JP6792798B2 - Manufacturing method of lithium ion secondary battery - Google Patents

Description

The present invention relates to a method for manufacturing a lithium ion secondary battery.

In a lithium ion secondary battery, a fluorinated solvent may be contained in a non-aqueous electrolytic solution for the purpose of improving durability and the like. For example, Patent Document 1 describes that the high temperature storage characteristics of a battery can be enhanced by including a fluorinated carboxylic acid ester, which is one of the fluorinated solvents, in a non-aqueous electrolytic solution.

Japanese Unexamined Patent Publication No. 2016-027548

The fluorinated carboxylic acid ester has high oxidation resistance (high oxidative decomposition potential) and is useful for suppressing a side reaction with the positive electrode (oxidative decomposition of the non-aqueous electrolyte solution). However, the fluorinated carboxylic acid ester has low reduction resistance as a trade-off. Therefore, according to the study by the present inventors, the side reaction between the negative electrode and the non-aqueous electrolyte solution increases during the first charging (first charging) after assembling the battery, and the input / output characteristics of the battery and the like. There was a problem that the cycle characteristics deteriorated.

The present invention has been made in view of the above points, and an object of the present invention is to provide a method for manufacturing a lithium ion secondary battery having excellent input / output characteristics and cycle characteristics.

The present inventors have considered forming a film having low resistance and excellent reduction resistance on the surface of the negative electrode. Then, after repeated diligent studies, the present invention was completed.
According to the present invention, a step of accommodating a positive electrode, a negative electrode, and a non-aqueous electrolytic solution in a battery case to construct an assembly, wherein the non-aqueous electrolytic solution includes a fluorinated carboxylic acid ester and a fluorinated cyclic carbonate. A method for producing a lithium ion secondary battery, which comprises a step of first charging the assembly at a high rate, which contains lithium bis (fluorosulfonyl) imide and a lithium salt having an oxalate complex as an anion. Provided.

By first charging the assembly having the above configuration at a high rate, a high-quality film containing components derived from "lithium bis (fluorosulfonyl) imide" and "lithium salt having an oxalate complex as an anion" is formed on the surface of the negative electrode. Specifically, it is possible to form a film having low resistance and high durability. As a result, the reduction resistance of the negative electrode can be improved and side reactions at the time of initial charging can be suppressed. Therefore, it is possible to realize a lithium ion secondary battery having excellent input / output characteristics and cycle characteristics.

Hereinafter, preferred embodiments of the present invention will be described. Matters other than those specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the prior art in the art. The present invention can be carried out based on the contents disclosed in the present specification and common general technical knowledge in the art.

The manufacturing method of the present embodiment includes (step 1) an assembly construction step and (step 2) an initial charging step. Hereinafter, each step will be described in order.

≪Step 1; Assembly construction process≫
In this step, the positive electrode, the negative electrode, and the non-aqueous electrolytic solution are housed in a battery case to construct an assembly. This step typically includes (step 1-A) a step of preparing the electrode body, (step 1-B) a step of preparing a non-aqueous electrolyte solution, and (step 1-C) an electrode body and a non-aqueous electrolyte solution. Containing process and. The order of steps 1-A and 1-B is not particularly limited.

(Step 1-A) Preparation Step of Electrode Body In this step, an electrode body including a positive electrode and a negative electrode is prepared. The electrode body can be manufactured by laminating the positive electrode and the negative electrode in an insulated state. For the insulation between the positive electrode and the negative electrode, a resin separator such as polyethylene (PE) or polypropylene (PP) can be used.

The positive electrode typically includes a positive electrode current collector and a positive electrode active material layer fixed on the positive electrode current collector. As the positive electrode current collector, a conductive member made of a metal having good conductivity (for example, aluminum) is suitable.

The positive electrode active material layer contains a positive electrode active material. Typical positive electrode active materials include lithium cobalt-based composite oxides (eg, LiCoO ₂ ), lithium manganese-based composite oxides (eg, LiMn ₂ O ₄ ), and lithium nickel-manganese-based composite oxides (eg, LiNi _{0). .5} Mn _1.5 O _4), lithium-nickel-cobalt-manganese-based composite oxide _{(e.g., LiNi x Co y Mn z O} 2 ( however, 0 <x <1,0 <y <1,0 <z <1, Examples thereof include lithium transition metal composite oxides such as x + y + z = 1)).

The positive electrode active material may include a high potential material having an operating upper limit potential (vs. Li / Li ⁺ ) of approximately 4.35 V or higher, for example 4.5 V or higher, within the operating voltage range of the lithium ion secondary battery. preferable. The operating upper limit potential (vs. Li / Li ⁺ ) of the high potential material is generally 4.7 V or more, and typically 5.5 V or less, for example 5.3 V or less. As a result, a battery having a high energy density can be stably realized. A preferred example of such a high-potential material is a lithium nickel-manganese-based composite oxide having a spinel structure.

The positive electrode active material layer may contain components other than the positive electrode active material, such as a conductive material, a positive electrode binder, and an inorganic phosphoric acid compound. Examples of the conductive material include a carbon material such as acetylene black. Examples of the positive electrode binder include vinyl halide resins such as polyvinylidene fluoride (PVdF). Examples of the inorganic phosphoric acid compound include phosphates containing alkali metal elements such as Li ₃ PO ₄ .

The negative electrode typically includes a negative electrode current collector and a negative electrode active material layer fixed on the negative electrode current collector. As the negative electrode current collector, a conductive material made of a metal having good conductivity (for example, copper) is suitable.

The negative electrode active material layer contains a negative electrode active material. Examples of the negative electrode active material include graphite-based carbons such as natural graphite, artificial graphite, and amorphous coated graphite. Here, the “graphite-based carbon” refers to a carbon having a proportion of graphite of about 50% by mass or more, typically 80% by mass or more.
The negative electrode active material layer may contain components other than the negative electrode active material, such as a thickener and a negative electrode binder. Examples of the thickener include celluloses such as carboxymethyl cellulose (CMC). Examples of the negative electrode binder include rubbers such as styrene-butadiene rubber (SBR) and vinyl halide resins such as polyvinylidene fluoride (PVdF).

(Step 1-B) Preparation step of non-aqueous electrolytic solution In this step, a non-aqueous electrolytic solution is prepared (typically prepared). In the techniques disclosed herein, the non-aqueous electrolyte solution is (a) a fluorinated carboxylic acid ester, (b) a fluorinated cyclic carbonate, (c) a lithium bis (fluorosulfonyl) imide, and (d) an oxalate complex. (Hereinafter, it may be referred to as “oxalate complex lithium salt”) and a lithium salt having an anion. The non-aqueous electrolyte solution typically exhibits a liquid state in a battery operating environment (typically in a temperature environment of -20 to + 60 ° C., for example, -10 to + 50 ° C.).

(A) The fluorinated carboxylic acid ester is a carboxylic acid ester substituted with fluorine, that is, a fluoride of the carboxylic acid ester. In this embodiment, the fluorinated carboxylic acid ester is the first fluorinated solvent. The fluorinated carboxylic acid ester is excellent in oxidation resistance because it contains a fluorine atom, and is useful for suppressing the oxidative decomposition of the non-aqueous electrolytic solution at the positive electrode. In addition, it has a higher dielectric constant than other non-aqueous solvents, which is useful for improving electron conductivity.

The fluorinated carboxylic acid ester is not particularly limited, and for example, methyl fluorinated acetate, ethyl fluorinated acetate, methyl fluorinated propionate, ethyl fluorinated propionate, methyl butyrate, methyl isobutyrate butyrate, methyl butyrate trimethylacetate and the like. The fluorinated chain carboxylic acid ester of is exemplified. A preferred example of the fluorinated chain carboxylic acid ester is one in which the carbon at the α-position is fluorinated, which is represented by the following formula (I).

式（Ｉ）において、Ｒ_１は、水素、フッ素、炭素数が１〜３の非フッ素アルキル基、または炭素数が１〜３のフッ素含有アルキル基を表す。Ｘは、水素またはフッ素を表す。Ｒ_２は、炭素数が１〜３の非フッ素アルキル基、または炭素数が１〜３のフッ素含有アルキル基である。

In the formula (I), R ₁ represents hydrogen, fluorine, a non-fluorine alkyl group having 1 to 3 carbon atoms, or a fluorine-containing alkyl group having 1 to 3 carbon atoms. X represents hydrogen or fluorine. R ₂ is a non-fluorine alkyl group having 1 to 3 carbon atoms or a fluorine-containing alkyl group having 1 to 3 carbon atoms.

As an example of the compound represented by the formula (I), methyl difluoroacetate (MDFA; R ₁ = H, X = F, R ₂ = CH ₃ ), methyl 2,3,3,3-tetrafluoropropionate (M2333TFP; R ₁ = CF ₃ , X = H, R ₂ = CH ₃ ), methyl 2,2,3,3-tetrafluoropropionate (M2233TFP; R ₁ = CHF ₂ , X = F, R ₂ = CH ₃ ), etc. Can be mentioned.

The content ratio of the fluorinated carboxylic acid ester in the non-aqueous electrolytic solution is approximately 50% by volume or more, for example 70% by volume or more, and approximately 95% by volume or less, for example 80% by volume or less, on a volume basis. preferable.

(B) The fluorinated cyclic carbonate is a fluoride of the cyclic carbonate. In this embodiment, the fluorinated cyclic carbonate is the second fluorinated solvent. The fluorinated cyclic carbonate is excellent in oxidation resistance because it contains a fluorine atom, and is useful for suppressing the oxidative decomposition of the non-aqueous electrolytic solution at the positive electrode. In addition, it has a lower viscosity than the fluorinated carboxylic acid ester, which is useful for reducing charge transfer resistance. A preferred example of the fluorinated cyclic carbonate is a 5-membered cyclic fluorinated cyclic carbonate represented by the following formula (II).

式（ＩＩ）において、Ｒ_３，Ｒ_４，Ｒ_５，Ｒ_６は、それぞれ独立して、水素、フッ素、またはフッ素含有アルキル基（例えば、炭素数が１〜５のフッ素含有アルキル基）である。Ｒ_３，Ｒ_４，Ｒ_５，Ｒ_６は、全てが異なっていてもよいし、全てあるいは一部が同一であってもよい（ただし、Ｒ_３，Ｒ_４，Ｒ_５，Ｒ_６の全てが水素である場合を除く）。

In formula (II), R ₃ , R ₄ , R ₅ , and R ₆ are independently hydrogen, fluorine, or fluorine-containing alkyl groups (for example, fluorine-containing alkyl groups having 1 to 5 carbon atoms). .. _{R 3, R 4, R 5} , R 6 may be have all different, all or part may be the same _{(however, R 3, R 4, R} 5, all _{R 6} is Except when it is hydrogen).

As an example of the compound represented by the formula (II), 4-fluoro-1,3-dioxolan-2-one (MFEC; R ₃ = F, R ₄ = R ₅ = R ₆ = H), 4,5-difluoro. -1,3-Dioxolane-2-one (DFEC; R ₃ = R ₅ = F, R ₄ = R ₆ = H), 4-trifluoromethyl-1,3-dioxolan-2-one (TFPC; R ₃₎ = CF ₃ , R ₄ = R ₅ = R ₆ = H).

The content ratio of the fluorinated cyclic carbonate in the non-aqueous electrolytic solution is preferably about 5% by volume or more, for example, 20% by volume or more, and about 50% by volume or less, for example, 30% by volume or less on a volume basis. ..

(C) Lithium bis (fluorosulfonyl) imide (LiFSI; LiN (SO ₂ F) ₂ ) functions as a so-called film-forming agent that forms a film on the surface of the negative electrode.
The molar concentration of LiFSI in the non-aqueous electrolyte solution is approximately 0.01 mol / L or more, for example 0.05 mol / L or more, which is typically lower than the solubility in a fluorinated solvent, and is approximately 1 mol / L or less. For example, it is preferably 0.5 mol / L or less. Thereby, a good quality film can be better formed on the surface of the negative electrode.

(D) The oxalate complex lithium salt functions as a so-called film-forming agent that forms a film on the surface of the negative electrode. No particular limitation is imposed on the oxalate complex lithium salts such as lithium bis (oxalato) borate, lithium difluoro Oki such Sarah oxalatoborate, at least one of oxalate ions to boron (B) atom as the central atom (C ₂ O ₄ ² Phosphorus as a central atom of B atom-containing oxalat complex lithium salt having a 4-coordinated structure coordinated by ⁻ ), lithium tetrafluorooxalat phosphate, lithium difluorobis (oxalate) oxalate, and lithium tris (oxalate) oxalate. P atom-containing oxalate complex lithium salt having a structure of at least one oxalate (C _{2 O} 4 ^_2-) 6 coordination which is coordinated is mentioned (P) atoms. Of these, an oxalate complex lithium salt containing a fluorine atom is preferable because of its high solubility in a fluorinated solvent.

The molar concentration of the oxalate complex lithium salt in the non-aqueous electrolytic solution is approximately 0.01 mol / L or more, for example 0.05 mol / L or more, which is typically lower than the solubility in a fluorinated solvent, and is approximately 1 mol / L. It is preferably L or less, for example, 0.5 mol / L or less. Thereby, a good quality film can be better formed on the surface of the negative electrode.
The molar concentration of the oxalate complex lithium salt is preferably about the same as the molar concentration of LiFSI (for example, the molar concentration of LiFSI ± 0.1 mol / L, preferably the molar concentration of LiFSI ± 0.05 mol / L).

In addition to the above four components, the non-aqueous electrolyte solution may optionally contain, for example, a supporting salt and various additives.
The supporting salt typically includes a lithium salt, for example, a fluorine-containing lithium salt such as LiPF ₆ or LiBF ₄ . The supporting salt dissociates in a non-aqueous solvent to produce a charge carrier. The molar concentration of the supporting salt is typically higher than the concentration of LiFSI or oxalate complex lithium salt, specifically approximately 0.7 to 2.0 mol / L, for example 0.9 to 1.5 mol / L. It would be nice to have it. The concentration of the supporting salt is preferably about 2 times or more, for example, 5 times or more, and about 20 times or less the concentration of the LiFSI or the oxalate complex lithium salt.

(Step 1-C) Storage Step of Electrode Body and Non-Aqueous Electrolyte In this step, the electrode body and the non-aqueous electrolytic solution are housed inside the battery case. As the material of the battery case, a relatively lightweight metal (for example, aluminum) is suitable. In this step, the assembly may or may not be hermetically sealed.
As described above, the assembly of the lithium ion secondary battery can be constructed.

≪Step 2 ； Initial charging process≫
In this step, the assembled assembly is charged for the first time at a predetermined charging rate. As a result, the non-aqueous electrolytic solution is electrically decomposed. Mainly, the components of the film-forming agent, that is, lithium bis (fluorosulfonyl) imide and / or the oxalate complex lithium salt are reduced and decomposed at the negative electrode. Then, a film containing components derived from these film forming agents, for example, these decomposition products, is formed on the surface of the negative electrode. As a result, even in the embodiment in which the fluorinated solvent, that is, the fluorinated carboxylic acid ester and the fluorinated cyclic carbonate are contained in the non-aqueous electrolytic solution, the reductive decomposition of the non-aqueous electrolytic solution at the negative electrode is suitably suppressed at the time of initial charging. can do.

In this embodiment, the initial charge is performed at a high rate. As a result, it is possible to form a high-quality film (for example, a film having low resistance and excellent reduction resistance) as compared with the case where the initial charge is performed at a low rate of about 0.1 to 1 C, for example. As a result, it is possible to realize a lithium ion secondary battery having excellent input / output characteristics and cycle characteristics. The upper limit of the charging rate is not particularly limited, but is typically 10 C or less, for example 5 C or less, from the viewpoint of forming a homogeneous film on the surface of the negative electrode.

The term "high rate" as used herein refers to a charging rate of approximately 1C or higher, typically 2C or higher, preferably 3C or higher. Further, 1C means a current value capable of fully charging the theoretical capacity (Ah) of the battery in one hour. For example, when the theoretical capacity is 24Ah, 1C = 24A.

The initial charge is until the negative electrode potential (vs. Li / Li ⁺ ) is below the reduction potential of the film-forming agent, that is, below the reduction potential of lithium bis (fluorosulfonyl) imide and / or the oxalat complex lithium salt. It is preferable to do so. In one preferred example, the assembly is charged until the potential of the negative electrode is 0.1 V (vs. Li / Li ⁺ ) or less. In another preferred example, the assembly is charged until the voltage between the positive and negative electrodes is 4.5 V or more and 5.0 V or less. In the first charge, it can be held (aged) for a predetermined period while maintaining the charged state. Further, charging may be performed once, and for example, charging may be repeated twice or more with a discharge in between.

As described above, the lithium ion secondary battery can be manufactured.
Such a battery contains at least two kinds of fluorinated solvents in a non-aqueous electrolytic solution. As a result, the oxidation resistance is excellent, and for example, the oxidative decomposition of the non-aqueous electrolytic solution at the positive electrode is better suppressed at the time of initial charging. As a result, the oxidative decomposition of the non-aqueous electrolytic solution is suitably suppressed.
Further, such a battery has a high-quality film containing a component derived from lithium bis (fluorosulfonyl) imide and a component derived from an oxalate complex lithium salt on the surface of the negative electrode. As a result, the reduction resistance is excellent, and for example, the reduction decomposition of the non-aqueous electrolytic solution at the negative electrode is better suppressed at the time of initial charging. As a result, the reductive decomposition of the non-aqueous electrolytic solution is suitably suppressed.
Due to these synergistic effects, the lithium ion secondary battery obtained by the manufacturing method disclosed herein is superior in input / output characteristics and cycle characteristics as compared with the conventional product. In a preferred embodiment, the energy density is further increased by raising the working upper limit potential of the positive electrode active material. Therefore, by taking advantage of such characteristics, it can be suitably used as a power source (driving power source) for a moving body such as a hybrid vehicle or an electric vehicle.

Hereinafter, examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in such examples.

<Construction of assembly>
First, a positive electrode was prepared. Specifically, first, NiMn spinel (LiNi _0.5 Mn _1.5 O ₄ ) as a positive electrode active material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are used. , LiNi _0.5 Mn _1.5 O ₄ : AB: PVdF = 87: 10: 3, weighed and mixed with N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry. .. This positive electrode slurry was applied to the surface of an aluminum foil (positive electrode current collector) and dried to prepare a positive electrode sheet having a positive electrode active material layer on the positive electrode current collector.

Next, a negative electrode was produced. Specifically, first, natural graphite-based carbon (C, average particle size: 20 μm) as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener are used. , C: SBR: CMC = 98: 1: 1 was weighed and mixed with water to prepare a negative electrode slurry. This negative electrode slurry was applied to the surface of a copper foil (negative electrode current collector) and dried to prepare a negative electrode sheet having a negative electrode active material layer on the negative electrode current collector.

Next, the positive electrode sheet and the negative electrode sheet produced above were used as a separator sheet (here, a PP / PE / PP three-layer structure in which polypropylene (PP) was laminated on both sides of polyethylene (PE). ) Was interposed, and the electrodes were laminated to prepare an electrode body.

Next, a non-aqueous electrolyte solution was prepared. Specifically, for each example, LiPF ₆ as a supporting salt was dissolved in a mixed solvent containing the non-aqueous solvent shown in Table 1 so as to have a concentration of 1.0 mol / L to prepare a base electrolytic solution. .. Then, the film-forming agent shown in Table 1 was added to this base electrolytic solution to prepare the non-aqueous electrolytic solution of each example. In the column of film forming agent in Table 1, "LiFSI" represents lithium bis (fluorosulfonyl) imide. Further, "LiDFOB" represents lithium difluorooxalate borate, "LiBOB" represents lithium bis (oxalate) borate, and "LiPFO" represents lithium difluorobis (oxalate) phosphate.

Then, the prepared electrode body and the non-aqueous electrolytic solution prepared above were housed in a battery case, and the battery case was sealed. As a result, a plurality of assemblies of each example were constructed. As shown in Table 1, the assemblies according to Test Examples 1 to 8 and Comparative Examples 1 to 5 differ only in the non-aqueous electrolytic solution (specifically, the non-aqueous solvent and the film forming agent).

<First charge / discharge>
The assembled assembly constructed above was first charged and discharged in a temperature environment of 25 ° C. Specifically, after constant current charging at a low rate (0.3C) or high rate (3.0C) charging rate until the voltage between the positive and negative electrodes becomes 4.9V, the voltage between the positive and negative electrodes becomes 3.5V. A constant current was discharged at a discharge rate of 0.3 C until it became. As a result, the batteries of each example were manufactured.

<Confirmation of initial capacity>
The manufactured battery is charged with a constant current at a charging rate of 0.2C until the voltage between the positive and negative electrodes reaches 4.9V in a temperature environment of 25 ° C., and then the constant voltage until the current value becomes 1 / 50C. It was charged and made fully charged. After that, constant current discharge was performed at a discharge rate of 0.2 C until the voltage between the positive and negative electrodes became 3.5 V, and the constant current discharge capacity at this time was used as the initial capacity.

<Evaluation of output characteristics>
The above battery was placed in a constant temperature bath at 25 ° C., and the IV characteristics at the time of discharge were evaluated. Specifically, after constant current charging at a charging rate of 0.3C until the charging depth (SOC) reaches 30%, the battery is moved to a constant temperature bath at −30 ° C. to 3C, 5C, 10C, 15C. Discharge was performed for 2 seconds at each discharge rate, and the battery voltage at this time was measured. Then, the IV resistance (Ω) at the time of discharge was calculated from the slope of the approximate straight line obtained by plotting the discharge current and the battery voltage. The results are shown in Table 1.

<Evaluation of input characteristics>
The above battery was placed in a constant temperature bath at 25 ° C., and the IV characteristics during charging were evaluated. Specifically, after constant current charging at a charging rate of 0.3C until the charging depth (SOC) reaches 60%, the battery is moved to a constant temperature bath at −10 ° C. to 3C, 5C, 10C, 15C. The batteries were charged at the charging rate for 10 seconds each, and the battery voltage at this time was measured. Then, the IV resistance (Ω) at the time of charging was calculated from the slope of the approximate straight line obtained by plotting the charging current and the battery voltage. The results are shown in Table 1.

<Evaluation of high temperature cycle characteristics (60 ° C)>
The above battery was installed in a constant temperature bath at 60 ° C., and the high temperature cycle characteristics were evaluated. Specifically, after constant current charging at a charging rate of 2C until the voltage between the positive and negative electrodes reaches 4.9V, constant current discharge is performed at a discharging rate of 2C until the voltage between the positive and negative electrodes reaches 3.5V. The discharge operation was set as one cycle, and this was repeated for 200 cycles. Then, the battery capacity (constant current discharge capacity) after the high temperature cycle test was measured in the same manner as the initial capacity, and the capacity retention rate (%) was calculated from the battery capacity before and after the high temperature cycle test. The results are shown in Table 1.

The evaluation results will be compared and examined based on Table 1.
In Comparative Examples 1 to 3 in which the fluorinated carboxylic acid ester and / or the fluorinated cyclic carbonate is not contained in the non-aqueous electrolytic solution, the initial charge is performed at a high rate (3C) as compared with a case where the initial charge is performed at a low rate (0.3C). The resistance increased and the input / output characteristics deteriorated. In addition, no difference in cycle characteristics was observed depending on the charge rate of the initial charge.
On the other hand, in Examples 1 to 8 in which both the fluorinated carboxylic acid ester and the fluorinated cyclic carbonate are contained in the non-aqueous electrolytic solution, the input / output characteristics and the cycle durability are obtained by performing the initial charge at a high rate. Significant improvement was observed.

Further, from the comparison of Test Examples 3, 6 to 8, in Test Examples 3, 7 and 8 using the fluorinated carboxylic acid ester in which the carbon at the α-position is fluorinated, the carbon at the α-position is not fluorinated. Compared with Test Example 6 using the fluorinated carboxylic acid ester (M333TFP), the improvement range of the input / output characteristics and the cycle characteristics was relatively large. Among them, in Test Example 3 using MDFA, the improvement range of the input / output characteristics and the cycle characteristics was the largest. From the above, it can be said that it is more preferable to use a fluorinated carboxylic acid ester in which the carbon at the α-position is fluorinated, particularly MDFA, in order to better improve the input / output characteristics and the cycle characteristics.

Further, from the comparison of Test Examples 3 to 5, Test Examples 3 and 5 using the fluorine-containing oxalate complex lithium salt were relatively contained as compared with Test Example 4 using the non-fluorine oxalate complex lithium salt (LiBOB). The improvement range of output characteristics and cycle characteristics was large. From the above, it can be said that it is more preferable to use a fluorine-containing oxalate complex lithium salt in order to better improve the input / output characteristics and the cycle characteristics.

Further, from the comparison between Test Example 3 and Comparative Examples 4 and 5, in Test Example 3 containing both LiFSI and oxalate complex lithium salt as a film-forming agent, Comparative Example 4 containing only LiFSI and oxalate complex lithium salt Compared with Comparative Example 5 containing only, the improvement range of the input / output characteristics and the cycle characteristics was relatively large.
The reason for this is not clear, but by containing both LiFSI and the oxalate complex lithium salt in the non-aqueous electrolyte solution, the LiFSI-derived components are mixed in the film formed by the reduction decomposition of the oxalate complex, resulting in good quality. It is considered that a good film was formed.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples illustrated above.

Claims (1)

A step of accommodating a positive electrode, a negative electrode, and a non-aqueous electrolytic solution in a battery case to construct an assembly, wherein the non-aqueous electrolytic solution is a fluorinated carboxylic acid ester, a fluorinated cyclic carbonate, and lithium bis (. Fluorosulfonyl) imide and a lithium salt anionized by an oxalate complex, and
The process of first charging the assembly at a charging rate of 3C or higher ,
A method for manufacturing a lithium ion secondary battery, including the above.