JP2016091724A - Lithium secondary battery and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery reduced in internal resistance, which can exhibit high battery characteristics.SOLUTION: A lithium secondary battery comprises a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a nonaqueous electrolyte, which are enclosed in a battery case. The nonaqueous electrolyte contains, at least, a lithium salt having a sulfonic acid skeleton expressed by the formula (I), and a vinylene carbonate compound. (Ris a straight or branched chain alkyl group with C1-12.)SELECTED DRAWING: None

Description

  The present invention relates to a lithium secondary battery and a method for manufacturing the same.

  In recent years, lithium secondary batteries (lithium ion secondary batteries) have been used as so-called portable power sources such as personal computers and portable terminals and power sources for driving vehicles. In particular, a lithium ion secondary battery that is lightweight and obtains a high energy density is preferably used as a high-output power source for driving vehicles such as electric vehicles and hybrid vehicles.

  In such a lithium secondary battery, a part of the non-aqueous electrolyte is decomposed during initial charging, and a coating (SEI coating) made of the decomposition product is formed on the surface of the negative electrode active material. Such a coating suppresses the decomposition of the non-aqueous electrolyte accompanying subsequent charging / discharging, so that the durability (cycle characteristics) of the battery can be improved. As a technology related to this, for example, Patent Document 1 discloses a lithium secondary battery including a vinylene carbonate compound and an alkyne compound in a nonaqueous electrolytic solution.

International Publication No. WO2005 / 008829

In Patent Document 1, by using a vinylene carbonate compound and an alkyne compound in combination, a strong SEI film can be formed on the negative electrode during initial charging, thereby improving battery durability (for example, cycle characteristics). (Patent Document 1, paragraphs 0027, 0028, etc.).
However, according to investigations by the inventors, the battery described in Patent Document 1 may not be sufficiently effective in reducing the internal resistance itself (internal resistance value). Since batteries with high internal resistance tend to have low input / output characteristics, reducing internal resistance is an important issue from the viewpoint of providing high-performance batteries. In particular, in a lithium secondary battery that is repeatedly used for charging and discharging at a high input / output density (for example, a lithium secondary battery that is repeatedly used for high-rate charging and discharging, such as a battery for vehicle use), high input / output characteristics, Reduction of internal resistance is strongly desired.
Further, according to the study by the present inventors, in the battery described in Patent Document 1, the durability of the battery may be reduced (for example, the cycle characteristics may be deteriorated) depending on the type and amount of the compound to be added. . For example, when the battery is used under severe conditions such as an in-vehicle battery (specifically, when it is stored for a long time in a high temperature environment or when charging and discharging are repeated at a high input / output density). In particular, it cannot be ignored.
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a lithium secondary battery capable of achieving both durability and input / output characteristics at a high level. In other words, it is to provide a lithium secondary battery that has reduced internal resistance and can exhibit higher cycle characteristics (for example, a high capacity retention ratio and a reduction in resistance increase).

The present inventors have, as one of the factors that the durability of the battery is lowered, the supporting salt in the nonaqueous electrolytic solution (e.g., LiPF ₆₎ fluorine anion can occur is hydrolyzed in the course of charging and discharging (F ^- ) And hydrogen fluoride (HF) have been found to be affected.
The supporting salt (for example, LiPF ₆ ) in the nonaqueous electrolytic solution can react (hydrolysis reaction) with a trace amount of water contained in the battery as follows.
LiPF ₆ + H ₂ O → POF ₃ + LiF + 2HF (S1)
POF ₃ + H ₂ O → PO ₂ F ₂ ⁻ + HF + H ⁺ (S2)
PO ₂ F ₂ ⁻ + H ₂ O → PO ₃ F ² + + HF + H ⁺ (S3)
^{_{PO 3 F 2- + H 2 O}} → PO 4 3- + HF + H + (S4)
Since the fluorine anion (F ⁻ ) generated by the hydrolysis reaction of LiPF ₆ is negatively charged, it is usually attracted to the positive electrode side when a voltage is applied. Then, it is oxidatively decomposed on the surface of the positive electrode (for example, the surface of the positive electrode active material) and becomes lithium fluoride (LiF) and is deposited on the positive electrode active material. Since such a film becomes a resistance component, an increase in internal resistance and a decrease in battery durability (for example, cycle characteristics) can be caused. In addition, the generated hydrogen fluoride (HF) accelerates the elution of constituent elements (typically transition metal elements such as manganese elements) from the positive electrode active material, thereby increasing the internal resistance and the crystal structure of the positive electrode active material. Can collapse.

  In addition, as one of the factors that the effect of reducing the internal resistance is insufficient, the inventors of the present invention have charge carriers (that is, lithium ions) on the negative electrode active material surface during charging (particularly during charging at a high input density). ) Was found to be affected. In other words, it has been found that the internal resistance can be reduced by increasing the charge carrier concentration (lithium ion concentration) on the surface of the negative electrode active material.

Therefore, the present inventors have conducted intensive studies and suppressed the influence of the fluorine anion (F ⁻ ) and hydrogen fluoride (HF) to improve the durability and increase the charge carrier concentration on the surface of the negative electrode active material. Thus, a means capable of reducing the internal resistance has been found, and the present invention has been completed.

  The present invention provides a lithium secondary battery in which a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte are accommodated in a battery case. Here, the non-aqueous electrolyte contains a lithium salt having a sulfonic acid skeleton represented by the following formula (I) and a vinylene carbonate compound.

（ここで、Ｒ^１は、炭素原子数１〜１２の直鎖状または分岐状のアルキル基である。）

(Here, R ¹ is a linear or branched alkyl group having 1 to 12 carbon atoms.)

  By including the vinylene carbonate compound in the non-aqueous electrolyte, an SEI film derived from the vinylene carbonate compound can be formed on the surface of the negative electrode active material. The SEI coating derived from the vinylene carbonate compound is a stable coating that is unlikely to be decomposed or deteriorated, and can favorably suppress reductive decomposition of the non-aqueous electrolyte during charge and discharge over a long period of time. That is, high durability (for example, cycle characteristics) can be realized by including a vinylene carbonate compound in the nonaqueous electrolytic solution.

In addition to the vinylene carbonate compound, the non-aqueous electrolyte contains a lithium salt having a sulfonic acid skeleton represented by the above formula (I) (hereinafter sometimes simply referred to as “lithium sulfonate”). Thus, after the initial charge, components derived from the lithium sulfonate (including decomposition products and modified products derived from the lithium sulfonate, the same shall apply hereinafter) are incorporated into the SEI coating derived from the vinylene carbonate compound. it can. Since the lithium sulfonate salt contains lithium element in the molecule, the amount of lithium element present on the surface of the negative electrode active material (charge carrier concentration on the surface of the negative electrode active material), that is, increase the charge carrier concentration in the lithium secondary battery. Can do. In addition, such lithium sulfonate has a molecular structure (molecular structure having many unshared electron pairs (law pairs)) with a large charge bias (polarization), and a cation (+ ion) approaches the molecule. Can be assisted (promoted). That is, lithium ions (Li ⁺ ) in the nonaqueous electrolytic solution can be attracted to the vinylene carbonate compound-derived film (that is, the negative electrode active material surface). This can also increase the charge carrier concentration on the negative electrode active material surface. With the above effects, it is possible to suppress the shortage of charge carriers (that is, lithium ions) on the surface of the negative electrode active material. That is, by including the vinylene carbonate compound and the sulfonic acid lithium salt in the nonaqueous electrolytic solution, it is possible to reduce the internal resistance of the battery.

Further, the lithium sulfonate in the non-aqueous electrolyte is typically reductively decomposed during charging (typically during initial charging), and the positive electrode active material surface and the negative electrode active material surface (typically vinylene carbonate). A part of the SEI film can be formed by binding (attaching) to the surface of the compound-derived SEI film. Such a film derived from lithium sulfonate has a molecular structure with many unshared electron pairs (lone pairs) and a large charge bias (polarization), so that lithium ions are positive and negative by electrostatic interaction. Can be approached. That is, by providing a coating derived from lithium sulfonate on the surfaces of the positive electrode active material and the negative electrode active material, it is possible to promote the approach of lithium ions (that is, charge carriers) in the nonaqueous electrolytic solution to the positive electrode and the negative electrode. it can. Thereby, the delivery of charge carriers between the positive and negative electrodes at the time of charging / discharging is performed smoothly, and the battery resistance can be reduced.
On the other hand, the coating derived from the lithium sulfonate salt represented by the formula (I) has many unshared electron pairs (lone pairs), and the fluorine anion approaches the positive electrode and the negative electrode due to electrostatic interaction and / or steric hindrance. This can be prevented. Thereby, the influence of the fluorine anion and hydrogen fluoride which can arise by hydrolysis of the support salt mentioned above can be suppressed. That is, by providing the positive electrode with a coating derived from a lithium sulfonate salt, it is possible to achieve a special effect that it is difficult to coat the positive electrode active material with lithium fluoride having high resistance. Further, by providing a coating derived from lithium sulfonate on the surface of the positive electrode active material, the oxidative decomposition of the non-aqueous electrolyte can be suppressed, and further the crystal structure of the positive electrode active material is maintained in a more stable state. be able to. In particular, since a film containing sulfur atoms is excellent in thermal stability, it does not easily decompose or deteriorate even in a high temperature environment, and can achieve high durability (for example, high temperature storage characteristics and high temperature charge / discharge cycle characteristics). For this reason, for example, even when a transition metal composite oxide containing a large amount of manganese that is easily eluted in a high-temperature environment (typically about 30 mol% to 40 mol%) is used as the positive electrode active material, it is stable for a long period of time. Performance can be demonstrated.

  As described above, the lithium secondary battery having the above-described configuration is a lithium secondary battery that has reduced internal resistance and can exhibit higher cycle characteristics (for example, high capacity retention rate and reduced resistance increase). That is, the lithium battery having the above configuration can achieve both durability and input / output characteristics at a high level.

In a preferred embodiment, R ¹ in the above formula (I) is an ethyl group. That is, in a lithium secondary battery according to a preferred embodiment disclosed herein, lithium ethoxysulfonate is included as the lithium salt having the sulfonic acid skeleton.
Lithium ethoxysulfonate is easy to be incorporated into the coating derived from the vinylene carbonate compound on the surface of the negative electrode active material, and can achieve the effect of increasing the charge carrier concentration on the surface of the negative electrode active material at a high level. Further, since lithium ethoxysulfonate is excellent in solubility in the non-aqueous electrolyte, a required amount of lithium ethoxysulfonate can be stably dissolved in the non-aqueous electrolyte.

In a lithium secondary battery according to a preferred embodiment disclosed herein, vinylene carbonate (C ₃ H ₂ O ₃ ) is included as the vinylene carbonate compound.
Vinylene carbonate can form a stable and strong SEI film on the negative electrode active material. For this reason, high durability is realizable. In addition, vinylene carbonate (C ₃ H ₂ O ₃ ) can easily incorporate the lithium sulfonate into the coating when the SEI coating is formed, and thus can achieve a high level of effect of increasing the charge carrier concentration on the surface of the negative electrode active material. .

In the lithium secondary battery according to a preferred aspect disclosed herein, a coating derived from the vinylene carbonate compound is formed on the surface of the negative electrode active material in terms of the vinylene carbonate compound consumed in the configuration of the coating. It is formed at a rate of 27 μmol or more and 64 μmol or less per unit surface area (1 m ² ) of the active material. And the component derived from the lithium salt which has the said sulfonic acid skeleton is contained in the film derived from the said vinylene carbonate compound. Furthermore, content of the component derived from lithium sulfonate contained in the coating is 0.04 mol or more and 0.15 mol or less in terms of sulfonic acid group per 1 mol of vinylene carbonate compound consumed in the configuration of the coating.
By setting the composition and the amount of the SEI coating derived from the vinylene carbonate compound on the surface of the negative electrode active material within the above range, a strong and stable SEI coating can be formed. In addition, by setting the amount of the coating within the above range, it is possible to suitably secure a field for the charge carrier reaction.
Moreover, the negative electrode active material by this sulfonic-acid lithium salt by making content (molar ratio in conversion of a sulfonic acid group) of the component derived from the sulfonic-acid lithium salt contained in the SEI film derived from a vinylene carbonate compound into the said range. The effect of increasing the charge carrier concentration on the surface can be suitably exhibited. Here, since the lithium sulfonic acid salt does not directly participate in the polymerization reaction in which the vinylene carbonate compound forms a film, if the content of the component derived from the lithium sulfonic acid salt in the film derived from the vinylene carbonate compound is too large, There exists a possibility that the intensity | strength of a film may fall. By setting the content of the component derived from lithium sulfonate in the SEI coating derived from the vinylene carbonate compound within the above range, the effect of increasing the charge carrier concentration on the negative electrode active material surface is preferable while ensuring the strength of the coating. Can be demonstrated.

The “amount of coating derived from the vinylene carbonate compound per unit surface area of the negative electrode active material (μmol / m ² )” is, for example, the consumption amount of the vinylene carbonate compound in the used non-aqueous electrolyte, that is, the decomposition amount (μmol). It is obtained by dividing by the total surface area (m ² ) of the negative electrode active material. The amount of vinylene carbonate compound consumed = decomposition amount (μmol) is the amount of vinylene carbonate compound remaining in the battery case (μmol) from the amount of vinylene carbonate compound supplied in the battery case (μmol) during battery construction. Can be calculated by subtracting. The residual amount (μmol) of the vinylene carbonate compound remaining in the battery case can be measured by, for example, a gas chromatography (GC) method. In addition, the measuring method of the vinylene carbonate compound by this GC is mentioned later. The “total surface area (m ² ) of the negative electrode active material” is, for example, the total mass (g) of the negative electrode active material used for forming the negative electrode active material layer and the BET specific surface area (m ² / g) of the active material. It can be obtained by the product of “BET specific surface area (m ² / g)” is, for example, a gas adsorption amount measured by a gas adsorption method (fixed capacity adsorption method) using nitrogen (N ₂ ) gas as an adsorbate, and a BET method (for example, It can be obtained by analyzing by the BET 1-point method.

The above “content (molar ratio) of components derived from a lithium salt having a sulfonic acid skeleton contained in a coating derived from a vinylene carbonate compound” is, for example, all lithium sulfonate present per unit area of the negative electrode active material layer Of the component derived from lithium sulfonate obtained by subtracting the amount of coating derived from lithium sulfonate (μmol / m ² ) per unit area of the negative electrode active material layer from the amount of component derived from salt (μmol / m ² ) the amount (μmol / ^{m 2),} Binirenkabone per unit area of the negative electrode active material layer - can be determined by dividing the coating weight of from bets compound (μmol / ^{m 2).}
The “amount of the component derived from the total sulfonic acid lithium salt present per unit area of the negative electrode active material layer (μmol / m ² )” is, for example, inductively coupled plasma emission spectroscopy (ICP-AES: Inductively Coupled Plasma-Atomic Emission). Spectrometry can be used for measurement. A method for measuring the amount of lithium salt in the vinylene carbonate compound using ICP-AES will be described later.
The “amount of coating derived from the vinylene carbonate compound per unit area of the negative electrode active material layer (μmol / m ² )” is the amount of vinylene carbonate compound consumed for forming the coating (decomposition amount) (μmol). Is divided by the formation area (m ² ) of the negative electrode active material layer. The “decomposition amount (μmol) of the vinylene carbonate compound” can be obtained by the above-described method.
The “amount of coating derived from lithium sulfonate per unit area of negative electrode active material layer (μmol / m ² )” can be measured by, for example, an ion chromatography (IC) method. . A method for measuring a film using the IC will be described later.

Moreover, in the lithium secondary battery according to a preferred embodiment disclosed herein, a coating derived from the lithium sulfonate salt has a unit of the positive electrode active material in terms of a sulfonic acid group on the surface of the positive electrode active material. It is formed at a rate of 8 μmol or more and 18 μmol or less per surface area (1 m ² ).
By setting the content of the component derived from the lithium sulfonate salt formed on the surface of the positive electrode active material (the amount of film formation) within the above range, it is possible to suitably secure the field of charge carrier reaction and The approach suppression effect and the charge carrier approach assist (promotion) effect can be exhibited at a high level.

The above “content of component derived from lithium salt having sulfonic acid skeleton per unit surface area of active material = film amount (μmol / m ² )” is measured by, for example, ion chromatography (IC: Ion Chromatography) method The content of the component derived from the lithium sulfonate salt = the coating amount (μmol / cm ² ) can be obtained by dividing the content by the surface area (m ² / cm ² ) of the active material contained per unit area. A method for measuring a film using the IC will be described later. Further, the “surface area of active material contained per unit area (m ² / cm ² )” is a product of the basis weight of active material (g / cm ² ) and the BET specific surface area of active material (m ² / g). Can be obtained. “BET specific surface area (m ² / g)” is, for example, a gas adsorption amount measured by a gas adsorption method (fixed capacity adsorption method) using nitrogen (N ₂ ) gas as an adsorbate, and a BET method (for example, It can be obtained by analyzing by the BET 1-point method.

The term “coating derived from a vinylene carbonate compound” or “coating derived from a lithium salt having a sulfonic acid skeleton” as used in the present specification is an expression used for components of the coating, and is formed after the initial charge. In the SEI coating, other components not derived from the vinylene carbonate compound or lithium sulfonate, such as decomposition products of other components constituting the nonaqueous electrolyte (specifically, supporting salts and nonaqueous solvents), etc. Of course, the “coating derived from a vinylene carbonate compound” or the “coating derived from a lithium salt having a sulfonic acid skeleton” in the present specification allows the presence of these other components. Is.
In this specification, the “lithium secondary battery” includes a non-aqueous electrolyte that is liquid at room temperature (for example, 25 ° C.) (typically, an electrolyte containing a charge carrier in a non-aqueous solvent). A battery that uses lithium ions as a charge carrier and is charged and discharged by the movement of lithium ions between positive and negative electrodes.

Moreover, this invention provides the method of manufacturing the lithium secondary battery of the structure disclosed here as another side surface. That is, the manufacturing method of the lithium secondary battery disclosed here is:
(1) housing a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte in a battery case, and (2) constructing a battery assembly. The initial charging process is performed so that the voltage between the two becomes a predetermined value.
And in the manufacturing method disclosed here, a non-aqueous electrolyte containing a sulfonic acid lithium salt represented by the following formula (I) and a vinylene carbonate compound is used as the non-aqueous electrolyte. And

（ここで、Ｒ^１は、炭素原子数１〜１２の直鎖状または分岐状のアルキル基である。）

(Here, R ¹ is a linear or branched alkyl group having 1 to 12 carbon atoms.)

During initial charging (conditioning), the vinylene carbonate compound is reduced and decomposed at the negative electrode, and an SEI coating derived from the vinylene carbonate compound is formed on the surface of the negative electrode active material. At this time, the component derived from the lithium sulfonate salt represented by the formula (1) is taken into the SEI coating derived from the vinylene carbonate compound. In addition, a part of the lithium sulfonate can be reduced and decomposed at the negative electrode during the initial charging (conditioning). A part of the R ¹ —SO ₃ group generated by such reductive decomposition moves to the positive electrode side, and a coating derived from lithium sulfonate (typically having a sulfonyloxy group) on the surface of the negative electrode active material and the positive electrode active material A film (for example, a film containing a sulfonyloxy group and lithium element) is bonded (attached).

In a preferred embodiment of the method for producing a lithium secondary battery disclosed herein, as the non-aqueous electrolyte, the concentration C _a (% by mass) of the vinylene carbonate compound in the non-aqueous electrolyte and the non-aqueous electrolyte A nonaqueous electrolytic solution having _a ratio (C _a / C _b ) to _a concentration C _b (mass%) of lithium sulfonate of 0.5 to 1.8 is used. By setting the (C _a / C _b ) ratio in the above range, an SEI coating containing a suitable amount of a component derived from lithium sulfonate in the coating is maintained while maintaining the strength of the coating derived from the vinylene carbonate compound. It can be formed on the active material layer.

In a preferred aspect of the method for producing a lithium secondary battery disclosed herein, the non-aqueous electrolyte has a sulfonic acid lithium salt concentration _Cb of 0.75% by mass to 2.0% by mass, and , the concentration C _a vinylene carbonate compound using a non-aqueous electrolyte is not more than 1.8 mass% to 0.7 mass%. By setting both the concentration of the vinylene carbonate compound and the concentration of the lithium sulfonic acid salt within the above ranges, a suitable amount of the component derived from the lithium sulfonic acid salt can be included in the coating derived from the vinylene carbonate compound. Therefore, the application effect of the present invention can be exhibited at a higher level.

  As described above, the lithium secondary battery disclosed herein (for example, a lithium ion secondary battery) is characterized in that internal resistance is reduced and high cycle characteristics (high capacity retention rate, low resistance increase rate, etc.) can be exhibited. And In other words, the battery disclosed herein has high initial battery characteristics (for example, initial input / output characteristics), and, for example, when the battery is stored for a long period of time in a high temperature environment or after a long period of use, the battery capacity is reduced. hard. Therefore, taking advantage of these features, applications that require high energy density, high output density, or high durability in a wide range of temperatures (for example, power sources for driving motors mounted on vehicles (drive power supplies)) And can be used particularly preferably.

It is a perspective view which shows typically the external shape of the lithium secondary battery which concerns on one Embodiment. It is a longitudinal cross-sectional view which follows the II-II line | wire in FIG. It is a schematic diagram which shows the structure of the wound electrode body which concerns on one Embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings as appropriate. Matters necessary for the implementation of the present invention other than matters specifically mentioned in the present specification can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In the following drawings, members / parts having the same action are described with the same reference numerals, and redundant descriptions may be omitted or simplified. Further, the dimensional relationship (length, width, thickness, etc.) in each drawing does not necessarily reflect the actual dimensional relationship.

  According to the present invention, there is provided a lithium secondary battery having a configuration in which a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte are accommodated in a battery case. Although not intended to be particularly limited, in the following, as a schematic configuration of a lithium secondary battery according to an embodiment, a flatly wound electrode body (wound electrode body) and a nonaqueous electrolyte solution are flattened. The present invention will be described in detail by taking as an example a lithium secondary battery that is housed in a rectangular parallelepiped (box) container.

1 and 2 show a schematic configuration of a lithium secondary battery according to an embodiment of the present invention. FIG. 1 is a perspective view schematically showing the outer shape of the lithium secondary battery 100. FIG. 2 is a longitudinal sectional view schematically showing a sectional structure taken along line II-II of the lithium secondary battery 100 shown in FIG.
As shown in FIGS. 1 and 2, the lithium secondary battery 100 includes a long positive electrode (positive electrode sheet) 50 and a long negative electrode (negative electrode sheet) 60 having a long separator (separator sheet) 70. An electrode body (winding electrode body) 20 that is wound flatly via a non-aqueous electrolyte solution (not shown) is housed in a flat box-shaped battery case 30.

≪Battery case 30≫
The battery case 30 includes a flat rectangular (box-shaped) battery case main body 32 having an open upper end, and a lid 34 that closes the opening. On the upper surface (that is, the lid 34) of the battery case 30, a positive terminal 42 for external connection that is electrically connected to the positive electrode of the wound electrode body 20, and a negative electrode that is electrically connected to the negative electrode of the wound electrode body 20. A terminal 44 is provided. The lid body 34 is also provided with a safety valve 36 for discharging the gas generated inside the battery case 30 to the outside of the battery case 30 as in the case of the battery case of the conventional lithium secondary battery.
Examples of the material of the battery case 30 include metal materials such as aluminum and steel; resin materials such as polyphenylene sulfide resin and polyimide resin. Among these, relatively light metals (for example, aluminum and aluminum alloys) can be preferably employed for the purpose of improving heat dissipation and increasing energy density. The shape of the case (outer shape of the container) is, for example, circular (cylindrical shape, coin shape, button shape), hexahedron shape (rectangular shape, cubic shape), bag shape, and a shape obtained by processing and deforming them. possible.

≪Winded electrode body 20≫
FIG. 3 is a schematic diagram showing a configuration of the wound electrode body 20 shown in FIG. As shown in FIG. 3, the wound electrode body 20 according to the present embodiment has a long sheet structure (sheet-like electrode body) in a stage before assembly. The wound electrode body 20 includes a positive electrode sheet 50 in which a positive electrode active material layer 54 is formed on one or both surfaces (here, both surfaces) of the long positive electrode current collector 52 along the longitudinal direction, and a long electrode body. A negative electrode sheet 60 in which a negative electrode active material layer 64 is formed along the longitudinal direction on one side or both sides (here, both sides) of the negative electrode current collector 62 is overlapped with a long separator sheet 70 to be long. It is formed into a flat shape by winding it in the direction and further crushing it from the side direction.

  In the central portion of the wound electrode body 20 in the winding axis direction, there is a wound core portion (that is, the positive electrode active material layer 54 of the positive electrode sheet 50, the negative electrode active material layer 64 of the negative electrode sheet 60, and the separator sheet 70). A densely stacked portion) is formed. In addition, at both ends of the wound electrode body 20 in the winding axis direction, a part of the positive electrode sheet 50 and the negative electrode sheet 60 where the electrode active material layer is not formed (52a, 62a) is outward from the wound core portion. It sticks out. The positive electrode side protruding portion and the negative electrode side protruding portion are respectively provided with a positive electrode current collecting plate 42a and a negative electrode current collecting plate 44a, and are electrically connected to the positive electrode terminal 42 (FIG. 2) and the negative electrode terminal 44 (FIG. 2), respectively. Has been.

≪Positive electrode sheet 50≫
The positive electrode sheet 50 includes a positive electrode current collector 52 and a positive electrode active material layer 54 including at least a positive electrode active material formed on the positive electrode current collector. A film derived from lithium sulfonate is formed on the surface of the positive electrode active material.
For the positive electrode current collector 52, a conductive member made of a metal having good conductivity (for example, aluminum, nickel, titanium, stainless steel, etc.) can be suitably used.

<Positive electrode active material layer 54>
The positive electrode active material layer 54 includes at least a positive electrode active material. As a positive electrode active material, 1 type, or 2 or more types of various materials known to be usable as a positive electrode active material of a lithium secondary battery can be adopted without particular limitation. Preferred examples include lithium composite metal oxides such as layered and spinel (LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiCrMnO ₄ , LiFePO _4, etc.). Can be mentioned. Among them, lithium nickel cobalt manganese composite oxide (for example, LiNi _1/3 Co) having a layered structure (typically a layered rock salt structure belonging to a hexagonal system) containing Li, Ni, Co, and Mn as constituent elements. _1/3 Mn _1/3 O ₂ ) is preferable because it is excellent in thermal stability and has a higher theoretical energy density than other compounds. In general, in a complex oxide containing a transition metal element (in particular, a manganese element), elution of constituent elements may be accelerated by hydrofluoric acid generated by hydrolysis of a supporting salt, for example. However, according to the technique disclosed here, the elution of the constituent elements is difficult to occur due to the coating on the surface of the positive electrode active material, and the crystal structure of the positive electrode active material can be maintained in a more stable state. For this reason, for example, even when a transition metal composite oxide containing a large amount of manganese that easily elutes under a high temperature environment (typically about 30 mol% to 40 mol%) is used as the positive electrode active material, it is high for a long period of time. The performance can be exhibited stably.

  Here, the lithium nickel cobalt manganese composite oxide is an oxide containing only Li, Ni, Co and Mn as constituent metal elements, and at least one other metal element in addition to Li, Ni, Co and Mn ( That is, it is meant to include oxides containing transition metal elements and / or typical metal elements other than Li, Ni, Co and Mn. Such metal elements include magnesium (Mg), calcium (Ca), strontium (Sr), titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), chromium (Cr), molybdenum (Mo), Tungsten (W), iron (Fe), rhodium (Rh), palladium (Pb), platinum (Pt), copper (Cu), zinc (Zn), boron (B), aluminum (Al), gallium (Ga), It may be one or more elements of indium (In), tin (Sn), lanthanum (La), and cerium (Ce). The addition amount (blending amount, content) of these metal elements is not particularly limited, but is usually 0.01% by mass to 5% by mass (for example, 0.05% by mass to 2% by mass, typically 0.1% by mass). % To 0.8% by weight). By setting the amount within the above range, excellent battery characteristics (for example, high energy density) can be realized.

Although the property of a positive electrode active material is not specifically limited, For example, it may be a particle form or a powder form. The average particle diameter of the particulate positive electrode active material may be 20 μm or less (typically 1 μm to 20 μm, for example, 5 μm to 15 μm). The specific surface area is 0.1 m ² / g or more (typically 0.7 m ² / g or more, for example, 0.8 m ² / g or more), and 5 m ² / g or less (typically 1.m ² / g or more). 3 m ² / g or less, for example 1.2 m ² / g or less). The positive electrode active material satisfying one or two of the above properties has high battery characteristics (for example, high input / output characteristics) because a reaction field of charge carriers is widely ensured even when a film is formed. It can be demonstrated.

In the present specification, the “average particle size” means a particle size distribution corresponding to 50% cumulative from the fine particle side in a volume-based particle size distribution measured by a particle size distribution measurement based on a general laser diffraction / light scattering method. (D ₅₀ particle diameter, also called median diameter).

A film derived from lithium sulfonate is formed on the surface of the positive electrode active material. Such a film typically contains an S element-containing group (for example, a sulfonyl group or a sulfonyloxy group). For example, an S element-containing group represented by SO _X (where X = 2 to 4) is included. Specifically, SO ₂ ²⁻ , SO ₃ ²⁻ , SO ₄ ^{2− and the} like may be included. By providing such a film, it is possible to suitably suppress the fluorine anion from approaching the positive electrode by utilizing electrostatic interaction and / or steric hindrance. Therefore, lithium fluoride having high resistance is hardly generated, and the resistance of the positive electrode can be kept lower. In particular, since a film containing sulfur atoms is excellent in thermal stability, it does not easily decompose or deteriorate even in a high temperature environment, and can achieve high durability (for example, high temperature storage characteristics and high temperature charge / discharge cycle characteristics).

The amount of the film derived from lithium sulfonate formed on the surface of the positive electrode active material is 8 μmol or more (preferably 10 μmol or more) and 18 μmol or less in terms of sulfonic acid group per unit surface area (1 m ² ) of the positive electrode active material. Preferably, it is 15 μmol or less. By setting the coating amount to 8 μmol or more, the effect of the present invention (for example, the effect of suppressing the approach of fluorine anions) can be exhibited at a high level. Further, by setting the coating amount to 18 μmol or less, a reaction field of charge carriers (that is, lithium ions) can be suitably secured, and the resistance can be suppressed low.

The above “content of component derived from lithium sulfonate per unit surface area of positive electrode active material = coating amount (μmol / m ² )” is the unit area of the positive electrode active material layer measured by ion chromatography (IC). The content of the component derived from the lithium sulfonate per liter = the coating amount (μmol / cm ² ) can be obtained by dividing by the surface area (m ² / cm ² ) of the positive electrode active material contained per unit area. . Specifically, first, the positive electrode active material layer 54 disassembled and taken out from the battery is immersed in an appropriate solvent (for example, EMC), and then cut into an appropriate size and collected. Next, by immersing the measurement sample in a 50% acetonitrile (CH ₃ CN) aqueous solution for a predetermined time (for example, about 1 to 30 minutes), the film component (typically lithium sulfonate) to be measured Components derived from (eg, sulfide ions) are extracted into a solvent. This solution is subjected to IC measurement, and the content (μmol) of ions (for example, SO ₂ ²⁻ , SO ₃ ²⁻ , SO ₄ ²⁻ ) to be measured is quantified from the obtained results. The total area (cm ² ) of the positive electrode active material layer subjected to measurement by summing the quantitative value (μmol) of each ion (typically, the area (cm ² ) in plan view of the positive electrode active material layer subjected to measurement) ), The coating amount (μmol / cm ² ) derived from the lithium sulfonic acid salt in the measurement sample can be determined in terms of sulfonic acid group. Then, by dividing this value by the product of the basis weight (g / cm ² ) of the positive electrode active material and the BET specific surface area (m ² / g) of the positive electrode active material, the “sulfone per unit surface area of the positive electrode active material” The coating amount derived from the lithium acid salt (μmol / m ² ) ”can be determined.

  In addition, although the case where IC was used was illustrated above as a technique for measuring the amount of the coating, it is not limited to this, and for example, a conventionally known inductively coupled plasma-atomic emission spectroscopy (ICP-AES) is used. ) And X-ray absorption fine structure analysis (XAFS: X-ray Absorption Fine Structure).

  The positive electrode active material layer 54 contains, in addition to the above positive electrode active material, one or more materials that can be used as a constituent component of the positive electrode active material layer 54 in a general lithium secondary battery as necessary. obtain. Examples of such materials include conductive materials and binders. As the conductive material, for example, carbon materials such as various carbon blacks (typically acetylene black and ketjen black), coke, activated carbon, graphite, carbon fiber, and carbon nanotube can be suitably used. As the binder, for example, a vinyl halide resin such as polyvinylidene fluoride (PVdF); a polyalkylene oxide such as polyethylene oxide (PEO); and the like can be preferably used.

  The proportion of the positive electrode active material in the entire positive electrode active material layer 54 is suitably about 60% by mass or more (typically 60% by mass to 99% by mass), and usually about 70% by mass to 95% by mass. % Is preferred. In the case of using a conductive material, the ratio of the conductive material to the entire positive electrode active material layer 54 can be, for example, about 2% by mass to 20% by mass, and usually about 3% by mass to 10% by mass. preferable. When using a binder, the ratio of the binder to the whole positive electrode active material layer 54 can be, for example, about 0.5 mass% to 10 mass%, and usually about 1 mass% to 5 mass%. preferable.

The mass (weight per unit area) of the positive electrode active material layer 54 provided per unit area of the positive electrode current collector 52 is 3 mg / cm ² or more per side of the positive electrode current collector 52 from the viewpoint of securing sufficient battery capacity (for example, 5 mg / cm ² or more, typically 7 mg / cm ² or more). Further, from the viewpoint of securing battery characteristics (for example, input / output characteristics), it is set to 100 mg / cm ² or less (for example, 70 mg / cm ² or less, typically 50 mg / cm ² or less) per side of the positive electrode current collector. it can. Thereby, the effect of this invention can be exhibited at a higher level. In the configuration having the positive electrode active material layer 54 on both surfaces of the positive electrode current collector 52 as in this embodiment, the mass of the positive electrode active material layer 54 provided on each surface of the positive electrode current collector 52 is approximately the same. It is preferable that

The average thickness per one side of the positive electrode active material layer 54 is, for example, 20 μm or more (typically 40 μm or more, preferably 50 μm or more), and may be 100 μm or less (typically 80 μm or less). The density of the positive electrode active material layer 54 can be, for example, 1 g / cm ^{3 to} 4 g / cm ³ (eg, 1.5 g / cm ^{3 to} 3.5 g / cm ³ ). The porosity (porosity) of the positive electrode active material layer 54 can be, for example, 10% to 50% by volume (typically 20% to 40% by volume).
In the case where one or more of the above properties are satisfied, an appropriate void can be maintained in the positive electrode active material layer 54, and the nonaqueous electrolyte can be sufficiently infiltrated. Therefore, a wide reaction field with the charge carrier can be secured, and high input / output characteristics can be exhibited. Moreover, the electrical conductivity in the positive electrode active material layer 54 can be kept good, and an increase in resistance can be suppressed. Furthermore, the mechanical strength (shape retention) of the positive electrode active material layer can be ensured, and good cycle characteristics can be exhibited. For this reason, the outstanding battery characteristic (for example, a high energy density and an input-output characteristic) can be exhibited by making one or two or more of the said characteristics into the said range.

Incidentally, the "porosity" in the present specification, multiplied by 100 and dividing the total pore volume obtained by the measurement of the mercury porosimeter a (cm ³⁾ in the apparent volume of the active material layer (cm ³⁾ value Say. The apparent volume can be calculated by the product of the area (cm ² ) and the thickness (cm) in plan view. Specifically, for example, a positive electrode sheet to be measured is first cut into a square or a rectangle with a punching machine or a cutter. Next, the area (cm ² ) and the thickness (cm) of the cut-out sample in the plan view of the positive electrode active material layer are measured, and the apparent volume is calculated by multiplying these values. The thickness can be measured by, for example, a micrometer or a thickness meter (for example, a rotary caliper meter).

  Although the method of producing such a positive electrode sheet 50 is not specifically limited, For example, it can carry out as follows. First, a positive electrode active material and a material used as necessary are dispersed in an appropriate solvent to prepare a paste-like or slurry-like composition (positive electrode active material layer forming slurry). And the prepared slurry for positive electrode active material layer formation is provided to the elongate positive electrode collector 52, and the solvent contained in this slurry is removed. Thereby, the positive electrode sheet 50 provided with the positive electrode active material layer 54 on the positive electrode current collector 52 can be produced. As the solvent, any of an aqueous solvent and an organic solvent can be used. For example, N-methyl-2-pyrrolidone (NMP) can be used. The operation of applying the slurry can be performed using an appropriate coating apparatus such as a gravure coater, a slit coater, a die coater, a comma coater, or a dip coater. Moreover, the removal of the solvent can also be performed by conventional general means (for example, heat drying or vacuum drying).

  In addition, the property (namely, average thickness, density, porosity) of the positive electrode active material layer 54 as described above is, for example, that the positive electrode sheet 50 is appropriately pressed after the positive electrode active material layer 54 is formed. Can be adjusted by. Various conventionally known press methods such as a roll press method and a flat plate press method can be employed for the press treatment. Further, such processing may be performed once or may be performed two or more times.

≪Negative electrode sheet 60≫
The negative electrode sheet 60 includes a negative electrode current collector 62 and a negative electrode active material layer 64 including at least a negative electrode active material formed on the negative electrode current collector. An SEI film derived from the vinylene carbonate compound is formed on the surface of the negative electrode active material. Such SEI coating contains components derived from lithium sulfonate. Further, on the surface of the negative electrode active material (typically the surface of the SEI coating derived from the vinylene carbonate compound), a coating derived from lithium sulfonate (a coating containing an S element-containing group) is further formed.
For the negative electrode current collector 62, a conductive material made of a metal having good conductivity (for example, copper, nickel, titanium, stainless steel, etc.) can be suitably used.

<Negative electrode active material layer 64>
The negative electrode active material layer 64 includes at least a negative electrode active material. As a negative electrode active material, 1 type, or 2 or more types of various materials known to be usable as a negative electrode active material of a lithium secondary battery can be used without particular limitation. Preferable examples include graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), carbon nanotubes, at least part of those having a combination of these, etc. The carbon material containing is mentioned. Especially, since a high energy density is obtained, graphite-based materials such as natural graphite (graphite) and artificial graphite can be preferably used. Usually, in a battery equipped with a carbon material as a negative electrode, when charging / discharging is repeated under severe conditions, for example, components (for example, nonaqueous solvent and supporting salt) contained in the nonaqueous electrolyte are gradually decomposed, resulting in energy density. Can be reduced. However, since the coating film derived from the vinylene carbonate compound is formed on the surface of the negative electrode active material disclosed herein, it has low resistance and can suitably suppress reductive decomposition of the non-aqueous electrolyte over a long period of time. it can.

Although the property of a negative electrode active material is not specifically limited, For example, it may be a particle form or a powder form. The average particle diameter of the particulate negative electrode active material can be, for example, 50 μm or less (typically 20 μm or less, for example, 1 μm to 20 μm, preferably 5 μm to 15 μm). The specific surface area is 1 m ² / g or more (typically 2.5 m ² / g or more, for example, 2.8 m ² / g or more), and 10 m ² / g or less (typically 3.5 m ² / G or less, for example 3.4 m ² / g or less). The negative electrode active material satisfying one or two of the above properties has high battery characteristics (for example, high input / output characteristics) because a reaction field of charge carriers is widely secured even when a film is formed. It can be demonstrated.

A SEI film derived from a vinylene carbonate compound is formed on the surface of the negative electrode active material. Such a film typically contains a C element-containing group (for example, a carbonyl group or a carboxylate group). Specifically, CO ²⁻ , CO ₂ ²⁻ , CO ₃ ^{2− and the} like may be included.
The vinylene carbonate compound can form a strong film on the negative electrode active material that can expand and contract following the volume change of the negative electrode active material accompanying charge and discharge. For this reason, high durability (for example, a high-rate charge / discharge characteristic, a cycle characteristic, etc.) can be implement | achieved by providing the coating film derived from this compound on a negative electrode.
In addition, according to the technique disclosed herein, the SEI coating derived from the vinylene carbonate compound contains a component derived from the lithium sulfonate salt in the coating, and therefore lithium in the coating (typically the surface of the negative electrode active material). The concentration (ie the concentration of charge carriers) can be increased. In addition, since the component derived from the lithium sulfonate salt has a molecular structure with a large charge bias (polarization), it has a characteristic of attracting cations using electrostatic interaction. For this reason, it can accelerate | stimulate suitably that the lithium ion in a nonaqueous electrolyte solution approaches the inside of a film (typically the negative electrode active material surface). That is, by providing the SEI film having such a configuration, the lithium concentration on the surface of the negative electrode active material can be suitably increased. Thereby, the resistance of the negative electrode can be kept low, and high input / output characteristics can be realized.

The amount of the SEI coating derived from the vinylene carbonate compound formed on the surface of the negative electrode active material is 27 μmol or more in terms of the vinylene carbonate compound consumed in the configuration of the coating per unit surface area (1 m ² ) of the negative electrode active material ( The amount is preferably 30 μmol or more and 64 μmol or less (preferably 60 μmol or less). Further, the content in terms of sulfonic acid group of the component derived from the lithium sulfonate salt contained in the SEI coating derived from the vinylene carbonate compound is 0.04 mol or more per 1 mol of the SEI coating derived from the vinylene carbonate compound (preferably 0.00. 07 mol or more) 0.15 mol or less (preferably 0.11 mol or less) is suitable.
The amount of the SEI coating derived from the vinylene carbonate compound per unit surface area (1 m ² ) of the negative electrode active material is 27 μmol / m ² or more (preferably 30 μmol / m ² ) in terms of the vinylene carbonate compound consumed in the configuration of the coating. With the above, it is possible to form a high-strength coating film (that is, a coating film having high durability against the volume change of the negative electrode active material) that can expand and contract appropriately following the volume change of the negative electrode active material. Thereby, the outstanding durability (for example, a high-rate charge / discharge characteristic, a cycle characteristic, etc.) is securable. In addition, the coating amount of the SEI coating derived from the vinylene carbonate compound per unit surface area (1 m ² ) of the negative electrode active material is 64 μmol / m ² or less (preferably 60 μmol / m) in terms of the vinylene carbonate compound consumed in the configuration of the coating. By setting it to m ² or less, a reaction field of charge carriers (that is, lithium ions) can be suitably secured, and the resistance can be kept low.
Moreover, while ensuring the intensity | strength of the film derived from a vinylene carbonate compound suitably by making the ratio (molar ratio) of the component derived from lithium sulfonate contained in the SEI film derived from a vinylene carbonate compound into the said range, This is preferable because the above-described effect of increasing the charge carrier concentration on the surface of the negative electrode active material can be suitably exhibited.

The “amount of the coating derived from the vinylene carbonate compound per unit surface area of the negative electrode active material (μmol / m ² )” is the vinylene carbonate compound consumed for film formation among the vinylene carbonate compounds in the non-aqueous electrolyte used. Is divided by the total surface area (total surface area) (m ² ) of the negative electrode active material used for forming the negative electrode active material layer.
The total surface area (m ² ) of the negative electrode active material used for forming the negative electrode active material layer is the total mass (g) of the negative electrode active material used for forming the negative electrode active material layer and the BET specific surface area (m ² ) of the negative electrode active material. / G). That is, the total surface area (m ² ) of the negative electrode active material used for the formation of the negative electrode active material layer is the BET specific surface area (m ² / g) of the negative electrode active material and the basis weight (g / cm ² ) of the negative electrode active material. It can be calculated from the product with the formation area (cm ² ) of the negative electrode active material layer.
Specifically, the amount (decomposition amount) (μmol) of the vinylene carbonate compound consumed for film formation can be determined as follows. First, the battery is disassembled and the non-aqueous electrolyte stored in the battery case is collected. In addition, the surface of the electrode body (typically between the electrodes) and the surface of the member that can come into contact with the non-aqueous electrolyte such as in the battery case is washed with an appropriate solvent (for example, EMC), and the washing solution is recovered. The amount of the vinylene carbonate compound (μmol) contained in these solutions is quantified by quantitatively analyzing the non-aqueous electrolyte and the cleaning solution by gas chromatography (GC). Then, the vinylene consumed for the formation of the coating film is subtracted from the amount (μmol) of the vinylene carbonate compound determined above from the amount (μmol) of vinylene carbonate contained in the non-aqueous electrolyte used for battery construction. The amount (decomposition amount) of the carbonate compound can be calculated.

  In addition, although the case where GC is used as an example of the method for measuring the amount of the coating derived from the vinylene carbonate compound is exemplified above, the present invention is not limited thereto, and for example, a conventionally known inductively coupled plasma emission spectroscopy (ICP-AES: Inductively) is used. It can be generally grasped by a coupled plasma-atomic emission spectrometry (XAFS) or an X-ray absorption fine structure analysis method (XAFS).

The proportion (molar ratio) of the component derived from lithium sulfonate contained in the vinylene carbonate compound-derived film is the amount of component derived from all lithium sulfonate (μmol / m) per unit area of the negative electrode active material layer. ² ) the amount of the component derived from lithium sulfonate (μmol / m ² ) obtained by subtracting the amount of the coating derived from lithium sulfonate per unit area of the negative electrode active material layer (μmol / m ² ) It can be determined by dividing by the coating amount (μmol / m ² ) derived from the vinylene carbonate compound per unit area of the active material layer.
The amount of coating (μmol / m ² ) derived from the vinylene carbonate compound per unit area of the negative electrode active material layer is the amount (decomposition amount) (μmol) of the vinylene carbonate compound consumed for forming the coating. By dividing by the formation area (m ² ) of the layer, it can be obtained in terms of vinylene carbonate compound consumed for the formation of the film. In addition, the amount (decomposition amount) (μmol) of the vinylene carbonate compound consumed for forming the coating can be obtained by the same method as that for obtaining the coating amount of the coating derived from the vinylene carbonate compound.
Specifically, the amount (μmol / m ² ) of the component derived from the total sulfonic acid lithium salt present per unit area of the negative electrode active material layer can be determined as follows. First, the negative electrode active material layer 64 taken out by disassembling the battery is immersed in an appropriate solvent (for example, EMC), cut out to an appropriate size, and collected. Next, by immersing the measurement sample in aqua regia for a predetermined time (for example, about 1 to 30 minutes), a component derived from a lithium sulfonate salt to be measured is extracted into a solvent. This solution is subjected to ICP-AES analysis, and the content (μmol) of the component derived from lithium sulfonate is quantified from the obtained result (typically the content of elemental sulfur). The area (m ² ) of the negative electrode active material layer subjected to the measurement of the content (μmol) of the component derived from the lithium sulfonate salt (typically, the area (m in plan view) of the negative electrode active material layer subjected to the measurement By dividing by ² )), the amount (μmol / m ² ) of components derived from all lithium sulfonates present per unit area of the negative electrode active material layer can be determined in terms of sulfonic acid groups.
The amount of the sulfonic acid lithium salt-derived film per unit area of the negative electrode active material layer (μmol / m ² ) is, for example, the above-described film of the lithium sulfonate salt derived from the unit surface area (1 m ² ) of the positive electrode active material. Similar to the case of obtaining the amount (μmol / m ² ), a 50% acetonitrile aqueous solution in which the negative electrode active material cut out to an appropriate size was immersed to extract the coating component was subjected to IC measurement, and measurement was performed from the obtained results. The content (μmol) of the target ion (for example, SO ₂ ²⁻ , SO ₃ ²⁻ , SO ₄ ²⁻ ) is quantified. The area (m ² ) of the negative electrode active material layer subjected to measurement by summing the quantitative value (μmol) of each ion (typically, the area (m ² ) in plan view of the negative electrode active material layer subjected to measurement) ), The amount of the sulfonic acid lithium salt-derived coating per unit area of the negative electrode active material layer (μmol / m ² ) can be determined in terms of sulfonic acid groups.

  In addition, although the case where ICP-AES is used is exemplified above as a method for measuring the amount of the component derived from the total sulfonic acid lithium salt present per unit area of the negative electrode active material layer, the present invention is not limited thereto. It can be generally grasped by a known IC, XAFS, MS or the like.

In a preferred embodiment, the surface of the negative electrode active material (typically, the surface of the SEI film derived from the vinylene carbonate compound formed on the surface of the negative electrode active material) has an S element-containing group (for example, a sulfonyl group or sulfonyloxy). A film containing a group, typically SO _X (herein, an S element-containing group represented by X = 2 to 4) (hereinafter, this film is also simply referred to as “S element-containing film”) is formed. Yes. Typically, the S element-containing group may be a decomposition product of lithium sulfonate. Further, the S element-containing coating has a form in which the S element-containing group is bonded or bonded (attached) to the surface of the negative electrode active material (typically, the surface of the vinylene carbonate compound-derived coating formed on the surface of the negative electrode active material). It can be. In other words, in addition to the SEI film derived from the vinylene carbonate compound, a film derived from a lithium sulfonate salt may be formed on the surface of the negative electrode active material. Typically, the component derived from the lithium sulfonate salt may be a part of the SEI film formed on the surface of the negative electrode active material layer.
S element-containing group represented by the S element-containing group (typically represented by SO _X (where X = 2 to 4), specifically SO ₂ ²⁻ , SO ₃ ²⁻ , SO ₄ ^2−, etc. ) Can be favorably promoted by the cation approaching the negative electrode surface because of the large bias of charge in the molecule. For this reason, by providing the S element-containing coating on the surface of the negative electrode active material (preferably, the outermost surface of the negative electrode active material), lithium ions approach the negative electrode using the electrostatic interaction of the S element-containing group. This can be favorably promoted. Therefore, the lithium ion concentration in the vicinity of the negative electrode active material can be increased, and the negative electrode resistance can be kept lower.

The amount of the coating derived from lithium sulfonate formed on the surface of the negative electrode active material is 8 μmol or more (preferably 10 μmol or more) and 23 μmol or less in terms of sulfonic acid group per unit surface area (1 m ² ) of the negative electrode active material. 20 μmol or less is preferable.
By setting the amount of the coating derived from the lithium sulfonate per unit surface area (1 m ² ) of the negative electrode active material to 8 μmol / m ² or more (preferably 10 μmol / m ² or more) in terms of sulfonic acid group, the above negative electrode The effect of promoting the approach of lithium ions to the active material surface can be exhibited at a high level. Further, the amount of coating from the lithium sulfonate of unit surface area (1 m ²⁾ per electrode active material, with a sulfonic acid group in terms of, 23μmol / ^{m 2} or less (preferably 20 [mu] mol / ^{m 2} or less) by a, A reaction field of charge carriers (Lithium, that is, lithium ions) can be suitably secured, and the resistance can be kept low.

The above-mentioned “amount (μmol / m ² ) of coating film derived from lithium sulfonate per unit surface area (1 m ² ) of negative electrode active material” is measured by, for example, ion chromatography (IC) as sulfonic acid group conversion. Obtaining by dividing the coating amount (μmol / cm ² ) derived from lithium sulfonate per unit area of the active material layer by the surface area (m ² / cm ² ) of the negative electrode active material contained per unit area. it can. For example, it can be obtained by the same method as in the case of obtaining the amount (μmol / m ² ) of the coating film derived from lithium sulfonate per unit surface area (1 m ² ) of the positive electrode active material described above.

  In addition to the above negative electrode active material, the negative electrode active material layer 64 may contain one or more materials that can be used as a constituent component of the negative electrode active material layer in a general lithium secondary battery, if necessary. . Examples of such materials include binders and various additives. As the binder, for example, a polymer material such as styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), or the like can be suitably used. In addition, various additives such as a thickener, a dispersant, and a conductive material can be used as appropriate. For example, carboxymethylcellulose (CMC) or methylcellulose (MC) can be suitably used as the thickener.

  The proportion of the negative electrode active material in the entire negative electrode active material layer 64 is suitably about 50% by mass or more, and is usually 90% by mass to 99% by mass (eg, 95% by mass to 99% by mass). Is preferred. When using a binder, the ratio of the binder to the whole negative electrode active material layer 64 can be, for example, about 1% by mass to 10% by mass, and usually about 1% by mass to 5% by mass is preferable. .

Negative electrode current collector 62 negative electrode active mass of the material layer 64 provided per unit area of (basis weight), the per side of the negative electrode current collector ^{62 5mg / cm 2 ~20mg / cm} 2 ( typically 7 mg / cm ^{2 to} 15 mg / cm ² ). In the configuration having the negative electrode active material layers 64 on both surfaces of the negative electrode current collector 62 as in this embodiment, the mass of the negative electrode active material layers 64 provided on each surface of the negative electrode current collector 62 is approximately the same. It is preferable to do.

The porosity of the negative electrode active material layer 64 may be, for example, about 5% to 50% by volume (preferably 35% to 50% by volume). Moreover, the thickness per one side of the negative electrode active material layer 64 is, for example, 40 μm or more (typically 50 μm or more), and can be 100 μm or less (typically 80 μm or less). Moreover, the density of the negative electrode active material layer 64 can be set to, for example, about 0.5 g / cm ^{3 to} 2 g / cm ³ (typically 1 g / cm ^{3 to} 1.5 g / cm ³ ). By setting the properties of the negative electrode active material layer in the above range, the interface with the non-aqueous electrolyte can be suitably maintained, and both durability (cycle characteristics) and output characteristics can be achieved at a high level during normal use. it can. In addition, hydrogen ions generated at the positive electrode can be suitably reduced during overcharge, and a large amount of gas can be generated quickly. In addition, the porosity, thickness, and density of the negative electrode active material layer 64 can be adjusted by performing an appropriate press process or the like, similarly to the positive electrode active material layer 54 described above.

  Although the method for producing such a negative electrode sheet 60 is not particularly limited, it can be performed, for example, as follows. First, a negative electrode active material and a material used as necessary are dispersed in a suitable solvent to prepare a paste-like or slurry-like composition (a slurry for forming a negative electrode active material layer). And the prepared slurry for negative electrode active material layer formation is provided to the elongate negative electrode collector 62, and the solvent contained in this slurry is removed. Thereby, the negative electrode sheet 60 provided with the negative electrode active material layer 64 on the negative electrode collector 62 can be produced. As the solvent, any of an aqueous solvent and an organic solvent can be used. For example, water can be used. Further, the application of the slurry, the removal of the solvent, the press treatment, and the like can be performed in the same manner as in the case of the positive electrode sheet 50.

≪Separator sheet 70≫
The separator sheet 70 interposed between the positive and negative electrode sheets 50 and 60 may be any sheet as long as it insulates the positive electrode active material layer 54 and the negative electrode active material layer 64 and has a nonaqueous electrolyte holding function and a shutdown function. . Preferable examples include porous resin sheets (films) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Among them, a polyolefin-based porous resin sheet (for example, PE or PP) has a shutdown temperature of 80 ° C. to 140 ° C. (typically 110 ° C. to 140 ° C., for example, 120 ° C. to 135 ° C.), and the heat resistant temperature of the battery. Since it is sufficiently lower than (typically about 200 ° C. or more), the shutdown function can be exhibited at an appropriate timing.

  Although the properties of the separator sheet 70 are not particularly limited, for example, the average thickness is usually 10 μm or more (typically 15 μm or more, for example, 17 μm or more) and 40 μm or less (typically 30 μm or less, for example, 25 μm or less). ) Is preferable. When the thickness of the separator sheet 70 is within the above range, the ion permeability is further improved, and an internal short circuit (separator film breakage) is less likely to occur even when foreign matter is mixed in the battery.

  Separator sheet 70 may have a single-layer structure, or may have a structure in which two or more porous resin sheets having different materials and properties (thickness, porosity, etc.) are laminated. As the multilayer structure, for example, a separator sheet having a three-layer structure in which a polypropylene (PP) layer is laminated on both sides of a polyethylene (PE) layer (that is, a three-layer structure of PP / PE / PP) can be suitably employed. . Further, the two separator sheets 70 provided in the wound electrode body 20 may be different in material and properties.

  Separator sheet 70 may be a heat-resistant separator having a porous heat-resistant layer on one side or both sides (typically one side) of the porous sheet. This heat-resistant layer can be, for example, a layer containing an inorganic filler and a binder. As the inorganic filler, for example, alumina, boehmite, silica, titania, calcia, magnesia, zirconia, boron nitride, aluminum nitride and the like can be preferably used. The average thickness of the heat-resistant layer can be, for example, about 1 μm to 10 μm.

≪Nonaqueous electrolyte≫
The nonaqueous electrolytic solution contains at least a supporting salt, a sulfonic acid lithium salt, and a vinylene carbonate compound in a nonaqueous solvent. The non-aqueous electrolyte exhibits a liquid state at normal temperature (for example, 25 ° C.), and in a preferred embodiment, the non-aqueous electrolyte always exhibits a liquid state under the battery usage environment (for example, a temperature environment of 0 ° C. to 60 ° C.).

  As the non-aqueous solvent, organic solvents such as various carbonates, ethers, esters, nitriles, sulfones, and lactones that are used in an electrolytic solution of a general lithium secondary battery can be used. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and the like. Such a non-aqueous solvent can be used individually by 1 type or in combination of 2 or more types as appropriate. Among these, EC having a high relative dielectric constant, DMC and EMC having a high oxidation potential (wide potential window) can be preferably used. For example, one or more carbonates are included as the non-aqueous solvent, and the total volume of these carbonates is 60% by volume or more (more preferably 75% by volume or more, more preferably 90% by volume) of the total volume of the non-aqueous solvent. % Or more and may be substantially 100% by volume).

As the supporting salt, those containing a charge carrier ion (that is, lithium ion) can be appropriately selected and used in the same manner as a general lithium secondary battery. For example, lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ are exemplified. Such a supporting salt can be used singly or in combination of two or more. LiPF ₆ may be mentioned as particularly preferred support salt. Moreover, it is preferable to prepare the non-aqueous electrolyte so that the concentration of the supporting salt is within a range of 0.7 mol / L to 1.3 mol / L. For example, it can be 1.1 mol / L.

As the lithium sulfonic acid salt, a lithium salt of an organic sulfonic acid compound having at least one —SO ₃ H group (sulfo group) and an alkoxy group can be used. For example, a lithium salt of alkoxysulfonic acid represented by the above formula (I) can be preferably used. Such lithium sulfonic acid salts are not particularly limited and those prepared by a known method or obtained by purchasing a commercially available product can be used alone or in combination of two or more.

In the formula (I), R ¹ represents 1 to 12 carbon atoms (preferably a methyl group, an ethyl group, a propyl group, an n-propyl group, an isopropyl group, an n-butyl group, a tert-butyl group, or a pentyl group). Are 1-6, more preferably 1-3) linear or branched alkyl groups. In a preferred embodiment, R ¹ in the above formula (I) may be an alkyl group having 1 to 3 carbon atoms (methyl group, ethyl group or propyl group). When such a lithium sulfonic acid salt is used, a low resistance and stable film can be formed on the surface of the positive electrode active material and the surface of the negative electrode active material. Further, such a coating can exhibit both a cation approach promoting effect and an anion approach inhibiting effect at a high level. In a particularly preferred embodiment, R ¹ may be an alkyl group having 2 carbon atoms (ethyl group). That is, the compound represented by the formula (I) preferably has an ethoxy group (CH ₃ —CH ₂ —O—). In such a case, the solubility of the lithium sulfonate in the non-aqueous electrolyte is improved, which is preferable.

  Specific examples of such lithium sulfonate include lithium methoxysulfonate, lithium ethoxysulfonate, lithium propoxysulfonate, lithium butoxysulfonate, and the like. Among these, lithium ethoxysulfonate represented by the following formula (II) can be preferably used.

As the vinylene carbonate compound, a compound represented by the following formula (III) can be used, and those prepared by a known method or those obtained by purchasing a commercially available product are not particularly limited, but one or two types The above can be used.
In the following formula (III), R ² and R ³ are each independently a hydrogen atom; an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, or a butyl group. Specific examples of the vinylene carbonate compound represented by the following formula (III) include vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, dimethyl vinylene carbonate, ethyl methyl vinylene carbonate, diethyl vinylene carbonate, propyl vinylene carbonate, butyl vinylene carbonate and the like. It is done. In a particularly preferred embodiment, both R ² and R ³ can be an elemental hydrogen. That is, vinylene carbonate can be suitably used as the vinylene carbonate compound.

  The sulfonic acid lithium salt and vinylene carbonate compound contained in the non-aqueous electrolyte are typically decomposed in the initial charge after the battery is constructed (assembled), whereby the positive electrode active material and / or the negative electrode active material are formed on the surface. A good quality film can be formed. Therefore, the total amount of these compounds contained in the non-aqueous electrolyte at the time of battery construction always remains in the non-aqueous electrolyte after charging / discharging (typically after initial charging, for example, after aging treatment). I don't need it. Typically, some of these compounds remain in the non-aqueous electrolyte even after charge / discharge (typically after initial charge, for example, after aging treatment), and therefore, non-aqueous electrolysis containing such compounds It can be grasped by confirming that these compounds (lithium sulfonate and vinylene carbonate compound) are present in the non-aqueous electrolyte solution.

Note that the amount of lithium sulfonate used in the battery configuration (in other words, the amount of lithium sulfonate supplied in the battery case) is determined by, for example, the above-described ICP-AES method. Quantifying the amount of lithium sulfonate incorporated into the film formed on the material; derived from lithium sulfonate bound to (attached to) the surface of the positive and negative electrode active material layers by the above-described ion chromatography technique The amount of SO ₂ ²⁻ , SO ₃ ²⁻ , and SO ₄ ²⁻ in the coating film (typically the SO _X adsorption layer (coating film)); The amount of chemical species derived from lithium sulfonic acid salts and their decomposition products is quantified by the above-described method;

  The non-aqueous electrolyte solution may contain components (additives) other than the non-aqueous solvent, the supporting salt, the vinylene carbonate compound, and the lithium sulfonic acid salt as long as the effects of the present invention are not significantly impaired. Examples of such additives include biphenyl compounds, alkylbiphenyl compounds, cycloalkylbenzene compounds, alkylbenzene compounds, organic phosphorus compounds, fluorine atom-substituted aromatic compounds, carbonate compounds, cyclic carbamate compounds, and aromatic compounds such as alicyclic hydrocarbons. Various additives such as a gas generating agent, a dispersant, a thickener, and the like.

≪Method for manufacturing lithium secondary battery≫
The lithium secondary battery as described above can be preferably manufactured by a manufacturing method including the following steps (1) and (2). That is, the method for manufacturing a lithium secondary battery disclosed herein includes (1) a battery assembly construction process and (2) a charging process (initial charging) process.
Hereinafter, each process is demonstrated in order.

<(1) Battery construction process>
In the battery construction process, the positive electrode, the negative electrode, and the non-aqueous electrolyte are housed in a battery case to construct a battery. As the positive electrode and the negative electrode, those already described above can be used.

  The non-aqueous electrolyte contains a sulfonic acid lithium salt and a vinylene carbonate compound in addition to the above-described non-aqueous solvent and supporting salt. As the constituent materials of these non-aqueous electrolytes, those described above can be used without particular limitation. A part of the vinylene carbonate compound and the lithium sulfonic acid salt can be decomposed in a charge treatment step (initial charge step) described later to form a film on the surface of the negative electrode active material and / or the positive electrode active material. Further, a part of the lithium sulfonate (and the component derived from the lithium sulfonate) is incorporated into the SEI coating derived from the vinylene carbonate compound.

The amount of vinylene carbonate compound added to the non-aqueous electrolyte may vary depending on, for example, the composition of the non-aqueous electrolyte, the type and properties of the negative electrode active material (for example, particle size and specific surface area), and the like. In general, if the amount added is too small, the formation efficiency of the film is lowered, and the SEI film formed on the surface of the negative electrode active material tends to be thin (the amount of film formation is reduced). For this reason, when the density | concentration of the vinylene carbonate compound in a non-aqueous electrolyte is too low, there exists a possibility that durability (for example, cycling characteristics, storage characteristics, etc.) of a battery may fall. On the other hand, when there is too much such addition amount, the formation amount of the SEI film formed on the negative electrode active material surface will become excessive, and there exists a possibility that the resistance accompanying charging / discharging may increase. Therefore, in a preferred embodiment, the amount of vinylene carbonate compound added to the non-aqueous electrolyte is 0.7% by mass or more (preferably 1.0% by mass) with respect to 100% by mass of the non-aqueous electrolyte. It is preferable to adjust the ratio to 1.8% by mass or less (preferably 1.5% by mass or less). Or you may adjust the addition amount of the vinylene carbonate compound added in a non-aqueous electrolyte so that it may become 40 to 110 micromol per unit surface area (1m < ² >) of a negative electrode active material.

  The amount of lithium sulfonate added in the non-aqueous electrolyte may vary depending on, for example, the composition of the non-aqueous electrolyte, the type and properties of the active material (for example, particle size and specific surface area), and the like. In general, if the amount added is too small, the content of the component derived from the lithium sulfonate salt contained in the SEI coating derived from the vinylene carbonate compound decreases, and the lithium sulfonate formed on the surface of the positive and negative electrodes There is a tendency that the amount of the film derived from the salt is lowered. Thereby, there is a possibility that the effect of increasing the charge carrier concentration on the negative electrode surface and the effect of suppressing the approach of anions (typically fluorine anions) cannot be sufficiently exhibited. On the other hand, when there is too much such addition amount, content of the component derived from lithium sulfonate contained in the SEI film derived from a vinylene carbonate compound will become excessive, and there exists a possibility that durability of this SEI film may fall. In addition, the amount of the coating derived from the lithium sulfonate salt formed on the surface of the positive and negative electrode active materials becomes excessive, and there is a concern that the resistance accompanying charge / discharge increases. Therefore, in a preferred embodiment, the amount of the sulfonic acid lithium salt added to the non-aqueous electrolyte is 0.75% by mass or more (preferably 1.0% by mass) with respect to 100% by mass of the non-aqueous electrolyte. % Or more) is preferably adjusted to a ratio of 2.0% by mass or less (preferably 1.5% by mass or less).

Furthermore, from the viewpoint of incorporating (incorporating) a suitable amount of a component derived from a lithium sulfonate into the film derived from the vinylene carbonate compound, the concentration (% by mass) of the vinylene carbonate compound in the nonaqueous electrolytic solution is nonaqueous. Vinylene carbonate so that the concentration (mass%) of the sulfonic acid lithium salt in the electrolytic solution is 0.5 times or more (preferably 0.7 times or more) and 1.8 times or less (preferably 1.5 times or less). It is preferable to adjust the addition amount of the compound and the addition amount of the lithium sulfonate. In other words, the ratio (C _a / C _b ) between the concentration C _a (% by mass) of the vinylene carbonate compound in the non-aqueous electrolyte and the concentration C _b (% by mass) of the lithium sulfonate in the non-aqueous electrolyte. Of vinylene carbonate compound added to the non-aqueous electrolyte so as to satisfy 0.5 ≦ C _a / C _b ≦ 2.0 (preferably 0.7 ≦ C _a / C _b ≦ 1.5) It is preferable to adjust the amount and the addition amount of the sulfonic acid lithium salt.

<(2) Charging process>
In the charging process, a charging process for applying a current between the positive electrode and the negative electrode is performed. This charging process is performed so that the potential of the negative electrode (vs. Li / Li ⁺ ) is equal to or lower than the reduction potential of the lithium sulfonate and vinylene carbonate compound contained in the non-aqueous electrolyte. In a preferred embodiment, the charge treatment is carried out until 0.05 V or more (typically 0.1 V or more, such as 0.3 V or more, particularly 0.5 V) lower than the reduction potential of these compounds contained in the electrolytic solution. I do. For example, the voltage between the positive and negative terminals (typically the highest voltage reached) in the charging process varies slightly depending on the type of lithium sulfonic acid salt or vinylene carbonate compound used, etc., but is about 3.95V to 4.05V. It can be.

  The charging process may be performed by, for example, a method of charging with a constant current (CC charging) from the start of charging until the negative electrode potential reaches a predetermined value (or until the negative electrode terminal voltage reaches a predetermined value), After charging with a constant current until the predetermined potential (or voltage) is reached, charging may be performed with a constant voltage (CCCV charging). The charging rate in CC charging is not particularly limited, but if it is too low, the processing efficiency tends to decrease. On the other hand, if it is too high, the quality of the formed film may be lowered, or the active material may be deteriorated. For this reason, it is preferable to set it as 0.1C-2C (typically 0.5C-1.5C, for example, 0.6C-1C), for example. As a result, it is possible to accurately form a film having a suitable denseness (that is, a low resistance and capable of sufficiently suppressing the reaction with the non-aqueous electrolyte) in a shorter time. This is also preferable from the viewpoint of work efficiency. “1C” means the amount of current that can charge the battery capacity (Ah) predicted from the theoretical capacity of the positive electrode in one hour.

  In a preferred aspect, the charging process is performed by a CCCV charging method. This makes it possible to form a suitable amount of a film having a suitable aspect on the positive and negative electrode surfaces. The time for performing CV charging (the time for holding at the above-mentioned potential or voltage) is not particularly limited, but if it is too short, the formation of the film may be insufficient or uneven, and charge / discharge efficiency and cycle characteristics may be reduced. obtain. On the other hand, if the length is too long, workability may be reduced, or depending on conditions or the like, the formation of a film may proceed too much, and the internal resistance (for example, initial resistance) of the battery may increase. Therefore, it is preferable to perform a simple preliminary experiment each time the battery components or the charging process conditions are changed, and to determine the result from the result. Alternatively, a suitable amount of a coating film is formed on the surface of the positive electrode active material by CC charging until reaching the predetermined potential (or voltage) and then aging for a certain period of time. Can do.

  In addition, the said charge process may be performed once, for example, can also be repeatedly performed twice or more on both sides of a discharge process process. Furthermore, other operations (for example, pressure load or ultrasonic irradiation) that can promote the reductive decomposition of the above compound can be used in combination as long as the battery characteristics are not adversely affected.

  Although the battery disclosed here can be used for various applications, the effect of forming a film on the surface of the active material (the effect of reducing internal resistance, the effect of improving cycle characteristics, etc.) is suitably exhibited, and the battery characteristics are better than those of the prior art. It is characterized by superiority (for example, excellent input / output characteristics, high durability, etc.). Therefore, taking advantage of such properties, for example, it can be suitably used as a driving power source mounted on a vehicle. The type of vehicle is not particularly limited, and examples include plug-in hybrid vehicles (PHV), hybrid vehicles (HV), electric vehicles (EV), electric trucks, motorbikes, electric assist bicycles, electric wheelchairs, electric railways, and the like. . Therefore, according to the present invention, there is provided a vehicle provided with any of the lithium secondary batteries disclosed herein, preferably as a power source. The lithium secondary battery provided in the vehicle may be in the form of an assembled battery in which a plurality of lithium secondary batteries are connected.

  Several examples (test examples) relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the specific examples.

  First, lithium secondary batteries according to Examples 1 to 10 were constructed by the following materials and processes.

[Construction of lithium secondary battery]
First, LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCM) was prepared as a positive electrode active material powder. Such LNCM, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder have a mass ratio of these materials of LNCM: AB: PVdF = 93.55: 3.75: 2.70. Was added to a kneader and kneaded while adjusting the viscosity with N-methylpyrrolidone (NMP) to prepare a positive electrode active material slurry. A positive electrode sheet (Example 1 to Example 10) having a positive electrode active material layer on the positive electrode current collector is obtained by applying the slurry to both surfaces of an aluminum foil (positive electrode current collector) having a thickness of 12 μm and pressing the slurry after drying. Produced.

  Next, natural graphite (C) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a dispersant, the mass ratio of these materials is C: SBR: CMC = The mixture was charged into a kneader so that the ratio was 99: 0.5: 0.5, and kneaded while adjusting the viscosity with ion-exchanged water to prepare a negative electrode active material slurry. A negative electrode sheet (Example 1 to Example) having a negative electrode active material layer on the negative electrode current collector by applying this slurry to both sides of a long copper foil (negative electrode current collector) having a thickness of 8 μm and pressing after drying. 10) was produced.

  A separator having a three-layer structure in which polypropylene (PP) is laminated on both sides of polyethylene (PE) and having a porous heat resistant layer (HRL) on one side was prepared. This heat-resistant layer was prepared by dispersing boehmite as an inorganic filler and SBR as a binder in water so that the mass ratio of these materials was 96: 4 to prepare an inorganic filler layer forming composition. This inorganic filler layer forming composition was applied to the surface (one side) of the separator substrate and dried to form a heat-resistant layer having a thickness of 4 μm on the separator substrate. In this way, a separator having a total thickness (average total thickness) of 16 μm was produced.

  The positive electrode sheet and the negative electrode sheet prepared above were wound together with the two separator sheets prepared as described above, and formed into a flat shape to prepare an electrode body. Here, the separator was laminated with the positive and negative electrode sheets so that the HRL layer was in the direction facing the positive electrode active material layer.

  Next, the positive electrode terminal and the negative electrode terminal were attached to the lid of the battery case, and these terminals were welded to the positive electrode current collector and the negative electrode current collector exposed at the ends of the wound electrode body, respectively. The wound electrode body thus connected to the lid body was housed inside the battery case from the opening, and the opening and the lid were welded.

And the non-aqueous electrolyte was inject | poured from the electrolyte solution injection hole provided in the said cover body, and the said electrolyte solution injection hole was sealed airtightly. As a non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC: DMC: EMC = 30: 40: 30 is used as a supporting salt. In which LiPF ₆ was dissolved at a concentration of 1.1 mol / L, and cyclohexylbenzene (CHB) and biphenyl (BP) as gas generating agents, lithium sulfonate, and a vinylene carbonate compound were contained. Using. Here, lithium ethoxysulfonate was used as the lithium sulfonate salt, and vinylene carbonate (VC) was used as the vinylene carbonate compound.
The lithium ethoxysulfonate is added in such a manner that the concentration of lithium ethoxysulfonate in the non-aqueous electrolyte is the concentration shown in the column of “LS concentration (% by mass)” in Table 1 with respect to 100% by mass of the non-aqueous electrolyte. I went to be. Further, the addition of the above-mentioned vinylene carbonate is such that the concentration of vinylene carbonate in the non-aqueous electrolyte becomes the concentration shown in the column of “VC concentration (% by mass)” in Table 1 with respect to 100% by mass of the non-aqueous electrolyte. went. At this time, the concentration ratio (C _a / C _b ) between the concentration C _a (mass%) of the vinylene carbonate compound in the non-aqueous electrolyte and the concentration C _b (mass%) of the sulfonic acid lithium salt in the non-aqueous electrolyte. Was calculated. This concentration ratio is shown in the column “Concentration ratio (C _a / C _b )” in Table 1. The CHB was added so that the CHB concentration in the non-aqueous electrolyte was 4% by mass with respect to 100% by mass of the non-aqueous electrolyte. The BP was added so that the BP concentration in the non-aqueous electrolyte was 1% by mass with respect to 100% by mass of the non-aqueous electrolyte.
In this way, battery assemblies according to Examples 1 to 10 were constructed.

About the battery assembly which concerns on Examples 1-10 constructed | assembled as mentioned above, the charging process (initial charge) and the aging process were performed, and the battery which concerns on each example was constructed | assembled. Specifically, as a charging process (initial charging process), a constant current charge (until the voltage between positive and negative terminals reaches 3.95 V at a charging rate (constant current) of 1 C in a temperature environment of 25 ° C. After performing (CC charge), constant voltage charge (CV charge) was performed until the current value reached 0.02C. And as an aging process, each battery after the said charge process was left to stand for 24 hours in a 60 degreeC temperature environment (typically in the thermostat adjusted to 60 degreeC).
In this way, lithium secondary batteries according to Examples 1 to 10 were constructed for battery characteristic evaluation and film analysis, respectively.

[Measurement of initial battery capacity (rated capacity)]
About the battery after the said aging process, the rated capacity was measured according to the following procedures 1-3 at the temperature of 25 degreeC and the voltage range of 3.0V to 4.1V.
(Procedure 1) After reaching 3.0 V by constant current discharge of 0.1 C, discharge at constant voltage discharge for 2 hours, and then rest for 10 minutes.
(Procedure 2) After reaching 4.1 V by constant current charging of 0.1 C, constant voltage charging is performed until the current becomes 1/100 C, and then rested for 10 minutes.
(Procedure 3) After reaching 3.0 V by constant current discharge of 0.1 C, constant voltage discharge until the current becomes 1/100 C, and then rest for 10 minutes.
And the discharge capacity (CCCV discharge capacity) in the discharge from the constant current discharge in the procedure 3 to the constant voltage discharge was made into the initial stage battery capacity.

[Measurement of initial resistance (IV resistance)]
Next, the initial resistance (IV resistance) of each battery constructed as described above was measured. First, CC charge was performed until SOC (State of Charge: charge state) reached 60%. Next, under a temperature condition of −10 ° C., each battery adjusted to 60% SOC was subjected to CC charging for 10 seconds at a discharge rate of 10 C, and a voltage increase value (V) was measured. Then, the IV resistance (mΩ) is calculated by dividing the measured voltage rise value (V) by the corresponding current value (typically the primary value of the plot value of current (I) −voltage (V)). The IV resistance (mΩ) was calculated from the slope of the approximate line), and the average value was taken as the initial resistance. The results are shown in the column of “Initial IV resistance” in Table 1.

[High temperature storage durability test]
Next, CC charge was performed until the SOC reached 85%. Each battery adjusted to SOC 85% was left (stored) for about 4800 hours (200 days) under a temperature environment of 60 ° C. (here, in a thermostatic chamber adjusted to 60 ° C.). And each battery after completion | finish of this high temperature storage durability test was taken out from the thermostat, and the battery capacity and IV resistance after a high temperature storage durability test were measured by the method similar to the said initial stage capacity | capacitance measurement and the said initial stage IV resistance measurement. Regarding the IV resistance after the high temperature storage durability test, the measurement results of each battery are shown in the column of “IV resistance after durability (mΩ)” in Table 1.
Subsequently, the capacity maintenance ratio (%) was calculated from the following formula: capacity maintenance ratio (%) = battery capacity after high-temperature storage durability test ÷ initial battery capacity × 100. The results are shown in the column “Capacity maintenance ratio (%)” in Table 1. Further, the resistance increase rate (%) was calculated from the following formula: resistance increase rate (%) = IV resistance after high-temperature storage durability test ÷ initial IV resistance × 100; The results are shown in the column of “resistance increase rate (%)” in Table 1.

[Coating analysis]
In addition, each separately prepared battery (the battery after aging treatment) was subjected to CC-CV discharge until the potential between the positive and negative terminals was 3 V (SOC 0%), and then disassembled to take out the electrode and the non-aqueous electrolyte. The coating was analyzed.

The coating amount derived from lithium sulfonate (μmol / m ² ) was measured by the following method. Specifically, first, each battery after the aging treatment was disassembled in a glove box, and the positive electrode and the negative electrode were taken out. Next, the positive electrode and the negative electrode were immersed in EMC using a non-aqueous electrolyte solution for about 10 minutes, and then each 10 sheets were cut out at an appropriate size (here, Φ40 mm). Then, the cut out positive electrode and negative electrode (sample for IC measurement) were immersed in a 50% acetonitrile (CH ₃ CN) aqueous solution for about 10 minutes to form a coating component derived from lithium sulfonate (component derived from lithium sulfonate) ) Was extracted. Next, this solution is quantitatively analyzed by IC, and the content (μmol) of ions to be measured (for example, SO ₂ ²⁻ , SO ₃ ²⁻ , SO ₄ ²⁻ ) is quantified from the obtained results. The total amount of each ion (μmol) is divided by the area (cm ² ) of the negative electrode active material layer subjected to the measurement, whereby the amount of the coating derived from lithium sulfonate per unit area of the active material layer (Μmol / cm ² ) was quantified in terms of sulfonic acid group. As an analyzer, an ion chromatograph (ICS-3000) manufactured by Nippon Dionex Co., Ltd. was used. Then, the coating amount (μmol / cm ² ) derived from the lithium sulfonic acid salt per unit area of the obtained active material layer, the BET specific surface area (m ² / g) of the active material and the basis weight of the active material (g / g) By dividing by the product of cm ² ), the coating amount (μmol / m ² ) per unit surface area (1 m ² ) of the positive electrode active material and the negative electrode active material was calculated in terms of sulfonic acid group. The results are shown in the column of “LS coating amount (μmol / m ² )” in Table 1.

The amount of SEI coating derived from the vinylene carbonate compound (μmol / m ² ) was measured by the following method. Specifically, first, each battery after the aging treatment was disassembled in a glove box, and the non-aqueous electrolyte stored in the battery case was recovered. In addition, the surface of the electrode body (typically between the electrodes) and the surface of the member that can come into contact with the nonaqueous electrolyte solution such as in the battery case was washed with an appropriate solvent (for example, EMC), and the washing solution was recovered. The amount of the vinylene carbonate compound (μmol) contained in these solutions was quantified by quantitatively analyzing the non-aqueous electrolyte and the cleaning solution by gas chromatography (GC). The column used was HP-1 column (length 60 m, inner diameter 0.32 mm, film thickness 1.00 μm) manufactured by Agilent Technologies, and the detector was an FID detector (Flame Ionization Detector). . The temperature condition of the column is that the temperature of the column adjusted to 50 ° C. is increased to 110 ° C. at a rate of 5 ° C./min, held at 110 ° C. for 3 minutes, and then the rate of 20 ° C./min. The temperature was raised to 280 ° C. Note that a gas chromatograph (GC17A) manufactured by Shimadzu Corporation was used as the analyzer.
Then, the amount of the vinylene carbonate compound (μmol) determined above was subtracted from the amount (μmol) of the vinylene carbonate compound contained in the non-aqueous electrolyte used for the construction of the battery. The amount (decomposition amount) of the vinylene carbonate compound was calculated. The decomposition amount (μmol) of the vinylene carbonate compound is defined as the sum of the surface areas of the active material (total surface area) (m ² ), that is, the total mass (g) of the negative electrode active material used for forming the negative electrode active material layer and the negative electrode active material. By dividing the product by the product with the BET specific surface area (m ² / g) of the material, the amount of coating (μmol / m ² ) per unit surface area (1 m ² ) of the negative electrode active material is consumed for the vinylene consumed in the composition of the coating The coating amount was calculated in terms of carbonate compound. The results are shown in the column of “VC coating amount (μmol / m ² )” in Table 1.

Moreover, the ratio (molar ratio) of the component derived from the lithium sulfonic acid salt contained in the film derived from the vinylene carbonate compound was measured by the following method.
First, each battery after the aging treatment was disassembled in a glove box, and the negative electrode was taken out. Next, this negative electrode was immersed in EMC used as a non-aqueous electrolyte solution for about 10 minutes, and then 10 pieces each were cut out at an appropriate size (here, Φ40 mm). And the cut-out negative electrode (sample for ICP-AES measurement) was immersed in aqua regia for about 10 minutes, and the component derived from lithium sulfonate used as a measuring object was extracted in the solvent. Next, the amount (μmol) of total sulfonic acid groups (typically S element) present per unit area of the negative electrode active material layer was quantified by ICP-AES analysis of the solution. That is, the content of components derived from all lithium sulfonates present per unit area of the negative electrode active material layer was measured in terms of sulfonic acid groups (typically S elements). Note that an ICP-AES analyzer (ICPS-8100) manufactured by Shimadzu Corporation was used as the analyzer. Then, by dividing the element amount (μmol) of the component derived from the obtained lithium sulfonic acid salt by the area of the negative electrode (sample for ICP-AES measurement) used for the measurement, per unit area of the negative electrode active material layer The amount (μmol / m ² ) of the component derived from the total sulfonic acid lithium salt present in the sulfonic acid group was calculated.
Then, from the amount of components from whole acid lithium salt present per unit area of the negative electrode active material layer obtained ^{(1m 2) (μmol / m} 2), unit area of the negative electrode active material layer (1 m ²⁾ per The coating amount (μmol / m ² ) derived from lithium sulfonate was subtracted. Here, as the coating amount (μmol / m ² ) derived from lithium sulfonate per unit area (1 m ² ) of the negative electrode active material layer, the negative electrode active material was obtained by the method described above (the method described in paragraph 0110). coating amount of from lithium sulfonate of unit surface area (1 m ²⁾ per (μmol / m ²⁾ coating weight of from sulfonic acid lithium salt per unit area of the negative electrode active material layer which is calculated in the process of measuring ([mu] mol / Cm ² ) was converted to a coating amount per 1 m ² (μmol / m ² ).
Next, the amount (decomposition amount) of the vinylene carbonate compound consumed for the formation of the SEI film derived from the vinylene carbonate compound on the surface of the negative electrode active material, measured by the method as described above, Divided by (m ² ). Thereby, the coating amount (μmol / m ² ) derived from vinylene carbonate per unit area of the negative electrode active material layer was calculated in terms of the vinylene carbonate compound consumed for forming the coating.
And as above-mentioned, the film | membrane derived from the lithium sulfonate salt per unit area of a negative electrode active material layer from the quantity (micromol / m < ² >) of the component derived from the total lithium sulfonate salt which exists per unit area of a negative electrode active material layer. The amount (μmol / m ² ) of the component derived from lithium sulfonic acid salt obtained by reducing the amount (μmol / m ² ) is the amount of coating derived from the vinylene carbonate compound per unit area of the negative electrode active material layer (μmol / m ^By dividing by ² ), the ratio (molar ratio) of the lithium salt having a sulfonic acid skeleton contained in the coating derived from the vinylene carbonate compound was calculated. The results are shown in the column of “LS content ratio in VC coating” in Table 1.

First, Examples 1 to 9 using both a vinylene carbonate compound and a lithium sulfonic acid salt are compared with Example 10 using only a vinylene carbonate compound without using a lithium sulfonic acid salt.
As shown in Table 1, in Examples 1 to 9 according to the present invention, the initial resistance is as low as 4 mΩ or less (preferably 3.9 mΩ or less), and the resistance after the durability test is 4.5 mΩ or less (preferably 4 .2 mΩ or less). The resistance increase rate after the durability test was also kept low at 130% or less (preferably 129% or less). Furthermore, the capacity retention rate after the durability test was also higher than 85% (more specifically, 89% or more). The reason for this is that (1) copolymerization of the vinylene carbonate compound progressed during the charging process by using the vinylene carbonate compound, and a high-quality (low resistance and strong) SEI film was formed on the negative electrode. (2) By using the vinylene carbonate compound and the lithium sulfonate, the component derived from the lithium sulfonate is taken into the SEI film derived from the vinylene carbonate compound, and the concentration of the charge carrier on the surface of the negative electrode active material is increased. (3) By using a lithium sulfonate, a component derived from a lithium sulfonate (typically SO _X (where X = 2 to 4)) is contained on the negative electrode. Group), the concentration of the charge carrier on the surface of the negative electrode active material layer increased, and (4) the use of lithium sulfonate, (In SO X _(wherein typically, X = 2 to 4) S element-containing group represented by) component derived from lithium acid salt coating with is formed, approaching the fluorine anion is suppressed, the resistance component It can be considered that the amount of lithium fluoride produced has decreased.

On the other hand, in Example 10 using only the vinylene carbonate compound, the initial resistance was high (initial characteristics were inferior). The reason for this is that the component derived from the lithium sulfonate salt was not incorporated into the coating derived from the vinylene carbonate compound, and the coating derived from the lithium sulfonate salt (typically SO _X (where, It is considered that the effect of increasing the charge carrier concentration on the surface of the negative electrode active material was not exhibited because the film having the S element-containing group represented by X = 2 to 4) was not formed. Further, in Example 10, the resistance after the durability test showed a high value, and the resistance increase rate was large. In Example 10, the capacity retention rate after the durability test was low. The reason for this is thought to be that lithium fluoride (resistance component) increased because the approach of the fluorine anion could not be suppressed because the coating having the S element-containing group was not formed on the positive electrode surface.
This result shows the technical significance of the present invention.

Further, as shown in Table 1, Examples 1 to 9 according to the present invention, the concentration of the concentration C _{a (wt%)} and acid lithium salt of vinylene carbonate compound in the nonaqueous electrolytic solution C _{b (wt%)} The ratio (C _a / C _b ) was in the range of 0.5 ≦ C _a / C _b ≦ 1.8. That is, the amount of vinylene carbonate compound added to the non-aqueous electrolyte and the lithium sulfonate so that the above ratio (C _a / C _b ) satisfies 0.5 ≦ C _a / C _b ≦ 1.8. It was confirmed that the effects of the present invention can be suitably exerted by adjusting the amount of addition.
This is because (1) when the C _a / C _b increases, the content ratio (molar ratio) of the component derived from lithium sulfonate contained in the SEI film derived from the vinylene carbonate compound tends to decrease. If the C _a / C _b is too large, the effect of increasing the charge carrier concentration on the negative electrode active material surface may not be sufficiently exhibited. (2) If the C _a / C _b is small, the vinylene carbonate compound is derived. Since the content ratio (molar ratio) of the component derived from the lithium sulfonate contained in the SEI coating tends to increase, if the C _a / C _b is too small, the strength of the SEI coating derived from the vinylene carbonate compound decreases. However, it is conceivable that the durability characteristics may deteriorate.
Especially, from the test results on the initial characteristics and the high-temperature storage durability characteristics of Examples 1 to 5, 7, and 9, the non-aqueous Ca / Cb satisfies the range of 0.7 ≦ C _a / C _b ≦ 1.5. It was confirmed that both the initial characteristics and the durability characteristics can be realized at a higher level by using the electrolytic solution. Here, in Examples 1 to 5, 7, and 9, the initial resistance is 3.6 mΩ or less, the capacity retention rate after the durability test is 90% or more (for example, 91% or more), and the resistance after the durability test is 4 The resistance increase rate after the durability test was 123% or less.

Moreover, as shown in Table 1, in Examples 1 to 9 according to the present invention, the amount of vinylene carbonate compound added to the non-aqueous electrolyte was 0.7% by mass or more and 1.8% by mass or less. . That is, it was confirmed that the effects of the present invention can be suitably achieved by adjusting the amount of the vinylene carbonate compound to be within the above range.
As this reason, the following can be considered, for example. When the amount of the vinylene carbonate compound added is too large, the amount of SEI coating derived from the compound formed on the negative electrode active material increases (the coating becomes thicker), and the occlusion and release of lithium ions are hindered. It is conceivable that the resistance and resistance after the durability test (that is, the absolute value of the resistance) may increase. On the other hand, if the amount of the vinylene carbonate compound added is too small, a sufficient amount of SEI film cannot be formed on the negative electrode active material, and the nonaqueous electrolytic solution is reduced and decomposed, resulting in decreased durability characteristics (capacity maintenance). It is conceivable that there are cases where the rate decreases, the resistance increases after the durability test, and the resistance increases after the durability test.
Among them, Examples 1 to 3 in which the concentration of the vinylene carbonate compound in the nonaqueous electrolytic solution is 1.0% by mass or more and 1.5% by mass or less are more initial characteristics and high temperature storage durability characteristics than Examples 7 and 8. None of them were excellent. In Examples 1 to 3, 7 and 8, the addition amount of the lithium sulfonate added to the non-aqueous electrolyte is the same and the addition amount of the vinylene carbonate compound is different. That is, it was confirmed that both the initial characteristics and the durability characteristics can be realized at a higher level by adjusting the addition amount of the vinylene carbonate compound to a range of 1.0 mass% to 1.5 mass%.

Moreover, as shown in Table 1, in Examples 1 to 9 according to the present invention, the addition amount of the sulfonic acid lithium salt added to the nonaqueous electrolytic solution was 0.75 mass% or more and 2 mass% or less. That is, it was confirmed that the effects of the present invention can be suitably achieved by adjusting the amount of lithium sulfonate added within the above range.
As this reason, the following reasons can be considered, for example. If the amount of the lithium sulfonate added is too large, the proportion of the lithium salt contained in the SEI coating derived from the vinylene carbonate compound will increase, and the strength of the SEI coating derived from the vinylene carbonate compound will decrease, resulting in durability characteristics. May decrease (decrease in capacity retention rate, increase in resistance after endurance test, increase in resistance increase rate after endurance test). On the other hand, when the amount of the sulfonic acid lithium salt added is too small, the proportion of the lithium salt-derived component contained in the SEI film derived from the vinylene carbonate compound decreases, and the charge carrier concentration on the negative electrode active material surface increases. It is possible that the effect may not be fully exhibited.
Among them, Examples 1, 3, and 4 in which the concentration of the lithium sulfonate in the non-aqueous electrolyte solution is 1.0% by mass or more and 1.5% by mass or less are higher in initial characteristics and higher temperature than Examples 6 and 9. All of the storage durability characteristics were excellent. Examples 1, 3, 4, 6, and 9 have the same amount of vinylene carbonate compound added to the non-aqueous electrolyte and different amounts of lithium sulfonate. That is, it was confirmed that both the initial characteristics and the durability characteristics can be realized at a higher level by adjusting the addition amount of the lithium sulfonic acid salt to a range of 1.0 mass% to 1.5 mass%. .

As shown in Table 1, in Examples 1 to 9, the surface of the negative electrode active material had a SEI coating derived from a vinylene carbonate compound, and the amount of the coating formed was determined by the unit surface area (1 m ^{2 of the} negative active material). ) In terms of vinylene carbonate compound consumed for forming the coating film, it was 25 μmol to 65 μmol (preferably 27 μmol to 64 μmol). In addition, in the SEI coating derived from the vinylene carbonate compound, 0.05 to 0.15 mol of a sulfonic acid lithium salt-derived component in terms of sulfonic acid group was contained per 1 mol of the vinylene carbonate compound constituting the coating. . That is, the amount of the SEI coating derived from the vinylene carbonate compound formed on the surface of the negative electrode active material and the content of the component derived from the lithium sulfonate salt contained in the SEI coating are within the above ranges. It was confirmed that the effect can be suitably exerted.
In particular, Examples 1 to 5 were superior to Examples 6 to 9 in both initial characteristics and high-temperature storage durability characteristics. In Examples 1 to 5, the amount of the SEI coating derived from the vinylene carbonate compound formed on the negative electrode surface was 30 μmol in terms of the vinylene carbonate compound consumed for forming the coating per unit surface area (1 m ² ) of the negative electrode active material. The SEI coating derived from the vinylene carbonate compound contains 0.07 to 0.11 mol of a sulfonic acid lithium salt-derived component per 1 mol of the vinylene carbonate compound constituting the coating. It was confirmed. From this, it is preferable to make the formation amount of the SEI coating derived from the vinylene carbonate compound formed on the surface of the negative electrode active material and the content of the component derived from the lithium sulfonate contained in the coating within the above range. Furthermore, in Examples 1 to 5, the coating amount of the sulfonic acid lithium salt-derived coating formed on the negative electrode active material surface is 10 μmol to 20 μmol per unit surface area (1 m ² ) of the negative electrode active material in terms of sulfonic acid group. there were. From this, in addition to setting the amount of the coating derived from the vinylene carbonate compound formed on the surface of the negative electrode active material and the content of the component derived from the lithium sulfonate contained in the coating within the above range, Furthermore, it is preferable that the coating amount of the coating derived from lithium sulfonate formed on the surface of the negative electrode active material is within the above range.

In particular, Examples 1 to 4 were superior to Example 5 in both initial characteristics and high-temperature storage durability characteristics. Comparing the results of analyzing the film formed on the positive electrode for Examples 1 to 4 and Example 5, Example 1 to 4 shows that the film derived from the lithium sulfonate salt formed on the positive electrode active material is a positive electrode. It was confirmed that 10 μmol to 15 μmol were formed per unit surface area (1 m ² ) of the active material in terms of sulfonic acid group salt. If the amount of the coating derived from the lithium sulfonate salt formed on the surface of the positive electrode active material is too large, it is considered that the coating on the surface of the positive electrode active material becomes thick and the occlusion and release of lithium ions may be hindered. On the other hand, if the amount of the coating derived from the lithium sulfonate salt formed on the surface of the positive electrode active material is too small, the nonaqueous electrolyte solution is oxidatively decomposed on the surface of the positive electrode, and the amount of LiF generated may increase. It is done. For this reason, it is preferable that the amount of the coating derived from lithium sulfonic acid salt formed on the surface of the positive electrode active material is in the above range.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here.

20 Winding electrode body 30 Battery case 32 Battery case body 34 Cover body 36 Safety valve 42 Positive electrode terminal 42a Positive electrode current collector plate 44 Negative electrode terminal 44a Negative electrode current collector plate 50 Positive electrode (positive electrode sheet)
52 Positive Electrode Current Collector 52a Positive Electrode Active Material Layer Non-Forming Part 54 Positive Electrode Active Material Layer 60 Negative Electrode (Negative Electrode Sheet)
62 Negative electrode current collector 62a Negative electrode active material layer non-formed portion 64 Negative electrode active material layer 70 Separator sheet (separator)
100 Lithium secondary battery (lithium ion secondary battery)

Claims (8)

A lithium secondary battery in which a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte are housed in a battery case,
The non-aqueous electrolyte is a lithium secondary battery, which is a non-aqueous electrolyte containing a lithium salt having a sulfonic acid skeleton represented by the following formula (I) and a vinylene carbonate compound.

(Here, R ¹ is a linear or branched alkyl group having 1 to 12 carbon atoms.)   The lithium secondary battery according to claim 1, comprising lithium ethoxysulfonate as the lithium salt having a sulfonic acid skeleton.   The lithium secondary battery according to claim 1 or 2, comprising vinylene carbonate as the vinylene carbonate compound. On the surface of the negative electrode active material, a film derived from the vinylene carbonate compound is 27 μmol or more and 64 μmol or less per unit surface area (1 m ² ) of the negative electrode active material in terms of the vinylene carbonate compound consumed in the structure of the film. Formed in proportion,
The coating derived from the vinylene carbonate compound contains a component derived from a lithium salt having the sulfonic acid skeleton, and the content of the component derived from a lithium salt having a sulfonic acid skeleton contained in the coating is The lithium secondary battery according to any one of claims 1 to 3, wherein the amount is 0.04 mol or more and 0.15 mol or less in terms of sulfonic acid group per 1 mol of the vinylene carbonate compound consumed in the structure. A film derived from a lithium salt having a sulfonic acid skeleton is formed on the surface of the positive electrode active material at a rate of 8 μmol or more and 18 μmol or less per unit surface area (1 m ² ) of the positive electrode active material in terms of sulfonic acid group. The lithium secondary battery according to any one of claims 1 to 4. A method for manufacturing a lithium secondary battery, comprising:
Housing a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte in a battery case;
Here, as the non-aqueous electrolyte, a non-aqueous electrolyte containing a lithium salt having a sulfonic acid skeleton represented by the following formula (I) and a vinylene carbonate compound is used; and Performing an initial charging process so that a voltage between the positive electrode and the negative electrode becomes a predetermined value;
A method for manufacturing a lithium secondary battery.

(Here, R ¹ is a linear or branched alkyl group having 1 to 12 carbon atoms.) As the non-aqueous electrolyte, the concentration C _b (mass%) of the lithium salt having the sulfonic acid skeleton in the non-aqueous electrolyte, the concentration C _a (mass%) of the vinylene carbonate compound in the non-aqueous electrolyte, and The method for producing a lithium secondary battery according to claim 6, wherein a nonaqueous electrolytic solution having _a ratio (C _a / C _b ) of 0.5 to 1.8 is used. As the nonaqueous electrolytic solution, the concentration C _b of the lithium salt having a sulfonic acid skeleton is 2.0 mass% or more 0.75% by mass, and the concentration C _a 0.7 mass of the vinylene carbonate compound The method for producing a lithium secondary battery according to claim 6 or 7, wherein a non-aqueous electrolyte solution having a concentration of from 1% to 1.8% by mass is used.

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