A kind of preparation method of lithium-sulfur cell
Technical field
The invention belongs to electrode material preparation field, particularly relate to a kind of lithium sulphur battery electrode material and utilize this kind of electrode material to prepare the method for lithium-sulfur cell.
Background technology
Lithium ion battery (Lithium-ionbattery, LIB), is also called lithium secondary battery, is a kind of portable power source equipment of charging capable of circulation.LIB has high-energy-density, high power density, has extended cycle life, cleans the plurality of advantages such as nontoxic and memory-less effect, and since the nineties in last century, Sony was by LIB commercialization, LIB obtains and develops rapidly and widely.Current LIB is own through becoming the power supply of most of mobile electronic device.In recent years, people had carried out going deep into and studying widely to LIB.In LIB, the performance of negative material on battery has very large impact, and the negative material of development excellence is also one of key factor improving LIB performance.Material with carbon element is topmost a kind of LIB negative material, and oneself is through there being hundreds of material with carbon element having different structure to be used as lithium ion battery negative at present, and these materials comprise native graphite, electrographite, coke, carbon fiber, carbonaceous mesophase spherules, carbon black etc.
But, there are problems in lithium-sulfur cell commercialization process, as lithium metal unstable chemcial property, during use, there is potential danger; When negative pole adopts metallic lithium foil, battery is after repeatedly discharge and recharge, and metallic lithium foil surface easily forms dendrite.The continuous growth of dendrite causes battery capacity to decline, and dendritic growth may pierce through barrier film, causes battery short circuit, causes safety problem.
Hard carbon is the RESEARCH OF PYROCARBON of high molecular polymer, even if be at high temperature also difficult to graphitization.The reversible capacity of hard carbon can be higher, and cycle performance is also fine.The shortcoming such as but hard carbon also exists, and electrode potential is too high, current potential is delayed (namely intercalation potential is less than de-lithium current potential) and circulation irreversible capacity is large first.
At present, most of lithium-sulfur cell all adopts lithium metal as negative pole.Lithium can cause being formed of a product by ten current densities inequalities as negative pole in repeatedly charge and discharge process.Branch product can cause barrier film to penetrate, and then battery is short-circuited, and are main potential safety hazard sources.If add Graphene in negative pole, the specific area of negative pole becomes large, and surface current density reduces, and meanwhile, loose Graphene provides the space of lithium deposition, thus makes the growth of lithium branch product more and more difficult.For cathode of lithium Problems existing, the improvement that researcher carries out and study less.Sum up and get up mainly to comprise two aspects: one is carry out modification from electrolysis additive, by adding different additives, as LiNO
3with PEO etc., impel cathode of lithium surface to form more stable SEI film fast in charge and discharge process, it is desirable to suppress Li dendrite and improve cycle performance.But additive is consumed gradually in charge and discharge process, affect stability and the continuity of battery.Two is start with from the preparation technology of lithium electrode, and by using the coated lithium powder of lithium compound or electrodeposit metals lithium, lithium paper tinsel surface increases the methods such as protective layer, improves cycle efficieny and cycle life, but operating process is also comparatively complicated.
Summary of the invention
In order to solve problems of the prior art, the object of this invention is to provide a kind of cathode size be prepared from by stable state lithium powder and special proportioning material with carbon element, and the lithium-sulfur cell to be prepared from by this slurry, which solve in prior art the technological deficiency that adopts the materials such as hard carbon to bring and solve stability and the technical problem such as poor continuity and complicated operation of the middle existence that cathode of lithium battery improves.
A preparation method for lithium-sulfur cell, comprises the following steps:
The preparation of step 1, positive plate: with poly-naphthalene/sulphur composite material be positive active material, the mixture that combines for 1:3 according to mass ratio of Ketjen black ECP600JD and carbon nano-fiber for conductive agent, polyvinylpyrrolidone and polymine are the mixed system that 2:1 mixes according to volume ratio is binding agent; The mass ratio of the poly-naphthalene in the anode sizing agent of sulfur-bearing/sulphur composite material, conductive agent and binding agent is 8:5:1; It is make solution in the solvent that mixes of 7:7:1 that mixture binding agent to be dissolved in by ethylene carbonate (EC), ethylene methacrylic ester (MA) and three fluoropropylene carbonates (TFPC) according to volume ratio; Wherein, according to Mass Calculation, the ratio being 30% according to solids content takes solvent, and solid comprises poly-naphthalene/sulphur composite material and conductive agent; After more poly-naphthalene/sulphur composite material being mixed in mass ratio with conductive agent, pour into and dissolve in the solvent of binding agent, be made into anode sizing agent;
Then the slurry obtained is uniformly coated on nickel foam collector.Be placed in vacuum drying chamber drier, except desolventizing and moisture, the temperature in vacuum drying chamber is 55 DEG C, drying time is 9h, by the slurry scraped clean of blade by nickel foam surface, then positive plate is flattened, then positive plate is placed in vacuum drying chamber again dry;
Prepared by step 2, negative plate: stable state lithium powder and material with carbon element are weighed according to mass ratio, is that the mixture that mixes of 7:7:1 is for solvent with ethylene carbonate (EC), ethylene methacrylic ester (MA) and three fluoropropylene carbonates (TFPC) according to volume ratio.Wherein, according to Mass Calculation, the ratio being 30% according to solids content takes solvent, and solid comprises stable state lithium powder and material with carbon element; First material with carbon element is dissolved in solvent, then stable state lithium powder is poured in above-mentioned solution, to be applied in after mixing on nickel foam collector thus to obtain negative plate; Negative plate is placed on heating plate and heats to make solvent evaporates; Then negative plate is flattened stand-by; Wherein, the mass ratio of stable state lithium powder and material with carbon element is 7-10:3-8; The temperature that heating plate heats is 70 DEG C, and heating time is 8h;
Step 3, battery are assembled: what use the obtained positive plate of step 1 and the obtained negative plate of step 2 is assembled into lithium-sulfur cell.
Further, by the slurry scraped clean of blade by nickel foam surface described in step 1, operating in vacuum glove box of positive plate pressing is completed.
Further, in step 2, negative plate is placed on heating plate and heats to make solvent evaporates, then negative plate being flattened stand-by operation is complete in vacuum glove box.
Further, the stable state lithium powder described in step 2 is made up of dropping liquid emulsifying technology (DET), and lithium powder diameter is 50 μm-70 μm.
A kind of lithium-sulfur cell negative material, is characterized in that comprising: in mass fraction, is made up of following feedstock composition: 7-10 part stable state lithium powder, 3-8 part material with carbon element and solvent.
Further, described stable state lithium powder is made up of dropping liquid emulsifying technology (DET), and lithium powder diameter is 50 μm-70 μm.
Further, described material with carbon element is vertical array column-shaped carbon nano-tube (VACNT) and mesoporous carbon is the mixture that 10:1 mixes according to mass ratio.
Further, described solvent is ethylene carbonate (EC), ethylene methacrylic ester (MA) and three fluoropropylene carbonates (TFPC) are the mixed solvent that 7:7:1 mixes according to volume ratio.
A preparation method for lithium-sulfur cell, adopts lithium-sulfur cell negative material as above as negative pole, it is characterized in that comprising the steps:
(1) anode sizing agent of sulfur-bearing is coated in collector and makes positive plate;
(2) stable state lithium powder and material with carbon element being weighed according to mass ratio, is that the mixture that mixes of 7:7:1 is for solvent with ethylene carbonate (EC), ethylene methacrylic ester (MA) and three fluoropropylene carbonates (TFPC) according to volume ratio; First described material with carbon element is dissolved in described solvent, then stable state lithium powder is poured in above-mentioned solution, to be applied in after mixing on collector thus to obtain negative plate; Negative plate is placed on heating plate and heats to make solvent evaporates; Then negative plate is flattened stand-by;
(3) positive pole, negative pole, barrier film are assembled into button cell.
Further, the anode sizing agent of the sulfur-bearing described in step (1) comprises: poly-naphthalene/sulphur composite material, conductive agent, binding agent and solvent; Described conductive agent is that 1:3 combines by Ketjen black ECP600JD and carbon nano-fiber according to mass ratio, described binding agent by polyvinylpyrrolidone and polymine be that 2:1 mixes according to volume ratio; Described solvent is that 7:7:1 mixes by ethylene carbonate (EC), ethylene methacrylic ester (MA) and three fluoropropylene carbonates (TFPC) according to volume ratio; In the mixed solvent first binding agent is dissolved in, after more poly-naphthalene/sulphur composite material being mixed in mass ratio with conductive agent, pour into and dissolve in the solvent of binding agent, be made into anode sizing agent, then by anode sizing agent uniform application on a current collector, positive plate is made.
Further, described positive plate need add heat abstraction moisture and solvent in vacuum drying chamber, then its surface is struck off and is flattened; Temperature in described vacuum drying chamber is 55 DEG C, and drying time is 9h.
Further, the mass ratio of the poly-naphthalene in the anode sizing agent of described sulfur-bearing/sulphur composite material, conductive agent and binding agent is 8:5:1.
Further, negative plate described in step (2) need, at 40 DEG C-70 DEG C heating 8h-11h to remove solvent, then flatten stand-by.
Further, the operation in step (2) and (3) all completes in the vacuum glove box being full of argon gas.
The lithium-sulfur cell negative material that the present invention prepares and lithium-sulfur cell have following beneficial effect:
(1) negative pole that the lithium-sulfur cell negative material that the present invention prepares is made by stable state lithium powder and the material with carbon element of specific proportioning is compared with common lithium foil electrode, specific area is larger, porosity is higher, more complete with electrolyte contacts, thus effectively machining area is larger, impedance is less, and effectively can suppress the growth of Li dendrite, can show good cycle performance and high rate performance.
(2) the lithium-sulfur cell negative material that the present invention prepares is made up of the material with carbon element of stable state lithium powder and specific proportioning, the volume that a large amount of carbon nano-tube wherein used effectively are taken into account serves the effect of material with carbon element and the effect of binding agent, effectively avoid the use of adhesive, the cost reduced cleverly, decrease processing step, also have important meaning to the ten actual energy density improving lithium-sulfur cell.
(3) vertical array column-shaped carbon nano-tube (VACNT) is adopted to have good orientation in the lithium-sulfur cell negative material that the present invention prepares, can good contact be formed with collector and form efficiently and directionally conducting matrix grain, effectively improve skeleton conductivity in lithium-sulfur cell negative material.It fully combines again the structural advantage of mesoporous carbon, and highly ordered mesosize pores carbon has that specific area is large, uniform pore diameter, pore volume are very high, loose structure and the high conductivity etc. of being mutually related feature.The present invention makes full use of the advantage of both structure, effectively can weaken shuttle back and forth effect and the dendritic growth in continuous charge and discharge process, show better cycle performance and high rate performance than conventional electrodes.
(4) in the conductive additive of positive pole; the present invention adds Ketjen black ECP600JD and carbon nano-fiber; the latter can form three-dimensional conductive network; the remote conductive ability in pole piece can be increased; not easily covered completely by the product formed in fair discharge process again, thus improve the surface texture of pole piece; The former utilizes rich space pore passage structure and the good adsorption properties of Ketjen black ECP600JD, also can improve the cycle performance of lithium-sulfur cell.
(5) positive active material of the present invention have selected poly-naphthalene/sulphur composite material, and poly-naphthalene is used for having some superiority in lithium-sulfur cell: (1) poly-naphthalene is conducting polymer, large in structure, and n key makes it be easy to conduction, obviously can improve the conductivity of sulfur electrode; (2) poly-naphthalene has the layer structure of similar graphite, its structure more easily and elemental sulfur be closely connected, the dissolving in the electrolytic solution of the many lithium sulfides of its electrode reaction product can be suppressed; (3) poly-naphthalene has certain capacity as electrode material, can produce act synergistically with sulfur electrode.
(6) the present invention has also selected the mixed system of polyvinylpyrrolidone and polymine as binding agent especially in positive electrode, thus with the strong loose structure of maintenance sulphur positive pole in cyclic process.
(7) the present invention has selected the mixed system solvent the most of three kinds of materials, through experiment, this solvent can better keep raw-material architectural feature and the advantage of various pole piece, same ethylene carbonate (EC), ethylene methacrylic ester (MA) can obtain good low temperature properties, add that again a small amount of three fluoropropylene carbonates (TFPC) can obtain good discharge capacity and cycle life.The selection of three kinds of solvents takes into account and considers the optimum combination performance of solvent and the factor of cost aspect, makes the product finally prepared have the quality of better stability and Geng Gao.
Embodiment
Embodiment one:
The preparation of positive plate: with poly-naphthalene/sulphur composite material be positive active material, the mixture that combines for 1:3 according to mass ratio of Ketjen black ECP600JD and carbon nano-fiber for conductive agent, polyvinylpyrrolidone and polymine are the mixed system that 2:1 mixes according to volume ratio is binding agent.
The mass ratio of the poly-naphthalene in the anode sizing agent of sulfur-bearing/sulphur composite material, conductive agent and binding agent is 8:5:1.It is make solution in the solvent that mixes of 7:7:1 that mixture binding agent to be dissolved in by ethylene carbonate (EC), ethylene methacrylic ester (MA) and three fluoropropylene carbonates (TFPC) according to volume ratio.Wherein, according to Mass Calculation, the ratio being 30% according to solids content takes solvent, and solid comprises poly-naphthalene/sulphur composite material and conductive agent.After more poly-naphthalene/sulphur composite material being mixed in mass ratio with conductive agent, pour into and dissolve in the solvent of binding agent, be made into anode sizing agent.
Then the slurry obtained is uniformly coated on nickel foam collector.Be placed in vacuum drying chamber drier, except desolventizing and moisture, the temperature in vacuum drying chamber is 55 DEG C, and drying time is 9h, by the slurry scraped clean of blade by nickel foam surface, then with certain pressure, positive plate is flattened.Then positive plate is placed in vacuum drying chamber again dry.More than operation all completes in vacuum glove box.
Prepared by negative plate: stable state lithium powder and material with carbon element are weighed according to mass ratio, is that the mixture that mixes of 7:7:1 is for solvent with ethylene carbonate (EC), ethylene methacrylic ester (MA) and three fluoropropylene carbonates (TFPC) according to volume ratio.Wherein, according to Mass Calculation, the ratio being 30% according to solids content takes solvent, and solid comprises stable state lithium powder and material with carbon element.
First material with carbon element is dissolved in solvent, then stable state lithium powder is poured in above-mentioned solution, to be applied in after mixing on nickel foam collector thus to obtain negative plate; Negative plate is placed on heating plate and heats to make solvent evaporates; Then negative plate is flattened stand-by; Wherein, the mass ratio of stable state lithium powder and material with carbon element is 10:8; The temperature that heating plate heats is 70 DEG C, and heating time is 8h.More than operation all completes in vacuum glove box.
Preparation method about poly-naphthalene/sulphur composite material: get appropriate poly-naphthalene and be scattered in deionized water, ultrasonic disperse, adds a certain amount of Na
2s
20
3.5H
2ultrasonic disperse again after 0; In mixture, slowly drip the hydrochloric acid solution of appropriate 1mol/L, be 7 to above-mentioned solution ph; Suction filtration after continuation stirring reaction, is placed in vacuum drying chamber by sample and dries, namely obtain poly-naphthalene/sulphur composite material.
Battery assembling and test: button battery assembles in the glove box being full of argon gas.With above-mentioned negative plate for negative pole, adopt Celgard2400 barrier film and 2025 type button batteries.Electrolyte is that 1MLiClO4,0.15MLiNO3 are dissolved in DOL:DME(volume ratio 1:1).Battery is placed in blue electrical testing system (CT2001A) and carries out constant current test.Charging/discharging voltage scope is 1.5-3.0V, and probe temperature is room temperature.
Embodiment two:
Compared with embodiment one, embodiment two is in negative plate preparation process, and the mass ratio changing stable state lithium powder and material with carbon element is 7:3, and the temperature that heating plate heats is 40 DEG C, and heating time is 11h.All the other operations and explanation are with embodiment one.
Embodiment three:
Compared with embodiment one, embodiment two is in negative plate preparation process, and the mass ratio changing stable state lithium powder and material with carbon element is 6:5, and the temperature that heating plate heats is 60 DEG C, and heating time is 9h.All the other operations and explanation are with embodiment one.
Compare common lithium foil electrode, when the negative pole of embodiment one, two and three uses stable state lithium powder and mixes material with carbon element, lithium-sulfur cell of the present invention can show better first charge-discharge specific capacity, and the rear capability retention of 100 circulations is all more than 95.8% simultaneously.
The button cell of each embodiment leaves standstill and is AC impedance contrast experiment after 24 hours.Experimental result shows, after embodiment one, two and three uses stable state lithium powder and mixing material with carbon element, compare common lithium foil electrode, the impedance of lithium-sulfur cell of the present invention reduces greatly, reason is that the specific area of stable state lithium powder is large, complete with electrolyte contacts, can show electron transmission and transfer faster.
Simultaneously, the lithium-sulfur cell negative material that the present invention prepares is made up of the material with carbon element of stable state lithium powder and specific proportioning, the volume that a large amount of carbon nano-tube wherein used effectively are taken into account serves the effect of material with carbon element and the effect of binding agent, effectively avoid the use of adhesive, the cost reduced cleverly, decrease processing step, also have important meaning to the ten actual energy density improving lithium-sulfur cell.
(3) vertical array column-shaped carbon nano-tube (VACNT) is adopted to have good orientation in the lithium-sulfur cell negative material that the present invention prepares, can good contact be formed with collector and form efficiently and directionally conducting matrix grain, effectively improve skeleton conductivity in lithium-sulfur cell negative material.It fully combines again the structural advantage of mesoporous carbon, and highly ordered mesosize pores carbon has that specific area is large, uniform pore diameter, pore volume are very high, loose structure and the high conductivity etc. of being mutually related feature.The present invention makes full use of the advantage of both structure, effectively can weaken shuttle back and forth effect and the dendritic growth in continuous charge and discharge process, show better cycle performance and high rate performance than conventional electrodes.
(4) in the conductive additive of positive pole; the present invention adds Ketjen black ECP600JD and carbon nano-fiber; the latter can form three-dimensional conductive network; the remote conductive ability in pole piece can be increased; not easily covered completely by the product formed in fair discharge process again, thus improve the surface texture of pole piece; The former utilizes rich space pore passage structure and the good adsorption properties of Ketjen black ECP600JD, also can improve the cycle performance of lithium-sulfur cell.
(5) positive active material of the present invention have selected poly-naphthalene/sulphur composite material, and poly-naphthalene is used for having some superiority in lithium-sulfur cell: (1) poly-naphthalene is conducting polymer, large in structure, and n key makes it be easy to conduction, obviously can improve the conductivity of sulfur electrode; (2) poly-naphthalene has the layer structure of similar graphite, its structure more easily and elemental sulfur be closely connected, the dissolving in the electrolytic solution of the many lithium sulfides of its electrode reaction product can be suppressed; (3) poly-naphthalene has certain capacity as electrode material, can produce act synergistically with sulfur electrode.
(6) the present invention has also selected the mixed system of polyvinylpyrrolidone and polymine as binding agent especially in positive electrode, thus with the strong loose structure of maintenance sulphur positive pole in cyclic process.
(7) the present invention has selected the mixed system solvent the most of three kinds of materials, through experiment, this solvent can better keep raw-material architectural feature and the advantage of various pole piece, same ethylene carbonate (EC), ethylene methacrylic ester (MA) can obtain good low temperature properties, add that again a small amount of three fluoropropylene carbonates (TFPC) can obtain good discharge capacity and cycle life.The selection of three kinds of solvents takes into account and considers the optimum combination performance of solvent and the factor of cost aspect, makes the product finally prepared have the quality of better stability and Geng Gao.
Above embodiment shows and describes general principle of the present invention, principal character and advantage of the present invention.The technical staff of the industry should understand; the present invention is not restricted to the described embodiments; what describe in above-described embodiment and specification just illustrates principle of the present invention; instead of limit the scope of the invention by any way; without departing from the scope of the invention; the present invention also has various changes and modifications, and these changes and improvements all fall in claimed scope.