JPWO2017056932A1 - Method of using non-aqueous electrolyte secondary battery and negative electrode active material for non-aqueous electrolyte secondary battery - Google Patents

Abstract

A positive electrode, a negative electrode using a negative electrode active material containing a silicon-based active material mainly composed of a silicon oxide represented by SiOx (provided that 0.5 ≦ x ≦ 1.6), and a nonaqueous electrolyte are provided. A method of using a non-aqueous electrolyte secondary battery, wherein the current amount corresponds to 1/5 of the battery capacity obtained by performing a second discharge of the battery at a current amount of 0.7 mA / cm @ 2 per unit area of the negative electrode. A method for using a non-aqueous electrolyte secondary battery, wherein the discharge cycle is performed with a current amount 20 times or more that when the battery discharge is performed for the third time.

Description

  The present invention relates to a method for using a nonaqueous electrolyte secondary battery and a negative electrode active material for a nonaqueous electrolyte secondary battery used therefor.

In recent years, small electronic devices typified by mobile terminals and the like have become widespread, and further downsizing, weight reduction, and long life have been strongly demanded. In response to such market demands, development of secondary batteries capable of obtaining a high energy density, in particular, being small and light is underway.
This secondary battery is not limited to a small electronic device, but is also considered to be applied to a large-sized electronic device represented by an automobile or the like, or an electric power storage system represented by a house.

  Among them, lithium ion secondary batteries are highly expected because they are small and easy to increase in capacity, and can obtain higher energy density than lead batteries and nickel cadmium batteries.

  Said lithium ion secondary battery is equipped with the electrolyte solution with the positive electrode, the negative electrode, and the separator, and the negative electrode contains the negative electrode active material in connection with charging / discharging reaction.

As this negative electrode active material, a carbon material is widely used, but further improvement in battery capacity is required due to recent market requirements.
In order to improve battery capacity, use of silicon as a negative electrode active material has been studied. This is because the theoretical capacity of silicon (4199 mAh / g) is 10 times or more larger than the theoretical capacity of graphite (372 mAh / g), so that significant improvement in battery capacity can be expected.
The development of a siliceous material as a negative electrode active material has been examined not only for silicon alone but also for compounds represented by alloys and oxides.
In addition, the shape of the active material has been studied from a standard coating type for carbon materials to an integrated type directly deposited on a current collector.

However, when silicon is used as the negative electrode active material as the main raw material, the negative electrode active material expands and contracts during charge / discharge, and therefore, it tends to break mainly near the surface of the negative electrode active material. Further, an ionic material is generated inside the active material, and the negative electrode active material is easily broken.
When the negative electrode active material surface layer is cracked, a new surface is generated thereby increasing the reaction area of the active material. At this time, a decomposition reaction of the electrolytic solution occurs on the new surface, and a coating that is a decomposition product of the electrolytic solution is formed on the new surface, so that the electrolytic solution is consumed. For this reason, the cycle characteristics are likely to deteriorate.

  So far, in order to improve the initial efficiency and cycle characteristics of the battery, various studies have been made on the negative electrode material for lithium ion secondary batteries mainly composed of a siliceous material and the electrode configuration as follows.

i. For the purpose of obtaining good cycle characteristics and high safety, silicon and amorphous silicon dioxide are simultaneously deposited using a vapor phase method (see, for example, Patent Document 1).
ii. In order to obtain high battery capacity and safety, a carbon material (electron conductive material) is provided on the surface layer of silicon oxide particles (see, for example, Patent Document 2).
iii. In order to improve cycle characteristics and obtain high input / output characteristics, an active material containing silicon and oxygen is produced, and an active material layer having a high oxygen ratio in the vicinity of the current collector is formed (for example, a patent) Reference 3).
iv. In order to improve the cycle characteristics, oxygen is contained in the silicon active material, the average oxygen content is 40 at% or less, and the oxygen content is increased at a location close to the current collector ( For example, see Patent Document 4).

v. Si phase in order to improve the initial charge-discharge efficiency is used nanocomposites containing SiO _2, M _y O metal oxide (for example, refer to Patent Document 5).
vi. In order to improve cycle characteristics, SiO _x (0.8 ≦ x ≦ 1.5, particle size range = 1 μm to 50 μm) and a carbon material are mixed and fired at a high temperature (see, for example, Patent Document 6).
vii. In order to improve the cycle characteristics, the molar ratio of oxygen to silicon in the negative electrode active material is 0.1 to 1.2, and the difference between the maximum value and the minimum value of the molar ratio in the vicinity of the active material and current collector interface is 0. The active material is controlled within a range of 4 or less (see, for example, Patent Document 7).
viii. In order to improve battery load characteristics, a metal oxide containing lithium is used (see, for example, Patent Document 8).
ix. In order to improve cycle characteristics, a hydrophobic layer such as a silane compound is formed on the surface of the siliceous material (see, for example, Patent Document 9).
x. In order to improve cycle characteristics, conductivity is imparted by using silicon oxide and forming a graphite film on the surface layer (see, for example, Patent Document 10). In Patent Document 10, with respect to the shift value obtained from the RAMAN spectrum for graphite coating, with broad peaks appearing at 1330 cm ^-1 and 1580 cm ^-1, their intensity ratio I ₁₃₃₀ / I ₁₅₈₀ is 1.5 <I ₁₃₃₀ / I ₁₅₈₀ <3.
xi. In order to improve high battery capacity and cycle characteristics, particles having a silicon microcrystalline phase dispersed in silicon dioxide are used (see, for example, Patent Document 11).
xii. In order to improve overcharge and overdischarge characteristics, a silicon oxide in which the atomic ratio of silicon and oxygen is controlled to 1: y (0 <y <2) is used (for example, see Patent Document 12).
xiii. In order to improve high battery capacity and cycle characteristics, a mixed electrode of silicon and carbon is produced, and the silicon ratio is designed at 5 wt% or more and 13 wt% or less (see, for example, Patent Document 13).

JP 2001-185127 A JP 2002-042806 A JP 2006-164955 A JP 2006-114454 A JP 2009-070825 A JP 2008-282819 A JP 2008-251369 A JP 2008-177346 A JP 2007-234255 A JP 2009-212074 A JP 2009-205950 A Japanese Patent No. 2999741 JP 2010-092830 A

As described above, in recent years, small mobile devices typified by electronic devices have been improved in performance and multifunction, and lithium ion secondary batteries, which are the main power sources, are required to have an increased battery capacity. Yes.
As one method for solving this problem, development of a lithium ion secondary battery composed of a negative electrode using a siliceous material as a main material is desired.
Moreover, the lithium ion secondary battery using a siliceous material is desired to have a cycle characteristic close to that of a lithium ion secondary battery using a carbon material.
However, no negative electrode has been proposed that exhibits cycle stability equivalent to that of a lithium ion secondary battery using a carbon material.

  The present invention has been made in view of the above problems, and uses a non-aqueous electrolyte secondary battery using a negative electrode capable of improving battery capacity, improving cycle characteristics and initial charge / discharge characteristics. And it aims at providing the negative electrode active material for nonaqueous electrolyte secondary batteries.

In order to achieve the above object, the present invention includes at least a silicon-based active material (SiO _x : 0.5 ≦ x ≦ 1.6) as a negative electrode active material in a negative electrode for a nonaqueous electrolyte secondary battery, For a non-aqueous electrolyte secondary battery using a negative electrode containing a silicon-based active material, discharge for the second time at a current amount of 0.7 mA / cm ² per unit area, corresponding to 1/5 of the obtained battery capacity Provided is a method for using a non-aqueous electrolyte secondary battery in which a discharge cycle is performed with a current amount 20 times or more that when the battery is discharged with a current amount (third time).
In the present invention, the first cycle is the time when the discharge cycle is started with a current amount 20 times or more that of the third discharge.

  In the silicon oxide used in such a secondary battery, a part of lithium silicate is decomposed at a potential higher than the inflection point in the vicinity of the discharge potential of about 0.65 V, and the battery cycle characteristics are deteriorated. By performing a battery cycle test using these charge / discharge conditions, it is possible to suppress the decomposition of the silicate, so that the battery cycle characteristics can be improved. This secondary battery is most suitable for a high-power battery represented by a hand drill, and it is a secondary battery that realizes a long-term cycle with an effect of improving the capacity of the silica material.

  At this time, the battery characteristics can be drastically improved by discharging with a current amount of 20 times or more. However, although it can be improved even by about 10 times, the life cannot be extended to around 500 cycles which is a general battery test. Compared to commercially available batteries, particularly high-power batteries using carbon as the mainstream, 20 times or more is desirable in order to realize similar battery characteristics.

  In particular, the life on the negative electrode side can be greatly extended by using it at 40 times or more. On the other hand, if it exceeds 80 times, the influence on the positive electrode side cannot be ignored, and the battery characteristics are deteriorated. However, this is an evaluation of the positive electrode material and the positive electrode composition implemented in the present invention, and it is possible to increase the current amount range by using a more improved material and composition.

It is desirable that the charge / discharge end potential of the battery is a negative electrode regulation. In particular, in a high-power battery, when battery termination is performed using a battery drop on the positive electrode side, not only the capacity becomes unstable, but battery deterioration may also progress. Therefore, it is desirable that the rate of change of the positive and negative electrode potentials at the battery end potential is larger at the negative electrode than at the positive electrode with respect to the potential when the battery capacity equivalent to half of the battery capacity obtained in the third cycle is discharged. The battery end potential greatly contributes to the change in the negative electrode.
Note that the potential regulation uses the potential change during the low rate discharge in the third cycle.

The negative electrode utilization rate is desirably 90% or more and 99% or less. If it exceeds 99%, Li precipitation tends to occur on the negative electrode side. On the other hand, if it is less than 90%, a decrease in battery capacity cannot be ignored.
The negative electrode utilization rate is obtained by the following formula.
[Positive electrode charge capacity (vs. Li: positive electrode capacity obtained at battery charge potential + 0.05V) −Negative electrode irreversible capacity (vs. Li: negative electrode irreversible capacity obtained in the range of 0V-1.2V)] / Negative electrode reversible capacity (vs. Li : Negative electrode discharge capacity obtained in the range of 0V-1.2V)

Silicon oxide has a large irreversible capacity, and the amount of reversible lithium decreases as the amount replaced with a carbon material increases, so improvement in efficiency is essential. In particular, by generating lithium silicate in the bulk of the silicon oxide in advance, it is possible to compensate for lithium that disappears when the battery is charged.
The lithium filling method is not particularly limited, and examples thereof include a thermal doping method, an electrochemical method, and a redox method. The thermal doping method can be obtained by mixing with LiH or the like and heating. The electrochemical method can insert and desorb necessary Li electrochemically using potential control. In the oxidation-reduction method, lithium supplementation can be performed using, for example, lithium dissolved in naphthalene.

In particular, the substitution amount of the total amount of the carbon-based active material and the silicon-based active material (silicon-based active material with respect to the negative electrode active material) is preferably 6 wt% or more. When a small amount is added, not only the capacity contribution ratio of the silicon oxide is small, but also the microscopic capacity increase / decrease of the negative electrode appears, so that the microscopic potential change according to the negative electrode capacity is present on the positive electrode side which is the counter electrode. It tends to occur.
Specifically, for example, when the charge capacity of silicon oxide is 2200 mAh / g and the carbon-based active material is 350 mAh / g, the opposing positive electrode is microscopically dispersed in a situation where silicon oxide is dispersed. Li is extracted until the specified battery potential is reached, resulting in a high charge voltage that exceeds the initially planned reached potential. Therefore, it is necessary to uniformly disperse the silicon oxide in the negative electrode active material layer in order to relax the dispersion state.

As a chemical shift value obtained from the ²⁹ Si-MAS-NMR spectrum of the silicon-based active material, it is desirable that the ratio of the peak intensity A attributed to lithium silicate to the peak intensity B attributed to silicon dioxide satisfies A> B. By replacing the silicon dioxide region with lithium silicate in advance as part of the irreversible capacity, a silicon-based active material with high initial efficiency can be produced.

  At this time, a test cell composed of a negative electrode and a counter electrode lithium prepared using a negative electrode active material in which the silicon-based active material and the carbon-based active material are mixed is charged and discharged, and the discharge capacity Q is set to the counter electrode lithium. When a graph showing the relationship between the differential value dQ / dV differentiated by the potential V of the negative electrode as a reference and the potential V is drawn, during discharge in which current flows so that the silicon-based active material desorbs lithium It is preferable that the potential V of the negative electrode has a peak in the range of 0.40 to 0.55V.

  The above peak in the V-dQ / dV curve is similar to the peak of the siliceous material, and the discharge curve on the higher potential side rises sharply, so that the capacity is easily developed when designing the battery.

  At this time, the silicon-based active material has a half-value width (2θ) of a diffraction peak due to the Si (111) crystal plane obtained by X-ray diffraction of 1.2 ° or more and a crystal due to the crystal plane. The child size (determined by Scherrer's equation based on the half width of the diffraction peak attributed to Si (111)) is preferably 7.5 nm or less. Since the silicon-based active material having such a half-value width and crystallite size has low crystallinity and a small amount of Si crystals, battery characteristics can be improved.

In view of the above, the present invention provides the following method of using a nonaqueous electrolyte secondary battery and a negative electrode active material for a nonaqueous electrolyte secondary battery.
[1]
A positive electrode, a negative electrode using a negative electrode active material containing a silicon-based active material whose main component is a silicon oxide represented by SiO _x (where 0.5 ≦ x ≦ 1.6), and a non-aqueous electrolyte The non-aqueous electrolyte secondary battery is used and corresponds to 1/5 of the battery capacity obtained by performing a second discharge with a current amount of 0.7 mA / cm ² per unit area of the negative electrode for the battery. A method for using a non-aqueous electrolyte secondary battery, characterized in that a discharge cycle is performed with a current amount 20 times or more that when a third battery discharge is performed with a current amount.
[2]
[1] The method according to [1], wherein the discharge cycle is performed at a current amount of 40 times to 80 times the current amount at the time of the third battery discharge.
[3]
[1] or [2] where the negative electrode potential change rate at the end potential is larger at the negative electrode than at the positive electrode with respect to the positive and negative electrode potential at 50% discharge of the discharge capacity obtained at the third cycle of the discharge cycle. Usage as described.
[4]
The usage method according to any one of [1] to [3], wherein the negative electrode utilization ratio is 90% or more and 99% or less.
[5]
The silicon-based active material contains at least one of Li ₂ SiO ₃ and Li ₄ SiO ₄ inside the silicon oxide, and the ratio of the silicon-based active material to the total amount of the negative electrode active material is 6% by mass or more. The usage method according to any one of [1] to [4].
[6]
The silicon-based active material has a peak intensity A derived from Li ₂ SiO ₃ given in the vicinity of −75 ppm as a chemical shift value obtained from a ²⁹ Si-MAS-NMR spectrum, and SiO ₂ given to −95 to −150 ppm. The method according to any one of [1] to [5], wherein the peak intensity B derived from the region satisfies a relationship of A> B.
[7]
The silicon-based active material has a half-width (2θ) of a diffraction peak due to the Si (111) crystal plane obtained by X-ray diffraction of 1.2 ° or more, and a crystallite size due to the crystal plane is The method according to any one of [1] to [6], which is 7.5 nm or less.
[8]
The method according to any one of [1] to [7], wherein the silicon-based active material is coated with conductive carbon.
[9]
The surface layer of the silicon-based active material containing at least one of Li ₂ SiO ₃ and Li ₄ SiO ₄ inside the silicon oxide represented by SiO _x (where 0.5 ≦ x ≦ 1.6) is carbon. A negative electrode active material for a non-aqueous electrolyte secondary battery, which is coated and contains 2% by mass or more of the silicon-based active material.
[10]
The silicon-based active material has a peak intensity A derived from Li ₂ SiO ₃ given in the vicinity of −75 ppm as a chemical shift value obtained from a ²⁹ Si-MAS-NMR spectrum, and SiO ₂ given to −95 to −150 ppm. The negative electrode active material according to [9], wherein a peak intensity B derived from the region satisfies a relationship of A> B.
[11]
Charge and discharge a test cell composed of a negative electrode prepared using a negative electrode active material obtained by mixing the silicon-based active material and the carbon-based active material and a counter electrode lithium, and the discharge capacity Q is based on the counter electrode lithium. The negative electrode during discharge in which a current flows so that the silicon-based active material desorbs lithium when a graph showing the relationship between the differential value dQ / dV differentiated by the potential V of the negative electrode and the potential V is drawn. The negative electrode active material according to [9] or [10], wherein the potential V has a peak in the range of 0.40 to 0.55V.
[12]
The silicon-based active material has a half-width (2θ) of a diffraction peak due to the Si (111) crystal plane obtained by X-ray diffraction of 1.2 ° or more, and a crystallite size due to the crystal plane is The negative electrode active material according to any one of [9] to [11], which is 7.5 nm or less.
[13]
The negative electrode active material according to any one of [9] to [12], wherein the silicon-based active material is coated with conductive carbon.

The silicon-based active material in the negative electrode for a non-aqueous electrolyte secondary battery of the present invention includes at least a silicon oxide (SiO _x : 0.5 ≦ x ≦ 1.6), and a negative electrode including the silicon-based active material. The nonaqueous electrolyte secondary battery used was discharged at a current amount equivalent to 1/5 of the battery capacity obtained by performing a second discharge at a current amount of 0.7 mA / cm ² per unit area. By performing the discharge cycle with a current amount of 20 times or more with respect to (third time), it is possible to improve the battery capacity and obtain stable battery cycle characteristics.

  The negative electrode for nonaqueous electrolyte secondary batteries using the negative electrode active material of the present invention and the nonaqueous electrolyte secondary battery using this negative electrode can improve battery capacity, cycle characteristics, and initial charge / discharge characteristics. Moreover, the same effect can be acquired also in the electronic device using the said secondary battery, an electric tool, an electric vehicle, an electric power storage system, etc., and is especially suitable for an electric tool etc.

It is sectional drawing which shows the structure of the negative electrode for nonaqueous electrolyte secondary batteries of this invention. It is explanatory drawing of the electrochemical method which modifies the negative electrode active material of this invention.

Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to this.
As described above, as one method for increasing the battery capacity of a lithium ion secondary battery, the use of a negative electrode using a silicon material as a main material as a negative electrode of a lithium ion secondary battery has been studied.
The lithium ion secondary battery using this silicon material is expected to have cycle characteristics similar to those of a lithium ion secondary battery using a carbon material, but the cycle is equivalent to that of a lithium ion secondary battery using a carbon material. A negative electrode that exhibits stability has not been proposed.

Therefore, the present inventors have made extensive studies on a negative electrode active material that can provide good cycle characteristics as a negative electrode of a lithium ion secondary battery, and have reached the present invention.
The negative electrode for a non-aqueous electrolyte secondary battery of the present invention contains a silicon oxide (SiO _x : 0.5 ≦ x ≦ 1.6) and a negative electrode containing a silicon-based active material containing the silicon oxide as a main component. A nonaqueous electrolyte secondary battery using an electrode discharges a battery at a current amount equivalent to 1/5 of the battery capacity obtained by performing a second discharge at a current amount of 0.7 mA / cm ² per unit area. The discharge cycle is performed with a current amount of 20 times or more as compared to the third time.
The first charging / discharging and the second charging are not particularly limited, but it is preferable to charge at least at the first or second battery potential of 4V or more.

  The negative electrode for nonaqueous electrolyte secondary batteries using the negative electrode active material for nonaqueous electrolyte secondary batteries of the present invention will be described. FIG. 1 shows a cross-sectional configuration of a negative electrode for a non-aqueous electrolyte secondary battery (hereinafter, simply referred to as “negative electrode”) according to an embodiment of the present invention.

[Configuration of negative electrode]
As shown in FIG. 1, the negative electrode 10 is configured to have a negative electrode active material layer 12 on a negative electrode current collector 11. The negative electrode active material layer 12 may be provided on both surfaces or only one surface of the negative electrode current collector 11. Furthermore, the negative electrode current collector 11 may be omitted as long as the negative electrode active material of the present invention is used.

[Negative electrode current collector]
The negative electrode current collector 11 is an excellent conductive material and is composed of a material having excellent mechanical strength. Examples of the conductive material that can be used for the negative electrode current collector 11 include copper (Cu) and nickel (Ni). This conductive material is preferably a material that does not form an intermetallic compound with lithium (Li).

  The negative electrode current collector 11 preferably contains carbon (C) or sulfur (S) in addition to the main element. This is because the physical strength of the negative electrode current collector is improved. In particular, in the case of having an active material layer that expands during charging, if the current collector contains the above-described element, there is an effect of suppressing electrode deformation including the current collector. Although content of said content element is not specifically limited, Especially, it is preferable that it is 100 ppm or less. This is because a higher deformation suppressing effect can be obtained.

  The surface of the negative electrode current collector 11 may be roughened or not roughened. The roughened negative electrode current collector is, for example, a metal foil subjected to electrolytic treatment, embossing treatment, or chemical etching. The non-roughened negative electrode current collector is, for example, a rolled metal foil.

[Negative electrode active material layer]
The negative electrode active material layer 12 includes a plurality of particulate negative electrode active materials (hereinafter also referred to as negative electrode active material particles) that can occlude and release lithium ions. Further, in terms of battery design, the negative electrode binder and the conductive auxiliary agent are further included. Other materials may be included.

  The negative electrode active material used for the negative electrode of the present invention includes a silicon-based active material and a carbon-based active material. The silicon-based active material contains a Li compound in a silicon oxide portion (surface or inside) capable of occluding and releasing lithium ions, and further has a carbon coating layer on the surface.

The silicon oxide used for the negative electrode of the present invention is a silicon oxide material represented by SiO _x (where 0.5 ≦ x ≦ 1.6), and the composition is preferably such that x is close to 1. This is because high cycle characteristics can be obtained. The silicon oxide composition in the present invention does not necessarily mean 100% purity, and may contain a trace amount of impurity elements.

The silicon-based active material contains at least one of Li ₂ SiO ₃ and Li ₄ SiO ₄ inside the silicon oxide particles, and the surface layer of the silicon-based active material is coated with carbon as described above. It is preferable. If it is such, the stable battery characteristic can be acquired.

Such silicon-based active material particles can be obtained by changing a part of the SiO ₂ component generated inside to a Li compound. Of these, Li ₄ SiO ₄ and Li ₂ SiO ₃ exhibit particularly good characteristics.
Li compounds can be quantified by NMR (nuclear magnetic resonance) and XPS (X-ray photoelectron spectroscopy). The XPS and NMR measurements can be performed, for example, under the following conditions.
XPS
-Equipment: X-ray photoelectron spectrometer-X-ray source: Monochromatic Al Kα ray-X-ray spot diameter: 100 μm
Ar ion gun sputtering conditions: 0.5 kV 2 mm x 2 mm
²⁹ Si-MAS-NMR (magic angle rotating nuclear magnetic resonance)
Apparatus: 700 NMR spectrometer manufactured by Bruker, Inc. Probe: 4 mmHR-MAS rotor 50 μL
Sample rotation speed: 10 kHz
・ Measurement environment temperature: 25 ℃

The nonaqueous electrolyte secondary battery using the negative electrode containing the silicon-based active material thus obtained is obtained by performing the second discharge at a current amount of 0.7 mA / cm ² per unit area of the negative electrode. When battery discharge is performed at a current amount corresponding to 1/5 of the battery capacity (third time), a discharge cycle is performed at a current amount 20 times or more. By suppressing partial decomposition of lithium silicate on the high potential side of the silicon oxide, battery cycle characteristics can be improved.

  In this case, the amount of current is desirably 20 times or more, and more desirably 40 times or more and 80 times or less. Even if it is less than 20 times, there is an effect of improving the cycle characteristics, but in order to obtain battery characteristics closer to those of the secondary battery using the carbon-based active material, it is necessary to be 20 times or more.

Most of the positive and negative electrode potentials associated with the end of the battery are desirably brought about by changes on the negative electrode side.
The positive / negative electrode potential change rate at the end potential is preferably larger at the negative electrode than at the positive electrode with respect to the positive / negative electrode potential at the time of 50% discharge of the discharge capacity obtained in the third cycle of the discharge cycle.

  The negative electrode utilization rate is desirably 90% or more and 99% or less. If it exceeds 99%, Li precipitation tends to occur on the negative electrode side. On the other hand, if it is less than 90%, a decrease in battery capacity cannot be ignored.

  Furthermore, in the present invention, it is preferable that the silicon-based active material has a ratio of the silicon-based active material to the total amount of the negative electrode active material of 2% by mass or more, particularly 6% by mass or more, thereby uniformizing the capacity of the negative electrode. More preferably, it is 10 mass% or more, and may be 100 mass%.

  The lower the crystallinity of the silicon-based active material contained in the negative electrode material of the present invention, the better. Specifically, the half-value width (2θ) of the diffraction peak due to the Si (111) crystal plane obtained by X-ray diffraction of the silicon-based active material is 1.2 ° or more, and the crystal due to the crystal plane The child size is desirably 7.5 nm or less. Particularly, since the crystallinity is low and the abundance of Si crystals is small, not only the battery characteristics are improved, but also a stable Li compound can be generated. The silicon-based active material may be amorphous.

As a chemical shift value obtained from the ²⁹ Si-MAS-NMR spectrum of the silicon-based active material, it is desirable that the ratio of the peak intensity A attributed to lithium silicate to the peak intensity B attributed to silicon dioxide satisfies A> B. By replacing the silicon dioxide region with lithium silicate in advance as part of the irreversible capacity, a silicon-based active material with high initial efficiency can be produced.

  In the present invention, the negative electrode active material other than the silicon-based active material preferably includes a carbon-based active material, and the carbon-based active material includes natural graphite, artificial graphite, MCMB, hard carbon, soft carbon, surface pitch. One type or two or more types such as layer-coated natural graphite are used.

  As described above, a silicon-based active material may be used alone as the negative electrode active material, but a silicon-based active material and a carbon-based active material can be used in combination. The ratio with respect to the carbon-based active material may be 2:98 to 100: 0, more preferably 6:94 to 100: 0, and still more preferably 10:90 to 100: 0 as a mass ratio. : The ratio of a silicon-type active material can be reduced by setting it as mass ratio of 94-30: 70.

  At this time, a test cell composed of a negative electrode and a counter electrode lithium prepared using a negative electrode active material in which the silicon-based active material and the carbon-based active material are mixed is charged and discharged, and the discharge capacity Q is set to the counter electrode lithium. When a graph showing the relationship between the differential value dQ / dV differentiated by the potential V of the negative electrode as a reference and the potential V is drawn, during discharge in which current flows so that the silicon-based active material desorbs lithium It is preferable that the potential V of the negative electrode has a peak in the range of 0.40 to 0.55V.

  The above peak in the V-dQ / dV curve is similar to the peak of the siliceous material, and the discharge curve on the higher potential side rises sharply, so that the capacity is easily developed when designing the battery.

  Examples of the negative electrode binder include one or more of polymer materials and synthetic rubbers. Examples of the polymer material include polyvinylidene fluoride, polyimide, polyamideimide, aramid, polyacrylic acid, lithium polyacrylate, and carboxymethylcellulose. The synthetic rubber is, for example, styrene butadiene rubber, fluorine rubber, or ethylene propylene diene.

  Examples of the negative electrode conductive assistant include one or more carbon materials such as carbon black, acetylene black, graphite, ketjen black, carbon nanotube (CNT), and carbon nanofiber. In particular, carbon nanotubes are suitable for obtaining electrical contacts between a silicon material and a carbon material having a high expansion / contraction rate.

  The negative electrode active material layer is formed by, for example, a coating method. The coating method is a method in which a negative electrode active material particle and the above-described binder, and the like, and a conductive additive and a carbon material are mixed as necessary, and then dispersed and coated in an organic solvent or water.

[Production method of negative electrode]
The method for producing negative electrode active material particles contained in the negative electrode material for a non-aqueous electrolyte secondary battery of the present invention will be described. First, a silicon oxide represented by SiO _x (0.5 ≦ x ≦ 1.6) is produced. To do. Next, it is preferable that Li is inserted into the silicon oxide to generate a Li compound inside the silicon oxide to modify the silicon oxide, and this is used as a silicon-based active material.

More specifically, the negative electrode active material particles are produced, for example, by the following procedure.
First, a raw material that generates silicon oxide gas is heated in a temperature range of 900 to 1600 ° C. in the presence of an inert gas or under reduced pressure to generate silicon oxide gas. In this case, the raw material is a mixture of metal silicon powder and silicon dioxide powder, and considering the surface oxygen of the metal silicon powder and the presence of trace amounts of oxygen in the reactor, the mixing molar ratio is 0.8 <metal silicon powder / Desirably, silicon dioxide powder <1.3. The Si crystallites in the particles are controlled by changing the preparation range and vaporization temperature, and by heat treatment after generation. The generated gas is deposited on the adsorption plate. The deposit is taken out in a state where the temperature in the reaction furnace is lowered to 100 ° C. or lower, and pulverized and pulverized using a ball mill, a jet mill or the like.

  Next, a carbon layer can be formed on the surface layer of the obtained powder material, but this step is not essential.

  Pyrolysis CVD is desirable as a method for generating a carbon layer on the surface layer of the obtained powder material. Thermal decomposition CVD fills a silicon oxide (hereinafter sometimes referred to as silicon oxide) powder set in the furnace and a hydrocarbon gas into the furnace to raise the temperature in the furnace. The decomposition temperature is not particularly limited, but is particularly preferably 1,200 ° C. or lower. More desirably, the temperature is 950 ° C. or lower, and disproportionation of the active material particles can be suppressed. The hydrocarbon gas is not particularly limited, but 3 ≧ n is desirable in the CnHm composition. This is because the low production cost and the physical properties of the decomposition products are good.

  Next, modification in the bulk of the powder material is performed. In-bulk reforming is desirably performed using an apparatus capable of electrochemically inserting and extracting Li. Although the apparatus structure is not particularly limited, for example, bulk reforming can be performed using the bulk reforming apparatus 20 shown in FIG. The in-bulk reformer 20 includes a bathtub 27 filled with an organic solvent 23, a positive electrode (lithium source, reforming source) 21 disposed in the bathtub 27 and connected to one of the power sources 26, And a separator 24 provided between the positive electrode 21 and the powder storage container 25. The powder storage container 25 is connected to the other side of the power source 26. The powder storage container 25 stores silicon oxide powder 22. The powder storage container stores silicon oxide particles, and a voltage is applied to the powder storage container and the positive electrode (lithium source) storing the silicon oxide particles by a power source. Thereby, since lithium can be inserted into and desorbed from the silicon oxide particles, the silicon oxide powder can be modified.

As the organic solvent in the bath, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, and the like can be used. Further, as an electrolyte salt contained in the organic solvent, lithium hexafluorophosphate (LiPF _6), or the like can be used lithium tetrafluoroborate (LiBF _4).

  The positive electrode may use a Li foil or a Li-containing compound. Examples of the Li-containing compound include lithium carbonate, lithium oxide, lithium cobaltate, lithium olivine, lithium nickelate, and lithium vanadium phosphate.

  The modification may be performed using a thermal doping method. In this case, for example, the powder material can be modified by mixing with LiH powder or Li powder and heating in a non-oxidizing atmosphere. For example, an Ar atmosphere can be used as the non-oxidizing atmosphere. More specifically, first, LiH powder or Li powder and silicon oxide powder are sufficiently mixed in an Ar atmosphere, sealed, and homogenized by stirring the sealed container. Thereafter, the reforming is performed by heating in the range of 700 to 750 ° C. In this case, in order to desorb Li from the silicon compound, a method of sufficiently cooling the heated powder and then washing with alcohol, alkaline water, weak acid or pure water can be used.

  In the reforming method using an acid reduction reaction, a 1 mol / L solution of biphenyl in tetrahydrofuran (THF) added with 10% by mass of lithium is impregnated at 20 ° C. for 10 hours, and then the powder is collected by filtration. / L solution was impregnated at 20 ° C. for 20 hours, and then the powder was collected by filtration. Next, p-benzoquinone was impregnated in THF 1 mol / L solution at 20 ° C. for 2 hours, and the powder was collected by filtration. Stir and filter off the powder. Next, the silicon compound after the washing treatment is dried under reduced pressure.

  Subsequently, the silicon-based active material and the carbon-based active material are mixed, and the negative electrode active material particles are mixed with other materials such as a negative electrode binder and a conductive additive to form a negative electrode mixture, and then an organic solvent. Or water etc. are added and it is set as a slurry.

  Next, a mixture slurry is applied to the surface of the negative electrode current collector and dried to form the negative electrode active material layer 12 shown in FIG. At this time, you may perform a heat press etc. as needed.

[Lithium ion secondary battery]
Next, a lithium ion secondary battery will be described as a specific example of a non-aqueous electrolyte secondary battery using the above-described negative electrode.

[Configuration of laminated film type secondary battery]
A laminated film type secondary battery is one in which a laminated electrode body is accommodated mainly in a sheet-like exterior member. This electrode body has a separator between a positive electrode and a negative electrode and is laminated. A positive electrode lead is attached to the positive electrode, and a negative electrode lead is attached to the negative electrode. The outermost peripheral part of the electrode body is protected by a protective tape.

  For example, the positive and negative electrode leads are led out in one direction from the inside of the exterior member to the outside. The positive electrode lead is formed of a conductive material such as aluminum, and the negative electrode lead is formed of a conductive material such as nickel or copper.

  The exterior member is, for example, a laminate film in which a fusion layer, a metal layer, and a surface protective layer are laminated in this order, and this laminate film is a fusion of two films so that the fusion layer faces the electrode body. The outer peripheral edge portions of the layers are bonded together with an adhesive or the like. The fused part is, for example, a film such as polyethylene or polypropylene, and the metal part is aluminum foil or the like. The protective layer is, for example, nylon.

  An adhesion film is inserted between the exterior member and the positive and negative electrode leads to prevent intrusion of outside air. This material is, for example, polyethylene, polypropylene, or polyolefin resin.

[Positive electrode]
The positive electrode has, for example, a positive electrode active material layer on both sides or one side of the positive electrode current collector, similarly to the negative electrode 10 of FIG.
The positive electrode current collector is made of, for example, a conductive material such as aluminum.
The positive electrode active material layer includes one or more positive electrode materials capable of occluding and releasing lithium ions, and includes other materials such as a binder, a conductive additive, and a dispersant depending on the design. You may go out. In this case, details regarding the binder and the conductive additive are the same as, for example, the negative electrode binder and the negative electrode conductive additive already described.

As the positive electrode active material, a lithium-containing compound is desirable. Examples of the lithium-containing compound include a composite oxide composed of lithium and a transition metal element, or a phosphate compound having lithium and a transition metal element. Among these described positive electrode materials, compounds having at least one of nickel, iron, manganese, and cobalt are preferable. These chemical formulas are represented by, for example, Li _y M ₁ O ₂ or Li _z M ₂ PO ₄ . In the formula, M ₁ and M ₂ represent at least one transition metal element. The values of y and z vary depending on the battery charge / discharge state, but are generally expressed as 0.05 ≦ y ≦ 1.10 and 0.05 ≦ z ≦ 1.10.

Examples of the composite oxide having lithium and a transition metal element include lithium cobalt composite oxide (Li _y CoO ₂ ), lithium nickel composite oxide (Li _z NiO ₂ ), and lithium nickel cobalt composite oxide. . Examples of the lithium nickel cobalt composite oxide include lithium nickel cobalt aluminum composite oxide (NCA) and lithium nickel cobalt manganese composite oxide (NCM).
Examples of the phosphoric acid compound having lithium and a transition metal element include a lithium iron phosphate compound (LiFePO ₄ ) or a lithium iron manganese phosphate compound (LiFe _1-u Mn _u PO ₄ (0 <u <1)). Is mentioned. This is because when these positive electrode materials are used, a high battery capacity can be obtained and excellent cycle characteristics can be obtained.

[Negative electrode]
The negative electrode has the same configuration as the negative electrode 10 for lithium ion secondary battery in FIG. 1 described above, and has, for example, a negative electrode active material layer on both sides of the current collector. This negative electrode preferably has a negative electrode charge capacity larger than the electric capacity (charge capacity as a battery) obtained from the positive electrode active material agent. Thereby, precipitation of lithium metal on the negative electrode can be suppressed.

  The positive electrode active material layer is provided on part of both surfaces of the positive electrode current collector, and the negative electrode active material layer is also provided on part of both surfaces of the negative electrode current collector. In this case, for example, the negative electrode active material layer provided on the negative electrode current collector is provided with a region where there is no opposing positive electrode active material layer. This is to perform a stable battery design.

  In the region where the negative electrode active material layer and the positive electrode active material layer do not face each other, there is almost no influence of charge / discharge. Therefore, the state of the negative electrode active material layer is maintained as it is, so that the composition and the like of the negative electrode active material can be accurately examined with good reproducibility without depending on the presence or absence of charge / discharge.

[Separator]
The separator separates the positive electrode and the negative electrode, and allows lithium ions to pass through while preventing current short-circuiting due to bipolar contact. This separator is formed of a porous film made of, for example, a synthetic resin or ceramic, and may have a laminated structure in which two or more kinds of porous films are laminated. Examples of the synthetic resin include polytetrafluoroethylene, polypropylene, and polyethylene.

[Electrolyte]
At least a part of the active material layer or the separator is impregnated with a liquid electrolyte (electrolytic solution). This electrolytic solution has an electrolyte salt dissolved in a solvent, and may contain other materials such as additives.

  For example, a non-aqueous solvent can be used as the solvent. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, 1,2-dimethoxyethane, and tetrahydrofuran. Among these, it is desirable to use at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. This is because better characteristics can be obtained. In this case, more advantageous characteristics can be obtained by combining a high viscosity solvent such as ethylene carbonate or propylene carbonate and a low viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate or diethyl carbonate. This is because the dissociation property and ion mobility of the electrolyte salt are improved.

  When using an alloy-based negative electrode, it is preferable that at least one of a halogenated chain carbonate or a halogenated cyclic carbonate is contained as a solvent. This is because a stable coating is formed on the surface of the negative electrode active material during charging / discharging, particularly during charging. The halogenated chain carbonate is a chain carbonate having halogen as a constituent element (at least one hydrogen is replaced by a halogen). The halogenated cyclic carbonate is a cyclic carbonate having halogen as a constituent element (at least one hydrogen is replaced by halogen).

  The type of halogen is not particularly limited, but fluorine is more preferable. This is because a film having a higher quality than other halogens is formed. Also, the larger the number of halogens, the better. This is because the resulting coating is more stable and the decomposition reaction of the electrolytic solution is reduced.

  Examples of the halogenated chain carbonate include fluoromethyl methyl carbonate and difluoromethyl methyl carbonate. Examples of the halogenated cyclic carbonate include 4-fluoro-1,3-dioxolan-2-one and 4,5-difluoro-1,3-dioxolan-2-one.

  The solvent additive preferably contains an unsaturated carbon bond cyclic carbonate. This is because a stable film is formed on the surface of the negative electrode during charging and discharging, and the decomposition reaction of the electrolytic solution can be suppressed. Examples of the unsaturated carbon bond cyclic ester carbonate include vinylene carbonate and vinyl ethylene carbonate.

  The solvent additive preferably contains sultone (cyclic sulfonic acid ester). This is because the chemical stability of the battery is improved. Examples of sultone include propane sultone and propene sultone.

  Furthermore, the solvent preferably contains an acid anhydride. This is because the chemical stability of the electrolytic solution is improved. Examples of the acid anhydride include propanedisulfonic acid anhydride.

The electrolyte salt can include any one or more of light metal salts such as lithium salts. Examples of the lithium salt include lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ).

  The content of the electrolyte salt is preferably 0.5 mol / kg or more and 2.5 mol / kg or less with respect to the solvent. This is because high ionic conductivity is obtained.

[Production method of laminated film type secondary battery]
First, a positive electrode is manufactured using the positive electrode material described above. First, a positive electrode active material and, if necessary, a binder, a conductive additive and the like are mixed to form a positive electrode mixture, and then dispersed in an organic solvent to form a positive electrode mixture slurry. Subsequently, the mixture slurry is applied to the positive electrode current collector with a coating apparatus such as a die coater having a knife roll or a die head, and dried with hot air to obtain a positive electrode active material layer. Finally, the positive electrode active material layer is compression molded with a roll press or the like. At this time, heating may be performed, and compression may be repeated a plurality of times.

  Next, a negative electrode is produced by forming a negative electrode active material layer on the negative electrode current collector using the same operation procedure as that for producing the negative electrode for a lithium ion secondary battery described above.

  When producing the positive electrode and the negative electrode, respective active material layers are formed on both surfaces of the positive electrode and the negative electrode current collector. At this time, the active material application length of both surface portions may be shifted in either electrode (see FIG. 1).

Subsequently, an electrolytic solution is prepared. Subsequently, the positive electrode lead is attached to the positive electrode current collector and the negative electrode lead is attached to the negative electrode current collector by ultrasonic welding or the like. Subsequently, a positive electrode and a negative electrode are laminated via a separator to produce an electrode body, and a protective tape is adhered to the outermost periphery. Next, the electrode body is molded so as to have a flat shape. Subsequently, after sandwiching the wound electrode body between the folded film-shaped exterior members, the insulating portions of the exterior members are bonded to each other by a thermal fusion method, and the electrode body is sealed in a released state only in one direction. . An adhesion film is inserted between the positive electrode lead and the negative electrode lead and the exterior member. A predetermined amount of the prepared electrolytic solution is introduced from the release section, and vacuum impregnation is performed. After impregnation, the release part is bonded by a vacuum heat fusion method.
As described above, a laminated film type secondary battery can be manufactured.

In the non-aqueous electrolyte secondary battery of the present invention such as the produced laminate film type secondary battery, the negative electrode utilization rate during charge / discharge is preferably 90% or more and 99% or less.
If the negative electrode utilization rate is in the range of 90% or more, the initial charge efficiency does not decrease, and the battery capacity can be greatly improved. Moreover, if the negative electrode utilization rate is in the range of 99% or less, Li is not precipitated and safety can be ensured.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these.

A laminate film type secondary battery was produced by the following procedure.
First, a positive electrode was produced. The positive electrode active material is 96 parts by mass of LiCo _0.33 Ni _0.33 Mn _0.33 O ₂ which is a lithium nickel cobalt manganese composite oxide (NCM), ₂ parts by mass of a positive electrode conductive additive (Ketjen Black), and a positive electrode binder (polyfluoride). 2 parts by mass of vinylidene chloride, PVDF) was mixed to obtain a positive electrode mixture. Subsequently, the positive electrode mixture was dispersed in an organic solvent (N-methyl-2-pyrrolidone, NMP) to obtain a paste slurry. Then, the slurry was apply | coated to both surfaces of the positive electrode electrical power collector (aluminum sheet) with the coating apparatus which has a die head, and it dried with the hot air type drying apparatus. At this time, the positive electrode current collector had a thickness of 15 μm. Finally, compression molding was performed with a roll press.

Next, a negative electrode was produced. The negative electrode active material is a mixture of metallic silicon and silicon dioxide, placed in a reactor, and vaporized in a vacuum atmosphere of 10 Pa is deposited on the adsorption plate. After cooling sufficiently, the deposit is taken out. It grind | pulverized with the ball mill. After adjusting the particle size, the carbon layer was coated by performing thermal decomposition CVD as necessary. The produced powder was thermally doped with LiH at 740 ° C. in an argon atmosphere for 2 hours. The produced powder was washed with pure water and ethanol mixed solution, and the residue and foreign matter were removed to obtain negative electrode silicon-based active material particles.
Subsequently, negative electrode silicon-based active material particles, artificial graphite, and natural graphite (some blended with hard carbon and soft carbon as needed) were blended at a weight ratio of 10:80:10. Next, the blended negative electrode active material, conductive auxiliary agent 1 (carbon nanotube, CNT), conductive auxiliary agent 2 (acetylene black), styrene butadiene copolymer (hereinafter referred to as SBR), carboxymethylcellulose (hereinafter referred to as CMC) 90 After mixing at a dry weight ratio of 5-92.5: 1: 1: 2.5: 3-5, the mixture was diluted with pure water to obtain a negative electrode mixture slurry. Finally, drying was performed at 100 ° C. for 1 hour in a vacuum atmosphere.

Further, after mixing silicon-based active material particles, conductive additive 1, conductive additive 2, and negative electrode binder precursor (polyamic acid) at a dry weight ratio of 83: 10: 2: 5, diluted with NMP. Thus, a paste-like negative electrode mixture slurry was obtained. In this case, NMP was used as a solvent for the polyamic acid. Subsequently, the negative electrode mixture slurry was applied to both surfaces of the negative electrode current collector with a coating apparatus and then dried. As this negative electrode current collector, an electrolytic copper foil (thickness = 15 μm) was used. Finally, baking was performed at 400 ° C. for 1 hour in a vacuum atmosphere. Thereby, the negative electrode binder (polyimide) was formed.
In this example, this composition was used only for silicon oxide 100%.

Next, after mixing solvent ethylene carbonate (EC) and dimethyl carbonate (DMC), electrolyte salt (lithium hexafluorophosphate: LiPF ₆ ) was dissolved to prepare an electrolytic solution. In this case, the composition of the solvent was EC: DMC = 30: 70 by volume, and the content of the electrolyte salt was 1.0 mol / kg with respect to the solvent. 2 wt% and 1 wt% of (4-fluoro-1,3-dioxolan-2-one (FEC)) and vinylene carbonate (VC) were added to the obtained electrolytic solution, respectively.

Next, a secondary battery was assembled as follows. First, a sheet having a positive electrode current collector portion and a coating portion was punched out. At this time, the width of the positive electrode application part was 32 mm × 35 mm. Subsequently, a sheet having a negative electrode current collector portion and a coating portion was punched out. The width of the negative electrode application part was 34 mm × 37 mm. Prepare a plurality of punched sheets, lay a sheet with the single-sided positive electrode coating part on the bottom, and stack 18 layers in the order of separator, double-sided negative electrode, separator, double-sided positive electrode. It laminated | stacked through the separator so that it might suit an application part.
An aluminum lead was ultrasonically welded to the positive electrode current collector, and a nickel lead was welded to the negative electrode current collector.
The laminate was fixed with a PET (polyethylene terephthalate) protective tape.
As the separator, a laminated film having a thickness of 10 μm was used in which a film mainly composed of porous polyethylene was sandwiched between films mainly composed of porous polypropylene. Subsequently, after sandwiching the electrode body between the exterior members, the outer peripheral edges except for one side were heat-sealed, and the electrode body was housed inside. As the exterior member, an aluminum laminated film in which a nylon film, an aluminum foil, and a polypropylene film were laminated was used. Subsequently, an electrolyte prepared from the opening was injected, impregnated in a vacuum atmosphere, and then heat-sealed and sealed.

The cycle characteristics were examined as follows. First, in order to stabilize the battery, charging and discharging were performed twice in an atmosphere at 25 ° C. Next, a third discharge was performed at a current value corresponding to 1/5 of the second discharge capacity. In the battery cycle test, the current value was doubled with respect to the numerical value (about 1 A in this experiment) obtained at the third discharge capacity, and the cycle test was performed. At this time, the first discharge in which the current value was increased was regarded as the first cycle. The current value during charging was 1/5 of the discharge capacity obtained in the second cycle.
Subsequently, charging / discharging was performed until the total number of cycles reached 500 (500 cycles excluding initial charge / discharge, second charge, and third charge / discharge), and the discharge capacity was measured each time. Finally, the discharge capacity at the 500th cycle was divided by the discharge capacity at the first cycle in which the current value was increased, and multiplied by 100 for% display to calculate the capacity maintenance rate. As the first and second charging / discharging conditions, the battery was charged at a constant current density of 0.7 mA / cm ² until 4.2 V was reached, and when the voltage reached 4.2 V, the current density was 0.25 mA / cm at 4.2 V constant voltage. Charged until ² was reached. During discharge, the battery was discharged at a constant current density of 0.7 mA / cm ² until the battery voltage reached 2.0V.
For the cycle characteristics, the current value calculated from the obtained battery capacity was used as the discharge rate. The charge rate was 1/5 of the discharge capacity obtained in the second cycle as described above.
The battery application area can be calculated by disassembling the battery. After the purchase, discharge was performed at 0.7 mA / cm ² to calculate the second discharge capacity (in the case of a commercial product, it was assumed that the first charge / discharge was performed). Discharging is performed with a current amount equivalent to 1/5 of the obtained discharge capacity (generally expressed as a C rate and corresponding to 0.2 C here). The amount of discharge current accompanying the first and subsequent cycles is defined from the capacity obtained at that time.

When examining the initial charge / discharge characteristics of the silicon-based active material, the initial efficiency (%) = (initial discharge capacity / initial charge capacity) × 100 was calculated. The ambient temperature was the same as when the cycle characteristics were examined. The silicon-based active material electrode was prepared by mixing a silicon-based active material and polyacrylic acid in a ratio of 85:15 wt%, coating, and drying at 90 ° C. for 1 hour. The electrode was punched with φ15, and CCCV charging was performed to 0 V with the counter electrode Li. The current density at this time was 0.2 mA / cm ² , and the current value was 0.1 mA at the end. Thereafter, CC discharge was performed, and the initial efficiency of the silicon-based active material was calculated from the capacity at 1.2 V.

[Examples 1-1 to 1-7, Comparative Examples 1-1 to 1-3]
SiO _x (x = 1.0) 10 wt%
Half width (2θ) of diffraction peak due to Si (111) crystal plane = 1.845 °, crystallite size due to crystal plane = 4.62 nm
End negative electrode regulation EC: DMC (3.7 vol%)
LiPF ₆ 1.0 mol / kg
FEC 2wt%, VC 1wt%
Positive electrode NCM
A> B
Negative electrode utilization rate 93%
dQ / dV = Yes SiO initial efficiency 80%
Li silicate available

The battery cycle characteristics were evaluated by increasing the battery discharge current.
Since the silicon-based active material has a lithium silicate capacity on the high potential side and shifts to the high potential side at low rates, the battery characteristics deteriorated due to partial decomposition of the lithium silicate.
By increasing the discharge current, the negative electrode discharge potential rises, and it becomes difficult to rise to a potential at which lithium silicate decomposes. As a result, the battery cycle characteristics were improved.

[Examples 2-1 to 2-5, Comparative examples 2-1 and 2-2]
SiO _x 10wt%
Half width (2θ) of diffraction peak due to Si (111) crystal plane = 1.845 °, crystallite size due to crystal plane = 4.62 nm
End negative electrode regulation EC: DMC (3.7 vol%)
LiPF ₆ 1.0 mol / kg
FEC 2wt%, VC 1wt%
Positive electrode NCM
A> B
Negative electrode utilization rate 93%
dQ / dV = Yes SiO initial efficiency 80%
Li silicate with current magnification 50 times

When there is not enough oxygen, the capacity retention rate is significantly deteriorated. Moreover, when there was too much oxygen amount, electroconductivity fall occurred and the capacity | capacitance of SiO material did not express as designed. Only the carbon material was charged / discharged, but the capacity increase was not obtained and the evaluation was interrupted. Thus, it was confirmed that good battery characteristics can be obtained in the range of SiO _x (0.5 ≦ x ≦ 1.6).

[Examples 3-1 and 3-2]
SiO _x (x = 1.0) 10 wt%
Half width (2θ) of diffraction peak due to Si (111) crystal plane = 1.845 °, crystallite size due to crystal plane = 4.62 nm
EC: DMC (3.7 vol%)
LiPF ₆ 1.0 mol / kg
FEC 2wt%, VC 1wt%
Positive electrode NCM
A> B
Negative electrode utilization rate 93%
dQ / dV = Yes Li silicate Yes Current amount magnification 50 times

The initial efficiency of the silicon-based active material was changed, and evaluation was made so that the end potential was applied by positive electrode regulation.
Since the discharge curve on the positive electrode side has a gentle slope, it is easily influenced by the battery impedance, and it is difficult to obtain a sufficient battery capacity when performing a high output cycle. Further, since the positive electrode is pulled to a potential lower than the inflection point at the end of discharge, the positive electrode is likely to deteriorate.

[Examples 1-4, 4-1 to 4-5]
SiO _x (x = 1.0) 10 wt%
Half width (2θ) of diffraction peak due to Si (111) crystal plane = 1.845 °, crystallite size due to crystal plane = 4.62 nm
End negative electrode regulation EC: DMC (3.7 vol%)
LiPF ₆ 1.0 mol / kg
FEC 2wt%, VC 1wt%
Positive electrode NCM
A> B
dQ / dV = Yes SiO initial efficiency 80%
Li silicate with current magnification 50 times

When the negative electrode utilization rate is less than 90%, the maintenance rate increases, but there are many parts that are not used as the negative electrode, which makes it difficult to improve the battery capacity.
Further, when the negative electrode utilization rate is set to 100%, the battery capacity is considered to increase. However, since there is a concern about Li precipitation in design, it is desirable to set the maximum utilization rate to 99%. From the above, it was found that the negative electrode utilization rate is desirably 90% or more and 99% or less in consideration of an increase in battery capacity.

[Examples 1-4 and 5-1]
SiO _x (x = 1.0) 10 wt%
Half width (2θ) of diffraction peak due to Si (111) crystal plane = 1.845 °, crystallite size due to crystal plane = 4.62 nm
End negative electrode regulation EC: DMC (3.7 vol%)
LiPF ₆ 1.0 mol / kg
FEC 2wt%, VC 1wt%
Positive electrode NCM
Negative electrode utilization rate 93%
dQ / dV = current amount magnification 50 times

When the silicon oxide is not modified, Li silicate is not generated, and the chemical shift peak ratio obtained from Si-MAS-NMR is also reversed.
In this case, the battery retention rate does not greatly decrease, but a system using silicon oxide having a large irreversible capacity is unlikely to increase the capacity of the battery.

[Examples 1-4, 6-1 to 6-6, Comparative Example 6-1]
SiO _x (x = 1.0)
Half width (2θ) of diffraction peak due to Si (111) crystal plane = 1.845 °, crystallite size due to crystal plane = 4.62 nm
End negative electrode regulation EC: DMC (3.7 vol%)
LiPF ₆ 1.0 mol / kg
FEC 2wt%, VC 1wt%
Positive electrode NCM
A> B
Negative electrode utilization rate 93%
dQ / dV = Yes SiO initial efficiency 80%
Li silicate with current magnification 50 times

The maintenance rate was evaluated by changing the proportion of the silicon-based active material in the negative electrode active material.
The carbon negative electrode without introducing the silicon-based active material has the result that the battery characteristics are most improved. However, since the negative electrode capacity is not improved, the battery capacity is not improved.
As a result, the maintenance rate was stabilized when the amount of the silicon-based active material exceeded 6 wt%.
In particular, since the silicon-based active material present in the negative electrode brings about a microscopic potential increase with respect to the positive electrode as the counter electrode, it is desirable to disperse as uniformly as possible. It is considered that the proportion of the silicon-based active material necessary for realizing uniform dispersion is 6 wt% or more.

[Examples 1-4, 7-1 to 7-9]
SiO _x (x = 1.0) 10 wt%
End negative electrode regulation EC: DMC (3.7 vol%)
LiPF ₆ 1.0 mol / kg
FEC 2wt%, VC 1wt%
Positive electrode NCM
A> B
Negative electrode utilization rate 93%
dQ / dV = Yes SiO initial efficiency 80%
Li silicate with current magnification 50 times

The capacity retention rate changed according to the crystallinity.
In particular, a high capacity retention ratio was obtained with a low crystalline material having a half width (2θ) of 1.2 ° or more and a crystallite size attributable to the Si (111) plane of 7.5 nm or less. In particular, the best battery characteristics were obtained in the non-crystalline region.

[Examples 1-4, 8-1, 8-2]
SiO _x (x = 1.0) 10 wt%
End negative electrode regulation EC: DMC (3.7 vol%)
LiPF ₆ 1.0 mol / kg
FEC 2wt%, VC 1wt%
Positive electrode NCM
A> B
Negative electrode utilization rate 93%
dQ / dV = Yes SiO initial efficiency 80%
Li silicate with current magnification 50 times

  As a result of producing the modification method using an electrochemical method or an oxidation-reduction method, when the modification is performed without applying heat, the crystal of silicon does not advance, so that the modification in a low crystalline state is possible. As a result, the battery cycle maintenance rate was improved.

[Examples 8-2 and 9-1]
Using a material having low crystallinity of Si, doping was performed in the same manner as in Example 8-2.

  In order for the discharge curve shape to rise more sharply, the silicon compound (SiOx) needs to exhibit a discharge behavior similar to that of silicon (Si). A silicon compound that does not exhibit a peak in the above range (0.40 to 0.55 V) after 30 charge / discharge cycles has a relatively gentle discharge curve, so the initial efficiency is slightly reduced when a secondary battery is used. As a result. If the peak appears within 30 charge / discharge cycles, a stable bulk was formed, and the capacity retention rate and initial efficiency were improved.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

DESCRIPTION OF SYMBOLS 10 Negative electrode 11 Negative electrode collector 12 Negative electrode active material layer 20 In-bulk reformer 21 Positive electrode 22 Silicon oxide powder 23 Organic solvent 24 Separator 25 Powder storage container 26 Power supply 27 Bathtub

Claims (13)

A positive electrode, a negative electrode using a negative electrode active material containing a silicon-based active material whose main component is a silicon oxide represented by SiO _x (where 0.5 ≦ x ≦ 1.6), and a non-aqueous electrolyte The non-aqueous electrolyte secondary battery is used and corresponds to 1/5 of the battery capacity obtained by performing a second discharge with a current amount of 0.7 mA / cm ² per unit area of the negative electrode for the battery. A method for using a non-aqueous electrolyte secondary battery, characterized in that a discharge cycle is performed with a current amount 20 times or more that when a third battery discharge is performed with a current amount.   The method according to claim 1, wherein the discharge cycle is performed with a current amount of 40 times or more and 80 times or less of a current amount during the third battery discharge.   The negative electrode has a larger rate of positive / negative electrode potential change at the end potential than that of the positive electrode with respect to the positive / negative electrode potential at the time of 50% discharge of the discharge capacity obtained in the third cycle of the discharge cycle. how to use.   The usage method according to any one of claims 1 to 3, wherein the utilization factor of the negative electrode is 90% or more and 99% or less. The silicon-based active material contains at least one of Li ₂ SiO ₃ and Li ₄ SiO ₄ inside the silicon oxide, and the ratio of the silicon-based active material to the total amount of the negative electrode active material is 6% by mass or more. The usage method of any one of Claims 1-4. The silicon-based active material has a peak intensity A derived from Li ₂ SiO ₃ given in the vicinity of −75 ppm as a chemical shift value obtained from a ²⁹ Si-MAS-NMR spectrum, and SiO ₂ given to −95 to −150 ppm. The use method according to claim 1, wherein the intensity B of the peak derived from the region satisfies a relationship of A> B.   The silicon-based active material has a half-width (2θ) of a diffraction peak due to the Si (111) crystal plane obtained by X-ray diffraction of 1.2 ° or more, and a crystallite size due to the crystal plane is It is 7.5 nm or less, The usage method of any one of Claims 1-6.   The use method according to any one of claims 1 to 7, wherein the silicon-based active material is coated with conductive carbon. The surface layer of the silicon-based active material containing at least one of Li ₂ SiO ₃ and Li ₄ SiO ₄ inside the silicon oxide represented by SiO _x (where 0.5 ≦ x ≦ 1.6) is carbon. A negative electrode active material for a non-aqueous electrolyte secondary battery, which is coated and contains 2% by mass or more of the silicon-based active material. The silicon-based active material has a peak intensity A derived from Li ₂ SiO ₃ given in the vicinity of −75 ppm as a chemical shift value obtained from a ²⁹ Si-MAS-NMR spectrum, and SiO ₂ given to −95 to −150 ppm. The negative electrode active material according to claim 9, wherein the intensity B of the peak derived from the region satisfies a relationship of A> B.   Charge and discharge a test cell composed of a negative electrode prepared using a negative electrode active material obtained by mixing the silicon-based active material and the carbon-based active material and a counter electrode lithium, and the discharge capacity Q is based on the counter electrode lithium. The negative electrode during discharge in which a current flows so that the silicon-based active material desorbs lithium when a graph showing the relationship between the differential value dQ / dV differentiated by the potential V of the negative electrode and the potential V is drawn. The negative electrode active material according to claim 9 or 10, wherein the potential V has a peak in the range of 0.40 to 0.55V.   The silicon-based active material has a half-width (2θ) of a diffraction peak due to the Si (111) crystal plane obtained by X-ray diffraction of 1.2 ° or more, and a crystallite size due to the crystal plane is It is 7.5 nm or less, The negative electrode active material of any one of Claims 9-11.   The negative electrode active material according to claim 9, wherein the silicon-based active material is coated with conductive carbon.

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