Patent Application
20230094647
Pursuant to 35 U.S.C. § 119(a), this application claims the benefits of the priority to Taiwan Patent Application No. 110135633, filed Sep. 24, 2021. The contents of the prior application are incorporated herein by its entirety.
The instant disclosure relates to hard carbon beads, their preparation, and an energy storage device comprising the same, more particularly to hard carbon beads for storage of lithium ion or sodium ion, their preparation, and an energy storage device comprising the same.
To solve the problems of energy shortage and increasing demand for electricity, people have put lots of effort on researches of high performance energy storage systems. Since lithium ion batteries (LIBs) have high energy density, high power density, and acceptable charge-discharge cycle life, they are widely used in various electronic products. Since sodium ion batteries (SIBs) have merits of high security, low cost and rich reserve of sodium raw material, they become highly valued new generation batteries.
Carbon usually serves as an active material in the negative electrode of a lithium ion battery. Carbon negative electrode material can be divided into natural graphite, artificial graphite, graphite-like carbon, and amorphous carbon material, and amorphous carbon material comprises soft carbon and hard carbon. Common precursors of hard carbon are artificial polymer and biomass. However, hard carbon produced by biomass has problems of uneven structure and difficulty of control due to impurity in biomass. Structure of hard carbon produced by artificial polymer can be controlled, which is beneficial to modify the property of lithium ion batteries.
Nowadays, artificial polymer needs to undergo pretreatment of cross-linking reaction before carbonization in production of hard carbon. However, conventional cross-linking reaction is carried out by heat treatment of 150° C. to 200° C. or long-term hydrothermal method for 6 hours to 24 hours. In addition to the defects of high energy consumption and uncontrollable curing extent, long staying in high temperature environment easily causes undesired side reaction. Aforesaid side reaction makes the hard carbon not suitable for lithium ion batteries or sodium ion batteries.
In view of this, an objective of the instant disclosure is to prepare hard carbon beads by adopting a microwave-assisted hydrothermal method instead
of the conventional hydrothermal method at high temperature. Microwave-assisted hydrothermal method can carry out fast cross-linking reactions. By aforesaid method, energy consumption can be reduced and the curing extent of obtained hard carbon beads can be controlled.
To achieve aforementioned objective, the instant disclosure provides a method of preparing hard carbon beads comprising:
step (a): dissolving phenol-formaldehyde resin, a cross-linking reagent and a protection reagent into a solvent to form a mixture and heating the mixture by microwave for cross-linking reaction to obtain a suspension containing phenol-formaldehyde beads, wherein the phenol-formaldehyde resin is set to be 100 parts by weight, the cross-linking reagent is greater than or equal to 5 parts by weight and less than or equal to 70 parts by weight, the protection reagent is greater than or equal to 1 part by weight and less than or equal to 10 parts by weight, the heating temperature of microwave is greater than or equal to 100° C. and less than or equal to 180° C., the cross-linking reagent is selected from the group consisting of: hexamethylenetetramine (HMTA), formaldehyde acetal, furfural, furfural alcohol and trimethylol phosphine oxide, and the protection reagent is selected from the group consisting of: polyvinyl alcohol (PVA), methyl cellulose (MC) and polyoxyethylene polyoxypropylene (POE-POP);
step (b): drying the suspension containing phenol-formaldehyde beads to obtain phenol-formaldehyde beads; and
step (c): subjecting the phenol-formaldehyde beads for carbonization under inert gas to obtain the hard carbon beads, wherein the carbonization temperature is greater than or equal to 500° C. and less than or equal to 1500° C.
By using the microwave-assisted hydrothermal method, fast cross-linking reaction of phenol-formaldehyde resin with moderate cross-linking reagent and protection reagent is carried out, which is beneficial to control cross-linking extent, to shorten the processing time and to save energy. Besides, carbonization under the atmosphere of inert gas and moderate temperature contributes to controllable graphitization extent of hard carbon beads, which makes the hard carbon beads have specific micro-graphitic structures and closed micropores. According to this, the hard carbon beads obtained by the method of the instant disclosure have good storage ability for lithium ion or sodium ion and render the lithium ion battery, sodium ion battery, lithium ion capacitor, and sodium ion capacitor enhanced economic values.
It should be explained that excess cross-linking reagent makes the cross-linking density of phenol-formaldehyde resin become uneven, which contributes to massive standard deviation of particle size of the obtained hard carbon beads. It should be explained that too high carbonization temperature makes some of the hard carbon beads subject to severe heat treatment, which contributes to massive standard deviation of particle size of the obtained hard carbon beads. However, carbonization without adequate temperature fails to make the obtained hard carbon beads have well-developed micro-graphitic structure.
Preferably, the number-average molecular weight (Mn) of aforesaid phenol-formaldehyde resin may be greater than or equal to 200 and less than or equal to 10000 and the viscosity of aforesaid phenol-formaldehyde resin may be greater than or equal to 35 cps and less than or equal to 2100 cps. In one of the embodiments, the Mn of aforesaid phenol-formaldehyde resin may be greater than or equal to 200 and less than or equal to 3000. In another embodiment, the Mn of aforesaid phenol-formaldehyde resin may be greater than or equal to 3000 and less than or equal to 10000.
According to the instant disclosure, aforesaid phenol-formaldehyde resin may be phenol-formaldehyde resin without nitrogen doping or nitrogen-doped doped phenol-formaldehyde resin. Aforesaid phenol-formaldehyde resin without nitrogen doping does not comprise any amino group or heteroaryl group comprising nitrogen. The Mn of phenol-formaldehyde resin without nitrogen doping may be greater than or equal to 200 and less than or equal to 3000. Aforesaid nitrogen-doped phenol-formaldehyde resin may comprise amino group, heteroaryl group comprising nitrogen or the combination thereof. The Mn of nitrogen-doped phenol-formaldehyde resin may be greater than or equal to 2000 and less than or equal to 4000.
According to the instant disclosure, aforesaid cross-linking reagent is a reagent which can be decomposed to an aldehyde during reaction. For example, aforesaid aldehyde is formaldehyde. Preferably, the phenol-formaldehyde resin is set to be 100 parts by weight in aforesaid step (a), the cross-linking reagent may be greater than or equal to 5 parts by weight and less than or equal to 50 parts by weight. More preferably, the phenol-formaldehyde resin is set to be 100 parts by weight in aforesaid step (a), the cross-linking reagent may be greater than or equal to 5 parts by weight and less than or equal to 30 parts by weight.
The function of protection reagent added in the method of preparing hard carbon beads of the instant disclosure is dispersing the phenol-formaldehyde resin evenly, which makes the extent of cross-linking reaction become controllable. Preferably, aforesaid protection reagent may be greater than or equal to 2.5 parts by weight and less than or equal to 7.5 parts by weight. Preferably, the protection reagent may be polyvinyl alcohol.
Aforesaid solvent may comprise 0 vol % to 100 vol % water and 0 vol % to 100 vol % alcohol and aforesaid alcohol may be methanol, ethanol or the combination thereof. In one of the embodiments, aforesaid solvent may comprise only one solvent (as known as single-solvent system). That is, aforesaid solvent may be water, methanol or ethanol. Single-solvent system is suitable for the phenol-formaldehyde resin without nitrogen doping having Mn of 200 to 3000. In another embodiment, aforesaid solvent may comprise two solvents (as known as double-solvent system). That is, aforesaid solvent may comprise 20 vol % to 80 vol % water and 20 vol % to 80 vol % methanol or 20 vol % to 80 vol % water and 20 vol % to 80 vol % ethanol. Double-solvent system is suitable for the nitrogen-doped phenol-formaldehyde resin having Mn of 2000 to 4000.
Preferably, the heating temperature of microwave in aforesaid step (a) may be greater than or equal to 110° C. and less than or equal to 140° C.
Preferably, the power of microwave in aforesaid step (a) may be greater than or equal to 60 watt and less than or equal to 100 watt.
Preferably, the microwave heating time in aforesaid step (a) may be greater than or equal to 5 minutes and less than or equal to 60 minutes. Compared to the conventional hydrothermal method for preparing hard carbon beads, the fast cross-linking reaction promoted by the microwave-assisted hydrothermal method is beneficial to save energy and to shorten the processing time in production. In one of the embodiments, the microwave heating time in aforesaid step (a) may be greater than or equal to 15 minutes and less than or equal to 30 minutes.
The drying method in aforesaid step (b) does not have any specific limitation. Aforesaid drying method may be air dry or drying at 60° C. to 90° C.
The inert gas in aforesaid step (c) does not have any specific limitation. For example, aforesaid inert gas may be nitrogen or argon.
Specifically, the carbonization temperature in step (c) may be 600° C. to 1500° C., 700° C. to 1200° C. or 800° C. to 1000° C.
In one of the embodiments, the carbonization in step (c) may be carried out in aforesaid temperature for 1 hour to 10 hours. In another embodiment, the carbonization in step (c) may be carried out in aforesaid temperature for 5 hours to 8 hours.
Besides, the instant disclosure provides a hard carbon bead having a maximum particle size and a minimum particle size, wherein a ratio of the maximum particle size to the minimum particle size is greater than or equal to 1 and less than or equal to 1.1.
In the present specification, aforesaid maximum particle size and minimum particle size are the particle sizes measured from the lines through the center of the same hard carbon bead. If the ratio of the maximum particle size to the minimum particle size is approximate to 1, the hard carbon bead is close to an ideal sphere.
Preferably, aforesaid hard carbon bead may be in the shape of a ball.
In one of the embodiments, aforesaid hard carbon bead may have a ratio of maximum particle size to minimum particle size greater than or equal to 1.021 and less than or equal to 1.098.
In one of the embodiments, aforesaid hard carbon bead may have an average group particle size greater than or equal to 3.5 μm and less than or equal to 4.8 μm. In another embodiment, aforesaid hard carbon bead may have an average group particle size greater than or equal to 3.8 μm and less than or equal to 4.6 μm.
In one of the embodiments, aforesaid hard carbon bead may have a standard deviation of particle size greater than or equal to 1.2 μm and less than or equal to 2.8 μm.
In one of the embodiments, the graphitic length La may be greater than or equal to 2.9 nm and less than or equal to 3.5 nm. In another embodiment, the graphitic length La may be greater than or equal to 3.0 nm and less than or equal to 3.4 nm.
In one of the embodiments, the Raman spectrum of aforesaid hard carbon bead has D1 band and G band. The ratio of the intensity of D1 band to the intensity of G band may be greater than or equal to 2.0 and less than or equal to 2.5.
According to the instant disclosure, the hard carbon beads obtained from aforesaid method may apply to negative electrode for the lithium ion battery, sodium ion battery, lithium ion capacitor and sodium ion capacitor.
The instant disclosure provides an energy storage device comprising a negative electrode and a lithium foil as a counter electrode, wherein the negative electrode comprises aforesaid hard carbon beads, the Galvanostatic charge-discharge curve (GCD curve) of the energy storage device comprises a plateau region ranging from 0.003 V to 0.12 V and a sloping area ranging from 0.12 V to 1.5 V, the specific capacity of the plateau region is greater than or equal to 90 mAh/g and less than or equal to 220 mAh/g, and the specific capacity of the sloping area is greater than or equal to 120 mAh/g and less than or equal to 320 mAh/g.
The energy storage device of the instant disclosure comprises a lithium ion battery, a sodium ion battery, a lithium ion capacitor, and a sodium ion capacitor. Since the GCD curve of the energy storage device has a significant plateau region and sloping area, the energy storage device has a higher total specific capacity (200 mAh/g to 500 mAh/g). Preferably, the energy storage device may have a total specific capacity greater than or equal to 280 mAh/g and less than or equal to 500 mAh/g.
In one of the embodiments, the energy storage device is a lithium ion battery. The specific capacity of the plateau region may be greater than or equal to 90 mAh/g and less than or equal to 220 mAh/g and the specific capacity of sloping area may be greater than or equal to 120 mAh/g and less than or equal to 290 mAh/g.
In another embodiment, the energy storage device is a sodium ion battery. The specific capacity of the plateau region may be greater than or equal to 90 mAh/g and less than or equal to 120 mAh/g and the specific capacity of sloping area may be greater than or equal to 120 mAh/g and less than or equal to 150 mAh/g.
Hereinafter, multiple examples are provided to illustrate the implementation of the method of preparing hard carbon beads of the instant disclosure, while multiple comparative examples are provided as comparison. A person having ordinary skill in the art can easily realize the advantages and effects of the instant disclosure from the following examples and comparative examples. The descriptions proposed herein are just preferable embodiments for the purpose of illustrations only, not intended to limit the scope of the instant disclosure. Various modifications and variations could be made in order to practice or apply the instant disclosure without departing from the spirit and scope of the instant disclosure.
Hard Carbon Bead
Phenolic-formaldehyde resin was used as starting material of Examples 1 to 10. By microwave-assisted hydrothermal method, fast cross-linking reaction was carried out and phenolic-formaldehyde beads in ball shape were obtained. Then after carbonization at appropriate temperature, Examples of hard carbon beads were obtained. With reference to
First, 846 g phenol (9 mol) and 1600 g of 30 wt % formaldehyde solution (16 mol) were mixed at 20° C. 38 wt % concentrated sodium hydroxide solution (about 110 ml) was added to aforesaid mixture with constant stirring and the pH value of the mixture was adjusted to be 9.5 to 10. Then the mixture was heated at 60° C. for 4 hours. After the reaction ended, the mixture was analyzed by titration and only 1 wt % formaldehyde was detected. Then aforesaid mixture was cooled down, about 5 wt % hydrochloric acid was added with constant stirring and the pH value of the mixture became almost neutral. Aforesaid mixture should not be acidic. Specifically, the pH value of the mixture should be about 7.2 to 7.5. Afterwards, water and excess phenol were evaporated under vacuum and the inner temperature reached about 60° C. Finally, 1360 g of viscous resin known as phenol-formaldehyde resin without nitrogen doping was obtained. Herein, the phenol-formaldehyde resin without nitrogen doping had a number average molecular weight around 200 and the viscosity around 35 cps.
Afterwards, 0.8 g phenol-formaldehyde resin without nitrogen doping was dissolved in 0.2 g methanol to obtain 1 g of 80 wt % phenol-formaldehyde resin solution without nitrogen doping. Phenol-formaldehyde resin without nitrogen doping was set to be 100 parts by weight. 5 parts by weight polyvinyl alcohol and 10 parts by weight to 50 parts by weight HMTA (vendor: SHOWA) were added to 1 g of 80 wt % phenol-formaldehyde resin solution without nitrogen doping. 19 ml deionized water was added to aforesaid mixture and the mixture was transferred to a reaction tube. The reaction tube was sealed with a lid and placed in a focused microwave reactor (model: CEM discover). The temperature of the focused microwave reactor was about 130° C., the power of the focused microwave reactor was about 60 watt, and the time of heating and constant stirring was 20 minutes. By microwave-assisted hydrothermal method, fast cross-linking reaction was carried out and a suspension containing phenol-formaldehyde beads without nitrogen doping was obtained.
Afterward, aforesaid suspension containing phenol-formaldehyde beads without nitrogen doping was cooled down to room temperature. Yellow phenol-formaldehyde beads without nitrogen doping were significantly suspended within aforesaid suspension. The suspension containing phenol-formaldehyde beads without nitrogen doping was rinsed by acetone two to three times and then aforesaid suspension was filtered. The solid product was obtained and placed in an 80° C. oven. After drying for 24 hours, phenol-formaldehyde beads without nitrogen doping were obtained.
Finally, aforesaid phenol-formaldehyde beads without nitrogen doping were put in a high-temperature furnace. The temperature of the high-temperature furnace was set to be about 600° C. to 1000° C. The temperature of the high-temperature furnace was raised at the speed of 1° C. to 50° C. per minute to the target temperature in nitrogen atmosphere. Carbonization was carried out at the target temperature for 6 hours and each Example of hard carbon beads was obtained.
The differences between Examples 1 to 10 were recruitment of HMTA and carbonization temperature. The parameters were shown in Table 1.
Examples 11 to 12 of hard carbon beads were rapidly produced by a similar microwave-assisted hydrothermal method and carbonization as stated in Examples 1 to 10. The differences were described as follows. (1) Different phenol-formaldehyde resin was used as starting material. (2) Polyvinyl alcohol was not added. The manufacturing process of Examples 11 to 12 was described as follows.
First, 0.8 g nitrogen-doped phenol formaldehyde resin (vendor: DIC Corporation, model: PHENOLITE LA-1356) was dissolved in methanol to obtain 1 g of 80 wt % nitrogen-doped phenol-formaldehyde resin solution. Nitrogen-doped phenol-formaldehyde resin was set to be 100 parts by weight. 70 parts by weight HMTA (vendor: SHOWA) was added to 1 g of 80 wt % nitrogen-doped phenol formaldehyde resin solution. 9.5 ml ethanol and 9.5 ml deionized water (total 19 ml liquid) were added to aforesaid mixture and the mixture was transferred to a reaction tube. The reaction tube was sealed with a lid and placed in a focused microwave reactor (model: CEM discover). The temperature of the focused microwave reactor was about 130° C., and the time of heating and constant stirring was 20 minutes. By microwave-assisted hydrothermal method, fast cross-linking reaction was carried out and a suspension containing nitrogen-doped phenol-formaldehyde beads was obtained.
Afterward, aforesaid suspension containing nitrogen-doped phenol-formaldehyde beads was cooled down to room temperature. Yellow nitrogen-doped phenol-formaldehyde beads were significantly suspended within aforesaid suspension. The suspension containing nitrogen-doped phenol-formaldehyde beads was rinsed by acetone two to three times and then aforesaid suspension was filtered. The solid product was obtained and placed in an 80° C. oven. After drying for 24 hours, nitrogen-doped phenol-formaldehyde beads were obtained.
Finally, aforesaid nitrogen-doped phenol-formaldehyde beads were put in a high-temperature furnace. The temperature of the high-temperature furnace was set to be about 900° C. to 1000° C. The temperature of the high-temperature furnace was raised at the speed of 1° C. to 50° C. per minute to the target temperature in nitrogen atmosphere. Carbonization was carried out at the target temperature for 6 hours and Examples 11 and 12 of hard carbon beads were obtained.
The difference between Examples 11 and 12 was the carbonization temperature. The carbonization temperature was 900° C. in Example 11 and the carbonization temperature was 1000° C. in Example 12.
Field-emission scanning electron microscope (vendor: Hitachi, model: SU8010) was used to observe Examples 1 to 12 of hard carbon beads in the test example. The results were shown as
IC Measure was used to analyze
As shown in Table 2, standard deviation of particle size of single particle of Examples 1 to 12 in the three kinds of particle sizes was less than 0.1 μm, which indicated that the values of particle size were centralized. The ratio of maximum particle size to minimum particle size of Examples 1 to 12 in the three kinds of particle sizes was greater than 1 and less than 1.1, which confirmed that Examples 1 to 12 of hard carbon beads were close to ideal ball type and different from conventional flake carbon material or lump carbon material.
Afterwards, field-emission scanning electron microscope and IC Measure were used to analyze the polydispersity index (PDI) of
The results in Table 3 and
The number of closed micropores in hard carbon beads and storage capacity of lithium ion and sodium ion were highly related. Transmission electron microscope (vendor: JEOL, model: JEM 2100F) was used to observe Example 1 of hard carbon beads in the test example. The HR-TEM and the partial enlargement thereof were shown as
X-ray diffractometer (vendor: Bruker, model: D8 Advance) was used to identify the crystal structures of Examples 1 to 4, and 7. A Cu Kα radiation source (λ=1.5405 Å) was used to measure aforesaid crystal structures. The results were shown as
The 2θ diffraction position of facet (002) and facet (100) ranged from 23° to 25° and 43° to 45° respectively. As shown in
To investigate the influence of recruitment of cross-linking reagent and carbonization temperature to micro-graphitic structure of hard carbon bead, X-ray diffraction curves of Examples 1 to 4 and 7 were combined into
Further analysis of XRD of Examples 1 to 9 was conducted to obtain 2θ002 of facet (002) and 2θ100 of facet (100). Interlayer d-spacing (d002) was rendered by Bragg's equation: nλ=2d002 sin θ002. Lc (graphitic length along c-axis) was rendered by Scherrer's equation: Lc=0.89λ/β002 cos θ002. β002 was the full width at half maximum of facet (002) characteristic peak. La (graphitic length along a-axis) was rendered by Scherrer's equation: La=1.84λ/β100 cos θ100. β100 was the full width at half maximum of facet (100) 5 characteristic peak. The results were shown in Table 4.
Besides, Raman spectra (model: JY HR 800) of Examples 1 to 9 were used to analyze the disordering degree of carbon structure. Origin (fitting mode: Gaussian) was used to carry out fitting analysis. As shown in
The ratio of the intensity of D1 band to the intensity of G band (ID1/IG) in Raman spectrum of each Example was used to evaluate the disordering degree of carbon structure. Aforesaid intensity of D1 band and intensity of G band were calculated by the signal areas of aforesaid two bands. The results were shown in Table 4.
d002
Lc
2θ100
As shown in Table 4, as cross-linking density of phenol-formaldehyde resin grew up, ID1/IG of hard carbon beads after carbonization was decreased. Aforesaid phenomenon indicated that the disordering degree was decreased. As shown in Table 4, each Raman spectrum of Examples 1 to 9 had D1 band and G band and the ratio of the intensity of D1 band to the intensity of G band was greater than or equal to 2.0 and less than or equal to 2.5.
As shown in Table 4, as cross-linking density of phenol-formaldehyde resin grew up, the graphitic length La micro structure was decreased due to the influence of closed micropore of micro-graphitic structure. As shown in Table 4, the graphitic length La micro structure of Examples 1 to 9 was greater than or equal to 2.9 nm and less than or equal to 3.5 nm.
Negative Electrode
Hard carbon beads of Examples 1 to 12 were used as negative electrode active material for preparing negative electrodes of Examples 1A to 12A. Each negative electrode of lithium ion batteries was obtained through following manufacturing process. The manufacturing process of Examples 1A to 12A was described as follows.
First, aforesaid hard carbon beads, carbon black (model: XC-72) and polyvinylidene fluoride (PVDF) were mixed at weight ratio of 85:5:10. Aforesaid mixture was dissolved in N-methyl-2-pyrrolidone (NMP) and the weight ratio of solid to liquid was 1:8. Then the negative electrode slurry was obtained.
Afterwards, the negative electrode slurry was coated on a copper foil by doctor blade method. The amount of hard carbon beads on the copper foil was around 2 mg per square centimeter. Then the copper foil coated with negative electrode slurry was placed in 80° C. vacuum environment for 24-hour drying to obtain a negative electrode containing hard carbon beads.
Negative electrodes of Comparative Examples 1A and 2A and Negative electrodes of Examples 1A to 12A were almost the same. The differences were that commercial mesocarbon microbeads (MCMB, vendor: China Steel Chemical Corporation, model: MG11) was used as negative electrode active material in Comparative Example 1A and that commercial soft carbon (vendor: China Steel Chemical Corporation, model: MSC-2) was used as negative electrode active material in Comparative Example 2A.
Lithium Ion Battery
Negative electrodes of Examples 1A to 9A and 11A to 12A with same kind of positive electrode and electrolyte were used for preparing lithium ion batteries of Examples 1B to 9B and 11B to 12B respectively. The manufacturing process of Examples 1B to 9B and 11B to 12B were described as follows.
Coin cell (model: CR2032) was used and aforesaid negative electrode and lithium foil (counter electrode) were divided by a glass fiber (grade: GF/A). Lithium hexafluorophosphate (LiPF6) was dissolved in a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) (volume ratio: 1:1:1) to obtain 1M LiPF6 solution as electrolyte. 1 wt % vinylene carbonate (VC) was added in aforesaid electrolyte. 80 μl aforesaid electrolyte was added to the coin cell in argon atmosphere (contents of moisture and oxygen less than 0.1 ppm) to obtain lithium ion batteries of Examples 1B to 9B and 11B to 12B. The content of water in aforesaid electrolyte was less than 10 ppm by measurement of Karl Fisher titration.
Lithium ion batteries of Comparative Examples 1B to 2B and lithium ion batteries of Examples 1B to 9B and 11B to 12B were almost the same. The differences were that negative electrode of Comparative Example 1A was used in Comparative Example 1B and that negative electrode of Comparative Example 2A was used in Comparative Example 2B.
Sodium Ion Battery
Sodium ion battery of Example 10C was almost the same as lithium ion battery of Example 1B. The differences were that negative electrode of Example 10A was used in sodium ion battery of Example 10C and that the electrolyte in Example 10C was 1M sodium hexafluorophosphate (NaPF6) solution. Aforesaid 1M NaPF6 solution was obtained by NaPF6 dissolving in the mixture of EC, EMC and DMC (volume ratio: 1:1:1).
Lithium ion batteries of Examples 1B to 4B and 7B were used as samples in this test example. The cyclic voltammetry was conducted between 0.003 V and 1.5V (vs. Li+/Li) at scanning rate of 1 mV/s and atmosphere of 1 atm. The results were shown in
As shown in
Lithium ion batteries of Examples 1B to 9B and 11B to 12B and sodium ion battery of Example 10C were used as samples in this test example. GCD cycle was conducted at a current density of 50 mA/g (0.2C), voltage ranging between 0.003 V and 1.5 V (vs. Li+/Li), and atmosphere of 1 atm. The results were shown in
As shown in Table 5, cross-linking density of phenol-formaldehyde resin had great influence on formation of closed micropore. Hard carbon bead carbonized by phenol-formaldehyde resin with low cross-linking density had more micro-graphitic structures and/or closed micropores, which was beneficial to lithium ion storage.
As shown in Table 5, cross-linking density of phenol-formaldehyde resin had decisive influence on specific capacity of plateau region. The specific capacity of plateau region of Example 4B was 200 mAh/g, and the total specific capacity of Example 4B was 480 mAh/g.
As shown in Table 5, GCD curves of Examples 1B to 9B and 11B to 12B had significant plateau region and sloping area. The specific capacity of aforesaid plateau region was greater than or equal to 90 mAh/g and less than or equal to 220 mAh/g, the specific capacity of aforesaid sloping area was greater than or equal to 180 mAh/g and less than or equal to 320 mAh/g, and the total specific capacity was greater than or equal to 280 mAh/g and less than or equal to 500 mAh/g.
As shown in
In one of the embodiments, the initial Faraday efficiency of lithium ion batteries of Examples 1B to 9B and 11B to 12B may be raised by pre-lithiation of negative electrode.
Lithium ion batteries of Examples 1B to 4B and 7B and Comparative Examples 1B to 2B were used as samples in this test example. The test was conducted at current density ranging from 50 mA/g to 2500 mA/g (0.2C to 10C) and atmosphere of 1 atm. The results were shown in
As shown in
Lithium ion battery of Example 4B was used as sample in this test example. Initial 3 charge-discharge cycles were measured at current density of 50 mA/g (0.2C) and atmosphere of 1 atm and subsequent 50 charge-discharge cycles were measured at current density of 250 mA/g (1C) and atmosphere of 1 atm. The result was shown as
As shown in
In summary, the method of preparing hard carbon beads involves a cross-linking reaction of phenol-formaldehyde resin heated by microwave. The method can reduce energy consumption, control the curing extent, and solve the problems of side reaction and high energy-consumption occurring at high temperature cross-linking reaction. Therefore, economic values of the negative electrode, lithium ion battery, sodium ion battery, lithium ion capacitor, and sodium ion capacitor comprising the hard carbon beads can be increased.
| Number | Date | Country | Kind |
|---|---|---|---|
| 110135633 | Sep 2021 | TW | national |
