All solid state battery

Abstract

To reduce the rate of increase in resistance after endurance.SOLUTION: An all-solid battery includes an electrode layer, the electrode layer includes an active material and composite particles, the composite particle includes a first solid electrolyte and a coating layer, the coating layer includes a polysiloxane compound, the coating layer covers at least a portion of the first solid electrolyte, and the coverage of the first solid electrolyte by the coating layer is less than 100%.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to all-solid-state batteries. [Background technology]

[0002] Patent Document 1 (JP 2020-181640 A) discloses a coated positive electrode active material for an all-solid-state battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-181640 A Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for lower resistance in all-solid-state batteries (hereinafter may be abbreviated as "batteries"). One of the resistance components in a battery is a low ion-conductive layer formed on the surface of an active material. The low ion-conductive layer is thought to be formed by oxidation of the surface of the active material. In order to inhibit the formation of the low ion-conductive layer, it has been proposed to cover the surface of the active material with a polysiloxane compound. This technology is expected to reduce the initial resistance. However, there is room for improvement in the rate of increase in resistance after endurance testing.

[0005] An object of the present disclosure is to reduce the rate of increase in resistance after durability testing. [Means for solving the problem]

[0006] [1] An electrode layer, the electrode layer includes an active material and composite particles; the composite particle includes a first solid electrolyte and a coating layer; The coating layer contains a polysiloxane compound, the coating layer coats at least a portion of the first solid electrolyte, A coverage of the first solid electrolyte with the covering layer is less than 100%.

[0007] Hereinafter, "solid electrolyte" may be abbreviated as "SE." The surface of the SE may be oxidized by repeated charge-discharge cycles. The oxidation of the SE may accelerate the deterioration of its performance.

[0008] In the electrode layer, a coating layer containing a polysiloxane compound covers at least a part of the surface of the first SE. The polysiloxane compound can improve the oxidation resistance of the SE. By improving the oxidation resistance of the SE, improvement in cycle characteristics is expected. However, the coverage of the first SE by the coating layer is less than 100%. When the coverage of the first SE by the coating layer is 100%, no ion conduction path is formed in the electrode layer.

[0009] [2] In the all-solid-state battery described in [1] above, the polysiloxane compound may include a structure represented by the following formula (1):

[0010] [ka]

[0011] In the above formula (1), R 1 and R 2 are each independently a hydrogen atom, a hydroxyl group, an alkyl group, a carbonyl group, an alkoxy group, a carboxylate group, or an acryloxy group, and n is a real number of 2 or more.

[0012] [3] In the all-solid-state battery according to the above [1] or [2], the electrode layer further contains a second solid electrolyte. [4] A positive electrode layer, the positive electrode layer includes a positive electrode active material and composite particles, the composite particle includes a first solid electrolyte and a coating layer; The coating layer contains a polysiloxane compound, the coating layer coats at least a portion of the first solid electrolyte, a coverage of the first solid electrolyte by the coating layer is less than 100%; The polysiloxane compound has the formula (1):

[0013] [ka]

[0014] The structure includes: In the formula (1), R 1 and R 2 each independently represents a hydrogen atom, a hydroxy group, an alkyl group, a carbonyl group, an alkoxy group, a carboxylate group, or an acryloxy group, An all-solid-state battery, where n is a real number greater than or equal to 2.

[0015] [5] In the all-solid-state battery according to the above [4], the positive electrode layer further contains a second solid electrolyte. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a conceptual diagram of an all-solid-state battery according to this embodiment. [Diagram 2] FIG. 2 is a conceptual diagram of a composite particle in this embodiment. [Diagram 3] FIG. 3 is a schematic flowchart of the method for producing an all-solid-state battery in this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present embodiment") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure.

[0018] <All-solid-state battery> Fig. 1 is a conceptual diagram of an all-solid-state battery in this embodiment. Fig. 1 conceptually shows a cross section parallel to the thickness direction of a battery 100. The battery 100 includes a power generating element 50. The battery 100 may include, for example, an exterior body (not shown). The exterior body may house the power generating element 50. The exterior body may be, for example, a pouch made of a metal foil laminate film, or a metal case.

[0019] The power generating element 50 includes a first electrode layer 10, a separator layer 30, and a second electrode layer 20. The power generating element 50 may include a plurality of the first electrode layers 10, the separator layers 30, and the second electrode layers 20. As an example, the power generating element 50 in FIG. 1 includes two each of the first electrode layers 10, the separator layers 30, and the second electrode layers 20. The separator layer 30 is interposed between the first electrode layer 10 and the second electrode layer 20. The separator layer 30 separates the first electrode layer 10 from the second electrode layer 20. The separator layer 30 may include, for example, a sulfide SE. The separator layer 30 may have a thickness of, for example, 1 to 100 μm.

[0020] The second electrode layer 20 has a polarity different from that of the first electrode layer 10. For example, when the first electrode layer 10 is a positive electrode layer, the second electrode layer 20 is a negative electrode layer. The power generating element 50 may further include a first current collector 11 and a second current collector 21. The first current collector 11 is in contact with the first electrode layer 10. The second current collector 21 is in contact with the second electrode layer 20. For example, when the first electrode layer 10 is a positive electrode layer, the first current collector 11 is a positive electrode current collector. For example, when the second electrode layer 20 is a negative electrode layer, the second current collector 21 is a negative electrode current collector. The first current collector 11 and the second current collector 21 may each independently have a thickness of, for example, 5 to 50 μm. The first current collector 11 and the second current collector 21 may each independently include, for example, an Al foil, an Al alloy foil, a Cu foil, a Ni foil, a stainless steel foil, or the like.

[0021] 《Electrode layer》 The first electrode layer 10 and the second electrode layer 20 are collectively referred to as the "electrode layer". The electrode layer may have a thickness of, for example, 10 to 1000 μm. The electrode layer contains an active material and composite particles. The electrode layer may further contain, for example, a conductive material, a binder, etc.

[0022] 《Active Material》 The active material may be, for example, particulate. The active material may have a D50 of, for example, 1 to 30 μm. "D50" indicates the particle diameter at which the cumulative frequency from the smaller particle diameters reaches 50% in the volume-based particle size distribution. D50 can be measured by a laser diffraction particle size distribution measuring device. The blending amount of the active material may be, for example, 60 to 95 parts by mass with respect to 100 parts by mass of the electrode layer.

[0023] The active material may be, for example, a positive electrode active material. The positive electrode active material may be, for example, LiCoO 2 , LiNiO 2 , LiMnO 2 , Li(NiCoMn)O 2 , and Li(NiCoAl)O 2 and may contain at least one selected from the group consisting of. For example, in "Li(NiCoMn)O 2 ", "(NiCoMn)" indicates that the total of the composition ratios within the parentheses is 1. As long as the total is 1, the individual component amounts are arbitrary.

[0024] The active material may be, for example, a negative electrode active material. The negative electrode active material may be, for example, natural graphite, artificial graphite, soft carbon, hard carbon, Si, SiO x (0 < x < 2), Si-based alloys, and Li 4 Ti 5 O 12 and may contain at least one selected from the group consisting of.

[0025] The active material may be coated with a film. The film may have a thickness of, for example, 5 to 500 nm. The film may contain, for example, an oxide SE, a polysiloxane compound, etc. The oxide SE may be, for example, LiNbO 3, Li 3 PO 4 etc. may be included.

[0026] 《Composite particles》 2 is a conceptual diagram showing a composite particle in this embodiment. The composite particle 5 includes a first solid electrolyte 1 (first SE1) and a coating layer 2. The composite particle 5 may form an aggregate, for example. That is, one composite particle 5 may include two or more first SE1. The composite particle 5 may have a D50 of, for example, 1 to 50 μm.

[0027] (1st solid electrolyte) The first SE1 can form an ion conduction path in the electrode layer. The first SE1 may be particulate. The first SE1 may have a D50 of, for example, 0.01 to 1 μm. The amount of the first SE1 may be, for example, 1 to 30 parts by mass with respect to 100 parts by mass of the electrode layer.

[0028] The first SE1 may be, for example, at least one selected from the group consisting of a sulfide SE, an oxide SE, and a fluoride SE. The sulfide SE may exhibit high ionic conductivity. The sulfide SE may include, for example, Li, P, and S. The sulfide SE may further include, for example, O, Ge, Si, etc. The sulfide SE may further include, for example, a halogen, etc. The sulfide SE may be, for example, a glass ceramic type or an argyrodite type. The sulfide SE may be, for example, LiI-LiBr-Li 3 P.S. 4 , Li 2 S-SiS 2 , LiI-Li 2 S-SiS 2 , LiI-Li 2 SP 2 S 5 , Li 2 SP 2 S 5 and Li 3 P.S. 4 may contain at least one selected from the group consisting of:

[0029] For example, "LiI-LiBr-Li 3 P.S. 4 " is LiI, LiBr and Li 3 P.S. 4 The sulfide SE may be synthesized by any method. The sulfide SE may be synthesized, for example, by a gas phase method, a solid phase method, or a liquid phase method. 2 SP 2 S 5 " is Li 3 P.S. 4 Includes: 3 P.S. 4 For example, Li 2 S and P 2 S 5 And "Li 2 S / P 2 S 5 = 75 / 25 (molar ratio)".

[0030] (covering layer) The coating layer 2 coats at least a portion of the first SE1. In the composite particle 5, the coverage of the surface of the first SE1 by the coating layer 2 is less than 100%. When the coverage is less than 100%, an ion conduction path is formed in the electrode layer. The coverage is not particularly limited as long as it is more than 0% and less than 100%. The coverage may be, for example, 92% or less, 73% or less, or 52% or less. The coverage may be, for example, 3% or more, 15% or more, or 23% or more.

[0031] The coverage can be measured by SEM-EDS (Scanning Electron Microscope-Energy Dispersive X-ray Spectrometry). That is, an SEM image of the composite particle 5 is obtained. The magnification of the SEM image is about 30,000 times. In the SEM image of the composite particle 5, elemental mapping of Si derived from the polysiloxane compound is performed and analyzed by image processing software "ImageJ". The area of ​​the part where Si is detected is calculated. The ratio (percentage) of the area of ​​the part where Si is detected to the area of ​​the entire composite particle 5 is the coverage. The coverage can be measured for 10 composite particles 5. The arithmetic average of the 10 coverages can be adopted as the measurement result.

[0032] The coating layer 2 may have a thickness of, for example, 1 to 100 nm. The thickness of the coating layer 2 can be measured in a cross-sectional SEM image of the composite particle 5. That is, the thickness of the coating layer 2 is measured at 10 points randomly selected in the cross-sectional SEM image of the composite particle 5. The arithmetic average of the 10 points can be used as the measurement result.

[0033] [Polysiloxane Compound] The coating layer 2 includes a polysiloxane compound. The polysiloxane compound can improve the oxidation resistance of the first SE1. By improving the oxidation resistance of the first SE1, it is expected that the cycle characteristics will be improved. The polysiloxane compound can also improve the oxidation resistance of the active material, the conductive material, and the like.

[0034] The polysiloxane compound includes a structure in which two or more siloxane bonds (-Si-O-) are linked. The polysiloxane compound may be, for example, linear, branched, or cyclic. The polysiloxane compound may include, for example, a structure represented by the following formula (1).

[0035] [ka]

[0036] In the above formula (1), R1 and R 2 are each independently a hydrogen atom, a hydroxyl group, an alkyl group, a carbonyl group, an alkoxy group, a carboxylate group, or an acryloxy group. These substituents may be further substituted. The polysiloxane compound may not contain an unsaturated bond such as "C=C". 1 and R 2 and may be bonded to each other to form a ring. In addition, in the above formula (1), n ​​is a real number of 2 or more. There is no particular limitation on n as long as it is a real number of 2 or more, and it may be, for example, 1000 or less, 500 or less, or 100 or less.

[0037] The polysiloxane compound may include, for example, 2,4,6,8-tetramethylcyclotetrasiloxane (TMCTS). TMCTS is a cyclic compound. In the above formula (1), R 1 is a hydrogen atom, and R 2 is a methyl group and n is 4.

[0038] The amount of the polysiloxane compound added is less than 50 parts by mass relative to 100 parts by mass of the first SE1. When the amount of the polysiloxane compound is 50 parts by mass or more, the coverage rate becomes 100%, and therefore, no ion conductive path is formed in the electrode layer.

[0039] 《Second solid electrolyte》 The electrode layer may include a second solid electrolyte (second SE). The second SE is not covered by a covering layer. The second SE may be the same as the first SE or may be different. Details of the second SE are omitted since they are the same as those of the first SE described above.

[0040] The content (volume %) of the composite particles and the second SE in the electrode layer is, for example, 100:0 to 1:99. By including the composite particles and the second SE in such a range, it is expected that the battery resistance will be reduced. In addition, from the viewpoint of cost reduction, it is preferable that the electrode layer includes the second SE.

[0041] Other Ingredients The electrode layer may contain a conductive material such as acetylene black (AB), vapor grown carbon fiber (VGCF), carbon nanotube (CNT), etc. The electrode layer may contain a binder such as styrene butadiene rubber (SBR), acrylate butadiene rubber (ABR), polyvinylidene fluoride (PVDF), etc. The amount of the conductive material and the binder to be mixed may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the electrode layer. EXAMPLES

[0042] <No.1> 《Synthesis of sulfide SE》 Li 2 S, P 2 S 5 The raw powder was prepared by weighing out the Li 2 S, P 2 S 5 The mixture ratio of Li 2 S / P 2 S 5 = 75 / 25 (molar ratio). Raw material powder and tetrahydrofuran (THF) were put into a glass container. The mixing ratio of the raw material and THF was "raw material powder / THF = 1 / 20 (mass ratio)". The raw material powder and THF were stirred for 72 hours at 25°C. After stirring, a precipitate (powder) was collected. The precipitate is a precursor of sulfide SE. The precursor was dried at 25°C under an argon atmosphere to form a dried product. The dried product was fired at 100°C for 1 hour under atmospheric pressure (open system) to form a first fired product. The first fired product was vacuum sealed in a quartz tube. The quartz tube was fired in a muffle furnace at 140°C for 12 hours to form a second fired product. The second fired product was pulverized to adjust the particle size. After pulverization, the second calcined product was calcined at 200° C. for 1 hour or more to obtain sulfide SE.

[0043] <<Creating Composite Particles>> At a dew point of -70°C, 100 parts by mass of sulfide SE and 100 parts by mass of a mixed solvent of heptane and dibutyl ether (heptane / dibutyl ether = 8 / 2 (volume ratio)) were mixed and stirred in a nitrogen atmosphere to obtain a slurry. 0.1 parts by mass of a polysiloxane compound was added to the slurry, stirred for 1 hour, and then vacuum dried at 120°C for 12 hours to obtain composite particles.

[0044] 3 is a schematic flow chart of the method for producing an all-solid-state battery in this embodiment. A test battery was produced according to the flow chart of FIG.

[0045] (a) Formation of electrode slurry A "Filmix (registered trademark)" manufactured by Plamix Corporation was prepared as a kneading device. 80 parts by mass of a positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 ), 9.51 parts by mass of composite particles, and 2.5 parts by mass of conductive material (VGCF) were added. Then, a binder dispersion (SBR dispersion, concentration 5%) and 32.21 parts by mass of a dispersion medium (tetralin) were added to the mixing vessel. The solid content was 69% (mass fraction). The mixture was further kneaded to form a positive electrode slurry. During kneading, the peripheral speed of the Filmix was adjusted within the range of 5 to 30 m / s.

[0046] (b) Formation of electrode layer The positive electrode slurry was applied to the surface of the positive electrode current collector (Al foil) using a blade applicator to form a coating film, which was then dried at 100°C for 30 minutes to form a positive electrode layer.

[0047] (c) Manufacturing of all-solid-state batteries (Formation of negative electrode layer) In the FILMICS, 18.6 parts by mass of the negative electrode active material (Si), 8.69 parts by mass of the sulfide SE, the binder dispersion (SBR dispersion, concentration 5%), and the dispersion medium (diisobutyl ketone) were mixed to form a negative electrode slurry. The solid content of the negative electrode slurry was 43% (mass fraction). During kneading, the peripheral speed of the FILMICS was adjusted within the range of 5 to 30 m / s. The negative electrode slurry was applied to the surface of the negative electrode current collector (Ni foil) by a blade-type applicator to form a coating film. The coating film was dried at 100°C for 30 minutes to form a negative electrode layer.

[0048] (Formation of separator layer) A separator slurry was formed by kneading 40 parts by mass of sulfide SE, a binder dispersion (ABR dispersion, concentration 5%), and a mixed dispersion medium (heptane: 25.62 parts by mass, diisobutyl ketone: 8 parts by mass) with an ultrasonic homogenizer. The solid content of the separator slurry was 50% (mass fraction). A coating film was formed by applying the separator slurry to the surface of a substrate (Al foil). The coating film was dried at 100°C for 30 minutes to form a separator layer.

[0049] (assembly) A separator layer and a positive electrode layer were sequentially pressed onto the surface of the negative electrode layer by a press working of 20 kN to form a power generating element. The power generating element was densified by applying roll pressing to the power generating element. The roll linear pressure was 4 ton / cm, and the roll gap was 200 μm. A positive electrode current collector (Al foil) was bonded to the positive electrode layer. A pouch made of Al laminated film was prepared as an exterior body. The power generating element was enclosed in the exterior body. A restraining member was attached to the outside of the exterior body so that a pressure of 5 MPa was applied to the power generating element. From the above, a test battery (an all-solid-state battery including a positive electrode layer) was manufactured.

[0050] (First charge / discharge) CCCV charging and discharging (upper limit charge voltage 4.55V, lower limit discharge voltage 2.5V) was performed. The design capacity of the cell was 0.3Ah. The hour rate during CC charging or CC discharging was 0.1C. At an hour rate of 1C, the design capacity is discharged in 1 hour.

[0051] <No.2~7> Test batteries were prepared in the same manner as No. 1, except that the amount of polysiloxane compound added was changed (see Table 1 below). The amount added in Table 1 below is the parts by weight of polysiloxane compound per 100 parts by weight of sulfide SE.

[0052] <No.8> A test cell was fabricated similarly to No. 1, except that in the formation of the positive electrode slurry, the composite particles were changed to sulfide SE.

[0053] <No.9> In No. 9, a coated positive electrode active material was formed by coating the positive electrode active material with a polysiloxane compound. The coating amount (addition amount of the polysiloxane compound) was 50 parts by mass per 100 parts by mass of the positive electrode layer. A test battery was manufactured in the same manner as No. 1, except that a coated positive electrode active material was used.

[0054] <No.10~20> Sulfide SE and the same composite particles as in No. 2 were prepared. Test cells were fabricated similarly to No. 1, except that the sulfide SE and the composite particles were added in the proportions listed in Table 1.

[0055] <Evaluation> (Coverage rate) The coverage of each composite particle was calculated using the method described above. The results are shown in Table 1.

[0056] (Rate of increase in resistance) The test battery was subjected to 1000 charge / discharge cycles, and the resistance increase rate was determined. The resistance increase rate was calculated by the following formula (2). The results are shown in Table 1. The resistance after 3 cycles was defined as the initial resistance.

[0057] Resistance increase rate (%) = 100 × (resistance after 1000 cycles – initial resistance) / initial resistance Equation (2)

[0058] [Table 1]

[0059] <Result> When composite particles with a coverage rate of less than 100% are used, the resistance increase rate tends to decrease (see Nos. 1 to 6).

[0060] When the content (volume %) of the composite particles and the sulfide SE in the positive electrode layer is 100:0 to 1:99, the resistance increase rate also tends to decrease (see Nos. 4 and 10 to 20). [Explanation of symbols]

[0061] 1 first solid electrolyte, 2 coating layer, 5 composite particle, 10 first electrode layer, 11 first current collector, 20 second electrode layer, 21 second current collector, 30 separator layer, 50 power generating element, 100 all-solid-state battery.

Claims

1. An electrode layer is included. the electrode layer includes an active material and composite particles; The composite particles include a first solid electrolyte, the first solid electrolyte has a coating layer on its surface, The coating layer contains a polysiloxane compound, the coating layer coats at least a portion of the first solid electrolyte, A solid-state battery, wherein a coverage of the first solid electrolyte by the covering layer is 3% or more and 73% or less.

2. The polysiloxane compound has the formula (1): 【Chemistry 1】 The structure includes: In the formula (1), R 1 and R 2 each independently represents a hydrogen atom, a hydroxy group, an alkyl group, a carbonyl group, an alkoxy group, a carboxylate group, or an acryloxy group, The solid-state battery according to claim 1 , wherein n is a real number of 2 or more.

3. The solid-state battery according to claim 1 , wherein the electrode layer further comprises a second solid electrolyte.

4. A positive electrode layer is included. the positive electrode layer includes a positive electrode active material and composite particles, The composite particles include a first solid electrolyte, the first solid electrolyte has a coating layer on its surface, The coating layer contains a polysiloxane compound, the coating layer coats at least a portion of the first solid electrolyte, a coverage of the first solid electrolyte by the coating layer is 3% or more and 73% or less; The polysiloxane compound has the formula (1): 【Chemistry 2】 The structure includes: In the formula (1), R 1 and R 2 each independently represents a hydrogen atom, a hydroxy group, an alkyl group, a carbonyl group, an alkoxy group, a carboxylate group, or an acryloxy group, A solid-state battery, wherein n is a real number greater than or equal to 2.

5. The solid-state battery according to claim 4 , wherein the positive electrode layer further comprises a second solid electrolyte.

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