Composite active material particle

Abstract

To provide composite active material particles that can produce a low resistance battery.SOLUTION: A composite active material particle that combines: Si particles having a porous structure; and a Li-ion conductor with a Young's modulus of 5 GPa or less and an ionic conductivity of 1×10-5S / cm or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to composite active material particles. [Background technology]

[0002] Conventionally, all-solid-state batteries have been known as lithium-ion batteries. Disclosed is a negative electrode for a lithium ion battery, which contains a negative electrode composite active material obtained by coating a negative electrode active material containing Si with a sulfide solid electrolyte, and plastic crystals containing at least one cation selected from the group consisting of pyrrolidinium, tetraalkylammonium, and tetraalkylphosphonium, and a carborane-based anion, wherein the coverage of the surface of the negative electrode active material with the sulfide solid electrolyte is 80% or more, and the volume ratio of the plastic crystals to the total of the sulfide solid electrolyte and the plastic crystals is 30 vol% to 75 vol%. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-131979 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, it has been considered to suppress the expansion of the electrode by forming voids by granulating the active material used in the electrode body of a solid-state battery. However, a binder is used to form the granules, which reduces the ionic conductivity inside the granules, resulting in a decrease in input and output when used as a battery. Therefore, composite active material particles that can provide a low-resistance battery have been desired.

[0005] An object of one embodiment of the present disclosure is to provide a composite active material particle that can provide a battery with low resistance. [Means for solving the problem]

[0006] Means for solving the above problems include the following embodiments. <1> Si particles having a porous structure; Young's modulus is 5 GPa or less, and ionic conductivity is 1×10 -5 A Li-ion conductor having a conductivity of 1.0 S / cm or more; A composite active material particle in which the above is combined. Effect of the Invention

[0007] An object of one embodiment of the present disclosure is to provide composite active material particles that can provide a battery with low resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] In the present disclosure, a numerical range indicated using "~" means a range that includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in the present disclosure. In the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples. In the present disclosure, combinations of two or more preferred embodiments are more preferred embodiments. In the present disclosure, when there are multiple substances corresponding to each component, the amount of each component means the total amount of the multiple substances, unless otherwise specified.

[0009] [Composite active material particles] The composite active material particles according to the embodiment of the present disclosure are made of Si particles having a porous structure and a Young's modulus of 5 GPa or less and an ionic conductivity of 1×10 -5 The composite active material particles are formed by combining the above-mentioned Li ion conductor.

[0010] According to the composite active material particles according to the embodiment of the present disclosure, a battery with low resistance can be obtained.

[0011] Conventionally, it has been considered to suppress the expansion of the electrode by forming voids by granulating the active material used in the electrode body of a solid-state battery. However, a polymer material with low ionic conductivity is generally used as a binder when producing the granules, and the ionic conductivity inside the granules is low, resulting in a decrease in input and output when the granules are used as a battery. Therefore, composite active material particles that can obtain a battery with low resistance have been desired.

[0012] In contrast, the composite active material particles according to the embodiment of the present disclosure use a Li ion conductor as a binder, and the Li ion conductor has a Young's modulus of 5 GPa or less and an ionic conductivity of 1×10 -5 That's it. By using a Li-ion conductor with high ionic conductivity, with a Young's modulus (elastic modulus) of 5 GPa or less, the ionic conductivity of the composite active material particles can be improved. In addition, by combining a Li-ion conductor with a high elastic modulus with Si particles, the Li-ion conductor follows the expansion and contraction of the Si particles, and low resistance can be maintained when the battery is formed. In addition, by using Si particles with a porous structure as the active material, the Li-ion conductor penetrates between the Si particles, and a granule can be formed by a physical anchor effect. This allows a battery with low resistance to be obtained in the embodiment of the present disclosure.

[0013] (Porous Si) The composite active material particles contain, as an active material, Si particles having a porous structure, where the porous structure refers to a structure in which the surfaces of the Si particles have numerous fine pores. Examples of the Si particles having a porous structure include single crystal silicon particles that have been made porous.

[0014] (Li-ion conductor) The composite active material particles have a Young's modulus of 5 GPa or less and an ionic conductivity of 1×10 -5 The above Li-ion conductors are included.

[0015] Young's Modulus The Young's modulus of the Li ion conductor is set to 5 GPa or less from the viewpoint of realizing low resistance when the Li ion conductor is used as a battery by following the expansion and contraction of the Si particles. From the viewpoint of low resistance in the battery, the Young's modulus is preferably 4 GPa or less, and more preferably 3 GPa or less. On the other hand, although not particularly limited, the lower limit of the Young's modulus of the Li-ion conductor is preferably 0.1 GPa or more, and more preferably 0.5 GPa or more. The Young's modulus of the Li-ion conductor is measured by nanoindentation.

[0016] Ionic conductivity The ionic conductivity of the Li-ion conductor is set to 1×10 in order to realize low resistance in a battery by improving the ionic conductivity of the composite active material particles. -5 The ionic conductivity of the Li-ion conductor is further increased to 2×10 -5 S / cm or more is preferable, and 3×10 -5 More preferably, it is S / cm or more. On the other hand, there is no particular limitation, and the higher the better, but the upper limit of the ionic conductivity of the Li ion conductor may be set to 1 S / cm or less.

[0017] The ionic conductivity of the Li-ion conductor is measured by the following method. Approximately 100 mg of Li-ion conductor is charged to 6 ton / cm. 2 The mixture is pressed at a pressure of 1000 .mu.m to obtain a pellet (diameter: 11.28 .mu.m) having a thickness of about 500 .mu.m. The thickness is measured using a micrometer. The ionic conductivity is calculated from the AC impedance measurement results. The measurement is performed using a Solartron 1260 at a frequency range of 10 MHz to 1 kHz, an applied voltage of ±10 mV, and a temperature of 25.degree. C.

[0018] Li-ion conductor material From the viewpoint of ion conductivity, it is preferable to use a lithium salt of a boron cluster anion as the Li ion conductor.

[0019] Boron cluster anions include boranes having 6 to 12 boron atoms with a total charge of -2, carboranes having one carbon and 5 to 11 boron atoms in a cluster structure with a total charge of -1, and carboranes having two carbon atoms and 4 to 10 boron atoms in a cluster structure with a total charge of -1 or -2. The boron cluster anion may have a substituent, and examples of the substituent include a halogen atom, an organic group, etc. Examples of the organic group include an alkyl group, an alkoxy group, etc. The boron cluster anion may be an anion represented by any one of the following formulas (1) to (5). (1) [B y H (y-z-i) R z X i ] -2 , (2) [CB (y-1) H (y-z-i) R z X i ] - (3) [C2B (y-2) H (y-t-j-1) R t X j ] - (4) [C2B (y-3) H (y-t-j) R t X j ] - (5) [C2B (y-3) H (y-t-j-1) R t X j ] -2 In formulas (1) to (5), y is an integer ranging from 6 to 12, (z+i) is an integer ranging from 0 to y, (t+j) is an integer ranging from 0 to (y-1), X is F, Cl, Br, I or a combination thereof, and R is an organic group or hydrogen. Examples of the organic group include an alkyl group and an alkoxy group.

[0020] A specific example of a lithium salt of a boron cluster anion is LiCB9H. 10 and LiCB 11 H12 A mixture of these two is also possible, i.e. Li(CB9H 10 ) x (CB 11 H 12 ) 1-x (x=more than 0 and less than 1). The value of x is preferably 0.6 or more and 0.8 or less, and more preferably 0.7.

[0021] ·Compounding The composite active material particles can be produced by mixing the above-mentioned porous Si particles with the above-mentioned Li ion conductor. The amount of the Li ion conductor added to the Si particles in the composite active material particles is preferably 10% by volume or more and 30% by volume or less, more preferably 15% by volume or more and 25% by volume or less.

[0022] [electrode] The composite active material particles according to the embodiment of the present disclosure can be used for an electrode (particularly a negative electrode) in a battery (particularly a lithium ion battery). This electrode may contain, in addition to the composite active material particles according to the embodiment of the present disclosure, for example, a conductive material, a solid electrolyte (SE), and the like. The battery (for example, a lithium ion battery) includes a positive electrode layer, a solid electrolyte layer, and a negative electrode layer. This battery may be an all-solid-state battery.

[0023] ·Porosity The electrode using the composite active material particles according to the embodiment of the present disclosure can increase the porosity. The reason for this is presumed to be as follows. When pressure is applied by a roll press or the like in the process of forming a general electrode, active materials such as Si are difficult to plastically deform, and the solid electrolyte undergoes plastic deformation to form an interface with the active material, filling the gaps in the electrode and improving the filling property. On the other hand, in the embodiment of the present disclosure, a secondary particle body is formed by compounding Si particles (active material) and a Li ion conductor, and voids are formed in the gaps between the active materials that are difficult to plastically deform. At this time, even if an active material is compounded with an ion conductor having a high Young's modulus (i.e., hard), the hard ion conductor is difficult to deform, so adhesion due to the anchor effect cannot be expected and the state of the secondary particle body cannot be maintained. It is believed that by using an ion conductor having a low Young's modulus (i.e., soft), the secondary particle body state due to the anchor effect and the voids can be maintained at the same time, and as a result, the voids in the electrode are increased. From the viewpoint of suppressing expansion of the electrode, the porosity of the electrode is preferably 10% or more, and more preferably 15% or more. On the other hand, although not particularly limited, the upper limit of the porosity of the electrode is preferably 40% or less, and more preferably 30% or less.

[0024] The porosity of the electrode is measured by the following method. First, a current of 0.5 mA / cm2 is applied to a battery (e.g., a lithium ion battery) at 60°C. 2 , 4.05Vcut, 10min rest, 0.5mA / cm 2 The charge-discharge cycle is repeated 20 times, with one cycle consisting of a 10-minute break and discharge at a 2.5V cut. After the charge-discharge cycle, the electrode is cut from the battery and its cross-sectional image is taken using a scanning electron microscope (SEM). From the cross-sectional image, the ratio of the void area to the cross-sectional area of ​​the cross-sectional image is measured using image processing software to determine the porosity.

[0025] The electrode can be manufactured by adding the composite active material particles according to an embodiment of the present disclosure, and other components as necessary, to a solvent to prepare a negative electrode mixture, and molding the mixture. EXAMPLES

[0026] The present disclosure will be described in more detail below with reference to examples, but the invention of the present disclosure is not limited to these examples.

[0027] <Comparative Example 1> 1. Preparation of the Positive Electrode Layer In an organic solvent, binder, conductive additive, solid electrolyte (SE), and LiNi 0.8 Co 0.15 Mn 0.05 O2 was added. After the addition, the mixture was kneaded using an ultrasonic homogenizer to obtain a positive electrode composite slurry. The obtained positive electrode composite slurry was applied to an Al foil to prepare a positive electrode layer.

[0028] 2. Preparation of the negative electrode layer A binder (poly(vinylidene fluoride-co-hexafluoropropylene: PVdF-HFP), a conductive additive, a solid electrolyte (SE), and Si having a porous structure (hereinafter referred to as "porous Si") as an active material were added to the organic solvent. After addition, the mixture was kneaded using an ultrasonic homogenizer to obtain a negative electrode composite slurry. The obtained negative electrode composite slurry was applied to a Cu foil to prepare a negative electrode layer. The Young's modulus (GPa) and ionic conductivity (S / cm) of the binder were the values ​​shown in Table 1. The amount of binder (binding agent) added to the active material (porous Si) was 20 volume % as shown in Table 1.

[0029] 3. Preparation of Solid Electrolyte Layer A binder and a solid electrolyte (SE) were added to the organic solvent. After the addition, the mixture was kneaded using an ultrasonic homogenizer to obtain a solid electrolyte slurry. The obtained solid electrolyte slurry was applied to an Al foil to prepare an SE layer.

[0030] 4. Battery Preparation Each layer prepared in 1. to 3. was molded into a rectangular shape. The composite surfaces of the positive electrode layer and the SE layer were aligned, roll pressed at 165°C and a pressure of 50 kN / cm, and the Al foil was peeled off to transfer the SE layer to the positive electrode layer. The composite surfaces of the negative electrode layer and the SE layer were aligned, roll pressed at 25°C and a pressure of 50 kN / cm, and the Al foil was peeled off to transfer the negative electrode layer to the SE layer. The negative electrode with the SE layer transferred was punched out with a punching machine of φ13.00 mm, and the positive electrode layer was punched out with a punching machine of φ11.28 mm. The SE layer was further transferred to the negative electrode with the SE layer transferred using a uniaxial press. Next, the punched negative electrode layer and the positive electrode layer were made to face each other to form a battery. Finally, current extraction tabs were attached to the positive electrode and the negative electrode, and they were sealed in an aluminum laminate using a vacuum lami sealer to produce an all-solid-state battery.

[0031] <Example 1> An all-solid-state battery was produced in the same manner as in Comparative Example 1, except that "2. Production of negative electrode layer" was changed as follows.

[0032] 2. Preparation of the negative electrode layer First, porous Si as the active material and a binder (Li(CB9H 10 ) 0.7 (CB 11 H 12 ) 0.3 The above was mixed in a mortar to prepare a Si composite. Next, other binders, conductive assistants, solid electrolyte (SE), and the Si composite were added to the organic solvent. After the addition, the mixture was kneaded using an ultrasonic homogenizer to obtain a negative electrode composite slurry. The obtained negative electrode composite slurry was applied to a Cu foil to prepare a negative electrode layer. The Young's modulus (GPa) and ionic conductivity (S / cm) of the binder were the values ​​shown in Table 1. The amount of binder (binding agent) added to the active material (porous Si) was 20 volume % as shown in Table 1.

[0033] <Battery performance evaluation> ·Porosity In the obtained all-solid-state battery, the porosity (%) in the cross section of the negative electrode was measured by the above-mentioned method. The results are shown in Table 1.

[0034] ·Initial resistance The voltage of the obtained all-solid-state battery was adjusted to 3.7 V, and the initial resistance (Ω) was calculated from the voltage drop after 5 seconds when the battery was discharged at a rate of 5 C. The results are shown in Table 1.

[0035] [Table 1]

[0036] As shown in Table 1, the battery of the embodiment had a lower resistance than the battery of the comparative example.

Claims

[Claim 1] Si particles having a porous structure; Young's modulus is 5 GPa or less, and ionic conductivity is 1×10 －５ S / cm or more of Li ion conductor; A composite active material particle in which the above is combined.

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