Negative electrode mixture, slurry, negative electrode, and battery

Abstract

A negative electrode mixture constituting a negative electrode layer, the negative electrode mixture containing particles of a solid electrolyte and particles of a conductive material disposed on the surfaces of the particles of the solid electrolyte. It is preferable that the solid electrolyte contains a crystal phase having an argyrodite-type crystal structure. Preferably, the conductive material is a carbon material or a metal material. It is also preferable that the viscosity of a slurry containing the negative electrode mixture, the binder, and the solvent is 0.05-3 Pa.s (inclusive) at 25 DEG C at a shear rate of 10 (1 / s).

Description

Technical Field

[0001] The invention relates to a negative electrode mixture, slurry, a negative electrode and a battery. Background Art

[0002] In recent years, secondary batteries have attracted widespread attention as a tool for reducing CO2 emissions and preventing global warming. Lithium-ion batteries, in particular, are widely used as power sources for portable electronic devices such as laptops and mobile phones due to their high energy density and ease of miniaturization and weight reduction. Furthermore, recent progress has been made in the development of high-power, high-capacity lithium-ion batteries for use in electric and hybrid vehicles.

[0003] However, when lithium foil is used in lithium-ion batteries, battery performance is compromised due to poor contact between the solid electrolyte layer and the negative electrode, or due to the influence of an oxide film formed on the surface of the lithium foil. To address this issue, a lithium-free battery has been proposed that uses LiCoO2 as the positive electrode material, Lipon as the solid electrolyte, and an in-situ deposition-type negative electrode. Instead of using lithium foil, the negative electrode utilizes lithium metal deposited on the current collector. However, the resulting battery capacity is insufficient, with a discharge current of only approximately 0.1 mAh.

[0004] To this end, Patent Document 1 proposes that a negative electrode containing solid electrolyte particles and having a porosity of 0.05 to 0.8 be sandwiched between a solid electrolyte layer and arranged opposite to a positive electrode. Even if metallic lithium is precipitated during charging, the contact state between the solid electrolyte layer and the negative electrode can be improved, thereby increasing the discharge current.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2012-146553 Summary of the Invention

[0008] However, the battery having the negative electrode described in Patent Document 1 has technical problems such as lithium (Li) crystals precipitating in a dendritic form, causing frequent short circuits and poor product yield.

[0009] Therefore, the technical problem of the present invention is to provide a negative electrode mixture capable of producing a negative electrode in which short circuiting of a battery, particularly a lithium ion battery, is suppressed.

[0010] The inventors have conducted in-depth research to suppress the short circuit of lithium-ion batteries. As a result, it was found that by forming a negative electrode layer comprising particles of a solid electrolyte and precipitating lithium (Li) crystals in the gaps between the particles of the solid electrolyte to replace the previous in-situ precipitation type negative electrode, it is possible to suppress the growth of lithium (Li) crystals into dendrites. On the other hand, when the negative electrode layer contains a conductive material, a solvent is usually made to contain a conductive material to form a slurry. However, it was found that the slurry viscosity increased, causing the particles of the solid electrolyte to be difficult to disperse evenly, thereby being unable to evenly form the gaps, and it is difficult to precipitate lithium (Li) crystals in the gaps. If a large amount of solvent is added to the slurry to adjust the slurry viscosity, the productivity of the negative electrode will decrease.

[0011] The present invention provides a negative electrode mixture, which constitutes a negative electrode layer.

[0012] The negative electrode mixture includes solid electrolyte particles and conductive material particles disposed on the surfaces of the solid electrolyte particles.

[0013] In addition, the present invention provides a slurry comprising a negative electrode mixture, a binder and a solvent.

[0014] The negative electrode mixture includes solid electrolyte particles and conductive material particles disposed on the surface of the solid electrolyte particles.

[0015] The viscosity of the slurry is 0.05 Pa·s or more and 3 Pa·s or less at a shear rate of 10 (1 / s) at 25°C.

[0016] Furthermore, the present invention provides a negative electrode comprising a negative electrode current collector and a negative electrode layer disposed on the negative electrode current collector and containing a negative electrode mixture.

[0017] The negative electrode mixture includes solid electrolyte particles and conductive material particles disposed on the surfaces of the solid electrolyte particles.

[0018] Furthermore, the present invention provides a battery comprising a negative electrode, a positive electrode, and a solid electrolyte layer disposed between the negative electrode and the positive electrode.

[0019] The negative electrode comprises a negative electrode current collector and a negative electrode layer disposed on the negative electrode current collector and containing a negative electrode mixture.

[0020] The negative electrode mixture includes solid electrolyte particles and conductive material particles disposed on the surfaces of the solid electrolyte particles. DETAILED DESCRIPTION

[0021] The present invention will be described below based on preferred embodiments. The negative electrode mixture of the present invention contains solid electrolyte particles and conductive material particles.

[0022] In the negative electrode mixture of the present invention, particles of a conductive material are arranged on the surface of particles of a solid electrolyte. In this technical field, conductive materials are generally mixed in order to improve the electronic conductivity of the negative electrode mixture and, in turn, the negative electrode layer. Therefore, in the past, the concentration of the slurry of the negative electrode mixture containing particles of a solid electrolyte and particles of a conductive material tended to increase. In contrast, in the present invention, it is preferred to coat the surface of the particles of the solid electrolyte with particles of a conductive material by a dry method described below, thereby arranging particles of a conductive material on the surface of the particles of the solid electrolyte, thereby reducing the viscosity of the slurry containing the negative electrode mixture. As a result, when the slurry is used to form a negative electrode layer, the particles of the solid electrolyte can be uniformly dispersed in the negative electrode layer. As a result, lithium (Li) crystals can be successfully precipitated in the gaps between the particles of the solid electrolyte, suppressing the precipitation of dendritic crystals and thus suppressing battery short circuits.

[0023] The solid electrolyte particles and the conductive material particles are preferably composited. Preferably, the solid electrolyte particles and the conductive material particles are "composite" to each other, meaning that the conductive material particles are inseparably integrated with the solid electrolyte particles and dispersed on the surface and inside of the solid electrolyte particles. Examples of "composite" include a method in which the conductive material particles are inseparably dispersed on the surface and / or inside of the solid electrolyte particles, and a method in which the solid electrolyte particles and the conductive material particles undergo a chemical reaction to form a bond.

[0024] The particles of the conductive material are inseparably dispersed on the surface and inside of the particles of the solid electrolyte, which refers to the following state, for example, when a scanning electron microscope (SEM-EDS) equipped with an energy dispersive X-ray spectrometer is used to observe the composite material obtained by the present manufacturing method, and when mapping the constituent elements of the solid electrolyte (such as sulfur element) and the constituent elements of the conductive material, the constituent elements of the solid electrolyte and the constituent elements of the conductive material exist in an overlapping manner. Or it refers to the following state, when the cross-section of the negative electrode layer in the negative electrode manufactured using the negative electrode mixture of the present invention is observed, the constituent elements of the solid electrolyte and the constituent elements of the conductive material exist in an overlapping manner. It should be noted that, for example, when the conductive material is a carbon material, the solid electrolyte and the conductive material react chemically to form a composite, and Raman spectroscopy and photoelectron spectroscopy can also be used to confirm the presence or absence of C-S bonds.

[0025] When the particles of the conductive material are arranged on the surface of the particles of the solid electrolyte, the ratio of the surface contacted by the particles of the conductive material relative to the surface of the particles of the solid electrolyte is preferably, for example, 10% or more, more preferably 20% or more, more preferably 30% or more, further preferably 50% or more, and particularly further preferably a state of contact in a manner covering the entire surface of the particles of the solid electrolyte, i.e., 80% or more or 90% or more.

[0026] The ratio of the face that the particle of the conductive material relative to the particle surface of solid electrolyte contacts can be measured by the following method.By for example cross section polishing instrument (CP) making the cross section sample of particle, and obtain the SEM image of this cross section.Can use image analysis software (MAC-View) to measure the contact length of the conductive material contacted with 1 particle of solid electrolyte, and obtain the ratio according to the girth of 1 particle of this contact length and solid electrolyte.Obtain the SEM image of 1 visual field under 5000 times, randomly select the particle of 5 solid electrolytes and obtain average value.

[0027] The thickness of the conductive material is not particularly limited as long as it is a thickness that can function as a conductive material. For example, it can be 0.01 μm or more, 0.05 μm or more, or 0.1 μm or more. The upper limit of the thickness of the conductive material depends on the negative electrode mixture and the amount of the conductive material contained in the negative electrode. For example, it is preferably 0.5 μm or less, and more preferably 0.2 μm or less.

[0028] The thickness of the conductive material can be measured by the following method. For example, a cross-section sample of the particles is prepared using a cross-section polisher (CP), and the thickness of the conductive material of a single solid electrolyte particle is measured from an SEM image of the cross-section. An SEM image of one field of view is obtained at 10,000x magnification, and five solid electrolyte particles are randomly selected from the image to determine the average value.

[0029] As a method of compounding the particles of the solid electrolyte with the particles of the conductive material so as to arrange the particles of the conductive material on the surface of the particles of the solid electrolyte, for example, a dry method is preferably used. Specifically, for the particles of the solid electrolyte and the particles of the conductive material, it is preferred to apply a compressive force / impact force or a shear force / friction force when they are mixed. Through this compounding, the increase in the viscosity of the slurry when the negative electrode is formed using the negative electrode mixture is suppressed, and the particles of the solid electrolyte are uniformly dispersed in the slurry, thereby optimizing the size of the gaps between the particles of the solid electrolyte.

[0030] It is preferred to apply mechanical energy such as compression / impact, shear / friction to the particles of the solid electrolyte and the conductive material in a mixed state to compound. In compounding, it is preferred to use a device that is mainly used to stir, mix, knead, granulate, crush, disperse and / or surface modify the powder. For example, a planetary ball mill, a ball mill, a jet mill, a bead mill, a stirring type crusher, a vibration mill, a hammer mill, a roller mill and an atomizer can be used. The type of main mechanical energy that can be applied using these devices varies depending on the device. For example, when a planetary ball mill is used, compression / impact is mainly applied to the particles of the solid electrolyte and the conductive material in a mixed state, thereby compounding the two. The centrifugal acceleration obtained when the device rotates is not particularly limited as long as it is the degree to which the particles of the solid electrolyte and the conductive material can be compounded. For example, it is preferably 10G or more, more preferably 15G or more, and more preferably 18G or more. In addition, the centrifugal acceleration is, for example, preferably 40G or less, more preferably 30G or less, and more preferably 25G or less. By setting the centrifugal acceleration within the above range, lithium short circuiting is less likely to occur in a battery including a negative electrode produced using the negative electrode mixture of the present invention.

[0031] In a state where the solid electrolyte particles and the conductive material particles are composited by the above method, the negative electrode mixture of the present invention preferably contains, for example, 1 part by mass or more of the conductive material relative to 100 parts by mass of the solid electrolyte, more preferably 2 parts by mass or more, and even more preferably 5 parts by mass or more. On the other hand, the negative electrode mixture preferably contains, for example, 50 parts by mass or less of the conductive material relative to 100 parts by mass of the solid electrolyte, more preferably 20 parts by mass or less, even more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less.

[0032] By mixing solid electrolyte particles with conductive material particles within the aforementioned range, the solid electrolyte acquires electronic conductivity. This suppresses the growth of lithium (Li) crystals in the spaces between the solid electrolyte particles and their dendritic growth. The relationship between the electronic conductivity of the solid electrolyte and the suppression of lithium (Li) crystal dendritic growth is a new discovery by the present inventors.

[0033] The negative electrode mixture of the present invention preferably does not contain a negative electrode active material. The negative electrode produced from the negative electrode mixture of the present invention also preferably does not contain a negative electrode active material. The negative electrode produced from the negative electrode mixture of the present invention does not contain a negative electrode active material during the first charge. However, after the first charge, metallic lithium can be deposited during charging, thereby functioning as an in-situ precipitation-type negative electrode containing a negative electrode active material (lithium).

[0034] The solid electrolyte particles contained in the negative electrode mixture of the present invention preferably have a specific particle size distribution. Specifically, the volume cumulative particle diameters at 10%, 50%, and 90% of the cumulative volume based on the laser diffraction scattering particle size distribution measurement method are respectively set as D 10 、D 50 and D 90 When the solid electrolyte (D 90 -D 10 ) / D 50 The value of is preferably less than 10.0, preferably less than 4.0, more preferably less than 3.8, and further preferably less than 2.2. (D 90 -D 10 ) / D 50 It is an indicator of the width of the particle size distribution. The closer the value is to 0, the more uniform the particle size distribution is. By making the particle size distribution uniform, uniform gaps are formed between the particles of the solid electrolyte in the negative electrode layer containing particles of the solid electrolyte. As a result, the lithium (Li) ions that migrate from the positive electrode during charging are successfully precipitated in the form of metallic lithium in the gaps. Therefore, unlike the previous in situ plating negative electrode, the negative electrode manufactured using the negative electrode mixture of the present invention can suppress the growth of lithium (Li) crystals into dendrites, and can suppress the occurrence of short circuits in the battery containing the negative electrode. (D 90 -D 10 ) / D 50 The lower limit of the value of is not particularly limited, and for example, it may be greater than 0, may be greater than 0.5, or may be greater than 0.8.

[0035] The measurement of the particle size distribution of the solid electrolyte particles based on the laser diffraction scattering particle size distribution measurement method can be carried out, for example, according to the following steps. Using an automatic sampler for a laser diffraction particle size distribution measurement device ("Microtorac SDC" manufactured by Nikkiso Co., Ltd.), 6 ml of the sample (slurry) is put into a non-aqueous solvent (toluene), the flow rate is set to 50%, and 30W ultrasonic waves are irradiated for 60 seconds. Then, the particle size distribution is measured using, for example, a laser diffraction particle size distribution measurement machine "MT3000II" manufactured by Nikkiso Co., Ltd., and the volume cumulative particle size D at 10% by volume, 50% by volume, and 90% by volume can be measured from the obtained volume reference particle size distribution diagram. 10 、D 50 and D 90 The value of .

[0036] When measuring particle size distribution, the non-water-soluble solvent should be passed through a 60μm filter. The solvent refractive index is set to 1.50, the particle permeability is set to transparent, the particle refractive index is set to 1.59, the particle shape is set to non-spherical, the measurement range is set to 0.133μm to 704.0μm, the measurement time is set to 10 seconds, and the average value of the two measurements is set as D 10 、D 50 and D 90 .

[0037] The sample (slurry) can be prepared by manually mixing 0.3 g of the solid electrolyte and 5.7 g of the dispersion (mass ratio of toluene: SN-DISPERSANT 9228 manufactured by San Nopco Corporation = 19:1).

[0038] In the present invention, the solid electrolyte has a specific particle size distribution and a volume cumulative particle size D at 95% of the cumulative volume based on the laser diffraction scattering particle size distribution measurement method. 95 For example, it is preferably less than 65 μm, more preferably less than 30 μm, and further preferably less than 10 μm. By making the solid electrolyte have a particle size distribution as described above and containing no coarse particles as much as possible, the size of the gaps between the particles of the solid electrolyte in the negative electrode layer containing the particles of the solid electrolyte is optimized. As a result, the lithium (Li) ions migrating from the positive electrode during charging are efficiently precipitated in the form of metallic lithium in the gaps, which can inhibit the growth of metallic lithium into dendrites. Therefore, it is possible to prevent a short circuit in a battery comprising a negative electrode manufactured from the negative electrode mixture of the present invention.

[0039] From the perspective of easily forming gaps of appropriate size between the particles of the solid electrolyte, the D 50 For example, it is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more. 50 For example, it is preferably 15 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less.

[0040] The BET specific surface area of ​​the solid electrolyte is preferably 2 m 2 / g or more, more preferably 3m 2 / g or more, more preferably 4m 2 / g or more. On the other hand, the BET specific surface area of ​​the solid electrolyte is preferably, for example, 30 m 2 / g or less, more preferably 20m 2 / g or less, more preferably 16m 2 / g or less, more preferably 10m 2 / g or less. By setting the BET specific surface area of ​​the solid electrolyte within the above range, lithium (Li) ions migrating from the positive electrode side during charging are more efficiently precipitated in the gaps between the particles of the solid electrolyte, which can suppress the growth of metallic lithium into dendrites. Therefore, it is possible to prevent short circuits in batteries containing negative electrodes manufactured using the negative electrode mixture of the present invention.

[0041] The BET specific surface area was calculated by the following method: using a specific surface area measuring apparatus "BELSORP-miniII" manufactured by Microtrac BEL, the adsorption and desorption isotherms were measured by the constant volume gas adsorption method, and the BET specific surface area was calculated by the multipoint method. The gas used was nitrogen.

[0042] In order to adjust the solid electrolyte (D 90 -D 10 ) / D 50 The value and particle size of the solid electrolyte can be determined by, for example, applying a suitable pulverization treatment to the solid electrolyte. Specifically, a ball mill or the like can be used to coarsely pulverize the solid electrolyte manufactured by a known method and then finely pulverize it in a wet manner to adjust the particle size distribution and particle size. Specifically, by controlling the pulverization conditions during wet fine pulverization, such as pulverization time, rotation speed of the pulverization device, material of the pulverization medium, particle size of the pulverization medium, concentration of the slurry, liquid feeding amount of the slurry, mass ratio of the solid electrolyte to the pulverization medium, etc., particles of the solid electrolyte having a target particle size distribution and particle size can be obtained. The discovery of these pulverization conditions falls within the scope of the technical common sense of those skilled in the art and is a matter that can be determined without placing an excessive burden on those skilled in the art.

[0043] From the perspective of suppressing the growth of dendritic lithium metal to a level sufficient to prevent short circuits, the solid electrolyte contained in the negative electrode mixture of the present invention preferably comprises, for example, lithium (Li), sulfur (S), and an element M. The element M is preferably at least one of phosphorus (P), germanium (Ge), antimony (Sb), silicon (Si), tin (Sn), aluminum (Al), titanium (Ti), iron (Fe), nickel (Ni), cobalt (Co), and manganese (Mn). In particular, the element M preferably includes at least phosphorus (P), and more preferably, the element M is solely P.

[0044] Examples of compounds containing Li, S, and M include compounds containing only Li, S, and M, namely, Li7PS6, Li 7+3x (P 5+ 1-x Fe 2+ x )S6、Li 7+x (P 5+ 1-x Si4+ x )S6 etc. (wherein, x represents a number greater than 0.1 and less than 1.0). In addition, as a compound comprising a Li element, an S element and an M element, a compound comprising other elements in addition to these three elements can also be used. As the other element, for example, a halogen (X) element can be listed. By using a compound comprising an X element in addition to the Li element, the S element and the M element, the properties of the composite material obtained by the present manufacturing method as an active material can be further improved. As the X element, at least one element selected from fluorine (F), chlorine (Cl), bromine (Br) and iodine (I) can be used.

[0045] From the perspective of being able to suppress the growth of dendritic lithium metal to the extent that short circuit can be suppressed, the compound containing Li element, S element, M element and X element is preferably composed of the composition formula (1): Li a MS b X c Represents (wherein, M is at least one element selected from P, Ge, Sb, Si, Sn, Al, Ti, Fe, Ni, Co and Mn. X is at least one element selected from F, Cl, Br and I).

[0046] From the perspective of improving lithium ion conductivity, in the composition formula (1), a is preferably 3.0 or greater, more preferably 3.5 or greater. On the other hand, a is preferably 9.0 or less, more preferably 8.0 or less. In particular, when the M element is a P element, the atomic ratio of the Li element to the P element, i.e., the value of a, is preferably, for example, 5.0 or greater, preferably 5.5 or greater, and particularly preferably 6.0 or greater. On the other hand, a is preferably, for example, 8.0 or less, preferably 7.8 or less, and particularly preferably 7.5 or less.

[0047] b is preferably 4.0 or greater, more preferably 4.5 or greater, and even more preferably 5.0 or greater. On the other hand, b is preferably 7.5 or less, more preferably 7.0 or less, and even more preferably 6.5 or less.

[0048] c is preferably 0.1 or greater, more preferably 0.2 or greater. On the other hand, c is preferably less than 2.0, more preferably less than 1.0, more preferably 0.8 or less, and even more preferably 0.6 or less.

[0049] The M element in the composition formula (1) is particularly preferably at least one of P, Ge, Sb, Sn, and Si, particularly preferably contains P, and more preferably contains only P. This can suppress the growth of dendritic lithium metal to a degree sufficient to prevent short circuits.

[0050] When the M element is the P element, the atomic ratio of the X element to the P element, i.e., the value of c, is preferably, for example, greater than 0.1, and preferably greater than 0.2. On the other hand, the value of c is preferably, for example, less than 2.0, further preferably less than 1.0, and preferably less than 0.8, particularly less than 0.6. When the M element is the P element, the atomic ratio of the Li element to the P element is preferably, for example, greater than 5.0, and preferably greater than 5.5, and particularly preferably greater than 6.0. On the other hand, the atomic ratio of the Li element to the P element is preferably, for example, less than 9.0, and preferably less than 8.0, and more preferably less than 7.5. It should be noted that when the M element contains the P element and other elements, the atomic ratio of the Li element to the P element can be, for example, less than 20.0, less than 15.0, or less than 9.0.

[0051] The solid electrolyte is particularly preferably composed of the formula (2)Li 7-d MS 6-d X d This is because the growth of dendritic lithium metal can be suppressed to a degree that can prevent short circuits. When the M element is a P element, the value of d, which is the atomic ratio of X to the P element, can be set to the same value as c in the above composition formula (1), and therefore is omitted here. In addition, when the M element is a P element, the atomic ratio of Li to the P element can also be set to the same value as in the above composition formula (1), and therefore is omitted here.

[0052] When the M element in the above composition formula (1) is an M1 element and an M2 element that are different from each other, the composition of the solid electrolyte can be Li a (M1 1-y M2 y )S b X c In addition, when the M element in the composition formula (2) is an M1 element and an M2 element that are different from each other, the composition of the solid electrolyte can be Li 7-d (M1 1-y M2 y )S 6-d X d y is preferably 0.010 or more, more preferably 0.020 or more, and even more preferably 0.050 or more. On the other hand, y is preferably 0.70 or less, more preferably 0.40 or less, and even more preferably 0.20 or less. It should be noted that the M1 element and the M2 element can be the same as the M element described in the composition formula (1), and therefore are omitted here.

[0053] The composition of each element in the solid electrolyte can be measured by, for example, ICP emission spectrometry.

[0054] In addition to the aforementioned elements, the solid electrolyte preferably also includes a crystalline phase having an argyrodite-type crystal structure. This further improves lithium ion conductivity. The solid electrolyte particularly preferably includes a crystalline phase having a cubic or orthorhombic argyrodite-type crystal structure. Whether the solid electrolyte contains a crystalline phase having an argyrodite-type crystal structure can be determined by analyzing the solid electrolyte using X-ray diffraction or total X-ray scattering. CuKα radiation, such as CuKα1 radiation, can be used as the radiation source in the X-ray diffraction method.

[0055] When the solid electrolyte has a cubic argyrodite-type crystal structure, it preferably has peaks at positions of 2θ=25.19°±1.00° and 29.62°±1.00° in an X-ray diffraction pattern measured using CuKα1 rays.

[0056] When the solid electrolyte has a cubic argyrodite-type crystal structure, it is further preferred that, in addition to the positions of 2θ=25.19°±1.00° and 29.62°±1.00°, in an X-ray diffraction pattern measured using CuKα1 radiation, there are also positions selected from the group consisting of 2θ=15.34°±1.00°, 17.74°±1.00°, 30.97°±1.00°, 44.37°±1.00°, 47.22°±1.00° and 51. .70°±1.00°, and more preferably, in addition to the positions of 2θ=25.19°±1.00° and 29.62°±1.00°, there are peaks at the positions of 2θ=15.34°±1.00°, 17.74°±1.00°, 30.97°±1.00°, 44.37°±1.00°, 47.22°±1.00° and 51.70°±1.00°.

[0057] When the solid electrolyte has an orthorhombic argyrodite-type crystal structure, the X-ray diffraction pattern measured using CuKα1 rays preferably has two peaks at 2θ=25.38°±1.00° and four peaks at 29.77°±1.00°.

[0058] In addition, when the solid electrolyte has an orthorhombic argyrodite-type crystal structure, it is further preferred that, in addition to having two peaks at 2θ = 25.38° ± 1.00° and four peaks at 29.77° ± 1.00°, in an X-ray diffraction pattern measured using CuKα1 radiation, there are also peaks selected from 2θ = 15.40° ± 1.00° (two peaks), 17.86° ± 1.00° (two peaks), 31.25° ± 1.00° (two peaks), 44.40° ± 1.00° (four peaks), 47.20° ± 1.00° (four peaks), and 52.00° ± 1.00°. °±1.00° (2 peaks), and more preferably, in addition to having 2 peaks at 2θ=25.38°±1.00° and 4 peaks at 29.77°±1.00°, it also has peaks at 2θ=15.40°±1.00° (2 peaks), 17.86°±1.00° (2 peaks), 31.25°±1.00° (2 peaks), 44.40°±1.00° (4 peaks), 47.20°±1.00° (4 peaks) and 52.00°±1.00° (2 peaks).

[0059] The peak position is expressed as ±1.00° from the center, but is preferably ±0.800° from the center, and more preferably ±0.500° from the center.

[0060] The solid electrolyte may contain other materials and other components as needed. Therefore, the solid electrolyte may be composed of a single phase, which is composed of a crystalline phase of an argyrodite-type crystal structure, or may contain other phases in addition to this phase. For example, in addition to the crystalline phase of the argyrodite-type crystal structure, the solid electrolyte may also contain a Li2S phase, a Li3PS4 phase, a Li4P2S6 phase, a LiCl or LiBr phase, etc. In particular, when the solid electrolyte contains a Li2S phase in addition to the crystalline phase of the argyrodite-type crystal structure, the lithium ion conductivity is further improved, so it is preferred. It is particularly preferred that the solid electrolyte contains a compound containing Li element, S element, M element and X element and containing a crystalline phase having an argyrodite-type crystal structure as the main material. In addition, in addition to the above-mentioned other materials and other components, the solid electrolyte may also contain unavoidable impurities that have a small adverse effect on the effect of the present invention (for example, less than 5% by mass, wherein less than 3% by mass).

[0061] Examples of the conductive material contained in the negative electrode mixture of the present invention include various metal materials and conductive non-metal materials. Any one of the metal material and the conductive non-metal material may be used, or both may be used in combination.

[0062] Examples of the metal material include various precious metal elements such as gold (Au), silver (Ag), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), and osmium (Os). Examples of the metal material include various transition metal elements such as copper (Cu), iron (Fe), and tin (Sn). These metal elements may be used alone or in combination of two or more.

[0063] As the conductive non-metallic material, for example, a carbon material can be used. Examples thereof include graphite, acetylene black, carbon black, carbon nanofibers, carbon nanotubes, nanographene, and fullerene nanowhiskers. These carbon materials can be used alone or in combination of two or more. When carbon black among these carbon materials is used, the initial capacity and discharge rate characteristics of the battery can be further improved. From the perspective of making this advantage more significant, acetylene black and furnace black are preferably used as the carbon black. Among them, oil furnace black is preferably used, and Ketjen black is particularly preferably used.

[0064] The conductive material has a particle form, and its particle size D1 is, for example, preferably 1 nm or more, more preferably 10 nm or more, and even more preferably 20 nm or more. Furthermore, D1 is, for example, preferably 600 nm or less, more preferably 500 nm or less, even more preferably 300 nm or less, and even more preferably 200 nm or less. The particle size D1 of the conductive material can be an average particle size (average value of 100 or more particles) of Feret diameter measured by direct observation of the particles using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0065] The particle size D1 of the conductive material is preferably smaller than the particle size (D 50 ).

[0066] It should be noted that, for example, when the conductive material is fibrous, such as the carbon nanotubes and carbon nanofibers described above, the fiber diameter can be used instead of the particle size. The fiber diameter D2 is, for example, preferably 50 nm or greater, more preferably 100 nm or greater, and even more preferably 150 nm or greater. Alternatively, D2 is, for example, preferably 10,000 nm or less, more preferably 5,000 nm or less, and even more preferably 2,000 nm or less.

[0067] The negative electrode mixture of the present invention can be used to prepare a slurry for manufacturing a negative electrode layer. The slurry comprises the negative electrode mixture, a binder, and a solvent. As described above, the negative electrode mixture comprises particles of a solid electrolyte and particles of a conductive material disposed on the surface of the particles of the solid electrolyte.

[0068] In the slurry, the concentration of the total amount of the solid electrolyte and the conductive material in the slurry is, for example, preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. On the other hand, the concentration is, for example, preferably 70% by mass or less, more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less. By making the concentration of the total amount of the solid electrolyte and the conductive material in the slurry within the range, the viscosity of the slurry can be adjusted to the desired range, and as a result, the negative electrode layer can be efficiently manufactured.

[0069] The viscosity of the slurry at 25° C. is, for example, preferably 0.05 Pa·s or more, more preferably 0.08 Pa·s or more, and even more preferably 0.1 Pa·s or more at a shear rate of 10 (1 / s).

[0070] On the other hand, the viscosity of the slurry at 25°C is, for example, preferably 4 Pa·s or less, more preferably 3 Pa·s or less, further preferably 2 Pa·s or less, and further preferably 1 Pa·s or less at a shear rate of 10 (1 / s).

[0071] The viscosity of the slurry is preferably 0.05 Pa·s or more, more preferably 0.1 Pa·s or more, at a shear rate of 100 (1 / s) at 25°C. Furthermore, the viscosity is preferably 4.0 Pa·s or less, more preferably 2.0 Pa·s or less, even more preferably 1.2 Pa·s or less, and even more preferably 0.8 Pa·s or less, at a shear rate of 100 (1 / s) at 25°C.

[0072] By setting the slurry to such a viscosity, the solid electrolyte particles can be uniformly dispersed in the negative electrode layer when the slurry is used to form the negative electrode layer. This allows lithium (Li) crystals to be successfully precipitated in the spaces between the solid electrolyte particles, suppressing the precipitation of dendritic crystals and thus preventing battery short circuits.

[0073] The viscosity of the slurry is measured, for example, by a rheometer.

[0074] Examples of the solvent include, but are not limited to, water, chloroform, methanol, ethanol, 1-propanol, 2-propanol, butanol, alcohols such as ethylene glycol, propylene glycol, and glycerol, and dimethyl sulfoxide (DMSO).

[0075] Examples of the binder include resin materials such as styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene.

[0076] The negative electrode can be manufactured by applying the slurry onto a negative electrode current collector and drying the slurry. The negative electrode comprises a negative electrode current collector and a negative electrode layer disposed on the negative electrode current collector and containing a negative electrode mixture. As described above, the negative electrode mixture comprises particles of a solid electrolyte and particles of a conductive material disposed on the surface of the particles of the solid electrolyte.

[0077] The negative electrode current collector can be made of a material with excellent conductivity, such as stainless steel, gold, platinum, zinc, nickel, tin, aluminum, molybdenum, niobium, tantalum, tungsten, titanium, and alloys thereof. The thickness of the negative electrode current collector is preferably 1 μm or greater, more preferably 3 μm or greater, and even more preferably 5 μm or greater.

[0078] On the other hand, the thickness of the negative electrode current collector may be, for example, 50 μm or less, preferably 30 μm or less, or 15 μm or less.

[0079] The negative electrode can be manufactured by the following methods: dropping the slurry on the negative electrode collector and wiping it with a scraper, bringing the negative electrode collector into contact with the slurry and then cutting it with an air knife, forming a coating by screen printing and then heating and drying to remove the solvent, etc.

[0080] A battery comprising a negative electrode made from the negative electrode mixture of the present invention may be a solid-state battery having, for example, a positive electrode, the negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode. More specifically, it can be used for a lithium solid-state battery. A lithium solid-state battery may be a primary battery or a secondary battery, and preferably a lithium secondary battery. In addition to solid-state batteries that do not contain any liquid or gel-like substances as electrolytes, a method comprising, for example, 50% by mass or less, 30% by mass or less, or 10% by mass or less of a liquid or gel-like substance as an electrolyte is also included in the "solid-state battery". In this case, the negative electrode manufactured using the negative electrode mixture of the present invention does not contain a negative electrode active material in the state before use, that is, before charging and discharging. That is, the negative electrode manufactured using the negative electrode mixture of the present invention does not contain a negative electrode active material when first charged, but after the first charge, it acts as a so-called in-situ precipitation-type negative electrode containing a negative electrode active material (lithium).

[0081] Regarding the above-mentioned embodiment, the present invention further discloses the following negative electrode mixture, slurry, negative electrode, and battery.

[0082] [1] A negative electrode mixture constituting a negative electrode layer,

[0083] The negative electrode mixture includes solid electrolyte particles and conductive material particles disposed on the surfaces of the solid electrolyte particles.

[0084] [2] The negative electrode mixture according to [1], wherein the ratio of the surface of the solid electrolyte particles to the surface of the solid electrolyte particles with which the particles of the conductive material are in contact is 10% or more.

[0085] [3] The negative electrode mixture according to [1] or [2], wherein the solid electrolyte contains lithium (Li), sulfur (S) and M, and M is at least one of phosphorus (P), germanium (Ge), antimony (Sb), silicon (Si), tin (Sn), aluminum (Al), titanium (Ti), iron (Fe), nickel (Ni), cobalt (Co) and manganese (Mn).

[0086] [4] The negative electrode mixture according to any one of [1] to [3], wherein the solid electrolyte contains a crystal phase having an argyrodite-type crystal structure.

[0087] [5] The negative electrode mixture according to any one of [1] to [4], wherein the conductive material is a carbon material or a metal material.

[0088] [6] A slurry comprising a negative electrode mixture, a binder and a solvent,

[0089] The negative electrode mixture includes solid electrolyte particles and conductive material particles disposed on the surface of the solid electrolyte particles.

[0090] The viscosity of the slurry is 0.05 Pa·s or more and 3 Pa·s or less at a shear rate of 10 (1 / s) at 25°C.

[0091] [7] The slurry according to [6], wherein the viscosity thereof is 0.1 Pa·s or more and 4.0 Pa·s or less at a shear rate of 100 (1 / s) at 25°C.

[0092] [8] A negative electrode comprising a negative electrode current collector and a negative electrode layer disposed on the negative electrode current collector and containing a negative electrode mixture,

[0093] The negative electrode mixture includes solid electrolyte particles and conductive material particles disposed on the surfaces of the solid electrolyte particles.

[0094] [9] The negative electrode according to [8], which can deposit metallic lithium during charging.

[0095]

[10] A battery comprising a negative electrode, a positive electrode, and a solid electrolyte layer disposed between the negative electrode and the positive electrode.

[0096] The negative electrode comprises a negative electrode current collector and a negative electrode layer disposed on the negative electrode current collector and containing a negative electrode mixture.

[0097] The negative electrode mixture includes solid electrolyte particles and conductive material particles disposed on the surfaces of the solid electrolyte particles.

[0098] Example 1

[0099] The present invention will be described in more detail below with reference to Examples. However, the scope of the present invention is not limited to these Examples. Unless otherwise specified, "%" means "mass %".

[0100] [Example 1]

[0101] Use Li2S powder, P2S5 powder, LiCl (Li 5.8 PS 4.5 Cl 1.2 ) powders were weighed to a total of 75 g, and mixed and pulverized using a planetary ball mill (P-7 manufactured by Fritsch) at a rotation speed of 600 rpm for 40 hours to obtain a composition of Li 5.8 PS 4.4 Br 0.8 Cl 0.8 Then, the sample was crushed using a mortar and pulverized using a ball mill, and then sized using a sieve with a mesh size of 53 μm to obtain a particle size of D 50 3.1μm, (D 90 -D 10 ) / D 50 The value of is 1.8 for the solid electrolyte particles.

[0102] Acetylene black was used as the conductive material, and the particle size D1 of the conductive material was 0.4 μm.

[0103] 95% of the solid electrolyte and 5% of the conductive material were compounded using Nobilta (NOB-MINI model manufactured by Hosokawa Micron Corporation). The planetary ball mill was operated at a rotation speed of 4000 rpm for 90 minutes.

[0104] The powder obtained by compounding was crushed in a mortar and sized using a sieve with a mesh size of 53 μm to obtain particles of a solid electrolyte compounded with particles of a conductive material. The particle size D of the solid electrolyte particles was 50 It is 2.9μm.

[0105] Next, the solid electrolyte particles composited with the conductive material particles, a binder, and a solvent were mixed to prepare a slurry. The concentration of the solid electrolyte particles composited with the conductive material particles in the slurry was 40%. The binder concentration was 0.4%, and the solvent concentration was 60%. The viscosity of the slurry is shown in Table 1 below.

[0106] The viscosity of the slurry was measured under the following conditions.

[0107] Device: RST rheometer

[0108] Model: RSTCPSPAHSIN

[0109] Manufacturer: AMETEK Brookfield

[0110] ·Measured at a shear rate of 0.05 to 1000 (1 / s) at 25°C

[0111] The slurry was applied to a negative electrode current collector made of SUS by a doctor blade method to a thickness of 100 μm, and then dried to produce a negative electrode.

[0112] The above operations were all carried out in a glove box that had been purged with sufficiently dry Ar gas (dew point below -60°C).

[0113] [Example 2]

[0114] A negative electrode was produced in the same manner as in Example 1, except that the solid electrolyte and the conductive material were compounded at a mass ratio of 90:10 to prepare a slurry. The viscosity of the slurry is shown in Table 1.

[0115] [Example 3]

[0116] In addition to the particle size D of the solid electrolyte particles 10 、D 50 and D 90 A negative electrode was produced in the same manner as in Example 1 except that the diameters were set to 0.4 μm, 0.7 μm, and 1.3 μm. The viscosity of the slurry is shown in Table 1.

[0117] [Example 4]

[0118] A negative electrode was produced in the same manner as in Example 1 except that carbon nanotubes (VGCF (registered trademark) manufactured by Resonac) were used as the conductive material. The viscosity of the slurry is shown in Table 1.

[0119] [Comparative Example 1]

[0120] A negative electrode was produced in the same manner as in Example 1, except that the compounding performed in Example 1 was not performed. The viscosity of the slurry is shown in Table 1.

[0121] 〔evaluate〕

[0122] Using the negative electrodes obtained in Examples and Comparative Examples, solid-state batteries were manufactured according to the following procedures.

[0123] The negative electrode was punched into a size of 25 mm × 25 mm. The punched negative electrode was overlapped with a 25 mm × 25 mm solid electrolyte layer and a 20 mm × 20 mm positive electrode, and then a pressure of 700 MPa was applied by cold isostatic pressing (CIP) to make a solid-state battery. As the solid electrolyte layer, the same solid electrolyte as in the embodiment was used. As the positive electrode, a current collector composed of aluminum was used to form a NCM622 (LiNi 0.6 Co 0.2 Mn 0.2 O2) is a positive electrode layer.

[0124] The resulting solid-state battery was charged and discharged at 25°C using a constant current and constant potential charge at 0.1C until it reached 4.3V, and then discharged at a constant current of 0.1C until it reached 2.5V. The battery was then inspected for short circuits. The final charge current was set at 0.05C. The results are shown in Table 1.

[0125] [Table 1]

[0126]

[0127] It can be seen from the results shown in Table 1 that the batteries made using the negative electrodes obtained in each embodiment did not suffer from short circuits during the above-mentioned charge and discharge process. The negative electrode comprises a negative electrode mixture in which particles of a conductive material are arranged on the surface of particles of a solid electrolyte. In contrast, the battery made using the negative electrode of Comparative Example 1 suffered from short circuits during the first charge and discharge process.

[0128] Industrial applicability

[0129] According to the present invention, there is provided a negative electrode mixture suitable for producing a negative electrode in which short circuiting is suppressed in a battery, particularly a lithium ion battery.

Claims

1. A negative electrode mixture, which constitutes a negative electrode layer, The negative electrode mixture includes solid electrolyte particles and conductive material particles disposed on the surfaces of the solid electrolyte particles.

2. The negative electrode mixture according to claim 1, wherein The ratio of the surface of the solid electrolyte particles to the surface of the solid electrolyte particles with which the particles of the conductive material are in contact is 10% or more.

3. The negative electrode mixture according to claim 1, wherein The solid electrolyte contains lithium (Li) element, sulfur (S) element and M element, and the M element is at least one of phosphorus (P), germanium (Ge), antimony (Sb), silicon (Si), tin (Sn), aluminum (Al), titanium (Ti), iron (Fe), nickel (Ni), cobalt (Co) and manganese (Mn).

4. The negative electrode mixture according to claim 3, wherein The solid electrolyte includes a crystal phase having an argyrodite-type crystal structure.

5. The negative electrode mixture according to any one of claims 1 to 4, wherein The conductive material is a carbon material or a metal material.

6. A slurry comprising a negative electrode mixture, a binder and a solvent, The negative electrode mixture includes solid electrolyte particles and conductive material particles disposed on the surface of the solid electrolyte particles. The viscosity of the slurry is 0.05 Pa·s or more and 3 Pa·s or less at a shear rate of 10 (1 / s) at 25°C. The slurry according to claim 6 , wherein the viscosity thereof is 0.1 Pa·s or more and 4.0 Pa·s or less at a shear rate of 100 (1 / s) at 25° C.

8. A negative electrode comprising a negative electrode current collector and a negative electrode layer disposed on the negative electrode current collector and containing a negative electrode mixture, The negative electrode mixture includes solid electrolyte particles and conductive material particles disposed on the surfaces of the solid electrolyte particles. 9 . The negative electrode according to claim 8 , which is capable of depositing metallic lithium during charging.

10. A battery comprising a negative electrode, a positive electrode, and a solid electrolyte layer disposed between the negative electrode and the positive electrode. The negative electrode comprises a negative electrode current collector and a negative electrode layer disposed on the negative electrode current collector and containing a negative electrode mixture. The negative electrode mixture includes solid electrolyte particles and conductive material particles disposed on the surfaces of the solid electrolyte particles.

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