JP2018160453A - Negative electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for a lithium ion secondary battery having excellent cycle characteristics and a lithium ion secondary battery. A negative electrode having a negative electrode active material layer having a negative electrode active material containing silicon on at least one of the main surfaces of a negative electrode current collector, in a Raman spectrum using an argon ion laser having a wavelength of 532 nm, The peak intensity ratio of the strongest peak located at 460±20 cm−1 to the peak intensity of the strongest peak located at 510±10 cm−1 on the surface of the negative electrode active material layer is A1, and the inside of the negative electrode active material layer is For a lithium ion secondary battery satisfying A1≧A2, where A2 is the peak intensity ratio of the strongest peak located at 460±20 cm−1 to the peak intensity of the strongest peak located at 510±10 cm−1. Negative electrode. [Selection diagram] Figure 1

Description

  The present invention relates to a negative electrode for a lithium ion secondary battery 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. In recent years, it has been used as a power source mounted for 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.

  Currently, carbon materials such as graphite are often used as negative electrode active materials for lithium ion secondary batteries. In recent years, a large number of alloy-based negative electrode active materials such as silicon (Si) and SiO having a larger discharge capacity than graphite have been studied. However, these alloy-based negative electrode active materials have a larger discharge capacity than graphite, and also have a large volume expansion associated with the charge / discharge reaction, and are more susceptible to particle cracking and isolation than graphite. The decrease was significant.

  Patent Documents 1 and 2 disclose that by adding a metal element to an alloy negative electrode to improve electron conductivity, a charge / discharge reaction can be uniformly performed in an electrode cross section, and cycle characteristics are improved. .

  In Patent Document 3, a lithium silicate layer that does not contribute to the charge / discharge reaction is formed at the interface between the negative electrode current collector and the negative electrode active material layer, whereby sufficient adhesion strength is obtained between the current collector and the active material layer. It is disclosed that the characteristics are improved.

JP 2007-27102 A International Publication No. 2007/046327 International Publication No. 2011/132428

  However, the method disclosed in the above prior art does not provide sufficient cycle characteristics, and further improvement is required.

  The present invention has been developed under such circumstances, and an object thereof is to provide a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery excellent in cycle characteristics.

In order to achieve the above object, a negative electrode for a lithium ion secondary battery according to the present invention is a negative electrode including a negative electrode active material layer having a negative electrode active material containing silicon on at least one of main surfaces of a negative electrode current collector. In the Raman spectrum using an argon ion laser having a wavelength of 532 nm, the most intense peak located at 460 ± 20 cm ⁻¹ with respect to the peak intensity of the strongest peak located at 510 ± 10 cm F ⁻¹ on the surface of the negative electrode active material layer. The peak intensity ratio of the strong peak is A1, and the peak intensity ratio of the strongest peak located at 460 ± 20 cm ⁻¹ with respect to the peak intensity of the strongest peak located at 510 ± 10 cm ⁻¹ inside the negative electrode active material layer is When A2, A1 ≧ A2 is satisfied.

  By satisfying the relationship of A1 ≧ A2, the expansion coefficient inside the negative electrode active material layer is lower than the surface of the negative electrode active material layer. For this reason, it is presumed that the cycle characteristics are improved because peeling between the negative electrode current collector and the negative electrode active material layer is suppressed.

  The ratio of the peak intensity ratio A2 to the peak intensity ratio A1 in the negative electrode active material layer satisfies 1 ≦ A1 / A2 ≦ 100, 0.1 ≦ A1 ≦ 10, and 0.1 ≦ A2 ≦ 10. Is preferred.

  In such peak intensity ratio, excellent cycle characteristics can be obtained.

  The ratio of A2 to the peak intensity ratio A1 in the negative electrode active material layer preferably satisfies 1.05 ≦ A1 / A2 ≦ 3.4.

  Particularly excellent cycle characteristics can be obtained at such peak intensity ratio.

  The average primary particle size of the silicon-based material is preferably 0.1 μm or more and 20 μm or less.

  With such a configuration, cycle characteristics are improved. Although this effect is not necessarily clear, the use of the silicon material in the above range can suppress the pulverization and cracking of the active material and further improve the cycle characteristics.

The negative electrode active material layer preferably contains at least one selected from the group consisting of Li ₄ SiO ₄ , Li ₆ Si ₂ O ₇ and Li ₂ Si ₃ O ₅ .

  With such a configuration, cycle characteristics are improved. Although this effect is not necessarily clear, by including the composition, excessive reaction of the silicon material with the electrolytic solution is suppressed, and cycle characteristics are further improved.

  The negative electrode active material layer preferably contains graphite.

  With such a configuration, cycle characteristics are improved. Although this effect is not necessarily clear, by mixing the silicon material and an active material having a small volume expansion during Li occlusion, separation and collapse of the mixture layer are alleviated, and cycle characteristics are further improved.

  ADVANTAGE OF THE INVENTION According to this invention, the negative electrode for lithium ion secondary batteries and the lithium ion secondary battery which were excellent in cycling characteristics can be provided.

It is a schematic cross section of the lithium ion secondary battery according to the present embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be appropriately combined.

(Lithium ion secondary battery)
FIG. 1 shows a cross-sectional configuration diagram of a lithium ion secondary battery 100 according to this embodiment. The lithium ion secondary battery 100 includes an outer body 50, a positive electrode 10 and a negative electrode 20 provided inside the outer body, and an electrode body 30 formed by being stacked via a separator 18 disposed therebetween. The separator 18 holds the non-aqueous electrolyte, which is a lithium ion transfer medium between the positive and negative electrodes during charging and discharging. Furthermore, one end is electrically connected to the negative electrode 20 and the other end protrudes outside the exterior body, and one end is electrically connected to the positive electrode 10. The other end is provided with a positive electrode lead 60 protruding outside the exterior body.

  There is no restriction | limiting in particular as a shape of a lithium ion secondary battery, For example, any, such as a cylindrical type, a square type, a coin type, a flat type, a laminate film type, may be sufficient. In the following examples, an aluminum laminated film type battery is produced and evaluated.

  The positive electrode 10 includes a positive electrode active material layer 14 containing a positive electrode active material that absorbs and releases lithium ions, a conductive additive, and a binder on at least one main surface of the positive electrode current collector 12. The negative electrode 20 includes a negative electrode active material layer 24 containing a negative electrode active material that absorbs and releases lithium ions, a conductive additive, and a binder on at least one main surface of the negative electrode current collector 22. Yes.

(Negative electrode)
The negative electrode active material layer 24 formed on the negative electrode 20 of the present embodiment contains a negative electrode active material, a binder, and a conductive additive.

  For the negative electrode active material layer 24, a paint containing a negative electrode active material, a binder, a conductive additive and a solvent is applied on the negative electrode current collector 22, and the solvent in the paint applied on the negative electrode current collector 22 is removed. Can be manufactured.

The negative electrode for a lithium ion battery according to this embodiment is a negative electrode including a negative electrode active material layer having a negative electrode active material containing silicon on at least one of main surfaces of a negative electrode current collector, and has an argon wavelength of 532 nm. In the Raman spectrum using an ion laser, the peak intensity ratio of the strongest peak located at 460 ± 20 cm ⁻¹ with respect to the peak intensity of the strongest peak located at 510 ± 10 cm ⁻¹ on the surface of the negative electrode active material layer. When the peak intensity ratio of the strongest peak located at 460 ± 20 cm ⁻¹ with respect to the peak intensity of the strongest peak located at 510 ± 10 cm ⁻¹ inside the negative electrode active material layer is A2,
A1 ≧ A2 is satisfied.

  By satisfying the relationship of A1 ≧ A2, the expansion coefficient inside the negative electrode active material layer is lower than the surface of the negative electrode active material layer. For this reason, it is presumed that the cycle characteristics are improved because peeling between the negative electrode current collector and the negative electrode active material layer is suppressed.

  In the negative electrode active material layer according to this embodiment, the ratio of the peak intensity ratio A2 to the peak intensity ratio A1 in the negative electrode active material layer satisfies 1 ≦ A1 / A2 ≦ 100, and 0.1 ≦ A1 ≦. 10 and 0.1 ≦ A2 ≦ 10 are preferably satisfied.

  Excellent cycle characteristics can be obtained at these peak intensity ratios.

The ratio of A2 to the peak intensity ratio A1 in the negative electrode active material layer according to this embodiment preferably satisfies 1.05 ≦ A1 / A2 ≦ 3.4.

  Particularly excellent cycle characteristics can be obtained at such peak intensity ratio.

  The average primary particle size of the silicon-based material according to this embodiment is preferably 0.1 μm or more and 20 μm or less.

  Thereby, pulverization and cracking of the active material can be suppressed, and the cycle characteristics are further improved.

The silicon material according to the present embodiment preferably has silicon oxide represented by SiO _x (0 <x ≦ 2).

The negative electrode active material layer according to this embodiment preferably contains at least one selected from the group consisting of Li ₄ SiO ₄ , Li ₆ Si ₂ O ₇ and Li ₂ Si ₃ O ₅ .

  Thereby, excessive reaction with the electrolytic solution of the silicon material is suppressed, and the cycle characteristics are further improved.

  The negative electrode active material according to this embodiment preferably further contains a carbon-based material.

  As the carbon material, a known carbon material that can be used for a lithium ion secondary battery can be used, and examples thereof include natural graphite, artificial graphite, and mesocarbon microbeads (MCMB). These carbon materials may be used individually by 1 type, and may use 2 or more types together.

  The mixing amount of the carbon material according to the present embodiment is preferably in the range of 0.4 ≦ d1 / d2 ≦ 2.3 when the weight ratio d1 of the negative electrode active material and the weight ratio d2 of the carbon material are set.

  The content of the negative electrode active material in the negative electrode active material layer 24 is preferably 50 to 95% by mass based on the sum of the masses of the negative electrode active material, the conductive additive and the binder, and is 75 to 93% by mass. More preferably. If it is said range, a negative electrode with a big capacity | capacitance can be obtained.

(Measurement method of A1, A2)
The peak intensity ratio A1 of the strongest peak located at 460 ± 20 cm ⁻¹ to the peak intensity of the strongest peak located at 510 ± 10 cm ⁻¹ on the surface of the negative electrode active material layer according to the present embodiment, the negative electrode active material layer The peak intensity ratio A2 of the strongest peak located at 460 ± 20 cm ⁻¹ with respect to the peak intensity of the strongest peak located at 510 ± 10 cm ⁻¹ is measured using an argon ion laser having a wavelength of 532 nm. can do.

  A1 and A2 can be measured by irradiating an arbitrary point in the negative electrode active material layer with an argon ion laser after polishing the negative electrode cross section with a cross section polisher or an ion milling device.

(binder)
The binder binds the negative electrode active materials to the current collector 22 while bonding the negative electrode active materials to each other. A binder will not be specifically limited if the above-mentioned coupling | bonding is possible. For example, a fluororesin such as polyvinylidene fluoride (PVDF), cellulose, styrene / butadiene rubber, polyimide, polyamideimide, polyacrylic acid, polyacrylonitrile, polyalginic acid, or the like can be used.

  The content of the binder in the negative electrode active material layer 24 is preferably 1 to 30% by mass, and preferably 5 to 15% by mass based on the sum of the masses of the negative electrode active material, the conductive additive and the binder. Is more preferable. If it is said range, a negative electrode with a big capacity | capacitance can be obtained.

(Conductive aid)
The conductive aid is not particularly limited as long as the conductivity of the negative electrode active material layer 24 is improved, and a known conductive aid can be used. Examples thereof include carbon blacks such as acetylene black, furnace black, channel black, and thermal black, vapor grown carbon fibers (VGCF), carbon fibers such as carbon nanotubes, and carbon materials such as graphite. More than seeds can be used.

  The content of the conductive auxiliary in the negative electrode active material layer 24 is not particularly limited, but when added, it is usually 1 to 10% by mass based on the sum of the mass of the negative electrode active material, conductive auxiliary and binder. Preferably there is.

(solvent)
The solvent is not particularly limited as long as it can form the above-described negative electrode active material, conductive additive, and binder. For example, N-methyl-2-pyrrolidone, N, N-dimethylformamide, and the like can be used. .

(Negative electrode current collector)
The negative electrode current collector 22 is preferably a conductive plate material having a small thickness, and is preferably a metal foil having a thickness of 8 to 30 μm. The negative electrode current collector 22 is preferably formed of a material that does not alloy with lithium, and a particularly preferable material is copper. Examples of such copper foil include electrolytic copper foil. For example, an electrolytic copper foil is prepared by immersing a metal drum in an electrolytic solution in which copper ions are dissolved, and flowing current while rotating the copper drum, thereby depositing copper on the surface of the drum and peeling it off. It is the obtained copper foil.

  Moreover, the rolled copper foil manufactured by rolling the cast copper lump to desired thickness may be sufficient, and copper is deposited on the surface of the rolled copper foil by an electrolytic method, and the surface is roughened. There may be.

  Thus, there is no restriction | limiting in particular as an application | coating method which apply | coats the coating material containing a negative electrode active material, a binder, a conductive support agent, and a solvent mentioned above, 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.

(Negative electrode active material layer)
The negative electrode active material layer satisfying A1 ≧ A2 according to the present embodiment can be produced by using a multilayer coating method or the like in which a plurality of paints produced using negative electrode active materials having different amounts of amorphous silicon are applied. .

  Amorphous silicon has a stronger peak at 460 ± 20 cm-1 in the Raman spectrum than crystalline silicon, so A1 / A2 is adjusted by adjusting the amount of amorphous silicon in the negative electrode active material layer. can do.

  A1 / A2 can be adjusted by using not only amorphous silicon but also amorphous silicon oxide. In addition, A1 / A2 in the negative electrode active material layer can be adjusted by doping part of the negative electrode active material layer with Li.

  The method for removing the solvent in the paint applied on the negative electrode current collector 22 is not particularly limited, and the negative electrode current collector 22 applied with the paint may be dried at, for example, 80 ° C. to 150 ° C.

  When preparing a negative electrode active material layer according to the present embodiment, when a plurality of coatings are applied in multiple layers, after the first coating is applied on the negative electrode current collector, the coating is dried once and then amorphous. After applying the second coating material produced using negative electrode active materials having different Si amounts, drying is performed again. A negative electrode active material can be produced by repeating these steps a plurality of times.

  In addition, when applying the second paint, the negative electrode active material layer may be prepared by applying the second paint on the first paint and then drying it in an undried state. Good.

  Then, the negative electrode 20 on which the negative electrode active material layer 24 is formed in this way may be subsequently subjected to a press treatment using, for example, a roll press device as necessary. The linear pressure of the roll press can be set to 100 to 5000 kgf / cm, for example.

(Nonaqueous electrolyte)
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.

  The cyclic carbonate is not particularly limited as long as it can solvate the electrolyte, and a known cyclic carbonate can be used. For example, ethylene carbonate, propylene carbonate, butylene carbonate, and the like can be used.

  The chain carbonate is not particularly limited as long as the viscosity of the cyclic carbonate can be reduced, and a known chain carbonate can be used. 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 Lithium salts such as CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (CF ₃ CF ₂ CO) ₂ , 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 conductivity.

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 conductivity 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.

(Positive electrode)
The positive electrode 10 of the present embodiment has a structure in which a positive electrode active material layer 14 containing a positive electrode active material is formed on one surface or both surfaces of a positive electrode current collector 12. The positive electrode active material layer 14 is coated on the positive electrode current collector 12 with a paint containing the positive electrode active material, a binder, a conductive additive, and a solvent in the same process as the negative electrode manufacturing method. It can be produced by removing the solvent in the applied paint.

Examples of the positive electrode active material include occlusion and release of lithium ions, desorption and insertion (intercalation) of lithium ions, or doping and dedoping of lithium ions and counter anions of the lithium ions (for example, ClO ₄ ⁻ ). Is not particularly limited as long as it can reversibly proceed, and a known electrode active material can be used. For example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganese spinel (LiMn ₂ O ₄ ), and a general formula: LiNi _x Co _y Mn _z O ₂ (x + y + z = 1) Examples include composite metal oxides, lithium vanadium compounds (LiV ₂ O ₅ ), and LiMPO ₄ (wherein M represents Co, Ni, Mn, Fe, or VO).

  In addition, oxides and sulfides capable of inserting and extracting lithium ions can be used as the positive electrode active material.

  Furthermore, each component (conductive auxiliary agent and binder) other than the positive electrode active material can be the same material as that used in the negative electrode 20.

  As the positive electrode current collector 12, various known metal foils used in current collectors for lithium ion secondary batteries can be used. For example, a metal foil such as aluminum, stainless steel, nickel, titanium, or an alloy thereof can be used, and an aluminum foil is particularly preferable.

(Separator)
As long as the separator 18 is formed of an insulating porous body, the material, the manufacturing method, and the like are not particularly limited, and a known separator used for a lithium ion secondary battery can be used. For example, as the insulating porous material, a known polyolefin resin, specifically, a crystalline homopolymer or copolymer obtained by polymerizing polyethylene, polypropylene, 1-butene, 4-methyl-1-pentene, 1-hexene, or the like. A polymer is mentioned. These homopolymers or copolymers can be used alone or in combination of two or more. Further, it may be a single layer or a multilayer.

  The outer package 50 is not particularly limited as long as it can prevent leakage of the electrolytic solution to the outside or entry of moisture or the like into the lithium ion secondary battery 100 from the outside, such as a metal can, an aluminum laminate film, or the like Can be used. The aluminum laminate film includes, for example, a structure that is configured as a three-layer structure in which polypropylene, aluminum, and nylon are laminated in this order.

  The negative electrode lead 62 and the positive electrode lead 60 may be formed of a conductive material such as aluminum or nickel.

  As mentioned above, although the example of this invention was described in detail by embodiment, this invention is not limited to the said embodiment, A various deformation | transformation is possible.

  About the produced lithium ion secondary battery, cycling characteristics were evaluated with the following method.

この容量維持率が高いほど、充放電サイクル特性が良好であることを意味する。実施例および比較例で作製したリチウムイオン二次電池は、上記の条件によって充放電を繰り返し、１００サイクル後の容量維持率を充放電サイクル特性として評価した。 (Measurement of charge / discharge cycle characteristics)
The cycle characteristic is a current value at 0.5 C when a voltage range is set to 3.0 V to 0.01 V using a secondary battery charge / discharge test apparatus and 1 C = 1600 mAh / g per weight of the negative electrode active material. The charge / discharge cycle characteristics may be evaluated under the condition of charging and discharging at a current value of 0.5C. The charge / discharge cycle characteristics are evaluated as capacity retention rate (%), and the capacity retention rate (%) is the ratio of the discharge capacity at each cycle number to the initial discharge capacity, with the discharge capacity at the first cycle being the initial discharge capacity. Yes, expressed by the following formula (1). 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.

A higher capacity retention rate means better charge / discharge cycle characteristics. The lithium ion secondary batteries produced in the examples and comparative examples were repeatedly charged and discharged under the above conditions, and the capacity retention rate after 100 cycles was evaluated as charge / discharge cycle characteristics.

  The method for measuring the peak of the Raman scattering spectrum in the negative electrode active material according to this embodiment is as follows. First, using an NRS-7100 manufactured by JASCO Corporation, using a green laser with a wavelength of 532 nm and Raman spectroscopy, a dimmer is used to adjust the irradiation intensity to 1 mW or less, and a Raman scattering spectrum at an excitation wavelength of 532 nm. Measure.

The Raman scattering spectrum is a graph showing the Raman shift wavenumber (cm ⁻¹ ) on the horizontal axis and the Raman scattering intensity obtained on the vertical axis. Using this graph, we determined the point P Raman scattering intensity is minimum, and a point Q Raman scattering intensity in a range of wavenumber 1900～2300Cm ^-1 is minimized within the range of wave numbers 500～900Cm ^-1, A straight line passing through these points P and Q is defined as base-in (BL), and is corrected to a graph obtained by removing peaks below the baseline from the graph of wave numbers 900 to 1900 cm ⁻¹ .

Next, the peak in each range is specified in the corrected graph. ^{Incidentally,} the fact that a peak in the range of 1330cm ^-1 ~1355cm -1, upon subtracting the baseline in the Raman scattering spectrum, the spectrum of the convex exists on for the baseline, half width There it means that the convex spectrum is 5 cm ^-1 or more 150 cm ^-1 or less is comprised in the range described above, the Raman shift position indicating the maximum Raman scattering intensity within the range are included within the range mentioned above Means. Furthermore, when there are a plurality of convex spectra in the range, the convex spectrum having the strongest Raman scattering intensity in each range may be set as the peak of the Raman scattering spectrum in each range.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in more detail, this invention is not limited to these Examples at all.

Example 1
(Preparation of positive electrode)
96% by weight of LiNi _0.85 Co _0.10 Al _0.05 O ₂ as a positive electrode active material, 2% by weight of carbon black as a conductive additive, 0.5% by weight of graphite, and 1 PVDF as a binder 0.5 wt% and N-methyl-2-pyrrolidone solvent were mixed and dispersed to prepare a paste-like positive electrode slurry.

The obtained positive electrode slurry was uniformly applied to both surfaces of an aluminum foil having a thickness of 20 μm using a comma roll coater so that the applied amount of the active material was 22.0 mg / cm ² . Next, a positive electrode active material layer was formed by drying the N-methyl-2-pyrrolidone solvent in the positive electrode active material in an air atmosphere at 110 ° C. in a drying furnace.

In addition, the thickness of the coating film of the positive electrode active material layer apply | coated to both surfaces of the said aluminum foil was adjusted to the substantially same film thickness. The positive electrode on which the positive electrode active material was formed was pressure-bonded to both surfaces of the positive electrode current collector by a roll press to produce a positive electrode so that the density of the positive electrode active material layer was 3.6 g / cm ³ . . The positive electrode sheet was obtained by the above.

(Preparation of negative electrode)
As the negative electrode active material, 87.59% by weight of silicon oxide having a D50 of 3 μm, 0.32% by weight of amorphous silicon oxide, 2.1% by weight of acetylene black, 10% by weight of polyamideimide resin, N— A first paint for forming an active material layer was prepared by mixing and dispersing a solvent of methyl-2-pyrrolidone. Next, a second coating material for forming an active material layer was prepared in the same manner as the first coating material except that the silicon oxide content was 87.60% by weight and the amorphous silicon oxide content was 0.30% by weight. .

The obtained second paint was applied to one side of a 10 μm thick copper foil so that the active material application amount was 1.5 mg / cm ^2, and the first paint was applied in an undried state. The negative electrode active material layer was formed by applying the active material so that the applied amount was 1.5 mg / cm ² and drying at 100 ° C. Thereafter, a negative electrode active material layer was similarly formed on the other surface of the negative electrode current collector.

In addition, the thickness of the coating film of the negative electrode active material layer apply | coated to both surfaces of the said copper foil was adjusted to the substantially same film thickness. The negative electrode on which the negative electrode active material was formed was pressure-bonded to both surfaces of the negative electrode current collector by a roll press, and the negative electrode was prepared so that the density of the negative electrode active material layer was 1.5 g / cm ³ . Thus, a negative electrode sheet was obtained.

(Example 2)
When forming the negative electrode active material layer, 87.63 wt% of silicon oxide is used as the negative electrode active material of the first paint, 0.27 wt% of amorphous silicon oxide, and silicon oxide is used as the negative electrode active material of the second paint. The negative electrode active material layer of Example 2 was formed in the same manner as in Example 1 except that 87.89% by weight and amorphous silicon oxide were changed to 0.01% by weight. Thus, a negative electrode was obtained. .

(Example 3)
When forming the negative electrode active material layer, 51.90% by weight of silicon oxide as the negative electrode active material of the first paint, 36.00% by weight of amorphous silicon oxide, and silicon oxide as the negative electrode active material of the second paint The negative electrode active material layer of Example 3 was formed in the same manner as in Example 1 except that 87.60 wt% and amorphous silicon oxide were changed to 0.30 wt% to obtain a negative electrode. .

Example 4
When forming the negative electrode active material layer, 15.90% by weight of silicon oxide, 72.00% by weight of amorphous silicon oxide as the negative electrode active material of the first paint, and silicon oxide as the negative electrode active material of the second paint The negative electrode active material layer of Example 4 was formed in the same manner as in Example 1 except that 87.66 wt% and amorphous silicon oxide were changed to 0.24 wt% to obtain a negative electrode. .

(Example 5)
When forming the negative electrode active material layer, 87.60 wt% of silicon oxide is used as the negative electrode active material of the first paint, 0.30 wt% of amorphous silicon oxide, and silicon oxide is used as the negative electrode active material of the second paint. The negative electrode active material layer of Example 5 was formed in the same manner as in Example 1 except that 87.60 wt% and amorphous silicon oxide were changed to 0.30 wt% to obtain a negative electrode. .

(Example 6)
When forming the negative electrode active material layer, 57.90% by weight of silicon oxide as the negative electrode active material of the first paint, 30.00% by weight of amorphous silicon oxide, and silicon oxide as the negative electrode active material of the second paint The negative electrode active material layer of Example 6 was formed in the same manner as in Example 1 except that 57.90 wt% and amorphous silicon oxide were changed to 30.00 wt%, thereby obtaining a negative electrode. .

(Example 7)
When forming the negative electrode active material layer, 73.62% by weight of silicon oxide, 14.28% by weight of amorphous silicon oxide as the negative electrode active material of the first paint, and silicon oxide as the negative electrode active material of the second paint The negative electrode active material layer of Example 7 was formed in the same manner as Example 1 except that 83.70% by weight and amorphous silicon oxide were changed to 4.20% by weight to obtain a negative electrode. .

(Example 8)
When forming the negative electrode active material layer, 72.15 wt% of silicon oxide is used as the negative electrode active material of the first paint, 15.75 wt% of amorphous silicon oxide, and silicon oxide is used as the negative electrode active material of the second paint. Was changed to 83.40% by weight and amorphous silicon oxide was changed to 4.50% by weight, in the same manner as in Example 1, the negative electrode active material layer of Example 8 was formed to obtain a negative electrode. .

Example 9
In forming the negative electrode active material layer, 60.90% by weight of silicon oxide, 27.00% by weight of amorphous silicon oxide as the negative electrode active material of the first paint, and silicon oxide as the negative electrode active material of the second paint The negative electrode active material layer of Example 9 was formed in the same manner as in Example 1 except that 86.40 wt% and amorphous silicon oxide were changed to 1.50 wt% to obtain a negative electrode. .

(Example 10)
When forming the negative electrode active material layer, 69.90% by weight of silicon oxide as the negative electrode active material of the first paint, 18.00% by weight of amorphous silicon oxide, and silicon oxide as the negative electrode active material of the second paint The negative electrode active material layer of Example 10 was formed in the same manner as in Example 1 except that 87.30 wt% and amorphous silicon oxide were changed to 0.60 wt% to obtain a negative electrode. .

(Example 11)
When forming the negative electrode active material layer, 57.90% by weight of silicon oxide as the negative electrode active material of the first paint, 30.00% by weight of amorphous silicon oxide, and silicon oxide as the negative electrode active material of the second paint The negative electrode active material layer of Example 11 was formed in the same manner as in Example 1 except that 87.60 wt% and amorphous silicon oxide were changed to 0.30 wt% to obtain a negative electrode. .

(Example 12)
A negative electrode active material layer of Example 11 was formed in the same manner as in Example 1 except that silicon oxide having a D50 of 0.06 μm was used as the negative electrode active material to obtain a negative electrode.

(Example 13)
A negative electrode active material layer of Example 13 was formed in the same manner as in Example 1 except that silicon oxide having a D50 of 0.09 μm was used as the negative electrode active material to obtain a negative electrode.

(Example 14)
A negative electrode active material layer of Example 14 was formed in the same manner as in Example 1 except that silicon oxide having a D50 of 22.0 μm was used as the negative electrode active material to obtain a negative electrode.

(Example 15)
A negative electrode active material layer of Example 15 was formed in the same manner as in Example 1 except that silicon oxide having a D50 of 28.0 μm was used as the negative electrode active material to obtain a negative electrode.

(Example 16)
A negative electrode active material layer of Example 16 was formed in the same manner as in Example 1 except that silicon oxide having a D50 of 0.1 μm was used as the negative electrode active material to obtain a negative electrode.

(Example 17)
A negative electrode active material layer of Example 17 was formed in the same manner as in Example 1 except that silicon oxide having a D50 of 5.0 μm was used as the negative electrode active material to obtain a negative electrode.

(Example 18)
A negative electrode active material layer of Example 18 was formed in the same manner as in Example 1 except that silicon oxide having a D50 of 20.0 μm was used as the negative electrode active material to obtain a negative electrode.

(Example 19)
Example 5 and Example 5 except that 99.5% by weight of silicon oxide, 0.5% by weight of Li ₄ SiO ₄ as an additive, and silicon oxide obtained by mixing with a planetary ball mill were used as the negative electrode active material. Similarly, the negative electrode active material layer of Example 19 was formed to obtain a negative electrode.

(Example 20)
Example 1 except that 99.5% by weight of silicon oxide, 0.5% by weight of Li ₄ SiO ₄ as an additive, and silicon oxide obtained by mixing with a planetary ball mill were used as the negative electrode active material. In the same manner as described above, the negative electrode active material layer of Example 20 was formed to obtain a negative electrode.

(Example 21)
Example 9 except that 99.5% by weight of silicon oxide, 0.5% by weight of Li ₄ SiO ₄ as an additive, and silicon oxide obtained by mixing with a planetary ball mill were used as the negative electrode active material. In the same manner as described above, the negative electrode active material layer of Example 21 was formed to obtain a negative electrode.

(Example 22)
Except that 99.5% by weight of silicon oxide, 0.5% by weight of Li ₆ Si ₂ O ₇ as an additive, and silicon oxide obtained by mixing with a planetary ball mill were used as the negative electrode active material. In the same manner as in Example 5, the negative electrode active material layer of Example 22 was formed to obtain a negative electrode.

(Example 23)
Except that 99.5% by weight of silicon oxide, 0.5% by weight of Li ₆ Si ₂ O ₇ as an additive, and silicon oxide obtained by mixing with a planetary ball mill were used as the negative electrode active material. The negative electrode active material layer of Example 23 was formed in the same manner as Example 1 to obtain a negative electrode.

(Example 24)
Except that 99.5% by weight of silicon oxide, 0.5% by weight of Li ₆ Si ₂ O ₇ as an additive, and silicon oxide obtained by mixing with a planetary ball mill were used as the negative electrode active material. In the same manner as in Example 9, the negative electrode active material layer of Example 24 was formed to obtain a negative electrode.

(Example 25)
Except for using 99.5% by weight of silicon oxide, 0.5% by weight of Li ₂ Si ₃ O ₅ as an additive, and silicon oxide obtained by mixing with a planetary ball mill as a negative electrode active material. The negative electrode active material layer of Example 25 was formed in the same manner as Example 5 to obtain a negative electrode.

(Example 26)
Except for using 99.5% by weight of silicon oxide, 0.5% by weight of Li ₂ Si ₃ O ₅ as an additive, and silicon oxide obtained by mixing with a planetary ball mill as a negative electrode active material. In the same manner as in Example 1, the negative electrode active material layer of Example 26 was formed to obtain a negative electrode.

(Example 27)
Except for using 99.5% by weight of silicon oxide, 0.5% by weight of Li ₂ Si ₃ O ₅ as an additive, and silicon oxide obtained by mixing with a planetary ball mill as a negative electrode active material. The negative electrode active material layer of Example 27 was formed in the same manner as Example 9 to obtain a negative electrode.

(Example 28)
When forming the negative electrode active material layer, 61.29% by weight of silicon oxide, 0.21% by weight of amorphous silicon oxide, 26.40% by weight of graphite as the negative electrode active material of the first paint, Except that the negative electrode active material of the paint was changed to 61.29 wt% silicon oxide, 0.21 wt% amorphous silicon oxide, and 26.40 wt% graphite, The negative electrode active material layer of Example 28 was formed to obtain a negative electrode.

(Example 29)
When forming the negative electrode active material layer, 61.28% by weight of silicon oxide, 0.22% by weight of amorphous silicon oxide, 26.40% by weight of graphite, Except that the negative electrode active material of the paint was changed to 61.29 wt% silicon oxide, 0.21 wt% amorphous silicon oxide, and 26.40 wt% graphite, The negative electrode active material layer of Example 29 was formed to obtain a negative electrode.

(Example 30)
When forming the negative electrode active material layer, 48.91 wt% silicon oxide, 12.59 wt% amorphous silicon oxide, 26.40 wt% graphite are used as the negative electrode active material of the first paint. As in Example 1, except that the negative electrode active material of the paint was changed to 61.08% by weight of silicon oxide, 0.42% by weight of amorphous silicon oxide, and 26.40% by weight of graphite. The negative electrode active material layer of Example 30 was formed to obtain a negative electrode.

(Example 31)
When forming the negative electrode active material layer, the negative electrode active material of the first paint is 26.31 wt% silicon oxide, 0.09 wt% amorphous silicon oxide, 61.50 wt% graphite, As in Example 1, except that the negative electrode active material of the paint was changed to 26.31 wt% silicon oxide, 0.09 wt% amorphous silicon oxide, and 61.50 wt% graphite. The negative electrode active material layer of Example 31 was formed to obtain a negative electrode.

(Example 32)
When forming the negative electrode active material layer, 26.30% by weight of silicon oxide, 0.10% by weight of amorphous silicon oxide, 61.50% by weight of graphite, As in Example 1, except that the negative electrode active material of the paint was changed to 26.31 wt% silicon oxide, 0.09 wt% amorphous silicon oxide, and 61.50 wt% graphite. The negative electrode active material layer of Example 32 was formed to obtain a negative electrode.

(Example 33)
When forming the negative electrode active material layer, as the negative electrode active material of the first paint, 20.99 wt% silicon oxide, 5.41 wt% amorphous silicon oxide, 61.50 wt% graphite, the second paint In the same manner as in Example 1, except that 26.22% by weight of silicon oxide, 0.18% by weight of amorphous silicon oxide, and 61.50% by weight of graphite were changed as the negative electrode active material. 33 negative electrode active material layers were formed to obtain a negative electrode.

(Comparative Example 1)
In forming the negative electrode active material layer, 85.40 wt% silicon oxide, 2.50 wt% amorphous silicon oxide as the negative electrode active material of the first paint, and silicon oxide as the negative electrode active material of the second paint The negative electrode active material layer of Comparative Example 1 was formed in the same manner as in Example 1 except that 87.40 wt% and amorphous silicon oxide were changed to 0.50 wt% to obtain a negative electrode. .

(Comparative Example 2)
When forming the negative electrode active material layer, 72.90 wt% of silicon oxide is used as the negative electrode active material of the first paint, 15.00 wt% of amorphous silicon oxide, and silicon oxide is used as the negative electrode active material of the second paint. The negative electrode active material layer of Comparative Example 2 was formed in the same manner as in Example 1 except that 86.40 wt% and amorphous silicon oxide were changed to 1.50 wt% to obtain a negative electrode. .

  The Raman scattering spectrum of the cross section of the obtained negative electrode active material layer was measured using an NRS-7100 manufactured by JASCO Corporation, using a green laser with a wavelength of 532 nm and Raman spectroscopy, and an irradiation intensity of 1 mW or less using a dimmer. And a Raman scattering spectrum at an excitation wavelength of 532 nm was measured. Tables 1 to 5 show values of A1, A2, and A1 / A2 for each negative electrode active material used.

(Production of evaluation lithium-ion secondary battery)
Using the positive electrode and the negative electrode prepared above, a separator made of a polyethylene microporous film is sandwiched between them and placed in an aluminum laminate pack. In this aluminum laminate pack, a 1M LiPF ₆ solution (solvent: EC) is used as an electrolytic solution. / DEC = 3/7 (volume ratio)) was injected, and then vacuum-sealed to produce a lithium ion secondary battery for evaluation.

The cycle characteristics of the lithium ion secondary batteries produced in Examples 1 to 33 and Comparative Examples 1 and 2 were evaluated. Table 1 shows the capacity retention ratio values after 100 cycles for each negative electrode active material used.

  Moreover, A1 in the negative electrode active material layer produced in Examples 1-32 and Comparative Examples 1 and 2 was measured by measuring the surface and the inside of the produced negative electrode active material layer using an argon ion laser having a wavelength of 532 nm. The results of calculating B2 and B2 are shown together in Table 1.

  From the results of Examples 1 to 11 and Comparative Examples 1 and 2, it was confirmed that the cycle characteristics were excellent because a high capacity retention ratio was exhibited when A1 ≧ A2. In addition, when 1 ≦ A1 / A2 ≦ 100 was satisfied, it was confirmed that the cycle characteristics were more excellent, and when 1.05 ≦ A1 / A2 ≦ 3.4 was satisfied, it was confirmed that the cycle characteristics were particularly excellent.

  From the results shown in Examples 12 to 18, it was confirmed that the cycle characteristics were excellent by optimizing the particle size of the silicon material. From the results shown in Examples 19 to 27, it was confirmed that the cycle characteristics were excellent by adding the above additives.

  From the results shown in Examples 28 to 33, it was confirmed that the cycle characteristics were excellent by mixing graphite with a silicon material.

  ADVANTAGE OF THE INVENTION According to this invention, the negative electrode for lithium ion secondary batteries and lithium ion secondary battery which are excellent in cycling characteristics can be provided.

DESCRIPTION OF SYMBOLS 10 ... Positive electrode, 12 ... Positive electrode collector, 14 ... Positive electrode active material layer, 18 ... Separator, 20 ... Negative electrode, 22 ... Negative electrode current collector, 24 ... Negative electrode active material layer, 30 ... Laminated body, 50 ... Outer body, 60 ... Positive electrode lead, 62 ... Negative electrode lead, 100 ... Lithium ion secondary battery

Claims (7)

A negative electrode comprising a negative electrode active material layer having a negative electrode active material containing silicon on at least one of main surfaces of a negative electrode current collector,
In a Raman spectrum using an argon ion laser having a wavelength of 532 nm,
The peak intensity ratio of the strongest peak located at 460 ± 20 cm ⁻¹ to the peak intensity of the strongest peak located at 510 ± 10 cm ⁻¹ on the surface of the negative electrode active material layer is A1,
When the peak intensity ratio of the strongest peak located at 460 ± 20 cm ⁻¹ to the peak intensity of the strongest peak located at 510 ± 10 cm ⁻¹ inside the negative electrode active material layer is A2,
A negative electrode for a lithium ion secondary battery satisfying A1 ≧ A2.   The ratio of the peak intensity ratio A2 to the peak intensity ratio A1 in the negative electrode active material layer satisfies 1 ≦ A1 / A2 ≦ 100, 0.1 ≦ A1 ≦ 10, and 0.1 ≦ A2 ≦ 10. Item 2. The negative electrode for a lithium ion secondary battery according to Item 1. The ratio of the peak intensity ratio A2 to the peak intensity ratio A1 in the negative electrode active material layer satisfies 1.05 ≦ A1 / A2 ≦ 3.4. Negative electrode for secondary battery.   4. The negative electrode for a lithium ion secondary battery according to claim 1, wherein an average primary particle size of the silicon-based material is 0.1 μm or more and 20 μm or less. 5. 5. The negative electrode active material layer according to claim 1, comprising at least one selected from the group consisting of Li ₄ SiO ₄ , Li ₆ Si ₂ O ₇ , and Li ₂ Si ₃ O _5. The negative electrode for lithium ion secondary batteries as described.   The negative electrode for a lithium ion secondary battery according to claim 1, wherein the negative electrode active material contains graphite. A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to any one of claims 1 to 6, a positive electrode, and an electrolyte.

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