JP6992362B2 - Lithium ion secondary battery - Google Patents

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 miniaturized and cordless, and there is an increasing demand for a secondary battery that is compact, lightweight, and has a high energy density as a power source for driving them. Further, under such a situation, a lithium ion secondary battery having a large charge / discharge capacity and a high energy density is attracting attention.

Currently, many alloy-based negative electrode active materials such as silicon and silicon oxide, which have a larger charge / discharge capacity than carbon materials such as graphite, are being studied as negative electrode active materials for electrochemical devices such as lithium ion secondary batteries. However, when such a material is used as the negative electrode active material, the negative electrode active material expands and contracts with charge and discharge, so that the binder expands by repeating charging and discharging, and between the active material particles and the current collector. Since the conductive path of the material is divided, the cycle characteristics are significantly deteriorated as compared with the carbon material.

Therefore, a technique has been reported in which the surface of an alloy-based negative electrode active material is coated with an inorganic compound rich in elasticity to suppress expansion and contraction and improve cycle characteristics. (Patent Document 1)

JP 2015-69863

However, the expansion and contraction of the negative electrode active material cannot be completely suppressed by the method of the prior art, and further improvement of the cycle characteristics is required.

As a result of diligent research, the authors have found that when the negative electrode active material repeatedly expands and contracts with the cycle, the pore distribution of the electrodes becomes non-uniform and the electrolyte does not penetrate evenly, which is one of the causes of the cycle deterioration. I found that it was.

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

In order to solve the above problems, the lithium ion secondary battery according to the present invention has a positive electrode composed of a positive electrode active material layer and a positive electrode current collector, a negative electrode composed of a negative electrode active material layer and a negative electrode current collector, and the positive electrode and the above. A lithium ion secondary battery including a separator located between the negative electrodes and an electrolytic solution, wherein the negative electrode active material layer contains silicon or a silicon compound, and the porosity of the negative electrode active material layer is 25% or more 38. % Or less, and the electrolytic solution contains fluorinated carbonate ester in an amount of 0.1% by volume or more and 5.0% by volume or less and a carboxylic acid ester, and the total mass of the positive electrode active material layer and the negative electrode active material layer. The weight of the electrolytic solution is 30% by mass or more and 45% by mass or less.

According to this, the porosity of the negative electrode active material layer is 25% or more and 38% or less, the mass of the electrolytic solution with respect to the total mass of the positive electrode active material layer and the negative electrode active material layer is 30% by mass or more and 45% by mass or less, and the viscosity is high. By using a low and highly wettable carboxylic acid ester, the electrolytic solution can be uniformly permeated into the electrode even after the cycle. Further, the fluorinated carbonic acid ester suppresses the reductive decomposition of the carboxylic acid ester, the consumption of the electrolytic solution can be prevented, and the cycle characteristics are improved.

Further, in the lithium ion secondary battery according to the present invention, the porosity of the negative electrode active material layer is preferably 30% or more and 35% or less.

According to this, it is suitable as the porosity of the negative electrode active material layer, and the cycle characteristics are further improved.

Further, in the lithium ion secondary battery according to the present invention, it is preferable that the carboxylic acid ester is represented by the following chemical formula (1).
(Here, R ₁ and R ₂ are linear or branched alkyl groups or substituted alkyl groups having 1 to 4 carbon atoms, and the total number of carbon atoms of R ₁ and R ₂ is 5 or less.)

According to this, it is suitable as a carboxylic acid ester, and the high temperature storage property is further improved.

Further, in the lithium ion secondary battery according to the present invention, it is preferable that the carboxylic acid ester is a propionic acid ester or an acetic acid ester.

According to this, it is suitable as a carboxylic acid ester, and the high temperature storage property is further improved.

Further, in the lithium ion secondary battery according to the present invention, it is preferable that the carboxylic acid ester is contained in the electrolytic solution in an amount of 50% by volume or more and 90% by volume or less.

According to this, the ratio of the carboxylic acid ester is suitable, and the high temperature storage property is further improved.

Further, in the lithium ion secondary battery according to the present invention, it is preferable that the lithium vanadium compound is LiVOPO ₄ .

INDUSTRIAL APPLICABILITY According to the present invention, a lithium ion secondary battery capable of improving cycle characteristics is provided.

It is a schematic cross-sectional view of the lithium ion secondary battery of this embodiment.

Hereinafter, preferred embodiments according to the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments. In addition, the components described below include those easily conceived by those skilled in the art and those substantially the same. Further, the components described below can be combined as appropriate.

<Lithium-ion secondary battery>
As shown in FIG. 1, the lithium ion secondary battery 100 according to the present embodiment is arranged adjacent to each other between the plate-shaped negative electrode 20 and the plate-shaped positive electrode 10 facing each other, and the negative electrode 20 and the positive electrode 10. A laminate 30 including a plate-shaped 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 are electrically connected to each other. It includes a lead 62 whose other end is projected to the outside of the case, and a lead 60 whose one end is electrically connected to the positive electrode 10 and whose other end is projected to the outside of the case.

The positive electrode 10 has a positive electrode current collector 12 and a positive electrode active material layer 14 formed on the positive electrode current collector 12. Further, the negative electrode 20 has 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 composed of a positive electrode active material layer and a positive electrode current collector.

(Positive current collector)
The positive electrode current collector 12 may be any conductive plate material, and for example, a thin metal plate (metal foil) such as aluminum or 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 auxiliary agent.

(Positive electrode active material)
As the positive electrode active material, the storage and release of lithium ions, the desorption and insertion (intercalation) of lithium ions, or the doping and dedoping of the counter anion of the lithium ions (for example, PF _6- ⁾ are reversibly performed. A known electrode active material can be used without particular limitation as long as it can be advanced. For example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganese spinel (LiMn ₂ O ₄ ), and chemical formula: LiNi _x Coy Mn _z MaO ₂ (x + _y + z + a = 1, 0 ≦ x ≦ 1). , 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ a ≦ 1, M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, and Cr). Material, Lithium vanadium compound Li _a (M) _b (PO ₄ ) _c (However, M = VO or V, and 0.9 ≦ a ≦ 3.3, 0.9 ≦ b ≦ 2.2, 0.9 ≦ c ≦ 3.3), olivine type LiMPO ₄ (where M indicates one or more elements or VO selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr), titanium Examples thereof include composite metal oxides such as lithium acid (Li ₄ Ti ₅ O ₁₂ ) and LiNi _x Coy Al _z O ₂ (0.9 <x + _y + z <1.1).

When a lithium vanadium compound is used among the positive electrode active materials, the effect of improving the cycle characteristics can be strongly obtained when combined with the negative electrode and the electrolytic solution according to the present embodiment. Among the lithium vanadium compounds, LiVOPO ₄ has a stronger effect of improving the cycle characteristics. The exact mechanism of the above action is still unknown, but it is presumed that vanadium ions complex with the carboxylic acid ester to form a film on the negative electrode.

(Binder for positive electrode)
The positive electrode binder binds the positive electrode active materials to each other, and also bonds the positive electrode active material layer 14 and the positive electrode current collector 12. The binder may be any as long as it can be bonded as described above, and is, for example, a fluororesin such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE), cellulose, styrene / butadiene rubber, ethylene / propylene rubber, or polyimide. A resin, a polyamide-imide resin, or the like may be used. Further, as the binder, an electron conductive conductive polymer or an ion conductive conductive polymer may be used. Examples of the electron-conducting conductive polymer include polyacetylene, polythiophene, polyaniline and the like. Examples of the ionic conductive polymer include a composite of a polyether polymer compound such as polyethylene oxide and polypropylene oxide and a lithium salt such as LiClO ₄ , LiBF ₄ , and LiPF ₆ . Be done.

The content of the binder in the positive electrode active material layer 14 is not particularly limited, but when added, it is preferably 0.5 to 5 parts by mass with respect to the mass of the positive electrode active material.

(Conductive aid for positive electrode)
The conductive auxiliary agent for the 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>
The negative electrode according to the present embodiment is composed of a negative electrode active material layer and a negative electrode current collector, and the negative electrode active material layer contains silicon or a silicon compound and has a porosity of 25% or more and 38% or less. There is.
(Negative electrode current collector)
The negative electrode current collector 22 may be a conductive plate material, and for example, a thin metal plate (metal leaf) 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 auxiliary agent.

The porosity of the negative electrode active material layer is 25% or more and 38% or less. In particular, it is preferably 30% or more and 35% or less. In the case of the above porosity, when combined with the electrolytic solution according to the present embodiment, the electrolytic solution can be uniformly permeated into the electrode even after the cycle, and the cycle characteristics are improved.

Here, the porosity of the negative electrode active material layer = the density of the negative electrode active material layer / the true density of the used negative electrode active material × 100 [%]. When the negative electrode active material layer contains two or more types of negative electrode active materials, the true density of each negative electrode active material is multiplied according to the composition ratio, and the total value thereof is taken as the porosity.

(Negative electrode active material)
The negative electrode active material contains silicon or a compound of silicon. For example, metallic silicon (Si) and silicon oxide (SiO _x ) may be mentioned, and these may be contained in an arbitrary ratio. Since the negative electrode active material repeats expansion and contraction with charge and discharge, fine cracks occur in the active material. When combined with the electrolytic solution according to the present embodiment, the electrolytic solution evenly permeates deep into the fine cracks, so that the cycle characteristics are improved. In particular, when the silicon material is contained in an amount of 5 parts by mass or more and 40 parts by mass or less, the above-mentioned improvement effect becomes remarkable.

Further, the negative electrode according to the present embodiment may contain silicon or other negative electrode active material other than the silicon compound. The other negative electrode active material is not particularly limited as long as it can reversibly proceed with the occlusion and release of lithium ions and the desorption and insertion (intercalation) of lithium ions, and known electrode active materials can be used. Can be used. Examples thereof include carbon-based materials such as graphite and hard carbon, metal oxides such as lithium titanate (LTO), and metal materials such as lithium, tin and zinc.

(Binder for negative electrode)
The binder for the negative electrode is not particularly limited, and the same binder as the binder for the positive electrode described above can be used.

(Conductive aid for negative electrode)
The conductive auxiliary agent for the negative electrode is not particularly limited, and the same conductive auxiliary agent for the positive electrode described above can be used.

<Electrolytic solution>
The electrolytic solution according to the present embodiment contains a fluorinated carbonic acid ester of 0.1% by volume or more and 5.0% by volume or less, and a carboxylic acid ester. Further, the mass of the electrolytic solution with respect to the total mass of the positive electrode active material layer and the negative electrode active material layer is 30% by mass or more and 45% by mass.

According to this, by using a carboxylic acid ester having a low viscosity and a high wettability, the electrolytic solution can be uniformly permeated into the electrode even after the cycle. Further, the fluorinated carbonic acid ester suppresses the reductive decomposition of the carboxylic acid ester, the consumption of the electrolytic solution can be prevented, and the cycle characteristics are improved.

In the electrolytic solution according to the present embodiment, the carboxylic acid ester is preferably represented by the chemical formula (1), and more preferably a propionic acid ester or an acetic acid ester.

According to this, it is suitable as a carboxylic acid ester, and the cycle characteristics are further improved.

In the electrolytic solution according to the present embodiment, it is preferable that the carboxylic acid ester is further contained in the electrolytic solution in an amount of 50% by volume or more and 90% by volume or less.

According to this, the ratio of the carboxylic acid ester is suitable, and the cycle characteristics are further improved.

(Other solvents)
As the electrolytic solution according to the present embodiment, a solvent generally used for a lithium ion secondary battery can be used in addition to the above carboxylic acid ester. The solvent is not particularly limited, and examples thereof include cyclic carbonate compounds such as ethylene carbonate (EC) and propylene carbonate (PC), and chain carbonate compounds such as diethyl carbonate (DEC) and ethyl methyl carbonate (EMC). Can be mixed and used in the ratio of.

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

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

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

[Example 1]
(Preparation of positive electrode)
LiVOPO ₄ 50 parts by mass, Li (Ni _0.80 Co _0.15 Al _0.05 ) O ₂ 35 parts by mass, carbon black 5 parts by mass, PVDF 10 parts by mass are dispersed in N-methyl-2-pyrrolidone (NMP). , The 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 amount of the positive electrode active material applied was 9.0 mg / cm ² , and dried at 100 ° C. to form a positive electrode active material layer. Then, it was pressure-molded by a roller press to prepare a positive electrode.

(Manufacturing of negative electrode)
As a silicon material, 20 parts by mass of SiO, 70 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, the negative electrode was pressure-molded by a roller press so that the porosity of the negative electrode active material layer was 32%, and a negative electrode was produced.

(Preparation of electrolytic solution)
Ethyl propionate was used as the carboxylic acid ester, and the volume ratio was adjusted to EC: ethyl propionate = 30:70, and LiPF ₆ was dissolved therein so as to have a concentration of 1.0 mol / L. rice field. Fluoroethylene carbonate (FEC) as a fluorocarbonic acid ester was added to the solution prepared as described above so as to be 2.0 wt% to prepare an electrolytic solution.

(Manufacturing of lithium-ion secondary battery for evaluation)
The positive electrode and the negative electrode prepared above and a separator made of a polyethylene microporous film were sandwiched between them and placed in an aluminum laminate pack. The electrolytic solution prepared above is injected into this aluminum laminate pack so as to be 35% by mass with respect to the total mass of the positive electrode active material layer and the negative electrode active material layer, vacuum-sealed, and lithium ion secondary for evaluation. A battery was made. In the second and subsequent examples, this amount of electrolytic solution is referred to as "injection amount".

(Measurement of capacity retention rate after 300 cycles)
For the evaluation lithium ion secondary battery manufactured above, a charging rate of 1.0 C (constant current charging at 25 ° C) was performed in 1 hour using a secondary battery charge / discharge test device (manufactured by Hokuto Denko Co., Ltd.). The battery was charged until the battery voltage reached 4.2 V by constant current charging (current value at which charging ends), and discharged until the battery voltage reached 2.8 V by constant current discharge at a discharge rate of 1.0 C. The above charge / discharge was set as one cycle, and 300 cycles of charge / discharge were continuously performed to obtain the capacity retention rate after 300 cycles (300th cycle discharge capacity / 1st cycle discharge capacity × 100). The results obtained are shown in Table 1.

[Example 2]
In the production of the negative electrode, the lithium ion secondary battery for evaluation of Example 2 was produced in the same manner as in Example 1 except that the porosity of the negative electrode active material layer was changed as shown in Table 1.

[Example 3]
In the production of the negative electrode, the lithium ion secondary battery for evaluation of Example 3 was produced in the same manner as in Example 1 except that the porosity of the negative electrode active material layer was changed as shown in Table 1.

[Example 4]
In the production of the negative electrode, the lithium ion secondary battery for evaluation of Example 4 was produced in the same manner as in Example 1 except that the porosity of the negative electrode active material layer was changed as shown in Table 1.

[Example 5]
In the production of the negative electrode, the lithium ion secondary battery for evaluation of Example 5 was produced in the same manner as in Example 1 except that the porosity of the negative electrode active material layer was changed as shown in Table 1.

[Example 6]
In the production of the negative electrode, the composition of the slurry for forming the negative electrode active material layer was 4 parts by mass of SiO, 86 parts by mass of natural graphite, 5 parts by mass of carbon black, and 5 parts by mass of PVDF as the silicon material, and the negative electrode was produced. A lithium ion secondary battery for evaluation of Example 6 was produced in the same manner as in Example 1 except for the above.

[Example 7]
In the production of the negative electrode, the composition of the slurry for forming the negative electrode active material layer was 5 parts by mass of SiO, 85 parts by mass of natural graphite, 5 parts by mass of carbon black, and 5 parts by mass of PVDF as the silicon material, and the negative electrode was produced. A lithium ion secondary battery for evaluation of Example 7 was produced in the same manner as in Example 1 except for the above.

[Example 8]
In the production of the negative electrode, the composition of the slurry for forming the negative electrode active material layer was 40 parts by mass of SiO, 50 parts by mass of natural graphite, 5 parts by mass of carbon black, and 5 parts by mass of PVDF as the silicon material, and the negative electrode was produced. A lithium ion secondary battery for evaluation of Example 8 was produced in the same manner as in Example 1 except for the above.

[Example 9]
In the production of the negative electrode, the composition of the slurry for forming the negative electrode active material layer was 41 parts by mass of SiO, 49 parts by mass of natural graphite, 5 parts by mass of carbon black, and 5 parts by mass of PVDF as the silicon material, and the negative electrode was produced. A lithium ion secondary battery for evaluation of Example 9 was produced in the same manner as in Example 1 except for the above.

[Example 10]
In the production of the lithium ion secondary battery for evaluation, the lithium ion secondary battery for evaluation of Example 10 was produced in the same manner as in Example 1 except that the injection amount was changed as shown in Table 1.

[Example 11]
In the production of the lithium ion secondary battery for evaluation, the lithium ion secondary battery for evaluation of Example 11 was produced in the same manner as in Example 1 except that the injection amount was changed as shown in Table 1.

[Example 12]
In the production of the lithium ion secondary battery for evaluation, the lithium ion secondary battery for evaluation of Example 12 was produced in the same manner as in Example 1 except that the injection amount was changed as shown in Table 1.

[Example 13]
In the preparation of the electrolytic solution, the lithium ion secondary battery for evaluation of Example 13 was prepared in the same manner as in Example 1 except that the amount of the fluorinated carbonic acid ester added was changed as shown in Table 1.

[Example 14]
In the preparation of the electrolytic solution, the lithium ion secondary battery for evaluation of Example 14 was prepared in the same manner as in Example 1 except that the amount of the fluorinated carbonic acid ester added was changed as shown in Table 1.

[Example 15]
In the preparation of the electrolytic solution, the lithium ion secondary battery for evaluation of Example 15 was prepared in the same manner as in Example 1 except that the amount of the fluorinated carbonic acid ester added was changed as shown in Table 1.

[Example 16]
A lithium ion secondary battery for evaluation of Example 16 was produced in the same manner as in Example 1 except that the amount of fluorinated carbonic acid ester added was changed as shown in Table 1 in the preparation of the electrolytic solution.

[Example 17]
In the preparation of the electrolytic solution, the lithium ion secondary battery for evaluation of Example 17 was prepared in the same manner as in Example 1 except that the carboxylic acid ester was changed as shown in Table 1.

[Example 18]
The evaluation lithium ion secondary battery of Example 18 was prepared in the same manner as in Example 1 except that the carboxylic acid ester was changed as shown in Table 1 in the preparation of the electrolytic solution.

[Example 19]
In the preparation of the electrolytic solution, the lithium ion secondary battery for evaluation of Example 19 was produced in the same manner as in Example 1 except that the composition ratio of the electrolytic solution was changed as shown in Table 1.

[Example 20]
In the preparation of the electrolytic solution, the lithium ion secondary battery for evaluation of Example 20 was produced in the same manner as in Example 1 except that the composition ratio of the electrolytic solution was changed as shown in Table 1.

[Example 21]
In the preparation of the electrolytic solution, the lithium ion secondary battery for evaluation of Example 21 was produced in the same manner as in Example 1 except that the composition ratio of the electrolytic solution was changed as shown in Table 1.

[Example 22]
In the preparation of the electrolytic solution, the lithium ion secondary battery for evaluation of Example 22 was produced in the same manner as in Example 1 except that the composition ratio of the electrolytic solution was changed as shown in Table 1.

[Example 23]
The evaluation lithium ion secondary battery of Example 23 was prepared in the same manner as in Example 1 except that the carboxylic acid ester was changed as shown in Table 1 in the preparation of the electrolytic solution.

[Example 24]
The evaluation lithium ion secondary battery of Example 24 was prepared in the same manner as in Example 1 except that the carboxylic acid ester was changed as shown in Table 1 in the preparation of the electrolytic solution.

[Example 25]
The evaluation lithium ion secondary battery of Example 25 was prepared in the same manner as in Example 1 except that the carboxylic acid ester was changed as shown in Table 1 in the preparation of the electrolytic solution.

[Example 26]
In the preparation of the electrolytic solution, the lithium ion secondary battery for evaluation of Example 26 was produced in the same manner as in Example 23 except that the composition ratio of the electrolytic solution was changed as shown in Table 1.

[Example 27]
In the preparation of the electrolytic solution, the lithium ion secondary battery for evaluation of Example 27 was produced in the same manner as in Example 23 except that the composition ratio of the electrolytic solution was changed as shown in Table 1.

[Example 28]
In the preparation of the electrolytic solution, the lithium ion secondary battery for evaluation of Example 28 was produced in the same manner as in Example 23 except that the composition ratio of the electrolytic solution was changed as shown in Table 1.

[Example 29]
In the preparation of the electrolytic solution, the lithium ion secondary battery for evaluation of Example 29 was produced in the same manner as in Example 23 except that the composition ratio of the electrolytic solution was changed as shown in Table 1.

[Example 30]
The evaluation lithium ion secondary battery of Example 30 was prepared in the same manner as in Example 1 except that the carboxylic acid ester was changed as shown in Table 1 in the preparation of the electrolytic solution.

[Example 31]
The evaluation lithium ion secondary battery of Example 31 was prepared in the same manner as in Example 1 except that the carboxylic acid ester was changed as shown in Table 1 in the preparation of the electrolytic solution.

[Example 32]
The evaluation lithium ion secondary battery of Example 32 was prepared in the same manner as in Example 1 except that the carboxylic acid ester was changed as shown in Table 1 in the preparation of the electrolytic solution.

[Example 33]
In the production of the negative electrode, the lithium ion secondary battery for evaluation of Example 33 was produced in the same manner as in Example 1 except that the silicon material was changed as shown in Table 1.

[Example 34]
In the production of the negative electrode, the lithium ion secondary battery for evaluation of Example 34 was produced in the same manner as in Example 1 except that the silicon material was changed as shown in Table 1.

[Example 35]
The evaluation lithium ion secondary battery of Example 35 was prepared in the same manner as in Example 1 except that difluorocarbonate (DFEC) was used as the fluorocarbonic acid ester in the preparation of the electrolytic solution.

[Example 36]
A lithium ion secondary battery for evaluation of Example 36 was produced in the same manner as in Example 35 except that the amount of fluorinated carbonic acid ester added was changed as shown in Table 1 in the preparation of the electrolytic solution.

[Example 37]
In the preparation of the electrolytic solution, the lithium ion secondary battery for evaluation of Example 37 was prepared in the same manner as in Example 35 except that the amount of fluorinated carbonic acid ester added was changed as shown in Table 1.

[Comparative Example 1]
In the production of the negative electrode, the lithium ion secondary battery for evaluation of Comparative Example 1 was produced in the same manner as in Example 1 except that the porosity of the negative electrode active material layer was changed as shown in Table 1.

[Comparative Example 2]
In the production of the negative electrode, the lithium ion secondary battery for evaluation of Comparative Example 2 was produced in the same manner as in Example 1 except that the porosity of the negative electrode active material layer was changed as shown in Table 1.

[Comparative Example 3]
In the production of the lithium ion secondary battery for evaluation, the lithium ion secondary battery for evaluation of Comparative Example 3 was produced in the same manner as in Example 1 except that the injection amount was changed as shown in Table 1.

[Comparative Example 4]
In the production of the lithium ion secondary battery for evaluation, the lithium ion secondary battery for evaluation of Comparative Example 4 was produced in the same manner as in Example 1 except that the injection amount was changed as shown in Table 1.

[Comparative Example 5]
A lithium ion secondary battery for evaluation of Comparative Example 5 was prepared in the same manner as in Example 1 except that a fluorocarbonic acid ester was not added in the preparation of the electrolytic solution.

[Comparative Example 6]
In the preparation of the electrolytic solution, the lithium ion secondary battery for evaluation of Comparative Example 6 was prepared in the same manner as in Example 1 except that the amount of the fluorinated carbonic acid ester added was changed as shown in Table 1.

[Comparative Example 7]
In the production of the negative electrode, the evaluation lithium ion secondary battery of Comparative Example 7 was produced in the same manner as in Example 1 except that the porosity of the silicon material and the negative electrode active material layer was changed as shown in Table 1.

[Comparative Example 8]
In the preparation of the electrolytic solution, the lithium ion secondary battery for evaluation of Comparative Example 8 was prepared in the same manner as in Example 1 except that the structure and the amount of the fluorinated carbonic acid ester added were changed as shown in Table 1.

For the evaluation lithium ion secondary batteries produced in Examples 2 to 37 and Comparative Examples 1 to 8, the capacity retention rate after 300 cycles was measured in the same manner as in Example 1. The results are shown in Table 1.

In each of Examples 1 to 37, the capacity retention rate after 300 cycles was improved as compared with Comparative Examples 1 to 8.

From Examples 1 to 5 and Comparative Examples 1 to 2, it was confirmed that the porosity of the negative electrode active material layer was optimized to improve the capacity retention rate after 300 cycles.

From Examples 6 to 9, it was confirmed that the capacity retention rate after 300 cycles was further improved by setting the ratio of the silicon compound in the negative electrode to 5 parts by mass or more and 40 parts by mass or less.

From Examples 10 to 12 and Comparative Examples 3 to 4, it was confirmed that the capacity retention rate after 300 cycles was improved by optimizing the injection amount of the electrolytic solution.

From Examples 13 to 16 and Comparative Examples 5 to 6, it was confirmed that the capacity retention rate after 300 cycles was improved by optimizing the addition amount of the fluorocarbonate ester.

From the results of Examples 17 to 18 and Examples 23 to 25, it was confirmed that the capacity retention rate after 300 cycles was improved by setting the total carbon number of the carboxylic acid to 5 or less.

From the results of Examples 19 to 22 and Examples 26 to 29, it was confirmed that the capacity retention rate after 300 cycles was improved by optimizing the composition of the electrolytic solution.

From the results of Examples 30 to 32, it was confirmed that the use of propionic acid or acetic acid ester as the carboxylic acid ester improved the volume retention rate after 300 cycles.

The present invention provides a lithium ion secondary battery capable of improving cycle characteristics.

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

Claims (4)

A lithium ion secondary comprising a positive electrode composed of a positive electrode active material layer and a positive electrode current collector, a negative electrode composed of a negative electrode active material layer and a negative electrode current collector, a separator located between the positive electrode and the negative electrode, and an electrolytic solution. It ’s a battery,
The negative electrode active material layer contains silicon or a compound of silicon, and the porosity of the negative electrode active material layer is 25% or more and 38% or less.
The electrolytic solution contains fluorinated carbonic acid ester in an amount of 0.1% by volume or more and 5.0% by volume or less and a carboxylic acid ester.
The carboxylic acid ester comprises one or more selected from ethyl propionate, propyl propionate, butyl propionate, ethyl acetate, butyl acetate, pentyl acetate, butyl butyrate, ethyl valerate and ethyl pivalate.
A lithium ion secondary battery characterized in that the mass of the electrolytic solution is 30% by mass or more and 45% by mass or less with respect to the total mass of the positive electrode active material layer and the negative electrode active material layer. The lithium ion secondary battery according to claim 1, wherein the negative electrode active material layer has a porosity of 30% or more and 35% or less. The lithium ion secondary battery according to claim 1 or 2 , wherein the carboxylic acid ester is contained in the electrolytic solution in an amount of 50% by volume or more and 90% by volume or less. The lithium ion secondary battery according to any one of claims 1 to 3 , wherein the positive electrode contains LiVOPO ₄ .

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