JP2011228058A - Negative electrode active material, and secondary battery and capacitor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode active material achieving the large capacity without reduction of the cycle life, and provide a secondary battery and a capacitor using the negative electrode active material.SOLUTION: A second battery comprises: a negative electrode that includes a porous aluminum alloy negative electrode active material 12 having at least one type of silicon or tin; a positive electrode that includes a positive electrode active material (LiCoO) 14 having lithium and capable of absorbing and releasing lithium; and a separator 15 provided between the negative electrode and the positive electrode and impregnated with ion conductivity electrolyte.

Description

  The present invention relates to a negative electrode active material, a secondary battery using the same, and a capacitor.

  Lithium (Li) ion batteries are used as secondary batteries because they are excellent in energy density (hereinafter also referred to as “capacity”). As the negative electrode active material for a secondary battery, a material in which Li is doped into graphite (C) is usually used, and it is theoretically possible to dope Li up to C6Li. At present, Li can be doped only up to a lower concentration (C10Li).

  Also, aluminum (Al) -Li alloys have been studied as a negative electrode for secondary batteries, and some of them have been put into practical use. This is an Al—Li alloy electrode for a non-aqueous secondary battery, and the electrode is made of an Al—Li alloy mainly containing Al and containing 4 to 12% by mass of Li, and the alloy is in a network eutectic structure. The LiAl compound has a size of 10 μm or less (see Patent Document 1).

  Moreover, since the output density of the capacitor is higher than that of the secondary battery, it is promising as a power storage device for renewable energy such as a main power source and an auxiliary power source of an electric vehicle or solar power generation and wind power generation. However, since the energy density is low (that is, the electric capacity is small), the following attempts to improve these have been proposed.

  As such a capacitor, for example, a Li ion hybrid capacitor in which a positive electrode and a negative electrode are immersed in an electrolytic solution through a separator, the positive electrode includes non-porous carbon as an active material, and the negative electrode includes Li as an active material. The thing of the structure which contains the carbon (C) material which can occlude / desorb ion reversibly and whose electrolyte solution is an aprotic organic solvent containing Li salt is known (refer patent document 2).

  In the Li-ion hybrid capacitor, the negative electrode active material is a carbonaceous porous powder that is an aggregate of porous carbon black having a pore structure and an average particle diameter of 12 to 300 nm bound with a carbon material. As the positive electrode active material, the same material as the carbon (C) material disclosed in Patent Document 2 is known (see Patent Document 3).

JP 63-51052 A JP 2007-294539 A JP 2008-150270 A

  However, since the Al—Li alloy as the negative electrode for secondary battery disclosed in Patent Document 1 has a plate shape, the stress due to volume expansion / contraction due to charge / discharge is not relieved and functions as a negative electrode active material. As a result, the Al-Li alloy is peeled off and the cycle life is insufficient.

  In addition, since the negative electrode disclosed in Patent Document 2 contains a carbon material as an active material, it is theoretically impossible to obtain a doping amount of Li equal to or higher than C6Li, and a large capacity cannot be expected in the first place. Furthermore, since the positive electrode stores electricity only by adsorption of anions, the capacity is considerably smaller than the negative electrode in the first place, and even the capacity of the negative electrode cannot be fully utilized.

  In addition, regarding the negative electrode disclosed in Patent Document 3, similarly to the negative electrode disclosed in Patent Document 3, since a carbon material is included as an active material, a doping amount of Li equal to or higher than C6Li is theoretically not obtained. In the first place, we cannot expect large capacity. Further, like the positive electrode disclosed in Patent Document 2, since the positive electrode stores electricity only by adsorption of anions, the capacity is considerably smaller than the negative electrode in the first place, and even the capacity of the negative electrode cannot be fully utilized.

  An object of the present invention is to provide a negative electrode active material capable of securing a large capacity without reducing the cycle life, and a secondary battery and a capacitor using the negative electrode active material.

  In order to achieve this object, an invention according to claim 1 of the present invention is a negative electrode active material for a secondary battery which is a porous aluminum alloy and contains at least one of silicon and tin.

  The invention described in claim 2 is the invention described in claim 1, wherein the silicon and tin are each 0.05 to 24 atomic% (provided that both silicon and tin are included, 30 atoms in total) % Or less).

  Invention of Claim 3 is a negative electrode active material for secondary batteries of Claim 2, Comprising: Magnesium is contained 0.02-5 atomic%, It is a negative electrode active material for secondary batteries characterized by the above-mentioned. .

  The invention described in claim 4 includes: a negative electrode having the negative electrode active material for secondary battery according to any one of claims 1 to 3; and a positive electrode active material containing lithium and capable of occluding and releasing lithium. A secondary battery comprising: a positive electrode provided; and an ion conductive electrolyte disposed between the negative electrode and the positive electrode.

  The invention according to claim 5 is a negative electrode active material for a capacitor, which is a porous aluminum alloy and contains lithium and at least one of silicon and tin.

  The invention according to claim 6 is the invention according to claim 5, wherein the silicon and tin are each 0.05 to 24 atom% (provided that both silicon and tin are included, 30 atoms in total) % Or less).

  The invention according to claim 7 is the negative electrode active material for capacitors according to claim 6, wherein the negative electrode active material for capacitors contains 0.02 to 5 atomic% of magnesium.

  The invention according to claim 8 is a negative electrode having the negative electrode active material for capacitors according to any one of claims 5 to 7, a positive electrode, and an ion conductive electrolyte disposed between the negative electrode and the positive electrode. And a capacitor.

  As described above, the negative electrode active material for a secondary battery of the present invention is a porous aluminum alloy, and includes at least one of silicon or tin, so that a large capacity can be ensured without reducing the cycle life. A negative electrode active material and a secondary battery using the same can be provided.

  Further, the negative electrode active material for a capacitor of the present invention is a porous aluminum alloy, and includes lithium and at least one of silicon and tin, so that a large capacity can be secured without reducing the cycle life. A negative electrode active material and a capacitor using the same can be provided.

It is a schematic block diagram for demonstrating one Embodiment of the secondary battery which concerns on this invention. It is a schematic block diagram for demonstrating one Embodiment of the capacitor based on this invention.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

(Preparation of negative electrode active material for secondary battery and negative electrode active material for capacitor)
(Pretreatment of aluminum foil)
1) First, an aluminum foil having a thickness of 110 μm and a predetermined composition (not including Li, for details, see Tables 1 and 2 below) was added to 5.5% hydrochloric acid, 1.5% phosphoric acid and 0.5% by mass. Etching in an aqueous solution containing 10% nitric acid and 2.0 mass% aluminum chloride in an electrolytic solution at 18 ° C. with a triangular wave alternating current of 10 Hz and a current density of 120 mA / cm ² for 10 seconds to 27 minutes, and washed with ion-exchanged water .
2) Next, it was immersed in a 5.0 mass% sulfuric acid aqueous solution at 60 ° C. for 2 to 3 minutes, and then washed with ion-exchanged water. As a result, the test No. in Table 1 below. The negative electrode active material 12 (see FIG. 1) as a negative electrode active material for a secondary battery that does not need to contain lithium (Li) as shown in 1 to 5 and 7 to 9 is completed. The negative electrode active material 12 has a large number of pores as will be described in detail below.

(Synthesis of secondary battery negative electrode active material and capacitor negative electrode active material)
When lithium (Li) is contained in the pre-treated aluminum foil, a lithium plate connected to each of the positive electrode side and the negative electrode side, and the pre-treated aluminum foil are used as an electrolyte {concentration of 1 mol; (LiPF ₆ ), an organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC) = 1: 1 mixed solution)) so that the aluminum foil has a potential of 25 mV (vs. Li / Li ⁺ ). Controlled and electrolyzed at 50 ° C. to form an alloy. A negative electrode active material 12 (see FIG. 1) as a negative electrode active material for a secondary battery shown in FIG. The negative electrode active material 12 (refer FIG. 2) as a negative electrode active material for capacitors shown in 11-21 was synthesize | combined, respectively. The negative electrode active material 12 obtained by these syntheses has a large number of pores. The term “pore” as used herein is a generic term including a case where some holes generated due to the pretreatment conditions of the aluminum foil are included. Moreover, the distribution state of the pores is almost uniform, and the proportion of the area occupied by the pores on the surface of the negative electrode active material 12 obtained by the synthesis is preferably 10% to 80%. The distribution state of the pores reflects the distribution state of the pores of the aluminum foil previously pretreated. Further, the lithium content in the porous negative electrode active material 12 having pores was calculated from the amount of electricity at the time of the synthesis experiment (see Tables 1 and 2 below).

(Formation of negative electrode)
As shown in FIGS. 1 and 2, the negative electrode active material 12 was used as a negative electrode.

(Embodiment 1)
FIG. 1 is a schematic configuration diagram for explaining an embodiment of a secondary battery according to the present invention.

In FIG. 1, 10 is a container, 13 is an aluminum current collector, 14 is LiCoO ₂ as a positive electrode active material containing lithium and capable of occluding and releasing lithium, and 15 is a synthesis of the negative electrode active material for the secondary battery. The separator is impregnated with the same electrolytic solution used in the above. The separator 15 is a configuration sandwiched between the LiCoO 2 ₁₄ provided by coating and drying on the negative electrode active material 12 and the current collector 13 for the secondary battery. The secondary battery constructed as described above was tested with the test numbers shown in Table 1 above. In accordance with the negative electrode active material 12 for secondary batteries 1 to 9, the test No. 1-9.

  The voltage of the secondary battery configured as shown in FIG. 1 was measured. Next, a cycle test (discharge depth 20%) was performed, and the cycle number in which the capacity was reduced to 80% of the initial value was defined as the cycle life. Further, the initial negative electrode capacity was obtained, and the surface of the negative electrode active material 12 was observed to confirm the presence or absence of dendrite formation. The results are shown in Table 3 above.

  As shown in Table 3 above, Test No. The target voltage of 3.5 to 3.9V is generated as the voltage of 1 to 9. In addition, Test No. Nos. 1 to 7 and 9 satisfy the target cycle life (600 times or more) of 970 to 1830 times. 8 fell below 320 times. This is the result of test no. In 1 to 7 and 9, the lithium content in the negative electrode active material 12 increases and the volume expands at the time of charging, but the influence is absorbed and relaxed throughout the negative electrode active material 12 because of the porous structure. It seems to be. On the other hand, test no. In No. 8, since the content of magnesium (Mg) is large, it seems that the cycle performance was deteriorated. In addition, Test No. 4 to 6 contain Mg and are advantageous in terms of cycle life because the mechanical strength of the negative electrode active material 12 is improved.

  In addition, as shown in Table 3 above, the test No. Although the initial negative electrode capacities of 1 to 7 satisfied the target capacity (800 mAh / g or more) of 810 to 1350 mAh / g, 8 and 9 were lower than 740 and 790, respectively. Thus, test no. The initial negative electrode capacities of 1-7 increased because the ability to occlude lithium was 2.3 times that of graphite, 4.4 times that of silicon (Si), and 4.4 times that of tin (Sn). It seems to be caused by being. Silicon and tin are each preferably 0.05 to 24 atoms (at)% (however, when both silicon and tin are included, the total is 30 atom% or less). This is because if it is less than 0.05 atomic%, the effect of occluding lithium is small, and if silicon or tin exceeds 24 atomic% or if the total of silicon and tin exceeds 30 atomic%, a porous negative electrode This is because it is difficult to produce an active material.

  In addition, Test No. In 1 to 9, no dendrite formation was observed. Summarizing the above results, in order to realize a negative electrode active material capable of securing a large capacity without reducing the cycle life and a secondary battery using the negative electrode active material, test no. It can be seen that 1 to 7 are suitable.

(Embodiment 2)
FIG. 2 is a schematic configuration diagram for explaining one embodiment of a capacitor according to the present invention.

  In FIG. 2, 20 is an aluminum current collector, 21 is a positive electrode active material, and 22 is a separator impregnated with an electrolytic solution. In the present embodiment, the same elements as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

The separator 22 was sandwiched between the negative electrode active material 12 for the capacitor and the positive electrode active material 21 having activated carbon (BET specific surface area: 800 to 1300 m ² / g) provided on the current collector 20 by coating and drying. It is a configuration. The electrolytic solution impregnated in the separator 22 is an electrolytic solution having a concentration of 1.5 mol composed of an electrolyte (LiBF ₄ ) and an organic solvent {a mixed solution of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 1: 1}. It is. The capacitor thus constructed was tested with the test numbers shown in Table 2 above. In accordance with the negative electrode active material 12 for capacitors 11 to 21, as shown in Table 4 below, It was set to 11-21.

The voltage of the capacitor configured as shown in FIG. 2 was measured. Further, the capacitor configured as shown in FIG. 2 was discharged to 1.0 V with a constant current in a thermostatic chamber at 25 ° C. The capacitance C at this time is calculated assuming that the discharge energy obtained by time integration of the product of the voltage V and the current I during discharge is equal to 1/2 CV ^2, and the capacitance C per unit weight of the negative electrode active material 12 is calculated. (F / g) was determined. The results are shown in Table 4 above.

  As shown in Table 4 above, Test No. The target voltage of 3.3 to 3.8 V is generated as the voltage of 11 to 21. In addition, Test No. The electrostatic capacity C of 11 to 19 satisfied the target predetermined electrostatic capacity (1800 F / g or more) of 1840 to 2450 F / g. 20 and 21 were lower than 1740 and 1790, respectively. Thus, test no. Capacitance C of 11 to 19 increased because the ability to occlude lithium was 2.3 times that of graphite, 4.4 times that of silicon (Si), and 4.4 times that of tin (Sn). It seems to be due to being doubled. Silicon and tin are each preferably 0.05 to 24 atomic% (however, when both silicon and tin are included, the total is 30 atomic% or less). This is because if it is less than 0.05 atomic%, the effect of occluding lithium is small, and if silicon or tin exceeds 24 atomic% or if the total of silicon and tin exceeds 30 atomic%, a porous negative electrode This is because it is difficult to produce an active material.

  Next, in a constant temperature bath at 25 ° C., the battery was charged to a predetermined voltage with a constant current and a constant voltage, discharged to 1.0 V with a constant current, and the cycle number in which the electrostatic capacity decreased to 70% of the initial value was defined as the cycle life. . Further, the surface of the negative electrode active material 12 was observed to confirm whether dendrite was generated. The results are shown in Table 4 above.

  As shown in Table 4 above, Test No. Nos. 11 to 19 and 21 satisfy the target cycle life (110,000 times or more) of 14,000 times to 110,000 times, but the test No. 20 fell below 3,000 times. This is the result of test no. In 11 to 19 and 21, the lithium content in the negative electrode active material 12 increases and the volume expands at the time of charging. However, because of the porous structure, the influence is absorbed and relaxed throughout the negative electrode active material 12. It seems to be. On the other hand, test no. In No. 20, since the Mg content is large, it seems that the effect of volume expansion was insufficiently mitigated. In addition, Test No. Nos. 14 to 18 contain Mg and are advantageous in satisfying a higher cycle life while increasing the capacity because the mechanical strength of the negative electrode active material 12 is improved.

  In addition, Test No. From 11 to 21, no dendrite formation was observed. Summarizing the above results, in order to realize a negative electrode active material capable of securing a large capacity without reducing the cycle life and a capacitor using the same, test no. It can be seen that 11 to 19 are suitable.

  In the present embodiment, the aluminum foil has been described as an example where the thickness is 110 μm, but the present invention is not necessarily limited to this, and an aluminum foil having a thickness of about 5 μm to 200 μm can be used. . Further, in this embodiment, as an anode active material for a secondary battery, as shown in Table 1 above, an example in which Si, Sn, and Mg are appropriately contained centering on Al has been described. The negative electrode active material may contain 0.05 at% or less of Fe, Cu, Mn, Zn, Ti, etc. as inevitable impurities. Further, in the present embodiment, as an anode active material for a capacitor, as shown in Table 2 above, an example in which Si, Sn, and Mg are appropriately contained centering on Al and Li has been described. The negative electrode active material may contain 0.05 at% or less of Fe, Cu, Mn, Zn, Ti, etc. as inevitable impurities. Moreover, the content of Li in the negative electrode active material for capacitors is preferably 5 at% to 70 at%. The reason is that if it is less than 5 at%, the energy density becomes small, and if it exceeds 70 at%, volume dendrite of the electrode tends to occur. More preferably, the Li content is 30 at% to 65 at%.

  In the first and second embodiments, the configuration in which a current collector is not separately provided for the negative electrode active material 12 has been described. However, the present invention is not necessarily limited thereto. For example, a current collector may be separately provided for the negative electrode active material 12 such that the negative electrode active material 12 is lightly pressed against a copper current collector via a conductive paste to form a negative electrode.

DESCRIPTION OF SYMBOLS 10 Container 12 Negative electrode active material 13, 20 Current collector 14 Positive electrode active material (LiCoO ₂ )
21 Positive electrode active material 15, 22 Separator impregnated with electrolyte

Claims (8)

  A negative electrode active material for a secondary battery, which is a porous aluminum alloy and contains at least one of silicon and tin.   2. The secondary according to claim 1, wherein the silicon and tin are each 0.05 to 24 atomic% (however, when both silicon and tin are included, the total is 30 atomic% or less). Negative electrode active material for batteries.   The negative electrode active material for a secondary battery according to claim 2, comprising 0.02 to 5 atomic% of magnesium.   A negative electrode having the negative electrode active material for a secondary battery according to any one of claims 1 to 3, a positive electrode having a positive electrode active material containing lithium and capable of occluding and releasing lithium, and the negative electrode and the positive electrode A secondary battery comprising: an ion conductive electrolyte solution disposed therebetween.   A negative electrode active material for a capacitor, which is a porous aluminum alloy and includes lithium and at least one of silicon and tin.   The said silicon and tin are 0.05-24 atomic%, respectively (however, when both silicon and tin are included, it is set as 30 atomic% or less in total), Negative electrode active material.   The negative electrode active material for capacitors according to claim 6, wherein the negative electrode active material for capacitors contains 0.02 to 5 atomic% of magnesium. A negative electrode having the negative electrode active material for a capacitor according to any one of claims 5 to 7, a positive electrode, and an ion conductive electrolyte disposed between the negative electrode and the positive electrode. Capacitor.

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