JP4787477B2 - Non-aqueous electrolyte battery electrolyte additive, battery non-aqueous electrolyte and non-aqueous electrolyte battery - Google Patents

Description

  The present invention relates to an additive for an electrolyte of a non-aqueous electrolyte battery, a non-aqueous electrolyte for a battery containing the additive, and a non-aqueous electrolyte battery including the non-aqueous electrolyte, and particularly improves the exothermic reaction start temperature. The present invention also relates to a non-aqueous electrolyte battery.

  In recent years, there has been a demand for a light, long-life battery with high energy density as a main power source or auxiliary power source for electric vehicles and fuel cell vehicles, or as a power source for small electronic devices. In contrast, a non-aqueous electrolyte battery using lithium as a negative electrode active material is known as one of batteries having a high energy density because the electrode potential of lithium is the lowest among metals and the electric capacity per unit volume is large. Many types of batteries, whether primary batteries or secondary batteries, are actively researched, and some of them are put into practical use and supplied to the market. For example, non-aqueous electrolyte primary batteries are used as power sources for cameras, electronic watches, and various memory backups. In addition, non-aqueous electrolyte secondary batteries are used as drive power sources for notebook computers and mobile phones, and are also being considered for use as main power sources or auxiliary power sources for electric vehicles and fuel cell vehicles. .

  In these non-aqueous electrolyte batteries, lithium as the negative electrode active material reacts violently with compounds having active protons such as water and alcohol, so that the electrolyte used in the batteries is non-ester compounds and ether compounds. Limited to protic organic solvents.

  However, although the aprotic organic solvent has low reactivity with the lithium of the negative electrode active material, for example, when a battery is short-circuited, a large current flows suddenly, and when the battery abnormally generates heat, it is vaporized and decomposed. Therefore, there is a high risk of generating gas, causing the battery to rupture or ignite due to the generated gas and heat, and sparks generated during a short circuit.

  In order to satisfy the guidelines for safety evaluation standards for non-aqueous electrolyte batteries (see Non-Patent Document 1), store the non-aqueous electrolyte battery in a 130 ° C heat oven for 60 minutes, and the battery will burst or ignite. However, if a non-aqueous electrolyte in which a supporting salt is simply dissolved in an aprotic organic solvent is used, the above guidelines cannot be satisfied. Therefore, in order to comply with the above guidelines, safety measures such as attaching a safety valve are usually taken for nonaqueous electrolyte batteries.

  In contrast, a phosphazene compound is added to the battery non-aqueous electrolyte to impart non-flammability, flame retardancy or self-extinguishing properties to the non-aqueous electrolyte, and the battery ignites and ignites in the event of an emergency such as a short circuit. Non-aqueous electrolyte batteries that greatly reduce the risk have been developed (see Patent Documents 1 and 2). In this case, the above guidelines can be satisfied without attaching a safety valve to the nonaqueous electrolyte battery.

Battery Industry Association Guidelines, Lithium Secondary Battery Safety Evaluation Standard Guidelines, 4.3. (3) -ii Environmental Test International Publication No. 02/21631 Pamphlet International Publication No. 03/041197 Pamphlet

  However, in recent years, it has been studied to further tighten the standard of not bursting or igniting when stored at 130 ° C for 60 minutes, and even if a phosphazene compound is added to the nonaqueous electrolyte for batteries, a safety valve is provided. Unless safety measures such as this are taken, there is a possibility that the new standard cannot be satisfied.

  Accordingly, an object of the present invention is to provide an additive for an electrolyte solution of a nonaqueous electrolyte battery that can increase the exothermic reaction start temperature of the nonaqueous electrolyte battery as compared with the conventional additive for electrolyte solution. It is in. Another object of the present invention is to provide a non-aqueous electrolyte for a battery containing such an additive, and a non-aqueous electrolyte battery comprising the non-aqueous electrolyte and having a greatly improved exothermic reaction start temperature. is there.

  As a result of intensive studies to achieve the above object, the present inventor added a cyclic phosphazene compound having a specific structure to the non-aqueous electrolyte, which significantly increased the exothermic reaction start temperature of the non-aqueous electrolyte battery. As a result, the present invention has been completed.

That is, the additive for electrolyte solution of the nonaqueous electrolyte battery of the present invention has the following formula (I):
(NPX ₂ ) _n ... (I)
Wherein each X is independently F or Cl, provided that all Xs are not the same; n is 3 or 4; To do.

  In a preferred example of the additive for an electrolyte solution of the nonaqueous electrolyte battery of the present invention, n in the formula (I) is 3, and 1 to 3 of the 6 Xs are Cl.

  In another preferred example of the additive for electrolyte solution of the nonaqueous electrolyte battery of the present invention, n in the formula (I) is 4, and 2 to 5 of 8 Xs are Cl.

  In another preferred embodiment of the additive for electrolyte solution of the nonaqueous electrolyte battery of the present invention, the number of Cl bonded to each P in the formula (I) is 0 or 1. That is, when two or more of X in the formula (I) are Cl, each Cl is preferably bonded to different Ps.

  Moreover, the non-aqueous electrolyte for batteries of the present invention is characterized by containing the above-mentioned additive for electrolyte, an aprotic organic solvent, and a supporting salt.

  Furthermore, the non-aqueous electrolyte battery of the present invention includes the non-aqueous electrolyte for a battery, a positive electrode, and a negative electrode, and may be a primary battery or a secondary battery. Here, the nonaqueous electrolyte battery of the present invention preferably has an exothermic reaction start temperature of 150 ° C. or higher.

  According to the present invention, it is possible to provide an additive for an electrolyte solution of a non-aqueous electrolyte battery, which is composed of a cyclic phosphazene compound having a specific structure and can greatly increase the exothermic reaction start temperature of the non-aqueous electrolyte battery. it can. In addition, it is possible to provide a non-aqueous electrolyte for a battery containing the additive and having greatly improved safety. Furthermore, it is possible to provide a non-aqueous electrolyte battery comprising the non-aqueous electrolyte for a battery and having a greatly improved exothermic reaction start temperature.

The present invention is described in detail below.
<Additive for electrolyte solution of non-aqueous electrolyte battery>
The additive for electrolyte of the nonaqueous electrolyte battery of the present invention is characterized by comprising a cyclic phosphazene compound represented by the above formula (I). The phosphazene compound has an effect of suppressing the exothermic reaction of the non-aqueous electrolyte, and the non-aqueous electrolyte battery including the non-aqueous electrolyte containing the phosphazene compound has a high exothermic reaction start temperature and high safety. . In addition, the phosphazene compound generates nitrogen gas and / or phosphate ester, etc. in an emergency of a non-aqueous electrolyte battery, thereby making the non-aqueous electrolyte non-flammable, flame retardant or self-extinguishing, etc. It also has the effect of greatly reducing the risk of

  The phosphazene compound constituting the additive for electrolyte of the nonaqueous electrolyte battery of the present invention is represented by the above formula (I). In formula (I), each X is independently F or Cl, provided that not all X are the same. Note that when a compound containing a halogen element is used, the generation of a halogen radical may be a problem. However, since the phosphorus element in the molecule captures the halogen radical and forms phosphorus halide, Such a problem does not occur.

  In the formula (I), n is 3 or 4. When n is 5 or more, it is not preferable because efficient synthesis of the phosphazene compound becomes difficult. Here, the viscosity of the phosphazene compound at 25 ° C. is preferably 10 mPa · s or less, and more preferably 5 mPa · s or less, from the viewpoint of sufficiently securing the charge / discharge characteristics of the battery. In the present invention, the viscosity is 1 rpm, 2 rpm, 3 rpm, 5 rpm, 7 rpm, 10 rpm, 20 rpm, and 50 rpm using a viscometer [R-type viscometer Model RE500-SL, manufactured by Toki Sangyo Co., Ltd.] It is a value measured at that time, measured at the rotational speed for 120 seconds, with the rotational speed when the indicated value is 50 to 60% as the analysis condition.

  Among the above phosphazene compounds, from the viewpoint of a low freezing point, n in the formula (I) is 3, 1 to 3 out of 6 Xs and the rest are F, and the formula (I N) is 4 and 2 to 5 of 8 Xs are Cl and the remainder is F. The freezing point of the phosphazene compound in which X in formula (I) is F or Cl is shown in Table 1 together with the boiling point and the viscosity at 25 ° C.

  As is apparent from Table 1, in the phosphazene compound in which X in the formula (I) is F or Cl, the boiling point rises as the Cl number increases (increase in molecular weight), but the freezing point is in a specific Cl number range. When n is 3, the Cl number is preferably in the range of 1 to 3, and when n is 4, the Cl number is preferably in the range of 2 to 5. Here, the phosphazene compound preferably has a freezing point of −10 ° C. or lower. By adding a phosphazene compound having a freezing point of −10 ° C. or lower to the non-aqueous electrolyte, the low-temperature characteristics of the non-aqueous electrolyte battery can be improved.

  In addition, a phosphazene compound in which two Cls are bonded to one P is that P electrons are attracted by two Cls and P is positive, and from the electron orbits of Cl and P. Due to the degeneracy of the unoccupied lowest molecular orbitals, the reduction potential of P is lowered. Moreover, since Cl is a large element, it is easy to desorb because of its steric hindrance. When such a compound is used as an additive, the phosphazene compound may undergo reductive decomposition depending on the potential used, and may not be satisfactory as a battery function. Therefore, the number of Cl bonded to each P is preferably 0 or 1. [Hereinafter, a phosphazene compound in which two Cls are bonded to one P is referred to as a geminal body, and each Cl May be referred to as non-geminal bodies].

The phosphazene compound can be synthesized, for example, by a method in which a commercially available phosphazene compound represented by (NPCl ₂ ) _n is reacted with a fluorinating agent such as sodium fluoride (NaF) in a nitrobenzene solvent and partially fluorinated. As a conventional synthesis method, a synthesis method described in J. Chem. Soc., Ser. A., pp. 2590 81968 is known, but since the yield is low in the synthesis method, the present inventor , Using its own synthesis process. More specifically, when synthesizing a phosphazene compound represented by the formula (I), n = 3, and Cl / F ratios of 1/5, 2/4, and 3/3, 0.4 M of (NPCl ₂ ) Each phosphazene compound can be obtained by reacting ₃ nitrobenzene solutions with 2 equivalents of NaF for the first time, then adding a very small amount of water, and further reacting with 1 equivalent of NaF, followed by distillation under reduced pressure. it can. In particular, when obtaining a phosphazene compound having a high Cl ratio, such as a phosphazene compound having a Cl / F ratio of 4/2, the amount of NaF added may be reduced, and conversely, when the Cl / F ratio is reduced. What is necessary is just to increase the addition amount of NaF. In this synthesis method, a phosphazene compound having a desired Cl / F ratio can be synthesized by changing the ratio of (NPCl ₂ ) _n / NaF. In addition, the said phosphazene compound may be used individually by 1 type, and may be used as a 2 or more types of mixture.

<Non-aqueous electrolyte for batteries>
The non-aqueous electrolyte for a battery of the present invention includes the above-described additive for a non-aqueous electrolyte, an aprotic organic solvent, and a supporting salt, and suppresses an exothermic reaction. The risk of ignition is very low.

  The aprotic organic solvent used in the nonaqueous electrolytic solution for batteries of the present invention is not particularly limited, but ether compounds and ester compounds are preferred from the viewpoint of keeping the viscosity of the electrolytic solution low. Specifically, 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), dimethyl carbonate (DMC), diethyl carbonate (DEC), diphenyl carbonate, ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), γ-valerolactone, ethyl methyl carbonate (EMC), methyl formate (MF) and the like are preferable. Among these, examples of the aprotic organic solvent for the non-aqueous electrolyte of the primary battery include cyclic ester compounds such as propylene carbonate and γ-butyrolactone, chain ester compounds such as dimethyl carbonate and ethyl methyl carbonate, and 1,2. A chain ether compound such as -dimethoxyethane is preferred, while an aprotic organic solvent for the non-aqueous electrolyte of the secondary battery includes cyclic ester compounds such as ethylene carbonate, propylene carbonate, and γ-butyrolactone, dimethyl carbonate, Chain ester compounds such as ethyl methyl carbonate and diethyl carbonate, and chain ether compounds such as 1,2-dimethoxyethane are preferred. In particular, a cyclic ester compound is suitable in that it has a high relative dielectric constant and excellent solubility in lithium salts and the like, and a chain ester compound and an ether compound have a low viscosity. This is preferable in terms of points. These may be used individually by 1 type, may use 2 or more types together, but it is suitable to use 2 or more types together. The viscosity of the aprotic organic solvent at 25 ° C. is not particularly limited, but is preferably 10 mPa · s (10 cP) or less, and more preferably 5 mPa · s (5 cP) or less.

As the supporting salt used in the non-aqueous electrolyte for a battery of the present invention, a supporting salt serving as a lithium ion source is preferable. The supporting salt is not particularly limited, and for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N and Li ( Preferable examples include lithium salts such as C ₂ F ₅ SO ₂ ) ₂ N. These supporting salts may be used individually by 1 type, and 2 or more types may be mixed and used for them.

  The concentration of the supporting salt in the battery non-aqueous electrolyte of the present invention is preferably in the range of 0.2 to 1.5 mol / L (M), more preferably in the range of 0.5 to 1 mol / L (M). If the concentration of the supporting salt is less than 0.2 mol / L, the conductivity of the electrolyte cannot be sufficiently ensured, and the discharge characteristics and charging characteristics of the battery may be hindered. Since the viscosity of the electrolytic solution increases and the mobility of lithium ions cannot be ensured sufficiently, the conductivity of the electrolytic solution cannot be sufficiently ensured in the same manner as described above, which may hinder battery discharge characteristics and charge characteristics. .

  The content of the phosphazene compound in the nonaqueous electrolytic solution for a battery of the present invention (that is, the content of an additive) improves the safety of the electrolytic solution and sufficiently increases the exothermic reaction start temperature of the battery. 2% by volume or more is preferable, and 5% by volume or more is more preferable.

<Nonaqueous electrolyte battery>
The non-aqueous electrolyte battery of the present invention includes the above-described non-aqueous electrolyte for a battery, a positive electrode, and a negative electrode, and is usually used in the technical field of non-aqueous electrolyte batteries such as a separator as necessary. It may be a primary battery or a secondary battery provided with other members. Since the nonaqueous electrolyte solution containing the above-mentioned additive is used in the nonaqueous electrolyte battery of the present invention, the exothermic reaction start temperature of the battery in ARC analysis is high, and preferably the exothermic reaction start temperature is 150 ° C. That's it.

The positive electrode active material of the non-aqueous electrolyte battery of the present invention is partially different between the primary battery and the secondary battery. For example, as the positive electrode active material of the non-aqueous electrolyte primary battery, fluorinated graphite [(CF _x ) _n ], MnO ₂ (which may be electrochemical synthesis or chemical synthesis), V ₂ O ₅ , MoO ₃ , Ag ₂ CrO ₄ , CuO, CuS, FeS ₂ , SO ₂ , SOCl ₂ , TiS _2, etc. Among these, MnO ₂ and fluorinated graphite are preferable from the viewpoints of high capacity, high safety, high discharge potential, and excellent wettability of the electrolytic solution. These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.

On the other hand, as the positive electrode active material of the non-aqueous electrolyte secondary battery, metal oxides such as V ₂ O ₅ , V ₆ O ₁₃ , MnO ₂ , MnO ₃ , LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFeO _{2 are used.} Preferable examples include lithium-containing composite oxides such as LiFePO ₄ , metal sulfides such as TiS ₂ and MoS ₂ , and conductive polymers such as polyaniline. The lithium-containing composite oxide may be a composite oxide containing two or three transition metals selected from the group consisting of Fe, Mn, Co, and Ni. In this case, the composite oxide includes: LiFe _x Co _y Ni [wherein, 0 ≦ x <1,0 ≦ y <1,0 <x + y ≦ 1] (1-xy) O 2, or represented by LiMn _x Fe _y O _2-xy like. Among these, LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are particularly preferable in terms of high capacity, high safety, and excellent electrolyte wettability. These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  The negative electrode active material of the nonaqueous electrolyte battery of the present invention is partially different between the primary battery and the secondary battery. For example, as the negative electrode active material of the nonaqueous electrolyte primary battery, lithium metal itself, lithium alloy, etc. Is mentioned. Examples of the metal that forms an alloy with lithium include Sn, Pb, Al, Au, Pt, In, Zn, Cd, Ag, and Mg. Among these, Al, Zn, and Mg are preferable from the viewpoints of rich reserves and toxicity. These negative electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  On the other hand, preferred examples of the negative electrode active material of the non-aqueous electrolyte secondary battery include lithium metal itself, an alloy of lithium and Al, In, Pb or Zn, a carbon material such as graphite doped with lithium, and the like. Among these, a carbon material such as graphite is preferable, and graphite is particularly preferable in view of higher safety and excellent wettability of the electrolytic solution. Here, examples of graphite include natural graphite, artificial graphite, mesophase carbon microbeads (MCMB), and the like, and widely include graphitizable carbon and non-graphitizable carbon. These negative electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  The positive electrode and the negative electrode can be mixed with a conductive agent and a binder as necessary. Examples of the conductive agent include acetylene black, and the binder includes polyvinylidene fluoride (PVDF) and polytetrafluoro. Examples include ethylene (PTFE), styrene / butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like. These additives can be used at a blending ratio similar to the conventional one.

  Moreover, there is no restriction | limiting in particular as a shape of the said positive electrode and a negative electrode, It can select suitably from well-known shapes as an electrode. For example, a sheet shape, a columnar shape, a plate shape, a spiral shape, and the like can be given.

  As another member used in the nonaqueous electrolyte battery of the present invention, a separator interposed in the nonaqueous electrolyte battery between the positive and negative electrodes to prevent a short circuit of current due to contact of both electrodes can be mentioned. As the material of the separator, it is possible to reliably prevent contact between the two electrodes and to allow the electrolyte to pass through or to contain, for example, synthesis of polytetrafluoroethylene, polypropylene, polyethylene, cellulose, polybutylene terephthalate, polyethylene terephthalate, etc. Preferred examples include resin non-woven fabrics and thin layer films. Of these, polypropylene or polyethylene microporous films having a thickness of about 20 to 50 μm, cellulose-based films, polybutylene terephthalate, polyethylene terephthalate, and the like are particularly suitable. In the present invention, in addition to the separators described above, known members that are normally used in batteries can be suitably used.

  The form of the non-aqueous electrolyte battery of the present invention described above is not particularly limited, and various known forms such as a coin-type, button-type, paper-type, square-type or spiral-type cylindrical battery are suitable. Can be mentioned. In the case of the button type, a non-aqueous electrolyte battery can be produced by preparing a sheet-like positive electrode and negative electrode and sandwiching a separator between the positive electrode and the negative electrode. In the case of a spiral structure, for example, a non-aqueous electrolyte battery can be produced by stacking and winding up a sheet-like positive electrode and a negative electrode via a separator.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

<Synthesis example 1 of phosphazene compound>
A 0.4 M (NPCl ₂ ) ₃ nitrobenzene solution was reacted with 2 equivalents of NaF for the first time, after which a very small amount of water was added, and then 1 equivalent of NaF was further reacted. The obtained reaction mixture was distilled under reduced pressure, represented by the formula (I), n = 3, Cl / F ratio of 1/5, 2/4 (geminal body and non-geminal body), 3/3. Each phosphazene compound was obtained. FIG. 1 shows a GC chart of GC-MS analysis of the reaction mixture before distillation under reduced pressure.

<Preparation of non-aqueous electrolyte for battery>
Next, 10% by volume of a phosphazene compound (additive) having a structure shown in Table 2 is added to 90% by volume of a mixed solvent (EC / EMC volume ratio = 1/2) of ethylene carbonate (EC) and ethyl methyl carbonate (EMC). In addition, LiPF ₆ (supporting salt) was dissolved in the obtained mixed solution at a concentration of 1M (mol / L) to prepare a nonaqueous electrolytic solution. The conventional non-aqueous electrolyte was prepared by dissolving LiPF ₆ at a concentration of 1M in a mixed solvent of EC and EMC (EC / EMC volume ratio = 1/2).

<Preparation of non-aqueous electrolyte secondary battery>
3 parts by mass of acetylene black (conductive agent) and 3 parts by mass of polyvinylidene fluoride (binder) are added to 94 parts by mass of LiCoO ₂ (positive electrode active material), and an organic solvent (ethyl acetate and ethanol) is added. 50/50% by mass mixed solvent), the kneaded product was applied to a 25 μm thick aluminum foil (current collector) with a doctor blade, and then dried with hot air (100 to 120 ° C.) to obtain a thickness. An 80 μm positive electrode sheet was produced. Further, 3 parts by mass of acetylene black (conductive agent) and 3 parts by mass of polyvinylidene fluoride (binder) are added to 94 parts by mass of graphite (carbon material), and an organic solvent (ethyl acetate and ethanol) is added. 50/50% by mass mixed solvent), the kneaded product was applied to a 25 μm thick aluminum foil (current collector) with a doctor blade, and then dried with hot air (100 to 120 ° C.) to obtain a thickness. A 150 μm negative electrode sheet was prepared. The positive electrode sheet and the negative electrode sheet were overlapped and rolled up through a separator (microporous film: made of polypropylene) having a thickness of 25 μm to produce a cylindrical electrode. The positive electrode length of the cylindrical electrode was about 260 mm. The above electrolytic solution was injected into the cylindrical electrode and sealed to prepare an AA lithium battery (non-aqueous electrolyte secondary battery). The obtained battery was charged under the conditions of 4.2 V and 3.7 mAh, and then ARC analysis was performed by the following method. The results are shown in FIGS. 2 and 3 and Table 2.

(1) ARC analysis method Under the measurement conditions of start temperature = 50 ° C., end temperature = 350 ° C., temperature step = 5 ° C., temperature sensitivity = 0.02 ° C./min, standby time = 17 minutes, analysis step temperature = 0.2 ° C. ARC analysis was performed on the battery using an ARC apparatus manufactured by Thermal Hazard Technology.

  As is clear from Table 1, a phosphazene compound represented by the formula (I), wherein X is F or Cl, provided that all Xs are not the same and n is 3 or 4, is added to the non-aqueous electrolyte. As a result, the exothermic reaction start temperature of the non-aqueous electrolyte battery can be increased. In addition, from the comparison between Example 1 and Example 2, in the phosphazene compound containing a plurality of Cls, the effect of improving the exothermic reaction start temperature of the battery is greater when each Cl is bonded to different P. Recognize.

The GC chart of GC-MS analysis of the reaction mixture obtained by the synthesis example 1 is shown. The result of the ARC analysis of the nonaqueous electrolyte secondary battery of a prior art example and a comparative example is shown. The result of the ARC analysis of the nonaqueous electrolyte secondary battery of a prior art example and an Example is shown.

Claims (7)

Formula (I) below:
(NPX ₂ ) _n ... (I)
[Wherein X is independently F or Cl, provided that all X are not the same; n is 3 or 4] Additive for battery electrolyte.   2. The additive for an electrolyte solution of a non-aqueous electrolyte battery according to claim 1, wherein n in the formula (I) is 3, and 1 to 3 of 6 Xs are Cl.   The additive for electrolyte solution of the non-aqueous electrolyte battery according to claim 1, wherein n in the formula (I) is 4, and 2 to 5 of 8 Xs are Cl.   2. The additive for an electrolyte solution of a nonaqueous electrolyte battery according to claim 1, wherein the number of Cl bonded to each P in the formula (I) is 0 or 1. 3.   A nonaqueous electrolytic solution for a battery comprising the additive for electrolytic solution according to any one of claims 1 to 4, an aprotic organic solvent, and a supporting salt.   A nonaqueous electrolyte battery comprising the battery nonaqueous electrolyte solution according to claim 5, a positive electrode, and a negative electrode.   The nonaqueous electrolyte battery according to claim 6, wherein the exothermic reaction start temperature is 150 ° C. or higher.

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