JP2009076260A - Lithium sulfur battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium-sulfur battery endowed with both a high output and excellent cycle characteristics. <P>SOLUTION: The lithium-sulfur battery comprises a cathode 20 made of nickel, an anode 16 made of lithium, and electrolyte containing lithium ion and an iron-sulfur complex. Since the iron-sulfur complex is thus fixed on the surface of the cathode 20 at an initial charging reaction, sulfide ion is prevented from eluting again into the electrolyte to restrain a self-discharge phenomenon. With this, the lithium-sulfur endowed with both the high output and the excellent cycle characteristics can be provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lithium sulfur battery.

  Conventionally, a lithium-sulfur battery using sulfur alone as a positive electrode active material is known. The theoretical capacity density of lithium is about 3862 mAh / g, and the theoretical capacity density of sulfur is about 1675 mAh / g. Therefore, by using sulfur as the positive electrode active material and lithium as the negative electrode active material, the energy density is very high. A secondary battery can be provided.

In a normal lithium-sulfur battery, sulfide ions (S ²⁻ ) in the electrolyte are oxidized to polysulfide ions (S _y ²⁻ ) in the charging reaction process at the positive electrode. And most of the produced polysulfide ions (S _y ²⁻ ) are further oxidized to be deposited as sulfur on the surface of the positive electrode. As shown in the following formula (1), the sulfur deposited on the positive electrode reacts with the polysulfide ions (S _(y-1) ²⁻ ) remaining in the vicinity of the positive electrode, thereby again producing polysulfide ions (S _y ^2- ) Elution into the electrolyte solution. The polysulfide ions eluted in the electrolyte react with the negative electrode and are reduced, whereby a discharge phenomenon (self-discharge phenomenon) occurs in the negative electrode. As a result, the charge / discharge cycle characteristics deteriorate.
S _(y-1) ^2- + S → S _y ^2- (1)

For this reason, several techniques for suppressing the self-discharge phenomenon have been reported. For example, in the lithium-sulfur battery described in Patent Document 1, sulfur is eluted into the electrolyte again by using a positive electrode containing a metal that forms a compound with sulfur, such as copper, and fixing the sulfur as a compound on the positive electrode. Prevents the self-discharge phenomenon.
JP 2005-251473 A

  However, in the lithium-sulfur battery described in Patent Document 1, the charge / discharge efficiency after the second cycle is approximately 100% and the cycle characteristics are good, but the current value that can be passed during charge / discharge is extremely low, and the high output There was a problem that could not get. That is, there is a problem that high output and good cycle characteristics cannot be combined.

  The present invention has been made in view of the above-described problems, and has as its main object to provide a lithium-sulfur battery having both high output and good cycle characteristics.

  In order to achieve the above-mentioned object, the present inventors assembled a lithium-sulfur battery in which nickel was added to the positive electrode, lithium was added to the negative electrode, and lithium ions and an iron-sulfur complex were added to the electrolyte. It has been found that it has characteristics, and the present invention has been completed.

  That is, the lithium-sulfur battery of the present invention includes a positive electrode containing at least one metal element of nickel and cobalt, a negative electrode containing a material that absorbs and releases lithium ions, and a nonaqueous electrolyte containing lithium ions, And at least one of the non-aqueous electrolytes contains a transition metal-sulfur complex.

The charge / discharge reaction of the lithium-sulfur battery of the present invention proceeds as follows, for example, when metallic lithium is used as the negative electrode active material and sulfur is used as the positive electrode active material.

  According to the lithium-sulfur battery of the present invention, an electrode containing at least one metal element of nickel and cobalt is used as a positive electrode, and a self-discharge phenomenon is suppressed by adding a transition metal-sulfur complex to the positive electrode or a non-aqueous electrolyte. can do. The reason why such an effect can be obtained is not clear, but by using an electrode containing at least one metal element of nickel and cobalt for the positive electrode, the transition metal-sulfur complex is immobilized on the positive electrode by the first charge. It is estimated that the suppression of the self-discharge phenomenon can be realized in a state where the sulfide ions can be prevented from being eluted again into the electrolyte and have both high output and good cycle characteristics.

  In the lithium-sulfur battery of the present invention, the negative electrode is not particularly limited as long as it contains a material that absorbs and releases lithium ions as a negative electrode active material. Here, examples of materials that occlude and release lithium ions include metal lithium and lithium alloys, metal oxides, metal sulfides, and carbonaceous substances that occlude and release lithium ions. Examples of the lithium alloy include alloys of lithium with aluminum, silicon, tin, magnesium, indium, calcium, and the like. Examples of the metal oxide include tin oxide, silicon oxide, lithium titanium oxide, niobium oxide, and tungsten oxide. Examples of the metal sulfide include tin sulfide and titanium sulfide. Examples of the carbonaceous material that absorbs and releases lithium ions include graphite, coke, mesophase pitch-based carbon fiber, spherical carbon, and resin-fired carbon.

  In the lithium-sulfur battery of the present invention, the positive electrode is not particularly limited as long as sulfur is a positive electrode active material and the positive electrode material contains at least one of nickel and cobalt. At this time, nickel or cobalt may be the main component, and at least one selected from the group consisting of copper, iron, manganese, nickel, and cobalt may be included. The positive electrode active material may be supplied as a transition metal-sulfur complex contained in the positive electrode material, or may be supplied by a transition metal-sulfur complex dissolved in an electrolyte described later. The positive electrode may be formed by mixing a predetermined amount of a conductive additive and a binder and then pressure bonding to a current collector. Here, the conductive auxiliary agent is not particularly limited as long as it is a conductive material. For example, carbon blacks such as ketjen black, acetylene black, channel black, furnace black, lamp black and thermal black may be used, and natural graphite such as flake graphite, graphite such as artificial graphite and expanded graphite may be used. Further, conductive fibers such as carbon fibers and metal fibers, metal powders such as copper, silver, nickel, and aluminum, or organic conductive materials such as polyphenylene derivatives may be used. These may be used alone or in combination. Although it does not specifically limit as a binder, A thermoplastic resin, a thermosetting resin, etc. are mentioned. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin) , Polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrif Examples include olefin copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, and ethylene-acrylic acid copolymer. . These materials may be used alone or in combination. As the current collector, a metal plate such as stainless steel, aluminum, copper, nickel, or a metal mesh can be used.

  In the lithium sulfur battery of the present invention, the shape of nickel or cobalt contained in the positive electrode is not limited. For example, when the case where nickel is included in the positive electrode is taken as an example, foamed nickel or nickel powder may be used. Further, regarding the composition, any electrode configuration may be used as long as the electrolyte can be impregnated into the electrode. For example, when nickel foam is used, it can be used alone. When nickel powder is used, the nickel powder is adhered to a constituent auxiliary agent having a high specific surface area such as ketjen black, carbon nanotube, and acetylene black. Can be used. A material in which nickel powder is adhered to a constituent auxiliary agent is preferable because cycle characteristics tend to be further improved as compared with the case of using foamed nickel. At this time, the proportion of the constituent auxiliary is preferably 70 wt% to 20 wt%, and more preferably 50 wt% to 30 wt%. If the proportion of the constituent auxiliary agent exceeds 70 wt%, the proportion of nickel for immobilizing the transition metal-sulfur complex decreases, which is not preferable, and if it is less than 20 wt%, the surface area of the positive electrode decreases, which is not preferable. Further, nickel and the constituent auxiliary may be mixed, or the constituent auxiliary may be plated. In the case where the constituent auxiliary agent is plated, nickel is positioned on the surface of the auxiliary constituent agent, and it is considered that the transition metal-sulfur complex can be more smoothly immobilized.

In the lithium-sulfur battery of the present invention, the nonaqueous electrolyte is not particularly limited as long as it contains lithium ions. For example, an electrolyte solution, a gel electrolyte, or a solid electrolyte containing lithium ions may be used. it can. Examples of the lithium-ion, but are not particularly limited, for example, may be a known supporting salt such as _{LiPF 6, LiClO 4, LiBF 4} , Li (CF 3 SO 2) 2 N. Although it does not specifically limit to the solvent of electrolyte solution, For example, carbonates, such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and dimethyl carbonate (DMC), (gamma) -butyrolactone, Cyclic esters such as γ-valerolactone, 3-methyl-γ-butyrolactone, 2-methyl-γ-butyrolactone, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyl-1 , 3-dioxolane, cyclic ethers such as 2-methyl-1,3-dioxolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, dimethyl ether, methyl ethyl ether, dipropyl ether, etc. Conventional ethers, etc. Organic solvents or their mixed solvents used in batteries and capacitors may be used. Alternatively, ionic liquids such as 1-methyl-3-propylimidazolium bis (trifluorosulfonyl) imide and 1-ethyl-3-butylimidazolium tetrafluoroborate can be used. The gel electrolyte is not particularly limited, but for example, a polymer such as polyvinylidene fluoride, polyethylene glycol, or polyacrylonitrile, or a saccharide such as an amino acid derivative or sorbitol derivative is added with an electrolyte containing a supporting salt. And a gel electrolyte. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes. As the inorganic solid electrolyte, for example, a nitride of Li, an oxyacid salt, and the like are well known. Among _{them, Li 4 SiO 4, Li 4} SiO 4 -LiI-LiOH, xLi 3 PO 4 - (1-x) Li 4 SiO 4, Li 2 SiS 3, Li 3 PO 4 -Li 2 S-SiS 2, sulfide Examples thereof include phosphorus compounds. Examples of the organic solid electrolyte include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyvinylidene fluoride, polyphosphazene, polyethylene sulfide, polyhexafluoropropylene, and derivatives thereof. These may be used alone or in combination. The nonaqueous electrolyte may contain a transition metal-sulfur complex.

In the lithium-sulfur battery of the present invention, the transition metal-sulfur complex is not particularly limited as long as it can be immobilized on the positive electrode. For example, the transition metal includes a group consisting of iron, nickel, and cobalt. At least one selected from the above may be used, an alkali metal ion, an alkaline earth metal ion, or an ammonium ion may be used as a counter ion, and S ₂ C _x H _2x (x is 1 to 5 may be a coordinated structure. Here, examples of the alkali metal include lithium, sodium, and potassium, and examples of the alkaline earth metal include calcium, strontium, and barium. C _x H _2x includes methylene, ethylene, 1,2-propylene, 1,3-propylene, 1,2-butylene, 1,3-butylene, 1,4-butylene, 1,2-pentylene, , 3-pentylene, 1,4-pentylene, 1,5-pentylene and the like. The transition metal-sulfur complex may be in an amount that can sufficiently fix the entire surface of the positive electrode, but when added to the non-aqueous electrolyte, the concentration is preferably higher and the battery is used. A saturated concentration or a slightly lower concentration is preferable in a temperature range (for example, around 25 ° C.). The transition metal-sulfur complex is fixed to the surface of the positive electrode when it is initially charged. However, since sulfur in the complex is also used as the positive electrode active material, a high concentration is desirable.

  The lithium sulfur battery of the present invention may include a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the lithium-sulfur battery. For example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or a microporous film of an olefin resin such as polyethylene or polypropylene Is mentioned. These may be used alone or in combination.

  The shape of the lithium-sulfur battery of the present invention is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Moreover, you may apply to the large sized thing etc. which are used for an electric vehicle etc.

  Hereinafter, specific examples of the present invention will be described using examples.

[Example 1]
The positive electrode used was 1.6 mm thick and φ14 mm foamed nickel (Celmet # 6 manufactured by Sumitomo Electric Toyama), dried at 80 ° C. for 10 hours under reduced pressure. The negative electrode used was a metal lithium having a thickness of 1 mm molded into φ18 mm. As the non-aqueous electrolyte, a non-aqueous electrolyte prepared using an iron-sulfur complex obtained by the method described later was used.

First, sodium methoxide (CH ₃ ONa, 84 mmol) and ethanedithiol (H ₂ (edt), 42 mmol) were dissolved in 100 mL of methanol, and a solution of iron chloride (FeCl ₃ , 20 mmol) dissolved in 70 mL of methanol was dissolved therein. Slowly added. This was stirred for 36 hours and then filtered through a glass filter under an Ar atmosphere. The obtained solid was washed with water, and the washing and the filtrate were combined. Tetrabutylammonium bromide (n-Bu ₄ N) Br dissolved in 10 mL of water was gently added and allowed to stand. This was recrystallized from acetonitrile to obtain a black iron-sulfur complex. In addition, the synthesis | combining method of this iron-sulfur complex is a method described in well-known literature (Inorganic Chemistry, Vol.14, No. 6,146-1429 (1975)).

Next, 1 mol / liter of lithium bis (trifluoromethylsulfonyl) imide: LiN (SO ₂ CF ₃ ) ₂ was added to a solution in which 1,2-dimethoxyethane and 1,3-dioxolane were mixed at a volume ratio of 9: 1. It melt | dissolved so that it might become the density | concentration of L. Then, the iron-sulfur complex synthesized by the above method was dissolved at about 25 ° C. until saturated, to prepare a nonaqueous electrolytic solution.

  An evaluation cell was prepared using the positive electrode, the negative electrode and the nonaqueous electrolytic solution thus obtained. FIG. 1 is an explanatory view of an evaluation cell, FIG. 1 (a) is a cross-sectional view before the evaluation cell 10 is assembled, and FIG. 1 (b) is a cross-sectional view after the evaluation cell 10 is assembled. In assembling the evaluation cell 10, first, the negative electrode 16 (the above-described metal lithium having a thickness of 1 mm and φ18 mm) is placed in the cavity 14 provided in the center of the upper surface of the stainless steel cylindrical base 12 having a thread groove on the outer peripheral surface. The separator 18 made of polyethylene (microporous polyethylene film, manufactured by Tonen Chemical Co., Ltd.) and the positive electrode 20 (foamed nickel having the thickness of 1.6 mm and φ14 mm described above) were laminated in this order. After filling the cavity 14 with 4 mL of the non-aqueous electrolyte described above, a stainless steel cylinder 24 fixed in a liquid-tight manner in the hole of the polyethylene ring 22 is placed on the positive electrode 20, and a stainless steel cup shape is formed. The lid 26 was screwed into the cylindrical base 12. Further, an insulating resin ring 27 made of PTFE is disposed on the cylinder 24, and a pressure bolt 25 having a through hole 25a in a screw groove carved in an inner peripheral surface of an opening 26a provided at the center of the upper surface of the lid 26. The negative electrode 16, the separator 18, and the positive electrode 20 were pressed and adhered. In this way, the evaluation cell 10 was assembled. In addition, since the diameter of the opening 26a provided in the upper surface center of the lid | cover 26 is larger than the diameter of the cylinder 24, the lid | cover 26 and the cylinder 24 are a non-contact state. In addition, since the packing 28 is disposed around the cavity 14, the electrolyte injected into the cavity 14 does not leak to the outside. In this evaluation cell 10, the lid 26, the pressure bolt 25, and the cylindrical base 12 are integrated with the negative electrode 16, so that the whole becomes the negative electrode side, and the column 24 is integrated with the positive electrode 20 and insulated from the negative electrode 16. Therefore, it becomes the positive electrode side.

Evaluation was performed using the evaluation cell thus prepared. First, at a discharging current of the cathode area per 0.5 mA / cm ^2, 2.8V after charging until the charging end potential of (vs.Li/Li ^+), the discharge current of the cathode area per 0.5 mA / cm ² Then, the battery was discharged to a discharge end potential of 1.5 V (vs. Li ^/ Li ⁺ ). Then, this cycle was evaluated as 10 cycles. In addition, evaluation was performed in a 25 degreeC thermostat. As a result, the initial charge capacity was 0.005 mAh and the discharge capacity was 0.032 mAh. The charge / discharge capacity after the second time changed as shown in FIG. As is apparent from FIG. 2, the lithium-sulfur battery of Example 1 has a charge / discharge efficiency of about 100% after the second cycle even when charge / discharge is performed at a high current of 0.5 mA / cm ² per positive electrode area. It can be said that it has high output and good cycle characteristics. The reason why the discharge capacity is about 6 times the charge capacity of the first cycle is unknown at present, but the first charge is due to the valence change from trivalent to divalent iron. The subsequent discharge may have a capacity in which iron and sulfur react with lithium.

[Example 2]
An evaluation cell was prepared in the same manner as in Example 1 except that ethanedithiol used in the synthesis of the iron-sulfur complex of Example 1 was replaced with propanedithiol. This evaluation cell was evaluated under the same conditions as in Example 1. The result is shown in FIG. As is clear from FIG. 3, the lithium-sulfur battery of Example 2 was charged / discharged at the second and subsequent cycles in the same manner as in Example 1 even when it was charged / discharged at a high current of 0.5 mA / cm ² per positive electrode area. The efficiency is almost 100%, and it can be said that it has high output and good cycle characteristics. Thus, even if the size of the ligand of the iron-sulfur complex is increased from S ₂ C ₂ H ₄ to S ₂ C ₃ H ₆ , the battery characteristics are not affected and good results can be obtained. Recognize.

[Example 3]
An evaluation cell was produced in the same manner as in Example 1 except that the positive electrode used in Example 1 was replaced with the positive electrode prepared by the following method. That is, first, Ketjen black (KB, ECP600JD manufactured by Ketjen Black International Co., Ltd.) as a conductive additive, nickel powder (Ni), and polytetrafluoroethylene (PTFE) as a binder are each weighted. It mixed so that it might become 47.5: 47.5: 5. This was bonded to a φ14 mm SUS mesh as a positive electrode, and was used under reduced pressure drying at 80 ° C. for 10 hours immediately before battery assembly.

Using the positive electrode thus obtained, an evaluation cell was prepared in the same manner as in Example 1 and evaluated under the same conditions as in Example 1. The result is shown in FIG. As is apparent from FIG. 4, the lithium-sulfur battery of Example 3 has a charge / discharge efficiency of about 100% after the second cycle even when charge / discharge is performed at a high current of 0.5 mA / cm ² per positive electrode area. It can be said that it has high output and good cycle characteristics. Moreover, in Example 3, even if it repeats the number of cycles compared with Examples 1 and 2, it turns out that a charge / discharge capacity does not fall easily.

[Example 4]
An evaluation cell was prepared in the same manner as in Example 1 except that the positive electrode used in Example 1 was replaced with the positive electrode prepared by the following method. That is, first, in order to perform nickel plating, Ketjen Black (ECP600JD made by Ketjen Black International Co., Ltd.) and Teflon (Teflon made by Daikin Co., Ltd. are registered) are mixed so that the weight is 90:10, and the length is 2 cm. X One of the electrodes (-) was molded to a width of 3 cm and a thickness t = 1 mm. Further, a nickel plate was used as the other electrode (+), and nickel plating was performed on the ketjen black surface by flowing a low current of 0.1 A for 3 minutes. The composition of the plating solution used at this time was nickel sulfate (NiSO ₄ .6H ₂ O) 240 g / L, nickel chloride (NiCL ₂ .6H ₂ O) 45 g / L, boric acid (H ₃ BO ₃ ) 30 g / L. is there. Using 100 mL of this, nickel plating was performed at room temperature. The negative electrode thus obtained was punched out to 14 mm to be a positive electrode of an evaluation cell.

Using the positive electrode thus obtained, an evaluation cell was produced in the same manner as in Example 1, and evaluated under the same conditions as in Example 1. The result is shown in FIG. From FIG. 5, the lithium-sulfur battery of Example 4 has a charge / discharge efficiency of about 100% after the second cycle even if it is charged / discharged at a high current of 0.5 mA / cm ² per positive electrode area. It can be seen that both have good cycle characteristics. Moreover, in Example 4, even if it repeats the cycle number compared with Examples 1 and 2, it turns out that charging / discharging capacity | capacitance hardly falls.

  Incidentally, when the iron-sulfur complex was supported on the positive electrode instead of dissolving the iron-sulfur complex in the electrolytic solution, almost the same results as in Examples 1 to 4 were obtained. This is presumably because the iron-sulfur complex supported on the positive electrode was eluted into the electrolyte solution to form the same as in Examples 1 to 4, and charging and discharging were repeated thereafter.

[Comparative Example 1]
An evaluation cell was produced in the same manner as in Example 3 except that the nickel powder in Example 3 was replaced with copper powder. This evaluation cell was evaluated under the same conditions as in Example 1. The result is shown in FIG. FIG. 6 shows that when copper is used for the positive electrode, the charge capacity increases as the number of cycles increases. This is presumably due to a self-discharge phenomenon caused by the positive electrode copper being ionized and dissolved in the electrolyte. That is, when copper is used for the positive electrode, unlike in Examples 1 to 4, it can be said that the self-discharge phenomenon cannot be suppressed.

[Comparative Example 2]
An evaluation cell was prepared in the same manner as in Example 1 except that the iron-sulfur complex of Example 1 was not added. In Comparative Example 2, it can also be said that a nonaqueous electrolyte battery was assembled in the same manner as in Example 2 except that the iron-sulfur complex of Example 2 was not added. Therefore, the comparative example 2 is a comparative example of the first embodiment and a comparative example of the second embodiment. This evaluation cell was evaluated under the same conditions as in Example 1. The result is shown in FIG. FIG. 7 shows that Comparative Example 2 does not function as a battery. That is, in Examples 1 to 4, the iron-sulfur complex is dissolved in the electrolytic solution, and this is immobilized on the positive electrode by charging, and further, reversibly reacts with lithium by subsequent discharging and charging. In contrast to Comparative Example 2, since the iron-sulfur complex was not dissolved in the electrolytic solution, it could be said that the battery did not become a secondary battery.

  The lithium-sulfur battery of the present invention can be used mainly in the electrochemical industry, for example, as a power source for hybrid vehicles and electric vehicles, as a power source for consumer electronics such as mobile phones and personal computers, and load leveling (load leveling). It can be used for electrochemical devices.

2 is a cross-sectional view of an evaluation cell 10. FIG. It is a graph showing the change of the charging / discharging capacity | capacitance of Example 1. FIG. It is a graph showing the change of the charging / discharging capacity | capacitance of Example 2. FIG. It is a graph showing the change of the charging / discharging capacity | capacitance of Example 3. FIG. It is a graph showing the change of the charging / discharging capacity | capacitance of Example 4. It is a graph showing the change of the charging / discharging capacity | capacitance of the comparative example 1. It is a graph showing the change of the charging / discharging capacity | capacitance of the comparative example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Evaluation cell, 12 Cylindrical base | substrate, 14 Cavity, 16 Negative electrode, 18 Separator, 20 Positive electrode, 22 Ring, 24 Cylinder, 25 Pressure bolt, 25a Through-hole, 26 Lid, 26a Opening, 27 Insulating resin ring, 28 Packing.

Claims (6)

A positive electrode containing at least one metal element of nickel and cobalt;
A negative electrode containing a material that occludes and releases lithium ions;
A non-aqueous electrolyte containing lithium ions;
With
Including a transition metal-sulfur complex in at least one of the positive electrode and the non-aqueous electrolyte,
Lithium sulfur battery. The positive electrode uses nickel foam,
The lithium sulfur battery according to claim 1. The positive electrode is obtained by adding nickel to the surface of carbon black.
The lithium sulfur battery according to claim 1. The transition metal is at least one selected from the group consisting of iron, nickel and cobalt.
The lithium sulfur battery according to any one of claims 1 to 3. The transition metal-sulfur complex has a structure in which S ₂ C _x H _2x (x is an integer of 1 to 5) is coordinated to a transition metal ion.
The lithium sulfur battery according to any one of claims 1 to 4. The transition metal-sulfur complex has an alkali metal ion, an alkaline earth metal ion or an ammonium ion as a counter ion.
The lithium sulfur battery according to any one of claims 1 to 5.