JP2015011843A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which enables the suppression of the worsening of cycle characteristics.SOLUTION: A nonaqueous electrolyte secondary battery that the present invention provides comprises a positive electrode, a negative electrode, a separator and a nonaqueous electrolyte. The positive electrode includes a positive electrode active material which contains a transition metal. Further, borosiloxane containing a vinyl group is included in the secondary battery. The borosiloxane is disposed on a surface of at least one member selected from the positive electrode, the negative electrode, and the separator, or included in the nonaqueous electrolyte.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. Specifically, the present invention relates to a non-aqueous electrolyte secondary battery applicable to a vehicle-mounted power source.

  Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries are preferably used as, for example, a high-output power source for driving a vehicle because they are lightweight and can provide a high energy density. In this type of battery, various compounds are blended depending on the purpose. For example, Patent Document 1 discloses an ion conductive polymer having borosiloxane as a compound that can be used for a solid electrolyte of a battery. Other prior art documents include Patent Documents 2 to 4.

JP 2002-179800 A JP 2012-209145 A JP 2010-238505 A International Publication No. 2013/046555

  By the way, in a secondary battery using a positive electrode active material containing a transition metal, the transition metal may be eluted from the positive electrode depending on charge / discharge conditions and the like. The eluted transition metal deactivates charge carriers that contribute to charge and discharge (for example, Li ions in the case of a lithium ion secondary battery) or deposits on the negative electrode surface, causing deterioration in cycle characteristics and the like. It is thought that it can become. As a result of intensive studies, the present inventor has found a compound capable of suppressing a decrease in cycle characteristics caused by the eluted transition metal, and has completed the present invention.

  The present invention relates to an improvement in a non-aqueous electrolyte secondary battery using a positive electrode active material containing a transition metal, and an object thereof is to provide a non-aqueous electrolyte secondary battery in which deterioration of cycle characteristics is suppressed. That is.

  In order to achieve the above object, the present invention provides a nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte. In the secondary battery, the positive electrode includes a positive electrode active material containing a transition metal. The secondary battery contains a borosiloxane containing a vinyl group (hereinafter also referred to as a vinyl group-containing borosiloxane). The borosiloxane is disposed on the surface (for example, at least part of the surface) of at least one member selected from the positive electrode, the negative electrode, and the separator, or is contained in the non-aqueous electrolyte. It is preferable. According to such a configuration, the vinyl group-containing borosiloxane acts to suppress a decrease in cycle characteristics due to the transition metal eluted from the positive electrode. Therefore, according to the present invention, a non-aqueous electrolyte secondary battery in which deterioration of cycle characteristics is suppressed is provided.

  In addition, according to the present invention, a method for producing a non-aqueous electrolyte secondary battery is provided. This method includes providing a positive electrode including a positive electrode active material containing a transition metal, a negative electrode, and a separator, and supplying a vinyl group-containing borosiloxane into the secondary battery. The borosiloxane may be supplied by adding the borosiloxane to at least one member selected from the positive electrode, the negative electrode, and the separator, and adding the borosiloxane to the non-aqueous electrolyte. Is preferably selected from.

  In the non-aqueous electrolyte secondary battery disclosed here, the deterioration of cycle characteristics is suppressed. Therefore, taking advantage of this feature, it can be suitably used as a drive power source for vehicles such as hybrid vehicles (HV), plug-in hybrid vehicles (PHV), electric vehicles (EV) and the like. According to the present invention, there is provided a vehicle equipped with the nonaqueous electrolyte secondary battery disclosed herein (which may be in the form of an assembled battery in which a plurality of batteries are connected).

It is a schematic cross section of a lithium ion secondary battery according to an embodiment.

  Hereinafter, preferred embodiments according to the lithium ion secondary battery will be described. It should be noted that the dimensional relationships (length, width, thickness, etc.) in the figure do not reflect actual dimensional relationships. Further, matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters for those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  As shown in FIG. 1, the lithium ion secondary battery 100 includes a battery case 10 and a wound electrode body 20 accommodated in the battery case 10. The battery case 10 has an opening 12 on the upper surface, and the opening 12 is sealed by the lid 14 after the wound electrode body 20 is accommodated in the battery case 10 from the opening 12. A non-aqueous electrolyte solution 25 is also accommodated in the battery case 10. The lid body 14 is provided with an external positive terminal 38 and an external negative terminal 48 for external connection, and a part of the terminals 38 and 48 protrudes to the surface side of the lid body 14. A part of the external positive terminal 38 is connected to the internal positive terminal 37 inside the battery case 10, and a part of the external negative terminal 48 is connected to the internal negative terminal 47 inside the battery case 10. These internal terminals 37 and 47 are connected to the positive electrode 30 and the negative electrode 40 constituting the wound electrode body 20, respectively.

  The wound electrode body 20 includes a long sheet-like positive electrode (positive electrode sheet) 30 and a long sheet-like negative electrode (negative electrode sheet) 40. The positive electrode sheet 30 includes a long positive electrode current collector 32 and a positive electrode active material layer 34 formed on at least one surface (typically both surfaces) thereof. The negative electrode sheet 40 includes a long negative electrode current collector 42 and a negative electrode active material layer 44 formed on at least one surface (typically both surfaces) thereof. The wound electrode body 20 also includes two long sheet-like separators (separator sheets) 50A and 50B. The positive electrode sheet 30 and the negative electrode sheet 40 are laminated via two separator sheets 50A and 50B. The laminated body is formed into a wound body by being wound in the longitudinal direction, and is further formed into a flat shape by crushing the rolled body from the side surface direction and causing it to be ablated. The electrode body is not limited to a wound electrode body. Depending on the shape of the battery and the purpose of use, an appropriate shape and configuration, such as a laminate mold, can be employed as appropriate.

  Next, each component which comprises the above-mentioned lithium ion secondary battery is demonstrated. As the positive electrode current collector constituting the positive electrode of the lithium ion secondary battery, for example, a foil-like material made of aluminum or an alloy containing aluminum as a main component can be used. In addition to the positive electrode active material, the positive electrode active material layer can contain additives such as a conductive material and a binder (binder) as necessary.

  As the positive electrode active material, for example, a lithium transition metal composite oxide having a spinel structure or a layered structure, a polyanion type (for example, olivine type) lithium transition metal compound, or the like can be used. More specifically, the following compounds can be used.

(1) Examples of the spinel-structure lithium transition metal composite oxide include a spinel-structure LiMn composite oxide containing at least Mn as a transition metal. More specifically, the general _{formula: Li p Mn 2-q M} q O 4 + α; represented by, LiMn composite oxide having a spinel structure. Here, p is 0.9 ≦ p ≦ 1.2; q is 0 ≦ q <2, and α is such that −0.2 ≦ α ≦ 0.2 and the charge neutrality condition is satisfied. It is a value determined by. When q is larger than 0 (0 <q), M may be one or more selected from any metal element other than Mn (preferably Ni) or a non-metal element. Specific examples include LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiCrMnO _{4 and the} like.

(2) The lithium transition metal composite oxide having a layered structure includes a compound represented by the general formula: LiMO ₂ ; Here, M includes at least one transition metal element such as Ni, Co, and Mn, and may further include another metal element or a nonmetal element. Specific examples include LiNiO ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ .
(3) Further, as the cathode active material, the general formula: _Li 2 MO _3; in it may be a lithium transition metal composite oxide represented. Here, M includes at least one transition metal element such as Mn, Fe, and Co, and may further include another metal element or a nonmetal element. Specific examples include Li ₂ MnO ₃ and Li ₂ PtO ₃ .
(4) Further, a lithium transition metal compound (phosphate) represented by the general formula: LiMPO ₄ ; Here, M includes at least one transition metal element such as Mn, Fe, Ni, and Co, and may further include another metal element or a nonmetal element. Specific examples include LiMnPO ₄ and LiFePO ₄ .
(5) In addition, as the positive electrode active material, the general _formula: Li 2 _MPO 4 F; lithium transition metal compound represented may be used (phosphate). Here, M includes at least one transition metal element such as Mn, Ni, and Co, and may further include another metal element or a nonmetal element. Specific examples include Li ₂ MnPO ₄ F.
(6) Furthermore, a solid solution of LiMO ₂ and Li ₂ MO ₃ can be used as the positive electrode active material. Here, LiMO ₂ refers to the composition represented by the general formula described in (2) above, and Li ₂ MO ₃ refers to the composition represented by the general formula described in (3) above. A specific example is a solid solution represented by 0.5LiNi _1/3 Mn _1/3 Co _1/3 O ₂ —0.5Li ₂ MnO ₃ .

  The positive electrode active materials described above can be used alone or in combination of two or more. Especially, it is preferable that a positive electrode active material consists of LiMn complex oxide (preferably LiNiMn complex oxide) of a spinel structure substantially.

  As the conductive material, for example, carbon black such as acetylene black (AB) can be preferably used. Examples of the binder include various polymer materials. For example, a vinyl halide resin such as polyvinylidene fluoride (PVdF) can be used. In addition, the said binder may be used as a thickener and other additives of the composition for positive electrode active material layer formation.

  As the negative electrode current collector constituting the negative electrode, for example, a foil-like one made of copper or an alloy containing copper as a main component can be used. The negative electrode active material layer contains one or more negative electrode active materials capable of occluding and releasing Li ions serving as charge carriers. Examples of such a negative electrode active material include carbon materials such as graphite carbon (graphite). In addition, oxides such as lithium titanate, simple substances such as silicon materials and tin materials, alloys, and the like can be used as the negative electrode active material. In addition to the negative electrode active material, the negative electrode active material layer can contain one or more binders, thickeners, and other additives as necessary. As the binder, for example, a material that can be contained in the positive electrode active material layer can be preferably used.

  The separator disposed so as to separate the positive electrode and the negative electrode may be a member that insulates the positive electrode active material layer and the negative electrode active material layer and allows the electrolyte to move. Preferable examples of the separator include those made of a porous polyolefin resin. The separator may be provided with a heat resistant layer. When a solid (gel-like) electrolyte in which a polymer is added to the electrolytic solution, for example, is used instead of the electrolytic solution, the separator itself is not necessary because the electrolyte itself can function as a separator. It can happen.

  The non-aqueous electrolyte contained in the lithium ion secondary battery can include at least a non-aqueous solvent and a supporting salt. A typical example is an electrolytic solution having a composition in which a supporting salt is contained in a suitable non-aqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like. Or 2 or more types can be mixed and used.

  Moreover, it is preferable that a non-aqueous electrolyte contains 1 type, or 2 or more types of fluorinated carbonates (for example, the fluorinated product of the above carbonates) as a non-aqueous solvent. In general, the non-aqueous electrolyte tends to be oxidatively decomposed under conditions where the positive electrode is charged to such a potential that the transition metal is eluted. However, the oxidative decomposition of the nonaqueous electrolytic solution is suppressed by using a nonaqueous electrolytic solution containing a fluorinated carbonate having excellent oxidation resistance.

  As the fluorinated carbonate, for example, a fluorinated cyclic carbonate represented by the following formula (C1) can be preferably used.

R ¹¹ , R ¹² and R ¹³ in the formula (C1) may be independently selected from a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms and a haloalkyl group, and a halogen atom other than fluorine. . Specific examples of the fluorinated cyclic carbonate represented by the above formula (C1) include monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC) and the like.

Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiI. 1 type, or 2 or more types of lithium compounds (lithium salt), such as these, can be used. The concentration of the supporting salt is not particularly limited, but can be about 0.1 to 5 mol / L.

  The technique disclosed here is characterized in that a vinyl group-containing borosiloxane is contained in a secondary battery. Here, the “vinyl group-containing borosiloxane” is a compound or mixture containing a silicon atom (Si) and an oxygen atom (O) in the main skeleton and a boron atom (B), and having a vinyl group. Say. Preferably, it may be a polyborosiloxane having a siloxane structure containing a Si—O bond, B being bonded to Si through O, and having a vinyl group.

  The borosiloxane has one or more (for example, two or more) vinyl groups. Moreover, it is preferable that at least one of the vinyl groups (for example, two or more of the vinyl groups, typically all of the vinyl groups) is directly bonded to Si constituting the borosiloxane.

The vinyl group-containing borosiloxane disclosed herein can typically have the following structural unit (a) and structural units (b) and / or (c).

  Here, R in the structural unit (c) may be a hydrogen atom or an organic group having 1 to 12 carbon atoms (for example, 1 to 4, typically 1 or 2). Examples of such an organic group include chain alkyl groups such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a t-butyl group; a cyclohexyl group, and the like. A cycloalkyl group, an alkenyl group, an alkynyl group, a halogenated alkyl group, and the like. Among these, from the viewpoint of suitably expressing the action of the borosiloxane, the organic group is preferably a methyl group, an ethyl group, a methoxy group, or an ethoxy group.

  The proportion of the structural unit (a) in the vinyl group-containing borosiloxane disclosed herein is 10 mol% or more (for example, 20 mol% or more, typically 30 mol% or more) from the viewpoint of improving cycle characteristics and the like. It is preferably 90 mol% or less (for example, 60 mol% or less, typically 40 mol% or less). In addition, the total proportion of the structural units (b) and (c) in the vinyl group-containing borosiloxane is 1 mol% or more (for example, 10 mol% or more, typically 20 mol% or more) from the viewpoint of improving cycle characteristics. It is preferably 90 mol% or less (for example, 50 mol% or less, typically 30 mol% or less).

  The vinyl group-containing borosiloxane as described above can be obtained, for example, by preparing an organosilane monomer having a vinyl group and boron oxide, mixing them at a desired molar ratio, and then heating. Heating is preferably performed at 80 ° C. or higher (for example, 100 to 180 ° C.). Further, by-products and unreacted materials may be removed by a technique such as distillation under reduced pressure or drying. Examples of the organic silane monomer having a vinyl group include vinyltrialkylsilanes such as vinyltrimethylsilane and vinyltriethylsilane; vinyldialkylmonoalkoxysilanes such as vinyldimethylmethoxysilane; vinylmethyldimethoxysilane and vinylmethyldiethoxysilane. Vinyl trialkoxysilanes such as vinyltrimethoxysilane; divinyldialkylsilanes; divinyl dialkoxysilanes; divinylalkylalkoxysilanes; These may be used alone or in combination of two or more.

  The vinyl group-containing borosiloxane in the technology disclosed herein is not particularly limited as long as it is contained in the secondary battery. The vinyl group-containing borosiloxane is, for example, a surface of at least one member selected from a positive electrode, a negative electrode, and a separator (typically constituting an electrode body in the secondary battery) in a secondary battery (for example, It is preferable to be disposed on at least a part of the surface. A typical example is a form in which the vinyl group-containing borosiloxane covers the member. Such a configuration can be obtained, for example, by applying the vinyl group-containing borosiloxane to the surface of the member. As a preferred example of such a method, a dispersion or solution (coating solution) in which the vinyl group-containing borosiloxane is dispersed or dissolved in water or an organic solvent such as tetrahydrofuran (THF) is applied to the surface of the member. And the method of making it dry as needed is mentioned. The concentration of the vinyl group-containing borosiloxane in the coating solution is not particularly limited as long as it is appropriately set. However, from the viewpoint of workability, for example, 0.1 to 10% by mass (typically 1 to 5% by mass) It is preferable to set the degree.

  Or it is preferable that the vinyl group containing borosiloxane in the technique disclosed here is contained in the non-aqueous electrolyte. The content (addition rate) of the vinyl group-containing borosiloxane in the non-aqueous electrolyte is not particularly limited, but is 0.01% by mass or more (for example 0.1 It is preferable that the content is at least mass%, typically at least 0.3 mass%. Further, from the viewpoint of suppressing deterioration of battery characteristics due to excessive addition, it is preferably 10% by mass or less (eg 5% by mass or less, typically 3% by mass or less).

  Next, some examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in the examples. In the following description, “parts” and “%” are based on mass unless otherwise specified.

<Preparation of vinyl group-containing borosiloxane>
Under an argon stream, the types and amounts of silane raw materials shown in Table 1 and the amount of boron oxide shown in Table 1 were put into a flask, and the mixture was heated and stirred at 80 ° C. for 1 hour. Thereafter, the temperature in the system was raised, and stirring was performed at 130 ° C. After one day, heating was terminated, and trimethyl borate as a by-product was distilled off under reduced pressure. This was dried under reduced pressure at 150 ° C. to obtain vinyl group-containing borosiloxane compounds A to D which were colorless solids. Hereinafter, including the table, the vinyl group-containing borosiloxane compounds A to D are simply abbreviated as compounds A to D, respectively.

<Example 1>
[Production of positive electrode]
Li-Ni _0.5 Mn _1.5 O ₄ powder as the positive electrode active material, AB as the conductive material, and PVdF as the binder, N-methyl so that the mass ratio of these materials is 85: 10: 5 A paste-like composition for forming a positive electrode active material layer was prepared by mixing with -2-pyrrolidone (NMP). This composition was uniformly applied to one surface of an aluminum foil (thickness: 15 μm) so that the amount applied was 6.5 mg / cm ² (solid content basis). The coated material was dried and pressed, and then cut into a predetermined size (circular shape with a diameter of 14 mm) to obtain a positive electrode.

[Production of negative electrode]
A composition for forming a negative electrode active material layer in the form of a paste by mixing graphite powder as a negative electrode active material and PVdF as a binder with NMP such that the mass ratio of these materials is 92.5: 7.5. A product was prepared. This composition was uniformly applied to one side of a copper foil (thickness: 15 μm) so that the amount applied was 4.3 mg / cm ² (based on solid content). The coated material was dried and pressed, and then cut into a predetermined size (circular shape with a diameter of 16 mm) to obtain a negative electrode.

[Production of lithium ion secondary battery]
A coin type (2032 type) battery was produced using the positive electrode and the negative electrode produced as described above. That is, the positive electrode and the negative electrode prepared above were laminated together with a separator impregnated with a nonaqueous electrolytic solution, accommodated in a container (negative electrode terminal), and then the electrolytic solution was further dropped. Next, the container was sealed with a gasket and a lid (positive electrode terminal) to obtain a battery. As the separator, a polypropylene porous film having a thickness of 25 μm cut into a predetermined size (a circle having a diameter of 19 mm) was used. As a non-aqueous electrolyte, about 1 mol / L LiPF ₆ was dissolved as a supporting salt in a 3: 4: 3 (volume ratio) mixed solvent of EC, EMC, and DMC, and the compound A obtained above was added to 0%. An electrolyte containing 5% concentration was used.

<Examples 2 to 5>
Coin-type batteries according to Examples 2 to 4 were produced in the same manner as Example 1 except that Compound A was replaced with Compounds B to D obtained above. A coin-type battery according to Example 5 was produced in the same manner as in Example 1 except that Compound A was not used.

<Example 6>
The positive electrode produced in Example 1 was immersed in a THF 3% solution of Compound A and then dried to produce a positive electrode coated with Compound A. Further, as the non-aqueous electrolyte, a non-aqueous electrolyte having the same composition as Example 1 was prepared except that the compound A was not included. A battery according to Example 6 was obtained in the same manner as in Example 1 except that the positive electrode coated with Compound A and a nonaqueous electrolytic solution were used.

<Example 7>
The negative electrode produced in Example 1 was immersed in a THF 3% solution of Compound A and then dried to produce a negative electrode coated with Compound A. Moreover, as the non-aqueous electrolyte, a non-aqueous electrolyte having the same composition as that used in Example 6 was prepared. A battery according to Example 7 was obtained in the same manner as Example 1 except that the negative electrode coated with Compound A and a nonaqueous electrolytic solution were used.

<Example 8>
The separator used in Example 1 was immersed in a THF 3% solution of Compound A and then dried to prepare a separator coated with Compound A. Moreover, as the non-aqueous electrolyte, a non-aqueous electrolyte having the same composition as that used in Example 6 was prepared. A battery according to Example 8 was obtained in the same manner as in Example 1 except that the separator coated with Compound A and a nonaqueous electrolytic solution were used.

<Examples 9 to 14>
Batteries according to Examples 9 to 11 were obtained in the same manner as Examples 6 to 8 except that Compound B was used instead of Compound A. Further, batteries according to Examples 12 to 14 were obtained in the same manner as Examples 6 to 8 except that Compound D was used instead of Compound A.

[Capacity maintenance rate after 100 cycles]
Each battery obtained above was subjected to a conditioning process, and then at a temperature environment of 60 ° C., constant current and constant voltage (CCCV) charging up to 4.9 V (1 C rate, 0.15 C cut), 3 A constant current (CC) discharge (1C rate) up to 5 V was repeated 100 cycles. The discharge capacity retention rate (%) after 100 cycles was determined with the discharge capacity (initial discharge capacity) at the first cycle as 100%. The obtained results are shown in Tables 2 and 3.

  As shown in Tables 2 and 3, batteries according to Examples 1 to 4 in which a vinyl group-containing borosiloxane is contained in a non-aqueous electrolyte, Examples 6 to 14 in which a vinyl group-containing borosiloxane is coated on a positive electrode, a negative electrode, or a separator. Compared with the battery according to Example 5 in which the vinyl group-containing borosiloxane was not used, the capacity retention rate after 100 cycles was improved. From these results, it is understood that the cycle characteristics can be improved by including the vinyl group-containing borosiloxane in the battery. The above-described improvement in cycle characteristics is considered to be realized by suppressing the deactivation of charge carriers (Li ions in the examples) caused by the transition metal eluted from the positive electrode.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The invention disclosed herein may include various modifications and alterations of the specific examples described above.

25 Nonaqueous electrolyte 30 Positive electrode 40 Negative electrode 50A, 50B Separator 100 Lithium ion secondary battery

Claims (1)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte,
The positive electrode includes a positive electrode active material containing a transition metal,
The secondary battery contains a borosiloxane containing a vinyl group,
The borosiloxane is disposed on the surface of at least one member selected from the positive electrode, the negative electrode, and the separator, and / or is contained in the nonaqueous electrolyte, and is a nonaqueous electrolyte secondary battery.

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