JP2019175652A - Lithium ion secondary battery - Google Patents

Abstract

To provide a lithium ion secondary battery which enables improvement of rapid charging capability.SOLUTION: A lithium ion secondary battery comprises: a positive electrode; a negative electrode; a separator located between the positive and negative electrodes; and an electrolyte solution containing a solvent and a supporting electrolyte. The solvent contains propylene carbonate. When impedance of the lithium ion secondary battery at 25°C and 100 kHz is Z(mΩ), impedance at 25°C and 1 kHz is Z(mΩ), and a capacity of the lithium ion secondary battery is Q(Ah), an in-pore liquid resistance index represented by (Z-Z)×Q is 20.0 mAhΩ or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion secondary battery.

  In recent years, electronic devices such as mobile phones and personal computers have been rapidly reduced in size and cordless, and there is an increasing demand for secondary batteries having a small size, light weight, and high energy density as power sources for driving these devices. Under such circumstances, a lithium ion secondary battery having a large charge / discharge capacity and a high energy density has attracted attention.

  The electrolyte for a lithium ion secondary battery is composed of a lithium salt that is an electrolyte and a non-aqueous organic solvent. Non-aqueous organic solvents are required to have a high dielectric constant in order to dissociate lithium salts, to exhibit high ionic conductivity in a wide temperature range, and to be stable in a battery. Since it is difficult to achieve these requirements with a single solvent, usually a combination of a high-boiling solvent typified by propylene carbonate and ethylene carbonate and a low-boiling solvent such as dimethyl carbonate and diethyl carbonate is used. ing.

  Among the above solvents, propylene carbonate is stable against oxidative decomposition and has a low freezing point (−70 ° C.), so that it is adopted as many commercially available electrolyte solutions for lithium ion secondary batteries. However, normally, when propylene carbonate is used alone, there is a problem that the co-insertion reaction into the graphite negative electrode proceeds, so that it is often used in combination with an appropriate additive such as ethylene carbonate or vinylene carbonate. The above problem can also be solved by surface coating on the graphite negative electrode. Patent Document 1 discloses a method of coating the surface of the graphite negative electrode with low crystalline carbon together with the use of ethylene carbonate.

JP-A-9-237638

  However, when an electrolytic solution containing propylene carbonate is used as in the prior art, there is a problem that rapid charging characteristics are deteriorated.

  As a result of diligent research, the inventors have found that when propylene carbonate is included in the electrolyte solution, the solvation radius of lithium ions increases due to the molecular structure of propylene carbonate, and it is difficult for solvated lithium ions to penetrate deep into the electrode, resulting in a large concentration overvoltage. It has been found that the occurrence of is a cause of the deterioration of the quick charge characteristics.

  The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide a lithium ion secondary battery capable of improving quick charge characteristics.

In order to solve the above problems, a lithium ion secondary battery according to the present invention comprises a positive electrode, a negative electrode, a separator positioned between the positive electrode and the negative electrode, and an electrolyte solution comprising a solvent and a supporting salt. A secondary battery, wherein the solvent contains propylene carbonate, the impedance of the lithium ion secondary battery at 25 ° C. and 100 kHz is Z ₁ (mΩ), the impedance at 25 ° C. and 1 kHz is Z ₂ (mΩ), and the lithium ion secondary battery When the capacity of the secondary battery is Q (Ah), the solution resistance index in pores represented by (Z ₂ −Z ₁ ) × Q is 20.0 mAhΩ or less.

In the lithium ion secondary battery according to the present invention, Z ₂ —Z ₁ can be used as an index representing the solution resistance in the pores when the pores existing in the electrode are modeled by a cylindrical model. Here, even when an electrolytic solution containing propylene carbonate as a solvent, which has a large solvation radius of lithium ions and does not easily penetrate into the deep part of the electrode, is used. Solution resistance in pores represented by (Z ₂ −Z ₁ ) × Q By setting the index to 20.0 mAhΩ or less, solvated lithium ions can quickly penetrate into the electrode deep portion. Thereby, quick charge characteristics are improved.

  In the lithium ion secondary battery according to the present invention, the solution resistance index in the pores is preferably 10.0 mAhΩ or less.

  According to this, it is more suitable as an intra-pore solution resistance index, and quick charge characteristics are further improved.

  In the lithium ion secondary battery according to the present invention, it is preferable that the proportion of propylene carbonate with respect to the total volume of the electrolytic solution is 10% by volume or more and 50% by volume or less.

  According to this, even if the proportion of propylene carbonate relative to the total volume of the electrolytic solution is 10% by volume or more and 50% by volume or less, if the lithium ion secondary battery according to the present invention is used, quick charge characteristics are improved. .

  ADVANTAGE OF THE INVENTION According to this invention, the lithium ion secondary battery which can improve a quick charge characteristic is provided.

It is a schematic cross section of the lithium ion secondary battery of this embodiment.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments according to the invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment. The constituent elements described below include those that can be easily conceived by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be appropriately combined.

<Lithium ion secondary battery>
As shown in FIG. 1, a lithium ion secondary battery 100 according to the present embodiment is disposed adjacent to each other between a plate-like negative electrode 20 and a plate-like positive electrode 10 facing each other, and the negative electrode 20 and the positive electrode 10. A plate-like separator 18, an electrolyte solution containing lithium ions, a case 50 containing these in a sealed state, and one end of the negative electrode 20 being electrically connected. A lead 62 whose other end protrudes outside the case and a lead 60 whose one end is electrically connected to the positive electrode 10 and whose other end protrudes outside the case are provided. The positive electrode 10 includes a positive electrode current collector 12 and a positive electrode active material layer 14 formed on the positive electrode current collector 12. The negative electrode 20 includes a negative electrode current collector 22 and a negative electrode active material layer 24 formed on the negative electrode current collector 22. The separator 18 is located between the negative electrode active material layer 24 and the positive electrode active material layer 14.

In addition, the lithium ion secondary battery according to this embodiment has an impedance at 25 ° C. and 100 kHz of Z ₁ (mΩ), an impedance at 25 ° C. and 1 kHz of Z ₂ (mΩ), and a capacity of the lithium ion secondary battery as Q (Ah). ), The pore solution resistance index represented by (Z ₂ −Z ₁ ) × Q is 20.0 mAhΩ or less, more preferably 10.0 mAhΩ or less.

In the lithium ion secondary battery according to the present embodiment, Z ₂ —Z ₁ can be used as an index representing the solution resistance in the pores when the pores existing in the electrode are imitated with a cylindrical model. Here, even when the electrolytic solution according to the present invention is used, the solvated lithium ion can be rapidly generated by setting the solution resistance index in pores represented by (Z ₂ −Z ₁ ) × Q to 20.0 mAhΩ or less. Can penetrate to the deep part of the electrode. Thereby, quick charge characteristics are improved.

  Moreover, it is preferable that the said impedance is measured in the uncharged state of a lithium ion secondary battery from a viewpoint of impedance analysis.

  An example of a technique for setting the solution resistance index in the pores to the specified numerical value is to change the void state of the positive and negative electrode active material layers. More specifically, when an active material having a small particle size or an active material having a flat particle shape is used, the formed voids tend to be small. In general, when an active material having a high packing property is used, voids formed are small, and the solution resistance index in the pores tends to be large. In addition, the solution resistance index in the pores can be controlled by the coverage of the binder used, the press pressure at the time of electrode preparation, the heat treatment after the electrode preparation, and the like. Further, it depends on the viscosity and wettability of the electrolyte used, and can be controlled effectively by the process after the electrode is manufactured. In the examples described below, the solution resistance index in the pores is set as a target value by combining these methods, but the solution resistance index in the pores may be controlled using a method other than described here, Such are within the scope of the present invention.

<Positive electrode>
(Positive electrode current collector)
The positive electrode current collector 12 may be a conductive plate material, and for example, a metal thin plate (metal foil) such as aluminum, an alloy thereof, or stainless steel can be used.

(Positive electrode active material layer)
The positive electrode active material layer 14 is mainly composed of a positive electrode active material, a positive electrode binder, and a positive electrode conductive additive.

(Positive electrode active material)
As the positive electrode active material, lithium ion occlusion and release, lithium ion desorption and insertion (intercalation), or doping and dedoping of a counter anion (for example, PF ₆ ⁻ ) of the lithium ion are reversibly performed. If it can be made to advance, it will not specifically limit, A well-known electrode active material can be used. For example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganese spinel (LiMn ₂ O ₄ ), and chemical formula: LiNi _x Co _y Mn _z M _a O ₂ (x + y + z + a = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ a ≦ 1, M is a composite represented by one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, and Cr) Metal oxide, lithium vanadium compound Li _a (M) _b (PO ₄ ) _c (where M = VO or V, and 0.9 ≦ a ≦ 3.3, 0.9 ≦ b ≦ 2.2, 0 .9 ≦ c ≦ 3.3), olivine-type LiMPO ₄ (wherein M represents one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and Zr or VO) , lithium titanate _(Li 4 T _{5 O 12), LiNi x Co} y Al z O 2 ( composite metal oxide such as 0.9 <x + y + z < 1.1) can be mentioned.

(Binder for positive electrode)
The positive electrode binder bonds the positive electrode active materials to each other and bonds the positive electrode active material layer 14 and the positive electrode current collector 12. The binder is not particularly limited as long as it can be bonded as described above. For example, fluorine resin such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), cellulose, styrene / butadiene rubber, ethylene / propylene rubber, polyimide A resin, a polyamideimide resin, or the like may be used. Alternatively, an electron conductive conductive polymer or an ion conductive conductive polymer may be used as the binder. Examples of the electron conductive conductive polymer include polyacetylene, polythiophene, and polyaniline. Examples of the ion conductive conductive polymer include those obtained by combining a polyether polymer compound such as polyethylene oxide and polypropylene oxide and a lithium salt such as LiClO ₄ , LiBF ₄ , and LiPF _6. It is done.

  Although content of the binder in the positive electrode active material layer 14 is not specifically limited, When adding, it is preferable that it is 0.5-5 mass parts with respect to the mass of a positive electrode active material.

(Conductive aid for positive electrode)
The conductive auxiliary agent for positive electrode is not particularly limited as long as it improves the conductivity of the positive electrode active material layer 14, and a known conductive auxiliary agent can be used. Examples thereof include carbon-based materials such as graphite and carbon black, metal fine powders such as copper, nickel, stainless steel, and iron, and conductive oxides such as ITO.

<Negative electrode>
(Negative electrode current collector)
The negative electrode current collector 22 may be a conductive plate material, and for example, a metal thin plate (metal foil) such as copper can be used.

(Negative electrode active material layer)
The negative electrode active material layer 24 is mainly composed of a negative electrode active material, a negative electrode binder, and a negative electrode conductive additive.

(Negative electrode active material)
The negative electrode active material is not particularly limited as long as it can reversibly advance occlusion and release of lithium ions and desorption and insertion (intercalation) of lithium ions, and a known electrode active material can be used. . For example, carbon-based materials such as graphite and hard carbon, silicon-based materials such as silicon oxide (SiO _x ) and metal silicon (Si), metal oxides such as lithium titanate (LTO), metals such as lithium, tin, and zinc Materials.

  When a metal material is not used as the negative electrode active material, the negative electrode active material layer 24 may further include a negative electrode binder and a negative electrode conductive additive.

(Binder for negative electrode)
There is no limitation in particular as a binder for negative electrodes, The thing similar to the binder for positive electrodes described above can be used.

(Conductive aid for negative electrode)
There is no limitation in particular as a conductive support agent for negative electrodes, The thing similar to the conductive support agent for positive electrodes described above can be used.

<Electrolyte>
The electrolytic solution according to the present embodiment includes propylene carbonate.

  According to this, propylene carbonate is easily solvated due to its high donor property among cyclic carbonates, and lithium ions solvated by propylene carbonate penetrate into the electrode deep due to its large solvation radius due to its molecular structure. Although quick charging characteristics are difficult to deteriorate, the quick charging characteristics can be improved with the configuration according to the present embodiment.

  In the electrolytic solution according to this embodiment, it is preferable that the proportion of propylene carbonate with respect to the total volume of the electrolytic solution is 10% by volume or more and 50% by volume or less.

  According to this, even if the proportion of propylene carbonate with respect to the total volume of the electrolytic solution is 10% by volume or more and 50% by volume or less, the quick charge characteristic is improved with the configuration according to the present embodiment.

(solvent)
In addition, as a solvent of the electrolytic solution, a solvent generally used in a lithium ion secondary battery may be mixed and used. For example, cyclic carbonate compounds such as ethylene carbonate (EC) and butylene carbonate, chain carbonate compounds such as diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), cyclic ester compounds such as γ-butyrolactone, propyl propionate, and propionic acid Examples thereof include chain ester compounds such as ethyl and ethyl acetate.

(Electrolytes)
The electrolyte is not particularly limited as long as it is a lithium salt used as an electrolyte of a lithium ion secondary battery. For example, inorganic acid anion salts such as LiPF ₆ , LiBF ₄ , lithium bisoxalate borate, LiCF ₃ SO ₃ , An organic acid anion salt such as (CF ₃ SO ₂ ) ₂ NLi, (FSO ₂ ) ₂ NLi, or the like can be used.

  As mentioned above, although preferred embodiment which concerns on this invention was described, this invention is not limited to the said embodiment.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

[Example 1]
(Preparation of positive electrode)
85 parts by mass of Li (Ni _0.80 Co _0.15 Al _0.05 ) O ₂ , 5 parts by mass of acetylene black and 10 parts by mass of PVDF are dispersed in N-methyl-2-pyrrolidone (NMP) to form a positive electrode active material layer The slurry for was prepared. This slurry was applied to one surface of an aluminum metal foil having a thickness of 20 μm so that the applied amount of the positive electrode active material was 6.0 mg / cm ² and dried at 100 ° C. to form a positive electrode active material layer. Then, it pressure-molded with the pressure of 1000 kg / cm of linear pressure with the roller press, and produced the positive electrode.

(Preparation of negative electrode)
A slurry for forming a negative electrode active material layer is prepared by dispersing 90 parts by mass of scaly artificial graphite whose surface is coated with amorphous carbon, 5 parts by mass of acetylene black, and 5 parts by mass of PVDF in N-methyl-2-pyrrolidone (NMP). did. The slurry was applied to one surface of a copper foil having a thickness of 20 μm so that the amount of the negative electrode active material applied was 4.0 mg / cm ² and dried at 100 ° C. to form a negative electrode active material layer. Thereafter, it was pressure-molded by a roller press at a linear pressure of 2400 kg / cm to produce a negative electrode.

(Preparation of electrolyte)
It was mixed so that EC / PC / DEC = 15/ 15/70 by volume, to which LiPF ₆ was dissolved at a concentration of 1.0 mol / L, to prepare an electrolyte solution.

(Production of evaluation lithium-ion secondary battery)
A laminate made of a polyethylene microporous membrane was sandwiched between the positive electrode and the negative electrode produced above, and the laminate was sealed in an aluminum laminate outer package to produce a dry cell having a capacity Q of 3.0 Ah. After the dry cell is dried at room temperature for 24 hours, the electrolytic solution prepared above is injected in an amount of injection obtained from the following formula, and sealed with a vacuum sealer (Fuji Impulse Co., Ltd.) for evaluation. A lithium ion secondary battery was prepared.
Injection volume (mL) = (Positive electrode volume + Negative electrode volume + Separator volume) x Injection coefficient Injection coefficient = 2.0
Positive electrode void volume (cm ³ ) = positive electrode active material layer volume × positive electrode porosity Negative electrode void volume (cm ³ ) = negative electrode active material layer volume × negative electrode porosity

(Measurement of impedance and derivation of solution resistance index in pores)
The evaluation lithium ion secondary battery prepared above was placed in a thermostatic chamber (manufactured by Espec Co., Ltd.) set at 25 ° C., and impedance Z at 25 ° C. and 100 kHz using an impedance analyzer (Bio-Logic). ₁ (mΩ) and impedance Z ₂ (mΩ) at 25 ° C. and 1 Hz were determined, and the solution resistance index in the pores was derived. The results are shown in Table 1.

(Battery)
The lithium ion secondary battery for evaluation produced above was charged at a constant current of 0.2C in a thermostat set at 25 ° C. using a charge / discharge test device (Hokuto Denko Co., Ltd.), and the battery voltage was 4 After charging until .2V, the battery was discharged with constant current discharge at a discharge rate of 0.2C until the battery voltage reached 2.8V. Here, X (C) indicates a current value at which charging is completed in 1 / X time when constant current charging is performed at 25 ° C.

(Confirmation of quick charge characteristics)
Charge the lithium ion secondary battery for evaluation made into a battery as described above into a constant-temperature charge at a charge rate of 0.2 C in a thermostatic chamber set at 25 ° C. using a charge / discharge test device until the battery voltage reaches 4.2V. It was carried out to determine the 0.2C charge capacity _{C 1.} After discharging the battery until the battery voltage becomes 2.8 V by constant current discharge at a discharge rate of 0.2 C, this time until the battery voltage becomes 4.2 V by constant current charge at a charge rate of 3.0 C and charges, was asked to 3.0C charge capacity _{C 2.}

From 0.2C charge capacity _{C 1} and 3.0C charge capacity _{C 2} obtained above, in accordance with the following equation to determine the rapid charging characteristics. The obtained results are shown in Table 1.
Rapid charge characteristics [%] = C ₂ / C ₁ × 100

[Example 2]
(Preparation of positive electrode)
85 parts by mass of Li (Ni _0.80 Co _0.15 Al _0.05 ) O ₂ , 5 parts by mass of acetylene black and 10 parts by mass of PVDF are dispersed in N-methyl-2-pyrrolidone (NMP) to form a positive electrode active material layer The slurry for was prepared. This slurry was applied to one surface of an aluminum metal foil having a thickness of 20 μm so that the applied amount of the positive electrode active material was 6.0 mg / cm ² and dried at 100 ° C. to form a positive electrode active material layer. Then, it pressure-molded by the pressure of 2000 kg / cm of linear pressure with the roller press, and produced the positive electrode.

(Preparation of negative electrode)
A slurry for forming a negative electrode active material layer is prepared by dispersing 90 parts by mass of scaly artificial graphite whose surface is coated with amorphous carbon, 5 parts by mass of acetylene black, and 5 parts by mass of PVDF in N-methyl-2-pyrrolidone (NMP). did. The slurry was applied to one surface of a copper foil having a thickness of 20 μm so that the amount of the negative electrode active material applied was 4.0 mg / cm ² and dried at 100 ° C. to form a negative electrode active material layer. Then, it pressure-molded with the pressure of 5000 kg / cm of linear pressure with the roller press, and produced the negative electrode.

(Preparation of electrolyte)
An electrolytic solution was prepared in the same manner as in Example 1.

(Production of evaluation lithium-ion secondary battery)
Using the positive electrode, negative electrode, and electrolytic solution prepared above, a lithium ion secondary battery for evaluation was manufactured following the method of Example 1.

[Example 3]
(Preparation of positive electrode)
A positive electrode was produced in the same manner as in Example 1.

(Preparation of negative electrode)
A negative electrode was produced in the same manner as in Example 1.

(Preparation of electrolyte)
It was mixed so that EC / PC / DEC = 25/ 15/60 by volume, to which LiPF ₆ was dissolved at a concentration of 1.2 mol / L, to prepare an electrolyte solution.
(Production of evaluation lithium-ion secondary battery)
Using the positive electrode, negative electrode, and electrolytic solution prepared above, a lithium ion secondary battery for evaluation was manufactured following the method of Example 1.

[Example 4]
(Preparation of positive electrode)
85 parts by mass of Li (Ni _0.80 Co _0.15 Al _0.05 ) O ₂ , 5 parts by mass of acetylene black and 10 parts by mass of PVDF are dispersed in N-methyl-2-pyrrolidone (NMP) to form a positive electrode active material layer The slurry for was prepared. This slurry was applied to one surface of an aluminum metal foil having a thickness of 20 μm so that the applied amount of the positive electrode active material was 6.0 mg / cm ² and dried at 100 ° C. to form a positive electrode active material layer. Then, the positive electrode was produced by press-molding with a roller press at a linear pressure of 400 kg / cm, and further heating at 80 ° C. for 24 hours.

(Preparation of negative electrode)
A slurry for forming a negative electrode active material layer is prepared by dispersing 90 parts by mass of scaly artificial graphite whose surface is coated with amorphous carbon, 5 parts by mass of acetylene black, and 5 parts by mass of PVDF in N-methyl-2-pyrrolidone (NMP). did. The slurry was applied to one surface of a copper foil having a thickness of 20 μm so that the amount of the negative electrode active material applied was 4.0 mg / cm ² and dried at 100 ° C. to form a negative electrode active material layer. Then, the negative electrode was produced by press-molding with a roller press at a linear pressure of 800 kg / cm and further heating at 80 ° C. for 24 hours.

(Preparation of electrolyte)
It was mixed so that EC / PC / DMC = 15/ 15/70 by volume, to which LiPF ₆ was dissolved at a concentration of 1.0 mol / L, to prepare an electrolyte solution.

(Production of evaluation lithium-ion secondary battery)
Using the positive electrode, negative electrode, and electrolytic solution prepared above, a lithium ion secondary battery for evaluation was manufactured following the method of Example 1.

[Example 5]
(Production of evaluation lithium-ion secondary battery)
A lithium ion secondary battery for evaluation was produced in the same manner as in Example 1 except that the capacity Q was 1.0 Ah.

[Example 6]
(Production of evaluation lithium-ion secondary battery)
A lithium ion secondary battery for evaluation was produced in the same manner as in Example 1 except that the capacity Q was 4.5 Ah.

[Example 7]
(Production of evaluation lithium-ion secondary battery)
A lithium secondary battery for evaluation was produced in the same manner as in Example 1 except that the electrolyte used was changed to 1.0 M LiPF ₆ EC / PC / DEC = 28/2/70.

[Example 8]
(Production of evaluation lithium-ion secondary battery)
A lithium secondary battery for evaluation was produced in the same manner as in Example 1 except that the electrolyte used was changed to 1.0 M LiPF ₆ EC / PC / DEC = 22/8/70.

[Example 9]
(Production of evaluation lithium-ion secondary battery)
A lithium secondary battery for evaluation was produced in the same manner as in Example 1 except that the electrolyte used was changed to 1.0 M LiPF ₆ EC / PC / DEC = 20/10/70.

[Example 10]
(Production of evaluation lithium-ion secondary battery)
A lithium secondary battery for evaluation was produced in the same manner as in Example 1 except that the electrolyte used was changed to 1.0 M LiPF ₆ EC / PC / DEC = 5/50/45.

[Example 11]
(Production of evaluation lithium-ion secondary battery)
A lithium secondary battery for evaluation was produced in the same manner as in Example 1 except that the electrolyte used was changed to 1.0 M LiPF ₆ PC / DEC = 55/45.

[Comparative Example 1]
(Preparation of positive electrode)
85 parts by mass of Li (Ni _0.80 Co _0.15 Al _0.05 ) O ₂ , 5 parts by mass of acetylene black and 10 parts by mass of PVDF are dispersed in N-methyl-2-pyrrolidone (NMP) to form a positive electrode active material layer The slurry for was prepared. This slurry was applied to one surface of an aluminum metal foil having a thickness of 20 μm so that the applied amount of the positive electrode active material was 6.0 mg / cm ² and dried at 100 ° C. to form a positive electrode active material layer. Then, it pressure-molded by the pressure of 2000 kg / cm of linear pressure with the roller press, and produced the positive electrode.

(Preparation of negative electrode)
A slurry for forming a negative electrode active material layer was prepared by dispersing 90 parts by mass of spherical artificial graphite whose surface was coated with amorphous carbon, 5 parts by mass of acetylene black, and 5 parts by mass of PVDF in N-methyl-2-pyrrolidone (NMP). . The slurry was applied to one surface of a copper foil having a thickness of 20 μm so that the amount of the negative electrode active material applied was 4.0 mg / cm ² and dried at 100 ° C. to form a negative electrode active material layer. Thereafter, it was pressure-molded with a roller press at a linear pressure of 5000 kg / cm to produce a negative electrode.

(Preparation of electrolyte)
It was mixed so that EC / PC / DEC = 15/ 15/70 by volume, to which LiPF ₆ was dissolved at a concentration of 1.5 mol / L, to prepare an electrolyte solution.

(Production of evaluation lithium-ion secondary battery)
Using the positive electrode, negative electrode, and electrolytic solution prepared above, a lithium ion secondary battery for evaluation was manufactured following the method of Example 1.

[Comparative Example 2]
(Preparation of positive electrode)
85 parts by mass of Li (Ni _0.80 Co _0.15 Al _0.05 ) O ₂ , 5 parts by mass of acetylene black and 10 parts by mass of PVDF are dispersed in N-methyl-2-pyrrolidone (NMP) to form a positive electrode active material layer The slurry for was prepared. This slurry was applied to one surface of an aluminum metal foil having a thickness of 20 μm so that the applied amount of the positive electrode active material was 6.0 mg / cm ² and dried at 100 ° C. to form a positive electrode active material layer. Then, it pressure-molded by the pressure of 2000 kg / cm of linear pressure with the roller press, and produced the positive electrode.

(Preparation of negative electrode)
A slurry for forming a negative electrode active material layer was prepared by dispersing 90 parts by mass of spherical artificial graphite whose surface was coated with amorphous carbon, 5 parts by mass of acetylene black, and 5 parts by mass of PVDF in N-methyl-2-pyrrolidone (NMP). . The slurry was applied to one surface of a copper foil having a thickness of 20 μm so that the amount of the negative electrode active material applied was 4.0 mg / cm ² and dried at 100 ° C. to form a negative electrode active material layer. Then, it pressure-molded with the pressure of 5000 kg / cm of linear pressure with the roller press, and produced the negative electrode.

(Preparation of electrolyte)
It was mixed so that PC / DEC = 55/45 by volume, to which LiPF ₆ was dissolved at a concentration of 1.5 mol / L, to prepare an electrolyte solution.

(Production of evaluation lithium-ion secondary battery)
Using the positive electrode, negative electrode, and electrolytic solution prepared above, a lithium ion secondary battery for evaluation was manufactured following the method of Example 1.

(Measurement of impedance and derivation of solution resistance index in pores)
Impedance of the lithium ion secondary batteries for evaluation produced in Examples 2 to 11 and Comparative Examples 1 and 2 was determined in the same manner as in Example 1 to derive the pore solution resistance index. The obtained results are shown in Table 1.

(Battery)
The evaluation lithium secondary batteries produced in Examples 2 to 11 and Comparative Examples 1 and 2 in which the impedance measurement and the solution resistance index in the pores were derived as described above were made into batteries by the same method as in Example 1. went.

(Confirmation of quick charge characteristics)
The quick charge characteristics of the evaluation lithium secondary batteries produced in Examples 2 to 11 and Comparative Examples 1 and 2 that were converted into batteries as described above were confirmed in the same manner as in Example 1. The obtained results are shown in Table 1.

  In each of Examples 1 to 11, it was confirmed that the quick charge characteristics were improved as compared with Comparative Examples 1 and 2 in which the pore resistance index was not optimized.

  From the results of Examples 7 to 11, it was confirmed that excellent quick charge characteristics could be obtained even when the ratio of PC to the entire electrolyte solution was changed. This is presumed that the effect of the present invention was obtained without depending on the ratio of PC because PC having the highest donor property is finally desolvated.

  According to the present invention, a lithium ion secondary battery capable of improving quick charge characteristics is provided.

  DESCRIPTION OF SYMBOLS 10 ... Positive electrode, 12 ... Positive electrode collector, 14 ... Positive electrode active material layer, 18 ... Separator, 20 ... Negative electrode, 22 ... Negative electrode collector, 24 ... Negative electrode active material layer, 30 ... Laminate, 50 ... Case, 60 62 ... Lead, 100 ... Lithium ion secondary battery.

Claims (3)

A lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator positioned between the positive electrode and the negative electrode, and an electrolyte solution comprising a solvent and a supporting salt,
The solvent comprises propylene carbonate;
When the impedance of the lithium ion secondary battery at 25 ° C. and 100 kHz is Z ₁ (mΩ), the impedance at 25 ° C. and 1 kHz is Z ₂ (mΩ), and the capacity of the lithium ion secondary battery is Q (Ah), (Z A lithium ion secondary battery having a solution resistance index in pores represented by ₂ −Z ₁ ) × Q of 20.0 mAhΩ or less.   The lithium ion secondary battery according to claim 1, wherein the solution resistance index in the pores is 10.0 mAhΩ or less. 3. The lithium ion secondary battery according to claim 1, wherein a ratio of propylene carbonate to a total volume of the electrolytic solution is 10% by volume or more and 50% by volume or less.

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