JP2012113933A - Negative electrode active material for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the mobility of lithium ions in a negative electrode active material for a lithium ion secondary battery containing a silicon-containing oxide, and to provide a lithium ion secondary battery offering high power and a long life, and capable of being charged and discharged in a short time.SOLUTION: A negative electrode active material for a lithium ion secondary battery in accordance with an embodiment of the present invention, contains a silicon-containing oxide, and halogen ions selected from the group consisting of Cl, Br, and Iare introduced into the silicon-containing oxide. A negative electrode for a lithium ion secondary battery in accordance with an embodiment of the present invention, contains the negative electrode active material for a lithium ion secondary battery. A lithium ion secondary battery in accordance with an embodiment of the present invention, comprises the negative electrode for a lithium ion secondary battery.

Description

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

The lithium ion secondary battery is a kind of non-aqueous secondary battery, and the charge / discharge reaction proceeds when lithium ions move between the positive electrode, the electrolyte, and the negative electrode. At present, the mainstream is to use a lithium ion oxide such as LiCoO ₂ , LiMn ₂ O ₄ , or LiNiO ₂ for the positive electrode and a carbon material such as graphite for the negative electrode. However, as mobile terminal devices such as mobile phones and PCs become more sophisticated, smaller, and hybrid vehicles and electric vehicles become more popular, there is a demand for higher capacity and longer life of lithium ion secondary batteries. The required capacity cannot be achieved by the combination of mainstream electrode materials. Therefore, application of a novel high capacity electrode material is desired.

  As a new high-capacity electrode material in the negative electrode, metallic lithium, an alloy of lithium and tin, lead, silicon, antimony, and the like have been studied (Non-patent Document 1). Among them, the alloy of lithium and silicon has a large theoretical electric capacity and can achieve the required value. Furthermore, silicon is the second most popular negative electrode material because it has the second largest number of Clarks and is rich in reserves. is there.

  However, since silicon undergoes a volume change that is four times as large as when alloyed with lithium ions, silicon is pulverized by continuous and large volume changes accompanying repeated charge and discharge, and a part of the silicon falls off from the current collector. The problem is that the electron conduction channel is lost and deteriorated, and sufficient cycle characteristics cannot be obtained.

As a negative electrode active material for solving this _{problem, SiO x (0 <x <} 2) or lithium silicate compound already containing the lithium SiO _x Li _y SiO _x and (y> 0,0 <x <2 ) using Thus, materials with reduced irreversible capacity have been proposed (Patent Documents 1 to 3). This SiO _x (0 <x <2) and Li _y SiO _x (y> 0, 0 <x <2) are microscopically SiO ₂ phase in which Si phase and SiO ₂ phase or lithium are bonded (hereinafter simply referred to as “Si ₂ phase”). (Sometimes referred to as “SiO ₂ phase”). Among them, the Si phase inserts and desorbs lithium ions, and the SiO ₂ phase surrounding the Si phase becomes a lithium ion conduction path between the Si phase and the electrolyte. Further, SiO ₂ phase surrounding the Si phase has a higher porosity an amorphous structure, and also plays a role of absorbing a large volume changes occurring upon lithium ion intercalation and deintercalation into Si phase, SiO _x ( 0 <x <2) and Li _y SiO _x (y> 0, 0 <x <2) as a whole, volume change is suppressed, and high cycle characteristics are achieved.

  In Patent Document 4, as the negative electrode active material, Group 3 of the periodic table, Group 4 excluding titanium Ti, Group 5 excluding vanadium V, Group 6 excluding tungsten W, Group 7 excluding manganese Mn, and iron Fe. Group 8 excluding Group 8, Group 10 excluding nickel Ni, Group 11 excluding nickel Ni, Group 2 excluding magnesium Mg, calcium Ca, Group 12 excluding zinc Zn, Group B excluding boron B, aluminum Al, and A silicon oxide containing one or more elements M selected from metal elements or similar metal elements of carbon C, arsenic As, antimony Sb, bismuth Bi, sulfur S, selenium Se, tellurium Te, and polonium Po is used. It is described.

JP 2000-243396 A JP 2004-119176 A JP 2010-73651 A JP 2000-82459 A

Journal of Power Sources, 81-82, 13 (1999) Journal of The Electrochemical Society, 153, A425 (2006) Journal of The Electrochemical Society, 151, A1572 (2004)

However, in the materials described in Patent Documents 1 to 3, since the ionic conductivity of lithium ions in the SiO ₂ phase, which is a lithium ion conduction path between the Si phase and the electrolyte, is extremely small, the negative electrode resistance is high and the output is small. Furthermore, since the movement speed of lithium ions is low, there arises a problem that the charge / discharge speed is slow. In practice, a large amount of negative electrode active material particles is a composite electrode in which a current collector is fixed to a current collector with a binder such as polyvinylidene fluoride (PVdF). Since the phase separation structure of the Si phase and SiO ₂ phase in the inside has non-uniformity, a portion where a high voltage is locally applied is generated without applying a voltage uniformly to the entire composite electrode during charging and discharging. In this case, there arises a problem that the electrolyte and the binder are decomposed to cause deterioration.

  Moreover, although the material described in Patent Document 4 can be expected to increase the mobility of lithium ions depending on the type of the element M, if the element M is contained to a certain degree, the electric capacity is reduced. Problem arises.

  In light of such a background, an object of the present embodiment is to increase lithium ion mobility in a negative electrode active material for a lithium ion secondary battery containing a silicon-containing oxide. Another object of the present embodiment is to provide a lithium ion secondary battery with high output, long life, and short charge / discharge time.

The present embodiment is a negative electrode active material for a lithium ion secondary battery containing a silicon-containing oxide, wherein a halogen ion selected from the group consisting of Cl ⁻ , Br ⁻ and I ⁻ is included in the silicon-containing oxide. It is the negative electrode active material for lithium ion secondary batteries characterized by being introduce | transduced.

  The present embodiment is a negative electrode for a lithium ion secondary battery comprising the above negative electrode active material for a lithium ion secondary battery.

  The present embodiment is a lithium ion secondary battery comprising the above-described negative electrode for a lithium ion secondary battery.

  According to this embodiment, the mobility of lithium ions in the negative electrode active material for lithium ion secondary batteries containing a silicon-containing oxide can be increased. As a result, according to the present embodiment, a lithium ion secondary battery with high output, long life, and short charge / discharge time can be obtained.

The negative electrode active material for a lithium ion secondary battery according to this embodiment contains a silicon-containing oxide. As the silicon-containing oxide, SiO _x (0 <x <2) or Li _y SiO _x (y> 0, 0 <x <2) can be used. In particular, Li _y SiO _x (y> 0, 0 <x <2) is preferably used because the lithium silicate synthesis reaction by lithium ions and silicon oxide generated at the first charge can be suppressed and the irreversible capacity is reduced. .

As described above, SiO ₂ phase SiO ₂ phase or lithium as a lithium ion conductive path between the Si phase and the electrolyte in the silicon-containing oxide is bound (hereinafter, may be simply referred to as "SiO ₂ phase".) In The ion conductivity of lithium ions is extremely small. Since the ionic conductivity of lithium ions is expressed by the product of the lithium ion concentration and the lithium ion mobility, high ionic conductivity can be obtained by increasing these as much as possible. However, since O ²⁻ ions have a relatively low ion polarizability, —Si—O 2 ⁻ contained in the SiO ₂ phase in the silicon-containing oxide interacts with lithium ions and strongly traps lithium ions. Realizing high ionic conductivity has been difficult.

In the silicon-containing oxide used in the present embodiment, a halogen ion selected from the group consisting of Cl ⁻ , Br ⁻ and I ⁻ is introduced. These halogen ions have a function of improving ion mobility of lithium ions moving in the active material phase by bonding (solid solution) to the SiO ₂ phase in the silicon-containing oxide.

That is, since the halogen ion has a higher ionic polarizability than the O ²⁻ ion, when the halogen ion is introduced into the silicon-containing oxide, non-bridging oxygen (—Si) contained in the SiO ₂ phase in the silicon-containing oxide. Part of —O ⁻ ) is replaced by the halogen ion. And the interaction with the lithium ions by the SiO ₂ phase is weakened, the lithium ion trapping ability is lowered, the lithium ions are easily moved, and the mobility of the lithium ions is increased. As a result, the resistance of the negative electrode is reduced, and the charge / discharge rate can be shortened. Since the resistance of the negative electrode is reduced, the output of the lithium secondary battery is increased, and the non-uniform voltage distribution applied to the negative electrode so far is relaxed, and the electrolyte and the connection in the part where the high voltage is locally generated are reduced. Degradation due to decomposition of the dressing is also avoided.

Since the ionic polarizability of the halogen ions has a relationship of Cl ⁻ <Br ⁻ <I ⁻ , the mobility of lithium ions is maximized when I ⁻ is introduced into the silicon-containing oxide. However, since the ion radius and the mass number are also in the relationship of Cl ⁻ <Br ⁻ <I ⁻ , the weight electric capacity and the volume electric capacity decrease as the halogen ions having a large ion polarizability are introduced. Therefore, it is necessary to adjust the type of halogen ion to be introduced in consideration of the required electric capacity. In addition, the halogen ion to introduce | transduce may be 1 type and 2 or more types may be sufficient as it.

  As the halogen ion introduction ratio increases, the mobility of lithium ions increases. However, since the weight electric capacity and the volume electric capacity are reduced, it is necessary to adjust the introduction ratio of the halogen ions in consideration of the required electric capacity.

Furthermore, it is preferable that a chalcogen ion selected from the group consisting of S ²⁻ , Se ^2−, and Te ²⁻ is introduced into the silicon-containing oxide used in the present embodiment. These chalcogen ions have a function of further improving the ion mobility of lithium ions moving in the active material phase by bonding (solid solution) to the SiO ₂ phase in the silicon-containing oxide.

That is, since the chalcogen ion has a larger ionic polarizability than the O ²⁻ ion, when the chalcogen ion is introduced into the silicon-containing oxide, non-crosslinked oxygen (—Si) contained in the SiO ₂ phase in the silicon-containing oxide. The O ²⁻ ion of —O ⁻ ) disappears and is replaced with the chalcogen ion. Since lithium ions move between non-crosslinked chalcogens (—Si—X ⁻ , X: S ⁻ , Se ⁻ or Te ⁻ ) having a small interaction, the lithium ion trapping ability by the SiO ₂ phase can be reduced. The lithium ion mobility is further decreased and the mobility of lithium ions is further increased.

Since the ion polarizability of the chalcogen ions is in a relationship of S ⁻ <Se ⁻ <Te ⁻ , the mobility of lithium ions is maximized when Te ⁻ is introduced into the silicon-containing oxide. However, since the ion radius and mass number are also in the relationship of S ⁻ <Se ⁻ <Te ⁻ , the weight electric capacity and the volume electric capacity decrease as the chalcogen ions having a large ion polarizability are introduced. Therefore, it is necessary to adjust the type of chalcogen ions to be introduced in consideration of the required electric capacity. The chalcogen ions to be introduced may be one type or two or more types.

When the introduction ratio of the chalcogen ions is in the range of 0 to 95%, the lithium ion mobility increases as the introduction ratio increases, but decreases as the introduction ratio increases. This is because if the introduction ratio of the chalcogen ions is large, a large amount of the chalcogen ions are bonded not only to the SiO ₂ phase but also to the Si phase, the ratio of the Si phase is reduced and the electric capacity is reduced. Therefore, it is necessary to adjust the introduction ratio of chalcogen ions in consideration of the required electric capacity.

  Since the ion polarizability has a relationship of halogen ion <chalcogen ion, the ion mobility of lithium ion is higher when the chalcogen ion is introduced. However, although the chalcogen ion depends on the silicon-containing oxide to be used, the introduction ratio is bonded to the Si phase from about 50%, and the ratio of the Si phase tends to decrease and the electric capacity tends to decrease. Therefore, by introducing both the halogen ion and the chalcogen ion, the chalcogen ion can be introduced at a rate at which the decrease in the electric capacity is not observed, and the ion mobility is increased while maintaining the electric capacity. Is possible.

In the SiO ₂ phase of SiO _x (0 <x <2) and Li _y SiO _x (y> 0, 0 <x <2), the composition of the lithium conductive phase when lithium ions move is Li ₂ SiO ₃ and Li ₄ Represented by SiO ₄ . Li ₂ SiO ₃ and Li ₄ SiO _{4 have} an ionic resistivity of about 10 ⁻¹⁰ Ωcm (room temperature), but the distance between the Si phase and the ionic conduction phase between the electrolyte is about 10 nm, and 0.5 mA / cm ² When a current density is applied and a voltage drop of 500 mV occurs in the ion conduction phase, the ionic specific resistance of the negative electrode active material according to the present embodiment decreases by 1 to 6 digits of Li ₂ SiO ₃ and Li ₄ SiO ₄ . Along with this, the voltage drop in the ion conduction phase is suppressed to a value (50 mV to 0.5 μV) that is one digit to six digits lower, so that an output improvement due to the voltage drop decrease due to the ion conduction phase is expected.

The ion mobility (cm / s) is inversely proportional to the ion resistivity. Therefore, when the number of lithium ions present per unit area of the ion conductive phase is the same, the ion mobility of the negative electrode active material according to the present embodiment is one digit higher than the ion mobility of Li ₂ SiO ₃ and Li ₄ SiO _4. Since it increases by ~ 6 digits, the time for lithium ions to travel the same distance is shortened by 1 to 6 digits. That is, since the time for moving between the active material phases in which lithium ions of the positive electrode and the negative electrode are actually inserted and desorbed is shortened accordingly, the time for moving in the ion conductive phase of the negative electrode active material provided in this embodiment is When charging / discharging at the same current value, the length is shortened by 1 to 6 digits with respect to Li ₂ SiO ₃ and Li ₄ SiO ₄ .

When the lithium ion conductive phase is Li ₂ SiO ₃ and Li ₄ SiO ₄ and a current density of 0.5 mA / cm ² is applied, a voltage drop of 50 mV occurs per 1 nm of the thickness of the ion conductive phase. Since the particle size of the silicon-containing oxide particles and the phase separation structure of the Si phase and the SiO ₂ phase in the silicon-containing oxide particles are not uniform, the thickness of the ion conductive phase is not uniform, and is several nm to several tens of nm. There is a difference, and a difference in applied voltage of several hundred mV appears locally. Furthermore, in practice, a large amount of silicon-containing oxide particles are fixed to the current collector with a binder such as polyvinylidene fluoride (PVdF), so that the entire composite electrode is evenly charged during the charge / discharge reaction. There is a portion where a voltage as high as several volts is locally applied without applying a voltage, and the electrolyte and the binder are decomposed at that portion, leading to a problem of deterioration. On the other hand, in the negative electrode active material according to the present embodiment, the voltage drop with respect to the thickness of 1 nm of the ion conductive phase is smaller by one to six digits than Li ₂ SiO ₃ and Li ₄ SiO _4. The difference is suppressed, and the decomposition of the electrolyte and the binder and the accompanying deterioration are also suppressed.

  The introduction of the halogen ion or chalcogen ion is performed by a method of doping ions into a silicon-containing oxide by a sputtering method or the like, a melting method using a compound containing a silicon-containing oxide and an ionic species as a starting material, or a press quenching method. Can do. Among these, the mechanochemical milling method is a method that can convert mechanical action force into chemical reaction energy, so that synthesis can be performed at low temperature, composition can be distributed relatively uniformly, and fine particles can be formed. This is an effective method.

  The negative electrode active material according to the present embodiment may be combined with an electron donating material. Specifically, silicon-containing oxides into which halogen ions are introduced, carbon materials such as graphite, hard carbon, soft carbon, amorphous carbon, and acetylene black, or nickel, copper, and alloys thereof that do not easily react with lithium ions Such a metal substance can be coated or mixed. When combined with an electron-imparting material, the electron conductivity is improved, and further charge / discharge characteristics can be expected.

  The negative electrode active material which concerns on this embodiment can be used as a negative electrode active material of the negative electrode for lithium ion secondary batteries. The negative electrode for a lithium ion secondary battery according to this embodiment can be used as a negative electrode for a lithium secondary battery or a lithium-air secondary battery. As the electrolytic solution of the lithium ion secondary battery, an electrolytic solution having any property such as an ionic liquid, a polymer electrolyte, and a solid electrolyte can be used in addition to the nonaqueous electrolytic solution. Other constituent members can be appropriately selected from conventionally known ones, for example.

  Hereinafter, examples of the present embodiment will be described.

[Example 1]
I ⁻ ions were introduced into SiO _x (0 <x <2) by a mechanochemical milling method. Specifically, in an inert atmosphere, 10 g of SiO _x (x = 1.34) and 0.15 g of iodine were pulverized and mixed at 300 rpm for about 10 hours using a planetary ball mill. In the obtained sample, a very small peak attributed to Si was observed by X-ray diffraction, but almost no remarkable peak was observed, and it was found that the structure had a glass structure in which fine particles of Si were mixed. It was. The average particle size of the obtained sample was about 800 nm. Thereafter, in order to increase the electron conductivity, the obtained sample was covered with a graphite film having a thickness of about 200 nm by a CVD method.

A slurry was prepared by mixing 100 g of the obtained SiO _x -I powder coated with the graphite film in 5 g of polyvinylidene fluoride and 10 g of N-methyl-2-pyrrolidone in an inert atmosphere. The slurry was applied on a copper current collector and vacuum dried at about 100 ° C. to produce a negative electrode. A coin cell having a diameter of about 16 mm is obtained by using a negative electrode, a Li foil as a counter electrode, and 1M-LiPF ₆ / EC + DMC (volume ratio: 1: 1) as an electrolytic solution with VC (weight ratio 2%) added thereto. And the following electrochemical characteristics were measured. The results are shown in Table 1.

<First charge / discharge efficiency and discharge capacity>
The initial charge and discharge efficiency and the discharge capacity were measured at 25 mA in a voltage of 0 to 1.5 V at a current density of 10 mA / g.

<Overvoltage>
From an OCV curve for each 1% SOC in a voltage of 0 to 1.5 V at a current density of 10 mA / g, 0.3 Vvs. The overvoltage at Li + / Li was measured.

<Charging time and discharging time>
The charging time and discharging time at an electric quantity of 0.9 C were measured.

<Electrode life>
As the electrode life, the reduction rate of the discharge capacity at 300 cycles with respect to the capacity at 10 cycles when the discharge capacity was stabilized was measured.

[Example 2]
I ⁻ ions were introduced into Li _y SiO _x (y> 0, 0 <x <2) by a mechanochemical milling method. Specifically, in an inert atmosphere, in addition to 10 g of SiO _x (x = 1.34) and 0.15 g of iodine, 0.7 g of lithium foil as a starting material, using a planetary ball mill for about 10 hours at 300 rpm, Crush and mix. It was found by X-ray diffraction that the obtained sample had a glass structure in which Si fine particles were mixed. Moreover, the average particle diameter of the obtained sample was about 900 nm. Thereafter, in order to increase the electron conductivity, the obtained sample was covered with a graphite film having a thickness of about 200 nm by a CVD method.

A coin cell was produced in the same manner as in Example 1 except that the Li _y SiO _x -I powder coated with the obtained graphite film was used, and its electrochemical characteristics were measured. The results are shown in Table 1.

[Comparative Examples 1-2]
A coin cell was prepared in the same manner as in Examples 1 and 2 except that iodine was not used, and its electrochemical characteristics were measured. The average particle size of the samples obtained by the mechanochemical milling method was about 800 nm. The results are shown in Table 1.

When Li _y SiO _x was used, the irreversible capacity at the initial charge was alleviated, so that the initial charge / discharge efficiency increased about twice as much as when SiO _x was used. In Example 1-2, I ^- since the Si content is reduced by performing the iontophoresis, I ^- discharge capacity is decreased as compared with Comparative Examples 1 and 2 was not performed iontophoresis.

I ^- Example 1-2 was performed iontophoresis, I ^- Comparative Example was not carried out iontophoresis 1-2 and initial charge-discharge efficiency was comparable. From this, it can be seen that even when I ⁻ ion introduction is performed, lithium ions are inserted and desorbed similarly to SiO _x or Li _y SiO _x .

I ^- Example 1-2 was performed iontophoresis, I ^- overvoltage is lower as compared with Comparative Examples 1 and 2 was not performed iontophoresis. This is because by introducing I ⁻ ions, a part of —Si—O ⁻ present in SiO _x or Li _y SiO _x is replaced with I ⁻ having a high polarizability, and the lithium ion trapping ability is reduced. This is probably because the resistance derived from ionic conduction decreased as a result of the increased mobility of lithium ions.

I ^- Example 1-2 was performed iontophoresis, I ^- in comparison with Comparative Examples 1-2 was not performed iontophoresis charging time and discharging time is shortened. This is presumably because the introduction of I ⁻ ions increased the mobility of lithium ions in the active material and shortened the migration time of lithium ions in the ion conduction phase in the active material.

I ^- Example 1-2 was performed iontophoresis, I ^- electrode life was improved as compared with Comparative Examples 1 and 2 was not performed iontophoresis. This is because the introduction of I ⁻ ions reduces the resistance in the ion conduction phase within the active material, reduces the voltage difference of the non-uniform voltage distribution that occurs across the composite electrode, and decomposes the electrolyte and binder. This is thought to be due to the suppression of deterioration caused by

[Examples 3 to 4]
In the same manner as in Example 2, halogen ions (Cl ⁻ ions or Br ⁻ ions) were introduced into Li _y SiO _x (y> 0, 0 <x <2). Incidentally, Cl ^- is using lithium chloride (LiCl) 0.001 g iontophoresis, Br ^- using lithium bromide (LiBr) 0.02 g The ion introduction. It was found by X-ray diffraction that the obtained samples all had a glass structure in which Si fine particles were mixed. In addition, the average particle size of the obtained samples was about 800 nm. Thereafter, in order to increase the electron conductivity, the obtained sample was covered with a graphite film having a thickness of about 200 nm by a CVD method.

  A coin cell was prepared in the same manner as in Example 1 except that each of the obtained powders was used, and its electrochemical characteristics were measured. The results are shown in Table 2.

Cl ^- ions or Br ^- also in Example 3-4 was performed iontophoresis, as compared with Comparative Example 2 not subjected to iontophoresis, overvoltage, charging time, discharge time and electrode life was improved. That is, the effect of increasing the mobility and reducing the resistance of lithium ions in the ionic conduction phase by introducing halogen ions appeared.

[Reference Examples 1 to 6]
In the same manner as in Example 1 or _{2, SiO x (0 <x} <2) or _{Li y SiO x (y> 0,0} <x <2) chalcogen ion (S ^2-ions to, Se ^2-ionic or Te ^2- ion) was introduced. For introduction of S ²⁻ ions, 0.001 g of simple substance S was used, 0.02 g of simple substance Se was used for introduction of Se ²⁻ ions, and 0.03 g of tellurium dioxide (TeO ₂ ) was used for introduction of Te ²⁻ ions. It was found by X-ray diffraction that the obtained samples all had a glass structure in which Si fine particles were mixed. In addition, the average particle size of the obtained samples was about 800 nm. Thereafter, in order to increase the electron conductivity, the obtained sample was covered with a graphite film having a thickness of about 200 nm by a CVD method.

  A coin cell was prepared in the same manner as in Example 1 except that each of the obtained powders was used, and its electrochemical characteristics were measured. The results are shown in Table 3.

  Even in Reference Examples 1 to 6 in which chalcogen ion introduction was performed, overvoltage, charging time, discharge time, and electrode life were improved as compared with Comparative Examples 1 and 2 in which ion introduction was not performed. Ion conduction by introduction of chalcogen ions The effect of increasing the mobility and reducing the resistance of lithium ions in the phase appeared.

[Examples 5 to 10]
In the same manner as in Example 2, halogen ions (I ⁻ ions, Cl ⁻ ions or Br ⁻ ions) and chalcogen ions (S ²⁻ ions, Se) to Li _y SiO _x (y> 0, 0 <x <2). ^2- ion or Te ^2- ion) was introduced. In addition, 0.15 g of iodine is used for introducing I ⁻ ions, 0.001 g of lithium chloride (LiCl) is used for introducing Cl ⁻ ions, and 0.02 g of lithium bromide (LiBr) is used for introducing Br ⁻ ions. For the introduction of S ²⁻ ions, 0.001 g of simple substance S was used, 0.02 g of simple substance Se was used for introduction of Se ²⁻ ions, and 0.03 g of tellurium dioxide (TeO ₂ ) was used for the introduction of Te ²⁻ ions. It was found by X-ray diffraction that the obtained samples all had a glass structure in which Si fine particles were mixed. In addition, the average particle size of the obtained samples was about 800 nm. Thereafter, in order to increase the electron conductivity, the obtained sample was covered with a graphite film having a thickness of about 200 nm by a CVD method.

  A coin cell was prepared in the same manner as in Example 1 except that each of the obtained powders was used, and its electrochemical characteristics were measured. The results are shown in Table 4.

  In Examples 5 to 10 in which halogen ions and chalcogen ions were introduced, overvoltage, charging time, discharge time, and electrode life were improved as compared with Comparative Example 2 in which no ion introduction was performed. Halogen ions and chalcogen ions The effect of increasing the mobility and reducing the resistance of lithium ions in the ionic conduction phase by introducing ions with a high polarizability.

  As apparent from the above results, according to the embodiment, the mobility of lithium ions in the negative electrode active material for a lithium ion secondary battery containing a silicon-containing oxide can be increased. As a result, according to the present embodiment, a lithium ion secondary battery with high output, long life, and short charge / discharge time can be obtained.

  Examples of utilization of this embodiment include negative electrode active materials of lithium ion secondary batteries and lithium-air secondary batteries.

Claims (8)

A negative electrode active material for a lithium ion secondary battery containing a silicon-containing oxide, wherein a halogen ion selected from the group consisting of Cl ⁻ , Br ⁻ and I ⁻ is introduced into the silicon-containing oxide. A negative electrode active material for a lithium ion secondary battery. 2. The lithium ion secondary battery according to claim 1, wherein chalcogen ions selected from the group consisting of S ²⁻ , Se ^2−, and Te ²⁻ are further introduced into the silicon-containing oxide. Negative electrode active material. The negative electrode active material for a lithium ion secondary battery according to claim 1, wherein the silicon-containing oxide is represented by SiO _x (0 <x <2). The negative electrode active material for a lithium ion secondary battery according to claim 1, wherein the silicon-containing oxide is represented by Li _y SiO _x (y> 0, 0 <x <2).   The negative electrode active material for a lithium ion secondary battery according to claim 1, wherein the negative electrode active material is combined with an electron-donating material.   The negative electrode active material for a lithium ion secondary battery according to claim 5, wherein the electron-donating material is a carbon material.   A negative electrode for a lithium ion secondary battery comprising the negative electrode active material for a lithium ion secondary battery according to any one of claims 1 to 6.   A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to claim 7.