Patent Application
20250033979
This application claims priority to Japanese Patent Application No. 2023-123369 filed on Jul. 28, 2023, incorporated herein by reference in its entirety.
The present disclosure relates to an electrode active material particle, an electrode composite material, and a lithium-ion battery.
In recent years, the development of batteries has been energetically performed. For example, in the automobile industry, the development of batteries that are used in battery electric vehicles or hybrid electric vehicles has been advanced. Further, silicon is known as an electrode active material that is used in batteries, particularly, lithium-ion batteries.
The silicon electrode active material has a high theoretical capacity, and is effective in increasing the energy density of the battery. On the other hand, the silicon electrode active material has a problem of a large expansion at the time of charging. In response, it is known that the expansion at the time of charging is restrained by using a silicon clathrate electrode active material as the silicon electrode active material.
For example, Japanese Unexamined Patent Application Publication No. 2021-158003 discloses a silicon clathrate electrode active material that has a crystal phase of type II silicon clathrate and has a composition of NaxSi136 (1.98<x<2.54).
The silicon clathrate electrode active material makes it possible to restrain the expansion at the time of charging, compared to ordinary silicon electrode active materials. However, it is desired to further restrain the expansion of the silicon clathrate electrode active material at the time of charging.
The present disclosure has an object to provide an electrode active material particle that reduces the expansion at the time of charging, and a lithium-ion battery that includes the electrode active material particle.
The disclosers of the present disclosure have found that the above problem can be solved by the following means.
An electrode active material particle including a silicon clathrate portion and an amorphous silicon portion, the electrode active material particle satisfying the following relational expression:
0 atom %<the number of silicon atoms in the amorphous silicon portion/(the number of silicon atoms in the amorphous silicon portion+the number of silicon atoms in the silicon clathrate portion)<50 atom %.
The electrode active material particle according to aspect 1, the electrode active material particle satisfying the following relational expression:
0 atom %<the number of silicon atoms in the amorphous silicon portion/(the number of silicon atoms in the amorphous silicon portion+the number of silicon atoms in the silicon clathrate portion)≤30 atom %.
An electrode composite material including the electrode active material particle according to aspect 1 or 2.
A lithium-ion battery including an electrode active material layer, in which
With the present disclosure, it is possible to provide an electrode active material particle that reduces the expansion at the time of charging, and a lithium-ion battery that includes the electrode active material particle.
Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein:
An embodiment of the present disclosure will be described below in detail. The present disclosure is not limited to the following embodiment, and can be carried out while being variously modified within the scope of the spirit of the present disclosure.
An electrode active material particle in the present disclosure includes a silicon clathrate portion and an amorphous silicon portion, and satisfies the flowing relational expression:
0 atom %<the number of silicon atoms in the amorphous silicon portion/(the number of silicon atoms in the amorphous silicon portion+the number of silicon atoms in the silicon clathrate portion)<50 atom %.
In a silicon clathrate particle, the change in expansion rate due to charging and discharging is small. However, the sensitivity to non-uniform reaction is high, and the expansion rate increases due to the progress of the non-uniform reaction. In this regard, the disclosers of the present disclosure have thought that the cause for the non-uniform reaction is that the ion conductivity of the silicon clathrate particle is low. Specifically, although the containment by any theory is not intended, it is thought that the reaction is concentrated on the particle surface because the ion conductivity of the silicon clathrate is low, and thereby the non-uniform reaction progresses.
In response, the disclosers of the present disclosure have found that it is possible to prevent the progress of the non-uniform reaction in the active material particle and thereby restrain the increase in expansion rate when the silicon electrode active material particle includes a silicon clathrate portion and an amorphous silicon portion that has a high ion conductivity.
In the present disclosure, the “electrode active material” can be used as a “positive-electrode active material” or a “negative-electrode active material”, and particularly, is used as the “negative-electrode active material”.
The electrode active material particle in the present disclosure includes a silicon clathrate portion and an amorphous silicon portion.
The electrode active material particle in the present disclosure satisfies the following relational expression:
0 atom %<the number of silicon atoms in the amorphous silicon portion/(the number of silicon atoms in the amorphous silicon portion+the number of silicon atoms in the silicon clathrate portion)<50 atom %.
The number of silicon atoms in the amorphous silicon portion/(the number of silicon atoms in the amorphous silicon portion+the number of silicon atoms in the silicon clathrate portion) may be 0.10 atom % or more, 0.30 atom % or more, 0.50 atom % or more, 0.70 atom % or more, 0.80 atom % or more, 0.90 atom % or more, or 0.95 atom % or more, and may be 45 atom % or less, 40 atom % or less, 35 atom % or less, 30 atom % or less, 25 atom % or less, 20 atom % or less, 15 atom % or less, 10 atom % or less, 5.0 atom % or less, 3.0 atom % or less, or 1.0 atom % or less.
As a method for quantitating the silicon clathrate portion and amorphous silicon portion in the electrode active material particle, there is a method in which a crystal orientation analysis system (ASTAR) attached to a transmission electron microscope (TEM) is used. More specifically, it is possible to quantitate the silicon clathrate portion and amorphous silicon portion in the electrode active material particle, by continuously collecting diffraction patterns while scanning a sample with an electron beam probe, using Nanomegas's ASTAR.
The ion conductivity of the electrode active material particle may be higher than 0.066 mS/cm. Further, the ion conductivity of the electrode active material particle may be 0.067 mS/cm or higher, 0.068 mS/cm or higher, or 0.069 mS/cm or higher, and may be 0.100 mS/cm or lower, 0.090 mS/cm or lower, 0.085 mS/cm or lower, or 0.080 mS/cm or lower.
The ion conductivity of the electrode active material particle can be measured by the following method. First, confining pressure is applied to a pellet obtained by pressing electrode active material particles. Then, in a state where the obtained sample is kept at 25° C., the calculation is performed by an alternating-current impedance method. For the measurement, Solartron 1260 of Solartron Analytical can be used. As the measurement condition, the applied voltage can be set to 5 mV, and the measurement frequency range can be set to 0.01 MHz to 1 MHz.
The method for producing the electrode active material particle in the present disclosure is, for example, a method including: mixing, heating and alloying silicon material and sodium material such that a powdery sodium-silicon (NaSi) alloy is obtained; and mixing and heating the obtained NaSi alloy and aluminum fluoride such that silicon clathrate is obtained as a clathrate compound, but is not limited to this.
The sodium material in the alloying process is sodium hydroxide, for example, but is not limited to this.
The heating temperature in the alloying process may be 350° C. or higher, 400° C. or higher, or 450° C. or higher, and may be 650° C. or lower, 600° C. or lower, or 550° C. or lower.
The heating temperature in the clathrate compound obtaining process may be 200° C. or higher, 250° C. or higher, or 270° C. or higher, and may be 400° C. or lower, 350° C. or lower, or 330° C. or lower.
The ratio between the silicon clathrate portion and amorphous silicon portion in the obtained electrode active material particle can be controlled, for example, by adjusting the heating temperatures in the alloying process and the clathrate compound obtaining process or using aluminum fluoride with a predetermined particle diameter in the clathrate compound obtaining process. Furthermore, this ratio can be controlled by charging the obtained electrode active material particle.
The silicon clathrate portion in the electrode active material in the present disclosure may be composed of porous silicon clathrate. The expansion due to charging and discharging can be absorbed by voids of porous silicon clathrate.
In the case where the silicon clathrate portion is composed of porous silicon clathrate, the method for producing the electrode active material particle in the present disclosure is, for example, a method including: obtaining a lithium-silicon (LiSi) alloy by mixing silicon and metallic lithium; obtaining porous silicon by the reaction of the obtained LiSi alloy and ethanol; and obtaining silicon clathrate as described above, using the obtained porous silicon as the silicon material, but is not limited to this.
An electrode composite material in the present disclosure includes the electrode active material particle. The electrode composite material in the present disclosure optionally contains a solid electrolyte, a conductive auxiliary agent, and a binder.
As for the electrode active material particle, it is possible to refer to the above description relevant to the electrode active material particle in the present disclosure.
The material of the solid electrolyte is not particularly limited, and it is possible to use a material that can be used as a solid electrolyte that is used in lithium-ion batteries. For example, the solid electrolyte may be a sulfide solid electrolyte.
Examples of the sulfide solid electrolyte include a sulfide amorphous solid electrolyte, a sulfide crystalloid solid electrolyte, and an argyrodite solid electrolyte, but are not limited to them. Specific examples of the sulfide solid electrolyte include a Li2S—P2S5 series (Li7P3S11, Li3PS4, Li8P2S9, and the like), Li2S—SiS2, LiI—Li2S—SiS2, LiI—Li2S—P2S5, LiI—LiBr—Li2S—P2S5, Li2S—P2S5—GeS2 (Li13GeP3S16, Li10GeP2S12, and the like), LiI—Li2S—P2O5, LiI—Li3PO4—P2S5, Li7-xPS6-xClx, and combinations of them, but are not limited to them.
The sulfide solid electrolyte may be glass or crystallized glass (glass ceramic).
The conductive auxiliary agent is not particularly limited. The conductive auxiliary agent may be vapor-grown carbon fiber (VGCF), acetylene black (AB), ketjen black (KB), carbon nanotube (CNT), or carbon nanofiber (CNF), for example, but is not limited to them.
The binder is not particularly limited. The binder may be materials such as polyvinylidene fluoride (PVDF), butadiene rubber (BR), and styrene-butadiene rubber (SBR), or combinations of them, for example, but is not limited to them.
In the present disclosure, “electrode composite material” means a composition matter that can compose an electrode active material layer by itself or by further containing another component. Further, in the present disclosure, “electrode composite material slurry” means a slurry that contains a dispersion medium in addition to the “electrode composite material” and that allows the electrode active material layer to be formed by the applying and drying of the slurry.
The lithium-ion battery in the present disclosure may be a liquid battery or a solid-state battery. In the present disclosure, the “solid-state battery” means a battery in which at least a solid electrolyte is used as the electrolyte, and accordingly, in the solid-state battery, a combination of a solid electrolyte and a liquid electrolyte is used as the electrolyte. Further, the solid-state battery in the present disclosure may be an all-solid-state battery, that is, a battery in which only the solid electrolyte is used as the electrolyte.
The lithium-ion battery in the present disclosure can be confined from both sides in the lamination direction of the above layer, by a confining member such as an end plate. The confining method is a method in which the confining torque of a bolt is used, for example, but is not limited to this.
The lithium-ion battery in the present disclosure includes the electrode active material layer, and the electrode active material layer contains the electrode composite material in the present disclosure. Particularly, in the lithium-ion battery in the present disclosure, the electrode composite material may be a negative-electrode composite material, and in this case, the lithium-ion battery in the present disclosure may include a negative-electrode current collector layer, a negative-electrode active material layer containing the electrode composite material in the present disclosure, a solid electrolyte layer, a positive-electrode active material layer, and a positive-electrode current collector layer, in this order.
The material that is used in the negative-electrode current collector layer is not particularly limited, and materials that can be used as the negative-electrode current collector of the battery can be appropriately employed. The material that is used in the negative-electrode current collector layer may be copper, a copper alloy, or a material in which nickel, chromium, carbon, or the like is plated or deposited on copper, for example, but is not limited to them.
The form of the negative-electrode current collector layer is not particularly limited, and for example, a foil form, a tabular form, a mesh form, or the like can be adopted. Among them, the foil form is preferable.
The negative-electrode active material layer contains the electrode composite material in the present disclosure. As for the electrode composite material, it is possible to refer to the above description relevant to the electrode composite material in the present disclosure.
In the case where the negative-electrode active material layer contains a solid electrolyte, the mass ratio (the mass of the electrode active material particle: the mass of the solid electrolyte) between the electrode active material particle and the solid electrolyte in the negative-electrode active material layer preferably should be 85:15 to 30:70, and more preferably should be 80:20 to 40:60.
The thickness of the negative-electrode active material layer may be 0.1 μm to 1000 μm, for example.
The solid electrolyte layer includes at least a solid electrolyte. In addition to the solid electrolyte, the solid electrolyte layer may include a binder or the like, as necessary. As for the solid electrolyte and the binder, it is possible to refer to the above description relevant to the electrode composite material in the present disclosure.
The thickness of the solid electrolyte layer is 0.1 μm to 300 μm, for example, and preferably should be 0.1 μm to 100 μm.
The positive-electrode active material layer is a layer that contains a positive-electrode active material and optionally contains a solid electrolyte, a conductive auxiliary agent, a binder, a thickening agent, or the like.
The material of the positive-electrode active material is not particularly limited. The positive-electrode active material may be lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), LiCO1/3Ni1/3Mn1/3O2, a heterologous element substitution Li—Mn spinel having a composition expressed as Li1+xMn2-x-yMyO4 (M is one or more kinds of metal elements selected from Al, Mg, Co, Fe, Ni, and Zn), lithium titanium oxide (LixTiOy), lithium metal phosphate (LiMPO4, M is one or more kinds of metals selected from Fe, Mn, Co, and Ni), or the like, for example, but is not limited to them.
The positive-electrode active material layer may include a covering layer. The covering layer is a layer that has lithium-ion conducting property, that has a low reactivity with the positive-electrode active material and the solid electrolyte, and that contains a substance that does not flow even in the case of the contact with the active material or the solid electrolyte and that allows the shape of the covering layer to be maintained. Specific examples of the material composing the covering layer include LiNbO3, Li4Ti5O12, and Li3PO4, but are not limited to them.
Examples of the form of the positive-electrode active material include a particle form. The average particle diameter (D50) of the positive-electrode active material, without being particularly limited, is 10 nm or more, for example, and may be 100 nm or more. Furthermore, the average particle diameter (D50) of the positive-electrode active material is 50 μm or less, for example, and may be 20 μm or less. For example, the average particle diameter (D50) can be calculated based on the measurement with a laser diffraction particle size analyzer or a scanning electron microscope (SEM).
As for the solid electrolyte, the conductive auxiliary agent, and the binder, it is possible to refer to the above description relevant to the electrode composite material in the present disclosure.
In the case where the positive-electrode active material layer contains a solid electrolyte, the mass ratio (the mass of the positive-electrode active material: the mass of the solid electrolyte) between the positive-electrode active material and solid electrolyte in the positive-electrode active material layer preferably should be 85:15 to 30:70, and more preferably should be 80:20 to 50:50.
The thickness of the positive-electrode active material layer is 0.1 μm to 1000 μm, for example, preferably should be 1 μm to 100 μm, and further preferably should be 30 μm to 100 μm.
The material that is used in the positive-electrode current collector layer is not particularly limited, and materials that can be used as the positive-electrode current collector of the battery can be appropriately employed. The material that is used in the positive-electrode current collector layer may be SUS, nickel, chromium, gold, platinum, aluminum, iron, titanium, zinc, or the like, or a material in which nickel, chromium, carbon, or the like is plated or deposited on these metals, for example, but is not limited to them.
The form of the positive-electrode current collector layer is not particularly limited, and for example, a foil form, a tabular form, a mesh form, or the like can be adopted. Among them, the foil form is preferable.
Si powder (Kojundo Chemical Laboratory Co., Ltd., SIEPB32) was prepared as the silicon (Si) material. The Si powder and metallic lithium (Li) were weighed at a molar ratio of Li/Si=4.0, and the weighed Si powder and Li were mixed in a mortar under an argon atmosphere, so that a lithium-silicon (LiSi) alloy was obtained. The obtained LiSi alloy was reacted with ethanol under an argon atmosphere, and by the treatment with hydrogen fluoride (HF), Si powder having voids within primary particles, that is, Si powder having a porous structure was obtained.
A sodium-silicon (NaSi) alloy was produced using the Si powder having the porous structure and sodium hydroxide (NaH) as a sodium (Na) material. As the NaH, a material that was previously washed by hexane was used. The NaH and the Si powder were weighed such that the molar ratio was 1.05:1, and the weighed NaH and Si powder having the porous structure were mixed by a cutter mill. The obtained mixture was heated in a heating furnace at 500° C. under an argon atmosphere for 40 hours, so that a powdered NaSi alloy was obtained.
The obtained NaSi alloy and aluminum fluoride (AlF3) particles were weighed such that the molar ratio was 1:0.35, and the weighed NaSi alloy and AlF3 particles were mixed by the cutter mill, so that a reaction material was obtained. The obtained powdered reaction material was put in a reaction container made of stainless steel, and was heated and reacted in the heating furnace at 310° C. under an argon atmosphere for 60 hours, so that a silicon clathrate was obtained. The obtained silicon clathrate was acid-washed using a mixed solvent in which HNO3 and H2O were mixed at a volume ratio of 10:90, and by-products in the reaction product were removed. After the washing, filtration was performed, and a solid content separated by the filtration was dried at 120° C. for 3 hours or more, so that a powdered silicon clathrate was obtained. Furthermore, the obtained silicon clathrate was washed in a 3 wt % hydrogen fluoride (HF) solution, and after filtration, was dried at 120° C. for 3 hours or more, so that an electrode active material particle in Synthesis Example 1 was obtained.
A NaSi alloy was obtained similarly to Synthesis Example 1, except that the Si powder (Kojundo Chemical Laboratory Co., Ltd., SIEPB32) was used in the alloying process, that is, the preparation of the porous silicon was not performed before the alloying process, and the heating was performed at 700° C. for 20 hours. The obtained NaSi alloy was heated in the heating furnace at 340° C. under an argon atmosphere for making a clathrate compound, and furthermore was crushed by a ball mill (manufactured by Fritsch), so that an electrode active material particle in Comparative Synthesis Example 1 was obtained.
Metallic lithium (Li) and the Si powder (Kojundo Chemical Laboratory Co., Ltd., SIEPB32) were weighed such that the molar ratio was 4:1, and are mixed and reacted in a mortar at room temperature under an argon atmosphere for 0.5 hours. Thereby, Li4Si was obtained. The obtained Li4Si was reacted with ethanol under an argon atmosphere. The filtration of the reaction product was performed, and a solid content separated by the filtration was dried at 120° C. for 3 hours or more, so that a powdered porous silicon was obtained. The porous silicon was washed in a 3 wt % HF solution, and after filtration, was dried at 120° C. for 3 hours or more, so that an electrode active material particle in Comparative Synthesis Example 2 was obtained.
An electrode active material particle in Comparative Synthesis Example 3 was obtained similarly to Synthesis Example 1, except that the clathrate compound obtaining process was executed using AlF3 crushed by the ball mill.
The surface of the electrode active material particle in each example may include coats and impurities that contain the O-element, the C-element, the N-element, and the like.
A 5 wt % butyl butyrate solution containing butyl butyrate and a polyvinylidene fluoride (PVDF) binder, a vapor-grown carbon fiber (VGCF) as a conductive auxiliary agent, the electrode active material particle in Synthesis Example 1, and a Li2S—P2S5 glass ceramic as a sulfide solid electrolyte were added in a polypropylene container, and were stirred for 30 seconds by an ultrasonic dispersing device (UH-50 manufactured by SMT Co., Ltd.). Next, the container was shaken for 30 minutes by a shaker (TTM-1 manufactured by Sibata Scientific Technology Ltd.), so that a slurry-formed negative-electrode composite material (negative-electrode composite material slurry) was obtained.
The obtained negative-electrode composite material slurry was applied on a copper (Cu) foil as a negative-electrode current collector layer by a blade method, using an applicator, and was dried on a hot plate heated at 100° C., for 30 minutes, so that a negative-electrode active material layer was formed on the negative-electrode current collector layer.
A 5 wt % heptane solution containing heptane and a butylene rubber (BR) binder, and a Li2SP2S5 glass ceramic as a sulfide solid electrolyte were added in a polypropylene container, and were stirred for 30 seconds by the ultrasonic dispersing device (UH-50 manufactured by SMT Co., Ltd.). Next, the container was shaken for 30 minutes by the shaker (TTM-1 manufactured by Sibata Scientific Technology Ltd.), so that a solid electrolyte slurry was obtained.
The obtained solid electrolyte slurry was applied on an aluminum (Al) foil as a release sheet by the blade method, using the applicator, and was dried on the hot plate heated at 100° C., for 30 minutes, so that a solid electrolyte layer was formed. A plurality of solid electrolyte layers was made.
A 5 wt % butyl butyrate solution containing butyl butyrate and a PVDF binder, LiNi1/3Co1/3Mn1/3O2 with an average particle diameter of 6 μm as a positive-electrode active material, a Li2S—P2S5 glass ceramic as a sulfide solid electrolyte, and VGCF as a conductive auxiliary agent were added in a polypropylene container, and were stirred for 30 seconds by the ultrasonic dispersing device (UH-50 manufactured by SMT Co., Ltd.). Next, the container was shaken for 3 minute by the shaker (TTM-1 manufactured by Sibata Scientific Technology Ltd.). Furthermore, the container was stirred for 30 seconds by the ultrasonic dispersing device, and was shaken for 3 minutes by the shaker, so that a slurry-formed positive-electrode composite material (positive-electrode composite material slurry) was obtained.
The obtained positive-electrode composite material slurry was applied on an Al foil as a positive-electrode current collector layer by the blade method, using the applicator, and was dried on the hot plate heated at 100° C., for 30 minutes, so that a positive-electrode active material layer was formed on the positive-electrode current collector layer.
The positive-electrode current collector layer, the positive-electrode active material layer, and the first solid electrolyte layer were laminated in this order. This laminate was set in a roll press machine, and was pressed at a press pressure of 100 kN/cm and a press temperature of 165° C., so that a positive-electrode laminated body was obtained.
The negative-electrode current collector layer, the negative-electrode active material layer, and the second solid electrolyte layer were laminated in this order. This laminate was set in the roll press machine, and was pressed at a press pressure of 60 kN/cm and a press temperature of 25° C., so that a negative-electrode laminated body was obtained.
Furthermore, the Al foils as the release sheets were released from solid electrolyte layer surfaces of the positive-electrode laminated body and the negative-electrode laminated body. Next, the Al foil as the release sheet was released from the third solid electrolyte layer.
The positive-electrode laminated body, the negative-electrode laminated body, and the third solid electrolyte layer were laminated such that the respective solid electrolyte layer sides of the positive-electrode laminated body and the negative-electrode laminated body face the third solid electrolyte layer. This laminated body was set in a planar uniaxial press machine, and was temporarily pressed at 100 MPa and 25° C. for 10 seconds. Finally, this laminated body was set in the planar uniaxial press machine, and was pressed at a press pressure of 200 MPa and a press temperature of 120° C. for 1 minute. Thereby, an all-solid-state battery in Example 1 was obtained.
A negative-electrode active material layer formed similarly to that in Example 1 was laminated on a solid electrolyte layer, and a charge and discharge test was executed at a condition of 3.17 V-4.16 V, 200 times, while lithium is adopted as a counter electrode. Thereafter, the negative-electrode active material layer was taken out, and the negative-electrode active material layer, a new solid electrolyte layer, and a positive-electrode active material layer were laminated similarly to those in Example 1, so that an all-solid-state battery in Example 2 was obtained.
All-solid-state batteries in Comparative Examples 1 to 3 were obtained similarly to those in Example 1, except that the electrode active material particles in Comparative Synthesis Examples 1 to 3 were used in the preparation of the negative-electrode composite material. The numbers of the comparative examples correspond to the numbers of the comparative synthesis examples.
A section of the electrode active material particle in Example 1 was picked up by a TEM. Further, the silicon clathrate portion and the amorphous silicon portion in the electrode active material particle were quantitated by an ASTAR attached to the TEM. Specifically, each silicon portion was quantitated by continuously collecting diffraction patterns while scanning the sample with an electron beam probe, using Nanomegas's ASTAR.
The ion conductivity of the electrode active material particle was measured by the following method. First, confining pressure was applied to a pellet obtained by pressing the electrode active material particle. Then, in a state where the obtained sample was kept at 25° C., the calculation was performed by the alternating-current impedance method. For the measurement, Solartron 1260 of Solartron Analytical was used. As the measurement condition, the applied voltage was 5 mV, and the measurement frequency range was set to 0.01 MHz to 1 MHz.
The made cell was confined at a predetermined confining pressure using a confining jig, and the confining pressure increase amount when charging at a constant current and a constant voltage was performed to 4.55 V at 10 hour rate ( 1/10 C) was measured. A large confining pressure increase amount means that the expansion amount of the active material is large. The confining pressure increase amount is the difference between the highest value and lowest value of the confining pressure, and the values in Examples ad Comparative Examples 2 and 3 are shown as relative values when the value in Comparative Example 1 is 100.
As shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-123369 | Jul 2023 | JP | national |
