JP5030414B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to an improvement in the negative electrode of a nonaqueous electrolyte secondary battery, and provides a nonaqueous electrolyte secondary battery having a high electric capacity and excellent charge / discharge cycle characteristics.

Non-aqueous electrolyte secondary batteries are capable of realizing a high energy density at a high voltage, and thus many studies have been conducted. The positive electrode of the non-aqueous electrolyte secondary battery includes a transition metal oxide or a transition metal chalcogen compound such as LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , V ₂ O ₅ , Cr ₂ O ₅ , MnO ₂ , TiS ₂ , MoS. ₂ etc. are used. These have a layered or tunnel-like crystal structure through which lithium ions can enter and exit. On the other hand, the negative electrode has a relatively small capacity, but is capable of reversibly inserting and extracting lithium, and provides a battery with excellent cycle life and safety, so a carbon material is used. A lithium ion battery using a carbon material as a negative electrode has been put into practical use.

However, since the theoretical capacity of the graphite material is 372 mAh / g and the theoretical density is relatively small at 2.2 g / cm ³ , it is expected to use a metal material capable of realizing a higher capacity than the graphite material as the negative electrode. Has been. Among metal materials, especially Si has a high capacity of 4199 mAh / g (theoretical density 2.33 g / cm ³ ), and many researches and developments have been conducted.

  Si can realize a high-capacity negative electrode, but has an important problem in the charge / discharge cycle characteristics of the battery. This is because during the charge and discharge reactions, the expansion and contraction of Si are repeated with the insertion and removal of lithium, the contact resistance between the particles inside the negative electrode increases, and the current collection network deteriorates. It is a problem that arises. The deterioration of the current collection network is a main factor for shortening the charge / discharge cycle life.

  In response to the above problems, the negative electrode material includes a solid phase A and a solid phase B that are capable of reversibly occluding and releasing lithium and having different compositions, and at least a part of the solid phase A is covered with the solid phase B An alloy material has been proposed in which the solid phase A includes silicon, tin, zinc, and the like, and the solid phase B includes a group 2A element, a transition element, a group 2B element, a group 3B element, a group 4B element, and the like. Yes. Further, it has been proposed that the solid phase A is preferably in an amorphous or low crystalline state (Patent Documents 1 and 2).

  Further, from the viewpoint of improving the cycle life, it includes an A phase mainly composed of Si and a B phase containing a compound of a transition metal and Si, and at least one of the A phase and the B phase is amorphous or low crystalline. A negative electrode active material in a state has also been proposed (Patent Document 3).

  According to the above related art, cracks at the time of expansion and contraction of the alloy material can be greatly suppressed, and there is a certain effect in that the deterioration of the current collecting network, which is the main factor of cycle characteristic deterioration, can be suppressed. However, as a result of detailed studies, it has been clarified that in the case where rapid charge / discharge is performed with a large current, the related technique may not provide a sufficient effect for suppressing deterioration of cycle characteristics.

  Reducing the particle size of the negative electrode active material has also been studied. For example, Si powder having an average particle diameter of 1 to 100 nm (Patent Document 4), 0.1 to 2.5 μm (Patent Document 5), 1 nm to 200 nm (Patent Document 6), and 0.01 to 50 μm (Patent Document 7) Each has been proposed. By using the fine-particle negative electrode active material, the alloying of lithium and Si proceeds uniformly during charging, and the localization of the reaction is suppressed. Therefore, volume expansion due to alloying during charging and volume contraction during discharging can be reduced, and the negative electrode is less susceptible to distortion. As a result, it is considered that a stable charge / discharge cycle can be repeated.

  However, a general negative electrode is produced using a negative electrode mixture. For example, the negative electrode of a coin-type battery is obtained by pressure-molding a negative electrode mixture into a disk-shaped pellet. The negative electrode mixture includes a negative electrode active material that is responsible for an electrochemical reaction, a conductive material that supplements the electron conductivity in the negative electrode, and a binder that joins them together. When the average particle size of the active material is small, the density of the negative electrode obtained by molding the negative electrode mixture is small. Therefore, the energy density per unit volume is reduced and the battery capacity is also reduced.

  Moreover, since the irreversible capacity | capacitance of a battery will increase when the average particle diameter of an active material is small, battery capacity will become still smaller. When the particle size of the active material is small, the reactivity between the active material and moisture contained in the electrolyte is increased, and gas is easily generated. Therefore, it is disadvantageous for cycle characteristics and storage characteristics.

On the other hand, if the average particle diameter of the active material is increased in order to obtain a high-density negative electrode or suppress gas generation, the distribution of the active material in the negative electrode becomes non-uniform. Therefore, the insertion and removal of lithium during charging and discharging are not uniform in the electrode, which is disadvantageous for the cycle life of the battery.
US Pat. No. 6,090,505 JP 2004-103340 A JP 2004-335272 A JP 2003-109590 A JP 2004-185810 A Japanese Patent Laid-Open No. 2004-214055 JP 2000-36323 A

  The proposals in Patent Document 1, Patent Document 2, and Patent Document 3 have a problem when performing rapid charge / discharge with a large current. Further, the proposals in Patent Document 4, Patent Document 5, Patent Document 6, and Patent Document 7 have a problem in balance between capacity and cycle characteristics. In particular, when a negative electrode is produced by forming a negative electrode mixture into pellets, it is difficult to obtain a non-aqueous electrolyte secondary battery having a high capacity and excellent cycle characteristics.

  The present inventors have conducted intensive studies for optimizing the states of the A phase and the B phase from the viewpoint of sufficiently suppressing deterioration of cycle characteristics even when rapid charge / discharge is performed with a large current. As a result, in an alloy material including an A phase mainly composed of Si and a B phase composed of an intermetallic compound of a transition metal element and Si, the presence of the A phase and the B phase together with the size of crystallites (crystal grains). The inventors have obtained the knowledge that it is effective to optimize the proportions and the composition thereof, and have completed the present invention.

That is, the present invention is a nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte capable of reversibly occluding and releasing lithium, and the negative electrode is an alloy capable of electrochemically occluding and releasing Li. Material (alloy forming material), and the alloy material includes an A phase mainly composed of Si and a B phase composed of an intermetallic compound of a transition metal element and Si, and the transition metal elements include Ti, Zr, Ni The ratio of the A phase to the total weight of the A phase and the B phase, which is at least one selected from the group consisting of Cu and Fe, and the A phase is a microcrystalline region having a crystallite size of 5 nm to 50 nm However, it is related with the nonaqueous electrolyte secondary battery which is more than 40 weight% and 95 weight% or less.

  In addition, when X-ray diffraction measurement of an alloy material is performed using CuKα ray as a radiation source, observation is performed in a diffraction angle 2θ = 10 ° to 80 ° or a diffraction angle 2θ = 20 ° to 35 ° of the obtained diffraction spectrum. The full width at half maximum of the strongest diffraction peak is preferably 0.1 ° or more.

When the transition metal element is Ti, the content of Si contained in the alloy material is desirably 72.4 to 97.7% by weight.
When the transition metal element is Zr, the content of Si contained in the alloy material is desirably 62.8 to 96.9% by weight.
When the transition metal element is Ni, the content of Si contained in the alloy material is desirably 69.4 to 97.45% by weight.
When the transition metal element is Cu, the content of Si contained in the alloy material is desirably 68.2 to 97.35% by weight.
When the transition metal element is Fe, the content of Si contained in the alloy material is desirably 70 to 97.5% by weight.
If the Si content in the alloy material is within the above range, the A phase content in the alloy material is in the range of 40 to 95% by weight.
When the transition metal element is Ti, B phase desirably includes TiSi _2.

  The average particle size of the alloy material (median diameter of volume cumulative particle size distribution: D50) is preferably 0.5 to 20 μm. The 10% diameter (D10) and 90% diameter (D90) of the volume cumulative particle size distribution of the alloy material are preferably 0.1 to 5 μm and 5 to 80 μm, respectively.

  In particular, the present invention has a coin-type battery case including a positive electrode can and a negative electrode can, and the positive electrode and the negative electrode are each in a disk shape and are accommodated in the positive electrode can and the negative electrode can, and between the positive electrode and the negative electrode The present invention relates to a coin-type non-aqueous electrolyte secondary battery in which a separator is interposed and an open end of a positive electrode can and an open end of a negative electrode can are fitted via an insulating gasket.

The density of the negative electrode is preferably 1.6 to 2.4 g / cm ³ . Here, the density of the negative electrode is synonymous with the density of the molded negative electrode mixture. The negative electrode mixture includes an alloy material that is an active material as an essential component, and includes a conductive material and a binder as optional components. Moreover, it is preferable that the porosity of a negative electrode is 16 to 43%. The porosity of the negative electrode is synonymous with the porosity of the molded negative electrode mixture.

  The present invention also includes a step of producing a disc-shaped positive electrode including a positive electrode active material capable of electrochemically inserting and extracting Li, a disc-shaped positive electrode including a negative electrode active material capable of electrochemically storing and releasing Li A process for producing a negative electrode, and a process for producing a negative electrode, comprising the steps of: housing a positive electrode and a negative electrode together with a non-aqueous electrolyte in a coin-type battery case; a) A phase mainly composed of Si by applying shearing force to a raw material containing Si and at least one transition metal selected from the group consisting of Ti, Zr, Ni, Cu and Fe by a mechanical alloying method And a B phase composed of an intermetallic compound of a transition metal element and Si, wherein at least one of the A phase and the B phase is composed of a microcrystalline or amorphous region, and the total weight of the A phase and the B phase Of phase A (B) stirring the alloy material together with the ball-shaped medium to obtain an average particle size (median diameter of volume cumulative particle size distribution: D50). A powder having a volume cumulative particle size distribution of 10% diameter (D10) and 90% diameter (D90) of 0.1 to 5 μm and 5 to 80 μm, respectively, and (c) The present invention relates to a method for producing a non-aqueous electrolyte secondary battery including a step of pressure-molding the obtained powder into a disk shape.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the nonaqueous electrolyte secondary battery which is high capacity | capacitance, is excellent in charging / discharging cycling characteristics, and has the cycling characteristics outstanding also when performing especially rapid charging / discharging. In the alloy material having the above-described configuration, it is considered that a state in which the resistance of the alloy material with respect to expansion during charging is improved is achieved.

  When the content of the A phase in the alloy material is 40 to 95% by weight, an extremely high capacity is achieved, but the expansion rate during charging is considered to be considerably large. According to the said structure, even if such a big expansion | swelling arises, degradation of a current collection network is suppressed. In particular, when the B phase contains at least one selected from the group consisting of Ti, Zr, Ni, Cu and Fe, cracking during charging is unlikely to occur, and it is extremely excellent even when performing rapid charge / discharge. Cycle characteristics are achieved.

  It is desirable that the alloy material is sized to an appropriate particle size distribution. By using an alloy material having an appropriate particle size distribution, the active material distribution in the negative electrode becomes uniform. Therefore, the expansion and contraction of the negative electrode during charging / discharging become uniform, which is advantageous for the cycle life of the nonaqueous electrolyte secondary battery. Moreover, the negative electrode which has sufficient density (mixture density) can be obtained by using the alloy material which has appropriate particle size distribution. Therefore, it is advantageous for increasing the capacity of the nonaqueous electrolyte secondary battery.

  The alloy material capable of electrochemically inserting and extracting Li according to the present invention has characteristics different from those of conventional alloy materials. The alloy material according to the present invention includes an A phase mainly composed of Si and a B phase composed of an intermetallic compound of a transition metal element and Si. This alloy material not only mitigates the influence of expansion, but also suppresses the decrease in electronic conductivity of the negative electrode that accompanies the expansion and contraction. Therefore, the negative electrode for a non-aqueous electrolyte secondary battery of the present invention containing this alloy material provides a battery with high capacity and excellent cycle characteristics.

  The A phase is a phase responsible for insertion and extraction of Li, and is a phase that can electrochemically react with Li. The phase A may be a phase mainly composed of Si, but is preferably a phase composed of Si alone (is preferably Si single phase). When the A phase is composed of Si alone, the amount of Li absorbed and released by the alloy material per unit weight or unit volume can be made extremely large. However, since Si simple substance is a semiconductor, it has poor electronic conductivity. Therefore, it is effective to add a trace amount of additive elements such as phosphorus (P), boron (B), hydrogen (H), etc., or transition metal elements to the A phase up to about 5% by weight.

The B phase is composed of an intermetallic compound of a transition metal element and Si. The intermetallic compound containing Si has a high affinity with the A phase, and cracking at the interface between the A phase and the B phase is unlikely to occur even when the alloy volume expands during charging. The B phase has higher electron conductivity and higher hardness than the A phase mainly composed of Si. Therefore, the B phase works to supplement the low electronic conductivity of the A phase and to maintain the shape of the alloy particles against the expansion stress. There may be a plurality of B phases. That is, two or more types of intermetallic compounds having different compositions may exist as the B phase. For example, when the transition metal element is represented by M, MSi ₂ and MSi may be present in the alloy particles. Further, intermetallic compounds containing different transition metal elements, for example, M ¹ Si ₂ and M ² Si ₂ (M ¹ and M ² are different) may be present in the alloy particles.

A phase consists of fine crystal region. When a crystalline alloy material is used, the alloy particles are liable to crack with the occlusion of Li, and the current collecting property of the negative electrode is rapidly reduced, resulting in a deterioration in battery characteristics. On the other hand, in the case of using an alloy material of fine crystals, breakage of the alloy particles due to expansion caused by the occlusion of Li is less likely to occur.

Region of fine crystals constituting the A-phase, the size of crystallites (crystal grains) is 5nm or more 50nm or less. Crystallite size is greater than 100 nm, especially for 50nm larger field case, the grain boundary between crystallites is reduced, the effect of suppressing particle cracking is reduced. Moreover, when the crystallite size is less than 5 nm, the grain boundary between the crystallites increases, and the electron conductivity in the alloy material may decrease. When the electronic conductivity of the alloy material is reduced, the polarization of the negative electrode is increased, and the battery capacity may be reduced.

The states of the A phase and the B phase constituting the alloy material can be known by the following X-ray diffraction measurement.
First, a sample holder is filled with a sample of an alloy material to be measured so as not to have orientation in all directions. For example, the alloy material is filled into the sample holder without applying pressure. Specifically, after the alloy material is put into the sample holder, the upper surface of the alloy material is covered with a flat plate so that the alloy material does not spill out from the sample holder. Thereafter, fine vibration is applied to the sample holder so that the alloy material does not spill from the sample holder even if the flat plate is removed.

  For the measurement object, the alloy powder before producing the negative electrode may be used, or the mixture is collected from the negative electrode after producing the negative electrode, and the particles in the mixture are sufficiently separated with a mortar. Also good. Further, in the case of X-ray diffraction measurement, if the sample surface on which X-rays are incident is a flat surface and the surface is made to coincide with the rotational axis of the goniometer, the measurement error of the diffraction angle and intensity can be minimized.

For the sample prepared as described above, X-ray diffraction measurement is performed using CuKα as an X-ray source and a diffraction angle 2θ in the range of 10 ° to 80 °. It is determined whether or not there is a peak attributed to the crystal plane of the A phase and / or the B phase in the diffraction spectrum obtained at that time.

  For example, in the case of a phase composed of Si, a peak corresponding to the crystal plane (111) is observed at a diffraction angle 2θ = 28.4 °, reflecting the crystal plane of Si, and the crystal plane (220) is observed at 47.3 °. A corresponding peak is observed, a peak corresponding to the crystal plane (311) is observed at 56.1 °, a peak corresponding to the crystal plane (400) is observed at 69.1 °, and a crystal plane is observed at 76.4 °. A peak corresponding to (331) is observed. In addition, the peak corresponding to the crystal plane (111) observed at the diffraction angle 2θ = 28.4 ° often has the strongest intensity. However, when the phase is composed of a microcrystalline region, a sharp peak is not observed and a relatively broad peak is observed. On the other hand, when the alloy material is made of an amorphous region, a broad halo pattern in which the half width cannot be recognized is observed in the diffraction spectrum of the alloy particles obtained by the X-ray diffraction measurement.

  The crystallite size can be determined by X-ray diffraction measurement. Specifically, the half-value width of a peak attributed to each phase in the diffraction spectrum of alloy particles obtained by X-ray diffraction measurement can be obtained, and calculated from the half-value width and the following Scherrer equation. When there are a plurality of peaks attributed to each phase, the half width of the peak with the highest intensity is obtained, and the Scherrer formula is applied thereto.

According to Scherrer's equation, the crystallite size D is given by the following equation (1):
D (nm) = 0.9 × λ / (β × cos θ) (1)
Given in.
However, in formula (1), λ, β, and θ represent the following.
λ = X-ray wavelength (nm) (in the case of CuKα, 1.5405 nm)
β = half-width of the peak (rad)
θ = half of the peak angle 2θ (rad)

  Usually, the peak with the highest intensity in the range of the diffraction angle 2θ of 10 ° to 80 ° may be noticed, but the peak of the highest intensity in the range of the diffraction angle 2θ of 20 ° to 35 ° is more focused. preferable.

  When X-ray diffraction measurement of an alloy material is performed using CuKα ray as a radiation source, the diffraction angle of the obtained diffraction spectrum is observed in the range of 2θ = 10 ° to 80 ° or diffraction angle 2θ = 20 ° to 35 °. The half width of the strongest diffraction peak is preferably 0.09 ° or more. In this case, it can be determined that the crystallite size is 100 nm or less.

  In addition, the cross-section of the alloy material particles can be observed using an AFM (Atomic Force Microscope), TEM (Transmission Electron Microscope), etc., and the crystallite size can be directly measured. The abundance ratio (phase composition) of the A phase and the B phase in the alloy material can be measured using EDX (energy dispersive X-ray spectroscopy (EDS)) or the like.

In the alloy material, the proportion of the A phase in the total weight of the A phase and the B phase is more than 40% by weight and 95% by weight or less. By increasing the proportion of the A phase to more than 40% by weight, a high capacity can be effectively achieved. Further, by making the ratio of the A phase 95% by weight or less, the low electron conductivity of the A phase can be supplemented and the effect of maintaining the shape of the alloy material particles can be maintained high. It becomes easy to make quality. From the viewpoint of prominent these effects, the proportion of the A phase in the total weight of the A phase and the B phase is desirably 65% by weight or more and 85% by weight or less,
It is particularly preferable that the content is 70% by weight or more and 80% by weight or less.

  The transition metal element is at least one selected from the group consisting of Ti, Zr, Ni, Cu and Fe, and preferably at least one selected from the group consisting of Ti and Zr. These element silicides have higher electronic conductivity and higher hardness than silicides of other elements.

  The content of Si contained in the alloy material according to the present invention is preferably 60% by weight or more. When the proportion of Si in the entire alloy material is 60% by weight or more, when the transition metal and Si occupying the remainder form an intermetallic compound (silicide), the proportion of the A phase exceeds 40% by weight, High capacity can be effectively realized.

Hereinafter, preferable Si content is exemplified for each transition metal element.
When the transition metal element is Ti, the content of Si contained in the alloy material is desirably 72.4 to 97.7% by weight. In the case the transition metal element is Ti, B phase desirably includes TiSi _2.

When the transition metal element is Zr, the content of Si contained in the alloy material is desirably 62.8 to 96.9% by weight.
When the transition metal element is Ni, the content of Si contained in the alloy material is desirably 69.4 to 97.45% by weight.
When the transition metal element is Cu, the content of Si contained in the alloy material is desirably 68.2 to 97.35% by weight.
When the transition metal element is Fe, the content of Si contained in the alloy material is desirably 70 to 97.5% by weight.

  From the viewpoint of balance between capacity and cycle characteristics, the average particle size of the alloy material (median diameter of volume cumulative particle size distribution: D50) is preferably 0.5 to 20 μm, and particularly preferably 1 to 10 μm. When the average particle size exceeds 20 μm, the distribution of the active material in the negative electrode becomes non-uniform, and the negative electrode expands and contracts easily during charge and discharge. If the negative electrode expands and contracts unevenly, the current collecting property deteriorates, which may be disadvantageous for cycle characteristics. On the other hand, when the average particle size is less than 0.5 μm, it is difficult to increase the negative electrode density, and it may be disadvantageous for cycle characteristics.

  From the viewpoint of balance between capacity and cycle characteristics, the 10% diameter (D10) and 90% diameter (D90) of the volume cumulative particle size distribution of the alloy material are preferably 0.1 to 5 μm and 5 to 80 μm, respectively. More preferably, it is 0.2-1 micrometer and 10-50 micrometers, and it is especially preferable that they are 0.2-0.9 micrometer and 11-50 micrometers.

  The alloy material having the particle size distribution as described above is particularly suitable for producing a disc-shaped negative electrode used for a coin-type non-aqueous electrolyte secondary battery. The disc-shaped negative electrode is produced by pressure forming a negative electrode mixture containing an alloy material. The negative electrode mixture can contain, for example, a binder or a conductive material.

  In the alloy materials as described above, the dislocation movement accompanying the expansion of the A phase during the insertion of Li is dammed at the grain boundaries between the crystallites, so that it is considered that the occurrence of particle cracking is remarkably suppressed. In this way, by suppressing particle cracking of the alloy material contained in the negative electrode, a nonaqueous electrolyte secondary battery with little deterioration associated with the charge / discharge cycle can be obtained.

  Although the manufacturing method of the alloy material which concerns on this invention is not specifically limited, For example, the casting method, gas atomizing method, liquid other than the mechanical alloy method currently disclosed by the metal material utilization dictionary (Industry Research Council, 870 (1999)) etc. Examples thereof include a rapid cooling method, an ion beam sputtering method, a vacuum deposition method, a plating method, and a gas phase chemical reaction method. Among these, a mechanical alloy method in which a raw material containing Si and a raw material containing a transition metal element are mixed and mechanical alloying is performed in that the control of the crystallite state of each phase can be easily performed. Is particularly preferred.

  Moreover, before performing a mechanical alloying process, you may perform the process which fuse | melts the mixture of a raw material and quenches and solidifies a molten material. However, in order to efficiently give the compounding effect (refining of crystallites by mixing different elements) to the raw material containing Si, the raw material containing Si and the raw material containing the transition metal element are mixed from the beginning. And the mechanical alloy method which performs a mechanical alloying process is especially preferable.

Although it does not specifically limit as a raw material of an alloy material, For example, a simple substance, an alloy, a solid solution, an intermetallic compound etc. can be used.
The mechanical alloying method is a method for synthesizing alloy materials in a dry atmosphere. The alloy material obtained by the mechanical alloying method has a feature that the width of the particle size distribution is very large. Therefore, the obtained alloy material is preferably subjected to a sizing treatment for controlling the particle size distribution.

  Examples of the sizing treatment method include a classification method in which particles having a large particle diameter are removed from the alloy material by passing through a sieve having a predetermined mesh size. Another example is a sedimentation classification method that utilizes the fact that the sedimentation rate of solid particles in a fluid medium varies depending on the particle size. However, these classification methods have the disadvantage that particles outside the predetermined particle size range cannot be effectively used, which is disadvantageous in terms of cost.

  As a method of sizing treatment, it is preferable to perform a treatment of pulverizing the alloy material. The grinding technique has been used in various industrial fields for a long time. However, it is important to select an efficient grinding method according to the object to be ground. By manipulating the grinding conditions, it is possible to simultaneously perform (1) pulverization and particle size adjustment of aggregated particles, (2) mixing and dispersion of several types of particles, or (3) surface modification and activation of particles. It is.

  Examples of the apparatus used for mechanical alloying and grinding of alloy materials include an attritor, a vibration mill, a ball mill, a planetary ball mill, a bead mill, and a jet mill.

The pulverization methods can be roughly classified into dry pulverization and wet pulverization. In the present invention, either method may be used.
The advantages of dry pulverization are that the coefficient of friction is large and a pulverization effect several times that of wet pulverization can be obtained. The disadvantage of dry pulverization is that the alloy material easily adheres to the ball-shaped medium that is put in the pulverization container together with the alloy material or the wall surface of the pulverization container. Aggregation of the particles of the alloy material also occurs, so that pulverization is hindered and the width of the particle size distribution may be relatively wide.

  On the other hand, in the wet pulverization, a liquid such as water is added to the alloy material to form a slurry to pulverize the alloy material. Therefore, adhesion of the alloy material to the ball-shaped medium and the wall surface of the pulverization container hardly occurs. Further, since the alloy material is dispersed in the liquid, it is easy to narrow the width of the particle size distribution of the alloy material as compared with dry pulverization.

  When wet pulverization is performed, a ball mill type pulverizer having a simple structure can be used. In addition, media made of various materials can be easily obtained as ball-shaped media that can be placed in the pulverization container together with the alloy material. Since the alloy material is pulverized at the contact points between the ball-shaped media, the pulverization progresses uniformly in very many places.

  As described above, in preparing the alloy material, it is desirable to control the particle size distribution of the alloy material by, for example, wet pulverization using a ball mill after obtaining the alloy material by a dry mechanical alloying method. For example, it is desirable to prepare an alloy material by a dry mechanical alloying method using a vibration ball mill or the like, and then wet pulverize the obtained alloy material with a ball mill. According to wet pulverization using such a ball mill, the average particle size (D50) of the alloy material is 0.5 to 20 μm, the 10% diameter (D10) of the volume cumulative particle size distribution is 0.1 to 5 μm, and the volume cumulative particle size. The 90% diameter (D90) of the distribution can be adjusted to 5 to 80 μm.

  According to wet grinding, a thin surface oxide film that prevents oxidation of the alloy material is easily formed. In addition, according to wet pulverization, a surface oxide film is gently formed on the alloy material. Therefore, it is not necessary to strictly control the oxygen concentration in the atmosphere during pulverization. However, when performing wet pulverization, a solid-liquid separation process and a drying process for removing the liquid are required.

  The average particle size of the alloy material (median diameter of volume cumulative particle size distribution: D50), 10% diameter of volume cumulative particle size distribution (D10), and 90% diameter of volume cumulative particle size distribution (D90) use the laser scattering method. Can be measured with a particle size distribution meter. The particle size of the amorphous particles is represented by, for example, a circle equivalent diameter or a Feret diameter. The particle size distribution can be measured using a microtrack method or particle image analysis. Here, the equivalent circle diameter is the diameter of the equivalent circle, and the equivalent circle is a circle having the same area as the area of the orthographic image of the particle.

  The microtrack method is a method of irradiating an alloy material dispersed in a medium such as water with a laser beam and examining its diffraction state. According to the microtrack method, the average particle size (median diameter of volume cumulative particle size distribution: D50), 10% diameter of volume cumulative particle size distribution (D10) and 90% diameter of volume cumulative particle size distribution (D90) are all measured. Can do. In addition to the laser scattering method, the particle size distribution can also be obtained by image processing of an observation image of the alloy material by a scanning battery microscope (SEM).

  The negative electrode according to the present invention can contain a conductive agent as necessary in addition to the alloy material. Examples of the conductive agent include graphite such as natural graphite (flaky graphite etc.), artificial graphite, expanded graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black, carbon Examples thereof include conductive fibers such as fibers and metal fibers, metal powders such as copper powder and nickel powder, and organic conductive materials such as polyphenylene derivatives. These may be used alone or in combination. Among these, it is preferable to use graphites from the viewpoints of density, stability to the electrolytic solution, capacity, price, and the like.

  When the conductive agent is included in the negative electrode, the amount of the conductive agent is not particularly limited, but is preferably 1 to 50 parts by weight and particularly preferably 1 to 40 parts by weight with respect to 100 parts by weight of the alloy material. However, since the alloy material according to the present invention itself has electronic conductivity, it is possible to obtain a sufficiently conductive negative electrode without using a conductive agent.

  The negative electrode is prepared by mixing, for example, an alloy material, a conductive agent, a binder, and a dispersion medium, if necessary, to prepare a negative electrode mixture, which is molded or applied to a current collector, and then dried. If you can get.

  The binder is preferably a material that is electrochemically inactive to Li in the working potential range of the negative electrode and does not affect other substances as much as possible. For example, styrene-butadiene copolymer rubber, polyacrylic acid, polyethylene, polyurethane, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene, carboxymethylcellulose, methylcellulose and the like are suitable. Since the negative electrode used in the present invention has a large volume change during charging, styrene-butadiene copolymer rubber that can handle the volume change relatively flexibly, and polyacrylic acid that can easily maintain a strong binding state even when the volume changes Etc. are preferred. The amount of the binder added is preferably as large as possible from the viewpoint of maintaining the structure of the negative electrode, but is preferably as small as possible from the viewpoint of improving battery capacity and improving discharge characteristics.

  The non-aqueous electrolyte secondary battery of the present invention includes the above-described negative electrode, a positive electrode capable of electrochemically inserting and extracting Li, and a non-aqueous electrolyte. The nonaqueous electrolytic solution may be a gel electrolyte or a solid electrolyte, but in general, an electrolytic solution composed of a nonaqueous solvent and a solute dissolved therein is used.

  Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), cyclic carbonates such as vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl. Chain carbonates such as methyl carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate and ethyl propionate, and γ-lactones such as γ-butyrolactone 1, 2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), chain ethers such as ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethylsulfoxy 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphate triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl -2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, dimethyl sulfoxide, N-methylpyrrolidone, butyl diglyme, methyl tetraglyme And aprotic organic solvents such as γ-butyllactone. These are preferably used in combination.

Examples of the solute dissolved in the non-aqueous solvent include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, LiCl, LiBr, LiI, lithium chloroborane, lithium tetraphenylborate, imides and the like can be mentioned. These may be used alone or in combination. The amount of these solutes dissolved in the non-aqueous solvent is not particularly limited, but is preferably 0.2 to 2.0 mol / L, and more preferably 0.5 to 1.5 mol / L.

If a positive electrode is proposed as a positive electrode of a nonaqueous electrolyte secondary battery, it can be used without limitation. The positive electrode generally includes a positive electrode active material, a conductive agent, and a binder. Any positive electrode active material can be used without particular limitation as long as it is proposed as a positive electrode active material for a non-aqueous electrolyte secondary battery, but a lithium-containing transition metal compound is preferred. As a typical example of a lithium-containing transition metal compound,
_{Li x CoO 2, Li x NiO} 2, Li x MnO 2, Li x MnO 2, Li x Co y Ni 1-y O 2, Li x Co y M 1-y O z, Li x Ni 1-y M y O _z , Li _x Mn ₂ O ₄ , Li _x Mn _{2 -y My} O ₄ , LiCo _1-x Mg _x O ₂ , LiNi _1-y Co _y O ₂ , LiNi _1-yz Co _y Mn _z O _{2 and the} like, but are not limited thereto. In these lithium-containing transition metal compounds, M is selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. It is at least one, and x = 0 to 1.2, y = 0 to 0.9, and z = 2.0 to 2.3. Further, the x value increases / decreases due to charging / discharging of the battery. Further, transition metal chalcogenides, vanadium oxides and lithium compounds thereof, niobium oxides and lithium compounds thereof, conjugated polymers using organic conductive substances, chevrel phase compounds, and the like can also be used as the positive electrode active material. It is also possible to use a combination of a plurality of active materials.

  As the separator interposed between the positive electrode and the negative electrode, a microporous thin film having high ion permeability, predetermined mechanical strength, and electronic insulation is used. A microporous thin film made of a material such as polypropylene, polyethylene, polyphenylene sulfide, polyethylene terephthalate, polyamide, or polyimide is preferably used because of its excellent resistance to non-aqueous solvents and hydrophobicity. These materials may be used alone or in combination. From the viewpoint of manufacturing cost, it is advantageous to use inexpensive polypropylene or the like. In addition, when imparting reflow resistance to the battery, it is preferable to use polyethylene terephthalate, polyamide, polyimide or the like having a heat distortion temperature of 230 ° C. or higher. Further, a sheet made of glass fiber or the like, a nonwoven fabric, a woven fabric, or the like is also used. The thickness of the separator is generally 10 to 300 μm, and the porosity of the separator is determined according to electron conductivity, ion permeability, material, etc., but is generally 30 to 80%. Is desirable.

  The present invention can be applied to non-aqueous electrolyte secondary batteries having various shapes such as a cylindrical shape, a flat shape, a coin shape, and a square shape, and the shape of the battery is not particularly limited. INDUSTRIAL APPLICABILITY The present invention can be applied to batteries of various sealing forms, including batteries that contain power generation elements such as electrodes and electrolytes in metal battery cans and laminated film cases. Is not particularly limited. However, the present invention is particularly suitable for a coin-type non-aqueous electrolyte secondary battery. A coin-type non-aqueous electrolyte secondary battery has a coin-type battery case including a positive electrode can and a negative electrode can, and the positive electrode and the negative electrode are each in a disc shape and are accommodated in the positive electrode can and the negative electrode can. A separator is interposed between the positive electrode and the negative electrode. The open end of the positive electrode can and the open end of the negative electrode can are fitted via an insulating gasket, and the battery is sealed. The battery is sealed after the positive electrode, the negative electrode, and the separator are impregnated with a lithium ion conductive nonaqueous electrolyte.

  Next, the present invention will be specifically described based on examples and comparative examples. However, the following examples illustrate preferred modes of the present invention, and the present invention is not limited to the following examples. Absent.

Example 1
In Examples and Comparative Examples, negative electrodes and coin-type batteries were produced in the following manner, and their cycle life and discharge capacity were evaluated.
(1) Manufacture of alloy material As a raw material of the transition metal element M, Ti, Zr, Ni, Cu, and Fe were used in a metal state. All of these were powders having a purity of 99.9% and a particle size of 100 to 150 μm. Si powder (purity 99.9%, average particle size 3 μm) was used as a raw material for Si.

When it is assumed that MSi ₂ constitutes the B phase, the raw materials are mixed at the following weight ratio so that the ratio of the A phase to the total weight of the A phase and the B phase in the alloy material to be generated is about 80%. did.
Ti: Si = 9.2: 90.8
Zr: Si = 12.4: 87.6
Ni: Si = 10.2: 89.8
Cu: Si = 10.6: 89.4
Fe: Si = 10.2: 89.8

  3.5 kg of each mixed powder is weighed and put into a vibration mill apparatus (manufactured by Chuo Kako Co., Ltd., model number FV-20). Further, a stainless steel ball (diameter 2 cm) is added to 70% by volume of the mill apparatus internal capacity. It was thrown to occupy. After evacuating the inside of the container, Ar (purity 99.999%, manufactured by Nippon Oxygen Co., Ltd.) was introduced so that the pressure became 1 atm. Mechanical alloying operation was performed under these conditions. The operating conditions of the mill device were an amplitude of 8 mm and a rotation speed of 1200 rpm. Under these conditions, mechanical alloying operation was performed for 80 hours.

  The Ti—Si alloy material, Zr—Si alloy material, Ni—Si alloy material, Cu—Si alloy material and Fe—Si alloy material obtained by the above operation were recovered and the particle size distribution was examined. It was found to have a broad particle size distribution of ˜80 μm. By classifying these alloy materials with a sieve (10 μm mesh size), a Ti—Si alloy material (hereinafter referred to as alloy material a) having a maximum particle size of 8 μm and an average particle size of 5 μm, a Zr—Si alloy material (hereinafter referred to as an alloy). Material b), Ni—Si alloy material (hereinafter referred to as alloy material c), Cu—Si alloy material (hereinafter referred to as alloy material d) and Fe—Si alloy material (hereinafter referred to as alloy material e) were obtained.

  When the alloy a was analyzed by X-ray diffraction measurement using CuKα rays as a radiation source, a spectrum showing microcrystals was obtained. Further, in the diffraction spectrum obtained by X-ray diffraction measurement, the half-value width of the strongest diffraction peak observed in the diffraction angle range of 2θ = 10 ° to 80 ° and the alloy calculated based on the Scherrer equation The grain size of the crystal grains (crystallites) of the material a was 10 nm.

From the result of the X-ray diffraction measurement, it was presumed that the Si material phase (A phase) and the TiSi ₂ phase (B phase) exist in the alloy material a. Assuming that only these two phases exist in the alloy material a and calculating the abundance ratio of the Si simple phase and the TiSi ₂ phase, it was found that Si: TiSi ₂ = 80: 20 (weight ratio). .
Regarding the alloy material b, the alloy material c, the alloy material d, and the alloy material e, X-ray diffraction measurement was performed to obtain the crystallite size and the A phase: B phase (weight ratio). was gotten.

When the cross section of the alloy material a was observed with a transmission electron microscope (TEM), an Si region consisting of an amorphous region, crystal grains (crystallites) having a particle size of about 10 nm, and crystal grains having a particle size of about 15 to 20 nm It was found that each TiSi ₂ phase having (crystallites) was present. When the same measurement was performed on the alloy material b, the alloy material c, the alloy material d, and the alloy material e, the same result as that of the alloy material a was obtained.

  In this example, HRA (MODEL No. 9320-X100), which is a particle size distribution measuring device manufactured by Microtrack, was used for measurement of the maximum particle size and the average particle size of the alloy material. Before measuring the particle size, the alloy material was mixed with water and ultrasonic dispersion was performed for 180 seconds. The same applies to the following examples and comparative examples.

(2) Production of negative electrode Using the alloy materials a to e obtained above, graphite, and a binder, a negative electrode was produced in the following manner.
An alloy material, graphite (manufactured by Nippon Graphite Industry Co., Ltd., SP-5030), and polyacrylic acid as a binder (manufactured by Wako Pure Chemical Industries, Ltd., average molecular weight 150,000) in a weight ratio of 70. The mixture was mixed at a ratio of 5: 21.5: 7 to obtain a negative electrode mixture. This negative electrode mixture was formed into a pellet shape having a diameter of 4 mm and a thickness of 0.3 mm, and then the pellet-shaped negative electrode was dried at 200 ° C. for 12 hours. The thickness of the negative electrode after drying was 300 μm, the porosity was 26.6%, and the mixture density was 1.721 g / cm ³ . Hereinafter, the pellet-shaped negative electrodes produced using the alloy materials a to e are referred to as negative electrodes a to e, respectively.

(3) Production of positive electrode Manganese dioxide and lithium hydroxide were mixed at a molar ratio of 2: 1, and the mixture was fired at 400 ° C. for 12 hours in air to obtain lithium manganate.
The obtained lithium manganate, carbon black as a conductive agent, and fluororesin (polytetrafluoroethylene) as a binder are mixed at a weight ratio of 88: 6: 6 to obtain a positive electrode mixture. It was. The binder was used in the form of an aqueous dispersion. This positive electrode mixture was formed into a pellet shape having a diameter of 4 mm and a thickness of 1.0 mm, and then the pellet-shaped positive electrode was dried at 250 ° C. for 12 hours.

(4) Production of Coin Type Battery A coin type non-aqueous electrolyte secondary battery having an outer diameter of 6.8 mm and a thickness of 2.1 mm as shown in FIG. 1 was produced.
The positive electrode can 1 also serves as a positive electrode terminal and is made of stainless steel having excellent corrosion resistance. The negative electrode can 2 also serves as a negative electrode terminal and is made of the same stainless steel as the positive electrode can 1. The gasket 3 insulates the positive electrode can 1 and the negative electrode can 2 and is made of polypropylene. Pitch is applied to the surfaces where the positive electrode can 1 and the negative electrode can 2 and the gasket 3 are in contact. Carbon pastes 8 a and 8 b were applied to the inner surfaces of the positive electrode can 1 and the negative electrode can 2.

  The alloy material (active material) contained in the pellet-shaped negative electrode 5 needs to be alloyed with lithium. Therefore, at the time of battery assembly, the lithium foil 4 was pressure bonded to the surface of the pellet-shaped negative electrode 5 obtained above. After the battery assembly, in the presence of an electrolyte, the lithium foil 4 was electrochemically occluded in the negative electrode, and a lithium alloy was generated inside the negative electrode 5.

A separator 6 made of a non-woven fabric made of polyethylene was disposed between the positive electrode 7 and the negative electrode 5 obtained above. Hereinafter, the batteries prepared using the pellet-shaped negative electrodes a to e are referred to as batteries a to e, respectively. The design capacity of this battery is 6 mAh.
As an electrolyte, a mixed solvent containing propylene carbonate (PC), ethylene carbonate (EC), and dimethoxyethane (DME) at a volume ratio PC: EC: DME = 1: 1: 1, LiN (CF ₃ SO _{3 2) 2} was used as dissolved at a concentration of 1 mol / L.

(5) Battery evaluation In a thermostat set at 20 ° C., the batteries a to e were charged at a constant current of charge current 2C (1C is 1 hour rate current), discharge current 0.2C, and battery voltage 2 200 cycles were repeated in the range of 0.0 to 3.3V.

  At that time, the discharge capacity at the second cycle was determined as the initial discharge capacity. In addition, the ratio of the discharge capacity at the 200th cycle to the discharge capacity at the second cycle was obtained as a percentage (%), and was used as the capacity maintenance rate. The closer the capacity retention rate is to 100 (%), the better the cycle life. Table 1 shows the results of the initial discharge capacity and capacity retention rate.

<< Comparative Example 1 >>
As a raw material for the transition metal element M, Co and Mn in a metal state were used. All of these were powders having a purity of 99.9% and a particle size of 100 to 150 μm.

Si powder (purity 99.9%, average particle size 3 μm) was used as a raw material for Si.
When it is assumed that the B phase constitutes MSi ₂ , the raw materials are mixed at the following weight ratio so that the ratio of the A phase to the total weight of the A phase and the B phase in the alloy material to be generated is about 80%. did.

Co: Si = 10.2: 89.8
Mn: Si = 9.9: 90.1
The mechanical alloying operation of each mixed powder was performed under the same conditions as in Example 1, the same classification was performed, and a Co—Si alloy material (hereinafter referred to as alloy material f) having a maximum particle size of 8 μm and an average particle size of 5 μm and A Mn—Si alloy material (hereinafter referred to as alloy material g) was obtained. Further, using the alloy materials f and g, pellet-shaped negative electrodes f and g were produced in the same manner as in Example 1, and batteries f and g were produced and evaluated using these. The results are shown in Table 2.

  The batteries a to e of Example 1 had a higher capacity retention rate at the 200th cycle than the batteries f and g of Comparative Example 1, and were excellent in life characteristics when the cycle by rapid charge / discharge was repeated. .

  Although details are unknown, it is thought that the main factor of cycle characteristic deterioration is deterioration of the current collection network accompanying charging / discharging. That is, due to the expansion and contraction of the alloy material that occurs when lithium is inserted and extracted, the connection between the particles in the electrode is broken, the particles are separated and displaced, the current collection property is deteriorated, and the entire negative electrode It is thought that the resistance increases. Such deterioration becomes prominent when rapid charge / discharge due to a large current is repeated.

  On the other hand, in Example 1, since the tolerance of the alloy material with respect to the expansion | swelling at the time of charge is improving, it is thought that the above deterioration is suppressed. Further, when Tables 1 and 2 are compared, it can be seen that the resistance of the alloy material against expansion varies significantly depending on the type of transition metal. The alloy material containing Ti, Zr, Ni, Cu and Fe has higher electronic conductivity and higher hardness than the alloy material containing Co and Mn. It is thought that the resistance of the alloy material to the expansion of time is improved.

  However, even the battery of Comparative Example 1 exhibited sufficiently excellent cycle characteristics under normal charge / discharge cycle conditions (for example, charge / discharge with a current of 1 hour rate). Therefore, even when rapid charge / discharge is required, superior performance can be expected as compared with a battery using a conventional alloy material.

Example 2
In this example, the crystallite size of the alloy material was examined in detail.
A phase: B phase in the same manner as in Example 1 except that the crystallite size of the alloy material was changed as shown in Table 3 by changing the mechanical alloying operation conditions (frequency and synthesis time). Various alloy materials are manufactured and classified so that (weight ratio) is 80:20, and Ti—Si alloy material, Zr—Si alloy material, Ni—Si having a maximum particle size of 8 μm and an average particle size of 5 μm are obtained. Alloy materials, Cu-Si alloy materials and Fe-Si alloy materials were obtained.

Here, as in Example 1, the crystallite size of the A phase was calculated from the half-width of the peak with the highest intensity obtained by X-ray diffraction measurement of the alloy material and the Scherrer equation.
In Table 3, only the crystallite size of the A phase is shown, but the crystallite size of the B phase is equivalent to that of the A phase.

The conditions of the mechanical alloying operation were controlled as follows, for example.
When obtaining an alloy material having a crystallite size of 0 nm, the operating conditions were an amplitude of 8 mm, a rotational speed of 1200 rpm, and a synthesis time of 2000 hours. Here, the case where the X-ray diffraction spectrum shows an amorphous spectrum and no peak capable of recognizing the half-value width was observed was defined as a crystallite size of 0 nm.

When obtaining an alloy material having a crystallite size of about 5 nm, the operating conditions were an amplitude of 8 mm, a rotational speed of 1200 rpm, and a synthesis time of 300 hours.
When obtaining an alloy material having a crystallite size of 50 nm, the operating conditions were an amplitude of 8 mm, a rotational speed of 1200 rpm, and a synthesis time of 4 hours.
When obtaining an alloy material having a crystallite size of 100 nm, the operating conditions were an amplitude of 8 mm, a rotational speed of 1200 rpm, and a synthesis time of 1 hour.
When obtaining an alloy material having a crystallite size of about 200 nm, the operating conditions were an amplitude of 8 mm, a rotational speed of 1200 rpm, and a synthesis time of 0.3 hours.
A pellet-shaped negative electrode was prepared in the same manner as in Example 1 except that the above alloy material was used, and a battery was prepared and evaluated using these. The results are shown in Table 3.

  As is apparent from Table 3, when the crystallite size of the A phase is 100 nm or less, the capacity retention rate after 200 cycles is increased at a high capacity. When the crystallite size is larger than 100 nm, the alloy material is likely to be cracked due to expansion and contraction of the alloy material during charge / discharge, and the current collecting network is considered to be deteriorated. Further, when the crystallite size was smaller than 5 nm, the capacity tended to decrease although it was slight. When the crystallite size is excessively small, the grain boundaries of the crystallite increase, so that the electrical conductivity is lowered, the resistance during charging / discharging is increased, and the capacity is slightly decreased. Therefore, it is desirable that the crystallite size is 5 nm to 100 nm. Further, it was shown that when the crystallite size is 5 nm to 50 nm, the capacity retention rate after 200 cycles is higher and the capacity is also increased.

Example 3
In this example, in the diffraction spectrum obtained by the X-ray diffraction measurement of the alloy material when CuKα ray is used as the radiation source, the strongest diffraction peak observed in the range of diffraction angle 2θ = 10 ° to 80 °. The full width at half maximum was examined in detail.

  Here, the half-value width of the strongest diffraction peak was changed as shown in Table 4 by changing the mechanical alloying operation conditions (frequency and synthesis time), as in Example 1. A variety of alloy materials are manufactured and classified so that the A phase: B phase (weight ratio) is 80:20, and a Ti—Si alloy material having a maximum particle size of 8 μm and an average particle size of 5 μm, Zr—Si Alloy materials, Ni-Si alloy materials, Cu-Si alloy materials and Fe-Si alloy materials were obtained.

  In Table 4, only the half width of the peak attributed to the A phase is shown, but the half width of the peak attributed to the B phase is also equivalent to that of the A phase.

The conditions of the mechanical alloying operation were controlled as follows, for example.
When obtaining an alloy material having a half width of 0.05 °, the operating conditions were an amplitude of 8 mm, a rotation speed of 1200 rpm, and a synthesis time of 0.35 hours.
When obtaining an alloy material having a half width of 0.1 °, the operating conditions were an amplitude of 8 mm, a rotation speed of 1200 rpm, and a synthesis time of 1.3 hours.
When obtaining an alloy material having a half width of 0.4 °, the operating conditions were an amplitude of 8 mm, a rotational speed of 1200 rpm, and a synthesis time of 18 hours.
When obtaining an alloy material having a half width of 0.5 °, the operating conditions were an amplitude of 8 mm, a rotation speed of 1200 rpm, and a synthesis time of 27 hours.
When obtaining an alloy material having a half width of 1 °, the operating conditions were an amplitude of 8 mm, a rotation speed of 1200 rpm, and a synthesis time of 100 hours.
When obtaining an alloy material having a half width of 2 °, the operating conditions were an amplitude of 8 mm, a rotation speed of 1200 rpm, and a synthesis time of 380 hours.

  A pellet-shaped negative electrode was prepared in the same manner as in Example 1 except that the above alloy material was used, and a battery was prepared and evaluated using these. Table 4 shows the results of the capacity retention rate after 200 cycles.

  When the half width was 0.1 or more, it was found that the capacity retention rate after 200 cycles was high. On the other hand, when the half width is smaller than 0.1, the crystallinity of the alloy material is relatively high and it cannot be said that it is in a microcrystalline state. For this reason, it is considered that the alloy material cannot sufficiently follow expansion and contraction during charge and discharge, cracks occur in the alloy material particles, and the current collecting network of the negative electrode is impaired.

Example 4
In this example, the ratio of the A phase in the alloy material was examined in detail.
When it is assumed that the B phase constitutes MSi ₂ , the ratio of the A phase in the total weight of the A phase and the B phase in the alloy material to be generated is the ratio shown in Table 5 (30 to 98 wt%). Except that the raw materials were mixed, various alloy materials were produced and classified in the same manner as in Example 1, and Ti—Si alloy material, Zr—Si alloy material, Ni—Si alloy material having a maximum particle size of 8 μm and an average particle size of 5 μm, Ni -Si alloy material, Cu-Si alloy material and Fe-Si alloy material were obtained.

  When CuKα ray was used as a radiation source and each alloy material was analyzed by X-ray diffraction measurement, a spectrum showing microcrystals was obtained. Further, in the diffraction spectrum obtained by the X-ray diffraction measurement, each calculated based on the half-value width of the strongest diffraction peak observed in the diffraction angle range of 2θ = 10 ° to 80 ° and the Scherrer equation. The grain size of crystal grains (crystallites) of the alloy material was 10 nm.

  A pellet-shaped negative electrode was prepared in the same manner as in Example 1 except that the above alloy material was used, and a battery was prepared and evaluated using these. Table 5 shows the results of the capacity retention rate after 200 cycles.

  It was shown that the capacity retention rate after 200 cycles was high when the proportion of the A phase in the alloy material was less than 95% by weight. Further, it was shown that when the proportion of the A phase in the alloy material is smaller than 40% by weight, the battery has a small capacity. Therefore, it was shown that the ratio of the A phase in the alloy material is in the range of 40 wt% to 95 wt% in which the capacity and the cycle characteristics are balanced.

<< Comparative Example 2 >>
When it is assumed that the B phase constitutes MSi ₂ , the ratio of the A phase in the total weight of the A phase and the B phase in the alloy material to be generated is the ratio shown in Table 6 (30 to 98 wt%). Except that the raw materials were mixed, various alloy materials were produced and classified in the same manner as in Comparative Example 1 to obtain Co—Si alloy materials and Mn—Si alloy materials having a maximum particle size of 8 μm and an average particle size of 5 μm. It was.

  When CuKα ray was used as a radiation source and each alloy material was analyzed by X-ray diffraction measurement, a spectrum showing microcrystals was obtained. Further, in the diffraction spectrum obtained by the X-ray diffraction measurement, each calculated based on the half-value width of the strongest diffraction peak observed in the diffraction angle range of 2θ = 10 ° to 80 ° and the Scherrer equation. The grain size of crystal grains (crystallites) of the alloy material was 10 nm.

  A pellet-shaped negative electrode was prepared in the same manner as in Example 1 except that the above alloy material was used, and a battery was prepared and evaluated using these. Table 6 shows the results of the capacity retention rate after 200 cycles.

When Co or Mn was used as the transition metal element, it was shown that when the proportion of the A phase was larger than 40% by weight, the capacity was increased, but the capacity retention rate after 200 cycles was significantly decreased. .
When Co or Mn is used as the transition metal element, it is considered that the resistance of the alloy material against expansion during charging cannot be improved so much that cracking of alloy particles during charging cannot be sufficiently suppressed.

  However, even the battery of Comparative Example 2 exhibited sufficiently excellent cycle characteristics under normal charge / discharge cycle conditions (for example, charge / discharge with a current of 1 hour rate). Therefore, even when rapid charge / discharge is required, superior performance can be expected as compared with a battery using a conventional alloy material.

Example 5
In this example, regarding the case where the transition metal element contained in the B phase is Ti, the particle size distribution of the alloy material was examined.
A Ti—Si alloy material was obtained in the same manner as in Example 1 except that the raw materials were mixed so that the A phase: B phase (weight ratio) was 80:20. When the particle size distribution of the obtained alloy material was examined, the particle size was widely distributed in the range of 0.5 to 200 μm. The average particle size (D50) was 50 μm. Moreover, the grain size of the crystal grain (crystallite) of the obtained alloy material was 10 nm.

  The Ti—Si alloy material was sieve classified to obtain alloy materials having various particle size distributions shown in Table 1. Except for using these alloy materials, a pellet-shaped negative electrode was produced in the same manner as in Example 1, and a battery was produced using these, and evaluated in the same manner as in Example 1. The results are shown in Table 7.

  From Table 7, the average particle size (D50) in the volume cumulative particle size distribution is 0.5 to 20 μm, the 10% diameter (D10) is 0.1 to 5 μm, and the 90% diameter (D90) is 5 to 80 μm. In some cases, the battery has a high capacity, and excellent cycle characteristics (capacity retention ratio) can be obtained.

  As the average particle size of the alloy material increased, the battery capacity increased, but the capacity retention rate decreased. This is presumably because when the average particle size of the alloy material is increased, the distribution of the active material in the negative electrode becomes non-uniform, and the negative electrode expands and contracts during charge and discharge, thereby causing current collection deterioration. On the other hand, when the average particle size of the alloy material was decreased, the capacity retention rate was increased, but the battery capacity was decreased. This is presumably because the density of the negative electrode mixture decreased.

Example 6
In this example, the types of transition metal elements contained in the B phase of the alloy material having a preferable particle size distribution were examined. As the transition metal element, Ti, Zr, Ni, Cu, Fe, Co, and Mn were used as shown in Table 8.

  Ti-Si alloy material, Zr-Si alloy material, Ni-Si alloy material, Cu, as in Example 1, except that the raw materials were mixed so that the A phase: B phase (weight ratio) was 80:20. -Si alloy material, Fe-Si alloy material, Co-Si alloy material and Mn-Si alloy material were obtained. The grain size of crystal grains (crystallites) of the obtained alloy material was 10 nm.

  These alloy materials were sieve classified so as to have the particle size distribution shown in Table 8. The average particle size (D50) of all alloy materials was unified to 1 μm. Except for using these alloy materials, a pellet-shaped negative electrode was produced in the same manner as in Example 1, and a battery was produced using these, and evaluated in the same manner as in Example 1. In addition, regarding all the alloy materials, the porosity of the negative electrode was unified to 22%. The results are shown in Table 8.

  As Table 8 shows, all the batteries showed good initial discharge capacity. On the other hand, the capacity retention rate was low in batteries using Co and Mn as transition metal elements. The main factor of the deterioration of the cycle characteristics is the deterioration of the current collecting property due to charge / discharge. The deterioration of current collection occurs because the electrode structure changes due to expansion and contraction of the negative electrode accompanying charge / discharge, and the resistance of the entire negative electrode increases. Such a phenomenon is affected by the type of transition metal element constituting the alloy material. By appropriately selecting the transition metal element, the strength of the alloy material is considered to be in a state suitable for expansion and contraction during charging and discharging.

  When Ti, Zr, Ni, Cu and Fe are used as the transition metal elements, the capacity retention rate is good, especially when Ti and Zr are used, and when Ti is used, the capacity is most favorable. It was. This is presumably because the strength of the alloy material was moderate and cracking during charging was suppressed. Even when Co or Mn is used as the transition metal element, good characteristics may be obtained by improving the conductivity of the electrode material or improving the type and amount of the conductive material.

Example 7
In this example, the particle size distribution was controlled by wet-grinding the alloy material obtained by the mechanical alloying method. Ti was used as the transition metal element.
Specifically, the following operations were performed.
First, a Ti—Si alloy material was obtained in the same manner as in Example 1 except that the raw materials were mixed so that the A phase: B phase (weight ratio) was 80:20. The obtained alloy material had an average particle size (D50) of 50 μm, and the crystal grains (crystallites) had a particle size of 10 nm.

  This Ti—Si alloy material was pulverized by a wet ball mill to obtain alloy materials having various particle size distributions shown in Table 9. A zirconia ball having a diameter of 5 mm was used as a ball-shaped medium. A polyethylene 500 ml container was used as the grinding container. Along with 120 ml of n-butyl acetate, 200 g of an alloy material and 100 zirconia balls were placed in a pulverization vessel. The rotation speed of the ball mill was 120 rpm. The grinding time was varied according to the desired particle size distribution. Thereafter, n-butyl acetate was removed to recover the alloy material.

  The yield of the alloy material obtained by wet grinding is shown in Table 9 together with the case of sieving classification in Example 5.

  As Table 9 shows, the yield of the alloy material was greatly improved when wet pulverization was performed as compared with the case of sieve classification. Therefore, it is desirable to control the particle size distribution of the alloy material by stirring and pulverizing the alloy material together with a ball-shaped medium.

  Here, the yield is a value expressed as a percentage (%) of the ratio of the weight of the alloy material recovered after classification to the charged weight of the alloy material before classification (sieving classification or pulverization). The closer the yield is to 100, the better the production method.

  In the wet pulverization, the difference between D50 and D10 and the difference between D90 and D50 were smaller than in the case of sieve classification, and the width of the particle size distribution was narrowed. Therefore, wet pulverization is suitable for obtaining an alloy material having a narrow particle size distribution.

  In particular, the present invention provides a non-aqueous electrolyte secondary battery that is optimal as a main power source and a memory backup power source for various electronic devices such as mobile phones and digital cameras, and further requires a high electric capacity. The present invention also provides a non-aqueous electrolyte secondary battery suitable for applications that require excellent cycle characteristics even when performing rapid charge / discharge with a large current.

It is sectional drawing of the coin-type battery which is an example of the nonaqueous electrolyte secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode can 2 Negative electrode can 3 Gasket 4 Lithium foil 5 Negative electrode 6 Separator 7 Positive electrode 8a, 8b Carbon paste

Claims (12)

A non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte capable of reversibly inserting and extracting lithium,
The negative electrode includes an alloy material capable of electrochemically inserting and extracting Li,
The alloy material includes an A phase mainly composed of Si, and a B phase composed of an intermetallic compound of a transition metal element and Si,
The transition metal element is at least one selected from the group consisting of Ti, Zr, Ni, Cu and Fe;
The A phase consists of microcrystalline regions ,
The microcrystalline region has a crystallite size of 5 nm to 50 nm,
Before Symbol ratio of the A phase relative to the total weight of the A phase and the B phase, more than 40 wt%, 95 wt% or less, the non-aqueous electrolyte secondary battery.   In the diffraction spectrum obtained by X-ray diffraction measurement of the alloy material when CuKα ray is used as the radiation source, the half-value width of the strongest diffraction peak observed in the diffraction angle range of 2θ = 10 ° to 80 °. The nonaqueous electrolyte secondary battery according to claim 1, wherein is 0.1 ° or more.   In the diffraction spectrum obtained by X-ray diffraction measurement of the alloy material using CuKα ray as the radiation source, the half-value width of the strongest diffraction peak observed in the diffraction angle range of 2θ = 20 ° to 35 ° The nonaqueous electrolyte secondary battery according to claim 1, wherein is 0.1 ° or more.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the transition metal element is Ti, and the content of Si contained in the alloy material is 72.4 to 97.7% by weight.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the transition metal element is Zr, and the content of Si contained in the alloy material is 62.8 to 96.9 wt%.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the transition metal element is Ni and the content of Si contained in the alloy material is 69.4 to 97.45 wt%.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the transition metal element is Cu and the content of Si contained in the alloy material is 68.2 to 97.35 wt%.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the transition metal element is Fe, and the content of Si contained in the alloy material is 70 to 97.5 wt%. The non-aqueous electrolyte secondary battery according to claim 1, wherein the transition metal element is Ti and the B phase contains TiSi ₂ .   The alloy material has an average particle size (median diameter of volume cumulative particle size distribution: D50) of 0.5 to 20 μm, and 10% diameter (D10) and 90% diameter (D90) of volume cumulative particle size distribution are each 0. The nonaqueous electrolyte secondary battery according to claim 1, which has a thickness of 1 to 5 μm and 5 to 80 μm.   A coin-shaped battery case including a positive electrode can and a negative electrode can, wherein the positive electrode and the negative electrode are each in a disc shape and are accommodated in the positive electrode can and the negative electrode can, and between the positive electrode and the negative electrode The nonaqueous electrolyte secondary battery according to claim 1, wherein a separator is interposed, and the open end of the positive electrode can and the open end of the negative electrode can are fitted via an insulating gasket. The nonaqueous electrolyte secondary battery according to claim 11 , wherein the density of the negative electrode is 1.6 to 2.4 g / cm ³ .

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