JP2004311429A - Electrode material for lithium secondary battery, electrode structure having the electrode material, and secondary battery having the electrode structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode material and an electrode for a lithium secondary battery exhibiting high lithium insertion/elimination efficiency. <P>SOLUTION: The electrode material for a lithium secondary battery comprises a particle 100 of an alloy containing silicon as a main component. The composition of the alloy is determined by a type of an element and an atomic ratio allowing component to completely melt together into a melted liquid state of the alloy. The alloy in a solid state comprises a phase selected from the group composed of a pure metal and a solid solution. The alloy particle 100 has a micro-structure in which microcrystalline or amorphous elements 102, 103 other than silicon are dispersed in microcrystalline silicon or amorphized silicon. A silicon content in the silicon alloy is not less than 50 wt.% and not more than 95 wt.%, and the silicon alloy is in the form of a fine particle. Further, the electrode material for a lithium secondary battery comprises silicon particles or silicon alloy particles wherein the silicon is doped with at least one element selected from a group composed of boron, aluminum, and gallium as a dopant in an atomic ratio of 10<SP>-8</SP>to 10<SP>-1</SP>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrode material for a lithium secondary battery comprising particles containing silicon as a main component, an electrode structure having the electrode material, and a secondary battery having the electrode structure.

  Recently, since the amount of CO2 gas contained in the atmosphere is increasing, it has been pointed out that global warming may occur due to the greenhouse effect. Thermal power plants convert thermal energy obtained by burning fossil fuels and the like into electric energy. However, it is difficult to construct a new thermal power plant because a large amount of CO2 gas is emitted by combustion. I have. Therefore, as an effective use of power generated by generators such as thermal power plants, surplus nighttime power is stored in secondary batteries installed in ordinary households and used during daytime when power consumption is high. A so-called load leveling has been proposed.

  In addition, development of a secondary battery with a high energy density is expected for electric vehicles having a feature of not emitting substances related to air pollution including COx, NOx, hydrocarbons and the like. Furthermore, in the power supply application of portable devices such as a book-type personal computer, a video camera, a digital camera, a mobile phone, and a PDA (Personal Digital Assistant), there is an urgent need to develop a small, lightweight, and high-performance secondary battery.

  Such a small, lightweight and high-performance secondary battery is formed by using a lithium intercalation compound that deintercalates lithium ions from the interlayer in the reaction during charging as a positive electrode material and lithium ions as carbon atoms. The so-called "lithium ion battery" of the rocking chair type using a carbon material typified by graphite that can be intercalated between layers of a six-membered ring network plane as the negative electrode material has been developed and put into practical use and generally used. ing.

  However, in this "lithium ion battery", the negative electrode composed of a carbon material can theoretically intercalate only a maximum of 1/6 lithium atoms per carbon atom. A secondary battery with a high energy density comparable to a primary battery cannot be realized.

  If, during charging, an attempt is made to intercalate a stoichiometric amount of lithium into the negative electrode made of carbon in a “lithium ion battery” or if the battery is charged under conditions of high current density, lithium metal is dendritic on the surface of the carbon negative electrode. It grows in a (dendritic) shape and may eventually lead to an internal short circuit between the negative electrode and the positive electrode due to repeated charge / discharge cycles. A "lithium-ion battery" exceeding the theoretical capacity of the graphite negative electrode has sufficient cycle life. Not been.

  On the other hand, a high-capacity lithium secondary battery using metallic lithium as a negative electrode has attracted attention as a secondary battery having a high energy density, but has not been put to practical use.

  The reason is that the charge / discharge cycle life is extremely short. The main cause of the extremely short charge / discharge cycle life is that metallic lithium reacts with impurities such as moisture in the electrolyte and organic solvents to form an insulating film, or the surface of the metallic lithium foil is not flat and the electric field concentrates It is considered that there is a point, and as a result, lithium metal grows in a dendrite shape due to repetition of charge / discharge, causing an internal short circuit between the negative electrode and the positive electrode to reach a life.

  A method of using a lithium alloy composed of lithium, aluminum, or the like for the negative electrode in order to suppress the progress of the reaction between lithium metal and water or an organic solvent in the electrolytic solution, which is a problem of a secondary battery using the above-described metal lithium anode. Has been proposed.

  However, in this case, since the lithium alloy is hard and cannot be wound in a spiral shape, a spiral cylindrical battery cannot be manufactured, the cycle life cannot be sufficiently extended, and the energy is comparable to that of a battery using metallic lithium for the negative electrode. At present, it has not been put to practical use in a wide range because of insufficient density and the like.

  By the way, in order to solve the above-mentioned problems, conventionally, as a secondary battery using a negative electrode for a lithium secondary battery made of silicon or tin, US Pat. No. 6,051,340, US Pat. No. 5,795,679, US Pat. No. 283627, Japanese Patent Application Laid-Open No. 2000-31681, and WO00 / 17948 have been proposed.

  Here, in U.S. Pat. No. 6,051,340, an electrode layer formed of a metal that alloys with lithium of silicon or tin and a metal that does not alloy with lithium of nickel or copper are formed on a current collector made of a metal material that does not alloy with lithium. A lithium secondary battery using the formed negative electrode has been proposed.

U.S. Pat. No. 5,795,679 discloses a lithium secondary battery using a negative electrode formed from an alloy powder of an element such as nickel or copper and an element such as tin. In U.S. Pat. No. 6,432,585, an electrode material layer has an average particle diameter of 0.5. Lithium secondary battery using a negative electrode having a particle size of silicon or tin of 35 to 60 μm in an amount of 35% by weight or more, a porosity of 0.10 to 0.86, and a density of 1.00 to 6.56 g / cm ³ Has been proposed.

  JP-A-11-283627 discloses a lithium secondary battery using a negative electrode having silicon or tin having an amorphous phase, and JP-A-2000-31681 discloses an amorphous tin having a non-stoichiometric composition. -A lithium secondary battery using a negative electrode made of transition metal alloy particles, and WO00 / 17948 proposes a lithium secondary battery using a negative electrode made of non-stoichiometric amorphous silicon-transition metal alloy particles. ing.

  However, in the lithium secondary batteries according to the above proposals, the efficiency of the amount of electricity associated with the release of lithium with respect to the amount of electricity associated with the first lithium insertion has not been obtained to the same level as that of the graphite anode, and the efficiency has been further improved. Was expected. Further, since the electrode of the lithium secondary battery proposed above has a higher resistance than the graphite electrode, it has been desired to reduce the resistance.

  In Japanese Patent Application Laid-Open No. 2000-21587, a metal layer or a metalloid capable of forming a lithium alloy, particularly, a carbon layer is formed on the surface of silicon particles by a chemical vapor deposition method of thermal decomposition such as benzene to improve conductivity. Thus, a lithium secondary battery having a high capacity and a high charge / discharge efficiency has been proposed, by suppressing volume expansion upon alloying with lithium to prevent electrode destruction.

However, in such a lithium secondary battery, while the theoretical storage capacity calculated from Li _4.4 Si as a compound of silicon and lithium is 4200 mAh / g, the amount of electricity exceeding 1000 mAh / g The development of a negative electrode having a high capacity and a long life has not been achieved yet because of the electrode performance that allows lithium insertion and desorption.

  Therefore, the present invention has been made in view of the above circumstances, a low resistance and high charge and discharge efficiency, a high capacity electrode material for a lithium secondary battery, an electrode structure having the electrode material, and It is an object of the present invention to provide a secondary battery having an electrode structure.

  The present invention provides an electrode material for a lithium secondary battery comprising particles of a solid-state silicon alloy containing silicon as a main component, wherein the particles of the solid-state alloy are contained in microcrystalline silicon or amorphous silicon. It is characterized in that microcrystals or amorphous materials composed of elements other than silicon are dispersed. Here, the solid state alloy preferably contains a pure metal or a solid solution. The composition of the alloy is preferably an elemental composition that completely dissolves in a liquid state in which the alloy is molten (an elemental composition that does not become two or more phases in a molten state (becomes a uniform phase)). Here, the element composition can be determined by the types of the elements constituting the alloy and the atomic ratio of those elements.

The present invention also provides an electrode material for a lithium secondary battery comprising silicon particles containing silicon as a main component, wherein the silicon contains one or more dopants selected from the group consisting of boron, aluminum, gallium, antimony, and phosphorus. Is doped in an atomic ratio of 1 × 10 ⁻⁸ to 2 × 10 ⁻¹ .

  According to the present invention, the silicon and the elements other than silicon constituting the silicon alloy become a homogeneous solution in a molten state, the crystallization of the intermetallic compound of silicon is small, and by selecting an element composition that includes a eutectic, Microstructured silicon alloy particles in which microcrystals or amorphous elements other than silicon are dispersed in microcrystalline silicon or amorphous silicon can be manufactured.

  By forming an electrode structure using a low-resistance, high charge-discharge efficiency, high-capacity electrode material for a lithium secondary battery formed by doping boron or the like into such a microstructured silicon alloy fine powder, The electrode structure is capable of repeatedly storing and releasing a large amount of lithium with high efficiency. Further, by using this electrode structure as a negative electrode to form a lithium secondary battery, a high capacity and high energy density secondary battery can be obtained. Can be made.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

  The present inventors investigated the relationship between the amount of insertion and desorption electricity of lithium and the potential of insertion and desorption of lithium in the following experiment.

  That is, a mixture of high-purity silicon, p-type silicon powder doped with boron, n-type silicon powder doped with phosphorus or antimony, graphite powder as a conductive auxiliary material, and a binder is coated on a copper foil. An electrode (silicon electrode) prepared by the above process was mixed with lithium metal as a counter electrode, and ethylene carbonate and diethyl carbonate as electrolytes in a volume ratio of 3: 7, and an organic solvent obtained by mixing 1 M of a salt of LiPF6 ( Using the dissolved electrolyte solution, the amount of electricity (the amount of lithium insertion / desorption electricity) associated with the insertion / desorption of lithium electrochemically to the silicon electrode was measured.

  As a result, in both highly doped n-type silicon and p-type silicon, the amount of insertion and desorption electricity of lithium and the desorption efficiency for insertion are large, the potential change with respect to lithium for insertion and desorption of lithium is small, and the amount of electricity during lithium desorption is small. The potential curve was flatter. In addition, it was found that the electric capacity and potential can be controlled to some extent by selecting the type and the doping amount of the dopant. Since highly doped silicon has low resistance, it has high electron conductivity, and when an electrode is formed from this silicon, it is considered that the electrode itself has low electric resistance and the electrochemical reaction proceeds smoothly.

  In addition, in the electrochemical repetition of the insertion and desorption of lithium, the boron particles doped with the silicon particles did not cause much reduction in the amount of lithium inserted and desorbed, and lithium was able to be stably inserted and extracted.

This is because
(I) Since p-type dopant atoms such as boron atoms replacing silicon atoms are ionized negatively, they do not hinder the insertion of lithium atoms that emit electrons and are easily ionized positively,
(Ii) doping silicon with a p-type dopant reduces the specific resistance of silicon and the resistance of the electrode;
Is mentioned.

  Here, FIG. 2 is a schematic diagram showing a reaction in which lithium is electrochemically inserted into a crystal of silicon. FIG. 2A shows a case of intrinsic semiconductor silicon containing no impurity atoms. It is. (It actually contains some impurity element.)

  FIG. 2B shows a case of p-type silicon doped with boron as an impurity atom. In this case, an attractive force acts between a lithium atom that is easily ionized to positive and a boron atom that is ionized to negative. Is expected, and it is assumed that insertion of lithium ions is easy.

  FIG. 2C shows the case of n-type silicon doped with phosphorus as an impurity atom. In this case, a repulsive force acts between a positively ionizable lithium atom and a positively ionized phosphorus atom. It is assumed that insertion of lithium ions is not easy.

  Also, the above results indicate that when p-type silicon, particularly boron-doped silicon, is used for the material of the negative electrode of the lithium secondary battery, the resistance of the negative electrode may of course be reduced and the insertion reaction of lithium ions may be easier. .

Here, the doping amount of the p-type dopant and the n-type dopant is preferably in a range in which the resistance of the electrode used in the lithium secondary battery is reduced and the storage capacity is increased. The range is preferably ^{−8 to} 2 × 10 ⁻¹ , more preferably 1 × 10 ⁻⁵ to 1 × 10 ⁻¹ . It is also preferable to simultaneously dope the p-type dopant and the n-type dopant from the viewpoint of reducing the resistance.

  In addition, aluminum and gallium are also effective as the p-type dopant, but boron having a small ionic radius is more preferable. Further, doping of boron, particularly addition of boron exceeding the solid solution limit, has an effect of facilitating amorphousization. Therefore, when particles or alloys containing boron-containing silicon as a main component are used as the negative electrode material of the lithium secondary battery, an electrode having a long repetitive life can be manufactured.

  Furthermore, the present inventors examined the amount of electricity, its efficiency, and the expansion rate of the electrode when electrochemical lithium insertion and desorption were repeatedly performed on the electrode using silicon alloy particles as the electrode material. As a result, when the distribution of elements in the alloy particles is less biased and the silicon crystal particles are smaller, a higher amount of lithium insertion / desorption electricity can be obtained, and the repetition of lithium insertion / desorption can be performed stably. It has been found that an electrode having a low expansion coefficient can be manufactured.

Further, as a preferred embodiment of the present invention, in order to reduce the deviation of the element distribution in the silicon alloy particles to be less uniform and to make the crystal grains of silicon smaller.
(1) A uniform solution of silicon and elements other than silicon constituting the silicon alloy in a molten state.
(2) The silicon alloy contains a eutectic,
(Note that this eutectic is a eutectic of silicon and a first element A described later, a eutectic of silicon and a second element E described later, and a eutectic of the first element A and the second element E. Including these combinations),
(3) less crystallization of intermetallic compounds formed between silicon and elements other than silicon constituting the silicon alloy;
It has been found that it is effective to produce a silicon alloy having such an element composition.

  Here, since the composition near the eutectic point tends to be amorphized easily, it is preferable in the present invention to employ a composition near the eutectic point.

  In addition, when an intermetallic compound is formed between silicon and an element other than silicon, the intrinsic ability of silicon to accumulate lithium decreases. Therefore, the alloy particles constituting the electrode material of the present invention preferably contain a pure metal or a solid solution. This is because a pure metal or a solid solution is considered to be superior to an intermetallic compound in lithium insertion and desorption. Of course, the existence of the intermetallic compound of silicon in the alloy is not denied, but it is preferable that the ratio of the intermetallic compound of silicon is 0 or smaller. In the preferred alloy particles used in the present invention, the pure metal and the solid solution may coexist, or one or both of the pure metal and the solid solution and the intermetallic compound may coexist.

  The content of silicon in the silicon alloy is preferably 50% by weight or more and 95% by weight or less, and more preferably 53% by weight or more in order to exhibit a high power storage performance as a negative electrode material of a lithium secondary battery. Is more preferably 90% by weight or less.

  Furthermore, in addition to the alloy composition of the above composition, silicon alloy particles having an average particle diameter of preferably 0.02 μm to 5 μm, more preferably 0.05 μm to 3 μm, and most preferably 0.1 μm to 1 μm Alternatively, it has been found that pulverization and further amorphousization of the silicon alloy are effective for obtaining the desired performance.

  Here, the term “amorphization” refers to a crystal structure having an amorphous phase. In the observation of a lattice image of the crystal with a high-resolution transmission electron microscope, in the case of a structure including this amorphous phase, a stripe is formed. A part where a pattern is not observed is recognized. The crystallite size of the silicon alloy particles as observed by transmission electron microscopy during amorphization is preferably in the range of 10 nm to 100 nm, more preferably in the range of 5 nm to 50 nm.

  By micronizing or pulverizing and / or amorphizing the silicon alloy having the above composition, the microstructure of the silicon alloy is changed into microcrystalline or amorphous silicon in a microcrystalline silicon or amorphous silicon. A structure in which quality is dispersed can be obtained. Here, “fine powder” is an aggregate of “fine particles”. Although silicon can electrochemically move a lot of lithium in and out, by reducing the crystallites of silicon, the insertion and desorption reactions of lithium can be made uniform, and the volume expansion and contraction due to repeated insertion and desorption can be made uniform. , Resulting in a longer cycle life.

  FIG. 1 schematically illustrates the cross-sectional structure of the finely divided and amorphized silicon alloy particles of the present invention. In FIGS. 1A and 1B, 100 denotes silicon alloy particles, 101 is a group of microcrystallized or amorphized silicon crystals, 102 is a group of microcrystallized or amorphized crystals of the first element A (other than silicon) contained in the silicon alloy, and 103 is silicon This is a group of microcrystallized or amorphous crystals of the second element E (other than silicon) contained in the alloy.

  That is, the silicon alloy particles 100 of FIG. 1A are alloy particles composed of at least a silicon element and the first element A, and the silicon alloy particles 100 of FIG. The alloy particles are composed of one element A and the second element E.

  Then, by forming a silicon alloy having an elemental composition according to (1) described above, solidification can be performed from a uniformly mixed molten liquid. However, when the difference between the melting point of the first element and the melting point of silicon, which is the second main component after silicon, is large, for example, when the first element is tin, even if the molten liquid is rapidly cooled, Tin having a low melting point segregates at the silicon grain boundary.

  Therefore, a uniform alloy composition cannot be obtained with an alloy of silicon and tin. In order to solve this problem, the alloy obtained by quenching the liquid obtained by melting the material of the alloy composition is once pulverized into fine powder, and then the alloy composition is mechanically alloyed using a pulverizer such as a ball mill. (Uniform dispersion of compositional elements in the alloy) and amorphization are simultaneously performed. Thus, alloy particles 100 more uniformly dispersed as shown in FIG. 1A or FIG. 1B can be produced without uneven distribution of elements other than silicon and the silicon element as constituent elements.

  Therefore, when the silicon alloy particles 100 according to one preferred embodiment of the present invention are used for a negative electrode material of a lithium secondary battery, lithium can be more uniformly inserted at the time of charging, and expansion at the time of lithium insertion can occur uniformly. Expansion is also reduced. For this reason, it is possible to manufacture a lithium secondary battery having an increased storage capacity, improved charge / discharge efficiency, and a long charge / discharge cycle life.

  The microstructure of the crystal of the silicon alloy particles 100 of the present invention can be observed with a transmission electron microscope and a selected area electron beam diffraction. The degree of microcrystallization or amorphization can be evaluated by measuring the half width of the X-ray diffraction peak. Here, when the ratio of the amorphous phase is increased due to the amorphization, the peak of the sharp X-ray diffraction chart which is crystalline is broadened and the half value width is broadened.

  Therefore, the half width of the diffraction intensity with respect to 2θ of the main peak of the X-ray diffraction chart is preferably 0.1 ° or more, more preferably 0.2 ° or more. The crystallite size calculated from the half width of the X-ray diffraction peak is preferably 60 nm or less, more preferably 30 nm or less.

  In order to reduce the crystallite size of silicon or a silicon alloy, it is effective to add a boron element having a solid solution limit or more, or add an yttrium or zirconium element. The addition amount of the boron element is preferably in the range of 0.1 to 5% by weight. The addition of the elements yttrium and zirconium is preferably in the range of 0.1 to 1% by weight.

  By the way, it is considered that the lithium insertion / desorption reaction occurs from the crystal grain boundary. However, since the silicon or silicon alloy crystal is microcrystallized or made amorphous to have many grain boundaries, lithium insertion / desorption is considered. The separation reaction can be performed uniformly, thereby increasing the storage capacity and the efficiency of charging and discharging.

  In addition, since microcrystallization or amorphization of a crystal loses the long-range order of the crystal structure, the degree of freedom is increased, and the change in the crystal structure when lithium is inserted is reduced. As a result, expansion during lithium insertion is reduced. Further, the repetition of insertion and extraction of lithium further promotes the amorphization of silicon.

  Thus, when the silicon alloy particles of the present invention are used as a negative electrode material of a lithium secondary battery, a secondary battery having high charge / discharge efficiency, high capacity, and long charge / discharge cycle life can be obtained. It is considered that the reason why the life is extended is that there is little change in the crystal structure of silicon due to insertion and desorption of lithium.

  When the silicon alloy is composed of silicon and the first element A having a lower atomic ratio than silicon but having the second highest atomic ratio after silicon (see FIG. 1A), as the first element A, From the viewpoints of (1), (2), and (3), one or more elements selected from the group consisting of tin, indium, gallium, copper, aluminum, silver, zinc, titanium, and germanium are preferable. Further, if the first element is an element selected from tin, indium, gallium, aluminum, zinc, silver, and germanium, which can electrochemically insert and desorb lithium, the same effect as the silicon crystal particles can be obtained. And a material having high performance as a negative electrode material of a lithium secondary battery can be obtained. Note that among the first elements, germanium is not suitable for providing an inexpensive electrode material because of its high price.

  In the case of an alloy of silicon, tin, indium, gallium, zinc, and silver, each is uniform in a molten solution state, and does not dissolve at all in a solid state. In the case of an alloy of silicon and silver, there is a eutectic crystallization of Si and Ag. In the case of an alloy of silicon and aluminum, it is uniform in a molten solution state, a solid solution is partially generated, and eutectic crystallization of Si and a Si-Al solid solution occurs.

  In the case of an alloy of silicon and titanium, the content of silicon is preferably 67 atomic% or more, and within this range, the molten solution is uniform. Further, it is more preferable that silicon has a composition of 85 atomic% or more. In this case, generation of an intermetallic compound of TiSi2 is small, and eutectic crystallization of Si and TiSi2 occurs. Therefore, the composition of the alloy formed from silicon and titanium preferably has a ratio of silicon atoms to titanium atoms of about 85:15. However, from the viewpoint of improving the power storage performance, it is preferable that the ratio of silicon is higher.

  In the case of an alloy of silicon and copper, in the case of the present invention in which silicon is 50 atomic% or more, it is uniform in a molten solution state, the generation of Cu3Si intermetallic compound is small, and the eutectic of Si and Cu3Si is formed. There is crystallization.

  The eutectic is effective in that the crystal grains in the alloy can be reduced. A composition near the eutectic point tends to be amorphous.

  Further, the silicon alloy is at least composed of silicon and a first element A having an atomic ratio lower than that of silicon but having an atomic ratio higher than that of silicon, and a second element E having an atomic ratio higher than that of silicon. (See FIG. 1 (b)), the first element A is at least one element selected from the group consisting of tin, aluminum, and zinc, and the second element E is copper, silver. , Zinc, titanium, aluminum, vanadium, yttrium, zirconium, and boron, the first element A and the second element E are different elements (A ≠ E ) Is more preferable.

  Here, the effect of the second element E is that the eutectic crystal with the first element A is crystallized and the crystal grains of the first element A are reduced, or the eutectic crystal with the silicon is crystallized to form a silicon crystal. The point is to make the grains smaller. Furthermore, the second element E is easier to form an oxide than silicon, and is effective in suppressing the formation of silicon oxide. If a large amount of silicon oxide is present in the silicon or silicon alloy, lithium oxide is formed by the electrochemical lithium insertion reaction, and the efficiency of desorption (release) with respect to the amount of lithium inserted decreases. It becomes a factor.

  Preferred and more specific examples of the silicon alloy (Si-AE alloy) composed of three or more elements include Si-Sn-Ti alloy, Si-Sn-Al alloy, Si-Sn-Zn alloy, Si-Sn -Ag alloy, Si-Sn-B alloy, Si-Sn-Sb-B alloy, Si-Sn-Cu-B alloy, Si-Sn-Cu-Sb-B alloy, Si-Al-Cu alloy, Si-Al -Ti alloy, Si-Al-Zn alloy, Si-Al-Ag alloy, Si-Zn-Ti alloy, Si-Zn-Sn alloy, Si-Zn-Al alloy, Si-Zn-Ag alloy, Si-Zn- Cu alloy, Si-Sn-Al-Ti alloy, Si-Sn-Zn-Ti alloy, Si-Sn-Ag-Ti alloy and the like can be mentioned.

  Here, the Sn-Zn-based alloy has a eutectic point near the atomic ratio Sn: Zn = 85: 15, and the Sn-Ag-based alloy has a eutectic point near the atomic ratio Sn: Ag = 95: 5. The Sn-Al alloy has a eutectic point near the atomic ratio Sn: Al = 97: 3, and the Al-Cu alloy has a eutectic point near the atomic ratio Al: Cu = 82: 18. Furthermore, an Al-Zn alloy has a eutectic point at an atomic ratio of Al: Zn = 89: 11.

  By crystallizing the eutectic, the crystal grains of Sn, Zn, Al, and Ag are reduced. In the silicon alloy, it is preferable to maintain a silicon ratio that can maintain the capacity as a negative electrode material of a lithium secondary battery, and to select a composition in which elements other than silicon are eutectic. In the case where tin, aluminum, zinc, and silver can be electrochemically inserted into and desorbed from lithium in a silicon alloy composed of the above three elements, so that these crystals become microcrystals or amorphous, It is preferable to select a composition near the eutectic point.

Of course, the silicon alloy contains one or more p-type dopants selected from the group consisting of boron, aluminum, gallium, antimony, and phosphorus in an atomic ratio with respect to silicon in order to reduce electric resistance and increase capacity. is preferably is doped with ¹ × ¹⁰ -8 ~2 × 10- 1 range, and more preferably is doped in the range of ^{1 × 10 -5 ~1 × 10 -1} . As the dopant, in particular, boron having a small ionic radius of a p-type dopant is more preferable.

  When aluminum or titanium, vanadium, yttrium, or zirconium is used as one of the constituent elements of the silicon alloy of the present invention, another effect is that oxygen and silicon react during the silicon alloy manufacturing process or the pulverizing process to oxidize. The formation of silicon can be suppressed. This is because aluminum atoms or titanium, vanadium, yttrium, and zirconium atoms form more stable bonds with oxygen atoms than silicon atoms. Note that when silicon oxide is formed, the efficiency of electrochemically inserting and removing lithium into the silicon alloy is reduced. This is presumed to be because lithium reacts with silicon oxide to form inactive lithium oxide.

  The average particle diameter of the primary particles of the silicon or silicon alloy of the present invention is preferably from 0.02 to 5 so that the lithium insertion and desorption reaction electrochemically occurs uniformly and quickly as a negative electrode material of a lithium secondary battery. It is preferably in the range of 0.0 μm, more preferably in the range of 0.05 to 3.0 μm, and most preferably in the range of 0.1 to 1.0 μm.

  If the average particle diameter is too small, handling becomes difficult, and the contact area between particles when an electrode is formed increases, and the contact resistance increases. Aggregating the primary particles to make the particles larger facilitates handling and leads to a reduction in electric resistance.

  Further, by forming a material selected from a carbon material, a metal magnesium, and a carbon material and a metal magnesium into the silicon particles containing silicon as a main component or the silicon alloy particles containing silicon as a main component, When used as a negative electrode material of a lithium secondary battery, it is possible to enhance the performance of the battery regarding charge / discharge efficiency, battery voltage, discharge current characteristics, charge / discharge repetition characteristics, and the like.

  The compounding of the carbon material can reduce fatigue due to volume expansion and contraction at the time of repeated insertion and desorption (release) of electrochemical lithium, and can extend the life. The amount of addition to the alloy containing silicon as a main component is preferably 1 to 10% by weight, and more preferably 2 to 5% by weight, without causing a significant decrease in the amount of lithium insertion / desorption (release).

  The composite of magnesium metal has the effect of increasing the battery voltage when a lithium secondary battery is formed. However, when the ratio of the magnesium metal to be composited is increased, the voltage of the produced battery is increased, but the electric capacity that can be stored is reduced because the ratio of silicon is reduced.

  Further, the outermost surface of the finely divided silicon powder or silicon alloy powder particles is preferably covered with a thin oxide layer of about 2 to 10 nm in order to suppress a rapid reaction with oxygen. The thickness of the oxide film can be measured, for example, by analyzing the oxygen element in the depth direction using a surface analyzer such as a scanning micro Auger analysis.

  In addition, in this specification, an "average particle size" means an average primary particle size (average particle size in the state where it does not aggregate).

  The microcrystallization or amorphization of the silicon or silicon alloy particles of the present invention can be evaluated by electron beam diffraction, neutron beam diffraction, observation with a high-resolution electron microscope, etc., in addition to the X-ray diffraction analysis. .

  In electron beam diffraction, a halo-shaped diffraction pattern is obtained when amorphization has progressed. In the high-resolution electron microscope observation, a striped lattice image indicating the presence of fine regular regions is observed (dotted stripes), or a labyrinthine pattern in which no striped lattice image is observed. Is observed, the structure of which is more amorphized.

  In addition, the radial distribution function from the atomic distribution function from the atomic distribution function obtained from the X-ray absorption fine structure (XAFS) analysis of the X-ray absorption fine structure (Extended X-ray absorption fine structure, commonly called EXAFS). Information about distance can be obtained. As a result, it is observed that the long-range order of the interatomic distance is lost if the amorphization is progressing.

  In the present invention, the crystallite size of the particles can be determined from the half width and the diffraction angle of the peak of the X-ray diffraction curve using CuKα as a radiation source using the following Scherrer's formula.

Lc = 0.94λ / (βcosθ) (Scherrer's formula)
Lc: crystallite size λ: wavelength of X-ray beam β: half width of peak (radian)
θ: Bragg angle of diffraction line

  The crystallite size obtained by the above equation becomes smaller as amorphization proceeds.

  The crystallite size of the electrode material of the present invention calculated from the above equation is preferably 60 nm or less, and more preferably 30 nm or less.

  In the case where the above-mentioned material that has become more amorphous is used as a negative electrode material of a lithium secondary battery, a change in expansion and contraction due to repetition of insertion and desorption (release) of lithium due to charge and discharge can be suppressed, and the repetition life is long.

  Next, a method for producing silicon particles and silicon alloy particles will be described.

  Silicon particles containing silicon of the present invention as a main component are obtained by mixing a predetermined amount of raw material silicon and a material of a doping element, melting and cooling the mixture to form a silicon ingot, It can be obtained as a fine powder having an average particle size of 1.0 μm. As the crushing apparatus used in the fine crushing step of the crushing step, a ball mill such as a planetary mill, a vibrating ball mill, a conical mill, and a tube mill, and a media mill such as an attritor type, a sand grinder type, an aniler mill type, and a tower mill type may be used. Can be. It is preferable to use zirconia, stainless steel, or steel as the material of the ball as the grinding media. As the dopant, boron, antimony, and phosphorus are preferable, and boron is more preferable.

  The silicon alloy particles of the present invention are obtained by mixing a predetermined amount of a metal material of a first element, a metal material of a second element, and a material of a doping element with silicon as a raw material, melting the molten metal to form a molten metal, Is cooled, and then powdery silicon alloy particles are produced. As a spraying method, a gas atomizing method of spraying with a high-pressure inert gas, a water atomizing method of spraying with high-pressure water, and the like can be used.

Preferably, the molten metal is cooled rapidly. This is because, in the state of the molten metal, the molten metal is in a uniformly molten state. Therefore, by rapidly cooling the molten metal, the composition in the silicon alloy composed of elements having different melting points becomes more uniform. Further, the cooling rate is desirably in the range of 10 ³ to 10 ⁸ K / s.

  Next, after forming an ingot of the silicon alloy, it is preferably subjected to a multi-stage pulverization process, preferably 0.02 to 5.0 μm, more preferably 0.05 to 3.0 μm, and still more preferably 0.1 to 1.0 μm Can be obtained as a fine powder having an average particle size of Further, it can be made amorphous by treatment with a ball mill or the like. As the crushing device for amorphization, a vibration mill, a planetary mill, a high-speed rotation mill, or the like is preferable.

  As a more preferable method, a method of mixing and melting materials as raw materials to form a molten metal, and then spraying with an inert gas to form powder (a so-called gas atomizing method), or blowing the powder into a rotating disk to form powder. After forming particle powder by atomization method (spraying method) such as method of spraying with high-pressure water (so-called water atomizing method), and method of pouring atomized metal into a high-speed rotating water stream, it is further pulverized. Silicon powder or silicon alloy powder having an average particle diameter of preferably 0.02 to 5.0 μm, more preferably 0.05 to 3.0 μm, and still more preferably 0.1 to 1.0 μm. Is obtained.

  By applying ultrasonic waves during the injection of the molten metal, the element composition inside the alloy particles obtained by the injection can be made more uniform. Further, by increasing the cooling rate in the above-mentioned atomization method, amorphousization is facilitated. Further, the powder obtained by the above atomization method is processed by an amorphizing pulverizing device such as a ball mill or the like to uniformize the distribution of constituent elements in the alloy and promote the amorphousization of the alloy. be able to.

  Also, after mixing and melting the materials as raw materials to form a molten metal, the powder or ribbon obtained at a high cooling rate of the gun method, the single roll method, or the twin roll method is further pulverized, whereby the present invention is obtained. A silicon powder or a silicon alloy powder having an average particle diameter of preferably 0.02 to 5.0 μm, more preferably 0.05 to 3.0 μm, and still more preferably 0.1 to 1.0 μm. Obtainable. Of course, the obtained powder can be further made amorphous by treatment with a ball mill or the like.

  In the ball mill treatment, it is preferable to add an antioxidant such as graphite, alcohol, or fatty acid to the silicon or silicon alloy powder for treatment in order to suppress the reaction of the treated fine powder with oxygen. Since graphite is hard and has poor malleability and ductility, it hardly solidifies, and has an effect of preventing material from adhering to the crushing container. Further, since it is chemically stable, hardly oxidized, and hardly alloyed, the oxidation can be suppressed by covering the surface of the finely pulverized negative electrode material particles.

  When a carbon material or magnesium metal is compounded into silicon or silicon alloy particles, it is preferable to carry out a pulverizing treatment such as a ball mill under a milder mixing condition than the condition for amorphization.

  Further, a material as a raw material of the silicon powder or the silicon alloy powder of the present invention is supplied to a plasma gas obtained by applying a high frequency to an inert gas, and the material is evaporated to have an amorphous particle diameter of 10 to 100 nm. Fine powder can be obtained. By applying a magnetic field when applying a high frequency, the plasma can be stabilized, and fine powder can be obtained more efficiently.

  Since the fine powder of silicon or silicon alloy is easily oxidized in the air and the dissolution reaction easily proceeds in an alkaline aqueous solution, it is preferable to cover the surface of the fine powder with an oxide film or a carbon film. By performing the pulverization step in a liquid such as alcohol, a thin oxide film can be formed on the surface of the fine powder.

  In addition, before removing the fine powder by pulverization, a process of exposing to an inert gas atmosphere such as a nitrogen gas or an argon gas containing a low concentration of an oxygen gas is performed so that a thin oxide film is formed on the surface. Powder can also be obtained.

  Here, the oxygen concentration in the nitrogen gas or the inert gas is preferably in the range of 0.01 to 5.0% by volume, and more preferably in the range of 0.05 to 2.0% by volume. The weight% of the oxygen element in the fine powder having a thin oxide film formed on the surface is preferably in the range of 0.1 to 15% by weight, more preferably in the range of 0.2 to 10% by weight, and more preferably in the range of 0.2 to 5% by weight. % Is most preferred.

  If the amount of the oxygen element and the amount of the oxide contained in the silicon powder or the silicon alloy powder of the present invention are large, a high discharge amount and high charge / discharge efficiency cannot be expected when used for an electrode material of a lithium secondary battery. This is because lithium and an oxide react during an insertion reaction of lithium and change into an inactive substance such as lithium oxide, and cannot be electrochemically released.

  Further, if the surface of the silicon powder or the silicon alloy powder of the present invention is not covered with sufficient oxygen content, i.e., oxide content, to be able to form an antioxidant film, it is easily oxidized in the air, and the charge / discharge reaction of the battery is difficult. An inactive reactant will be formed.

  The carbon film for preventing oxidation can be formed by mixing fine powder carbon such as graphite powder and acetylene black when pulverizing or amorphizing silicon or a silicon alloy.

  The silicon fine particles or silicon alloy fine particles of the present invention can also be formed by a method such as sputtering, electron beam evaporation, cluster ion beam evaporation, and the like.

  When silicon is used as a raw material of the present invention, it may contain impurities such as Ca, Al, and Fe. In order to provide an inexpensive negative electrode material for a lithium secondary battery, the purity is preferably 99.99% or less, more preferably 99.9% or less, and still more preferably 99.6% or less.

  FIG. 3 shows a schematic sectional structure of the electrode structure of the present invention. In FIG. 3A, reference numeral 302 denotes an electrode structure. The electrode structure 302 includes an electrode material layer 301 and a current collector 300. The electrode material layer 301 is formed as shown in FIG. As shown in FIG. 1, it is composed of particles (silicon Si or silicon alloy powder) 303 containing silicon as a main component, a conductive auxiliary material 304 and a binder 305. Although the electrode material layer 301 is provided only on one surface of the current collector 300 in FIG. 3, depending on the form of the battery, the electrode material layer 301 may be formed on both surfaces of the current collector 300. Good.

  Here, the content of the conductive auxiliary material 304 is preferably 5% by weight or more and 40% by weight or less, more preferably 10% by weight or more and 30% by weight or less. The content of the binder 305 is preferably 2% by weight or more and 20% by weight or less, more preferably 5% by weight or more and 15% by weight or less. The content of the particles (powder) 303 containing silicon as a main component contained in the electrode material layer 301 is preferably in a range of 40% by weight to 93% by weight.

  Examples of the conductive auxiliary material 304 include amorphous carbon such as acetylene black and Ketjen black, a carbon material having a graphite structure such as graphite, carbon fiber, and carbon nanotube, nickel, copper, silver, titanium, platinum, aluminum, and cobalt. , Iron, chromium and the like can be used, and graphite is particularly preferable. As the shape of the conductive auxiliary material, preferably, a shape selected from a sphere, a flake, a filament, a fiber, a spike, a needle and the like can be adopted. Furthermore, by employing powders of two or more different shapes, the packing density at the time of forming the electrode material layer can be increased and the impedance of the electrode structure 302 can be reduced.

  Examples of the material of the binder 305 include water-soluble polymers such as polyvinyl alcohol, water-soluble ethylene-vinyl alcohol copolymer, polyvinyl butyral, polyethylene glycol, carboxymethyl cellulose sodium, and hydroxyethyl cellulose, polyvinylidene fluoride, and vinylidene fluoride-hexafluoropropylene. Examples include fluororesins such as polymers, polyolefins such as polyethylene and polypropylene, styrene-butadiene rubber, polyimide, polyamic acid (polyimide precursor), and polyamideimide. As a material used for the binder, a material having a tensile strength of 100 to 400 MPa and an elongation of 40 to 100% is preferable, and polyimide, polyamic acid (polyimide precursor), and polyamideimide are more preferable.

  When forming an electrode, the binder may be further added with a polymer material such as polyacrylonitrile or polymethyl methacrylate which absorbs and gels the electrolyte to form a composite, and the penetration of the electrolyte may be improved. However, it is preferable in that the electric resistance of the electrode is reduced.

  In addition, since the current collector 300 efficiently supplies a current consumed in the electrode reaction at the time of charging, or plays a role of collecting a current generated at the time of discharging, the current collector 300 particularly functions as a secondary electrode. When applied to the negative electrode of a battery, as a material for forming the current collector 300, a material having high electric conductivity and inert to a battery reaction is desirable. Preferred materials include those made of one or more metal materials selected from copper, nickel, iron, stainless steel, titanium, and platinum. As a more preferable material, copper which is inexpensive and has low electric resistance is used.

  The shape of the current collector is a plate shape, but the “plate shape” is not specified in the practical range of the thickness, and is called a “foil” having a thickness of about 100 μm or less. Also encompasses forms. In addition, a plate-shaped member such as a mesh, a sponge, or a fiber, a punched metal, an expanded metal, or the like may be used.

  Next, a procedure for manufacturing the electrode structure 302 will be described.

  First, a conductive auxiliary material powder and a binder 305 are mixed with a powder of silicon or a silicon alloy, which is particles containing silicon as a main component of the present invention, and a solvent for the binder 305 is appropriately added and kneaded. Prepare a slurry. Next, the prepared slurry is applied to the current collector 300, dried to form the electrode material layer 301, and then subjected to a press treatment to adjust the thickness and density of the electrode material layer 301 to form the electrode structure 302. I do.

  As the above-mentioned coating method, for example, a coater coating method and a screen printing method can be applied. In addition, the main material and the conductive auxiliary material 304 and the binder 305 are added without adding a solvent, or only the negative electrode material and the conductive auxiliary material 304 are added onto the current collector without mixing the binder 305. The electrode material layer 301 can be formed by pressing.

Here, if the density of the electrode material layer 301 is too high, the expansion at the time of insertion of lithium increases, and the electrode material layer 301 peels off from the current collector 300. If the density is too low, the resistance of the electrode increases, so that the charging / discharging efficiency decreases and the voltage drop at the time of discharging the battery increases. Therefore, the density of the electrode material layer 301 of the present invention is more it is preferably in the range of 0.8 to 2.0 g / cm ^3, in the range of 0.9~1.5g / cm ³ preferable.

  Note that the electrode structure 302 formed using only silicon particles or silicon alloy particles of the present invention without using the conductive auxiliary material 304 or the binder 305 can be formed by a method such as sputtering, electron beam evaporation, or cluster ion beam evaporation. Thus, it can be manufactured by directly forming the electrode material layer 301 on the current collector 300.

  However, when the thickness of the electrode material layer 301 is increased, peeling is likely to occur at the interface with the current collector 300. Therefore, the above evaporation method is not suitable for forming the thick electrode structure 302. In order to prevent peeling at the interface, a metal layer, an oxide layer, or a nitride layer having a thickness of 1 to 10 nm is provided on the current collector 300 to form irregularities on the current collector 300, and the adhesion of the interface is reduced. It is preferable to improve the properties. As a more specific oxide layer or nitride layer, a silicon or metal oxide layer or nitride layer is preferably used.

  Incidentally, the secondary battery according to the present invention includes a negative electrode, an electrolyte, and a positive electrode using the electrode structure having the above-described features, and utilizes a lithium oxidation reaction and a lithium ion reduction reaction.

  FIG. 4 is a diagram showing a basic configuration of such a lithium secondary battery of the present invention. In FIG. 4, reference numeral 401 denotes a negative electrode using the electrode structure of the present invention, 402 denotes an ion conductor, and 403 denotes a positive electrode. , 404 is a negative terminal, 405 is a positive terminal, and 406 is a battery case (housing).

  Here, in the secondary battery, an ion conductor 402 is stacked between the negative electrode 401 and the positive electrode 403 to form an electrode group, and in a dry air or dry inert gas atmosphere where the dew point is sufficiently controlled, After inserting the electrode group into the battery case, the electrodes 401 and 403 are connected to the electrode terminals 404 and 405, and the battery case is sealed.

  In the case where a material obtained by holding an electrolytic solution in a microporous plastic film as the ion conductor 402 is used, a microporous plastic film is sandwiched between the negative electrode 401 and the positive electrode 403 as a separator for preventing short circuit. After forming the electrode group, it is inserted into a battery case, the electrodes 401 and 403 are connected to the electrode terminals 404 and 405, and an electrolyte is injected before the battery case is sealed to assemble the battery.

  A lithium secondary battery using the electrode structure made of the electrode material of the present invention as a negative electrode has high charge / discharge efficiency, capacity, and energy density due to the beneficial effects of the negative electrode.

  Here, the positive electrode 403 serving as a counter electrode of the lithium secondary battery using the above-described electrode structure of the present invention as a negative electrode is at least a lithium ion source and is formed of a positive electrode material serving as a lithium ion host material, and is preferably lithium. It is composed of a current collector and a layer formed from a positive electrode material serving as an ion host material. Further, the layer formed from the positive electrode material is preferably made of a material in which a positive electrode material serving as a host material of lithium ions and a binder, and in some cases, a conductive auxiliary material are added thereto.

  The positive electrode material which is a lithium ion source and a host material used in the lithium secondary battery of the present invention includes lithium-transition metal (composite) oxide, lithium-transition metal (composite) sulfide, and lithium-transition metal (composite). Nitride and lithium-transition metal (composite) phosphor oxide are more preferred. The transition metal element of the transition metal oxide, transition metal sulfide, transition metal nitride, and transition metal phosphate compound is, for example, a metal element having a d-shell or an f-shell, and is Sc, Y, a lanthanoid, an actinoid. , Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pb, Pt, Cu, Ag, and Au are used. In particular, Co, Ni, Mn, Fe, Cr, and Ti are preferably used. Lithium-transition metal (composite) oxide, lithium-transition metal (composite) sulfide, lithium-transition metal (composite) nitride, lithium-transition metal (composite) phosphate, particularly lithium-transition metal The (composite) oxide contains 0.001-0.01 element of yttrium Y or element of Y and zirconium Zr with respect to lithium Li1.0 to make crystal grains finer and more. Can be repeatedly and stably performed.

  When the shape of the positive electrode active material is a powder, a positive electrode is manufactured by using a binder or by sintering or vapor deposition to form a positive electrode active material layer on a current collector. When the conductivity of the positive electrode active material powder is low, it is necessary to appropriately mix a conductive auxiliary material in the same manner as in the formation of the active material layer of the electrode structure. As the conductive auxiliary material and the binder, those used for the above-described electrode structure 302 of the present invention can be similarly used.

  Here, as the current collector material used for the positive electrode, aluminum, titanium, nickel, and platinum, which are materials having high electric conductivity and inert to a battery reaction, are preferable. Specifically, nickel, stainless steel, Titanium and aluminum are preferred, and aluminum is more preferred because of its low cost and high electrical conductivity. The shape of the current collector is a plate shape, but the “plate shape” is not specified in the practical range of the thickness, and is called a “foil” having a thickness of about 100 μm or less. Also encompasses forms. In addition, a plate-shaped member such as a mesh, a sponge, or a fiber, a punched metal, an expanded metal, or the like may be used.

In addition, the ion conductor 402 of the lithium secondary battery of the present invention has a separator holding an electrolytic solution (an electrolytic solution prepared by dissolving an electrolyte in a solvent), a solid electrolyte, and a gel made of a polymer gel or the like. A lithium ion conductor such as a solidified electrolyte, a composite of a polymer gel and a solid electrolyte, or the like can be used. Here, the conductivity of the ion conductor 402 as a value at 25 ° C. is preferably 1 × 10 ⁻³ S / cm or more, more preferably 5 × 10 ⁻³ S / cm or more.

As the electrolyte, for example, lithium ion (Li ⁺ ) and Lewis acid ion (BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , ClO ₄ ⁻ , CF ₃ SO ₃ ⁻ , BPh ₄ ⁻ (Ph: phenyl group) ) Comprising LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiBPh ₄ , LiSbF ₆ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (CF ₃ SO ₂₎ ) ₃ C and the like, and their mixed salts. It is desirable that the salt is sufficiently dehydrated and deoxidized by heating under reduced pressure.

  Further, as a solvent for the electrolyte, for example, acetonitrile, benzonitrile, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethylformamide, tetrahydrofuran, nitrobenzene, dichloroethane, diethoxyethane, 1,2-dimethoxyethane, Chlorobenzene, γ-butyrolactone, dioxolane, sulfolane, nitromethane, dimethylsulfide, dimethylsulfoxide, methyl formate, 3-methyl-2-oxidazolidinone, 2-methyltetrahydrofuran, 3-propylsidone, sulfur dioxide, phosphoryl chloride, thionyl chloride, Sulfuryl chloride or a mixture thereof can be used. As a solvent for the electrolyte, a combination of ethylene carbonate, γ-butyrolactone, and diethyl carbonate is more preferable because a decomposition reaction hardly occurs even at a higher charging voltage.

  The solvent is, for example, dehydrated with activated alumina, molecular sieve, phosphorus pentoxide, calcium chloride, or the like, or, depending on the solvent, is also subjected to impurity removal and dehydration by distillation in the presence of an alkali metal in an inert gas. Is good.

  In order to prevent leakage of the electrolyte, it is preferable to use a solid electrolyte or a solidified electrolyte. Examples of the solid electrolyte include glass such as an oxide including a lithium element, a silicon element, an oxygen element, a phosphorus element, and a sulfur element, and a polymer complex of an organic polymer having an ether structure. As the solidified electrolyte, those obtained by gelling the electrolytic solution with a gelling agent and solidifying are preferable.

  As the gelling agent, it is desirable to use a polymer which absorbs the solvent of the electrolytic solution and swells, or a porous material having a large liquid absorption such as silica gel. Further, as the polymer, polyethylene oxide, polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, vinylidene fluoride-hexafluoropropylene copolymer and the like are used. Further, the polymer is more preferably one having a crosslinked structure.

  Note that the ion conductor 402 which forms a separator that plays a role in preventing a short circuit between the negative electrode 401 and the positive electrode 403 in the secondary battery sometimes has a role of holding an electrolytic solution. It is necessary to have a large number and to be insoluble and stable in the electrolytic solution.

  Therefore, as the ion conductor 402 (separator), for example, a material having a micropore structure or a nonwoven fabric such as glass, polyolefin such as polypropylene or polyethylene, or a fluororesin is preferably used. Further, a metal oxide film having fine pores or a resin film in which a metal oxide is compounded can be used.

  Next, the shape and structure of the secondary battery will be described.

  Specific shapes of the secondary battery of the present invention include, for example, a flat shape, a cylindrical shape, a rectangular parallelepiped shape, and a sheet shape. In addition, examples of the structure of the battery include a single-layer type, a multilayer type, and a spiral type. Among them, a spiral cylindrical battery is characterized in that the electrode area can be increased by winding a separator between the negative electrode and the positive electrode, and a large current can flow during charging and discharging. Further, a rectangular parallelepiped or sheet type battery has a feature that a storage space of a device configured to store a plurality of batteries can be effectively used.

  Next, the shape and structure of the battery will be described in more detail with reference to FIGS. FIG. 5 is a cross-sectional view of a single-layer flat (coin-shaped) battery, and FIG. 6 is a cross-sectional view of a spiral cylindrical battery. The lithium secondary battery having these shapes has basically the same configuration as that of FIG. 4 and includes a negative electrode, a positive electrode, an ion conductor, a battery housing, and an output terminal.

  5 and 6, 501 and 603 are negative electrodes, 503 and 606 are positive electrodes, 504 and 608 are negative electrode caps or negative cans as negative electrode terminals, 505 and 609 are positive electrode cans or positive electrode caps as positive electrode terminals, 502 and 607 Is an ion conductor, 506 and 610 are gaskets, 601 is a negative electrode current collector, 604 is a positive electrode current collector, 611 is an insulating plate, 612 is a negative electrode lead, 612 is a positive electrode lead, and 614 is a safety valve.

  Here, in the flat type (coin type) secondary battery shown in FIG. 5, a positive electrode 503 including a positive electrode material layer and a negative electrode 501 including a negative electrode material layer are formed, for example, by an ion formed by a separator holding at least an electrolytic solution. The laminate is stacked via a conductor 502. The laminate is accommodated in a positive electrode can 505 as a positive electrode terminal from the positive electrode side, and the negative electrode side is covered with a negative electrode cap 504 as a negative electrode terminal. Then, a gasket 506 is arranged in another portion inside the positive electrode can.

  In the spiral cylindrical secondary battery shown in FIG. 6, a positive electrode 606 having a positive electrode (material) layer 605 formed on a positive electrode current collector 604 and a negative electrode (material) formed on a negative electrode current collector 601 are formed. A) A negative electrode 603 having a layer 602 faces, for example, via an ionic conductor 607 formed of at least a separator holding an electrolytic solution, and forms a multilayer structure having a cylindrical structure wound in multiple layers.

  The laminate having the cylindrical structure is accommodated in a negative electrode can 608 serving as a negative electrode terminal. In addition, a positive electrode cap 609 as a positive electrode terminal is provided on the opening side of the negative electrode can 608, and a gasket 610 is disposed in another portion inside the negative electrode can. The stacked body of the electrodes having the cylindrical structure is separated from the positive electrode cap side via the insulating plate 611.

  The positive electrode 606 is connected to a positive electrode cap 609 via a positive electrode lead 613. The negative electrode 603 is connected to the negative electrode can 608 via the negative electrode lead 612. A safety valve 614 for adjusting the internal pressure inside the battery is provided on the positive electrode cap side. As described above, the layer made of the above-described negative electrode material fine powder of the present invention is used for the active material layer of the negative electrode 601 and the active material layer 602 of the negative electrode 603.

Next, an example of a method of assembling the battery shown in FIGS. 5 and 6 will be described.
(1) The ion conductors 502 and 607 as separators are interposed between the negative electrodes 501 and 603 and the molded positive electrodes 503 and 606, and are incorporated in the positive electrode can 505 or the negative electrode can 608.
(2) After injecting the electrolytic solution, the negative electrode cap 504 or the positive electrode cap 609 and the gaskets 506 and 610 are assembled.
(3) The above (2) is swaged.

  Thereby, the battery is completed. The above-described preparation of the lithium battery material and assembly of the battery are desirably performed in dry air from which moisture is sufficiently removed or in a dry inert gas.

  Next, members constituting such a secondary battery will be described.

  As a material of the gaskets 506 and 610, for example, a fluorine resin, a polyolefin resin, a polyamide resin, a polysulfone resin, and various rubbers can be used. As a method for sealing the battery, a method such as glass sealing tube, adhesive, welding, soldering, or the like is used in addition to “caulking” using a gasket as shown in FIGS. As the material of the insulating plate 611 in FIG. 6, various organic resin materials and ceramics are used.

  The outer can of the battery includes a battery positive or negative electrode can 505, 608 and a negative or positive electrode cap 504, 609. As a material for the outer can, stainless steel is preferably used. As other materials for the outer can, aluminum alloy, titanium-clad stainless steel, copper-clad stainless steel, nickel-plated steel plate and the like are often used.

  Since the positive electrode can 505 in FIG. 5 and the negative electrode can 608 in FIG. 6 also serve as a battery housing (case) and terminals, the above stainless steel is preferable. However, when the positive electrode can 505 or the negative electrode can 608 does not double as a battery housing and a terminal, besides stainless steel, use metal such as zinc, plastic such as polypropylene, or a composite material of metal or glass fiber and plastic. Can be.

  As the safety valve 614 provided in the lithium secondary battery as a safety measure when the internal pressure of the battery increases, for example, rubber, a spring, a metal ball, a rupture foil, or the like can be used.

  Hereinafter, the present invention will be described in more detail by way of examples.

(Preparation of electrode material)
First, an example of preparing a negative electrode material will be described.

(Example 1)
Granular silicon (purity: 99.6%) and bulk titanium were mixed at an atomic ratio of 85:15 (weight ratio: 76.8: 23.2), and a Si—Ti alloy was prepared under vacuum with an arc melting apparatus. Next, the Si-Ti alloy previously obtained by arc melting was melted by a single-roll method apparatus, and the molten metal was sprayed with an argon gas onto a rotating copper roll and rapidly cooled to produce a Si-Ti alloy. Next, the Si—Ti alloy was ground with a planetary ball mill using silicon nitride balls in an argon gas atmosphere for 2 hours to obtain a fine powder electrode material.

(Example 2)
Granular silicon (purity 99.6%), bulk titanium, and bulk boron are mixed at an atomic ratio of 85: 15: 0.85 (weight ratio: 76.8: 23.2: 0.3), and an arc melting apparatus is applied under vacuum. Was used to prepare a boron-doped Si-Ti alloy. Next, the boron-doped Si-Ti alloy previously obtained by arc melting is melted by a single-roll method apparatus, and the molten metal is sprayed with an argon gas on a rotating copper roll to quench the boron-doped Si-Ti alloy. Produced. Next, the boron-doped Si-Ti alloy was pulverized for 2 hours in a planetary ball mill using silicon nitride balls in an argon gas atmosphere to obtain a fine powder electrode material.

(Example 3)
Granular silicon (purity: 99.6%) and bulk titanium were mixed at an atomic ratio of 85:15 (weight ratio: 76.8: 23.2), and a Si—Ti alloy was prepared under vacuum with an arc melting apparatus. Next, granular tin was added to the Si-Ti alloy obtained by the arc melting at an atomic ratio of Si: Sn: Ti = 76.2: 10.3: 13.5 (weight ratio 53.3: 30.5: 16.05) was melted by a single-roll method apparatus, and the molten metal was sprayed with an argon gas onto a rotating copper roll to be rapidly cooled to produce a Si-Sn-Ti alloy. Next, the Si-Sn-Ti alloy was ground using a silicon nitride ball in an argon gas atmosphere with a planetary ball mill for 2 hours to obtain a fine powder electrode material.

(Example 4)
In the above-mentioned Example 3, granular tin was added to the Si—Ti alloy obtained by arc melting in an atomic ratio of Si: Sn: Ti = 76.4: 20.0: 3.6 (weight ratio: 60: 35: 5). The resulting mixture was melted by a single-roll method apparatus, and the molten metal was sprayed with an argon gas onto a rotating copper roll to be quenched to produce a Si-Sn-Ti alloy. Otherwise, in the same manner as in Example 3, an electrode material of a Si-Sn-Ti alloy fine powder was obtained.

(Example 5)
Silicon, tin, and aluminum are mixed at an atomic ratio of 74.0: 19.4: 6.6 (weight ratio: 60: 35: 5), melted by a single roll method apparatus, and the molten metal is rotated with argon gas. This was sprayed onto a copper roll and quenched to obtain a Si-Sn-Al alloy powder. Next, the obtained Si-Sn-Al alloy powder was further pulverized for 2 hours by using a silicon nitride ball in an argon gas atmosphere with a planetary ball mill to obtain a fine powder electrode material.

(Example 6)
Silicon, zinc, and aluminum were mixed in an atomic ratio of 69.0: 27.6: 0.4 (weight ratio: 50.5: 47.1: 2.4), melted in an argon gas atmosphere, and the molten metal was mixed with argon. Si-Zn-Al alloy powder was obtained by a gas atomization method in which a gas was injected. Next, the obtained Si-Zn-Al alloy powder was pulverized in isopropyl alcohol with a media mill using zirconia beads, and an electrode of Si-Zn-Al alloy fine powder having an average particle diameter of 0.3 µm was obtained. The material was obtained. Further, the obtained fine powder of Si—Zn—Al alloy was pulverized for 2 hours using silicon nitride balls in an argon gas atmosphere by a planetary ball mill to obtain a fine powder electrode material.

(Example 7)
Silicon, aluminum, and copper are mixed in an atomic ratio of 73.5: 21.9: 4.6 (weight ratio: 70:20:10), melted by a single roll method device, and the molten metal is rotated with argon gas. The mixture was sprayed onto a copper roll and quenched to obtain a Si-Al-Cu alloy powder. Next, the obtained Si-Al-Cu alloy powder was further pulverized for 2 hours using a silicon nitride ball in an argon gas atmosphere with a planetary ball mill to obtain an electrode material of Si-Al-Cu alloy fine powder. Was.

(Example 8)
According to the gas atomization method of Example 6, silicon, tin, aluminum, and titanium were 84.1: 11.5: 0.4: 4.0 in atomic ratio (59.8: 35.0 in weight ratio). 0.2: 5.0) An electrode material of Si-Sn-Al-Ti alloy fine powder was obtained by the same operation as in Example 6, except that a Si-Sn-Al-Ti alloy powder of (0.2: 5.0) was obtained.

(Example 9)
Silicon, tin, and zinc are mixed in an atomic ratio of 81.0: 16.2: 2.8 (weight ratio: 51.9: 43.9: 4.2) and melted in an argon gas atmosphere to form a molten metal. After that, a Si—Sn—Zn alloy powder was obtained by a water atomization method in which the molten metal was injected with high-pressure water. Next, the obtained Si—Sn—Zn alloy powder was pulverized in isopropyl alcohol with a media mill using zirconia balls to obtain a fine Si—Sn—Zn alloy powder having an average particle diameter of 0.3 μm. Next, the obtained Si-Sn-Zn alloy fine powder was further pulverized for 2 hours using a silicon nitride ball in an argon gas atmosphere using a planetary ball mill to obtain a fine powder electrode material.

(Example 10)
In the single-roll method apparatus of Example 5, silicon, tin, and silver are 81.8: 17.1: 1.1 atomic ratio (63: 35: 2 by weight ratio) Si—Sn—Ag alloy powder. Was obtained in the same manner as in Example 5 except that the electrode material of Example 5 was obtained.

(Example 11)
According to the water atomization method of Example 9, silicon, tin, zinc, and titanium were 82.7: 11.3: 2.0: 4.0 in atomic ratio (58.0: 33.9 in weight ratio: An electrode material of Si-Sn-Zn-Ti alloy fine powder was obtained by the same operation as in Example 5, except that 3.3: 4.8) Si-Sn-Zn-Ti alloy powder was obtained.

(Example 12)
In the same manner as in Example 5, silicon, tin, and boron were mixed at a weight ratio of 62: 36: 2, melted by a single-roll method apparatus, and the molten metal was sprayed with argon gas onto a rotating copper roll to rapidly cool the same. Thus, a Si-Sn-B alloy powder was obtained. Next, the obtained Si-Sn-B alloy powder was further pulverized for 2 hours using a silicon nitride ball in an argon gas atmosphere by a planetary ball mill to obtain a fine powder electrode material.

(Example 13)
Same as Example 12, except that silicon, tin, and antimony were mixed at a weight ratio of 58: 34: 8 in the same manner as in Example 12, and a Si-Sn-Sb alloy powder was obtained using a single-roll method apparatus. By operation, the electrode material of the Si-Sn-Sb alloy fine powder was obtained.

(Example 14)
Except that silicon, tin, antimony, and boron were mixed at a weight ratio of 60: 35: 4: 1 in the same manner as in Example 12, and a Si-Sn-Sb-B alloy powder was obtained using a single-roll method apparatus. By the same operation as in Example 12, an electrode material of Si-Sn-Sb-B alloy fine powder was obtained.

(Example 15)
In the same manner as in Example 12, except that silicon, tin, copper, and boron were mixed at a weight ratio of 59: 34: 5: 2, and a Si-Sn-Cu-B alloy powder was obtained using a single-roll method apparatus. By the same operation as in Example 12, an electrode material of a Si-Sn-Cu-B alloy fine powder was obtained.

(Example 16)
In the same manner as in Example 12, except that silicon, tin, aluminum, and boron were mixed at a weight ratio of 59: 34: 5: 2, and a Si-Sn-Al-B alloy powder was obtained using a single-roll method apparatus. By the same operation as in Example 12, an electrode material of a Si-Sn-Al-B alloy fine powder was obtained.

(Example 17)
In the same manner as in Example 12, except that silicon, tin, aluminum, and antimony were mixed at a weight ratio of 56: 33: 4: 7, and a Si-Sn-Al-Sb alloy powder was obtained using a single roll method apparatus. By the same operation as in Example 12, an electrode material of Si-Sn-Al-Sb alloy fine powder was obtained.

(Example 18)
In the same manner as in Example 12, silicon, tin, aluminum, antimony, and boron were mixed at a weight ratio of 58: 34: 5: 2: 1, and a Si-Sn-Al-Sb-B alloy was formed using a single-roll method apparatus. An electrode material of Si-Sn-Al-Sb-B alloy fine powder was obtained in the same manner as in Example 12, except that powder was obtained.

(Reference Example 1)
Silicon powder having an average particle diameter of 10 μm and a purity of 99.6% by weight was pulverized in isopropyl alcohol by a media mill using zirconia balls to obtain silicon fine powder having an average particle diameter of 0.3 μm. Then, using a silicon nitride ball in an argon gas atmosphere using a planetary ball mill, the ball was pulverized for 2 hours to obtain an electrode material of silicon fine powder.

(Reference Example 2)
Granular silicon (purity: 99.6% by weight) and bulk titanium were mixed at an atomic ratio of 65:35 (weight ratio: 52:48), and a Si—Ti alloy was first prepared under vacuum with an arc melting apparatus. Next, the Si-Ti alloy previously obtained by arc melting was melted by a single-roll method apparatus, and the molten metal was sprayed with an argon gas onto a rotating copper roll and rapidly cooled to produce a Si-Ti alloy. Next, the obtained Si—Ti alloy was ground with a planetary ball mill using silicon nitride balls in an argon gas atmosphere for 2 hours to obtain a fine powder electrode material.

Note that the above composition of silicon and titanium partially melts in a molten liquid state, that is, a composition in which liquids having different concentrations exist, and is a composition in which TiSi ₂ is easily crystallized in a solid state.

(Reference Example 3)
Granular silicon (purity: 99.6% by weight) and granular nickel were mixed at an atomic ratio of Si: Ni = 65.9: 34.1 (weight ratio: 48:52), and the Si-Ni alloy was vacuum-arc-melted using an arc melting apparatus. Prepared. Next, the Si-Ni alloy previously obtained by arc melting was melted by a single-roll method apparatus, and the molten metal was sprayed with an argon gas onto a rotating copper roll to be rapidly cooled to produce a Si-Ni alloy. Next, the obtained Si—Ni alloy was pulverized for 2 hours using a silicon nitride ball in an argon gas atmosphere with a planetary ball mill, to obtain a fine powder electrode material.

It is known that silicon and nickel form various intermetallic compounds (NiSi ₂ , NiSi, Ni ₂ Si ₃ , Ni ₂ Si, etc.), and in the above composition of silicon and nickel, Si ₂ Ni is formed. Easy composition.

  Next, the results of analyzing the electrode materials obtained in Examples 1 to 18 and Reference Examples 1 to 3 will be described.

  The analysis of the electrode material of the above silicon alloy is based on the microcrystal or amorphization of the silicon crystal, which is considered to affect the performance of the negative electrode of the lithium secondary battery, and the crystal of the other element forming the alloy. The analysis was performed from the viewpoint of element distribution in the alloy.

  The crystal structure of the silicon alloy of the present invention suitable for a negative electrode material of a lithium secondary battery has a low intermetallic compound of silicon, which is considered to have a low ability to store lithium, and the crystals of each element forming the alloy are microcrystals, or The crystal structure has advanced amorphization, and the distribution of elements in the alloy is less unevenly distributed and more uniformly distributed.

  As an analysis method, X-ray diffraction analysis, observation by a transmission electron microscope, energy dispersive X-ray spectroscopy (energy dispersive X-ray spectroscopy aka EDXS) analysis, electron beam diffraction analysis, and the like were used.

  Here, the formation of the intermetallic compound can be confirmed from the pattern of X-ray diffraction or electron beam diffraction. Further, when the crystal becomes microcrystals or becomes amorphous, the half-width of the X-ray diffraction peak becomes broad, and the crystallite size calculated from the Scherrer's formula becomes small. The pattern changes from a ring pattern to a halo pattern. From a high-resolution observation with a transmission electron microscope, a fine stripe pattern or a maze pattern of a crystal lattice is observed.

  Further, when the distribution of elements in the alloy is less unevenly distributed and more uniformly distributed, it is observed as an image with less uneven distribution of density in the alloy particles by transmission electron microscope observation (particularly dark field image), In the element mapping by EDXS analysis combined with the transmission electron microscope, a small deviation of the element distribution in the particles is observed.

  First, in the analysis and evaluation of the crystal structures of the electrode materials obtained in Examples 1 to 18, the half width of the X-ray diffraction peak was broad, and fine stripes or labyrinths were observed by transmission electron microscope observation. Was observed. From this, it was found that each of the examples was a material having a structure in which microcrystals or amorphization were advanced. In addition, when the Scherrer crystallite size was determined from the measurement results of X-ray diffraction, all were in the range of 7 to 40 nm.

  In the EDXS analysis on the element distribution of the electrode materials obtained in Examples 1 to 18, the deviation of the elements in the alloy particles was small, and as shown in the schematic diagram of FIG. It turned out that it is uniformly distributed. The detection of the intermetallic compound of silicon in Examples 1 to 18 was carried out by X-ray diffraction and selected area electron diffraction with a transmission electron microscope, using titanium or copper of Examples 1 to 4, 7, 8, 11, and 15 in Examples. Only a small amount was observed in alloys containing

On the other hand, in the analysis and evaluation of the crystal structure of the electrode material obtained in Reference Examples 2 and 3, the half-width of the X-ray diffraction peak was narrower than that in Examples 1 to 18 and the X-ray diffraction peak was smaller than that in Examples 1 to 18 by the transmission electron microscope. A large stripe pattern in the target area was observed. From the X-ray diffraction peak pattern and the selected area electron beam diffraction pattern, in Reference Example 2, an intermetallic compound of TiSi ₂ was confirmed, and in Reference Example 3, an intermetallic compound of NiSi ₂ was confirmed.

  In addition, in the transmission electron microscope observations (especially dark-field images) of Reference Examples 2 and 3, an image with large uneven distribution of density was observed in the alloy particles, and the particle mapping was confirmed from the element mapping by EDXS analysis combined with the transmission electron microscope. It was confirmed that the above titanium or nickel element was unevenly distributed.

  Next, an electrode structure was prepared using various silicon or silicon alloy fine powders obtained by the above-described procedure as described below, and the performance of lithium insertion / desorption of the electrode structure was evaluated.

First, 66.5% by weight of various silicon or silicon alloy fine powders obtained by the above-mentioned procedure and flat graphite powder (specifically, approximately 5 μm in diameter and approximately 1 μm in thickness) were used as conductive auxiliary materials. 10.0% by weight of disc-shaped graphite powder), 6.0% by weight of graphite powder (substantially spherical, having an average particle size of 0.5 to 1.0 μm), and acetylene black (substantially spherical) 4.0 wt% of an average particle size of 4 × 10 ⁻² μm), 10.5 wt% of polyvinyl alcohol as a binder and 3.0 wt% of carboxymethyl cellulose sodium were mixed, Water was added and kneaded to prepare a slurry.

  Next, the slurry thus prepared was applied on a 15 μm-thick electric field copper foil (electrochemically produced copper foil) with a coater, dried, and the thickness was adjusted by a roll press to obtain a thickness of 25 μm. The electrode structure of the active material layer was manufactured. Then, the electrode structure was cut into a size of 2.5 cm × 2.5 cm, and a copper tab was welded to form a silicon electrode.

[Evaluation procedure of lithium storage / release amount]
Next, a lithium electrode was fabricated by pressing a 100 μm-thick lithium metal foil on a copper foil. Next, 1 M (mol / l) of a salt of LiPF ₆ was dissolved in an organic solvent obtained by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 3: 7 to prepare an electrolyte solution.

  Then, the electrolytic solution was impregnated into a porous polyethylene film having a thickness of 25 μm, and the silicon electrode described above was disposed on one surface of the film, and the lithium electrode described above was disposed on the other surface. To sandwich the polyethylene film. Next, in order to obtain flatness, it was sandwiched between glass plates from both sides, and further covered with an aluminum laminate film to prepare an evaluation cell.

  The aluminum laminated film used was a three-layer film in which the outermost layer was a nylon film, the middle layer was an aluminum foil having a thickness of 20 μm, and the inner layer was a polyethylene film. Note that the lead terminal portion of each electrode was sealed without being laminated by fusing.

  Then, in order to evaluate the function of the electrode structure as a negative electrode, a lithium insertion / desorption cycle test (charge / discharge cycle test) was performed.

That is, the above-described cell for evaluation was connected to a charging / discharging device using the lithium electrode as the anode and the silicon electrode as the cathode. First, the current density was 0.112 mA / cm ² (70 mA per gram of the active material layer of the silicon electrode, that is, 70 mA). / Electrode layer weight g) to discharge the evaluation cell to insert lithium into the silicon electrode layer. Next, the cell for evaluation was charged at a current density of 0.32 mA / cm ² (200 mA / g of electrode layer), and lithium was desorbed from the silicon layer to remove the weight of the silicon electrode layer or the lithium per silicon powder or silicon alloy powder. The amount of electricity involved in insertion and desorption was evaluated in the voltage range of 0 to 1.2V.

  The performance evaluation results of lithium insertion and desorption of the above electrode structure were as follows.

  First, as a result of evaluating the ratio (efficiency) of the amount of electricity accompanying the release of lithium to the amount of electricity accompanying the insertion of lithium in the first and tenth times, the efficiency in the first example was about 85% in Reference Examples 2 and 3. The efficiency of the tenth time was 98% or less, whereas the efficiency of the first time was about 90% or more and the efficiency of the tenth time was 99% in the electrodes made from the electrode materials of Examples 1 to 12 of the present invention. 0.5% or more.

  In the tenth test, the amount of lithium released from the electrodes manufactured using the electrode materials of Reference Examples 2 and 3 was reduced to 87% or less in the first test. However, the amount of lithium released from the electrode made of the electrode material of this example was maintained at almost 100% of that of the first time even in the tenth time.

  In the electrode using the silicon powder of Reference Example 1, the insertion and desorption efficiencies of the first and tenth lithium insertions were 89% and 98%, respectively. It decreased to 70% of the first time.

  The amount of electricity accompanying the first lithium release was as follows. The electrodes prepared from the electrode material of the silicon alloy fine powder of Examples 1 to 18 all showed an electric charge of 1400 to 1800 mAh / g per electrode layer weight (excluding the current collector weight). The electrode manufactured from the silicon fine powder of Reference Example 1 showed a lithium emission electricity amount of 2000 mAh / g per electrode layer weight. The electrodes made from the silicon alloy fine powders of Reference Examples 2 and 3 showed only a lithium discharge electric quantity of 400 mAh / g or less.

  It was found that the silicon alloy electrode manufactured in this example has a long cycle life, and can store and discharge about 4 to 6 times the amount of electricity (the amount of electricity per electrode layer weight) of an electrode made of graphite. .

  In addition, regarding Examples 4, 5, 7, 10, 12 to 18, the half value of the peak related to silicon near the diffraction angle 2Θ = 28.4 ° by X-ray diffraction analysis before and after the ball mill treatment of the produced alloy powder. The width, the desorption (release) efficiency for the first insertion, and the electricity associated with Li release when performing electrochemical Li insertion and desorption reactions on electrodes made using alloy fine powder after ball milling The amounts are summarized in Table 1.

  From the results in Table 1 above, it was found that the desorption (release) efficiency for the first lithium insertion was extremely high, and the amount of electricity associated with Li release per electrode layer weight was also extremely high. In addition, although amorphousization can be promoted by ball milling, alloys with a high concentration of boron generally have a large half-value width of the peak related to silicon in the X-ray diffraction chart even before the ball milling, and the amorphous state is high. It was confirmed that the conversion was easily promoted. From empirical data, it is known that a lithium secondary battery using a negative electrode material in which amorphization has been promoted has a long repeated charge / discharge life.

  Next, the resistance of the electrode layer was evaluated.

  Using each of the electrode materials of Examples 1 to 18, a slurry was prepared in the same procedure as in the preparation of the electrode structure, the slurry was applied to a polyester sheet, dried, and then pressed with a roll press to form an electrode layer. Were prepared. When the sheet resistance of the electrode layer prepared by the above method was measured by a four-point needle measurement method, in each case, the electrode layer formed from the boron-doped electrode material was more sheet than the non-boron-doped electrode material. The result was a low resistance value.

  Next, a secondary battery was fabricated as Example 19 of the present invention.

(Example 19)
In this example, an electrode structure in which electrode layers were provided on both surfaces of a current collector using the negative electrode material of the present invention was manufactured, and the manufactured electrode structure was used as a negative electrode. No. 18650 (diameter 18 mmφ × height 65 mm) lithium secondary battery was manufactured.

(1) Production of Negative Electrode 603 Using silicon alloy fine powder as an electrode material in Examples 1 to 18, 69% by weight of silicon alloy fine powder and flat graphite powder as a conductive auxiliary material (specifically, 10% by weight of a substantially disc-shaped graphite powder having a diameter of about 5 μm and a thickness of about 1 μm), and 6% by weight of a graphite powder (substantially spherical and having an average particle size of 0.5 to 1.0 μm); 4% by weight of acetylene black (having a substantially spherical shape and an average particle size of 4 × 10 ⁻² μm) and N of polyamic acid (polyimide precursor) having a solid content of 14% as a binder -Methyl-2-pyrrolidone solution was mixed with 11% by weight in terms of solid content, and N-methyl-2-pyrrolidone was added and kneaded to prepare a slurry. Next, the slurry thus prepared was applied to both sides of a 15 μm thick electric field copper foil (electrochemically produced copper foil) with a coater, dried, and the thickness was adjusted by a roll press to obtain a thickness of 25 μm. The electrode structure of the active material layer was manufactured. The electrode structure obtained in the above procedure was cut into a predetermined size, and a lead of a nickel ribbon was connected to the electrode by spot welding to obtain a negative electrode 603.

(2) Production of positive electrode 606
(a) Lithium citrate and cobalt nitrate are mixed at a molar ratio of 1: 3, and an aqueous solution in which citric acid is added and dissolved in ion-exchanged water is sprayed into an air stream at 200 ° C. A cobalt oxide precursor was prepared.
(b) The lithium-cobalt oxide precursor obtained in (a) above was further heat-treated at 850 ° C. in an oxygen stream.
(c) 3% by weight of graphite powder and 5% by weight of polyvinylidene fluoride powder were mixed with 92% by weight of the lithium-cobalt oxide prepared in (b) above, and N-methyl-2-pyrrolidone was added thereto to form a slurry. Was prepared.
(d) After applying and drying the slurry obtained in (c) on both surfaces of the current collector 604 of a 20-μm-thick aluminum foil, the thickness of the positive electrode active material layer on one side is adjusted to 90 μm by a roll press. did. Further, an aluminum lead was connected by an ultrasonic welding machine, and dried under reduced pressure at 150 ° C. to produce a positive electrode 606.

(3) Preparation procedure of electrolyte
(a) A solvent was prepared by mixing ethylene carbonate and diethyl carbonate from which water had been sufficiently removed at a volume ratio of 3: 7.
(b) A solution obtained by dissolving 1 M (mol / L) of lithium hexafluorophosphate (LiPF ₆ ) in the solvent obtained in (a) above was used as an electrolytic solution.

(4) Separator 607
A 25 micron thick polyethylene microporous film was used as the separator.

(5) Assembling of Battery Assembling was all performed under a dry atmosphere in which moisture at a dew point of −50 ° C. or less was controlled.
(a) A separator 607 was sandwiched between the negative electrode 603 and the positive electrode 606, wound in a spiral shape so as to have a configuration of separator / positive electrode / separator / negative electrode / separator, and inserted into a stainless steel negative electrode can 608.
(b) Next, the negative electrode lead 612 was connected to the bottom of the negative electrode can 608 by spot welding. A neck was formed on the upper part of the negative electrode can by a necking device, and a positive electrode lead 613 was welded to a positive electrode cap 609 having a gasket 610 made of polypropylene by a spot welding machine.
(c) Next, after injecting the electrolytic solution, the positive electrode cap was covered, and the positive electrode cap and the negative electrode can were caulked with a caulking machine to form a battery.

  This battery was a battery with a positive electrode capacity regulation in which the capacity of the negative electrode was larger than that of the positive electrode.

(6) Evaluation Each battery was charged and discharged, and the discharge capacity was measured.

  As a result, the discharge capacity of each of the lithium secondary batteries using the electrode structures formed from the electrode materials of Examples 1 to 18 as the negative electrode exceeded 2800 mAh, and the average operating voltage was 3.3 V. .

(Example 20)
In this example, an electrode structure in which electrode layers were provided on both surfaces of a current collector using the negative electrode material of the present invention was manufactured, and the manufactured electrode structure was used as a negative electrode. No. 18650 (diameter 18 mmφ × height 65 mm) lithium secondary battery was manufactured.

(1) Production of Negative Electrode 603 Silicon, tin, and boron were mixed at a weight ratio of 74.5: 25.0: 0.5, and melted under an argon gas atmosphere to form a molten metal. A Si—Sn—B alloy powder was obtained by pouring a metal atomized with argon gas into the mixture. Next, the obtained Si—Sn—B alloy powder was pulverized in isopropyl alcohol with a media mill using zirconia balls to obtain a fine Si—Sn—B alloy powder having an average particle diameter of 0.3 μm. Next, the obtained Si-Sn-B alloy fine powder was further pulverized for 2 hours using a stainless steel ball in an argon gas atmosphere with an attritor, and further reduced to 100 parts by weight of the Si-Sn-B alloy fine powder. On the other hand, 2 parts of graphite powder, 1 part of carbon fiber and 1 part of multi-walled carbon nanotube were added and pulverized to obtain an electrode material of a silicon alloy fine powder in which a carbon material was composited.

  Next, 69% by weight of a silicon alloy fine powder obtained by compounding the obtained carbon material, and flat graphite powder (specifically, a substantially disk-shaped powder having a diameter of about 5 μm and a thickness of about 1 μm as a conductive auxiliary material). 10% by weight of graphite powder, 10% by weight of graphite powder (substantially spherical and having an average particle size of 0.5 to 1.0 μm), and N of polyamic acid (polyimide precursor) having a solid content of 14%. -Methyl-2-pyrrolidone solution was mixed with 11% by weight in terms of solid content, and N-methyl-2-pyrrolidone was added and kneaded to prepare a slurry. Next, the slurry thus prepared was applied on both sides of a 10 μm thick electric field copper foil (electrochemically produced copper foil) with a coater, dried, and the thickness was adjusted by a roll press to obtain a thickness of 25 μm. The electrode structure of the active material layer was manufactured. The electrode structure obtained by the above procedure was cut into a predetermined size, a lead of a nickel ribbon was connected to the electrode by spot welding, and dried under reduced pressure at 200 ° C. to obtain a negative electrode 603.

(2) Production of positive electrode 606
(a) Lithium citrate and cobalt nitrate are mixed at a molar ratio of 1: 3, and an aqueous solution in which citric acid is added and dissolved in ion-exchanged water is sprayed into an air stream at 200 ° C. A cobalt oxide precursor was prepared.
(b) The lithium-cobalt oxide precursor obtained in (a) above was further heat-treated at 850 ° C. in an oxygen stream.
(c) A mixture of 93% by weight of the lithium-cobalt oxide prepared in (b) above, 3% by weight of graphite powder and 1% by weight of carbon fiber, and 3% by weight of a solid component of polyamic acid (polyimide precursor) A slurry was prepared by adding an N-methyl-2-pyrrolidone solution of a polyamic acid so as to obtain a slurry.
(d) After applying and drying the slurry obtained in (c) on both surfaces of the current collector 604 made of aluminum foil having a thickness of 17 μm, the thickness of the positive electrode active material layer on one side is adjusted to 90 μm with a roll press. did. Further, an aluminum lead was connected with an ultrasonic welding machine, and dried under reduced pressure at 200 ° C. to produce a positive electrode 606.

  A battery was produced in the same manner as in Example 19, except that the above-described negative electrode and positive electrode were prepared and a microporous polyethylene film having a thickness of 17 μm was used as a separator.

  As a result of performing a charge / discharge test with constant current-constant voltage charging (maximum voltage of 4.2 V), the discharge capacity exceeded 3400 mAh in all cases, and the average operating voltage was 3.3 V. Also, from the results of the repeated charge / discharge test of the obtained battery, the charge / discharge rate of the battery using the carbon material-composite anode material was 1.5 times or more that of the battery not using the carbon material. It was found that repeated life was obtained.

(Example 21)
A lithium secondary battery of 18650 size (diameter 18 mmφ × height 65 mm) having a cross-sectional structure shown in FIG. 6 was prepared in the same manner as in Example 20 except for the following (1) preparation of a negative electrode.
(1) Preparation of Negative Electrode 603 Silicon, tin, and boron are mixed in a weight ratio of 74.5: 25.0: 0.5, melted in an argon gas atmosphere to form a molten metal, and then the molten metal is sprayed with high-pressure water. A water atomizing method was used to obtain a Si-Sn-B alloy powder. Next, the obtained Si—Sn—B alloy powder was pulverized in isopropyl alcohol with a media mill using zirconia balls to obtain a fine Si—Sn—B alloy powder having an average particle diameter of 0.3 μm.

  Next, the obtained Si-SnSi-Sn-B alloy fine powder was further pulverized for 2 hours using an stainless steel ball in an argon gas atmosphere with an attritor, and further, the Si-Sn-B alloy fine powder weight 100 3 parts of graphite powder, 2 parts of carbon fiber, and 30 parts of metal magnesium powder were added to each part and pulverized to obtain an electrode material of a silicon alloy fine powder in which a carbon material and magnesium metal were combined. As a result of X-ray diffraction analysis, a peak of metallic magnesium was observed in the obtained alloy fine particles.

  Next, 69% by weight of a silicon alloy fine powder obtained by compounding the obtained carbon material, and flat graphite powder (specifically, a substantially disk-shaped powder having a diameter of about 5 μm and a thickness of about 1 μm as a conductive auxiliary material). 10% by weight of graphite powder, 10% by weight of graphite powder (substantially spherical and having an average particle size of 0.5 to 1.0 μm), and N of polyamic acid (polyimide precursor) having a solid content of 14%. -Methyl-2-pyrrolidone solution was mixed with 11% by weight in terms of solid content, and N-methyl-2-pyrrolidone was added and kneaded to prepare a slurry.

  Next, the slurry thus prepared was applied on both sides of a 10 μm thick electric field copper foil (electrochemically produced copper foil) with a coater, dried, and the thickness was adjusted by a roll press to obtain a thickness of 25 μm. The electrode structure of the active material layer was manufactured. The electrode structure obtained by the above procedure was cut into a predetermined size, a lead of a nickel ribbon was connected to the electrode by spot welding, and dried under reduced pressure at 200 ° C. to obtain a negative electrode 603.

  Otherwise, the battery produced in the same manner as in Example 20 was subjected to a constant current-constant voltage charge (maximum voltage: 4.2 V) charge / discharge test. As a result, the discharge capacity exceeded 3000 mAh in all cases, and the average operating voltage was It was 3.5V.

(Example 22)
Except for the preparation of the positive electrode of (2) below and the use of the electrolytic solution of (3) below, lithium of 18650 size (diameter 18 mmφ × height 65 mm) having a cross-sectional structure shown in FIG. A secondary battery was manufactured.

(2) Production of positive electrode 606
(a) lithium citrate and 1 cobalt nitrate were mixed in a molar ratio of 3 for Li element of lithium citrate, 0.1 mol ratio of preparative yttrium nitrate _{Y (NO 3) 3 · 6H} 2 O and An aqueous solution obtained by adding zirconium oxyacetate ZrO (CH ₃ COO) _{2 in a} molar ratio of 0.4 to the Li element and citric acid and dissolving in ion-exchanged water was sprayed into an air stream at 200 ° C. A finely divided lithium-cobalt oxide precursor was prepared.
(b) The precursor of the lithium-cobalt oxide containing the yttrium element and the zirconium element obtained in (a) above was further heat-treated at 850 ° C. in an oxygen stream.
(c) 3% by weight of graphite powder and 5% by weight of polyvinylidene fluoride powder are mixed with 92% by weight of the lithium-cobalt oxide containing the yttrium element and the zirconium element prepared in the above (b), and then mixed with N-methyl-2. -A slurry was prepared by adding pyrrolidone.
(d) After applying and drying the slurry obtained in (c) on both surfaces of the current collector 604 of a 20-μm-thick aluminum foil, the thickness of the positive electrode active material layer on one side is adjusted to 90 μm by a roll press. did. Further, an aluminum lead was connected by an ultrasonic welding machine, and dried under reduced pressure at 150 ° C. to produce a positive electrode 606.

(3) Preparation procedure of electrolyte
(a) A solvent was prepared by mixing ethylene carbonate, γ-butyrolactone, and diethyl carbonate at a volume ratio of 1.5: 1.5: 7 from which water had been sufficiently removed.
(b) A solution obtained by dissolving lithium tetrafluoroborate (LiBF ₄ ) in a concentration of 1.5 M (mol / liter) in the solvent obtained in the above (a) was used as an electrolytic solution.

  A battery prepared in the same manner as in Example 20 except for the above operation was subjected to a charge / discharge test under constant current-constant voltage charging (maximum voltage 4.4 V). As a result, the discharge capacity exceeded 3700 mAh in all cases, and the average operation was performed. The voltage was 3.3V.

FIG. 2 is a schematic cross-sectional view of the silicon alloy particles of the present invention. The figure for explaining the reaction which lithium ion inserts into intrinsic silicon, p-type silicon, and n-type silicon. FIG. 1 is a conceptual diagram schematically showing a cross section of an embodiment of an electrode structure made of fine powder of a negative electrode material of a lithium secondary battery of the present invention. FIG. 1 is a conceptual diagram schematically showing a cross section of one embodiment of a secondary battery (lithium secondary battery) of the present invention. FIG. 3 is a cross-sectional view of a single-layer flat (coin-shaped) battery. FIG. 2 is a cross-sectional view of a spiral cylindrical battery.

Explanation of reference numerals

REFERENCE SIGNS LIST 100 Particles of silicon alloy 101 Microcrystal group of silicon 102 Microcrystal group of first element 103 Microcrystal group of second element 301 Electrode material layer 302 Electrode structure 303 Negative material fine powder 304 Conductive auxiliary agent 305 Binder 401, 501, 603 Negative electrodes 403, 503, 606 Positive electrodes 402, 502, 607 Ion conductor 404 Negative terminal 405 Positive terminal 406 Battery case (battery housing)
506 Negative electrode cap 505 Positive electrode can 506, 610 Gasket 601 Negative electrode current collector 602 Negative electrode active material layer 604 Positive electrode current collector 605 Positive electrode active material layer 608 Negative electrode can (negative electrode terminal)
611 Insulating plate 612 Negative lead 613 Positive lead 614 Safety valve

Claims (19)

In an electrode material for a lithium secondary battery comprising particles of a solid-state alloy containing silicon as a main component,
An electrode for a lithium secondary battery, wherein the particles of the solid-state alloy are microcrystalline silicon or amorphous silicon, in which microcrystalline or amorphous elements other than silicon are dispersed. material.   The electrode material for a lithium secondary battery according to claim 1, wherein the solid state alloy contains a pure metal or a solid solution.   The electrode material for a lithium secondary battery according to claim 1, wherein the composition of the alloy is an elemental composition that completely dissolves in a liquid state in which the alloy is molten.   The alloy is composed of silicon and at least a first element A having an atomic ratio lower than that of silicon, and the first element A is selected from the group consisting of tin, indium, gallium, copper, aluminum, silver, zinc, and titanium. The electrode material for a lithium secondary battery according to claim 1, wherein the electrode material is at least one element.   The alloy is composed of silicon and at least a first element A and a second element E having an atomic ratio lower than that of silicon, the atomic ratio of the first element is higher than the atomic ratio of the second element, and The first element A is at least one element selected from the group consisting of tin, aluminum and zinc, and the second element E is copper, silver, zinc, titanium, aluminum, vanadium, yttrium, zirconium, boron The at least one element selected from the group consisting of: the first element A and the second element E are different elements (A ≠ E). Electrode material for lithium secondary batteries.   The electrode material for a lithium secondary battery according to claim 1, wherein the content of silicon in the alloy is 50% by weight or more and 95% by weight or less.   The electrode material for a lithium secondary battery according to claim 1, wherein the alloy contains a eutectic. The eutectic is
(A) a eutectic of silicon and the first element A,
(B) a eutectic of silicon and the second element E,
(C) a eutectic of the first element A and the second element E (d) a eutectic of a combination of the above (a), (b) and (c). 8. The electrode material for a lithium secondary battery according to 7. At least one element as a dopant selected from the group consisting of boron, aluminum, gallium, antimony, and phosphorus is doped into silicon of the alloy in an atomic ratio of 1 × 10 ⁻⁸ to 2 × 10 ^−1. The electrode material for a lithium secondary battery according to claim 1, wherein: In an electrode material for a lithium secondary battery composed of silicon particles containing silicon as a main component,
The silicon is doped with at least one element as a dopant selected from the group consisting of boron, aluminum, gallium, antimony, and phosphorus in an atomic ratio of 1 × 10 ⁻⁸ to 2 × 10 ⁻¹ . An electrode material for a lithium secondary battery, comprising: The electrode material for a lithium secondary battery according to claim 9, wherein a ratio of the dopant to silicon is in an atomic ratio of 1 × 10 ⁻⁵ to 1 × 10 ⁻¹ .   The electrode material for a lithium secondary battery according to any one of claims 9 to 11, wherein the dopant is boron.   11. The lithium according to claim 1, wherein an average particle diameter of the alloy particles containing silicon as a main component or the particles containing silicon as a main component is 0.02 μm to 5 μm. 12. Electrode material for secondary batteries.   11. The lithium secondary battery according to claim 1, wherein the shape of the alloy particles containing silicon as a main component or the particles containing silicon as a main component is fine powder. Electrode material.   2. A material selected from the group consisting of a carbon material, metallic magnesium, and a carbon material and metallic magnesium is combined with the alloy particles containing silicon as a main component or the particles containing silicon as a main component. Alternatively, the electrode material for a lithium secondary battery according to claim 10.   An electrode structure comprising the electrode material according to claim 1, a conductive auxiliary material, a binder, and a current collector.   The electrode structure according to claim 16, wherein the conductive auxiliary material is a carbon material.   A secondary battery comprising a negative electrode, an electrolyte, and a positive electrode using the electrode structure according to claim 16, wherein a lithium oxidation reaction and a lithium ion reduction reaction are used. 19. The secondary battery according to claim 18, wherein the positive electrode material forming the positive electrode is a lithium-transition metal composite oxide containing at least an element selected from the group consisting of yttrium and yttrium and zirconium.

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