Secondary batteries and secondary battery systems

Abstract

To improve durability of a secondary cell using silicon negative electrode active materials.SOLUTION: A secondary cell includes a negative electrode 10, an electrolyte layer 20, and a positive electrode 30, the negative electrode 10 including Si particles as negative electrode active materials, the positive electrode 30 including Li-containing compounds as positive electrode active materials, the Si particles having a clathrate structure, where a ratio C1 / C2 of a basis weight C1 of the Li-containing compounds in the positive electrode 30 to a basis weight C2 of the Si particles in the negative electrode 10 is equal to or larger than 3.40 and equal to or smaller than 8.33.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application discloses a secondary battery and a secondary battery system using a silicon-based negative electrode active material. [Background Art]

[0002] Batteries using a silicon-based negative electrode active material are known. For example, Patent Document 1 discloses a lithium ion secondary battery using a silicon oxide as a negative electrode active material. Further, Patent Document 2 discloses a lithium ion secondary battery using silicon clathrate II as a negative electrode active material. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2020-113547 [Patent Document 2] Japanese Patent Application Laid-Open No. 2021-034279 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] Batteries using a silicon-based negative electrode active material still have room for improvement in durability. [Means for Solving the Problem]

[0005] As one of the means for solving the above problems, the present application provides: a secondary battery comprising a negative electrode, an electrolyte layer, and a positive electrode, the negative electrode comprising Si particles serving as a negative electrode active material, the positive electrode comprising a Li-containing compound serving as a positive electrode active material, the Si particles having a clathrate structure, a ratio C1 / C2 of a basis weight C1 of the Li-containing compound in the positive electrode to a basis weight C2 of the Si particles in the negative electrode is 8.33 or less, a secondary battery Disclose the following.

[0006] In the secondary battery of this disclosure, the ratio C1 / C2 may be 2.87 or greater.

[0007] In the secondary battery disclosed herein, The Li-containing compound may contain, as constituent elements, at least Li, at least one of Ni, Co, and Mn, and O.

[0008] This application is one means of solving the above problem, The secondary battery disclosed herein, A control unit for controlling the charging and discharging of the secondary battery, Equipped with, The control unit controls the charging voltage of the secondary battery to 4.2V or less. Secondary battery system Disclose the following. [Effects of the Invention]

[0009] The secondary battery of this disclosure has excellent durability. [Brief explanation of the drawing]

[0010] [Figure 1] This shows a schematic representation of the configuration of a secondary battery. [Modes for carrying out the invention]

[0011] 1. Secondary battery The secondary battery of this disclosure comprises a negative electrode, an electrolyte layer, and a positive electrode. Here, the negative electrode has Si particles as a negative electrode active material, and the positive electrode has a Li-containing compound as a positive electrode active material. The Si particles have a clathrate structure. The ratio C1 / C2 of the basis weight C1 of the Li-containing compound in the positive electrode to the basis weight C2 of the Si particles in the negative electrode is 8.33 or less. Figure 1 schematically shows the configuration of a secondary battery 100 according to one embodiment. As shown in Figure 1, the secondary battery 100 comprises a negative electrode 10, an electrolyte layer 20, and a positive electrode 30.

[0012] 1.1 Negative electrode The negative electrode 10 contains Si particles as a negative electrode active material. As shown in Figure 1, the negative electrode 10 may comprise a negative electrode active material layer 11 and a negative electrode current collector 12, in which case the negative electrode active material layer 11 may contain Si particles as a negative electrode active material.

[0013] 1.1.1 Negative electrode active material layer The negative electrode active material layer 11 contains Si particles as a negative electrode active material, and may optionally also contain an electrolyte, a conductive additive, a binder, etc. The negative electrode active material layer 11 may also contain various other additives. The content of each component in the negative electrode active material layer 11 is not particularly limited and can be appropriately determined according to the performance of the target battery. For example, if the entire negative electrode active material layer 11 (total solid content) is taken as 100% by mass, the content of the negative electrode active material may be 40% by mass or more, 50% by mass or more, or 60% by mass or more, or 100% by mass or less, or 90% by mass or less. The thickness of the negative electrode active material layer 11 is also not particularly limited and may be, for example, 1 μm or more, 10 μm or more, or 30 μm or more, or 1 mm or less, 500 μm or less, or 100 μm or less.

[0014] The Si particles used as the negative electrode active material have a clathrate structure. The presence of a clathrate structure in the Si particles reduces the expansion and contraction of the Si particles during battery charging and discharging, thus improving the battery's durability. Whether or not the Si particles have a clathrate structure can be easily determined from Raman spectroscopy or XRD. In this application, the measurement was 325±10 cm² using Raman spectroscopy. -1 Maximum peak intensity I 325 And, 205±10cm -1 Maximum peak intensity I 205 Ratio I 325 / I 205 If the value is within the range of 1.03 to 1.21, the Si particles are considered to have a clathrate structure. Furthermore, the Si particles used as the negative electrode active material may have an oxide film and may contain impurities such as carbon.

[0015] The size of the Si particles as the negative electrode active material is not particularly limited. The average particle diameter of the Si particles may be, for example, 0.1 μm or more, 0.3 μm or more, 0.5 μm or more, or 0.7 μm or more, and may also be 50 μm or less, 30 μm or less, 10 μm or less, or 5 μm or less. Here, the average particle diameter of Si particles refers to the particle diameter (median diameter) at an integrated value of 50% in a volume-based particle size distribution determined by the laser diffraction / scattering method.

[0016] The negative electrode active material layer 11 may contain other negative electrode active materials in addition to the above Si particles as the negative electrode active material. For example, as other negative electrode active materials, the negative electrode active material layer 11 may contain at least one selected from the group consisting of: silicon-based active materials other than clathrate silicon, such as Si other than clathrate silicon, Si alloys, and silicon oxide; carbon-based active materials such as graphite and hard carbon; various oxide-based active materials such as lithium titanate; and metallic lithium and lithium alloys. The proportion of Si particles having a clathrate structure in the negative electrode active material contained in the negative electrode active material layer 11 may be, for example, more than 50 mass%, 70 mass% or more, 90 mass% or more, or 95 mass% or more. Alternatively, the negative electrode active material layer 11 may contain only Si particles having a clathrate structure as the negative electrode active material.

[0017] The electrolyte may be a solid electrolyte or a liquid electrolyte (electrolytic solution). When the secondary battery 100 is an all-solid-state battery, the negative electrode active material layer 11 may contain a solid electrolyte as the electrolyte. Further, when the secondary battery 100 is an electrolytic solution battery, the negative electrode active material layer 11 may contain an electrolytic solution as the electrolyte.

[0018] As the solid electrolyte, any solid electrolyte known as a solid electrolyte for secondary batteries may be used. The solid electrolyte may be an inorganic solid electrolyte or an organic polymer electrolyte. In particular, inorganic solid electrolytes are preferable because they are excellent in ionic conductivity and heat resistance. Examples of the inorganic solid electrolyte include lithium lanthanum zirconate, LiPON, Li 1+X Al X Ge 2-XExamples of oxide solid electrolytes include (PO4)3, Li-SiO glass, and Li-Al-SO glass; and sulfide solid electrolytes such as Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Si2S-P2S5, Li2S-P2S5-LiI-LiBr, LiI-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, and Li2S-P2S5-GeS2. In particular, sulfide solid electrolytes, especially those containing Li2S-P2S5, exhibit high performance. The solid electrolyte may be amorphous or crystalline. The solid electrolyte may also be particulate, for example. One type of solid electrolyte may be used alone, or two or more types may be used in combination.

[0019] The electrolyte may contain, for example, lithium ions as carrier ions. The electrolyte may be aqueous or non-aqueous. The composition of the electrolyte may be the same as that known for lithium-ion battery electrolytes. For example, a solution of lithium salt dissolved in a carbonate-based solvent at a predetermined concentration can be used as the electrolyte. Examples of carbonate-based solvents include fluoroethylene carbonate (FEC), ethylene carbonate (EC), and dimethyl carbonate (DMC). Examples of lithium salts include LiPF6.

[0020] Examples of conductive additives include carbon materials such as vapor-processed carbon fiber (VGCF), acetylene black (AB), Ketjenblack (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metallic materials such as nickel, aluminum, and stainless steel. Conductive additives may be in particulate or fibrous form, and their size is not particularly limited. Conductive additives may be used alone or in combination of two or more types.

[0021] Examples of binders include polyimide (PI) binders, butadiene rubber (BR) binders, butylene rubber (IIR) binders, acrylate butadiene rubber (ABR) binders, styrene butadiene rubber (SBR) binders, polyvinylidene fluoride (PVdF) binders, and polytetrafluoroethylene (PTFE) binders. In particular, when the negative electrode active material layer 11 contains polyimide as a binder, the expansion and contraction of Si particles are more easily suppressed. The polyimide may be obtained by heating a polyamic acid to induce an imidation reaction (dehydration and cyclization). The polyamic acid may be aromatic or aliphatic, but from the viewpoint of being able to become a high-strength binder when it becomes polyimide, one having an aromatic ring is particularly preferred. The binder may be used alone or in combination of two or more types.

[0022] 1.1.2 Negative electrode current collector The negative electrode current collector 12 can be any of the materials commonly used as negative electrode current collectors for secondary batteries. The negative electrode current collector 12 may also be in the form of foil, plate, mesh, perforated metal, or foam. The negative electrode current collector 12 may be a metal foil or metal mesh, or a carbon sheet. Metal foil is particularly advantageous in terms of handling. The negative electrode current collector 12 may consist of multiple foils or sheets. Examples of metals constituting the negative electrode current collector 12 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. In particular, from the viewpoint of ensuring reduction resistance and avoiding alloying with lithium, the negative electrode current collector 12 may contain at least one metal selected from Cu, Ni, and stainless steel. The negative electrode current collector 12 may have some kind of coating layer on its surface for purposes such as adjusting resistance. Furthermore, the negative electrode current collector 12 may be a metal foil or a substrate on which the above-mentioned metal is plated or deposited. Also, if the negative electrode current collector 12 consists of multiple metal foils, there may be some layer between the multiple metal foils. The thickness of the negative electrode current collector 12 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, or 1 mm or less or 100 μm or less.

[0023] 1.2 Electrolyte layer The electrolyte layer 20 contains at least an electrolyte. If the secondary battery 100 is a solid-state battery (a battery containing a solid electrolyte, which may or may not contain a liquid), the electrolyte layer 20 contains a solid electrolyte and may optionally contain a binder or the like. In this case, the content of the solid electrolyte and the binder or the like in the electrolyte layer 20 is not particularly limited. On the other hand, if the secondary battery 100 is an electrolyte battery, the electrolyte layer 20 contains an electrolyte and may also have a separator or the like to hold the electrolyte and prevent contact between the negative electrode 10 and the positive electrode 30. The thickness of the electrolyte layer 20 is not particularly limited and may be, for example, 0.1 μm or more or 1 μm or more, or 2 mm or less or 1 mm or less.

[0024] The solid electrolyte, electrolyte solution, and binder are as described above. The separator can be any separator commonly used in secondary batteries, such as those made of polyethylene (PE), polypropylene (PP), polyester, and polyamide resins. The separator may have a single-layer structure or a multi-layer structure. Examples of multi-layer separators include a PE / PP two-layer separator, or a PP / PE / PP or PE / PP / PE three-layer separator. The separator may also be made of a nonwoven fabric such as cellulose nonwoven fabric, resin nonwoven fabric, or glass fiber nonwoven fabric.

[0025] 1.3 Positive electrode The positive electrode 30 contains positive electrode active material. As shown in Figure 1, the positive electrode 30 may comprise a positive electrode active material layer 31 and a positive electrode current collector 32, in which case the positive electrode active material layer 31 may contain positive electrode active material.

[0026] 1.3.1 Cathode active material layer The positive electrode active material layer 31 contains a positive electrode active material and may optionally contain an electrolyte, a conductive additive, a binder, etc. The positive electrode active material layer 31 may also contain various other additives. The content of each component in the positive electrode active material layer 31 is not particularly limited and can be appropriately determined according to the performance of the battery to be used. For example, if the entire positive electrode active material layer 31 is taken as 100% by mass, the content of the positive electrode active material may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 100% by mass or less, or 90% by mass or less. The thickness of the positive electrode active material layer 31 is also not particularly limited and may be, for example, 1 μm or more, 10 μm or more, 30 μm or more, 1 mm or less, 500 μm or less, or 100 μm or less.

[0027] As the positive electrode active material, any known positive electrode active material for secondary batteries can be used. Among the known active materials, a material whose potential for intercalation and release of lithium ions (charge / discharge potential) is nobler than the charge / discharge potential of Si particles having the above-mentioned clathrate structure can be used as the positive electrode active material. Examples of such positive electrode active materials include various Li-containing compounds. More specifically, lithium cobaltate, lithium nickelate, and Li can be used as positive electrode active materials. 1±α Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O 2±δ Lithium manganate, spinel-type lithium compounds (Li 1+x Mn 2-x-y M y Various lithium-containing oxides may be used, such as heteroatom-substituted Li-Mn spinel (e.g., O4, where M is one or more selected from Al, Mg, Co, Fe, Ni, and Zn), lithium titanate, and metallic lithium phosphate (e.g., LiMPO4, where M is one or more selected from Fe, Mn, Co, and Ni). In particular, a higher effect can be expected when the Li-containing compound used as the positive electrode active material contains at least Li, at least one of Ni, Co, and Mn, and O as constituent elements. The positive electrode active material may be used alone or in combination of two or more types. The positive electrode active material may be particulate, for example, and its size is not particularly limited. The particles of the positive electrode active material may be solid or hollow. The particles of the positive electrode active material may be primary particles or secondary particles formed by the aggregation of multiple primary particles. The average particle diameter of the positive electrode active material particles may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, or it may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less.

[0028] A protective layer containing a Li ion conductive compound may be formed on the surface of the positive electrode active material. That is, the positive electrode active material layer 31 may contain a composite comprising the positive electrode active material and a protective layer provided on its surface. This makes it easier to suppress reactions between the positive electrode active material and sulfides (such as sulfide solid electrolytes). Examples of Li ion conductive compounds include Li3BO3, LiBO2, Li2CO3, LiAlO2, Li4SiO4, Li2SiO3, Li3PO4, Li2SO4, Li2TiO3, and Li4Ti5O 12 Examples include Li2Ti2O5, Li2ZrO3, LiNbO3, Li2MoO4, and Li2WO4. The coverage rate (area ratio) of the protective layer on the surface of the positive electrode active material may be, for example, 70% or more, 80% or more, or 90% or more. The thickness of the protective layer may be, for example, 0.1 nm or more, 1 nm or more, 100 nm or less, or 20 nm or less.

[0029] The electrolyte, conductive additive, and binder may be selected from the examples provided as possible components of the negative electrode active material layer 11. Each of the electrolyte, conductive additive, and binder may be used individually or in combination of two or more types.

[0030] 1.3.2 Positive electrode current collector The positive electrode current collector 32 can be any of the commonly used positive electrode current collectors for secondary batteries. The positive electrode current collector 32 may be in the form of foil, plate, mesh, perforated metal, or foam. The positive electrode current collector 32 may be composed of metal foil or metal mesh. Metal foil, in particular, offers superior handling. The positive electrode current collector 32 may consist of multiple foils. Examples of metals constituting the positive electrode current collector 32 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. In particular, the positive electrode current collector 32 may contain Al to ensure oxidation resistance. The positive electrode current collector 32 may have some kind of coating layer on its surface for purposes such as adjusting resistance. Furthermore, the positive electrode current collector 32 may be a metal foil or substrate on which the above metals are plated or vapor-deposited. Furthermore, if the positive electrode current collector 32 consists of multiple metal foils, there may be some layer between the multiple metal foils. The thickness of the positive electrode current collector 32 is not particularly limited. For example, it may be 0.1 μm or more, or 1 μm or more, or 1 mm or less, or 100 μm or less.

[0031] 1.4 Estimated amount of active material Conventionally, negative electrodes using Si particles as the negative electrode active material have attracted attention for their high energy density. However, when Si particles are used as the negative electrode active material, the expansion and contraction of the Si particles during charging and discharging are large, making them prone to cracking and other damage. Until now, adverse effects related to the expansion and contraction of Si particles have been suppressed by methods such as silicideization of Si and mixing with graphite, but in this case, the proportion of other elements increases, and in some cases, elements other than Si may account for more than 50% by mass, which can lead to a decrease in energy density.

[0032] On the other hand, Si particles with a clathrate structure exhibit less expansion and contraction during charging and discharging, making it easier to improve the durability of secondary batteries compared to ordinary Si particles. Furthermore, according to the inventors' new findings, when Si particles with a clathrate structure are used as the negative electrode active material, there is a correlation between the usable capacity of the negative electrode during charging (utilization rate of Si particles, i.e., the Li absorption rate of Si particles) and the durability of the secondary battery. In other words, as the utilization rate of Si particles with a clathrate structure decreases, the proportion of the non-expansion region increases, further significantly reducing the amount of expansion and contraction. It is also possible to suppress the collapse of the clathrate structure due to excessive expansion and contraction, and the clathrate structure is more easily maintained even after repeated charging and discharging. As a result, the durability of the secondary battery is further improved. Here, as far as the inventors have confirmed, the utilization rate of Si particles during charging correlates with the basis weight of the positive and negative electrode active materials in approximately a 1:1 ratio. That is, the higher the basis weight of the positive electrode active material, and the lower the basis weight of the negative electrode active material, the higher the utilization rate of the negative electrode active material.

[0033] In the secondary battery 100, it is important that the ratio C1 / C2 of the basis weight C1 of the Li-containing compound in the positive electrode 30 to the basis weight C2 of the Si particles in the negative electrode 10 is 8.33 or less. By having a ratio of C1 / C2 of 8.33 or less, the utilization rate of Si particles is sufficiently reduced as described above, and the expansion of Si particles during charging is suppressed. As a result, the durability of the secondary battery 100 can be increased, and the capacity of the secondary battery 100 does not easily decrease even after repeated charging and discharging. Furthermore, the lower limit of the ratio C1 / C2 should be set within a range that can secure the necessary capacity for the secondary battery 100. For example, it is preferable that the ratio C1 / C2 is 0.50 or more, 1.00 or more, 1.50 or more, 2.00 or more, 2.50 or more, 2.87 or more, 3.00 or more, or 3.40 or more.

[0034] The basis weight of Si particles in the negative electrode 10 and the basis weight of the Li-containing compound in the positive electrode 30 can be appropriately adjusted according to the desired battery performance, within the range where the above ratio C1 / C2 is satisfied. For example, the basis weight of Si particles in the negative electrode 10 is 0.1 mg / cm³. 2 More than 0.5mg / cm 2 More than 1.0mg / cm2 More than 1.5mg / cm 2 2.0 mg / cm³ or more 2 It may be greater than or equal to 10.0 mg / cm³. 2 Below, 8.5mg / cm 2 The following or 7.0 mg / cm³ 2 The following may also apply: The basis weight of the Li-containing compound in the positive electrode 30 is, for example, 0.5 mg / cm³. 2 More than 1.0mg / cm 2 More than 12.5mg / cm 2 It may be 15.0 mg / cm² or more, or 40.0 mg / cm² or more. 2 Below 30mg / cm 2 The following or 25.0 mg / cm³ 2 That's fine.

[0035] The basis weight of the active material in an electrode can be determined by various methods. For example, the basis weight of the active material can be determined by observing the cross-section of the electrode with a scanning electron microscope (SEM) and determining the proportion of active material contained in the active material layer through elemental analysis. Alternatively, the active material layer can be peeled off from a secondary battery, the mass of the active material contained in the layer can be measured, and the basis weight of the active material can be determined from this mass and the electrode area.

[0036] 1.5 Other Configurations The secondary battery 100 may have all of the above components housed inside an outer casing. Any known battery casing can be used. Furthermore, multiple secondary batteries 100 may be electrically connected and stacked as desired to form a battery pack. In this case, the battery pack may be housed inside a known battery case. The secondary battery 100 may also have other obvious components such as necessary terminals. Examples of shapes for the secondary battery 100 include coin-type, laminate-type, cylindrical, and prismatic types.

[0037] 1.6 Method for manufacturing secondary batteries The secondary battery 100 can be manufactured by applying known methods. For example, it can be manufactured as follows. However, the manufacturing method of the secondary battery 100 is not limited to the following method, and each layer may be formed by, for example, dry molding. (1) A slurry for the negative electrode layer is obtained by dispersing the negative electrode active material and other materials constituting the negative electrode active material layer in a solvent. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. Then, the slurry for the negative electrode layer is applied to the surface of the negative electrode current collector using a doctor blade or the like, and then dried to form a negative electrode active material layer on the surface of the negative electrode current collector, which serves as the negative electrode. (2) A slurry for the positive electrode layer is obtained by dispersing the positive electrode active material and other materials constituting the positive electrode active material layer in a solvent. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. The slurry for the positive electrode layer is applied to the surface of the positive electrode current collector using a doctor blade or the like, and then dried to form a positive electrode active material layer on the surface of the positive electrode current collector, which serves as the positive electrode. (3) An electrolyte layer (solid electrolyte layer or separator) is sandwiched between the negative electrode and the positive electrode to obtain a laminate having a negative electrode current collector, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector in this order. Other components such as terminals are attached to the laminate as needed. (4) The laminate is housed in a battery case, and in the case of an electrolyte battery, the battery case is filled with electrolyte, the laminate is immersed in the electrolyte, and the laminate is sealed inside the battery case to form a secondary battery. In the case of an electrolyte battery, the negative electrode active material layer, separator and positive electrode active material layer may be made to contain the electrolyte at the stage of (3) above.

[0038] 2. Secondary battery system The technology disclosed herein also has an aspect as a system for controlling the charging and discharging of a secondary battery. That is, the secondary battery system disclosed herein comprises the secondary battery 100 described above and a control unit (not shown) for controlling the charging and discharging of the secondary battery 100, characterized in that the control unit controls the charging voltage of the secondary battery 100 to 4.2V or less. By controlling the charging voltage of the secondary battery 100 to 4.2V or less, the utilization rate of Si particles as the negative electrode active material can be kept low, and the durability of the secondary battery 100 can be improved based on the mechanism described above.

[0039] The control unit only needs to be capable of controlling the charging and discharging of the secondary battery 100 as described above. For example, when charging the secondary battery by supplying electricity from a power source, the voltage of the secondary battery can be measured sequentially, and the supply of electricity from the power source can be continued or stopped so that the measured voltage does not exceed 4.2V, thereby continuing or stopping the charging. When the charging and discharging of the secondary battery 100 is controlled by the control unit, the lower limit of the charging voltage and the upper and lower limits of the discharging voltage of the secondary battery 100 are not particularly limited, and the lower limit of the charging voltage can be determined according to the desired battery performance. If the charging voltage is too low, sufficient performance may not be obtained from the secondary battery 100.

[0040] 3. Supplement As described above, according to the technology disclosed herein, by using Si particles having a clathrate structure as the negative electrode active material and controlling the utilization rate of said Si particles, the proportion of the non-expansion region of the Si particles increases during charging, the expansion and contraction of the Si particles during charging and discharging is suppressed, and the collapse of the clathrate structure due to excessive expansion and contraction is also suppressed. As a result, the clathrate structure is more easily maintained even after repeated charging and discharging. Consequently, the durability of the secondary battery is improved. It is believed that such effects are achieved regardless of the type of secondary battery (electrolyte battery, solid-state battery). [Examples]

[0041] The technology of this disclosure will be described in more detail below with reference to examples, but the technology of this disclosure is not limited to the following examples.

[0042] 1. Fabrication of silicon anode active material Crystalline silicon and clathrate silicon were prepared as silicon anode active materials.

[0043] 1.1 Fabrication of crystalline silicon Si particles (high-purity chemicals, 5 μm) were micronized using a planetary ball mill (Fritsch Classic Line) to obtain crystalline silicon powder. This crystalline silicon did not have a clathrate structure.

[0044] 1.2 Fabrication of Clathrate Silicon Si particles and Na particles were mixed in a 1:1 molar ratio and heated at 700°C to synthesize NaSi. Subsequently, desodiumization was performed by heating at 340°C. Further desodiumization was carried out by heating at 430°C, and then the mixture was finely milled using a planetary ball mill at 150 rpm for 3 hours to obtain a powder. The resulting powder had a clathrate structure (clathrate silicon).

[0045] 2. Preparation of the positive electrode In a PP container, NMP is used as the solvent, a 5 wt% butyl butyrate solution of PVDF-based binder is used, and LiNi is used as the positive electrode active material. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (average particle size 6 μm) and VGCF as a conductive additive were added and stirred for 10 minutes in an Awatori Rentaro (Sinky Co., Ltd. ARE-310) to obtain a positive electrode slurry. The positive electrode slurry was coated onto Al foil (Showa Denko Co., Ltd.) using an applicator and the blade method. The coated electrodes were dried on an 80°C hot plate for 60 minutes. The basis weight of the positive electrode active material was varied by adjusting the concentration of the positive electrode slurry and the amount of coating.

[0046] 3. Fabrication of the negative electrode In a PP container, NMP as a solvent, polyamic acid (U varnish A, manufactured by Ube Industries) as a binder (polyimide), silicon active material as the negative electrode active material, and VGCF and KB as conductive additives were added and stirred for 10 minutes using a foam mixer (ARE-310, manufactured by Thinky Co., Ltd.) to obtain a negative electrode slurry. Using an applicator, the slurry was coated onto Cu foil (manufactured by Furukawa Electric Co., Ltd.) using the blade method. The coated electrodes were dried on an 80°C hot plate for 60 minutes. The basis weight of the negative electrode active material was varied by adjusting the concentration of the negative electrode slurry and the amount of coating.

[0047] 4. Making a battery The fabricated positive electrode was punched out to a diameter of φ14 mm, while the negative electrode was punched out to a diameter of φ16 mm. After this, they were set in a roll press and pressed at 20 kN / cm. Subsequently, the negative electrode was fired in an Ar atmosphere at 350°C for 2 hours to induce the imidation reaction of the polyamic acid. Each electrode was moved to a glove box, and 1 ml of electrolyte (1.2 M LiPF6 solution; solvent FEC:EC:EMC:DMC = 1:2:4:3 vol%) was dropped onto the active material layer of the negative electrode. A separator (made of PP) was then stacked, another 1 ml of electrolyte was dropped, and the positive electrode was stacked. A coin cell was then fabricated using an automatic coin cell crimping machine (manufactured by Hosen Co., Ltd.).

[0048] 4.1 Comparative Example 1 Positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The estimated amount of O2 is 28.480 mg / cm³. 2 The basis weight of the negative electrode active material (crystalline silicon) at the negative electrode is 4.838 mg / cm³. 2 This was done by setting the ratio C1 / C2 of the basis weight of the positive electrode active material C1 at the positive electrode to the basis weight of the negative electrode active material C2 at the negative electrode to 5.89.

[0049] 4.2 Comparative Example 2 Positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The estimated amount of O2 is 17.978 mg / cm³. 2The basis weight of the negative electrode active material (crystalline silicon) at the negative electrode is 6.660 mg / cm³. 2 This was done by setting the ratio C1 / C2 of the basis weight of the positive electrode active material C1 at the positive electrode to the basis weight of the negative electrode active material C2 at the negative electrode to 2.70.

[0050] 4.3 Comparative Example 3 Positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The estimated amount of O2 is 20.114 mg / cm³. 2 The basis weight of the negative electrode active material (crystalline silicon) at the negative electrode is 2.050 mg / cm³. 2 This was done by setting the ratio C1 / C2 of the basis weight of the positive electrode active material C1 at the positive electrode to the basis weight of the negative electrode active material C2 at the negative electrode to 9.81.

[0051] 4.4 Example 1 Positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The estimated amount of O2 is 23.674 mg / cm³. 2 The basis amount of the negative electrode active material (clathrate silicon) at the negative electrode is 4.756 mg / cm³. 2 This was done by setting the ratio C1 / C2 of the basis weight of the positive electrode active material C1 at the positive electrode to the basis weight of the negative electrode active material C2 at the negative electrode to 4.98.

[0052] 4.5 Example 2 Positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The estimated amount of O2 is 19.224 mg / cm³. 2 The basis amount of the negative electrode active material (clathrate silicon) at the negative electrode is 5.658 mg / cm³. 2 This was done by setting the ratio C1 / C2 of the basis weight of the positive electrode active material C1 at the positive electrode to the basis weight of the negative electrode active material C2 at the negative electrode to 3.40.

[0053] 4.6 Example 3 Positive electrode active material (LiNi 1 / 3 Co1 / 3 Mn 1 / 3 The estimated amount of O2 is 21.182 mg / cm³. 2 The basis amount of the negative electrode active material (clathrate silicon) at the negative electrode is 2.542 mg / cm³. 2 This was done by setting the ratio C1 / C2 of the basis weight of the positive electrode active material C1 at the positive electrode to the basis weight of the negative electrode active material C2 at the negative electrode to 8.33.

[0054] 4.7 Comparative Example 4 Positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The estimated amount of O2 is 22.517 mg / cm³. 2 The base amount of negative electrode active material (clathrate silicon) at the negative electrode is 1.804 mg / cm³. 2 This was done by setting the ratio C1 / C2 of the basis weight of the positive electrode active material C1 at the positive electrode to the basis weight of the negative electrode active material C2 at the negative electrode to 12.48.

[0055] 5. Charge / Discharge Cycle Test The fabricated coin cells were charged with a constant current of 0.2mA to 4.2V, and then discharged with 0.2mA to 2.5V. The battery capacity at this point was taken as the initial capacity. A charge-discharge test was repeated 50 times, in which the cells were charged with a constant current of 2mA to 4.2V, and then discharged with a constant current of 2mA. Subsequently, the battery capacity was measured after charging with a constant current of 0.2mA to 4.2V and then discharged with 0.2mA to 2.5V. The durability performance after 50 cycles was confirmed by calculating the ratio to the initial capacity. The durability performance of Comparative Examples 2-4 and Examples 1-3 was evaluated relative to the durability performance of Comparative Example 1, which was set as the baseline (100%).

[0056] Furthermore, the negative electrode was removed after the initial charge and discharge, and measurements were performed using Raman spectroscopy (wavelength 532 nm). The obtained Raman spectrum was analyzed, and a value of 325 ± 10 cm was obtained. -1 Maximum peak intensity I 325 and 205±10cm -1 Maximum peak intensity I 205 Ratio I 325 / I 205 The ratio I was calculated.325 / I 205 If the value is within the range of 1.03 to 1.21, then the Si particles can be said to have a clathrate structure.

[0057] 6. Evaluation Results The evaluation results are shown in Table 1 below.

[0058] [Table 1]

[0059] The results shown in Table 1 reveal the following: First, a comparison between Comparative Examples 1-3 and Examples 1-3 shows that the durability of the secondary battery is higher when using clathrate silicon as the negative electrode active material than when using crystalline silicon. This is thought to be due to the fact that clathrate silicon expands and contracts less with charging and discharging the battery compared to crystalline silicon.

[0060] Furthermore, a comparison of Comparative Example 4 with Examples 1-3 reveals that even when clathrate silicon is used as the negative electrode active material, if the active material basis ratio C1 / C2 is too large (i.e., there is more positive electrode active material than negative electrode active material, and too much negative electrode active material is used), the durability of the secondary battery decreases. This is presumed to be due to the following mechanism: In a secondary battery, the higher the utilization rate of Si particles during charging, the greater the expansion of Si particles, and the greater the expansion, the more likely the Si particles are to crack or the more likely the clathrate structure is to collapse. In Comparative Example 4, it is thought that cracking of Si particles and collapse of the clathrate structure occurred during charging, resulting in a significant decrease in the negative electrode capacity.

[0061] 7. Consideration of Solid-State Batteries We also considered the case where the technology disclosed herein is applied to solid-state batteries (batteries containing a solid electrolyte).

[0062] 7.1 Fabrication of the negative electrode In a polypropylene container, the above-mentioned negative electrode active material (crystalline silicon or clathrate silicon), sulfide solid electrolyte (Li2S-P2S5 glass ceramic), conductive additive (VGCF), a butyl butyrate solution containing 5% by weight of a PVdF binder, and butyl butyrate were added and stirred for 30 seconds using an ultrasonic disperser (SMT UH-50). Next, the container was shaken for 30 minutes using a shaker (Shibata Scientific Co., Ltd., TTM-1). Using an applicator, the mixture was coated onto a negative electrode current collector (Cu foil, UACJ) by the blade method and dried on a hot plate at 100°C for 30 minutes. This yielded a negative electrode having a negative electrode current collector and a negative electrode active material layer.

[0063] 7.2 Preparation of the positive electrode A polypropylene container contains a positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 A butyl butyrate solution containing 5% by weight of O2 (average particle size 6 μm), a sulfide solid electrolyte (Li2S-P2S5 glass ceramic), a conductive additive (VGCF), and a PVdF binder, along with butyl butyrate, was added and stirred for 30 seconds using an ultrasonic disperser (SMT UH-50). Next, the container was shaken for 3 minutes using a shaker (Shibata Scientific Co., Ltd., TTM-1). Using an applicator, the solution was coated onto a positive electrode current collector (Al foil, Showa Denko) using the blade method and dried on a hot plate at 100°C for 30 minutes. This yielded a positive electrode having a positive electrode current collector and a positive electrode active material layer. The area of ​​the positive electrode was made smaller than the area of ​​the negative electrode.

[0064] 7.3 Fabrication of the Solid Electrolyte Layer A heptane solution containing a sulfide solid electrolyte (Li2S-P2S5 glass ceramic) and a butylene rubber binder in a ratio of 5% by weight, along with heptane, was added to a polypropylene container and stirred for 30 seconds using an ultrasonic disperser (SMT UH-50). Next, the container was shaken for 30 minutes using a shaker (Shibata Scientific Co., Ltd., TTM-1). Using an applicator, the mixture was coated onto a release sheet (Al foil) using the blade method and dried on a hot plate at 100°C for 30 minutes. This yielded a transfer member having a release sheet and a solid electrolyte layer.

[0065] 7.4 Making a Battery A solid electrolyte layer for bonding was placed on the positive electrode active material layer of the positive electrode, and the assembly was set in a roll press and pressed at 100 kN / cm and 165°C. This obtained the first laminate. Next, the negative electrode was set in the roll press and pressed at 60 kN / cm and 25°C. This obtained the pressed negative electrode. Then, the solid electrolyte layer for bonding and the transfer member were placed in order from the negative electrode active material layer side. At this time, the solid electrolyte layer for bonding and the solid electrolyte layer in the transfer member were positioned to face each other. The obtained laminate was set in a flat uniaxial press and pre-pressed for 10 seconds at 100 MPa and 25°C. Then, the release sheet was peeled off from the solid electrolyte layer. This obtained the second laminate. Next, the solid electrolyte layer for bonding in the first laminate and the solid electrolyte layer in the second laminate were positioned to face each other, and the assembly was set in a flat uniaxial press and pressed at 400 MPa and 135°C for 1 minute. This obtained a solid battery for evaluation.

[0066] 7.4.1 Comparative Example 5 Crystalline silicon was used as the negative electrode active material, and the ratio C1 / C2 of the basis weight of the positive electrode active material C1 to the basis weight of the negative electrode active material C2 was set to 5.50.

[0067] 7.4.2 Example 4 Clathrate silicon was used as the negative electrode active material, and the ratio C1 / C2 of the basis weight of the positive electrode active material C1 to the basis weight of the negative electrode active material C2 was set to 2.87.

[0068] 7.4.3 Example 5 Clathrate silicon was used as the negative electrode active material, and the ratio C1 / C2 of the basis weight of the positive electrode active material C1 to the basis weight of the negative electrode active material C2 was set to 3.71.

[0069] 7.5 Charge-discharge cycle test For each sulfide solid battery prepared as described above, the durability performance after 50 cycles was confirmed, similar to Examples 1-3 and Comparative Examples 1-4. The durability performance of Comparative Example 5 was used as the baseline (100%), and the durability performance of Examples 4 and 5 was evaluated relative to it. In addition, the negative electrode was removed after the initial charge and discharge, and measured by Raman spectroscopy (wavelength 532 nm). The obtained Raman spectrum was analyzed to obtain a value of 325 ± 10 cm⁻¹. -1 Maximum peak intensity I 325 and 205±10cm -1 Maximum peak intensity I 205 Ratio I 325 / I 205 The ratio I was calculated. 325 / I 205 If the value is within the range of 1.03 to 1.21, then the Si particles can be said to have a clathrate structure.

[0070] 7.6 Evaluation Results The evaluation results are shown in Table 2 below. As shown in Table 2 below, it can be seen that the technology of this disclosure produces the same effects as electrolyte batteries even in solid-state batteries.

[0071] [Table 2]

[0072] 8. Summary Based on the above results, a secondary battery having the following configuration (1) to (4) can be said to have excellent durability. (1) The negative electrode contains Si particles as the negative electrode active material. (2) The positive electrode contains a Li-containing compound as the positive electrode active material. (3) The Si particles have a clathrate structure. (4) The ratio C1 / C2 of the basis weight C1 of the Li-containing compound at the positive electrode to the basis weight C2 of the Si particles at the negative electrode shall be 8.33 or less.

[0073] In addition, although the above embodiments show examples using specific positive electrodes and electrolytes, there are no particular restrictions on the types of positive electrodes and electrolytes in the technology of this disclosure. Furthermore, although the above embodiments show configurations using specific current collectors, binders, and conductive additives in the negative electrode, there are no particular restrictions on the configuration of the negative electrode other than the negative electrode active material in the technology of this disclosure. Based on the above estimated mechanism, it is considered that the durability of a secondary battery is improved by using a specific negative electrode active material and adjusting the active material basis ratio C1 / C2 within a predetermined range, regardless of the type of battery (electrolyte battery, solid battery) or materials. [Explanation of Symbols]

[0074] 10 negative electrode 11 Negative electrode active material layer 12 Negative electrode current collector 20 Electrolyte layer 30 positive electrode 31 Positive electrode active material layer 32 Positive electrode current collector 100 Secondary battery

Claims

1. A secondary battery having a negative electrode, an electrolyte layer, and a positive electrode, The negative electrode has Si particles as a negative electrode active material, The positive electrode has a Li-containing compound as a positive electrode active material, The aforementioned Si particles were measured by Raman spectroscopy at 325 ± 10 cm². －１ Maximum peak intensity I ３２５ And, 205 ± 10 cm －１ Maximum peak intensity I ２０５ Ratio I ３２５ / I ２０５ The value is within the range of 1.03 to 1.

21. The basis weight C of the Li-containing compound in the positive electrode １ and the basis weight C of the Si particles in the negative electrode ２ the ratio C １ / C ２ is 8.33 or less, Secondary battery.

2. Said ratio C １ / C ２ However, it is 2.87 or higher. The secondary battery according to claim 1.

3. The Li-containing compound comprises, as constituent elements, at least Li, at least one of Ni, Co, and Mn, and O. The secondary battery according to claim 1 or 2.

4. The electrolyte layer includes a solid electrolyte. A secondary battery according to any one of claims 1 to 3.

5. A secondary battery according to any one of claims 1 to 4, A control unit for controlling the charging and discharging of the secondary battery, Equipped with, The control unit controls the charging voltage of the secondary battery to 4.2V or less. Secondary battery system.

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