JP6331395B2 - Negative electrode active material for power storage device and method for producing the same - Google Patents

Description

  The present invention relates to a method for producing a negative electrode active material used for an electricity storage device such as a lithium ion secondary battery used in a portable electronic device or an electric vehicle, for example.

  In recent years, with the widespread use of portable electronic devices, electric vehicles, and the like, there is an increasing demand for higher capacity and smaller size of power storage devices such as lithium ion secondary batteries. If the capacity of the electricity storage device is increased, it will be easy to reduce the size of the battery. Therefore, there is an urgent need to develop the capacity of the electricity storage device.

For example, high potential type LiCoO ₂ , LiCo _1-x Ni _x O ₂ , LiNiO ₂ , LiMn ₂ O _{4 and the} like are widely used as the positive electrode active material for lithium ion secondary batteries. On the other hand, a carbon material is generally used for the negative electrode active material. These materials function as an electrode active material that reversibly occludes and releases lithium ions by charging and discharging, and a so-called rocking chair type secondary battery that is electrochemically connected by a non-aqueous electrolyte or a solid electrolyte. Configure. For example, a binder or a conductive auxiliary agent is added to these electrode active materials, and the electrode active material is used as an electrode by applying it to the surface of a metal foil or the like that serves as a current collector.

  Examples of the carbon material used for the negative electrode active material include graphitic carbon material, pitch coke, fibrous carbon, and soft carbon. However, the carbon material has a problem that it is difficult to increase the capacity of the battery because only 0.17 lithium atoms can be occluded and released per carbon atom. Specifically, even if a stoichiometric amount of lithium insertion capacity can be realized, the battery capacity of the carbon material is limited to about 372 mAh / g.

  As a negative electrode active material capable of inserting and extracting lithium ions and having a higher capacity density than a negative electrode active material made of a carbon material, a negative electrode active material containing Si or Sn exists. However, the negative electrode active material containing Si and Sn has a remarkably large volume change due to the insertion and release reaction of lithium ions during charge and discharge, and therefore the structure of the negative electrode active material deteriorates and cracks when repeatedly charged and discharged. It tends to occur. As cracks progress, in some cases, cavities are formed in the negative electrode active material and may be pulverized. As a result, since the electron conduction network is divided, there has been a problem of a decrease in discharge capacity (cycle characteristics) after repeated charge and discharge.

  Thus, in Patent Document 1, a negative electrode active material containing SiO as a negative electrode active material capable of inserting and extracting lithium ions and having excellent cycle characteristics as compared with a negative electrode active material containing Si or Sn. Has been proposed.

This negative electrode active material is produced by a gas phase synthesis method shown by the following procedure. First, Si powder and SiO ₂ powder are mixed and granulated in advance, and this is heated and vaporized at 1250 to 1350 ° C. in a vacuum, so that SiO is deposited on the deposition substrate provided in the vacuum vessel, and the solid state of SiO Get things. Next, this solid matter is taken out from the vacuum vessel, pulverized and classified to produce powdery SiO.

WO2006 / 011290

  The negative electrode active material made of SiO produced by this production method has a problem that although the cycle characteristics are improved, the discharge capacity is lowered (for example, 400 to 501 mAh / g).

The cause of this is not clarified, but it is presumed that a part of SiO causes a disproportionation reaction when SiO is deposited, and phase separation occurs between the Si component and the SiO ₂ component. At this time, since the SiO ₂ component does not contribute to the charge / discharge reaction, the discharge capacity of the negative electrode active material is considered to be low.

  This invention is made | formed in view of the above situations, and it aims at providing the negative electrode active material for electrical storage devices which has favorable cycling characteristics and high discharge capacity, and its manufacturing method.

The method for producing a negative electrode active material for an electricity storage device according to the present invention includes an oxide material containing SiO ₂ and a non-oxide material containing at least one selected from Si, Al, Ti, Li, Mg, Zr, and Ca. And a step of subjecting the raw material containing the material to mechanical milling.

Furthermore, the oxide material, in mass%, preferably contains more _SiO 2 30%. Glass may be used as the oxide material.
Furthermore, the raw material preferably contains a carbon material.

Furthermore, it is preferable that the said raw material contains 5 to 95% of oxide materials, 5 to 95% of non-oxide materials, and 0 to 20% of carbon materials by mass%.
Furthermore, the mechanical milling treatment is preferably performed in a non-oxidizing atmosphere.

  The negative electrode active material for an electricity storage device of the present invention is preferably produced by the production method.

The negative electrode active material for an electricity storage device of the present invention is represented by a general formula SiM _x O ₂ (0 <x <4, M is at least one selected from Si, Al, Ti, Li, Mg, Zr, and Ca). Including material.

Moreover, it is preferable that the negative electrode active material for electrical storage devices of this invention contains a carbon material.
Furthermore, it is preferable that a carbon material is dispersed in a material represented by the general formula SiM _x O ₂ .

The crystallite size of Si is preferably 100 nm or less.
Further, the negative electrode active material for an electricity storage device of the present invention may contain a glass component other than SiO ₂ .

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the negative electrode active material for electrical storage devices which has favorable cycling characteristics and high discharge capacity.

The method for producing a negative electrode active material for an electricity storage device of the present invention is referred to as an oxide material containing SiO ₂ and at least one selected from Si, Al, Ti, Li, Mg, Zr, and Ca (hereinafter referred to as M component). And a non-oxide material containing a material, and a mechanical milling process for the raw material.

By subjecting the raw material to mechanical milling, high impact energy can be imparted to the raw material. Due to the high impact energy, the SiO ₂ component contained in the oxide material reacts with the M component contained in the non-oxide material, and the SiO ₂ component is efficiently reduced to contain the SiO component and the M _x O component. A negative electrode active material is formed. The SiO component in the negative electrode active material plays a role of occluding and releasing Li ions and electrons, and the M _x O component plays a role of mitigating volume changes associated with the insertion and removal of Li ions and electrons of the SiO component. . As a result, the SiO ₂ component is reduced to the SiO component at a very high rate, and the remaining SiO 2 component and M component are reduced, so that a negative electrode active material having good cycle characteristics and high discharge capacity can be obtained. .

By making M contained in the non-oxide raw material at least one selected from Si, Al, Ti, Li, Mg, Zr, and Ca, SiO ₂ can be reduced. More preferred are Si, Al, Mg, and Zr that are easy to handle, and most preferred is Si that is inexpensive.

  For the mechanical milling process, a general pulverizer such as a mortar, a rake machine, a ball mill, an attritor, a vibration ball mill, a satellite ball mill, a planetary ball mill, a jet mill, or a bead mill can be used. In particular, it is preferable to use a planetary ball mill. The planetary ball mill can efficiently generate very high impact energy by rotating the platform while the pot rotates.

The content of SiO ₂ in the oxide material is preferably 30% or more, 50% or more, or 60% or more, and more preferably 95% or more, in mass%. When SiO ₂ content is too low, SiO component is reduced to be formed in the negative electrode active material, negative electrode active material is difficult to obtain with a high discharge capacity.

SiO ₂ in the oxide material may be either crystalline or amorphous. Crystals are preferred because they are less expensive.

Further, glass may be used as the oxide material. As the glass, glass having a high SiO ₂ content is preferable. Specifically, the content of SiO _{2 in} the glass is 30% by mass, preferably 30% or more, more preferably 40% or more, and particularly preferably 50% or more. Specific examples of the glass include borosilicate glass, soda lime glass, aluminoborosilicate glass, alkali aluminosilicate glass, phosphosilicate glass, and tin silicate glass.

  The shape of the oxide material and the non-oxide material is not particularly limited, and examples thereof include a bulk shape, a film shape, and a powder shape. Preferably, it is in powder form.

Furthermore, the raw material preferably contains a carbon material. By containing the carbon material, SiO ₂ in the oxide material can be reduced in a shorter time.

  Examples of the carbon material include highly conductive carbon black such as acetylene black and ketjen black, carbon powder such as graphite, and carbon fiber. Of these, acetylene black having a high electron conductivity is preferable.

  Moreover, it is preferable that the said raw material contains 5 to 95% of oxide materials, 5 to 95% of non-oxide materials, and 0 to 20% of carbon materials by mass%. More preferably, the oxide material is 25 to 90%, the non-oxide material is 5 to 74%, and the carbon material is 1 to 10%. With this configuration, a negative electrode active material having good cycle characteristics and high discharge capacity can be obtained.

  The mechanical milling treatment is preferably performed in a non-oxidizing atmosphere. By setting it as a non-oxidizing atmosphere, the oxidation of SiO formed by the mechanical milling process can be suppressed. The non-oxidizing atmosphere includes a reducing atmosphere and an inert atmosphere.

In order to obtain a reducing atmosphere, it is preferable to supply a reducing gas during the mechanical milling process. The reducing gas is preferably in a volume% of N ₂ 90 to 99.5%, H ₂ 0.5 to 10%, particularly N ₂ 92 to 99% and H ₂ 1 to 4%.

  In order to obtain an inert atmosphere, it is preferable to supply an inert gas during the mechanical milling process. As the inert gas, it is preferable to use any of nitrogen, argon, and helium.

  The negative electrode active material for an electricity storage device manufactured by the above manufacturing method preferably contains an amorphous phase. In this case, the crystallinity of the oxide material is preferably 95% or less, 80% or less, 70% or less, 50% or less, particularly 30% or less. The smaller the degree of crystallinity (the larger the proportion of the amorphous phase), the more the volume change during repeated charge / discharge can be relaxed, and the better the cycle characteristics can be obtained.

The degree of crystallinity is obtained from a diffraction line profile of 10 to 60 degrees as a 2θ value obtained by powder X-ray diffraction measurement using CuKα rays. Specifically, the integrated intensity obtained by peak-separating a broad diffraction line (amorphous halo) at 10 to 45 ° from the total scattering curve obtained by subtracting the background from the diffraction line profile is Ia, 10 When the total integrated intensity obtained by peak separation of each crystalline diffraction line detected at ˜60 ° is Ic, the crystallinity Xc can be obtained from the following equation.
Xc = [Ic / (Ic + Ia)] × 100 (%)

  The crystallite size of Si can be measured by powder X-ray diffraction measurement using CuKα rays. The crystallite size of Si is preferably 100 nm or less, more preferably 80 nm or less, and particularly preferably 50 nm or less. By reducing the crystallite size of Si, cycle characteristics are improved. The lower limit of the Si crystallite size is not particularly limited, but is generally preferably 0.3 nm or more.

  The shape of the negative electrode active material for an electricity storage device is not particularly limited, but is preferably a powder. In the case of a powder, the average particle size is preferably 0.1 to 20 μm, 0.3 to 15 μm, 0.5 to 10 μm, particularly 1 to 5 μm. The maximum particle size is preferably 150 μm or less, 100 μm or less, 75 μm or less, particularly 55 μm or less. If the average particle size or the maximum particle size is too large, the volume change of the negative electrode active material associated with insertion and extraction of lithium ions during charge / discharge cannot be alleviated, and the current collector tends to peel off. As a result, repeated charge / discharge tends to significantly reduce the discharge capacity. On the other hand, if the average particle size is too small, the powder is in a poorly dispersed state when formed into a paste, and it tends to be difficult to produce a uniform electrode.

  Here, the average particle size and the maximum particle size are D50 (50% volume cumulative diameter) and D99 (99% volume cumulative diameter), respectively, as the median diameter of primary particles, and were measured by a laser diffraction particle size distribution analyzer. Value.

Note that the negative electrode active material for an electricity storage device manufactured by the above-described manufacturing method using a raw material containing an oxide material and a non-oxide material has a general formula of SiM _x O ₂ (0 <x <4, where M is Si , Al, Ti, Li, Mg, Zr, and Ca).

In addition, when the raw material includes a carbon material, the negative electrode active material for an electricity storage device manufactured by the above manufacturing method includes a carbon material.
Moreover, the negative electrode active material for an electricity storage device tends to have a configuration in which a carbon material is dispersed in a material represented by the general formula SiM _x O ₂ .

Further, by using the glass as an oxide material, a negative electrode active material obtained, glass components other than SiO _2. Examples of glass components other than SiO ₂ include Al ₂ O ₃ , P ₂ O ₅ , B ₂ O ₃ , Bi ₂ O ₃ , MgO, CaO, SrO, BaO, TiO ₂ , ZrO ₂ , Li ₂ O, and Na. ₂ O, K ₂ O, SnO, MnO, ZnO and the like can be mentioned. The content of the glass component other than SiO ₂ in the negative electrode active material is mass%, preferably 70% or less, more preferably 50% or less, and particularly preferably 40% or less. The lower limit of the content of the glass component other than the SiO ₂ of the negative electrode active material is not particularly limited, is generally 5% or more.

  A negative electrode for an electricity storage device is obtained by adding a binder or a conductive additive to the negative electrode active material for an electricity storage device obtained by the production method of the present invention.

  Examples of the binder include cellulose derivatives such as carboxymethylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, hydroxyethylcellulose, ethylcellulose, hydroxymethylcellulose, and water-soluble polymers such as polyvinyl alcohol; thermosetting polyimide, phenolic resin, epoxy resin, urea Examples thereof include thermosetting resins such as resins, melamine resins, unsaturated polyester resins, and polyurethanes; polyvinylidene fluoride.

Examples of the conductive assistant include highly conductive carbon black such as acetylene black and ketjen black, carbon powder such as graphite, and carbon fiber.
The negative electrode active material for an electricity storage device can be used as an anode for an electricity storage device by applying it to the surface of a metal foil or the like that serves as a current collector.

  In addition, after charging / discharging the electrical storage device produced using the negative electrode active material of this invention, metal lithium, lithium oxide (an oxide, such as a silicic acid, phosphoric acid, boric acid, and a lithium atom are contained in a negative electrode active material. Oxide (including complexed lithium composite oxide), Si metal, Si-Li alloy, and the like may be included.

  The negative electrode active material produced by the method of the present invention is not only a lithium ion secondary battery, but also other non-aqueous secondary batteries, and further, a negative electrode active material for lithium ion secondary batteries and a non-aqueous electric double layer The present invention can also be applied to a hybrid capacitor combined with a positive electrode active material for a capacitor.

  A lithium ion capacitor, which is a hybrid capacitor, is one type of asymmetric capacitor that has different charge / discharge principles for a positive electrode and a negative electrode. The lithium ion capacitor has a structure in which a negative electrode for a lithium ion secondary battery and a positive electrode for an electric double layer capacitor are combined. Here, the positive electrode forms an electric double layer on the surface and is charged / discharged by utilizing a physical action (electrostatic action), whereas the negative electrode has a lithium ion chemistry similar to the lithium ion secondary battery described above. Charge and discharge by reaction (occlusion and release).

  For the positive electrode of the lithium ion capacitor, a positive electrode active material made of carbonaceous powder having a high specific surface area such as activated carbon, polyacene, or mesophase carbon is used. On the other hand, a negative electrode active material produced by the method of the present invention can be used for the negative electrode.

[Example]
EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to this Example.

(Examples 1-3 and Comparative Examples 1-3)
(1) negative active material prepared in Examples 1 to 3 of the negative electrode active material, an oxide containing SiO ₂ material, a non-oxide material, mass% according to the raw material consisting of acetylene black is a carbon material in Table 1 And 30 g of the raw material and 1 kg of φ5 mm ZrO ₂ balls are placed in a 500 mL ZrO ₂ pot, and mechano-milling is performed under the processing conditions shown in Table 1 using a planetary ball mill (P6 made by Fritch). It was produced by.

  The negative electrode active materials of Comparative Examples 1 to 3 were crystalline Si powder, metal Sn powder, and SiO powder produced by a vapor phase synthesis method, respectively.

  About the obtained negative electrode active material, the crystallinity degree and crystallite size of the negative electrode active material were measured by said powder X-ray-diffraction measurement, and the result was shown in Table 1. The crystallite size is the crystallite size of Si.

(2) Production of negative electrode The obtained negative electrode active material, conductive additive and binder were weighed in a weight percentage of 80: 5: 15, dispersed in dehydrated N-methylpyrrolidone, and then rotated. -It stirred sufficiently with the revolution mixer and was made into the slurry. Here, SuperC65 (manufactured by Timcal) was used as the conductive assistant, and thermosetting polyimide resin was used as the binder.

  Next, using a doctor blade with a gap of 75 μm, the obtained slurry was coated on a 20 μm thick copper foil as a negative electrode current collector, vacuum-dried with a dryer at 70 ° C., and then between a pair of rotating rollers. An electrode sheet was obtained by pressing through. This electrode sheet was punched to a diameter of 11 mm with an electrode punching machine and dried under reduced pressure at a temperature of 200 ° C. for 8 hours to obtain a circular working electrode (a negative electrode for a non-aqueous secondary battery).

(3) Preparation of test battery The working electrode was placed on the lower lid of the coin cell with the copper foil surface facing down, and dried on the top at 70 ° C. for 8 hours under reduced pressure for 16 hours in a polypropylene porous membrane (Hoechst Cera A separator comprising Cellguard # 2400 manufactured by Needs Co., Ltd. and metallic lithium as a counter electrode were laminated to prepare a test battery. As the electrolytic solution, 1M LiPF ₆ solution / EC: DEC = 1: 1 (EC = ethylene carbonate, DEC = diethyl carbonate) was used. The test battery was assembled in an environment with a dew point temperature of −40 ° C. or lower.

(4) Charge / Discharge Test The test battery is charged at a 0.2C rate from 1 V to 0 V with CC (constant current) charge (occlusion of lithium ions into the negative electrode active material) and charged in the unit weight of the negative electrode active material. The charge amount (mAh / g) was calculated | required by calculating | requiring the amount of electricity performed. Next, the battery was discharged from 0 V to 1 V at a constant current of 0.2 C rate (release of lithium ions from the negative electrode active material), and the amount of electricity discharged in the unit weight of the negative electrode active material was determined to determine the discharge capacity (mAh / g ) Table 2 shows the results of the charge / discharge characteristics. The discharge capacity retention rate is the ratio between the initial discharge capacity and the 50th cycle discharge capacity.

  As described above, the negative electrode active materials produced in Examples 1 to 3 had a high initial discharge capacity of 670 to 752 mAh / g and a favorable discharge capacity retention rate of 94 to 96%. On the other hand, the negative electrode active materials of Comparative Examples 1 and 2 had a high initial discharge capacity, but the discharge capacity retention rate was significantly reduced to 21 to 31%. The negative electrode active material of Comparative Example 3 had a discharge capacity retention rate as low as 79%, and the initial discharge capacity was as low as 483 mAh / g.

(Examples 4-9 and Comparative Examples 4-5)
A raw material composed of acetylene black, which is an oxide material, non-oxide material, and carbon material containing SiO ₂ , was weighed so as to have the composition shown in Table 3, and in the same manner as in Examples 1 to 3, the negative electrode An active material was produced. In Examples 4 and 5, a high-purity silica stone powder (product name: Wacomjir: product number HS6-3000, average particle size: 11 μm) manufactured by Nichetsu Co., Ltd., similar to Examples 1 to 3 above, is used as the oxide material. It was. In Examples 6 to 9, glass was used as the oxide material.

In Comparative Example 4, the same raw material as in Example 4 was used, and the raw material that was a mixture was used as the negative electrode active material without performing mechanical milling. In Comparative Example 5, Al ₂ O ₃ powder was used as the oxide material.
About the obtained negative electrode active material, the crystallinity degree and crystallite size of the negative electrode active material were measured by said powder X-ray-diffraction measurement, and the result was shown in Table 3.

  Using the obtained negative electrode active material, a test battery was produced in the same manner as in Examples 1 to 3, and a charge / discharge test was performed. The results are shown in Table 4.

  As described above, the negative electrode active materials produced in Examples 4 to 9 have a Si crystallite size of 100 nm or less, a high initial discharge capacity of 708 to 1466 mAh / g, and a discharge capacity retention ratio of 85 to 99. % And good. On the other hand, the negative electrode active material of Comparative Example 4 had a low discharge capacity retention rate of 5% and a low initial discharge capacity of 506 mAh / g. Further, the negative electrode active material of Comparative Example 5 had a high initial discharge capacity, but the discharge capacity retention rate was significantly reduced to 53%.

  The negative electrode active material for an electricity storage device obtained by the present invention can be used for applications such as a main power source for mobile communication devices, portable electronic devices, electric bicycles, electric motorcycles, electric vehicles, and the like.

Claims (6)

A raw material comprising an oxide material containing SiO ₂ , a non-oxide material containing at least one selected from Si, Al, Ti, Li, Mg, Zr, and Ca, and highly conductive carbon black is mechanically used. The manufacturing method of the negative electrode active material for electrical storage devices characterized by including the process of milling. The method for producing a negative electrode active material for an electricity storage device according to claim 1, wherein the oxide material contains 30% or more of SiO _{2 by} mass.   The method for producing a negative electrode active material for an electricity storage device according to claim 1, wherein glass is used as the oxide material. The raw material contains, by mass%, an oxide material of 5 to 95%, a non-oxide material of 5 to 95%, and a highly conductive carbon black of 0 to 20% (excluding 0%). The manufacturing method of the negative electrode active material for electrical storage devices in any one of claim | item 1-3.   The method for producing a negative electrode active material for an electricity storage device according to claim 1, wherein the mechanical milling treatment is performed in a non-oxidizing atmosphere. The negative electrode active material for electrical storage devices manufactured by the manufacturing method in any one of Claims 1-5.