JP4037560B2 - Non-aqueous secondary battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous secondary battery having excellent cycle characteristics.
[0002]
[Prior art]
With the rapid spread of notebook PCs and mobile phones, the need for small and rechargeable secondary batteries is increasing. Among secondary batteries, a lithium secondary battery having a particularly high energy density is rapidly expanding the market. Currently, lithium secondary batteries use LiPF ₆ , LiBF ₄ , LiClO ₄ or the like as an electrolyte, and a high dielectric solvent such as ethylene carbonate or propylene carbonate and a low viscosity solvent such as diethyl carbonate and the like. The electrolyte solution using the mixed solvent which combined these is mainly used.
[0003]
[Problems to be solved by the invention]
However, LiPF ₆ is, although having a high ion conductivity and withstand voltage compared to other electrolytes, i) HF remains used in the preparation, or ii) an electrolyte solution which is a typical electrolyte of a lithium secondary battery Since it reacts with H ₂ O, or is thermally unstable, it decomposes to produce HF or PF ₅ , thereby deteriorating cycle characteristics. Further, for example, Japanese Patent Laid-Open No. 7-29602 proposes to use silicon, which can be expected to have a high capacity, as a negative electrode active material instead of a conventional carbonaceous material. However, in this case, the problem that HF or the like deteriorates the cycle characteristics is remarkable.
[0004]
Accordingly, an object of the present invention is to provide a non-aqueous secondary battery having an electrolyte that gives excellent cycle characteristics when silicon that can be expected to have a high capacity is used as a negative electrode active material.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the non-aqueous secondary battery of the present invention includes a compound represented by the general formula LiB [C ₆ H _5-n F _n ] ₄ (where n is an integer of 1 to 5) and An electrolyte solution containing at least one of compounds represented by LiB [C ₆ H _{5 -m} (CF ₃ ) _m ] ₄ (where m is an integer of 1 to 5) as an electrolyte, and an active material mainly composed of silicon And a negative electrode.
According to the present invention, by using a compound comprising a fluorine-containing substituted aromatic lithium borate represented by the above general formula for an electrolyte, the thermal stability of the electrolyte is increased, and the generation of HF due to decomposition of the electrolyte is increased. It is suppressed and the cycle characteristics can be improved. In addition, since the electron-withdrawing fluoro group or trifluoromethyl group reduces the electron density at the center of the anion, the Coulomb force of the ion pair is reduced and the degree of ion dissociation is increased. It can be secured.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The electrolyte used in the present invention has a general formula LiB [C ₆ H _5-n F _n ] ₄ (where n is an integer of 1 to 5), and a general formula LiB [C ₆ H _5-m (CF ₃ ) _m ] _4. (Where m is an integer of 1 to 5). These electrolytes can be used alone or in combination. Here, in LiB [C ₆ H _5-n F _n ] ₄ , lithium tetrakis [pentafluorophenyl] borate LiB [C ₆ F ₅ ] ₄ , LiB [C ₆ H _5-m (CF in _{3) m] 4,} lithium tetrakis m is 2 [3,5-di (trifluoromethyl) phenyl] borate _{LiB [C 6 H 3 (CF} 3) 2 -3,5] 4 are preferred. High thermal stability and withstand voltage can be obtained.
[0007]
These electrolytes can be produced by known methods (for example, the paper by Lambert et al. Organometallics, 13 , 2430 (1994)).
[0008]
Solvents for dissolving the electrolyte used in the present invention include known solvents for non-aqueous secondary batteries, for example, chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethylene Examples thereof include cyclic carbonates such as carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate.
[0009]
Moreover, the density | concentration which dissolves these electrolytes in a solvent can be used in 0.05-2 mol / l, Preferably it is 0.1-1.2 mol / l.
[0010]
Moreover, you may add and use the electrolyte conventionally used in the range which does not impair the objective of this invention to the electrolyte used for this invention.
[0011]
The negative electrode used in the secondary battery of the present invention preferably contains silicon as an active material. In particular, it is preferable to use a sintered body obtained by heat-treating silicon powder in a non-oxidizing atmosphere in the presence of a carbon material or a material carbonized by heat treatment.
[0012]
Moreover, the positive electrode active material which consists of a well-known material which can occlude / release lithium ion can be used for the positive electrode used for the secondary battery of this invention. Examples of the positive electrode active material include Li _x CoO ₂ , Li _x NiO ₂ , MnO ₂ , Li _x MnO ₂ , Li _x Mn ₂ O ₄ , Li _x Mn _{2 -y} O ₄ , α-V ₂ O ₅ , TiS _2. Etc. can be used.
[0013]
【Example】
Example.
Li ₂ CO ₃ powder and CoCO ₃ are mixed at a molar ratio of Li / Co = 1/1 and calcined at 800 ° C. for 1 hour in an air atmosphere. Next, this was pulverized, pressed, and fired at 800 ° C. for 10 hours in an air atmosphere to obtain a positive electrode made of a sintered body having a diameter of 20 mm and a thickness of 0.5 mm.
[0014]
Further, 80 parts of crystalline silicon powder having a purity of 99.9% and an average particle diameter of 1 μm and 40 parts of pitch-based carbon powder (residual carbon ratio 50%) were mixed and fired at 1000 ° C. for 3 hours. Next, this was pulverized, PVDF and NMP were added to form a paste, applied onto a copper foil, dried, punched out to a diameter of 20 mm, and pressed with a press. This copper foil-containing coating film was baked at 800 ° C. for 3 hours in a nitrogen atmosphere to obtain a negative electrode.
[0015]
The above positive electrode and negative electrode are laminated via a separator, and are housed in a battery case. In a mixed solvent of ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 1, 0.4 mol / l lithium tetrakis [pentafluorophenyl] borate _{LiB [(C 6 F 5)} ] after the ₄ electrolyte solution plus infusion, a coin-type battery was produced by sealing the case. And the charging / discharging test was done using this battery. Good cycle characteristics were obtained compared to the comparative example.
[0016]
Comparative example.
A coin battery was manufactured in the same manner as in the example except that 1 mol / l LiPF ₆ was used as a mixed solvent of ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 1 as an electrolytic solution, and a charge / discharge test was performed.
[0017]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a non-aqueous secondary battery including an electrolyte that provides excellent cycle characteristics even when silicon is used as a negative electrode active material.

Claims (1)

A non-aqueous secondary battery having an electrolytic solution containing LiB [C ₆ F ₅ ] ₄ as an electrolyte and a negative electrode containing an active material mainly composed of silicon.