JP2019179731A - All solid-state battery negative electrode and all solid lithium secondary battery - Google Patents

Abstract

To provide a new negative electrode successfully forming interface contact between a silicon-based negative electrode active material and a Li ion conductive resin so that the utilization efficiency of a negative electrode active material is increased thereby to achieve an increase in charge/discharge efficiency, relating to a negative electrode used in an all solid-state battery and containing the negative electrode active material.SOLUTION: There is proposed an all solid-state battery negative electrode including a Li ion conductive resin, a Si-containing negative electrode active material, and a conductive material.SELECTED DRAWING: None

Description

  The present invention relates to a negative electrode constituting an all solid state battery using a solid electrolyte (referred to as an “all solid state battery negative electrode”), and an all solid state lithium secondary battery using the negative electrode.

  The lithium secondary battery is a secondary battery having a structure in which lithium is melted as ions from the positive electrode during charging and transferred to the negative electrode and stored, and lithium ions are returned from the negative electrode to the positive electrode during discharging. Such a lithium secondary battery has features such as high energy density and long life, so it can be used for home appliances such as video cameras, portable electronic devices such as notebook computers and mobile phones, and power tools. It is widely used as a power source for power tools such as electric tools, and recently, it is also applied to large batteries mounted on electric vehicles (EV) and hybrid electric vehicles (HEV).

  This type of lithium secondary battery is generally composed of a positive electrode, a negative electrode, and an ion conductive layer sandwiched between the two electrodes. The ion conductive layer includes a porous film such as polyethylene or polypropylene. A separator filled with a non-aqueous electrolyte has been generally used. However, because flammable organic electrolytes are used in this way, it was necessary to improve the structure and materials in order to prevent volatilization and leakage, and the installation of safety devices that suppress the temperature rise during short circuits Improvements in structure and materials were also necessary to prevent short circuits.

  On the other hand, all solid-state lithium secondary batteries do not require a flammable organic electrolyte solution, so that the safety device can be simplified and the manufacturing cost and productivity can be improved. In addition, it has a feature that high voltage can be achieved by stacking in series in the cell. Moreover, in the solid electrolyte, since only Li ions do not move, side reactions due to the movement of anions do not occur, and it is expected to lead to improvements in safety and durability.

  Solid electrolytes used in all solid-state lithium secondary batteries are required to have as high an ionic conductivity as possible and to be chemically and electrochemically stable. For example, lithium halide, lithium nitride, lithium oxyacid salt or These derivatives are known as material candidates.

On the other hand, a negative electrode used for a lithium secondary battery is generally prepared by mixing active material particles made of a material capable of inserting lithium ions by charging with a binder, a conductive material, and a solvent, and collecting the resulting mixture. It is manufactured by applying to the surface of the body and drying to form a coating film, followed by pressing.
However, most of the negative electrodes of commercially available batteries use a carbon material (also referred to as “graphite”) as the negative electrode active material. However, the capacity has already reached the theoretical limit, and a new negative electrode active material is used. There is a need for material development. One possible candidate is a negative electrode active material containing silicon (also referred to as a “silicon-based negative electrode active material”).

  The silicon-based negative electrode active material has a potential that the capacity per mass is 5 to 10 times that of graphite. However, the volume change due to insertion / desorption of lithium ions is large, and expansion and contraction are repeated during the charge / discharge cycle. Therefore, separation from the conductive material occurs easily as charge / discharge is repeated, resulting in cycle deterioration and energy. It has a problem of causing a decrease in density and reducing the safety of the battery.

  In order to solve this problem, for example, Patent Document 1 discloses active material particles having an average particle diameter of 5 μm or more and 25 μm or less with respect to active material particles containing silicon. By setting the average particle size of the active material particles to 5 μm or more, the specific surface area of the original active material can be reduced, thereby reducing the contact area between the electrolyte and the new active material surface, thereby improving the cycle characteristics and expanding the active material It is described that the suppression effect of is increased.

  In Patent Document 2, etc., as an electrode material having high lithium insertion / extraction efficiency, an electrode material for a lithium secondary battery composed of particles of a solid state alloy mainly composed of silicon, the solid state alloy Disclosed is an electrode material for a lithium secondary battery, characterized in that microparticles or amorphous materials composed of elements other than silicon are dispersed in microcrystalline silicon or amorphous silicon. Yes.

  Patent Document 3 includes a positive electrode, a separator, and a negative electrode facing the positive electrode through the separator, wherein the negative electrode includes a negative electrode active material containing at least a silicon-based compound and polyimide as a binder. A lithium ion secondary battery using an electrolytic solution is disclosed.

JP 2008-123814 A JP 2010-135336 A International Publication No. 2013/042610

  In the case of a liquid-type lithium secondary battery negative electrode using a silicon-based negative electrode active material, a Li ion conductive resin binder such as polyimide (also referred to as “Li ion conductive resin”), and an electrolyte, Li ion conductivity Since the resin exists in a state of being fixed to a part of the surface of the silicon-based negative electrode active material in the electrolytic solution, and the resin binder is in a swollen state, the exchange of Li ions is mainly performed with the silicon-based negative electrode active material. Performed at the electrolyte interface. On the other hand, when a solid electrolyte is used, the exchange of Li ions is considered to be performed at the contact point between the silicon-based negative electrode active material and the Li ion conductive resin.

When using an electrolytic solution as the electrolyte, even if the volume of the silicon-based negative electrode active material changes due to insertion / extraction of Li ions, the electrolytic solution is fluid, so that the contact between the silicon-based negative electrode active material and the electrolytic solution is good. The exchange of Li ions can also be maintained satisfactorily.
On the other hand, when a solid electrolyte is used as the electrolyte, if the volume of the silicon-based negative electrode active material is greatly changed due to insertion / extraction of lithium ions, the contact between the solid electrolyte and the silicon-based negative electrode active material particles cannot be taken, or Since a contact cannot be obtained even between the negative electrode layer and the solid electrolyte layer, the utilization factor of the active material is lowered, and as a result, a problem that charge / discharge efficiency is lowered is assumed.

  Therefore, the present invention relates to an all-solid battery negative electrode containing a silicon-based negative electrode active material, and satisfactorily forms an interface contact between the negative electrode active material and a Li ion conductive resin to increase the utilization rate of the negative electrode active material. It is an object of the present invention to provide a new all-solid-state battery negative electrode and an all-solid-type lithium secondary battery using the same that can increase the discharge efficiency.

  The present invention proposes an all solid state battery negative electrode comprising a Li ion conductive resin, a negative electrode active material containing Si, and a conductive material.

  The present invention also proposes an all-solid battery negative electrode in which a negative electrode active material containing Si and a conductive material are combined with a Li ion conductive resin as a binder.

  The present invention proposes an all-solid-state battery negative electrode comprising a Li ion conductive resin, a negative electrode active material containing Si, which is continuously covered with the Li ion conductive resin, and a conductive material.

  The present invention is also an all-solid-state lithium secondary battery comprising the all-solid battery negative electrode, a solid electrolyte, and a positive electrode active material, wherein the negative electrode layer and the solid electrolyte layer are in contact with each other. We propose an all-solid-state lithium secondary battery equipped with

The all-solid-state battery negative electrode proposed by the present invention includes a negative electrode active material containing Li ion conductive resin and Si, and a conductive material, thereby favorably forming an interface contact between the negative electrode active material and the Li ion conductive resin. The utilization factor of the negative electrode active material can be increased, and as a result, the charge / discharge efficiency can be improved. At this time, by combining a negative electrode active material containing Si with a Li ion conductive resin as a binder and a conductive material, volume change of the negative electrode can be effectively suppressed. be able to.
Furthermore, by adjusting the type and amount of the Li ion conductive resin, it is possible to reduce the irreversible trapping of Li ions, and the charge / discharge efficiency can be further improved.

  Next, the present invention will be described based on an example of the embodiment. However, this invention is not limited to an example of embodiment described below.

[This negative electrode]
An all-solid battery negative electrode according to an example of the present embodiment, that is, a negative electrode used for an all-solid battery (hereinafter referred to as “main negative electrode”) includes a Li ion conductive resin, a negative electrode active material containing Si, and a conductive material. Is.

  The present negative electrode may be one in which a solid electrolyte is present in addition to the Li ion conductive resin, or may be one in which no solid electrolyte is present. In addition, it is one of the characteristics of this invention that it functions as a negative electrode of an all-solid-state battery negative electrode even if a solid electrolyte does not exist in this negative electrode.

The negative electrode can have a pellet shape, a sheet shape, or other shapes as its form. Especially, it is preferable to exhibit a sheet form from a viewpoint which can handle easily and can respond to enlargement.
As an example of the form of the present negative electrode, there can be mentioned, for example, a Li-ion conductive resin, a Si-based negative electrode active material and a conductive material, and a negative electrode in the form of a sheet in which a solid electrolyte is present if necessary.

<Li ion conductive resin>
The Li ion conductive resin is a resin capable of reversibly transporting Li ions as the battery is charged and discharged.
Examples of the Li ion conductive resin include any one of polyimide, polyamide, and polyamideimide, or a combination of two or more thereof (hereinafter, these are collectively referred to as “polyimide and the like”). . Conductive resins other than these may be used in combination.

  The polyimide or the like preferably has a functional group capable of transporting and storing Li ions from the viewpoint of improving the transport capability of Li ions. Moreover, the functional group may have polarity. Examples of the functional group include aromatics and ethers. However, it is not limited to these.

As the polyimide or the like, a polyimide having an alkyl group, an alkoxy group, an acyl group, a phenyl group, or a phenoxy group can be used.
As an alkyl group, a C1-C6 thing is preferable, a methyl group, an ethyl group, or a propyl group is more preferable, and a methyl group is especially preferable.
As an alkoxy group, a C1-C6 thing is preferable, a methoxy group, an ethoxy group, or a propoxy group is more preferable, and a methoxy group is especially preferable.
As an acyl group, a C2-C6 thing is preferable and an acetyl group, a propionyl group, etc. can be mentioned.
The reason why a polyimide having such a structure is preferable is that, when charged, the Li ions are occluded to suppress the ring opening of the imide ring and to bind firmly to the active material. .
Among the above, from the viewpoint of securing the conduction path of Li ions and obtaining the effect of promoting the transport of Li ions, it is preferably a wholly aromatic polyimide, among them pyromellitic acid-based, and diphenyl ether or alkylbiphenyl, It is preferable to have an alkylpolyphenyl group, and among them, it is particularly preferable to have diphenyl ether.

The Li ion conductive resin in the present negative electrode is preferably present in a proportion of 2 to 20 wt% in the negative electrode (excluding the current collector).
If the Li ion conductive resin is present in the negative electrode in an amount of 2 wt% or more, the volume change of the negative electrode can be effectively suppressed, while if it is 20 wt% or less, the charge / discharge efficiency can be improved. preferable.
From such a viewpoint, the Li ion conductive resin in the present negative electrode is preferably present in a proportion of 2 to 20 wt% in the negative electrode, more than 4 wt%, or less than 20 wt%, and more than 6 wt%. Alternatively, it is preferably present at a ratio of less than 16 wt%, particularly more than 8 wt%, or less than 12 wt%.

<This Si negative electrode active material>
As described above, the Si-based negative electrode active material (referred to as “the present Si-based negative electrode active material”) in the present negative electrode is preferably present in a state of being bonded to the conductive material using Li ion conductive resin as a binder.
At this time, it can be confirmed by observing the cross section of the negative electrode with an electron microscope that the Si negative electrode active material and the conductive material are in a state of being bonded with the Li ion conductive resin as a binder. .

  When the Si-based negative electrode active material constitutes the Li ion conductive resin, the conductive material, and the negative electrode, the utilization factor of the negative electrode active material can be increased, and the charge / discharge efficiency can be improved. In addition, even if the Si-based negative electrode active material expands and contracts, since the Li ion conductive resin functions as a binder, volume change of the negative electrode can be effectively suppressed, thereby improving cycle characteristics. Can be made compatible.

  In order to make this Si type negative electrode active material and a conductive material combined with Li ion conductive resin as a binder, for example, the amount of Li ion conductive resin is adjusted or the shape of the present Si type negative electrode active material The particle size may be adjusted, the kneading method may be adjusted, or the like. At this time, it can be said that when the Si-based negative electrode active material is spherical and finer, the Si-based negative electrode active material and the conductive material are more likely to be combined with the Li ion conductive resin as a binder.

The Si-based negative electrode active material in the present negative electrode is preferably present in the negative electrode (excluding the current collector) at a ratio of 70 wt% or more.
If the negative electrode active material is present in the main negative electrode in an amount of 70 wt% or more, the active material contributing to charging / discharging increases, so that the capacity and energy density can be increased. On the other hand, if it is 98% or less, an ion conductive resin or a conductive material can be included, and a Li ion conduction path can be secured, so that cycle characteristics can be improved.
From this point of view, the Si-based negative electrode active material in the present negative electrode is preferably present in the negative electrode in a proportion of 70 wt% or more, more preferably in a proportion of 98 wt% or less, and in particular, greater than 75 wt%. Or more preferably less than 95 wt%, more preferably greater than 80 wt%, or even less than 92 wt%, especially greater than 84 wt% or less than 88 wt%.

  The Si-based negative electrode active material may be a negative electrode active material containing silicon (Si).

(Si)
Examples of the present Si-based negative electrode active material include, in addition to pure silicon as a main component, silicon oxides such as SiO and SiO ₂ , and silicon-containing materials such as Si ₃ N ₄ and SiC as main components. be able to. Among these, those containing pure silicon as the main component are preferable from the viewpoint of improving the capacity.
Here, “consisting of pure silicon as a main component” means that pure silicon occupies 45 wt% or more of silicon (Si), especially 50 wt% or more, of which 55 wt% or more.

In addition to Si, the present Si-based negative electrode active material suppresses cracking due to expansion and contraction, and element A (A is Li, Al, P, B, Ti, V, Mn, Fe, Co, Ni, Cu, Y , Zr, Nb, Mo, Ta, and W are preferably used.
In this case, in the present Si-based negative electrode active material, the content of the element A other than Si is preferably 40 at% or less, more than 0 at% or less than 25 at%, particularly more than 1 at% or less than 15 at%. Of these, more than 2 at% or less than 10 at% is preferable.

As the state of the element A, it may be dissolved in Si, or another compound (for example, a silicide represented by TiSi ₂ , CoSi ₂ , NiSi ₂ , Mn ₁₁ Si ₁₉ ) may be formed.

The content of oxygen atoms (O) contained in the present Si-based negative electrode active material is preferably less than 30 wt%.
In the present Si-based negative electrode active material, if the content of oxygen atoms (O) is less than 30 wt%, the ratio of oxygen atoms (O) that do not contribute to charge / discharge decreases, and the capacity and charge / discharge efficiency can be increased. It is preferable. However, when oxygen atoms (O) are not contained at all, a rapid reaction with oxygen in the atmosphere occurs, and there is a risk of heat generation and ignition, which is not preferable.
From this point of view, the content of oxygen atoms (O) contained in the present Si-based negative electrode active material is preferably less than 30 wt%, more than 0 wt%, or less than 20 wt%, and more than 0.1 wt%. It is preferably less than 15 wt%, more preferably more than 0.2 wt% or less than 10 wt%, more preferably more than 0.6 wt% or less than 5 wt%.

(Method for producing the present Si-based negative electrode active material)
The present Si-based negative electrode active material is silicon or a silicon-containing material, an element A-containing material as required, and other raw material materials mixed as necessary, heated and melted to be atomized, and if necessary Crushing and classification can be performed. However, it is not limited to such a method.

  A known method may be employed as the atomization method. For example, silicon or a silicon-containing material, an element A-containing material as necessary, and other raw material materials as necessary may be mixed and heated to form a melt, and then atomized by an atomizing method or the like Then, after forming the melt, it may be cast by a roll casting method and further pulverized in a non-oxygen atmosphere to be atomized. Further, after that, particles may be passed through plasma generated using a DC plasma apparatus to form a spherical fine powder.

From the viewpoint of imparting electron conductivity, the Si-based negative electrode active material is preferably coated on the surface with a material having electron conductivity, particularly a material having higher electron conductivity than the inside of the particles. Examples of the substance include metals, metalloids, and compounds thereof. Carbon is particularly preferable from the viewpoint that it hardly reacts with the sulfur component.
In this case, the substance may be present as particles, may be present as aggregated particles obtained by agglomerating particles, or may be present in a layered form.
Here, “exists as a layer” means a state in which the entire surface or a part of the surface of the Si-based negative electrode active material is covered.

Examples of the method of coating the surface of the Si-based negative electrode active material with carbon include a CVD method, a spray pyrolysis method, a planetary ball mill method, and a method of applying to the surface of the active material using a rolling fluidized bed. be able to. However, it is not limited to these methods.
In addition, the state by which the surface of this Si type negative electrode active material is coat | covered with carbon can be confirmed with a scanning transmission electron microscope (TEM), for example.
At this time, the ratio of the surface of the Si-based negative electrode active material covered with carbon, that is, the coverage of carbon is preferably 1% or more, or less than 100%, and more preferably, more than 10% or 80%. Less than that, more preferably more than 20% or less than 50%.
By setting it as such a range, electronic conductivity can be provided, without forming an interface resistance layer.

The present Si-based negative electrode active material may contain unavoidable impurities derived from raw materials.
At this time, in the present Si-based negative electrode active material, the content of inevitable impurities is preferably less than 2 wt%, more preferably less than 1 wt%, and particularly preferably less than 0.5 wt%.

  The Si-based negative electrode active material can be used as a single negative electrode active material, or can be used in combination with graphite.

(Particle shape)
The particle shape of the Si-based negative electrode active material is not particularly limited. For example, a spherical shape, a polyhedral shape, a spindle shape, a plate shape, a scale shape, an amorphous shape, or a combination thereof can be used. Among these, from the viewpoint of uniform expansion and contraction, a shape having good symmetry, for example, a spherical shape is preferable.
For example, it has been confirmed that when it is sphered by gas atomization and pulverized by a jet mill or the like, the particle breaks along the grain boundary, resulting in an indefinite shape.

(Specific surface area)
The specific surface area (SSA) of the present Si-based negative electrode active material is preferably 2 m ² / g or more.
If the specific surface area (SSA) of the present Si-based negative electrode active material is 2 m ² / g or more, the area in which Li ions can be inserted and desorbed increases, so that the resistance can be lowered.
From this point of view, the specific surface area (SSA) of the present Si-based negative electrode active material is preferably 2 m ² / g or more, more preferably less than 140 m ² / g, of which more than 2 m ² / g or 60m less than ² / g, ^{30 m} less than 2 / g among them, particularly preferably more 2.5 m ² / g less than greater than or ^{20 m} 2 / g among them.
In order to adjust the SSA of the present Si-based negative electrode active material within the above range, it is preferable to adjust the pulverization conditions and the modification conditions. However, it is not limited to these adjustment methods.

Ratio of content ratio of Li ion conductive resin: L (wt%) to specific surface area (SSA): M (m ² / g) of the present Si-based negative electrode active material: L / M (wt% / (m ² / g)) is preferably from 0.01 to 10.0.
There are two methods for increasing L / M. One is to increase L and the other is to decrease M. The former means that a large amount of Li ion conductive resin exists with respect to the negative electrode active material, so that a conductive path of Li ions can be secured, and improvement in cycle characteristics is expected. In the latter case, for example, when M is reduced by increasing the particle size, the degree of expansion and contraction of the negative electrode active material is increased, and there is a concern that the cycle characteristics may deteriorate. From the above, it is considered that there is an appropriate range for L / M. When the value of L / M is small, it is considered that the reverse operation to the above-described content occurs.
From this point of view, there is an appropriate range for L / M, and the L / M is preferably 0.01 to 10.0, more preferably 0.02 or more, or 5.0 or less, of which 0.05 Above or 4.5 or less, especially 4.0 or less, more preferably 0.1 or more or 3.5 or less.

(D50)
The laser diffraction / scattering particle size distribution measurement method is a measurement method in which agglomerated particles are regarded as one particle (aggregated particle) and the particle size is calculated. D50 by the measurement method means 50% volume cumulative particle diameter, that is, a diameter of 50% cumulative from the finer one of the cumulative percentage notation of the particle size measurement value converted into volume in the volume reference particle size distribution chart.

The D50 of the present Si-based negative electrode active material is preferably less than 4 μm. If D50 is less than 4 μm, it is preferable because the influence of expansion and contraction can be reduced. However, if the Si-based negative electrode active material is too small, the specific surface area increases, and it becomes difficult to adjust and knead the amount of Li ion conductive resin for bonding the active material.
From this point of view, the D50 of the present Si-based negative electrode active material is preferably less than 4 μm, more preferably greater than 0.01 μm or less than 3.5 μm, more preferably greater than 0.05 μm or less than 3.0 μm, and even more preferably 0 More preferably, it is larger than 0.1 μm or smaller than 2.7 μm, and more preferably, it is larger than 0.2 μm or smaller than 2.0 μm.
In order to adjust the D50 of the present Si-based negative electrode active material to the above range, it is preferable to adjust the starting material, the melting temperature or the melting time, or the D50 by crushing and pulverization after melting. However, it is not limited to these adjustment methods.

The ratio of the content of Li ion conductive resin: L (wt%) to the particle size (D50): P (μm) of the Si-based negative electrode active material: L / P (wt% / (μm) is from 0.5 It is large and preferably 100 or less.
There are two methods for increasing L / P. One is to increase L, and the other is to decrease P.
The former means that a large amount of Li ion conductive resin exists with respect to the negative electrode active material, so that a conductive path of Li ions can be secured, and improvement in cycle characteristics is expected.
On the other hand, when there is too much content rate of Li ion conductive resin, there exists a risk that charging / discharging efficiency will fall. The latter means that the particle size is reduced. When P is reduced, the degree of expansion and contraction of the negative electrode active material is also reduced, so that improvement in cycle characteristics is expected. From the above, it is considered that there is an appropriate range for L / P. When the value of L / P is small, it is considered that the reverse operation to the above-described content occurs.
From this point of view, there is an appropriate range for L / P, and the L / P is preferably greater than 0.5 and less than or equal to 100, more preferably greater than 0.7, or less than 60. It is preferably greater than 0 or less than 50, particularly preferably less than 35, and more preferably greater than 2.0 or less than 20.

<Conductive material>
As the conductive material of the present negative electrode, for example, metal fine powder, powder of conductive carbon material such as carbon nanotube, acetylene black, or the like can be used. Boron (B) or phosphorus (P) or a compound containing these can also function as a conductive material.
When metal fine powder is used, it is preferable to use fine powder such as a conductive metal such as Sn, Zn, Ag and In or an alloy of these metals.

  Examples of the shape of the conductive material include a spherical shape, a fiber shape, and an indefinite shape. Among them, the spherical shape and the fiber shape are preferable from the viewpoint of maintaining the electron conductive path.

  The conductive material in the negative electrode is preferably 1 to 15 wt% in the negative electrode (excluding the current collector), more preferably 10 wt% or less.

<Solid electrolyte>
As described above, in the present negative electrode, a solid electrolyte may be present in addition to the Li ion conductive resin.
The presence of a solid electrolyte in addition to the Li ion conductive resin can increase the Li ion conductivity of the electrode.

  The “solid electrolyte” described in the present specification is not a film (so-called SEI (Solid Electrolyte Interface)) generated at the electrode material interface in the first charge / discharge reaction after the battery is manufactured, but in the battery design, the electrolyte solution and It refers to a solid having Li ion conductivity that can be used as an alternative to a separator.

The solid electrolyte may be an oxide solid electrolyte, a sulfide solid electrolyte, a polymer solid electrolyte, or other solid electrolyte. For example, lithium halide, lithium nitride, lithium phosphate, lithium oxyacid salt, or derivatives thereof can be given.
Among them, a sulfide-based solid electrolyte, and among them, those containing a sulfide-based compound having an Argyrodite type crystal structure are preferable, and among them, those containing as a main phase are preferable. Here, the “main phase” means a composition that is contained most in the compound by a molar ratio.

The sulfide solid electrolyte may be any of a crystalline material, glass ceramics, and glass. For example, Li ₃ PS ₄ , Li ₁₀ GeP ₂ S ₁₂ , Li _3.25 Ge _0.25 P _0.75 S ₄ , 30Li ₂ S · 26B ₂ S ₃ · 44LiI, 63Li ₂ S · 36SiS ₂ · Li ₃ PO ₄ 57Li ₂ S · 38SiS ₂ · 5Li ₄ Si ₄ , 70Li ₂ S · 30P ₂ S ₅ , 50Li ₂ S · 50GeS ₂ , Li ₇ P ₃ S ₁₁ , Li _3.25 P _0.95 S _{4 and the} like. Can be mentioned.

The main phase containing a sulfide compound having an Argyrodite type crystal structure has a cubic Argyrodite type crystal structure, among which Li _7-x PS _6-x Ha _x (Ha: halogen, x: 0. 2-1.8) are preferred. When the above compound is used, Li ions can move more quickly, so that the cycle characteristics can be improved while improving the rate characteristics, and the effects of the present invention can be further enjoyed.

  When a solid electrolyte is present in the negative electrode, it is preferable that the Si-based negative electrode active material and the solid electrolyte exist so as to have a contact.

When a solid electrolyte is present in the negative electrode, the content of the solid electrolyte in the negative electrode (excluding the current collector) is preferably 1 to 15 wt%, more preferably 10 wt% or less, and more preferably 5 wt%. The following is preferable.
The amount of the solid electrolyte is preferably smaller than the amount of the Li ion conductive resin.

<Method for producing the present negative electrode>
This negative electrode is prepared by mixing the present Si-based negative electrode active material (particulate), Li ion conductive resin, conductive material, solvent, and other materials such as graphite as necessary, and mixing them with a kneader. A negative electrode mixture is prepared by smelting, and this negative electrode mixture is applied to the surface of a current collector made of Cu or the like and dried to form a negative electrode active material layer, and then the active material layer is formed as necessary. It can be formed by pressing.

  In the above manufacturing method, the Si-based negative electrode active material is uniformly dispersed in the electrode and is closely adhered to the Li-ion conductive resin, thereby bonding the Si-based negative electrode active material and the conductive material using the Li-ion conductive resin as a binder. And a conductive path of Li ions can be secured.

  Drying after applying the negative electrode mixture to the surface of the current collector is performed for 1 hour to 10 hours, particularly 1 hour to 7 hours in an air atmosphere or a non-oxygen atmosphere such as a nitrogen atmosphere or an argon atmosphere. Can do. Among these, it is preferable to perform drying in a non-oxygen atmosphere, for example, a nitrogen atmosphere or an argon atmosphere.

In addition, when using a polyimide as Li ion conductive resin, it is preferable to use the precursor compound of a polyimide as Li ion conductive resin used when preparing the said negative mix.
A polyamic acid (polyamide acid) can be used as the polyimide precursor compound.

If a negative electrode mixture is apply | coated to the surface of an electrical power collector, while heating a coating film and volatilizing a solvent, the precursor compound of a polyimide can be polymerized and it can be set as a polyimide.
As a result of the study by the present inventors, it has been found that it is advantageous to perform multi-stage heating as the polymerization condition of the precursor compound. In particular, it is advantageous to carry out heating in at least 2 stages, preferably at least 3 stages, more preferably 4 stages. For example, when two-stage heating is performed, the first-stage heating is preferably performed at 100 to 150 ° C., and the second-stage heating is preferably performed at 200 to 400 ° C.

Regarding the heating time, it is preferable that the heating time of the first stage is equal to or longer than the heating time of the second stage. For example, the first stage heating time is preferably set to 120 to 300 minutes, particularly 180 minutes or more and 240 minutes or less, and the second stage heating time is set to 30 to 120 minutes, particularly 30 to 60 minutes.
When three-stage heating is performed, the third stage preferably employs a heating temperature intermediate between the first and second stages.
The third stage heating temperature is preferably 150 to 190 ° C. The heating time is preferably the same as the time of the first stage and the second stage or a time intermediate between the first stage and the second stage. That is, when performing heating in three stages, it is preferable that the heating time be the same in each stage, or that the heating time be shortened as the stages progress.
Furthermore, when performing four steps of heating, it is preferable to employ a higher heating temperature for the fourth step than for the third step.
By performing the above multi-stage heating, the organic solvent contained in the negative electrode mixture can be gradually volatilized, thereby making it possible to sufficiently increase the molecular weight of the precursor compound such as polyimide, and the entire negative electrode The strength of can be increased.

Regardless of the number of stages of heating, the heating is preferably performed in an inert atmosphere such as nitrogen or argon.
In the heat treatment, it is also preferable to hold the active material layer with a pressing member such as a glass plate. By doing so, the polyamic acid can be polymerized in a state in which the organic solvent is abundant, that is, in a state where the polyamic acid is saturated in the organic solvent. Because it becomes.

<This solid battery>
As the all-solid-state lithium secondary battery (referred to as “present solid battery”) according to the present embodiment, the negative electrode described above, a solid electrolyte layer containing a solid electrolyte, and a positive electrode layer containing a positive electrode active material were provided. An all solid-state lithium secondary battery can be mentioned.

The present solid battery preferably has a structure in which the negative electrode layer and the solid electrolyte layer are in contact with each other.
The state of contact can be confirmed by, for example, a scanning electron microscope (SEM).
When the negative electrode layer and the solid electrolyte layer are in contact with each other, a Li ion conduction path can be secured satisfactorily.

  In order to configure the negative electrode layer and the solid electrolyte layer to be in contact with each other on the surface, for example, a crimping press may be performed using a parallel plate. However, it is not limited to this method.

(Negative electrode layer)
The said negative electrode layer should just consist of this main negative electrode mentioned above.

(Positive electrode layer)
The positive electrode layer should just contain the positive electrode active material and the electrically conductive material, and the form is arbitrary. For example, the form can present a pellet form and a sheet form. Especially, it is preferable to exhibit a sheet form from a viewpoint of resistance reduction.

  The positive electrode layer can be prepared, for example, by preparing a positive electrode mixture containing a positive electrode active material, a solid electrolyte, and a conductive material and a binder as necessary, and coating or placing this positive electrode mixture on a current collector. it can. You may dry, press, and heat as needed.

Here, as the positive electrode active material, those conventionally known in the technical field can be used without particular limitation. For example, various lithium transition metal composite oxides can be used. Examples of such materials include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiMn _1.5 Ni _0.5 O ₄ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiCo _0.5 Ni _0.5 O _2. , LiNi _0.7 Co _0.2 Mn _0.1 O ₂ , Li (Li _x Mn _2x Co _1-3x ) O ₂ (where 0 <x <1/3), LiFePO ₄ , LiMn _1-z M _z PO ₄ ( In the formula, 0 <z ≦ 0.1, and M is at least one metal element selected from the group consisting of Co, Ni, Fe, Mg, Zn, and Cu. In addition, from the viewpoint of suppressing the formation of the resistance layer due to the reaction with the solid electrolyte, one or more elements selected from the group consisting of Ti, Zr, Ta, Nb, Zn, W, and Al and O are included. It is preferably coated with a compound.

(Solid electrolyte layer)
The solid electrolyte layer may be a layer made of the solid electrolyte. The form can mention a sheet-like shape, for example.

  When forming the solid electrolyte layer into a sheet, for example, after the solid electrolyte powder is made into a slurry, the solid electrolyte sheet can be obtained by removing the solvent. The solid electrolyte powder may be slurried and applied directly to the positive or negative electrode layer. If necessary, it may be pressed and fired by, for example, an isotropic pressure press.

  The thickness of the solid electrolyte layer is preferably 500 μm or less, more preferably 100 μm or less, of which 50 μm or less, and even more preferably 20 μm or less.

<Explanation of words>
In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), unless otherwise specified, “X is preferably greater than X” or “preferably Y”. It also includes the meaning of “smaller”.
In addition, when expressed as “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), it is “preferably greater than X” or “preferably less than Y”. Includes intentions.

  Hereinafter, the present invention will be described in more detail based on the following examples and comparative examples. However, the present invention is not limited to the following examples.

<Example 1>
As a negative electrode active material, Si powder (D50: 2.7 μm, specific surface area (SSA): 2.6 m ² / g) manufactured by roll casting, acetylene black, and Li ion conductive resin as pyromellitic acid type And a polyimide containing diphenyl ether, these are mixed so as to have a mixing ratio of negative electrode active material: acetylene black: polyimide = 85: 5: 10 (wt%), and N-methylpyrrolidone is put into them, A paste was prepared by stirring. This paste was applied onto Cu foil, dried by heating to 80 ° C. using a hot plate, pressed at a linear pressure of 500 kg using a roll press, and further 1.5 hours under a reduced pressure Ar atmosphere. The temperature was raised to 350 ° C., and the temperature was maintained at 350 ° C. for 1 hour to prepare a negative electrode (sample).
Tables 1 and 2 show various powder properties and element addition amounts of the negative electrode and the negative electrode active material.

<Examples 2-3>
A negative electrode (sample) was produced in the same manner as in Example 1 except that various powder physical properties of the negative electrode active material were changed. Tables 1 and 2 show various powder properties of the negative electrode active material.

<Example 4>
A negative electrode (sample) was prepared in the same manner as in Example 3, except that the mixing ratio of the negative electrode active material, acetylene black, and polyimide was changed to negative electrode active material: acetylene black: polyimide = 77.5: 15: 7.5. Produced.
Tables 1 and 2 show various powder properties and element addition amounts of the negative electrode and the negative electrode active material.

<Example 5>
A negative electrode (sample) was produced in the same manner as in Example 1 except that the particle surface was coated with carbon as the negative electrode active material.
Tables 1 and 2 show various powder properties and element addition amounts of the negative electrode and the negative electrode active material.

<Examples 6 to 8>
In Example 6, except that Ti was added to the negative electrode active material, in Example 7, B and Al were added and atomization was performed, and in Example 8, P and Ni were added and atomization was performed. A negative electrode (sample) was produced in the same manner as in Example 1 except that the preparation was performed.
Tables 1 and 2 show various powder properties and element addition amounts of the negative electrode and the negative electrode active material.

<Comparative Example 1>
As a negative electrode active material, boron (B) is added to a silicon (Si) ingot, roll cast, and then passed through DC plasma. Si spherical particle powder (D50: 0.7 μm, specific surface area (SSA): 20.0 m ² / g) was prepared.
This negative electrode active material, Li _5.8 PS _4.8 Cl _1.2 , which is a sulfide compound having an Argyrodite-type crystal structure as a solid electrolyte, and acetylene black, negative electrode active material: solid electrolyte: acetylene black = These were mixed so as to have a mixing ratio of 45.7: 45.7: 5 (wt%), and dry-mixed in a mortar to obtain a mixed powder. The mixed powder, the positive electrode mixed powder, and the solid electrolyte powder are filled in an insulating cylinder (φ10.5 mm) of a sealed cell so as to form an all-solid lithium secondary battery, and uniaxially molded at 550 MPa to form a pellet. A negative electrode (sample) was prepared.
Tables 1 and 2 show various powder properties and element addition amounts of the negative electrode and the negative electrode active material.

<Measuring method of various physical properties>
Various physical property values of the negative electrodes (samples) obtained in Examples and Comparative Examples were measured as follows.

(D50)
Using an automatic sample feeder for a laser diffraction particle size distribution measuring device (Microtrac Bell Co., Ltd., device name “microtorac SDC”), the negative electrode active materials obtained in Examples and Comparative Examples were converted into ultrasonic homogenizers. The dispersion was dispersed in water and used, and the dispersion was put into a water-soluble solvent. The particle size distribution was measured using a laser diffraction particle size distribution analyzer “MT3300II” manufactured by Microtrack Bell Co., Ltd. at a flow rate of 40 mL / sec, and D50 was determined from the obtained volume reference particle size distribution chart.

(SSA)
The specific surface area (SSA) of the negative electrode active materials obtained in Examples and Comparative Examples was measured as follows. First, 1.0 g was weighed into a glass cell (standard cell) for a fully automatic specific surface area measuring apparatus (manufactured by Mountec, apparatus name “Macsorb”), and set in an autosampler. Next, after replacing the inside of the glass with nitrogen gas, heat treatment was performed in the nitrogen gas at 250 ° C. for 15 minutes. Thereafter, cooling was performed for 4 minutes while flowing a mixed gas of nitrogen and helium. After cooling, the sample was measured by the BET single point method. The adsorbed gas at the time of cooling and measurement was a mixed gas of nitrogen 30 volume%: helium: 70 volume%.

(Analysis of additive elements)
About the negative electrode active material obtained by the Example and comparative example which added the element, content of the additional element was measured by the inductively coupled plasma (ICP) emission spectroscopic analysis. Table 2 shows the results (at%).

(Confirmation of carbon coating)
As a result of observing the coating state by TEM for each of the negative electrode active materials obtained in Examples 1 to 8 with carbon coating, the coverage was 40 to 60%, although there was variation depending on the position.

(Confirmation of presence of negative electrode active material)
As a result of observing the cross-section of each of the negative electrodes (samples) obtained in Examples 1 to 8 with an electron microscope at a magnification of 10,000 times, all of the negative electrodes (samples) obtained in Examples 1 to 8 were a negative electrode active material and It was confirmed that the conductive material was in a state of being bound using Li ion conductive resin as a binder.

<Production of battery>
Samples prepared in Examples and Comparative Examples were used as the negative electrode active material, Nb-coated Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ was used as the positive electrode active material, and Argyrodite-type crystals as the solid electrolyte powder A powder represented by Li _5.8 PS _4.8 Cl _1.2 , which is a sulfide-based compound having a structure, was used.
The positive electrode mixture powder was Nb-coated Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ and a solid electrolyte powder (composition formula: Li _5.8 PS _4.8 Cl _1.2 ) and Showa Denko VGCF (registered trademark) powder, which is a conductive material manufactured by Co., Ltd., was prepared by mixing in a mortar at a ratio of 60: 37: 3.
A solid cell is filled with 50 mg of a solid electrolyte in an insulating cylinder (φ10.5 mm) of a sealed cell, and a negative electrode coating electrode and a positive electrode mixture powder are placed on both sides of the solid electrolyte layer, and parallel plates are used. Each layer was brought into contact with the surface by uniaxial molding at 550 MPa. Then, it tightened with the pressurization screw and produced the all-solid-type lithium secondary battery. In addition, about a filling amount, it is a capacity | capacitance (N / P ratio) of the negative electrode active material with respect to the capacity | capacitance of a positive electrode active material, and a comparative example is 2.0-2. The amount of the positive electrode active material was adjusted to be 5.

<Evaluation of battery characteristics>
(Battery performance evaluation test)
Using the all solid lithium secondary battery cell prepared as described above, initial activity was performed by the method described below. The produced all solid lithium secondary battery cell was charged by the CC-CV method with an upper limit voltage of 4.5V only during the first cycle, and discharged by the CC method with a lower limit voltage of 2.5V. Charging and discharging were performed at 0.1C. The charge / discharge efficiency (%) at the first cycle is shown in Table 3 as an index with Comparative Example 1 taken as 100.
The second cycle was charged by the CC-CV method with an upper limit voltage of 4.3V, and the discharge was performed by the CC method with a lower limit voltage of 2.5V. Charging and discharging were performed at a current value of 0.1C.
From the third cycle onward, the battery was charged by the CC-CV method with an upper limit voltage of 4.3V, and the discharge was repeatedly charged and discharged by the CC method with a lower limit voltage of 2.5V. Charging and discharging were performed at a current value of 0.2C.
The cycle characteristics (discharge capacity retention rate (%)) are shown as a quotient obtained by dividing the discharge capacity at the 51st cycle by the discharge capacity at the 3rd cycle. The actually set current value was calculated from the content of the positive electrode active material in the positive electrode. The cycle characteristics are shown in Table 3 as an index with Comparative Example 1 taken as 100.

From the above examples and the results of tests conducted by the present inventors, the negative electrode active material is an all solid state battery negative electrode including a Li ion conductive resin, a negative electrode active material containing Si, and a conductive material. It has been found that the interface contact between Li and the Li ion conductive resin can be satisfactorily formed, and the utilization factor of the negative electrode active material can be increased. At this time, by combining a negative electrode active material containing Si with a Li ion conductive resin as a binder and a conductive material, volume change of the negative electrode can be effectively suppressed. be able to.
Furthermore, it was found that by adjusting the type and amount of the Li ion conductive resin, it is possible to reduce the irreversible trapping of Li ions and to further improve the charge / discharge efficiency. .

Claims (16)

  An all-solid-state battery negative electrode comprising a Li ion conductive resin, a negative electrode active material containing Si, and a conductive material.   2. The all-solid-state battery negative electrode according to claim 1, wherein the negative electrode active material containing Si and the conductive material are in a state of being bonded with a Li ion conductive resin as a binder.   The all-solid-state battery negative electrode according to claim 1, further comprising a solid electrolyte.   The all-solid battery negative electrode according to claim 3, wherein the solid electrolyte includes a sulfide-based solid electrolyte.   5. The all-solid battery negative electrode according to claim 1, wherein a content ratio of the negative electrode active material in the all-solid battery negative electrode is 70 wt% or more.   The all-solid-state battery negative electrode according to any one of claims 1 to 5, wherein a content ratio of the Li ion conductive resin in the all-solid-state battery negative electrode is 2 to 20 wt%.   The all-solid-state battery negative electrode according to any one of claims 3 to 6, wherein the solid electrolyte includes a sulfide-based compound having an Argyrodite type crystal structure. The all-solid-state battery negative electrode according to claim 1, wherein the negative electrode active material has a specific surface area (SSA) of 2.0 m ² / g or more. The ratio of the Li ion conductive resin content: L (wt%) to the specific surface area (SSA): M (m ² / g) of the negative electrode active material: L / M (wt% / (m ² / g) )) Is 0.01-10.0, The all-solid-state battery negative electrode in any one of Claims 1-8 characterized by the above-mentioned.   The all-solid-state battery negative electrode according to claim 1, wherein D50 of the negative electrode active material is less than 4.0 μm.   The ratio of the content of the Li ion conductive resin: L (wt%) to the particle size (D50): P (μm) of the negative electrode active material: L / P (wt% / μm) is greater than 0.5, The all-solid-state battery negative electrode according to claim 1, which is 100 or less.   The negative electrode active material is composed of element A (A is Li, Al, P, B, Ti, V, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ta, and W in addition to Si. The all-solid-state battery negative electrode in any one of Claims 1-11 containing 1 type, or 2 or more types of elements chosen from the group.   The all-solid-state battery negative electrode according to any one of claims 1 to 12, wherein the negative electrode active material is surface-coated with a substance having higher electron conductivity than the inside of the particles.   The all-solid-state battery negative electrode according to claim 1, wherein the negative electrode active material is coated with carbon.   The all-solid-state battery negative electrode in any one of Claims 1-14 which exhibit a sheet form. An all solid state lithium secondary battery comprising the all solid state battery negative electrode according to any one of claims 1 to 15, a solid electrolyte, and a positive electrode active material, wherein the negative electrode and the solid electrolyte are in contact with each other on a surface. All-solid-state lithium secondary battery.