JP4789032B2 - Negative electrode active material particles for lithium secondary battery and method for producing negative electrode - Google Patents

Description

The present invention relates to a novel high-capacity negative electrode active material particle for a lithium secondary battery and a method for producing the same, and more particularly, to a negative electrode active material particle for a lithium secondary battery that electrochemically occludes and releases lithium. Alloy particles having amorphous regions in which all or part of silicon or tin is alloyed with other metal elements on all or part of the surface of low melting point metal particles or low melting point alloy particles, and / or low temperature firing A carbon material composed of carbon, acetylene black, ketjen black, carbon fiber or graphite is fixed, and the low melting point metal particles or the low melting point alloy particles are at least partially or partially alloyed amorphous regions. A negative active material particle for a lithium secondary battery, and a production thereof, characterized by having an average particle size larger than that of the silicon or tin alloy particles having Law on.

Lithium secondary batteries are used in particular for portable devices. Batteries that are used with many functions added to mobile phones and portable electronic devices such as portable devices such as recent portable devices, personal computers, PDAs, and output voltage according to the operating voltage of the device, and usage time There is a need to increase the battery capacity to affect. In particular, with regard to an increase in battery capacity for prolonging the usage time, the capacity of the battery cannot be increased other than increasing the energy density of the active material that stores electrical energy in a limited battery space.

The positive electrode active material of a typical lithium secondary battery conventionally used is lithium cobaltate, and the negative electrode active material is graphite. With such a battery material configuration, it is difficult to increase the volumetric energy efficiency to 400 Wh / L or more. In particular, since the theoretical energy amount of graphite as a negative electrode active material is 372 mAh / g, there is a limit to further improve the battery capacity, and the use of other types of negative electrode active materials is not limited to each research institution or battery manufacturing. Researched and developed by the manufacturer.

Examples of negative electrode active material materials that are considered in this context include silicon, tin, and lithium metal. For metal lithium, lithium dendrite is generated, and for silicon and tin, volume expansion and contraction associated with insertion and extraction of lithium ions. There is a problem that the utilization rate is lowered due to the destruction of the crystal structure due to crystallization and the isolation due to fine particles, and various improvements have been made.
JP-A-8-50922 Japanese Patent Laid-Open No. 8-213008 JP 2001-332254 A Japanese Patent Laid-Open No. 2003-77529 JP 2003-109589 A JP 2002-83594 A WO00 / 17949 International Publication WO01 / 029912 International Publication

Silicon and tin as the negative electrode active material have a large volume expansion / contraction ratio associated with occlusion / release of lithium ions, and since the particles are easily atomized, the electrical connection is hindered, along with the charge / discharge cycle. There is a problem that it becomes difficult to charge and discharge.

The negative electrode active material is coated on the surface of the negative electrode current collector by a method such as sputtering, vacuum deposition, or plating. The thickness of the coating layer that can be formed by such a surface treatment method is about several μm at most. When the thickness of the layer is made too thick, there is a problem that cracks are generated in the coating layer due to a volume change at the time of occlusion / release of lithium ions, resulting in fine pulverization.

Furthermore, in order to increase the battery capacity of the lithium secondary battery, it is necessary to increase the coating amount of the negative electrode active material to be coated, but the thickness of the coating layer that can be formed by the surface treatment method is limited. There was a problem that it was not practical, for example, the manufacturing time was extremely long.

On the other hand, in order to increase the amount of the negative electrode active material to be coated, other surface treatment methods such as coating the negative electrode active material particles with a coating liquid kneaded with a conductive material and a binder have been used. In this method, the conductivity of the coated layer is poor compared to the surface treatment method, and when pulverized, the electrical conduction between the particles is cut off and the battery capacity of the lithium secondary battery is reduced. There was a problem of a rapid decrease.

Therefore, the present invention has been developed for the purpose of solving the above-mentioned problems, and its main purpose is (1) the fineness of particles associated with occlusion / release of lithium ions of negative electrode active material particles. And (2) negative electrode active material particles for lithium secondary batteries capable of reducing the surface treatment load while increasing the amount of negative electrode active material particles coated on the negative electrode current collector, and It is in providing the manufacturing method.

A negative electrode active material particle and a method for producing the same according to the present invention include an amorphous material in which all or part of silicon or tin is alloyed with another metal element on all or part of the surface of low melting point metal particles or low melting point alloy particles. It is characterized in that it is surface-modified with an alloy particle having a region and / or a carbon material composed of low-temperature-fired carbon, acetylene black, ketjen black, carbon fiber or graphite, and its manufacturing method, particularly electrochemically Negative electrode active material particles for lithium secondary batteries that occlude and release lithium, wherein all or part of the surface of low melting point metal particles or low melting point alloy particles is all or part of silicon or tin is another metal element Alloy particles having an amorphous region alloyed with carbon and / or low-temperature-fired carbon, acetylene black, ketjen black, carbon fiber or The carbon material made of graphite is fixed, and the low melting point metal particles or the low melting point alloy particles are larger in average than the silicon or tin alloy particles having an amorphous region in which at least all or a part is alloyed. Provided are negative electrode active material particles having good electrical characteristics and a method for producing the same by surface treatment with a particle size.

That is, according to the negative electrode active material particle and the method for producing the same according to the present invention, the low melting point metal particle or the low melting point alloy particle is used as a base material, and the low melting point metal particle or the low melting point alloy is further formed on the whole or a part of the surface. Alloy particles having an amorphous region made of silicon or tin having an average particle size smaller than the particles, and / or a carbon material made of low-temperature fired carbon, acetylene black, ketjen black, carbon fiber or graphite The negative electrode active material particles having a complicated shape are provided by fixing them in a fibrous state or coating them in layers.

The alloy particles made of silicon or tin coated on the surface of the anode active material particles and / or the carbon material made of low-temperature fired carbon, acetylene black, ketjen black, carbon fiber or graphite are low melting point metal particles or low Because it is strongly bonded to the melting point alloy particles, the low melting point metal particles or the low melting point alloy particles that are the cores of each ensure the direct electrical contact between the negative electrode current collector and the negative electrode active material particles adjacent thereto, Furthermore, conductive materials such as carbon fibers present around them serve to ensure indirect contact between the negative electrode current collector and the negative electrode active material particles adjacent thereto.

In such a form, since an alloy mainly composed of silicon or tin is bonded as negative electrode active material particles to the surfaces of the low melting point metal particles or the low melting point alloy particles serving as the nucleus, the lithium secondary battery is charged and discharged. On the contrary, the distance between the negative electrode active material particles is reduced during the volume expansion / contraction, so that the contact between the negative electrode active material particles becomes better than before charge / discharge.

In addition, the alloy particles made of silicon or tin having an amorphous structure functioning as the negative electrode active material itself have been miniaturized due to strain fatigue due to structural changes due to volume changes associated with insertion and extraction of lithium ions. The alloy particles having an amorphous structure mainly composed of silicon or tin are coated on the surface with conductive metal particles composed of low melting point metal particles or low melting point alloy particles as a core ( In the case of fixed negative electrode active material particles, if the size of the alloy particles made of silicon or tin itself is suppressed to 5 μm or less in a state where lithium ions are not occluded, the progress rate of miniaturization can be extremely reduced. Can do.

Furthermore, such a negative electrode active material particle has a form in which an appropriate gap is formed between each particle and the negative electrode current collector by coating the negative electrode active material particle with a predetermined thickness on the negative electrode current collector. In combination with the ease of deformation of the low-melting-point metal particles or low-melting-point alloy particles that support the negative electrode active material particles, it acts to absorb the volume change of the coating layer that accompanies occlusion / release of lithium ions. As a result, the negative electrode active material particles according to the present invention also contribute to reducing the volume change of the coating layer itself due to charge / discharge.

At this time, the porosity of the coating layer formed on the negative electrode surface by the negative electrode active material particles according to the present invention is preferably in the range of 30 to 65%.

When such a porosity is less than 30%, it is difficult for the electrolyte to penetrate into the coating layer formed of the negative electrode active material particles, and a large amount of time is required for vacuum impregnation of the electrolyte. The battery performance may be deteriorated due to insufficient amount of impregnation, and an internal short circuit is likely to occur due to movement of the electrode within a limited volume. On the other hand, when the porosity is larger than 65%, a predetermined amount of the negative electrode active material cannot be disposed in the limited volume, resulting in a problem that the battery capacity is reduced.

Therefore, in order to maintain such an appropriate gap in the coating layer of the negative electrode, the negative electrode for the lithium secondary battery is formed by appropriately pressure-molding the negative electrode for the lithium secondary battery after the surface treatment. This is very important. When a lithium secondary battery is produced in a state where the porosity is lowered by applying pressure more than necessary, the thickness of the negative electrode increases by repeating charge and discharge, and finally the negative electrode thickness as designed can be maintained. It becomes impossible to destroy the lithium secondary battery.

The average particle diameter of the alloy particles made of silicon or tin present on the surface of the negative electrode active material particles according to the present invention is preferably 5 μm or less, more preferably the alloy particles having an average particle diameter of 2 μm or less are lithium. It was found that stress strain is effectively suppressed and miniaturization is suppressed in response to the volume change during occlusion and release of ions. Also, it has been found that if the average particle size of the low melting point metal particles or low melting point alloy particles that are cores combined at this time is suppressed to 15 μm or less, the generation of stress strain can be effectively prevented and miniaturization can be suppressed. did.

On the other hand, the average particle size of the negative electrode active material particles is that the alloy particles made of silicon or tin are fixed on the surface of the low melting point metal particles or the low melting point alloy particles, so the average particle size of the particles as a whole is 35 μm or less. More preferably, when the thickness is 15 μm or less, the negative electrode current collector can be uniformly coated, and the electrical contact can be maintained against the volume change of the particles when the lithium ions are occluded and released. I understood.

When the average particle diameter of the alloy particles made of silicon or tin is larger than 5 μm, irregularities are generated on the negative electrode covering surface, and the average particle diameter of the low melting point metal particles or the low melting point alloy particles as the core is more than 15 μm. When it becomes large, the thickness of the coating layer coated on the negative electrode current collector becomes larger than necessary, and as a result, the negative electrode in which the negative electrode active material particles are surface-treated particularly on the negative electrode current collector partially having corners. When the battery was used, it was confirmed by disassembling the broken lithium ion battery that an internal short circuit occurred at a rate of about 16% to damage the separator.

Thus, when the average particle diameter of the whole negative electrode active material particles in which the alloy particles made of silicon or tin are fixed to the outer surface of the low melting point metal particles or the low melting point alloy particles is larger than 35 μm, the silicon fixed to the outer surface Alternatively, it has been found that the adhesion thickness of the alloy particles made of tin becomes too large, and the alloy particles made of silicon or tin peel off and become isolated as the charge / discharge cycle passes.

On the other hand, when alloy particles having an average particle size of 2 μm or less are used, voids formed between the particles absorb the stress strain at the time of occlusion and release of lithium ions. It turned out that it can suppress more effectively. In particular, when the average particle diameter of the low melting point metal element or low melting point alloy element serving as the nucleus is suppressed to 3 μm or less, this effect becomes even more remarkable.

That is, when the average particle diameter of the negative electrode active material particles as a whole is suppressed to 15 μm or less, the alloy particles made of silicon or tin are divided into a maximum of 3 to 4 layers on the outer surface of the low-melting-point metal particles or the low-melting-point alloy particles serving as nuclei. It has been found that the solid particles are fixed in a stacked state, can withstand expansion and contraction of alloy particles made of silicon or tin, and the shape does not collapse. Further, when the low melting point metal particles or the low melting point alloy particles are bonded to the outer surface of the alloy particles made of silicon or tin in a state where they are stacked in one layer, if the average particle diameter of the whole negative electrode active material particles becomes 7 μm or less, the composite It was found that the stability of the converted negative electrode active material particles was further increased.

In addition, the shape of the alloy particles made of silicon or tin having an amorphous region is a particle shape close to a sphere in order to alleviate the uneven distribution of stress strain generated at the time of occlusion and release of lithium ions and to make it uniform. It has been found that the smaller the particle shape, the more difficult it is to refine the particles.

Next, the alloy particles made of silicon or tin made of silicon or tin and other metal elements according to the present invention preferably have an amorphous region in whole or in part.

Further, since the alloy particles made of silicon or tin according to the present invention need only have an amorphous region in all or part thereof, the other metal elements do not need to be alloyed with all of silicon or tin, It may be alloyed with a part of silicon or tin.

This amorphous region is formed by the method described below.

The other metal element added for amorphizing silicon or tin is the first other element added to promote the amorphization of silicon or tin depending on the purpose and process of addition. And a second other metal element added for amorphization and coating of silicon or tin.

First, in order to promote the amorphization of silicon or tin, the first other metal element is 0.1 wt% or less of the total weight of the final negative electrode active material particles by using a general alloy manufacturing method. Pre-silicon or tin alloy particles are produced so that

Thus, pre-silicon or tin alloy particles are prepared by adding about 0.1 wt% of another metal element to silicon or tin in advance, for example, in the subsequent amorphization process. When processing using a ball mill or the like, the amorphization of silicon or tin takes about 30 to 48 hours when the first other metal element is not added, but in a short time of about several hours. It could also be made amorphous.

The alloy composition after the pre-silicon or tin alloy particles described above are alloyed and amorphized with a second other metal element, which will be described later, is increased by adding the second other metal element. One metal element is contained at a lower rate than 0.1 wt% of the total weight of alloy particles made of amorphous silicon or tin. Further, when iron is used as the first other metal element in the silicon alloy particles, iron is contained with a content of 0.1 wt% or more because the iron contains a small amount of silicon. Sometimes.

As described above, suitable first metal elements to be added in advance in order to promote the amorphization of silicon or tin include iron, aluminum, chromium, antimony, and magnesium. Here, the pre-silicon or tin alloy particles made of silicon or tin and the first other metal element were alloyed by adding silicon or tin and a plurality of different first other alloy elements. It may be a thing.

Next, for example, the pre-silicon or tin alloy particles are mixed with a second other metal element, and one or more selected from at least a mechanical alloying method, a mechanical gliding method, a liquid quenching method, and a gas quenching method. Thus, alloy particles made of silicon or tin having an amorphous region in whole or in part are produced.

In addition, since the produced alloy particles made of silicon or tin need only have an amorphous region in all or a part thereof, other metal elements do not need to be alloyed with all of silicon or tin. It may be alloyed with a part of silicon or tin. Further, in order to surface-modify amorphous alloy particles made of silicon or tin, which will be described later, a mixed powder of alloy particles made of silicon or tin produced by these different production methods is used. You can also.

As described above, the second other metal elements mixed with the alloy particles made of pre-silicon or tin in order to make silicon or tin amorphous may include iron, aluminum, cobalt, copper, nickel, chromium, There are magnesium, lead, zinc, bismuth and antimony, and further, tin is an effective metal element for making silicon amorphous. Also, the amorphous alloy particles made of silicon or tin are made amorphous by mixing the second other alloy element which is the same as or different from the first other metal element. It may be.

Here, in the case of silicon, there are amorphous silicon, microcrystalline silicon, polycrystalline silicon, and single crystal silicon due to the difference in the crystal structure of silicon as silicon having an amorphous region manufactured by the above-described manufacturing method. In the present invention, silicon having a microcrystalline region is included in addition to silicon having an amorphous region.

Amorphous silicon is one in which a peak in the vicinity of 480 cm ⁻¹ corresponding to the amorphous region is detected in Raman spectroscopic analysis, whereas a peak in the vicinity of 520 cm ⁻¹ corresponding to the crystalline region is not substantially detected. It is. Microcrystalline silicon is a substance in which both a peak near 520 cm ⁻¹ corresponding to a crystalline region and a peak near 480 cm ⁻¹ corresponding to an amorphous region are substantially detected in Raman spectroscopic analysis. In other words, microcrystalline silicon is substantially composed of a crystalline region and an amorphous region. On the other hand, in polycrystalline silicon and single crystal silicon, a peak in the vicinity of 520 cm ⁻¹ corresponding to the crystalline region is detected in Raman spectroscopic analysis, while a peak in the vicinity of 480 cm ⁻¹ corresponding to the amorphous region is substantially detected. It is not detected.

As described above, the reason for using amorphous silicon or tin as the negative electrode active material is that the negative electrode active material such as silicon or tin, which has been regarded as promising conventionally, absorbs or releases lithium ions. One of the drawbacks is that the volume expansion change in this case is very large, 3 to 4 times. As a result, the crystals cannot withstand the volume change and are finely pulverized. Is blocked and does not contribute to the electrochemical reaction, whereas amorphized silicon or tin is due to the strong bonding force between elements by alloying with other metal elements. The durability against the expansion and contraction is increased, and the volume change of the particles themselves can be reduced by amorphization, and as a result, the blocking of the electrical connection path in the negative electrode due to the fine pulverization of the particles is suppressed. Pole to do Te is because it is effective.

In addition, when a solid electrolyte is used at the interface in contact with the negative electrode, when such amorphous silicon or tin is used, components contained in the electrolyte are diffused into the negative electrode surface treatment layer made of negative electrode active material particles. As a result, the adhesion between the negative electrode surface-treated with the negative electrode active material particles and the solid electrolyte may be improved.

In addition, when the adhesion between the negative electrode and the solid electrolyte is increased, the ion conductivity is improved and a higher charge / discharge capacity is obtained. When charge / discharge is repeated, the volume of the negative electrode active material particles changes. A decrease in the contact property with the solid electrolyte is also suppressed, and more excellent charge / discharge cycle characteristics can be obtained. Furthermore, as described above, when the component contained in the solid electrolyte is in a solid solution in the negative electrode active material particles at the interface where the negative electrode and the solid electrolyte contact, as if an intermetallic compound was formed, Even better charge / discharge cycle characteristics can be obtained without the charge and discharge separating the component contained in the solid electrolyte from the negative electrode active material and reducing the adhesion.

In this way, the charge / discharge cycle characteristics of the lithium secondary battery are improved by enhancing the durability against expansion / contraction of the negative electrode active material in the negative electrode, suppressing pulverization, and further improving the adhesion between the negative electrode and the solid electrolyte. In order to improve the above, it is necessary that the ratio of the amorphous region in the total weight of the alloy particles made of at least silicon or tin is 80 wt% or more.

When the proportion of the amorphous region in the total weight of the alloy particles made of silicon or tin is 80 wt% or more, 50 cycles of charge and discharge of the lithium secondary battery are suppressed by suppressing the structural breakdown due to volume expansion / contraction of the alloy particles. The capacity decay rate is improved to about 1/20 later, and the effect of suppressing the attenuation of the lithium secondary battery capacity can be further enhanced as compared with the case of using silicon particles or silicon alloy particles that are not amorphized. .

In addition, according to the present invention, the surface of the low melting point metal particles or the low melting point alloy particles is coated (fixed) with the alloy particles made of silicon or tin having an average particle size smaller than the particles. Works to efficiently fill the voids formed between the low melting point metal particles or the low melting point alloy particles as the core while maintaining constant contact, and is also composed of silicon or tin for the storage and release of lithium ions. Negative electrode active material particles by expanding and contracting the volume in the voids formed between the particles without changing the relative position of the low melting point metal particles or the low melting point alloy particles whose core is the alloy particles alone The contact between the particles as a whole, that is, the electrical resistance between the negative electrode active material particles hardly changes when the lithium ions are occluded / released. Charge-discharge cycle characteristics of the lithium secondary battery so obtained was.

Further, in order to prevent inactivation of lithium ions caused by oxidation of the produced negative electrode active material particles, pre-silicon or tin alloy particles are made amorphous or amorphous silicon or The coating (adhering) with the alloy particles made of tin is preferably performed in an inert gas atmosphere.

When pre-silicon or tin alloy particles and second metal element, and silicon or tin alloy particles and low melting point metal particles or low melting point alloy particles are fixed and surface treated in an inert gas atmosphere It is possible to suppress the generated metal oxide to a predetermined amount or less, and the suppression of the generation of the metal oxide in such an inert gas atmosphere is caused by each metal particle constituting the negative electrode active material particle according to the present invention. It also excludes reacting with the atmospheric gas to produce other metal products.

Further, when the proportion of the metal oxide generated at this time in the total weight of the negative electrode active material particles exceeds 1 wt%, the utilization factor of the initial negative electrode active material particles becomes 90% or less due to a synergistic effect. The ratio of the metal oxide to the total weight of the active material particles is preferably suppressed to 1 wt% or less.

Further, the negative electrode active material particles according to the present invention include low-melting point metal particles or low-melting point alloy particles whose surface is entirely or partly made of alloy particles made of silicon or tin, and / or low-temperature fired carbon, Coating with a carbon material made of acetylene black, ketjen black, carbon fiber or graphite (adhesion, binding, fusion, bonding, pressure bonding, etc.) gives an extremely complicated shape.

The shape of the composite negative electrode active material particles is such that, after the surface treatment is performed on the negative electrode current collector, the coating layer formed of the negative electrode active material particles by the appropriate voids formed between the particles is accompanied by charge / discharge. Absorbs the volume change, and even when the volume changes, it fills the gaps between the resulting particles to ensure electrical connection between the particles, and as a result, as described below There are many additional effects.

For example, a negative electrode active material particle according to the present invention and a conductive material that hardly absorbs carbon or lithium ions such as ketjen black and a binder are added to the surface of a negative electrode current collector made of a copper foil or a copper-plated film. The case of a negative electrode produced by applying and drying a coating liquid obtained by kneading with a diluting liquid so as to have a predetermined film thickness will be described as a first effect. The negative electrode active material particles are coated (adhered to) the negative electrode active material for inserting and extracting lithium ions with alloy particles made of silicon or tin having a small particle diameter with respect to the low melting point metal particles or the low melting point alloy particles. Therefore, the conductive path through the alloy particles made of silicon or tin is shortened, and the negative electrode active material particles are applied between the negative electrode active material particles and the negative electrode active material particles. And it was possible to reduce the electrical resistance of the negative electrode.

As the second function and effect, the negative electrode active material particles according to the present invention increase the ratio of the volume of the low melting point metal particles or the low melting point alloy particles exhibiting high conductivity to the total volume of the negative electrode active material particles. The electrical resistance of the material particles and the negative electrode to which the anode active material particles are applied depends on the physical properties of the low melting point metal element or low melting point alloy element, and the influence of the alloy particles made of silicon or tin having a smaller volume is It was possible to obtain an almost uniform electrical resistance that was minimized.

Further, as a third effect, conventionally, in order to provide electrical connection between the negative electrode active material particles filled in the electrode, such as ketjen black or acetylene black having a nano-unit ultrafine shape, etc. Whereas a conductive material was used, in the negative electrode active material particles according to the present invention, the conductive material having these ultrafine shapes can be replaced with particles having a large particle diameter such as low-temperature fired carbon or graphite, As a result, the negative electrode capacity increased and the electrical resistance could be reduced. In addition, when used in combination with ketjen black or acetylene black, the electrical conductivity is further improved.

Further, as a fourth function and effect, when the negative electrode to which the negative electrode active material particles according to the present invention are applied is used, the surface of the low melting point metal particles or the low melting point alloy particles that become nuclei particularly when a lithium secondary battery is charged. Since the alloy particles made of silicon or tin coated (adhered) on the surface increase with occlusion of lithium ions so as to fill the voids formed between the respective negative electrode active material particles, electrical connection between the respective negative electrode active material particles Can be made even stronger.

In this way, the surface modified composite negative electrode active material pre-particles can be formed by sintering low melting point metal particles or low melting point alloy particles using a sintering method or a surface modification composite method (multiple types of powders collide at high speed. This is a method of alloying and surface treatment by circulating in the container while using a method called hybridizing method and grinding heat and pressure when the powder is pressed by the gap between the container inner wall and the central axis. And alloying and surface-treating mechano-fusion manufacturing method, etc.), and surface treatment is performed with alloy particles made of silicon or tin that has been amorphousized. Moreover, the negative electrode active material particles according to the present invention may be those using a mixed powder of negative electrode active material pre-particles produced by these different production methods.

Furthermore, low melting point metal particles or low melting point alloy particles surface-treated with amorphous silicon or tin alloy particles, that is, low temperature fired carbon or graphite having a relatively large particle diameter on the surface of the negative electrode active material pre-particles. In order to fix a carbon material such as the above, the surface of the surface-treated negative electrode active material metal particles is coated with a polymer organic material solution and baked in an inert gas atmosphere. It is carried out by carbonization or volatilization.

Among the above production methods, in particular, the alloying particles made of amorphous silicon or tin are coated on the surface of the low melting point metal particles or the low melting point alloy particles using the mechanical alloying method or the mechanical grinding method, Further, when the negative electrode active material particles according to the present invention in which carbon materials such as low-temperature-fired carbon and graphite are fixed by low-temperature firing are produced, even if the particle shape is destroyed due to occlusion / release of lithium ions, these silicon or tin And / or a carbon material composed of low-temperature-fired carbon, ketjen black, acetylene black, carbon fiber, or graphite remains while forming irregularities on the surface of the low-melting-point metal particles or low-melting-point alloy particles. In order to maintain a conductive network formed in a grid, alloy particles made of bonded silicon or tin and And / or electrical connection between the particulate carbon material as a medium is maintained, a decrease in battery capacity of the lithium ion battery is suppressed.

As a result, the surface resistance of the negative electrode without such surface treatment was 9 Ωcm, but was reduced to 1.5 Ωcm or less and improved.

As described above, the low melting point metal particles or the low melting point alloy particles and / or the carbon material composed of the low-temperature-fired carbon, carbon fiber, or graphite are bonded to the negative electrode current collector and the conductivity between the particles as described above. Therefore, as the low melting point alloy particles for achieving this purpose, the metal itself such as lead solder, lead-free solder, and conductor paste is soft and has a temperature of about 850 ° C. or less. What can be processed at low temperature is preferable, and specifically, Sn-Pb alloy, Sn-Sb alloy, Sn-Ag alloy, Sn-Bi alloy, Sn-In alloy, Sn-Zn alloy, Sn-Ag-In-Bi. One or more types of lead solder selected from the group consisting of alloys and lead-free solder are preferred.

Similarly, preferable low melting point metal particles include one or more metal elements selected from the group consisting of iron, aluminum, copper, nickel, lead and zinc.

Further, as a carbon material that complements the function of the conductive network formed in a mesh shape and can function as a negative electrode active material itself, low-temperature calcined carbon calcined between about 300 ° C. and 1,000 ° C., One or more carbon materials selected from the group consisting of carbon fibers and graphite can be used for surface modification by compositing particles composed of low melting point metal particles or low melting point alloy particles.

Furthermore, in order to achieve the above object according to the present invention, the first and second other metal elements contained in the alloy particles made of silicon or tin constituting the negative electrode active material particles account for the total weight of the alloy particles. The ratio is preferably in the range of 10 to 83 wt%.

When the ratio of the first and second other metal elements to the total weight of the alloy particles made of silicon or tin is less than 10 wt%, fatigue of structural change strain accompanying volume expansion / contraction during insertion and extraction of lithium ions Since the alloy particles made of silicon or tin have been refined, the electrical contact tends to be poor due to isolation. Further, when the amount is more than 83 wt%, the problem that the electrical contact becomes poor due to isolation by suppressing the miniaturization due to volume expansion / contraction of the alloy particles made of silicon or tin against the insertion and release of lithium ions. Although the point is improved, there arises a problem that the battery capacity as the negative electrode active material particles becomes extremely small.

As described above, the negative electrode active material particles according to the present invention are made of metal or alloy particles having a low softening point (or melting point) as a base material, and an alloy made of silicon or tin having an average particle size smaller than that of the base material particles on the surface. Since the particles (substantially, alloy particles contributing to occlusion / release of lithium ions as negative electrode active material particles) are coated (fixed), the low melting point metal particles or the low melting point alloy particles and silicon or tin Bonding between the metal and the alloy particles made of the metal can easily proceed, and negative electrode active material particles that are firmly coated (fixed) can be provided.

Further, the configuration of the negative electrode active material particles according to the present invention enables the negative electrode current collector particles to be coated on the surface of the negative electrode current collector at a low temperature, so that the negative electrode current collector is deformed or altered due to thermal history, etc. In addition, it is possible to form an electrical network having high conductivity by the strong bonding between the negative electrode current collector, the coating layer, and the negative electrode active material particles formed in the coating layer.

Next, the negative electrode active material particles according to the present invention and a method for forming a negative electrode for a lithium secondary battery using the same will be described.

A method for producing negative electrode active material particles for a lithium secondary battery according to the present invention is a method for producing negative electrode active material particles for a lithium secondary battery that occludes and releases lithium in an electrochemistry,
A first step for alloying all or part of silicon or tin with a first other metal element to produce alloy particles comprising silicon or tin;
All or a part of the surface of the alloy particles made of silicon or tin is further alloyed and / or surface-treated with the second other metal element to modify the alloy particles made of silicon or tin having an amorphous region. A second step for
A third step for fixing the alloy particles made of silicon or tin to the surface of the low melting point metal particles or the low melting point alloy particles to form negative electrode active material pre-particles;
The surface of the negative electrode active material pre-particles is coated with a polymer organic material solution and baked in an inert gas atmosphere, and the polymer organic material solution is carbonized or volatilized to fix the carbon material to the negative electrode. A fourth step for forming active material particles, and the third step has an amorphous region in which the low melting point metal particles or the low melting point alloy particles are at least partially or alloyed. 1 or 2 having an average particle size larger than that of the alloy particles made of silicon or tin, and selected from at least a mechanical alloying method, a mechanical gliding method, a mechanofusion method, a hybridizing method, and a sintering method The alloy particles made of silicon or tin are fixed by the above manufacturing method.

A method for producing a negative electrode for a lithium secondary battery according to the present invention is a method for producing a negative electrode for a lithium secondary battery that electrochemically occludes and releases lithium,
A first step for alloying all or part of silicon or tin with a first other metal element to produce alloy particles comprising silicon or tin;
All or a part of the surface of the alloy particles made of silicon or tin is further alloyed and / or surface-treated with the second other metal element to modify the alloy particles made of silicon or tin having an amorphous region. A second step for
A third step for fixing the alloy particles made of silicon or tin to the surface of the low melting point metal particles or the low melting point alloy particles to form negative electrode active material pre-particles;
The surface of the negative electrode active material pre-particles is coated with a polymer organic material solution and baked in an inert gas atmosphere, and the polymer organic material solution is carbonized or volatilized to fix the carbon material to the negative electrode. A fourth step for forming active material particles;
And a fifth step for forming a negative electrode by surface-treating a coating material containing the negative electrode active material particles on a negative electrode current collector, and the third step includes the low melting point metal particles or the low melting point alloy. The particles have an average particle size larger than that of the alloy particles made of silicon or tin having at least all or partly alloyed amorphous regions, and at least mechanical alloying method, mechanical gliding method, mechanofusion The alloy particles comprising silicon or tin are fixed by one or more production methods selected from a method, a hybridizing method and a sintering method.

Here, as a feature of the negative electrode active material particles according to the present invention and a method for forming a negative electrode for a lithium secondary battery using the same, the specific material used in the third step is combined with the manufacturing method used in this step. Thus, the negative electrode active material particles according to the present invention having a desired shape and bonding state are provided for the first time.

That is, the low-melting-point metal particles or low-melting-point alloy particles used in the third step have a larger average particle size than the alloy particles made of silicon or tin having an amorphous region, In combination with the method, the alloy particles made of silicon or tin are strongly fixed to the surface of the low melting point metal particles or the low melting point alloy particles, and the negative electrode active material pre-particles are formed so as to have a complicated shape as a whole. .

Further, in the fourth step, the surface of the negative electrode active material pre-particles is coated with a polymer organic material solution and fired in an inert gas atmosphere to carbonize or volatilize the polymer organic material solution. Thus, a carbon material such as low-temperature calcined carbon or graphite having a relatively large particle diameter is firmly fixed to the surface of the negative electrode active material pre-particles.

The first step may produce pre-silicon or tin alloy particles by using silicon or tin and a first other metal element, for example, a general alloying method such as a melting method. it can.

In the second step, the pre-silicon or tin alloy particles and the second other metal element are mixed and selected from at least a mechanical alloying method, a mechanical gliding method, a liquid quenching method, and a gas quenching method. Alternatively, the pre-silicon or tin alloy particles are made amorphous by using two or more production methods, and alloy particles made of silicon or tin having an amorphous region in all or part thereof are produced.

In addition, since the alloy particles made of silicon or tin need only have an amorphous region in all or part thereof, the other metal elements do not need to be alloyed with all of silicon or tin, It may be alloyed with a part of silicon or tin. Furthermore, in the third step for coating (adhering) alloy particles made of amorphous silicon or tin, which will be described later, on the surface of low melting point metal particles or low melting point alloy particles that are the core, It is also possible to use a mixed powder of alloy particles made of silicon or tin produced by these different production methods.

Further, in order to prevent inactivation of lithium ions due to oxidation of the produced negative electrode active material particles, the pre-silicon or tin alloy particle amorphization treatment in the second step, and third The coating (fixing) treatment of the low melting point metal particles or the low melting point alloy particles with the amorphized silicon or tin alloy particles in the step is preferably performed in an inert gas atmosphere.

When pre-silicon or tin alloy particles and second metal element, and alloy particles made of silicon or tin and low melting point metal particles or low melting point alloy particles are fixed and surface treated in an inert gas atmosphere It is possible to suppress the generated metal oxide to a predetermined amount or less, and the suppression of the generation of the metal oxide in such an inert gas atmosphere is caused by each metal particle constituting the negative electrode active material particle according to the present invention. It also excludes reacting with the atmospheric gas to produce other metal products.

In addition, when the proportion of the metal oxide generated at this time in the total weight of the negative electrode active material particles exceeds 1 wt%, the utilization factor of the initial negative electrode active material particles becomes 90% or less due to a synergistic effect. It is preferable that the ratio of the metal oxide in the total weight of the particles is suppressed to 1 wt% or less.

The formation of the negative electrode active material pre-particles having a complicated shape in the third step is a mechanical alloying method or a sintering method using a planetary ball mill or the like on the whole or a part of the surface of the low melting point metal particles or the low melting point alloy particles. , And other surface modification compounding methods (a method of alloying and surface-treating by circulating in the container while colliding multiple types of powders at high speed, such as a method called hybridizing, There are processes called alloying and surface treatment using the frictional heat and pressure applied when the powder is pressed by the gap between the center axis and the center axis, which are called mechanical gliding method or mechanofusion method. ) To surface-treat the amorphous alloy particles made of silicon or tin. Moreover, the negative electrode active material particles according to the present invention may be those using a mixed powder of negative electrode active material pre-particles produced by these different production methods.

Furthermore, the surface of the low melting point metal particles or the low melting point alloy particles surface-treated with the alloy particles made of silicon or tin made amorphous in the fourth step, that is, the surface of the negative electrode active material pre-particles has a relatively large particle size. In order to fix a carbon material such as low-temperature fired carbon or graphite, the surface of the surface-treated negative electrode active material pre-particles is coated with a polymer organic material solution and fired in an inert gas atmosphere. This is performed by carbonizing or volatilizing the molecular organic material solution.

The surface of the low melting point metal particles or low melting point alloy particles is coated (fixed) with alloy particles made of amorphous silicon or tin using the mechanical alloying method or mechanical grinding method in particular. In addition, when the anode active material particles according to the present invention to which carbon materials such as low-temperature-fired carbon and graphite are fixed are produced by low-temperature firing, even if the particle shape is destroyed due to occlusion / release of lithium ions, these silicon Alternatively, alloy particles made of tin and / or carbon material made of low-temperature fired carbon, ketjen black, acetylene black, carbon fiber or graphite remain while forming irregularities on the surface of the low-melting-point metal particles or the low-melting-point alloy particles. To maintain a conductive network formed in the form of a mesh, and is composed of bonded silicon or tin. And particles, and / or electrical connection between the particulate carbon material as a medium is maintained, a decrease in battery capacity of the lithium ion battery is suppressed.

In the fifth step, the negative electrode using the negative electrode active material particles is formed by forming a negative electrode current collector made of copper foil or the like into the negative electrode active material particles according to the present invention, iron, aluminum, copper, nickel, chromium, lead, tin. Coating a coating material containing one or more conductive materials selected from the group consisting of tin solder, zinc and conductive carbon material and a binder, heat drying, and roll pressing to a predetermined thickness Thus, a negative electrode for a lithium secondary battery that has been surface-treated with a coating layer having a predetermined porosity can be produced.

Such a coating method on the negative electrode current collector according to the present invention is obtained by roughening the surface of the negative electrode current collector as described in other patents to a columnar silicon having a thickness of several μm. Since the coating layer can be made thicker than the surface treatment method that forms the film by ion sputtering, PVD, CVD, plating, etc., and the porous coating layer can be formed, the electrode capacity is increased and the volume efficiency is increased. Can be increased.

The formation of the negative electrode using the negative electrode active material particles in the fifth step is performed on the surface of the negative electrode current collector made of a copper foil or a resin film plated with copper without using a conductive material and a binder. The negative electrode active material particles are directly arranged and subjected to surface treatment on the negative electrode current collector by cold rolling method, coating method, sintering method, melt dropping method or thermal spraying method, or press treatment or heating / pressing Surface treatment can also be performed by a production method (heat press method) in which treatments are performed simultaneously.

In this case, the coating method on the negative electrode current collector according to the present invention is a porous material having a predetermined void that makes it possible to effectively absorb the volume change of the negative electrode active material particles accompanying the insertion and extraction of lithium ions. It is particularly useful for forming a conductive coating layer, and the negative electrode active without changing the thickness of the negative electrode because the binder can be omitted in the coating method in which a solution in which a binder and a conductive material are kneaded is applied and dried. As a result of the increased packing density of the substance particles, the battery capacity per unit volume can be increased.

Further, in the fourth step, the coating (adhering) of the negative electrode active material pre-particles with the carbon material is performed by converting the coating material containing the negative electrode active material pre-particles and the polymer organic material solution according to the present invention into an inert gas in the fifth step. By subjecting the negative electrode current collector to surface treatment by a hot press method in an atmosphere, the polymer organic material solution can be carbonized or volatilized on the surface of the negative electrode active material pre-particles, and the negative electrode can be formed simultaneously. .

As a result, the lithium secondary battery using the negative electrode according to the present invention has a battery capacity of approximately the same as that of 0.2C up to 2C in the case of an electrode having a thickness of 90 μm for high rate charge / discharge. It can also be applied to small electric devices.

The porosity of the coating layer formed on the negative electrode is preferably within the range of 37% to 65% of the porosity of the coating layer in a state where the front and back surfaces of the negative electrode current collector are coated with the negative electrode active material particles. In this way, the negative electrode active material particles can absorb the volume expansion associated with the insertion and extraction of lithium ions only inside the coating layer and suppress an increase in the thickness of the negative electrode, so that the negative electrode is incorporated as a whole. In addition, the shape change of the lithium secondary battery can be minimized. More preferably, when the porosity of the coating layer is about 30% in a state where occlusion of lithium ions is completed during charging, the shape change of the lithium secondary battery can be further suppressed. The particle size, filling amount, filling density, and electrode thickness of the negative electrode active material particles at the time of production can be appropriately selected.

Alloy particles made of silicon or tin, which should be called the gist of the present invention, and / or negative electrode active material particles according to the present invention, to which a carbon material made of low-temperature-fired carbon, acetylene black, ketjen black, carbon fiber or graphite is fixed Coating a coating material composed of a mixture of a conductive material such as carbon and a binder on the surface of the negative electrode current collector makes it possible to form a network-like conductive network having a strong electrical connection in the electrode and the negative electrode current collector. Because it helps to form on the surface of the body, and as a result, it suppresses particle shape collapse due to volume expansion / contraction associated with the charge / discharge cycle of lithium secondary batteries, and maintains electrical connection even if miniaturized. The cycle characteristics of the lithium secondary battery could be improved.

As a result, the negative electrode active material particles according to the present invention are: (1) suppression of particle refinement associated with lithium ion occlusion / release of the negative electrode active material particles; and (2) occlusion / release of lithium ions of the negative electrode active material particles. Even if the particles become finer as a result of this, the electrical connection of the finely divided fine particles can be maintained.

Further, the negative electrode according to the present invention has (3) a network-like conductive network bonded to the surface of the negative electrode current collector, and the conductive network exists even if the negative electrode active material particles are finely divided. Therefore, electrical conductivity between each particle is ensured, and it can contribute to the electrochemical reaction of lithium ions.

In addition, the negative electrode according to the present invention is (4) relatively simple by heating the negative electrode active material particles according to the present invention on the surface of the negative electrode current collector, and dissolving or softening the low melting point metal particles or the low melting point alloy particles. Negative electrode active material particles for lithium secondary battery that can be manufactured without oxidizing the negative electrode active material particles in a simple process and can reduce volume change at the time of occlusion and release of lithium ions, a method for manufacturing the same, and negative electrode active material particles A negative electrode and a lithium secondary battery can be provided.

Furthermore, the negative electrode active material particles according to the present invention can provide (5) a lithium secondary battery having high charge / discharge efficiency, no reduction in cycle life and energy density, and no increase in internal resistance.

In addition, the individual ratio of the other metal elements in the present invention, the particle size of the raw material, and the particle size and particle size of each of the alloy particles having an amorphized region and the low melting point metal particles or the low melting point alloy particles as the core thereof The ratio and the like are not particularly limited as long as the technical idea of the present invention is followed. For example, the low melting point alloy particles are not limited to solder, but are metal elements that can be dissolved and bonded to each other at a temperature that does not alter the negative electrode active material particles. And other conductive pastes can also be used, and further, it can be used for a positive electrode active material with poor conductivity, and is appropriately selected according to the use, capacity, and form of the lithium secondary battery.

Hereinafter, the negative electrode using the negative electrode active material particles according to the present invention and the lithium secondary battery using the negative electrode will be described in detail using examples, and a comparative example will show that charge and discharge cycle characteristics are improved. Cite and clarify.

FIG. 1 shows an external perspective view of a thin lithium secondary pack battery 1 using negative electrode active material particles 5 according to the present invention. The battery 1 is provided with a positive electrode terminal 2 and a negative electrode terminal 3, respectively.

FIG. 2 is a perspective view of the negative electrode used in FIG. 1. The negative electrode active material particles 5 according to the present invention are displayed on the front and back surfaces of the negative electrode current collector 4 made of a copper foil having a thickness of about 8 μm. The film is hot press-molded so that the thickness is approximately 40 μm by slightly shifting the position on the back surface.

The negative electrode active material particles 5 have an average particle diameter of 2 μm in which 0.07% aluminum, 0.01% chromium, 0.1% iron and 0.01% magnesium are added in advance to silicon by a usual melt alloying method. Pre-silicon alloy powder particles were prepared and used.

Next, the pre-silicon alloy particles, nickel powder particles and magnesium powder particles having an average particle diameter of 5 μm are mixed at a weight ratio of 0.6: 0.3: 0.1, and an argon gas atmosphere is mixed. It is stored in a planetary ball mill container below, and the container is sealed and rotated at a high speed for about 10 hours (mechanical alloying method) to alloy pre-silicon alloy particles with nickel particles and magnesium powder particles to be amorphous. Qualified.

When the silicon alloy particles 7 produced at this time were subjected to XRD analysis, no silicon element peak was detected. Therefore, it is considered that all silicon was amorphized.

Next, the mechano-fusion apparatus is blended so that the weight ratio of the amorphous silicon alloy powder particles 7 having an average particle diameter of 2 μm and Zn powder particles 6 having an average particle diameter of 8 μm is 16: 1. Using the surface modification composite treatment for 15 minutes, the negative electrode active material pre-particles having the Zn powder particles 6 as nuclei and the silicon alloy powder particles 7 fixed on the surface were prepared and classified at 25 μm or less. Used as raw material powder.

Further, after adding an appropriate amount of a 5% PVA (polyvinyl alcohol) solution as an organic polymer to the classified negative electrode active material pre-particle powder, the organic polymer was applied to the surface by stirring and mixing, and then argon gas was applied. And 5% hydrogen gas in a mixed gas atmosphere at a temperature of about 750 ° C. to deposit and form low-temperature calcined carbon 8 on the surface of the particles, thereby producing negative electrode active material particles 5 according to the present invention.

The negative electrode active material particles 5 thus produced have a weight ratio of 92: 4: 4 of ketjen black 9 as a conductive material for further increasing the conductivity and a binder for binding them. And the solution obtained by kneading this is applied to the surface of the negative electrode current collector 4 made of a copper foil having a thickness of 8 μm, and then dried at about 140 ° C. to obtain negative electrode active material particles according to the present invention. A negative electrode to which 5 was applied was produced.

FIG. 3 shows an enlarged schematic view of the negative electrode cross section (wherein the particles indicate the surface morphology) to which the negative electrode active material particles 5 according to the present invention were applied. On the surface of the negative electrode current collector 4, negative electrode active material particles 5 in which the silicon powder particles 7 and the low-temperature calcined carbon 8 are fixed on the surface with the Zn powder particles 6 as nuclei are combined with the conductive material 9 by a binder. A conductive network is formed by linking connections. In addition, the conductive material 9 also serves to agglomerate and connect the negative electrode active material particles 5 electrically and structurally.

Next, the thickness of the negative electrode coating layer to which the negative electrode active material particles 5 according to the present invention having such a structure are applied is pressed to 77 μm, and the porosity of the negative electrode coating layer is 53% according to the present invention. A negative electrode was produced.

After the negative electrode according to the present invention wound in a coil shape thus produced is cut into a predetermined width, the negative electrode terminal 2 to which the adhesive film is thermally bonded is connected to the end of the negative electrode current collector 4. Inside the battery pack that is ultrasonically welded to the coated part, wound in a flat shape while being stacked via a positive electrode current collector coated with a positive electrode active material after vacuum drying and a separator, and further formed with an aluminum laminate film The battery was heat sealed with one side left, and the electrolyte solution was vacuum impregnated from the unsealed portion, and then the unsealed portion was heat sealed under vacuum to form a lithium secondary battery 1.

The theoretical battery capacity in design of the thin pack battery having the negative electrode coated with the negative electrode active material particles 5 according to the present invention thus produced is about 1,900 mAh.

As another example, the negative electrode active material particles 5 were pre-added with 0.1% iron and 0.1% aluminum in tin by the melt alloying method in the same manner as in Example 1. Next, after pulverization, pre-tin alloy particles having an average particle diameter of 4 μm and cobalt particles having an average particle diameter of 6 μm are mixed at a weight ratio of 80:20, and stored in a planetary ball mill container under an argon gas atmosphere and sealed. Then, it was made amorphous by rotating at a high speed by applying 150 G for about 90 minutes (mechanical alloying method). When the obtained alloy particles were subjected to XRD analysis, the peaks of tin element and cobalt element were not detected, so it is considered that all of them became amorphous.

Further, the crushed tin-cobalt alloy powder particles 7 were mixed with low melting point alloy particles 6 made of Zn—Sn alloy in an inert Ar gas atmosphere and sealed in a container. This was set in a hybridizing machine and operated for about 4 minutes to subject the tin-cobalt alloy particles 7 to surface modification composite treatment. It was observed that the negative electrode active material particles 5 thus produced were bonded to the surface of the Zn—Sn alloy particles 6 with the tin-cobalt alloy particles 7 having an average particle diameter of 2 μm scattered. Furthermore, in order to prevent unevenness of the surface when applied to the negative electrode current collector, the particles were classified so that the maximum particle size was 12 μm or less.

The classified negative electrode active material particles 5 were discharged by a slit nozzle having a certain gap from the surface of the negative electrode current collector 4 made of copper foil, and deposited on the surface of the negative electrode current collector 4 to have a certain thickness. Then, it further roll-pressed with the rolling roll heated at about 170 degreeC, and the negative electrode to which the negative electrode active material particle 5 by this invention was applied was produced. The negative electrode produced in this way is slightly smaller than the negative electrode active material particles 5 of Example 1 shown in FIG. 3 by crushing a part of the Zn—Sn alloy particles 6 serving as nuclei to other particles. It was observed that the negative electrode active material particles 5 were connected to and bonded to the negative electrode current collector 4 and other particles in a dense state.

Using this negative electrode, a lithium secondary battery 1 was produced in the same manner as in Example 1. The theoretical battery capacity in design at that time was 1,950 mAh.

The production conditions of the other main lithium secondary batteries 1 in Examples 1 and 2 produced at this time are as follows.

(1) Negative electrode

In Example 1, dissolution was performed by adding an appropriate amount of a solvent (N-methylpyrrolidone) to a negative electrode mixture composed of 88 wt% of a negative electrode active material, 4 wt% of a conductive agent (Ketjen black), and 8 wt% of a binder (polyvinylidene fluoride). The solution was then applied to the negative electrode current collector 4 (copper foil having a thickness of 8 μm) so that the dry coating film had a thickness of about 60 μm. In Example 2, the negative electrode active material 100 wt% was dissolved by adding an appropriate amount of a solvent (N-methylpyrrolidone) to form a solution, and this was made into a negative electrode current collector 4 (8 μm thick copper foil). The dried coating film was coated so that the thickness was about 60 μm.

(2) Separator

A multilayer polyethylene film having a thickness of about 20 μm was used.

(3) Positive electrode

Mixing of 40 wt% lithium cobaltate, 10 wt% lithium iron phosphate, 90 wt% positive electrode active material consisting of 40 wt% nickel-cobalt lithium, 5 wt% conductive agent (Ketjen Black) and 5 wt% binder (polyvinylidene fluoride) Then, an appropriate amount of a solvent (N-methylpyrrolidone) is added to dissolve it to form a solution, and this is applied to a positive electrode current collector (aluminum foil having a thickness of about 15 μm), and the density of the dried coating film after pressing is 3 The coating was performed so that the thickness was about 70 μm.

(4) Electrolyte

LiPF ₆ was dissolved in a 1: 1 mixture of ethylene carbonate and diethyl carbonate so as to have a concentration of 1M.

FIG. 4 shows a result of a charge / discharge cycle at a 5-hour rate of a lithium secondary battery to which the negative electrode active material particles and the negative electrode according to the present invention are applied, and a low melting point metal as a nucleus as a comparative example. Apply a kneaded solution of a negative electrode active material particle consisting only of silicon alloy particles having an amorphous region that does not have particles or low melting point alloy particles to a conductive agent and a binder to a predetermined thickness with a coating machine. The characteristics of the battery when it is subjected to a charge / discharge cycle at a 5-hour rate by a lithium secondary battery using a negative electrode produced by drying at about 150 ° C. for about 10 minutes and then subjected to press treatment are shown.

Here, the curves indicated by A1 and A2 in FIG. 4 are the charge characteristics and discharge characteristics of the lithium secondary battery in Example 1 according to the first embodiment of the present invention, and the curves indicated by A3 and A4 are 45 cycles. These are the charging characteristics and discharging characteristics of the eyes. B1 and B2 are the charge characteristics and discharge characteristics at the fifth cycle of the lithium secondary battery in Example 2 according to the present invention, and the curves indicated by B3 and B4 are the charge characteristics and discharge characteristics at the 45th cycle. On the other hand, the curves indicated by C1 and C2 are the charge characteristics and discharge characteristics at the fifth cycle of the lithium secondary battery of Comparative Example 2, and the curves indicated by C3 and C4 are the charge characteristics at the 45th cycle. And the discharge characteristics.

According to FIG. 4, it was found that the lithium secondary battery of Example 1 according to the present invention has a battery capacity of 1,900 mAh as originally designed due to the characteristic A. In addition, since the battery capacity is about 1,840 mAh even after the 45th cycle, it is proved that the battery capacity of about 96.8% of the initial design value can be maintained even after the 45th cycle. It was.

Moreover, it was found that the lithium secondary battery of Example 2 according to the present invention has a battery capacity of 1,950 mAh as originally designed due to the characteristic B. Further, since the battery capacity of about 1,900 mAh is exhibited even after the 45th cycle, it is proved that the battery capacity of about 97.4% of the initially measured value can be maintained even after the 45th cycle. It was.

On the other hand, the characteristic C of the lithium secondary battery according to the comparative example shows a battery capacity substantially equal to the designed value of about 1,950 mAh in the initial charge, while the initial designed battery capacity value is about 2,000 mAh. However, it was found that the battery capacity was significantly attenuated at about 1,740 mAh at the 5th cycle and about 940 mAh at the 45th cycle. This is because the resistance layer is formed on the surface of the negative electrode active material particles along with the charge / discharge cycle of the lithium secondary battery, and the electrical connection between each particle is destroyed while repeatedly expanding and contracting and becomes poor it is conceivable that.

As described above, the decrease in the battery capacity after the charging / discharging cycle of the lithium secondary battery according to the present invention is small because the volume of the coating layer composed of the negative electrode active material particles according to the present invention in the negative electrode due to the insertion / extraction of lithium ions. This is presumably because the change in expansion / contraction is small and the coating layer has a strength capable of resisting stress strain caused by the volume change.

More importantly, all or a part of the surface of the low melting point metal particles or the low melting point alloy particles, and / or alloy particles made of silicon or tin, and / or low temperature fired carbon, acetylene black, ketjen black, carbon fiber or graphite The carbon material composed of the carbon material was fixed to form a network-like conductive network, and the connection between the individual particles and the negative electrode current collector could be strengthened through the alloy particles composed of silicon or tin and / or the carbon material. There is. As a result, even if the negative electrode active material particles are further miniaturized due to repeated expansion and contraction associated with the charge / discharge cycle, the surface of the negative electrode active material particles formed into a complicated shape by the surface modification composite treatment effect has a conductive function. Even if the negative electrode active material particles are detached from the negative electrode current collector, an electrical connection network within the negative electrode is secured, and sufficient electron movement during charge / discharge can be achieved. It was.

In addition, in the case where silicon or tin and other metal elements are mixed as the negative electrode active material particles and all or a part thereof is alloyed and adjusted, a plurality of other metal elements are mixed to achieve higher charge / discharge efficiency. It has been found that there are other combinations of other metal elements that are optimal.

For example, aluminum, copper and tin are easily alloyed with other metal elements, lead and antimony promote alloying with other metal elements, and magnesium and cobalt are volume expansions associated with insertion and extraction of lithium ions. It has been found that the tendency to maintain the conductive mechanism by suppressing the refinement of alloy particles made of silicon or tin against shrinkage, that is, the charge-discharge cycle deterioration suppression is strong.

On the other hand, since aluminum, iron, magnesium and nickel are very active metal elements, heat generation due to oxidation occurs unless attention is paid to the atmosphere when alloying with silicon or tin. Since it reduces the charge / discharge efficiency of the lithium secondary battery, it needs to be handled with care. If the metal oxide is present even in a part of the alloy particles made of silicon or tin, when lithium ions are occluded, the lithium ions are oxidized and inactivated, thereby reducing the capacity of the lithium ion battery. It will be. It has been found that the lifetime of the lithium secondary battery is improved by setting the moisture content of all materials used for the lithium secondary battery to 10 ppm or less.

The perspective view of the thin pack battery using the negative electrode active material by this invention is shown. The perspective view of the negative electrode which coated the negative electrode active material by this invention is shown. The principal part expansion model structure sectional drawing of a negative electrode by this invention (however, particle | grains show surface form) is shown. The charging / discharging cycle characteristic of the lithium secondary battery with which the negative electrode by this invention was applied and the lithium secondary battery of a comparative example is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thin battery pack 2 Negative electrode terminal 3 Positive electrode terminal 4 Negative electrode collector 5 Negative electrode active material particle 6 Low melting point alloy particle 7 Silicon alloy particle 8 Low-temperature-fired carbon 9 Conductive material

Claims (9)

A method for producing negative electrode active material particles for a lithium secondary battery that occludes and releases lithium in electrochemistry,
A first step for producing alloy particles comprising silicon or tin by alloying a first other metal element to form an amorphous region in all or part of silicon or tin;
All or a part of the surface of the alloy particles made of silicon or tin is further alloyed and / or surface-treated with the second other metal element to modify the alloy particles made of silicon or tin having an amorphous region. A second step for
A third step for fixing the alloy particles made of silicon or tin to the surface of the low melting point metal particles or the low melting point alloy particles to form negative electrode active material pre-particles;
The surface of the negative electrode active material pre-particles is coated with and fixed to one or more carbon materials selected from the group consisting of low-temperature calcined carbon, acetylene black, ketjen black, carbon fiber and graphite, and the negative electrode active material A fourth step for forming particles, and
In the second step, alloying and / or surface treatment is performed by at least one production method selected from mechanical alloying method, mechanical gliding method, liquid quenching method and gas quenching method,
In the third step, the low melting point metal particles or the low melting point alloy particles have an average particle size larger than that of the alloy particles made of silicon or tin having an amorphous region in which at least all or a part is alloyed. In addition, the alloy particles made of silicon or tin are fixed by at least one production method selected from mechanical alloying method, mechanical gliding method, mechanofusion method, hybridizing method and sintering method. Yes,
The first other metal element is at least one selected from the group consisting of iron, aluminum, chromium, antimony, and magnesium, and the second other metal element is iron, aluminum, cobalt, copper, nickel , Chromium, magnesium, lead, zinc, bismuth, antimony and tin (however, tin is used when silicon is used in the first step), and the low Melting point metal elements are tin (Sn) -lead (Pb) alloy, tin (Sn) -antimony (Sb) alloy, tin (Sn) -silver (Ag) alloy, tin (Sn) -bismuth (Bi) alloy, tin (Sn) -indium (In) alloy, tin (Sn) -zinc (Zn) alloy, tin (Sn) -zinc (Zn) -aluminum (Al) alloy, tin (Sn) -silver (Ag) -indium (I ) - bismuth (Bi) alloys, iron, aluminum, copper, nickel, lead, and wherein the at least one selected from the group consisting of zinc, method of preparing a negative active material particle for lithium secondary batteries. 2. The method for producing negative electrode active material particles for a lithium secondary battery according to claim 1, wherein the average particle diameter of the low melting point metal particles or the low melting point alloy particles is 15 μm or less. 3. The method for producing negative electrode active material particles for a lithium secondary battery according to claim 1, wherein an average particle diameter of the alloy particles made of silicon or tin is 5 μm or less. A method of manufacturing a negative electrode for a lithium secondary battery that electrochemically occludes and releases lithium, wherein a first other metal element is used to form an amorphous region in all or part of silicon or tin. First step for producing alloy particles made of silicon or tin by alloying
All or a part of the surface of the alloy particles made of silicon or tin is further alloyed and / or surface-treated with the second other metal element to modify the alloy particles made of silicon or tin having an amorphous region. A second step for
A third step for fixing the alloy particles made of silicon or tin to the surface of the low melting point metal particles or the low melting point alloy particles to form negative electrode active material pre-particles;
The surface of the negative electrode active material pre-particles is coated with and fixed to one or more carbon materials selected from the group consisting of low-temperature calcined carbon, acetylene black, ketjen black, carbon fiber and graphite, and the negative electrode active material A fourth step for forming particles;
And a fifth step for surface-treating a coating material containing the negative electrode active material particles on a negative electrode current collector to form a negative electrode, and
In the second step, alloying and / or surface treatment is performed by at least one production method selected from mechanical alloying method, mechanical gliding method, liquid quenching method and gas quenching method,
In the third step, the low melting point metal particles or the low melting point alloy particles have an average particle size larger than that of the alloy particles made of silicon or tin having an amorphous region in which at least all or a part is alloyed. In addition, the alloy particles made of silicon or tin are fixed by at least one production method selected from mechanical alloying method, mechanical gliding method, mechanofusion method, hybridizing method and sintering method. Yes,
The first other metal element is at least one selected from the group consisting of iron, aluminum, chromium, anitimon, and magnesium, and the second other metal element is iron, aluminum, cobalt, copper, nickel. , Chromium, magnesium , lead, zinc, bismuth, antimony and tin (however, tin is used when silicon is used in the first step), and the low Melting point metal elements are tin (Sn) -lead (Pb) alloy, tin (Sn) -antimony (Sb) alloy, tin (Sn) -silver (Ag) alloy, tin (Sn) -bismuth (Bi) alloy, tin (Sn) -indium (In) alloy, tin (Sn) -zinc (Zn) alloy, tin (Sn) -zinc (Zn) -aluminum (Al) alloy, tin (Sn) -silver (Ag) -indium (I ) - bismuth (Bi) alloys, iron, aluminum, copper, nickel, lead, and wherein the at least one selected from the group consisting of zinc, method for producing a negative electrode for a lithium secondary battery. In the carbon material of the fourth step, the surfaces of the low melting point metal particles or the low melting point alloy particles to which the alloy particles made of silicon or tin are fixed are coated with a polymer organic material solution and fired in an inert gas atmosphere. The negative electrode active material particles for a lithium secondary battery according to any one of claims 1 to 4, wherein the polymer organic material solution is carbonized or volatilized and fixed. Manufacturing method of negative electrode. The method for producing a negative electrode active material particle for a lithium secondary battery or a negative electrode according to any one of claims 1 to 5, wherein the second and third steps are performed under an inert gas atmosphere. . In the fifth step, the coating material containing the negative electrode active material particles is subjected to surface treatment on the negative electrode current collector by cold rolling method, coating method, sintering method, melt dropping method, DLC method or plasma / thermal spraying method, and then pressed. The manufacturing method of the negative electrode for lithium secondary batteries in any one of Claims 2-6 characterized by the manufacturing method to process, or the manufacturing method to heat-press. The method for producing a negative electrode for a lithium secondary battery according to any one of claims 2 to 7, wherein the porosity of the coating layer of the negative electrode for a lithium secondary battery is 30 to 65%. A method for producing a lithium secondary battery, wherein the negative electrode obtained by the method according to claim 2 is used.

Images