from room temperature to 500 ° C. over 1.5 hours while passing a nitrogen stream, and then the temperature was maintained at 500 ° C. And the gas discharged | emitted from the annular furnace for 10 minutes from the time of the temperature maintenance start was extract | collected, and the component in the gas extract | collected by gas chromatography was quantified.

Table 3 shows the types of generated gas and the composition ratio of hydrogen, carbon monoxide, and carbon dioxide.

  It can be seen from Table 3 that hydrogen and carbon monoxide, which are reducing chemical species, are generated more in the pyrolysis process of glucose than in the pyrolysis process of glutamic acid. In the heat treatment step of the negative electrode active material of Example 7, it is considered that the tin dioxide of the composite was reduced by these reducing chemical species, and a large amount of tin monoxide and tin were generated.

About the negative electrode active material of Example 6, Example 7, and Comparative Example 2, the specific surface area per 1g of negative electrode active materials was measured by the nitrogen adsorption method. Table 4 shows the results.

  From Table 4, the negative electrode active material of Example 7 containing an amorphous carbon layer obtained by pyrolysis of glucose had a specific surface area lower than that of the negative electrode active material of Comparative Example 2 not containing an amorphous carbon layer. I understand that. Moreover, it turns out that the negative electrode active material of Example 6 containing the amorphous carbon layer obtained by thermal decomposition of glutamic acid has a specific surface area significantly lower than the negative electrode active materials of Example 7 and Comparative Example 2. . From these results, it was found that the specific surface area of the negative electrode active material (composite) was reduced by forming the amorphous carbon layer. In the negative electrode active material of Example 7, the composite is covered with a sparse amorphous carbon layer, whereas in the negative electrode active material of Example 6, the composite is covered with a dense amorphous carbon layer. It was judged.

b. Preparation of half-cell 1M LiPF ₆ ethylene carbonate / diethyl carbonate obtained by adding 30% by mass of polyvinylidene fluoride to 0.7 mg of each of the negative electrode active materials of Examples 4 to 7 and Comparative Example 2 to form a negative electrode A half-cell was prepared using the 1: 1 solution as the electrolyte and the counter electrode as lithium.

c. Charging / Discharging Characteristics For the half-cells using the negative electrode active materials of Examples 4 to 7 and Comparative Example 2, a potential range of 0 to 2 V (including a conversion reaction region) under constant current conditions at a rate of 0.2 C (298 mA / g). The range was evaluated for charge / discharge characteristics. Although this evaluation is an evaluation as a half battery, the same effect can be expected in all batteries using the positive electrode. Table 5 summarizes the irreversible capacity and the reversible capacity in the first charge / discharge.

  From Table 5, it can be seen that any of the negative electrode active materials has a reversible capacity significantly increased from the theoretical capacity of 372 mAh / g of conventional graphite. Moreover, when the measurement result (refer Table 2) about the negative electrode active material of the comparative example 1 is compared with the measurement result (refer Table 5) about the negative electrode active material of the comparative example 2, the negative electrode active material of the comparative example 2 fell. It turns out that it has capacity. This result shows that the content of tin oxide in the negative electrode active material is increased by coating the tin oxide particles with the pyrolyzate of polyvinyl alcohol in the production process of the negative electrode active material of Comparative Example 2, and the content of ketjen black This is considered to reflect the fact that it was possible to reduce Further, as can be seen from Table 5, the negative electrode active materials of Examples 5 to 7, that is, the negative electrode active material having an amorphous carbon film covering the surface of ketjen black, are the negative electrode active materials of Comparative Example 2. Compared with negative electrode active material that does not have an amorphous carbon coating covering the surface of the material, ketjen black and has the same amount of tin content, the reversible capacity is slightly reduced and greatly It had a reduced irreversible capacity. Therefore, it can be seen that the negative electrode active materials of Examples 5 to 7 achieve a reduction in reversible capacity and a significant reduction in irreversible capacity.

  The negative electrode active material of Example 4 and the negative electrode active material of Example 3 are both negative electrode active materials having tin oxide powder, iron oxide and an amorphous carbon film on the surface of ketjen black, and tin oxide in the negative electrode active material And the content of the iron oxide is the same, and the anode active material is different only in the kind of the amorphous carbon precursor used in the production process. The negative electrode active material of Example 6 and the negative electrode active material of Example 7 both have tin oxide powder, iron oxide, and an amorphous carbon film coated on the surface of ketjen black with a pyrolyzate of polyvinyl alcohol. It is a negative electrode active material, the content of tin oxide and iron oxide in the negative electrode active material is the same, and the negative electrode active material is different only in the type of amorphous carbon precursor used in the production process. From Table 2 and Table 5, the negative electrode active material of Example 4 and Example 6 having an amorphous carbon film derived from glutamic acid is the negative electrode active material of Example 3 and Example 7 having an amorphous carbon film derived from glucose. In comparison, it can be seen that it has a significantly reduced irreversible capacity. This result reflected that the amorphous carbon film derived from glutamic acid was denser than the amorphous carbon film derived from glucose, and the electrochemical decomposition of the electrolyte was effectively suppressed by this dense amorphous carbon film. It is thought to be a thing. In particular, the negative electrode active material of Example 6 containing a dense amorphous carbon layer obtained from pyrolysis of glutamic acid and iron oxide had a significantly reduced initial irreversible capacity.

About the half cells using the negative electrode active materials of Examples 5 to 7 and Comparative Example 2 having the same tin content, a potential range of 0 to 2 V (including a conversion reaction region) under a constant current condition of a rate of 0.5 C. Range) was conducted. Table 6 summarizes the reversible capacity maintenance rates after the 20th and 100th charge / discharge cycle tests.

  The negative electrode active materials of Examples 5 and 6 and Comparative Example 2 showed an equivalent capacity maintenance rate, and showed a capacity maintenance rate exceeding 75% even after experiencing 100 charge / discharge cycle tests. Therefore, the negative electrode active materials of Examples 5 and 6 were negative electrode active materials having a high reversible capacity, a significantly reduced initial irreversible capacity, and excellent cycle characteristics. In the negative electrode active material of Example 7, the complex tin dioxide was reduced by the reducing chemical species, and a large amount of aggregated tin was generated. Therefore, it is considered that the stability in the charge / discharge cycle test was lowered.

  Since the negative electrode active material of the present invention has a reduced initial irreversible capacity and a high reversible capacity, it is promising as a negative electrode active material replacing graphite, and is suitably used for the next-generation lithium ion secondary battery. And is also suitable as a negative electrode active material for a hybrid capacitor.

Claims (12)

A negative electrode active material capable of occluding and releasing lithium containing nano-sized conductive carbon powder and tin oxide powder,
It further contains a metal oxide other than tin oxide,
The conductive carbon powder has voids;
The tin oxide powder has an average particle size smaller than the conductive carbon powder;
96% by mass of primary particles of the tin oxide powder are present in a non-aggregated state,
The tin oxide powder is present in the voids of the conductive carbon powder and is in contact with the surface of the conductive carbon powder;
The negative electrode active material, wherein the metal oxide is amorphous or nano-sized microcrystals and is in contact with the surface of the conductive carbon powder.   The negative electrode active material according to claim 1, wherein the tin oxide powder is a spherical particle. The negative electrode active material according to claim 2, wherein the conductive carbon powder is ketjen black (registered trademark) .   The negative electrode active material according to claim 2 or 3, further comprising a low-conductivity amorphous carbon film covering the surface of the conductive carbon powder. A negative electrode active material capable of occluding and releasing lithium containing nano-sized conductive carbon powder and tin oxide powder,
The conductive carbon powder has voids;
The tin oxide powder has an average particle size smaller than the conductive carbon powder;
96% by mass of primary particles of the tin oxide powder are present in a non-aggregated state,
The tin oxide powder is present in the voids of the conductive carbon powder and is in contact with the surface of the conductive carbon powder;
A negative electrode active material, further comprising an amorphous carbon film having low conductivity and covering a surface of the conductive carbon powder. The negative electrode active material according to claim 5 , wherein the tin oxide powder is a spherical particle. The negative electrode active material according to claim 6 , wherein the conductive carbon powder is ketjen black (registered trademark) . It is a manufacturing method of the negative electrode active material of Claim 2 or 3,
Introducing a reaction solution in which the conductive carbon powder is added to a solution in which a tin oxide precursor and a metal oxide precursor other than the tin oxide precursor are dissolved in a swirlable reactor; and
The reactor was swirled, and a hydrolysis reaction and a polycondensation reaction of the tin oxide precursor and the metal oxide precursor were performed while applying a shear stress and a centrifugal force to the reaction solution. A method for producing a negative electrode active material, comprising a step of supporting a reaction product on the conductive carbon powder. It is a manufacturing method of the negative electrode active material of Claim 4 , Comprising:
A step of obtaining a kneaded product of the negative electrode active material and the amorphous carbon precursor obtained by the method for producing a negative electrode active material according to claim 8 , and
A method for producing a negative electrode active material, comprising: thermally treating the kneaded material to thermally decompose the amorphous carbon precursor to form a low-conductivity amorphous carbon film. It is a manufacturing method of the negative electrode active material of Claim 6 or 7 ,
Introducing a reaction solution in which the conductive carbon powder is added to a solution in which a tin oxide precursor is dissolved in a swirlable reactor,
The reactor is swirled to perform hydrolysis reaction and polycondensation reaction of the tin oxide precursor while applying shear stress and centrifugal force to the reaction solution, and at the same time, the obtained reaction product is converted to the conductive property. A process of supporting the carbon powder;
Obtaining a kneaded product of the conductive carbon powder carrying the reaction product and an amorphous carbon precursor; and
A method for producing a negative electrode active material, comprising: thermally treating the kneaded material to thermally decompose the amorphous carbon precursor to form a low-conductivity amorphous carbon film. The method for producing a negative electrode active material according to claim 9 or 10, wherein the amorphous carbon precursor is glutamic acid. A negative electrode containing a negative active material according to any one of claims 1 to 7 positive and negative electrode and a lithium ion secondary that includes a separator which holds the placed nonaqueous electrolyte between the positive electrode battery.

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