WO2021152381A1

WO2021152381A1 - Nitrogen-doped carbonaceous anode for metal ion battery and method of making

Info

Publication number: WO2021152381A1
Application number: PCT/IB2020/061697
Authority: WO
Inventors: Wenli Zhang; Husam Niman Alshareef
Original assignee: King Abdullah University Of Science And Technology
Priority date: 2020-01-29
Filing date: 2020-12-09
Publication date: 2021-08-05

Abstract

A carbonaceous anode (1302) for a metal ion battery (1300) includes three-dimensional nitrogen-doped, turbostratic carbons (320) including atoms of oxygen, hydrogen, nitrogen and carbon. A total nitrogen doping level is between 20 and 23 at. %, and an edge-nitrogen doping level is between 14 and 17 at. %.

Description

NITROGEN-DOPED CARBONACEOUS ANODE

FOR METAL ION BATTERY AND METHOD OF MAKING

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 62/967,109, filed on January 29, 2020, entitled “NITROGEN-DOPED CARBONACEOUS ANODES FOR METAL ION BATTERIES,” and U.S. Provisional Patent Application No. 63/036,061, filed on June 8, 2020, entitled “NITROGEN- DOPED CARBONACEOUS ANODE FOR METAL ION BATTERY AND METHOD OF MAKING,” the disclosures of which are incorporated herein by reference in their entirety.

BACKGROUND

TECHNICAL FIELD

[0002] Embodiments of the subject matter disclosed herein generally relate to an anode for a battery and method for making the anode, and more particularly, to a nitrogen-doped carbonaceous material having a turbostratic structure and a carbonization method that is applied to a mixture of precursors of the cathode material, where the individual precursors are sublimated by the carbonization unless in the mixture. DISCUSSION OF THE BACKGROUND

[0003] Lithium-ion batteries (LIB) have been playing an increasingly vital role in hand-held electronics, electric vehicles, and energy storage in the past decades. Considering the limited lithium supplies present in earth’s crust (20 ppm), and the growing need for large-scale renewable energy storage, there is a desire to develop alternative rechargeable battery chemistries based on more earth-abundant elements, such as sodium (earth abundance 23,000 ppm), and potassium (earth abundance 17,000 ppm). The past decade has witnessed the rapid development in sodium-ion battery (SIB) research, while the potassium-ion battery (PIB) remains less explored. One of the main reasons for this situation is the lack of suitable high- performance PIB anodes.

[0004] Graphite is the standard Li-intercalating anode, which can be fully lithiated (stage I, UC6 graphite intercalation compound), giving a capacity of 372 mAh g^_1. However, when used as the anode for the SIB, in carbonate electrolyte, the graphite can only be sodiated into a stage VIII NaC64. The failure of graphite to achieve a high-capacity anode in the SIB has triggered the interest in intercalating other ions in the graphite, such as the potassium ions. In this regard, the graphite can form a fully-potassiated stage I KCs compound, corresponding to a theoretical capacity of 278 mAh g^_1. Nonetheless, the rate capability and cycling stability of the graphite anode for the PIB are still limited due to the large volume variation (61%) during (de)potassiation, low-diffusion coefficient of K⁺ ions, and the irreversible trapping of K atoms in the graphite lattices. [0005] To compete with the LIB technology, the capacity of carbonaceous anodes for PIB should be improved to be comparable to the specific capacity of LiC6. To enhance the performance of the graphite anode in PIB, several parameters need to be controlled including: (1) the (002) lattice spacing of graphite should be made larger for efficient (de)intercalation, and (2) the nitrogen-doping-induced adsorption mechanism should be engineered to enhance potassium storage beyond the intercalation mechanism.

[0006] Nitrogen-doping of carbonaceous materials have been demonstrated as PIB anodes owing to the increased negativity of defective sites for efficient adsorption of K atoms. In addition, edge-nitrogen (pyrrolic and pyridinic) doping, as demonstrated by calculation and experimental studies, has higher adsorption energy than sp² hybridized graphitic nitrogen doping. However, the state-of-art pyrolysis methods for preparing nitrogen-doped carbons from nitrogen-abundant organics are mostly done by trial and error approaches. In these methods, the nitrogen doping of carbonaceous products cannot be precisely tuned into edge-nitrogen configurations. For instance, low-temperature pyrolysis (around 650 °C) of polypyrrole, which is a typical precursor of the nitrogen-doped carbons, leads to a high nitrogen doping level (13.8%), but also to a low edge-nitrogen doping ratio (55%).

[0007] Thus, the traditional methods for synthesizing the carbonaceous materials with both high-nitrogen doping level and high-percentage (doping ratio) of edge-nitrogen are needed to enhance the K ion storage capability of carbonaceous PIB anodes. Therefore, there is a need for a new anode that overcomes these problems and a new method for manufacturing this anode. BRIEF SUMMARY OF THE INVENTION

[0008] According to an embodiment, there is a carbonaceous anode for a metal ion battery, and the anode includes three-dimensional nitrogen-doped, turbostratic carbons having atoms of oxygen, hydrogen, nitrogen and carbon. A total nitrogen doping level is between 20 and 23 at. %, and an edge-nitrogen doping level is between 14 and 17 at. %.

[0009] According to another embodiment, there is a metal ion battery that includes an anode, a separator, a cathode, and an electrolyte placed between the anode and the cathode. The anode includes three-dimensional nitrogen-doped, turbostratic carbons having atoms of oxygen, hydrogen, nitrogen and carbon. A total nitrogen doping level is between 20 and 23 at. %, and an edge-nitrogen doping level is between 14 and 17 at. %.

[0010] According to another embodiment, there is a method for making an anode for a metal ion battery. The method includes mixing a first organic monomer with a second organic monomer mechanically or in an aqueous solution to form a mixture of super-molecules, heating the mixture of super-molecules to form an amide structure by releasing a water molecule, heating the amide structure to form an imide structure by releasing another water molecule, and carbonizing the imide structure to form three-dimensional nitrogen-doped, turbostratic carbons having atoms of oxygen, hydrogen, nitrogen and carbon. A total nitrogen doping level is between 20 and 23 at. %, and an edge-nitrogen doping level is between 14 and 17 at. %. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0012] Figure 1A is a schematic diagram of a turbostratic structure and Figure 1 B is a schematic diagram of a graphite structure;

[0013] Figure 2 illustrates pyridinic nitrogen, pyrrolic nitrogen, and graphitic nitrogen in a given molecule;

[0014] Figure 3 illustrates the synthesis process of three-dimensional nitrogen-doped, turbostratic carbons;

[0015] Figure 4 illustrates amidation, imidization and carbonization of various intermediary products for obtaining the three-dimensional nitrogen-doped, turbostratic carbons;

[0016] Figure 5 illustrates the thermogravimetric curves of the precursors of the three-dimensional nitrogen-doped, turbostratic carbons;

[0017] Figure 6 shows the chemical composition of the various precursors of the three-dimensional nitrogen-doped, turbostratic carbons and associated reactions during the synthesis process;

[0018] Figure 7 shows the electronic microscope image of the obtained three- dimensional nitrogen-doped, turbostratic carbons; [0019] Figure 8 illustrates (002) broad hump peaks of the obtained three- dimensional nitrogen-doped, turbostratic carbons;

[0020] Figure 9 illustrates the nitrogen doping levels of the obtained three- dimensional nitrogen-doped, turbostratic carbons for two different temperatures; [0021] Figure 10 illustrates the XPS spectra of the obtained three-dimensional nitrogen-doped, turbostratic carbons;

[0022] Figure 11 illustrates the structures of two different three-dimensional nitrogen-doped, turbostratic carbons;

[0023] Figure 12A shows the current curve for the obtained three-dimensional nitrogen-doped, turbostratic carbons, Figure 12B shows the galvanostatic charge- discharge for the same carbons, and Figure 12C shows a comparison of the total nitrogen doping level, edge-nitrogen doping level, and the stabilized reversible capacities between the obtained three-dimensional nitrogen-doped, turbostratic carbons and high-performance traditional carbonaceous anodes;

[0024] Figure 13 illustrates a potassium ion battery that uses the obtained three-dimensional nitrogen-doped, turbostratic carbons as an anode and perylenetetracarboxylic dianhydride (PTCDA) as a cathode; and [0025] Figure 14 is a flowchart of a method for manufacturing three- dimensional nitrogen-doped, turbostratic carbons.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The following description of the embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.

The following embodiments are discussed, for simplicity, with regard to an anode for a PIB battery. However, the embodiments to be discussed next are not limited to an anode or a PIB battery, but they may be applied to other systems different from batteries.

[0027] Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0028] According to an embodiment, a novel method for manufacturing highly edge-nitrogen doped carbons (ENDC) as anodes for PIB is introduced. This method is called herein polymerization during pyrolysis. The method uses organic monomers as the precursors and applies a polymerization-assisted pyrolysis to enable the monomers to be polymerized as polymers that can be carbonized. Simultaneously, the nitrogen is doped in the carbon skeleton. Three-dimensional nitrogen-doped, turbostratic carbon (3D-NTC) with an ultra-high edge-nitrogen doping level of 14 to 17 at. % (e.g., 16.8 at. %) is obtained through this novel method, using general direct pyrolyzing super-molecule strategy. Highly edge-nitrogen doped 3D-NTC shows remarkable performance towards potassium-ion storage. In one embodiment, a high- performance potassium-ion full battery is assembled using a 3D-NTC anode and perylenetetracarboxylic dianhydride (PTCDA) as the cathode.

[0029] To improve the anode capacities for the carbonaceous potassium ion batteries, it is possible to implement edge-nitrogen doping into the anode, which enhances the reversible capacity of the carbonaceous anodes by effectively increasing the K-ion adsorption energy. However, this process has been challenging, especially if the goal is to achieve both (1) high overall nitrogen doping of the anode, and (2) a high edge-nitrogen doping ratio. The inventors have found that improved carbon-based anodes with ultra-high, edge-nitrogen doping that achieve a high- performance can be made by using self-assembled super-molecules from pyromellitic acid and melamine as carbon precursors in a direct pyrolysis process. The amidation and imidization reactions before carbonization facilitates the carbonization of pyromellitic acid-melamine super-molecules. The obtained carbon, termed as three-dimensional nitrogen-doped, turbostratic carbon, possesses a three- dimensional framework composed of carbon nano-sheets, turbostratic crystalline structure, and ultra-high, edge-nitrogen-doping level between 14 and 17 at. % (e.g., 16.8 at. %, i.e. , the product of the edge-nitrogen doping ratio of 73.85 % of the total nitrogen doping of the material of about 22.8 at. %; the edge-nitrogen doping ratio can be between 70 and 74 at. % and the total nitrogen doping of the material is between 20 and 23 at. %). These features endow the 3D-NTC material with a remarkable performance for the PIB anodes.

[0030] Specifically, the manufactured 3D-NTC anode displays a high stable reversible capacity of 473 mAh g^_1, a high initial Coulombic efficiency of 61% (a high value among carbonaceous PIB anodes reported in recent years), robust rate capability, and a long cycle life of 500 cycles with a high capacity retention of 93.1%. [0031] The turbostratic carbon is considered to have a unique configuration, having a structural ordering between an amorphous carbon phase and crystalline graphite phase, as shown in Figure 1A. While the crystalline graphite phase has the sheets 110 of carbon atoms located in ordered and parallel plans, as shown in Figure 1B, the turbostratic carbon has sheets 102 of carbon atoms randomly folded or crumpled together. Although the chemical composition of the carbon materials shown in Figures 1A and 1B might be the same, their properties are very different because of the orientation of the sheets of carbon. Thus, in the following, a turbostratic carbon material is considered to be different from a crystalline graphite material or an amorphous carbon material or any other carbon based material, for example, graphene.

[0032] Nitrogen doping is a powerful strategy to increase the potassium-ion storage capacity of carbonaceous materials. As demonstrated by computational and experimental methodologies, edge-nitrogen-induced defects are active sites for adsorbing potassium ions compared with graphitic-nitrogen-doped carbon, and un doped carbons. The edge-nitrogen doping ratio is defined herein as follows. The nitrogen N can bond to a graphene layer 200, in at least three different ways. If the N atom bonds to the graphene layer 200 to form a single covalent bond 202 with a carbon atom and a double covalent bond 204 with another carbon atom, then this structure is called pyridinic N 210. If the N atom bonds with two carbon atoms through single covalent bonds 202, then this structure is called pyrrolic N 220. If the N atom bonds with three different C atoms, then this structure is called graphitic N 230. It is noted that the pyridinic N 210 and the pyrrolic N 220 leave the N atom with the capacity to bond to another atom, for example, the K ions in the battery, while the graphitic N 230 cannot bond with any other foreign atom. For this reason, each of the pyridinic N 210 and the pyrrolic N 220 are considered to be on the edge, while the graphitic N 230 is not on the edge. Thus, the edge-nitrogen doping ratio is considered to be the ratio of (1) the sum of the pyridinic N 210 and the pyrrolic N 220 atoms in a given material and (2) the sum of the total N atoms, irrespective of their bonding type in that given material, i.e., the pyridinic N 210, the pyrrolic N 220, and the graphitic N 230 in the example shown in Figure 2. Thus, this ratio is expressed as atoms (at.) %.

[0033] On the other hand, the total amount of N atoms, irrespective of the bonding type, are considered when calculating the total nitrogen doping, i.e., it is the ratio of (1) all the N atoms in a given material, and (2) all atoms in that given material. An edge-nitrogen doping level (which is different from the edge-nitrogen doping ratio) is defined as the total number of the pyridinic N 210 and the pyrrolic N 220 atoms (edge atoms) relative to the total number of atoms in that given material. [0034] Most known nitrogen-doped carbonaceous materials possess low nitrogen doping ratios <10 at.% and a large portion is electrochemically inactive graphitic nitrogen, which is too low to exert their potassium-ion storage capability. Some carbonaceous materials could achieve an edge-nitrogen doping ratio of -90% [1], but they possess rather an overall low nitrogen doping level (4.32 at.%). Thus, carbonaceous materials with both high nitrogen doping level and high edge-nitrogen doping ratios are very useful for enhancing the potassium-ion storage capacity of carbonaceous materials.

[0035] According to an embodiment, carbons with ultra-high edge-nitrogen doping level for use as anodes in PIB are discussed with regard to a method illustrated in Figures 3 and 4. The method starts in step 300 by providing two organic monomers 301 and 303, for example, a pyromellitic acid (PMA) 301 and a melamine (MA) 303, to realize the ultra-high edge-nitrogen doping level in carbonaceous materials. Other monomers may be used as discussed later. Pure PMA and MA monomers 301 and 303 cannot be carbonized because of sublimation. To avoid this problem, the inventors have determined that the self-assembled PMA-MA super molecules 310 can be carbonized due to the pre-carbonization reactions of amidation and imidization between the PMA and MA monomers.

[0036] More specifically, the PMA and MA molecules are placed together in step 302, for example, in an aqueous mixing, and they self-assembly to form the super-molecule 310. Specifically, the PMA and MA monomers first react in water and form the cubic, self-assembled, super-molecule (PMA-MA) crystals 310 (see Figures 3 and 4) due to the strong hydrogen bonding 311 between the PMA and MA molecules, as specifically shown in Figure 4. The detailed chemical structure of the super-molecule 310 is shown in Figure 4. The formation of the PMA-MA super molecule 310 was confirmed by the inventors by X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectroscopy.

[0037] After a one-step pyrolysis process 304, see Figure 3, the PMA-MA super-molecule 310 was successfully carbonized into 3D-NTC 320. The 3D-NTC samples obtained at annealing temperatures of 750 and 900 °C are termed herein as 3D-NTC750 and 3D-NTC900, respectively.

[0038] The one-step pyrolysis process 304 is shown in more details in Figure 4, and includes amidation and imidization reactions 306, which result in amide and imide structures 312 formed before carbonization, which greatly enhance the thermostability of the PMA and MA, which makes the PMA and MA carbonizable. Then, in step 308, the amide and imide structures 312 are carbonized, which results in the three-dimensional nitrogen-doped, turbostratic carbon (3D-NTC) 320 with an ultra-high, edge-nitrogen doping level of 14 to 17 at. %, e.g., 16.8 at. %. Note that the step 306 of amidation and imidization and the step 308 of carbonization shown in Figure 4 correspond to the single step 304 of pyrolysis in Figure 3.

[0039] In a specific embodiment, 9 mmol PMA and 12 mmol MA were placed into 100 ml_ deionized water in a glass bottle and magnetically stirred for 10 hours at room temperature (25 °C). Then, the glass bottle was sealed with a plastic cap and placed into an air-flow oven, which was maintained at 110 °C for 24 hours. The as- prepared precipitate was then dried in a 120 °C air-flow oven overnight to obtain the white-color pyromellitic acid melamine (PMA-MA) super-molecule powders. To obtain three-dimensional nitrogen-doped, turbostratic carbons (3D-NTCs), the PMA- MA super-molecule powders were heat-treated in a capped alumina crucible placed in a quartz tube for 2 hours with a heat ramping rate of 5 °C per min under an argon flow of 100 seem.

[0040] As noted above, other monomers than the PMA and the MA may be used for generating the 3D-NTCs. The preparation conditions for the 3D-NTC750s derived from poly(acrylic acid) (PAA), or terephthalic acid (benzene-1, 4-dioic acid, BDC), or citric acid (CA) were the same with 3D-NTC derived from PMA and MA except for the carboxylic precursors. In each synthesis, PAA, BDC, and CA were mixed with 12 mmol MA providing that equal mole ratios of carboxyl groups and amino groups were mixed to form the super-molecule.

[0041] The ultra-high, edge-nitrogen doping level in the 3D-NTC 320 material make it a good candidate for a PIB anode. Specifically, the 3D-NTC anode obtained with the method illustrated in Figures 3 and 4 shows a high stabilized reversible capacity of 473 mAh g^_1, robust rate capability, and a long cycle life of 500 cycles with a high capacity retention of 93.1%. Furthermore, this high-performance 3D-NTC anode was assembled into a high-performance PIB using perylenetetracarboxylic dianhydride (PTCDA) as cathode, as discussed later.

[0042] Pure PMA cannot be carbonized since PMA sublimes at a temperature of ca. 280 °C as illustrated by curve 500 in Figure 5. Likewise, pure MA faces sublimation and decomposition at temperatures above ca. 350 °C as illustrated by curve 510 in Figure 5. The MA molecules polymerize into graphitic carbon nitride (g- C3N4) at temperatures around 500 °C. The g-C3l\l4 fully decomposes at temperatures above 650 °C, as illustrated in Figure 5. On the contrary, the PMA-MA super-molecule 310 can be carbonized at high temperatures ranging from 400 to 1000 °C, as demonstrated by the increased thermostability through thermogravimetric analysis (TGA) illustrated by curve 520 in Figure 5. The differential scanning calorimetry (DSC) curve 530 in Figure 5 shows three endothermic peaks 532, 534, and 536 at temperatures ranging from 100 to 350 °C. These three endothermic peaks belong to the pre-carbonization processes 306. [0043] The inventors have tracked the pyrolysis behavior of the PMA-MA super-molecule 310 by mass spectroscopy (MS). The release of NH2 groups at 295 °C is attributed to the partial sublimation or decomposition of the MA molecule, while the release of CO2 at 298 °C is attributed to the partial sublimation or decomposition of the PMA molecule. MS spectra show three H2O release peaks at 141 , 236, and 295 °C, respectively. The H2O release peak at 141 °C results from the releasing of the crystal water in the PMA-MA super-molecules. The second (236 °C) and the third (295 °C) H2O release peaks are attributed to the amidation and imidization reactions, respectively. These three water-releasing reactions are endothermic. In the imidization of the PMA-MA super-molecule 310, the PMA 301 and MA 303 first react to form an amide structure 600 releasing one water molecule, as illustrated in Figures 4 and 6. The formed amide structure 600 further reacts to form an imide structure 610 by releasing another water molecule, as also shown in Figures 4 and 6. The amide and imide structures enable the PMA-MA super-molecule 310 to be highly thermostable and carbonizable. After the imidization process, there is some edge-locating un-imidized carboxylic acid (C(O)OH) and amine (NH2) groups due to the slow reaction kinetics of imidization. The un-imidized C(0)0H groups decompose around 483 °C, which results in the exfoliation of the 3D-NTC 320 by the released pyrolysis gases, and the final formation of the laminar nano-sheet frameworks of the 3D-NTCs. The decomposition of the s-triazine structure in the MA with the releasing of NCNH2 at higher temperatures around 521 °C may result in the formation of edge-nitrogen defect structures in the 3D-NTC. The different releasing temperatures of the C(0)0H and s-triazine demonstrate that in the amide and imide structure formed by amidation and imidization of PMA and MA, the pristine structure of PMA is less stable than MA. The high-nitrogen concentration in MA (67.7 at.% with respect to total atoms of carbon and nitrogen) and the high thermostability of amide and imide structures formed in pre-carbonization are likely to result in the highly nitrogen-doped, turbostratic carbon structures. On the one hand, since the s- triazine structure is more stable than C(0)0H in PMA, the 3D-NTC may have a higher nitrogen doping level compared with other carbonaceous materials prepared with the pyrolysis methods. On the other hand, the release of the NCNH2 may create defective edge sites for neighboring nitrogen atoms, which enables most doped nitrogen atoms to be of edge-nitrogen configurations.

[0044] The laminar sheet-like framework and the turbostratic crystalline structure of the 3D-NTC750 material were studied by electron microscopy characterization. The 3D-NTC750 material shows laminar frameworks consisting of thin carbon nano-sheets (as shown in the scanning electron microscopy (SEM) image in Figure 7). The thickness of the carbon sheets of the 3D-NTC750 material obtained by transmission electron microscopy (TEM) image is around 7-12 nanometers. The crystalline structure of the 3D-NTC750 material is turbostratically amorphous with most inter-atom distances ranging from 4.4 to 5.2 A, while a small amount of inter-atom spacing of 3.5 A has been observed. The high-resolution TEM (HRTEM) image shows some defect sites that result from the breakage of chemical bonds in the original PMA or MA structures as demonstrated by the TGA-MS study. The turbostratically amorphous structure of the 3D-NTC750 material with large inter atom spacing could facilitate the (de)potassiation process.

[0045] SEM and TEM images of the 3D-NTC900 configuration also show three-dimensional laminar frameworks similar to the 3D-NTC750 material. However, different from the 3D-NTC750 material, the 3D-NTC900 material shows developed long-range ordered GNDs observed in its HRTEM images. The developed long- range ordered GNDs of the 3D-NTC900 material originates from the higher annealing temperature. The GND of the 3D-NTC900 material is of turbostratic structure with wide distributed interlayer spacings, which is beneficial for the intercalation of potassium ion into a carbon matrix from where GND has large interlayer spacing.

[0046] Nitrogen is successfully doped in the carbon skeleton of the 3D- NTC750 material as demonstrated by the energy-dispersive X-ray spectroscopy (EDS) mapping. To demonstrate that this imidization-assisted pyrolysis is a new general strategy that can be generally extended to prepare other 3D-NTCs materials using MA and easy-accessible carboxylic acids, the inventors prepared 3D-NTCs using MA and general carboxylic acids such as poly(acrylic acid)(PAA), terephthalic acid (benzene-1, 4-dioic acid, BDC), and citric acid (CA). These carboxylic acids form amide structures with MA, and the highly thermostable amide structures can be carbonized successfully to prepare 3D-NTCs. The laminar frameworks and the turbostratic crystalline structures of the 3D-NTC750PAA, 3D-NTC750BDC, and 3D- NTC750PAA materials were characterized by physicochemical techniques, such as SEM, TEM, HRTEM, XRD and Raman. These results show that this approach constitutes a general strategy that can be extended to various carboxylic acids and amines for preparing various edge nitrogen-doped turbostratic carbons.

[0047] The (002) broad hump peaks of 3D-NTCs centering at 26.5° illustrated in Figure 8 prove that the 3D-NTCs 320 do not have well-defined interlayer spacing, consistent with the image illustrated in Figure 7. The R value introduced by Dahn (see, Y. Liu, J. S. Xue, T. Zheng, J. R. Dahn, Carbon N. Y. 1996, 34, 193), to a certain extent, can be used as an indicator to describe the order degree of the amorphous carbons. The much higher R value (4.5) of the 3D-NTC900 material than the value (2.36) of the 3D-NTC750 material demonstrates its better graphitic structure. The high ID/IG ratios of 0.99 for the 3D-NTC750 material and 0.94 for the 3D-NTC900 material obtained from the Raman spectra imply their amorphous structural natures. The pore size distribution and Brunauer-Emmett-Teller (BET) surface areas of the 3D-NTCs were evaluated by N2 adsorption/desorption isotherms. The 3D-NTC750 sample has a small BET surface area of 23.9 m² g^_1 and a large average pore size of 26.8 nm. The 3D-NTC900 sample has a relatively small BET surface area of 31.6 m² g^_1 and a relatively small average pore size of 20.9 nm, respectively. Both the 3D-NTC750 and 3D-NTC900 materials are mesoporous carbons with layer-structured pores and wide mesopore-dominated pore size distributions from 2 to 60 nanometers, which is consistent with the SEM and TEM characterization. The mesoporous structure of the 3D-NTCs could enable fast electrolyte diffusion in the electrode. The low BET surface areas of the 3D-NTCs could help reduce side reactions and improve their initial Coulombic efficiencies (ICE) towards a practical PIB anode.

[0048] The nitrogen doping levels of the 3D-NTCs were tested by X-ray photoelectron spectroscopy (XPS) analysis as illustrated in Figure 9. The 3D- NTC750 sample shows an unexpected, ultra-high nitrogen doping level between 20 and 23 at. %, for example, 22.8 at. %. This ultra-high nitrogen doping level has not been previously reported in similar carbonaceous materials obtained by pyrolysis. The nitrogen doping level of the 3D-NTC750 material was also confirmed by FTIR and TGA. The ultra-high nitrogen doping level results from the formation of stable amide and imide structures, and the high nitrogen content in the MA molecules. The other reason for this ultra-high nitrogen doping level in the 3D-NTC750 material is that PMA is less stable than MA, which indicates that MA may contribute more in the final carbon matrix of the 3D-NTC750 material.

[0049] The 3D-NTC900 sample shows lower nitrogen doping level of 9.9 at.

%, which is still higher than most recently reported nitrogen-doped amorphous carbons. The nitrogen bonding was analyzed by fitting N 1s XPS spectra deconvoluted into different configurations of pyridinic (N-6), pyrrolic (N-5), graphitic (N-Q), and oxidized (N-O) nitrogen, as illustrated in Figure 10. The relative ratios of N-6, N-5, N-Q and N-0 to the total number of N atoms, for the 3D-NTC750 sample are 41.44, 32.41, 12.73, and 13.42% respectively. The corresponding values for the 3D-NTC900 sample are 23.38, 23.15, 39.73, and 13.75, respectively. Based on these findings, the edge-nitrogen doping ratio (N-6 and N-5) of the 3D-NTC750 material is calculated to be between 70 and 74 at. % (e.g., 73.85 at. %), which is attributed to the unique decomposition behavior of the PMA-MA super-molecules. [0050] The 3D-NTC900 sample shows a lower edge-nitrogen doping ratio of 46.53%, which is attributed to the fact that at the high annealing temperature, most edge-nitrogen configurations decompose or form in-plane graphitic nitrogen. The 3D- NTC750 sample has an ultra-high, edge-nitrogen-doping level of 14 to 17 at. %, e.g., 16.8 at. %. The ultra-high edge-nitrogen doping level in the 3D-NTC750 material could contribute to high potassium-ion storage capacity and provide facile intercalation pathways.

[0051] The carbon bonding was analyzed by fitting C 1s spectra. The 3D- NTC900 sample shows a high sp² C=C ratio due to the formation of better graphene nanodomains (GNDs). The edge-nitrogen doping effect was further studied by electron paramagnetic resonance (EPR) spectroscopy, as shown in Figure 11. The 3D-NTC750 and 3D-NTC9800 materials exhibit Lorentzian EPR lines centering at different g values of 2.0032 and 2.0022, respectively. The line width (L.W.) of the 3D- NTC750 sample is 11.16 G, while the L.W. of the 3D-NTC900 sample is 224.68 G. The low L.W. of the 3D-NTC750 material indicates that the unpaired electrons in the 3D-NTC750 material are more localized due to the existence of high concentrations of edge-nitrogen configurations compared with the delocalized unpaired electrons in the 3D-NTC900 material. The g-value of 2.0032 for the 3D-NTC750 material, which is higher than the g-value 2.0022 of the 3D-NTC900 material, implies a strong nitrogen doping effect. Through EPR spectra, the inventors found that the 3D- NTC750 material is full of edge-nitrogen doping configurations that separate its carbon matrix into small GNDs. The unique ultra-high, edge-nitrogen doped structure of the 3D-NTC750 material agrees well with HRTEM, XPS, and TGA-MS studies.

The GND of the 3D-NTC900 material develops into large sizes due to the high annealing temperatures. The high nitrogen-edge doping of the 3D-NTC750 material could enhance the potassium adsorption capacity, while the small GND could enhance the rate performances of the 3D-NTC750 material. The well-developed GNDs in the 3D-NTC900 material could contribute to the intercalation capacity. [0052] The electrochemical performances of these materials were also studied. The electrochemical performance of the 3D-NTC750 electrode was first studied by cyclic voltammetry (CV). The cathodic peak starting from ca. 0.7 V is attributed to the formation of solid electrolyte interphase. After the 1st cycle, the CV curves become increasingly stabilized, which indicates that the capacity decreases during the several initial cycles, as illustrated in Figure 12A. Galvanostatic charge- discharge (GCD) analysis was used to evaluate their potassium-ion storage capabilities, as illustrated in Figure 12B. At a current density of 50 mA g^_1, the 3D- NTC750 electrode displays an initial discharge capacity of 995 mAh g^_1, while its initial charge capacity is around 606 mAh g^_1.

[0053] The initial Coulombic efficiency (ICE) of the 3D-NTC750 material is 61%, which is the highest among carbonaceous PIB anodes reported in recent years. The capacity of the 3D-NTC electrode decreases in the initial cycles at a current density of 50 mA g^_1, but then stabilized after 10 cycles. The 3D-NTC900 electrode shows a lower first charge capacity of 578 mAh g^_1 with a lower discharge plateau, which is attributed to its well-developed GNDs in its carbon skeleton. The well-developed GNDs in the 3D-NTC900 electrode has a lower initial capacity of 100 mAh g^_1, but a higher intercalation capacity than the 3D-NTC750 material.

[0054] The 3D-NTC750 electrode shows a ultra-high capacity due to its ultra- high, edge-nitrogen doping level of 14 to 17 at. %, e.g., 16.8 at. %, which is effective for the adsorption and release of the potassium ions. The intercalation-adsorption mechanism for the potassiation of the 3D-NTC750 electrode is demonstrated by energy-dispersive X-ray spectroscopy (EDS) elemental mapping. The atomic ratio of nitrogen, edge-nitrogen doping level and stabilized reversible capacity of the 3D- NTC750 electrode are the highest among all the reported carbonaceous anodes for PIB, as illustrated by Figure 12C. It is necessary to note that some studies reported high nitrogen doping level, such as PNCM (18.9 at. %) [2] or a high edge-nitrogen doping level, such as NHC2-NH3/Ar (9.2 at. %) [3] However, no studies have shown a 3D-NTC750 material that can achieve both a high nitrogen doping level (higher than 20 at. %, e.g., 22.8 at. %) and a high edge-nitrogen-doping level (higher than 14 at. %, e.g., 16.8 at. %), as discovered by the inventors.

[0055] Both the 3D-NTC750 and the 3D-NTC900 materials show a high-rate capability. The 3D-NTC750 electrode displays a higher rate capability. The 3D- NTC750 electrode displays capacities of 518, 436, 378, 313, 265, 212, and 119 mAh g^_1 at current densities of 50, 100, 200, 500, 1000, 2000, and 5000 mA g^_1, respectively. After the current density is switched back to 50 mA g^_1 , the capacity is recovered to 473 mAh g^_1, which demonstrates its high reversibility. The 3D-NTC900 displays capacities of 469, 358, 310, 260, 216, 147, 66 mAh g^_1 at current densities of 50, 100, 200, 500, 1000, 2000, and 5000 mA g^_1, respectively. The capacity of the 3D-NTC900 material is recovered to 413 mAh g^_1, after the GCD current density is switched back to 50 mA g^_1.

[0056] The long-term cycling stabilities of the 3D-NTCs electrodes were tested at a current density of 1000 mA g^_1. The tested 3D-NTC//K half cells failed at 500 and 600 GCD cycles due to the potassium dendrite penetration through the separator. The 3D-NTC750 electrode displays a high capacity retention of 93.1% after 500 GCD cycles. The 3D-NTC900 electrode shows a high capacity retention of 94% after 600 cycles.

[0057] Further, the 3D-NTC750 electrodes show unchanged morphologies before and after GCD cycling test, which demonstrates their high structural stability during (de)potassiation. The capacitive contribution was calculated based on Dunn’s method (W. Zhang, J. Ming, W. Zhao, X. Dong, M. N. Hedhili, P. M. F. J. Costa, H.

N. Alshareef, Adv. Funct. Mater. 2019, 29, 1903641). The inventors found that the 3D-NTC750 electrode has a higher capacitive contribution of 49.8% than the 3D- NTC900 electrode (38.6%). The higher capacitive contribution of the 3D-NTC750 material results from the undeveloped GNDs and large inter-atom spacing, which enables fast potassium adsorption and release. The 3D-NTC900 electrode has a smaller interlayer spacing, which may impede the diffusion of potassium ions. The capacitive contribution calculated at different scan rates confirms this tendency. [0058] A 3D-NTC750 anode 1302 was assembled into a 3D-NTC750//PTCDA PIB full cell 1300 using a (PTCDA) cathode 1310, as illustrated in Figure 13. The chemical composition of the anode and cathode is illustrated in the figure. The figure also shows a separator 1320 and the electrolyte 1330. The PTCDA electrode 1310 shows a capacity around 120 mAh g^_1 as a PI B cathode. The first discharge plateau of the 3 D- N TC750//PTC D A PIB full cell 1300 is between 2.5 and 3.0 V. A 4.5 V LED can be lit by two PIB full cells in series. The PIB full cell 1300 has a good rate performance and high operational voltages at various GCD current densities ranging from 30 to 200 mA g^_1. The cycling performance of the PIB full cell was tested under a current density of 200 mA g^_1. After 100 GCD cycles, the PIB full cell still can deliver a high capacity of 241 mAh g^_1. The cycling stability of this 3D- NTC750//PTCDA PIB full cell could be further enhanced by optimizing the electrolyte. The 3D-NTC750//PTCDA PIB full cell shows a self-discharge rate of 0.088% per hour.

[0059] In one embodiment, the PIB full cell 1300 was prepared as follows.

The 3D-NTC electrode 1302 was prepared by slurry (containing 80 wt. % 3D-NTCs, 10 wt. % acetylene black, and 10 wt. % sodium carboxymethyl cellulose) casting on copper foil with blade coating technique, and dried in a 70 °C vacuum oven for at least 24 hours. The mass loadings of the 3D-NTC electrode are around 1.0 mg cm^-2. The PTCDA electrodes were prepared by slurry (containing 70 wt. % PTCDA, 20 wt. % acetylene black, and 10 wt. % sodium carboxymethyl cellulose) casting on carbon coated aluminum, and dried in a 70 °C vacuum oven for at least 24 hours. The mass loadings of PTCDA electrodes are around 2-3 mg cm^-2.

[0060] The 3D-NTC electrode was placed in 3D-NTC//K half cells assembled in 2032 coin cells, in which, the 3D-NTC electrode was used as a working electrode, and a potassium foil was used as both the counter and quasi-reference electrode. Home-made 0.8 mol L¹ potassium hexafluorophosphate (KPF6) in ethylene carbonate: diethyl carbonate (EC: DEC, equal volume) was used as the electrolyte 1330. Two pieces of glass fiber mat were used as the separator 1320. The 3D- NTC//K half-cells were tested within the potential range from 3.0 to 0.01 V, and the PTCDA//K half-cells were tested within the potential range from 1.5 to 3.5 V with respect to the potassium quasi-reference electrode.

[0061] For the assembly of the 3D-NTC//PTCDA full cell, the 3D-NTC750 electrode was first cycled at a GCD current density of 50 mA g^_1 for 10 cycles, and then discharged to 0.01 V to make the 3D-NTC750 fully potassiated. A fully potassiated 3D-NTC750 anode was then assembled with a fresh PTCDA cathode. The newly assembled full cell was then discharged to 0.5 V and charged to 3.3 V. To avoid the potassium dendrite formation, the anode capacity is 20% in excess of the cathode capacity. All the measurements were conducted in ambient conditions. [0062] The obtained carbon anodes show a turbostratically amorphous structure with an ultra-high, total nitrogen doping level of 20 to 23 at. % (e.g., 22.8 at. %) and an ultra-high, edge-nitrogen-doping level of 14 to 17 at. % (e.g., 16.8 at. %). The ultra-high, edge-nitrogen doping level and unique defect-rich turbostratic structures of the carbon anode results in its remarkable performance as PIB anodes. This novel strategy can be extended to prepare a family of highly nitrogen-doped carbonaceous materials for other alkaline ion batteries.

[0063] According to an embodiment illustrated in Figure 14, a method for making the anode 1302 for the metal ion battery 1300 includes a step 1400 of mixing the first organic monomer 301 with the second organic monomer 303 in an aqueous solution to form a mixture of super-molecules 310, a step 1402 of heating the mixture of super-molecules 310 to form an amide structure 600 by releasing a water molecule, a step 1404 of heating the amide structure 600 to form an imide structure 610 by releasing another second water molecule, and a step 1406 of carbonizing the imide structure 610 to form the three-dimensional nitrogen-doped, turbostratic carbons 320 having atoms of oxygen, hydrogen, nitrogen and carbon. A total nitrogen doping level is between 20 and 23 at. %, and an edge-nitrogen doping level is between 14 and 17 at. %.

[0064] In one embodiment, the total nitrogen doping level is 22.8 at. % and the edge-nitrogen doping level is 16.8 at. %. In still another embodiment or the same embodiment, an edge-nitrogen doping ratio is between 70 and 74 at. %. In yet another embodiment or the same embodiment, an edge-nitrogen doping ratio is 73.85 at. %.

[0065] The first organic monomer may be pyromellitic acid (PMA) and the second organic monomer may be melamine (MA). The steps of heating take place at a temperature between 750 and 900°C. Each of the first and second organic monomers sublimates at a temperature below the 750 to 900°C range.

[0066] The disclosed embodiments provide a carbonaceous anode for a metal ion battery and the anode includes three-dimensional nitrogen-doped, turbostratic carbons having a high total nitrogen doping level and a high edge-nitrogen doping level. It should be understood that this description is not intended to limit the invention. On the contrary, the embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.

[0067] Although the features and elements of the present embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein. [0068] This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.

References

[1] Z. Liu, L. Zhang, L. Sheng, Q. Zhou, T. Wei, J. Feng, Z. Fan, Adv. Energy Mater. 2018, 8, 1802042.

[2] Y. Xie, Y. Chen, L. Liu, P. Tao, M. Fan, N. Xu, X. Shen, C. Yan, Adv. Mater.

2017, 29, 1702268.

[3] W. Yang, J. Zhou, S. Wang, W. Zhang, Z. Wang, F. Lv, K. Wang, Q. Sun, S. Guo, Energy Environ. Sci. 2019, 12, 1605.

Claims

WHAT IS CLAIMED IS:

1. A carbonaceous anode (1302) for a metal ion battery (1300), the anode (1302) comprising: three-dimensional nitrogen-doped, turbostratic carbons (320) including atoms of oxygen, hydrogen, nitrogen and carbon, wherein a total nitrogen doping level is between 20 and 23 at. %, and wherein an edge-nitrogen doping level is between 14 and 17 at. %.

2. The anode of Claim 1, wherein the total nitrogen doping level is 22.8 at. % and the edge-nitrogen doping level is 16.8 at. %.

3. The anode of Claim 1 , wherein an edge-nitrogen doping ratio is between 70 and 74 at. %.

4. The anode of Claim 1, wherein an edge-nitrogen doping ratio is 73.85 at.

%.

5. A metal ion battery (1300) comprising: an anode (1302); a separator (1320); a cathode (1310); and an electrolyte (1330) placed between the anode (1302) and the cathode (1310), wherein the anode (1302) includes three-dimensional nitrogen-doped, turbostratic carbons (320) having atoms of oxygen, hydrogen, nitrogen and carbon, wherein a total nitrogen doping level is between 20 and 23 at. %, and wherein an edge-nitrogen doping level is between 14 and 17 at. %.

6. The battery of Claim 5, wherein the total nitrogen doping level is 22.8 at. % and the edge-nitrogen doping level is 16.8 at. %.

7. The battery of Claim 5, wherein an edge-nitrogen doping ratio is between 70 and 74 at. %.

8. The battery of Claim 5, wherein an edge-nitrogen doping ratio is 73.85 at.

%.

9. The battery of Claim 5, wherein the electrolyte includes potassium.

10. The battery of Claim 5, wherein the electrolyte includes potassium hexafluorophosphate.

11. The battery of Claim 10, wherein the potassium hexafluorophosphate is mixed with equal parts of ethylene carbonate and diethyl carbonate.

12. The battery of Claim 9, wherein the cathode includes perylenetetracarboxylic dianhydride.

13. The battery of Claim 5, wherein the battery is a potassium ion battery.

14. A method for making an anode (1302) for a metal ion battery (1300), the method comprising: mixing (1400) a first organic monomer (301) with a second organic monomer (303) mechanically or in an aqueous solution to form a mixture of super-molecules (310); heating (1402) the mixture of super-molecules (310) to form an amide structure (600) by releasing a water molecule; heating (1404) the amide structure (600) to form an imide structure (610) by releasing another water molecule; and carbonizing (1406) the imide structure (610) to form three-dimensional nitrogen-doped, turbostratic carbons (320) having atoms of oxygen, hydrogen, nitrogen and carbon, wherein a total nitrogen doping level is between 20 and 23 at. %, and wherein an edge-nitrogen doping level is between 14 and 17 at. %.

15. The method of Claim 14, wherein the total nitrogen doping level is 22.8 at. % and the edge-nitrogen doping level is 16.8 at. %.

16. The method of Claim 14, wherein an edge-nitrogen doping ratio is between 70 and 74 at. %.

17. The method of Claim 14, wherein an edge-nitrogen doping ratio is 73.8 at.

%.

18. The method of Claim 14, wherein the first organic monomer is pyromellitic acid (PMA) and the second organic monomer is melamine (MA).

19. The method of Claim 14, wherein the first organic monomer includes a carboxylic acid and the second organic monomer includes an organic amine.

20. The method of Claim 14, wherein the steps of heating take place at a temperature between 750 and 900°C and each of the first and second organic monomers sublimates at a temperature below 750°C.