JP5728720B2 - Non-aqueous electrolyte lithium ion battery with carbonaceous negative electrode - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte lithium ion battery having a negative electrode using a carbonaceous material as a negative electrode active material, and more particularly to a lithium ion battery containing an ionic liquid in a non-aqueous electrolyte. The present invention also provides an ionic liquid comprising a fluorosulfonyl (trifluoromethylsulfonyl) amide (FTA) anion and a 1-ethyl-3-methylimidazolium imidazolium (EMI) cation as an electrolyte for a lithium ion battery. Regarding use.

  A fluorosulfonyl (trifluoromethylsulfonyl) amide (FTA) anion is known as an anion of an ionic liquid (Patent Documents 1 and 2), and 1-ethyl-3-methylimidazolium (EMI) is an ionic liquid. Widely used as a cation (Patent Document 3).

  Currently, non-aqueous electrolytes for lithium ion batteries are mainly cyclic carbonates and / or chain carbonates. However, these carbonates are flammable, and there is a risk of explosion of lithium ion batteries. There is a need for non-flammable electrolytes.

  In a lithium ion battery using a carbonaceous material as a negative electrode active material, bis (trifluoromethane) sulfonylamide (TFSA) cannot be used because its charge / discharge capacity is significantly reduced when used as a non-aqueous electrolyte.

JP2007-141489 WO2009 / 136608 Table 2006-070545

  The present invention has been made in view of the above problems, and there is no risk of explosion, and even when a carbonaceous material is used as a negative electrode active material, non-aqueous electrolysis has a practical charge / discharge capacity. An object is to provide a liquid lithium ion battery.

The present invention relates to the use of the following non-aqueous electrolyte lithium ion battery and ionic liquid.
Item 1. In a nonaqueous electrolyte lithium ion battery including a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte containing a lithium salt and an ionic liquid, the anion of the ionic liquid is fluorosulfonyl (trifluoromethylsulfonyl) amide (FTA) The cation of the ionic liquid is 1-ethyl-3-methylimidazolium (EMI), NN-diethyl-N-methyl- (2-methoxyethylammonium (DEME), N-methyl-N-propylpyrrolidinium (Py13). ), N-methyl-N-propylpiperidinium (PP13), azonia spiro [4.4.] Nonane (AS44), and the negative electrode active material used for the negative electrode is a carbonaceous material. Lithium ion battery.
Item 2. Item 4. The ionic liquid according to Item 1, wherein the cation of the ionic liquid is EMI.
Item 3. The use of an ionic liquid in a non-aqueous electrolyte of a non-aqueous electrolyte lithium ion battery having a negative electrode whose negative electrode active material is a carbonaceous material, wherein the anion of the ionic liquid is fluorosulfonyl (trifluoromethylsulfonyl) amide ( FTA), and the cation of the ionic liquid is 1-ethyl-3-methylimidazolium (EMI), NN-diethyl-N-methyl- (2-methoxyethylammonium (DEME), N-methyl-N-propylpyrrole Use, selected from the group consisting of dinium (Py13), N-methyl-N-propylpiperidinium (PP13), azonia spiro [4.4.] Nonane (AS44).
Item 4. Item 4. The use according to Item 3, wherein the cation of the ionic liquid is EMI or Azonia spiro [4.4.] Nonane (AS44).

  According to the present invention, a nonaqueous electrolyte battery having high energy density and excellent charge / discharge characteristics while ensuring high safety obtained by using an ionic liquid for a nonaqueous electrolyte without using an organic solvent. Can be provided.

The charge / discharge characteristics of a non-aqueous electrolyte lithium ion battery using an ionic liquid composed of EMI, DEME, Py13, PP13, AS44, FTA (Example 1), and TFSA (Comparative Example 1) as an electrolyte are shown. The thermal decomposition behavior of K [FTA], K [TFSA], K [FSA] is shown.

  The non-aqueous electrolyte lithium ion battery of the present invention uses an ionic liquid instead of a conventional organic solvent such as ethylene carbonate, propylene carbonate, dimethyl carbonate and the like. By using no organic solvent, it is possible to obtain a safe non-aqueous electrolyte lithium ion battery with no danger of explosion.

The ionic liquid in the present invention contains N-methyl-N-ethylimidazolium (EMI), NN-diethyl-N-methyl- (2-methoxyethylammonium (DEME), N-methyl-N-propylpyrrolidi as cations. At least one selected from the group consisting of nium (Py13), N-methyl-N-propylpiperidinium (PP13), and azonia spiro [4.4.] Nonane (AS44) is used, and fluorosulfonyl (trifluoromethylsulfonyl) is used as the anion. ) Amide (FTA ⁻ ) is used.

  The structures of the anion used in the present invention and the comparative anion are shown below.

As the anion of the lithium salt constituting the non-aqueous electrolyte in the present invention, FTA is preferable, but other anions (for example, ClO ₄ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆₎ within the range not impairing the effects of the present invention. ^{_{-, SbF 6 -, CN -}} , COO -, N (CF 3 SO 2) 2 -, N (C 2 F 5 SO 2) 2 -, N (CF 3 SO 2) (C 2 F 5 SO 2) - , CF ₃ SO ₃ ⁻ , N (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) ⁻ , C (CF ₃ SO ₂ ) ₃ ⁻ , C (C ₂ F ₅ SO ₂ ) ₃ ^{− and the} like) are used. be able to.

Typical lithium salts used in the electrolyte include LiCF ₃ SO ₃ , LiPF ₆ , LiClO ₄ , LiI, LiBF ₄ , LiBF ₃ CF ₃ , LiBF ₃ C ₂ F ₅ , LiCF ₃ CO ₂ , LiSCN, LiN ( SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) _{2 and the} like.

  The lithium cation content in the non-aqueous electrolyte is desirably 0.3 to 5 mol / l, and preferably 0.5 to 3 mol / l.

  Examples of the negative electrode active material that is a main component of the negative electrode of the nonaqueous electrolyte battery in the present invention include carbonaceous materials (for example, coal, coke, polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, carbonized product of organic matter, natural graphite) Artificial graphite, synthetic graphite, mesocarbon microbeads, organic graphitized products and graphite fibers), and materials modified by adding phosphorus or boron for the purpose of improving negative electrode characteristics. Among carbonaceous materials, graphite has a working potential very close to that of metallic lithium. Therefore, when lithium salt is used as an electrolyte salt, self-discharge can be reduced, and irreversible capacity in charge / discharge can be reduced, which is preferable as a negative electrode active material. . Graphite crystals include the well-known hexagonal system and others belonging to the rhombohedral system. In particular, rhombohedral graphite has a wide selectivity for a solvent in an electrolytic solution. For example, an organic compound that easily co-inserts with lithium ions or an organic compound that is easily reductively decomposed at a relatively noble potential can be obtained using a non-aqueous solution. Even when it is used as a constituent material of an electrolyte, it is desirable because delamination is suppressed and excellent charge / discharge efficiency is exhibited.

As the positive electrode of the non-aqueous electrolyte lithium ion battery, it is preferable to use a positive electrode obtained by applying a positive electrode active material to an aluminum current collector. As the positive electrode active material, a known positive electrode active material used in a lithium ion battery can be used. In particular, an active material that operates at a potential of 3 to 5 V based on lithium is preferably used. As a specific example of the positive electrode active material, in order to obtain a high voltage, lithium cobalt oxide (Li _x CoO ₂ , x = 0.4 to 1), lithium nickel oxide (Li _x NiO ₂ , x = 0. 3-1), lithium manganese oxide (Li _x MnO ₂ , x = 0 to 1), transition metal substituted lithium manganese oxide (Li _x Mn _{1- y My} O ₂ , M = Co, Al, Ni, Cr Or Bi, x = 0 to 1, y = 0.01 to 0.25), lithium nickel cobalt oxide (Li _x Ni _1-yz Co _y M _z O ₂ , M = Al or Mn, x = 0 .3-1, y = 0.1-0.4, z = 0.01-0.2), olivine phase compound LiMPO ₄ (M = Fe or Co), etc. can be used. Among these, the lithium manganese oxide may have either a spinel phase or a layered structure, and the olivine phase compound LiMPO ₄ may contain a small amount of transition metals such as Mn and Ni. Each oxide may be a mixture of oxides having different compositions.

Further, in order to obtain a high capacity, manganese oxide _MnO x (x = _1.5~2), vanadium oxide _{Li x V y O 5 (x} = 0~3, y = 1.5~3.5 ) Or a composite oxide of these. A positive electrode active material can be used individually by 1 type or in mixture of 2 or more types.

  The positive electrode can be produced according to a conventional method. Usually, a positive electrode can be produced by adding a conductive agent, a binder, and the like to the above-described positive electrode active material, applying the mixture onto a current collector, and pressing the mixture. Known components can be used for the conductive agent, binder and the like. For example, acetylene black, natural graphite, artificial graphite, synthetic graphite or the like can be used as the conductive agent.

  An electrolytic solution containing an ionic liquid is usually used by impregnating the gap between the separator and the electrode.

  The nonaqueous electrolyte lithium ion battery of the present invention including the positive electrode, the negative electrode, the separator, and the nonaqueous electrolyte containing a lithium salt and an ionic liquid can further contain additives other than the organic solvent.

  Each of the above-described constituent elements can be sealed in a well-known various battery exterior such as a coin type, a cylindrical type, or a laminate package to form a lithium ion battery.

  As the lithium ion battery, a lithium secondary battery is preferable.

  Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited to these descriptions.

Reference production example 1
(1) A commercially available product was used for K [(CF ₃ SO ₂ ) N] (KTFSA).

_{(2) K [CF 3 SO} 2 NSO 2 F] K Synthesis <br/> anhydrous _Et 2 in O (980 ml) of _{(KFTA) [CF 3 SO 2} NH] (60.0 g, 0.32 mol (FSO ₂ ) ₂ O ¹⁾ (69.5 g, 0.38 mol) was added dropwise at −20 ° C. over 30 minutes. The mixture was kept stirring at −20 ° C. for 3 hours and filtered.
The crude product (21.5 g) was washed with MeOH and filtered. The solvent was removed in vacuo and recrystallized from acetone / CHCl ₃ to give the product. ¹⁹ F NMR (CD ₃ OD, CFCl ₃ , 470.6 MHz) δ 56.8 (s, 1F), −78.0 (s, 3F); MS m / z (%) 230 (100) [CF ₃ SO ₂ NSO ₂ F] ⁻ ; Anal Calcd. for CF ₄ O ₄ S ₂ NK: C, 4.46; N, 5.20; Found: C, 4.28; N, 5.35.

(3) A commercially available product was used for K [(FSO ₂ ) ₂ N] (KFSA).

Reference production example 2
FTA ionic liquid unnecessary in water produced by mixing equimolar amounts of the above-mentioned potassium salt of FTA and bromide of known N-methyl-N-ethylimidazolium cation (EMI ⁺ ) was extracted with dichloromethane, several times After washing with water, dichloromethane was distilled off to obtain an ionic liquid composed of a fluorosulfonyl (trifluoromethylsulfonyl) amide (FTA) anion and a 1-ethyl-3-methylimidazolium (EMI) cation.

  Similarly, DEME-FTA, Py13-FTA, PP13-FTA, and AS44-FTA as ionic liquids were obtained in the same manner as above except that EMI was replaced with DEME, Py13, PP13, and AS44.

Reference production example 3
TFSA, which is an ionic liquid, in the same manner as in Reference Production Example 1, using a known potassium salt of bis (trifluoromethylsulfonyl) amide (TFSA) and bromide of N-methyl-N-ethylimidazolium cation (EMI ⁺ ) -Obtained EMI.

  Similarly, ionic liquids DEME-TFSA, Py13-TFSA, and PP13-TFSA were obtained in the same manner as described above except that EMI was changed to DEME, Py13, and PP13.

Reference production example 4
A nonaqueous electrolytic solution was obtained by mixing Li-TFSA as an electrolyte lithium salt in the ionic liquids obtained in Reference Production Examples 2 to 3 so as to be 20 to 24% by mass.

Example 1 and Comparative Example 1
An electrolytic solution containing the ionic liquid of the present invention (EMI-FTA, DEME-FTA, Py13-FTA, PP13-FTA, AS44-FTA) obtained in Reference Production Example 4, the ionic liquid of Comparative Example 1 (EMI-TFSA, DEME-TFSA, Py13-TFSA, PP13-TFSA), and as a control, an electrolyte obtained by dissolving LiPF ₆ at a concentration of 1M in a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC), Carbonaceous negative electrode (artificial graphite mesocarbon microbeads, heat treatment temperature 2800 ° C, binder: PVDF, conductive additive: acetylene black mixed negative electrode) and separator, half cell made of aluminum laminate as exterior material (counter electrode = lithium) The charge / discharge characteristics of (metal) were evaluated.

  The test temperature for the discharge capacity test was 25 ° C. Charging was performed up to a final voltage of 0.05 V in the CCCV mode. Discharge was performed up to a final voltage of 1.5 V in the CC mode. FIG. 1 shows the obtained capacity at the time of discharge with respect to the time rate. This suggests that the ionic liquid composed of FTA anion can be charged / discharged at a higher current density than the ionic liquid composed of TFSA anion which has been conventionally known. It became clear that ionic liquids composed of EMI cations, which are considered difficult to use due to insertion / desorption reaction in the negative electrode, can be used by using FTA.

  In addition, the thermal decomposition behavior of potassium salt, which is a raw material for producing ionic liquid, was investigated. The results are shown in FIG. It can be seen that the FTA anion has a thermal stability comparable to the TFSA anion. From the results shown in FIGS. 1 and 2, the present invention shows that the FTA anion shows high thermal stability, and even the ionic liquid composed of EMI, which is difficult with TFSA, can use the carbon negative electrode and has high rate characteristics. It was done. Thus, the present invention is required for constructing a non-aqueous electrolyte lithium ion battery having sufficient charge / discharge characteristics, high thermal stability, and safe and practical charge / discharge capacity. It was clarified that the carbon negative electrode can be operated in an ionic liquid.

Claims (4)

In a nonaqueous electrolyte lithium ion battery including a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte containing a lithium salt and an ionic liquid, the anion of the ionic liquid is fluorosulfonyl (trifluoromethylsulfonyl) amide (FTA) The cation of the ionic liquid is selected from the group consisting of 1-ethyl-3-methylimidazolium (EMI) and N-methyl-N-propylpyrrolidinium (Py13), and the negative electrode active material used for the negative electrode is carbon (However, when the cation of the ionic liquid is EMI, the negative electrode active material is not natural spherical graphite, and the positive electrode forms an active material layer containing lithium element on the current collector foil. The lithium element concentration is different in the thickness direction of the layer, and the lithium element concentration D1 on the surface side of the active material layer is Excluding those higher than the concentration D2 elementary) a non-aqueous electrolyte lithium-ion batteries. The ionic liquid according to claim 1, wherein the cation of the ionic liquid is EMI. The use of an ionic liquid in a non-aqueous electrolyte of a non-aqueous electrolyte lithium ion battery having a negative electrode whose negative electrode active material is a carbonaceous material, wherein the anion of the ionic liquid is fluorosulfonyl (trifluoromethylsulfonyl) amide ( FTA), and the cation of the ionic liquid is selected from the group consisting of 1-ethyl-3-methylimidazolium (EMI) and N-methyl-N-propylpyrrolidinium (Py13), and the negative electrode active used for the negative electrode The substance is a carbonaceous material (however, when the cation of the ionic liquid is EMI, the negative electrode active material is not natural spherical graphite, and the positive electrode forms an active material layer containing lithium element on the current collector foil) The concentration of the lithium element in the thickness direction of the active material layer is different, and the concentration D1 of the lithium element on the surface side of the active material layer is the lithium element on the current collector foil side. Of excluding those higher than the concentration D2), used. Use according to claim 3, wherein the cation of the ionic liquid is EMI.

Images