A cathode material for a lithium-ion capacitor, a preparation method thereof, and a lithium-ion capacitor using the cathode material

Abstract

The present invention discloses a cathode material for a lithium-ion capacitor, a preparation method thereof, and a lithium-ion capacitor using this cathode material. The cathode material is an activated carbon material. The activated carbon material has a spherical porous structure, and some carbon spheres are in a collapsed state. The BET specific surface area is 300-1000 m<supgt;2< / supgt> / g, and it is a porous spherical material rich in mesoporous structure. The advantages of the present invention compared with the prior art are as follows: By simultaneously utilizing the synergistic effect of the high content of moisture introduced during the spraying process, sodium hydroxide and sodium oxide decomposed from sodium salts in paper-making black liquor, and high temperature, the carbonization and activation pore formation of paper-making black liquor can be achieved in one step during the high-temperature pyrolysis process, obtaining an activated carbon material with a high specific surface area and rich pores. Using this activated carbon as the cathode, a lithium-ion capacitor with a high energy density is prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of capacitors and their positive electrode materials, and specifically refers to a positive electrode material for a lithium-ion capacitor, a preparation method thereof, and a lithium-ion capacitor using such a positive electrode material. Background Art

[0002] Lithium-ion capacitors or supercapacitors have characteristics such as high power, long cycle life, and fast charge and discharge speed. They are very characteristic power-type energy storage devices. Activated carbon materials are the key electrode materials for lithium-ion capacitors or supercapacitors, significantly affecting the device performance. An ideal activated carbon material should have a suitable microstructure and morphology, a high specific surface area, a reasonable pore size distribution, etc.

[0003] Paper-making black liquor is a dark brown wastewater containing a large amount of lignin produced by the alkaline pulping process, and also contains some hemicellulose, residual alkali, etc. At present, paper-making black liquor is mainly discharged after treatment, or incinerated as fuel after concentration, or lignin is extracted by acidification precipitation method, membrane separation method, flocculation precipitation method, etc. The obtained lignin is further used to prepare water coal slurry additives, fertilizers, activated carbon, etc. Among them, the preparation of activated carbon requires processes such as carbonization and activation after lignin extraction. The above methods for treating or utilizing paper-making black liquor have problems such as large pollution, low resource utilization rate, or complex operation and long process.

[0004] Spray pyrolysis is a powder material preparation method developed in recent years. After the precursor solution is atomized, a series of physical and chemical processes such as solvent evaporation, solid particle formation, particle drying, thermal decomposition, and sintering molding are completed instantaneously in the reaction furnace, and finally ultrafine powder is formed. Its process is simple and the finished product can be obtained in one step.

[0005] The purpose of this project is to efficiently utilize high-molecular organic substances such as lignin and hemicellulose in paper-making black liquor, directly prepare a high-capacity activated carbon material by spray pyrolysis, use this activated carbon as the positive electrode, develop a lithium-ion capacitor with a high energy density, and realize the short-process high-value application of paper-making black liquor. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an activated carbon material prepared from concentrated paper-making black liquor in a short process, its production method, and a lithium-ion capacitor using such an activated carbon material, aiming at the problems of the positive electrode material of the lithium-ion capacitor and the treatment of paper-making black liquor mentioned in the above background art.

[0007] To solve the above technical problem, the technical solution provided by the present invention is: A positive electrode material for a lithium-ion capacitor, the positive electrode material is an activated carbon material, the activated carbon material has a spherical porous structure, some carbon spheres are in a collapsed state, and the BET specific surface area is 300 - 1000m 2 / g, is a porous spherical material rich in mesoporous structure. The diameter of the spherical activated carbon is about 0.2 - 3 μm, the wall thickness is about 20 - 50 nm, and the interlayer spacing (d 002 ) of the (002) crystal plane is 0.36 - 0.37 nm. The average thickness (L c ) along the c-axis direction is 0.7 - 0.85 nm, and the average width (L a ) along the a-axis direction is 9.5 - 12 nm..

[0008] The preparation method of the activated carbon material is as follows: The papermaking black liquor is atomized, and an inert gas is used as the carrier gas. The atomized droplets and the inert gas enter the atmosphere protection furnace together. In the atmosphere protection furnace, the high-temperature pyrolysis of the black liquor and the activation and pore formation of the carbon material are completed in one step. After collection, washing, and drying, the activated carbon material is obtained.

[0009] As an improvement, the total dissolved solids in the papermaking black liquor (including lignin, hemicellulose and their derivatives, sodium salts, residual alkali, etc.) is 50 - 600 g / L, the total carbon content (TOC) is 10 - 100 g / L, the content of hydroxide (OH - ) is 2 - 30 g / L, and the content of sodium (Na) is 10 - 100 g / L.

[0010] As an improvement, the collection is to introduce the pyrolyzed solid material and tail gas into a collector filled with dilute sodium hydroxide solution.

[0011] As an improvement, the inert gas contains at least one of nitrogen and argon.

[0012] As an improvement, the water partial pressure in the atmosphere protection furnace is 0.4 - 0.7 atm.

[0013] As an improvement, the temperature of the high-temperature pyrolysis and activation and pore formation is 600 - 720 °C.

[0014] As an improvement, the atomization includes ultrasonic atomization and centrifugal atomization.

[0015] Using the activated carbon material described above as the positive electrode material, using one or several of artificial graphite, graphitized mesophase carbon microspheres, and hard carbon as the negative electrode material, and the electrolyte is 1.3 - 1.5 mol / L LiPF 6 ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio x:1 - x, x = 0.15 - 0.3) solution, and adding 5 - 15 wt.% ethyl acetate (EA) and 5 - 10 wt.% fluoroethylene carbonate (FEC), 1 - 1.5 wt.% biphenyl (BP) as additives, a high-voltage lithium-ion capacitor is prepared, and it is charged and discharged between 2.0 - 4.0 V, and the energy density is 110 - 124 Wh·kg-1.

[0016] After adopting the above materials and preparation methods, the present invention has the following advantages: (1) The concentrated papermaking black liquor is used to prepare activated carbon materials through a short spray pyrolysis process, which is used as the positive electrode material of a high-capacity lithium-ion capacitor, realizing the high-efficiency value addition of papermaking black liquor.

[0017] (2) Spherical porous carbon materials are obtained by spray pyrolysis. At the same time, by utilizing the synergistic effect of the high content of moisture brought in during the spraying process, sodium oxide decomposed from sodium hydroxide and sodium salts in papermaking black liquor, and high temperature, the carbonization and activation pore formation of papermaking black liquor can be achieved in one step during the high-temperature pyrolysis process.

[0018] (3) The pyrolyzed solid materials and tail gas are introduced into a collector filled with dilute sodium hydroxide solution, simultaneously achieving the purposes of sealing the atmosphere protection furnace, collecting porous carbon materials, absorbing and treating pyrolysis tail gas, and removing soluble impurities.

[0019] (4) The prepared activated carbon material has a spherical porous structure, and some carbon spheres are collapsed

[0020] in shape, with a BET specific surface area of 300 - 1000 m 2 / g, an average pore diameter of 1.8 - 3 nm. It is a porous spherical material rich in mesoporous structure. The diameter of the spherical activated carbon is about 0.2 - 3 um, the wall thickness is about 20 - 50 nm, and the interlayer spacing d 002 is 0.36 - 0.37 nm. The average thickness L c along the c-axis direction is 0.7 - 0.85 nm, and the average width L a along the a-axis direction is 9.5 - 12 nm, meeting the requirements of high capacity of activated carbon for lithium-ion capacitors.

[0021] (5) Using porous spherical activated carbon with high-capacity characteristics as the positive electrode material, and using one or several of artificial graphite, graphitized mesophase carbon microspheres, and hard carbon as the negative electrode material, the electrolyte is an EC / DMC solution of 1.3 - 1.5 mol / L LiPF 6 (with a volume ratio of x:1 - x, x = 0.15 - 0.3), and adding 5 - 15 wt.% of EA and 5 - 10 wt.% of FEC, 1 - 1.5 wt.% of BP (biphenyl) as additives, a high-voltage lithium-ion capacitor is prepared, which can be charged and discharged within a relatively wide voltage range (2.0 - 4.0 V) and has a large energy density. Description of the Drawings

[0022] Figure 1 It is a SEM image of an activated carbon material of a positive electrode material for a lithium-ion capacitor, its preparation method, and a lithium-ion capacitor using this positive electrode material;

[0023] Figure 2It is a positive electrode material for a lithium-ion capacitor, its preparation method, and SEM images of the activated carbon material of the lithium-ion capacitor using this positive electrode material;

[0024] Figure 3 It is a positive electrode material for a lithium-ion capacitor, its preparation method, and TEM images of the activated carbon material of the lithium-ion capacitor using this positive electrode material;

[0025] Figure 4 It is a charge-discharge curve graph of a lithium-ion capacitor using this positive electrode material. Specific embodiments

[0026] The following further describes the present invention in detail with reference to the accompanying drawings.

[0027] Combined with the attached Figures 1-4 , a positive electrode material for a lithium-ion capacitor, the positive electrode material is an activated carbon material, the activated carbon material has a spherical porous structure, some carbon spheres are in a collapsed state, the BET specific surface area is 300 - 1000 m 2 / g, the average pore diameter is 1.8 - 3 nm, it is a porous spherical material rich in mesoporous structure, the diameter of the spherical activated carbon is about 0.2 - 3 um, the wall thickness is about 20 - 50 nm, the interplanar spacing (d 002 ) of the (002) crystal plane is 0.36 - 0.37 nm, the average thickness (L c ) along the c-axis direction is 0.7 - 0.85 nm, and the average width (L a ) along the a-axis direction is 9.5 - 12 nm.

[0028] A preparation method of a positive electrode material for a lithium-ion capacitor: The paper-making black liquor is atomized, an inert gas is used as the carrier gas, the atomized droplets and the inert gas enter the atmosphere protection furnace together, and the high-temperature pyrolysis of the black liquor and the activation and pore formation of the carbon material are completed in one step in the atmosphere protection furnace. After collection, washing, and drying, the activated carbon material is obtained. The total dissolved solids (including lignin, hemicellulose and their derivatives, sodium salts, residual alkali, etc.) in the paper-making black liquor is 50 - 600 g / L, the total carbon content (TOC) is 10 - 100 g / L, the content of hydroxide (OH - ) is 2 - 30 g / L, and the content of sodium (Na) is 10 - 100 g / L. The collection is to introduce the pyrolyzed solid material and the tail gas into a collector filled with dilute sodium hydroxide solution. The inert gas contains at least one of nitrogen and argon. The water partial pressure in the atmosphere protection furnace is 0.4 - 0.7 atm. The temperature of the high-temperature pyrolysis and activation and pore formation is 600 - 720 °C. The atomization includes ultrasonic atomization and centrifugal atomization.

[0029] Using the activated carbon material described above as the positive electrode material, and using one or more of artificial graphite, graphitized mesophase carbon microspheres, and hard carbon as the negative electrode material, the electrolyte is 1.3 - 1.5 mol / L LiPF 6 ethylene carbonate (EC) / dimethyl carbonate (DMC) solution (volume ratio x:1 - x, x = 0.15 - 0.3), and adding 5 - 15 wt.% ethyl acetate (EA) and 5 - 10 wt.% fluoroethylene carbonate (FEC), 1 - 1.5 wt.% biphenyl (BP) as additives to prepare a high - voltage type lithium ion capacitor, which is charged and discharged between 2.0 - 4.0 V, and the energy density is 110 - 124 Wh·kg-1.

[0030] Specific Example 1: Papermaking black liquor (total dissolved solids 62 g / L, TOC 10.6 g / L, OH - 2.8 g / L, Na 10.4 g / L) is ultrasonically atomized, using nitrogen as the carrier gas. The atomized droplets enter the atmosphere - protected furnace together with nitrogen (3 L / min). In the atmosphere - protected furnace (p H2O = 0.45 atm), the high - temperature pyrolysis of black liquor and the activation and pore - forming of carbon materials are completed in one step at 700 °C. The obtained carbon materials and tail gas are introduced into a collector containing dilute sodium hydroxide solution. After the spray pyrolysis, filtration, washing, and drying are carried out to obtain the activated carbon material.

[0031] It is measured that the obtained activated carbon material has a spherical porous structure, and some carbon spheres are in a collapsed state. The BET specific surface area is 345.8 m 2 / g, the average pore diameter is 1.9 nm, and it is a porous spherical material rich in mesoporous structure. The diameter of the spherical activated carbon is about 0.2 - 3 μm, the wall thickness is about 20 - 50 nm, and the layer spacing d 002 is 0.365 nm, the average thickness L c along the c - axis direction is 0.81 nm, and the average width L a along the a - axis direction is 11 nm. Using the obtained activated carbon as the positive electrode material, a coin - type battery is assembled with a lithium metal sheet, a separator, and an electrolyte, and is charged and discharged at a current density of 50 mA / g between 2 - 4 V. The reversible capacity is 60.8 mAh / g (109.4 F / g).

[0032] As a comparison, using Kuraray YP50 as the positive electrode material, a coin - type battery is assembled and charged and discharged in the same way, and the reversible capacity is 50 mAh / g (90 F / g).

[0033] Using the activated carbon material prepared in this example as the positive electrode material of the lithium capacitor, and using artificial graphite as the negative electrode material to assemble a lithium capacitor (the mass ratio of positive and negative active substances is 2:1), the electrolyte is 1.4 mol / L LiPF 6A solution of ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio x:1 - x, x = 0.25), with 10 wt.% ethyl acetate (EA) and 7 wt.% fluoroethylene carbonate (FEC) added, and 1.2 wt.% biphenyl (BP) as an additive, was used to prepare a high-voltage lithium-ion capacitor, which was charged and discharged between 2.0 - 4.0 V, and the energy density was 110 Wh·kg -1 (taking the sum of the masses of the positive and negative active materials as the total mass).

[0034] Specific Example 2: Papermaking black liquor (total dissolved solids 62 g / L, TOC 10.6 g / L, OH - 2.8 g / L, Na 10.4 g / L) was ultrasonically atomized, with nitrogen as the carrier gas. The atomized droplets and nitrogen (2 L / min) entered the atmosphere protection furnace together. In the atmosphere protection furnace (p H2O = 0.7 atm), the high-temperature pyrolysis of the black liquor and the activation and pore formation of the carbon material were completed in one step at 600 °C. The obtained carbon material and tail gas were introduced into a collector containing dilute sodium hydroxide solution. After the spray pyrolysis, filtration, washing, and drying were carried out to obtain the activated carbon material.

[0035] It was determined that the obtained activated carbon material had a spherical porous structure, and some carbon spheres were in a collapsed state. The BET specific surface area was 305 m 2 / g, the average pore diameter was 3 nm. It was a porous spherical material rich in mesoporous structure. The diameter of the spherical activated carbon was about 0.2 - 3 um, the wall thickness was about 20 - 50 nm, and the layer spacing d 002 was 0.37 nm, and the average thickness L c along the c-axis direction was 0.71 nm, and the average width L a along the a-axis direction was 9.5 nm. The obtained activated carbon was used as the positive electrode material, and a button battery was assembled with a lithium metal sheet, a separator, and an electrolyte. It was charged and discharged at a current density of 50 mA / g between 2 - 4 V, and the reversible capacity was 60.1 mAh / g (108.2 F / g).

[0036] Using the activated carbon material prepared in this example as the positive electrode material of the lithium capacitor, a lithium capacitor was assembled with graphitized mesophase carbon microspheres as the negative electrode material (the mass ratio of the positive and negative active materials was 2.5:1),

[0037] The electrolyte was a solution of ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio x:1 - x, x = 0.3) with 1.5 mol / L LiPF6, and 15 wt.% ethyl acetate (EA) and 5 wt.% fluoroethylene carbonate (FEC) were added, and 1 wt.% biphenyl (BP) was used as an additive. A high-voltage lithium-ion capacitor was prepared, which was charged and discharged between 2.0 - 4.0 V, and the energy density was 115 Wh·kg-1 (Taking the sum of the masses of the positive and negative active materials as the total mass).

[0038] Specific Example 3: Papermaking black liquor (total dissolved solids 580 g / L, TOC 98 g / L, OH - 28 g / L, Na 95 g / L) is centrifugally atomized, and nitrogen is used as the carrier gas. The atomized droplets enter the atmosphere protection furnace together with nitrogen (10 L / min). In the atmosphere protection furnace (p H2O = 0.4 atm), the high-temperature pyrolysis of the black liquor and the activation and pore formation of the carbon material are completed in one step at 720 °C. The obtained carbon material and tail gas are introduced into a collector filled with dilute sodium hydroxide solution. After the spray pyrolysis, filtration, washing, and drying are carried out to obtain the activated carbon material.

[0039] It is measured that the obtained activated carbon material has a spherical porous structure, and some carbon spheres are in a collapsed state. The BET specific surface area is 980 m 2 / g, the average pore diameter is 1.8 nm. It is a porous spherical material rich in mesoporous structure. The diameter of the spherical activated carbon is about 0.2 - 3 um, the wall thickness is about 20 - 50 nm, and the interlayer spacing d 002 is 0.362 nm, and the average thickness L c along the c-axis direction is 0.84 nm, and the average width L a along the a-axis direction is 11.9 nm. Using the obtained activated carbon as the positive electrode material, it is assembled with a lithium metal sheet, a separator, and an electrolyte into a coin cell, and charged and discharged at a current density of 50 mA / g between 2 - 4 V. The reversible capacity is 62.5 mAh / g (112.5 F / g).

[0040] Using the activated carbon material prepared in this example as the positive electrode material of the lithium capacitor, a lithium capacitor assembled with hard carbon as the negative electrode material (the mass ratio of the positive and negative active materials is 3:1), and the electrolyte is 1.3 mol / L LiPF 6 ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio x:1 - x, x = 0.15) solution, and 5 wt.% ethyl acetate (EA) and 10 wt.% fluoroethylene carbonate (FEC), 1.5 wt.% biphenyl (BP) are added as additives to prepare a high-voltage type lithium ion capacitor, which is charged and discharged between 2.0 - 4.0 V, and the maximum energy density is 124 Wh·kg -1 (Taking the sum of the masses of the positive and negative active materials as the total mass).

[0041] Specific Example 4: Papermaking black liquor (total dissolved solids 124 g / L, TOC 21.3 g / L, OH -5.5 g / L, Na₂O 0.8 g / L) was ultrasonically atomized, with nitrogen as the carrier gas. The atomized droplets and nitrogen (4 L / min) entered the atmosphere protection furnace together. In the atmosphere protection furnace (p H2O = 0.4 atm), the high-temperature pyrolysis of black liquor and the activation and pore formation of carbon materials were completed in one step at 650 °C. The obtained carbon materials and tail gas were introduced into a collector containing dilute sodium hydroxide solution. After the spray pyrolysis, filtration, washing, and drying were carried out to obtain activated carbon materials.

[0042] It was measured that the obtained activated carbon materials had a spherical porous structure. Some carbon spheres were in a collapsed state. The BET specific surface area was 482 m 2 / g, the average pore diameter was 2.5 nm. It was a porous spherical material rich in mesoporous structure. The diameter of the spherical activated carbon was about 0.2 - 3 μm, the wall thickness was about 20 - 50 nm, and the layer spacing d 002 was 0.37 nm. The average thickness L c along the c-axis direction was 0.77 nm, and the average width L a along the a-axis direction was 10.5 nm. The obtained activated carbon was used as the positive electrode material, and a button battery was assembled with a lithium metal sheet, a separator, and an electrolyte. Charging and discharging were carried out at a current density of 50 mA / g between 2 - 4 V, and the reversible capacity was 62.8 mAh / g (113.0 F / g).

[0043] Using the activated carbon material prepared in this example as the positive electrode material of a lithium capacitor, a lithium capacitor was assembled with graphitized mesocarbon microbeads as the negative electrode material (the mass ratio of the positive and negative electrode active substances was 2:1). The electrolyte was a solution of ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio of x:1 - x, x = 0.2) with 1.35 mol / L LiPF 6 , and 10 wt.% ethyl acetate (EA) and 8 wt.% fluoroethylene carbonate (FEC), 1.25 wt.% biphenyl (BP) were added as additives. A high-voltage type lithium-ion capacitor was prepared. Charging and discharging were carried out between 2.0 - 4.0 V, and the maximum energy density was 113 Wh·kg -1 (using the sum of the masses of the positive and negative electrode active substances as the total mass).

[0044] The above describes the present invention and its embodiments. This description is not restrictive, and the actual structure is not limited thereto. Generally speaking, if those of ordinary skill in the art are inspired by it and design similar structural forms and embodiments without creative efforts without departing from the purpose of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. A positive electrode material for a lithium ion capacitor, characterized in that: The positive electrode material is an activated carbon material, which has a spherical porous structure, some carbon balls are collapsed, and the BET specific area is 300-1000 m 2 / g, with an average pore size of 1.8-3nm, and is a porous spherical material rich in mesoporous structure. The diameter of the spherical activated carbon is 0.2-3um, the wall thickness is 20-50nm, and the (002) crystal plane interlayer spacing (d 002 ) is 0.36-0.37 nm, and the average thickness along the c-axis (L c ) is 0.7-0.85 nm, and the average width along the a-axis (L a ) is 9.5-12 nm.

2. The method for preparing a positive electrode material for a lithium ion capacitor according to claim 1, characterized in that: The papermaking black liquor is atomized, and an inert gas is used as a carrier gas. The atomized droplets enter the atmosphere protection furnace together with the inert gas. The high-temperature pyrolysis of the black liquor and the activation and pore formation of the carbon material are completed in one step in the atmosphere protection furnace. The activated carbon material is obtained by collection, washing and drying.

3. The method for preparing a positive electrode material for a lithium ion capacitor according to claim 2, characterized in that: The total dissolved solids in the papermaking black liquor include lignin, hemicellulose and their derivatives, sodium salt, residual alkali, the total dissolved solids are 50-600g / L, the total carbon content (TOC) is 10-100g / L, the hydroxide (OH - ) content is 2-30 g / L, and the sodium (Na) content is 10-100 g / L.

4. The method for preparing a positive electrode material for a lithium ion capacitor according to claim 2, characterized in that: The collection is to introduce the pyrolyzed solid materials and tail gas into a collector filled with a dilute sodium hydroxide solution.

5. The method for preparing a positive electrode material for a lithium ion capacitor according to claim 2, characterized in that: The water partial pressure in the atmosphere protection furnace is 0.4-0.7atm.

6. The method for preparing a positive electrode material for a lithium ion capacitor according to claim 2, characterized in that: The temperature of the high temperature pyrolysis and activation pore formation is 600-720°C.

7. The method for preparing a positive electrode material for a lithium ion capacitor according to claim 2, characterized in that: The atomization includes ultrasonic atomization and centrifugal atomization.

8. A lithium ion capacitor using the lithium ion capacitor positive electrode material according to claim 1, characterized in that: The activated carbon material according to claim 1 is used as the positive electrode material, one or more of artificial graphite, graphitized mesophase carbon microbeads, and hard carbon are used as the negative electrode material, the electrolyte is 1.3-1.5 mol / L LiPF6 ethylene carbonate (EC) / dimethyl carbonate (DMC) solution, the volume ratio of EC to DMC is x:1-x, x=0.15-0.3, and 5-15 wt.% of ethyl acetate (EA) and 5-10 wt.% of fluoroethylene carbonate (FEC), 1-1.5 wt.% of biphenyl (BP) are added as additives to prepare a high-voltage lithium ion capacitor, which is charged and discharged between 2.0-4.0 V and has an energy density of 110~124 Wh·kg -1 .

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