WO2019064728A1 - Negative electrode active material containing oxygen-containing silicon material, and method for producing same - Google Patents

Abstract

Provided are: a negative electrode active material which contains a silicon material and makes it possible to modify the capacity maintenance rate of a secondary battery to a suitable value; and a method for producing the negative electrode active material. A negative electrode active material characterized by containing an oxygen-containing silicon material having an oxygen content (WO %) of 16 to 27% by mass exclusive (i.e., 16 < WO < 27) and a silicon content (WSi %) of 62 to 81% by mass exclusive (i.e., 62 < WSi < 81).

Description

Negative electrode active material containing oxygen-containing silicon material and method of manufacturing the same

The present invention relates to a negative electrode active material containing an oxygen-containing silicon material.

Silicon is known to be used as a component of semiconductors, solar cells, secondary batteries and the like, and hence research on silicon is actively conducted.

For example, Patent Document 1 discloses that a layered silicon compound mainly composed of layered polysilane from which CaSi ₂ is reacted with an acid to remove Ca is synthesized, and the layered silicon compound is heated at 300 ° C. or higher to generate hydrogen. A lithium ion secondary battery is described which has produced a detached silicon material and which comprises the silicon material as a negative electrode active material.

International Publication No. 2014/080608

When a silicon material is employed as a negative electrode active material of a secondary battery, it is silicon itself that exhibits the function as a negative electrode active material for storing and releasing charge carriers. Therefore, to improve the function of inserting and extracting charge carriers, it is necessary to increase the purity of the silicon material. However, in a secondary battery using a silicon material with a high proportion of silicon as the negative electrode active material, although the initial efficiency indicated by (initial discharge capacity) / (initial charge capacity) is improved, when charging and discharging are repeated It was found that the capacity of

The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a negative electrode active material containing a silicon material and a method of manufacturing the same, which can optimize the capacity retention rate of a secondary battery.

The inventor repeated trial and error and examined a method of manufacturing a silicon material. As a result, it has been found that a secondary battery employing a silicon material containing an element other than silicon to some extent is excellent in capacity retention rate.
The present invention relates to an oxygen-containing silicon material focusing on oxygen as an element other than silicon, and in particular, to provide a manufacturing method capable of controlling the oxygen content of the oxygen-containing silicon material.

The negative electrode active material of the present invention has an oxygen mass% (W 2 _O %) of 16 <W 2 _O <27 and an silicon mass% (W _Si %) of 62 <W _Si <81 (hereinafter referred to as And the oxygen-containing silicon material of the present invention).

One embodiment of a method for producing a negative electrode active material containing the oxygen-containing silicon material of the present invention is
a-1) reacting CaSi ₂ with an aqueous acid solution at 15 to 50 ° C. to synthesize an oxygen-containing layered silicon compound containing layered polysilane,
b) heating the oxygen-containing layered silicon compound at 300 ° C. or higher to synthesize an oxygen-containing silicon material;
It is characterized by including.

Another aspect of the method for producing a negative electrode active material containing the oxygen-containing silicon material of the present invention is
a-2-1) reacting CaSi ₂ with an aqueous acid solution at −20 to 10 ° C.,
a-2-2) a step of synthesizing an oxygen-containing layered silicon compound containing layered polysilane with the temperature of the reaction liquid being set to 15 to 50 ° C., following the above step a-2-1),
b) heating the oxygen-containing layered silicon compound at 300 ° C. or higher to synthesize an oxygen-containing silicon material;
It is characterized by including.

According to the present invention, it is possible to provide a negative electrode active material containing an oxygen-containing silicon material and a method for producing the same, which can optimize the capacity retention rate of a secondary battery.

It is a graph which shows the relationship of the integral capacity and discharge capacity of each lithium ion secondary battery in evaluation example 2. FIG. It is a graph which shows the relationship of the integral capacity and discharge capacity of each lithium ion secondary battery in evaluation example 9. FIG.

Below, the form for implementing this invention is demonstrated. Incidentally, unless otherwise specified, the numerical range “ab” described in the present specification includes the lower limit a and the upper limit b in that range. And a numerical range can be constituted by combining these arbitrarily including the upper limit and lower limit, and the numerical value listed in the example. Furthermore, numerical values arbitrarily selected from these numerical ranges can be used as new upper and lower numerical values.

The negative electrode active material of the present invention contains an oxygen-containing silicon material in which oxygen mass% (W 2 _O %) is 16 <W 2 _O <27 and silicon mass% (W _Si %) is 62 <W _Si <81. It is characterized by

The oxygen-containing silicon material of the present invention can be used as a negative electrode active material of a secondary battery such as a lithium ion secondary battery. Since the oxygen-containing silicon material of the present invention has an appropriate ratio of oxygen to silicon, the secondary battery comprising the oxygen-containing silicon material of the present invention satisfies all of the capacity retention rate, capacity, and initial efficiency in a well-balanced manner. .

An oxygen-containing silicon material having an excessively low oxygen mass% and an excessively high silicon mass% is excellent in capacity and initial efficiency as a negative electrode active material, but is inferior in capacity retention rate. On the other hand, an oxygen-containing silicon material having an excessively high oxygen content by mass and an excessively low silicon content by mass is inferior in capacity and initial efficiency as a negative electrode active material.

Oxygen mass% in the oxygen-containing silicon material of the present invention _(W O%) is preferably 16.5 ≦ _{W O} ≦ 26.5, and more preferably 17 ≦ _{W O} ≦ 26, is 18 ≦ _{W O} ≦ 25.5 More preferably, 19 ≦ W _o ≦ 25 is particularly preferred.
The silicon mass% (W _Si %) in the oxygen-containing silicon material of the present invention preferably satisfies 65 ≦ W _Si ≦ 80, more preferably 68 ≦ W _Si ≦ 79, and 70 ≦ W _Si ≦ It is further preferable to satisfy 78, and it is particularly preferable to satisfy 70 ≦ W _Si ≦ 76.

The oxygen-containing silicon material of the present invention may contain elements other than oxygen and silicon. As such an element, Al is preferable. The oxygen-containing silicon material of the present invention containing Al has a reduced resistance. Therefore, it can be said that the oxygen-containing silicon material of the present invention containing Al is excellent in the function as a negative electrode active material.

Further, it is known that, under charge and discharge conditions of a secondary battery, constituents of the electrolytic solution are decomposed to form an SEI (Solid Electrolyte Interphase) film containing oxygen on the surface of the negative electrode active material. Here, when the negative electrode active material contains silicon, there is a concern that silicon is oxidized by oxygen contained in the SEI film to be degraded.
However, since the oxygen-containing silicon material of the present invention containing Al contains Al, it is considered that the oxidative degradation of silicon is suppressed. The reason is that Al is considered to bind preferentially and stably to oxygen since it has lower electronegativity than silicon, and that Al-O bond of Al and oxygen is more stable than Si-O bond. Also, oxygen having a stable Al—O bond can be said to be less likely to be involved in the oxidation of silicon which is more electronegative than Al.
Therefore, a secondary battery having the oxygen-containing silicon material of the present invention containing Al as a negative electrode active material can be expected to have a long life.

It is preferable that Al mass% (W _Al %) in the oxygen-containing silicon material of the present invention satisfy 0 <W _Al <1, and more preferably 0 <W _Al ≦ 0.8. It is further preferable to satisfy ≦ W _Al ≦ 0.6, and it is particularly preferable to satisfy 0.05 ≦ W _Al ≦ 0.4.

The oxygen-containing silicon material of the present invention may contain an impurity derived from a manufacturing process or an impurity derived from a raw material. As described later, in the method for producing an oxygen-containing silicon material of the present invention, an acid is used. The element derived from the anion of the acid is likely to be contained as an impurity in the oxygen-containing silicon material of the present invention.
In the oxygen-containing silicon material of the present invention, the element mass% (W _x %) derived from the acid anion is preferably a small value. When W _x % is large, the irreversible capacity of the oxygen-containing silicon material is increased, thereby reducing the initial efficiency. As a range of W _x %, 0 <W _x <8 can be illustrated. The range of W _x % preferably satisfies 0 <W _x <6, more preferably 0 <W _x ≦ 4, and still more preferably 0 <W _x ≦ 3. It is particularly preferred to satisfy W _x ≦ 2. When the acid anion is a halogen, the element mass% (W _x %) derived from the acid anion is read as halogen mass% (W _x %).

Examples of impurities that can be contained in the oxygen-containing silicon material of the present invention include Ca and Fe. Ca is derived from the raw material CaSi ₂ . Fe is an impurity in the raw material.

The Ca mass% (W _Ca %) in the oxygen-containing silicon material of the present invention is preferably a small value. Ca mass% in the oxygen-containing silicon material of the present invention _{(W Ca%)} is preferably satisfies 0 ≦ _{W Ca} <5, more preferably satisfies _{0 ≦ W Ca ≦ 1, 0} ≦ W Ca ≦ It is further preferable to satisfy 0.5, and it is particularly preferable to satisfy 0 ≦ W _Ca ≦ 0.3. In view of easiness of mixing and removal of _Ca , it is assumed that Ca mass% (W _Ca %) in the oxygen-containing silicon material of the present invention is 0 <W _Ca.

The Fe mass% (W 2 _Fe %) in the oxygen-containing silicon material of the present invention is preferably a small value. Fe wt% in the oxygen-containing silicon material of the present invention _{(W Fe%)} is preferably satisfies 0 ≦ _{W Fe} ≦ 3, more preferably satisfies _{0 ≦ W Fe ≦ 1, 0} ≦ W Fe ≦ It is more preferable to satisfy 0.5, particularly preferably to satisfy 0 ≦ W _Fe ≦ 0.3, and most preferably to satisfy 0 ≦ W _Fe ≦ 0.1. In view of easiness of mixing of Fe and difficulty of removal, it is assumed that Fe mass% (W 2 _Fe %) in the Al-containing silicon material of the present invention is 0 <W 2 _Fe .
Moreover, it is preferable that the relationship of Al mass% (W _Al %) and Fe mass% (W _Fe %) satisfies W _Al > W _Fe, and more preferably W _Al > 2 × W _Fe .

From the viewpoint of structure, the oxygen-containing silicon material of the present invention preferably has a structure in which a plurality of plate-like silicon bodies are stacked in the thickness direction. This laminated structure can be confirmed by observation with a scanning electron microscope or the like. Considering using the oxygen-containing silicon material of the present invention as a negative electrode active material of a lithium ion secondary battery, the plate-like silicon body has a thickness of 10 nm for efficient insertion and desorption reaction of lithium ions. Those in the range of ̃100 nm are preferable, and those in the range of 20 nm to 50 nm are more preferable. The length of the plate-like silicon body in the long axis direction is preferably in the range of 0.1 μm to 50 μm. The plate-like silicon body preferably has a (longitudinal direction length) / (thickness) in the range of 2 to 1,000. The layered structure of the plate-like silicon body is considered to be the remnant of the Si layer in CaSi ₂ of the raw material.

The oxygen-containing silicon material of the present invention may contain either or both of amorphous silicon and silicon crystals. The size of the silicon crystal is preferably nano-sized. Specifically, the size of the silicon crystal is preferably in the range of 0.5 nm to 300 nm, more preferably in the range of 1 nm to 100 nm, still more preferably in the range of 1 nm to 50 nm, particularly preferably in the range of 1 nm to 10 nm preferable. In addition, the size of the silicon crystal is calculated from the Scheller equation using the half value width of the diffraction peak of the Si (111) surface of the obtained XRD chart by performing X-ray diffraction measurement (XRD measurement) on the silicon material. Ru.

The ratio of crystal to amorphous in silicon of the oxygen-containing silicon material of the present invention is 0: 100 to 100: 0, 1: 99 to 50: 50, 0: 100 to 30: 70, 5: 95 to 30: The range of 70, 10: 90 to 20: 80 can be exemplified.

The oxygen-containing silicon material of the present invention is preferably in the form of powder, and is preferably an aggregate of particles exhibiting a certain particle size distribution. The average particle diameter of the oxygen-containing silicon material of the present invention is preferably in the range of 0.5 to 30 μm, more preferably in the range of 1 to 20 μm, and still more preferably in the range of 2 to 10 μm. In the present specification, the average particle size means the D ₅₀ as measured by conventional laser diffraction type particle size distribution measuring apparatus.

The BET specific surface area of the oxygen-containing silicon material of the present invention is in the range of 0.5 to 15 m ² / g, in the range of 0.5 to 10 m ² / g, in the range of 1 to 10 m ² / g, 3 to The range of 10 m ² / g can be exemplified.

Next, a method for producing a negative electrode active material containing the oxygen-containing silicon material of the present invention (hereinafter, sometimes simply referred to as “the production method of the present invention”) will be described.
The key to the production method of the present invention is to set the temperature of the reaction solution to 15 to 50 ° C. in the step of reacting CaSi ₂ with an aqueous acid solution to synthesize an oxygen-containing layered silicon compound containing layered polysilane. And controlling the oxygen content in the oxygen-containing layered silicon compound containing layered polysilane and the oxygen-containing silicon material of the present invention.

One aspect of the production method of the present invention is
a-1) A step of synthesizing an oxygen-containing layered silicon compound containing layered polysilane by reacting CaSi ₂ with an aqueous acid solution of 15 to 50 ° C. (hereinafter simply referred to as “a-1) step”. ),
b) A step of synthesizing the oxygen-containing silicon material by heating the oxygen-containing layered silicon compound at 300 ° C. or higher (hereinafter simply referred to as “step b”). And the like.

When an aqueous hydrogen chloride solution (hydrochloric acid) is used as the aqueous acid solution in step a-1), the reaction represented by the following formula (1) proceeds, and then, for example, on the surface of Si ₆ H ₆ which is a layered polysilane: It is considered that the reaction represented by the formula (2) proceeds. Therefore, the step a-1) can be said to be a key step for determining the oxygen content in the oxygen-containing layered silicon compound containing the layered polysilane and the oxygen-containing silicon material of the present invention.
Formula (1) 3CaSi ₂ +6 HCl → Si ₆ H ₆ +3 CaCl ₂
Formula (2) Si ₆ H ₆ + 3H ₂ O → Si ₆ H ₃ (OH) ₃ + 3H ₂ ↑

The temperature in the step a-1) is preferably in the range of 18 to 45 ° C., and more preferably in the range of 20 to 40 ° C. a-1) In order to control the temperature in the step, a thermostat such as a thermostat may be used. The treatment time of step a-1) may be 1 to 50 hours, 5 to 40 hours, or 10 to 30 hours.

Instead of the step a-1), the following steps a-2-1) and a-2-2) may be employed.
a-2-1) A step of reacting CaSi ₂ with an aqueous acid solution at -20 to 10 ° C a-2-2) Subsequent to the step a-2-1), the temperature of the reaction liquid is changed to 15 to 50 ° C to form a layer Process for synthesizing an oxygen-containing layered silicon compound containing polysilane

In the a-2-1) step, the reaction represented by the formula (1) is considered to proceed, and in the a-2-2) step, the reaction represented by the formula (2) is considered to proceed. Therefore, it can be said that the step a-2-2) is a key step for determining the oxygen content in the oxygen-containing layered silicon compound containing the layered polysilane and the oxygen-containing silicon material of the present invention.

Examples of the timing at which the step a-2-1) is switched to the step a-2-2) include a point at which the heat generation resulting from the reaction has taken a break, and a point at which bubbling from the reaction solution has taken a break. In order to switch the a-2-1) step to the a-2-2) step, the temperature-controlled device used in the a-2-1) step may be heated, or it may be used in the a-2-1) step The same thermostat may be replaced with another thermostat which has been previously adjusted to a temperature range of 15 to 50.degree.

The temperature in the step a-2-1) is preferably in the range of -10 to 5 ° C, more preferably in the range of -5 to 5 ° C. As a specific time of the step a-2-1), for example, 10 minutes, 20 minutes, 1 hour or 2 hours, etc. can be exemplified after the completion of mixing of CaSi ₂ and the aqueous acid solution.
The temperature in the step a-2-2) is preferably in the range of 18 to 45 ° C., and more preferably in the range of 20 to 40 ° C. As a specific time of step a-2-2), 1 to 50 hours, 5 to 40 hours, and 10 to 30 hours can be exemplified.

Hereinafter, the process of reacting CaSi ₂ with an aqueous acid solution to synthesize an oxygen-containing layered silicon compound containing layered polysilane may be collectively referred to as a process a).

CaSi ₂ which is a raw material generally has a structure in which a Ca layer and a Si layer are laminated. CaSi ₂ may be synthesized by a known production method, or a commercially available one may be adopted. CaSi ₂ used in step a), previously crushed, it is preferable to powdered.

CaSi ₂ preferably contains Al. The content of Al is preferably less than 4.5%, more preferably in the range of 0.01 to 3%, still more preferably in the range of 0.05 to 2%, and in the range of 0.1 to 1% Is particularly preferred.

As the acid, hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, phosphoric acid, formic acid, acetic acid, methanesulfonic acid, tetrafluoroboric acid, hexafluorophosphoric acid, hexafluoro acid Arsenic acid, fluoroantimonic acid, hexafluorosilicic acid, hexafluorogermanic acid, hexafluorotin (IV) acid, trifluoroacetic acid, hexafluorotitanic acid, hexafluorozirconic acid, trifluoromethanesulfonic acid, fluorosulfonic acid are exemplified. Ru. These acids may be used alone or in combination.

The acid is preferably used in an amount capable of supplying 2 mol or more of protons to 1 mol of CaSi ₂ . The reason for using water as a solvent in step a) is that, from the technical point of view, removal of unnecessary substances such as CaCl ₂ is easy and oxygen is extremely introduced into the layered polysilane produced in step a). It is an easy point.

The concentration of the acid in the aqueous acid solution is preferably 5 to 36% by mass, more preferably 5 to 30% by mass, still more preferably 10 to 30% by mass, particularly preferably 13 to 25% by mass, and 15 to 20% by mass Is most preferred. If the concentration of the acid is too low, the progress of the reaction will be slow and the production efficiency will be reduced. On the other hand, when the concentration of the acid is too high, an element derived from the acid anion is contained in a large amount in the oxygen-containing silicon material of the present invention.

The reaction conditions in the step a) are preferably under an inert gas atmosphere such as nitrogen, helium or argon, and are preferably under stirring conditions.

In order to isolate the oxygen-containing layered silicon compound obtained in the step a), a filtration step, a washing step, and a drying step may be appropriately carried out. In order to control the oxygen content of the oxygen-containing layered silicon compound, it is preferable to carry out these steps under an inert gas atmosphere such as nitrogen, helium or argon.

Next, the step b) will be described. The step b) is a step of heating the oxygen-containing layered silicon compound at 300 ° C. or higher.

From the chemical point of view, the step b) is a step of synthesizing an oxygen-containing silicon material by releasing hydrogen or the like from the oxygen-containing layered silicon compound by heating. The reaction formula when hydrogen is released from the layered polysilane in step b) is as follows.
Si ₆ H ₆ → ₆ Si + 3 H ₂ ↑

The step b) is preferably carried out under a non-oxidizing atmosphere having a lower oxygen content than under normal atmosphere. As the non-oxidizing atmosphere, a reduced pressure atmosphere including vacuum, an inert gas atmosphere such as nitrogen, helium, argon and the like can be exemplified. The heating temperature is preferably in the range of 300 ° C. to 1000 ° C., more preferably in the range of 500 ° C. to 900 ° C., and still more preferably in the range of 600 ° C. to 800 ° C. If the heating temperature is too low, desorption of hydrogen may not be sufficient. On the other hand, if the heating temperature is too high, crystallization of silicon in the oxygen-containing silicon material may proceed excessively, which may lead to a decrease in performance as a negative electrode active material. The heating time may be appropriately set in accordance with the heating temperature, and it is also preferable to determine the heating time while measuring the amount of hydrogen and the like which leaks out of the reaction system. By appropriately selecting the heating temperature and the heating time, the ratio of amorphous silicon and silicon crystals contained in the oxygen-containing silicon material to be produced, and the size of silicon crystals can also be prepared, and further, it is produced It is also possible to adjust the shape and size of a nano-level thick layer including amorphous silicon and silicon crystals contained in the oxygen-containing silicon material.

The oxygen-containing silicon material of the present invention may be pulverized or classified into particles having a constant particle size distribution.

As already stated, the oxygen-containing silicon material of the present invention can be used as a negative electrode active material of a secondary battery such as a lithium ion secondary battery. At that time, it is preferable to use the oxygen-containing silicon material of the present invention coated with carbon. This is because the carbon coating improves the conductivity.
As a method of carbon coating, a mechanical milling method in which a mixture of oxygen-containing silicon material and carbon powder is subjected to strong pressure and then stirred and integrated, or carbon generated from a carbon source is vapor-deposited onto the oxygen-containing silicon material Can be exemplified by chemical vapor deposition (CVD).

The CVD method is preferable as a carbon coating method in that the surface of the oxygen-containing silicon material can be uniformly coated with a thin carbon layer. Then, among the CVD methods, a thermal CVD method in which a gaseous organic substance which is a carbon source is decomposed by heat to generate carbon is preferable.

The carbon mass% (W _C %) in the carbon-coated oxygen-containing silicon material of the present invention preferably satisfies 1 ≦ W _C ≦ 10, more preferably 3 ≦ W _C ≦ 9, and 5 It is further preferable to satisfy ≦ W _c ≦ 8. As for the content of elements other than carbon in the carbon-coated oxygen-containing silicon material of the present invention, the numerical range described for the oxygen-containing silicon material of the present invention is incorporated.

Hereinafter, a secondary battery including the oxygen-containing silicon material of the present invention as a negative electrode active material will be described by taking a lithium ion secondary battery as an example. Hereinafter, a lithium ion secondary battery including the oxygen-containing silicon material of the present invention as a negative electrode active material is referred to as a lithium ion secondary battery of the present invention. Specifically, the lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode including the oxygen-containing silicon material of the present invention as a negative electrode active material, an electrolytic solution, and a separator as necessary.

The positive electrode has a current collector and a positive electrode active material layer bonded to the surface of the current collector.

The current collector refers to a chemically inert electron conductor for keeping current flowing to the electrode during discharge or charge of the lithium ion secondary battery. As the current collector, at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, stainless steel, etc. A metal material can be illustrated. The current collector may be coated with a known protective layer. What processed the surface of a collector by a well-known method may be used as a collector.

The current collector can take the form of a foil, a sheet, a film, a line, a rod, a mesh or the like. Therefore, as the current collector, for example, metal foils such as copper foil, nickel foil, aluminum foil, and stainless steel foil can be suitably used. When the current collector is in the form of a foil, a sheet or a film, the thickness is preferably in the range of 1 μm to 100 μm.

The positive electrode active material layer contains a positive electrode active material and, if necessary, a conductive aid and / or a binder.

As the positive electrode active material, a layered compound _{Li a Ni b Co c Mn d} D e O f (0.2 ≦ a ≦ 2, b + c + d + e = 1,0 ≦ e <1, D is Li, Fe, Cr, Cu, At least one element selected from Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 3 ), Li _a Ni _b Co _c Al _{d DeO f} (0.2 ≦ a ≦ 2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, Zn, Ca, Mg, S , At least one element selected from Si, Na, K, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 3), Li ₂ MnO ₃ Can. In addition, as a positive electrode active material, spinel such as LiMn ₂ O ₄ and a solid solution composed of a mixture of spinel and layered compound, LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ (M in the formula is Co, Ni, Mn, Polyanionic compounds represented by (at least one of Fe) and the like can be mentioned. Furthermore, as the positive electrode active material, tavorite compound (the M a transition metal) LiMPO ₄ F, such as LiFePO ₄ F represented by, Limbo ₃ such LiFeBO ₃ (M is a transition metal) include borate-based compound represented by be able to. Any metal oxide used as a positive electrode active material may have the above composition formula as a basic composition, and one obtained by replacing the metal element contained in the basic composition with another metal element can also be used. In addition, as a positive electrode active material, a positive electrode active material containing no lithium ion contributing to charge and discharge, for example, a simple substance of sulfur, a compound of sulfur and carbon, a metal sulfide such as TiS ₂ , V ₂ O ₅ , MnO Oxides such as ₂ , polyaniline and anthraquinone, and compounds containing these aromatics in the chemical structure, conjugated materials such as conjugated diacetic acid organic substances, and other known materials can also be used. Furthermore, a compound having a stable radical such as nitroxide, nitronyl nitroxide, galvinoxyl, phenoxyl or the like may be adopted as the positive electrode active material. In the case of using a positive electrode active material containing no lithium, it is necessary to add ions to the positive electrode and / or the negative electrode by a known method. Here, in order to add the ions, a metal or a compound containing the ions may be used.

A conductive aid is added to enhance the conductivity of the electrode. Therefore, the conductive additive may be optionally added when the conductivity of the electrode is insufficient, and may not be added when the conductivity of the electrode is sufficiently excellent. The conductive support agent may be any chemically active high electron conductor, and carbon black fine particles such as carbon black, graphite, vapor grown carbon fiber, and various metal particles are exemplified. Ru. Examples of the carbon black include acetylene black, ketjen black (registered trademark), furnace black, channel black and the like. These conductive assistants can be added to the active material layer singly or in combination of two or more.

The compounding ratio of the conductive aid in the active material layer is, in mass ratio, preferably active material: conductive aid = 1: 0.005 to 1: 0.5, 1: 0.01 to 1: 0 The ratio is more preferably 0.2, and more preferably 1: 0.02 to 1: 0.15. If the amount of the conductive additive is too small, efficient conductive paths can not be formed. If the amount of the conductive additive is too large, the formability of the active material layer deteriorates and the energy density of the electrode decreases.

The binder plays the role of anchoring the active material and the conductive aid to the surface of the current collector and maintaining the conductive network in the electrode. The binder may, for example, be a fluorine-containing resin such as polyvinylidene fluoride, polytetrafluoroethylene or fluororubber, a thermoplastic resin such as polypropylene or polyethylene, an imide resin such as polyimide or polyamideimide, an alkoxysilyl group-containing resin, Examples include acrylic resins such as meta) acrylic acid, styrene-butadiene rubber (SBR), and carboxymethyl cellulose. These binders may be used alone or in combination.

The blending ratio of the binder in the active material layer is, in mass ratio, preferably active material: binder = 1: 0.05 to 1: 0.3, 1: 0.01 to 1: 0 The ratio is more preferably 0.2, and more preferably 1: 0.02 to 1: 0.15. When the amount of the binder is too small, the formability of the electrode decreases, and when the amount of the binder is too large, the energy density of the electrode decreases.

The negative electrode includes a current collector and a negative electrode active material layer bonded to the surface of the current collector. As the current collector, one described for the positive electrode may be appropriately adopted appropriately. The negative electrode active material layer contains a negative electrode active material and, if necessary, a conductive aid and / or a binder.

As the negative electrode active material, any material containing the oxygen-containing silicon material of the present invention may be used, and only the oxygen-containing silicon material of the present invention may be adopted, and the oxygen-containing silicon material of the present invention and the known negative electrode active material You may use together.

As the conductive auxiliary and the binder used for the negative electrode, those described for the positive electrode may be appropriately adopted at the same mixing ratio.

In addition, a crosslinked polymer in which a carboxyl group-containing polymer such as polyacrylic acid or polymethacrylic acid as disclosed in WO 2016/063882 is crosslinked with a polyamine such as diamine may be used as a binder.

Examples of the diamine used for the cross-linked polymer include alkylene diamines such as ethylene diamine, propylene diamine and hexamethylene diamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, isophorone diamine, bis (4-aminocyclohexyl) methane and the like. Saturated carbocyclic ring diamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylether, bis (4-aminophenyl) sulfone, benzidine, o-tolidine, 2,4- Aromatic diamines such as tolylene diamine, 2,6-tolylene diamine, xylylene diamine and naphthalene diamine can be mentioned.

In order to form an active material layer on the surface of a current collector, current collection can be performed using conventionally known methods such as roll coating, die coating, dip coating, doctor blade method, spray coating, and curtain coating. The active material may be applied to the surface of the body. Specifically, the active material, the solvent, and, if necessary, the binder and / or the conductive auxiliary agent are mixed to prepare a slurry. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone and water. The slurry is applied to the surface of a current collector and then dried. The dried one may be compressed to increase the electrode density.

The electrolytic solution contains a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent.

As the non-aqueous solvent, cyclic carbonate, cyclic ester, chain carbonate, chain ester, ethers and the like can be used. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate. Examples of cyclic esters include gamma butyrolactone, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain carbonates include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, and ethyl methyl carbonate. Examples of chain esters include propionic acid alkyl ester, malonic acid dialkyl ester, acetic acid alkyl ester and the like. As the ethers, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane can be exemplified. As the non-aqueous solvent, a compound in which part or all of hydrogens in the chemical structure of the above specific solvent is substituted with fluorine may be adopted.

Examples of the electrolyte include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ and LiN (FSO ₂ ) ₂ .

As electrolyte solution, 0.5 to 3.5 mol of lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiN (FSO ₂ ) ₂ and the like in nonaqueous solvents such as ethylene carbonate, dimethyl carbonate, propylene carbonate, diethyl carbonate and the like A solution dissolved at a concentration of 1 / L, 1 to 3 mol / L, or 1.6 to 2.5 mol / L can be exemplified.

The separator separates the positive electrode and the negative electrode, and allows lithium ions to pass while preventing a short circuit due to the contact of the both electrodes. As a separator, synthetic resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polyamide), polyester, polyacrylonitrile, etc., polysaccharides such as cellulose and amylose, natural substances such as fibroin, keratin, lignin and suberin Examples thereof include porous bodies, non-woven fabrics, and woven fabrics using one or more kinds of electrically insulating materials such as polymers and ceramics. In addition, the separator may have a multilayer structure.

Next, a method of manufacturing a lithium ion secondary battery of the present invention using a positive electrode, a negative electrode and an electrolytic solution will be described.

For example, the positive electrode and the negative electrode sandwich a separator to form an electrode body. The electrode body may be any of a laminated type in which a positive electrode, a separator and a negative electrode are stacked, or a wound type in which a laminate of a positive electrode, a separator and a negative electrode is wound. After connecting the current collector of the positive electrode and the current collector of the negative electrode to the positive electrode terminal and the negative electrode terminal leading to the outside using a current collection lead or the like, an electrolytic solution is added to the electrode body to form a lithium ion secondary battery. Good.

The shape of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as cylindrical, square, coin, and laminate types can be adopted.

The lithium ion secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle using electric energy from a lithium ion secondary battery for all or part of its power source, and may be, for example, an electric vehicle, a hybrid vehicle, or the like. When a lithium ion secondary battery is mounted on a vehicle, a plurality of lithium ion secondary batteries may be connected in series to form a battery pack. As an apparatus which mounts a lithium ion secondary battery, various household appliances driven by a battery, such as a personal computer and a mobile communication apparatus, as well as a vehicle, an office apparatus, an industrial apparatus and the like can be mentioned. Furthermore, the lithium ion secondary battery of the present invention can be used in wind power generation, solar power generation, hydroelectric power generation, storage devices and power smoothing devices for electric power systems, power sources for power and / or accessories of ships, etc., aircraft, Power supply source for power of spacecraft and / or accessories, auxiliary power supply for vehicles not using electricity as power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, You may use for the electrical storage apparatus which stores temporarily the electric power required for charge in the charge station etc. for electric vehicles.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. In the range which does not deviate from the summary of the present invention, it can carry out with various forms which gave change, improvement, etc. which a person skilled in the art can make.

Hereinafter, the present invention will be described more specifically by showing Examples and Comparative Examples. The present invention is not limited by these examples.

Example 1
a) Step a-1) Step CaSi ₂ powder containing Fe as an impurity was prepared.
The reaction vessel containing 35 mass% hydrochloric acid was placed in a thermostat at 18 ° C. After confirming that the temperature of hydrochloric acid had reached 18 ° C., the above CaSi ₂ powder was gradually introduced into the hydrochloric acid under a nitrogen gas atmosphere and under stirring conditions. Stirring was continued for 2 hours after the addition of the CaSi ₂ powder, and then the reaction solution was filtered. The residue was washed with distilled water and then with methanol and dried under reduced pressure to obtain the oxygen-containing layered silicon compound of Example 1.

b) Step The oxygen-containing layered silicon compound of Example 1 was heated at 900 ° C. for 1 hour in a nitrogen gas atmosphere to obtain an oxygen-containing silicon material. This was used as the oxygen-containing silicon material of Example 1.

The negative electrode and the lithium ion secondary battery of Example 1 were produced as follows.

A polyacrylic acid having a weight average molecular weight of 800,000 was dissolved in N-methyl-2-pyrrolidone to prepare a polyacrylic acid solution containing 10% by mass of polyacrylic acid. In addition, a solution of 4,4'-diaminodiphenylmethane was prepared by dissolving 0.2 g (1.0 mmol) of 4,4'-diaminodiphenylmethane in 0.4 mL of N-methyl-2-pyrrolidone. Under stirring conditions, the entire amount of 4,4'-diaminodiphenylmethane solution is added dropwise to 7 mL of a polyacrylic acid solution (corresponding to 9.5 mmol in terms of acrylic acid monomer), and the resulting mixture is allowed to stand at room temperature for 30 minutes. It stirred. Then, using a Dean-Stark apparatus, the mixture was stirred at 130 ° C. for 3 hours to allow the dehydration reaction to proceed, thereby producing a binder solution.

72.5 parts by mass of the oxygen-containing silicon material of Example 1 as a negative electrode active material, 13.5 parts by mass of acetylene black as a conduction aid, and 14 parts by mass of solid content as a binder And, an appropriate amount of N-methyl-2-pyrrolidone was mixed to prepare a slurry. A copper foil was prepared as a current collector for the negative electrode. The slurry was applied in the form of a film on the surface of the copper foil using a doctor blade. The copper foil coated with the slurry was dried to remove N-methyl-2-pyrrolidone. Thereafter, the resultant was pressed and baked at 180 ° C. to produce the negative electrode of Example 1 in which the negative electrode active material layer was formed.

A solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L was used as an electrolytic solution in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1.

The negative electrode was cut to a diameter of 11 mm and used as an evaluation electrode. A metal lithium foil having a thickness of 500 μm was cut to a diameter of 13 mm and used as a counter electrode. A glass filter (Hoechst Celanese) and celgard 2400 (Polypore Co., Ltd.) which is a single-layer polypropylene were prepared as a separator. The two types of separators were sandwiched between the counter electrode and the evaluation electrode in the order of the counter electrode, the glass filter, celgard 2400, and the evaluation electrode to form an electrode body. The electrode body was housed in a coin-type battery case CR2032 (Hohsen Co., Ltd.). The electrolytic solution was injected into the battery case, and the battery case was sealed to manufacture the lithium ion secondary battery of Example 1.

(Example 2)
The oxygen-containing layered silicon compound, the oxygen-containing silicon material, the negative electrode, and the lithium ion secondary battery of Example 2 are the same as in Example 1 except that in the step a), the temperature of the constant temperature bath is 40 ° C. Manufactured.

(Comparative example 1)
The oxygen-containing layered silicon compound, the oxygen-containing silicon material, the negative electrode, and the lithium ion secondary battery of Comparative Example 1 are prepared in the same manner as in Example 1 except that the temperature of the constant temperature bath is set to 0 ° C. in step a). Manufactured.

(Comparative example 2)
The oxygen-containing layered silicon compound, the oxygen-containing silicon material, the negative electrode, and the lithium ion secondary battery of Comparative Example 2 are the same as in Example 1 except that in the step a), the temperature of the constant temperature bath is 60 ° C. Manufactured.

(Evaluation example 1)
Elemental analysis of Si, Cl, Fe and Ca with respect to the oxygen-containing silicon materials of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 using a fluorescent X-ray analyzer (XRF) went. In addition, with respect to the oxygen-containing silicon materials of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 using an oxygen-nitrogen-hydrogen analyzer (inert gas melting method), an element targeted for oxygen Analysis was carried out.
The results of these elemental analyzes are shown in Table 1 as mass%. It can be seen from Table 1 that as the temperature of the process a) increases, the silicon content decreases and the oxygen content increases.

(Evaluation example 2)
The lithium ion secondary batteries of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 are charged to 0.01 V at a current of 0.2 mA, and then discharged to 1.0 V at a current of 0.2 mA. The initial charge and discharge was performed.
Furthermore, the lithium ion secondary batteries of Example 1 and Example 2 and Comparative Examples 1 and 2 after the initial charge and discharge are charged to 0.01 V at a current of 0.5 mA, and then at a current of 0.5 mA. The charge and discharge cycle of discharging to 1.0 V was performed 50 times.

The initial efficiency and capacity retention rate were calculated by the following formulas.
Initial efficiency (%) = 100 × (initial discharge capacity) / (initial charge capacity)
Capacity retention rate (%) = 100 × (discharge capacity at 50 cycles) / (discharge capacity at 1 cycle)
The results of the initial efficiency and capacity retention are shown in Table 2 along with some of the elemental analysis results. Further, FIG. 1 shows the relationship between the integrated capacity and the discharge capacity of each lithium ion secondary battery in 50 charge and discharge cycles.

From the results of the initial efficiency in Table 2, it can be seen that the value of the initial efficiency in the lithium ion secondary battery of Comparative Example 2 is extremely low. It can be said that the oxygen-containing silicon material having a high silicon mass% and a low oxygen mass% is superior to the oxygen-containing silicon material of Comparative Example 2 in the initial efficiency. From the viewpoint of production conditions, it can be said that the temperature of the step a) is less than 60 ° C., which is a suitable condition for producing an oxygen-containing silicon material excellent in initial efficiency.

From the results of the capacity retention rates in Table 2, it can be seen that the value of the capacity retention rate in the lithium ion secondary battery of Comparative Example 1 is extremely low. From the results of elemental analysis in Table 2, it is considered that there is a significant difference in capacity retention rate between the oxygen-containing silicon material whose oxygen mass% is 16% or less and the oxygen-containing silicon material whose oxygen mass% exceeds 16%.
From the viewpoint of production conditions, it can be said that the temperature of the step a) is more than 0 ° C., which is advantageous for the introduction of oxygen, and a condition for producing an oxygen-containing silicon material excellent in capacity retention.

Further, it is understood from the graph of FIG. 1 showing the relationship between the cumulative capacity and the discharge capacity of each lithium ion secondary battery that the oxygen-containing silicon materials of Example 1 and Example 2 are particularly excellent negative electrode active materials. .

(Evaluation example 3)
The BET specific surface areas of the oxygen-containing silicon materials of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were measured.
In addition, Raman spectroscopy of each oxygen-containing silicon material was measured by a Raman spectroscopy apparatus. In each Raman spectrum, a peak derived from silicon crystal was observed at around 520 cm ^-1 and a peak derived from amorphous silicon was observed at around 480 cm ^-1 . The sample which mixed amorphous silicon and a silicon crystal by weight ratio 1: 1 was measured, and the ratio of the silicon crystal and the amorphous silicon was computed from the intensity ratio of each peak on the basis of the measurement result of the sample concerned.
The above results are shown in Table 3.

From Table 3, the BET specific surface area of the oxygen-containing silicon material tends to increase as the temperature in the step a) rises, but it can be said that it becomes substantially constant at 40 ° C. or higher. The proportions of silicon crystals and amorphous silicon in the oxygen-containing silicon material are considered to have no correlation with the temperature in the step a).

(Example 3)
An Al-containing CaSi ₂ powder was prepared as follows.
Ca, Al and Si were weighed in a carbon crucible. The elemental composition ratio of Ca and Si was 1: 2, and the amount of Al added was 1% with respect to the total mass of Ca, Al and Si. A carbon crucible was heated at around 1300 ° C. in a high frequency induction heating apparatus under an argon gas atmosphere to obtain a molten metal containing Ca, Al and Si. The molten metal is poured into a predetermined mold to cool and solidify. The solid was crushed into CaSi ₂ powder and then subjected to a) step.

a) Process a-2-1) Process A reaction vessel containing 18 mass% hydrochloric acid was placed in a thermostat at 0 ° C. After confirming that the temperature of the hydrochloric acid reached 0 ° C., the CaSi ₂ powder was gradually introduced into the hydrochloric acid under a nitrogen gas atmosphere and under stirring conditions. Stirring was continued for 15 minutes after the addition of the CaSi ₂ powder.
a-2-2) Step After the step a-2-1), the temperature of the thermostat was raised to 20 ° C. at a rate of 1 ° C./min, and the reaction solution was stirred overnight. Thereafter, the reaction solution was filtered. The residue was washed with distilled water and then with methanol and dried under reduced pressure to obtain the oxygen-containing layered silicon compound of Example 3.

b) Step The oxygen-containing layered silicon compound of Example 3 was heated at 900 ° C. for 1 hour in a nitrogen gas atmosphere to obtain an oxygen-containing silicon material. This was used as the oxygen-containing silicon material of Example 3.

Thereafter, in the same manner as in Example 1, a negative electrode and a lithium ion secondary battery of Example 3 were produced.

(Example 4)
The oxygen-containing layered silicon compound of Example 4, oxygen-containing in the same manner as in Example 3 except that in the step a-2-2) the temperature of the thermostatic chamber was raised to 30 ° C. at a rate of 1 ° C./min. A silicon material, a negative electrode and a lithium ion secondary battery were manufactured.

(Example 5)
The oxygen-containing layered silicon compound of Example 5, oxygen-containing in the same manner as in Example 3 except that in the step a-2-2) the temperature of the thermostatic chamber was raised to 40 ° C. at a rate of 1 ° C./min. A silicon material, a negative electrode and a lithium ion secondary battery were manufactured.

(Example 6)
The oxygen-containing layered silicon compound, the oxygen-containing silicon material, the negative electrode, and the lithium ion secondary battery of Example 6 were manufactured in the same manner as in Example 3 except that the process a) was performed as follows.
a-1) Step A reaction vessel containing 18 mass% hydrochloric acid was placed in a thermostat at 20 ° C. After confirming that the temperature of the hydrochloric acid reached 20 ° C., the CaSi ₂ powder was gradually added to the hydrochloric acid under a nitrogen gas atmosphere and under stirring conditions. After charging of the CaSi ₂ powder, the reaction solution was stirred overnight. Thereafter, the reaction solution was filtered. The residue was washed with distilled water and then with methanol and dried under reduced pressure to obtain the oxygen-containing layered silicon compound of Example 6.

(Comparative example 3)
In the step a-2-2), the oxygen-containing layered silicon compound of Comparative Example 3 and the oxygen-containing silicon material in the same manner as in Example 3 except that the constant temperature bath is not heated and maintained at 0 ° C. Negative electrodes and lithium ion secondary batteries were manufactured.

(Comparative example 4)
Oxygen-containing layered silicon compound of Comparative Example 4 in the same manner as in Example 3 except that in the step a-2-2) the temperature of the thermostatic chamber was raised to 60 ° C. at a rate of 1 ° C./min A silicon material, a negative electrode and a lithium ion secondary battery were manufactured.

(Evaluation example 4)
Elemental analysis was performed on the oxygen-containing silicon materials of Examples 3 to 6 and Comparative Examples 3 to 4 in the same manner as in Evaluation Example 1. The results of these elemental analyzes are shown in Table 4 as mass%.

From the results in Table 4, it can be seen that as the reaction temperature in the step a-2-2) increases, the oxygen content increases. a-2-2) It is considered that the reaction rate of the following formula (2) can be controlled by controlling the temperature of the step.
Formula (2) Si ₆ H ₆ + 3H ₂ O → Si ₆ H ₃ (OH) ₃ + 3H ₂ ↑

Further, in comparison with the oxygen-containing silicon material of Example 1 using 35 mass% hydrochloric acid, Cl in the oxygen-containing silicon materials of Examples 3 to 5 and Comparative Examples 3 to 4 using 18 mass% hydrochloric acid It can be seen that the content is very low.

(Evaluation example 5)
The lithium ion secondary batteries of Examples 3 to 6 and Comparative Examples 3 to 4 are charged to 0.01 V at a current of 0.2 mA, and then discharged to 1.0 V at a current of 0.2 mA. The initial charge and discharge was performed.
Furthermore, the lithium ion secondary batteries of Example 3 to Example 5 and Comparative Example 3 to Comparative Example 4 after the initial charge and discharge are charged to 0.01 V at a current of 0.5 mA, and then at a current of 0.5 mA. The charge and discharge cycle of discharging to 1.0 V was performed 50 times.

The initial efficiency and capacity retention rate were calculated by the following formulas.
Initial efficiency (%) = 100 × (initial discharge capacity) / (initial charge capacity)
Capacity retention rate (%) = 100 × (discharge capacity at 50 cycles) / (discharge capacity at 1 cycle)
The results of the initial charge capacity, the initial discharge capacity, the initial efficiency, and the capacity retention rate are shown in Tables 5 and 6 together with part of the results of the elemental analysis.

From the results of Tables 5 and 6, it is understood that the values of the initial charge capacity, the initial discharge capacity and the initial efficiency of Comparative Example 4 in which the temperature in the step a-2-2) is 60 ° C. are extremely low. The result is that the reaction of the formula (2), which is an oxygen introduction reaction, excessively proceeds because the temperature of the step a-2-2) is 60 ° C., and the oxygen content in the oxygen-containing silicon material is It can be said that what was too high was reflected.
Further, from the results in Table 6, it is understood that the value of the capacity retention rate of Comparative Example 3 in which the temperature in the step a-2-2) is 0 ° C. is extremely low. This result indicates that the reaction of formula (2), which is an oxygen introduction reaction, became slow because the temperature of the step a-2-2) was 0 ° C., and the silicon content in the oxygen-containing silicon material is It can be said that what was too high was reflected.

From Tables 5 and 6, the temperature at the time of CaSi ₂ powder introduction is 0 ° C., and then the temperature at the time of CaSi ₂ powder introduction is 20 ° C., and the temperature at 20 ° C. is 20 ° C. It can be said that Example 6 maintained shows equivalent results in terms of battery characteristics. From the viewpoint of safety in terms of work, it is reasonable to adopt a production method in which the reaction is allowed to proceed under low temperature conditions and the temperature is gradually raised when CaSi ₂ powder in which a relatively vigorous reaction occurs is caused .

(Example 7)
An Al-containing CaSi ₂ powder was prepared as follows.
Ca, Al and Si were weighed in a carbon crucible. The elemental composition ratio of Ca and Si was 1: 2, and the amount of Al added was 1% with respect to the total mass of Ca, Al and Si. A carbon crucible was heated at around 1300 ° C. in a high frequency induction heating apparatus under an argon gas atmosphere to obtain a molten metal containing Ca, Al and Si. The molten metal is poured into a predetermined mold to cool and solidify. The solid was crushed into CaSi ₂ powder and then subjected to a) step.

a) Process a-2-1) Process A reaction vessel containing 18 mass% hydrochloric acid was placed in a thermostat at 0 ° C. After confirming that the temperature of the hydrochloric acid reached 0 ° C., the CaSi ₂ powder was gradually introduced into the hydrochloric acid under a nitrogen gas atmosphere and under stirring conditions. Stirring was continued for 15 minutes after the addition of the CaSi ₂ powder.

a-2-2) Step After the step a-2-1), the temperature of the thermostat was raised to 20 ° C. at a rate of 1 ° C./min, and the reaction solution was stirred overnight. Thereafter, the reaction solution was filtered. The residue was washed with distilled water and then with methanol and dried under reduced pressure to obtain the oxygen-containing layered silicon compound of Example 7.

b) Step The oxygen-containing layered silicon compound of Example 7 was heated at 900 ° C. for 1 hour in a nitrogen gas atmosphere to obtain an oxygen-containing silicon material. The oxygen-containing silicon material was pulverized using a jet mill to obtain a powder having an average particle size of 5 μm.
This powder was used as the oxygen-containing silicon material of Example 7.

Carbon Coating Step The oxygen-containing silicon material of Example 7 was placed in a rotary kiln type reactor, and thermal CVD was performed at 880 ° C. for 60 minutes under aeration of propane-argon mixed gas, and carbon coated. An oxygen-containing silicon material was obtained. This was used as the carbon-coated oxygen-containing silicon material of Example 7.

The negative electrode and lithium ion secondary battery of Example 7 were produced as follows.

A polyacrylic acid having a weight average molecular weight of 800,000 was dissolved in N-methyl-2-pyrrolidone to prepare a polyacrylic acid solution containing 10% by mass of polyacrylic acid. In addition, a solution of 4,4'-diaminodiphenylmethane was prepared by dissolving 0.2 g (1.0 mmol) of 4,4'-diaminodiphenylmethane in 0.4 mL of N-methyl-2-pyrrolidone. Under stirring conditions, the entire amount of 4,4'-diaminodiphenylmethane solution is added dropwise to 7 mL of a polyacrylic acid solution (corresponding to 9.5 mmol in terms of acrylic acid monomer), and the resulting mixture is allowed to stand at room temperature for 30 minutes. It stirred. Then, using a Dean-Stark apparatus, the mixture was stirred at 130 ° C. for 3 hours to allow the dehydration reaction to proceed, thereby producing a binder solution.

78.5 parts by mass of the carbon-coated silicon material of Example 7 as a negative electrode active material, 10.5 parts by mass of acetylene black as a conductive additive, and the above-mentioned binding in an amount such that the solid content is 11 parts by mass as a binder The slurry was prepared by mixing the agent solution and an appropriate amount of N-methyl-2-pyrrolidone. A copper foil was prepared as a current collector for the negative electrode. The slurry was applied in the form of a film on the surface of the copper foil using a doctor blade. The copper foil coated with the slurry was dried to remove N-methyl-2-pyrrolidone. Thereafter, pressing and baking at 180 ° C. were performed to manufacture the negative electrode of Example 7 in which the negative electrode active material layer was formed.

96 parts by mass of LiNi _82/100 Co _14/100 Al _4/100 O ₂ as a positive electrode active material, 2 parts by mass of acetylene black as a conduction aid, 2 parts by mass of polyvinylidene fluoride as a binder, and an appropriate amount of N-methyl The -2-pyrrolidone was mixed to produce a slurry. An aluminum foil was prepared as a positive electrode current collector. The slurry was applied in the form of a film on the surface of the aluminum foil using a doctor blade. The N-methyl-2-pyrrolidone was removed by drying the aluminum foil to which the slurry was applied. Thereafter, pressing and baking at 120 ° C. were performed to manufacture a positive electrode in which a positive electrode active material layer was formed on the surface of the positive electrode current collector.

Dimethyl carbonate, ethyl methyl carbonate and fluoroethylene carbonate were mixed at a volume ratio of 63:27:10 to give a mixed organic solvent. LiPF ₆ was dissolved in a mixed organic solvent at a concentration of 2 mol / L to form an electrolyte.

A porous membrane made of polyethylene was prepared as a separator.

The separator was sandwiched between the positive electrode and the negative electrode of Example 7 to form an electrode plate group. The electrode plate group was covered with a pair of laminate films, the three sides were sealed, and then an electrolytic solution was injected into the bag-like laminate film. By sealing the remaining one side, the four sides were airtightly sealed to obtain a lithium ion secondary battery in which the electrode plate group and the electrolytic solution were sealed. This battery was used as a lithium ion secondary battery of Example 7.

(Example 8)
The oxygen-containing layered silicon compound of Example 8, oxygen-containing in the same manner as in Example 7 except that in the step a-2-2) the temperature of the thermostatic chamber was raised to 40 ° C. at a rate of 1 ° C./min. Silicon materials, carbon coated-oxygen containing silicon materials, negative electrodes and lithium ion secondary batteries were manufactured.

(Comparative example 5)
In the step a-2-2), the oxygen-containing layered silicon compound of Comparative Example 5, the oxygen-containing silicon material, and the method of Comparative Example 5 are carried out in the same manner as in Example 7 except that Carbon coated-oxygen containing silicon materials, negative electrodes and lithium ion secondary batteries were manufactured.

(Comparative example 6)
Oxygen-containing layered silicon compound of Comparative Example 6 in the same manner as in Example 7 except that in the step a-2-2), the temperature of the thermostatic chamber was raised to 60 ° C. at a rate of 1 ° C./min. Silicon materials, carbon coated-oxygen containing silicon materials, negative electrodes and lithium ion secondary batteries were manufactured.

(Comparative example 7)
The negative electrode of Comparative Example 7 and lithium ion in the same manner as in Example 7 except that carbon-coated SiO (Shin-Etsu Chemical Co., Ltd.), which is a carbon-coated, oxygen-containing silicon material, was employed as the negative electrode active material. The following battery was manufactured.

(Evaluation example 6)
Elemental analysis was performed on the carbon-coated oxygen-containing silicon materials of Examples 7 to 8 and Comparative Examples 5 to 7 in the same manner as in Evaluation Example 1. However, elemental analysis for carbon was performed using a carbon / sulfur analyzer.
The results of these elemental analyzes are shown in Table 7 as mass%.

(Evaluation example 7)
The lithium ion secondary batteries of Examples 7 to 8 and Comparative Examples 5 to 7 are charged to a voltage of 4.28 V under conditions of 25 ° C., and then discharged to a voltage of 3 V, The initial discharge capacity was measured.
In addition, with respect to each lithium ion secondary battery adjusted to SOC 15%, a voltage was measured in the case of discharging at constant current for 10 seconds under the condition of 25 ° C. The measurements were performed under multiple conditions of varying current. From the obtained results, a constant current (mA) at which the discharge time up to a voltage of 2.5 V is 10 seconds was calculated for each lithium ion secondary battery of SOC 15%, and 2.5 V was multiplied by the current value. The value was set to 25 ° C. for 10 seconds output (mW).
Furthermore, with respect to each lithium ion secondary battery adjusted to SOC 15%, the voltage in the case of discharging at constant current for 5 seconds under the condition of 0 ° C. was measured. The measurements were performed under multiple conditions of varying current. From the obtained results, a constant current (mA) at which the discharge time up to a voltage of 2.5 V is 5 seconds was calculated for each lithium ion secondary battery of SOC 15%, and 2.5 V was multiplied by the current value. The value is 0 ° C. for 5 seconds output.
The above results are shown in Table 8.

From Table 8, it can be seen that Comparative Example 6 and Comparative Example 7 having a high oxygen content have low initial discharge capacity. It can be said that Example 7 and Example 8 in which the oxygen content and the silicon content are in appropriate ranges are all excellent in the initial discharge capacity, the 25 ° C. output and the 0 ° C. output.
Further, from the results of Comparative Example 6 and Comparative Example 7 in which the oxygen content and the silicon content are equal, it is understood that the lithium ion secondary battery of Comparative Example 6 is more excellent in battery characteristics. An oxygen-containing silicon material based on CaSi ₂ has a unique structure in which a plurality of plate-like silicon bodies are stacked in the thickness direction, which is not observed in general SiO. The reason why the lithium ion secondary battery of Comparative Example 6 is superior in output characteristics when Comparative Example 6 and Comparative Example 7 are compared is that a plurality of plate shapes possessed by the oxygen-containing silicon material of Comparative Example 6 It is considered that the silicon body is in the structure of being stacked in the thickness direction.

(Example 9)
An Al-containing CaSi ₂ powder was prepared as follows.
Ca, Al and Si were weighed in a carbon crucible. The elemental composition ratio of Ca and Si was 1: 2, and the amount of Al added was 1% with respect to the total mass of Ca, Al and Si. A carbon crucible was heated at around 1300 ° C. in a high frequency induction heating apparatus under an argon gas atmosphere to obtain a molten metal containing Ca, Al and Si. The molten metal is poured into a predetermined mold to cool and solidify. The solid was crushed into CaSi ₂ powder and then subjected to a) step.

a) Process a-2-1) Process A reaction vessel containing 18 mass% hydrochloric acid was placed in a thermostat at 0 ° C. After confirming that the temperature of the hydrochloric acid reached 0 ° C., the CaSi ₂ powder was gradually introduced into the hydrochloric acid under a nitrogen gas atmosphere and under stirring conditions. Stirring was continued for 15 minutes after the addition of the CaSi ₂ powder.

a-2-2) Step After the step a-2-1), the temperature of the thermostat was raised to 20 ° C. at a rate of 1 ° C./min, and the reaction solution was stirred overnight. Thereafter, the reaction solution was filtered. The residue was washed with distilled water and then with methanol and dried under reduced pressure to obtain the oxygen-containing layered silicon compound of Example 9.

b) Step The oxygen-containing layered silicon compound of Example 9 was heated at 900 ° C. for 1 hour in a nitrogen gas atmosphere to obtain an oxygen-containing silicon material. The oxygen-containing silicon material was pulverized using a jet mill to obtain a powder having an average particle size of 5 μm.
This powder was used as the oxygen-containing silicon material of Example 9.

Carbon Coating Step The oxygen-containing silicon material of Example 9 was placed in a rotary kiln type reactor, and thermal CVD was performed at 880 ° C. and a residence time of 60 minutes under aeration of a propane-argon mixed gas, and carbon coated. An oxygen-containing silicon material was obtained. This was used as the carbon-coated oxygen-containing silicon material of Example 9.

The negative electrode and lithium ion secondary battery of Example 9 were produced as follows.

A polyacrylic acid having a weight average molecular weight of 800,000 was dissolved in N-methyl-2-pyrrolidone to prepare a polyacrylic acid solution containing 10% by mass of polyacrylic acid. In addition, a solution of 4,4'-diaminodiphenylmethane was prepared by dissolving 0.2 g (1.0 mmol) of 4,4'-diaminodiphenylmethane in 0.4 mL of N-methyl-2-pyrrolidone. Under stirring conditions, the entire amount of 4,4'-diaminodiphenylmethane solution is added dropwise to 7 mL of a polyacrylic acid solution (corresponding to 9.5 mmol in terms of acrylic acid monomer), and the resulting mixture is allowed to stand at room temperature for 30 minutes. It stirred. Then, using a Dean-Stark apparatus, the mixture was stirred at 130 ° C. for 3 hours to allow the dehydration reaction to proceed, thereby producing a binder solution.

78.5 parts by mass of the carbon-coated silicon material of Example 9 as a negative electrode active material, 10.5 parts by mass of acetylene black as a conductive additive, and the above-mentioned binding in an amount such that the solid content is 11 parts by mass as a binder The slurry was prepared by mixing the agent solution and an appropriate amount of N-methyl-2-pyrrolidone. A copper foil was prepared as a current collector for the negative electrode. The slurry was applied in the form of a film on the surface of the copper foil using a doctor blade. The copper foil coated with the slurry was dried to remove N-methyl-2-pyrrolidone. After that, pressing and baking at 180 ° C. manufactured a negative electrode of Example 9 in which a negative electrode active material layer was formed.

A solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L was used as an electrolytic solution in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1.

The negative electrode was cut to a diameter of 11 mm and used as an evaluation electrode. A metal lithium foil having a thickness of 500 μm was cut to a diameter of 13 mm and used as a counter electrode. A glass filter (Hoechst Celanese) and celgard 2400 (Polypore Co., Ltd.) which is a single-layer polypropylene were prepared as a separator. The two types of separators were sandwiched between the counter electrode and the evaluation electrode in the order of the counter electrode, the glass filter, celgard 2400, and the evaluation electrode to form an electrode body. The electrode body was housed in a coin-type battery case CR2032 (Hohsen Co., Ltd.). An electrolytic solution was injected into the battery case, the battery case was sealed, and a lithium ion secondary battery of Example 9 was manufactured.

(Example 10)
The oxygen-containing layered silicon compound of Example 10, oxygen-containing in the same manner as Example 9, except that in the step a-2-2) the temperature of the thermostatic chamber was raised to 40 ° C. at a rate of 1 ° C./min. Silicon materials, carbon coated-oxygen containing silicon materials, negative electrodes and lithium ion secondary batteries were manufactured.

(Comparative example 8)
In the step a-2-2), the oxygen-containing layered silicon compound of Comparative Example 8 and the oxygen-containing silicon material of Comparative Example 8 are the same as in Example 9 except that the temperature of the constant temperature bath is not increased and maintained at 0 ° C. Carbon coated-oxygen containing silicon materials, negative electrodes and lithium ion secondary batteries were manufactured.

(Comparative example 9)
The oxygen-containing layered silicon compound of Comparative Example 9 in the same manner as in Example 9 except that in the step a-2-2) the temperature of the thermostatic chamber was raised to 60 ° C. at a rate of 1 ° C./min. Silicon materials, carbon coated-oxygen containing silicon materials, negative electrodes and lithium ion secondary batteries were manufactured.

(Evaluation example 8)
Elemental analysis was performed on the carbon-coated oxygen-containing silicon materials of Examples 9 to 10 and Comparative Examples 8 to 9 in the same manner as in Evaluation Example 6. The results of these elemental analyzes are shown in Table 9 as mass%.

(Evaluation example 9)
A charge and discharge test was performed on the lithium ion secondary batteries of Examples 9 to 10 and Comparative Examples 8 to 9 in the same manner as in Evaluation Example 2. The results are shown in Table 10. Further, FIG. 2 shows the relationship between the integrated capacity and the discharge capacity of each lithium ion secondary battery in 50 charge and discharge cycles.

From the results of Table 10 and FIG. 2, the lithium ion secondary battery comprising the oxygen-containing silicon material of Example 9 and Example 10, in which oxygen mass% and silicon mass% are in appropriate ranges, has initial efficiency and capacity retention It can be said that the rate and integrated capacity are satisfied in a well-balanced manner.

(Example 11)
An Al-containing CaSi ₂ powder was prepared as follows.
Ca, Al and Si were weighed in a carbon crucible. The elemental composition ratio of Ca and Si was 1: 2, and the amount of Al added was 1% with respect to the total mass of Ca, Al and Si. A carbon crucible was heated at around 1300 ° C. in a high frequency induction heating apparatus under an argon gas atmosphere to obtain a molten metal containing Ca, Al and Si. The molten metal is poured into a predetermined mold to cool and solidify. The solid was crushed into CaSi ₂ powder and then subjected to a) step.

a) Process a-2-1) Process A reaction vessel containing 18 mass% hydrochloric acid was placed in a thermostat at 0 ° C. After confirming that the temperature of the hydrochloric acid reached 0 ° C., the CaSi ₂ powder was gradually introduced into the hydrochloric acid under a nitrogen gas atmosphere and under stirring conditions. Stirring was continued for 15 minutes after the addition of the CaSi ₂ powder.

a-2-2) Step After the step a-2-1), the temperature of the thermostat was raised to 40 ° C. at a rate of 1 ° C./min, and the reaction solution was stirred overnight. Thereafter, the reaction solution was filtered. The residue was washed with distilled water and then with methanol and dried under reduced pressure to obtain the oxygen-containing layered silicon compound of Example 11.

b) Step The oxygen-containing layered silicon compound of Example 11 was heated at 700 ° C. for 1 hour in a nitrogen gas atmosphere to obtain an oxygen-containing silicon material. The oxygen-containing silicon material was pulverized using a jet mill to obtain a powder having an average particle size of 5 μm.
This powder was used as the oxygen-containing silicon material of Example 11.

Carbon Coating Step The oxygen-containing silicon material of Example 11 was placed in a rotary kiln type reactor, and thermal CVD was performed under the conditions of 700 ° C. and a residence time of 60 minutes under aeration of a hexane-argon mixed gas, and carbon coated. An oxygen-containing silicon material was obtained. This was used as the carbon-coated oxygen-containing silicon material of Example 11.

The negative electrode and lithium ion secondary battery of Example 11 were produced as follows.

72.5 parts by mass of the carbon-coated silicon material of Example 11 as a negative electrode active material, 13.5 parts by mass of acetylene black as a conductive additive, 14 parts by mass of polyamideimide as a binder, and an appropriate amount of N-methyl The -2-pyrrolidone was mixed to produce a slurry. A copper foil was prepared as a current collector for the negative electrode. The slurry was applied in the form of a film on the surface of the copper foil using a doctor blade. The copper foil coated with the slurry was dried to remove N-methyl-2-pyrrolidone. After that, pressing and baking at 180 ° C. manufactured a negative electrode of Example 11 in which a negative electrode active material layer was formed.

A solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L was used as an electrolytic solution in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1.

The negative electrode was cut to a diameter of 11 mm and used as an evaluation electrode. A metal lithium foil having a thickness of 500 μm was cut to a diameter of 13 mm and used as a counter electrode. A glass filter (Hoechst Celanese) and celgard 2400 (Polypore Co., Ltd.) which is a single-layer polypropylene were prepared as a separator. The two types of separators were sandwiched between the counter electrode and the evaluation electrode in the order of the counter electrode, the glass filter, celgard 2400, and the evaluation electrode to form an electrode body. The electrode body was housed in a coin-type battery case CR2032 (Hohsen Co., Ltd.). An electrolytic solution was injected into the battery case, and the battery case was sealed to manufacture a lithium ion secondary battery of Example 11.

(Example 12)
In the step of preparing the CaSi ₂ powder containing Al, the procedure is the same as in Example 11 except that the addition amount of Al is set to 0.5% with respect to the total mass of Ca, Al and Si. The oxygen-containing layered silicon compound of Example 12, the oxygen-containing silicon material, the carbon-coated oxygen-containing silicon material, the negative electrode and the lithium ion secondary battery were manufactured.

(Example 13)
At the step of preparing a CaSi ₂ powder containing Al, without adding Al, except preparing the CaSi ₂ powder not containing Al is in the same manner as in Example 11, the oxygen-containing layered silicon of Example 13 Compounds, oxygen-containing silicon materials, carbon coated-oxygen-containing silicon materials, negative electrodes and lithium ion secondary batteries were manufactured.

(Example 14)
b) In the same manner as in Example 11 except that the heating temperature in the step is 900 ° C., and the conditions for the carbon coating step are 880 ° C. and a residence time of 60 minutes under aeration of a propane-argon mixed gas. An oxygen-containing layered silicon compound, an oxygen-containing silicon material, a carbon-coated oxygen-containing silicon material, a negative electrode and a lithium ion secondary battery of Example 14 were manufactured.

(Example 15)
b) In the same manner as in Example 13, except that the heating temperature in the step is 900 ° C., and the conditions for the carbon coating step are 880 ° C. and a residence time of 60 minutes under aeration of propane-argon mixed gas. An oxygen-containing layered silicon compound, an oxygen-containing silicon material, a carbon-coated oxygen-containing silicon material, a negative electrode and a lithium ion secondary battery of Example 15 were manufactured.

(Evaluation example 10)
Elemental analysis was performed on the carbon-coated oxygen-containing silicon material of Example 11 to Example 15 in the same manner as in Evaluation Example 6. The results of these elemental analyzes are shown in Table 11 as mass%.

(Evaluation example 11)
The BET specific surface area of the carbon-coated oxygen-containing silicon material of Example 11 to Example 15 was measured. The results are shown in Table 12 together with the features of the production methods other than the step a).

(Evaluation example 12)
The lithium ion secondary batteries of Examples 11 to 15 were charged to 0.01 V at a current of 0.2 mA and then discharged to 1.0 V at a current of 0.2 mA. went.
Furthermore, the lithium ion secondary batteries of Examples 11 to 15 after the initial charge and discharge are charged to 0.01 V with a current of 0.5 mA, and then discharged to 1.0 V with a current of 0.5 mA. The charge and discharge cycle of 50 cycles was performed.

The initial efficiency and capacity retention rate were calculated by the following formulas.
Initial efficiency (%) = 100 × (initial discharge capacity up to 0.8 V) / (initial charge capacity)
Capacity retention rate (%) = 100 × (discharge capacity at 50 cycles) / (discharge capacity at 1 cycle)
The above results are shown in Table 13 together with data such as elemental analysis of carbon-coated oxygen-containing silicon material.

From the results in Table 13, it can be said that the preferred oxygen-mass% carbon-coated oxygen-containing silicon material exhibits excellent characteristics as a negative electrode active material. Further, it can be seen that the oxygen mass%, silicon mass% and Al mass% of the carbon-coated silicon-containing silicon material affect the capacity retention rate of the secondary battery.

Claims (16)

1. a-1) reacting CaSi ₂ with an aqueous acid solution at 15 to 50 ° C. to synthesize an oxygen-containing layered silicon compound containing layered polysilane,
   b) heating the oxygen-containing layered silicon compound at 300 ° C. or higher to synthesize an oxygen-containing silicon material;
   A method of manufacturing a negative electrode active material comprising an oxygen-containing silicon material, characterized in that the method comprises:
2. a-2-1) reacting CaSi ₂ with an aqueous acid solution at −20 to 10 ° C.,
   a-2-2) a step of synthesizing an oxygen-containing layered silicon compound containing layered polysilane with the temperature of the reaction liquid being set to 15 to 50 ° C., following the above step a-2-1),
   b) heating the oxygen-containing layered silicon compound at 300 ° C. or higher to synthesize an oxygen-containing silicon material;
   A method of manufacturing a negative electrode active material comprising an oxygen-containing silicon material, characterized in that the method comprises:
3. The method for producing a negative electrode active material containing an oxygen-containing silicon material according to claim 1 or 2, wherein the concentration of the acid in the aqueous acid solution is in the range of 5 to 30% by mass.
4. The oxygen-containing silicon according to claim 3, wherein the oxygen-containing silicon material contains an element derived from the anion of the acid, and the element mass% (W _x %) in the oxygen-containing silicon material is 0 <W _x <6. The manufacturing method of the negative electrode active material containing a material.
5. The method for producing a negative electrode active material including the oxygen-containing silicon material according to any one of claims 1 to 4, wherein oxygen mass% (W 2 _O %) in the oxygen-containing silicon material is 16 <W 2 _O <27.
6. The method for producing a negative electrode active material containing an oxygen-containing silicon material according to any one of claims 1 to 5, wherein the silicon mass% (W _Si %) in the oxygen-containing silicon material is 62 <W _Si <81.
7. The oxygen-containing silicon according to any one of claims 1 to 6, wherein the CaSi ₂ contains Al, and the Al mass% (W _Al %) in the oxygen-containing silicon material is 0 <W _Al <1. The manufacturing method of the negative electrode active material containing a material.
8. The negative electrode active material containing oxygen-containing silicon material according to any one of claims 1 to 7, wherein the ratio of silicon crystal to amorphous silicon in the oxygen-containing silicon material is in the range of 0: 100 to 30: 70. Manufacturing method.
9. A method of manufacturing a negative electrode using a negative electrode active material containing an oxygen-containing silicon material manufactured by the method according to any one of claims 1 to 8.
10. The manufacturing method of a secondary battery using the negative electrode manufactured by the manufacturing method of Claim 9.
11. A negative electrode active material comprising an oxygen-containing silicon material having an oxygen mass% (W 2 _O %) of 16 <W 2 _O <27 and a silicon mass% (W 2 _Si %) of 62 <W 2 _Si <81.
12. The negative electrode active material according to claim 11, wherein the oxygen-containing silicon material contains Al at Al mass% (W _Al %): 0 <W _Al <1.
13. The negative electrode active material according to claim 11, wherein the oxygen-containing silicon material contains a halogen at a halogen mass% (W _x %): 0 <W _x <6.
14. The negative electrode active material according to any one of claims 11 to 13, wherein the ratio of silicon crystals to amorphous silicon in the oxygen-containing silicon material is in the range of 0: 100 to 30:70.
15. A negative electrode comprising the negative electrode active material according to any one of claims 11 to 14.
16. A secondary battery comprising the negative electrode according to claim 15.

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