JP2011228293A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which has a high ratio of a low-SOC output with respect to a high-SOC output and a high energy density.SOLUTION: A nonaqueous electrolyte secondary battery has a positive electrode including a first active material containing a lithium transition metal complex oxide expressed by general formula LiNiMnCoO(x+y+z=1, x>0, y>0 and z>0), and a second active material containing LiFePO, and has a 1-kHz impedance equal to or less than 1.27 mΩ, which makes possible to offer a nonaqueous electrolyte secondary battery having a high ratio of a low-SOC output with respect to a high-SOC output, and a high energy density.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  Nonaqueous electrolyte secondary batteries have been widely used in recent years as power sources for mobile devices typified by mobile phones, taking advantage of their high energy density. In addition to power supplies for small devices, it is expected to be used for medium and large-sized industrial applications such as power storage, electric vehicles and hybrid vehicles.

A nonaqueous electrolyte secondary battery generally includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator, and a nonaqueous electrolyte containing a nonaqueous solvent and a lithium salt.
The positive electrode active material constituting the nonaqueous electrolyte secondary battery is a lithium transition metal composite oxide, the negative electrode active material is a carbon material typified by graphite, and the nonaqueous electrolyte is mainly composed of ethylene carbonate. A solution in which an electrolyte such as lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a non-aqueous solvent is widely known.

At present, there are many positive electrode active materials for non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, but the most commonly known is a lithium cobalt composite whose operating voltage is around 4V. It is a lithium transition metal composite oxide having a basic structure of oxide (LiCoO ₂ ), lithium nickel composite oxide (LiNiO ₂ ), lithium manganese composite oxide (LiMn ₂ O ₄ ) having a spinel structure, or the like. Among them, LiCoO ₂ is widely adopted as a positive electrode active material for small-capacity lithium ion secondary batteries up to a battery capacity of 2 Ah because of its excellent charge / discharge characteristics and energy density.

However, since cobalt has less abundance, is expensive, lithium-transition metal composite oxide part of the cobalt in LiCoO ₂ was replaced with nickel and manganese _{LiNi x Mn y Co z O 2} (0 ≦ x <1, Development of 0 ≦ y <1, 0 <z <1, x + y + z = 1) is in progress, but has a problem that it is inferior in high rate discharge performance compared to LiCoO ₂ . Therefore, as a means for improving the high rate discharge performance of LiNi _x Mn _y Co _z O ₂ , a technique for improving the diffusibility of lithium ions by increasing the specific surface area or by making fine particles has been studied. There is a problem that the charge / discharge capacity is lowered and the safety is remarkably lowered.

  In addition, considering the development of medium-sized and large-sized products in the future, especially industrial applications where large demand is expected, there are applications where batteries are used in high-temperature environments that are not used in small-sized consumer products. Safety is very important.

Therefore, it has been proposed to use a lithium transition metal phosphate compound, which is a positive electrode active material having high safety, alone or in combination with a lithium transition metal composite oxide. Lithium transition metal phosphate compounds typified by LiFePO ₄ having an olivine type crystal structure are high in oxygen because they form a covalent bond with phosphorus, so that oxygen is not generated even when exposed to a high temperature environment in a charged state. Safety can be obtained.

For the purpose of “providing a non-aqueous electrolyte secondary battery that can easily detect a charged state without using a complicated electronic circuit” (paragraph 0006), Patent Document 1 describes “lithium ions. A non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode that can be inserted and removed, and the positive electrode includes two or more positive electrode active materials, and the non-aqueous electrolyte secondary battery is charged and discharged. When the charge / discharge curve representing the relationship between the remaining capacity and the battery voltage has the remaining battery capacity on the horizontal axis and the battery voltage on the vertical axis, the battery voltage becomes substantially flat and the battery with respect to the change in the remaining battery capacity It has two or more flat parts with a small voltage change, and the slope part where the change of the battery voltage with respect to the change of the battery remaining capacity is larger than the flat part is interposed between the flat parts. To Invention is disclosed that "(paragraph 0007). Patent Document 1 states that, in this case, the positive electrode active material includes a lithium-containing transition metal composite oxide having an olivine crystal structure, a lithium-containing transition metal composite oxide having a layered crystal structure, and a lithium containing spinel crystal structure. In this case, the lithium-containing transition metal composite oxide having an olivine crystal structure may be represented by the chemical formula Li _{1 + y} M _1-y PO ₄ (M is Mn, Co, Ni). , Cr, Al, Mg, Fe, or a transition metal element selected from the group consisting of a compound represented by the chemical formula Li _{1 + y} M _1-y PO ₄ and carbon. And a lithium-containing transition metal composite oxide having a layered crystal structure as a compound represented by the chemical formula Li _{1 + x} M _1-x O ₂ The lithium-containing transition metal composite oxide having a spinel crystal structure may be a compound represented by the chemical formula Li _{1 + x} M _2−x O ₄ ”(paragraph 0009). Examples of Patent Document 1 include “a lithium-containing transition metal composite oxide having a layered crystal structure represented by a chemical formula LiCo _0.33 Mn _0.33 Ni _0.34 O ₂ , and a chemical formula LiFePO _4. A laminated film-covered battery 1 using a mixed positive electrode active material obtained by mixing a lithium-containing transition metal composite oxide having an olivine crystal structure with a compound supporting carbon of 10% by weight in a weight ratio of 2: 1. When the laminated film exterior battery is used, “the battery charge state can be detected at a stage where the remaining battery capacity is sufficient, so the device is immediately stopped. That is, it is easy to detect the state of charge even with low-accuracy voltage detection, and the operation of the device can be ensured even after detection. "(Paragraph 0037) It is shown.

Patent Document 2 states that “the battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, and the capacity of the negative electrode includes a capacity component due to insertion and extraction of lithium and a capacity component due to lithium precipitation and dissolution. The positive electrode contains lithium and iron (Fe) and contains a first positive electrode active material made of a phosphorus oxide having an olivine structure ”(paragraph 0008). "The positive electrode further contains lithium, nickel, a first element and oxygen (O), and the first element is iron, cobalt (Co), manganese (Mn), Copper (Cu), zinc (Zn), aluminum (Al), tin (Sn), boron (B), gallium (Ga), chromium (Cr), vanadium (V), titanium (Ti), magnesium (M ), Calcium (Ca), and strontium (Sr), and a second positive electrode active material in which the proportion of nickel and nickel in the first element is 50 mol% or more is included. The ratio by mass ratio of the first positive electrode active material and the second positive electrode active material (first positive electrode active material: second positive electrode active material) is set within the range of 30:70 to 90:10. In this case, the thermal stability can be further improved and the capacity can be increased. "(Paragraph 0010), and" the content of the first positive electrode active material is relative to the total amount of the positive electrode active material. In the range of 30% by mass or more and 90% by mass or less, and more preferably in the range of 30% by mass or more and 55% by mass or less, if the content of the first positive electrode active material is small, Improved stability That effect is not sufficient, the content is large, capacity is lowered. "(Paragraph 0023) that have been described. In an example of Patent Document 2, in a secondary battery in which the capacity ratio between the positive electrode and the negative electrode material is 120: 100, LiFePO ₄ is used as the first active material, and LiNi _{0.6 is} used as the second active material. When Co _0.2 Mn _0.2 O ₂ or LiNi _0.5 Co _0.3 Mn _0.2 O ₂ is used, “the ratio of the first positive electrode active material increases, As the ratio decreased, good results were obtained in the nail cutting test, and the discharge capacity was increased as the ratio of the second cathode active material increased and the ratio of the first cathode active material decreased. Furthermore, the ratio (first positive electrode active material: second positive electrode active material) by the mass ratio between the first positive electrode active material and the second positive electrode active material was changed from 30:70 to 90:10. In each of the examples within the range, the capacity of the negative electrode is lithium insertion and extraction. Represented by a capacity component by the higher discharge capacity than the comparative example 1-3 was called lithium ion secondary battery were obtained. "(Paragraph 0093) that has been shown.

Patent Document 3 states that “an electrochemically active material is replaced by I) lithium and one element selected from Mg, Al, B, Ti, Si, Zr, Fe, Zn, and Cu. A composite oxide of at least one transition metal selected from Ni and Co, and II) a general formula Li _t M ² _z PO ₄ from phosphorus, lithium, and at least one transition metal, wherein 0 ≦ t ≦ 3, and a mixture with a composite oxide of z = 1 or 2), and the content of the composite oxide from phosphorus, lithium, and at least one transition metal is the weight of the mixture A lithium rechargeable electrochemical cell comprising a liquid electrolyte and the electrochemically active material for a positive electrode is provided, characterized in that it is in the range of 1% to 50%. Is “It is preferable that the composite oxide of phosphorus, lithium, and a transition metal is selected from LiFePO ₄ , LiVPO ₄ F, and Li ₃ Fe ₂ PO ₄ ” (paragraph 0013). . In an example of Patent Document 3, an electrochemical cell containing LiFePO ₄ and LiNi _0.80 Co _0.15 Al _0.05 O ₂ in a ratio of 20:80 is described, and the electrochemical cell is LiFePO _4. Or a reversible capacity higher than expected from the case of using LiNi _0.80 Co _0.15 Al _0.05 O ₂ alone, and when performing an overuse overcharge test, "Using the active material of the present invention for a lithium battery can reduce the total amount of gas released by about one-half compared to prior art batteries" (paragraph 0043). .

For the purpose of providing a non-aqueous electrolyte secondary battery having excellent overdischarge performance and showing a continuous potential change during charging and discharging (paragraph 0009), Patent Document 4 describes, In a non-aqueous electrolyte secondary battery including a positive electrode including, a negative electrode including a carbon material, and a non-aqueous electrolyte, the positive electrode active material is LiCoO ₂ , LiMnO _2, and a general formula LiFe _1-x M _x PO ₄ (however, , 0 ≦ x ≦ 0.13, M is a compound represented by at least one metal selected from Mg, Co, Ni, Mn, and Zn), and the ratio of LiCoO ₂ to the positive electrode active material is 50% by weight to 80% by weight, the ratio of LiMnO ₂ is 10% by weight to 30% by weight, and the ratio of LiFe _1-x M _x PO ₄ is 10% by weight to 30% by weight. It is characterized. "(Paragraph 0 10) the invention is disclosed. In an example of Patent Document 4, a non-aqueous electrolyte using a positive electrode active material in which LiCoO ₂ , LiMnO ₂ , and LiFePO ₄ are mixed in a weight ratio of 70:20:10 to 50:20:30. A secondary battery is shown, “In a ternary system of LiCoO ₂ , LiMnO ₂ and LiFePO ₄ , a flat region of about 3.6 V, about 3.3 V, and about 2.5 V has a flat region of 4 V to 2. It showed a continuous discharge curve up to 5V "(paragraph 0069).

Patent Document 5 states that “a secondary battery using the above-described layered rock salt structure LiCoO ₂ , LiNiO ₂ , spinel structure LiMn ₂ O _4, or the like as a positive electrode active material depends on its charge state (SOC). In order to solve the problem of “the density changed” (paragraph 0004), “a positive electrode using a lithium transition metal composite oxide as a positive electrode active material, a negative electrode, and a lithium salt dissolved in an organic solvent” A lithium secondary battery comprising a non-aqueous electrolyte, wherein an output density at an SOC of 50% and an input density are 1500 W / kg or more, respectively, and an output density in an SOC range of 25% to 80% The invention is disclosed that the rate of change and the rate of change of input density are each 20% or less. "(Paragraph 0007). Patent Document 5 states that “a lithium transition metal composite oxide used as a positive electrode active material of a secondary battery is not particularly limited. A secondary battery that has high input density and high output density and does not depend on SOC. For example, it is preferable to use one having a composition formula LiMePO ₄ and a crystal structure having an olivine structure ”(paragraph 0014),“ in this case, the composition formula LiMePO ₄ , Me is at least one selected from divalent transition metals, and examples thereof include Fe, Mn, Ni, Co, Mg, etc. Among them, they are abundant and inexpensive in terms of resources and have an environmental burden. It is desirable that Me be Fe because it is small ”(paragraph 0015). In the example of Patent Document 5, a LiFe _0.85 Mn _0.15 PO ₄ compounded with carbon material fine particles was used as a positive electrode active material # 3, and “LiNiO ₂ was used as a positive electrode active material # 5 Secondary battery, Li
The Mn ₂ O ₄ was secondary battery # 6 those as the positive electrode active material. (Paragraph 0061), "the power density of the secondary batteries of # 5 and # 6 was significantly changed by the SOC as compared with the secondary battery of # 3." (Paragraph 0062). "As described above, the secondary battery of the present invention using the olivine-structured lithium transition metal composite oxide as the positive electrode active material has both high output density and high input density, and little change in input / output density due to SOC. It was confirmed that the battery was a secondary battery ”(paragraph 0064).

JP 2007-250299 A JP 2007-317538 A JP 2005-183384 A JP 2003-346799 A JP 2003-036889 A

Non-aqueous electrolyte secondary batteries used in hybrid vehicles and electric vehicles are required to have high output performance in any state of charge (SOC) in addition to high energy density and high safety. That is, a nonaqueous electrolyte secondary battery having a high ratio of output at low SOC to output at high SOC is desired.
Patent Document 5 discloses a battery in which the change in input / output density due to SOC is reduced by using LiFePO ₄ as a positive electrode active material, but LiFePO ₄ has an energy density per mass and per volume of the active material. Since it is low, the battery using this for a positive electrode has the subject that it does not have sufficient energy density.

  The present invention has been made in view of the above problems, and it is an object of the present invention to provide a non-aqueous electrolyte secondary battery having a high ratio of output at low SOC to output at high SOC and high energy density. To do.

  The technical configuration and operational effects of the present invention are as follows. However, the action mechanism includes estimation, and its correctness does not limit the present invention.

The nonaqueous electrolyte secondary battery according to the present invention includes a lithium transition metal composite oxide represented by a general formula LiNi _x Mn _y Co _z O ₂ (x + y + z = 1, x> 0, y> 0, z> 0). A non-aqueous electrolyte secondary battery comprising a positive electrode containing a first active material containing and a second active material containing LiFePO ₄ and having an impedance of 1 kHz of 1.27 mΩ or less.
That is, the nonaqueous electrolyte secondary battery of the present invention is a lithium transition metal composite oxide represented by the general formula LiNi _x Mn _y Co _z O ₂ (x + y + z = 1, x> 0, y> 0, z> 0). By including LiFePO ₄ , it has high safety and excellent input / output performance, and further, the impedance of 1 kHz is 1.27 mΩ or less, which is due to the change in SOC. A non-aqueous electrolyte secondary battery having a small change in input / output density can be obtained.

In the nonaqueous electrolyte secondary battery of the present invention, the ratio of the second active material to the sum of the first active material and the second active material contained in the positive electrode is 5% by mass or more and 25%. It is characterized by being not more than mass%.
In the non-aqueous electrolyte secondary battery of the present invention, when the ratio of the second active material to the sum of the first active material and the second active material is 5% by mass or more, high safety is achieved. In addition to ensuring the output performance, the output performance at the low SOC with respect to the output at the high SOC can be remarkably increased. Moreover, it is set as the nonaqueous electrolyte secondary battery which has a high energy density because the ratio of the said 2nd active material with respect to the sum of a said 1st active material and a said 2nd active material shall be 25 mass% or less. be able to.

The non-aqueous electrolyte secondary battery of the present invention, the first active _{material, LiNi x Mn y Co z O} 2 (x + y + z = 1,1 / 4 ≦ x ≦ 1 / 3,1 / 4 ≦ y ≦ It is preferable to contain a lithium transition metal composite compound represented by 1/3, 1/3 ≦ z ≦ 1/2). It is preferable that x, y, and z in the lithium transition metal composite oxide be in the range of these values because the effects of the present invention become remarkable.

  In the nonaqueous electrolyte secondary battery of the present invention, it is preferable that a carbonaceous material is disposed on the second active material. By arranging the carbonaceous material in the second active material, the electrical conductivity is improved and the effect of the present invention can be made more remarkable.

  ADVANTAGE OF THE INVENTION According to this invention, the ratio of the output in low SOC with respect to the output in high SOC can be high, and the nonaqueous electrolyte secondary battery which has a high energy density can be provided.

Structural schematic diagram of batteries according to Examples 1 to 10 and Comparative Example 2 Structural schematic diagram of batteries according to Comparative Examples 1 and 3

  Embodiments of the present invention are illustrated below, but the present invention is not limited to these descriptions.

The nonaqueous electrolyte secondary battery according to the present invention includes a lithium transition metal composite oxide represented by a general formula LiNi _x Mn _y Co _z O ₂ (x + y + z = 1, x> 0, y> 0, z> 0). A non-aqueous electrolyte secondary battery comprising a positive electrode containing a first active material containing and a second active material containing LiFePO ₄ and having an impedance of 1 kHz of 1.27 mΩ or less.
Specifically, the non-aqueous electrolyte secondary battery of the present invention is a lithium transition metal composite oxide represented by the general formula LiNi _x Mn _y Co _z O ₂ (x + y + z = 1, x> 0, y> 0, z> 0). A positive electrode containing a first active material containing a material and a second active material containing LiFePO ₄ , a negative electrode, and a non-aqueous electrolyte containing an electrolyte salt and a non-aqueous solvent, and an impedance of 1 kHz is 1. 27 mΩ or less.
Furthermore, the nonaqueous electrolyte secondary battery of the present invention may be provided with a separator between the positive electrode and the negative electrode. Moreover, the exterior body which packages these structures may be provided.
In addition, the aspect of the non-aqueous electrolyte secondary battery is not particularly limited. For example, a coin battery or a button battery having a positive electrode, a negative electrode, and a single-layer or multi-layer separator, a positive electrode, a negative electrode, and a roll. And a cylindrical battery, a square battery, a flat battery, and the like having a cylindrical separator.

The first active material is selected from the group of lithium transition metal composite oxides represented by the general formula LiNi _x Mn _y Co _z O ₂ (x + y + z = 1, x> 0, y> 0, z> 0). It contains at least one compound and has an α-NaFeO ₂ type crystal structure.
In the lithium transition metal composite oxide, a part of Li, Ni, Mn and / or Co in the above general formula does not impair the effects of the present invention, such as Fe, Al, Cr, Mg, V and Ti It may be substituted with a metal element, and a part of oxygen may be substituted with F, S or the like. In addition, lithium represented by LiNi _x Mn _y Co _z O ₂ (x + y + z = 1, 1/4 ≦ x ≦ 1/3, 1/4 ≦ y ≦ 1/3, 1/3 ≦ z ≦ 1/2) The transition metal composite oxide is preferable because the effect of the present invention becomes remarkable. Moreover, it is preferable that | x−y | ≦ 0.05 because it is excellent in thermal stability and charge / discharge cycle performance.
Examples of the first active material include LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _1/6 Mn _1/6 Co _2/3 O ₂ , LiNi _1/4 Mn _1/4 Co _{1 / 2} O ₂ , LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , etc., and LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _1/4 Mn _1/4 Co _{1 / 2} O ₂ is preferred.

The second active material is represented by the general formula LiFePO ₄ . The second active material according to the present invention includes Co, Al, Cr, Mg, Mn, Ni, Ti, and the like as long as a part of Fe and / or Li in the above general formula does not impair the effects of the present invention. It does not exclude those substituted with a metal element other than Fe or Li. In addition, the phosphoric acid moiety (PO ₄ ) may contain a small amount of other anions such as (BO ₃ ), (WO ₄ ), (MoO ₄ ), (SiO ₄ ), and the like Is also included in the scope of rights of the present invention.

  In the non-aqueous electrolyte secondary battery according to the present invention, various methods are used in order to set the impedance at 1 kHz to 1.27 mΩ or less. The impedance value of 1 kHz can be used as an index representing the magnitude of the internal resistance. In general, the resistance of a material is proportional to thickness and inversely proportional to electrical conductivity and area. Here, in the battery, the thickness corresponds to the distance between the electrodes, and varies depending on the thickness of the electrode or separator or the current collecting structure. In order to reduce the internal resistance, it is preferable to reduce the thickness of the electrode and use a thin separator. Moreover, about a current collection structure, internal resistance can be reduced by shortening the distance from an active material application part to a current collection board, or enlarging the cross-sectional area of a current collection board and / or a current collection terminal. The electrical conductivity varies depending on the composition and shape of the active material, the composition of the mixture, the composition of the electrolyte solution, or the current collecting structure. For example, the active material is coated with a conductive material, the current collector is undercoated, Increasing the thickness of the electric body, increasing the proportion of the conductive agent contained in the electrode mixture, using a non-aqueous solvent having a low viscosity or a high dielectric constant, or a current collector and a current collector plate or Reducing the resistance between the current collector plate and the current collector terminal is effective for increasing the electrical conductivity. The area corresponds to the electrode area, and the internal resistance can be reduced by increasing the electrode area. In the examples described later, the maximum distance between the current collector plate and the active material, the electrode area, and the electrode thickness will be described. However, if the technique is to reduce the 1 kHz impedance of the battery to 1.27 mΩ or less. Means other than those described herein may be used, and such are within the scope of the present invention.

The impedance of 1 kHz of the nonaqueous electrolyte secondary battery according to the present invention can be measured by a commercially available impedance measuring instrument. The impedance measurement must be performed in an open circuit state in which no load is applied to the battery (a state in which no current is passed), and the impedance of 1 kHz in the present invention means that no load is applied to the SOC 0% battery. The value measured at the time of the condition. The amplitude during measurement is preferably 10 mV or less. In addition, with SOC
Indicates how much the battery has been charged, and in the range of battery voltage that can be reversibly charged and discharged, the charging state at which the upper limit battery voltage is obtained is 100%, that is, the fully charged state, It means the state of charge when the state of charge in which the battery voltage is obtained is 0%, that is, the state of discharge. Usually, it is known that the impedance of 1 kHz becomes maximum at SOC 0%. Therefore, a battery having a 1 kHz impedance of 1.27 mΩ or less in any charged state is within the scope of the present invention. In the present specification, the impedance may be referred to as an internal resistance.

  The method for synthesizing the active material according to the present invention is not particularly limited. Specific examples include a solid phase method, a liquid phase method, a sol-gel method, and a hydrothermal method.

The lithium transition metal composite oxide which is the first active material according to the present invention basically includes a raw material containing a metal element (Li, Ni, Mn, Co) constituting the active material as a target active material. It can be obtained by adjusting the precursor (mixture) contained according to the composition and firing it. Also for LiFePO _{4 as} the second active material, a precursor containing a raw material containing metal elements (Li, Fe) constituting the active material and a raw material serving as a phosphoric acid source according to the composition of the target active material ( It can be obtained by adjusting the mixture) and firing it. At this time, a precursor containing a metal element other than Li according to the composition of the target active material may be prepared in advance, and a Li source may be added later. In addition, the composition of the compound actually obtained may vary slightly compared with the composition calculated from the charged composition ratio of the raw materials. The present invention can be carried out without departing from the technical idea or the main features thereof, and the scope of the present invention is only that the composition of the product obtained as a result of production does not exactly match the above general formula. Needless to say, it should not be construed as not belonging to. In particular, it is known that a part of the lithium source easily volatilizes during firing. For this reason, it is common practice to charge the precursor or raw material before firing with a lithium source larger than the stoichiometric ratio.

As a raw material containing Li, lithium carbonate (Li ₂ CO ₃ ), lithium hydroxide (LiOH), lithium nitrate (LiNO ₃ ), lithium acetate (CH ₃ COOLi), or the like is used. As a raw material containing Fe, iron acetate, iron nitrate, iron lactate and the like can be used. As the phosphate source, ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and the like can be used. Moreover, as a raw material containing Ni, Mn or Co, carbonate, nitrate, acetate or sulfate of each metal is used. In addition, in the synthesis of an aqueous solution system such as a liquid phase method and a sol-gel method, the compound used as a metal source is preferably one that dissolves in water. It is good to change the above or to dissolve each raw material in purified water beforehand. Furthermore, as the phosphoric acid source containing Li, lithium phosphate _(Li 3 _PO 4), it is also possible to use lithium dihydrogen phosphate _(LiH 2 PO _4).

Moreover, it is preferable to adhere and coat carbon on the surface of the active material particles mechanically or by thermal decomposition of organic matter for the purpose of supplementing electron conductivity.
In particular, in LiFePO ₄ which is the second active material according to the present invention, it is important to sufficiently ensure the electron conduction between particles with carbon or the like in order to sufficiently develop the effects of the present invention.

  In the present invention, the method for adhering or coating the carbon on the surface of the active material particles used for the electrode is not limited. For example, a solid or liquid organic substance or carbon source such as carbon and the positive electrode active material particles It can be obtained by heat treatment. The heat treatment temperature needs to be equal to or higher than the temperature at which the carbon source is thermally decomposed. Examples of the carbon source include sucrose, polyvinyl alcohol, and acetylene black. Alternatively, a method may be employed in which positive electrode active material particles are placed in a temperature rising atmosphere and carbon is deposited and vapor-phase grown on the surface of the active material particles by introducing a gaseous organic material. Examples of the gaseous organic substance include vaporized monohydric alcohols such as methanol, ethanol, isopropanol, and butanol, ethylene gas, propylene gas, and the like. In addition, when synthesizing by a hydrothermal method or the like, organic substances such as citric acid and ascorbic acid may be added to the water bath for the purpose of preventing oxidation. In such a case, the active material which is the final product is used. Since carbon derived from the organic matter may adhere or be coated on the surface, it can be used as it is. Of course, you may use together the prescription using the above-mentioned solid or liquid organic substance or gaseous organic substance. For any of the above-mentioned prescriptions, for example, Examples and Comparative Examples in International Publication No. 2007/043665 pamphlet are useful.

The lithium transition metal composite oxide as the first active material and the LiFePO _{4 as} the second active material according to the present invention are preferably powders having an average particle size of 100 μm or less. In particular, in order to effectively bring out the effects of the present invention, a smaller particle size is preferable, and the average particle size of secondary particles is preferably 0.5 to 50 μm. By making the secondary particle diameter small, it becomes possible to make it uniform when the positive electrode paste is applied to the current collector. The primary particle diameter of LiFePO ₄ is more preferably 50 to 500 nm. By reducing the primary particle size of LiFePO _4, since it is possible to shorten the diffusion path length of the solid electron conduction path length and Li ions Aiuchi, it is possible to maximize use of the performance of LiFePO _4.
The average particle size of secondary particles is determined by particle size distribution measurement by liquid phase precipitation method or laser diffraction / scattering method, and the average particle size of primary particles is determined by image analysis of the results of transmission electron microscope (TEM) observation. Can be sought.

The BET specific surface area by the nitrogen adsorption method of the lithium transition metal composite oxide as the first active material is preferably large in order to achieve the effects of the present invention significantly, preferably 0.1 m ² / g or more, 0.5 m ² / g or more is more preferable. Further, by making the specific surface area of the lithium transition metal composite oxide preferably 20 m ² / g or less, more preferably 10 m ² / g or less, the thermal stability of the positive electrode in the charged state is improved and the charge / discharge capacity is reduced. It can be made sufficiently high.
The BET specific surface area by the nitrogen adsorption method of LiFePO ₄ as the second active material is preferably large so that the effects of the present invention are remarkably exhibited, preferably 1 m ² / g or more, and more preferably 5 m ² / g or more. preferable. Further, if the BET specific surface area is too large, it is necessary to increase the amount of the binder to be contained in the paste at the time of producing the electrode, and the packing density of the active material is reduced. Therefore, it is preferably 100 m ² / g or less, 80 m ² / g or less is more preferable.
In the present invention, the specific surface area of the LiFePO ₄ particles is preferably larger than the specific surface area of the lithium transition metal composite oxide.

  In order to obtain the powder of the active material contained in the electrode of the present invention in a predetermined shape, a pulverizer or a classifier can be used. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, or the like can be used. At the time of pulverization, wet pulverization in which an organic solvent such as water or alcohol or hexane coexists may be used. The classification method is not particularly limited, and a sieve, an air classifier or the like can be used in a dry or wet manner as necessary.

The general formulas of the first active material and the second active material according to the present invention can be obtained by analyzing elements other than oxygen (Li, Ni, Mn, Co or Li, Fe, It is obtained by examining the ratio of P). Examples of analysis techniques include ICP emission spectroscopy, ICP mass spectrometry, atomic absorption, and fluorescent X-ray analysis. The crystal structures of the first active material and the second active material can be examined by X-ray diffraction (XRD) measurement.
Further, the amount of the conductive carbonaceous material arranged in the active material used for the electrode according to the present invention can be determined by high-frequency overheating firing in an oxygen stream-infrared absorption method, thermogravimetry (TG), or the like. Further, it can be confirmed by observation using a transmission electron microscope (TEM) that the conductive carbonaceous material is arranged in the active material.

  Other positive electrode materials can be mixed and used for the positive electrode as long as the effects of the present invention are not impaired. Examples of other positive electrode materials include transition metal oxides, transition metal sulfides, lithium transition metal composite oxides, and the like. Examples of the transition metal oxide include manganese oxide, iron oxide, copper oxide, nickel oxide, vanadium oxide, and examples of the transition metal sulfide include molybdenum sulfide and titanium sulfide. Examples of the lithium transition metal composite oxide include lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, and lithium nickel manganese composite oxide. Furthermore, conductive polymer compounds such as disulfide, polypyrrole, polyaniline, polyparastyrene, polyacetylene, and polyacene materials, pseudographite-structured carbonaceous materials, and the like are exemplified, but the invention is not limited thereto.

The organic solvent constituting the nonaqueous electrolyte contained in the nonaqueous electrolyte secondary battery according to the present invention is not limited, and is generally an organic solvent used in a nonaqueous electrolyte provided for a nonaqueous electrolyte secondary battery. A solvent can be used.
For example, cyclic carbonate such as propylene carbonate, ethylene carbonate, butylene carbonate, styrene carbonate, catechol carbonate, 1-phenyl vinylene carbonate, 1,2-diphenyl vinylene carbonate, cyclic such as γ-butyrolactone, γ-valerolactone, propiolactone, etc. Carboxylic acid esters, linear carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, linear carboxylic acid esters such as methyl acetate and methyl butyrate, tetrahydrofuran or derivatives thereof, 1,3-dioxane, dimethoxyethane, diethoxyethane, Simple substances such as ethers such as methoxyethoxyethane and methyldiglyme, nitriles such as acetonitrile and benzonitrile, dioxalane or derivatives thereof Examples thereof include, but are not limited to, one or a mixture of two or more thereof.
Moreover, these organic solvents can be mixed and used in arbitrary ratios.

The lithium salt constituting the non-aqueous electrolyte is not limited, and lithium salts that are generally used in non-aqueous electrolyte secondary batteries and that are stable in a wide potential region can be used. For example, LiBF ₄ , LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) _{3 and the} like. These may be used alone or in combination of two or more.

  The concentration of the electrolyte salt in the nonaqueous electrolyte is preferably 0.1 mol / l to 5.0 mol / l, more preferably, in order to reliably obtain a nonaqueous electrolyte secondary battery having excellent high rate discharge characteristics. 0.8 mol / l to 2.0 mol / l.

The nonaqueous electrolyte contained in the nonaqueous electrolyte secondary battery according to the present invention can contain an arbitrary amount of a compound other than the organic solvent and the lithium salt as long as the effects of the present invention are not impaired.
Examples of such other compounds include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; Partially fluorinated products of the above aromatic compounds such as -fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5 -Overcharge inhibitors such as fluorine-containing anisole compounds such as difluoroanisole; vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate, succinic anhydride, glutar anhydride Negative electrode film forming agents such as maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone, propene sultone, butane sultone, methyl methanesulfonate Cathodic protective agents such as, busulfan, methyl toluene sulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, thioanisole, diphenyl disulfide, dipyridinium disulfide, etc. Is mentioned.

  Two or more of the above compounds may be used in combination. The combined use of a negative electrode film forming agent and a positive electrode protective agent, or the combined use of an overcharge inhibitor, a negative electrode film forming agent and a positive electrode protective agent is particularly preferred.

  The content ratio of these other compounds in the non-aqueous electrolyte is not particularly limited, but is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and still more preferably, with respect to the entire non-aqueous electrolyte. Is 0.2% by mass or more, and the upper limit is preferably 5% by mass or less, more preferably 3% by mass or less, and still more preferably 2% by mass or less. By adding these compounds, safety can be further improved, and capacity maintenance performance and cycle performance after high-temperature storage can be improved.

  There is no restriction | limiting in particular as a material of a positive electrode electrical power collector, A well-known thing can be used arbitrarily. Specific examples include metal materials such as aluminum, nickel-plated steel, titanium, and tantalum; and carbonaceous materials such as carbon cloth and carbon paper. Of these, aluminum is particularly preferable.

  The negative electrode active material used in the non-aqueous electrolyte secondary battery of the present invention is not particularly limited as long as it can electrochemically occlude and release lithium ions, such as carbonaceous materials, tin oxide and silicon oxide. Examples thereof include metal oxides, lithium transition metal composite oxides such as lithium titanate, lithium alloys such as lithium alone and lithium aluminum alloys, metals that can form alloys with lithium such as Sn and Si, and the like. These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio. Of these, carbonaceous materials or lithium transition metal composite oxides are preferably used from the viewpoint of safety.

  Examples of the carbonaceous material include natural graphite, artificial graphite, coke, non-graphitizable carbon, low-temperature calcinable graphitizable carbon, fullerene, carbon nanotube, carbon black, activated carbon and the like.

  As the current collector for the negative electrode, a known one can be arbitrarily used. For example, metal materials such as copper, nickel, stainless steel, nickel-plated steel, and chrome-plated steel can be used, and copper is particularly preferable from the viewpoint of ease of processing and cost.

  The capacity balance between the positive electrode and the negative electrode in the non-aqueous electrolyte secondary battery according to the present invention is designed so that the amount of charged electricity in the negative electrode is 1.05 times or more and less than 1.50 times the amount of charged electricity in the positive electrode. It is preferable. In order to avoid the risk of Li deposition on the negative electrode without receiving the amount of Li released from the positive electrode during charging, the negative charge is preferably 1.05 times or more of the positive charge. . If the amount of charged electricity in the negative electrode is too large, the number of negative electrodes that are not used increases, and as a result, the weight energy density and volume energy density decrease. . Therefore, the amount of charge in the negative electrode is preferably 1.05 to less than 1.50 times the amount of charge in the positive electrode, more preferably 1.05 to 1.30 times, and even more preferably 1.10 to 1.20 times. .

  As the separator, it is preferable to use a microporous membrane or a nonwoven fabric alone or in combination. Examples of the material constituting the separator include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexafluoropropylene copolymer. , Vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoro Acetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoro Ethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer. In particular, in the present invention, a microporous film mainly composed of a polyolefin resin typified by polyethylene, polypropylene or the like is preferable.

  Other battery components include conductive agents and / or binders used for positive and negative electrodes, terminals, insulating plates, battery cases, etc., but these components may be used as they are. Absent.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example and a comparative example, this invention is not limited to the following embodiment.

Lithium transition metal composite oxide LiNi _x Mn _y Co _z O ₂ (x + y + z = 1, x> 0, y> 0, z> 0) used in the following examples and comparative examples, and carbon-coated LiFePO ₄ Was synthesized by a known method. The LiFePO ₄ is already carbon coated at the time of synthesis. The amount of the carbon coat occupies 1.1 mass% of the entire LiFePO ₄ . The average particle diameter of the LiFePO ₄ was 10.0 μm, and the BET specific surface area determined by the nitrogen adsorption method was 10.5 m ² / g.

[Example 1]
(Preparation of positive electrode)
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ as the first active material and the LiFePO ₄ as the second active material were mixed at a mass ratio of 90:10. The average particle diameter of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ and the BET specific surface area determined by the nitrogen adsorption method were 12.1 μm and 1.1 m ² / g, respectively. This active material mixture was used as the positive electrode active material in this example. The positive electrode active material, a carbon material as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder are contained in a mass ratio of active material mixture: carbon material: PVdF = 88: 7: 5, N -A positive electrode paste using methyl-2-pyrrolidone (NMP) as a solvent was prepared. The positive electrode paste was applied to both surfaces of a 15 μm thick aluminum foil and dried at 80 ° C. to remove NMP. The coating mass of the positive electrode was 13.16 mg / cm ² . The positive electrode was pressure-molded with a roller press heated to 120 ° C. to form a positive electrode active material layer, and then dried under reduced pressure at 150 ° C. for 12 hours to remove moisture in the electrode plate. The total thickness of the aluminum foil and the positive electrode active material layer after the roller press was 119 μm. At this time, the porosity of the electrode plate was 35%. The positive electrode produced in this way is designated as positive electrode a.

(Preparation of negative electrode)
A negative electrode paste containing graphite as a negative electrode active material and PVdF as a binder in a mass ratio of graphite: PVdF = 94: 6 and using N-methyl-2-pyrrolidone (NMP) as a solvent was prepared. . The negative electrode paste was applied to both sides of a 10 μm thick copper foil and dried at 80 ° C. to remove NMP. The coating mass of the negative electrode is 6.85 mg / cm ² . The negative electrode was pressure-molded with a roller press heated to 120 ° C. to form a negative electrode active material layer, and then dried under reduced pressure at 150 ° C. for 12 hours to remove moisture in the electrode plate. The total thickness of the copper foil and the positive electrode active material layer after the roller press was 106 μm. At this time, the porosity of the electrode plate was 35%. The negative electrode produced in this way is referred to as negative electrode a.

(Preparation of non-aqueous electrolyte)
In a mixed solvent in which ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are mixed at a volume ratio of 1: 1: 1, LiPF ₆ which is a fluorine-containing electrolyte salt is dissolved at a concentration of 1.0 mol / l, and a non-aqueous electrolyte is obtained. Was made. The amount of water in the non-aqueous electrolyte was less than 50 ppm.

(Preparation of non-aqueous electrolyte secondary battery)
A schematic diagram of the battery of the example is shown in FIG. As the separator, a polyethylene microporous film having a thickness of 27 μm, an air permeability of 95 seconds and a porosity of 50% is used, and the separator (13) is positioned between the positive electrode a (11) and the negative electrode a (12). Thus, the positive electrode, the negative electrode, and the separator were wound into a flat shape to produce a power generation element (14). The area where the positive electrode and the negative electrode face each other (opposing area) was 6825 cm ² . Here, the positive electrode and the negative electrode are wound while being shifted in a direction away from each other along the winding axis. That is, one of the axial ends of the power generation element (14) protrudes from the separator (13), and the other of the axial ends of the power generation element (14) forms the negative electrode. Metal foil sticks out. The positive electrode current collector plate made of aluminum was disposed at a position (15) across the thickness direction with respect to the power generation element on the portion of the metal foil constituting the positive electrode that protruded from the separator, and then welded to the metal foil. Similarly, on the negative electrode side, a copper negative electrode current collector plate was placed on a portion of the metal foil constituting the negative electrode that protruded from the separator at a position (16) across the thickness direction with respect to the power generation element, and then the metal Welded with foil. At this time, the distance (17) from the current collecting plate to the farthest active material was the length in the width direction of the power generation element, and this distance was within 10 cm. A power generation element (14) made of a positive electrode, a negative electrode, and a separator prepared as described above was welded with a positive and negative current collector plate, and an aluminum square battery case (height 81 mm, width 111.6 mm, thickness 20. 6 mm), and positive and negative terminals were attached. 76 g of nonaqueous electrolyte was injected into the container and then sealed to prepare a nonaqueous electrolyte secondary battery having a design capacity of 11.5 Ah. This battery is referred to as a battery A of the present invention.

[Example 2]
(Preparation of positive electrode)
An active material mixture obtained by mixing LiNi _1/4 Mn _1/4 Co _1/2 O ₂ as the first active material and the LiFePO ₄ as the second active material at a mass ratio of 90:10 is used as the positive electrode active material. Example 1 except that the coating mass of the positive electrode was 13.23 mg / cm ² and the total thickness of the aluminum foil and the positive electrode active material layer after pressure molding was 118 μm. In the same manner as above, a positive electrode b was produced. The average particle diameter of the LiNi _1/4 Mn _1/4 Co _1/2 O ₂ and the BET specific surface area determined by the nitrogen adsorption method were 6.2 μm and 0.62 m ² / g, respectively.

(Preparation of negative electrode)
A negative electrode b was produced in the same manner as in Example 1, except that the coating mass of the negative electrode was 6.89 mg / cm ² . At this time, the porosity of the electrode plate was 35%.

(Preparation of non-aqueous electrolyte secondary battery)
A battery B of the present invention was produced in the same manner as in Example 1 except that the positive electrode b and the negative electrode b were used.

[Example 3]

(Preparation of non-aqueous electrolyte secondary battery)
A battery C of the present invention was produced in the same manner as in Example 2 except that the facing area between the positive electrode and the negative electrode was 7037 cm ² .

[Example 4]
(Preparation of positive electrode)
Except that the coating mass of the positive electrode was 14.20 mg / cm ² and the total thickness of the aluminum foil and the positive electrode active material layer after pressure molding was 125 μm, the same as in Example 2, A positive electrode d was produced.

(Preparation of negative electrode)
Except that the coating mass of the negative electrode was 7.40 mg / cm ² and the total thickness of the copper foil and the negative electrode active material layer after pressure molding was 113 μm, the same as in Example 2, A negative electrode d was produced. At this time, the porosity of the electrode plate was 35%.

(Preparation of non-aqueous electrolyte secondary battery)
A battery D of the present invention was produced in the same manner as in Example 1 except that the positive electrode d and the negative electrode d were used and the opposing area of the positive and negative electrodes was 6675 cm ² .

[Example 5]
(Preparation of positive electrode)
An active material mixture obtained by mixing the LiNi _1/4 Mn _1/4 Co _1/2 O ₂ as the first active material and the LiFePO ₄ as the second active material at a mass ratio of 92: 8 is used as the positive electrode active material. Example except that it was used as a substance, the coating mass of the positive electrode was 13.52 mg / cm ² , and the total thickness of the aluminum foil and the positive electrode active material layer after pressure molding was 120 μm In the same manner as in Example 1, a positive electrode e was produced.

(Preparation of negative electrode)
Except that the coating mass of the negative electrode was 7.05 mg / cm ² and that the total thickness of the copper foil and the negative electrode active material layer after pressure molding was 108 μm, the same as in Example 1, A negative electrode e was produced. At this time, the porosity of the electrode plate was 35%.

(Preparation of non-aqueous electrolyte secondary battery)
A battery E of the present invention was produced in the same manner as in Example 1 except that the positive electrode e and the negative electrode e were used and the opposing area of the positive and negative electrodes was 6989 cm ² .

[Example 6]
(Preparation of non-aqueous electrolyte secondary battery)
A battery F of the present invention was produced in the same manner as in Example 5 except that the facing area between the positive electrode and the negative electrode was 7289 cm ² and the thickness of the separator was 22 μm.

[Example 7] (Preparation of positive electrode)
The mass ratio contained in the positive electrode paste was set to a mass ratio of active material mixture: carbon material: PVdF = 89: 6: 5, the positive electrode coating mass was set to 13.37 mg / cm ² , and pressure molding A positive electrode g was produced in the same manner as in Example 5 except that the total thickness of the later aluminum foil and the positive electrode active material layer was 117 μm.

(Preparation of non-aqueous electrolyte secondary battery)
A battery G of the present invention was produced in the same manner as in Example 1 except that the positive electrode g and the negative electrode e were used and the opposing area of the positive and negative electrodes was 7049 cm ² .

[Example 8]
(Preparation of positive electrode)
A positive electrode h was produced in the same manner as in Example 5 except that the coating mass of the positive electrode was 13.53 mg / cm ² .

(Preparation of negative electrode)
A negative electrode h was produced in the same manner as in Example 5 except that the total thickness of the copper foil after the pressure molding and the negative electrode active material layer was 117 μm. The porosity of the electrode plate at this time was 40%.

(Preparation of non-aqueous electrolyte secondary battery)
A battery H of the present invention was produced in the same manner as in Example 1 except that the positive electrode h and the negative electrode h were used and the facing area of the positive and negative electrodes was 7043 cm ² .

[Example 9] (Preparation of positive electrode)
Except that the coating mass of the positive electrode was 12.57 mg / cm ² and that the total thickness of the aluminum foil after the pressure molding and the positive electrode active material layer was 113 μm, the same as in Example 1. A positive electrode i was produced.

(Preparation of negative electrode)
A negative electrode containing graphite as a negative electrode active material, styrene butadiene rubber (SRB) and carboxymethyl cellulose (CMC) as a binder in a mass ratio of graphite: binder = 97: 3, and water as a solvent. The paste was adjusted. The negative electrode paste was applied to both sides of a 10 μm thick copper foil and dried at 80 ° C. The coating mass of the negative electrode is 6.37 mg / cm ² . The negative electrode was pressure-molded with a roller press at room temperature to form a negative electrode active material layer, and then dried under reduced pressure at 150 ° C. for 12 hours to remove moisture in the electrode plate. The total thickness of the copper foil and the positive electrode active material layer after the roller press was 94 μm. The porosity of the electrode plate at this time was 30%. The negative electrode produced in this manner is designated as negative electrode i.

(Preparation of non-aqueous electrolyte secondary battery)
A battery H of the present invention was produced in the same manner as in Example 1 except that the positive electrode i and the negative electrode i were used and the facing area of the positive and negative electrodes was 7293 cm ² .

[Example 10]
(Preparation of positive electrode)
An active material mixture obtained by mixing the LiNi _1/3 Mn _1/3 Co _1/3 O ₂ as the first active material and the LiFePO ₄ as the second active material at a mass ratio of 80:20 is used as the positive electrode active material. Example except that it was used as a material, the coating mass of the positive electrode was 12.92 mg / cm ² , and the total thickness of the aluminum foil and the positive electrode active material layer after pressure molding was 118 μm In the same manner as in Example 1, a positive electrode j was produced.

(Preparation of negative electrode)
Except that the coating mass of the negative electrode was 6.78 mg / cm ² and the total thickness of the copper foil and the negative electrode active material layer after pressure molding was 103 μm, the same as in Example 1, A negative electrode e was produced. At this time, the porosity of the electrode plate was 35%.

(Preparation of non-aqueous electrolyte secondary battery)
A battery J of the present invention was produced in the same manner as in Example 1 except that the positive electrode j and the negative electrode j were used and the facing area of the positive and negative electrodes was 7433 cm ² .

[Comparative Example 1]
(Preparation of positive electrode)
The positive electrode k was the same as that of Example 1 except that the coating mass of the positive electrode was 11.13 mg / cm ² and the total thickness of the aluminum foil after the pressure molding and the positive electrode active material layer was 103 μm. Was made.

(Preparation of negative electrode)
The negative electrode k was the same as that of Example 1, except that the coating mass of the negative electrode was 5.8 mg / cm ² and the total thickness of the copper foil and the negative electrode active material layer after pressure molding was 91 μm. Was made. At this time, the porosity of the electrode plate was 35%.

(Preparation of non-aqueous electrolyte secondary battery)
A schematic diagram of the battery of Comparative Example 1 is shown in FIG. As the separator, a polyethylene microporous film having a thickness of 27 μm, an air permeability of 95 seconds, and a porosity of 50% is used so that the separator (23) is positioned between the positive electrode e (21) and the negative electrode e (22). Then, the positive electrode, the negative electrode, and the separator were wound into a flat shape to produce a power generation element (24). The opposing area of the positive and negative electrodes at this time is 415.1 cm ² . Here, since the positive electrode and the negative electrode are wound so that both ends coincide with each other along the winding axis, the metal foil does not protrude from both ends in the axial direction of the power generation element (24). The positive electrode current collector plate made of aluminum and the negative electrode current collector plate made of copper were respectively disposed at the end (25) of the winding end of the power generation element, and welded to the positive electrode and the negative electrode. At this time, the distance from the current collector plate to the active material farthest was the length from the start to the end of winding of the positive and negative electrodes, and this distance was 65 cm. The positive and negative current collector plates welded to the power generation element composed of the positive electrode, the negative electrode, and the separator thus produced were made of aluminum square battery case (height 49.3 mm, width 33.7 mm, thickness 5.17 mm). ) And attached positive and negative terminals. After 3.2 g of nonaqueous electrolyte was injected into the container, the container was sealed to produce a nonaqueous electrolyte secondary battery having a design capacity of 0.65 Ah. This battery is referred to as a comparative battery K.

[Comparative Example 2]
(Preparation of positive electrode)
The LiNi _1/3 Mn _1/3 Co _1/3 O ₂ was used alone as a positive electrode active material. The positive electrode active material, a carbon material as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder are contained in a mass ratio of positive electrode active material: carbon material: PVdF = 90: 5: 5, N -A positive electrode paste using methyl-2-pyrrolidone (NMP) as a solvent was prepared. The positive electrode paste was applied to both surfaces of a 15 μm thick aluminum foil and dried at 80 ° C. to remove NMP. The coating mass of the positive electrode was 13.43 mg / cm ² . The positive electrode was pressure-molded with a roller press heated to 120 ° C. to form a positive electrode active material layer, and then dried under reduced pressure at 150 ° C. for 12 hours to remove moisture in the electrode plate. The total thickness of the aluminum foil and the positive electrode active material layer after the roller press was 116 μm. The positive electrode produced in this way is designated as positive electrode l.

(Preparation of negative electrode)
Except that the coating mass of the negative electrode was 7.37 mg / cm ² and the total thickness of the copper foil and the negative electrode active material layer after pressure molding was 113 μm, the same as in Example 1, A negative electrode 1 was produced. At this time, the porosity of the electrode plate was 35%.

(Preparation of non-aqueous electrolyte secondary battery)
A comparative battery L was produced in the same manner as in Example 1 except that the positive electrode 1 and the negative electrode 1 were used and the opposing area of the positive and negative electrodes was 6681 cm ² .

[Comparative Example 3]
(Preparation of positive electrode)
Positive electrode m in the same manner as in Comparative Example 2 except that the coating mass of the positive electrode was 10.00 mg / cm ² and that the total thickness of the aluminum foil and the positive electrode active material layer after pressure molding was 90 μm. Was made.

(Preparation of negative electrode)
Except that the coating mass of the negative electrode was 5.51 mg / cm ² and that the total thickness of the copper foil and the negative electrode active material layer after pressure molding was 87 μm, the same as in Example 1, A negative electrode m was produced. At this time, the porosity of the electrode plate was 35%.

(Preparation of non-aqueous electrolyte secondary battery)
A comparative battery M was produced in the same manner as in Comparative Example 1 except that the positive electrode m and the negative electrode m were used and the opposing area of the positive and negative electrodes was 471.9 cm ² .

<Capacity confirmation test>
In order to confirm that the designed charge / discharge capacity was obtained, a capacity confirmation test was performed on the battery of the present invention and the comparative battery produced as described above.
For all the batteries of the present invention and comparative batteries L, charging current 11.5A, charging voltage 4.2V, constant current constant voltage charging with a total charging time 3 hours, discharging current 11.5A, end voltage 2.0V Three cycles of charging / discharging consisting of constant current discharge were performed. For Comparative Example K and Comparative Battery M, charging current 0.65A, charging voltage 4.2V, constant current constant voltage charging with a total charging time 3 hours, and discharging current 0.65A, constant voltage with end voltage 2.0V Three cycles of charging / discharging consisting of discharge were performed. The discharge capacity at the third cycle in each charge / discharge was defined as the rated capacity, and it was confirmed that the rated capacity was substantially equal to the design capacity. The value of the current for discharging the rated discharge capacity in one hour is referred to as 1CA. In the battery of the present invention and the comparative battery L, 1CA = 11.5A, and in the comparative example K and the comparative battery M, 1CA = 0.65A.

<Impedance measurement at 1 kHz>
With respect to all the present invention batteries and comparative batteries, an impedance of 1 kHz was measured using an AC milliohm high tester manufactured by Hioki Electric Co., Ltd. with a SOC of 0%. The results are shown in Table 1.
Here, the “state of charge (SOC)” indicates how much the battery is charged in a reversibly chargeable / dischargeable battery voltage range, and in this embodiment, SOC 100% means a fully charged state immediately after a constant current and constant voltage charge with a charging current of 1 CA, a charging voltage of 4.2 V, and a total charging time of 3 hours. SOC 0% means a discharging current of 1 CA and a final voltage of 2.0 V. The state of charge immediately after performing constant current discharge.

As can be seen from Table 1, the present invention battery and the comparative battery L in which the opposing area of the positive and negative electrodes is increased and the maximum distance between the current collector and the active material is shortened are the comparative example K and the comparative battery M. The impedance at 1 kHz was significantly reduced as compared with FIG. A book using a positive electrode active material in which LiNi _1/3 Mn _1/3 Co _1/3 O ₂ as a first active material and LiFePO ₄ as a second active material are mixed at a mass ratio of 90:10. A positive electrode active material in which the inventive battery A, LiNi _1/4 Mn _1/4 Co _1/2 O ₂ as the first active material, and LiFePO _{4 as} the second active material are mixed at a mass ratio of 90:10 In comparison with the present invention battery B using the present invention, the present invention battery A had a lower impedance but a lower impedance. Therefore, as the first active material, LiNi _1/3 Mn _1/3 Co _{1 / It} can be seen that ₃ O ₂ is preferably used. In addition, since the impedance of the present invention battery D is higher than that of the present invention battery B, it is preferable to reduce the impedance of 1 kHz by increasing the electrode area and reducing the thickness of the active material layer. I understood. From the above, it can be seen that the impedance of 1 kHz, that is, the internal resistance can be reduced by increasing the opposing area of the positive and negative electrodes, that is, the electrode area, and shortening the maximum distance between the current collector and the active material. It was.

  Here, the internal resistance refers to the property of the material used for the positive and negative electrode active materials and the nonaqueous electrolyte, that is, the resistance that varies depending on the chemical prescription, and the current collector that varies depending on the physical prescription such as the electrode area and the current collector mounting position It can be considered as the sum of resistance. In this example, the example in which the current collection resistance is reduced and the internal resistance is reduced by changing the physical prescription of the battery is shown. However, the composition and shape of the active material and the nonaqueous electrolyte are changed. Therefore, the internal resistance can be reduced, and the present invention can be implemented by such a method.

<Output test>
For some of the above-described batteries of the present invention and comparative batteries, output performance tests were performed in a charged state of SOC 10%, SOC 20%, and SOC 50%. The battery voltages in the charged state of SOC 10%, SOC 20% and SOC 50% are 3.49V, 3.53V and 3.68V, respectively.

  The output performance test in the state of charge of each SOC was performed according to the following procedure. First, the test battery was charged to a SOC of 10% by constant current and constant voltage charging with a charging current of 1 CA, a charging voltage of 3.49 V, and a total charging time of 2 hours. Thereafter, the battery was discharged at a discharge current of 1CA for 30 seconds, and then charged for 30 seconds at the same current value as the previous discharge current. Similarly, the discharge and charge were performed in the same manner except that the discharge current value was changed to 3, 5 and 10 CA. The VI characteristic was drawn by plotting the voltage after 10 seconds in each discharge current and the discharge current value at that time. In the VI characteristic, after performing linear approximation by the least square method, a maximum output current value corresponding to the discharge end voltage is calculated, and further, the maximum output current value is multiplied by the discharge end voltage. The SOC 10% output was determined. The discharge final voltage was 2.0V.

  The SOC 20% output was obtained in the same manner as the output test, except that the charging voltage was 3.53 V, and the SOC was charged to 20%.

  The SOC 50% output was determined in the same manner as the output test except that the charging voltage was 3.68V and the SOC was 50% charged.

  The output ratio A (%) was calculated by dividing the SOC 20% output by the SOC 50% output and multiplying by 100. The output ratio B (%) was calculated by dividing the SOC 10% output by the SOC 50% output and multiplying by 100.

  The results are shown in Table 2. It should be noted that the test is not performed on the columns in Table 2 where no numbers are written.

As shown in Table 2, the batteries A to J of the present invention in which the impedance at 1 kHz is 1.27 mΩ or less as compared with the comparative battery K having a high impedance of 1 kHz of 37.6 mΩ are high in output ratio and high SOC 20% output. Alternatively, SOC 10% output was shown. In particular, the battery A of the present invention using LiNi _1/3 Mn _1/3 Co _1/3 O ₂ as the first active material has a high output ratio A of 72.3% and a high power of 2.76 W / cc. An SOC 20% output, a high output ratio B of 74.7%, and a high SOC 10% output of 2.85 W / cc were shown.

Further, as can be seen from the comparison with Comparative Example 2, even when the impedance at 1 kHz is 1.27 mΩ or less, the general formula LiNi _x Mn _y Co _z O ₂ (x + y + z = 1, x> 0, y> 0, z When the lithium transition metal composite oxide represented by> 0) was used alone, the output performance was not excellent.

From the above, the first active material containing the lithium transition metal composite oxide represented by the general formula LiNi _x Mn _y Co _z O ₂ (x + y + z = 1, x> 0, y> 0, z> 0) By providing a non-aqueous electrolyte secondary battery having a positive electrode containing a second active material containing LiFePO ₄ and having an impedance of 1 kHz of 1.27 mΩ or less, an output at a low SOC relative to an output at a high SOC is achieved. It was found that a non-aqueous electrolyte secondary battery having a high ratio and a high energy density can be provided.

DESCRIPTION OF SYMBOLS 11 Positive electrode 12 Negative electrode 13 Separator 14 Electric power generation element 15 Positive electrode current collection board attachment position 16 Negative electrode current collection board attachment position 17 Distance to the active material furthest from the current collection board 21 Positive electrode 22 Negative electrode 23 Separator 24 Electric power generation element 25 Current collection board attachment position

Claims (4)

A first active material containing a lithium transition metal composite oxide represented by the general formula LiNi _x Mn _y Co _z O ₂ (x + y + z = 1, x> 0, y> 0, z> 0) and a first active material containing LiFePO ₄ . A nonaqueous electrolyte secondary battery comprising a positive electrode containing 2 active materials and having an impedance of 1 kHz of 1.27 mΩ or less. The ratio of the second active material to the sum of the first active material and the second active material contained in the positive electrode is 5% by mass or more and 25% by mass or less. The nonaqueous electrolyte secondary battery as described. The first active material is LiNi _x Mn _y Co _z O ₂ (x + y + z = 1, 1/4 ≦ x ≦ 1/3, 1/4 ≦ y ≦ 1/3, 1/3 ≦ z ≦ 1/2. The non-aqueous electrolyte secondary battery according to claim 1, comprising a lithium transition metal composite compound represented by the formula: The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the second active material is provided with a carbonaceous material.