JP2016051622A - Active material for negative electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a lithium ion battery, which is superior in charge and discharge cycles.SOLUTION: An active material (B) for a negative electrode comprises porous silicon particles (A) of which the 50%-particle diameter (d50) is 10 to 1000 nm. The difference between the 90%-particle diameter (d90) of the porous silicon particles (A) and the 10%-particle diameter (d10) is preferably 10 to 500 nm. The surfaces of the porous silicon particles (A) are preferably coated with a conducting agent (D). A method for manufacturing the active material (B) for a negative electrode comprises the step of removing a supercritical or subcritical fluid (J) from a mixture (K) arranged by mixing porous silicon particles (A) of which the 50%-particle diameter (d50) is 10 to 1000 nm with a conducting agent (D) in the supercritical or subcritical fluid (J).SELECTED DRAWING: None

Description

  The present invention relates to a negative electrode active material, a method for producing the negative electrode active material, a lithium ion battery electrode having the negative electrode active material, a lithium ion battery having the electrode, and a method for producing the negative electrode active material.

  Non-aqueous electrolyte secondary batteries such as lithium ion batteries are characterized by high voltage and high energy density, so they are widely used in the field of portable information equipment, and the demand for them is rapidly expanding. A position as a standard battery for mobile information devices such as telephones and notebook computers has been established. Of course, along with the high performance and multi-functionality of portable devices, etc., even higher performance (for example, higher capacity and higher energy density) for non-aqueous electrolyte secondary batteries as its power source It has been demanded. In order to meet this demand, various methods, for example, higher density by improving the filling rate of electrodes, improvement of the depth of use of current active materials (especially negative electrodes), development of new high-capacity active materials, etc. are being carried out. . In reality, the capacity of the non-aqueous electrolyte secondary battery is reliably increased by these methods.

As a technique for increasing the capacity of a lithium ion battery, a technique using silicon, tin, or the like in place of the conventionally used graphite-based active material has been studied. Since these elements form an alloy with lithium, they have a very high theoretical capacity compared to graphite (graphite: 372 mAh / g, silicon: 4200 mAh / g, tin: 994 mAh / g). However, these alloy-forming active materials have a problem that the cycle characteristics are greatly inferior to those of the graphite-based active materials because the volume change accompanying charging / discharging is large.

  For example, Patent Document 1 discloses a technique using fluoroethylene carbonate to solve the problem of deterioration of cycle characteristics of a silicon-based active material. Patent Document 2 discloses a technique using triallyl isocyanate. Patent Document 3 discloses a technique of adding a spiro ammonium salt to an electrolytic solution. Further, Patent Document 4 discloses a technique for improving cycle characteristics by using a porous silicon active material.

JP 2011-49114 A JP 2014-73733 A Special table 2013-542562 gazette Special table 2013-509687 gazette

However, these techniques have not yet achieved satisfactory cycle characteristics.
An object of this invention is to provide the electrode for lithium ion batteries excellent in the charge / discharge cycle.

  As a result of intensive studies to achieve the above object, the present inventors have reached the present invention. That is, the present invention is a negative electrode active material containing porous silicon particles (A), wherein the 50% particle diameter (d50) of (A) is 10 to 1000 nm. A negative electrode (H) for a lithium ion battery containing the active material (B) for use; a lithium ion battery having the negative electrode (H) for a lithium ion battery; the porous silicon in a supercritical fluid or a subcritical fluid (J) It is a manufacturing method of the active material for negative electrodes (B) including the process of removing (J) from what mixed particle | grains (A) and electrically conductive agent (D) (K).

  The lithium ion battery which consists of an electrode which has the active material for negative electrodes (B) of this invention is excellent in cycling characteristics. Moreover, the lithium ion battery which consists of an electrode which has the active material for negative electrodes (B) which consists of porous silicon particles (A) coat | covered with the electrically conductive agent (D) obtained by the manufacturing method of this invention is cycling characteristics and output characteristics. Excellent.

The negative electrode active material (B) of the present invention contains porous silicon particles (A), and the 50% particle diameter (d50) of (A) is 10 to 1000 nm.
The negative electrode active material (B) contains porous silicon particles (A) as an essential component. Components other than (A) contained in (B) include graphite, amorphous carbon, polymer compound fired bodies (for example, those obtained by firing and carbonizing phenol resin and furan resin), cokes (for example, pitch coke, needle coke). And petroleum coke), carbon fibers, conductive polymers (for example, polyacetylene and polypyrrole), tin and the like. Of these, graphite is preferably used. The content of (A) in (B) is preferably 0.1 to 100% by weight, more preferably 1.0 to 90% by weight.

  The porous silicon particles (A) used in the present invention can be obtained by a known method. For example, there are a method of electrochemical etching, a method of crushing with ultrasonic waves, and a method of using these in combination. Among these, a method of crushing by using electrochemical etching and ultrasonic waves in combination is particularly preferably used.

The porous silicon particles (A) used in the present invention have a 50% particle diameter (d50) of 10 to 1000 nm, preferably 20 to 800 nm, more preferably 40 to 600, and most preferably. 60-400 nm. If the d50 of (A) is less than 10 nm, the dispersibility in the electrode for a lithium ion battery will be poor, and if the d50 of (A) is greater than 1000 nm, the expansion / contraction of silicon particles accompanying charge / discharge increases. It is not preferable from the viewpoint of cycle characteristics.
In the present invention, the 50% particle diameter (d50) is a value obtained by integrating the number. d50 means the particle diameter when the particle diameter is accumulated from the smallest, and the relative particle amount becomes 50%. d50 is a value often used when comparing particle size distributions. In the present invention, the 50% particle size (d50) is measured using a dynamic scattering method.

The difference between the 90% particle diameter (d90) and the 10% particle diameter (d10) (hereinafter referred to as d90-d10) of the porous silicon particles (A) used in the present invention is preferably 10 to 500 nm. More preferably, it is 20-400 nm, More preferably, it is 30-300 nm, Most preferably, it is 40-200 nm. If d90-d10 is larger than 10 nm, it is preferable from the viewpoint of yield, and if it is smaller than 500 nm, it is preferable from the viewpoint of cycle characteristics.
In d90-d10, the 90% particle size (d90) and the 10% particle size (d10) are the particle sizes when 90% and 10% are used instead of 50% of the above d50. The smaller the difference between d90 and d10, the smaller the particle size distribution.

The method for producing the porous silicon particles (A) having d90-d10 of 10 to 500 nm can be produced by a known method. Examples thereof include a method of electrochemically etching a silicon wafer, a method of obtaining a silicon film by ultrasonic treatment, and a method of ultrasonicating the silicon wafer after electrochemical pulse treatment.

The porous silicon particles (A) of the present invention are preferably coated with a conductive agent (D).
That (A) is covered with the conductive agent (D) means that (A) is uniformly coated on the surface with (D). At this time, (D) indicates not only the state in which (A) is completely covered, but also a state in which (D) covers (A) but has a portion that is not partially covered. Shall be included.
(D) can be used if it has a high electron conductivity. Specific examples of (D) include graphite-based conductive agents (for example, natural graphite and artificial graphite), carbon black-based conductive agents (for example, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black). , Carbon nanotube-based conductive agents, metal-based conductive agents (for example, aluminum powder and nickel powder), metal compound-based conductive agents (for example, zinc oxide and titanium oxide), and conductive polymers (for example, polythiophene, polypyrrole, polyaniline), and the like. .
As a method of coating (A) with (D), in addition to a method of treating in a supercritical fluid or subcritical fluid (J) described later, a method of directly contacting without solvent, mixing in a solvent and removing the solvent And a method of vapor deposition in a vacuum. Here, they are described as supercritical fluid (J1) and subcritical fluid (J2).

As a method of processing in the supercritical fluid or subcritical fluid (J), the mixture (C) in which the conductive agent (D) is dispersed or dissolved in (J) and the porous silicon particles (A) are mixed. Then, the process of removing (J) is included. Since (D) can be uniformly coated with respect to (A) by treating with (J), preferable performance is obtained from the viewpoint of battery characteristics.

  As a supercritical fluid (J1), it exists as a non-aggregating high-density fluid in a temperature / pressure region that exceeds the limit (critical point) where gas and liquid can coexist, and does not aggregate even when compressed. As long as the fluid is in a state of a critical pressure or higher, there is no particular limitation, and it can be appropriately selected according to the purpose, but a fluid having a low critical temperature is preferable. This supercritical fluid includes, for example, carbon monoxide, carbon dioxide, ammonia, nitrogen, water, methanol, ethanol, ercol solvents such as n-butanol, ethane, propane, 2,3-dimethylbutane, benzene, toluene and the like. Hydrocarbon solvents, halogen solvents such as methylene chloride and chlorotrifluoromethane, and ether solvents such as dimethyl ether are preferred. Among these, carbon dioxide is particularly preferable because it has a critical pressure of 7.3 MPa and a critical temperature of 31 ° C., so that it can easily create a supercritical state and is nonflammable and easy to handle. These fluids may be used alone or in combination of two or more.

  The critical temperature and critical pressure of the supercritical fluid are not particularly limited and can be appropriately selected according to the purpose. However, the critical temperature is preferably −273 ° C. or more and 300 ° C. or less, particularly 0 ° C. or more and 200 ° C. or less. preferable.

The subcritical fluid (J2) used in the present invention is not particularly limited as long as it exists as a high pressure liquid in the temperature and pressure regions near the critical point, and can be appropriately selected according to the purpose. The compound mentioned as a supercritical fluid mentioned above can be used conveniently also as a subcritical fluid.

  The critical temperature and critical pressure of the subcritical fluid (J2) are not particularly limited and can be appropriately selected according to the purpose, but the critical temperature is preferably in the range of −50 ° C. to 300 ° C.

Furthermore, an organic solvent can also be added to the above-mentioned supercritical fluid and subcritical fluid. Although it does not necessarily limit as addition amount of an organic solvent, it is preferable that it is 10-1000 volume% with respect to a supercritical fluid, More preferably, it is 50-700 volume%.
By adding an organic solvent, the solubility in the supercritical fluid can be adjusted more easily. Such an organic solvent is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, ethyl formate, ethyl acetate, and n acetate. Ester solvents such as -butyl, ether solvents such as diisopropyl ether, dimethoxyethane, tetrahydrofuran, dioxolane, or dioxane, N, N-dimethylformamide, N, N-dimethylacetamide, or N-methyl-2-pyrrolidone Amide solvents, dichloromethane, chloroform, bromoform, methyl iodide, dichloroethane, trichloroethane, trichloroethylene, chlorobenzene, o-dichlorobenzene, fluorobenzene, bromobenzene, iodobenzene Is a halogenated hydrocarbon solvent such as 1-chloronaphthalene, n-pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene, benzene, toluene, o-xylene, m- Examples thereof include hydrocarbon solvents such as xylene, p-xylene, ethylbenzene, and cumene.

The negative electrode for lithium ion battery (H) of the present invention is obtained by dispersing the active material for negative electrode (B) and binder (E) of the present invention in a solvent to obtain a slurry, and then coating the slurry on a current collector. And it can obtain by drying a solvent. The negative electrode for lithium ion batteries of the present invention may contain a negative electrode active material (F) and / or a conductive additive (G) other than (B) as necessary.

  Examples of the binder (E) include high molecular compounds such as starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, and polypropylene.

  The negative electrode active material (F) other than (B) contained as an optional component in the negative electrode for lithium ion battery (H) of the present invention includes graphite, amorphous carbon, polymer compound fired body (for example, phenol resin and furan resin). Baked and carbonized), cokes (for example, pitch coke, needle coke and petroleum coke), carbon fibers, conductive polymers (for example, polyacetylene and polypyrrole), tin and the like. Of these, graphite is preferably used.

  The conductive auxiliary agent (G) contained as an optional component in the negative electrode (H) for lithium ion batteries of the present invention includes carbon blacks (for example, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black and thermal Black) and metal powder (for example, aluminum powder and nickel powder), conductive metal oxide (for example, zinc oxide and titanium oxide), and the like.

  Examples of the solvent used in preparing the electrode of the present invention include water, N-methylpyrrolidone, acetone and toluene.

Each preferred content of (B), (E), and conductive additive (G) based on the total weight of the negative electrode active material (B) and the binder (E) in the negative electrode (H) for lithium ion batteries of the present invention. The amounts are as follows.

The content of (B) is preferably 50 to 98% by weight, more preferably 70 to 95% by weight from the viewpoint of battery capacity.
The content of the binder (E) is preferably 2 to 50% by weight, and more preferably 5 to 30% by weight from the viewpoint of battery capacity.
The content of the conductive auxiliary agent (G) is preferably 0 to 29% by weight, more preferably 1 to 10% by weight, from the viewpoint of battery output.

  The lithium ion battery of the present invention is obtained by using the negative electrode for a lithium ion battery of the present invention as a negative electrode when an electrolyte is injected into a battery can containing a positive electrode, a negative electrode, and a separator to seal the battery can. Can do.

  As a separator in a lithium ion battery, a microporous film made of polyethylene or polypropylene film, a multilayer film of porous polyethylene film and polypropylene, a nonwoven fabric made of polyester fiber, aramid fiber, glass fiber, etc., and silica, alumina on the surface thereof And those having ceramic fine particles such as titania attached thereto.

  As the battery can in the lithium ion battery, metal materials such as stainless steel, iron, aluminum and nickel-plated steel can be used, but plastic materials can also be used depending on the battery application. Further, the battery can can be formed into a cylindrical shape, a coin shape, a square shape, or any other shape depending on the application.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not limited to these. Hereinafter, unless otherwise specified, “%” represents “% by weight” and “parts” represents “parts by weight”.

  The particle size and particle size distribution in this example were measured by dispersing in water using a particle size distribution meter (manufactured by Horiba: nano Partica SZ-100).

<Example 1>
Preparation of Active Material for Negative Electrode (B-1) A porous silicon wafer etched with hydrogen fluoride was placed on an aluminum foil, and a current was applied at 50 mA / cm ² for 8 seconds. Next, a current was applied at 400 mA / cm ² for 0.5 seconds. After repeating this cycle 30 times, the porous silicon wafer was peeled off from the aluminum foil. Porous silicon particles (A-1) were obtained by treatment with an ultrasonic cleaner in water. d50 was 250 nm and d90-d10 was 80 nm. (A-1) was used as the negative electrode active material (B-1).

<Example 2>
Preparation of active material for negative electrode (B-2) Porous silicon particles (A-2) were obtained in the same manner as in Example 1 except that the current flow time for 8 seconds was 16 seconds. d50 was 450 nm and d90-d10 was 120 nm. (A-2) was used as the negative electrode active material (B-1).

<Example 3>
Preparation of Active Material for Negative Electrode (B-3) Porous silicon particles (A-3) were obtained in the same manner as in Example 1 except that the current flowing time for 8 seconds was 25 seconds. d50 was 800 nm and d90-d10 was 420 nm. (A-3) was used as the negative electrode active material (B-3).

<Example 4>
Preparation of Active Material for Negative Electrode (B-4) (A-1) 90.0 parts, Ketjen Black [Ketjen Black EC300J, manufactured by Lion Corporation, 40 nm particle size] 5 parts was charged into a pressure-resistant reaction vessel, The temperature was raised to 40 ° C. After heating, carbon dioxide was supplied to 10 MPa, and the mixture was stirred for 10 minutes. Then, the contents were taken out from the take-out nozzle to return to normal pressure, carbon dioxide was removed, and porous silicon particles (with a coating layer formed on the surface layer) ( A-4) was obtained. d50 was 300 nm and d90-d10 was 140 nm. (A-4) was used as the negative electrode active material (B-4). The presence or absence of the coating layer was confirmed with a scanning electron microscope (manufactured by JEOL, JSM-7100F).

<Example 5>
Preparation of Active Material for Negative Electrode (B-5) 10 parts of (A-1) and 90 parts of natural graphite were mixed to obtain an active material for negative electrode (B-5).

<Comparative Example 1>
Preparation of Comparative Active Material (B′-1) Comparative silicon particles (A′-1) were obtained in the same manner as in Example 1 except that the current flow time for 8 seconds was 40 seconds. d50 was 1350 nm and d90-d10 was 720 nm. (A′-1) was used as the negative electrode active material (B′-1).

<Comparative Example 2>
Silicon powder (manufactured by Aldrich, d50 = 10 μm, d90-d10 = 4.5 μm) was used as the negative electrode active material (B′-2).

  Table 1 summarizes the negative electrode active material (B) of the example and the comparative active material (B ') of the comparative example.

<Examples 6 to 10 and Comparative Examples 3 to 4>
Evaluation of Lithium Ion Battery, Electrode, Electrolyte Solution A negative electrode for a lithium ion battery having the above active material for negative electrode (B) or comparative active material (B ′) was prepared by the following method, and the following negative electrode was used. A lithium ion battery was produced by this method.
The results of evaluating charge / discharge cycle characteristics and low-temperature charge / discharge cycle characteristics by the following methods are shown in Table 2.

[Production of positive electrode for lithium ion battery]
9 parts by weight of LiCoO ₂ powder, 5 parts by Kechen Black [manufactured by Sigma Aldrich Co., Ltd.], 5 parts by polyvinylidene fluoride [manufactured by Sigma Aldrich Co., Ltd.] and the parts shown in Table 2 (B) or (B ′ ) In a mortar, 70.0 parts of 1-methyl-2-pyrrolidone [manufactured by Tokyo Chemical Industry Co., Ltd.] was added, and further mixed well in a mortar to obtain a slurry. The obtained slurry was applied to one side of an aluminum electrolytic foil having a thickness of 20 μm using a wire bar in the air, dried at 80 ° C. for 1 hour, and further under reduced pressure (1.3 kPa) at 80 ° C. It was dried for 2 hours and punched out to 15.95 mmφ to produce a positive electrode for a lithium ion battery.

[Production of negative electrode for lithium ion battery]
90.0 parts of the negative electrode active material obtained in Examples 1 to 5 and Comparative Examples 1 to 2, 7.5 parts of polyvinylidene fluoride and 200 parts of 1-methyl-2-pyrrolidone [manufactured by Tokyo Chemical Industry Co., Ltd.] The slurry was sufficiently mixed with a mortar. The obtained slurry was applied to one side of a 20 μm-thick copper foil in the air using a wire bar, dried at 80 ° C. for 1 hour, and further under reduced pressure (1.3 kPa) at 80 ° C. for 2 hours. It dried, punched to 16.15 mmphi, and 30 micrometers in thickness was made with the press, and the negative electrode for lithium ion batteries of Examples 6-10 and Comparative Examples 3-4 was produced.

[Production of lithium-ion batteries]
The positive electrode and the negative electrode of Examples 6 to 10 and Comparative Examples 3 to 4 are arranged at both ends in the 2032 type coin cell so that the coated surfaces face each other, and a separator (polypropylene nonwoven fabric) is inserted between the electrodes, and lithium An ion battery cell was produced. The solution was poured and sealed in a cell in which an electrolytic solution was prepared by dissolving LiPF ₆ in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1: 1) at a ratio of 12 wt%. The charge / discharge cycle characteristics and output characteristics were evaluated by the following methods.

<Evaluation of charge / discharge cycle characteristics>
Using a charge / discharge measuring device “Battery Analyzer 1470” [manufactured by Toyo Technica Co., Ltd.] at room temperature, the battery was charged to a voltage of 4.3 V with a current of 0.1 C, and after a pause of 10 minutes, 0.1 C The battery voltage was discharged to 3.5 V with this current, and this charge / discharge was repeated. At this time, the battery capacity at the first charge and the battery capacity at the 30th cycle charge were measured, and the charge / discharge cycle characteristics were calculated from the following formula. It shows that charging / discharging cycling characteristics are so favorable that a numerical value is large.
Charging / discharging cycle characteristics (%) = (battery capacity at 30th charge / battery capacity at first charge) × 100

<Evaluation of output characteristics>
Using a charge / discharge measuring device “Battery Analyzer 1470” [manufactured by Toyo Technica Co., Ltd.], charge to a voltage of 4.5 V with a current of 0.1 C, and after a pause of 10 minutes, apply a voltage with a current of 0.1 C The battery was discharged to 3.5 V, and the discharge capacity (hereinafter referred to as 0.1 C discharge capacity) was measured. Next, the battery was charged to a voltage of 4.5 V with a current of 0.1 C, and after 10 minutes of rest, the voltage was discharged to 3.5 V with a current of 1 C, and the capacity (hereinafter referred to as 1 C discharge capacity) was measured. The capacity maintenance rate at the time of 1C discharge is calculated. The larger the value, the better the output characteristics.
Capacity maintenance rate during 1 C discharge (%) = (1 C discharge capacity / 0.1 C discharge capacity) × 100

  As is clear from Examples 6 to 10 and Comparative Examples 3 and 4, the active material that satisfies the requirements of the present invention is excellent in charge / discharge cycle characteristics. In particular, it was found that Example 9 in which a conductive agent coating was applied, and porous silicon particles 10 and 10 using graphite in combination as other active materials were particularly excellent. In Example 9, it is considered that the surface of the active material was uniformly coated with a conductive agent with a supercritical fluid. In Example 10, it is considered that the gap between graphite particles as other active materials could be filled in a preferred form.

  The electrode for a lithium ion battery using the negative electrode active material (B) of the present invention is effective for a lithium ion battery, and can be suitably used particularly for a lithium ion battery for an electric vehicle. Moreover, it is applicable also to electrochemical devices (electric double layer capacitor, nickel metal hydride battery, nickel cadmium battery, air battery, alkaline battery, etc.) other than those disclosed in the present invention.

Claims (6)

  A negative electrode active material containing porous silicon particles (A), wherein the 50% particle diameter (d50) of (A) is 10 to 1000 nm.   The negative electrode active material (B) according to claim 1, wherein the difference between the 90% particle diameter (d90) and the 10% particle diameter (d10) of the porous silicon particles (A) is 10 to 500 nm.   The negative electrode active material (B) according to claim 1 or 2, wherein the surface of the porous silicon particles (A) is coated with a conductive agent (D).   The negative electrode (H) for lithium ion batteries containing the active material for negative electrodes (B) of any one of Claims 1-3.   The lithium ion battery which has the negative electrode (H) for lithium ion batteries of Claim 4. From a supercritical fluid or subcritical fluid (J) in which a porous silicon particle (A) having a 50% particle size (d50) of 10 to 1000 nm and a conductive agent (D) are mixed (K), supercritical The manufacturing method of the active material for negative electrodes (B) including the process of removing a fluid or a subcritical fluid (J).