JP2018073650A - Lithium occlusion/release material, electrode, lithium ion secondary battery, and method for producing lithium occlusion/release material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium occlusion/release material which can be applied as an electrode material of a lithium ion secondary battery which stably has excellent charge and discharge characteristics without requiring high-speed cooling in a manufacturing process.SOLUTION: The lithium occlusion/release material has a composition containing Si and Ni, and includes a Si phase and NiSiphase. An average diameter of crystals calculated from a peak of Si in an X-ray diffraction spectrum of the lithium occlusion/release material by the Scherrer equation is 100 nm or less.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a lithium storage / release material, an electrode, a lithium ion secondary battery, and a method for producing a lithium storage / release material.

  In recent years, with the rapid development of electronic devices and communication devices and the development of miniaturization technology, various portable devices have become widespread. As a power source for these portable devices, development of a secondary battery having high capacity and excellent life characteristics is strongly demanded from the viewpoints of economy, miniaturization and weight reduction of the device.

  As such a small, lightweight, high-capacity secondary battery, a lithium intercalation compound that releases lithium ions from the interlayer is used as a cathode material, and lithium ions are occluded and released during charging / discharging between layers between crystal planes ( The development of rocking chair type lithium ion batteries using a carbonaceous material typified by graphite or the like that can be intercalated as a negative electrode material has been developed and put into practical use.

  Non-aqueous electrolyte secondary batteries that use lithium compounds as negative electrodes have high voltage and high energy density. Among them, lithium metal is the subject of many researches as an active material for negative electrode due to its abundant battery capacity. Became. However, when lithium metal is used as the negative electrode, a lot of dendritic lithium is deposited on the surface of the negative electrode lithium during charging, so that the charge / discharge efficiency is reduced, or the dendritic lithium grows, causing a short circuit with the positive electrode. However, because of the instability of lithium itself, that is, high reactivity, it is sensitive to heat and impact, so there are still problems in commercialization.

  Therefore, a carbon-based negative electrode that occludes and releases lithium has been used as a negative electrode active material instead of lithium metal. The carbon-based negative electrode has greatly contributed to the widespread use of lithium ion batteries by solving various problems of lithium metal. However, as various portable devices are gradually reduced in size, weight and performance, increasing the capacity of lithium ion secondary batteries has emerged as an important issue.

A lithium ion secondary battery using a carbon-based negative electrode has a substantially low battery capacity due to the porous structure of carbon. For example, even in the case of graphite having the highest crystallinity as the carbon used, the theoretical capacity is about 372 mAh / g when the composition is LiC ₆ . This is only about 10% compared to the theoretical capacity of lithium metal being 3860 mAh / g. Therefore, in spite of the existing problems of the metal negative electrode, research has been actively conducted to improve the battery capacity by introducing a metal such as lithium again into the negative electrode.

In recent years, Si has attracted the most attention as a material that can replace carbon-based materials. The reason is that Si forms a compound represented by Li ₂₂ Si ₅ and can occlude a large amount of lithium, so that the capacity of the negative electrode can be increased as compared with the case where a carbon-based material is used. This is because it has the potential to increase the storage capacity of secondary batteries, capacitors and solid state batteries.

  However, when Si is used alone as a negative electrode material, the Si phase is pulverized by repetition of expansion when alloying with lithium during charging and contraction when dealloying with lithium during discharging. There is a problem that the life of the electricity storage device is extremely short because troubles such as the Si phase dropping off from the electrode substrate during use or the electrical conductivity between the Si phases being lost can occur.

  Furthermore, Si has a lower electrical conductivity than carbon-based materials and metal-based materials, and the efficient movement of electrons associated with charge / discharge is limited. Therefore, the negative electrode material supplements conductivity such as carbon-based materials. Although it is used in combination with the material, even in that case, there was a problem in the initial charge / discharge characteristics and the highly efficient charge / discharge characteristics.

  As a method for solving such a defect when using the Si phase as a negative electrode, a material in which at least a part of the Si phase is wrapped with a metal compound typified by Si and a transition metal and a manufacturing method thereof are disclosed in, for example, a patent. It is proposed in Document 1.

JP 2001-297757 A

Nagasaki Seizo and Hirabayashi Shinko, “Binary Alloy Phase Diagrams”, 2nd edition, Agne Technology Center, Inc., May 30, 2013, p234

  Patent Document 1 discloses that a melt of a master alloy having a composition in which a phase that is not a phase capable of occluding and releasing lithium (lithium occluding / releasing phase) is precipitated as a primary crystal is 100 ° C./second or more. It is described that a material having a high charge / discharge capacity and a high capacity retention rate can be obtained by performing the process of cooling at 1. It is not easy to increase productivity with materials that require such rapid cooling in the manufacturing process.

  An object of the present invention is to provide a lithium occlusion / release material that can be applied as an electrode material of a lithium ion secondary battery that stably has excellent charge / discharge characteristics without requiring such high-speed cooling. To do. Another object of the present invention is to provide a method for producing such a lithium storage / release material. Another object of the present invention is to provide an electrode including the above lithium storage / release material and a lithium ion secondary battery including the electrode as a negative electrode.

The present invention provided to solve the above problems is as follows.
(1) A lithium occlusion / release material having a composition containing Si and Ni and comprising an Si phase and an NiSi ₂ phase, wherein the Scherrer formula (from the Si peak in the X-ray diffraction spectrum of the lithium occlusion / release material) The average diameter of the crystal calculated by the formula (i) described later (the arithmetic average value of the crystal size calculated from five peaks described later, which corresponds to the size of the Si phase) is 100 nm or less. Lithium storage / release material.

(2) The lithium storage / release material according to (1) above, wherein an atomic ratio of Si to Ni (Si / Ni ratio) is 2.2 or more and 4.2 or less.

(3) The lithium storage / release material has a composition further containing Fe, and the atomic ratio of Fe to Ni (Fe / Ni ratio) is 0.08 or less, according to (1) or (2) above Lithium storage / release material.

(4) The lithium storage / release material according to any one of (1) to (3), further including a NiSi phase.

(5) An electrode comprising the lithium storage / release material according to any one of (1) to (4).

(6) A lithium ion secondary battery comprising the electrode described in (5) as a negative electrode.

(7) A raw material containing a silicon source and a nickel source made of metallic silicon is heated to obtain a molten material containing Si and Ni and having a composition in which the atomic ratio of Si to Ni is 2.08 or more. A method for producing a lithium occlusion / release material, wherein the material is cooled to 50 ° C. or less with a cooling time of 3 hours or more to obtain a lithium occlusion / release material.

(8) A raw material containing a nickel source, a silicon source and a carbon source is heated and reacted at 1,100 to 1,650 ° C. in an inert gas atmosphere for 0.5 to 30 hours. And obtaining a lithium occlusion / release material by cooling the melted substance to 50 ° C. or less with a cooling time of 3 hours or more. A method for producing a lithium storage / release material.

(9) The above (7) or (8), wherein the nickel source contains one or more selected from the group consisting of new nickel, used sponge nickel catalyst, and electric furnace residual nickel silicon alloy semi-finished product A method for producing a lithium storage / release material according to claim 1. (In the present invention, refined nickel is referred to as “new nickel”.)

(10) The lithium as described in (9) above, wherein the new nickel has a purity of 99.5% by weight or more, and the contents of S, P, As and halogen elements are all inevitable impurity levels. A method for producing a release material.

(11) The spent sponge nickel catalyst has a purity of 50 to 70% by weight, a Si content of 30 to 50% by weight, and a Fe content of 4% by weight or less (9) Or the manufacturing method of the lithium occlusion release material as described in (10).

(12) The method for producing a lithium storage / release material according to any one of (8) to (11), wherein the silicon source includes one or more selected from the group consisting of silica and metal silicon.

(13) The silica has a purity of 99.0% by weight or more, a calcium oxide content of 0.1% by weight or less, an aluminum oxide content of 0.2% by weight or less, and a magnesium oxide content The method for producing a lithium storage / release material according to (12), wherein the amount is 0.1% by weight or less.

(14) The metal silicon has a purity of 99.0% by weight or more, an Fe content of 0.5% by weight or less, an Al content of 0.1% by weight or less, and a Ca content of The method for producing a lithium storage / release material according to (12) or (13), wherein the content is 0.3% by weight or less.

(15) The method for producing a lithium storage / release material according to any one of (8) to (14), wherein the carbon source includes one or more selected from the group consisting of charcoal and oga charcoal.

(16) The method for producing a lithium storage / release material according to any one of (8) to (15), wherein the carbon source has an inevitable impurity level in any of S, P, As, and halogen contents.

(17) The method for producing a lithium storage / release material according to any one of (7) to (16), wherein heating is performed in a state where the raw material is mixed in advance.

(18) The method for producing a lithium storage / release material according to any one of (7) to (17), wherein an average cooling rate of the molten material is 0.5 ° C./second or less.

  According to the present invention, there is provided a lithium occlusion / release material that can be applied as an electrode material of a lithium ion secondary battery having excellent charge / discharge characteristics even when it is repeatedly charged and discharged not only for the first time. According to this invention, the manufacturing method of this lithium occlusion / release material, the electrode containing said lithium occlusion / release material, and a lithium ion secondary battery provided with this electrode as a negative electrode are also provided.

2 is a Ni—Si alloy state diagram shown in Non-Patent Document 1. FIG. It is a general | schematic apparatus installation flow chart which shows a specific example of the manufacturing method of the lithium occlusion / release material which concerns on one Embodiment of this invention. 2 is an X-ray photoelectron spectrum (wide scan) of the lithium storage / release material according to Example 1. FIG. 2 is an X-ray photoelectron spectrum (narrow scan including a Si peak) of the lithium storage / release material according to Example 1; 2 is an X-ray photoelectron spectrum (narrow scan including a Ni peak) of the lithium storage / release material according to Example 1; 2 is an X-ray diffraction spectrum of a lithium storage / release material according to Example 1. FIG.

The lithium storage / release material according to an embodiment of the present invention has a composition containing Si and Ni, and includes a Si phase and a NiSi ₂ phase.

Si is a direct constituent element of the Si phase, which is a lithium storage / release phase. Ni is a kind of element constituting the NiSi ₂ phase that restrains the Si phase. As shown in FIG. 1, under the thermodynamic equilibrium condition, the Si content in the Ni—Si binary alloy is 67.5 atomic% or more (the atomic ratio of Si to Ni (herein, “Si / It is also referred to as “Ni ratio”.) When converted to 2.08 or more), NiSi ₂ phase and Si phase are mainly formed. Therefore, the lithium occlusion / release material according to an embodiment of the present invention has a composition in which the Si / Ni ratio is 2.08 or more.

When the Si / Ni ratio of the lithium storage / release material is 2.08 or more, a structure mainly including the Si phase and the NiSi ₂ phase is obtained, and the electrode including the lithium storage / release material according to one embodiment of the present invention is provided. The charge / discharge characteristics of a lithium ion secondary battery (hereinafter sometimes referred to as “the present battery”) provided as a negative electrode are improved. From the viewpoint of more stably realizing such charge / discharge characteristics, the Si / Ni ratio is preferably 2.2 or more, more preferably 2.4 or more, and 2.5 The above is particularly preferable.

As a basic tendency, the higher the Si / Ni ratio, the higher the proportion of the Si phase that is the lithium occlusion / release phase, and the above charge / discharge characteristics are improved. Increase. However, when the Si / Ni ratio increases, the existence ratio of the NiSi ₂ phase, which is a constrained phase, relatively decreases. For this reason, when the Si / Ni ratio becomes excessively high, it becomes difficult to properly restrain the Si phase by the NiSi ₂ phase, and the capacity retention ratio when repeatedly charged / discharged (charge amount after repeated charge / discharge / initial charge (Charge amount, unit:%) tends to decrease. From the viewpoint of more stably realizing the capacity retention appropriately, the Si / Ni ratio may be preferably 4.2 or less, and more preferably 4.0 or less. There is.

  The lithium occlusion / release material according to one embodiment of the present invention may contain other elements such as Fe as optional addition elements in addition to Si and Ni. Fe, like Ni, is an iron group element and has high reactivity with Si. Therefore, Fe is also easily contained in the material containing Si and Ni, and it is not easy to completely remove Fe from such material. In the case where the lithium storage / release material according to an embodiment of the present invention has the above charge / discharge characteristics, when Fe contains Fe, the present invention can be achieved more stably from the viewpoint of achieving better charge / discharge characteristics. The Fe content in the lithium storage / release material according to an embodiment of the present invention is preferably such that the atomic ratio of Fe to Ni (hereinafter sometimes referred to as “Fe / Ni ratio”) is 0.08 or less. .

  As optional addition elements other than Fe in the lithium occlusion / release material according to one embodiment of the present invention, transition metal elements such as Co, Cu, Ag, Au, Pt, Ti, V, Zr, Nb, Zn, T, and W, Examples are B, C, Al, S, K, Na, Ca, Mg, Sn, Ge and the like. The smaller the content of these optional added elements, the better. Ca, Al, Mg and the like form a composite oxide together with Si, and Si contained in the formed composite oxide cannot fulfill the function of occluding and releasing lithium. The lithium storage / release material according to one embodiment of the present invention preferably contains substantially no halogen element such as Cl, P, S and As. These elements may corrode other materials included in the battery, particularly metal-based materials.

As described above, the phase constituting the lithium storage / release material according to the embodiment of the present invention includes the Si phase that is the lithium storage / release phase and the NiSi ₂ phase that is the constraining phase. When the shape of the Si phase is excessively large, the constraint by the constraint phase may not be performed properly. Therefore, the Si phase is preferably not excessively large. The size of the Si phase can be estimated by the average diameter of the crystal calculated by the Scherrer equation from the Si peak in the X-ray diffraction spectrum of the lithium storage / release material.

When X-ray diffraction measurement (ray source: Cu Kα) is performed on the lithium storage / release material according to one embodiment of the present invention, a plurality of peaks attributed to Si are detected in the obtained X-ray diffraction spectrum. . Among these peaks, the full width at half maximum FWHM (unit: radians) is obtained for five peaks (peak 1 to peak 5) in which the angle (2θ) of the peak position is approximately the following value, and is expressed by the following formula (i): The crystal size τ (unit: nm) is determined from the Scherrer equation.
Peak 1: 56.14 °
Peak 2: 69.14 °
Peak 3: 76.38 °
Peak 4: 88.04 °
Peak 5: 94.95 °
τ = k × λ / (FWHM × COS (θ)) (i)
here,
τ: Crystal size (nm)
k: Scherrer's constant (0.94)
λ: X-ray wavelength (nm)
FWHM: Full width at half maximum (rad)
θ: Bragg angle (rad)

  In the present specification, the arithmetic average value of the five crystal sizes τ thus obtained is defined as the size of the Si phase in the lithium storage / release material according to one embodiment of the present invention. In the lithium storage / release material according to one embodiment of the present invention, the size of the Si phase obtained by the above method is 100 nm or less. When the size of the Si phase exceeds 100 nm, the tendency for the capacity retention rate to decrease when the battery is repeatedly charged and discharged becomes significant. From the viewpoint of more stably suppressing the decrease in capacity retention, the size of the Si phase may be preferably 90 nm or less, and more preferably 85 nm or less.

The lithium occlusion / release material according to one embodiment of the present invention may include a phase other than the Si phase and the NiSi ₂ phase. An example of such a phase is a NiSi phase.

An electrode according to an embodiment of the present invention includes the lithium storage / release material according to the above-described embodiment of the present invention. As described above, since the lithium occlusion / release material according to the embodiment of the present invention includes the Si phase appropriately defined in size and the NiSi ₂ phase that is a constrained phase, the lithium occlusion / release is appropriately performed. be able to. Therefore, the lithium occlusion / release material according to one embodiment of the present invention can be suitably used as an electrode of a lithium ion secondary battery, particularly as a negative electrode.

  The lithium ion secondary battery according to an embodiment of the present invention including such a negative electrode has good charge / discharge characteristics. Moreover, in a preferred example, the capacity retention rate is unlikely to decrease even when the battery is repeatedly charged and discharged.

  The manufacturing method of the lithium occlusion / release material according to an embodiment of the present invention is not limited. If it manufactures with the method demonstrated below, the lithium occlusion / release material which concerns on one Embodiment of this invention can be manufactured efficiently.

  In the method for producing a lithium occlusion / release material according to an embodiment of the present invention, first, a raw material containing a nickel source, a silicon source and a carbon source is heated to 1,100 to 1,650 ° C. and an inert gas. By reacting in an atmosphere for 0.5 to 30 hours, a molten material containing Si and Ni and having a composition in which the atomic ratio of Si to Ni (Si / Ni ratio) is 2.08 or more is obtained.

Since Si is an element having high affinity with oxygen, the silicon source often contains an oxide of Si. Therefore, in the manufacturing method according to an embodiment of the present invention, a carbon source is used, and a Si oxide as shown in the following formula (ii) (SiO ₂ is shown as a specific example in the following formula (ii)). ) To obtain Si.
SiO ₂ + 2C → Si + 2CO (ii)

  In order to make this reduction reaction proceed appropriately, the raw material is heated until it is melted in an inert gas atmosphere, and the molten state is maintained for 0.5 to 30 hours. The heating temperature is a temperature at which a molten state is reached. A specific temperature range of the heating temperature is appropriately set depending on the composition of the raw material. Usually, it is in the range of 1,100 to 1,650 ° C, preferably in the range of 1,200 to 1,650 ° C, more preferably in the range of 1,300 to 1,500 ° C. There is a case. A heating means is arbitrary and an electric furnace is mentioned as a specific example. The maintenance time of a molten state should be set suitably, and the time which the reaction shown by said formula (ii) is completed appropriately based on the composition of a raw material is set.

  The composition of the molten material is arbitrary as long as the Si / Ni ratio is 2.08 or more. From the viewpoint of improving the properties of the obtained lithium storage / release material, the Si / Ni ratio in the molten material may be preferably 2.2 or more and 4.2 or less, and may be 2.5 or more and 4.0 or less. It may be more preferable.

  The composition of the nickel source contained in the raw material is arbitrary as long as it contains Ni. It may be preferable that the nickel source contains one or more selected from the group consisting of new nickel, a used sponge nickel catalyst, and an electric furnace residual nickel silicon alloy semi-finished product.

  The new nickel is smelted nickel and preferably has a purity (Ni content) of 99.5% by weight or more. Such new nickel is readily available from the market. From the viewpoint of suppressing corrosion of metallic materials other than the lithium occlusion / release material of the battery, it is preferable that the content of S, P, As, and halogen elements in the new nickel are all inevitable impurity levels.

  The used sponge nickel catalyst is obtained after a member made of a sponge-like (porous) nickel alloy is used as a catalyst for hydrogenation reaction or the like. The used sponge nickel catalyst preferably has a purity (Ni content) of 50 to 70% by weight, a Si content of 30 to 50% by weight, and an Fe content of 4% by weight or less. Since Si is one of the essential constituent elements of the lithium storage / release material according to an embodiment of the present invention, it does not matter that the used sponge nickel catalyst contains Si. Since Fe easily forms an intermetallic compound with Si, the Fe content in the used sponge nickel catalyst is preferably as small as possible. In addition, as shown in the Example mentioned later, even if it is sponge nickel before using as a catalyst, and the sponge nickel after using as a catalyst, the function as a nickel source is equivalent. Therefore, it is preferable to use sponge nickel after it has been used as a catalyst because it is a valuable resource for recycling.

  In this specification, “an electric furnace residual nickel silicon alloy semi-finished product” means a nickel silicon alloy semi-finished product remaining in the electric furnace, which is generated in the process of producing the nickel alloy using the electric furnace. Since this semi-finished product contains Ni and Si, it is suitable as a raw material for the lithium storage / release material according to one embodiment of the present invention. Elements other than Ni and Si may be included, but the smaller the content, the better.

An example of the nickel source analysis method is as follows.
Purity (Ni content): JIS H 1151 According to pure (Ni + Co) quantification method.
S content: According to JIS H 1151 12.2 Hydrogen sulfide vaporization separation methylene blue spectrophotometry. Detection limit: 0.0001% by weight
P content: Conforms to the method for determining phosphorus in JIS H 1278 nickel and nickel alloys. Detection limit: 0.0005% by weight
As content: Conforms to JIS G 1225 arsenic trichloride distillation separation molybdoarsenate blue absorption photometric method. Detection limit: 0.0005% by weight
Halogen element content: According to sample combustion ion chromatography. Detection limit: 10 mass ppm

  The composition of the silicon source contained in the raw material is arbitrary as long as it contains Si. It may be preferred that the silicon source contains one or more selected from the group consisting of silica and metallic silicon.

  Silica stone is a type of material suitable as a silicon source because it contains an oxide of Si and is easily available. The silica is preferably 99.0% by weight or more in purity (silicon dioxide content). The quartzite preferably has a calcium oxide content of 0.1% by weight or less, an aluminum oxide content of 0.2% by weight or less, and a magnesium oxide content of 0.1% by weight or less. Ca, Al, and Mg, alone or in a plurality of types, form a hardly soluble complex oxide with Si and become an inhibitory factor for obtaining Si by the reaction of the above formula (ii).

An example of a method for analyzing quartzite is as follows.
Purity (content of silicon dioxide): Conforms to JIS M 8852: 1998 8.3 Dehydration gravimetric analysis and spectrophotometric analysis combined method. Detection limit: 0.1% by weight
Calcium oxide: Conforms to JIS M 8852: 1998 9.3 ICP emission analysis. Detection limit: 0.005% by weight
Aluminum oxide: According to JIS M 8852: 1998 13.3 ICP emission analysis method. Detection limit: 0.02% by weight
Magnesium oxide: Conforms to JIS M 8852: 1998 14.3 ICP emission analysis. Detection limit: 0.002% by weight

  Metallic silicon is also readily available, and is a material that has already undergone a reduction treatment to some extent, and is therefore suitable as a silicon source. The metal silicon preferably has a purity (Si content) of 99.0% by weight or more. The metal silicon preferably has an Fe content of 0.5% by weight or less, an Al content of 0.1% by weight or less, and a Ca content of 0.3% by weight or less.

An example of a method for analyzing metal silicon is as follows.
Purity (Si content): JIS G 1322-1: 2010 5. Silicon determination method Follows the gravimetric method. Detection limit: 0.1% by weight
Fe content: JIS G 1322-5: 2010 7. Conforms to silicon isolation ICP emission spectroscopy. Detection limit: 0.001% by weight
Al content: JIS G 1322-6: 2010 6. Conforms to silicon isolation ICP emission spectroscopy. Detection limit: 0.001% by weight
Ca content: JIS G 1322-7: 2010 6. Conforms to silicon isolation ICP emission spectroscopy. Detection limit: 0.001% by weight
P content: JIS G 1322-3: 2010 6. Conforms to silicon isolation ICP emission spectroscopy. Detection limit: 0.002% by weight
B content: JIS G 1322-3: 2010 6. Conforms to silicon separation ICP emission analysis. Detection limit: 1 ppm by mass

  The carbon source contained in the raw material is arbitrary as long as it contains C. Since the availability is high, the carbon source may preferably include one or more selected from the group consisting of charcoal and oga charcoal.

  Since S, P, As, Bi, and halogen corrode the metal-based material constituting the lithium ion secondary battery, the carbon source contains unavoidable impurity levels of any of S, P, As, Bi, and halogen. It is preferable that

An example of the carbon source analysis method is as follows.
S content: According to the sample combustion ion chromatography method. Detection limit: 10 mass ppm
P content: According to ICP emission analysis. Detection limit: 1 ppm by mass
As content: According to ICP emission analysis. Detection limit: 1 ppm by mass
Bi content: According to ICP emission analysis. Detection limit: 1 ppm by mass
Halogen element content: According to sample combustion ion chromatography. Detection limit: 10 mass ppm

  When the silicon source includes silica, the amount of the carbon source in the raw material is set so that the silicon oxide contained in the silica can be reduced. From the viewpoint of stably producing the reduction of the silica, the amount of C in the carbon source is preferably 3 mol times or more of Si contained in the silica.

  From the viewpoint of improving uniformity when heating each material (nickel source, silicon source and carbon source) constituting the raw material in a furnace to obtain a molten material, the materials constituting the raw material are mixed in advance. It is preferable to perform heating.

By cooling the molten material obtained by heating the raw material to 50 ° C. or lower with a cooling time of 3 hours or longer, a lithium occlusion / release material can be obtained. As will be described later in Examples, the obtained lithium storage / release material includes a Si phase, a NiSi ₂ phase, and a NiSi phase. That is, the process for obtaining the lithium storage / release material from the molten material can be represented by the following formula (ii).
xNi + ySi → (NiSi ₂ ) _a (NiSi) _b (Si) _c (iii)

  Since the melted substance has a Si / Ni ratio of 2.08 or more, as shown in Non-Patent Document 1, the primary crystal becomes the Si phase if it is cooled. In Patent Document 1, the Si phase that is the lithium occlusion / release phase is regarded as an initial crystal, which is not preferable because the lithium occlusion / release phase may become coarse, but when the cooling rate is slow, Even when the lithium occlusion / release phase is the initial phase, it is possible to obtain a lithium occlusion / release material that can be used as a negative electrode material of a lithium ion secondary battery having excellent charge / discharge characteristics and high capacity retention when repeatedly charged / discharged. .

  From the viewpoint of obtaining a lithium occlusion / release material having an appropriate structure, the average cooling rate in the cooling process may be preferably 0.5 ° C./second or less, more preferably 0.3 ° C./second or less. It may be preferable, and it may be particularly preferable that it is 0.1 ° C./second or less.

  FIG. 2 is a schematic flow sheet of equipment installation showing a specific example of a method for producing a lithium storage / release material according to an embodiment of the present invention. Hereinafter, a manufacturing example will be described with reference to FIG.

  First, a predetermined amount of raw material is mixed well in a mixer and then stored in a container. It is preferable to feed the raw materials to the electric furnace after homogeneously mixing the raw materials in advance with a mixer (MX-101). If the mixing is insufficient, the silica that is the silicon source is not sufficiently reduced to silicon by the carbon source and remains in the electric furnace (in this example, the arc furnace) as insoluble silica. This residue can be a factor that hinders continuous operation.

  Next, the preparation of the furnace is completed according to the operation procedure of the electric furnace. After the preparation of the furnace is completed, the operation of the furnace is raised to the normal operating temperature (1,200 to 1,650 ° C.) according to the startup procedure. During operation, the temperature in the furnace is maintained in the range of 1,200 to 1,650 ° C, more preferably 1,350 to 1,500 ° C. When a state where normal operation can be continued is reached, the well-mixed raw material of the container is transferred to the raw material stock pan, and the required amount is charged into the arc furnace at a predetermined speed to produce an alloy. It usually takes 1 to 2 hours to stabilize the internal state of the electric furnace (arc furnace). Thereafter, the reaction is further carried out for 4 to 30 hours. In this way, a molten material is obtained.

  Subsequently, the obtained molten material is drawn out into a tray every predetermined time. A molten lithium occlusion / release material is obtained by cooling the molten material extracted to the tray to 50 ° C. over 3 hours or more. This is pulverized by a crusher (not shown), and then classified into a size according to the purpose of use to obtain a lithium occluding / releasing material having a uniform size. The dust generated during work is No. 1 blower (BL-101), No. 1 Aspirate with 2 blowers (BL-102). Dust collector and No2. Remove with a dust collector. Dust collected is stored in a flexible container and processed.

  The embodiment described above is described for facilitating understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

  For example, in the above method for producing a lithium storage / release material, the raw material contains a carbon source. However, if a refined (reduced) silicon material such as metallic silicon is used as the silicon source, the carbon source is used. Thus, the process of reducing the oxide of Si may not be performed. However, Si is easy to oxidize, and if an oxide of Si remains in the lithium occlusion / release material, Si contained in the oxide cannot fulfill the function of occlusion / release of lithium. Therefore, it is preferable to reduce the Si in the molten material sufficiently by performing a reduction process in producing the molten material.

  EXAMPLES Hereinafter, although an Example etc. demonstrate this invention further more concretely, the scope of the present invention is not limited to these Examples etc.

(Example 1)
Using 306.6 kg of silica as a silicon source and 184.0 kg of charcoal as a carbon source for 100 kg of new nickel as a raw material nickel source, a lithium storage / release material is produced by the method described in the production flow sheet shown in FIG. did. The composition of the molten material was controlled such that the atomic ratio of Fe to Ni (Fe / Ni ratio) in the lithium storage / release material was 0.063 or less. In other examples and comparative examples, the management of the Fe / Ni ratio of the lithium storage / release material was the same. The molten material was cooled by cooling to 50 ° C. over 3 hours from the molten state. In this case, the average cooling rate was 0.1 ° C./second. Thus, a lithium occlusion / release material having an atomic ratio of silicon to nickel (Si / Ni ratio) of 3.0 was obtained in a yield of 99%.

(Measurement Example 1) X-ray Photoelectron Spectroscopy The lithium storage / release material produced in Example 1 was measured by X-ray photoelectron spectroscopy (XPS). The measurement conditions were as follows.
Equipment: “Quantera SXM ULXAC-PHI” manufactured by ULVAC-PHI Co., Ltd.
X-ray source target: Al (monochromatic light source)
X-ray beam diameter and output: 100 μm, 15 KV, 25 W
Take-off Angle. : 45 ° (analysis depth about 7nm)

The measurement results (X-ray photoelectron spectroscopy spectrum) are shown in Table 1 and FIGS. As shown in Table 1, the Si / Ni ratio (ratio of metal Si to metal Ni) on the surface of the lithium occlusion / release material manufactured according to Example 1 is 5.6, and Si is relatively present on the surface. It was confirmed that there were many.

(Measurement Example 2) X-ray diffraction spectrum The X-ray diffraction measurement of the lithium occlusion / release material produced in Example 1 was performed. The measurement conditions were as follows.
Device: Smart Lab (manufactured by Rigaku Corporation)
Radiation source: Cu Kα (output: 45 kV x 200 mA)
Measurement mode: 2θ-ω measurement (concentration method)
Range: 5-150 °
Step width: 0.01 °
Counting time: 0.1 ° / min Sample setting method: Apply to glass plate

The measurement result (X-ray diffraction spectrum) was collated with a known Ni _x Si _y pattern in ICDD (powder diffraction database) attached to the apparatus. In FIG. 6, the peak due to Si is indicated by a broken line (marked with ■ at the top), the peak due to NiSi ₂ is indicated by a dotted line (marked with 頂 at the top), and the peak due to NiSi is indicated by a dotted line (Δ at the top). Attached). As shown in FIG. 6 (particularly, a peak group near 76 °, a peak group near 88 °, and a peak group near 95 °), a peak attributed to Si and a peak attributed to NiSi ₂ were detected. It was. In addition, the other small peaks included some attributed to NiSi. Therefore, it was confirmed that the lithium occlusion / release material manufactured according to Example 1 includes a Si phase and a NiSi ₂ phase, and further includes a trace amount of NiSi crystals. FIG. 6 also shows an X-ray diffraction spectrum obtained by enlarging the range of 55 ° to 58 °, the range of 68 ° to 71 °, the range of 75 ° to 78 °, and the range of 87 ° to 90 °. Table 5 shows the calculation results of peak positions (unit: ° (degree)) and lattice spacing for five peaks assigned to Si in the X-ray diffraction spectrum.

(Measurement Example 3) Measurement of Si Phase Size The full width at half maximum FWHM (unit: rad) is obtained for the five peaks assigned to Si in the X-ray diffraction spectrum measured in Measurement Example 2, and the above formula (i) is obtained. The Si crystal size τ (unit: nm) at each peak was calculated using the Scherrer equation shown (see Table 2). The arithmetic average value of the obtained five crystal sizes was defined as the size of the Si phase of the lithium occlusion / release material manufactured in Example 1. The size of the Si phase thus determined was 47 nm.

(Example 2)
Production of lithium occlusion / release material by the method described in the production flow sheet shown in FIG. 2, using 255.5 kg of silica as a silicon source and 153.2 kg of charcoal as a carbon source for 100 kg of new nickel as a raw material nickel source did. The molten material was cooled by cooling to 50 ° C. over 3 hours from the molten state. In this case, the average cooling rate was 0.1 ° C./second. Thus, a lithium occlusion / release material having an atomic ratio of silicon to nickel (Si / Ni ratio) of 2.5 was obtained in a yield of 99%.

(Example 3)
Production of lithium occlusion / release material by the method described in the production flow sheet shown in FIG. 2, using 408.9 kg of silica as a silicon source and 245.3 kg of charcoal as a carbon source for 100 kg of new nickel as a raw material nickel source. did. The molten material was cooled by cooling to 50 ° C. over 3 hours from the molten state. In this case, the average cooling rate was 0.1 ° C./second. Thus, a lithium occlusion / release material having an atomic ratio of silicon to nickel (Si / Ni ratio) of 4.0 was obtained in a yield of 99%. The size of the Si phase measured in the same manner as in Measurement Example 3 was 84 nm.

Example 4
As a raw material nickel source, 100 kg of nickel silicon hydrogenation catalyst (hydrogenation catalyst) (composition: Ni 53.5 kg, Si 43 kg, Fe 2.5 kg), using 71.9 kg of silica as a silicon source and 43.1 kg of charcoal as a carbon source A lithium occlusion / release material was produced by the method described in the production flow sheet shown in FIG. The molten material was cooled by cooling to 50 ° C. over 3 hours from the molten state. In this case, the average cooling rate was 0.1 ° C./second. Thus, a lithium occlusion / release material having an atomic ratio of silicon to nickel (Si / Ni ratio) of 3.0 was obtained in a yield of 99%.

(Example 5)
As a raw material nickel source, 100 kg of used sponge nickel catalyst (hydrogenation recovery catalyst) (composition: Ni 63 kg, Si 34 kg, Fe 3 kg), 120.3 kg of silica as a silicon source, and 72.1 kg of charcoal as a carbon source, FIG. A lithium occlusion / release material was produced by the method described in the production flow sheet shown in FIG. The molten material was cooled by cooling to 50 ° C. over 3 hours from the molten state. In this case, the average cooling rate was 0.1 ° C./second. Thus, a lithium occlusion / release material having an atomic ratio of silicon to nickel (Si / Ni ratio) of 3.0 was obtained in a yield of 99%.

(Example 6)
A molten material was obtained in a high frequency induction melting furnace using 143.1 kg of metallic silicon as a silicon source for 100 kg of new nickel as a raw material nickel source. The molten material was cooled by cooling to 50 ° C. over 3 hours from the molten state. In this case, the average cooling rate was 0.1 ° C./second. Thus, a lithium occlusion / release material having an atomic ratio of silicon to nickel (Si / Ni ratio) of 3.0 was obtained in a yield of 99%.

(Example 7)
Production of lithium storage and release material by the method described in the production flow sheet shown in FIG. 2, using 235.1 kg of silica as a silicon source and 141.1 kg of charcoal as a carbon source for 100 kg of new nickel as a raw material nickel source did. The molten material was cooled by cooling to 50 ° C. over 3 hours from the molten state. In this case, the average cooling rate was 0.1 ° C./second. Thus, a lithium occlusion / release material having an atomic ratio of Si to nickel (Si / Ni ratio) of 2.3 was obtained in a yield of 99%.

(Comparative Example 1)
As a raw material nickel source, 100 kg of used sponge nickel catalyst (composition: Ni 63 kg, Si 34 kg, Fe 3 kg), 30.2 kg of silica as a silicon source, 18.1 kg of charcoal as a carbon source, and the production flow sheet shown in FIG. A silicon-nickel alloy for hydrogenation was produced by the method described in 1. The molten material was cooled by cooling to 50 ° C. over 3 hours from the molten state. In this case, the average cooling rate was 0.1 ° C./second. Thus, a hydrogenating silicon-nickel alloy having an atomic ratio of Si to nickel (Si / Ni ratio) of 1.6 was obtained in a yield of 99%.

(Comparative Example 2)
Lithium occlusion / release materials were produced by the method described in the production flow sheet shown in FIG. 2, using 460 kg of silica as a silicon source and 276 kg of charcoal as a carbon source for 100 kg of new nickel as a raw material nickel source. The molten material was cooled by cooling to 50 ° C. over 3 hours from the molten state. In this case, the average cooling rate was 0.1 ° C./second. Thus, a lithium occlusion / release material having an atomic ratio of Si to nickel (Si / Ni ratio) of 4.5 was obtained in a yield of 99%. The size of the Si phase measured in the same manner as in Measurement Example 3 was 130 nm.

(Example 8)
Lithium occlusion / release material was manufactured by the method described in the manufacturing flow sheet shown in FIG. 2 using 245 kg of silica as a silicon source and 147 kg of charcoal as a carbon source for 100 kg of new nickel as a raw material nickel source. The molten material was cooled by cooling to 50 ° C. over 3 hours from the molten state. In this case, the average cooling rate was 0.1 ° C./second. Thus, a lithium occlusion / release material having an atomic ratio of Si to nickel (Si / Ni ratio) of 2.4 was obtained in a yield of 99%.

(Comparative Example 3)
As a raw material nickel source, 2 kg of new nickel, 6 kg of silica as a silicon source, and 3.7 kg of charcoal as a carbon source were melted in a high frequency furnace to obtain a molten material. The obtained molten material was rapidly cooled to 50 ° C. in 20 minutes to produce a lithium storage / release material. In this case, the average cooling rate was 1 ° C./second. Thus, a lithium storage / release material having an atomic ratio of Si to nickel (Si / Ni ratio) of 3.0 was obtained in a yield of 99%.

(Measurement Example 4) Production and characteristic evaluation of lithium ion secondary battery A 2032 type coin battery was produced. The bulk lithium occlusion / release material produced in Examples and Comparative Examples was pulverized to about 1 mmφ by a pulverizer, and the pulverized product obtained using a planetary ball mill was further pulverized to obtain a fine powder of about 1 μmφ. A negative electrode was prepared using this fine powder. Metallic lithium was used as the counter electrode (positive electrode), and a microporous polypropylene film was used as the separator. A solution obtained by adding 5% by weight of fluoroethylene carbonate to a 1: 1 (volume ratio) mixed solvent of ethylene carbonate and diethyl carbonate in which LiPF ₆ was dissolved at a rate of 1 mol / L was used as an electrolytic solution.

  The charge / discharge characteristics of the lithium ion secondary battery using the negative electrode containing the lithium storage / release material of the present invention were measured as follows. Using “BTS2005W” manufactured by Nagano Co., Ltd., constant current charging was performed at a current of 100 mA per gram of active material until reaching 0.001 V with respect to the lithium electrode. Next, constant voltage charging was carried out while maintaining a voltage of 0.001 V until the current reached a current value of 20 mA or less per gram of active material. The cell that had been fully charged was subjected to a constant current discharge at a current of 100 mA per gram of active material until the voltage reached 1.5 V after a rest period of about 30 minutes.

  The charge capacity was calculated from the integrated current value until the constant voltage charge was completed, and the discharge capacity was calculated from the integrated current value until the battery voltage reached 1.5V. At the time of switching between charge and discharge, the circuit was paused for 30 minutes.

  Table 3 shows the measurement results of the charge / discharge characteristics. The capacity retention rate is a ratio (unit:%) of the 50th charge amount to the second charge amount.

  As shown in Table 3, when the hydrogenated silicon-nickel alloy of Comparative Example 1 was used, both the initial charge amount and the initial discharge amount of the lithium ion secondary battery were extremely low. This is considered because the Si / Ni ratio of the alloy of Comparative Example 1 is less than 2.08. On the other hand, in the lithium ion secondary battery using the lithium occlusion / release material according to the example in which the Si / Ni ratio is 2.08 or more, both the initial charge amount and the initial discharge amount are 400 mAh / g or more, which is favorable. Charge / discharge characteristics were obtained. In particular, in the lithium ion secondary battery using the lithium occlusion / release material according to Examples (Examples 1, 2, 3 and 8) having a Si / Ni ratio of 2.4 or more, the initial charge amount is 500 mAh / g or more. It became.

Further, in the lithium ion secondary battery using the lithium occlusion / release materials according to Examples 1 and 3 in which the size of the Si phase is 100 nm or less and the Si / Ni ratio is 2.08 or more and 4.2 or less, The capacity retention rate was 85% or more, and the capacity when repeatedly charged and discharged could be properly maintained. On the other hand, in the lithium ion secondary battery using the lithium occlusion / release material according to Comparative Example 2 (Si phase equivalent diameter = 65 nm, Si / Ni ratio = 4.5), the capacity retention rate decreases, and repeated charge / discharge The capacity could not be maintained. In the case of Comparative Example 2, it is considered that the Si phase in the lithium occlusion / release material is excessively large, and the NiSi ₂ phase is not properly restrained when repeatedly charged and discharged.

  In order to evaluate the relationship between the nickel source and the lithium storage / release material (Si / Ni ratio = 3.0), the measurement results of Examples 1, 4 and 5 are shown in Table 4.

  As shown in Table 4, the properties of the obtained lithium storage / release materials were almost equal even when the lithium sources were different. In particular, even when the used sponge nickel catalyst was used as the nickel source, the results were not significantly different from the case where the new nickel or the hydrogenation catalyst before use was used as the nickel source. It has become clear that it can be reused as a nickel source for producing lithium storage / release materials.

  The results of Examples 1 and 6 are shown in Table 5 in order to evaluate the influence of the difference in the production method of the lithium storage / release material, particularly the production method of the molten material, on the charge / discharge characteristics. In Example 1, a reduction method including a carbon source in a raw material was performed, and a molten material was produced using an electric furnace (an arc furnace). On the other hand, in Example 6, the new nickel and metallic silicon were used as raw materials, and the molten material was manufactured using a high frequency induction melting furnace.

  As shown in Table 5, it was confirmed that the influence of the difference in the manufacturing method of the molten material was not great. Even if an unreduced material (silica stone) is included in a part of the raw material, the reduced material (new nickel, metallic silicon) is obtained by actively performing the reduction process in the manufacturing process of the molten material (Example 1). Compared with the case where the reduction process is not actively performed using the raw material made of (Example 6), the charge / discharge characteristics of the lithium ion secondary battery using the obtained lithium ion storage / release material are improved. Was confirmed.

  Table 6 shows the measurement results of Examples 1 and 3 and Comparative Example 2 in order to evaluate the influence of the size of the Si phase in the lithium storage / release material on the charge / discharge characteristics.

  As shown in Table 6, when the size of the Si phase is 100 nm or less, preferably 85 nm, good charge / discharge characteristics can be obtained, and the capacity can be properly maintained even when repeatedly charged / discharged. It was confirmed that the capacity retention decreased when the size was excessive.

  The results of Example 1 and Comparative Example 4 are shown in Table 7 in order to evaluate the effect on the charge / discharge characteristics of the production method of the lithium storage / release material, particularly the difference in the process of obtaining the lithium storage / release material by cooling the molten material. It was.

  As shown in Table 7, by reducing the cooling rate of the molten material, specifically, by setting the average cooling rate to about 0.1 ° C./second, it was repeatedly charged and discharged with excellent charge / discharge characteristics. Lithium ion storage / release material that can be used as an electrode material for a lithium ion secondary battery that can maintain the capacity appropriately can be obtained. When the average cooling rate is about 1 ° C./second, lithium ion having excellent charge / discharge characteristics It was confirmed that a lithium storage / release material giving a secondary battery could not be obtained.

  The lithium storage / release material of the present invention can be suitably used as a negative electrode material for a lithium ion secondary battery.

Claims (18)

A lithium storage / release material having a composition containing Si and Ni, comprising a Si phase and a NiSi ₂ phase,
The lithium occlusion / release material is characterized in that the average diameter of the crystal calculated by the Scherrer equation from the Si peak in the X-ray diffraction spectrum of the lithium occlusion / release material is 100 nm or less.   The lithium occlusion / release material according to claim 1, wherein an atomic ratio of Si to Ni is 2.2 or more and 4.2 or less.   The lithium storage / release material according to claim 1 or 2, wherein the lithium storage / release material has a composition further containing Fe, and an atomic ratio of Fe to Ni is 0.08 or less.   The lithium storage / release material according to any one of claims 1 to 3, further comprising a NiSi phase.   The electrode containing the lithium occlusion / release material according to any one of claims 1 to 4.   A lithium ion secondary battery comprising the electrode according to claim 5 as a negative electrode. Heating a raw material containing a silicon source and a nickel source made of metallic silicon to obtain a molten material containing Si and Ni and having a composition in which the atomic ratio of Si to Ni is 2.08 or more,
A method for producing a lithium occlusion / release material, wherein the molten material is cooled to 50 ° C. or less with a cooling time of 3 hours or more to obtain a lithium occlusion / release material. A raw material containing a nickel source, a silicon source and a carbon source is heated and reacted at 1,100 to 1,650 ° C. in an inert gas atmosphere for 0.5 to 30 hours to contain Si and Ni. Obtaining a molten material having a composition in which the atomic ratio of Si to Ni is 2.08 or more;
A method for producing a lithium occlusion / release material, wherein the molten material is cooled to 50 ° C. or less with a cooling time of 3 hours or more to obtain a lithium occlusion / release material.   9. The lithium occlusion / release of claim 7, wherein the nickel source includes one or more selected from the group consisting of new nickel, a used sponge nickel catalyst, and an electric furnace residual nickel-silicon alloy semi-finished product. Material manufacturing method.   10. The production of a lithium storage / release material according to claim 9, wherein the new nickel has a purity of 99.5% by weight or more, and the contents of S, P, As, and a halogen element are all inevitable impurity levels. Method.   11. The spent sponge nickel catalyst has a purity of 50 to 70% by weight, a Si content of 30 to 50% by weight, and a Fe content of 4% by weight or less. Manufacturing method of lithium storage / release material.   The method for producing a lithium storage / release material according to any one of claims 8 to 11, wherein the silicon source includes one or more selected from the group consisting of silica and metal silicon.   The silica has a purity of 99.0% by weight or more, a calcium oxide content of 0.1% by weight or less, an aluminum oxide content of 0.2% by weight or less, and a magnesium oxide content of 0. The method for producing a lithium storage / release material according to claim 12, wherein the content is 1% by weight or less.   The metal silicon has a purity of 99.0% by weight or more, an Fe content of 0.5% by weight or less, an Al content of 0.1% by weight or less, and a Ca content of 0.3% by weight. The method for producing a lithium storage / release material according to claim 12 or 13, wherein the lithium storage / release material has a weight% or less.   The method for producing a lithium storage / release material according to any one of claims 8 to 14, wherein the carbon source includes one or more selected from the group consisting of charcoal and oga charcoal.   The method for producing a lithium storage / release material according to any one of claims 8 to 15, wherein the carbon source has an inevitable impurity level in the contents of S, P, As, and halogen.   The method for producing a lithium storage / release material according to any one of claims 7 to 16, wherein heating is performed in a state where the raw material is mixed in advance.   The method for producing a lithium storage / release material according to any one of claims 7 to 17, wherein an average cooling rate of the molten material is 0.5 ° C / second or less.