JP2020126835A - Negative electrode active material for lithium-ion battery - Google Patents

Abstract

To provide a negative electrode active material for a lithium-ion battery having a well-balanced and improved cycle characteristics, initial discharge capacity, and initial Coulombic efficiency.SOLUTION: A negative electrode active material for a lithium-ion battery is configured to include a Si phase, a Si-Zr compound phase, and a Sn-X compound phase. An element X is one or more elements selected from the group consisting of Cu, Ti, Co, Fe, Ni, and Zr. Further, the proportion of the Sn-X compound phase in the whole is 0.1 to 18 mass%, and the amount of Si phase is 10 to 80 mass%.SELECTED DRAWING: Figure 1

Description

The present invention relates to a negative electrode active material for lithium ion batteries.

Lithium-ion batteries have the advantages of high capacity, high voltage, and miniaturization, and are widely used as power sources for mobile phones, notebook computers, and the like. Further, in recent years, great expectations have been placed on it as a power source for power applications such as electric vehicles and hybrid vehicles, and its development has been actively promoted.

In this lithium ion battery, lithium ions (hereinafter referred to as Li ions) move between the positive electrode and the negative electrode to perform charging and discharging, and on the negative electrode side, Li ions are occluded in the negative electrode active material during charging, During discharge, Li ions are released from the negative electrode active material.

Conventionally, lithium cobalt oxide (LiCoO ₂ ) has been generally used as the positive electrode side active material, and graphite has been widely used as the negative electrode active material. However, the negative electrode active material, graphite, has a theoretical capacity of only 372 mAh/g, and further higher capacity is desired. Therefore, as a substitute material for the carbon-based negative electrode active material, a metal material such as Si (theoretical capacity of Si is 4198 mAh/g), which is expected to have a higher capacity, has been actively researched recently.

However, since Si absorbs Li ions by an alloying reaction with Li, a large volume expansion/contraction occurs with the absorption/release of Li ions. Therefore, when the negative electrode active material is composed of Si alone, the expansion/contraction stress causes the Si particles to be cracked or peeled from the current collector, which deteriorates the cycle characteristics which are the capacity maintenance characteristics when charging and discharging are repeated. There was a problem.

In order to solve such a problem, various proposals have been made for alloying Si in a negative electrode active material using Si (for example, refer to Patent Document 1 below). In the negative electrode active material containing an element that forms an alloy with Si together with Si, the Si compound phase formed around the Si phase acts to absorb the expansion stress of the Si phase when the Si phase expands. Collapse is suppressed and cycle characteristics can be improved.

On the other hand, miniaturizing Si in the negative electrode active material is also known as an effective method for improving cycle characteristics. However, in the negative electrode active material obtained by alloying Si, the Li storage property of the Si compound phase, that is, the Li pass characteristic is not high. Therefore, when miniaturized, it becomes difficult for Li ions to diffuse and move in the Si compound phase to reach the Si phase, and as a result, the initial discharge capacity and the initial Coulombic efficiency decrease.

JP, 2017-224499, A

The present invention has been made in view of the above circumstances, and an object thereof is to provide a negative electrode active material for a lithium ion battery in which cycle characteristics, initial discharge capacity, and initial Coulomb efficiency are improved in a well-balanced manner.

Thus, the present invention comprises a Si phase, a Si-Zr compound phase and a Sn-X compound phase, and the element X is selected from the group consisting of Cu, Ti, Co, Fe, Ni and Zr. One or more elements of
The ratio of the Sn—X compound phase in the whole is 0.1 to 18% by mass, and the amount of Si phase is 10 to 80% by mass.

In the process of cooling and solidifying the molten metal, the Si-Zr alloy has an Si-Zr compound phase in an island shape and an Si phase in a sea shape. Since most of the sea-like Si phase is located on the outermost surface, the stress applied to the Si-Zr compound phase during Si phase expansion is reduced, and particle collapse can be suppressed. In addition, since the Si-Zr compound phase arranged in an island shape does not expand, it plays a role of an aggregate that maintains the structure of the particles, and it is possible to more effectively suppress the collapse of the particles, and when charging and discharging are repeated. It is possible to improve the capacity maintenance characteristic, that is, the cycle characteristic.

Furthermore, the present invention is characterized in that it is configured to include a Sn-X compound phase. An Sn-X compound composed of Sn and an element selected from the group consisting of Cu, Ti, Co, Fe, Ni, and Zr has a higher Li ion diffusivity than a Si-Zr compound, and therefore is contained in alloy particles. By dispersing the Sn-X compound together with the Si-Zr compound, it becomes easy to secure the diffusion path of Li ions. Therefore, even when the Si phase is miniaturized to improve the cycle characteristics, it is possible to suppress a decrease in the initial discharge capacity and the initial Coulombic efficiency.

Here, in the present invention, the proportion of the Sn—X compound phase in the whole is 0.1 to 18% by mass. Although the Sn-X compound phase is smaller than Sn alone, it expands due to the reaction with Li ions, so if the proportion of the Sn-X compound phase is too high, the cycle characteristics may deteriorate. Therefore, in the present invention, the proportion of the Sn-X compound phase is set to 0.1 to 18% by mass. A more preferable ratio of the Sn-X compound phase is 1 to 10% by mass.

Further, in the present invention, the amount of Si phase is set to 10 to 80 mass %. When the amount of Si that occludes Li ions is small, the initial discharge capacity is reduced, and conversely, when the amount of Si is large, the amount of the Si compound phase is relatively reduced and the cycle characteristics may be deteriorated. Therefore, in the present invention, the amount of Si phase is in the range of 10 to 80 mass %. A more preferable Si phase amount is 20 to 65 mass %.

Here, the Si phase is preferably refined so that the maximum size is 500 nm or less.

According to the present invention as described above, it is possible to provide a negative electrode active material for a lithium ion battery in which cycle characteristics, initial discharge capacity and initial Coulombic efficiency are improved in a well-balanced manner.

3 is a microstructure photograph of a negative electrode active material according to Example 2 by a scanning electron microscope.

Next, a negative electrode active material for a lithium ion battery of one embodiment of the present invention (hereinafter may be simply referred to as a negative electrode active material), a lithium ion battery using the negative electrode active material for a negative electrode (hereinafter may be simply referred to as a battery) ) Will be specifically described.

1. Present Negative Electrode Active Material The present negative electrode active material is made of a Si—Zr—Sn—X alloy and is configured to include a Si phase, a Si—Zr compound phase, and a Sn—X compound phase. Here, the element X is at least one element selected from the group consisting of Cu, Ti, Co, Fe, Ni, and Zr. Elements other than these main constituent elements (Si, Zr, Sn, element X) are not included except those inevitable.

The Si phase is a phase mainly containing Si. From the viewpoint of increasing the amount of absorbed Li, the single phase of Si is preferable. However, unavoidable impurities may be contained in the Si phase.

The Si-Zr compound phase is a phase mainly containing Si ₂ Zr, but inevitably other Zr silicide phases (Si ₄ Zr, Si ₃ Zr ₂ , Si ₅ Zr ₄ , SiZr, SiZr ₂ etc.) May be included. The shape of the Si-Zr compound phase dispersed in the matrix phase (Si phase) is not particularly limited, but considering that the Si-Zr compound phase suppresses expansion and contraction of the Si phase. , A flat shape that increases the contact area with the Si phase is desirable.

On the other hand, the Sn-X compound phase is a phase composed of a compound of Sn and an element selected from the group consisting of Cu, Ti, Co, Fe, Ni and Zr. The feature of the Sn-X compound is that it has a higher Li ion diffusivity than the Si-Zr compound. Comparing the Li reactivities, the Si—Zr compound has 100 mAh/g and the Sn simple substance has 930 mAh/g, whereas the Sn—X compound has 150 to 600 mAh/g.

That is, in the negative electrode active material of this example, the diffusion path of Li ions is easily secured via the Sn—X compound phase. On the other hand, since the degree of expansion due to the reaction with Li ions is smaller than that of Sn, which has high reactivity with Li ions, the adverse effect on the cycle characteristics due to the formation of the Sn-X compound can be suppressed to a low level. .. The Sn-X compound phase may be composed not only of one kind of compound but also of two kinds of Sn-Zr compound and Sn-Cu compound, for example. As described above, the negative electrode active material of the present example is composed of the phases of Si, Si-Zr compound, and Sn-X compound, but if the proportion of the whole is 5 mass% or less, the non-compound Sn simple substance is an impurity. May be included as.

The form of the negative electrode active material is not particularly limited. Specific examples include flakes and powders. From the viewpoint of easy application to the production of the negative electrode, the powder is preferable. The negative electrode active material of the present invention may be dispersed in a suitable solvent.

The negative electrode active material of the present invention can be manufactured by a method including a step of rapidly cooling a molten alloy having a predetermined chemical composition to form a quenched alloy. When the obtained quenched alloy is not in a powder form or when it is desired to reduce the diameter, a step of pulverizing the quenched alloy by an appropriate pulverizing means to form a powder may be added. Further, if necessary, a step of classifying the obtained quenched alloy to adjust it to an appropriate grain size may be added. It is also possible to produce the negative electrode active material of the present invention by separately producing Si, a Si-Zr compound, and a Sn-X compound and mixing them.

The particle size (average particle size (d50)) of the active material is preferably within the range of 1 to 20 μm. The average particle diameter (d50) in the present invention means a volume standard, and can be measured using a laser diffraction/scattering type particle size distribution measuring device (Microtrac MT3000).
Even when a Si alloy is used as an active material, a volume expansion/contraction of the active material itself occurs due to a charge/discharge reaction, which causes a negative electrode active material to bind with a binder, that is, a conductive material layer. Stress is generated in the film. In this case, if the binder cannot withstand the stress, the binder collapses, and as a result, the conductive film peels from the current collector, resulting in a decrease in conductivity in the electrode and deterioration in charge/discharge cycle characteristics. To do. However, when the average particle diameter of the active material is set to 1 to 20 μm, the contact area with the binder is increased due to the miniaturization of the active material, whereby the collapse of the binder is satisfactorily suppressed. As a result, cycle characteristics can be improved.

In the above-mentioned manufacturing method, specifically, the molten alloy is, for example, each raw material is weighed so as to have a predetermined chemical composition, and each weighed raw material is melted by an arc furnace, a high frequency induction furnace, a heating furnace, or the like. It can be obtained by dissolving with.

As a method for quenching the molten alloy, specifically, liquids such as roll quenching method (single roll quenching method, twin roll quenching method, etc.), atomizing method (gas atomizing method, water atomizing method, centrifugal atomizing method, etc.) Although a quenching method and the like can be exemplified, it is particularly preferable to use a roll quenching method having a high cooling rate.

Here, when the negative electrode active material of the present invention is manufactured using the molten alloy containing Si and Zr, specifically, the following method may be used.
That is, when the roll quenching method is applied, the molten alloy that has been tapped into a chamber such as a quenching and recovery chamber and continuously (downwardly) flows downward is rotated at a peripheral speed of 10 m/s to 100 m/s. (The material may be Cu, Fe, or the like, and the surface of the roll may be plated). The molten alloy turns into an alloy material that is foiled or cut into pieces by being cooled on the roll surface. In this case, a powdery negative electrode active material is obtained by crushing the alloy material by an appropriate crushing means such as a ball mill, a disk mill, a coffee mill, or a mortar, and then performing classification or further fine crushing as necessary. To be

On the other hand, when the atomizing method is applied, a gas such as N ₂ , Ar, or He is jetted at a high pressure (for example, 1 to 10 MPa) with respect to the molten alloy that is discharged into the spray chamber and continuously (bar-shaped) flows downward. Add and cool the molten metal while crushing it. The cooled molten metal approaches a sphere while free-falling in the spray chamber while being semi-molten, and a powdery negative electrode active material is obtained. Further, from the viewpoint of improving the cooling effect, high pressure water may be sprayed instead of the gas.

2. Present Battery The present battery is configured using a negative electrode containing the present negative electrode active material.

The negative electrode has a conductive base material and a conductive film laminated on the surface of the conductive base material. The conductive film contains at least the above-described present negative electrode active material in a binder. The conductive film may further contain a conductive auxiliary material, if necessary. When the conductive auxiliary material is contained, it becomes easy to secure a conductive path for electrons.

Further, the conductive film may contain an aggregate, if necessary. When the aggregate is contained, expansion and contraction of the negative electrode during charge and discharge can be easily suppressed, and collapse of the negative electrode can be suppressed, so that cycle characteristics can be further improved.

The conductive base material functions as a current collector. Examples of the material include Cu, Cu alloys, Ni, Ni alloys, Fe, Fe-based alloys, and the like. Preferably, it is Cu or Cu alloy. Moreover, as a specific form of the conductive base material, a foil shape, a plate shape, and the like can be exemplified. The foil shape is preferable from the viewpoints of reducing the volume of the battery and improving the degree of freedom in shape.

Examples of the material of the binder include polyvinylidene fluoride (PVdF) resin, fluororesin such as polytetrafluoroethylene, polyvinyl alcohol resin, polyimide resin, polyamide resin, polyamideimide resin, styrene-butadiene rubber (SBR), polyacrylic acid. And the like can be preferably used. These may be used alone or in combination of two or more. Of these, a polyimide resin is particularly preferable because it has high mechanical strength, can withstand the volume expansion of the active material, and prevents the conductive film from being peeled off from the current collector due to the destruction of the binder.

Examples of the conductive aid include carbon black such as Ketjen black, acetylene black, and furnace black, graphite, carbon nanotubes, fullerenes, and the like. These may be used alone or in combination of two or more. Of these, Ketjen black, acetylene black, and the like can be preferably used from the viewpoint of easily ensuring the electronic conductivity.

The content of the conductive additive is preferably 0 to 30 parts by mass, more preferably 4 to 13 parts by mass with respect to 100 parts by mass of the present negative electrode active material, from the viewpoint of the degree of conductivity improvement, the electrode capacity, and the like. It is good to be within the range. The average particle diameter (d50) of the conductive additive is preferably 10 nm to 1 μm, and more preferably 20 to 50 nm from the viewpoint of dispersibility, handleability, and the like.

As the aggregate, a material that does not expand/contract during charging/discharging or has very little expansion/contraction can be preferably used. For example, graphite, alumina, calcia, zirconia, activated carbon and the like can be exemplified. These may be used alone or in combination of two or more. Of these, graphite and the like can be preferably used from the viewpoint of conductivity, Li activity, and the like.

The content of the aggregate is preferably 10 to 400 parts by mass, and more preferably 43 to 100 parts by mass with respect to 100 parts by mass of the present negative electrode active material from the viewpoint of improving cycle characteristics. And good. The average particle size of the aggregate is preferably 10 to 50 μm, and more preferably 20 to 30 μm from the viewpoint of functionality as an aggregate, control of the electrode film thickness, and the like. The average particle size of the aggregate is a value measured using a laser diffraction/scattering type particle size distribution measuring device.

The present negative electrode is, for example, in a binder dissolved in an appropriate solvent, the present negative electrode active material, and if necessary, a conductive additive and an aggregate are added in a necessary amount to form a paste, which is then applied to the surface of the conductive base material. It can be produced by coating, drying and, if necessary, subjecting it to consolidation, heat treatment, or the like.

When a lithium ion battery is formed using the present negative electrode, the positive electrode, the electrolyte, the separator, and the like, which are the basic constituent elements of the battery other than the present negative electrode, are not particularly limited.

Specific examples of the positive electrode include those in which a layer containing a positive electrode active material such as LiCoO ₂ , LiNiO ₂ , LiFePO ₄ , and LiMnO ₂ is formed on the surface of a current collector such as an aluminum foil. You can

Specific examples of the electrolyte include an electrolyte solution in which a lithium salt is dissolved in a non-aqueous solvent. In addition, a polymer in which a lithium salt is dissolved, a polymer solid electrolyte obtained by impregnating a polymer with the above electrolytic solution, and the like can be used.

Specific examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. These may be contained alone or in combination of two or more.

Specific examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCF ₃ SO ₃ , and LiAsF ₆ . These may be contained alone or in combination of two or more.

Further, other battery components include a separator, a can (battery case), a gasket, and the like, and any of them may be appropriately used as long as it is a material usually adopted in a lithium ion battery. A battery can be formed by combining them.

The shape of the battery is not particularly limited, and may be any shape such as a cylindrical shape, a square shape, and a coin shape, and can be appropriately selected according to its specific application.

Hereinafter, the present invention will be described more specifically with reference to examples. The% of the alloy composition is mass% unless otherwise specified.

1. Preparation of Negative Electrode Active Material Each raw material was weighed so that the alloy composition shown in Table 1 below was obtained. Each of the weighed raw materials was heated and melted using a high frequency induction furnace to obtain an alloy melt. The obtained alloy melts were rapidly cooled using a single roll quenching method to obtain each quenched alloy ribbon. The roll peripheral speed was 42 m/s and the nozzle distance was 3 mm. Each of the obtained quenched alloy ribbons was mechanically crushed using a mortar to produce each powdery negative electrode active material. In addition, if necessary, a planetary ball mill was used to perform miniaturization so that the desired Si phase size could be obtained.

2. Structure Observation of Negative Electrode Active Material, etc. The structure of the negative electrode active material according to each of Examples and Comparative Examples was observed with a scanning electron microscope (SEM). In addition, analysis by XRD (X-ray diffraction) was also performed, and it was confirmed that the phase consisted of Si, Si-Zr compound, and Sn compound. The types of compound phases confirmed are shown in Table 2 below. In addition, XRD analysis measured the range of the angle of 120 degrees-20 degrees using the Co tube.

As a representative example of this example, a scanning electron micrograph of the negative electrode active material according to Example 2 made of a Si—Zr—Sn—Cu alloy is shown in FIG. It can be seen that a large number of gray flat Si compound phases in the figure are dispersed in the matrix phase composed of the black Si phase in the figure. During the process of cooling and solidifying the molten alloy, the Si-Zr compound crystallizes first, and then the Si (Si phase) crystallizes, so that the Si-Zr compound phase is formed into islands and the Si phase is formed into sea. It In FIG. 1, what appears to be dispersed in white is the Sn—Cu compound phase crystallized after Si.

3. Evaluation of Size of Si Phase The Si phase was photographed with a SEM at a magnification of 10,000 times. The size of the Si phase was measured from the captured image. More specifically, five fields of view were photographed, the maximum length of the Si phase in each field of view was measured, and the maximum value was taken as the size of the Si phase. When the Si phase spreads like a sea, the connected Si phase was regarded as one Si phase, and the maximum length thereof was measured. The results are shown in Table 2.

4. Calculation of Si phase amount and Sn-X compound phase amount Regarding the calculation method of the Si phase amount and Sn-X compound phase amount shown in Table 2, the calculation method will be described by taking the case of Example 7 containing Si, Zr, and Sn as an example. explain.
(1) First, confirm the constituent phase. In the case of Example 7, Si, Si ₂ Zr and Sn ₂ Zr were confirmed as a result of the XRD analysis (see Table 2).
(2) Sn ₂ Zr is 72.3[Sn]-27.7[Zr] in terms of mass% ratio. The total amount of Sn is a compound, and correspondingly, the amount of Zr converted into a Sn compound is 3.6×27.7/72.3=1.4 (mass %).
(3) The amount of remaining Zr, 40.8-1.4=39.4 (mass %), corresponds to the amount of Zr that is converted into a Si compound.
(4) Si ₂ Zr is 38.1[Si]-61.9[Zr] in terms of mass% ratio. Since the amount of Zr compounded into Si is 39.4 (mass %) as in (3) above, the amount of Si compounded corresponding to this is 39.4×38.1/61.9=24.3 (mass %). ..
(5) Therefore, the Si phase amount obtained by subtracting the compounded Si amount from the total Si amount can be calculated as 55.6−24.3=31.3 (mass %).
(6) The Sn-X compounds (Sn ₂ Zr) Airyo can be calculated as 3.6 (Sn amount) × 100 / 72.3 = 5.0 (% by weight).

5. Evaluation of Negative Electrode Active Material 5.1 Preparation of Coin-Type Battery for Charge/Discharge Test First, 100 parts by mass of each negative electrode active material and 6 parts by mass of Ketjen Black (manufactured by Lion Corporation) as a conductive auxiliary material were bonded together. 19 parts by mass of a polyimide (thermoplastic resin) binder as a binder was mixed, and this was mixed with N-methyl-2-pyrrolidone (NMP) as a solvent to prepare each paste containing each negative electrode active material.

Each coin type half battery was produced as follows. Here, for the sake of simple evaluation, the electrode prepared using the negative electrode active material was used as the test electrode, and the Li foil was used as the counter electrode. First, each paste was applied to a SUS316L foil (thickness 20 μm) surface serving as a negative electrode current collector so as to have a thickness of 50 μm using a doctor blade method and dried to form each negative electrode active material layer. After formation, the negative electrode active material layer was compacted by roll pressing. Thus, test electrodes according to the examples and comparative examples were produced.

Next, the test electrodes according to the examples and the comparative examples were punched out into a disk shape having a diameter of 11 mm to obtain each test electrode.

Then, a Li foil (thickness: 500 μm) was punched out into a shape substantially the same as that of the test electrode to prepare each counter electrode. Further, LiPF ₆ was dissolved in a mixed solvent of an equal amount of ethylene carbonate (EC) and diethyl carbonate (DEC) at a concentration of 1 mol/l to prepare a non-aqueous electrolytic solution.

Next, each test electrode is housed in each positive electrode can (each test electrode should be a negative electrode in a lithium ion battery, but when the counter electrode is a Li foil, the Li foil becomes a negative electrode and the test electrode becomes a positive electrode). ), the counter electrode was housed in each negative electrode can, and the polyolefin microporous membrane separator was arranged between each test electrode and each counter electrode.

Then, the above nonaqueous electrolytic solution was injected into each can, and each negative electrode can and each positive electrode can were crimped and fixed.

5.2 Charge/Discharge Test Using each coin type battery, constant current charge/discharge with a current value of 0.2 mA was carried out for one cycle, and the capacity (mAh) used at the time of releasing Li was divided by the amount of active material (g). The value was defined as the initial discharge capacity C ₀ (mAh/g). Further, the ratio of the discharge capacity to the charge capacity in the above charge/discharge cycle was obtained as a percentage of discharge capacity/charge capacity to obtain the initial Coulombic efficiency (%).

Regarding the measured initial discharge capacity C ₀ , 1000 (mAh/g) or more was evaluated as “⊚”, 500 to less than 1000 was evaluated as “Δ”, and less than 500 was evaluated as “x”, and the results are shown in Table 2. There is.
Regarding the initial Coulombic efficiency, 70% or more was evaluated as “⊚”, 65 to less than 70% was evaluated as “Δ”, and less than 65% was evaluated as “x”, and the results are shown in Table 2.

After the second cycle, a charge/discharge test was performed at a rate of 1/5C (C rate: the amount of electricity C ₀ required to (charge) and discharge the electrode is set to 1C as a current value for (charge) discharging in 1 hour. It will take 12 minutes for 5C and 5 hours for 1/5C. Then, the charge/discharge cycle was repeated 50 times to evaluate the cycle characteristics. Then, the capacity retention ratio (discharge capacity after 50 cycles/initial discharge capacity (discharge capacity at 1st cycle)×100) was obtained from each of the obtained discharge capacities. Regarding the capacity retention rate, 70% or more was evaluated as “⊚”, 60 to less than 70% was evaluated as “Δ”, and less than 60% was evaluated as “x”, and the results are shown in Table 2.

The comprehensive judgment in Table 2 is based on the evaluation results of each item of initial discharge capacity, initial Coulombic efficiency, and capacity retention rate. here,
"◎ (pass)" when each item is "◎"
"○ (pass)" when any one item is "△" and the other items are "◎"
When any two items were “Δ”, or when any one item was “X”, it was determined as “X (fail)”.

The following can be seen from the results of Table 2 obtained as described above.
Comparative Examples 1 to 4 are examples that do not include a Sn-X compound phase. In Comparative Examples 2 and 3 in which the Si phase amount is 40% or more, the initial discharge capacity and the initial Coulombic efficiency are high, but the capacity retention rate is low.
In Comparative Example 1 in which the Si phase amount is 33%, the capacity retention ratio is improved, but the target (70% or more) is not achieved.
In Comparative Example 4 in which the Si size is reduced to 300 nm, the capacity retention rate is high, but the initial discharge capacity and the initial Coulombic efficiency are reduced. In each of Comparative Examples 1 to 4, the comprehensive determination is “x”.

Comparative Example 5 is an example in which an active material is produced by mechanical milling using Si—Zr alloy powder and Sn powder, and a Sn phase having high reactivity with Li ions is formed instead of the Sn—X compound. .. Therefore, in Comparative Example 5, the initial discharge capacity and the initial Coulombic efficiency are high, but the capacity retention rate is low and the evaluation is “x”.

Comparative Example 6 is an example in which a Si—Fe compound was formed in place of the Si—Zr compound phase, but the capacity retention rate was low and the evaluation was “x”. In Comparative Example 6, since the Si phase is island-shaped and the silicide phase is a sea-island structure, the stress generated when Si expands is applied to the silicide phase and the particles collapse, resulting in poor cycle characteristics. It is estimated that

On the other hand, in each of the examples, the comprehensive judgment is “⊚” or “∘”, which shows that the cycle characteristics, the initial discharge capacity, and the initial Coulomb efficiency are improved in a well-balanced manner. Particularly, in Examples in which the Si phase amount is 20 to 65%, the Si phase size is 500 nm or less, and the Sn-X compound phase amount is 1 to 10%, a high evaluation is obtained.

Although the negative electrode active material for a lithium ion battery and the lithium ion battery of the present invention have been described above in detail, the present invention is not limited to the above-described embodiments and examples, and various modifications are possible within the scope of the present invention. It can be modified.

Claims (4)

It is configured to include a Si phase, a Si-Zr compound phase, and a Sn-X compound phase, and the element X is one or more elements selected from the group consisting of Cu, Ti, Co, Fe, Ni, and Zr. There
The negative electrode active material for a lithium ion battery, wherein the proportion of the Sn-X compound phase in the whole is 0.1 to 18 mass% and the amount of Si phase is 10 to 80 mass %. The negative electrode active material for a lithium ion battery according to claim 1, wherein the maximum size of the Si phase is 500 nm or less. The negative electrode active material for a lithium ion battery according to claim 1, wherein the amount of the Si phase is 20 to 65 mass %. The negative electrode active material for a lithium ion battery according to any one of claims 1 to 3, wherein a ratio of the Sn-X compound phase is 1 to 10% by mass.