JP6676305B2 - Negative electrode active material for non-aqueous electrolyte secondary battery, and negative electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery using the same - Google Patents

Description

  The present invention relates to a negative electrode active material for a non-aqueous electrolyte secondary battery, and a negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the same.

  Currently, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries used for mobile devices such as mobile phones have been commercialized. Non-aqueous electrolyte secondary batteries generally include a positive electrode in which a positive electrode active material or the like is applied to a current collector, and a negative electrode in which a negative electrode active material or the like is applied to a current collector. It is configured to be connected via an electrolyte layer holding an electrolyte gel. Then, ions such as lithium ions are occluded and released in the electrode active material, and a charge / discharge reaction of the battery occurs.

  By the way, in recent years, it has been required to reduce the amount of carbon dioxide to cope with global warming. Therefore, non-aqueous electrolyte secondary batteries having a low environmental load are being used not only for portable devices and the like but also for power supply devices for electric vehicles such as hybrid vehicles (HEV), electric vehicles (EV), and fuel cell vehicles. .

  Non-aqueous electrolyte secondary batteries intended for application to electric vehicles are required to have high output and high capacity. As the positive electrode active material used for the positive electrode of the nonaqueous electrolyte secondary battery for electric vehicles, a lithium composite oxide which is a layered composite oxide can obtain a high voltage and has a high energy density, It is already widely used. On the other hand, as the negative electrode active material used for the negative electrode, a material containing carbon such as natural graphite is widely used because of its high capacity and excellent durability. Here, in the lithium ion secondary battery, when the battery is repeatedly charged and discharged, the nonaqueous solvent in the electrolyte is electrochemically decomposed by reacting with the negative electrode active material, and the decomposed product generated at that time is used as the negative electrode active material. The SEI (Solid Electrolyte Interface) film is deposited on the surface of the substance. Thereby, the chemical stability of the negative electrode is ensured.

  However, gas is generated as a by-product during the SEI film formation. When gas is generated, the outer package of the battery expands in the flat laminate type battery, and the thickness of the battery increases. In addition, since the distance between the electrodes is also increased, there is a problem that the reaction between the electrodes becomes difficult to progress and the capacity is deteriorated. For this reason, it is necessary to design a battery in which the volume of generated gas is secured in advance in anticipation of battery swelling, so that a limited battery volume cannot be effectively used as a volume for packing the active material. Has become.

  In addition, when the battery is stored at a high temperature, there is a problem that the SEI film is likely to be deteriorated, and the negative electrode and the electrolyte react at the deteriorated portion to generate more gas. Since the amount of generated gas is greatly affected by the stability of the SEI film, many studies have been made to form a good SEI film.

  For example, Patent Document 1 discloses that after natural graphite is subjected to an acid treatment with concentrated sulfuric acid or the like, the amount of surface functional groups is adjusted by performing a heat treatment at 100 to 600 ° C., thereby forming a good SEI film. A technique for reducing the amount of generated gas and reducing the irreversible capacity has been disclosed.

JP 2010-219036 A

  According to the study of the present inventors, it has been found that even with the technique described in Patent Document 1, the amount of generated gas (and eventually the swelling of the battery) cannot be sufficiently suppressed. It has also been found that there is still room for improvement in terms of long-term cycle durability such as 1000 cycles.

  Therefore, the present invention provides a negative electrode active material for a non-aqueous electrolyte secondary battery containing carbon as a main component, which suppresses gas generation accompanying the progress of charging and discharging and swelling of the battery due to this, and has a long cycle durability of 1000 cycles. It is an object of the present invention to provide means capable of improving the performance.

The present inventors have intensively studied to solve the above problems. As a result, in the negative electrode active material for a non-aqueous electrolyte secondary battery containing carbon as a main component, the R value (R _A ) obtained by Raman spectroscopy and the charge / discharge of 1000 cycles using the active material were performed. The initial desorbed carbon dioxide molecule measured so that the R value (R _B ) of the sample satisfies a predetermined relationship, or measured by a temperature-programmed desorption gas analysis (TDS) at a temperature rise from 50 ° C. to 400 ° C. By controlling the (CO ₂ ) number to be a value within a predetermined range and the R value obtained by Raman spectroscopy to be a value within the predetermined range, a non-water solution that can solve the above problem They have found that a negative electrode active material for an electrolyte secondary battery can be provided, and have completed the present invention.

That is, according to one embodiment of the present invention, a negative electrode active material for a nonaqueous electrolyte secondary battery containing carbon as a main component, the R value (R _A ) obtained by Raman spectroscopy, and the use of the active material The value of R (R _B ) after 1000 cycles of charging and discharging is related to the following:

A negative electrode active material for a non-aqueous electrolyte secondary battery, characterized in that:

According to another aspect of the present invention, there is provided a negative electrode active material for a non-aqueous electrolyte secondary battery containing carbon as a main component, wherein the temperature-dependent desorption gas analysis (TDS) at a temperature rise from 50 ° C. to 400 ° C. ), The initial number of desorbed carbon dioxide molecules (CO ₂ ) is 1.5 to 3.1 × 10 ¹⁵ [pieces / 2 mg], and the R value obtained by Raman spectroscopy is 0. A negative electrode active material for a non-aqueous electrolyte secondary battery, wherein the negative electrode active material has a particle diameter of 41 to 0.45.

Further, according to still another aspect of the present invention, there is provided a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery containing carbon as a main component, the method comprising heat-treating an active material precursor, The initial number of desorbed carbon dioxide molecules (CO ₂ ) measured before and after the temperature rise desorption gas analysis (TDS) at a temperature increase from 50 ° C. to 400 ° C. was N ₁ (before heat treatment) and N ₁ , respectively. ₂ (after heat treatment)
Assuming that R values before and after the heat treatment determined by Raman spectroscopy are R ₁ (before heat treatment) and R ₂ (after heat treatment), respectively, the following relationship:

A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, characterized by satisfying the following.

  In the negative electrode active material according to the present invention, adsorbed substances and functional groups on the surface of the negative electrode active material are sufficiently removed, and the crystallinity of carbon as a main component is controlled to a certain low level. As a result, a side reaction between the adsorbed material or functional group on the surface and the electrolytic solution is suppressed, and gas generation accompanying the progress of charge and discharge and swelling of the battery due to the gas generation can be suppressed. Further, the SEI film can be formed uniformly, and the long-term cycle durability such as 1000 cycles can be improved.

FIG. 2 is a schematic cross-sectional view schematically illustrating an outline of a nonaqueous electrolyte secondary battery that is an embodiment of the battery of the present invention, and is a schematic cross-sectional view along the line AA shown in FIG. 2 described below. FIG. 1 is a perspective view showing the appearance of a flat nonaqueous electrolyte secondary battery which is a typical embodiment of the battery of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. In addition, the dimensional ratios in the drawings are exaggerated for convenience of description, and may be different from the actual ratios.

According to one embodiment of the present invention, a negative electrode active material for a non-aqueous electrolyte secondary battery containing carbon as a main component, the R value (R _A ) obtained by Raman spectroscopy, and 1000 times using the active material The R value (R _B ) after the charge and discharge of a cycle is related to the following relationship:

And a negative electrode active material for a non-aqueous electrolyte secondary battery (hereinafter, also referred to as a “first negative electrode active material”). According to another aspect of the present invention, there is provided a negative electrode active material for a non-aqueous electrolyte secondary battery containing carbon as a main component, wherein the temperature-dependent desorption gas analysis (TDS) at a temperature rise from 50 ° C. to 400 ° C. ), The initial number of desorbed carbon dioxide molecules (CO ₂ ) is 1.5 to 3.1 × 10 ¹⁵ [pieces / 2 mg], and the R value obtained by Raman spectroscopy is 0. A negative electrode active material for a nonaqueous electrolyte secondary battery (hereinafter, also referred to as a “second negative electrode active material”), which is 41 to 0.45, is provided.

  As described above, in the present invention, first, the negative electrode active material is provided. When the negative electrode active material is included in the negative electrode active material layer on the surface of the current collector, the current collector and the negative electrode active material layer form a negative electrode. The negative electrode constitutes a power generating element together with a positive electrode in which a positive electrode active material layer is formed on the surface of a current collector and an electrolyte layer, and is a main component of a nonaqueous electrolyte secondary battery. Hereinafter, the negative electrode active material according to the embodiment will be described.

[Negative electrode active material]
The negative electrode active material (first negative electrode active material and second negative electrode active material) according to the present invention contains carbon as a main component. Here, that the negative electrode active material is “having carbon as a main component” means that the ratio of carbon atoms in the negative electrode active material is 50% by mass or more, and this ratio is preferably 70% by mass or more. And more preferably 90% by mass or more, and still more preferably 95% by mass or more.

In the first negative electrode active material, the R value (R _A ) obtained by Raman spectroscopy and the R value (R _B ) after 1000 cycles of charge / discharge using the active material have the following relationship. :

The feature is that it satisfies.

Here, the R value obtained by Raman spectroscopy is the peak intensity in the 1360 cm ^-1 (G band) region relative to the peak intensity in the 1580 cm ^-1 (G band) region in the Raman spectrum of carbon as the main component of the negative electrode active material. Ratio (R = I1360 / I1580). The absorption in the D band region in the Raman spectrum of carbon is due to the turbulent layer structure, and the absorption in the G band region is due to the graphite crystal structure. That is, the higher the crystallinity of the surface (the closer to the crystalline carbon), the stronger the absorption in the G band region, and the greater the degree of amorphousness, the stronger the absorption in the D band region.

According to a first negative electrode active material, by the R _A and R _B as described above satisfies the above relationship, while suppressing the expansion of the battery due to gas generation and this with the progress of charge and discharge, 1000 cycles It is also possible to improve the long-term cycle durability. The mechanism that achieves such an effect is presumed as follows. That is, the adsorbate and the functional group on the surface of the negative electrode active material are sufficiently removed, and the crystallinity of carbon as the main component is controlled to a certain low level. As a result, a side reaction between the adsorbed material or functional group on the surface and the electrolytic solution is suppressed, and gas generation accompanying the progress of charge and discharge and swelling of the battery due to the gas generation can be suppressed. Further, it is considered that the SEI film can be formed uniformly and the long-term cycle durability such as 1000 cycles can be improved.

The method for measuring the R value is not particularly limited. However, when the measured value varies depending on the measurement method, a Raman spectrum is detected using a known laser Raman spectrometer using an argon laser, and peaks at 1360 cm ⁻¹ (D band) and 1580 cm ⁻¹ (G band) are detected. Respectively, and calculating the peak intensity ratio (I1360 / I1580) to obtain the R value.

As described above, the first negative electrode active material has an R value (R _A ) determined by Raman spectroscopy, and an R value (R _B ) after 1000 cycles of charge and discharge using the active material. Satisfy the above-mentioned predetermined relationship. Here, the charge-discharge conditions for the "1000 cycles of the charge and discharge" for determining the R _B is, be as described in the column of Examples described later.

First negative electrode active material satisfies the value of the _"R B / _{R A} × 100" is from 87.5 to 92.7. This value is preferably from 90.5 to 92.7, and more preferably from 91.0 to 92.7. In these preferred ranges, the swelling and long-term cycle durability of the battery can be further improved.

Subsequently, the second negative electrode active material has an initial number of desorbed carbon dioxide molecules (CO ₂ ) of 1. as measured by temperature-programmed desorption gas analysis (TDS) at a temperature rise from 50 ° C. to 400 ° C. It is characterized in that it is 5 to 3.1 × 10 ¹⁵ [pieces / 2 mg] and the R value obtained by Raman spectroscopy is 0.41 to 0.45.

Here, the method of obtaining the R value by Raman spectroscopy is as described above for the first negative electrode active material. The method for determining the initial number of desorbed carbon dioxide molecules (CO ₂ ) by temperature-programmed desorption gas analysis (TDS) at a temperature rise from 50 ° C. to 400 ° C. is as described in the Examples section described later. I do.

In the second negative electrode active material, it is essential that the initial number of desorbed carbon dioxide molecules (CO ₂ ) is 1.5 to 3.1 × 10 ¹⁵ [pieces / 2 mg], but this value is preferable. Is 1.5 to 2.4 × 10 ¹⁵ [pieces / 2 mg], and more preferably 1.5 to 1.6 × 10 ¹⁵ [pieces / 2 mg]. Further, in the second negative electrode active material, it is essential that the R value obtained by Raman spectroscopy is 0.41 to 0.45, and this value is preferably 0.41 to 0.44. , More preferably 0.41 to 0.42. From the above, in a preferred embodiment of the second negative electrode active material, the number of desorbed carbon dioxide molecules is 1.5 to 2.4 × 10 ¹⁵ [pieces / 2 mg], and R determined by Raman spectroscopy. The value is between 0.41 and 0.44. In a more preferred embodiment of the second negative electrode active material, the number of desorbed carbon dioxide molecules is 1.5 to 1.6 × 10 ¹⁵ [particles / 2 mg], and R determined by Raman spectroscopy. The values are between 0.41 and 0.42. In these preferred ranges, the swelling and long-term cycle durability of the battery can be further improved.

Although there is no particular limitation on the method for producing the first and second negative electrode active materials, according to still another embodiment of the present invention, a preferable method for producing the first and second negative electrode active materials is provided. You. The production method is a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery containing carbon as a main component, and includes heat-treating an active material precursor. Then, the manufacturing method includes measuring an initial number of desorbed carbon dioxide molecules (CO ₂ ) measured by a thermal desorption spectroscopy (TDS) at a temperature rise from 50 ° C. to 400 ° C. before and after the heat treatment. Where N ₁ (before heat treatment) and N ₂ (after heat treatment), respectively, and R values obtained by Raman spectroscopy before and after the heat treatment are R ₁ (before heat treatment) and R ₂ (after heat treatment), respectively. The following relationship:

The feature is that it satisfies. The negative electrode active material thus manufactured can improve long-term cycle durability such as 1000 cycles while suppressing gas generation due to progress of charging and discharging and swelling of the battery due to the gas generation.

  The carbon material used as a raw material of the negative electrode active material is not particularly limited. For example, carbon particles containing, as a main component, artificial or natural graphite having a graphite structure can be used as a raw material carbon material.

  Amorphous carbon particles can also be used as the raw carbon particles. As the amorphous carbon particles, carbon black, a 5-membered or 6-membered cyclic hydrocarbon compound or an oxygen-containing cyclic organic compound synthesized by thermal decomposition can be used.

  The shape of the carbon particles as the raw material is preferably spherical, massive, or flat spherical. The average particle diameter (D50) of the carbon particles is preferably in the range of 1 to 50 μm, more preferably in the range of 2 to 30 μm, and even more preferably in the range of 5 to 25 μm. The preferred form of the average particle size value similarly applies to the average particle size values of the first and second negative electrode active materials.

  The shape of the raw carbon particles may be a shape having a large aspect ratio, such as a flake shape or a fibrous shape. However, even if such carbon particles are used as a raw material, the aspect ratio of the produced negative electrode active material is preferably in the range of 1 to 5, and more preferably in the range of 1 to 3. The c-axis length Lc of the raw carbon particles may be within a range that satisfies the above aspect ratio. When the aspect ratio exceeds the above range, the ratio of large amorphous particles increases. Since the filling property of the negative electrode active material using such carbon particles as a raw material is low, the density of the negative electrode tends to be difficult to increase, and a high energy density cannot be obtained, which is not preferable.

  The method for measuring the average particle size of the carbon particles is not particularly limited. For example, it can be measured using a particle size distribution measuring device (for example, Microtrack) using laser scattering.

The production method according to this embodiment includes using the above-described raw material such as carbon particles as an active material precursor and heat-treating the same. There is no particular limitation on the specific form of the heat treatment, and the heat treatment may be controlled so that the values of “N ₂ / N ₁ × 100” and “R ₂ / R ₁ × 100” fall within the above-mentioned predetermined ranges. Where these values have the following relationship:

Preferably, the following relationship is satisfied:

It is more preferable to satisfy the following. In these preferred ranges, the swelling and long-term cycle durability of the battery can be further improved.

As an example of the heat treatment conditions, the temperature of the heat treatment is preferably 90 to 190 ° C, more preferably 100 to 190 ° C, still more preferably 150 to 190 ° C, and particularly preferably 180 to 190 ° C. Typically, when the heat treatment temperature is reduced, the values of “N ₂ / N ₁ × 100” and “R ₂ / R ₁ × 100” tend to increase, and when the heat treatment temperature is increased, these values become It tends to be smaller. The heat treatment time is preferably about 1 to 5 hours. Further, the heat treatment atmosphere may be an air atmosphere or an inert gas atmosphere such as argon or nitrogen. Further, the atmospheric pressure may be normal pressure or a reduced pressure of about 10 to 1000 Pa.

  According to still another aspect of the present invention, there is provided a negative electrode for a non-aqueous electrolyte secondary battery including a current collector and a negative electrode active material layer including a negative electrode active material, which is disposed on a surface of the current collector. Also provided is a negative electrode for a non-aqueous electrolyte secondary battery using the first or second negative electrode active material according to the present invention or the negative electrode active material manufactured by the manufacturing method according to the present invention as the negative electrode active material. Is done.

[Non-aqueous electrolyte secondary battery]
FIG. 1 is a schematic cross-sectional view schematically showing an outline of a nonaqueous electrolyte secondary battery (hereinafter, also simply referred to as a “stacked battery”) which is one embodiment of a negative electrode active material and a negative electrode according to the present invention. FIG. 3 is a schematic sectional view taken along the line AA shown in FIG. In this specification, a flat (laminated) lithium ion secondary battery which is not a bipolar type shown in FIG. 1 will be described in detail as an example, but the technical scope of the present invention is limited to only such a form. Not limited to

  First, the overall structure of a nonaqueous electrolyte secondary battery according to the present invention will be described with reference to the drawings.

[Overall structure of battery]
As shown in FIG. 1, the stacked battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a battery exterior material 29 which is an exterior body. Have. Here, the power generation element 21 has a configuration in which a positive electrode, a separator 17, and a negative electrode are stacked. The separator 17 contains an electrolyte (in the present embodiment, a liquid electrolyte (electrolyte) containing an additive). The positive electrode has a structure in which a positive electrode active material layer 15 is disposed on both surfaces of a positive electrode current collector 12. The negative electrode has a structure in which a negative electrode active material layer 13 is disposed on both surfaces of a negative electrode current collector 11. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are stacked in this order such that one positive electrode active material layer 15 and the negative electrode active material layer 13 adjacent thereto are opposed via the separator 17. Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10 illustrated in FIG. 1 has a configuration in which a plurality of unit cell layers 19 are stacked and electrically connected in parallel.

  In each of the outermost layer positive electrode current collectors located on both outermost layers of the power generation element 21, the negative electrode active material layer 13 is disposed only on one surface, but the active material layers may be provided on both surfaces. That is, a current collector having an active material layer on both surfaces may be used as it is as an outermost current collector, instead of a current collector dedicated to the outermost layer having an active material layer provided only on one surface. Also, the arrangement of the positive electrode and the negative electrode is reversed from that of FIG. 1 so that the outermost layer positive electrode current collector is located on both outermost layers of the power generating element 21, and the single-sided positive electrode active material of the outermost layer positive electrode current collector The layers may be arranged.

  The positive electrode current collector 12 and the negative electrode current collector 11 are respectively provided with a positive electrode current collector (tab) 27 and a negative electrode current collector (tab) 25 that are electrically connected to each electrode (positive electrode and negative electrode). And is led out of the battery exterior material 29 so as to be sandwiched between the ends of the battery. The positive electrode current collector 27 and the negative electrode current collector 25 are each ultrasonically welded to the positive electrode current collector 12 and the negative electrode current collector 11 of each electrode via a positive electrode lead and a negative electrode lead (not shown) as necessary. Or may be attached by resistance welding or the like.

  Note that FIG. 1 illustrates a stacked (stacked) battery that is not a bipolar battery, but includes a positive electrode active material layer electrically connected to one surface of a current collector and an opposite side of the current collector. And a negative electrode active material layer electrically coupled to the surface of the negative electrode. In this case, one current collector also serves as a positive electrode current collector and a negative electrode current collector.

  Hereinafter, each member constituting the non-aqueous electrolyte lithium ion secondary battery which is one embodiment of the present invention will be described.

[Positive electrode]
The positive electrode has a current collector and a positive electrode active material layer formed on the surface of the current collector.

(Current collector; common to positive and negative electrodes)
The material constituting the current collector is not particularly limited, but a metal is preferably used. Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, copper, and other alloys. In addition, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plated material of a combination of these metals can be preferably used. Further, a foil having a metal surface coated with aluminum may be used. Among them, aluminum, stainless steel, and copper are preferable from the viewpoint of electron conductivity and battery operating potential. Aluminum is optimal for the positive electrode current collector, and copper is optimal for the negative electrode current collector.

  The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery requiring a high energy density, a current collector having a large area is used. There is no particular limitation on the thickness of the current collector. The thickness of the current collector is usually about 1 to 100 μm.

(Positive electrode active material layer)
The positive electrode active material layer contains a positive electrode active material. The specific configuration of the positive electrode active material is not particularly limited, and a conventionally known material can be used. For example, the positive electrode active material preferably includes a spinel-based lithium manganese composite oxide and / or a lithium nickel-based composite oxide. Hereinafter, preferred embodiments of these positive electrode active materials will be described.

Spinel-based lithium-manganese composite oxide The spinel-based lithium-manganese composite oxide is typically a composite oxide having a composition of LiMn ₂ O ₄ and having a spinel structure and essentially containing lithium and manganese, For its specific configuration and manufacturing method, conventionally known knowledge can be appropriately referred to.

  The spinel lithium manganese composite oxide has a configuration of secondary particles formed by aggregating primary particles. The secondary particles have an average particle size (average secondary particle size; D50) of preferably 5 to 50 μm, and more preferably 7 to 20 μm. The measurement of the average secondary particle size is performed by a laser diffraction method.

-Lithium nickel composite oxide The composition of the lithium nickel composite oxide is not specifically limited as long as it is a composite oxide containing lithium and nickel. A typical example of a composite oxide containing lithium and nickel is a lithium nickel composite oxide (LiNiO ₂ ). However, a composite oxide in which a part of nickel atoms of a lithium nickel composite oxide is substituted with another metal atom is more preferable. As a preferable example, a lithium-nickel-manganese-cobalt composite oxide (hereinafter simply referred to as “NMC composite oxide”) is used. Oxide) has a layered crystal structure in which a lithium atomic layer and a transition metal (Mn, Ni and Co are arranged in order) atomic layer are alternately stacked via an oxygen atomic layer. One Li atom is contained per atom, and the amount of Li that can be taken out is twice that of the spinel-based lithium manganese oxide, that is, the supply capacity is doubled, and a high capacity can be obtained. In addition, since it has higher thermal stability than LiNiO ₂ , it is particularly advantageous among nickel-based composite oxides used as a positive electrode active material.

  In this specification, the NMC composite oxide also includes a composite oxide in which part of a transition metal element is replaced by another metal element. Other elements in this case include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu , Ag, Zn, etc., preferably, Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably, Ti, Zr, P, Al, Mg, Cr, and more preferably, Ti, Zr, Al, Mg, and Cr from the viewpoint of improving cycle characteristics.

NMC composite oxide, since the theoretical discharge capacity is high, preferably the general formula _{(1): Li a Ni b} Mn c Co d M x O 2 ( In the formula, a, b, c, d, x Satisfies 0.9 ≦ a ≦ 1.2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, and b + c + d = 1. At least one element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr). Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Mn, d represents the atomic ratio of Co, and x represents the atomic ratio of M. Represents From the viewpoint of cycle characteristics, it is preferable that 0.4 ≦ b ≦ 0.6 in the general formula (1). The composition of each element can be measured by, for example, inductively coupled plasma (ICP) emission spectrometry.

  Generally, it is known that nickel (Ni), cobalt (Co) and manganese (Mn) contribute to capacity and output characteristics from the viewpoint of improving the purity of a material and improving electronic conductivity. Ti and the like partially replace the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element is replaced by another metal element, and it is particularly preferable that 0 <x ≦ 0.3 in the general formula (1). Since at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr forms a solid solution, the crystal structure is stabilized. It can be considered that the battery capacity can be prevented from being reduced even by repeating the above, and excellent cycle characteristics can be realized.

In the NMC composite oxide, the present inventors have found that when the metal composition of nickel, manganese, and cobalt is not uniform, such as LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , It has been found that the influence of strain / cracking of the composite oxide at the time increases. This is presumably because the metal composition is non-uniform, so that stress is applied to the inside of the particles during expansion and contraction, and the composite oxide is more likely to crack. Therefore, for example, a composite oxide in which the abundance ratio of Ni is rich (for example, LiNi _0.8 Mn _0.1 Co _0.1 O ₂ ) or a composite oxide in which the abundance ratios of Ni, Mn, and Co are uniform (For example, LiNi _0.33 Mn _0.33 Co _0.33 O ₂ ), the long-term cycle characteristics are significantly reduced. On the other hand, by adopting the configuration according to the present embodiment, surprisingly, even in a composite oxide having a non-uniform metal composition such as LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , the cycle characteristics are surprisingly low. It has been found to be improved.

  Therefore, in the general formula (1), b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, and 0.19 ≦ d ≦ 0.26. Is preferable. With such a configuration, a battery having an excellent balance between capacity characteristics and output characteristics can be provided.

  The lithium nickel-based composite oxide also has a configuration of secondary particles formed by aggregating primary particles. The average particle size of the primary particles (average primary particle size; D50) is preferably 0.9 μm or less, more preferably 0.20 to 0.6 μm, and still more preferably 0.25 to 0.5 μm. It is. The average particle size of the secondary particles (average secondary particle size; D50) is preferably 5 to 20 μm, more preferably 5 to 15 μm. Further, the value of these ratios (average secondary particle size / average primary particle size) is preferably larger than 11, more preferably 15 to 50, and even more preferably 25 to 40. The primary particles constituting the lithium nickel-based composite oxide usually have a hexagonal crystal structure having a layered structure, and the size of the crystallite has a correlation with the size of the average primary particle size. Have. Here, the “crystallite” means the largest collection that can be regarded as a single crystal, and can be measured by a method of refining the crystal structure parameters from the diffraction intensity obtained by powder X-ray diffraction measurement or the like. The specific value of the crystallite diameter of the primary particles constituting the lithium nickel composite oxide is not particularly limited, but is preferably 1 μm or less, more preferably 360 nm or less, from the viewpoint of life characteristics. Preferably it is 310 nm or less. With such a configuration, it is possible to reduce the amount of displacement during expansion and contraction of the active material, to suppress the occurrence of miniaturization (cracking) of secondary particles due to repeated charge and discharge, and to improve the cycle characteristics. It can contribute to improvement. The lower limit of the crystallite diameter is not particularly limited, but is usually 20 nm or more. Here, in the present specification, the value of the crystallite diameter in the positive electrode active material particles is measured by the Rietveld method in which the crystallite diameter is calculated from the diffraction peak intensity obtained by powder X-ray diffraction measurement.

The tap density of the lithium-nickel-based composite oxide is preferably 2.3 g / cm ^3, more preferably 2.4~2.9g / cm ^3. With such a configuration, high density of the primary particles constituting the secondary particles of the positive electrode active material is sufficiently ensured, and the effect of improving the cycle characteristics can be maintained.

Further, BET specific surface area of the lithium nickel composite oxide is preferably 0.1~1.0m ² / g, more preferably 0.3~1.0m ² / g, particularly preferably 0. 3 to 0.7 m ² / g. When the specific surface area of the active material is within such a range, a reaction area of the active material is secured and the internal resistance of the battery is reduced, so that the occurrence of polarization during electrode reaction can be minimized.

Further, for the lithium nickel-based composite oxide, the diffraction peak of the (104) plane and the diffraction peak of the (003) plane obtained by powder X-ray diffraction measurement are defined as a diffraction peak intensity ratio ((003) / (104)). It is preferably 1.28 or more, more preferably 1.35 to 2.1. Further, the diffraction peak integrated intensity ratio ((003) / (104)) is preferably 1.08 or more, and more preferably 1.10 to 1.45. These rules are preferred for the following reasons. That is, the lithium nickel-based composite oxide has a layered rock salt structure in which a Li ⁺ layer and a Ni ³⁺ layer exist between oxygen layers. However, ^{Ni 3+} is easily reduced to ^{Ni 2+,} and because substantially equal to the ^{Ni 2+} ion radius (0.83Å) is Li ⁺ ion radius (0.90 Å), Ni to Li ⁺ defect occurring during active material synthesized ²⁺ is easily mixed. When Ni ²⁺ is mixed into the Li ⁺ site, a locally electrochemically inactive structure is formed and diffusion of Li ⁺ is prevented. Therefore, when an active material having low crystallinity is used, there is a possibility that the charge / discharge capacity of the battery is reduced and the durability is reduced. The above definition is used as an index of the degree of crystallinity. Here, as a method of quantifying the crystallinity, as described above, the ratio of the intensity of the diffraction peak of the (003) plane to the intensity of the diffraction peak of the (104) plane and the ratio of the integrated intensity of the diffraction peak by the crystal structure analysis using X-ray diffraction are described above. Was used. When these parameters satisfy the above rules, the number of defects in the crystal is reduced, and a decrease in battery charge / discharge capacity and a decrease in durability can be suppressed. Note that such a crystallinity parameter can be controlled by a raw material, a composition, a firing condition, and the like.

  A lithium nickel-based composite oxide such as an NMC composite oxide can be prepared by selecting various known methods such as a coprecipitation method and a spray drying method. It is preferable to use the coprecipitation method because the preparation of the composite oxide according to this embodiment is easy. Specifically, as a method for synthesizing an NMC composite oxide, for example, a nickel-cobalt-manganese composite oxide is produced by a coprecipitation method as in the method described in JP-A-2011-105588. -It can be obtained by mixing and sintering a manganese composite oxide and a lithium compound.

  When the positive electrode active material includes a spinel-based lithium manganese composite oxide and a lithium nickel-based composite oxide, the mixing ratio thereof is not particularly limited. The content is preferably 15 to 40% by mass, more preferably 30 to 40% by mass, based on the content of lithium nickel-based composite oxide of 100% by mass.

  The positive electrode active material layer includes, in addition to the positive electrode active material described above, a conductive auxiliary agent, a binder, an electrolyte (a polymer matrix, an ion conductive polymer, an electrolytic solution, and the like), and a lithium salt for enhancing ion conductivity, as necessary. It further contains other additives. However, the content of a material that can function as an active material in the positive electrode active material layer and the negative electrode active material layer described below is preferably 85 to 99.5% by mass.

(Conduction aid)
The conductive additive refers to an additive compounded to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Examples of the conductive assistant include carbon materials such as carbon black such as Ketjen black and acetylene black, and carbon fibers. When the active material layer contains a conductive additive, an electron network inside the active material layer is effectively formed, which can contribute to improvement in output characteristics of the battery.

(binder)
The binder used for the positive electrode active material layer is not particularly limited, and examples thereof include the following materials. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile, polyacrylonitrile, polyimide, polyamide, cellulose, carboxymethyl cellulose (CMC) and its salts, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR) ), Isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and its hydrogenated product, styrene / isoprene / styrene block copolymer and its hydrogenated Polymer, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (F P), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE) ), Fluororesins such as polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubber (VDF-HFP) -TFE fluororubber), vinylidene fluoride-pentafluoropropylene fluororubber (VDF-PFP fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene Fluorine rubber (VDF-PFP-TFE fluorine rubber), vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene fluorine rubber (VDF-PFMVE-TFE fluorine rubber), vinylidene fluoride-chlorotrifluoroethylene fluorine Vinylidene fluoride fluororubbers such as rubber (VDF-CTFE fluororubber), epoxy resins, and the like. These binders may be used alone or in combination of two or more.

As the electrolyte salt (lithium _{salt), LiPF 6, LiBF 4,} LiClO 4, LiAsF 6, LiTaF 6, LiSbF 6, LiAlCl 4, Li 2 B 10 Cl 10, LiI, LiBr, LiCl, LiAlCl, LiHF 2, LiSCN , etc. Inorganic acid anion salt, LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiBOB (lithium bisoxide borate), LiBETI (lithium bis (perfluoroethylenesulfonylimide); Li (C ₂ F ₅ SO ₂₎ ) such as 2 _N with described) organic acid anion salts, and the like. These electrolyte salts may be used alone or in the form of a mixture of two or more.

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  The mixing ratio of the components contained in the positive electrode active material layer and the negative electrode active material layer described later is not particularly limited. The compounding ratio can be adjusted by appropriately referring to known knowledge about the lithium ion secondary battery. There is also no particular limitation on the thickness of each active material layer, and conventionally known knowledge about batteries can be appropriately referred to. For example, the thickness of each active material layer is about 2 to 100 μm.

[Negative electrode active material layer]
The negative electrode active material layer contains an active material, and if necessary, a conductive additive, a binder, an electrolyte (a polymer matrix, an ion conductive polymer, an electrolytic solution, etc.), and other additions such as a lithium salt for enhancing ion conductivity. And an agent. Other additives such as a conductive auxiliary agent, a binder, an electrolyte (a polymer matrix, an ion-conductive polymer, an electrolytic solution, etc.) and a lithium salt for enhancing ion conductivity are described in the above-mentioned column of the positive electrode active material layer. Is the same as

As described above, the negative electrode active material essentially includes the first or second negative electrode active material according to the present invention or the negative electrode active material manufactured by the manufacturing method according to the present invention. Although the ratio of the “first or second negative electrode active material according to the present invention, or the negative electrode active material manufactured by the manufacturing method according to the present invention” to the negative electrode active material included in the negative electrode active material layer is not particularly limited, , Preferably 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass. As the negative electrode active material other than “the first or second negative electrode active material according to the present invention, or the negative electrode active material manufactured by the manufacturing method according to the present invention”, conventionally known materials can be used. Examples thereof include carbon materials such as graphite, soft carbon, and hard carbon, lithium-transition metal composite oxides (for example, Li ₄ Ti ₅ O ₁₂ ), metal materials, and lithium alloy-based negative electrode materials.

The BET specific surface area (SSA) of the negative electrode active material is preferably from 0.5 to 10 m ² / g, more preferably from 1.0 to 6.0 m ² / g, and still more preferably from 2.0 to 4.0 m ² / g. 2 m ² / g. When the specific surface area of the negative electrode active material is equal to or more than the lower limit, the possibility that the low-temperature characteristics deteriorate due to an increase in the internal resistance is reduced. On the other hand, if the value is equal to or less than the upper limit, it is possible to prevent the side reaction from proceeding with an increase in the contact area with the electrolyte. In particular, if the specific surface area is too large, an overcurrent flows locally in the electrode surface due to gas generated at the time of the first charge (the film formed by the electrolyte additive is not fixed), and the gas flows into the electrode surface. In some cases, the coating becomes non-uniform and the life characteristics are deteriorated. However, if the value is equal to or less than the upper limit, the risk can be reduced.

  The negative electrode active material layer preferably contains at least an aqueous binder. The aqueous binder has a high binding force. In addition to the fact that water as a raw material is easy to procure, water vapor is generated during drying, which significantly reduces capital investment in production lines and reduces environmental impact. There is.

  The aqueous binder refers to a binder using water as a solvent or a dispersion medium, and specifically includes a thermoplastic resin, a polymer having rubber elasticity, a water-soluble polymer, or a mixture thereof. Here, the binder containing water as a dispersion medium includes all expressed as a latex or an emulsion, and refers to a polymer that is emulsified with water or suspended in water, for example, a polymer latex that is emulsion-polymerized in a self-emulsifying system. And the like.

  Specific examples of the aqueous binder include styrene-based polymers (styrene-butadiene rubber, styrene-vinyl acetate copolymer, styrene-acrylic copolymer, etc.), acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, ) Acrylic polymer (polyethyl acrylate, polyethyl methacrylate, polypropyl acrylate, polymethyl methacrylate (methyl methacrylate rubber), polypropyl methacrylate, polyisopropyl acrylate, polyisopropyl methacrylate, polybutyl acrylate, polybutyl methacrylate, polyhexyl acrylate , Polyhexyl methacrylate, polyethylhexyl acrylate, polyethylhexyl methacrylate, polylauryl acrylate, polylauryl meth Acrylate, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polybutadiene, butyl rubber, fluorine rubber, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer Poly (vinyl pyridine), chlorosulfonated polyethylene, polyester resin, phenol resin, epoxy resin; polyvinyl alcohol (average degree of polymerization is preferably 200 to 4000, more preferably 1000 to 3000, and saponification degree is preferably 80. Mol% or more, more preferably 90 mol% or more) and a modified product thereof (ethylene / vinyl acetate = 1/80 mol% of vinyl acetate units of a copolymer having a molar ratio of 2/98 to 30/70). , 1 to 50 mol% of vinyl alcohol partially acetalized product), starch and modified products thereof (oxidized starch, phosphorylated esterified starch, cationized starch, etc.), and cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, hydroxyethylcellulose) And salts thereof), polyvinylpyrrolidone, polyacrylic acid (salt), polyethylene glycol, a copolymer of (meth) acrylamide and / or (meth) acrylate [(meth) acrylamide polymer, (meth) acrylamide- (Meth) acrylate copolymer, alkyl (meth) acrylate (C1-4) ester- (meth) acrylate copolymer, etc., styrene-maleate copolymer, Mannich of polyacrylamide Denatured form , Formalin condensation type resin (urea-formalin resin, melamine-formalin resin, etc.), polyamide polyamine or dialkylamine-epichlorohydrin copolymer, polyethyleneimine, casein, soybean protein, synthetic protein, and water-soluble polymer such as mannangalactan derivative And the like. These aqueous binders may be used alone or in combination of two or more.

  From the viewpoint of binding properties, the aqueous binder may include at least one rubber-based binder selected from the group consisting of styrene-butadiene rubber, acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, and methyl methacrylate rubber. preferable. Further, the water-based binder preferably contains a styrene-butadiene rubber because of good binding properties.

  When styrene-butadiene rubber is used as the aqueous binder, it is preferable to use the above water-soluble polymer in combination from the viewpoint of improving coatability. Water-soluble polymers suitable for use in combination with styrene-butadiene rubber include polyvinyl alcohol and modified products thereof, starch and modified products thereof, cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxyethylcellulose, and salts thereof), polyvinyl alcohol and the like. Examples include pyrrolidone, polyacrylic acid (salt), or polyethylene glycol. Especially, it is preferable to combine styrene-butadiene rubber and carboxymethylcellulose (salt) as a binder. The content mass ratio of the styrene-butadiene rubber to the water-soluble polymer is not particularly limited, but is preferably styrene-butadiene rubber: water-soluble polymer = 1: 0.1 to 10, More preferably, it is 0.5 to 2.

  Among the binders used for the negative electrode active material layer, the content of the aqueous binder is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and preferably 100% by mass.

[Separator (electrolyte layer)]
The separator has a function of retaining electrolyte and ensuring lithium ion conductivity between the positive electrode and the negative electrode, and a function as a partition between the positive electrode and the negative electrode.

  Examples of the form of the separator include a porous sheet separator and a nonwoven fabric separator made of a polymer or a fiber that absorbs and retains the electrolyte.

  As a separator of a porous sheet made of a polymer or a fiber, for example, a microporous membrane can be used. Specific forms of the porous sheet made of the polymer or the fiber include, for example, polyolefins such as polyethylene (PE) and polypropylene (PP); and a laminate of a plurality of these (for example, three layers of PP / PE / PP) And a microporous (microporous membrane) separator made of polyimide, aramid, a hydrocarbon resin such as polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), glass fiber, or the like.

  The thickness of the microporous (microporous membrane) separator cannot be uniquely defined because it varies depending on the intended use. As an example, in a use such as a secondary battery for driving a motor such as an electric vehicle (EV), a hybrid electric vehicle (HEV), and a fuel cell vehicle (FCV), the thickness is 4 to 60 μm in a single layer or a multilayer. Is desirable. It is desirable that the micropore diameter of the microporous (microporous membrane) separator is 1 μm or less at maximum (usually, the pore diameter is about several tens nm).

  As the nonwoven fabric separator, conventionally known materials such as cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; polyimides and aramids are used alone or in combination. The bulk density of the nonwoven fabric is not particularly limited as long as sufficient battery characteristics can be obtained by the impregnated polymer gel electrolyte. Further, the thickness of the nonwoven fabric separator may be the same as that of the electrolyte layer, preferably 5 to 200 μm, and particularly preferably 10 to 100 μm.

  Here, the separator is preferably a separator in which a heat-resistant insulating layer is laminated on a porous substrate (a separator with a heat-resistant insulating layer). The heat-resistant insulating layer is a ceramic layer containing inorganic particles and a binder. As the separator with a heat-resistant insulating layer, a high heat-resistant separator having a melting point or a thermal softening point of 150 ° C. or higher, preferably 200 ° C. or higher is used. By having the heat-resistant insulating layer, the internal stress of the separator, which increases when the temperature rises, is reduced, so that the effect of suppressing heat shrinkage can be obtained. As a result, induction of a short circuit between the electrodes of the battery can be prevented, so that a battery configuration in which performance degradation due to a rise in temperature hardly occurs is obtained. In addition, by having the heat-resistant insulating layer, the mechanical strength of the separator with the heat-resistant insulating layer is improved, and the separator is hardly broken. Further, the separator is unlikely to curl in the battery manufacturing process due to the effect of suppressing heat shrinkage and the high mechanical strength.

The inorganic particles in the heat-resistant insulating layer contribute to the mechanical strength of the heat-resistant insulating layer and the effect of suppressing heat shrinkage. The material used as the inorganic particles is not particularly limited. Examples include oxides of silicon, aluminum, zirconium, and titanium (SiO ₂ , Al ₂ O ₃ , ZrO ₂ , TiO ₂ ), hydroxides, and nitrides, and composites thereof. These inorganic particles may be derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine and mica, or may be artificially produced. In addition, one kind of these inorganic particles may be used alone, or two or more kinds may be used in combination. Among these, from the viewpoint of cost, it is preferable to use silica (SiO ₂ ) or alumina (Al ₂ O ₃ ), and it is more preferable to use alumina (Al ₂ O ₃ ).

The weight of the heat-resistant particles is not particularly limited, but is preferably 5 to 15 g / m ² . Within this range, sufficient ion conductivity is obtained, and the heat resistance is preferably maintained.

  The binder in the heat-resistant insulating layer has a role of bonding the inorganic particles or the inorganic particles and the resin porous substrate layer. With the binder, the heat-resistant insulating layer is formed stably, and peeling between the porous substrate layer and the heat-resistant insulating layer is prevented.

  The binder used for the heat-resistant insulating layer is not particularly limited, and for example, carboxymethylcellulose (CMC), polyacrylonitrile, cellulose, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), isoprene rubber Compounds such as butadiene rubber, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), and methyl acrylate can be used as the binder. Among them, it is preferable to use carboxymethylcellulose (CMC), methyl acrylate, or polyvinylidene fluoride (PVdF). One of these compounds may be used alone, or two or more of them may be used in combination.

  The content of the binder in the heat-resistant insulating layer is preferably 2 to 20% by mass based on 100% by mass of the heat-resistant insulating layer. When the content of the binder is 2% by mass or more, the peel strength between the heat-resistant insulating layer and the porous base layer can be increased, and the vibration resistance of the separator can be improved. On the other hand, when the content of the binder is 20% by mass or less, the gap between the inorganic particles is appropriately maintained, so that sufficient lithium ion conductivity can be secured.

The heat shrinkage of the separator with a heat-resistant insulating layer is preferably 10% or less for both MD and TD after holding for 1 hour at 150 ° C. and ² gf / cm ² . By using such a material having high heat resistance, the heat generation of the positive electrode increases, and even if the internal temperature of the battery reaches 150 ° C., the contraction of the separator can be effectively prevented. As a result, induction of a short circuit between the electrodes of the battery can be prevented, so that a battery configuration in which performance degradation due to a rise in temperature hardly occurs is obtained.

(Electrolytes)
As described above, the separator includes an electrolyte. The electrolyte is not particularly limited as long as it can exert such a function, and a liquid electrolyte or a gel polymer electrolyte is used. By using the gel polymer electrolyte, the distance between the electrodes is stabilized, the occurrence of polarization is suppressed, and the durability (cycle characteristics) is improved.

The liquid electrolyte has a function as a carrier for lithium ions. The liquid electrolyte has a form in which a lithium salt is dissolved in an organic solvent. Examples of the organic solvent to be used include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate. As the lithium _{salt, Li (CF 3 SO 2)} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiClO 4, LiAsF 6, LiTaF such 6, LiCF ₃ SO ₃ Compounds that can be added to the active material layer of the electrode can be employed as well.

  The liquid electrolyte may further include additives other than the above-described components. Specific examples of such compounds include, for example, vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate, phenyl vinylene carbonate, diphenyl vinylene carbonate, ethyl vinylene carbonate, diethyl vinylene carbonate, vinyl ethylene carbonate, and 1,2-divinyl ethylene carbonate. , 1-methyl-1-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1-ethyl-1-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, vinylvinylene carbonate, allylethylene carbonate, vinyl Oxymethylethylene carbonate, allyloxymethylethylene carbonate, acryloxymethylethylene carbonate, Oxy methylethylene carbonate, ethynyl ethylene carbonate, propargyl carbonate, ethynyloxy methylethylene carbonate, propargyloxy ethylene carbonate, methylene carbonate, etc. 1,1-dimethyl-2-methylene-ethylene carbonate. Among them, vinylene carbonate, methyl vinylene carbonate and vinyl ethylene carbonate are preferred, and vinylene carbonate and vinyl ethylene carbonate are more preferred. One of these cyclic carbonates may be used alone, or two or more thereof may be used in combination.

  The gel polymer electrolyte has a configuration in which the above liquid electrolyte is injected into a matrix polymer (host polymer) made of an ion conductive polymer. The use of a gel polymer electrolyte as the electrolyte is excellent in that the fluidity of the electrolyte is lost and the ionic conductivity between the layers is cut off to facilitate the flow. Examples of the ion conductive polymer used as the matrix polymer (host polymer) include, for example, polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene ( PVdF-HEP), poly (methyl methacrylate (PMMA), and copolymers thereof.

  The matrix polymer of the gel electrolyte can exhibit excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, a suitable polymerization initiator is used to polymerize a polymerizable polymer for forming a polymer electrolyte (eg, PEO or PPO) by heat polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, or the like. A polymerization treatment may be performed.

[Positive current collector and negative current collector]
The material constituting the current collectors (25, 27) is not particularly limited, and a known highly conductive material conventionally used as a current collector for a lithium ion secondary battery can be used. As a constituent material of the current collector, for example, a metal material such as aluminum, copper, titanium, nickel, stainless steel (SUS), or an alloy thereof is preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. In addition, the same material may be used for the positive electrode current collector 27 and the negative electrode current collector 25, or different materials may be used.

[Positive electrode lead and negative electrode lead]
Although not shown, the current collector 11 and the current collector (25, 27) may be electrically connected via a positive electrode lead or a negative electrode lead. As the constituent materials of the positive electrode and the negative electrode lead, materials used in known lithium ion secondary batteries can be similarly employed. In addition, the parts removed from the exterior may be in contact with peripheral equipment or wiring, etc., causing a short circuit, which will not affect products (for example, automobile parts, especially electronic equipment, etc.). It is preferable to coat with a tube or the like.

[Battery exterior]
As the battery outer casing 29, a known metal can case can be used, and a bag-shaped case that can cover the power generating element and that uses a laminated film containing aluminum can be used. As the laminate film, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used, but the present invention is not limited thereto. Laminated films are desirable from the viewpoint that they are excellent in high output and cooling performance and can be suitably used for batteries for large-sized devices for EV and HEV. In addition, since the group pressure applied to the power generation element from the outside can be easily adjusted and the thickness of the electrolyte layer can be easily adjusted to a desired value, the exterior body is more preferably an aluminate laminate.

[Cell size]
FIG. 2 is a perspective view showing the appearance of a flat lithium ion secondary battery which is a typical embodiment of the secondary battery.

  As shown in FIG. 2, the flat lithium ion secondary battery 50 has a rectangular flat shape, and a positive electrode tab 58 and a negative electrode tab 59 for extracting electric power are drawn out from both sides thereof. I have. The power generating element 57 is wrapped by the battery outer material 52 of the lithium ion secondary battery 50 and the periphery thereof is heat-sealed, and the power generating element 57 is hermetically sealed with the positive electrode tab 58 and the negative electrode tab 59 drawn out. Have been. Here, the power generating element 57 corresponds to the power generating element 21 of the lithium ion secondary battery 10 described above and shown in FIG. The power generation element 57 includes a plurality of unit cell layers (single cells) 19 each including a positive electrode (positive electrode active material layer) 15, an electrolyte layer 17, and a negative electrode (negative electrode active material layer) 13.

  Note that the lithium ion secondary battery is not limited to a stacked flat battery. The wound lithium ion secondary battery may have a cylindrical shape, or may have such a cylindrical shape deformed into a rectangular flat shape. It is not particularly limited. In the case of the cylindrical shape, there is no particular limitation, for example, a laminate film may be used for the exterior material, or a conventional cylindrical can (metal can) may be used. Preferably, the power generating element is clad with an aluminum laminated film. With this configuration, weight reduction can be achieved.

  The removal of the tabs 58 and 59 shown in FIG. 2 is not particularly limited. As shown in FIG. 2, the positive electrode tab 58 and the negative electrode tab 59 may be pulled out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality of parts and taken out from each side. It is not limited to. In a wound lithium ion battery, terminals may be formed using, for example, a cylindrical can (metal can) instead of a tab.

  In a general electric vehicle, the battery storage space is about 170L. Since cells and auxiliary equipment such as charge / discharge control devices are stored in this space, the storage space efficiency of the normal cells is about 50%. The cell loading efficiency in this space is a factor that governs the cruising distance of the electric vehicle. If the size of the single cell is reduced, the above-mentioned loading efficiency is impaired, and the cruising distance cannot be secured.

  Therefore, in the present invention, it is preferable that the battery structure in which the power generation element is covered with the outer package is large. Specifically, the length of the short side of the laminated cell battery is preferably 100 mm or more. Such a large battery can be used for vehicle use. Here, the length of the short side of the laminate cell battery refers to the shortest side. The upper limit of the length of the short side is not particularly limited, but is usually 400 mm or less.

[Volume energy density and rated discharge capacity]
In a general electric vehicle, the driving distance (cruising distance) per charge is required to be 100 km in the market. In consideration of such a cruising distance, the battery preferably has a volume energy density of 157 Wh / L or more, and a rated capacity of 20 Wh or more.

In addition, as a viewpoint of a larger battery, which is different from the viewpoint of the physical size of the electrode, the size of the battery can be specified from the relationship between the battery area and the battery capacity. For example, in the case of a flat laminated type laminated battery, the value of the ratio of the battery area to the rated capacity (projected area of the battery including the battery exterior body) is 5 cm ² / Ah or more, and the rated capacity is 3 Ah or more. In a certain battery, since the battery area per unit capacity is large, the problem to be solved by the present embodiment is more likely to become more apparent. Therefore, the non-aqueous electrolyte secondary battery according to the present embodiment is preferably a large-sized battery as described above, since the merit of the operation and effect of the embodiment is greater. Furthermore, the aspect ratio of the rectangular electrode is preferably 1 to 3, and more preferably 1 to 2. Note that the aspect ratio of the electrode is defined as the aspect ratio of the rectangular positive electrode active material layer. By setting the aspect ratio in such a range, there is an advantage that both the required performance of the vehicle and the mounting space can be achieved.

[Battery pack]
An assembled battery is formed by connecting a plurality of batteries. More specifically, at least two or more are used for serialization and / or parallelization. It is possible to freely adjust the capacity and the voltage by making them serial and parallel.

  A plurality of batteries may be connected in series or in parallel to form a detachable small assembled battery. Then, a plurality of the small battery packs which can be attached and detached are further connected in series or in parallel, and a large capacity and a large capacity suitable for a vehicle drive power supply and an auxiliary power supply requiring a high volume energy density and a high volume output density are required. A battery pack having an output can also be formed. How many batteries are connected to create a battery pack, and how many small battery packs are stacked to produce a large capacity battery pack, depends on the battery capacity of the vehicle (electric vehicle) to be mounted. It may be determined according to the output.

[vehicle]
The nonaqueous electrolyte secondary battery of the present invention maintains a discharge capacity even after long-term use, and has good cycle characteristics. Further, the volume energy density is high. Vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles require higher capacity and larger size and longer life than electric and portable electronic device applications. . Therefore, the nonaqueous electrolyte secondary battery can be suitably used as a vehicle power supply, for example, as a vehicle drive power supply or an auxiliary power supply.

  Specifically, a battery or an assembled battery obtained by combining a plurality of these batteries can be mounted on a vehicle. According to the present invention, since a long-life battery having excellent long-term reliability and output characteristics can be formed, when such a battery is mounted, a plug-in hybrid electric vehicle having a long EV mileage or an electric vehicle having a long charge mileage can be formed. . For example, a hybrid vehicle, a fuel cell vehicle, an electric vehicle (all four-wheel vehicles (commercial vehicles such as passenger cars, trucks, buses, light vehicles, etc.) This is because the use in a motorcycle (including a motorcycle) and a three-wheeled vehicle) results in a vehicle having a long life and high reliability. However, the application is not limited to automobiles. For example, other vehicles, for example, various power supplies for moving objects such as trains can be applied, and a mounting power supply such as an uninterruptible power supply. It is also possible to use as.

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

<< Production of laminated battery >>
[Comparative Example 1]
(1) Preparation of Positive Electrode NMC composite oxide (LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , average secondary particle size (D50) = 10 μm) as a positive electrode active material was 95% by mass, and a conductive auxiliary agent And 2% by mass of conductive carbon black (super-P), 3% by mass of polyvinylidene fluoride (PVdF) as a binder, and N-methyl-2-pyrrolidone (NMP) as a slurry viscosity adjusting solvent. An active material slurry was prepared.

The obtained positive electrode active material slurry was applied to both surfaces of an aluminum foil (thickness: 20 μm) as a positive electrode current collector, dried at 120 ° C. for 3 minutes, and compression-molded with a roll press to form a positive electrode active material layer. A positive electrode having a coating amount on one side (excluding the current collector) of 18 mg / cm ² and a density of the positive electrode active material layer of 3.1 g / cm ³ was produced.

(3) Preparation of Negative Electrode Natural graphite (having an amorphous coating layer on its surface, average particle size (D50) = 18 μm, BET specific surface area (SSA) = 1.6 m ² / g) was used as the negative electrode active material. 96% by mass of a negative electrode active material, 1% by mass of conductive carbon black (super-P) as a conduction aid, 1% by mass of carboxymethyl cellulose (CMC) as a binder, and 2% by mass of styrene-butadiene copolymer (SBR) in purified water To prepare a negative electrode active material slurry. The negative electrode active material used here is also referred to as “active material (1)”.

The obtained negative electrode active material slurry was applied to both surfaces of a copper foil (thickness: 10 μm) as a negative electrode current collector, dried at 120 ° C. for 3 minutes, and then compression-molded with a roll press to form a negative electrode active material layer. A negative electrode having a coating amount on one side (excluding the current collector) of 9.5 g / cm ² and a density of the negative electrode active material layer of 1.5 g / cm ³ was produced.

(4) Preparation of Laminated Battery The positive electrode (cut to 200 mm square) and the negative electrode (cut to 202 mm square) obtained above were alternately laminated via separators (Celgard 2500, polypropylene microporous membrane, size 204 mm square). (Three layers of the positive electrode and four layers of the negative electrode), a laminate was produced. Tabs (current collectors) were welded to the positive and negative electrodes of the laminate, and the three sides were sealed with an aluminum laminate film. Thereafter, a predetermined amount of a non-aqueous electrolyte was injected, and the remaining sides were vacuum-sealed to produce a laminated battery. As a non-aqueous electrolyte, vinylene carbonate was used as an additive in a solution in which 1.0 M LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio of 3: 7, 3EC7DEC). At a concentration of 1% by mass (% by mass based on the total mass of the electrolyte salt and the mixed solvent). The amount of the nonaqueous electrolyte injected was such that the ratio of the amount of the nonaqueous electrolyte to the total pore volume of the positive electrode, the negative electrode, and the separator (liquid coefficient L) was 1.5.

The rated capacity (Ah) of the obtained laminated battery of Comparative Example 1 and the ratio of the battery area to the rated capacity were 4.5 Ah and 70 cm ² / Ah, respectively.

[Example 1]
In “(3) Preparation of negative electrode”, the active material (1) subjected to a heat treatment at 90 ° C. for 3 hours under an air atmosphere was used as the negative electrode active material instead of the active material (1). Except for this, a laminated battery was produced in the same manner as in Comparative Example 1 described above.

[Example 2]
In “(3) Preparation of negative electrode”, the active material (1) subjected to a heat treatment at 100 ° C. for 3 hours under an air atmosphere was used as the negative electrode active material instead of the active material (1). Except for this, a laminated battery was produced in the same manner as in Comparative Example 1 described above.

[Example 3]
In “(3) Preparation of negative electrode”, the active material (1) subjected to a heat treatment at 180 ° C. for 3 hours under an air atmosphere was used as the negative electrode active material instead of the active material (1). Except for this, a laminated battery was produced in the same manner as in Comparative Example 1 described above.

[Example 4]
In “(3) Preparation of negative electrode”, a material obtained by subjecting active material (1) to a heat treatment at 180 ° C. for 3 hours in an argon (Ar) atmosphere in place of active material (1) was used as a negative electrode active material. A laminated battery was produced in the same manner as in Comparative Example 1 except that the battery was used as Comparative Example 1.

[Example 5]
In “(3) Preparation of negative electrode”, the active material (1) was subjected to a heat treatment at 180 ° C. for 3 hours in a nitrogen (N ₂ ) atmosphere in place of the active material (1). A laminated battery was produced in the same manner as in Comparative Example 1 except that the laminated battery was used as a substance.

[Example 6]
In “(3) Preparation of negative electrode”, the active material (1) was subjected to a heat treatment at 180 ° C. for 3 hours under a reduced pressure (100 Pa) atmosphere in place of the active material (1). A laminated battery was produced in the same manner as in Comparative Example 1 except that the battery was used as Comparative Example 1.

[Example 7]
In “(3) Preparation of negative electrode”, the active material (1) subjected to a heat treatment at 190 ° C. for 3 hours under an air atmosphere was used as the negative electrode active material instead of the active material (1). Except for this, a laminated battery was produced in the same manner as in Comparative Example 1 described above.

[Comparative Example 2]
In “(3) Preparation of negative electrode”, the active material (1) subjected to a heat treatment at 200 ° C. for 3 hours under an air atmosphere was used as the negative electrode active material instead of the active material (1). Except for this, a laminated battery was produced in the same manner as in Comparative Example 1 described above.

[Comparative Example 3]
In “(3) Preparation of negative electrode”, the active material (1) subjected to a heat treatment at 210 ° C. for 3 hours under an air atmosphere was used as the negative electrode active material instead of the active material (1). Except for this, a laminated battery was produced in the same manner as in Comparative Example 1 described above.

The rated capacity (Ah) of the obtained laminated batteries of Examples 1 to 7 and Comparative Examples 2 to 3 and the ratio of the battery area to the rated capacity were all 4.5 Ah and 70 cm ² / Ah, respectively.

≫Evaluation of laminated battery≫
[Evaluation of physical properties of negative electrode active material]
The amount (number) of carbon dioxide (CO ₂ ) molecules desorbed from the negative electrode active material used in each of the examples and comparative examples using a temperature rising desorption gas analyzer TDS-1200 manufactured by Electronic Science. Was measured and analyzed. Specifically, the number (number of 2 mg) of carbon dioxide molecules (CO ₂ ) desorbed from the negative electrode active material at a temperature rise from 50 ° C. to 400 ° C. was measured by thermal desorption gas analysis (TDS). . The results are shown in Table 1 below.

In the TDS, a sample stage for setting a negative electrode active material as a sample is made of quartz, and a sample dish is made of SiC. Further, the heating rate was 10 ° C./min. The temperature rise was controlled by monitoring the sample surface temperature. The mass of the sample was 2 mg, and was corrected by the measured mass. A quadrupole mass spectrometer was used for detection, and the applied voltage was 1000 V. Mass number used for the analysis of the measured value [M / z] are _{H 2} are 2, _{H 2} O is 18, CO is a 28, CO ₂ is 44, the gas corresponding to the mass number, all of the above, respectively Each substance was assumed to be. Note that, as the sample temperature in TDS (that is, the temperature of the negative electrode active material), not the ambient temperature but the sample surface temperature was used.

Next, the R value of the produced negative electrode active material was measured using a laser Raman spectrometer (NRS-2100 manufactured by JASCO Corporation). An argon laser was used as a measurement light source. In the measurement, the raw material carbon particles as a sample were irradiated with an argon laser, and the peak intensities at 1360 cm ^-1 (D band) and 1580 cm ^-1 (G band), I1360 and I1580, were determined from the scattered light spectrum. The R value, which is the intensity ratio (I1360 / I1580), was calculated. The measurement of the R value was also performed on the negative electrode active material obtained by disassembling the laminated battery after the measurement of the capacity retention after 1000 cycles described later. The results are shown in Table 1 below.

[Capacity maintenance rate after 1000 cycles]
With the current density with respect to the positive electrode being ² mA / cm ² , the laminated batteries produced in each of the examples and comparative examples were charged to a cutoff voltage of 4.15 V to obtain an initial charge capacity, and a cutoff voltage of 3.0 V after a one-hour pause. The capacity when the battery was discharged to the maximum was defined as the initial discharge capacity. This charge / discharge cycle was repeated 1000 times. Then, the ratio of the discharge capacity at the 1000th cycle to the initial discharge capacity was calculated. The results are shown in Table 1 below.

[Evaluation of cell swelling]
The cell swelling was evaluated by comparing the volume of the laminated battery immediately after fabrication with the volume of the laminated battery after measuring the 1000 cycle capacity retention rate. Here, the volume of the laminated battery was measured by the Archimedes method. The results are shown in Table 1 below. In addition, UX6200H manufactured by Shimadzu Corporation was used as the electronic balance. In addition, a thermometer YOKOGAWA TX1001 and a thermocouple Type K were used for measuring the underwater temperature, and ion-exchanged water was used as the water (recommended ion conductivity of 0.1 to 100 μS / cm). Further, the measurement environment temperature was 25 ° C. ± 3 ° C. The specific procedure is shown below.

  1) A laminated battery is hung on an electronic balance, and the mass in the atmosphere is measured.

  Next, the water tank is raised, all parts of the laminated battery are submerged in water, and the mass in water is measured. Then, the place where the cell mass is stabilized is defined as the mass in water (about 2 minutes).

  2) The cell volume is calculated using the following equation (1). Note that the density at the temperature during the volume measurement is used as the density of water.

From the results shown in Table 1, the rate of change of the R value by Raman spectroscopy after 1000 cycles of charge / discharge is a value within a predetermined range, or the amount of the heated desorption gas (CO ₂ ) is a predetermined value. By configuring a non-aqueous electrolyte secondary battery using a negative electrode active material having a value within a range, and an initial R value according to Raman spectroscopy being a value within a predetermined range, the charge-discharge proceeds It is understood that it is possible to improve long-term cycle durability such as 1000 cycles while suppressing gas generation and battery swelling caused by the gas generation.

  In addition, it was also found that heat treatment of the active material functions as a factor affecting these parameters, and in particular, it was also found that the temperature conditions during the heat treatment show a certain tendency with respect to changes in the parameters.

  The laminated batteries obtained in the examples and comparative examples are large-sized, large-capacity, and large-area laminated batteries, as can be seen from the rated capacity and the ratio of the battery area to the rated capacity. Thus, although the effects of the present invention are not limited by the capacity and size of the battery, it was confirmed that the present invention is particularly useful for a large-sized, large-capacity, and large-area non-aqueous electrolyte secondary battery.

10, 50 lithium ion secondary battery,
11 negative electrode current collector,
12 positive electrode current collector,
13 negative electrode active material layer,
15 positive electrode active material layer,
17 separator,
19 cell layers,
21, 57 power generation elements,
25 negative electrode current collector,
27 positive electrode current collector,
29, 52 Battery exterior material,
58 positive electrode tab,
59 Negative electrode tab.

Claims (10)

A negative electrode active material for a non-aqueous electrolyte secondary battery, wherein the proportion of carbon atoms in the active material is 50% by mass or more ,
The initial number of desorbed carbon dioxide molecules (CO ₂ ) measured by thermal desorption spectroscopy (TDS) at a temperature rise from 50 ° C. to 400 ° C. is 1.5 to 3.1 × 10 ¹⁵ [pieces / piece] 2 mg], and the R value determined by Raman spectroscopy is 0.41 to 0.45. The negative electrode active material for a non-aqueous electrolyte secondary battery. 2. The number of desorbed carbon dioxide molecules is 1.5 to 2.4 × 10 ¹⁵ [pieces / 2 mg], and an R value obtained by Raman spectroscopy is 0.41 to 0.44. 3. The negative electrode active material for a non-aqueous electrolyte secondary battery according to 1. The number of the desorbed carbon dioxide molecules is 1.5 to 1.6 × 10 ¹⁵ [pieces / 2 mg], and the R value determined by Raman spectroscopy is 0.41 to 0.42. The negative electrode active material for a non-aqueous electrolyte secondary battery according to 1. When the R value is R _A , the following relationship is established between the R _A and the R value (R _B ) after 1000 cycles of charge / discharge using the active material under the following charge / discharge conditions. :
The negative electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, which satisfies the following :
(Charging and discharging conditions)
One charge / discharge cycle is to charge to a cutoff voltage of 4.15 V at a current density of ² mA / cm ² with respect to the positive electrode, and discharge to a cutoff voltage of 3.0 V after a one-hour pause. A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, wherein the proportion of carbon atoms in the active material is 50% by mass or more ,
Heat-treating artificial or natural graphite or amorphous carbon at a heat treatment temperature of 90 to 190 ° C. and a heat treatment time of 1 to 5 hours ,
Before and after the heat treatment, the number of desorbed carbon dioxide molecules (CO ₂ ) measured at the temperature rise from 50 ° C. to 400 ° C. by thermal desorption spectroscopy (TDS) was N ₁ (before heat treatment). ) And N ₂ (after heat treatment)
Assuming that R values before and after the heat treatment determined by Raman spectroscopy are R ₁ (before heat treatment) and R ₂ (after heat treatment), respectively, the following relationship:
Wherein N ₂ is 1.5 to 3.1 × 10 ¹⁵ [pieces / 2 mg], and R ₂ is 0.41 to 0.45. A method for producing a negative electrode active material for an electrolyte secondary battery. The following relationship:
The method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 5, which satisfies the following. The following relationship:
The method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 6, which satisfies the following. Current collector,
A negative electrode active material layer including a negative electrode active material disposed on the surface of the current collector,
A negative electrode for a non-aqueous electrolyte secondary battery having
The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material is a negative electrode active material for a non-aqueous electrolyte secondary battery.   A non-aqueous electrolyte secondary battery comprising the negative electrode for a non-aqueous electrolyte secondary battery according to claim 8. 10. The non-aqueous electrolyte according to claim 9, wherein a value of a ratio of a battery area to a rated capacity (projected area of the battery including the battery exterior body) is 5 cm ² / Ah or more, and a rated capacity is 3 Ah or more. Next battery.