JP6115780B2 - Composite negative electrode active material body, negative electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a composite negative electrode active material body including a negative electrode active material for a nonaqueous electrolyte secondary battery, a negative electrode for a nonaqueous electrolyte secondary battery using the composite negative electrode active material body, and a nonaqueous electrolyte using the negative electrode The present invention relates to a secondary battery.

  Non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries are small and have a large capacity, and are therefore used in a wide range of fields such as mobile phones and laptop computers. In recent years, the use of a lithium ion secondary battery as a drive source for a vehicle has also been studied.

  A lithium ion secondary battery, which is a type of nonaqueous electrolyte secondary battery, has an active material capable of inserting and removing lithium (Li) as a charge carrier in the positive electrode and the negative electrode, and Li moves between the positive and negative electrodes. Works by. In recent years, a technique using a material containing silicon (Si) (hereinafter referred to as a silicon-based negative electrode active material) as a negative electrode active material for a lithium ion secondary battery has been proposed. Since Si is an element that can be alloyed with Li and has a large theoretical capacity, it is considered useful as a negative electrode active material for a lithium ion secondary battery. On the other hand, however, the volume of Si greatly changes with the insertion and extraction of Li during charge and discharge. Due to this volume change, Si may be pulverized and fall off or peel from the current collector, and it is difficult to greatly improve the charge / discharge cycle life of the battery.

For example, the use of silicon oxide (SiO _x : generally, x is about 0.5 ≦ x ≦ 1.5) as a negative electrode active material has been studied. SiO _x is a general formula that represents a general term for amorphous silicon oxides obtained using metal silicon (Si) and silicon dioxide (SiO ₂ ) as raw materials. It is known that SiO _x decomposes into silicon (Si) and silicon dioxide (SiO ₂ ) when heat-treated. This is called disproportionation reaction. If the ratio of Si and O is a homogeneous solid silicon monoxide (SiO) of approximately 1: 1, the silicon (Si) phase and silicon dioxide (SiO ₂ ) Separate into two phases. The Si phase obtained by separation is very fine and is dispersed in the SiO ₂ phase. Further, the SiO ₂ phase covering the Si phase has a function of suppressing decomposition of the electrolytic solution. Therefore, a lithium ion secondary battery using a negative electrode active material composed of SiO _x decomposed into Si and SiO ₂ has excellent cycle characteristics. That is, by using SiO _x as the negative electrode active material, it is possible to suppress a volume change associated with insertion and extraction of Li during charge and discharge as compared to the case of using Si as the negative electrode active material.

By the way, SiO _x is relatively inferior in conductivity. Therefore, the negative electrode is also poor in conductivity containing SiO _x as the negative electrode active material. Therefore, it is desired to improve the conductivity of the negative electrode containing SiO _x . For example, by providing a carbon (C) coat layer made of graphite or an amorphous carbon material as a raw material on the negative electrode active material layer to form a composite negative electrode active material body, conductivity corresponding to the amount of C coat can be obtained. It can be applied to the negative electrode. For example, Patent Document 1 proposes a technique of providing a C coat layer on the surface of a negative electrode active material layer made of SiO _x .

JP 2006-196247 A

  By the way, also when using the above-mentioned silicon oxide as a negative electrode active material, the expansion | swelling and shrinkage | contraction of a negative electrode accompanying charging / discharging of a nonaqueous electrolyte secondary battery cannot be suppressed completely. Therefore, for example, even when a negative electrode active material made of silicon oxide is covered with a C coat layer, it is only possible to improve the conductivity of the negative electrode, and it is difficult to improve the durability of the negative electrode. That is, after the cycle, the C coat layer that could not follow the expansion and contraction of the negative electrode active material layer might peel from the negative electrode active material layer. If the C coat layer is peeled off, the battery capacity of the nonaqueous electrolyte secondary battery may be reduced.

  The present invention has been made in consideration of the above circumstances, and is a composite negative electrode active material body that is excellent in cycle characteristics while using a silicon-based negative electrode active material, and for a non-aqueous electrolyte secondary battery using the composite negative electrode active material body An object is to provide a negative electrode and a nonaqueous electrolyte secondary battery including the negative electrode.

  As a result of earnest research, the inventors of the present invention have determined that a transition metal nitride is formed between the C coat layer and the negative electrode active material layer when forming the C coat layer on the negative electrode active material layer containing the silicon-based negative electrode active material. It was found that the cycle characteristics of the nonaqueous electrolyte secondary battery can be improved by interposing the layer.

That is, the composite negative electrode active material body for a non-aqueous electrolyte secondary battery of the present invention that solves the above problems includes silicon particles made of a silicon-based negative electrode active material containing silicon (Si),
A transition metal nitride layer provided on the silicon grains, including a nitride of at least one transition metal selected from tungsten (W), titanium (Ti), and tantalum (Ta);
And a C coat layer containing carbon (C) and provided on the transition metal nitride layer.

The composite negative electrode active material body for a non-aqueous electrolyte secondary battery of the present invention preferably includes any one of the following (1) to (4), and more preferably includes a plurality.
(1) The amount of C when the mass of the silicon grains is 100 mass% is 0.25 mass% or more and 10.0 mass% or less.
(2) The element amount of the transition metal when the mass of the silicon particles is 100% is 0.5% by mass or more and 5.0% by mass or less.
(3) The amount of C when the mass of the silicon particles is 100% by mass is 0.5% by mass or more and 5.0% by mass or less.
(4) The silicon-based negative electrode active material is made of a silicon oxide represented by SiO _x (0.3 ≦ x ≦ 1.6).

Moreover, the composite negative electrode active material body for a non-aqueous electrolyte secondary battery of the present invention that solves the above-described problems includes silicon particles made of a silicon-based negative electrode active material containing silicon (Si),
A transition metal nitride layer including at least one nitride selected from tungsten (W), titanium (Ti), and tantalum (Ta), and provided on the silicon grains;
A method for producing a composite negative electrode active material body for a non-aqueous electrolyte secondary battery comprising carbon (C) and a C coat layer provided on the transition metal nitride layer,
The method includes a reactive sputtering step of forming the transition metal nitride layer on the silicon grains in the presence of nitrogen gas using at least one of the transition metals as a target.

  The negative electrode for a non-aqueous electrolyte secondary battery of the present invention that solves the above-described problems includes any of the above-described composite negative electrode active material for a non-aqueous electrolyte secondary battery of the present invention.

  The nonaqueous electrolyte secondary battery of the present invention that solves the above problems includes the above-described negative electrode for a nonaqueous electrolyte secondary battery of the present invention.

  According to the composite negative electrode active material body for a non-aqueous electrolyte secondary battery of the present invention, the cycle characteristics of the non-aqueous electrolyte secondary battery can be improved while using the silicon-based negative electrode active material.

It is explanatory drawing which represents typically the composite negative electrode active material body for nonaqueous electrolyte secondary batteries and the negative electrode for nonaqueous electrolyte secondary batteries of this invention. It is a graph showing the relationship between the quantity (carbon content) of C coat layer, and electrical conductivity. It is a graph showing the relationship between the quantity (carbon content) of C coat layer, and electrical conductivity. It is a graph showing the initial efficiency of the nonaqueous electrolyte secondary battery of the samples 10-16.

  The nonaqueous electrolyte secondary battery of the present invention includes the negative electrode for a nonaqueous electrolyte secondary battery of the present invention, and the negative electrode for a nonaqueous electrolyte secondary battery of the present invention includes a composite negative electrode active material body. Hereinafter, unless otherwise specified, the negative electrode for a nonaqueous electrolyte secondary battery of the present invention is simply referred to as a negative electrode of the present invention, and the composite negative electrode active material for a nonaqueous electrolyte secondary battery of the present invention is simply referred to as the present invention. It is called a composite negative electrode active material body. Moreover, the manufacturing method of the composite negative electrode active material body for nonaqueous electrolyte secondary batteries of this invention is only called the manufacturing method of this invention.

  As shown in the schematic diagram of FIG. 1, the composite negative electrode active material body of the present invention is provided with a transition metal nitride layer 12 on silicon particles 11 made of a silicon-based negative electrode active material. A C coat layer 13 is further provided thereon. The negative electrode 1 of the present invention includes the composite negative electrode active material body 10 described above. The composite negative electrode active material body 10 can be disposed on the current collector 15 together with additives (not shown) such as a conductive additive and a binder.

  The C coat layer contains a carbon (C) element and contributes to improving the conductivity of the negative electrode. The transition metal nitride layer is interposed between the C coat layer and the silicon grains, and contributes to improving the adhesion between them. The transition metal nitride layer may cover the entire surface of the silicon grain, or may cover only a part of the surface of the silicon grain. The C coat layer may cover the entire surface of the transition metal nitride layer, or may cover only part of the surface of the transition metal nitride layer. Furthermore, when the transition metal nitride layer covers only part of the surface of the silicon grain, the C coat layer may cover part or all of the exposed surface of the silicon grain. However, the amount of the C coat layer needs to be within an appropriate range. Specifically, when the mass of silicon particles is 100% by mass, the amount of C is 0.25% by mass to 10.0% by mass. The capacity of the nonaqueous electrolyte secondary battery when C is the negative electrode active material is significantly smaller than the capacity of the nonaqueous electrolyte secondary battery when Si is the negative electrode active material. For this reason, if the amount of C is excessive, the proportion of Si in the composite negative electrode active material body is greatly reduced, and as a result, the capacity of the nonaqueous electrolyte secondary battery may be reduced. If the amount of C is within this range, the ratio of Si in the composite negative electrode active material body is sufficiently large, and the capacity reduction of the nonaqueous electrolyte secondary battery can be suppressed. Moreover, if the amount of C is within this range, the conductivity (S / cm) of the composite negative electrode active material body becomes as high as that of carbon (C). Preferably, when the mass of silicon particles is 100% by mass, the amount of C is preferably 0.3% by mass or more and 5.0% by mass or less, and 0.5% by mass or more and 5.0% by mass or less. Is more preferable.

  The method for forming the C coat layer is not particularly limited, and a known method such as vapor deposition, sputtering, or mechanical milling may be used. As the carbon material, a general carbon material such as artificial graphite, natural graphite, soft carbon, or hard carbon may be used. These carbon materials can be used alone or in combination of two or more. Note that the sputter-formed C coat layer tends to be peeled off more easily than, for example, a CVD (chemical vapor deposition) C coat layer. However, in the composite negative electrode active material body of the present invention, since the transition metal nitride layer is provided between the silicon grains and the C coat layer, even the sputtered C coat layer is difficult to peel off.

  The transition metal nitride layer may include at least one transition metal nitride selected from tungsten (W), titanium (Ti), and tantalum (Ta), and each transition in the case of including a plurality of transition metal nitrides. There are no particular limitations on the mixing ratio of the metal. The amount of the transition metal is not particularly limited, but the amount of the transition metal when the mass of the silicon particles is 100% by mass is preferably 0.5% by mass to 5.0% by mass. If the amount of the transition metal is too small, the amount of the transition metal nitride layer interposed between the silicon grains and the C coat layer may be too small, and the effect of the transition metal nitride layer may be reduced. Further, if the amount of the transition metal nitride layer is excessive, the proportion of Si in the composite negative electrode active material body is greatly reduced, the capacity of the non-aqueous electrolyte secondary battery may be reduced, and binder aggregation may occur. Can happen.

  The method for forming the transition metal nitride layer is not particularly limited as in the case of the C coat layer, and known methods such as vapor deposition, sputtering, and mechanical milling can be used. Of these, when the transition metal nitride layer is formed by sputtering, it is not necessary to heat the transition metal nitride layer and the silicon grains, so the Si crystallites in the silicon grains are coarsened, the silicon grains themselves are coarsened, and The reaction between the transition metal and silicon can be suppressed. When the transition metal nitride layer is formed by sputtering, the transition metal nitride itself can be used as a target, or the transition metal nitride layer is sputtered (reactive sputtering) in a nitrogen gas atmosphere using the transition metal as a target. Is also possible. The reason for this is not clear, but as will be described later, when the transition metal nitride layer is formed by reactive sputtering, the improvement in cycle characteristics (suppression of the decrease in capacity retention rate) is significant. In consideration of Li ion conductivity and the like, the transition metal nitride layer is preferably thin. Specifically, the thickness is preferably 10 μm or less.

The negative electrode for a non-aqueous electrolyte secondary battery of the present invention includes silicon particles made of a silicon-based negative electrode active material. As the silicon-based negative electrode active material, a known negative electrode active material containing a silicon (Si) element can be used while functioning as a negative electrode active material. For example, as the silicon-based negative electrode active material, Si alone, the above-described SiO _x , silicon nanosheet (siloxene), or the like can be used, but is not limited thereto. The SiO _x and silicon nanosheet will be described in detail below.

As described above, it is preferable to use SiO _x (0.3 ≦ x ≦ 1.6) that is disproportionated into two phases of Si phase and SiO ₂ phase. The Si phase consists of simple silicon and can occlude and release Li ions. This Si phase undergoes a volume change (ie, expansion and contraction) as Li ions are occluded and released. The SiO ₂ phase is made of SiO ₂ and can absorb the expansion and contraction of the Si phase. To sufficiently exhibit the buffering effect of such a SiO ₂ phase are preferably coated with Si phase SiO ₂ phase. Furthermore, a plurality of Si phase was finer coated by SiO ₂ phase, Si phase and SiO ₂ phase and is particularly preferable to form the particles together. If x is less than the lower limit, the Si ratio becomes excessive, so that the volume change at the time of charging / discharging becomes too large and the cycle characteristics deteriorate. On the other hand, if x exceeds the upper limit value, the Si ratio becomes too small and the energy density decreases. The range of x is more preferably 0.5 ≦ x ≦ 1.5, and further preferably 0.7 ≦ x ≦ 1.2.

In SiO _x , the mass of the SiO ₂ phase relative to the Si phase is preferably 1 to 3 times that of the Si phase. When the mass of the SiO ₂ phase is smaller than the mass of the Si phase, that is, when the mass of the SiO ₂ phase is less than the mass of the Si phase, the volume change of SiO _x becomes large. If this volume change is excessive, cracks may occur in the negative electrode containing SiO _x . On the other hand, when the mass of the SiO ₂ phase exceeds three times the mass of the Si phase, the amount of insertion and extraction of Li ions in the negative electrode active material is small, and the battery capacity may be reduced. This is mainly because the Si phase is involved in the insertion and release of Li ions. Preferably, Si and SiO ₂ are contained in a 1: 1 (molar ratio).

As SiO _x , those produced by a general method can be used. For example, a raw material powder containing silicon monoxide (SiO) can be used. In this case, SiO in the raw material powder is disproportionated into two phases of SiO ₂ phase and Si phase. SiO is a homogeneous solid (SiO _n : n is 0.5 ≦ n ≦ 1.5) in which the atomic ratio of Si and O is approximately 1: 1. And is separated into two phases of SiO ₂ phase and Si phase. By this disproportionation, a SiO _x powder containing a SiO ₂ phase and a Si phase can be obtained. This disproportionation proceeds by applying energy to the raw material powder. For example, the raw material powder is heated, milled, and the like.

In the case of heating the raw material powder, it is generally assumed that almost all SiO is disproportionated and separated into two phases at 800 ° C. or higher if oxygen is turned off. Specifically, the raw material powder containing the amorphous SiO powder is subjected to a heat treatment at 800 to 1200 ° C. for 1 to 5 hours in an inert atmosphere such as in a vacuum or an inert gas, whereby an amorphous state is obtained. SiO _x powder containing two phases of a crystalline SiO ₂ phase and a crystalline Si phase can be obtained.

When milling the raw material powder, a part of the mechanical energy of the milling contributes to chemical atomic diffusion at the solid phase interface of the raw material powder, thereby disproportionating SiO into the SiO ₂ phase and the Si phase. . Specifically, the raw material powder is mixed using a mixer in a low-pressure inert gas atmosphere (for example, in argon gas). As the mixer, a known apparatus represented by a V-type mixer, a ball mill, an attritor, a jet mill, a vibration mill, a high energy ball mill, or the like may be used. By further heat treatment after milling, SiO disproportionation may be further promoted.

  The silicon nanosheet is a silicon-based layered compound also called siloxene. Specifically, the silicon nanosheet is composed of a silicate matrix and nano-sized silicon particles dispersed in the matrix. Of the silicon particles and silicate, at least the silicon particles are in an amorphous state.

  Such silicon nanosheets are described, for example, in “'Layered polysilane: thermolysis and photoluminescence” J. He, J. S. Tse, * D. K. Krug and K. F. Preston J. Mater. Chem., 1998, 8 ( 3) The layered polysilane disclosed in 705, 710 ", etc. can be used as a raw material. Specifically, this layered polysilane has a structure in which a plurality of six-membered rings composed of silicon atoms are connected in a basic skeleton, and among these, a silicon atom has a layered structure in which at least one of a hydroxyl group and a hydrogen group is bonded. .

In order to produce a silicon nanosheet using the layered polysilane as a raw material, first, the layered polysilane and the alkoxysilane are mixed in an organic solvent to obtain a layered compound in which the alkoxysilane is infiltrated between the layers of the layered polysilane. The alkoxysilane used at this time is represented by the general formula Si (OR) ₄ . R is an alkyl group such as a methyl group, an ethyl group, a propyl group or a butyl group, an alkene group such as a vinyl group, an alkyne group such as an ethynyl group or an acetyl group, a phenyl group, a biphenyl group, a naphthyl group or an anthryl group. An aromatic group, an acyl group, etc. are illustrated. Moreover, as an organic solvent used at this time, the thing which does not react with alkoxysilane and can dissolve alkoxysilane can be used. Examples of such an organic solvent include alcohols. Specifically, methanol, ethanol, propanol, butanol and the like can be used alone or in combination of two or more. In this step, a solution in which alkoxysilane is dissolved permeates between layers of layered polysilane, thereby forming a layered compound in which alkoxysilane is introduced between layers of layered polysilane. At this time, if the temperature is raised to about 60 ° C., it is considered that the solution penetrates between the layers of the layered polysilane relatively easily. This is because a part of the alkoxysilane is considered to aggregate between the layers of the layered polysilane.

  Next, the aqueous solution of the alkali compound and the layered compound are mixed to hydrolyze the alkoxysilane between the layers of the layered polysilane and form a silicate. Specifically, at this time, the alkoxysilane is hydrolyzed between the layers of the layered polysilane to be gelled, and is reacted with an alkali compound to form a silicate. Thereafter, the organic solvent contained in the reaction system, alcohol generated by hydrolysis of alkoxysilane, and the like are removed, and a silicon nanosheet precursor is obtained. This precursor is in a state in which polysilane layers and silicate layers are laminated approximately alternately. In addition, as an alkali compound at this time, what is soluble in water, such as an alkali metal or alkaline earth metal hydroxide and carboxylate, can be preferably used. For example, when silicon nanosheets are used as a negative electrode active material for a lithium ion secondary battery, lithium hydroxide, lithium formate, lithium acetate, alkoxylithium, and the like can be particularly preferably used as the alkali compound.

  Next, the above precursor is heated in a non-oxidizing atmosphere. Then, the layered polysilane is decomposed to obtain amorphous silicon particles. The silicon particles try to aggregate with each other, but the aggregation of the silicon particles is suppressed by the silicate layer interposed between the polysilane layers. As a result, grain growth of silicon particles is suppressed, and nano-sized fine silicon particles are obtained. That is, the silicon nanosheet obtained by the above method is composed of a silicate matrix and nano-sized silicon particles dispersed in the matrix, and at least the silicon particles are in an amorphous state. More preferably, the silicate is also in an amorphous state. Since the silicon particles are in an amorphous state, the initial capacity of the nonaqueous electrolyte secondary battery is increased. Further, since the silicate is in an amorphous state, the cycle characteristics of the nonaqueous electrolyte secondary battery are improved. In addition, it can confirm by XRD diffraction that at least one part of a silicon nanosheet is an amorphous state. In addition, the presence of Si—Si bonds in the silicon nanosheet can be confirmed by Raman spectrum analysis.

  The particle size of the silicon particles in the silicon nanosheet is preferably about 0.5 nm to 20 nm, and more preferably about 1 nm to 10 nm. This particle size may be a number average particle size observed with a TEM or the like, a particle size obtained by Scherrer's equation from an XRD peak, or an average particle size measured by other methods. The molar ratio of silicon particles to silicate is preferably about 0.1 to 1.5 mol of silicate with respect to 1 mol of silicon particles. It is more preferable that the amount is about 0.5 to 1.0 mol of silicate with respect to 1 mol of silicon particles.

Other examples of the silicon-based negative active material, the main component and Si phase and SiO ₂ phase, may be used those containing other known active materials. More specifically, it is Me _w Si _y O _z . Note that Me is Li, Ca, and the like, and w, y, and z are integers.

The negative electrode for a non-aqueous electrolyte secondary battery of the present invention may contain two or more silicon-based negative electrode active materials (for example, two or more selected from the above-mentioned SiO _x , silicon nanosheet and Me _w Si _y O _z ). Moreover, as a negative electrode active material, you may include things other than silicon type negative electrode active materials, such as graphite and carbon, for example. The particle diameter of the silicon particles is not particularly limited, but the average particle diameter of the silicon particles is preferably 0.5 μm or more and 50 μm or less. This is because the presence of particles exceeding 50 μm causes polarization in the particles, leading to a decrease in Coulomb efficiency. In addition, the average particle diameter here refers to the mass average particle diameter in the particle size distribution measurement by a laser beam diffraction method.

  A negative electrode can be comprised with the negative electrode compound-material layer containing the negative electrode active material mentioned above, and a collector. The negative electrode mixture layer may be laminated on the current collector, or in some cases, a layer integrated with the current collector may be formed. In some cases, the laminate of the negative electrode mixture layer and the current collector may be further heated. As the current collector, for example, a general material such as a metal mesh such as copper or copper alloy or a metal foil can be used. The negative electrode mixture constituting the negative electrode mixture layer may contain a binder, a conductive additive, and the like in addition to the silicon-based negative electrode active material described above.

  The binder is not particularly limited, and a known one may be used. For example, it is preferable to use a resin that does not decompose even at a high potential, such as a fluorine-containing resin such as polytetrafluoroethylene or polyvinylidene fluoride. The blending ratio of the binder is preferably a mass ratio in the range of negative electrode active material: binder = 1: 0.05 to 1: 0.5. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

  As a conductive support agent, a material generally used for an electrode of a nonaqueous electrolyte secondary battery may be used. For example, finely divided metal particles such as acetylene black, ketjen black, carbon black, carbon nanotube, vapor grown carbon fiber, graphite and copper may be used. The blending ratio of the conductive assistant is, in mass ratio, negative electrode active material: conductive assistant = 1: 0.01 to 1: 0.5.

  The positive electrode used in the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, and a general positive electrode of a nonaqueous electrolyte secondary battery, that is, a material containing a positive electrode active material capable of occluding and releasing lithium ions is used. Can do.

As the positive electrode active material, for example, metallic lithium, a lithium-containing composite oxide, or the like can be used. The lithium-containing composite oxide is a metal composite oxide of lithium and a transition metal such as a lithium / manganese composite oxide, a lithium / cobalt composite oxide, or a lithium / nickel composite oxide. More specifically, LiCoO ₂ , LiCo _p Ni _q Mn _r O ₂ (p + q + r = 1, 0 <p <1, 0 ≦ q <1, 0 ≦ r <1), Li ₂ MnO ₂ , Li ₂ MnO ₃ Etc. Among these, as LiCo _p Ni _q Mn _r O ₂ (p + q + r = 1, 0 <p <1, 0 ≦ q <1, 0 ≦ r <1), LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiCo _2/10 Ni _5/10 Mn _3/10 O ₂ is preferably used. Furthermore, as the positive electrode active material, an active material that does not contain lithium, for example, sulfur alone or a sulfur-modified compound can be used. When both the positive electrode and the negative electrode do not contain lithium, it is necessary to pre-dope lithium. The positive electrode may include a binder, a conductive additive, and the like in addition to the positive electrode active material. The positive electrode may be integrated with the current collector. The conductive auxiliary agent and the binder are not particularly limited, and any conductive auxiliary agent and binder may be used as long as they can be used for the non-aqueous electrolyte secondary battery, similarly to the conductive auxiliary agent and binder for the negative electrode described above.

  As the current collector for the positive electrode, a material generally used for a positive electrode of a non-aqueous electrolyte secondary battery such as aluminum, nickel, stainless steel or the like may be used. The shape of the current collector may be a general shape such as a mesh shape or a foil shape, like the current collector for the negative electrode.

The electrolytic solution is not particularly limited as long as a supporting electrolyte (supporting salt) is dissolved in an organic solvent. As the organic solvent, an aprotic organic solvent such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), or the like is used. be able to. The supporting electrolyte is preferably a lithium metal salt that is soluble in an organic solvent. For example, at least one selected from the group consisting of LiPF ₆ , LiBF ₄ , LIASF ₆ , LiI, LiClO ₄ , and LiCF ₃ SO ₃ is used. It is preferred to use. The supporting electrolyte is preferably dissolved in the organic solvent at a concentration of about 0.5 mol / l to 1.7 mol / l.

  A separator may be interposed between the positive electrode and the negative electrode as necessary. The separator separates the positive electrode and the negative electrode and holds the electrolytic solution, and a thin microporous film such as polyethylene or polypropylene can be used.

  The shape of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, and a connection between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal connected to the outside using a current collecting lead or the like. After that, the electrode body is preferably impregnated with a non-aqueous electrolyte solution to form a non-aqueous electrolyte secondary battery.

  The shape of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited. Various shapes such as a cylindrical shape, a laminated shape, a coin shape, and a laminated shape can be employed. Regardless of the shape, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body, and the current collector is connected between the positive electrode current collector and the negative electrode current collector and the positive electrode terminal and the negative electrode terminal. After connecting using the lead for this etc., this electrode body is sealed with a battery case (or laminate film) with electrolyte solution, and it becomes a battery.

  The nonaqueous electrolyte secondary battery of the present invention may be, for example, a lithium ion secondary battery or a lithium secondary battery. Alternatively, a charge carrier other than lithium (for example, sodium) may be used. The nonaqueous electrolyte secondary battery of the present invention may be mounted on a vehicle. Since the nonaqueous electrolyte secondary battery using the negative electrode of the present invention can be used for a long time with a large capacity and a large output, it is suitable for driving a traveling motor for a vehicle. The vehicle may be a vehicle that uses electric energy from a non-aqueous electrolyte secondary battery for part or all of its power source. Specifically, they are so-called electric vehicles (EV vehicles), hybrid vehicles (HV vehicles), and the like. When a nonaqueous electrolyte secondary battery is mounted on a vehicle, it is preferable to use it as an assembled battery in which a plurality of nonaqueous electrolyte secondary batteries are connected in series.

  The nonaqueous electrolyte secondary battery of the present invention can be used for various applications other than the above-described vehicle. For example, it is preferably used as a battery for various home appliances, office equipment, and industrial equipment driven by a battery such as a personal computer and a portable communication device.

  Hereinafter, the composite negative electrode active material body, the negative electrode, and the nonaqueous electrolyte secondary battery of the present invention will be described with specific examples.

(Sample 1)
First, commercially available SiO powder was put in a ball mill and milled at 450 rpm for 20 hours in an Ar atmosphere. Thereafter, heat treatment was performed for 2 hours at 900 ° C. in an inert gas atmosphere. Thus, SiO powder is disproportionated, particulate silicon oxide (SiO _x) was obtained. When X-ray diffraction (XRD) measurement using CuKα was performed on this SiO _x , a unique peak derived from simple silicon and silicon dioxide was confirmed. Therefore, the simple substance of silicon and silicon dioxide is produced in SiO _x, that is, it was found that the SiO _x is disproportionation. The average particle diameter D50 of SiO _x was 5 μm or less.

The above-mentioned SiO _x in the form of particles was used as silicon particles. First, a transition metal layer was provided on the surface of the silicon grains. Specifically, 1 g of silicon particles was placed in a vacuum chamber of a sputtering apparatus (SPM-302 manufactured by Canon Tokki). Further, Ta and C as targets were respectively arranged in the vacuum chamber. And vacuuming was performed to 1.4 Pa. Then, while Ar gas was circulated in the vacuum chamber to be about 1 Pa,
The silicon particles were flowed by rotating or vibrating the container containing the silicon particles, and sputtering was performed using Ta as a target. After a Ta sputtered film having a maximum thickness of about 10 nm was formed on the silicon grains, sputtering was performed using C as a target. The film thickness of the C sputtered film at this time was about 5 nm at the maximum. Through the above steps, a composite in which a transition metal layer (Ta sputtered film) is provided on silicon particles made of a negative electrode active material (SiO _x ), and a C coat layer (C sputtered film) is provided on the transition metal layer. A negative electrode active material body was obtained. Sample 1 contains 0.5% by mass of C and 3.0% by mass of Ta when the mass of silicon grains, that is, SiO _x is 100% by mass.

  The composite negative electrode active material, graphite (SMG), acetylene black (AB), and polyamideimide (PAI) are combined into the composite negative electrode active material: SMG: AB: PAI = 45: 40: 5: 10 (mass ratio). Weighed out and mixed. And the obtained mixture (namely, negative electrode compound material) was formed into a film on the single side | surface of the copper foil which is a collector using a doctor blade. The obtained current collector-negative electrode composite film was dried at 80 ° C. for 0.5 hours to evaporate the solvent, then pressed at a predetermined pressure and punched into a predetermined shape. Then, it vacuum-dried at 200 degreeC for 2 hours, and stood to cool after that. As a result, a negative electrode (evaluation electrode) in which the negative electrode active material layer was fixed on the current collector surface was obtained.

As the counter electrode, metal lithium foil was used. The diameter of the counter electrode was 13.0 mm, and the diameter of the evaluation electrode was 11.0 mm. A polypropylene porous membrane (thickness: 25 μm) as a separator was sandwiched between the counter electrode and the evaluation electrode to obtain an electrode body battery. This electrode body battery was accommodated in a battery case (CR2032 coin cell manufactured by Hosen Co., Ltd.). An electrolytic solution was further injected into the battery case. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as a supporting electrolyte in an organic solvent at a concentration of 1 mol / l was used. As the organic solvent, a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at 30:70 (volume ratio) was used. After injecting the electrolytic solution, the battery case was sealed to obtain a nonaqueous electrolyte secondary battery of Sample 1.

(Sample 2)
The negative electrode of Sample 2 is the same as the negative electrode of Sample 1 except that a transition metal nitride layer (TaN sputtered film) is provided instead of the transition metal layer. The negative electrode manufacturing method of sample 2 is the same as the negative electrode manufacturing method of sample 1 except that TaN is used instead of Ta as a sputtering target. The nonaqueous electrolyte secondary battery of sample 2 is the same as the nonaqueous electrolyte secondary battery of sample 1 except for the negative electrode.

In the method for producing the negative electrode of Sample 2, the vacuum chamber is evacuated to 1.4 Pa during sputtering, and then ArN is circulated in the vacuum chamber so that the pressure is about 1 Pa, and sputtering is performed using TaN as a target. I did it. After a TaN sputtered film having a maximum thickness of about 10 nm was formed on the silicon grains, sputtering using C as a target was subsequently performed. At this time, the maximum thickness of the C sputtered film was about 5 nm. Through the above steps, the transition metal nitride layer (TaN sputtered film) is provided on the silicon particles made of the negative electrode active material (SiO _x ), and the C coat layer (C sputtered film) is provided on the transition metal nitride layer. A composite negative electrode active material body was obtained. The composite negative electrode active material body in the negative electrode of Sample 2 contains 0.5% by mass of C and 3.0% by mass of Ta when the mass of silicon particles, that is, SiO _x is 100% by mass. .

(Sample 3)
The negative electrode of Sample 3 is the same as the negative electrode of Sample 1 except that a transition metal nitride layer (TaN reactive sputtered film) is provided instead of the transition metal layer. The nonaqueous electrolyte secondary battery of sample 3 is the same as the nonaqueous electrolyte secondary battery of sample 1 except for the negative electrode. The negative electrode manufacturing method of sample 3 is the same as the negative electrode manufacturing method of sample 1 in that Ta is used as a sputtering target. However, the negative electrode of sample 1 is different in that a TaN sputtered film is formed by reactive sputtering. Different from the manufacturing method.

Specifically, in the method for producing the negative electrode of Sample 3, the vacuum chamber is evacuated to 1.4 Pa during sputtering, and then Ta is introduced into the vacuum chamber so that the pressure is about 1 Pa, while Ta is circulated. Sputtering was performed as a target. Ta and nitrogen gas reacted on the silicon grains to produce TaN, and a TaN sputtered film having a maximum thickness of about 10 nm was formed on the silicon grains. Thereafter, sputtering was performed using C as a target while Ar gas was circulated in the vacuum chamber instead of nitrogen gas. The film thickness of the C sputtered film at this time was about 5 nm at the maximum. Through the above steps, the transition metal nitride layer (TaN reactive sputtered film) is provided on the silicon particles made of the negative electrode active material (SiO _x ), and the C coat layer (C sputtered film) is formed on the transition metal nitride layer. A composite negative electrode active material body provided with a was obtained. The composite negative electrode active material body in the negative electrode of Sample 3 contains 0.5% by mass of C and 3.0% by mass of Ta when the mass of silicon particles, that is, SiO _x is 100% by mass. .

(Sample 4)
The negative electrode of Sample 4 is the same as the negative electrode of Sample 1 except that the transition metal layer in the composite negative electrode active material body is a Ti sputtered film. The nonaqueous electrolyte secondary battery of sample 4 is the same as the nonaqueous electrolyte secondary battery of sample 1 except for the negative electrode.

In addition, the composite negative electrode active material body in the negative electrode of Sample 4 contains 0.5% by mass of C and 3.0% by mass of Ti when the mass of silicon particles, that is, SiO _x is 100% by mass. .

(Sample 5)
The negative electrode of Sample 5 is the same as the negative electrode of Sample 1 except that a transition metal nitride layer (TiN sputtered film) is provided instead of the transition metal layer. The nonaqueous electrolyte secondary battery of Sample 5 is the same as the nonaqueous electrolyte secondary battery of Sample 1 except for the negative electrode. The negative electrode manufacturing method of Sample 5 is the same as the negative electrode manufacturing method of Sample 2 except that Ti is used as a sputtering target.

The composite negative electrode active material body in the negative electrode of Sample 5 contains 0.5% by mass of C and 3.0% by mass of Ti when the mass of silicon particles, that is, SiO _x is 100% by mass. .

(Sample 6)
The negative electrode of Sample 6 is the same as the negative electrode of Sample 1 except that a transition metal nitride layer (TiN reactive sputtered film) is provided instead of the transition metal layer. The nonaqueous electrolyte secondary battery of Sample 6 is the same as the nonaqueous electrolyte secondary battery of Sample 1 except for the negative electrode. The negative electrode manufacturing method of Sample 6 is the same as the negative electrode manufacturing method of Sample 3 except that Ti is used as a sputtering target.

In addition, the composite negative electrode active material body in the negative electrode of Sample 6 contains 0.5% by mass of C and 3.0% by mass of Ti when the mass of silicon particles, that is, SiO _x is 100% by mass. .

(Sample 7)
The negative electrode of Sample 7 is the same as the negative electrode of Sample 1 except that the transition metal layer in the composite negative electrode active material body is a W sputtered film. The nonaqueous electrolyte secondary battery of Sample 7 is the same as the nonaqueous electrolyte secondary battery of Sample 1 except for the negative electrode.

The composite negative electrode active material body in the negative electrode of Sample 7 contains 0.5% by mass of C and 3.0% by mass of W when the mass of silicon particles, that is, SiO _x is 100% by mass. .

(Sample 8)
The negative electrode of Sample 8 is the same as the negative electrode of Sample 1 except that a transition metal nitride layer (WN sputtered film) is provided instead of the transition metal layer. The nonaqueous electrolyte secondary battery of Sample 8 is the same as the nonaqueous electrolyte secondary battery of Sample 1 except for the negative electrode. The method for producing the negative electrode of Sample 8 is the same as the method for producing the negative electrode of Sample 2 except that W is used as a sputtering target.

The composite negative electrode active material body in the negative electrode of Sample 8 contains 0.5% by mass of C and 3.0% by mass of W when the mass of silicon particles, that is, SiO _x is 100% by mass. .

(Sample 9)
The negative electrode of Sample 9 is the same as the negative electrode of Sample 1 except that a transition metal nitride layer (WN reactive sputtered film) is provided instead of the transition metal layer. The nonaqueous electrolyte secondary battery of Sample 9 is the same as the nonaqueous electrolyte secondary battery of Sample 1 except for the negative electrode. The negative electrode manufacturing method of Sample 9 is the same as the negative electrode manufacturing method of Sample 3 except that W is used as a sputtering target.

In addition, the composite negative electrode active material body in the negative electrode of Sample 9 contains 0.5% by mass of C and 3.0% by mass of W when the mass of silicon particles, that is, SiO _x is 100% by mass. .

(Sample 10)
The negative electrode of Sample 10 is the same as the negative electrode of Sample 1 except that the C-coat layer, the transition metal nitride layer, and the transition metal layer are not provided on the composite negative electrode active material body. The nonaqueous electrolyte secondary battery of Sample 10 is the same as the nonaqueous electrolyte secondary battery of Sample 1 except for the negative electrode.

(Sample 11)
The negative electrode of Sample 11 is the same as the negative electrode of Sample 10 except that the composite negative electrode active material body was not provided with the transition metal nitride layer and the transition metal layer, and the amount of the C coat layer. The nonaqueous electrolyte secondary battery of Sample 11 is the same as the nonaqueous electrolyte secondary battery of Sample 1 except for the negative electrode.

In addition, the composite negative electrode active material body in the negative electrode of Sample 11 contains 0.25% by mass of C when the mass of silicon particles, that is, SiO _x is 100% by mass.

(Sample 12)
The negative electrode of Sample 12 is the same as the negative electrode of Sample 1 except that the transition metal nitride layer and the transition metal layer are not provided in the composite negative electrode active material body. Further, the nonaqueous electrolyte secondary battery of Sample 12 is the same as the nonaqueous electrolyte secondary battery of Sample 1 except for the negative electrode.

In addition, the composite negative electrode active material body in the negative electrode of the sample 12 contains 0.5 mass% of C when the mass of silicon particles, that is, SiO _x is 100 mass%.

(Sample 13)
The negative electrode of Sample 13 is the same as the negative electrode of Sample 1 except that the composite negative electrode active material body was not provided with the transition metal nitride layer and the transition metal layer, and the amount of the C coat layer. Further, the non-aqueous electrolyte secondary battery of Sample 13 is the same as the non-aqueous electrolyte secondary battery of Sample 1 except for the negative electrode.

In addition, the composite negative electrode active material body in the negative electrode of Sample 13 contains 1.0 mass% of C when the mass of silicon particles, that is, SiO _x is 100 mass%.

(Sample 14)
The negative electrode of Sample 14 is the same as the negative electrode of Sample 1 except that the composite negative electrode active material body was not provided with the transition metal nitride layer and the transition metal layer, and the amount of the C coat layer. Further, the nonaqueous electrolyte secondary battery of Sample 14 is the same as the nonaqueous electrolyte secondary battery of Sample 1 except for the negative electrode.

In addition, the composite negative electrode active material body in the negative electrode of Sample 14 contains 1.5% by mass of C when the mass of silicon particles, that is, SiO _x is 100% by mass.

(Sample 15)
The negative electrode of Sample 15 is the same as the negative electrode of Sample 1 except that the composite negative electrode active material body was not provided with the transition metal nitride layer and the transition metal layer, and the amount of the C coat layer. The nonaqueous electrolyte secondary battery of Sample 15 is the same as the nonaqueous electrolyte secondary battery of Sample 1 except for the negative electrode.

In addition, the composite negative electrode active material body in the negative electrode of Sample 15 contains 3.0 mass% C when the mass of silicon particles, that is, SiO _x is 100 mass%.

(Sample 16)
The negative electrode of Sample 16 is the same as the negative electrode of Sample 1 except that the composite negative electrode active material body was not provided with the transition metal nitride layer and the transition metal layer, and the amount of the C coat layer. Further, the nonaqueous electrolyte secondary battery of Sample 16 is the same as the nonaqueous electrolyte secondary battery of Sample 1 except for the negative electrode.

In addition, the composite negative electrode active material body in the negative electrode of the sample 16 contains 5.0 mass% of C when the mass of silicon particles, that is, SiO _x is 100 mass%.

  The composition and amount of the C coat layer and the transition metal nitride layer in the composite negative electrode active material bodies of Samples 1 to 16 are shown in Table 1 below.

(Conductivity evaluation test)
About the negative electrode of samples 10-15, electrical conductivity (S / cm) was measured. Specifically, the negative electrodes of Samples 10 to 15 that were cut into 20 mm × 50 mm were prepared as measurement samples. Using a measuring device (MCP-T610) manufactured by Mitsubishi Chemical Corporation, a needle was applied from the negative electrode active material side of the measurement sample, and the conductivity (S / cm) was measured by a four-probe method. The measurement results are shown in FIGS. 2 and 3 are graphs showing the relationship between the amount of C coat layer (carbon content) and electrical conductivity. As shown in FIG. 3, if the carbon (C) content is 0.25% by mass or more, the conductivity is sufficiently high. As shown in FIG. 2, this conductivity is a value close to a C content of 100 mass% (that is, carbon itself). When the C content exceeds 0.25% by mass, the conductivity of the negative electrode is further closer to that of carbon itself, and becomes substantially the same as that of carbon itself at 0.5 mass. For this reason, considering the electrical conductivity, the amount of C contained in the composite negative electrode active material body (the amount of the C coat layer) may be 0.25% by mass or more when the mass of the silicon particles is 100% by mass. It is preferably 0.3% by mass or more, and more preferably 0.5% by mass or more.

(Charge / discharge test)
About each nonaqueous electrolyte secondary battery of samples 1-16, after performing constant current constant voltage (CC-CV) charge at 0.2 mA to charge final voltage 0.8V, 0.2 mA to discharge final voltage 0.08V A constant current and constant voltage discharge was performed. For the nonaqueous electrolyte secondary batteries of Sample 1 to Sample 10 and Sample 12, this charge / discharge was repeated 50 cycles. Based on the result of the first charge / discharge, the initial efficiency was calculated for the nonaqueous electrolyte secondary batteries of Sample 10 to Sample 16. The initial efficiency is a percentage of a value obtained by dividing the initial discharge capacity by the initial charge capacity, and is obtained by (initial discharge capacity / initial charge capacity) × 100. A graph showing the initial efficiency of the nonaqueous electrolyte secondary batteries of Sample 10 to Sample 16 is shown in FIG. As shown in FIG. 4, when the C content of the composite negative electrode active material body is 0.1% by mass or more, the initial efficiency of the nonaqueous electrolyte secondary battery is that the entire surface of the silicon particles is covered with the C coat layer. A value equivalent to the initial efficiency of the sample 16 is obtained. In addition, when the C content of the composite negative electrode active material body is 0.05% by mass or more, the initial efficiency of the nonaqueous electrolyte secondary battery becomes a value close to the initial efficiency of the sample 16. That is, considering the initial efficiency, the C content of the composite negative electrode active material body is preferably 0.05% by mass or more, and more preferably 0.1% by mass or more. From the viewpoint of initial efficiency, it can be said that it is sufficient that the C content of the composite negative electrode active material body is 0.1% by mass. In other words. In consideration of the initial efficiency, the C content of the composite negative electrode active material body is preferably 0.05% by mass or more, and more preferably 0.1% by mass or more. From the viewpoint of initial efficiency, it can be said that it is sufficient if the carbon content of the composite negative electrode active material body is 0.1 mass%.

  For the nonaqueous electrolyte secondary batteries of Sample 1 to Sample 10 and Sample 12, the capacity retention rate after 50 cycles was calculated. The capacity retention rate (%) is obtained by (charge capacity at the time of 50 cycles / initial charge capacity) × 100. Table 2 shows the capacity retention rates of the nonaqueous electrolyte secondary batteries of Samples 1 to 10 and Sample 12.

  As shown in Table 2, the cycle characteristics (capacity maintenance ratio) of the non-aqueous electrolyte secondary batteries of Sample 1, Sample 4 and Sample 7 in which the transition metal layer is interposed between the C coat layer and the silicon grains are silicon It is superior to the cycle characteristics of the non-aqueous electrolyte secondary battery of Sample 12 in which only the C coat layer is provided on the grains.

  Further, for each metal species, when comparing a non-aqueous electrolyte secondary battery having a transition metal nitride layer on a silicon grain and a non-aqueous electrolyte secondary battery having a transition metal layer on a silicon grain, the silicon grain A non-aqueous electrolyte secondary battery having a transition metal nitride layer provided thereon is superior in cycle characteristics. From this, it can be seen that the cycle characteristics are further improved by interposing the transition metal nitride layer between the silicon grains and the C coat layer instead of a mere transition metal layer. This is because the transition metal nitride layer is interposed between the C coat layer and the surface of the silicon grains, so that the adhesion between the C coat layer and the silicon grains is further improved. This is thought to be due to the suppression of layer peeling. From the results shown in Table 2, it can be seen that it is particularly preferable that at least a part of the transition metal nitride layer is made of Ta in view of the initial capacity.

(Other)
The present invention is not limited to the embodiments described above and shown in the drawings, and can be implemented with appropriate modifications within the scope not departing from the gist.

1: Negative electrode 10: Composite negative electrode active material body 11: Silicon grain 12: Transition metal nitride layer 13: C coat layer 15: Current collector

Claims (8)

Silicon particles composed of a silicon-based negative electrode active material containing silicon (Si);
A transition metal nitride layer provided on the silicon grains, including a nitride of at least one transition metal selected from tungsten (W), titanium (Ti), and tantalum (Ta);
A composite negative electrode active material body for a non-aqueous electrolyte secondary battery, comprising: a C coat layer containing carbon (C) and provided on the transition metal nitride layer.   2. The composite negative electrode active material for a nonaqueous electrolyte secondary battery according to claim 1, wherein the amount of C when the mass of the silicon particles is 100 mass% is 0.25 mass% or more and 10.0 mass% or less. body. 2. The composite negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein an element amount of the transition metal when the mass of the silicon particles is 100% is 0.5% by mass or more and 5.0% by mass or less. body.   The amount of the C when the mass of the silicon particles is 100 mass% is 0.5 mass% or more and 5.0 mass% or less. The non-water according to any one of claims 1 to 3. A composite negative electrode active material body for an electrolyte secondary battery. The non-aqueous electrolyte secondary battery according to claim 1, wherein the silicon-based negative electrode active material is made of a silicon oxide represented by SiO _x (0.3 ≦ x ≦ 1.6). Composite negative electrode active material body. Silicon particles composed of a silicon-based negative electrode active material containing silicon (Si);
A transition metal nitride layer provided on the silicon grains, including a nitride of at least one transition metal selected from tungsten (W), titanium (Ti), and tantalum (Ta);
A method for producing a composite negative electrode active material body for a non-aqueous electrolyte secondary battery comprising carbon (C) and a C coat layer provided on the transition metal nitride layer,
Production of a composite negative electrode active material body for a non-aqueous electrolyte secondary battery including a reactive sputtering step of forming the transition metal nitride layer on the silicon grains in the presence of nitrogen gas using at least one of the transition metals as a target Method.   The negative electrode for nonaqueous electrolyte secondary batteries containing the composite negative electrode active material body for nonaqueous electrolyte secondary batteries as described in any one of Claims 1-5.   A nonaqueous electrolyte secondary battery comprising the negative electrode for a nonaqueous electrolyte secondary battery according to claim 7.

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