Lithium ion secondary battery negative electrode active material, method for manufacturing same, and lithium ion secondary battery negative electrode

Abstract

The purpose of the present invention is to provide a lithium ion secondary battery negative electrode active material capable of suppressing deterioration of a discharge capacity retention rate (cycle characteristics) even if charge and discharge are repeated by suppressing collapse of silicon particles due to expansion and contraction of the silicon particles accompanying storage and release of lithium. In this lithium ion secondary battery negative electrode active material in which silicon particles are dispersed in a lithium silicate phase, the lithium silicate phase is a composite having a barium-containing glass material as a main phase.

Description

Negative electrode active material for lithium-ion secondary batteries, method for manufacturing the same, and negative electrode for lithium-ion secondary batteries

[0001] This invention relates to a negative electrode active material for lithium-ion secondary batteries, a method for producing the same, and a negative electrode for lithium-ion secondary batteries. More specifically, it relates to a negative electrode active material for lithium-ion secondary batteries having excellent cycle characteristics, in which silicon particles are dispersed in a matrix mainly composed of a barium-containing glass material with excellent sinterability, a method for producing the same, and a negative electrode for lithium-ion secondary batteries.

[0002] Rechargeable batteries are now widely used in devices such as mobile phones, personal computers, power tools, hybrid electric vehicles (HEVs), and electric vehicles (PEVs). In particular, lithium-ion batteries have high power output and high energy density, and are widely used as batteries for portable devices and in vehicles. The negative electrode active material of lithium-ion batteries is mainly graphite. Although the negative electrode of lithium-ion batteries using graphite as the negative electrode active material has good cycle characteristics, its charge capacity is relatively small, at around 372 mAh / g.

[0003] In recent years, with the increasing demand for lithium-ion batteries as automotive batteries, there is a strong desire for even higher energy density in lithium-ion batteries. To improve the energy density of lithium-ion batteries, it is necessary to improve the charging capacity by changing the negative electrode active material contained in the negative electrode of the lithium-ion battery. From this perspective, silicon-based negative electrodes, which use silicon material as the negative electrode active material and have a charging capacity of 4200 (mA·h / g) that is more than 10 times that of graphite material, are attracting attention, and research and development are being actively carried out.

[0004] Silicon-based anodes that have been put into practical use include Si anodes, which are made only from pure silicon, and Si and SiO ２This is an SiO anode composed of SiO, which is a mixture of silicon and lithium. Here, the SiO anode has a structure in which silicon is dispersed in silicon oxide. The SiO anode has superior cycle characteristics compared to the Si anode, which is composed of silicon alone, because the silicon oxide suppresses the expansion and contraction of silicon. However, in the SiO anode, during the initial charge, the silicon oxide reacts with lithium as a side reaction, and Li ４ SiO ４ This process reduces Coulomb efficiency. For this reason, development is underway on Li-Si-O based anodes, in which lithium is pre-doped into the SiO anode. However, Li-Si-O based anodes have inferior cycle characteristics compared to graphite-based anodes, so technical challenges remain.

[0005] Patent Document 1 discloses an SiO powder that can be used as a negative electrode material for a lithium secondary battery capable of intercalating and deintercalating lithium using a lithium-ion conductive non-aqueous electrolyte, and a method for producing the same. The SiO powder described in Patent Document 1 is a secondary battery SiO powder used as a negative electrode material for a lithium secondary battery, and has a hydrogen content of 80 ppm or more.

[0006] Patent Document 2 discloses a powder for the negative electrode of a lithium-ion secondary battery, in which reactivity with water is suppressed. The negative electrode powder for a lithium-ion secondary battery described in Patent Document 2 contains lithium-containing silicon oxide powder, and when X-ray diffraction measurement is performed using CuKα rays, the diffraction angle 2θ appears within a predetermined range. ２ Si ２ O ５ The peak height P1 caused by this and the diffraction angle 2θ appear within a predetermined range of Li ２ SiO ３ The peak height P2 resulting from this satisfies a certain relationship.

[0007] Patent Document 3 discloses a negative electrode active material for lithium-ion secondary batteries that can suppress the decrease in discharge capacity retention rate (cycle characteristics) even after repeated charging and discharging. The negative electrode active material for lithium-ion secondary batteries described in Patent Document 3 is a composite in which silicon particles are dispersed in a matrix containing lithium aluminosilicate having a three-dimensional network structure, and the lithium aluminosilicate is represented by a predetermined general formula.

[0008] Patent Document 4 discloses a negative electrode active material for secondary batteries that can increase the cycle capacity retention rate of secondary batteries. The negative electrode active material for secondary batteries described in Patent Document 4 is a negative electrode active material comprising a lithium silicate phase and a silicon phase dispersed within the lithium silicate phase. In the negative electrode active material for secondary batteries described in Patent Document 4, the lithium silicate phase constituting the negative electrode active material for secondary batteries contains element M and has a spot image in the electron diffraction pattern on a transmission electron microscope.

[0009] Japanese Patent Publication No. 4531762, Japanese Unexamined Patent Publication No. 2015-153520, Japanese Patent Publication No. 7116518, International Publication No. 2021 / 241618

[0010] However, the above-mentioned prior art has the following problems. Specifically, a lithium secondary battery equipped with a negative electrode using SiO powder as the negative electrode material disclosed in Patent Document 1 can prevent the breakdown of the conductive network and suppress cycle performance degradation, but it can only slightly reduce the volume expansion of the negative electrode.

[0011] Furthermore, the negative electrode powder contained in the negative electrode of the lithium-ion secondary battery disclosed in Patent Document 2 has suppressed reactivity with water. For this reason, the negative electrode powder described in Patent Document 2 can be used to produce a slurry using the negative electrode powder, water, and an aqueous binder to manufacture the working electrode of the negative electrode of a lithium-ion secondary battery. In other words, the negative electrode powder contained in the negative electrode of the lithium-ion secondary battery disclosed in Patent Document 2 only enables the good formation of the negative electrode of the lithium-ion secondary battery and does not focus on the cycle characteristics of the lithium-ion secondary battery.

[0012] Furthermore, the negative electrode active material for lithium-ion secondary batteries disclosed in Patent Document 3 is a composite in which silicon particles are dispersed in a matrix containing lithium aluminosilicate having a three-dimensional network structure. The components forming the lithium aluminosilicate contained in this negative electrode active material for lithium-ion secondary batteries are limited to silicon, aluminum, and oxygen, and the ratio of silicon to aluminum must be set within a predetermined range.

[0013] On the other hand, the negative electrode active material for secondary batteries described in Patent Document 4 comprises a lithium silicate phase and a silicon phase dispersed within the lithium silicate phase, and the lithium silicate phase contains element M. The element M contained in the lithium silicate phase constituting the negative electrode active material for secondary batteries described in Patent Document 4 includes a group 2 element. However, Patent Document 4 does not specify the specific composition of the lithium silicate phase when a particular group 2 element is selected and used as element M constituting the lithium silicate phase constituting the negative electrode active material for secondary batteries.

[0014] As described above, the negative electrode active materials for lithium-ion secondary batteries disclosed in Patent Documents 1 to 4 list various elements as element M in the lithium silicate phase constituting the negative electrode active material, such as alkali metal elements (excluding lithium), group 2 elements, and rare earth elements. However, they do not adopt a specific group 2 element, and are therefore insufficient from a technical standpoint to achieve extremely good cycle characteristics for lithium-ion secondary batteries. Consequently, in negative electrode materials containing the negative electrode active material for lithium-ion secondary batteries disclosed in Patent Documents 1 to 4 and silicon particles, the silicon particles disintegrate due to the expansion and contraction of the silicon particles accompanying the intercalation and deintercalation of lithium.

[0015] In other words, in negative electrode materials that use silicon particles as the active material, the expansion and contraction rate of silicon is large in response to the intercalation and deintercalation of lithium, causing the silicon particles to collapse due to the expansion and contraction of the silicon particles during charging and discharging. Ultimately, the discharge capacity decreases with each repeated charging and discharging of the lithium-ion secondary battery, and the cycle characteristics of the lithium-ion secondary battery deteriorate. In short, lithium-ion secondary batteries equipped with negative electrode electrodes containing the negative electrode active material disclosed in Patent Documents 1 to 4 have the problem that their charge and discharge capacity decreases with each repeated charging and discharging, resulting in a decrease in discharge capacity retention rate (cycle characteristics).

[0016] This invention has been made in view of the problems of these prior arts, and aims to provide a negative electrode active material for lithium-ion secondary batteries, a method for producing the same, and a negative electrode for lithium-ion secondary batteries that can suppress the collapse of silicon particles due to the expansion and contraction of silicon particles accompanying the intercalation and release of lithium, thereby suppressing the decrease in discharge capacity retention rate (cycle characteristics) even after repeated charging and discharging.

[0017] The negative electrode active material for lithium-ion secondary batteries targeted by this invention is a composite in which silicon particles are dispersed in a matrix mainly composed of a sinterable barium-containing glass material. To achieve the above objective, this invention utilizes a sinterable barium-containing glass material as the matrix for dispersing the silicon particles contained in the negative electrode active material for lithium-ion secondary batteries. This suppresses the collapse of silicon particles due to expansion and contraction associated with the intercalation and release of lithium, enabling a balanced combination of discharge capacity characteristics and charge / discharge capacity retention rate of the negative electrode active material for lithium-ion secondary batteries. It was discovered that this also results in suitable cycle characteristics for automotive lithium-ion secondary batteries, leading to the development of this invention.

[0018] In other words, firstly, the present invention provides a negative electrode active material for a lithium-ion secondary battery, wherein silicon particles are dispersed in a lithium silicate phase, and the lithium silicate phase is a composite mainly composed of a barium-containing glass material.

[0019] In addition, as the negative electrode active material for the lithium ion secondary battery, (a) the softening point of the composite is 500 to 560 ° C and its crystallization temperature is 600 to 650 ° C, (b) the content of the silicon particles contained in the negative electrode active material for the lithium ion secondary battery is 40 to 90% by mass, (c) the average particle diameter of the silicon particles is 5 to 100 nm, and (d) the barium-containing glass material contains boron, etc. are considered preferable means.

[0020] Second, the present invention is a method for producing a negative electrode active material for a lithium ion secondary battery in which silicon particles are dispersed in a matrix mainly composed of a barium-containing glass material having sinterability, and step (I); lithium carbonate, barium carbonate, and silicon dioxide are mixed and pulverized, and then fired at a temperature of 600 to 1000 ° C in an atmospheric pressure atmosphere to produce a barium-containing glass material, and step (II); a step of producing a negative electrode active material precursor by mixing and pulverizing the barium-containing glass material produced in the step (I) and silicon particles, and step (III); a step of sintering the negative electrode active material precursor produced in the step (II) in an inert gas atmosphere.

[0021] Third, the present invention is a negative electrode for a lithium ion secondary battery characterized by containing the above negative electrode active material for a lithium ion secondary battery.

[0022] The negative electrode active material for a lithium ion secondary battery and the negative electrode for a secondary battery containing the negative electrode active material for a lithium ion secondary battery according to the present invention are excellent in discharge capacity characteristics and discharge capacity maintenance rate (cycle characteristics). Therefore, according to the present invention, it becomes possible to reduce the size and weight of the lithium ion secondary battery, and by mounting the lithium ion secondary battery on a mobile phone, a personal computer, a power tool, a hybrid electric vehicle (HEV), or an electric vehicle (PEV), it becomes possible to provide a product having high exercise performance.

[0023] It is a graph showing the result of measuring the pore distribution of the negative electrode active material for a lithium ion secondary battery according to the present invention. As the negative electrode active material for a lithium ion secondary battery, Li ２ Si ２O ５ This is a graph showing the results of pore distribution measurement after adopting the material. This is a flow diagram showing each step of the method for manufacturing the negative electrode active material for lithium-ion secondary batteries according to the present invention. This is a model diagram showing the structure of a secondary battery equipped with a negative electrode containing the negative electrode active material for lithium-ion secondary batteries according to the present invention. This is a graph showing the measurement results of the discharge capacity retention rate (cycle characteristics) with respect to the number of discharge cycles of a laminate cylindrical secondary battery equipped with a negative electrode material containing the negative electrode active material manufactured in Example 1 and Comparative Examples 1-2. This is an SEM image of the surface of the negative electrode (negative electrode active material consisting of a composite material containing silicon particles and barium-containing glass material) of a secondary battery equipped with a negative electrode containing the negative electrode active material manufactured in Example 1 after 500 cycles. ２ Si ２ O ５ This is an SEM image of the surface of the negative electrode active material (which consists of a composite containing [a specific component]).

[0024] [First Embodiment] The negative electrode active material for lithium-ion secondary batteries of the first embodiment will be described. The negative electrode active material for lithium-ion secondary batteries of this embodiment is characterized by being a composite in which silicon particles are dispersed in a matrix mainly composed of a barium-containing glass material. That is, the matrix constituting the negative electrode active material for lithium-ion secondary batteries of this embodiment mainly consists of a barium-containing glass material. Here, "main phase" means that the barium-containing glass material is contained in the matrix at a concentration of 50% by mass or more. Furthermore, "main phase" means that the matrix constituting the negative electrode active material for lithium-ion secondary batteries of this embodiment is composed solely of barium-containing glass material, and the barium-containing glass material may be contained in the matrix at a concentration of 100% by mass. That is, the barium-containing glass material according to this embodiment is contained in the matrix at a concentration of 50 to 100% by mass, preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0025] Furthermore, as a matrix for dispersing silicon particles contained in the negative electrode active material for the non-aqueous electrolyte lithium-ion secondary battery of this embodiment, a barium-containing glass material containing boron in addition to lithium, barium, silicon, and oxygen, which constitute the barium-containing glass material, can preferably be used. Moreover, a barium-containing glass material can be used in which boron is replaced with Al, K, Na, Mg, Ti, V, Fe, Ta, Y, Zr, Bi, Mn, W, Co, Mo, Cu, Cr, Ni, Zn, etc., which have chemical properties similar to boron.

[0026] Figure 1 is a graph showing the results of pore distribution measurement of a barium-containing glass material, which is a negative electrode active material for lithium-ion secondary batteries according to the present invention. As shown in Figure 1, the pore width of the pores in the negative electrode active material for lithium-ion secondary batteries according to this embodiment is 3.0 to 75.0 nm. Furthermore, the cumulative pore volume of the pores in this negative electrode active material for lithium-ion secondary batteries is 0.0010 to 0.0030 cm³. ３ It is / g, and in particular, 0.0017 cm ３ It is approximately / g. Furthermore, the differential pore volume of the pores in the negative electrode active material for lithium-ion secondary batteries according to this embodiment is 1.0 × 10⁻⁶. －５ ~4.0 x 10 －５ That is the case.

[0027] On the other hand, Figure 2 shows Li as a negative electrode active material for lithium-ion secondary batteries. ２ Si ２ O ５ This graph shows the results of pore distribution measurement after selecting Li as the negative electrode active material for lithium-ion secondary batteries. As shown in Figure 2, Li was selected as the negative electrode active material for lithium-ion secondary batteries. ２ Si ２ O ５ The pore width is 2.0 to 72.0 nm. Furthermore, the cumulative pore volume of the pores in this lithium-ion secondary battery negative electrode active material is 0.0056 cm³. ３ It is approximately / g. Also, Li is used as a negative electrode active material for lithium-ion secondary batteries. ２ Si ２ O ５ The differential pore volume of the pores in the selected negative electrode active material for lithium-ion secondary batteries is 2.5 × 10⁻⁶. －５~1.8 x 10 －４ That is the case.

[0028] Furthermore, the method used to measure the pore distribution of the barium-containing glass material shown in Figures 1 and 2 is the gas adsorption method, because the pores of the negative electrode active material for lithium-ion secondary batteries according to this embodiment are in the micro-mesopore region.

[0029] As is clear from the comparison between Figure 1 and Figure 2, the negative electrode active material for lithium-ion secondary batteries according to this embodiment is composed of a composite in which silicon particles are dispersed in a matrix mainly composed of barium-containing glass material, and therefore has a structure with extremely few pores. Moreover, the cumulative pore volume of the barium-containing glass material, which is the negative electrode active material for lithium-ion secondary batteries, is Li ２ Si ２ O ５ It is understood that the cumulative pore volume is approximately one-third. For this reason, the barium-containing glass material, which is the negative electrode active material for lithium-ion secondary batteries, is considered to have a structure that makes it difficult for electrolytes and other components contained in lithium secondary batteries using this negative electrode active material to penetrate the pores. Thus, the negative electrode active material for lithium-ion secondary batteries according to this embodiment has a structure with extremely few pores. Furthermore, even when the negative electrode active material for lithium-ion secondary batteries according to this embodiment is used as the negative electrode material for a lithium secondary battery, the penetration of carbon components such as electrolytes and binders contained in the lithium secondary battery is suppressed. As a result, a lithium secondary battery using the negative electrode active material for lithium-ion secondary batteries according to this embodiment can achieve a high discharge capacity retention rate even after repeated charging and discharging.

[0030] In the negative electrode active material for lithium-ion secondary batteries according to this embodiment, a barium-containing glass material containing boron (B) can be preferably used. Covalent bonds are formed between B-Si-O atoms, forming a three-dimensional structure between these atoms, with a high proportion of covalent bonds and a branched structure. The three-dimensional structure referred to here is a structure in which elements other than lithium, which is a mobile ion, are covalently bonded in three dimensions.

[0031] Lithium ions can move arbitrarily within the Li-B-Si-O compound during charge-discharge reactions. By bonding with elements other than lithium to form a three-dimensional structure without the involvement of lithium, it is possible to maintain lithium ion conductivity while aiming for improved strength due to the three-dimensional structure of the barium-containing glass material.

[0032] The composite material used as the negative electrode active material for lithium-ion secondary batteries according to this embodiment preferably has a softening point of 500 to 560°C and a crystallization temperature of 600 to 650°C as its physical and thermal properties. In other words, the negative electrode active material for lithium-ion secondary batteries according to this embodiment is a composite material with extremely excellent sinterability. Because the negative electrode active material for lithium-ion secondary batteries has excellent sinterability, a robust three-dimensional structure and a structure with few pores can be realized in each step of the manufacturing method for the negative electrode active material for lithium-ion secondary batteries described later.

[0033] In this way, the electrical conductivity of silicon particles in a negative electrode containing the above-mentioned negative electrode active material can be ensured, using a composite material consisting of silicon particles constituting the negative electrode active material for lithium-ion secondary batteries and a barium-containing glass material used as the main phase of the matrix. Furthermore, the barium-containing glass material has high strength and low porosity, and even after charging and discharging the lithium-ion secondary battery equipped with the above-mentioned negative electrode, the structure in which the barium-containing glass material is present around the silicon particles, which are the active material, can be maintained. Therefore, the expansion and contraction of the silicon particles, which are the active material contained in the negative electrode active material for lithium-ion secondary batteries, is suppressed by the barium-containing glass material present around them. As a result, the disintegration of the silicon particles, which are the active material contained in the negative electrode active material for lithium-ion secondary batteries, is suppressed even after charging and discharging the lithium-ion secondary battery equipped with the above-mentioned negative electrode.

[0034] The average particle size of the silicon particles is preferably 5 to 100 nm. An average particle size of 5 nm or more is preferable because it stabilizes the microstructure of the negative electrode active material for lithium-ion secondary batteries. An average particle size of 100 nm or less is preferable because the miniaturization of the silicon particles suppresses the expansion of silicon particles due to volume changes during charging and discharging of a lithium-ion secondary battery equipped with a negative electrode electrode using the negative electrode active material for lithium-ion secondary batteries of this embodiment. The average particle size of the silicon particles can be calculated by performing an XRD measurement of the negative electrode active material for lithium-ion secondary batteries of this embodiment and using the Sherler formula from the full width at half maximum of the Si peak. Here, the Sherler formula is expressed as D = Kλ / Bcosθ, where D: crystal size (nm), K: Sherler constant, λ: X-ray wavelength (nm), B: full width at half maximum (rad), and θ: Bragg angle (rad).

[0035] The silicon particle content (Si particles) in the negative electrode active material for lithium-ion secondary batteries of this embodiment is preferably 40 to 90% by mass. A silicon particle content of 40% by mass or more is preferable because it ensures the electrical conductivity of the silicon particles in the negative electrode containing the negative electrode active material, which uses a matrix mainly composed of silicon particles and a sinterable barium-containing glass material, and enables charging and discharging of the lithium-ion secondary battery equipped with the negative electrode. On the other hand, a silicon particle content of 90% by mass or less is preferable because it improves the discharge capacity retention rate (cycle characteristics) of the lithium-ion secondary battery equipped with the negative electrode.

[0036] As described above, the negative electrode active material for the lithium-ion secondary battery according to this embodiment is mainly composed of a sinterable barium-containing glass material as the matrix of silicon particles, thereby suppressing the collapse of silicon particles and providing a lithium-ion secondary battery with excellent discharge capacity retention rate (cycle characteristics).

[0037] [Second Embodiment] Next, a method for manufacturing a negative electrode active material for a lithium-ion secondary battery according to the second embodiment will be described. Figure 3 is a flow chart showing each step of the method for manufacturing a negative electrode active material for a lithium-ion secondary battery according to this embodiment. As shown in Figure 3, the method for manufacturing a negative electrode active material for a lithium-ion secondary battery according to this embodiment is a method for manufacturing a negative electrode active material for a lithium-ion secondary battery in which silicon particles are dispersed in a matrix mainly composed of a barium-containing glass material having sinterability, and includes the following steps (I) to (III). Each step will be described below.

[0038] <Step (I): Step for manufacturing barium-containing glass material> The method for manufacturing a negative electrode active material for a lithium-ion secondary battery according to this embodiment includes Step (I): Step for manufacturing barium-containing glass material. The raw materials for the barium-containing glass material manufactured in Step (I) are, for example, barium carbonate, lithium oxide, and silicon dioxide. In addition, as shown in Figure 3, boron oxide may also be included in the raw materials, and furthermore, oxides of elements having chemical properties similar to boron may also be included in the raw materials. A predetermined amount of these glass material raw materials is weighed out. When boron oxide is also included in the raw materials as shown in Figure 3, the mixing ratio (mass ratio) of barium carbonate, boron oxide, lithium oxide, and silicon dioxide is not particularly limited, but as a preferred example, the mass ratio of barium carbonate:boron oxide:lithium carbonate:silicon dioxide is 2.0:2.5:2.5:0.8. In addition to lithium oxide used as a raw material in Step (I), lithium carbonate, lithium hydroxide, lithium oxide, and lithium sulfate can also be used. In process (I), in addition to boron oxide as a raw material, boron hydroxide, boron sulfate, etc., can also be used.

[0039] Next, a predetermined amount of lithium oxide, silicon dioxide, barium oxide, and more preferably boron oxide, which are the raw materials for barium-containing glass material, are mixed and pulverized. The mixing and pulverization of these raw materials is carried out for a predetermined time using a device such as a ball mill. After mixing and pulverization, the raw materials become a mixture of lithium oxide, silicon dioxide, barium oxide, and more preferably boron oxide having a predetermined particle size.

[0040] Furthermore, the raw materials obtained above are fired at a temperature of 600 to 1000°C under atmospheric pressure. A firing temperature of 600°C or higher and 1000°C or lower is preferable because it can firmly maintain the structure of the barium-containing glass material contained in the negative electrode active material for lithium-ion secondary batteries according to this embodiment.

[0041] <Step (II): Step for manufacturing a negative electrode active material precursor> The method for manufacturing a negative electrode active material for a lithium-ion secondary battery according to this embodiment includes a step of manufacturing a negative electrode active material precursor by mixing and pulverizing the barium-containing glass material and silicon particles manufactured in step (I). The negative electrode active material precursor manufactured in step (II) includes barium-containing glass material and silicon particles. In step (II), the barium-containing glass material and silicon particles are mixed and pulverized. Specifically, the barium-containing glass material and silicon particles are placed in a container such as a ball mill, and then the ball mill is rotated to mix and pulverize the barium-containing glass material and silicon particles.

[0042] Here, the mass ratio of barium-containing glass material to silicon particles is preferably 10 to 60% by mass of barium-containing glass material and 40 to 90% by mass of silicon particles. It is preferable that the mass ratio of barium-containing glass material is within the above range because it allows for a structure in which the barium-containing glass material is present around the silicon particles contained in the negative electrode active material for lithium-ion secondary batteries.

[0043] Furthermore, if the mass ratio of silicon particles is within the above range, it is preferable because it can maintain the cycle characteristics of the lithium-ion secondary battery. In step (II), a precursor of a negative electrode active material for a lithium-ion secondary battery is formed, consisting of a barium-containing glass material having excellent sinterability and silicon particles. In step (II), the silicon particles mixed with the barium-containing glass material play the role of an active substance for the negative electrode active material of the lithium-ion secondary battery.

[0044] In step (II), the particle size of the silicon particles in the mixture consisting of barium-containing glass material and silicon particles before mixing and grinding is preferably 0.2 to 100 μm. By setting the particle size of the silicon particles before mixing and grinding within the above range, the particle size of the silicon particles in the negative electrode active material precursor obtained by mixing and grinding the barium-containing glass material and silicon particles can be set to 5 to 100 nm.

[0045] <Step (III): Step of sintering the negative electrode active material precursor in an inert gas atmosphere> The method for producing a negative electrode active material for a lithium-ion secondary battery according to this embodiment includes, as step (III), a step of sintering the negative electrode active material precursor produced in step (II) in an inert gas atmosphere. By sintering the negative electrode active material precursor in an inert gas atmosphere, the negative electrode active material precursor becomes a negative electrode active material for a lithium-ion secondary battery. Furthermore, in step (III), in order to control the oxygen nonstoichiometry of the barium-containing glass material, which is the main phase of the matrix constituting the negative electrode active material for a lithium-ion secondary battery, sintering may be performed in an oxygen atmosphere before sintering in an inert gas atmosphere.

[0046] Furthermore, in step (III), in order to control the oxygen nonstoichiometry of the barium-containing glass material, which is the main phase of the matrix constituting the negative electrode active material for lithium-ion secondary batteries, sintering may be performed in the presence of a reducing agent before sintering in an inert gas atmosphere. In this way, by performing step (III) as a preceding step, sintering the negative electrode active material precursor in an inert gas atmosphere or in the presence of a reducing agent, oxygen vacancies and metal vacancies due to excess oxygen can be compensated for.

[0047] The sintering temperature of the negative electrode active material precursor is preferably 500 to 1000°C. A sintering temperature of 500°C or higher is preferable because heating the negative electrode active material precursor stabilizes the structure of the negative electrode active material for lithium-ion secondary batteries, while a temperature of 1000°C or lower is preferable because decomposition of the negative electrode active material precursor does not occur. The heat treatment time for the negative electrode active material precursor is preferably 0.5 to 40 hours, and particularly preferably 1 to 20 hours. A heat treatment time of 0.5 hours or more is preferable because the reaction of the precursor proceeds, while a time of 40 hours or less is preferable because the volatilization of Li can be suppressed.

[0048] Furthermore, the sintering of the negative electrode active material precursor is carried out in the presence of an inert gas such as nitrogen or argon. This is because the negative electrode active material precursor does not react with oxygen in the atmosphere, and the three-dimensional structure of the composite in which silicon particles are dispersed in a matrix mainly composed of a sinterable barium-containing glass material becomes strong, thereby obtaining a stable negative electrode active material for lithium-ion secondary batteries. The negative electrode active material for lithium-ion secondary batteries produced by going through step (III) included in the method for producing the negative electrode active material for lithium-ion secondary batteries according to this embodiment is cooled, then crushed to a predetermined particle size and classified, and used as a material for the negative electrode of a lithium-ion secondary battery.

[0049] The negative electrode active material for lithium-ion secondary batteries produced by the method for producing the negative electrode active material for lithium-ion secondary batteries of this embodiment, which is obtained by mixing a matrix mainly composed of barium-containing glass material with silicon particles, can firmly maintain its microstructure even after charging and discharging a lithium-ion secondary battery equipped with the negative electrode containing the negative electrode active material. In other words, the negative electrode active material for lithium-ion secondary batteries produced by the method for producing the negative electrode active material for lithium-ion secondary batteries of this embodiment has a technical feature in that, by containing a barium-containing glass material with excellent sinterability, it can firmly maintain the structure formed between barium (Ba), silicon (Si), oxygen (O), and more preferably boron (B), which form the basis of its microstructure, even after charging and discharging a lithium-ion secondary battery equipped with the negative electrode containing the negative electrode active material.

[0050] As described above, according to the method for manufacturing a negative electrode active material for lithium-ion secondary batteries of this embodiment, bonds of barium (Ba), silicon (Si), and oxygen (O), more preferably boron (B), are formed three-dimensionally. Furthermore, according to the method for manufacturing a negative electrode active material for lithium-ion secondary batteries of this embodiment, a composite negative electrode active material for lithium-ion secondary batteries can be manufactured in which silicon particles are dispersed in a matrix with a low pore size even after charging and discharging, using a barium-containing glass material having excellent sinterability as the main phase.

[0051] [Third Embodiment] A negative electrode for a lithium-ion secondary battery according to a third embodiment will be described. The negative electrode for a lithium-ion secondary battery according to this embodiment contains the negative electrode active material for a lithium-ion secondary battery of the above embodiment. The negative electrode containing the negative electrode active material for a lithium-ion secondary battery of this embodiment can be doped and dedoped with lithium ions at a lower potential than the positive electrode. Examples of the negative electrode for a lithium-ion secondary battery according to this embodiment include a negative electrode in which a negative electrode mixture containing the negative electrode active material for a lithium-ion secondary battery of the above embodiment is supported on a negative electrode current collector, and a negative electrode composed only of the negative electrode active material for a lithium-ion secondary battery of the above embodiment.

[0052] (Other negative electrode active materials) The negative electrode active material for lithium-ion secondary batteries included in the negative electrode electrode for lithium-ion secondary batteries of this embodiment may include other negative electrode active materials in the negative electrode active material for lithium-ion secondary batteries of the above embodiment, to the extent that it does not hinder the objectives of the present invention. Other negative electrode active materials may include carbon materials, oxides, sulfides, nitrides, metals, or alloys that can be doped and dedoped with lithium ions at a lower potential than that of the positive electrode.

[0053] Other carbon materials that can be used as negative electrode active materials include graphite such as natural graphite and artificial graphite, coke, carbon black, pyrolytic carbons, carbon fibers, and calcined organic polymer compounds. These carbon materials, oxides, sulfides, nitrides, etc. may be used individually or in combination of two or more. Furthermore, these carbon materials, oxides, sulfides, nitrides, etc. may be crystalline or amorphous.

[0054] Among the other negative electrode active materials mentioned above, carbon materials mainly composed of graphite, such as natural graphite and artificial graphite, are preferred for reasons such as the fact that the potential of the negative electrode hardly changes from the uncharged state to the fully charged state during charging (good potential flatness), a low average discharge potential, and a high capacity retention rate when repeatedly charged and discharged (good cycle characteristics). The shape of the carbon material may be any of the following: for example, flakes like natural graphite, spheres like mesocarbon microbeads, fibers like graphitized carbon fibers, or aggregates of fine powder.

[0055] Other negative electrode active materials may contain a binder as needed. Examples of binders include thermoplastic resins, specifically polyvinylidene fluoride, thermoplastic polyimide, carboxymethylcellulose, polyethylene, and polypropylene.

[0056] (Negative electrode current collector) The negative electrode current collector of the lithium-ion secondary battery negative electrode containing the negative electrode active material for lithium-ion secondary batteries according to this embodiment can be a strip-shaped member formed from a metallic material such as copper (Cu), nickel (Ni), or stainless steel. Among these, a thin film made of copper (Cu) is preferred because it is difficult to form alloys with lithium and is easy to process.

[0057] Methods for supporting the negative electrode compound on such a negative electrode current collector include pressure molding, and a method in which the compound is formed into a paste using a solvent, applied to the negative electrode current collector, dried, and then pressed to adhere it.

[0058] As described above, the negative electrode for lithium-ion secondary batteries according to this embodiment contains a negative electrode active material for lithium-ion secondary batteries, which is a composite in which silicon particles are dispersed in a matrix mainly composed of barium-containing glass material. For this reason, a secondary battery equipped with the negative electrode for lithium-ion secondary batteries of this embodiment has excellent charge / discharge capacity retention rate (cycle characteristics), and also has cycle characteristics that are particularly suitable for automotive lithium-ion secondary batteries.

[0059] [Fourth Embodiment] A lithium-ion secondary battery of the fourth embodiment will be described. Figure 4 is a model diagram showing the structure of a lithium-ion secondary battery equipped with a negative electrode for a lithium-ion secondary battery. As shown in Figure 4, the lithium-ion secondary battery of this embodiment is equipped with the negative electrode for a lithium-ion secondary battery of the above embodiment. As for the shape of the negative electrode for the lithium-ion secondary battery, for example, when the electrode is cut perpendicular to the winding axis, the cross-sectional shape can be a circle, an ellipse, a rectangle, or a columnar shape with rounded corners.

[0060] Furthermore, as a specific example of a lithium-ion secondary battery having such electrodes, the shape of the lithium secondary battery can be one that is specified in IEC 60086 or JIS C8500, which are standards for batteries established by the International Electrotechnical Commission (IEC). For example, preferred shapes for the negative electrode of the lithium-ion secondary battery include cylindrical and prismatic shapes. Moreover, the negative electrode of a lithium-ion secondary battery is not limited to the wound configuration described above, but may also be a laminated configuration in which a laminated structure of positive electrode, separator, negative electrode, and separator is repeatedly stacked. Examples of laminated lithium secondary batteries include so-called coin-type batteries, button-type batteries, paper-type (or sheet-type) batteries, and laminated cylindrical batteries.

[0061] The lithium-ion secondary battery of this embodiment includes, in addition to the negative electrode for the lithium-ion secondary battery of the above embodiment, a positive electrode mainly containing a positive electrode active material, an electrolyte, and a separator. Each component will be described below.

[0062] (Positive electrode) The positive electrode of the lithium-ion secondary battery of this embodiment can be manufactured by preparing a positive electrode mixture containing a positive electrode active material, a conductive material, and a binder, and supporting the positive electrode mixture on a positive electrode current collector.

[0063] (Positive electrode active material) As the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) can be used. Specifically, one or more composite oxides of lithium with metals such as cobalt, manganese, nickel, or combinations thereof can be used. Specific examples of positive electrode active materials include lithium cobaltate, lithium nickelate, and lithium manganeseate.

[0064] (Conductive Material) As the conductive material included in the positive electrode of the lithium-ion secondary battery of this embodiment, a carbon material can be used. Examples of carbon materials include graphite powder, carbon black (e.g., acetylene black), and fibrous carbon material. Because carbon black is fine and has a large surface area, adding a small amount to the positive electrode mixture can increase the conductivity inside the positive electrode, thereby improving the charge / discharge efficiency and output characteristics. On the other hand, if too much carbon black is added, the binding force between the positive electrode mixture and the positive electrode current collector by the binder, as well as the binding force inside the positive electrode mixture, will decrease, which can actually increase the internal resistance.

[0065] The proportion of conductive material in the positive electrode mixture is preferably 2 to 20 parts by mass per 100 parts by mass of positive electrode active material. When using fibrous carbon materials such as graphitized carbon fibers or carbon nanotubes as the conductive material, this proportion can be reduced.

[0066] (Binder) A thermoplastic resin can be used as the binder for the positive electrode. Examples of such thermoplastic resins include polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer, hexafluoropropylene / vinylidene fluoride copolymer, tetrafluoroethylene / perfluorovinyl ether copolymer, and other fluororesins, as well as polyolefin resins such as polyethylene and polypropylene. Two or more of these thermoplastic resins may be used in combination.

[0067] (Positive electrode current collector) As the positive electrode current collector of this embodiment, a strip-shaped member made of a metal material such as aluminum (Al), nickel (Ni), or stainless steel can be used. Among these, a thin film made of aluminum (Al) is preferred because it is easy to process and inexpensive.

[0068] One method for supporting the positive electrode mixture on a positive electrode current collector is to press-molde the positive electrode mixture onto the positive electrode current collector. Alternatively, the positive electrode mixture may be made into a paste using an organic solvent, and the resulting paste may be applied to at least one side of the positive electrode current collector, dried, and then pressed to fix it in place.

[0069] When forming a paste from the positive electrode mixture, suitable organic solvents include amine solvents such as N,N-dimethylaminopropylamine and diethylenetriamine, ether solvents such as tetrahydrofuran, ketone solvents such as methyl ethyl ketone, ester solvents such as methyl acetate, and amide solvents such as dimethylacetamide and N-methyl-2-pyrrolidone.

[0070] Methods for applying the positive electrode mixture paste to the positive electrode current collector include, for example, slit die coating, screen coating, curtain coating, knife coating, gravure coating, and electrostatic spraying.

[0071] (Separator) As the separator in the lithium-ion secondary battery of this embodiment, for example, a material having the form of a porous membrane, nonwoven fabric, woven fabric, etc., made of materials such as polyethylene, polyolefin resin such as polypropylene, fluororesin, nitrogen-containing aromatic polymer, etc. may be used. Furthermore, two or more of these materials may be used to form the separator, or these materials may be laminated to form the separator.

[0072] In the lithium-ion secondary battery of this embodiment, the separator is preferably configured such that, in order to allow good permeability of the electrolyte during battery use (charging and discharging), the air permeability resistance determined by the Gurley method as defined in JIS P8117 is 50 seconds / 100cc or more and 300 seconds / 100cc or less, and more preferably 50 seconds / 100cc or more and 200 seconds / 100cc or less.

[0073] (Electrolyte) The electrolyte of the lithium-ion secondary battery of this embodiment may contain an electrolyte and an organic solvent. The electrolyte included in the electrolyte is LiClO ４ LiPF ６ LiAsF６ LiSbF ６ LiBF ４ LiCF ３ SO ３ , LiN (SO ２ CF ３ ) ２ , LiN (SO ２ C ２ F ５ ) ２ , LiN (SO ２ CF ３ ) (COCF ３ ), Li(C ４ F ９ SO ３ ), LiC (SO ２ CF ３ ) ３ Li ２ B １０ Cl １０ LiBOB (where BOB represents bis(oxalato)borate), LiFSI (where FSI represents bis(fluorosulfonyl)imide), lithium salts of lower aliphatic carboxylates, LiAlCl ４ Examples of lithium salts include those listed above. Alternatively, a mixture of two or more electrolytes selected from these electrolytes may be used. Examples of electrolytes include LiPFA containing fluorine. ６ LiAsF ６ LiSbF ６ LiBF ４ LiCF ３ SO ３ , LiN (SO ２ CF ３ ) ２ and LiC (SO ２ CF ３ ) ３ It is preferable to use one that includes at least one selected from the group consisting of the following.

[0074] (Organic solvents) As organic solvents, carbonates, ethers, nitriles, carbamates, and sulfur-containing compounds can be used. Examples of carbonates include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di(methoxycarbonyloxy)ethane. Examples of ethers include 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyldifluoromethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of esters include methyl formate, methyl acetate, and γ-butyrolactone. Examples of nitriles include acetonitrile and butyronitrile. Examples of amides include N,N-dimethylformamide and N,N-dimethylacetamide. Examples of carbamates include 3-methyl-2-oxazolidone. Examples of sulfur-containing compounds include sulfolanes, dimethyl sulfoxides, and 1,3-propanesalton.

[0075] It is preferable to use a mixture of two or more of these as the organic solvent. Among these, a mixed solvent containing carbonates is preferred, and a mixed solvent of cyclic carbonates and acyclic carbonates and a mixed solvent of cyclic carbonates and ethers are even more preferred.

[0076] A solid electrolyte may be used instead of an electrolyte solution. As a solid electrolyte, for example, an organic polymer electrolyte such as a polyethylene oxide-based polymer compound, a polymer compound containing at least one of polyorganosiloxane chains, or a polyoxyalkylene chain can be used. Alternatively, a so-called gel type, in which a non-aqueous electrolyte is held within a polymer compound, can also be used. Furthermore, Li ２ S-SiS ２ Li ２ S-GeS ２ Li ２ S-P ２ S５ , Li ２ S-B ２ S ３ , Li ２ S-SiS ２ -Li ３ PO ４ , Li ２ S-SiS ２ -Li ２ SO ４ , Li ２ S-GeS ２ -P ２ S ５ Examples of the inorganic solid electrolyte include sulfides such as these, and mixtures of two or more of these may also be used.

[0077] Also, in the lithium-ion secondary battery of this embodiment, when a solid electrolyte is used, the solid electrolyte may serve as a separator, and in that case, a separator may not be required.

[0078] The lithium-ion secondary battery of this embodiment is a secondary battery and can be repeatedly charged and discharged. Therefore, the lithium-ion secondary battery of this embodiment is suitable, for example, as a vehicle-mounted battery. In particular, the lithium-ion secondary battery of this embodiment can be suitably used as a battery to be mounted on an EV vehicle (electric vehicle) that drives a motor using the electricity of the battery. EV vehicles (electric vehicles) include BEV vehicles (battery electric vehicles) and HV vehicles (hybrid vehicles) that use only the electricity of the battery. When applying the lithium-ion secondary battery of this embodiment to an HV vehicle (hybrid vehicle), it is not limited to only the use as a hybrid vehicle battery in a form that supplies power to a motor for driving an automobile, and it may be applied in a form that supplies power to a starter motor for restarting an engine in an automobile having an idling stop function. Note that the secondary battery includes the primary battery-like use of the secondary battery (use for the purpose of only one discharge after charging).

[0079] As described above, the lithium-ion secondary battery according to the present embodiment includes a negative electrode containing a negative electrode active material for a lithium-ion secondary battery, which is a composite in which silicon particles are dispersed in a matrix mainly composed of a barium-containing glass material. Therefore, it has excellent charge-discharge capacity retention rate (cycle characteristics), and particularly has cycle characteristics suitable for a lithium-ion secondary battery for vehicle-mounted use.

[0080] [Other Embodiments] Although the invention of the present application has been described with reference to the embodiments, the invention of the present application is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the invention of the present application within the technical scope of the invention of the present application.

[0081] (Example 1) A barium-containing glass material was prepared as a matrix for dispersing silicon particles. This barium-containing glass material was weighed so as to be 38% by mass and silicon particles 62% by mass. Using the barium-containing glass material, a negative electrode active material for a lithium-ion secondary battery was produced. The barium-containing glass material was, in mass%, Li ２ O = 12.5%, SiO ２ = 12.2%, CaO = 18.8%, B2O ３ = 35.9%, BaO = 20.6%. Then, a negative electrode was produced using this negative electrode active material for a lithium-ion secondary battery. Furthermore, a laminated cylindrical secondary battery, which is a lithium-ion secondary battery provided with this negative electrode, was produced. And the evaluation (discharge capacity retention rate (cycle characteristics)) of the produced laminated cylindrical secondary battery was carried out. Specifically, a negative electrode active material, a negative electrode, and a laminated cylindrical secondary battery were produced as follows, and the laminated cylindrical secondary battery was evaluated.

[0082] <Production of Negative Electrode Active Material> The matrix material of the negative electrode active material for a lithium-ion secondary battery was put into a container rotation and rocking type powder mixer (rocking mixer; "RM10-3" manufactured by Aichi Electric Co., Ltd.), the rotation speed was set to 2 rpm, and dry mixing was carried out for 15.0 hours. Then, a matrix mainly composed of a barium-containing glass material was obtained by firing at 600 to 1000 °C in an atmospheric pressure atmosphere.

[0083] For the dry mixing process, chromium steel balls (diameter φ: 20 mm) were used as the media and fed into a planetary ball mill (Classic Line P-5, manufactured by Fritsch GmbH, Germany). The mixture was ground at a rotation speed of 200 rpm for 15.0 hours. For the silicon particles (Si), silicon particles with an average particle size of 10 μm were used. Chromium steel balls (diameter Φ20 mm) were used as the media for grinding. After the completion of the dry mixing process, the resulting mixed powder (sample) was formed into a circular shape and heat-treated at 500-1000°C to obtain a sintered body. The obtained sintered body was further ground in a tungsten mortar and pestle, and the sample that fell through a 75 μm sieve was collected. The collected sample and pitch were mixed and heat-treated under a nitrogen atmosphere. After the heat treatment, the sample that fell through the sieve was collected again by passing it through a 75 μm sieve.

[0084] A slurry for negative electrodes (for coin batteries) was manufactured using the obtained negative electrode active material. The slurry for negative electrodes consists of slurry raw materials for negative electrodes (negative electrode active material, graphite), binder CMC, and binder SBR. The slurry for negative electrodes contains 97.0% by mass of slurry raw material powder (composed of 85% by mass of graphite negative electrode and 15% by mass of Si negative electrode sample), and the slurry raw material powder and binder CMC powder are weighed so that the mass ratio of the slurry raw material powder and binder CMC is 1.5% by mass. Here, the slurry raw material for negative electrodes consists of 15% by mass of negative electrode active material and 85% by mass of graphite. The weighed powder of the slurry raw material for the negative electrode and the powder of the binder CMC were mixed with deionized water, and then kneaded using a rotary-orbit mixer (product name "Awatori Rentaro ARE-310" manufactured by THINKY Co., Ltd.) with the rotation speed set to 2000 rpm and the stirring time set to 1.0 hour.

[0085] After mixing, the slurry for the negative electrode was prepared by adding deionized water dropwise to a liquid containing the powder raw material for the negative electrode, the powder of binder CMC, and deionized water to adjust the viscosity. Then, binder SBR was added at a mass ratio of 1.5 mass% so that the amount of SBR in the negative electrode slurry reached a predetermined mass ratio. The mixture was then mixed again by stirring with the rotation speed set to 1000 rpm and the stirring time set to 1.0 hour to obtain a slurry for the negative electrode (slurry for coating the negative electrode). This slurry for the negative electrode was coated onto copper (Cu) foil, dried at a drying temperature of 60°C, and rolled using a roll mill to produce the negative electrode.

[0086] <Manufacturing of Laminated Cylindrical Secondary Battery> As an example of a lithium-ion secondary battery shown in Figure 4, a laminated cylindrical secondary battery 100 was manufactured as follows. The laminated cylindrical secondary battery 100 comprises a coated negative electrode 101 containing a slurry for the negative electrode (slurry for coating the negative electrode), a separator 102 laminated on the upper surface of the coated negative electrode 101, and a coated positive electrode 103 laminated on the upper surface of the separator 102. The coated positive electrode 103 contains nickel (Ni), cobalt (Co), and manganese (Mn) as constituent elements. The molar ratio of these components is nickel (Ni):cobalt (Co):manganese (Mn) is 5:2:3. Therefore, the coated positive electrode 103 can be represented as NCM523. The coated negative electrode 101 has a negative electrode terminal 111 at its end. Separator 102 has a separator terminal 121 on the same end as the positive electrode terminal 111. Coated positive electrode 103 has a positive electrode terminal 131 on the end opposite to the positive electrode terminal 111. A laminated cylindrical secondary battery 100 was manufactured by laminating and fixing the coated negative electrode 101, separator 102, coated positive electrode 103, and separator 102 in this order. Specifically, the coated negative electrode 101, which is the negative electrode, was cut to a width of 3.5 cm x length of 18.0 cm, and the laminate, which is the positive electrode, coated positive electrode 103 and separator 102 wound around it, was vacuum dried at a drying temperature of 90°C for a drying time of 15.0 h. The vacuum-dried laminate was placed in a glove box, and in the glove box, LiPF4 with a concentration of 1.0 mol / L was used. ６ Electrolyte (electrolyte LiPF ６A laminated cylindrical secondary battery was assembled using an electrolyte solution (ethylene carbonate (EC) 3: diethyl carbonate (DEC) 7).

[0087] Specifically, a laminated cylindrical secondary battery was fabricated using a coated negative electrode (3.5 cm wide x 18.0 cm long), a coated positive electrode (lithium nickel cobalt manganese ternary material for lithium-ion batteries: "NCM523"), a separator (wet-processed PE), a Ni-plated Cu tab (for the negative electrode), and an Al tab (for the positive electrode). The fabricated laminate was wrapped in aluminum laminate film, sealed leaving an electrolyte inlet, and vacuum-dried at 90°C for 15 hours before being placed in a glove box. Inside the glove box, the electrolyte was ethylene carbonate (EC):diethyl carbonate (DEC) = 3:7LiPF ６ -1.0 mol / L was injected into the cell, and the laminate film was sealed.

[0088] <Evaluation of Laminated Cylindrical Secondary Batteries> The manufactured laminated cylindrical secondary batteries were set in a charge / discharge device and charged / discharge tests were performed using CCCV charging - CC discharging, at 2.5 to 4.2 V, and a rate of 0.5 C to 1.0 C (50 mA to 100 mA). The performance of the negative electrode active material was evaluated by assessing the discharge capacity retention rate (cycle characteristics) of the laminated cylindrical secondary batteries.

[0089] Specifically, a laminated cylindrical secondary battery was placed in a charge / discharge device and charged for 6 hours under the conditions of CC charging, 4.2V, and a rate of 0.1C (10mA). After that, the secondary battery was removed from the charge / discharge device and left in a 45°C constant temperature bath for 24 hours (aging process). Subsequently, the film edges of the aged cells were cut in a glove box to expel the gas generated during the aging process, and the film was resealed. The laminated cylindrical secondary battery was then placed in a charge / discharge device and a charge / discharge cycle test was performed under the conditions of CCCV charging (0.5C, 50mA) - CC discharge (1.0C → 0.2C, 100mA → 20mA) and 4.2-2.5V.

[0090] The porosity [%] of the negative electrode active material produced in Example 1 was calculated. The results are shown in Table 1. The porosity [%] of the negative electrode active material was measured according to the Archimedes method.

[0091] (Comparative Example 1) Lithium carbonate (Li) is used as a raw material to be included in the negative electrode active material. ２ CO ３ ), silicon dioxide (SiO ２ ) to Li ２ Si2O ５ A negative electrode active material for a lithium-ion secondary battery was manufactured in the same manner as in Example 1, except that a matrix was prepared for dispersing silicon particles by weighing the materials to achieve a composition of (mol% Li = 33.3%, Si = 66.7%). Furthermore, in Comparative Example 1, a negative electrode was manufactured using the manufactured negative electrode active material. Then, a lithium-ion secondary battery equipped with this negative electrode was manufactured in the same manner as in Example 1, and the lithium-ion secondary battery was evaluated. The porosity [%] of the negative electrode active material manufactured in Comparative Example 1 was calculated. The results are shown in Table 1.

[0092] (Comparative Example 2) Lithium carbonate (Li) is used as a raw material in the negative electrode active material. ２ CO ３ ), silicon dioxide (SiO ２ ), calcium carbonate (CaCO3) ３ ), boron oxide (B ２ O ３ ), calcium-containing Li ２ SiO ５ Using this method, Li is expressed in mass percent. ２ O=17.5%, SiO ２ =70.3%, CaO=5.5%, B ２ O ２ A negative electrode active material for a lithium-ion secondary battery was manufactured in the same manner as in Example 1, except that a matrix for dispersing silicon particles was prepared by weighing the material to achieve a composition of 6.8%. Furthermore, in Comparative Example 2, a negative electrode was manufactured using the manufactured negative electrode active material. Then, a lithium-ion secondary battery equipped with this negative electrode was manufactured in the same manner as in Example 1, and the lithium-ion secondary battery was evaluated. The porosity [%] of the negative electrode active material manufactured in Comparative Example 2 was calculated. The results are shown in Table 1.

[0093]

[0094] Furthermore, negative electrode electrodes containing the negative electrode active materials produced in Example 1 and Comparative Examples 1-2 were manufactured, and the discharge capacity retention rate (cycle characteristics) of a laminated cylindrical secondary battery, which is a lithium-ion secondary battery equipped with this negative electrode, was evaluated in the same manner as in Example 1. Figure 5 shows the measurement results of the discharge capacity retention rate (cycle characteristics) against the number of discharge cycles for laminated cylindrical secondary batteries equipped with negative electrode materials containing the negative electrode active materials produced in Example 1 and Comparative Examples 1-2.

[0095] (Evaluation Results) The discharge capacity retention rate (cycle characteristics) of the secondary battery equipped with a negative electrode containing the negative electrode active material manufactured in Example 1 is compared with the discharge capacity retention rate (cycle characteristics) of the secondary batteries equipped with a negative electrode containing the negative electrode active material manufactured in Comparative Examples 1 and 2. As is clear from Figure 5, the discharge capacity retention rate (500 cycles) of the secondary battery equipped with a negative electrode containing the negative electrode active material manufactured in Example 1 is approximately 78%, while the discharge capacity retention rate of Comparative Examples 1 and 2 at the same number of cycles is approximately 65%, showing a significant difference.

[0096] Furthermore, as is clear from Figure 5, the discharge capacity retention rate in the examples consistently exceeds that of the comparative examples, and this difference becomes more pronounced with increasing charge-discharge cycle counts. From these evaluation results, it is clear that the secondary battery equipped with a negative electrode containing the negative electrode active material of the present invention exhibits a good discharge capacity retention rate (cycle characteristics).

[0097] Furthermore, the discharge capacity retention rate (cycle characteristics) after 500 cycles of a secondary battery equipped with a negative electrode containing the negative electrode active material manufactured in Example 1 was compared with the discharge capacity retention rate (cycle characteristics) after 500 cycles of secondary batteries equipped with negative electrode containing the negative electrode active material manufactured in Comparative Examples 1 and 2. The evaluation results are shown in Table 2.

[0098] The comparison between the discharge capacity retention rate after 500 cycles of the secondary battery equipped with a negative electrode containing the negative electrode active material manufactured in Example 1 and the discharge capacity retention rate after 500 cycles of the secondary batteries equipped with a negative electrode containing the negative electrode active material manufactured in Comparative Examples 1 and 2 was evaluated by expressing the discharge capacity retention rate after 500 cycles of Example 1 and Comparative Example 2 relatively, with the discharge capacity retention rate after 500 cycles in Comparative Example 1 set to 100.

[0099]

[0100] Figure 6 is an SEM image of the surface of the negative electrode (a composite containing silicon particles and glass material) of a secondary battery equipped with a negative electrode containing the negative electrode active material manufactured in Example 1, after 500 cycles. As shown in Figure 7, the negative electrode active material manufactured in Example 1 exhibits an extremely small degradation range from the surface of the Si particles contained in the negative electrode material.

[0101] The reason for this is that the negative electrode active material produced in Example 1 is made from a barium-containing glass material with an extremely low porosity. Another reason is that the barium-containing glass material constituting the negative electrode active material produced in Example 1 has little chemical interaction with the binder, electrolyte, etc., which are C components contained in lithium-ion secondary batteries. Therefore, it is possible to suppress the intrusion of the electrolyte, etc., contained in lithium-ion secondary batteries through the pores of the negative electrode active material.

[0102] As a result, the breakdown of silicon particles constituting the negative electrode active material manufactured in Example 1 can be effectively suppressed. Furthermore, a secondary battery equipped with a negative electrode containing the negative electrode active material manufactured in Example 1 can maintain a good discharge capacity retention rate even after repeated charging and discharging.

[0103] Figure 7 shows the negative electrode (silicon particles and Li) of a secondary battery equipped with a negative electrode containing the negative electrode active material manufactured in Comparative Example 1 after 500 cycles. ２ Si ２ O ５This is an SEM image of the surface of a composite material containing the above. As shown in Figure 7, the negative electrode active material produced in Comparative Example 1 has an extremely large degradation range from the surface of the Si particles contained in the negative electrode material.

[0104] The reason is that the negative electrode active material produced in Comparative Example 1 has a large porosity of Li ２ Si ２ O ５ This is because it is formed from [unclear material]. Therefore, it is not possible to prevent the electrolyte contained in the lithium-ion secondary battery from entering through the pores of the negative electrode active material. As a result, it is not possible to effectively suppress the collapse of the silicon particles constituting the negative electrode active material manufactured in Comparative Example 1. Furthermore, a secondary battery equipped with a negative electrode containing the negative electrode active material manufactured in Comparative Example 1 cannot maintain a good discharge capacity retention rate even after repeated charging and discharging.

[0105] Thus, the fundamental effect expected from the barium-containing glass material having excellent sinterability and appropriate pore distribution contained in the negative electrode active material for lithium-ion secondary batteries according to the present invention is the improvement of the discharge capacity maintenance rate (cycle characteristics) of a secondary battery equipped with a negative electrode containing the said negative electrode active material for lithium-ion secondary batteries, by suppressing the collapse of silicon particles (Si particles). In other words, the fundamental effect of the negative electrode active material for lithium-ion secondary batteries according to the present invention is considered to be the same whether the electrolyte of the lithium-ion secondary battery is a non-aqueous electrolyte or a solid electrolyte.

[0106] When the electrolyte of a lithium-ion secondary battery is a liquid electrolyte (non-aqueous electrolyte), the expansion and contraction of silicon particles (Si particles) are suppressed by the effect of the barium-containing glass material with excellent sinterability contained in the negative electrode active material for lithium-ion secondary batteries. As a result, the collapse of silicon particles (Si particles) contained in the negative electrode active material for lithium-ion secondary batteries, that is, the detachment of silicon particles (Si particles) from the negative electrode of the secondary battery, and the deactivation of silicon particles (Si particles) due to reaction of the electrolyte with silicon particles (Si particles) can be prevented. Thus, when a negative electrode electrode containing the negative electrode active material for lithium-ion secondary batteries according to the present invention is provided and the electrolyte is a liquid electrolyte (non-aqueous electrolyte), the life characteristics of the secondary battery are improved.

[0107] On the other hand, when the electrolyte of a lithium-ion secondary battery is a solid electrolyte, the expansion and contraction of silicon particles (Si particles) are suppressed by the effect of the barium-containing glass material with excellent sinterability contained in the negative electrode active material for lithium-ion secondary batteries. As a result, it becomes easier to maintain a state of close contact between the negative electrode active material for lithium-ion secondary batteries, which is a composite in which silicon particles are dispersed in a matrix mainly containing barium-containing glass material with excellent sinterability, and the solid electrolyte, thereby improving the lifespan characteristics of the lithium-ion secondary battery.

[0108] Furthermore, by adopting a solid electrolyte as the electrolyte for lithium-ion secondary batteries, it becomes possible to create entirely solid-state lithium-ion secondary batteries. As a result, the safety and reliability of lithium-ion secondary batteries will be dramatically improved, and higher energy density and output will be possible.

[0109] The lithium-ion secondary battery anode active material of the present invention exhibits excellent discharge capacity, cycle life characteristics, and high-rate discharge characteristics. Therefore, it is suitable not only as an anode material for alkaline storage batteries used in hybrid vehicles and idle-stop vehicles, but can also be suitably used in alkaline storage batteries for electric vehicles, making it industrially useful in industries such as the electrical industry and the automotive industry.

[0110] 100 Laminated cylindrical secondary battery 101 Coated negative electrode 111 Negative electrode terminal 102 Separator 121 Separator terminal 103 Coated positive electrode 131 Positive electrode terminal

Claims

1. A negative electrode active material for a lithium-ion secondary battery, wherein silicon particles are dispersed in a lithium silicate phase, and the lithium silicate phase is a composite mainly composed of a barium-containing glass material.

2. The negative electrode active material for lithium-ion secondary batteries according to claim 1, characterized in that the composite has a softening point of 500 to 560°C and a crystallization temperature of 600 to 650°C.

3. The negative electrode active material for lithium-ion secondary batteries according to claim 1, characterized in that the content of silicon particles contained in the negative electrode active material for lithium-ion secondary batteries is 40 to 90% by mass.

4. The negative electrode active material for lithium-ion secondary batteries according to claim 1, characterized in that the average particle diameter of the silicon particles is 5 to 100 nm.

5. The negative electrode active material for lithium-ion secondary batteries according to claim 1, characterized in that the barium-containing glass material contains boron.

6. A method for producing a negative electrode active material for a lithium-ion secondary battery, comprising: step (I); a step of producing a barium-containing glass material by mixing and pulverizing lithium carbonate, barium carbonate, and silicon dioxide, and then firing it at a temperature of 600 to 1000°C under atmospheric pressure; step (II); a step of producing a negative electrode active material precursor by mixing and pulverizing the barium-containing glass material produced in step (I) with silicon particles; and step (III); a step of sintering the negative electrode active material precursor produced in step (II) under an inert gas atmosphere.

7. A negative electrode for a lithium-ion secondary battery, characterized by comprising the negative electrode active material for a lithium-ion secondary battery described in any one of claims 1 to 5.

Images