JP5125029B2 - battery - Google Patents

Description

  The present invention relates to a battery including a negative electrode containing at least one of silicon (Si) and tin (Sn).

  In recent years, portable electronic devices (information terminal devices) such as mobile phones and notebook computers have been remarkably reduced in size and weight. Along with this, research and development for reducing the weight and increasing the output of the power source for driving these portable information terminal devices has been actively conducted. In particular, lithium ion secondary batteries using a lithium compound as an active material have features such as light weight, high voltage, and high energy density, and thus have been widely put into practical use as the driving power source.

  Recently, with the improvement in performance of portable electronic devices, there has been a demand for further improvement in the capacity of secondary batteries, and it is considered to use silicon or tin with a large theoretical capacity instead of carbon materials as the negative electrode active material. Has been. This is because the theoretical capacity of silicon, 4199 mAh / g, is much larger than the theoretical capacity of graphite, 372 mAh / g, so that an improvement in capacity can be expected. In particular, a negative electrode in which a silicon thin film is formed on a current collector can maintain a relatively large discharge capacity without pulverization of the negative electrode active material due to insertion and extraction of lithium (Li).

  In general, an organic solvent such as cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC) is often used as an electrolytic solution for a lithium ion secondary battery. Since these solvents are high dielectric constant solvents, they can easily dissolve the lithium salt as the supporting electrolyte, and have a wide potential window, which is advantageous for ensuring stability at a high potential. However, the organic solvent of carbonic acid esters has a relatively high viscosity, which is disadvantageous for efficient ion transfer. Moreover, it has a high melting point and may solidify at a low temperature. For this reason, a low-viscosity chain carbonate such as dimethyl carbonate (DMC) is usually used in combination.

  In addition, by adding a cyclic carbonate having an unsaturated bond such as vinylene carbonate (VC) or vinyl ethylene carbonate (VEC) to the electrolyte, decomposition of the solvent during charging and discharging is suppressed, and cycle characteristics are improved. It has been known. This is because, when the battery is charged for the first time, the unsaturated cyclic carbonate is reduced and decomposed, so that a stable film is formed on the surface of the electrode, which prevents contact between the electrode and solvent molecules, resulting in decomposition of the solvent. It is thought to be suppressed.

Furthermore, by adding a room temperature molten salt that has a high electrical conductivity that is less volatile than organic solvents and that has a high flash point, the battery is designed to achieve high performance and high safety. Development is underway (see, for example, Patent Documents 1 to 3).
JP 2003-331918 A JP 2005-183195 A JP 2001-351681 A

  However, recently, with the increase in demand for portable electronic devices, they are often placed under high temperature conditions during transportation or use, and deterioration of battery characteristics under such conditions has become a problem. . This is considered to be because a part of the lithium salt decomposes as the temperature increases, and a free acid is generated, resulting in self-discharge. Therefore, not only improvement of characteristics at room temperature but also improvement of characteristics at high temperature is a problem.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a battery that has a high capacity and can exhibit excellent high-temperature characteristics.

The battery of the present invention includes an electrolyte solution together with a positive electrode and a negative electrode, the negative electrode includes at least one of silicon (Si) and tin (Sn) as a negative electrode active material, and the electrolyte solution melts at room temperature together with a solvent having difluoroethylene carbonate. It contains salt. The ambient temperature molten salt in the electrolyte includes a five-membered or six-membered cyclic cation having at least one hetero atom, (CF ₃ SO ₂ ) ₂ N ⁻ , (CF ₃ CF ₂ SO ₂ ) ₂ ) N ^−. , PF ₆ ⁻ , BF ₄ ⁻ and an anion having at least one of them.
The cyclic cation includes 1-methyl-3-n-butylimidazolium ion, 1,2-dimethylpyrrolium ion, 1-methyl-2-n-butylpyrazolium ion, 1-methyl-1-n-propylpiperidin Of 1-n-butyl-4-methylpyridinium ion, 1-ethylpyridazinium ion, 1-n-propylpyrimidinium ion, 1-ethylpyrazinium ion, 2,3-dimethylthiazolium ion It contains at least one kind.

  Since the battery of the present invention has a negative electrode containing at least one of silicon and tin, a larger capacity than that of the negative electrode made of graphite is ensured, and a predetermined cyclic cation contained in the room temperature molten salt in the electrolytic solution And the decomposition reaction of the electrolyte solution under a high temperature environment is suppressed by the anion.

According to the battery of the present invention, the negative electrode active material includes at least one of silicon and tin, and a predetermined cyclic cation, (CF ₃ SO ₂ ) ₂ N ⁻ , (CF ₃ CF ₂ SO ₂ ) ₂ ) N ^{_{-, PF 6 -, BF 4}} - since as added to the electrolyte ambient temperature molten salt comprising an anion having at least one of, it is possible to realize a high capacity and excellent high-temperature characteristics.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration of a secondary battery 1 as an embodiment of the present invention. This secondary battery 1 is a so-called coin-type battery, in which a negative electrode 4 accommodated in an exterior cup 5 and a positive electrode 2 accommodated in an exterior can 3 are stacked via a separator 6. It is.

  The peripheral portions of the outer cup 5 and the outer can 3 are sealed by caulking through an insulating gasket 7. Between the gasket 7, the negative electrode 4 and the positive electrode 2, an electrolytic solution 8 which is a liquid electrolyte is filled. The electrolytic solution 8 is also impregnated in the separator 6. The exterior cup 5 is made of, for example, a metal such as stainless steel, aluminum, or iron whose surface is nickel-plated. The exterior cup 5 is a petri dish-like container that accommodates the negative electrode 4 and serves as an external negative electrode of the secondary battery 1.

  The outer can 3 has a shallow dish shape that accommodates the positive electrode 2, a so-called petri dish shape, and serves as an external positive electrode of the secondary battery 1. The outer can 3 is made of, for example, stainless steel, aluminum, or a metal having a laminated structure in which aluminum, stainless steel, and nickel are sequentially laminated in the thickness direction from the side of the accommodated positive electrode 2.

  The negative electrode 4 has, for example, a structure in which a negative electrode current collector 11 is provided with a negative electrode active material layer 12. The negative electrode current collector 11 is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil.

The negative electrode active material layer 12 includes a negative electrode material capable of inserting and extracting lithium (Li) as an electrode reactant as a negative electrode active material. The negative electrode active material layer 12 may include a conductive material such as a carbon material and a binder such as polyvinylidene fluoride or styrene butadiene rubber as necessary. The negative electrode material capable of inserting and extracting lithium contains at least one of silicon and tin. Silicon and tin have a large ability to occlude and release lithium, and a high energy density can be obtained. In particular, silicon is preferable because of its larger theoretical capacity. Silicon or tin may be contained as a simple substance, as an alloy, as a compound, or as a mixture of two or more thereof. _{Specifically, M r Si, M s Sn} , M t Si 2, M u Sn 2 (M is Si, is one or more elements other than Sn, r, s, t, u is 0 or more numeric SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi ₂ , Cu ₅ Si, FeSi ₂ , MnSi ₂ , NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi ₂ and other silicon compounds and tin compounds. Further, as oxide compounds, nitrogen compounds, or carbonized compounds containing silicon or tin, for example, SiC, Si ₃ N ₄ , Si ₂ N ₂ O, SiO _v (0 <v ≦ 2), SnO _w (0 <w ≦) 2), LiSiO, LiSnO and the like. Furthermore, as an alloy of silicon, for example, at least one selected from the group consisting of tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony and chromium in addition to silicon The thing containing is mentioned. Examples of the tin alloy include, in addition to tin, at least one selected from the group consisting of silicon, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium. Things.

  The negative electrode active material layer 12 is preferably formed at least partly by, for example, one or more methods selected from the group consisting of a vapor phase method, a liquid phase method, a firing method, and a thermal spray method. It may be formed by combining two or more. Specific examples include a mechanical alloying method, a melt spinning method, a gas atomizing method, and a water atomizing method. Breakage due to expansion / contraction of the negative electrode active material layer 12 due to charge / discharge can be suppressed, the negative electrode current collector 11 and the negative electrode active material layer 12 can be integrated, and electrons in the negative electrode active material layer 12 can be integrated. This is because the conductivity can be improved. Note that the “firing method” means that a layer formed by mixing a powder containing an active material and a binder is heat-treated in a non-oxidizing atmosphere or the like, so that the volume density is higher than that before the heat treatment and the denser. It means the method of forming a layer.

  The negative electrode active material layer 12 is preferably alloyed with the negative electrode current collector 11 at least at a part of the interface with the negative electrode current collector 11. Specifically, the constituent elements of the negative electrode current collector 11 are diffused in the negative electrode active material layer 12, the constituent elements of the negative electrode active material layer 12 are diffused in the negative electrode current collector 11, or they are mutually diffused at the interface. preferable. This is because the adhesion can be improved and the negative electrode active material layer 12 can be prevented from falling off the negative electrode current collector 11 due to expansion and contraction.

  The positive electrode 2 includes, for example, a positive electrode current collector 10 and a positive electrode active material layer 9 provided on the positive electrode current collector 10 such that the positive electrode active material layer 9 side faces the negative electrode active material layer 12. Is arranged. The positive electrode current collector 10 is made of, for example, net-like or foil-like aluminum, nickel, or stainless steel.

The positive electrode active material layer 9 includes, for example, any one or more of positive electrode materials capable of inserting and extracting lithium as a positive electrode active material, and a conductive material such as a carbon material and the like as necessary. A binder such as polyvinylidene fluoride may be included. As a positive electrode material capable of inserting and extracting lithium, for example, a lithium-containing metal composite oxide represented by the general formula Li _x MIO ₂ is preferable. This is because the lithium-containing metal composite oxide can generate a high voltage and has a high density, so that the secondary battery 1 can be further increased in capacity. MI is one or more kinds of transition metals, and for example, at least one of cobalt and nickel is preferable. x varies depending on the charge / discharge state of the secondary battery 1 and is usually a value in the range of 0.05 ≦ x ≦ 1.10. Specific examples of such a lithium-containing metal composite oxide include LiCoO ₂ , LiNiO ₂ , or Li _x Ni _y Co _1-y O ₂ (x and y differ depending on the charge / discharge state of the secondary battery 1, 0 <x <1, 0.7 <y <1.02.). Other positive electrode materials include specific polymers such as TiS ₂ , MoS ₂ , NbSe ₂ , V ₂ O _{5 and} other lithium-free metal sulfides, metal oxides, polyaniline, or LiMn ₂ O _4. Examples include spinel-type lithium / manganese composite oxides.

  The positive electrode 2 is prepared, for example, by mixing a positive electrode material, a conductive material, and a binder to prepare a mixture, and dispersing the mixture in a dispersion medium such as N-methyl-2-pyrrolidone to produce a mixture slurry. The mixture slurry can be applied to the positive electrode current collector 10 made of a metal foil, dried, and then compression molded to form the positive electrode active material layer 9.

  The separator 6 separates the negative electrode 4 and the positive electrode 2 and allows lithium ions to pass through while preventing a short circuit of current due to contact between both electrodes. The separator 6 includes, for example, a microporous film having many fine pores. The microporous membrane is preferably a resin membrane having a large number of micropores having an average pore diameter of about 5 μm or less. Moreover, the material of the separator 6 can utilize what was used for the conventional battery, for example, Among these, the polypropylene which is excellent in the short-circuit prevention effect and can improve the safety | security of the battery by the shutdown effect. Polyolefin resins such as polyethylene and polyethylene are preferred. The separator 6 has a thickness in the range of, for example, 5 μm or more and 50 μm or less, and more preferably has a porosity representing a void volume ratio in the entire volume of 20% or more and 60% or less. . By using such a separator 6, the secondary battery 1 excellent in manufacturing yield, output characteristics, cycle characteristics, and safety can be obtained.

  As described above, the separator 6 is impregnated with the electrolytic solution 8. The electrolytic solution 8 includes a solution having difluoroethylene carbonate as a solvent and a room temperature molten salt, and a lithium salt as an electrolyte salt dissolved in the solution, and includes an additive as necessary. Also good.

  The electrolytic solution 8 contains difluoroethylene carbonate and a room temperature molten salt, so that the decomposition reaction at a high temperature is suppressed and the stability is improved. In particular, when the concentration of difluoroethylene carbonate in the solution is 0.01% by mass or more and 50% by mass or less, more preferably 30% by mass or more and 40% by mass or less, a good-quality film is formed on the electrode surface, and the electrolytic solution 8 The decomposition reaction of is sufficiently suppressed. As difluoroethylene carbonate, for example, 4,5-difluoro-1,3-dioxolan-2-one can be used. 4,5-Difluoro-1,3-dioxolan-2-one may be either a cis isomer or a trans isomer, or a mixture thereof.

The room temperature molten salt has (CF ₃ SO ₂ ) ₂ N ⁻ , (CF ₃ CF ₂ SO ₂ ) ₂ ) N ⁻ , PF ₆ ⁻ together with a 5- or 6-membered cyclic cation having at least one heteroatom. , BF ₄ ^- includes anions having at least one of. The cyclic cation here is the imidazolium cation shown in Chemical formula 1, the pyrrolium cation shown in Chemical formula 2, the pyrazolium cation shown in Chemical formula 3, the pyrrolidinium cation shown in Chemical formula 4, and the chemical formula 5. Piperidinium cation, pyridinium cation shown in Chemical formula 6, pyridazinium cation shown in Chemical formula 7, pyrimidinium cation shown in Chemical formula 8, pyrazinium cation shown in Chemical formula 9, thia shown in Chemical formula 10 It contains at least one of zolium cations.

（Ｒ１，Ｒ３は炭素数が１から５の炭化水素基であり、Ｒ２は水素原子または炭素数が１から５の炭化水素基のいずれかである。）

（Ｒ４は水素原子または炭素数が１から５の炭化水素基であり、Ｒ５は炭素数が１から５の炭化水素基である。）

（Ｒ６は水素原子または炭素数が１から５の炭化水素基であり、Ｒ７は炭素数が１から５の炭化水素基である。）

（Ｒ８，Ｒ９は炭素数が１から５の炭化水素基である。）

（Ｒ１０，Ｒ１１は炭素数が１から５の炭化水素基である。）

（Ｒ１２，Ｒ１３は水素原子または炭素数が１から５の炭化水素基である。）

（Ｒ１４，Ｒ１５は水素原子または炭素数が１から５の炭化水素基である。）

（Ｒ１６，Ｒ１７は水素原子または炭素数が１から５の炭化水素基である。）

（Ｒ１８，Ｒ１９は水素原子または炭素数が１から５の炭化水素基である。）

（Ｒ２０は炭素数が１から５の炭化水素基であり、Ｒ２１は水素原子または炭素数が１から５の炭化水素基である。）

(R1 and R3 are hydrocarbon groups having 1 to 5 carbon atoms, and R2 is either a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms.)

(R4 is a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms, and R5 is a hydrocarbon group having 1 to 5 carbon atoms.)

(R6 is a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms, and R7 is a hydrocarbon group having 1 to 5 carbon atoms.)

(R8 and R9 are hydrocarbon groups having 1 to 5 carbon atoms.)

(R10 and R11 are hydrocarbon groups having 1 to 5 carbon atoms.)

(R12 and R13 are a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms.)

(R14 and R15 are hydrogen atoms or hydrocarbon groups having 1 to 5 carbon atoms.)

(R16 and R17 are a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms.)

(R18 and R19 are hydrogen atoms or hydrocarbon groups having 1 to 5 carbon atoms.)

(R20 is a hydrocarbon group having 1 to 5 carbon atoms, and R21 is a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms.)

  As the solvent, in addition to the above, for example, one or more of carbonic acid esters such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate may be included.

Examples of lithium salts include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), and lithium trifluoromethanesulfonate. (CF ₃ SO ₃ Li), bis (trifluoromethanesulfonyl) imidolithium ((CF ₃ SO ₂ ) ₂ NLi), tris (trifluoromethanesulfonyl) methyllithium ((CF ₃ SO ₂ ) ₃ CLi), and the like. Any one of the above may be used alone, or two or more may be mixed and used.

  In manufacturing the secondary battery 1, for example, a negative electrode 4, a separator 6 impregnated with an electrolyte solution 8 containing a predetermined room temperature molten salt together with difluoroethylene carbonate, and a positive electrode 2 are laminated, and an outer cup 5 and an outer can 3 are laminated. And injecting the electrolyte solution 8 as necessary, and then caulking them.

  In the secondary battery 1, when charged, for example, lithium ions are extracted from the positive electrode 2 and inserted in the negative electrode 4 through the electrolytic solution 8. When discharging is performed, for example, lithium ions are extracted from the negative electrode 4 and inserted into the positive electrode 2 through the electrolytic solution 8.

  Thus, according to the present embodiment, a larger battery capacity can be ensured by using a negative electrode containing at least one of silicon and tin. Furthermore, since the room temperature molten salt containing a predetermined cyclic cation and anion is added to the electrolytic solution 8 containing difluoroethylene carbonate, the electrical conductivity of the electrolytic solution 8 is improved not only at the normal temperature but also at a high temperature. Ion conductivity can be obtained, and the decomposition reaction of the electrolyte solution 8 is suppressed by the effect of the film formed on the electrode surface, so that excellent cycle characteristics can be obtained.

Further, specific examples of the present invention will be described in detail.
(Examples 1-1 to 1-12)
In this example, the secondary battery 1 described in the above embodiment was manufactured in the following manner.

  First, a negative electrode active material layer 12 having a thickness of 5 μm made of silicon or tin was formed on the negative electrode current collector 11 made of a copper foil having a thickness of 15 μm by an electron beam evaporation method. After that, the negative electrode 4 was produced by punching into a pellet having a diameter of 16 mm. At that time, the amount of lithium-cobalt composite oxide and silicon or tin is adjusted so that the charge capacity of silicon or tin is larger than the charge capacity of the positive electrode 2, and lithium metal is added to the negative electrode 4 during the charge. It was made not to precipitate. After that, the negative electrode current collector 11 on which the negative electrode active material layer 12 was formed was punched into a circle having a diameter of 16 mm.

Further, lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) are mixed at a ratio of Li ₂ CO ₃ : CoCO ₃ = 0.5: 1 (molar ratio), and 5 ° C. at 900 ° C. in the air. After firing for a time, lithium-cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material was obtained. Next, 94 parts by mass of this lithium-cobalt composite oxide, 3 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder were prepared, and then a positive electrode mixture was prepared. A positive electrode mixture slurry was prepared by dispersing in some N-methyl-2-pyrrolidone. Subsequently, the positive electrode mixture slurry was applied to a positive electrode current collector 10 made of an aluminum foil having a thickness of 20 μm, dried, and then compression molded to form the positive electrode active material layer 9. After that, the positive electrode 2 was produced by punching into a pellet having a diameter of 15.5 mm.

Subsequently, the positive electrode 2 and the negative electrode 4 produced as described above were placed on the outer can 3 via the separator 6 made of a microporous polypropylene film, and an electrolytic solution 8 having a predetermined component was injected thereon. After that, the outer cup 5 was covered and caulked. As shown in Table 1 below, the electrolyte solution 8 was prepared by mixing LiPF ₆ as an electrolyte salt at a concentration of 1 mol / dm ³ in a mixture (that is, a solution) of a solvent and a room temperature molten salt whose composition was changed according to each example. What was dissolved in was used.

Specifically, a solvent comprising difluoroethylene carbonate (DFEC) and dimethyl carbonate (DMC), a cyclic cation and an imide anion ((CF ₃ SO ₂ ) shown in the following chemical formulas 11 (1) to 11 (10) ₂ N ⁻ ) and room temperature molten salt were prepared, and their composition was changed. Here, chemical formula 11 (1) is 1-methyl-3-n-butylimidazolium ion, chemical formula 11 (2) is 1,2-dimethylpyrrolium ion, and chemical formula 11 (3) is 1-methyl. 2-n-butylpyrazolium ion, wherein 11 (4) is 1-ethyl-1-methylpyrrolidinium ion and 11 (5) is 1-methyl-1-n-propylpiperidinium ion Chemical formula 11 (6) is 1-n-butyl-4-methylpyridinium ion, chemical formula 11 (7) is 1-ethylpyridazinium ion, chemical formula 11 (8) is 1-n-propylpyridium ion. It is a midinium ion, chemical formula 11 (9) is a 1-ethylpyrazinium ion, chemical formula 11 (10) is a 2,3-dimethylthiazolium ion.

  Moreover, the secondary battery as Comparative Examples 1-1 to 1-9 with respect to Examples 1-1 to 1-12 was produced as follows. First, the secondary battery of Comparative Example 1-1 was the same as Examples 1-1 to 1-12 except that a solvent consisting only of ethylene carbonate (EC) and dimethyl carbonate (DMC) was used. Produced. Further, in the secondary batteries of Comparative Example 1-2 and Comparative Example 1-3, none of the room temperature molten salts containing the cyclic cations shown in Chemical Formulas 11 to 20 was added to the solvent, and the other Example 1- It produced similarly to 1-1-12. Further, in the secondary batteries as Comparative Examples 1-4 to 1-9, difluoroethylene carbonate (DFEC) was not used as a solvent. Instead, ethylene carbonate (EC), fluoroethylene carbonate (FEC), or propylene carbonate ( Except for the addition of (PC), the others were produced in the same manner as in Examples 1-1 to 1-9. In addition, the constituent material of the negative electrode 4 used in Examples 1-1 to 1-12 and Comparative Examples 1-1 to 1-9, the composition of the solution, and the composition ratio (% by mass) are as shown in Table 1. In Table 1, Chemical Formula I to Chemical Formula X represent room temperature molten salts containing the cyclic cations represented by Chemical Formula 11 (1) to Chemical Formula 11 (10), respectively.

  For the fabricated secondary batteries of Examples 1-1 to 1-12 and Comparative Examples 1-1 to 1-9, a charge / discharge test was performed to examine high-temperature storage characteristics and high-temperature cycle characteristics. The high-temperature storage characteristics include two cycles of charging and discharging at 23 ° C., charging again and leaving it in a constant temperature bath at 60 ° C. for 30 days, then discharging again at 23 ° C. and discharging after storage with respect to the discharge capacity before storage. It was determined from the ratio of capacity, that is, (discharge capacity after storage / discharge capacity value before storage) × 100. The discharge capacity before storage is the discharge capacity at the second cycle, and the discharge capacity after storage is the discharge capacity immediately after storage, that is, the discharge capacity at the third cycle as a whole.

  The high-temperature cycle characteristics are as follows. After charging and discharging at 23 ° C. for 2 cycles, charging and discharging are repeated for 100 cycles in a constant temperature bath at 60 ° C. It was determined from the ratio of the discharge capacity, that is, (discharge capacity at 100th cycle at 60 ° C./discharge capacity value at the second cycle at 23 ° C.) × 100. The obtained results are shown in Table 1.

In addition, charge and discharge are all under the same conditions, and charge is 1 mA. Until the battery voltage reaches 4.2V at a constant current of 4.2V, then until the current reaches 0.02mA at a constant voltage of 4.2V, and discharge is performed until the battery voltage reaches 3V at a constant current of 1mA. It was.

  As shown in Table 1, an example in which both difluoroethylene carbonate (DFEC) and a room temperature molten salt (including any cyclic cation of Chemical Formula 11 (1) to Chemical Formula 11 (10)) was added. According to 1-1 to 1-12, compared with Comparative Examples 1-2 to 1-9 lacking any one of them or Comparative Example 1-1 not including any of them, the high temperature storage characteristics and Both high-temperature cycle characteristics could be improved.

  In addition, according to the comparison between Examples 1-1 to 1-4 and Comparative Examples 1-2 and 1-3, difluoroethylene carbonate was used regardless of whether silicon was used as the negative electrode material or tin was used. It was also found that the effect of adding room temperature molten salt can be obtained.

From the above, when using a simple substance, alloy or compound of silicon or tin as a negative electrode active material capable of occluding and releasing lithium, it is excellent if the electrolyte contains a predetermined room temperature molten salt together with difluoroethylene carbonate. It was found that a secondary battery exhibiting high temperature characteristics can be realized.
(Examples 2-1 to 2-5)
Secondary battery 1 was produced in the same manner as in Examples 1-1 to 1-12. At that time, silicon was used as a negative electrode material. Further, the composition ratio of the solution in the electrolytic solution was changed as shown in Table 2 below. For the secondary batteries 1 of Examples 2-1 to 2-5, charge and discharge tests were performed in the same manner as in Examples 1-1 to 1-12, and high temperature storage characteristics and high temperature cycle characteristics were examined. The results are shown in Table 2 together with Example 1-1 and Comparative Example 1-5.

  As shown in Table 2, according to Examples 2-1 to 2-5, Example 1-1, and Comparative Example 1-5, the content of difluoroethylene carbonate is 0.01% by mass or more to 50% of the entire solution. It was found that the high temperature storage characteristics and the high temperature cycle characteristics higher than those of Comparative Example 1-5 containing no difluoroethylene carbonate were obtained when the content was less than or equal to mass%. In particular, it was found that more excellent high temperature characteristics can be obtained at 30% by mass or more and 40% by mass or less.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. In the above embodiments and examples, a battery using lithium as an electrode reactant has been described. However, other alkali metals such as sodium or potassium, alkaline earth metals such as magnesium or calcium, or other light metals such as aluminum The present invention can also be applied to the case where is used. In that case, as a negative electrode active material, the thing similar to the said embodiment etc. can be used, for example.

  In the above embodiments and examples, the coin-type secondary battery has been described. However, the present invention is not limited to a secondary battery having another shape such as a cylindrical shape, a button shape, or a square shape, or a laminate film. The present invention can be similarly applied to a secondary battery using an exterior member and a secondary battery having another structure. Further, the present invention is not limited to the secondary battery, and can be similarly applied to other batteries such as a primary battery.

  Furthermore, in the above-described embodiments and examples, the case where a liquid electrolytic solution is used as the electrolyte has been described. However, a gel electrolyte in which the electrolytic solution is held by a holding body such as a polymer compound may be used. . Examples of such a polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, and polyphosphazene. , Polysiloxane, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene or polycarbonate. In particular, polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene, or polyethylene oxide is preferable from the viewpoint of electrochemical stability. Although the ratio of the polymer compound to the electrolytic solution varies depending on the compatibility thereof, it is usually preferable to add a polymer compound corresponding to 5% by mass or more and 50% by mass or less of the electrolytic solution.

  Furthermore, in the above-described embodiments and examples, the appropriate range derived from the results of the examples was described for the composition of the electrolytic solution in the battery of the present invention, but the description is out of the range described above for the composition. The possibility is not completely denied. In other words, the appropriate range described above is a particularly preferable range for obtaining the effect of the present invention, and the content may be slightly deviated from the above range as long as the effect of the present invention is obtained.

It is sectional drawing showing the structure of the secondary battery which concerns on one embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Secondary battery, 2 ... Positive electrode, 3 ... Outer can, 4 ... Negative electrode, 5 ... Outer cup, 6 ... Separator, 7 ... Gasket, 8 ... Electrolyte, 9 ... Positive electrode active material layer, 10 ... Positive electrode collector , 11 ... negative electrode current collector, 12 ... negative electrode active material layer.

Claims (2)

A battery comprising an electrolyte solution together with a positive electrode and a negative electrode,
The negative electrode includes at least one of silicon (Si) and tin (Sn) as a negative electrode active material,
The electrolyte includes a room temperature molten salt together with a solvent having difluoroethylene carbonate,
The room temperature molten salt includes 1-methyl-3-n-butylimidazolium ion shown in Chemical Formula 1 (1), 1,2-dimethylpyrrolium ion shown in Chemical Formula 1 (2), and Chemical Formula 1 (3). 1-methyl-2-n-butylpyrazolium ion shown, 1-methyl-1-n-propylpiperidinium ion shown in Chemical formula 1 (4), 1-n-butyl-shown in Chemical formula 1 (5) 4-methylpyridinium ion, 1-ethylpyridazinium ion shown in Chemical Formula 1 (6), 1-n-propylpyrimidinium ion shown in Chemical Formula 1 (7), 1- shown in Chemical Formula 1 (8) A cyclic cation containing at least one of ethylpyrazinium ion, 2,3-dimethylthiazolium ion shown in Chemical Formula 1 (9) , (CF ₃ SO ₂ ) ₂ N ⁻ , (CF ₃ CF ₂ SO _{2) ^{) 2) N -, PF 6}} -, BF 4 - small of Including an anion having a Kutomo one
Batteries.

Content of the difluoroethylene carbonate to the whole of the solvent and the ambient temperature molten salt, Ru der 50 wt% or less than 0.01 wt%
請 Motomeko 1 battery described.

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