Anode material for lithium-ion secondary batteries, anode for lithium-ion secondary batteries, and lithium-ion secondary batteries

Abstract

To provide a negative electrode material for high-capacity lithium-ion secondary batteries with a long cycle life. [Solution] The system comprises a Si phase and two compound phases selected from a SiA compound phase, a SiB compound phase, and a SiC compound phase. The SiA compound phase comprises a SiA compound of Si and at least one of the elements A1 and A2. The SiB compound phase comprises a SiB compound of Si and B1 and B2. The SiC compound phase comprises a SiC compound of Si and C1 and C2. A1 and A2 are derived from Mn, Fe, Y, La, Ce, Gd, Dy, and Sm. A negative electrode material for lithium-ion secondary batteries, wherein A1 and A2 are different elements, B1 and B2 are different elements, C1 is Mn, Fe, Y, La, Ce, Gd, Dy, or Sm, and C2 is Ti, V, Cr, Zr, Nb, Mo, Ta, or W.

Description

[Technical Field]

[0001] This disclosure relates to anode materials for lithium-ion secondary batteries, anodes for lithium-ion secondary batteries, and lithium-ion secondary batteries. [Background technology]

[0002] Lithium-ion rechargeable batteries offer higher energy density and voltage compared to conventional batteries, allowing for miniaturization and rapid charging. Therefore, they are widely used as power sources for small portable electronic devices such as smartphones, personal computers (primarily notebook computers), and tablet devices. In recent years, they have also been used as stationary power sources for storing electricity generated by wind and solar power, as well as in-vehicle power sources for electric vehicles and hybrid vehicles, creating a demand for even higher performance.

[0003] In lithium-ion rechargeable batteries, charging and discharging occur through the movement of lithium ions between the positive and negative electrodes. On the negative electrode side, lithium ions are absorbed into the negative electrode active material during charging, and released from the negative electrode active material during discharging.

[0004] Graphite is widely used as a negative electrode active material, but its theoretical capacity is 372 mAhg -1 Therefore, alternative materials are being considered to achieve even higher capacity. For example, Si has a theoretical capacity of 4198 mAhg. -1 It has more than 10 times the capacity of graphite, and is being actively researched because it is expected to enable higher capacity applications.

[0005] However, silicon undergoes significant volume changes during the intercalation and release of lithium ions. Therefore, when a single-phase silicon material is used as the negative electrode active material, the electrode collapses due to these volume changes, leading to a decrease in capacity retention characteristics and a poor cycle life after repeated charging and discharging cycles.

[0006] In response to this, attempts have been made to solve the above problem by using Si compounded with metal silide as the negative electrode active material. Patent Document 1 proposes that the cycle life can be improved by using a Si compound consisting of three elements including Si as the negative electrode active material, and Patent Document 2 proposes that the cycle life can be improved by using a Si compound consisting of four elements including Si as the negative electrode active material. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2021-22438 [Patent Document 2] Japanese Patent Publication No. 2024-58816 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, while the Si composites disclosed in conventional technologies do have some effect in improving cycle life, the effect is not sufficient, and further improvements are desired. This disclosure aims to provide a negative electrode material for high-capacity lithium-ion secondary batteries with a long cycle life. [Means for solving the problem]

[0009] Some embodiments of this disclosure are illustrated below. [1] Complies with a Si phase and two compound phases selected from a SiA compound phase, a SiB compound phase, and a SiC compound phase, wherein the SiA compound phase comprises a SiA compound of Si and at least one of the elements A1 and A2, the SiB compound phase comprises a SiB compound of Si and B1 and B2, and the SiC compound phase comprises a SiC compound of Si and C1 and C2, where A1 and A2 are Mn, Fe, Y, La, Ce, Gd, Dy, and Sm A negative electrode material for lithium-ion secondary batteries, wherein A1 and A2 are different elements, B1 and B2 are different elements, C1 is Mn, Fe, Y, La, Ce, Gd, Dy, or Sm, and C2 is Ti, V, Cr, Zr, Nb, Mo, Ta, or W. [2] The negative electrode material for lithium-ion secondary battery according to [1], wherein the SiB compound phase is included, and the SiB compound is a silicide compound of Cr and one element selected from the group consisting of V, Nb, Mo, Ta, W, Zr, and Ti. [3] The SiB compound is a silicide compound containing Cr and V, the negative electrode material for lithium-ion secondary batteries according to [1] or [2]. [4] The negative electrode material for lithium-ion secondary battery according to [1], wherein the SiB compound phase is included, and the SiB compound is a silicide compound of Nb and one element selected from the group consisting of V, Mo, Ta, W, Zr, and Ti. [5] The SiB compound phase is a silicide compound containing Nb and Mo, as described in [4], for a lithium-ion secondary battery negative electrode material. [6] When the SiB compound phase is included, if the atomic weight of B1 is greater than that of B2, the molar ratio of B1 to the total amount of B1 and B2 is 0.3 to 0.7, the negative electrode material for lithium-ion secondary batteries according to any one of [1] to [5]. [7] The negative electrode material for a lithium-ion secondary battery according to any one of [1] to [6], wherein, when the SiA compound phase and the SiB compound phase are included, the mass ratio of the SiA compound to the total amount of the SiA compound and the SiB compound is 0.1 to 0.9. [8] The negative electrode material for a lithium-ion secondary battery according to any one of [1] to [7], wherein the SiA compound phase is included, and the SiA compound is a silicide compound containing La. [9] A negative electrode material for lithium-ion secondary batteries according to any one of [1] to [8], wherein the amount of Si phase obtained by subtracting the amount of Si compounded from the total amount of Si in the negative electrode material is 20 to 90 mass%. A negative electrode for a lithium-ion secondary battery, comprising the negative electrode material for lithium-ion secondary batteries described in any one of

[10] [1] to [9].

[11] A lithium-ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises a lithium-ion secondary battery negative electrode material described in any one of [1] to [9]. [Effects of the Invention]

[0010] According to this disclosure, it is possible to provide a negative electrode material for high-capacity lithium-ion secondary batteries with a long cycle life. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a graph showing the cycle life of a coin-type battery when a sulfide-type solid electrolyte is used in the example. [Figure 2] Figure 2 is a graph showing the cycle life of a coin-type battery when an ionic liquid electrolyte is used in the example. [Figure 3] Figure 3 is a graph showing the cycle life of a coin-type battery when an ionic liquid electrolyte is used in the example. [Modes for carrying out the invention]

[0012] The embodiments described below are illustrative and not limited to these examples.

[0013] According to this embodiment, the material comprises a Si phase and two compound phases selected from a SiA compound phase, a SiB compound phase, and a SiC compound phase, wherein the SiA compound phase comprises a SiA compound of Si and at least one of the elements A1 and A2, the SiB compound phase comprises a SiB compound of Si and B1 and B2, and the SiC compound phase comprises a SiC compound of Si and C1 and C2, and A1 and A2 are from the group consisting of Mn, Fe, Y, La, Ce, Gd, Dy, and Sm. A negative electrode material for lithium-ion secondary batteries can be provided, wherein A1 and A2 are different elements, B1 and B2 are different elements, C1 is Mn, Fe, Y, La, Ce, Gd, Dy, or Sm, and C2 is Ti, V, Cr, Zr, Nb, Mo, Ta, or W.

[0014] Hereafter, the negative electrode material for lithium-ion secondary batteries will be simply referred to as negative electrode material, the negative electrode for lithium-ion secondary batteries will be referred to as negative electrode, and the lithium-ion secondary battery will be referred to as secondary battery.

[0015] In this embodiment, the negative electrode material is a three-phase material comprising a Si phase and two compound phases selected from a SiA compound phase, a SiB compound phase, and a SiC compound phase. The SiB compound phase is ternated with Si, B1, and B2, and the SiC compound phase is ternated with Si, C1, and C2. In other words, since any combination of the SiA compound phase, SiB compound phase, and SiC compound phase contains either a SiB compound or a SiC compound, the negative electrode material in this embodiment is a multi-phase and diversified material.

[0016] Here, the silicide compound of Si with one element selected from the group consisting of Mn, Fe, Y, La, Ce, Gd, Dy, and Sm, which is included in the SiA compound phase, has elastic mechanical properties. Furthermore, the silicide compound of Si with two elements selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Ta, and W, which is included in the SiB compound phase, has rigid mechanical properties. The SiC compound phase contains both elements that can impart elastic or rigid properties through diversification with Si, but when multiphased with the SiA compound phase, it becomes relatively rigid, and when multiphased with the SiB compound phase, it becomes relatively elastic. By containing these two types of silicide compounds with different mechanical properties, the negative electrode material can alleviate stress caused by volume changes due to Li absorption during charging and discharging. Furthermore, it can obtain mechanical properties suitable for the support structure, improving cycle life. While possessing these characteristics, the negative electrode material can also have an appropriate battery capacity.

[0017] Furthermore, by ternating SiB and SiC compounds, in addition to the mechanical properties mentioned above, it is possible to adjust electronic conductivity, Li diffusion, thermodynamic stability, etc., thereby further improving cycle life.

[0018] Thus, by combining the above-mentioned multiphase and diversification, the negative electrode material can achieve further improvements in cycle life.

[0019] [Negative electrode material] In this embodiment, the negative electrode material comprises a Si phase and two compound phases selected from a SiA compound phase, a SiB compound phase, and a SiC compound phase. The SiA compound phase, SiB compound phase, and SiC compound phase can be formed as Si alloy phases around the Si phase by applying high energy to a mixture of raw material metal powders using a mechanical alloying method, thereby alloying the metal powders while they remain in a solid state. Alternatively, the mixture of raw material metal powders can be melted at a high temperature, and the Si alloy can be rapidly cooled to form the Si alloy phases around the Si phase. As a result, in the negative electrode material, two compound phases selected from the SiA compound phase, SiB compound phase, and SiC compound phase are mixed around the Si phase, and it is desirable that the Si phase is distributed in a sea-island pattern. Furthermore, each phase may have a heterogeneous microstructure such as a sea-island structure, a fibrous structure, a co-continuous structure, or a composite structure thereof, but is not limited to these.

[0020] The Si phase is a single phase that primarily contains silicon. In addition to silicon, the Si phase may contain unavoidable impurities.

[0021] The Si phase may be doped with impurity elements (dopants). Examples of impurity elements include phosphorus (P), arsenic (As), antimony (Sb), boron (B), aluminum (Al), and gallium (Ga). It is preferable for the Si phase to be doped with phosphorus. The doping amount is preferably 100 to 1600 ppm relative to the total mass of Si contained in the Si phase.

[0022] The average size of the Si phase is preferably 1000 nm or less, more preferably 500 nm or less, and even more preferably 200 nm or less. Having the average size of the Si phase within these ranges allows the surrounding SiA or SiC compound phase to more easily relieve the stress generated by the volume expansion of the Si phase. This prevents the collapse of the negative electrode and further improves the cycle life. The average size of the Si phase may be 1 nm or more, 10 nm or more, 50 nm or more, or 100 nm or more. This can further improve the charge-discharge cycle life and volume expansion. For example, the average size of the Si phase may be between 1 nm and 1000 nm.

[0023] In this disclosure, the average size of the Si phase is calculated based on observations using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Specifically, the maximum diameters of multiple Si phases are observed in a field of view containing a significant number of particles, and their arithmetic mean is taken.

[0024] The SiA compound phase includes SiA compounds of Si with one or two elements selected from the group consisting of Mn, Fe, Y, La, Ce, Gd, Dy, and Sm. Because SiA compound phases containing these elements are highly elastic, they can relieve stress caused by volume changes during charging and discharging, thereby further improving cycle life.

[0025] The SiB compound phase contains SiB compounds of two elements selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Ta, and W, and SiB. Because the SiB compound phase containing these elements is rigid, it can function as a support framework that can withstand stress from the Si phase, thereby further improving cycle life.

[0026] The SiC compound phase includes SiC compounds with C1 (Mn, Fe, Y, La, Ce, Gd, Dy, or Sm), C2 (Ti, V, Cr, Zr, Nb, Mo, Ta, or W), and Si. SiC compound phases containing these elements possess both the elastic properties of C1 and the rigid properties of C2, and can complement the elastic or rigid properties of SiA or SiB compound phases, thereby further improving cycle life.

[0027] In this embodiment, the negative electrode material contains, in addition to the Si phase, two compound phases selected from the above SiA compound phase, SiB compound phase, and SiC compound phase, so that the respective effects on improving the cycle life can be obtained synergistically, and the cycle life can be further improved.

[0028] The SiA compound is a compound of Si and at least one of the elements A1 and A2. A1 and A2 are elements respectively selected from the group consisting of Mn, Fe, Y, La, Ce, Gd, Dy, and Sm. A1 and A2 are different elements from each other. The SiA compound phase may contain unavoidable impurities. The SiA compound is preferably a silicide compound containing La or Ce. More preferably, when the SiA compound is LaSi2 containing La, the SiA compound phase can obtain more elastic properties and the cycle life can be further improved.

[0029] The SiA compound may be a ternary silicide compound of Si, A1, and A2. In the case of a ternary system, all are mutually soluble. The ternary silicide compound usually phase-separates into a Si phase, one silicide compound phase, and the other silicide compound phase. However, when A1 and A2 are respectively selected from the group consisting of Mn, Fe, Y, La, Ce, Gd, Dy, and Sm, the Si-A1 compound phase and the Si-A2 compound phase are difficult to form, and the Si-A1-A2 compound phase can be formed. Specifically, the ternary SiA compound (A1 1-x A2 x Si2) is Gd 1-x Y x Si2, Dy 1-x Y x Si2, Gd 1-x Dy x Si2, La 1-x Ce x Si2, Mn 1-x Ce x Si2, Mn 1-x Fe x Si2, Gd 1-x La x Si2, Gd 1-x Sm xSi2, Dy 1-x La x Si2, Dy 1-x Sm x Si2, Y 1-x La x Si2, Y 1-x Ce x Si2, Y 1-x Sm x Si2 or Ce 1-x Fe x It may be Si2 (0 < x < 1).

[0030] The ternary SiA compound is preferably a silicide compound of either La and Ce and the remaining element. In this case, elements with the same crystal structure may be used for A1 and A2. More preferably, the SiA compound contains La, La 1-x A2 x By being Si2 (0 < x < 1), the SiA compound phase can obtain more elastic properties and can further improve the cycle life. For example, it is more preferably a silicide compound of La and Mn, Fe or Ce.

[0031] In the ternary silicide compound where the SiA compound contains A1 and A2, when the atomic weight of A1 is greater than that of A2, the molar ratio of A1 to the total amount of A1 and A2 is preferably 0.1 to 0.9, more preferably 0.2 to 0.8, and even more preferably 0.3 to 0.7. By having this atomic ratio within these ranges, mechanical properties, electronic conductivity, Li diffusivity, thermodynamic stability, etc. can be more adjusted, and the cycle life can be further improved.

[0032] SiB compounds are compounds of Si and B1 and B2. B1 and B2 are different elements. The SiB compound phase may contain unavoidable impurities. Ternary silicide compounds usually separate into a Si phase, one silicide compound phase, and the other silicide compound phase. However, when B1 and B2 are selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Ta, and W, the Si-B1 compound phase and Si-B2 compound phase are less likely to form, and the Si-B1-B2 compound phase may be formed. Specifically, ternary SiB compounds (B1 1-y B2 y Si2) is Nb 1-y Ta y Si2, Nb 1-y V y Si2, Ta 1-y Mo y Si2, Cr 1-y Mo y Si2, Cr 1-y V y Si2, Mo 1-y V y Si2, Mo 1-y Nb y Si2, Zr 1-y Ti y Si2, W 1-y Ta y Si2, Zr 1-y W y Si2, W 1-y Mo y Si2, Zr 1-y Nb y Si2, W 1-y V y Si2, Zr 1-y Ta y Si2, W 1-y Cr y Si2, Zr 1-y Mo y Si2, Nb 1-y Cr y Si2, Zr 1-y V y Si2, Ta 1-y V y Si2, Ti 1-y W y Si2, Ta 1-y Cr y Si2, Ti 1-y Nby Si2, Ti 1-y Ta y Si2, Ti 1-y Mo y Si2, Ti 1-y V y Si2, Ti 1-y Cr y Si2, or W 1-y Nb y It may be Si2 (0 < y < 1).

[0033] The SiB compound is preferably a silicide compound of one of Cr and Nb and the remaining elements. In this case, it is preferable to use elements with the same crystal structure for B1 and B2. More preferably, the SiB compound contains Nb in B1 1-y Nb y Si2 (0 < y < 1), or Cr containing Cr 1-y B2 y By being Si2 (0 < y < 1), the mechanical, electrical, and thermodynamic properties of the SiB compound phase are finely adjusted. Furthermore, the SiB compound contains Mo and Nb in Mo 1-y Nb y Si2 (0 < y < 1), or Cr containing Cr and V 1-y V y It is preferably Si2 (0 < y < 1). By the SiB compound containing Mo and Nb, or Cr and V, each property of the SiB compound phase can be finely adjusted, and the cycle life can be further improved.

[0034] When the atomic weight of B1 is greater than that of B2, the molar ratio of B1 to the total amount of B1 and B2 is preferably 0.1 to 0.9, more preferably 0.2 to 0.8, and even more preferably 0.3 to 0.7. By this atomic ratio being within these ranges, mechanical properties, electron conductivity, Li diffusivity, thermodynamic stability, etc. can be further adjusted, and the cycle life can be further improved.

[0035] The SiC compound is a compound of Si, C1, and C2. C1 and C2 are different elements from each other. The SiC compound phase may contain inevitable impurities. The ternary silicide compound usually phase-separates into a Si phase, one silicide compound phase, and the other silicide compound phase. However, when C1 is selected from the group consisting of Mn, Fe, Y, La, Ce, Gd, Dy, and Sm, and C2 is selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Ta, and W, the Si-C1 compound phase and the Si-C2 compound phase are difficult to form, and the Si-C1-C2 compound phase can be formed. In this case, it is preferable to use elements with the same crystal structure for C1 and C2. When the SiC compound is C1 (1-z) C2 (z) is Si2(0 < z < 1), by appropriately changing the value of Z, the SiC compound phase can obtain rigid properties or elastic properties, and the cycle life can be further improved.

[0036] Specifically, the ternary SiC compound is Gd 1-z Zr z Si2, Dy 1-z Zr z Si2, La 1-z W z Si2, Ce 1-z W z Si2, Gd 1-z W z Si2, La 1-z Ti z Si2, Sm 1-z Zr z Si2, Gd 1-z Nb z Si2, La 1-z Nb z Si2, Sm 1-z Nb z Si2, Gd 1-z Ta z Si2, La 1-z Ta z Si2, Sm 1-z Ta z Si2, Dy 1-z W z Si2, La 1-z Mo z Si2, Mn 1-z Ti zSi2, Dy 1-z Nb z Si2, La 1-z V z Si2, Mn 1-z W z Si2, Dy 1-z Ta z Si2, La 1-z Cr<00,00142>Si2, Mn 1-z Mo z Si2, Dy 1-z Mo z Si2, Ce 1-z Zr z Si2, Mn 1-z V z Si2, Y 1-z Zr z Si2, Ce 1-z Ti z Si2, Mn 1-z Cr z Si2, Y 1-z Ti z Si2, Ce 1-z Nb z Si2, Fe 1-z Ti z Si2, Y 1-z W z Si2, Ce 1-z Ta z Si2, Fe 1-z V z Si2, Y 1-z Nb z Si2, Ce 1-z Mo z Si2, Fe 1-z Cr z Si2, Y 1-z Ta z Si2, Ce 1-z V z Si2, Y 1-z Mo z Si2 or Ce 1-z Cr z It may be Si2 (0 < z < 1).

[0037] When the atomic weight of C1 is greater than that of C2, the molar ratio of C1 to the total amount of C1 and C2 is preferably 0.1 to 0.9, more preferably 0.2 to 0.8, and even more preferably 0.3 to 0.7. By having this mass ratio within these ranges, mechanical properties, electronic conductivity, Li diffusivity, thermodynamic stability, etc., can be further adjusted, and the cycle life can be further improved.

[0038] In the anode material, two compound phases selected from the SiA compound phase, SiB compound phase, and SiC compound phase undergo phase separation. Phase separation is promoted by identifying the elements constituting each of the two compound phases. Furthermore, phase separation can be promoted by following the manufacturing method of the anode material described later. Whether the Si phase and the two compound phases have separated can be confirmed by XRD (X-ray diffraction).

[0039] In the anode material, the independent presence of the Si phase allows for an increase in Li storage capacity. Two compound phases selected from SiA, SiB, and SiC compound phases exhibit elastic and rigid properties in relation to the volume expansion of the Si phase, thereby suppressing the collapse of the anode material. In the anode material, the presence of regions exhibiting elastic and rigid properties, respectively, due to the phase separation of the two selected compound phases, not only effectively relieves the stress generated by the volume expansion of the Si phase but also enables resistance to stress. In this disclosure, it has been found that while the suppression effect on the volume expansion of the Si phase was limited with binary silicide compounds, the effect is further enhanced by using ternary silicide compounds for the SiB or SiC compound phase, resulting in a further improvement in cycle life.

[0040] The negative electrode material may contain a Si phase, a SiA compound phase, and a SiB compound phase. In this case, the SiA compound phase exhibits elastic properties, and the SiB compound phase exhibits rigid properties. When the mixture contains both an SiA compound phase and a SiB compound phase, the mass ratio of the SiA compound to the total amount of the SiA and SiB compounds is preferably 0.1 to 0.9, more preferably 0.2 to 0.8, and even more preferably 0.3 to 0.7. Having this mass ratio within this range enhances the synergistic effect of the two compound phases on improving cycle life.

[0041] The negative electrode material may contain a Si phase, a SiA compound phase, and a SiC compound phase. In this case, the SiA compound phase exhibits elastic properties, and the SiC compound phase exhibits rigid properties. In this combination, the SiC compound should preferably have a high ratio of C2 atoms to C1 atoms. When a SiA compound phase and a SiC compound phase are included, the mass ratio of the SiA compound to the total amount of the SiA compound and SiC compound is preferably 0.1 to 0.9, more preferably 0.2 to 0.8, and even more preferably 0.3 to 0.7. Having this mass ratio within this range enhances the synergistic effect of the two compound phases on improving cycle life.

[0042] The negative electrode material may contain a Si phase, a SiB compound phase, and a SiC compound phase. In this case, the SiB compound phase exhibits rigid properties, and the SiC compound phase exhibits elastic properties. In this combination, the SiC compound should preferably have a low atomic ratio of C2 to C1. When a SiB compound phase and a SiC compound phase are included, the mass ratio of the SiB compound to the total amount of the SiB compound and SiC compound is preferably 0.1 to 0.9, more preferably 0.2 to 0.8, and even more preferably 0.3 to 0.7. Having this mass ratio within this range enhances the synergistic effect of the two compound phases on improving cycle life.

[0043] In this embodiment, it is preferable that the Si phase amount, obtained by subtracting the amount of Si compounded from the total amount of Si in the negative electrode material, be 20 to 90% by mass. If the Si phase amount is low, at 90% by mass or less, two compound phases selected from SiA compound phase, SiB compound phase, and SiC compound phase can be sufficiently included in the negative electrode material, thereby improving cycle life. On the other hand, if the Si phase amount is high, at 20% by mass or more, the negative electrode capacity can be increased, and the battery can be made to have a high energy density. It is preferable to adjust the Si phase amount according to the application.

[0044] The negative electrode material can take the form of flakes, granules, etc., but is not limited to these. A composite electrode can be prepared by dispersing the negative electrode material together with a conductive additive and a binder in a suitable solvent to make a paste or slurry, which is then applied to a current collector substrate and dried. Alternatively, a gas deposition electrode can be prepared by forming a film of the negative electrode material on a current collector using a gas deposition method.

[0045] The average particle size (D50) of the negative electrode material is preferably 1 to 20 μm. In this disclosure, the average particle size (D50) refers to the volume-based median diameter and can be measured using a laser diffraction / scattering particle size distribution analyzer. When the negative electrode material contains a single phase of Si or a silicide compound, volume expansion and contraction of the negative electrode material itself occur with charge-discharge reactions, which can generate stress in the composite layer, i.e., the conductive film, that binds the negative electrode material with a binder. If the binder collapses due to such stress, the conductive film may peel off from the current collector, resulting in a decrease in conductivity within the electrode and a reduction in cycle life. When the average particle size (D50) of the negative electrode material is 1 to 20 μm, the negative electrode material is refined, increasing the contact area with the binder, which suppresses binder collapse and, as a result, can improve cycle life.

[0046] In a negative electrode material, when the average particle size (D50) of the negative electrode material is 1 to 20 μm, and the size of the Si phase is 1 to 500 nm, two compound phases selected from SiA compound phase, SiB compound phase, and SiC compound phase will be present around the Si phase in appropriate proportions. This further promotes the absorption and suppression of volume expansion of the Si phase, thereby improving the cycle life.

[0047] Next, an example of a method for manufacturing the negative electrode material according to this embodiment will be described. Note that the negative electrode material according to this embodiment is specified by the configuration described above, and is not limited to the manufacturing method.

[0048] In one embodiment, the negative electrode material can be manufactured by a method that involves rapidly cooling a molten alloy having a predetermined chemical composition to form a rapidly cooled alloy. If the obtained rapidly cooled alloy is not in powder form or if it is desired to reduce its diameter, an additional step may be added to grind the rapidly cooled alloy into a powder using appropriate grinding means. Furthermore, if necessary, an additional step may be added to classify the obtained rapidly cooled alloy to adjust it to an appropriate particle size.

[0049] In the above manufacturing method, the molten alloy can be obtained, for example, by weighing out each raw material to achieve a predetermined chemical composition, and then melting each weighed-out raw material using a melting means such as an arc furnace, a high-frequency induction furnace, or a heating furnace.

[0050] Methods for rapidly cooling molten alloys include liquid quenching methods such as roll quenching (single-roll quenching, double-roll quenching, etc.) and atomization (gas atomization, water atomization, centrifugal atomization, etc.), but it is preferable to use roll quenching, which has a particularly high cooling rate.

[0051] One example of applying the roll quenching method is to cool molten alloy, which is dispensed into a chamber such as a quenching and recovery chamber and flows continuously (in a rod shape) downwards, on a rotating roll that rotates at a peripheral speed of approximately 10 m / s to 100 m / s. The molten alloy is cooled on the roll surface, resulting in an alloy material that is foil-like or flaked. In this case, the alloy material can be crushed using a suitable grinding means such as a ball mill, disc mill, coffee mill, or mortar and pestle, and classified as necessary to obtain a powdered negative electrode material. The material of the rotating roll may be, for example, Cu, Fe, etc., and the roll surface may be plated.

[0052] One example of applying the atomization method is to spray a gas containing N2, Ar, He, etc., at high pressure (e.g., 1-10 MPa) onto a molten alloy that is dispensed into a spray chamber and flows continuously (in a rod shape) downwards, thereby pulverizing and cooling the molten metal. The cooled molten metal, while remaining semi-molten, free-falls within the spray chamber and approaches a spherical shape, yielding a powdered negative electrode material. Alternatively, high-pressure water may be sprayed instead of gas to improve the cooling effect.

[0053] In another embodiment, the anode material can be manufactured by a method that involves alloying using a mechanical alloying method. In the mechanical alloying method, a mixed powder is used in which the component amounts of each raw material are adjusted to form the target constituent phase. By grinding this mixed powder, the raw material powder is subjected to physical impact and alloying is carried out. As for the grinding method, a dry grinding method such as a planetary ball mill is preferable. Since the mechanical alloying method performs grinding along with alloying, the resulting anode material can be made finer. The anode material obtained by the mechanical alloying method has a Si phase and two compound phases selected from a SiA compound phase, a SiB compound phase, and a SiC compound phase surrounding the Si phase.

[0054] [Negative electrode] According to this embodiment, it is possible to provide a negative electrode for a lithium-ion secondary battery that includes the negative electrode material for lithium-ion batteries described above. For example, the negative electrode has a conductive substrate and a conductive film laminated on the surface of the conductive substrate. The conductive film contains the negative electrode material according to this embodiment as a negative electrode active material in a binder. The conductive film may further contain a binder, a conductive additive, etc. When a conductive additive is included, it becomes easier to secure the conductive path of electrons.

[0055] The conductive substrate described above functions as a current collector. Examples of materials for the conductive substrate include Cu, Cu alloy, Ni, Ni alloy, Fe, Fe alloy, and stainless steel (SUS). Cu and Cu alloy are preferred. The specific form of the conductive substrate may be foil-shaped, plate-shaped, etc. A foil shape is preferred from the viewpoint of reducing the volume of the secondary battery and improving the degree of freedom in shape. The current collector may be Cu foil, Cu alloy foil, SUS foil, etc.

[0056] The binder material may be, for example, polyvinylidene fluoride (PVdF) resin, fluororesins such as polytetrafluoroethylene, polyvinyl alcohol resin, polyimide resin, polyamide resin, polyamide-imide resin, styrene-butadiene rubber (SBR), styrene-butadiene copolymer and its hydrogenated products, polyacrylic acid, carboxymethylcellulose, etc. These may be used individually or in combination of two or more.

[0057] From the viewpoint of improving conductivity and strength, the binder content is preferably 1 to 30 parts by mass, and more preferably 5 to 25 parts by mass, per 100 parts by mass of the negative electrode material.

[0058] Examples of the above-mentioned conductive additives include carbon black such as Ketjenblack, acetylene black, and furnace black, graphite, carbon nanotubes, and fullerenes. These may be used individually or in combination of two or more. Of these, Ketjenblack, acetylene black, etc., are preferred from the viewpoint of easily ensuring electronic conductivity.

[0059] From the viewpoint of improving conductivity and electrode capacity, the content of the conductive additive is preferably 0 to 30 parts by mass, and more preferably 5 to 25 parts by mass, per 100 parts by mass of the negative electrode material. Furthermore, from the viewpoint of dispersibility and ease of handling, the average particle size (D50) of the conductive additive is preferably 10 nm to 1 μm, and more preferably 20 nm to 50 nm.

[0060] The negative electrode can be manufactured, for example, by adding the required amount of negative electrode material and, if necessary, a conductive additive to a binder dissolved in a suitable solvent to form a paste, coating this paste onto the surface of a conductive substrate, drying it, and, if necessary, compacting or heat treatment.

[0061] In another embodiment, the negative electrode can be manufactured by a method that involves a film deposition process using a gas deposition method. In the gas deposition method, the negative electrode material powder is aerosolized with a carrier gas such as argon or helium, and then sprayed onto a substrate under pressure. The differential pressure is preferably 0.6 MPa. In the gas deposition method, it is preferable to uniformly control the particle size of the negative electrode material powder. For example, the negative electrode material powder should have a primary particle size of 1 μm or less and a secondary aggregated average particle size of 5 to 20 μm. This increases the packing density of the alloy deposited film and increases the discharge capacity of the secondary battery.

[0062] The gas deposition method offers a fast film deposition rate and makes it easier to maintain the target constituent phase. Furthermore, the gas deposition method allows for the deposition of the negative electrode without the use of a binder. Because the gas deposition method does not use a binder, the packing density can be increased by controlling the particle size of the negative electrode material, thereby increasing the discharge capacity of the secondary battery.

[0063] [Lithium-ion rechargeable battery] According to this embodiment, a lithium-ion secondary battery can be provided that includes a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode includes the lithium-ion battery negative electrode material described above. In this embodiment, the components of the battery other than the negative electrode, such as the positive electrode, electrolyte, and separator, are not particularly limited.

[0064] Examples of the above-mentioned positive electrode include those in which a layer containing a positive electrode material such as LiCoO2, LiNiO2, LiFePO4, or LiMnO2 is formed on the surface of a current collector such as aluminum foil.

[0065] The electrolyte may be either a solid electrolyte or a liquid electrolyte. Examples of electrolytes include liquid electrolytes obtained by dissolving a lithium salt in a non-aqueous solvent. Other options include polymers in which a lithium salt is dissolved, and polymer solid electrolytes obtained by impregnating a polymer with the above-mentioned liquid electrolyte.

[0066] Examples of the lithium salts mentioned above include LiFSA, LiPF6, LiBF4, LiClO4, and LiCF3SO3. These may be present individually or in combination of two or more. The concentration of the Li salt may be 0.1-10M, 0.5-5M, or 1-3M.

[0067] Examples of the above-mentioned non-aqueous solvents include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and the like. These may be present individually or in combination of two or more.

[0068] Furthermore, as the liquid electrolyte, a solution of LiFSA salt dissolved in an ionic liquid of N-methyl-N-propylpyrrolidinium (Py13) and bis(fluoromethylsulfonyl)amide (FSA) (Py13-FSA), or a solution of LiTFSA salt dissolved in an ionic liquid of N-methyl-N-propylpyrrolidinium (Py13) and bis(trifluoromethylsulfonyl)amide (TFSA) (Py13-FSA) may be used.

[0069] The liquid electrolyte may contain additives. Examples of additives include film-forming additives (such as vinylene carbonate and fluoroethylene carbonate) and flame-retardant additives (such as triethyl phosphate).

[0070] As the solid electrolyte, one or more known types can be used in combination. Inorganic solid electrolytes may be used, as well as oxide solid electrolytes, sulfide-type solid electrolytes, complex hydride solid electrolytes, nitride solid electrolytes, halogenated solid electrolytes, polymer electrolytes, etc. Among these, sulfide-type solid electrolytes are preferred.

[0071] Examples of sulfide-type solid electrolytes include Li6PS5Cl, Li6PS5Br, Li6PS5I, xLi2S-(1-x)P2S5, xLi2S-(1-x)GeS2, xLi2S-yGeS2-(1-xy)P2S5, xLi4GeS4-(1-x)Li3PS4, Li 9.54 Si 1.74 P 1.44 S 11.7 C l0.3 , Li4SnS4, Li3PS4, xLi2S-(1-x)P2S5, xLi2S-yP2S5-(1-xy)Li3N, Li5B7S 13 Examples include Li3BS3 and Li2B2S5. Here, 0 <x<1、0<y<1、0<(1-x-y)<1である。

[0072] Other battery components include separators, casings (battery cases), and gaskets. These components can also be appropriately combined to construct a battery using those commonly used in lithium-ion secondary batteries.

[0073] The battery shape is not particularly limited and can be cylindrical, rectangular, coin-shaped, or any other shape, and can be selected as appropriate according to the specific application. [Examples]

[0074] The present invention will be described more specifically below using examples, but the present invention is not limited to the specific examples described below. Unless otherwise specified, the percentages of alloy composition are given in mass percent.

[0075] [Fabrication of negative electrode materials] Each raw material was weighed to achieve the alloy composition shown in Table 1 below. The weighed raw materials were mixed, and powdered negative electrode materials were produced using a mechanical alloying method with a planetary ball mill. The rotation speed of the planetary ball mill was 380 rpm, and the processing time was 5 to 100 hours.

[0076] [Table 1]

[0077] [Microstructure observation of negative electrode materials, etc.] The negative electrode materials of each example and comparative example were observed using a transmission electron microscope (TEM). XRD (X-ray diffraction) analysis was also performed to confirm the presence of phases such as the Si phase, SiA compound phase, and SiB compound phase. The XRD analysis was performed using a Cu tube, measuring angles between 80° and 20°.

[0078] [Method for calculating the amount of each ingredient] The amount of each raw material was adjusted so that the amount of each phase matched the target constituent phases shown in Table 1. The amount of each component was calculated based on the chemical composition. The calculation method will be explained below using Example 2, which contains Si, La, Cr, and V, as an example. In this example, the atomic weights of each atom were calculated as Si=28, La=139, Cr=52, V=51, Mo=96, and Nb=93. In Example 2, LaSi2 accounts for 35% by mass of the total. Since the atomic weight of Si is 28 and the atomic weight of La is 139, the amount of La contained in the total composition is 35 × 139 / (139 + 28 × 2) = 24.95% by mass. Also, Cr 0.5 V 0.5Si2 makes up 35% by mass of the total. Since the atomic weight of Si is 28, the atomic weight of Cr is 52, and the atomic weight of V is 51, the amount of Cr in the total composition is 35 × 52 × 0.5 / (52 × 0.5 + 51 × 0.5 + 28 × 2) = 8.47% by mass, and the amount of V is 35 × 51 × 0.5 / (52 × 0.5 + 51 × 0.5 + 28 × 2) = 8.30% by mass. Since the rest is all Si, the total composition contains 100 - (24.95 + 8.47 + 8.30) = 58.28 mass% Si. Table 1 shows the molar ratio of B1 / (B1+B2) when B1 is Cr and B2 is V, or when B1 is Mo and B2 is Nb.

[0079] [Fabrication of a test coin-type battery] Coin-type batteries were fabricated as follows. For a simplified evaluation, a gas deposition electrode made using the negative electrode material was used as the test electrode, and a Li metal foil was used as the counter electrode. A copper foil with a thickness of 20 μm and a diameter of 10 mm was used as the substrate, and the negative electrode material was deposited on it to a thickness of 2 μm and a diameter of approximately 5 mm to be used as the gas deposition electrode.

[0080] When using a solid electrolyte, a SUS foil, a Li-In counter electrode (lithium-indium), and solid electrolyte powder were layered in that order, and a pressure of 100 MPa was applied to this layer to form a solid electrolyte layer. A sulfide-type solid electrolyte (Li7PS6Cl) was used as the solid electrolyte. Next, a negative electrode mixture powder (active material (negative electrode material): solid electrolyte: conductive additive = 47.5:47.5:5.0 (volume ratio)) and SUS foil were layered on top of the solid electrolyte phase, and a pressure of 100 MPa was applied. Finally, the cell was restrained with a pressure of 150 MPa using bolts and nuts. The test electrode and counter electrode were disc-shaped with a diameter of 11.2 mm. In this way, an all-solid-state battery was fabricated.

[0081] When using a liquid electrolyte, half-cells were fabricated using each test electrode and Li metal as the counter electrode. The counter electrode was a disc shape with a diameter of 8 mm. A glass fiber filter (19 mm in diameter, 0.3 mm thick) was used as the separator. The liquid electrolyte was 1 mol / dm³.3 LiFSA / Py13-FSA was used. 1 mol / dm 3 LiFSA / Py13-FSA is prepared by adding the LiFSA salt to an ionic liquid (Py13-FSA) of N-methyl-N-propylpyrrolidinium (Py13) and bis(fluoromethylsulfonyl)amide (FSA) at a concentration of 1 mol / dm³. 3 It was dissolved in such a manner. A coin-shaped cell was then fabricated.

[0082] [Evaluation of negative electrode materials] <Cycle life> The test coin-type batteries prepared as described above were subjected to repeated charge and discharge cycles, and the discharge capacity was measured. The results for Comparative Examples 1-4 and Examples 2 and 4 when a solid electrolyte was used are shown in the graph in Figure 1. The results for Comparative Examples 1-4 and Example 2 when a liquid electrolyte was used are shown in the graph in Figure 2. The results for Comparative Examples 1, 4, and 5 and Examples 1-3 when a liquid electrolyte was used are shown in the graph in Figure 3. In these graphs, the horizontal axis represents the number of cycles, and the vertical axis represents the discharge capacity.

[0083] The details of the method for measuring cycle life are as follows: <In the case of all-solid-state batteries> 1.0~0.05 V vs. Li + Two pre-cycles were performed within the potential range of / Li. Constant current charging was performed at a rate of 0.1C, and after reaching the predetermined potential, constant voltage charging was performed until the current value dropped to the equivalent of 0.01C. Similarly, constant current discharge was followed by constant voltage discharge on the discharge side. In this test, constant current tests were performed within the above potential range at a rate of 0.2C on the charging side and 0.5C on the discharging side. In addition, no capacity restriction was applied during the pre-cycle, and in this test, 1000mAhg per Si single-phase weight was used. -1 The charging capacity was restricted. The 1C rate is 4200mAh. -1 That's reasonable.

[0084] [Evaluation of negative electrode materials] <Cycle life> The test coin-type batteries prepared as described above were subjected to repeated charge and discharge cycles, and the discharge capacity was measured. For Comparative Examples 1-4 and Example 2, the results when a solid electrolyte was used are shown in the graph in Figure 1, and the results when a liquid electrolyte was used are shown in the graph in Figure 2. Furthermore, for Comparative Examples 1, 4, 5 and Examples 1-3, the results when a liquid electrolyte was used are shown in the graph in Figure 3. In these graphs, the horizontal axis represents the number of cycles, and the vertical axis represents the discharge capacity.

[0085] <In the case of a coin-type half-cell> 2.0~0.5V vs. Li + One pre-cycle was performed within the potential range of / Li. Constant current charging was performed at a rate of 0.1C, and 0.5V vs Li. + The potential was maintained for 12 hours after reaching / Li. Subsequently, constant current discharge was performed at a rate of 0.1C until it reached 2.0V vs. Li+ / Li. This test involved constant current charge and discharge tests at a rate of 1C on both the charging and discharging sides within the above potential range. Furthermore, no capacity restrictions were imposed during the pre-cycle, and this test used 1000mAhg per single-phase Si weight. -1 The charging capacity was restricted. The 1C rate is 3600mAh. -1 That's reasonable.

[0086] Figure 1 shows that when the electrolyte is solid, it is formed in three phases of Si, LaSi2, and CrSi2, and CrSi2 is Cr 0.5 V 0.5 Example 2, in which Si is ternated as Si2, and in which Si, LaSi2 and NbSi2 are triphase, and NbSi2 is Mo 0.5 Nb 0.5 This shows that Example 4, which is ternated as Si2, has a better cycle life than Comparative Example 1, which is a single-phase Si phase; Comparative Example 2, which is a two-phase Si and CrSi2; Comparative Example 3, which is a two-phase Si and LaSi2; and Comparative Example 4, which is a three-phase Si, LaSi2, and CrSi2 but is not diversified.

[0087] Figure 2 shows that when the electrolyte is a liquid electrolyte, Si, LaSi2, and CrSi2 form a three-phase system, and CrSi2 is Cr0.5 V 0.5 Example 2 tripled as Si2 shows that the cycle life is improved compared to Comparative Example 1 with a single Si phase, Comparative Example 2 dual-phased with Si and CrSi2, Comparative Example 3 dual-phased with Si and LaSi2, and Comparative Example 4 tri-phased with Si, LaSi2, and CrSi2 but not diversified.

[0088] Figure 3 shows that when the electrolyte is a liquid electrolyte, it is tri-phased with Si, LaSi2, and CrSi2, and CrSi2 is Cr 1-y V y Examples 1 to 3 tripled as Si2(0 < y < 1) show that the cycle life is superior to Comparative Example 4 which is tri-phased with Si, LaSi2, and CrSi2 but not tripled.

[0089] As described above, the negative electrode material for a lithium-ion secondary battery and the lithium-ion secondary battery of the present invention have been described in detail. However, the present invention is not limited to the specific examples described in the above embodiments and examples, and various modifications are possible without departing from the spirit of the present invention.

Industrial Applicability

[0090] In the present disclosure, by combining the diversification and multiphase formation of silicide compounds, we have successfully improved the cycle life of a lithium-ion secondary battery using Si as a negative electrode material. The negative electrode material according to the present disclosure can also be applied to driving power sources used in vehicles driven by motors such as electric vehicles and hybrid vehicles, power sources used in portable small electronic devices such as smartphones, personal computers typified by notebooks, tablet terminals, stationary power sources, small batteries for medical wearable terminals, etc. Further, with the progress of the practical application of lithium-ion secondary batteries using Si-based negative electrodes according to the present disclosure, the entire chemical industry is expected to be activated.

Claims

1. It comprises a Si phase and two compound phases selected from SiA compound phase, SiB compound phase, and SiC compound phase. The SiA compound phase comprises an SiA compound of Si and at least one of the elements A1 and A2. The SiB compound phase comprises Si and SiB compounds of B1 and B2. The SiC compound phase comprises Si and SiC compounds of C1 and C2. A1 and A2 are elements selected from the group consisting of Mn, Fe, Y, La, Ce, Gd, Dy, and Sm, and A1 and A2 are different elements from each other. B1 and B2 are elements selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Ta, and W, and B1 and B2 are different elements from each other. C1 is Mn, Fe, Y, La, Ce, Gd, Dy, or Sm, and C2 is Ti, V, Cr, Zr, Nb, Mo, Ta, or W. Anode material for lithium-ion secondary batteries.

2. The negative electrode material for a lithium-ion secondary battery according to claim 1, wherein, when the SiB compound phase is included, the SiB compound is a silicide compound of Cr and one element selected from the group consisting of V, Nb, Mo, Ta, W, Zr, and Ti.

3. The anode material for a lithium-ion secondary battery according to claim 2, wherein the SiB compound is a silicide compound containing Cr and V.

4. The negative electrode material for a lithium-ion secondary battery according to claim 1, wherein, when the SiB compound phase is included, the SiB compound is a silicide compound of Nb and one element selected from the group consisting of V, Mo, Ta, W, Zr, and Ti.

5. The anode material for a lithium-ion secondary battery according to claim 4, wherein the SiB compound phase is a silicide compound containing Nb and Mo.

6. The negative electrode material for a lithium-ion secondary battery according to claim 1, wherein, when the SiB compound phase is included, if the atomic weight of B1 is greater than that of B2, the molar ratio of B1 to the total amount of B1 and B2 is 0.3 to 0.

7.

7. The negative electrode material for a lithium-ion secondary battery according to claim 1, wherein, when the material contains the SiA compound phase and the SiB compound phase, the mass ratio of the SiA compound to the total amount of the SiA compound and the SiB compound is 0.1 to 0.

9.

8. The negative electrode material for a lithium-ion secondary battery according to claim 1, wherein, when the SiA compound phase is included, the SiA compound is a silicide compound containing La.

9. The anode material for a lithium-ion secondary battery according to claim 1, wherein the amount of Si phase obtained by subtracting the amount of Si compounded from the total amount of Si in the anode material is 20 to 90% by mass.

10. A negative electrode for a lithium-ion secondary battery, comprising the negative electrode material for a lithium-ion secondary battery described in any one of claims 1 to 9.

11. A lithium-ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises a negative electrode material for a lithium-ion secondary battery according to any one of claims 1 to 9.

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