JP2011054334A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery capable of achieving both a high power and long life. <P>SOLUTION: The lithium ion secondary battery 25 houses a wound-around group 16 and nonaqueous electrolyte solution in a battery can 17. The wound-around group 16 has a positive and a negative electrode plates wound around through a separator 15. As a cathode active material, lithium transition metal complex oxide of a lamellar crystal structure containing manganese and nickel and lithium transition metal complex oxide of a spinel crystal structure containing manganese are mixed and used. A composition ratio of nickel to transition metal elements other than lithium of the complex oxide of the lamellar crystal structure is adjusted at ≥50% in a molar ratio. An interlayer distance of the lamellar crystal structure is expanded with the nickel. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery including a positive electrode plate and a negative electrode plate capable of inserting and removing lithium ions.

  Lithium secondary batteries are widely used as power sources for consumer devices such as VTR cameras, notebook computers, and mobile phones, taking advantage of their high energy density. In the automobile industry, in order to deal with environmental problems, an electric vehicle using only a lithium secondary battery as a power source, or a hybrid electric vehicle using both an internal combustion engine and a lithium secondary battery as power sources Etc. are being developed.

  In general, in a lithium secondary battery used as a power source for a mobile object such as an electric vehicle, it is important to ensure a predetermined output in a low temperature environment in order to ensure traveling performance in extreme cold. Therefore, it is required to increase the output of the battery not only in a normal temperature environment but also in a low temperature environment. In addition, in consideration of environmental problems and cost reduction, there is a demand for longer battery life. That is, in the development of a lithium secondary battery for mobile bodies, the main technical problem is that it is possible to suppress a decrease in battery output and supply necessary electric energy over a long period of time.

  In order to solve this, improvement of the positive electrode material has been promoted in the lithium secondary battery. For example, by using a lithium nickel composite oxide having a layered crystal structure in which the composition ratio of nickel is less than 50% in molar ratio to a transition metal element other than lithium and a lithium manganese composite oxide having a spinel crystal structure as a positive electrode active material. A technique for improving output characteristics in a low temperature environment has been disclosed (see Patent Document 1). In addition, the positive electrode active material includes a layered crystal structure lithium manganese complex oxide and a spinel crystal structure lithium manganese complex oxide, and the reversible capacity of the positive electrode is less than the reversible capacity of the negative electrode, thereby increasing the battery capacity and extending the life. The technique which tries is disclosed (refer patent document 2).

JP 2004-259511 A JP 2003-36846 A

  However, in order to use a lithium secondary battery as a power source for a mobile body, not only high capacity but also high output that affects acceleration performance and the like are required. In addition, there is a demand for longer battery life in order to cope with a long use period. At present, lithium secondary batteries having sufficient performance are not obtained in response to these requirements. For example, although the technique of Patent Document 1 can improve battery output in a low temperature environment, it cannot be said to be sufficient for extending battery life. Further, with the technique of Patent Document 2, although the battery life can be extended, it is difficult to sufficiently exhibit the high output performance in a low temperature environment required for the mobile battery.

  In view of the above-described case, an object of the present invention is to provide a lithium secondary battery that can achieve both high output and long life.

  In order to solve the above-described problems, the present invention provides a lithium transition metal composite oxide having a layered crystal structure capable of inserting and releasing lithium ions and containing manganese and nickel, and a lithium transition metal composite having a spinel crystal structure containing manganese. A positive electrode plate coated with a positive electrode active material containing an oxide; and a negative electrode plate coated with a negative electrode active material capable of inserting and releasing lithium ions, the positive electrode active material having the layered crystal structure The composition ratio of nickel to the transition metal element other than lithium in the lithium transition metal composite oxide is 50% or more in terms of molar ratio.

  In the present invention, the positive electrode active material contains a lithium transition metal composite oxide having a layered crystal structure and a lithium transition metal composite oxide having a spinel crystal structure. The lithium ion diffusibility is ensured and the battery life can be extended, and the composition ratio of nickel to the transition metal element other than lithium in the lithium transition metal composite oxide having a layered crystal structure can be increased. By setting the molar ratio to 50% or more, the interlayer distance of the layered crystal structure is expanded, and lithium ions can be easily inserted and removed during charging and discharging, thereby improving the diffusibility of lithium ions and increasing the output. it can.

  In this case, the mixing ratio of the lithium transition metal composite oxide having a layered crystal structure and the lithium transition composite oxide having a spinel crystal structure is preferably in the range of 60:40 to 95: 5 by weight ratio. Moreover, it is preferable that the composition ratio of nickel with respect to transition metal elements other than lithium in the lithium transition metal composite oxide having a layered crystal structure is 80% or less in terms of molar ratio.

  According to the present invention, the positive electrode active material includes the lithium transition metal composite oxide having a layered crystal structure and the lithium transition metal composite oxide having a spinel crystal structure. Since it is less affected and lithium ion diffusibility is ensured, the battery life can be extended and the composition of nickel with respect to transition metal elements other than lithium in the layered crystal structure lithium transition metal composite oxide By setting the ratio to 50% or more in terms of molar ratio, the interlayer distance of the layered crystal structure is increased, and lithium ions can be easily inserted and released during charge and discharge, so that the diffusibility of lithium ions is improved and the output is increased. Can be obtained.

It is sectional drawing of the cylindrical lithium ion secondary battery of embodiment to which this invention is applied.

  Embodiments of a cylindrical lithium ion secondary battery to which the present invention is applied will be described below with reference to the drawings.

(Constitution)
As shown in FIG. 1, the cylindrical lithium ion secondary battery 25 of the present embodiment has a bottomed cylindrical battery can 17 made of iron plated with nickel and serving as a battery container. The battery can 17 accommodates a wound group 16 in which strip-like positive and negative electrode plates are wound.

  In the winding group 16, the positive and negative electrode plates are wound in a spiral shape through a polyethylene microporous membrane separator 15. In this example, the separator 15 has a thickness of 40 μm. A ribbon-like positive electrode tab terminal 19 made of aluminum and having one end fixed to the positive electrode plate is led out from the upper end surface of the wound group 16. The other end of the positive electrode tab terminal 19 is joined by ultrasonic welding to the lower surface of a disk-shaped battery lid 18 that is disposed on the upper side of the wound group 16 and serves as a positive electrode external terminal. On the other hand, a ribbon-shaped negative electrode tab terminal 21 made of copper and having one end fixed to the negative electrode plate is led out to the lower end surface of the winding group 16. The other end of the negative electrode tab terminal 21 is joined to the inner bottom portion of the battery can 17 by resistance welding. Accordingly, the positive electrode tab terminal 19 and the negative electrode tab terminal 21 are led out to the opposite sides of the both end surfaces of the wound group 16, respectively. An insulation coating (not shown) is applied to the entire outer peripheral surface of the wound group 16.

The battery lid 18 is caulked and fixed to the upper portion of the battery can 17 via an insulating resin gasket 20. For this reason, the inside of the lithium ion secondary battery 25 is sealed. In addition, a non-aqueous electrolyte (not shown) is injected into the battery can 17. Examples of the non-aqueous electrolyte include lithium hexafluorophosphate (LiPF ₆ ) in a carbonate-based mixed solvent having a volume ratio of 1: 1: 1 of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC). ) Can be used by dissolving 1 mol / liter. The injection amount of the non-aqueous electrolyte is set to 5 ml in this example.

  The positive electrode plate constituting the wound group 16 has an aluminum foil 13 as a positive electrode current collector. The thickness of the aluminum foil 13 is set to 20 μm in this example, and can be set in the range of 15 to 25 μm. On both surfaces of the aluminum foil 13, a positive electrode mixture containing a positive electrode active material is applied substantially evenly to form a positive electrode mixture layer 14. In addition to the positive electrode active material, for example, graphite powder and acetylene black and a binder (binder) polyvinylidene fluoride (hereinafter abbreviated as PVDF) are blended in the positive electrode mixture. When the positive electrode mixture is applied to the aluminum foil 13, the positive electrode mixture is dispersed in N-methylpyrrolidone (hereinafter abbreviated as NMP) as a viscosity adjusting solvent to prepare a slurry solution. At this time, the dispersion solution is agitated using a mixer equipped with a rotor blade. This solution is applied to the aluminum foil 13 by a roll-to-roll transfer method. After drying, the positive electrode plate is integrated by pressing and cut. In this example, the thickness of the positive electrode mixture application portion that does not include the aluminum foil 13 of the positive electrode plate is adjusted to 70 μm. A positive electrode tab terminal 19 is joined to the substantially central portion in the longitudinal direction of the positive electrode plate by ultrasonic welding.

In the positive electrode active material contained in the positive electrode mixture, lithium transition metal composite oxide (hereinafter referred to as layered composite oxide) having a layered rock salt type crystal structure capable of inserting and releasing lithium ions and containing manganese and nickel, And a lithium transition metal composite oxide having a spinel crystal structure containing manganese (hereinafter referred to as a spinel composite oxide). The mixing ratio of the layered complex oxide and the spinel complex oxide is adjusted in the range of 60:40 to 95: 5. The average particle diameter of the layered composite oxide is in the range of 8.0 to 17.5 μm, and the specific surface area can be set in the range of 0.7 to 1.2 m ² / g. As the spinel composite oxide, a chemical formula represented by LiMn ₂ O ₄ , an average particle diameter of 10 μm, and a specific surface area of 0.8 m ² / g can be used. Moreover, the composition ratio of nickel in the layered composite oxide is adjusted to 50% or more in terms of a molar ratio with respect to the transition metal element other than lithium. The composition ratio of nickel can be adjusted by the mixing ratio of the raw materials.

  On the other hand, the negative electrode plate has a rolled copper foil 11 as a negative electrode current collector. The thickness of the rolled copper foil 11 is set to 10 μm in this example, and can be set to a range of 5 to 20 μm. On both surfaces of the rolled copper foil 11, a negative electrode mixture containing amorphous carbon powder as a negative electrode active material is applied substantially evenly to form a negative electrode mixture layer 12. In addition to the negative electrode active material, for example, acetylene black as a conductive material and PVDF as a binder are blended in the negative electrode mixture. At this time, the mass ratio of the negative electrode active material, the conductive material, and PVDF can be set to 80:10:10. When the negative electrode mixture is applied to the rolled copper foil 11, the slurry is prepared by dispersing the negative electrode mixture in the viscosity adjusting solvent NMP. At this time, the dispersion solution is agitated using a mixer equipped with a rotor blade. This solution is applied to the rolled copper foil 11 by a roll-to-roll transfer method. After drying, the negative electrode plate is integrated by pressing and cut. In this example, the thickness of the negative electrode mixture application part thickness not including the rolled copper foil 11 of the negative electrode plate is adjusted to 70 μm. A negative electrode tab terminal 21 is joined to one end of the negative electrode plate in the longitudinal direction by ultrasonic welding.

(Production of battery)
In the production of the battery, first, the obtained positive and negative electrode plates are wound through the separator 15 to produce a wound group 16. At this time, the negative electrode tab terminal 21 is wound so as to be positioned on the outermost periphery of the wound group 16. The wound group 16 is inserted into the battery can 17, and the negative electrode tab terminal 21 is welded to the inner bottom portion of the battery can 17. After injecting a non-aqueous electrolyte into the battery can 17, a battery lid 18, in which the other end of the positive electrode tab terminal 19 is welded in advance, is fitted to the upper part of the battery can 17 via a gasket 20. The assembly of the lithium ion secondary battery 25 is completed by caulking and fixing the upper part of the battery can 17.

  Next, examples of the lithium ion secondary battery 25 manufactured according to the present embodiment will be described in detail. In addition, it describes together about the battery of the comparative example produced for the comparison.

Example 1
As shown in Table 1 below, in Example 1, a layered composite oxide having a composition ratio of nickel with respect to a transition metal element other than lithium in a molar ratio of 50% was used. The average particle diameter of the layered composite oxide is in the range of 8.0 to 17.5 μm, and the specific surface area is 0.7 to 1.2 m ² / g. As the spinel composite oxide, one represented by the chemical formula LiMn ₂ O ₄ and having an average particle diameter of 10 μm and a specific surface area of 0.8 m ² / g was used. The battery of Example 1 was fabricated by mixing the layered composite oxide and the spinel composite oxide in a weight ratio of 80:20 to obtain a positive electrode active material. At this time, 13% by weight of a mixture of graphite and acetylene black powder was added as a conductive material for the positive electrode.

(Examples 2-3)
As shown in Table 1, in Example 2, as the layered composite oxide, the composition ratio of nickel with respect to the transition metal element other than lithium was 60% in terms of molar ratio and 20% in terms of cobalt was used. A battery was fabricated in the same manner as in Example 1 except for the above. In Example 3, a battery was fabricated in the same manner as in Example 1 except that the layered composite oxide had a nickel composition ratio of 80% in terms of a molar ratio to the transition metal element other than lithium.

(Comparative Examples 1-2)
As shown in Table 1, in Comparative Example 1, a layered composite oxide having a composition ratio of nickel to a transition metal element other than lithium in a molar ratio of 33% and containing cobalt in a molar ratio of 34% was used. A battery was manufactured in the same manner as in Example 1 except for the above. Further, in Comparative Example 2, Example 1 was used except that the layered composite oxide had a nickel composition ratio of 40% in terms of a molar ratio with respect to a transition metal element other than lithium and 20% of cobalt in a molar ratio. A battery was produced in the same manner as described above.

(Examples 4 to 7)
As shown in Table 2 below, in Examples 4 to 7, batteries were produced in the same manner as in Example 2 except that the mixing ratio of the layered composite oxide and the spinel composite oxide was changed. That is, the mixing ratio of the layered complex oxide and the spinel complex oxide is a weight ratio of 95: 5 in Example 4, 90:10 in Example 5, 70:30 in Example 6, and 60: in Example 7. Each was adjusted to 40. In Table 2, Example 2 is also shown.

(Comparative Examples 3-5)
As shown in Table 2, in Comparative Examples 3 to 5, batteries were produced in the same manner as in Example 2 except that the mixing ratio of the layered composite oxide and the spinel composite oxide was changed. That is, the mixing ratio of the layered composite oxide and the spinel composite oxide was adjusted to a weight ratio of 100: 0 in Comparative Example 3, 50:50 in Comparative Example 4, and 40:60 in Comparative Example 5, respectively.

(Test / Evaluation 1)
About the lithium ion secondary battery of each Examples 1-3 and Comparative Examples 1-2, the initial stage discharge capacity was confirmed and the output characteristic was measured. The initial discharge capacity was measured after charging each battery and then discharging the battery at an ambient temperature of 23 to 27 ° C. The charging conditions were a 4.2 V constant voltage, a limiting current of 5 A, and a charging time of 2.5 hours. The discharge conditions were a 5 A constant current and a final voltage of 2.7 V. After the initial discharge capacity measurement, each battery was charged under the same charging conditions, 5A constant current discharge was performed, and after charging, 25A constant current discharge was performed again, and charging was performed again to discharge 50A constant current. The voltage at the 10th second in the discharge at each current value was measured to calculate the output. The measurement was performed in a normal temperature atmosphere of 25 ± 2 ° C. and a low temperature atmosphere of −10 ± 2 ° C., respectively. The output measurement results are shown in Table 3 below. Table 3 shows relative values with the output of the lithium ion secondary battery of Comparative Example 1 in a room temperature atmosphere being 100.

  As shown in Table 3, in Comparative Example 1 and Comparative Example 2, the output characteristics were around 100% at room temperature and low temperature atmosphere, whereas in Examples 1 to 3, the output characteristics were 110% or more and greatly increased. Improved. In Examples 1 to 3, the composition ratio of nickel to the transition metal element other than lithium is 50% or more in molar ratio, the interlayer distance of the layered crystal structure is expanded by nickel, and lithium ions are inserted during charge and discharge. This is probably because the diffusibility of lithium ions was improved and the output could be increased because it became easier to detach. When the composition ratio of nickel in the layered composite oxide exceeds 80% in terms of the molar ratio with respect to the transition metal element other than lithium, the layered crystal structure with the expanded interlayer distance becomes unstable, and it is expected that the battery performance is deteriorated on the contrary. Is done. For this reason, it is preferable that the composition ratio of nickel in the layered composite oxide is 80% or less.

(Test / Evaluation 2)
Moreover, about the lithium ion secondary battery of each Example 4-7, Example 2, and Comparative Examples 3-5, the high temperature life characteristic was evaluated after the initial stage discharge capacity measurement. That is, charging and discharging under the same charging and discharging conditions as the measuring conditions of the discharging capacity were repeated 300 times in an atmosphere having an environmental temperature of 48 to 52 ° C. Thereafter, the discharge capacity was measured in the same manner in an atmosphere at an ambient temperature of 23 to 27 ° C., and the ratio of the discharge capacity at the 300th cycle to the initial discharge capacity was obtained as a percentage to obtain the capacity maintenance rate at the 300th cycle. Table 4 below shows the measurement results of the capacity retention rate at the 300th cycle.

  As shown in Table 4, in Comparative Examples 3 to 5, the capacity maintenance rate is 90% or less, whereas in Examples 4 to 7 and Example 2, the capacity maintenance rate is 90% or more and at a high temperature. The result that there was little deterioration of was obtained. This is because, in Examples 4 to 7 and Example 2, the mixing ratio of the layered composite oxide and the spinel composite oxide is in the range of 60:40 to 95: 5 by weight ratio. This is considered to be because the stability was increased and the diffusibility of lithium ions was ensured for a long time even at high temperatures, and the battery life could be extended.

(Function)
Next, the operation and the like of the lithium ion secondary battery 25 of the present embodiment will be described.

  In the lithium ion secondary battery 25 of this embodiment, a layered composite oxide and a spinel composite oxide are mixed and used for the positive electrode active material. In a layered complex oxide, lithium ions are inserted and released during charge and discharge, whereby the crystal lattice repeatedly expands and contracts, and the life characteristics tend to be lowered. On the other hand, in the spinel composite oxide, even when lithium ions are inserted and released during charging and discharging, the crystal lattice is three-dimensional and stable, so that the expansion and contraction of the crystal lattice is reduced. For this reason, when the layered composite oxide and the spinel composite oxide are mixed in the positive electrode active material, the stability of the positive electrode active material as a whole is increased, and the positive electrode composite is not affected even if the layered composite oxide expands or contracts. Omission of the material layer 14 can also be suppressed. Accordingly, the diffusibility of lithium ions is ensured over a long period of time, so that the lifetime can be extended.

  In the lithium ion secondary battery 25 of the present embodiment, a layered composite oxide and a spinel composite oxide are mixed and used as the positive electrode active material. In the layered complex oxide, the lithium ion diffusion path is two-dimensional, so that it is excellent in lithium ion diffusibility at room temperature and inherently excellent in output characteristics. However, at low temperatures, the diffusibility of lithium ions is reduced due to the shrinkage of the crystal lattice, resulting in lower output characteristics. In contrast, the spinel composite oxide has a three-dimensional crystal lattice and excellent stability, is hardly affected by temperature, and has excellent output characteristics at low temperatures. Therefore, in this embodiment, the lithium ion diffusibility of the layered composite oxide acts at room temperature, and the spinel composite oxide lithium ion diffusivity functions at a low temperature. Battery output can be ensured even underneath.

  Furthermore, in the lithium ion secondary battery 25 of the present embodiment, the composition ratio of nickel to the transition metal element other than lithium in the layered composite oxide of the positive electrode active material is in the range of 50 to 80%. Nickel has a larger atomic radius than manganese, which is frequently used as a transition metal element constituting the layered composite oxide. Therefore, the interlayer distance of the layered crystal structure is increased by nickel, and lithium ions are easily inserted and removed during charge and discharge. Therefore, when the composition ratio of nickel in the layered composite oxide is 50% or more, the diffusibility of lithium ions is improved, and high output can be achieved. If the composition ratio of nickel in the layered composite oxide exceeds 80%, the crystal structure instability increases and the diffusion of lithium is inhibited, so that the output characteristics deteriorate.

  Furthermore, in the lithium ion secondary battery 25 of this embodiment, the mixing ratio of the layered composite oxide and the spinel composite oxide contained in the positive electrode active material is in the range of 60:40 to 95: 5. When the proportion of the spinel composite oxide is 5% or less, the amount of the spinel composite oxide is small and the entire positive electrode active material is not sufficiently stabilized. (See also Comparative Example 3). When the spinel composite oxide ratio is 40% or higher, the crystal lattice of the spinel composite oxide is three-dimensional and stable. When used, the capacity retention rate tends to decrease (see also Comparative Examples 4 and 5). Therefore, when the mixing ratio of the layered composite oxide and the spinel composite oxide is in the range of 60:40 to 95: 5, the stability of the positive electrode active material is increased, and the lithium ion diffusibility is less affected by temperature. Therefore, the battery life can be extended.

  In the present embodiment, the composite oxide having a layered rock salt type crystal structure is exemplified as the layered composite oxide. However, the present invention is not limited to this, and a layered structure in which a sufficient amount of lithium is inserted in advance. Any crystal structure can be applied.

  In the present embodiment, a part of the transition metal element contained in the layered complex oxide or the spinel complex oxide may be substituted or doped with another transition metal element (cation). In the layered composite oxide, examples of cations other than lithium, nickel and manganese include cobalt, aluminum, iron, chromium, magnesium, titanium, tin, and indium, and may include a plurality of cations. Moreover, in spinel complex oxide, aluminum, cobalt, nickel, chromium, magnesium etc. can be mentioned as cations other than lithium and manganese. Furthermore, a material in which part of oxygen in the crystal of the layered complex oxide or the spinel complex oxide is substituted or doped with sulfur, phosphorus, or the like may be used.

  Furthermore, in the present embodiment, a mixture of graphite and acetylene black powder is exemplified as the conductive material of the positive electrode, but the present invention is not limited to this. For example, what is necessary is just to have electroconductivity, such as a carbon material. In the present embodiment, an example in which a mixer equipped with a stirring means such as a rotary blade is used for mixing positive and negative electrode slurries is shown, but the present invention is not limited to this, and the slurry is uniform. What is necessary is just to use the means mixed.

  Furthermore, in this embodiment, although amorphous carbon was illustrated as a negative electrode active material, this invention is not limited to this. As the negative electrode active material, any material capable of inserting and releasing lithium ions may be used, and materials usually used for lithium secondary batteries can be used. Examples of the negative electrode active material used in other than the present embodiment include carbon materials such as graphite. Of course, graphite and amorphous carbon may be mixed and used.

  Furthermore, in the present embodiment, the cylindrical battery is exemplified, but the present invention is not limited to the shape of the battery, and can be applied to a rectangular battery or other polygonal batteries. Moreover, in this embodiment, although the large sized lithium secondary battery used as a power supply for moving bodies, such as an electric vehicle, was illustrated, this invention is not restrict | limited to the capacity | capacitance, size, shape, etc. of a battery.

  Further, in the present embodiment, the winding type battery in which the strip-like positive and negative electrode plates are wound is illustrated, but the present invention is not limited to this. For example, a stacked battery may be used in which a bag-like separator is used, electrodes are accommodated therein, and these are sequentially stacked. Furthermore, the structure to which the present invention can be applied may be other than a battery having a structure in which the battery lid 18 is sealed with the battery can 17 described above. As an example of such a structure, a battery in a state where positive and negative electrode tab terminals penetrate through the battery lid and are pressed through the shaft core in the battery container can be mentioned.

Furthermore, although the microporous polyethylene film was illustrated as the separator 15 in this embodiment, this invention is not limited to this, A polypropylene etc. may be used for a material and even if it laminates | stacks a some film Good. In this embodiment, a non-aqueous electrolyte solution in which LiPF ₆ having a concentration of 1M is dissolved in a mixed solvent of EC, DEC, and DMC is exemplified. However, a general lithium salt is used as an electrolyte, and this is dissolved in an organic solvent. The nonaqueous electrolyte solution may be used, and the present invention is not particularly limited to the lithium salt or organic solvent used.

  The present invention contributes to the manufacture and sale of lithium secondary batteries in order to provide a lithium secondary battery that can achieve both high output and long life, and thus has industrial applicability.

12 Negative electrode mixture layer 14 Positive electrode mixture layer 16 Winding group 25 Cylindrical lithium ion secondary battery (lithium secondary battery)

Claims (3)

A positive electrode active material capable of inserting and releasing lithium ions and including a lithium transition metal composite oxide having a layered crystal structure containing manganese and nickel and a lithium transition metal composite oxide having a spinel crystal structure containing manganese is applied. Positive electrode plate,
A negative electrode plate coated with a negative electrode active material capable of inserting and removing lithium ions;
With
The lithium secondary battery, wherein the positive electrode active material has a molar ratio of nickel to a transition metal element other than lithium in the layered crystal structure lithium transition metal composite oxide in a molar ratio of 50% or more.   The mixing ratio of the lithium transition metal composite oxide having the layered crystal structure and the lithium transition metal composite oxide having the spinel crystal structure is in a range of 60:40 to 95: 5 by weight. 2. The lithium secondary battery according to 1.   3. The lithium secondary battery according to claim 2, wherein a composition ratio of nickel to a transition metal element other than lithium in the lithium transition metal composite oxide having a layered crystal structure is 80% or less in terms of molar ratio.

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