KR20050020571A - Negative active material for rechargeable lithium battery, method of preparing same and rechargeable lithium battery comprising same - Google Patents

Abstract

PURPOSE: Provided are a negative electrode active material for a lithium secondary battery which inhibits the expansion and contraction of powder itself and prevents the decomposition of an electrolyte solution at the surface of powder, its preparation method, and a lithium secondary battery containing the active material. CONSTITUTION: The negative electrode active material comprises a multi-phase alloy powder(1) comprising a Si phase(2), a SiM phase(3) and at least one(4) of an X phase and a SiX phase, and the amount of the Si phase at the particle surface of the multi-phase alloy powder is smaller than that of the Si phase at the inside of particle, wherein M is at least one selected from the group consisting of Ni, Co, As, B, Cr, Cu, Fe, Mg, Mn and Y; X is at least one selected from the group consisting of Ag, Cu and Au; and both M and X are not Cu simultaneously. Preferably a micropore(5) is formed on the particle surface of the multi-phase alloy powder.

Description

A negative electrode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery comprising the same TECHNICAL FIELD

[Industrial use]

The present invention relates to a negative electrode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same.

[Prior art]

The study of increasing the capacity of the negative electrode active material of a lithium secondary battery has been actively studied mainly on metal materials such as Si, Sn, and Al until the battery system using the negative electrode active material as carbon, and has been practically used. The main reason is that during charging and discharging, metals such as Si, Sn, and Al are alloyed with lithium to cause volume expansion and shrinkage, which causes micronization of the metal and deteriorates cycle characteristics. In order to solve this problem, as described in Japanese Patent Laid-Open No. 2002-216746, an amorphous alloy, "The 42nd Battery Discussion Meeting Preliminary Proceedings", the Korean Electrochemical Society Battery Technology Committee, November 21, 2013 , p. 296-297 or the 43rd Annual Battery Debate Preliminary Proceedings, The Korean Society of Electrochemical Society Battery Technology Committee, Pyongyang October 21, 14, p. As with the Ni-Si based alloys described in 326-327, amorphous alloys composed of metals that can be alloyed with lithium and metals that are not alloyed with lithium have been studied.

However, when Si powder is used as a negative electrode active material, the possibility of characteristic deterioration is pointed out by the decomposition reaction of electrolyte solution in the surface of Si powder other than expansion shrinkage of the powder itself as a factor of cycle characteristic deterioration.

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a negative electrode active material capable of preventing expansion and contraction of the powder itself and preventing the decomposition reaction of the electrolyte solution on the surface of the powder, a method for producing the same, and a lithium secondary battery using the negative electrode active material. For the purpose of

In order to achieve the above object, the present invention adopts the following configuration.

The negative electrode active material for a lithium secondary battery of the present invention is composed of a polyphase alloy powder which includes a Si phase and a SiM phase, and also includes either or both of an X phase and a SiX phase, and on the particle surface of the polyphase alloy powder. The amount of the Si phase is less than the amount of the Si phase inside the particles. Provided that M is at least one or more elements selected from the group consisting of Ni, Co, As, B, Cr, Cu, Fe, Mg, Mn and Y, and element X is at least one or more of Ag, Cu, Au Is an element, and Cu is not selected at the same time as the element M and the element X.

According to the said negative electrode active material, since the amount of Si phase in particle surface is less than the amount of Si phase in particle | grains, or almost no Si phase exists, electrolyte solution decomposition reaction by the Si phase which is a main negative electrode active material is suppressed, and a cycle characteristic is carried out. Can improve.

In addition, since the element M is an alloy alloyed with Si and not alloyed with Li, since the particles contain a SiM phase in addition to the Si phase, the amount of expansion and contraction of the particles themselves can be reduced as compared with the Si layer alone. Therefore, it is possible to prevent the micronization of the particles themselves, thereby improving cycle characteristics.

In addition, since any one or two of the X phase or SiX phase having a lower resistance than the Si phase, the specific resistance of the negative electrode active material can be reduced.

In addition, Cu is an element having an amphoteric property of the element M and the element X because alloying with Si and lower resistance than Si. Therefore, in the present invention, Cu is added to both the element M and the element X, but Cu is not selected simultaneously as the element M and the element X.

In addition, the negative electrode active material for a lithium secondary battery of the present invention is the above-described negative electrode active material for a lithium secondary battery, characterized in that fine pores are formed on the particle surface of the multiphase alloy powder.

According to the said negative electrode active material, since the micropore is formed in the particle | grain surface, a particle specific surface area is high, it can occlude and discharge lithium quickly, and can improve high rate charge-discharge characteristic.

Further, the average particle diameter of the fine pores is preferably in the range of 10 nm or more and 5 m or less.

In addition, the negative electrode active material for a lithium secondary battery of the present invention is the above-described negative electrode active material for a lithium secondary battery, and the multiphase alloy powder is selected from the group consisting of Ni, Co, As, B, Cr, Cu, Fe, Mg, Mn, and Y. Quenching an alloy melt containing at least one or more elements M and at least one or more elements X and Si selected from the group consisting of Ag, Cu, and Au to prepare a quench alloy powder, and the quench alloy powder is added to an alkaline solution. It is characterized by being formed by removing part or all of the Si phase on the particle surface by impregnation. However, Cu should not be selected simultaneously as the element M and the element X.

According to the negative electrode active material, the amount of the Si phase on the particle surface can be made smaller than the amount of the Si phase inside the particles, thereby suppressing the electrolytic solution decomposition reaction by the Si phase and improving the cycle characteristics. In addition, since the Si phase having the highest resistance is reduced among the phases forming the alloy particles, the surface resistance of the particles can be reduced, and the high rate characteristic can be improved.

Moreover, the negative electrode active material for lithium secondary batteries of this invention is the above-mentioned negative electrode active material for lithium secondary batteries, and the ratio of Si content a on the particle surface of the said polyphase alloy powder obtained by the surface analysis of the electron microscope, and Si content b of the particle cross section is 0.5 <= a / b ≤ 0.95. However, since it is difficult to quantitatively distinguish between alloy phase SiM phase and single phase Si phase by surface analysis, in this case, the Si amount also includes Si of SiM phase.

The negative electrode active material for a lithium secondary battery of the present invention is the above-described negative electrode active material for a lithium secondary battery, and the alloy molten metal is quenched by a gas atomizing method, a water atomizing method, or a roll quenching method.

According to such a negative electrode active material, the polyphase alloy powder which necessarily contains a Si phase and a SiM phase, and contains either or both of an X phase and a SiX phase can be obtained easily. In particular, according to the gas atomization method or the water atomization method, since the spherical powder is obtained, the packing density of the negative electrode active material can be increased, and the energy density of the negative electrode active material can be increased.

Next, the lithium secondary battery of the present invention is characterized by containing any one of the negative electrode active materials described above.

According to this lithium secondary battery, since the said negative electrode active material is included, the decomposition reaction of electrolyte solution can be suppressed and the expansion shrinkage amount of particle | grains itself can be reduced, and cycling characteristics can be improved.

Subsequently, the manufacturing method of the negative electrode active material for lithium secondary batteries of the present invention is at least one element M selected from the group consisting of Ni, Co, As, B, Cr, Cu, Fe, Mg, Mn, and Y, Ag, Cu And quenching an alloy melt containing at least one or more elements X selected from the group consisting of Au and Si, to prepare a quench alloy powder, and impregnating the quench alloy powder with an alkaline solution to partially or all of the Si phase on the particle surface. It characterized in that to remove. However, Cu should not be selected simultaneously as the element M and the element X.

According to the method for producing the negative electrode active material, as the alloy molten metal including the element M, element X and Si is quenched, the Si phase and the SiM phase are necessarily included, and any one or both of the X phase and the SiX phase are included. The quench alloy powder can be easily obtained. Subsequently, the obtained quenching alloy powder can be impregnated with an alkaline solution to remove part or all of the Si phase on the particle surface, so that the amount of the Si phase on the particle surface is smaller than the amount of the Si phase inside the particles. The negative electrode active material thus obtained can suppress the decomposition reaction of the electrolyte solution, reduce the surface resistance of the particles, and reduce the amount of expansion and shrinkage of the particles themselves, thereby improving cycle characteristics.

In addition, the resistivity of the negative electrode active material may be reduced since it includes any one or two of an X phase or a SiX phase having a lower resistance than the Si phase.

In addition, Cu is an element having an amphoteric property of the element M and the element X because alloying with Si and lower resistance than Si. Therefore, although Cu can be used for both the element M and the element X in this invention, Cu is not selected simultaneously as the element M and the element X.

Moreover, the manufacturing method of the negative electrode active material for lithium secondary batteries of this invention is the manufacturing method mentioned above, It is characterized by quenching the said molten metal by the gas atomizing method, the water atomizing method, or the roll quenching method.

According to the said manufacturing method, the polyphase alloy powder which necessarily contains a Si phase and a SiM phase, and contains either or both of an X phase and a SiX phase can be obtained easily. In particular, according to the gas atomization method or the water atomization method, since the spherical powder is obtained, the packing density of the negative electrode active material can be increased, and the energy density of the negative electrode active material can be increased. Among them, in the case of gas atomization, since helium gas is used as the cooling gas, each structure in the alloy particles can be made fine, so that the cycle characteristics can be further improved.

Moreover, the manufacturing method of the negative electrode active material for lithium secondary batteries of this invention is the manufacturing method mentioned above, Alkaline solution so that the specific surface area of the powder after Si phase removal may be 1.2 times or more and 50 times or less of the specific surface area of the quenching alloy powder before Si phase removal. It is characterized in that the impregnation treatment.

According to such a manufacturing method, since the impregnation process is performed so that the specific surface area may be 1.2 times or more initially, Si of a particle surface elutes, reaction of Si and electrolyte solution can be suppressed, and cycling characteristics can be improved.

The removal of the Si phase with the alkaline solution is preferably carried out so that the specific surface area of the powder after removing the Si phase is 50 times or less of the specific surface area of the quench alloy powder before removing the Si phase. When the amount is 50 times or more, the amount of Si used as the active material is reduced, the capacity is greatly reduced, and the particles are structurally broken, collapsed by expansion and contraction due to charge and discharge, and the cycle characteristics are deteriorated, which is not preferable.

Embodiments of the present invention will be described below with reference to the drawings.

The negative electrode active material for lithium secondary battery of this embodiment consists of a polyphase alloy powder which necessarily contains a Si phase and a SiM phase, and also contains either or both of an X phase and a SiX phase, and the Si on the particle surface of a polyphase alloy powder is carried out. The amount of phase is comprised less than the amount of Si phase inside a particle. In FIG. 1, an example of an external appearance schematic diagram of one particle constituting the polyphase alloy powder is illustrated, and FIG. 2 illustrates an example of a cross-sectional schematic diagram of one particle illustrated in FIG. 1.

As shown in FIG. 1 and FIG. 2, the structure of the polyphase alloy powder particle 1 which comprises a negative electrode active material contains the Si phase 2, the SiM phase 3, and the Si phase or SiX phase 4.

Si phase 2 exists more inside a particle than a particle surface. This Si phase 2 is alloyed with lithium at the time of charging to form a LiSi _x phase, and at the time of charging, lithium is released to return to the Si phase. In addition, since the Si phase does not remain or is small on the particle surface, the Si phase is less in direct contact with the electrolyte solution, and the decomposition reaction of the electrolyte solution by the Si phase is suppressed.

In addition, the SiM phase 3 maintains the shape of the particles 1 without reacting with lithium during charge and discharge to control expansion and contraction of the particles 1 itself. The element M constituting the SiM phase 3 is a metal element which is not alloyed with lithium and is at least one element selected from the group consisting of Ni, Co, As, B, Cr, Cu, Fe, Mg, Mn, and Y. to be. It is particularly preferable to use Ni as the element M, in which case the composition of the SiM phase is a Si ₂ Ni phase.

In addition, the X phase 4 imparts conductivity to the polyphase alloy powder and reduces the specific resistance of the negative electrode active material itself. The element X constituting the X phase 4 is a metal element having a specific resistance of 3 Pa · m or less, and is at least one element selected from the group consisting of Ag, Cu, or Au. Cu is particularly preferable because it does not alloy with lithium and has an expansion inhibiting effect. In addition, since Ag hardly alloys with Si, it is preferable to select a metal which does not alloy with Ag as the element M, so that Ag exists in a single phase and the conductivity of the particles can be improved.

In addition, Cu is an element having both properties of the element M and the element X because alloying with Si and lower resistance than Si. Therefore, although Cu can be used for both the element M and the element X in this invention, it is assumed that Cu is not selected by the element M and the element X simultaneously.

In addition, the SiX phase may be precipitated instead of the X phase 4 or together with the X phase 4. The SiX phase, like the X phase 4, imparts conductivity to the multiphase alloy powder, thereby reducing the specific resistance of the negative electrode active material itself.

The crystal forms of the Si phase (2), the SiM phase (3), the X phase (4), and the SiX phase are determined by the quench rate, the alloy composition, and the presence or absence of heat treatment after quenching. In the negative electrode active material of this embodiment, the whole phase may be a crystalline phase, an amorphous phase may be sufficient, and a crystalline phase and an amorphous phase may be mixed. In addition to the Si phase, SiM phase, X phase, and SiX phase, other alloy phases may be included.

Next, when the alloy composition is described, since Si is an element which forms the Si single phase, the SiM phase and the SiX phase, the composition ratio is selected so as to generate the Si single phase even when the SiM phase and the SiX phase are formed by analyzing the state diagram of the alloy. As a result, Si capacity can be obtained. However, when the Si amount is excessively increased, a large amount of Si phase is precipitated, and the amount of expansion and shrinkage of the entire negative electrode active material increases during charging and discharging, and the negative electrode active material is undifferentiated to deteriorate cycle characteristics. Specifically, the range of the Si composition ratio of 30 mass% or more and 70 mass% or less in the negative electrode active material is preferable.

Since element M forms an SiM phase with Si, it is preferable to add so that the whole amount of element M may alloy with Si by analyzing the state diagram of an alloy. When the amount of M is increased to an amount that can be alloyed with Si, Si is slipped and alloyed, so that the capacity can be greatly reduced, which is not preferable. If the amount of M is small, the amount of SiM phase is small, the effect of suppressing expansion of the Si phase is small, and cycle characteristics are deteriorated. In addition, a plurality of elements may be present, such as elements different from M phase, M1 phase, M2 phase, and M3 phase. The composition ratio of M is not particularly limited since the Si and solid solution limits vary depending on the element, but it is preferable to select the composition ratio so that Si still exists even when Si and M are alloyed to the solid solution limit. In addition, since the element M is not alloyed with lithium, no irreversible capacity appears. Moreover, it is preferable that element M is insoluble about an alkaline solution.

In addition, when the composition ratio of X is large, the specific resistance is reduced, so that the Si phase is relatively decreased, thereby reducing the charge and discharge capacity. On the other hand, when the X composition ratio is reduced, the specific resistance of the negative electrode active material is increased to reduce the charge and discharge efficiency. For this reason, it is preferable that X composition ratio in a negative electrode active material is the range of 1 mass% or more and 30 mass% or less. Moreover, it is preferable that element X is insoluble about an alkaline solution.

The average particle diameter of the polyphase alloy powder is preferably in the range of 5 µm or more and 30 µm or less. In general, the alloy powder containing Si has a higher resistance than the graphite powder used as a conventional negative electrode material of a lithium ion battery, and therefore, it is preferable to use a conductive material. However, when the average particle diameter is 5 µm or less, the phase diameter of the conductive assistant is multiphase. The case where the average particle diameter of an alloy powder is small arises, the effect of a conductive support is acquired, and battery characteristics, such as a capacity | capacitance and a cycle characteristic, fall, and are unpreferable. Moreover, when the average particle diameter exceeds 30 micrometers, the charge density of a negative electrode active material falls in a lithium battery, and is unpreferable.

1 and 2, a plurality of fine pores 5 are formed on the particle surface of the polyphase alloy powder. The fine pores 5 are formed by quenching the molten alloy and then impregnating the alkaline solution, and are traces of the elution of the Si phase exposed to the particle surface immediately after quenching. As a result, since Si is not exposed to the particle surface, the reaction with the electrolyte is suppressed during charging, and as the fine pores 5 are formed, the specific surface area of the polyphase alloy powder is increased, and the contact area with the electrolyte is increased, thereby charging and discharging. The efficiency is improved.

The average pore particle size of the fine pores 5 is preferably in the range of 10 nm or more and 5 μm or less. In addition, the thickness of the fine pores 5 is preferably in the range of 10 nm or more and 1 m or less. The specific surface area of the polyphase alloy powder is preferably in the range of 0.2 m ² / g or more and 5 m ² / g or less.

According to the said negative electrode active material, since the amount of Si phase in particle surface becomes less than the amount of Si phase in particle inside, electrolyte solution decomposition reaction by a Si phase can be suppressed and a cycle characteristic can be improved. In addition, since the particles contain a SiM phase and an X phase in addition to the Si phase, the amount of expansion and shrinkage of the particles themselves can be reduced as compared with the Si phase alone, and the fineness of the particles itself is prevented and the conductivity is improved and the cycle is achieved. Properties can be improved.

In addition, fine pores are formed on the surface of the particles, the specific surface area of the particles is increased, it is possible to quickly occlude and release the lithium ions, it is possible to improve the high rate charge and discharge characteristics.

Next, the lithium secondary battery using the said negative electrode active material is demonstrated. This lithium secondary battery contains at least the negative electrode, the positive electrode, and the electrolyte containing the negative electrode active material.

The negative electrode of a lithium secondary battery can illustrate that the polyphase alloy powder which comprises a negative electrode active material solidified-molded in the sheet form by the binder, for example. In addition, the cathode is not limited to being solidified in a sheet form, and pellets solidified in a columnar shape, a disk shape, a plate shape or a cylindrical shape may be used.

The binder may be either organic or inorganic, but any binder may be used as long as the binder is dispersed or dissolved in a solvent together with the negative electrode active material alloy powder, and then the alloy powders are bound together by removing the solvent. In addition, it is also possible to bind the alloy powders together by dissolving together with the alloy powder and performing solidification molding such as pressure molding. As such a binder, for example, a vinyl resin, a cellulose resin, a phenol resin, a thermoplastic resin, a thermosetting resin, or the like can be used. For example, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, styrenebutadiene Resin, such as rubber, can be illustrated.

In the negative electrode of the present invention, carbon black, graphite powder, carbon fiber, metal powder, metal fiber, or the like may be added as a conductive material in addition to the negative electrode active material and the binder.

Subsequently, the positive electrode can occlude and release lithium such as LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , V ₂ O ₅ , TiS, MoS, and an organic sulfide compound and an organic polysulfide compound. The composite oxide containing a positive electrode active material and Ni, Mn, Co type | system | group etc. can be illustrated. In addition to the positive electrode active material, a binder such as polyvinylidene fluoride and a conductive additive such as carbon black may be added to the positive electrode.

Specific examples of the positive electrode and the negative electrode may be one in which the positive electrode or the negative electrode is applied to a conductor made of a metal foil or a metal mesh and molded into a sheet.

Moreover, as electrolyte solution, the organic electrolyte solution which the lithium salt melt | dissolved in the aprotic solvent can be illustrated, for example.

Examples of aprotic solvents include propylene carbonate, ethylene carbonate, butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetoamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate, methyl ether carbonate, diethyl carbonate, methylpropyl Examples of aprotic solvents such as carbonate, methyl isopropyl carbonate, ethyl butyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, diethylene glycol, and dimethyl ether, or a mixed solvent in which two or more kinds of these solvents are mixed. Propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC) It is always necessary to include any one of the dimethyl carbonate, methyl ethyl carbonate (MEC), diethyl carbonate (DEC) is also preferably included.

LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF3SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural water), LiCl, LiI, etc., any one, or a mixture of two or more lithium salts will be exemplified. In particular, it is preferable to include any one of LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , and LiN (C ₂ F ₅ SO ₂ ).

As another example of the electrolyte, so-called polymer electrolytes such as a mixture of any one of the lithium salts described above with a polymer such as PEO and PVA, and an organic electrolyte solution impregnated with a highly expandable polymer may be used.

In addition, the lithium secondary battery of the present invention is not limited to the positive electrode, the negative electrode, and the electrolyte, and may include other members or the like as necessary, and may include, for example, a separator that separates the positive electrode and the negative electrode.

According to such a lithium secondary battery, since the expansion and contraction accompanying charge / discharge is reduced, including the negative electrode active material, there is no fear that the negative electrode active material is undifferentiated or detached from the current collector, and the contact with the conductive material is also maintained, thereby charging. The cycle characteristics can be improved while improving the discharge capacity.

In addition, since the amount of precipitation of the Si phase on the surface of the polyphase alloy particles decreases, the decomposition reaction of the nonaqueous electrolyte solution is suppressed, so that the charge and discharge capacity can be improved, and the cycle characteristics can be improved.

In addition, a plurality of fine pores are formed on the surface of the particles of the polyphase alloy powder, and when used as a negative electrode active material of a lithium secondary battery, the fine pores are impregnated with the nonaqueous electrolyte and have a high conductivity X phase, thereby increasing the diffusion of lithium ions. It can be performed efficiently and high rate charge / discharge can be attained.

Next, the manufacturing method of the negative electrode active material for lithium secondary batteries of this embodiment is demonstrated. The manufacturing method of the negative electrode active material for lithium secondary batteries of this embodiment is roughly comprised by the process of manufacturing the quenching alloy powder containing Si, the element M, and the element X, and the process of impregnating the obtained quenching alloy powder in alkaline solution. . Hereinafter, each process is demonstrated in order.

First, in the process of manufacturing a quenching alloy powder, the molten alloy containing Si, the element M, and the element X is quenched and a quench alloy powder is manufactured. The molten alloy is at least one element selected from the group consisting of Ni, Co, As, B, Cr, Cu, Fe, Mg, Mn, and Y, and at least one member selected from the group consisting of Ag, Cu, and Au. The above-mentioned element X and Si are included, and one or these alloys are melt | dissolved simultaneously, for example by a high frequency induction heating method, and are manufactured.

In the molten alloy, the Si content is preferably in the range of 30% by mass or more and 70% by mass or less. When the Si content in the molten alloy is out of the above range, the Si content becomes too small, the Si phase is not precipitated, and the amount of Si is too large, so that a negative electrode active material which is easy to expand and contract is obtained, which is not preferable.

As a method of quenching the molten alloy, for example, a gas atomizing method, a water atomizing method, a roll quenching method, or the like can be used. A powdery quenching alloy is obtained by the gas atomizing method and a water atomizing method, and a thin band-shaped quenching alloy is obtained by the roll quenching method. The thin strip of quench alloy is ground again to produce a powder. The average particle diameter of the quenched alloy powder produced thereby becomes the particle diameter of the polyphase alloy powder finally obtained. Therefore, when manufacturing a quenching alloy powder, it is required to adjust this average particle diameter to the range of 5 micrometers or more and 30 micrometers or less.

The quenching alloy powder obtained from the molten alloy is a quenching alloy in which the entire structure is in an amorphous phase, a quenching alloy in which some are in an amorphous phase and the remainder is a crystalline phase or a quenching alloy in which the entire structure is in a crystalline phase. Alternatively, the quench alloy powder necessarily includes a SiX phase and a SiM phase, and also includes either or both of an X phase and a SiX phase. In addition, each of these Si phase, SiM phase, X phase, and SiX phase is a state mixed uniformly in alloy structure.

In the case of quenching, the quenching speed is preferably 100 K / sec or more. If the quenching rate is less than 100 K / sec, there is a fear that each phase of the Si phase, SiM phase, X phase, and SiX phase may not be uniformly precipitated in the alloy structure, or the crystal size of each phase is too large, resulting in a uniform expansion and contraction effect, It is unpreferable since electroconductivity provision effect is not acquired.

Next, in the step of impregnating the quench alloy with the alkaline solution, the Si phase precipitated on the particle surface of the quench alloy powder is eluted and removed. Specifically, the quench alloy powder is impregnated with an alkaline solution, followed by washing and drying. The condensing conditions are preferably conditions to be performed while stirring slowly at room temperature for about 30 minutes to 5 hours. As the alkaline solution, for example, an aqueous solution of sodium hydroxide and potassium hydroxide is preferably used, and the concentration is preferably in the range of 1 to 5N.

However, the impregnation conditions described here are the final targets, and in reality, impregnation conditions can be determined in which only the Si phase precipitated on the particle surface is confirmed to be eluted and removed. Excessive impregnation treatment elutes not only the surface but also the Si phase inside the particles, and the charge and discharge capacity of the negative electrode active material is lowered, which is not preferable. In addition, when the agitation conditions are insufficient, the Si phase remains on the surface of the particles and causes an electrolyte solution decomposition reaction, which is not preferable.

Specifically, it is preferable to impregnate the alkaline solution so that the specific surface area of the powder after removing the Si phase becomes 1.2 times or more of the specific surface area of the quench alloy powder before removing the Si phase. By performing the impregnation treatment until the specific surface area reaches 1.2 times or more initially, part or all of the Si on the surface can be removed, and the reaction with the electrolyte solution can be suppressed.

Moreover, even if there is little specific surface area after Si phase removal, it is good to impregnate an alkaline solution so that it may become 50 times or less of the specific surface area of the quenching alloy powder before Si phase removal. As a result, it is possible to prevent dissolution of Si more than necessary and to prevent reduction of battery capacity.

By performing the said impregnation process, the Si phase precipitated on the particle surface of the quenching alloy powder is eluted and removed, and the SiM phase, X phase, or SiX phase remains on the particle surface. In addition, fine pores are formed in the portion from which the Si phase is removed. In addition, since the Si phase on the particle surface is removed, the amount of the Si phase on the particle surface becomes smaller than the amount of the Si phase inside the particles.

However, since the element M and the element X are insoluble with respect to the alkaline solution, and the SiM phase and the SiX phase are difficult to dissolve in the alkali solution, the Si phase is eluted predominantly.

According to the method for producing the negative electrode active material, as the molten alloy containing the element M, element X and Si is quenched, the SiX phase and the SiM phase are necessarily included, and the polyphase including any one or both of the X phase and the SiX phase. Alloy powder can be easily formed. Subsequently, the obtained quenching alloy powder can be impregnated with an alkaline solution to remove the Si phase on the particle surface, and the amount of the Si phase on the particle surface can be made smaller than the amount of the Si phase inside the particles. The negative electrode active material thus obtained can suppress the decomposition reaction of the electrolyte solution and reduce the amount of expansion and contraction of the particles themselves, thereby improving the cycle characteristics.

In addition, it is possible to easily form a multiphase alloy powder that necessarily includes a SiX phase and a SiM phase, and also includes either or both of an X phase and a SiX phase. In particular, according to the gas atomizing method or the water atomizing method, since the spherical powder is obtained, the packing density of the negative electrode active material can be increased, and the energy density of the negative electrode active material can be increased.

Example 1

55 parts by weight of massive Si powder, 35 parts by weight of Ni powder, and 10 parts by weight of Ag powder were prepared, respectively, and they were mixed and dissolved in an argon atmosphere by high frequency heating to prepare an alloy molten metal. The molten alloy was quenched by a gas atomization method using helium gas at 80 kg / cm ² pressure to prepare a quench alloy powder having an average particle diameter of 10 µm. The quenching rate at this time was 1 × 10 ⁵ K / sec.

Subsequently, the obtained quenching alloy powder was added to 5N aqueous sodium hydroxide solution, and it was impregnated over 4 hours, stirring gradually at room temperature. Thereafter, the solution was sufficiently washed with pure water and dried to prevent sodium remaining, and then the particle size was adjusted to an average particle diameter of 10 µm. Thus, the negative electrode active material of Experimental Example 1 was prepared.

As a result of performing X-ray diffraction on the obtained powder, a structure in which the crystalline phase and the Ag crystalline phase of the composition consisting of Si crystalline phase and NiSi ₂ were mixed was confirmed.

Moreover, the shape observation was performed with the electron microscope about the quenching alloy particle before the joining process and the quenching alloy particle after the impregnation process. The results are shown in FIGS. 3 and 4. As shown in FIG. 3, it can be seen that the quench alloy powder particles before the impregnation process are spherical and the surface is relatively smooth. However, the photograph shown to FIG. 3 and FIG. 4 is a secondary electron image, and in FIG. 3, a Si phase is shown to be comparatively dark gray. As shown in Fig. 3, the Si phase shows a long and slender improvement in appearance. In addition, in Fig. 3, the NiSi ₂ phase is seen to be relatively light gray. As shown in FIG. 3, the NiSi ₂ phase is located around the Si phase.

On the other hand, the quenching alloy powder particles after the impregnation treatment, it can be seen that a large number of fine pores are formed on the surface, as shown in FIG. It can also be seen that the color of the particle surface is relatively one. The micropores on the surface are thought to be formed by eluting the Si phase exposed on the surface. In addition, the color of the particle surface is relatively one because the Si phase elutes, the surface is occupied by the NiSi ₂ phase and the surface composition becomes uniform.

As described above, as the molten alloy containing Ni, Ag and Si is quenched, the quench alloy powder having the Si phase, the NiSi ₂ phase (SiM phase) and the Ag phase (X phase) can be easily formed. Therefore, as the obtained quenching alloy powder is impregnated with the alkaline solution to remove the Si phase on the particle surface, the Si phase on the particle surface can be reduced.

(Example 2)

A negative electrode active material of Experimental Example 2 was prepared in the same manner as in Experiment 1 except that Cu powder was used for the Ag powder.

In addition, the negative electrode active material of Experimental Example 3 was prepared in the same manner as in Experimental Example 1 except that the treatment time of the impregnation treatment was 1 hour.

Further, the negative electrode active material of Experimental Example 4 was prepared in the same manner as in Experiment 1 except that the treatment temperature of the impregnation treatment was 40 ° C. and the treatment time was 1 hour.

The negative electrode active material of Experimental Example 5 was prepared in the same manner as in Example 1 except that the treatment temperature of the impregnation treatment was 60 ° C. and the treatment time was 1 hour.

In addition, the negative electrode active material of Experimental Example 6 was prepared in the same manner as in Experiment 1 except that the impregnation treatment was not performed.

A lithium secondary battery was manufactured using the negative electrode active material of Experimental Example 1 prepared in Experimental Examples 2 to 6 and Example 1. 70 parts by weight of each of the negative electrode active materials of Experimental Examples 1 to 6, 20 parts by weight of graphite powder having an average particle diameter of 3 μm as a conductive material, and 10 parts by weight of polyvinylidene fluoride were mixed, N-methylpyrrolidone was added and stirred, Slurry was prepared. Subsequently, this slurry was applied onto a copper foil having a thickness of 14 µm and dried, and then rolled to prepare a cathode having a thickness of 40 µm. The prepared negative electrode was cut into a circle having a diameter of 13 mm, and metal negative electrode was used as a counter electrode via a porous polypropylene separator, and 1.3 mol / l of LiPF ₆ was added in a mixed solvent of EC: DEC3: 7 in terms of capacity ratio. Coin-type titanium secondary batteries were prepared by pouring the electrolyte solution prepared by adding L at a concentration.

The obtained lithium secondary battery was repeatedly charged and discharged at a current density of 0.2 C in a battery voltage of 0 V to 1.5 V for 50 cycles. At this time, the initial discharge capacity, the first charge and discharge efficiency, and the capacity retention rate after 50 cycles were determined. The results are shown in Table 1. Table 1 also shows the specific surface area of the negative electrode active materials of Examples 1 to 6 and the ratio (a / b) of Si content a on the particle surface of the polyphase alloy powder obtained by surface analysis of an electron microscope and Si content b on the particle cross section. Together. In addition, Si amount was measured based on the intensity | strength of Si characteristic X-ray.

Initial capacity (mAh / g) Initial charge and discharge efficiency (%) Capacity retention rate (%) Specific surface area (m ² / g) a / b Example 1 721 92.3 92.8 1.8 0.86 Example 2 637 91.5 95.0 1.9 0.82 Example 3 783 92.2 85.0 0.9 0.91 Example 4 680 92.2 90.3 2.8 0.78 Example 5 600 87.0 65.7 13.0 0.62 Example 6 920 92.8 80.0 0.15 0.99

As shown in Table 1, it can be seen that the capacity retention rate of the lithium secondary batteries of Experimental Examples 1 to 4 subjected to the impregnation treatment of the negative electrode active material is higher than that of the lithium secondary battery of Experimental Example 6 not subjected to the impregnation treatment. This is considered to be because in Experimental Examples 1 to 4, since the Si phase on the particle surface of the negative electrode active material was removed by the impregnation treatment, the decomposition reaction of the electrolyte solution was suppressed by the Si phase. In addition, it is considered that the Si phase having a high specific resistance is removed by the impregnation treatment, which contributes to the reduction of the surface resistance of the particle surface and the improvement of capacity retention. However, if the impregnation treatment is excessively carried out as in Experimental Example 5, the Si inside the particles is also eluted, so that the strength of the particles is lowered, and the cycle characteristics are lowered without being able to withstand expansion.

Moreover, when comparing Experimental Example 1 and 2, it turns out that the capacity retention rate of Experimental Example 2 is high. This is because Ag used as the element X in Experimental Example 1 is alloyed with Li, and thus the capacity retention rate of Experimental Example 1 is lowered, while Cu used as the element X in Experimental Example 2 is not alloyed with Li. do.

In Experiment 3, the impregnation time was shorter than that of Experiment 1, and therefore, the Si phase slightly remained on the particle surface. Therefore, the capacity retention rate is lower than that of Experimental Example 1, but it can be seen that capacity retention is superior to Experimental Example 6.

In addition, the impregnation temperature of Experimental Example 4 was higher than that of Experimental Example 1, and thus eluted to the Si phase inside the particles. Therefore, although the capacity retention rate is the same as that of Experimental Example 1, the initial dose was lower than that of Experimental Example 1.

In addition, the impregnation temperature of Experimental Example 5 was higher than that of Experimental Example 4, and therefore eluted to the Si phase inside the particles. Therefore, the capacity | capacitance retention and initial stage capacity fell more significantly than Experimental example 1.

As described above, when the impregnation treatment is appropriately performed, it is understood that the Si phase inside the particles can be eluted and removed, thereby improving the cycle life and the charge / discharge capacity of the lithium secondary battery at the same time.

As described above, according to the negative electrode active material for a lithium secondary battery of the present invention, the decomposition reaction of the electrolyte solution can be suppressed by the Si phase, the resistance of the particle surface can be reduced, and the amount of expansion and shrinkage of the particles themselves can be reduced, By preventing the micronization of the particles themselves, the cycle characteristics can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic diagram which showed the negative electrode active material for lithium secondary batteries of embodiment of this invention.

2 is a schematic cross-sectional view showing a negative electrode active material for a lithium secondary battery of an embodiment of the present invention.

3 is an electron micrograph (secondary electron image) of the negative electrode active material of Experimental Example 1 before the impregnation treatment.

4 is an electron micrograph (secondary electron image) of the negative electrode active material of Experimental Example 1 after the impregnation treatment.

Claims (10)

A polyphase alloy powder comprising a Si phase and a SiM phase and comprising either or both of an X phase and a SiX phase, and the amount of Si phase on the particle surface of the multiphase alloy powder is the amount of Si phase in the particles. A negative electrode active material for a lithium secondary battery, characterized in that less, wherein M is at least one or more elements selected from the group consisting of Ni, Co, As, B, Cr, Cu, Fe, Mg, Mn and Y, element X Is at least one element selected from the group consisting of Ag, Cu, and Au, and Cu is not selected at the same time as the element M and the element X. The negative electrode active material of claim 1, wherein fine pores are formed on a particle surface of the multiphase alloy powder. The negative electrode active material of claim 2, wherein the average particle diameter of the fine pores is 10 nm or more and 5 µm or less. The at least one element M according to any one of claims 1 to 3, wherein the polyphase alloy powder is selected from the group consisting of Ni, Co, As, B, Cr, Cu, Fe, Mg, Mn and Y. And quenching the molten alloy containing at least one element X selected from the group consisting of Ag, Cu, and Au and Si, to form a quench alloy powder, and impregnating the quench alloy powder into an alkaline solution to form a particle surface. A negative electrode active material for lithium secondary batteries, wherein a part or all of Si phases are removed to form Cu, wherein Cu is not simultaneously selected from element M and element X. The negative electrode for a lithium secondary battery according to claim 1, wherein a ratio of Si content a on the surface of the particles of the polyphase alloy powder obtained by electron microscope surface analysis and Si content b of the particle cross section is 0.5 ≦ a / b ≦ 0.95. Active material. The negative electrode active material for lithium secondary battery according to claim 4, wherein the molten alloy is quenched by a gas atomizing method, a water atomizing method, or a roll quenching method. The lithium secondary battery containing the negative electrode active material for lithium secondary batteries in any one of Claims 1-6. At least one element M selected from the group consisting of Ni, Co, As, B, Cr, Cu, Fe, Mg, Mn and Y, and at least one element X selected from the group consisting of Ag, Cu and Au; And quenching the molten alloy containing Si to produce a quench alloy powder, and impregnating the quench alloy powder with an alkaline solution to remove part or all of the Si phase on the surface of the particle. As a method for producing a negative electrode active material for a lithium secondary battery, wherein Cu is not simultaneously selected as an element M and an element X. The method for producing a negative electrode active material for a lithium secondary battery according to claim 8, wherein the molten metal is quenched by a gas atomizing method, a water atomizing method or a roll quenching method. 10. The alkaline solution according to claim 8 or 9, wherein the alkaline solution is impregnated so that the specific surface area of the powder after removing the Si phase is 1.2 times or more and 50 times or less the specific surface area of the hot water alloy powder before removing the Si phase. The manufacturing method of the negative electrode active material for lithium secondary batteries.