JP2013122859A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery that contains a nickel-containing lithium complex oxide composed of secondary particles that are aggregates of primary particles, and resisting breakage that may occur at the interfaces between the primary particles and may cause degradation in charge-discharge cycle characteristics.SOLUTION: A positive electrode active material is composed of a lithium complex oxide represented by LiNiCoAlO, where 0.9<x<1.3, 0.1<y<0.3, and 0.0<z<0.3 are satisfied. The positive electrode active material is composed of secondary particles that are aggregates of primary particles, and contains a conductive agent among the primary particles constituting the secondary particles.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery.

  In recent years, with the reduction in size and weight of electronic devices such as mobile phones and notebook computers, there is a demand for higher capacities for secondary batteries as power sources. As a battery that satisfies this requirement, a non-aqueous electrolyte secondary battery, for example, a lithium whose negative electrode active material includes metallic lithium, a lithium alloy, or a material that can intercalate and deintercalate lithium ions (for example, a carbon material) A secondary battery is mentioned.

Lithium ion secondary batteries using lithium cobalt oxide (LiCoO ₂ ) as a positive electrode material and graphite or amorphous carbon as a negative electrode material have been developed and commercialized. Further, higher energy density is desired, and lithium nickelate (LiNiO ₂ ) is expected as a positive electrode material replacing LiCoO ₂ .

LiNiO ₂ is expected to have a higher energy density than LiCoO ₂ and is being developed in various directions. However, since the polarization during charging is large and Li can not be extracted sufficiently, it reaches the oxidative decomposition voltage of the electrolyte. The expected large capacity was not obtained.

  In order to solve such a problem, a nonaqueous electrolyte secondary battery using a positive electrode active material obtained by substituting a part of Ni element with Co has been proposed.

  For example, in Patent Document 1, lithium composite nickel-cobalt oxide is synthesized by mixing lithium carbonate, cobalt carbonate, and nickel carbonate and firing at 900 ° C.

  Moreover, in patent document 2, in lithium nickel complex oxide, the content rate of the aluminum or cobalt in a particle | grain surface layer part has description of a primary particle higher than the inside of a particle | grain.

JP 62-256371 A JP 2010-211925 A

  However, since lithium nickelate has poor cycle characteristics of lithium insertion and desorption, the primary particles that form the secondary particles have sub-micron order particle diameters that form fine voids in the secondary particles and come into contact with the electrolyte. If the area is not increased, good charge / discharge cycle characteristics cannot be obtained. However, secondary particles composed of aggregates of primary particles are apt to collapse because stress is generated at the grain boundaries of the primary particles forming the secondary particles by the process of compressing the electrode plate and the repetition of the charge / discharge cycle.

  On the other hand, a positive electrode mixture layer of a lithium ion battery, which is a general non-aqueous electrolyte secondary battery, contains a conductive agent such as carbon in order to provide conductivity between active materials. However, when the active material collapses at the primary particle interface, the electronic resistance between the primary particles increases, and the charge / discharge cycle characteristics tend to deteriorate.

  An object of the present invention is to provide a non-aqueous electrolyte secondary battery having a high capacity and excellent charge / discharge cycle characteristics.

A non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode and a negative electrode that reversibly occlude and release lithium ions, and an organic electrolyte in which the electrolyte containing the lithium ions is dissolved. The positive electrode and the negative electrode are porous insulating. In the non-aqueous electrolyte secondary battery disposed through the layers, the positive electrode active material has a general formula of Li _x Ni _1-yz Co _y Al _z O ₂ (x: 0.9 <x <1.3 0.1 <y <0.3, 0.0 <z <0.3), and the positive electrode active material is a secondary particle made of an aggregate of primary particles. The nonaqueous electrolyte secondary battery is characterized in that a conductive agent is contained between the primary particles.

  By containing a conductive agent between the primary particles that make up the secondary particles, even if the secondary particles collapse, the electrical conductivity between the primary particles is unlikely to decrease, preventing a significant decrease in charge / discharge cycle characteristics. can do.

  The conductive agent is preferably a carbon material from the viewpoint of electrochemical stability in the operating voltage range of the nonaqueous electrolyte secondary battery and chemical stability with respect to the nonaqueous electrolyte.

  The primary particles of the positive electrode active material preferably have an increased amount of aluminum from the inside to the surface. By containing a large amount of aluminum on the primary particle surface, the reaction between the electrolytic solution and nickel on the primary particle surface can be suppressed, and the increase in resistance on the primary particle surface can be suppressed. Since it can suppress, it is more preferable.

  According to the present invention, since the conductive agent is contained between the primary particles constituting the secondary particles, even if the secondary particles are collapsed, the conductivity between the primary particles is unlikely to decrease, so that the charge / discharge cycle characteristics Therefore, a non-aqueous electrolyte secondary battery having a high capacity and excellent charge / discharge cycle characteristics can be provided.

1 is a schematic longitudinal sectional view showing a schematic structure of a lithium ion secondary battery according to an embodiment of the present invention.

The lithium ion secondary battery of the present invention has a general formula of Li _x Ni _1-yz Co _y Al _z O ₂ (x: 0.9 <x <1.3, 0.1 <y <0.3, 0.0 <z <0.3), and the positive active material is a secondary particle composed of an aggregate of primary particles, and constitutes a secondary particle. A conductive agent is included between the primary particles.
The compound represented by the general formula Li _x Ni _1-yz Co _y Al _z O ₂ as the positive electrode active material is excellent in safety, high energy density, and good cycle characteristics.

  In the positive electrode active material, x indicating Ni composition is 0.6 to 0.75, y indicating Co composition is 0.1 to 0.3, and z indicating Al composition is 0.0 to 0.00. 3 is desirable, and x indicating the Ni composition is preferably 0.6 to 0.7.

  The following points can be considered as these reasons. When the Ni composition in the positive electrode active material is larger than 0.75, that is, when the addition amount of the dissimilar metal is less than 0.25, the stabilization effect due to the bond between the added metal and oxygen is reduced.

  Since the effect of stabilizing the crystal structure increases as the amount of added metal increases, the Ni composition is particularly preferably 0.7 or less. Conversely, when the Ni composition is less than 0.6, the charge / discharge capacity tends to decrease, which is not preferable.

  On the other hand, it was expected that the larger the amount of Co added, the more stable the crystal structure and the effect of safety, but substitution exceeding 0.3 is not possible because a uniform crystal structure cannot be obtained. .3 or less is desirable.

  Al has the effect of improving the reversibility of lithium occlusion and release in addition to the effect of stabilizing the crystal structure. However, when Al is more than 0.15, the amount of occlusion and release of lithium decreases. Therefore, the optimum Al addition amount is around 0.1, and the Co composition is preferably in the range of 0.2 to 0.3.

  The positive active material is a secondary particle composed of an aggregate of primary particles, and the size of the primary particle is preferably 0.5 μm to 3.0 μm. If it is 0.5 μm or less, the surface area of the primary particles will increase, so a large amount of conductive agent will be required to ensure the conductivity between the primary particles, leading to a decrease in the amount of active material packed in the battery. It is not preferable because the capacity is lowered. On the other hand, if the size of the primary particles is 3.0 μm or more, the contact area of the active material with the electrolytic solution is lowered, which causes a significant decrease in reactivity, which is not preferable.

  The conductive agent has a high electronic conductivity, and it is preferable to use a carbon material from the viewpoint of electrochemical stability in the operating voltage range of the nonaqueous electrolyte secondary battery and chemical stability with respect to the nonaqueous electrolyte.

  As the carbon material, it is preferable to use a material having a high surface area such as acetylene black having a high surface area or carbon nanofibers in order to obtain a high effect with a small amount of addition. The amount added varies depending on the carbon material used, but is preferably 0.1 wt% to 10 wt%. The effect that the added amount is 0.1 wt% or less cannot be sufficiently obtained, and if the added amount is 10 wt% or more, the amount of the active material is lowered, which is not preferable.

  The presence of a large amount of Al oxide on the surface of the primary particles can suppress a side reaction with the electrolytic solution on the surface of the active material, and an effect of including a conductive agent between the primary particles can be obtained.

  Hereinafter, the lithium secondary battery of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of a lithium secondary battery according to an embodiment of the present invention.

  A positive electrode 11, a separator 12, a negative electrode 13, and a separator 12 that are stacked and wound in this order are housed in a battery can 18 together with an upper insulating plate 16 and a lower insulating plate 17. A positive electrode tab 14 is attached to the positive electrode 11, and a negative electrode tab 15 is attached to the negative electrode 13. The positive electrode tab 14 is connected to the positive electrode terminal 20 provided on the battery inner lid 19, and the negative electrode tab 15 is connected to the battery can 18. .

  Next, an example of the lithium secondary battery of the present invention will be shown and described in detail.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. Needless to say, the present invention is not limited to these examples.

  In this example, a lithium ion secondary battery was produced, the capacity of the produced lithium ion secondary battery was measured, and the charge / discharge cycle characteristics were evaluated.

Example 1
(Preparation of positive electrode active material)
Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ having an average particle diameter of 1 μm, 100 parts by weight, 0.5 parts by weight of carbon nanotubes having a fiber diameter of 15 nm and an aspect ratio of 100, and carbonylmethylcellulose 0.5 as a binder After dispersing a weight part in water, it was granulated using a spray dryer so as to have a particle diameter of 15 μm. The resulting granulated particles were then calcined at 765 ° C. for 20 hours. The obtained fired body was cooled to room temperature in an electric furnace to obtain a spherical fired powder in which primary particles were aggregated. In this powder, carbon nanotubes were scattered between primary particles.

(Preparation of positive electrode)
First, 0.5 part by weight of acetylene black (conductive agent), 1.0 part by weight of polyvinylidene fluoride (PVDF (poly (vinylidene fluoride))) (binder) and 100 parts by weight of Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ (positive electrode active material) and N-methylpyrrolidone were mixed to obtain a positive electrode mixture paste.

  This positive electrode mixture paste was applied to both surfaces of a 15-μm thick aluminum foil made in Japan (A8021H-H18-15RK) and dried. The positive electrode plate thus obtained was rolled and then heated at 280 ° C. for 60 seconds and then cut to obtain a positive electrode having a thickness of 0.157 mm, a width of 57 mm, and a length of 564 mm.

(Preparation of negative electrode)
First, the flaky artificial graphite was pulverized and classified so that the average particle diameter was about 20 μm.

  Next, 100 parts by weight of flaky artificial graphite was added and mixed with 3 parts by weight of styrene / butadiene rubber as a binder and 100 parts by weight of an aqueous solution containing 1% by weight of carboxymethylcellulose to obtain a negative electrode mixture paste. It was. Thereafter, the negative electrode mixture paste was applied to both sides of a copper foil (negative electrode current collector) having a thickness of 8 μm and dried. The negative electrode plate thus obtained was rolled and then heated at 190 ° C. and then cut to obtain a negative electrode having a thickness of 0.156 mm, a width of 58.5 mm, and a length of 750 mm.

(Preparation of non-aqueous electrolyte)
5 wt% vinylene carbonate was added to a mixed solvent in which the volume ratio of ethylene carbonate to dimethyl carbonate was 1: 3, and LiPF ₆ was dissolved to a concentration of 1.4 mol / m ³ . In this way, a nonaqueous electrolytic solution was obtained.

(Production of cylindrical battery)
First, a positive electrode lead made of aluminum was connected to the positive electrode current collector, and a negative electrode lead made of nickel was connected to the negative electrode current collector. Next, it wound in the state which pinched | interposed the polyethylene-made separator between the positive electrode and the negative electrode, and produced the electrode group.

  Next, insulating plates were respectively arranged above and below the electrode group, the negative electrode lead was welded to the battery case, and the positive electrode lead was welded to a sealing plate having an internal pressure actuated safety valve. The electrode group was housed inside the battery case.

Thereafter, a non-aqueous electrolyte was injected into the battery case by a reduced pressure method. Then, the battery 1 was produced by caulking the open end of the battery case with a sealing plate via a gasket. The battery capacity of the battery was 2900 mAh. The battery capacity was charged at a constant current of 1.4 A up to 4.2 V in a 25 ° C. environment, and then charged at a constant voltage of 4.2 V until the current value reached 50 mA, and then the battery capacity was reduced to 0. This is the capacity when discharging to 2.5 V with a constant current value of 56 A.

(Example 2)
A battery of Example 2 was produced in the same manner as in Example 1 except that 0.5 part by weight of acetylene black was added instead of 0.5 part by weight of carbon nanotubes during the production of the positive electrode active material.

(Example 3)
A battery of Example 2 was produced in the same manner as in Example 1 except that 0.5 part by weight of acetylene black was added instead of 0.5 part by weight of carbon nanotubes during the production of the positive electrode active material.

(Comparative Example 1)
A battery of Comparative Example 1 was produced in the same manner as in Example 1 except that no carbon nanotubes were added during the production of the positive electrode active material.

<Evaluation of cycle characteristics>
About the nonaqueous electrolyte secondary battery of the batteries 1-8, the following charging / discharging cycle was repeated 500 times at 45 degreeC.

Constant current charging: Charging current value 1450mA / end-of-charge voltage 4.2V
Constant voltage charging: Charging voltage value 4.2V / end-of-charge current 50mA
Constant current discharge: discharge current value 2750 mA / discharge end voltage 2.5 V
And according to the following formula | equation, the capacity | capacitance maintenance factor (%) was calculated | required. The results are shown in Table 1.

Capacity retention rate (%) = (500th discharge capacity / first discharge capacity) × 100
The results are shown in Table 1.

  The present invention is useful not only for power sources for portable electronic devices but also for power sources for driving automobiles or power sources for supplying household power.

DESCRIPTION OF SYMBOLS 11 Positive electrode 12 Separator 13 Negative electrode 14 Positive electrode tab 15 Negative electrode tab 16 Upper insulating plate 17 Lower insulating plate 18 Battery can 19 Battery inner lid 20 Positive electrode terminal

Claims (3)

A non-aqueous electrolyte secondary comprising a positive electrode and a negative electrode that reversibly occlude and release lithium ions, and an organic electrolyte in which an electrolyte containing the lithium ions is dissolved, and the positive electrode and the negative electrode are disposed via a porous insulating layer In batteries,
The positive electrode active material has a general formula of Li _x Ni _1-yz Co _y Al _z O ₂ (x: 0.9 <x <1.3, 0.1 <y <0.3, 0.0 < z <0.3), and the positive electrode active material is secondary particles composed of aggregates of primary particles, and a conductive agent is included between the particles of the primary particles. A non-aqueous electrolyte secondary battery characterized by comprising:   The non-aqueous electrolyte secondary battery according to claim 1, wherein the conductive agent is made of a carbon material.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the primary particles of the positive electrode active material have an increased amount of aluminum from the inside to the surface thereof.