JP2017224554A - Secondary battery including separator of metal organic structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery including a novel configuration of a separator capable of suppressing capacity drop, even when using an active material of such a kind that may cause capacity drop due to shuttle phenomenon, like a lithium sulfur secondary battery.SOLUTION: A separator including a film of a metal organic structure (MOF) is used in a secondary battery. The film of the metal organic structure may be formed of a mixture of metal organic structure particles and adhesive or resin, and the separator may have a structure obtained by laminating or bonding a metal organic structure film to a porous support, or by laminating the metal organic structure film and a graphene oxide film, via an adhesive or not via the adhesive but directly, two layers or alternating three or more layers.SELECTED DRAWING: Figure 12

Description

  The present invention relates to a secondary battery including a metal organic structure film as a separator. More specifically, such a decrease in capacity can be suppressed even when an active material or the like of a type that causes a decrease in capacity due to the shuttle phenomenon, as exemplified by a lithium-sulfur secondary battery, is used. Next battery.

Due to environmental and energy problems in recent years, electric vehicles (EV and HEV) are becoming popular. Currently, lithium-ion batteries are installed in electric vehicles, but their performance is not sufficient, and there is a need for the development of high-performance storage batteries that can travel longer distances (for example, non-patented Reference 1). Lithium-sulfur secondary batteries are advanced storage batteries for lithium-ion batteries, and are theoretically researched because they can expect batteries with a weight energy density that is about twice as high as the current level (for example, non-patent literature) 2).
However, the intermediate polysulfide produced by the discharge reaction is easily eluted into the electrolyte. The eluted polysulfide ions are repeatedly reciprocated between the positive electrode and the negative electrode, and the oxidation-reduction reaction is performed. As a result, the capacity of the lithium-sulfur secondary battery greatly deteriorates with the progress of the charge / discharge cycle. Yes. (For example, refer to Patent Documents 1 to 3 and Non-Patent Documents 3 to 5).

Special Table 2015-507340 WO2015 / 092959 WO2015 / 083314

Tarascon JM, Armand M. Issues and challenges facing rechargeable lithium batteries.Nature414, 359-367 (2001). Bruce PG, Freunberger SA, Hardwick LJ, Tarascon JM. Li-O2and Li-S batteries with high energy storage (vol 11, pg 19, 2012). Nat Mater 11, 19-29 (2012). Pang Q, Kundu D, Cuisinier M, Nazar LF.Surface-enhanced redox chemistry of polysulphides on a metallic and polar host for lithium-sulphur batteries. Nat Commun5, 4759 (2014). Yao HB, et al. Improving lithium-sulphur batteries through spatial control of sulphur species deposition on a hybrid electrode surface.Nat Commun5, 3943 (2014). Zhou GM, et al. A Graphene-Pure-Sulfur Sandwich Structure for Ultrafast, Long-Life Lithium-Sulfur Batteries. Adv Mater26, 625-631 (2014). Ji XL, Lee KT, Nazar LF.A highly ordered nanostructured carbon-sulphur cathode for lithium-sulphur batteries. Nat Mater8, 500-506 (2009) Yin YX, Xin S, Guo YG, Wan LJ. Lithium-Sulfur Batteries: Electrochemistry, Materials, and Prospects.Angew Chem Int Edit52, 13186-13200 (2013). Park K, et al. Trapping lithium polysulfides of a Li-S battery by forming lithium bonds in a polymer matrix.Energ Environ Sci8, 2389-2395 (2015). Mao YY, et al. General incorporation of diverse components inside metal-organic frameworkthin films at room temperature.Nat Commun5, 5532 (2014). Dikin DA, et al. Preparation and characterization of graphene oxide paper.Nature448, 457-460 (2007). Huang JQ, Zhuang TZ, Zhang Q, Peng HJ, Chen CM, Wei F. Permselective Graphene Oxide Membrane for Highly Stable and Anti-Self-Discharge Lithium-Sulfur Batteries.Acs Nano9, 3002-3011 (2015). Chui SSY, Lo SMF, Charmant JPH, Orpen AG, Williams ID. A chemically functionalizable nanoporous material [Cu-3 (TMA) (2) (H2O) (3)] (n). Science283, 1148-1150 (1999). Zhu K, Qiu HL, Zhang YQ, Zhang D, Chen G, Wei YJ.Synergetic Effects of Al3 + Doping and Graphene Modification on the Electrochemical Performance of V2O5Cathode Materials.Chemsuschem8, 1017-1025 (2015).

  In the lithium-sulfur secondary battery, the intermediate polysulfide produced by the discharge reaction is easily eluted into the electrolytic solution. The eluted polysulfide ions are repeatedly reciprocated between the positive electrode and the negative electrode to cause an oxidation-reduction reaction, so that the capacity of the lithium-sulfur secondary battery is significantly deteriorated with the progress of the charge / discharge cycle. The present inventor has recognized that the same capacity degradation problem due to the shuttle phenomenon can also occur in a lithium ion secondary battery using an organic positive electrode material, a nickel metal hydride secondary battery containing a nitrogen compound as an impurity, and the like.

The present invention is based on the background of the prior art as described above, and it is an object of the present invention to provide a secondary battery having a novel separator configuration that can solve the above-described problems.
In addition, the present invention is of a type that can cause a capacity drop due to a shuttle phenomenon, such as a lithium-sulfur secondary battery, a lithium-ion secondary battery using an organic positive electrode material, and a nickel-hydrogen secondary battery containing a nitrogen compound as an impurity. Even when an active material or the like is used, it is an object to provide a secondary battery that can suppress such a decrease in capacity.
Another object of the present invention is to provide a lithium-sulfur secondary battery, a lithium-ion secondary battery using an organic positive electrode material, a nickel-hydrogen secondary battery, and the like that can suppress capacity reduction due to the shuttle phenomenon.

  In order to solve the problems of the conventional technology as described above, conventionally, a technology for suppressing polysulfide elution from the positive electrode has been basically developed (see Patent Document 1, Non-Patent Documents 3 to 8). However, the present inventor has recognized that it is difficult to completely prevent elution of polysulfide from the positive electrode, and studied a method for preventing the eluted polysulfide from going to the negative electrode side. In the prior art, the use of a cation exchange membrane or a polymer non-woven fabric having a sulfone group as a separator has been studied (see Patent Documents 2 and 3). It was recognized that this was insufficient to completely prevent the movement of the product to the negative electrode side. In such a study process, we focused on metal-organic structures, which are molecular sieves that have been commonly used for adsorption and separation of gas molecules.

  Metal-organic framework (Metal-Organic Framework, hereinafter referred to as “MOF”) is a material with a porous coordination network structure by the interaction of metal and organic ligand (ligand). It is. The molecular sieving effect is a three-dimensional micropore whose size can be controlled from several angstroms to several nanometers. The inventor has selected a metal organic structure having fine pores smaller than polysulfide ions and used it as a separator for a lithium-sulfur secondary battery. Furthermore, in order to prevent the fragile defects of the metal organic structure which is a crystal, a composite metal organic structure film (= MOF @ GO) in which a metal organic structure layer and a graphene oxide layer are laminated is synthesized and the generated flexibility A composite metal organic structure film was developed on the separator of a lithium-sulfur secondary battery to suppress the conventional shuttle phenomenon and to prevent a decrease in charge / discharge capacity and deterioration of cycle characteristics. Stable charge / discharge cycle characteristics were confirmed over a long period of time.

The present invention has been completed based on the findings obtained in the above-described research process, and the present invention provides the following inventions.
<1> A secondary battery, wherein the separator includes a film of a metal organic structure.
<2> The secondary battery according to <1>, wherein the metal organic structure film is formed from a mixture including the metal organic structure and an adhesive or a resin.
<3> The secondary battery according to <1>, wherein the separator has a laminated structure including a graphene layer and a metal organic structure layer.
<4> The metal organic structure according to any one of <1> to <3>, wherein the metal is selected from Cu, Ni, Zn, Mn, Co, and Zr. Secondary battery.
<5> The secondary battery according to <4>, wherein the metal of the metal organic structure is Cu.
<6> The metal organic structure according to any one of <1> to <5>, wherein the size of the three-dimensional micropore is in a range of several angstroms to several nanometers (3 to 6 nm). Secondary battery.
<7> The secondary battery according to any one of <1> to <6>, wherein metallic lithium is used as the negative electrode active material and sulfur is used as the positive electrode active material.
<8> The secondary battery according to <7>, wherein the intermediate product ion _Sn ^2- (4 ≦ n ≦ 8) dissolved in the positive electrode side electrolyte is prevented from moving to the negative electrode side.

Furthermore, the present invention can include the following aspects.
<9> The secondary battery according to <1> or <2>, wherein the separator includes a porous support that supports the metal organic structure film.
<10> The secondary battery according to <9>, wherein the metal organic structure film is formed directly on the porous support with or without an adhesive.
<11> The secondary battery according to <1>, <2>, <9>, or <10>, including a plurality of metal organic structure films or layers.
<12> The secondary battery according to <3>, including a separator in which three or more metal organic structure layers and graphene oxide layers are alternately formed.
<13> The secondary battery according to <3> or <12>, wherein the metal organic structure layer and the graphene oxide layer are laminated with or without an adhesive.
<14> A lithium-sulfur secondary battery, wherein the separator includes a film of a metal organic structure.
<15> The lithium-sulfur secondary battery according to <14>, wherein the separator has a laminated structure including a graphene layer and a metal organic structure layer.

The secondary battery of the present invention includes a film or layer of a novel metal organic structure (MOF) as a structure and structure of the separator, and the separator passes ions necessary for charging and discharging. In addition to being allowed, contact between the positive electrode (or positive electrode active material) and the negative electrode (or negative electrode active material) can be prevented, so that it can function effectively in the same manner as a normal secondary battery.
In particular, decomposition products of electrode active materials dissolve in the electrolyte, such as lithium-sulfur secondary batteries, lithium-ion secondary batteries using organic cathode materials, nickel-hydrogen secondary batteries containing nitrogen compounds as impurities, etc. However, when applied to a secondary battery that may cause a shuttle phenomenon, the degradation product of one electrode active material can be prevented from moving to the other electrode. It can be remarkably suppressed and good cycle characteristics can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS Drawing which shows typically the lithium sulfur secondary battery of the Example of this invention. Drawing which shows typically the manufacturing process of the separator used for the secondary battery of the Example of this invention. The schematic drawing which shows the crystal structure (HKUST-1) of a metal organic structure, and its micropore. The powder X-ray-diffraction figure of the MOF @ GO separator of the Example of this invention. The black line indicates the theoretical calculated value (Simulated) of the MOF film, the light gray line indicates before charging (Before Charged), and the dark gray line indicates after 200 cycles of charging (After Charged 200 ^th cycles). (A) is a scanning electron micrograph of the multilayer MOF @ GO separator used in the secondary battery of the example of the present invention (inset is an optical photograph). (B) is a scanning electron micrograph showing the GO layer of the GO separator of the comparative example (inset is an optical photograph). The figure which shows the permeation | transmission test apparatus of a separator. The figure which shows the permeation | transmission test result of the MOF @ GO separator of the Example of this invention. The figure which shows the permeation | transmission test result of the GO separator of the comparative example of this invention. The drawing which shows transition of the discharge capacity and coulomb efficiency accompanying cycle progress at the time of repeating charge / discharge to 500 cycles on 0.5 C conditions about the lithium sulfur secondary battery of the Example of this invention. About the lithium sulfur secondary battery of the Example (gray line) of the present invention and the comparative example (black line), it shows the transition of capacity and coulombic efficiency with the progress of the cycle when charging and discharging are repeated up to 1500 cycles under the condition of 1C. Drawing. It shows in comparison with a secondary battery of a comparative example having a GO separator. (In addition, the transition line of the Coulomb efficiency is substantially the same in the example (gray line) and the comparative example (black line) and is displayed overlapping.) The charge / discharge curves in the first, 155th, and 250th cycles of the lithium-sulfur secondary battery of the example of the present invention are shown. (Note that the charge / discharge curves of the 155th cycle and the 250th cycle are substantially the same and overlapped). For the lithium-sulfur secondary batteries of the example (gray line) of the present invention and the comparative example (black line), the current conditions were sequentially changed to 0.2C, 0.5C, 1C, 2C, 3C, and 0.2C during the cycle. Drawing which shows the rate performance (change of the discharge capacity accompanying a cycle progress) at the time of repeating charging / discharging to a cycle. About the lithium sulfur secondary battery of the comparative example of this invention, the charging / discharging curve at the time of charging / discharging on 0.1C, 0.2C, 0.5C, or 1C electric current conditions is shown. The charging / discharging curve at the time of charging / discharging on the constant current conditions of 0.1C, 0.2C, 0.5C, or 1C about the lithium sulfur secondary battery which comprises the MOF @ GO separator of the Example of this invention is shown.

  The secondary battery of the present invention is characterized in that a separator including a novel metal organic structure (MOF) film is used as the structure (or structure) of the separator. That is, although MOF has been conventionally used as a molecular sieve for adsorbing and separating gas molecules, it has not been known to be used as a main component of a secondary battery separator. The present inventor allows the MOF film to allow passage of necessary ions during charging and discharging, and can prevent contact between the positive electrode (or positive electrode active material) and the negative electrode (or negative electrode active material), In particular, by acting as a barrier that does not allow permeation of polysulfides dissolved in the electrolyte, capacity reduction due to the shuttle phenomenon can be remarkably suppressed, and good cycle characteristics can be obtained. Thus, the present invention has been achieved.

The separator including the MOF membrane according to the present invention partitions the secondary battery containing the electrolyte into a positive electrode chamber and a negative electrode chamber, allows passage of ions necessary for charging and discharging, and positive electrode (or positive electrode active). Material) and the negative electrode (or negative electrode active material) can be prevented from contacting each other. Therefore, the present invention can be applied to any ordinary secondary battery, but when applied to a type of secondary battery in which capacity reduction due to the shuttle phenomenon can occur, the capacity reduction due to the shuttle phenomenon is effective. This is particularly desirable.
Examples of secondary batteries that can cause capacity reduction due to the shuttle phenomenon include, but are not limited to, lithium-sulfur secondary batteries, lithium-ion secondary batteries using organic cathode materials, and nickel metal hydride containing nitrogen compounds as impurities. A secondary battery etc. are mentioned.

A schematic structure when the present invention is applied to a lithium-sulfur secondary battery is shown in FIG. The separator includes a film of a metal organic structure, and lithium ions (Li ⁺ ) can pass through the micropores (in this example, about 9 mm), but the polysulfide dissolved in the electrolyte on the cathode chamber side Object ions (S _n ²⁻ ) cannot pass through the micropores and cannot reach the negative electrode. Therefore, the capacity reduction due to the polysulfide shuttle phenomenon can be effectively suppressed.

  As the metal organic structure in the present invention, a metal selected from Cu, Ni, Zn, Mn, Co, and Zr can be used. In particular, when Cu is used, the pore size can be reduced to about 9 mm. Therefore, when applied to lithium-sulfur secondary batteries, the migration of polysulfides to the negative electrode side is prevented, and the polysulfide shuttle phenomenon occurs. It is considered that the capacity reduction due to can be effectively prevented.

Since the MOF is relatively fragile, the separator can include a material for MOF membrane reinforcement. Such a reinforcing material is not limited, but various adhesives such as organic adhesives, resin materials, carbon materials, and the like can be used.
As the organic adhesive, for example, various curable adhesives such as a reactive curable adhesive, a thermosetting adhesive, and an ultraviolet curable adhesive can be suitably used.
The resin material is not limited, but is preferably a curable resin such as an epoxy resin, a melamine resin, a silicon resin, or an unsaturated polyester resin, or a heat resistant resin such as a fluororesin.
Examples of the carbon material include carbon fiber woven or non-woven fabric, graphene, and the like, and a graphene oxide (hereinafter sometimes referred to as “GO”) film is preferable.
These reinforcing materials may be porous films or sheets that support the MOF membrane.
When a GO film is used, the MOF film and the GO film can be formed in two layers or in alternating layers.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these Examples.

<Manufacture of MOF-GO composite separator and GO separator>
The manufacturing process of the MOF-GO composite (hereinafter sometimes referred to as “MOF @ GO”) separator used in the examples of the present invention is schematically shown in FIG.
A film of MOF particles was first formed on a filter (Filter membrane, manufactured by Millipore Co. Ltd., diameter 47 mm, pore size 0.2 μm). MOF particles were synthesized in the same manner as in Non-Patent Documents 9 and 12. That is, a mixed solution containing 0.966 g (4 mmol) of copper (II) nitrate trihydrate [Cu (NO ₃ ) ₂ · 3H ₂ O] and 0.42 g (2 mmol) of 1,3,5-benzenetricarboxylic acid (BTC) Was vacuum filtered on a filter. Through this process, crystalline MOF particles were synthesized and self-assembled to form a MOF film.
Next, in the same manner as in Non-Patent Documents 10 and 11, by supplying and filtering a diluted graphene oxide solution (Diluted GO solutions), graphene oxide (GO) is formed on the MOF film formed on the filter. A layer was formed. Adjacent MOF and GO layers were strongly bonded on the filter. Graphene oxide (GO) is prepared from graphite powder (purity 99.8% or higher, Alfa Aesar (registered trademark)) by the revised version method of the hammer method (Hummers' method, Non-Patent Document 13), and is sonicated to 0.1 mg ml. Used diluted.
In order to manufacture a good separator, the MOF layer is then formed with a mixed solution of copper (II) nitrate and BTC (shown as “Ligand Solution” in FIG. 2), and the diluted GO solution (“GO” in FIG. The process consisting of GO layer formation by “GO solution” can be repeated 2 or 3 times. In that case, the continuous growth of MOF nanoparticles would fill the void space and eliminate the apparent gap along the grain boundary.
Finally, the formed MOF-GO composite (MOF @ GO) was peeled from the filter to obtain a self-supporting separator.
The GO separator of the comparative example was manufactured by performing the same operation as the GO layer formation in the MOF @ GO until the film thickness was about the same as that of the MOF @ GO without including MOF particles.
The manufactured MOF @ GO separator and GO separator were each separated from the filter and stored in a suitable dewatering environment until use.

<Structural features of MOF @ GO separator>
Powder X-ray diffraction (PXRD) data for the MOF @ GO separator was measured using an X-ray diffractometer (Bruker D8 Advanced diffractometer), using an X-ray source: CuKα ray (λ = 1.5418Å), acceleration voltage: 40 kV, acceleration Current: 40 mA, obtained under ambient temperature conditions. Fig. 4 shows the MOF film theoretically calculated (black line), before charging (light gray line), and after 200 cycles of charging / discharging (dark gray line) as described below. The powder X-ray diffraction (PXRD) pattern of is shown. The MOF particles in the separator were the same as HKUST-1 oriented in the (001) direction. In addition, the structural framework of MOF in the MOF @ GO separator remained unchanged throughout the charging and discharging processes over 200 cycles.

FIG. 5A shows a scanning electron micrograph (inset is an optical photograph) of the multilayer structure of the MOF @ GO separator. It is clear that the MOF film is composed of MOF particles and GO layer. For the MOF @ GO separator, the nitrogen adsorption isotherm was measured at 77K and atmospheric pressure and analyzed based on the non-local density functional theory (NLDFT). The pore size distribution was about 9 mm. It was calculated.
FIG. 5B shows a scanning electron micrograph (inset is an optical photograph) of a GO separator made of a GO laminate. Regarding the GO separator, peeling was observed after 200 cycles of charge / discharge as described below. Such peeling of the GO laminate is consistent with the results of the transmission test described below. Soluble polysulfides are thought to deteriorate the function of the GO separator because they diffuse and penetrate widely between GO layers to form voids and cracks. The SS chain length of lithium polysulfide (Li ₂ S _n , 4 ≦ n ≦ 8) is in the range of 2.09 mm to 2.39 mm, and the bond length between Li and S is considered to be slightly shorter than 2.6 mm, The GO separator cannot perform the barrier function against polysulfide molecules because it is shorter due to the spatial distance between GOs.

<Permeation test of MOF-GO composite separator>
The permeation test is performed using a self-made permeation test apparatus consisting of two glass tubes arranged in a V shape and a MOF @ GO separator or GO separator sandwiched between the two glass tubes, as shown in FIG. It was. Each separator was carefully inspected for cracks and holes, and then fixed with a transparent adhesive to the 20 mm opening at the bottom of each glass tube so that the two glass tubes were connected via the separator. .
In the transmission test, a crimson polysulfide solution (electrolyte containing 0.1M Li ₂ S ₆ ) is gently applied to the left glass tube, and a transparent electrolyte not containing polysulfide is gently added to the right glass tube. The liquid level was maintained at the same level on the left and right sides, and the presence / absence or degree of permeation of polysulfide from the left glass tube to the right glass tube (deep red color diffusion) over time of 0 to 48 hours was examined.
The permeation test result using the MOF @ GO separator of the example is shown in FIG. 7, and the permeation test result using the GO separator of the comparative example is shown in FIG.
In the permeation test using the MOF @ GO separator of the example, the polysulfide cannot permeate the separator at all within 48 hours, and the MOF @ GO separator clearly shows the permeation-preventing effect of the polysulfide as an ion sieve. It was shown to.
On the other hand, in the permeation test using the GO separator of the comparative example, permeation of polysulfides could not be sufficiently prevented. The polysulfide that permeated through the GO separator was slight within 1 hour, but about 1/8 of the right side liquid was occupied by the crimson polysulfide solution in 3 hours, and then the permeation accelerated. Then, the diffusion progressed to the entire right side liquid in 12 hours.

<Production of lithium-sulfur secondary battery>
(Preparation of positive electrode)
CMK-3 / S (carbon / sulfur produced by introducing sulfur into mesoporous carbon CMK-3 having a periodic structure prepared by using silica as a template in the same manner as described in Non-Patent Document 6. Complex) was prepared. The prepared CMK-3 / S was mixed with carbon black [Super P (registered trademark)], polyvinylidene fluoride binder in a weight ratio of 80:10:10 in N-methyl-2-pyrrolidone, and the resulting slurry was mixed. The positive electrode current collector was coated and dried under vacuum to produce a positive electrode. As measured by thermogravimetric analysis (TGA), the sulfur component in the carbon-sulfur composite (CMK-3 / S) was about 70 wt% and about 56 wt% of the positive electrode mixture.

(Assembly of lithium-sulfur secondary battery)
A normal 2032 coin cell was assembled in a glove box filled with argon gas using the MOF @ GO separator or GO separator obtained above, the positive electrode, and a negative electrode of a lithium metal foil. As electrolytes, 1,2-dimethoxyethane (DME, manufactured by Tokyo Chemical Industry Co., Ltd., purity 99.8%) and 1,3-dioxolane (DOL, manufactured by Tokyo Chemical Industry Co., Ltd., purity 99.8%) are 1: 1. A mixture containing 1M lithium-bis (trifluoromethanesulfonyl) imide (LiTFSI, manufactured by Tokyo Chemical Industry Co., Ltd., purity 99.9%) and 0.1M LiNO ₃ in a mixed solvent in a volume ratio was used. The separator was cut to a diameter of 16 mm and used after being washed with a blank electrolyte in a glove box.

<Performance test of lithium-sulfur secondary battery 1: discharge capacity, coulomb efficiency>
The constant current cycle test was performed in a range of a cut-off voltage of 1.5 to 3.0 V (Li ⁺ / Li) using a charge / discharge device (Hokuto Denko).
In a lithium-sulfur secondary battery, an initial active cycle is required due to the large intermediate contact area between the carbon carrier and sulfur in the positive electrode. Due to the higher sulfur content and electronic conductivity, the close connection between the sulfur particles plays an important role in improving the ion transport capability within the mesoporous carbon particles. In the secondary battery fabricated this time, the initial process of about 100 cycles is an activation cycle for achieving an electrochemical state with high reversible stability.

The secondary battery having the MOF @ GO separator was charged and discharged under a constant current condition of 0.5 C (1C = 1673 mAg ⁻¹ ) for more than 500 cycles. FIG. 9 shows the capacity change (gray line) and the Coulomb efficiency change (black line) as the cycle progresses. The initial discharge capacity was 1126 mAhg ⁻¹ , but gradually decreased to 100 cycles. However, the discharge capacities at the 100th, 300th and 500th cycles are still 813 mAhg ^-1 , 807 mAhg ^-1 and 799 mAhg ^-1 respectively, and excellent capacity retention after the 100th cycle. showed that. Moreover, the lost capacity in the range from the 100th cycle to the 500th cycle falls within 14 mAhg ⁻¹ , indicating excellent cycle stability and negligible capacity decay. On the other hand, the charge / discharge voltage in the constant current charge / discharge at 0.5 C coincided with that of a typical lithium-sulfur secondary battery (see FIG. 11).

In addition, for each lithium-sulfur secondary battery having the MOF @ GO separator of the example and the GO separator of the comparative example, the capacity change with the cycle progress when charging / discharging under a constant current condition of 1 C up to more than 1500 cycles (lower side) 10) and the Coulomb efficiency change (the two lines almost overlapping on the upper side) are shown in FIG. 10 (the gray line is an example and the black line is a comparative example).
The GO separator secondary battery had a relatively large initial capacity of 1000 mAhg ⁻¹ , but thereafter showed dramatic capacity decay. The capacities of the 100th cycle, 400th cycle, 800th cycle and 1000th cycle are 611 mAhg ^-1 , 363 mAhg ^-1 , 258 mAhg ^-1 and 234 mAhg ^-1 respectively. It was only about 23%. This can be explained by the short blocking effect of the GO separator. This result is consistent with the transmission test results described above.
On the other hand, the secondary battery with the MOF @ GO separator has a relatively large capacity reduction up to the 100th cycle, as is evident from the initial capacity of 1207 mAhg- ¹ and the capacity of the 100th cycle of 870 mAhg- ^1. is there. The capacity reduction at this stage is considered as a secondary battery activation process. The cycle performance was stable from the 100th cycle to the 1500th cycle, and was maintained at about 855 mAhg- ¹ . The capacity retention rate reaches about 71%, and the capacity loss rate per cycle up to 1500 cycles is as small as 0.019%, which suggests that the secondary battery of the present invention has high efficiency and dynamic characteristics.

<Performance test 2 of lithium-sulfur secondary battery: Rate characteristics and charge / discharge voltage profile>
For each lithium-sulfur secondary battery equipped with the GO separator of the comparative example and the MOF @ GO separator of the example, a cycle test was performed by sequentially changing the current conditions to 0.2C, 0.5C, 1C, 2C, 3C, 0.2C. went. FIG. 12 shows the change in discharge capacity as the cycle progresses.
In the comparative example equipped with the GO separator (black line), the initial capacity at 0.2 C reached 885 mAhg ⁻¹ but decreased to 718 mAhg ⁻¹ . In addition, the discharge capacities were dramatically reduced to 452 mAhg ⁻¹ , 296 mAhg ⁻¹ , 141 mAhg ⁻¹ , and 84 mAhg ⁻¹ by increasing the rate to 0.5C, 1C, 2C, and 3C. At the final 0.2C, the recovery was only 580 mAhg ^-1 .
In contrast, the MOF @ GO separator of the example (gray line) showed a rate characteristic far superior to that of the comparative example. The initial capacity at 0.2 C reached approximately 1072 mAhg ⁻¹ and the retention capacity reached 969 mAhg ⁻¹ . Further, 0.5C, 1C, 2C, the discharge capacity at the time of the 3C and high ^{rate, 801 mAhg -1, 612 mAhg -1} , 537 mAhg -1, at 488 mAhg ^-1, the last 0.2C at 876 mAhg ^- Recovered to ¹ .

The charging / discharging voltage profiles when charging / discharging at various rates in a predetermined charging / discharging cycle of each lithium-sulfur secondary battery including the GO separator of the comparative example or the MOF @ GO separator of the example are shown in FIGS. Shown in Both separator secondary batteries showed two plateaus whose discharge curves were similar to those typically observed in lithium-sulfur secondary batteries with carbon-sulfur composite cathodes. On the other hand, in the secondary battery of the example equipped with the MOF @ GO separator, two distinct plateaus were observed even at low rate charging of 0.1C and 0.2C, but at high rates, irregular charging was observed. A voltage profile was observed. Furthermore, the flat area during charging in the MOF @ GO separator was not as clear as in the GO separator.

Claims (8)

  A secondary battery, wherein the separator includes a film of a metal organic structure.   The secondary battery according to claim 1, wherein the metal organic structure film is formed from a mixture including the metal organic structure and an adhesive or a resin.   The secondary battery according to claim 1, wherein the separator has a laminated structure including a graphene layer and a metal organic structure layer.   The secondary battery according to any one of claims 1 to 3, wherein the metal organic structure is one in which the metal is selected from Cu, Ni, Zn, Mn, Co, and Zr.   The secondary battery according to claim 4, wherein the metal of the metal organic structure is Cu.   6. The secondary battery according to claim 1, wherein the metal organic structure has a three-dimensional micropore size ranging from several angstroms to several nanometers (3 to 6 nm).   The secondary battery according to claim 1, wherein metallic lithium is used as the negative electrode active material and sulfur is used as the positive electrode active material. The secondary battery according to claim 7, wherein intermediate product ions _Sn ²⁻ (4 ≦ n ≦ 8) dissolved in the positive electrode side electrolyte are prevented from moving to the negative electrode side.

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