JP2019175650A - Lithium ion secondary battery - Google Patents

Abstract

To provide a lithium ion secondary battery which enables the improvement of lithium precipitation on a negative electrode after a cycle.SOLUTION: A lithium ion secondary battery comprises a positive electrode 10 which contains a lithium nickel compound represented by LiNi(M)(M)O(where Mis at least one kind selected from Co and Mn, and Mrepresents at least one element selected from Al, Fe, Cr and Mg; 0.9≤w≤1.3; 0.75≤x≤0.95; 0.01≤y≤0.25; and 0≤z≤0.25), and a negative electrode 20. When the impedance of the negative electrode at 25°C and 1 kHz is denoted by Z(mΩ), the impedance at 25°C and 1 Hz is Z(mΩ), and the capacity of the lithium ion secondary battery is denoted by Q (Ah), a unit volume impedance index given by (Z-Z)×Q is 100.0 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.

To increase the energy density of lithium ion secondary batteries, it is urgent to develop positive electrode active materials with high potential and high capacity. In recent years, a battery voltage of around 4 V has appeared, and lithium transition metal composite oxides mainly composed of nickel and cobalt such as LiNiO ₂ and LiCoO ₂ are considered as one of promising materials. Among these, lithium nickel compounds having a high nickel ratio such as NCA and NCM811 exist that have a discharge capacity exceeding 200 mAh / g, and it is expected that the energy density of the lithium ion secondary battery will be dramatically improved by using this. Has been.

  However, the lithium nickel compound has a problem that a transition metal element that gradually constitutes elutes in the electrolytic solution with charge and discharge. In particular, lithium nickel compounds having a high nickel ratio such as NCA and NCM811, the tendency is remarkable, and it is considered that the cycle characteristics and rate characteristics of the battery are greatly affected.

  Therefore, in Patent Document 1, an organometallic compound containing at least one of Al, Mg, Sn, Ti, Zn, and Zr is added to a lithium nickel compound, and mechanically pulverized. A method of performing heat treatment at a temperature of 700 ° C. or lower has been proposed. According to this, the particle surface of the lithium nickel compound is stabilized and the cycle characteristics are improved by mechanically crushing the particle surface and attaching the organometallic compound, followed by high-temperature treatment.

JP-A-2005-346955

  However, it is difficult to completely suppress the elution of the transition metal element even by the prior art method, and the eluted transition metal element is taken into the solid electrolyte interface (SEI) film of the negative electrode, and the negative electrode resistance continuously increases. End up. Thereby, there existed a subject by which dendritic precipitation of lithium was caused on a negative electrode with progress of a cycle.

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide a lithium ion secondary battery capable of improving lithium deposition on the negative electrode after the cycle has elapsed.

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. In the secondary battery, the positive electrode is Li _w Ni _x (M ₁ ) _y (M ₂ ) _z O ₂ (where M ₁ is at least one selected from Co and Mn, and M ₂ is Al, Fe, Cr) And at least one element selected from Mg, 0.9 ≦ w ≦ 1.3, 0.75 ≦ x ≦ 0.95, 0.01 ≦ y ≦ 0.25, 0 ≦ z ≦ 0. .25), the impedance of the negative electrode at 25 ° C. and 1 kHz is Z ₁ (mΩ), the impedance at 25 ° C. and 1 Hz is Z ₂ (mΩ), and the capacity of the lithium ion secondary battery is Q (Ah) and When _{in, (Z} 2 -Z ₁₎ Lithium ion secondary batteries, characterized by unit volume impedance index represented by × Q is less than 100.0MAhomega.

When a lithium nickel compound having a high nickel ratio is used as the positive electrode as in the lithium ion secondary battery according to the present invention, transition metal ions are likely to elute with the progress of the cycle, and are taken into the SEI film on the negative electrode and have a high capacitance. Easy to convert. Along with this, the time constant also changes in a decreasing direction. Therefore, when the impedance at 25 ° C. and 1 kHz is Z ₁ , and the impedance at 25 ° C. and 1 Hz is Z ₂ , Z ₂ −Z ₁ is used as an index representing the impedance of the negative electrode. be able to. By setting the unit capacity impedance index obtained by standardizing this value with the battery capacity Q to 100 mAhΩ or less, uniform SEI with low resistance can be formed on the negative electrode, and lithium deposition after the cycle can be suppressed.

  In the lithium ion secondary battery according to the present invention, the unit capacity impedance index is preferably 70.0 mAhΩ or less.

  According to this, it is more suitable as a unit capacity impedance index, and lithium deposition after the cycle can be further suppressed.

  In the lithium ion secondary battery according to the present invention, the capacity Q is preferably 3.0 Ah or more.

  According to this, since the variation in SEI film formation is likely to occur, even if it is a lithium ion secondary battery having a capacity band in which lithium deposition is likely to be caused, by adopting the configuration according to the present invention, the cycle progress Later lithium deposition can be suppressed.

  In the lithium ion secondary battery according to the present invention, the positive electrode preferably further contains a lithium vanadium compound.

  According to this, even if it is a lithium ion secondary battery including a lithium vanadium compound composed of a vanadium ion that is likely to be a nucleus of lithium deposition on the positive electrode, the configuration according to the present invention allows lithium after the cycle to be performed. Precipitation can be suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium ion secondary battery which can suppress the lithium precipitation after progress of a cycle 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.

<Positive electrode>
The positive electrode according to the present embodiment is Li _w Ni _x (M ₁ ) _y (M ₂ ) _z O ₂ (where M ₁ is at least one selected from Co and Mn, and M ₂ is Al, Fe, Cr, and Mg) And at least one element selected from the group consisting of 0.9 ≦ w ≦ 1.3, 0.75 ≦ x ≦ 0.95, 0.01 ≦ y ≦ 0.25, and 0 ≦ z ≦ 0.25. The lithium nickel compound represented by this is included.

  According to this, even if a lithium nickel compound having a high nickel ratio that easily elutes transition metal ions with the progress of the cycle is used as the positive electrode, the lithium ion battery according to the present embodiment can be used as the lithium after the cycle has elapsed. Precipitation can be suppressed.

  The positive electrode according to this embodiment preferably further contains a lithium vanadium compound.

  According to this, even if it is a lithium ion secondary battery containing a lithium vanadium compound composed of vanadium ions that are likely to be nuclei of lithium deposition on the positive electrode, by configuring the lithium ion battery according to this embodiment, Lithium deposition after the cycle can be suppressed.

The lithium vanadium compound is not particularly limited, but Li _a M _b (PO ₄ ) _c (where M represents V and VO. Also, 1 ≦ a ≦ 4, 1 ≦ b ≦ 2, 1 ≦ c ≦ 3) The lithium vanadium lithium compound represented by the formula etc. can be used.

  Hereinafter, an example of the configuration of the positive electrode according to the present embodiment will be described.

(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.

(Other positive electrode active materials)
As the positive electrode active material, other positive electrode active materials capable of inserting and extracting lithium ions and desorbing and inserting lithium ions can be mixed and used. For example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganese spinel (LiMn ₂ O ₄ ), 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, and M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, and Cr) Etc.

(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>
When the impedance at 25 ° C. and 1 kHz is Z ₁ (mΩ), the impedance at 25 ° C. and 1 Hz is Z ₂ (mΩ), and the capacity of the lithium ion secondary battery is Q (Ah), the negative electrode according to this embodiment is (Z _The unit capacitance impedance index represented by ₂ −Z ₁ ) × Q is 100.0 mAhΩ or less, more preferably 70.0 mAhΩ or less.

  Examples of the method for setting the unit capacitance impedance index to the specified value include, for example, use of a negative electrode active material having different lithium ion conductivity, or changing the ratio of the conductive auxiliary agent contained in the negative electrode. The unit capacitance impedance index can be controlled by changing the resistance of the layer. Alternatively, the unit capacitance impedance index can be controlled by changing the resistance of the negative electrode active material surface, such as adding an appropriate additive to the negative electrode slurry, or coating the negative electrode active material with a material having different electrolyte wettability. I can do it. Furthermore, after the battery is made into a battery, the unit capacity impedance index can be controlled by the magnitude of the charging current and the temperature at that time. In the embodiments described later, the unit capacitance impedance index is set as a target value by combining these methods, but the unit capacitance impedance index may be controlled by using a method other than those described here. Are also within the scope of the present invention.

  In particular, even in the case of a lithium ion battery having a Q of 3.0 Ah or higher, which is likely to cause variations in SEI film formation and cause lithium deposition, the lithium deposition after cycle elapses with the configuration according to the present invention. Can be effectively suppressed.

  As a method for measuring the impedance of the negative electrode, a method using a triode cell in which a reference electrode is incorporated in a battery is well known. By connecting the negative electrode to the positive electrode with a current terminal and connecting the negative electrode to the reference electrode with a voltage terminal and measuring with an impedance analyzer, the impedance of the negative electrode can be obtained separately. From the viewpoint of not adversely affecting the battery, it is preferable to use lithium metal for the reference electrode and nickel for the electrode outlet.

  In addition, as a method for measuring the impedance of the negative electrode, a method using a symmetrical cell in which the negative electrodes are opposed to each other is also known. A symmetrical cell can be obtained by disassembling the battery to be measured under an inert atmosphere such as a glove box, taking out the negative electrode, and facing and resealing via a separator. The impedance of the negative electrode can also be obtained separately by measuring the symmetric cell with an impedance analyzer.

  Hereinafter, an example of the configuration of the negative electrode according to the present embodiment will be described.

(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>
(solvent)
The solvent of the electrolytic solution is not particularly limited as long as it is a solvent generally used in lithium ion secondary batteries. For example, cyclic carbonate compounds such as ethylene carbonate (EC) and propylene carbonate (PC), diethyl carbonate (DEC) ), A chain carbonate compound such as ethyl methyl carbonate (EMC), a cyclic ester compound such as γ-butyrolactone, a chain ester compound such as propyl propionate, ethyl propionate, and ethyl acetate, etc. Can be used.

(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 carbon 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 9.0 mg / cm ² and dried at 100 ° C. to form a positive electrode active material layer. Then, it pressure-molded with the roller press and produced the positive electrode.

(Preparation of negative electrode)
90 parts by mass of natural graphite, 5 parts by mass of carbon black, and 5 parts by mass of PVDF were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a slurry for forming a negative electrode active material layer. 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 6.0 mg / cm ² and dried at 100 ° C. to form a negative electrode active material layer. Then, it pressure-molded with the roller press and produced the negative electrode.

(Preparation of electrolyte)
Were mixed so that EC / DEC = 3/7 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

(Battery)
The lithium ion secondary battery for evaluation produced above was charged at a charge rate of 0.00 in a thermostatic chamber set at 25 ° C. using a thermostatic chamber (manufactured by Espec Co., Ltd.) and a charge / discharge test apparatus (manufactured by Hokuto Denko Co., Ltd.). After charging at a constant current of 2C until the battery voltage reached 4.2V, discharging was performed until the battery voltage reached 2.8V at a constant current discharge at a discharge rate of 0.2C. 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.

(Measurement of negative electrode impedance)
A part of the evaluation lithium-ion secondary battery package that has been made into a battery as described above is opened in a glove box under an inert atmosphere, and then the reference electrode in which metallic lithium is plated on a nickel wire is short-circuited. It was introduced with care and resealed using a vacuum sealer. The evaluation lithium secondary battery into which this reference electrode was introduced was measured using an impedance analyzer (Bio-Logic), the current terminal was negative (+)-positive (-), and the voltage terminal was negative (+)-reference electrode. It was connected to a thermostatic chamber (manufactured by Espec Corp.) set at 25 ° C. so as to be (−), and impedance Z ₁ (mΩ) at ₁ kHz and impedance Z ₂ (mΩ) at 1 Hz were obtained. The results are shown in Table 1.

(Confirmation of lithium deposition after 100 cycles)
The lithium ion secondary battery for evaluation whose negative electrode impedance was measured as described above was charged until the battery voltage became 4.2 V by constant current charging at a charging rate of 2.0 C in a thermostat set at 25 ° C., and then Then, the battery was discharged until the battery voltage became 2.8 V by constant current discharge at a discharge rate of 1.0 C. The charge / discharge pattern was defined as one cycle, and 100 cycles of charge / discharge were performed. Regarding the battery after 100 cycles, the battery was disassembled in an inert atmosphere in the glove box and the negative electrode surface was confirmed. As a result, lithium deposition was not confirmed.

[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 carbon 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 13.5 mg / cm ² and dried at 100 ° C. to form a positive electrode active material layer. Then, it pressure-molded with the roller press and produced the positive electrode.

(Preparation of negative electrode)
90 parts by mass of natural graphite, 5 parts by mass of carbon black, and 5 parts by mass of PVDF were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a slurry for forming a negative electrode active material layer. 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 9.0 mg / cm ² and dried at 100 ° C. to form a negative electrode active material layer. Then, it pressure-molded 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. The capacity Q was set to 3.0 Ah.

(Battery)
Batterization was carried out in the same manner as in Example 1.

(Measurement of negative electrode impedance)
The negative electrode impedance of the evaluation lithium ion secondary battery made into a battery as described above was measured in the same manner as in Example 1. The results are shown in Table 1.

(Confirmation of lithium deposition during cycle test)
The lithium ion secondary battery for evaluation made into a battery was observed for the negative electrode surface of the battery after 100 cycles in the same manner as in Example 1. As a result, lithium deposition was slightly confirmed. (About 1% of the total area of the negative electrode)

[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)
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. The capacity Q was set to 3.0 Ah.

(Battery)
The lithium ion secondary battery for evaluation produced above was charged until the battery voltage became 4.2 V by constant current charging at a charge rate of 0.2 C in a thermostat set at 25 ° C., and then the discharge rate. The battery was discharged at a constant current discharge of 0.2 C until the battery voltage reached 2.8V. The lithium ion secondary battery that was charged and discharged as described above was allowed to stand for 30 minutes in a thermostatic chamber set at 60 ° C., and the battery was formed.

(Confirmation of lithium deposition during cycle test)
Regarding the lithium ion secondary battery for evaluation made into a battery as described above, as in Example 1, the negative electrode surface of the battery after 100 cycles was observed, and lithium deposition was not confirmed.

[Example 4]
(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 / DEC / DMC = 2/ 2/6 by volume, to which LiPF ₆ was dissolved at a concentration of 1.2 mol / L. Then, vinylene carbonate was added so that it might become a 1.0 wt% density | concentration, and electrolyte solution was produced.

(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. The capacity Q was 3.0 Ah, and the injection coefficient was 2.2.

(Battery)
The lithium ion secondary battery for evaluation produced above was charged until the battery voltage became 3.9 V by constant current charging at a charge rate of 0.05 C in a thermostat set at 25 ° C., and then the charge rate It switched to the constant current charge of 0.1C, and it charged until the battery voltage became 4.2V. Then, it discharged until the battery voltage became 2.8V by the constant current discharge of the discharge rate 0.2C.

(Measurement of negative electrode impedance)
The negative electrode impedance of the evaluation lithium ion secondary battery made into a battery as described above was measured in the same manner as in Example 1. The results are shown in Table 1.

(Confirmation of lithium deposition during cycle test)
Regarding the lithium ion secondary battery for evaluation made into a battery as described above, as in Example 1, the negative electrode surface of the battery after 100 cycles was observed, and lithium deposition was not confirmed.

[Example 5]
In the production of the evaluation lithium ion secondary battery, the evaluation lithium ion secondary battery of Example 5 was produced in the same manner as in Example 1, except that the capacity Q was changed to 1.0 Ah.

(Measurement of negative electrode impedance)
The negative electrode impedance of the evaluation lithium ion secondary battery made into a battery as described above was measured in the same manner as in Example 1. The results are shown in Table 1.

(Confirmation of lithium deposition during cycle test)
Regarding the lithium ion secondary battery for evaluation made into a battery as described above, as in Example 1, the negative electrode surface of the battery after 100 cycles was observed, and lithium deposition was not confirmed.

[Example 6]
A lithium ion secondary battery for evaluation of Example 6 was produced in the same manner as in Example 1 except that the capacity Q was changed to 4.5 Ah in the production of the evaluation lithium ion secondary battery.

(Measurement of negative electrode impedance)
The negative electrode impedance of the evaluation lithium ion secondary battery made into a battery as described above was measured in the same manner as in Example 1. The results are shown in Table 1.

(Confirmation of lithium deposition during cycle test)
Regarding the lithium ion secondary battery for evaluation made into a battery as described above, as in Example 1, the negative electrode surface of the battery after 100 cycles was observed, and lithium deposition was not confirmed.

[Example 7]
(Preparation of positive electrode)
80 parts by mass of Li (Ni _0.80 Co _0.15 Al _0.05 ) O ₂ , 5 parts by mass of LiVOPO _4, 5 parts by mass of carbon black, and 10 parts by mass of PVDF are dispersed in N-methyl-2-pyrrolidone (NMP). Then, a slurry for forming the positive electrode active material layer 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 9.0 mg / cm ² and dried at 100 ° C. to form a positive electrode active material layer. Then, it pressure-molded with the roller press and produced the positive electrode.

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

(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. The capacity Q was set to 3.0 Ah.

(Battery)
Batterization was carried out in the same manner as in Example 1.

(Measurement of negative electrode impedance)
The negative electrode impedance of the evaluation lithium ion secondary battery made into a battery as described above was measured in the same manner as in Example 1. The results are shown in Table 1.

(Confirmation of lithium deposition during cycle test)
Regarding the lithium ion secondary battery for evaluation made into a battery as described above, as in Example 1, the negative electrode surface of the battery after 100 cycles was observed, and lithium deposition was not confirmed.

[Comparative Example 1]
(Preparation of positive electrode)
A negative 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)
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. The capacity Q was set to 3.0 Ah.

(Battery)
The lithium ion secondary battery for evaluation prepared above was charged until the battery voltage became 4.2 V by constant current charging at a charging rate of 0.2 C in a thermostat set at 60 ° C., and then the discharge rate. The battery was discharged at a constant current discharge of 0.2 C until the battery voltage reached 2.8V. The lithium ion secondary battery that was charged and discharged as described above was allowed to stand for 2 hours in a thermostatic chamber set at 80 ° C., and battery formation was performed.

(Measurement of negative electrode impedance)
The negative electrode impedance of the evaluation lithium ion secondary battery made into a battery as described above was measured in the same manner as in Example 1. The results are shown in Table 1.

(Confirmation of lithium deposition during cycle test)
The lithium ion secondary battery for evaluation made into a battery as described above was subjected to observation of the negative electrode surface of the battery after 100 cycles in the same manner as in Example 1. As a result, lithium deposition was confirmed. (About 5% of the total area of the negative electrode)

[Comparative Example 2]
(Production of evaluation lithium-ion secondary battery)
In the same manner as in Example 7, a positive electrode, a negative electrode, and an electrolytic solution were produced, and a lithium ion secondary battery for evaluation was produced. The capacity Q was set to 3.0 Ah.

(Battery)
A battery was produced in the same manner as in Comparative Example 1.

(Measurement of negative electrode impedance)
The negative electrode impedance of the evaluation lithium ion secondary battery made into a battery as described above was measured in the same manner as in Example 1. The results are shown in Table 1.

(Confirmation of lithium deposition during cycle test)
As for the lithium ion secondary battery for evaluation made into a battery as described above, the negative electrode surface of the battery after 100 cycles was observed in the same manner as in Example 1. As a result, many lithium depositions were confirmed. (About 10% of the total area of the negative electrode)

  In each of Examples 1 to 7, it was confirmed that lithium deposition was suppressed more than Comparative Examples 1 and 2 in which the unit capacitance impedance index was not optimized.

  From the results of Example 7 and Comparative Example 2, it was confirmed that when the positive electrode contains a lithium vanadium compound, the lithium precipitation suppressing action can be obtained more effectively.

  The present invention provides a lithium ion secondary battery capable of improving lithium deposition on the negative electrode after the cycle has elapsed.

  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 (4)

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 positive electrode is Li _w Ni _x (M ₁ ) _y (M ₂ ) _z O ₂ (where M ₁ is at least one selected from Co and Mn, M ₂ is at least selected from Al, Fe, Cr and Mg) One element, 0.9 ≦ w ≦ 1.3; 0.75 ≦ x ≦ 0.95; 0.01 ≦ y ≦ 0.25; 0 ≦ z ≦ 0.25) Including lithium nickel compounds,
When the impedance of the negative electrode at 25 ° C. and 1 kHz is Z ₁ (mΩ), the impedance of the negative electrode at 25 ° C. and 1 Hz is Z ₂ (mΩ), and the capacity of the lithium ion secondary battery is Q (Ah), (Z ₂ A unit capacity impedance index represented by -Z ₁ ) × Q is 100.0 mAhΩ or less.   The lithium ion secondary battery according to claim 1, wherein the unit capacity impedance index is 70.0 mAhΩ or less.   The lithium ion secondary battery according to claim 1, wherein the capacity Q is 3.0 Ah or more. The lithium ion secondary battery according to any one of claims 1 to 3, wherein the positive electrode contains a lithium vanadium compound.

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