JP7111005B2 - Negative electrode for all-solid-state lithium-ion secondary battery - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to a negative electrode for an all-solid lithium ion secondary battery.

As a negative electrode active material used in lithium-ion secondary batteries, compared to the carbon-based negative electrode active material that has been widely used in the past, the volume change accompanying charging and discharging is small, and as a negative electrode active material that provides excellent cycle characteristics, spinel type Lithium titanate Li ₄ Ti ₅ O ₁₂ is known. However, batteries using spinel-type lithium titanate as a negative electrode active material have a problem of low energy density.

In Patent Document 1, in a negative electrode for a lithium ion secondary battery using a liquid nonaqueous electrolyte as a nonaqueous electrolyte, a niobium-titanium composite oxide having a larger theoretical capacity per weight than spinel-type lithium titanate is used as a negative electrode active material. , discloses that in a negative electrode layer containing active material particles containing a niobium-titanium composite oxide, the mode diameter in the pore size distribution obtained by mercury porosimetry is in the range of 0.1 μm to 0.2 μm.

On the other hand, in the field of batteries such as lithium-ion secondary batteries, development of all-solid-state batteries using solid electrolytes instead of liquid electrolytes is underway. An all-solid-state battery does not use a combustible organic solvent in the battery, so it is thought that the safety device can be simplified and the manufacturing cost and productivity are excellent.
The present applicant discloses in Patent Document 2 that a negative electrode for an all-solid-state battery using composite particles having a carbon material containing Si or Sn with a specific particle size as a negative electrode active material, and the porosity of the negative electrode is 5% to 5%. 30%.

Patent No. 6193285 JP 2017-54720 A

However, the liquid battery technology disclosed in Patent Document 1 ensures ion conduction by impregnating the pores of the negative electrode with an electrolytic solution. Due to the pores, it is difficult to obtain contact between the solid electrolyte and the negative electrode active material, and ion conduction paths and electronic conduction paths become insufficient, resulting in problems of increased resistance and decreased capacity.
The negative electrode for an all-solid-state battery of Patent Document 2 suppresses deterioration of battery performance after charging and discharging, but since it is a technology that uses specific composite particles as a negative electrode active material, various negative electrode active materials are used. A possible technology is desired.

In view of the above circumstances, the present disclosure is an all-solid lithium ion secondary battery that can use various negative electrode active materials to improve the energy density of the battery and can suppress deterioration in battery performance after charging and discharging. An object of the present invention is to provide a negative electrode for

The negative electrode for an all-solid lithium ion secondary battery of the present disclosure is a negative electrode for an all-solid lithium ion secondary battery having a negative electrode active material layer,
Before initial charging, the peak diameter in the pore size distribution of the negative electrode active material layer measured by a mercury intrusion method is 0.1 μm or less, and the porosity of the negative electrode active material layer is 10% or more and 25% or less,
The negative electrode active material contained in the negative electrode active material layer has a volume expansion rate of 15% or less at full charge compared to before initial charge.

According to the present disclosure, in the negative electrode active material layer in which the volume expansion coefficient of the negative electrode active material at full charge compared to before initial charge is equal to or less than the specific value, the pore size distribution before initial charge is equal to or less than the specific value, and the initial Provided is a negative electrode for an all-solid-state lithium-ion secondary battery that can suppress deterioration in battery performance after charging and discharging, regardless of the type of negative electrode active material, because the porosity before charging is within the specific range. can do.

BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram which shows an example of the all-solid-state lithium ion secondary battery provided with the negative electrode for all-solid-state lithium ion secondary batteries of this indication. 4 is a graph showing the pore size distribution of the negative electrode active material layer of the negative electrode for an all-solid lithium ion secondary battery of Example 1, measured by mercury porosimetry.

The negative electrode for an all-solid lithium ion secondary battery of the present disclosure is a negative electrode for an all-solid lithium ion secondary battery having a negative electrode active material layer,
Before initial charging, the peak diameter in the pore size distribution of the negative electrode active material layer measured by a mercury intrusion method is 0.1 μm or less, and the porosity of the negative electrode active material layer is 10% or more and 25% or less,
The negative electrode active material contained in the negative electrode active material layer has a volume expansion rate of 15% or less at full charge compared to before initial charge.

In the negative electrode for all-solid-state lithium ion secondary batteries, when using a negative electrode active material that can cause volume change due to charge and discharge in order to improve the energy density of the battery, the expansion and contraction of the negative electrode active material due to charge and discharge causes the negative electrode cracks may occur. In all-solid-state batteries, conduction is achieved by physical contact, so cracks in the electrodes cut the ionic conduction path and electronic conduction path, resulting in deterioration of battery performance such as a decrease in output and capacity. becomes a problem.
The negative electrode for an all-solid-state lithium ion secondary battery of the present disclosure adjusts the negative electrode capacity according to the type of negative electrode active material so that the volume expansion rate of the negative electrode active material at full charge is 15% or less compared to before initial charge. used as The researchers found that the peak diameter (hereinafter sometimes referred to as the pore peak diameter) in the pore size distribution of the negative electrode active material layer measured by the mercury intrusion method is 0.1 μm or less before initial charging, and , the porosity of the entire negative electrode active material layer is within a specific range of 10% or more and 25% or less, so that the ion conduction path and the electron conduction path are performed well, and the volume expansion coefficient of the negative electrode active material is 15 % or less, the battery performance is likely to be maintained for a long period of time even after charging and discharging.
Since the negative electrode for an all-solid lithium ion secondary battery of the present disclosure has a pore peak diameter of 0.1 μm or less before initial charging, the size of each pore in the negative electrode active material layer is sufficiently small, and ion It is presumed that deterioration in battery performance is suppressed because the conduction path and the electron conduction path are less likely to be cut. In addition, the negative electrode for an all-solid lithium ion secondary battery of the present disclosure has a porosity of 10% or more and 25% or less in the entire negative electrode active material layer before initial charge, so that from before initial charge to full charge It is considered that a sufficient space is secured to accommodate the volume change of the negative electrode active material. Therefore, in the negative electrode for an all-solid lithium ion secondary battery of the present disclosure, even after the negative electrode active material expands and contracts due to charging and discharging, the size and porosity of each pore in the negative electrode active material layer are easily maintained. After that, it is presumed that cracking of the negative electrode is suppressed, and deterioration of battery performance due to disconnection of ion-conducting paths and electron-conducting paths is suppressed.
Cracking of the negative electrode due to expansion and contraction of the negative electrode active material during charging and discharging can also be suppressed by, for example, providing a battery restraining mechanism in the battery pack and applying sufficient restraining pressure to the battery. However, there is a problem that the energy density of the battery pack decreases as the proportion of equipment other than batteries increases in the battery pack. In contrast, by using the negative electrode for an all-solid-state lithium ion secondary battery of the present disclosure, it is possible to sufficiently suppress deterioration of battery performance with a simple restraint mechanism, so the restraint mechanism provided in the battery pack can be simplified. , and the energy density in the battery pack can be improved.
Hereinafter, the negative electrode for an all-solid lithium ion secondary battery of the present disclosure will be described in detail.

The negative electrode for an all-solid-state lithium ion secondary battery of the present disclosure has at least a negative electrode active material layer, and if necessary, may further include other components such as a negative electrode current collector.
In addition, in the present disclosure, the negative electrode may be one before being incorporated into the battery, or may be one after being incorporated into the battery.

<Negative electrode active material layer>
The negative electrode active material layer of the negative electrode for an all-solid lithium ion secondary battery of the present disclosure contains at least a negative electrode active material, and if necessary, other components such as a solid electrolyte, a binder, and a conductive aid. may contain.
In the negative electrode for an all-solid lithium ion secondary battery of the present disclosure, the negative electrode active material layer has a specific pore peak diameter and porosity, and the negative electrode active material contained in the negative electrode active material layer has a specific It is characterized by having a volume expansion coefficient.

(pore peak diameter)
The negative electrode active material layer has a peak diameter of 0.1 μm or less in a pore size distribution measured by a mercury porosimetry method, that is, a pore peak diameter, before initial charging. The pore peak diameter is preferably 0.08 μm or less from the viewpoint of easily suppressing deterioration of battery performance.
In the mercury intrusion method, mercury is forced into the pores of a solid sample by pressurizing it, and the diameter and volume of the pores are calculated from the pressure applied to the mercury and the amount of mercury injected into the pores. . When mercury to which a pressure P is applied can enter a pore having a diameter D, the diameter D of the pore can be obtained from the pressure P, the contact angle θ of mercury, and the surface tension σ of mercury according to Equation 1 below. Desired. Also, the pore volume is calculated from the amount of mercury injected into the pores. In addition, in this disclosure, the pore diameter is the diameter of the pore.
(Formula 1)
−4σ cos θ=PD
In the present disclosure, the pore size distribution measured by the mercury intrusion method is a graph plotting the Log differential pore volume (cm ³ /g)) against the average pore size (μm) of the section of each measurement point. where the horizontal axis is the pore diameter (μ) and the vertical axis is the log differential pore volume (cm ³ /g).
In the present disclosure, the peak diameter in the pore size distribution is the pore size at the top of the highest peak in the pore size distribution.
The pore peak diameter of the negative electrode active material layer depends on the type, size, and blending amount of the negative electrode active material contained in the negative electrode active material layer, the pressure during pressing when forming the negative electrode active material layer, and the like. can be adjusted.

The measurement of the pore size distribution by the mercury intrusion method is performed on the negative electrode active material layer before initial charging. For example, using a measurement sample obtained by punching the negative electrode for an all-solid lithium ion secondary battery of the present disclosure incorporated in a battery into a predetermined shape before initial charging, the negative electrode activity of the measurement sample For the substance layer, the pore size distribution can be measured by the mercury porosimetry. The measurement sample should have at least the negative electrode active material layer on its surface, and may further have other components such as a negative electrode current collector.
The shape of the measurement sample used for the measurement of the pore peak diameter is not particularly limited, but may be, for example, a coin shape or a cylindrical shape.

The measurement of the pore size distribution by the mercury intrusion method can be performed, for example, using an apparatus such as Autopore IV9500 series manufactured by Micromeltics. During measurement, the measurement sample is enclosed in a sample container in an inert atmosphere, mercury is injected into the sample container, and pressure is applied to the mercury. Here, the pressure applied to the mercury is appropriately adjusted according to the size of the pore diameter that the measurement sample may have, and is not particularly limited, but for example, from 0.5 psi (3.4 kPa) to 60000 psi (413400 kPa). It is preferable to measure by changing the pressure, because the pore size can be measured over a wide range.

(porosity)
The negative electrode active material layer has a porosity of 10% or more and 25% or less before initial charging. The porosity is preferably 10% or more and 24% or less in order to easily suppress deterioration of battery performance.
The porosity of the negative electrode active material layer is determined by using a measurement sample obtained by punching the negative electrode for an all-solid lithium ion secondary battery of the present disclosure into a predetermined shape before initial charging. Based on the weight and volume of the negative electrode active material layer, it is obtained according to Equation 2 below. In Equation 2 below, the theoretical specific gravity of the material constituting the negative electrode active material layer can be obtained from the true specific gravity and compounding ratio of each material.
(Formula 2)
Porosity [%]=100−{(weight of negative electrode active material layer/volume of negative electrode active material layer)/theoretical specific gravity of material constituting negative electrode active material layer}×100
The porosity of the negative electrode active material layer may be adjusted by adjusting the type, size and blending amount of the negative electrode active material contained in the negative electrode active material layer, the pressure during pressing when forming the negative electrode active material layer, and the like. can be done.
As the measurement sample used for measuring the porosity, the same measurement sample as used for determining the pore peak diameter can be used.

(Negative electrode active material)
The negative electrode active material contained in the negative electrode active material layer is not particularly limited, but the use of a negative electrode active material that undergoes a volume change due to charging and discharging has the effect of suppressing deterioration in battery performance after charging and discharging according to the present disclosure. is preferable because it is easy to obtain. Examples of negative electrode active materials whose volume changes due to charging and discharging include carbon-based negative electrode active materials such as niobium-titanium composite oxides and graphite, alloy-based negative electrode active materials such as silicon and tin, SiOx, and these negative electrode active materials. Composite materials and the like can be mentioned. Examples of the negative electrode active material whose volume increase upon lithium ion absorption is 15% or less of the volume upon lithium ion release include carbon-based negative electrode active materials such as niobium-titanium composite oxides and graphite.
Among them, from the viewpoint of improving the energy density and increasing the capacity of the battery, the negative electrode active material layer preferably contains a niobium-titanium composite oxide as a negative electrode active material, and a niobium-titanium composite oxide having a monoclinic structure. Containing is more preferable. In the present disclosure, in the niobium-titanium composite oxide, part of niobium (Nb) and titanium (Ti) may be replaced with different elements. Examples of the dissimilar elements include Mg, Sr, Mo, W, Ta and V. Examples of the _{niobium - titanium composite oxide include TiNb2O7} , _Ti2Nb10O29 , _TiNb24O62 , _TiNb14O37 , and _{Ti2Nb2O9 .} TiNb ₂ O ₇ is preferable from the viewpoint of improving the energy density of the battery and increasing the capacity.

In the negative electrode of the present disclosure, the negative electrode active material contained in the negative electrode active material layer has a volume expansion rate of 15% or less at full charge compared to before initial charge. Note that the volume expansion coefficient is satisfied for all negative electrode active materials contained in the negative electrode active material layer.
The lower limit of the volume expansion rate of the negative electrode active material is not particularly limited, but when it is 3% or more, the effect of suppressing deterioration of battery performance after charging and discharging can be easily obtained.

The volumetric expansion rate of the negative electrode active material at full charge compared to before initial charge is obtained according to Equation 3 below.
(Formula 3)
Volume expansion rate [%] = {(volume of negative electrode active material at full charge−volume of negative electrode active material before initial charge)/volume of negative electrode active material before initial charge}×100
Here, "before initial charging" means before initial charging of a battery incorporating the negative electrode for an all-solid-state lithium ion secondary battery of the present disclosure. The fully charged time is the time when a battery incorporating the negative electrode for an all-solid-state lithium ion secondary battery of the present disclosure is charged to the maximum voltage. A battery incorporating the negative electrode for an all-solid-state lithium ion secondary battery of the present disclosure is preferably charged at a rate of 0.1 C or more and 0.5 C or less from the viewpoint of sufficiently charging the battery.
The volume expansion coefficient of the negative electrode active material can be confirmed by observing the change in lattice constant obtained by X-ray diffraction before and after charging and the particle size by SEM.

The volume expansion rate of the negative electrode active material can be adjusted according to the type of the negative electrode active material and the negative electrode capacity of the negative electrode for an all-solid lithium ion secondary battery of the present disclosure. For example, the volume expansion rate of the negative electrode active material can be set to 15% or less by using a negative electrode active material whose volume increase amount when absorbing lithium ions is 15% or less of the volume when releasing lithium ions. . When the negative electrode active material contains a volume increase of 15% or more of the volume when releasing lithium ions, for example, the volume expansion rate of the negative electrode active material is 15% or less. By suppressing the negative electrode capacity, the volume expansion rate of the negative electrode active material can be set to 15% or less. Note that the negative electrode capacity can be adjusted, for example, by the capacity ratio between the positive electrode and the negative electrode.

The size of the negative electrode active material is not particularly limited, but from the viewpoint of slurry preparation, the median diameter (D50) is preferably 0.1 μm or more, more preferably 0.2 μm or more. On the other hand, from the viewpoint of the solid diffusion of the negative electrode active material, the median diameter (D50) is preferably 5 μm or less, more preferably 3 μm or less.
The median diameter (D50) is a particle size corresponding to a cumulative frequency of 50% by volume from fine particles having a smaller particle size in a volume-based particle size distribution based on a laser diffraction light scattering method.

The content of the negative electrode active material is not particularly limited, but from the viewpoint of increasing the energy density, the content of the negative electrode active material is 30 parts by mass with respect to the total amount of 100 parts by mass of the negative electrode active material layer. It is preferably 40 parts by mass or more, and on the other hand, it is preferably 90 parts by mass or less from the viewpoint of sufficiently containing other components other than the negative electrode active material in the negative electrode active material layer. Preferably, it is 80 parts by mass or less.
In addition, the content of the negative electrode active material in a total of 100 parts by mass of the negative electrode active material and the solid electrolyte described later is preferably 40 parts by mass or more from the viewpoint of increasing the energy density, and is preferably 50 parts by mass or more. On the other hand, it is preferably 90 parts by mass or less, more preferably 80 parts by mass or less, from the viewpoint of sufficiently containing the solid electrolyte to improve ion conductivity.

(solid electrolyte)
The negative electrode active material layer preferably further contains a solid electrolyte in order to improve ion conductivity and improve battery performance.
Examples of the solid electrolyte that the negative electrode active material layer may contain include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, and nitride solid electrolytes. From this point of view, a sulfide solid electrolyte can be preferably used.
Examples of sulfide solid electrolytes include Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiI, Li ₂ SP ₂ S ₅ -LiI-LiBr, Li ₂ SP ₂ S ₅ —Li ₂ O, Li ₂ SP ₂ S ₅ —Li ₂ O—LiI, Li ₂ S—SiS ₂ , Li ₂ S—SiS ₂ —LiI, Li ₂ S—SiS ₂ —LiBr, Li ₂ S—SiS ₂ -LiCl, _{Li2S - SiS2 - B2S3 -} LiI, _{Li2S - SiS2 - P2S5 -} LiI, _{Li2S -} B2S3, Li2SP2S5- Z _m S _n (where m and n are positive numbers and Z is Ge, Zn or Ga), Li ₂ S—GeS ₂ , Li ₂ S—SiS ₂ —Li ₃ PO ₄ , Li 2S—SiS _{2 —Li x} MO _y (where x and y are positive numbers, and M is P, Si, Ge, B, Al, Ga or In). Among them, those containing Li _{2 SP 2 S 5 are more preferable, and Li 2 SP 2 S 5 -LiI -} LiBr is particularly preferable, because of their high ionic conductivity. The description of "Li ₂ SP _{2 S 5 " means a sulfide solid electrolyte using a raw material composition containing Li 2 S and P 2 S 5 , and} the same applies to other descriptions. .

The content of the solid electrolyte is not particularly limited, but the content of the solid electrolyte in a total of 100 parts by mass of the negative electrode active material and the solid electrolyte improves the ion conductivity, It is preferably 10 parts by mass or more, more preferably 20 parts by mass or more. On the other hand, from the viewpoint of increasing the energy density by sufficiently containing the negative electrode active material, it is preferably 70 parts by mass or less. It is more preferably 60 parts by mass or less.

When the negative electrode active material layer contains a solid electrolyte other than a sulfide solid electrolyte as a solid electrolyte, from the viewpoint of improving ion conductivity, The proportion of the sulfide solid electrolyte is preferably 70 parts by mass or more, more preferably 80 parts by mass or more, and even more preferably 90 parts by mass or more.

(Binder)
The negative electrode active material layer may further contain a binder.
Examples of the binder that may be contained in the negative electrode active material layer include polyvinylidene fluoride (PVDF) and a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (PVDF-HFP). , polytetrafluoroethylene (PTFE), butylene rubber (BR), styrene-butadiene rubber (SBR), polyvinyl butyral (PVB), acrylic resin, and the like.

The content of the binder is not particularly limited, but from the viewpoint of sufficiently expressing the function as a binder, the content of the binder in the total amount of 100 parts by mass of the negative electrode active material layer is 0. It is preferably 3 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 5 parts by mass or less in order to sufficiently contain other materials.

(Conductivity aid)
The negative electrode active material layer may further contain a conductive aid in order to improve electron conductivity.
As the conductive aid that may be contained in the negative electrode active material layer, those used in conventional all-solid-state batteries can be appropriately selected and used, and are not particularly limited. and carbon materials such as carbon nanotubes such as carbon fiber) and carbon nanofibers.

The content of the conductive aid is not particularly limited, but from the viewpoint of ensuring a large number of electron conduction paths in the negative electrode, the content of the conductive aid in the total amount of 100 parts by mass of the negative electrode active material layer is preferably 1.0 parts by mass or more, and preferably 15 parts by mass or less from the viewpoint of sufficiently containing other materials.

The thickness of the negative electrode active material layer is not particularly limited, but may be, for example, 10 μm or more and 100 μm or less, or may be 10 μm or more and 50 μm or less.

<Negative electrode current collector>
The negative electrode for an all-solid lithium ion secondary battery of the present disclosure may further have a negative electrode current collector. The negative electrode current collector has a function of collecting current for the negative electrode active material layer.
In the present disclosure, as the negative electrode current collector, a known negative electrode current collector that can be used for all-solid-state batteries can be appropriately selected and used, and is not particularly limited.
Examples of materials for the negative electrode current collector include SUS, Cu, Ni, Fe, Ti, Co, and Zn.
Examples of the shape of the negative electrode current collector include a foil shape, a plate shape, and a mesh shape.
The negative electrode for an all-solid lithium ion secondary battery of the present disclosure may further include a negative electrode lead connected to the negative electrode current collector.

<Method for producing negative electrode for all-solid lithium ion secondary battery>
The method for manufacturing the negative electrode for the all-solid lithium ion secondary battery of the present disclosure is not particularly limited as long as it is a method capable of manufacturing the negative electrode for the all-solid lithium ion secondary battery of the present disclosure described above. Among them, since the negative electrode active material layer tends to have the specific pore peak diameter and porosity, the method of forming the negative electrode active material layer is to use a slurry or paste composition for a negative electrode active material layer as a support. and drying to form a coating film for the negative electrode active material layer; and pressing the coating film for the negative electrode active material layer to form the negative electrode active material layer. Preferably.
The composition for a negative electrode active material layer is obtained by adding a dispersion medium to each component constituting the negative electrode active material layer and mixing them to form a slurry or a paste.
In the method for forming the negative electrode active material layer, by using the negative electrode current collector as the support, at least one of the negative electrode current collectors has the negative electrode active material layer. A negative electrode for the next battery can be easily obtained.

In the step of pressing the negative electrode active material layer coating film, for example, the negative electrode structure having the negative electrode active material layer coating film on the support can be subjected to the pressing treatment. The step of pressing the negative electrode active material layer coating film may be performed before or after the negative electrode structure is incorporated into the battery. When the pressing step is performed before incorporating the negative electrode structure into the battery, the negative electrode for an all-solid lithium ion secondary battery of the present disclosure is obtained before being incorporated into the battery. When the pressing step is performed after the negative electrode structure is built into the battery, the negative electrode for an all-solid lithium ion secondary battery of the present disclosure is obtained after being built into the battery. Above all, if the pressing step is carried out after the negative electrode structure is incorporated into the battery, the ionic conduction path and the electronic conduction path between the negative electrode active material layer and the solid electrolyte layer in the battery tend to be improved. It is preferable from the point of view. The pressure of the press is not particularly limited, and can be, for example, 20 MPa or more and 1000 MPa or less.

<All solid state lithium ion secondary battery>
An all-solid-state lithium-ion secondary battery using the all-solid-state lithium-ion secondary battery negative electrode of the present disclosure includes the above-described all-solid-state lithium-ion secondary battery negative electrode of the present disclosure as a negative electrode. In the all-solid-state lithium-ion secondary battery including the negative electrode of the present disclosure described above, the deterioration of the performance of the negative electrode is suppressed even after charging and discharging, so the deterioration of the battery performance is suppressed. In addition, the all-solid-state lithium ion secondary battery equipped with the negative electrode of the present disclosure suppresses cracking of the negative electrode, and suppresses deterioration in battery performance due to disconnection of the ion-conducting path and the electron-conducting path. , the restraining mechanism for applying the restraining pressure to the battery can be simplified. By simplifying the restraint mechanism provided inside the battery pack, the energy density inside the battery pack can be improved.
In addition, in the all-solid-state lithium ion secondary battery including the negative electrode of the present disclosure, the configuration other than the negative electrode can adopt the same configuration as a known all-solid-state lithium ion secondary battery, and is not particularly limited.

As an all-solid lithium ion secondary battery comprising the negative electrode of the present disclosure, for example, all-solid lithium having the negative electrode of the present disclosure described above, a positive electrode, and a solid electrolyte layer disposed between the negative electrode and the positive electrode An ion secondary battery can be mentioned. FIG. 1 is a cross-sectional schematic diagram showing an example of an all-solid-state lithium-ion secondary battery comprising the negative electrode of the present disclosure. The all-solid lithium ion secondary battery 100 shown in FIG. and a negative electrode 17, and the negative electrode 17 is the above-described negative electrode for an all-solid lithium ion secondary battery of the present disclosure.
The all-solid lithium ion secondary battery comprising the negative electrode of the present disclosure may be a cell assembly by integrating and electrically connecting a plurality of single cells as shown in FIG. At least one of the plurality of negative electrodes may be the negative electrode for the all-solid lithium ion secondary battery of the present disclosure. This is preferable because subsequent deterioration in battery performance is easily suppressed.

EXAMPLES The present disclosure will be described in more detail below with reference to Examples, but the present disclosure is not limited only to these Examples. Examples 5 and 6 are reference examples.

[Example 1]
(1) Synthesis of negative electrode active material Titanium oxide (anatase type, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and niobium oxide (manufactured by Kishida Chemical Co., Ltd.) It was weighed so that the ratio (Ti:Nb) was 1:2. These raw materials, zirconia beads with a diameter of 5 mm, and ethanol were placed in a planetary ball mill (manufactured by Fritsche) and mixed for 2 hours at a rotation speed of 200 rpm. After mixing, the dried mixture was sintered in the air at 1100° C. for 12 hours to obtain TiNb ₂ O ₇ powder. The obtained TiNb ₂ O ₇ powder, zirconia beads with a diameter of 0.5 mm, and ethanol were placed in a planetary ball mill, wet-ground at 400 rpm for 3 hours, and then dried. After that, in order to restore the crystallinity that had been reduced by the pulverization treatment, it was re-fired at 700° C. for 5 hours to obtain TiNb ₂ O ₇ with a monoclinic structure and a median diameter (D50) of 0.3 μm. rice field.

(2) Fabrication of Negative Electrode Structure As a sulfide solid electrolyte, each raw material was blended so that the molar ratio of _Li2S : _P2S5 :LiBr:LiI was 56.25:18.75: ₁₅ :10. As a result, a sulfide solid electrolyte (10LiI-15LiBr-75 (0.75Li ₂ S-0.25P ₂ S ₅ )) was obtained.
The TiNb ₂ O ₇ (D50 is 0.3 μm) as a negative electrode active material and the sulfide solid electrolyte (10LiI-15LiBr-75 (0.75Li ₂ S-0.25P ₂ S ₅ )) were combined as negative electrode active materials. : The mass ratio of the sulfide solid electrolyte was 75: 25. Furthermore, a PVDF-HFP binder (manufactured by Solvay, Soref (registered trademark)) was added as a binder to 100 parts by mass of the negative electrode active material. 21510) was weighed in. Furthermore, methyl isobutyl ketone (dehydrated grade, manufactured by Nacalai Tesque Co., Ltd.) as the main solvent and n-decane (Tokyo Kasei Kogyo Co., Ltd.) was mixed so that the volume ratio of the main solvent: the sub-solvent was 90: 10. These raw materials were mixed and kneaded for 1 minute using an ultrasonic homogenizer to obtain a slurry. After that, the composition for the negative electrode active material layer was applied to the surface of a Ni foil as a negative electrode current collector using a doctor blade, and dried naturally for 30 minutes. After that, it was dried by heating at 100° C. for 30 minutes to form a coating film for a negative electrode active material layer, thereby obtaining a negative electrode structure.

(3) Preparation of positive electrode structure LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (manufactured by Nichia Corporation) as a positive electrode active material, and the sulfide solid electrolyte (10LiI-15LiBr-75 (0.75Li ₂ S-0.25P ₂ S ₅ ) was weighed so that the mass ratio of positive electrode active material:sulfide solid electrolyte was 75:25. , PVDF-HFP binder (manufactured by Solvay, Soref (registered trademark) 21510) 1.5 parts by weight, and conductive aid (vapor-grown carbon fiber, manufactured by Showa Denko K.K.) 3.0 parts by weight were weighed. Furthermore, methyl isobutyl ketone (dehydration grade, manufactured by Nacalai Tesque Co., Ltd.) as a main solvent and n-decane (manufactured by Tokyo Chemical Industry Co., Ltd.) as a secondary solvent dehydrated with molecular sieves are used as the main solvent. : A secondary solvent was mixed so that the volume ratio was 90: 10. These raw materials were mixed and kneaded for 1 minute using an ultrasonic homogenizer to prepare a slurry composition for a positive electrode active material layer. After that, the positive electrode active material layer composition was applied to the surface of an aluminum foil (manufactured by Showa Denko KK) as a positive electrode current collector using a doctor blade, and dried naturally for 30 minutes. By heating and drying at 100° C. for 30 minutes, a positive electrode active material layer coating film was formed to obtain a positive electrode structure.

(4) Preparation of all-solid lithium ion secondary battery In an Ar atmosphere glove box, the sulfide solid electrolyte (10LiI-15LiBr-75 (0.75Li ₂ S-0.25P ₂ S ₅ ) 100 parts by mass Then, 1 part by mass of a PVDF-HFP binder (Soref (registered trademark) 21510, manufactured by Solvay) was weighed, and methyl isobutyl ketone (dehydrated grade, manufactured by Nacalai Tesque Co., Ltd.) was added as a main solvent to a solid content of 35. % by mass, and kneaded using an ultrasonic homogenizer to obtain a solid electrolyte layer slurry.On the surface of an aluminum foil, a doctor blade is used to apply the solid electrolyte layer slurry, A solid electrolyte layer was formed by drying, and then the positive electrode structure and the negative electrode structure were laminated by roll pressing.Specifically, the solid electrolyte layer and the positive electrode of the positive electrode structure were laminated. The positive electrode structure was laminated so that the active material layer coating film faced each other, and cold-pressed at room temperature at 4.3 ton/cm ^2. After that, the aluminum foil in contact with the solid electrolyte layer was peeled off, The negative electrode structure was laminated so that the negative electrode active material layer coating film of the negative electrode structure and the solid electrolyte layer faced each other, and hot pressing was performed at 135° C. and 4.3 tons/cm ² . After that, by sealing with a laminate, an all-solid lithium ion secondary battery of Example 1 was obtained.

[Example 2]
The all-solid lithium ion secondary battery obtained in Example 1 was further provided with a restraining mechanism to apply a restraining pressure of 5 MPa to the battery cells, thereby obtaining an all-solid lithium ion secondary battery of Example 2.

[Example 3]
In "(1) Synthesis of Negative Electrode Active Material" of Example 1, zirconia beads with a diameter of 1 mm were used instead of zirconia beads with a diameter of 0.5 mm when the powder of TiNb ₂ O ₇ was wet pulverized. obtained TiNb ₂ O ₇ having a monoclinic structure and a median diameter (D50) of 0.9 μm in the same manner as in Example 1.
In Example 1, instead of TiNb ₂ O ₇ having a monoclinic structure and a median diameter (D50) of 0.3 μm, TiNb 2 O 7 having a monoclinic structure and a median diameter (D50) of 0.3 μm was used as the negative electrode active material. An all-solid lithium ion secondary battery of Example 3 was obtained in the same manner as in Example 1, except that 9 μm TiNb ₂ O ₇ was used.

[Example 4]
The all-solid lithium ion secondary battery obtained in Example 3 was further provided with a restraining mechanism to apply a restraining pressure of 5 MPa to the battery cells, thereby obtaining an all-solid lithium ion secondary battery of Example 4.

[Example 5]
In "(1) Synthesis of Negative Electrode Active Material" of Example 1, zirconia beads with a diameter of 1.5 mm were used instead of the zirconia beads with a diameter of 0.5 mm when the powder of TiNb ₂ O ₇ was wet pulverized. An all-solid lithium ion secondary battery of Example 5 was obtained in the same manner as in Example 1, except that

[Example 6]
The all-solid lithium ion secondary battery of Example 6 was obtained by further providing a restraining mechanism to the all-solid lithium-ion secondary battery obtained in Example 5 to apply a restraining pressure of 5 MPa to the battery cells.

[Comparative Example 1]
Same as Example 1 except that the pressure during hot pressing was changed from 4.3 ton/cm ² to 5.0 ton/cm ² in "(4) Fabrication of all-solid-state lithium-ion secondary battery" of Example 1. Similarly, an all-solid lithium ion secondary battery of Comparative Example 1 was obtained.

[Comparative Example 2]
The all-solid lithium ion secondary battery obtained in Comparative Example 1 was further provided with a restraining mechanism to apply a restraining pressure of 5 MPa to the battery cells, whereby an all-solid lithium ion secondary battery of Comparative Example 2 was obtained.

[Comparative Example 3]
An all-solid lithium ion secondary battery of Comparative Example 3 was produced in the same manner as in Example 3, except that the pressure during hot pressing was changed from 4.3 ton/cm ² to 3.2 ton/cm ² . Obtained.

[Comparative Example 4]
The all-solid lithium ion secondary battery obtained in Comparative Example 3 was further provided with a restraining mechanism to apply a restraining pressure of 5 MPa to the battery cells, whereby an all-solid lithium ion secondary battery of Comparative Example 4 was obtained.

[Comparative Example 5]
An all-solid lithium ion secondary battery of Comparative Example 5 was produced in the same manner as in Example 5, except that the pressure during hot pressing was changed from 4.3 ton/cm ² to 3.2 ton/cm ² . Obtained.

[Comparative Example 6]
The all-solid lithium ion secondary battery obtained in Comparative Example 5 was further provided with a restraining mechanism to apply a restraining pressure of 5 MPa to the battery cells, whereby an all-solid lithium ion secondary battery of Comparative Example 6 was obtained.

[Example 7]
_In Example 1, Si powder (manufactured by Kojundo Chemical Laboratory Co., Ltd., product name: _SIE23PB , Purity: 3N, size: about 5 μm), and the negative electrode capacity was adjusted so that the volume expansion rate of Si at full charge compared to before initial charge was 15%. No. 7 all-solid lithium ion secondary battery was obtained.

[Example 8]
The all-solid lithium ion secondary battery obtained in Example 7 was further provided with a restraining mechanism to apply a restraining pressure of 5 MPa to the battery cells to obtain an all-solid lithium ion secondary battery of Example 8.

[Comparative Example 7]
In Example 7, the all-solid lithium-ion dichloride of Comparative Example 7 was prepared in the same manner as in Example 7, except that the negative electrode capacity was adjusted so that the volume expansion coefficient of Si at full charge compared to before initial charge was 25%. I got the following battery.

[Comparative Example 8]
The all-solid lithium ion secondary battery obtained in Comparative Example 7 was further provided with a restraining mechanism to apply a restraining pressure of 5 MPa to the battery cells, whereby an all-solid lithium ion secondary battery of Comparative Example 8 was obtained.

[Comparative Example 9]
In Example 7, the all-solid lithium ion dipole of Comparative Example 9 was prepared in the same manner as in Example 7, except that the negative electrode capacity was adjusted so that the volume expansion coefficient of Si at full charge compared to before initial charge was 20%. I got the following battery.

[Comparative Example 10]
The all solid lithium ion secondary battery obtained in Comparative Example 9 was further provided with a restraining mechanism to apply a restraining pressure of 5 MPa to the battery cells, thereby obtaining an all solid lithium ion secondary battery of Comparative Example 10.

[Example 9]
_In Example ₁ , natural graphite (C) (manufactured by Mitsubishi Chemical Corporation, graphite, An all-solid lithium ion secondary battery of Example 9 was obtained in the same manner as in Example 1, except that the average particle size was 10 μm.

[Example 10]
The all-solid lithium ion secondary battery of Example 10 was obtained by further providing a restraining mechanism to the all-solid lithium-ion secondary battery obtained in Example 9 to apply a restraining pressure of 5 MPa to the battery cells.

[Comparative Example 11]
An all-solid lithium ion secondary battery of Comparative Example 11 was produced in the same manner as in Example 9, except that the pressure during hot pressing was changed from 4.3 ton/cm ² to 5.0 ton/cm ² in Example 9. Obtained.

[Comparative Example 12]
The all-solid lithium ion secondary battery obtained in Comparative Example 11 was further provided with a restraining mechanism to apply a restraining pressure of 5 MPa to the battery cells, thereby obtaining an all-solid lithium ion secondary battery of Comparative Example 12.

[Comparative Example 13]
In "(1) Synthesis of Negative Electrode Active Material" of Example 1, as the negative electrode active material, instead of TiNb ₂ O ₇ having a monoclinic structure and a median diameter (D50) of 0.3 μm, spinel-type titanium An all-solid lithium ion secondary battery of Comparative Example 13 was obtained in the same manner as in Example 1, except that lithium oxide Li ₄ Ti ₅ O ₁₂ was used.

[Comparative Example 14]
The all-solid lithium ion secondary battery obtained in Comparative Example 13 was further provided with a restraining mechanism to apply a restraining pressure of 5 MPa to the battery cells, thereby obtaining an all-solid lithium ion secondary battery of Comparative Example 14.

[evaluation]
(1) Measurement of pore peak diameter From the all-solid lithium ion secondary battery before initial charge, the negative electrode is punched out from five locations using a cylindrical mold with an inner diameter of 15 mm, and the negative electrode active material layer is formed on one side of the negative electrode current collector. A total of five cylindrical measurement samples were obtained for each negative electrode. In an inert atmosphere, a sample for measurement was enclosed in a sample container made of 6 sheets of glass, and measurement was performed under the following measurement conditions to obtain a pore size distribution. As an example, FIG. 2 shows the pore size distribution of the negative electrode active material layer of the all-solid lithium ion secondary battery of Example 1. As shown in FIG.
(Measurement condition)
・ Apparatus (Autopore IV9510, manufactured by Micromeltics)
・ Pressure: initial pressure 0.5 psi, final pressure 60000 psi
・Mercury contact angle: 141.3°C
・Mercury surface tension: 484dyn/cm
The pore diameter peaks of five measurement samples per negative electrode were measured, and the average of the pore diameter peaks was taken as the pore diameter peak of the negative electrode active material layer of the negative electrode.

(2) Measurement of porosity From the all-solid lithium ion secondary battery before initial charge, the negative electrode is punched out from five locations using a cylindrical mold with an inner diameter of 15 mm, and the negative electrode active material layer is formed on one side of the negative electrode current collector. A total of 5 cylindrical samples for measurement were obtained for each negative electrode. The weight and film thickness of the negative electrode active material layer of the measurement sample were measured, and the porosity of the negative electrode active material layer was calculated according to Equation 2 above. The weight of the negative electrode active material layer was obtained by subtracting the weight of the negative electrode current collector from the weight of the measurement sample. The volume of the negative electrode active material layer was calculated from the area of the bottom surface (a circle with a diameter of 15 mm) of the cylindrical measurement sample and the thickness of the negative electrode active material layer. The theoretical specific gravity of the material constituting the negative electrode active material layer was calculated from the true specific gravity and the compounding ratio of the components other than the solvent in the negative electrode active material layer composition.
The porosity of five measurement samples per negative electrode was measured, and the average of the measurements was taken as the porosity of the negative electrode active material layer of the negative electrode.

(3) Measurement of initial output retention rate Under a temperature condition of 25 ° C., the all-solid-state lithium ion secondary battery was charged with constant current and constant voltage (CCCV) to SOC 100%, and then the current density was changed to 0.2C or 2. Constant current (CC) discharge is performed to each SOC 0% at 0 C, and the initial discharge capacity when discharged at a current density of 0.2 C and the initial discharge capacity when discharged at a current density of 2.0 C are obtained, The initial output retention rate was obtained by the following formula.
Initial output retention rate [%] = (initial discharge capacity at 2.0C/initial discharge capacity at 0.2C) x 100

(4) Measurement of post-cycle capacity retention rate Under a temperature condition of 25°C, an all-solid-state lithium ion secondary battery was CCCV charged to SOC 100%, and then CC discharged to SOC 0% (current density: 0.2C). was performed, and the discharge capacity during the CC discharge was taken as the initial capacity.
Then, under the temperature condition of 25° C., 100 cycles were performed, one cycle being CCCV charging to SOC 100% and then CC discharging (current density: 1 C) to SOC 0%. The discharge capacity at the 100th cycle was defined as the post-cycle capacity, and the post-cycle capacity retention rate was determined by the following formula.
Post-cycle capacity retention rate [%] = (post-cycle capacity/initial capacity) x 100

(5) Measurement of post-cycle output retention rate Under a temperature condition of 25°C, an all-solid-state lithium ion secondary battery is CCCV charged to an SOC of 100%, and then CC-discharged to an SOC of 0% (current density: 1C). One cycle of charging and discharging was performed, and 100 cycles were performed. After that, after performing CCCV charging to SOC 100% under a temperature condition of 25 ° C., the current density is set to 0.2C or 2.0C, and constant current (CC) discharge is performed to SOC 0%, respectively, and the current density is 0.2C. The post-cycle discharge capacity when discharged at a current density of 2.0 C was determined, and the post-cycle output retention rate was determined by the following formula.
Output retention rate after cycle [%] = (discharge capacity after cycle at 2.0C/discharge capacity after cycle at 0.2C) x 100

Regarding the initial output retention rate, the post-cycle capacity retention rate, and the post-cycle output retention rate, the results of the battery in which a confining pressure of 5 MPa was applied to the battery cells (when confined to 5 MPa) were compared to the results of the battery in which no confining pressure was applied to the battery cells. A ratio (0 MPa/5 MPa in Table 1) of the results (when unconstrained) was calculated. The closer the ratio of the result under 5 MPa restraint to the result under no restraint is to 1, the more the deterioration of the battery performance due to the volume change of the negative electrode active material is suppressed, and the restraint mechanism in the battery pack can be simplified. means
Regarding each of the results of the initial output retention rate, post-cycle capacity retention rate, and post-cycle output retention rate, the ratio (0 MPa/5 MPa) of the result of unconstrained to the result of 5 MPa constraint is 0.95 or more. desirable.

From Table 1, in Examples 1 to 10, the negative electrode included in the all-solid-state lithium ion secondary battery has a pore peak diameter of 0.1 μm or less measured by a mercury intrusion method of the negative electrode active material layer before initial charging. and the porosity of the negative electrode active material layer was 10% or more and 25% or less, and the _volume expansion rate of the negative electrode active material at full charge was 15% or less compared to that before initial charge. _7. When using either Si or natural graphite (C), the initial output retention rate, the capacity retention rate and the output retention rate after cycling were high, and the deterioration of the battery performance after charging and discharging was suppressed. there were. In addition, in Examples 1 to 10, when comparing the results of the initial output retention rate, the capacity retention rate after the cycle, and the output retention rate for the batteries under the same conditions other than the confining pressure applied to the battery cells, when constrained to 5 MPa The ratio of the results when unrestrained to the results of is all 0.95 or more, and excellent battery performance can be exhibited even in an unrestrained state. It was revealed that the battery can improve the energy density.
In Comparative Examples 1 to 6, the porosity of the negative electrode active material layer before initial charging was less than 10% or more than 25%, or the pore peak diameter was more than 0.1 μm, so the same type of negative electrode active material was used. Among the used Examples 1 to 6, when the confining pressure applied to the battery cell is the same, both the initial output retention rate and the capacity retention rate and output retention rate after cycling are reduced, and the battery performance was declining.
In Comparative Examples 7 to 10, the volume expansion rate of the negative electrode active material at full charge was more than 15% compared to before initial charge, so among Examples 7 and 8 using the same type of negative electrode active material, When the applied confining pressure was the same, both the initial output retention rate, the capacity retention rate and the output retention rate after cycling decreased, and the battery performance decreased.
In Comparative Examples 11 and 12, the porosity of the negative electrode active material layer before the initial charge was less than 10%. When compared with the battery with the same value, both the initial output retention rate and the capacity retention rate and output retention rate after cycling decreased, indicating a decrease in battery performance.
In Comparative Examples 13 and 14, since Li ₄ Ti ₅ O ₁₂ was used as the negative electrode active material, the volume change of the negative electrode active material due to charging and discharging was small, so the battery performance was maintained even after charging and discharging. The battery had insufficient density.
In the comparative examples, the battery cells in which a confining pressure of 5 MPa was applied had better battery performance than those in which the confining pressure was not applied to the battery cells. As a result, cracking of the negative electrode caused by expansion and contraction of the negative electrode active material was suppressed, or the contact between the negative electrode active material and the solid electrolyte became good, and the ionic conductivity and the like improved.

11 solid electrolyte layer 12 positive electrode active material layer 13 negative electrode active material layer 14 positive electrode current collector 15 negative electrode current collector 16 positive electrode 17 negative electrode 100 all-solid lithium ion secondary battery

Claims (2)

A negative electrode for an all-solid lithium ion secondary battery having a negative electrode active material layer,
Before initial charging, the peak diameter in the pore size distribution of the negative electrode active material layer measured by a mercury intrusion method is 0.08 μm or less, and the porosity of the negative electrode active material layer is 10% or more and 25% or less. ,
A negative electrode for an all-solid lithium ion secondary battery, wherein the negative electrode active material contained in the negative electrode active material layer has a volume expansion rate of 15% or less at full charge compared to before initial charge. 2. The negative electrode for an all-solid lithium ion secondary battery according to claim 1, containing a niobium-titanium composite oxide as said negative electrode active material.

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