JP6735060B2 - 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 having excellent conductivity in an electricity storage device such as a lithium-ion secondary battery, a hybrid capacitor, and an all-solid-state lithium-ion secondary battery that moves lithium ions during charging and discharging, and an electrode using the same. It is a thing.

2. Description of the Related Art In recent years, with the spread of mobile devices, high-performance secondary batteries centering on lithium-ion batteries have been actively developed. Further, a lithium-ion secondary battery and a hybrid capacitor in which its reaction mechanism is applied to the negative electrode have been actively developed as a stationary electric storage device for automobiles and homes. As a negative electrode material of such an electricity storage device, a carbonaceous material capable of inserting and extracting lithium ions, such as natural graphite, artificial graphite, or coke is used. However, since these carbonaceous materials intercalate lithium ions between the carbon faces, the theoretical capacity when used for the negative electrode is limited to 372 mAh/g, which is a new material replacing the carbonaceous material for the purpose of increasing the capacity. Is being actively explored.

On the other hand, Si has attracted attention as a material replacing carbonaceous materials. The reason is that Si can form a compound represented by Li22Si5 and can occlude a large amount of lithium, so that the capacity of the negative electrode can be significantly increased as compared with the case of using a carbonaceous material, and as a result, This is because it has the potential to increase the storage capacity of lithium-ion secondary batteries, hybrid capacitors, and all-solid-state batteries.

However, when Si is used alone as the negative electrode material, the Si phase is pulverized due to repeated expansion during alloying with lithium during charging and contraction during dealloying with lithium during discharging. However, there is a problem that the life of the electricity storage device is extremely short due to problems such as the loss of Si phase from the electrode substrate during use and the loss of electrical conductivity between Si phases.

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

As a method of solving such a drawback when using the Si phase as a negative electrode, a material in which at least a part of a parent lithium phase such as Si is surrounded by an intermetallic compound of Si and a metal represented by a transition metal, A manufacturing method thereof has been proposed, for example, in Japanese Patent Laid-Open No. 2001-297757 (Patent Document 1) and Japanese Patent Laid-Open No. 10-31804 (Patent Document 2).

Further, 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 does not alloy with lithium and a method for manufacturing the electrode are disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-228059. 3) and Japanese Patent 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 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 by a method such as Cu plating before or after the step of forming the active material containing the Si phase on the electrode. In addition, there is a problem in that it takes a lot of time and effort to control the coating film thickness industrially.
A material in which at least a part of the parent lithium phase such as Si is surrounded by the intermetallic compound is an industrially preferable process because the parent lithium phase and the intermetallic compound are formed during the solidification process after melting. However, there is a problem in that sufficient charge/discharge cycle characteristics cannot be obtained by itself.

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

In order to solve the above problems, as a result of intensive development by the inventors, as a result, the fineness of the structure, excellent ionic and electronic conductivity, control of the component system for enhancing the stress relaxation effect, and Si phase and By controlling the crystallite size of the intermetallic compound phase, the inventors have found a Si-based alloy negative electrode material that provides excellent battery characteristics.

Therefore, as a means for solving the problems of the present invention,
According to the means of claim 1, a negative electrode material made of a Si-based alloy for a power storage device, in which lithium ions move during charge and discharge, wherein the negative electrode material made of the Si-based alloy is a Si main phase made of Si and Si and Si. Other than the above, a compound phase composed of one or more elements other than the above, the compound phase having a phase containing a phase composed of Si and Cr, or Si, Cr and Ti, and the Si crystallite size of the Si main phase. Is 30 nm or less, and the crystallite size of the compound phase consisting of Si and Cr or Si, Cr and Ti is 40 nm or less, and the total content of Cr and Ti is 21.1 to 40 at. %, and Cr%/(Cr%+Ti%), which is the ratio of Cr to Ti, is in the range of 0.15 to 1.00, which is a negative electrode material made of a Si-based alloy for an electricity storage device.

According to a second aspect of the present invention, the compound phase of the negative electrode material comprising the Si-based alloy for an electricity storage device according to the first aspect is selected from the group consisting of Cu, V, Mn, Fe, Ni, Nb, Zn and Al. At least one element or more, and the total content is 0.05 at. % To 5 at. % Is a negative electrode material composed of a Si-based alloy for an electricity storage device.

According to a third aspect of the present invention, the compound phase of the negative electrode material comprising the Si-based alloy for an electricity storage device according to any one of the first and second aspects is selected from the group consisting of Mg, B, P and Ga. At least one element is contained, and the total content is 0.05 at. % To 5 at. %, a negative electrode material made of a Si-based alloy for a power storage device.

According to a fourth aspect of the present invention, in an electrode using the negative electrode material made of the Si-based alloy for an electricity storage device according to any one of claims 1 to 3, particularly for a electricity storage device, a polyimide binder is included. It is a negative electrode made of a Si-based alloy.

In the alloy of the present invention, Cr is an essential element that produces Si ₂ Cr that is effective in forming a fine eutectic structure with the Si phase, and Ti is replaced with Cr to increase the lattice constant of Si ₂ Cr and increase the lithium ion conductivity. It is supposed to increase. Furthermore, when the Si phase has a crystallite size of 30 nm or less, and the crystallite size of the compound phase of Si and Cr, or the compound phase of Si, Cr, and Ti is 40 nm or less, when lithium is absorbed or released into Si. It plays the role of relaxing the stress caused by the volume expansion of Si and preventing the electrical isolation due to the pulverization of Si, and excellent charge/discharge cycle characteristics can be obtained.

Further, by controlling the chemical composition of the Si-based alloy negative electrode material for the 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 21.1 to 40 at. %, and when Cr%/(Cr%+Ti%) is controlled in the range of 0.15 to 1.00, the effect is large.

In addition, Si and Cr of Si-based alloy negative electrode materials for power storage devices, and Si and Cr and Ti samples were Cu.
, V, Mn, Fe, Ni, Nb, Pd, Zn, Al, one or more additive elements in a total amount of 0.05 at. % To 5 at. %, and by controlling the crystallite size, the compound phase surrounds the periphery of the fine Si phase, relieves the stress caused by the pulverization of Si, the volume expansion when lithium is occluded and released into Si, and the electrode It plays a role in preventing collapse and electrical isolation of Si. In an electrode using these Si-based alloy negative electrode materials for power storage devices, particularly when a polyimide binder having a high binding force is included, excellent battery characteristics are provided.

In addition, Si and Cr or Si, Cr and Ti samples of the Si-based alloy negative electrode material for power storage devices were tested with M
g, B, P, Ga, one or more additive elements, with a total amount of 0.05 at. % To 5 at. %, and by controlling the crystallite size, the compound phase surrounds the periphery of the fine Si phase, relieves the stress caused by the pulverization of Si, the volume expansion when lithium is occluded and released into Si, and the electrode It plays a role in preventing collapse and electrical isolation of Si. Further, by taking a P-type semiconductor structure by adding B, it plays a role of improving the electric conductivity of Si. By taking an N-type semiconductor structure by adding P, it plays a role of improving the electric conductivity of Si. In an electrode using these Si-based alloy negative electrode materials for power 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, which has a high capacity and excellent cycle characteristics during repeated charge and 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.

The present invention will be described in detail below.
The charge/discharge capacity of the lithium-ion secondary battery is determined by the amount of transferred lithium. There is a need for a substance that can store and release a large amount of lithium. Therefore, it is most efficient to use lithium metal as the negative electrode material, but there is a problem in safety such as ignition of the battery caused by the formation of dendride due to charge and discharge. Therefore, research on alloys capable of absorbing and releasing a larger amount of lithium is currently underway, and among these alloys, Si is regarded as a promising substance capable of absorbing and releasing a large amount of lithium. Therefore, Si is adopted as the main phase of the alloy phase.

However, Si causes a volume expansion of about 400% when absorbing and releasing lithium, so that Si is separated and dropped from the electrode, and Si cannot maintain contact with the current collector, which results in charge and discharge accompanying the cycle. 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 of Si that easily reacts with lithium, cracks occur, and then the unreacted Si phase inside expands. In addition, Si is repeatedly pulverized, which causes cracks. As a result, Si peels off/falls off from the electrode, or Si cannot maintain contact with the current collector, so that the charge/discharge capacity rapidly decreases with the cycle.

A feature of the present invention is that Cr is used as an additional element for obtaining a eutectic alloy. FIG. 1 is a cross-sectional structural diagram of a eutectic alloy of Si—Si ₂ Cr according to the present invention, which is a scanning electron micrograph, and a black phase is a Si phase and a white phase is a Si ₂ Cr phase. As shown in FIG. 1, both the Si phase and the CrSi ₂ phase are extremely fine. In addition, as compared with other elements such as Fe and V, the reason why the addition of Cr has an extremely fine eutectic structure and is excellent in charge and discharge characteristics is presumed as follows.

The amount of the additional element required to obtain the eutectic of the Si phase and the silicide is determined by the kind of the element. For example, in the case of Fe, the addition amount is 26.5%, and in the case of V, the addition amount is 3%. All of these can be read from the phase diagram of Si and the additional element. Here, when a relatively large addition amount such as Fe is necessary to obtain a eutectic, the amount of silicide is inevitably increased and coarsens easily, and the ratio of the Si phase that absorbs and releases Li decreases. However, a high discharge capacity cannot be obtained.

On the other hand, in the case of forming an eutectic crystal with an extremely small addition amount such as V, the ratio of the silicide in the eutectic structure is small and the Si phase is inevitably coarsened, and the volume change of the Si phase at the time of charging and discharging. The effect of the silicide that controls the temperature cannot be obtained. On the other hand, the addition amount of Cr which becomes a eutectic is intermediate between these, and it is considered that both the Si phase and the silicide are fine. Therefore, Si-Si ₂ Cr eutectic alloy can combine a high discharge capacity and excellent cycle life.

Further, by substituting a part of Cr with Ti, the charge/discharge characteristics can be further improved. The inventor has conducted a detailed study of substituting Cr for Ti in a Si—Si ₂ Cr eutectic alloy, and as a result, Ti is replaced by Cr of Si ₂ Cr, and the lattice constant is 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 having a changed Cr/Ti ratio. 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. Thought to be a thing.

It is speculated that the increase in the lattice constant of Si ₂ Cr due to the substitution of Ti for Cr in the present invention may serve to smooth the passage of Li in the silicide and reduce the accompanying volume change. As described above, in the study of utilizing a eutectic alloy of Si and a silicide as a negative electrode active material for a lithium ion battery, almost no studies have been made to the structure of a silicide.

By controlling the crystallite size in addition to the eutectic structure of Si and Cr and Si, Cr and Ti, further improvement of lithium ion secondary battery characteristics is expected. If the Si phase size is too large, Si does not react with lithium up to the internal Si phase, and expands from the surface layer of Si that easily reacts with lithium, cracks occur, and then the unreacted Si phase inside expands. Further, Si is repeatedly pulverized, causing cracks to occur. As a result, Si peels off/falls off from the electrode, or Si cannot maintain contact with the current collector, so that the charge/discharge capacity rapidly decreases with the cycle. From this, it is necessary to form a fine structure to a size at which differentiation does not occur, and it is preferable to control the crystallite size of the Si phase of the lithium ion secondary battery negative electrode material to 30 nm or less. More preferably, the thickness is 25 nm or less. Particularly, it is preferable that the thickness is 10 nm or less.

The crystallite size of the Si phase can be controlled not only by controlling the components defined above, but also by controlling the cooling rate during solidification after melting the raw material powder. Examples of the manufacturing method include, but not limited to, water atomization, single roll quenching method, twin roll quenching method, gas atomizing method, disc atomizing method, and centrifugal atomizing method. If the cooling effect is insufficient in the above process, mechanical milling or the like can be performed. Milling methods include, but are not limited to, ball mills, bead mills, planetary ball mills, attritors, and vibrating ball mills.

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 1.54059Å is used as an X-ray source, and measurement is performed in the range of 2θ=20° to 80°. In the obtained diffraction spectrum, a relatively broad diffraction peak is observed as the crystallite size becomes smaller. From the full width at half maximum of the peak obtained by powder X-ray diffraction analysis, it can be obtained using Scherrer's formula (D(Å)=(K×λ)/(β×cos θ) D: crystallite size, K : Scherrer's constant, λ: wavelength of X-ray tube used, β: spread of diffraction line due to size of crystallite, θ: diffraction angle).

Regarding the crystallite size, not only the Si main phase but also the crystallite size of the intermetallic compound phase is important. By reducing the crystallite size of intermetallic compounds such as Si and Cr and Si, Cr and Ti, it is expected that the yield stress of the intermetallic compounds can be increased and the ductility and toughness can be improved. When received, it is possible to suppress the occurrence of cracks and the like, and ensure good ionic conductivity and electronic conductivity. Further, since the crystallite size of the intermetallic compound becomes smaller, the crystal particles come into contact with the Si phase with a larger specific surface area than that of large particles, and it is possible to efficiently absorb and relax the stress due to the volume expansion and contraction of the Si phase. Furthermore, by contacting the Si phase with a larger specific surface area, it is expected that lithium ion conductivity and electron conductivity paths will increase, and a smoother charge/discharge reaction will be performed. Therefore, it is preferable to control the crystallite size to 40 nm or less. More preferably, it is 20 nm or less. Particularly, it is preferable that the thickness is 10 nm or less.

The crystallite size of the intermetallic compound can also 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 1.54059Å is used as an X-ray source, and measurement is performed in the range of 2θ=20° to 80°. In the obtained diffraction spectrum, a relatively broad diffraction peak is observed as the crystallite size becomes smaller. From the full width at half maximum of the peak obtained by powder X-ray diffraction analysis, it can be obtained using Scherrer's formula (D(Å)=(K×λ)/(β×cos θ) D: crystallite size, K : Scherrer's constant, λ: wavelength of X-ray tube used, β: spread of diffraction line due to size of crystallite, θ: diffraction angle). The crystallite size of the intermetallic compound can be controlled by controlling the cooling rate during solidification after melting the raw material powder. Examples of the manufacturing method include, but not limited to, water atomization, single roll quenching method, twin roll quenching method, gas atomizing method, disc atomizing method, and centrifugal atomizing method. If the cooling effect is insufficient in the above process, mechanical milling or the like can be performed. Milling methods include, but are not limited to, ball mills, bead mills, planetary ball mills, attritors, and vibrating ball mills.

The reason why the total content of Cr and Ti is 21.1 to 40% (including the case where Ti is 0 at. %) and Cr%/(Cr%+Ti%) is within the range of 0.15 to 1.00 is In the invention alloy, Cr is an essential element that forms Si ₂ Cr that forms a eutectic structure with the Si phase, and Ti is an effective element that substitutes Cr and increases the lattice constant of Si ₂ Cr. Further, it is recognized that the Si compound phase compensates for the poor electrical and electronic conductivity of Si, and that the initial capacity reversibility is improved by Cr or Ti. If it is less than 21.1%, it is impossible for the Si compound phase to alleviate the volume expansion and contraction of Si during charge and discharge, resulting in electrical and electronic isolation of the active material in the electrode, resulting in remarkable cycle characteristics. to degrade. On the other hand, if it is 40% or more, the proportion of the Si phase that absorbs and releases Li decreases, and a high discharge capacity cannot be obtained. Therefore, by setting Cr and Ti to a total of 21.1 to 40%, the electric and electronic conductivity of the electrode is enhanced, and the amount of the Si compound phase that can suppress the stress due to the volume expansion and contraction of the Si phase during charge and discharge is secured. It becomes possible to do. In the total of Cr and Ti, the preferable range is 22 to 35, and more preferably 23 to 30. The preferable range of Cr%/(Cr%+Ti%) is 0.15 to 0.90, more preferably 0.20 to 0.80.

Further, in a SixCry alloy which is an alloy of Si and Cr forming an intermetallic compound and a Six(Cr,Ti)y alloy which is an alloy of Cr and Ti, the composition of the Six(Cr,Ti)y phase is x> It must be y. It is when x>y that the Si main phase, which is essential for high capacity, crystallizes out, and preferably x=2 and y=1.

In addition, regarding the negative electrode material for a lithium ion secondary battery according to claim 1, a eutectic alloy is formed with Si in addition to Cr and Ti to obtain a fine Si phase, and a metal having better conductivity and flexibility than Si. One or more additive elements such as Cu, V, Mn, Fe, Ni, Nb, Zn, and Al that form 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, and the stress caused by the pulverization of Si and the volume expansion at the time of inserting and extracting lithium into Si is relaxed. In addition, it plays a role of preventing the collapse of the electrode and the electrical isolation of Si.

Further, in the negative electrode material for a lithium ion secondary battery according to claim 1, a eutectic alloy is formed with Si other than Cr and Ti to obtain a fine Si phase, and a metal having better conductivity and flexibility than Si. One or more additive elements such as Mg, B, P, and Ga that form intermetallic compounds, and the total amount is 0.05 at. % To 5 at. %, and by controlling the crystallite size, the compound phase surrounds the periphery of the fine Si phase, relieves the stress caused by the pulverization of Si, the volume expansion when lithium is occluded and released into Si, and the electrode It plays a role in preventing collapse and electrical isolation of Si. Further, by taking a P-type semiconductor structure by adding B, it plays a role of improving the electric conductivity of Si. By taking an N-type semiconductor structure by adding P, it plays a role of improving the electric conductivity of Si.

In order to impart the effect of reducing the stress relaxation effect 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, but 5 at. If it exceeds %, the amount of lithium inactive element increases, which causes a decrease in charge/discharge capacity. Therefore, the total content of the additive elements contained in at least one of Cu, V, Mn, Fe, Ni, Nb, Pd, Zn, and Al is 0.05 at. % To 5 at. % Is desirable. More preferably 0.1 at. %-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 contained is 0.05 at. % To 5 at. It is desirable to set it as %.

In order to impart the effect of reducing the effect such as 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, but 5 at. If it exceeds %, the amount of lithium inactive element increases, which causes a decrease in charge/discharge capacity. Therefore, the total content of the additive elements contained in at least one of Mg, B, P, and Ga is 0.05 at. % To 5 at. % Is desirable. More preferably 0.1 at. %-3 at. %. In addition, for Co, Zr, Pd, Bi, In, Sb, Sn, and Mo aiming for the same effect, the total content of at least one additive element is 0.05 at. % To 5 at. It is desirable to set it as %.

By using the above-mentioned lithium ion secondary battery negative electrode material, a battery having high capacity and excellent cycle characteristics upon repeated charge/discharge and excellent charge/discharge efficiency at the beginning of the cycle is exhibited.
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 adhesiveness with a current collector such as Cu is enhanced, and charging/discharging while maintaining a high capacity. An 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 the single-roll quenching method, the gas atomizing method, etc. described below. Regarding 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 a pore at the bottom, high frequency melting is performed in an Ar atmosphere to form a molten metal, and the molten metal of a rotating copper roll is rotated. After tapping on the surface, a quenching ribbon was produced in which the crystallite size of the Si phase was miniaturized by the quenching effect of the copper roll. Then, the quenched ribbon was sealed in a zirconia, SUS304, or SUJ2 pot container together with zirconia balls, SUS304 balls, or SUJ2 balls in an Ar atmosphere, and milled for the purpose of processing into particles. It was Examples of the milling include a ball mill, a bead mill, a planetary ball mill, an attritor, a vibrating ball mill and the like.

Regarding the gas atomizing method, a raw material of a predetermined composition is placed in a quartz crucible having a pore in the bottom, heated and melted in a high-frequency induction melting furnace in an Ar gas atmosphere, and then gas is sprayed and tapped in an Ar gas atmosphere. Then, the gas atomized fine powder was obtained by rapid solidification. Regarding the disk atomization method, a raw material having a predetermined composition is put in a quartz crucible having a pore in the bottom, and is heated and melted in a high-frequency induction melting furnace in an Ar gas atmosphere, and then in an Ar gas atmosphere at 40,000 to 60,000 r. p. m. The molten metal was poured onto the rotating disk of No. 3 and rapidly solidified to obtain a disk atomized fine powder. Thereafter, the atomized fine powder produced was sealed in an Ar atmosphere together with zirconia balls or SUS304 balls and SUJ2 balls in a pot container made of zirconia or SUS304, SUJ2, and powdered by mechanical milling to control the crystallite size. went. Examples of mechanical milling include ball mills, bead mills, planetary ball mills, attritors, and vibration ball mills. In the processing by mechanical milling, the Si crystallite size of the atomized powder and the crystallite size of the intermetallic compound that utilize rapid solidification can be controlled by setting the milling time, the rotation speed, and the like.

Hereinafter, a specific method for producing a negative electrode will be described.
In order to evaluate the electrode performance of the above negative electrode in a single electrode, a so-called bipolar coin-type cell in which lithium metal was used 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 by an electronic balance, and mixed slurry with a dispersion liquid (N-methylpyrrolidone). After the state, it was evenly applied onto a current collector (such as Cu). After application, the solvent was evaporated under reduced pressure with a vacuum drier to evaporate the solvent, followed by roll pressing if necessary, and then punching into a shape suitable for the coin cell. Similarly, for the lithium of the counter electrode, a metal lithium foil 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 higher in order to exert its performance sufficiently. 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, and LiPF ₆ (lithium hexafluorophosphate) was used as the supporting electrolyte, and 1 mol was dissolved in the electrolyte. Since the electrolytic solution needs to be handled in an inert atmosphere with dew point control, all the cells were assembled in a glove box in an inert atmosphere. The separator was cut into a shape suitable for the coin cell and then kept in the electrolytic solution under reduced pressure for several hours in order to allow the electrolytic solution to sufficiently penetrate into the separator. After that, the negative electrode punched out in the previous step, the separator, and the counter electrode lithium were assembled in this order, and the inside of the battery was sufficiently filled with the electrolytic solution.

To measure the charge capacity and the discharge capacity, the bipolar cell was used, the temperature was 25° C., the charge was performed at a current density of 0.50 mA/cm ² until the potential (0 V) equivalent to that of the metal lithium electrode was obtained, and the same. At a current value (0.50 mA/cm ² ), discharging was performed up to 1.5 V, and this charging-discharging was set as one cycle. As the cycle life, the above measurement was repeated.

No. 1 of the present invention example. 1 to 12 include a Si main phase and a phase composed of Si, Cr and Ti, the crystallite size of Si is 30 nm or less, and the crystallite size of the compound phase composed of Si, Cr and Ti satisfies 40 nm or less. doing.

Inventive Example No. In No. 4, the main phase of Si, Si, Cr, and Ti are included, the crystallite size of Si is 3 nm, and the condition that the crystallite size of Si is 30 nm or less is satisfied. In addition, the crystallite size of the compound phase composed of Si, Cr and Ti is 31 nm, and the condition that the crystallite size of the compound phase composed of Si, Cr and Ti is 40 nm or less is satisfied. Further, as described above, the conditions of the present invention were satisfied, the initial discharge capacity was 789 mAh/g, the discharge capacity retention ratio after 50 cycles was 92%, and both the charge and discharge capacity and the cycle life showed good characteristics.

No. 1 of the present invention example. Nos. 13 to 18 include a Si main phase and a phase composed of Si and Cr, the crystallite size of Si is 30 nm or less, and the crystallite size of the compound phase composed of Si and Cr is 40 nm or less.

Inventive Example No. 14 contains Si main phase and Si and Cr, and the crystallite size of Si is 5n.
m, which satisfies the condition that the crystallite size of Si is 30 nm or less. In addition, the crystallite size of the compound phase composed of Si and Cr is 14 nm, and the condition that the crystallite size of the compound phase composed of Si and Cr is 40 nm or less is satisfied. Further, as described above, the conditions of the present invention were satisfied, the discharge capacity was 989 mAh/g, the discharge capacity retention rate after 50 cycles was 83%, and both the charge and discharge capacity and the cycle life showed good characteristics.

No. 1 of the present invention example. 19 to 24 include a Si main phase and a phase composed of Si, Cr, and Ti, the crystallite size of Si is 30 nm or less, and the crystallite size of the compound phase composed of Si, Cr, and Ti satisfies the condition of 40 nm or less. doing.

Inventive Example No. In No. 23, the main phase of Si, Si, Cr and Ti are contained, the crystallite size of Si is 9 nm, and the condition of the crystallite size of Si is 30 nm or less is satisfied. The crystallite size of the compound phase composed of Si, Cr and Ti is 15 nm, and the crystallite size of the compound phase composed of Si, Cr and Ti is 40 nm or less. Further, as described above, the conditions of the present invention were satisfied, the discharge capacity was 674 mAh/g, the discharge capacity retention ratio after 50 cycles was 84%, and good characteristics were shown in both charge and discharge capacity and cycle life.

No. 1 of the invention example . Nos. 25 to 48 include a Si main phase and 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 is 30 nm or less and 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. Further, the total content of the additive elements contained in at least one or more of Cu, V, Mn, Fe, Ni, Nb, Zn, and Al is 0.05 at. % To 5 at. %. Moreover, the total content of the additive elements contained in at least one or more of Mg, B, P, and Ga is 0.05 at. % To 5 at. %. It also includes trace additions of Co, Zr, Pd, Bi, In, Sb, Sn and the like aiming at the same effect.

For example, No. In No. 39, the main phase of Si, Si, Cr, and Ti are included, the crystallite size of Si is 15 nm, and the condition of the crystallite size of Si is 30 nm or less is satisfied. In addition, the crystallite size of the compound phase composed of Si, Cr and Ti is 32 nm, and the condition that the crystallite size of the compound phase composed of Si, Cr and Ti is 40 nm or less is satisfied. 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 included. In addition, 0.01 at. % Co, 0.14 at. % Bi, 0.15 at. % In, 0.15 at. % Sb, 0.15 at. % Sn is included. As described above, the conditions of the present invention were satisfied, the discharge capacity was 1079 mAh/g, the discharge capacity retention ratio after 50 cycles was 85%, and both the charge and discharge capacity and the cycle life showed good characteristics.

For example, Comparative Example No. No. 81, the total content of Cr and Ti was 21.1 to 40 at. %, and the ratio of Cr to Ti, Cr%/(Cr%+Ti%), is not in the range of 0.15 to 1.00, and the condition of Si crystallite size of 30 nm or less is not satisfied. Therefore, the conditions of the present invention are not satisfied. Comparative Example No. 106, the total content of Cr and Ti is 21.1 to 40 at. %, the ratio of Cr and Ti, Cr%/(Cr%+Ti%), is not in the range of 0.15 to 1.00, and the condition of Si crystallite size of 30 nm or less is not satisfied. The condition of the present invention is not satisfied because the condition that the crystallite size of the compound phase is 40 nm or less is not satisfied.

As described above, the composition is refined, the components that enhance the excellent ionic conductivity and electronic conductivity, and the stress relaxation effect are controlled, the Si phase crystallite size is controlled, and the crystallite size of the intermetallic compound phase is also controlled. By doing so, a smoother charge/discharge reaction can be carried out, and the charge/discharge cycle characteristics can be improved. Further, by including a polyimide-based binder, the adhesion with the current collector such as Cu is enhanced, and the strength that can withstand the stress due to the volume expansion and contraction of Si also has a high charge/discharge capacity and an excellent cycle life. It has an extremely excellent effect.


Patent applicant Sanyo Special Steel Co., Ltd.
Attorney Attorney Shiina Akira

Claims (4)

A negative electrode material made of a Si-based alloy for an electricity storage device in which lithium ions move during charge and discharge, wherein the negative electrode material made of the Si-based alloy is composed of a Si main phase made of Si and Si and one or more elements other than Si. And a compound phase having a phase including Si and Cr or a phase including Si, Cr and Ti, and the Si crystallite size of the Si main phase is 30 nm or less, and , Si and Cr or the compound phase consisting of Si, Cr and Ti has a crystallite size of 40 nm or less, and the total content of Cr and Ti is 21.1 to 40 at. %, and Cr%/(Cr%+Ti%), which is the ratio of Cr and Ti, is in the range of 0.15 to 1.00, wherein the negative electrode material is made of a Si-based alloy for an electricity storage device. At least one element selected from the group consisting of Cu, V, Mn, Fe, Ni, Nb, Zn, and Al is added to the compound phase of the negative electrode material made of the Si-based alloy for an electricity storage device according to claim 1. Including the total content of 0.05 at. % To 5 at. %, a negative electrode material made of a Si-based alloy for a power storage device. The at least 1 type or more element selected from the group which consists of Mg, B, P, Ga is contained in the said compound phase of the negative electrode material which consists of Si type alloys for electrical storage devices as described in any one of Claims 1-2. , A total content of 0.05 at. % To 5 at. %, a negative electrode material made of a Si-based alloy for a power storage device. Any electrode odor using the anode material consisting of Si-based alloy for a power storage device as described in one of claims 1 to 3 Te, a negative electrode comprising a Si-based alloy for an electricity storage device which comprises a polyimide-based binder ..

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