Living material secondary particles, negative electrode composite material, method for producing the same, and secondary battery

Abstract

To provide a new technique for reducing the resistance of a secondary battery and improving its cycle characteristics.SOLUTION: In a negative electrode of a secondary battery, a specific active material secondary particle is used. The active material secondary particle includes a plurality of negative electrode active material particles and a perfluoropolyether.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present application discloses active material secondary particles, a negative electrode composite material, methods for manufacturing these, and a secondary battery.

Background Art

[0002] Patent Document 1 discloses using predetermined porous silicon particles as a negative electrode active material in order to suppress an increase in the restraint pressure of a battery during charging. Patent Document 2 discloses causing a compound containing a perfluoropolyether group to be present on the surface of an electrode in order to enhance the storage stability of the electrode.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The negative electrode of a secondary battery can be formed by pressing a negative electrode composite material containing a negative electrode active material. Here, in order to increase the filling rate of the negative electrode and reduce the resistance of the negative electrode, if the negative electrode composite material is pressed at high pressure, there is a risk that the negative electrode active material will be crushed. On the other hand, in order to avoid crushing of the negative electrode active material or the like, if the negative electrode composite material is pressed at low pressure, the filling rate of the negative electrode decreases and the resistance of the negative electrode tends to increase.

[0005] Moreover, during charging or discharging of a secondary battery, the volume of the negative electrode active material changes as the negative electrode active material occludes or releases carrier ions. Along with such a volume change of the negative electrode active material, voids and cracks may occur in the negative electrode of the secondary battery, and the cycle characteristics of the secondary battery may deteriorate.

[0006] As described above, there is room for improvement in the conventional secondary battery in terms of achieving both reduction of resistance and improvement of cycle characteristics.

Means for Solving the Problems

[0007] This application discloses the following multiple aspects as means for solving the above problems. <Aspect 1> Active material secondary particles containing a plurality of negative electrode active material particles and perfluoropolyether. Active material secondary particles. <Aspect 2> The negative electrode active material particles contain Si, Active material secondary particles of Aspect 1. <Aspect 3> The volume ratio of the perfluoropolyether in the total of the negative electrode active material particles and the perfluoropolyether is 2% by volume or more and 30% by volume or less, Active material secondary particles of Aspect 1 or 2. <Aspect 4> The viscosity of the perfluoropolyether at 25 °C is 5 mPa·s or more and 3000 mPa·s or less, Active material secondary particles of any one of Aspects 1 to 3. <Aspect 5> The average particle diameter of the negative electrode active material particles is 0.1 μm or more and 5.0 μm or less, The average particle diameter of the active material secondary particles is 0.5 μm or more and 20.0 μm or less, Active material secondary particles of any one of Aspects 1 to 4. <Aspect 6> At least containing active material secondary particles of any one of Aspects 1 to 5 and a solid electrolyte, Negative electrode composite material. <Aspect 7> Mixing a plurality of negative electrode active material particles and perfluoropolyether, and bonding the plurality of negative electrode active material particles to each other through the perfluoropolyether, A method for manufacturing active material secondary particles. <Aspect 8> Mixing active material secondary particles of any one of Aspects 1 to 5 and a solid electrolyte, A method for manufacturing a negative electrode composite material, comprising: <Aspect 9> A secondary battery having a negative electrode, an electrolyte layer, and a positive electrode, wherein the negative electrode contains active material secondary particles according to any one of Aspects 1 to 5. Secondary battery.

Advantages of the Invention

[0008] When a secondary battery is configured using the active material secondary particles of the present disclosure, the secondary battery is likely to have low resistance and excellent cycle characteristics.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments of the technology of the present disclosure will be described, but the technology of the present disclosure is not limited to the following embodiments.

[0011] 1. Active Material Secondary Particles As shown in FIG. 1, an active material secondary particle 1 according to an embodiment includes a plurality of negative electrode active material particles 1a and a perfluoropolyether 1b. In the active material secondary particle 1, for example, as shown in FIG. 1, the plurality of negative electrode active material particles 1a are connected to each other via the perfluoropolyether 1b.

[0012] During charging or discharging of a secondary battery, the volume of the negative electrode active material changes as the negative electrode active material occludes or releases carrier ions. Excessive volume change of the negative electrode active material causes voids and cracks in the negative electrode, which may have an adverse effect on the cycle characteristics and the like of the secondary battery. On the other hand, as described above, the active material secondary particle 1 of the present disclosure includes a plurality of negative electrode active material particles 1a and perfluoropolyether 1b, and as shown in FIG. 1, the plurality of negative electrode active material particles 1a can be connected via the perfluoropolyether 1b. In the active material secondary particle 1, voids may exist between the plurality of negative electrode active material particles 1a, or the voids may be filled with the perfluoropolyether 1b. When voids or perfluoropolyether 1b exist between the negative electrode active material particles 1a, even if the negative electrode active material particles 1a occlude carrier ions and expand, the expansion can be absorbed by the voids or perfluoropolyether 1b, and the expansion of the entire secondary particle can be alleviated. That is, the volume change of the entire secondary particle is likely to be small. Further, since the active material secondary particle 1 includes the perfluoropolyether 1b together with the negative electrode active material particles 1a, when the volume of the negative electrode active material particles 1a changes, the arrangement of the negative electrode active material particles 1a in the active material secondary particle 1 easily changes smoothly via the perfluoropolyether 1b. From this point as well, the volume change of the entire active material secondary particle 1 is likely to be small. In addition, since the arrangement of the negative electrode active material particles 1a in the active material secondary particle 1 changes smoothly, local stress concentration on the negative electrode active material particles 1a is less likely to occur, and cracking and crushing of the negative electrode active material particles 1a are easily suppressed. For example, even when pressure is applied to the active material secondary particle 1 by press molding or the like, the arrangement of the negative electrode active material particles 1a in the active material secondary particle 1 changes smoothly, and cracking and crushing of the negative electrode active material particles 1a can be suppressed. Similarly, stress concentration due to expansion and contraction of the negative electrode active material particles 1a is also suppressed, and from this point as well, cracking and crushing of the negative electrode active material particles 1a can be suppressed.Furthermore, by constructing a secondary battery using the active material secondary particles 1, even after the construction of the secondary battery, the perfluoropolyether 1b is arranged in the vicinity of the negative electrode active material particles 1a, and it is considered that it is unlikely that ion conduction (for example, ion conduction between solid electrolytes) and electron conduction in the negative electrode of the secondary battery are inhibited by the perfluoropolyether. By constructing a secondary battery with such active material secondary particles 1, the cycle characteristics of the secondary battery are likely to be improved and the resistance is likely to be reduced.

[0013] 1.1 Negative electrode active material particles The negative electrode active material particles 1a are particles made of a material known as a negative electrode active material of a secondary battery. As the negative electrode active material, various materials having a potential (charge-discharge potential) for occluding and releasing a predetermined carrier ion (for example, lithium ion) that is lower than that of the positive electrode active material described later can be adopted.

[0014] 1.1.1 Types of negative electrode active materials The negative electrode active material constituting the negative electrode active material particles 1a includes at least one selected from silicon-based active materials such as Si, Si alloys, and silicon oxides; 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. In particular, when the negative electrode active material is one or both of a silicon-based active material and a carbon-based active material, the performance of the secondary battery is likely to be enhanced. The negative electrode active material may be used alone as a single type, or two or more types may be combined and used. As described above, the technology of the present disclosure can easily suppress the volume change of the entire active material secondary particles 1 even when the volume change of the negative electrode active material particles 1a themselves during charge and discharge is large. In this regard, the technology of the present disclosure is also applicable when the negative electrode active material particles 1a contain Si (for example, the silicon-based active material described above). That is, although the negative electrode active material particles 1a containing Si have a large volume change accompanying the occlusion and release of carrier ions, as described above, the volume change of the entire secondary particles is suppressed by forming the negative electrode active material particles 1a into secondary particles together with the perfluoropolyether 1b. When the negative electrode active material particles 1a contain Si, their chemical composition is not particularly limited. The proportion of the Si element in all the elements contained in the negative electrode active material particles 1a may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more. In addition to the Si element, the negative electrode active material particles 1a may contain other elements such as alkali metal elements such as Li and Na elements. Examples of the other elements include at least one element selected from alkali metal elements such as Li and Na elements, Sn element, Fe element, Co element, Ni element, Ti element, Cr element, B element, and P element. Further, the negative electrode active material particles 1a may contain impurities such as oxides. The negative electrode active material particles 1a may be amorphous or crystalline. The crystal phase contained in the negative electrode active material particles 1a is not particularly limited.

[0015] 1.1.2 Particle size The negative electrode active material particles 1a may be primary particles or secondary particles. That is, the active material secondary particles 1 may contain a plurality of negative electrode active material particles 1a that are primary particles, may contain a plurality of negative electrode active material particles 1a that are secondary particles, or may contain a combination of negative electrode active material particles 1a that are primary particles and negative electrode active material particles 1a that are secondary particles. The size of the negative electrode active material particles 1a is not particularly limited. The average particle diameter of the negative electrode active material particles 1a may be, for example, 10 nm or more, 30 nm or more, 50 nm or more, 0.1 μm or more, or 0.2 μm or more, and may be 20.0 μm or less, 15.0 μm or less, 10.0 μm or less, 5.0 μm or less, 3.0 μm or less, 2.0 μm or less, or 1.0 μm or less. In particular, when the average particle diameter of the negative electrode active material particles 1a is 0.1 μm or more and 5.0 μm or less, and the average particle diameter of the active material secondary particles 1 is 0.5 μm or more and 20.0 μm or less, a higher effect is more easily obtained. The average particle diameter of the negative electrode active material particles 1a can be determined by observation with an electron microscope such as SEM. For example, it is determined as the average value of the maximum Feret diameters of each of a plurality of particles. The number of samples is preferably large, for example, 20 or more, may be 50 or more, or may be 100 or more. The average particle diameter of the negative electrode active material particles 1a can be appropriately adjusted, for example, by appropriately changing its manufacturing conditions or performing a classification process.

[0016] 1.1.3 Void The negative electrode active material particles 1a may have voids or may be porous. When the negative electrode active material particles 1a have voids, the expansion of the entire negative electrode active material particles 1a during charging can be alleviated by the voids. There is no particular limitation on the form of the voids in the negative electrode active material particles 1a. The negative electrode active material particles 1a may be particles containing nanoporous silicon. Nanoporous silicon refers to silicon having a plurality of pores with pore diameters on the order of nanometers (less than 1000 nm, preferably 100 nm or less). The negative electrode active material particles 1a may be porous silicon particles containing pores with a diameter of 55 nm or less. The pores with a diameter of 55 nm or less are difficult to be crushed by pressing. That is, the porous silicon particles containing pores with a diameter of 55 nm or less are likely to maintain a porous state even after pressing. For example, per 1 g of the porous silicon particles, the pores with a diameter of 55 nm or less may be contained in an amount of 0.21 cc or more, 0.22 cc / g or more, or 0.23 cc / g or more, and may be contained in an amount of 0.30 cc / g or less, 0.28 cc / g or less, or 0.26 cc / g or less. The amount of the pores with a diameter of 55 nm or less contained in the porous silicon particles can be determined, for example, from the pore size distribution by the nitrogen gas adsorption method or the DFT method.

[0017] When the negative electrode active material particles 1a are porous, their porosity is not particularly limited. The porosity of the negative electrode active material particles 1a may be, for example, 1% or more, 5% or more, 10% or more, or 20% or more, and may be 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, or 30% or less. The porosity of the negative electrode active material particles 1a can be determined, for example, by observation using a scanning electron microscope (SEM). It is preferable that the number of samples is large, for example, 100 or more. The porosity can be the average value obtained from these samples.

[0018] 1.1.4 Number of Particles The number of the negative electrode active material particles 1a contained in one active material secondary particle 1 is not particularly limited. The number may be 2 or more, 5 or more, 10 or more, or 50 or more, and may be 1000 or less, 500 or less, or 100 or less.

[0019] 1.2 Perfluoropolyether (PFPE) As described above, in the active material secondary particles 1 of the present disclosure, by including the perfluoropolyether 1b together with the negative electrode active material particles 1a, the volume change of the entire active material secondary particles 1 during charge and discharge is likely to be suppressed, and also, cracking and crushing of the negative electrode active material particles 1a are likely to be suppressed. Further, since the perfluoropolyether 1b has an ether bond, it is considered to have a high affinity for the surfaces of various battery materials, and for example, it is considered to be likely to appropriately stay between the negative electrode active material particles 1a. Thereby, for example, excellent lubricity can be imparted between the negative electrode active material particles 1a.

[0020] 1.2.1 Chemical Structure The perfluoropolyether 1b has a perfluoropolyether chain, and any one can be used as long as it can impart lubricity between the negative electrode active material particles 1a. For example, the perfluoropolyether 1b may be represented by the following formula (1).

[0021] E1-Rf1-R F -O-Rf2-E2 (1) [In formula (1), Rf1 and Rf2 are each independently a C1-16 divalent alkylene group which may be substituted by one or more fluorine atoms, E1 and E2 are each independently a monovalent group selected from the group consisting of a fluorine group, a hydrogen group, a hydroxyl group, an aldehyde group, a carboxylic acid group, a C1-10 alkyl ester group, an amide group which may have one or more substituents, and an amino group which may have one or more substituents, R F is a divalent fluoropolyether group.]

[0022] In the above formula (1), Rf1 and Rf2 are each independently a C1-16 divalent alkylene group which may be substituted by one or more fluorine atoms.

[0023] In one embodiment, the "C1-16 divalent alkylene group" in the C1-16 divalent alkylene group which may be substituted by one or more fluorine atoms may be linear or branched, preferably a linear or branched C1-6 alkylalkylene group, particularly a C1-3 alkylene group, and more preferably a linear C1-6 alkylene group, particularly a C1-3 alkylene group.

[0024] In one embodiment, the "C1-16 divalent alkylene" in the C1-16 divalent alkylene group which may be substituted by one or more fluorine atoms may be linear or branched, preferably a linear or branched C1-6 fluoroalkylene group, particularly a C1-3 fluoroalkylene group, specifically, -CF2CH2- and -CF2CF2CH2- may be used, and more preferably a linear C1-6 perfluoroalkylene group, particularly a C1-3 perfluoroalkylene group, specifically, a group selected from the group consisting of -CF2-, -CF2CF2-, and -CF2CF2CF2- may be used.

[0025] In the above formula (1), E1 and E2 are each independently a monovalent group selected from the group consisting of a fluorine group, a hydrogen group, a hydroxyl group, an aldehyde group, a carboxylic acid group, a C1-10 alkyl ester group, an amide group which may have one or more substituents, and an amino group which may have one or more substituents.

[0026] Perfluoropolyether 1b has low reactivity with respect to the sulfide solid electrolyte described below. Therefore, even when perfluoropolyether 1b and the sulfide solid electrolyte are in contact, a decrease in ionic conductivity due to alteration or deterioration of the sulfide solid electrolyte is unlikely to occur. In particular, when perfluoropolyether 1b has a non-polar group as a terminal group, the reaction between perfluoropolyether 1b and the sulfide solid electrolyte is further suppressed, and a higher effect can be expected. In this regard, each of E1 and E2 is preferably a fluorine group, independently. In one embodiment, each of E1-Rf1 and E2-Rf2 may independently be a group selected from the group consisting of -CF3, -CF2CF3, and -CF2CF2CF3.

[0027] In the above formula (1), R F is, in each occurrence, independently a divalent fluoropolyether group.

[0028] R F is preferably of formula (2): -(OC6F 12 ) a -(OC5F 10 ) b -(OC4F8) c -(OC3R Fa ) d -(OC2F4) e -(OCF2) f - (2) [In formula (2): R Fa is, in each occurrence, independently a hydrogen atom, a fluorine atom, or a chlorine atom, a, b, c, d, e, and f are each independently an integer from 0 to 200, the sum of a, b, c, d, e, and f is 1 or more, the order of existence of each repeating unit enclosed in parentheses with a, b, c, d, e, or f attached is arbitrary in the formula, provided that when all R Fa are hydrogen atoms or chlorine atoms, at least one of a, b, c, e, and f is 1 or more.] is a group represented by.

[0029] R Fa is preferably a hydrogen atom or a fluorine atom, more preferably a fluorine atom.

[0030] a, b, c, d, e and f may preferably each independently be an integer from 0 to 100.

[0031] The sum of a, b, c, d, e and f is preferably 5 or more, more preferably 10 or more, and may be, for example, 15 or more or 20 or more. The sum of a, b, c, d, e and f is preferably 200 or less, more preferably 100 or less, still more preferably 60 or less, and may be, for example, 50 or less or 30 or less.

[0032] These repeating units may be linear or branched. For example, -(OC6F 12 )- may be any of -(OCF2CF2CF2CF2CF2CF2)-, -(OCF(CF3)CF2CF2CF2CF2)-, -(OCF2CF(CF3)CF2CF2CF2)-, -(OCF2CF2CF(CF3)CF2CF2)-, -(OCF2CF2CF2CF(CF3)CF2)-, and -(OCF2CF2CF2CF2CF(CF3))-. -(OC5F 10 )- may be any of -(OCF2CF2CF2CF2CF2)-, -(OCF(CF3)CF2CF2CF2)-, -(OCF2CF(CF3)CF2CF2)-, -(OCF2CF2CF(CF3)CF2)-, and -(OCF2CF2CF2CF(CF3))-. -(OC4F8)- may be any of -(OCF2CF2CF2CF2)-, -(OCF(CF3)CF2CF2)-, -(OCF2CF(CF3)CF2)-, -(OCF2CF2CF(CF3))-, -(OC(CF3)2CF2)-, -(OCF2C(CF3)2)-, -(OCF(CF3)CF(CF3))-, -(OCF(C2F5)CF2)-, and -(OCF2CF(C2F5))-. -(OC3F6)- (i.e., in the above formula (2), when R Fa is a fluorine atom) may be any of -(OCF2CF2CF2)-, -(OCF(CF3)CF2)-, and -(OCF2CF(CF3))-. -(OC2F4)- may be any of -(OCF2CF2)- and -(OCF(CF3))-.

[0033] In one embodiment, R F may, in each occurrence, be independently a group represented by any of the following formulas (2-1) to (2-5).

[0034] -(OC3F6) d -(OC2F4) e - (2-1) [In formula (2-1), d is an integer from 1 to 200, and e is 0 or 1.]

[0035] -(OC4F8) c -(OC3F6) d -(OC2F4) e -(OCF2) f - (2-2) [In formula (2-2), c and d are each independently an integer from 0 to 30, e and f are each independently an integer from 1 to 200, the sum of c, d, e, and f is 2 or more, and the order of existence of each repeating unit enclosed in parentheses with subscripts c, d, e, or f is arbitrary in the formula.],

[0036] -(R 6 -R 7 ) g - (2-3) [In formula (2-3), R 6 is OCF2 or OC2F4, R 7 is OC2F4, OC3F6, OC4F8, OC5F 10 and OC6F 12a group selected from, or a combination of two or three groups selected from these groups, g is an integer from 2 to 100.];

[0037] -(OC6F 12 ) a -(OC5F 10 ) b -(OC4F8) c -(OC3F6) d -(OC2F4) e -(OCF2) f - (2-4) [In formula (2-4), e is an integer of 1 or more and 200 or less, a, b, c, d and f are each independently an integer of 0 or more and 200 or less, The order of existence of each repeating unit enclosed in parentheses with a, b, c, d, e or f is arbitrary in the formula.]

[0038] -(OC6F 12 ) a -(OC5F 10 ) b -(OC4F8) c -(OC3F6) d -(OC2F4) e -(OCF2) f - (2-5) [In formula (2-5), f is an integer of 1 or more and 200 or less, a, b, c, d and e are each independently an integer of 0 or more and 200 or less, The order of existence of each repeating unit enclosed in parentheses with a, b, c, d, e or f is arbitrary in the formula.]

[0039] In the above formula (2-1), d is preferably an integer of 5 to 200, more preferably 10 to 100, still more preferably 15 to 50, for example 25 to 35. The above formula (2-1) is preferably -(OCF2CF2CF2) d -, or, -(OCF(CF3)CF2) d - represented by a group, more preferably, -(OCF2CF2CF2) dIt is a group represented by -. In one embodiment, e is 0. In another embodiment, e is 1.

[0040] In the above formula (2-2), e and f are each independently preferably an integer of 5 to 200, more preferably 10 to 200. Also, the sum of c, d, e and f is preferably 5 or more, more preferably 10 or more, and may be, for example, 15 or more or 20 or more. In one embodiment, the above formula (2-2) is preferably -(OCF2CF2CF2CF2) c -(OCF2CF2CF2) d -(OCF2CF2) e -(OCF2) f It is a group represented by -. In another embodiment, formula (2-2) is -(OC2F4) e -(OCF2) f It may be a group represented by -.

[0041] In the above formula (2-3), R 6 is preferably OC2F4. In the above (2-3), R 7is preferably a group selected from OC2F4, OC3F6 and OC4F8, or a combination of two or three groups independently selected from these groups, more preferably a group selected from OC3F6 and OC4F8. The combination of two or three groups independently selected from OC2F4, OC3F6 and OC4F8 is not particularly limited, and examples thereof include -OC2F4OC3F6-, -OC2F4OC4F8-, -OC3F6OC2F4-, -OC3F6OC3F6-, -OC3F6OC4F8-, -OC4F8OC4F8-, -OC4F8OC3F6-, -OC4F8OC2F4-, -OC2F4OC2F4OC3F6-, -OC2F4OC2F4OC4F8-, -OC2F4OC3F6OC2F4-, -OC2F4OC3F6OC3F6-, -OC2F4OC4F8OC2F4-, -OC3F6OC2F4OC2F4-, -OC3F6OC2F4OC3F6-, -OC3F6OC3F6OC2F4-, and -OC4F8OC2F4OC2F4-. In the above formula (2-3), g is preferably an integer of 3 or more, more preferably 5 or more. The above g is preferably an integer of 50 or less. In the above formula (2-3), OC2F4, OC3F6, OC4F8, OC5F 10、 and OC6F 12 may be either linear or branched, preferably linear. In this embodiment, the above formula (2-3) is preferably -(OC2F4-OC3F6) g -, or -(OC2F4-OC4F8) g -.

[0042] In the above formula (2-4), e is preferably an integer of 1 or more and 100 or less, more preferably 5 or more and 100 or less. The sum of a, b, c, d, e and f is preferably 5 or more, more preferably 10 or more, for example 10 or more and 100 or less.

[0043] In the above formula (2-5), f is preferably an integer of 1 or more and 100 or less, more preferably 5 or more and 100 or less. The sum of a, b, c, d, e and f is preferably 5 or more, more preferably 10 or more, for example 10 or more and 100 or less.

[0044] In one aspect, the above R F is a group represented by the above formula (2-1).

[0045] In one aspect, the above R F is a group represented by the above formula (2-2).

[0046] In one aspect, the above R F is a group represented by the above formula (2-3).

[0047] In one aspect, the above R F is a group represented by the above formula (2-4).

[0048] In one aspect, the above R F is a group represented by the above formula (2-5).

[0049] R F In R, the ratio of e to f (hereinafter referred to as "e / f ratio") may be 0.5 to 4, preferably 0.6 to 3, more preferably 0.7 to 2, and even more preferably 0.8 to 1.4. By setting the e / f ratio to 4 or less, the lubricity and chemical stability are further improved. The smaller the e / f ratio, the more the lubricity is improved. On the other hand, by setting the e / f ratio to 0.5 or more, the stability of the compound can be further enhanced. The larger the e / f ratio, the more the stability of the fluoropolyether structure is improved. In this case, the value of f is preferably 0.8 or more.

[0050] In one aspect, the above R F is the following formula (2-6): -(OCF2CF2CF2) a -(OCF(CF3)CF2) b -(OCF2CF(CF3)) c -(OCF2CF2) d -(OCF(CF3)) e -(OCF2) f - (2-6) [In formula (2-6), a, b, c, d, e, and f are each independently an integer from 0 to 200, the sum of a, b, c, d, e, and f is 1 or more, and the order of existence of each repeating unit enclosed in parentheses with a, b, c, d, e, or f attached is arbitrary in the formula.] It may be a group represented by

[0051] In one aspect, the above R F is the following formula (2-7): -(OCF2CF2) d -(OCF(CF3)) e -(OCF2) f - (2-7) [In formula (2-7), d, e, and f are each independently an integer from 0 to 200, the sum of d, e, and f is 1 or more, and the order of existence of each repeating unit enclosed in parentheses with d, e, or f attached is arbitrary in the formula.] It may be a group represented by

[0052] In R F , the ratio of d to f (hereinafter referred to as "d / f ratio") may be 0.5 to 4, preferably 0.6 to 3, more preferably 0.7 to 2, and even more preferably 0.8 to 1.4. By setting the d / f ratio to 4 or less, the lubricity and chemical stability are further improved. The smaller the d / f ratio, the more improved the lubricity. On the other hand, by setting the d / f ratio to 0.5 or more, the stability of the compound can be further enhanced. The larger the d / f ratio, the more improved the stability of the fluoropolyether structure. In this case, the value of f is preferably 0.8 or more.

[0053] In the above fluoropolyether group-containing compound, the number average molecular weight of the R F portion is not particularly limited, but is, for example, 500 to 30,000, preferably 1,500 to 30,000, and more preferably 2,000 to 10,000. In this specification, the number average molecular weight of R F is19 Let it be a value measured by F-NMR.

[0054] 1.2.2 Viscosity The viscosity of perfluoropolyether 1b is not particularly limited. In particular, when the viscosity of perfluoropolyether 1b at 25°C is 1 mPa·s or more and 5000 mPa·s or less, and especially 5 mPa·s or more and 3000 mPa·s or less, perfluoropolyether 1b tends to remain in the active material secondary particles 1, and a higher lubricating effect is more likely to be exhibited in the active material secondary particles 1. The viscosity may be 5 mPa·s or more and 1000 mPa·s or less. The viscosity of perfluoropolyether 1b is the viscosity at 25°C measured by a B-type viscometer and can be measured in accordance with JIS K7117-1:1999.

[0055] 1.3 Volume ratio The volume ratio of the negative electrode active material particles 1a to the perfluoropolyether 1b in the active material secondary particles 1 is not particularly limited as long as it can maintain a certain shape as the active material secondary particles 1. For example, when the volume ratio of the perfluoropolyether 1b in the total of the negative electrode active material particles 1a and the perfluoropolyether 1b is 1% by volume or more and 50% by volume or less, particularly 2% by volume or more and 30% by volume or less, the shape as the active material secondary particles 1 is more appropriately maintained, and it is likely to become an active material secondary particle 1 with better handleability. The volume ratio of the negative electrode active material particles 1a to the perfluoropolyether 1b in the active material secondary particles 1 can be measured, for example, as follows. That is, the volume of the entire active material secondary particles 1 is measured using an optical microscope or SEM. The volume of the perfluoropolyether 1b can be specified by washing the active material secondary particles 1 with a solvent (one that can dissolve the perfluoropolyether 1b and does not dissolve other negative electrode active material particles 1a), collecting the filtrate in which the perfluoropolyether 1b is dissolved by suction filtration or the like, and analyzing the collected solvent by GC-MS. Alternatively, when the solvent has a significantly different boiling point from the perfluoropolyether 1b, it can be extracted by distillation, and the volume of the perfluoropolyether 1b can be directly measured. Thereby, the volume ratio of the perfluoropolyether 1b and the volume ratio of the negative electrode active material particles 1a in the volume of the active material secondary particles 1 measured in advance can be calculated.

[0056] 1.4 Mass ratio The mass ratio of the negative electrode active material particles 1a to the perfluoropolyether 1b in the active material secondary particles 1 is not particularly limited as long as it can maintain a certain shape as the active material secondary particles 1. For example, when the active material secondary particles 1 contain 1 part by mass or more and 50 parts by mass or less, particularly 10 parts by mass or more and 40 parts by mass or less of the perfluoropolyether 1b with respect to 100 parts by mass of the negative electrode active material particles 1a, the shape as the active material secondary particles 1 is more appropriately maintained, and it is likely to become an active material secondary particle 1 with better handleability

[0057] 1.5 Other matters The active material secondary particle 1 may or may not contain some secondary components together with the above-mentioned negative electrode active material particles 1a and perfluoropolyether 1b. The active material secondary particle 1 may contain, for example, a total of the negative electrode active material particles 1a and perfluoropolyether 1b in an amount of 90% by mass or more and 100% by mass or less, 95% by mass or more and 100% by mass or less, or 99% by mass or more and 100% by mass or less. The active material secondary particle 1 may consist essentially of only the negative electrode active material particles 1a and perfluoropolyether 1b. Further, the active material secondary particle 1 may not contain a solid electrolyte, a conductive assistant, and a binder.

[0058] The average particle diameter of the active material secondary particle 1 is not particularly limited. For example, the average particle diameter of the active material secondary particle 1 may be 50 nm or more, 0.1 μm or more, 0.5 μm or more, 1.0 μm or more, or 2.0 μm or more, and may be 80.0 μm or less, 60.0 μm or less, 40.0 μm or less, 20.0 μm or less, or 15.0 μm or less. In particular, as described above, when the average particle diameter of the negative electrode active material particles 1a is 0.1 μm or more and 5.0 μm or less, and the average particle diameter of the active material secondary particle 1 is 0.5 μm or more and 20.0 μm or less, a higher effect is more easily obtained.

[0059] 2. Negative electrode composite material As described above, by applying the active material secondary particles 1 of the present disclosure to the negative electrode composite material constituting the negative electrode of the secondary battery, the secondary battery is likely to have excellent cycle characteristics and low resistance. The negative electrode composite material may form the negative electrode active material layer described later. The negative electrode composite material according to one embodiment may include at least the above-described active material secondary particles 1 and a solid electrolyte. Further, the negative electrode composite material may include at least the above-described active material secondary particles 1, a solid electrolyte, and at least one of a conductive assistant and a binder, and may include at least the above-described active material secondary particles 1, a solid electrolyte, a conductive assistant, and a binder. Further, the negative electrode composite material may contain various additives and the like. For example, the negative electrode composite material may or may not contain perfluoropolyether separately from the above-described active material secondary particles 1. The content of each component in the negative electrode composite material may be appropriately determined according to the target battery performance. For example, assuming the total amount of the negative electrode composite material is 100% by mass, the content of the above-described active material secondary particles 1 may be 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, and may be less than 100% by mass or 90% by mass or less. Further, assuming the total amount of the negative electrode composite material is 100% by mass, the content of the solid electrolyte may be more than 0% by mass or 10% by mass or more, and may be 60% by mass or less, 50% by mass or less, 40% by mass or less, or 30% by mass or less. Further, when the total amount of perfluoropolyether contained in the negative electrode composite material is 100% by mass, the perfluoropolyether 1b constituting the above-described active material secondary particles 1 may be 90% by mass or more, 95% by mass or more, or 99% by mass or more, and 100% by mass or less.

[0060] 2.1 Negative electrode active material The negative electrode composite material includes the above-described active material secondary particles 1. Further, the negative electrode composite material may independently contain other negative electrode active materials in addition to the above-described active material secondary particles 1. However, it is considered that the effect of the technology of the present disclosure increases as the content of other active materials decreases. For example, when the total amount of the negative electrode active material contained in the negative electrode composite material is 100% by mass, the negative electrode active material particles 1a constituting the above-described active material secondary particles 1 may occupy 90% by mass or more, 95% by mass or more, or 99% by mass or more, and 100% by mass or less.

[0061] 2.2 Solid electrolyte As the solid electrolyte that can be included in the negative electrode composite material, those known as solid electrolytes 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 excellent in ionic conductivity and heat resistance. Examples of inorganic solid electrolytes include oxide solid electrolytes and sulfide solid electrolytes. Among inorganic solid electrolytes, in particular, sulfide solid electrolytes, and among them, sulfide solid electrolytes containing at least Li, S, and P as constituent elements have high performance. The solid electrolyte may be amorphous or crystalline. The solid electrolyte may be in the form of particles. The average particle diameter (D50) of the solid electrolyte may be, for example, 10 nm or more and 10 μm or less. Note that the average particle diameter D50 referred to in the present application is the particle diameter (median diameter) at the integrated value of 50% in the volume-based particle size distribution determined by the laser diffraction / scattering method. The ionic conductivity of the solid electrolyte at 25°C is, for example, 1×10 -4 S / cm or more, or 1×10 -3 S / cm or more. Only one type of solid electrolyte may be used alone, or two or more types may be used in combination.

[0062] The oxide solid electrolyte may be one or more selected from lithium lanthanum zirconate, LiPON, Li 1+X Al X Ge 2-X (PO4)3, Li-SiO-based glass, Li-Al-S-O-based glass, etc.

[0063] The sulfide solid electrolyte may be a glass-based sulfide solid electrolyte (sulfide glass), a glass-ceramic-based sulfide solid electrolyte, or a crystalline sulfide solid electrolyte. Sulfide glass is amorphous. Sulfide glass may have a glass transition temperature (Tg). Also, when the sulfide solid electrolyte has a crystalline phase, examples of the crystalline phase include a Thio-LISICON type crystalline phase, an LGPS type crystalline phase, and an argyrodite type crystalline phase.

[0064] The sulfide solid electrolyte may contain, for example, Li element, X element (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, In), and S element. Further, the sulfide solid electrolyte may further contain at least one of O element and halogen element. Also, the sulfide solid electrolyte may contain S element as the main component of the anion element.

[0065] The sulfide solid electrolyte is, for example, Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-GeS2, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-LiI-LiBr, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-ZmSn (where m and n are positive numbers. Z is any of Ge, Zn, Ga.), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers. M is any of P, Si, Ge, B, Al, Ga, In.) and may be at least one selected therefrom.

[0066] The composition of the sulfide solid electrolyte is not particularly limited, and examples thereof include xLi2S·(100-x)P2S5 (70 ≦ x ≦ 80), yLiI·zLiBr·(100-y-z)(xLi2S·(1-x)P2S5) (0.7 ≦ x ≦ 0.8, 0 ≦ y ≦ 30, 0 ≦ z ≦ 30), etc. Alternatively, the sulfide solid electrolyte has the general formula: Li 4-x Ge 1-x P xIt may have a composition represented by S4(0 < x < 1). In the above general formula, at least a part of Ge may be substituted with at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the above general formula, at least a part of P may be substituted with at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the above general formula, a part of Li may be substituted with at least one of Na, K, Mg, Ca, and Zn. In the above general formula, a part of S may be substituted with a halogen (at least one of F, Cl, Br, and I). Alternatively, the sulfide solid electrolyte is Li 7-a PS 6-a X a (X is at least one of Cl, Br, and I, and a is a number of 0 or more and 2 or less). a may be 0, or may be greater than 0. In the latter case, a may be 0.1 or more, may be 0.5 or more, or may be 1 or more. Also, a may be 1.8 or less, or may be 1.5 or less.

[0067] 2.3 Conductive Aid Examples of the conductive aid that can be included in the negative electrode composite material include carbon materials such as vapor grown carbon fiber (VGCF), acetylene black (AB), ketjen black (KB), carbon nanotube (CNT), and carbon nanofiber (CNF); and metal materials such as nickel, aluminum, and stainless steel. The conductive aid may be, for example, particulate or fibrous, and its size is not particularly limited. Only one type of conductive aid may be used alone, or two or more types may be used in combination.

[0068] 2.4 Binder Examples of the binder that can be included in the negative electrode composite material include, for example, butadiene rubber (BR)-based binders, isobutylene rubber (IIR)-based binders, acrylate butadiene rubber (ABR)-based binders, styrene butadiene rubber (SBR)-based binders, polyvinylidene fluoride (PVdF)-based binders, polytetrafluoroethylene (PTFE)-based binders, polyimide (PI)-based binders, polyacrylic acid-based binders, and the like. Only one type of binder may be used alone, or two or more types may be used in combination.

[0069] 3. Secondary battery The technology of the present disclosure also has an aspect as a secondary battery having the above active material secondary particles 1. As shown in FIG. 2, a secondary battery 100 according to an embodiment has a negative electrode 10, an electrolyte layer 20, and a positive electrode 30. Here, the negative electrode 10 contains the above active material secondary particles 1.

[0070] 3.1 Negative electrode The negative electrode 10 may contain the above active material secondary particles 1 and may have various configurations as long as it can function appropriately as the negative electrode of the secondary battery. As shown in FIG. 2, the negative electrode 10 may include a negative electrode active material layer 11 and a negative electrode current collector 12. In this case, the negative electrode active material layer 11 may contain the above active material secondary particles 1.

[0071] 3.1.1 Negative electrode active material layer The negative electrode active material layer 11 may be made of the above-described negative electrode composite material. The shape of the negative electrode active material layer 11 is not particularly limited, and for example, it may be in the form of a sheet having a substantially flat surface. The thickness of the negative electrode active material layer 11 is not particularly limited, and for example, it may be 0.1 μm or more, 1 μm or more, or 10 μm or more, and may also be 2 mm or less, 1 mm or less, or 500 μm or less.

[0072] 3.1.2 Negative electrode current collector As shown in FIG. 2, the negative electrode 10 may include a negative electrode current collector 12 that contacts the above-described negative electrode active material layer 11. Any of the commonly used materials for the negative electrode current collector of a secondary battery can be adopted as the negative electrode current collector 12. Further, the negative electrode current collector 12 may be in the form of a foil, a plate, a mesh, a punched metal, a foam, or the like. The negative electrode current collector 12 may be a metal foil or a metal mesh, or may be a carbon sheet. In particular, a metal foil is excellent in handleability and the like. The negative electrode current collector 12 may be composed of a plurality of foils or sheets. Examples of the metal constituting the negative electrode current collector 12 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, and the like. In particular, from the viewpoints of ensuring reduction resistance and being difficult to alloy 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 coating layer on its surface for the purpose of adjusting resistance or the like. Further, the negative electrode current collector 12 may be a metal foil or a substrate on which the above metal is plated or vapor-deposited. Further, when the negative electrode current collector 12 is composed of a plurality of metal foils, there may be some layer between the plurality of 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, and may be 1 mm or less or 100 μm or less.

[0073] 3.2 Electrolyte layer The electrolyte layer 20 is disposed between the negative electrode 10 and the positive electrode 30 and can function as a separator. The electrolyte layer 20 contains at least an electrolyte, and may further optionally contain a binder or the like. The electrolyte layer 20 may further contain various additives or the like. The content of each component in the electrolyte layer 20 is not particularly limited and may be appropriately determined according to the intended battery performance. The shape of the electrolyte layer 20 is not particularly limited, and for example, it may be in the form of a sheet having a substantially flat surface. The thickness of the electrolyte layer 20 is not particularly limited, and for example, it may be 0.1 μm or more or 1 μm or more, and may be 2 mm or less or 1 mm or less.

[0074] 3.2.1 Electrolyte As the electrolyte contained in the electrolyte layer 20, any of those known as electrolytes for secondary batteries can be adopted. In particular, the performance of the electrolyte layer 20 containing a solid electrolyte, among which a sulfide solid electrolyte, and among them a sulfide solid electrolyte containing at least Li, S, and P as constituent elements, is high. The details of the solid electrolyte are as described above. The type of electrolyte contained in the electrolyte layer 20 may be the same as or different from the type of electrolyte that can be contained in the above-described negative electrode composite material. Only one type of electrolyte may be used alone, or two or more types may be used in combination.

[0075] 3.2.2 Binder The binder that can be contained in the electrolyte layer 20 may be appropriately selected, for example, from among those exemplified as the binder that can be contained in the above-described negative electrode composite material. The type of binder contained in the electrolyte layer 20 may be the same as or different from the type of binder that can be contained in the above-described negative electrode composite material. Only one type of binder may be used alone, or two or more types may be used in combination.

[0076] 3.3 Positive Electrode The positive electrode 30 may have any configuration as long as it can function appropriately as the negative electrode of the secondary battery. As shown in FIG. 2, the positive electrode 30 may include a positive electrode active material layer 31 and a positive electrode current collector 32.

[0077] 3.3.1 Positive Electrode Active Material Layer The positive electrode active material layer 31 contains at least a positive electrode active material. Further, the positive electrode active material layer 31 may optionally contain an electrolyte, a conductive assistant, a binder, etc. Furthermore, the positive electrode active material layer 31 may contain various additives, etc. The content of each component in the positive electrode active material layer 31 may be appropriately determined according to the target battery performance. For example, taking the total solid content of the positive electrode active material layer 31 as 100% by mass, the content of the positive electrode active material may be 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, and may also be 100% by mass or less, 95% by mass or less, or 90% by mass or less. Alternatively, taking the entire positive electrode active material layer 31 as 100% by volume, the positive electrode active material and optionally the electrolyte, the conductive assistant, and the binder may be contained in a total of 85% by volume or more, 90% by volume or more, or 95% by volume or more, and the balance may be voids or other components. The shape of the positive electrode active material layer 31 is not particularly limited, and for example, it may be in the form of a sheet having a substantially flat surface. The thickness of the positive electrode active material layer 31 is not particularly limited, and for example, it may be 0.1 μm or more, 1 μm or more, or 10 μm or more, and may also be 2 mm or less, 1 mm or less, or 500 μm or less.

[0078] As the positive electrode active material, those known as the positive electrode active material of a secondary battery may be used. Among the known active materials, a substance with a relatively high potential (charge-discharge potential) for occluding and releasing a predetermined carrier ion (for example, lithium ion) is used as the positive electrode active material, and a substance with a relatively low potential is used as the above-mentioned negative electrode active material. The positive electrode active material may be, for example, at least one selected from various lithium-containing compounds, elemental sulfur, sulfur compounds, etc. The lithium-containing compound as the positive electrode active material is lithium cobaltate, lithium nickelate, Li 1±α Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O 2±δ 、 lithium manganate, spinel-type lithium compound (Li 1+x Mn 2-x-y M yHetero-element substituted Li-Mn spinel represented by O4 (M is one or more selected from Al, Mg, Co, Fe, Ni, and Zn), etc., lithium titanate, lithium metal phosphate (such as LiMPO4, M is one or more selected from Fe, Mn, Co, and Ni), and various lithium-containing oxides may be used. In particular, when the cathode active material contains a lithium-containing oxide containing at least Li, at least one of Ni, Co, and Mn, and O as constituent elements, the performance of the secondary battery is more likely to be enhanced. Only one type of cathode active material may be used alone, or two or more types may be used in combination.

[0079] The shape of the cathode active material may be a general shape as the cathode active material of the secondary battery. The cathode active material may be, for example, particulate. The cathode active material may have voids, for example, it may be porous or hollow. The cathode active material may be primary particles or secondary particles formed by aggregation of a plurality of primary particles. The average particle diameter D50 of the cathode active material may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may also be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Incidentally, the average particle diameter D50 of the cathode active material is the particle diameter (median diameter) at the integrated value of 50% in the volume-based particle size distribution determined by the laser diffraction / scattering method.

[0080] A protective layer containing an ion-conductive oxide may be formed on the surface of the cathode active material. Thereby, the reaction between the cathode active material and a sulfide (for example, a sulfide solid electrolyte) etc. is likely to be suppressed. Examples of the ion-conductive oxide include Li3BO3, LiBO2, Li2CO3, LiAlO2, Li4SiO4, Li2SiO3, Li3PO4, Li2SO4, Li2TiO3, Li4Ti5O 12, such as Li2Ti2O5, Li2ZrO3, LiNbO3, Li2MoO4, Li2WO4, etc. The ion-conductive oxide may be one in which some elements are substituted by doping elements such as P and B. 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 or 1 nm or more, and may be 100 nm or less or 20 nm or less.

[0081] The electrolyte that can be included in the positive electrode active material layer 31 may be a solid electrolyte, a liquid electrolyte (electrolyte solution), or a combination thereof. The positive electrode active material layer 31 may include a solid electrolyte, particularly a sulfide solid electrolyte, and more particularly a sulfide solid electrolyte containing Li, S, and P as constituent elements. The conductive assistant that can be included in the positive electrode active material layer 31 may be appropriately selected from those exemplified as the conductive assistants that can be included in the above-mentioned negative electrode composite material. The type of the conductive assistant included in the positive electrode active material layer 31 may be the same as or different from the type of the conductive assistant that can be included in the above-mentioned negative electrode composite material. Only one type of conductive assistant may be used alone, or two or more types may be combined and used. The binder that can be included in the positive electrode active material layer 31 may be appropriately selected from those exemplified as the binders that can be included in the above-mentioned negative electrode composite material. The type of the binder included in the positive electrode active material layer 31 may be the same as or different from the type of the binder that can be included in the above-mentioned negative electrode composite material. Only one type of binder may be used alone, or two or more types may be combined and used.

[0082] 3.3.2 Positive Electrode Current Collector As shown in FIG. 2, the positive electrode 30 may include a positive electrode current collector 32 that contacts the above-described positive electrode active material layer 31. Any commonly used positive electrode current collector of a secondary battery can be adopted as the positive electrode current collector 32. Further, the positive electrode current collector 32 may be in the form of a foil, a plate, a mesh, a punching metal, a foam, or the like. The positive electrode current collector 32 may be composed of a metal foil or a metal mesh. In particular, a metal foil is excellent in terms of handleability and the like. The positive electrode current collector 32 may be composed of a plurality of foils. Examples of the metal constituting the positive electrode current collector 32 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, and the like. In particular, from the viewpoint of ensuring oxidation resistance, etc., the positive electrode current collector 32 may contain Al. The positive electrode current collector 32 may have some coating layer on its surface for the purpose of adjusting resistance or the like. Further, the positive electrode current collector 32 may be a metal foil or a base material on which the above metal is plated or vapor-deposited. Also, when the positive electrode current collector 32 is composed of a plurality of metal foils, there may be some layer between the plurality of 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, and may be 1 mm or less or 100 μm or less.

[0083] 3.4 Other Configurations The secondary battery 100 may be one in which each of the above-described configurations is housed inside an exterior body. Any known exterior body of a battery can be adopted as the exterior body. Also, a plurality of secondary batteries 100 may be arbitrarily electrically connected and arbitrarily stacked to form a battery pack. In this case, the battery pack may be housed inside a known battery case. The secondary battery 100 may further include obvious configurations such as necessary terminals. Examples of the shape of the secondary battery 100 include a coin type, a laminate type, a cylindrical type, and a rectangular type.

[0084] 4. Method for Manufacturing Active Material Secondary Particles The technology of the present disclosure also has an aspect as a method for manufacturing active material secondary particles. As shown in FIG. 1, a method for manufacturing active material secondary particles 1 according to an embodiment includes mixing a plurality of negative electrode active material particles 1a and perfluoropolyether 1b and bonding the plurality of negative electrode active material particles 1a to each other via the perfluoropolyether 1b. The mixing of the negative electrode active material particles 1a and the perfluoropolyether 1b can be carried out using a known mixing device or the like. The mixing conditions are not particularly limited as long as the negative electrode active material particles 1a and the perfluoropolyether 1b can be formed into secondary particles. The mixing ratio (volume ratio or mass ratio) is as described above.

[0085] 5. Method for manufacturing negative electrode composite material The technology of the present disclosure also has an aspect as a method for manufacturing a negative electrode composite material. For example, a method for manufacturing a negative electrode composite material according to an embodiment includes mixing the above-described active material secondary particles 1 and a solid electrolyte. As described above, the negative electrode composite material may include a conductive auxiliary agent, a binder, and various additives in addition to the above-described active material secondary particles 1 and the solid electrolyte. For example, the method for manufacturing the negative electrode composite material may include mixing the above-described active material secondary particles 1 and at least one of a solid electrolyte, a conductive auxiliary agent, and a binder, or may include mixing the above-described active material secondary particles 1, a solid electrolyte, a conductive auxiliary agent, and a binder. The mixing of the active material secondary particles 1 and the solid electrolyte or the like can be carried out using a known mixing device or the like. The mixing conditions are not particularly limited as long as each component can be uniformly mixed. The types and mixing ratios of the respective components are as described above.

[0086] 6. Method for manufacturing secondary battery The technology of the present disclosure also has an aspect as a method for manufacturing a secondary battery. The secondary battery 100 can be manufactured by applying a known method. For example, it can be manufactured as follows. However, the method for manufacturing the secondary battery 100 is not limited to the following method. For example, each layer may be formed by dry forming or the like. (1) The active material secondary particles 1 and the like that constitute the negative electrode active material layer are dispersed in a solvent to obtain a negative electrode slurry. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. Then, using a doctor blade or the like, the negative electrode slurry is applied to the surface of the negative electrode current collector or the electrolyte layer described later, and then dried to form a negative electrode active material layer on the surface of the negative electrode current collector or the electrolyte layer, thereby obtaining a negative electrode. Here, the negative electrode active material layer may be press-molded. (2) The positive electrode active material and the like that constitute the positive electrode active material layer are dispersed in a solvent to obtain a positive electrode slurry. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. Then, using a doctor blade or the like, the positive electrode slurry is applied to the surface of the positive electrode current collector or the electrolyte layer described later, and then dried to form a positive electrode active material layer on the surface of the positive electrode current collector or the electrolyte layer, thereby obtaining a positive electrode. Here, the positive electrode active material layer may be press-molded. (3) Each layer is laminated so that the electrolyte layer is sandwiched between the negative electrode and the positive electrode, and 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 is obtained. The electrolyte layer may be, for example, obtained by molding an electrolyte binder containing an electrolyte and a binder, or may be obtained by press-molding. Alternatively, the electrolyte layer may be transferred to the above-described negative electrode active material layer or positive electrode active material layer. The laminate may be further press-molded. Other members such as terminals are attached to the laminate as necessary. (4) A secondary battery is obtained by housing the laminate in a battery case and sealing it.

[0087] 7. Method for improving the cycle characteristics of a secondary battery The technology of the present disclosure also has an aspect as a method for improving the cycle characteristics of a secondary battery. That is, the method of the present disclosure is characterized in that, in the negative electrode of the secondary battery, by adopting the above-described active material secondary particles 1, the cycle characteristics of the secondary battery are improved. The details of the configuration of the secondary battery and the active material secondary particles are as described above.

[0088] 8. Vehicle As described above, the secondary battery of the present disclosure has excellent cycle characteristics and low resistance. Such a secondary battery can be suitably used, for example, in at least one vehicle selected from a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), and a battery electric vehicle (BEV). That is, the technology of the present disclosure also has an aspect as a vehicle having a secondary battery, wherein the secondary battery has a negative electrode, an electrolyte layer, and a positive electrode, and the negative electrode contains the above-described active material secondary particles 1. The details of the configuration of the secondary battery are as described above.

[0089] 9. Supplementary The technology of the present disclosure can be applied not only to lithium-ion secondary batteries but also to secondary batteries other than lithium-ion secondary batteries (for example, sodium-ion secondary batteries). However, the technology of the present disclosure is more likely to exhibit a higher effect when applied to lithium-ion secondary batteries.

Examples

[0090] Hereinafter, the technology of the present disclosure will be described in more detail while showing examples, but the technology of the present disclosure is not limited to the following examples.

[0091] 1. Preparation of Positive Electrode for Pressing A binder (PVdF), a conductive assistant (VGCF), a sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5), and a positive electrode active material (LiNi 0.80 Co 0.15 Mn 0.05 O2) were added to an organic solvent and kneaded using an ultrasonic homogenizer to obtain a positive electrode composite slurry. The obtained positive electrode composite slurry was coated on an Al foil and dried to obtain a positive electrode for pressing.

[0092] 2. Preparation of Negative Electrode for Pressing When producing the negative electrode composite material, when perfluoropolyether (PFPE) was not included (Comparative Examples 1 and 2), when the negative electrode active material particles, the solid electrolyte, etc. and PFPE were mixed simultaneously (when the negative electrode active material particles and PFPE were not secondary particleized, Comparative Examples 3 and 4), and when the negative electrode active material particles and PFPE were secondary particleized in advance and the secondary particles were mixed with the solid electrolyte, etc. (Examples 1 and 2), a negative electrode for pressing was produced. In Comparative Examples 3 and 4 and Examples 1 and 2, as PFPE, one having a chemical structure represented by the following formula (I) was used. Further, the PFPE had a viscosity of 60 mPa·s at 25°C.

[0093] F3C-(CF2CF2CF2O) n -CF3(I)

[0094] 2.1 Comparative Example 1 A binder (PVdF), a conductive assistant (VGCF), a sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5), and negative electrode active material particles (porous Si particles, average particle diameter: 0.5 μm) were added to an organic solvent, and kneaded using an ultrasonic homogenizer to obtain a negative electrode composite material slurry. The mixing ratio of the binder, the conductive assistant, the sulfide solid electrolyte, and the negative electrode active material particles contained in the negative electrode composite material was, by mass ratio, binder:conductive assistant:sulfide solid electrolyte:negative electrode active material particles = 2.5:5:41:51.5. The obtained negative electrode composite material slurry was coated on a Cu foil and dried to obtain a negative electrode for pressing.

[0095] 2.2 Comparative Example 2 A negative electrode for pressing was obtained in the same manner as in Comparative Example 1, except that graphite particles (average particle diameter: 1.0 μm) were used instead of the porous Si particles as the negative electrode active material. The mass ratio of the binder, the conductive assistant, the sulfide solid electrolyte, and the negative electrode active material particles contained in the negative electrode composite material was also the same as in Comparative Example 1.

[0096] 2.3 Comparative Example 3 A binder (PVdF), a conductive additive (VGCF), a sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5), negative electrode active material particles (porous Si particles, average particle diameter: 0.5 μm), and PFPE were added to an organic solvent and kneaded using an ultrasonic homogenizer to obtain a negative electrode composite slurry. The mixing ratio of the binder, conductive additive, sulfide solid electrolyte, negative electrode active material particles, and PFPE contained in the negative electrode composite was, by mass ratio, binder:conductive additive:sulfide solid electrolyte:negative electrode active material particles:PFPE = 2:4:37:47.5:9.5 (that is, in the negative electrode for pressing, 20 parts by mass of PFPE was contained with respect to 100 parts by mass of the negative electrode active material particles). The obtained negative electrode composite slurry was coated on a Cu foil and dried to obtain a negative electrode for pressing.

[0097] 2.4 Comparative Example 4 A negative electrode for pressing was obtained in the same manner as in Comparative Example 3, except that graphite particles (average particle diameter: 1.0 μm) were used instead of the porous Si particles as the negative electrode active material. The mixing ratio of the binder, conductive additive, sulfide solid electrolyte, negative electrode active material particles, and PFPE contained in the negative electrode composite was also the same as in Comparative Example 3.

[0098] 2.5 Example 1 2.5.1 Preparation of Active Material Secondary Particles Negative electrode active material particles (porous Si particles, average particle diameter: 0.5 μm) and PFPE were mixed in a mortar to obtain active material secondary particles containing a plurality of negative electrode active material particles and PFPE. Here, 20 parts by mass of PFPE was mixed with 100 parts by mass of the negative electrode active material. In this case, in the active material secondary particles, the volume ratio of the negative electrode active material particles in the total of the negative electrode active material particles and PFPE was 81% by volume. Also, the average particle diameter of the active material secondary particles was 8 μm.

[0099] 2.5.2 Preparation of Negative Electrode Composite and Negative Electrode A binder (PVdF), a conductive additive (VGCF), a sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5), and the above active material secondary particles were added to an organic solvent and kneaded using an ultrasonic homogenizer to obtain a negative electrode composite material slurry. The mixing ratio of the binder, conductive additive, sulfide solid electrolyte, and active material secondary particles contained in the negative electrode composite material was 2:4:37:57 by mass ratio (binder:conductive additive:sulfide solid electrolyte:active material secondary particles). The obtained negative electrode composite material slurry was coated on a Cu foil and dried to obtain a negative electrode for pressing.

[0100] 2.6 Example 2 Active material secondary particles were produced in the same manner as in Example 1 except that graphite particles (average particle diameter: 1.0 μm) were used instead of porous Si particles as the negative electrode active material, and a negative electrode for pressing was obtained. That is, the active material secondary particles contain 20 parts by mass of PFPE with respect to 100 parts by mass of the negative electrode active material. In this case, in the active material secondary particles, the volume ratio of the negative electrode active material particles in the total of the negative electrode active material particles and PFPE was 83% by volume. The mixing ratio of the binder, conductive additive, sulfide solid electrolyte, and active material secondary particles contained in the negative electrode composite material was the same as in Example 1. Also, the average particle diameter of the active material secondary particles was 10 μm.

[0101] 3. Preparation of Electrolyte Layer for Pressing A binder (PVdF) and a sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5) were added to an organic solvent and kneaded using an ultrasonic homogenizer to obtain an electrolyte composite material slurry. The obtained electrolyte composite material slurry was coated on an Al foil and dried to obtain an electrolyte layer for pressing.

[0102] 4. Fabrication of Battery The positive electrode, negative electrode, and electrolyte layer for pressing were each formed into strip shapes. After overlapping the composite material surface of the positive electrode for pressing and the composite material surface of the electrolyte layer for pressing, roll pressing was performed at 165 °C under a pressure of 50 kN / cm, and by peeling off the Al foil of the electrolyte layer for pressing, a laminate (A) of the Al foil, positive electrode active material layer, and electrolyte layer was obtained. On the other hand, after overlapping the composite material surface of the negative electrode for pressing and the composite material surface of the electrolyte layer for pressing, roll pressing was performed at 25 °C under a pressure of 50 kN / cm, and by peeling off the Al foil of the electrolyte layer for pressing, a laminate (B) of the Cu foil, negative electrode active material layer, and electrolyte layer was obtained. The laminate (A) was punched out to φ11.28 mm, and the laminate (B) was punched out to φ13.00 mm. Using a uniaxial press machine for the laminate (B), after further transferring the electrolyte layer, the laminate (A) and the laminate (B) were overlapped to obtain an electrode body having a structure of Al foil / positive electrode active material layer / electrolyte layer / negative electrode active material layer / Cu foil. Current extraction tabs were attached to the Al foil and Cu foil of the electrode body, respectively, and an evaluation battery was fabricated by enclosing it in a laminate pack using a vacuum laminator.

[0103] 5. Evaluation of Battery Resistance The resistance of the evaluation battery fabricated as described above was measured. Specifically, the voltage of the battery was adjusted to 3.7 V, and the resistance value (initial resistance) of the battery was calculated from the voltage drop 5 seconds after discharging at a 5C rate.

[0104] 6. Evaluation of Battery Cycle Characteristics Regarding the evaluation battery fabricated as described above, a charge-discharge test was repeated 100 times at 25 °C, in which after constant current charging to SOC93% at a 2C rate, constant current discharging to SOC10% at a 2C rate was performed. The ratio C A of the capacity C B after 100 cycles to the capacity C B / C A was determined as the capacity retention rate.

[0105] 7. Evaluation Results The results are shown in Table 1 below.

[0106]

Table 1

[0107] The following can be said from the results shown in Table 1. (1) As is clear from the results of Comparative Examples 1 and 2 and Comparative Examples 3 and 4, when PFPE was mixed with the negative electrode active material particles, the solid electrolyte, the conductive assistant, and the binder to obtain a negative electrode composite material (Comparative Examples 3 and 4), the initial resistance of the secondary battery decreased and the cycle characteristics improved compared to the case where PFPE was not mixed (Comparative Examples 1 and 2). (2) As is clear from the results of Comparative Examples 3 and 4 and Examples 1 and 2, when secondary particles of the negative electrode active material particles and PFPE were prepared in advance and then the secondary particles, the solid electrolyte, and the conductive assistant were mixed to obtain a negative electrode composite material (Examples 1 and 2), the initial resistance of the secondary battery decreased and the cycle characteristics improved compared to the case where PFPE was mixed with the negative electrode active material particles, the solid electrolyte, the conductive assistant, and the binder without preparing secondary particles in advance (Comparative Examples 3 and 4).

[0108] Regarding Comparative Examples 3 and 4 and Examples 1 and 2, the reasons why the initial resistance of the secondary battery decreased and the cycle characteristics improved are considered as follows. That is, since PFPE is contained in the negative electrode, PFPE functions as a lubricant, and when the negative electrode is pressed, the materials constituting the negative electrode composite material move (flow) smoothly, increasing the filling rate of the negative electrode, and thereby it is considered that the resistance of the negative electrode has decreased. Further, during charge and discharge of the secondary battery, due to the lubricating effect of PFPE, cracks and the like of the negative electrode active material when the negative electrode active material expands and contracts are suppressed, and the materials constituting the negative electrode composite material move (flow) smoothly to suppress the generation of voids and the like, and thereby it is considered that the cycle characteristics of the secondary battery have improved.

[0109] In particular, in Examples 1 and 2, a plurality of negative electrode active material particles are connected via perfluoropolyether, and it is considered that voids exist between the plurality of negative electrode active material particles or the voids are filled with perfluoropolyether (FIG. 1). When perfluoropolyether or voids exist between the negative electrode active material particles, even if the negative electrode active material particles expand during charging of the secondary battery, it is considered that the expansion amount of the entire secondary particles is alleviated. That is, it is considered that the volume change of the entire secondary particles becomes small. Further, in Examples 1 and 2, when the volume of the negative electrode active material particles changes, the arrangement of the negative electrode active material particles in the active material secondary particles changes smoothly via perfluoropolyether, and thus, it is considered that the volume change of the entire active material secondary particles also becomes small. In addition, since the arrangement of the negative electrode active material particles in the active material secondary particles changes smoothly, it is considered that local stress concentration on the negative electrode active material particles is less likely to occur and cracking of the negative electrode active material particles is suppressed. Further, in Examples 1 and 2, when the negative electrode is pressed, the arrangement of the negative electrode active material particles in the active material secondary particles changes smoothly via PFPE, the filling rate of the negative electrode increases, and crushing of the negative electrode active material particles is suppressed. Furthermore, in Examples 1 and 2, by pre-secondary particleizing the negative electrode active material particles and PFPE, it is considered that PFPE is arranged only in the vicinity of the negative electrode active material particles even after the secondary battery is constructed, and it is considered that ion conduction (for example, ion conduction between solid electrolytes) and electron conduction in the negative electrode are hardly inhibited by PFPE. As a result of these effects being combined in a complex manner, in Examples 1 and 2, it is considered that the initial resistance of the secondary battery is significantly reduced and the cycle characteristics are significantly improved.

[0110] In addition, in the above examples, PFPE having a specific chemical structure was exemplified, but the chemical structure of PFPE is not limited thereto. Further, in the above examples, the case where porous Si particles and graphite particles are used as the negative electrode active material particles was exemplified, but the type of the negative electrode active material particles is not limited thereto. Also, the composite material compositions of the positive electrode, the electrolyte layer, and the negative electrode are not limited to those described above.

[0111] As described above, by using active material secondary particles containing a plurality of negative electrode active material particles and perfluoropolyether to form a negative electrode composite material or a secondary battery, the secondary battery is likely to have low resistance and excellent cycle characteristics.

Explanation of Signs

[0112] 1 Active material secondary particle 1a Negative electrode active material particle 1b Perfluoropolyether 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. An active material secondary particle comprising a plurality of negative electrode active material particles and a perfluoropolyether connecting the plurality of negative electrode active material particles to each other, and a sulfide solid electrolyte, A negative electrode composite material containing

2. The negative electrode active material particles contain Si, The negative electrode composite material according to claim 1.

3. The volume ratio of the perfluoropolyether in the total of the negative electrode active material particles and the perfluoropolyether is 2% by volume or more and 30% by volume or less, The negative electrode composite material according to claim 1.

4. The viscosity of the perfluoropolyether at 25° C. is 5 mPa·s or more and 3000 mPa·s or less, The negative electrode composite material according to claim 1.

5. The average particle diameter of the negative electrode active material particles is 0.1 μm or more and 5.0 μm or less, The average particle diameter of the active material secondary particles is 0.5 μm or more and 20.0 μm or less, The negative electrode composite material according to claim 1.

6. Mixing a plurality of negative electrode active material particles and a perfluoropolyether, and bonding the plurality of negative electrode active material particles to each other via the perfluoropolyether to produce active material secondary particles, and Mixing the active material secondary particles and a sulfide solid electrolyte, A method for manufacturing a negative electrode composite material including

7. A secondary battery having a negative electrode, an electrolyte layer, and a positive electrode, The negative electrode contains the negative electrode composite material according to any one of claims 1 to 5, Secondary battery.

Images