Silicon alloy for lithium-ion battery anode

Abstract

To provide a silicon alloy for a lithium-ion battery anode with a new composition that has excellent cycle characteristics.SOLUTION: A silicon alloy for a lithium-ion battery anode is an Si alloy having an Si phase, an SiX phase that is a first Si compound phase, and an SiY phase that is a second Si compound phase. The amount of Si phase in the entire Si alloy is 20 to 90 mass%, the element X is at least one element selected from the group consisting of Fe, Co, Zr, Ti, Cr, V, Mo, Ta, Nb, and W, and the element Y is at least one element selected from the group consisting of La, Sm, Ni, Ce, Mn, and Cu.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This invention relates to a Si alloy for use in the negative electrode of a lithium ion battery. [Background technology]

[0002] Lithium-ion batteries have the advantages of being high capacity, high voltage, and compact, and are widely used as power sources for mobile phones, laptops, etc. In recent years, they have also attracted great expectations as a power source for electric vehicles, hybrid vehicles, etc., and their development is being actively pursued.

[0003] In this lithium-ion battery, charging and discharging are performed by the movement of lithium ions (hereinafter sometimes referred to as Li ions) between the positive electrode and the negative electrode. On the negative electrode side, Li is absorbed into the negative electrode active material during charging, and Li is released as ions from the negative electrode active material during discharging.

[0004] Conventionally, lithium cobalt oxide (LiCoO 2 ) was used, and graphite was widely used as the negative electrode active material. However, the theoretical capacity of the negative electrode active material graphite is only 372mAh / g, and there is a demand for even higher capacity. Therefore, in recent years, there has been active research into metal materials such as silicon (theoretical capacity of silicon is 4198mAh / g) that are expected to increase capacity as an alternative to carbon-based negative electrode active materials.

[0005] However, because Si absorbs Li through an alloying reaction with Li, large volume expansion and contraction occurs as the Li is absorbed and released. Therefore, if the negative electrode active material is made of Si alone, the expansion and contraction stress causes the Si particles to crack or peel off from the current collector, resulting in a problem of deterioration in cycle characteristics, which are the capacity retention characteristics when charging and discharging repeatedly.

[0006] For this reason, various proposals have been made to alloy Si in negative electrode active materials using Si, as shown in the following Patent Document 1. In the alloying of Si, the Si compound phase formed around the Si phase acts to relieve stress caused by volume expansion during Li absorption in Si, thereby suppressing cracking and collapse of the Si phase and enabling improvement of cycle characteristics. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2016-62660 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, although the previously proposed alloying with Si has been found to have a certain effect on improving cycle characteristics, the effect is not sufficient and there is still room for improvement. The present invention has been made against the background described above, with an object to provide a Si alloy for use in the negative electrode of a lithium ion battery having a novel structure and excellent cycle characteristics. [Means for solving the problem]

[0009] As a result of various investigations to solve the above problems, the present inventors have found that by combining two types of Si compounds with different physical properties, specifically, by combining two types of SiX phases with high hardness and SiY phases with high indentation work ratio to form a Si compound phase, the cycle characteristics of a lithium ion battery can be improved. The present invention is based on such findings.

[0010] The present invention relates to a Si alloy having a Si phase, a first Si compound phase, a SiX phase, and a second Si compound phase, a SiY phase, The amount of the Si phase in the entire Si alloy is 20 to 90 mass %, The element X is at least one element selected from the group consisting of Fe, Co, Zr, Ti, Cr, V, Mo, Ta, Nb, and W; The element Y is characterized by being at least one element selected from the group consisting of La, Sm, Ni, Ce, Mn, and Cu.

[0011] In the Si alloy for lithium ion battery negative electrode of the present invention thus specified, the SiX phase is unlikely to deform even when stress is applied from the outside, and is considered to act to suppress the expansion of the Si phase when Li is absorbed. Also, the SiY phase is considered to elastically deform when the Si phase expands, and to act to buffer the increase in stress in the Si alloy. Based on the effect of combining these, the Si alloy for lithium ion battery negative electrode of the present invention can bring about further improvement in cycle characteristics.

[0012] Here, the mass % ratio of the SiX compound to the SiY compound, represented by SiX / SiY, is preferably set to 0.20 to 5.0.

[0013] In the present invention, the alloy may further contain one or more elements selected from the group consisting of Sn, Al, In and Bi, and the total content thereof may be 10 mass % or less. Sn, Al, In, and Bi, which do not form compounds with Si and exist alone, are thought to elastically deform like the SiY phase and function as a buffer against the stress caused by Si expansion, thereby improving cycle characteristics.

[0014] In addition, in the present invention, the average size of the Si phase is set to 500 nm or less, thereby making it possible to further improve the cycle characteristics. [Brief description of the drawings]

[0015] [Figure 1] 1 is a structural photograph of a negative electrode Si alloy according to Example 6 taken by a scanning electron microscope (SEM). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Next, a specific description will be given of a Si alloy for a negative electrode of a lithium ion battery according to one embodiment of the present invention (hereinafter, may be simply referred to as a Si alloy for a negative electrode), and a lithium ion battery (hereinafter, may be simply referred to as a battery) using this Si alloy for a negative electrode in its negative electrode.

[0017] 1.Si alloy for negative electrode The Si alloy for negative electrodes is mainly composed of Si, element X, and element Y. Here, element X is one or more elements selected from the group consisting of Fe, Co, Zr, Ti, Cr, V, Mo, Ta, Nb, and W, and element Y is one or more elements selected from the group consisting of La, Sm, Ni, Ce, Mn, and Cu. No elements other than these main constituent elements (Si, element X, element Y) are included, except for unavoidable impurity elements. Examples of unavoidable impurity elements include nitrogen (N), sulfur (S), and phosphorus (P). The upper limits of each are N≦0.10 mass%, S≦0.10 mass%, and P≦0.10 mass%.

[0018] The metal structure of the present Si alloy for negative electrodes includes a Si phase, a SiX phase which is a first Si compound phase, and a SiY phase which is a second Si compound phase.

[0019] The Si phase is a phase that mainly contains Si. From the viewpoint of increasing the amount of Li absorption, it is preferable that the Si phase is a single phase of Si. However, the Si phase may contain unavoidable impurities.

[0020] In the present Si alloy for negative electrode, if the ratio of the Si phase that absorbs Li is low, the initial discharge capacity decreases. Therefore, in this embodiment, the amount of the Si phase is set to 20 mass% or more, preferably 25 mass% or more, and more preferably 30 mass% or more. However, if the proportion of the Si phase is high, the proportion of the Si compound phase decreases relatively, and cycle characteristics deteriorate. Therefore, in this embodiment, the amount of the Si phase is set to 90 mass % or less, preferably 80 mass % or less, and more preferably 70 mass % or less.

[0021] The average size of the Si phase is preferably 500 nm or less, because by making the Si finer, the amount of expansion and contraction of each Si is reduced, thereby improving cycle characteristics.

[0022] The Si compound phase is a phase that mainly contains Si compounds, although the Si compound phase may contain unavoidable impurities.

[0023] In this embodiment, the Si compound phase includes a SiX phase which is a first Si compound phase, and a SiY phase which is a second Si compound phase. The SiX compound constituting the SiX phase is a compound of Si and the element X, specifically, Si 2 Nb, Si 2 Cr, Si 2 Examples of such compounds include Mo. The SiX compounds have a higher hardness than the other SiY compounds, and are less likely to deform even when external stress is applied, which is thought to act to suppress the expansion that occurs when the Si phase absorbs Li.

[0024] The SiY compound constituting the SiY phase is a compound of Si and the element Y, specifically, Si 2 La, Si 2 Sm, Si 2 An example of this is Ni. The SiY compound has a higher indentation work ratio (i.e., is more elastically deformable) than the other SiX compound, and is therefore considered to act to buffer the increase in stress in the Si alloy by elastically deforming when the Si phase expands.

[0025] In this embodiment, by combining these two phases with different physical properties, it is possible to improve cycle characteristics compared to a case where the Si compound phase is composed of only either the SiX phase or the SiY phase. According to the research of the present inventors, the effect of improving the cycle characteristics varies depending on the mass % ratio of the SiX compound to the SiY compound, expressed as SiX / SiY. From the viewpoint of improving the cycle characteristics, in this embodiment, the value of SiX / SiY is set within the range of 0.20 to 5.0. It is preferably within the range of 0.25 to 4.0, and more preferably within the range of 0.40 to 2.5. It is preferable that the SiX phase is contained at 10 mass % or more, and the SiY phase is contained at 10 mass % or more. It is also preferable that the content of the SiX phase is 80 mass % or less, and the content of the SiY phase is 80 mass % or less.

[0026] The negative electrode Si alloy of this embodiment may further contain one or more elements selected from the group consisting of Sn, Al, In, and Bi. These Sn, Al, In, and Bi exist alone without forming a compound with Si, and are considered to elastically deform when an external stress is applied, and to function as a buffer against the stress, similar to the SiY compound. Furthermore, by containing these elements, the Li pass characteristic can be improved, and as a result, the utilization rate of Si can be increased. However, since these elements expand by absorbing Li, excessive addition reduces cycle characteristics, so the total content of the elements selected from the above group is desirably 10 mass % or less.

[0027] The form of the Si alloy for the negative electrode of this embodiment is not particularly limited. Specifically, the form may be a flake form, a powder form, or the like. Preferably, the Si alloy for the negative electrode of the present invention is in the form of a powder, from the viewpoint of being easily applicable to the manufacture of the negative electrode. In addition, the Si alloy for the negative electrode of the present invention may be dispersed in a suitable solvent.

[0028] The Si alloy for negative electrode of this embodiment can be manufactured by a method that includes a step of quenching a molten alloy having a predetermined chemical composition to form a quenched alloy. If the quenched alloy obtained is not in a powder form or if it is desired to reduce the diameter, a step of pulverizing the quenched alloy into a powder form by a suitable pulverizing means may be added. In addition, if necessary, a step of classifying the quenched alloy obtained to adjust it to an appropriate particle size may be added.

[0029] The particle size (average particle size (d50)) of the present Si alloy for negative electrode is preferably within the range of 1 to 20 μm. The average particle size (d50) in the present invention means a volumetric standard, and can be measured using a laser diffraction / scattering type particle size distribution analyzer (Microtrac MT3000). Even when a Si alloy is used as the negative electrode material, the volume of the negative electrode material itself expands and contracts during charge and discharge reactions, which generates stress in the composite layer formed by binding the negative electrode material with the binder, i.e., the conductive film. In this case, if the binder cannot withstand the stress, the binder collapses, resulting in peeling of the conductive film from the current collector, which results in a decrease in the conductivity within the electrode and a decrease in the charge and discharge cycle characteristics. However, when the average particle size of the present Si alloy for the negative electrode is set to fine particles of 1 to 20 μm, the contact area with the binder increases due to the fineness of the present Si alloy for the negative electrode, which effectively suppresses the collapse of the binder, thereby improving the cycle characteristics.

[0030] In the above-described manufacturing method, the molten alloy can be obtained, for example, by weighing out each raw material so as to obtain a predetermined chemical composition, and melting the weighed out raw materials using a melting means such as an arc furnace, a high-frequency induction furnace, or a heating furnace.

[0031] Specific examples of methods for quenching the molten alloy include roll quenching (single roll quenching, twin roll quenching, etc.) and liquid quenching methods such as atomization (gas atomization, water atomization, centrifugal atomization, etc.).

[0032] When the roll quenching method is applied, the molten alloy is poured into a chamber such as a quenching and recovery chamber and flows downward continuously (in a rod shape), and is cooled on a rotating roll (material is Cu, Fe, etc., the roll surface may be plated) rotating at a peripheral speed of about 10 m / s to 100 m / s. The molten alloy is cooled on the roll surface to become a foil or foil-flaked alloy material. In this case, the alloy material is pulverized by a suitable pulverizing means such as a ball mill, disk mill, coffee mill, or mortar grinder, and classified as necessary to obtain a powdered negative electrode material.

[0033] On the other hand, when the atomization method is applied, the molten alloy is poured into the atomization chamber and flows downward continuously (in a rod shape). 2 Gas such as Ar, He, etc. is sprayed at high pressure (for example, 1 to 10 MPa) to crush and cool the molten metal. The cooled molten metal approaches a spherical shape while falling freely in the spray chamber while remaining semi-molten, and a powdered Si alloy for the negative electrode is obtained. In order to improve the cooling effect, high-pressure water may be sprayed instead of gas.

[0034] 2. This battery The present battery is constructed using a negative electrode containing the present Si alloy for the negative electrode.

[0035] 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 present Si alloy for negative electrodes described above in a binder. The conductive film may also contain a conductive auxiliary material as necessary. When the conductive auxiliary material is contained, it becomes easier to ensure a conductive path for electrons.

[0036] Furthermore, the conductive film may contain an aggregate as necessary. When an aggregate is contained, it becomes easier to suppress the expansion and contraction of the negative electrode during charging and discharging, and the collapse of the negative electrode can be suppressed, so that the cycle characteristics can be further improved.

[0037] The conductive base material functions as a current collector. Examples of the material include Cu, Cu alloy, Ni, Ni alloy, Fe, and Fe-based alloy. Preferably, the conductive base material is Cu or a Cu alloy. Specific examples of the conductive base material include a foil shape and a plate shape. Preferably, the conductive base material is a foil shape, from the viewpoint of reducing the volume of the battery and improving the degree of freedom in shape.

[0038] As the material of the binder, for example, polyvinylidene fluoride (PVdF) resin, fluororesin such as polytetrafluoroethylene, polyvinyl alcohol resin, polyimide resin, polyamide resin, polyamideimide resin, styrene butadiene rubber (SBR), polyacrylic acid, etc. can be suitably used. These can be used alone or in combination of two or more. Among these, polyimide resin is particularly preferred in the sense that it has high mechanical strength, can withstand the volume expansion of the negative electrode material well, and can effectively prevent the conductive film from peeling off from the current collector due to the destruction of the binder.

[0039] Examples of the conductive assistant include carbon black such as Ketjen black, acetylene black, furnace black, graphite, carbon nanotubes, fullerene, etc. These may be used alone or in combination of two or more. Among these, Ketjen black, acetylene black, etc. are preferably used from the viewpoint of easily securing electronic conductivity.

[0040] The content of the conductive assistant is preferably 0 to 30 parts by mass, more preferably 4 to 13 parts by mass, relative to 100 parts by mass of the present negative electrode Si alloy, from the viewpoints of improved conductivity, electrode capacity, etc. The average particle size (d50) of the conductive assistant is preferably 10 nm to 1 μm, more preferably 20 to 50 nm, from the viewpoints of dispersibility, ease of handling, etc.

[0041] As the aggregate, a material that does not expand or contract during charging and discharging or that expands or contracts very little can be preferably used. Examples of the aggregate include graphite, alumina, calcia, zirconia, and activated carbon. These may be used alone or in combination of two or more. Of these, graphite is preferably used from the viewpoints of electrical conductivity, Li activity, and the like.

[0042] The content of the aggregate is preferably 10 to 400 parts by mass, more preferably 43 to 100 parts by mass, relative to 100 parts by mass of the present negative electrode Si alloy, from the viewpoint of improving cycle characteristics, etc. The average particle size of the aggregate is preferably 10 to 50 μm, more preferably 20 to 30 μm, from the viewpoint of functionality as an aggregate, control of electrode film thickness, etc. The average particle size of the aggregate is a value measured using a laser diffraction / scattering type particle size distribution measuring device.

[0043] The present negative electrode can be produced, for example, by adding the present negative electrode Si alloy, and, if necessary, a conductive additive and an aggregate in required amounts to a binder dissolved in an appropriate solvent to form a paste, which is then applied to the surface of a conductive base material, dried, and, if necessary, compacted or heat-treated.

[0044] When the present negative electrode is used to construct a lithium ion battery, the basic components of the battery other than the present negative electrode, such as the positive electrode, electrolyte, and separator, are not particularly limited.

[0045] Specifically, the positive electrode is, for example, a LiCoO 2 , LiNiO 2 , LiFePO 4 , LiMnO 2 , LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O 2 Examples of the positive electrode material include a layer containing the above positive electrode material.

[0046] Specific examples of the electrolyte include an electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent, etc. In addition, a lithium salt is dissolved in a polymer, and a polymer solid electrolyte in which the electrolytic solution is impregnated in a polymer can also be used.

[0047] 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. In addition, an ionic liquid electrolyte may also be used.

[0048] Specific examples of the lithium salt include LiPF 6 , LiBF 4 , LiClO 4 , LiCF 3 SO 3 These may be included as one or more of them.

[0049] Other battery components include a separator, a can (battery case), a gasket, etc., and any of these can be appropriately combined to form a battery as long as they are typically used in lithium ion batteries.

[0050] The shape of the battery is not particularly limited and may be any shape such as cylindrical, rectangular, or coin-shaped, and may be appropriately selected according to the specific application. EXAMPLES

[0051] The present invention will now be described in more detail with reference to examples. Note that % in the alloy composition is by mass % unless otherwise specified.

[0052] 1. Preparation of Si alloy for negative electrode Each raw material was weighed so as to obtain the alloy composition shown in the following Table 1. Each weighed raw material was heated and melted using a high-frequency induction furnace to obtain a molten alloy. The resulting molten alloys were quenched using a single roll quenching method to obtain quenched alloy ribbons, with the roll peripheral speed set to 42 m / s and the nozzle distance set to 3 mm. The resulting quenched alloy ribbons were mechanically pulverized in a mortar to produce powdered Si alloys for the negative electrodes, and in the case of Examples 37 and 38, further pulverization was performed using a planetary ball mill.

[0053] [Table 1]

[0054] 2. Structural observation of negative electrode Si alloy The structure of the negative electrode Si alloys according to each of the Examples and Comparative Examples was observed using a scanning electron microscope (SEM). XRD (X-ray diffraction) analysis was also performed, and it was confirmed that the phases of Si, SiX compounds, SiY compounds, etc. shown in the table were generated. The XRD analysis was performed using a Co tube over an angle range of 120° to 20°.

[0055] As a representative example of this embodiment, Si as the first Si compound phase 2 Cr phase and Si as a second Si compound phase 2 FIG. 1 shows a structural photograph of the Si alloy for negative electrodes according to Example 6, which has a La phase, taken by a scanning electron microscope. Here, the dark grey in the low-magnification photograph is the Si phase, and the light grey in the photograph is the Si compound phase (silicide phase). In this example, in the process of cooling and solidifying the molten alloy, Si crystallizes first, and then the Si compound crystallizes, so that the Si phase is formed in islands and the Si compound phase is formed in a sea. As shown in the high-magnification photograph, the Si compound phase is a light grey Si 2 Cr phase and white Si in the figure 2 It is composed of two types of La phase.

[0056] 3.Evaluation of the size of the Si phase The Si phase was photographed at a magnification of 30,000 times using a SEM (scanning electron microscope). The size of the Si phase was measured from the photographed image. Specifically, 1 to 5 visual fields were photographed, and the maximum diameter of 15 Si phases selected from each visual field was measured and averaged to determine the size of the Si phase. The results are shown in Table 2 below. Note that for Si phases smaller than 1 μm, which are difficult to measure with an SEM, their sizes were measured by observation with a TEM.

[0057] 4. Calculation method for the amount of Si phase The amount of Si phase shown in Table 2 was calculated based on the chemical components in Table 1. The calculation method will be explained below using the example 6 containing Si, Cr, and La as an example. In the case of Example 6, the Si compound phase formed is Si 2 Cr and Si 2 It's La. S 2 The mass percentage of Cr is 52[Si]-48[Cr], and Si 2 La is expressed as 29.1 [Si] - 70.9 [La] in mass % ratio. When the Cr content is 16.8 mass %, the amount of Si that is compounded = 52 × 16.8 / 48 = 18.2 (mass %), and when the La content is 24.8 mass %, the amount of Si that is compounded = 29.1 × 24.8 / 70.9 = 10.2 (mass %). The amount of Si phase that contributes to the Li absorption reaction is the amount obtained by subtracting the amount of Si that is compounded from the total Si amount, so it can be calculated as the amount of Si phase = 58.4 - 28.4 = 30.0 (mass %). The results of the calculation in this way are shown in Table 2.

[0058] 5. Vickers hardness measurement of SiX compounds Separate from the negative electrode Si alloy, metal particles consisting of only SiX compounds were prepared, embedded in resin, polished, and measured with a Vickers hardness tester. Hardness was measured with reference to the JIS Z 2244 Vickers hardness test, by pressing a diamond indenter into the test piece (pressing load 100g). Hardness was measured at 10 points (1 point for each of 10 metal particles) and the average value is shown in Table 2. The value of 3.2 GPa shown in Comparative Example 1 is Si 2 This is the measured value for La.

[0059] 6. Measurement of indentation work ratio of SiY compound Separate from the Si alloy for the negative electrode, metal particles consisting of only SiY compounds were prepared, and these were deposited on a copper foil substrate and measured with a microhardness tester. The indentation work ratio was measured by a load-unloading test (using a diamond triangular pyramid indenter, test force 4.9N) in accordance with ISO14577-1. The indentation work ratio is defined as the ratio of the work of elastic deformation to the total amount of mechanical work (the sum of the work of plastic deformation and the work of elastic deformation), and measurements were performed at 10 points or more (10 different points on one test piece), and the average values ​​are shown in Table 2.

[0060] 7. Evaluation of charge / discharge characteristics 7.1 Preparation of coin-type batteries for charge / discharge tests First, 100 parts by mass of each Si alloy for the negative electrode, 6 parts by mass of Ketjen Black (manufactured by Lion Corporation) as a conductive additive, and 19 parts by mass of polyimide (thermoplastic resin) binder as a binding agent were blended, and this was mixed with N-methyl-2-pyrrolidone (NMP) as a solvent to prepare each paste containing each negative electrode material.

[0061] Each coin-type half cell was prepared as follows. Here, for simple evaluation, an electrode prepared using a Si alloy for the negative electrode was used as the test electrode, and Li foil was used as the counter electrode. First, each paste was applied to a thickness of 50 μm by a doctor blade method on the surface of SUS316L foil (thickness 20 μm) that serves as the negative electrode current collector, and then dried to form each negative electrode material layer. After formation, the negative electrode material layer was consolidated by roll pressing. In this way, the test electrodes according to the examples and comparative examples were prepared.

[0062] Next, the test electrodes according to the example and comparative example were punched out into disk shapes having a diameter of 11 mm to prepare the respective test electrodes.

[0063] Next, Li foil (thickness 500 μm) was punched out to approximately the same shape as the test electrode to prepare each counter electrode. 6was dissolved at a concentration of 1 mol / l to prepare a non-aqueous electrolyte solution.

[0064] Next, each test electrode was housed in its own positive electrode can (each test electrode would be a negative electrode in a lithium ion battery, but when the counter electrode was Li foil, the Li foil became the negative electrode and the test electrode became the positive electrode), and the counter electrode was housed in its own negative electrode can, with a polyolefin-based microporous membrane separator being disposed between each test electrode and each counter electrode.

[0065] Next, the non-aqueous electrolyte was poured into each can, and the negative electrode can and the positive electrode can were each fixed by crimping.

[0066] 7.2 Charge / discharge test Each coin battery was charged and discharged at a constant current of 0.2 mA for one cycle, and the discharge capacity was recorded as the initial discharge capacity C 0 From the second cycle onwards, the charge / discharge test was carried out at a 1 / 5C rate (C rate: the amount of electricity required to (charge) and discharge the electrode, C 0 The current value at which the battery is discharged in 1 hour is set to 1C. At 5C, it takes 12 minutes, and at 1 / 5C, it takes 5 hours.) The capacity (mAh) used during this discharge is divided by the amount of negative electrode material (g) to determine each discharge capacity (mAh / g). The initial discharge capacity C 0 The results are shown in Table 2.

[0067] In this example, the cycle characteristics were evaluated by repeating the charge-discharge cycle 50 times. The capacity retention rate (discharge capacity after 50 cycles / initial discharge capacity (discharge capacity at the first cycle)×100) was calculated from each discharge capacity obtained. The results are shown in Table 2.

[0068] [Table 2]

[0069] The results obtained in Table 2 as described above reveal the following. In Examples 1 to 5, the amount of Si phase is 30%, and the Si compound phase is Si 2Nb phase (SiX phase) and Si 2 These are examples of Si alloys for negative electrodes having two types of phases, a La phase (SiY phase) and a Si phase. 2 Comparative Example 1, which is made up of a single La phase, and Comparative Example 2, which is made up of a single La phase and a Si compound phase with a Si phase content of 30%. 2 Compared with Comparative Example 2, which is made of a single Nb phase, the capacity retention rate is higher while maintaining the same or higher initial discharge capacity. 2 Nb and Si 2 The capacity retention rate of Example 1, in which the ratio of the SiX compound to the SiY compound represented by SiX / SiY is 1, is particularly high.

[0070] Examples 6 to 12 are examples in which the SiX compound is different from that of Example 1. For example, in Example 6, the Si compound phase is Si 2 Cr phase (SiX phase) and Si 2 This is an example of a Si alloy for negative electrodes that has two types of Si compound phases: La phase (SiY phase) and SiY phase. 2 Comparative Example 1 with a single La phase and a Si compound phase with Si 2 Compared with Comparative Example 3, which uses a single Cr phase, the capacity retention rate is higher while maintaining approximately the same initial discharge capacity. 2 Cr and Si 2 La) is clearly effective. Furthermore, in Examples 7 to 12, approximately the same capacity retention rate as in Example 6 was obtained.

[0071] Examples 13 to 18 are examples in which an element other than La was selected as the Y element. For example, in Example 13, the Si compound phase is Si 2 Nb phase (SiX phase) and Si 2 This is an example of a negative electrode Si alloy that has two types of Si compound phases: Sm phase (SiY phase) and SiY phase. 2 Comparative Example 2, which is made of a single Nb phase, and Comparative Example 3, which is made of a single Si compound phase, 2Compared with Comparative Example 4, which is made of a single Sm phase, the capacity retention rate is higher while maintaining the same or higher initial discharge capacity. 2 Nb and Si 2 The effect of using the 100% 100% 15 ... In Example 15, the Si compound phase was Si 2 Cr phase (SiX phase) and Si 2 This is an example of a negative electrode Si alloy that has two types of Si compound phases: Sm phase (SiY phase) and SiY phase. 2 Comparative Example 3, which is made of a single Cr phase, and Comparative Example 4, which is made of a single Si compound phase, 2 Compared with Comparative Example 4, which is made of a single Sm phase, the capacity retention rate is higher while maintaining approximately the same initial discharge capacity. 2 Cr and Si 2 The effect of using the 100% 100% 15 ... In addition, in Examples 16 to 18 in which Ni was selected as the Y element, the capacity retention rate tended to be slightly lower than in the other examples. 2 This is presumably due to the low indentation work ratio of Ni).

[0072] In Examples 19 to 23, the amount of Si phase was 20%, and the Si compound phase was Si 2 Nb phase (SiX phase) and Si 2 This is an example in which the ratio of the SiX compound and the SiY compound represented by SiX / SiY was changed in a negative electrode Si alloy having two types of phases, La and SiY. The capacity retention ratio was highest in Example 19 where SiX / SiY was 1, and the capacity retention ratio tended to decrease as SiX / SiY became smaller than 1, and also decreased as SiX / SiY became larger than 1.

[0073] Examples 24 to 28 are examples in which the Si phase amount is 60% and the ratio of the SiX compound to the SiY compound, expressed as SiX / SiY, is changed. The same tendency as in the case of the Si phase amount being 20% ​​(Examples 19 to 23) was observed.

[0074] Examples 29 and 30 are examples in which the amount of Si phase is further increased. Although there is generally a trade-off between the initial discharge capacity and the cycle characteristics, Examples 29 and 30 show that the initial discharge capacity can be increased while suppressing the decrease in the capacity retention rate.

[0075] Examples 31 to 33 are examples in which Sn, which does not form a compound with Si, was further added. Compared to Example 1, Examples 31 and 32 showed higher capacity retention rates, and it is clear that the addition of Sn is effective in improving cycle characteristics. However, in Example 33, which contains 10% Sn, a decrease in capacity retention rate was observed, and it is clear that the Sn content is preferably 10% or less.

[0076] Examples 34 to 36 are examples in which Al, which does not form a compound with Si, was further contained. The same tendency as in the case of containing Sn (Examples 31 to 33) was observed.

[0077] Examples 37 and 38 are examples in which the Si phase size is refined to less than 1 μm compared to Examples 1 and 32. The capacity retention rates are higher than those of Examples 1 and 32. In particular, Example 38, in which the Si phase size is 0.3 μm, had a high capacity retention rate of 99%.

[0078] Although the Si alloy for the negative electrode of a lithium ion battery and the lithium ion battery of the present invention have been described in detail above, the present invention is not limited to the above-mentioned embodiment and examples. For example, the Si alloy for the negative electrode of the present invention can be applied to the negative electrode material for a liquid lithium ion battery as in the above-mentioned embodiment, as well as to the negative electrode material for an all-solid-state lithium ion battery, and various modifications can be made to the present invention without departing from the spirit thereof.

Claims

1. A Si alloy having a Si phase, a SiX phase which is a first Si compound phase, and a SiY phase which is a second Si compound phase, The amount of the Si phase in the entire Si alloy is 20 to 90 mass %, The element X is at least one element selected from the group consisting of Fe, Co, Zr, Ti, Cr, V, Mo, Ta, Nb, and W; A Si alloy for a lithium ion battery negative electrode, wherein the element Y is at least one element selected from the group consisting of La, Sm, Ni, Ce, Mn, and Cu.

2. 2. The Si alloy for lithium ion battery negative electrode according to claim 1, wherein the mass % ratio of the SiX compound to the SiY compound, represented by SiX / SiY, is 0.20 to 5.

0.

3. 2. The Si alloy for a lithium ion battery negative electrode according to claim 1, further comprising one or more elements selected from the group consisting of Sn, Al, In, and Bi, the total content of which is 10 mass % or less.

4. The Si alloy for lithium ion battery negative electrodes according to any one of claims 1 to 3, wherein the average size of the Si phase is 500 nm or less.

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