JP6371504B2 - Si-based alloy negative electrode material for power storage device and electrode using the same - Google Patents

Description

  The present invention relates to a Si-based alloy negative electrode material that is excellent in conductivity of an electricity storage device that involves movement of lithium ions during charge and discharge, such as a lithium ion secondary battery, a hybrid capacitor, and an all solid lithium ion secondary battery, and an electrode using the same Is.

  In recent years, with the spread of portable devices, development of high-performance secondary batteries centering on lithium-ion batteries has been actively conducted. Furthermore, lithium-ion secondary batteries and hybrid capacitors using the reaction mechanism of the lithium ion secondary battery as a negative electrode as active storage devices for automobiles and households have been actively developed. As a negative electrode material for these electricity storage devices, carbonaceous materials such as natural graphite, artificial graphite, and coke that can occlude and release lithium ions are used. However, since these carbonaceous materials insert lithium ions between the carbon surfaces, the theoretical capacity when used for the negative electrode is limited to 372 mAh / g, which is a new material that replaces carbonaceous materials for the purpose of increasing capacity. The search for is being actively conducted.

On the other hand, Si has attracted attention as a material that can replace carbonaceous materials. The reason is that Si can form a compound represented by Li ₂₂ Si ₅ and occlude a large amount of lithium, so that the capacity of the negative electrode can be greatly increased compared to the case of using a carbonaceous material. As a result, there is a possibility that the storage capacity of the lithium ion secondary battery, the hybrid capacitor, or the all solid state battery can be increased.

  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 as an electricity storage device is extremely short because problems 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.

  In addition, Si has poor electrical conductivity compared to carbonaceous materials and metal-based materials, and the efficient movement of electrons associated with charge / discharge is limited. Therefore, as a negative electrode material, a material that supplements conductivity, such as a carbonaceous material. However, even in that case, initial charge / discharge characteristics and charge / discharge characteristics with high efficiency are also problems.

  As a method for solving the drawbacks of using such a Si phase as a negative electrode, a material in which at least part of a parent lithium phase such as Si is surrounded by an intermetallic compound of Si and a metal typified by a transition metal, The manufacturing method is proposed by Unexamined-Japanese-Patent No. 2001-297757 (patent document 1) and Unexamined-Japanese-Patent No. 10-31804 (patent document 2), for example.

  As another solution, an electrode in which a phase of an active material containing a Si phase is coated with a conductive material such as Cu that is not alloyed with lithium and a method for manufacturing the same are disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-228059 (Patent Document). 3) and Japanese Patent Application Laid-Open No. 2005-44672 (Patent Document 4).

JP 2001-297757 A JP 10-31804 A JP 2004-228059 A JP 2005-44672 A

However, in the above-described method of coating the active material phase with a conductive material such as Cu, it is necessary to coat the active material containing the Si phase with a method such as Cu plating before or after the step of forming the active material on the electrode. Further, there is a problem that it takes time and labor from the industrial point of view, such as control of the coating thickness.
A material in which at least a part of a parent lithium phase such as Si is surrounded by an intermetallic compound is an industrially preferable process because a parent lithium phase and an intermetallic compound are formed during the solidification process after melting. , There is a problem that sufficient charge / discharge cycle characteristics cannot be obtained.

  Therefore, the problem to be solved by the present invention is to control the chemical composition, structure, structure size, etc. of the Si phase or intermetallic compound phase in the Si-based alloy at a high level, thereby enabling the lithium ion secondary battery or hybrid to be controlled. It is to propose a Si-based alloy negative electrode material that is excellent in charge / discharge characteristics with respect to an electricity storage device that moves lithium ions during charge / discharge, such as a capacitor and an all solid state battery.

  In order to solve the problems as described above, the inventors have intensively developed, and as a result, refinement of the structure, excellent ion conductivity and electron conductivity, control of the component system that enhances the stress relaxation effect, Si phase and The present inventors have found a Si-based alloy negative electrode material capable of obtaining excellent battery characteristics by controlling the crystallite size of the intermetallic compound phase.

Therefore, as means for solving the problems of the present invention,
According to the first aspect of the present invention, a negative electrode material made of a Si-based alloy for an electricity storage device accompanied by movement of lithium ions during charge / discharge, wherein the negative electrode material made of the Si-based alloy is composed of Si main phase made of Si, Si and Si A compound phase composed of one or more elements other than the above, wherein the compound phase has a phase composed of Si and Cr, or a phase composed of Si, Cr and Ti, and the Si crystallite size of the Si main phase There are at 30nm or less, and Si and Cr or the crystallite size of the compound phase consisting of Si, Cr and Ti, is Ri der less 40 nm, and the compound phase of the negative electrode material composed of Si-based alloy for an electricity storage device , Cu, V, Mn, Fe, Ni, Nb, Zn, Al, and at least one element selected from the group consisting of Al and a total content of 0.05 at. % To 3 at. % , A negative electrode material made of a Si-based alloy for power storage devices.

  According to a second aspect of the present invention, in the negative electrode material made of the Si-based alloy for an electricity storage device according to claim 1, the total content of Cr and Ti of the negative electrode material made of the Si-based alloy is 12 to 21 at. %, And the ratio of Cr to Ti, Cr% / (Cr% + Ti%) is in the range of 0.15 to 1.00.

According to a third aspect of the present invention, the compound phase of the negative electrode material made of the Si-based alloy for an electricity storage device according to the first or second aspect has at least one selected from the group consisting of Mg, B, P, and Ga. Elements, and a total content of 0.05 at. % To 3 at. % Negative electrode material comprising a Si-based alloy for power storage devices.

In the means of Claim 4 , in the electrode using the negative electrode material which consists of Si type alloys for electrical storage devices as described in any one of Claims 1-3 , a polyimide-type binder is included, Si for electrical storage devices characterized by the above-mentioned. It is a negative electrode made of an alloy.

In the alloy of the present invention, Cr is an essential element for generating Si ₂ Cr effective for the formation of a Si phase and a fine eutectic structure. Ti is substituted by Cr to increase the lattice constant of Si ₂ Cr, thereby improving lithium ion conductivity. Presumed to increase. Furthermore, when the crystallite size of the Si phase is 30 nm or less, and the crystallite size of the compound phase of Si and Cr, and the compound phase of Si, Cr and Ti is 40 nm or less, when lithium is occluded / released in Si It plays the role which relieves the stress caused by the volume expansion of silicon and prevents electrical isolation due to the pulverization of Si, and provides excellent charge / discharge cycle characteristics.

  Further, by controlling the chemical component of the Si-based alloy negative electrode material for an electricity storage device, excellent charge / discharge cycle characteristics can be obtained. The total content of Cr and Ti in the phase composed of Si and Cr or Si, Cr and Ti is 12 to 21 at. %, And Cr% / (Cr% + Ti%) is controlled within the range of 0.15 to 1.00.

Further, Si and Cr, Si and Cr and Ti samples of Si-based alloy negative electrode materials for power storage devices contain one or more additive elements such as Cu, V, Mn, Fe, Ni, Nb, Zn, and Al, and the total content is 0.00. 05at. % To 3 at. % And containing, by controlling the crystallite size, compound phase surrounds the periphery of the fine Si phase, the stress relieve occurring and pulverization of Si, the volume expansion at the time of occlusion and release of lithium to the Si, the electrode Plays a role in preventing the collapse of silicon and electrical isolation of Si. In an electrode using these Si-based alloy negative electrode materials for electricity storage devices, particularly when a polyimide binder having a high binding force is included, excellent battery characteristics are provided.

In addition, Si and Cr, Si and Cr and Ti samples of Si-based alloy negative electrode materials for power storage devices were used.
One or more additive elements such as g, B, P, and Ga, and the total amount is 0.05 at. % To 5 at. By controlling the crystallite size, the compound phase surrounds the periphery of the fine Si phase, and mitigates the stress caused by the pulverization of Si and the volume expansion at the time of insertion and extraction of lithium into and from the Si. It plays a role in preventing collapse and electrical isolation of Si. Also, by taking a P-type semiconductor structure by adding B, it plays a role of improving the electrical conductivity of Si. By taking an N-type semiconductor structure by adding P, it plays a role of improving the electrical conductivity of Si. In an electrode using these Si-based alloy negative electrode materials for electricity storage devices, particularly when a polyimide binder having a high binding force is included, excellent battery characteristics are provided.

As described above, the present invention has an extremely excellent effect of providing a Si-based alloy negative electrode material for an electricity storage device having a high capacity and excellent cycle characteristics during repeated charge / discharge.

Cross-sectional SEM image of the Si-Si ₂ Cr eutectic alloy is a diagram showing a. It is an XRD of Cr / Ti ratio Si-Si ₂ Cr eutectic alloy with varying. SEM images of Cr and the total amount of change in the Si-Si ₂ Cr eutectic alloy was of Ti is a diagram showing a. (A) When the total amount of Cr and Ti is 17%, (b) When the total amount of Cr and Ti is 19%

The present invention is described in detail below.
The charge / discharge capacity of a lithium ion secondary battery is determined by the amount of lithium transferred. There is a need for a material that can occlude and release large amounts of lithium. Therefore, although lithium metal is most effective when used as the negative electrode material, there are safety problems such as battery ignition caused by the formation of dendrites during charging and discharging. Therefore, studies on alloys that can occlude and release more lithium are currently underway, and among these alloys, Si is promising as a substance that can occlude and release lithium in large quantities. Therefore, Si is adopted as the main phase of the alloy phase.

  However, since Si causes volume expansion of about 400% when lithium is occluded / released, Si is peeled off or dropped from the electrode, or Si cannot maintain contact with the current collector. A sudden drop in capacity occurs. Also, if the Si phase size is too large, Si does not react with lithium up to the internal Si phase, but expands from the surface layer that easily reacts with lithium of Si, cracks occur, and then the internal unreacted Si phase expands. In addition, the Si is pulverized repeatedly such that cracks occur. As a result, Si peels off from the electrode, or Si cannot maintain contact with the current collector, resulting in a rapid decrease in charge / discharge capacity associated with the cycle.

A feature of the present invention is that Cr is used as an additive element for obtaining a eutectic alloy. FIG. 1 is a cross-sectional structure diagram of a Si—Si ₂ Cr eutectic alloy according to the present invention, taken by a scanning electron micrograph, wherein the black phase is the Si phase and the white phase is the Si ₂ Cr phase. As shown in FIG. 1, both the Si phase and the CrSi ₂ phase are extremely fine. In addition, compared with other elements, such as Fe and V, the following is estimated about the cause by which Cr addition becomes an extremely fine eutectic structure and is excellent also in a charge / discharge characteristic.

  The amount of added element necessary to obtain a eutectic of Si phase and silicide is determined by the kind of element. For example, 26.5% for Fe and 3% for V are necessary. These can be read from the phase diagrams of Si and additive elements. Here, when a relatively large amount of addition is required, such as Fe, in order to obtain a eutectic, the amount of silicide is inevitably increased and coarsening is likely, and the proportion of the Si phase that occludes / releases Li decreases. However, a high discharge capacity cannot be obtained.

On the other hand, when it becomes eutectic with an extremely small addition amount like V, the proportion of silicide in the eutectic structure is small, and the Si phase tends to be coarsened, and the volume change of the Si phase during charge / discharge The effect of the silicide to control is not obtained. On the other hand, Cr is added in the middle amount of eutectic, and it is considered that both the Si phase and the silicide become fine. Therefore, the Si—Si ₂ Cr eutectic alloy can have both a high discharge capacity and an excellent cycle life.

Moreover, the charge / discharge characteristics can be further improved by replacing a part of Cr with Ti. As a result of detailed examination of substituting Cr for Ti in the Si—Si ₂ Cr eutectic alloy, the inventor found that Ti was replaced by Cr in Si ₂ Cr, and the lattice constant was changed without changing its crystal structure. It was thought to increase.

FIG. 2 is a diagram showing X-ray diffraction of a Si—Si ₂ Cr eutectic alloy in which the Cr / Ti ratio is changed. As shown in this figure, by replacing a part of Cr with Ti, the diffraction peak position of Si ₂ Cr is shifted to the lower angle side without changing the crystal structure, and the lattice constant is increased. It is considered a thing.

The increase in the lattice constant of Si ₂ Cr due to Ti substitution into Cr in the present invention is presumed to play a role of smoothing the passage of Li in the silicide and reducing the volume change associated therewith. Thus, in the study of utilizing a eutectic alloy of Si and silicide as a negative electrode active material for a lithium ion battery, there has been almost no research so far that has gone into the structure of silicide.

In addition to the eutectic structure of Si and Cr, Si, Cr and Ti, the characteristics of the lithium ion secondary battery can be further improved by controlling the crystallite size. If the Si phase size is too large, Si does not react with lithium up to the internal Si phase, but expands from the surface layer that reacts easily with lithium of Si, cracks occur, and then the internal unreacted Si phase expands, Moreover, the pulverization of Si which repeats that a crack arises is caused. As a result, Si peels off from the electrode, or Si cannot maintain contact with the current collector, resulting in a rapid decrease in charge / discharge capacity associated with the cycle. For this reason, it is necessary to make the microstructure to a size that does not cause differentiation, and it is preferable to control the crystallite size of the Si phase of the negative electrode material for a lithium ion secondary battery to 30 nm or less. More preferably, it is 25 nm or less. In particular, it is preferably 10 nm or less.

  Control of the crystallite size of the Si phase is possible by controlling the cooling rate at the time of solidification after dissolving the raw material powder in addition to the control of the components defined above. Examples of the production method include water atomization, single-roll quenching method, twin-roll quenching method, gas atomization method, disk atomization method, and centrifugal atomization, but are not limited thereto. Further, when the cooling effect is insufficient in the above process, mechanical milling or the like can be performed. Examples of the milling method include a ball mill, a bead mill, a planetary ball mill, an attritor, and a vibration ball mill, but are not limited thereto.

Further, the Si crystallite size of the Si main phase can be directly observed by a transmission electron microscope (TEM). Alternatively, it can be confirmed by using powder X-ray diffraction. A CuKα ray having a wavelength of 1.54059 mm is used as an X-ray source, and measurement is performed in a range of 2θ = 20 degrees to 80 degrees. In the obtained diffraction spectrum, a relatively broad diffraction peak is observed as the crystallite size decreases. From the full width at half maximum of the peak obtained by powder X-ray diffraction analysis, it can be determined using the Scherrer equation (D (Å) = (K × λ) / (β × cos θ) D: crystallite size, K : Scherrer's constant, λ: wavelength of X-ray tube used, β: broadening of diffraction line depending on crystallite size, θ: diffraction angle).

In the crystallite size, not only the Si main phase but also the crystallite size of the intermetallic compound phase becomes important. By reducing the crystallite size of intermetallic compounds such as Si and Cr, Si and Cr and Ti, it is possible to increase the yield stress of the intermetallic compounds and improve ductility and toughness. When it is received, the occurrence of cracks and the like can be suppressed, and good ion conductivity and electron conductivity can be secured. Further, since the crystallite size of the intermetallic compound is reduced, it is possible to contact the Si phase with a larger specific surface area than to the larger particles, and to efficiently absorb and relax the stress due to the volume expansion and contraction of the Si phase. Furthermore, contact with the Si phase with a larger specific surface area is expected to increase the lithium ion conductivity and the electron conductivity path, and to perform a smoother charge / discharge reaction. Therefore, it is preferable to control the crystallite size to 40 nm or less. More preferably, it is 20 nm or less. In particular, it is preferably 10 nm or less.

The crystallite size of the intermetallic compound can also be directly observed with a transmission electron microscope (TEM). Alternatively, it can be confirmed by using powder X-ray diffraction. A CuKα ray having a wavelength of 1.54059 mm is used as an X-ray source, and measurement is performed in a range of 2θ = 20 degrees to 80 degrees. In the obtained diffraction spectrum, a relatively broad diffraction peak is observed as the crystallite size decreases. From the full width at half maximum of the peak obtained by powder X-ray diffraction analysis, it can be determined using the Scherrer equation (D (Å) = (K × λ) / (β × cos θ) D: crystallite size, K : Scherrer constant, λ: wavelength of X-ray tube used, β: broadening of diffraction line depending on crystallite size, θ: diffraction angle). The crystallite size of the intermetallic compound can be controlled by controlling the cooling rate during solidification after dissolving the raw material powder. Examples of the production method include water atomization, single-roll quenching method, twin-roll quenching method, gas atomization method, disk atomization method, and centrifugal atomization, but are not limited thereto. Further, when the cooling effect is insufficient in the above process, mechanical milling or the like can be performed. Examples of the milling method include a ball mill, a bead mill, a planetary ball mill, an attritor, and a vibration ball mill, but are not limited thereto.

Furthermore, although the detailed cause is unknown about the effect which substitutes a part of Cr to Ti, the following unexpected advantages were also discovered. The normal eutectic structure is a unique structure with a single additive element amount. If the added amount fluctuates back and forth, it becomes a hypoeutectic or hypereutectic alloy, and an extremely coarse primary crystal is crystallized. Therefore, a high production technique is required to obtain a eutectic structure strictly. However, in the alloy of the present invention in which a part of Cr is substituted with Ti, a fine structure is obtained in a wide range where the total of Cr and Ti is about 12 to 21%, and the amount added may fluctuate back and forth depending on the production lot. But there is no extreme organizational change. FIG. 3 is a cross-sectional structure diagram of a scanning electron micrograph of a Si—Si ₂ Cr eutectic alloy in which the total amount of Cr and Ti is changed. FIG. 3A shows a case where the total amount of Cr and Ti is 17%, and FIG. 3B shows a case where the total amount of Cr and Ti is 19%.

The reason why the total content of Cr and Ti is 12 to 21% (including the case where Ti is 0 at.%) And Cr% / (Cr% + Ti%) is in the range of 0.15 to 1.00. In the above, Cr is an essential element for generating Si ₂ Cr that forms a fine eutectic structure with the Si phase, and Ti is an effective element that substitutes for Cr and increases the lattice constant of Si ₂ Cr. If the total amount is less than 12%, it becomes a hypoeutectic structure and a coarse primary Si phase is crystallized. If it exceeds 21%, it becomes a hypereutectic structure and coarse Si ₂ Cr is crystallized, both of which have some influence on the cycle life. Effect. Further, the Cr% / (Cr% + Ti %) is Si ₂ Ti phase is produced in addition to the Si ₂ Cr phase is less than 0.15, to coarsen Si phase, some impact in the same manner as described above the cycle life . Therefore, the total range of Cr and Ti is preferably 13 to 20, more preferably 14 to 19. Moreover, the preferable range of Cr% / (Cr% + Ti%) was 0.15-0.90, More preferably, it was 0.20-0.80.

  Further, in the SixCry alloy that is an alloy of Si and Cr that forms an intermetallic compound, and the Six (Cr, Ti) y alloy that is an alloy of Cr and Ti, the composition of the Six (Cr, Ti) y phase is x> It must be y. The Si main phase indispensable for high capacity is crystallized when x> y, and preferably x = 2 and y = 1.

Further, regarding the negative electrode material for lithium ion secondary battery according to claim 1, a fine Si phase can be obtained by forming a eutectic alloy with Si in addition to Cr and Ti, and a metal that is more conductive and flexible than Si. One or more additive elements such as Cu, V, Mn, Fe, Ni, Nb, Zn, and Al forming an intermetallic compound can be further contained. By controlling the crystallite size of the intermetallic compound by adding these, the compound phase surrounds the periphery of the fine Si phase, relieving the stress caused by volumetric expansion when Si is pulverized and lithium is absorbed into and released from Si. And it plays the role which prevents the collapse of an electrode and the electrical isolation of Si.

  Further, regarding the negative electrode material for lithium ion secondary battery according to claim 1, a fine Si phase can be obtained by forming a eutectic alloy with Si in addition to Cr and Ti, and a metal that is more conductive and flexible than Si. One or more additive elements such as Mg, B, P, and Ga that form intermetallic compounds, with a total amount of 0.05 at. % To 5 at. By controlling the crystallite size, the compound phase surrounds the periphery of the fine Si phase, and mitigates the stress caused by the pulverization of Si and the volume expansion at the time of insertion and extraction of lithium into and from the Si. It plays a role in preventing collapse and electrical isolation of Si. Also, by taking a P-type semiconductor structure by adding B, it plays a role of improving the electrical conductivity of Si. By taking an N-type semiconductor structure by adding P, it plays a role of improving the electrical conductivity of Si.

In order to give the effect of reducing the effect of stress relaxation caused by the volume expansion and contraction of Si, the total content of Cu, V, Mn, Fe, Ni, Nb, Pd, Zn, and Al is 0.05 at. % Or more is necessary, but 5 at. If it exceeds 50%, the amount of lithium inactive elements increases, which causes a decrease in charge / discharge capacity. Therefore, the total content of additive elements contained at least one of Cu, V, Mn, Fe, Ni, Nb, Pd, Zn, and Al is 0.05 at. % To 3 at. % Is desirable. More preferably, 0.1 at. % To 3 at. %. In addition, for Co, Zr, Pd, Bi, In, Sb, Sn, and Mo aiming at the same effect, the total content of at least one additive element is set to 0.05 at. % To 5 at. % Is desirable.

  In order to give the effect of reducing the effect of stress relaxation caused by the volume expansion and contraction of Si, the total content of Mg, B, P, and Ga is 0.05 at. % Or more is necessary, but 5 at. If it exceeds 50%, the amount of lithium inactive elements increases, which causes a decrease in charge / discharge capacity. For this reason, the total content of additive elements contained at least one or more of Mg, B, P, and Ga is 0.05 at. % To 5 at. % Is desirable. More preferably, 0.1 at. % To 3 at. %. In addition, for Co, Zr, Pd, Bi, In, Sb, Sn, and Mo aiming at the same effect, the total content of at least one additional element is set to 0.05 at. % To 5 at. % Is desirable.

By using the above-mentioned lithium ion secondary battery negative electrode material, the battery characteristics are excellent in high capacity, excellent cycle characteristics during repeated charge / discharge, and excellent charge / discharge efficiency in the initial cycle.
In addition, in the electrode using the lithium ion secondary battery negative electrode material, by including a polyimide-based binder having excellent binding properties, the adhesion with a current collector such as Cu is improved, and charging and discharging are performed while maintaining a high capacity. The effect of improving cycle characteristics is expected.

Hereinafter, the present invention will be specifically described with reference to examples.
Negative electrode material powders for lithium ion secondary batteries having the compositions shown in Tables 1 and 2 were produced by a single roll quenching method, a gas atomizing method, or the like described below. For the liquid quenching method, which is a single roll quenching method, a raw material having a predetermined composition is placed in a quartz tube having pores at the bottom, melted at a high frequency in an Ar atmosphere to form a molten metal, and a copper roll that rotates this molten metal. After the hot water was discharged on the surface, a quenching ribbon was prepared in which the crystallite size of the Si phase was refined by the quenching effect of the copper roll. The milled ribbon is then sealed in an Ar atmosphere together with zirconia balls, SUS304 balls, or SUJ2 balls in a zirconia, SUS304, or SUJ2 pot container and milled for the purpose of processing into particles. It was. As for milling, a ball mill, a bead mill, a planetary ball mill, an attritor, a vibrating ball mill, and the like can be given.

  Regarding the gas atomization method, a raw material having a predetermined composition is placed in a quartz crucible having pores at the bottom, heated and melted in a high-frequency induction melting furnace in an Ar gas atmosphere, and then subjected to gas injection in an Ar gas atmosphere and a tapping hot water. Then, gas atomized fine powder was obtained by rapid solidification. In the disk atomization method, a raw material having a predetermined composition is placed in a quartz crucible having pores at the bottom, heated and melted in a high-frequency induction melting furnace in an Ar gas atmosphere, and then in an Ar gas atmosphere, 40000 to 60000 r. p. m. The hot water was discharged onto a rotating disk of No. 1 and rapidly solidified to obtain a disk atomized fine powder. Thereafter, the produced atomized fine powder is sealed in a zirconia or SUS304 / SUJ2 pot container together with zirconia balls, SUS304 balls, or SUJ2 balls in an Ar atmosphere, and powdered by mechanical milling to control the crystallite size. went. Examples of mechanical milling include a ball mill, a bead mill, a planetary ball mill, an attritor, and a vibrating ball mill. In the processing by mechanical milling, the crystallite size of the atomized powder and the intermetallic compound using rapid solidification can be controlled by setting the milling time and the number of rotations.

Hereinafter, a specific method for preparing a negative electrode will be described.
In order to evaluate the electrode performance of the negative electrode as a single electrode, a so-called bipolar coin-type cell using lithium metal as a counter electrode was used. First, a negative electrode active material (Si-Cr-Ti, etc.), a conductive material (acetylene black), a binder material (polyimide, polyvinylidene fluoride, etc.) are weighed with an electronic balance, and mixed with a dispersion (N-methylpyrrolidone). After making it into a state, it was uniformly applied on a current collector (Cu or the like). After coating, the solvent was evaporated by vacuum drying with a vacuum dryer, and then roll-pressed as necessary, and then punched into a shape suitable for the coin cell. Similarly, lithium for the counter electrode was punched into a shape suitable for the coin cell. In the vacuum drying of the slurry-coated electrode, when the polyimide binder material was used, it was dried at a temperature of 200 ° C. or more in order to fully exhibit performance. When using polyvinylidene fluoride or the like, it was dried at a temperature of about 160 ° C.

The electrolyte used for the lithium ion battery was a 3: 7 mixed solvent of ethylene carbonate and dimethyl carbonate, LiPF ₆ (lithium hexafluorophosphate) was used as the supporting electrolyte, and 1 mol was dissolved in the electrolyte. Since the electrolyte solution must be handled in an inert atmosphere with dew point control, the cells were all assembled in a glove box with an inert atmosphere. The separator was cut out in a shape suitable for a coin cell and then held in the electrolyte for several hours under reduced pressure in order to sufficiently permeate the electrolyte into the separator. Thereafter, the negative electrode punched out in the previous step, the separator, and the counter electrode lithium were combined in this order, and the inside of the battery was sufficiently filled with the electrolytic solution.

The measurement of charge capacity and discharge capacity was performed using the above-mentioned bipolar cell, at a temperature of 25 ° C., and charged at a current density of 0.50 mA / cm ² until the same potential (0 V) as that of the metal lithium electrode. At a current value (0.50 mA / cm ² ), discharging was performed up to 1.5 V, and this charging-discharging was defined as one cycle. In addition, as the cycle life, the above measurement was repeated.

As shown in Tables 1-2 , no. 1-24 are examples of the present invention, No. as shown in Table 2-4 25-93 shows a comparative example. These characteristics are determined by the initial discharge capacity and the discharge capacity maintenance rate after 50 cycles. The standard is that it is 1000 mAh / g or more and the cycle life is 60% or more [discharge capacity maintenance ratio (%) after 50 cycles].

No. of the example of the present invention. 4 to 24 include a Si main phase and a phase composed of Si and Cr, or Si, Cr and Ti. The Si main phase has a Si crystallite size of 30 nm or less, and is composed of Si and Cr, or Si, Cr and Ti. The crystallite size of the compound phase satisfies the condition of 40 nm or less. In addition, the total content of additive elements contained at least one or more of Cu, V, Mn, Fe, Ni, Nb, Zn, and Al is 0.05 at. % To 5 at. %. Further, the total content of additive elements contained in at least one of Mg, B, P, and Ga is 0.05 at. % To 5 at. %. The addition of trace amounts of Co, Zr, Pd, Bi, In, Sb, Sn and the like aiming at the same effect is also included.

For example, no. No. 8 contains Si main phase, Si, Cr, and Ti, the crystallite size of Si is 17 nm, and the condition that the crystallite size of Si is 30 nm or less is satisfied. And the crystallite size of the compound phase consisting of Si, Cr and Ti is 38 nm, and the crystallite size of the compound phase consisting of Si, Cr and Ti is 40 nm or less. In addition, 0.01 at. % Cu, 0.03 at. % V, 0.01 at. % Mn, 0.01 at. % Fe, 0.01 at. % Ni, 0.02 at. % Zn, 0.02 at. % Al is contained. In addition, 1.01 at. % Mg, 1.79 at. % B, 1.03 at. % P, 1.12 at. % Ga is contained. As described above, the conditions of the present invention were satisfied, the discharge capacity was 1179 mAh / g, the discharge capacity retention rate after 50 cycles was 80%, and both the charge / discharge capacity and the cycle life showed good characteristics.

Comparative Example No. Since 25 to 27 and 37 to 38 do not contain Cr, the conditions of the present invention are not satisfied. Comparative Example No. Since 28 to 30 and 39 do not contain Cr and do not satisfy the condition of the Si crystallite size of 30 nm or less, the conditions of the present invention are not satisfied. Comparative Example No. 31 to 33 and 40 satisfy the condition that the crystallite size of Si is 30 nm or less, but do not contain Cr and do not satisfy the condition of the present invention because the crystallite size of the compound phase does not satisfy the condition of 40 nm or less. Comparative Example No. 34 to 36 and 41 do not contain Cr, do not satisfy the condition of the Si crystallite size of 30 nm or less, and do not satisfy the condition of the crystallite size of the compound phase of 40 nm or less.

Comparative Example No. Nos. 42 to 59 include a phase composed of Si and Cr, or Si, Cr and Ti, and the crystallite size of the compound phase composed of Si and Cr or Si, Cr and Ti satisfies the condition of 40 nm or less. Since the Si crystallite size of the Si main phase does not satisfy the condition of 30 nm or less, the conditions of the present invention are not satisfied. Comparative Example No. 60 to 75 include a phase composed of Si and Cr or Si and Cr and Ti, and the Si crystallite size of the Si main phase satisfies the condition of 30 nm or less. However, Si and Cr, or Si and Cr Since the crystallite size of the compound phase composed of Ti does not satisfy the condition of 40 nm or less, the present invention condition is not satisfied. Comparative Example No. 76 to 93 include a phase composed of Si and Cr, or Si, Cr and Ti, but the Si crystallite size of the Si main phase does not satisfy the condition of 30 nm or less, and Si and Cr, or Si and Cr and Ti. Since the crystallite size of the compound phase consisting of does not satisfy the condition of 40 nm or less, the condition of the present invention is not satisfied.

As described above, refinement of the structure, control of components that enhance the excellent ion conductivity and electron conductivity, stress relaxation effect, control of the Si phase crystallite size, and further control of the crystallite size of the intermetallic compound phase By doing so, a smoother charge / discharge reaction can be performed, and charge / discharge cycle characteristics can be improved. Furthermore, by including a polyimide-based binder, it has high strength to withstand current stress due to volume expansion and contraction of Si, and has high charge / discharge capacity and excellent cycle life. It has an extremely excellent effect.


Patent Applicant Sanyo Special Steel Co., Ltd.
Attorney: Attorney Shiina

Claims (3)

A negative electrode material made of a Si-based alloy for an electricity storage device accompanied by movement of lithium ions during charge / discharge, wherein the negative electrode material made of the Si-based alloy is composed of a Si main phase made of Si and one or more elements other than Si and Si. And the compound phase has a phase comprising Si and Cr, or a phase composed of Si, Cr and Ti, and the Si main phase has a Si crystallite size of 30 nm or less, and , Si and Cr, or a compound phase composed of Si, Cr and Ti has a crystallite size of 40 nm or less, and Cu, V, Mn, Fe , Ni, Nb, Zn, Al, at least one element selected from the group consisting of Al, and a total content of 0.05 at. % To 3 at. % Der is,
The total content of Cr and Ti is 12 to 21 at. % And it is the ratio of Cr and Ti Cr% / (Cr% + Ti%) is negative electrode material composed of Si-based alloy for a power storage device, wherein the range der Rukoto of 0.15 to 1.00. The negative electrode material comprising the Si-based alloy for an electricity storage device according to claim 1 contains at least one element selected from the group consisting of Mg, B, P, and Ga, and the total content is 0. 05at. % To 5 at. % Negative electrode material comprising a Si-based alloy for power storage devices. The electrode using the negative electrode material which consists of Si type alloys for electrical storage devices described in Claim 1 or 2 WHEREIN: Polyimide type binder is included, The negative electrode which consists of Si type alloys for electrical storage devices characterized by the above-mentioned.