JP5368908B2 - Storage device processing method - Google Patents

Description

The present invention relates to a treatment method capable of improving cycle characteristics, particularly high-temperature cycle characteristics, in an electricity storage device using a titanate compound represented by H ₂ Ti ₁₂ O ₂₅ as an electrode active material.

Lithium secondary batteries have been rapidly spreading in recent years because of their excellent cycle characteristics. Conventionally, a carbon material has been used as a negative electrode active material for a lithium secondary battery. However, a titanate compound having a high charge / discharge potential and an excellent safety has attracted attention. For example, H ₂ Ti ₁₂ O ₂₅ The electrode active material (patent document 1) using the titanic acid compound represented by these is known. However, since the titanic acid compound easily decomposes the electrolyte solution at high temperatures, it is inferior in high-temperature cycle characteristics, for example, it is difficult to use for large power storage devices such as motorcycles and automobiles used at high temperatures, and for power generation. There's a problem.

International Publication WO2008 / 111465 Pamphlet

  The present invention provides a method for improving battery characteristics, particularly high-temperature cycle characteristics, of an electricity storage device using the titanate compound.

  As a result of intensive studies, the present inventors improved the battery characteristics of this electricity storage device by performing an initial treatment by a specific method immediately after producing the electricity storage device using the titanate compound as an electrode. The present invention has been completed by finding out what can be done.

That is, the present invention provides (1) an electricity storage device comprising at least a positive electrode containing a positive electrode active material, a negative electrode containing a titanate compound represented by H ₂ Ti ₁₂ O ₂₅ , and an electrolyte containing lithium ions. This is a method for treating an electricity storage device in which the negative electrode is initially charged so that the potential of the negative electrode is in the range of 0.1 to 1.3 V with respect to the potential of metallic lithium and then held in the charged state. Alternatively, (2) an electricity storage device including at least a positive electrode containing a titanate compound represented by H ₂ Ti ₁₂ O ₂₅ , a negative electrode containing lithium or an alloy thereof, and an electrolytic solution containing lithium ions is used as the positive electrode This is a method for treating an electricity storage device that is initially discharged so that its potential is in a range of 0.1 to 1.3 V with respect to the potential of metallic lithium and then held in the discharged state.

  The electricity storage device treated according to the present invention has excellent battery characteristics, particularly high temperature cycle characteristics.

FIG. 1 shows high-temperature cycle characteristics of Examples 1 and 2 and Comparative Example 1 (Samples A, B, and a).

The present invention is a method for treating an electricity storage device, wherein the first invention is a positive electrode including a positive electrode active material, a negative electrode including a titanate compound represented by H ₂ Ti ₁₂ O ₂₅ , and an electrolysis including lithium ions. An electrical storage device comprising at least a liquid is initially charged so that the potential of the negative electrode is in a range of 0.1 to 1.3 V with respect to the potential of metallic lithium, and then held in the charged state. To do. According to a second aspect of the present invention, there is provided an electricity storage device including at least a positive electrode including a titanate compound represented by H ₂ Ti ₁₂ O ₂₅ , a negative electrode including lithium or an alloy thereof, and an electrolytic solution including lithium ions. The initial discharge is performed so that the potential of the positive electrode is in the range of 0.1 to 1.3 V with respect to the potential of the metallic lithium, and then the discharge state is maintained. In the first invention, an initial charge is performed at a voltage in the above range, and in the second invention, an initial discharge is performed at a voltage in the above range. It is considered that a stable film derived from the components is formed. Since the formation of this film does not hinder the insertion / extraction of lithium ions into the positive / negative electrode and the positive / negative electrode is difficult to directly contact with the electrolyte, the decomposition of the electrolyte is suppressed, and the battery It is estimated that the characteristics are improved. In particular, the effect of suppressing the decomposition of the electrolytic solution at a high temperature is high, and the high-temperature cycle characteristics are considered to be improved.

  In any of the inventions, the holding temperature after the initial charge or after the initial discharge is preferably less than 40 ° C., more preferably at room temperature, that is, in the range of 20 to 30 ° C. In addition, if the holding period is at least 1 week, the desired effect can be easily obtained, and it is difficult to obtain a further effect even if performed for more than 1 month.

The titanic acid compound can be prepared according to a known method, for example, the method described in Patent Document 1. That is, a mixture of a sodium compound and titanium oxide is baked in air at a temperature of 600 ° C. or higher to obtain sodium titanate represented by the composition formula: Na ₂ Ti ₃ O _7. To obtain a titanic acid compound represented by the composition formula: H ₂ Ti ₃ O ₇ , and the obtained H ₂ Ti ₃ O ₇ is dehydrated by heating at a temperature in the range of 150 ° C. or higher and lower than 280 ° C. Can be obtained.

  In the first invention, the positive electrode and the negative electrode are mixed with a positive electrode active material or the titanic acid compound with a conductive agent and a binder, and further added with a solvent as necessary. It is obtained by forming the active material layer on the surface of the substrate. Examples of positive electrode active materials include lithium / manganese composite oxides, lithium / cobalt composite oxides, lithium / nickel composite oxides, lithium / transition metal composite oxides such as lithium / vanadine composite oxides, and lithium / iron / composite phosphates. It is preferable to use at least one lithium-containing composite oxide selected from olivine type compounds such as compounds.

In the second invention, as in the first invention, a mixture obtained by adding the titanic acid compound to the positive electrode and a conductive agent, a binder, and an appropriate solvent is supported on the surface of the current collector as an active material layer.

  In 1st and 2nd invention, the said titanic acid compound contained in an active material layer, or the positive electrode active material used for this counter electrode, metallic lithium, or its alloy is 40-about with respect to 100 weight part of active material layers. A range of 95 parts by weight is preferred.

  Examples of the conductive agent include carbon black, acetylene black, ketjen black, and graphite. The binder includes fluorine resin (polyfluoroethylene, polytetrafluoroethylene, polyvinylidene fluoride, etc.), vinyl resin (polyvinyl alcohol, polyvinylpyrrolidone, etc.), cellulose resin (hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, etc.), polyolefin resin (Polyethylene, polypropylene, etc.) are mentioned, and among them, a fluororesin is preferable.

  For the current collector, copper, nickel, or the like or an alloy thereof can be used. Further, the current collector may be mesh, sheet or the like.

The electrolytic solution is prepared by dissolving a lithium salt such as LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₄ in a solvent. Examples of the solvent include carbonate solvents (propylene carbonate, ethylene carbonate, etc.), ether solvents (1,2-dimethoxyethane, tetrahydrofuran, etc.), and mixed solvents thereof. The concentration of the electrolyte in the electrolytic solution is preferably in the range of 0.1 to 10 mol / liter, more preferably in the range of 0.1 to 5 mol / liter.

  An electricity storage device can be manufactured by sandwiching a separator between the positive electrode and the negative electrode, storing the separator in a battery case, filling an electrolyte containing lithium ions, and then sealing the battery case.

  For the separator, polyolefin films such as polyethylene, polypropylene, and copolymers thereof are preferable, and porous polyolefin films are particularly preferable.

As the battery case, a metal case such as stainless steel or aluminum or a laminate film is appropriately selected. Further, the form of the electricity storage device may be any of a button type, a coin type, a cylindrical type, a square type, a sheet type, a laminate type, and the like, and is not particularly limited.

  Examples of the present invention are shown below, but these do not limit the present invention.

Example 1 (second invention)
A titanic acid compound represented by a composition formula: H ₂ Ti ₁₂ O ₂₅ , acetylene black powder as a conductive agent, and polytetrafluoroethylene resin as a binder are mixed at a weight ratio of 50:40:10, N-methyl-2-pyrrolidone was added as a solvent and kneaded in a mortar to prepare a paste. This paste was applied on a copper foil, dried at a temperature of 120 ° C. for 10 minutes, punched into a circle having a diameter of 12 mm, and pressed at 17 MPa to produce a positive electrode.

This positive electrode was vacuum-dried at a temperature of 120 ° C. for 4 hours, and then incorporated in a sealable coin-type cell in a glove box having a dew point of −70 ° C. or less. A coin type cell made of stainless steel (SUS316), having an outer diameter of 20 mm and a height of 3.2 mm was used. As the negative electrode, a metal lithium having a thickness of 0.5 mm formed into a circle having a diameter of 12 mm was used. As the non-aqueous electrolyte, a mixed solution of ethylene carbonate and dimethyl carbonate (mixed in a volume ratio of 1: 2) in which LiPF ₆ was dissolved at a concentration of 1 mol / liter was used.

  The positive electrode was placed in a lower can of a coin-type cell, a porous polypropylene film was placed thereon as a separator, and a nonaqueous electrolyte was dropped from above. Further, a negative electrode, a 0.5 mm-thickness spacer for adjusting the thickness, and a spring (all made of SUS316) were placed thereon, and an upper can with a propylene gasket was put on and the outer peripheral edge portion was caulked and sealed. (Sample a).

  The coin-type cell was initially discharged at a constant current at a temperature of 25 ° C. with a discharge current set to 0.2 mA until the potential of the negative electrode was 0.7 V with respect to the potential of metallic lithium. . In this discharge state, the electricity storage device was processed by holding it in a thermostatic chamber set at 25 ± 5 ° C. for 1 week (sample A).

Example 2 (second invention)
In Example 1, the treatment was performed in the same manner as in Example 1 except that the holding period was 2 weeks (Sample B).

Comparative Example 1
Sample a was set as Comparative Example 1.

Evaluation: Evaluation of high-temperature cycle characteristics The power storage devices of Examples 1 and 2 and Comparative Example 1 (samples A, B, and a) were charged in a high-temperature bath at 60 ° C. with a charge / discharge current of 0.2 mA and a cut-off potential of 1. The battery was charged and discharged for 50 cycles at 0V to 2.5V. The discharge capacities at the second cycle and the 50th cycle were taken as the respective storage capacities, and (the electric capacity at the 50th cycle / the electric capacity at the second cycle) × 100 was taken as the high temperature cycle characteristics. The results are shown in Table 1. Moreover, transition of each capacity maintenance rate is shown in FIG. It can be seen that the present invention is excellent in high-temperature cycle characteristics.

  The electricity storage device treated in the present invention has a high discharge potential, excellent safety, and excellent high-temperature cycle characteristics, so that it is not only a small electricity storage device for mobile phones, notebook computers, etc. It is also useful as a large power storage device for cars and power generation.

Claims (2)

An electric storage device comprising at least a positive electrode containing a titanate compound represented by H ₂ Ti ₁₂ O ₂₅ , a negative electrode containing lithium or an alloy thereof, and an electrolytic solution containing lithium ions, and the potential of the positive electrode is metallic lithium A method for treating an electricity storage device in which initial discharge is performed so as to be in a range of 0.1 to 1.3 V with respect to the potential of the battery, and then held in the discharged state for at least one week . Processing method of an electric storage device according to claim 1, wherein performing holding in the discharge state of the at a temperature below 40 ° C..

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