JP2018147673A - Negative electrode active material, negative electrode and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode active material superior in rapid charging capability, a negative electrode and a lithium ion secondary battery.SOLUTION: A negative electrode active material comprises a carbon material, Al and P, wherein the content of Al is 0.002 mass% or more and 0.2 mass% or less, and the content of P is 0.06 mass% or more and 1.5 mass% or less. A negative electrode 30 is a negative electrode 30 having a negative electrode current collector 32, and a negative electrode active material layer 34 provided on the negative electrode current collector 32. The negative electrode active material layer 34 includes the negative electrode active material. A lithium ion secondary battery 100 comprises the negative electrode 30, a positive electrode 20 and an electrolyte solution.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a negative electrode active material, a negative electrode, and a lithium ion secondary battery.

  Lithium ion secondary batteries are widely applied as power sources for portable electronic devices because they are lighter and have a higher capacity than nickel cadmium batteries, nickel metal hydride batteries, and the like. It is also a promising candidate as a power source for use in hybrid vehicles and electric vehicles. With the recent miniaturization and higher functionality of portable electronic devices, further increase in capacity is expected for lithium ion secondary batteries that serve as these power sources.

  The capacity of the lithium ion secondary battery mainly depends on the active material of the electrode. In general, a carbon material such as graphite is used as the negative electrode active material. However, the theoretical capacity of graphite is 372 mAh / g, and a battery of about 350 mAh / g has already been used in a battery that has been put into practical use. Therefore, in order to obtain a nonaqueous electrolyte secondary battery having a sufficient capacity as an energy source for future high-performance portable devices, it is necessary to further increase the capacity.

  In recent years, in addition to higher capacities, there has also been a growing demand for rapid discharge due to the rapid charging characteristics and improved use of lithium-ion secondary batteries such as power tools and cordless home appliances for improved convenience. It's getting on.

In Patent Document 1, in a lithium ion secondary battery using a high energy density electrode with low porosity, high salt charge / discharge characteristics are obtained by setting the salt concentration of the nonaqueous electrolyte to 1.3 mol · dm ⁻³ or more. Yes. In Patent Document 2, a non-aqueous electrolyte for a lithium ion secondary battery is prepared by using lithium salt containing LiPF ₆ and LiBF ₄ ; and (a) cyclic carbonate composed of ethylene carbonate or a mixture of ethylene carbonate and propylene carbonate; and (b) propionate. High rate charge / discharge characteristics are obtained when the mixing volume ratio (a: b) with a linear ester such as a series ester is about 10:90 to about 70:30.

JP 2003-173821 A Special table 2010-539670 gazette

  However, in the lithium ion secondary batteries described in Patent Documents 1 and 2 described above, quick charge characteristics may not be sufficient.

  This invention is made | formed in view of the said problem, and it aims at providing the negative electrode active material, negative electrode, and lithium ion secondary battery which are excellent in a quick charge characteristic.

The inventors of the present invention have a lithium ion secondary battery using a carbon material and a composition containing a predetermined amount of Al and P as a negative electrode active material. It has been found that the ease of insertion (input characteristics) is improved.
That is, this invention provides the following means in order to solve the said subject.

(1) The negative electrode active material according to the first aspect contains a carbon material, Al and P, and the content of the Al is 0.002% by mass to 0.2% by mass, Content is 0.06 mass% or more and 1.5 mass% or less.

(2) The negative electrode active material according to the above aspect may further contain Ti, and the content of Ti may be 0.05% by mass or more and 1.5% by mass or less with respect to the carbon material.

(3) In the negative electrode active material according to the above aspect, the carbon material may be artificial graphite, and the bulk density may be 0.5 g / cm ³ or more and 2.0 g / cm ³ or less.

(4) In the negative electrode active material according to the above aspect, the carbon material may have a specific surface area of 0.1 m ² / g or more and 2 m ² / g or less.

(5) The negative electrode according to the second aspect is a negative electrode having a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, wherein the negative electrode active material layer is the above-described aspect. Negative electrode active material.

(6) The lithium ion secondary battery according to the third aspect includes the negative electrode according to the aspect, a positive electrode, and an electrolytic solution.

  The negative electrode active material, the negative electrode, and the lithium ion secondary battery according to the above aspect are excellent in quick charge characteristics.

It is a cross-sectional schematic diagram of the lithium ion secondary battery concerning this embodiment.

  Hereinafter, the present embodiment will be described in detail with appropriate reference to the drawings. In the drawings used in the following description, in order to make the characteristics of the present invention easier to understand, there are cases where the characteristic parts are enlarged for the sake of convenience, and the dimensional ratios of the respective components are different from actual ones. is there. The materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be appropriately modified and implemented without departing from the scope of the invention.

[Lithium ion secondary battery]
FIG. 1 is a schematic cross-sectional view of a lithium ion secondary battery according to this embodiment. A lithium ion secondary battery 100 shown in FIG. 1 mainly includes a laminated body 40, a case 50 that accommodates the laminated body 40 in a sealed state, and a pair of leads 60 and 62 connected to the laminated body 40. Although not shown, the electrolyte solution is housed in the case 50 together with the laminate 40.

  The stacked body 40 is configured such that the positive electrode 20 and the negative electrode 30 are disposed to face each other with the separator 10 interposed therebetween. The positive electrode 20 is obtained by providing a positive electrode active material layer 24 on a plate-like (film-like) positive electrode current collector 22. The negative electrode 30 is obtained by providing a negative electrode active material layer 34 on a plate-like (film-like) negative electrode current collector 32.

  The positive electrode active material layer 24 and the negative electrode active material layer 34 are in contact with both sides of the separator 10. Leads 62 and 60 are connected to the ends of the positive electrode current collector 22 and the negative electrode current collector 32, respectively, and the ends of the leads 60 and 62 extend to the outside of the case 50. In FIG. 1, the case 50 has one laminated body 40 in the case 50, but a plurality of laminated bodies 40 may be laminated.

"Negative electrode"
The negative electrode 30 includes a negative electrode current collector 32 and a negative electrode active material layer 34 provided on the negative electrode current collector 32.

(Negative electrode current collector)
The negative electrode current collector 32 may be a conductive plate material, and for example, a thin metal plate of aluminum, copper, or nickel foil can be used.

(Negative electrode active material layer)
The negative electrode active material layer 34 includes a negative electrode active material and a negative electrode binder, and optionally includes a negative electrode conductive material.

(Negative electrode active material)
The negative electrode active material contains a carbon material and Al and P.

  Examples of the carbon material include natural graphite, artificial graphite, mesocarbon microbeads (MCMB) and the like. These carbon materials may be used individually by 1 type, and may use 2 or more types together. Among these carbon materials, artificial graphite is preferable.

The artificial graphite preferably has a bulk density of 0.5 g / cm ³ or more and 2.0 g / cm ³ or less. The negative electrode active material layer formed using artificial graphite having a bulk density in the above range is likely to have a relatively large void that allows the electrolyte to enter, and facilitates lithium ion movement between the artificial graphite and the electrolyte. There is a tendency for quick charge characteristics to be further improved. The bulk density is a ratio between the weight of the artificial graphite and the volume of the container when the artificial graphite is filled in a container having a predetermined capacity.

The carbon material preferably has a specific surface area of 0.1 m ² / g or more and 2 m ² / g or less. The negative electrode active material layer formed using artificial graphite with a specific surface area in the above range has a wide contact surface between the artificial graphite and the electrolytic solution, facilitating lithium ion movement between the artificial graphite and the electrolytic solution, and rapid charging. There is a tendency for the characteristics to be improved. The specific surface area is a value measured by the BET method using nitrogen gas adsorption.

  Al and P contained in the negative electrode active material of the present embodiment have an effect of improving the quick charge characteristics of the lithium ion secondary battery. The reason why the rapid charge characteristics of a lithium ion secondary battery using a negative electrode active material containing Al and P is improved is considered as follows. Al ions and P ions have invaded between carbon material layers in advance, and the carbon material layers are expanded. Therefore, it is considered that Li ions can be easily inserted and removed from the carbon material, and the quick charge characteristics of the lithium ion secondary battery are improved.

  There is no particular limitation on the form of Al and P contained in the negative electrode active material before being incorporated in the lithium ion secondary battery. However, it is preferable that Al and P contained in the negative electrode active material penetrate between layers of the carbon material. Al and P may exist in the state of oxides, such as aluminum oxide and phosphorus pentoxide, for example. Further, aluminum phosphate may be formed of Al and P.

  In this embodiment, the content of Al in the negative electrode active material is set to 0.002% by mass or more and 0.2% by mass or less with respect to the total amount of the negative electrode active material. Further, the content of P in the negative electrode active material is set to 0.06 mass% or more and 1.5 mass% or less with respect to the total amount of the negative electrode active material. The content ratio of A and P in the negative electrode active material is preferably 5 or more and 40 or less as the mass ratio of Al to P (P / Al).

The negative electrode active material of this embodiment further contains Ti, and the content of Ti is preferably 0.05% by mass or more and 1.5% by mass or less with respect to the carbon material. A lithium ion secondary battery using a negative electrode active material containing Ti in the above range tends to further improve quick charge characteristics. This is because the three kinds of elements of Al, P, and Ti penetrate between the layers of the carbon material, thereby further expanding the layers of the carbon material and facilitating the desorption / insertion of lithium ions into the carbon material. it is conceivable that. In addition, there is no restriction | limiting in particular in the form of Ti contained in the negative electrode active material before incorporating in a lithium ion secondary battery. Ti is contained as titanium oxide, aluminum titanate, titanium phosphate, lithium titanate, lithium aluminum titanium phosphate (Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ , 0 <x ≦ 0.5). Also good.

(Method for producing negative electrode active material)
The negative electrode active material of the present embodiment is, for example, a carbon material, an Al source, a P source, and further, if necessary, a Ti source, and weighed the Al amount, the P amount, and the Ti amount in the above ranges, It can be produced by mixing them. Mixing may be performed wet or dry. As the mixing apparatus, a mixing apparatus used for mixing general powders such as a ball mill can be used.

(Negative electrode conductive material)
Examples of the conductive material include carbon powder such as carbon black, carbon nanotube, carbon material, fine metal powder such as copper, nickel, stainless steel and iron, a mixture of carbon material and fine metal powder, and conductive oxide such as ITO. It is done. Among these, carbon powders such as acetylene black and ethylene black are particularly preferable. In the case where sufficient conductivity can be ensured with only the negative electrode active material 36, the lithium ion secondary battery 100 may not include a conductive material.

(Negative electrode binder)
The binder bonds the active materials to each other and bonds the active material to the negative electrode current collector 32. The binder is not particularly limited as long as the above-described bonding is possible. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene- Perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF) ) And the like.

  In addition to the above, as the binder, for example, vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-) TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluorine rubber (VDF-PFP-TFE fluorine rubber), Vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluoro rubber (VDF-PFMVE-TFE fluoro rubber), vinylidene fluoride-chlorotrifluoroethylene fluoro rubber The containing rubbers (VDF-CTFE-based fluorine rubber) vinylidene fluoride-based fluorine rubbers such as may be used.

Alternatively, an electron conductive conductive polymer or an ion conductive conductive polymer may be used as the binder. Examples of the electron conductive conductive polymer include polyacetylene. In this case, since the binder also functions as a conductive material, it is not necessary to add a conductive material. Examples of the ion conductive conductive polymer include monomers of polymer compounds (polyether polymer compounds such as polyethylene oxide and polypropylene oxide, polyphosphazenes, etc.), LiClO ₄ , LiBF ₄ , LiPF _{6, and the} like. Examples include a composite of a lithium salt or an alkali metal salt mainly composed of lithium. Examples of the polymerization initiator used for the combination include a photopolymerization initiator or a thermal polymerization initiator that is compatible with the above-described monomer.

  In addition, for example, cellulose, styrene / butadiene rubber, ethylene / propylene rubber, polyimide resin, polyamideimide resin, acrylic resin, or the like may be used as the binder.

  The contents of the negative electrode active material 36, the conductive material, and the binder in the negative electrode active material layer 34 are not particularly limited. The constituent ratio of the negative electrode active material 36 in the negative electrode active material layer 34 is preferably 90% or more and 98% or less by mass ratio. The constituent ratio of the conductive material in the negative electrode active material layer 34 is preferably 0% or more and 3.0% or less in terms of mass ratio, and the constituent ratio of the binder in the negative electrode active material layer 34 is 2.0% by mass ratio. It is preferably 5.0% or less.

  By making content of a negative electrode active material and a binder into the said range, it can prevent that the quantity of a binder is too small and it becomes impossible to form a strong negative electrode active material layer. In addition, the amount of the binder that does not contribute to the electric capacity increases, and the tendency that it is difficult to obtain a sufficient volume energy density can be suppressed.

"Positive electrode"
The positive electrode 20 includes a positive electrode current collector 22 and a positive electrode active material layer 24 provided on the positive electrode current collector 22.

(Positive electrode current collector)
The positive electrode current collector 22 may be a conductive plate material, and for example, a thin metal plate of aluminum, copper, or nickel foil can be used.

(Positive electrode active material layer)
The positive electrode active material used for the positive electrode active material layer 24 includes lithium ion occlusion and release, lithium ion desorption and insertion (intercalation), or counter ions (for example, PF ⁶⁻ ) of lithium ions and lithium ions. An electrode active material capable of reversibly proceeding doping and dedoping can be used.

For example, lithium cobalt oxide (LiCoO _2), lithium nickelate (LiNiO _2), lithium manganate (LiMnO _2), lithium manganese spinel (LiMn ₂ O _4), and the general _{formula: LiNi x Co y Mn z M} a O ₂ (x + y + z + a = 1, 0 ≦ x <1, 0 ≦ y <1, 0 ≦ z <1, 0 ≦ a <1, M is one type selected from Al, Mg, Nb, Ti, Cu, Zn, Cr Complex metal oxides represented by the above elements), lithium vanadium compounds (LiV ₂ O ₅ ), olivine-type LiMPO ₄ (where M is Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr) One or more elements selected from VO), LiNi _x Co _y Al _z O ₂ (0.9 <x + y + z <1.1) and other complex metal oxides, polyacetylene, Polyaniline, polypyrrole, polythiophene, polyacene and the like can be mentioned.

(Conductive material)
Examples of the conductive material include carbon powder such as carbon black, carbon nanotube, carbon material, fine metal powder such as copper, nickel, stainless steel and iron, a mixture of carbon material and fine metal powder, and conductive oxide such as ITO. . In the case where sufficient conductivity can be ensured only by the positive electrode active material, the lithium ion secondary battery 100 may not include a conductive material.

(Positive electrode binder)
The binder used for the positive electrode can be the same as that for the negative electrode.

  The constituent ratio of the positive electrode active material in the positive electrode active material layer 24 is preferably 80% or more and 96% or less by mass ratio. The constituent ratio of the conductive material in the positive electrode active material layer 24 is preferably 2.0% or more and 10% or less by mass ratio, and the constituent ratio of the binder in the positive electrode active material layer 24 is 2.0% by mass ratio. It is preferable that it is 10% or less.

"Separator"
The separator 10 only needs to be formed of an electrically insulating porous structure, for example, a single layer of a film made of polyethylene, polypropylene, or polyolefin, a stretched film of a laminate or a mixture of the above resins, or cellulose, polyester, and Examples thereof include a fiber nonwoven fabric made of at least one constituent material selected from the group consisting of polypropylene.

"Electrolyte"
As the electrolytic solution, an electrolyte solution containing lithium salt (electrolyte aqueous solution, electrolyte solution using an organic solvent) can be used. However, since the electrolytic aqueous solution has a low decomposition voltage electrochemically, the withstand voltage during charging is limited to be low. Therefore, an electrolyte solution (nonaqueous electrolyte solution) using an organic solvent is preferable.

  The nonaqueous electrolytic solution has an electrolyte dissolved in a nonaqueous solvent, and may contain a cyclic carbonate and a chain carbonate as a nonaqueous solvent.

  As cyclic carbonate, what can solvate electrolyte can be used. For example, ethylene carbonate, propylene carbonate, butylene carbonate, and the like can be used.

  The chain carbonate can reduce the viscosity of the cyclic carbonate. Examples thereof include diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate. In addition, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, and the like may be mixed and used.

  The ratio of the cyclic carbonate and the chain carbonate in the non-aqueous solvent is preferably 1: 9 to 1: 1 by volume.

Examples of the electrolyte include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , LiCF ₃ CF ₂ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF _{2 SO 2) 2, LiN (} CF 3 SO 2) (C 4 F 9 SO 2), LiN (CF 3 CF 2 CO) 2, lithium salts such as LiBOB can be used. In addition, these lithium salts may be used individually by 1 type, and may use 2 or more types together. In particular, LiPF ₆ is preferably included from the viewpoint of the degree of ionization.

When LiPF ₆ is dissolved in a non-aqueous solvent, the concentration of the electrolyte in the non-aqueous electrolyte is preferably adjusted to 0.5 to 2.0 mol / L. When the concentration of the electrolyte is 0.5 mol / L or more, the lithium ion concentration of the nonaqueous electrolytic solution can be sufficiently secured, and a sufficient capacity can be easily obtained during charging and discharging. Moreover, by suppressing the electrolyte concentration to within 2.0 mol / L, it is possible to suppress an increase in the viscosity of the non-aqueous electrolyte, to sufficiently secure the mobility of lithium ions, and to obtain a sufficient capacity during charging and discharging. It becomes easy.

Even when LiPF ₆ is mixed with another electrolyte, the lithium ion concentration in the non-aqueous electrolyte is preferably adjusted to 0.5 to 2.0 mol / L, and the lithium ion concentration from LiPF ₆ is 50 mol%. More preferably, it is contained.

"Case"
The case 50 seals the laminated body 40 and the electrolytic solution therein. The case 50 is not particularly limited as long as it can suppress leakage of the electrolytic solution to the outside and entry of moisture and the like into the lithium ion secondary battery 100 from the outside.

  For example, as the case 50, as shown in FIG. 1, a metal laminate film in which a metal foil 52 is coated with a polymer film 54 from both sides can be used. For example, an aluminum foil can be used as the metal foil 52 and a film such as polypropylene can be used as the polymer film 54. For example, the material of the outer polymer film 54 is preferably a polymer having a high melting point, such as polyethylene terephthalate (PET) or polyamide, and the material of the inner polymer film 54 is polyethylene (PE) or polypropylene (PP). Etc. are preferred.

"Lead"
The leads 60 and 62 are made of a conductive material such as aluminum. Then, the leads 60 and 62 are respectively welded to the positive electrode current collector 22 and the negative electrode current collector 32 by a known method, and a separator is provided between the positive electrode active material layer 24 of the positive electrode 20 and the negative electrode active material layer 34 of the negative electrode 30. 10 is inserted into the case 50 together with the electrolyte, and the entrance of the case 50 is sealed.

[Method for producing lithium ion secondary battery]
Next, a method for manufacturing the lithium ion secondary battery 100 will be specifically described.

  First, a negative electrode active material, a binder, and a solvent are mixed to prepare a paint. A conductive material may be further added as necessary. As the solvent, for example, water, N-methyl-2-pyrrolidone or the like can be used. The constituent ratio of the negative electrode active material, the conductive material, and the binder is preferably 90 wt% to 98 wt%: 0 wt% to 3.0 wt%: 2.0 wt% to 5.0 wt% in mass ratio. These mass ratios are adjusted so as to be 100 wt% as a whole.

  The mixing method of these components constituting the paint is not particularly limited, and the mixing order is not particularly limited. The paint is applied to the negative electrode current collector 32. There is no restriction | limiting in particular as an application | coating method, The method employ | adopted when producing an electrode normally can be used. Examples thereof include a slit die coating method and a doctor blade method. Similarly, the positive electrode paint is applied on the positive electrode current collector 22 for the positive electrode.

  Subsequently, the solvent in the paint applied on the positive electrode current collector 22 and the negative electrode current collector 32 is removed. The removal method is not particularly limited. For example, the positive electrode current collector 22 and the negative electrode current collector 32 to which the paint is applied may be dried in an atmosphere of 80 ° C. to 150 ° C.

  Then, the electrode on which the positive electrode active material layer 24 and the negative electrode active material layer 34 are formed in this way is subjected to a press treatment by a roll press device or the like as necessary.

  Next, the positive electrode 20 having the positive electrode active material layer 24, the negative electrode 30 having the negative electrode active material layer 34, the separator 10 interposed between the positive electrode and the negative electrode, and the electrolytic solution are sealed in a case 50.

  For example, the positive electrode 20, the negative electrode 30, and the separator 10 are stacked, and the positive electrode 20 and the negative electrode 30 are heated and pressed with a press tool from a direction perpendicular to the stacking direction, and the positive electrode 20, the separator 10, and the negative electrode 30. Adhere. For example, the laminated body 40 is put into a bag-like case 50 prepared in advance.

  Finally, the lithium ion secondary battery is manufactured by injecting the electrolytic solution into the case 50. Instead of injecting the electrolytic solution into the case, the laminate 40 may be impregnated with the electrolytic solution.

  As described above, since the negative electrode active material according to the present embodiment contains Al and P in predetermined amounts, it is considered that the interlayer of the carbon material is expanded. For this reason, the lithium ion secondary battery containing the negative electrode active material concerning this embodiment improves a quick charge characteristic (input characteristic).

  The embodiments of the present invention have been described in detail with reference to the drawings. However, the configurations and combinations of the embodiments in the embodiments are examples, and the addition and the omission of the configurations are within the scope not departing from the gist of the present invention. , Substitutions, and other changes are possible.

[Example 1]
(Preparation of negative electrode active material)
Artificial graphite (bulk density: 2.5 g / cm ³ , specific surface area: 0.05 m ² / g) was prepared as a carbon material, Al ₂ O ₃ was prepared as an Al source, and P ₂ O ₅ was prepared as a P source. The prepared artificial graphite, Al ₂ O ₃ and P ₂ O ₅ have an Al ₂ O ₃ content of 0.002% by mass as an Al amount and a P ₂ O ₅ content of 0.060% by mass as a P amount. Weighed at the ratio Artificial graphite and _Al 2 _{O 3} and _P 2 _{O 5} were weighed and dry-mixed in a ball mill, to prepare a negative electrode active material.
The bulk density is determined by dropping the artificial graphite from the discharge part 8 mmφ of the funnel, filling the container with a capacity of 100 cm ³ , scraping the artificial graphite overflowing from the container, and then weighing the artificial graphite filled in the container. It measured and computed from the measured weight of artificial graphite and the volume of the container. The specific surface area was measured by a BET method using nitrogen gas adsorption using a specific surface area measuring device.

(Preparation of negative electrode)
94 parts by mass of the produced negative electrode active material, 2 parts by mass of acetylene black as a conductive auxiliary agent, and 4 parts by mass of polyvinylidene fluoride (PVDF) as a binder were weighed and mixed to obtain a negative electrode mixture. . Subsequently, the negative electrode mixture was dispersed in N-methyl-2-pyrrolidone to obtain a paste-like negative electrode mixture paint. This paint was applied to both surfaces of an electrolytic copper foil having a thickness of 10 μm so that the amount of the negative electrode active material applied was 6.1 mg / cm ² and dried at 100 ° C. to form a negative electrode active material layer. . Then, it pressure-molded with the roll press and produced the negative electrode.

(Preparation of positive electrode)
90 parts by mass of LiCoO ₂ as a positive electrode active material, 5 parts by mass of acetylene black as a conductive auxiliary agent, and 5 parts by mass of polyvinylidene fluoride (PVDF) as a binder are mixed together to obtain a positive electrode mixture. It was. Subsequently, the positive electrode mixture was dispersed in N-methyl-2-pyrrolidone to obtain a paste-like positive electrode mixture paint. This paint was applied to both surfaces of an aluminum foil having a thickness of 20 μm so that the applied amount of the positive electrode active material was 12.5 mg / cm ² and dried at 100 ° C. to form a positive electrode active material layer. Then, it pressure-molded with the roll press and produced the positive electrode.

(Production of evaluation lithium-ion secondary battery)
The produced negative electrode and positive electrode were alternately laminated through a polypropylene separator having a thickness of 16 μm, and a laminate was produced by laminating three negative electrodes and two positive electrodes. Furthermore, in the negative electrode of the laminated body, a negative electrode lead made of nickel is attached to the protruding end portion of the copper foil not provided with the negative electrode active material layer. On the other hand, in the positive electrode of the laminated body, aluminum without the positive electrode active material layer is provided. An aluminum positive electrode lead was attached to the protruding end of the foil by an ultrasonic welding machine. And this laminated body is inserted into the outer package of the aluminum laminate film and heat-sealed except for one peripheral portion to form a closed portion, and EC (ethylene carbonate) / DEC (diethyl carbonate) is formed in the outer package. After injecting a non-aqueous electrolyte to which 1M (mol / L) LiPF ₆ was added as a lithium salt into a solvent blended at a volume ratio of 3: 7, the remaining one part was decompressed by a vacuum sealer. While being sealed with heat seal, a lithium ion secondary battery was produced.

(Measurement of quick charge characteristics)
The quick charge characteristics of the produced lithium ion secondary battery were measured using a secondary battery charge / discharge test apparatus. The voltage range was 3.0 V to 4.2 V, and 1C = 340 mAh / g per negative electrode active material weight, and the 3C capacity retention rate (%) was evaluated. Here, the 3C capacity maintenance rate is a ratio of the charging capacity at the time of 3C constant current charging to the 0.2C charging amount with respect to the constant current-constant voltage charging capacity at the time of 0.2C charging. ). Note that 1C is a current value at which charging / discharging is completed in exactly one hour after a constant current charge or constant current discharge is performed on a battery cell having a nominal capacity value. The results are shown in Table 1.

[Examples 2-8, Comparative Examples 1-8]
In the production of the negative electrode active material, artificial graphite, Al ₂ O ₃ and P ₂ O ₅ were used, and the amounts of Al ₂ O ₃ and P ₂ O ₅ were the amounts shown in Table 1 below as the amounts of Al and P, respectively. A lithium ion secondary battery was produced in the same manner as in Example 1 except that it was weighed at the ratio described above. And the quick charge characteristic (3C capacity | capacitance maintenance factor (%)) of the produced lithium ion secondary battery was measured. The results are shown in Table 1.

  From the results shown in Table 1, Example 1 in which the Al content is 0.002% by mass to 0.2% by mass and the P content is 0.06% by mass to 1.5% by mass. It was confirmed that all of -8 exhibited a high value with a 3C capacity maintenance ratio of 68% or more. On the other hand, Comparative Examples 1 to 8, in which the content of at least one of Al and P is less or greater than the range of the present invention, all showed a low value of 3C capacity maintenance rate of 60% or less.

[Examples 9 to 16]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that Ti was added to the negative electrode active material as TiO ₂ . That is, in the production of the negative electrode active material, artificial graphite, Al ₂ O ₃ , P ₂ O ₅ and TiO ₂ , the content of Al ₂ O ₃ is 0.080 mass% as the amount of Al, and the content of P ₂ O ₅ Lithium ion secondary battery in the same manner as in Example 1, except that the P content was 0.750% by mass, and the TiO ₂ content was weighed in the proportion of Ti as described in Table 2 below. Was made. And the quick charge characteristic (3C capacity | capacitance maintenance factor (%)) of the produced lithium ion secondary battery was measured. The results are shown in Table 2. In Table 2, Example 4 in which the content of Al ₂ O ₃ of the negative electrode active material was 0.080 mass% as the Al amount and the content of P ₂ O ₅ was 0.750 mass% as the P amount. The measurement results of the quick charge characteristics of are described.

  From the results shown in Table 2, it was confirmed that the 3C capacity retention rate was improved by further adding Ti. In particular, in Examples 11 to 14 in which the Ti content was 0.05% by mass or more and 1.5% by mass or less, the 3C capacity retention rate was improved.

[Examples 17 to 24]
A lithium ion secondary battery was produced in the same manner as in Example 11 except that the bulk density of the artificial graphite was adjusted by sieving the artificial graphite. That is, in the production of the negative electrode active material, a lithium ion secondary battery was produced in the same manner as in Example 11 except that artificial graphite having a bulk density adjusted to the value shown in Table 3 below was used as the carbon material. did. And the quick charge characteristic (3C capacity | capacitance maintenance factor (%)) of the produced lithium ion secondary battery was measured. The results are shown in Table 3.

  In addition, the bulk density of Example 17 was adjusted by removing 0 to 10% and 90 to 100% of the artificial graphite of the cumulative volume of the particle size distribution of the artificial graphite by sieving. Similarly, in Example 18, artificial graphite of 0 to 8% and 92 to 100% of the cumulative volume was removed. In Example 19, 0 to 7% and 93 to 100% of the artificial graphite of the cumulative volume was removed. In Example 20, artificial graphite of 0 to 5% and 95 to 100% of the cumulative volume was removed. In Example 21, 0 to 3% of the cumulative volume and 97 to 100% of artificial graphite were removed. In Example 22, 0-2% and 98-100% of the artificial graphite was removed. In Example 23, 0 to 1% and 99 to 100% of artificial graphite in the cumulative volume were removed. Example 24 was not sieved (ie, equivalent to Example 11). By doing so, the bulk density shown in Table 3 was obtained without changing the specific surface area.

From the results shown in Table 3, it was confirmed that the 3C capacity retention rate was improved by adjusting the bulk density of the artificial graphite. In particular, in Examples 19 to 22 in which the bulk density was 0.5 g / cm ³ or more and 2.0 g / cm ³ or less, the 3C capacity retention rate was significantly improved.

[Examples 25 to 32]
A lithium ion secondary battery was produced in the same manner as in Example 18 except that the specific surface area of the artificial graphite was adjusted by pulverizing the artificial graphite. That is, in the production of the negative electrode active material, a lithium ion secondary battery was produced in the same manner as in Example 18 except that artificial graphite having a specific surface area adjusted to the value shown in Table 4 below was used as the carbon material. did. And the quick charge characteristic (3C capacity | capacitance maintenance factor (%)) of the produced lithium ion secondary battery was measured. The results are shown in Table 4.

  The artificial graphite was pulverized by dry pulverization using a ball mill. However, in Example 25, pulverization was not performed (that is, corresponding to Example 18). Example 26 has a grinding time of 0.5 hour, Example 27 has a grinding time of 1 hour, Example 28 has a grinding time of 2 hours, Example 29 has a grinding time of 3 hours, and Example 30 has a grinding time of 4 hours. Time, Example 31 had a grinding time of 5 hours, and Example 32 had a grinding time of 6 hours.

From the results shown in Table 4, it was confirmed that the 3C capacity retention rate was improved by adjusting the specific surface area of the artificial graphite. In particular, in Examples 27 to 30 having a specific surface area of 0.1 m ² / g or more and 2 m ² / g or less, the 3C capacity retention rate was significantly improved.

DESCRIPTION OF SYMBOLS 10 ... Separator, 20 ... Positive electrode, 22 ... Positive electrode collector, 24 ... Positive electrode active material layer, 30 ... Negative electrode, 32 ... Negative electrode collector, 34 ... Negative electrode active material layer, 40 ... Laminate, 50 ... Case, 52 ... Metal foil, 54 ... Polymer film, 60, 62 ... Lead, 100 ... Lithium ion secondary battery

Claims (6)

  A carbon material, Al and P are contained, and the content of Al is 0.002% by mass or more and 0.2% by mass or less, and the content of P is 0.06% by mass or more and 1.5% by mass. A negative electrode active material that is:   2. The negative electrode active material according to claim 1, further comprising Ti, wherein the content of Ti is 0.05% by mass or more and 1.5% by mass or less. The negative electrode active material according to claim 1, wherein the carbon material is artificial graphite, and the bulk density of the artificial graphite is 0.5 g / cm ³ or more and 2.0 g / cm ³ or less. 4. The negative electrode active material according to claim 1, wherein the carbon material has a specific surface area of 0.1 m ² / g or more and 2 m ² / g or less. A negative electrode having a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector,
The negative electrode in which the said negative electrode active material layer contains the negative electrode active material as described in any one of Claims 1-4.   The lithium ion secondary battery which has a negative electrode of Claim 5, a positive electrode, and electrolyte solution.

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