Negative electrode active material for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery using same, and method for producing negative electrode active material for non-aqueous electrolyte secondary battery

Abstract

The disclosed negative electrode active material for a non-aqueous electrolyte secondary battery includes active material particles containing silicon, and a surface layer formed on the surface of the active material particles. The surface layer includes a reaction product obtained as a result of a compound being reacted so as to form a siloxane bond. The compound includes a structure represented by Si-R1-Si. R1 is an atomic group having a chain part that includes, as constituent elements, an alkylene group and at least one substance selected from the group consisting of sulfur atoms, oxygen atoms, and nitrogen atoms. At least one atomic group selected from the group consisting of C1-C6 alkoxy groups and the like is bonded to each of the two Si.

Description

Negative electrode active material for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery using the same, and method for manufacturing negative electrode active material for non-aqueous electrolyte secondary battery

[0001] The present disclosure relates to a negative electrode active material for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery using the same, and a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery.

[0002] Silicon materials, such as silicon (Si) and silicon oxides (SiOx), are known to be able to store more lithium ions per unit volume than carbon materials such as graphite, and their application to the negative electrodes of lithium-ion batteries and the like has been investigated. Non-aqueous electrolyte secondary batteries using silicon materials as the negative electrode active material have the problem of lower charge-discharge efficiency compared to those using graphite as the negative electrode active material. Therefore, the use of lithium silicate as the negative electrode active material has been proposed to improve charge-discharge efficiency.

[0003] Patent Document 1 (JP 2003-160328 A) describes a compound having the general formula SiLi ｘ O ｙ The patent application discloses a lithium-containing silicon oxide powder represented by the formula (1), wherein the ranges of x and y are 0<x<1.0 and 0<y<1.5, and wherein lithium is fused and part of it is crystallized.

[0004] Patent Document 2 (JP 2014-150068 A) states that "the surface moisture content per unit specific surface area (200-300°C) is 0.1 to 20 ppm / (m ２ / g) with a silane coupling agent.

[0005] Non-Patent Document 1 reports that the capacity retention rate during charge-discharge cycles is improved by adding a vinyl group-containing silane coupling agent to the electrolyte of a single-electrode battery using a Si / C composite.

[0006] JP 2003-160328 A JP 2014-150068 A

[0007] Ionics, 2018, 24, 3691-3698

[0008] There is a need for non-aqueous electrolyte secondary batteries that further suppress the decrease in discharge capacity during repeated charge-discharge cycles. In this situation, one object of the present disclosure is to provide a negative electrode active material that can be used to form a non-aqueous electrolyte secondary battery with a high capacity retention rate during charge-discharge cycles.

[0009] One aspect of the present disclosure relates to a negative electrode active material for a non-aqueous electrolyte secondary battery. The negative electrode active material includes silicon-containing active material particles and a surface layer formed on the surface of the active material particles. The surface layer includes a reaction product formed by a reaction of a compound to form a siloxane bond. The compound has a structure represented by Si-R1-Si, where R1 is an atomic group having a chain portion containing, as components, at least one selected from the group consisting of a sulfur atom, an oxygen atom, and a nitrogen atom and an alkylene group. One of the two Si atoms contains an alkoxy group or an oxyalkylene group having a carbon number of 1 to 6, and is represented by —O—(C ｘ１ H ２ｘ１＋１ O ｙ１ ) (x1 is an integer of 2 or more and 6 or less, and y1 is an integer of 1 or more and 3 or less), a chloro group, and at least one atomic group selected from the group consisting of a hydroxyl group, and the other of the two Si's is an alkoxy group or oxyalkylene group having a carbon number of 1 to 6, and is represented by -O-(C ｘ２ H ２ｘ２＋１ O ｙ２ ) (x2 is an integer of 2 or more and 6 or less, and y2 is an integer of 1 or more and 3 or less), a chloro group, and a hydroxyl group.

[0010] Another aspect of the present disclosure relates to a non-aqueous electrolyte secondary battery, which includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the negative electrode includes the negative electrode active material according to the present disclosure.

[0011] Another aspect of the present disclosure relates to a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery. The method includes a first step of contacting a compound or a liquid in which the compound is dissolved with silicon-containing active material particles, and a second step of reacting the compound with the active material particles while the compound or the liquid is in contact with the active material particles to form a siloxane bond, the compound having a structure represented by Si-R1-Si, where R1 is an atomic group having a chain portion containing at least one selected from the group consisting of sulfur atoms, oxygen atoms, and nitrogen atoms and an alkylene group as constituent elements, and one of the two Si atoms contains an alkoxy group or oxyalkylene group having a carbon number in the range of 1 to 6, and is represented by the formula -O-(C ｘ１ H ２ｘ１＋１ O ｙ１ ) (x1 is an integer of 2 or more and 6 or less, and y1 is an integer of 1 or more and 3 or less), a chloro group, and at least one atomic group selected from the group consisting of a hydroxyl group, and the other of the two Si's is an alkoxy group or oxyalkylene group having a carbon number of 1 to 6, and is represented by -O-(C ｘ２ H ２ｘ２＋１ O ｙ２ ) (x2 is an integer of 2 or more and 6 or less, and y2 is an integer of 1 or more and 3 or less), a chloro group, and a hydroxyl group.

[0012] According to the present disclosure, a negative electrode active material capable of forming a nonaqueous electrolyte secondary battery with a high capacity retention rate during charge / discharge cycles is obtained. Furthermore, according to the present disclosure, a nonaqueous electrolyte secondary battery using the negative electrode active material is obtained. While novel features of the present invention are set forth in the appended claims, the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0013] 1 is a partially cutaway plan view schematically illustrating the structure of a nonaqueous electrolyte secondary battery according to one embodiment of the present invention. 2 is a cross-sectional view taken along line XX' of the nonaqueous electrolyte secondary battery shown in FIG.

[0014] Hereinafter, embodiments according to the present disclosure will be described using examples, but the embodiments according to the present disclosure are not limited to the examples described below. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "numerical value A or more and numerical value B or less." In the following description, when a lower limit and an upper limit are exemplified for numerical values ​​of specific physical properties or conditions, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit.

[0015] (Negative Electrode Active Material for Non-Aqueous Electrolyte Secondary Battery) The negative electrode active material for a non-aqueous electrolyte secondary battery according to the present disclosure comprises silicon-containing active material particles and a surface layer formed on the surface of the active material particles. Hereinafter, the negative electrode active material and the surface layer may be referred to as "negative electrode active material (N)" and "surface layer (L)." The surface layer (L) contains a reaction product in which a predetermined compound has reacted to form a siloxane bond. Hereinafter, the compound may be referred to as "compound (1)." Compound (1) has a structure represented by Si-R1-Si. R1 is an atomic group having a chain portion containing, as constituent elements, at least one selected from the group consisting of a sulfur atom, an oxygen atom, and a nitrogen atom and an alkylene group. One of the two Si atoms has an alkoxy group or oxyalkylene group having a carbon number in the range of 1 to 6, and is represented by -O-(C ｘ１ H ２ｘ１＋１ O ｙ１ ) (x1 is an integer of 2 or more and 6 or less, and y1 is an integer of 1 or more and 3 or less), a chloro group, and a hydroxyl group. The other of the two Si has an alkoxy group or oxyalkylene group having a carbon number of 1 to 6, and is bonded to at least one atomic group selected from the group consisting of -O-(C ｘ２ H ２ｘ２＋１ O ｙ２ ) (x2 is an integer of 2 or more and 6 or less, and y2 is an integer of 1 or more and 3 or less), a chloro group, and a hydroxyl group.

[0016] The oxyalkylene group is —O—C ｘ H ２ｘ It is a group represented by -.ｘ１ H ２ｘ１＋１ O ｙ１ ) and a group represented by —O—(C ｘ２ H ２ｘ２＋１ O ｙ２ In the group represented by —O—(C), the oxygen atom of the oxyalkylene group is bonded to Si. Hereinafter, the term —O—(C) refers to an oxyalkylene group containing an oxygen atom bonded to Si. ｘ H ２ｘ＋１ O ｙ ) (where x is an integer of 2 or more and 6 or less, and y is an integer of 1 or more and 3 or less) is sometimes referred to as an "oxyalkyl group." In all oxyalkyl groups bonded to Si in compound (1), y (for example, y1, y2, and y6 described below) may be 1 or 2. Examples of oxyalkyl groups include -OC ｘ４ H ２ｘ４ -OC ｘ５ H ２ｘ５＋１ (x4 is an integer of 1 or more and 3 or less, and x5 is an integer of 1 or more and 3 or less), for example, —OCH ２ CH ２ OCH ３ These include:

[0017] The compound (1) may be a compound represented by the following formula (1):

[0018] [In formula (1), at least one selected from the group consisting of R2, R3, and R4 each independently contains an alkoxy group or an oxyalkylene group having 1 to 6 carbon atoms, and is —O—(C ｘ１ H ２ｘ１＋１ O ｙ１ ) (x1 is an integer of 2 or more and 6 or less, and y1 is an integer of 1 or more and 3 or less), a chloro group, or a hydroxyl group. At least one selected from the group consisting of R5, R6, and R7 each independently contains an alkoxy group or an oxyalkylene group having 1 to 6 carbon atoms, and is represented by —O—(C ｘ２ H ２ｘ２＋１ O ｙ２) (x2 is an integer of 2 or more and 6 or less, and y2 is an integer of 1 or more and 3 or less), a chloro group, or a hydroxyl group. The remainder of R2 to R7 are each independently a hydrocarbon group having 1 to 6 carbon atoms, a hydrogen atom, or a C ｘ３ H ２ｘ３＋ｙ３＋１ N ｙ３ O ｚ３ S ｗ３ (wherein x3 is an integer of 1 or more and 6 or less, y3 is an integer of 0 or more and 3 or less, z3 is an integer of 0 or more and 3 or less, and w3 is an integer of 0 or more and 3 or less, and 1≦y3+z3+w3). R2 to R7 may be the same or different.)

[0019] Examples of the hydrocarbon group having 1 to 6 carbon atoms include alkyl groups, alkenyl groups, and alkynyl groups having 1 to 6 carbon atoms. ｘ３ H ２ｘ３＋ｙ３＋１ N ｙ３ O ｚ３ S ｗ３ is not an alkoxy group having 1 to 6 carbon atoms and is not an alkoxy group having —O—(C ｘ１ H ２ｘ１＋１ O ｙ１ ) is not the above group represented by the formula (I). y3, Z3, and w3 may each independently be an integer of 0 to 2 or an integer of 0 to 1. The sum of y3, z3, and w3 may be in the range of 1 to 3, or in the range of 1 to 2. The sum of y3, z3, and w3 may be 1 or 2, and in one example, is 1. C ｘ３ H ２ｘ３＋ｙ３＋１ N ｙ３ O ｚ３ S ｗ３ Examples of the group represented by the formula: ｘ３ H ２ｘ３＋１ O ｙ３ C includes groups represented by the formula: C, alkylamino groups having 1 to 6 carbon atoms, and mercaptoalkyl groups having 1 to 6 carbon atoms. ｘ３ H ２ｘ３＋１ O ｙ３ The group represented by the formula (I) is bonded to Si via a carbon atom. ｘ３ H ２ｘ３＋１ O ｙ３Examples of the group represented by the formula (I) include a hydroxyalkyl group. The remaining R2 to R7 may each independently be a hydrocarbon group having 1 to 6 carbon atoms or a hydrogen atom.

[0020] In compound (1), the alkoxy group having 1 to 6 carbon atoms and the above-mentioned oxyalkylene group are collectively referred to as "an alkoxy group bonded to Si or an oxyalkylene group bonded to Si, and -O-(C ｘ６ H ２ｘ６＋１ O ｙ６ ) (x6 is an integer of 2 or more and 6 or less, and y6 is an integer of 0 or more and 3 or less)." Alternatively, the alkoxy group having 1 to 6 carbon atoms and the above-mentioned oxyalkylene group may be collectively read as "a group containing an alkoxy group and having 1 to 6 carbon atoms."

[0021] From another perspective, the surface layer formed on the surface of the active material particles contains a reaction product of compound (0) reacting to form a siloxane bond. Compound (0) is a compound containing two silicon atoms bonded to atomic groups capable of forming a siloxane bond upon reaction, and R1 connecting the two silicon atoms. The number of atomic groups bonded to one silicon atom ranges from 1 to 3, preferably 2, and more preferably 3. Examples of atomic groups capable of forming a siloxane bond upon reaction include alkoxy groups, hydroxyl groups, chloro groups, and the above-mentioned oxyalkyl groups. Hereinafter, alkoxy groups, hydroxyl groups, chloro groups, and the above-mentioned oxyalkyl groups having carbon atoms ranging from 1 to 6 may be collectively referred to as "atomic group (G)." Reactions to form siloxane bonds by reacting a compound having an alkoxysilyl group (e.g., hydrolysis / condensation reaction) are widely known. The R1 in compound (0) can be the same as the R1 exemplified for compound (1). Examples of compound (0) include at least some of the examples of compound (1).

[0022] Compound (0) and compound (1) may be commercially available compounds, or may be synthesized by a known synthesis method.

[0023] In a typical example of compound (1), the chain of the chain portion of R1, which connects the two silicon atoms, is composed of at least one atom selected from the group consisting of a sulfur atom, an oxygen atom, and a nitrogen atom, and a carbon atom in the alkylene group.

[0024] In the negative electrode active material (N) according to the present disclosure, the surface of the active material particles is protected by the reaction product of compound (1). At least a portion of compound (1) forms a siloxane bond with silicon in the active material particles. Compound (1) connects the silyl groups that form the siloxane bond via R1. Therefore, the two silyl groups form a siloxane bond with silicon in the active material particles, thereby protecting the surface of the active material particles. Because the reaction product of compound (1) contains the R1 moiety, it flexibly follows the expansion and contraction of the active material particles accompanying charge and discharge, and the surface protection layer is less likely to be damaged even when the active material particles repeatedly expand and contract during charge and discharge cycles. Therefore, according to the present disclosure, side reactions between the active material particle surface and components in the electrolyte can be suppressed. As a result, according to the present disclosure, the capacity retention rate during charge and discharge cycles can be increased.

[0025] Among R2 to R7, those that are not the above-mentioned atomic group (G) may each independently be the above-mentioned groups. Specifically, among R2 to R7, those that are not the above-mentioned atomic group (G) may each independently be a hydrocarbon group having 1 to 6 carbon atoms, a hydrogen atom, or a group represented by the above formula C ｘ３ H ２ｘ３＋ｙ３＋１ N ｙ３ O ｚ３ S ｗ３ It may also be a group represented by the following formula:

[0026] Formula (1) preferably satisfies the following condition (V1) or (V2), and more preferably may satisfy the following condition (V3) or (V4). Formula (1) may also satisfy the following condition (V5) or (V6). (V1) Each of R2 to R7 contains 4 or less carbon atoms. (V2) At least two selected from the group consisting of R2, R3, and R4 are alkoxy groups having 1 to 4 carbon atoms, and at least two selected from the group consisting of R5, R6, and R7 are alkoxy groups having 1 to 4 carbon atoms. Of R2 to R7, those that are not alkoxy groups having 1 to 4 carbon atoms are hydrocarbon groups (alkyl groups, alkenyl groups, alkynyl groups) having 1 to 6 carbon atoms, or hydrogen atoms. (V3) All of R2 to R7 are alkoxy groups having 1 to 4 carbon atoms (e.g., 1 to 3 carbon atoms). (V4) All of R2 to R7 are independently methoxy groups or ethoxy groups. R2 to R7 may be methoxy groups or ethoxy groups. For example, all of R2 to R7 may be methoxy groups, or all of R2 to R7 may be ethoxy groups. (V5) In condition (V2), all occurrences of "the number of carbon atoms is in the range of 1 to 4" are replaced with "the number of carbon atoms is in the range of 1 to 3". (V6) In condition (V2), all occurrences of "the number of carbon atoms is in the range of 1 to 4" are replaced with "the number of carbon atoms is 1 or 2".

[0027] A preferred example of formula (1) satisfies any of the above conditions (V1) to (V6) and satisfies the following condition (W1). A preferred example of formula (1) satisfies any of the above conditions (V1) to (V6) and satisfies condition (W2) or (W3). In these cases, formula (1) may further satisfy condition (W4) or (W5). (W1) R1 is an atomic group including a chain portion formed of at least one selected from the group consisting of a sulfur atom, an oxygen atom, and a nitrogen atom, and an alkylene group. (W2) R1 includes a chain portion formed of at least one heteroatom selected from the group consisting of a sulfur atom, an oxygen atom, and a nitrogen atom, and two alkylene groups forming the chain portion so as to sandwich the at least one heteroatom. The two alkylene groups each independently have 2 to 4 carbon atoms. The two alkylene groups may be directly bonded to the heteroatom. (W3) R1 is not an atomic group including -(CH ２ ) ｐ S ｎ (CH ２ ) ｑ -(1≦n≦6, 2≦p≦4, 2≦q≦4), -(CH ２ ) ｐ O (CH ２ ) ｑ -(2≦p≦4, 2≦q≦4), -(CH ２ ) ｐ O (CH ２ ) ｒ O (CH ２ ) ｑ -(2≦p≦4, 2≦q≦4, 2≦r≦4), and -(CH ２ ) ｐ NH (CH ２ ) ｑ-(2≦p≦4, 2≦q≦4). In this case, p=q=3 may be satisfied, and r may be 2 or 3. Note that n, p, q, and r are each natural numbers. (W4) In condition (W1) or (W2), the number of atoms constituting the chain portion of the chain moiety is 2 or more, 3 or more, 5 or more, or 6 or more, and 20 or less, 15 or less, or 10 or less. For example, the number of atoms may be in the range of 3 to 20, 3 to 15, or 3 to 10. The lower limit of these ranges may be replaced with 5 or 6. Here, the number of atoms constituting the chain portion of the chain moiety refers only to the number of atoms constituting the chain connecting two silicon atoms. For example, in the case of an alkylene group, only the number of carbon atoms constituting the chain is counted. (W5) In condition (W1), (W2), or (W4), R1 is a straight chain containing no branched chains.

[0028] The greater the number of alkoxy groups contained in formula (1), the more easily a three-dimensional network is formed by the reaction of compounds (1) with each other. Part of this network bonds with silicon present on the surface of the negative electrode active material particles. Even when a three-dimensional network is formed, the R1 moiety is present in the network, so the formed network is thought to have high flexibility. It is thought that the formation of a highly flexible three-dimensional network can produce a greater effect.

[0029] When R1 contains at least one heteroatom selected from the group consisting of a sulfur atom, an oxygen atom, and a nitrogen atom, the ion coordination ability of the heteroatom is thought to cause lithium ions to dissociate as carrier ions from the lithium salt in the electrolyte solution, thereby promoting lithium ion conduction in the surface layer, which is thought to reduce the inhibition of lithium ion exchange between the active material and the electrolyte during charge and discharge.

[0030] When R1 contains a nitrogen atom, R1 may contain an amide bond. When formula (1) satisfies condition (W1), compound (1) represented by formula (1) may be a sulfide, an ether, or an amine.

[0031] The mass of the reaction product of compound (1) contained in the surface layer may be in the range of 0.001% to 10% (e.g., 0.05% to 1%) of the mass of the active material particles. This proportion may be determined by ICP analysis or the like.

[0032] The reaction product may have a chemical structure in which Si in the Si-R1-Si structure is bonded to Si in the active material particles by a siloxane bond. That is, the surface layer (L) may include a chemical structure (reaction product of compound (1)) in which Si in a plurality of Si-R1-Si structures is bonded to Si in the active material particles by a siloxane bond. The reaction product may have a structure in which Si in a plurality of Si-R1-Si structures is bonded to each other and to Si in the active material particles by a siloxane bond. That is, the surface layer (L) may include a chemical structure (reaction product of compound (1)) in which Si in a plurality of Si-R1-Si structures is bonded to each other and to Si in the active material particles by a siloxane bond.

[0033] (Compound (1) in which the chain portion of R1 contains sulfur) In compound (1) (for example, a compound represented by formula (1)), the chain portion of R1 may contain sulfur. For example, compound (1) may be a bis(alkoxysilylalkyl)sulfide. An example of compound (1) in which the chain portion of R1 contains sulfur will be described below. R1 is C ｔ１ H ２ｔ１ S ｚ where t1 and z are each an integer of 1 or more. At least one of R2 to R4 is at least one selected from the group consisting of an alkoxy group having 1 to 6 carbon atoms, the above-mentioned alkyloxy group, a hydroxyl group, and a chloro group. At least one of R5 to R7 is at least one selected from the group consisting of an alkoxy group having 1 to 6 carbon atoms, the above-mentioned alkyloxy group, a hydroxyl group, and a chloro group. The remaining R2 to R7 may each independently be the above-mentioned groups. Specifically, of R2 to R7, those that are not the above-mentioned atomic group (G) each independently are a hydrocarbon group having 1 to 6 carbon atoms, a hydrogen atom, or a group represented by the above formula C ｘ３ H ２ｘ３＋ｙ３＋１ N ｙ３ O ｚ３ Sｗ３ It may be a group represented by the following formula:

[0034] The atomic group (G) included in R2 to R4 and R5 to R7 can form an X-O-Si-R1 bond with the surface of a silicon-containing material, and the surface of the silicon-containing material can be covered with a Si-R1-Si structure having stable siloxane bonds at both ends. That is, the surface of the silicon-containing material can be covered with a coating containing a bissilyl sulfide structure (a coating formed from the reaction product of compound (1), hereinafter sometimes referred to as an "SSS coating").

[0035] In formula (1), C ｔ１ H ２ｔ１ S ｚ The sulfide group (R1) represented by R11-S ｚ The compound may have a structure represented by —R12, where R11 and R12 are each independently an alkylene group having one or more carbon atoms. Such an R1 has excellent flexibility and is also suitable for S ｚ It is believed that the electron shielding effect due to the structure is high, and the effect of suppressing side reactions is greater.

[0036] The greater the number of carbon atoms in R11 and R12, the greater the flexibility, and therefore the easier the reversible deformation of the SSS coating. However, if the number of carbon atoms in R11 and R12 is excessively large, the alkylene chain becomes too long, which reduces the density of the SSS coating and the effect of suppressing side reactions. Therefore, it is desirable that the number of carbon atoms in R11 and R12 be 1 to 6, and more desirably 2 to 4. Bis(alkoxysilyl alkyl) sulfides are bis(alkoxysilyl C １－６ alkyl) sulfide, and bis(alkoxysilyl C ２－４ It may also be a sulfide.

[0037] In addition, S constituting R1 ｚ The more consecutive sulfur groups there are, the more flexible the SSS coating is, facilitating reversible deformation of the SSS coating. However, if the number of sulfur groups is too large, the density of the SSS coating decreases and the S ｚ The group itself may cause side reactions. ｚThe number of sulfur atoms in the group is preferably 1 to 6, and more preferably 2 to 4. That is, the bis(alkoxysilyl alkyl) sulfide is a bis(alkoxysilyl C １－６ Alkyl)S １－６ It is preferably a sulfide, and bis(alkoxysilyl C ２－４ Alkyl)S ２－４ It may also be a sulfide.

[0038] R2 to R7 have been described above, so redundant explanations will be omitted. From the viewpoint of increasing the reactivity with the surface of the silicon-containing material, the alkoxy group may have 1 to 3 carbon atoms, and the oxyalkyl group may have 2 to 3 carbon atoms.

[0039] The rest of R2 to R7 may be the above-mentioned groups. Specifically, among R2 to R7, those that are not the above-mentioned atomic group (G) are each independently a hydrocarbon group having 1 to 6 carbon atoms, a hydrogen atom, or a group represented by the above formula C ｘ３ H ２ｘ３＋ｙ３＋１ N ｙ３ O ｚ３ S ｗ３ From the viewpoint of reducing steric hindrance during the reaction, it may have 1 to 3 carbon atoms. R2 to R4 are each independent, and R2 to R4 may all have the same number of carbon atoms, or may all have different numbers of carbon atoms, or two of R2 to R4 may have the same number of carbon atoms. Similarly, R5 to R7 are each independent, and R5 to R7 may all have the same number of carbon atoms, or may all have different numbers of carbon atoms, or two of R5 to R7 may have the same number of carbon atoms.

[0040] The two alkoxysilyl groups (RRRSi- or RRRSi-) linked to R1 may be the same or different, although the two alkoxysilyl groups linked to R1 may have the same structure in order to increase the symmetry of the SSS coating structure and make it more stable.

[0041] Bis(trialkoxysilyl C １－６ Alkyl)S １－６Among sulfides, at least one selected from the group consisting of bis(triethoxysilylpropyl) sulfide, bis(triethoxysilylpropyl) disulfide, bis(triethoxysilylpropyl) trisulfide, and bis(triethoxysilylpropyl) tetrasulfide can be easily obtained. Bis(triethoxysilylpropyl) tetrasulfide (TESPT, also known as bis[3-(triethoxysilyl)propyl]tetrasulfide) is shown below. These may be commercially available products or may be synthesized by known methods.

[0042]

[0043] (Compound (1) in which the chain portion of R1 contains nitrogen) In compound (1) (e.g., a compound represented by formula (1)), the chain portion of R1 may contain nitrogen. For example, compound (1) may be a bis(alkoxysilylalkyl)amine. In the case where the chain portion of R1 contains nitrogen, the compound (1) is the same as the compound (1) in which S is mentioned above in the description of compound (1) in which the chain portion of R1 contains sulfur. ｚ The compound may be a compound in which the nitrogen atom is replaced with a secondary amino group (—NH—) or a tertiary amino group. In the case of a tertiary amino group, examples of the side chain bonded to the nitrogen atom include an alkyl group and an alkoxysilylalkyl group. An example of a bis(alkoxysilylalkyl)amine is shown below. These may be commercially available products or may be synthesized by known methods.

[0044]

[0045] The amino group constituting R1 may have a structure represented by R11-N-R12, where R11 and R12 are each independently an alkylene group having one or more carbon atoms. Such an R1 is thought to have excellent flexibility and high electron shielding properties, thereby further enhancing the effect of suppressing side reactions.

[0046] The greater the number of carbon atoms in the amino group, the more flexible it is, facilitating the reversible deformation of the coating film formed from the reaction product of compound (1). However, if the number of carbon atoms in the amino group is excessively large, R1 becomes too long, which is thought to reduce the density of the coating film and reduce the effect of suppressing side reactions. Therefore, the number of carbon atoms in the alkylene group is preferably 1 to 6, and more preferably 2 to 4. For example, bis(alkoxysilylalkyl)amines are prepared by adding bis(alkoxysilyl C １－６ alkyl)amine, and bis(alkoxysilyl C ２－４ It may also be a (alkyl)amine.

[0047] (Compound (1) in which the chain portion of R1 contains an amide bond) The compound (1) in which the chain portion of R1 contains an amide bond is the same as the compound (1) in which the chain portion of R1 contains sulfur, except that S ｚ The compound may be a compound in which the group is replaced with an amide group.

[0048] (Compound (1) in which the chain portion of R1 contains an ether bond) In compound (1) (e.g., a compound represented by formula (1)), the chain portion of R1 may contain an ether bond. In this case, compound (1) may be a compound in which R1 in the above description of compound (1) in which the chain portion of R1 contains sulfur is replaced with an atomic group containing an ether bond.

[0049] When R1 of the compound (1) contains an ether bond, R1 in the formula (1) is R11-(O-R12) ｎThe (O-R12) unit may have a structure represented by the formula: —O—R13. Here, R11, R12, and R13 are each independently an alkylene group having 1 or more carbon atoms, and n is an integer of 0 or more. Such an R1 has excellent flexibility, and the oxygen bonding R11 and R12 and the oxygen bonding R12 and R13 coordinate to cations, thereby promoting the movement of cations into and out of the silicon-containing material. This is thought to increase the cationic conductivity and further enhance the effect of suppressing a decrease in capacity retention. Note that when n is 2 or more, the multiple R12s contained in the (O-R12) unit may all be the same alkylene group, or may contain alkylene groups with different numbers of carbon atoms.

[0050] The greater the number of carbon atoms in R11 and R13, the more flexible the coating formed from the reaction product of compound (1), and the easier it is to reversibly deform the coating. However, if the number of carbon atoms in R11 and R13 is excessively large, the alkylene chain becomes too long, which is thought to reduce the density of the coating and the effect of suppressing side reactions. Therefore, it is desirable that the number of carbon atoms in R11 and R13 be 1 to 6, and more desirably 2 to 4. Bis(alkoxysilyl alkyl) ethers are bis(alkoxysilyl C １－６ alkyl) ether, and bis(alkoxysilyl C ２－４ It may also be an alkyl ether.

[0051] Furthermore, the —O— groups constituting R1 increase cationic conductivity and contribute to improving the capacity retention rate. However, since an excessively large number of —O— groups reduces the denseness of the coating film, the number of —O— groups is preferably 1 to 5, and more preferably 1 to 3. That is, the number n of (O-R12) units contained in the above R1 is preferably 0 to 4, and more preferably 0 to 2.

[0052] On the other hand, the number of carbon atoms in R12 is preferably 4 or less, more preferably 2 or more and 4 or less, from the viewpoint of promoting the transfer of cations between adjacent oxygen atoms.

[0053] R1 is -C ３ H ６ -O-C ３ H ６ -or-C２ H ４ -O-C ２ H ４ -O-C ３ H ６ Each of R2 to R7 may be a methoxy group.

[0054] Specific examples of desirable alkoxysilyl compounds include bis(alkoxysilylalkyl) ethers represented by the following formula:

[0055]

[0056]

[0057] The surface layer (L) of the negative electrode active material (N) may contain conductive carbon. In this case, it is preferable that formula (1) satisfies the above-mentioned condition (V2) or (V5). Active materials containing silicon have low conductivity and are prone to capacity loss during charge-discharge cycling. By disposing conductive carbon on the surface of the active material, capacity loss during charge-discharge cycling can be suppressed. However, simply disposing conductive carbon on the surface reduces adhesion between the active material and the conductive carbon due to expansion and contraction of the active material during charge-discharge cycling, resulting in reduced conductivity between them. In contrast, by including the surface layer (L) in the reaction product of compound (1) and conductive carbon, the charge-discharge efficiency of the silicon-containing negative electrode active material can be significantly improved. This may be due to the network formed by the reaction product of compound (1), which maintains adhesion between the active material and the conductive carbon.

[0058] Examples of conductive carbon that can be used include amorphous carbon, graphite, easily graphitized carbon (soft carbon), and hardly graphitized carbon (hard carbon). Among these, amorphous carbon is preferred because it is easy to form a thin conductive layer that covers the surface of the composite particles. Examples of amorphous carbon include carbon black, burned pitch, coke, and activated carbon. Examples of graphite include natural graphite, artificial graphite, and graphitized mesophase carbon.

[0059] (Active material particles) The active material particles contain silicon (silicon element). Materials containing silicon are sometimes treated as a type of alloy material. Here, alloy material refers to a material containing an element capable of forming an alloy with lithium. Examples of elements capable of forming an alloy with lithium include silicon and tin, with silicon (Si) being particularly promising. There are no limitations on the method for producing the active material particles. The active material particles may be produced by a known method, or commercially available particles may be used.

[0060] The silicon-containing material may be a silicon alloy, a silicon compound, or a composite material. Among these, a composite material containing a lithium ion conductive phase and silicon particles dispersed in the lithium ion conductive phase is particularly promising. Examples of the lithium ion conductive phase that can be used include a silicon oxide phase, a silicate phase, and a carbon phase. The silicon oxide phase is a material with a relatively high irreversible capacity. On the other hand, the silicate phase is preferred because it has a low irreversible capacity.

[0061] The main component of the silicon oxide phase (for example, 95 to 100 mass %) may be silicon dioxide. The composition of the composite material containing the silicon oxide phase and silicon particles dispersed therein is generally SiO ｘ SiOx is a material in which silicon particles are amorphous SiO ２ The oxygen content ratio x to silicon is, for example, 0.5≦x<2.0, and more preferably 0.8≦x≦1.5.

[0062] The silicate phase may contain, for example, at least one element selected from the group consisting of Group 1 and Group 2 elements of the long periodic table. Examples of Group 1 elements of the long periodic table and Group 2 elements of the long periodic table include lithium (Li), potassium (K), sodium (Na), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Other elements may include aluminum (Al), boron (B), lanthanum (La), phosphorus (P), zirconium (Zr), and titanium (Ti). Among these, a silicate phase containing lithium (hereinafter also referred to as a lithium silicate phase) is preferred due to its small irreversible capacity and high initial charge / discharge efficiency.

[0063] The lithium silicate phase may be an oxide phase containing lithium (Li), silicon (Si), and oxygen (O), and may contain other elements. The atomic ratio of O to Si in the lithium silicate phase, O / Si, is, for example, greater than 2 and less than 4. Preferably, O / Si is greater than 2 and less than 3. The atomic ratio of Li to Si in the lithium silicate phase, Li / Si, is, for example, greater than 0 and less than 4. The lithium silicate phase has the formula: Li ２ｚ SiO ２＋ｚ (0<z<2). Preferably, z satisfies the relationship 0<z<1, and more preferably z=1 / 2. Examples of elements other than Li, Si, and O that can be contained in the lithium silicate phase include iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), and aluminum (Al).

[0064] The carbon phase may be composed of, for example, amorphous carbon with low crystallinity (i.e., amorphous carbon). The amorphous carbon may be, for example, hard carbon, soft carbon, or other.

[0065] The active material particles (N) and the negative electrode mixture layer may each contain, in addition to a material containing silicon element, a material that electrochemically absorbs and desorbs lithium ions, lithium metal, a lithium alloy, etc. As the material that electrochemically absorbs and desorbs lithium ions, a carbon material is preferred. Examples of the carbon material include graphite, easily graphitized carbon (soft carbon), and hardly graphitized carbon (hard carbon). Among them, graphite is preferred because of its excellent charge / discharge stability and low irreversible capacity.

[0066] The active material particles are Li ｘ SiO ｙ The composite particles may be those containing a lithium silicate phase represented by (0<x≦4, 0<y≦4) and a silicon phase dispersed in the lithium silicate phase. Note that x and y are unrelated to x and y in compound (1). Such composite particles may be produced, for example, by a method described in the Examples, or may be produced by a known method. The crystallite size of the silicon phase may be in the range of 1 nm to 1000 nm (for example, in the range of 200 nm to 500 nm).

[0067] The crystallite size of the silicon phase is calculated by Scherrer's formula from the half-width of the diffraction peak attributable to the (111) plane of the silicon phase (simple element Si) in the X-ray diffraction pattern.

[0068] The active material particles may be composite particles containing a carbon phase and a silicon phase dispersed within the carbon phase. The carbon phase may be composed of, for example, amorphous carbon. The amorphous carbon may be, for example, hard carbon, soft carbon, or other. Amorphous carbon generally refers to a carbon material in which the average interplanar spacing d002 of the (002) plane measured by X-ray diffraction exceeds 0.34 nm.

[0069] (Method for producing negative electrode active material (N)) The production method according to the present disclosure is a method for producing the negative electrode active material (N) for a non-aqueous electrolyte secondary battery according to the present disclosure. However, the negative electrode active material (N) may be produced by a method other than the method described below. The matters described for the negative electrode active material (N) can be applied to the production method below, and therefore, redundant explanations may be omitted. The matters described for the production method below can also be applied to the negative electrode active material according to the present disclosure.

[0070] This production method includes a first step and a second step, in this order. The first and second steps are carried out under conditions in which compound (1) forms a siloxane bond. The first and second steps may be carried out under conditions similar to those in which a known silane coupling agent containing an alkoxysilyl group undergoes hydrolysis and condensation to form a siloxane bond.

[0071] (First Step) The first step is a step of bringing compound (1) or a liquid in which compound (1) is dissolved into contact with silicon-containing active material particles. Hereinafter, this liquid may be referred to as "liquid (S)." The first step may be a step of dispersing silicon-containing active material particles in compound (1) or liquid (S). Alternatively, the first step may be a step of applying compound (1) or liquid (S) to the surface of silicon-containing active material particles.

[0072] The compound (1) is the above-described compound and is represented by formula (1). The active material particles are the above-described active material particles. The liquid (S) can be prepared by dissolving the compound (1) in a solvent. Note that, before the second step is performed, a portion of the compound (1) may have reacted to form a siloxane bond. The solvent may contain a lower alcohol (e.g., ethanol), water, and an acid. Examples of the acid include hydrochloric acid.

[0073] The content of the reaction product of compound (1) in the negative electrode active material (N) can be changed by changing the concentration of compound (1) in the liquid (S). The concentration of compound (1) in the liquid (S) may be in the range of 0.0001 to 10 mol / L (e.g., 0.001 to 0.1 mol / L). The mass of compound (1) per 1 g of the mass of the active material particles dispersed in the liquid (S) may be in the range of 0.0001 to 1 g (e.g., 0.001 to 0.1 g).

[0074] (Second Step) The second step is a step of reacting compound (1) with the active material particles in a state where compound (1) or liquid (S) is in contact with the active material particles to form siloxane bonds. The second step may be carried out, for example, by maintaining the liquid (S) and the active material particles at a predetermined temperature for a predetermined period of time. When the active material particles are dispersed in the liquid (S), the liquid (S) may be stirred in the second step. The predetermined temperature may be in the range of 10 to 200°C (e.g., in the range of 40 to 100°C). The predetermined time may be in the range of 1 to 120 hours (e.g., in the range of 12 to 72 hours).

[0075] The second step yields the negative electrode active material (N). The negative electrode active material (N) obtained in the second step may be washed and / or dried as necessary.

[0076] The production method according to the present disclosure may include step (a) of disposing conductive carbon on the surface of the active material particles before step 1, between step 1 and step 2, or after step 2. By performing step (a), a surface layer (L) containing the reaction product of compound (1) and conductive carbon can be formed.

[0077] Step (a) may be performed by heat-treating a mixture of active material particles and conductive carbon. Examples of materials that can be used for the conductive carbon include coal pitch, coal tar pitch, petroleum pitch, and phenolic resin. The heat treatment may be performed by heating at a temperature of 450 to 1000°C for 1 to 10 hours. The conductive carbon may be any of the conductive carbons described above. Alternatively, step (a) may involve forming a conductive carbon layer by reacting a hydrocarbon gas on the surface of the composite particles using a gas-phase method such as CVD. Examples of hydrocarbon gases that can be used include acetylene and methane. These methods can form a conductive layer that can be infiltrated by the reaction product of compound (1).

[0078] (Negative electrode for non-aqueous electrolyte secondary battery) The present disclosure provides a negative electrode for a non-aqueous electrolyte secondary battery. The negative electrode includes a negative electrode active material (N) according to the present disclosure.

[0079] (Non-aqueous electrolyte secondary battery) A non-aqueous electrolyte secondary battery according to the present disclosure includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode includes a negative electrode active material (N). The configuration other than the negative electrode is not particularly limited, and known configurations used in non-aqueous electrolyte secondary batteries may be applied. Except for the inclusion of the negative electrode active material (N), the configuration of the negative electrode is not particularly limited. Known components of negative electrodes for non-aqueous electrolyte secondary batteries may be applied as components of the negative electrode other than the negative electrode active material (N). An example of a negative electrode according to the present disclosure includes a negative electrode current collector and a negative electrode mixture layer disposed on the surface of the negative electrode current collector. Except for the use of the negative electrode active material (N), the method for manufacturing a non-aqueous electrolyte secondary battery according to the present disclosure is not particularly limited, and the battery may be manufactured by a known method.

[0080] An example of the configuration of a nonaqueous electrolyte secondary battery according to the present disclosure will be described below. However, except for the use of the negative electrode active material (N), the configuration of the nonaqueous electrolyte secondary battery is not limited to the following configuration.

[0081] (Negative Electrode) The negative electrode includes, for example, a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector. The negative electrode mixture layer includes a negative electrode active material (N) as an essential component, and may include optional components such as a binder, a conductive material, and a thickener. The negative electrode mixture layer may include, in addition to the negative electrode active material (N), an active material for the negative electrode other than the negative electrode active material (N). Known materials can be used for the optional components such as the binder, the conductive material, and the thickener.

[0082] The negative electrode mixture layer can be formed, for example, by applying a negative electrode slurry, in which a negative electrode mixture containing the negative electrode active material (N) and predetermined optional components is dispersed in a dispersion medium, to the surface of the negative electrode current collector and drying the resulting coating. The dried coating may be rolled as necessary. The negative electrode mixture layer may be formed on one surface or both surfaces of the negative electrode current collector.

[0083] The negative electrode current collector may be, for example, a metal sheet or a metal foil, and examples of the material for the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, and copper alloy.

[0084] (Positive Electrode) The positive electrode includes, for example, a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector. The positive electrode mixture layer includes a positive electrode active material as an essential component, and may include optional components such as a binder, a conductive material, and a thickener. Known materials can be used for the optional components such as the binder, the conductive material, and the thickener.

[0085] The positive electrode mixture layer can be formed, for example, by applying a positive electrode slurry, in which a positive electrode mixture containing a positive electrode active material and predetermined optional components is dispersed in a dispersion medium, to the surface of the positive electrode current collector and drying the applied film. The dried coating may be rolled as necessary. The positive electrode mixture layer may be formed on one surface or both surfaces of the positive electrode current collector.

[0086] As the positive electrode active material, for example, a lithium-containing composite oxide can be used. ａ CoO ２ , Li ａ NiO ２ , Li ａ MnO ２ , Li ａ Co ｂ Ni １－ｂ O２ , Li ａ Co ｂ Me １－ｂ O ｃ , Li ａ Ni １－ｂ Me ｂ O ｃ , Li ａ Mn ２ O ４ , Li ａ Mn ２－ｂ Me ｂ O ４ , LiMePO ４ , Li ２ MeP.O. ４ F (Me is at least one selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B). Here, a = 0 to 1.2, b = 0 to 0.9, and c = 2.0 to 2.3. The value a, which indicates the molar ratio of lithium, increases or decreases with charge and discharge.

[0087] Among them, Li ａ Ni ｂ Me １－ｂ O ２ (Me is at least one selected from the group consisting of Mn, Co, and Al, and 0<a≦1.2, and 0.3≦b≦1) is preferred. From the viewpoint of increasing capacity, it is more preferred that 0.85≦b<1 is satisfied. From the viewpoint of stability of the crystal structure, Li-nickel composite oxides containing Co and Al as Me are preferred. ａ Ni ｂ Co ｃ Al ｄ O ２ (0<a≦1.2, 0.85≦b<1, 0<c<0.15, 0<d≦0.1, b+c+d=1) is more preferable.

[0088] Positive electrode active materials (especially lithium-containing composite oxides) usually have the form of secondary particles formed by aggregation of primary particles. The average particle diameter of the positive electrode active material may be, for example, 2 μm or more and 20 μm or less. Here, the average particle diameter refers to the median diameter at which the cumulative volume in the volume-based particle size distribution is 50%. The volume-based particle size distribution can be measured using a laser diffraction particle size distribution measuring device.

[0089] The positive electrode current collector may be, for example, a metal sheet or a metal foil, and may be made of, for example, stainless steel, aluminum, an aluminum alloy, or titanium.

[0090] Examples of the conductive material used in the positive electrode mixture layer and the negative electrode mixture layer include carbon materials such as carbon black (CB), acetylene black (AB), ketjen black (KB), carbon nanotubes (CNT), graphite, etc. These may be used alone or in combination of two or more.

[0091] Examples of binders used in the positive electrode mixture layer and the negative electrode mixture layer include fluororesins (polytetrafluoroethylene, polyvinylidene fluoride, etc.), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. These may be used alone or in combination of two or more.

[0092] (Separator) Non-aqueous electrolyte secondary batteries typically include a separator disposed between the positive electrode and the negative electrode. The separator has high ion permeability and adequate mechanical strength and insulating properties. Examples of separator materials include microporous membranes, woven fabrics, and nonwoven fabrics. Examples of separator materials include polyolefins (polypropylene, polyethylene, etc.).

[0093] (Non-aqueous electrolyte) The non-aqueous electrolyte (or non-aqueous electrolyte solution from another perspective) contains a non-aqueous solvent and a salt (solute) dissolved in the non-aqueous solvent. The salt (solute) is an electrolyte salt that ionically dissociates in the non-aqueous solvent. When the non-aqueous electrolyte is used in a lithium ion secondary battery, the salt contains at least a lithium salt. The non-aqueous electrolyte may contain additives other than the non-aqueous solvent and the salt. For example, the non-aqueous electrolyte may contain compound (1) and / or a reaction product of compound (1).

[0094] Examples of non-aqueous solvents that can be used include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and chain carboxylic acid esters. Examples of cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC). Examples of chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP). One type of non-aqueous solvent may be used alone, or two or more types may be used in combination.

[0095] Among these, chain carboxylic acid esters are suitable for preparing a low-viscosity nonaqueous electrolyte solution. Therefore, the nonaqueous electrolyte solution may contain 1 mass % or more and 90 mass % or less of the chain carboxylic acid ester. Among the chain carboxylic acid esters, methyl acetate has a particularly low viscosity. Therefore, 90 mass % or more of the chain carboxylic acid ester may be methyl acetate.

[0096] Other examples of the non-aqueous solvent include cyclic ethers, chain ethers, nitriles such as acetonitrile, and amides such as dimethylformamide.

[0097] Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, and crown ethers.

[0098] Examples of chain ethers include 1,2-dimethoxyethane, dimethyl ether, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0099] These solvents may be fluorinated solvents in which some of the hydrogen atoms are substituted with fluorine atoms, such as fluoroethylene carbonate (FEC).

[0100] Examples of the lithium salt include lithium salts of chlorine-containing acids (LiClO ４ , LiAlCl ４ , LiB １０ Cl １０ etc.), lithium salts of fluorine-containing acids (LiPF ６ , LiPF ２ O ２ , LiBF ４ , LiSbF ６ , LiAsF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ etc.), lithium salt of fluorine-containing acid imide (LiN(FSO ２ ) ２ , LiN(CF ３ SO ２ ) ２ , LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ ), LiN(C ２ F５ SO ２ ) ２ Lithium salts such as lithium halides (LiCl, LiBr, LiI, etc.) can be used. One type of lithium salt can be used alone, or two or more types can be used in combination.

[0101] The concentration of the lithium salt in the non-aqueous electrolyte may be 0.5 mol / L or more and 2 mol / L or less, or may be 1 mol / L or more and 1.5 mol / L or less. By controlling the lithium salt concentration within the above range, a non-aqueous electrolyte having excellent ionic conductivity and low viscosity can be obtained.

[0102] Examples of additives include 1,3-propane sultone, methylbenzenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, and fluorobenzene.

[0103] An example of a nonaqueous electrolyte secondary battery includes an outer casing, an electrode group, and a nonaqueous electrolyte housed in the outer casing. The electrode group may be a wound electrode group formed by winding a positive electrode and a negative electrode with a separator interposed therebetween. Alternatively, an electrode group of another form may be used instead of the wound electrode group. For example, the electrode group may be a laminated electrode group formed by stacking a positive electrode and a negative electrode with a separator interposed therebetween. The nonaqueous electrolyte secondary battery may be in any form, such as a cylindrical type, a prismatic type, a coin type, a button type, or a sheet type (laminate type).

[0104] A nonaqueous electrolyte secondary battery according to one embodiment of the present invention will be described below with reference to Figures 1 and 2. Figure 1 is a partially cutaway plan view schematically showing an example of the structure of a nonaqueous electrolyte secondary battery. Figure 2 is a cross-sectional view taken along line XX' in Figure 1.

[0105] As shown in FIGS. 1 and 2, the nonaqueous electrolyte secondary battery 100 is a sheet-type battery, and includes an electrode plate group 4 and an exterior case 5 that houses the electrode plate group 4.

[0106] The electrode plate group 4 has a structure in which a positive electrode 10, a separator 30, and a negative electrode 20 are stacked in this order, with the positive electrode 10 and the negative electrode 20 facing each other with the separator 30 interposed therebetween, thereby forming the electrode plate group 4. The electrode plate group 4 is impregnated with a non-aqueous electrolyte (not shown).

[0107] The positive electrode 10 includes a positive electrode active material layer 1a and a positive electrode current collector 1b. The positive electrode active material layer 1a is formed on the surface of the positive electrode current collector 1b.

[0108] The negative electrode 20 includes a negative electrode mixture layer 2 a and a negative electrode current collector 2 b. The negative electrode mixture layer 2 a is formed on the surface of the negative electrode current collector 2 b. The negative electrode mixture layer 2 a includes the negative electrode active material (N) according to the present disclosure.

[0109] A positive electrode tab lead 1c is connected to the positive electrode current collector 1b, and a negative electrode tab lead 2c is connected to the negative electrode current collector 2b. The positive electrode tab lead 1c and the negative electrode tab lead 2c each extend to the outside of the outer case 5.

[0110] The positive electrode tab lead 1c and the outer case 5, and the negative electrode tab lead 2c and the outer case 5 are insulated from each other by insulating tab films 6, respectively.

[0111] (Example of a method for synthesizing compound (1) in which the chain portion of R1 contains oxygen) An example of compound (1) in which the chain portion of R1 contains oxygen may be synthesized by the following method. First, 1.0 g of allyl ether and dichloroethane (C ２ H ４ Cl ２ ) 40.0 mL, trimethoxysilane (HSi(OMe) ３ ) 3.7 g, cyclooctadiene iridium chloride dimer ([Ir(COD)Cl] ２ ) was added and stirred, allowing the reaction shown in the following formula to proceed. The mixture was heated and stirred from room temperature to 50°C until the raw material allyl ether was consumed. After confirming that the raw material had been consumed, heating and stirring were stopped. Next, dichloroethane (solvent) was distilled off from the reaction mixture using an evaporator, yielding brown oil K1 (4.0 g) as a crude product containing alkoxysilyl compound A.

[0112]

[0113] Next, 5.0 g of allyl ether and dichloroethane (C ２ H ４ Cl ２ ) 200 mL, trimethoxysilane (HSi(OMe) ３ ) 18.6 g, cyclooctadiene iridium chloride dimer ([Ir(COD)Cl] ２ ) was added, and the mixture was heated and stirred from room temperature to 50°C. After confirming that the raw materials had disappeared, heating and stirring were stopped. Next, dichloroethane (solvent) was distilled off from the reaction solution using a vacuum pump. Brown oil K1 was added to the crude product after distillation, and distillation purification was carried out using a distillation purification apparatus connected to a flask, a T-shaped tube, a thermometer, a condenser, a vacuum pump, and a pressure gauge at an oil bath temperature of 190°C and a vacuum of 0.1-0.01 mmHg, to obtain brown oil K2 (9.3 g) containing alkoxysilyl compound A.

[0114] Furthermore, 5.0 g of allyl ether and dichloroethane (C ２ H ４ Cl ２ ) 200 mL, trimethoxysilane (HSi(OMe) ３ ) 18.6 g, cyclooctadiene iridium chloride dimer ([Ir(COD)Cl] ２ ) was added, and the mixture was heated and stirred from room temperature to 50°C. After confirming that the raw materials had disappeared, heating and stirring was stopped. Next, dichloroethane (solvent) was distilled off from the reaction solution using a vacuum pump. Brown oil K2 was added to the crude product after distillation, and distillation purification was carried out again at an oil bath temperature of 190°C and a vacuum of 0.1-0.01 mmHg, yielding colorless oil compound K3 (13.3 g, 38.8 mol, yield 34.6%) containing alkoxysilyl compound A. １ The purity was confirmed by H-NMR and gas chromatography (GC).

[0115] (Another example of a method for synthesizing compound (1) in which the chain portion of R1 contains oxygen) At room temperature, ethylene glycol monovinyl ether (5.0 g, 1.0 eq.), 50 mL of ultra-dehydrated dimethylformamide (DMF), and allyl bromide (7.55 g, 1.1 eq.) were added to a 200 mL reactor. To this solution, NaH (2.27 g, 1.0 eq.) was added slowly in multiple portions over 20 minutes while stirring, yielding a white suspension. The white suspension was stirred at room temperature for 16 hours, allowing the reaction shown in the following formula to proceed. After stirring, water was added to quench the reaction, yielding a reaction solution containing compound B.

[0116]

[0117] The reaction solution was placed in a separatory funnel, 30 mL of diethyl ether was added, and the mixture was stirred. The organic phase was extracted three times. The extracted organic phases were combined and placed in the separatory funnel again. 100 mL of water was added and the mixture was stirred, and the aqueous phase was then discharged. This operation was repeated three times. Subsequently, 100 mL of saturated saline was added and the mixture was stirred, and the aqueous phase was then discharged. 20 g of anhydrous sodium sulfate was then added to the remaining organic phase and stirred to remove moisture, and the anhydrous sodium sulfate was removed by filtration. Subsequently, diethyl ether was removed at a bath temperature of 50°C under normal pressure, and the residue was purified by distillation (vacuum degree: 20 mmHg, oil bath temperature: 70°C, vapor temperature: 50°C) using a distillation purification apparatus connected to a flask, a T-junction tube, a thermometer, a condenser, a vacuum pump, and a pressure gauge, to obtain a colorless liquid Y1 containing compound B.

[0118] Subsequently, a 50 mL reactor was charged with Compound B (1.0 g, 1.0 eq.), 30 mL of ultra-dehydrated dichloromethane, and cyclooctadiene iridium chloride dimer ([Ir(COD)Cl] ２ ) (52 g, 0.01 eq.) was added to obtain an orange solution. Trimethoxysilane (HSi(OMe) ３ ) (3.0 mL, 3.0 eq.) was slowly added dropwise over 15 minutes. The solution was stirred at room temperature for 2 hours, and the reaction shown in the following formula was allowed to proceed, yielding a solution Y2 containing an alkoxysilyl compound C.

[0119]

[0120] Furthermore, at room temperature, a 50 mL reactor was charged with Compound B (5.0 g, 1.0 eq.), 125 mL of ultra-dehydrated dichloromethane, and cyclooctadiene iridium chloride dimer ([Ir(COD)Cl] ２ 0.26 g of trimethoxysilane (HSi(OMe)) was added to the orange solution while stirring. ３ ) (14.9 mL, 3.0 eq.) was slowly added dropwise over 15 minutes. The solution was stirred at room temperature for 2 hours, and then solution Y2 was added to the stirred solution. A distillation purification apparatus was attached to the reactor, and dichloromethane was removed at a bath temperature of 50°C, and volatile components were further removed under reduced pressure of 20 mmHg / 70°C. The residue was purified by distillation (vacuum degree: 0.1-0.3 mmHg, oil bath temperature: 180-195°C, vapor temperature: 139-142°C) to obtain compound C (10.4 g, 27.9 mol, yield 59.6%) as a light brown solution.

[0121] The present disclosure will be specifically described below based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0122] <Battery (A1-1)> [Preparation of negative electrode active material] Lithium carbonate (Li ２ CO ３ ) and silicon dioxide (SiO ２ ) and Li ２ CO ３ : SiO ２ The lithium silicate composite oxide was mixed in a molar ratio of 34:66, and the mixture was heated in an inert gas atmosphere at 1500°C for 5 hours to obtain a melt. The melt was passed through a metal roller to form a flaky solid, and the solid was heat-treated at 750°C for 5 hours to obtain a lithium silicate composite oxide existing as a mixed phase of amorphous and crystalline phases. The obtained lithium silicate composite oxide was pulverized to an average particle size of 10 μm.

[0123] Next, in an inert gas atmosphere, Si particles (3N, average particle size 10 μm) and the above-mentioned lithium silicate composite oxide were mixed in a mass ratio of Si particles:lithium silicate composite oxide = 58:42, and the mixture was loaded into a pot (SUS (stainless steel), volume: 500 mL) of a planetary ball mill (Fritsch, P-5). Twenty-four SUS balls (diameter 20 mm) were placed in the pot, the lid was closed, and the mixture was pulverized at 200 rpm for 50 hours to obtain a powder. The obtained powder was then removed from the inert gas atmosphere and heat-treated at 800°C for 4 hours in the inert gas atmosphere to obtain a sintered body of Si-containing lithium silicate composite oxide. That is, by the above process, composite particles containing a lithium silicate phase and a silicon phase dispersed in the lithium silicate phase were produced.

[0124] The sintered body was then pulverized and passed through a 40 μm mesh. The particles that passed through the mesh were then mixed with coal pitch (MCP250, manufactured by JFE Chemical Corporation) to obtain a mixture. The mixture was then heat-treated in an inert gas atmosphere at 800°C for 5 hours to coat the particle surfaces with conductive carbon and form a conductive layer. The amount of the conductive layer coated was 5 mass% relative to the total mass of the Si-containing lithium silicate composite oxide particles and the conductive layer. Active material particles with an average particle size of 5 μm and a conductive layer were then obtained using a sieve. The active material particles and the conductive layer formed on their surfaces may hereinafter be collectively referred to as "active material particles (a0)."

[0125] [Analysis of Active Material Particles] The cross section of the active material particle (a0) was observed by TEM, and the average particle size of the Si particles (Si phase) was found to be less than 50 nm. The cross section of the active material particle (a0) was observed by SEM. As a result, it was confirmed that a large number of Si particles (Si phase) were dispersed almost uniformly within the silicate phase.

[0126] The XRD pattern of the active material particles (a0) contains Si, Li ２ Si ２ O ５ A peak due to SiO was confirmed near 2θ=25°. ２ The active material particles (a0) were measured by Si-NMR, and as a result, a peak due to SiO２ The content was below the detection limit.

[0127] [Coating Treatment 1-1 of Negative Electrode Active Material] 342 mL of ethanol, 10 mL of pure water, and 326 μL of hydrochloric acid (concentration: 37% by mass) were mixed to prepare a solution of about pH 4.5 (hereinafter sometimes referred to as "mother liquor"). Bis[3-(triethoxysilyl)propyl]tetrasulfide (commercially available product, hereinafter sometimes referred to as "P1") was added to the above mother liquor so that the concentration was 0.5% by mass, and mixed to prepare a P1 solution. Next, 22 g of active material particles (a0) were mixed with the P1 solution to form a suspension, which was then stirred at 50 ° C. for 24 hours using a stirrer. This allowed P1 to react to form siloxane bonds.

[0128] Next, the suspension was suction filtered using a polytetrafluoroethylene (PTFE) membrane filter and rinsed with 500 mL of ethanol, followed by 500 mL of pure water. The recovered particles were vacuum dried at 100°C for 24 hours, and this was designated as negative electrode active material (a1-1). A cross section of this negative electrode active material (a1-1) was observed using a TEM-EDX device (JEM-F200, manufactured by JEOL Ltd.). As a result, it was confirmed that a surface layer was formed on the Si-containing lithium silicate composite oxide particles. It was confirmed that the surface layer contained a conductive layer (a layer of conductive carbon) and a substance derived from P1 (including a reaction product of P1) infiltrated into the conductive layer.

[0129] [Coating Treatment 1-2 of Negative Electrode Active Material] 0.77% by mass of P1 was added to 17 mL of pure water and mixed to prepare a P1 aqueous solution. 31 g of the active material particles (a0) was mixed with the P1 aqueous solution to obtain a paste. Next, the paste was vacuum-dried at 100°C for 24 hours. This caused P1 to react to form siloxane bonds, and a powdered negative electrode active material (a1-2) was obtained.

[0130] A cross section of the negative electrode active material (a1-2) was observed using a TEM-EDX apparatus (JEM-F200, manufactured by JEOL Ltd.), and it was confirmed that a surface layer was formed on the Si-containing lithium silicate composite oxide particles. It was confirmed that the surface layer contained a conductive layer (a layer of conductive carbon) and a substance derived from P1 (including a reaction product of P1) that had infiltrated the conductive layer.

[0131] [Coating Treatment 2-1 of Negative Electrode Active Material] 342 mL of ethanol, 10 mL of pure water, and 326 μL of hydrochloric acid (concentration: 37% by mass) were mixed to prepare a solution of approximately pH 4.5 (hereinafter referred to as "mother liquor"). 0.5% by mass of the above-mentioned compound C was added to the above mother liquor and mixed to prepare a solution of compound C. Next, 22 g of active material particles (a0) were mixed with the solution of compound C to form a suspension, and the suspension was stirred at 50 ° C. for 24 hours using a stirrer. Thereafter, the suspension was suction filtered using a PTFE membrane filter and rinsed with 500 mL of ethanol, followed by 500 mL of pure water. The recovered particles were vacuum-dried at 100 ° C. for 24 hours to obtain a negative electrode active material (a2-1). The cross section of this negative electrode active material (a2-1) was observed using a TEM-EDX device (manufactured by JEOL Ltd., JEM-F200). As a result, it was confirmed that a surface layer was formed on the Si-containing lithium silicate composite oxide particles. It was confirmed that the surface layer contained a conductive layer (a layer of conductive carbon) and a substance derived from compound C (including a reaction product of compound C) that had infiltrated the conductive layer.

[0132] [Coating Treatment 2-2 of Negative Electrode Active Material] 0.6% by mass of compound C was added to 17 mL of pure water and mixed to prepare an aqueous solution of compound C. 31 g of active material particles (a0) was mixed with the aqueous solution of compound C to obtain a paste. Next, the paste was vacuum dried at 100°C for 24 hours to obtain a powdered negative electrode active material (a2-2). A cross section of this negative electrode active material (a2-2) was observed using a TEM-EDX device (manufactured by JEOL Ltd., JEM-F200). As a result, it was confirmed that a surface layer was formed on the Si-containing lithium silicate composite oxide particles. It was confirmed that the surface layer contained a conductive layer (a layer of conductive carbon) and a substance derived from compound C (including a reaction product of compound C) infiltrated into the conductive layer.

[0133] [Preparation of Negative Electrode] An active material mixture containing a negative electrode active material (a1-1) and graphite in a mass ratio of negative electrode active material (a1-1):graphite = 5:95 was mixed with a sodium salt of carboxymethyl cellulose (CMC-Na) and styrene-butadiene rubber (SBR) in a mass ratio of active material mixture:CMC-Na:SBR = 97.5:1.0:1.5, and water was added to obtain a mixture. The mixture was stirred using a mixer (T.K. Hibismix, manufactured by Primix) to prepare a negative electrode slurry. Next, the negative electrode slurry was applied to both sides of a copper foil (negative electrode current collector), the coating was dried, and then rolled to obtain a copper foil having a density of 1.6 g / cm. ３ Thus, a negative electrode having the above negative electrode mixture layer formed thereon was obtained.

[0134] [Preparation of Positive Electrode] Lithium cobalt oxide, acetylene black (HS100, manufactured by Denki Kagaku Kogyo Co., Ltd.), and polyvinylidene fluoride (PVdF) were mixed in a mass ratio of lithium cobalt oxide:acetylene black:PVdF = 98.7:0.7:0.6. N-methyl-2-pyrrolidone (NMP) was added to the mixture as a dispersion medium, and the mixture was stirred using a mixer (T.K. Hibismix, manufactured by Primix Corporation) to prepare a positive electrode slurry. Next, the positive electrode slurry was applied to both sides of an aluminum foil (positive electrode current collector), the coating film was dried, and then rolled with a rolling roller to form a positive electrode current collector with a density of 3.6 g / cm on both sides. ３ A positive electrode having the positive electrode mixture layer formed thereon was fabricated.

[0135] [Preparation of Non-Aqueous Electrolyte] A mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC:EMC:DMC=4:1:15 was added to a non-aqueous electrolyte solution containing lithium hexafluorophosphate (LiPF ６ ) was added in an amount of 1.3 mol / L to prepare a non-aqueous electrolyte solution.

[0136] [Preparation of Non-Aqueous Electrolyte Secondary Battery] A tab was attached to each of the electrodes. Next, a wound electrode assembly was prepared by spirally winding the positive electrode, the negative electrode, and the separator so that the separator was disposed between the positive electrode and the negative electrode. At this time, the electrode plates were wound so that the tab was located at the outermost periphery. The obtained electrode plate assembly was inserted into an outer casing composed of an aluminum laminate sheet having a height of 62 mm and a width of 35 mm, and vacuum dried at 105°C for 2 hours. Next, the non-aqueous electrolyte solution was injected into the outer casing, and the opening of the outer casing was sealed. In this way, a non-aqueous electrolyte secondary battery (A1-1) was prepared. The design capacity of this battery was 360 mAh.

[0137] <Battery (A1-2)> A battery (A1-2) was produced under the same conditions as those for the battery (A1-1), except that the negative electrode active material (a1-2) was used instead of the negative electrode active material (a1-1).

[0138] <Battery (A2-1)> A battery (A2-1) was produced under the same conditions as those for the battery (A1-1), except that the negative electrode active material (a2-1) was used instead of the negative electrode active material (a1-1).

[0139] <Battery (A2-2)> Battery (A2-2) was produced under the same conditions as battery (A1-1), except that negative electrode active material (a2-2) was used instead of negative electrode active material (a1-1). <Battery B> Comparative battery B was produced under the same conditions as battery (A1-1), except that active material particles (a0) were used instead of negative electrode active material (a1-1).

[0140] (Charge-Discharge Cycle Characteristics) A total of 400 charge-discharge cycles were performed on the nonaqueous electrolyte secondary battery at a temperature of 25° C. The charge-discharge cycles were performed by repeating a set of 100 charge-discharge cycles four times. One set of charge-discharge cycles was performed by repeating one charge-discharge cycle under the following charge-discharge condition 1, one charge-discharge cycle under charge-discharge condition 2, and then repeating 98 charge-discharge cycles under charge-discharge condition 3.

[0141] [Charge / Discharge Condition 1] The battery was charged at a constant current of 0.3 C (1 C is the current value required to discharge the design capacity in 1 hour) until the battery voltage reached 4.2 V, and then at a constant voltage of 4.2 V, constant voltage charging was performed until the current value reached 0.02 C. After a 20-minute pause, constant current discharging was performed at a constant current of 0.05 C until the battery voltage reached 2.5 V, and then a 20-minute pause was performed. [Charge / Discharge Condition 2] The battery was charged at a constant current of 0.05 C until the battery voltage reached 4.2 V, and then at a constant voltage of 4.2 V, constant voltage charging was performed until the current value reached 0.02 C. After a 20-minute pause, constant current discharging was performed at a constant current of 0.5 C until the battery voltage reached 2.5 V, and then a 20-minute pause was performed. Thereafter, constant current discharging was performed at a constant current of 0.2 C until the battery voltage reached 2.5 V, and then a 20-minute pause was performed. [Charge / Discharge Condition 3] Constant current charging was performed at a constant current of 0.5 C until the battery voltage reached 4.2 V, and constant voltage charging was performed at a constant voltage of 4.2 V until the current value reached 0.05 C. After a 20-minute pause, constant current discharging was performed at a constant current of 0.7 C until the battery voltage reached 2.5 V, and then a 20-minute pause was performed.

[0142] [Capacity Retention Rate after 400 Cycles] The discharge capacity at the third cycle and the discharge capacity at the 400th cycle under the above charge / discharge conditions were measured, and the capacity retention rate after 400 cycles was calculated using the following formula. The results are shown in Table 1.

[0143] Capacity retention rate after 400 cycles (%)=(discharge capacity at 400th cycle / discharge capacity at 3rd cycle)×100

[0144]

[0145] Battery B is a comparative example, and the others are batteries according to the present disclosure. Compared to Battery B of the comparative example, Batteries A1-1 to A2-2 according to the present disclosure were able to suppress the decrease in capacity retention rate associated with charge-discharge cycling. In Batteries A1-1 to A2-2, the surfaces of the negative electrode active materials (a1-1) to (a2-2) are protected by the reaction product of Compound (1). This is thought to have suppressed the reaction (side reaction) between Si and the electrolyte, thereby suppressing the decrease in capacity retention rate.

[0146] The present disclosure can be used for negative electrode active materials for non-aqueous electrolyte secondary batteries and non-aqueous electrolytes using the same. Although the present invention has been described with reference to presently preferred embodiments, such disclosure should not be construed as limiting. Various modifications and variations will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. Accordingly, the appended claims should be construed to include all modifications and variations that do not depart from the true spirit and scope of the present invention.

[0147] 1a: positive electrode mixture layer, 1b: positive electrode current collector, 1c: positive electrode tab lead, 2a: negative electrode mixture layer, 2b: negative electrode current collector, 2c: negative electrode tab lead, 4: electrode plate assembly, 5: exterior case, 6: insulating tab film, 10: positive electrode, 20: negative electrode, 30: separator, 100: nonaqueous electrolyte secondary battery

Claims

1. A negative electrode active material for a non-aqueous electrolyte secondary battery, comprising: active material particles containing silicon; a surface layer formed on the surface of the active material particle, the surface layer comprises a reaction product in which compounds have reacted to form siloxane bonds; The compound includes a structure represented by Si-R1-Si, R1 is an atomic group having a chain portion containing, as components, at least one selected from the group consisting of a sulfur atom, an oxygen atom, and a nitrogen atom and an alkylene group; One of the two Si's is an alkoxy group or an oxyalkylene group having a carbon number of 1 to 6, and is -O-(C ｘ１ H ２ｘ１＋１ O ｙ１ wherein x1 is an integer of 2 or more and 6 or less, and y1 is an integer of 1 or more and 3 or less, a chloro group, and a hydroxyl group are bonded to at least one atomic group selected from the group consisting of The other of the two Si's is an alkoxy group or oxyalkylene group having a carbon number of 1 to 6, and is -O-(C ｘ２ H ２ｘ２＋１ O ｙ２ ) (x2 is an integer of 2 or more and 6 or less, and y2 is an integer of 1 or more and 3 or less), a chloro group, and a hydroxyl group.

2. The negative electrode active material according to claim 1 , wherein the compound is a compound represented by the following formula (1): 【Chemistry 1】 [In formula (1), at least one selected from the group consisting of R2, R3, and R4 each independently contains an alkoxy group or an oxyalkylene group having a carbon number of 1 to 6, and is —O—(C ｘ１ H ２ｘ１＋１ O ｙ１ ) (x1 is an integer of 2 or more and 6 or less, and y1 is an integer of 1 or more and 3 or less), a chloro group, or a hydroxyl group. At least one selected from the group consisting of R5, R6, and R7 is independently an alkoxy group or an oxyalkylene group having a carbon number of 1 to 6, and is represented by -O-(C ｘ２ H ２ｘ２＋１ O ｙ２ ) (x2 is an integer of 2 to 6, and y2 is an integer of 1 to 3), a chloro group, or a hydroxyl group. The remainder of R2 to R7 are each independently a hydrocarbon group having a carbon number of 1 to 6, a hydrogen atom, or a C ｘ３ H ２ｘ３＋ｙ３＋１ N ｙ３ O ｚ３ S ｗ３ (x3 is an integer of 1 or more and 6 or less, y3 is an integer of 0 or more and 3 or less, z3 is an integer of 0 or more and 3 or less, and w3 is an integer of 0 or more and 3 or less, and 1≦y3+z3+w3). R2 to R7 may be the same or different.

3. 3. The negative electrode active material according to claim 2, wherein in the formula (1), R2 to R7 are methoxy groups or ethoxy groups.

4. R1 includes at least one heteroatom selected from the group consisting of a sulfur atom, an oxygen atom, and a nitrogen atom, and two alkylene groups constituting the chain portion so as to sandwich the at least one heteroatom, 2. The negative electrode active material according to claim 1, wherein the carbon numbers of the two alkylene groups are each independently in the range of 2 to 4.

5. The R1 is -(CH ２ ) ｐ S ｎ (CH ２ ) ｑ -(1≦n≦6, 2≦p≦4, 2≦q≦4), -(CH ２ ) ｐ O (CH ２ ) ｑ -(2≦p≦4, 2≦q≦4), -(CH ２ ) ｐ O (CH ２ ) ｒ O (CH ２ ) ｑ -(2≦p≦4, 2≦q≦4, 2≦r≦4), and -(CH ２ ) ｐ NH (CH ２ ) ｑ 2. The negative electrode active material according to claim 1, wherein n, p, q, and r are each a natural number.

6. The negative electrode active material according to claim 1 , wherein the surface layer comprises conductive carbon.

7. The active material particles are ｘ SiO ｙ 2. The negative electrode active material according to claim 1, which is a composite particle including a lithium silicate phase represented by (0<x≦4, 0<y≦4) and a silicon phase dispersed in the lithium silicate phase.

8. The negative electrode active material according to claim 7, wherein the crystallite size of the silicon phase is in the range of 1 nm to 1000 nm.

9. The negative electrode active material according to claim 1 , wherein the active material particles include a carbon phase and a silicon phase dispersed within the carbon phase.

10. A positive electrode, a negative electrode, and a non-aqueous electrolyte, The negative electrode of a non-aqueous electrolyte secondary battery comprises the negative electrode active material according to any one of claims 1 to 9.

11. A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, comprising: A first step of contacting a compound or a liquid in which the compound is dissolved with silicon-containing active material particles; a second step of reacting the compound or the liquid with the active material particles to form a siloxane bond, The compound includes a structure represented by Si-R1-Si, R1 is an atomic group having a chain portion containing, as components, at least one selected from the group consisting of a sulfur atom, an oxygen atom, and a nitrogen atom and an alkylene group; One of the two Si's is an alkoxy group or an oxyalkylene group having a carbon number of 1 to 6, and is -O-(C ｘ１ H ２ｘ１＋１ O ｙ１ wherein x1 is an integer of 2 or more and 6 or less, and y1 is an integer of 1 or more and 3 or less, a chloro group, and a hydroxyl group are bonded to at least one atomic group selected from the group consisting of The other of the two Si's is an alkoxy group or oxyalkylene group having a carbon number of 1 to 6, and is -O-(C ｘ２ H ２ｘ２＋１ O ｙ２ ) (x2 is an integer of 2 or more and 6 or less, and y2 is an integer of 1 or more and 3 or less), a chloro group, and a hydroxyl group.

12. The method according to claim 11 , wherein the compound is a compound represented by the following formula (1): 【Chemistry 2】 [In formula (1), at least one selected from the group consisting of R2, R3, and R4 each independently contains an alkoxy group or an oxyalkylene group having a carbon number of 1 to 6, and is —O—(C ｘ１ H ２ｘ１＋１ O ｙ１ ) (x1 is an integer of 2 or more and 6 or less, and y1 is an integer of 1 or more and 3 or less), a chloro group, or a hydroxyl group. At least one selected from the group consisting of R5, R6, and R7 is independently an alkoxy group or an oxyalkylene group having a carbon number of 1 to 6, and is represented by -O-(C ｘ２ H ２ｘ２＋１ O ｙ２ ) (x2 is an integer of 2 to 6, and y2 is an integer of 1 to 3), a chloro group, or a hydroxyl group. The remainder of R2 to R7 are each independently a hydrocarbon group having a carbon number of 1 to 6, a hydrogen atom, or a C ｘ３ H ２ｘ３＋ｙ３＋１ N ｙ３ O ｚ３ S ｗ３ (x3 is an integer of 1 or more and 6 or less, y3 is an integer of 0 or more and 3 or less, z3 is an integer of 0 or more and 3 or less, and w3 is an integer of 0 or more and 3 or less, and 1≦y3+z3+w3). R2 to R7 may be the same or different.

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