JP5124975B2 - Negative electrode material for lithium ion secondary battery and method for producing the same - Google Patents

Description

  The present invention relates to a negative electrode material for a lithium ion secondary battery that realizes a lithium ion secondary battery having excellent cycle characteristics and a method for producing the same.

  Lithium ion secondary batteries have a higher capacity per unit volume than other secondary batteries such as nickel metal hydride batteries. Because of this excellent feature, it is used for power supply in portable devices such as mobile phones and notebook computers. The lithium ion secondary battery is composed of a positive electrode, a negative electrode facing the positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte solution, and a graphite particle layer covering the current collector plate and the current collector plate surface. Lithium ion secondary batteries equipped with a negative electrode comprising the above are mainly put into practical use. When charging and discharging are repeated in such a battery, graphite repeatedly occludes and releases lithium, and accordingly, the graphite expands and contracts, which causes deterioration of the cycle characteristics of the lithium ion secondary battery.

  Incidentally, as described above, lithium ion secondary batteries using graphite have been put into practical use. However, the market demands a higher capacity of lithium ion secondary batteries. In order to meet this demand, there is a demand for practical application of a lithium ion secondary battery using a high capacity negative electrode material such as silicon or tin having a capacity larger than that of graphite. At the time of charging, graphite expands to about 1.1 times. On the other hand, the high-capacity negative electrode material expands significantly more than graphite (for example, silicon expands about 4 times and tin expands about 3 times). The expansion of the high-capacity negative electrode material during charging is accompanied by contraction during discharge, and repeated expansion and contraction are likely to cause collapse of the high-capacity negative electrode material, and are said to reduce the conductivity between the negative electrode materials. Therefore, the lithium ion secondary battery using such a high capacity negative electrode material has a problem that it is difficult to ensure excellent cycle characteristics.

  In order to commercialize lithium-ion secondary batteries that use high-capacity negative electrode materials, it is necessary to improve the cycle characteristics by suppressing the collapse of the negative electrode material that accompanies expansion and contraction. Is underway.

  For example, Patent Document 1 discloses using composite particles of a silicon acid compound and a metal coated with carbon as a negative electrode material. Since the particles used in this negative electrode material are coated with carbon, it is disclosed in Patent Document 1 that particle collapse is suppressed.

  On the other hand, Patent Document 2 discloses composite particles of a fibrous graphite material coated with a carbonaceous material and a high capacity member such as silicon as a negative electrode material. The composite particles are in close contact with the carbonaceous material that forms the outer skin, and there are no voids between them, but there are voids in the composite particles, and these voids are It can be expected to mitigate expansion. However, in order to put this composite particle into practical use as a negative electrode material, it is desired that the expansion is further relaxed.

Patent Document 3 discloses the use of sintered particles of silicon, a silicon alloy or silicon oxide fine particles (such as constituent silicon) and an organic silicon compound or an organic silicon mixture as a negative electrode material. The sintered particles further form a carbon-deposited outer skin. In the sintered body particles formed with such an outer skin, there are no voids between the outer skin and the sintered body particles, but there are voids that can be expected to relax in the sintered body particles. . However, like the composite particles disclosed in Patent Document 2, it is desired to further improve the expansion suppression of the entire sintered particles having the outer skin. Moreover, the particle | grains currently disclosed by patent document 3 use a constituent silicon etc., and are not manufactured using other high capacity | capacitance materials, such as tin. Furthermore, since it is a sintered body, various production conditions such as raw materials, temperature, and time must be highly controlled in order to adjust the void amount.
JP 2005-294079 A JP 2005-310760 A JP 2005-310759 A

  An object of this invention is to provide the negative electrode material for lithium ion secondary batteries which can implement | achieve the outstanding cycling characteristics in view of the said situation, and the manufacturing method of this negative electrode material.

  The present invention is a negative electrode material for a lithium ion secondary battery, comprising an outer skin, a hollow part enclosed in the outer skin, and an inclusion member having a first lithium ion storage member disposed in the hollow part. It is characterized by. In the present invention, in order to increase the capacity of the lithium ion secondary battery, it is preferable that the outer skin has a second lithium ion storage member. In order to reduce the electric resistance of the negative electrode material, it is preferable that the inclusion member has a conductive material.

  When the first lithium ion storage member and the second lithium ion storage member store lithium ions, it is preferable that the second lithium ion storage member has a lower expansion coefficient than the first lithium ion storage member. In this case, since the second lithium ion storage member having a low expansion rate is disposed on the outside of the first lithium ion storage member, expansion of the first lithium ion storage member is suppressed by the second lithium ion storage member, Improve cycle characteristics of lithium ion secondary batteries.

The charge capacity of the first lithium ion storage member may be larger than the charge capacity of the second lithium ion storage member. Here, the size of the charge capacity is two types of lithium ion secondary batteries that use lithium metal for the positive electrode and differ only in the type of the negative electrode material (one is the first lithium ion storage member as the negative electrode material and the other is 2nd lithium ion storage member is used as negative electrode material), each lithium ion secondary battery is charged under the same conditions, then discharged under the same conditions, and the discharge results of each battery are compared, Can be determined. The charging conditions and discharging conditions for determining the size of the charging capacity are, for example, as follows. The charging conditions were such that the current density with respect to the electrode area was set to a constant current value of 0.37 mA / cm ² until the potential difference between the positive electrode and the negative electrode was 0 V, and then the current value was 0.06 mA / cm at a constant potential of 0 V. do down to cm ^2. On the other hand, the discharge conditions are 0.37 mA / cm ² and discharge to 1V.

  The first lithium ion storage member may be a metal that can be alloyed with lithium, such as Si or Sn.

  Moreover, this invention is a lithium ion secondary battery provided with the negative electrode for lithium ion secondary batteries provided with the said negative electrode material for lithium ion secondary batteries, and this negative electrode.

  In addition, the present invention provides the negative electrode material for a lithium ion secondary battery comprising an outer skin, a hollow portion enclosed in the outer skin, and an inner member having a first lithium ion storage member disposed in the hollow portion. A method for preparing a core material in which a vaporizable member that vaporizes by heating and a first lithium ion storage member are mixed; a coating step for forming a coating film on a surface of the core material; It has the heating process which heats the core material in which the said coating film was formed, and vaporizes the said vaporizable member.

In the core material preparation step, it is preferable to prepare the core material by mixing conductive materials.
In the coating step, a coating film having a second lithium ion storage member may be formed. In the heating step, the coating film may be changed to an outer skin by heating, and a second lithium ion storage member may be generated in the outer skin.

  In the method for producing a negative electrode material for a lithium ion secondary battery, the second lithium ion occlusion member may have a lower expansion coefficient than the first lithium ion occlusion member during lithium ion occlusion. The charge capacity of one lithium ion storage member may be larger than the charge capacity of the second lithium ion storage member.

  In the method for producing a negative electrode material for a lithium ion secondary battery, the first lithium ion storage member may be a metal that can be alloyed with lithium.

  The present invention also provides a method for producing a negative electrode for a lithium ion secondary battery comprising a step of using the method for producing a negative electrode material for a lithium ion secondary battery, and a lithium ion secondary battery comprising a step of using this production method. It is a manufacturing method.

  According to the negative electrode material for a lithium ion secondary battery of the present invention, the inner member is arranged in the hollow portion enclosed in the outer skin, and the gap for receiving the expansion of the inner member accompanying the occlusion of lithium is between the outer skin and the inner member. Therefore, the expansion of the negative electrode material itself is suppressed, and as a result, a lithium ion secondary battery having excellent cycle characteristics can be realized.

  Moreover, according to the manufacturing method of the negative electrode material for lithium ion secondary batteries of this invention, the quantity of a vaporizable member and a 1st lithium storage member is set arbitrarily, and a hollow part is formed in an outer skin only by heating. Therefore, the amount of voids in the outer skin can be set freely and easily.

  A negative electrode material for a lithium ion secondary battery according to the present invention and a method for producing the negative electrode material will be described below based on the embodiments.

  First, the negative electrode material for a lithium ion secondary battery according to this embodiment will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view for explaining a negative electrode material for a lithium ion secondary battery according to this embodiment. The illustrated negative electrode material AM includes an outer skin SS, a hollow portion IE included in the outer skin SS, and an inner member IM disposed in the hollow portion IE.

  The smaller the average particle size of the negative electrode material AM, the larger the specific surface area of the negative electrode material AM, and the initial efficiency calculated by dividing the initial discharge amount of the lithium ion secondary battery by the initial charge amount tends to decrease. Therefore, the average particle diameter of the negative electrode material AM is preferably 5 μm or more, preferably 7 μm or more, and more preferably 10 μm or more. On the other hand, the upper limit of the average particle diameter should be appropriately set according to the thickness of the negative electrode material layer in the negative electrode of the lithium ion secondary battery, and should not be particularly limited, but is preferably 100 μm or less. When the thickness of the negative electrode material layer is generally 60 μm, the average particle size is preferably 50 μm or less, and preferably 40 μm or less in order to uniformly provide the negative electrode material on the current collector plate surface.

  Here, the “average particle diameter” means a median diameter obtained by using a laser diffraction particle size distribution measuring device for a sample dispersed in water. For example, “SALD-2000” manufactured by Shimadzu Corporation is used. Can be measured using. The meaning of this average particle diameter applies to all average particle diameters in the present invention.

Below, description of negative electrode material AM is demonstrated for every structure.
The inclusion member IM includes a plurality of first lithium ion storage members IA and a plurality of conductive materials IC. These constituent members are arranged in the hollow portion IE as a granular or granular aggregate, and the hollow portion IE can accept the expansion of the inclusion member IM, thereby suppressing the expansion of the entire negative electrode material AM. In the present embodiment, only the first lithium ion storage member IA and the conductive material IC have the configuration of the inclusion member IM. However, in the present invention, members other than the first lithium ion storage member and the conductive material are used. It is allowed to adopt the configuration of the enclosing member.

  The 1st lithium ion occlusion member IA which is the structure of the inclusion member IM will not be specifically limited if it is a member which can be used for the negative electrode material for lithium ion secondary batteries. Therefore, the first lithium ion storage member IA includes a carbon material such as graphite, coke, and hard carbon having lithium ion storage ability; and Al, Pb, Zn, Sn, Bi, In, Mg, Ga, Cd, Ag, One type or two or more types selected from Si, B, Au, Pt, Pd, Sb, Ge, and Ni are included, and the charge capacity per unit weight (hereinafter referred to as “charge capacity per unit weight”) is higher than that of graphite. A high capacity material such as a metal, an alloy, an oxide, a nitride, or a carbide having a large unit capacity) may be selected. When a carbon material is selected, graphite is preferably selected. On the other hand, when a high-capacity material is selected, from the viewpoint of unit capacity, a metal or oxide containing Si or Sn is preferably selected. A carbon material and a high-capacity material may be arbitrarily selected and combined.

  The selection of the first lithium ion storage member is arbitrarily performed according to the characteristics of the target negative electrode material. Therefore, if the purpose is to increase the capacity of the negative electrode material, a material having a larger unit capacity than the second lithium ion storage member described later may be selected as the first lithium ion storage member IA. In this case, even if the expansion coefficient is higher than that of the second lithium ion storage member, the expansion of the first lithium ion storage member IA is alleviated by the hollow portion IE. As the first lithium ion storage member IA having a higher capacity and a higher expansion coefficient than the second lithium ion storage member, when a carbon material such as graphite is selected for the second lithium ion storage member, the above high capacity material is used. It can be illustrated.

  The average particle diameter of the first lithium ion storage member IA is set according to the average particle diameter of the negative electrode material AM. Therefore, the average particle diameter is not particularly limited, but is usually 0.05 to 5 μm, preferably 0.1 to 3 μm, and more preferably 0.5 to 2 μm.

  The conductive material IC which is the configuration of the other inclusion member IM reduces the electrical resistance value of the negative electrode material AM itself, and improves the cycle characteristics of the lithium ion secondary battery. The conductive material IC is selected from materials having higher electrical conductivity than the first lithium ion storage member IA. For example, when the first lithium ion storage member IA is metal Si, it may be selected from conductive carbon materials such as carbon black, fibrous carbon, amorphous carbon, and graphite; and metals such as copper. The conductive material IC may have a lithium ion storage capability as long as it has a higher electrical conductivity than the first lithium ion storage member IA.

  The average particle diameter of the conductive material IC is set according to the average particle diameter of the negative electrode material AM, as with the first lithium ion storage member IA.

  The first lithium ion storage member IA and the conductive material IC of the present embodiment are as described above. The filling rate of the inclusion member IM in the hollow portion IE can suppress the expansion of the negative electrode material AM as the filling rate is lower, while the capacity of the negative electrode material AM can be increased as the filling rate is higher. Therefore, the filling rate in the hollow portion IE is appropriately set from the viewpoints of the cycle characteristics of the lithium ion secondary battery that are affected by the magnitude of expansion of the negative electrode material AM and the desired lithium ion secondary battery capacity. Usually, it is good to be 10 to 90%, preferably 20 to 80%, more preferably 30 to 70%.

  The outer skin SS is configured to provide a hollow portion IE inside the negative electrode material AM. The outer skin SS in the present embodiment is a porous film, and includes a second lithium ion storage member (not shown) having a lithium ion storage capability in order to increase the capacity of the negative electrode material AM. The second lithium ion storage member is not particularly limited as long as it has a lithium ion storage capability. Therefore, the same material as the first lithium ion storage member IA can be selected as the second lithium ion storage member.

  As described above, the second lithium ion storage member can be selected from materials having lithium ion storage capability, but when the second lithium ion storage member has a lower expansion coefficient than the first lithium ion storage member IA, the negative electrode material AM itself. Is preferable because it has a lower expansion coefficient. When realizing such a low-expansion negative electrode material AM, when a high-capacity material such as Si metal is selected for the first lithium ion storage member IA, for example, graphite or petroleum carbon or coal pitch carbonized by heating is used. It can be illustrated.

  The negative electrode material AM of the present embodiment is as described above. As described above, the first lithium ion storage member IA and the second lithium ion storage member can be arbitrarily selected. For example, by increasing the amount of graphite in the lithium ion storage member, the negative electrode composed only of graphite It is also possible to realize a lithium ion secondary battery that exhibits an electromotive force equivalent to that of a lithium ion secondary battery using the material.

  Next, the manufacturing method of the negative electrode material AM of this embodiment mentioned above is explained in full detail. The manufacturing method of the negative electrode material AM in this embodiment includes a core material preparation step of preparing a core material particle in which a vaporizable member that vaporizes by heating and a first lithium ion storage member are mixed, and a surface of the core material particle. In this method, a coating process for forming a coating film and a heating process for heating the core material particles on which the coating film is formed to vaporize the vaporizable member in the coating film are sequentially performed. FIG. 2 is a diagram for explaining a method for producing a negative electrode material in the present embodiment, and FIG. 2 (a) is a diagram showing the core material particles NP prepared in the core material preparation step, and FIG. FIG. 2B is a diagram illustrating the core material particle NP on which the coating film OS is formed in the coating process, and FIG. 2C is a diagram illustrating the negative electrode material AM manufactured through the heating process. Hereinafter, it demonstrates for every process.

  First, the core material particle preparation step will be described. In this step, the core material particle NP is prepared by mixing the vaporizable member GM that is vaporized by heating, the first lithium ion storage member IA, and the conductive material IC.

  The vaporizable member GM is preferably selected from thermally decomposable resins that decompose or volatilize by heating, and examples thereof include polystyrene and polyethylene. Further, the first lithium ion storage member IA and the conductive material IC are arbitrarily selected from the materials described above.

  In the preparation of the core material particles NP, an arbitrary amount of the vaporizable member GM, the first lithium ion storage member IA, and the conductive material IC are mixed and integrated according to characteristics such as the capacity of the target negative electrode material AM. If this integration is possible, the mixing method is not particularly limited. For example, (a) a method in which the first lithium ion storage member IA and the conductive material IC are mixed with the thermally meltable vaporizable member GM, and then cooled and solidified; (b) N-methylpyrrolidone in which the vaporizable member GM is dissolved, etc. A method of mixing the first lithium ion occlusion member IA and the conductive material IC in a solvent and then evaporating the solvent to solidify can be cited as a mixing method.

  By pulverizing the core material integrated by the above mixing, the core material particles NP shown in FIG. 2A having a desired average particle diameter are prepared.

  In the next coating step, as shown in FIG. 2B, the coating film OS is formed on the entire outer surface of the core material particle NP. The coating film OS contains a binder in order to enhance the adhesion with the core material particles NP in addition to the second lithium ion storage member (not shown).

  When forming the coating film OS, in order to easily form the coating film OS on the surface of the core material particle NP, it is preferable to use a liquid material as the coating film material. At this time, the second lithium ion storage member and / or the member that changes to the second lithium ion storage member by heating is used as one material of the coating film. The second lithium ion storage member is not particularly limited as long as it is a member having lithium ion storage capability such as graphite as described above. On the other hand, coal pitch and petroleum pitch can be illustrated as a member which changes to a lithium ion occlusion member by heating.

  Moreover, as a binder to be used, it is good to use well-known organic binders, such as carboxymethylcellulose which carbonizes by the heating at the next heating process. In addition, as long as the function as a binder is exhibited, the use of a member that changes to a lithium ion storage member by heating, such as coal pitch or petroleum pitch, is allowed.

  In the coating film material, the ratio between the second lithium ion storage member and / or the member that changes to the lithium ion storage member by heating and the binder is appropriately set for the purpose of forming the coating film OS. Usually, the second lithium ion occlusion member and / or the member that changes to the lithium ion occlusion member by heating: Binder = 1: 0.001-0.1 (weight ratio), preferably 1: 0.002- It is 0.08, More preferably, it is 1: 0.005-0.05.

  In the next heating step, as shown in FIG. 2 (c), the vaporizing member GM contained in the coating film OS is vaporized and reduced to form the hollow portion IE. The heating temperature at this time is set to be equal to or higher than the temperature at which the vaporizable member GM is thermally decomposed and volatilized, and is preferably set to a temperature at which the binder used in the coating film OS is carbonized. For example, when petroleum pitch, coal pitch, or carboxymethyl cellulose is used as the binder, the binder can be carbonized at a temperature of about 800 ° C. In this heating step, heating is performed in an inert gas such as nitrogen in order to prevent oxidation of the lithium ion storage member.

  Note that, in the heating in the main heating step, a part of the components of the coating film OS is vaporized by thermal decomposition or volatilization, like the vaporizable member GM. Therefore, the coating film OS changes to a porous film, and the vaporized material of the vaporizable member GM flows out of the core material particles NP through the coating film OS. Further, when the heating is continued, the binder in the coating film OS is carbonized and changed to the outer skin SS. As a result, the negative electrode material AM of the present embodiment is obtained.

  Next, the negative electrode for a lithium ion secondary battery will be described. The negative electrode material AM of this embodiment is used for the negative electrode of this embodiment. The negative electrode can be produced by a known method. For example, it can be manufactured by applying a slurry in which the negative electrode material AM of the present embodiment and a binder are dispersed to the surface of the current collector plate, and then drying. As the current collector plate, a copper foil is generally used. The binder may be a fluorine-based polymer compound such as polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer, or carboxymethyl cellulose. Styrene-butadiene rubber, acrylonitrile-butadiene rubber, etc. are used. This binder is usually used after being dissolved in a solvent.

Next, a lithium ion secondary battery will be described. The lithium ion secondary battery according to the present embodiment mainly includes a positive electrode, an electrolytic solution, and a separator in addition to the negative electrode, and the negative electrode according to the present embodiment is used as the negative electrode. To exemplify the positive electrode material, LiCoO ₂ and _{LiNiO 2, LiNi 1-y Co} y O 2, LiMnO 2, LiMn 2 O 4, etc. LiFeO ₂ and the like. Moreover, as a binder of a positive electrode, polyvinylidene fluoride, polytetrafluoroethylene, etc. are employable. Further, carbon black or the like may be mixed as a conductive material. As the electrolytic solution, for example, an organic solvent such as ethylene carbonate, or a mixed solvent of the organic solvent and a low boiling point solvent such as dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, diethoxymethane, ethoxymethoxyethane, A solution in which an electrolyte solution solute (electrolyte salt) such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCF ₃ SO ₃ , or LiAsF ₆ is dissolved is used. As the separator, for example, a nonwoven fabric, a cloth, a microporous film, or the like whose main component is a polyolefin such as polyethylene or polypropylene is used.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples, and may be appropriately modified and implemented within a range that can meet the purpose described above and below. All of which are within the scope of the present invention.

Example 1
The negative electrode material of Example 1 was produced by the following procedures of preparation of core material particles, formation of a coating film, and heat treatment.

(Preparation of nuclear material particles)
Core material particles were prepared as follows using metal Si having an average particle diameter of 1 μm as a first lithium ion occlusion member, flaky graphite having an average particle diameter of 3 μm as a conductive material, and fine powder polystyrene as a vaporizable member. First, 20 g of a first lithium ion occlusion member, 20 g of a conductive material, and 10 g of a vaporizable member are mixed, and 50 g of N-methylpyrrolidone (NMP) is added to the mixture to dissolve the vaporizable member. Obtained. NMP was evaporated from the slurry, solidified, and then pulverized to prepare core material particles having an average particle size of 20 μm.

(Formation of coating film)
A coating film was formed as follows using flaky graphite having an average particle size of 3 μm as a second lithium ion storage member and carboxymethylcellulose (CMC) as a binder. After mixing 50 g of the core material particles and 10 g of the second lithium ion storage member, 10 g of a 2% by weight binder aqueous solution was added while stirring at 3000 rpm, and then water was evaporated to cover the surface of the core material particles. A covering film was formed.

(Heat treatment)
The core material particles on which the coating film is formed are heat-treated at 800 ° C. for 2 hours in a nitrogen stream, and the vaporizing member in the core material particles is vaporized to form a hollow portion inside the outer skin, so that the average particle size is A negative electrode material of Example 1 having a thickness of 27 μm was obtained.

(Example 2)
Except for the matters described below, a negative electrode material B of Example 2 having an average particle size of 27 μm was produced in the same manner as in the production method of the negative electrode material of Example 1.

(Preparation of nuclear material particles)
Core material particles were prepared using 10 g of CMC as a vaporizing member, and using 20 g of water instead of NMP.
(Formation of coating film)
Instead of the 2% by mass CMC aqueous solution, 10 g of NMP containing 5% by mass of coal tar pitch was used to form a coating film.

(Example 3)
A negative electrode material of Example 3 having an average particle size of 28 μm was produced in the same manner as in the production method of the negative electrode material of Example 1, except for the matters described below.

(Preparation of nuclear material particles)
Core material particles were prepared using 10 g of CMC as a vaporizing member, and using 20 g of water instead of NMP.
(Coating of outer skin)
15 g of coal tar pitch was used instead of graphite as the second lithium ion storage member, and 10 g of NMP was used instead of 2 mass% CMC aqueous solution to form a coating film.

(Comparative Example 1)
30 g of scaly graphite having an average particle size of 25 μm was mixed with metal Si having an average particle size of 1 μm, and this was used as the negative electrode material of Comparative Example 1.

(Comparative Example 2)
20 g of metal Si having an average particle diameter of 1 μm, 50 g of coal tar pitch, and 20 g of NMP were mixed and heat-treated at 800 ° C. for 2 hours in a nitrogen stream. Then, it grind | pulverized to the average particle diameter of 25 micrometers, and was set as the negative electrode material of the comparative example 2.

  Lithium ion secondary batteries were fabricated using the negative electrode materials of the above examples and comparative examples. The load characteristics and cycle characteristics of this battery were evaluated. A battery manufacturing method and a battery evaluation method are as follows.

(Production of lithium ion secondary battery)
(1) Production of Negative Electrode 100 parts by mass of Example or Comparative Example negative electrode material, 50 parts by mass of binder aqueous solution (2.0% by mass carboxymethylcellulose aqueous solution), and 20 parts by mass of 5.0% by mass styrene butadiene rubber aqueous solution. And 30 parts by mass of water were added to form a slurry. The obtained slurry was applied onto a copper foil having a thickness of 18 μm and dried for 10 minutes with a dryer (100 ° C.). After drying, it was punched out into a circle with a diameter of 1.6 cm, and the coating amount excluding the copper foil was 18 mg. This film was pressed with a roller press so that the density of the coating applied on the copper foil was 1.40 g / cc, and a negative electrode for a lithium ion secondary battery was produced.

(2) Production of lithium ion secondary battery As a positive electrode for a lithium ion secondary battery, a lithium foil is used for a lithium ion secondary battery for calculating low temperature charge characteristics and load characteristics, and cycle characteristics are calculated. Therefore, an electrode using LiCoO ₂ as an active material was used for the lithium ion secondary battery. An electrode using LiCoO ₂ as an active material was produced as follows. To 90 parts by mass of LiCoO _2, 5 parts by mass of polyvinylidene fluoride as a binder and 5 parts by mass of carbon black as a conductive material were mixed, and 200 parts by mass of NMP were added thereto to prepare a slurry. The obtained slurry was applied onto an aluminum foil having a thickness of 30 μm and dried with a dryer (100 ° C.) for 20 minutes. After the dried film was punched out into a circle having a diameter of 1.6 cm, the coating amount excluding the aluminum foil was measured to be 45 mg. This film was pressed with a roller press so that the density of the coating applied on the aluminum foil was 2.8 g / cc to produce a positive electrode for a lithium ion secondary battery.

(3) Assembly of lithium ion secondary battery The positive electrode and the negative electrode were opposed to each other through a separator and incorporated in a stainless steel cell to produce a lithium ion secondary battery (coin type). The battery is assembled in an argon gas atmosphere. As the electrolyte, 0.05 mL of 1M LiPF ₆ / (ethylene carbonate + dimethyl carbonate) is used, and “Celguard # 3501 (trade name)” manufactured by Celgard is used as the separator. Using. The electrolytic solution is obtained by dissolving LiPF ₆ to a concentration of 1M in a solvent in which ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1: 1 (trade name “Sollite”, manufactured by Mitsubishi Chemical Corporation).

(Evaluation of load characteristics)
The battery is charged at a constant current value of 0.37 mA / cm ² (0.1 C) with respect to the electrode area until the potential difference between the positive electrode and the negative electrode becomes 0 V, and then the current value at a constant potential of 0 V. Until 0.06 mA / cm ² was reduced. From the discharge capacity discharged to 1 V at 0.37 mA / cm ² (0.1 C) and the discharge capacity discharged to 1 V at 9.2 mA / cm ² (2.5 C) after charging, the following formula was used.
Load characteristics (%) = 100 × ((discharge capacity was discharged at 9.2mA / cm ²⁾ / (discharge capacity was discharged at 0.37mA / cm ²⁾⁾

(Evaluation of cycle characteristics)
The battery was charged to 4.2 V at a current value of 6.4 mA, and then continuously until the current value reached 0.2 mA at a constant voltage of 4.2 V. Next, discharging was performed at a current value of 6.4 mA until 3.0 V was reached. This charging and discharging were repeated a predetermined number of times, and the cycle characteristics were calculated by the following formula.
Cycle characteristics (%) of the nth cycle = 100 × ((discharge capacity of the nth cycle) / (discharge capacity of the first cycle))

  Table 1 shows the evaluation results of load characteristics and cycle characteristics.

  Comparing the examples and comparative examples in Table 1, it can be confirmed that the cycle characteristics of the lithium ion secondary battery are clearly superior to those using the negative electrode materials of the examples than the comparative examples. .

It is a cross-sectional schematic diagram for demonstrating the negative electrode material for lithium ion secondary batteries which concerns on embodiment of this invention. It is a figure for demonstrating the manufacturing method of the negative electrode material for lithium ion secondary batteries which concerns on embodiment of this invention.

Explanation of symbols

AM negative electrode material IE hollow part IM inclusion member IA first lithium ion occlusion member IC conductive material SS outer skin GM vaporizable member NP core material particle OS coating film

Claims (14)

An outer skin, a hollow portion encapsulated in the outer skin, and an encapsulating member having a granular first lithium ion storage member and a conductive material disposed in the hollow portion,
The outer skin has graphite as a second lithium ion storage member,
The first lithium ion storage member has a metal that can be alloyed with lithium,
A negative electrode material for a lithium ion secondary battery, wherein the filling rate of the inclusion member in the hollow portion is 10 to 90%.   2. The lithium according to claim 1, wherein when the first lithium ion storage member and the second lithium ion storage member store lithium ions, the second lithium ion storage member has a lower expansion coefficient than the first lithium ion storage member. Negative electrode material for ion secondary battery.   The negative electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein a charge capacity of the first lithium ion storage member is larger than a charge capacity of the second lithium ion storage member. The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the outer skin is a porous film having graphite as a second lithium ion storage member. The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the conductive material is at least one selected from the group consisting of particles, granular aggregates, fibers, and scales. The negative electrode for lithium ion secondary batteries provided with the negative electrode material for lithium ion secondary batteries in any one of Claims 1-5 . The lithium ion secondary battery provided with the negative electrode for lithium ion secondary batteries of Claim 6 . It is a manufacturing method of the negative electrode material for lithium ion secondary batteries of any one of Claims 1-5 ,
A core material preparation step of preparing a core material mixed with a vaporizable member that is vaporized by heating, a granular first lithium ion storage member having a metal that can be alloyed with lithium, and a conductive material;
A coating step of forming a coating film having graphite as the second lithium ion storage member on the surface of the core material;
A method for producing a negative electrode material for a lithium ion secondary battery, comprising a heating step of heating the core material on which the coating film is formed to vaporize the vaporizable member. The method for producing a negative electrode material for a lithium ion secondary battery according to claim 8 , wherein in the heating step, the coating film is changed to an outer skin by heating, and a second lithium ion storage member is generated in the outer skin. During lithium ion occlusion of the first lithium ion occluding member and the second lithium ion occluding member, wherein the than the first lithium ion occluding member second lithium ion absorbing member according to claim 8 or 9 which is a low expansion Manufacturing method of negative electrode material for lithium ion secondary battery. The method for producing a negative electrode material for a lithium ion secondary battery according to any one of claims 8 to 10 , wherein a charge capacity of the first lithium ion storage member is larger than a charge capacity of the second lithium ion storage member. The method for producing a negative electrode material for a lithium ion secondary battery according to any one of claims 8 to 11 , wherein the coating film becomes a porous coating film by the heating step. Any process method for producing a negative electrode for a lithium ion secondary battery comprising a the use of a manufacturing method of a lithium ion secondary battery negative electrode material according to claim 8-12. The manufacturing method of a lithium ion secondary battery provided with the process of using the manufacturing method of the negative electrode for lithium ion secondary batteries of Claim 13 .

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