WO2021241752A1 - Titanium oxide-silicon composite and use of same - Google Patents

Abstract

This composite contains a Ti oxide and Si element and has, in a powder X-Ray diffraction method (CuKα radiation), at least (1) a halo pattern at a 2θ value within the range 12.0-18.0º and has (2) at least one peak at a 2θ value within the range 24.5-26.0º and (3) at least one peak at a 2θ value within the range 28.0-30.0º. The ratio (I3/I2) of the peak intensity I3 of the largest peak within the range (3) and the peak intensity I2 of the largest peak within the range (2) is less than 1.2. A Ti oxide domain contains Si element.

Description

Titanium Oxide-Silicone Complex and Its Applications

The present invention relates to a titanium oxide-silicon complex and its use.

Mobile electronic devices are becoming more multifunctional at a speed that exceeds the power saving of electronic components, and the power consumption of portable electronic devices is increasing. Therefore, there is a strong demand for higher capacity and smaller size of lithium ion secondary batteries, which are the main power sources for portable electronic devices. In addition, the demand for electric vehicles is increasing, and there is a strong demand for higher capacity lithium-ion secondary batteries used in them.

In recent years, various studies have been conducted to meet such demands.
For example, it is being considered to use Si, that is, a simple substance of silicon as a material for a negative electrode. However, although it is possible to increase the capacity by using Si as compared with the carbon material, it has been known that Si, particularly crystalline Si, has a large volume change during charging and discharging and is severely deteriorated. In order to make up for such a defect of Si, a negative electrode material in which Si and a carbon material are combined has been conventionally proposed. For example, various measures have been taken such as making Si into nanoparticles, applying a coating material to Si, and doping Si with a dissimilar metal. In fact, these studies are improving the cycle life while maintaining high capacity.

Amorphous Si has an isotropic expansion when it reacts with Li compared to crystalline Si, and it is considered that there is less deterioration when viewed as a structure of the entire negative electrode. However, it has been said that amorphous Si is disadvantageous in terms of energy density as compared with crystalline Si because the charge / discharge curve becomes sloped when it reacts with Li. In the reaction between amorphous Si and Li, the slope-like charge / discharge curve is a unique characteristic of the material itself.

As another study, for example, in Patent Document 1, a composite containing lithium titanium oxide and bronze phase titanium oxide, Si can be used as an element constituting the lithium titanium oxide, and the composite is described. The negative electrode active material and the like including the above have been disclosed (see, for example, Patent Document 1, [Claim 1], [Claim 2] and [Claim 18]). However, even if the negative electrode active material disclosed in Patent Document 1 is used, it is not possible to obtain a lithium ion secondary battery having a sufficient charge / discharge capacity.

Further, titanium oxide having a special crystal structure called _{TiO 2 (B) is known.} It has been known that the TiO ₂ (B) can be used as a negative electrode material for a lithium ion secondary battery because its crystal structure has a tunnel structure and Li ^{+ can easily move (for example, non-patented).} See Documents 1 and 2).

Japanese Unexamined Patent Publication No. 2013-105744

When amorphous Si is used as the negative electrode material for lithium-ion batteries, the charge / discharge curve becomes sloped. Therefore, it is disadvantageous in terms of energy density as compared with the case of using crystalline Si having a plateau-like charge / discharge curve. No attempt has been made to solve this problem in the past.

An object of the present invention is to provide a lithium ion secondary battery having a high energy density, and as a negative electrode material for a lithium ion secondary battery and the negative electrode material capable of providing such an excellent lithium ion secondary battery. The purpose is to provide a complex that can be used.

The present inventors have conducted diligent studies in order to solve the above-mentioned problems. As a result, it has been found that a lithium ion secondary battery that solves the above-mentioned problems can be obtained by using a composite obtained by introducing an Si element into a specific titanium oxide as a negative electrode material for a lithium ion secondary battery. , The present invention has been completed.

That is, the present invention includes, for example, the following aspects.
[1] A complex (A) containing a Ti oxide and a Si element, wherein 2θ is obtained by powder X-ray diffraction method (CuKα ray), and (1) 12.0-18.0 deg. It has a halo pattern between the two, and (2) 24.5-26.0 deg. And (3) 28.0-30.0 deg. Has one or more peaks in any of
The ratio (I3 / I2) of the peak intensity I3 of the largest peak in (3) to the peak intensity I2 of the largest peak in (2) is less than 1.2, and the Ti oxide domain. Complex (A) containing Si element.
[2] The complex (A) according to [1], which contains carbon.
[3] The complex (A) according to [2], which comprises the complex composed of the carbon and the Si element.
[4] The complex (A) according to any one of [1] to [3], wherein the _{50% particle size DV50} in the volume-based cumulative particle size distribution is 0.1 μm or more and 20 μm or less.
[5] The complex (A) according to any one of [1] to [4], wherein the content of Si element is 5% by mass or more and 70% by mass or less.
[6] A negative electrode material for a lithium ion secondary battery containing the complex (A) according to any one of [1] to [5].
[7] A negative electrode having a current collector and an electrode mixture layer covering the current collector, the electrode mixture layer including a binder and a negative electrode material for a lithium ion secondary battery according to [6].
[8] The lithium ion secondary battery having the negative electrode according to [7].

By using the composite according to the embodiment of the present invention as a negative electrode material for a lithium ion secondary battery, it becomes possible to provide a lithium ion secondary battery having a high energy density and a high initial Coulomb efficiency.

The results of SEM-EDX analysis of the complex (A) -1 obtained in Example 1 are shown in FIG. The initial charge / discharge curves of Example 1 and Comparative Example 1 are shown in FIG. The profiles of the X-ray diffraction measurements of Examples 1 and 2 are shown in FIG.

Next, the present invention will be specifically described. In the present invention, "peak intensity" means "peak height" from the baseline to the peak of the peak.

(Definition of words)
First, some terms related to the present invention will be described.

"Lithium-ion secondary battery": A lithium-ion secondary battery has at least one selected from the group consisting of a non-aqueous electrolyte solution and a non-aqueous polymer electrolyte, a positive electrode, and a negative electrode, and lithium is between the positive electrode and the negative electrode. It is a secondary battery that charges and discharges when ions move.

"Full cell" and "half cell": In the present invention, the full cell refers to a cell that is composed of a positive electrode and a negative electrode and is controlled by a voltage like the lithium ion secondary battery. In the present invention, the half cell has a bipolar structure in which either the positive electrode or the negative electrode of the lithium ion battery is the working electrode and the Li metal is the counter electrode, and is controlled by the potential based on the redox potential of Li. Refers to the cell in which it is. The Li counter electrode is an electrode paired with a working electrode for passing an electric current.

"Potential" and "voltage": The electromotive force of the battery when the reference electrode and a certain active material-containing electrode system are combined is called the potential of the active material-containing electrode system. The difference in potential when the two types of active material-containing electrode systems are combined is called a voltage.

"CC mode", "CV mode", and "CC-CV mode": CC mode is a constant current mode, in which the voltage (potential) of the battery is changed while always maintaining a constant current value. This is the mode in which the reaction proceeds. The CV mode is a constant voltage (potential) mode, which is a mode in which the reaction of the battery is advanced by changing the current value of the battery while always maintaining a constant voltage (potential). The CC-CV mode is a mode in which the CV mode is executed after the CC mode. ^{In the present specification, Li +} is inserted into the complex (A) in CC-CV mode, ^{and Li +} is released from the complex (A) in CC mode. This is called a charge / discharge test.

"Charge / discharge curve": Electrochemical capacity [mAh / g, Ah / g, etc.] or time [seconds, minutes, hours, etc.] is set on the horizontal axis, and voltage [V] or potential [V vs. A graph with [Ref] set. Lithium-ion secondary battery-related potentials are generally based on the redox potential of lithium [V vs. The unit Li / Li ⁺ ] is used. A constant current test is performed on a lithium ion secondary battery (full cell) or a half cell when the electrode to be tested (for example, the negative electrode using the negative electrode material for the lithium ion secondary battery of the present invention) is used as the working electrode. Then, a charge / discharge curve is drawn.

"Plateautability of charge / discharge curve", "Slope property of charge / discharge curve": When a full cell or half cell is charged / discharged in a constant current test, the redox reaction proceeds at the potential or voltage at which the redox reaction proceeds. A constant potential or voltage may be maintained until the reaction is complete. When the charge / discharge curve is kept horizontal (or a straight line at an angle close to horizontal) with respect to the capacity or time on the horizontal axis when the redox reaction is occurring, it is said to have plateau property. On the other hand, when the redox reaction is in progress and the charge / discharge curve is not horizontal with respect to the capacity or time on the horizontal axis, it is said to have a slope property. Generally, when it has a plateau property, a two-phase coexistence reaction is proceeding. On the other hand, when it has a slope property, a multi-step reaction is proceeding, or a reaction ^{having a high redox reaction resistance (electron resistance, Li +} diffusion resistance, etc.) is proceeding. In addition, the state where the charge / discharge curve shows slope property is also expressed as the charge / discharge curve becomes slope-like, and the state where the charge / discharge curve shows plateau property is also expressed as the charge / discharge curve becomes plateau shape. do.

"Energy density": Obtained by the product of electrochemical capacity and voltage (potential). Energy density per weight and energy density per volume are commonly used.

Hereinafter, the Ti oxide and the Si element constituting the composite (A) of the present invention will be described, and then the composite (A), the negative electrode material for a lithium ion secondary battery, etc., which is one embodiment of the present invention, will be sequentially described. explain.

(Ti oxide)
The complex (A) according to an embodiment of the present invention contains a Ti oxide. The Ti oxide exists, for example, as secondary particles in which primary particles are aggregated. The shape of the Ti oxide is not particularly limited, and examples thereof include a lump, a scale, a spherical shape, a fibrous shape, and a rod shape.

The Ti oxide usually contains at least TiO ₂ (B).
In producing the complex (A) according to the embodiment of the present invention, the simple substance of Ti oxide, which is a raw material, has pores into which a gas phase raw material such as monosilane, which is a raw material of a substance containing Si element, can enter. Is preferable. Since monosilane has a molecular size of about 3 Å, it is preferable that it has pores larger than this, and TiO ₂ (B) has pores of 5 to 6 Å, and Ti contained in the complex (A). Preferred as an oxide. The Ti oxide _{preferably contains TIO 2} (B) as a main component. _{Specifically, 80 to 100% by mass of TiO 2} (B) is preferably contained in 100% by mass of Ti oxide, and 90 to 100% by mass is more preferable. It is most preferable that the Ti oxide contains substantially _{only TiO 2} (B), specifically, 99 to 100% by mass of _{TiO 2} (B) in 100% by mass of the Ti oxide.

The Ti oxide may contain a crystal structure other than TiO ₂ (B), as the crystal structure other than _{TiO 2 (B), TiO 2} ( anatase), TiO ₂ (rutile), TiO ₂ (brookite), TiO ₂ (bronze _{type), Li 4 Ti 5 O 12} , a 2 Ti n O 2n + 1 (a is Li, Na, alkali metals such as K) can be exemplified. When the Ti oxide has _{a crystal structure other than TiO 2} (B), it may have one of the structures or two or more of the structures.

In the Ti oxide, a part of the crystal lattice in the crystal structure is C, N, B, S, P, Na, Mg, Al, K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu. , Zn, Mo, Ru, Rh, Pd, Pt, Be, Nb, Nd, Ce, W, Ta, Ag, Au, Cd, Ga, In, Sb, Ba, and vacancies may be substituted.

The Ti oxide is 2θ in the powder X-ray diffraction method (CuKα ray), and (1) 12.0-18.0 deg. It has a halo pattern between the two, and (2) 24.5-26.0 deg. And (3) 28.0-30.0 deg. If any of the above has one or more peaks, the complex (A) also has a halo pattern in the range of (1) and peaks in the ranges of (2) and (3). Has.

The Ti oxide has a ratio (I3 / I2) of the peak intensity I3 of the largest peak in (3) to the peak intensity I2 of the largest peak in (2) less than 1.2. Yes, preferably less than 1.1.

In the complex (A) according to the embodiment of the present invention, it is preferable that the Ti oxide is used as a scaffold for the Si element described later, that is, as a carrier. By using the above-mentioned specific Ti oxide as a scaffold, the present inventors presume that the shape of the charge / discharge curve when the Si atom and Li react is not a slope shape but a plateau shape.

The TiO ₂ (B) is known in, for example, Non-Patent Document 1 and Non-Patent Document 2. The TiO ₂ (B) is any one of ICDD # 00-035-0088, # 00-046-1237, # 00-046-1238 of the powder diffraction database of the International Center for Diffraction Data (ICDD). It means titanium oxide containing a powder X-ray diffraction profile that corresponds to the peak position of.

When the crystallite size is calculated from Scherrer's equation using the half width of the peak with the highest intensity in the powder X-ray diffraction profile of Ti oxide, it is preferably 20 nm or less. It is more preferably 10 nm or less. More preferably, it is 8 nm or less. The crystallite size is usually 2 nm or more.

The content of Ti oxide in the composite (A) is preferably 0.10% by mass or more and 95% by mass or less, more preferably 0.95% by mass or more and 92% by mass or less, and further preferably 1% by mass or more and 90. It is less than mass%. When the content of Ti oxide is within the above range, Si enters in a certain proportion or more and the electrochemical capacity increases, and at the same time, TiO ₂ (B) is also contained in a certain proportion or more, so that Si easily develops a high energy density. Therefore, it is preferable.

In the present invention, by selecting appropriate conditions, the silicon component is eluted from the pores and the surface of the complex (A) particles, and the Ti oxide in the complex (A) particles is the same impurities as before the complex. It can be recovered in the state of concentration and pore structure.

As an example of the above-mentioned appropriate conditions, the complex (A) is stirred in an aqueous KOH solution at a temperature of 50 ° C. for 1 to 5 days, evacuated every other day, and then filtered, washed and dried. To do. The concentration of the KOH aqueous solution and the number of treatment days are adjusted each time according to the Ti oxide species. Conditions may be appropriately selected and carried out in which Si is dissolved but Ti oxide is not dissolved.

The method for synthesizing the Ti oxide is not particularly limited, but a method using a titanium alkoxide-based sol-gel reaction and a rearrangement reaction to a Ti oxide using the positional relationship between Ti and O of a polynuclear Ti complex. The method using the above is preferable. _{From the viewpoint that the ratio of TiO 2} (B) in the Ti oxide can be increased, the latter transition reaction based on the polynuclear Ti complex is preferable.

The above-mentioned method using a transition based on a polynuclear Ti complex is a method formed by a polynuclear Ti complex, which is heated and pressurized while maintaining the positional relationship between Ti and O to obtain Ti oxide. ₂ This is a method for obtaining a Ti oxide having a special crystal structure such as (B).

(Si element)
The complex (A) according to an embodiment of the present invention contains a Si element. The Si element may be contained in the complex (A) as a substance containing the Si element, and is not particularly limited, but a substance containing Si as a main component, which can occlude and release Li, is usually used. Examples of the substance containing a Si element include a simple substance of Si, a compound containing a Si element, a mixture, a eutectic or a solid solution. The content of the Si element in 100% by mass of the substance containing the Si element is preferably 90% by mass or more, more preferably 95% by mass or more. In the composite (A) according to the embodiment of the present invention, it is preferable that a substance containing a Si element is present on the Ti oxide as a scaffold material and inside the crystal lattice of the Ti oxide.

As an example of the substance containing the Si element, a substance represented by a simple substance of Si or a substance represented by the _{general formula: M m Si containing an element M other than Si and Li can be mentioned.} The substance is a compound, a mixture, a eutectic or a solid solution containing the element M in a ratio of m mol to 1 mol of Si.

Specific examples of the element M, which is an element other than Li, include B, C, N, O, S, P, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Rh, Pd, Pt, Be, Nb, Nd, Ce, W, Ta, Ag, Au, Cd, Ga, In, Sb, Ba and the like can be mentioned. The element M may be one kind of element or two or more kinds of elements. When two or more kinds of elements are contained as the element M, the ratio thereof is not particularly limited, and the total amount of the elements M may be m. In the formula, m is preferably 0.01 or more and 0.3 or less, more preferably 0.02 or more and 0.2 or less, and further preferably 0.03 or more and 0.1 or less.

Specific examples of substances containing Si elements include Si alone, an alloy of Si and an alkaline earth metal; an alloy of Si and a transition metal; an alloy of Si and a semi-metal; Si and Be, Ag, Al, Au. , Cd, Ga, In, Sb or Zn and solid soluble alloy or eutectic alloy; CaSi, CaSi ₂ , Mg ₂ Si, BaSi ₂ , Cu ₅ Si, FeSi, FeSi ₂ , CoSi ₂ , Ni ₂ Si, NiSi ₂ , MnSi, MnSi ₂ , MoSi ₂ , CrSi ₂ , Cr ₃ Si, TiSi ₂ , Ti ₅ Si ₃ , NbSi ₂ , NdSi ₂ , CeSi ₂ , WSi ₂ , W ₅ Si ₃ , TaSi ₂ , Ta ₅ Si ₃ , Silicide such as PtSi, V ₃ Si, VSi ₂ , PdSi, RuSi, RhSi; SiO ₂ , SiC, Si ₃ N _{4 and the} like can be mentioned.

The content of the Si element in the complex (A) is preferably 5% by mass or more, more preferably 8% by mass or more, and further preferably 10% by mass or more. When the content of Si element is 5% by mass or more, it is preferable because the superiority in terms of volume energy density and weight energy density can be maintained.

The content of the Si element in the complex (A) is preferably 70% by mass or less, more preferably 60% by mass or less, and further preferably 55% by mass or less. When the content of Si element is 70% by mass or less, the resistance of the composite (A) does not become too large, which is preferable. The content of Si element in the complex (A) can be examined by, for example, fluorescent X-ray analysis using the fundamental parameter method (FP method).

The substance containing the Si element can be produced by any of the solid phase method, the liquid phase method, and the gas phase method, but the vapor phase method is preferable. In particular, a method of producing Si element by a CVD method from a vapor phase Si raw material (Si element-containing gas) such as monosilane is preferable.

(Complex (A))
The complex (A) according to the embodiment of the present invention contains the Ti oxide and the Si element, and the Si element is contained in the Ti oxide domain. The Ti oxide domain means a crystal domain constituting the Ti oxide. Since the composite (A) contains a Si element in the Ti oxide domain, the energy density becomes high when it is used as a negative electrode material for a lithium ion secondary battery. The inclusion of the Si element in the Ti oxide domain can be confirmed, for example, by the cross-section SEM-EDX of the Ti oxide domain of the composite (A) particles. The lower limit of the value range of Si mass concentration / Ti mass concentration is preferably 0.05 or more, more preferably 0.10 or more, still more preferably 0.15 or more, and the upper limit is preferably 0.65 or less. It is more preferably 0.50 or less, still more preferably 0.30 or less.

Specifically, in the composite (A), it is preferable that the Si element is present in the gaps in the crystal lattice of the Ti oxide and the interface of the primary particles of the Ti oxide. The gaps in the crystal lattice of Ti oxide are micropores, and the primary particles of Ti oxide include mesopores in addition to micropores. The above-mentioned micropores mean pores having a pore diameter of less than 2 nm, and mesopores mean pores having a pore diameter of 2 nm or more and less than 50 nm. Since the Si element that has entered the micropores has only about 1 to 4 atoms in the micropore radial direction, the expansion of this Si due to lithium insertion is very small.

By using the composite (A) according to the embodiment of the present invention as a negative electrode material for a lithium ion secondary battery, the charge / discharge curve of the lithium ion secondary battery exhibits plateau properties. When the redox reaction is occurring and the charge / discharge curve remains horizontal (or straight at an angle close to horizontal) with respect to the capacitance or time on the horizontal axis, that is, when it shows plateau properties. It means that the two-phase coexistence reaction is proceeding in the electrode (negative electrode), which is preferable.

The complex (A) may contain carbon. Examples of the carbon-containing complex (A) include a complex (A) containing a complex composed of carbon and Si elements, and the surface of carbon-containing particles coated with the Ti oxide. The complex (A) in which the Si element is supported can be mentioned. Further, as another form of the complex (A) containing carbon, there is also a form in which a complex in which a Si element is supported on a titanium oxide is coated with carbon.

The carbon may be amorphous carbon such as hard carbon or soft carbon, or crystalline carbon such as graphite, carbon fiber, graphene, or carbon nanotube. Further, the carbon may be porous. In the case of porous carbon, it can be suitably used as long as ^{the pore volume is 0.2 cm 3 / g or more.} Examples of the porous carbon include activated carbon and molecular shedding carbon.

_{The 50% particle size DV50} in the volume-based cumulative particle size distribution of the complex (A) according to the embodiment of the present invention is preferably 0.1 μm or more. It is more preferably 1.0 μm or more, still more preferably 2.5 μm or more. When the _DV50 is 0.1 μm or more, the specific surface area does not become excessively high, so that a side reaction with the electrolytic solution occurs only slightly, and the initial Coulomb efficiency is excellent.

50% particle diameter D _V50 volume-based cumulative particle size distribution of the composite according to an embodiment of the present invention (A) is preferable equal to or less than 20.0 .mu.m. It is more preferably 15.0 μm or less, still more preferably 10.0 μm or less. When the _DV50 is 20 μm or less, the electron transfer distance to the inside of the complex (A) or the carbon coated by the complex (A) and the Li ⁺ diffusion distance are short, and the rate characteristics are excellent. _{The 50% particle size DV50} in the volume-based cumulative particle size distribution of the complex (A) according to the embodiment of the present invention can be measured by, for example, a laser diffraction type particle size distribution measuring device.

_{The BET specific surface area (S BET} ) of the complex (A) according to the embodiment of the present invention ^{is preferably 1.0 m 2} / g or more. It is more preferably 2.0 m ² / g or more, and further preferably 3.0 m ² / g or more. When the BET specific surface area (S _BET ) is 1.0 m ² / g or more, the surface of the composite (A) ^{has a sufficient entrance for Li +} to enter, and the input / output characteristics are excellent.

_{The BET specific surface area (S BET} ) of the complex (A) according to the embodiment of the present invention ^{is preferably 10.0 m 2} / g or less. It is more preferably 5.0 m ² / g or less, still more preferably 4.0 m ² / g or less. When the BET specific surface area (S _BET ) is 10.0 m ² / g or less, the coatability and handleability are excellent. Further, since it is not necessary to use a large amount of binder for electrode production, the electrode density can be increased, and the initial Coulomb efficiency does not decrease due to a side reaction with the electrolytic solution. _{The BET specific surface area (S BET} ) of the complex (A) according to the embodiment of the present invention can be measured by, for example, a BET multipoint method using nitrogen gas as a probe.

The complex (A) has a 2θ of (1) 12.0-18.0 deg in the powder X-ray diffraction method (CuKα ray). It has a halo pattern between the two, and (2) 24.5-26.0 deg. And (3) 28.0-30.0 deg. It has one or more peaks in any of the above, and the ratio of the peak intensity I3 of the largest peak in (3) above to the peak intensity I2 of the largest peak in (2) above (2). I3 / I2) is less than 1.2.

Having the above-mentioned halo pattern (1) means that a crystal system in which a large number of micropores are developed is formed among Ti oxides. Here, having a halo pattern means that the complex (A) has a 10.0-80.0 deg. 12.0-18.0 deg. For maximum peak intensity in the range of. It means that the ratio of the maximum peak intensities in the range of (12.0-18.0 deg. Maximum peak intensity in the range / 10.0-80.0 deg. Maximum peak intensity in the range) is 0.05 or more.

The above-mentioned peak (2) is a peak peculiar to Ti oxide in general. The peak of (2) includes a peak derived from _{TiO 2 (B).} The peak of (3) described above also _{includes a peak of titanium oxide having micropores such as TiO 2} (B), and at the same time, a peak of Si (111) is also included. When I3 / I2 is less than 1.2, it means that Si is Si having very weak crystallinity. I3 / I2 is more preferably less than 1.0. Further, I3 / I2 preferably exceeds 0.1, and more preferably more than 0.3.

(Manufacturing method of complex (A))
As a method for producing a composite body according to one embodiment of the present invention (A), for example by combining the TiO ₂ (B) in a known manner, TiO ₂ (B) is used as a Ti oxide, the Ti oxide On the other hand, for example, a chemical vapor deposition (CVD) method may be performed with a Si element-containing gas such as silane gas. This makes it possible to allow the Si element to enter the inside of the crystal lattice of the Ti oxide and the interface of the primary particles, and the complex (A) can be produced. The CVD can be carried out according to a known method.

When the composite (A) contains carbon, for example, the surface of the particles containing porous carbon is coated with the Ti oxide, and the composite (A) in which the Si element is supported on the porous carbon and the Ti oxide. Examples of the manufacturing method of the above include the following manufacturing methods. _{A porous material in which a Ti oxide containing TiO 2} (B) is formed on the surface of carbon-containing particles such as porous carbon particles is prepared, and then the porous carbon and Ti oxidation are performed by a chemical vapor phase growth (CVD) method. The complex (A) can be obtained by precipitating the Si element in the pores of the object. Examples of the method for forming Ti oxide on the surface of carbon-containing particles include a physical vapor deposition (PVD) method in the vapor phase method, and a titanium oxide precursor coated on the surface of carbon-containing particles in the liquid phase method. Then, a method of heating / pressurizing and the like can be mentioned, and in the solid phase method, a method of forming a complex by mechanochemical treatment and the like can be mentioned.

As another method, for example, porous carbon and Ti oxide are separately CVD-treated to precipitate Si elements, and then the porous carbon in which Si is precipitated and the Ti oxide in which Si is precipitated are subjected to mechanochemical treatment. It may be compounded with. The CVD method can be carried out, for example, by exposing the porous material to a Si element-containing gas, preferably a silane gas, at a high temperature.

Further, another form of the composite (A) containing carbon, which is a form in which a composite in which a Si element is supported on a titanium oxide is coated with carbon, specifically, a titanium oxide in which a Si element is supported. The manufacturing method is as follows. The gas phase method is a method of depositing carbon by CVD or PVD, the liquid phase method is a method of supporting a carbon source (for example, sucrose or citric acid) and then heating, and the solid phase method is a carbon source (for example). , Carbon nanotubes, carbon black, graphene and other conductive carbon materials) and mechanochemical treatment methods.

(Negative electrode material for lithium-ion secondary batteries)
The negative electrode material for a lithium ion secondary battery according to an embodiment of the present invention includes the complex (A). In the present invention, the "negative electrode material for a lithium ion secondary battery" is also simply referred to as a "negative electrode material". In the present invention, the negative electrode material refers to a negative electrode active material or a composite of a negative electrode active material and another material.

The negative electrode material for a lithium ion secondary battery according to an embodiment of the present invention may be formed only from the composite (A), or may be formed from the composite (A) and another negative electrode material. May be good.
As the other negative electrode material, a substance generally used as a negative electrode active material of a lithium ion secondary battery can be used. Specific examples include carbon-containing materials such as graphite and hard carbon _{, alloy-based active materials such as lithium titanate (Li 4} Ti ₅ O ₁₂ ), silicon and tin, and composite materials thereof. These negative electrode materials are usually in the form of particles. As the other negative electrode material, one type may be used or two or more types may be used. Among them, graphite (graphite particles) and hard carbon are particularly preferably used.

When the negative electrode material for a lithium ion secondary battery is formed of the composite (A) and another negative electrode material, the composite (A) is used per 100% by mass of the negative electrode material for the lithium ion secondary battery. It preferably contains 4 to 99% by mass, more preferably 8 to 40% by mass.

(Adjusting the capacity of the negative electrode material for lithium-ion secondary batteries, etc.)
For the purpose of improving battery performance, adjusting the capacity of the negative electrode material for lithium-ion secondary batteries, and adjusting the density of the electrode mixture layer constituting the negative electrode, assisting conductivity, and expanding / contracting. For the purpose of relaxation, a mixture of the composite (A) and another negative electrode material containing carbon may be used as the negative electrode material for a lithium ion secondary battery. A plurality of types of materials containing carbon to be mixed may be used. As the material containing carbon, graphite having a high capacity is preferable. As the graphite, natural graphite or artificial graphite can be selected and used. At this time, it is preferable to use a complex (A) having a relatively high capacity (700 mAh / g or more) because the cost of the negative electrode material for the lithium ion secondary battery can be reduced. This carbon-containing material for volume adjustment is mixed with the complex (A) in advance, and additives such as a binder, a solvent, and an optional conductive auxiliary agent are added thereto to prepare a paste for a negative electrode. May be good. Further, an additive such as a complex (A), a carbon-containing material, a binder, a solvent, and an optionally used conductive auxiliary agent may be mixed at the same time to prepare a paste for a negative electrode. The mixing order and method may be appropriately determined in consideration of the handleability of the powder and the like.

(Paste for negative electrode)
The paste for a negative electrode according to an embodiment of the present invention contains the negative electrode material, a binder, and a solvent, and further contains an additive such as a conductive auxiliary agent, if necessary. This negative electrode paste can be obtained, for example, by kneading the negative electrode material, a binder, a solvent, and if necessary, a conductive auxiliary agent or the like. The negative electrode paste can be formed into a sheet shape, a pellet shape, or the like.

The material used as the binder is not particularly limited, and is, for example, carboxymethyl cellulose, polyethylene, polypropylene, ethylene propylene tarpolymer, butadiene rubber, styrene butadiene rubber, butyl rubber, acrylic rubber, polyvinylidene fluoride, polyethylene oxide, polyepicrolhydrin, polyphosphazene. , Polyacrylonitrile and the like. One kind of binder may be used alone, or two or more kinds of binders may be used. The amount of the binder is preferably 0.5 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the negative electrode material.

The conductive auxiliary agent is not particularly limited as long as it has a role of imparting conductivity and electrode stability (the action of absorbing the volume change of the negative electrode material at the time of insertion / removal of Li) to the electrode. For example, carbon black, carbon nanotubes, carbon nanofibers, gas phase growth method carbon fibers (for example, "VGCF (registered trademark)" manufactured by Showa Denko Co., Ltd.), conductive carbon black (for example, "Denka Black (registered trademark)" electricity. Chemical Industry Co., Ltd., "SUPER C65" Imeris Graphite & Carbon Co., Ltd., "SUPER C45" Imeris Graphite & Carbon Co., Ltd.), Conductive Graphite (for example, "KS6L" Imeris Graphite & Carbon Co., Ltd., "SFG6L" Imeris Graphite & Carbon Co., Ltd.) and the like. Further, two or more kinds of the conductive auxiliary agents can be used. The amount of the conductive auxiliary agent is preferably 1 to 3 parts by mass with respect to 100 parts by mass of the negative electrode material.

In the present embodiment, it is preferable to include carbon nanotubes, carbon nanofibers, and vapor phase carbon fibers, and the fiber length of these conductive aids is preferably 1/2 or more of _{DV50 of the composite (A).} .. With this length, these conductive auxiliaries can be bridged between the negative electrode materials including the composite (A), and the cycle characteristics can be improved. Single-wall type and multi-wall type carbon nanotubes and carbon nanofibers having a fiber diameter of 15 nm or less are preferable because the number of bridges increases with the same amount of addition as compared with thicker carbon nanotubes and carbon nanofibers. It is also preferable from the viewpoint of improving the electrode density because it is more flexible.

The solvent is not particularly limited, and N-methyl-2-pyrrolidone, dimethylformamide, isopropanol, water, etc. can be used. In the case of a binder that uses water as a solvent, it is preferable to use a thickener in combination. The amount of the solvent may be adjusted so that the paste has a viscosity that makes it easy to apply to the current collector.

(Negative electrode)
The negative electrode according to an embodiment of the present invention has a current collector (for example, a sheet-shaped current collector) and an electrode mixture layer that covers the current collector, and the electrode mixture layer is a binder and the lithium ion battery. It contains a negative electrode material for a secondary battery, and if necessary, the conductive auxiliary agent and the like.

Examples of the current collector include a sheet-like material such as nickel foil, copper foil, nickel mesh or copper mesh.

The electrode mixture layer contains a binder and the above-mentioned negative electrode material. When the negative electrode paste contains a conductive auxiliary agent, the electrode mixture layer also contains the conductive auxiliary agent. The electrode mixture layer can be obtained, for example, by applying the negative electrode paste on a current collector and drying it. The method of applying the negative electrode paste is not particularly limited. The thickness of the electrode mixture layer is preferably 50 to 200 μm. If the electrode mixture layer becomes too thick, it may not be possible to accommodate the negative electrode in a standardized battery container. The thickness of the electrode mixture layer can be adjusted by the amount of paste applied. It can also be adjusted by pressure molding after the paste is dried. Examples of the pressure forming method include forming methods such as roll pressurization and press pressurization. The pressure during press molding is preferably about 100 to 500 MPa.

The electrode density of the negative electrode (negative electrode density) can be calculated as follows, for example. That is, the negative electrode after pressing is punched into a circular shape having a diameter of 16 mm, and its mass and thickness are measured. The mass and thickness of the collector foil (punched into a circular shape with a diameter of 16 mm) measured separately are subtracted from the mass and thickness to obtain the mass and thickness of the electrode mixture layer, and the electrode density (negative electrode) is based on that value. Density) is calculated.

(Lithium-ion secondary battery)
The lithium ion secondary battery according to the embodiment of the present invention has the negative electrode. Since the lithium ion secondary battery of the present invention has the negative electrode, it is excellent in energy density. Further, the lithium ion secondary battery of the present invention has a low electrode expansion rate of the negative electrode, a high initial Coulomb efficiency, and a high capacity retention rate, and therefore has a long battery life and is suitably used as a power source for various devices. Can be done.

The lithium ion secondary battery has at least one selected from the group consisting of a non-aqueous electrolyte solution and a non-aqueous polymer electrolyte, a positive electrode, and the negative electrode.
The positive electrode used in the present invention is not particularly limited, including those conventionally used for lithium ion secondary batteries. As the positive electrode, specifically, an electrode containing a positive electrode active material can be used. Examples of the positive electrode active material include LiNiO ₂ , LiCoO ₂ , LiMn ₂ O ₄ , LiNi _0.34 Mn _0.33 Co _0.33 O ₂ , LiFePO _{4, and the} like.

The non-aqueous electrolyte solution and the non-aqueous polymer electrolyte used in the lithium ion secondary battery are not particularly limited. For example, _{lithium salts such as LiClO 4} , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF ₃ , CH ₃ SO ₃ Li can be used as ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, butylene carbonate, acetonitrile. , Propionitrile, dimethoxyethane, tetrahydrofuran, γ-butyrolactone and other organic electrolytes; gel-like polymer electrolytes containing polyethylene oxide, polyacrylic nitrile, polyvinylidene fluoride, polymethylmethacrylate and the like. A solid polymer electrolyte containing a polymer having an ethylene oxide bond or the like can be mentioned.

Further, a small amount of additives generally used for lithium ion secondary batteries may be added to the electrolytic solution. Examples of the substance include vinylene carbonate (VC), biphenyl, propane sultone (PS), fluoroethylene carbonate (FEC), ethylene sultone (ES) and the like. The addition amount is preferably 0.01% by mass or more and 50% by mass or less.

A separator can be provided between the positive electrode and the negative electrode in the lithium ion secondary battery. Examples of the separator include non-woven fabrics mainly composed of polyolefins such as polyethylene and polypropylene, cloths, micropore films, and those obtained by combining them.

Lithium-ion secondary batteries are obtained from the power supply of electronic devices such as mobile phones, mobile personal computers, and mobile information terminals; the power supply of electric motors such as electric drills, electric vacuum cleaners, and electric vehicles; fuel cells, solar power generation, and wind power generation. It can be used for storing the generated power.

Examples and comparative examples of the present invention will be shown below, and the present invention will be described in more detail. It should be noted that these are merely examples for explanation, and the present invention is not limited thereto.
In addition, the measurement of each physical property and the evaluation of the battery performance were performed as follows.

[50% particle size _DV50 ]
Add 2 tablespoons of powder (complex (A)) and 2 drops of nonionic surfactant (TRITON®-X; Roche Applied Science) to 50 ml of water for more than 3 minutes. The sound was dispersed. This dispersion was put into a laser diffraction type particle size distribution measuring device (LMS-2000e, manufactured by Seishin Enterprise Co., Ltd.), and the volume-based cumulative particle size distribution was measured to obtain a 50% particle size _DV50 (μm).

[BET specific surface area]
Using a specific surface area / pore distribution measuring device (NOVA 4200e (registered trademark) manufactured by Kantachrome Instruments), using nitrogen gas as a probe, and using a BET multipoint method with relative pressures of 0.1, 0.2, and 0.3. The BET specific surface area S _BET (m ² / g) was measured.

[Total pore volume]
About 5 g of the carbon material was weighed in a glass cell and dried at 300 ° C. under a reduced pressure of 1 kPa or less for about 3 hours to remove adsorbed components such as water, and then the mass of the carbon material was measured. Then, the adsorption isotherm of the nitrogen gas of the carbon material after drying under the cooling of liquid nitrogen was measured with Autosorb (registered trademark) -1 manufactured by Quantachrome. The total pore volume (μL / g) was determined from the amount of nitrogen adsorbed at the measurement points of the obtained adsorption isotherm at P / P0 = 0.992 to 0.995 and the mass of the carbon material after drying.

[Profile of complex (A) by powder X-ray diffraction method]
The complex (A) was filled in a non-reflective Si plate (sample plate window 5 mmφ, depth 0.2 mm), and measurement was performed under the following conditions.
X-ray diffractometer: Rigaku SmartLab®
X-ray type: CuKα ray Kβ ray removal method: Ni filter X-ray output: 45kV, 200mA
Measurement range: 5.0-80.0 deg

Scan speed: 10.0 deg / min.
The obtained waveform was subjected to background removal, Kα2 component removal, and profile fitting. Based on the result, the peak intensity was calculated. 2θ = 28.0-30.0 deg. The peak intensity (I3) of the maximum peak at 2θ = 24.5-26.0deg. The ratio I3 / I2 of the peak intensity (I2) of the largest peak in was calculated.

[Content rate (mass%) of Si element in complex (A) by fluorescent X-ray analysis]
The measurement was performed under the following conditions.
X-ray fluorescence device: NEX CG manufactured by Rigaku
Tube voltage: 50kV
Tube current: 1.00mA
Sample cup: Φ32, 12mL, CH1530
Sample (complex (A)) weight: 3 g
Sample height: 11 mm
The powder was introduced into the sample cup, and the content of Si element was calculated by mass% using the FP method.

[Si position in complex (A) by scanning electron microscope (SEM) observation and energy dispersive X-ray analysis (EDX)]
A carbon double-sided tape was attached to the Si wafer, and the powder of the complex (A) was supported on the carbon tape. The powder of the complex (A) supported on the end face of the carbon tape was polished with a cross-session polisher (registered trademark; manufactured by JEOL Ltd.) to generate a cross section of particles. This polished surface was observed with a scanning electron microscope (SEM) (Regulus® 8220; manufactured by Hitachi High-Tech) at a magnification of 50,000. Energy dispersive X-ray analysis (EDX) was performed at the magnification (SEM-EDX analysis).

SEM-EDX analysis was performed with a view that the entire Ti oxide domain of the complex (A) could be mapped. The elements to be measured were four elements, Ti, C, O, and Si. (Si mass concentration) / (Ti mass concentration) when the central part of the Ti oxide domain was point-EDX analyzed was calculated.

[Manufacturing of working electrode]
Carboxymethyl cellulose (CMC; manufactured by Daicel, CMC1300) and styrene butadiene rubber (SBR) were used as binders. Specifically, an aqueous solution in which 2% by mass of CMC powder was dissolved and an aqueous dispersion in which 40% by mass of SBR was dispersed were used.

Carbon black and gas phase growth method carbon fiber (VGCF (registered trademark) -H, manufactured by Showa Denko KK) were prepared as conductive auxiliaries and mixed at a ratio of 3: 2 (mass ratio). And said.

The complex (A) produced in Examples and Comparative Examples described later was mixed with graphite for the purpose of adjusting the initial Li desorption capacity within a certain range. As a result, the content of Si element in the working electrode was adjusted to 2.0 to 3.3% by mass. This mixture (acting electrode material) was mixed by 90 parts by mass, the mixed conductive auxiliary agent by 5 parts by mass, the CMC aqueous solution by 125 parts by mass, and the SBR aqueous dispersion by 6.25 parts by mass. The obtained mixture was kneaded with a rotation / revolution mixer to obtain a paste for working electrodes.

The above-mentioned paste for working electrode was uniformly applied onto a copper foil having a thickness of 20 μm using a doctor blade so as to have a thickness of 150 μm, dried on a hot plate, and then vacuum dried to obtain a working electrode. The dried electrode was pressed with a uniaxial press at a pressure of 300 MPa to obtain a working electrode for battery evaluation. The thickness of the obtained working electrode was 62 μm including the thickness of the copper foil.

[Making evaluation batteries]
The following operations were carried out in a dry room with a dew point of −80 ° C. to −60 ° C.

[Making a coin-shaped half cell]
In a coin cell (inner diameter of about 18 mm), the working electrode and a metal lithium foil punched to 16 mmφ were sandwiched between separators (polypropylene microporous film (cell guard 2400)) and laminated, and an electrolytic solution was added to form a coin-type half cell. The work was performed in a dry room.

[Definition of charging and discharging]
In this embodiment and the comparative example, an increase in the cell voltage (increasing the potential difference) is referred to as charging, and decreasing the cell voltage (decreasing the potential difference) is referred to as discharging. In the case of a coin-type half cell having a Li metal as a counter electrode, the Li metal has a lower redox potential than the above-mentioned working electrode. Therefore, when Li is inserted into the working electrode, the voltage decreases (the potential difference decreases), resulting in discharge. On the contrary, when Li is discharged from the working electrode, the voltage increases (the potential difference increases), so that charging is performed. In an actual lithium ion secondary battery, a material having a redox potential higher than that of the working electrode (for example, lithium cobalt oxide, lithium nickel manganese cobalt oxide, etc.) is opposed to the working electrode, so that the working electrode is a negative electrode. ..

[Measurement test of initial Li insertion capacity and initial Coulomb efficiency]
The test was conducted using the above coin-shaped half cell. From OCP (Open Circuit Potential) 0.005 V vs. CC mode was discharged with a current value of 0.1 C up to Li / Li ^+. Next, 0.005V vs. The discharge was switched to CV mode with Li / Li ⁺ , and the discharge was performed with a cutoff current value of 0.005 C. The capacity at this time is defined as the initial Li insertion capacity. Upper limit potential 1.5V vs. CC mode charging was performed at 0.1 C as Li / Li ^+. The capacity at this time is defined as the initial Li desorption capacity.

The test was conducted in a constant temperature bath set at 25 ° C. Further, the value obtained by expressing the initial Li desorption capacity / initial Li insertion capacity as a percentage was defined as the initial Coulomb efficiency.
For Example 1 and Comparative Example 1, the initial charge / discharge curves obtained in the above test are shown in FIG.

The materials used in the following examples and comparative examples are as follows.
(Dio ₂ (B) raw material for synthesis)
-Ti metal powder (CAS No. 7440-32-6; powder, average particle size 45 μm, 99.9%, Fuji Film Wako Pure Chemical Industries, Ltd.)
・ Ammonia water (CAS No. 1336-21-6; Kanto Chemical Co., Inc.)
-Hydrogen peroxide solution (CAS No. 7722-84-1; Kanto Chemical Co., Inc.)
-Glycolic acid (CAS No. 79-14-1; Kanto Chemical Co., Inc.)
・ Sulfuric acid (CAS No. 7664-93-9; Kanto Chemical Co., Inc.)
(Porous carbon)
· KDPW-SP (CO., LTD YOU e-es, D _V50 = 5.6μm)
(Graphite particles)
In the example below, Table 1 shows the physical properties of artificial graphite particles [manufactured by Showa Denko KK] (graphite (1)) used as a carbon-containing material for the purpose of adjusting the capacity together with the complex (A). ..

_DV50 , total pore volume and BET specific surface area were measured by the method described above. d ₀₀₂ indicates the average plane spacing of the (002) plane by the powder X-ray diffraction method. Lc indicates the thickness of the crystallites of the graphite particles in the C-axis direction. In the present specification, d ₀₀₂ and Lc can be measured by a known method using the powder X-ray diffraction (XRD) method (Michio Inagaki, "Carbon", 1963, No. 36, 25-3 4). Page; Iwashita et al., Carbon vol. 42 (2004), p. 701-714).

The I ₁₁₀ / I _004, the ratio of the peak intensity I ₀₀₄ of the diffraction peak profile obtained by powder X-ray diffraction method and the peak intensity I ₁₁₀ of the 110 plane of graphite crystal 004 side. Specifically, the waveform obtained by the powder X-ray diffraction method was subjected to background removal, Kα2 component removal, and profile fitting. Was calculated and the results peak strength of the resulting 004 surface I ₀₀₄ intensity ratio becomes orientation index from the peak intensity I ₁₁₀ of the 110 plane I ₁₁₀ / I _004. As for the peaks on each surface, the one with the highest intensity in the following range was selected as each peak.
Surface (004): 54.0 to 55.0 deg
Surface (110): 76.5 to 78.0 deg

(Example 1)
After adding 0.9572 g of Ti metal powder to 80 mL of hydrogen peroxide solution, 20 mL of ammonia water was added. After the Ti metal powder was dissolved, 2.282 g of glycolic acid was added and the mixture was stirred at 80 ° C. for 3 hours. 40 mL of water and 2.6 mL of sulfuric acid were added thereto, and hydrothermal treatment was performed at 200 ° C. for 1 hour in an autoclave. The obtained solid content was washed with water _{to obtain TiO 2} (B).

The TiO ₂ (B) was dried under vacuum at 400 ° C. for 3 hours, and then the atmosphere was replaced with He gas. Then, silane gas was circulated for 6 hours at a silane flow rate of 0.28 g / h and a reaction temperature of 400 ° C. After the silane gas treatment, the supply of silane gas was stopped and switched to the He gas flow. The silane gas was purged while cooling to obtain complex (A) -1.

Table 2 shows the results of X-ray diffraction measurement, fluorescent X-ray analysis, and SEM-EDX analysis of this complex (A) -1. The results of SEM-EDX analysis are shown in FIG. From this, it was confirmed that the Si element was contained in the Ti oxide domain. The profile of the X-ray diffraction measurement is shown in FIG. In addition, 10.0-80.0 deg. 12.0-18.0 deg. For maximum intensity peak intensity in the range. Since the ratio of the maximum peak intensity in the range (12.0-18.0 deg. Maximum peak intensity in the range / 10.0-80.0 deg. Maximum peak intensity in the range) was 0.308, there is a halo pattern. I decided.
Using a mixture of 11.2 parts by mass of complex (A) -1 and 88.8 parts by mass of graphite (1), working electrodes were prepared by the above method, and the results of measuring the battery characteristics are shown in Table 3. show.

(Example 2)
Obtained by the phenolic resin steam activation _{(900 ℃), D V50 =} 6.6μm, to the activated carbon is BET specific surface area = 2361m ² / g, subjected to silane gas treated in the same manner as in Example 1, complex (B) was obtained. The complex (A) -1 of 1.0 g and the complex (B) of 9.0 g were combined with a rotary cutter mill for 30 seconds to obtain a complex (A) -2.

Table 2 shows the results of X-ray diffraction measurement, fluorescent X-ray analysis, and SEM-EDX analysis of this complex (A) -2. From this, it was confirmed that the Si element was contained in the Ti oxide domain. The X-ray diffraction profile is also shown in FIG. In addition, 10.0-80.0 deg. 12.0-18.0 deg. For maximum intensity peak intensity in the range. Since the ratio of the maximum peak intensity in the range (12.0-18.0 deg. Maximum peak intensity in the range / 10.0-80.0 deg. Maximum peak intensity in the range) was 0.191, there is a halo pattern. I decided.
Table 3 shows the results of measuring the battery characteristics by preparing working electrodes using a mixture of 10.9 parts by mass of complex (A) -2 and 89.1 parts by mass of graphite (1).

(Comparative Example 1)
The complex (A) -c1 was obtained by the same method as in Example 1 except _{that the TiO 2} (B) was replaced with the porous carbon "KDPW-SP" during the silane gas treatment. Table 2 shows the results of X-ray diffraction measurement, fluorescent X-ray analysis, and SEM-EDX analysis of this complex (A) -c1. In addition, 10.0-80.0 deg. 12.0-18.0 deg. For maximum intensity peak intensity in the range. Since the ratio of the maximum peak intensity in the range (12.0-18.0 deg. Maximum peak intensity in the range / 10.0-80.0 deg. Maximum peak intensity in the range) was 0.001, there is a halo pattern. I decided not to.
Table 3 shows the results of measuring the battery characteristics by preparing working electrodes using a mixture of 10.8 parts by mass of the complex (A) -c1 and 89.2 parts by mass of graphite (1).

(Comparative Example 2)
_{After obtaining TIO 2} (B) by the same method as in Example 1, _{82 parts by mass of TiO 2} (B) and 18 parts by mass of Si particles (BET specific surface area 52 m ² / g, density 2.3 g / cm ^{3) were added.} It was put into a rotary cutter mill, and nitrogen gas was circulated to maintain an inert atmosphere, and the mixture was stirred at high speed at 2500 rpm and mixed to obtain a complex (A) -c2. Table 2 shows the results of X-ray diffraction measurement, fluorescent X-ray analysis, and SEM-EDX analysis of this complex (A) -c2.
Table 3 shows the results of measuring the battery characteristics by preparing working electrodes using a mixture of 11.2 parts by mass of the complex (A) -c2 and 88.8 parts by mass of graphite (1).

Energy density *: Working poles prepared in Examples and Comparative Examples and 1500 mV vs. A full cell consisting of a positive electrode (a material having a redox potential higher than that of the working electrode) that expresses the same capacity as the working electrode at a constant potential of Li / Li ^{+ is set.} At the time of discharging the full cell, the working potential is 350 mV vs. The value of the energy density of the part above Li / Li ^{+ (Si reaction part).}

Comparing Example 1 and Comparative Example 1 with respect to the results shown in Table 3, Comparative Example 1 uses porous carbon as a scaffolding material. Therefore, it takes time for ^{Li +} to reach the entire Si filled inside the porous carbon. Therefore, it is considered that the charge / discharge curve of Comparative Example 1 is sloped and the energy density is lower than that of Example 1.

_{From this point, it can be seen that TiO 2} (B) is superior to porous carbon as a scaffolding material. Further, Comparative Example 1 has a lower initial Coulomb efficiency than Example 1. It is considered that this is because the porous carbon surface is more non-uniform and unstable as an energy field than the _{TiO 2 (B) surface.}

Comparing Example 1 and Comparative Example 2 with respect to the results shown in Table 2, the values of I3 / I2 are very large in Comparative Example 2. This means that the peak intensity of the powder X-ray diffraction of Si (111) is very high, and the crystallinity of Si is high. It is considered that when Si with high crystallinity is used, the expansion of Si becomes anisotropic and the electrode structure is destroyed. In fact, when the electrochemical evaluation was carried out, as shown in Table 3, the initial Li insertion capacity showed the same value as that of Example 1, whereas the initial Li desorption capacity was significantly lower than that of Example 1. It has become. This is because the expansion of Si is anisotropic in Comparative Example 2 as compared with Example 1, so that the electrode structure is greatly destroyed by the first Li insertion, and the electron conduction path is reduced during Li desorption. It is thought that it has been done.

Comparing Example 1 and Example 2 with respect to the results shown in Table 3, the value of the energy density is large in Example 2. This is due to the influence of the complex (B) having a large electrochemical capacity carrying more Si. _{That is, by combining a complex having a large electrochemical capacity and a complex based on TiO 2} (B) having a plateau on the charge / discharge curve, a material having a high electrochemical capacity and expressing a plateau can be obtained. It is considered that the energy density was further improved.

Claims (8)

1. It is a complex (A) containing a Ti oxide and a Si element, and 2θ in the powder X-ray diffraction method (CuKα ray) is (1) 12.0-18.0 deg. It has a halo pattern between the two, and (2) 24.5-26.0 deg. And (3) 28.0-30.0 deg. Has one or more peaks in any of
   The ratio (I3 / I2) of the peak intensity I3 of the largest peak in (3) to the peak intensity I2 of the largest peak in (2) is less than 1.2, and the Ti oxide domain. Complex (A) containing Si element.
2. The complex (A) according to claim 1, which contains carbon.
3. The complex (A) according to claim 2, which comprises the complex composed of the carbon and the Si element.
4. The complex (A) according to any one of claims 1 to 3, wherein the _{50% particle size DV50} in the volume-based cumulative particle size distribution is 0.1 μm or more and 20 μm or less.
5. The complex (A) according to any one of claims 1 to 4, wherein the content of Si element is 5% by mass or more and 70% by mass or less.
6. A negative electrode material for a lithium ion secondary battery containing the complex (A) according to any one of claims 1 to 5.
7. A negative electrode having an electrode mixture layer covering the current collector and the current collector, and the electrode mixture layer includes a binder and a negative electrode material for a lithium ion secondary battery according to claim 6.
8. The lithium ion secondary battery having the negative electrode according to claim 7.

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